No abstract

Md 30 is defined as the temperature at which 50 vol.% of α'-martensite is formed at a true tensile strain of 0.3 in metastable austenitic steels. The effect of C concentration on Md 30 is known to be identical to that of N, as shown by Nohara's equation. However, we found that Md 30 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 Md 30 and C and N concentration is not linear. The effect of C and N concentration on Md 30 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 Md 30 of an Fe-Cr-Ni alloy system. The modified Md 30 equation is shown below: