	US 12,442,062 B2
	Hot-rolled steel sheet
Daisuke Ito, Tokyo (JP); Akifumi Sakakibara, Tokyo (JP); Teruki Hayashida, Tokyo (JP); and Tatsuo Yokoi, Tokyo (JP)
Assigned to NIPPON STEEL CORPORATION, Tokyo (JP)
Appl. No. 18/027,800
Filed by NIPPON STEEL CORPORATION, Tokyo (JP)
PCT Filed Jan. 7, 2022, PCT No. PCT/JP2022/000308 § 371(c)(1), (2) Date Mar. 22, 2023, PCT Pub. No. WO2022/153927, PCT Pub. Date Jul. 21, 2022.
Claims priority of application No. 2021-005008 (JP), filed on Jan. 15, 2021.
Prior Publication US 2023/0357908 A1, Nov. 9, 2023
Int. Cl. C22C 38/58 (2006.01); C21D 1/18 (2006.01); C21D 6/00 (2006.01); C21D 8/02 (2006.01); C21D 9/46 (2006.01); C22C 38/00 (2006.01); C22C 38/02 (2006.01); C22C 38/04 (2006.01); C22C 38/06 (2006.01); C22C 38/12 (2006.01); C22C 38/14 (2006.01); C22C 38/28 (2006.01); C22C 38/32 (2006.01); C22C 38/42 (2006.01); C22C 38/50 (2006.01); C22C 38/54 (2006.01)

CPC C22C 38/58 (2013.01) [C21D 1/18 (2013.01); C21D 6/002 (2013.01); C21D 6/004 (2013.01); C21D 6/005 (2013.01); C21D 6/008 (2013.01); C21D 8/0205 (2013.01); C21D 8/0226 (2013.01); C21D 8/0263 (2013.01); C21D 9/46 (2013.01); C22C 38/001 (2013.01); C22C 38/002 (2013.01); C22C 38/02 (2013.01); C22C 38/04 (2013.01); C22C 38/06 (2013.01); C22C 38/12 (2013.01); C22C 38/14 (2013.01); C22C 38/28 (2013.01); C22C 38/32 (2013.01); C22C 38/42 (2013.01); C22C 38/50 (2013.01); C22C 38/54 (2013.01); C21D 2211/008 (2013.01)]

9 Claims

1. A hot-rolled steel sheet having a chemical composition which contains, in % by mass,

C: 0.050 to 0.150%,

Si: 0.01 to 1.00%,

Mn: 1.00 to 2.50%,

P: 0.100% or less,

S: 0.020% or less,

N: 0.0050% or less,

Al: 0.001 to 0.300%,

Ti: 0.001 to 0.100%,

B: 0.0005 to 0.0050%,

Nb: 0 to 0.100%,

Cr: 0 to 1.00%,

V: 0 to 0.30%,

Cu: 0 to 0.30%,

Ni: 0 to 0.30%, and

Ca: 0 to 0.0050%,

wherein the remainder comprises Fe and impurities,

Vc represented by the following Expressions (1) to (3) is 10 to 40,

a microstructure contains, in area ratio,

at a location at ¼ a sheet thickness,

a total amount of 90% or more of one or more of martensite and tempered martensite and

a total amount of 10% or less of one or more ferrite, bainite, and pearlite,

at a location of 200 μm from a surface,

a total amount of 70% or more and less than 90% of one or more of martensite and tempered martensite and

a total amount of more than 10% and 30% or less of one or more of ferrite, bainite, and pearlite:

when an effective amount of B≥0.0005% by mass is satisfied,

Vc=10^{2.94−0.75×(2.7×C+0.4×Si+Mn+0.45×Ni+0.8×Cr)}

when an effective amount of B<0.0005% by mass is satisfied,

Vc=10^{3.69−0.75×(2.7×C+0.4×Si+Mn+0.45×Ni+0.8×Cr)} (1),

an effective amount of B=10.81×(B/10.81−solid solution N amount/14.01) (2), and

solid solution N amount=14.01×(N/14.01−Ti/47.88) (3),

here, each element symbol in the above Expression (1) is the content of the element in % by mass, and when the element is not contained, 0 is substituted,

B in the above Expression (2) is, in % by mass, a B content,

when the effective amount of B is a negative value, the effective amount of B is set to 0,

N and Ti in the above Expression (3) are, in % by mass, contents, and

when the solid solution N amount is a negative value, the solid solution N amount is 0.