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The corrosion types and definition
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In many of the industrial use, stainless steel can provide people satisfied with the corrosion resistance performance. According to use experience, in addition to the mechanical failure, stainless steel corrosion mainly displays in: stainless steel of a serious corrosion form is local corrosion (i.e. the stress corrosion cracking, point corrosion, inter crystal corrosion and corrosion fatigue and crevice corrosion). These local corrosion in the case of the failure of accounts for almost half the cases of failure. In fact, many failure accidents can be through the reasonable selection and to avoid.
Stress corrosion cracking (SCC) : refers to the stress of the alloy in corrosive environment due to the expansion of the fierce lines and alternate failure of a general term. The stress corrosion cracking have brittle fracture morphology, but it can also occur in high toughness of material. The stress corrosion cracking occurred the necessary condition is to have stress (whether residual stress or applied stress, or both) and specific corrosion medium existence. The formation and extension of grain roughly and tensile stress direction perpendicular. This lead to stress value of the stress corrosion cracking, than when there are no corrosive medium material faults need to stress value of the much smaller. In on microscopic, across the grain of the crack called wear crystal crackle, and expanding the graph grain boundaries along the crack the intergranular called crack, when the stress corrosion cracking extended to a depth (here, loads of materials on the cross to the stress of it in the air of the fracture stress), the material is the normal crack (in the toughness materials, usually through the microscopic defect of the polymerization) and disconnect. Therefore, because of the failure of the stress corrosion cracking and the section of parts, will contain a stress corrosion cracking of regional characteristics and has the defect of the polymerization are associated with the "toughening nest" area.
Some corrosion: is a lead to the corrosion of the local corrosion form.
Intergranular corrosion: between grain boundary is crystallography orientation of different grain disorder or wrong between world city, therefore, they are all kinds of solute segregation in steel elements or metal compounds (such as carbide and δ phase) precipitation exhalation the advantageous area of the city. So, in some corrosive medium, grain boundary between may first be corrosion but not surprising. This type of corrosion intergranular corrosion is called, most of the metal and alloy in particular the corrosive medium of intergranular corrosion may be present.
Crevice corrosion: is a form of local corrosion, it can get the solution of stagnation in aperture of the surface or shielding inside. Such gaps in metals and metal or metal and nonmetal locations at the form, for example, in and rivet, bolts, gasket, seat, loose surface sediment and sea creatures into the place of candle formation.
Comprehensive corrosion: is used to describe the whole alloy on the surface of all the way to compare what happened the terms of corrosion phenomena. When there is a comprehensive corrosion, village due to corrosion and material gradually become thinner, and even material corrosion failure. Stainless steel in acid and alkali corrosion may be present in full. Comprehensive corrosion caused by failure problem is not how worrying, because, the corrosion can usually through simple soak test or consult literature material and corrosion predict it.
2. All kinds of stainless steel corrosion resistance performance
304 is one kind of universal stainless steel, which is widely used for requirements of making good comprehensive performance (corrosion resistance and formability) equipment and parts.
301 stainless steel in deformation presents the obvious when the work-hardening, be used to demand higher strength of all sorts of circumstances.
302 stainless steel is essentially carbon content of higher 304 stainless steel varieties, through the cold rolling mill can make it to gain higher strength.
302 B is a kind of content of silicon higher stainless steel, it has high resistance to high temperature oxidation performance.
303 and 303 Se is containing sulfur and selenium were cutting stainless steel, main requirements for cutting and table and light hao degree is high occasion. 303 Se stainless steel also used to make need hot heading machine parts of, because in this kind of condition, the stainless steel has good heat processing.
304 L is carbon content lower 304 stainless steel varieties, used for welding occasion. Low carbon content in near the welding line of that heat affected zone of the precipitation to minimize carbide, and separation of carbide could lead to stainless steel in some environment intergranular corrosion produced (welding erosion).
04 N is a kind of nitrogen stainless steel, add nitrogen is in order to improve the strength of steel.
305 and 384 stainless steel contains high nickel, its processing sclerosis rate is low, suitable for cold forming sex requirement of high on various occasions.
308 stainless steel used to make rod.
309, 310, 314 and 330 stainless steel of nickel, chrome content is higher, to improve the steel under high temperature antioxidant properties and creep strength. And S5 and 310 S but 30 309 and 310 variations of the stainless steel, the carbon content of different is low, in order to make the separation of carbide weld nearby minimized. 330 stainless steel has a special high anti-permeability carbon ability and thermal shock resistance.
316 and 317 stainless steel contains aluminium, thus in the ocean and chemical industry environment of corrosion resistance points better than 304 stainless steel ability greatly. Among them, 316 stainless steel by varieties including low carbon stainless steel 316 L, nitrogen high strength stainless steel 316, N and close of sulfur in higher cutting stainless steel 316 F.
In 321, 347 and 348 respectively is in titanium, niobium and tantalum and niobium stabilization of the stainless steel, suitable for high temperature of welding components use. 348 is a kind of applicable to the nuclear power industry stainless steel, tantalum and drill for the reasonable to have the certain restrictions..
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