| 摘要 |
PROBLEM TO BE SOLVED: To provide a cold rolled steel sheet excellent in both deep drawability and fatigue characteristic, and to provide its manufacturing method.SOLUTION: A steel containing, by mass%, C:0.015 to 0.15%; Si:2.0% to less; Mn:0.1 to 3.0%; P:0.05% or less; S:0.05% or less; sol.Al:0.001 to 0.1%; N:0.001 to 0.01%; and O:0.01% or less is subjected to multisteps pass hot rolling with conditions of time of rolling passes between just before a final rolling pass and the final rolling pass of 0.3 to 4.0 seconds, a finish temperature of the final rolling pass of Arpoint to 780°C, a cooling time by 720°C after completion of rolling within 0.4 seconds, then cold rolling with a rolling reduction of 40 to 90%, and then annealed. The obtained cold rolled steel sheet has TS[=(TS+2×TS+TS)/4] of 300 MPa or more, YR[=(YR+2×YR+YR)/4] of 0.67 or more, |&Dgr;r| of 0.20 or less, r/|&Dgr;r| of 4.7 or less, where [&Dgr;r=(r-2×r+r)/2, r=(r+2×r+r)/4]. Subscripts 0, 45 and 90 mean a rolling direction, a 45° direction to the rolling direction and a 90° direction to the rolling direction respectively. |
