Due to the strain-induced martensitic transformation (SIMT) during plastic deformation under cold working conditions, a TRIP (Transformation-Induced Plasticity) phenomenon in which an elongation increases at one temperature range is generated. The microstructure of TRIP steels is retained austenite embedded in a primary matrix of ferrite. In addition to a minimum of five-volume percent of retained austenite, hard phases such as martensite and bainite are present in varying amounts.

Transformation-induced plasticity can increase the ductility of material during the deformation process and delay the necking and cracking of material because the retained austenite transfers into martensite. Then TRIP steels have received increased attention to improving manufacturability, safety, and lightweight of the automobile, for its high ductility. As a result of their high energy absorption capacity and fatigue strength, TRIP steels are particularly well-suited for automotive structural and safety parts such as cross members, longitudinal beams, B-pillar reinforcements, sills, and bumper reinforcements. Strain-induced martensitic transformation increases the strain hardening rate, leading to excellent combinations of strength and elongation, as displayed at room temperature in metastable austenitic stainless steels and some TRIP steels. In this project, the effect of strain-induced martensitic transformation on mechanical properties is studied.