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Steel is an
alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductilit ...
made up of
iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
with added
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...
to improve its
strength Strength may refer to: Physical strength *Physical strength, as in people or animals * Hysterical strength, extreme strength occurring when people are in life-and-death situations *Superhuman strength, great physical strength far above human c ...
and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are
corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...
- and
oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
-resistant typically need an additional 11% chromium. Because of its high
tensile strength Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or F_\text within equations, is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials t ...
and low cost, steel is used in
building A building, or edifice, is an enclosed structure with a roof and walls standing more or less permanently in one place, such as a house or factory (although there's also portable buildings). Buildings come in a variety of sizes, shapes, and fu ...
s, infrastructure,
tool A tool is an object that can extend an individual's ability to modify features of the surrounding environment or help them accomplish a particular task. Although many animals use simple tools, only human beings, whose use of stone tools dates ba ...
s,
ship A ship is a large watercraft that travels the world's oceans and other sufficiently deep waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research, and fishing. Ships are generally distinguished ...
s,
train In rail transport, a train (from Old French , from Latin , "to pull, to draw") is a series of connected vehicles that run along a railway track and transport people or freight. Trains are typically pulled or pushed by locomotives (often ...
s, cars, machines, electrical appliances,
weapons A weapon, arm or armament is any implement or device that can be used to deter, threaten, inflict physical damage, harm, or kill. Weapons are used to increase the efficacy and efficiency of activities such as hunting, crime, law enforcement, s ...
, and
rockets A rocket (from it, rocchetto, , bobbin/spool) is a vehicle that uses jet propulsion to accelerate without using the surrounding air. A rocket engine produces thrust by reaction to exhaust expelled at high speed. Rocket engines work entirely ...
. Iron is the
base metal A base metal is a common and inexpensive metal, as opposed to a precious metal such as gold or silver. In numismatics, coins often derived their value from the precious metal content; however, base metals have also been used in coins in the past ...
of steel. Depending on the temperature, it can take two crystalline forms (allotropic forms): body-centred cubic and face-centred cubic. The interaction of the allotropes of iron with the alloying elements, primarily carbon, gives steel and
cast iron Cast iron is a class of iron– carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impur ...
their range of unique properties. In pure iron, the
crystal structure In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric patterns ...
has relatively little resistance to the iron atoms slipping past one another, and so pure iron is quite
ductile Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...
, 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
dislocation In materials science, a dislocation or Taylor's dislocation is a linear crystallographic defect or irregularity within a crystal structure that contains an abrupt change in the arrangement of atoms. The movement of dislocations allow atoms to s ...
s. The carbon in typical steel alloys may contribute up to 2.14% 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), impedes the movement of the dislocations that make pure iron ductile, and thus controls and enhances its qualities. These qualities include the
hardness In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard ...
, quenching behaviour, need for annealing, tempering behaviour,
yield strength In materials science and engineering, the yield point is the point on a stress-strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Below the yield point, a material will deform elastically and ...
, and
tensile strength Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or F_\text within equations, is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials t ...
of the resulting steel. The increase in steel's strength compared to pure iron is possible only by reducing iron's ductility. Steel was produced in bloomery furnaces for thousands of years, but its large-scale, industrial use began only after more efficient production methods were devised in the 17th century, with the introduction of the blast furnace and production of
crucible steel Crucible steel is steel made by melting pig iron (cast 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 ...
. This was followed by the
open-hearth furnace An open-hearth furnace or open hearth furnace is any of several kinds of industrial Industrial furnace, furnace in which excess carbon and other impurities are burnt out of pig iron to Steelmaking, produce steel. Because steel is difficult to ma ...
and then the
Bessemer process The Bessemer process was the first inexpensive industrial process for the mass production of steel from molten pig iron before the development of the open hearth furnace. The key principle is removal of impurities from the iron by oxidation ...
in
England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...
in the mid-19th century. With the invention of the Bessemer process, a new era of
mass-produced Mass production, also known as flow production or continuous production, is the production of substantial amounts of standardized products in a constant flow, including and especially on assembly lines. Together with job production and ba ...
steel began. Mild steel replaced
wrought iron Wrought iron is an iron alloy with a very low carbon content (less than 0.08%) in contrast to that of cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag inclusions (up to 2% by weight), which give it a wood-like "grain" ...
. The German states saw major steel prowess over Europe in the 19th century. Further refinements in the process, such as
basic oxygen steelmaking Basic oxygen steelmaking (BOS, BOP, BOF, or OSM), also known as Linz-Donawitz steelmaking or the oxygen converter processBrock and Elzinga, p. 50. is a method of primary steelmaking in which carbon-rich molten pig iron is made into steel. Blowin ...
(BOS), largely replaced earlier methods by further lowering the cost of production and increasing the quality of the final product. Today, steel is one of the most commonly manufactured materials in the world, with more than 1.6 billion tons produced annually. Modern steel is generally identified by various grades defined by assorted standards organisations. The modern steel industry is one of the largest manufacturing industries in the world, but is one of the most energy and
greenhouse gas emission Greenhouse gas emissions from human activities strengthen the greenhouse effect, contributing to climate change. Most is carbon dioxide from burning fossil fuels: coal, oil, and natural gas. The largest emitters include coal in China and ...
intense industries, contributing 8% of global emissions. However, steel is also very reusable: it is one of the world's most-recycled materials, with a recycling rate of over 60% globally.


Definitions and related materials

The noun ''steel'' originates from the
Proto-Germanic Proto-Germanic (abbreviated PGmc; also called Common Germanic) is the reconstructed proto-language of the Germanic branch of the Indo-European languages. Proto-Germanic eventually developed from pre-Proto-Germanic into three Germanic bran ...
adjective ''stahliją'' or ''stakhlijan'' 'made of steel', which is related to ''stahlaz'' or ''stahliją'' 'standing firm'. The carbon content of steel is between 0.002% and 2.14% by weight for plain carbon steel (
iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
-
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...
alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductilit ...
s). Too little carbon content leaves (pure) iron quite soft, ductile, and weak. Carbon contents higher than those of steel make a brittle alloy commonly called pig iron.
Alloy steel Alloy steel is steel that is alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to improve its mechanical properties. Alloy steels are broken down into two groups: low alloy steels and high alloy steels. The differe ...
is steel to which other alloying elements have been intentionally added to modify the characteristics of steel. Common alloying elements include:
manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...
,
nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow ...
, chromium, molybdenum, boron,
titanium Titanium is a chemical element with the Symbol (chemistry), symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resista ...
, vanadium,
tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...
,
cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, p ...
, and niobium. Additional elements, most frequently considered undesirable, are also important in steel:
phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
, sulfur,
silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ta ...
, and traces of
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
,
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
, and
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
. Plain carbon-iron alloys with a higher than 2.1% carbon content are known as
cast iron Cast iron is a class of iron– carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impur ...
. With modern
steelmaking Steelmaking is the process of producing steel from iron ore and carbon/or scrap. In steelmaking, impurities such as nitrogen, silicon, phosphorus, sulfur and excess carbon (the most important impurity) are removed from the sourced iron, and alloy ...
techniques such as powder metal forming, it is possible to make very high-carbon (and other alloy material) steels, but such are not common. Cast iron is not malleable even when hot, but it can be formed by
casting Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a ''casting'', which is ejected ...
as it has a lower
melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depen ...
than steel and good
castability Castability is the ease of forming a quality casting. A very castable part design is easily developed, incurs minimal tooling costs, requires minimal energy, and has few rejections.Ravi, p. 2 Castability can refer to a part design or a material pro ...
properties. Certain compositions of cast iron, while retaining the economies of melting and casting, can be heat treated after casting to make malleable iron or
ductile iron Ductile iron, also known as ductile cast iron, nodular cast iron, spheroidal graphite iron, spheroidal graphite cast iron and SG iron, is a type of graphite-rich cast iron discovered in 1943 by Keith Millis. While most varieties of cast iron are ...
objects. Steel is distinguishable from
wrought iron Wrought iron is an iron alloy with a very low carbon content (less than 0.08%) in contrast to that of cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag inclusions (up to 2% by weight), which give it a wood-like "grain" ...
(now largely obsolete), which may contain a small amount of carbon but large amounts of slag.


Material properties


Origins and production

Iron is commonly found in the Earth's crust in the form of an
ore Ore is natural rock or sediment that contains one or more valuable minerals, typically containing metals, that can be mined, treated and sold at a profit.Encyclopædia Britannica. "Ore". Encyclopædia Britannica Online. Retrieved 7 Apr ...
, usually an iron oxide, such as
magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With th ...
or hematite. Iron is extracted from iron ore by removing the oxygen through its combination with a preferred chemical partner such as carbon which is then lost to the atmosphere as carbon dioxide. This process, known as
smelting Smelting is a process of applying heat to ore, to extract a base metal. It is a form of extractive metallurgy. It is used to extract many metals from their ores, including silver, iron, copper, and other base metals. Smelting uses heat and a ...
, was first applied to metals with lower
melting Melting, or fusion, is a physical process that results in the phase transition of a substance from a solid to a liquid. This occurs when the internal energy of the solid increases, typically by the application of heat or pressure, which inc ...
points, such as
tin Tin is a chemical element with the symbol Sn (from la, stannum) and atomic number 50. Tin is a silvery-coloured metal. Tin is soft enough to be cut with little force and a bar of tin can be bent by hand with little effort. When bent, t ...
, which melts at about , and
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
, which melts at about , and the combination, bronze, which has a melting point lower than . In comparison, cast iron melts at about . Small quantities of iron were smelted in ancient times, in the solid-state, by heating the ore in a charcoal fire and then
welding Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct from lower temperature techniques such as bra ...
the clumps together with a hammer and in the process squeezing out the impurities. With care, the carbon content could be controlled by moving it around in the fire. Unlike copper and tin, liquid or solid iron dissolves carbon quite readily. All of these temperatures could be reached with ancient methods used since the
Bronze Age The Bronze Age is a historic period, lasting approximately from 3300 BC to 1200 BC, characterized by the use of bronze, the presence of writing in some areas, and other early features of urban civilization. The Bronze Age is the second prin ...
. Since the oxidation rate of iron increases rapidly beyond , it is important that smelting take place in a low-oxygen environment. Smelting, using carbon to reduce iron oxides, results in an alloy ( pig iron) that retains too much carbon to be called steel. The excess carbon and other impurities are removed in a subsequent step. Other materials are often added to the iron/carbon mixture to produce steel with the desired properties.
Nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow ...
and
manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...
in steel add to its tensile strength and make the
austenite Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 K ...
form of the iron-carbon solution more stable, chromium increases hardness and melting temperature, and vanadium also increases hardness while making it less prone to
metal fatigue In materials science, fatigue is the initiation and propagation of cracks in a material due to cyclic loading. Once a fatigue crack has initiated, it grows a small amount with each loading cycle, typically producing striations on some parts o ...
. To inhibit corrosion, at least 11% chromium can be added to steel so that a hard oxide forms on the metal surface; this is known as stainless steel. Tungsten slows the formation of
cementite Cementite (or iron carbide) is a compound of iron and carbon, more precisely an intermediate transition metal carbide with the formula Fe3C. By weight, it is 6.67% carbon and 93.3% iron. It has an orthorhombic crystal structure. It is a hard, bri ...
, keeping carbon in the iron matrix and allowing
martensite Martensite is a very hard form of steel crystalline structure. It is named after German metallurgist Adolf Martens. By analogy the term can also refer to any crystal structure that is formed by diffusionless transformation. Properties M ...
to preferentially form at slower quench rates, resulting in
high-speed steel High-speed steel (HSS or HS) is a subset of tool steels, commonly used as cutting tool material. It is often used in power-saw blades and drill bits. It is superior to the older high-carbon steel tools used extensively through the 1940s in tha ...
. The addition of
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
and sulfur decrease grain size, thereby making the steel easier to turn, but also more brittle and prone to corrosion. Such alloys are nevertheless frequently used for components such as nuts, bolts, and washers in applications where toughness and corrosion resistance are not paramount. For the most part, however,
p-block A block of the periodic table is a set of elements unified by the atomic orbitals their valence electrons or vacancies lie in. The term appears to have been first used by Charles Janet. Each block is named after its characteristic orbital: s-blo ...
elements such as sulfur,
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
,
phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
, and lead are considered contaminants that make steel more brittle and are therefore removed from the steel melt during processing.


Properties

The
density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...
of steel varies based on the alloying constituents but usually ranges between , or . Even in a narrow range of concentrations of mixtures of carbon and iron that make steel, several different metallurgical structures, with very different properties can form. Understanding such properties is essential to making quality steel. At room temperature, the most stable form of pure iron is the
body-centred cubic In crystallography, the cubic (or isometric) crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals. There are three main varieties of ...
(BCC) structure called alpha iron or α-iron. It is a fairly soft metal that can dissolve only a small concentration of carbon, no more than 0.005% at and 0.021 wt% at . The inclusion of carbon in alpha iron is called ferrite. At 910 °C, pure iron transforms into a
face-centred cubic In crystallography, the cubic (or isometric) crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals. There are three main varieties of ...
(FCC) structure, called gamma iron or γ-iron. The inclusion of carbon in gamma iron is called austenite. The more open FCC structure of austenite can dissolve considerably more carbon, as much as 2.1%, (38 times that of ferrite) carbon at , which reflects the upper carbon content of steel, beyond which is cast iron. When carbon moves out of solution with iron, it forms a very hard, but brittle material called cementite (Fe3C). When steels with exactly 0.8% carbon (known as a eutectoid steel), are cooled, the
austenitic Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 ...
phase (FCC) of the mixture attempts to revert to the ferrite phase (BCC). The carbon no longer fits within the FCC austenite structure, resulting in an excess of carbon. One way for carbon to leave the austenite is for it to
precipitate In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...
out of solution as
cementite Cementite (or iron carbide) is a compound of iron and carbon, more precisely an intermediate transition metal carbide with the formula Fe3C. By weight, it is 6.67% carbon and 93.3% iron. It has an orthorhombic crystal structure. It is a hard, bri ...
, leaving behind a surrounding phase of BCC iron called ferrite with a small percentage of carbon in solution. The two, ferrite and cementite, precipitate simultaneously producing a layered structure called
pearlite Pearlite is a two-phased, lamellar (or layered) structure composed of alternating layers of ferrite (87.5 wt%) and cementite (12.5 wt%) that occurs in some steels and cast irons. During slow cooling of an iron-carbon alloy, pearlite form ...
, named for its resemblance to
mother of pearl Nacre ( , ), also known as mother of pearl, is an organicinorganic composite material produced by some molluscs as an inner shell layer; it is also the material of which pearls are composed. It is strong, resilient, and iridescent. Nacre is f ...
. In a hypereutectoid composition (greater than 0.8% carbon), the carbon will first precipitate out as large inclusions of cementite at the austenite
grain boundaries In materials science, a grain boundary is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundaries are two-dimensional defects in the crystal structure, and tend to decrease the electrical and thermal ...
until the percentage of carbon in the
grains A grain is a small, hard, dry fruit (caryopsis) – with or without an attached hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and legumes ...
has decreased to the eutectoid composition (0.8% carbon), at which point the pearlite structure forms. For steels that have less than 0.8% carbon (hypoeutectoid), ferrite will first form within the grains until the remaining composition rises to 0.8% of carbon, at which point the pearlite structure will form. No large inclusions of cementite will form at the boundaries in hypoeuctoid steel. The above assumes that the cooling process is very slow, allowing enough time for the carbon to migrate. As the rate of cooling is increased the carbon will have less time to migrate to form carbide at the grain boundaries but will have increasingly large amounts of pearlite of a finer and finer structure within the grains; hence the carbide is more widely dispersed and acts to prevent slip of defects within those grains, resulting in hardening of the steel. At the very high cooling rates produced by quenching, the carbon has no time to migrate but is locked within the face-centred austenite and forms
martensite Martensite is a very hard form of steel crystalline structure. It is named after German metallurgist Adolf Martens. By analogy the term can also refer to any crystal structure that is formed by diffusionless transformation. Properties M ...
. Martensite is a highly strained and stressed, supersaturated form of carbon and iron and is exceedingly hard but brittle. Depending on the carbon content, the martensitic phase takes different forms. Below 0.2% carbon, it takes on a ferrite BCC crystal form, but at higher carbon content it takes a
body-centred tetragonal In crystallography, the tetragonal crystal system is one of the 7 crystal systems. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a squa ...
(BCT) structure. There is no thermal
activation energy In chemistry and physics, activation energy is the minimum amount of energy that must be provided for compounds to result in a chemical reaction. The activation energy (''E''a) of a reaction is measured in joules per mole (J/mol), kilojoules p ...
for the transformation from austenite to martensite. There is no compositional change so the atoms generally retain their same neighbors.. Martensite has a lower density (it expands during the cooling) than does austenite, so that the transformation between them results in a change of volume. In this case, expansion occurs. Internal stresses from this expansion generally take the form of
compression Compression may refer to: Physical science *Compression (physics), size reduction due to forces *Compression member, a structural element such as a column *Compressibility, susceptibility to compression * Gas compression *Compression ratio, of a ...
on the crystals of martensite and
tension Tension may refer to: Science * Psychological stress * Tension (physics), a force related to the stretching of an object (the opposite of compression) * Tension (geology), a stress which stretches rocks in two opposite directions * Voltage or el ...
on the remaining ferrite, with a fair amount of
shear Shear may refer to: Textile production *Animal shearing, the collection of wool from various species **Sheep shearing *The removal of nap during wool cloth production Science and technology Engineering *Shear strength (soil), the shear strength ...
on both constituents. If quenching is done improperly, the internal stresses can cause a part to shatter as it cools. At the very least, they cause internal
work hardening In materials science, work hardening, also known as strain hardening, is the strengthening of a metal or polymer by plastic deformation. Work hardening may be desirable, undesirable, or inconsequential, depending on the context. This strengt ...
and other microscopic imperfections. It is common for quench cracks to form when steel is water quenched, although they may not always be visible.


Heat treatment

There are many types of
heat treating Heat treating (or heat treatment) is a group of industrial, thermal and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are als ...
processes available to steel. The most common are annealing,
quenching In materials science, quenching is the rapid cooling of a workpiece in water, oil, polymer, air, or other fluids to obtain certain material properties. A type of heat treating, quenching prevents undesired low-temperature processes, such as pha ...
, and tempering. Annealing is the process of heating the steel to a sufficiently high temperature to relieve local internal stresses. It does not create a general softening of the product but only locally relieves strains and stresses locked up within the material. Annealing goes through three phases:
recovery Recovery or Recover may refer to: Arts and entertainment Books * ''Recovery'' (novel), a Star Wars e-book * Recovery Version, a translation of the Bible with footnotes published by Living Stream Ministry Film and television * ''Recovery'' (fil ...
, recrystallization, and
grain growth In materials science, grain growth is the increase in size of grains (crystallites) in a material at high temperature. This occurs when recovery and recrystallisation are complete and further reduction in the internal energy can only be achieved ...
. The temperature required to anneal a particular steel depends on the type of annealing to be achieved and the alloying constituents. Quenching involves heating the steel to create the austenite phase then quenching it in water or
oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...
. This rapid cooling results in a hard but brittle martensitic structure. The steel is then tempered, which is just a specialized type of annealing, to reduce brittleness. In this application the annealing (tempering) process transforms some of the martensite into cementite, or
spheroidite Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states: * no minimum content is specified or required for chromium, coba ...
and hence it reduces the internal stresses and defects. The result is a more ductile and fracture-resistant steel.


Production

When iron is
smelted Smelting is a process of applying heat to ore, to extract a base metal. It is a form of extractive metallurgy. It is used to extract many metals from their ores, including silver, iron, copper, and other base metals. Smelting uses heat and a c ...
from its ore, it contains more carbon than is desirable. To become steel, it must be reprocessed to reduce the carbon to the correct amount, at which point other elements can be added. In the past, steel facilities would
cast Cast may refer to: Music * Cast (band), an English alternative rock band * Cast (Mexican band), a progressive Mexican rock band * The Cast, a Scottish musical duo: Mairi Campbell and Dave Francis * ''Cast'', a 2012 album by Trespassers William ...
the raw steel product into
ingot An ingot is a piece of relatively pure material, usually metal, that is cast into a shape suitable for further processing. In steelmaking, it is the first step among semi-finished casting products. Ingots usually require a second procedure of sha ...
s which would be stored until use in further refinement processes that resulted in the finished product. In modern facilities, the initial product is close to the final composition and is continuously cast into long slabs, cut and shaped into bars and extrusions and heat treated to produce a final product. Today, approximately 96% of steel is continuously cast, while only 4% is produced as ingots. The ingots are then heated in a soaking pit and
hot rolled In metalworking, rolling is a metal forming process in which metal stock is passed through one or more pairs of rolls to reduce the thickness, to make the thickness uniform, and/or to impart a desired mechanical property. The concept is simil ...
into slabs,
billets A billet is a living-quarters to which a soldier is assigned to sleep. Historically, a billet was a private dwelling that was required to accept the soldier. Soldiers are generally billeted in barracks or garrisons when not on combat duty, al ...
, or blooms. Slabs are hot or
cold rolled In metalworking, rolling is a metal forming process in which metal stock is passed through one or more pairs of rolls to reduce the thickness, to make the thickness uniform, and/or to impart a desired mechanical property. The concept is simil ...
into
sheet metal Sheet metal is metal formed into thin, flat pieces, usually by an industrial process. Sheet metal is one of the fundamental forms used in metalworking, and it can be cut and bent into a variety of shapes. Thicknesses can vary significantly; ex ...
or plates. Billets are hot or cold rolled into bars, rods, and wire. Blooms are hot or cold rolled into structural steel, such as
I-beam An I-beam, also known as H-beam (for universal column, UC), w-beam (for "wide flange"), universal beam (UB), rolled steel joist (RSJ), or double-T (especially in Polish, Bulgarian, Spanish, Italian and German), is a beam with an or -shape ...
s and
rails Rail or rails may refer to: Rail transport *Rail transport and related matters *Rail (rail transport) or railway lines, the running surface of a railway Arts and media Film * ''Rails'' (film), a 1929 Italian film by Mario Camerini * ''Rail'' ( ...
. In modern steel mills these processes often occur in one
assembly line An assembly line is a manufacturing process (often called a ''progressive assembly'') in which parts (usually interchangeable parts) are added as the semi-finished assembly moves from workstation to workstation where the parts are added in se ...
, with ore coming in and finished steel products coming out. Sometimes after a steel's final rolling, it is heat treated for strength; however, this is relatively rare.


History


Ancient

Steel was known in antiquity and was produced in bloomeries and
crucible A crucible is a ceramic or metal container in which metals or other substances may be melted or subjected to very high temperatures. While crucibles were historically usually made from clay, they can be made from any material that withstands te ...
s. The earliest known production of steel is seen in pieces of ironware excavated from an
archaeological site An archaeological site is a place (or group of physical sites) in which evidence of past activity is preserved (either prehistoric or historic or contemporary), and which has been, or may be, investigated using the discipline of archaeology a ...
in
Anatolia Anatolia, tr, Anadolu Yarımadası), and the Anatolian plateau, also known as Asia Minor, is a large peninsula in Western Asia and the westernmost protrusion of the Asian continent. It constitutes the major part of modern-day Turkey. The ...
(
Kaman-Kalehöyük Kaman-Kalehöyük is a multi-period archaeological site in Kırşehir Province, Turkey, around 100 km south east of Ankara, 6 km east of the town center of Kaman. It is a tell or mound site that was occupied during the Bronze Age, Iron ...
) and are nearly 4,000 years old, dating from 1800 BC. Horace identifies steel weapons such as the ''
falcata The falcata is a type of sword typical of pre-Roman Iberia. The falcata was used to great effect for warfare in the ancient Iberian peninsula, and is firmly associated with the southern Iberian tribes, among other ancient peoples of Hispania. ...
'' in the
Iberian Peninsula The Iberian Peninsula (), ** * Aragonese and Occitan: ''Peninsula Iberica'' ** ** * french: Péninsule Ibérique * mwl, Península Eibérica * eu, Iberiar penintsula also known as Iberia, is a peninsula in southwestern Europe, def ...
, while
Noric steel Noric steel was a steel from Noricum, a Celtic kingdom located in modern Austria and Slovenia. The proverbial hardness of Noric steel is expressed by Ovid: ''"...durior ..ferro quod noricus excoquit ignis..."'' which roughly translates to "...har ...
was used by the
Roman military The military of ancient Rome, according to Titus Livius, one of the more illustrious historians of Rome over the centuries, was a key element in the rise of Rome over "above seven hundred years" from a small settlement in Latium to the capital o ...
. The reputation of ''Seric iron'' of India (wootz steel) grew considerably in the rest of the world. Metal production sites in Sri Lanka employed wind furnaces driven by the monsoon winds, capable of producing high-carbon steel. Large-scale
Wootz steel Wootz steel, also known as Seric steel, is a crucible steel characterized by a pattern of bands and high carbon content. These bands are formed by sheets of microscopic carbides within a tempered martensite or pearlite matrix in higher carbon ...
production in
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
using crucibles occurred by the sixth century BC, the pioneering precursor to modern steel production and metallurgy. The
Chinese Chinese can refer to: * Something related to China * Chinese people, people of Chinese nationality, citizenship, and/or ethnicity **''Zhonghua minzu'', the supra-ethnic concept of the Chinese nation ** List of ethnic groups in China, people of ...
of the
Warring States period The Warring States period () was an era in ancient Chinese history characterized by warfare, as well as bureaucratic and military reforms and consolidation. It followed the Spring and Autumn period and concluded with the Qin wars of conquest ...
(403–221 BC) had quench-hardened steel, while Chinese of the
Han dynasty The Han dynasty (, ; ) was an imperial dynasty of China (202 BC – 9 AD, 25–220 AD), established by Liu Bang (Emperor Gao) and ruled by the House of Liu. The dynasty was preceded by the short-lived Qin dynasty (221–207 BC) and a warr ...
(202 BC—AD 220) created steel by melting together wrought iron with cast iron, thus producing a carbon-intermediate steel by the 1st century AD.Gernet, Jacques (1982). ''A History of Chinese Civilization''. Cambridge: Cambridge University Press. p. 69. . There is evidence that carbon steel was made in Western
Tanzania Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands ...
by the ancestors of the
Haya people The Haya (or Bahaya) are a Bantu ethnic group based in Kagera Region, northwestern Tanzania, on the western side of Lake Victoria. With over one million people, it is estimated the Haya make up approximately 2% of the population of Tanzania. Hi ...
as early as 2,000 years ago by a complex process of "pre-heating" allowing temperatures inside a furnace to reach 1300 to 1400 °C.


Wootz and Damascus

Evidence of the earliest production of high carbon steel in
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
are found in Kodumanal in
Tamil Nadu Tamil Nadu (; , TN) is a state in southern India. It is the tenth largest Indian state by area and the sixth largest by population. Its capital and largest city is Chennai. Tamil Nadu is the home of the Tamil people, whose Tamil language ...
, the Golconda area in
Andhra Pradesh Andhra Pradesh (, abbr. AP) is a state in the south-eastern coastal region of India. It is the seventh-largest state by area covering an area of and tenth-most populous state with 49,386,799 inhabitants. It is bordered by Telangana to the ...
and
Karnataka Karnataka (; ISO: , , also known as Karunāḍu) is a state in the southwestern region of India. It was formed on 1 November 1956, with the passage of the States Reorganisation Act. Originally known as Mysore State , it was renamed ''Karnat ...
, and in the
Samanalawewa The Samanala Dam ( Sinhala: සමනලවැව වේල්ල) is a dam primarily used for hydroelectric power generation in Sri Lanka. Commissioned in 1992, the Samanalawewa Project (''Samanala Reservoir Project'') is the third-largest hydro ...
, Dehigaha Alakanda, areas of Sri Lanka. This came to be known as
Wootz steel Wootz steel, also known as Seric steel, is a crucible steel characterized by a pattern of bands and high carbon content. These bands are formed by sheets of microscopic carbides within a tempered martensite or pearlite matrix in higher carbon ...
, produced in South India by about the sixth century BC and exported globally. The steel technology existed prior to 326 BC in the region as they are mentioned in literature of Sangam Tamil, Arabic, and Latin as the finest steel in the world exported to the Romans, Egyptian, Chinese and Arab worlds at that time – what they called ''Seric Iron''. A 200 BC Tamil trade guild in Tissamaharama, in the South East of Sri Lanka, brought with them some of the oldest iron and steel artifacts and production processes to the island from the classical period. The Chinese and locals in
Anuradhapura Anuradhapura ( si, අනුරාධපුරය, translit=Anurādhapuraya; ta, அனுராதபுரம், translit=Aṉurātapuram) is a major city located in north central plain of Sri Lanka. It is the capital city of North Central ...
, Sri Lanka had also adopted the production methods of creating Wootz steel from the Chera Dynasty Tamils of South India by the 5th century AD. In Sri Lanka, this early steel-making method employed a unique wind furnace, driven by the monsoon winds, capable of producing high-carbon steel.Coghlan, Herbert Henery. (1977). ''Notes on prehistoric and early iron in the Old World''. Oxprint. pp. 99–100 Since the technology was acquired from the
Tamilians The Tamil people, also known as Tamilar ( ta, தமிழர், Tamiḻar, translit-std=ISO, in the singular or ta, தமிழர்கள், Tamiḻarkaḷ, translit-std=ISO, label=none, in the plural), or simply Tamils (), are a Drav ...
from South India, the origin of steel technology in India can be conservatively estimated at 400–500 BC. The manufacture of what came to be called Wootz, or
Damascus steel Damascus steel was the forged steel of the blades of swords smithed in the Near East from ingots of Wootz steel either imported from Southern India or made in production centres in Sri Lanka, or Khorasan, Iran. These swords are characterized by ...
, famous for its durability and ability to hold an edge, may have been taken by the Arabs from Persia, who took it from India. It was originally created from several different materials including various
trace element __NOTOC__ A trace element, also called minor element, is a chemical element whose concentration (or other measure of amount) is very low (a "trace amount"). They are classified into two groups: essential and non-essential. Essential trace elements ...
s, apparently ultimately from the writings of
Zosimos of Panopolis Zosimos of Panopolis ( el, Ζώσιμος ὁ Πανοπολίτης; also known by the Latin name Zosimus Alchemista, i.e. "Zosimus the Alchemist") was a Greco-Egyptian alchemist and Gnostic mystic who lived at the end of the 3rd and beginning ...
. In 327 BC,
Alexander the Great Alexander III of Macedon ( grc, Ἀλέξανδρος, Alexandros; 20/21 July 356 BC – 10/11 June 323 BC), commonly known as Alexander the Great, was a king of the ancient Greek kingdom of Macedon. He succeeded his father Philip II to ...
was rewarded by the defeated King
Porus Porus or Poros ( grc, Πῶρος ; 326–321 BC) was an ancient Indian king whose territory spanned the region between the Jhelum River (Hydaspes) and Chenab River (Acesines), in the Punjab region of the Indian subcontinent. He is only ment ...
, not with gold or silver but with 30 pounds of steel. A recent study has speculated that
carbon nanotubes A scanning tunneling microscopy image of a single-walled carbon nanotube Rotating single-walled zigzag carbon nanotube A carbon nanotube (CNT) is a tube made of carbon with diameters typically measured in nanometers. ''Single-wall carbon na ...
were included in its structure, which might explain some of its legendary qualities, though, given the technology of that time, such qualities were produced by chance rather than by design. Natural wind was used where the soil containing iron was heated by the use of wood. The ancient Sinhalese managed to extract a ton of steel for every 2 tons of soil, a remarkable feat at the time. One such furnace was found in Samanalawewa and archaeologists were able to produce steel as the ancients did.
Crucible steel Crucible steel is steel made by melting pig iron (cast 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 ...
, formed by slowly heating and cooling pure iron and carbon (typically in the form of charcoal) in a crucible, was produced in
Merv Merv ( tk, Merw, ', مرو; fa, مرو, ''Marv''), also known as the Merve Oasis, formerly known as Alexandria ( grc-gre, Ἀλεξάνδρεια), Antiochia in Margiana ( grc-gre, Ἀντιόχεια ἡ ἐν τῇ Μαργιανῇ) and ...
by the 9th to 10th century AD. In the 11th century, there is evidence of the production of steel in
Song China The Song dynasty (; ; 960–1279) was an imperial dynasty of China that began in 960 and lasted until 1279. The dynasty was founded by Emperor Taizu of Song following his usurpation of the throne of the Later Zhou. The Song conquered the rest ...
using two techniques: a "berganesque" method that produced inferior, inhomogeneous steel, and a precursor to the modern
Bessemer process The Bessemer process was the first inexpensive industrial process for the mass production of steel from molten pig iron before the development of the open hearth furnace. The key principle is removal of impurities from the iron by oxidation ...
that used partial
decarbonization Climate change mitigation is action to limit climate change by reducing emissions of greenhouse gases or removing those gases from the atmosphere. The recent rise in global average temperature is mostly caused by emissions from fossil fuels b ...
via repeated forging under a
cold blast Cold blast, in ironmaking, refers to a metallurgical furnace where air is not preheated before being blown into the furnace. This represents the earliest stage in the development of ironmaking. Until the 1820s, the use of cold air was thought to b ...
.


Modern

Since the 17th century, the first step in European steel production has been the smelting of iron ore into pig iron in a blast furnace.Tylecote, R.F. (1992) ''A history of metallurgy'' 2nd ed., Institute of Materials, London. pp. 95–99 and 102–105. . Originally employing charcoal, modern methods use coke, which has proven more economical.


Processes starting from bar iron

In these processes pig iron was refined (fined) in a
finery forge A finery forge is a forge used to produce wrought iron from pig iron by decarburization in a process called "fining" which involved liquifying cast iron in a fining hearth and removing carbon from the molten cast iron through oxidation. Finery ...
to produce
bar iron Wrought iron is an iron alloy with a very low carbon content (less than 0.08%) in contrast to that of cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag inclusions (up to 2% by weight), which give it a wood-like "grain" t ...
, which was then used in steel-making. The production of steel by the cementation process was described in a treatise published in Prague in 1574 and was in use in
Nuremberg Nuremberg ( ; german: link=no, Nürnberg ; in the local East Franconian dialect: ''Nämberch'' ) is the second-largest city of the German state of Bavaria after its capital Munich, and its 518,370 (2019) inhabitants make it the 14th-largest ...
from 1601. A similar process for
case hardening Case-hardening or surface hardening is the process of hardening the surface of a metal object while allowing the metal deeper underneath to remain soft, thus forming a thin layer of harder metal at the surface. For iron or steel with low carbon ...
armor and files was described in a book published in
Naples Naples (; it, Napoli ; nap, Napule ), from grc, Νεάπολις, Neápolis, lit=new city. is the regional capital of Campania and the third-largest city of Italy, after Rome and Milan, with a population of 909,048 within the city's adminis ...
in 1589. The process was introduced to England in about 1614 and used to produce such steel by Sir Basil Brooke at
Coalbrookdale Coalbrookdale is a village in the Ironbridge Gorge in Shropshire, England, containing a settlement of great significance in the history of iron ore smelting. It lies within the civil parish called the Gorge. This is where iron ore was first s ...
during the 1610s. The raw material for this process were bars of iron. During the 17th century, it was realized that the best steel came from
oregrounds iron Oregrounds iron was a grade of iron that was regarded as the best grade available in 18th century England. The term was derived from the small Swedish city of Öregrund, the port from which the bar iron was shipped. It was produced using the Wal ...
of a region north of Stockholm, Sweden. This was still the usual raw material source in the 19th century, almost as long as the process was used. Crucible steel is steel that has been melted in a
crucible A crucible is a ceramic or metal container in which metals or other substances may be melted or subjected to very high temperatures. While crucibles were historically usually made from clay, they can be made from any material that withstands te ...
rather than having been
forged Forging is a manufacturing process involving the shaping of metal using localized compressive forces. The blows are delivered with a hammer (often a power hammer) or a die. Forging is often classified according to the temperature at which it ...
, with the result that it is more homogeneous. Most previous furnaces could not reach high enough temperatures to melt the steel. The early modern crucible steel industry resulted from the invention of
Benjamin Huntsman Benjamin Huntsman (4 June 170420 June 1776) was an English inventor and manufacturer of cast or crucible steel. Biography Huntsman was born the fourth child of William and Mary (née Nainby) Huntsman, a Quaker farming couple, in Epworth, Li ...
in the 1740s. Blister steel (made as above) was melted in a crucible or in a furnace, and cast (usually) into ingots.


Processes starting from pig iron

The modern era in
steelmaking Steelmaking is the process of producing steel from iron ore and carbon/or scrap. In steelmaking, impurities such as nitrogen, silicon, phosphorus, sulfur and excess carbon (the most important impurity) are removed from the sourced iron, and alloy ...
began with the introduction of
Henry Bessemer Sir Henry Bessemer (19 January 1813 – 15 March 1898) was an English inventor, whose steel-making process would become the most important technique for making steel in the nineteenth century for almost one hundred years from 1856 to 1950. H ...
's
process A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management *Business process, activities that produce a specific se ...
in 1855, the raw material for which was pig iron. His method let him produce steel in large quantities cheaply, thus mild steel came to be used for most purposes for which wrought iron was formerly used. The Gilchrist-Thomas process (or ''basic Bessemer process'') was an improvement to the Bessemer process, made by lining the converter with a basic material to remove phosphorus. Another 19th-century steelmaking process was the Siemens-Martin process, which complemented the Bessemer process. It consisted of co-melting bar iron (or steel scrap) with pig iron. These methods of steel production were rendered obsolete by the Linz-Donawitz process of
basic oxygen steelmaking Basic oxygen steelmaking (BOS, BOP, BOF, or OSM), also known as Linz-Donawitz steelmaking or the oxygen converter processBrock and Elzinga, p. 50. is a method of primary steelmaking in which carbon-rich molten pig iron is made into steel. Blowin ...
(BOS), developed in 1952, and other oxygen steel making methods. Basic oxygen steelmaking is superior to previous steelmaking methods because the oxygen pumped into the furnace limited impurities, primarily nitrogen, that previously had entered from the air used, and because, with respect to the open hearth process, the same quantity of steel from a BOS process is manufactured in one-twelfth the time. Today,
electric arc furnace An electric arc furnace (EAF) is a furnace that heats material by means of an electric arc. Industrial arc furnaces range in size from small units of approximately one-tonne capacity (used in foundries for producing cast iron products) up to ...
s (EAF) are a common method of reprocessing
scrap metal Scrap consists of recyclable materials, usually metals, left over from product manufacturing and consumption, such as parts of vehicles, building supplies, and surplus materials. Unlike waste, scrap has monetary value, especially recovered me ...
to create new steel. They can also be used for converting pig iron to steel, but they use a lot of electrical energy (about 440 kWh per metric ton), and are thus generally only economical when there is a plentiful supply of cheap electricity.


Industry

The steel industry is often considered an indicator of economic progress, because of the critical role played by steel in infrastructural and overall
economic development In the economics study of the public sector, economic and social development is the process by which the economic well-being and quality of life of a nation, region, local community, or an individual are improved according to targeted goals and ...
. In 1980, there were more than 500,000 U.S. steelworkers. By 2000, the number of steelworkers had fallen to 224,000. The
economic boom An economic expansion is an increase in the level of economic activity, and of the goods and services available. It is a period of economic growth as measured by a rise in real GDP. The explanation of fluctuations in aggregate economic activit ...
in China and India caused a massive increase in the demand for steel. Between 2000 and 2005, world steel demand increased by 6%. Since 2000, several Indian and Chinese steel firms have risen to prominence, such as
Tata Steel Tata Steel Limited is an Indian multinational steel-making company, based in Jamshedpur, Jharkhand and headquartered in Mumbai, Maharashtra. It is a part of the Tata Group. Formerly known as Tata Iron and Steel Company Limited (TISCO), Tata S ...
(which bought
Corus Group Corus may refer to: Places *Çörüş, Gazipaşa, a village in Antalya Province, Turkey Facilities and structures * Corus Quay, Toronto, Ontario, Canada; an office tower Fictional locations * Corus, a fictional world that is the setting for the ...
in 2007),
Baosteel Group China Baowu Steel Group Corp., Ltd., commonly known as Baowu, is a state-owned iron and steel company headquartered in the Baosteel Tower in Pudong, Shanghai, China. The company was formed by Baosteel Group absorbing its smaller state-owned pe ...
and Shagang Group. , though,
ArcelorMittal ArcelorMittal S.A. is a Luxembourgian multinational steel manufacturing corporation headquartered in Luxembourg City. It was formed in 2006 from the takeover and merger of Arcelor by Indian-owned Mittal Steel. ArcelorMittal is the second la ...
is the world's largest steel producer. In 2005, the British Geological Survey stated China was the top steel producer with about one-third of the world share; Japan, Russia, and the US followed respectively. The large production capacity of steel results also in a significant amount of carbon dioxide emissions inherent related to the main production route. In 2021, it was estimated that around 7% of the global greenhouse gas emissions resulted from the steel industry. Reduction of these emissions are expected to come from a shift in the main production route using cokes, more recycling of steel and the application of carbon capture and storage or carbon capture and utilization technology. In 2008, steel began trading as a commodity on the
London Metal Exchange The London Metal Exchange (LME) is a futures and forwards exchange with the world's largest market in standarised forward contracts, futures contracts and options on base metals. The exchange also offers contracts on ferrous metals and precious ...
. At the end of 2008, the steel industry faced a sharp downturn that led to many cut-backs.


Recycling

Steel is one of the world's most-recycled materials, with a recycling rate of over 60% globally; in the United States alone, over were recycled in the year 2008, for an overall recycling rate of 83%. As more steel is produced than is scrapped, the amount of recycled raw materials is about 40% of the total of steel produced - in 2016, of crude steel was produced globally, with recycled.


Contemporary


Carbon

Modern steels are made with varying combinations of alloy metals to fulfill many purposes. Carbon steel, composed simply of iron and carbon, accounts for 90% of steel production.
Low alloy steel Alloy steel is steel that is alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to improve its mechanical properties. Alloy steels are broken down into two groups: low alloy steels and high alloy steels. The differe ...
is alloyed with other elements, usually molybdenum, manganese, chromium, or nickel, in amounts of up to 10% by weight to improve the hardenability of thick sections. High strength low alloy steel has small additions (usually < 2% by weight) of other elements, typically 1.5% manganese, to provide additional strength for a modest price increase. Recent Corporate Average Fuel Economy (CAFE) regulations have given rise to a new variety of steel known as Advanced High Strength Steel (AHSS). This material is both strong and ductile so that vehicle structures can maintain their current safety levels while using less material. There are several commercially available grades of AHSS, such as
dual-phase steel Dual-phase steel (DP steel) is a high-strength steel that has a ferritic– martensitic microstructure. DP steels are produced from low or medium carbon steels that are quenched from a temperature above A1 but below A3 determined from continuous c ...
, which is heat treated to contain both a ferritic and martensitic microstructure to produce a formable, high strength steel. Transformation Induced Plasticity (TRIP) steel involves special alloying and heat treatments to stabilize amounts of
austenite Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 K ...
at room temperature in normally austenite-free low-alloy ferritic steels. By applying strain, the austenite undergoes a
phase transition In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states o ...
to martensite without the addition of heat. Twinning Induced Plasticity (TWIP) steel uses a specific type of strain to increase the effectiveness of work hardening on the alloy. Carbon Steels are often
galvanized Galvanization or galvanizing ( also spelled galvanisation or galvanising) is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanizing, in which the parts are submerged ...
, through hot-dip or electroplating in
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
for protection against rust.


Alloy

Stainless steels contain a minimum of 11% chromium, often combined with nickel, to resist
corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...
. Some stainless steels, such as the
ferritic A ferrite is a ceramic material made by mixing and firing large proportions of iron(III) oxide (Fe2O3, rust) blended with small proportions of one or more additional metallic elements, such as strontium, barium, manganese, nickel, and zinc. Th ...
stainless steels are magnetic, while others, such as the
austenitic Austenite, also known as gamma-phase iron (γ-Fe), is a metallic, non-magnetic allotrope of iron or a solid solution of iron with an alloying element. In plain-carbon steel, austenite exists above the critical eutectoid temperature of 1000 ...
, are nonmagnetic. Corrosion-resistant steels are abbreviated as CRES. Alloy steels are plain-carbon steels in which small amounts of alloying elements like chromium and vanadium have been added. Some more modern steels include
tool steel Tool steel is any of various carbon steels and alloy steels that are particularly well-suited to be made into tools and tooling, including cutting tools, dies, hand tools, knives, and others. Their suitability comes from their distinctive har ...
s, which are alloyed with large amounts of tungsten and
cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, p ...
or other elements to maximize solution hardening. This also allows the use of
precipitation hardening Precipitation hardening, also called age hardening or particle hardening, is a heat treatment technique used to increase the yield strength of malleable materials, including most structural alloys of aluminium, magnesium, nickel, titanium, and ...
and improves the alloy's temperature resistance. Tool steel is generally used in axes, drills, and other devices that need a sharp, long-lasting cutting edge. Other special-purpose alloys include
weathering steel Weathering steel, often referred to by the genericised trademark COR-TEN steel and sometimes written without the hyphen as corten steel, is a group of steel alloys which were developed to eliminate the need for painting, and form a stable r ...
s such as Cor-ten, which weather by acquiring a stable, rusted surface, and so can be used un-painted.
Maraging steel Maraging steels (a portmanteau of " martensitic" and "aging") are steels that are known for possessing superior strength and toughness without losing ductility. ''Aging'' refers to the extended heat-treatment process. These steels are a special cla ...
is alloyed with nickel and other elements, but unlike most steel contains little carbon (0.01%). This creates a very strong but still
malleable Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...
steel.
Eglin steel Eglin steel (ES-1) is a high- strength, high-performance, low-alloy, low-cost steel, developed for a new generation of bunker buster type bombs, e.g. the Massive Ordnance Penetrator and the improved version of the GBU-28 bomb known as EGBU-28. It ...
uses a combination of over a dozen different elements in varying amounts to create a relatively low-cost steel for use in
bunker buster A bunker buster is a type of munition that is designed to penetrate hardened targets or targets buried deep underground, such as military bunkers. Armor piercing shells Germany Röchling shells were bunker-busting artillery shells, developed ...
weapons. Hadfield steel (after Sir
Robert Hadfield Sir Robert Abbott Hadfield, 1st Baronet FRS (28 November 1858 in Sheffield – 30 September 1940 in Surrey) was an English metallurgist, noted for his 1882 discovery of manganese steel, one of the first steel alloys. He also invented silicon ...
) or manganese steel contains 12–14% manganese which when abraded strain-hardens to form a very hard skin which resists wearing. Examples include tank tracks, bulldozer blade edges, and cutting blades on the
jaws of life Hydraulic rescue tools, also known as jaws of life, are used by emergency rescue personnel to assist in the extrication of victims involved in vehicle accidents, as well as other rescues in small spaces. These tools include cutters, spreaders, ...
.


Standards

Most of the more commonly used steel alloys are categorized into various grades by standards organizations. For example, the
Society of Automotive Engineers SAE International, formerly named the Society of Automotive Engineers, is a United States-based, globally active professional association and standards developing organization for engineering professionals in various industries. SAE Internatio ...
has a series of grades defining many types of steel. The
American Society for Testing and Materials ASTM International, formerly known as American Society for Testing and Materials, is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, an ...
has a separate set of standards, which define alloys such as
A36 steel A36 steel is a common structural steel alloy utilized in the United States.''Steel Construction Manual'', 8th Edition, second revised edition, American Institute of Steel Construction, 1986, Ch. 1 pp. 1–5. The A36 (UNS K02600) standard was establ ...
, the most commonly used structural steel in the United States. The JIS also defines a series of steel grades that are being used extensively in Japan as well as in developing countries.


Uses

Iron and steel are used widely in the construction of roads, railways, other infrastructure, appliances, and buildings. Most large modern structures, such as
stadiums A stadium ( : stadiums or stadia) is a place or venue for (mostly) outdoor sports, concerts, or other events and consists of a field or stage either partly or completely surrounded by a tiered structure designed to allow spectators to stand o ...
and skyscrapers, bridges, and airports, are supported by a steel skeleton. Even those with a concrete structure employ steel for reinforcing. It sees widespread use in major appliances and
cars A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, Car seat, seat one to eight people, have four wheels, and mainly transport private transport#Personal transport, people in ...
. Despite the growth in usage of
aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
, steel is still the main material for car bodies. Steel is used in a variety of other construction materials, such as bolts, nails and
screw A screw and a bolt (see '' Differentiation between bolt and screw'' below) are similar types of fastener typically made of metal and characterized by a helical ridge, called a ''male thread'' (external thread). Screws and bolts are used to f ...
s and other household products and cooking utensils. Other common applications include
shipbuilding Shipbuilding is the construction of ships and other floating vessels. It normally takes place in a specialized facility known as a shipyard. Shipbuilders, also called shipwrights, follow a specialized occupation that traces its roots to befo ...
, pipelines,
mining Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the economic ...
,
offshore construction Offshore construction is the installation of structures and facilities in a marine environment, usually for the production and transmission of electricity, oil, gas and other resources. It is also called maritime engineering. Construction a ...
,
aerospace Aerospace is a term used to collectively refer to the atmosphere and outer space. Aerospace activity is very diverse, with a multitude of commercial, industrial and military applications. Aerospace engineering consists of aeronautics and astr ...
,
white goods A major appliance, also known as a large domestic appliance or large electric appliance or simply a large appliance, large domestic, or large electric, is a non-portable or semi-portable machine used for routine housekeeping tasks such as cookin ...
(e.g.
washing machine A washing machine (laundry machine, clothes washer, washer, or simply wash) is a home appliance used to wash laundry. The term is mostly applied to machines that use water as opposed to dry cleaning (which uses alternative cleaning fluids and ...
s), heavy equipment such as bulldozers, office furniture, steel wool,
tool A tool is an object that can extend an individual's ability to modify features of the surrounding environment or help them accomplish a particular task. Although many animals use simple tools, only human beings, whose use of stone tools dates ba ...
, and armour in the form of personal vests or
vehicle armour Military vehicles are commonly armoured (or armored; see spelling differences) to withstand the impact of shrapnel, bullets, shells, rockets, and missiles, protecting the personnel inside from enemy fire. Such vehicles include armoured fi ...
(better known as
rolled homogeneous armour Rolled homogeneous armour (RHA) is a type of vehicle armour made of a single steel composition hot-rolled to improve its material characteristics, as opposed to layered or cemented armour. Its first common application was in tanks. After World ...
in this role).


Historical

Before the introduction of the
Bessemer process The Bessemer process was the first inexpensive industrial process for the mass production of steel from molten pig iron before the development of the open hearth furnace. The key principle is removal of impurities from the iron by oxidation ...
and other modern production techniques, steel was expensive and was only used where no cheaper alternative existed, particularly for the cutting edge of
knives A knife ( : knives; from Old Norse 'knife, dirk') is a tool or weapon with a cutting edge or blade, usually attached to a handle or hilt. One of the earliest tools used by humanity, knives appeared at least 2.5 million years ago, as evidenced ...
,
razors A razor is a bladed tool primarily used in the removal of body hair through the act of shaving. Kinds of razors include straight razors, safety razors, disposable razors, and electric razors. While the razor has been in existence since before ...
, swords, and other items where a hard, sharp edge was needed. It was also used for springs, including those used in clocks and watches. With the advent of speedier and thriftier production methods, steel has become easier to obtain and much cheaper. It has replaced wrought iron for a multitude of purposes. However, the availability of plastics in the latter part of the 20th century allowed these materials to replace steel in some applications due to their lower fabrication cost and weight.
Carbon fiber Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...
is replacing steel in some cost insensitive applications such as sports equipment and high-end automobiles.


Long

* As reinforcing bars and mesh in reinforced concrete *
Railroad tracks A railway track (British English and UIC terminology) or railroad track (American English), also known as permanent way or simply track, is the structure on a railway or railroad consisting of the rails, fasteners, railroad ties (sleepers, ...
* Structural steel in modern buildings and bridges *
Wire Overhead power cabling. The conductor consists of seven strands of steel (centre, high tensile strength), surrounded by four outer layers of aluminium (high conductivity). Sample diameter 40 mm A wire is a flexible strand of metal. Wire is c ...
s * Input to reforging applications


Flat carbon

*
Major appliance A major appliance, also known as a large domestic appliance or large electric appliance or simply a large appliance, large domestic, or large electric, is a non-portable or semi-portable machine used for routine housekeeping tasks such as cookin ...
s * Magnetic cores * The inside and outside body of automobiles, trains, and ships.


Weathering (COR-TEN)

*
Intermodal container An intermodal container, often called a shipping container, is a large standardized shipping container, designed and built for intermodal freight transport, meaning these containers can be used across different modes of transport – from ship ...
s * Outdoor sculptures *
Architecture Architecture is the art and technique of designing and building, as distinguished from the skills associated with construction. It is both the process and the product of sketching, conceiving, planning, designing, and constructing building ...
* Highliner
train car A railroad car, railcar ( American and Canadian English), railway wagon, railway carriage, railway truck, railwagon, railcarriage or railtruck (British English and UIC), also called a train car, train wagon, train carriage or train truck, is ...
s


Stainless

* Cutlery *
Ruler A ruler, sometimes called a rule, line gauge, or scale, is a device used in geometry and technical drawing, as well as the engineering and construction industries, to measure distances or draw straight lines. Variants Rulers have long ...
s *
Surgical instrument A surgical instrument is a tool or device for performing specific actions or carrying out desired effects during a surgery or operation, such as modifying biological tissue, or to provide access for viewing it. Over time, many different kinds of ...
s *
Watch A watch is a portable timepiece intended to be carried or worn by a person. It is designed to keep a consistent movement despite the motions caused by the person's activities. A wristwatch is designed to be worn around the wrist, attached b ...
es *
Gun A gun is a ranged weapon designed to use a shooting tube (gun barrel) to launch projectiles. The projectiles are typically solid, but can also be pressurized liquid (e.g. in water guns/cannons, spray guns for painting or pressure washing, p ...
s * Rail passenger vehicles * Tablets * Trash Cans * Body piercing jewellery * Inexpensive
rings Ring may refer to: * Ring (jewellery), a round band, usually made of metal, worn as ornamental jewelry * To make a sound with a bell, and the sound made by a bell :(hence) to initiate a telephone connection Arts, entertainment and media Film and ...
* Components of
spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...
and space stations


Low-background

Steel manufactured after
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...
became
contaminated Contamination is the presence of a constituent, impurity, or some other undesirable element that spoils, corrupts, infects, makes unfit, or makes inferior a material, physical body, natural environment, workplace, etc. Types of contamination ...
with radionuclides by
nuclear weapons testing Nuclear weapons tests are experiments carried out to determine nuclear weapons' effectiveness, yield, and explosive capability. Testing nuclear weapons offers practical information about how the weapons function, how detonations are affected by ...
. Low-background steel, steel manufactured prior to 1945, is used for certain radiation-sensitive applications such as Geiger counters and
radiation shielding Radiation protection, also known as radiological protection, is defined by the International Atomic Energy Agency (IAEA) as "The protection of people from harmful effects of exposure to ionizing radiation, and the means for achieving this". Exposur ...
.


See also

*
Bulat steel Bulat is a type of steel alloy known in Russia from medieval times; it was regularly mentioned in Russian legends as the material of choice for cold steel. The name ''булат'' is a Russian transliteration of the Persian word ''fulad'', meani ...
* Carbon steel *
Damascus steel Damascus steel was the forged steel of the blades of swords smithed in the Near East from ingots of Wootz steel either imported from Southern India or made in production centres in Sri Lanka, or Khorasan, Iran. These swords are characterized by ...
* Galvanising * Global steel industry trends *
Iron in folklore Iron has a long and varied tradition in the mythology and folklore of the world. While iron is now the name of a chemical element, the traditional meaning of the word "iron" is what is now called wrought iron. In East Asia, cast iron was also ...
*
Knife metal Blade materials are materials used to make the blade of a knife or other simple edged hand tool or weapon, such as a hatchet or sword. Blades can be made from a variety of materials. The most common being carbon steel, stainless steel, tool s ...
*
Machinability Machinability is the ease with which a metal can be cut (machined) permitting the removal of the material with a satisfactory finish at low cost.Degarmo, p. 542. Materials with good machinability (free machining materials) require little power to c ...
*
Noric steel Noric steel was a steel from Noricum, a Celtic kingdom located in modern Austria and Slovenia. The proverbial hardness of Noric steel is expressed by Ovid: ''"...durior ..ferro quod noricus excoquit ignis..."'' which roughly translates to "...har ...
* Pelletizing *
Rolling Rolling is a type of motion that combines rotation (commonly, of an axially symmetric object) and translation of that object with respect to a surface (either one or the other moves), such that, if ideal conditions exist, the two are in contact ...
*
Rolling mill In metalworking, rolling is a metal forming process in which metal stock is passed through one or more pairs of rolls to reduce the thickness, to make the thickness uniform, and/or to impart a desired mechanical property. The concept is simil ...
*
Rust Belt The Rust Belt is a region of the United States that experienced industrial decline starting in the 1950s. The U.S. manufacturing sector as a percentage of the U.S. GDP peaked in 1953 and has been in decline since, impacting certain regions an ...
*
Second Industrial Revolution The Second Industrial Revolution, also known as the Technological Revolution, was a phase of rapid scientific discovery, standardization, mass production and industrialization from the late 19th century into the early 20th century. The Fi ...
*
Silicon steel Electrical steel (E-steel, lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) is an iron alloy tailored to produce specific magnetic properties: small hysteresis area resulting in low power loss per cycle ...
* Steel abrasive * Steel mill *
Tamahagane ''Tamahagane'' (玉鋼) is a type of steel made in the Japanese tradition. The word ''tama'' means "precious". The word ''hagane'' means "steel". Tamahagane is used to make Japanese swords, knives, and other kinds of tools. The carbon content ...
, used in Japanese swords *
Tinplate Tinplate consists of sheets of steel coated with a thin layer of tin to impede rusting. Before the advent of cheap milled steel, the backing metal was wrought iron. While once more widely used, the primary use of tinplate now is the manufacture ...
*
Toledo steel Toledo steel, historically known for being unusually hard, is from Toledo, Spain, which has been a traditional sword-making, metal-working center since about the Roman period, and came to the attention of Rome when used by Hannibal in the Punic W ...
*
Wootz steel Wootz steel, also known as Seric steel, is a crucible steel characterized by a pattern of bands and high carbon content. These bands are formed by sheets of microscopic carbides within a tempered martensite or pearlite matrix in higher carbon ...


References


Bibliography

* * * * * * * Verein Deutscher Eisenhüttenleute (Ed.). ''Steel – A Handbook for Materials Research and Engineering, Volume 1: Fundamentals''. Springer-Verlag Berlin, Heidelberg and Verlag Stahleisen, Düsseldorf 1992, 737 p. . * Verein Deutscher Eisenhüttenleute (Ed.). ''Steel – A Handbook for Materials Research and Engineering, Volume 2: Applications''. Springer-Verlag Berlin, Heidelberg and Verlag Stahleisen, Düsseldorf 1993, 839 pages, . *


Further reading

* Mark Reutter,
Making Steel: Sparrows Point and the Rise and Ruin of American Industrial Might
'. University of Illinois Press, 2005. * Duncan Burn,
The Economic History of Steelmaking, 1867–1939: A Study in Competition
'. Cambridge University Press, 1961. * Harukiyu Hasegawa,
The Steel Industry in Japan: A Comparison with Britain
'. Routledge, 1996. * J.C. Carr and W. Taplin,
History of the British Steel Industry
'. Harvard University Press, 1962. * H. Lee Scamehorn,
Mill & Mine: The Cf&I in the Twentieth Century
'. University of Nebraska Press, 1992. * Warren, Kenneth,
Big Steel: The First Century of the United States Steel Corporation, 1901–2001
'. University of Pittsburgh Press, 2001.


External links


Official website
of the
World Steel Association World Steel Association, often abbreviated as worldsteel, is the international trade body for the iron and steel industry. The association is one of the largest and most dynamic industry associations in the world, with members in every major st ...
(worldsteel) *
steeluniversity.org
Online steel education resources, an initiative of World Steel Association
Metallurgy for the Non-Metallurgist
from the
American Society for Metals ASM International, formerly known as the American Society for Metals, is an association of materials-centric engineers and scientists. ASM provides several information resources, including technical books, various digital databases, and ASM Han ...

MATDAT Database of Properties of Unalloyed, Low-Alloy and High-Alloy Steels
– obtained from published results of material testing {{Authority control 2nd-millennium BC introductions Building materials Roofing materials