Advanced formable high- and ultra high-strength trip-aided sheet steels

Many formable high or ultra-high strength TRIP-aided steels have been developed to realize a drastic weight reduction and excellent crash worthiness of vehicles since 1987. In general, formability of the low alloy TRIP-aided steels is principally influenced by chemical composition, heat treatment conditions and forming conditions, which control the retained austenite characteristics and matrix microstructure of the steels. In this study, microstructure, retained austenite characteristics, tensile properties and formability of three types of TRIP-aided steels with different matrix structure, polygonal ferrite, annealed martensite or bainitic ferrite are introduced. In addition, the effects of alloying elements, heat treatment conditions and forming conditions on these properties are discussed. (AU)