Corrosion Types Of Metallic Materials
Metal materials in industrial production due to corrosion and lose the capacity is a variety of forms. Different materials in different load and different media environment, the corrosion of the main forms are the following categories:
metal exposed surface of a large area of relatively uniform corrosion, although reducing the effective area of the component and its service life, but less harmful than the local corrosion.
refers to the corrosion along the material sector, so that the connection of the grain was destroyed. This corrosion is the most harmful, it can make the metal brittle or loss of strength, percussion lost metal sound, easily lead to a sudden accident. Intergranular corrosion is the main form of corrosion of austenitic stainless steel, which is due to the grain boundary region and the crystal composition or stress are different, causing grain boundary area electrode potential caused by a significant reduction in electrode potential caused by the difference.
Stress corrosion: metal in the corrosive medium and tensile stress (external stress or internal stress) under the joint action of the phenomenon of rupture. The fracture is mainly along the crystal, but also transgranate, which is a dangerous low stress brittle fracture, in the chlorinated medium and alkaline oxide or other water-soluble medium often stress corrosion, in many equipment accidents accounted for A considerable proportion.
Point corrosion: point corrosion is occurring in the local surface of the metal surface of a corrosion damage form, after the formation of corrosion can quickly develop into the depth, and finally penetrate the metal. Point corrosion is very harmful, especially for a variety of containers is extremely unfavorable. Appear after the point of corrosion should be polished or painted in order to avoid corrosion to deepen.
Corrosion fatigue: metal in the corrosive medium and the role of alternating stress occurred under the destruction, which is characterized by corrosion pits and a large number of cracks. Significantly reduce the fatigue strength of steel, leading to premature fracture. Corrosion fatigue is different from mechanical fatigue, it does not have a certain fatigue limit, with the increase in the number of cycles, fatigue strength has been declining.
In addition to the various forms of corrosion, there are corrosion due to the role of macro batteries. For example, rivets in metal structures are different from riveted materials, dissimilar metals are welded, and hulls and propeller materials are different from corrosion due to electrode potential differences.
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