Patent ID: 8852360
Filing Date: 2014-10-07
Classification: C21D,C22C,C23C

Abstract:
1. A high strength hot-rolled steel sheet that is superior in an acid pickling property, a chemical conversion processability, a fatigue property, a hole expandability, and a resistance to surface deterioration during forming, and that has isotropic strength and isotropic ductility, the steel sheet consisting of, in terms of percent by mass: C: 0.05 to 0.12%; Si: 1.0 to 1.2%; Mn: 1.6 to 2.2%; Al: 0.30 to 0.6%; P: 0.05% or less; S: 0.005% or less; N: 0.01% or less; and the remainder of Fe and unavoidable impurities, wherein a microstructure comprises: 60 area % or more of ferrite phases; more than 10 area % of martensite phases; and 0 to less than 1 area % of residual austenite phases, or the microstructure comprises: 60 area % or more of ferrite phases; more than 10 area % of martensite phases; less than 5 area % of bainite phases; and 0 to less than 1% of residual austenite phases, and a maximum concentration of Al detected by a glow discharge emission spectroscopic analysis is in a range of 0.75 mass % or less in a region from a surface of the steel sheet to a thickness of 500 nm after being acid-pickled.