A comparative study of single and duplex treatment of martensitic AISI 420 stainless steel using plasma nitriding and plasma nitriding-plus-nitrogen ion implantation techniques

Martensitic AISI 420 is a high chromium mold steel which is suitable for tools for molding corrosive plastics. In this study, micro-pulsed plasma nitriding and plasma nitriding + nitrogen ion implantation techniques have been used to improve the surface hardness and tribological properties of AISI 420 substrates. Firstly polished-AISI 420 samples are nitrided at 530 °C for 15 h at a pressure of 10 mbar. Then nitrided samples are implanted with nitrogen ions to a dose of 2 × 1017 ions/cm2. Mechanical characterization of both of the modified and unmodified samples has been carried out by means of nano-hardness, wear resistance, friction coefficient and surface roughness measurements. It is found that the nano-hardness, wear resistance, friction coefficient and surface roughness values improve 1.6, 3.5, 1.4 and 10 times for plasma nitrided samples, and 2.0, 4.6, 1.1 and 9 times for plasma nitrided-plus-N+ ion implanted samples, respectively, in comparison with unmodified AISI 420 samples. Both the plasma nitriding process and the plasma nitriding-plus-N+ ion implantation treatment sample results are also compared. The improvement of the samples modified using nitriding-plus-N+ ion implantation process is found to be better than that of samples modified by the nitriding process.