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/*728*90 created on 2018/5/16*/ var cpro_id = "u3440131"; Home>Bearing knowledge>The disadvantages of quality after bearing parts heat treatment Defects in the quality of bearing parts after heat treatment
1. . Heat treatment of deformed bearing parts during heat treatment; there are thermal stresses and arrangement stresses; such internal stresses can be superimposed or partially offset; they are complex and variable; because they can follow heating temperature, heating rate, cooling method, cooling rate, parts The shape and the size change; therefore, the heat treatment deformation is inevitable. Knowing and grasping the changing rules can make the deformation of the bearing parts (such as the ellipse of the ferrule, the scale increase, etc.) on a controllable scale; Of course. Mechanical bumps during heat treatment can also cause deformation of the parts; but this deformation can be reduced and prevented by improved operation. /*250*250 was created on 2017/12/25*/ var cpro_id = 'u3171089';
2. Overheating can be investigated from the rough mouth of the bearing part to the overheating of the microscopic arrangement after quenching. However, it is necessary to investigate the microscopic arrangement when discriminating the degree of overheating. If coarse acicular martensite is present in the quenching arrangement of GCr15 steel, then Arrangement for quenching and overheating. The cause of the formation may be that the quenching heating temperature is too high or the heating and holding time is too long to form all the overheating, or the original arrangement of the banded carbide is severe; the low carbon region between the two bands constitutes part of Markov The needle is coarse; the part is overheated. The retained austenite is increased in the superheating arrangement; the dimensional stability is reduced. Because the quenching arrangement is overheated; the crystal of the steel is coarse; the resistance of the part is reduced; the impact resistance is reduced; the life of the bearing is reduced Also reduced.
3. If the under-heat quenching temperature is low or the cooling is poor, the tortite arrangement that exceeds the canonical rules will be attacked in the microscopic arrangement; it is called the underheating arrangement; it reduces the hardness; the wear resistance is drastically reduced; and the bearing life is affected.
4. . The soft spot is lack of heating; the poor cooling; the hardening operation is not suitable. The appearance of the bearing part is not the hardness of the surface. It is called quenching soft point. It can form the same wear resistance and fatigue strength as the outer surface decarburization.
5. The outer decarburization bearing parts are in the heat treatment process; if it is heated in an oxidizing medium; the surface will have an oxidation effect to reduce the mass fraction of the surface carbon of the part; the outer surface decarburization will be formed. The depth of the outer decarburization layer exceeds the final processing allowance. The part will be invalidated. The depth of the decarburization layer can be determined by metallographic method and microhardness method in the metallographic examination.
6. Quenching cracked bearing parts are called quenching cracks due to internal stress during quenching and cooling. The causes of such cracks are: because the quenching heating temperature is too high or the cooling is too fast; the thermal stress and the metal mass volume change the arrangement stress It is greater than the fracture strength of the steel, the original defects of the work appearance (such as fine cracks or scratches on the surface) or the internal defects of the steel (such as slag inclusions, severe non-metallic inclusions, white spots, shrinkage holes, etc.) during quenching Constitutive stress gathering, severe surface decarburization and carbide segregation, lack of tempering after quenching of parts or tempering in time, the cold pressing stress of the previous process is too large, casting folding, deep turning tool marks, oil groove sharp edge Et al. The cause of quenching cracks may be one or more of the above factors; the existence of internal stress is the main cause of quenching cracks.
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Defects in the quality of bearing parts after heat treatment
Source: China Bearing Network Time: 2014-10-10