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Steps of heat treatment process technology

Date:2023-09-26 09:51:57 Hits:257 From:Ningbo Zhenhai Bright Heat Treatment Plant

Metal heat treatment processes can generally be divided into overall heat treatment, surface heat treatment, local heat treatment, and chemical heat treatment. Depending on the heating medium, heating temperature, and cooling method, each major category can be divided into several different heat treatment processes. Different heat treatment processes can be used for the same metal to obtain different microstructures and thus exhibit different properties. Steel is the most widely used metal in industry, and its microstructure is also the most complex, resulting in a wide variety of steel heat treatment processes.

Overall heat treatment is a metal heat treatment process that heats the workpiece as a whole and then cools it at an appropriate rate to change its overall mechanical properties.

heating

Heating is one of the important steps in heat treatment. There are many heating methods for metal heat treatment, initially using charcoal and coal as heat sources, and then applying liquid and gas fuels. The application of electricity makes heating easy to control and has no environmental pollution. These heat sources can be used for direct heating, as well as indirect heating through molten salts or metals, as well as floating particles.

When metal is heated, the workpiece is exposed to air and often undergoes oxidation and decarburization (i.e., the carbon content on the surface of steel parts decreases), which has a very adverse impact on the surface performance of the parts after heat treatment. Therefore, metals should usually be heated in a controlled or protective atmosphere, molten salt, and vacuum, and can also be protected and heated using coatings or packaging methods.

Heating temperature is one of the important process parameters in heat treatment process, and selecting and controlling the heating temperature is the main issue to ensure the quality of heat treatment. The heating temperature varies depending on the metal material being treated and the purpose of the heat treatment, but generally it is heated above the phase transition temperature to obtain the required structure. In addition, the transformation requires a certain amount of time. Therefore, when the surface of the metal workpiece reaches the required heating temperature, it is necessary to maintain this temperature for a certain period of time, so that the internal and external temperatures are consistent and the microstructure transformation is complete. This period of time is called insulation time. When using high-energy density heating and surface heat treatment, the heating speed is extremely fast, and generally there is no insulation time or the insulation time is very short, while the insulation time of chemical heat treatment is often longer.

cooling

It is also an indispensable step in the heat treatment process, and the cooling method varies depending on the process, mainly controlling the cooling speed. Generally, annealing has the slowest cooling rate, normalizing has a faster cooling rate, and quenching has a faster cooling rate. But there are also different requirements for different types of steel, such as air hardened steel, which can be quenched at the same cooling rate as normalizing.
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