What Are the Types of Gear Heat Treatment?

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1. Gear normalizing heat treatment

Normalizing treatment can eliminate excessive stress inside the gear, increase the toughness of the gear, and improve the cutting performance of the material. Normalizing is often 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 quenched and tempered gears, and the hardness is HB163～217. Therefore, for large-diameter gears that do not require high mechanical properties or are not suitable for quenching or quenching and tempering, normalizing treatment is often used.

2.Gear quenching and tempering heat treatment

Quenching and tempering treatment is often used for gears made of high-quality carbon steel or alloy steel with a carbon content of 0.3% to 0.5%. The quenching and tempering treatment can refine the crystal grains and obtain a uniform fine spherical pearlite structure with a certain degree of dispersion and excellent comprehensive mechanical properties-tempered sorbite. Generally, after quenching and tempering, the hardness of the gear teeth can reach HB220～285. For smaller gears, the hardness can be higher. The overall performance of quenched and tempered gears is higher than that of normalized gears. Its yield limit and impact toughness are about 40% higher than that of normalized gears, and its strength limit and reduction of area are also higher by 5% to 6% (for carbon steel). Quenched and tempered gears are easy to run-in during operation, have a large tooth root strength margin, and have strong impact resistance. They occupy a considerable proportion in heavy gear transmission. In order to improve the anti-gluing ability of soft tooth surface gears and considering that the small gears work harder than the large gears, the small gears commonly used for quenching and tempering are matched with the normalized or quenched and tempered large gears, and the hardness difference is often HB20-50.

3.Gear surface hardening

Gears need to be tempered at low temperature after surface quenching to reduce internal stress and brittleness. The tooth surface hardness is generally HRC45~55. The surface-hardened gear has high load-bearing capacity and can withstand impact loads. Generally, the roughened gears can be normalized or quenched and tempered first, so that the tooth center of the gear has a certain strength and toughness.

4. Gear carburizing and quenching

Carburized and hardened gears are usually 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. Generally, tooth grinding or honing is required to eliminate the deformation caused by heat treatment. This type of gear has high contact strength and bending strength, and can withstand greater impact loads. Important gears in various trucks are often carburized and quenched.

5. Gear 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 extremely small, and no grinding or fine grinding is required. Nitrided gear materials mainly include 38CrMoAlA, 30CrMoSiA, 20CrMnTi, etc. Nitrided gears have the risk of peeling off the hardened layer due to the thin nitriding layer (0.15～0.75mm), and their bearing capacity is generally not as high as that of carburized gears, so they are not suitable for use in occasions with impact load or strong wear.

6. Other heat treatment methods for steel gears

Steel gears can also be treated by methods such as integral quenching or cyanidation (carbonitriding). The overall hardened gear has high hardness, but has large deformation, poor toughness, and is not resistant to impact, so it is less used. Cyanide gears have the advantages of high hardness, good wear resistance, small deformation and high productivity. They are suitable for carbon steel and alloy steel. However, the hardened layer is brittle, not impact resistant, and cyanide is highly toxic, so safety facilities must be provided .

After the gear is carburized, the surface layer of the product has high hardness and wear resistance, and the core still maintains the toughness and plasticity of low carbon steel.

Shanghai Geheng Vacuum Technology Co., Ltd has a number of multi-purpose furnace production lines, which can select quenching oil treatments with different cooling speeds according to the precision of the gears to control the amount of deformation. For gear heat treatment, please choose Gehang heat treatment, we believe that quality determines success or failure!

Editing by Baccata

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