Formation Mechanisms And Properties Of Affected Layers Induced By Surface Grinding Of Hardened AISI 52100 Steel

Hardened AISI 52100 steel has high bearing capacity and good comprehensive performance,and is widely used in bearings,molds,turbofan blades and other important parts.Grinding is an important method for precision machining of the above key parts because of its good surface quality and high shape accuracy.However,the hardened AISI 52100 steel generates more heat and has poor heat dissipation performance in the grinding process,so an affected layers are often generated on the machined surface,which are different from the microstructure of the matrix,and has a great influence on the mechanical properties and service life of the parts.Therefore,surface grinding experiments of hardened AISI 52100 steel were carried out in this paper,and the microstructure,mechanical properties,microstructure and formation mechanisms of the grinding affected layers were systematically studied.The main research contents are as follows:(1)The microstructure and properties of grinding affected layers of hardened AISI 52100 steel were studied.Research shows that:The grinding affected layers usually contain white layer and dark layer,and the affected layers are distributed on the grinding surface and sub-surface discretely and locally.The reason is that the grinding heat accumulation on the workpiece surface is discrete due to the randomness of grinding wheel abrasive wear,and the impact of abrasive particles on the workpiece surface is also accidental.As a result,the white layer in the affected layers presents discontinuity and inhomogeneity on the surface and its related sub-surface.The experimental results show that the microstructure of the affected layers formed at different grinding depths is also different,which is closely related to the formation mechanism of the metamorphic layer under different thermal-mechanical coupling conditions.(2)The formation mechanisms of grinding affected layers of hardened AISI 52100 steel were studied.The research shows that the formation mechanisms of grinding affected layers can be divided into thermal induced formation mechanism and mechanical induced formation mechanism.The affected layers produced by thermally induced formation mechanism is composed of white layer,hybrid structure and dark layer.The multiplication of retained austenite during the formation of the thermal induced affected layers confirms that there is a phase transformation process and re-austenitizing occurs.The affected layers produced by mechanical induction mechanism is composed of white layer and hybrid structure.During the formation process,under the coupling action of stress shock and deformation induced martensitic transformation,the austenite decomposed into ferrite and cementite,resulting in a significant decrease in the content,which is completely opposite to the re-austenitizing phenomenon in the formation mechanism of heat-induced affected layers.In addition,the formation process of dark layer in metamorphic layer is similar to high temperature tempering,during which austenite is decomposed and cementite is precipitated,accompanied by continuous dynamic recovery and dynamic recrystallization.(3)The influence of grinding affected layers on tensile properties of workpiece was investigated.Tensile test results show that the hardness of grinding white layer tissues in the affected layers,thickness and uniformity,continuity of the surface area of the reinforcement ratio on the tensile properties of workpiece played a key influence,especially the white layer thickness uniformity and surface distribution continuity,uniform and dense tissue can improve the total surface energy,make the crack initiation and propagation,be suppressed,The tensile strength of the workpiece is improved.