Iron is a chemical element with symbol Fe and atomic number 26. It is a metal, that belongs to group 8 of the periodic table, it is by mass the most common element on Earth, forming much of Earth's inner core. It is the fourth most common element in the Earth's crust. Pure iron is rare on the Earth's crust being limited to meteorites. Iron ores are quite abundant, but extracting usable metal from them requires kilns or furnaces capable of reaching 1500 °C or higher, about 500 °C higher than what is enough to smelt copper. Humans started to dominate that process in Eurasia only about 2000 BCE, iron began to displace copper alloys for tools and weapons, in some regions, only around 1200 BCE; that event is considered the transition from the Bronze Age to the Iron Age. Iron alloys, such as steel and special steels are now by far the most common industrial metals, because of their mechanical properties and their low cost. Pristine and smooth pure iron surfaces are mirror-like silvery-gray. However, iron reacts with oxygen and water to give brown to black hydrated iron oxides known as rust.
Unlike the oxides of some other metals, that form passivating layers, rust occupies more volume than the metal and thus flakes off, exposing fresh surfaces for corrosion. The body of an adult human contains about 3 to 5 grams of elemental iron in hemoglobin and myoglobin; these two proteins play essential roles in vertebrate metabolism oxygen transport by blood and oxygen storage in muscles. To maintain the necessary levels, human iron metabolism requires a minimum of iron in the diet. Iron is the metal at the active site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants and animals. Chemically, the most common oxidation states of iron are +2 and +3. Iron shares many properties of other transition metals, including the other group 8 elements and osmium. Iron forms compounds in a wide range of oxidation states, −2 to +7. Iron forms many coordination compounds. At least four allotropes of iron are known, conventionally denoted α, γ, δ, ε; the first three forms are observed at ordinary pressures.
As molten iron cools past its freezing point of 1538 °C, it crystallizes into its δ allotrope, which has a body-centered cubic crystal structure. As it cools further to 1394 °C, it changes to its γ-iron allotrope, a face-centered cubic crystal structure, or austenite. At 912 °C and below, the crystal structure again becomes the bcc α-iron allotrope; the physical properties of iron at high pressures and temperatures have been studied extensively, because of their relevance to theories about the cores of the Earth and other planets. Above 10 GPa and temperatures of a few hundred kelvin or less, α-iron changes into another hexagonal close-packed structure, known as ε-iron; the higher-temperature γ-phase changes into ε-iron, but does so at higher pressure. Some controversial experimental evidence exists for a stable β phase at pressures above 50 GPa and temperatures of at least 1500 K, it is supposed to have a double hcp structure. The inner core of the Earth is presumed to consist of an iron-nickel alloy with ε structure.
The melting and boiling points of iron, along with its enthalpy of atomization, are lower than those of the earlier 3d elements from scandium to chromium, showing the lessened contribution of the 3d electrons to metallic bonding as they are attracted more and more into the inert core by the nucleus. This same trend appears for ruthenium but not osmium; the melting point of iron is experimentally well defined for pressures less than 50 GPa. For greater pressures, published data still varies by tens of gigapascals and over a thousand kelvin. Below its Curie point of 770 °C, α-iron changes from paramagnetic to ferromagnetic: the spins of the two unpaired electrons in each atom align with the spins of its neighbors, creating an overall magnetic field; this happens because the orbitals of those two electrons do not point toward neighboring atoms in the lattice, therefore are not involved in metallic bonding. In the absence of an external source of magnetic field, the atoms get spontaneously partitioned into magnetic domains, about 10 micrometres across, such that the atoms in each domain have parallel spins, but different domains have other orientations.
Thus a macroscopic piece of iron will have a nearly zero overall magnetic field. Application of an external magnetic field causes the domains that are magnetized in the same general direction to grow at the expense of adjacent ones that point in other directions, reinforcing the external field; this effect is exploited in devices that needs to channel magnetic fields, such as electrical transformers, magnetic recording heads, electric motors. Impurities, lattice defects, or grain and particle boundaries can "pin" the domains in the new positions, so that the effect persists after the external field is removed -- thus turning the iron object into a magnet. Similar behavior is exhibited by some iron compounds, such as the fer
Ductile iron 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 weak in tension and brittle, ductile iron has much more impact and fatigue resistance, due to its nodular graphite inclusions. On October 25, 1949, Keith Dwight Millis, Albert Paul Gagnebin and Norman Boden Pilling received US patent 2,485,760 on a Cast Ferrous Alloy for ductile iron production via magnesium treatment. Augustus F. Meehan was awarded a patent in January 1931 for inoculating iron with calcium silicide to produce ductile iron subsequently licensed as Meehanite, still produced in 2017. Ductile iron is not a single material but part of a group of materials which can be produced with a wide range of properties through control of their microstructure; the common defining characteristic of this group of materials is the shape of the graphite. In ductile irons, graphite is in the form of nodules rather than flakes as in grey iron.
Whereas sharp graphite flakes create stress concentration points within the metal matrix, rounded nodules inhibit the creation of cracks, thus providing the enhanced ductility that gives the alloy its name. Nodule formation is achieved by adding nodulizing elements, most magnesium and, less now, cerium. Tellurium has been used. Yttrium a component of mischmetal, has been studied as a possible nodulizer. "Austempered Ductile Iron" was discovered in the 1950s but was commercialized and achieved success only some years later. In ADI, the metallurgical structure is manipulated through a sophisticated heat treating process; the "aus" portion of the name refers to austenite. A typical chemical analysis of this material: Carbon 3.2 to 3.60% Silicon 2.2 to 2.8% Manganese 0.1 to 0.2% Magnesium 0.03 to 0.04% Phosphorus 0.005 to 0.04% Sulfur 0.005 to 0.02% Copper <0.40% Iron balanceElements such as copper or tin may be added to increase tensile and yield strength while reducing ductility. Improved corrosion resistance can be achieved by replacing 15% to 30% of the iron in the alloy with varying amounts of nickel, copper, or chromium.
Much of the annual production of ductile iron is in the form of ductile iron pipe, used for water and sewer lines. It competes with polymeric materials such as PVC, HDPE, LDPE and polypropylene, which are all much lighter than steel or ductile iron. Ductile iron is useful in many automotive components, where strength must surpass that of aluminum but steel is not required. Other major industrial applications include off-highway diesel trucks, Class 8 trucks, agricultural tractors, oil well pumps. In wind power industry nodular cast iron is used for structural parts like machine frames. Nodular cast iron is suitable for high loads. SG iron is used in many grand piano harps. Malleable iron Smith, William F.. Ductile Iron Society Ductile Iron Pipe Research Association
Smelting is a process of applying heat to ore in order to extract out a base metal. It is a form of extractive metallurgy, it is used to extract many metals from their ores, including silver, iron and other base metals. Smelting uses heat and a chemical reducing agent to decompose the ore, driving off other elements as gases or slag and leaving the metal base behind; the reducing agent is a source of carbon, such as coke—or, in earlier times, charcoal. The carbon removes oxygen from the ore; the carbon thus oxidizes in two stages, producing first carbon monoxide and carbon dioxide. As most ores are impure, it is necessary to use flux, such as limestone, to remove the accompanying rock gangue as slag. Plants for the electrolytic reduction of aluminium are generally referred to as aluminium smelters. Labourers working in the smelting industry have reported respiratory illnesses inhibiting their ability to perform the physical tasks demanded by their jobs. Smelting involves more than just melting the metal out of its ore.
Most ores are the chemical compound of the metal and other elements, such as oxygen, sulfur, or carbon and oxygen together. To extract the metal, workers must make these compounds undergo a chemical reaction. Smelting therefore consists of using suitable reducing substances that combine with those oxidizing elements to free the metal. In the case of carbonates and sulfides, a process called "roasting" drives out the unwanted carbon or sulfur, leaving an oxide, which can be directly reduced. Roasting is carried out in an oxidizing environment. A few practical examples: Malachite, a common ore of copper, is copper carbonate hydroxide Cu22; this mineral undergoes thermal decomposition to 2CuO, CO2, H2O in several stages between 250 °C and 350 °C. The carbon dioxide and water are expelled into the atmosphere, leaving copper oxide, which can be directly reduced to copper as described in the following section titled Reduction. Galena, the most common mineral of lead, is lead sulfide; the sulfide is oxidized to a sulfite, which thermally decomposes into lead oxide and sulfur dioxide gas.
The sulfur dioxide is expelled, the lead oxide is reduced as below. Reduction is the final, high-temperature step in smelting, in which the oxide becomes the elemental metal. A reducing environment pulls the final oxygen atoms from the raw metal; the required temperature varies over a large range, both in absolute terms and in terms of the melting point of the base metal. Examples: Iron oxide becomes metallic iron at 1250 °C 300 degrees below iron's melting point of 1538 °C. Mercuric oxide becomes vaporous mercury near 550 °C 600 degrees above mercury's melting point of -38 °C. Flux and slag can provide a secondary service after the reduction step is complete: they provide a molten cover on the purified metal, preventing contact with oxygen while still hot enough to oxidize; this prevents impurities from forming in the metal. Metal workers use fluxes in smelting for several purposes, chief among them catalyzing the desired reactions and chemically binding to unwanted impurities or reaction products.
Calcium oxide, in the form of lime, was used for this purpose, since it could react with the carbon dioxide and sulfur dioxide produced during roasting and smelting to keep them out of the working environment. Of the seven metals known in antiquity, only gold occurred in native form in the natural environment; the others – copper, silver, tin and mercury – occur as minerals, though copper is found in its native state in commercially significant quantities. These minerals are carbonates, sulfides, or oxides of the metal, mixed with other components such as silica and alumina. Roasting the carbonate and sulfide minerals in air converts them to oxides; the oxides, in turn, are smelted into the metal. Carbon monoxide was the reducing agent of choice for smelting, it is produced during the heating process, as a gas comes into intimate contact with the ore. In the Old World, humans learned to smelt metals in prehistoric times, more than 8000 years ago; the discovery and use of the "useful" metals — copper and bronze at first iron a few millennia — had an enormous impact on human society.
The impact was so pervasive that scholars traditionally divide ancient history into Stone Age, Bronze Age, Iron Age. In the Americas, pre-Inca civilizations of the central Andes in Peru had mastered the smelting of copper and silver at least six centuries before the first Europeans arrived in the 16th century, while never mastering the smelting of metals such as iron for use with weapon-craft. In the Old World, the first metals smelted were lead; the earliest known cast lead beads were found in the Çatal Höyük site in Anatolia, dated from about 6500 BC, but the metal may have been known earlier. Since the discovery happened several millennia before the invention of writing, there is no written record about how it was made; however and lead can be smelted by placing the ores in a wood fire, leaving the possibility that the discovery may have occurred by accident. Lead is a common metal, but its discovery had little impact in the ancient world, it is too soft to use for structural elements or weapons, though its high density relative to other metals makes it ideal for sling projectiles.
However, since it was
The Zhou dynasty was a Chinese dynasty that followed the Shang dynasty and preceded the Qin dynasty. The Zhou dynasty lasted longer than any other dynasty in Chinese history; the military control of China by the royal house, surnamed Ji, lasted from 1046 until 771 BC for a period known as the Western Zhou and the political sphere of influence it created continued well into Eastern Zhou for another 500 years. During the Zhou Dynasty, centralized power decreased throughout the Spring and Autumn period until the Warring States period in the last two centuries of the Zhou Dynasty. In this period, the Zhou court had little control over its constituent states that were at war with each other until the Qin state consolidated power and formed the Qin dynasty in 221 BC; the Zhou Dynasty had formally collapsed only 35 years earlier, although the dynasty had only nominal power at that point. This period of Chinese history produced; the Zhou dynasty spans the period in which the written script evolved into its almost-modern form with the use of an archaic clerical script that emerged during the late Warring States period.
According to Chinese mythology, the Zhou lineage began when Jiang Yuan, a consort of the legendary Emperor Ku, miraculously conceived a child, Qi "the Abandoned One", after stepping into the divine footprint of Shangdi. Qi was a culture hero credited with surviving three abandonments by his mother and with improving Xia agriculture, to the point where he was granted lordship over Tai and the surname Ji by his own Xia king and a posthumous name, Houji "Lord of Millet", by the Tang of Shang, he received sacrifice as a harvest god. The term Hòujì was a hereditary title attached to a lineage. Qi's son, or rather that of the Hòujì, Buzhu is said to have abandoned his position as Agrarian Master in old age and either he or his son Ju abandoned agriculture living a nomadic life in the manner of the Xirong and Rongdi. Ju's son Liu, led his people to prosperity by restoring agriculture and settling them at a place called Bin, which his descendants ruled for generations. Tai led the clan from Bin to Zhou, an area in the Wei River valley of modern-day Qishan County.
The duke passed over his two elder sons Taibo and Zhongyong to favor Jili, a warrior who conquered several Xirong tribes as a vassal of the Shang kings Wu Yi and Wen Ding before being treacherously killed. Taibo and Zhongyong had already fled to the Yangtze delta, where they established the state of Wu among the tribes there. Jili's son Wen moved the Zhou capital to Feng. Around 1046 BC, Wen's son Wu and his ally Jiang Ziya led an army of 45,000 men and 300 chariots across the Yellow River and defeated King Zhou of Shang at the Battle of Muye, marking the beginning of the Zhou dynasty; the Zhou enfeoffed a member of the defeated Shang royal family as the Duke of Song, held by descendants of the Shang royal family until its end. This practice was referred to Three Reverences. According to Nicholas Bodman, the Zhou appear to have spoken a language not different in vocabulary and syntax from that of the Shang. A recent study by David McCraw, using lexical statistics, reached the same conclusion.
The Zhou emulated extensively Shang cultural practices to legitimize their own rule, became the successors to Shang culture. At the same time, the Zhou may have been connected to the Xirong, a broadly defined cultural group to the west of the Shang, which the Shang regarded as tributaries. According to the historian Li Feng, the term "Rong" during the Western Zhou period was used to designate political and military adversaries rather than cultural and ethnic'others.' King Wu maintained the old capital for ceremonial purposes but constructed a new one for his palace and administration nearby at Hao. Although Wu's early death left a young and inexperienced heir, the Duke of Zhou assisted his nephew King Cheng in consolidating royal power. Wary of the Duke of Zhou's increasing power, the "Three Guards", Zhou princes stationed on the eastern plain, rose in rebellion against his regency. Though they garnered the support of independent-minded nobles, Shang partisans and several Dongyi tribes, the Duke of Zhou quelled the rebellion, further expanded the Zhou Kingdom into the east.
To maintain Zhou authority over its expanded territory and prevent other revolts, he set up the fengjian system. Furthermore, he countered Zhou's crisis of legitimacy by expounding the doctrine of the Mandate of Heaven while accommodating important Shang rituals at Wangcheng and Chengzhou. Over time, this decentralized system became strained as the familial relationships between the Zhou kings and the regional dynasties thinned over the generations. Peripheral territories developed local prestige on par with that of the Zhou; when King You demoted and exiled his Jiang queen in favor of the beautiful commoner Bao Si, the disgraced queen's father the Marquis of Shen joined with Zeng and the Quanrong barbarians to sack Hao in 771 BC. Some modern scholars have surmised that the sack of Haojing might have been connected to a Scythian raid from the Altai before their westward expansion. With King You dead, a conclave of nobles declared the Marquis's grandson King Ping; the capital was moved eastward to Wangcheng, marking the end of the "Western Zhou" and the beginning of the "Eastern Zhou" dynasty.
The Eastern Zhou was characterized by an accelerating collapse of royal authority, although the king's ritual importance allowed over five more cent
Brill is a Dutch international academic publisher founded in 1683 in Leiden, Netherlands. With offices in Leiden, Boston and Singapore, Brill today publishes 275 journals and around 1200 new books and reference works each year. In addition, Brill is a provider of primary source materials online and on microform for researchers in the humanities and social sciences. Brill publishes in the following subject areas: The roots of Brill go back to May 17, 1683, when a certain Jordaan Luchtmans was registered as a bookseller by the Leiden booksellers' guild; as was customary at the time, Luchtmans combined his bookselling business with publishing activities. These were in the fields of biblical studies, Oriental languages, ethnography. Luchtmans established close ties with the University of Leiden, one of the major centers of study in these areas. In 1848, the business passed from the Luchtmans family to that of a former employee. In order to cover the financial obligations that he inherited, E. J. Brill decided to liquidate the entire Luchtmans book stock in a series of auctions that took place between 1848 and 1850.
Brill continued to publish in the traditional core areas of the company, with occasional excursions into other fields. Thus, in 1882, the firm brought out a two-volume Leerboek der Stoomwerktuigkunde. More programmatically, however, in 1855 Het Gebed des Heeren in veertien talen was meant to publicize Brill's ability to typeset non-Latin alphabets, such as Hebrew, Samaritan, Coptic, Arabic, among several others. In 1896, Brill became a public limited company, when E. J. Brill's successors, A. P. M. van Oordt and Frans de Stoppelaar, both businessmen with some academic background and interest, died. A series of directors followed, his directorship marked a period of unprecedented growth in the history of the company, due to a large extent to Folkers' cooperation with the German occupying forces during World War II. For the Germans, Brill printed foreign-language textbooks so that they could manage the territories they occupied, but military manuals, such as "a manual which trained German officers to distinguish the insignias of the Russian army".
In 1934, the company had a turnover of 132,000 guilders. After the war, the Dutch denazification committee determined the presence of "enemy money" in Brill's accounts. Folkers was arrested in September 1946, deprived of the right to hold a managerial post; the company itself, escaped the aftermath of the war unscathed. Brill's path in the post-war years was again marked by ups and downs, though the company remained faithful in its commitment to scholarly publishing; the late 1980s brought an acute crisis due to over-expansion, poor management, as well as general changes in the publishing industry. Thus, in 1988–91 under new management the company underwent a major restructuring, in the course of which it closed some of its foreign offices, including Cologne, its London branch was closed by then. Brill, sold its printing business, which amounted "to amputat its own limb"; this was considered necessary to save the company as a whole. No jobs were lost in the process; the reorganization managed to save the company, which has since undergone an expansion that as as 1990 had been inconceivable.
As of 2008, Brill was publishing around 600 books and 100 journals each year, with a turnover of 26 million euros. Brill publishes several open access journals and is one of thirteen publishers to participate in the Knowledge Unlatched pilot. In 2013, Brill created the IFLA/Brill Open Access Award for initiatives in the area of open access monograph publishing together with the International Federation of Library Associations and Institutions. Brill is a member of the Open Access Scholarly Publishers Association. List of Brill academic journals Books in the Netherlands The most up-to-date history of the company is Sytze van der Veen, Brill: 325 Years of Scholarly Publishing, ISBN 978-90-04-17032-2 Tom Verde, "Brill's Bridge to Arabic", Aramco World, 66, nr. 3, pp. 30–39 online edition. Brill Annual Report 2012 Official website A list of books published by E. J. Brill Leiden
A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals pig iron, but others such as lead or copper. Blast refers to the combustion air being "forced" or supplied above atmospheric pressure. In a blast furnace, fuel and flux are continuously supplied through the top of the furnace, while a hot blast of air is blown into the lower section of the furnace through a series of pipes called tuyeres, so that the chemical reactions take place throughout the furnace as the material falls downward; the end products are molten metal and slag phases tapped from the bottom, waste gases exiting from the top of the furnace. The downward flow of the ore and flux in contact with an upflow of hot, carbon monoxide-rich combustion gases is a countercurrent exchange and chemical reaction process. In contrast, air furnaces are aspirated by the convection of hot gases in a chimney flue. According to this broad definition, bloomeries for iron, blowing houses for tin, smelt mills for lead would be classified as blast furnaces.
However, the term has been limited to those used for smelting iron ore to produce pig iron, an intermediate material used in the production of commercial iron and steel, the shaft furnaces used in combination with sinter plants in base metals smelting. Cast iron has been found in China dating to the 5th century BC, but the earliest extant blast furnaces in China date to the 1st century AD and in the West from the High Middle Ages, they spread from the region around Namur in Wallonia in the late 15th century, being introduced to England in 1491. The fuel used in these was invariably charcoal; the successful substitution of coke for charcoal is attributed to English inventor Abraham Darby in 1709. The efficiency of the process was further enhanced by the practice of preheating the combustion air, patented by Scottish inventor James Beaumont Neilson in 1828. Archaeological evidence shows that bloomeries appeared in China around 800 BC, it was thought that the Chinese started casting iron right from the beginning, but this theory has since been debunked by the discovery of'more than ten' iron digging implements found in the tomb of Duke Jing of Qin, whose tomb is located in Fengxiang County, Shaanxi.
There is however no evidence of the bloomery in China after the appearance of the blast furnace and cast iron. In China blast furnaces produced cast iron, either converted into finished implements in a cupola furnace, or turned into wrought iron in a fining hearth. Although cast iron farm tools and weapons were widespread in China by the 5th century BC, employing workforces of over 200 men in iron smelters from the 3rd century onward, the earliest extant blast furnaces were built date to the Han Dynasty in the 1st century AD; these early furnaces used phosphorus-containing minerals as a flux. Chinese blast furnaces ranged from around two to ten meters depending on the region; the largest ones were found in modern Sichuan and Guangdong, while the'dwarf" blast furnaces were found in Dabieshan. In construction, they are both around the same level of technological sophistication The effectiveness of the Chinese blast furnace was enhanced during this period by the engineer Du Shi, who applied the power of waterwheels to piston-bellows in forging cast iron.
Donald Wagner suggests that early blast furnace and cast iron production evolved from furnaces used to melt bronze. Though, iron was essential to military success by the time the State of Qin had unified China. Usage of the blast and cupola furnace remained widespread during Tang Dynasties. By the 11th century, the Song Dynasty Chinese iron industry made a switch of resources from charcoal to coke in casting iron and steel, sparing thousands of acres of woodland from felling; this may have happened as early as the 4th century AD. The primary advantage of the early blast furnace was in large scale production and making iron implements more available to peasants. Cast iron is more brittle than wrought iron or steel, which required additional fining and cementation or co-fusion to produce, but for menial activities such as farming it sufficed. By using the blast furnace, it was possible to produce larger quantities of tools such as ploughshares more efficiently than the bloomery. In areas where quality was important, such as warfare, wrought iron and steel were preferred.
Nearly all Han period weapons are made of wrought iron or steel, with the exception of axe-heads, of which many are made of cast iron. Blast furnaces were later used to produce gunpowder weapons such as cast iron bomb shells and cast iron cannons during the Song dynasty; the simplest forge, known as the Corsican, was used prior to the advent of Christianity. Examples of improved bloomeries are the Stückofen or the Catalan forge, which remained until the beginning of the 19th century; the Catalan forge was invented in Catalonia, during the 8th century. Instead of using natural draught, air was pumped in by a trompe, resulting in better quality iron and an increased capacity; this pumping of airstream in with bellows is known as cold blast, it increases the fuel efficiency of the bloomery and improves yield. The Catalan forges can be built bigger than natural draught bloomeries; the oldest known blast furnaces in the West were built in Dürstel in Switzerland, the Märkische Sauerland in Germany, at Lapphyttan in Sweden, where the complex was active between 1205 and 1300.
At Noraskog in the Swedish parish of Järnboås, there have been fou
Electric arc furnace
An electric arc furnace is a furnace that heats charged material by means of an electric arc. Industrial arc furnaces range in size from small units of one ton capacity up to about 400 ton units used for secondary steelmaking. Arc furnaces used in research laboratories and by dentists may have a capacity of only a few dozen grams. Industrial electric arc furnace temperatures can be up to 1,800 °C, while laboratory units can exceed 3,000 °C. Arc furnaces differ from induction furnaces in that the charge material is directly exposed to an electric arc and the current in the furnace terminals passes through the charged material. In the 19th century, a number of men had employed an electric arc to melt iron. Sir Humphry Davy conducted an experimental demonstration in 1810; the first successful and operational furnace was invented by James Burgess Readman in Edinburgh, Scotland in 1888 and patented in 1889. This was for the creation of phosphorus. Further electric arc furnaces were developed by Paul Héroult, of France, with a commercial plant established in the United States in 1907.
The Sanderson brothers formed The Sanderson Brothers steel Co. in Syracuse, New York, installing the first electric arc furnace in the U. S; this furnace is now on display at Station Square, Pennsylvania. "electric steel" was a specialty product for such uses as machine tools and spring steel. Arc furnaces were used to prepare calcium carbide for use in carbide lamps; the Stassano electric furnace is an arc type furnace that rotates to mix the bath. The Girod furnace is similar to the Héroult furnace. While EAFs were used in World War II for production of alloy steels, it was only that electric steelmaking began to expand; the low capital cost for a mini-mill—around US$140–200 per ton of annual installed capacity, compared with US$1,000 per ton of annual installed capacity for an integrated steel mill—allowed mills to be established in war-ravaged Europe, allowed them to compete with the big United States steelmakers, such as Bethlehem Steel and U. S. Steel, for low-cost, carbon steel "long products" in the U.
S. market. When Nucor—now one of the largest steel producers in the U. S.—decided to enter the long products market in 1969, they chose to start up a mini-mill, with an EAF as its steelmaking furnace, soon followed by other manufacturers. Whilst Nucor expanded in the Eastern U. S. the companies that followed them into mini-mill operations concentrated on local markets for long products, where the use of an EAF allowed the plants to vary production according to local demand. This pattern was followed globally, with EAF steel production used for long products, while integrated mills, using blast furnaces and basic oxygen furnaces, cornered the markets for "flat products"—sheet steel and heavier steel plate. In 1987, Nucor made the decision to expand into the flat products market, still using the EAF production method. An electric arc furnace used for steelmaking consists of a refractory-lined vessel water-cooled in larger sizes, covered with a retractable roof, through which one or more graphite electrodes enter the furnace.
The furnace is split into three sections: the shell, which consists of the sidewalls and lower steel "bowl". The roof supports the refractory delta in its centre, through which one or more graphite electrodes enter; the hearth may be hemispherical in shape, or in an eccentric bottom tapping furnace, the hearth has the shape of a halved egg. In modern meltshops, the furnace is raised off the ground floor, so that ladles and slag pots can be maneuvered under either end of the furnace. Separate from the furnace structure is the electrode support and electrical system, the tilting platform on which the furnace rests. Two configurations are possible: the electrode supports and the roof tilt with the furnace, or are fixed to the raised platform. A typical alternating current furnace is powered by a three-phase electrical supply and therefore has three electrodes. Electrodes are round in section, in segments with threaded couplings, so that as the electrodes wear, new segments can be added; the arc forms between the charged material and the electrode, the charge is heated both by current passing through the charge and by the radiant energy evolved by the arc.
The electric arc temperature reaches around 3000 °C, thus causing the lower sections of the electrodes to glow incandescently when in operation. The electrodes are automatically raised and lowered by a positioning system, which may use either electric winch hoists or hydraulic cylinders; the regulating system maintains constant current and power input during the melting of the charge though scrap may move under the electrodes as it melts. The mast arms holding the electrodes can either carry heavy busbars or be "hot arms", where the whole arm carries the current, increasing efficiency. Hot arms can be made from copper-clad steel or aluminium. Large water-cooled cables connect the bus tubes or arms with the transformer located adjacent to the furnace; the transformer is installed in a vault and is wa