Effect of carbon and silicon on the structure and corrosion resistance of 18cr‐8ni cast steel in concentrated nitric acid solutions

Abstract

The solutions of nitric acid can be divided into two concentration ranges: range I from 0 to 60–70% and range II from 80 to 100%. The 18Cr‐8Ni cast steel with about 4% Si and up to 0.12% C exhibits very good corrosion resistance in concentrated nitric acid solutions (up to 98%); however, it is slightly inferior to a corresponding 18 Cr‐13 Ni grade. The investigations were concentrated on the effect of the carbon and silicon contents on structure and corrosion resistance of an 18 Cr‐8 Ni cast steel in cold nitric acid solutions. The following materials were used in these studies: a cast stainless steel of type 18Cr‐8Ni with 0.48–6.75% Si and 0.021–0.220% C. A detailed analysis of the main result shows that in cold HNO3 solutions of concentrations above 80% the silicon content in a cast steel must not be lower than 2.5‐3.0%; the 18Cr‐8Ni cast steel containing more than 4% Si and up to 0.12‐0.13% carbon is practically not susceptible to corrosion in cold HNO3 over the whole range of concentrations.