Effect Of MnS Inclusions On Meso-damage And Microstructure Evolution Of Matrix At High Temperature

As the core component of heavy equipment,large forgings cannot avoid the existence of non-metallic inclusions in the production and manufacturing process.As a typical non-metallic inclusion,MnS has good plastic deformation ability at high temperature.However,due to its different physical and mechanical properties from the metal matrix,MnS inclusions reduce the continuity of the matrix,leading to defects such as micro-cracks during hot working(e.g.,forging and rolling),and induce damage failure behavior and affects hot ductility and fracture behavior of the matrixas well as generate additional interfaces in the matrix,which change the microstructure of the matrix and affect the evolution of grains microstructure,thus improving or worsening the related mechanical properties of the material.Therefore,it is of great significance to investigate effect of MnS inclusions on meso-damage and microstructure evolution of matrix at high temperature.In this paper,the macroscopic mechanical curves of materials with and without MnS inclusions were obtained through thermal tensile experiments.Through comparative analysis,it can be seen that the presence of MnS inclusions improves the strength of the material and reduces the plasticity of the material at the same time.By Optical Microscope(OM),Scanning Electron Microscope(SEM),Energy Dispersive Spectroscopy(EDS)and Electron Backscattered Diffraction(EBSD),we investigeted the damage and fracture mechanism of the matrix under the combined action of MnS inclusions and deformation temperature.The results show that MnS inclusions accelerate the damage evolution during plastic deformation,while the dynamic recrystallization(DRX)behavior near MnS inhibits damage propagation.Based on the response surface method,the GTN damage parameters at different deformation temperatures are determined,and the effects of MnS inclusion and deformation temperature on the damage parameters of GTN were discussed.The result shows the accelerating factor of void growth(k)can describe the effect of MnS and deformation temperature on the evolution of voids in the matrix during the necking and fracture stage of the material.Through hot compression experiments,the microstructure before and after deformation was characterized by EBSD technique.The effect of MnS on the dynamic recrystallization and the evolution of twin boundaries in matrix was studied.The particle stimulated nucleation mechanism induced by MnS promoted the development of DRX.Simultaneously,The particle stimulated nucleation induced by MnS inclusions produces dynamic recrystallized new grains containing twin boundaries,which increases the content of twin boundaries.