A thermochemical model was presented for the stacking-fault energy in the Fe–Mn–C system with few percent of added Cu, Cr, Al or Si. Aluminium strongly increased the stacking-fault energy, contrary to chromium, while the effect of silicon was more complex. Copper also increased the stacking-fault energy, but strongly decreased the Néel temperature. The stacking-fault energy was the relevant parameter that controlled mechanical twinning, which was known to be at the origin of the excellent mechanical properties of these steels. Using this model, copper containing Fe–Mn–C grades were elaborated with stacking-fault energy below 18mJ/m2, in the range where ε-martensite platelets formed instead of micro-twins during plastic deformation. This substitution of deformation modes, confirmed by X-ray diffraction, did not significantly damage the mechanical properties, as long as the stacking-fault energy was greater than 12mJ/m2, which avoids the formation of α′-martensite.

Influence of Addition Elements on the Stacking-Fault Energy and Mechanical Properties of an Austenitic Fe–Mn–C Steel. A.Dumay, J.P.Chateau, S.Allain, S.Migot, O.Bouaziz: Materials Science and Engineering: A, 2008, 483-484, 184-7