The impact of cold work and hard phases on cavitation and corrosion resistance of high interstitial austenitic FeCrMnMoCN stainless steels

High interstitial austenitic stainless steels have been shown to exhibit superior mechanical properties, which include a unique combination of high strength and high toughness, due to the positive effects of the combination of carbon and nitrogen in solid solution. By the addition of molybdenum, a significant improvement of their localized corrosion resistance has been achieved. Further strengthening is necessary in the case of application in environments featuring both high mechanical loads and corrosive attack, e.g. in bearings in sea water. It can be induced by cold work hardening as well as the addition of hard phases, which in turn can affect the wear and corrosion resistance. In this study, the impact of cold work and the precipitation of niobium carbonitrides on the resistance to cavitation erosion, localized, and general corrosion has been investigated. Two newly developed high interstitial FeCrMnMoCN steels were analyzed by vibratory cavitation testing in distilled water and potentiodynamic polarization measurements in sodium chloride solution and sulfuric acid after cold work strengthening. The latter was induced by cold rolling to different degrees. Microstructural characterization was performed by hardness testing, optical, and scanning electron microscopy. The results show improved strength but decreased cavitation erosion resistance caused by the hard phases. In contrast, neither the localized nor the general corrosion resistance seem severely affected. The cold rolling leads to intense work hardening and enhanced cavitation erosion resistance, while the corrosion behavior is not significantly influenced. In the case of cavitation erosion, the improved resistance of the cold work hardened steel matrix seems to dominate the negative effect of the hard phases. The combination of high wear and high corrosion resistance, even in severely cold work strengthened condition, makes the FeCrMnMoCN austenitic stainless steels promising candidates for application in harsh environments.