Abstract: Surface modification of the 25Cr2Ni4WA steel specimens with thickness of 2 mm was carried out with programable ion permeation (PIP) technology. The main processes were nitriding temperature of 530 ℃, cyanate concentration of 32%, nitriding time of 20, 40, 60 and 90 min, respectively, and after nitriding, oxygenation treatment was carried out, with oxygenation temperature of 450 ℃ and oxygenation time of 15 min. The microstructure, surface hardness, cross section hardness, tensile properties and fracture morphologies of the specimens treated by different PIP processes were analyzed. The results show that the structure of the permeation layer is composed of oxide film, loose layer, bright white layer and diffusion layer. The thickness of permeation layer increases with the extension of nitriding time, but the growth rate of infiltration layer decreases. PIP treatment can significantly improve the hardness of the specimens, in which the hardness of the specimens with nitriding time of 60 min is the highest and 2.3 times of the substrate one. After PIP treatment, the tensile properties of the specimens decrease, and the deeper the penetration layer, the more the decrease, and the specimens as a whole show ductile-brittle mixed fracture.

Key words: programmable ion permeation (PIP), nitriding process, microstructure, surface hardness