Metallurgy

Metallurgy is a domain of 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.

History

See also: Bronze Age

See also: History of ferrous metallurgy

See also: Iron Age

See also: Metallurgy in pre-Columbian Mesoamerica

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]

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^[3]^[4]

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 first established in ancient China long before Europeans mastered these crafts (such as the innovation of the trip hammers, etc.)^[5].

A 16th century book by 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"^[6]

Extractive metallurgy

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 ductile iron are also part of the iron-carbon system.

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 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, creep.

Metal Working Processes

Metals are shaped by processes such as gas cutters and bent into shape.

"microscopic defects in the metal, which resist further changes of shape.

Various forms of continuous casting.

Joining

Main article: 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.

Main article: 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. Brazing results in a mechanical and metallurgical bond between work pieces.

Main article: Soldering

Soldering is a method of joining metals below their melting points using a filler metal. Soldering results in a mechanical joint and occurs at lower temperatures than brazing.

Heat Treatment

Main article: Heat treatment

Metals can be 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.

Surface Treatment

Main article: Plating

zinc to the surface of the product. It is used to reduce corrosion as well as to improve the product's aesthetic appearance.

Main article: Thermal spray

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

Main article: 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, gold are used in power lines, wires, printed circuit boards and integrated circuits.

Metallurgical techniques

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.

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.

References

^ History of Gold. Gold Digest. Retrieved on 2007-02-04.
^ W. Keller (1963) The Bible as History page 156 ISBN 0 340 00312 X
^ W. Keller (1963) The Bible as History page 177 ISBN 0 340 00312 X
^ B. W. Anderson (1975) The Living World of the Old Testament page 154 ISBN 0-582-48598-3
^ R. F. Tylecote (1992) A History of Metallurgy ISBN 0-901462-88-8
^ Karl Alfred von Zittel (1901) History of Geology and Palaeontology page 15

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Metallurgy

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