Heat treatment process, characteristics and functions of automobile gears

Update:07-05-2022
Summary:

As a key part of automobiles, automobile gears are main […]

As a key part of automobiles, automobile gears are mainly used to transmit power and motion, and through them to change the speed ratio of engine crankshaft and main shaft gears. Since the driving condition of the automobile changes randomly with the road conditions, the working condition of the automobile gear is very complicated, which requires the automobile gear to have good internal quality.Yuhuan FaShiEr gear Co, LTD is located in Yuhuan-China automobile parts production base. our factory is a professional manufacturer of the various precision forging differential gears, Precision Forged Gears with all kinds of mechanical processing equipment.

Heat treatment process, characteristics and functions of automobile gears

The intrinsic quality of automobile gears mainly means that the microstructure and mechanical properties of the gears meet the technical requirements, and other defects must be controlled within the specified technical scope.

The quality of the internal quality of automobile gears is the key to determining the quality of the gears, which depends entirely on the quality of heat treatment, and is the key factor for the gears to achieve low noise, high precision and long life.

Automotive gear heat treatment (process) includes: first, ordinary heat treatment, such as annealing, normalizing, quenching, tempering, quenching and tempering; second, surface heat treatment, which includes surface quenching (such as induction quenching, laser quenching, etc.) and chemical heat treatment (such as carburizing, carbonitriding, nitriding, nitrocarburizing, etc.).

tempering

Quenching and tempering is an operation in which parts such as gears are quenched and then tempered at high temperature (500~650℃). 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% (mass fraction).

Quenching and tempering can refine the grains and obtain a tempered sorbite structure with uniform, certain dispersion and excellent mechanical properties. Generally, after quenching and tempering, the gear hardness can reach 220~285HBW. The comprehensive performance of quenched and tempered gears is better than that of normalizing.

Quenching and tempering is often used for preliminary heat treatment of gears (such as nitriding, quenching and tempering before induction hardening) and final heat treatment.

surface hardening

The quenching hardness of gear tooth surface is generally 45~55HRC. Case hardened gears have high load-carrying capacity and are able to withstand shock loads. Usually, the blanks of surface-hardened gears are normalized or quenched and tempered, so that the core of the gears has a certain strength and toughness.

Surface quenching mainly includes induction quenching, laser quenching and flame quenching. Compared with carburizing and quenching, surface quenching has small deformation, low cost and high efficiency.

The surface quenching of automobile gears mainly adopts induction quenching process. Due to the high speed of induction heating, there is almost no oxidation and decarburization, the gear deformation is very small, and it is easy to realize local heating and automatic production, and the heat treatment cost is low. Therefore, it is widely used in the modern automobile industry.

Carburizing and Carbonitriding

Carburizing and Quenching

Carburizing and quenching is to first put gears and other parts into carburizing medium, heat and keep warm at 880~950℃ to increase the surface of gears, and then quench.

Gas carburizing process is commonly used in automobile gears. The surface hardness of the gear after carburizing, quenching and tempering is generally 58~63HRC. At present, carburizing and quenching has become the dominant heat treatment process for important automotive gears (such as differential gears, drive axle drive-driven and driven spiral bevel gears, transmission gears, etc.).

Carbonitriding

In recent years, the actual temperature of the tooth surface of the AIT carburized gear of the automatic transmission for automobiles during operation is about 300℃, which is much higher than the normal tempering temperature (150~200℃). The temperature of this surface will cause a reduction in hardness, which can lead to pitting corrosion. Fatigue strength can be improved by carbonitriding followed by shot peening. During carbonitriding, with the increase of nitrogen content, the ΔHV (hardness drop) increases, and the tempering resistance improves, and the tempering resistance temperature reaches 300 °C.

Nitriding and nitrocarburizing

Nitriding

Nitriding is a chemical heat treatment process in which nitrogen atoms are infiltrated into the surface of parts such as gears to form a nitride layer. Nitriding can improve the surface hardness, wear resistance, fatigue strength and corrosion resistance of gears. The nitriding temperature is low, so the gear deformation is small, and no grinding or fine grinding is required.

Nitrocarburizing is a chemical heat treatment process in which nitriding is mainly nitriding and carbon is infiltrated. Nitrocarburizing can significantly improve the wear resistance, anti-glue and scratch resistance, fatigue resistance and corrosion resistance of gears. At present, gas nitrocarburizing is used in parts such as transmission gears for cars and light buses.

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