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Heat treatment knowledge
Metal heat treatment is one of the important processes in mechanical manufacturing. Compared with other processing techniques, heat treatment generally does not change the shape and overall chemical composition of the workpiece, but changes the microstructure inside the workpiece or changes the chemical composition of the surface of the workpiece. , to give or improve the performance of the workpiece. It is characterized by improving the intrinsic quality of the workpiece, which is generally not visible to the naked eye.
Thermal treatment process generally comprises heating, insulation, three processes of cooling, has only two processes of heating and cooling sometimes. These processes are interconnected and cannot be interrupted. Metal heat treatment process can be roughly divided into overall heat treatment, surface heat treatment, local heat treatment and chemical heat treatment, etc.
It is to heat the workpiece to an appropriate temperature, adopt different holding times according to the material and the size of the workpiece, and then slowly cool it. The purpose is to make the internal structure of the metal reach or approach the equilibrium state, obtain good process performance and use performance, or do further quenching. organization preparation
overall heat treatment
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 change its overall mechanical properties. The overall heat treatment of steel generally has four basic processes: annealing, normalizing, quenching and tempering. Annealing, normalizing, quenching, and tempering are the "four fires" in the overall heat treatment. Among them, quenching and tempering are closely related, and they are often used together, and both are indispensable.
It is to heat the workpiece to a suitable temperature and then cool it in the air. The effect of normalizing is similar to that of annealing, but the obtained structure is finer. It is often used to improve the cutting performance of low-carbon materials, and sometimes it is used for some parts with low requirements. as final heat treatment.
After the workpiece is heated and kept warm, it is rapidly cooled in a quenching medium such as water, oil or other inorganic salts or organic aqueous solutions. After quenching, the steel becomes hard, but at the same time becomes brittle.
In order to reduce the brittleness of the steel parts, the quenched steel parts are kept at an appropriate temperature higher than room temperature but lower than 650 ° C for a long time, and then cooled.