Abstract: 8620H steels with low hardenability and high hardenability were prepared by modifying chemical composition, and application on the intermediate shaft of the auxiliary box was studied. The results show that under the same heat treatment process, the high hardenability 8620H2 steel has a deeper effective hardened layer depth and higher core hardness than that of the low hardenability 8620H steel auxiliary box intermediate shaft. In addition, the heat treatment work station take time of the low hardenability 8620H steel auxiliary box intermediate shaft is 25.5 min, while that of the high hardenability 8620H2 steel can be significantly decreased to 20.5 min. It should be noted that, when developing the heat treatment process for the part of the 8620H2 steel with high hardenability, the technical indexes of heat treatment and the accuracy of tooth after heat treatment should be comprehensively considered.

Key words: hardenability, refined grading, heat treatment, tooth accuracy