HIGH-STRENGTH STEEL SHEET HAVING EXCELLENT ROOM-TEMPERATURE FORMABILITY AND WARM FORMABILITY, AND WARM FORMING METHOD THEREOF

摘要

This high-strength steel plate has a component composition including, by mass %, C: 0.02-0.3%, Si: 1-3%, Mn: 1.8-3%, P: 0.1% or less, S: 0.01% or less, Al: 0.001-0.1%, N: 0.002-0.03%, the rest consisting of iron and impurities. Said steel plate has a microstructure including, in terms of area ratio relative to the entire microstructure, each of the following phases: bainitic ferrite: 50-85%; retained γ; 3% or greater; martensite+the aforementioned retained γ; 10-45%; and ferrite: 5-40%. The C concentration (CγR) in the aforementioned retained austenite is 0.3-1.2 mass %, part or all of the N in the aforementioned component composition is solid solution N, and the amount of said solid solution N is 30-100 ppm.

主权项

1. A steel sheet having a composition 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, and part or all of N in the composition is dissolved, and an amount of the dissolved N is from 30 to 100 ppm.