Metal heat treatment protectio

Metal heat treatment process

Update time: 2018-05-30

Review

The heat treatment process generally includes three processes of heating, heat preservation and cooling, and sometimes only heating and cooling processes. These processes are connected with each other and cannot be interrupted.

heating

Heating is one of the important processes of heat treatment. There are many heating methods for metal heat treatment. The earliest use of charcoal and coal as heat sources led to the use of liquid and gaseous fuels. The application of electricity makes heating easy to control and no environmental pollution. These heat sources can be used for direct heating, as well as for indirect heating via molten salts or metals as well as floating particles.
When the metal is heated, the workpiece is exposed to the air and oxidation and decarburization often occur (ie, the surface carbon content of the steel parts is reduced), which has a negative effect on the surface properties of the heat-treated parts. Thus metals should generally be heated in controlled atmospheres or protective atmospheres, in molten salts and in vacuum, but also protected by coatings or packaging methods.
The heating temperature is one of the important process parameters of the heat treatment process. Selecting and controlling the heating temperature is a major problem in ensuring the quality of the heat treatment. The heating temperature varies depending on the metal material being processed and the purpose of the heat treatment, but generally it is heated above a certain characteristic transformation temperature to obtain a high temperature structure. In addition, the transformation requires a certain time, so when the surface of the metal workpiece reaches the required heating temperature, it must be maintained at this temperature for a certain time, so that the internal and external temperatures are the same, so that the microstructure changes completely. This time is called holding time. With high energy density heating and surface heat treatment, the heating rate is extremely fast, generally there is no heat preservation time, and the heat treatment time of chemical heat treatment is often longer.

cool down

Cooling is also an indispensable step in the heat treatment process, and the cooling method differs depending on the process, mainly controlling the cooling rate. In general, the cooling rate of the annealing is the slowest, the normalized cooling rate is faster, and the quenching cooling rate is faster. However, there are different requirements depending on the type of steel. For example, an empty hard steel can be hardened with a normal cooling rate.
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