What are the commonly used heat treatment processes after carbonitriding?

The commonly used carbonitriding temperature is 820-880℃ (840-860℃ for low carbon steel and low alloy steel). The following process methods are commonly used for heat treatment after carbonitriding:

01 Direct quenching + low temperature tempering

After carbonitriding, quench directly from the quenching temperature (820-860℃), and then perform low temperature tempering 160-200℃×2-3h. This process is simple and suitable for medium and low carbon steel and low alloy steel, and can obtain satisfactory surface and core structure. Oil quenching (or water quenching) is generally selected.

02 Gradual quenching + low temperature tempering

After carbonitriding, quench directly from the quenching temperature 820-860℃ in 110-200℃ hot oil or alkali bath for 1-15min, then air cool, and then perform low temperature tempering at 160-200℃. This process has small deformation of the workpiece and is suitable for alloy steel parts with strict dimensional requirements.

03 Secondary heating quenching + low temperature tempering

After carbonitriding, air cool or slow cool in the cooling pit, then reheat quenching + low temperature tempering heat treatment. Suitable for workpieces that need to be machined after carbonitriding or are not suitable for direct quenching for various reasons.

04 Direct quenching, cold treatment + low temperature tempering

After carbonitriding, directly quench from the carbonitriding temperature, then cold treat at -80 to -70℃, and then perform low temperature tempering to reduce the residual austenite on the surface, increase the hardness, and stabilize the size. Suitable for alloy steels containing more chromium and nickel, such as 12CrNiA, 20Cr2Ni4A, 18CrNiWA, etc.

05 Slow cooling, high temperature tempering, and then reheat quenching + low temperature tempering

After carbonitriding, air cool or slow cool in the cooling pit, then perform high temperature tempering heat treatment (should be in pig iron chips or protective atmosphere) to reduce the residual austenite, and then reheat quenching + low temperature tempering. It is suitable for alloy steels containing more chromium and nickel, as well as parts that need to be machined after carbonitriding.