Powder metallurgy has lots of advantages, such as material saving, energy saving, high efficiency, suitable for mass production, good size and shape repetition, low noise and low wear when gears are running etc., so it has been widely used. The main defects are impacting resistance and poor impact function. Therefore, it is very important to enhance its strength.

A. Strength characteristics of powder metallurgy gears

1. The expansion coefficient of materials and the accuracy of dies mostly depend on the accuracy of powder metallurgical gears. Generally, the domestic die for gear within 50 diameters is between 8-9 grades, while the imported die is between 7-8 grades. If it is helical gear, it can also be a higher grade. The greatest advantage of powder metallurgy gear is that it can be produced in large quantities and has good consistency.

2. For ordinary FN0205 powder metallurgy gear, it can carry torque up to 14NM, warm-pressed parts can reach 20NM, and warm-pressed FD0405 can reach 25NM. Therefore, in the case of professional powder metallurgy design, gears weight can still be reduced by 30-40%.

B. Increasing the strength of powder metallurgical gears

1. For high strength powder metallurgical gears, they should have high density and follow the process of "pressing-preheating-reheating-heat treatment".

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2. Lower carbon content can ensure that the product has high surface hardness and wear resistance in heat treatment. Low carbon will make the product have excellent impact resistance.

3. Adding 2%-3% Ni and 2% Cu into the material can obviously improve material impact strength after sintering.

4. Compared with carburizing and quenching, carbonitriding products have excellent wear resistance. Lower carbonitriding temperature guarantees parts core strength and reduces the quenching deformation.

Powder metallurgy gears are commonly used parts in automotive. Through one-time forming and finishing process, the requirement of gear accuracy can be achieved completely without other post-processing, and the processing efficiency can be effectively promoted.