The role of quenching

What is the purpose of quenching fluid

Ensure that the austenite can be cooled at a rate exceeding the critical cooling rate, so as to obtain the martensite structure and obtain the purpose of quenching. Of course, the cooling capacity requirements of the quenching liquid are very different for different steel grades. Austenitic The higher the body stability, the lower the requirement for the cooling capacity of the quenching liquid, and vice versa. For example, carbon steel needs to be quenched with water (salt\alkali water), and alloy steel is generally quenched with oil (low cooling capacity).

What is tempering and quenching, and its function

Tempering is also called matching fire. A type of metal heat treatment process. The quenched workpiece is reheated to an appropriate temperature lower than the lower critical temperature, and after a period of heat preservation, it is a metal heat treatment that is cooled in air, water, oil and other media. Or heat the quenched alloy workpiece to an appropriate temperature, keep it for a certain period of time, and then cool it slowly or quickly. Generally used to reduce or eliminate the internal stress in the quenched steel, or reduce its hardness and strength to improve its ductility or toughness. According to different requirements, low temperature tempering, medium temperature tempering or high temperature tempering can be used. Generally, as the tempering temperature increases, the hardness and strength decrease, and the ductility or toughness gradually increases.

Quenching is a metal heat treatment process in which a metal workpiece is heated to an appropriate temperature and maintained for a period of time, and then immersed in a quenching medium for rapid cooling. The purpose of quenching is to make the supercooled austenite martensite or bainite Transformation to obtain martensite or bainite structure, and then temper with different temperatures to greatly improve the strength, hardness, wear resistance, fatigue strength and toughness of the steel, so as to meet the different requirements of various mechanical parts and tools. Requirements. It can also be quenched to meet the ferromagnetic, corrosion resistance and other special physical and chemical properties of certain special steels. (Guide: Eliminate the three major problems of anchor bolts)

• Surface hardening of steel

Some parts are subjected to alternating loads and impact loads such as torsion and bending during the workpiece, and its surface layer bears higher stress than the core. In the occasion of friction, the surface layer is continuously worn. Therefore, the surface layer of some parts is required to have high strength, high hardness, high wear resistance and high fatigue limit. Only surface strengthening can meet the above requirements. Because surface quenching has the advantages of small deformation and high productivity, it is widely used in production.

According to different heating methods, surface quenching mainly includes induction heating surface quenching, flame heating surface quenching, electric contact heating surface quenching and so on.

• Induction heating surface hardening

Induction heating is the use of electromagnetic induction to generate eddy currents in the workpiece to heat the workpiece. Compared with ordinary quenching, induction heating surface quenching has the following advantages:

1. The heat source is on the surface of the workpiece, the heating speed is fast, and the thermal efficiency is high

2. Because the workpiece is not heated as a whole, the deformation is small

3. The heating time of the workpiece is short, and the amount of surface oxidation and decarburization is small

4. The surface hardness of the workpiece is high, the notch sensitivity is small, and the impact toughness, fatigue strength and wear resistance are greatly improved. It is helpful to realize the potential of materials, save material consumption, and increase the service life of parts

5. The equipment is compact, easy to use, and good working conditions

6. Facilitate mechanization and automation

7. Not only used in surface quenching, but also in penetration heating and chemical heat treatment.

• The basic principle of induction heating

Put the workpiece in the inductor, when the alternating current passes through the inductor, an alternating magnetic field with the same frequency as the current is generated around the inductor, and an induced electromotive force is generated in the workpiece correspondingly, and an induction is formed on the surface of the workpiece Electric current, that is, eddy current. Under the action of the resistance of the workpiece, the electric energy is converted into heat energy by the eddy current, so that the surface temperature of the workpiece reaches the quenching heating temperature, and the surface quenching can be realized.

• Performance after induction surface hardening

1. Surface hardness: The surface hardness of workpieces that are surface-quenched by high- and medium-frequency induction heating is often 2 to 3 units (HRC) higher than ordinary quenching.

2. Wear resistance: The wear resistance of the workpiece after high-frequency quenching is higher than that of ordinary quenching. This is mainly due to the combination of small martensite grains in the hardened layer, high carbide dispersion, high hardness, and high surface compressive stress.

3. Fatigue strength: high and medium frequency surface quenching greatly improves the fatigue strength and reduces the notch sensitivity. For a workpiece of the same material, the depth of the hardened layer is within a certain range. As the depth of the hardened layer increases, the fatigue strength increases, but when the depth of the hardened layer is too deep, the surface layer is compressive stress, so the fatigue strength of the hardened layer increases and the fatigue strength decreases. Increased brittleness. Generally, the depth of the hardened layer is δu003d(10~20)%D. More appropriate, among them D. Is the effective diameter of the workpiece.

More related metal processing industry news: