Effects of heat treatment and Si addition on the mechanical properties of 0.1 wt% C TRIP-aided cold-rolled steels

Abstract

The purpose of the present study was understanding the effects of heat treatment and silicon content on the microstructure and mechanical properties of low-carbon TRIP-aided cold-rolled steel sheets. Two steels of the same base composition, 0.10%C-1.5%Mn-Si-0.5%Cu (hereafter all in weight percent), but containing 0.94% Si and 1.48% Si were cold rolled to I mm thick sheet. The sheets were intercritically annealed and isothermally treated in the temperature range of bainite reaction in order to vary the volume fraction of retained austenite and the mechanical properties. The fractions of retained austenite increased with decreasing intercritical annealing and isothermal treatment temperatures, resulting in the improvement in tensile strength, elongation,,and the strength-ductility balance. In the steel having the higher silicon content, a higher fraction of retained austenite and better mechanical properties were achieved than in the steel having the lower silicon content. The findings indicate that partitioning of C and Mn to the austenite during intercritical annealing, together with a higher Si content, increase the stability of the austenite and affect the optimum intercritical and isothermal heat treatment temperatures.