Effect of microstructure on transformation-induced plasticity of silicon-containing low-alloy steel

Fe-0.6C-1.5Si-0.8Mn steel was studied to determine the effect of the microstructure on transformation-induced plasticity (TRIP) of silicon-containing low-alloy steel. A remarkable increase in elongation through TRIP can develop in the steel subjected to the following heat treatments: (1) austemper combined with subcritical annealing (SA Aus-T): subcritical annealing at 993K followed by austempering at 673K and then light tempering (after austenitization at 1173K); (2) austemper coupled with interrupted quenching (IQ Aus-T): interrupted quenching at 533K followed by austempering at 673K and light tempering (after austenitization at 1173K). Aus-T treatment produced the triple structures of carbide-free upper bainite, retained austenite (γR), and free ferrite. As a result of the IQ Aus-T treatment, the triple structures of carbide-free upper bainite, γR, and tempered martensite appeared. The results are described and microstructural factors in TRIP are discussed.