Austenitic stainless steels at cryogenic temperatures: The compositional dependence of the Ms

The problem of predicting the likelihood of martensitic transformations in austenitic stainless steels at low temperatures remains an important one, in which there is still much uncertainty. Spontaneous transformations in the absence of plastic strains have generally been analysed in terms of the Eichelman and Hull equation or its variants. This equation is useful in that its predictions are qualitatively correct when applied to the AISI 300 stainless steels but are not really accurate enough for deciding where the dividing line between transforming and non-transforming steels lies in any one grade of steel. A re-examination of the existing M_S data shows that the elemental coefficients in linear equations are approximate and that a quadratic equation is more likely. Our analysis shows that the exact range of validity of the Eichelman and Hull equation is more restricted than thought hitherto and that the elemental coefficients show systematic deviations as the composition changes towards the practically important steels in the AISI 300 grades of steel.