Bearing parts common quality defects after heat treatment: quenching microstructure overheating, less heat, quenching cracks, hardness is not enough, heat treatment variant surface decarburization, soft spots.
   1 overheating
Accurate determination of its overheating the extent necessary to observe the microstructure. Thrown in the the GCr15 steel quenching organization coarse acicular martensite, compared the quenching overheating Organization. The causes may be the comprehensive overheating quenching temperature is too high or the heating temperature and time is too long; may also be due to severe original organization ribbon carbide, a local martensite needle-like thick low carbon zone between the two belts , causing local overheating. Overheating tissue retained austenite increased size chaos of decline. Quenched structure overheating, thick steel crystal, will lead to the toughness of the part down, the fight against functional decline, also reduces joint bearing life. Overheating may even cause severe quenching cracks.
   2 due to heat
Quenching temperature is low or poor cooling but it will produce over scale delineation of the trust′s tissue microstructure, called due to heat tissue, decrease in hardness, wear resistance is drastically reduced, affecting the joints bearing life.
  3 quenching cracks
Bearing parts known as quenching cracks cracks formed due to the internal stress in the quench process. The reason for this crack: quenching temperature is too high or cooling too fast. Thermal stress and metal mass volume change when the stress is greater than the fracture resistance of the steel; original work surface of the defect (eg, surface micro-cracks or scratches) or internal defects of steel (such as slag, severe non-metallic inclusions , white point, residual shrinkage) stress concentration quenching; severe surface decarburization and the carbide segregation; parts after quenching the fire or tempering in a timely manner; excessive the cold punching stress caused by the previous process, casting folding, deep turning marks, oil hook sharp edges and corners.
  4 heat treatment deformation
Bearing parts during heat treatment, there is thermal stress and stress is complex, because it can follow the heating temperature, heating rate, cooling method, the cooling rate, the part shape and size changes, so the heat treatment distortion is inevitable the. Familiar with and grasp the variation deformation of the joint bearing parts (such as sets of oval, size up big, and so on) in a controlled range, is conducive to the production progresses. Of course, the mechanical collision during the heat treatment also causes Part deformed, but this deformation can be improved manipulated to reduce or 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 overhaul in metallurgical available Metallographic and microhardness method. To the surface microhardness announced this quasi-curve measurement method, do Arbitration criterion.
  6 soft spots
Because of lack of heating, cooling poor local hardness of the surface of the joint bearing parts is not enough phenomenon known as quenching caused by improper operation and other reasons this quenching soft spots. It is like the surface decarburization can cause severe surface wear resistance and fatigue degree drop.