Heat Treatment Process

Heat treatment process generally includes three processes: heating, heat preservation and cooling, sometimes only heating and cooling. 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. Charcoal and coal are used as heat sources, and liquid and gas fuels are used recently. The application of electricity makes heating easy to control and no environmental pollution. These heat sources can be used to heat directly, or indirectly through molten salt or gold, or even floating particles. When the metal is heated, the workpiece is exposed to the air, which often occurs oxidation and decarburization (that is, the carbon content on the surface of steel parts is reduced), which has a very adverse effect on the surface performance of parts after heat treatment. Therefore, the metal should be heated in controllable or protective atmosphere, molten salt and vacuum, and can also be protected by coating or packaging. Heating temperature is one of the important process parameters of heat treatment process. The selection and control of heating temperature is the main problem to ensure the quality of heat treatment. The heating temperature varies with the metal material being treated and the purpose of heat treatment, but it is generally heated above the phase change temperature to obtain high temperature structure. In addition, the transformation needs a certain time, so when the surface of the metal workpiece reaches the required heating temperature, the temperature must be maintained for a certain time, so that the internal and external temperatures are the same, and the microstructure can be transformed. This time is called the holding time. When density heating and surface heat treatment are adopted, the heating speed is extremely fast, and there is no heat preservation time generally, while the heat preservation time of chemical heat treatment is often longer.