STEEL SHEET
A steel sheet according to an aspect of the present invention includes a predetermined chemical composition; in which a metallographic structure in a ¼ t portion contains residual austenite of 4 volume % to 70 volume %; [Mn] γ /[Mn] ave >1.5 is satisfied in the ¼ t portion; f γs /f γ ≤0.30 and [C]×[Mn]≥0.15 are satisfied in the ¼ t portion.
1 . A steel sheet comprising, by unit mass %,
C: 0.03% to 0.40%,
Si: 0.01% to 5.00%,
Mn: 0.50% to 12.00%,
Al: 0.001% to 5.000%,
P: 0.150% or less,
S: 0.0300% or less,
N: 0.0100% or less,
O: 0.0100% or less,
Cr: 0% to 5.00%,
Mo: 0% to 5.00%,
Ni: 0% to 5.00%,
Cu: 0% to 5.00%,
Nb: 0% to 0.500%,
Ti: 0% to 0.500%,
V: 0% to 0.500%,
W: 0% to 0.500%,
B: 0% to 0.0030%,
Ca: 0% to 0.0500%,
Mg: 0% to 0.0500%,
Zr: 0% to 0.0500%,
REM: 0% to 0.0500%,
Sb: 0% to 0.0500%,
Sn: 0% to 0.0500%,
As: 0% to 0.0500%,
Te: 0% to 0.0500%, and
a remainder including Fe and impurities,
wherein a metallographic structure in a ¼ t portion contains residual austenite of 4 volume % to 70 volume %,
an average Mn concentration [Mn] γ in the residual austenite by unit mass % satisfies Expression 1 with respect to an average Mn concentration [Mn] ave of the entire ¼ t portion by unit mass %, in the ¼ t portion,
a volume fraction f γs of the residual austenite having an aspect ratio of 2.0 or less and a volume fraction f γ of all the residual austenite satisfy Expression 2, in the ¼ t portion, and
a C content [C] and a Mn content [Mn] by unit mass % satisfy Expression 3.
[Mn] γ /[Mn] ave >1.5 (Expression 1)
f γs /f γ ≤0.30 (Expression 2)
[C]×[Mn]≥0.15 (Expression 3)
2 . The steel sheet according to claim 1 , comprising, by unit mass %,
Mn: 3.50% to 12.00%.
3 . The steel sheet according to claim 1 , comprising, by unit mass %, one or more selected from the group consisting of
Cr: 0.01% to 5.00%,
Mo: 0.01% to 5.00%,
Ni: 0.01% to 5.00%,
Cu: 0.01% to 5.00%,
Nb: 0.005% to 0.500%,
Ti: 0.005% to 0.500%,
V: 0.005% to 0.500%,
W: 0.005% to 0.500%,
B: 0.0001% to 0.0030%,
Ca: 0.0001% to 0.0500%,
Mg: 0.0001% to 0.0500%,
Zr: 0.0005% to 0.0500%,
REM: 0.0005% to 0.0500%,
Sb: 0.0050% to 0.0500%,
Sn: 0.0050% to 0.0500%,
As: 0.0050% to 0.0500%, and
Te: 0.0050% to 0.0500%.
4 . The steel sheet according to claim 1 , comprising:
a hot dip galvanized layer on a surface of the steel sheet.
5 . The steel sheet according to claim 1 , comprising:
a galvannealed layer on a surface of the steel sheet.
6 . The steel sheet according to claim 2 , comprising, by unit mass %, one or more selected from the group consisting of
Cr: 0.01% to 5.00%,
Mo: 0.01% to 5.00%,
Ni: 0.01% to 5.00%,
Cu: 0.01% to 5.00%,
Nb: 0.005% to 0.500%,
Ti: 0.005% to 0.500%,
V: 0.005% to 0.500%,
W: 0.005% to 0.500%,
B: 0.0001% to 0.0030%,
Ca: 0.0001% to 0.0500%,
Mg: 0.0001% to 0.0500%,
Zr: 0.0005% to 0.0500%,
REM: 0.0005% to 0.0500%,
Sb: 0.0050% to 0.0500%,
Sn: 0.0050% to 0.0500%,
As: 0.0050% to 0.0500%, and
Te: 0.0050% to 0.0500%.
7 . The steel sheet according to claim 2 , comprising:
a hot dip galvanized layer on a surface of the steel sheet.
8 . The steel sheet according to claim 3 , comprising:
a hot dip galvanized layer on a surface of the steel sheet.
9 . The steel sheet according to claim 6 , comprising:
a hot dip galvanized layer on a surface of the steel sheet.
10 . The steel sheet according to claim 2 , comprising:
a galvannealed layer on a surface of the steel sheet.
11 . The steel sheet according to claim 3 , comprising:
a galvannealed layer on a surface of the steel sheet.
12 . The steel sheet according to claim 6 , comprising:
a galvannealed layer on a surface of the steel sheet.