What are the corrosion performance of stainless steel

Many instruments and instruments are made of stainless steel. Here we come to understand that the 'stainlessness' of stainless steel is also relative. It may also rust under certain conditions. For example, austenitic stainless steel will crystallize at 400-850°C. The tendency of inter-corrosion is prone to stress corrosion under the combined action of tensile stress and close-up corrosion media, and crevice corrosion may also occur. However, this corrosion can be caused by stainless steel in many instruments and instruments. Here we come to understand that the 'stainlessness' of stainless steel is also relative. It may also rust under certain conditions, such as austenitic stainless steel at 400-850 There is a tendency for intergranular corrosion to occur at ℃, stress corrosion is prone to occur under the combined action of tensile stress and close-up corrosion media, and crevice corrosion may also occur. But this corrosion can be avoided by taking measures. At present, stainless steel is still the magnificent protagonist on the alloy steel stage. In many industrial applications, stainless steel can provide satisfactory corrosion resistance. According to experience in use, in addition to mechanical failure, the corrosion of stainless steel is mainly manifested in: a serious form of corrosion of stainless steel is localized corrosion (ie stress corrosion cracking, pitting corrosion, intergranular corrosion, corrosion fatigue and crevice corrosion) . 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 of materials. Stress Corrosion Cracking (SCC): A general term that refers to the mutual failure of stress-bearing alloys in a corrosive environment due to the expansion of streaks. Stress corrosion cracking has a brittle fracture morphology, but it may also occur in materials with high toughness. The necessary condition for stress corrosion cracking is the existence of tensile stress (whether it is residual stress or applied stress, or both) and a specific corrosive medium. The formation and expansion of the pattern is roughly perpendicular to the direction of tensile stress. This stress value that causes stress corrosion cracking is much smaller than the stress value required for material fracture when there is no corrosive medium. At the microscopic level, the cracks passing through the grains are called transgranular cracks, and the cracks extending along the grain boundaries are called intergranular cracks. When the stress corrosion cracking extends to a certain depth (here, the cross-section of the material under load When the stress reaches its fracture stress in the air), the material will be broken according to normal cracks (in ductile materials, usually through the aggregation of microscopic defects). Therefore, the section of the part that fails due to stress corrosion cracking will contain the characteristic area of u200bu200bstress corrosion cracking and the 'dimple' area associated with the aggregation of the micro-defects. Pitting corrosion: It is a form of localized corrosion that causes corrosion. Intergranular corrosion: Grain boundaries are the boundary cities where the crystal grains with different crystallographic orientations are disordered and mixed. Therefore, they are advantageous for the segregation of various solute elements in steel or the precipitation of metal compounds (such as carbides and δ phase). District city. Therefore, in some corrosive media, it is not surprising that the grain boundaries may be corroded first. This type of corrosion is called intergranular corrosion. Most metals and alloys may exhibit intergranular corrosion in certain corrosive media. Crevice corrosion: It is a form of local corrosion, which may occur in the crevice where the solution stagnates or in the shielded surface. Such gaps can be formed at the junction of metal and metal or metal and non-metal, for example, where they meet with rivets, bolts, gaskets, valve seats, loose surface deposits, and sea creatures. General corrosion: It is a term used to describe the corrosion phenomenon that occurs on the entire alloy surface in a relatively uniform manner. When overall corrosion occurs, the material will gradually become thinner due to corrosion, and even the material will fail to corrode. Stainless steel may exhibit general corrosion in strong acids and alkalis. The failure problem caused by general corrosion is not very worrying, because this kind of corrosion can usually be predicted by a simple immersion test or by consulting the literature on corrosion.