Stacking fault energy and deformation mechanisms in Fe-xMn-0.6C-yAl TWIP steel

The deformation mechanisms and mechanical properties of Fe-Mn-C-Al twinning-induced plasticity (TWIP) steels with a chemical composition range of 12-18 wt% Mn and 0-3 wt% Al, are reviewed. The in-depth microstructural analysis revealed that all the investigated TWIP steels exhibit deformation twinning as the main deformation mechanism in addition to dislocation glide. The Al-free TWIP steels have a much more complex deformation behavior than the Al-added TWIP steels. The deformation of Fe-15Mn-0.6C steel is accompanied by the formation of a very small amount of strain-induced ε martensite, in addition to deformation twinning. Deformation of Fe-12Mn-0.6C steel is accompanied by several deformation mechanisms which are simultaneously activated: strain-induced ε martensite, formation of shear bands and strain-induced α′ martensite, in addition to deformation twinning. The upper limit for the value of SFE for strain-induced martensitic transformation is determined to be approximately 13 mJ/m2. The results confirm that the SFE is the key parameters affecting the strength and the ductility of TWIP steel. A linear relation between the ultimate tensile strength (UTS) and the SFE is proposed, with the UTS increasing with decreasing SFE.