Microstructure Evolution Of Cutting Metamorphic Layer Of H13 Steel Based On Plastic Deformation Mechanism

AISI Hl3 steel has high hardness and good red hardness,and is widely used in hot forging dies and hot extrusion dies.The die is subjected to extreme conditions such as high temperature,high pressure and thermal shock during the service process;therefore it is required to have good geometric integrity and physical integrity during machining.The coupled thermo-mechanical effects in hard cutting of H13 steel will change the microstructure of the machined surface and affect the quality of the die steel.The microstructure of the machined surface has a very important influence on the fatigue strength,wear resistance and corrosion resistance of the workpiece.It is of great significance to study the relationship between the service performance of the workpiece and the processing conditions.However,the research on the microstructure evolution model of the machined surface and the relationship between the service performance and the microstructure of machined surface is still lacking.In this paper,H13 steel is taken as the research object,and the orthogonal test of hard cutting is carried out.The prediction model of the thickness of the surface metamophic layer on the cutting parameters is established.The finite element model of the hard cutting is established.The stress,strain and temperature field data during the cutting process are obtained.A microstructure evolution model based on plastic deformation was established,this model was used to predict the dislocation density and grain size of the surface metamophic layer coupling finite element model.The main contents and conclusions of the thesis are as follows:(1)By carrying out the orthogonal experiments of Hl3 steel hard cutting,the regression model of the thickness of the metamophic layer on the cutting parameters was established.The orthogonal experiments of 3 factors and 5 levels of hard cutting was carried out.The degree of plastic deformation was characterized by the thickness of the metamophic layer.The relationship between the degree of plastic deformation and the grain size of the machined surface was studied.The results show that the grain refinement degree is related to the thickness of the metamophic layer during low-speed cutting.During high-speed cutting,the cutting temperature is higher,which weakens the grain refinement.The regression model of the thickness of the metamophic layer on the cutting parameters is established.(2)The finite element simulation model of H13 steel hard cutting was established.Based on Abaqus finite element software,the finite element model of H13 steel hard cutting was established by selecting reasonable material model,friction model,mesh property,boundary condition and contact model.Compared with the experimental results,errors of the simulated chip shape and cutting force are less than 15%,which verifies the accuracy of the finite element model.The distribution of stress field,temperature field and strain field during the cutting process is analyzed,which provides a basis for the subsequent microstructure evolution model.(3)Based on the Abaqus user-defined subroutine,a microstructure evolution model based on plastic deformation mechanism was established.The subroutine calculates the dislocation density and grain size of the machined surface according to the dislocation theory and was verified by experiments.The dislocation density and grain size distribution of the machined surface under different cutting speeds and different tool rake angles were studied.The results show that the grain size on the cutting surface is remarkably reduced and gradually transits to the original grain size along the cutting depth.The dislocation density of the cutting surface increases with the increase of the cutting speed.and the grain size increases with the cutting speed.The thickness of the metamophic layer increases with the increase of cutting speed;the dislocation density of the machined surface decreases with the increase of the rake angle of the tool,and the grain size increases with the increase of the rake angle of the tool,and the thickness of the metamophic layer varies with the tool.The rake angle increases and decreases.In this study,the dislocation density and grain size distribution of the machined surface were analyzed by the plastic deformation mechanism.Technical support can be provided to reveal the milling mechanism of H13 steel,guide the milling process and obtain good surface quality.