A METHOD OF PRODUCING DUAL-PHASE HIGH-STRENGTH STEEL SHEETS HAVING HIGH IMPACT ENERGY ABSORPTION PROPERTIES

摘要

The invention relates to dual-phase type high-strength steel sheets, for automobiles, which have excellent dynamic deformation properties and exhibit impact absorption properties, and are intended to be used as structural members and reinforcing materials primarily for automobiles, as well as to a method of producing them, which dual-phase type high-strength steel sheets with excellent dynamic deformation properties are characterized in that the final microstructure of the steel sheets is a composite microstructure wherein the dominating phase is ferrite, and the second phase is another low temperature product phase containing martensite at a volume fraction between 3% and 50% after 5% deformation of the steel sheet, wherein the difference between the quasi-static deformation strength Ãs when deformed in a strain rate range of 5 x 10 -4 - 5 x 10 -3 (s -1 ) after pre-deformation of more than 0% and less than or equal to 10% of equivalent strain, and the dynamic deformation strength Ãd when deformed in a strain rate range of 5 x 10 2 - 5 x 10 3 (s -1 ) after the aforementioned pre-deformation, i.e. (Ãd - Ãs), is at least 60 MPa, and the work hardening coefficient at 5-10% strain is at least 0.13.