THE MECHANISM OF THE END GRAIN CORROSION OF STAINLESS-STEEL IN NITRIC-ACID SOLUTIONS AND ITS PREVENTION

Austenitic stainless steels with low carbon content have good corrosion resistance in nitric acid solutions. However, these steels are susceptible to corrosion in nitric acid solutions which contain highly oxidizing ions such as Cr2O72-, Ru-n+ etc. One of these is called ''End Grain Corrosion'' or ''Tunnelling Corrosion''. In this type of corrosion, a part of the cross-section of plate is preferentially attacked severely. In this study, it was clarified that the end grain corrosion was caused by intergranular corrosion (IGC) at phosphorus segregated areas which were induced during casting. And it was also found that the decrease of P content less than 0.015%, and heat treatments to reduce segregation of P were very effective to prevent the end grain corrosion.