Microstructure and mechanical behavior of cold-rolled CMnAlSi TRIP-aided steel sheets

The microstructure, mechanical properties and retained austenite stability of CMnAlSi-TRIP steels were investigated. Optical microscopy and X-ray diffractometry were used to analyze the microstructure, volume fraction and carbon concentration of retained austenite, while the tensile tests were performed to study the retained austenite stability against strain-induced martensitic transformation. The results show that the mechanical properties of the CMnAlSi cold-rolled TRIP-aided steels fabricated by proper heat treatment display good combination of strength and ductility after isothermal bainitic transformation (IBT) treatment at 420–450 °C for 60–120 s. The austenite transformation kinetics is influenced significantly by the IBT temperature, and the high mechanical stability of retained austenite, governed by its carbon concentration, and determines high strain hardening during deformation.