The dual phase die high intensity cold rolling steel sheet and the production manner null which are superior in dynamic deformation

摘要

PROBLEM TO BE SOLVED: To provide a dual-phase-type high strength cold rolled steel sheet for automobile use, aiming at the use principally for an automobile structural member and reinforcement, having superior collision-proof stability, and excellent in dynamic deformability, and its production. ;SOLUTION: In the dual-phase-type high strength cold rolled steel sheet excellent in dynamic deformability, the microstructure of the steel sheet as a final product has a composite structure consisting of a main phase composed of ferrite and a second phase composed of the other phase forming at low temperature and containing 3-50% martensite by volume fraction after 5% forming of the steel sheet. Moreover the difference (σd-σs), between the quasistatic deformation strength σs when pre-deformation of 0 to 10% equivalent strain is applied and deformation is performed at 5×10-4 to 5×10-3 (s-1) strain rate and the dynamic deformation strength σd when pre-deformation is applied and deformation is performed at 5×102 to 5×103 (s-1), is regulated to ≥60 MPa and also the work hardening index at 5 to 10% strain satisfies ≥0.13.;COPYRIGHT: (C)2000,JPO