Crucible steel is steel made by melting pig iron, iron, and sometimes steel, often along with sand, glass, ashes, and other fluxes, in a crucible. In ancient times steel and iron were impossible to melt using charcoal or coal fires, which could not produce temperatures high enough. However, pig iron, having a higher carbon content and thus a lower melting point, could be melted, and by soaking wrought iron or steel in the liquid pig-iron for a long time, the carbon content of the pig iron could be reduced as it slowly diffused into the iron, turning both into steel. Crucible steel of this type was produced in South and Central Asia during the medieval era. This generally produced a very hard steel, but also a composite steel that was inhomogeneous, consisting of a very high-carbon steel and a lower-carbon steel. This often resulted in an intricate pattern when the steel was forged, filed or polished, with possibly the most well-known examples coming from the wootz steel used in Damascus swords. The steel was often much higher in carbon content and in quality in comparison with other methods of steel production of the time because of the use of fluxes. The steel was usually worked very little and at relatively low temperatures to avoid any decarburization, hot short crumbling, or excess diffusion of carbon; just enough hammering to form the shape of a sword. With a carbon content close to that of cast iron, it usually required no heat treatment after shaping other than air cooling to achieve the correct hardness, relying on composition alone. The higher-carbon steel provided a very hard edge, but the lower-carbon steel helped to increase the toughness, helping to decrease the chance of chipping, cracking, or breaking.
"Kirk nardeban" pattern of a sword blade made of crucible steel, Zand period: 1750–1794, Iran. (Moshtagh Khorasani, 2006, 506)
"Woodgrain" pattern of a sword blade made of crucible steel, Zand or Early Qajar period: (Zand) 1750–1794 AD; (Qajar) 1794–1952 AD, Iran.(Moshtagh Khorasani 2006, 516)
Crucibles next to the furnace room at Abbeydale, Sheffield
Steel is an alloy of iron and carbon with improved strength and fracture resistance compared to other forms of iron. Because of its high tensile strength and low cost, steel is one of the most commonly manufactured materials in the world. Steel is used in buildings, as concrete reinforcing rods, in bridges, infrastructure, tools, ships, trains, cars, bicycles, machines, electrical appliances, furniture, and weapons.
The steel cable of a colliery winding tower
An incandescent steel workpiece in a blacksmith's art
Iron ore pellets used in the production of steel
A Bessemer converter in Sheffield, England