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 degrees C; and the work hardening followed by steady-state flow is caused during the deformation at 600 and 900 degrees 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. (C) 2013 Elsevier B.V. All rights reserved.