Wrought iron is a very pure form of commercial
iron having a very small carbon content. It is tough, malleable,
ductile and can be easily welded.
However, wrought iron it is too soft to make blades from; steel,
with a carbon content between wrought and the high-carbon brittle
cast iron.
Cast iron is made by remelting pig iron, often
along with substantial quantities of scrap iron, and taking various
steps to remove undesirable contaminants such as silica, phosphorus
and sulfur, which weaken the material. Carbon content is carefully
reduced to the desired level, which may be anywhere from 2% to 3.5%
depending on the application. (Carbon steel has less than 0.45% carbon.)The
salient feature of its manufacture is that the mix of about 3.5%
carbon with iron makes an alloy that has a minimum melting point
(1420-1470 K), and therefore can be created at temperatures at least
300 K lower than the melting point of pure iron.
Wrought iron has been used for thousands of years, and represents
the "iron" that is referred to throughout history. Wrought iron was
originally produced by a variety of methods today known as a bloomery.
Bloomeries used charcoal-heated smelters,
typically in the form of small pots or ladles, into which the ore
was poured and then covered with a thin layer of charcoal. Air was
blown onto the charcoal after lighting it on fire, the heat produced
would melt the ore. As the ore melted it would give up its oxygen
(ore is iron oxide, or rust), mixing with the charcoal to release
carbon dioxide.
This way little carbon entered the iron directly. In a bloomery,
the fire does not get hot enough to melt the iron completely, so
you are left with a spongy mass containing iron and silicates from
the ore -- this is iron bloom from which the technique gets its name.
The bloom was then mechanically worked to break off the masses of
slag and impurities. This process gives rise to the name "wrought",
as the iron was pounded and twisted.