Note that after the heat treatment of the bearing components of quality defects

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1 overheating

   The rough mouth from the bearing parts can be observed in the microstructure after quenching overheating. But to determine exactly the extent of the overheating must obse rve the microstructure. If coarse acicular martensite in GCr15 steel quenching organization, compared the quenching overheating Organization. Formation may be due to the quenching temperature is too high or the heating holding time is too long comprehensive overheating; serious original organization ribbon carbide, formed in the area between the two with a low-carbon the local martensite needle-like thick, caused by local overheating. Overheating tissue retained austenite is increased, decreased dimensional stability. Overheating due to the quenching structure, the coarse crystals of steel, will cause the parts of the decrease in toughness, impact resistance is reduced, and also reduces the life of the bearing. Serious overheating even cause quenching cracks.

   2 due to heat

   Quenching temperature is low or poor cooling will be generated in the microstructure than the standard provisions of the trust s tissue called due to heat ti ssue, decrease in hardness, wear resistance is drastically reduced, affect the bearing life.ball roller bearing

   3 quenching cracks

   Bearing parts in the process of quenching cracks formed due to the internal stress that the quenching cracks. The reason for this crack: fracture resistance due to the quenching temperature is too high or cooling too quickly, the stress when the thermal stress and the quality of metal volume change greater than steel; original work surface defects (such as surface micro-cracks or scratches) or internal defects of steel (such as slag, serious non-metallic inclusions, the white point, the residual shrinkage) is formed in the quenching concentration of stress; severe surface decarburization and carbide segregation; parts after quenching and tempering or tempered in a timely manner; exc essive the cold punching stress caused by the previous process, forging folding, deep turning marks, sharp edges and corners of the oil groove. In short, the reason causing quenching cracks may be one or more of the above factors, the presence of the internal stress is the main reason of forming the quenching cracks. Quenching cracks are deep and slender, straight fracture, fracture surface oxide color. It often longitudinal straight cracks or ring of cracking on the bearing rings; steel ball bearings on the shape of the S-shaped, T-shaped or ring. Organizational characteristics of the quenching cracks on both sides of the crack without decarburization significant difference between forging cracks and material crack.

   (4) heat treatment deformation

   The bearing parts during heat treatment, there is thermal stress and stress, this internal stress can be superimposed on each other or partially offset, is complex, because it as the heating temperature, heating rate, cooling, cooling rate, the shape of parts changes and changes in the size, heat treatment distortion is inevitable. Understand and grasp the variation of deformation of the bearing parts (such as rings oval, size up, etc.) in a controlled range, is conducive to production. Of course, the mechanical collision during the heat treatment also causes Part deformed, but this deformation can be reduced with improved operation and avoid.

   (5) surface decarburization

   Bearing parts in the heat treatment process, if it is heated in an oxidizing medium, the surface oxidation occurs to reduce the carbon mass fraction of the surface of the part, causing surface decarburization. Surface decarburization depth over the last processing allowance will be scrapped parts. Determination of surface decarburization depth available metallographic method metallographic examination and microhardness method. The surface m icrohardness distribution curve measurements shall do the arbitration criterion.thin section ball bearing

   6 soft spots

   Due to the lack of heating, poor cooling, quenching improper operation caused the local hardness of the surface of the bearing parts is not enough phenomenon known as quenching soft spots. It is like the surface decarburization can result in a serious decline in surface wear resistance and fatigue strength.