Cast iron

A painted cast iron decorative grate (l) and cast iron cooking skillet (r)

Steels
Phases
Ferrite Austenite Cementite Martensite Graphite
Microstructures
Spheroidite Pearlite Bainite Ledeburite Tempered martensite Widmanstätten structures
Classes
Crucible steel Carbon steel Spring steel Alloy steel Maraging steel Stainless steel High-speed steel Weathering steel Tool steel
Other iron-based materials
Cast iron Gray iron White iron Ductile iron Malleable iron Wrought iron

Cast iron is a class of iron–carbon alloys with a carbon content of more than 2% and silicon content around 1–3%.^[1] Its usefulness derives from its relatively low melting temperature. The alloying elements determine the form in which its carbon appears: white cast iron has its carbon combined into an iron carbide named cementite, which is very hard, but brittle, as it allows cracks to pass straight through; grey cast iron has graphite flakes which deflect a passing crack and initiate countless new cracks as the material breaks, and ductile cast iron has spherical graphite "nodules" which stop the crack from further progressing.

Carbon (C), ranging from 1.8 to 4 wt%, and silicon (Si), 1–3 wt%, are the main alloying elements of cast iron. Iron alloys with lower carbon content are known as steel.

Cast iron tends to be brittle, except for malleable cast irons. With its relatively low melting point, good fluidity, castability, excellent machinability, resistance to deformation and wear resistance, cast irons have become an engineering material with a wide range of applications and are used in pipes, machines and automotive industry parts, such as cylinder heads, cylinder blocks and gearbox cases. Some alloys are resistant to damage by oxidation. In general, cast iron is notoriously difficult to weld.

The earliest cast-iron artefacts date to the 5th century BC, and were discovered by archaeologists in what is now Jiangsu, China. Cast iron was used in ancient China to mass-produce weaponry for warfare, as well as agriculture and architecture.^[2] During the 15th century AD, cast iron became utilized for cannons and shot in Burgundy, France, and in England during the Reformation. The amounts of cast iron used for cannons required large-scale production.^[3] The first cast-iron bridge was built during the 1770s by Abraham Darby III, and is known as the Iron Bridge in Shropshire, England. Cast iron was also used in the construction of buildings.