Release Source:NAIGOO
|Release Time:2019/07/29
|Number of Views:0
1. Normalization treatment
Normalization treatment can eliminate excessive stress inside the gear, increase the toughness of the gear, and improve the cutting performance of the material. Normalization treatment is commonly used for gears made of high-quality carbon steel or alloy steel with a carbon content of 0.3% to 0.5%. The strength and hardness of normalized gears are lower than those of quenched or tempered gears, with a hardness of HB163-217. Therefore, for large-diameter gears that do not require high mechanical performance or are not suitable for quenching or tempering, normalizing treatment is often used.
2. Quenching and tempering treatment
Quenching and tempering treatment is commonly used for gears made of high-quality carbon steel or alloy steel with a carbon content of 0.3% to 0.5%. Quenching and tempering treatment can refine the grain size and obtain a uniform fine spherical pearlite like structure with a certain degree of dispersion and excellent comprehensive mechanical properties - tempered martensite. After quenching and tempering treatment, the hardness of the gear teeth can reach HB220-285, and for smaller gears, the hardness can be even higher. The comprehensive performance of quenched and tempered gears is higher than that of normalized gears, with a yield limit and impact toughness that can be increased by about 40% compared to normalized gears. The strength limit and cross-sectional shrinkage rate are also 5% to 6% higher (for carbon steel). Tempered gears are prone to running in during operation, with a large margin of tooth root strength and strong impact resistance, and occupy a considerable proportion in heavy-duty gear transmission. In order to improve the anti sticking ability of soft tooth surface gears and considering that small gears work more heavily than large gears, commonly used quenched and tempered small gears are matched with normalized or quenched and tempered large gears, with a hardness difference of HB20-50.
3. Surface quenching
After surface quenching, gears need to undergo low-temperature tempering to reduce internal stress and brittleness. The tooth surface hardness is generally HRC 45-55. Surface quenched gears have high load-bearing capacity and can withstand impact loads. Usually, the blank of quenched gears can be first subjected to normalizing or tempering treatment to give the tooth center a certain strength and toughness.
4. Carburizing and quenching
Carburizing and quenching gears are commonly made of alloy steel or high alloy steel with a carbon content of 0.10% to 0.25%. After carburizing and quenching, the tooth surface hardness is HRC58-62, and generally requires grinding or honing to eliminate deformation caused by heat treatment. This type of gear has high contact strength and bending strength, and can withstand large impact loads. Important gears in various heavy-duty vehicles are often subjected to carburizing and quenching treatment.
5. Nitriding
Nitriding can improve the surface hardness, wear resistance, fatigue strength, and corrosion resistance of gear teeth. The nitriding treatment temperature is low, so the gear deformation is minimal and does not require grinding or only requires precision grinding. The materials for nitriding gears mainly include 38CrMoAlA, 30CrMoSiA, 20CrMnTi, etc. Nitrided gears have a thin nitriding layer (0.15-0.75mm) and a risk of peeling off the hardened layer. Their load-bearing capacity is generally not as high as that of carburized gears, and they are not suitable for use in situations where they can withstand impact loads or experience strong wear.
6. Other heat treatment methods for steel gears
Steel gears can also be treated using methods such as integral quenching or cyanide (carbonitriding). The overall hardness of quenched gears is relatively high, but they have large deformation, poor toughness, and are not resistant to impact, so their application is limited. Cyanide gears have the advantages of high hardness, good wear resistance, small deformation, and high productivity, and are suitable for carbon steel and alloy steel. But its hardened layer is brittle, not resistant to impact, and cyanide is highly toxic, so safety facilities must be in place.
