Environmentally Assisted Cracking: Concerns for Cadmium Replacement

Abstract

Abstract : Recently, cadmium replacement has become the topic of an Environmental Security Technology Certification Program. As a direct result of this program, replacement coating systems will be developed and scrutinized. A fundamental starting point for corrosion-resistant coatings development work consists of a target for the overall chemical potential (galvanic series) and pH of the coating system and the substrate. This work developed the data necessary to determine the target for several high strength steels. Hydrogen is widely recognized as having a detrimental embrittling effect on high strength materials, especially high strength steel. Many of these materials show a strong dependence of hydrogen on chemical potential and pH. This work focused on determining the effect of hydrogen on the environmentally assisted cracking critical stress intensity values (K(sub IEAC)) for several common high strength structural steels. Evaluating the effects of hydrogen on K(sub IEAC) over a range of chemical potential and pH will make the optimum chemical potential and pH evident for each material. It then becomes possible for the coating system designers to tailor a prospective coating system around those optimum values with the various substrates. If a system were designed at the optimum values for chemical potential and pH, the substrate material would be at the most tolerant conditions for resisting detrimental hydrogen effects, regardless of the source of the hydrogen.