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What are the forms of corrosion of stainless steel?

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2022-06-27 00:00

Stainless steel may have excellent corrosion resistance in many media, but in others, corrosion may occur due to its low chemical stability. Therefore, stainless steel cannot be resistant to all media. In numerous industrial applications, stainless steel can provide the correct anti-corrosion function for modern people. According to experience, the corrosion of stainless steel is mainly manifested in the following aspects in addition to mechanical failure: the serious corrosion form of stainless steel is localized corrosion (ie stress corrosion cracking, pitting corrosion, intergranular corrosion, corrosion fatigue and crack corrosion). The failure cases caused by localized corrosion accounted for more than half of the failure cases. In fact, many variations can be avoided by judicious choice of materials. According to the corrosion mechanism, metal corrosion can be divided into three types: special corrosion, chemical corrosion and electrochemical corrosion. In life and engineering, metal corrosion is mostly electrochemical corrosion. Stress Corrosion Cracking (SCC): A general term referring to the interaction of stress corrosion alloys under corrosive conditions due to the propagation of severe cracks. Stress corrosion cracking is characterized by brittle fracture, but can also occur in highly ductile materials. The preconditions for stress corrosion cracking are tensile stress (residual stress or external stress, or both) and the presence of specific corrosive media. The formation and expansion of the graph is perpendicular to the purpose of the tensile stress scale. The stress value that causes stress corrosion cracking is much smaller than the stress required to fracture the material in the absence of a corrosive medium. The cracks that pass through the grain are called transgranular cracks, and the cracks that propagate along the grain boundaries are called intergranular cracks. When a stress corrosion crack propagates to its depth (here, the stress on the cross-section of the loaded material reaches its breaking stress in air), the material will behave as a normal crack (presumably in ductile materials, usually by aggregation of microscopic defects) And broken. Therefore, a cross-section of a part that fails due to stress corrosion cracking will contain both characteristic areas of stress corrosion cracking and recessed areas associated with microdefect aggregation. Pitting corrosion: Pitting corrosion refers to metal materials with high segregation, no erosion or light and fine local erosion in general. The common corrosion point size is less than 1.00mm, and the depth is often larger than the general hole diameter. There are shallow pits in light, and even perforations in heavy. Intergranular corrosion: The intergranular boundary is the boundary of disordered dislocations between grains of different crystal orientations. Therefore, they are favorable regions for the segregation of various solute elements or the precipitation of metallic compounds such as carbides and delta phases in steel. Therefore, in some corrosive media, the intergranular boundaries may be eroded first, but one after the other. This type of corrosion is called intergranular corrosion. Intergranular corrosion occurs in most metals and alloys in specific corrosive media.

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