High-strength galvanized steel sheet, high-strength alloyed hot-dip galvanized sheet, and high-strength cold-rolled steel sheet which excel in moldability and weldability, and manufacturing method for the same

TLDR: This cold-rolled steel sheet includes, in terms of mass %, C: not less than 0.05%, C: 0.095%, Cr: 0., Cr: 1.5% and Cr content within the martensite is 1.1 to 2.5 times the Cr content in the polygonal ferrite, and the tensile strength is at least 880 MPa.

Abstract: This cold-rolled steel sheet includes, 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 contains as the remainder, iron and unavoidable impurities, wherein the microstructure of the steel sheet includes mainly polygonal ferrite having a crystal grain size of not more than 4 µm, and hard microstructures of bainite and martensite, the block size of the martensite is not more than 0.9 µm, the Cr content within the martensite is 1.1 to 1.5 times the Cr content within the polygonal ferrite, and the tensile strength is at least 880 MPa.