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 ( M S ) 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 M S , refined lath martensitic microstructure and slightly enhanced hardness. With decreasing the ausforming temperature the M S and martensite lath thickness decrease markedly. The strain and strain rate do not have strong effects on the M S and lath thickness. In addition, the ausforming can decrease the tetragonality of martensite and facilitate the formation of dislocation substructured martensite.