Warm Deformation Behavior Of T12 Steel With Different Microstructures

In this work, the flow curves of a high carbon steel, T12, prepared for different heat treatment were studied by warm compressive tests on Gleeble3500 machine. The processing parameters of the temperature were in 550～700℃, the strain were in 50% and the strain rate were in 1.0～0.001s-1. The difference with normal quenching structure and spheroidizing annealing structure was investigated especially. The corresponding microstructures and mechanical properties were also investigated with TEM, SEM, and microhardness tests.The results show that their flow stresses decrese with decreasing temperature or increase with decreasing strain rate. These two flow curves have an intersection point at a temperatures between 600℃and 700℃. The corresponding strain is called critical strain. When the strain is lower than the critical strain, the flow stress with martensite structure is higher than those with ferrite and granular cementite. When it is higher than the critical strain, the flow stress with martensite structure is lower than those with ferrite and granular cementite. Related constitutive equations of the warm deformation are set up. Strain rate sensitivity and power dissipation efficiency are determined under different deformed conditions. Processing maps are established to determine the region of plastic instability. The above results are effective for the further research.The results by TEM and SEM show that the main softening mechanism of martensite structures is dynamic recrystallization. As the softening is stronger, the flow curves have obviously descending. The main softening mechanism of the steel with ferrite and granular cementite structures is dynamic recovery. As the softening weak, the flow curves become smoothly.