Transpassivity
Transpassivity is the state in which the passive protective layer of a metal loses its protective effect due to chemical decomposition or dissolution. This leads to corrosion and reduced service life.
Physical-Chemical Mechanism of Action
The passive protective layer of a metal, such as a steel edge, consists of a dense oxide layer that prevents corrosion. At elevated positive potentials, this layer can be destroyed by chemical decomposition or dissolution, leading to transpassivity.
Metallurgical Relevance & Risks in Welding
Transpassivity can occur during welding when the metal is in a corrosive environment. This leads to corrosion and a reduction in the service life of the weld. It can also cause cracks and deformations in the metal.
Workshop Practice & Action Guidelines
To avoid transpassivity, the metals should be cleaned before welding and kept in a dry environment. In corrosive environments, it is important to apply a suitable protective layer or corrosion Corrosion Inhibitor.