HIGH-STRENGTH COLD ROLLED STEEL SHEET HAVING EXCELLENT FORMABILITY AND WELDABILITY, HIGH-STRENGTH HOT DIP GALVANIZED STEEL SHEET, HIGH-STRENGTH ALLOYED GALVANNEALED STEEL SHEET, PRODUCTION METHOD OF HIGH-STRENGTH COLD ROLLED STEEL SHEET, PRODUCTION METHOD OF HIGH-STRENGTH HOT DIP GALVANIZED STEEL SHEET, AND PRODUCTION METHOD OF HIGH-STRENGTH ALLOYED GALVANNEALED STEEL SHEET

摘要

PROBLEM TO BE SOLVED: To provide a high-strength cold rolled steel sheet having maximum tensile strength (TS) of≥780 MPa, a yield ratio (RY) of 0.5 to 0.7, and excellent moldability and spot weldability. SOLUTION: The high-strength cold rolled steel sheet contains, by mass%, 0.06 to <0.1% C, 0.4 to 0.8% Si, 1.8 to 2.2% Mn, 0.014 to 0.029% Nb, 0.014 to 0.029% Ti,≤0.04% P,≤0.01% S,≤0.1% Al,≤0.01% N, and 0.0005 to 0.007% O, consists of the balance Fe and inevitable impurities, having the yield ratio of 0.5 to 0.7, the tensile strength of≥780 MPa, and the excellent moldability and weldability, and may be subjected, as necessary, to hot dip galvanizing or alloying after the hot dip galvanizing. COPYRIGHT: (C)2007,JPO&INPIT