Surface heat treatment technology
Surface heat treatment technology refers to a heat treatment process that only heats, keeps warm, and cools the surface of metal materials to change their surface structure and obtain the required mechanical properties. Different from overall heat treatment, surface heat treatment only changes the properties of the metal surface, while the core still maintains its original toughness and plasticity, so that the parts have both wear-resistant and fatigue-resistant surfaces and good impact resistance. This technology is particularly suitable for mechanical parts that are subjected to friction, impact and alternating loads, such as gears, shafts, bearings, etc. For example, after surface heat treatment, the tooth surface hardness of automobile transmission gears is significantly improved and the wear resistance is enhanced, while the tooth center still maintains good toughness, can withstand impact loads, and extend the service life of the gears. Therefore, surface heat treatment technology is widely used in the machinery manufacturing industry and is one of the key processes to improve the quality and reliability of parts.
There are many types of surface heat treatment technologies, the most common of which include flame hardening, induction hardening, laser surface hardening, carburizing and quenching, and nitriding. Flame hardening uses an oxygen-acetylene flame to rapidly heat the metal surface. Once the metal reaches the austenitizing temperature, it is immediately cooled by spraying water to achieve surface hardening. This method requires simple equipment and is flexible to operate, making it suitable for localized surface hardening of large parts. However, the heating temperature is difficult to control, and overheating and uneven heating can occur. Induction hardening, on the other hand, utilizes the principle of electromagnetic induction to generate eddy currents on the metal surface, rapidly heating and hardening the surface. It offers advantages such as fast heating speed, stable quenching quality, and high production efficiency, and is widely used for surface treatment of parts such as shafts and gears.
Laser surface quenching is a new type of surface heat treatment technology that uses a high-energy laser beam to scan and heat the metal surface, causing the surface layer to quickly heat up to above the phase transition point, and then relies on the metal’s own heat conduction to quickly cool it to achieve quenching. Laser quenching has the characteristics of extremely fast heating speed, small heat-affected zone, and small deformation. It can accurately quench local areas of complex-shaped parts, such as the cutting edge of the mold and the tooth surface of the gear. In addition, the surface hardness and wear resistance are high after laser quenching, and no subsequent processing is required, saving process costs. Carburizing and quenching is to first place the parts in a carburizing medium to allow carbon atoms to penetrate the surface, and then quench and low-temperature tempering are performed to obtain a high-hardness carburized layer and a tough core. It is suitable for low-carbon steel and low-alloy steel parts and can significantly improve their surface hardness and wear resistance.
The quality of surface heat treatment technology depends on the control of multiple process parameters, such as heating temperature, holding time, and cooling rate. If the heating temperature is too low, complete austenitization cannot be achieved, resulting in insufficient hardness after quenching; if the heating temperature is too high, the grains will be coarse, oxidation and decarburization will occur on the surface, and the performance of the part will be reduced. The holding time needs to be determined according to the part size and heating method to ensure uniform heating of the surface. The cooling rate is a key factor affecting the quality of quenching. Different metal materials require different cooling rates to obtain the desired martensitic structure. For example, carbon steel requires a faster cooling rate to obtain martensite, while alloy steel can be quenched at a slower cooling rate. Therefore, during the surface heat treatment process, various process parameters must be precisely controlled according to the type of material and part requirements to ensure the treatment effect.
With the continuous advancement of industrial technology, surface heat treatment technology is also constantly innovating and developing. New heating methods such as electron beam heating and plasma heating are gradually being applied to surface heat treatment. These technologies have the advantages of high heating efficiency, high control precision, and low environmental pollution. The introduction of intelligent technologies, such as computer simulation of surface heat treatment processes and automatic control of heating and cooling parameters, has improved the stability and repeatability of the process. At the same time, environmentally friendly surface heat treatment processes have also become a research hotspot, such as the use of non-toxic carburizing media and low-temperature nitriding processes to reduce the emission of harmful gases. In the future, surface heat treatment technology will pay more attention to the combination with other surface treatment technologies, such as coating treatment after surface quenching, to further improve the comprehensive performance of parts to meet increasingly stringent industrial use requirements.
