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DO you know how many kinds of pre-heat treatment and final heat treatment?

Annealing,normalized, quenching, tempering… Do you know the difference of all this heat treatment ways? The role of heat treatment is to improve the mechanical properties of materials, eliminate residual stress and improve the cutting effency.According to different purposes, Heat treatment process can be divided into two types: preparing heat treatment and final heat treatment.

Heat treatment of steel

1.Preparing heat treatment

The purpose of pre-heat treatment is to improve processing performance, eliminate internal stress, and prepare good gold -phase tissue for final heat treatment,which include annealing, normalizing, aging treatment etc.

1) Annealing and Normalizing

Annealing and normalizing are used for Hot working blanks. Carbon steel and alloy steel with a carbon content greater than 0.5% are often annealed to reduce their hardness and facilitate cutting; Carbon steel and alloy steel with a carbon content below 0.5% are normalized to avoid tool sticking during cutting due to low hardness. Annealing and normalizing can still refine grains and uniform structure, preparing for future heat treatment. Annealing and normalizing are often arranged after rough manufacturing and before rough machining.

2) Aging treatment

Aging treatment is mainly used to eliminate internal stress generated during rough manufacturing and mechanical processing.

To avoid excessive transportation workload, for parts with general accuracy, an aging treatment can be arranged before precision machining. However, for parts with high precision requirements (such as the box of a coordinate boring machine, etc.), two or several aging treatment processes should be arranged. Simple parts generally do not require aging treatment.

In addition to castings, for some precision parts with poor rigidity (such as precision screws), in order to eliminate internal stress generated during processing and stabilize the machining accuracy of the parts, multiple aging treatments are often arranged between rough machining and semi precision machining. Some shaft parts need to be processed with aging treatment after the straightening process.

3) Tempering

Quenching and tempering refers to high-temperature tempering treatment after quenching, which can obtain a uniform and fine tempered sorbite structure, preparing for reducing deformation during subsequent surface quenching and nitriding treatment. Therefore, quenching and tempering can also serve as a preparatory heat treatment.

Due to the good comprehensive mechanical properties of the quenched and tempered parts, some parts with low requirements for hardness and wear resistance can also be used as the final heat treatment process.

2.Final heat treatment

The ultimate purpose of heat treatment is to improve mechanical properties such as hardness, wear resistance, and strength.

1) Quenching

Quenching includes surface quenching and overall quenching.Surface quenching is widely used due to its small deformation, oxidation, and decarburization. Moreover, surface quenching has the advantages of high external strength and good wear resistance, while maintaining good toughness and strong impact resistance internally. To improve the mechanical properties of surface quenched parts, heat treatment such as quenching and tempering or normalizing is often required as a preparatory heat treatment. The general process route is: cutting → forging → normalizing (annealing) → rough machining → quenching and tempering → semi precision machining → surface quenching → precision machining.

2) Carburizing quenching

Carburization quenching is suitable for low carbon steel and low alloy steel. Firstly, the carbon content of the surface layer of the part is increased, and after quenching, the surface layer obtains high hardness, while the core still maintains a certain strength and high toughness and plasticity. Carburization is divided into overall carburization and local carburization. During local carburization, anti-seepage measures (copper plating or anti-seepage material plating) should be taken for the non carburized parts. Due to the large deformation caused by carburizing and quenching, and the carburizing depth is generally between 0.5~2mm, the carburizing process is generally arranged between semi precision machining and precision machining.

The general process route is: cutting → forging → normalizing → rough and semi precision machining → carburizing and quenching → precision machining. When the non carburized part of a partially carburized part adopts the process plan of cutting off the excess carburized layer after increasing the margin, the process of cutting off the excess carburized layer should be arranged after carburizing and before quenching.

3) Nitriding treatment

Nitriding is a treatment method that allows nitrogen atoms to penetrate into the surface of a metal to obtain a layer of nitrogen-containing compounds. Nitriding layer can improve the surface hardness, wear resistance, fatigue strength, and corrosion resistance of parts. Due to the low temperature, small deformation, and thin nitriding layer (generally not exceeding 0.6-0.7mm) of nitriding treatment, the nitriding process should be arranged as far back as possible. To reduce deformation during nitriding, high temperature tempering to relieve stress is generally required after cutting.


Shandong Dajin Metal Material specialized in all kinds of heat treatment.We can suggest the right heat treatment ways according to client’s final usage and final properties requirement.Welcome come to our factory and send inquiry to us!