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Significant portion of Medical ID Bracelets and ID tags
are made from stainless steel. It is done so, due to
exceptional properties of this material to prevent human
body "rejection" or allergy, be rust free and maintain
attractive shiny appearance for a long time. Stainless steel
used for medical ID jewelry is also quite easy to clean
and does not oxidize over time as does other types of
semi-precious materials.
This material
is known by now for more than one hundred years.
A little
History
A few corrosion-resistant iron artifacts survive from
antiquity. A famous (and very large) example is the Iron
Pillar of Delhi, erected by order of Kumara-Gupta-First
around the year AD 400. However, unlike stainless steel,
these artifacts owe their durability not to chromium, but to
their high phosphorus content, which together with favorable
local weather conditions promotes the formation of a solid
protective passivation layer of iron oxides and phosphates,
rather than the non-protective, cracked rust layer that
develops on most ironwork.
The corrosion resistance of iron-chromium alloys was first
recognized in 1821 by the French metallurgist Pierre
Berthier, who noted their resistance against attack by some
acids and suggested their use in cutlery. However, the
metallurgists of the 19th century were unable to produce the
combination of low carbon and high chromium found in most
modern stainless steels, and the high-chromium alloys they
could produce were too brittle to be of practical interest.
This situation changed in the late 1890s, when Hans
Goldschmidt of Germany developed an aluminothermic (thermite)
process for producing carbon-free chromium. In the years
1904–1911, several researchers, particularly Leon Guillet of
France, prepared alloys that would today be considered
stainless steel.
In 1911, Philip Monnartz of Germany reported on the
relationship between the chromium content and corrosion
resistance of these alloys.
Harry Brearley of the Brown-Firth research laboratory in
Sheffield, England is most commonly credited as the
"inventor" of stainless steel. In 1913, while seeking an
erosion-resistant alloy for gun barrels, he discovered and
subsequently industrialized a martensitic stainless steel
alloy. However, similar industrial developments were taking
place contemporaneously at the Krupp Iron Works in Germany,
where Eduard Maurer and Benno Strauss were developing an
austenitic alloy (21% chromium, 7% nickel), and in the
United States, where Christian Dantsizen and Frederick
Becket were industrializing ferritic stainless.
Already in the year 1908 Krupp had built a famous
sailing-yacht featuring a chrome-nickel steel hull, or so it
seems - its wreck being currently investigated by the Bureau
of Archaeological Research of the State of Florida.
Types of stainless steel
Surgical
stainless steel used for Medical ID tags is a variation of
steel consisting of an alloy of chromium (12-20%),
molybdenum (0.2-3%), and sometimes nickel (8-12%).
The chromium gives the metal its sheen, scratch-resistance
and corrosion resistance. The molybdenum gives
corrosion-resistance, and helps maintaining a cutting edge.
The 'surgical' refers to the fact that these types of steel
are quite well-suited for making surgical implants and
equipment: they are easy to clean and sterilize, strong and
corrosion-resistant, although some patients may have immune
response issues with nickel.
Most surgical equipment is made out of martensitic steel -
it is much harder than austenitic steel, and easier to keep
sharp. Depending on the type of equipment, the alloy recipe
is varied slightly to get more sharpness, or strength.
Implants and equipment that are put under pressure (bone
fixation screws, prostheses, body piercing jewelry), are
made out of austenitic steel, often 316L and 316LVM, because
it is less brittle.
In metallurgy, stainless steel (inox) is defined as a
ferrous alloy with a minimum of 10.5% chromium content. The
name originates from the fact that stainless steel stains,
corrodes or rusts less easily than ordinary steel. In the
United States and world-wide, particularly in the aviation
industry, this material is also called corrosion resistant
steel when it is not detailed exactly to its alloy type and
grade.
Properties
Stainless steels have higher resistance to oxidation (rust)
and corrosion in many natural and man made environments,
however, it is important to select the correct type and
grade of stainless steel for the particular application.
High oxidation resistance in air at ambient temperature is
normally achieved with additions of more than 12% (by
weight) chromium. The chromium forms a passivation layer of
chromium(III) oxide (Cr2O3) when exposed to oxygen. The
layer is too thin to be visible, meaning the metal stays
shiny. It is, however, impervious to water and air,
protecting the metal beneath. Also, when the surface is
scratched this layer quickly reforms. This phenomenon is
called passivation by materials scientists, and is seen in
other metals, such as aluminum. When stainless steel parts
such as nuts and bolts are forced together, the oxide layer
can be scraped off causing the parts to weld together. When
disassembled, the welded material may be torn and pitted, an
effect that is known as galling.
Commercial value of
stainless steel
As we
mentioned before, stainless steel's resistance to corrosion
and staining, low maintenance, and familiar luster make it
an ideal base material for a medical ID bracelets.
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