What is Heat Treatment?
Metal heat treatment is one of the important processes in mechanical manufacturing. It refers to a metal thermal processing to obtain the desired structure and properties via heating,warming,cooling method.
Compared with other processing techniques, heat treatment generally does not change the shape of the workpiece and the overall chemical composition. Instead, it improves the performance of the workpiece by changing the microstructure inside the workpiece or changing the chemical composition of the surface of the workpiece. It is characterized by improved internal quality of the workpiece, which is not visible to the naked eye. The essence of heat treatment is the physical change of the object. It is a process that improves its performance, service performance and service life by strictly controlling the heating and cooling process of the material.
Heat Treatment Process
The heat treatment process generally includes three processes of heating, warming and cooling. Sometimes there are only two processes of heating and cooling. These processes are connected to each other and cannot be interrupted.
When the metal is heated, the workpiece is exposed to the air, and oxidation and decarburization. That is to say, the carbon content on the surface of the steel part often occur. It has a detrimental effect on the surface properties of the parts after the heat treatment. Thus the metal should normally be heated in a controlled or protective atmosphere, in molten salt and in a vacuum. Protective heating can also be carried out by coating or packaging methods.
Heating temperature is one of the important process parameters of heat treatment process. Selecting and controlling heating temperature is the main problem to ensure the quality of heat treatment. The heating temperature varies depending on the metal material to be treated and the purpose of the heat treatment. However, it is generally heated above the phase transition temperature to obtain a high temperature structure. In addition, the transformation takes a certain time. Therefore, when the surface of the metal workpiece reaches the required heating temperature. It must be kept at this temperature for a certain period of time. So that the internal and external temperatures are uniform, and the microstructure is completely transformed. This time is called the holding time.
When high-energy density heating and surface heat treatment are used, the heating rate is extremely fast. Generally, there is no holding time, and the heat treatment time of the chemical heat treatment tends to be long.
Cooling is also an indispensable step in the heat treatment process. The cooling method varies from process to process, mainly to control the cooling rate.
Metal heat treatment processes can be roughly divided into three categories: overall heat treatment, surface heat treatment and chemical heat treatment. Depending on the heating medium, heating temperature and cooling method. Each category can be divided into several different heat treatment processes. The same metal uses different heat treatment processes to obtain different microstructures and thus different properties. Steel is the most widely used metal in the industry. Its microstructure is also the most complex. Therefore, there are many kinds of steel heat treatment processes.
The overall heat treatment is a metal heat treatment process that heats the workpiece as a whole and then cools it at an appropriate speed to obtain the desired metallographic structure to change its overall mechanical properties. The overall heat treatment of steel has four basic processes: annealing, normalizing, quenching and tempering.
What is the purpose of heat treatment?
The purpose of heat treatment: to change the size of the shape of the material and improve its performance. Including the performance and process performance, the potential of the material can be fully utilized to improve the intrinsic quality of the part.