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Various types of stainless steel are identified by their microstructure or predominant crystal phase. These are generally grouped into martensitic, austenitic, ferritic, duplex and precipitation handling. Chromium, nickel, and molybdenum are most commonly used as alloying elements affecting the features of steel. Stainless steel is generally segregated into five types – ferritic, austenitic, martensitic, duplex and precipitation handling. Ferritic steel is made up of iron and chromium, based on the Type 430 composition of 17% chromium, having a similar microstructure to carbon and low alloy steel. Lack of toughness in welds makes them limited in use to relatively thin sections. However, in non-welding applications, they can find usage. This steel shows resistance to stress corrosion cracking. With additions of molybedenum, this steel can be used in aggressive conditions such as sea water. Austenitic steel is an alloy structured around iron, 18% chromium and 8% nickel along with the addition of manganese and nitrogen. The combination gives the steel its characteristic combination of weldability and formability. The steel cannot be hardened by heat treatment, but has the property of being work hardened while retaining a level of ductility and toughness. Type 304 is the most familiar stainless steel containing 18-20% chromium and 8-10% nickel. Higher nickel austenitic steel shows increased resistance to stress corrosion cracking. Martensitic steel is low carbon material based on the Type 410 composition of iron along with 12% chromium and 0.12% carbon. The hardened steel gains on this attribute, but also has reduced toughness and brittleness. This steel is used in applications that require high strength and moderate corrosion resistance. They find more common usage in long products than in sheet and plate form. Duplex steel is approximately 50% ferritic and 50% austenitic, which gives them higher strength as well as resistance to stress corrosion cracking. Superduplex steel demonstrates increased strength and resistance to all forms of corrosion. Lean duplex steel has comparable corrosion resistance to standard austenitic steel; however, it has enhanced resistance to stress corrosion cracking. Elements like copper, niobium and aluminum are added to the steel for precipitation hardening (PH) which lends very high strength. The steel can be machined to intricate shapes requiring good tolerances before the final aging treatment is done to ensure that there is minimal distortion. The steel is available in the form of plate, foil, bar, wire, sheet, strip, pipes and tubes. Alloying elements that are added to the stainless steel to gain certain performance include nickel, copper, sulphur, selenium, molybdenum, titanium, aluminum, silicon, niobium and nitrogen. The most common grades of stainless steel in the US are Type 304, Type 316, Type 409, Type 410 and Type 430. Type 304 is the most commonly specified austenitic stainless steel that withstands ordinary corrosion in architecture and resists most chemicals. Type 316 has greater resistance to various forms of deterioration, Type 409 is suitable for high temperatures, Type 410 is a low-cost, heat-treatable grade while Type 430 is a general-purpose corrosion resistance grade that finds usage in decorative applications. Blue Steel Services is counted among the leading suppliers of industrial stainless steel pipes and tubes in the US. Click here to know about their product line that includes ERW pipe, spiral weld pipe, fire sprinkler pipe and a range of other stuff. Visit Bluesteelservices.com for additional information. Author of this article is associated with Blue Steel Services LLC, which is engaged in OCTG sales, steel coils, electrical conduits, water well casing and pipes.
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