	US 12,319,977 B2
	Hot rolled steel sheet and production method thereof
Masaharu Oka, Tokyo (JP); Nobusato Kojima, Tokyo (JP); and Mitsuru Yoshida, Tokyo (JP)
Assigned to NIPPON STEEL CORPORATION, Tokyo (JP)
Appl. No. 17/788,672
Filed by NIPPON STEEL CORPORATION, Tokyo (JP)
PCT Filed Jan. 29, 2021, PCT No. PCT/JP2021/003289 § 371(c)(1), (2) Date Jun. 23, 2022, PCT Pub. No. WO2021/153746, PCT Pub. Date Aug. 5, 2021.
Claims priority of application No. 2020-013713 (JP), filed on Jan. 30, 2020; and application No. 2020-047558 (JP), filed on Mar. 18, 2020.
Prior Publication US 2023/0034898 A1, Feb. 2, 2023
Int. Cl. C21D 9/46 (2006.01); B21C 47/02 (2006.01); C21D 8/02 (2006.01); C22C 38/00 (2006.01); C22C 38/02 (2006.01); C22C 38/04 (2006.01); C22C 38/06 (2006.01); C22C 38/14 (2006.01); C23C 2/04 (2006.01)

CPC C21D 8/0226 (2013.01) [B21C 47/02 (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 38/14 (2013.01); C23C 2/04 (2013.01); C21D 2211/001 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01)]

20 Claims

1. A hot-rolled steel sheet comprising, as a chemical composition, by mass %:

C: 0.08% to 0.25%;

Si: 0.01% to 1.00%;

Mn: 0.8% to 2.0%;

P: 0.020% or less;

S: 0.001% to 0.010%;

Al: 0.005% to 1.000%;

N: 0.0010% to 0.0100%;

Ti: 0.005% to 0.30%;

Ca: 0.0005% to 0.0100%;

Nb: 0% to 0.30%;

V: 0% to 0.50%;

Cr: 0% to 3.0%;

Mo: 0% to 3.0%;

Ni: 0% to 5.0%;

Cu: 0% to 3.0%;

B: 0% to 0.0100%;

Mg: 0% to 0.0100%;

Zr: 0% to 0.0500%;

REM: 0% to 0.050%; and

a remainder including Fe and impurities,

wherein a microstructure includes 99% or more of martensite by volume fraction and a remainder in microstructure including residual austenite and ferrite, wherein the martensite refers to one or more of fresh martensite and tempered martensite,

in a cross section parallel to a rolling direction,

an average aspect ratio of prior austenite grains is less than 3.0,

a proportion of sulfides having an aspect ratio of more than 3.0 among sulfides having an area of 1.0 μm²or more is 1.0% or less, and

in a thickness middle portion, a pole density of {211}<011> orientation is 3.0 or less, and

a tensile strength TS is 980 MPa or higher.