Influence of nitrogen on the cavitation erosion resistance of martensitic stainless steel

ABSTRACT The addition of nitrogen on stainless steels has been studied as an alternative to the production of materials which combine good mechanical properties, corrosion and wear resistance. Some nitrogen enrichment methods are supported by diffusive processes such as low and high temperatures nitriding. Among these processes, it is worth mentioning the Solution Heat Treatment after Plasma Nitriding (SHTPN), which consists in performing plasma nitriding, with the purpose of adding nitrogen to the material, followed by a solubilization heat treatment, which dissolves the nitrates, causing the nitrogen to appear in interstitial solid solution. In this paper, the SHTPN technique was applied to ASTM CA-6NM martensitic stainless steel. Plasma nitriding was performed at 630 °C for 3 hours and three different solubilization conditions were used (1200 °C for 30 minutes, 1200 °C for 1 hour e 1100 °C for 1 hour). The samples were analyzed through x-ray diffraction, optical microscopy and microhardness measurements in the transverse section of the sample. All samples had an increase in surface hardness of ASTM CA-6NM steel, and no stabilization of the austenite phase was observed in the surface area richer in nitrogen. The cavitation experiment was conducted according to the ASTM G32/09 standard, using the indirect method, in which the sample is not directly fixed on the vibrating horn. The cavitated area of the samples was analyzed by scanning electron microscopy. The treatment increased cavitation erosion resistance of all samples and differences were observed among the various solubilization conditions.