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
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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 degrees C for 15 It at a pressure of 10 mbar. Then nitrided samples are implanted with nitrogen ions to a dose of 2 x 10(17) ions/cm(2). 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 nanohardness, 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. (c) 2007 Elsevier B.V. All rights reserved.