metallurgy(redirected from Metalurgy)
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metallurgy(mĕt`əlûr'jē), science and technology of metalsmetal,
chemical element displaying certain properties by which it is normally distinguished from a nonmetal, notably its metallic luster, the capacity to lose electrons and form a positive ion, and the ability to conduct heat and electricity.
..... Click the link for more information. and their alloysalloy
[O. Fr.,=combine], substance with metallic properties that consists of a metal fused with one or more metals or nonmetals. Alloys may be a homogeneous solid solution, a heterogeneous mixture of tiny crystals, a true chemical compound, or a mixture of these.
..... Click the link for more information. . Modern metallurgical research is concerned with the preparation of radioactive metals, with obtaining metals economically from low-grade ores, with obtaining and refining rare metals hitherto not used, and with the formulation of alloys. Powder metallurgy deals with the manufacture of ferrous and nonferrous parts by compacting elemental metal or alloy powders in a die. The resultant shapes are then heated in a controlled-atmosphere furnace to bond the particles so that the part will retain the shape at normal temperatures and pressures. Weldingwelding,
process for joining separate pieces of metal in a continuous metallic bond. Cold-pressure welding is accomplished by the application of high pressure at room temperature; forge welding (forging) is done by means of hammering, with the addition of heat.
..... Click the link for more information. and soldering (see soldersolder
, metal alloy used in the molten state as a metallic binder. The type of solder to be used is determined by the metals to be united. Soft solders are commonly composed of lead and tin and have low melting points. Hard solders (i.e.
..... Click the link for more information. ) are techniques for joining metals metallurgically. Extractive metallurgy is the study and practice of separating metals from their ores and refining them to produce a pure metal. This article discusses the extraction of metals in general terms, but methods for the treatment of ores are quite diverse; see also aluminumaluminum
, called in British countries aluminium
, metallic chemical element; symbol Al; at. no. 13; at. wt. 26.98154; m.p. 660.37°C;; b.p. 2,467°C;; sp. gr. 2.6989 at 20°C;; valence +3.
..... Click the link for more information. , coppercopper,
metallic chemical element; symbol Cu [Lat. cuprum=copper]; at. no. 29; at. wt. 63.546; m.p. 1,083.4°C;; b.p. 2,567°C;; sp. gr. 8.96 at 20°C;; valence +1 or +2. Copper and some of its alloys have been used by humanity since the Bronze Age.
..... Click the link for more information. , goldgold,
metallic chemical element; symbol Au [Lat. aurum=shining dawn]; at. no. 79; at. wt. 196.96657; m.p. 1,064.43°C;; b.p. 2,808°C;; sp. gr. 19.32 at 20°C;; valence +1 or +3.
..... Click the link for more information. , ironiron,
metallic chemical element; symbol Fe [Lat. ferrum]; at. no. 26; at. wt. 55.845; m.p. about 1,535°C;; b.p. about 2,750°C;; sp. gr. 7.87 at 20°C;; valence +2, +3, +4, or +6. Iron is biologically significant.
..... Click the link for more information. , leadlead,
metallic chemical element; symbol Pb [Lat. plumbum]; at. no. 82; at. wt. 207.2; m.p. 327.502°C;; b.p. about 1,740°C;; sp. gr. 11.35 at 20°C;; valence +2 or +4.
..... Click the link for more information. , nickelnickel,
metallic chemical element; symbol Ni; at. no. 28; at. wt. 58.6934; m.p. about 1,453°C;; b.p. about 2,732°C;; sp. gr. 8.902 at 25°C;; valence 0, +1, +2, +3, or +4.
..... Click the link for more information. , silversilver,
metallic chemical element; symbol Ag [Lat. argentum]; at. no. 47; at. wt. 107.8682; m.p. 961.93°C;; b.p. 2,212°C;; sp. gr. 10.5 at 20°C;; valence +1 or +2.
..... Click the link for more information. , tintin,
metallic chemical element; symbol Sn [Lat. stannum]; at. no. 50; at. wt. 118.710; m.p. 231.9681°C;; b.p. 2,270°C;; sp. gr. 5.75 (gray), 7.3 (white); valence +2 or +4. Tin exhibits allotropy; above 13.
..... Click the link for more information. , and zinczinc,
metallic chemical element; symbol Zn; at. no. 30; at. wt. 65.38; m.p. 419.58°C;; b.p. 907°C;; sp. gr. 7.133 at 25°C;; valence +2. Zinc is a lustrous bluish-white metal. It is found in Group 12 of the periodic table.
..... Click the link for more information. for special procedures followed.
Concentration of the Ore
When an ore has a low percentage of the desired metal, a method of physical concentration must be used before the extraction process begins. In one such method, the ore is crushed and placed in a machine where, by shaking, the heavier particles containing the metal are separated from the lighter rock particles by gravity. Another method is the flotation processflotation process,
in mineral treatment and mining, process for concentrating the metal-bearing mineral in an ore. Crude ore is ground to a fine powder and mixed with water, frothing reagents, and collecting reagents.
..... Click the link for more information. , used commonly for copper sulfide ores. In certain cases (as when gold, silver, or occasionally copper occur "free," i.e., uncombined chemically in sand or rock), mechanical or ore dressing methods alone are sufficient to obtain relatively pure metal. Waste material is washed away or separated by screening and gravity; the concentrated ore is then treated by various chemical processes.
Separation of the Metal
Processes for separating the metal from the impurities it is found with or the other elements with which it is combined depend upon the chemical nature of the oreore,
metal-bearing mineral mass that can be profitably mined. Nearly all rock deposits contain some metallic minerals, but in many cases the concentration of metal is too low to justify mining the ore.
..... Click the link for more information. to be treated and upon the properties of the metalmetal,
chemical element displaying certain properties by which it is normally distinguished from a nonmetal, notably its metallic luster, the capacity to lose electrons and form a positive ion, and the ability to conduct heat and electricity.
..... Click the link for more information. to be extracted. Gold and silver are often removed from the impurities associated with them by treatment with mercury, in which they are soluble. Another method for the separation of gold and silver is the so-called cyanide processcyanide process
method for extracting gold from its ore. The ore is first finely ground and may be concentrated by flotation; if it contains certain impurities, it may be roasted.
..... Click the link for more information. . The Parkes process, which is based on silver being soluble in molten zinc while lead is not, is used to free silver from lead ores. Since almost all the metals are found combined with other elements in nature, chemical reactions are required to set them free. These chemical processes are classified as pyrometallurgy, electrometallurgy, and hydrometallurgy.
Pyrometallurgy, or the use of heat for the treatment of an ore, includes smeltingsmelting,
in metallurgy, any process of melting or fusion, especially to extract a metal from its ore. Smelting processes vary in detail depending on the nature of the ore and the metal involved, but they are typified in the use of the blast furnace.
..... Click the link for more information. and roasting. If the ore is an oxide, it is heated with a reducing agent, such as carbon in the form of coke or coal; the oxygen of the ore combines with the carbon and is removed in carbon dioxide, a gas (see oxidation and reductionoxidation and reduction,
complementary chemical reactions characterized by the loss or gain, respectively, of one or more electrons by an atom or molecule. Originally the term oxidation
..... Click the link for more information. ). The waste material in the ore is called gangue; it is removed by means of a substance called a flux which, when heated, combines with it to form a molten mass called slag. Being lighter than the metal, the slag floats on it and can be skimmed or drawn off. The flux used depends upon the chemical nature of the ore; limestone is usually employed with a siliceous gangue. A sulfide ore is commonly roasted, i.e., heated in air. The metal of the ore combines with oxygen of the air to form an oxide, and the sulfur of the ore also combines with oxygen to form sulfur dioxide, which, being a gas, passes off. The metallic oxide is then treated with a reducing agent. When a carbonate ore is heated, the oxide of the metal is formed, and carbon dioxide is given off; the oxide is then reduced.
Electrometallurgy includes the preparation of certain active metals, such as aluminum, calcium, barium, magnesium, potassium, and sodium, by electrolysiselectrolysis
, passage of an electric current through a conducting solution or molten salt that is decomposed in the process. The Electrolytic Process
The electrolytic process requires that an electrolyte, an ionized solution or molten metallic salt, complete an
..... Click the link for more information. : a fused compound of the metal, commonly the chloride, is subjected to an electric current, the metal collecting at the cathode.
Hydrometallurgy, sometimes called leaching, involves the selective dissolution of metals from their ores. For example, certain copper oxide and carbonate ores are treated with dilute sulfuric acid, forming water-soluble copper sulfate. The metal is recovered by electrolysis of the solution. If the metal obtained from the ore still contains impurities, special refiningrefining,
any of various processes for separating impurities from crude or semifinished materials. It includes the finer processes of metallurgy, the fractional distillation of petroleum into its commercial products, and the purifying of cane, beet, and maple sugar and many
..... Click the link for more information. processes are required.
See R. E. Reed-Hill et al., Physical Metallurgy Principles (1991); H. Chandler, Metallurgy for the Non-Metallurgist (1998); D. A. Brandt et al., Metallurgy Fundamentals (1999).
in the original, narrow sense, the art of extracting metals from ore; in the modern sense, the area of science and technology and the branch of industry encompassing the processes of production of metals from ores or other materials, as well as processes related to the alteration of the chemical composition and structure, and hence the properties, of metal alloys. Metallurgy involves the preliminary treatment of mined ores, the production and refining of metals and alloys, and the process of imparting to the latter a particular shape and specific properties.
In modern technology, a historical distinction has been made between ferrous and nonferrous metallurgy. Ferrous metallurgy encompasses the production of iron alloys (pig iron, steel, and ferroalloys). The production of ferrous metals accounts for 95 percent of the world metal production. Nonferrous metallurgy includes the production of most other metals. The production of radioactive metals is developing in connection with the use of atomic energy. Metallurgical processes are also used in the production of semiconductors and nonmetals (silicon, germanium, selenium, tellurium, arsenic, phosphorus, and sulfur), some of which are obtained as byproducts in metal refining. On the whole, modern metallurgy deals with processes for obtaining almost all the elements of the periodic table, with the exception of halogens and gases.
Archaeological findings show that metallurgy originated in antiquity. In the 1950’s and 1960’s, traces of copper smelting dating to the seventh to sixth millennia B.C. were discovered in southwestern Asia Minor. It was approximately at that time that man became acquainted with native ores (gold, silver, and copper) and subsequently with meteoric iron. At first, metal objects were made by cold working. Copper and iron do not lend themselves readily to such treatment and therefore did not become widely used.
After the invention of hot forging, copper objects became common (the Aneolithic period). The mastery of the art of smelting copper from oxidized copper ores and of producing the desired shape by casting (fifth and fourth millennia B.C.) led to a rapid rise in copper production and a significant expansion of its use. However, the small size of deposits of oxidized copper ores made necessary the much more complicated method of processing sulfide ores involving preliminary roasting of the ore and refining of the copper by repeated melting. The appearance of this process dates to about the mid-second millennium B.C. in the Middle East and central Europe.
Widespread use of objects made of bronze (an alloy of copper with tin) began in the second millennium B.C. The quality of such objects was significantly better than that of copper objects. Bronze tools and weapons had increased corrosion resistance, resilience, hardness, and blade sharpness. In addition, bronze had a lower melting point than copper and better filled casting molds. All types of objects were more easily cast from bronze. The replacement of copper by bronze marked the transition to the Bronze Age. In the late third millennium and in the second millennium B.C., the main center of copper and bronze metallurgy on the present-day territory of the USSR was the Caucasus.
In about the mid-second millennium B.C., man mastered the art of obtaining iron from ore. At first wood fires and later special smelting pits (Catalan forges) were used. The pits were lined with rock and charged with charcoal and easily reduced ore. The draft required for combustion of the charcoal was supplied to the hearth from below (at first by natural ventilation and then by means of bellows). The gases formed (carbon monoxide) reduced the iron oxides. The relatively low temperature of the process and the large quantity of iron slag impeded carburization of the metal and permitted only the production of iron with a low carbon content. The process had low productivity and provided extraction of only about half of the iron in the ore.
Iron metallurgy developed very slowly, even though iron ores are much more common than copper ores and the temperature for their reduction is lower. The reason for the earlier development of copper metallurgy lay in the significantly lower quality of bloomery iron relative to copper. This was primarily because, at the temperatures attainable at the time, copper was produced in the molten state, whereas iron was produced in the form of a doughy mass with many slag and unburned coal inclusions. As a result of its low carbon content, bloomery iron was soft, and tools and weapons made from it rapidly became blunt and bent. They were not tempered and were inferior in quality to bronze implements. Improvement of the primitive bloomery process and, most importantly, mastery of the process of carburization and subsequent tempering of iron—that is, the production of steel—were required for expansion of the production and use of iron. In the first millennium B.C., these improvements gave iron a predominant position among the materials used by man. Toward the turn of the Common Era, iron metallurgy was almost universally found in Europe and Asia.
Over a period of almost three millennia, iron metallurgy did not undergo any basic changes. The process was gradually improved: the Catalan forges were enlarged and their shape improved and draft capacity increased. As a result, the Catalan forges were converted into small bloomery furnaces.
In the mid-14th century, further increase in the size of bloomery furnaces led to the appearance of small blast furnaces. An increase in the height of the furnaces and a more intense blast provided an increase in temperature and significantly stronger reduction and carburization of the metal. Instead of the semiliquid mass of bloomery iron, blast furnaces yielded a high-carbon iron alloy with silicon and manganese impurities, called pig iron. In the 14th century, the growth of pig iron production led to the discovery of bloomery conversion, a means of converting pig iron into malleable iron. The pig iron was melted in the bloomery, and impurities were removed by oxidizing them with an oxygen draft and a special ferruginous slag. Bloomery conversion gradually replaced the previous inefficient processes for the production of steel based on bloomery iron, in spite of the extremely high quality of the metal produced by means of the earlier processes. Thus, a two-stage method for producing iron took shape; it has retained its significance and is the basis of modern steel production techniques.
The next step in the development of steel metallurgy in Europe was the appearance in England in 1740 of crucible smelting (which had long been known in the East) and, in the last quarter of the 18th century, of puddling. The crucible method was a technique for producing cast steel by smelting in crucibles made of refractory clay and installed in special furnaces. Both the puddling process and bloomery conversion produced malleable iron: pig iron was refined on the hearth of a reverberatory furnace to remove carbon and other impurities.
In spite of their great importance in the development of technology of their time, the crucible and puddling processes could not meet the demand for steel. The metallurgy of pig iron developed rapidly, leading to the introduction of water blast pipes, bellows driven by waterwheels (beginning in the 15th century), and steam blast machines (1782). In the late 18th century, the use of coke became widespread; the use of a hot blast and careful priming of the ore for blastfurnace smelting date to the 19th century. The low level of development of steel-smelting production was manifested in the fact that, until the early 20th century, the production of pig iron exceeded steel production.
Three new processes in the production of cast steel played a major role in the advance of steel production: the Bessemer process (1856), the open-hearth process (1864), and the basic Bessemer process (1878). As a result of the widespread use of these processes—above all the open-hearth process, which uses large quantities of metal scrap—pig iron production in the mid-20th century was only 70 percent of steel production.
The further development of steel smelting in the second half of the 20th century was related to the significant increase in the capacity and efficiency of steel mills, the widespread use of oxygen to increase the efficiency of various metallurgical processes, the appearance of a new, rapidly developing method of steel production in oxygen converters, the development of vacuum refining of steel outside the furnace, the treatment of steel with synthetic slags and inert gas, the introduction of continuous steel casting, and the extensive mechanization and automation of production processes. An important role in modern iron metallurgy is played by the production of high-quality steels, including alloy steel, which has been produced mainly in electric furnaces since the early 20th century.
In the second half of the 20th century, remelting of metals in vacuum arc furnaces and in electro slag, electron-beam, and plasma installations has come to be used in the production of certain nonferrous metals, and also of steels for particularly critical uses. In the extraction of iron from ores, various methods of direct iron production are developing, in addition to blast-furnace production, whose expansion is continuing. These processes, which make possible the production of iron suitable for steel smelting in electric furnaces, have a highly promising future.
In addition to iron, in the ancient world gold, silver, copper, tin, lead, and mercury were mined and used. Many other metals, including some that were unknown to the ancients, were used in alloys, minerals, or compounds.
In prehistoric times, gold was mined in the form of nuggets or native ores by ore washing. Gold-bearing sand was subjected to hot forging or smelting in crucibles to produce gold objects. This method usually yielded alloys of gold with silver and other elements, which brought about wide variations in color and in the casting and mechanical properties of the metal.
The refining of gold and its separation from silver began in the second half of the second millennium B.C. but spread very slowly until the sixth century B.C. The removal of impurities (together with the lead added to improve the refining process) was carried out by oxidizing them with air. Silver was separated by chlorinating the alloy by heating it in the presence of common salt, with subsequent distillation or solution of the volatile chlorides. Another method of separating silver consisted in its conversion into a sulfide by heating the alloy in the presence of sulfides and charcoal. The use of nitric acid for separating silver from gold began as early as the 13th and 14th centuries.
The method of amalgamation was also known in the ancient world, but there is no certainty that it was used to extract gold from ores and sand. After the discovery by the Russian scientist P. R. Bagration in 1843 of the principles of cyaniding gold ores, and particularly after the work of the English metallurgists J. S. MacArthur and the brothers R. and W. Forrest (1887–88), the process became predominant in gold metallurgy. Cyaniding is sometimes used in conjunction with amalgamation. Flotation and gravity concentration are used successfully in gold metallurgy.
In antiquity, silver was produced mainly as a by-product with lead from galenite. The origin of the joint smelting of the two metals dates to the third millennium B.C. in Asia Minor; the process became widespread only 1,500–2,000 years later. The technology used is presumed to have included roasting of the ore, smelting in a furnace, separation smelting (segregation and liquation), and cupellation. In the second half of the 20th century, lead has been produced primarily from complex ores by flotation concentration, agglomerative roasting, reduction smelting in shaft furnaces, and refining of the product, called crude lead. Silver (as well as gold, if it is present) is also extracted in this refining process.
Large-scale production of copper began after the discovery by V. A. Semennikov in 1866 of the conversion of copper matte. The idea of blowing the melt from the side (rather than from below, as in the Bessemer process for producing steel from pig iron), which was proposed in 1880, played an important role in the development of converter processing of matte. With blowing from the side, the air passes directly into the melt being refined, bypassing the easily solidified copper that accumulates on the bottom of the converter.
Flotation concentration, which was invented at the turn of the 20th century, had great significance in the development of large-scale copper production. The process makes possible the successful treatment of ores with a copper content of less than 1 percent. Nonfloating low-grade oxidized ores, containing less than 0.7 percent copper, are processed by the hydrometallurgical method (leaching). Sulfide ores may be leached at the site of the ore deposit without mining, using bacteria to increase the efficiency of leaching (bacterial lixiviation).
In antiquity, tin was smelted in simple shaft furnaces, and impurities were eliminated by liquation or oxidation processes. Before smelting, native tin ores were crushed and underwent enrichment by a very simple method; placer ore was mined by washing. In modern metallurgy, the necessity of using low-grade tin ores with a significant concentration of the impurities sulfur, arsenic, antimony, bismuth, and silver has led to the production of tin by complex treatment of the ore. The treatment includes enrichment, roasting, leaching of impurities from the ore concentrates, magnetic separation of impurities, and reduction smelting in reverberatory, shaft, or electrical furnaces (the last is the best method) to give crude tin, which is then refined mainly by pyrometallurgical methods (electrolysis is sometimes used).
The first methods of producing mercury apparently consisted of roasting the ore in piles; the mercury condensed on cold objects. The ceramic retort appeared later. The methods of mercury production described by the German scientist G. Agricola in the 16th century consisted of roasting the ore in ceramic vessels with various condensers. Iron retorts appeared in the 17th century (1641). Later, with the increasing demand for mercury, more efficient batch and, subsequently, continuous shaft furnaces, reverberatory furnaces (beginning in 1842), and rotary tube furnaces (since the early 20th century) appeared; they are now the main furnaces for processing mercury ores. A promising method of producing mercury, involving the treatment of ore in fluidized-bed furnaces, has been successfully introduced in the USSR.
The processes of production of other metals, which have become important only during recent centuries (and sometimes only in recent years), are discussed in the corresponding articles (seeALUMINUM, ZINC, MANGANESE, CHROMIUM, NICKEL, and MAGNESIUM).
Modern metallurgy as a complex of basic technological operations in the production of metals and alloys includes the following: (1) preparation of ore (including concentration) for extraction of metal; (2) pyrometallurgical, hydrometallurgical, and electrolytic processes for extraction and refining of metals; (3) production of objects from metal powder by sintering; (4) crystal-physical methods of refining metals and alloys; (5) pouring of metals and alloys to produce ingots and castings; (6) pressure working of metals; (7) thermal, thermomechanical, and thermochemical treatment of metals to impart the required properties to them; (8) application of protective coatings.
Metallurgy is closely tied to the by-product coke industry and the production of refractory materials.
The preparation of ores for extraction of metal begins with crushing, grinding, screening, and classification. The next stage of treatment is concentration. The materials are usually roasted or dried during or after concentration. Fluidized-bed roasting is very promising. Flotation, gravity, magnetic, and electrical methods of concentration are most widespread. Flotation processes are used to treat more than 90 percent of the ore of nonferrous and rare metals. Heavy-media concentration, jigging, and table concentration are common gravity methods.
The great importance of concentration processes in modern metallurgy results from the desire to increase the efficiency of metallurgical production, and also from the use of lower-grade ores required by the growth of metal smelting. The direct metallurgical treatment of such ores without concentration is usually not economically feasible and is sometimes even impossible.
The final operations in the preparation of ores for smelting are usually blending and mixing, as well as pelletizing by means of sintering or briquetting. Pelletizing is necessary because of the undesirability or impossibility of using the finely ground products of ore concentration in various types of smelting operations.
Pyrometallurgical (high-temperature) methods of metal extraction and refining are extremely varied. Such processes are carried out in shaft, reverberatory, or electrical furnaces and in converters. In pyrometallurgical processes, concentration of metals and impurities takes place in various phases of the system that forms upon heating or melting of the materials being processed. Gases, liquid metals, slag, matte, or solids may be such phases. After separation, one or more phases undergoes further treatment. Both oxidation and reduction methods are used to accomplish the necessary processes in pyrometallurgy. Gaseous oxygen, as well as chlorine and potassium nitrate, is used to intensify the oxidation. Carbon, carbon monoxide, hydrogen, or certain metals may be used as reducing agents. Examples of reduction processes are blast-furnace smelting; the melting of secondary copper, tin, and lead in shaft furnaces; and the production of ferroalloys and titanium slag in electric reducing furnaces. For example, magnesiothermic reduction is used in the production of titanium. Oxidation refining is a necessary element in open-hearth and converter production of steel and the production of anode copper and lead.
Methods of extraction and refining of metals based on the formation of sulfides, chlorides, iodides, and carbonyls are very widely used. Processes involving evaporation and condensation (distillation, rectification, vacuum separation, and sublimation) are also very important. Methods for refining steel that are performed outside the furnace have developed, as have vacuum smelting and argon smelting, which have come to be used in the production of chemically reactive metals (titanium, zirconium, and molybdenum) and steel.
Hydrometallurgical methods of extraction and refining of metals that do not require high temperatures are based on the use of aqueous solutions. Leaching with aqueous solutions of acids, bases, or salts is used to transfer the metals into solution. Carburizing, crystallization, adsorption, precipitation, or hydrolysis are used to remove elements from solution. Sorption of metals by ion exchangers (mainly synthetic resins) and extraction (by means of organic liquids) have become widespread. Modern sorption and extraction methods are characterized by high efficiency. They make possible the extraction of metals not only from solutions but also from pulp, bypassing settling, washing, and filtration operations. Among other hydrometallurgical processes, autoclave treatment of materials at high temperatures and pressures, and also fluidized-bed purification of solutions, should be noted. Amalgamation, which is the extraction of metals (for example, gold) from ores using mercury, is important in a number of industries.
Electrolytic precipitation for the production or refining of nonferrous metals, both from aqueous solutions (copper, nickel, cobalt, and zinc) and from melts (aluminum and magnesium), is very significant. For example, aluminum is produced by means of electrolysis of a cryolite-alumina melt.
The production of items from metal powders, or powder metallurgy, is also used. In a number of instances, this process provides higher quality of the manufactured item and better technical and economic characteristics of the production process than traditional methods.
Crystal-physical methods of refining (zone melting and extraction of single crystals from solution) based on the difference in composition of the solid and liquid phases during crystallization of metal from a melt are used for the production of ultrahigh-purity metals and semiconductors.
Processes of production of castings from molten metals and alloys, and alsoof ingots for subsequent pressure working, have been known to man for many centuries. The major technical advances in this area are related to the shift to continuous casting of steel and alloys and to combined processes of casting and pressure working of ingots (for example, the continuous production of wire or sheets from molten aluminum, copper, and zinc).
Pressure working of metals has also long been known (for example, forging was an essential element in the working of bloomery pig iron). Forging, stamping, and molding are the most important elements of machine building. Rolling is the main method of pressure working of metals and alloys in modern metallurgical factories. The rolling mill, which apparently was proposed as early as 1495 by Leonardo da Vinci, has become a large-scale, highly automated complex with an annual production capacity of several million tons of metal. In addition to sheet and sectional metal, pipes, bent and regular shapes, and bimetal are produced by rolling. Drawing is widely used for producing wire.
Heat treatment, which makes possible production of the most suitable structure of metals and alloys, also has very ancient origins. Such processes as carburizing, hardening, annealing, and tempering of metals were known and had been mastered in practice even in remote antiquity. The scientific grounding of the heat treatment of metals was developed by D. K. Chernov.
In modern technology the heat treatment of metals and alloys, as well as thermomechanical, chemical-mechanical, and chemical heat treatment, is very widely used in industry. In addition to finished parts, which are processed at machine-building plants, many types of products are heat-treated at metallurgical works. Among such products are steel rails (volume and head hardening), thick sheets and reinforcement steel (strengthening), and thin sheets of transformer steel (annealing for improvement of magnetic properties).
Processes for application of various protective coatings to metals are gaining great importance in modern metallurgy. Such processes are tinning, zinc plating, and application of plastic coatings that significantly improve the quality and durability of metals.
The importance of metallurgy in the creation of modern civilization is extremely great. Without metals, the material culture of society is unthinkable. Metallurgy is the basis for the production of means of production and transportation and communications equipment, as well as for civil construction and military affairs. Metals play a great role in agriculture and in the production of consumer goods. (For data on the volume and dynamics of the production of steel, pig iron, and the most important nonferrous metals and other information on metallurgy as branches of industry, seeFERROUS METALLURGY and NONFERROUS METALLURGY.)
REFERENCESOsnovy metallurgii, vols. 1–6. Moscow, 1961–73.
Metallovedenie i termicheskaia obrabotka stall: Spravochnik, 2nd ed. Moscow, 1961–62.
Prokatnoe proizvodstvo: Spravochnik, vols. 1–2. Moscow, 1962.
Domennoe proizvodstvo: Spravochnik, vols. 1–2. Moscow, 1963.
Staleplavil’noe proizvodstvo: Spravochnik, vols. 1–2. Moscow, 1964.
Aitchison, L. A History of Metals, vols. 1–2. London, 1960.
A. IA. STOMAKHIN
The technology and science of metallic materials. Metallurgy as a branch of engineering is concerned with the production of metals and alloys, their adaptation to use, and their performance in service. As a science, metallurgy is concerned with the chemical reactions involved in the processes by which metals are produced and the chemical, physical, and mechanical behavior of metallic materials.
The field of metallurgy may be divided into process metallurgy (production metallurgy, extractive metallurgy) and physical metallurgy. In this system metal processing is considered to be a part of process metallurgy and the mechanical behavior of metals a part of physical metallurgy.
Process metallurgy, the science and technology used in the production of metals, employs some of the same unit operations and unit processes as chemical engineering. These operations and processes are carried out with ores, concentrates, scrap metals, fuels, fluxes, slags, solvents, and electrolytes. Different metals require different combinations of operations and processes, but typically the production of a metal involves two major steps. The first is the production of an impure metal from ore minerals, commonly oxides or sulfides, and the second is the refining of the reduced impure metal, for example, by selective oxidation of impurities or by electrolysis. See Electrometallurgy, Hydrometallurgy, Ore dressing, Pyrometallurgy, Steel manufacture
Physical metallurgy investigates the effects of composition and treatment on the structure of metals and the relations of the structure to the properties of metals. Physical metallurgy is also concerned with the engineering applications of scientific principles to the fabrication, mechanical treatment, heat treatment, and service behavior of metals. See Alloy, Heat treatment (metallurgy)
The structure of metals consists of their crystal structure, which is investigated by x-ray, electron, and neutron diffraction, their microstructure, which is the subject of metallography, and their macrostructure. Crystal imperfections, which provide mechanisms for processes occurring in solid metals, are investigated by x-ray diffraction and metallographic methods, especially electron microscopy. The microstructure is determined by the constituent phases and the geometrical arrangement of the microcrystals (grains) formed by those phases. Macrostructure is important in industrial metals. It involves chemical and physical inhomogeneities on a scale larger than microscopic. Examples are flow lines in steel forgings and blowholes in castings. See Metallography
Phase transformations occurring in the solid state underlie many heat-treatment operations. The thermodynamics and kinetics of these transformations are a major concern of physical metallurgy. Physical metallurgy also investigates changes in the structure and properties resulting from mechanical working of metals.