Correlations between microstructure and surface properties in a high nitrogen martensitic stainless steel

Nitrided and tempered AISI 410S stainless steel was tested under corrosion-erosion conditions and compared to conventional AISI 420 martensitic stainless steel. The corrosion-erosion resistance of the nitrided specimens was higher than that of the AISI 420 steel when tempered at 200 degreesC, but it decreased with tempering temperature in the range between 200 and 600 degreesC. The higher corrosion-erosion resistance of the high-nitrogen steel was credited to a more homogeneous distribution of chromium in martensite and a lower number of coarse second-phase particles, especially for tempering temperatures below 550 degreesC. The hexagonal epsilon-nitride was identified in specimens tempered at 200 degreesC, while finely distributed cubic CrN nitrides were observed in specimens tempered between 400 and 600 degreesC. Hexagonal Cr2N nitrides were observed at 550 and 600 degreesC. These coarse, high-chromium precipitates were responsible for the drop in corrosion resistance of the nitrided specimens. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.