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 gamma -> epsilon -> alpha' martensitic transformation occurred at -196 degrees C, whereas epsilon- or alpha'-martensite was not found in the 1.0C-18Mn steel. After the dynamic compressive test, on the other hand, the gamma -> epsilon martensitic transformation occurred at -196 degrees C without the formation of alpha'-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 gamma -> alpha' transformation was prevented under the dynamic compressive loading because the increase in molar volume was required for the gamma -> alpha' transformation, whereas it was promoted to induce the gamma -> epsilon -> alpha'' transformation under dynamic tensile loading. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.