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Rotary Support Heat Treatment Defects
May 22, 2017

1, heat treatment deformation

Rotational support parts in the heat treatment, there is thermal stress and tissue stress, the internal stress can be superimposed on each other or partially offset, is complex and varied, because it can with the heating temperature, heating speed, cooling, cooling speed, parts Shape and size changes, so heat treatment deformation is inevitable. Knowing and mastering the law of change can make the deformation of the slewing bearing parts (such as the ellipse of the ring, the size of the large, etc.) placed in a controlled range, is conducive to the production. Of course, the mechanical collision during the heat treatment also causes the part to be deformed, but this deformation can be reduced and avoided by improved operation.


2, overheating

The microstructure of the microstructure after quenching can be observed from the rough surface of the rotary support part. But to determine the extent of its overheating must observe the microstructure. If the coarse needle-like martensite appears in the quenched tissue of GCr15 steel, it is quenched and superheated. The formation of the reasons may be quenching heating temperature is too high or heating and holding time is too long caused by a comprehensive overheating; may also be due to the original organization of ribbon carbide serious, in the low band between the two areas of the formation of local martensite needle- Caused by local overheating. In the superheated tissue, the retained austenite increases and the dimensional stability decreases. Due to the overheating of the quenched structure, the crystal of the steel is coarse, the toughness of the part is reduced, the impact resistance is reduced, and the life of the slewing ring is reduced.


3, less heat

Quenching temperature is low or poor cooling will produce in the microstructure of the standard than the provisions of the organization, known as less thermal tissue, it reduces the hardness, abrasion resistance drastically reduced, affecting the rotation support life.


4, soft point

Due to lack of heating, poor cooling, quenching improper operation and other reasons caused by the surface of the rotary support parts of the local hardness is not enough phenomenon called quenching soft point. It is like surface decarburization can cause surface abrasion and fatigue strength of a serious decline.


5, surface decarburization

Rotational support parts in the heat treatment process, if it is heated in the oxidizing medium, the surface will be oxidized to the surface of the carbon content of the surface to reduce the weight, resulting in surface decarburization. The depth of the surface decarburization layer exceeds the final processing of the amount will make the parts scrapped. Determination of surface decarburization depth The metallographic method and microhardness method can be used in the metallographic examination.


6, quenching crack

Rotary support parts in the quenching process due to internal stress caused by cracks, said quenching crack. The reason for this crack is due to the fact that the hardening temperature is too high or the cooling is too fast. The stress of the thermal stress and the mass change of the metal mass is larger than that of the steel. The original defects of the working surface (such as surface micro- (Such as slag, severe non-metallic inclusions, white spots, shrinkage, etc.) in the quenching of the formation of stress concentration; severe surface decarburization and carbide segregation; parts quenched after tempering Or not timely tempering; the previous process caused by the cold punch stress is too large, forging folding, deep turning knife marks, oil groove sharp edges and corners.