ASPECTS OF DUCTILITY, TOUGHNESS AND FORMABILITY OF STEEL SHEET IN RELATION TO TRANSFORMATION PLASTICITY

Transformation plasticity, the macroscopic plastic strain associated with phase transformations under stress, has allowed the achievement of improved mechanical properties in a wide range of materials. In metastable fully-austenitic steels, transformation plasticity is responsible for the significant enhancement of ductility and toughness. The ultra-high-strength martensitic steels toughness enhancement of the order of 40% is attributable to the transformation of precipitated austenite, a phenomenon called dispersed-phase transformation toughening. These concepts are explored further towards the development of triple-phase microstructures in low-alloy steels where the transformation plasticity of dispersed austenite leads to the enhanced stretch-formability required for automotive applications.