Corrosion of AISI 316 stainless steel containing Cu and Sn in acid media

Abstract

The influence of Cu and Sn additions on the corrosion resistance of AISI 316 stainless steels has been evaluated in various acid media (boiling 50 wt-%H₃PO₄, boiling 65 wt-%HNO₃, 3 wt-%HCl at 25°C and 30 wt-%H₂SO₄ at 50°C). A kinetic study of the corrosion process was carried out using gravimetric tests. The nature of the corrosion products was analysed by SEM, X-ray mapping and X-ray photoelectron spectroscopy both before and after accelerated corrosion tests. The steels displayed high chemical resistance to the nitric, hydrochloric and phosphoric acid media. An increase in Cu and Sn concentration did not significantly affect the corrosion resistance in boiling 50 wt-% phosphoric acid, boiling 65 wt-% nitric acid or 3 wt-% hydrochloric acid. The behaviour of AISI 316 in sulphuric acid solution was greatly improved by increasing the Cu concentration, whether alone or in combination with Sn. The effect of Sn addition in decreasing the corrosion rate was minor in comparison with that of Cu.