Kinetics of Structure Evolution During Deformation Enhanced Transformation in a Low Carbon Steel SS400
低碳钢SS400形变强化相变组织演变的动力学

Quantitative characterization of microstructural evolution during deformation enhanced transformation in a low carbon steel SS400 was investigated on a Gleeble 1500 machine. General conclusions of the austenite transformation kinetics were formulated. It was shown that the transformation process can be divided into three stages according to the characteristics of transformation kinetics: The kinetics equations of two early stages fitted well in with the J-M-A equation. The kinetics of the first stage obeys Cahn's site saturation mechanism, the kinetics parameter n=4 which indicates the ferrite nucleates at austenite grain boundaries and triple points. Kinetics of the second stage doesn't obey Cahn's theory, the kinetics parameter n=1.0-1.5, corresponding to ferrite nucleating repeatedly at the high stored energy areas in front of the ferrite/austenite interface. The kinetics doesn't obey the J-M-A equation anymore in the final stage, and only few nucleation sites left at this moment. Deformation promotes the growth of ferrite grains, the growing rate of ferrite in the early stage of DEFT was calculated.