Diesel multiple unit
A diesel multiple unit or DMU is a multiple-unit train powered by on-board diesel engines. A DMU requires no separate locomotive, as the engines are incorporated into one or more of the carriages. Diesel-powered single-unit railcars are generally classed as DMUs. Diesel-powered units may be further classified by their transmission type: diesel–electric, diesel–mechanical or diesel–hydraulic; the diesel engine may be located under the floor. Driving controls can be on one end, or in a separate car. DMUs are classified by the method of transmitting motive power to their wheels. In a diesel–mechanical multiple unit, the rotating energy of the engine is transmitted via a gearbox and driveshaft directly to the wheels of the train, like a car; the transmissions can be shifted manually by the driver, as in the great majority of first-generation British Rail DMUs, but in most applications, gears are changed automatically. In a diesel–hydraulic multiple unit, a hydraulic torque converter, a type of fluid coupling, acts as the transmission medium for the motive power of the diesel engine to turn the wheels.
Some units feature a hybrid mix of hydraulic and mechanical transmissions reverting to the latter at higher operating speeds as this decreases engine RPM and noise. In a diesel–electric multiple unit, a diesel engine drives an electrical generator or an alternator which produces electrical energy; the generated current is fed to electric traction motors on the wheels or bogies in the same way as a conventional diesel–electric locomotive. In modern DEMUs, such as the Bombardier Voyager family, each car is self-contained and has its own engine and electric motors. In older designs, such as the British Rail Class 207, some cars within the consist may be unpowered or only feature electric motors, obtaining electric current from other cars in the consist which have a generator and engine. A train composed of DMU cars scales well, as it allows extra passenger capacity to be added at the same time as motive power, it permits passenger capacity to be matched to demand, for trains to be split and joined en route.
It is not necessary to match the power available to the size and weight of the train, as each unit is capable of moving itself. As units are added, the power available to move the train increases by the necessary amount. DMUs may have better acceleration capabilities, with more power-driven axles, making them more suitable for routes with frequent spaced stops, as compared with conventional locomotive and unpowered carriage setups. Distribution of the propulsion among the cars results in a system, less vulnerable to single-point-of-failure outages. Many classes of DMU are capable of operating with faulty units still in the consist; because of the self-contained nature of diesel engines, there is no need to run overhead electric lines or electrified track, which can result in lower system construction costs. Such advantages must be weighed against the underfloor noise and vibration that may be an issue with this type of train. Diesel traction has several downsides compared to electric traction, namely higher fuel costs, more noise and exhaust as well as worse acceleration and top speed performance.
The power to weight ratio tends to be worse. DMUs have further disadvantages compared to diesel locomotives in that they cannot be swapped out when passing onto an electrified line, necessitating either passengers to change trains or Diesel operation on electrified lines; the lost investment once electrification reduces the demand for diesel rolling stock is higher than with locomotive hauled trains where only the locomotive has to be replaced. Diesel multiple units are in constant use in Croatia, operated by national operator Croatian Railways. On Croatian Railways, DMUs have important role since they cover local and distant lines across the country. Two largest towns in Croatia and Split, are daily connected with DMU tilting trains "RegioSwinger" that provide Inter City service between those two towns since 2004. In the early 1990s, luxury DMU series 7021 provided some of higher ranked lines across the country. DMU series HŽ series 7121, 7122 and Croatian-built series 7022 and 7023 are nowadays in high use covering country's local and regional services in country's interior on the tracks that are not electrified.
In the Republic of Ireland the Córas Iompair Éireann, which controlled the republic's railways between 1945 and 1986, introduced DMUs in the mid-1950s and they were the first diesel trains on many main lines. The first significant use of DMUs in the United Kingdom was by the Great Western Railway, which introduced its small but successful series of diesel–mechanical GWR railcars in 1934; the London and North Eastern Railway and London and Scottish Railway experimented with DMUs in the 1930s, the LMS both on its own system, on that of its Northern Irish subsidiary, but development was curtailed by World War II. After nationalisation, British Railways revived the concept in the early 1950s. At that time there was an urgent need to move away from expensive steam traction which led to many experimental designs using diesel propulsion and multiple units; the early DMUs proved successful, under BR's 1955 Modernisation Plan the building of a large fleet was authorised. These BR "First Generation" DMUs were built between 1956 and 1963.
BR required that contracts for the design and manufacture of new locomotives and rolling stock be split between n
History of rail transport in Great Britain 1948–1994
This article is part of a series on the History of rail transport in Great BritainThe history of rail transport in Great Britain 1948–1994 covers the period when the British railway system was nationalised under the name of British Rail, until its eventual privatisation in 1994. The railway system in this period underwent modernisation and rebranding, some of which proved controversial; the use of steam locomotives on the network ended in this period. Due to falling passenger numbers, rail subsidies from the government were necessary to keep the railways financially viable. Concerns about the levels of these contributed to the Beeching cuts which closed down many less well used lines; the Transport Act 1947 nationalised nearly all forms of mass transport in Great Britain and came into effect on 1 January 1948. British Railways came into existence as the business name of the Railway Executive of the British Transport Commission on 1 January 1948 when it took over the assets of the Big Four railway companies.
A small number of independent light railways and industrial railways, which did not contribute significant mileage to the system, were not included in British Railways. The Northern Counties Committee lines owned by the London, Midland & Scottish Railway were sold to the Northern Ireland government, becoming part of the Ulster Transport Authority as a result of the Ireland Act 1949. Under the BTC's Railway Executive, the railways were organised into six regions: Eastern Region – LNER lines south of Shaftholme Junction, Doncaster North Eastern Region – LNER lines in England north of Shaftholme Junction London Midland Region – LMS lines in England and Wales. Scottish Region – LMS and LNER lines in Scotland Southern Region – Southern Railway lines Western Region – Great Western Railway linesThe first priority of the new British Railways Board was to repair the infrastructure of the railways damaged by bombing, clear the backlog of maintenance that had built up, make good losses in locomotives and rolling stock.
By the start of the 1950s, British Railways were making a working profit, albeit a small one. However, Britain had fallen well behind the rest of Europe in terms of dieselisation and electrification of its railways. There were political as well as practical reasons behind the resistance to dieselisation in particular: the Labour Government of Clement Attlee did not want to reduce the demand for domestically-produced coal in favour of imported oil, thus both affecting the balance of payments and causing unemployment. Robin Riddles, the British Railways' Chief Mechanical Engineer, disagreed with the dieselisation programme, arguing that it would be too expensive to import oil given the large amounts of domestically available coal, he continued to order steam locomotives on a large scale and from 1948 to 1953, 1,487 steam locomotives were built. Although the initial focus was on repairing and renewing, some pre-war capital investment schemes that had stopped upon the outbreak of hostilities were restarted, for example the Manchester–Sheffield–Wath electrification over the Woodhead route and the Great Eastern suburban electrification.
The new BR regions, formed around the management structures of the old "Big Four" companies, remained autonomous in terms both of organisation and production of locomotives and rolling stock continuing with pre-war designs - indeed, some designs were older: the workhorse LNER Class J17 was designed in 1898. As a whole, the equipment of the new British Railways was outdated unreliable, in urgent need of a refurbishment. Only the Southern Region with its large electrified suburban network in South London inherited from the Southern Railway operated a significant number of non-steam-powered trains. In 1951, the British Transport Commission approved a new series of standard locomotives and coaches incorporating design features from the London, Midland & Scottish Railway but the other pre-nationalisation companies; these standard designs were designed to be long-lasting but in the event few served to their full potential before being withdrawn during the 1960s. By the middle of the decade, however, it was clear that British Railways were in trouble in the freight haulage business to which they were losing ground to road and air traffic.
The government ordered a review. The report formally known as Modernisation and Re-Equipment of the British Railways, more the "Modernisation Plan", was published in December 1954, it was intended to bring the railway system up to date. A government White Paper produced in 1956 stated that modernisation would help eliminate BR's financial deficit by 1962; the aim was to increase speed, reliability and line capacity, through a series of measures which would make services more attractive to passengers and freight operators, thus recovering traffic, being lost to the roads. The important areas were: Electrification of principal main lines, in the Eastern Region, Kent and Central Scotland; however most railway historians
Bristol is a city and county in South West England with a population of 459,300. The wider district has the 10th-largest population in England; the urban area population of 724,000 is the 8th-largest in the UK. The city borders North Somerset and South Gloucestershire, with the cities of Bath and Gloucester to the south-east and north-east, respectively. South Wales lies across the Severn estuary. Iron Age hill forts and Roman villas were built near the confluence of the rivers Frome and Avon, around the beginning of the 11th century the settlement was known as Brycgstow. Bristol received a royal charter in 1155 and was divided between Gloucestershire and Somerset until 1373, when it became a county of itself. From the 13th to the 18th century, Bristol was among the top three English cities after London in tax receipts. Bristol was surpassed by the rapid rise of Birmingham and Liverpool in the Industrial Revolution. Bristol was a starting place for early voyages of exploration to the New World.
On a ship out of Bristol in 1497 John Cabot, a Venetian, became the first European since the Vikings to land on mainland North America. In 1499 William Weston, a Bristol merchant, was the first Englishman to lead an exploration to North America. At the height of the Bristol slave trade, from 1700 to 1807, more than 2,000 slave ships carried an estimated 500,000 people from Africa to slavery in the Americas; the Port of Bristol has since moved from Bristol Harbour in the city centre to the Severn Estuary at Avonmouth and Royal Portbury Dock. Bristol's modern economy is built on the creative media and aerospace industries, the city-centre docks have been redeveloped as centres of heritage and culture; the city has the largest circulating community currency in the UK—the Bristol pound, pegged to the Pound sterling. The city has two universities, the University of Bristol and the University of the West of England, a variety of artistic and sporting organisations and venues including the Royal West of England Academy, the Arnolfini, Spike Island, Ashton Gate and the Memorial Stadium.
It is connected to London and other major UK cities by road and rail, to the world by sea and air: road, by the M5 and M4. One of the UK's most popular tourist destinations, Bristol was selected in 2009 as one of the world's top ten cities by international travel publishers Dorling Kindersley in their Eyewitness series of travel guides; the Sunday Times named it as the best city in Britain in which to live in 2014 and 2017, Bristol won the EU's European Green Capital Award in 2015. The most ancient recorded name for Bristol is the archaic Welsh Caer Odor, consistent with modern understanding that early Bristol developed between the River Frome and Avon Gorge, it is most stated that the Saxon name Bricstow was a simple calque of the existing Celtic name, with Bric a literal translation of Odor, the common Saxon suffix Stow replacing Caer. Alternative etymologies are supported by numerous orthographic variations in medieval documents, with Samuel Seyer enumerating 47 alternative forms; the Old English form Brycgstow is used to derive the meaning place at the bridge.
Utilizing another form, Rev. Dr. Shaw derived the name from the Celtic words bras, or braos and tuile; the poet Thomas Chatterton popularised a derivation from Brictricstow linking the town to Brictric, a leading landholder in the area. It appears that the form Bricstow prevailed until 1204, the Bristolian'L' is what changed the name to Bristol. Archaeological finds, including flint tools believed to be between 300,000 and 126,000 years old made with the Levallois technique, indicate the presence of Neanderthals in the Shirehampton and St Annes areas of Bristol during the Middle Palaeolithic. Iron Age hill forts near the city are at Leigh Woods and Clifton Down, on the side of the Avon Gorge, on Kings Weston Hill near Henbury. A Roman settlement, existed at what is now Sea Mills. Isolated Roman villas and small forts and settlements were scattered throughout the area. Bristol was founded by 1000. By 1067 Brycgstow was a well-fortified burh, that year the townsmen beat off a raiding party from Ireland led by three of Harold Godwinson's sons.
Under Norman rule, the town had one of the strongest castles in southern England. Bristol was the place of exile for Diarmait Mac Murchada, the Irish king of Leinster, after being overthrown; the Bristol merchants subsequently played a prominent role in funding Richard Strongbow de Clare and the Norman invasion of Ireland. The port developed in the 11th century around the confluence of the Rivers Frome and Avon, adjacent to Bristol Bridge just outside the town walls. By the 12th century Bristol was an important port, handling much of England's trade with Ireland, including slaves. There was an important Jewish community in Bristol from the late 12th century through to the late 13th century when all Jews were expelled from England; the stone bridge built in 1247 was replaced by the current bridge during the 1760s. The town incorporated neighbouring suburbs and became a county in 1373, the first town in England to be given this status. During this period, Bristol became manufacturing centre. By the 14th centur
A railway brake is a type of brake used on the cars of railway trains to enable deceleration, control acceleration or to keep them immobile when parked. While the basic principle is familiar from road vehicle usage, operational features are more complex because of the need to control multiple linked carriages and to be effective on vehicles left without a prime mover. Clasp brakes are one type of brakes used on trains. In the earliest days of railways, braking technology was primitive; the first trains had brakes operative on the locomotive tender and on vehicles in the train, where "porters" or, in the United States brakemen, travelling for the purpose on those vehicles operated the brakes. Some railways fitted a special deep-noted brake whistle to locomotives to indicate to the porters the necessity to apply the brakes. All the brakes at this stage of development were applied by operation of a screw and linkage to brake blocks applied to wheel treads, these brakes could be used when vehicles were parked.
In the earliest times, the porters travelled in crude shelters outside the vehicles, but "assistant guards" who travelled inside passenger vehicles, who had access to a brake wheel at their posts, supplanted them. The braking effort achievable was limited and it was unreliable, as the application of brakes by guards depended upon their hearing and responding to a whistle for brakes. An early development was the application of a steam brake to locomotives, where boiler pressure could be applied to brake blocks on the locomotive wheels; as train speeds increased, it became essential to provide some more powerful braking system capable of instant application and release by the train operator, described as a continuous brake because it would be effective continuously along the length of the train. In the UK, the Abbots Ripton rail accident in January 1876 was aggravated by the long stopping distances of express trains without continuous brakes, which -it became clear- in adverse conditions could exceed those assumed when positioning signals.
This had become apparent from the trials on railway brakes carried out at Newark in the previous year, to assist a Royal Commission considering railway accidents. In the words of a contemporary railway official, these showed that under normal conditions it required a distance of 800 to 1200 yards to bring a train to rest when travelling at 45½ to 48½ mph, this being much below the ordinary travelling speed of the fastest express trains. Railway officials were not prepared for this result and the necessity for a great deal more brake power was at once admitted Trials conducted after Abbots Ripton reported the following However, there was no clear technical solution to the problem, because of the necessity of achieving a reasonably uniform rate of braking effort throughout a train, because of the necessity to add and remove vehicles from the train at frequent points on the journey.. The chief types of solution were: A spring system: James Newall, carriage builder to the Lancashire and Yorkshire Railway, in 1853 obtained a patent for a system whereby a rotating rod passing the length of the train was used to wind up the brake levers on each carriage against the force of conical springs carried in cylinders.
The rod, mounted on the carriage roofs in rubber journals, was fitted with universal joints and short sliding sections to allow for compression of the buffers. The brakes were controlled from one end of the train; the guard wound up the rod, to release the brakes. When the ratchet was released the springs applied the brakes. If the train divided, the brakes were not held off by the ratchet in the guard's compartment and the springs in each carriage forced the brakes onto the wheel. Excess play in the couplings limited the effectiveness of the device to about five carriages; this apparatus was sold to a few companies and the system received recommendation from the Board of Trade. The L&Y conducted a simultaneous trial with a similar system designed by another employee, Charles Fay, but little difference was found in their effectiveness. In Fay's version, patented in 1856, the rods passed beneath the carriages and the spring application, which offered the important "automatic" feature of Newall but could act too fiercely, was replaced by a worm and rack for each brake.
The chain brake, such as the Heberlein brake, in which a chain was connected continuously along the train. When pulled tight it activated a friction clutch that used the rotation of the wheels to tighten a brake system at that point. Hydraulic brakes; as with car brakes. These found some favor in the UK, but water was used as the hydraulic fluid and in the UK "Freezing possibilities told against the hydraulic brakes, though the Great Eastern Railway, which used them for a while, overcame this by the use of salt water" The simple vacuum system. An ejector on the locomotive created a vacuum in a continuous pipe along the train, allowing the external air pressure to operate brake cylinders on every vehicle; this system was cheap and effective, but it had the major weakness that it became inoperative if the train became divided or if the tra
British Railways, which from 1965 traded as British Rail, was the state-owned company that operated most of the overground rail transport in Great Britain between 1948 and 1997. It was formed from the nationalisation of the "Big Four" British railway companies and lasted until the gradual privatisation of British Rail, in stages between 1994 and 1997. A trading brand of the Railway Executive of the British Transport Commission, it became an independent statutory corporation in 1962 designated as the British Railways Board; the period of nationalisation saw sweeping changes in the national railway network. A process of dieselisation and electrification took place, by 1968 steam locomotion had been replaced by diesel and electric traction, except for the Vale of Rheidol Railway. Passengers replaced freight as the main source of business, one third of the network was closed by the Beeching Axe of the 1960s in an effort to reduce rail subsidies. On privatisation, responsibility for track and stations was transferred to Railtrack and that for trains to the train operating companies.
The British Rail "double arrow" logo is formed of two interlocked arrows showing the direction of travel on a double track railway and was nicknamed "the arrow of indecision". It is now employed as a generic symbol on street signs in Great Britain denoting railway stations, as part of the Rail Delivery Group's jointly-managed National Rail brand is still printed on railway tickets; the rail transport system in Great Britain developed during the 19th century. After the grouping of 1923 under the Railways Act 1921, there were four large railway companies, each dominating its own geographic area: the Great Western Railway, the London and Scottish Railway, the London and North Eastern Railway and the Southern Railway. During World War I the railways were under state control, which continued until 1921. Complete nationalisation had been considered, the Railways Act 1921 is sometimes considered as a precursor to that, but the concept was rejected. Nationalisation was subsequently carried out after World War II, under the Transport Act 1947.
This Act made provision for the nationalisation of the network, as part of a policy of nationalising public services by Clement Attlee's Labour Government. British Railways came into existence as the business name of the Railway Executive of the British Transport Commission on 1 January 1948 when it took over the assets of the Big Four. There were joint railways between the Big Four and a few light railways to consider. Excluded from nationalisation were industrial lines like the Oxfordshire Ironstone Railway; the London Underground – publicly owned since 1933 – was nationalised, becoming the London Transport Executive of the British Transport Commission. The Bicester Military Railway was run by the government; the electric Liverpool Overhead Railway was excluded from nationalisation. The Railway Executive was conscious that some lines on the network were unprofitable and hard to justify and a programme of closures began immediately after nationalisation. However, the general financial position of BR became poorer, until an operating loss was recorded in 1955.
The Executive itself had been abolished in 1953 by the Conservative government, control of BR transferred to the parent Commission. Other changes to the British Transport Commission at the same time included the return of road haulage to the private sector. British Railways was divided into regions which were based on the areas the former Big Four operated in. Notably, these included the former Great Central lines from the Eastern Region to the London Midland Region, the West of England Main Line from the Southern Region to Western Region Southern Region: former Southern Railway lines. Western Region: former Great Western Railway lines. London Midland Region: former London Midland and Scottish Railway lines in England and Wales. Eastern Region: former London and North Eastern Railway lines south of York. North Eastern Region: former London and North Eastern Railway lines in England north of York. Scottish Region: all lines, regardless of original company, in Scotland; the North Eastern Region was merged with the Eastern Region in 1967.
In 1982, the regions were abolished and replaced by "business sectors", a process known as sectorisation. The Anglia Region was created in late 1987, its first General Manager being John Edmonds, who began his appointment on 19 October 1987. Full separation from the Eastern Region – apart from engineering design needs – occurred on 29 April 1988, it handled the services from Fenchurch Street and Liverpool Street, its western boundary being Hertford East and Whittlesea. The report, latterly known as the "Modernisation Plan", was published in January 1955, it was intended to bring the railway system into the 20th century. A government White Paper produced in 1956 stated that modernisation would help eliminate BR's financial deficit by 1962, but the figures in both this and the original plan were produced for political reasons and not based on detailed analysis; the aim was to increase speed, reliability and line capacity through a series of measures that would make services more attractive to passengers and freight operators, thus recovering traffic lost to the roads.
Important areas included: Electrification of principal main lines, in the Eastern Region, Birmingham to Liverpool/Manchester and Central Scotland Large-scale dieselisation to replace steam locomotives New passenger and freight rolling stock R
A supercharger is an air compressor that increases the pressure or density of air supplied to an internal combustion engine. This gives each intake cycle of the engine more oxygen, letting it burn more fuel and do more work, thus increasing power. Power for the supercharger can be provided mechanically by means of a belt, shaft, or chain connected to the engine's crankshaft. Common usage restricts the term supercharger to mechanically driven units. In 1848 or 1849, G. Jones of Birmingham, England brought out a Roots-style compressor. In 1860, brothers Philander and Francis Marion Roots, founders of Roots Blower Company of Connersville, patented the design for an air mover for use in blast furnaces and other industrial applications; the world's first functional tested engine supercharger was made by Dugald Clerk, who used it for the first two-stroke engine in 1878. Gottlieb Daimler received a German patent for supercharging an internal combustion engine in 1885. Louis Renault patented a centrifugal supercharger in France in 1902.
An early supercharged race car was built by Lee Chadwick of Pottstown, Pennsylvania in 1908 which reached a speed of 100 mph. The world's first series-produced cars with superchargers were Mercedes 6/25/40 hp and Mercedes 10/40/65 hp. Both models had Roots superchargers, they were distinguished as "Kompressor" models, the origin of the Mercedes-Benz badging which continues today. On March 24, 1878 Heinrich Krigar of Germany obtained patent #4121, patenting the first screw-type compressor; that same year on August 16 he obtained patent #7116 after modifying and improving his original designs. His designs show a two-lobe rotor assembly with each rotor having the same shape as the other. Although the design resembled the Roots style compressor, the "screws" were shown with 180 degrees of twist along their length; the technology of the time was not sufficient to produce such a unit, Heinrich made no further progress with the screw compressor. Nearly half a century in 1935, Alf Lysholm, working for Ljungströms Ångturbin AB, patented a design with five female and four male rotors.
He patented the method for machining the compressor rotors. There are two main types of superchargers defined according to the method of gas transfer: positive displacement and dynamic compressors. Positive displacement blowers and compressors deliver an constant level of pressure increase at all engine speeds. Dynamic compressors do not deliver pressure at low speeds. Positive-displacement pumps deliver a nearly fixed volume of air per revolution at all speeds. Major types of positive-displacement pumps include: Roots Lysholm twin-screw Sliding vane Scroll-type supercharger known as the G-Lader Positive-displacement pumps are further divided into internal and external compression types. Roots superchargers, including high helix roots superchargers, produce compression externally. External compression refers to pumps that transfer air at ambient pressure. If an engine equipped with a supercharger that compresses externally is running under boost conditions, the pressure inside the supercharger remains at ambient pressure.
Roots superchargers tend to be mechanically efficient at moving air at low pressure differentials, whereas at high pressure rations, internal compression superchargers tend to be more mechanically efficient. All the other types have some degree of internal compression. Internal compression refers to the compression of air within the supercharger itself, which at or close to boost level, can be delivered smoothly to the engine with little or no back flow. Internal compression devices use a fixed internal compression ratio; when the boost pressure is equal to the compression pressure of the supercharger, the back flow is zero. If the boost pressure exceeds that compression pressure, back flow can still occur as in a roots blower; the internal compression ratio of this type of supercharger can be matched to the expected boost pressure in order to optimize mechanical efficiency. Positive-displacement superchargers are rated by their capacity per revolution. In the case of the Roots blower, the GMC rating pattern is typical.
The GMC types are rated according to how many two-stroke cylinders, the size of those cylinders, it is designed to scavenge. GMC has made 2–71, 3–71, 4–71, the famed 6–71 blowers. For example, a 6–71 blower is designed to scavenge six cylinders of 71 cubic inches each and would be used on a two-stroke diesel of 426 cubic inches, designated a 6–71. However, because 6–71 is the engine's designation, the actual displacement is less than the simple multiplication would suggest. A 6–71 pumps 339 cubic inches per revolution. Aftermarket derivatives continue the trend with 8–71 to current 16–71 blowers used in different motor sports. From this, one can see that a 6–71 is twice the size of a 3–71. GMC made 53 cu in series in 2–, 3–, 4–, 6–, 8–53 sizes, as well as a "V71" series for use on engines using a V configuration. Dynamic compressors rely on accelerating the air to high speed and t
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