Spur Gear Transmission

Material for M4 spur gear: 

Low carbon alloy carburized steel or carbonitriding steel shall be selected for gears with heavy load, high speed or medium speed and subject to large impact load. Such as 20Cr, 20CrMnTi, 20crni3, 18Cr2Ni4WA, 40Cr, 30crmnti and other steels. The heat treatment adopts carburizing, quenching and low-temperature tempering. The gear surface obtains high hardness of hrc58 ~ 63. Due to high hardenability, the gear core has high strength and toughness. The surface wear resistance, fatigue strength, bending strength of tooth root and impact resistance of heart of this gear are higher than those of surface hardened gears. When the accuracy requirements are high, grinding is generally arranged at last. It is applicable to the gearbox and rear axle gear of automobiles and tractors with poor working conditions. Compared with carburizing, carbonitriding has the advantages of small heat treatment deformation, short production cycle and high mechanical properties. It is also applied to medium carbon steel or medium carbon alloy steel. Therefore, carbonitriding can be used to replace carburizing process for many gears. The load and working conditions of variable speed gears on internal combustion engines, tanks and aircraft are heavier and worse than those of automobiles, which requires higher performance of materials. Alloy carburized steel with high alloy elements should be selected to obtain higher strength and wear resistance.

Precision transmission  M4 spur gear or hard tooth surface gear with difficulty in gear grinding (such as internal gear) mainly requires high precision and small heat treatment deformation. Nitride steel should be used. Such as 35CrMo, 38CrMoAlA and other steels. Quenching and tempering and nitriding are adopted for heat treatment. After nitriding, the tooth surface hardness is as high as HV850 ~ 1200 (equivalent to HRC65 ~ 70), with good thermal stability (high hardness can be maintained at 500 ~ 550 ℃) and certain corrosion resistance. Its disadvantage is that the hardening layer is thin and not resistant to impact, so it is not suitable for heavy-duty gears with frequent load changes, but mostly used for precision transmission gears with stable load and good lubrication or internal gears with difficult tooth grinding. In recent years, due to the development of soft nitriding and ion nitriding process, the process cycle is shortened, the steel grade is widened, and the gears treated with nitriding are gradually widely used.

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