Dual-phase and other formable steels

Abstract

While high-strength low-alloy steels have been available for some considerable time, and have found extensive application, their use in certain areas has been restricted by other property requirements, such as formability. Developments in improved stretch-forming steels are reviewed. The ability of high-Si or rephosphorized steels to give moderate strength increases with improved formability is well established. and such steels are finding application in coldrolled gauges for body sheeting. A more recent development is the improvement in formability attained by the use of ‘dual-phase’ ferrite-martensite structures. The mechanisms involved in the attainment of improved strength-ductility combinations are described. Developments in fracture resistance within the past decade are also considered. Inclusion shape control was developed during the mid-1960s to improve transverse properties. The advent of secondary-steelmaking practices capable of producing steels with very low inclusion contents is currently being exploited for formable steels. The application of these newly developed steels has been mixed, some finding immediate acceptance, while uses for others are still being sought. The factors controlling acceptance are complex, and consideration is given to the supplementary property requirements. cost benefits. and design philosophy, particularly with respect to dual-phase steels.