Influence of Pickling High Alloyed CrNi-Steels and Nickel Base Alloys with Citric Acid on the Composition of their Tarnish Oxides

 Extra-ordinary mechanical features and high corrosion resistance are essential qualities of CrNi-steels and nickel base alloys. The corrosion resistance of these materials fundamentally depends on their surface conditions. Tarnish colours and welding scale, formed during thermal treatment or joining, are removed by pickling components made of these alloys with sulphuric acid, nitric acid and hydrofluoric acid as well. By this kind of surface refinement several million tons per annum of aggressive waste waters are produced, that cause high environmental risks and not acceptable employee endangerings. Therefore, a project was promoted by the DECHEMA e.V. to replace hydrofluoric acid by organic complexing agents. The related surface analytical examinations are reported in this publication.