The test method test was divided into two groups of 8 gear samples each. One group adopts the conventional carburizing process, and is heated to 920 in the well type carburizing furnace for carburizing, and then cooled to 870 and directly discharged to the oil quenching, and then subjected to 180120 min tempering treatment, the depth of the infiltration layer is 08 mm 12 mm, and the surface carbon content For the other group of 0955. The following measures were taken: furnace loading method: fixed furnace installation in the manner shown. Controlled cooling: slow cooling after carburizing, and then heated to 830 in a salt bath furnace to quench oil. Elimination of residual stress: After roughing, 5502h to eliminate internal stress treatment, cooling with the furnace to 300 outlet air cooling. (Improvement of the quenching method: after the bevel gear is heated by the salt bath furnace, the salt bath on the gear is quickly removed, and then placed on the press bed for a short time, after releasing for 3s4s, and then pressure quenching. For the two groups of gears before and after quenching the common normal line Length and diameter of the inner hole.
During the heat treatment of the gear, the distortion is not only related to its raw materials, original structure, heat treatment process, but also to the geometry of the gear.
After the gear is carburized, the carbon content on the surface increases, causing the phase transition between the core and the surface to be different. The martensitic transformation occurs on the surface, the specific volume increases, and the temperature difference between the inside and the outside will inevitably lead to distortion. It can be seen that after the first group of gears is carburized and quenched, the length of the common normal line is obviously enlarged, and it increases with the increase of the modulus and the depth of the layer. For the larger diameter gear, it can even reach 012mm019mm. It is related to the change of the heat treatment stress due to the large cross-sectional size. The diameter of the inner hole also swells, mainly because the height dimension of the bevel gear is small, and the residual stress after quenching and cooling is mainly based on the tissue stress, so that the gear is elongated along the maximum line direction [5]. It can be seen from the results of carburizing and quenching of the second group of gears that, by improving the furnace charging method, controlling the cooling and quenching methods, on the one hand, the residual stress is effectively eliminated, and the heat treatment distortion of the gear is reduced; on the other hand, when the parts are in a high temperature state, When the yield strength is low, press it on the press for a short time, the distortion caused by carburizing and salt bath heating and salt explosion can be corrected, and then the recovery of 3s4s can reduce the quenching temperature and make the gear quenching and cooling distortion. Also got control. The surface hardness and core hardness of the two sets of gears are basically the same, reaching the technical requirements of the parts.
Conclusion After controlling the deformation of the bevel gear heat treatment from the aspects of furnace charging mode, cooling control and improvement of quenching method, the length of the common normal line is expanded by <007mm, and the inner hole is expanded by <005mm. The process of improving the gear is reduced. The heat treatment of the gear is distorted, and its surface hardness and core hardness are not reduced, which fully meets the technical requirements of the part.
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