There are two kinds of internal stresses in the heat treatment, namely thermal stress and tissue stress. The reason why the heat treatment deforms is that the tensile stress on the surface of the part is greater than the yield strength of the material. The spline gear is a deformable part. Due to the high temperature of carburizing and quenching, the temperature difference between the quenching heating temperature and the cooling medium is large, the cooling capacity of the cooling medium is strong, and the thermal stress of the part after quenching is large; on the other hand, the superheated carburizing, A large amount of retained austenite and coarse martensite after quenching increase the internal stress, so the deformation of the part is large. After repeated trials, the 980e@3min high-temperature salt bath was used to replace the original carburizing and quenching process by rapid heating quenching, and the method of increasing the temperature of the quenching cooling medium was adopted, and the quenching of 120140e hot oil was used, and a remarkable effect was obtained. The results of process test and production verification show that the workpiece clamping and furnace loading method has a great influence on the deformation of the gear spline hole. After the tooling is improved, the product qualification rate is obviously improved.
Process and tooling improvement, high-temperature salt bath rapid heating and quenching to select a suitable heat treatment process, reduce the amount of deformation of the spline inner hole, using the scrapped gears, high-temperature salt bath rapid heating quenching and different process tests, 980e@3min high temperature After rapid heating and quenching, the amount of deformation of the inner hole is reduced by about 100,400 Lm on the basis of the original carburizing and quenching process, showing a shrinking tendency. Rapid heating causes the surface of the workpiece to reach the quenching temperature. When the heat is too late to pass to the core, it is rapidly cooled. Since the core of the workpiece is still below the phase transition point, the quenching deformation can be reduced. According to the test results of the spline gear deformation of different heat treatment processes, the large-sized bevel gear of the turntable is rapidly heated by a 980e high-temperature salt bath, and the heating coefficient is K=410s/mm. In the test, the gear was preheated, heated in a 980e salt bath for 3 min, and cooled in oil for 4 min to remove the temper. At this time, not only the heating speed was fast, but also the heating effect was stable.
Improved effect. The high-temperature salt bath was used for rapid heating and quenching, and 20 products were processed with the spline mandrel lifting process. The pass rate was 95. The metallographic examination results showed that the tooth surface and the tooth root were grade 2 retained austenite, and the tooth angle carbide grade 1 The heart is a grade 3 ferrite, the core hardness is 4243HRC, and the tooth top hardness is 6062HRC, all of which meet the design requirements. The main disadvantage of body carburizing is that the production cycle is long and the parts are deformed greatly. It is difficult to guarantee the design drawings and the final product quality in the original process.
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