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Types and definitions of corrosion
Sep 22, 2017

Types and definitions of corrosion
In many industrial USES, stainless steel can provide a satisfactory corrosion resistance. According to the use of experience, in addition to the mechanical failure, the corrosion of stainless steel mainly displays in: the a serious corrosion of stainless steel in the form of local corrosion (i.e. stress corrosion cracking, pitting corrosion, intergranular corrosion, crevice corrosion and corrosion fatigue). The failure cases caused by these local corrosion accounted for almost half of the failure cases. In fact, many failure accidents can be avoided through reasonable selection.

Stress corrosion cracking (SCC) : a generic term used to describe the failure of an alloy subjected to stress in corrosive environment.

Stress corrosion cracking has brittle fracture appearance, but it can also occur in materials with high toughness. The necessary conditions for stress corrosion cracking are tensile stress (whether residual stress or external stress, or both) and specific corrosive media. The formation and extension of pattern pattern is roughly perpendicular to the direction of tensile stress. The stress value that causes stress corrosion cracking is much smaller than the stress required for material fracture when there is no corrosive medium. In the micro level, through the crack in grain called transgranular crack, and the cracks along the grain boundary expansion graph called the intergranular crack, when the stress corrosion cracking extended to one depth (here, the load stress on the section of materials to achieve its fracture stress) in the air, the material is according to the normal crack (in ductile material, usually through microscopic defect aggregation) and disconnect. Therefore, the section of the parts that fail due to stress corrosion cracking will include the feature area with stress corrosion cracking and the "ductile" area associated with the polymerization of the microdefect.

Spot corrosion: a form of local corrosion that causes corrosion.
Intergranular corrosion: grain boundary of different crystallographic orientation is intergranular disorder malocclusion of world city, therefore, they are all elements of the solute segregation in steel or metal compounds (e.g., carbide and delta facies) precipitate out the favorable area city. Therefore, in some corrosive media, it is not surprising that the boundary of grain may be corrupted first. This type of corrosion is known as intercrystalline corrosion, and most metals and alloys may present intergranular corrosion in certain corrosive media.
Crevice corrosion: a form of local corrosion that may be found in the cracks of the solution or the surface of the shield. This gap can be in metal and the formation of joint of metal or metal and nonmetal, for example, with rivets, bolts, gaskets, valve seat, the surface of the loose sediment and formed into the sea creatures candle.

Total corrosion: a term used to describe the corrosion phenomenon that occurs on the surface of the entire alloy by comparing the average scoop. When total corrosion occurs, the village is gradually thinning due to corrosion and even corrosion of materials. Stainless steel may be completely corroded in strong acid and strong base. The failure problem caused by the full corrosion is not very worrying, because the corrosion can be predicted by simple immersion tests or access to the literature on corrosion.

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