US 11,913,088 B2
High-strength steel sheet and method for producing same
Tadao Murata, Kakogawa (JP); Muneaki Ikeda, Kakogawa (JP); and Toshio Murakami, Kobe (JP)
Assigned to Kobe Steel, Ltd., Kobe (JP)
Appl. No. 17/760,969
Filed by Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.), Kobe (JP)
PCT Filed Sep. 14, 2020, PCT No. PCT/JP2020/034736
§ 371(c)(1), (2) Date Mar. 16, 2022,
PCT Pub. No. WO2021/054290, PCT Pub. Date Mar. 25, 2021.
Claims priority of application No. 2019-168392 (JP), filed on Sep. 17, 2019.
Prior Publication US 2022/0349020 A1, Nov. 3, 2022
Int. Cl. C21D 9/46 (2006.01); B32B 15/01 (2006.01); C21D 6/00 (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 2/40 (2006.01)
CPC C21D 9/46 (2013.01) [B32B 15/013 (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); 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 2/40 (2013.01); C21D 2211/001 (2013.01); C21D 2211/005 (2013.01); C21D 2211/008 (2013.01)] 20 Claims
OG exemplary drawing
 
1. A high-strength steel sheet, comprising:
0.10% to 0.35% of C;
0.5% to 3.0% of Si+Al;
1.0% to 3.0% of Mn;
more than 0% and 0.05% or less of P; and
more than 0% and 0.01% or less of S, in terms of mass percentage,
wherein the high-strength steel sheet has a metallographic microstructure having a ferrite fraction of 0% to 10%, a Fresh-Martensite/Retained-Austenite (MA) fraction in a range of from 0% to 30%, a hard phase other than ferrite and MA in a range of from 70% to 100% in terms of area proportion, and
a retained austenite fraction in a range of from 5% to 30% in terms of volume proportion, and
wherein a skewness of image quality (IQ) as analyzed by an Electron Back Scatter Diffraction (EBSD) method is in a range of from −1.2 to −0.3, when the skewness is expressed by Formula (1) in a case where crystal grains having a bcc structure and a bet structure are regarded as an aggregation of regions having an area of 0.05 μm2:

OG Complex Work Unit Math
wherein, in Formula (1),
n is total number of regions having a bcc structure and a bct structure and an area of 0.05 μm2,
s is standard deviation of the IQ in a region having an area of 0.05 μm2,
xi is the IQ of a region i having an area of 0.05 μm2, and
xave is an average IQ of regions having a bee structure and a bet structure and an area of 0.05 μm2.