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As the name implies, stainless steels are more resistant
to rusting and staining than are plain carbon and lower
allooy steels. This superior corrosion resistance is
brought about by addition of the element chromium to
alloys of iron and carbon.
The minimum amount of chromium necessary to confer this superior
corrosion resistance depends upon the corroding agent. The American
Iron and Steel Institute has chosen 10 per cent chromium as the
dividing line between “alloy” steel and “stainless” steel. Most
of these types are available in the main product forms such as
plates, bars, shapes, sheet, strip, and tubes.
In 1912 Harry Brearley, head of the Brown - Firth Research
Laboratory in England, while attempting to develop steels
to resist the fouling and corrosion encountered in gun
barrels, reported that a composition of 12.8 per cent
chromium and 0.24 per cent carbon was quite resistant
to corrosion.
The austenitic iron-chromium-nickel alloys were developed
in Germany during the years 1909-1912 by Benno Strauss
and Edward Maurer . Further work by Strauss and others
ultimately led to the versatile 18 per cent chromium,
8 per cent nickel steels popularly called 18-8 which
are used so widely today.
The resistance to attack is due to the naturally occurring
chromiun rich oxide film formed on the surface of the
steel. Although extremely thin, this invisible, inert
film is tightly adherent to the metal and extremely protective
in a wide range of corrosive media. This film is rapidly
self reparing in the presence of oxygen, and damage by
abrassion, cutting or machining is quickly repaired.
Benefits of Stainless Steel are:
corrosion resistance
ease of fabrication
aesthetic and higienic appeal
high and low temperature resistance
low maintenance cost
life cycle characteristics
100% recyclable
In addition to chromium, nickel, molybdenum, titanium,
niobium and other elements may also be added to stainless
steels in varaying quantities to produce a range of sainless
steel grades, each with different properties.
1. Austenitic
2. Ferritic
3. Martensitic
4. Duplex
Chemical Composition, Mechanical and Physical Properties
table.
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