Coke is a grey and porous fuel with a high carbon content and few impurities, made by heating coal or oil in the absence of air — a destructive distillation process. It is an important industrial product, used in iron ore smelting, but as a fuel in stoves and forges when air pollution is a concern; the unqualified term "coke" refers to the product derived from low-ash and low-sulfur bituminous coal by a process called coking. A similar product called pet coke, is obtained from crude oil in oil refineries. Coke may be formed by geologic processes. Historical sources dating to the 4th century describe the production of coke in ancient China; the Chinese first used coke for heating and cooking no than the ninth century. By the first decades of the eleventh century, Chinese ironworkers in the Yellow River valley began to fuel their furnaces with coke, solving their fuel problem in that tree-sparse region. In 1589, a patent was granted to Thomas Proctor and William Peterson for making iron and steel and melting lead with "earth-coal, sea-coal and peat".
The patent contains a distinct allusion to the preparation of coal by "cooking". In 1590, a patent was granted to the Dean of York to "purify pit-coal and free it from its offensive smell". In 1620, a patent was granted to a company composed of William St. John and other knights, mentioning the use of coke in smelting ores and manufacturing metals. In 1627, a patent was granted to Sir John Hacket and Octavius de Strada for a method of rendering sea-coal and pit-coal as useful as charcoal for burning in houses, without offense by smell or smoke. In 1603, Hugh Plat suggested that coal might be charred in a manner analogous to the way charcoal is produced from wood; this process was not employed until 1642. It was considered an improvement in quality, brought about an "alteration which all England admired"—the coke process allowed for a lighter roast of the malt, leading to the creation of what by the end of the 17th century was called pale ale. In 1709, Abraham Darby I established a coke-fired blast furnace to produce cast iron.
Coke's superior crushing strength allowed blast furnaces to become larger. The ensuing availability of inexpensive iron was one of the factors leading to the Industrial Revolution. Before this time, iron-making used large quantities of charcoal, produced by burning wood; as the coppicing of forests became unable to meet the demand, the substitution of coke for charcoal became common in Great Britain, coke was manufactured by burning coal in heaps on the ground so that only the outer layer burned, leaving the interior of the pile in a carbonized state. In the late 18th century, brick beehive ovens were developed, which allowed more control over the burning process. In 1768, John Wilkinson built a more practical oven for converting coal into coke. Wilkinson improved the process by building the coal heaps around a low central chimney built of loose bricks and with openings for the combustion gases to enter, resulting in a higher yield of better coke. With greater skill in the firing and quenching of the heaps, yields were increased from about 33% to 65% by the middle of the 19th century.
The Scottish iron industry expanded in the second quarter of the 19th century, through the adoption of the hot-blast process in its coalfields. In 1802, a battery of beehives was set up near Sheffield, to coke the Silkstone seam for use in crucible steel melting. By 1870, there were 14,000 beehive ovens in operation on the West Durham coalfields, capable of producing 4,000,000 long tons of coke; as a measure of the extent of the expansion of coke making, it has been estimated that the requirements of the iron industry were about 1,000,000 long tons a year in the early 1850s, whereas by 1880 the figure had risen to 7,000,000 long tons, of which about 5,000,000 long tons were produced in Durham county, 1,000,000 long tons in the South Wales coalfield, 1,000,000 long tons in Yorkshire and Derbyshire. In the first years of steam railway locomotives, coke was the normal fuel; this resulted from an early piece of environmental legislation. This was not technically possible to achieve until the firebox arch came into use, but burning coke, with its low smoke emissions, was considered to meet the requirement.
This rule was dropped, cheaper coal became the normal fuel, as railways gained acceptance among the public. In the US, the first use of coke in an iron furnace occurred around 1817 at Isaac Meason's Plumsock puddling furnace and rolling mill in Fayette County, Pennsylvania. In the late 19th century, the coalfields of western Pennsylvania provided a rich source of raw material for coking. In 1885, the Rochester and Pittsburgh Coal and Iron Company constructed the world's longest string of coke ovens in Walston, with 475 ovens over a length of 2 km, their output reached 22,000 tons per month. The Minersville Coke Ovens in Huntingdon County, were listed on the National Register of Historic Places in 1991. Between 1870 and 1905, the number of beehive ovens in the US skyrocketed from about 200 to 31,000, which produced nearly 18,000,000 tons of coke in the Pittsburgh area alone. One observer boasted that if loaded into a train, “the year's production would make up a train so long that the engine in front of it would go to
A wetland is a distinct ecosystem, inundated by water, either permanently or seasonally, where oxygen-free processes prevail. The primary factor that distinguishes wetlands from other land forms or water bodies is the characteristic vegetation of aquatic plants, adapted to the unique hydric soil. Wetlands play a number of functions, including water purification, water storage, processing of carbon and other nutrients, stabilization of shorelines, support of plants and animals. Wetlands are considered the most biologically diverse of all ecosystems, serving as home to a wide range of plant and animal life. Whether any individual wetland performs these functions, the degree to which it performs them, depends on characteristics of that wetland and the lands and waters near it. Methods for assessing these functions, wetland ecological health, general wetland condition have been developed in many regions and have contributed to wetland conservation by raising public awareness of the functions and the ecosystem services some wetlands provide.
Wetlands occur on every continent. The main wetland types are swamp, marsh and fen. Many peatlands are wetlands; the water in wetlands is either brackish, or saltwater. Wetlands can be non-tidal; the largest wetlands include the Amazon River basin, the West Siberian Plain, the Pantanal in South America, the Sundarbans in the Ganges-Brahmaputra delta. The UN Millennium Ecosystem Assessment determined that environmental degradation is more prominent within wetland systems than any other ecosystem on Earth. Constructed wetlands are used to treat municipal and industrial wastewater as well as stormwater runoff, they may play a role in water-sensitive urban design. A patch of land that develops pools of water after a rain storm would not be considered a "wetland" though the land is wet. Wetlands have unique characteristics: they are distinguished from other water bodies or landforms based on their water level and on the types of plants that live within them. Wetlands are characterized as having a water table that stands at or near the land surface for a long enough period each year to support aquatic plants.
A more concise definition is a community composed of hydric soil and hydrophytes. Wetlands have been described as ecotones, providing a transition between dry land and water bodies. Mitsch and Gosselink write that wetlands exist "...at the interface between terrestrial ecosystems and aquatic systems, making them inherently different from each other, yet dependent on both."In environmental decision-making, there are subsets of definitions that are agreed upon to make regulatory and policy decisions. A wetland is "an ecosystem that arises when inundation by water produces soils dominated by anaerobic and aerobic processes, which, in turn, forces the biota rooted plants, to adapt to flooding." There are four main kinds of wetlands – marsh, swamp and fen. Some experts recognize wet meadows and aquatic ecosystems as additional wetland types; the largest wetlands in the world include the swamp forests of the Amazon and the peatlands of Siberia. Under the Ramsar international wetland conservation treaty, wetlands are defined as follows: Article 1.1: "...wetlands are areas of marsh, peatland or water, whether natural or artificial, permanent or temporary, with water, static or flowing, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres."
Article 2.1: " may incorporate riparian and coastal zones adjacent to the wetlands, islands or bodies of marine water deeper than six metres at low tide lying within the wetlands." Although the general definition given above applies around the world, each county and region tends to have its own definition for legal purposes. In the United States, wetlands are defined as "those areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, that under normal circumstances do support, a prevalence of vegetation adapted for life in saturated soil conditions. Wetlands include swamps, marshes and similar areas"; this definition has been used in the enforcement of the Clean Water Act. Some US states, such as Massachusetts and New York, have separate definitions that may differ from the federal government's. In the United States Code, the term wetland is defined "as land that has a predominance of hydric soils, is inundated or saturated by surface or groundwater at a frequency and duration sufficient to support a prevalence of hydrophytic vegetation adapted for life in saturated soil conditions and under normal circumstances supports a prevalence of such vegetation."
Related to this legal definitions, the term "normal circumstances" are conditions expected to occur during the wet portion of the growing season under normal climatic conditions, in the absence of significant disturbance. It is not uncommon for a wetland to be dry for long portions of the growing season. Wetlands can be dry during the dry season and abnormally dry periods during the wet season, but under normal environmental conditions the soils in a wetland will be saturated to the surface or inundated such that the soils become anaerobic, those conditions will persist through the wet portion of the growing season; the most important factor producing wetlands is flooding. The duration of flooding or prolonged soil saturation by groundwater determines whether the resulting wetland has aquatic, marsh or swamp vegetation
Mining is the extraction of valuable minerals or other geological materials from the earth from an ore body, vein, reef or placer deposit. These deposits form a mineralized package, of economic interest to the miner. Ores recovered by mining include metals, oil shale, limestone, dimension stone, rock salt, potash and clay. Mining is required to obtain any material that cannot be grown through agricultural processes, or feasibly created artificially in a laboratory or factory. Mining in a wider sense includes extraction of any non-renewable resource such as petroleum, natural gas, or water. Mining of stones and metal has been a human activity since pre-historic times. Modern mining processes involve prospecting for ore bodies, analysis of the profit potential of a proposed mine, extraction of the desired materials, final reclamation of the land after the mine is closed. De Re Metallica, Georgius Agricola, 1550, Book I, Para. 1Mining operations create a negative environmental impact, both during the mining activity and after the mine has closed.
Hence, most of the world's nations have passed regulations to decrease the impact. Work safety has long been a concern as well, modern practices have improved safety in mines. Levels of metals recycling are low. Unless future end-of-life recycling rates are stepped up, some rare metals may become unavailable for use in a variety of consumer products. Due to the low recycling rates, some landfills now contain higher concentrations of metal than mines themselves. Since the beginning of civilization, people have used stone and metals found close to the Earth's surface; these were used to make early weapons. Flint mines have been found in chalk areas where seams of the stone were followed underground by shafts and galleries; the mines at Grimes Graves and Krzemionki are famous, like most other flint mines, are Neolithic in origin. Other hard rocks mined or collected for axes included the greenstone of the Langdale axe industry based in the English Lake District; the oldest-known mine on archaeological record is the Ngwenya Mine in Swaziland, which radiocarbon dating shows to be about 43,000 years old.
At this site Paleolithic humans mined hematite to make the red pigment ochre. Mines of a similar age in Hungary are believed to be sites where Neanderthals may have mined flint for weapons and tools. Ancient Egyptians mined malachite at Maadi. At first, Egyptians used the bright green malachite stones for ornamentations and pottery. Between 2613 and 2494 BC, large building projects required expeditions abroad to the area of Wadi Maghareh in order to secure minerals and other resources not available in Egypt itself. Quarries for turquoise and copper were found at Wadi Hammamat, Tura and various other Nubian sites on the Sinai Peninsula and at Timna. Mining in Egypt occurred in the earliest dynasties; the gold mines of Nubia were among the largest and most extensive of any in Ancient Egypt. These mines are described by the Greek author Diodorus Siculus, who mentions fire-setting as one method used to break down the hard rock holding the gold. One of the complexes is shown in one of the earliest known maps.
The miners crushed the ore and ground it to a fine powder before washing the powder for the gold dust. Mining in Europe has a long history. Examples include the silver mines of Laurium. Although they had over 20,000 slaves working them, their technology was identical to their Bronze Age predecessors. At other mines, such as on the island of Thassos, marble was quarried by the Parians after they arrived in the 7th century BC; the marble was shipped away and was found by archaeologists to have been used in buildings including the tomb of Amphipolis. Philip II of Macedon, the father of Alexander the Great, captured the gold mines of Mount Pangeo in 357 BC to fund his military campaigns, he captured gold mines in Thrace for minting coinage producing 26 tons per year. However, it was the Romans who developed large scale mining methods the use of large volumes of water brought to the minehead by numerous aqueducts; the water was used for a variety of purposes, including removing overburden and rock debris, called hydraulic mining, as well as washing comminuted, or crushed and driving simple machinery.
The Romans used hydraulic mining methods on a large scale to prospect for the veins of ore a now-obsolete form of mining known as hushing. They built numerous aqueducts to supply water to the minehead. There, the water stored in large tanks; when a full tank was opened, the flood of water sluiced away the overburden to expose the bedrock underneath and any gold veins. The rock was worked upon by fire-setting to heat the rock, which would be quenched with a stream of water; the resulting thermal shock cracked the rock, enabling it to be removed by further streams of water from the overhead tanks. The Roman miners used similar methods to work cassiterite deposits in Cornwall and lead ore in the Pennines; the methods had been developed by the Romans in Spain in 25 AD to exploit large alluvial gold deposits, the largest site being at Las Medulas, where seven long aqueducts tapped local rivers and sluiced the deposits. Spain was one of the most important mining regions, but all regions of the Roman Empire were exploited.
In Great Britain the natives had mined minerals for millennia, but after the Roman conquest, the scale of the operations increased as the Romans needed Britannia's resources gold, silver
ArcelorMittal S. A. is a multinational steel manufacturing corporation headquartered in Luxembourg City. It was formed in 2006 from the merger of Arcelor by Indian-owned Mittal Steel. ArcelorMittal is the world's largest steel producer, with an annual crude steel production of 92.5 million metric tonnes as of 2018. It is ranked 123 in the 2017 Fortune Global 500 ranking of the world's biggest corporations. ArcelorMittal was created by the takeover of Western European steel maker Arcelor by Indian-owned multinational steel maker Mittal Steel in 2006, at a cost of €40.37 per share $33 billion total. Mittal Steel launched a hostile takeover bid which replaced a previous planned merger between Arcelor and Severstal, which had lacked sufficient shareholder approval; the resulting merged business was headquartered in Luxembourg City. The resulting firm produced 10% of the world's steel, was by far the world's largest steel company. Total revenues in 2007 were $105 billion; the company earned revenues f $105 billion in 2007.
By February 2008, the company had 320,000 employees in 60 countries. In October 2008, the market capitalisation of ArcelorMittal was over $30 billion, after peaking at $32.5 billion in September 2008. At the end of 2008, the company reported operating income of around $12 billion. In December 2008, ArcelorMittal announced several plant closings, including the Bethlehem Steel plant in Lackawanna, New York, LTV Steel in Hennepin, Illinois. After purchase of Kryvorizhstal, Ukraine's largest steel producer, employment was scaled back from 57,000 employees to 30,000. In 2010, the company's operating income had fallen to $4.9 billion, with sales down 10 percent from the year earlier, income down 50 percent as steel prices slumped. In 2011, the company began curtailing its European production to match the reduced demand for steel, it sold Skyline Steel and Astralloy to a rival, for $605 million. On 26 January 2011, the stainless steel division split off as Aperam; as of 2012, due to overcapacity and reduced demand in Europe it had idled 9 of 25 blast furnaces.
On 31 October 2012, the company reported a third-quarter loss of $709 million as compared to a $659 million profit for the same period a year ago, citing the slow down in China's economy. In 2012 ArcelorMittal had $22 billion of debt. In January 2013, ArcelorMittal bid $1.5 billion to acquire ThyssenKrupp AG's rolling mill in Calvert, United States. On 26 February 2014, ThyssenKrupp sold their Calvert carbon steel facility to ArcelorMittal and Nippon Steel for $1.55 billion, as a new joint venture. The facility was renamed AM/NS Calvert through the 50/50 joint partnership with Nippon Steel & Sumitomo Metal Corp; the firm entered into a $2.2 billion contract to develop an iron ore deposit in Senegal. This included construction of a 750 km railway line. After stalling on the contract and failing to build according to schedule the Government of Senegal sued. In September 2013, the government of Senegal won a court case before an international tribunal to rescind a $2.2 billion deal with ArcelorMittal after the company suspended work on an iron ore mine in the country.
In June 2014, the International Chamber of Commerce's arbitration court in Paris awarded Senegal $150 million. Dealing with price and demand fluctuations in the steel market, from 2012 to 2014 ArcelorMittal restructured its European division by reducing employee numbers and closing plants. In May, 2014, ArcelorMittal, citing economic self-interest, declared its opposition to sanctions on Russia; as of June 2014, ArcelorMittal accounted for 7 percent of world steel production. After being shut out of the Chinese steel industry in 2005 along with other foreign companies, in 2014 the company announced it was planning new plants in China. In 2014, the company had an annual crude steel production of 98.1 million tons. Following an investigation first launched in 2008, in August 2016 the South African Competition Commission found the company guilty of price fixing. ArcelorMittal was fined US$110.9 million, as part of the settlement agreed to invest R4.64 billion in capital over five years. According to the findings, the firm had been part of a 17 steel member groups nicknamed "Club Zürich" that became known as "Club Europe."
Between January 1984 and September 2002, the companies fixed the market and exchanged confidential corporate information. In 2015, the company had a net loss of $7.9 billion. Between February 2015 and February 2016, share value dropped 60%, making the company the "worst performer" in the FTSEurofirst300 index; the CEO said the company had performed poorly in 2015 due to "Chinese exports depressing prices." Early in 2016, the company announced it had raised $3 billion in new investment capital to help reduce debt to $11.7 billion of debt. In early 2016 the company announced a program to boost core profit by $3 billion by 2020 "through a mixture of cost-cutting, increased production and a focus on higher-value forms of steel." Chairman Lakshmi Mittal announced doubled earnings the following year in May 2017. Along with the increase in capital, the company sold its 35% stake in Gestamp Automacion for $979 million, with the goal of reducing ArcelorMittal's debt to less than $12 billion. By February 2016, the company made about 6% of the world's steel.
It ranked 108th in the 2016 Fortune Global 500 ranking of the world's biggest corporations. In February 2017 ArcelorMittal announced its first annual profits in five years. In February 2017, ArcelorMittal and Votorantim announced plans to combine their long steel operations in Brazil. Under th
Basic oxygen steelmaking
Basic oxygen steelmaking known as Linz–Donawitz-steelmaking or the oxygen converter process is a method of primary steelmaking in which carbon-rich molten pig iron is made into steel. Blowing oxygen through molten pig iron lowers the carbon content of the alloy and changes it into low-carbon steel; the process is known as basic because fluxes of burnt lime or dolomite, which are chemical bases, are added to promote the removal of impurities and protect the lining of the converter. The process was developed in 1948 by Swiss engineer Robert Durrer and commercialized in 1952–1953 by the Austrian steelmaking company VOEST and ÖAMG; the LD converter, named after the Austrian towns Linz and Donawitz is a refined version of the Bessemer converter where blowing of air is replaced with blowing oxygen. It reduced capital cost of the plants, time of smelting, increased labor productivity. Between 1920 and 2000, labor requirements in the industry decreased by a factor of 1,000, from more than three man-hours per metric ton to just 0.003.
The majority of steel manufactured in the world is produced using the basic oxygen furnace. In 2000, it accounted for 60% of global steel output. Modern furnaces will take a charge of iron of up to 400 tons and convert it into steel in less than 40 minutes, compared to 10–12 hours in an open hearth furnace; the basic oxygen process developed outside of traditional "big steel" environment. It was developed and refined by a single man, Swiss engineer Robert Durrer, commercialized by two small steel companies in allied-occupied Austria, which had not yet recovered from the destruction of World War II. In 1856, Henry Bessemer patented a steelmaking process involving oxygen blowing for decarbonizing molten iron. For nearly 100 years commercial quantities of oxygen were not available or were too expensive, the invention remained unused. During WWII German and Swiss engineers proposed their versions of oxygen-blown steelmaking, but only Durrer and Heilbrugge brought it to mass-scale production. In 1943, Durrer a professor at the Berlin Institute of Technology, returned to Switzerland and accepted a seat on the board of Roll AG, the country's largest steel mill.
In 1947 he purchased the first small 2.5-ton experimental converter from the US, on April 3, 1948 the new converter produced its first steel. The new process could conveniently process large amounts of scrap metal with only a small proportion of primary metal necessary. In the summer of 1948 Roll AG and two Austrian state-owned companies, VOEST and ÖAMG, agreed to commercialize the Durrer process. By June 1949, VOEST developed an adaptation of Durrer's process, known as the LD process. In December 1949, VOEST and ÖAMG committed to building their first 30-ton oxygen converters, they were put into operation in November 1952 and May 1953 and temporarily became the leading edge of the world's steelmaking, causing a surge in steel-related research. Thirty-four thousand businesspeople and engineers visited the VOEST converter by 1963; the LD process reduced processing time and capital costs per ton of steel, contributing to the competitive advantage of Austrian steel. VOEST acquired the rights to market the new technology.
Errors by the VOEST and the ÖAMG management in licensing their technology made control over its adoption in Japan impossible. By the end of the 1950s the Austrians lost their competitive edge. In the original LD process, oxygen was blown over the top of the molten iron through the water-cooled nozzle of a vertical lance. In the 1960s steelmakers introduced bottom-blown converters and introduced inert gas blowing for stirring the molten metal and removing phosphorus impurities. In the Soviet Union, some experimental production of steel using the process was done in 1934, but industrial use was hampered by lack of efficient technology to produce liquid oxygen. In 1939, the Russian physicist Pyotr Kapitsa perfected the design of the centrifugal turboexpander; the process was put to use in 1942-1944. Most turboexpanders in industrial use since have been based on Kapitsa's design and centrifugal turboexpanders have taken over 100% of industrial gas liquefaction, in particular the production of liquid oxygen for steelmaking.
Big American steelmakers were late adopters of the new technology. The first oxygen converters in the US were launched at the end of 1954 by McLouth Steel in Trenton, which accounted for less than 1% of the national steel market. U. S. Steel and Bethlehem Steel introduced the oxygen process in 1964. By 1970 half of the world's and 80% of Japan's steel output was produced in oxygen converters. In the last quarter of the 20th century use of basic oxygen converters for steel production was partially replaced by the electric arc furnace using scrap steel and iron. In Japan the share of LD process decreased from 80% in 1970 to 70% in 2000. Basic oxygen steelmaking is a primary steelmaking process for converting molten pig iron into steel by blowing oxygen through a lance over the molten pig iron inside the converter. Exothermic heat is generated by the oxidation reactions during blowing; the basic oxygen steel-making process is as follows: Molten pig iron from a blast furnace is poured into a large refractory-lined container called a ladle.
The metal in the ladle is sent directly to a pretreatment stage. High purity oxygen at a pressure of 700–1,000 kilopascals is introduced at supersonic speed onto the surface of the iron bath through a water-cooled lance, suspended in the vessel
Steel is an alloy of iron and carbon, sometimes other elements. Because of its high tensile strength and low cost, it is a major component used in buildings, tools, automobiles, machines and weapons. Iron is the base metal of steel. Iron is able to take on two crystalline 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, it is the interaction of the allotropes of iron with the alloying elements carbon, that gives steel and cast iron their range of unique properties. In pure iron, the crystal structure has little resistance to the iron atoms slipping past one another, so pure iron is quite ductile, or soft and formed. In steel, small amounts of carbon, other elements, 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, slows the movement of those dislocations that make pure iron ductile, thus controls and enhances its qualities. These qualities include such things as the hardness, quenching behavior, need for annealing, tempering behavior, yield strength, 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 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 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 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 identified by various grades defined by assorted standards organizations; the noun steel originates from the Proto-Germanic adjective stahliją or stakhlijan, related to stahlaz or stahliją. The carbon content of steel is between 0.002% and 2.14% by weight for plain iron–carbon alloys. These values vary depending on alloying elements such as manganese, nickel, so on. 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 iron quite soft and weak. Carbon contents higher than those of steel make a brittle alloy 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, chromium, boron, vanadium, tungsten and niobium. Additional elements, most considered undesirable, are important in steel: phosphorus, sulfur and traces of oxygen 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 high-carbon steels, but such are not common. Cast iron is not malleable when hot, but it can be formed by casting as it has a lower melting point than steel and good castability properties. Certain compositions of cast iron, while retaining the economies of melting and casting, can be heat treated after casting to make malleable iron or ductile iron objects. Steel is distinguishable from wrought iron, which may contain a small amount of carbon but large amounts of slag. Iron is found in the Earth's crust in the form of an ore 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, 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, copper, which melts at about 1,100 °C, the combination, which has a melting point lower than 1,083 °C. In comparison, cast iron melts at about 1,375 °C. Small quantities of iron were smelted in ancient times, in the solid state, by heating the ore in a charcoal fire and 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 beyond 800 °C, it is important that smelting take place in a low-oxygen environment. Smelting, using carbon to reduce iro
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