The Effects of Iron on the Corrosion Resistance of Zirconium Available to Purchase

Zirconium is one of the few metals that resists attack by sulfuric acid up to 75% concentration. However, selective corrosion may be found in welds at somewhat lower concentrations of sulfuric acid. It is generally believed that iron in zirconium plays an important role in degrading zirconium’s corrosion resistance. Zirconium-iron alloys were then prepared for corrosion testing. Zirconium crystal bar and pure iron were used to make Zr-50,240,460, and 800 ppm Fe alloys by using the consumable electrode technique. These ingots were also hot and then cold rolled to sheet material as required. Specimen conditions included as-cast, as-cast and heat treated, cold rolled, cold rolled and heat treated, welded, and welded and heat treated. Heat treatment was performed at 760 C for one hour. Standard immersion tests were conducted in 60, 65, 70, 75, and 77.5% H₂SO₄ at boiling temperature. Metallography was used to study the effect of heat treatment on the distribution of second phase particles. Potential differences between pure zirconium and pure iron in testing solutions were also determined. It has been found that lowering iron content can not really ensure zirconium’s corrosion resistance in sulfuric acid solutions. Heat treatment is an effective method to improve zirconium’s corrosion resistance. Corrosion rates of Zr-Fe alloys in sulfuric acid solutions can decrease up to two orders by the heat treatment method.