Dynamic tension-compression asymmetry of martensitic transformation in austenitic Fe-(0.4, 1.0)C-18Mn steels for cryogenic applications

In this study, cryogenic-temperature dynamic mechanical properties of austenitic Fe-(0.4, 1.0)C-18Mn steels were evaluated by conducting dynamic tensile and compressive tests, and deformation mechanisms including tension-compression asymmetry of martensitic transformation behavior were interpreted by microstructural evolution of dynamically tensioned or compressed specimens. After the dynamic tensile test of the 0.4C-18Mn steel, the γ → ɛ → α′ martensitic transformation occurred at −196 °C, whereas ɛ- or α′-martensite was not found in the 1.0C-18Mn steel. After the dynamic compressive test, on the other hand, the γ → ɛ martensitic transformation occurred at −196 °C without the formation of α′-martensites in the 0.4C-18Mn steel. This dynamic tensile-compressive asymmetry of martensitic transformation was plausibly interpreted by austenite stability in relation with difference in molar volume, hydrostatic stress distribution, and adiabatic heating. The γ → α′ transformation was prevented under the dynamic compressive loading because the increase in molar volume was required for the γ → α′ transformation, whereas it was promoted to induce the γ → ɛ → α′ transformation under dynamic tensile loading.