Influence of Microelement Addition on the Pitting Corrosion Resistance of Nitrogen-Containing Stainless Steel

To improve the performance of stainless steel, we subjected solidstate steel to a nitrogen absorption treatment. In the fabrication process, a commercially available highchromium ferritic stainless steel (Fe22Cr1Mo) was heattreated at 1423 K in a nitrogen atmosphere. The heattreatment transformed the ferric phase into the austenite phase. This process loaded over 1 mass of nitrogen into the steel material. Most of the added nitrogen formed a solid solution in the matrix, but a minor portion formed nitrides with the very small quantities of elements such as titanium and aluminum that preexisted in the steel. The nitrogencontaining steels were then analyzed by pitting potential measurements and ferric chloride corrosion examination. The pitting corrosion resistance of Fe22Cr1Mo1N exceeded that of conventional materials such as Fe18Cr12Ni and Fe22Cr1Mo. However in the ferric chloride corrosion tests, pits developed in Fe22Cr1Mo1N at temperatures above 323 K. These pits were possibly initiated at the sites of minute nitride resulting from the nitrogen absorption process. [doi:10.2320/jinstmet.J2015004]