Microstructural and mechanical characterization of C-Mn-Al-Si cold-rolled TRIP-aided steel

摘要

Retained austenite characteristics and tensile properties in a 0.21C-1.77Mn-1.2Al-0.283Si, high strength cold-rolled TRIP steel were investigated. The microstructure of this steel is comprised of ferrite, bainite and retained austenite, which is obtained by controlled cooling from the intercritical annealing temperature to the isothermal bainitic holding temperature. The effects of cooling rate from intercritical annealing temperature to isothermal transformation temperature, as well as effect of isothermal transformation time on microstructure and mechanical properties, were studied using optical microscopy, SEM, TEM, XRD, dilatometry and mechanical testing. These studies revealed that the microstructure of the steel mainly consisted of bainitic ferrite lath matrix, blocky martensites and stable retained austenite films of 7-8 vol%. When austempered at temperatures above M_S temperature, the steel possessed high tensile strength of 600 MPa, total elongation of 28-32% and n-value 0.2. The present paper deals with the effect of heat treatment on microstructure and mechanical properties of C-Mn-Al-Si cold-rolled TRIP steel.