Abstract: Effect of titanium on conventional plasma nitriding process of 42CrMo steel under different nitriding time was studied. The microstructure and hardness of the nitrided layers on specimen under different nitriding processes were characterized and analyzed. The results show that the surface hardness and nitrided layer depth of the titanium-catalyzed plasma nitrided specimen are obviously higher than those of the conventional plasma nitrided specimen. Under the process condition of 535 ℃×3 h, the surface hardness and the depth of the nitrided layer reach 887.4 HV0.2 and 400 μm, respectively. The addition of titanium promotes the infiltration and diffusion of nitrogen, and generates high hardness compound TiN on the surface. Compared with the conventional plasma nitriding under the same nitriding time, the surface hardness and the depth of the nitrided layer are increased by 60 HV0.2 and by 80 μm, respectively, and the nitriding efficiency is increased by about 25%. The titanium-catalyzed plasma nitriding process has more significant advantages than conventional plasma nitriding, which not only improves the microstructure and hardness of the nitrided layer, enhances the nitriding effect, but also improves the nitriding efficiency and significantly shortens the nitriding cycle.

Key words: 42CrMo steel, Ti-catalyzed plasma nitriding, microstructure, hardness