Sonderflle der Korrosion der Metalle. Die mechanischen Eigenschaften der Sthle wissenschaftliche Grundlagen und Forderungen der Praxis

Under the earthly atmosphere conditions, i. e. in water or in oxygen, the technically important metallic materials are thermodynamic unstable. Their more or less slow destruction especially by water and oxygen by chemical and electrochemical reactions is called corrosion. The high stability against corrosion of a certain class of metals depends upon the formation of reaction products at the surface which separate metal and the agressive medium. By local destruction of these surface films special cases of corrosion are caused which lead to localised rapid and at the beginning frequently unnoticed destruction of constructions. If the destruction of the surface films is the result of a local chemical attack pitting corrosion appears. In- vestigations have shown that the speed of the growth of pits corresponds with thc corrosion of the active metal, i. e. the metal free of surface films. Furthermore the surface films may be locally destructed by yielding. This is the reason of the frequently noticed preferred attack of slip bands in de- formed metals. If yielding of a metal occurs in a specific corrosion medium the relative velocities of rupture and repair of surface films can lead to the formation of cracks by localised anodic dissolution which can penetrate into the metal with high speed. The conditions for the appearance of this kind of corrosion, the so-called stress corrosion cracking, are discussed by means of own measurements and the literature.