Production of Formable TS98OMPa Grade Cold-rolled Steel

Abstract

Influences of continuous annealing conditions on strength and ductility of 0.1%C-1.0%Mn cold-rolled dual phase steel were investigated as a preliminary study to find the concepts on optimum microstructure which gives high strength and good ductility. It was found that the highest strength ductility balance is obtained by the two phase microstructure consisting of a small amount of carbon enriched martensite and fully ductile ferrite.
In applying the results to the production of TS980MPa grade cold-rolled steel, the appropriate strengthening methods were discussed. Consequently, it was found that some solution hardening of ferrite should be added, because of the both limitations in carbon enrichment in martensite phase and in increase in its volume fraction for maintaining good ductility.The additional investigation showed that hardening by silicon is most desirable.
Spot weldability and phosphatability were also considered for the determination of steel chemistry. The result of mill production carried out upon these basic investigations indicated that the developed TS980MPa grade steel is applicable to the stringent cold forming for such as a door impact beam bracket.