Patent ID: 11970752
Assignee: NIPPON STEEL CORPORATION
Field: Materials, metallurgy (Chemistry)
Classification: CPC C | IPC C

Claim 0:
1. A steel sheet, having a chemical composition comprising, by mass %:
C: 0.15 to 0.40%;
Si: 0.01 to 2.00%;
Mn: 0.10 to 5.00%;
P: 0.0001 to 0.0200%;
S: 0.0001 to 0.0200%;
Al: 0.001 to 1.000%;
N: 0.0001 to 0.0200%;
Co: 0 to 0.50%;
Ni: 0 to 1.00%;
Mo: 0 to 1.00%;
Cr: 0 to 2.000%;
O: 0 to 0.0200%;
Ti: 0 to 0.500%;
B: 0 to 0.0100%;
Nb: 0 to 0.500%;
V: 0 to 0.500%;
Cu: 0 to 0.500%;
W: 0 to 0.100%;
Ta: 0 to 0.100%;
Sn: 0 to 0.050%;
Sb: 0 to 0.050%;
As: 0 to 0.050%;
Mg: 0 to 0.0500%;
Ca: 0 to 0.050%;
Y: 0 to 0.050%;
Zr: 0 to 0.050%;
La: 0 to 0.050%;
Ce: 0 to 0.050%; and
a balance of Fe and impurities,
wherein
the steel sheet comprises, by area ratio:
ferrite: 5.0% or less; and
a total of martensite and tempered martensite: 90.0% or more, wherein when there is a balance structure, the balance structure is composed of at least one of bainite, pearlite, and retained austenite,
a standard deviation σ of Mn concentration satisfies a 0.15 Mnave (wherein, Mnave represents an average Mn concentration), and
a region with a Mn concentration of higher than (Mnave+1.3σ) has a circle-equivalent diameter of less than 10.0 μm.