Austenite deformation behavior and the effect of ausforming process on martensite starting temperature and ausformed martensite microstructure in medium-carbon Si–Al-rich alloy steel

Deformation behavior of austenite/supercooled austenite in a medium-carbon Si–Al-rich alloy steel is investigated on a thermomechanical simulator and an optical microscope. Effects of ausforming temperature, strain rate and strain on martensite start temperature (MS) and ausformed martensite microstructure are studied in detail. Results show that power-law-type work hardening is caused during supercooled austenite deformation at 300°C; and the work hardening followed by steady-state flow is caused during the deformation at 600 and 900°C. The ausforming can decrease MS, refined lath martensitic microstructure and slightly enhanced hardness. With decreasing the ausforming temperature the MS and martensite lath thickness decrease markedly. The strain and strain rate do not have strong effects on the MS and lath thickness. In addition, the ausforming can decrease the tetragonality of martensite and facilitate the formation of dislocation substructured martensite.