
Cast
iron has higher carbon and silicon contents than steel. Because of the
higher carbon content, the structure of cast iron, as opposed to that of
steel, exhibits a rich carbon phase. Depending primarily on composition,
cooling rate and melt treatment, cast iron can solidify according to the
thermodynamically metastable Fe-Fe3C system or the stable Fe-Gr system.

Various
types of cast irons are widely used in industry, especially for valves,
pumps, pipes, filters and certain mechanical parts. Cast iron can be
considered an alloy of Fe, Si and C. The carbon concentration is between
1.7 and 4.5 %, most of which is present in insoluble form (e.g. graphite
flakes or nodules). Such material is, however, normally called unalloyed
cast iron and exists in four main types:
- White iron, which is brittle and glass hard.
- Unalloyed gray iron, which is soft but still brittle, and
which is the most common form of unalloyed cast iron.
- More ductile malleable iron.
- Nodular or ductile cast iron, the best modern form of cast
iron, which has superior mechanical properties and equivalent
corrosion resistance.
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In addition there are a number of alloy cast irons, many of
which have improved (corrosion) resistance and substantially modified
mechanical and physical properties. Some of the most wellknown classes
include the high-silicon and nickel cast irons.