Correlation between warm deformation characteristics and mechanical properties of a new TRIP-assisted Fe-MN-Ni steel

The warm deformation behavior of a Fe-12Mn-3Ni steel was investigated and the governing deformation mechanisms were determined. The compressive deformation was applied at various temperatures from room temperature to reverse austenite formation temperature. The subsequent mechanical properties were evaluated through a shear punch testing method. The phase characterization was carried out using scanning electron microscopy, X-ray diffraction analysis and ferritescope measurements. The results showed that the dynamic α′-martensite transformation occurs during deformation at relatively low temperatures (below 100 °C). In the moderate temperature range (i.e. 200-400 °C), α′-martensite formation takes place holding a lower kinetic at upper temperature limit due to the higher stability of austenite. At temperatures around 500 °C, the fraction of α′-martensite decreases due to α′→γ reverse transformation phenomenon. These findings are confirmed by stacking fault energy and γ→α′ chemical driving force thermodynamic calculations. According to shear punch results on processed specimens, a good combination of strength and ductility is achieved for the deformed material at 500 °C. This is related to the occurrence of TRIP effects due to the higher fraction of retained austenite in the microstructure.