Martensite Formation and Recrystallization Behavior in 17Mn0.06C2Si3Al1Ni TRIP/TWIP Steel after Hot and Cold Rolling

This work evaluates the evolution of the microstructure and its influence on the mechanical behavior of steel containing 17% Mn, 0.06% C, 2% Si, 3% Al, and 1% Ni after hot rolling at 1070 degrees C, cold rolling with 44% reduction, and annealing at 700 degrees C for different time periods. The resultant athermal, strain-induced martensite and austenite grains were analyzed by optical and scanning electron microscopy (SEM). The volume fractions of the gamma, epsilon, and alpha' phases of martensite were confirmed by X-ray diffraction, dilatometry, and SEM-electron backscatter diffraction (EBSD) techniques. It was found that cold reduction results in the formation of more alpha' martensite. The Vickers microhardness values were higher for the cold-rolled condition and lower for recrystallized samples, as expected. However, this reduction is counterbalanced by the formation of athermal epsilon and alpha' martensite during the cooling process. The sizes of the recrystallized grains change exponentially during their growth and remain within 1-3 mu m. The yield and tensile strength of the hot-rolled steel reach values close to 250 and 800 MPa, respectively, with a total elongation of 40%, which demonstrates the high work-hardening rate of the steel.