Improving the wear resistance of heavy-duty gear steels by cyclic carburizing

In this work, we adopted a cyclic carburizing method to improve the wear resistance and antifriction properties of 17CrNiMo6 heavy-gear steel. The possibility of achieving cyclic carburization is described in terms of diffusion thermodynamics and carburization kinetics. The results indicated that the phase transmation during cyclic carburization can significantly refine the microstructure, and the change of carbon concentration provides a guarantee for cyclic carburization to obtain a high hardness, dense and thick hardened layer. As the number of cycles increases, the friction coefficient of surface wear of the carburized layer at room temperature gradually decreases, while the wear rate after surface removal of 50 µm is significantly diminished and wear rate was the minimum (0.69 ×10-14 mm3N-1m-1) after 4 cycles carburization. At 100 ℃, the oxidation of wear scars on the surface of carburized layer increases. In the case of oil lubrication, the friction coefficient of the cyclic carburized layer was clearly declined. Wear analysis revealed that the wear mechanism of the circulating carburized layer was mainly abrasive wear and oxidation wear with a small amount of adhesive wear.