A Temperature–Stress Phase Diagram of Carbon-Supersaturated bcc-Iron, Exhibiting “Beyond-Zener” Ordering

Abstract

Carbon ordering in supersaturated body-centered iron was investigated by means of atomic-scale simulations. Beyond the well-known Zener ordering of carbon atoms, our results reveal a first-order transition occurring upon temperature change when a single crystal is subjected to axial compression. This ordering produces orthorhombic martensite due to unequal carbon redistribution over the three octahedral interstitial sites. The resulting phase diagram is of the rare homotectoid type. Connection is made with the thermoelastic behavior of martensitic alloys, which proves to be similar to that of shape-memory alloys.