Role of corrosion inhibitors or grain boundary corrosion control of Cr-Mn-Cu stainless steel in pickling solution

A study has been made to investigate the effect of various additives on the scale and metal dissolution of stainless steel in 6.8% HNO3 + 0.9%HF + 3.5% H2SO4 solution. The additives namely Urea, methanol, boric acid, phosphoric acid and sodium chloride, were chosen for study as they are reported to have beneficial effect on oxide dissolution of other metals and alloys and also in some cases exhibit corrosion inhibitive effect. Potentiostatic polarization, mass loss, optical microscopic and scanning electron microscopic studies have been performed to assess the performance and to understand the mechanism of action of the above additives. Amongst the reagents studied, phosphoric and boric acids are found to have the most promising results. During the dissolution of the alloy, it is observed that enriching of Cu takes place near the grain boundaries.