Heat Treatment Process of Painted Packing Steel Strip

The heat treatment process generally includes three processes of heating, heat preservation, and cooling, sometimes only two processes of heating and cooling. These processes are connected and uninterrupted.
　　 Heating is one of the important steps of heat treatment. There are many heating methods for the heat treatment of painted and packaged steel strips. The earliest heat source was charcoal and coal, and then liquid and gas fuels were used. The application of electricity makes heating easy to control, and there is no environmental pollution. These heat sources can be used for direct heating, or indirect heating by molten salt or metal, or even floating particles.
　　 When the painted steel strip is heated, the steel strip is exposed to the air, and often oxidizes and decarburizes (that is, the carbon content of the surface of the steel parts is reduced), which has a very adverse effect on the surface properties of the parts after heat treatment. Therefore, the painted packaging steel strip should usually be heated in a controlled atmosphere or protective atmosphere, molten salt and vacuum, and it can also be heated by coating or packaging methods.
　　The heating temperature is one of the important process parameters of the heat treatment process. The selection and control of the heating temperature is the main issue to ensure the quality of the heat treatment. The heating temperature varies with the metal material being processed and the purpose of the heat treatment, but it is generally heated above the phase transition temperature to obtain the required structure. In addition, the transformation takes a certain time. Therefore, when the surface of the painted and packaged steel strip reaches the required heating temperature, it must be maintained at this temperature for a certain period of time to make the internal and external temperatures consistent and complete the microstructure transformation. This period of time is called Holding time. When using high-energy density heating and surface heat treatment, the heating speed is extremely fast, generally there is no holding time or the holding time is very short, and the holding time of chemical heat treatment is often longer.