Microstructure evolution and deformation mechanism change in 0.98C–8.3Mn–0.04N steel during compressive deformation

The microstructure evolution and the deformation mechanism change in 0.98C–8.3Mn–0.04N steel during compressive deformation at room temperature have been studied as a function of the reduction in the range of 20–60%. Experimental results show that with the reduction increasing the microstructure of the deformed sample changes from dislocation substructures into the dominant twins plus dislocations. This suggests that the plastic deformation mechanism changes from the dislocation slip to the dominant deformation twinning. The minimum reduction for deformation twins starting is estimated to be at between 30 and 40%. With the reduction further increases to more than 40%, the deformation twinning is operative and the thickness of deformation twins gradually decreases to nanoscale and shear bands occur. These high-density twins can be curved by the formation of shear bands. In addition, both transmission electron microscopy and X-ray diffraction examinations confirm the inexistence of deformation-induced martensites in these deformed samples.