In response to an increasing demand of high strength steel sheets for automobiles, study was carried out to develop TS 980MPa (100kgf/mm2) grade cold rolled dual phase steel sheet which can be used for the manufacturing of, for instance, bumper reinforcement and door impact beams.
First, the process conditions of water-quenching-type continuous annealing were investigated to establish the concepts on the optimum dual phase microstructure which guarantees high strength and good ductility.
Secondly, solution hardening by typical chemical elements: carbon, silicon, manganese and phosphorus, was discussed to find the most beneficial way to maintain good ductility in the strengthening of the steel sheet.
Mill production of the TS 980MPa grade steel sheet proved to have good ductility which now can replace the conventional TS 784MPa grade steel sheet.