[Title of the Invention] COLD ROLLED STEEL SHEET,
ELECTROGALVANIZED COLD-ROLLED STEEL SHEET, HOT-DIP
GALVANIZED COLD-ROLLED STEEL SHEET, ALLOYED HOT-DIP
5 GALVANIZED COLD ROLLED STEEL SHEET, AND
MANUFACTURING METHODS OF THE SAME
[Technical Field]
[0001] The present invention relates to a cold-rolled steel sheet excellent
in rigidity and deep drawability, an electrogalvanized cold-rolled steel sheet, a
10 hot-dip galvanized cold-rolled steel sheet, an alloyed hot-dip galvanized
cold-rolled steel sheet, and manufacturing methods of the same.
[Background Art]
[0002] In the field of automobiles, in terms of improvement of he1
efficiency, there is a growing need for a weight reduction of vehicle body, and
15 in tetms of securing collision safety, various high-strength steel sheets are
applied to automobile meinbers. However, even when yield strength and
tensile strength of a steel product are irnproved by using a strengthening
mechanism such as structure strengthening or a grain refining effect, a
Young's ~nodulus does not change. Therefore, when a sheet thickness of a
20 steel sheet is thinned for weight reduction, member rigidity is decreased, so
that it becomes difficult to achieve sheet thinning.
[0003] On the other hand, the Young's lnodulus of iron is 206 GPa or so
generally, but it is possible to increase a Young's modulus in a specific
direction by controlling a crystal orientation (texture) of a polycrystalline iron.
25 There have been made many inventions with regard to a steel sheet in which a
Young's modulus in a direction perpendicular to a rolling direction (to be
referred to as a transverse direction, hereinafter) is increased by increasing the
integration degree to the { 1 12)<1 10> orientation, for example, so fac
However, the {112}<110> orientation is an orientation to significantly
decrease r values in the rolling direction and in the transverse direction, so
5 that there is a problem that deep drawability deteriorates significantly.
Further, the Young's rnodulus in a rolling 45' direction decreases more than
that of a noimal steel sheet, so that the steel sheets can be applied only to a
member long in one direction such as a fiame member, and there is a problem
that they cannot be applied to, for example, a panel member and a member
10 required to have Young's lnodulus in plural directions such as torsional
rigidity.
[0004] Patent Docurnents 1 to 4 are each related to an orientation group
including {112)<110> or a steel sheet in which an orientation group including
{112}<110> is developed. Patent Documents 1 to 4 are each related to a
15 technique in which a high Young's lnodulus is obtained in a transverse
direction and a ceitain direction of a lneinber is suited to the transverse
direction, thereby making it possible to increase rigidity in the direction.
However, in each of Patent Doculnents 1 to 4, there is no description other
than the Young's modulus in the transverse direction. Patent Document 3
20 among them is one related to a high-strength steel with ductility and a
Young's modulus both achieved, but has no description on deep drawability.
Furthel; Patent Document 4 is one related to a steel sheet excellent in hole
expandability being one of indices of workability and in a Young's modulus,
but has no description on deep drawability.
25 [0005] Further, some of the present inventors and the like have disclosed
a hot-rolled steel sheet having a high Young's inodulus in a rolling direction, a
cold-rolled steel sheet, and manufacturing methods of the same (see Patent
Docu~nents 5 and 6, for example). These Patent Docu~nents 5 and 6 are a
technique of increasing Young's modulus in a rolling direction and in a rolling
perpendicular direction by using the {110}<111> orientation and the
5 {112)<111> orientation. However, with regard also to the steel sheets
described in these respective Patent documents, there are descriptions on hole
expandability and ductility, but there is no description on deep drawability.
[0006] Fui-ther, Patent Document 7 discloses a technique of increasing
Young's modulus in a rolling direction and in a transverse direction of a
10 cold-rolled steel sheet, but has no description on deep drawability.
Ful-ther, Patent Document 8 discloses a technique of increasing a
Young's modulus and deep drawability by using an ultralow carbon steel.
However, the technique described in Patent Document 8 has a problem that
due to perfor~ningro lling with the total reduction amount of 85% or more in a
15 temperature range of As3 to As3 + 150°C or lower, and the like, a load on a
rolling Inill is high. Fui-ther, Patent Document 8 is not the one capable of
obtaining significant rigidity at all because the Young's lnodulus in a 45"
direction is not necessarily high and a crystal orientation to be developed is
not also proper.
20 [Prior Art Document]
[Patent Document]
[0007] Patent Document 1: Japanese Laid-open Patent Publication No.
2006-1 83 130
Patent Document 2: Japanese Laid-open Patent Publication No.
25 2007-92128
Patent Document 3: Japanese Laid-open Patent Publication No.
2008-240 125
Patent Document 4: Japanese Laid-open Patent Publication No.
2008-240 123
Patent Document 5: Japanese Laid-open Patent Publication No.
5 2009-19265
Patent Document 6: Japanese Laid-open Patent Publication No.
2007-146275
Patent Document 7: Japanese Laid-open Patent Publication No.
2009-13478
10 Patent Document 8: Japanese Laid-open Patent Publication No.
05-255804
[Disclosure of the Invention]
[Problems to Be Solved by the Invention]
[0008] The present invention has been made in consideration of the
15 above-described problems, and has an object to provide a cold-rolled steel
sheet whose Young's modulus in all directions are increased as compared to a
conventional product and whose rigidity and deep drawability are excellent,
an electrogalvanized cold-rolled steel sheet, a hot-dip galvanized cold-rolled
steel sheet, an alloyed hot-dip galvanized cold-rolled steel sheet, and
20 manufacturing methods of the same.
[Means for Solving the Problems]
[0009] The present inventors performed earnest examinations in order to
solve the above-described problems. As a result, they learned that to a steel
whose added amount of C is decreased and whose amount of solid-solution C
25 is further decreased as much as possible by adding Nb and Ti thereto, Mn, P,
and B are further added in proper ranges and hot rolling conditions are
optimized, thereby making it possible to improve rigidity and deep
drawability of a cold-rolled steel sheet. That is, they found that by
employing the above-described condition, during cold rolling and annealing
to be perfolmed later, the Young's modulus are increased, {557}<9 16 5>
5 being an orientation with a relatively high r value is developed, and the
{332}<110> orientation being an orientation to decrease the Young's modulus
in a rolling direction is decreased, thereby making it possible to obtain
excellent rigidity and deep drawability.
The present invention is the cold-rolled steel sheet excellent in rigidity
10 and deep drawability, the electrogalvanized cold-rolled steel sheet, the hot-dip
galvanized cold-rolled steel sheet, the alloyed hot-dip galvanized cold-rolled
steel sheet, and the manufacturing methods of the same as described above,
and the gist thereof is as follows.
[0010] [I] A cold-rolled steel sheet, contains:
15 in mass%,
C: 0.0005 to 0.0045%;
Mn: 0.80 to 2.50%;
Ti: 0.002 to 0.150%;
B: 0.0005 to 0.01%;
20 Si: 0 to 1.0%;
Al: 0 to 0.10%;
Nb: 0 to 0.040%;
Mo: 0 to 0.500%;
Cr: 0 to 3.000%;
25 W: 0 to 3.000%;
Cu: 0 to 3.000%;
Ni: 0 to 3.000%;
Ca: 0 to 0.1000%;
Rem: 0 to 0.1000%;
V: 0 to 0.100%;
5 P: 0.15% or less;
S: 0.010% or less;
N: 0.006% or less,
in which (I) Expression below is satisfied, and
a balance being composed of iron and impurities, in which
10 at the position of 114 thickness of a sheet thickness, a random intensity ratio
(A) of the {332)<110> orientation is 3 or less, a random intensity ratio (B) of
the {557)<9 16 5> orientation and a random intensity ratio (C) of the
{111)<112> orientation are both 7 or more, and {(B)/(A) 2 5) and {(B) >
(C)) are satisfied.
15 0.07 5 (Mn (mass%) - Mn* (mass%))/(B (ppm) - B* (ppm)) 5 0.2
.....(I)
(1) Expression above is set as follows.
Mn* (mass%) = 55s (mass%)/32
B* (ppm) = low (mass%) - 14Ti (mass%)/48)/14 x 10000
20 In the case of Mn* < 0 and BY < 0, B* is set to 0.
[0011] [2] The cold-rolled steel sheet according to [I], contains:
one or two of, in mass%,
Si: 0.01 to 1.0%; and
Al: 0.010 to 0.10%.
25 [0012] [3] The cold-rolled steel sheet according to [l] or [2], contains:
in mass%,
Nb: 0.005 to 0.040%.
[0013] [4] The cold-rolled steel sheet according to any one of [l] to [3],
contains:
5 one or two or more of, in mass%,
Mo: 0.005 to 0.500%;
Cr: 0.005 to 3.000%;
W: 0.005 to 3.000%;
Cu: 0.005 to 3.000%; and
10 Ni: 0.005 to 3.000%.
[0014] [5] The cold-rolled steel sheet according to any one of [I] to [4],
contains:
one or two or more of, in mass%,
Ca: 0.0005 to 0.1000%;
15 Rem: 0.0005 to 0.1000%; and
V: 0.001 to 0.100%.
[0015] [6] The cold-rolled steel sheet according to any one of [l] to [5],
in which
a Young's lnodulus in a rolling perpendicular direction is 225 GPa or more, a
20 Young's ~nodulus in a rolling direction and a Young's ~nodulus in a 45"
direction with respect to the rolling direction are both 206 GPa or more, and
an average r value is 1.4 or more.
[0016] [7] An electrogalvanized cold-rolled steel sheet, in which
on the surface of the cold-rolled steel sheet according to any one of [I] to [6],
25 electrogalvanizing is perfor~ned.
[0017] [8] A hot-dip galvanized cold-rolled steel sheet, in which
on the surface of the cold-rolled steel sheet according to any one of [I] to [6],
hot-dip galvanizing is performed.
[0018] [9] An alloyed hot-dip galvanized cold-rolled steel sheet, in which
on the surface of the cold-rolled steel sheet according to any one of [I] to [6],
5 alloying hot-dip galvanizing is perfor~ned.
[0019] [lo] A manufacturing method of a cold-rolled steel sheet, includes:
on a steel billet containing:
in ~nass%,
C: 0.0005 to 0.0045%;
10 Mn: 0.80 to 2.50%;
Ti: 0.002 to 0.150%;
B: 0.0005 to 0.01%;
Si: 0 to 1 .O%;
Al: 0 to 0.10%;
15 Nb: 0 to 0.040%;
Mo: 0 to 0.500%;
Cr: 0 to 3.000%;
W: 0 to 3.000%;
Cu: 0 to 3.000%;
20 Ni: 0 to 3.000%;
Ca: 0 to 0.1000%;
Rem: 0 to 0.1000%;
V: 0 to 0.100%;
P: 0.15% or less;
25 S: 0.010% or less;
N: 0.006% or less,
in which (1) Expression below is satisfied, and
a balance being composed of iron and impurities,
performing heating to 11 50°C or higher, and next performing rolling with a
shape ratio (X) determined by (2) Expression below of 4.4 or less for at least
5 one pass or more in a temperature range of 1000 to 950°C with a finish rolling
starting temperature set to 1000 to llOO°C, and next performing rolling with
the shape ratio (X) determined by (2) Expression below of 3.0 to 4.2 for at
least one pass or more in a temperature range of not lower than a telnperature
50°C lower than an A3 transfor~nation temperature obtained by (3)
10 Expression below nor higher than 950°C, and next stal-ting cooling within 2
seconds after finish of final rolling, cooling the temperature within a range
down to 700°C at an average cooling rate of 15"C/s or more, and then
performing coiling in a temperature range of 500 to 650°C, and next
performing pickling, and then performing cold rolling at a reduction ratio of
15 50 to 90%, heating the temperature in a range of room temperature to 650°C
at an average heating rate of 2 to 20°C/s, and further heating the temperature
f?om 650°C to 700°C at an average heating rate of 2 to 15OC/s, and next
performing annealing to perform holding for 1 second or longer in a
temperature range of not lower than 700°C nor higher than 900°C.
20 0.07 5 (Mn (mass%) - Mn* (mass%))/(B (ppm) - B* (ppm)) 5 0.2
.....(I)
(1) Expression above is set as follows.
Mn* (mass%) = 55s (tnass%)/32
B* (ppmn) = 10(N (mass%) - 14Ti (mass%)/48)/14 x 10000
25 In the case of Mn* < 0 and B* < 0, B* is set to 0.
X (shape ratio) = ldlhm .....(2)
(2) Expression above is set as follows.
Id (contact arc length of hot-rolling roll and steel sheet): d (x~ (h in - hout)/2)
hm: (hin + hout)/2
L: roll diameter (mm)
5 hin: rolling roll ently side sheet thickness (mm)
hout: rolling roll exit side sheet thickness (mm)
A3 ("C) = 937.2 - 476.5C + 56Si - 19.7Mn - 16.3Cu - 26.6Ni - 4.9Cr
+ 38.1Mo + 136.3Ti - 19.1Nb + 124.8V + 198.4A1+ 3315.0B .....(3)
In (3) Expression above, C, Si, Mn, P, Cu, Ni, Cr, Mo, Ti, Nb, V, Al,
10 and B are the contents of the respective elements [mass%]. With regard to a
steel sheet in which Si, Al, Cu, Ni, Cr, Mo, Nb, and V are not intended to be
contained, it is calculated with content percentages of these each being 0%.
[0020] [ll] A manufacturing method of an electrogalvanized cold-rolled
steel sheet, includes:
15 performing electrogalvanizing on the surface of the steel sheet manufactured
by the method according to [lo].
[0021] [12] A manufacturing method of a hot-dip galvanized cold-rolled
steel sheet, includes:
performing hot-dip galvanizing on the surface of the steel sheet manufactured
20 by the method according to [lo].
[0022] [13] A manufacturing method of an alloyed hot-dip galvanized
cold-rolled steel sheet, includes:
on the surface of the steel sheet manufactured by the method
according to [lo], performing hot-dip galvanizing, and then fusther
25 performing a heat tseatment for 10 seconds or longer in a temperature range
of 450 to 600°C.
[Effect of the Invention]
[0023] According to the cold-rolled steel sheet, the electrogalvanized
cold-rolled steel sheet, the hot-dip galvanized cold-rolled steel sheet, the
alloyed hot-dip galvanized cold-rolled steel sheet, and the manufacturing
5 methods of the same of the present invention, the above-described
constitution makes it possible to obtain a cold-rolled steel sheet whose rigidity
is excellent because Young's modulus in both the directions are 206 GPa or
more, a Young's modulus in the rolling perpendicular direction is 225 GPa or
more, and a static Young's modulus in the rolling direction improves and
10 whose deep drawability is excellent because an average r value is 1.4 or more,
an electrogalvanized cold-rolled steel sheet, a hot-dip galvanized cold-rolled
steel sheet, or an alloyed hot-dip galvanized cold-rolled steel sheet. Thus,
application of the present invention to an automobile member such as a panel
member, for example, makes it possible to suff~cientlye njoy merits of fuel
15 efficiency improvelnent and reduction in vehicle body weight associated with
sheet thinning of a member achieved by improvement in rigidity in addition
to improvement in workability, so that social contributions are immeasurable.
[Brief Description of the Drawings]
[0024] [FIG. 11 FIG. 1 is a view to explain a cold-rolled steel sheet
20 excellent in deep drawability being an embodiment of the present invention,
an electrogalvanized cold-rolled steel sheet, a hot-dip galvanized cold-rolled
steel sheet, an alloyed hot-dip galvanized cold-rolled steel sheet, and
manufacturing methods of the same, and is a view showing positions of
respective ciystal orientations on an ODF (Ciystallite Orientation Distribution
25 Function; $2 = 45' cross section).
[Mode for Carrying out the Invention]
[0025] Hereinafter, there will be explained a cold-rolled steel sheet
excellent in rigidity and deep drawability being an embodiment of the present
invention, an electrogalvanized cold-rolled steel sheet, a hot-dip galvanized
cold-rolled steel sheet, an alloyed hot-dip galvanized cold-rolled steel sheet,
5 and manufacturing methods of the same. Incidentally, this embodiment is to
be explained in detail for a better understanding of the spirit of the present
invention, and thus is not the one to limit the present invention unless
otherwise specified.
[0026] Generally, it is known that a Young's modulus and an r value of a
10 steel sheet both rely on ciystal orientations and values of them largely change.
The present inventor and the like examined a y fiber ({111)<112> to
(1 11)<110> orientation group) to be well known as an orientation to increase
an r value of a steel sheet, and Young's modulus anisotropy of an orientation
close to it. Then, the present inventor and the like found that the orientation
15 of {557)<9 16 5> a little deviating from the y fiber is an orientation where
deterioration of the r value is relatively small, Young's modulus in both
in-plane directions are high, and the Young's modulus in a transverse
direction in particular is increased, and further the {332)<110> orientation is
an orientation to decrease the Young's ~nodulusi n a rolling direction and in a
20 transverse direction conversely.
[0027] Thus, as a result that the present inventor and the like repeated
earnest examination on a method of intensifying the {557)<9 16 5>
orientation and weakening {332)<110>, the following things were made
cleac
25 That is, a component base with the amount of C decreased to 0.0045%
or less and Nb andlor Ti added thereto is limited to a component base in
which appropriate amounts of solid-solution Mn and solid-solution B remain,
and hot rolling conditions are optimized, and thereby grains of a hot-rolled
sheet are refined, the shape of grains of the hot-rolled sheet is made bainitic,
and a nucleation site of {557)<9 16 5> during annealing increases, and
5 conversely development of the (33214 10> orientation is suppressed.
Further, they newly found that when, on the occasion of cold rolling and
annealing of the hot-rolled sheet with strongly developed transfor~nation
texture, recovery at the time of annealing is suppressed appropriately due to
the existence of solid-solutions Mn and B, the {557}<9 16 5> orientation is
10 more intensified. Further, they found that when a random intensity ratio of
{557}<9 16 5> is set to (A) and a random intensity ratio of {332)<110> is set
to (B), it is impostant to satisfy the following expression {(A)/(B) 2 5) for
achievement of high Young's modulus. Ful-ther, the (1 11 } orientation
is known as an orientation to increase the r value, and it is important to make
15 a random intensity ratio (C) of the orientation become 7 or more in terms of
deep drawability, but when the rand0111 intensity ratio (C) is more intensified
than the random intensity ratio (A), the Young's modulus in the transverse
direction decreases, so that it is also impoi-tant to satisfy the following
expression {(A) > (C)}.
20 Incidentally, for the Young's modulus described in the present
invention, a value obtained by a dynamic oscillation method or a static tensile
method may also be used.
[0028] [Cold-rolled steel sheet]
The cold-rolled steel sheet of the present invention contains, in mass%,
25 C: 0.0005 to 0.0045%; Mn: 0.80 to 2.50%; Ti: 0.002 to 0.150%; B: 0.0005 to
0.01%; Si: 0 to 1.0%; Al: 0 to 0.10%; Nb: 0 to 0.040%; Mo: 0 to 0.500%; Cr:
0 to 3.000%; W: 0 to 3.000%; Cu: 0 to 3.000%; Ni: 0 to 3.000%; Ca: 0 to
0.1000%; Rem: 0 to 0.1000%; V: 0 to 0.100%; P: 0.15% or less; S: 0.010% or
less; N: 0.006% or less, in which (1) Expression below is satisfied, and a
balance being cornposed of iron and impurities, in which at the position of 114
5 thickness of a sheet thickness, a random intensity ratio (A) of the {332)<110>
orientation is 3 or less, a random intensity ratio (B) of the {557}<9
16 5> orientation and a random intensity ratio (C) of the {I 11}<112>
orientation are both 7 or more, and {(B)/(A) 2 5) and {(B) > (C)) are
satisfied.
10 0.07 5 (Mn (mass%) - Mn* (mass%))/(B (pptn) - B* (pp~n)) 5 0.2
.....(I)
(1) Expression above is set as follows.
Mn* (mass%) = 55s (mass%)/32
B* (ppm) = lO(N (mass%) - 14Ti (mass%)/48)/14 x 10000
15 In the case of Mn* < 0 and B* < 0, B* is set to 0.
[0029] [Steel composition]
Hereinafter, there will be explained reasons for limiting a steel
composition in the present invention in hrther detail. Incidentally, in the
following explanation, "%" relating to the steel colnposition indicates mass%
20 unless otherwise specified.
[0030] [Essential comnponents]
(C: carbon) 0.0005 to 0.0045%
C is an element necessary for irnproving strength of a steel sheet.
However, when C remains in a solid solution state in a hot-rolled sheet, a
25 shear zone is formed in a grain during cold rolling and the {110}<001>
orientation to decrease the Young's lnodulus in the rolling direction develops,
so that the content is set to 0.0045% or less. Further, from this viewpoint,
the amount of C is desirably set to 0.004% or less, and is further desirably
0.0035% or less. On the other hand, when the amount of C is set to less than
0.0005%, the cost of a vacuum degassing treatment increases too much, and
5 thus the lower lirnit of C is set to 0.0005%.
[0031] (Mn: manganese) 0.80 to 2.50%
Mn is an important element in the present invention. Mn has an
effect of increasing hardenability during cold rolling after finish of hot rolling
and turning structure of a hot-rolled sheet into bainitic ferrite. Further, Mn is
10 contained with B in a colnposite manner, and thereby recovery during
annealing after cold rolling is suppressed. As above, in worked grains in the
y fiber orientation, of which the recovely is suppressed, {557)<9 16 5> is
likely to reciystalize and the Young's modulus improves. Therefore, in the
present invention, 0.8% or more of Mn is contained. Ful-thel; fiom this
15 viewpoint, 1 .O% or more of Mn is desirably contained.
[0032] On the other hand, when greater than 2.5% of Mn is contained,
recrystallization is delayed, the {112}<110> orientation develops, and the
Young's ~nodulus in the 45" direction deteriorates. Therefore, the upper
liinit of Mn is set to 2.5%. Fui-ther, froin this viewpoint, Mn is more
20 desirably set to 2.0% or less, and is still more desirably 1.5% or less.
[0033] (Ti: titanium) 0.002 to 0.150%
Ti is an impostant element contributing to improve~nent in deep
drawability and Young's modulus. Ti forins nitride in a y phase
high-temperature zone, and suppresses recrystallization caused when a y
25 phase is worked in hot rolling similarly to Nb to be described later. Further,
during coiling, Ti precipitates as Tic to thereby decrease the amount of
solid-solution C and improve deep drawability in pai-ticular. Ful-thel; TiN is
formed at high temperature, and thereby precipitation of BN is suppressed,
and thus solid-solution B can be secured, so that developinent of a texture
favorable for improvement in Young's modulus is promoted. In order to
5 obtain this effect, 0.002% or more of Ti needs to be contained. On the other
hand, when 0.150% or more of Ti is contained, a recrystallization te~nperature
increases and workability deteriorates significantly, so that this value is set to
the upper limit. Further, from this viewpoint, the amount of Ti is preferably
set to 0.100% or less, and is fui-ther preferably 0.060% or less.
10 [0034] (B: boron) 0.0005 to 0.01%
B is also an important element in the present invention similarly to Ti.
B optimizes hardenability and a microstructure and a texture of a hot-rolled
sheet. Further, B is contained with Mn in a composite manner, thereby
moderately delaying recovely during annealing after cold rolling to contribute
15 to optimal texture foimation. From this viewpoint, 0.0005% or more of B is
contained, and 0.001% or more of B is more desirably contained. On the
other hand, containing greater than 0.01% of B increases a recrystallization
temperature significantly to cause deterioration of workability, so that this
value is set to the upper limit. Further, fkoin this viewpoint, the amount of B
20 is desirably set to 0.004% or less, and is further desirably 0.003% or less.
[0035] [Optional components]
In the present invention, in addition to the above-described essential
components, the following optional components may also be fui-ther
contained in predetermined ranges.
25 [0036] For deoxidation, one or both of Si and A1 inay also be contained.
(Si: silicon) 0 to 1.0%
The lower limit of Si is not defined, but Si is a deoxidixing element,
so that 0.01% or more is desirably contained. Further, Si is an element to
increase strength by solid-solution strengthening, to thus be contained with
the upper limit being 1.0% as usage. When greater than 1.0% of Si is
5 contained, deterioration of workability is caused, so that this value is set to the
upper limit. Fulther, the containing of Si causes a scale flaw that occurs
during hot rolling, which is called a Si scale, and further decreases
adhesiveness of plating, so that it is more desirably set to 0.8% or less.
Fuither, fkom this viewpoint, the content of Si is still more desirably 0.6% or
10 less.
[0037] (Al: aluininumn) 0 to 0.10%
A1 is a deoxidation preparing agent, and its lower limit is not limited
in particular, but in terms of a deoxidation effect, it is preferably set to
0.010% or more. On the other hand, Al is an element to significantly
15 increase a transforlnation point, and when greater than 0.10% of Al is added,
y-region rolling becomes difficult to be performed, so that the upper limit is
set to 0.10%.
[0038] (Nb: niobium) 0 to 0.040%
Further, Nb is more desirably contained in a predetermined range.
20 Nb significantly suppresses recrystallization caused when a y phase is worked
in hot rolling and significantly prolnotes formation of a worked texture in a y
phase. Further, Nb forms NbC during coiling to decrease solid-solution C to
thereby contribute to irnprovelnent in deep drawability. From this viewpoint,
0.005% or more of Nb is desirably contained, and 0.015% or more of Nb is
25 Inore desirably contained. However, when the content of Nb exceeds
0.040%, recrystallization at the time of annealing is suppressed and deep
drawability deteriorates. Therefore, the upper limit of the content of Nb is
set to 0.04%. Further, from this viewpoint, the content of Nb is Inore
desirably set to 0.03% or less, and is still more desirably 0.025% or less.
[0039] Further, in the present invention, as an element for improving steel
5 properties, one or two or more of Mo, Cr, W, Cu, and Ni are more desirably
contained. Concretely, one or two or more of Mo of 0.005 to 0.500% and Cs,
W, Cu, and Ni each in a range of 0.005 to 3.000% are desirably contained.
[0040] (Mo: molybdenum) 0 to 0.500%
Mo is an element improving hardenability and having an effect of
10 increasing strength by forming carbide. Therefore, when Mo is contained,
0.005% or more is desirably contained. On the other hand, when greater
than 0.5% of Mo is contained, ductility and weldability are decreased. From
this viewpoint, Mo is desirably contained in a range of not less than 0.005%
nor more than 0.500% according to need.
15 [0041] (Cr: chromium) 0 to 3.000%
Cr is also an element improving hardenability and having an effect of
increasing strength by forming carbide. Therefore, when Cr is contained,
0.005% or more is desirably contained. On the other hand, when greater
than 3.000% of Cr is contained, ductility and weldability are decreased.
20 From this viewpoint, Cr is desirably contained in a range of not less than
0.005% nor more than 3.000% according to need.
[0042] (W: tungsten) 0 to 3.000%
W is also an eleinent improving hardenability and having an effect of
increasing strength by forming carbide. Therefore, when W is contained,
25 0.005% or more is desirably contained. On the other hand, when greater
than 3.000% of W is contained, ductility and weldability are decreased.
From this viewpoint, W is desirably contained in a range of not less than
0.005% nor more than 3.000% according to need.
[0043] (Cu: copper) 0 to 3.000%
Cu is an element increasing strength of a steel sheet and improving
5 corrosion resistance and removability of scales. Therefore, when Cu is
contained, 0.005% or more is desirably contained. On the other hand, when
greater than 3.000% of Cu is contained, Cu causes a surface flaw, so that Cu
is desirably contained in a range of not less than 0.005% nor more than
3.000% according to need.
10 [0044] (Ni: nickel) 0 to 3.000%
Ni is an element increasing strength of a steel sheet and improving
toughness. Therefore, when Ni is contained, 0.005% or more is desirably
contained. On the other hand, when greater than 3.000% of Ni is contained,
Ni causes ductility deterioration, so that Ni is desirably contained in a range
15 of not less than 0.005% nor more than 3.000% according to need.
[0045] (Ca: 0 to 0.1000%, REM: 0 to 0.1000%, and V: 0 to 0.100%)
Further, in the present invention, as an element for obtaining an effect
of increasing strength and improving material of a steel sheet, one or two or
more of Ca, REM (rare-earth element), and V are hrther contained
20 preferably.
[0046] When the contents of Ca and REM are each less than 0.0005%
and the added amount of V is less than 0.001%, the above-described effect is
not sometimes obtained sufficiently. On the other hand, when the contents
of Ca and REM are each greater than 0.1000% and the content of V is greater
25 than 0.100%, ductility is sometimes impaired. Thus, when Ca, REM, and V
are contained, Ca is preferably contained in a range of 0.0005 to 0.1000%,
REM is preferably contained in a range of 0.0005 to 0.1000%, and V is
preferably contained in a range of 0.001 to 0.100% respectively.
[0047] The balance other than the above is Fe and impurities. As the
impurities, one contained in a raw material of ore, scrap, and the like and one
5 contained in a manufacturing step can be exemplified. In the present
invention, as representative impurities, P, S, N, and the like are exemplified.
[0048] (P: phosphorus) 0.15% or less
P is contained in steel as an impurity. The lower limit of P is not
limited, but P is an element capable of improving strength inexpensively, so
10 that greater than 0.01% may also be contained. Ful-thel; from this viewpoint,
0.02% or more of P is desirably contained. On the other hand, containing
0.15% or more of P causes a seconda~yw orking crack, so that 0.15% is set to
the upper limit. Ful-thel; fiom this viewpoint, the amount of P is more
desirably set to 0.1% or less, and is still more desirably 0.08% or less.
15 [0049] (S: sulfur) 0.010% or less
S is contained in steel as an impurity. S forms MnS to cause
deterioration of workability and decrease the amount of solid-solution Mn, so
that 0.010% is set to the upper limit. Further, from this viewpoint, the
amount of S is further desirably set to 0.008% or less.
20 [0050] (N: nitrogen) 0.006% or less
N is an impurity contained in steel, and its lower limit is not set in
particular, but when N is set to less than 0.0005%, the cost of steel~naking
increases, so that it is preferably set to 0.0005% or more. On the other hand,
N forms TiN with Ti at high temperature and suppresses recrystallization in a
25 y phase, but when the amount of TiN is increased too much, workability
deteriorates, so that the upper limit of N is set to 0.006%. Further, from this
viewpoint, the amount of N is set to 0.0040%, and is more preferably set to
0.0020% or less. Incidentally, when N that is equal to or more than the Ti
equivalent (48Til14) of TiN is contained, remaining N forms BN and the
amount of solid-solution B is decreased, resulting in that a hardenability effect
5 and a recovery suppression effect decrease. Therefore, the amount of N is
fulther desirably set to 48Ti/14 or less.
[005 11 Further, the steel of the present invention may also further contain
elements for improving steel propelties in addition to the above elements, and
further as the balance, iron is contained, and elements to be mixed inevitably
10 such as Sn and As (inevitable impurities) may also be contained.
[0052] (Relational expression of the amount of Mn and the amount of B)
Next, there will be explained (1) Expression below being a relational
expression of the amount of Mn and the amount of B in detail.
In the present invention, Mn and B are contained in the ranges
15 satisfying the relation expressed by (1) Expression below.
0.07 5 (Mn (mass%) - Mn* (mass%))/(B (ppm) - B* (ppm)) 5 0.2
.....(I)
However, (1) Expression above is set as follows.
Mn* (mass%) = 55s (mass%)/32
20 B* (ppm) = 10(N (mass%) - 14Ti (mass%)/48)/14 x 10000
In the case of Mn* < 0 and B* < 0, B* is set to 0.
[0053] (1) Expression above expresses the ratio of the amount of
solid-solution Mn and the amount of solid-solution B. When solid-solution
Mn and solid-solution B coexist, the interaction with dislocation is brought,
25 recovely is delayed, the {557)<9 16 5> orientation develops, and the
{332}<110> orientation decreases. However, when the value expressed by
(1) Expression above is less than 0.07, an abundance ratio of Mn to B is too
small, so that the delay of recovery obtained by the interaction becomes
insufficient to cause an increase in the {332)<110> orientation and a decrease
in the {557)<9 16 5> orientation, and {111)<112> becomes the main
5 orientation. Therefore, this value being 0.07 is set to the lower limit. From
this viewpoint, with regard to the value expressed by (1) Expression above,
0.1 is more desirably set to the lower limit, and 0.1 1 is still more desirably set
to the lower limit. On the other hand, even when the value expressed by (I)
Expression above exceeds 0.2, no special effect can be obtained, and further
10 another workability such as ductility decreases. Therefore, this value being
0.2 is set to the upper limit. Further, fsom this viewpoint, this value is
hither desirably 0.19 or less.
[0054] [Crystal orientation]
Next, there will be explained crystal orientations of the cold-rolled
15 steel sheet of the present invention.
With regard to the cold-rolled steel sheet of the present invention, at
the position of 114 thickness of a sheet thickness, the random intensity ratio
(A) of the (33214 10> orientation is 3 or less, the random intensity ratio (B)
of the {557}<9 16 5> orientation and the random intensity ratio (C) of the
20 {111)<112> orientation are both 7 or more, and {(B)/(A) 2 5) and {(B) >
(C)) are satisfied.
[0055] FIG. 1 shows an ODF (Clystallite Orientation Distribution
Function) of a 42 = 45" cross section where the crystal orientations of the
cold-rolled steel sheet of the present invention are shown. Here, with regard
25 to the orientations of crystals, normally, the orientation veltical to a sheet
surface is represented as [hkl] or {hkl) and the orientation parallel to a rolling
direction is represented as (uvw) or . {hkl) and are generic
terms of equivalent planes, and [hkl] and (uvw) indicate individual crystal
planes. That is, in the present invention, a b. c. c. structure is intended, so
that for example, (1 1 I), (-1 ll), (1-ll), (1 1-l), (-1-1 I), (-1 1-11> (1-1-11> and
5 (-1-1-1) planes are equivalent to one another and cannot be distinguished
from one another. In such a case, these orientations are referred to as (1 11)
generically.
[0056] Incidentally, the ODF is used also for showing orientations of a
low sylnlnetric crystal structure, to thus be expressed by $1 = 0 to 360°, @ = 0
10 to 180°, and $2 = 0 to 360' in general, and the individual orientations are
represented by [hkl](uvw). However, in the present invention, a high
symmetric body-centered cubic crystal is intended, so that with regard to cD
and 42, they are expressed in the range of 0 to 90°. Ful-ther, with regard to
$1, its range changes depending on whether or not symmetry due to
15 deformation is considered when calculation is performed, but in the present
invention, symmetry is considered and the orientations are expressed by 41 =
0 to 90°, and namely in the present invention, a method in which the average
value of the same orientations expressed by 41 = 0 to 360° is shown on the
ODF of 0 to 90" is selected. In this case, [hkl](uvw) and {hkl) are
20 synonymous. Thus, for example, the random intensity ratio of (110)[1-111
of the ODF on the 42 = 45' cross section shown in FIG. 1 is the random
intensity ratio of the (1 10}<111> orientation.
[0057] Here, the random intensity ratios of the {332)<110> orientation,
the {557)<9 16 5> orientation, and the (11 1)<112> orientation may be
25 obtained from a crystallite orientation distribution function (ODF: Orientation
Distribution Function) showing a three-dimensional texture calculated by a
series expansion method based on plural pole figures among the (1 101, {loo),
(2111, and (310) pole figures measured by X-ray diffsaction. Incidentally,
the random intensity ratio is a numerical value obtained by measuring X-ray
intensities of a standard sample not having accumulation to a specific
5 orientation and a test salnple under the same conditions by X-ray
diffractometry or the like and dividing the obtained X-ray intensity of the test
sample by the X-ray intensity of the standard sample.
[0058] As shown in FIG. 1, {332)<110> that is one of the crystal
orientations of the cold-rolled steel sheet of the present invention is expressed
10 by $1 = O0, @ = 65O, and 42 = 45" on the ODF. However, measurement
errors caused by working of a test piece and setting of a salnple sometimes
occur, so that the value of the random intensity ratio (A) of the (33214 10>
orientation is set to the maximum random intensity ratio in the range of $1 =
0 to 2" and = 63 to 67O and the upper limit of the value is set to 3. When
15 this value becomes greater than 3.0, the Young's modulus in the transverse
direction in particular decreases, so that this value is set to the upper limit.
Further, fiom this viewpoint, (A) is desirably set to 2.0 or less, and is further
desirably 1.5 or less. The lower limit of the value of the random intensity
ratio (A) is not defined in particular, but the value of less than 0 is
20 meaningless in principle, so that this value is set to the lower limit.
[0059] Furthel; the {557}<9 16 5> orientation is expressed by $1 = 20°,
@ = 45", and 42 = 45' on the ODF. As described above, in the present
invention, in consideration of the measurement errors caused by working of a
test piece and the like, the value of the randoln intensity ratio (B) of the
25 {557)<9 16 5, orientation is set to the maximum randoln intensity ratio in the
range of $1 = 18 to 22' and @ = 43 to 47' and the lower limit of the value is
set to 7. Further, fsom this viewpoint, the value of the random intensity ratio
(B) is more desirably 9 or more, and is still more desirably 11 or more. This
orientation is a favorable orientation capable of i~nproving the Young's
modulus in both the directions to 220 GPa or more, so that the upper limit of
5 the random intensity ratio (B) is not set, but the random intensity ratio
becoming 30 or more indicates that all the orientations of clystal grains in the
steel sheet are aligned, namely the steel sheet is turned into a single clystal,
and deterioration of workability and the like might be caused, so that it is
desirably set to less than 30.
10 [0060] Ful-ther, the (1 11 )<112> orientation is expressed by $1 = 90°, @ =
5S0, and $2 = 45" on the ODF. In the present invention, in consideration of
the measurement errors caused by working of a test piece and the like
described above, the value of the random intensity ratio (C) of the
(1 11)<112> orientation is set to the maximum random intensity ratio in the
15 range of $1 = 88 to 90' and = 53 to 57O and the lower limit of the value is
set to 7. When this value is less than 7, a high average r value cannot be
obtained. However, when the value of the random intensity ratio (C) is
higher than that of the random intensity ratio (B), the Young's modulus in the
transverse direction decreases, so that the relation of {(B) > (C)) is
20 established. Further, fsom this viewpoint, the relation of {(B) > 1.2(C)) is
more desirably satisfied.
[OOGl] Further, the random intensity ratio (A) of the {332)<110>
orientation and the random intensity ratio (B) of the {557)<9 16 5>
orientation satisfy ({(B)/(A) 2 5). When this value is less than 5, it
25 becomes difficult to achieve a high Young's ~nodulus in the transverse
direction, which is 225 GPa or more. Ful-ther, fsom this viewpoint, the value
expressed by the above-described expression is more desirably 10 or more.
[0062] Incidentally, preparation of samples for X-ray diffraction is
performed as follows.
First, the steel sheet is polished to a predetermined position in the
5 sheet thickness direction by mechanical polishing, chemical polishing, or the
like to be finished into a mirror surface by buffing, and then at the same time
as strain removal by electrolytic polishing or chemical polishing, the steel
sheet is adjusted so that a 114 sheet thickness portion may become a
measurement surface. Here, it is difficult to precisely position the
10 measurement surface at a predetermined sheet thickness position, so that it is
sufficient to prepare the sample so that a region within the range of 3% of the
sheet thickness may become the measurement surface with the target position
being the center. Further, when measurement by X-ray diffraction is
difficult to be performed, by an EBSP (Electron Back Scattering Pattern)
15 method or an ECP (Electron
Channeling Pattern) method, a statistically sufficient number of
measurements may also be performed.
[0063] [Manufacturing method]
Next, there will be explained manufacturing conditions of the
20 cold-rolled steel sheet of the present invention in detail.
In the manufacturing method of the cold-rolled steel sheet of the
present invention, first a steel billet having the above-described chemical
components is heated to 1150°C or higher. Next, in the temperature range of
1000 to 950°C, rolling with a shape ratio (X) determined by (2) Expression
25 below of 4.4 or less is performed for at least one pass or more with a finish
rolling starting temperature set to 1000 to 11 OO°C. Next, in the temperature
range of not lower than a temperature 50°C lower than an A3 transformation
temperature obtained by (3) Expression below (A3 transformation
temperature - 50°C) nor higher than 950°C, rolling with the shape ratio (X)
determined by (2) Expression below of 3.0 to 4.2 is performed for at least one
5 pass or more. Next, after finish of final rolling, cooling is started within 2
seconds, the temperature within a range down to 700°C is cooled at an
average cooling rate of 15"C/s or more, and then coiling is performed in the
temperature range of 500 to 650°C. Next, after pickling is perfosmed, cold
rolling at a reduction ratio of 50 to 90% is performed. Then, the temperature
10 in a range of room temperature to 650°C is heated at an average heating rate
of 2 to 20°C/s, and fulther the temperature from 650°C to 700°C is heated at
an average heating rate of 2 to 15"C/s. Next, annealing to perform holding
for 1 second or longer in the temperature range of not lower than 700°C nor
higher than 900°C is performed.
X (shape ratio) = l d h ...-(2)
(2) Expression above is set as follows.
Id (contact arc length of hot-rolling roll and steel sheet): d (x~ (h in - hout)/2)
hm: (hin + hout)/2
L: roll diameter
20 hin: rolling roll entry side sheet thickness
hout: rolling roll exit side sheet thickness
A3 ("C) = 937.2 - 476.5C + 56% - 19.7Mn - 16.3Cu - 26.6Ni - 4.90
+ 38.1Mo + 136.3Ti - 19.1Nb + 124.8V + 198.4A+ 3315.0B ..-.(3)
In (3) Expression above, C, Si, Mn, P, Cu, Ni, Cs, Mo, Ti, Nb, V, Al,
25 and B are the contents of the respective elements [mass%]. With regard to a
steel sheet in which Si, Al, Cu, Ni, Cr, Mo, Nb, and V are not intended to be
contained, it is calculated with content percentages of these each being 0%.
(That is, when Si is less than 0.01%, it is set to 0%. When A1 is less than
0.010%, it is set to 0%. When Cu is less than 0.005%, it is set to 0%.
When Ni is less than 0.005%, it is set to 0%. When Cr is less than 0.005%,
5 it is set to 0%. When Mo is less than 0.005%, it is set to 0%. When Nb is
less than 0.005%, it is set to 0%. When V is less than 0.001%, it is set to
O%.)
[0064] In the manufacturing method of the present invention, first, a steel
is melted and cast by ordinary methods to obtain a steel billet to be subjected
10 to hot rolling. This steel billet may be the one obtained by forging or rolling
a steel ingot, but in terms of productivity, the steel billet is preferably
manufactured by continuous casting. Further, it may also be manufactured
by using a thin slab caster, or the like.
[0065] Further, the steel billet is normally cast to then be cooled and is
15 heated again for performing hot rolling. In this case, a heating temperature
of the steel billet when performing hot rolling is set to 1150°C or higher.
This is because when the heating temperature of the steel billet is lower than
11 50°C, Nb and Ti are not sufficiently solid-dissolved, and thereby formation
of a texture suitable for achievement of high Young's modulus is inhibited
20 during hot rolling. Further, also fsoin the viewpoint of efficient uniform
heating of the steel billet, the heating temperature is set to 1150°C or higher.
The upper limit of the heating temperature is not defined, but when it is
heated to higher than 1300°C, a crystal grain diameter of the steel sheet
becomes coarse to sometimes impair workability. Incidentally, a process
25 such as
continuous casting-direct rolling (CC-DR), in which a molten steel is cast to
then be hot rolled directly, may also be employed.
[0066] In the present invention, the finish rolling starting temperature is
important, and its temperature range is set to 1000 to llOO°C. When the
finish rolling starting telnperature is higher than 1 100°C, strain during rolling
5 at a stage prior to finish rolling is not acculnulated sufficiently, and during hot
rolling, a worked texture does not develop and grains of a hot-rolled sheet do
not become fine, so that after cold rolling and annealing, the {332)<110>
orientation develops. Further, fsom this viewpoint, finish rolling is more
desirably started at 1050°C or lower. On the other hand, when rolling is
10 started at lower than 1000°C, it becomes difficult to finish the hot rolling at
(the A3 transformation temperature - 50)"C or higher, which is obtained by
(3) Expression above, and the orientation to impair the Young's modulus
develops, so that 1000°C is set to the lower limit.
[0067] Further, in the manufacturing method of the present invention, in
15 the temperature zone of 1000 to 950°C, rolling with the shape ratio (X)
determined by (2) Expression above of 4.4 or less is performed for at least
one pass or more. By the rolling in this temperature range, a hot-rolled
austenite structure is reclystallized to thereby make a grain diameter of the
hot-rolled sheet fine, and an effect of suppressing development of the
20 {332)<110> orientation after cold rolling and annealing is obtained.
However, when the shape ratio exceeds 4.4, at the time of cold rolling and
recrystallization annealing, the {557)<9 16 5> orientation is not easily
formed in the vicinity of the surface, so that the upper limit of the shape ratio
is limited to 4.4. The preferable range is 4.2 or less.
25 [0068] Subsequently to the above-described rolling, in the temperature
zone of not lower than (the A3 transforlnation temperature - 50)"C nor higher
than 950°C, rolling with the shape ratio (X) determined by (2) Expression
above of 3.0 to 4.2 is performed for at least one pass or more.
[0069] The A3 transfolmation temperature is obtained by (3) Expression
above. When the rolling is performed at lower than (the A3 transformation
5 te~nperature - 50)"C, the rolling results in a-region hot rolling and the
{100)<001> orientation to decrease the Young's modulus develops, and the
grain diameter of the hot-rolled sheet is decreased and the {332)<110>
orientation becomes weak. Therefore, this temperature is set to the lower
limit. On the other hand, unless moderate shear deformation is applied in
10 the temperature zone of 950°C or lower where recrystallization is suppressed,
an initial structure to be a nucleation site of the {557)<9 16 5> orientation is
not formed at the time of cold rolling and rec~ystallizationa nnealing, so that
this temperature is set to the upper limit. Fui-ther, fsom this viewpoint, the
above-described rolling temperature is preferably set to 930°C or lower.
15 [0070] When in the rolling to be performed in the temperature zone of
not lower than (the A3 transformation temperature - 50)"C nor higher than
950°C, the shape ratio detelmined by (2) Expression above is less than 3.0,
sufficient shear deformation is not applied, so that this value is set to the
lower limit. On the other hand, when the rolling is performed with the shape
20 ratio of 4.2 or more, in the uppermost layer of the hot-rolled sheet, the
orientation to increase anisotropy of the r value develops after cold rolling
and annealing, so that this value is set to the upper limit. Incidentally, the
rolling roll diameter L is measured at room temperature, and flattening during
hot rolling does not have to be considered. Further, of each rolling roll, the
25 entry side sheet thickness hin and the exit side sheet thickness hout may be
measured on site by using radiations or the like, or may also be obtained by
calculation in consideration of defolmation resistance and the like by a rolling
load.
[0071] Next, after final finish rolling is finished, cooling is started within
2 seconds and cooling is performed down to 700°C at an average cooling rate
5 of 15"CIs or more. The time period until start of cooling is desirably 1.5
seconds or shorter. When the time period until start of cooling after finish of
final finish rolling exceeds 2 seconds, the grain diameter of the hot-rolled
sheet becomes coarse, and at the time of cold rolling and recrystallization
annealing, the {332)<110> orientation is intensified. Further, when an
10 attainment telnperature of cooling is higher than 700°C and a cooling rate
becomes less than 15"C/s, hardenability becomes insufficient, the grain
diameter of the hot-rolled sheet increases, the structure is turned into
polygonal fel-rite, and the (3321x1 10> orientation is intensified. Therefore,
in the present invention, 15"CIs is set to the lower limit of the average cooling
15 rate. Incidentally, the upper limit of the average cooling rate is not defined,
but cooling at 100°C/s or more requires an excessive facility to be provided,
and no special effect can also be obtained, so that cooling is desirably
performed at a rate of less than 100°C/s.
[0072] After the cooling perfor~ned on the above-described condition,
20 coiling is perfor~ned in the temperature range of 500 to 650°C. When a
coiling telnperature becomes lower than 500°C, Tic or NbC does not
precipitate, solid-solution C remains, and the r value decreases, so that this
value is set to the lower limit of the coiling temperature. On the other hand,
when the coiling temperature becomes higher than 650°C, the grain diameter
25 of the hot-rolled sheet increases, the structure is turned into polygonal ferrite
having linear grain boundaries, and the {332)<110> orientation increases.
Thus, in the present invention, 650°C is set to the upper limit of the coiling
temperature. Further, from this viewpoint, the coiling temperature is more
desirably set to 600°C or lower.
[0073] Next, the hot-rolled steel sheet manufactured by the
5 above-described method is pickled, to then be subjected to cold rolling at a
reduction ratio in the range of 50 to 90%. When the reduction ratio in the
cold rolling is set to less than 50%, a sufficient cold-rolled texture does not
develop and the r value decreases, so that this value is set to the lower limit.
Further, from this viewpoint, the reduction ratio in the cold rolling is more
10 desirably 60% or more, and is still more desirably 65% or more. On the
other hand, when the reduction ratio becomes greater than 90%, a load on a
cold rolling mill increases, and integration degree of the { 11 0)<001>
orientation being an orientation to increase the anisotropy of the r value and
integration degree of the { 1 10)<0 12> orientation to decrease the absolute
15 values of the r value and the Young's modulus increase, so that this value is
set to the upper limit. Further, ftom this viewpoint, the reduction ratio in the
cold rolling is more desirably set to 85% or less, and is still more desirably
80% or less.
[0074] Next, annealing is performed. On this occasion, an average
20 heating rate from room temperature to 650°C is set to 2 to 20°C/s. When
this heating rate is less than 2"C/s, recrystallization occurs at low temperature
and the {557)<9 16 5> orientation becomes weak, so that this value is set to
the lower limit. Further, fiom this viewpoint, the heating rate is more
desirably set to 4OC/s or more. On the other hand, when the heating rate
25 exceeds 20°C/s, recrystallization does not start during heating and the
( 1 12)<110> orientation develops, so that a decrease in the r value in the 45"
direction is caused. Further, fkom this viewpoint, the heating rate is more
desirably set to 15"CIs or less.
[0075] Next, heating is performed in the range of 650°C to 700°C, and an
average heating rate in this temperature range is set to 2 to 15"CIs. When
5 this heating rate is less than 2"C/s, the {557)<9 16 5> orientation becomes
weak, so that this value is set to the lower limit. Further, from this viewpoint,
the heating rate is more desirably set to 4"CIs or more. On the other hand,
when the heating rate exceeds 15"C/s, recrystallization does not start during
heating and the {112}<110> orientation develops, so that a decrease in the r
10 value in the 45" direction is caused and hither the {332}<110> orientation is
intensified. From this viewpoint, the heating rate is more desirably set to
1 O°C/s or less.
[0076] After heating is performed up to 700°C at the above-described
heating rate, heating is further performed to not lower than 700°C nor higher
15 than 900°C for 1 second or longer. When an annealing temperature is 700°C
or lower, a worked structure formed at the time of cold rolling remains as it is,
and thus for~nability decreases significantly, so that this temperature is set to
the lower limit value of annealing. On the other hand, when the annealing
temperature becomes higher than 900°C, a texture is broken and shape
20 fixability deteriorates, so that this is set to the upper limit.
[0077] Incidentally, in the manufacturing method of the cold-rolled steel
sheet of the present invention, after the annealing performed on the
above-described condition, temper rolling at a reduction ratio of 10% or less
may also be performed in-line or off-line.
25 [0078] [Electrogalvanized cold-rolled steel sheet, Hot-dip galvanized
cold-rolled steel sheet, and Alloyed hot-dip galvanized cold-rolled steel sheet]
The electrogalvanized cold-rolled steel sheet of the present invention
is one in which on the surface of the cold-rolled steel sheet of the
above-described present invention, electrogalvanizing is furtl~erp erformed.
Further, the hot-dip galvanized cold-rolled steel sheet of the present invention
5 is one in which on the surface of the cold-rolled steel sheet of the
above-described present invention, hot-dip galvanizing is further performed.
Fui-ther, the alloyed hot-dip galvanized cold-rolled steel sheet of the present
invention is one in which on the surface of the cold-rolled steel sheet of the
above-described present invention, alloying hot-dip galvanizing is further
10 performed. As above, in the present invention, on the surface of the
cold-rolled steel sheet, electrogalvanizing, hot-dip galvanizing, or alloying
hot-dip galvanizing may also be perfonned as usage.
[0079] With regard to a manufacturing method of the electrogalvanized
cold-rolled steel sheet of the present invention, on the surface of the
15 cold-rolled steel sheet manufactured on the above-described conditions and
by the above-described steps, electrogalvanizing is performed by a
conventional well-known method. Further, with regard to a manufacturing
method of the hot-dip galvanized cold-rolled steel sheet (alloyed hot-dip
galvanized cold-rolled steel sheet) of the present invention, on the surface of
20 the cold-rolled steel sheet manufactured on the above-described conditions
and by the above-described steps, hot-dip galvanizing is performed by a
conventional well-known method.
On this occasion, the co~npositiono f the galvanizing is not limited in
particular, and in addition to zinc, Fe, Al, Mn, Cr, Mg, Pb, Sn, Ni, and the like
25 may also be contained according to need.
By the above-described methods, the electrogalvanized cold-rolled
steel sheet and the hot-dip galvanized cold-rolled steel sheet of the present
invention can be obtained.
[0080] Then, in the case of manufacturing the alloyed hot-dip galvanized
cold-rolled steel sheet of the present invention, on the hot-dip galvanized
5 cold-rolled steel sheet of the present invention obtained by the
above-described method, a heat treatment is performed for 10 seconds or
longer in a temperature range of 450 to 600°C, which is set to a method of
performing an alloying treatment.
[0081] The above-described alloying treatment (heat treatment) needs to
10 be performed in the range of 450 to 600°C. When this temperature is lower
than 450°C, there is caused a problem that alloying does not progress
sufficiently. Ful-ther, when it is 600°C or higher, alloying progresses
excessively and a plating layer becomes brittle, so that a problem such as
peeling of plating caused by working such as pressing is caused.
15 [0082] Further, the time period for the alloying treatment is set to 10
seconds or longer. When the time period for the alloying treatment is shol-ter
than 10 seconds, alloying does not progress sufficiently. Incidentally, the
upper limit of the time period of the alloying treatment is not defined in
particular, but the alloying treatment is normally performed by heat treatment
20 equipment installed in a continuous line, so that when it is performed for
longer than 3000 seconds, productivity is impaired, or a facility investment is
required and the manufacturing cost is increased, and thus this is preferably
set to the upper limit.
[0083] Incidentally, in the present invention, prior to the above-described
25 alloying treatment, annealing at an Ac3 transformation temperature or lower
may also be performed beforehand according to the structure of a
manufacturing facility. As long as the temperature of the annealing to be
performed before the alloying treatment is a temperature in the
above-described temperature zone or lower, the texture hardly changes, so
that it is possible to suppress a decrease in Young's modulus.
5 Further, in the present invention, the above-described temper rolling
may also be performed after the electrogalvanizing, the galvanizing, and the
alloying treatment.
[0084] According to the cold-rolled steel sheet excellent in rigidity and
deep drawability, the electrogalvanized cold-rolled steel sheet, the hot-dip
10 galvanized cold-rolled steel sheet, the alloyed hot-dip galvanized cold-rolled
steel sheet, and the manufacturing methods of the same of the present
invention that are explained above, the above-described constitution makes it
possible to obtain a cold-rolled steel sheet whose rigidity is excellent because
the Young's modulus in both the directions are 206 GPa or more, the Young's
15 modulus in the rolling perpendicular direction is 225 GPa or more, and the
static Young's modulus in the rolling direction improves and whose deep
drawability is excellent because the average r value is 1.4 or more, an
electrogalvanized cold-rolled steel sheet, a hot-dip galvanized cold-rolled
steel sheet, or an alloyed hot-dip galvanized cold-rolled steel sheet.
20 Thus, application of the present invention to an automobile member
such as a panel member, for example, makes it possible to sufficiently enjoy
merits of fuel efficiency improvement and reduction in vehicle body weight
associated with sheet thinning of a inember achieved by iinprove~nent in
rigidity in addition to improvement in workability, so that social contributions
25 are immeasurable.
Example
[0085] Hereinafter, the present invention will be explained more
concretely by citing examples of the cold-rolled steel sheet, the
electrogalvanized cold-rolled steel sheet, the hot-dip galvanized cold-rolled
steel sheet, the alloyed hot-dip galvanized cold-rolled steel sheet, and the
5 manufacturing methods of the same of the present invention. The present
invention is not limited to the following examples, and can also be cassied out
with appropriate modification being added within a range conforming to the
spirit described above and the spirit to be described later, and they are all
included in the technical scope of the present invention.
10 [0086] In this example, steels having compositions shown in Table 1 were
first melted to manufacture steel billets. Each of the steel billets in Table 1
was heated to be subjected to rough rolling in hot working, and then was
subjected to finish.rolling under conditions shown in Table 2 subsequently.
A finish rolling stand is made of seven stages in total, and a roll diameter is
15 650 to 830 mm. Further, a finished sheet thickness after the final pass is set
to 2.3 mm to 4.5 mm.
[0087] In Table 1, each underline attached to a numerical value means
that an alloy component is outside the range of the present invention. "-"
means that each alloy component is not contained intentionally. Further,
20 "(1) EXPRESSION Mn/B" shown in Table 1 is a value of "(Mn (mass%) -
MnX (mass%))/(B (ppm) - BX (ppm))" in (1) Expression above. "(3)
EXPRESSION (A3 - 50)"C" is a value of the temperature 50°C lower than
the A3 transformation temperature obtained by (3) Expression above (the A3
transformation temperature - 50°C).
25 [0088] In Table 2, each underline attached to a numerical value means
that a manufacturing condition is outside the range of the present invention.
SRT ["C] represents a heating temperature of the steel billet, FOT ["C]
represents an entry side temperature of the first pass of finish rolling (a finish
rolling stasting temperature), FT ["C] represents a temperature after the final
pass of finish rolling, namely an exit side temperature of finish rolling, t [s]
5 represents a time period until start of cooling after final finish rolling, a
cooling rate indicates an average cooling rate down to 700°C after finish of
finish rolling, and CT ["C] represents a coiling temnperature. A shape ratio 1
indicates a shape ratio of the fourth pass of finish rolling perfor~ned in the
temperature zone of 1000°C to 950°C, and a shape ratio 2 indicates a shape
10 ratio of the seventh pass of finish rolling performed in the temperature zone of
not lower than (the A3 transformation temperature - 50)"C nor higher than
950°C. A cold rolling ratio is a value of a difference between a sheet
thickness of a hot-rolled sheet and a sheet thickness after finish of cold rolling
divided by the sheet thickness of the hot-rolled sheet to be shown in
15 percentage. A heating rate 1 indicates an average heating rate from room
temperature to 650°C. A heating rate 2 indicates an average heating rate
from 650°C to 700°C.
[0089] [Table 11
[0090] [Table 21
[0091] From each of obtained cold-rolled steel sheets, a tensile test piece
based on JIS Z 2201 was taken with the rolling perpendicular direction being
a longitudinal direction, a tensile test was performed based on JIS Z 2241, and
a tensile strength was measured.
With regard to the r value, in the same manner as that in the tensile
test, tensile test pieces based on JIS Z 2201 were taken with the rolling
direction, the 45" direction, and the rolling perpendicular direction each being
a longitudinal direction, and values were measured with 15% of a strain
amount.
[0092] With regard to measurement of the Young's modulus, it was
measured by both the above-described static terlsile method and an oscillation
method.
The measurement of the Young's modulus by the static tensile method
5 was performed by using a tensile test piece based on JIS Z 2201 and applying
a tensile stress equivalent to 112 of a yield strength of the steel sheet. On this
occasion, the measurement was performed five times, and among Young's
modulus calculated based on a slope of a stress-strain diagram, an average
value of three measurement values excluding the maximum value and the
10 minimum value was found as the Young's ~nodulus by the static tensile
method, and this was shown in Table 3 as a tensile Young's modulus.
Incidentally, with regard to an electrogalvanized steel sheet, a hot-dip
galvanized steel sheet, and an alloyed hot-dip galvanized steel sheet to be
described later, the measurement was performed after a plating layer on the
15 surface was peeled off.
[0093] The random intensity ratios of the {332)<110>, {557)<9 16 7>,
and (1 11)<112> orientations at the position of 114 sheet thickness of the steel
sheet were measured as follows. First, a sample obtained in a manner that
the steel sheet was mechanically polished and buffed, and then was further
20 electrolytic polished to remove strain and was adjusted so that a 114 sheet
thickness portion became a measurement surface was used to be subjected to
X-ray diffraction. Incidentally, X-ray diffraction of a standard sample
without having accumulation to a specific orientation was also performed on
the same condition.
Next, based on the {110}, {loo}, (2111, and (310) pole figures
obtained by the X-ray diffraction, an ODF was obtained by a series expansion
method. Then, fi-om this ODF, the random intensity ratios of the
above-described orientations were determined.
[0094] Further, among these steel sheets, the case where
electrogalvanizing was performed after cold rolling and annealing was shown
5 as "ELECTRO" in Table 2, the case where hot-dip galvanizing was performed
was shown as "HOT DIP" in Table 2, and further the case where after the
hot-dip galvanizing, an alloying treatment to perform holding for 15 seconds
at 520°C was performed and alloying hot-dip galvanizing was perfor~nedw as
shown as "ALLOY."
10 Incidentally, as an electrogalvanizing treatment in this exa~npleZ, n-Ni
plating (Ni = 11 mass%) was performed.
Each weight was set to 20 gh2.
[0095] Results in this example are shown in Table 3. Incidentally, in the
colutnn of Young's modulus in Table 3, RD means the rolling direction
15 (Rolling Direction), 45" means 45" with respect to the rolling direction, and
TD means the transverse direction (Transverse Direction) respectively.
[0096] [Table 31
I) KANDOXI INTENSITY RATIO (A) OF THE (332)clID ORIENTATION
2) RANDOXI INTENSITY RATIO (B) OFTHE (537)- 16 5-'ORIENTATION
3) RANDOM INTENSITY RATIO (C) OF THE (I1 I J c l l D ORIENTATION
[0097] As is clear fiom the results shown in Table 3, in the case of the
present invention examples in which the steel having the chemical
co~nponents of the present invention was manufactured on the proper
conditions (the present invention examples in the column of note in Tables 1
to 3), the Young's modulus in the rolling direction and in the 45" direction
both became 206 GPa or more, the Young's ~nodulus in the transverse
direction became 225 GPa or more, and the average r value became 1.4 or
5 more. Thereby, it is clear that the present invention examples are each high
in rigidity and excellent in deep drawability.
[0098] On the other hand, Manufactures No. 45 to 52 are comparative
examples using Steels No. P to W each having the chemical components
falling outside the range of the present invention. Manufacture No. 45 and
10 Manufacture No. 48 are an example of the case where (1) Expression was not
able to be satisfied because the content of S was high in Manufacture No. 45
and the content of Mn was low in Manufacture No. 48. In this case,
recovely during annealing was not suppressed sufficiently, so that the random
intensity ratios (A) and (C) were intensified and no sufficient Young's
15 modulus in the transverse direction was able to be obtained.
[0099] Manufacture No. 46 indicates an example of the case where no Ti
is contained. In this case, TiN precipitation does not occur and a y grain
diameter becomes coarse, so that the random intensity ratio (A) increases.
Additionally, at the stage of the hot-rolled sheet, solid-solution C remains, so
20 that the random intensity ratio (A) hrther develops but the development of
the randoin intensity ratios (B) and (C) is suppressed, resulting in that the
Young's illodulus in the transverse direction decreases and the r value also
deteriorates.
Manufacture No. 47 is the case where the added amount of C is too
25 high. In this case, solid-solution C remains in the hot-rolled sheet, so that
development of all the orientations of the randoin intensity ratios (A), (B),
and (C) is suppressed.
Manufacture No. 49 is an example of the case where Mn is too high.
In this case, recrystallization is delayed, the random intensity ratios (B) and
(C) become weak, the Young's modulus in the transverse direction cannot be
5 satisfied, and the r value also decreases.
Manufacture No. 50 is the case where the amount of B is small. In
this case, recovely is not suppressed, so that the random intensity ratio (C)
develops and the random intensity ratio (B) decreases, and thus it is not
possible to satisfy the Young's modulus in the transverse direction.
10 Manufacture No. 5 1 is the case where the added amount of Ti is too
high, and Manufacture No. 52 is the case where the added amount of B is too
high. In each of these cases, the recrystallization temperature when
annealing becomes too high, so that workability deteriorates, the random
intensity ratio (B) becomes weak, the Young's modulus in the 45" direction
15 decreases, and the r value also decreases.
[OlOO] As is Manufacture No. 3 with Steel No. A being a comparative
example, when the heating rate 2 is too large, the r value decreases and the
random intensity ratio (A) develops, so that the Young's modulus in the
transverse direction and in the rolling direction decrease.
20 As is Manufacture No. 4 with Steel No. A being a compasative
example, when the shape ratio 1 is too high, the r value decreases and the
random intensity ratio (B) does not develop, so that the Young's modulus in
the transverse direction and in the rolling direction decrease.
[OlOl] As is Manufacture No. 7 with Steel No. B being a comparative
25 example, when the time period t until start of cooling after final finish rolling
is too long, the random intensity ratio (A) develops, so that the Young's
modulus in the transverse direction and in the rolling direction decrease.
As is Manufacture No. 8 with Steel No. B being a comparative
example, when the heating rate 2 is too small, the r value decreases and the
random intensity ratio (B) does not develop, so that the Young's modulus in
5 the transverse direction and in the rolling direction decrease.
[0102] As is Manufacture No. 11 with Steel No. C being a comparative
example, when the shape ratio of the hot rolling final pass is too low, no
sufficient shear deformation is introduced and the random intensity ratio (B)
does not develop, so that the Young's modulus in the transverse direction
10 decreases.
[0103] As is Manufacture No. 14 with Steel No. D being a comparative
example, when the shape ratio 1 is too high, the r value decreases and the
random intensity ratio (B) does not develop, so that the Young's modulus in
the transverse direction and in the rolling direction decrease.
15 [O104] As is Manufacture No. 17 with Steel No. E being a comparative
example, when the heating temperature is low to make it impossible to secure
sufficient FOT and FT, the random intensity ratio (B) is intensified, but the
random intensity ratio (C) becomes weak, so that the r value cannot be
secured.
20 As is Manufacture No. 18 with Steel No. E being a comparative
example, when the heating rate 2 is too large, the r value decreases and the
random intensity ratio (A) develops, so that the Young's modulus in the
transverse direction and in the rolling direction decrease.
[0105] As is Manufacture No. 21 with Steel No. F being a comparative
25 example, when the annealing temperature is too high, the annealing results in
y-region annealing, so that the texture becomes weak and the Young's
modulus and the r value both decrease.
[0106] As is Manufacture No. 24 with Steel No. G being a comparative
example, when FOT and FT are too high, the random intensity ratio (A) is
intensified too nluch, so that the Young's modulus in the transverse direction
5 decreases.
[0107] As is Manufacture No. 26 with Steel No. H being a comparative
example, when the cooling rate after hot rolling is small and the cold rolling
ratio is low, the random intensity ratio (A) is intensified too much and the
random intensity ratios (B) and (C) become weak, so that the Young's
10 modulus and the r value both decrease.
As is Manufacture No. 27 with Steel No. H being a comparative
example, when the time period t until start of cooling after final finish rolling
is too long, the random intensity ratio (A) develops, so that the Young's
lnodulus in the transverse direction and in the rolling direction decrease.
15 [0108] As is Manufacture No. 30 with Steel No. I being a comparative
example, when the coiling temperature is too low, solid-solution C remains in
the hot-rolled sheet, so that the randoln intensity ratios (B) and (C) do not
develop sufficiently, the Young's modulus decreases, and the r value also
deteriorates.
20 [0109] As is Manufacture No. 34 with Steel No. K being a comparative
example, when the coiling temperature increases too much and the cold
rolling ratio increases too much, the randoln intensity ratio (A) is intensified
too much and the integration degree of the {100}<012> orientation to
decrease the absolute values of the r value and the Young's modulus increases,
25 resulting in that both the r value and the Young's modulus cannot be secured.
[0110] As is Manufacture No. 38 with Steel No. M being a comparative
exatnple, when the heating rate when annealing (the heating rates 1 and 2) is
too fast, the {112}<110> orientation is intensified and the random intensity
ratio (B) becomes weak, and thereby the Young's modulus in the 45" direction
decreases and the r value also deteriorates.
5 [Olll] As is Manufacture No. 41 with Steel No. N being a comparative
example, when the annealing temperature is too low, reclystallization does not
progress sufficiently and non-recrystallization remains, so that ductility
decreases, and the Young's modulus in the 45" direction and the r value
deteriorate.
10 [0112] As is Manufacture No. 44 with Steel No. 0 being a colnparative
example, when the shape ratio 2 is too high, after cold rolling and annealing,
the random intensity ratio (B) does not develop as compared to the random
intensity ratio (C), so that the Young's modulus in the transverse direction
decreases.
15 [0113] From the results of the examples explained above, it is clear that
the present invention enables the cold-rolled steel sheet excellent in rigidity
and deep drawability, the electrogalvanized cold-rolled steel sheet, the hot-dip
galvanized cold-rolled steel sheet, and the alloyed hot-dip galvanized
cold-rolled steel sheet to be fabricated.
20 [Industrial Applicability]
[O114] The cold-rolled steel sheet of the present invention is used fol; for
example, automobiles, home electric appliances, buildings, and so on.
Fusther, the cold-rolled steel sheet of the present invention includes
narrowly-defined cold-rolled steel sheets without a surface treatment
25 perfor~nedt hereon and broadly-defined cold-rolled steel sheets with a surface
treatment such as hot-dip Zn plating, alloying hot-dip Zn plating, or
electrogalvanizing performed thereon for the purpose of rust prevention.
This surface treatment includes aluminum-based plating, forming of an
organic coating film and an inorganic coating film on surfaces of various
plated steel sheets, coating, and treatments combined with them. Then, the
5 cold-rolled steel sheet of the present invention has a high Young's modulus,
and thus as compared to a conventional steel sheet, a decrease in sheet
thickness, namely a reduction in weight can be achieved, and it is possible to
contribute to global environmental conservation. Further, the cold-rolled
steel sheet of the present invention is also improved in shape fixability, so that
10 application of a high-strength steel sheet to a pressed part such as an
automobile member is facilitated. Further, members obtained by forming
and working the steel sheet of the present invention are also excellent in
collision energy absorbing property, to thus contribute also to safety
improvement of automobiles, resulting in that social contributions are
I 5 im~neasurable.
Claim
[Claim 11 (after amendment) A cold-rolled steel sheet, comprising:
in mass%,
C: 0.0005 to 0.0045%;
Mn: 0.80 to 2.50%;
Ti: 0.002 to 0.150%;
B: 0.0005 to 0.01%;
Si: 0 to 1.0%;
Al: 0 to 0.10%;
Nb: 0 to 0.040%;
Mo: 0 to 0.500%;
Cr: 0 to 3.000%;
W: 0 to 3.000%;
Cu: 0 to 3.000%;
Ni: 0 to 3.000%;
Ca: 0 to 0.1000%;
Rem: 0 to 0.1000%;
V: 0 to 0.100%;
P: 0.15% or less;
S: 0.010% or less;
N: 0.006% or less,
in which (1) Expression below is satisfied, and
a balance being composed of iron and impurities, wherein
at the position of 114 thickness of a sheet thickness, a random intensity ratio
(A) of the (332)<110> orientation is 3 or less, a random intensity ratio (B) of
the (557)<9 16 5> orientation and a random intensity ratio (C) of the
(11 1)<112> orientation are both 7 or more, and {(B)/(A) 2 5) and {(B) >
(C)) are satisfied.
0.07 5 (Mn (mass%) - Mn* (mass%))/(B (ppin) - B* (ppm)) 5
0.2 .....( 1)
(1) Expression above is set as follows.
Mn* (mass%) = 55s (mass%)/32
B* (ppm) = 10(N (mass%) - 14Ti (mass%)/48)/14 x 10000
In the case of Mn* < 0 and B* < 0, B* is set to 0.
[Claim 21 The cold-rolled steel sheet according to claim 1, comprising:
one or two of, in mass%,
Si: 0.01 to 1.0%; and
Al: 0.010 to 0.10%.
[Claim 31 The cold-rolled steel sheet according to claim 1 or 2,
comprising:
in mass%,
Nb: 0.005 to 0.040%.
[Claim 41 The cold-rolled steel sheet according to any one of claims 1 to
3, comprising:
one or two or more of, in mass%,
Mo: 0.005 to 0.500%;
Cr: 0.005 to 3.000%;
W: 0.005 to 3.000%;
Cu: 0.005 to 3.000%; and
Ni: 0.005 to 3.000%.
[Claim 51 The cold-rolled steel sheet according to any one of claims 1 to
4, comprising:
one or two or more of, in mass%,
Ca: 0.0005 to 0.1000%;
Rem: 0.0005 to 0.1000%; and
V: 0.001 to 0.100%.
[Claim 61 The cold-rolled steel sheet according to any one of claims 1 to
5, wherein
a Young's ~nodulusin a rolling perpendicular direction is 225 GPa or more, a
Young's modulus in a rolling direction and a Young's modulus in a 45"
direction with respect to the rolling direction are both 206 GPa or more, and
an average r value is 1.4 or more.
[Claim 71 An electrogalvanized cold-rolled steel sheet, wherein
on the surface of the cold-rolled steel sheet according to any one of claims 1
to 6, electrogalvanizing is performed.
[Claim 81 A hot-dip galvanized cold-rolled steel sheet, wherein
on the surface of the cold-rolled steel sheet according to any one of claims 1
to 6, hot-dip galvanizing is performed.
[Claim 91 An alloyed hot-dip galvanized cold-rolled steel sheet, wherein
on the surface of the cold-rolled steel sheet according to any one of claims 1
to 6, alloying hot-dip galvanizing is perfolmed.
[Claim 101 (after amendment) A manufacturing method of a
cold-rolled steel sheet, comprising:
on a steel billet containing:
in mass%,
C: 0.0005 to 0.0045%;
Mn: 0.80 to 2.50%;
Ti: 0.002 to 0.150%;
B: 0.0005 to 0.01%;
Si: 0 to 1.0%;
Al: 0 to 0.10%;
Nb: 0 to 0.040%;
Mo: 0 to 0.500%;
Cr: 0 to 3.000%;
W: 0 to 3.000%;
Cu: 0 to 3.000%;
Ni: 0 to 3.000%;
Ca: 0 to 0.1000%;
Rem: 0 to 0.1000%;
V: 0 to 0.100%;
P: 0.15% or less;
S: 0.010% or less;
N: 0.006% or less,
in which (1) Expression below is satisfied, and
a balance being composed of iron and impurities,
performing heating to 1 150°C or higher, and next perfor~ning rolling with a
shape ratio (X) determined by (2) Expression below of 4.4 or less for at least
one pass or more in a temperature range of 1000 to 950°C with a finish
rolling starting temperature set to 1000 to llOO°C, and next perfor~ning
rolling with the shape ratio (X) determined by (2) Expression below of 3.0 to
4.2 for at least one pass or more in a temperature range of not lower than a
temperature 50°C lower than an A3 transfor~nation temperature obtained by
(3) Expression below nor higher than 950°C, and next starting cooling within
2 seconds after finish of final rolling, cooling the temperature within a range
down to 700°C at an average cooling rate of 15"CIs or more, and then
perfor~ning coiling in a telnperature range of 500 to 650°C, and next
perfor~ningp ickling, and then perfor~ningc old rolling at a reduction ratio of
50 to 90%, heating the temperature in a range of room telnperature to 650°C
at an average heating rate of 2 to 20°C/s, and fusther heating the temperature
f?om 650°C to 700°C at an average heating rate of 2 to 15OC/s, and next
perfor~ning annealing to perfor~n holding for 1 second or longer in a
temperature range of not lower than 700°C nor higher than 900°C.
0.07 5 (Mn (mass%) - Mn* (mass%))/(B (ppm) - B* (ppm)) 5
0.2 .....( 1)
(1) Expression above is set as follows.
Mn* (mass%) = 55s (mass%)/32
BY (ppm) = 1 O(N (mass%) - 14Ti (mass%)/48)/14 x 10000
In the case of Mn* < 0 and BY < 0, B* is set to 0.
X (shape ratio) = ldlhm ...-(2)
(2) Expression above is set as follows.
Id (contact arc length of hot-rolling roll and steel sheet): d (x~ (h in - hout)/2)
hm: (hin + hout)/2
L: roll diameter (mm)
hin: rolling roll ent~ysi de sheet thickness (mm)
hout: rolling roll exit side sheet thickness (mm)
A3 ("C) = 937.2 - 476.5'2 + 56% - 19.7Mn - 16.3Cu - 26.6Ni - 4.9Cr
+ 38.1Mo + 136.3Ti - 19.1Nb + 124.8V + 198.4Al+ 3315.0B --(3)
In (3) Expression above, C, Si, Mn, P, Cu, Ni, Cr, Mo, Ti, Nb, V, Al,
and B are the contents of the respective elements [mass%]. With regard to a
steel sheet in which Si, Al, Cu, Ni, Cr, Mo, Nb, and V are not intended to be
contained, it is calculated with content percentages of these each being 0%.
[Claim 111 A manufacturing method of an electrogalvanized cold-rolled
steel sheet, comprising:
performing electrogalvanizing on the surface of the steel sheet manufactured
by the method according to claim 10.
[Claim 121 A manufacturing method of a hot-dip galvanized cold-rolled
steel sheet, comprising:
performing hot-dip galvanizing on the surface of the steel sheet manufactured
by the method according to claim 10.
[Claim 131 A manufacturing method of an alloyed hot-dip galvanized
cold-rolled steel sheet, comprising:
on the surface of the steel sheet manufactured by the method
according to claim 10, perfolming hot-dip galvanizing, and then further
perfoi~ning a heat treatment for 10 seconds or longer in a temperature range
of 450 to 600°C.