Steel is an alloy of iron and carbon, and sometimes 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 and face centered cubic, depending on its temperature. In the body-centered cubic arrangement, there is an iron atom in the center and eight atoms at the vertices of each cubic unit cell; in the face-centered cubic, there is one atom at the center of each of the six faces of the cubic unit cell and eight atoms at its vertices. 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 2.14% 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), 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 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 production of blister steel and then crucible steel. With the invention of the Bessemer process in the mid-19th 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 iron.

Further refinements in the process, such as basic oxygen steelmaking (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 common manmade 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 organizations.

Definitions and related materials

The noun steel originates from the Proto-Germanic adjective stahliją or stakhlijan (made of steel), which is related to stahlaz or stahliją (standing firm).[1]

The carbon content of steel is between 0.002% and 2.14% by weight for plain ironcarbon alloys.[2] These values vary depending on alloying elements such as manganese, chromium, nickel, tungsten, and so on. Basically, steel is an iron-carbon alloy that does not undergo eutectic reaction. In contrast, cast iron does undergo eutectic reaction. 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. While iron alloyed with carbon is called carbon steel, alloy steel is steel to which other alloying elements have been intentionally added to modify the characteristics of steel. Common alloying elements include: manganese, nickel, chromium, molybdenum, boron, titanium, vanadium, tungsten, cobalt, and niobium.[3] Additional elements, most frequently considered undesirable, are also important in steel: phosphorus, sulfur, silicon, and traces of oxygen, nitrogen, and copper.

Plain carbon-iron alloys with a higher than 2.1% carbon content are known as cast iron. With modern steelmaking 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 as it has a lower melting point than steel and good castability properties.[3] 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 objects. Steel is distinguishable from wrought iron (now largely obsolete), which may contain a small amount of carbon but large amounts of slag.

Material properties

Iron carbon phase diagram
Iron-carbon equilibrium phase diagram, showing the conditions necessary to form different phases

Iron is commonly found in the Earth's crust in the form of an ore, usually an iron oxide, such as magnetite 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, was first applied to metals with lower melting points, such as tin, which melts at about 250 °C (482 °F), and copper, which melts at about 1,100 °C (2,010 °F), and the combination, bronze, which has a melting point lower than 1,083 °C (1,981 °F). In comparison, cast iron melts at about 1,375 °C (2,507 °F).[4] Small quantities of iron were smelted in ancient times, in the solid state, by heating the ore in a charcoal fire and then welding 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. Since the oxidation rate of iron increases rapidly beyond 800 °C (1,470 °F), 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.[4] 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 desired properties. Nickel and manganese in steel add to its tensile strength and make the austenite 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.[5]

To inhibit corrosion, at least 11% chromium is 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, keeping carbon in the iron matrix and allowing martensite to preferentially form at slower quench rates, resulting in high speed steel. On the other hand, sulfur, nitrogen, and phosphorus are considered contaminants that make steel more brittle and are removed from the steel melt during processing.[5]

The density of steel varies based on the alloying constituents but usually ranges between 7,750 and 8,050 kg/m3 (484 and 503 lb/cu ft), or 7.75 and 8.05 g/cm3 (4.48 and 4.65 oz/cu in).[6]

Even in a narrow range of concentrations of mixtures of carbon and iron that make a steel, a number of 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-centered cubic (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 0 °C (32 °F) and 0.021 wt% at 723 °C (1,333 °F). The inclusion of carbon in alpha iron is called ferrite. At 910 °C, pure iron transforms into a face-centered cubic (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%[7] (38 times that of ferrite) carbon at 1,148 °C (2,098 °F), which reflects the upper carbon content of steel, beyond which is cast iron.[8] 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 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 out of solution as cementite, 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, named for its resemblance to mother of pearl. 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 until the percentage of carbon in the grains 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.[9] 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-centered austenite and forms martensite. 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-centered tetragonal (BCT) structure. There is no thermal activation energy for the transformation from austenite to martensite. Moreover, there is no compositional change so the atoms generally retain their same neighbors.[10]

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 on the crystals of martensite and tension on the remaining ferrite, with a fair amount of shear 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 and other microscopic imperfections. It is common for quench cracks to form when steel is water quenched, although they may not always be visible.[11]

Heat treatment

There are many types of heat treating processes available to steel. The most common are annealing, quenching, and tempering. Heat treatment is effective on compositions above the eutectoid composition (hypereutectoid) of 0.8% carbon. Hypoeutectoid steel does not benefit from heat treatment.

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, recrystallization, and grain growth. The temperature required to anneal a particular steel depends on the type of annealing to be achieved and the alloying constituents.[12]

Quenching involves heating the steel to create the austenite phase then quenching it in water or oil. This rapid cooling results in a hard but brittle martensitic structure.[10] 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 and hence it reduces the internal stresses and defects. The result is a more ductile and fracture-resistant steel.[13]

Steel production

LightningVolt Iron Ore Pellets
Iron ore pellets for the production of steel

When iron is smelted 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 the raw steel product into ingots 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 only a small fraction is cast into ingots. Approximately 96% of steel is continuously cast, while only 4% is produced as ingots.[14]

The ingots are then heated in a soaking pit and hot rolled into slabs, billets, or blooms. Slabs are hot or cold rolled into sheet metal 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-beams and rails. In modern steel mills these processes often occur in one assembly line, with ore coming in and finished steel products coming out.[15] Sometimes after a steel's final rolling, it is heat treated for strength; however, this is relatively rare.[16]

History of steelmaking

Bas fourneau
Bloomery smelting during the Middle Ages

Ancient steel

Steel was known in antiquity and was produced in bloomeries and crucibles.[17][18]

The earliest known production of steel is seen in pieces of ironware excavated from an archaeological site in Anatolia (Kaman-Kalehöyük) and are nearly 4,000 years old, dating from 1800 BC.[19][20] Horace identifies steel weapons such as the falcata in the Iberian Peninsula, while Noric steel was used by the Roman military.[21]

The reputation of Seric iron of South India (wootz steel) grew considerably in the rest of the world.[18] Metal production sites in Sri Lanka employed wind furnaces driven by the monsoon winds, capable of producing high-carbon steel. Large-scale Wootz steel production in Tamilakam using crucibles and carbon sources such as the plant Avāram occurred by the sixth century BC, the pioneering precursor to modern steel production and metallurgy.[17][18]

The Chinese of the Warring States period (403–221 BC) had quench-hardened steel,[22] while Chinese of the Han dynasty (202 BC – 220 AD) created steel by melting together wrought iron with cast iron, gaining an ultimate product of a carbon-intermediate steel by the 1st century AD.[23][24]

Wootz steel and Damascus steel

Evidence of the earliest production of high carbon steel in the Indian Subcontinent are found in Kodumanal in Tamil Nadu area, Golconda in Andhra Pradesh area and Karnataka, and in Samanalawewa areas of Sri Lanka.[25] This came to be known as Wootz steel, produced in South India by about sixth century BC and exported globally.[26][27] 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.[28] 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.[29][30][31] The Chinese and locals in Anuradhapura, 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.[32][33] In Sri Lanka, this early steel-making method employed a unique wind furnace, driven by the monsoon winds, capable of producing high-carbon steel.[34][35] Since the technology was acquired from the Tamilians from South India, the origin of steel technology in India can be conservatively estimated at 400–500 BC.[26][35]

The manufacture of what came to be called Wootz, or Damascus steel, 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 a number of different materials including various trace elements, apparently ultimately from the writings of Zosimos of Panopolis. In 327 BC, Alexander the Great was rewarded by the defeated King Porus, not with gold or silver but with 30 pounds of steel.[36] Recent studies have suggested that carbon nanotubes 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.[37] 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,[34] a remarkable feat at the time. One such furnace was found in Samanalawewa and archaeologists were able to produce steel as the ancients did.[34][38]

Crucible steel, formed by slowly heating and cooling pure iron and carbon (typically in the form of charcoal) in a crucible, was produced in Merv by the 9th to 10th century AD.[27] In the 11th century, there is evidence of the production of steel in Song China using two techniques: a "berganesque" method that produced inferior, inhomogeneous steel, and a precursor to the modern Bessemer process that used partial decarbonization via repeated forging under a cold blast.[39]

Modern steelmaking

Bessemer Converter Sheffield
A Bessemer converter in Sheffield, England

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.[40] Originally employing charcoal, modern methods use coke, which has proven more economical.[41][42][43]

Processes starting from bar iron

In these processes pig iron was refined (fined) in a finery forge to produce bar iron, which was then used in steel-making.[40]

The production of steel by the cementation process was described in a treatise published in Prague in 1574 and was in use in Nuremberg from 1601. A similar process for case hardening armor and files was described in a book published in Naples in 1589. The process was introduced to England in about 1614 and used to produce such steel by Sir Basil Brooke at Coalbrookdale during the 1610s.[44]

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 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.[45][46]

Crucible steel is steel that has been melted in a crucible rather than having been forged, 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 in the 1740s. Blister steel (made as above) was melted in a crucible or in a furnace, and cast (usually) into ingots.[46][47]

Processes starting from pig iron

Siemens Martin Ofen Brandenburg
A Siemens-Martin steel oven from the Brandenburg Museum of Industry.
Allegheny Ludlum steel furnace
White-hot steel pouring out of an electric arc furnace.

The modern era in steelmaking began with the introduction of Henry Bessemer's Bessemer process in 1855, the raw material for which was pig iron.[48] 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.[49] 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.[46] 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 (BOS), developed in the 1950s, 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.[50] Today, electric arc furnaces (EAF) are a common method of reprocessing scrap metal 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.[51]

Steel industry

Steel production by country map
Steel production (in million tons) by country in 2007

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.[52] In 1980, there were more than 500,000 U.S. steelworkers. By 2000, the number of steelworkers fell to 224,000.[53]

The economic boom 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[54] and Chinese steel firms have risen to prominence, such as Tata Steel (which bought Corus Group in 2007), Baosteel Group and Shagang Group. As of 2017, though, ArcelorMittal is the world's largest steel producer.[55] 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.[56]

In 2008, steel began trading as a commodity on the London Metal Exchange. At the end of 2008, the steel industry faced a sharp downturn that led to many cut-backs.[57]


Steel is one of the world's most-recycled materials, with a recycling rate of over 60% globally;[58] in the United States alone, over 82,000,000 metric tons (81,000,000 long tons; 90,000,000 short tons) were recycled in the year 2008, for an overall recycling rate of 83%.[59]

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, 1,628,000,000 tonnes (1.602×109 long tons; 1.795×109 short tons) of crude steel was produced globally, with 630,000,000 tonnes (620,000,000 long tons; 690,000,000 short tons) recycled.[60]

Contemporary steel

Bethlehem Steel
Bethlehem Steel (Bethlehem, Pennsylvania facility pictured) was one of the world's largest manufacturers of steel before its closure in 2003

Carbon steels

Modern steels are made with varying combinations of alloy metals to fulfill many purposes.[5] Carbon steel, composed simply of iron and carbon, accounts for 90% of steel production.[3] Low alloy steel 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.[3] 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.[61]

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, which is heat treated to contain both a ferritic and martensitic microstructure to produce a formable, high strength steel.[62] Transformation Induced Plasticity (TRIP) steel involves special alloying and heat treatments to stabilize amounts of austenite at room temperature in normally austenite-free low-alloy ferritic steels. By applying strain, the austenite undergoes a phase transition to martensite without the addition of heat.[63] Twinning Induced Plasticity (TWIP) steel uses a specific type of strain to increase the effectiveness of work hardening on the alloy.[64]

Carbon Steels are often galvanized, through hot-dip or electroplating in zinc for protection against rust.[65]

Alloy steels

Stainless steels contain a minimum of 11% chromium, often combined with nickel, to resist corrosion. Some stainless steels, such as the ferritic stainless steels are magnetic, while others, such as the austenitic, are nonmagnetic.[66] Corrosion-resistant steels are abbreviated as CRES.

Some more modern steels include tool steels, which are alloyed with large amounts of tungsten and cobalt or other elements to maximize solution hardening. This also allows the use of precipitation hardening and improves the alloy's temperature resistance.[3] 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 steels such as Cor-ten, which weather by acquiring a stable, rusted surface, and so can be used un-painted.[67] Maraging steel is alloyed with nickel and other elements, but unlike most steel contains little carbon (0.01%). This creates a very strong but still malleable steel.[68]

Eglin steel uses a combination of over a dozen different elements in varying amounts to create a relatively low-cost steel for use in bunker buster weapons. Hadfield steel (after Sir Robert Hadfield) or manganese steel contains 12–14% manganese which when abraded strain-hardens to form an incredibly hard skin which resists wearing. Examples include tank tracks, bulldozer blade edges and cutting blades on the jaws of life.[69]


Most of the more commonly used steel alloys are categorized into various grades by standards organizations. For example, the Society of Automotive Engineers has a series of grades defining many types of steel.[70] The American Society for Testing and Materials has a separate set of standards, which define alloys such as A36 steel, the most commonly used structural steel in the United States.[71] The JIS also define series of steel grades that are being used extensively in Japan as well as in developing countries.


A roll of steel wool

Iron and steel are used widely in the construction of roads, railways, other infrastructure, appliances, and buildings. Most large modern structures, such as stadiums and skyscrapers, bridges, and airports, are supported by a steel skeleton. Even those with a concrete structure employ steel for reinforcing. In addition, it sees widespread use in major appliances and cars. Despite growth in usage of aluminium, it is still the main material for car bodies. Steel is used in a variety of other construction materials, such as bolts, nails, and screws and other household products and cooking utensils.[72]

Other common applications include shipbuilding, pipelines, mining, offshore construction, aerospace, white goods (e.g. washing machines), heavy equipment such as bulldozers, office furniture, steel wool, tools, and armour in the form of personal vests or vehicle armour (better known as rolled homogeneous armour in this role).


Carbon steel knife
A carbon steel knife

Before the introduction of the Bessemer process and other modern production techniques, steel was expensive and was only used where no cheaper alternative existed, particularly for the cutting edge of knives, razors, swords, and other items where a hard, sharp edge was needed. It was also used for springs, including those used in clocks and watches.[46]

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.[73] Carbon fiber is replacing steel in some cost insensitive applications such as aircraft, sports equipment and high end automobiles.

Long steel

The viaduct La Polvorilla, Salta Argentina
A steel bridge
Steel tower
A steel pylon suspending overhead power lines

Flat carbon steel

Weathering steel (COR-TEN)

Stainless steel

Sauce boat
A stainless steel gravy boat

Low-background steel

Steel manufactured after World War II became contaminated with radionuclides by nuclear weapons testing. Low-background steel, steel manufactured prior to 1945, is used for certain radiation-sensitive applications such as Geiger counters and radiation shielding.

See also


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Further reading

External links


An alloy is a combination of metals and of a metal or another element. Alloys are defined by a metallic bonding character. An alloy may be a solid solution of metal elements (a single phase) or a mixture of metallic phases (two or more solutions). Intermetallic compounds are alloys with a defined stoichiometry and crystal structure. Zintl phases are also sometimes considered alloys depending on bond types (see also: Van Arkel–Ketelaar triangle for information on classifying bonding in binary compounds).

Alloys are used in a wide variety of applications. In some cases, a combination of metals may reduce the overall cost of the material while preserving important properties. In other cases, the combination of metals imparts synergistic properties to the constituent metal elements such as corrosion resistance or mechanical strength. Examples of alloys are steel, solder, brass, pewter, duralumin, bronze and amalgams.

The alloy constituents are usually measured by mass percentage for practical applications, and in atomic fraction for basic science studies. Alloys are usually classified as substitutional or interstitial alloys, depending on the atomic arrangement that forms the alloy. They can be further classified as homogeneous (consisting of a single phase), or heterogeneous (consisting of two or more phases) or intermetallic.

Andrew Carnegie

Andrew Carnegie ( kar-NAY-gee, but commonly KAR-nə-ghee or kar-NEG-ee; November 25, 1835 – August 11, 1919) was a Scottish-American industrialist, business magnate, and philanthropist.

Carnegie led the expansion of the American steel industry in the late 19th century and is often identified as one of the richest people (and richest Americans) in history. He became a leading philanthropist in the United States and in the British Empire. During the last 18 years of his life, he gave away about $350 million to charities, foundations, and universities – almost 90 percent of his fortune. His 1889 article proclaiming "The Gospel of Wealth" called on the rich to use their wealth to improve society, and stimulated a wave of philanthropy.

Carnegie was born in Dunfermline, Scotland, and immigrated to the United States with his parents in 1848. Carnegie started work as a telegrapher, and by the 1860s had investments in railroads, railroad sleeping cars, bridges, and oil derricks. He accumulated further wealth as a bond salesman, raising money for American enterprise in Europe. He built Pittsburgh's Carnegie Steel Company, which he sold to J. P. Morgan in 1901 for $303,450,000. It became the U.S. Steel Corporation. After selling Carnegie Steel, he surpassed John D. Rockefeller as the richest American for the next couple of years.

Carnegie devoted the remainder of his life to large-scale philanthropy, with special emphasis on local libraries, world peace, education, and scientific research. With the fortune he made from business, he built Carnegie Hall in New York, NY, and the Peace Palace and founded the Carnegie Corporation of New York, Carnegie Endowment for International Peace, Carnegie Institution for Science, Carnegie Trust for the Universities of Scotland, Carnegie Hero Fund, Carnegie Mellon University, and the Carnegie Museums of Pittsburgh, among others.


ArcelorMittal S.A. (French pronunciation: ​[aʁsəlɔʁmiˈtal]) is an Indian 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 world's largest steel producer, with an annual crude steel production of 98.1 million tons as of 2014. It is ranked 123 in the 2017 Fortune Global 500 ranking of the world's biggest corporations.

Battle of Okinawa

The Battle of Okinawa (Japanese: 沖縄戦, Hepburn: Okinawa-sen) (Okinawan: 沖縄戦, translit. Uchinaa ikusa), codenamed Operation Iceberg, was a major battle of the Pacific War fought on the island of Okinawa by United States Marine and Army forces against the Imperial Japanese Army. The initial invasion of Okinawa on April 1, 1945, was the largest amphibious assault in the Pacific Theater of World War II. The 82-day battle lasted from April 1 until June 22, 1945. After a long campaign of island hopping, the Allies were planning to use Kadena Air Base on the large island of Okinawa as a base for Operation Downfall, the planned invasion of the Japanese home islands, 340 mi (550 km) away.

The United States created the Tenth Army, a cross-branch force consisting of the 7th, 27th, 77th, and 96th infantry divisions of the US Army with the 1st, 2nd, and 6th divisions of the Marine Corps, to fight on the island. The Tenth was unique in that it had its own tactical air force (joint Army-Marine command), and was also supported by combined naval and amphibious forces.

The battle has been referred to as the "typhoon of steel" in English, and tetsu no ame ("rain of steel") or tetsu no bōfū ("violent wind of steel") in Japanese. The nicknames refer to the ferocity of the fighting, the intensity of Japanese kamikaze attacks, and the sheer numbers of Allied ships and armored vehicles that assaulted the island. The battle was one of the bloodiest in the Pacific, with approximately 160,000 casualties on both sides: at least 75,000 Allied and 84,166–117,000 Japanese, including drafted Okinawans wearing Japanese uniforms. 149,425 Okinawans were killed, committed suicide or went missing, a significant proportion of the estimated pre-war 300,000 local population.In the naval operations surrounding the battle, both sides lost considerable numbers of ships and aircraft, including the Japanese battleship Yamato. After the battle, Okinawa provided a fleet anchorage, troop staging areas, and airfields in proximity to Japan in preparation for the planned invasion.

Bethlehem Steel

The Bethlehem Steel Corporation (commonly called Bethlehem Steel) was a steel and shipbuilding company that began operations in 1904 and was America's second-largest steel producer and largest shipbuilder.

The Bethlehem Steel roots trace back to 1857 with the establishment of the Bethlehem Iron Company; the Bethlehem Iron Company (also known as Bethlehem Iron Works or simply Bethlehem Iron) was established as the Saucona Iron Company and ceased operations in 1901. However, the Bethlehem Steel legacy began in 1899 with the formation of the first Bethlehem Steel, the Bethlehem Steel Company which was two years before the Bethlehem Iron Company ceased operations. The Bethlehem Steel Company (also known as Bethlehem Steel Works) leased all properties from the Bethlehem Iron Company from 1899 to 1901 and assumed ownership of all properties from the Bethlehem Iron Company after the Bethlehem Iron Company ceased operations.

The Bethlehem Steel Company became the primary subsidiary company of the Bethlehem Steel Corporation in 1904. The Bethlehem Steel Company is the first Bethlehem Steel while the Bethlehem Steel Corporation is the second Bethlehem Steel; both companies existed simultaneously after 1904, but the Bethlehem Steel Company was eventually merged into the Bethlehem Steel Corporation in the 1960s.

The Bethlehem Steel Corporation (using the Bethlehem Steel Company) and the Bethlehem Shipbuilding Corporation, which was also a Bethlehem Steel Corporation subsidiary, were two of the most powerful symbols of American industrial manufacturing leadership. Their demise is often cited as one of the most prominent examples of the U.S. economy's shift away from industrial manufacturing, its failure to compete with cheap foreign labor, and management's penchant for short-term profits.

After a decline in the American steel industry and other problems leading to the company's bankruptcy in 2001, the Bethlehem Steel Corporation was dissolved and the remaining assets sold to International Steel Group in 2003; Bethlehem Steel Corporation did not merge with/into International Steel Group.

Business magnate

A business magnate or industrialist is an entrepreneur of great influence, importance, or standing in a particular enterprise or field of business. The term characteristically refers to a wealthy entrepreneur or investor who controls, through personal business ownership or dominant shareholding position, a firm or industry whose goods or services are widely consumed. Such individuals may also be called czars, moguls, proprietors, tycoons, taipans, barons, or oligarchs.

Carbon steel

Carbon steel is a steel with carbon content up to 2.1% by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states:

Steel is considered to be carbon steel when:

no minimum content is specified or required for chromium, cobalt, molybdenum, nickel, niobium, titanium, tungsten, vanadium or zirconium, or any other element to be added to obtain a desired alloying effect;

the specified minimum for copper does not exceed 0.40 percent;

or the maximum content specified for any of the following elements does not exceed the percentages noted: manganese 1.65, silicon 0.60, copper 0.60.The term "carbon steel" may also be used in reference to steel which is not stainless steel; in this use carbon steel may include alloy steels.

As the carbon percentage content rises, steel has the ability to become harder and stronger through heat treating; however, it becomes less ductile. Regardless of the heat treatment, a higher carbon content reduces weldability. In carbon steels, the higher carbon content lowers the melting point.

Damascus steel

Damascus steel was the forged steel comprising the blades of swords smithed in the Near East from ingots of wootz steel imported from India and Sri Lanka. These swords are characterized by distinctive patterns of banding and mottling reminiscent of flowing water. Such blades were reputed to be tough, resistant to shattering, and capable of being honed to a sharp, resilient edge.The steel is named after Damascus, the capital city of Syria and one of the largest cities in the ancient Levant. It may either refer to swords made or sold in Damascus directly, or it may just refer to the aspect of the typical patterns, by comparison with Damask fabrics (which are themselves named after Damascus).The original method of producing wootz is not known. Modern attempts to duplicate the metal have not been entirely successful due to differences in raw materials and manufacturing techniques. Several individuals in modern times have claimed that they have rediscovered the methods by which the original Damascus steel was produced.The reputation and history of Damascus steel has given rise to many legends, such as the ability to cut through a rifle barrel or to cut a hair falling across the blade. A research team in Germany published a report in 2006 revealing nanowires and carbon nanotubes in a blade forged from Damascus steel. Although many types of modern steel outperform ancient Damascus alloys, chemical reactions in the production process made the blades extraordinary for their time, as Damascus steel was superplastic and very hard at the same time. During the smelting process to obtain Wootz steel ingots, woody biomass and leaves are known to have been used as carburizing additives along with certain specific types of iron rich in microalloying elements. These ingots would then be further forged and worked into Damascus steel blades. Research now shows that carbon nanotubes can be derived from plant fibers, suggesting how the nanotubes were formed in the steel. Some experts expect to discover such nanotubes in more relics as they are analyzed more closely.


Iron is a chemical element with symbol Fe (from Latin: ferrum) and atomic number 26. It is a metal in the first transition series. It is by mass the most common element on Earth, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust. Its abundance in rocky planets like Earth is due to its abundant production by fusion in high-mass stars, where it is the last element to be produced with release of energy before the violent collapse of a supernova, which scatters the iron into space.

Like the other group 8 elements, ruthenium and osmium, iron exists in a wide range of oxidation states, −2 to +7, although +2 and +3 are the most common. Elemental iron occurs in meteoroids and other low oxygen environments, but is reactive to oxygen and water. Fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give hydrated iron oxides, commonly known as rust. Unlike the metals that form passivating oxide layers, iron oxides occupy more volume than the metal and thus flake off, exposing fresh surfaces for corrosion.

Iron metal has been used since ancient times, although copper alloys, which have lower melting temperatures, were used even earlier in human history. Pure iron is relatively soft, but is unobtainable by smelting because it is significantly hardened and strengthened by impurities, in particular carbon, from the smelting process. A certain proportion of carbon (between 0.002% and 2.1%) produces steel, which may be up to 1000 times harder than pure iron. Crude iron metal is produced in blast furnaces, where ore is reduced by coke to pig iron, which has a high carbon content. Further refinement with oxygen reduces the carbon content to the correct proportion to make steel. Steels and iron alloys formed with other metals (alloy steels) are by far the most common industrial metals because they have a great range of desirable properties and iron-bearing rock is abundant.

Iron chemical compounds have many uses. Iron oxide mixed with aluminium powder can be ignited to create a thermite reaction, used in welding and purifying ores. Iron forms binary compounds with the halogens and the chalcogens. Among its organometallic compounds is ferrocene, the first sandwich compound discovered.

Iron plays an important role in biology, forming complexes with molecular oxygen in hemoglobin and myoglobin; these two compounds are common oxygen-handling proteins in vertebrates (hemoglobin for oxygen transport, and myoglobin for oxygen storage). Iron is also the metal at the active site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants and animals. Iron is distributed throughout the human body, and is especially abundant in hemoglobin. Total iron content of the adult human body is approximately 3.8 grams in males and 2.3 grams in females. Iron is a critical element in the metabolism of hundreds of proteins and enzymes involved in diverse body functions, such as oxygen transport, DNA synthesis, and cell growth.

Man of Steel (film)

Man of Steel is a 2013 superhero film based on the DC Comics character Superman. It is a British-American venture produced by DC Entertainment, Legendary Pictures and Syncopy, and distributed by Warner Bros. Pictures. It is the first installment in the DC Extended Universe (DCEU). The film is directed by Zack Snyder, written by David S. Goyer, and stars Henry Cavill, Amy Adams, Michael Shannon, Kevin Costner, Diane Lane, Laurence Fishburne, Antje Traue, Ayelet Zurer, Christopher Meloni and Russell Crowe. Man of Steel is a reboot of the Superman film series that portrays the character's origin story. In the film, Clark Kent learns that he is a superpowered alien from the planet Krypton. He assumes the role of superhero as Superman when faced with the threat of humanity's destruction from General Zod and wrestles with saving the world while remaining emotionally distant.

Development began in 2008, when Warner Bros. took pitches from comic book writers, screenwriters, and directors, opting to reboot the franchise. In 2009, a court ruling resulted in Jerry Siegel's family recapturing the rights to Superman's origins and Siegel's copyright. The decision stated that Warner Bros. did not owe the families additional royalties from previous films, but if they did not begin production on a Superman film by 2011, then the Shuster and Siegel estates would be able to sue for lost revenue on an unproduced film. Producer Christopher Nolan pitched Goyer's idea after story discussion on The Dark Knight Rises, and Snyder was hired as the film's director in October 2010. Principal photography began in August 2011 in West Chicago, Illinois, before moving to Vancouver and Plano, Illinois.

Man of Steel was released in theaters on June 14, 2013, in conventional 2D, 3D, and IMAX formats. Despite receiving mixed reviews, the film became a box office success, grossing more than $668 million worldwide. Critics praised the film's visuals and Hans Zimmer's score, but criticized its pacing and lack of character development. A follow-up entitled Batman v Superman: Dawn of Justice was released on March 25, 2016.

Pedal steel guitar

The pedal steel guitar is a console-type of steel guitar with pedals and levers added to enable playing more varied and complex music which had not been possible with antecedent steel guitar designs. Like other steel guitars, it shares the ability to play unlimited glissandi (sliding notes) and deep vibrati—characteristics in common with the human voice. Pedal steel is most commonly associated with American country music.

Pedals and knee levers were added to a steel guitar in the 1950s, allowing the performer to play scales without moving the bar and also to push the pedals while striking a chord, making passing notes slur or bend up into harmony with existing notes. The latter creates a unique sound that has been particularly embraced by country and western music—a sound not previously possible on a non-pedal steel guitar of any type.

From its first use in Hawaii in the 19th century, the steel guitar sound became popular in the United States in the first half of the 20th century and spawned a family of instruments designed specifically to be played with the guitar a horizontal position, also known as "Hawaiian-style". The first instrument in this chronology was the Hawaiian guitar also called a lap steel; next was a lap steel with a resonator to make it louder, first made by National and Dobro Corporation. The electric guitar pickup was invented in 1934, allowing steel guitars to be heard equally with other instruments. Electronic amplification enabled subsequent development of the electrified lap steel, then the console steel, and finally the pedal steel guitar.

Playing the pedal steel has unusual physical requirements in requiring simultaneous coordination of both hands, both feet and both knees (knees operate levers on medial and lateral sides of each knee); the only other instrument with similar requirements is the American reed organ. Pioneers in development of the instrument include Buddy Emmons, Bud Isaacs, Zane Beck, and Paul Bigsby. In addition to American country music and Hawaiian music, the instrument is common in sacred music (called Sacred Steel), jazz, Nigerian Music, and Indian music.

Professional wrestling match types

Many types of wrestling matches, sometimes called "concept" or "gimmick matches" in the jargon of the business, are performed in professional wrestling. Some of them occur relatively frequently while others are developed so as to advance an angle and such match types are used rarely. Because of professional wrestling's long history over decades, many things have been recycled (many match types often being variations of previous match types). These match types can be organized into several loose groups.

Reinforced concrete

Reinforced concrete (RC) (also called reinforced cement concrete or RCC) is a composite material in which concrete's relatively low tensile strength and ductility are counteracted by the inclusion of reinforcement having higher tensile strength or ductility. The reinforcement is usually, though not necessarily, steel reinforcing bars (rebar) and is usually embedded passively in the concrete before the concrete sets. Reinforcing schemes are generally designed to resist tensile stresses in particular regions of the concrete that might cause unacceptable cracking and/or structural failure. Modern reinforced concrete can contain varied reinforcing materials made of steel, polymers or alternate composite material in conjunction with rebar or not. Reinforced concrete may also be permanently stressed (concrete in compression, reinforcement in tension), so as to improve the behaviour of the final structure under working loads. In the United States, the most common methods of doing this are known as pre-tensioning and post-tensioning.

For a strong, ductile and durable construction the reinforcement needs to have the following properties at least:

High relative strength

High toleration of tensile strain

Good bond to the concrete, irrespective of pH, moisture, and similar factors

Thermal compatibility, not causing unacceptable stresses (such as expansion or contraction) in response to changing temperatures.

Durability in the concrete environment, irrespective of corrosion or sustained stress for example.

Stainless steel

In metallurgy, stainless steel, also known as inox steel or inox from French inoxydable (inoxidizable), is a steel alloy, with highest percentage contents of iron, chromium, and nickel, with a minimum of 10.5% chromium content by mass and a maximum of 1.2% carbon by mass.Stainless steels are most notable for their corrosion resistance, which increases with increasing chromium content. Additions of molybdenum increase corrosion resistance in reducing acids and against pitting attack in chloride solutions. Thus, there are numerous grades of stainless steel with varying chromium and molybdenum contents to suit the environment the alloy must endure. Stainless steel's resistance to corrosion and staining, low maintenance, and familiar luster make it an ideal material for many applications where both the strength of steel and corrosion resistance are required.

Stainless steels are rolled into sheets, plates, bars, wire, and tubing to be used in: cookware, cutlery, surgical instruments, major appliances; construction material in large buildings, such as the Chrysler Building; industrial equipment (for example, in paper mills, chemical plants, water treatment); and storage tanks and tankers for chemicals and food products (for example, chemical tankers and road tankers). Stainless steel's corrosion resistance, the ease with which it can be steam cleaned and sterilized, and no need for surface coatings has also influenced its use in commercial kitchens and food processing plants.

Steel guitar

Steel guitar is a type of guitar or the method of playing the instrument. Developed in Hawaii by Joseph Kekuku in the late 19th and early 20th centuries, a steel guitar is usually positioned horizontally; strings are plucked with one hand, while the other hand changes the pitch of one or more strings with the use of a bar or slide called a steel (generally made of metal, but also of glass or other materials). The earliest use of an electrified steel guitar was first made in the early 1930s by Bob Dunn of Milton Brown and His Brownies, a western swing band from Fort Worth, Texas; the instrument was perfected in the mid to late 1930s by Fort Worth's Leon McAuliffe, who played for western swing band Bob Wills and His Texas Playboys. Nashville later picked up the use of the steel guitar in the early days of the late 1940s and early 1950s "Honky Tonk" country & western music with a number of fine steel guitarists backing names like Hank Williams, Lefty Frizzell and Webb Pierce. The term steel guitar is often mistakenly used to describe any metal body resophonic guitar.

Steel guitar can describe:

The slide technique of playing slide guitar is generally by using a steel bar. Resonator guitars, including round necked varieties, are particularly suitable for this style, yet are seldom referred to as "steel guitars", but rather referred to generally as a Dobro, acoustic slide guitar, or square neck resonator guitars. Dobro is also a brand name of one of the leading manufacturers of resonator guitars.

A specialized instrument built for playing in steel guitar fashion. These are of several types:

Lap steel guitar, which may be:

Lap slide guitar, with a conventional wooden guitar box.

The square-necked variety of resonator guitar.

Electric lap steel guitar.

Electric console steel guitar.

Electric pedal steel guitar.

Tata Group

Tata Group () is an Indian multinational conglomerate holding company headquartered in Mumbai, Maharashtra, India. Founded in 1868 by Jamsetji Tata, the company gained international recognition after purchasing several global companies. One of India's largest conglomerates, Tata Group is owned by Tata Sons.Each Tata company operates independently under the guidance and supervision of its own board of directors and shareholders.

Significant Tata companies and subsidiaries include Tata Steel, Tata Motors, Jaguar Land Rover, Tata Consultancy Services, Tata Advanced Systems Limited , Tata Power, Tata Chemicals, Tata Global Beverages, Tata Coffee, Tata Teleservices, Titan, Voltas, TATA cliq, Tata Communications, and The Indian Hotels Company Limited (Taj Hotels).

Tata Steel

Tata Steel Limited formerly Tata Iron and Steel Company Limited (TISCO) is an Indian multinational steel-making company headquartered in Mumbai, Maharashtra, India, and a subsidiary of the Tata Group.

It is one of the top steel producing companies globally with annual crude steel deliveries of 27.5 million tonnes (in FY17), and the second largest steel company in India (measured by domestic production) with an annual capacity of 13 million tonnes after SAIL.Tata Steel has manufacturing operations in 26 countries, including Australia, China, India, the Netherlands, Singapore, Thailand and the United Kingdom, and employs around 80,500 people. Its largest plant is located in Jamshedpur, Jharkhand. In 2007 Tata Steel acquired the UK-based steel maker Corus. It was ranked 486th in the 2014 Fortune Global 500 ranking of the world's biggest corporations. It was the seventh most valuable Indian brand of 2013 as per Brand Finance.

U.S. Steel

United States Steel Corporation (NYSE: X), more commonly known as U.S. Steel, is an American integrated steel producer headquartered in Pittsburgh, Pennsylvania, with production operations in the United States and Central Europe. As of 2016, the company was the world's 24th-largest steel producer and second-largest domestic producer, trailing only Nucor Corporation.

Though renamed USX Corporation in 1986, the company returned to its present name in 2001 after spinning off its energy business, including Marathon Oil, and other assets from its core steel concern. The company experienced significant downsizing during the 1980s; a decline in market capitalization resulted in its removal from the S&P 500 Index in 2014.

Wrought iron

Wrought iron is an iron alloy with a very low carbon (less than 0.08%) content in contrast to cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag inclusions (up to 2% by weight), which gives it a "grain" resembling wood that is visible when it is etched or bent to the point of failure. Wrought iron is tough, malleable, ductile, corrosion-resistant and easily welded. Before the development of effective methods of steelmaking and the availability of large quantities of steel, wrought iron was the most common form of malleable iron. It was given the name wrought because it was hammered, rolled or otherwise worked while hot enough to expel molten slag. The modern functional equivalent of wrought iron is mild or low carbon steel. Neither wrought iron nor mild steel contain enough carbon to be hardenable by heating and quenching.It is a highly refined iron with a small amount of slag forged out into fibres. The chemical analysis of the metal shows as much as 99 percent of iron. The slag characteristic of wrought iron is useful in blacksmithing operations and gives the material its peculiar fibrous structure. The non-corrosive slag constituent causes wrought iron to be resistant to progressive corrosion. Moreover, the presence of slag produces a structure which diminishes the effect of fatigue caused by shocks and vibrations.Historically, a modest amount of wrought iron was refined into steel, which was used mainly to produce swords, cutlery, chisels, axes and other edged tools as well as springs and files. The demand for wrought iron reached its peak in the 1860s, being in high demand for ironclad warships and railway use. However, as properties such as brittleness of mild steel improved with better ferrous metallurgy and as steel became less costly to make thanks to the Bessemer process and the Siemens-Martin process, the use of wrought iron declined.

Many items, before they came to be made of mild steel, were produced from wrought iron, including rivets, nails, wire, chains, rails, railway couplings, water and steam pipes, nuts, bolts, horseshoes, handrails, wagon tires, straps for timber roof trusses, and ornamental ironwork, among many other things.Wrought iron is no longer produced on a commercial scale. Many products described as wrought iron, such as guard rails, garden furniture and gates, are actually made of mild steel. They retain that description because they are made to resemble objects which in the past were wrought (worked) by hand by a blacksmith (although many decorative iron objects, including fences and gates, were often cast rather than wrought).

Iron and steel production
Iron production
(Steel mill)
Production by country
Heat treatment methods
See also

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