Experimental Study And Modeling Of Stress- Induced Martensitic Transformation In Cr5 Steel

Numerical simulation of heat treatment is a complicated process, which mainly involves the interaction among temperature, phase transformation, stress/strain. There are two main aspects of coupling stress affected phase transformation and transformation plasticity, in which the transformation plasticity effects greatly on the results of the numerical simulation. Using Cr5 steel for backup rollers, the transformation plasticity of martensitic transformation is studied via dilatometric experiments under uniaxial external loading in this article on a Gleeble-1500D experiment device.The two mechanisms of transformation plasticity are analyzed. In the condition of Cr5 steel, a type of the medium-carbon low alloy steel, the transformation plasticity model can be built based on Greenwood-Johnson mechanism, and Magee mechanism can be neglected under a small applied stress.A summary of experimental methods are made and some experimental criterions are founded during the martensitic transformation process. A method is introduced to separate the transformation strain from total strains. The error and the feasibility of various methods are studied. With the experimental data, the values of transformation plasticity parameters are obtained through linear fitting between the transformation plasticity strain and stress.Based on Greenwood-Johnson mechanism, a transformation prediction model was established with the data of the obtained yield stress of austenite and the transformation volume strain of martensite. The model gives good results in prediction of transformation plasticity strain and radial strain in martensitic transformation under external loading. By analyzing the error caused in simulation, some suggestions were proposed to improve theprediction model. In addition, the model is able to be extended to some other applications.The Ms point and yield stress of austenite at the Ms point were predicted by the means of the carbon-equivalent method with the transformation thermodynamics ternary regular solution model. The uniaxial stress effect on Ms point is studied by comparing with experimental data using the Patel and Cohen model.A radial strain prediction model in pearlite-austenite transformation is established during an experimental study of the effects of heating rates on P-A transformation under continuous heating conditions. Some suggestions are proposed to the extended application of the model under variable heating rate condition.