Effect of carbon and nitrogen on md30 in metastable austenitic stainless steel

Md30 is defined as the temperature at which 50 vol.% of martensite is formed at a true tensile strain of 0.3 in metastable austenitic steels. The effect of C concentration on Md30 is known to be identical to that of N, as shown by Nohara's equation. However, we found that Md30 of C-added steel is lower than that of N-added steel, which indicates that the effect of C concentration on the mechanical stability of austenite is more significant than that of N. In addition, the relationship between Md30 and C and N concentration is not linear. The effect of C and N concentration on Md30 is higher at lower C and N concentration (0.1%). As this effect was not considered in the previous study, the austenite-stabilizing effects of these elements were underestimated. Therefore, in this study, new equations were proposed to accurately estimate Md30 of an Fe-Cr-Ni alloy system. The modified Md30 equation is shown below: Md30 K 800 333 Ceq10.3Si 12.5Mn 10.5Cr 24.0Ni 5.6Mo Ceq (C equivalent) is a function of C and N concentrations and temperature. Ceq C aN a=0.931 0.000281exp0.0219T These equations show that the difference in austenite-stabilizing effects of C and N increases with increasing temperature due to the difference in stacking fault energy between C- and N-added steels.