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Metallurgy is a domain of of Metalworking . HISTORY See Also: Bronze Age See Also: History of ferrous metallurgy See Also: Iron Age See Also: Metallurgy in pre-Columbian Mesoamerica s, from the ''Nong Shu'', by Wang Zhen, 1313 AD, during the Chinese Yuan Dynasty .]] 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.1 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"W. Keller (1963) ''The Bible as History'' page 156 ISBN 0 340 00312 X. 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 W. Keller (1963) ''The Bible as History'' page 177 ISBN 0 340 00312 XB. W. Anderson (1975) ''The Living World of the Old Testament'' page 154 ISBN 0-582-48598-3 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 Roman s 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 first established in ancient China long before Europeans mastered these crafts (such as the innovation of the Blast Furnace , Cast Iron , Steel , Hydraulic -powered Trip Hammer s, etc.) R. F. Tylecote (1992) A History of Metallurgy ISBN 0-901462-88-8. A 16th century book by Georg Agricola called De Re Metallica describes the highly developed and complex processes of metal extraction and metallurgy of the time. Agricola has been described as the "father of metallurgy" Karl Alfred Von Zittel (1901) ''History of Geology and Palaeontology'' page 15 EXTRACTIVE METALLURGY 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 a 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. IMPORTANT COMMON ALLOY SYSTEMS Common engineering Metal s 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 Steel s and Cast Iron s. 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 Superalloy s 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. PRODUCTION ENGINEERING OF METALS 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 . Metal Working Processes 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 Machine s, and Drill s cut the cold metal to shape. With fabrication, sheets of metal are cut with Guillotine s or Gas Cutters and bent into shape. " Cold Work ing" processes, where the product’s shape is altered by rolling, fabrication or other processes while the product is cold, can increase the strength of the product by a process called Work Hardening . Work hardening creates Microscopic Defects in the metal, which resist further changes of 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 . Joining See Also: Welding Welding is a technique for joining metal components by melting the base material. A filler material of similar composition may also be melted into the joint. See Also: Brazing Brazing is a technique for joining metals 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. See Also: Soldering Soldering is a method of joining metallic electrical conductors where high strength is not required. Heat Treatment See Also: Heat treatment Metals can be Heat Treated by to alter the properties of 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. Surface Treatment See Also: Plating 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. See Also: Thermal spray Thermal spraying techniques are another popular finishing option, and often have better high temperature properties than electroplated coatings. See Also: Case hardening 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. ELECTRICAL AND ELECTRONIC ENGINEERING Metallurgy is also applied to electrical and electronic materials where metals such as Aluminium , Copper , Tin and Gold are used in power lines, wires, Printed Circuit Board s and Integrated Circuit s. METALLURGICAL TECHNIQUES Metallurgists study the microscopic and macroscopic properties using Metallography . 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 or X-ray s or Electron s, 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. REFERENCES SEE ALSO
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