The quality of heat treatment is directly related to the quality of subsequent processing and ultimately affects the performance and life of parts.At the same time,heat treatment is a major energy consumer and a major polluter in the machinery industry.The heat treatment quality control of bearing parts is the most stringent in the entire machinery industry.

　　The following editor will briefly summarize the common quality defects of bearing parts after heat treatment:

　　1.Overheating

　　The overheating of the microstructure after quenching can be observed from the roughness of the bearing parts.

　　But to determine the degree of overheating,the microstructure must be observed.If thick acicular martensite appears in the quenched structure of GCr15 steel,it is a quenched superheated structure.The reason for the formation may be the overall overheating caused by the excessively high quenching heating temperature or the heating and holding time for too long;it may also be caused by the serious band-like carbides of the original structure,and the formation of local martensite needle-like coarseness in the low-carbon zone between the two belts.Local overheating caused by.The retained austenite in the superheated structure increases and the dimensional stability decreases.Due to the overheating of the quenched structure and the coarse steel crystals,the toughness of the parts will decrease,the impact resistance will decrease,and the life of the bearing will also decrease.Severe overheating may even cause quenching cracks.

　　2.Low heat

　　Low quenching temperature or poor cooling will produce a troostite structure in the microstructure that exceeds the standard,called underheated structure,which reduces the hardness and the wear resistance sharply,which affects the life of the bearing.

　　3.Quenching crack

　　The cracks formed by internal stress in the quenching and cooling process of bearing parts are called quenching cracks.The reasons for this kind of cracks are:because the quenching heating temperature is too high or the cooling is too rapid,the thermal stress and the structural stress of the metal mass volume change are greater than the fracture strength of the steel;the original defects of the working surface(such as surface micro cracks or scratches)Marks)or internal defects of the steel(such as slag inclusions,serious non-metallic inclusions,white spots,shrinkage residuals,etc.)that form stress concentration during quenching;severe surface decarburization and carbide segregation;insufficient tempering of parts after quenching Or not tempered in time;excessive cold punching stress caused by the previous process,forging folding,deep turning tool marks,sharp edges and corners of the oil groove,etc.In short,the reason for quenching cracks may be one or more of the above factors,and the existence of internal stress is the main reason for quenching cracks.The quenching crack is deep and slender,the fracture is straight,and the fracture surface has no oxidation color.It is often a longitudinal straight crack or annular crack on the bearing ring;the shape on the bearing steel ball is S-shaped,T-shaped or ring-shaped.The structural feature of quenching crack is that there is no decarburization on both sides of the crack,which is obviously different from forging crack and material crack.