Effect of annealing temperature on carbide precipitation, microstructure and mechanical properties of Fe-Mn-C- (Cr, Mo, W, Ni, Nb, Ti, V) multi-alloying TWIP steel

The effect of annealing temperature on the microstructure, carbide precipitation and mechanical properties of a cold-rolled multi-alloying TWIP steel were investigated by means of Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) analysis, tensile and impact tests. As the temperature increases from 400 °C to 800 °C, the amount of carbides climbed to the peak at 700 °C and then decreased, having a strong opposite relationship with the impact energy, which was minimum 26 J at 700 °C. The main distribution of carbides underwent a transition from intragranular, intragranular + intergranular to intergranular, and the composition of carbides changed from (Nb, Ti and W) to (Cr, Mo and W). Compared with the cold-rolled sample, Fe21W2C6 precipitated out at low annealing temperature of 400 °C, when the tensile and yield strengths and elongation were all simultaneously improved due to the precipitation recovery annealing. And the 600 °C annealing sample exhibited identical yield and tensile strengths. Subsequently, the yield strengths decreased but the tensile strengths and elongation increased at 650 °C and 700 °C attributed to the interaction of carbide precipitation and recrystallization. The recrystallization started at 650 °C and finished at 750 °C. And Fe3Mo3C was identified at 750 °C.