Although the strength of mechanical gear bearing capacity does not entirely depend on gear hardness, improving gear hardness is still one of the main factors affecting gear bearing capacity. The effective heat treatment method to improve the gear hardness is deep carburizing and quenching. The higher the relative content of nickel, the greater the austenite shape, the lower the carbon content of eutectoid composition, and the easier carbides are formed on the surface during carburizing, resulting in the lower carbon content of surface austenite than that of subsurface austenite. Therefore, in order to reduce the grade difference and low hardness of carbide, martensite and retained austenite. If air cooling after carburizing, troostite will be produced in the surface layer and martensite will be produced in the subsurface layer.
However, for the Ni Cr Mo steel system, the influence of the above adverse phenomena is less than that of the Ni Cr Mo steel system because of the molybdenum content and the less nickel content in the Ni Cr Mo steel system. Therefore, it is only necessary to control the carbon concentration gradient of the carburized surface layer and the whole carburized layer in an appropriate range, and directly carburize and quench at an appropriate quenching temperature and medium. In addition, the deformation of Ni Cr Mo steel system is smaller than that of Ni Cr steel system after heat treatment. The mechanical properties of Ni Cr Mo steel system after heat treatment are better than that of Ni Cr steel system, which improves the accuracy and strength of gear, reduces the noise and vibration during working, and improves the service life of gear. The hardenability of Ni Cr Mo steel system is better than that of Ni Cr steel system.
Therefore, for the Ni Cr Mo steel system with hard tooth surface steel such as chromium steel, the correct heat treatment process should be selected, which is carburizing at 930 ℃, quenching at 820 ℃, engine oil cooling at 60 ℃ and low temperature tempering at 180 ℃. Compared with Ni Cr steel, it has shorter production cycle and lower cost. The depth of infiltration layer is generally 0.1 ~ 0.15m, which belongs to medium infiltration layer and is mainly used for surface hardening. The surface microstructure is martensite, carbide and retained austenite, and the surface stress state is high residual compressive stress. After quenching, the surface hardness can reach 58 ~ 65hr carbon, and the core hardness can generally reach 30hr carbon. It has good wear resistance, contact fatigue strength, bending fatigue strength, anti adhesion ability and high impact toughness. It has great deformation tendency after heat treatment, but it is not easy to crack.
Because in daily production, machinery often needs to bear too much pressure, the strengthening treatment of gear surface also involves the gear core, and at present the most widely used is to enhance the strength of the core to avoid gear failure, but the reasonable discussion is how to effectively control the mechanical gear cracking, so the ball impact gear can be used to improve its strength.
The surface of mechanical gear with large load is usually in the maximum stress state, and the environmental dust content is high. Most of the failure and failure starts from the surface and surface of gear. The proportion of gears which break or deform due to the insufficient overall strength of materials is relatively small. Therefore, in order to improve the surface wear resistance, corrosion resistance, strength and fatigue resistance of the material, extend the service life of gear, ensure the reasonable configuration performance and system stability of mechanical gears, surface strengthening technology must be carried out for the gears. Surface strengthening can improve the surface performance of gear, improve fatigue strength and wear resistance, and also improve corrosion resistance. If some residual pressure stress is introduced into the surface of gear, the surface hardness and surface structure are improved, the fatigue strength and wear resistance of gear can be improved significantly.
In addition, the lubrication optimization of gear can reduce the wear force on the surface of gear, and attention should be paid to it. During the process, the gear should be avoided from cracking due to external force. Through the research on the cracking and control of mechanical gears, it can be found that the surface strength, toughness, hardness and wear resistance of gears are the important problems to be considered for effective control due to the problems of heavy load, strong noise and dust pollution in mechanical production. Through the optimization design of these factors, the stability of mechanical appliances can be improved, the safety of production can be guaranteed and the production efficiency can be improved.