Patent ID: 11970758
Assignee: NIPPON STEEL CORPORATION
Field: Materials, metallurgy (Chemistry)
Classification: CPC C | IPC C

Claim 0:
1. A hot-rolled steel sheet comprising, as a chemical composition, by mass %:
C: 0.100% to 0.250%;
Si: 0.05% to 3.00%;
Mn: 1.00% to 4.00%;
Nb: 0.005% to 0.050%;
sol. Al: 0.001% to 2.000%;
P: 0.100% or less;
S: 0.0300% or less;
N: 0.1000% or less;
0: 0.0100% or less;
Ti: 0% to 0.300%;
V: 0% to 0.500%;
Cu: 0% to 2.00%;
Cr: 0% to 2.00%;
Mo: 0% to 1.000%;
Ni: 0% to 2.00%;
B: 0% to 0.0100%;
Ca: 0% to 0.0200%;
Mg: 0% to 0.0200%;
REM: 0% to 0.1000%;
Bi: 0% to 0.020%;
one or two or more of Zr, Co, Zn, and W: 0% to 1.00% in total;
Sn: 0% to 0.050%; and
a remainder including Fe and impurities,
wherein a metallographic structure at a sheet thickness ¼ depth from a surface and at a center position in a sheet width direction in a sheet width cross section parallel to a rolling direction contains, by area %,
77.0% to 94.0% of bainite and tempered martensite in total,
0% to 5.0% of ferrite,
0% to 5.0% of pearlite,
6.0% or more of residual austenite, and
0% to 10.0% of martensite,
an average grain size of the metallographic structure excluding the residual austenite is 7.0 μm or less,
a C concentration in the residual austenite is 0.5 mass % or more, and
a number density of iron-based carbides having a diameter of 20 nm or more is 1.0×106 carbides/mm2 or more.