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There is hardly a material thinkable
that has found its way to so many applications in such a short period
of time as stainless steel. Only developed in the first decade of the
20th century stainless steels are irreplaceable in the world today.
Although kitchen sinks, refrigerators and other consumer goods are
probably the most visible applications it is the industrial
application where stainless steel has its biggest impact on our daily
lives. Some chemicals couldn't be produced without the use of
corrosion resistant vessels and piping systems. Oil & gas production
would often be close to impossible or very costly without the
successful application of stainless steel.
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Stainless steels represent the most diverse and complex
family of all steels. The single most important property of stainless
steels, and the reason for their existence and widespread use, is
their corrosion resistance. Stainless steels are stainless because a
protective layer spontaneously forms on their surfaces and reduces the
rate of corrosion to almost negligible levels. Under normal
conditions, this layer heals very rapidly if scratched, so that if
stainless steels only suffered from uniform corrosion, they could
survive for literally millions of years.
Passivity
As mentioned above, the reason for the good
corrosion resistance of stainless steels is that they form a very
thin, invisible surface film in oxidizing environments. This film is
an oxide that protects the steel from attack in an aggressive
environment. As chromium is added to steel, a rapid reduction in
corrosion rate is observed to around 10% because of the formation of
this protective layer or passive film. In order to obtain a compact
and continuous passive film, a chromium content of about 17% is
needed. This is the reason why many stainless steels contain 17-18%
chromium.
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Stainless steels are stainless because a
protective layer spontaneously forms on their surfaces and reduces the
rate of corrosion to almost negligible levels. Under normal conditions,
this layer heals very rapidly if scratched, so that if stainless steels
only suffered from uniform corrosion, they could survive for literally
millions of years. This thin, invisible surface layer is an oxide
that protects the steel from attack in an aggressive environment. As
chromium is added to steel, a rapid reduction in corrosion rate is
observed to around 10% because of the formation of this protective layer
or passive film.
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In
metallurgy, stainless steel is defined1 as a
ferrous
alloy
with a minimum of 10.5%
chromium content. Such
steels
have higher resistance to
oxidation (rust)
and
corrosion in several environments |
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BSS Steelstrip, specialise in small quantities of spring steel strip
including type 301 hard rolled for feeler gauges, springs and
applications where high tensile strengths are required, please visit
our website
for more information. |
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Common stainless steel grades, properties and
analyses can be found here
SUPPLIERS OF STAINLESS STEEL STRIP |
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| Stainless
steels are classified by their
crystalline structure:
Austenitic stainless steels comprise over 70% of total stainless
steel production. They contain a maximum of 0.15% carbon, a minimum of
16% chromium and sufficient nickel and/or manganese to retain an
austenitic structure at all temperatures from the cryogenic region to
the melting point of the alloy. A typical composition is 18% chromium
and 8% nickel, commonly known as 18/8 stainless.
Ferritic stainless steels are highly corrosion resistant, but far
less durable than austenitic grades and cannot be hardened by heat
treatment. They contain between 10.5% and 27% chromium and very little
nickel, if any. Most recipes include
molybdenum; some, aluminium or
titanium. Common ferritic grades include 18Cr-2Mo, 26Cr-1Mo,
29Cr-4Mo, and 29Cr-4Mo-2Ni.
Martensitic stainless steels are not as corrosion resistant as the
other two classes, but are extremely strong and tough as well as
highly
machineable, and can be hardened by heat treatment. They contain
11.5 to 18% chromium and significant amounts of carbon. Some grades
include additional alloying elements in small quantities.
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