When colliding which possesses high dynamic flow stress for bombardment absorption it is good the processability high intensity cold rolling steel sheet and the production manner

摘要

PROBLEM TO BE SOLVED: To improve the striking energy absorption power of a steel sheet by allowing the difference between the average value of the deformation stress in the case deformation is generated in a specified strain rate range after the application of predeformation in a specified range of equivalent strain to a steel having a specified compsn. and the average value of the deformation stress in the case deformation is generated in a very small strain rate range to satisfy specified relation. ;SOLUTION: The microstructure of a steel sheet is the one contg. ferrite and bainite, in which either of them is used as the main phase and the third phase contg. ≥3 vol.% retained austenite. The difference between the average value σ dyn (MPa) of the deformation stress in the equivalent strain of 3 to 10% in the case deformation is generated at the strain rate of 500 to 5,000 (1/s) after the application of predeformation of 0 to 10% at equivalent strain to thin steel sheet and the average value σ st (MPa) of the deformation stress in the case deformation is generated at 5×10^-4 to 5×10^-3 (1/s) satisfies the inequality of (σ dyn-σ st) ≥-0.272×TS+300 expressed by the maximum stress TS (MPa) in a dynamic tension test measured at the strain rate of 5×10^-4 to 5×10^-3 (1/s).;COPYRIGHT: (C)1999,JPO