Overall heat treatment

Overall heat treatment is a metal heat treatment technology that heats the entire workpiece and then cools it at an appropriate rate to change its overall mechanical properties. The overall heat treatment of steel generally has four basic techniques: annealing, normalizing, quenching and tempering.

Annealing is to heat the workpiece to an appropriate temperature, select 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, achieve excellent technical performance and application performance, or to further Quenching for arrangement preparation. Normalizing 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 resulting arrangement is finer. It is often used to improve the cutting performance of the material, and sometimes it is used for some parts with low demand. Heat treated as a finish. Quenching is to rapidly cool the workpiece in a quenching medium such as water, oil or other inorganic salts, organic aqueous solutions, etc. after heating and maintaining the workpiece. After quenching, the steel becomes hard, but also becomes brittle. In order to reduce the brittleness of steel parts, the quenched steel parts are kept warm for a long time at an appropriate temperature higher than room temperature but lower than 650 ℃, and then cooled. This technique is called tempering. Annealing, normalizing, quenching, and tempering are the "four fires" in the overall heat treatment. The quenching and tempering are closely related, and they are often used together and are indispensable. The "four fires" have evolved different heat treatment technologies with different heating temperatures and cooling methods. In order to obtain a certain strength and resistance, the technology of combining quenching and high temperature tempering is called quenching and tempering. After some alloys are quenched to form a supersaturated solid solution, they are kept at room temperature or a slightly higher appropriate temperature for a long time to improve the hardness, strength or electrical and magnetic properties of the alloy. Such a heat treatment technique is called aging treatment. The method of effectively and closely combining pressure deformation and heat treatment to make the workpiece achieve excellent strength and tolerance is called deformation heat treatment; heat treatment in a negative pressure atmosphere or vacuum is called vacuum heat treatment, which not only makes The workpiece is not oxidized or decarburized, and the surface of the workpiece is kept clean after treatment, which improves the performance of the workpiece, and can also be chemically heat treated with a penetration agent.