Heat Treatment

Heat treatment process

1. Annealing

By heating to the appropriate temperature, holding for a period of time, and then slowly cooling, to eliminate the residual stress inside the material, reduce hardness, improve plasticity and toughness, and improve processing performance. Common types are complete annealing, incomplete annealing, isothermal annealing, spheroidizing annealing and so on.

2. Normalize

The steel is heated to Ac3(austenitizing temperature) above 30-50 ° C, and the air is cooled after insulation to refine the grains, improve the strength and toughness of the material, and improve the cutting performance.

3. Quench

The steel is heated to austenitizing temperature, and then cooled rapidly (such as water cooling, oil cooling) to obtain a high-hardness martensitic structure. Quenching is a key step to improve the hardness and wear resistance of steel, but it is often accompanied by increased brittleness and needs to be used with tempering.

4. Temper

After quenching, the steel is heated and held at a temperature below the critical temperature, and then cooled to room temperature to adjust the excessive hardness and brittleness generated by quenching, and obtain the required comprehensive mechanical properties. According to the different tempering temperature, it can be divided into low temperature tempering, medium temperature tempering and high temperature tempering.

5. Conditioning treatment

Tempering refers to the process of quenching and tempering the entire workpiece to achieve a uniform hardness distribution.

6. Surface hardening

Surface hardening is a treatment that hardens only the surface layer of the metal while leaving the core soft. Common methods include carburizing, nitriding, and cyaniding. These treatments can make the surface of the part have high hardness and wear resistance, while the core maintains good toughness.

7. Preheat treatment

Preheat treatment refers to the heating of metal prior to certain welding operations to reduce the risk of cracks caused by welding.

Each heat treatment process has its specific application range, and which process is chosen depends on the desired final properties as well as the type of metal. Heat treatment can be applied not only to steel materials, but also to other types of alloys. The correct heat treatment can greatly affect the functional life and reliability of metal components.

Heat treatment advantage

1. Improve mechanical properties

Improve the hardness: through the heat treatment process such as quenching, the hardness of metal materials can be significantly improved to enhance its wear resistance and scratch resistance. For example, after proper heat treatment of tool steel, the hardness can reach a very high value, so that it can maintain a sharp edge in the cutting, stamping and other processing processes, extending the service life.
Increase strength: Heat treatment can greatly increase the strength of the metal and can withstand greater loads. For example, after quenching and tempering treatment, the strength of structural steel is significantly improved, and it can be used to manufacture mechanical parts and engineering structures that can withstand heavy loads.
Improve toughness: Reasonable heat treatment process can improve the strength at the same time, maintain or improve the toughness of the material, to avoid the material is too brittle and hard and easy to break. For example, quenching stress can be eliminated by tempering, so that the toughness of the material can be restored and its impact resistance can be improved.
2. Optimized processing performance

Improve machinability: For some materials with high hardness, the hardness can be reduced by heat treatment processes such as annealing, making it easier to cut. For example, high carbon steel is spheroidized and annealed before cutting, which can spheroidize carbides, reduce the hardness and brittleness of the material, and improve the cutting performance.
Easy to cold processing: Heat treatment can improve the plasticity of metal materials, which is conducive to cold processing deformation. For example, brass is annealed before processing to improve its plasticity and facilitate cold working operations such as stretching and stamping.
3. Stable size and shape

Elimination of residual stress: Residual stress occurs during the processing and manufacturing of metals, which can cause problems such as deformation and cracking of parts. Through appropriate heat treatment processes, such as stress relief annealing, residual stress can be eliminated and the size and shape of the part can be stabilized. For example, the stress relief annealing of welded structural parts after welding can prevent the formation of welding deformation and cracks.
Improve dimensional accuracy: Heat treatment can make the organization of the material more uniform, reduce internal defects, thereby improving the dimensional accuracy of the parts. For example, after heat treatment of precision mechanical parts, higher dimensional stability can be obtained to meet the processing requirements of high precision.
4. Improve corrosion resistance

Forming a protective film: Some heat treatment processes can form a dense oxide film or other protective film on the surface of the metal to improve the corrosion resistance of the material. For example, the solid solution treatment and passivation treatment of stainless steel at high temperatures can form a stable chromium oxide protective film to enhance its corrosion resistance.
Improve the uniformity of the structure: Heat treatment can make the structure of the metal more uniform and reduce the occurrence of local corrosion. For example, after the homogenization annealing treatment of aluminum alloy, the composition of the tissue is more uniform, reducing the sensitivity of local corrosion.
5. Special properties

Obtain special physical properties: Heat treatment can change the physical properties of the metal, such as magnetism, electrical conductivity, coefficient of thermal expansion, etc. For example, the magnetic properties of electrical steel can be adjusted through heat treatment, so that it has higher permeability and lower iron loss, improving the efficiency of motors and transformers.
Produce special organizational structure: Heat treatment can make the metal form a special organizational structure, such as martensite, bainite, etc., giving the material special properties. For example, after quenching and tempering treatment, the martensite and carbide structure formed by high-speed steel makes it have high hardness, high red hardness and wear resistance, which is suitable for high-speed cutting.