Patent ID: 8163108
Filing Date: 2012-04-24
Classification: C21D,C22C,C23C,Y10T

Abstract:
1. A cold-rolled steel sheet, comprising, in terms of mass %: C: not less than 0.05% and not more than 0.095%; Cr: not less than 0.15% and not more than 2.0%; B: not less than 0.0003% and not more than 0.01%; Si: not less than 0.3% and not more than 2.0%; Mn: not less than 1.7% and not more than 2.6%; Ti: not less than 0.005% and not more than 0.14%; P: not more than 0.03%; S: not more than 0.01%; Al: not more than 0.1%; N: less than 0.005%; O: not less than 0.0005% and not more than 0.005%; and containing as the remainder, iron and unavoidable impurities, wherein a microstructure of said steel sheet comprises mainly polygonal ferrite having a crystal grain size of not more than 4 μm, and hard microstructures of bainite and martensite, a volume fraction of said polygonal ferrite is in a range of 50% to 90%, a volume fraction of said hard microstructure is in a range of less than 50%, and a volume fraction of said bainite is in a range of less than 20%, a block size of said martensite is not more than 0.9 μm, a Cr content within said martensite is 1.1 to 1.5 times a Cr content within said polygonal ferrite, and a tensile strength is at least 880 MPa.