Prediction Model for Phase Transformation Initiation of TRIP Type Duplex Stainless Steel under Cyclic Loading
Strain induced martensitic transformation has an important effect on the cyclic properties of TRIP type duplex stainless steel,and the clarification of the martensitic transformation initiation law is the basis for further development and application of high-performance TRIP type duplex stainless steels.The martensitic transformation law of TRIP type duplex stainless steel under monotonic loading has been relatively clear,but the law under cyclic loading condition needs further study.From the perspectives of phase transformation thermodynamics and plastic deformation energy,calculate the chemical driving force and mechanical driving force of phase transformation for TRIP type duplex stainless steel.Based on the first law of thermodynamics,a prediction model of martensitic transformation initiation cycles is established under the cyclic loading.In-situ tests of martensitic transformation with strain amplitudes of 0.5％,0.7％,0.9％and 1.3％are carried out by using Ferrite Measuring Instrument(FISHER FMP30)and hydraulic servo fatigue testing machine(INSTRON 8801).Analyze the variation law of the martensitic transformation amount with the change of cycles,determine the transformation initiation cycle,and solve the parameters of the transformation initiation cycle prediction model.Finally,EBSD and TEM microstructure observation experiments under the characteristic cycles with strain amplitude of 1.1％are carried out to study the initiation characteristics of martensitic transformation and verify the established prediction model of cyclic transformation initiation.The results can provide a theoretical reference for the study of martensitic transformation under cyclic loading conditions,and provide theoretical support for the further development and application of high-performance TRIP steels.
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