Taking the constant velocity universal joint drive shaft of a car under torsional load as an example

a heat treatment-hardness gradient design method based on the strength gradient was proposed.That was

the ideal strength gradient distribution was obtained according to the maximum stress and its gradient distribution of the dangerous section of the structure.Then

the ideal hardness gradient distribution was obtained from the hardness-strength conversion relation.Finally

the actual hardness gradient was matched according to the ideal hardness gradient distribution combined with the material end quenching curve.The hardness gradient matching of the drive shafts made of 40Cr

UC2 and 38B3 materials was carried out respectively

and the static strength test of the transmission shaft after the hardness gradient matching was carried out.The test results show that the static strength of the transmission shafts made of different materials can meet the test requirements after the heat treatment-hardness gradient matching.