Effect of heat treatment on microstructure and mechanical properties of a medium-carbon TRIP steel

The effect of quenching-tempering(QT) treatment and austempering(AT) treatment on microstructure and mechanical properties of 0.4C-1.5Si-1.5Mn TRIP steel was investigated.The results show that the microstructure of AT specimen consists of ferrite,bainite,retained austenite and/or a small quantity of martensite,and the initial volume fraction of retained austenite in AT specimen is higher.This kind duplex microstructure makes the mechanical properties of AT specimen be superior to that of QT specimen.Moreover,the observation of microstructure shows that upper bainite aand lower bainite are interlaced in bainitic ferrite matrix,and favorable mechanical properties,homogeneous microstructure,higher amount of retained austenite is obtained for the steel austempered at 400℃ for 600s,which induces obvious TRIP effect.