Retained austenite characteristics and tensile properties in a TRIP type bainitic sheet steel

Abstract

Retained austenite characteristics and tensile properties in a 0.2C-1.5Si-1.5Mn, mass%, high-strength cold-rolled `TRIP type bainitic steel' which was associated with the transformation induced plasticity (TRIP) of the retained austenite were investigated. The steel mainly consisted of bainitic ferrite lath matrix, blocky martensites and stable retained austenite films of 5-12 vol %. When austempered at temperatures above Ms temperature, the steel possessed high tensile strength of 900 MPa, large total elongation of 15-20% and large reduction of area of 40-60%. The good ductility was mainly owing to uniform fine lath structure, initial martensite and the TRIP effect of retained austenite, as well as a small contribution of long range internal stress resulting from untransformed retained austenite films.