If you remember waking up to hash browns sizzling in a heavy
black pan on your grandmother's stove, or have ever enjoyed
tender bits of meat and gravy out of an old-fashioned Dutch
oven, chances are good that you have enjoyed the benefits of
cast iron. Cast iron is a hard, albeit, brittle iron alloy
commonly used to make cookware. In times past, it was also used
in architecture to make gutters, drainpipes and decorations. It
is still used today to construct manhole covers. Most cast irons
are composed of six primary elements.
Iron
Iron is the primary element in cast iron and is responsible for
its hard composition and great weight. Hematite and magnetite
are common iron ores, and are heated together with coke, a
carbon-based substance, and limestone to produce the chemical
reaction that separates the iron from the ore. Gray, ductile,
compacted graphite, malleable and white iron alloys are used to
make varieties of cast iron, each with unique properties.
Carbon
Carbon is the second most abundant element in cast iron, and is
largely what differentiates cast iron from steel. Steel is also
an iron-carbon alloy, but contains less than 2 percent carbon,
while cast iron contains 2 percent to 4 percent. This abundance
of carbon lowers the boiling point of the alloy, which is part
of what makes this alloy good for making castings.
Silicon
Silicon is a natural component of all cast irons, but is
especially prevalent in certain types of high-alloy cast irons.
When additional silicon is added, the resulting alloy is called
high-silicon (Silal) cast iron. While normal cast iron can have
silicon concentrations up to three percent, high-silicon irons
are from five to 18 percent silicon, and exhibit a greater
resistance to heat and acid corrosion.
Manganese, Sulfur and Phosphorous
Manganese, sulfur and phosphorous also occur in cast iron in
small concentrations. Manganese is a metal harder than iron and
contributes to the strength of alloy. It reacts with sulfur to
create a compound that causes iron to form graphite, which
arranges in different configurations to give different types of
cast iron different properties. Phosphorous, like carbon, lowers
the melting point of the alloy and helps to make it highly fluid
when liquefied.
Other Elements
Small amounts of other elements affect how cast iron behaves.
For example, adding chromium and nickle creates high-alloy cast
irons, which are more resistant to heat, corrosion and wear.
Bismuth and tellurium aid in the production of malleable iron,
and trace amounts of magnesium cause the graphite in the iron to
form into spheres, which creates ductile iron.
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