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

Abstract

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.