	US 12,421,566 B2
	Hot-rolled steel sheet and manufacturing method thereof
Eisaku Sakurada, Tokyo (JP); Takashi Yasutomi, Tokyo (JP); and Genki Abukawa, Tokyo (JP)
Assigned to NIPPON STEEL CORPORATION, Tokyo (JP)
Appl. No. 17/908,553
Filed by NIPPON STEEL CORPORATION, Tokyo (JP)
PCT Filed Apr. 21, 2021, PCT No. PCT/JP2021/016130 § 371(c)(1), (2) Date Sep. 1, 2022, PCT Pub. No. WO2021/225073, PCT Pub. Date Nov. 11, 2021.
Claims priority of application No. 2020-082655 (JP), filed on May 8, 2020.
Prior Publication US 2023/0140766 A1, May 4, 2023
Int. Cl. C21D 8/02 (2006.01); B21C 47/02 (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 38/22 (2006.01); C22C 38/24 (2006.01); C22C 38/26 (2006.01); C22C 38/28 (2006.01); C22C 38/32 (2006.01); C23C 2/40 (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 38/22 (2013.01); C22C 38/24 (2013.01); C22C 38/26 (2013.01); C22C 38/28 (2013.01); C22C 38/32 (2013.01); C23C 2/40 (2013.01); C21D 2211/001 (2013.01); C21D 2211/002 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01); C21D 2211/009 (2013.01)]

7 Claims

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

C: 0.085% to 0.190%;

Si: 0.40% to 1.40%;

Mn: 1.70% to 2.75%;

Al: 0.01% to 0.55%;

Nb: 0.006% to 0.050%;

P: 0.080% or less;

S: 0.010% or less;

N: 0.0050% or less;

Ti: 0.004% to 0.180%;

B: 0.0004% to 0.0030%;

Mo: 0% to 0.150%;

V: 0% to 0.300%;

Cr: 0% to 0.500%;

Ca: 0% to 0.0020%; and

a remainder consisting of Fe and an impurity,

wherein, in metallographic structures at a ¼ position in a sheet thickness direction from a surface and at a ½ position in the sheet thickness direction from the surface, by vol %,

residual austenite is 3.0% to 12.0%,

bainite is 75.0% or more and less than 97.0%,

ferrite is 10.0% or less,

martensite is 10.0% or less, and

pearlite is 3.0% or less,

in a metallographic structure of a region from the surface to a 100 μm position in the sheet thickness direction from the surface,

an average grain diameter of prior austenite grains is 25.0 μm or less,

a ratio between a maximum depth of a region where, on one surface, a rotation angle between a normal line of the one surface and a (011) pole near the normal line of the one surface is 5° or less and a maximum depth of a region where, on the other surface, a rotation angle between a normal line of the other surface and a (011) pole near the normal line of the other surface is 5° or less is 1.00 to 1.20, and

a tensile strength is 1150 MPa or more.