What are the commonly used heat treatment processes after carbonitriding?

The common temperature of carbonitriding is 820 ~ 880℃ (low carbon steel and low alloy steel are 840 ~ 860℃). The following processes are commonly used for heat treatment after carbonitriding.

01. Direct quenching and low tempering

After carbonitriding, it is quenched directly by the temperature of the carbonitriding (820 ~ 860℃) and then tempered at low temperature 160 ~ 200℃×2 ~ 3h. This process is simple and suitable for medium and low carbon steel and low alloy steel. Generally choose oil quenching (or water quenching).

Step quenching + low temperature tempering

After carbonitriding, the temperature of the carbonitriding was 820 ~ 860℃, and the temperature was 110-200 ℃. After quenching in hot oil or alkali bath for 1 ~ 15min, the temperature was 160 ~ 200℃. The deformation of the workpiece is small, suitable for alloy steel with strict size requirements.

03. Second heating quenching and low tempering

After carbonitriding, air cooling or slow cooling in the cooling pit, and then re-heating quenching + low-temperature tempering heat treatment. It is suitable for the workpiece that needs to be machined or not quenched directly due to various reasons.

04. Direct quenching, cold treatment and low temperature tempering

After the carbonitride, it is quenched directly from the temperature of the carbonitride, then cold treated in the mesocarbon at -80 ~ -70℃, followed by low-temperature tempering to reduce the surface residual austenite, improve the hardness and stabilize the size. Suitable for alloy steel with more chromium and nickel, such as 12CrNiA, 20Cr2Ni4A, 18CrNiWA, etc.

05. Slow cooling, high tempering, and then restart

Heat quenching + low temperature tempering

After carbonitriding, air cooling or slow cooling in the cooling pit, then a high temperature tempering heat treatment (should be in the cast iron or protective atmosphere) to reduce residual austenite, and then re-heating quenching + low temperature tempering. Suitable for alloy steel with more chromium and nickel, as well as mechanical workpieces after carburizing.