Influence of pickling high alloyed CrNi-steels and nickel base alloys withcitric acid on the composition of their tarnish oxides

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