Vacuum heat treatment process

Heat treatment process generally includes heating, heat preservation, cooling three processes, sometimes only heating and cooling two processes. These processes are interlinked and uninterrupted.

Heating is one of the important processes of heat treatment. There are many heating methods for metal heat treatment. The earliest method is to use charcoal and coal as heat sources, and then to use liquid and gas fuels. The application of electricity makes heating easy to control and no environmental pollution. These heat sources can be directly heated or indirectly heated by molten salts or metals or even floating particles.

When metal is heated, the workpiece is exposed to air, and oxidation and decarbonization often occur (i.e. the carbon content on the surface of iron and steel parts decreases), which have a negative impact on the surface performance of the parts after heat treatment. Therefore, metals should be heated in controllable or protective atmosphere, molten salt and vacuum. Coatings or packaging can also be used for protective heating.

The heating temperature of high vacuum sintering furnace is one of the important technological parameters of heat treatment process. Selecting and controlling the heating temperature is the main problem to ensure the quality of heat treatment. The heating temperature varies with the purpose of the treated metal material and heat treatment, but it is generally heated to a phase transition temperature above, in order to obtain high temperature structure. In addition, the transformation takes a certain time, so when the surface of the metal workpiece reaches the required heating temperature, it must also maintain a certain time at this temperature, so that the internal and external temperatures are consistent, so that the transformation of the microstructures is complete. This period is called holding time. When high energy density heating and surface heat treatment are used, the heating speed is very fast. Generally, there is no heat preservation time, while the heat preservation time of chemical heat treatment is often longer.

Cooling is also an indispensable step in the process of heat treatment. Cooling methods vary according to different processes, mainly controlling the cooling rate. Generally, the cooling speed of annealing is the slowest, normalizing is faster and quenching is faster. But there are different requirements for different kinds of steel. For example, air-hardened steel can be hardened at the same cooling rate as normalized steel.

Metal heat treatment process can be roughly divided into three categories: integral heat treatment, surface heat treatment and chemical heat treatment. According to the different heating medium, heating temperature and cooling method, each type can be divided into several different heat treatment processes. Different microstructures and properties of the same metal can be obtained by different heat treatment processes. Iron and steel is the most widely used metal in industry, and its microstructure is also the most complex, so there are many kinds of heat treatment processes for iron and steel.

Vacuum Heat Treatment Furnace