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Stainless Steel

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Materials

Stainless steel, also referred to as inox or rostfrei, is an alloy of two elements that have been melted together—ordinary steel and at least 11 percent metal chromium. The result is a shiny material resistant to rust, corrosion, and stain—unique characteristics that set it a part from other forms of steel.[1]

Stainless steel is not a coated material, unlike many other forms of steel that may contain zinc, nickel, or chromium coatings. Commonly used in equipment manufacturing factories in the construction, agricultural, mining, forestry and transportation industries, it exists in more than 100 different grades containing an alloy of different elements with varying percentages of chromium.

The first person to realize the potential of stainless steel was an English metallurgist in 1913. Harry Brearly was involved in a project to improve rifle barrels and noticed that the addition of chromium to low carbon steel made it resistant to stain.[2]

The original stainless steel contained iron with 12 percent chromium alloy. Although there are many types of stainless steel, the three main types are: austenitic, ferritic, and martensitic.

Austenitic steel comprises austenite as the primary phase and contains an alloy of chromium and nickel, sometimes manganese and nitrogen, and the Type 302 composition of iron, 18 percent chromium, and eight percent nickel. Unlike many other elements, it cannot be hardened by heat; however, it is the most common form of stainless steel.

Ferritic stainless steel comprises ferrite as the main phase and Type 430 composition (17 percent chromium with iron). This type of stainless steel also cannot be hardened by heat and is, by nature, less ductile than austenitic steel.

Martensitic steel comprises the Type 410 composition of iron with 12 percent chromium and 0.12 percent carbon. In order to be hardened it has to be tempered, but the process also reduces the strength of the material, making it brittle.[3]

[edit] References

  1. Stainless Steel. WorldStainless. 2008-10-08.
  2. About. Metals and Alloys. 2008-10-09.
  3. Metals and Alloys. About. 2008-10-09.