The transformation behavior, microstructural evolution and mechanical properties were compared in a coldrolled Nb-Mo microalloyed 6.5Mn alloy after intercritical annealing (IA) and quenching and partitioning (Q & P), respectively. The thermodynamic calculation and theoretical analysis were used to determine the optimal heat treatment parameters. The Q & P samples exhibited relatively higher strength with relatively low ductility, mainly due to the hard martensite matrix, which resulted in continuous yielding behavior upon loading, whereas the IA samples showed the significantly improved ductility, which benefited from the more sufficient transformation-induced plasticity (TRIP) effects and the softer ultrafine ferrite matrix. The dependence of yield point elongation (YPE) of IA samples on grain size demonstrated that the YPE value was in the reverse proportional relationship to the average grain size, which agreed well with theoretical analysis.
Hot deformation behavior of a high Allow Si transformation-induced plasticity (TRIP) steel was studied by an MMS-300 thermo-simulation machine at the temperature range of 1050-1200°C and strain rate range of 0.01-10 s-1. The constitutive equations of the TRIP steel were established at high temperature by fitting the strain factor with a sixth-order polynomial. The instability during hot rolling was discussed using processing maps. The results reveal that two types of flow stress curves (dynamic recrystallization and dynamic recovery) were observed during the hot compression of the high Allow Si TRIP steel. Flow stress decreased with increasing deformation temperature and decreasing strain rate. The predicted flow stress of experimental TRIP steel is in agreement with the experimental values with an average absolute relative error of 4.49% and a coefficient of determination of 0.9952. According to the obtained processing maps, the TRIP steel exhibits a better workability at strain rate of 0.1 s-1 and deformation temperature of 1200°C as compared to other deformation conditions.
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