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Corrosion resistance of stainless steel
Jul 20, 2017

Types and definitions of corrosion
In many industrial applications, stainless steel can provide a satisfactory corrosion resistance. According to the experience of the use, in addition to mechanical failure, stainless steel corrosion is mainly manifested in: Stainless steel a serious form of corrosion is local corrosion (that is, stress corrosion cracking, pitting corrosion, intergranular corrosion, corrosion fatigue and crevice corrosion). The failure cases caused by these localized corrosion almost accounted for more than half of the failure cases. In fact, many failure accidents can be avoided through reasonable selection.
Stress corrosion Cracking (SCC): A general term used to refer to an alloy subjected to stress to alternate failure due to the expansion of strong lines in corrosive environments.
Stress corrosion cracking has brittle fracture morphology, but it may also occur in high toughness materials. The necessary conditions for the occurrence of stress corrosion cracking are tensile stress (whether residual stress or external stress, or both) and specific corrosive medium. The formation and expansion of the pattern are roughly perpendicular to the tensile stress direction. The stress value which leads to the stress corrosion cracking is much smaller than the stress value needed for material fracture without corrosive medium. In microscopic, the crack through the grain is called the crack, and the crack along the grain boundary enlargement is called the intergranular crack, when the stress corrosion cracking expands to one depth (here, the stress on the cross-section of the material under load reaches its breaking stress in the air), the material is broken down by normal cracks (in ductile materials, usually through the polymerization of microscopic imperfections). Therefore, the section of the part which is broken due to the stress corrosion cracking will contain the characteristic area of the stress corrosion cracking and the "dimple" area associated with the micro-defect polymerization.
Point corrosion: It is a localized corrosion form that causes corrosion.
Intergranular Corrosion: intergranular boundary is a boundary city with different crystalline orientations, which is a favorable region for the segregation of solute elements or metal compounds (such as carbides and δ facies) in steels. Therefore, it is not surprising that in some corrosive media, the grain boundary may be corroded in advance. This type of corrosion is known as intergranular corrosion, and most metals and alloys may exhibit intergranular corrosion in a particular corrosive medium.
Crevice corrosion: It is a form of localized corrosion that may be made entirely in a stagnant crevice or in a shielding surface. Such gaps can be formed between metals and metal or metal or non-metallic junctions, for example, in the form of rivets, bolts, gaskets, seat, loose surface sediments, and marine bio-junction Candle.
Total corrosion: A term used to describe corrosion phenomena occurring in a way that is compared to a spoon on the surface of an entire alloy. When full-scale corrosion occurs, the material of the village becomes thinner due to corrosion and even the corrosion of materials is ineffective. Stainless steel may exhibit total corrosion in strong acids and alkalis. The failure problem caused by total corrosion is not a cause for concern, because this corrosion can usually be predicted by simple immersion tests or by consulting the literature on corrosion.

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