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Metal heat treatment process and purpose

Heat treatment process for the industry should be very familiar with, but for the new line of friends is not to be missed. Next, we will introduce the common heat treatment process and its purpose. The commonly used heat treatment process includes annealing, quenching, tempering, solution heat treatment, carburizing, surface treatment and composite heat treatment.


1. Metal heat treatment annealing

Annealing mainly refers to the heat treatment process of exposing the material to high temperature for a long time and then cooling it slowly. To be exact, annealing is a kind of heat treatment process for materials, including metal materials and non-metal materials.


Annealing purpose of metal heat treatment:

1. Refine grains, improve mechanical properties, and prepare for the next process.

2. Reduce the hardness, improve the plasticity, improve the cutting and pressure processing performance.

3. Eliminate the internal stress produced by cold and hot working.


2. Metal heat treatment normalizing

Normalizing is a metal heat treatment process in which the workpiece is heated to a proper temperature (30-50 ℃ above AC3 or ACCM) (see steel microstructure) and cooled in air after heat preservation. Normalizing is mainly used for steel parts. Normalizing is usually used as a pre heat treatment process for forgings, weldments and carburized parts. For low carbon and medium carbon carbon structural steel and low alloy steel with low performance requirements, it can also be used as the final heat treatment. For general medium and high alloy steel, air cooling can lead to complete or partial quenching, so it can not be used as the final heat treatment process.


Metal heat treatment normalizing purpose:

1. Refine grains, improve mechanical properties, and prepare for the next process.

2. Eliminate the internal stress produced by cold and hot working.

3. Reduce the hardness, improve the plasticity, improve the cutting and pressure processing performance.


3. Metal heat treatment and quenching

Quenching, a heat treatment process for metals and glass. The quenching of steel is a heat treatment process in which the steel is heated to a critical temperature above AC3 (hypoeutectoid steel) or AC1 (hypereutectoid steel) for a period of time to make all or part of austenite 1-turn, and then cooled to a temperature below MS (or isothermal near MS) at a cooling rate faster than the critical cooling rate for martensite (or bainite) transformation. Generally, the solution treatment of aluminum alloy, copper alloy, titanium alloy, toughened glass and other materials or the heat treatment process with rapid cooling process are also called quenching.


Purpose of metal heat treatment and quenching:

Generally, the purpose of quenching is to obtain martensite structure with high hardness. Sometimes, when quenching some high alloy steels (such as stainless steel and wear-resistant steel), it is to obtain single and uniform austenite structure, so as to improve wear resistance and corrosion resistance.


4. Metal heat treatment and tempering

Tempering is a process in which the quenched steel is heated below the austenitic transformation temperature and cooled after holding for 1 to 2 hours. Tempering is often accompanied by quenching and is the last process of heat treatment. After tempering, the structure of the steel tends to be stable, the brittleness of the quenched steel is reduced, the toughness and plasticity are improved, the quenching stress is eliminated or reduced, the shape and size of the steel are stabilized, the deformation and cracking of the quenched parts are prevented, and the cutting performance can also be improved by high temperature tempering.


Purpose of metal heat treatment and tempering:

1. Adjust the hardness, improve the plasticity and toughness, and obtain the required mechanical properties.

2. Reduce or eliminate the internal stress after quenching, reduce the deformation and cracking of workpiece.

3. Stabilize workpiece size.


5. Metal heat treatment and tempering

Quenching and tempering is the comprehensive heat treatment process of quenching and high temperature tempering.

Most of the quenched and tempered parts work under relatively large dynamic load. They bear the effects of tension, compression, bending, torsion or shear. Some surfaces also have friction, which requires certain wear resistance and so on. In a word, the parts work under various compound stresses. Such parts are mainly structural parts of various machines and mechanisms, such as shafts, connecting rods, bolts, gears, etc., which are widely used in manufacturing industries such as machine tools, automobiles and tractors. Especially for large parts in heavy machine manufacturing, quenching and tempering treatment is more used. Therefore, tempering treatment plays an important role in heat treatment.

Purpose of metal heat treatment and tempering:

1. Reduce the deformation and cracking during quenching.

2. Good comprehensive mechanical properties were obtained.

3. Improve the cutting performance and surface finish.


Aging of metal heat treatment:

Aging refers to the effect that can occur in a certain period of time; after a period of time, the strength of metal or alloy increases gradually due to the desolvention of supersaturated solid solution and lattice precipitation.

Aging purpose of metal heat treatment:

1. Reduce the internal stress after quenching and grinding, and stabilize the shape and size.

2. Stabilize the structure of steel parts after quenching and reduce the deformation during storage or use.


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