HIGH STRENGTH HOT ROLLED STEEL SHEET EXCELLENT IN FORMABILITY

摘要

A hot rolled high strength steel sheet having a satisfactory strength - elongation balance and an stretch frangibility and with excellent formability comprising a steel, which contains: C : 0.05 SIMILAR 0.15% Si : 0.5 SIMILAR 2.0% Mn : 0.5 SIMILAR 2.0% P : 0.05% or less S : 0.010% or less Al : 0.005 SIMILAR less than 0.10%, and the balance of Fe and inevitable impurities, and in which the metal structure mainly comprises three phases of ferrite, retained austenite and bainite, the amount of the ferrite ÄV(F)Ü is 60 SIMILAR 95 area%, the amount of the retained austenite ÄV( gamma )Ü is 3 SIMILAR 15 vol%, the amount of the bainite ÄV(B)Ü in the area ratio is 1.5 times or more of the amount of the retained austenite ÄV( gamma )Ü, and the average hardness of the bainite is 240 - 400 Hv.