Description
Steel is an alloy of iron and carbon and other elements. Because of
its high tensile strength and low cost, it is a major component
used in buildings, infrastructure, tools, ships, automobiles,
machines, appliances, and weapons.
Iron is the base metal of steel. Iron is able to take on two
crystalline forms (allotropic forms), body centered cubic (BCC) and
face centered cubic (FCC), depending on its temperature. In the
body-centred cubic arrangement, there is an iron atom in the centre
of each cube, and in the face-centred cubic, there is one at the
center of each of the six faces of the cube. It is the interaction
of the allotropes of iron with the alloying elements, primarily
carbon, that gives steel and cast iron their range of unique
properties.
In pure iron, the crystal structure has relatively little
resistance to the iron atoms slipping past one another, and so pure
iron is quite ductile, or soft and easily formed. In steel, small
amounts of carbon, other elements, and inclusions within the iron
act as hardening agents that prevent the movement of dislocations
that are common in the crystal lattices of iron atoms.
The carbon in typical steel alloys may contribute up to 2.*4% of
its weight. Varying the amount of carbon and many other alloying
elements, as well as controlling their chemical and physical makeup
in the final steel (either as solute elements, or as precipitated
phases), slows the movement of those dislocations that make pure
iron ductile, and thus controls and enhances its qualities. These
qualities include such things as the hardness, quenching behavior,
need for annealing, tempering behavior, yield strength, and tensile
strength of the resulting steel. The increase in steel\'s strength
compared to pure iron is only possible by reducing iron\'s
ductility.
Steel was produced in bloomery furnaces for thousands of years, but
its large-scale, industrial use only began after more efficient
production methods were devised in the *7th century, with the
production of blister steel and then crucible steel. With the
invention of the Bessemer process in the mid**9th century, a new
era of mass-produced steel began. This was followed by the
Siemens-Martin process and then the Gilchrist-Thomas process that
refined the quality of steel. With their introductions, mild steel
replaced wrought
