Abstract: Effects of rare earth elements on microstructure and hardness of 42CrMo steel under nitriding heat treatment were investigated. The results show that after nitriding treatment, the white layer of the 42CrMo steel added with rare earth elements, is obviously thickened, the surface hardness and effective hardening layer depth are significantly increased, and the pulse structure of the permeability layer is improved. It shows that the rare earth microalloying has an obvious effect on the nitriding process of the 42CrMo steel, it can accelerate the diffusion of nitrogen atoms, and increase nitriding speed.

Key words: gas nitriding, microalloying, 42CrMo steel, hardness of nitrided layer, rare earth