| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-strength cold rolled steel sheet excellent in yield strength and formability, and to provide a producing method thereof.SOLUTION: A cold rolled steel sheet has a component composition comprising C:0.10 to 0.25%, Si:0.50 to 2.40%, Mn:1.00 to 3.00%, Al:0.001 to 0.10%, Ti:0.02 to 0.30%, P:0.100% or less (including 0%), S:0.010% or less (including 0%), N:0.006% or less (including 0%) and the balance iron with inevitable impurities, and a structure comprising 30 to 75% of a ferrite α by area ratio and the balance tempered martensite (M) having a hardness of 330 to 450 Hv. The α includes an α having a particle diameter of 3 to 6 μm: 20 to 60%, an α having a particle diameter of less than 3 μm: 10 to 20%, an α having a particle diameter of larger than 6 μm: less than 5% (including 0%) and an average particle diameter of Ti-containing precipitates included in the α having a circle-equivalent diameter of 3 to 6 μm is 10 nm or less by circle-equivalent diameter and a mutual connection ratio of the αs is 0.25 or less. |
