Patent ID: 9657381
Date: 2017-05-23
CPC Classifications: B21D,C21D,C22C

Claim:
1. A steel sheet, comprising, by mass percent: C: 0.02 to 0.3%; Si: 1.0 to 3.0%; Mn: 1.8 to 3.0%; P: 0.1% or less, including 0%; S: 0.01% or less, including 0%; Al: 0.001 to 0.1%; N: 0.01 to 0.03%; and a remainder comprising iron and impurities, and having a microstructure comprising phases of, by area ratio to an entire microstructure: bainitic ferrite: 50 to 85%; retained austenite: 3% or more; martensite and a retained austenite in total: 10 to 45%; and ferrite: 5 to 40%, wherein C concentration (CγR) in the retained austenite is from 0.3 to 1.2 mass percent, part or all of N in the composition is dissolved, and an amount of the dissolved N is from 30 to 100 ppm, and wherein a dislocation density in the entire microstructure is 5×10