THE SURFACE-COMPOSITION AND CORROSION BEHAVIOR OF AISI-304 STAINLESS-STEEL AFTER IMMERSION IN 20-PERCENT HNO3 SOLUTION

This work describes results comparing the influence of surface treatments (grinding, and immersion in 20% HNO3 solutions and distilled water) on (i) the corrosion resistance in 10% FeCl3 and 3.5% NaCl solutions, and (ii) the composition of passive films of AISI 304 stainless steel. Both immersion in HNO3 and in distilled water cause an increase in Cr concentration in the films. The acid treatment produces a more intense attack in 10% FeCl3 and increases the corrosion rate in 3.5% NaCl, whereas immersion in distilled water produces no changes in corrosion behaviour. It is argued that the improvement in pit initiation resistance often observed with stainless steel after a HNO3 treatment is essentially associated with removal of sulphide inclusions, and not with Cr enrichment in the film.