What are the main processes of carburizing and quenching

Carburizing and quenching is a common heat treatment process for metal materials. It can make the surface of carburized workpiece obtain high hardness and improve its wear resistance. The process mainly includes low temperature tempering, precooling direct quenching, primary heating quenching, carburizing high temperature tempering, secondary quenching cold treatment, induction heating after carburizing and other processes.

Low temperature tempering can't refine the grain of steel, the quenching deformation of workpiece is larger, the amount of retained austenite on the surface of carburized alloy steel is more, and the surface hardness is lower. Simple operation and low cost are used to deal with the parts with little deformation and impact load, which are suitable for gas carburizing and liquid carburizing processes.

Pre cooling direct quenching and low temperature tempering, the quenching temperature is 800-850 ℃. It can reduce the quenching deformation of workpieces, the amount of retained austenite in the layer can also be slightly reduced, and the surface hardness is slightly increased, but the austenite grains have not changed. Simple operation, small oxidation, decarburization and quenching deformation, widely used in fine grain steel manufacturing tools.

The quenching temperature is 820-850 ℃ or 780-810 ℃. For those with higher requirements on the strength of the core, 820-850 ℃ quenching is used, the core is low carbon m, and the surface hardness is high. 780-810 ℃ quenching can refine the grains. It is suitable for carbon steel and low alloy steel workpieces, gas and liquid carburized coarse grain steel, some workpieces that are not suitable for direct quenching after carburizing and parts that need machining after carburizing.

The secondary quenching and low temperature tempering mainly improve the structure of the infiltrated layer. When the requirements for the core performance are not high, it can be quenched between ac1-ac3 of the material, and when the requirements for the core performance are high, it should be quenched above AC3. It is mainly used for important carburized parts with high mechanical properties, especially for coarse grain steel. However, after carburizing, it needs two times of high temperature heating, which makes the workpiece deformation and oxidation decarburization increase, and the heat treatment process is more complex.

When the temperature of secondary quenching and cold treatment is higher than that of AC1 or AC3, the surface of high alloy has more residual, and the transformation is promoted by cold treatment, so the surface hardness and wear resistance are improved. It is mainly used for high alloy steel workpiece without machining after carburizing. Induction hardening and low temperature tempering after carburizing. It can refine the permeable layer and the structure near the permeable layer. The quenching deformation is small, and the parts that are not allowed to harden do not need to be impervious in advance.

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