| Non-quenched and tempered steel does not require quenching and tempering treatment,which reduces the high energy consumption of heat treatment links,which can reduce energy consumption and energy conservation.With the development of non-quenched and tempered steel,the current production of cars used by most of the key equipment such as power components,connecting functional parts,wheel steering components are using non-quenched and tempered steel for processing.These automotive parts will bear continuous tensile,impact,bending and other more complex load,which requires the material after forging forming has a high strength,better toughness,high anti-fatigue.The good comprehensive mechanical properties depend on the evolution of hot forging and forging cooling.Therefore,it is important to study the microstructural evolution of non-quenched and tempered steel during forming and cooling.Through the combination of model and actual production,it can effectively reduce the waste of materials and improve the quality of products,which has a great significance for domestic non-quenched and tempered steel research and application.In this paper,38 MnVTi steel as the experimental object,the hot compression process of microstructure evolution were discussed.According to the results of single pass compression test,the high temperature flow stress model was established,and the parameters of high temperature flow stress model were determined by linear regression method.Based on the metallographic data of 38 MnVTi steel,the corresponding dynamic recrystallization rule and the corresponding grain size model was established.The static recrystallization dynamics model and the corresponding size model are established on the basis of the double pass hot compression test.The factors influencing the static recrystallization volume fraction such as the temperature of the deformation,the strain of the first pass and the rate of deformation are discussed.The main factors influencing the static recrystallization volume fraction are the temperature of deformation and the amount of strain of the first pass but the rate of deformation has little effect on it.The effect of the holding time and the heating temperature on the grain size of the austenite region was investigated by the austenite grain growth experiment.The results show that the residence time of the temperature is approximately parabolic in relation to the grain size.The heating temperature and the grain size is approximately exponentially.Finally,the corresponding grain size model is obtained by averaging the grain size.The relationship between temperature and cooling rate of non-quenched and tempered steel 's microstructure was discussed by means of physical experiment.As the steel used in this paper is a typical ferrite-pearlitic steel,the pavement spacing of pearlite has a great influence on the comprehensive performance of non-quenched and tempered steel.So the influence of cooling temperature and cooling rate for pearlite layer spacing was obtained by means of scanning electron microscopy.Finally,the effect of cooling rate on grain orientation difference and texture of 38 MnVTi non-quenched and tempered steel was studied by means of EBSD technique.It was concluded that the cooling rate had some influence on the texture of 38 MnVTi non-quenched and tempered steel,but there was no fixed law.In this paper,the microstructural evolution model of 38 MnVTi non-quenched and tempered steel in forging process is established by a large number of experiments.The experimental model is compared with the experimental data,and the experimental value is in good agreement with the model.The effects of cooling parameters on the microstructure of the cooling process after hot forging were studied by metallographic technique and EBSD technique.The experimental results provide effective theoretical guidance for the optimization of process parameters in the actual production process. |
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