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Iron & Steel Info
Steel From Wikipedia, the free encyclopedia
For other uses, see Steel (disambiguation).
The steel cable of a colliery winding tower.Look up steel in Wiktionary, the free dictionary.Steel is an alloy consisting mostly of iron, with a carbon content between 0.02% and 1.7 or 2.04% by weight (C:1000–10,8.67Fe), depending on grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese and tungsten.[1] Carbon and other elements act as a hardening agent, preventing dislocations in the iron atom crystal lattice from sliding past one another. Varying the amount of alloying elements and form of their presence in the steel (solute elements, precipitated phase) controls qualities such as the hardness, ductility, and tensile strength of the resulting steel. Steel with increased carbon content can be made harder and stronger than iron, but is also more brittle. The maximum solubility of carbon in iron (in austenite region)is 2.14% by weight, occurring at 1149 °C; higher concentrations of carbon or lower temperatures will produce cementite. Alloys with higher carbon content than this are known as cast iron because of their lower melting point.[1] Steel is also to be distinguished from wrought iron containing only a very small amount of other elements, but containing 1-3% by weight of slag in the form of particles elongated in one direction, giving the iron a characteristic grain. It is more rust-resistant than steel and welds more easily. But at present time this term is rarely used in steel industry. It is common today to talk about 'the iron and steel industry' as if it were a single entity, but historically they were separate products.
Though steel had been produced by various inefficient methods long before the Renaissance, its use became more common after more efficient production methods were devised in the 17th century. With the invention of the Bessemer process in the mid-19th century, steel became a relatively inexpensive mass-produced good. Further refinements in the process, such as basic oxygen steelmaking, further lowered the cost of production while increasing the quality of the metal. Today, steel is one of the most common materials in the world and is a major component in buildings, tools, automobiles, and appliances. Modern steel is generally identified by various grades of steel defined by various standards organizations.
Contents 1 Material properties 2 History of steelmaking 2.1 Ancient steel 2.2 Early modern steel 2.2.1 Blister steel 2.2.2 Crucible steel 2.3 Modern steelmaking 3 Steel industry 4 Recycling 5 Contemporary steel 6 Modern production methods 7 Uses of steel 7.1 Historically 7.2 Since 1850 7.2.1 Long steel 7.2.2 Flat carbon steel 7.2.3 Stainless steel 8 See also 9 References 10 Further reading 11 External links
Material properties v • d • e Iron alloy phases Austenite (?-iron; hard) Bainite Martensite Cementite (iron carbide; Fe3C) Ledeburite (ferrite - cementite eutectic, 4.3% carbon) Ferrite (a-iron, d-iron; soft) Pearlite (88% ferrite, 12% cementite) Spheroidite
Types of Steel Plain-carbon steel (up to 2.1% carbon) Stainless steel (alloy with chromium) HSLA steel (high strength low alloy) Tool steel (very hard; heat-treated)
Other Iron-based materials Cast iron (>2.1% carbon) Wrought iron (almost no carbon) Ductile iron
Iron, like most metals, is not usually found in the Earth's crust in an elemental state.[2] Iron can be found in the crust only in combination with oxygen or sulfur. Typical iron-containing minerals include Fe2O3—the form of iron oxide found as the mineral hematite, and FeS2—pyrite (fool's gold).[3] Iron is extracted from ore by removing the oxygen by combining it with a preferred chemical partner such as carbon. This process, known as smelting, was first applied to metals with lower melting points. Copper melts at just over 1000 °C, while tin melts around 250 °C. Cast iron—iron alloyed with greater than 1.7% carbon—melts at around 1370 °C. All of these temperatures could be reached with ancient methods that have been used for at least 6000 years (since the Bronze Age). Since the oxidation rate itself increases rapidly beyond 800 °C, it is important that smelting take place in a low-oxygen environment. Unlike copper and tin, liquid iron dissolves carbon quite readily, so that smelting results in an alloy containing too much carbon to be called steel.[4]
Even in the narrow range of concentrations that make up steel, mixtures of carbon and iron can form into a number of different structures, with very different properties; understanding these is essential to making quality steel. At room temperature, the most stable form of iron is the body-centered cubic (BCC) structure ferrite or a-iron, a fairly soft metallic material that can dissolve only a small concentration of carbon (no more than 0.021 wt% at 910 °C). Above 910 °C ferrite undergoes a phase transition from body-centered cubic to a face-centered cubic (FCC) structure, called austenite or ?-iron, which is similarly soft and metallic but can dissolve considerably more carbon (as much as 2.03 wt% carbon at 1154 °C).[5] As carbon-rich austenite cools, the mixture attempts to revert to the ferrite phase, resulting in an excess of carbon. One way for carbon to leave the austenite is for cementite to precipitate out of the mix, leaving behind iron that is pure enough to take the form of ferrite, resulting in a cementite-ferrite mixture. Cementite is a stoichiometric phase with the chemical formula of Fe3C. Cementite forms in regions of higher carbon content while other areas revert to ferrite around it. Self-reinforcing patterns often emerge during this process, leading to a patterned layering known as pearlite (Fe3C:6.33Fe) due to its pearl-like appearance, or the similar but less beautiful bainite.
Iron-carbon phase diagram, showing the conditions necessary to form different phases.Perhaps the most important allotrope is martensite, a chemically metastable substance with about four to five times the strength of ferrite. A minimum of 0.4 wt% of carbon (C:50Fe) is needed in order to form martensite. When the austenite is quenched to form martensite, the carbon is "frozen" in place when the cell structure changes from FCC to BCC. The carbon atoms are much too large to fit in the interstitial vacancies and thus distort the cell structure into a body-centered tetragonal (BCT) structure. Martensite and austenite have an identical chemical composition. As such, it requires extremely little thermal activation energy to form.
The heat treatment process for most steels involves heating the alloy until austenite forms, then quenching the hot metal in water or oil, cooling it so rapidly that the transformation to ferrite or pearlite does not have time to take place. The transformation into martensite, by contrast, occurs almost immediately, due to a lower activation energy.
Iron ore pellets for the production of steel.Martensite has a lower density than 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, these 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 water quenched, although they may not always be visible.[6]
At this point, if the carbon content is high enough to produce a significant concentration of martensite, the result is an extremely hard but very brittle material. Often, steel undergoes further heat treatment at a lower temperature to destroy some of the martensite (by allowing enough time for cementite, etc., to form) and help settle the internal stresses and defects. This softens the steel, producing a more ductile and fracture-resistant metal. Because time is so critical to the end result, this process is known as tempering, which forms tempered steel.[7]
Other materials are often added to the iron-carbon mixture to tailor the resulting properties. Nickel and manganese in steel add to its tensile strength and make austenite more chemically stable, chromium increases the hardness and melting temperature, and vanadium also increases the hardness while reducing the effects of metal fatigue. Large amounts of chromium and nickel (often 18% and 8%, respectively) are added to stainless steel so that a hard oxide forms on the metal surface to inhibit corrosion. Tungsten interferes with the formation of cementite, allowing martensite to form with slower quench rates, resulting in high speed steel. On the other hand sulfur, nitrogen, and phosphorus make steel more brittle, so these commonly found elements must be removed from the ore during processing.[8]
When iron is smelted from its ore by commercial processes, it contains more carbon than is desirable. To become steel, it must be melted and reprocessed to remove the correct amount of carbon, at which point other elements can be added. Once this liquid is cast into ingots, it usually must be "worked" at high temperature to remove any cracks or poorly mixed regions from the solidification process, and to produce shapes such as plate, sheet, wire, etc. It is then heat-treated to produce a desirable crystal structure, and often "cold worked" to produce the final shape. In modern steelmaking these processes are often combined, with ore going in one end of the assembly line and finished steel coming out the other. These can be streamlined by a deft control of the interaction between work hardening and tempering.
History of steelmaking
Bloomery smelting during the Middle Ages.Main article: History of ferrous metallurgy
Ancient steel Steel was known in antiquity, and may have been produced by managing the bloomery so that the bloom contained carbon.[9] Some of the first steel comes from East Africa, dating back to 1400 BC[10]. In the 4th century BC steel weapons like the Falcata were produced in the Iberian peninsula. The Chinese of the Han Dynasty (202 BC - 220 AD) created steel by melting together wrought iron with cast iron, gaining ultimate product of a carbon intermediate—steel—by the 1st century BC.[11][12] Along with their original methods of forging steel, the Chinese had also adopted the production methods of creating Wootz steel, an idea imported from India to China by the 5th century AD.[13] Wootz steel was produced in India and Sri Lanka from around 300 BC. This early steel-making method employed the use of a wind furnace, blown by the monsoon winds.[14] Also known as Damascus steel, wootz is famous for its durability and ability to hold an edge. It was originally created from a number of different materials including various trace elements. It was essentially a complicated alloy with iron as its main component. Recent studies have suggested that carbon nanotubes were included in its structure, which might explain some of its legendary qualities, though given the technology available at that time, they were probably produced more by chance than by design.[15] Crucible steel was produced in Merv by 9th to 10th century AD.
In the 11th century, there is evidence of the production of steel in Song China using two techniques: a "berganesque" method that produced inferior, inhomogoneous steel and a precursor to the modern Bessemer process that utilized partial decarbonization via repeated forging under a cold blast. [16]
Early modern steel
A Bessemer converter in Sheffield, England. Blister steel Main article: Cementation process Blister steel, produced by the cementation process was first made in Italy in the early 17th century AD and soon after introduced to England. It was probably produced by Sir Basil Brooke at Coalbrookdale during the 1610s. The raw material for this was bars of wrought iron. During the 17th century it was realised that the best steel came from oregrounds iron from a region of Sweden, north of Stockholm. This was still the usual raw material in the 19th century, almost as long as the process was used.[17][18]
Crucible steel Main article: Crucible steel Crucible steel is steel that has been melted in a crucible rather than being 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 in a furnace, and cast (usually) into ingots.[18]
Modern steelmaking
A Siemens-Martin steel oven from the Brandenburg Museum of Industry.See also History of the modern steel industry. The modern era in steelmaking began with the introduction of Henry Bessemer's Bessemer process in the late 1850s. This enabled steel to be produced in large quantities cheaply, so that mild steel is now used for most purposes for which wrought iron was formerly used.[19] This was only the first of a number of methods of steel production. The Gilchrist-Thomas process (or basic Bessemer process) was an improvement to the Bessemer process, lining the converter with a basic material to remove phosphorus. Another was the Siemens-Martin process of open hearth steelmaking which like the Gilchrist-Thomas process complemented, rather than replaced, the original Bessemer process.[18]
These were rendered obsolete by the Linz-Donawitz process of basic oxygen steelmaking, developed in the 1950s, and other oxygen steelmaking processes.[20]
Steel industry
Tata Steel plant in the United Kingdom. Steel output in 2005Because of the critical role played by steel in infrastructural and overall economic development, the steel industry is often considered to be an indicative for economic prowess.
The economic boom in China has caused a massive increase in the demand for steel in recent years. Between 2000 and 2005, world steel demand increased by 6%.[21] Since 2000, several Indian[22] and Chinese steel firms have rose to prominence like Tata Steel (which bought Corus Group in 2007), Shanghai Baosteel Group Corporation and Shagang Group. Arcelor-Mittal is however the world's largest steel producer.[21]
The British Geological Survey reports that in 2005, China was the top producer of steel with about one-third world share followed by Japan, Russia and the USA.
See also: List of steel producers and Global steel industry trends
Recycling Steel is the most widely recycled material in North America. The steel industry has been actively recycling for more than 150 years, in large part because it is economically advantageous to do so. It is cheaper to recycle steel than to mine iron ore and manipulate it through the production process to form 'new' steel. Steel does not lose any of its inherent physical properties during the recycling process, and has drastically reduced energy and material requirements than refinement from iron ore. The energy saved by recycling reduces the annual energy consumption of the industry by about 75%, which is enough to power eighteen million homes for one year.[23] Recycling one ton of steel saves 1,100 kilograms of iron ore, 630 kilograms of coal, and 55 kilograms of limestone.[24] 76 million tons of steel were recycled in 2005.[23]
A pile of steel scrap in Brussels, waiting to be recycled.In recent years, about three quarters of the steel produced annually has been recycled. However, the numbers are much higher for certain types of products. For example, in both 2004 and 2005, 97.5 % of structural steel beams and plates were recycled.[25] Other steel construction elements such as reinforcement bars are recycled at a rate of about 65 %. Indeed, structural steel typically contains around 95 % recycled steel content, whereas lighter gauge, flat rolled steel contains about 30 % reused material.
Because steel beams are manufactured to standardized dimensions, there is often very little waste produced during construction, and any waste that is produced may be recycled. For a typical 2000-square-foot two-story house, a steel frame is equivalent to about six recycled cars, while a comparable wooden frame house may require as many as 40-50 trees.[23]
Global demand for steel continues to grow, and though there are large amounts of steel existing, much of it is actively in use. As such, recycled steel must be augmented by some first-use metal, derived from raw materials. Commonly recycled steel products include cans, automobiles, appliances, and debris from demolished buildings. A typical appliance is about 65% steel by weight and automobiles are about 66% steel and iron.
While some recycling takes place through the integrated steel mills and the basic oxygen process, most of the recycled steel is melted electrically, either using an electric arc furnace (for production of low-carbon steel) or an induction furnace (for production of some highly-alloyed ferrous products).
Contemporary steel Modern steels are made with varying combinations of alloy metals to fulfill many purposes.[8] Carbon steel, composed simply of iron and carbon, accounts for 90% of steel production.[1] 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.[26] 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.[1] Stainless steels and surgical stainless steels contain a minimum of 10% chromium, often combined with nickel, to resist corrosion (rust). Some stainless steels are magnetic, while others are nonmagnetic.[27]
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.[1] 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.[28]
Many other high-strength alloys exist, such as dual-phase steel, which is heat treated to contain both a ferrite and martensic microstructure for extra strength.[29] Transformation Induced Plasticity (TRIP) steel involves special alloying and heat treatments to stabilize amounts of austentite at room temperature in normally austentite-free low-alloy ferritic steels. By applying strain to the metal, the austentite undergoes a phase transition to martensite without the addition of heat.[30] Maraging steel is alloyed with nickel and other elements, but unlike most steel contains almost no carbon at all. This creates a very strong but still malleable metal.[31] Twinning Induced Plasticity (TWIP) steel uses a specific type of strain to increase the effectiveness of work hardening on the alloy.[32] Eglin Steel uses a combination of over a dozen different elements in varying amounts to create a relatively low-cost metal for use in bunker buster weapons. Hadfield steel (after Sir Robert Hadfield) or manganese steel contains 12-14% manganese which when abraded forms an incredibly hard skin which resists wearing. Examples include tank tracks, bulldozer blade edges and cutting blades on the jaws of life.[33] A special class of high-strength alloy, the superalloys, retain their mechanical properties at extreme temperatures while minimizing creep. These are commonly used in applications such as jet engine blades where temperatures can reach levels at which most other alloys would become weak.[34]
Most of the more commonly used steel alloys are categorized into various grades by standards organizations. For example, the American Iron and Steel Institute has a series of grades defining many types of steel ranging from standard carbon steel to HSLA and stainless steel.[35] 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.[36]
Though not an alloy, galvanized steel is a commonly used variety of steel which has been hot-dipped or electroplated in zinc for protection against rust.[37]
Modern production methods
White-hot steel pouring out of an electric arc furnace.Blast furnaces have been used for two millennia to produce pig iron, a crucial step in the steel production process, from iron ore by combining fuel, charcoal, and air. Modern methods use coke instead of charcoal, which has proven to be a great deal more efficient and is credited with contributing to the British Industrial Revolution.[38] Once the iron is refined, converters are used to create steel from the iron. During the late 19th and early 20th century there were many widely used methods such as the Bessemer process and the Siemens-Martin process. However, basic oxygen steelmaking, in which pure oxygen is fed to the furnace to limit impurities, has generally replaced these older systems. Electric arc furnaces 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 great deal of electricity (about 440 kWh per metric ton), and are thus generally only economical when there is a plentiful supply of cheap electricity.[39]
Uses of steel Iron and steel are used widely in the construction of roads, railways, infrastructure and buildings. Most large modern structures, such as stadiums and skyscrapers, are supported by a steel skeleton. Even those with a concrete structure will employ steel for reinforcing. In addition to widespread use, in electrical appliances and motor vehicles (despite growth in usage of aluminium, it is still the main material for car bodies), steel is used in a variety of other construction-related applications, such as bolts, nails, and screws.[40] Other common applications include shipbuilding, oil and gas pipelines, mining, aerospace, 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).
A piece of steel wool Historically 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.[41]
A carbon steel knife Since 1850 With the advent of faster and more efficient steel production methods, steel has been easier to obtain and much cheaper. It has replaced wrought iron for a multitude of purposes. However, the availability of plastics during the later 20th century allowed these materials to replace steel in many products due to their lower cost and weight.[42]
Long steel
A stainless steel sauce boat.As supports in reinforced concrete Wires railroad tracks Structural steel in modern buildings and bridges
Flat carbon steel
A steel pylon suspending overhead powerlines.The inside and outside body of automobiles, trains, and ships. Major appliances Magnetic cores
Stainless steel
A steel roller coaster.Main article: Stainless steel Cutlery Rulers Wrist watches Surgical equipment
See also Cold rolling Foundry Global steel industry trends Hot rolling Pelletizing Rolling Rolling mill Silicon steel Steel producers Steel mill Tinplate
http://en.wikipedia.org/wiki/Steel
Iron From Wikipedia, the free encyclopedia
For other uses, see Iron (disambiguation). 26 manganese ? iron ? cobalt - ? Fe ? Ru Periodic Table - Extended Periodic Table
General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge
Standard atomic weight 55.845(2)?g·mol-1 Electron configuration [Ar] 4s2 3d6 Electrons per shell 2, 8, 14, 2 Physical properties Phase solid Density (near r.t.) 7.86 g·cm-3 Liquid density at m.p. 6.98 g·cm-3 Melting point 1811 K (1538 °C, 2800 °F) Boiling point 3134 K (2861 °C, 5182 °F) Heat of fusion 13.81 kJ·mol-1 Heat of vaporization 340 kJ·mol-1 Heat capacity (25 °C) 25.10 J·mol-1·K-1 Vapor pressure P/Pa 1 10 100 1 k 10 k 100 k at T/K 1728 1890 2091 2346 2679 3132
Atomic properties Crystal structure body-centered cubic a=286.65 pm; face-centered cubic between 1185–1667 K Oxidation states 2, 3, 4, 6 (amphoteric oxide) Electronegativity 1.83 (Pauling scale) Ionization energies (more) 1st: 762.5 kJ·mol-1 2nd: 1561.9 kJ·mol-1 3rd: 2957 kJ·mol-1 Atomic radius 140 pm Atomic radius (calc.) 156 pm Covalent radius 125 pm Miscellaneous Magnetic ordering ferromagnetic 1043 K Electrical resistivity (20 °C) 96.1 nO·m Thermal conductivity (300 K) 80.4 W·m-1·K-1 Thermal expansion (25 °C) 11.8 µm·m-1·K-1 Speed of sound (thin rod) (r.t.) (electrolytic) 5120 m·s-1 Young's modulus 211 GPa Shear modulus 82 GPa Bulk modulus 170 GPa Poisson ratio 0.29 Mohs hardness 4.0 Vickers hardness 608 MPa Brinell hardness 490 MPa CAS registry number 7439-89-6 Selected isotopes Main article: Isotopes of iron iso NA half-life DM DE (MeV) DP 54Fe 5.8% >3.1×1022y 2e capture ? 54Cr 55Fe syn 2.73 y e capture 0.231 55Mn 56Fe 91.72% Fe is stable with 30 neutrons 57Fe 2.2% Fe is stable with 31 neutrons 58Fe 0.28% Fe is stable with 32 neutrons 59Fe syn 44.503 d ß 1.565 59Co 60Fe syn 1.5×106 y ß- 3.978 60Co
References This box: view • talk • edit Iron (IPA: /'a??(?)n/) is a chemical element with the symbol Fe (Latin: ferrum) and atomic number 26. Iron is a group 8 and period 4 metal. Iron is a lustrous, silvery soft metal. Iron and nickel are notable for being the final elements produced by stellar nucleosynthesis, and thus are the heaviest elements which do not require a supernova or similarly cataclysmic event for formation. Iron and nickel are therefore the most abundant metals in metallic meteorites and in the dense-metal cores of planets such as Earth.
Contents 1 Characteristics 2 Applications 2.1 Iron compounds 3 History 4 Occurrence 5 Production of iron from iron ore 6 Isotopes 7 Iron in organic synthesis 8 Iron in biology 8.1 Nutrition and dietary sources 8.2 Regulation of iron uptake 9 Bibliography 10 References 11 See also 12 External links
Characteristics Iron is believed to be the tenth most abundant element in the universe, and the fourth most abundant on earth. The concentration of iron in the various layers in the structure of the Earth ranges from high (probably greater than 80%, perhaps even a nearly pure iron crystal) at the inner core, to only 5% in the outer crust. Iron is second in abundance to aluminium among the metals and fourth in abundance in the crust. Iron is the most abundant element by mass of our entire planet, making up 35% of the mass of the Earth as a whole.
Iron is a metal extracted from iron ore, and is almost never found in the free elemental state. In order to obtain elemental iron, the impurities must be removed by chemical reduction. Iron is the main component of steel, and it is used in the production of alloys or solid solutions of various metals, as well as some non-metals, particularly carbon. The many iron-carbon alloys, which have very different properties, are discussed in the article on steel.
Nuclei of iron have some of the highest binding energies per nucleon, surpassed only by the nickel isotope 62Ni. The universally most abundant of the highly stable nuclides is, however, 56Fe. This is formed by nuclear fusion in stars. Although a further tiny energy gain could be extracted by synthesizing 62Ni, conditions in stars are unsuitable for this process to be favoured, and iron abundance on Earth greatly favors iron over nickel, and also presumably in supernova element production.[citation needed] When a very large star contracts at the end of its life, internal pressure and temperature rise, allowing the star to produce progressively heavier elements, despite these being less stable than the elements around mass number 60, known as the "iron group". This leads to a supernova.
Iron (as Fe2+, ferrous ion) is a necessary trace element used by almost all living organisms, the only exceptions a few prokaryotic organisms which live in iron-poor conditions (such as the lactobacilli in iron-poor milk) which use manganese for catalysis, instead. Iron-containing enzymes, usually containing heme prosthetic groups, participate in catalysis of oxidation reactions in biology, and in transport of a number of soluble gases. See hemoglobin, cytochrome, and catalase.
Applications Iron is the most used of all the metals, comprising 95% of all the metal tonnage produced worldwide. Its combination of low cost and high strength make it indispensable, especially in applications like automobiles, the hulls of large ships, and structural components for buildings. Steel is the best known alloy of iron, and some of the forms that iron can take include:
Pig iron has 4% – 5% carbon and contains varying amounts of contaminants such as sulfur, silicon and phosphorus. Its only significance is that of an intermediate step on the way from iron ore to cast iron and steel. Cast iron contains 2% – 4.0% carbon , 1% – 6% silicon , and small amounts of manganese. Contaminants present in pig iron that negatively affect the material properties, such as sulfur and phosphorus, have been reduced to an acceptable level. It has a melting point in the range of 1420–1470 K, which is lower than either of its two main components, and makes it the first product to be melted when carbon and iron are heated together. Its mechanical properties vary greatly, dependent upon the form carbon takes in the alloy. 'White' cast irons contain their carbon in the form of cementite, or iron carbide. This hard, brittle compound dominates the mechanical properties of white cast irons, rendering them hard, but unresistant to shock. The broken surface of a white cast iron is full of fine facets of the broken carbide, a very pale, silvery, shiny material, hence the appellation. In grey iron the carbon exists free as fine flakes of graphite, and also renders the material brittle due to the stress-raising nature of the sharp edged flakes of graphite. A newer variant of grey iron, referred to as ductile iron is specially treated with trace amounts of magnesium to alter the shape of graphite to spheroids, or nodules, vastly increasing the toughness and strength of the material. Carbon steel contains between 0.4% and 1.5% carbon, with small amounts of manganese, sulfur, phosphorus, and silicon. Wrought iron contains less than 0.2% carbon. It is a tough, malleable product, not as fusible as pig iron. It has a very small amount of carbon, a few tenths of a percent. If honed to an edge, it loses it quickly. Wrought iron is characterised, especially in old samples, by the presence of fine 'stringers' or filaments of slag entrapped in the metal. Wrought iron does not rust particularly quickly when used outdoors. It has largely been replaced by mild steel for "wrought iron" gates and blacksmithing. Mild steel does not have the same corrosion resistance but is cheaper and more widely available. Alloy steels contain varying amounts of carbon as well as other metals, such as chromium, vanadium, molybdenum, nickel, tungsten, etc. They are used for structural purposes, as their alloy content raises their cost and necessitates justification of their use. Recent developments in ferrous metallurgy have produced a growing range of microalloyed steels, also termed 'HSLA' or high-strength, low alloy steels, containing tiny additions to produce high strengths and often spectacular toughness at minimal cost. Iron(III) oxides are used in the production of magnetic storage media in computers. They are often mixed with other compounds, and retain their magnetic properties in solution. The main drawback to iron and steel is that pure iron, and most of its alloys, suffer badly from rust if not protected in some way. Painting, galvanization, plastic coating and bluing are some techniques used to protect iron from rust by excluding water and oxygen or by sacrificial protection.
Iron is believed to be the critical missing nutrient in the ocean that limits the growth of plankton. Experimental iron fertilization of areas of the ocean using iron(II) sulfate has proven successful in increasing plankton growth[1][2][3]. Larger scaled efforts are being attempted with the hope that iron seeding and ocean plankton growth can remove carbon dioxide from the atmosphere, thereby counteracting the greenhouse effect that is generally agreed by climatologists to cause global warming[4].
Iron compounds See also iron compounds.
Iron chloride hexahydrateIron(III) acetate (Fe(C2H3O2)3 is used in the dyeing of cloth. Iron(III) ammonium oxalate (Fe(NH4)3(C2O4)4) is used in blueprints. Iron(III) arsenate (FeAsO4) is used in insecticide. Iron(III) chloride (FeCl3) is used: in water purification and sewage treatment, in the dyeing of cloth, as a coloring agent in paints, as an additive in animal feed, and as an etching material for engravement, photography and printed circuits. Iron(III) chromate (Fe2(CrO4)3) is used as a yellow pigment for paints and ceramic. Iron(III) hydroxide (Fe(OH)3) is used as a brown pigment for rubber and in water purification systems. Iron(III) phosphate (FePO4) is used in fertilizer and as an additive and human and animal food. Iron(II) acetate (Fe(C2H3O2)2 is used in the dyeing of fabrics and leather, and as a wood preservative. Iron(II) gluconate (Fe(C6H11O7)2) is used as a dietary supplement in iron pills. Iron(II) oxalate (FeC2O4) is used as yellow pigment for paints, plastics, glass and ceramic, and in photography. Iron(II) sulfate (FeSO4) is used in water purification and sewage treatment systems, as a catalyst in the production of ammonia, as an ingredient in fertilizer and herbicide, as an additive in animal feed, in wood preservative and as an additive to flour to increase iron levels. Iron-Fluorine complex (FeF6)3- is found in solutions containing both Fe(III) ions and fluoride ions.
History Main article: History of ferrous metallurgy
The puddling process of smelting iron ore to make pig iron from wrought iron, with the right illustration displaying men working a blast furnace, from the Tiangong Kaiwu encyclopedia, published 1637 by Song Yingxing.The first iron used by mankind, far back in prehistory, came from meteors. The smelting of iron in bloomeries probably began in Anatolia or the Caucasus in the second millennium BC or the latter part of the preceding one. Cast iron was first produced in China about 550 BC, but not in Europe until the medieval period. During the medieval period, means were found in Europe of producing wrought iron from cast iron (in this context known as pig iron) using finery forges. For all these processes, charcoal was required as fuel.
Steel (with a smaller carbon content than pig iron but more than wrought iron) was first produced in antiquity. New methods of producing it by carburizing bars of iron in the cementation process were devised in the 17th century AD. In the Industrial Revolution, new methods of producing bar iron without charcoal were devised and these were later applied to produce steel. In the late 1850s, Henry Bessemer invented a new steelmaking process, involving blowing air through molten pig iron, to produce mild steel. This and other 19th century and later processes have led to wrought iron no longer being produced.
Occurrence
The red appearance of this water is due to iron in the rocks.Iron is one of the most common elements on Earth, making up about 5% of the Earth's crust. Most of this iron is found in various iron oxides, such as the minerals hematite, magnetite, and taconite. The earth's core is believed to consist largely of a metallic iron-nickel alloy. About 5% of the meteorites similarly consist of iron-nickel alloy. Although rare, these are the major form of natural metallic iron on the earth's surface.
The reason for Mars's red colour is thought to be an iron-oxide-rich soil.
See also Iron minerals.
Production of iron from iron ore Main article: Blast furnace
How Iron was extracted in the 19th century Iron output in 2005 This heap of iron ore pellets will be used in steel production.Industrially, iron is produced starting from iron ores, principally haematite (nominally Fe2O3) and magnetite (Fe3O4) by a carbothermic reaction (reduction with carbon) in a blast furnace at temperatures of about 2000 °C. In a blast furnace, iron ore, carbon in the form of coke, and a flux such as limestone (which is used to remove impurities in the ore which would otherwise clog the furnace with solid material) are fed into the top of the furnace, while a blast of heated air is forced into the furnace at the bottom.
In the furnace, the coke reacts with oxygen in the air blast to produce carbon monoxide:
6 C + 3 O2 ? 6 CO The carbon monoxide reduces the iron ore (in the chemical equation below, hematite) to molten iron, becoming carbon dioxide in the process:
6 CO + 2 Fe2O3 ? 4 Fe + 6 CO2 The flux is present to melt impurities in the ore, principally silicon dioxide sand and other silicates. Common fluxes include limestone (principally calcium carbonate) and dolomite (calcium-magnesium carbonate). Other fluxes may be used depending on the impurities that need to be removed from the ore. In the heat of the furnace the limestone flux decomposes to calcium oxide (quicklime):
CaCO3 ? CaO + CO2 Then calcium oxide combines with silicon dioxide to form a slag.
CaO + SiO2 ? CaSiO3 The slag melts in the heat of the furnace, which silicon dioxide would not have. In the bottom of the furnace, the molten slag floats on top of the more dense molten iron, and apertures in the side of the furnace are opened to run off the iron and the slag separately. The iron once cooled, is called pig iron, while the slag can be used as a material in road construction or to improve mineral-poor soils for agriculture.
Pig iron is not pure iron, but has 4-5% carbon dissolved in it. This is subsequently reduced to steel or commercially pure iron, known as wrought iron, using other furnaces or converters.
In 2005, approximately 1,544Mt (million tons) of iron ore was produced worldwide. China was the top producer of iron ore with atleast one-fourth world share followed by Brazil, Australia and India, reports the British Geological Survey.
Isotopes Naturally occurring iron consists of four isotopes: 5.845% of radioactive 54Fe (half-life: >3.1×1022 years), 91.754% of stable 56Fe, 2.119% of stable 57Fe and 0.282% of stable 58Fe. 60Fe is an extinct radionuclide of long half-life (1.5 million years).
Much of the past work on measuring the isotopic composition of Fe has centered on determining 60Fe variations due to processes accompanying nucleosynthesis (i.e., meteorite studies) and ore formation. In the last decade however, advances in mass spectrometry technology have allowed the detection and quantification of minute, naturally-occurring variations in the ratios of the stable isotopes of iron. Much of this work has been driven by the Earth and planetary science communities, although applications to biological and industrial systems are beginning to emerge.[5]
The isotope 56Fe is of particular interest to nuclear scientists. A common misconception is that this isotope represents the most stable nucleus possible, and that it thus would be impossible to perform fission or fusion on 56Fe and still liberate energy. This is not true, as both 62Ni and 58Fe are more stable, being the most stable nuclei. However, since 56Fe is much more easily produced from lighter nuclei in nuclear reactions, it is the endpoint of fusion chains inside extremely massive stars and is therefore common in the universe, relative to other metals.
In phases of the meteorites Semarkona and Chervony Kut a correlation between the concentration of 60Ni, the daughter product of 60Fe, and the abundance of the stable iron isotopes could be found which is evidence for the existence of 60Fe at the time of formation of the solar system. Possibly the energy released by the decay of 60Fe contributed, together with the energy released by decay of the radionuclide 26Al, to the remelting and differentiation of asteroids after their formation 4.6 billion years ago. The abundance of 60Ni present in extraterrestrial material may also provide further insight into the origin of the solar system and its early history. Of the stable isotopes, only 57Fe has a nuclear spin (-1/2).
Iron in organic synthesis The usage of iron metal filings in organic synthesis is mainly for the reduction of nitro compounds.[6] Additionally, iron has been used for desulfurizations[7], reduction of aldehydes[8], and the deoxygenation of amine oxides[9].
Iron in biology
Structure of Heme bMain article: human iron metabolism Iron is essential to nearly all known organisms. In cells, iron is generally stored in the centre of metalloproteins, because "free" iron -- which binds non-specifically to many cellular components -- can catalyse production of toxic free radicals.
In animals, plants, and fungi, iron is often incorporated into the heme complex. Heme is an essential component of cytochrome proteins, which mediate redox reactions, and of oxygen carrier proteins such as hemoglobin, myoglobin, and leghemoglobin. Inorganic iron also contributes to redox reactions in the iron-sulfur clusters of many enzymes, such as nitrogenase (involved in the synthesis of ammonia from nitrogen and hydrogen) and hydrogenase. Non-heme iron proteins include the enzymes methane monooxygenase (oxidizes methane to methanol), ribonucleotide reductase (reduces ribose to deoxyribose; DNA biosynthesis), hemerythrins (oxygen transport and fixation in marine invertebrates) and purple acid phosphatase (hydrolysis of phosphate esters).
Iron distribution is heavily regulated in mammals, partly because iron has a high potential for biological toxicity. Iron distribution is also regulated because many bacteria require iron, so restricting its availability to bacteria (generally by sequestering it inside cells) can help to prevent or limit infections. This is probably the reason for the relatively low amounts of iron in mammalian milk. A major component of this regulation is the protein transferrin, which binds iron absorbed from the duodenum and carries it in the blood to cells.[10]
Nutrition and dietary sources Good sources of dietary iron include red meat, fish, poultry, lentils, beans, leaf vegetables, tofu, chickpeas, black-eyed peas, potatoes with skin, bread made from completely whole-grain flour, molasses, teff and farina. Iron in meat is more easily absorbed than iron in vegetables.[11]
Iron provided by dietary supplements is often found as iron (II) fumarate, although iron sulfate is cheaper and is absorbed equally well. Elemental iron, despite being absorbed to a much smaller extent (stomach acid is sufficient to convert some of it to ferrous iron), is often added to foods such as breakfast cereals or "enriched" wheat flour (where it is listed as "reduced iron" in the list of ingredients). Iron is most available to the body when chelated to amino acids - iron in this form is ten to fifteen times more bioavailable than any other, and is also available for use as a common iron supplement. Often the amino acid chosen for this purpose is the cheapest and most common amino acid, glycine, leading to "iron glycinate" supplements.[12] The RDA for iron varies considerably based on age, gender, and source of dietary iron (heme-based iron has higher bioavailability)[13]. Infants will require iron supplements if they are not breast-fed. Blood donors are at special risk of low iron levels and are often advised to supplement their iron intake.
Regulation of iron uptake Excessive iron can be toxic, because free ferrous iron reacts with peroxides to produce free radicals, which are highly reactive and can damage DNA, proteins, lipids, and other cellular components. Thus, iron toxicity occurs when there is free iron in the cell, which generally occurs when iron levels exceed the capacity of transferrin to bind the iron.
Iron uptake is tightly regulated by the human body, which has no physiological means of excreting iron, so controls iron levels solely by regulating uptake. Although uptake is regulated, large amounts of ingested iron can cause excessive levels of iron in the blood, because high iron levels can cause damage to the cells of the gastrointestinal tract that prevents them from regulating iron absorption. High blood concentrations of iron damage cells in the heart, liver and elsewhere, which can cause serious problems, including long-term organ damage and even death.
Humans experience iron toxicity above 20 milligrams of iron for every kilogram of mass, and 60 milligrams per kilogram is a lethal dose.[14] Over-consumption of iron, often the result of children eating large quantities of ferrous sulfate tablets intended for adult consumption, is one of the most common toxicological cause of death in children under six[14]. The DRI lists the Tolerable Upper Intake Level (UL) for adults as 45 mg/day. For children under fourteen years old the UL is 40 mg/day.
Regulation of iron uptake is impaired in some people as a result of a genetic defect that maps to the HLA-H gene region on chromosome 6. In these people, excessive iron intake can result in iron overload disorders, such as hemochromatosis. Many people have a genetic susceptibility to iron overload without realizing it or being aware of a family history of the problem. For this reason, it is advised that people should not take iron supplements unless they suffer from iron deficiency and have consulted a doctor. Hemochromatosis is estimated to cause disease in between 0.3 and 0.8% of Caucasians.
The medical management of iron toxicity is complex, and can include use of a specific chelating agent called deferoxamine to bind and expel excess iron from the body.
Bibliography
Los Alamos National Laboratory — Iron H. R. Schubert, History of the British Iron and Steel Industry ... to 1775 AD (Routledge, London, 1957) R. F. Tylecote, History of Metallurgy (Institute of Materials, London 1992). R. F. Tylecote, 'Iron in the Industrial Revolution' in J. Day and R. F. Tylecote, The Industrial Revolution in Metals (Institute of Materials 1991), 200-60. http://www.webelements.com/webelements/elements/text/Fe/xtal.html
http://en.wikipedia.org/wiki/Iron
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Types of steel
The various steels are alloys in which iron is mixed with carbon and other elements. Steels are described as mild, medium- or high-carbon steels according to the percentage of carbon they contain, which is never greater than about 1.5%.
Type of steel
Mild steel - Up to 0.25% carbon Medium carbon steel - 0.25% to 0.45% carbon High carbon steel - 0.45% to 1.50% carbon
Adding metals such as nickel, chromium, and tungsten to iron produces a wide range of alloy steels, including stainless steel and high speed steels.
Stainless Steel
Stainless steel is defined as a ferrous alloy with a minimum of 10.5% chromium content. Stainless steel does not stain, corrode or rust as easily as ordinary steel. There are different accessible grades and surface finishes of stainless steel, to suit the environment to which the material will be used. Common uses of stainless steel are the everyday cutlery and watch straps.
Heat Treatment
Heat treatment is given to steel to control its properties. Cooling a red-hot tool steel rapidly in cold water makes it harder and more brittle. The same piece can be made softer by heating it red hot for an extended period and then cooling it slowly.
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