Influence of Copper in Super Duplex Stainless Steels on Iso-Corrosion Curves in Hydrochloric Acid and Dilute Sulfuric Acid

摘要

Iso-corrosion curves of super duplex stainless steels have been discussed over the years. It has earlier been shown that the test method, especially whether activation has been performed or not, has a large influence on the results. Some have claimed that addition of copper has a beneficial effect on super duplex stainless steels in hydrochloric acid and sulfuric acid. However, there have been uncertainties about the magnitude of the claimed effect since the same test method has not been used in all investigations. In this work experimental heats of 25% chromium super duplex stainless steel were investigated with different copper contents between 0.02 and 2.01 weight-%. In order to maintain similar ferrite content the nickel content was adjusted but the rest of the elements remained constant. The uniform corrosion resistance was investigated with mass loss by immersion testing with activated specimens in both hydrochloric acid and sulfuric acid. The results indicate that copper addition has no beneficial effect on the iso-corrosion curves in hydrochloric acid. On the contrary, the results indicate that the two heats with highest copper content had a lower corrosion limit. In dilute sulfuric acid, with up to 40 weight-% sulfuric acid, copper was also found have either a negligible or a detrimental effect on the iso-corrosion curves.