Technical Field [0001]
The present invention relates to a galvamiealed steel sheet which is subjected to
press-forming and which is mainly utilized for automobiles, and relates to a method for
10 producing the same. Specifically, the present invention relates to a galvannealed steel
sheet for press-forming which is excellent in surface appearance, and relates to a method
for producing the same.
Background Art
15 [0002]
In recent years, in order to prevent the global warming, it has been required to improve the fuel efficiency of the automobiles. For example, an improvement target for the fiiel efficiency of the automobiles has been newly set for emission control of carbon dioxide. In order to improve the fuel efficiency of the automobiles, a weight reduction
20 of an automobile body is effective. Thus, for the weight reduction, it has been required to thin the steel sheet for the automobile body. On the other hand, for the safety of the automobile body, it has been required to strengthen the steel sheet for the automobile body.
[0003]
25 In addition to the above mentioned requirements of thimiing and strengthening
the steel sheet, it has been required for the steel sheet for the automobile body which is press-formed to complex shapes to be excellent in surface corrosion resistance and electrophoretic paintability and to be excellent in surface appearance. [0004]

2
In general, in a high tensile strength steel sheet (HTSS), solid solution
strengthening elements such as Si (Silicon), Mn (Manganese), P (Phosphorus), or the like
are included in the steel for strengthening the steel sheet.
[0005]
5 In the galvannealed steel sheet which includes the elements such as Si, Mn, P, or
the like as the chemical composition, surface defects such as line defects, stripe defects,
or the like may appear after press-forming. Since the surface defects may remain after
painting, the surface defects are undesirable for the surface appearance and have been
concerns.
10 [0006]
In order to suppress the surface defects, it has been mainly proposed to grind a
steel piece (slab) before hot-rolling, to grind a hot-rolled steel sheet or a cold-rolled steel
sheet before coating, or the like.
[0007]
15 For example, as a method for producing a galvannealed steel sheet which has
not many patternlike defects on coating surface and in which a steel sheet including Ti (Titanium) and an ultra-low carbon is utilized for base material, Patent Document 1 discloses a method to considerably reduce an amount of scarfing a cast piece or grinding a steel sheet which has been conducted for suppressing the patternlike defects in a 20 mamier that element segregation in the cast piece is suppressed by conducting the electromagnetic stirring during continuous casting. As a method for producing a galvamiealed steel sheet which is excellent in the surface appearance, coating adhesion, and formability and in which high-Si-based steel sheet or high-P-based steel sheet is utilized for base material, Patent Document 2 discloses a method to grind a surface of a 25 coating steel sheet so as to control surface rougliness Ra to 0.3 to 0.6, to immerse it in galvanizing bath, and thereafter, to conduct heating and alloying treatment. [0008]
In general, although P is included in the steel to strengthen the steel sheet, P is the element to be readily segregated. Thus, P which is segregated to a slab surface is 30 elongated along a longitudinal direction of the steel sheet by hot-rolling and cold-rolling, and thereby, a concentrated layer of P is formed in a coil surface. Alloying at the concentrated layer of P is delayed during coating, which causes the line defects of the galvannealed steel sheet. For the problem, as a method for producing a galvamiealed

3 steel sheet in which a steel sheet including 0.03% or more of P is utilized for base material, Patent Document 3 discloses a method to grind a surface of a steel sheet by a grinding amount depending on a P content in the steel slieet in order to suppress unevenness in the surface of the steel sheet, and thereafter, to conduct alloying treatment 5 by induction heating in an alloying furnace. [0009]
In addition. In order to suppress occurrence of chevron stripes on a surface of a pickled steel sheet. Patent Document 4 discloses a method to pickle a hot-rolled steel sheet under ordinary conditions, and thereafter, to ftirther pickle it so as to dissolve a 10 surface layer by 1.0 jim or more. [0010]
In order to suppress the linear pattern defects of the galvannealed steel sheet in a case Nvhere a steel sheet including Ti, an ultra-low carbon, and 0.03% or more of P is utilized, for example, the prior arts conduct scarfing a surface of a continuous cast piece 15 by 3 mm or more and fijrther grinding a surface of a steel sheet before coating by 5 |jm or more. As a result, the prior arts suppress the occun'cnce of the patternlike defects after coating and obtain surface quality Even when a steel sheet including Ti, an iiltra-low carbon, and a low P is utilized, in the present situation, the prior arts conduct scarfing a surface of a cast piece by 3 mm or more, grinding a surface of a steel sheet after 20 cold-rolling by 2 [im or more using a brush for heavy duty grinding, and scarfing it after pickling by 1 |.im or more in order to suppress the chevron stripes. The above-mentioned situation causes a decrease in yield.
Related Art Documents 25 Patent Documents
[0011]
[Patent Document 1] Japanese Unexamined Patent Application, First
Publication No. 2004-149866
[Patent Document 2] Japanese Unexamined Patent Application, First
30 Publication No. 2004-169160
[Patent Document 3] Japanese Patent (Granted) Publication No. 2576329

4 [Patent Document 4] Japanese Unexamined Patent Application, First
Publication No. 2005-281775
Summary of Invention 5 Technical Problem to be Solved [0012]
An aspect of the present invention relates to a galvamiealed steel sheet which includes a high tensile strength steel sheet as base material whose base elements correspond to an ultra-low carbon steel for improving formability and which includes P
10 for improving strength. An object of the present invention is to provide the
galvamiealed steel sheet which is subjected to press-forming and which is excellent in surface appearance even after the press-forming, and is to provide a method for producing the same. In addition, the object of the present invention is to provide the galvamiealed steel sheet for the press-forming in which it is possible for the steel sheet to
15 reduce and optimize an amount of surface-removing which is conducted for suppressing surface defects having linear pattern or the like and for obtaining the excellent surface appearance, and is to provide a method for producing the same. In other word, the steel sheet according to the aspect of the present invention is to be excellent in a production cost.
20
Solution to Problem [0013]
The present inventors have thoroughly investigated an occurrence cause of unevenness of P concentration which results in surface defects having linear pattern or
25 the like for a high tensile strength galvannealed steel sheet whose base elements
correspond to an ultra-low carbon steel and which includes P for improving strength. As a result, the following knowledge has been found. Alloying rate during galvamiealing decreases in an area where P is segregated in a surface part of steel sheet, when a galvanized steel sheet is galvannealed. Unevemiess of coating thickness is
30 caused by difference in the alloying rate. The uneveimess of coating thickness results in the surface defects having longitudinal pattern (linear pattern) which have whitish or blackish appearance. After conducting press-forming the galvaimealed steel sheet

5 having the surface defects, the patterns become excessive because a convex area which forms the linear pattern on steel sheet surface is peeled off. In addition, when P, Ni (Nickel), and Cu (Copper) are segregated to the same part near an interface between scale (oxide layer) and steel of a hot-rolled steel sheet, the segregated part is not pickled and 5 remains even after the pickling. As a result, the surface defects having linear pattern or the like become excessive. [0014]
Therefore, in order to suppress the occurrence of the surface defects having linear pattern during the galvannealing after the galvanizing, it is preferable to remove 10 the segregated part where the above elements are segregated near the interface between the scale and the steel after the hot-roIHng. As a result of the above removing, a P-segregated part which is harmful to surface quality is simultaneously removed and invalidated.
[0015]
15 An aspect of the present invention employs the following.
[0016]
(1) A galvannealed steel sheet according to an aspect of the present invention includes:
a scale-removed rolled steel sheet which includes, as a chemical composition, by
mass%,
20 0.0005% to 0.01% of C,
0.001% to 1.0% of Si,
0.01% to 2.0% of Mn,
0.005% to 0.1% of P,
0.01% to 0.10% of Al,
25 0.02% or less of S,
0.1% or less of Ni, 0.1% or less of Qi, 0.01% or less of N, and
a balance consisting of Fe and unavoidable impurities; and
30 a galvannealed layer ananged on the scale-removed rolled steel sheet,
wherein, when ten measurement points of the galvannealed steel sheet are set in a transverse direction by equally dividing a line-segment having a reference length of 50 mm by 10,

6
a minimum P content of the galvannealed layer in the ten measurement points of the galvannealed steel sheet is 50% or more as compared Avith a maximum P content therein.
(2) In the galvamiealed steel sheet according to (1),
5 the scale-removed rolled steel sheet may fiiither include, as the chemical
composition, by mass%, at least one selected from
0.0001% to 0.0050% of B,
0.001% to 0.1% ofNb,
0.001% to 0.1% of Ti, and
10 0.001% to 0.1% of Mo.
(3) In the galvannealed steel sheet according to (2),
when ten measurement points of the scale-removed rolled steel sheet are set in the transverse direction by equally dividing a line-segment having a reference length of 50 mm bj^ 10, when a surface part of the scale-removed rolled steel sheet is from a
15 surface of the scale-removed rolled steel sheet to 0.1 jun in depth along a thickness
direction, and when a base part of the scale-removed rolled steel sheet is from the surface of the scale-removed rolled steel sheet to more than 2 fim in depth along the thickness direction,
in each of the ten measurement points of the scale-removed rolled steel sheet, a
20 P content, a Ni content, and a Cu content of the surface part of the scale-removed rolled steel sheet may be respectively 105% to 150% as compared with a P content, a Ni content, and a Cu content of the base part of the scale-removed rolled steel sheet.
(4) In the galvarmealed steel sheet according to (1),
when ten measurement points of the scale-removed rolled steel sheet are set in 25 the transverse direction by equally dividing a line-segment having a reference length of 50 nmi by 10, when a surface part of the scale-removed rolled steel sheet is from a surface of the scale-removed rolled steel sheet to 0. i [im in depth along a thickness direction, and when a base part of the scale-removed rolled steel sheet is from the surface of the scale-removed rolled steel sheet to more than 2 j.im in depth along the thickness 30 direction,
in each of the ten measurement points of the scale-removed rolled steel sheet, a P content, a Ni content, and a Cu content of the surface part of the scale-removed rolled steel sheet may be respectively 105% to 150% as compared with a P content, a Ni

7 content, and a Cu content of the base part of the scale-removed rolled steel sheet. (5) A method for producing a galvannealed steel sheet includes:
casting a molten steel which includes, as a chemical composition, by mass %,
0.0005% to 0.01% of C,
5 0.001% to 1.0% of Si,
0.01% to 2.0% of Mn,
0.005%. to 0.1% of P,
0.01% to 0.10% of Al,
0.02% or less of S,
10 0.1% or less of Ni,
0.1% or less of Cu, 0.01% or less of N, and
a balance consisting of Fe and unavoidable impurities in order to obtain a slab;
heating the slab in 1100°C to 1300°C;
15 hot-rolling the slab after the heating under conditions such that a finishing
temperature is in 800°C to 1050°C and a coiling temperature is in 500°C to 800°C in order to obtain a hot-rolled steel sheet;
surface-removing the hot-rolled steel sheet within a range in |im of GL expressed by a following Expression I or more and GU expressed by a following 20 Expression 2 or less from an interface toward a steel along a thickness direction in order to obtain a scale-removed rolled steel sheet, when ten measurement points of the hot-rolled steel sheet are set in a transverse direction by equally dividing a line-segment having a reference length of 50 mm by 10, when a steel surface part of the hot-rolled steel sheet is from the interface between a scale and the steel to 2 |.im in depth toward the 25 steel along the thickness direction, and when a Nimax ai^d a Cu,„ax are respectively a
maximum Ni content and a maximum Cu content in mass % of the steel surface part in the ten measurement points of the hot-rolled steel sheet;
galvanizing the scale-removed rolled steel sheet after the surface-removing in
order to obtain a galvanized steel sheet; and
30 gaivanneaiing the galvanized steel sheet after the galvanizing in order to obtain a
galvannealed steel sheet.
GL= (Ni„,ax + 0.8 X Cumax) >^ 0.2 ■■•(Expression 1) GU = (Nimax + 0.8 X Cu„,ax) ^4 ■ • -(Expression 2)

8
(6) In the method for producing the galvannealed steel sheet according to (5),
the molten steel may further include, as the chemical composition, by mass %, at least one selected from
0.0001% to 0.0050% of B,
5 0.001% to 0.1% of Nb,
0.001% to 0.1% of Ti, and 0.001% to 0.1% of Mo.
(7) The method for producing the galvannealed steel sheet according to (6) may include
pickling a surface of the scale-removed rolled steel sheet at least before the 10 surface-removing or after the surface-removing.
(8) The method for producing the galvannealed steel sheet according to (5) may include
pickling a surface of the scale-removed rolled steel sheet at least before the surface-removing or after the surface-removing.
(9) The method for producing the galvannealed steel sheet according any one of (5) to
15 (8) may include;
cold-roiling the scale-removed rolled steel sheet before the galvanizing under a cold-reduction of 50% to 95%; and
amiealing the scale-removed rolled steel sheet after the cold-rolling in a temperature which is a recrystallization temperature or higher. 20
Effects of Invention [0017] The galvaimealed steel sheet according to the above aspects of the present
invention satisfies the mechanical properties such as tensile strength, is excellent in the 25 formability, includes the galvannealed layer which has not many surface defects such as
linear pattern defects, and simultaneously, maintains excellent surface appearance even
after press-forming.
In addition, since it is possible for the hot-rolled steel sheet to comparatively reduce and
optimize the amount of surface-removing which is conducted for suppressing the surface 30 defects having linear pattern or the like when the galvannealed steel sheet is produced, it
is possible to obtain the prominent effects such that the loss of steel and the production
cost can be reduced.

9 Detailed Description of Preferred Embodiments [0018]
Hereinafter, a preferable embodiment of the present invention will be described
in detail.
5 [0019]
A galvannealed steel sheet according to an embodiment of the present invention includes a galvannealed layer arranged on a scale-removed rolled steel sheet. Herein, the scale-removed rolled steel sheet is defined as a rolled steel sheet which is subjected to surface-removing in a surface-removing process as explained below. In order to obtain 10 the galvannealed steel sheet which is excellent in surface quality (surface appearance), it is needed to reduce unevenness of P content in the galvamiealed layer. Specifically, wdien equally-spaced ten measurement points of the galvannealed steel sheet are set in a transverse direction by equally dividing a line-segment having a reference length of 50 mm by 10, it is needed to control a minimum P content of the galvannealed layer in the 15 ten measurement points to be 50% or more (and 100% or less) as compared with a maximum P content therein. [0020]
When the minimum P content of the galvannealed layer in the ten measurement points is less than 50% as compared with the maximum P content of the galvannealed 20 layer therein, difference in alloying rate during galvaimealing after a galvanizing process becomes excessive. As a result, surface defects having linear pattern or the like of the galvannealed steel sheet become excessive. Thus, the P content in the galvamiealed layer needs to satisfy the above requirement. It is preferable that the minimum P content of the galvannealed layer in the ten measurement points is 60% or more as 25 compared with the maximum P content of the galvamiealed layer therein. [0021]
The P content of the galvannealed layer may be measured by using a Glow Discharge Spectroscopy (GDS) or the like. The equally-spaced ten measurement points of the galvannealed steel sheet may be set in the transverse direction by equally dividing 30 the line-segment having the reference length of 50 mm by 10, and thus, the P content in each measurement point may be measured by using the GDS. [0022] hi addition, in order to obtain the galvannealed steel sheet which is excellent in

10
the surface quality (surface appearance), it is preferable to reduce unevenness of
thickness in the galvannealed layer. Specifically, it is preferable to control a minimum
thickness of the galvannealed layer in the ten measurement points to be 50% or more
(and 100% or less) as compared with a maximum thickness therein.
5 [0023]
When the minimum thickness of the galvannealed layer in the ten measurement points is less than 50% as compared with the maximum thickness of the galvaimealed layer therein, a thick area in the galvannealed layer may be peeled off at press-forming the galvannealed steel sheet, and as a result, the surface defects having linear pattern or
10 the like may become excessive. Thus, it is preferable that the thickness of the galvannealed layer satisfies the above requirement. It is more preferable that the minimum thickness of the galvaimealed laj^er in the ten measurement points is 60% or more as compared with the maximum thickness of the galvannealed layer therein. [0024]
15 In consideration of occurrence of the surface defects having linear pattern
parallel to a rolling direction, the thickness of the galvannealed layer may be measured on a cross section that is planarly cut along a thickness direction so that an observed section corresponds to the transverse direction perpendicular to the rolling direction of the galvannealed steel sheet. When equally-spaced ten measurement points of the
20 galvannealed steel sheet are set in the transverse direction by equally dividing a line-segment having a reference length of 50 nmi by 10, the thickness of the galvannealed layer in each measurement point may be measured by observing the cross section. For example, the observation on the cross section may be conducted under a magnification in which a visual field is to be 1000 \xm or less in the transverse direction.
25 [0025]
In order to obtain the teclmical features of the galvannealed steel sheet according to the embodiment, it is preferable that P, Ni, and Cu are not segregate to a steel sheet surface in the scale-removed rolled steel sheet wliich is the base material of the galvamiealed steel sheet. Specifically, it is preferable that, when equally-spaced ten
30 measurement points of the scale-removed rolled steel sheet are set in the transverse
direction by equally dividing a line-segment having a reference length of 50 imn by 10, when a surface part of the scale-removed rolled steel sheet is from the surface of the scale-removed rolled steel sheet to 0.1 |im in depth along the thickness direction, and

11
when a base part of the scale-removed rolled steel sheet is from the surface of the scale-removed rolled steel sheet to more than 2 },im in depth along the thickness direction, in each of the ten measurement points of the scale-removed rolled steel sheet, a P content, a Ni content, and a Cu content of the surface part of the scale-removed rolled steel sheet 5 are respectively 105% to 150% as compared with a P content, a Ni content, and a Cu content of the base part of the scale-removed rolled steel sheet.
[0026]
When the P content, the Ni content, and the Cu content of the surface part of the scale-removed rolled steel sheet are respectively more than 150% as compared with the P 10 content, the Ni content, and the Cu content of the base part of the scale-removed rolled steel sheet, a segregated part of P, Ni, and Cu may remain in the surface of the scale-removed rolled steel sheet even after pickling the scale-removed rolled steel sheet, and thereby, the surface defects having linear pattern or the like in the galvannealed steel sheet maj' become excessive. When the above contents are less than 105%, an amount 15 of surface-removing for the scale-removed rolled steel sheet may be excessive, and
thereby, a time or equipment for surface-removing is further required, which results in a decrease in a yield of the steel. Thus, the P content, the Ni content, and the Cu content of the surface part of the scale-removed rolled steel sheet are to satisfy the above requirement. It is more preferable that the above range is 110% or more and 130% or 20 less.
[0027]
The P content, theNi content, and the Cu content of the scale-removed rolled
steel sheet may be measured by using the GDS. Herein, a measured average from the
surface of the scale-removed rolled steel sheet to 0.1 [im along the thickness direction is
25 regarded as a measurement result of the surface part of the scale-removed rolled steel
sheet, and a measured average from the surface to more than 2 pm is regarded as a
measurement result of the base part of the scale-removed rolled steel sheet. In addition,
it is preferable that a measured depth is more than 2 pni to 4fjm when the base part of the
scale-renroved rolled steel sheet is measured by using the GDS.
30 [0028]
The details which led to the above technical features will be described below.
[0029]
It is required to thin the steel sheet for improving the fuel efficiency of

12
automobiles and to strengthen the steel sheet for ensurhig the safety of automobile bodies.
In addition, it is required for the steel sheet for automobile bodies to be excellent in the
surface appearance and the press-formability.
[0030]
5 For strengthening the steel sheet, P-included steel sheet is utilized as the coating
steel sheet. However, P is the element to be readily segregated, P which is segregated to a slab surface is elongated along a longitudinal direction of the steel sheet bj^ hot-rolling and cold-roiling, and thereby, a P-segregated part is formed in a steel sheet surface. When the above steel sheet is subjected to galvamiealing treatment, alloying rate during
10 galvamiealing becomes uneven in the P-segregated part, and thereby, concavity and convexity of the surface of the galvamiealed steel sheet is formed. As a result, the surface defects having linear pattern or the like appear. When the above galvamiealed steel sheet is subjected to press-forming, the convex area is peeled off, and thereby, the linear pattern becomes excessive.
15 [0031]
The present inventors have thoroughly investigated an occuirence cause of the surface defects having linear pattern or the like for the galvannealed steel sheet which utilizes a high tensile strength hot-rolled steel sheet whose base elements coirespond to an ultra-low carbon steel and which includes P for improving strength. As a result, the
20 following knowledge has been found. When P, Ni, and Cu are segregated to the same part near an interface between scale and steel of the hot-rolled steel sheet, the segregated part remains even after the pickling process. Unevenness of coating thickness is formed in the segregated part during the galvaimealing after the galvanizing, and thereby, the surface defects having linear pattern or the like appear.
25 [0032]
With respect to a segregation mechanism of P, Ni, and Cu, which causes the occurrence of the surface defects having linear pattern or the like on the surface of the galvannealed steel sheet, the following mechanism is considered. [0033]
30 In general, the galvamiealed steel sheet is produced by continuous-casting a slab,
by heating it in a heating ftmiaee, by hot-rolling it after surface-removing, by coiling it in order to obtain a hot-rolled steel sheet, by cold-rolling and annealing the hot-rolled steel sheet as necessary, and by conducting a galvannealing treatment.

13 [0034]
In the heating process of the slab, when the continuously cast slab which includes P, Ni, and Cu is heated in tlie heating furnace in 1100°C to 1300°C, Fe (iron) in a slab surface is oxidized and becomes primary scale. HoAvever, since Ni and Cu which 5 are steel elements are hardly oxidized, Ni and Cu segregate to the interface between the primary scale and the steel without the oxidation. [0035]
Although the primary scale is removed by the scale-removing (descaling) which
is conducted as necessary, Ni and Cu which segregate to the steel surface are not
10 removed and still remain. In the hot-rolling process, when the above slab is hot-rolled,
Ni- and Cu-segregated part is elongated along the longitudinal direction of the steel sheet,
and thereb}^, the thickness of Ni- and Cu-segregated pai1 is thinned. At the same time,
secondary scale is formed by the oxidation of the steel sheet surface during the
hot-roiling, and thereby, Ni and Cu further segregate to the steel surface.
15 [0036]
During the coiling after the hot-roliing, P segregates to the interface between the
scale and the steel or to grain boundaries. When P is segiegated to the same part with
Ni and Cu, the above P is not removed and remains in the steel surface part even after
conducting the pickling process.
20 [0037]
When the hot-rolled steel sheet is subjected to the cold-rolling and the amiealing as necessary, and thereafter, is subjected to the galvannealing treatment, the surface defects having linear pattern or the like appear. The pail where the surface defects appear corresponds to the part where P, Ni, and Cu coincidently segregate. Thus, it is 25 possible to conclude that the occurrence of the surface defects having linear pattern or the like does not result from only the segregation of P but results from the coincidently segregation of P, Ni, and Cu to the surface part. [0038]
The present inventors have statistically investigated the suppression of the 30 P-segregated part which segregates to the steel sheet surface by using various steel sheets. Since P remains in the part where Ni and Cu segregate, the present inventors have focused attention on the Ni- and Cu-segregated part which is located in the interface between the scale and the steel in the hot-rolled steel sheet. As a result, the following

14 knowledge has been found. Depending on the Ni content and the Cu content in the steel surface part which is from the interface toward the steel, the amount of surface-removing which is required to invalidate P increases correiatively. Specifically, when equally-spaced ten measurement points of the hot-rolled steel sheet are set in the 5 transverse direction by equally dividing a iine-segment having a reference length of 50 min by 10, when the steel surface part of the hot-rolled steel sheet is from the interface between the scale and the steel to 2 |jm in depth toward the steel along the thickness direction, and when a Nimax and a Cumax are respectively regarded as a maximum Ni content and a maximum Cu content in mass % of the steel surface part in the ten
10 measurement points of the hot-rolled steel sheet, the hot-rolled steel sheet is subjected to the surface-removing within a range in [im of GL or more and GU or less, GL being expressed by a following Expression A and GU being expressed by a following Expression B, from the interface toward the steel along the thickness direction in order to obtain the scale-removed rolled steel sheet. Thereby, it is possible to remove and
15 invalidate the P-segregated part in addition to the Ni- and Cu-segregated part. In other word, it is difficult to remove the P-, Ni-, and Cu-segi'egated part by the pickling process, and thus, it is important to conduct the surface-removing so as to control the removing amount to be within the above range in order to remove the segregated part. In addition, the above amount of surface-removing is optimized, and thus, it is possible to sufficiently
20 remove the P-segregated part with the removing amount which is less than that of the prior arts.
GL - (Ninm + 0.8 X Cu„,axO ^ 0.2 •■ -(Expression A) GU = (Nima.x + 0.8 X CuniaO X 4 -" ■ (Exprcssiou B) [0039]
25 The scale-removed rolled steel sheet after the surface-removing is used as the
base material and is subjected to the galvaimealing, and thereby, it is possible to obtain the galvannealed steel sheet which includes the galvamiealed layer without the surface defects having linear pattern or the like and which maintains the excellent surface appearance even after press-forming. In addition, even when the scale-removed rolled
30 steel sheet after the surface-removing is subjected to the cold-rolling process or the annealing process as necessary, and thereafter, is subjected to the galvannealing, it is possible to obtain the same effect as described above. [0040]

15
Next, the chemical composition of the scale-removed rolled steel sheet which is the base material of the galvannealed steel sheet according to the embodiment will be described in detail. In addition, % as described below is mass%.
[0041]
5 It is required for an automobile steel sheet to simultaneously satisfy the high
tensile strength and the press-formability such as deep drawability. For the scale-removed rolled steel sheet which is the base material of the gaivamiealed steel sheet according to the embodiment, a high tensile strength steel sheet as base material whose base elements correspond to an ultra-low carbon steel for improving formability and 10 which includes Si, Mn, P, or the like for improving strength may be used. Hereinafter, the reasons for addition and limitation of base elements will be described.
[0042]
C: 0.0005% to 0.01%
C (carbon) is an element which decreases ductility and r value (Lankford-value) 15 which are related to the press-formability. It is preferable that the C content be small. However, in order to decrease the C content to less than 0.0005%, production cost for steel making is excessive, and thus, it is industrially difficult to control the C content to be less than 0.0005%. On the other hand, when the C content is more than 0.01%, the r value which is a factor of the formability deteriorates, and thus, an upper limit is to be 20 0.01%. The upper limit may be preferably 0.008%..
[0043]
Si:0.00i%to 1.0%
Si (silicon) is an element enliancing the steel strength and is utilized in combination to the other strengthening elements. When the Si content is less than 25 0.001%, the above effect is not obtained. On the other hand, when the Si content is more than 1.0%, Si-oxides are formed on the steel sheet surface, bare spots occur, and coating adhesion deteriorates during the galvanizing. Also, the r value which is a factor of the formability deteriorates the ductilitj' or the r value which is the factor of the formability deteriorates. In order to further enliance the tensile strength, the Si content 30 may be preferably 0.1% or more.
[0044]
Mn: 0.01% to 2.0%
Mn (manganese) is an element enliancing the steel strength and is utilized in

16 combination to the other strengthening elements. When the Mn content is less than 0.01%, the above effect is not obtained. Also, the production cost for steel making is excessive, and thus, a lower limit is to be 0.01%. On the other hand, when the Mn content is more than 2.0%, the r value which is the factor of the formability deteriorates 5 because the steel sheet is hardened, the galvanizability deteriorates because Mn-oxides are formed on the steel sheet surface, and thus, an upper limit is to be 2.0%. In order to fiiither enhance the tensile strength, the Mn content may be preferably 0.15% or more. [0045]
P: 0.005% to 0.1%
10 P (phosphorus) is an element which is significantly effective in enhancing the
steel strength and which almost never has the negative influence of the formability as
compared with Si, Mn, or the like. Thus, P is usefiil for enhancing the steel strength.
When the P content is less than 0.005%, the above effect is not obtained. In order to
fiirther enhance the tensile strength, the P content may be preferably 0.01% or more.
15 On the other hand, P is an element which delay the galvannealing after the galvanizing,
which deteriorates the surface quality by forming the linear pattern on coating surface,
and which negatively affects the spot weldabilit>^ Thus, an upper limit of the P content
is to be 0.1%.
[0046]
20 Al: 0.01% to 0.10%
Al (aluminum) is a deoxidizing element of the steel and an element enhancing the steel strength. When the Al content is less than 0.01 %, the above effect is not obtained. Also, the oxides remain because the deoxidation is insufficient, and thus, the formability deteriorates. On the other hand, when the Al content is more than 0.10%, 25 the r value which is the factor of the formability deteriorates. Thus, an upper limit is to be 0.10%.
[0047]
In addition to the above base elements, at least one selected from the group consisting of B, Nb, Ti, and Mo may be additionally included as optional elements. 30 Hereinafter, the reasons for addition and limitation of the optional elements will be described. In addition, % as described below is mass%. [0048] B: 0.0001% to 0.0050%

17 B (boron) has a high affinity for N (Nitrogen), forms the nitrides during soUdification or hot-rolling, and thus, has the effects on enhancing the steel strength and enliancing the formabilit)' by decreasing the solid-soluted N in the steel. In order to obtain the effects, the B content may be preferably 0.0001% or more. On the other hand, 5 when the B content is more than 0.0050%, a weld zone and a heat affected zone may harden during welding, and thus, the toughness may deteriorate. Also, the strength of the hot-rolled steel sheet may increase, and thus, a cold-rolling load may increase. Also, the recrystallization temperature may increase, the in-plane anisotropy of the r value which is the factor of the formability may increase, and thus, the press-formability may 10 deteriorate. Thus, the B content may be preferably 0.0001% to 0.0050%. In addition, when the B content is 0% to 0.0050%, the characteristic values of the galvaimealed steel sheet are not negatively affected. [0049]
Nb: 0.001% to 0.1%
15 Nb (Niobium) has a high affmity for C and N, forms the carbonitrides during
solidification or hot-rolling, and thus, has the effects on enhancing the steel strength and
enhancing the formability by decreasing the solid-soluted C and N in the steel. In order
to obtain the effects, the Nb content may be preferably 0.001% or more. On the other
hand, when the Nb content is more than 0.1%, the recrystallization temperature may
20 increase, the in-plane anisotropy of the r value which is the factor of the formability may
increase, and thus, the press-formability may deteriorate. Also, the toughness of the
weld zone may deteriorate. Thus, the Nb content may be preferably 0.001% to 0.1%.
In addition, when the Nb content is 0% to 0.1%, the characteristic values of the
galvamiealed steel sheet are not negatively affected.
25 [0050]
Ti: 0.001% to 0.1%
Ti (titanium) is an element which enliances the steel strength and enliances the formability by decreasing the solid-soluted N by fixing N in the steel as TiN. In order to obtain the effects, the Ti content may be preferably 0.001% or more. On the other 30 hand, when the Ti content is more than 0.1%, the effects may be saturated, on the
contrary, the r value which is the factor of the formability^ may deteriorate by forming TiC. Thus, the Ti content may be preferably 0.001% to 0.1%. The Ti content may be more preferably 0.015% to 0.09%. In addition, when the Ti content is 0% to 0.1%, the

18
characteristic values of the galvamiealcd steel sheet are not negatively affected.
[0051]
Mo: 0.001% to 0.1%
Mo (molybdenum) is an element which makes it possible to obtain the slow 5 aging properties, because the aging is suppressed with a small amount of addition. In order to obtain the effects, the Mo content may be preferably 0.001% or more. On the other hand, when the Mo content is more than 0.1%, the effects may be saturated, on the contrary, the formability may deteriorate because the steel sheet is hardened. Thus, the Mo content may be preferably 0.001% to 0.1%. In addition, when the Mo content is 0% 10 to 0.1%, the characteristic values of the galvannealed steel sheet are not negatively affected.
[0052]
In addition to the above mentioned elements, the scale-removed rolled steel sheet which is the base material of the galvannealed steel sheet according to the 15 embodiment includes unavoidable impurities. Herein, the unavoidable impurities indicate elements such as S, Ni, Cu, N, Mg, Pb, Sb, Sn, Cd, or the like which are unavoidably contaminated from auxiliary materials such as scrap and from the galvanizing process. It is preferable that S, Ni, Cu, and N in the elements are limited to the following in order to obtain satisfactory the effects of the present invention. Since it 20 is preferable that the amount of the unavoidable impurities is as small as possible, the limited range of the unavoidable impurities includes 0%. In addition, % as described below is mass%.
[0053]
S : 0.02% or less
25 S (suffur) is an impurity which is unavoidably contaminated in the steel. When
the S content is more than 0.02%, the r value which is the factor of the deep drawability may deteriorate. When the S content is limited to 0% or more and 0.02% or less, the range is acceptable substantially without the negative influence.
[0054]
30 Ni: 0.1% or less
Ni is an element which is difficult to be removed at controlling the steel compositions in the steel making, and thus, a small amount of Ni is included (for example, 0.001% or more). When the Ni content is more than 0.1%, some patterns tend

19
to appear on the galvanized steel sheet. Thus, tlie Ni content is limited to 0% or more
and 0.1% or less. In addition, when the Ni content is excessive, the cost may rise
because the expensive Ni needs to be consciously added. Thus, an upper limit of Ni is
to be 0.1%.
5 [0055]
Cu: 0.1% or less
In conmion with Ni, Cu is also the element which is difficult to be removed at controlling the steel compositions in the steel making, and thus, a small amount of Cu is included (for example, 0.001% or more). When the Cui content is more than 0.1%, 10 some patterns tend to appear on the galvanized steel sheet, the grain boundaries may embrittled, and the cost may rise. Thus, the Cu content is limited to 0% or more and 0.1% or less.
[0056]
N: 0.01% or less
15 N is the impurit}' which is unavoidably contaminated in the steel. When the N
content is more than 0.01%, the r value which is the factor of the deep drawability may
deteriorate. When the N content is limited to 0% or more and 0.01% or less, the range
is acceptable substantially without the negative influence.
[0057]
20 Next, the method for producing the galvannealed steel sheet according to the
embodiment will be described. [0058]
In a casting process, the molten steel which satisfies the above mentioned chemical composition is cast in order to obtain a slab. Although a casting method is not 25 particularly limited, a vacuum casting method, a continuous casting method, or the like may be employed. [0059]
In a heating process, the slab is heated in 1100°Cto 1300°C. The reasons why the slab is heated in 1100°C to 1300°C are as follows. When the heating is lower than 30 1100°C, a hot-rolling load increases, and it is difficult to ensure the predetermined finishing temperature for hot-rolling. On the other hand, when the heating is higher than 1300°C, the cost may rise because the energy is excessively used. In addition, as a first scale-removing process after the heating process, the scale -removing (descaling)

20
may be conducted as necessary in order to remove the primary scale on the slab surface.
[0060]
In a hot-rolling process, the slab after the heating process is hot-rolled under conditions such that the finishing temperature is in 800°C to 1050°C and a coiling 5 temperature is in 500°C to 800°C in order to obtain the hot-rolled steel sheet. When the finishing temperature for the hot-rolling is lower than 800°C, the duplex grain structure is formed, which causes the unevemiess of the material properties. Also, since the rolling temperature is low, the steel strength increases, and the r value which is the factor of the formabilit}' deteriorates. On the other hand, when the finishing temperature is higher 10 than 1050°C, the cost may rise because the heating temperature needs to be high. Also, the steel strength may decrease. Thus, the finishing temperature for the hot-rolling is to be80D°Ctol050°C.
[0061]
When the coiling temperature is lower than 500°C, a defective shape may occur.
15 On the other hand, when the coiling temperature is higher than 800°C, scale defects tend
to be fonned. Thus, the coiling temperature is to be 500°C to 800°C. In addition, as a
pickling process after the hot-rolling process and before the below-mentioned
surface-removing process, the pickling may be conducted as necessary in order to pickle
and remove the scale on the hot-rolled steel sheet.
20 [0062]
In a surface-removing process, the hot-rolled steel sheet is surface-removed. Specifically, when equally-spaced ten measurement points of the hot-rolled steel sheet are set in the transverse direction by equally dividing a line-segment having a reference length of 50 mm by 10, when the steel surface part of the hot-rolled steel sheet is from 25 the interface between the scale and the steel to 2 pm in depth toward the steel along the thickness direction, and when the Ni„,ax and the Cumax aie respectively regarded as the maximum Ni content and the maximum Cu content in mass % of the steel surface part in the ten measurement points of the hot-rolled steel sheet, the hot-rolled steel sheet is subjected to the surface-removing within a range in |.an of GL or more and GU or less, 30 GL being expressed by a following Expression C and GU being expressed by a following Expression D, from the interface toward the steel along the thickness direction in order to obtain the scale-removed rolled steel sheet.
GL - (Ni,„ax + 0.8 X CumaO ^0-2 ■ ■ -(Expression C)

21
GU = (Ni,„ax + 0.8 X CuniiLv) X 4 ■ ■ -(Expression D)
[0063]
As the surface-removing method, macliining is convenient. For example, a wire brusli roil, an abrasive grain belt, shot blasting, or the like may be used. However, 5 any methods may be used in so far as the above range of removing is satisfied.
[0064]
When the removing amount is less than GL in |.un, the P-, Ni-, and Cu-segregated part remain in the steel surface part. When the removing amount is more than GU in |.un, the time or equipment for removing is further required, the cost rises, and 10 the yield of the steel decreases.
[0065]
The Ni content and the Cu content in the steel surface part may be measured by
using a Glow Discharge Spectroscopy (GDS), an Electron Probe Micro Analyzer
(EPMA), or the like. The equally-spaced ten measurement points of the hot-rolled steel
15 sheet may be set in the transverse direction by equally dividing the line-segment having
the reference length of 50 mm by 10, and thus, the Ni content and the Cu content in each
measurement point may be measured by using the GDS or the EPMA. In a case of
using the GDS for the analysis, from a standpoint of saving the measuring time, it is
preferable that the GDS measurement is conducted after preliminarily removing the
20 surface scale of GDS test sample. In a ease of using the EPMA for the analysis, it is
preferable that, after polishing a cross section that is planarly cut along the thickness
direction so that the observed section corresponds to the transverse direction
perpendicular to the rolling direction of the hot-rolled steel sheet, the EPMA
measurement is conducted on the cross section.
25 [0066]
In addition, as a pickling process after the surface-removing process, the pickling may be conducted as necessary in order to pickle and remove the surface on the scale-removed rolled steel sheet. Although a pickling method is not particularly limited, a general pickling method such as sulftiric acid, or nitric acid may be applied. As 30 mentioned above, it is preferable to conduct at least one of the pickling process after the hot-rolling process and before the surface-removing process or the pickling process after the surface-removing process and before the below-mentioned galvanizing process, in order to pickle the surface of the scale-removed rolled steel sheet. It is difficult to

22 remove the P-, Ni-, and Cii-segregated part by the pickling process, and tlius, it is needed to conduct the surface-removing so as to control tlie removing amount to be within the above range in order to remove the segregated part. By conducting the picl<:ling process, the adhesion between the scale-removed rolled steel sheet and the galvannealed layer is 5 preferably improved. [0067]
In general, P, Ni, and Cu segregate to the interface between the scale and the
steel in the steel sheet during the heating process and the hot-rolling process. The
segregated part is elongated along the longitudinal direction of the steel sheet by
10 hot-rolling, and thereby, the P-, Ni-, and Cu-segregated part is linearly formed. During
the coiling in the hot-rolling process, P further segregates to the interface between the
scale and the steel. Ni and Cu are not removed by the pickling. Thus, when the Ni-
and Cu-segregated part remains in the steel sheet after the surface-removing process, the
Ni- and Cu-segregated part still remains in the steel sheet surface even after conducting
15 the pickling process. P which exists in the Ni- and Cu-segregated part delays the
alloying reaction during the galvannealing process, and thereby, the surface defects
having linear pattern or the like appear. When P independently segregates, P is removed
and invalidated by the pickling process, and thereby, the surface defects having linear
pattern or the like hardly appear.
20 [0068]
In the method for producing the galvannealed steel sheet according to the embodiment, by optimally conducting the surface-removing for the hot-rolled steel sheet, P which exists in the Ni- and Cu-segregated part is removed and invalidated. The above amount of surface-removing is optimized, and thus, it is possible to sufficiently remove 25 the P-segregated part with the removing amount which is less than that of the prior arts. [0069]
In addition, as a cold-rolling process after the surface-removing process or after the pickling process, the scale-removed rolled steel sheet may be cold-roiled as necessary under a cold-reduction of 50% to 95%. By cold-rolling under the cold-reduction of 30 50% to 95%, it is possible to preferably control the scale-removed roiled steel sheet to be the predetermined thickness in addition to ensuring the r value and the formability. When the cold-reduction is less than 50%, a coil length of the hot-rolled steel sheet may be elongated in the hot-rolling process, and the cost may equipmently rise. On the other

23 hand, when the cold-reduction is more than 95%, the cold-rolling mill for high load may be needed, and the cost may rise. In addition, in a case where both the pickling process and the cold-roliing process are conducted after the surface-removing process, the process order may be the surface-removing process, the pickling process, and the 5 cold-rolling process. [0070]
In addition, as an annealing process after the cold-rolling process, the
scale-removed rolled steel sheet may be amiealed as necessary in a temperature which is
the recrystallization temperature or higher. When the annealing is conducted in the
10 temperature which is the recrystallization temperature or higher, the strain derived from
the rolling may be relieved, and the formability may be improved by softening, hi
addition, even when the scale-removed rolled steel sheet is subjected to the cold-rolling
process or the annealing process as necessaiy, it is possible to unchangingly obtain the
effects according an aspect of the present invention.
15 [0071]
In a galvanizing process after the surface-removing process, after the pickling process, after the cold-rolling process, or after the annealing process, the scale-removed rolled steel sheet is galvanized in order to obtain the galvanized steel sheet. When the galvanizing process is conducted, it is preferable that the scale-removed rolled steel sheet 20 after the annealing process and before the galvanizing process is not cooled and is continuously subjected to the treatment by using the continuous annealing furnace. [0072]
In a galvamiealing process after the galvanizing process, the galvanized steel sheet is galvannealed in order to obtain the galvannealed steel sheet. At the time, it is 25 preferable that the galvanized steel sheet after the galvanizing process and before the galvamiealing process is not cooled and is continuously subjected to the treatment by using the continuous annealing furnace.
Example 30 [0073]
Hereinafter, the effects of an aspect of the present invention will be described in
detail with reference to the following examples. However, the condition in the

24 examples is an example condition employed to confirm the opeiability and the effects of
the present invention, so that the present invention is not limited to the example condition.
The present invention can employ various types of conditions as long as the conditions
do not depart from the scope of the present invention and can achieve the object of the
5 present invention.
[0074]
The galvannealed steel sheet was produced by the steel compositions as shown
in Table 1 and by the production conditions as shown in Tables 2 and 3. Specifically,
the cast piece (slab) as the test material which had the steel compositions as shown in
10 Table 1 was made by the continuous casting. The slab was heated and held in the
heating furnace (heating process), was scale-removed (descaling) after being taken out, and was hot-rolled under the conditions such as the finishing temperature and the coiling temperature as shown in Table 2 (hot-rolling process). The surface of the hot-rolled steel sheet after the hot-rolling process was pickled as necessary (pickling process), and
15 the hot-rolled steel sheet was surface-removed in order to obtain the scale-removed rolled steel sheet (surface-removing process). The surface of the scale-removed rolled steel sheet was pickied and cleaned as necessary (pickling process). The scale-removed rolled steel sheet was cold-rolled as necessary to the predetermined thickness (cold-rolling process), and was annealed as necessary in the continuous annealing
20 furnace (annealing process). The scale-removed rolled steel sheet was galvanized by dipping it into the coating bath (galvanizing process), and was galvannealed in order to obtain the galvannealed steel sheet (galvannealing process). In the Tables 2 and 3, for example, "CO. (Carrying Out)" indicates that the pickling was conducted, and "Not CO. (Not Carrying Out)" indicates that the pickling was not conducted. The other processes
25 are indicated in the same manner.

25 [0075]
In addition, the balance of the steel compositions as shown in Table 1 consisted
of Fe and unavoidable impurities. In addition, in the Tables, underlined values indicate
out of the range of the present invention.
5 [0076]
In the Table 2, the conditions of the surface-removing (surface-removing
process) for the hot-rolled steel sheet are shown. Herein, by using the hot-rolled steel
sheet before the siuTace-removing, the Nin,ax and the Cu,„a\ were measured in the steel
surface part which was from the interface between the scale and the steel to 2 \im in
10 depth toward the steel along the thickness direction, and the GL and the GU which
corresponded to the appropriate range for the surface-removing were calculated in fim.
Also, the actual removing amount was shown in the Table 2. In addition, the Ni^ax and
the Cuniax were measured b}^ using the Election Probe Micro Analyzer (EPMA). The
ten measurement points of the hot-rolled steel sheet were set in the transverse direction
15 by equally dividing the line-segment having the i'eference length of 50 mm by 10, and
thus, the Ni content and the Cu content in each measurement point were measured by
using the EPMA. Herein, the measurement result of the steel surface part was regarded
as the measured average from the above interface of the hot-rolled steel sheet to 2 }.im
toward the steel along the thickness direction. Also, the Nimax and the Cumax were
20 regarded as the maximum Ni content and the maximum Cu content in mass % in the ten
measurement points.
[0077]
Similarly, the P content, the Ni content, and the Cu content were measured in the
surface part and the base part of the scale-removed rolled steel sheet after the
25 surface-removing, and thereby, the segregating situation was checked. The ten

26 measurement points of the scale-removed rolled steel sheet were set in the transverse
direction by equally dividing the line-segment having the reference length of 50 mm by
10, and thus, the P content, the Ni content, and the Cu content in each measurement point
in the ten measurement points were measured by using the GDS. Herein, the
5 measurement result of the surface part of the scale-removed rolled steel sheet was
regarded as the measured average from the surface of the scale-removed rolled steel sheet
to 0.1 i-un along the thickness direction, and the measurement result of the base part of
the scale-removed rolled steel sheet was regarded as the measured average from the
surface to the range of more than 2 [im to 4(am. The segregating situation was
10 expressed in percentage by respectively comparing the P content, the Ni content, and the Cu content of the surface part of the scale-removed rolled steel sheet with the P content, the Ni content, and the Cu content of the base part of the scale-removed rolled steel sheet. When the comparing result in each element was within 105% or more and 150% or less, it was judged to be acceptable. The Table 5 shows the measurement result of the
15 segregating situation of P, Ni, and Cu which are expressed as the ratio of the surface part of the scale-removed rolled steel sheet to the base part of the scale-removed rolled steel sheet. Herein, the Table 5 only shows the result of the one measurement point which is the farthest value from 127.5% (intermediate value between 105% and 150%) among the measurement results of the segregating situation of P, Ni, and Cu in tiie ten measurement
20 points.
[0078]
For each galvannealed steel sheet of examples and comparative examples which ware produced by the above method, the tensile characteristics, the r value (Lankford-value) which is the factor of the deep drawabilhy, and the surface quality were
25 evaluated. The evaluation method will be described below.

27 [0079]
The tensile test was conducted, for example, based on JIS Z 2241:2011 or ISO
6892-1: 2009 by using JIS No. 5 test samples which were prepared from each
galvarmealed steel sheet so that a tensile direction was perpendicular to the rolling
5 direction and the thickness direction, and the tensile strength (TS) in MPa and the
elongation (EL) in % were evaluated as the tensile characteristics. When the tensile
strength was 320 MPa or more and the elongation was 20% or more, it was judged to be
acceptable.
[0080]
10 The r value which was the factor of the deep drawability was measured and
evaluated, for example, based on JIS Z 2254: 2008 or ISO 10113-1: 2006 by using JIS No. 5 test samples which were prepared from each gah'anneaied steel sheet from three directions which were the direction parallel to the rolling direction, the direction making an angle of 45° with the rolling direction, and the direction perpendicular to the rolling
15 direction. For example, the r value may be measured by measuring the thickness
change and the width change at the point of approximately 10% tensile deformation in the tensile test and by calculating the ratio of the width change to the thickness change. When ro w^as the r value in the direction parallel to the rolling direction, r45 was the r value in the direction making the angle of 45° with the rolling direction, and rgo was the r
20 value in the direction perpendicular to the rolling direction, the r value was evaluated by rave which was the average of the r values in the directions and which was calculated using the following Expression E. In the present example, when the rave was 1.2 or more, it was judged to be acceptable.
I'ave = (t'o + 2 X r45 + rgo) / 4 ■ ■■ (Expression E)
25 [0081]

28 The surface quality was evaluated by investigating the P content in the
gaivannealed layer, by investigating the unevenness of the galvannealed layer thickness,
and by observing the existence of the patternlike defects.
[0082]
5 The P content in the galvannealed layer was measured by using the GDS. The
ten measurement points of the galvannealed steel sheet were set in the transverse
direction by equally dividing the line-segment having the reference length of 50 nmi by
10, and thus, the P content in each measurement point in the galvannealed layer was
measured by using the GDS. When the minimum P content in the ten measurement
iO points in the galvannealed layer of the galvannealed steel sheet was 50% or more as compared with the maximum P content therein, it was judged to be acceptable. [0083]
The galvannealed layer thickness was measured on the cross section that was planarly cut along the thickness direction so that the observed section corresponded to
15 the transverse direction perpendicular to the rolling direction of the galvannealed steel sheet. The ten measurement points of the galvannealed steel sheet were set in the transverse direction by equally dividing the line-segment having the reference length of 50 mm by 10, and thus, the galvatmealed layer thickness in each measurement point was measured by observing the metallographic structure on the cross section. The
20 metallographic structure was observed under the magnification in which the visual field Avas to be 1000 i-un or less in the transverse direction. When the minimum thickness in the ten measurement points in the galvannealed layer of the galvannealed steel sheet was 50% or more as compared with the maximum thickness content therein, it was judged to be acceptable.
25 [0084]

29 The existence of the patternlike defects was visually observed after scrubbing
tlie surface of tlie galvannealed steel sheet with the grindstone. The scrubbing with the
grindstone simulated the abrasion at the press-forming. By the method, it was possible
to generally judge whether the patternlike defects would appear or not after the actual
5 press-forming, hi the Table 5, "Good" indicates that the patternlike defects did not
appear after conducting the method in the galvamiealed steel sheet, and "Bad" indicates
that the patternlike defects appeared in the galvarmealed steel sheet.
[0085]
The results are shown in the following Tables. Table 4 shows the tensile
10 strength, the elongation, and the rave value as the mechanical propeilies. Table 5 shows
the segregating situation of P, Ni, and Cu in the scale-removed rolled steel sheet, the
unevenness of the P content in the galvannealed layer, the unevenness of the
galvannealed layer thickness, and the existence of the patternlike defects.
[0086]
15 As shown in the Tables 4 and 5, in the examples in the galvannealed steel sheets,
the mechanical properties were satisfied, the formability was excellent, the unevenness of
the P content in the galvannealed layer and the unevenness of the galvannealed layer
thickness were small, and simultaneously, the patternlike defects on the surface did not
appear.
20 [0087]
On the other hand, the other galvannealed steel sheets were the comparative
examples which were out of the range of the present invention.
In the Steel No. C and the Steel No. M, since the removing amount was less than
GL which was the lower limit, the P, Ni, and Cu were segregated to the steel surface pai1
25 even after the surface-removing process. Thus, the minimum P content in the

30 galvannealed layer and the minimum thickness of the galvannealed layer were less than
50% as compared with the maximum therein, and the linear pattern defects appeared.
In the Steel No. G and the Steel No. J, the removing amount was more than the
upper limit. Thus, the removing amount was not optimum and excessive, it took time
5 for the removing, and thus, the cost rose.
In the Steel No. Q which was the comparative example, the P content was more
than the upper limit. Thus, in the galvannealed steel sheet, the alloying rate delayed, the
surface quality became iineven, and the linear pattern defects partially appeared.
In the Steel No. R which was the comparative example, the Mn content was
10 more than the upper limit. Thus, in the galvamiealed steel sheet, the r value was the low
value such as 1.1. Also, since the galvanizability deteriorated, the linear pattern defects
partially appeared.
In the Steel No. S which was the comparative example, the C content was more
than the upper limit, and the removing amount was more than the upper limit. Thus, in
15 the galvannealed steel sheet, since the r value was 0.9, the formability was insufficient.
Also, since the removing amount was not optimum and excessive, the cost rose.
In the Steel No. T which was the comparative example, the Ti content was more
than the upper limit. Thus, in the galvamiealed steel sheet, since the r value was 0.9, the
formability was insufficient.
20 In the Steel No. U which was the comparative example, the Ni content was more
than the upper limit. In the Steel No. V which was the comparative example, the Cu
content was more than the upper limit. In addition, in the galvannealed steel sheets, the
removing amount was less than the lower limit. Thus, in the galvamiealed steel sheets,
the surface quality became uneven, and the pattern defects appeared.
25 In the Steel No. W which was the comparative example, the Nb content was

31 more than the upper limit. Thus, in the galvannealed steel sheet, since the r value was
1.1, the formability was insufficient.
In the Steel No. KK which was the comparative example, the C content was less
than the lower limit. Thus, in the galvannealed steel sheet, since the steel making
5 needed to be excessively conducted in order to decrease the C content, the cost rose.
In the Steel No. LL which was the comparative example, the C content was
more than the upper limit. Thus, in the galvannealed steel sheet, the formability was
insufficient.
In the Steel No. MM wliich was the comparative example, the Si content was
10 less than the lower limit. Thus, in the galvaimealed steel sheet, the tensile strength was
insufficient.
In the Steel No. NN which was the comparative example, the Si content was
more than the upper limit. Thus, in the galvannealed steel sheet, the formability was
insufficient.
15 In the Steel No. 00 which was the comparative example, the Mn content was
less than the lower limit. Thus, in the galvannealed steel sheet, the tensile strength was
insufficient.
In the Steel No. PP which was the comparative example, the P content was less
than the lower limit. Thus, in the galvannealed steel sheet, the tensile strength was
20 insufficient.
In the Steel No. QQ which was the comparative example, the Al content was
less than the lower limit. Thus, in the galvannealed steel sheet, since the deoxidation
was insufficient and the oxides remained, the formability was insufficient.
In the Steel No. RR which was the comparative example, the Al content was
25 more than the upper limit. Thus, in the galvamiealed steel sheet, the formability was

32 insufficient.
In the Steel No. SS \vhich was the comparative example, the S content was more
than the upper limit. Thus, in the galvannealed steel sheet, the formability was
insufficient.
5 In the Steel No. TT which was the comparative example, the B content was
more than the upper limit. Thus, in the galvannealed steel sheet, the formability was
insufficient.
In the Steel No. UU which was the comparative example, the heating
temperature in the heating process was lower than the lower limit, and the finishing
10 temperature in the hot-rolling process was lower than the lower limit. Thus, in the
galvamiealed steel sheet, the formability was insufficient.
In the Steel No. VV which was the comparative example, the finishing
temperature in the hot-rolling process was lower than the lower limit. Thus, in the
galvannealed steel sheet, the formability was insufficient.
15 In the Steel No. WW which was the comparative example, the coiling
temperature in the hot-rolling process was lower than the lower limit. Thus, in the
galvannealed steel sheet, since the defective shape occurred, the product was not usable.
In the Steel No. XX which was the comparative example, the coiling
temperature in the hot-rolling process was higher than the upper limit. Thus, in the
20 galvannealed steel sheet, since the scale defects were excessive, the product was not
usable.
In the Steel No. AB which was tlie comparative example, the Mo content was
more than the upper limit. Thus, in the galvamiealed steel sheet, the formability was
insufficient.
25 In the Steel No. AC which was the comparative example, the N content was

33
more than the upper hmit. Thus, in the galvannealed steel sheet, the formabihty was
insufficient.
[0088]
[Table 1]
5 Table 1 (continued 1 of 2)
SfEEOCHEHlCAL COMPOSITION
No. ""C r~Sl I Mn I P I Al I S I Ni I Cu I N r~B I Nb I Ti I Mo
(mass%) (niass%) (rnassS) (niass%) (massji) [mass%) (mass%) Onasjji) (fnass%) (mass%) (mass%) (niass%) ([i]as$%)
A 0.0007 0.004 0.11 0.010 0.030 0.003 Q.OlO 0.010 Q.002 0.0006 0.070
B 0.0015 0.015 2.00 0.015 0.040 0.006 0.005 0.020 0.002 0.0004 0.011
C 0.0020 0.010 0.13 0.006 0.050 0.012 0.050 0.010 0.003 0.015 0.02
P 0.0005 0.010 0.20 0.010 0.035 0.010 0.020 0.050 0.002
E 0.0005 0.020 0.18 0.008 0.060 0.020 0.030 0.005 0.0O3
F 0.0022 0.007 0.57 0.023 0.050 0.006 0.010 0.015 0.002 0.0012 0.013
G 0.0055 0.040 0.65 0.045 0.030 0.020 0.015 0.004 0.002 0.0015 0.020 0.01
H 0.0032 0.440 0.40 0.020 0.043 0.013 0.024 0.011 O.O02
1 0.0040 0.040 0.65 0.045 0.075 0.020 0.037 0.026 0.002 0.0O25 0.027
J 0.0021 0.008 0.30 0.018 0.060 O.QI 2 0.015 0.010 0.Q02 0.0013 0.017 0.02
K 0.0050 0.034 0.45 0.045 0.070 0.020 0.040 0.040 0.002 0.0015 0.030
L 0.0035 0.023 0.80 0.015 0.022 0.014 0.016 0.Q29 0.003 0.028
M 0.0025 0.250 0.10 0.080 0.050 0.018 0.020 0.015 0.002 0.020 0.01
N 0.0028 0.294 1.20 0.059 0.060 0-015 0.030 0.004 0.002 0.0035 0.095
O 0.0022 0.550 1.20 0.027 0.050 0.003 0.002 0.005 0.O02 0.0015 0.030 0.03
P 0.0035 0.950 1.50 0.100 0.080 0.015 0.010 0.002 0.002 0.080
Q 0.0034 0.021 0.11 0.200 0.050 0.005 0.042 0.020 0.002
R 0.0018 0.012 2.80 0.010 0.035 0.016 0.024 0.033 0.005 0.050
S 0^300 0.040 0.42 0.023 0.070 0.010 0.010 0.020 0.002 0,0048 0.05
T 0.0100 0.360 0.10 0.015 0.060 0.013 0.020 0.016 0.002 QM
U 0.0031 0.546 1.06 0.040 0.045 0.011 0300 0.013 0.003 0.0007 0.016
V 0.0021 0.360 1.43 0.070 0.054 0.014 0.030 0500 0.002 ——--
W 0.0018 0.550 1.24 0.054 0.045 0.007 0.020 0,010 0.002 0.0008 0.500 0.02
X 0.0095 0.O08 1.10 0.050 0.043 0.013 0.024 0.011 0.002
Y 0.0020 0.(X)8 0.02 0.050 0,043 0.013 0.024 0.011 0.002
Z 0.0020 0,008 1.10 0.050 0.043 0.013 0.093 0.011 0.002
Table 1 (continued 2 of 2)

34
STEELlCHEHICAL COMPOSITION
No. ~C r^i I Mn I P I Al I S | Ni | Cu I N [""B | Nb I Tt | Ho
Cmass%) (mass%) (niass%) (niass%) (mass%) (fliass%) (fliass%) (mass%) [mass%) ;mass%) Crnass%) [mass%) (mass%)
AA 0.0020 0.008 1.10 0.050 0.043 0.013 0.024 0.096 D.002
BB 0.0020 0.008 1.10 0.050 0.043 0.013 0.024 0.011 0.002 0.ODO1
GC 0.0020 0.008 1.10 0.050 0.043 0.013 0.024 0.011 0.002 0.0027
DP 0.0020 0.008 1.10 0.050 0.043 0.013 0.024 0.011 0.002 OOOl
EE 0.0020 O.QOS 1.10 0.050 0-043 0.013 0.024 0.011 0.002 0.090
FF 0.0020 0.003 1.10 0.050 0.043 0.013 0.024 0.011 0.002 OOO!
GG 0.0020 0.008 1.10 0.050 0.043 0.013 0.024 0.011 0.002 0050
HH 0.0020 0.008 1.10 0.050 0.043 0.013 0.024 0.011 0.002 OOWOS
II 0.0020 0.008 1.10 0.050 0.043 0.013 0.024 0.011 0.002 0.0007
JJ 0.0020 0.008 1.10 0.050 0-043 0.013 0.Q24 0.011 0.002 0.0008
KK 0.0004 0.008 1.10 0.050 0.043 0.013 0.024 0.011 0.002
LL OQltQ 0.008 1.10 0.050 0.043 0.013 0.024 0.011 0.002
MM 0.0020 0^008 0.01 0-005 0.043 0.013 0.024 0011 0.002
NN 0.0020 1.100 1.10 0.050 0.043 0.013 0.024 0.011 0.QO2
00 0.0020 0.008 0.009 0.005 0.043 0,013 0.024 0.011 0.002
PP 0.0020 0.008 0.01 0.003 0-043 0.013 0.024 0.011 0.002
QQ 0.0020 0.008 1.10 0.050 0^8 0.013 0.024 0.011 0.002
RR 0.0020 0.008 1.10 0.050 QAM 0.013 0.024 0.011 0.002
SS 0.0020 0.008 1.10 0.050 0.043 0,022 0.024 0.011 0.002
TT 0.0020 0.008 1.10 0.050 0.043 0.013 0.024 0.011 0.002 0.0052
UU 0.0020 0.008 1.10 0.050 0.043 0.013 0.024 0.011 0.Q02
W 0.0020 0.008 1.10 0.050 0.043 0.013 0.024 0.011 0.002
WW 0.0020 0.008 1.10 0.050 0.043 0.013 0.024 0.011 0.002
XX 0.0020 0.008 1-10 0.050 0.043 0.013 0.024 0.011 0.002
YY 0.0020 0.008 1.10 0.050 Q.Q43 0.013 0.024 0.011 0.002
ZZ 0.0030 0.011 0.57 0.020 Q-050 0.008 0.010 0.020 O.O03 0.0014 0.015 0.001 O.024
AB 0.0040 0.014 0.62 0.017 0.058 0.008 0.010 0.035 0-003 0.0012 _001_6 0.150
AC 0.0020 0.008 1.10 0.050 0.043 0.012 0.024 0.011 0.012
AD 0.0020 0.008 1.10 Q-050_ _Q-Q43 0013 0.024 0.011 0.002 0.0009
[0089] [Table 2]
Table 2 (continued 1 of 2)

35
STEEL I HEATING I HOT-ROLL IHG I PICKLING I SURFACE-REMOVING PROCESS ^~-—
Mo PROCESS PROCESS PROCESS
tsriTiiv^ nmcu.i-,. I miniv^ PICKLIKG SURFACE-REMOVIHG iDPiinuiurl "' ^^ ^ ^™^ I ^'^^^ ^^ ^
mum mmm CfllLIKG BEFORE ^""•^^^'^ """'ifM REMOVING m cTcn MPCIM: DIDT KunuiiM luniBn
IEKPERATMTEKPERATURETEMUM KE ''ETHOD AMOUNT I" STEEL MCE PART MIfKAM
rc) ra m -REVOVIHG (uni) "'^^ cit^^x GL GU
^^^ ^ ^ ^^^ PROCESS ^^""^ (mass%) (mass^) (/Jm) (//m)
A 1230 905 650 CO. GRINDER 0.7 0.108 0.12O 0.041 0.816
B 1230 905 650 CO. WIRE BRUSH ROLL 0.35 0.089 0.308 0-067 1.342
C 1230 905 650 CO. WIRE BRUSH ROLL OJ. 1.120 0.186 0.254 5.075
D 1230 905 650 Not CO. GRINDER 1.5 0.300 0.815 0.190 3.808
E 1230 905 650 CO. WIRE BRUSH ROLL 0.3 0.258 0.047 0.059 1.1S2
F 1230 905 650 CO. SHOT BLASTING 0.5 0.130 0.125 0.046 0.920
G 1230 905 650 CO. GRINDER 01 0.090 0.049 0.026 Q.517
H 1230 905 650 CO. GRINDER 0.6 0.139 0.055 0.037 0.732
I 1230 905 650 CO. WIRE BRUSH ROLL 0.15 0.477 0.299 0.143 2.865
J 1230 905 650 CO. GRINDER 21 0.170 0.068 0.045 0.898
K 1230 905 650 CO. GRINDER 0.8 0.348 0.348 0.125 2.508
L 1230 905 650 CO. GRINDER 0.4 0.157 0.229 0.068 1.361
M 1230 905 650 CO. WIRE BRUSH ROLL OM 0.328 0.186 0.095 1.907
N 1230 905 650 CO. WIRE BRUSH ROLL 0.95 0.237 0.045 0.055 1.092
O 1230 905 650 CO. GRINDER 0.1 0.013 0,042 0.0O9 0.186
P 1230 905 650 CO. WIRE BRUSH ROLL 0.6 0.253 0.040 0.057 1.140
Q 1230 905 650 CO. GRINDER 1.1 0.281 0.108 0.073 1.470
R 1230 905 650 CO. SHOT BLAST ING 1.45 0.226 0.284 0.091 1.813
S 1230 905 650 CO. GRINDER 2J. 0.146 0.288 0.075 1.506
T 1230 905 650 CO. WIRE BRUSH ROLL 0.6 0.350 0.286 0.116 2,315
U 1230 905 650 CO. GRINDER 04 2.700 0.086 0.555 11.107
V 1230 905 650 CO. WIRE BRUSH ROLL 05 0.150 2.950 0.502 10.040
V/ 1230 905 650 CO. GRINDER 0.6 0.148 0.069 0.041 0.813
X 1230 905 650 CO. GRINDER 0.6 0.139 0.055 0.037 0.732
Y 1230 905 650 Not CO. GRINDER 0.6 0.139 0.055 0.037 0.732
Z I 1230 I 905 I 650 | CO- | GRINDER | 0.6 | 0.539 j 0.055 | 0.117 | 2.33"
Table 2 (continued 2 of 2)

36
TEMTlRETEVf£RATlR£TE«TURE sEI METHOD AMOUNT ■" S^ WCE PART mm mm
^^' ^^^ ^^^ PROCESS ^ ^ (mass%) (mass%) (f/m) (//m)
AA 1230 905 650 CO. GRlfJDER 0.6 0.139 0.480 0.1Q5 2.092
BB 1230 905 650 CO. GRIHDER 0.6 0.139 0.055 0.Q37 0.732
CC 1230 905 650 CO. GRIKDER 0.6 0.139 0.055 0.037 0.732
DP 1230 905 650 CO. GRINDER 0.6 0.139 0.055 0.037 0.732
EE 1230 905 650 CO. GRIHDER 0.8 0.139 0.055 0.037 0.732
FF 1230 905 650 CO- GRIHDER 0.6 0.139 0.055 0.037 0.732
GG 1230 905 650 CO. GRIHDER 0.6 0.139 0.055 0.037 0.732
HH 1230 905 650 CO. GRINDER 0.6 0.139 0.055 0.037 0.732
II 1230 905 650 CO. GRINDER 0.6 0.139 0.055 0.037 0.732
J J 1230 905 650 CO. GRIHDER 0.6 0.139 0.055 0.037 0.732
KK 1230 905 650 CO. GRINDER 0.6 0.139 0.055 0.037 0.732
LL 1230 905 650 CO. GRIHDER 0.6 0.139 0.055 0.037 0.732
MM 1230 905 650 CO. GRINDER 0.6 0.139 0.055 0.037 0.732
NN 1230 905 650 CO. GRIHDER 0.6 0.139 0.055 0.O37 0.732
OO 1230 . 905 650 CO. GRIHDER 0.6 0.139 0.055 0.037 0.732
PP 1230 905 650 CO. GRIHDER 0.6 0.139 0.055 0.037 0.732
QQ 1230 905 650 CO- GRIHDER 0.6 0.139 0.055 0.037 0.732
RR 1230 9Q5 650 CO. GRIHDER 0.6 0.139 0.055 0.037 0.732
SS 1230 905 650 CO. GRIHDER 0.6 0.139 0.055 0.037 0.732
TT 1230 905 650 CO. GRIHDER 0.6 0.139 0.055 0.037 0.732
UU 1080 780 650 CO. GRINDER 0.6 0.139 0.055 0.037 0.732
W 1230 790 650 0.0. GRIHDER 0.6 0.139 0.055 0.037 0.732
mi 1230 905 480 Not CO. - Hot CO. - -
XX 1230 905 BIO Hot 0-0- - IMMQ. I I -
YY 1230 905 650 Not 0.0. GRINDER 0.6 0.139 0.055 0.037 0.732
ZZ 1230 905 650 CO. SHOT BLASTIHG 0.5 0.130 0.166 0.O53 1.051
AB 1230 905 650 CO. SHOT BLASTING 0.5 0.130 0.291 0-072 1.450
AG 1230 905 650 CO. GRINDER 0.6 0.139 0.055 0.037 0.732
AD 1230 905 650 CO. GRIHDER 0.6 I 0.139 0.055 0.037 0.732
[0090]
[Table 3] Table 3 (continued 1 of 2)

37
STEEL I PICKLING I COLD-ROLLING I ANNEALING PROCESS iGALVAfilZIHGlGALVAHflEALIfJG
No. PROCESS PROCESS PROCESS PROCESS
PICKLING 1 AFTER "CO." COLD "CO." ANNEALING "CO." "CC"
SURFACE OR REDUCTION OR TEMPERATURE OR OR
-REMOVING "NOT C. 0." (%) "NOT C 0." Cc) "NOT C 0." "NOT C 0. "
PROCESS I
A " CO. CO. 80 0.0. 790 CO. CO.
B CO. CO. 80 CO. 790 G.O. CO.
C 0.0. CO. 80 CO. 790 CO. CO.
D CO. CO. 80 CO. 790 CO CO.
E CO. CO. 80 CO. 790 CO. CO.
F CO. 0.0. 8Q CO. 790 CO. CO.
G 0.0. CO. 80 0.0. 790 CO. CO.
H CO. CO. 80 CO. 790 G.O. 0.0.
I CO. CO. 80 CO. 790 CO. CO.
J CO. CO. 80 CO. 790 CO. 0.0.
K CO. CO. 80 CO. 790 CO. P.O.
L CO. CO. 80 CO. 790 CO. CO.
M CO. CO. 80 CO. 790 CO. CO.
N CO. CO. 80 CO. 790 CO. CO.
0 CO. CO. 80 CO. 790 CO. G.O.
P G.O. CO. 80 G.O. 790 CO. CO.
Q G.O. G.O. 80 G.O. 790 CO. CO.
R G.O. CO. 80 G.O. 790 0.0. P.O.
S CO. G.O. 80 G.O. 790 CO. CO.
T CO. CO. 80 CO. 790 CO. CO.
U CO. G.O. 80 CO. 790 CO. P.O.
_y CO. G.O. 80 G.O. 790 CO. CO.
W G.O. G.O. 80 CO. 790 CO. CO.
X G.O. CO. 80 G.O. 790 CO. G.O.
Y Not CO. 0.0. 80 CO. 790 CO. CO.
Z Not CO. I CO. I 80^" CO. I 790 | CO. | CO.
Table 3 (continued 2 of 2)

38
STEEL I PICKLING I COLD-ROLLING I ANNEALING PROCESS I GALVANIZING lOALVANHEALIfiG
No. PROCESS PROCESS PROCESS PROCESS
PICKLING \ AFTER "CO." COLD "CO." ANNEALING "CO." "CC"
SURFACE OR REDUCTI ON OR TEMPERATURE OR OR
-REMOVING "NOT CC" (%) "NOT CC" CO "NOT CC" "NOT CC"
PROCESS
AA CO. 0.0. 80 CO. 790 CO. CO.
BB P.O. CO. 80 CO. 790 CO. CO.
CO CO. Not CO. - Not CO. - CO. CO.
DP CO. CO. 80 CO. 790 CO. CO.
BE CO. 0.0. 80 CO 790 CO. CO.
FF CO. 0.0. 80 CO. 790 CO. CO.
GG 0.0. Not CO. - Not CO. CO. CO.
HH CO. CO. 80 CO. 790 CO. 0.0.
II CO. CO. 80 CO. 790 CO. CO.
JJ CO. CO. 80 CO. 790 CO. 0.0.
KK CO. CO^ 80 CO. 790 CO. CO.
LL CO. 0.0. 80 CO. 790 CO. CO.
MM CO. CO. 80 CO. 790 CO. CO.
NN CO. 0.0. 80 CO. 790 CO. CO.
00 CO. CO. 80 CO 790 CO. CO.
PP CO. CO. 80 CO. 790 CO. CO.
QQ 0.0. CO. 80 CO. 790 CO. CO.
RR CO. CO. 80 CO. 790 CO. 0.0.
SS CO. CO. 80 CO. 790 CO. CO.
TT CO. CO. 80 CO. 790 0.0. CO.
UU CO. CO. 80 CO. 790 CO. CO.
W CO. CO. 80 CO. 790 CO. 0.0.
WW Not CO. Not CO. - Not CO. - Not CO. Not CO.
XX Not CO. Not CO. - Not CO. - Not CO. Not CO.
YY Not CO. Not CO. - Not CO. - CO. CO.
ZZ CO. CO. 80 CO. 790 CO. CO.
AB CO. _ 0.0. 80 C.O^ 790 CO. CO-
AC CO. CO. 80 CO. 790 CO. CO.
^_^AD CO. CO. 80 CO. __ 790 _ CO. CO.
[0091] [Table 4] Table 4 (continued 1 of 2)

39
STEEL I TENSILE I ELONGATION I r.^eVALUE I "
No STRENGTH TS EL
"_ (MPa) (%)
A 329 47 1.9 EXAMPLE
B 440 37 1.3 EXAMPLE
C 327 47 1.8 COHPARATIVE EXAMPLE
D 335 46 1.7 EXAMPLE
E 336 46 1.8 EXAMPLE
F 366 44 1^6 EXAMPLE
G 394 41 1.5 COMPARATIVE EXAMPLE
H 405 41 1.5 EXAMPLE
I 395 41 1.6 EXAMPLE
J 347 45 1.7 COJ^PARATIVE EXAMPLE
K 383 42 1.6 EXAMPLE
L 374 43 1.7 EXAMPLE
M 420 39 1.4 COMPARATIVE EXAMPLE
N 463 35 1.2 EXAMPLE
0 465 35 1.2 EXAMPLE
P _575 26 1.2 EXAMPLE
Q 504 32 1.2 g^PARATIVE EXAMPLE
R 469 34 1.1 COMPARATIVE EXAMPLE
S 497 32 0.9 COMPARATIVE EXAMPLE
T 395 42 0.9 COMPARATIVE EXAMPLE
U 474 34 1.2 COMPARATIVE EXAMPLE
V 475 33 1.2 COMPARATIVE EXAMPLE
W 491 33 1.1 COMPARATIVE EXAMPLE
X 455 36 1.2 EXAMPLE
Y 363 44 1.5 EXAMPLE
Z I 420 I 43 I 1.4 I EXAMPLE
Table 4 (continued 2 of 2)

40
STEEL I TENSILE IELONGATIONI r„„eVALUE I
Nn STRENGTH IS EL
(MPa) (%)
AA 409 40 1.4 EXAMPLE
BB 415 39 U EXAMPLE
CC 436 38 U EXAMPLE
DP 413 40 1.4 EXAMPLE
EE 442 37 1.3 EXAMPLE
FF 417 39 1.4 EXAMPLE
GG 435 38 U EXAMPLE
HH 405 40 1.4 EXAMPLE
II 405 41 U EXAMPLE
JJ 405 41 1.4 EXAMPLE
KK 378 43 1.7 COIilPARATlVE EXAMPLE
LL 460 35 1.1 COfilPARATIVE EXAMPLE
MM 315 47 1.8 COMPARATIVE EXAMPLE
NN 545 24 0.9 COMPARATIVE EXAMPLE
QO 313 48 1.8 COMPARATIVE EXAMPLE
PP 302 47 1.8 COMPARATIVE EXAMPLE
QQ 435 24 0.9 COMPARATIVE EXAMPLE
RR 478 32 1.1 COMPARATIVE EXAMPLE
SS 405 36 1.0 COMPARATIVE EXAMPLE
TT 456 34 1.0 COMPARATIVE EXAMPLE
UU 564 26 0.9 COMPARATIVE EXAMPLE
VV 551 27 1.0 COMPARATIVE EXAMPLE
WW 2 COMPARATIVE EXAMPLE
XX - COMPARATIVE EXAMPLE
YY 402 41 1.4 EXAMPLE
ZZ 345_ 41 1.6 EXAMPLE
AB 486 31 1.1 COMPARATIVE EXAMPLE
AC 472 34 1.0 COMPARATIVE EXAMPLE
AD I 405 I 40 I 1.4 I EXAMPLE
[0092] [Table 5] Table 5 (continued 1 of 2)

41
STEEL I SEGREGATING SITUATION OF I ,„„„,.„„^^ ^^ iEXISTENGEJ REMARKS I
M„ P, Ni, AND Cu IN UNEVENNESS OF Qp
"°- SCALE-REMOVED GALVANNEALEO UYER ■ ,NFAR
ROLLED STEEL SHEET {HINIHUM-MMIMUH) 0/™^
(SURFACE PART-f BASE PART) ^ ncclnro
P Ni Cu P CONTENT ^^AYER „
(%) (%) (%) (^) ™^^ OR "Bad"
A 115 113 111 77 85 Good EXAMPLE
B 139 142 135 68 75 Good EXAMPLE
G 169 183 179 40 42 Bad - COMPARATIVE EXAMPLE
D 134 131 129 77 89 Good - EXAMPLE
E 145 139 144 61 72 Good EXAMPLE
F 124 132 129 72 87 Good EXAMPLE
G 103 102 101 79 92 Good COST ROSE COMPARATIVE EXAMPLE
H 113 116 118 70 84 Good EXAMPLE
I 135 128 126 65 68 Good EXAMPLE
J 99 101 102 75 92 Good COST ROSE COMPARATIVE EXAMPLE
K 139 145 141 82 93 Good - EXAMPLE
L 132 125 141 66 79 Good EXAMPLE
M 178 181 173 8 31 Bad - COMPARATIVE EXAMPLE
N 105 106 106 75 84 Good - EXAMPLE
O 110 108 109 87 86 Good EXAMPLE
P 125 118 123 75 74 Good ~ EXAMPLE
Q 125 lie 116 42 43 Bad - COMPARATIVE EXAMPLE
R 107 105 108 72 94 Good - COMPARATIVE EXAMPLE
S 104 103 103 81 92 Good COST ROSE COMPARATIVE EXAMPLE
T 150 149 147 77 74 Good - COMPARATIVE EXAMPLE
U 168 172 165 22 39 Bad - COMPARATIVE EXAMPLE
V 155 163 161 17 46 Bad - COMPARATIVE EXAMPLE
W 123 131 138 68 76 Good - COMPARATIVE EXAMPLE
X 113 116 118 70 84 Good - EXAMPLE
Y 113 116 118 70 84 Good EXAMPLE
~ Z I 143 I 141 I 136 I 58 I 59 I Good | - | EXAMPLE
Table 5 (continued 2 of 2)

42
STEEL I SEGREGATING SITUATION OF I „^,^„^„„„^ ^^ IEXISTENGEI REMARKS I
No P, Ni, AND Cu IN UNEVENNESS OF QF
" ■ SCALE-REMOVED GALVANNEALEO LAYER ■ ,ur.n
ROLLED STEEL SHEET (MINIMUM-^MAXIMUH) pVnFRfj
(SURFACE PART-^BASE PART) ^J™
I 1 I I Avco DEFEGTS
P Ni Gu P CONTENT LAYER „^^^^„
(%) (%) (%) (^) ^^" OR "Bad"
AA t41 136 143 _ 56 57 Good - EXAMPLE
BB 113 116 118 70 84 Good ^ EXAMPLE
CC 113 116 118 70 84 Good ^ EXAMPLE
DP 113 116 118 7j 84 Good - EXAMPLE
EE 113 116 118 _ 70 84 Good - EXAMPLE
FF 113 116 118 70 84 Good ~ EXAMPLE
GG 113 116 118 70 84 Good EXAMPLE
HH 113 116 118 70 84 Good - EXAMPLE
I[ 113 118 118 70 84 Good - EXAMPLE
JJ 113 116 118 70 84 Good - EXAMPLE
KK 113 116 118 70 84 Good COST ROSE CfflmilVE EXAIRE
LL 113 116 118 70 84 Good COVPARATIVE EXME
MM 113 116 118 70 84 Good (^tfPARATIVE EXAJTIE
NN 113 116 118 70 84 Good COi«^ARATIVE EXAIRE
00 113 116 118 70 84 Good CpyfARATIVE EXAiPLE
PP 105 116 118 82 94 Good COMPARATIVE EXAIPIE
QQ 113 116 118 70 84 Good IMARATIVE EXAffLE
RR 113 116 118 70 84 Good COMPARATIVE EXAiffLE
SS 113 116 118 70 84 Good QJItPARATIVE EXAJFLE
TT 113 116 118 70 84 Good COi/PARATIVE EXAIfflE
UU 113 116 118 70 84 Good COMPARATIVE EXAiffLE
W 113 116 118 70 84 Good COMPARATIVE EXAiffLE
WW - -_ - - [fftClH^S^J^tCCORia COMPARATIVE EXAiffLE
XX - 2 : SCALE DEFECTS (^PARATIVE EXAiffLE
YY 113 116 118 70 84 Good ~ EXAMPLE
ZZ 127 129 129 72 85 Good EXAMPLE
AB 125 132 128 71 75 Good COMPARATIVE EXAiffLE
AC 113 116 118 70 84 Good COMPARATIVE EXAiffLE
"~ AD 1 113 I 116 I 118 I 70 I 84 ["Good | - _1__JXAMPLE
Industrial Applicability
[0093]
5 According to the above aspects, it is possible to provide the galvannealed steel
sheet which is subjected to the press-forming and which satisfies the mechanical properties such as tensile strength, is excellent in the formability, includes the galvamiealed layer which has not many surface defects such as linear pattern defects, and simultaneously, maintains excellent surface appearance even after press-forming. Also,

43 it is possible to provide tlic method for producing the same. Accordingly, the present
invention has significant industrial applicability'.

WE CLAIMS:-
1. A galvannealed steei sheet comprising:
a scale-removed rolled steel sheet which comprises, as a chemical composition, 5 by mass%,
0.0005% to 0.01% of C,
0.001% to 1.0% of Si,
0.01% to 2.0% of Mn,
0.005% to 0.1% of P,
10 0.01% to 0.10% of Al,
0.02% or less of S,
0.1% or less of Ni,
0.1% or less of Cii,
0.01% or less of N, and
15 a balance consisting of Fe and unavoidable impurities; and
a galvannealed layer arranged on the scale-removed rolled steel sheet,
wherein, when ten measurement points of the galvannealed steel sheet are set in
a transverse direction by equally dividing a line-segment having a reference length of 50
mm by 10,
20 a minimum P content of the galvamiealed layer in the ten measurement points of
the galvamiealed steel sheet is 50% or more as compared with a maximum P content therein.
2. The galvannealed steel sheet according to claim 1,
25 wherein the scale-removed rolled steel sheet further comprises, as the chemical

45 composition, by mass%, at least one selected from
0.0001% to 0.0050% of B,
0.001% to 0.1% of Nb,
0.001% to 0.1% of Ti, and
5 0.001% to 0.1% of Mo.
3. The galvannealed steel sheet according to claim 2,
wherein, when ten measurement points of the scale-removed rolled steel sheet are set in the transverse direction by equally dividing a line-segment having a reference
10 length of 50 mm by 10, when a surface part of the scale-removed rolled steel sheet is from a surface of the scale-removed rolled steel sheet to 0.1 |.im in depth along a thickness direction, and when a base part of the scale-removed rolled steel sheet is from the surface of the scale-removed rolled steel sheet to more than 2 fxm in depth along the thickness direction,
15 in each of the ten measurement points of the scale-removed rolled steel sheet, a
P content, aNi content, and a Cu content of the surface part of the scale-removed rolled steel sheet are respectively 105% to 150% as compared with a P content, a Ni content, and a Cu content of the base part of the scale-removed rolled steel sheet.
20 4. The galvannealed steel sheet according to claim 1,
wherein, when ten measurement points of the scale-removed rolled steel sheet are set in the transverse direction by equally dividing a line-segment having a reference length of 50 nmi by 10, when a surface part of the scale-removed rolled steel sheet is from a surface of the scale-removed rolled steel sheet to 0.1 jam in depth along a
25 thickness direction, and when a base part of the scale-removed rolled steel sheet is from

46 the surface of the scale-removed rolled steel sheet to more than 2 fim in depth along the
thickness direction,
in each of the ten measurement points of the scale-removed rolled steel sheet, a
P content, a Ni content, and a Cu content of the surface part of the scale-removed rolled
5 steel sheet are respectively 105% to 150% as compared with a P content, a Ni content,
and a Cu content of the base part of the scale-removed rolled steel sheet.
5. A method for producing a galvaimealed steel sheet, the method comprising:
casting a molten steel which comprises, as a chemical composition, by mass %,
10 0.0005% to 0.01% of C,
0.001% to 1.0% of Si,
0.01% to 2.0% of Mn,
0.005% to 0.1% of P,
0.01% to 0.10% of Al,
15 0.02% or less of S,
0.1% or less of Ni, 0.1% or less of Cu, 0.01% or less of N, and
a balance consisting of Fe and unavoidable impurities in order to obtain 20 a slab;
heating the slab in 1100°C to 1300°C;
hot-rolling the slab after the heating under conditions such that a finishing
temperature is in 800°C to 1050°C and a coiling temperature is in 500°C to 800°C in
order to obtain a hot-rolled steel sheet;
25 surface-removing the hot-rolled steel sheet within a range in \im of GL

47 expressed by a following Expression 1 or more and GU expressed by a following
Expression 2 or less from an interface toward a steel along a thickness direction in order
to obtain a scale-removed rolled steel sheet, when ten measurement points of the
hot-rolled steel sheet are set in a transverse direction by equally dividing a line-segment
5 having a reference length of 50 mm by 10, when a steel surface pait of the hot-rolled
steel sheet is from the interface between a scale and the steel to 2 jim in depth toward the
steel along the thickness direction, and when a Ni,i,ax and a Cu„,av: are respectively a
maximum Ni content and a maximum Cu content in mass % of the steel surface part in
the ten measurement points of the hot-rolled steel sheet;
10 galvanizing the scale-removed rolled steel sheet after the surface-removing in
order to obtain a galvanized steel sheet; and
gal^'annealing the galvanized steel sheet after the galvanizing in order to obtain a
galvannealed steel sheet,
GL = (Niniax + 0.8 X Cumax) >< 0.2 " - -(Exprcssion 1),
15 GU = (Ni,„a,x + 0.8 X Cuniax) ^4 -(Expression 2).
6. The method for producing the galvannealed steel sheet according to claim 5,
wherein the molten steel ftiither comprises, as the chemical composition, by
mass %, at least one selected from
20 0.0001% to 0.0050% of B,
0.001% to 0.1% ofNb, 0.001% to 0.1% of Ti, and 0.001% to 0.1% of Mo.
25 7. The method for producing the galvannealed steel sheet according to claim 6, the

48 method comprising
pickling a surface of the scale-removed rolled steel sheet at least before the
surface-removing or after the surface-removing.
5 8. The method for producing the galvamiealed steel sheet according to claim 5, the
method comprising
pickling a surface of the scale-removed rolled steel sheet at least before the surface-removing or after the surface-removing.
10 9. The method for producing the galvannealed steel sheet according to claims 5 to
8, the method comprising:
cold-rolling the scale-removed rolled steel sheet before the galvanizing under a
cold-reduction of 50% to 95%; and
annealing the scale-removed rolled steel sheet after the cold-rolling in a 15 temperature which is a recrystallization temperature or higher.