Study On Metamorphic Layers’ Composite Microstructure Transformation And Macroscopic Performance Characterization In Grinding Hardening

Grinding hardening is a green and efficient composite machining technology.The strong nonlinear dynamic thermal-mechanical effect in the grinding contact zone during the machining process,which will cause a series of metallurgical transformation behaviors of the surface matrix microstructure.Including the austenite transformation and dynamic recrystallization process oft he matrix microstructure in the high temperature thermal deformation stage,and bainite transformation and martensitic transformation of supercooled austenite during continuous cooling stage.Finally,the metamorphic layer is formed on the processed surface to effectively improve the mechanical properties of the processed surface.However,the dynamic thermal-mechanical effect is not uniformly distributed along the direction of grinding depth in the surface processing,which leads to the difference ofmetallurgical behavior of the metamorphic layer.At the same time,dynamic thermal-mechanical effect of contact zone is affected by grinding parameters,which will determine the quality and distribution range of the metamorphic layer.Meanwhile,the mechanical properties and surface quality of machined surface are significantly affected by grinding parameters.In order to realize the scientific evaluation and characterization of the mechanical properties of the machined surface,in this paper,the metallurgical transformation process of the metamorphic layer in the abrasive grinding hardening process was taken as the research object.Through the combination of simulation and experimental measurement,the distribution law of the strong nonlinear dynamic thermalmechanical effect in the grinding contact zone along the layer was explored.Meanwhile,the effect mechanism of different grinding parameters on the quality and distribution range of the metamorphic layer was solved.On this basis,the formation mechanism of the metamorphic layer and macroscopic properties characterization of grinding surface are studied,and a parameterized control method for the quality of the metamorphic layer is proposed.The main research contents ofthis paper are as follows:(1)The strong nonlinear dynamic thermal-mechanical effect in grinding contact zone was studied.The finite difference method and the finite element method were used to construct discrete digital models of the dynamic temperature and strain fields respectively.The spatio-temporal distribution of the dynamic thermal-mechanical effect under different grinding parameters was solved.and the diversity of the metallurgical transformation process of the matrix tissue of the metamorphic layer was analyzed.The effect laws of different grinding parameters on dynamic thermal-mechanical effect were compared to exploring the high temperature thermal deformation process of the surface metal layer with the moving heat source.(2)The astonishing transformation process and the dynamic recrystallization process are studied respectively.Based on the dynamic thermal-mechanical effect,the austenitic transformation and dynamic recrystallization behavior of the matrix were simulated by cellular automata method The difference of austenite transformation process along the layers and the influence mechanism of different grinding parameters on the transformation process were investigated.At the same time,the dynamic recrystallization process of austenite grains in the grinding contact zone during high temperature thermal deformation was studied,and the variation of grain size along the depth of the modified layer was investigated,as well as the comprehensive effect of different grinding parameters on the distribution of the refined layer.(3)The metallurgical transformation process and the distribution characteristics of composite microstructure of metamorphic layer during continuous cooling were studied.Firstly,a coupling model of pearlitic transformation and bainite transformation was established to simulate the transformation process of ferrite equiaxed crystal to lamellar crystal.Then,the dynamic conditions of martensite transformation were analyzed and the rapid shear process of martensite was simulated by the space phase field method.Finally,a hybrid cellular automaton-phase field model(C-PL model)was established to investigate the distribution of composite microstructure along the layers and the influence mechanism of different grinding parameters on the morphological characteristics of composite microstructure in metamorphic layer.(4)Experimental research on abrasive grinding hardening under different grinding parameters was carried out.Firstly,the experimental platform was built,and the comparative experiments were designed.Then the experimental results were observed and the model parameters were modified.Finally,based on the experimental results and model analysis,a parameterized control method for the quality of the metamorphic layer was proposed,which can be used to guide the production practice.In this paper,a series of metallurgical transformation processes of the matrix microstructure and the nonlinear dynamic thermal-mechanical effect of the grinding contact zone in the process of abrasive grinding hardening were studied.By combining modeling and simulation with experimental observation,the distribution difference of composite microstructure along the layers was investigated.Meanwhile the influence mechanism of different grinding parameters on the metallurgical transformation process ofthe metamorphic layer was also investigated.Finally,a parameterized control method for the quality of the modified layer is proposed,which is helpful to further explore the processing mechanism,optimize the process and scientific characterization of the machined surface properties,which provide research basis for the development of grinding hardening.