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Stainless steels are iron alloys with a minimum of Chromium and Carbon, and with eventually other elements such as Nickel, Molybdenum, Silicon, Titanium, etc...
Stainless steel is defined as stainless because when exposed to an oxidant environment develops over its surface a protective film of absorbed oxygen. |
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This invisible film, which has the width of an atom acts as a barrier to oxidation and corrosion, and if it is damaged it will normally self repair. For this condition it is necessary an enough quantity of chromium, which must be a minimum of 1.11%. |
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Depending on the structure, which is the chemical composition, stainless steels are divided into: |
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Martensitic
With a variable function depending on the temperature and therefore extremely strong due to thermic treatment. Martensitic stainless steels contain mostly chromium (11-18%) and other small quantities of other elements such as nickel, which however will never be more than 2.5%, and carbon which may vary between 0.08% and 1.20%. |
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Ferritici
With a ferritic structure independent from the temperature. FERRITIC stainless steels have a low carbon content (under 0.1%) and contain chromium as the main alloying element, typically between 16% and 18%. |
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Austenitic
With an austenitic structure independent from the temperature.
Chromium-Nickel austenitic stainless steel contains carbon between 0.03% and 0.12%; Chromium between 17% and 26%; Nickel between 7% and 22% and eventually Molybdenum
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