Deep carburising and quenching distortion analysis of heavy-duty hardened gear

For heavy-duty hardened gear with the large module, deep carburising and quenching are necessary to achieve surface strengthening. Deep carburising involves prolonged cycles, making it challenging to achieve the desired case depth and carbide morphology. Meanwhile, quenching distortion is prone to occur and difficult to control. This study focused on the difficulties of deep carburising and quenching processes, and combining a numerical analysis model of carburising-quenching, the deep carburising and quenching distortion of the heavy-duty slewing rack were analysed. The multi-stage cyclic carburising was designed and performed on the rack. It effectively reduced the carbon potential on the surface of the rack by increasing multiple diffusion stages and reducing the boost time. By comparison with the conventional two-stage carburising, the multi-stage cyclic carburising would achieve a carburised layer of 5.5 mm on the rack without generating network carbides. Meanwhile, the concave bending of the quenched rack decreased from 2.74 mm to 1.08 mm by optimising the process and employing reverse deformation method, which met the technical requirements of the rack.