Surface quenching
Surface hardening of steel
When some parts are in the workpiece, under the action of alternating load and impact load such as torsion and bending, the surface layer bears higher stress than the center. In the case of friction, the surface layer is also constantly 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, etc.
Induction heating surface quenching
Induction heating is to use electromagnetic induction to generate eddy current 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, with fast heating speed and high thermal efficiency
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 oxidation and decarburization on the surface 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 conducive to give full play to the potential of materials, save material consumption and improve the service life of parts
5. Compact equipment, easy to use and good working conditions
6. It is convenient for mechanization and automation
7. It can be used not only for surface quenching, but also for penetration heating and chemical heat treatment.
Basic principle of induction heating
Place the workpiece in the inductor. When the inductor passes through the alternating current, an alternating magnetic field with the same frequency as the current will be generated around the inductor. The induced electromotive force will be generated in the workpiece accordingly, and the induced current, namely eddy current, will be formed on the surface of the workpiece. Under the action of the resistance of the workpiece, the electric energy is converted into heat energy to make the surface temperature of the workpiece reach the quenching heating temperature, which can realize surface quenching.
Properties after induction surface quenching
1. Surface hardness: the surface hardness of workpieces quenched by high and medium frequency induction heating is often 2 ~ 3 units (HRC) higher than that of 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 fine martensite grain, high carbide dispersion, high hardness and high compressive stress on the surface of the hardened layer.
3. Fatigue strength: high and medium frequency surface quenching greatly improves the fatigue strength and reduces the notch sensitivity. For the workpiece of the same material, the depth of the hardened layer is within a certain range, and the fatigue strength increases with the increase of the depth of the hardened layer, but when the depth of the hardened layer is too deep, the surface layer is compressive stress, so the fatigue strength decreases with the increase of the depth of the hardened layer, and the brittleness of the workpiece increases. General hardened layer depth δ＝（ 10～20）％D。 More appropriate, where D. Is the effective diameter of the workpiece.
As a springs maker, we know that Surface quenching is very important process to improve material properties.
