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Stainless steel
  • 2016-10-29

Stainless steel is a common and versatile metal that does not stain, corrode or rust easily. It is also known as corrosion resistant steel or chromium steel, and is defined by the fact that it is alloyed with a minimum of 10% chromium. Regular steel often contains smaller amounts of chromium to enhance properties of strength and hardness, but stainless steel has the something extra that makes it less scratchable and just as strong and durable.

Stainless steel alloys develop a passivation layer of chromium oxide on their outer surface, effectively coating the steel and protecting it from the harmful oxidation that occurs between exposed iron and oxygen molecules in the air, which makes stainless steel more affective and attractive then regular steel.. This protecting layer of chromium oxide easily reforms when scratched, making stainless steel an excellent, durable solution with no surface cracking or pores. Austenitic Stainless Steel has the highest ratio of chromium, and is by far the most common type. Stainless steel is produced in over a hundred different grades, which differ depending on their alloys, strengths, temperature resistances and applications. One of the most popular stainless steel grades, 316 stainless steel, is super corrosion resistant because it contains more nickel. Steel service centers manufacture stainless steel into a variety of shapes and products, including stainless steel foil, stainless steel strip, stainless steel wire, stainless steel plate, stainless steel bars, stainless steel rods, stainless steel coil and stainless steel sheets via hot rolling and forming processes. It is used to make consumer goods, including domestic kitchen supplies and tableware, sinks, laundry equipment, flatware and electronic appliances, and in the food and beverage industry to make silos, vats, kegs and large kitchen equipment. Stainless steel is also found in the construction and engineering industries as roofing, gutters, elevator doors, public seating, and is used to build large skyscrapers. Automotive parts, bus frames, pipes, valves, pumps and industrial mixers are also often made out of stainless steel.

There are 3 main types of stainless steel which combine nickel, carbon and molybdenum in different ratios to achieve different qualities. Austenitic stainless steel combines the largest ratios of chromium, nickel and molybdenum and accounts for about 70% of fabricated stainless steel, with the most common grade being 18/10 stainless, an alloy which is very hard, durable and resistant to corrosion. Austenitic steels have a great strength-to-weight advantage over other materials; they also provide impact resistance and toughness in extreme temperatures, making them suitable for cryogenic applications. Ferritic stainless steel has very low nickel content, higher carbon content and is very corrosion resistant but less strong and durable than austenitic stainless. Martensitic stainless steel contains higher levels of carbon and often molybdenum, making it extremely strong and durable with lower corrosion resistance. Some types of stainless steel can transform from martensite to austenitic under heat treatment or with the addition of chromium. For example, maraging steel, a specialty low-carbon ultra-high strength steel alloy, is transformed into martensite when a portion of the alloy's nickel content is substituted by chromium to enhance corrosion resistance and hardness.
There are 150 grades of steel, which are classified in 4 different groups according to their varying corrosion resistance and mechanical properties. 200 series stainless steels are non magnetic, austenitic, and have the most resistance to attack. They contain 17% chromium, 4% nickel and 7% manganese. 300 level series are almost identical to 200, except they are a bit less attack-resistant and contain slightly more chromium and 8% nickel. 316 Stainless Steel is a 300 level steel, and because it contains more nickel, it has superior corrosion resistance. 400 series stainless steels are magnetic, martenistic, have a poor corrosion resistance and contain 11% chromium and 1% manganese. Finally, 600 series steels, often referred to as precipitation hardening, can be heat treated to very high strength levels and are therefore very resistant against water and chloride attack.
Manufacturing stainless steel is a 7 step process, and produces many different forms and parts. First, the raw materials are melted together in an electric furnace for 8 to 12 hours, until they reach their recrystallization temperature. The molten steel is then cast into semi-finished forms called blooms, billets, slabs, rods and tube rounds. The unfinished shapes then undergo a forming process via hot rolling, where blooms and billets become bars, wire and coil, and slabs form plates, strips, sheets and foil. They are then heat treated through annealing, where the steel is heated and then cooled through quenching or air hardening. The steel hardens or softens, depending on the amount of time it is let to cool. When it has cooled, the stainless steel is descaled, which removes any buildup by pickling or electrocleaning. It is then cut to obtain its final desired shape and size by shearing, blanking, nibbling or flame cutting. Further processing to acquire a certain finish, dull or shiny, is done through hot rolling, cold rolling, annealing, descaling, or different combinations of these processes. Before becoming parts and components in industrial and commercial products, all stainless steel must meet specific requirements, such as toughness or corrosion resistance, put fourth by the American Society for Testing and Materials (ASTM) to ensure quality and safety.

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