Introduction to Heat Treatment Processes
Aug 12, 2025
What is heat treatment?
Heat treatment improves a workpiece's performance by changing its internal microstructure or surface chemical composition.
When is heat treatment necessary?
After a customer places an order, the sawing shop cuts the mold steel to size according to their needs. The mold then undergoes a series of grinding or milling operations.
The mold, after rough machining, is returned to the factory for heat treatment based on the needs of the specific material.
Heat treatment process classifications
Heat treatment processes include quenching, tempering, nitriding, cryogenic cooling, and oxidation. What do these processes mean?
I. Quenching
1. What is quenching?
This is a heat treatment process in which steel is austenitized and then cooled at an appropriate rate to induce an unstable microstructure transformation, such as martensite, across the entire cross-section or within a specific area of the workpiece.
2. What is the purpose of quenching?
1) To improve the mechanical properties of the finished metal or part. For example: improving the hardness and wear resistance of tools and bearings, increasing the elastic limit of springs, and improving the overall mechanical properties of shaft parts.
2) Improving the material or chemical properties of certain special steels. For example, improving the corrosion resistance of stainless steel and increasing the permanent magnetism of magnetic steel.
II. Tempering
1. What is tempering?
A heat treatment process in which a quenched workpiece is heated to an appropriate temperature below the critical point AC1 for a specified period of time, followed by cooling using a suitable method to achieve the desired microstructure and properties.
2. Purpose of tempering?
1) Reducing internal stress and brittleness. Quenched parts are subject to significant stress and brittleness. If not tempered promptly, they often deform or even crack.
2) Adjusting the mechanical properties of the workpiece. After quenching, workpieces are hard and brittle. To meet the varying performance requirements of various workpieces, tempering can be used to adjust hardness, strength, plasticity, and toughness.
3) Stabilizing workpiece dimensions. Tempering stabilizes the metallographic structure, ensuring that deformation does not occur during subsequent use.
4) Improving the cutting performance of certain alloy steels.
III. Nitriding
1. What is nitriding?
Nitriding is a chemical heat treatment process in which nitrogen atoms are introduced into the surface of a workpiece at a specific temperature and in a specific medium.
2. What is the purpose of nitriding?
To impart excellent wear resistance, fatigue resistance, corrosion resistance, and high-temperature resistance to the product. Nitriding is a chemical heat treatment process in which nitrogen atoms are introduced into the surface of a workpiece at a specific temperature and in a specific medium.
IV. Cryogenics
1. What is cryogenics?
Cryogenics involves treating metals at temperatures below -160°C, converting almost all of the soft retained austenite into high-strength martensite.
2. What is the purpose of cryogenics?
Eliminating retained austenite (after quenching and tempering, retained austenite is approximately 8-20%. Austenite is very unstable and easily transforms into martensite when subjected to external forces or changes in ambient temperature. Martensite, which is larger than austenite, can cause irregular expansion of the material and reduce the dimensional accuracy of the workpiece). After deep cooling, the retained austenite is reduced to below 2%, reducing residual stress, making the metal matrix more stable, and increasing the strength and toughness of the metal material, significantly improving its red hardness.
5. Oxidation
What is oxidation?
Oxidation treatment forms a dense, protective oxide film on the surface of steel parts. Its primary component is magnetic iron oxide (Fe₃O₄), which has an anti-adhesion effect. The FeS film obtained by surface sulfidation can also reduce wear and prevent adhesion. It can also improve corrosion resistance and high-temperature oxidation resistance.
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