What are the common quality defects bearing heat treatment

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Bearing parts common quality defects after heat treatment: quenching microstructure overheating, due to thermal quenching cracks, hardness is not enough, heat treatment distortion the surface decarburizati on soft spot.

1. Overheating

Overheating of the microstructure after quenching can be observed from the bearing parts rough port, but to determine exactly the degree of overheating of the microstructure must be observed. If in gcr15 steel quenched structure in coarse acicular martensite, compared with quenching overheating organizations. Formation may be due to the quenching temperature is too high or too long caused heated holding time comprehensive overheating; may be due to the serious the original organization ribbon carbide, low-carbon zone between the two with the formation of local coarse martensitic acicular caused by local overheating. Overheating organization residual austenite increases, the dimensional stability is lowered. , Steel, coarse crystal, cause parts toughness decreased, impact resistance is reduced, the life of the bearing is also reduced due to overheating of the quenched structure. Severe or even cause overheating quenching crac ks.roll bearings

2. Due to heat

Low quenching temperature or cooling adverse will be produced in the microstructure exceed standard requirements troostite tissue, called subcooled tissue, which decrease in hardness, abrasion resistance is drastically reduced, and affect bearing life.bearing manufacturer

3. Quenching cracks

The cracks formed by the bearing parts in the quenching process due to the internal stress, said quenching cracks. This crack: quenching temperature or cooling too quickly, the organizations stress is greater than the volume change of the thermal stress and metal quality steel fracture resistance; original work surface defects (such as surface micro-cracks or scratches) or steel internal defects (such as slag, serious non-metallic inclusions, white point, residual shrinkage, etc.) formed in the quenching stress concentration; the surface decarburization carbide segregation; parts quenching and tempering and or timely tempering; previous process caused by cold punching too much stress, forging folding, deep knife marks the turning oil groove sharp edges and corners. In short, the reasons causing quenching cracks may be one or more of the above factors, the presence of the internal stress is to form the main reason for the quenching cracks. Quenching cracks deep, slender, straight fracture, fracture surface oxidation color. It on the bearing rings are often cracking straightness of longitudinal cracks or annular; the shape of the bearing balls on the s-shaped, t-shaped, or ring. Organizing feature of quenching cracks cracks on both sides of decarburization obvious difference with forging cracks and the material crack.thin section bearing