Thu, 02 Aug 2018 02:02:41 +0000
Vacuum carburizing heat treatment
The critical phase change points Ac1 and Ac3 of steel are moved down due to the infiltration of nitrogen, which can reduce the quenching temperature appropriately and provide the possibility of further reducing the quenching deformation. The infiltration of nitrogen also increases the hardenability, so in addition to alloy steel, carbon steel can also implement carbon and nitrogen co-infiltration and oil quenching treatment, so as to improve the hardness and surface wear resistance.
1) the leachate used by the technology is: refined ammonia gas + kerosene; Potassium absorbent atmosphere + fusible gas + ammonia gas; Nitrogen base atmosphere + methanol + propane + ammonia, etc.
2) co-infiltration mechanism: no matter which infiltrant contains oxygen-containing media, C and N simultaneously infiltrate into the metal. Chemical reaction of the metal surface and diffusion of C and N into the metal interior are balanced. According to the co-infiltration results, the infiltration layer has a grain boundary oxidation layer.
3) pre-pumped vacuum carburizing technology: from the perspective of C and N sources and the use of infiltrating agents, the mechanism and results of carburizing are the same as that of gas carburizing, and there are still oxygen-containing media in the infiltrating agent. There is still a surface grain boundary oxidation layer in the infiltration layer, which cannot be eliminated. However, due to the use of vacuum exhaust and sealing technology, this method not only shortens the process, improves the efficiency, slightly reduces the use of infiltrating agent, but also reduces the depth of the oxidation layer at the grain boundary.
The new technology of injecting propane and ammonia into the vacuum furnace can improve the surface hardness of alloy steel and carbon steel, and the control of the process in vacuum can affect the carbon and nitrogen concentration of metal surface and the depth of infiltration layer. The characteristics of the technology: in the vacuum furnace, the workpiece is heated to the carburizing temperature, carburizing and diffusing through the carburizing gas, then reducing the temperature, and then entering the nitriding gas into the vacuum furnace for nitriding. Carbon steel or surface-hardened steel with this new technology can obtain the required surface hardness, depth and toughness.