Patent ID: 8480819

Claim:
A cold-rolled steel sheet containing in mass %: C: 0.10-0.3%, Si: 1.0-3.0%, Mn: 1.5-3%, Al: 0.005-0.2%, and satisfying: P: 0.1% or below, S: 0.05% or below the balance comprising iron with inevitable impurities, wherein; the metallurgical structure of the steel sheet comprises bainite, residual austenite and tempered martensite, (1) when the metallurgical structure is observed with a scanning electron microscope; bainite is constituted of complex structure of high temperature range forming bainite with 1 μm or above average distance between neighboring residual austenite and/or carbide and low temperature range forming bainite with below 1 μm average distance between neighboring residual austenite and/or carbide, and when the area ratio of the high temperature range (400° C. ≦T1(° C.) ≦540° C.) forming bainite with respect to total metallurgical structure is made a and the total area ratio of the low temperature range (200° C.≦T2(° C.)≦400° C.) forming bainite and the tempered martensite with respect to the total metallurgical structure is made b, a: 20-80%, b: 20-80%, and a+b: 70% or above are satisfied, and (2) the volumetric ratio of residual austenite measured by a saturation magnetization method is 3% or above with respect to the total metallurgical structure.