The principle of laser heating surface quenching is the same as that of ordinary heat treatment, but its heating time is very short, the area is small, and the cooling time is short. That is, the laser is used as a heat source to rapidly heat a small area of the metal surface, make it austenitic, and then quench for hardening. Both theory and practice confirm that the surface temperature and thermal penetration depth are proportional to the square root of the laser irradiation duration. Therefore, by properly adjusting the spot size, scanning speed and laser power, its surface temperature and thermal penetration depth can be controlled. When the laser beam leaves the heated surface, the heat there is quickly transmitted to the remaining cold part of the surface, equivalent to self-quenching, and no other rapid cooling measures are required. When the laser beam is scanning, the power density can also be adjusted by changing the amplitude and frequency of the beam swing, so as to control the depth of the hardening layer and the coverage area.
Because the laser spot or beam swing amplitude is very small, it can only be heated by scanning the surface of the parts one by one. In order not to temper and soften the hardened part of the previous strip due to the heat at the edge of the latter scan strip, efforts should be made to make the energy distribution at the beam edge or oscillating surface as steep as possible. This can be done using rasters.
Similar to induction heating surface quenching, the microstructure of general steel after laser surface quenching is also divided into surface completely quenched area, stratified incomplete quenched area and core unquenched area.
Compared with ordinary heat treatment, laser heating surface quenching has the following characteristics.
1. The heating speed is very fast, and the workpiece thermal deformation is very small. Due to the high power density of the laser, the heating speed is as high as 1010℃/s, the heat-affected zone is small, and the thermal deformation of the workpiece is small.
2. The cooling speed is very fast. If the quality of the workpiece is sufficient, the cooling speed can reach 1023℃/s; Self-cooling quenching does not require a cooling medium and relies on heat conduction from the surface to the interior.
3. After laser quenching, the surface of the workpiece obtains a fine martensitic structure and has high surface hardness and wear resistance.
4. Because the laser beam scanning (heating) area is very small, it can be very precise machining of complex shapes of the workpiece (such as small grooves, blind holes, small holes, thin-walled parts, etc.) or part processing. Different treatments can also be performed on different parts of the same site as needed.
5. It does not need a heating medium, and will not emit gas pollution to the environment, which is conducive to environmental protection.
save energy, workpiece surface clean. There is no need to grind after treatment, and it can be used as the last process of workpiece finishing.
6. Laser heating surface quenching can achieve personalized customization and flexible processing. For metal parts of different materials, shapes and sizes, personalized customization and flexible processing can be achieved through laser heating surface quenching technology. At the same time, this technology can also achieve automated production, improve production efficiency and reduce costs.
In summary, laser heating surface quenching technology is a metal surface treatment technology with high hardness, high precision, high efficiency and environment-friendly characteristics. It has been more and more widely used in the field of metal manufacturing and processing and has become one of the important development directions of metal heat treatment technology. With the continuous progress of science and technology and the continuous expansion of application fields, laser heating surface quenching technology will continue to improve and develop, bringing more innovation and change to the metal manufacturing and processing industry.
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