High-strength cold-rolled steel sheet having a tensile strength of 980 MPa or more excellent in workability and impact property and a method for manufacturing the same

摘要

A high strength cold rolled steel sheet having a tensile strength of 980 MPa or higher, which has good processability evaluated by ductility and elongation flangeability, and which is excellent in collision characteristics, and a process for producing the same. A high strength cold rolled steel sheet in which the metal structure at the 1/4 position of the sheet thickness satisfies the following (1) to (4). (1) the area ratio of the ferrite is more than 10% and not more than 65%, and the remainder is at least one selected from the group consisting of bainitic ferrite, bainite and tempering martensite, including quenched martensite and retained austenite Lt; / RTI (2) The volume ratio V _? Of the retained austenite is 5% or more and 30% or less. (3) the area ratio V _MA of the MA structure in which quenched martensite and retained austenite are combined is 3% or more and 25% or less, and the average circle-equivalent diameter of the MA structure is 2.0 μm or less. (4) The ratio V _MA / V _? Of the area ratio V _MA of the MA structure to the volume ratio V _? Of the retained austenite is 0.50 to 1.50.