On the effect of Mn-content on the strength-ductility balance in Ni-free high N transformation induced plasticity steels

The present work deals with the room temperature microstructure-mechanical properties relationship in Ni-free high N transformation induced plasticity steels. The tensile properties of the alloy with lower Mn content of 4%, and thus lower austenite fraction and austenite stability, was mainly controlled through sequential (extended) transformation route of ?????? . The extended route resulted in a higher strain hardening rate and lower ductility value. In addition, the formation of thermally-induced martensite before plastic deformation reduced the capacity of strain partitioning and load transition between the austenite and ferrite. In contrast, the tensile properties of the alloy holding higher Mn content of 8% with higher austenite fraction and stability was mainly governed by twin-aided transformation route of ???twinned??? . It was found that the higher strain compatibility between austenite and ferrite resulted in a substantially high uniform elongation and moderate strain hardening rate.