Effects of C and N contents on the tensile properties and deformation behaviors at low temperatures have been investigated to obtain an alloy design basis on SUS 304 and 316 austenitic stainless steels for cryogenic application.
Increase in C and N contents led to the increase in temperature dependency of 0.2% yield strength for both SUS 304 and 316 steels. However, SUS 316 steel showed larger temperature dependency than SUS 304 at the same level of (C + N) content, probably due to the solution strengthening effect of Mo.
The results of multiple regression analyses on the effects of C and N contents on the 0.2% yield strength at each temperature indicated that the contributions of both C and N increase with decreasing temperature and that the contribution of N is larger than that of C at low temperatures.
The deformation behavior of metastable austenitic steels could be comprehensively explained in relation to austenite stability. Increase in austenite stability resulted in increase in onset strain at which strain-induced martensitic transformation occurred. And increase in austenite stability also led to the decrease in transformation rate which in turn gave rise to lowering strain-hardening exponent. It has been also found that tensile elongation shows maximum at around M_d30 temperature.