High-temperature tempering of steel 20Kh2N4A after deep carburizing

Conclusions

• 1. Single tempering at 580–600\dg is sufficient for complete decomposition of retained austenite in steel 20Kh2N4A with a carbon concentration in the case of 0.8% or less or with cooling after carburizing at 30\dg or lower.

  Incomplete cooling from the carburizing temperature and a carbon content of the case larger than 0.8% require double tempering with intermediate cooling to 30°.

• 2. To ensure the possibility of machining the parts, it is necessary that they be tempered at 650\dg to reduce the hardness before low-temperature quenching.

• 3. To obtain a case after high-temperature tempering that consists of pearlite with evenly distributed carbides (without cementite platelets), it is necessary that carburizing be conducted at a temperature no higher than 950\dg and that a steel with fine grains be used for this purpose.

• 4. The workability of carburized parts (especially after deep carburizing) depends to a considerable extent on the conditions of high-temperature tempering.

• 5. The quality of high-temperature tempering can be determined from the microstructure (sections of retained austenite cannot be permitted).

  The homogeneity of pearlite should match the special scale developed at the All-Union Scientific Design-Engineering Institute of the Bearing Industry (VNIPP).