In many industrial applications, stainless steel can provide satisfactory corrosion resistance. According to the use of experience, in addition to mechanical failure, corrosion of stainless steels mainly displays in: stainless steel is a kind of serious corrosion is a form of localized corrosion (i.e., stress corrosion cracking, corrosion, intergranular corrosion, corrosion fatigue and crevice corrosion ). These localized corrosion caused by the failure cases accounted for almost half of the above failures. In fact, many failure accidents can be avoided by reasonable selection of the.
Stress corrosion cracking ( SCC ): refers to withstand the stress of alloy in corrosion environment due to strong lines and the expansion of alternate failure of a general term. Stress corrosion cracking of brittle fracture surface, but it may also occur in the high toughness of materials. Stress corrosion cracking is the necessary condition to tensile stress (whether residual stress as well as the applied stress, or the two have both at the same time ) and specific corrosion medium. Type pattern formation and extend generally perpendicularly to the direction of the tensile stress. This leads to stress corrosion cracking stress value, than no corrosive medium exists when the material fracture need to stress the value of much smaller. At the micro level, through the grain crack called transgranular crack along the grain boundaries, and the expansion of crack called intergranular crack stress corrosion cracking, when extended to its depth when (here, the load bearing material section on the stress to reach it in the air in the fracture stress, the material ) according to the normal crack ( in the ductile material, usually through microscopic defects in polymerization and disconnect ). Therefore, due to stress corrosion cracking and invalidation of parts of the cross, will contain the stress corrosion cracking of characteristic region and has defects of polymerization is linked to the " dimple " area.
Point corrosion: is a leading cause of corrosion localized corrosion form.
Intergranular corrosion: grain boundary is the crystallographic orientation of different grain disorders malocclusion circle city, therefore, they are a variety of solute segregation in steel or metal compounds (such as carbide andδ phase ) precipitation the advantageous area of city. Therefore, in some corrosion media, grain boundary corrosion may go ahead of the rest is be not at all surprising. This type of corrosion is called the intergranular corrosion, most metals and alloys in particular corrosion medium may exhibit intergranular corrosion.
Crevice corrosion localized corrosion: is a form, it may happen in solution stagnant gap or shielding surface. Such a gap in metal to metal or metal and non metal junction formation, for example, in the rivet, bolt, gasket, and the valve seat, loosening of the surface sediments and marine organisms that formed with candle.
Total corrosion: is used to describe the alloy surface in order to compare all spoon way occurs corrosion phenomenon terminology. When the comprehensive corrosion, materials due to corrosion and gradually becomes thinner, and even material corrosion failure. Stainless steel in acid and alkali corrosion may present a comprehensive. Comprehensive corrosion failure problems do not worry, because, this kind of corrosion can often through simple immersion test or inspection of corrosion of data and predict it.
2, all kinds of stainless steel corrosion resistance
304 stainless steel is one kind of universal, which is widely used in production requirements of good comprehensive performance ( corrosion resistance and moldability ) equipment and parts.
301 stainless steel during deformation showing significant work hardening phenomenon, be used to require a higher intensity of various occasions.
302 stainless steel is essentially carbon content is higher 304 stainless steel variants, through a cold can make its obtain high strength.
302B is a silicon containing high content of stainless steel, it has high resistance to high temperature oxidation property.
303 and 303Se respectively with sulfur and selenium free-cutting stainless steel, used for the main requirements of easy cutting and surface K. ho degrees high occasions. 303Se stainless steel is also used to make need hot upsetting machine, because in this kind of condition, the stainless steel has good heat processing.
304L carbon content is low 304 stainless steel variants, used to weld occasion. Low carbon content in weld heat affected zone near the precipitated carbide minimized the precipitation of carbide, and may result in stainless steel in some environments of intergranular corrosion ( welding erosion ).
04N is a kind of nitrogen containing stainless steel, nitrogen is added to increase the strength of steel.
In 305 and 384 stainless steel containing high nickel, its working hardening rate low, suitable for cold forming of high requirements of various occasions.
308 stainless steel for the production of welding rod.
309, 310, 314 and 330 stainless steel nickel, chromium content is higher, in order to improve the steel in high temperature oxidation resistance and creep strength. While 30S5 and 310S are 309 and 310 stainless steel variants, the difference is the low carbon content, as is the adjacent to the welds the precipitated carbide minimized. 330 stainless steel has a particularly high carburizing resistance ability and resistance to thermal shock.
316 and type 317 stainless steel containing aluminum, thus in the ocean and chemical industrial environment in anti corrosion ability greatly superior to 304 stainless steel. Among them, type 316 stainless steel by variants include low carbon stainless steel 316L, nitrogen containing high strength stainless steel 316N and sulfur content high stainless steel 316F.
In 321, 347 and 348 respectively with titanium, niobium and tantalum, niobium stabilized stainless steel, suitable for use under high temperature welding components. 348 is a suitable for nuclear power industry of stainless steel, tantalum and the drilling of a certain limit.