Surface heat treatment technology for low carbon steel and low carbon alloy steel
Statistics show that more than 80% of the scrap parts in mechanical products are caused by surface failure, while the failure rate of parts that are genuinely broken or deformed due to insufficient overall strength of materials is very small (in fact, many parts break, and their cracks are first generated from the surface). Therefore, improving the wear resistance, corrosion resistance, fatigue resistance and strength of the material surface is the key to prolong the service life of components, reasonable configuration performance and ensure the stability of the system. Therefore, the surface heat treatment technology has attracted great attention and developed rapidly, playing an increasingly important role in improving the performance of various components.
The depth of the infiltrated layer is generally 0.1~1.5mm, which is of medium depth and is mainly used for surface hardening. The microstructure of the surface layer is (martensite + carbide + retained austenite), and the stress state of the surface layer is high residual compressive stress. After quenching, the surface hardness can reach 58 ~ 65HRC, and the core hardness is generally about 30HRC. It has good wear resistance, good contact fatigue strength, bending fatigue strength, anti-adhesion and high impact toughness. Heat treatment tends to have large deformation, but it is not easy to crack. This process is suitable for low carbon steel and low carbon alloy steel, such as 15, 20, 12CeNi3, 20Cr2Ni4, 20Cr, 15CrMo, 20CrMo, 20CrMnTi and other iron-based powder metallurgical materials, mainly used for wear-resisting and fatigue-resisting parts with good toughness at the core. The cost of steel used in this process is low or medium, and the investment in equipment is high. The process is shallow, generally 0.1~1.0mm, mostly used for surface hardening. The surface microstructure is (carbonitride + nitrogen-containing martensite + retained austenite), and the surface is in high residual compressive stress state. After quenching, the surface hardness reaches 60 ~ 65HRC, and the wear resistance is high. It has good contact fatigue strength, good bending fatigue strength, good anti-occlusion ability and good impact toughness.
The compound layer of the infiltrating layer is generally 0.005~0.020mm, mainly used for surface hardening. The microstructure of the surface hardened layer is surface carbonitride layer + internal nitrogen diffusion layer and the surface is in a state of high residual compressive stress. After nitrocarburizing, the surface hardness is generally 500 ~ 800HV (50 ~ 63HRC), the wear resistance is higher, the contact fatigue strength and bending fatigue strength are better, and the anti-occlusion ability is the best. The deformation tendency and cracking tendency of nitrocarburizing treatment are very small. Nitrocarburizing is usually the last step and no processing is allowed. Depending on the frequency of selection, the hardened layer is 0.8~50mm, mainly used for surface hardening. The surface structure is martensite and the surface is high residual compressive stress state. Surface hardness can reach 55 ~ 65HRC with high wear resistance, good contact fatigue strength, good bending fatigue strength and good anti-bite ability. Deformation and cracking tend is small.
After induction hardening, grinding is generally required. Flame hardened surface hardened layer is usually 1~12mm, mainly used for surface hardening. The surface structure is quenched martensite and the surface is a high compressive stress state. The surface hardness can reach 55~63 HRC, and the surface has high wear resistance, good contact fatigue strength, good bending fatigue strength and good anti-occlusion ability. Quenching deformation and cracking tendency is smaller. After flame quenching, grinding is usually done. The technology is suitable for medium carbon steel or medium carbon alloy steel. It is mainly used for parts with wearable surface.
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Post time: 02-15-2019