Abstract: During the assembly process of 20Cr2Ni4A steel gimbal shaft, it was found that cracks were located at the oil hole and pin hole on the outer side of the frame. The physical and chemical analysis results show that there are suspected carburized layers and high hardness phenomenon. The simulation analysis shows that the stress values of the oil through-hole and the pin hole in the carburized and non-carburized states are different, and that of the carburized state is significantly higher than that of the non-carburized state. By quenching test, it is found that when the temperature is kept at 800 ℃ for 60 min and a higher carbon potential is applied, the surface of the 20Cr2Ni4A steel have different degrees of carburization. Based on the above analysis and production verification, it can be concluded that the cause of crack formation is the existence of carburized layer on the wall of pin hole and oil hole, and the stress reaches the cracking critical state during quenching, which leads to cracks in part of the gimbal axis.

Key words: 20Cr2Ni4A steel, gimbal axis, crack, carburized layer, quenching