1
[Name of Document] DESCRIPTION
[Title of the Invention] HIGH-STRENGTH HOT-DIP GALVANIZED STEEL SHEET AND HIGH-STRENGTH ALLOYED HOT-DIP GALVANIZED STEEL SHEET HAVING EXCELLENT FORMABILITY AND SMALL MATERIAL ANISOTROPY 5 WITH ULTIMATE TENSILE STRENGTH OF 980 MPa OR MORE AND MANUFACTURING METHOD THEREFOR [Technical Field] [0001]
The present invention relates to a high-strength plated steel sheet and a
10 high-strength alloyed hot-dip galvanized steel sheet having excellent plating adhesion and formability with an ultimate tensile strength (TS) of 980 MPa or more which is particularly suitable for a structural member, a reinforcing member, and a suspension member of automobiles.
This application claims priority on Japanese Patent Application No, 2011-218040,
15 filed on September 30,2011, the content of which is incorporated herein by reference. [Background Art] [0002]
Reduction of weight of members such as cross members and side members of automobiles has been considered so as to support trends for reduction of fuel consumption
20 in recent years. In terms of materials, from the viewpoint of securing strength and impact safety even when being thinned, a steel sheet has been made higher in strength. However, the formability of materials deteriorates along with the rise of strength thereof. In order to implement lighter weight of the members, a steel sheet which satisfies both of the press formability and the high strength has to be produced. In particular, excellent ductility is
25 required in the case of forming the structural member or the reinforcing member of automobiles that has a complicated shape.

2
[0003]
Recently, as a frame member of the automobile, a steel sheet having ultimate
tensile strength of 440 MPa or 590 MPa is mainly used. In order to further reduce the
weight, development of a high strength steel sheet of 980 MPa or more is preferred. In 5 particular, when the steel sheet of 590 MPa class is replaced with the steel sheet of 980
MPa class, it requires an elongation equivalent to the 590 MPa class. Thus, development
of a steel sheet of 980 MPa or more having excellent elongation is desired.
[0004]
As the steel sheet having excellent total elongation (El) in a tensile test, there are 10 complex stmcture steel sheets in which a soft ferrite serving as a primary phase is used in a
steel sheet structure to ensure the ductility and a residual austenite is dispersed as a second
phase to ensure strength.
As the steel obtained by dispersing the residual austenite, there is a TRIP
(TRansformation Induced Plasticity) steel which uses martensite transformation of the 15 residual austenite at the time of plastic processing, and applications thereof has been
expanded, recently.
[0005]
In particular, the TRIP steel has excellent elongation compared with precipitation
strengthened steel and DP steel (steel consisting of ferrite and martensite), and thus 20 expanded application is highly desirable. However, since this steel ensures excellent
formability using martensite transformation at the time of forming, large amounts of
residual austenite are required to ensure the formability. In order to ensure the residual
austenite, it is required to add large amounts of Si. Further, in order to ensure the strength
of 980 MPa or more, there is a tendency that alloy elements are added in large amounts and 25 a texture easily develops. In particularly, the development of the texture of orientation
groups {100} <011> to {223} <110> or the texture of an orientation {332} <113>

3
promotes a material anisotropy. For example, as compared with the total elongation in the case of performing the tensile test on a steel strip in a direction parallel to a rolling direction, the total elongation in the case of performing the tensile test in a vertical direction is greatly inferior. Consequently, even though the steel sheet has characteristics 5 of a good elongation in one direction and an excellent formability, it is difficult to apply to a member having a complicated shape. [0006]
On the other hand, hot-dip galvanized steel sheet and alloyed hot-dip galvanized steel sheet having excellent corrosion resistance has been known as a steel sheet for
10 automobile. The steel sheet is provided with a plated layer made of a zinc containing Fe of 15% or less on a surface of the steel sheet to have the excellent corrosion resistance. The hot-dip galvanized steel sheet and the alloyed hot-dip galvanized steel sheet are manufactured in a continuous-type hot-dip galvanizing line (hereinafter, referred to as a CGL) in many cases. In the CGL, the steel sheet is degreased, then is annealed by an
15 indirect heating with radiant tubes under a reducing atmosphere which contains H2 and N2, then is cooled to near a temperature of a galvanizing bath, and then is dipped in a hot-dip galvanizing bath. Thereafter, the steel sheet is subjected to a plating treatment. [0007]
In the case of manufacturing the alloyed hot-dip galvanized steel sheet, the steel
20 sheet is dipped in the galvanizing bath and is then re-heated, so that the galvanized layer is subjected to an alloying treatment. At this time, an in-rurnace atmosphere is an atmosphere at which Fe is reduced, and the steel sheet can be manufactured without oxidizing Fe, so that it is widely used as a manufacturing facility of a galvanized steel sheet.
25 However, Si is easily oxidized compared with Fe, and Si oxide is formed on the
surface of the steel sheet while passing through the CGL. The Si oxide is responsible for

4
galvanizing faults due to poor wettability with the hot-dip galvanizing. Alternatively,
since the oxide inhibits an alloying reaction of Fe and zinc, there has a problem in that the
alloyed hot-dip galvanized steel sheet cannot be manufactured.
[0008]
5 With respect to this problem, a method of achieving both of the excellent
formability and a plating property, in particular, a means of improving the plating property of steel containing Si in large amounts is disclosed in Patent Literature 1 in which annealing is performed once, then pickling is performed to remove the oxide on the surface of the steel sheet, and then the hot-dip galvanizing treatment is performed once again.
10 However, this method is undesirable in that the annealing of two times is performed, and thus the pickling after heat treatment and a passage of the galvanizing line leads to a significant increase of processes and an increase of cost. [0009]
As the means of improving the plating property of the steel containing Si, a
15 method of suppressing oxides of Si or Mn by making in-furnace atmosphere to be a reducing atmosphere of easily oxidizable elements such as Si and Mn or a method of reducing the formed oxides is disclosed in Patent Literature 2. In this method, pre-plating or surface grinding is performed on materials having a poor plating property prior to entering the galvanizing line. However, as a process of the pre-plating or the surface
20 grinding increases, the cost increases. In addition, since the high strength steel sheet generally contains Si and Mn in large amounts, it is difficult to achieve an atmosphere capable of reducing Si in the steel sheet containing Si of 0.5 wt% or more which is a target of the present invention, and thus huge facility investment is required, resulting in increasing the cost. In addition, since oxygen released from the reduced oxides of Si and
25 Mn changes the in-furnace atmosphere into an oxidizing atmosphere of Si, it is difficult to stabilize the atmosphere in the case of performing massive production. As a result, there

5
is a concern in that defects such as unevenness of plating wettability or alloying unevenness occur in a longitudinal direction or a width direction of the steel sheet. [0010]
As a means of achieving both of the excellent ductility and a plating property, 5 Patent Literature 3 discloses a method in which cold-rolling is performed, then the surface of the steel sheet is subjected to a pre-plating treatment with metals such as Ni, Fe, or Co and is subjected to a plating treatment while passing through a heat-treatment line. This relates to a method of pre-plating metals, which are difficult to oxidize compared with Si and Mn, on a surface layer of the steel sheet and manufacturing the steel sheet not
10 containing Si and Mn on the surface layer of the steel sheet. However, even when the surface of the steel sheet is subjected to the pre-plating treatment, these elements diffuse into the inside of the steel sheet during the heat treatment, and thus a large amount of pre-plating should be performed. Therefore, there is a problem in that the cost remarkably increases.
15 [0011]
As a means of solving these problems, Patent Literatures 4 to 6 propose a method in which Si oxide is not formed on the surface of the steel sheet but is formed inside the steel sheet. This can increase oxygen potential in the furnace and can oxidize Si inside the steel sheet to suppress diffusion of Si into the surface of the steel sheet and formation
20 of the Si oxide on the surface. [0012]
In addition, Patent Literatures 7 and 8 do not relate to TRIP steel but to galvanized steel sheet and disclose a method of setting the inside of the furnace to be the reducing atmosphere at an annealing process of CGL. Moreover, Patent Literature 9 discloses a
25 method of providing a jet flow of a predetermined flow rate in a galvanizing bath to prevent galvanizing faults by scum.

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However, the conventional techniques are extremely difficult to simultaneously
provide the corrosion resistance, the high strength, and the ductility.
[Prior Art Literature (s)]
[Patent Literature(s)] 5 [0013]
[Patent Literature 1] JP3521851B
[Patent Literature 2] JP 4-26720A
[Patent Literature 3] JP 3598087B
[Patent Literature 4] JP 2004-323970A 10 [Patent Literature 5] JP 2004-315960A
[Patent Literature 6] JP 2008-214752A
[Patent Literature 7] JP 2011 -111674A
[Patent Literature 8] JP 2009-030159A
[Patent Literature 9] JP2008-163388A 15 [Summary of the Invention]
[Problem(s) to Be Solved by the Invention]
[0014]
The present invention is to provide a high-strength hot-dip galvanized steel sheet
and a high-strength alloyed hot-dip galvanized steel sheet having excellent plating 20 adhesion and formability with ultimate tensile strength (TS) of 980 MPa or more.
[Means for Solving the Problem(s)]
[0015]
From the result obtained by an earnest examination, in order to achieve both of
the ultimate tensile strength (TS) of 980 MPa or more and the excellent formability, the 25 present inventors have found that it is important to fully utilize Si as a strengthening
element and to contain ferrite of 40% or more by volume fraction and a residual austenite

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of 8% or more by volume fraction. In addition, the inventors have found that even in a cold-rolled steel sheet containing a large amount of additive elements, it is possible to manufacture a steel sheet, in which anisotropy of a material is reduced and the formability is excellent, by controlling rough rolling and finishing rolling within a specific range. 5 [0016]
On the other hand, the plating property and alloying of the steel containing a large amount of Si were ensured by allowing the molten zinc to flow in a galvanizing bath at 10 to 50 m/min and suppressing a reaction between zinc oxide (scum) and the steel sheet which is responsible for galvanizing faults. In the case where the flow does not occur in
10 the bath, a fine zinc oxide is incorporated into a galvanized layer and the alloying reaction is inhibited.
In addition, the detailed mechanism is unclear, but when oxides of Si and Mn exist in the surface of the steel sheet, the galvanizing faults due to the zinc oxide and the alloying delay become more remarkable to have significantly an adverse influence on the
15 plating property. The suppression of the reaction between the scum and the steel sheet which is responsible for the galvanizing faults and the alloying delay also has a significant effect in facilitating the alloying process.
By the improvement of the plating property, it is possible to add a large amount of Si to the hot-dip galvanized steel sheet and the alloyed hot-dip galvanized steel sheet.
20 [0017]
The present invention relates to a high-strength hot-dip galvanized steel sheet and a high-strength alloyed hot-dip galvanized steel sheet having small material anisotropy and excellent formability with the ultimate tensile strength (TS) of 980 MPa or more and the gist thereof is as follows.
25 [0018]
[1] A high-strength hot-dip galvanized steel sheet having small material anisotropy

and excellent formability with an ultimate tensile strength of 980 MPa or more, the hot-dip galvanized steel sheet comprising a hot-dip galvanized layer formed on a surface of a base steel sheet,
wherein the base steel sheet contains: by mass%,
5 C: 0.1 to less than 0.40%;
Si: 0.5 to 3.0%;
Mn: 1.5 to 3.0%;
O: limited to 0.006% or less;
P: limited to 0.04% or less;
10 S: limited to 0.01% or less;
Al: limited to 2.0% or less;
N; limited to 0.01% or less; and
a balance including Fe and inevitable impurities,
a microstructure of the base steel sheet contains ferrite of 40% or more, residual 15 austenite of 8 to less than 60%, by volume fraction, and a balance being bainite or martensite,
an average value of pole densities of orientation groups {100} <011> to {223}
<110> represented by each of crystal orientations {100} <011>, {116} > {114}
<110>, {113} <110>, {112} , {335} <110>, and {223} <110> in a sheet thickness
20 range of 5/8 to 3/8 from the surface of the base steel sheet is 6.5 or less and a pole density
of a crystal orientation {332} <113> is 5.0 or less, and
the hot-dip galvanized layer contains Fe: less than 7 mass% and a balance
including Zn, Al, and inevitable impurities.
[0019]
25 [2] The high-strength hot-dip galvanized steel sheet having the small material
anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or

9
more according to [1], wherein the base steel sheet further contains one or two or more of: by mass%,
Cr: 0.05 to 1.0%;
Mo: 0.01 to 1.0%;
5 Ni: 0.05 to 1.0%;
Cu: 0.05 to 1.0%;
Nb: 0.005 to 0.3%;
Ti: 0.005 to 0.3%;
V: 0.005 to 0.5%; and
10 B: 0.0001 to 0.01%.
[0020]
[3] The high-strength hot-dip galvanized steel sheet having the small material
anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or more according to [1], wherein the base steel sheet further contains, by mass%, 0.0005 to 15 0.04% in total of one or two or more selected from Ca, Mg, and REM. [0021]
[4] A high-strength alloyed hot-dip galvanized steel sheet having small material
anisotropy and excellent formability with an ultimate tensile strength of 980 MPa or more, the alloyed hot-dip galvanized steel sheet comprising an alloyed hot-dip galvanized layer 20 formed on & surface of a base steel sheet,
wherein the base steel sheet contains: by mass%,
C: 0.10 to less than 0.4%;
Si: 0.5 to 3.0%;
Mn: 1.5 to 3.0%;
25 O: limited to 0.006% or less;
P: limited to 0.04% or less;

10
S: limited to 0.01% or less;
Al: limited to 2.0% or less;
N: limited to 0.01% or less; and
a balance including Fe and inevitable impurities,
5 a microstructure of the base steel sheet contains ferrite of 40% or more, residual
austenite of 8 to less than 60%, by volume fraction, and a balance being bainite or martensite,
an average value of pole densities of orientation groups {100} <011> to {223}
<110> represented by each of crystal orientations {100} <011>, {116} <110>, {114}
10 <110>, {113} <110>, {112} <110>, {335} <110>, and {223} <110> in a sheet thickness
range of 5/8 to 3/8 from the surface of the base steel sheet is 6.5 or less and a pole density
of a crystal orientation {332} <113> is 5.0 or less, and
the alloyed hot-dip galvanized layer contains Fe: 7 to 15 mass% and a balance including Zn, Al, and inevitable impurities. 15 [0022]
[5] The high-strength alloyed hot-dip galvanized steel sheet having the small material
anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or
more according to [4], wherein the base steel sheet further contains one or two or more of:
by mass%,
20 Cr: 0.05 to 1.0%;
Mo: 0.01 to 1.0%;
Ni: 0.05 to 1.0%;
Cu: 0.05 to 1.0%;
Nb: 0.005 to 0.3%;
25 Ti: 0.005 to 0.3%;
V: 0.005 to 0.5%; and

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B; 0.0001 to 0.01%. [0023]
[6] The high-strength alloyed hot-dip galvanized steel sheet having the small material
anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or 5 more according to [4], wherein the base steel sheet further contains, by mass%, 0.0005 to 0.04% in total of one or two or more selected from Ca, Mg, and REM. [0024]
[7] A manufacturing method of a high-strength hot-dip galvanized steel sheet having
small material anisotropy and excellent formability with an ultimate tensile strength of 980 10 MPa or more, the manufacturing method comprising:
with respect to a steel billet containing; by mass%,
C: 0.10 to less than 0.4%;
Si: 0.5 to 3.0%;
Mn: 1.5 to 3.0%;
15 O: limited to 0.006% or less;
P: limited to 0.04% or less;
S: limited to 0.01% or less;
Al: limited to 2.0% or less;
N: limited to 0.01% or less; and
20 a balance including Fe and inevitable impurities,
performing first hot rolling in which rolling at a reduction ratio of 40% or more is carried out one time or more at a temperature range of 1000°C or higher and 1200°C or lower;
setting an austenite grain diameter to 200 jam or less by the first hot rolling;
25 performing second hot rolling in which rolling at a reduction ratio of 30% or more
is carried out in one pass at least one time at a temperature region of Tl + 30°C or higher

12
and Tl + 200°C or lower determined by Expression (1) below;
setting a total reduction ratio in the second hot rolling to 50% or more;
performing a final reduction at a reduction ratio of 30% or more in the second hot rolling and then starting cooling before cold rolling in such a manner that a waiting time t 5 (second) satisfies Expression (2) below;
setting an average cooling rate to 50°C/second or more and a temperature change to be in a range of 40°C or higher and 140°C or lower in the cooling before cold rolling;
coiling at a temperature region of 700°C or lower;
performing cold rolling at a reduction ratio of 40% or more and 80% or less;
10 heating to an annealing temperature of 750°C or higher and 900°C or lower and
then annealing in a continuous hot-dip galvanizing line;
cooling to 500°C from the annealing temperature at 0.1 to 200°C/second; and
performing hot-dip galvanizing after holding for 10 to 1000 seconds between 500
and 350°C,
15 Tl (°C) = 850 + 10 x (C + N) x Mn + 350 x Nb + 250 x Ti + 40 x B + 10 x Cr +
100 x Mo + 100 x V - Expression (1)
where, C, N, Mn, Nb, Ti, B, Cr, Mo, and V each represent the content of each element (mass%, Ti, B, Cr, Mo, and V are calculated as zero when not being contained).
t < 2.5 x tl ■•■ Expression (2)
20 where, tl is obtained by Expression (3) below.
tl = 0.001 x ((Tf - Tl) x Pl/100)2 - 0.109 x ((Tf - Tl) x Pl/100) + 3.1 -Expression (3)
where, in Expression (3) above, Tf represents a temperature of the steel billet obtained after a final reduction at a reduction ratio of 30% or more, and PI represents a 25 reduction ratio of a final reduction at 30% or more. [0025]

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[8] The manufacturing method of the high-strength hot-dip galvanized steel sheet
having the small material amsotropy and the excellent formability with the ultimate tensile strength of 980 MPa or more according to [7], wherein the total reduction ratio in a temperature range below Tl + 30°C is 30% or less. 5 [0026]
[9] The manufacturing method of the high-strength hot-dip galvanized steel sheet
having the small material anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or more according to [7], wherein, in a case of heating to the annealing temperature in the continuous hot-dip galvanizing line, an average heating rate
10 of room temperature or higher and 650°C or lower is set to HRl (°C/second) expressed by Expression (4) below, and an average heating rate from a temperature exceeding 650°C to the annealing temperature is set to HR2 (°C/second) expressed by Expression (5) below. HRl >0.3-Expression(4) HR2 < 0.5 x HRl - Expression (5)
15 [0027]
[10] The manufacturing method of the high-strength hot-dip galvanized steel sheet having the small material anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or more according to [7], wherein when the hot-dip galvanizing is performed, a temperature of a base steel sheet is (temperature of hot-dip galvanizing bath -
20 40)°C or higher and (temperature of hot-dip galvanizing bath + 50)°C or lower. [0028]
[11] The manufacturing method of the high-strength hot-dip galvanized steel sheet having the small material anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or more according to [7], wherein a flow rate of 10 m/min or faster
25 and 50 m/min or slower is provided in a galvanizing bath when the hot-dip galvanizing is performed.

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[0029]
[12] A manufacturing method of a high-strength alloyed hot-dip galvanized steel sheet
having small material anisotropy and excellent formability with an ultimate tensile strength
of 980 MPa or more, the manufacturing method comprising:
5 with respect to a steel billet containing: by mass%,
C: 0.10 to less than 0.4%;
Si: 0.5 to 3.0%;
Mn: 1.5 to 3.0%;
O: limited to 0.006% or less;
10 P: limited to 0.04% or less;
S: limited to 0.01% or less;
Al: limited to 2.0% or less;
N: limited to 0.01% or less; and
a balance including Fe and inevitable impurities,
15 performing first hot rolling in which rolling at a reduction ratio of 40% or more is
carried out one time or more at a temperature range of 1000°C or higher and 1200°C or lower;
setting an austenite grain diameter to 200 jam or less by the first hot rolling; performing second hot rolling in which rolling at a reduction ratio of 30% or more 20 is earned out in one pass at least one time at a temperature region of Tl + 30°C or higher and Tl + 200°C or lower determined by Expression (1) below;
setting a total reduction ratio in the second hot rolling to 50% or more; performing a final reduction at a reduction ratio of 30% or more in the second hot rolling and then starting cooling before cold rolling in such a manner that a waiting time t 25 (second) satisfies Expression (2) below;
setting an average cooling rate to 50°C/second or more and a temperature change

15
to be in a range of 40°C or higher and 140°C or lower in the cooling before cold rolling;
coiling at a temperature region of 700°C or lower;
performing cold rolling at a reduction ratio of 40% or more and 80% or less;
heating to an annealing temperature of 750°C or higher and 900°C or lower and 5 then annealing in a continuous hot-dip galvanizing line;
cooling to 500°C from the annealing temperature at 0.1 to 200°C/second;
performing hot-dip galvanizing after holding for 10 to 1000 seconds between 500 and350°C;and
performing an alloying treatment at a temperature of 460°C or higher,
10 Tl (°C) = 850 + 10 x (C + N) x Mn + 350 x Nb + 250 x Ti + 40 x B + 10 x Cr +
100 x Mo + 100 x V - Expression (1)
where, C, N, Mn, Nb, Ti, B, Cr, Mo, and V each represent the content of each element (mass%, Ti, B, Cr, Mo, and V are calculated as zero when not being contained).
t < 2.5 x tl - Expression (2)
15 where, tl is obtained by Expression (3) below.
tl = 0.001 x ((Tf - Tl) x Pl/100)2 - 0.109 x ((Tf - Tl) x Pl/100) + 3.1 -Expression (3)
where, in Expression (3) above, Tf represents a temperature of the steel billet obtained after a final reduction at a reduction ratio of 30% or more, and PI represents a 20 reduction ratio of a final reduction at 30% or more. [0030]
[13] The manufacturing method of the high-strength alloyed hot-dip galvanized steel sheet having the small material anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or more according to [12], wherein the total reduction ratio in 25 a temperature range below Tl + 30°C is 30% or less. [0031]

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[14] The manufacturing method of the high-strength alloyed hot-dip galvanized steel sheet having the small material anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or more according to [12], wherein, in a case of heating to the annealing temperature in the continuous hot-dip galvanizing line, an average heating rate 5 of room temperature or higher and 650°C or lower is set to HRl (°C/second) expressed by Expression (4) below, and an average heating rate from a temperature exceeding 650°C to the annealing temperature is set to HR2 (°C/second) expressed by Expression (5) below. HRl > 0.3 - Expression (4) HR2 < 0.5 x HRl - Expression (5)
10 [0032]
[15] The manufacturing method of the high-strength alloyed hot-dip galvanized steel sheet having the small material anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or more according to [12], wherein when the hot-dip galvanizing is performed, a temperature of a base steel sheet is (temperature of hot-dip
15 galvanizing bath - 40)°C or higher and (temperature of hot-dip galvanizing bath + 50)°C or lower. [0033]
[16] The manufacturing method of the high-strength alloyed hot-dip galvanized steel sheet having the small material anisotropy and the excellent formability with the ultimate
20 tensile strength of 980 MPa or more according to [12], wherein a flow rate of 10 m/min or faster and 50 m/min or slower is provided in a galvanizing bath when the hot-dip galvanizing is performed. [Effect(s) of the Invention] [0034]
25 According to the present invention, the high-strength hot-dip galvanized steel
sheet and the high-strength alloyed hot-dip galvanized steel sheet having the small material

17
anisotropy and excellent formability with the ultimate tensile strength (TS) of 980 MPa or more, which is suitable for a structural member, a reinforcing member, and a suspension member of automobiles, are provided at a low cost. [Brief Description of the Drawing(s)] 5 [0035]
[FIG. 1] FIG. 1 is a diagram illustrating a relation between AE1 and an average value of pole densities of orientation groups {100} <011> to {223} <110>.
[FIG. 2] FIG. 2 is a diagram illustrating a relation between AE1 and a pole density
of an orientation {332} <113>.
10 [FIG. 3] FIG. 3 is an explanatory diagram of a continuous hot rolling line.
[Mode(s) for Carrying out the Invention] [0036]
From the result obtained by an earnest examination on the hot-dip galvanized steel sheet and the alloyed hot-dip galvanized steel sheet to solve the above problems, the 15 present inventors have found to exhibit the ultimate tensile strength of 980 MPa or more and the excellent formability when the primary phase of a microstructure of the base steel sheet is ferrite and the residual austenite is contained. In addition, the inventors have found that even in the steel sheet containing a large amount of Si and Mn, it is possible to manufacture the cold-rolled steel sheet having the small material anisotropy by controlling 20 the hot-rolled conditions within a specific range. Further, even in the steel sheet containing a large amount of Si, the plating wettability and the alloying are ensured by allowing the molten zinc to flow in the galvanizing bath. [0037]
Hereinafter, the present invention will be described in detail. 25 (Crystal orientation of base steel sheet)
An average value of pole densities of orientation groups {100} <011> to {223}

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<110> and a pole density of a crystal orientation {332} <113>, in a sheet thickness range of 5/8 to 3/8 from a surface of a base steel sheet are particularly important characteristic values in the present invention. As illustrated in FIG. 1, in the case of calculating the pole density of each orientation by performing an X-ray diffraction in the sheet thickness range 5 of 5/8 to 3/8 from the surface of the base steel sheet, when the average value of the pole density of the orientation groups {100} <011> to {223} <110> is 6.5 or less, a high strength steel sheet having small material anisotropy and excellent formability is obtained. The average value of the orientation groups {100} <011> to {223} <110> is preferably 4.0 or less.
10 [0038]
Orientations included in the orientation groups {100} <011> to {223} <110> are {100} <011>, {116} <110>, {114} <110>, {113} , {112} <110>, {335} <110>, and {223}<110>. [0039]
15 A steel sheet having large material anisotropy means a steel sheet in which AE1 [=
(L-El) - (C-El)], which is defined by a difference between a total elongation (L-El) in the case of performing a tensile test in a direction parallel to a rolling direction and a total elongation (C-El) in the case of performing the tensile test in a direction vertical to the rolling direction, exceeds 5%. A steel sheet containing a large amount of alloying
20 elements has large anisotropy due to the development of texture and has a small C-El in particular. As a result, even though the L-El is excellent, it is difficult to apply such a steel sheet to members to be machined in various directions. [0040]
In the present invention, the AE1 was less than 5%, but even though the difference
25 in the total elongation is less than -5%, the material anisotropy becomes large to deviate from the range of the present invention. However, generally, the above-described range

19
was considered from the fact that the texture develops and the C-El deteriorates.
Preferably, the AE1 is 3% or less.
[0041]
The pole density is synonymous with an X-ray random intensity ratio. The pole 5 density (X-ray random intensity ratio) is a numerical value obtained by measuring X-ray intensities of a standard sample not having accumulation in a specific orientation and a test sample using an X-ray diffraction method or the like under the same conditions and by dividing the X-ray intensity of the test sample by the X-ray intensity of the standard sample. The pole density is measured using X-ray diffraction, EBSD (Electron Back
10 Scattering Diffraction) or the like. In addition, the pole density can be measured by either an EBSP (Electron Back Scattering Pattern) method or an ECP (Electron Channeling Pattern) method. It may be obtained from a three-dimensional texture calculated by a vector method based on a pole figure of {110} or may be obtained from a three-dimensional texture calculated by a series expansion method using a plurality
15 (preferably, three or more) of pole figures out of pole figures of {110}, {100}, {211}, and {310}. [0042]
For example, for the pole density of each of the crystal orientations, each of intensities of (001) [1-10], (116) [1-10], (114) [1-10], (113) [1-10], (112) [1-10], (335)
20 [1-10], and (223) [1-10] at 2 = 45° cross-section in the three-dimensional texture (ODF) may be used as it is. [0043]
The average value of the pole densities of the orientation groups {100} <011> to {223} <110> is an arithmetic average of the pole density of each orientation. When all of
25 the intensities of these orientations are not obtained, the aritlimetic average of the pole density of each orientation {100} <011>, {116} <110>, {114} <110>, {112} <110>, or

20
{223} <110> may be used as a substitute.
[0044]
Similarly, as illustrated in FIG. 2, the pole density of the crystal orientation {332}
<113> in the sheet thickness range of 5/8 to 3/8 from the surface of the base steel sheet has 5 to be 5.0 or less. Preferably, the pole density may be 3.0 or less. When the pole density
of the crystal orientation {332} <113> is 5.0 or less, the AE1 is 5% or less and a steel sheet
for satisfying a relation of (ultimate tensile strength x total elongation > 16000 MPa x %)
is produced.
[0045]
10 The sample to be subjected to the X-ray diffraction may be measured while
adjusting the sample by the above-described method in such a manner that the steel sheet is
reduced in thickness from the surface to a predetermined sheet thickness by mechanical
polishing or the like, a strain is then removed by chemical polishing, electrolytic polishing
or the like, and an appropriate plane becomes a measuring plane in the sheet thickness 15 range of 3/8 to 5/8.
[0046]
As a matter of course, when the limitation relating to the above-described X-ray
intensity is satisfied not only near a center portion of the sheet thickness but also at as
many thickness portions as possible, the material anisotropy becomes further smaller. 20 However, the range of 3/8 to 5/8 from the surface of the steel sheet is measured to make it
possible to represent material properties of the entire steel sheet in general. Thus, 5/8 to
3/8 of the sheet thickness is defined as the measuring range.
[0047]
Further, the crystal orientation represented by {hkl} means that the normal 25 direction of a steel sheet plane is parallel to and a rolling direction is parallel to
. With respect to the crystal orientation, normally, orientations vertical to the sheet

21
plane are represented by [hkl] or {hkl} and orientations parallel to the rolling direction are represented by (uvw) or . {hkl} and are collective terms for equivalent planes, [hkl] and (uvw) represent individual crystal planes. That is, since a body-centered cubic structure is applied to the present invention, for example, (111), (-111), (1-H), (11-1), 5 (-1-11), (-11-1), (1-1-1), and (-1-1-1) planes are equivalent and cannot be distinguished from each other. In such a case, these orientations are collectively called {111}. Since an ODF representation is also used for representing orientations of other low symmetric crystal structures, individual orientations are generally represented by [hkl] (uvw), but, in the present invention, [hkl] (uvw) and {hkl} are synonymous with each other.
10 The measurement of the crystal orientation by an X-ray is performed according to a method disclosed in, for example, Cullity, Theory of X-ray diffraction (issued in 1986, translated by MATSUMURA, Gentaro, published by AGNE Inc.) on pages 274 to 296. [0048]
In the present invention, the anisotropy was estimated using the total elongation in
15 the tensile test, but the same anisotropy also occurs in the steel sheet, in which the texture is developed, with respect to uniform elongation or bendability. In the steel sheet of the present invention, therefore, the anisotropy of the bendability or uniform elongation is also small.
In the present invention, the excellent formability means that a steel sheet satisfies
20 the relation of (ultimate tensile strength x total elongation (C-El) > 16000 MPa-%) represented by the product of the ultimate tensile strength and the total elongation in the direction vertical to the rolling direction. The formability is preferably 18000 MPa-% or more and is more preferably 20000 MPa-% or more. [0049]
25 (Microstructure of base steel sheet)
Next, a microstructure of the base steel sheet will be described.

22
In the present invention, the base steel sheet is provided such that a primary phase is a ferrite of 40% or more by volume fraction and a residual austenite is dispersed with 8% or more and less than 60% by volume fraction to ensure the ultimate tensile strength of 980 MPa or more and excellent formability. Thus, it is necessary to contain the residual 5 austenite. Moreover, the ferrite phase may be a form of an acicular ferrite in addition to a polygonal ferrite. [0050]
By using the primary phase as the ferrite, a ferrite having high ductility becomes the primary phase, and thus the ductility is improved. By containing the residual
10 austenite as a second phase, high strengthening and the further improvement of the ductility are achieved at the same time. When the residual austenite is less than 8% by volume fraction, since the effect is difficult to obtain, a lower limit of the residual austenite is 8%. A bainite structure is inevitably contained to stabilize of the residual austenite. In order to achieve the further high strengthening, martensite may be contained. In
15 addition, when the volume fraction is less than 10%, a pearlite structure may be contained. [0051]
Furthermore, each phase of the microstructures such as ferrite, martensite, bainite, austenite, pearlite, and residual structures can be identified and their locations and volume fraction can be observed and quantitatively measured using an optical microscope having a
20 magnification of 1000 times and a scanning and transmission electron microscope having a magnification of 1000 times to 100000 times after a cross section of the steel sheet in a rolling direction or a cross section in the right angle direction of the rolling direction is etched using a Nital reagent and the reagent as disclosed in JP 59-219473A. The area fraction of each structure can be obtained by each observing 20 or more fields and
25 applying the point-count method or image analysis. Then, the obtained area fraction is defined as the volume fraction of each structure.

23
[0052]
(Chemical composition of base steel sheet)
Next, reasons for restricting the amounts of the composition will be described. Moreover, % means % by mass. In the present invention, the base steel sheet contains, by 5 mass %, C: 0.1 to less than 0.40%, Si: 0.5 to 3.0%, and Mn: 1.5 to 3.0%, O: limited to 0.006% or less, P: limited to 0.04% or less, S: limited to 0.01% or less, Al: limited to 2.0% or less, N: limited to 0.01% or less, and a balance including Fe and inevitable impurities. [0053]
C: C is an element which can increase the strength of the steel sheet. However,
10 when the content is less than 0.1%, it is difficult to achieve both of the tensile strength of 980 MPa or more and the workability. On the other hand, when the content exceeds 0.40%, it is difficult to ensure the spot weldability. For this reason, the range is limited to 0.1 to 0.40% or less. [0054]
15 Si: Si is a strengthening element and is effective for increasing the strength of the
steel sheet. The addition is essential because of suppressing precipitation of cementite and contributing to stabilizing the residual austenite. However, when the content is less than 0.5%, the effect of high strengthening is small. On the other hand, when the content exceeds 3.0%, the workability is decreased. Accordingly, the content of Si is limited to
20 the range of 0.5 to 3.0%. [0055]
Mn: Mn is a strengthening element and is effective for increasing the strength of the steel sheet. However, when the content is less than 1.5%, it is difficult to obtain the tensile strength of 980 MPa or more. Conversely, when the content is a large quantity, it
25 facilitates co-segregation with P and S and leads to a remarkable deterioration in the workability, and thus the upper limit is 3.0%. More preferably, the range is 2.0 to 2.7%.

24
[0056]
0: 0 forms oxides to cause a deterioration in the bendability and hole expandability, and thus it is necessary to restrict an additive amount. In particular, the oxides often exist in the form of inclusions, and when these exist in a punched out edge or 5 a cut cross-section, then notch-like surface defects or coarse dimples may form at the edge surface. As a result, stress concentration tends to occur during hole expansion or large deformation process, which can then act as an origin for crack formation; therefore, dramatic deterioration in the hole expandability and bendability occurs. When the content of 0 exceeds 0.006%, then these tendencies become remarkable, and therefore the
10 upper limit of the content of O is 0.006% or less. When the content is less than 0.0001%, the cost excessively increases and thus it is undesirable economically. Accordingly, this value is a substantial lower limit. [0057]
P: P tends to segregate at the center part of thickness of the steel sheet and causes
15 the weld zone to become brittle. When the content exceeds 0.04%, the embrittlement of the weld zone becomes remarkable, so the suitable range is limited to 0.04% or less. The lower limit value of P is not particularly determined, but when the lower limit is less than 0.0001%, it is disadvantageous economically, so this value is preferably set to the lower limit value.
20 [0058]
S: S has an adverse effect on the weldability and on the manufacturability at the time of casting and hot rolling. For this reason, the upper limit value was 0.01% or less. The lower limit value of S is not particularly determined, but when the lower limit is less than 0.0001%, it is disadvantageous economically, so this value is preferably set to the
25 lower limit value. Since S combines with Mn to form coarse MnS, which deteriorates the bendability and the hole expandability, the content of S is necessary to reduce as much as

25
possible.
[0059]
Al: Al promotes the formation of ferrite, which improves the ductility, and may
therefore be added. Furthermore, Al can also act as a deoxidizing material. However, 5 excessive addition increases the number of Al-based coarse inclusions, which can cause the
deterioration in hole expandability as well as surface defects. For this reason, the upper
limit for the Al addition is 2.0%. Preferably, the upper limit is 0.05% or less. The lower
limit is not particularly limited, but it is difficult to set to be less than 0.0005%, so this
value is a substantial lower limit. 10 [0060]
N: N forms coarse nitrides and causes the deterioration of the bendability and hole
expandability, so it is necessary to restrict the additive amount. This is because when the
content of N exceeds 0.01%, the above tendency becomes remarkable, so the content of N
is in a range of 0.01% or less. In addition, this causes blowholes to occur at the time of 15 welding, so the less the better. The effect of the present invention is exhibited without
particularly limiting the lower limit, but when the content of N is less than 0.0005%, the
manufacturing cost dramatically increases, so this value is a substantial lower limit.
[0061]
In the present invention, the base steel sheet may further contain any one or two or 20 more of the following elements which are conventionally used for, for example, strength
enhancement.
[0062]
Mo: Mo is a strengthening element and is important for improvement of
hardenability. However, when the content is less than 0.01%, these effects cannot be 25 obtained, so the lower limit value was 0.01%. Conversely, when the content exceeds 1%,
it has an adverse effect on the manufacturability at the time of manufacturing and hot

26
rolling, so the upper limit value was 1%.
[0063]
Cr: Cr is a strengthening element and is important for improvement of
hardenability. However, when the content is less than 0.05%, these effects cannot be 5 obtained, so the lower limit value was 0.05%. Conversely, when the content exceeds 1%,
it has an adverse effect on the manufacturability at the time of manufacturing and hot
rolling, so the upper limit value was 1%.
[0064]
Ni; Ni is a strengthening element and is important for improvement of 10 hardenability. However, when the content is less than 0.05%, these effects cannot be
obtained, so the lower limit value was 0.05%. Conversely, when the content exceeds 1%,
it has an adverse effect on the manufacturability at the time of manufacturing and hot
rolling, so the upper limit value was 1%. In addition, it may be added to cause the
improvement of the wettability and the promotion of the alloying reaction. 15 [0065]
Cu: Cu is a strengthening element and is important for improvement of
hardenability. However, when the content is less than 0.05%, these effects cannot be
obtained, so the lower limit value was 0.05%. Conversely, when the content exceeds 1%,
it has an adverse effect on the manufacturability at the time of manufacturing and hot 20 rolling, so the upper limit value was 1%. In addition, it may be added to cause the
improvement of the wettability and the promotion of the alloying reaction.
[0066]
B is effective for grain boundary strengthening and steel strengthening by addition
of 0.0001 mass% or more, but when the additive amount thereof exceeds 0.01 mass%, not 25 only the effect of addition becomes saturated, but the manufacturability at the time of hot
rolling is decreased, so the upper limit thereof was 0.01%.

27
[0067]
Ti: Ti is a strengthening element. It helps to increase the strength of the steel sheet through precipitate strengthening, grain-refining strengthening due to the growth inhibition of ferrite crystal grains, and dislocation strengthening due to the inhibition of 5 recrystallization. When the additive amount is less than 0.005%, these effects cannot be obtained, so the lower limit value was 0.005%. When the content exceeds 0.3%, carbonitride precipitation increases and the formability tends to deteriorate, so the upper limit was 0.3%. [0068]
10 Nb: Nb is a strengthening element. It helps to increase the strength of the steel
sheet through the precipitate strengthening, the grain-refining strengthening due to the growth inhibition of ferrite crystal grains, and the dislocation strengthening due to the inhibition of recrystallization. When the additive amount is less than 0.005%, these effects cannot be obtained, so the lower limit value was 0.005%. When the content
15 exceeds 0.3%, the carbonitride precipitation increases and the formability tends to deteriorate, so the upper limit was 0.3%. [0069]
V: V is a strengthening element. It helps to increase the strength of the steel sheet through the precipitate strengthening, the grain-refining strengthening due to the
20 growth inhibition of ferrite crystal grains, and the dislocation strengthening due to the inhibition of recrystallization. When the additive amount is less than 0.005%, these effects cannot be obtained, so the lower limit value was 0.005%. When the content exceeds 0.5%, the carbonitride precipitation increases and the formability tends to deteriorate, so the upper limit was 0.5%.
25 [0070]
One or two or more elements selected from Ca, Mg, and REM may be added by

28
0.0005 to 0.04% in total. Ca, Mg, and REM are elements used for deoxidation and one or two or more elements of 0.0005% or more are preferably contained in total. REM indicates a rare earth metal. However, when the content exceeds 0.04% in total, this may cause deterioration of the formability. Therefore, the total content of the elements is 5 0.0005 to 0.04%. Further, in the present invention, REM is generally added in a mischmetal, which in addition to La and Ce may also contain other lanthanoid series elements in combination. The effects of the present invention are exhibited even when the lanthanoid series elements other than La and Ce are contained as inevitable impurities. However, the effects of the present invention are exhibited even when metals such as La
10 and Ce are added. [0071] (Chemical composition of hot-dip galvanized layer and alloyed hot-dip galvanized layer)
In the present invention, a hot-dip galvanized layer formed on the surface of the base steel sheet contains less than 7 mass% Fe, the balance being Zn, Al, and inevitable
15 impurities. In addition, an alloyed hot-dip galvanized layer contains 7 to 15 mass% Fe, and the balance being Zn, Al, and inevitable impurities. Further, when the base steel sheet is subjected to a hot-dip galvanizing treatment by dipping in a hot-dip galvanizing bath, a hot-dip galvanized layer containing less than 7 mass% Fe is formed on the surface of the base steel sheet. In addition, after the galvanizing treatment, when an alloying
20 treatment is subsequently performed, an alloyed hot-dip galvanized layer containing 7 to 15 mass% Fe is formed on the surface of the base steel sheet.
Depending on the presence or absence of the alloying treatment, the galvanized layer is formed of zinc or an alloy of Fe-zinc. Zinc oxide may be contained in the surface of the galvanized layer, but when the content (%) of Fe contained in the galvanized layer is
25 within a range of the present invention, the effect of the present invention can be obtained. In addition, since the base steel sheet of the present invention contains Si, Mn, or Al, even

29
though the oxide formed during the annealing may exist in a boundary between the base
steel sheet and the galvanized layer or exist in the galvanized layer, the effect of the present
invention is exhibited in either case.
[0072]
5 In the case where spot weldability and a coating property are desired, it is possible
to improve these properties by forming the alloyed hot-dip galvanized layer containing 7 to 15 mass% Fe on the surface of the base steel sheet. Specifically, when the base steel sheet is subjected to the alloying treatment after being dipped in the galvanizing bath, Fe is incorporated into the galvanized layer, and thus the high-strength alloyed hot-dip
10 galvanized steel sheet having an excellent coating property and spot weldability can be obtained. When the content of Fe after the alloying treatment is less than 7 mass%, the spot weldability becomes insufficient. On the other hand, when the content of Fe exceeds 15 mass%, the adhesion of the galvanized layer itself is impaired, and the galvanized layer is broken and fractured and dropped out in machining, thereby causing scratches when
15 forming by adhering to a mold. Accordingly, the content of Fe contained in the galvanized layer during the alloying treatment is within a range of 7 to 15 mass%. [0073]
Further, in a case where the alloying treatment is not performed, even when the content of Fe contained in the galvanized layer is less than 7 mass%, the corrosion
20 resistance, the formability, and hole expandability which are effects obtained by the alloying are good except for the spot welding. [0074]
Further, the galvanized layer may contain AI, Mg, Mn, Si, Cr, Ni, Cu or the like in addition to Fe.
25 [0075]
In order to measure the content of Fe and Al contained in the galvanized layer, a

30
method of dissolving the galvanized layer with an acid and chemically analyzing the dissolved solution may be used. For example, with respect to the alloyed hot-dip galvanized steel sheet cut into 30 mm x 40 mm, only the galvanized layer is dissolved while suppressing elution of the base steel sheet with an inhibitor-added 5% HC1 aqueous 5 solution. Then, the content of Fe and Al is quantified using signal intensities obtained by ICP emission analysis of the dissolved solution and a calibration curve prepared from concentration-known solutions. Further, in consideration of measured variation of samples, an average value is employed obtained by measuring at least three samples which are cut out from the same alloyed hot-dip galvanized steel sheet.
10 [0076]
The coated amount of the plating is not particularly limited, but is preferably 5 g/m or more in the coated amount on a single surface of the base steel sheet from the viewpoint of corrosion resistance. In addition, the coated amount on the single surface is preferably no greater than 100 g/m from the viewpoint of ensuring the plating adhesion.
15 [0077]
(Manufacturing method of steel sheet)
In order to obtain a steel sheet having a small material anisotropy of 980 MPa or more in the present invention, it is important to provide a steel sheet in which formation of a specific texture is suppressed. Hereinafter, details of manufacturing conditions will be
20 described to simultaneously satisfy these factors. [0078]
A manufacturing method prior to hot rolling is not limited in particular. That is, subsequently to melting by a shaft furnace, an electric, furnace, or the like, secondary refining may be variously performed, and then casting may be performed by normal
25 continuous casting, or by an ingot method, or further by thin slab casting, or the like. In the case of a continuous casting, it is possible that a continuous cast slab is once cooled

31
down to low temperature and thereafter is reheated to then be subjected to hot rolling, or it
is also possible that a continuous cast slab is subjected to hot rolling continuously. A
scrap may also be used for a raw material of the steel.
[0079] 5 (First hot rolling)
A slab extracted from a heating furnace is subjected to a rough rolling process
being first hot rolling to be rough rolled, and thereby a rough bar is obtained. The present
inventive steel sheet needs to satisfy the following requirements. First, an austenite grain
diameter after the rough rolling, namely an austenite grain diameter before finish rolling is 10 important. The austenite grain diameter before the finish rolling is desirably small, and
the austenite grain diameter of 200 um or less greatly contributes to making crystal grains
fine and homogenization of crystal grains.
[0080]
In order to obtain the austenite grain diameter of 200 um or less before the finish 15 rolling, it is necessary to perform rolling at a reduction ratio of 40% or more one time or
more in the rough roiling in a temperature region of 1000 to 1200°C.
[0081]
The austenite grain diameter before the finish rolling is desirably 160 um or less
or 100 \xm or less, and in order to obtain this grain diameter, rolling at 40% or more is 20 performed two times or more. However, in the rough rolling, when the reduction is
greater than 70% or rolling is performed greater than 10 times, there is a concern in that the
rolling temperature decreases or a scale is generated excessively.
[0082]
It is supposed that an austenite grain boundary after the rough rolling (namely, 25 before the finish rolling) functions as one of recrystallization nuclei during the finish
rolling. The austenite grain diameter after the rough rolling is confirmed in a manner that

32
a steel sheet piece before being subjected to the finish rolling is quenched as much as possible, (which is cooled at 10°C/second or more, for example), and a cross section of the steel sheet piece is etched to make austenite grain boundaries appear, and the austenite grain boundaries are observed by an optical microscope. On this occasion, at 50 or more 5 magnifications, the austenite grain diameter of 20 visual fields or more is measured by image analysis or a point counting method. [0083] (Second hot rolling)
After the rough rolling process (first hot rolling) is completed, a finish rolling
10 process being second hot rolling is started. The time between the completion of the rough rolling process and the start of the finish rolling process is desirably set to 150 seconds or shorter. [0084]
In the finish rolling process (second hot rolling), a finish rolling start temperature
15 is desirably set to 1000°C or higher. When the finish rolling start temperature is lower than 1000°C, at each finish rolling pass, the temperature of the rolling to be applied to the rough bar to be rolled is decreased, the reduction is performed in a non-recrystallization temperature region, the texture develops, and thus the isotropy deteriorates. [0085]
20 Incidentally, the upper limit of the finish rolling start temperature is not limited in
particular. However, when it is 1150°C or higher, a blister to be the starting point of a scaly spindle-shaped scale defect is likely to occur between a steel sheet base iron and a surface scale before the finish rolling and between passes, and thus the finish roiling start temperature is desirably lower than 1150°C.
25 [0086]
In the finish rolling, a temperature determined by the chemical composition of the

33
steel sheet is set to Tl, and in a temperature region of Tl + 30°C or higher and Tl + 200°C or lower, the rolling at 30% or more is performed in one pass at least one time. Further, in the finish rolling, the total reduction ratio is set to 50% or more. By satisfying this condition, at the range of 5/8 to 3/8 in sheet thickness from the surface of the steel sheet, 5 the average value of the pole densities of the orientation groups {100} <011> to {223} <110> becomes 6.5 or less and the pole density of the crystal orientation {332} <113> becomes 5.0 or less. Thus, the high strength steel sheet having the small material anisotropy can be obtained. [0087]
10 Here, Tl is the temperature calculated by Expression (1) below.
Tl (°C) - 850 + 10 x (C + N) x Mn + 350 x Nb + 250 x Ti + 40 x B + 10 x Cr + 100 x Mo + 100 x V - Expression (1)
C, N, Mn, Nb, Ti, B, Cr, Mo, and V each represent the content of each element (mass%). Further, Ti, B, Cr, Mo, and V are calculated as zero when not being contained
15 [0088]
Heavy reduction in the temperature region of Tl + 30°C or higher and Tl + 150°C or lower and light reduction at equal to or higher than Tl and lower than Tl + 30°C thereafter control the average value of the pole densities of the orientation groups {100} <011> to {223} <110> and the pole density of the crystal orientation {332} <113> at the
20 range of 5/8 to 3/8 in sheet thickness from the surface of the steel sheet, and thereby the material anisotropy of the final product are drastically improved, as indicated Tables 2 and 3 of Example to be described later. [0089]
This Tl temperature itself is obtained empirically. The present inventors learned
25 empirically by experiments that the recrystallization in an austenite region of each steel is promoted based on the Tl temperature. In order to obtain better material uniformity, it is

34
important to accumulate strain by the heavy reduction, and the total reduction ratio of 50% or more is essential in the finish rolling. Further, it is desired to take reduction at 70% or more, and on the other hand, when the reduction ratio greater than 90% is taken, securing a temperature and an excessive rolling load are as a result added. 5 [0090]
When the total reduction ratio in the temperature region of Tl + 30°C or higher and Tl + 200°C or lower is less than 50%, rolling strain to be accumulated during the hot rolling is not sufficient and the recrystallization of austenite does not advance sufficiently. Therefore, the texture develops and the isotropy deteriorates. When the total reduction
10 ratio is 70% or more, the sufficient isotropy can be obtained even though variations ascribable to temperature fluctuation or the like are considered. On the other hand, when the total reduction ratio exceeds 90%, it becomes difficult to obtain the temperature region of Tl + 200°C or lower due to heat generation by working, and further a rolling load increases to cause a risk that the rolling becomes difficult to be performed
15 [0091]
In the finish rolling, in order to promote the uniform recrystallization caused by releasing the accumulated strain, the rolling at 30% or more is performed in one pass at least one time at Tl + 30°C or higher and Tl + 200°C or lower. [0092]
20 Incidentally, in order to accelerate uniform recrystallization through releasing of
accumulated strain, it is necessary to suppress as much as possible the working amount in a temperature range of lower than Tl + 30°C after the heavy reduction at Tl + 30°C or higher and Tl + 200°C or lower. For this reason, the reduction ratio at lower than Tl 4-30°C is desirably 30% or less. The reduction ratio of 10% or more is desirable in terms
25 of improving the sheet shape, but a reduction ratio of 0% is desirable in the case where the hole expandability is further focused. In addition, when the reduction ratio at less than Tl

35
+ 30°C is large, recrystallized austenite grains are expanded, and, when a retention time
after the finish rolling is short, recrystallization does not sufficiently proceed, and the
material anisotropy becomes large. That is, in the manufacturing conditions of the
present invention, when the austenite is uniformly and finely recrystallized in the finish 5 rolling, the texture of the product is controlled and the material anisotropy is improved.
[0093]
A rolling ratio can be obtained by actual performances or calculation from the
rolling load, sheet thickness measurement, or/and the like. The temperature can be
actually measured by a thermometer between stands, or can be obtained by calculation 10 simulation in consideration of the heat generation by working from a line speed, the
reduction ratio or the like. Alternatively, it is possible to be obtained by both of them.
[0094]
The hot rolling (first hot rolling and second hot rolling) performed as described
above is finished at a temperature of AQ transformation temperature or higher. When the 15 hot rolling is finished at Ai*3 or lower, the hot rolling becomes two-phase region rolling of
austenite and ferrite, and accumulation to the orientation groups {100} <011> to {223}
becomes strong. As a result, the material anisotropy is promoted.
[0095]
(Cooling before cold-rolling)
20 After final reduction at a reduction ratio of 30% or more is performed in the finish
rolling, a cooling before cold-rolling is started in such a manner that a waiting time t
second satisfies Expression (2) below.
t < 2.5 x tl - Expression (2)
Here, tl is obtained by Expression (3) below.
25 tl - 0.001 x ((Tf - Tl) x Pl/100)2 - 0.109 x ((Tf - Tl) x Pl/100) + 3.1 -
Expression (3)

36
Here, in Expression (3) above, Tf represents the temperature of a steel billet
obtained after the final reduction at a reduction ratio of 30% or more, and PI represents the
reduction ratio of the final reduction at 30% or more.
[0096]
5 Incidentally, the "final reduction at a reduction ratio of 30% or more" indicates the
rolling performed finally in the rolling processes whose reduction ratio becomes 30% or more out of the rolling processes in a plurality of passes performed in the finish rolling. For example, in the rolling processes in a plurality of passes performed in the finish rolling, when the reduction ratio of the rolling performed at the final stage is 30% or more, the
10 rolling performed at the final stage is the "final reduction at a reduction ratio of 30% or more." Further, in the rolling processes in a plurality of passes performed in the finish rolling, when the reduction ratio of the rolling performed prior to the final stage is 30% or more and after the rolling performed prior to the final stage (rolling at a reduction ratio of 30% or more) is performed, the rolling whose reduction ratio becomes 30% or more is not
15 performed, the rolling performed prior to the final stage (rolling at a reduction ratio of 30% or more) is the "final reduction at a reduction ratio of 30% or more." [0097]
In the finish rolling, after the final reduction at a reduction ratio of 30% or more is performed, the waiting time t second until the cooling before cold-rolling is started greatly
20 affects the austenite grain diameter and strongly affects the structure after cold rolling and annealing. When the waiting time t exceeds tl x 2.5, grain coarsening is progressed and the elongation is remarkably reduced. [0098]
The waiting time t second further satisfies Expression (2a) below, thereby making
25 it possible to preferentially suppress the growth of the crystal grains. Consequently, even though the recrystallization does not advance sufficiently, it is possible to sufficiently

37
improve the elongation of the steel sheet and to improve a fatigue property simultaneously.
t < tl ■•• Expression (2a) [0099]
At the same time, the waiting time t second further satisfies Expression (2b) below, 5 and thus the recrystallization advances sufficiently and the crystal orientations are randomized. Therefore, it is possible to sufficiently improve the elongation of the steel sheet and to greatly improve the isotropy simultaneously.
tl < t < tl x 2.5 - Expression (2b)
[0100]
10 Here, as illustrated in FIG. 3, on a continuous hot rolling line 1, the steel billet
(slab) heated to a predetermined temperature in the heating furnace is rolled in a roughing mill 2 and in a finishing mill 3 sequentially to be a hot-rolled steel sheet 4 having a predetermined thickness, and the hot-rolled steel sheet 4 is carried out onto a run-out-table 5. In the manufacturing method of the present invention, in the rough rolling process 15 (first hot rolling) performed in the rougiiing mill 2, the rolling at a reduction ratio of 40% or more is performed on the steel billet (slab) one time or more in the temperature range of 1000°C or nigher and 1200°C or lower. [0101]
The rough bar rolled to a predetermined thickness in the roughing mill 2 in this 20 manner is next finish rolled (is subjected to the second hot rolling) through a plurality of rolling stands 6 of the finishing mill 3 to be the hot-rolled steel sheet 4. Then, in the finishing mill 3, the rolling at 30% or more is performed in one pass at least one time in the temperature region of Tl + 30°C or higher and Tl 4- 200°C or lower. Further, in the finishing mill 3, the total reduction ratio becomes 50% or more. 25 [0102]
Further, in the finish rolling process, after the final reduction at a reduction ratio

38
of 30% or more is performed, the cooling before cold-rolling is started in such a manner that the waiting time t second satisfies Expression (2) above or either Expression (2a) or (2b) above. The start of this cooling before cold-rolling is performed by inter-stand cooling nozzles 10 disposed between the respective two of the rolling stands 6 of the 5 finishing mill 3, or cooling nozzles 11 disposed in the run-out-table 5. [0103]
For example, when the final reduction at a reduction ratio of 30% or more is performed only at the rolling stand 6 disposed at the front stage of the finishing mill 3 (on the left side in FIG. 3, on the upstream side of the rolling) and the rolling whose reduction
10 ratio becomes 30% or more is not performed at the rolling stand 6 disposed at the rear stage of the finishing mill 3 (on the right side in FIG. 3, on the downstream side of the rolling), when the start of the cooling before cold-rolling is performed by the cooling nozzles 11 disposed in the run-out-table 5, a case where the waiting time t second does not satisfy Expression (2) above or Expressions (2a) and (2b) above is sometimes caused. In
15 such a case, the cooling before cold-rolling is started by the inter-stand cooling nozzles 10 disposed between the respective two of the rolling stands 6 of the finishing mill 3. [0104]
Further, for example, when the final reduction at a reduction ratio of 30% or more is performed at the rolling stand 6 disposed at the rear stage of the finishing mill 3 (on the
20 right side in FIG. 3, on the downstream side of the rolling), even though the start of the cooling before cold-rolling is performed by the cooling nozzles 11 disposed in the run-out-table 5, there is sometimes a case where the waiting time t second can satisfy Expression (2) above or Expressions (2a) and (2b) above. In such a case, the cooling before cold-rolling may also be started by the cooling nozzles 11 disposed in the
25 run-out-table 5. Needless to say, as long as the performance of the final reduction at a reduction ratio of 30% or more is completed, primary cooling before cold-rolling may be

39
also started by the inter-stand cooling nozzles 10 disposed between the respective two of
the rolling stands 6 of the finishing mill 3.
[0105]
Then, in this cooling before cold-rolling, the cooling that at an average cooling 5 rate of 50°C/second or more, a temperature change (temperature drop) becomes 40°C or higher and 140°C or lower is performed. [0106]
When the temperature change is less than 40°C, the recrystallized austenite grains grow and low-temperature toughness deteriorates. The temperature change is set to 40°C
10 or more, thereby making it possible to suppress coarsening of the austenite grains. When the temperature change is less than 40°C, the effect cannot be obtained. On the other hand, when the temperature change exceeds 140°C, the recrystallization becomes insufficient to make it difficult to obtain a targeted random texture. Further, a ferrite phase effective for the elongation is also not obtained easily and the hardness of a ferrite
15 phase becomes high, and thereby the formability also deteriorates. Further, when the temperature change is higher than 140°C, an overshoot to/below an Ar3 transformation point temperature is likely to be caused. In the case, even by the transformation from recrystallized austenite, as a result of sharpening of variant selection, the texture is formed and the isotropy decreases consequently.
20 [0107]
When the average cooling rate in the cooling before cold-rolling is slower than 50°C/second, as expected, the recrystallized austenite grains grow and the low-temperature toughness deteriorates. The upper limit of the average cooling rate is not determined in particular, but in terms of the steel sheet shape, 200°C/second or less is considered to be
25 proper. [0108]

40
In addition, as has been described previously, in order to promote the uniform recrystallization, it is preferable that a working amount at a temperature region of lower than Tl + 30°C be as small as possible and the reduction ratio at the temperature region lower than Tl + 30°C be 30% or less. For example, in the finishing mill 3 of the 5 continuous hot rolling line 1 illustrated in FIG. 3, when passing through one or two or more rolling stands 6 disposed at the front-stage side (the left side in FIG. 3, the upstream side of the rolling), the steel sheet is in a temperature region of Tl + 30°C or higher and Tl + 200°C or lower, and when passing through one or two or more rolling stands 6 disposed at the rear-stage side (the right side in FIG. 3, the downstream side of the rolling), the steel
10 sheet is in a temperature region lower than Tl + 30°C. When passing through one or two or more rolling stands 6 disposed at the rear-stage side (the right side in FIG. 3, the downstream side of the rolling), the reduction is not performed, or even though the reduction is performed, the reduction ratio at lower than Tl + 30°C is preferably 30% or less in total. In terms of the sheet thickness accuracy and the sheet shape, the reduction
15 ratio at lower than Tl + 30°C is preferably 10% or less in total. In the case of requiring a more isotropy, the reduction ratio at the temperature region lower than Tl + 30°C is preferably 0%. [0109]
In the manufacturing method of the present invention, a rolling speed is not
20 limited in particular. However, when the rolling speed on the final stand side of the finish rolling is less than 400 mpm, y grains grow to be coarse, regions in which ferrite can be precipitated to obtain the ductility are decreased, and thus the ductility is likely to deteriorate. Even though the upper limit of the rolling speed is not limited in particular, the effect of the present invention can be obtained, but it is realistic that the rolling speed is
25 1800 mpm or less due to facility restriction. Therefore, in the finish rolling process, the rolling speed is preferably 400 mpm or more and 1800 mpm or less. Further, in the hot

41
rolling, the finishing rolling may be continuously performed by joining the sheet bar
(rough bar) after the rough rolling. At this time, the rough bar is once coiled in a coil
shape and is stored in a cover having a thermal insulation function as required. Then, the
rough bar may be joined after being again re-coiled. 5 [0110]
(Coiling)
After being obtained in this manner, the hot-rolled steel sheet can be coiled at
700°C or lower. When a coiling temperature exceeds 700°C, a coarse ferrite or pearlite
structure occurs in the hot-rolled structure and structural unhomogeneity after annealing 10 increases. As a result, the material anisotropy of the final product is increased. In
addition, when the hot-rolled steel sheet is coiled at a temperature exceeding 700°C, a
thickness of oxide formed on the surface of the steel sheet excessively increases and it is
difficult to perform the pickling. Even though the lower limit of the coiling temperature
is not defined in particular, the effects of the present invention are exhibited. However, 15 since it is technically difficult to coil at a temperature of room temperature or lower, the
room temperature is substantially the lower limit.
[0111]
(Pickling)
Pickling is performed on the hot-rolled steel sheet prepared in this manner. The 20 pickling is an important process to remove the oxide on the surface of the base steel sheet
and to improve a plating property. In addition, the pickling may be performed once or a
plurality of times.
[0112]
(Cold rolling)
25 Next, cold rolling is performed on the hot-rolled steel sheet after the pickling at
the reduction ratio of 40 to 80%. In the case where the reduction ratio is less than 40%, it

42
is difficult to maintain the flattened shape. Further, in this case, since the ductility of the final product is deteriorated, the lower limit of the reduction ratio is 40%. On the other hand, when the cold rolling is performed at the reduction ratio exceeding 80%, a cold rolling load is excessively large and it is difficult to perform the cold rolling. For this 5 reason, the upper limit of the reduction ratio is 80%. More preferably, the reduction ratio is in the range of 45 to 70%. The effects of the present invention can be exhibited without pai ticularly defining the number of rolling passes and the reduction ratio of each pass. [0113]
10 (Hot-dip galvanizing)
After the cold rolling, the base steel sheet is subjected to hot-dip galvanizing through a continuous hot-dip galvanizing line (CGL). [0114] (Annealing)
15 The steel sheet (base steel sheet) which has been subjected to the cold rolling is
then heated to an annealing temperature of 750 to 900°C in the continuous hot-dip galvanizing line. When the annealing temperature is lower than 750°C, a re-solid of carbide formed during the hot rolling requires a long time, all or a part of carbide remain, and thus it is difficult to ensure the strength of 980 MPa or more. From this reason, the
20 lower limit of the annealing temperature is 750°C. On the other hand, since the heating to an excessive temperature leads to increase in cost, it is unfavorable economically and the sheet shape become poor or the lifetime of the roll is reduced. Therefore, the upper limit of the annealing temperature is 900°C. A holding time at the annealing temperature is not. limited in particular, but the heat treatment is preferably performed for 10 seconds or
25 longer to dissolve the carbide. On the other hand, when the heat treatment time becomes longer than 600 seconds, it leads to the increase in cost, which is unfavorable economically.

43
The effects of the present invention may be exhibited by performing isothermal-holding at
the annealing temperature of 750 to 900°C and even by starting to cool it immediately after
the steel sheet reaches the maximum temperature by performing gradient heating.
[0115]
5 In heating the base steel sheet to the annealing temperature, an average heating
rate from the room temperature or higher to 650°C or lower is set to HR1 (°C/second) expressed by Expression (4) below, and an average heating rate from the temperature exceeding 650°C to the annealing temperature is set to HR2 (°C/second) expressed by Expression (5) below.
10 HR1 > 0.3 - Expression (4)
HR2 < 0.5 x HR1 - Expression (5) [0116]
The hot rolling is performed under the above-described condition, and further the cooling prior to the cold rolling is performed. Thus, both of the refinement of the crystal
15 grains and randomization of the crystal orientations are achieved. However, by the cold rolling to be performed thereafter, the strong texture develops and the texture becomes likely to remain in the steel sheet. As a result, the isotropy of the steel sheet decreases. Thus, it is preferred to make the texture, which has developed by the cold rolling, disappear as much as possible by appropriately performing the heating to be performed
20 after the cold rolling. For this reason, it is necessary to divide the average heating rate of the heating into two stages expressed by Expressions (4) and (5) above. [0117]
The detailed reason why the texture and properties of the base steel sheet are improved by this two-stage heating is unclear, but this effect is considered to be related to
25 the recovery of dislocation and the recrystallization introduced at the time of the cold rolling. That is, a driving force of the recrystallization to occur in the steel sheet by the

44
heating is strain accumulated in the steel sheet by the cold rolling. When the average heating rate HR1 at the temperature range from the room temperature or higher to 650°C or lower is small, the dislocation introduced by the cold rolling recovers and the recrystallization does not occur. As a result, the texture which has developed at the time 5 of the cold rolling remains as it is and the properties such as the isotropy deteriorate. When the average heating rate HR1 at the temperature range from the room temperature or higher to 650°C or lower is less than 0.3°C/second, the dislocation introduced by the cold rolling recovers, resulting in that the strong texture formed at the time of the cold rolling remains. Therefore, it is necessary to set the average heating rate HR1 at the temperature
10 range from the room temperature or higher to 650°C or lower to 0.3 (°C/second) or more. When the average heating rate HR1 is 0.3 (°C/second) or more, it is possible to make the recrystallization from the ferrite (recovery of the dislocation is slow) having a large dislocation density, recrystallized grains having different crystal orientations are formed, the texture is randomized, and thus the anisotropy is reduced. In addition, when the
15 heating rate exceeds 100 (°C/second), facility investment becomes excessive, and thus it is unfavorable economically. Therefore, the upper limit of the average heating rate HR1 is substantially 100 (°C/second). [0118]
On the other hand, when the average heating rate HR2 from the temperature
20 exceeding 650°C to the annealing temperature is large, ferrite existing in the steel sheet after the cold rolling does not recrystallize and non-recrystallized ferrite in a state of being worked remains. When the steel containing C of over 0.1% in particular is heated to a two-phase region of ferrite and austenite, the formed austenite inhibits the growth of recrystallized ferrite, and thus non-recrystallized ferrite becomes more likely to remain.
25 This non-recrystallized ferrite has a strong texture, to thus adversely affect the isotropy, and this non-recrystallized ferrite contains a lot of dislocations to thus drastically

45
deteriorate the ductility. For this reason, at the temperature range from the temperature exceeding 650°C to the annealing temperature, the average heating rate HR2 needs to be 0.5 x HR1 (°C/second) or less. When the average heating rate HR2 exceeds 0.5 x HR1 (°C/second), the carbide becomes the austenite prior to the recrystallization, and the 5 formed austenite grains delay the growth of the recrystallized grains. As a result, the texture in a state of being cold-rolled remains, and thus the anisotropy increases. [0119]
From results obtained by earnestly investigating the relation between manufacturing conditions and the texture in detail, the inventors have found that the
10 randomization of the texture and the reduction of the anisotropy can be achieved when the HR1 is twice or above of the HR2. It is difficult to obtain the randomization of the texture by controlling such a heating rate by a conventional annealing in which the heating rate is constant. [0120]
15 (Cooling after annealing)
Alter being subjected to the annealing, the base steel sheet is cooled to 500°C from the annealing temperature at an average cooling rate of 0.1 to 200°C/second. When the average cooling rate is slower than 0.1°C/second, the productivity is largely impaired. On the other hand, when the cooling rate excessively rises, the manufacturing cost
20 increases. Accordingly, the upper limit of the average cooling rate is 200°C/second. Further, the cooling rate in the temperature region of 650 to 500°C is preferably 3 to 200°C/second. When the cooling rate is very slow, the austenite structure is transformed into the pearlite structure in the cooling process. Since it is difficult to ensure the austenite of 8% or more by volume fraction, the cooling rate is preferably 3°C/second or
25 faster. Example of a cooling method may include roll cooling, air cooling, water cooling, and any one of combinations of these cooling methods.

46
[0121]
(Temperature-holding)
Thereafter, the temperature is held between 500 and 350°C for 10 to 1000 seconds.
In the temperature-holding process, bainite transformation occurs and the residual austenite 5 is stabilized. The reason why the upper limit of the holding temperature is set to 500CC is
because the bainite transformation occurs at this temperature or lower. On the other hand,
when the temperature is held at the temperature region of below 3 50°C, it takes a long time
for the bainite transformation to occur, the facilities are excessive, and thus the
productivity is decreased. Accordingly, the holding temperature is 500 to 350°C. The 10 lower limit of the holding time is 10 seconds. The reason is because the bainite
transformation is not sufficiently progressed at the holding of less than 10 seconds, the
residual austenite is not stabilized, and the excellent formability is not obtained. On the
other hand, the holding of exceeding 1000 seconds deteriorates the productivity.
Furthermore, the holding does not indicate only the isothermal-holding, but also includes a 15 cold removal and heating at this temperature region.
[0122]
(Hot-dip galvanizing and alloyed hot-dip galvanizing)
The cold-rolled steel sheet (base steel sheet) manufactured in this manner is then
dipped in a hot-dip galvanizing bath and is subjected to a hot-dip galvanizing treatment, so 20 that the high-strength hot-dip galvanized steel sheet of the present invention is
manufactured. In addition, after the galvanizing treatment, when an alloying treatment is
subsequently performed, the high-strength alloyed hot-dip galvanized steel sheet of the
present invention is manufactured.
[0123]
25 Preferably, a temperature of the base steel sheet to be dipped in the hot-dip
galvanizing bath is in a range from a temperature lower than 40°C compared with the

47
temperature of the hot-dip galvanizing bath to a temperature higher than 50°C compared with the temperature of the hot-dip galvanizing bath. When the temperature of the base steel sheet to be dipped is below "temperature of hot-dip galvanizing bath - 40" (°C), the heat loss upon dipping into the galvanizing bath becomes large and a part of the molten 5 zinc is solidified, thereby leading to a deterioration of the galvanized external appearance in some cases. Before being dipped in the galvanizing bath, the base steel sheet may be dipped by re-heating the sheet to a temperature of the (temperature of hot-dip galvanizing bath - 40)°C or higher. In addition, when the temperature of the base steel sheet is above "temperature of hot-dip galvanizing bath + 50)°C, operational problems associated with a
10 temperature rise of the galvanizing bath are induced. [0124]
In addition, the alloying treatment of the galvanized layer is performed at 460°C or higher. When the alloying treatment temperature is lower than 460°C, the progress of the alloying is delayed and the productivity is decreased. The upper limit is not limited in
15 paiticular, but when the alloying treatment temperature is over 600°C, the carbide is formed and the volume fraction of a hard structure (martensite, bainite, residual austenite) is reduced, so that it is difficult to ensure the excellent ductility. Therefore, the upper limit is substantially 600°C. [0125]
20 In order to suppress galvanizing faults and to promote the alloying, it is preferable
that a jet flow of 10 m/min or more and 50 m/min or less be provided in the galvanizing bath. Scum, which is an oxide film of Zn or Al, is floated on the surface of the galvanizing bath. When the oxide film remains on the surface of the base steel sheet in large amounts, the scum adheres to the surface of the base steel sheet at the time of dipping
25 in the galvanizing bath and the galvanizing faults easily occur. Further, the scum adhering to the steel sheet causes not only the galvanizing faults but also the alloying

48
delay. [0126]
This property is particularly remarkable in the steel sheet containing a lot of Si and Mn, The detailed mechanism is unclear, but it is considered that the galvanizing 5 faults and the alloying delay are facilitated by reacting between the oxide of Si and Mn, which is formed on the surface of the base steel sheet, and the scum as the oxide as well. The reason for setting the flow rate of the jet flow to 10 m/min or more and 50 m/min or less is because the suppressing effect of the galvanizing faults due to the jet flow cannot be obtained at the flow rate slower than 10 m/min. The reason for setting the flow rate to 50
10 m/min or less is because the suppressing effect of the galvanizing faults is saturated and a high cost due to the excessive facility investment is also avoided.
The purpose of setting the flow rate of the molten zinc in the bath to 10 m/min or more and 50 m/min or less is to prevent the adhesion of dross onto the surface of the base steel sheet. From this reason, it is mainly preferable that the flow rate be within the above
15 range up to a depth of the base steel sheet which is dipped in the galvanizing bath. Meanwhile, the dross may be deposited on the bottom of the galvanizing bath in some cases. In this case, when the molten zinc near the bottom of the bath flows, it is increasingly concerned that the dross adheres to the surface of the base steel sheet by a splashing of the deposited dross. Thus, the flow rate is preferably set to a region from the
20 surface of the galvanizing bath to the depth of the base steel sheet which is dipped in the galvanizing bath. The size of the galvanizing bath may be any width as long as the base steel sheet can be dipped, but the size of the steel sheet for automotive exterior is generally up to about 2 m of a width. The size of the galvanizing bath may be sufficiently larger than the above size. Since the dross is deposited on the bottom of the galvanizing bath,
25 the zinc flows in the bath by the passing sheet, and thus it is concerned that the dross adheres to the surface of the base steel sheet by the splashing of the dross. Therefore, the

49
depth of the bath is preferably deep. [0127]
In addition, the galvanizing bath may contain Fe, Al, Mg, Mn, Si, Cr and the like in addition to pure zinc. 5 [0128]
Further, in order to further improve the plating adhesion, before the annealing in the continuous hot-dip galvanizing line, the base steel sheet may be subjected to the plating treatment using materials consisting of a single or a plurality of Ni, Cu, Co, or Fe. In addition, examples of the plating treatment include a sendimir method of "degreasing,
10 pickling, then heating in a nonoxidizing atmosphere, annealing under a reducing atmosphere which contains H2 and N2, then cooling to near the galvanizing bath temperature, and dipping in the galvanizing bath", a total reduction furnace method of "adjusting the atmosphere at the time of annealing to first oxidize the surface of the steel sheet, then using reduction to perform cleaning before the plating, and dipping in the
15 galvanizing bath", or a flux method of "degreasing and pickling the steel sheet, then using ammonium chloride or the like for flux treatment, then dipping in the galvanizing bath". However, the present invention can be exhibited even when the treatment is performed in any conditions. [0129]
20 Further, in the case of manufacturing the alloyed hot-dip galvanized steel sheet, an
effective Al concentration in the galvanizing bath is preferably controlled in the range of 0.05 to 0.500 mass% to control the properties of the galvanized layer. Here, the effective Al concentration in the galvanizing bath is a value obtained by subtracting a Fe concentration in the galvanizing bath from an Al concentration in the galvanizing bath.
25 [0130]
When the effective Al concentration is less than 0.05 mass%, the dross

50
significantly occurs and a good appearance cannot be obtained. On the other hand, the effective Al concentration is more than 0.500 mass%, the alloying is delayed and the productivity is decreased. For this reason, the upper limit of the effective Al concentration in the galvanizing bath is preferably 0.500 mass%. 5 [0131]
Further, when the alloying is performed at a low temperature, the alloying treatment can be utilized to facilitate the bainite transformation. [0132]
Meanwhile, in order to improve the coating property and weldability, the surfaces
10 of the hot-dip galvanized steel sheet and the alloyed hot-dip galvanized steel sheet of the present invention are subjected to upper layer plating and to a variety of treatments, for example, a chromate treatment, a phosphate treatment, a lubricity-improving treatment, a weldability-improving treatment or the like. [0133]
15 In addition, the hot-dip galvanized steel sheet and the alloyed hot-dip galvanized
steel sheet of the present invention may be further subjected to skin pass rolling. The reduction ratio of the skin pass rolling is preferably in a range of 0.1 to 1.5%. When the reduction ratio is less than 0.1%, the effect is small and the control is also difficult. When the reduction ratio exceeds 1.5%, the productivity is remarkably decreased. The skin pass
20 rolling may be performed in-line or off-line. Further, the skin pass of the intended reduction ratio may be performed once or in several times. [Example(s)] [0134]
The present invention will be now described in detail by way of examples.
25 Incidentally, conditions of the examples are condition examples employed for confirming the applicability and effects of the present invention, and the present invention is not

51
limited to these condition examples. The present invention can employ various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention. Chemical compositions of respective steels used in the examples are illustrated in Table 1. Respective manufacturing conditions are illustrated in 5 Tables 2 and 3. Further, structural constitutions and mechanical properties of respective steel types under the manufacturing conditions of Table 2 are illustrated in Table 4. Incidentally, underlines in each Table indicate that a numeral value is out of the range of the present invention or is out of the range of a preferred range of the present invention. [0135]
10 There will be described results of examinations using inventive steels "A to S" and
using comparative steels "a to d" which have compositions illustrated in Table 1. Incidentally, in Table 1, each numerical value of the chemical compositions indicates mass%. In Tables 2 to 4, English letters A to U and English letters a to g, which are attached to the steel types, indicate compositions of the inventive steels A to U and the
15 comparative steels a to g in Table 1 respectively. [0136]
These steels (inventive steels A to S and comparative steels a to d) were heated to 1200°C and then were subjected to the hot rolling under the conditions indicated in Table 2, and thereafter, the hot rolling was finished at an Ar3 transformation temperature or higher.
20 [0137]
In the hot rolling, first, in rough rolling as first hot rolling, the rolling was performed one time or more at a reduction ratio of 40% or more in a temperature region of 1000°C or higher and 1200°C or lower. However, with respect to steel types A2, C2, E2, J2, and 02, in the rough rolling, the rolling at the reduction ratio of 40% or more in one
25 pass was not performed. In the rough roiling, the number of times of reduction at the reduction ratio of 40% or more, each reduction ratio (%), and an austenite grain diameter

52
(urn) after the rough rolling (before finish rolling) are indicated in Table 2. Further, a
temperature Tl (°C) of the respective steel types is indicated in Table 2.
[0138]
After the rough rolling was finished, the finish rolling as second hot rolling was 5 performed. In the finish rolling, rolling at a reduction ratio of 30% or more was performed in one pass at least one time in a temperature region of Tl + 30°C or higher and Tl + 200°C or lower, and in a temperature range below Tl + 30°C, the total reduction ratio was set to 30% or less. Incidentally, in the finish rolling, rolling at a reduction ratio of 30% or more in one pass was performed in a final pass in the temperature region of Tl +
10 30°C or higher and Tl + 200°C or lower. [0139]
However, with respect to steel types C3, E3, J3, and 03, the rolling at a reduction ratio of 30% or more was not performed in the temperature region of Tl + 30°C or higher and Tl + 200°C or lower. Further, with regard to steel types A4 and C4, the total
15 reduction ratio in the temperature range below Tl + 30°C was greater than 30%. [0140]
Further, in the finish rolling, the total reduction ratio was set to 50% or more. However, with regard to steel types A3, C3, E3, J3, and 03, the total reduction ratio in the temperature region of Tl + 30°C or higher and Tl + 200°C or lower was less than 50%.
20 [0141]
Table 2 indicates the total reduction ratio (%) in the temperature region of Tl + 200°C or lower, a temperature (°C) after the reduction in the final pass in the temperature region of Tl + 30°C or higher, and Tl + 30°C or higher and Tl + 200°C or lower, and PI: the reduction ratio of the final reduction of 30% or more (the reduction ratio in the final
25 pass in the temperature region of Tl + 30°C or higher and Tl + 200°C or lower) (%), in the finish rolling. Further, Table 2 indicates the reduction ratio (%) at the time of the

53
reduction in the temperature range below Tl + 30°C in the finish rolling. [0142]
After the final reduction in the temperature region of Tl + 30°C or higher and Tl + 200°C or lower was performed in the finish rolling, cooling before cold-rolling was 5 started before a waiting time t (second) passes 2.5 x tl. In the cooling before cold-rolling, an average cooling rate was set to 50°C/second or more. Further, a temperature change (a cooled temperature amount) in the cooling before cold-rolling was set to fall within a range of 40°C or higher and 140°C or lower. [0143]
10 However, with respect to steel types A6, C4, E4, J4, and 03, the cooling before
cold-rolling (after hot rolling-finish rolling-cooling) was started after the waiting time t (second) passes 2.5 x tl from the final reduction in the temperature region of Tl + 30°C or higher and Tl + 200°C or lower in the finish rolling. With regard to steel types A22, C16, E12, and E13, the temperature change (after hot rolling-finish rolling-cooling amount) in
15 the cooling before cold-rolling was less than 40°C, and with regard to steel types A21, C15, and Ell, the temperature change (after hot rolling-finish rolling-cooling amount) in the cooling before cold-rolling was higher than 140°C. With regard to steel types A22, C16, and E13, the average cooling rate (after hot rolling-finish rolling-cooling rate) in the cooling before cold-rolling was slower than 50°C/second.
20 [0144]
Table 2 indicates tl (second) of each steel type, the waiting time t (second) from the final reduction in the temperature region of Tl + 30°C or higher and Tl + 200°C or lower to the start of the cooling before cold-rolling in the finish rolling, t/tl, the temperature change (cooling amount) (°C) in the cooling before cold-rolling, and the
25 average cooling rate (°C/second) in the cooling before cold-rolling. [0145]

54
After the cooling before cold-rolling, coiling was performed at 700°C or lower, and hot-rolled original sheets each having a thickness of 2 to 4.5 mm were obtained. [0146]
However, with respect to steel types A7 and C8, a coiling temperature was higher 5 than 700°C. With respect to each of the steel types, the cooling stop temperature (coiling temperature) (°C) of the cooling before cold-rolling was indicated in Table 2. [0147]
Next, the hot-rolled original sheets were pickled and then were subjected to the cold rolling at a reduction ratio of 40% or more and 80% or less such that the thickness
10 after the cold rolling became 1.2 mm. However, with regard to steel types A17, E9, and J15, the reduction ratio of the cold rolling was less than 40%. In the cold rolling, the reduction ratio of each steel type is indicated in Table 3. Further, when the reduction ratio of the cold rolling was 80%, a rolling load became too high and thus the cold rolling could not be performed to a predetermined sheet thickness. Therefore, the substantial upper
15 limit of the reduction ratio is about 80%. [0148]
Thereafter, the cold-rolled sheet (base steel sheet) was subjected to the heat treatment and the hot-dip galvanizing treatment in the continuous hot-dip galvanizing line. [0149]
20 In the continuous hot-dip galvanizing line, first, the cold-rolled sheet was heated
to a temperature region of 750 or higher and 900°C or lower, was held for 10 seconds or more and 600 seconds or less at the temperature region, and then was subjected to the annealing treatment. In addition, when the heating was performed up to the temperature region of 750 to 900°C, an average heating rate HRl (°C/second) of room temperature or
25 higher and 650°C or lower was set to 0.3 or more (HRl > 0.3), and an average heating rate HR2 (°C/second) from above 650°C to 750 to 900°C was set to 0.5 x HRl or less (HR2 ^

55
0.5 x HR1). Table 3 indicates the heating temperature (annealing temperature), the
heating holding time (time to a primary cooling start after cold rolling) (second), and the
average heating rates HR1 and HR2 (°C/second) of each steel type.
[0150]
5 However, with respect to steel type A20, the annealing temperature exceeded
900°C. With respect to steel types A7, C4, E5, J5, and 04, the annealing temperature was
less than 750°C. With respect to steel types C3, E6, and J5, the holding time was shorter
than one second. With respect to steel types Al 8 and C13, the holding time exceeded 600
seconds. Further, with respect to steel type C12, the average heating rate HR1 was slower 10 than 0.3 (°C/second). With respect to steel types A12, A13, A15, A15, C3, C4, C9, Cll,
J10, Jll, J13, J14, and O10, the average heating rate HR2 (°C/second) exceeded 0.5 x
HR1.
[0151]
After the annealing, the cooling was performed from the annealing temperature to 15 500°C at the average cooling rate of 0.1 to 200°C/second. With respect to steel types Al 9
and C13, the average cooling rate was slower than 0.1°C/second. The average cooling
rate (°C/second) of each steel sheet is indicated in Table 3.
[0152]
After the cooling treatment, the holding was performed between 500 and 350°C 20 for 10 to 1000 seconds. The holding time of each steel sheet is indicated in Table 3.
However, with respect to steel sheets A8, C5, J6, and 05, the holding time was less than 10
seconds.
[0153]
Then, the base steel sheet was dipped in the hot-dip galvanizing bath controlled to 25 a predetermined condition and then was cooled to the room temperature. The temperature
of the galvanizing bath was managed to 440 to 470°C. In addition, when the hot-dip

56
galvanizing was performed, the temperature of the base steel sheet was (temperature of hot-dip galvanizing bath - 40)°C or higher and (temperature of hot-dip galvanizing bath + 50)°C or lower, The effective Al concentration in the hot-dip galvanizing bath was in the range of 0.09 to 0.17 mass%. After being dipped in the hot-dip galvanizing bath, a part of 5 the steel sheet was subjected to the alloying treatment at 460°C or higher and 600°C or lower and then was cooled to the room temperature. At that time, the weight per unit area was each about 35 g/m on both surfaces. Finally, the obtained steel sheet was subjected to the skin pass rolling at the reduction ratio of 0.4%. [0154]
10 In order to suppress the plating and to promote the alloying, a jet flow of 10
m/min or more and 50 m/min or less was provided in the galvanizing bath. Table 3 indicates the speed (m/min) of the jet flow provided in the galvanizing bath and the alloying treatment temperature at the time of performing the hot-dip galvanizing on each of the steels. However, with respect to steel types A9, C5, C8, E7, J7, and 06, the speed of
15 the jet flow provided in the galvanizing bath was slower than 10 m/min. In addition, with respect to steel types All, C8, E9, J9, and 09, the alloying treatment temperature exceeded 600°C. [0155]
Table 4 indicates an average value of pole densities of orientation groups {100}
20 <011> to {223} <110> and a pole density of a crystal orientation {332} <113> in a sheet thickness range of 5/8 to 3/8 from a steel sheet surface of each steel type, and volume fractions (structural fractions) (%) of ferrite, bainite, residual austenite, martensite, and pearlite in a metal structure of each steel type. In addition, each of the volume fractions (structural fractions) was evaluated by the structural fraction before the skin pass rolling.
25 Further, Table 4 indicated, as mechanical properties of each steel type, the tensile strength TS (MPa), the elongation (L-El), the difference in elongation (AE1), the balance (TS x El)

57
of the strength (TS) - total elongation (C-El), In addition, the presence or absence of
galvanizing faults, Fe concentration (mass%) of the hot-dip galvanized layer, and Fe
concentration (mass%) of the alloyed hot-dip galvanized layer are indicated.
[0156]
5 The tensile test was performed fay sampling a JIS No. 5 test piece from a sheet of
1.2 mm thick in a direction vertical to and parallel to the rolling direction to evaluate tensile properties. A difference (AE1) between an elongation (L-El) in the case of performing the tensile test in the direction parallel to the rolling direction and an elongation (C-El) in the case of performing the tensile test in the direction vertical to the rolling
10 direction was calculated from the obtained elongation value. The tensile test was performed on each of five test pieces and an average value of values was obtained, so the elongation and TS were calculated from the average value. In addition, as for a steel sheet having large material anisotropy, there was a tendency that the elongation value was varied. A steel having the balance (TS x El) of the strength (TS) - the total elongation
15 (C-El) exceeding 16000 (MPa-%) was defined as a high strength steel sheet having excellent formability. [0157]
The plating property and the alloying reaction were evaluated as follows, respectively.
20 O: No galvanizing fault is present.
A: Some galvanizing faults are present. X: Numerous galvanizing faults are present. [0158]
The tensile property, the plating property, and the content (%) of Fe contained in
25 the galvanized layer which were measured are indicated in Table 4. It was figured out that all of the steel sheets of the present invention were excellent in both of the formability

5
10
15
20
25

58 and the plating property.

[0159] [Table 1]

59

60
[0160] [Table 2]

Reli^ln It fl: Alia lit A-^llrf
utaintf rebcfiJS Asfcdu niani M»*"jff fi^kcf rtfcg- tdfcg-
JFiatttt aixrcil gin >?C L-4 l^nul i&jis^ TI4 2WC rfMirr rfJWo lafcufcss tniig ™&g C«SE3 CdSg
1W/C» llXfCtr rfr* abiu on rat IIiHC lis na taud {«7M fl 0 ui 333 15} 111 m S3 SVJ
All 814 45 45 1SS to *M 1) 0 131 127 2.43 184 so S3 SCO
AH S54 4545 16) E0 f» 4) 0 lti 3E9 1J) 0.81 (0 6) 5M
AM S54 4343 1» so 9)4 4) a 135 3J3 153 11! 3) « }»
All ES4 4345 IB so S» 43 0 L79 447 063 034 ' ISO 113 353
A12 EH 4545 17) 10 »7J 4) 0 019 045 030 1(1 3 ii (CO
Bl S33 4343 1M 75 935 4) 0 SS) 151 06) 103 53 5) O)
CI £55 4545 It) 15 sa 43 0 01) 05! 03! 2.31 SO 70 (CO
CI S3! '1 250. to E5) t) o 334 8.33 1(0 030 SO S3 (1)
O SSS 4341 130 s K3 30 0 IB 711 OSO OS 13) 110 1»
C4 £15 4545 16) so fa 4) a 4(3 1L73 ua> IB SO S3 (CO
ci as 4545 163 10 SSS 30 0 15) 417 IK Oil SO 5) 5»
« 535 454! IB il Ml 45 0 m 251 OS) OS »0 5) Q)
C? 155 50 130 SO ST3 4) 0 2-23 S-Q 05) 0)3 7) 6) 61)
cs SJJ 5) 123 10 SO 30 0 0S1 2.36 IP) 1« 11) S3 23
cs SJJ 4313 1« so 925 4) IS OK 231 06) 0(3 KO KO 55!
CM SJS 4313 14! SO EiJ 4) 0 1(2 4M 1-13 OH 11) SO SS)
cu SIS 4545 It! S3 (CO *3 <] 1.(7 IS 06) 041 BO 73 (CO
C12 fJJ 45 4! in SO 9H « 0 111 2 SO OKI 051 81 6) »)
CI3 US 4543 ISO H K3 4) 0 1C9 121 OS) 05S 110 53 (2)
C14 SJS 45 43 It! SO 911 30 0 LS 113 06) 047 S3 « (CO
CU as 45 45 It) 60 fi5 30 0 IIS 14S o» Oil S> ISO 513
CK US 45 45 1*1 B 55S 30 0 072 ISO 133 ISO s a (10
Ol OS 5J 1M Si SO « 0 0!J 0 44 0.43 151 7) 113 5»
m SJS 45 4J IM SO 532 43 0 OSS 171 on OB SO 9) !*)
El us 4343 150 SO »:« 41 0 IB 173 ID) 091 173 SO (3)
El ESS ■1 25 S) 911 43 0 LIS 2S5 030 OH SO 50 653
a SJ5 S IS) 2) 501 35 5) 151 ISO 05) 033 9) SO 62)
u 655 4343 150 BJ Sil 4) 0 L6I 1» ISM 9.78 11! 40 (CO
L! 655 4545 it: SO SM 40 io lit SSS 10) 071 Kfl 6) 5»
U 655 4313 120 SO 911 4) 0 07S LSI 01) 0)1 133 SO 62)
n 65S 45 45 130 so SOS 10 0 151 329 0.4) O30 S3 50 633
L5 l» 4S45 113 SO SS7 43 0 US 154 OM Oli 7) 5) 510
E9 S54 (51J 130 S3 92) 13 0 OSS It) 0(0 on 9) 70 B)
EM 855 43 4S 170 S3 91) 4) 0 LIS 170 QM OM » 113 (10
111 fis 4S45 11! 10 S« 5! 0 ire 322 0E0 033 m 21) 61)
Ell S)6 45.41 12) 8) 512 13 0 0)3 133 li) 11) 5) H B)
El) sss 43 43 If) S3 S3 12 0 Q14 0J4 OM 413 ; B 610
Fl SM 4)4) l» 55 !!S 13 0 10) ID OSO 07S ID m £1)
n S54 43 41 151 S3 932 « 0 070 1M 01) 0)7 111 D) 62)
01 SS> 4)«i) 153 •n 92S IS 0 a<5 170 1.20 177 S3 )JD 5M
(a S57 45.45 !53 SO 530 13 0 077 191 0.4) 0)2 11) so 633
HI 652 4141 111 E! 942 13 23 OH 1(1 OSO 093 153 so fit)
K3 SSI 4341 113 S3 SS) 43 0 LE5 46J 01) 01S tl3 so 653
11 SSS 4S4S 15) SO 555 13 0 0S3 2.U 07) OSS SO 63 61)
11 SSS 4141 1!) s> 954 45 0 063 174 0-3) 013 et 11) 610
n' US •tiDt) IS) S3 5)5 33 0 0M 165 113 IKS so 70 5»
22 £51 •1 2» SS 91) 13 J! 074 164 OSO 081 110 S3 K-)
a SSI » 150 li 5)! i) 0 0(9 7.23 OtJ 045 IM SO U)
» SS) 5) 13) S3 934 3) 0 1« 2(4 440 415 130 70 61)
» SS) 5) IS) S3 913 ii 0 014 259 0J0 OSO SO t» 5»
M te) 4141 IS) SS 9M 1) X tw 1(1 10) 095 so 12) IS)
n SS) 45.11 15) S3 94! 43 11 06! ie 0(0 OS 73 SO SCO
JS SS) 4141 14) 65 93) 1) 0 OSS 137 OSO 034 30 M (B
n SS) 4)4) D) S3 Sr25 4) 23 107 IS! 110 111 6) 11) (J!
J19 SS) 4541 1M SO SS) 1) 0 Oil 1C1 1(0 IS) so t.» sw
Jll £61 4141 1*1 ta 9M 1) 0 041 1(1 ICO 21? 120 SO 150
J13 SSI 4141 If) so 541 1) a 034 OSS 110 Ill *M 63 591
J]} f*J 414) IB so 95) 4) 0 a is 139 It) 195 SO » 570
J14 SSI 4541 15) so 94! 1) 0 0£4 1(0 110 172 13) so 4»
11) (fl 4141 H3 so 945 1) 0 0f4 1(0 110 171 153 70 JSO
XI SSS 40 411) 15) 75 931 1) 0 0S4 234 OSO OS) SO 63 15)
LI £33 4141 12) 5>) 944 45 0 039 05S 0(0 133 SO SO !2)
Ml £1 30 D) S5 »X 4) a LIS 117 OH 03! 5) 13 ISO
Nl 174 1 454) li) SO vx 43 0 173 1)7 OSO a 44 15) 12) EM
Ol S57 2 4545 1M 75 932 45 0 07) 191 1*3 1J) 53 9) O)
02 SST 9 '1 2£l a 911 45 0 054 131 0(0 0(4 170 » 430
03 SJJ 5) 13) & i23 J) 0 4S2 10 SO is a; 17) 6) 70 5S0
CM £17 5! It) so ¥/S H 0 133 14) 103 073 SO S) 3M
0) U7 50 150 so S91 45 0 ia f$ 0 4) 0 24 50 It) 5(0
m 117 1 4545 1» so 954 45 0 135 3.11 053 04) 113 13) !70
OT 817 2 4511 It) 7) Ko 4) 0 U) 15! 213 155 113 33> 3>!
oi 637 ! 1343 IM 7) sw 43 0 124 113 06) an SO 8) SSO
09 SJ7 1 4545 13) SO 91-3 45 0 107 its 030 023 63 7) 613
Oil S17 2 4545 ia 71 9M 10 0 099 IS 103 1M 63 9) 330
Oil 6)7 2 4345 IS) 71 9)3 4) 0 112 1S1 06) 03) 12) 120 (CO
Oil 8)7 1 4545 1M ;> SS3 « 0 171 4)1 063 031 13) 7) (CO
11 SSS 2 431! 1H to 9M 4) 0 (171 1S3 0-M 017 ») » 550
01 6(0 1 4545 It) so S40 45 0 01! IIS 03) 063 (0 4) sso
HI S3! 1 !0 15C 50 911 4) 0 1S1 4)1 050 05) SO 9) 430
SI S17 2 451! 1M 7) 5« 4) 0 IM 3-1) 113 0(1 (0 It) 540
■1 SS6 J 4315 1H 50 SSS 4) 0 170 42S 443 021 so S3 (SO
SI Ol >i 15) SO M4 « a OTi 15) 0(0 077 (0 6) 4?)
d £)1 2 451! 12) 71 Kl 43 0 117 3.1! OSO 071 70 S3 SI3
: i. t>Jtf-f-*'l.-f* tf <-* pf*?-* rr-.T^rtF
•lirrit&EiHiBtsffE.^rptci^cf^iccnif^flrrtfofj^

61
[0161] [Table 3]

A«r«i! A*TIB|«
653 "CU Adrift
>■—-TVI* " ■="*e HiS« B:V5-^ n^tja Biiitx^
CiUrftj rrim tf 65J*C ttzztn^xt- lice 6xeg b=e diri^g L^^ fc| U150U Jet-JV™riaii Afc;i«
rct> ;rti**r:Hftl HSJ m.kg m£4 U». *c Bi'c fcaJ-^ir-Sfcei lc=ytieziB
SiHRw Kt /■C't /"Ci .•c \ (*C 1 'Ci Ic'ib l-C
A] 6) 353 113 EH M 4 3! M ■•1
Al 6) 551 7 ID S23 SO 4 53 M *•*
AJ 61 3.5] 111 Ef] » 4 3) 20 -•1
A4 63 SSI 111 113 *3 4 63 2) -•1
A) (0 553 15) Bj3 93 4 33 M -•2
Ai 6} 5-51 710 KO 63 4 SO >3 -•1
A7 73 551 1*3 m 63 4 33 23 -•1
A! « SSI 113 SCO W 4 i 23 -•1
A! 53 SSI 123 SB 63 4 3) 1 -•J
AID 73 55J HI S20 63 4 23 J5 5*)
All (0 353 11) KO 63 4 33 3) sa
All 61 151 HM 610 SO 4 33 13 493
A13 63 SSI 5 31 SIC M 4 3D M 4?3
AH 63 SSI LW E'3 » 4 31 M SDO
A15 6D m 13 SM 5>3 4 3) 11 491
A1S 63 t» 71) ST3 SO 4 3) 23 SQ
A17 21 153 1(0 »3 113 4 33 15 HO
All 63 an 0(S S13 7)2 4 53 21 513
Al» a SSI LM EM so a 51 n m
AM a SSI IK 5*3 113 4 6) n •8
AH » iSJ 1(0 KO 93 4 63 M 5D0
A?! 63 5 51 1(0 ill SO 4 33 23 )H
HI 43 551 71) ice 30 4 3) 23 -•2
CI 63 3 51 113 t25 61 4 3) n -•1
CI 63 SSJ 113 SO 63 3 3) M -*2
C3 n 12 5 53 361 3 I IS) 10 -*2
C4 » iS !5! JM 63 4 53 2) -•1
CS 63 S51 713 tw 63 4 s 3 -•2
CS 63 353 11) sn 61 4 ]» 11 «0
C7 63 5 51 12) S21 63 4 15 13 JM
a 60 i» 12) »23 63 4 4! 2 SH
C9 63 111 1761 sia 60 4 33 23 «0
CU 63 551 16) ill 61 4 33 21 4»
Cll 63 1161 1163 (19 60 4 3D 13 SCO
Cll m 014 DCS &] 93 4 5) il 60
CIS m 353 12) in IJSl 0 5) 11 il-3
CU 6D 553 12) S IE) 4 53 11 570
CL5 63 551 71) JM 61 4 3) 15 323
CIS 151 71) fl) MO 1 63 15 363
Dl 63 SSI 121 t)l M 5 6) 11 -•2
D: SO 153 72) !*1 61 7 J) 11 SB
II (0 153 12) KM 63 4 1« 21 .'2
12 50 551 11) BD 6D 2 1) 13 -•2
13 50 S53 123 Ml 61 3 3D 13 -*2
14 53 S53 123 KO 60 3 3) 13 -■2
ES S3 553 123 7?1 61 1 3) 11 -•1
U 5) 551 72) 7?1 ! 1 1) 11 .'2
17 » 553 71) SJ1 6) 1 63 7 -'2
IS 43 553 72) f&l 30 1 M 15 363
IS 4) 5)3 12) KO SI 1 >» ID m
£13 a 550 22) m » 2 63 11 511
Ell « 553 22) HI 61 4 53 11 «0
It) « 15) 72) I:J ]JD 4 « IS 521
1)3 « 153 720 ii) 6D 4 SO 21 551
11 63 55) 1» no SO 3 33 13 -•2
n 50 553 121 7» 61 1 6) 45 )13
Ol 53 15) IN TO 63 1 J3 15 .'1
ia 53 15) 22) 7/3 91 I 73 11 J13
HI Si 5 5) in 800 3) 2 33 13 -'2
H3 S3 Ji) 220 TW SO 1 7) 45 330
II a) 55) 715 7» 51 2 33 ID -•2
1! 63 JM 221 S» 4! I 73 3) 330
)I 60 IS) L43 S) 63 2 » 2) •'1
n SO IK) 1_»3 7S3 93 1 63 15 •'1
n 50 ISO L*3 JS3 SO 1 63 2) -'1
14 50 18) 1*0 7» SO 1 30 15 -'2
JS 53 is) 1+3 2J ! S 30 2) -■2
js ■0 J SO L»3 SO 9) 2 i }) -■1
i7 53 3-f) 1*3 CO 9) 1 30 1 -'1
I! 51 IS) 1*3 7S) SO 1 33 2D 493
H 51 IB) 1*0 7)1 SO 1 30 25 (43
313 J] !B soi e» 9) 1 30 2) 550
311 n 3 50 3S3 KO 9) I 13 20 4»
III 53 IK OH E13 9) M 20 ■tel
m 5) 13a is ») SO 1 33 23 to
in 53 ico 2M K» 93 33 2) I'D
ju 13 IS) OfO Sio SO 30 2) J2D
Kl 63 3)3 213 KO ' 40 60 10 •'1
LI 60 350 223 St) J3 SB 20 -'1
ill 63 353 ITS E2'3 53 33 11 -•1
M 43 55) IN SID 5) 33 2) -•1
CI 43 SJ3 ll1! SS) 6) 30 H ■•1
Ol 43 353 113 i» SO 3D 20 ■•1
O) 53 353 223 TM 93 33 20 -'1
04 51 553 723 ») SO » 2) -■1
0) 50 353 in s;o 93 4 20 -'1
OS 61 553 7M SM SO 3D } -■1
07 63 353 123 110 SO 61 4S «D
01 63 353 113 SCO 93 11 20 531
Ol 63 353 111 S.0 93 33 15 «3
Oil 5D £S HO so SO 3D 2) 4?3
Oil 51 l» 711 7M 113 3D 23 fSO
on S3 551 721 sa SO 3D 2) «0
Fl 4) 5)3 111 KO M 3D 20 -'1
Qi JJ 353 111 7S3 53 31 20 •'1
HI S3 553 723 6!0 63 61 « •'1
SI 53 153 in !23 33 211 2) -•1
ll 43 55) 713 !?) 53 31 3) -■1
M 73 55) 713 SO 33 1 S 31 2) -■2
cl 51 5)3 113 (13 63 31 2) •'1
41 63 553 .in »3 33 31 21 -'1
Uo5f[fci1 h5?£* td IIIZHII «U P pJ of tc -T--^r tf $* piir^t F^rfa.
•2- bats cuti »ifie CJ '1^E«^ttitetl ii m pti&Ezsi

£ee = 22gsgS8SS8S225EES££ = = ~B:: = Kfc*3B:: = :=E!SGS;3:;S^
EEKEECKSSSESSEESKKKSlSlBESEfcSSfi^^
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HS§£g52S£23SSSE5S5i=5gs=5gSgSEEg£55£E5|gg^
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63
[Industrial Applicability] [0163]
The present invention is to provide the high-strength galvanized steel sheet having the small material anisotropy and excellent formability with the ultimate tensile strength of 980 MPa or more, which is suitable for the structural member, the reinforcing member, and the suspension member of automobiles, at a low cost. Accordingly, the present invention can be expected to greatly contribute to the lighter-weight of automobiles and is extremely high in effect in industry.

64

[Name of Document] CLAIMS [Claim 1]
A high-strength hot-dip galvanized steel sheet having small material anisotropy and excellent formability with an ultimate tensile strength of 980 MPa or more, the hot-dip 5 galvanized steel sheet comprising a hot-dip galvanized layer formed on a surface of a base steel sheet,
wherein the base steel sheet contains: by mass%,
C: 0.1 to less than 0.40%;
Si: 0.5 to 3.0%;
10 Mn: 1.5 to 3.0%;
. O: limited to 0.006% or less;
P: limited to 0.04% or less;
S: limited to 0.01% or less;
Al: limited to 2.0% or less;
15 N: limited to 0.01% or less; and
a balance including Fe and inevitable impurities,
a microstructure of the base steel sheet contains ferrite of 40% or more, residual
austenite of 8 to less than 60%, by volume fraction, and a balance being bainite or
martensite,
20 an average value of pole densities of orientation groups {100} <011> to {223}
<110> represented by each of crystal orientations {100} <011>, {116} <110>, {114}
<110>, {113} <110>, {112} , {335} <110>, and {223} <110> in a sheet thickness
range of 5/3 to 3/8 from the surface of the base steel sheet is 6.5 or less and a pole density
of a crystal orientation {332} <113> is 5.0 or less, and
25 the hot-dip galvanized layer contains Fe: less than 7 mass% and a balance
including Zn, Al, and inevitable impurities.

65
Claim 2]
The high-strength hot-dip galvanized steel sheet having the small material anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or 5 more according to claim 1, wherein the base steel sheet further contains one or two or more of: by mass%,
Cr: 0.05 to 1.0%;
Mo: 0.01 to 1.0%;
Ni: 0.05 to 1.0%;
10 Cu: 0.05 to 1.0%;
Nb: 0.005 to 0.3%; Ti: 0.005 to 0.3%; V: 0.005 to 0.5%; and B: 0.0001 to 0.01%. 15
[Claim 3]
The high-strength hot-dip galvanized steel sheet having the small material anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or more according to claim 1, wherein the base steel sheet further contains, by mass%, 0.0005 20 to 0.04% in total of one or two or more selected from Ca, Mg, and REM.
[Claim 4]
A high-strength alloyed hot-dip galvanized steel sheet having small material anisotropy and excellent formability with an ultimate tensile strength of 980 MPa or more, 25 the alloyed hot-dip galvanized steel sheet comprising an alloyed hot-dip galvanized layer formed on a surface of a base steel sheet,

66
wherein the base steel sheet contains: by mass%,
C: 0.10 to less than 0.4%;
Si: 0.5 to 3.0%;
Mn: 1.5 to 3.0%;
5 O: limited to 0.006% or less;
P: limited to 0.04% or less;
S: limited to 0.01% or less;
Al: limited to 2.0% or less;
N: limited to 0.01% or less; and
10 a balance including Fe and inevitable impurities,
a microstructure of the base steel sheet contains ferrite of 40% or more, residual austenite of 8 to less than 60%, by volume fraction, and a balance being bainite or martensite,
an average value of pole densities of orientation groups {100} <011> to {223}
15 <110> represented by each of crystal orientations {100} <011>, {116} <110>, {114}
<110>, {113} <110>, {112} <110>, {335} <110>, and {223} <110> in a sheet thickness
range of 5/8 to 3/8 from the surface of the base steel sheet is 6.5 or less and a pole density
of a crystal orientation {332} <113> is 5.0 or less, and
the alloyed hot-dip galvanized layer contains Fe: 7 to 15 mass% and a balance 20 including Zn, Al, and inevitable impurities.
[Claim 5]
The high-strength alloyed hot-dip galvanized steel sheet having the small material anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or 25 more according to claim 4, wherein the base steel sheet further contains one or two or more of: by mass%,

61
Cr: 0.05 to 1.0%;
Mo: 0.01 to 1.0%;
Ni: 0.05 to 1.0%;
Cu: 0.05 to 1.0%;
5 Nb: 0.005 to 0.3%;
Ti: 0.005 to 0.3%; V: 0.005 to 0.5%; and B: 0.0001 to 0.01%.
10 [Claim 6]
The high-strength alloyed hot-dip galvanized steel sheet having the small material anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or more according to claim 4, wherein the base steel sheet further contains, by mass%, 0.0005 to 0.04% in total of one or two or more selected from Ca, Mg, and REM. 15
[Claim 7]
A manufacturing method of a high-strength hot-dip galvanized steel sheet having
small material anisotropy and excellent formability with an ultimate tensile strength of 980
MPa or more, the manufacturing method comprising:
20 with respect to a steel billet containing: by mass%,
C: 0.10 to less than 0.4%;
Si: 0.5 to 3.0%;
Mn: 1.5 to 3.0%;
O: limited to 0.006% or less;
25 P: limited to 0.04% or less;
S: limited to 0.01% or less;

68
Al: limited to 2.0% or less;
N: limited to 0.01% or less; and
a balance including Fe and inevitable impurities,
performing first hot rolling in which rolling at a reduction ratio of 40% or more is 5 carried out one time or more at a temperature range of 1000°C or higher and 1200°C or lower;
setting an austenite grain diameter to 200 um or less by the first hot rolling;
performing second hot rolling in which rolling at a reduction ratio of 30% or more is carried out in one pass at least one time at a temperature region of Tl + 30°C or higher 10 and Tl + 200°C or lower determined by Expression (1) below;
setting a total reduction ratio in the second hot rolling to 50% or more;
performing a final reduction at a reduction ratio of 30% or more in the second hot
rolling and then starting cooling before cold rolling in such a manner that a waiting time t
(second) satisfies Expression (2) below;
15 setting an average cooling rate to 50°C/second or more and a temperature change
to be in a range of 40CC or higher and 140°C or lower in the cooling before cold rolling;
coiling at a temperature region of 700°C or lower;
performing cold rolling at a reduction ratio of 40% or more and 80% or less;
heating to an annealing temperature of 750°C or higher and 900°C or lower and 20 then annealing in a continuous hot-dip galvanizing line;
cooling to 500°C from the annealing temperature at 0.1 to 200°C/second; and
performing hot-dip galvanizing after holding for 10 to 1000 seconds between 500 and 350°C,
Tl (°C) - 850 + 10 x (C + N) x Mn + 350 x Nb + 250 x Ti + 40 x B + 10 x Cr + 25 100 x Mo + 100 x V - Expression (1)
where, C, N, Mn, Nb, Ti, B, Cr, Mo, and V each represent the content of each

69
element (mass%, Ti, B, Cr, Mo, and V are calculated as zero when not being contained),
t < 2.5 x tl— Expression (2)
where, tl is obtained by Expression (3) below.
tl - 0.001 x ((Tf - Tl) x Pl/100)2 - 0.109 x ((Tf - Tl) x Pl/100) + 3.1 -5 Expression (3)
where, in Expression (3) above, Tf represents a temperature of the steel billet obtained after a fmal reduction at a reduction ratio of.30% or more, and PI represents a reduction ratio of a final reduction at 30% or more.
10 [Claim 8]
The manufacturing method of the high-strength hot-dip galvanized steel sheet having the small material amsotropy and the excellent formability with the ultimate tensile strength of 980 MPa or more according to claim 7, wherein the total reduction ratio in a temperature range below Tl + 30°C is 30% or less.
15
[Claim 9]
The manufacturing method of the high-strength hot-dip galvanized steel sheet having the small material anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or more according to claim 7, wherein, in a case of heating to the
20 annealing temperature in the continuous hot-dip galvanizing line, an average heating rate of room temperature or higher and 650°C or lower is set to HR1 (°C/second) expressed by Expression (4) below, and an average heating rate from a temperature exceeding 650°C to the annealing temperature is set to HR2 (°C/second) expressed by Expression (5) below. HR1 > 0.3-Expression (4)
25 HR2 < 0.5 x HR1 - Expression (5)

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[Claim 10]
The manufacturing method of the high-strength hot-dip galvanized steel sheet
having the small material anisotropy and the excellent formability with the ultimate tensile
strength of 980 MPa or more according to claim 7, wherein when the hot-dip galvanizing is
5 performed, a temperature of a base steel sheet is (temperature of hot-dip galvanizing bath -
40)°C or higher and (temperature of hot-dip galvanizing bath + 50)°C or lower.
[Claim 11]
The manufacturing method of the high-strength hot-dip galvanized steel sheet
10 having the small material anisotropy and the excellent formability with the ultimate tensile
strength of 980 MPa or more according to claim 7, wherein a flow rate of 10 m/min or
faster and 50 rn/min or slower is provided in a galvanizing bath when the hot-dip
galvanizing is performed.
15 [Claim 12]
A manufacturing method of a high-strength alloyed hot-dip galvanized steel sheet having small material anisotropy and excellent formability with an ultimate tensile strength of 980 MPa or more, the manufacturing method comprising:
with respect to a steel billet containing: by mass%,
20 C: 0.10 to less than 0.4%;
Si: 0.5 to 3.0%;
Mn: 1.5 to 3.0%;
O: limited to 0.006% or less;
P: limited to 0.04% or less;
25 S: limited to 0.01% or less;
Al: limited to 2.0% or less;

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N: limited to 0.01% or less; and
a balance including Fe and inevitable impurities,
performing first hot rolling in which rolling at a reduction ratio of 40% or more is carried out one time or more at a temperature range of 1000°C or higher and 1200°C or 5 lower;
setting an austenite grain diameter to 200 um or less by the first hot rolling;
performing second hot rolling in which rolling at a reduction ratio of 30% or more
is earned out in one pass at least one time at a temperature region of Tl + 30°C or higher
and Tl + 200°C or lower determined by Expression (1) below;
10 setting a total reduction ratio in the second hot rolling to 50% or more;
performing a final reduction at a reduction ratio of 30% or more in the second hot rolling and then starting cooling before cold rolling in such a manner that a waiting time t (second) satisfies Expression (2) below;
setting an average cooling rate to 50°C/second or more and a temperature change 15 to be in a range of 40°C or higher and 140°C or lower in the cooling before cold rolling;
coiling at a temperature region of 700°C or lower;
performing cold rolling at a reduction ratio of 40% or more and 80% or less;
heating to an annealing temperature of 750°C or higher and 900°C or lower and
then annealing in a continuous hot-dip galvanizing line;
20 cooling to 500°C from the annealing temperature at 0.1 to 200°C/second;
performing hot-dip galvanizing after holding for 10 to 1000 seconds between 500 and 350°C; and
performing an alloying treatment at a temperature of 460°C or higher,
Tl (°C) - 850 + 10 x (C + N) x Mn + 350 x Nb + 250 x Ti + 40 x B + 10 x Cr + 25 100 x Mo + 100 x V - Expression (1)
where, C, N, Mn, Nb, Ti, B, Cr, Mo, and V each represent the content of each element

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(mass%, Ti, B, Cr, Mo, and V are calculated as zero when not being contained).
t < 2.5 x tl - Expression (2)
where, tl is obtained by Expression (3) below.
tl = 0.001 x ((Tf - Tl) x Pl/100)2 - 0.109 x ((Tf - Tl) x Pl/100) + 3.1 -5 Expression (3)
where, in Expression (3) above, Tf represents a temperature of the steel billet obtained after a final reduction at a reduction ratio of 30% or more, and PI represents a reduction ratio of a final reduction at 30% or more.
10 [Claim 13]
The manufacturing method of the high-strength alloyed hot-dip galvanized steel sheet having the small material anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or more according to claim 12, wherein the total reduction ratio in a temperature range below Tl + 30°C is 30% or less.
15
[Claim 14]
The manufacturing method of the high-strength alloyed hot-dip galvanized steel sheet having the small material anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or more according to claim 12, wherein, in a case of heating to
20 the annealing temperature in the continuous hot-dip galvanizing line, an average heating rate of room temperature or higher and 650°C or lower is set to HR1 (°C/second) expressed by Expression (4) below, and an average heating rate from a temperature exceeding 650°C to the annealing temperature is set to HR2 (°C/second) expressed by Expression (5) below.
25 HR1 > 0.3 - Expression (4)
HR2 < 0.5 x HR1 - Expression (5)

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[Claim 15]
The manufacturing method of the high-strength alloyed hot-dip galvanized steel sheet having the small material anisotropy and the excellent formability with the ultimate 5 tensile strength of 980 MPa or more according to claim 12, wherein when the hot-dip galvanizing is performed, a temperature of a base steel sheet is (temperature of hot-dip galvanizing bath - 40)°C or higher and (temperature of hot-dip galvanizing bath + 50)°C or lower,
10 [Claim 16]
The manufacturing method of the high-strength alloyed hot-dip galvanized steel sheet having the small material anisotropy and the excellent formability with the ultimate tensile strength of 980 MPa or more according to claim 12, wherem a flow rate of 10 m/min or faster and 50 m/min or slower is provided in a galvanizing bath when the hot-dip
15 galvanizing is performed.
ATTORNEY FOR THE APPLICANTS]