Deformation substructure and strain-hardening characteristics of metastable Fe−Mn austenites

Abstract

The 500° and 550°C strain-hardening characteristics of manganese austenites based on Fe-14 pct Mn-0.4 pct C with carbide forming elements (Cr, V, Mo), were determined and deformation substructures were examined by transmission electron microscopy. Of the carbide formers investigated, molybdenum is the most effective in enhancing the strain-hardening rate of manganese austenite, followed closely by vanadium. The effect of chromium is relatively small. The effectiveness of carbide formers is independent of the strain-induced precipitation reaction, though this varies greatly in extent. Examination of thin foils revealed widely extended stacking faults which persist after heavy deformation, indicating a low stacking fault energy. It is tentatively suggested that the essential role of molybdenum, vanadium, and chromium is to progresively lower the stacking fault energy of a manganese austenite, and thereafter enhance its strain-hardening rate. The lower stacking fault energy postpones cross-slip and, as a result of stacking fault-dislocation interaction, increases the dislocation density and strain-hardening rate. It is concluded that the precipitates play only a minor role in strain-hardening manganese austenites.