Metallurgy

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Posted by pompos 03/24/2009 @ 14:07

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Metallurgy

Georg Agricola, author of De re metallica, an important early book on metal extraction

Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use. Metallurgy is commonly used in the craft of metalworking.

The earliest recorded metal employed by humans appears to be gold which can be found free or "native". Small amounts of natural gold have been found in Spanish caves used during the late Paleolithic period, c. 40,000 BC.

Silver, copper, tin and meteoric iron can also be found native, allowing a limited amount of metalworking in early cultures. Egyptian weapons made from meteoric iron in about 3000 B.C. were highly prized as "Daggers from Heaven". However, by learning to get copper and tin by heating rocks and combining copper and tin to make an alloy called bronze, the technology of metallurgy began about 3500 B.C. with the Bronze Age.

The extraction of iron from its ore into a workable metal is much more difficult. It appears to have been invented by the Hittites in about 1200 B.C., beginning the Iron Age. The secret of extracting and working iron was a key factor in the success of the Philistines.

Historical developments in ferrous metallurgy can be found in a wide variety of past cultures and civilizations. This includes the ancient and medieval kingdoms and empires of the Middle East and Near East, ancient Egypt and Anatolia (Turkey), Carthage, the Greeks and Romans of ancient Europe, medieval Europe, ancient and medieval China, ancient and medieval India, ancient and medieval Japan, etc. Of interest to note is that many applications, practices, and devices associated or involved in metallurgy were possibly established in ancient China before Europeans mastered these crafts (such as the innovation of the blast furnace, cast iron, steel, hydraulic-powered trip hammers, etc.). However, modern research suggests that Roman technology was far more sophisticated than hitherto supposed, especially in mining methods, metal extraction and forging. They were for example expert in hydraulic mining methods well before the Chinese, or any other civilization of the time.

Extractive metallurgy is the practice of removing valuable metals from an ore and refining the extracted raw metals into a purer form. In order to convert a metal oxide or sulfide to a purer metal, the ore must be reduced either physically, chemically, or electrolytically.

Extractive metallurgists are interested in three primary streams: feed, concentrate (valuable metal oxide/sulfide), and tailings (waste). After mining, large pieces of the ore feed are broken through crushing and/or grinding in order to obtain particles small enough where each particle is either mostly valuable or mostly waste. Concentrating the particles of value in a form supporting separation enables the desired metal to be removed from waste products.

Mining may not be necessary if the ore body and physical environment are conducive to leaching. Leaching dissolves minerals in an ore body and results in an enriched solution. The solution is collected and processed to extract valuable metals.

Ore bodies often contain more than one valuable metal. Tailings of a previous process may be used as a feed in another process to extract a secondary product from the original ore. Additionally, a concentrate may contain more than one valuable metal. That concentrate would then be processed to separate the valuable metals into individual constituents.

The properties of metals make them suitable for different uses in daily life.

Pure elemental metals are often too soft to be of practical use which is why much of metallurgy focuses on formulating useful alloys.

Common engineering metals include aluminium, chromium, copper, iron, magnesium, nickel, titanium and zinc. These are most often used as alloys. Much effort has been placed on understanding the iron-carbon alloy system, which includes steels and cast irons. Plain carbon steels are used in low cost, high strength applications where weight and corrosion are not a problem. Cast irons, including ductile iron are also part of the iron-carbon system.

Stainless steel or galvanized steel are used where resistance to corrosion is important. Aluminium alloys and magnesium alloys are used for applications where strength and lightness are required.

Cupro-nickel alloys such as Monel are used in highly corrosive environments and for non-magnetic applications. Nickel-based superalloys like Inconel are used in high temperature applications such as turbochargers, pressure vessels, and heat exchangers. For extremely high temperatures, single crystal alloys are used to minimize creep.

In production engineering, metallurgy is concerned with the production of metallic components for use in consumer or engineering products. This involves the production of alloys, the shaping, the heat treatment and the surface treatment of the product. The task of the metallurgist is to achieve balance between material properties such as cost, weight, strength, toughness, hardness, corrosion and fatigue resistance, and performance in temperature extremes. To achieve this goal, the operating environment must be carefully considered. In a saltwater environment, ferrous metals and some aluminium alloys corrode quickly. Metals exposed to cold or cryogenic conditions may endure a ductile to brittle transition and lose their toughness, becoming more brittle and prone to cracking. Metals under continual cyclic loading can suffer from metal fatigue. Metals under constant stress at elevated temperatures can creep.

Metals are shaped by processes such as casting, forging, flow forming, rolling, extrusion, sintering, metalworking, machining and fabrication. With casting, molten metal is poured into a shaped mould. With forging, a red-hot billet is hammered into shape. With rolling, a billet is passed through successively narrower rollers to create a sheet. With extrusion, a hot and malleable metal is forced under pressure through a die, which shapes it before it cools. With sintering, a powdered metal is compressed into a die at high temperature. With machining, lathes, milling machines, and drills cut the cold metal to shape. With fabrication, sheets of metal are cut with guillotines or gas cutters and bent into shape.

Various forms of casting exist in industry and academia. These include sand casting, investment casting (also called the “lost wax process”), die casting and continuous casting.

Welding is a technique for joining metal components cohesively by melting the base material, making the parts into a single piece. A filler material of similar composition (welding rod) may also be melted into the joint.

Brazing is a technique for joining metals adhesively at a temperature below their melting point. A filler with a melting point below that of the base metal is used, and is drawn into the joint by capillary action.Two part borex and one part boric acid is also used at the time of joining. Brazing results in a mechanical and metallurgical bond between work pieces.

Soldering is a method of joining metals below their melting points using a filler metal. Soldering, like brazing, results in an adhesive joint and occurs at lower temperatures than brazing, specifically below 450 C (840 F).

Metals can be heat treated to alter the properties of strength, ductility, toughness, hardness or resistance to corrosion. Common heat treatment processes include annealing, precipitation strengthening, quenching, and tempering. The annealing process softens the metal by allowing recovery of cold work and grain growth. Quenching can be used to harden alloy steels, or in precipitation hardenable alloys, to trap dissolved solute atoms in solution. Tempering will cause the dissolved alloying elements to precipitate, or in the case of quenched steels, improve impact strength and ductile properties.

Electroplating is a common surface-treatment technique. It involves bonding a thin layer of another metal such as gold, silver, chromium or zinc to the surface of the product. It is used to reduce corrosion as well as to improve the product's aesthetic appearance.

Thermal spraying techniques are another popular finishing option, and often have better high temperature properties than electroplated coatings.

Case hardening is a process in which an alloying element, most commonly carbon or nitrogen, diffuses into the surface of a monolithic metal. The resulting interstitial solid solution is harder than the base material, which improves wear resistance without sacrificing toughness.

Metallurgy is also applied to electrical and electronic materials where metals such as aluminium, copper, tin, silver, and gold are used in power lines, wires, printed circuit boards and integrated circuits.

Metallurgists study the microscopic and macroscopic properties using metallography, a technique invented by Henry Clifton Sorby. In metallography, an alloy of interest is ground flat and polished to a mirror finish. The sample can then be etched to reveal the microstructure and macrostructure of the metal. A metallurgist can then examine the sample with an optical or electron microscope and learn a great deal about the sample's composition, mechanical properties, and processing history.

Crystallography, often using diffraction of x-rays or electrons, is another valuable tool available to the modern metallurgist. Crystallography allow the identification of unknown materials and reveals the crystal structure of the sample. Quantitative crystallography can be used to calculate the amount of phases present as well as the degree of strain to which a sample has been subjected.

The physical properties of metals can be quantified by mechanical testing. Typical tests include tensile strength, compressive strength, hardness, impact toughness, fatigue and creep life.

For example: The dull appearance of the metal lead is due to a coating of lead oxide.

If the surface is scratched then the shiny lead metal can be seen underneath.

Schools such as University of Illinois, The Ohio State University and California Polytechnic State University College of Engineering offer a degree in Materials Sciences.

Schools such as Don Bosco Technical Institute have offered a degree in Metallurgy, though that has been phased out in favor of Materials Science.

From 1965 to 1971, the Boy Scouts of America offered a Metallurgy merit badge. From 1972 to 1995 they offered a Metals Engineering Merit Badge.

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History of ferrous metallurgy

Willamette Meteorite, the sixth largest in the world, is an iron-nickel meteorite

The history of ferrous metallurgy began far back in prehistory, most likely with the use of iron from meteorites. The smelting of iron in bloomeries began in the 12th century BC in India, Anatolia or the Caucasus. Iron use, in smelting and forging for tools, appeared in Sub-Saharan Africa by 1200 BC. The use of cast iron was known in the 1st millennium BC. 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.

Because meteorites fall from the sky, some linguists have conjectured that the English word iron (OE īsern), which has cognates in many northern and Western European languages, derives from the Etruscan aisar which means "the gods". Even if this is not the case, the word is likely a loan into pre-Proto-Germanic from Celtic or Italic. Krahe compares Old Irish, Illyrian, Venetic and Messapic forms). The meteoric origin of iron in its first use by humans is also alluded to in the Quran: "and We sent down Iron in which has incredible strength and many benefits for mankind".

Iron was in limited use long before it became possible to smelt it. The first signs of iron use come from Ancient Egypt and Sumer, where around 4000 BC small items, such as the tips of spears and ornaments, were being fashioned from iron recovered from meteorites. However, their use appears to be ceremonial, and iron was probably an expensive metal, perhaps more expensive than gold. About 6% of meteorites are composed of an iron-nickel alloy, and iron recovered from meteorite falls allowed ancient peoples to manufacture small numbers of iron artefacts.

In Anatolia, smelted iron was occasionally used for ornamental weapons: an iron-bladed dagger with a bronze hilt has been recovered from a Hattic tomb dating from 2500 BC. Also, the Egyptian ruler Tutankhamun died in 1323 BC and was buried with an iron dagger with a golden hilt. An Ancient Egyptian sword bearing the name of pharaoh Merneptah as well as a battle axe with an iron blade and gold-decorated bronze shaft were both found in the excavation of Ugarit (see Ugarit). The early Hittites are known to have bartered iron for silver, at a rate of 40 times the iron's weight, with Assyria.

Meteoric iron was also fashioned into tools in precontact North America. Beginning around the year 1000, the Thule people of Greenland began making harpoons and other edged tools from pieces of the Cape York meteorite. These artefacts were also used as trade goods with other Arctic peoples: tools made from the Cape York meteorite have been found in archaeological sites more than 1,000 miles (1,600 km) away. When the American polar explorer Robert Peary shipped the largest piece of the meteorite to the American Museum of Natural History in New York City in 1897, it still weighed over 33 tons.

About 1500 BC, increasing numbers of smelted iron objects (distinguishable from meteoric iron by the lack of nickel in the product) appear in Mesopotamia, Anatolia, and Egypt.

During the Early Iron Age (12th to 10th centuries BCE) iron came to replace bronze as the dominant metal used for tools and weapons across the Eastern Mediterranean (the Levant, Cyprus, Greece, Crete, Anatolia, and Egypt). Although iron objects are known from the Bronze Age across the Eastern Mediterranean, they occur only sporadically and are statistically insignificant compared to the quantity of bronze objects during this time.

The traditional explanation of the rise of iron was that the Hittites of Anatolia had mastered iron technology during the Late Bronze Age. They maintained a monopoly on ironworking, which allowed them to establish their empire based on iron's superiority over bronze. The invasions of the Sea Peoples at the end of the Late Bronze Age that brought an end to the Hittite empire broke up the monopoly, spreading the technological knowledge throughout the Eastern Mediterranean as a result of their migrations. This theory is no longer held in the mainstream of scholarship. One problem with it is that there is no archaeological evidence that the Hittites held a monopoly on iron during the Bronze Age. While there are some iron objects from Bronze Age Anatolia, the number is comparable to iron objects found in Egypt and other places of the same time period, and only a small number of these objects are weapons.

A more recent theory for the rise of iron has been that the collapse of the empires at the end of the Late Bronze Age disrupted the trade routes necessary for bronze production. Copper and, more importantly, tin were not widely available and needed to be transported over long distances. It is assumed that during the Early Iron Age this was not possible on a scale necessary to satisfy the needs of metalworkers. Since iron ore is more abundant naturally, metalworkers exploited this more universal metal. So, the rise of iron was the result of necessity due principally to the shortage of tin. The problem with this theory is that there is nothing archaeologically that would suggest a bronze or tin shortage in the Early Iron Age. Bronze objects are still abundant and these objects have the same percentage of tin as those from the Late Bronze Age.

Mesopotamia was fully into the Iron Age by 900 BC, central Europe by 800 BC. Egypt, on the other hand, did not experience such a rapid transition from the bronze to iron ages: although Egyptian smiths did produce iron artifacts, bronze remained in widespread use there until after Egypt's conquest by Assyria in 663 BC.

Concurrent with the transition from bronze to iron was the discovery of carburization, which was the process of adding carbon to the irons of the time. Iron was recovered as sponge iron, a mix of iron and slag with some carbon and/or carbide, which was then repeatedly hammered and folded over to free the mass of slag and oxidise out carbon content, so creating the product wrought iron. Wrought iron was very low in carbon content and was not easily hardened by quenching. The people of the Middle East found that a much harder product could be created by the long term heating of a wrought iron object in a bed of charcoal, which was then quenched in water or oil. The resulting product, which had a surface of steel, was harder and less brittle than the bronze it began to replace. Quench-hardening was also known by this time.

Iron smelting at this time was based on the bloomery, a furnace where bellows were used to force air through a pile of iron ore and burning charcoal. The carbon monoxide produced by the charcoal reduced the iron oxides to metallic iron, but the bloomery was not hot enough to melt the iron. Instead, the iron collected in the bottom of the furnace as a spongy mass, or bloom, whose pores were filled with ash and slag. The bloom then had to be reheated to soften the iron and melt the slag, and then repeatedly beaten and folded to force the molten slag out of it. The result of this time-consuming and laborious process was wrought iron, a malleable but fairly soft alloy containing little carbon.

The Delhi iron pillar is an example of the iron extraction and processing methodologies of India. The iron pillar at Delhi has withstood corrosion for the last 1600 years.

Archaeological sites in India, such as Malhar, Dadupur, Raja Nala Ka Tila and Lahuradewa in present day Uttar Pradesh show iron implements in the period between 1800 BC - 1200 BC. Early iron objects found in India can be dated to 1400 BC by employing the method of radio carbon dating. Spikes, knives, daggers, arrow-heads, bowls, spoons, saucepans, axes, chisels, tongs, door fittings etc. ranging from 600 BC to 200 BC have been discovered from several archaeological sites of India. Some scholars believe that by the early 13th century BC, iron smelting was practiced on a bigger scale in India, suggesting that the date the technology's inception may be placed earlier. In Southern India (present day Mysore) iron appeared as early as 11th to 12th centuries BC; these developments were too early for any significant close contact with the northwest of the country.

The beginning of the 1st millennium BC saw extensive developments in iron metallurgy in India. Technological advancement and mastery of iron metallurgy was achieved during this period of peaceful settlements. The coming years saw several advancements being made to the technology involved in metallurgy during the politically stable Maurya period.

Greek historian Herodotus wrote the first western account of the use of iron in India. The Indian mythological texts, the Upnishads, have mentions of weaving, pottery, and metallurgy as well.

Dagger and its scabbard, India, 17th–18th century. Blade: Damascus steel inlaid with gold; hilt: jade; scabbard: steel with engraved, chased and gilded decoration.

Perhaps as early as 300 BC, although certainly by AD 200, high quality steel was being produced in southern India also by what Europeans would later call the crucible technique. In this system, high-purity wrought iron, charcoal, and glass were mixed in a crucible and heated until the iron melted and absorbed the carbon. Iron chain was used in Indian suspension bridges as early as the 4th century.

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. 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.

The iron pillar of Delhi, the capital city of India, is one of the world's foremost metallurgical curiosities, standing in the famous Qutb complex. The pillar—almost seven meters high and weighing more than six tonnes—was erected by Chandragupta II Vikramaditya. The pillar is made up of 98% wrought iron of pure quality, and is a testament to the high level of skill achieved by ancient Indian iron smiths in the extraction and processing of iron. It has attracted the attention of archaeologists and metallurgists as it has withstood corrosion for the last 1,600 years, despite harsh weather.

Historians of metallurgy hold that Indian iron smelters had acquired an advanced and precise knowledge about the production of iron and steel, and the related details including the thermo-mechanical aspects and heat treatment. The Indians developed wootz, which was popular in international markets. The Dutch carried wootz from South India to Europe, where it subsequently spread through mass production.

Radio-carbon dating evidence shows that Sri Lankans were producing steel since 300 BC. archaeometallurgists believed that the high temperatures required for the process could only be generated through bellows-driven furnaces, the ancient Sinhalese however used a previously unknown and an advanced technique which didnt use bellows driven furnaces but the design of the furnaces were such that it utilized the winds were driven through the furnace.

The furnaces consists of long trenches which are dug into the crests of hills, these were made of clay and the air vents were positioned at the front. This allowed the wind to be diverted to the furnace thus creating a high pressure zone in front and a low pressure zone above the furnace bed. The differential of these pressures drew air into the furnace through the vents. Computer simulations done by scientists show that the design would easily provide the furnaces with enough winds to generate enough heat and the iron which is made in these furnaces would be of better qulaity than the bellow driven furnaces. Steel made in Sri Lanka were traded extensively within the region and in the Islamic world.

Axe made of iron, dating from Swedish Iron Age, found at Gotland, Sweden.

Ironworking is first introduced to Central Europe in Hallstatt C (8th century BC). Throughout the 7th to 6th centuries, iron artefacts remain luxury items reserved for an elite. This changes dramatically shortly after 500 BC with the rise of the La Tène culture, from which time iron metallurgy also becomes common in Northern Europe and Britain. The spread of ironworking in Central and Western Europe is associated with Celtic expansion. By the 1st century BC, Noric steel was famous for its quality and sought-after by the Roman military.

Western historians debate whether bloomery-based ironworking ever spread to China from the Middle East. Around 500 BC, however, metalworkers in the southern state of Wu developed an iron smelting technology that would not be practiced in Europe until late medieval times. In Wu, iron smelters achieved a temperature of 1130°C, hot enough to be considered a blast furnace which could create cast iron. At this temperature, iron combines with 4.3% carbon and melts. As a liquid, iron can be cast into molds, a method far less laborious than individually forging each piece of iron from a bloom.

Cast iron is rather brittle and unsuitable for striking implements. It can, however, be decarburized to steel or wrought iron by heating it in air for several days. In China, these ironworking methods spread northward, and by 300 BC, iron was the material of choice throughout China for most tools and weapons. A mass grave in Hebei province, dated to the early third century BC, contains several soldiers buried with their weapons and other equipment. The artifacts recovered from this grave are variously made of wrought iron, cast iron, malleabilized cast iron, and quench-hardened steel, with only a few, probably ornamental, bronze weapons.

During the Han Dynasty (202 BC–AD 220), the government established ironworking as a state monopoly (yet repealed during the latter half of the dynasty, returned to private entrepreneurship) and built a series of large blast furnaces in Henan province, each capable of producing several tons of iron per day. By this time, Chinese metallurgists had discovered how to puddle molten pig iron, stirring it in the open air until it lost its carbon and became wrought iron. (In Chinese, the process was called chao, literally, stir frying.) By the 1st century BC, Chinese metallurgists had found that wrought iron and cast iron could be melted together to yield an alloy of intermediate carbon content, that is, steel. According to legend, the sword of Liu Bang, the first Han emperor, was made in this fashion. Some texts of the era mention "harmonizing the hard and the soft" in the context of ironworking; the phrase may refer to this process. Also, the ancient city of Wan (Nanyang) from the Han period forward was a major center of the iron and steel industry. 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. The Chinese during the ancient Han Dynasty were also the first to apply hydraulic power (ie. a waterwheel) in working the inflatable bellows of the blast furnace. This was recorded in the year 31 AD, an innovation of the engineer Du Shi, Prefect of Nanyang. Although Du Shi was the first to apply water power to bellows in metallurgy, the first drawn and printed illustration of its operation with water power came in 1313 AD, in the Yuan Dynasty era text called the Nong Shu. In the 11th century, there is evidence of the production of steel in Song China using two techniques: a "berganesque" method that produced inferior, heterogeneous steel and a precursor to the modern Bessemer process that utilized partial decarbonization via repeated forging under a cold blast. By the 11th century, there was also a large amount of deforestation in China due to the iron industry's demands for charcoal. However, by this time the Chinese had figured out how to use bituminous coke to replace the use of charcoal, and with this switch in resources many acres of prime timberland in China were spared. This switch in resources from charcoal to coal was later used in Europe by the 17th century.

During the Islamic Golden Age and Muslim Agricultural Revolution, Muslim chemists, inventors and engineers were making significant advances in metallurgy.

Muslim engineers invented the first stamp mills and steel mills. By the 11th century, every province throughout the Islamic world had these industrial mills in operation, from al-Andalus and North Africa to the Middle East and Central Asia. The first geared gristmills were invented by Muslim engineers for many industrial uses such as crushing metallic ores before extraction. In order to adapt water wheels for gristmilling purposes, cams were used for raising and releasing trip hammers to fall on a material. The first wind-powered gristmills driven by windmills were built in what are now Afghanistan, Pakistan and Iran in the 9th and 10th centuries. The first forge to be driven by a hydropowered watermill rather than manual labour, also known as a finery forge, was invented in 12th century Islamic Spain. The first factory milling installations were also built by Muslim engineers throughout every city and urban community in the Islamic world, particularly Baghdad, since the 10th century. The first large milling installations in Europe were built in 12th century Islamic Spain.

One of the most famous steels produced in the medieval Near East was Damascus steel used for swordmaking, and mostly produced in Damascus, Syria, in the period from 900 to 1750. This was produced using the crucible steel method, based on the earlier Indian wootz steel. This process was further refined in the Middle East using locally produced steels. The exact process remains unknown, but allowed carbides to precipitate out as micro particles arranged in sheets or bands within the body of a blade. The carbides are far harder than the surrounding low carbon steel, allowing the swordsmith to make an edge which would cut hard materials with the precipitated carbides, while the bands of softer steel allowed the sword as a whole to remain tough and flexible. A team of researchers based at the Technical University of Dresden that uses x-rays and electron microscopy to examine Damascus steel discovered the presence of cementite nanowires and carbon nanotubes. Peter Paufler, a member of the Dresden team, says that these nanostructures give Damascus steel its distinctive properties and are a result of the forging process.

Inhabitants at Termit, in eastern Niger became the first iron smelting people in West Africa and among the first in the world around 1500 BC. Iron and copper working then continued to spread southward through the continent, reaching the Cape around AD 200. The widespread use of iron revolutionized the Bantu-speaking farming communities who adopted it, driving out and absorbing the rock tool using hunter-gatherer societies they encountered as they expanded to farm wider areas of savannah. The technologically superior Bantu-speakers spread across southern Africa and became wealthy and powerful, producing iron for tools and weapons in large, industrial quantities.

There was no fundamental change in the technology of iron production in Europe for many centuries. Iron continued to be made in bloomeries. However there were two separate developments in the Medieval period. One was the application of water power to the bloomery process in various places (as outlined above). The other was the first European production in cast iron.

Sometime in the medieval period, water power was applied to the bloomery process. It is possible that this was at the Cistercian Abbey of Clairvaux as early as 1135, but it was certainly in use in France by the early 13th century there and in Sweden. In England, the first clear documentary evidence for this is the accounts of a forge of the Bishop of Durham, near Bedburn in 1408, but that was certainly not the first such ironworks. In the Furness district of England, powered bloomeries were in use into the beginning of the 18th century, and near Garstang until about 1770.

The Catalan Forge was a variety of powered bloomery. Bloomeries with hot blast were used in upstate New York in the mid 19th century.

Cast iron development lagged in Europe, as the smelters could only achieve temperatures of about 1000 C; or perhaps they did not want hotter temperatures, as they were seeking to produce blooms as a precursor of wrought iron, not cast iron. Through a good portion of the Middle Ages, in Western Europe, iron was thus still being made by the working of iron blooms into wrought iron. Some of the earliest casting of iron in Europe occurred in Sweden, in two sites, Lapphyttan and Vinarhyttan, between 1150 and 1350 CE. Some scholars have speculated the practice followed the Mongols across Russia to these sites, but there is no clear proof of this hypothesis, and it would certainly not explain the pre-mongol datings of many of these iron-production centres. In any event, by the late fourteenth century, a market for cast iron goods began to form, as a demand developed for cast iron cannonballs.

Iron from furnaces such as Lapphyttan was refined into wrought iron by the osmond process. The pig iron from the furnace was melted in front of a blast of air and the droplets caught on a staff (which was spun). This formed a ball of iron, known as an osmond. This was probably a traded commodity by c.1200.

An alternative method of decarburising pig iron seems to have been devised in the region around Namur in the 15th century. This Walloon process spread by the end of that century to the Pay de Bray on the eastern boundary of Normandy before the end of that century, and to then to England, where it became the main method of making wrought iron by 1600. It was introduced to Sweden by Louis de Geer in the early 17th century and was used to make the oregrounds iron favoured by English steelmakers.

A variation on this was the German process. This became the main method of producing bar iron in Sweden.

In the early 17th century, ironworkers in Western Europe had found a means (called cementation) to carburize wrought iron. Wrought iron bars and charcoal were packed into stone boxes, then held at a red heat for up to a week. During this time, carbon diffused into the iron, producing a product called cement steel or blister steel (see cementation process). One of the earliest places where this was used in England was at Coalbrookdale, where Sir Basil Brooke had two cementation furnaces (recently excavated). For a time in the 1610s, he owned a patent on the process, but had to surrender this in 1619. He probably used Forest of Dean iron as his raw material, but it was soon found that oregrounds iron was more suitable.

The quality of the steel could be improved by faggoting, producing shear steel. However in the 1740s, Benjamin Huntsman found a means of melting blister steel, made by the cementation process in crucibles; this was cast usually as ingots as crucible steel. This is more homogeneous than blister steel.

Early iron smelting used charcoal as both the heat source and the reducing agent. By the 18th century, the availability of wood for making charcoal was limiting the expansion of iron production, so that England became increasingly dependent for a considerable part of the iron required by its industry, on Sweden (from the mid 17th century) and then from about 1725 also on Russia.

Smelting with coal (or its derivative coke) was a long sought objective. The production of pig iron with coke was probably achieved by Dud Dudley in the 1620s, and with a mixed fuel made from coal and wood again in the 1670s. However this was probably only a technological rather than a commercial success. Shadrach Fox may have smelted iron with coke at Coalbrookdale in Shropshire in the 1690s, but only to make cannon balls and other cast iron products such as shells. However, in the peace after the Nine Years War, there was no demand for these.

In 1707, Abraham Darby patented a method of making cast iron pots. His pots were thinner and hence cheaper than those of his rivals. Needing a larger supply of pig iron he leased the blast furnace at Coalbrookdale in 1709. There, he made iron using coke, thus establishing the first successful business in Europe to do so. His products were all of cast iron, though his immediate successors attempted (with little commercial success) to fine this to bar iron.

Bar iron thus continued normally to be made with charcoal pig iron until the mid 1750s. In 1755 Abraham Darby II (with partners) opened a new coke-using furnace at Horsehay in Shropshire, and this was followed by others. These supplied coke pig iron to finery forges of the traditional kind for the production of bar iron. The reason for the delay remains controversial.

Schematic drawing of a puddling furnace.

It was only after this that economically viable means of converting pig iron to bar iron began to be devised. A process known as potting and stamping was devised in the 1760s and improved in the 1770s, and seems to have been widely adopted in the West Midlands from about 1785. However, this was largely replaced by Henry Cort's puddling process, patented in 1784, but probably only made to work with grey pig iron in about 1790. These processes permitted the great expansion in the production of iron that constitutes the Industrial Revolution for the iron industry.

In the early 19th century, Hall discovered that the addition of iron oxide to the charge of the puddling furnace caused a violent reaction, in which the pig iron was decarburised, this became known as 'wet puddling'. It was also found possible to produce steel by stopping the puddling process before decarburisation was complete.

The efficiency of the blast furnace was improved by the change to hot blast, patented by James Beaumont Neilson in Scotland in 1828. This further reduced production costs. Within a few decades, the practice was to have a 'stove' as large as the furnace next to it into which the waste gas (containing CO) from the furnace was directed and burnt. The resultant heat was used to preheat the air blown into the furnace.

Apart from some production of puddled steel, English steel continued to be made by the cementation process, sometimes followed by remelting to produce crucible steel. These were batch-based processes whose raw material was bar iron, particularly Swedish oregrounds iron.

The problem of mass-producing cheap steel was solved in 1855 by Henry Bessemer, with the introduction of the Bessemer converter at his steelworks in Sheffield, England. (An early converter can still be seen at the city's Kelham Island Museum). In the Bessemer process, molten pig iron from the blast furnace was charged into a large crucible, and then air was blown through the molten iron from below, igniting the dissolved carbon from the coke. As the carbon burned off, the melting point of the mixture increased, but the heat from the burning carbon provided the extra energy needed to keep the mixture molten. After the carbon content in the melt had dropped to the desired level, the air draft was cut off: a typical Bessemer converter could convert a 25-ton batch of pig iron to steel in half an hour.

Finally, the basic oxygen process was introduced at the Voest-Alpine works in 1952; a modification of the basic Bessemer process, it lances oxygen from above the steel (instead of bubbling air from below), reducing the amount of nitrogen uptake into the steel. The basic oxygen process is used in all modern steelworks; the last Bessemer converter in the U.S. was retired in 1968. Furthermore, the last three decades have seen a massive increase in the mini-mill business, where scrap steel only is melted with an electric arc furnace. These mills only produced bar products at first, but have since expanded into flat and heavy products, once the exclusive domain of the integrated steelworks.

Until these 19th century developments, steel was an expensive commodity and only used for a limited number of purposes where a particularly hard or flexible metal was needed, as in the cutting edges of tools and springs. The widespread availability of inexpensive steel powered the Second Industrial Revolution and modern society as we know it. Mild steel ultimately replaced wrought iron for almost all purposes, and wrought iron is no longer commercially produced. With minor exceptions, alloy steels only began to be made in the late 19th century. Stainless steel was developed on the eve of the First World War and was not widely used until the 1920s.

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Salamander (metallurgy)

Salamander at Henrichshütte/Hattingen/Germany

A salamander (or deadman's foot) in the metallurgy dialect means all liquid and solidified materials in the hearth of a blast furnace below the tap hole.

After blowdown of the furnace the salamander remains as solid block. It is very imperishable, and normally it is left inside.

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Polling (metallurgy)

Polling in metallurgy is the process of refining a crude metal which has its own oxide as impurity. The molten metal is stirred with logs of green wood in a tank. The heat from the molten metal decomposes the wood which liberates hydrocarbon gases which reduce the oxide impurity into the metal. This method is generally used for refining copper and tin.

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Converting (metallurgy)

PierceSmith.gif

Converting is a term used to describe a number of metallurgical smelting processes. The most commercially important use of the term is in the treatment of molten metal sulfides to produce crude metal and slag, as in the case of copper and nickel converting. Another, now uncommon, use of the term referred to batch treatment of pig iron to produce steel by the Bessemer process. The vessel used was called the Bessemer converter.

After the first portion of slag is poured off the converter, a new portion of matte is added, and the converting operation is repeated many times until the converter is filled with the purified copper sulfide. The converter slag is usually recycled to the smelting stage due to the high content of copper in this by-product. Converter gas contains more than 10% of sulfur dioxide, which is usually captured and subjected to the production sulfuric acid.

Copper content in the obtained blister copper is typically more than 95%. Blister copper is the final product of converting.

The converting process occurs in a converter. Two kinds of converters are widely used: horizontal and vertical.

Horizontal converters of the Pierce-Smith type prevail in the metallurgy of non ferrous metals. Such a converter is a horizontal barrel lined with refractory material inside. A hood for the purpose of the loading/unloading operations is located on the upper side of the converter. Two belts of tuyeres come along the axis on either sides of the converter.

Molten sulfide material, referred to as matte, is poured through the hood into the converter during the operation of loading. Air is distributed to tuyeres from the two tuyere collectors which are located on opposite sides of the converter. Collector pipes vary in diameter with distance from the connection to air supplying trunk; this is to provide equal pressure of air in each tuyere.

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Source : Wikipedia