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Wrought iron is one of the oldest materials used in
architecture and house decoration. Wrought iron refers to metal that is
hammered or bent into shape as opposed to being cast or poured at a
foundry. Today, wrought iron is usually produced in industrial
quantities, much to the disadvantage of the hand made craft. The wrought
iron of today most commonly consists of mild steel, which was discovered
in 1856 and is made by melting cast iron and removing the carbon and
slag.
Steel castings as cast have relatively low fatigue resistance with an
endurance ratio (fatigue strength/ultimate strength) as low a 0.4. This
ratio can be improved by heat treatment and improvement of the surface
finish. Wrought iron is able to retain a thicker layer of finish than
smoother metal.
The commercial wrought iron is actually simply "bent work," for example
mild-steel bars, tubing, or strips that have been cut, heated, and bent.
Wrought Iron is no longer produced in commercial quantities; the wrought
iron that survives contains less than 0.035 percent carbon. The term
"wrought iron" should normally be applied only to iron that has been
worked by the crafted Hammersmith; when he heats the metal to make it
flow and then reshapes it into the desired form. A distinguishing
characteristic of wrought iron is a fragmented or irregular fracture, as
contrasted with a fibrous or crystalline type in steel.
Wrought iron is unlike cast, in that it is not brittle, and seldom
breaks.
For this reason, wrought iron work is frequently far more delicate,
although years of paint can obscure this.
Cast iron is more difficult to
weld than steel because the high carbon content may lead to brittle
structures on cooling, thereby causing cracking. Cast iron is most
frequently identified by its repetitive nature, and forms, which could
be carved in a wooden pattern, but not made by hammer and anvil. Similar
steel and steel alloy specifications are available to those for Forged
and drawn steel products. The notes provided for carbon steel and alloy
steel generally applies for cast steel.
Stainless steel refers to shiny steel that contains chromium, making it
resistant to corrosion. One of the major advantages of the stainless
steels, and the austenitic grades in particular, is their ability to be
fabricated by all the standard fabrication techniques. Stainless steel
is a very popular metal in furniture construction because of its
attractive appearance and environmentally friendly nature.
Telling wrought iron from mild steel is often more difficult, as both
will bend, and not break Frequently, however, work in mild steel is
readily identified by the lower standards of workmanship often used.
Wrought iron owes its rust proof properties to its fibrous nature. In
modern terms, the refining of iron is a crude process, and results in
the inclusion of non-corrodible slags in the structure of the metal.
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