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Home » FAQs » Corrosion and corrosion resistance of stainless steel
Corrosion and corrosion resistance of stainless steel
2017-04-01 09:24:09

 1, corrosion types and definitions

In many industrial applications, stainless steel can provide people with satisfactory corrosion resistance. According to the experience, in addition to mechanical failure, the corrosion of stainless steel is mainly manifested in a serious form of corrosion of stainless steel is local corrosion (i.e. stress corrosion cracking, pitting corrosion, intergranular corrosion, crevice corrosion and corrosion fatigue). The failure cases caused by local corrosion account for more than half of the failure cases. In fact, many failures can be avoided by reasonable selection.
Stress corrosion cracking (SCC): a general term for the failure of an alloy subjected to stress in corrosive environments due to the expansion of a strong pattern. The stress corrosion cracking has a brittle fracture morphology, but it may also occur in the material with high toughness. The necessary condition for the occurrence of stress corrosion cracking is the presence of tensile stresses (whether residual or applied stresses, or both) and the presence of a particular corrosion medium. The formation and expansion of the pattern are perpendicular to the tensile stress. The stress value of the stress corrosion cracking is much smaller than that of the material when there is no corrosive medium. In the micro crack, through the grains called transgranular cracks, and cracks along the grain boundaries of the expansion graph is called intergranular crack, stress corrosion cracking when extended to a depth (the material section here, the load on the stress of it in the air, then the fracture stress) materials according to the normal crack (in ductile materials, usually through polymerization micro defects) and disconnect. Therefore, the section of the part due to the stress corrosion cracking will contain the characteristic area of the stress corrosion cracking and the "dimple" zone associated with the polymerization of the micro defects.
Pitting corrosion is a form of localized corrosion that leads to corrosion.
Intergranular corrosion: grain boundary is grain crystallographic orientation between different disorder malrelated circle city, therefore, they are all the solute segregation of steel or metal compounds (such as carbide and delta facies) advantage region precipitation. Therefore, it is not surprising that in some corrosive media, it is possible that the grain boundaries may be corroded in advance. This type of corrosion is known as intergranular corrosion, and most of the metals and alloys may exhibit intergranular corrosion in certain corrosive media.
Crevice corrosion: a form of localized corrosion, which may occur in the surface of a stagnant solution or in a shielded surface. Such a gap can be formed in the joints of metals and metals or metals and nonmetals, for example, in the form of rivets, bolts, gaskets, valve seats, loose surface deposits, and sea creatures.
Total corrosion is a term used to describe the corrosion phenomena occurring in the same way as on the surface of the alloy. When the total corrosion occurs, the material becomes thinner and thinner, and even the material corrosion failure. Stainless steel in the strong acid and alkali may present a comprehensive corrosion. The problem of failure caused by total corrosion is not so worrying, because it can be predicted by a simple immersion test or a review of the literature on corrosion.
2 corrosion resistance of stainless steel
304: it is a kind of universal stainless steel, it is widely used to produce good comprehensive performance (corrosion resistance and formability) of the equipment and parts.
301: stainless steel in the deformation showed a clear work hardening phenomenon, is used for a variety of occasions requiring high strength.
302: stainless steel is essentially a higher carbon content of the variant of the 304 stainless steel, cold rolling can make it get a higher strength.
302B: it is a kind of stainless steel with high silicon content, it has high resistance to high temperature oxidation.
303 and 303Se respectively containing sulfur and selenium free cutting stainless steel, the main requirements for cutting and surface Guanghao high occasions. 303Se stainless steel is also used to make hot upsetting parts, because in this kind of condition, the stainless steel has good machinability.
304L: a variant of 304 stainless steel with a low carbon content for use in welding applications. The lower carbon content reduces the amount of carbides precipitated in the heat affected zone near the weld, and the precipitation of carbides may lead to intergranular corrosion (corrosion) of stainless steel in some environments.
04N: stainless steel containing nitrogen, nitrogen is used to improve the strength of steel.
305 and 384: stainless steel containing high nickel, the low rate of work hardening, suitable for cold forming requirements of various occasions.
308: stainless steel used for making electrode.
309, 310, 314 and 330: stainless steel nickel, chromium content is relatively high, in order to improve the oxidation resistance and creep strength of steel at high temperature. The 30S5 and 310S are 309 and 310 stainless steel variants, the difference is only a low carbon content, in order to make the vicinity of the weld carbide to reduce the minimum. 330 stainless steel has a very high resistance to carburizing and thermal shock resistance
316 and 317: type stainless steel containing aluminum, and therefore in the marine and chemical industry in the environment of the resistance to pitting corrosion is much better than the 304 stainless steel. Among them, the type 316 stainless steel consists of variants of low carbon stainless steel 316L, nitrogen containing high strength stainless steel 316N and high sulfur free cutting stainless steel 316F.
321, 347 and 348 are titanium, niobium and tantalum, niobium stabilized stainless steel, suitable for use at high temperature welding components. 348 is a kind of stainless steel for nuclear power industry

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