Corrosion-erosion behaviour of austenitic and martensitic high nitrogen stainless steels

The corrosion-erosion resistance of high nitrogen austenitic and martensitic stainless steels (HNSS) has been studied. A high temperature gas nitriding process was used in order to obtain 1.5 mm thick cases with nitrogen contents in solid solution up to 0.5 wt% for the austenitic steel and 0.4 wt% for the martensitic steel. Austenitic and martensitic samples without nitrogen were used as reference materials. The corrosion-erosion tests were performed in slurry composed of 3.5% NaCl with 10 wt.% of quartz particles. The impingement velocity and impact angle were fixed and the testing temperature was monitored. In order to establish the interactions between corrosion and erosion, we determined electrochemical parameters from potentiodynamic polarization curves in static conditions and under the influence of a slurry jet. In addition, scanning electron images were used to assess the dominant damage mechanisms and to support the results obtained by electrochemical measurements. The results showed that nitrogen addition improved the corrosion-erosion resistance in both stainless steels, owing to the strengthening effect of nitrogen in solid solution and to the increase of repassivation ability of the passive layer.