HIGH STRENGTH HOT-ROLLED STEEL PLATE EXHIBITING EXCELLENT ACID PICKLING PROPERTY, CHEMICAL CONVERSION PROCESSABILITY, FATIGUE PROPERTY, STRETCH FLANGEABILITY, AND RESISTANCE TO SURFACE DETERIORATION DURING MOLDING, AND HAVING ISOTROPIC STRENGTH AND DUCTILITY, AND METHOD FOR PRODUCING SAID HIGH STRENGTH HOT-ROLLED STEEL PLATE

摘要

This high strength hot-rolled steel sheet includes: in terms of percent by mass, C: 0.05 to 0.12%; Si: 0.8 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; and N: 0.01% or less, with the remainder being Fe and unavoidable impurities, wherein a microstructure includes: 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 includes: 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.