What are the types of gear heat treatment?

Different materials, sizes, working conditions and properties of gears affect the selection of heat treatment process. So, what kind of heat treatment does gear machining need? Today, I will introduce the heat treatment method of the lower gear to you.

1. Gear normalizing heat treatment

Normalizing treatment can eliminate the 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 carbon content of 0.3% - 0.5%. The strength and hardness of normalized gear is lower than that of quenched or tempered gear, and the hardness is hb163-217. Therefore, normalizing is often used for large-diameter gears with low mechanical properties or unsuitable for quenching or tempering.

2. Gear tempering heat treatment

Quenching and tempering treatment is often used for gears made of high quality carbon steel or alloy steel with carbon content of 0.3% - 0.5%. After quenching and tempering, the grains can be refined, and the fine pearlite like structure tempered sorbite with certain dispersion and excellent comprehensive mechanical properties can be obtained. Generally, the hardness of gear teeth can reach hb220-285 after quenching and tempering. For smaller size gears, the hardness can be higher. The comprehensive performance of quenched and tempered gear is higher than that of normalized gear, its yield limit and impact toughness are about 40% higher than that of normalized gear, and its strength limit and reduction of area are 5% - 6% higher than that of normalized gear (for carbon steel). The quenched and tempered gears are easy to run in, have large root strength margin and strong impact resistance in operation, and account for a considerable proportion in heavy gear transmission. In order to improve the anti scuffing ability of the soft tooth surface gear and consider that the work of the small gear is heavier than that of the big gear, the hardness difference between the commonly used hardened and tempered small gear and the normalized or tempered big gear is usually in hb20-50.

3. Gear surface hardening

After surface quenching, the gears need to be tempered at low temperature in order to reduce the internal stress and brittleness. The hardness of tooth surface is generally hrc45-55. The surface hardened gear has high bearing capacity and can bear impact load. Generally, the rough of hardened gear can be normalized or tempered first, so that the center of gear teeth has certain strength and toughness.

4. Gear carburizing and quenching

Carburized and quenched gears are usually made of alloy steel or high alloy steel with carbon content of 0.10% - 0.25%. After carburizing and quenching, the hardness of the tooth surface is HRC58-62. Generally, grinding or honing is required to eliminate the deformation caused by heat treatment. This kind of gear has high contact strength and bending strength, and can bear large impact load. The important gears in all kinds of 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 temperature of nitriding treatment is low, so the deformation of gear is very small, no grinding or only fine grinding is needed. The materials of nitriding gear mainly include 38CrMoAlA, 30crmosia, 20CrMnTi, etc. Because of the thin nitriding layer (0.15-0.75mm), the hardened layer of the nitriding gear is in danger of peeling off, and its bearing capacity is generally lower than that of the carburizing gear, so it is not suitable for the occasion of bearing impact load or strong wear.

6. Other heat treatment methods of steel gear

Steel gears can also be treated by integral quenching or cyaniding (carbonitriding). The hardness of the whole hardened gear is high, but the deformation is large, the toughness is poor, and it is not resistant to impact, so it is seldom used. Cyaniding gear has the advantages of high hardness, good wear resistance, small deformation and high productivity, which is suitable for carbon steel and alloy steel. However, the hardening layer is brittle, impact resistant, and cyanide is highly toxic, so safety facilities must be provided.

After carburizing, the surface of the gear has high hardness and wear resistance, while the core still keeps the toughness and plasticity of low carbon steel. Qingdao Fengdong heat treatment Co., Ltd. has a number of multi-purpose furnace production lines, which can select quenching oil treatment with different cooling rates according to gear accuracy to control deformation. Please contact us for gear heat treatment. We believe that quality determines success or failure!

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