| 摘要 |
PROBLEM TO BE SOLVED: To provide a dual-phase-type high-strength cold rolled steel sheet combining elongation in a tensile test with bore expandability and having an excellent balance between strength and formability. SOLUTION: The cold rolled steel sheet has a composition containing, by mass, 0.02 to 0.25% C, 0.02 to 4.0% Si and 0.15 to 3.5% Mn and also has a structure composed of a composite structure of a ferritic phase and a martensitic phase. The average hardness of the martensitic phase is Hv 400 to 480, and the volume fraction of the ferritic phase is 30 to 60%, and further, the volume fraction of retainedγin the composite structure measured by a saturation magnetization measurement method is≤1 vol.% including 0 vol.%. COPYRIGHT: (C)2005,JPO&NCIPI
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