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Steel

Steel


Steel is an alloy of iron with about 1 percent carbon. It may also contain other elements, such as manganese. Whereas pure iron is a relatively soft metal that rusts easily, steel can be hard, tough, and corrosion-resistant. Used to make almost everything from skyscraper girders, automobiles, and appliances to thumb tacks and paper clips, steel is one of the world's most vital materials. Among all the metals, iron is second only to aluminum in natural abundance, making up 4.7 percent of the earth's crust, and occurring mainly as its various oxides. The main product made from iron is steel, the least expensive and most widely used of all metals.

History

It appears that ancient peoples were using iron as early as 4000b.c.e. for making various tools, weapons, and other objects. They apparently obtained the iron from meteorites. The composition of those earliest iron artifacts was higher in nickel than native iron ores on Earth, in keeping with the composition of meteorites. In fact, the word "iron" comes from an ancient term meaning "metal from the sky." It is interesting to note that when Admiral Robert Peary visited Greenland in the 1890s, he found that the Inuit had for many years been making iron tools from a 30-ton iron meteorite that had fallen there centuries earlier.

While it is not known exactly when people learned how to remove iron from its ores, by 1200 b.c.e. iron ore was being mixed with burning wood or charcoal and turned into hot masses from which iron metal could be "wrought" by repeated hammering. Placing the iron back in burning charcoal seemed to make it harder and stronger. The iron picked up carbon from the charcoal, especially along its surface, turning it into the hard material that has come to be known as steel.

During the first millennium b.c.e. a highly superior steel product was made in India, in a region near Hyderabad. Well known for its strength and its wavy patterned surface, it was especially desirable for making sword blades. Some think that the ore found in that area just happened to have the right impurities to give the steel special properties. The hot iron was repeatedly forged and folded to produce a metal of extremely high quality that became famous all over the ancient world. It was especially sought after by Europeans, who called it "wootz"; by Moors living in Spain, who used it to make their Toledo blades; and by Arabs, who used it in their famous Damascus swords.

Making Steel

Over the years various countries have excelled in making steel. During the eighteenth century a relatively small amount of steel was made, but Sweden was the main producer. In the nineteenth century Great Britain became dominant. In the twentieth century the United States was the largest steel producer in the world until about 1970, when it was surpassed by the Soviet Union. At the start of the twenty-first century, China led the world in steel production.

Three primary installations in an integrated steel plant are the blast furnace, the steel furnaces, and the rolling mills. The blast furnace converts iron ore to pig iron; the steel furnaces convert the pig iron to steel; and the rolling mills shape the steel into sheets, slabs, or bars.

Blast furnace. A blast furnace is a chimney-like structure in which iron ores (mainly FeO, Fe2O3, and Fe3O4) are converted into iron metal. Iron ore, coke, and limestone are loaded into the top of the furnace, while air is blown in from below. The coke is converted to carbon monoxide (CO), which then acts as the reducing agent:

2 C + O2 2 CO

3 CO + Fe2O3 2 Fe + 3 CO2

The molten iron falls to the bottom of the furnace, and the limestone reacts with silicate impurities to form a molten slag, which floats on top of the iron. The two layers are drawn off separately, and the iron is poured into molds. Because the molten iron yields ingots that resemble little pigs, the product is referred to as "pig iron."

Steel furnaces. In the steel furnace, sulfur and phosphorus impurities and excess carbon are burned away, and manganese and other alloying ingredients are added. During the nineteenth century most steel was made by the Bessemer process, using big pear-shaped converters. During the first half of the twentieth century, the open hearth furnace became the main type of steel furnace. This gave way mid-century to the basic oxygen process, which used pure oxygen instead of air, cutting the process time from all day to just a few hours. In the twenty-first century, most new steel plants use electric furnaces, the most popular being the electric-arc furnace. It is cheaper to build and more efficient to operate than the basic oxygen furnace. In the electric-arc furnace a powerful electric current jumps (or arcs) between the electrodes, generating intense heat, which melts the iron scrap that is typically fed into it. The most modern process for making steel is the continuous process, which bypasses the energy requirements of the blast furnace. Instead of using coke, the iron ore is reduced by hydrogen and CO derived from natural gas. This direct reduction method is especially being used in developing countries where there are not any large steel plants already in operation.

Finishing processes. A final step in processing steel is shaping. Liquid steel can be cast into ingots or various other forms. They can then be sent to rolling mills. There are hot rolling mills and cold rolling mills. Various kinds of steel slabs are rolled into sheets, strips, bars, or other kinds of products. Sometimes the steel is forged into shape with hammers or presses, or the hot steel is extruded through dies to give it some desired shape. For example, steel wire is made by drawing hot steel rods through smaller and smaller dies. Some steel is finished by grinding or polishing, and some is coated with zinc or electroplated with tin.

World Steel Production

The three top steel producers in the world are China, the United States, and Japan, in that order. The United States and Japan each produce around 100 million tons (90 million metric tons) of steel per year, and China had an output in 2000 of about 140 million tons (127 million metric tons). Iron and steel make up approximately 90 percent of all the metal produced in the world. The largest steel company in the United States is United States Steel, which produces about 20 percent of the country's steel.

TYPES OF STEEL

Carbon Steel. This is the most widely used kind of steel. Its carbon content is under 2 percent and is usually less than 1 percent. It often also contains a little manganese.

Stainless Steel. This is the most corrosion-resistant kind of steel. It normally contains at least 12 percent (and sometimes up to 30 percent) chromium, and it usually also contains nickel. A very popular stainless steel formulation is 18-8, 18 percent chromium and 8 percent nickel.

Alloy Steels. These contain a little carbon, and sometimes silicon, but they mainly contain added metals, such as manganese (hardness), nickel (strength), molybdenum (improved wear), tungsten (high temperature strength), chromium (corrosion resistance), and vanadium (toughness).

Galvanized Steel. This steel is coated with zinc to protect against corrosion. The coating is usually done by a hot dip process.

Electroplated Steel. This steel has a coating of another metal, usually tin, applied by the use of an electric current. Tin-plated steel is widely used for making cans and other containers.

Tool Steel. This is very hard steel made by tempering (heating to a very high temperature and then quickly cooling).

Damascus Steel. This was a very high quality ancient steel with a beautiful wavy surface pattern used in making sword blades. It seems to have come mainly from India.

Wootz Steel. This was actually a European mispronunciation of ukku, the very fine steel made in ancient India that they called "wook." (It is probably the same material as Damascus steel.)

Steel plants vary widely in size. Some large integrated plants include coke ovens, blast furnaces, several kinds of steelmaking furnaces, and various mills for rolling the steel into sheets or slabs. Some companies dig their own ore and run their own coal mines and limestone quarries, and some even operate their own railroads and barges. Other steel plants consist of a single electric furnace for melting scrap with a small mill for turning the melted steel into bars. These scrap recycling plants are known as

"minimills," and they now account for about half of steel production in the United States. There were about 160 steel plants operating in the United States in 2003, and most of them were minimills.

see also Iron.

Doris K. Kolb

Bibliography

Ohashi, Nobuo (1992). "Modern Steelmaking." American Scientist November-December: 540555.

Paxton, Harry (1997). "Steel." Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 22. New York: John Wiley.

Pehlke, Robert D. (2002). "Steel Manufacture." McGraw-Hill Encyclopedia of Science and Technology, 19th edition, Vol. 17. New York: McGraw-Hill.

Raymond, Robert (1984). Out of the Fiery Furnace: The Impact of Metals on the History of Mankind. University Park: Pennsylvania State University Press.

Stwertka, Albert (1998). A Guide to the Elements. New York: Oxford University Press.

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steel

steel, alloy of iron, carbon, and small proportions of other elements. Iron contains impurities in the form of silicon, phosphorus, sulfur, and manganese; steelmaking involves the removal of these impurities, known as slag, and the addition of desirable alloying elements.

Production

Steel was first made by cementation, a process of heating bars of iron with charcoal in a closed furnace so that the surface of the iron acquired a high carbon content. The crucible method, originally developed to remove the slag from cementation steel, melts iron and other substances together in a fire-clay and graphite crucible. The famous blades of Damascus and of Toledo, Spain, were made by the cementation and crucible techniques.

The Bessemer process, the open-hearth process, and the basic oxygen process are more widely used in modern steelmaking. The open-hearth uses a type of furnace called a regenerative furnace; instead of a firebox at one end and a flue at the other, it has devices at each end for the intake and outflow of both fuel and air. The air is preheated by a system of current reversals that causes very high temperatures. This process, developed c.1866 by Sir William Siemens, uses iron ore and pig iron. In the basic oxygen process, or Linz-Donawitz process, developed in the 1950s, the design of the furnace is changed, and oxygen added to the air intake permits more rapid refining of the charge (material in the furnace). The electric-arc furnace is another modern development; it provides a means of making large quantities of high-grade steel, with the advantages of positive temperature control, freedom from contamination of the product by the fuel, and simultaneous deoxidation and desulfurization actions.

Steel is shaped for commercial use in rolling mills, where successive passages of the red-hot ingot between variously shaped rollers give it the desired form. Pittsburgh, one of the world's great steel centers, built its first rolling mill in 1811; Bessemer steel rails were rolled in Chicago as early as 1865.

Types and Uses

Steel is often classified by its carbon content: a high-carbon steel is serviceable for dies and cutting tools because of its great hardness and brittleness; low- or medium-carbon steel is used for sheeting and structural forms because of its amenability to welding and tooling. Alloy steels, now most widely used, contain one or more other elements to give them specific qualities. Aluminum steel is smooth and has a high tensile strength. Chromium steel finds wide use in automobile and airplane parts on account of its hardness, strength, and elasticity, as does the chromium-vanadium variety. Nickel steel is the most widely used of the alloys; it is nonmagnetic and has the tensile properties of high-carbon steel without the brittleness. Nickel-chromium steel possesses a shock resistant quality that makes it suitable for armor plate. Wolfram (tungsten), molybdenum, and high-manganese steel are other alloys. Stainless steel, which was developed in England, has a high tensile strength and resists abrasion and corrosion because of its high chromium content.

Bibliography

See R. M. Brick, Structure and Properties of Alloys (1965); K. Warren, The American Steel Industry, 1850–1970 (1973).

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steel

steel. Following the use of cast and wrought iron in buildings, steel (a strong, malleable metal, mostly iron, with added carbon and sometimes small amounts of other metals) was employed for tall structures, notably skyscrapers in America from the 1880s. One of the first to have a full skeletal frame, supporting all the floors, etc., without the help of brick or masonry stiffeners, was Jenney's Manhattan Building, Chicago, IL (1889–90), but the frame was not entirely of steel, and consisted of cast and wrought iron as well as steel. Jenney had used steel in the upper storeys of the Home Insurance Company Building, Chicago (1884–5), which was really a prototypical skyscraper, but the structure was a hybrid, and did not have a true steel skeleton. Steel, strong and capable of being assembled quickly, had been proved in bridge construction and elsewhere, so its potential for industrialized building and skyscrapers became apparent in the closing years of C19, although full expression of steel structure had to wait until C20. Steel is liable to fail at high temperatures, so it has to be protected against fire, and this seems to have inhibited designers at first, who disguised the frames behind masonry and other façades. Elegant uses of steel structures were demonstrated by Mies van der Rohe much later.Cor-Ten Steel, which oxidizes to give a brown finish, can be used for exterior work, as it does not need paint protection.

Bibliography

Blanc et al. (1993);
N. Jackson (1996);
Mainstone (1975)

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steel

steel Group of iron alloys containing a little carbon. The great strength of steel makes it an extremely important material in construction and manufacturing. The most common type is called plain carbon steel, because carbon is the main alloying material. This kind of steel usually contains less than 1% of carbon by weight. Alloy steels contain some carbon, but owe their special properties to the presence of manganese, nickel, chromium, vanadium, or molybdenum. Low-alloy steels, with less than 5% of alloying metals, are exceptionally strong, and are used in buildings, bridges, and machine parts. High-alloy steels contain more than 5% of alloying metals. This groups includes various forms of stainless steel

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steel

steel / stēl/ • n. a hard, strong, gray or bluish-gray alloy of iron with carbon and usually other elements, used extensively as a structural and fabricating material. ∎  used as a symbol or embodiment of strength and firmness: nerves of steel | [as adj.] a steel will. ∎  a rod of roughened steel on which knives are sharpened. • v. [tr.] mentally prepare (oneself) to do or face something difficult: I speak quickly, steeling myself for a mean reply.

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steel

steel sb. OE. (Angl.) *stēle, (WS). *stīele, stȳle = OS. stehli :- WGmc. *staχlja-, f. Gmc. *staχla-, repr. by MLG. stāl, MDu. stael (Du. staal), OHG. stahal (G. stahal), prob. rel. to STAY1.
Hence steel vb. edge, etc., with steel OE. (first in pp. steeled); (fig.) XVI. steely (-Y1) XVI. Comp. steelyard (YARD2) balance consisting of a lever with unequal arms, moving on a fulcrum. XVII.

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steel

steelallele, anele, anneal, appeal, Bastille, Beale, Castile, chenille, cochineal, cockatiel, conceal, congeal, creel, deal, eel, Emile, feel, freewheel, genteel, Guayaquil, heal, heel, he'll, keel, Kiel, kneel, leal, Lille, Lucille, manchineel, meal, misdeal, Neil, O'Neill, ordeal, peal, peel, reel, schlemiel, seal, seel, she'll, spiel, squeal, steal, steel, Steele, teal, underseal, veal, weal, we'll, wheel, zeal •airmobile • Dormobile • snowmobile •Popemobile • bookmobile •automobile • piecemeal •sweetmeal, wheatmeal •fishmeal • inchmeal • cornmeal •wholemeal • bonemeal • oatmeal •kriegspiel • bonspiel • Glockenspiel •newsreel • imbecile • Jugendstil •cartwheel • treadwheel • millwheel •pinwheel • flywheel • gearwheel •waterwheel

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Steel

Steel

Raw materials

Manufacturing processes

Quality control

Byproducts and waste

The future

Resources

Steel is a strong metal alloy whose major component is iron, along with a minor amount of carbon, from 0.02 to 2.0% by weight, and other lesser elements such as chromium, manganese, and nickel. It is the most widely used of all metals, with uses ranging from concrete reinforcement in highways and in highrise buildings to automobiles, aircraft, and vehicles in space. Steel is more ductile (able to deform without breakage) and durable than cast iron and is generally forged, rolled, or drawn into various shapes.

Since the beginning of the Iron Age, about 1000 BC, humankinds progress has been greatly dependent on tools and equipment made with iron. The iron tools were then used to fashion many other needed goods. Eventually, this was followed by the Industrial Revolution, a period of change beginning in the middle of the eighteenth century in England where extensive mechanization of production systems resulted in a shift from home manufacturing and farms to largescale factory production. Machine tools and other equipment made of iron and steel significantly changed the economy of both farms and cities.

The history of iron and steel began at least 6,000 years ago. It is speculated that early humankind first learned to use iron from fallen meteorites. Many meteorites are composed of iron and nickel, which forms a much harder metal than pure iron. The ancients could make crude tools and weapons by hammering and chipping this metal. Because this useful metal came from the heavens, early human beings probably did not associate it with the iron found in the ground. It is likely that metallic iron was found in the ashes of fires that had been built on outcroppings of red iron ore, also called iron oxide. The red ore was called paint rock, and fires were built against banks of ore that had been exposed to wind and weather. Iron ore is found worldwide on each of the seven continents.

Smelting iron, a primitive direct reduction method of separating iron from its ore using a charcoal forge or furnace, probably began in China and India and then spread westward to the area around the Black Sea. Unlike copper ores, which yielded molten copper in these furnaces, iron would not melt at temperatures below 2,799°F (1,537°C) and the highest temperature that could be reached in these primitive smelters appears to have been about 2,192°F (1,200°C). Iron ore subjected to that temperature does not melt, but instead results in a spongy mass (called sponge iron) mixed with impurities called slag. The ironworker removed this spongy mass from the furnace and then squeezed the slag out of it by hammering. This wrought iron had less tendency to corrode and had a fibrous quality from the stringers of slag which gave it a certain toughness.

The Hittites, an ancient tribe living in Asia Minor and northern Syria, produced iron starting about 2500 BC. The Chalybes, a subject tribe of the Hittites, invented a cementation process about 1400 BC to make the iron stronger. The iron was hammered and heated in contact with charcoal. The carbon absorbed from the charcoal produced a much harder iron. With the fall of the Hittite empire, the various tribes scattered, carrying the knowledge of smelting and the cementation process with them to Syria, Egypt, and Macedonia. Widespread use of iron for weapons and tools began about 1000 BC, marking the beginning of the Iron Age.

The ancient Egyptians learned to increase smelting temperature in the furnace by blowing a stream of air into the fire using blowpipes and bellows. Around 500 BC, Greek soldiers used iron weapons that had been hardened by quenching the hot metal in cold water. The Romans learned to reheat the iron after quenching in a process called tempering, which made the iron less brittle.

During the Middle Ages, from about AD 500 to 1500, the old methods of smelting and cementation continued. Early blacksmiths made chain mail, weapons, nails, horseshoes, and tools such as iron plows. The Stückofen, a furnace first developed by the Romans, was made larger and higher for better air draft. This was a forerunner of the modern blast furnace. Waterwheels came into use for iron making between 1200 and 1350. The waterwheels converted the energy of swift stream currents into work that moved air bellows, forcing blasts of air into the furnace. The resulting higher temperature melted the iron, which was then formed into pigs (so named because as the pig iron was cast, the runners and series of ingots resembled pigs suckling their mother) of cast iron. As time progressed, these early blast furnaces were built larger and better, reaching 30 ft (9 m) in height and able to operate continuously for weeks at a time.

About 1500, iron makers faced wood shortages that affected their source of charcoal. Increased warfare and the resulting demand for more iron weapons forced iron makers to use coal as an alternate source of fuel. A major problem with coal was that it contained impurities such as sulfur and phosphorus that tended to make the iron brittle. In 1709, Abraham Darby of England used coke, the residue left after soft coal was heated to remove impurities, to successfully smelt pig iron. Benjamin Huntsman, of England, invented crucible cast steel around 1740. A clay crucible, or cup, of iron ore was placed in a furnace andwhenmolten, wascast. The resulting cast steel was of very high purity since the molten steel did not come into contact with the fuel. In 1784, another improvement was made by Henry Cort, an English iron maker, who invented the puddling of molten pig iron. Puddling involved stirring air into the liquid iron by a worker who stood near the furnace door. A reverberatory furnace was used in which the coal was separated from the iron to prevent contamination. After the pig iron had been converted into wrought iron, it was run through a rolling mill, which used grooved rollers to press out the remaining slag. Corts rolling mill was patented in 1783 and could make iron bars about 15 times faster than the old hammer method.

From 1850 to 1865, great advances were made in iron and steel processing. Steel was gaining more popularity than iron beginning around 1860 as less expensive manufacturing methods were discovered and greater quantity and quality were being produced.

William Kelly of the United States, and Henry Bessemer of England, both working independently, discovered the same method for converting iron into steel. They subjected molten pig iron to a blast of air, which burned out most of the impurities and the carbon contained in the molten iron acted as its own fuel. Kelly built his first converter in 1851 and received an American patent in 1857. He also went bankrupt the same year and the method finally became known as the Bessemer process. In 1856, Bessemer completed his vertical converter and, in 1860, he patented a tilting converter, which could be tilted to receive molten iron from the furnace and also to pour out its load of liquid steel. The Bessemer converter made possible the high tonnage production of steel for ships, railroads, bridges, and large buildings in the midnineteenth century. However, the steel was brittle from the many impurities that remained, especially phosphorus and sulfur, and by the oxygen from the air blast. English metallurgist Robert F. Mushet discovered in 1856 that adding an iron alloy (spiegeleisen) containing manganese would remove the oxygen. Around 1875, Sidney G. Thomas and Percy Gilchrist, two English chemists, discovered that by adding limestone to the converter they could remove the phosphorus and most of the sulfur.

In England, another new furnace was introduced in 1861 by two brothers, William and Frederick Siemans. This was the openhearth furnace, also known as the regenerative openhearth because the outgoing hot gases were used to preheat the incoming air. Pierre Émile Martin of France improved the process in 1864 by adding scrap steel to the molten iron to speed purification. During this period, hardened alloy steels came into commercial use; Mushet made a high carbon steel in 1868 that gave tools longer life in France; a chromium steel alloy was produced in 1877; and a nickel steel alloy in 1888. Englishman Sir Robert Hadfield discovered in 1882 how to harden manganese tool steel by heating it to a high temperature and then quenching it in water.

Around 1879, the electric furnace was developed by William Siemans. This furnace was used very little prior to 1910 because of the high electrical costs and the poor quality of electrodes used to produce the arc for melting.

The openhearth furnace was the most popular method of steel production until the early 1950s. Pure oxygen became more economical to produce in large quantities and, in 1954, the first basic oxygen process facility opened for production in the United States. Today, most of the worlds steel is made by either a basic oxygen furnace or an electric furnace.

Raw materials

The ores used in making iron and steel are iron oxides, which are compounds of iron and oxygen. The major iron oxide ores are hematite, which is the most plentiful, limonite, also called brown ore, taconite, and magnetite, a black ore. Magnetite is named for its magnetic property and has the highest iron content. Taconite, named for the Taconic Mountains in the northeastern United States, is a lowgrade, but important ore, which contains both magnetite and hematite.

Ironmaking furnaces require at least a 50% iron content ore for efficient operation. In addition, the cost of shipping iron ores from the mine to the smelter can be greatly reduced if the unwanted rock and other impurities can be removed prior to shipment. This requires that the ores undergo several processes called beneficiation. These processes include crushing, screening, tumbling, floatation, and magnetic separation. The refined ore is enriched to over 60% iron by these processes and is often formed into pellets before shipping. Taconite ore powder, after beneficiation, is mixed with coal dust and a binder and rolled into small balls in a drum pelletizer where it is, then, baked to hardness. About two tons of unwanted material is removed for each ton of taconite pellets shipped.

The three raw materials used in making pig iron (which is the raw material needed to make steel) are the processed iron ore, coke (residue left after heating coal in the absence of air, generally containing up to 90% carbon) and limestone (CaCO3) or burnt lime (CaO), which are added to the blast furnace at intervals, making the process continuous. The limestone or burnt lime is used as a fluxing material that forms a slag on top of the liquid metal. This has an oxidizing effect on the liquid metal underneath that helps to remove impurities. Approximately two tons of ore, one ton of coke, and a half ton of limestone are required to produce one ton of iron.

There are several basic elements which can be found in all commercial steels. Carbon is a very important element in steel since it allows the steel to be hardened by heat treatment. Only a small amount of carbon is needed to produce steel: up to 0.25% for low carbon steel, 0.25 to 0.50% for medium carbon steel, and 0.50 to 1.25% for high carbon steel. Steel can contain up to 2% carbon, but over that amount it is considered to be cast iron, in which the excess carbon forms graphite. The metal manganese is used in small amounts (0.03 to 1.0%) to remove unwanted oxygen and to control sulfur. Sulfur is difficult to remove from steel and the form it takes in steel (iron sulfide, FeS) allows the steel to become brittle, or hotshort, when forged or rolled at elevated temperatures. Sulfur content in commercial steels is kept below 0.05%. A small quantity of phosphorus (usually below 0.04%) is present, which tends to dissolve in the iron, slightly increasing the strength and hardness. Phosphorus in larger quantities reduces the ductility or formability of steel and can cause the material to crack when cold worked in a rolling mill, making it coldshort. Silicon is another element present in steel, usually between 0.5 to 0.3%. The silicon dissolves in the iron and increases the strength and toughness of the steel without greatly reducing ductility. The silicon also deoxidizes the molten steel through the formation of silicon dioxide (SiO2), which makes for stronger, less porous castings. Another element that plays an important part in the processing of steel is oxygen. Some large steel mills have installed their own oxygen plants, which are located near basic oxygen furnaces. Oxygen injected into the mix, or furnace charge, improves and speeds up steel production.

Steel can be given many different and useful properties by alloying the iron with other metals such as chromium, molybdenum, nickel, aluminum, cobalt, tungsten, vanadium, and titanium, and with nonmetals such as boron and silicon.

Manufacturing processes

Most steel is produced using one of four methods: Bessemer converters, openhearth furnaces, basic oxygen furnaces, and electric furnaces. The basic oxygen process is the most efficient, while the Bessemer and openhearth methods have become obsolete. Electric furnaces are used to produce high quality steels from selected steel scrap, lime, and mill scale (an iron oxide that forms on the surface of hot steel and falls off as black scale).

Until 1909, most steel made in the United States came from Bessemer converters. A Bessemer converter looks like a huge pearshaped pot and can hold anywhere from 5 to 25 tons. It is balanced on axles so that its open top can be tilted one way to take a charge and the other way to pour out steel. After the converter is charged with hot metal, it is swung to the upright position. Air is then blown through holes in its bottom at a typical rate of 30,000 cubic feet per minute. Sparks and thick, brown smoke pour from the converters mouth as the oxygen in the blow combines with the iron, silicon, and manganese to form slag. Then 30ft (9m) flames replace the smoke as the oxygen combines with the carbon fuel and burns. The whole process took less than 15 minutes. Unfortunately, the blowing air contained contaminants (such as nitrogen) and also removed some desirable elements such as carbon and manganese. This was solved by adding the necessary elements back into the converter after the blow. Because of stricter air pollution regulations and more efficient processes, the Bessemer converter is no longer used in countries with such safeguards.

From 1909 until the 1960s, the openhearth process was the most popular method of steel production. Openhearth furnaces got their name from a shallow area called a hearth that is exposed to a blast of flames that alternately sweeps across the hearth from one side for a period of time and then to the side of the furnace. To make a heat, or one batch of steel, pig iron, limestone, and scrap steel, are initially charged, or loaded, into the hearth. These materials are heated for about two hours at temperatures from 2,700 to 3,000°F (1,482 to 1,649°C) until they begin to fuse. Then the furnace is charged with many tons of molten pig iron. Scrap is placed in the furnace with a charging machine that usually serves a series of openhearth furnaces in a single building. Other elements, such as fluxing agents, carbon (usually in the form of anthracite coal pellets), and alloying materials, are then added to improve the steel. These elements can be added either in the furnace charge, the melt or bath, ladle, or the ingot molds to meet the desired chemical composition of the finished steel or to eliminate or counteract the effect of oxides or other impurities. Fluxing agents (primarily lime, added in the form of either limestone or burnt lime and supplemented by magnesia, MgO, and lime from the furnace bottom and sides) melt and combine with the impurities to form slag at the top of the melt that is poured off into a separate slag pot. Mill scale, a form of iron oxide (Fe3O4), is used to reduce carbon content. Aluminum ferrosilicon is added if the steel is to be killed. A killed steel is one that has been deoxidized to prevent gas evolution in the ingot mold, making a more uniform steel. Rimmed steel is steel that has not been deoxidized and gas pockets and holes from free oxygen form in the center of the ingot while the rim near the surface of the ingot is free of defects. Rolling processes are used in later operations to remove these defects. Semikilled steels are a compromise between rimmed and killed steels and are mainly limited to steels to be rolled into sheet bar, plate, and structural sections. The quantity of deoxidizers used must be closely controlled to allow a limited evolution of gas from the carbonoxygen reaction.

When the contents of the heat are acceptable and the temperature is correct, the furnace is tapped and the molten metal is poured into a ladle. An openhearth furnace is tapped through a hole in the furnaces bottom. A heat is refined into steel during an 8712 hour timeperiod. Oxygen released from the ore and additional injected oxygen combines with carbon in the molten pig iron to form carbon gases. These, along with any additional gases from the burned fuel, are used to heat incoming air and this is why the openhearth process is sometimes called the regenerative openhearth.

The basic oxygen converter resembles a Bessemer converter. It receives materials from the top and tips to pour off the finished steel into ladles. The main element is a watercooled oxygen lance, which is placed into the top of the converter after it is charged with scrap steel, molten pig iron, and fluxing agents. The lance, lowered to within a few feet of the charge, directs highpurity oxygen at supersonic speeds into the molten metal. This burns out the impurities and, also, enables the making of steel with a minimum amount of nitrogen, which can make steel brittle. The oxidation of the carbon and impurities causes a violent rolling agitation, which brings all the metal into contact with the oxygen stream. The furnace ladle is, first, tipped to remove slag and, then, rotated to pour molten steel into a ladle. The speed and efficiency of the oxygen process has had a significant impact on the steel industry. An oxygen converter can produce a heat of quality steel in 3045 minutes. An openhearth furnace without an oxygen lance requires as much as eight hours to produce steel of a similar quality. Recent advances in refractory brick, the insulating ceramics that protect vessels from the hot steel, have allowed injection of oxygen from the bottom of a vessel without a large complicated lance. This allows for a much more efficient use of the oxygen and can lower the capital costs in constructing a basic oxygen facility, especially if the building and cranes of a retired openhearth facility is used.

Highquality carbon and alloy steels, such as tool and stainless steels, are produced in electric arc furnaces. These furnaces can make 150200 tons (136181 tonnes) in a single heat in as little as 90 minutes. The charge is melted by the arcing between carbon electrodes and high quality scrap steel. Some of the electrodes can be 2 ft (0.6 m) in diameter and 24 ft (7.2 m) long. The entire electric furnace is tilted during a tapping operation in which molten steel flows into a waiting ladle. Electric furnaces are the most competitive where lowcost electricity is available and where very little coal or iron ore is found.

After the steel in the ladle has cooled to the desired temperature, the ladle is moved by a traveling crane to either a pouring platform for ingot production or to a continuous caster. Ingots may be square, rectangular, or round and weigh anywhere from a few hundred pounds to 40 tons (36 tonnes). A small amount of steel is cast directly into the desired shape in molds of fine sand and fireclay. Small rail cars carrying a series of heavy cast iron ingot molds wait alongside the pouring platform. The steel is teemed, or poured, into the molds through a fireclay nozzle in the bottom of the ladle. After the steel in the molds has solidified, the cars are pulled under a stripping crane. The cranes plunger holds down the ingot top as its jaws lift the mold from the glowing hot ingot. The ingots are then taken to soaking pits for further processing.

An underground soaking pit is used to heat the steel ingots to a uniform temperature throughout. The ingots must be the same temperature throughout so that they can be easily plastically deformed and to prevent damage to the heavy machinery of the mills. The jaws of the crane clamp onto the ingots and lower them into the open soaking pits. The roof of the pits is then closed and burning oil or gas heats the ingots to about 2,200°F (1,204°C). After soaking in the pits for several hours, the ingots are then lifted out by crane and transported by rail to the blooming and slabbing mills.

The mechanical working of steel, such as rolling, forging, hammering, or squeezing, improves it in several ways. Cavities and voids are closed, harmful concentrations of nonmetallic impurities are broken up and more evenly disbursed, and the grain structure is refined to produce a more homogeneous or uniform product. Some ingots are sent directly to a universal plate mill for immediate rolling of steel plates. Most ingots, however, are sent to semifinishing mills (also known as slabbing or blooming mills) for reduction and shaping into slabs, blooms, or billets. A slab is generally a large flat length of steel wider than a bloom, a bloom is a length of steel either square or rectangular with a crosssectional area larger than 36 in (90 cm), and a billet is generally two to five inches square, although some billets can be round or rectangular. The exact sizes of slabs, blooms, and billets depend on the requirements of further processing.

In slabbing and blooming mills, the steel ingot is gradually squeezed between heavy rolls. To make billets, the steel is first shaped into blooms, then further reduced in a billet mill. Each time the ingot is forced through the rolls, it is further reduced in one dimension. Blooming mills can be classified as either twohigh or threehigh, depending on the number of rolls used. The two rolls of the twohigh mill can be reversed so that the ingot is flattened and lengthened as it passes back and forth between the rolls. The top and bottom rolls of the threehigh mill turn in one direction while the middle roll turns in the opposite direction. The ingot is flattened first between the bottom and middle rolls and ends up on a runout table. The table rises and the steel is then fed through the top and middle rolls. The continuous, or crosscountry, mill is a third type of blooming mill. This mill has a series of twohigh rolls. As many as 15 passes may be required to reduce an ingot 21 in2 (135 cm2) in crosssection to a bloom 8 in2 (52 cm2) in cross section. The two and threehigh blooming mills roll the top and bottom of the steel in every pass. After one or two passes, mechanical manipulators on the runout table turn the steel to bring the side surfaces under the rolls for a uniform material. After the steel is rolled, the uneven ends are sheared off, and the single long piece is cut into shorter lengths. The sheared off ends are reused as scrap. Most of the rolls used in these mills are horizontal, but there are also vertical rolls that squeeze the blooms or slabs from the sides. Highpressure water jets are used to remove mill scale that forms on the surface. Surface defects on the finished blooms and slabs are burned off, or scarfed, with an oxygen flame. The hot lengths of steel are moved from one station to another on a series of roller conveyors. Workers in an overhead glassenclosed room called a pulpit automatically control the mill operations. The slabs, blooms, and billets are then taken to finishing mills where they are formed into special shapes and forms such as bars, beams, plates, and sheets. The steel is still not completely finished but it is closer to the form in which it will eventually be used in manufactured goods. Blooms and billets are finished into rails, wire rods, wires, bars, tubes, seamless pipe, and structural shapes such as I and H beams. Slabs are converted into plates, sheets, strips, and welded pipe.

After they are hot rolled, steel plates or shapes undergo further processing such as cleaning and pickling by chemicals to remove surface oxides, cold rolling to improve strength and surface finish, annealing (also known as stress relieving), and coating (galvanizing or aluminizing) for corrosion resistance.

Continuous, or strand, casting of steel eliminates the need to produce ingots and the use of soaking pits. In addition to costing less, continuously cast steels have more uniform compositions and properties than ingot cast steels. Continuous casting of steel produces an endless length of steel, which is cut into long slabs or blooms that are ready for shaping in rolling mills. Molten steel is poured into the top of a continuous casting machine and is cooled by passing through a watercooled mold. Pinch rolls draw the steel downward as it solidifies. Water sprays along the travel path of the solidifying metal provide additional cooling. The thickness of the steel strand is typically 10 in (25 cm) but new developments have reduced this thickness to 1 in (2.5 cm) or less. The thinner strand reduces the number of rolling operations required and improves the economy of the overall process. Some continuous cast machines bend the steel while it is still hot and flexible so that it comes out of the bottom in a horizontal position. Other machines cut the steel into sections while it is still in a vertical position. The continuous cast process has become the most economical method to produce large quantities of conventional steels. Small heats of alloy and specialty steels are still cast in ingots because the small size makes the continuous cast process impractical.

Some steel shapes are produced from powder. There are several chemical, electrochemical, and mechanical ways to make steel powder. One method involves improving the ore by magnetically separating the iron. A ball mill is then used to grind the ore into a powder that is then purified with hot hydrogen. This powder, under heat and pressure, is pressed into molds to form irregularly shaped objects; objects that would be hard to form any other way.

Quality control

To specify the various physical and mechanical properties of the finished product, various tests, both destructive and nondestructive, are performed. Metallurgical, hardness, hardenability, tension, ductility, compression, fatigue, impact, wear, corrosion, creep, machinability, radiography, magnetic particle, ultrasonic, and eddy current are some of the major tests that are performed by quality control personnel.

Metallurgical testing is used to determine the quality of steel by analyzing the microstructure of a sample under a microscope. A cross section of a sample is first highly polished and then examined at a magnification from 100 to 500 diameters. The microstructure of steel consists of grains of different compositions and sizes. Generally, a sample of steel with fine grains is tougher than one with large grains. Different characteristics are produced through alloying the steel with other substances. It is possible to determine grain size and the size, shape, and distribution of various phases and inclusions (nonmetallic material) which have a great effect on the mechanical properties of the metal. Some grains are made of ferrite, or pure metallic iron; graphite, a crystal form of carbon; pearlite, an alloy of iron of carbon; cementite, also called iron carbide, a hard compound of iron and carbon and other carbideforming elements; austenite, a solid solution of carbon in gamma iron, a nonmagnetic form of iron; and martensite, an extremely hard constituent of steel produced by heattreating. The sample can also be etched to make visible many structural characteristics of the metal or alloy by a preferential attack on the different constituents. The microstructure will reveal the mechanical and thermal treatment of the metal, and it may be possible to predict its expected behavior under a given set of conditions.

Hardness is not a fundamental property of a material, but is related to its elastic and plastic properties. The hardness value obtained in a particular test serves only as a comparison between materials or treatments. The test procedure and sample preparation are simple and the results may be used in estimating other mechanical properties. Rockwell and Brinell are two popular hardness tests that are widely used for inspection and control. These tests are usually performed by impressing into the test specimen, which is resting on a rigid platform, an indenter of fixed and known geometry, under a known static load.

Hardenability is a property that determines the depth and distribution of hardness induced by quenching. The standardized test used is called the endquench hardenability test, also known as the Jominy test. A 1in (2.54 cm) round 4in (10 cm) long sample is heated uniformly to the austenitizing temperature (this temperature depends on the material composition, ranging from 1,500 to 1,900°F [816 to 1,038°C]). The sample is removed from the furnace and placed on a fixture. Then, a jet of water contacts the bottom face of the sample. After ten minutes on the fixture, the sample is removed and two flat parallel surfaces are ground on the sample. Rockwell hardness readings are taken along the ground surfaces at certain intervals from the quenched end. The results are expressed as a curve of hardness values versus distance from the quenched end. Plain carbon steels tend to be hard on the surface, near the quenched end, but remain relatively soft at the core, or further away from the quenched end. Alloyed steels, in general, have an increased depth of hardenability which is one of the main advantages of using alloyed steels.

Next to the hardness test, the tensile test is the most frequently performed test to determine certain mechanical properties. A specifically prepared tensile sample is placed in the heads of a testing machine and an axial load is placed on the sample through a hydraulic loading system. The tensile test is used to determine several important material properties such as yield strength, where the material starts to exhibit plastic or permanent deformation, and the ultimate tensile or breaking strength.

Ductility of a material is indicated by the amount of deformation that is possible until fracture and can be determined by measuring elongation and reduction in area of a tensile sample that has been tested to failure.

Compression tests are performed on small cylinders, blocks, or strips to determine the ability of a material to undergo large plastic deformations (a mechanical property also known as malleability) and its limits. Stressstrain relations determined from this testing are used to predict the pressures and forces arising in industrial forming operations such as rolling, forging, or extrusion. Samples are placed between anvils or pressure plates and are compressed (friction is also a factor to consider as the material slides sidewise over the anvils).

The fatigue test is used to determine the behavior of materials when subjected to repeated or fluctuating loads. It is used to simulate stress conditions developed in materials under service conditions. The fatigue potential, or endurance limit, is determined by counting the number of cycles of stress, applied first in one direction and then another, to which the metal can be subjected before it breaks. Fatigue tests can be used to study the material behavior under various types and ranges of fluctuating loads and also the effect of corrosion, surface conditions, temperature, size, and stress concentrations.

Impact tests are used to determine the behavior of materials when subjected to high rates of loading, usually in bending, tension, or torsion. The quantity measured is the energy absorbed in breaking the specimen in one blow, two such tests are called the Charpy and the Izod, which use notched bar specimens. A swinging pendulum of fixed weight raised to a standard height is used to strike the specimen. Some of the energy of the pendulum is used to rupture the specimen so that the pendulum rises to a lower height than the standard height. The weight of the pendulum times the difference in heights indicates the energy absorbed by the specimen, usually measured in footpounds.

Wear resistance is represented by few standardized tests because of its complex nature. One test is the pin on disk method, where a pin is moved against a disk of the test material. Usually, wear testing is application specific and the equipment is designed to simulate actual service conditions.

Corrosion involves the destruction of a material by chemical, electrochemical, or metallurgical interaction between the environment and the material. Various types of environmental exposure testing is done to simulate actual use conditions, such as salt bath immersion testing. Zinc coating, or galvanizing, is commonly applied to sheet and structural steel used for outdoor applications to protect against corrosion.

Creep tests are used to determine the continuing change in the deformation of a material at elevated temperatures when stressed below the yield strength. This is important in the design of parts exposed to elevated temperatures. Creep may be defined as a continuing slow plastic flow under constant load conditions. A creep test is a tension test run at a constant load and temperature. The percent elongation of the sample is measured over time.

Machinability is the ease with which a metal may be machined. Many factors are considered in arriving at machinability ratings. Some of the more important factors are the rate of metal removal, quality of the finished surface, and tool life. Machinability ratings are expressed as a percentage, in comparison with AISI 1112 steel, which is rated at 100%. Metals which are more difficult to machine have a rating of less than 100% while metals which machine easily have a rating more than 100%.

Radiography of metals involves the use of x rays or gamma rays. The shortwavelength electromagnetic rays are capable of going through large thickness of metal and are typically used to nondestructively test castings and welded joints for shrinkage voids and porosity.

Magnetic particle inspection (also called Magnaflux) is a method of detecting cracks, tears, seams, inclusions, and similar discontinuities in iron and steel. This method will detect surface defects too fine to be seen by the naked eye and will also detect discontinuities just below the surface. The sample is magnetized and, then, covered with a fine iron powder. The presence of an imperfection is indicated by a pattern that assumes the approximate shape of the defect.

Ultrasonic testing utilizes sound waves above the audible range with a frequency of one to five million Hz (cycles per second). Ultrasonics allow for fast, reliable, nondestructive testing which employs electronically produced highfrequency sound waves to penetrate metals and other materials at speeds of several thousand feet per second. If there is a flaw in the path of the ultrasonic wave, part of the energy will be reflected and the signal received by a receiving transducer will be reduced. Ultrasonic inspection is used to detect and locate such defects as shrinkage voids, internal cracks, porosity, and large nonmetallic inclusions.

Eddy current inspection is used to inspect electrically conducting materials for defects and variations in composition. Eddy current testing involves placing a varying magnetic field (which is produced by connecting alternating current to a coil) near an electrically conducting sample. Eddy currents are induced in the sample, which then produces a magnetic field of its own. A detection unit measures this new magnetic field and converts the signal into a voltage, which can be read on a meter for comparison. Properties such as hardness, alloy composition, chemical purity, and heat treat condition influence the magnetic field and may be measured through the use of eddy current testing.

Byproducts and waste

There are a number of waste byproducts from the steel making process. Mine tailings from the ore beneficiation process are returned to the mining site. Growing vetches (a species of plant valuable for fodder), grasses, and trees on some of these barren landscapes has been a project of biologists and foresters. Gases that are given off from the coke ovens, blast furnaces, and steel furnaces are largely recovered for reuse. After use in iron and steelmaking, most slags are used for other purposes such as railroad ballast and road fill, an ingredient in cement or blocks, insulating material, or fertilizer.

The future

In the future there will be many new developments involving computer controls and automation that will improve economy and quality and lower energy consumption and pollution. More automation will also lead to more robots replacing humans in hazardous areas. Computers can be used to control several rolling mills operating as a continuous unit. The decreasing material thickness can be maintained automatically as it passes through the various mills to produce a uniform final sheet. Continued research and development is ongoing to connect continuous casting machines with rolling mills to provide a single continuous process from molten metal to the final product. This will produce energy and cost savings because the material would not have to be reheated for processing, and result in a higher quality end product.

The use of 100% scrap in charging electric furnaces has cut the dependence on pig iron and ores, and has resulted in the development of more small steel mills, also called minimills, which can be located far from natural resources to serve wider geographical areas.

More net steel shapes will be formed using powder metallurgy as direct reduction processes produce steel powders directly from iron ore, bypassing the blast furnace and making difficult shapes easier to form.

In 2005, according to the International Iron and Steel Institute, the companies that produced the most steel worldwide were (in millions of metric ton of crude steel): Mittal Steel (63.0, the Netherlands); Arcelor (46.7, Luxembourg); Nippon Steel (32.0, Japan); POSCO (30.5, South Korea); and JFE (29.9, Japan). (Of note, Arcelor and Mittal Steel merged in 2006 to form Arcelor Mittal, now the worlds largest manufacturer of steel.)

See also Metal production; Metallurgy.

Resources

BOOKS

Byars, Mel. Design in Steel. London, UK: Laurence King, 2003.

Ghosh, Ahindra. Secondary Steelmaking: Principles and Applications. Boca Raton, FL: CRC Press, 2001.

Kalpakjian, Serope. Manufacturing Processes for Engineering Materials. 4th ed. Upper Saddle River, NJ: Prentice Hall, 2003.

Walsh, Ronald A. New York: McGrawHill Machining and Metalworking Handbook. McGrawHill, Inc., 2006.

PERIODICALS

ASM Publication. ASM Metals Handbook Vol. 1: Properties and Selection: Irons, Steels, and High Performance Alloys

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Steel

Steel

Steel is the most widely used of all metals, with uses ranging from concrete reinforcement in highways and in high-rise buildings to automobiles, aircraft , and vehicles in space. Steel is iron combined or alloyed with other metals or nonmetals such as carbon . Steel is more ductile (able to deform without breakage) and durable than cast iron and is generally forged, rolled, or drawn into various shapes.

Since the beginning of the Iron Age, about 1000 b.c., mankind's progress has been greatly dependent on tools and equipment made with iron. The iron tools were then used to fashion many other much needed goods. Eventually, this was followed by the Industrial Revolution , a period of change beginning in the middle of the eighteenth century in England where extensive mechanization of production systems resulted in a shift from home manufacturing and farms to large-scale factory production. Machine tools and other equipment made of iron and steel significantly changed the economy of both farm and city.

The history of iron and steel began at least 6,000 years ago. It is speculated that early mankind first learned to use iron from fallen meteorites. Many meteorites are composed of iron and nickel, which forms a much harder metal than pure iron. The ancients could make crude tools and weapons by hammering and chipping this metal. Because this useful metal came from the heavens, early human beings probably did not associate it with the iron found in the ground. It is likely that metallic iron was found in the ashes of fires that had been built on outcroppings of red iron ore , also called iron oxide. The red ore was called paint rock, and fires were built against banks of ore that had been exposed to wind and weather . Iron ore is found worldwide on each of the seven continents.

Smelting iron, a primitive direct reduction method of separating iron from its ore using a charcoal forge or furnace, probably began in China and India and then spread westward to the area around the Black Sea. Unlike copper ores, which yielded molten copper in these furnaces, iron would not melt at temperatures below 2,799°F (1,537°C) and the highest temperature that could be reached in these primitive smelters appears to have been about 2,192°F (1,200°C). Iron ore subjected to that temperature does not melt, but instead results in a spongy mass (called "sponge" iron) mixed with impurities called slag. The iron worker removed this spongy mass from the furnace and then squeezed the slag out of it by hammering. This "wrought" iron had less tendency to corrode and had a fibrous quality from the stringers of slag which gave it a certain toughness.

The Hittites, an ancient tribe living in Asia Minor and northern Syria, produced iron starting about 2500 b.c. The Chalybes, a subject tribe of the Hittites, invented a cementation process about 1400 b.c. to make the iron stronger. The iron was hammered and heated in contact with charcoal. The carbon absorbed from the charcoal produced a much harder iron. With the fall of the Hittite empire, the various tribes scattered, carrying the knowledge of smelting and the cementation process with them to Syria, Egypt, and Macedonia. Widespread use of iron for weapons and tools began about 1000 b.c., marking the beginning of the Iron Age.

The ancient Egyptians learned to increase smelting temperature in the furnace by blowing a stream of air into the fire using blowpipes and bellows. Around 500 b.c., the Greek soldiers used iron weapons which had been hardened by quenching the hot metal in cold water . The Romans learned to reheat the iron after quenching in a process called tempering which made the iron less brittle.

During the Middle Ages, from about a.d. 500 to a.d. 1500, the old methods of smelting and cementation continued. Early blacksmiths made chain mail, weapons, nails, horseshoes, and tools such as iron plows. The Stückofen, a furnace first developed by the Romans, was made larger and higher for better air draft. This was a forerunner of the modern blast furnace. Waterwheels came into use for ironmaking between a.d. 1200 and a.d. 1350. The waterwheels converted the energy of swift stream currents into work that moved air bellows, forcing blasts of air into the furnace. The resulting higher temperature melted the iron, which was then formed into "pigs" (so named because as the pig iron was cast, the runners and series of ingots resembled pigs suckling their mother) of cast iron. As time progressed, these early blast furnaces were built larger and better, reaching 30 ft (9 m) in height and able to operate continuously for weeks at a time.

About a.d. 1500, ironmakers faced wood shortages that affected their source of charcoal. Increased warfare and the resulting demand for more iron weapons forced ironmakers to use coal as an alternate source of fuel. A major problem with coal was that it contained impurities such as sulfur and phosphorus that tended to make the iron brittle. In 1709 Abraham Darby of England used "coke," the residue left after soft coal was heated to remove impurities, to successfully smelt pig iron. Crucible cast steel was invented around 1740 by Benjamin Huntsman of England. A clay crucible, or cup, of iron ore was placed in a furnace and when molten, was cast. The resulting cast steel was of very high purity since the molten steel did not come into contact with the fuel. In 1784 another improvement was made by Henry Cort, an English ironmaker, who invented the puddling of molten pig iron. Puddling involved stirring air into the liquid iron by a worker who stood near the furnace door. A reverberatory furnace was used in which the coal was separated from the iron to prevent contamination . After the pig iron had been converted into wrought iron, it was run through a rolling mill which used grooved rollers to press out the remaining slag. Cort's rolling mill was patented in 1783 and could make iron bars about 15 times faster than the old hammer method.

From 1850 to 1865, great advances were made in iron and steel processing. Steel was gaining more popularity than iron beginning around 1860 as less expensive manufacturing methods were discovered and greater quantity and quality were being produced.

William Kelly of the United States, and Henry Bessemer of England, both working independently, discovered the same method for converting iron into steel. They subjected molten pig iron to a blast of air which burned out most of the impurities and the carbon contained in the molten iron acted as its own fuel. Kelly built his first converter in 1851 and received an American patent in 1857. He also went bankrupt the same year and the method finally became known as the Bessemer process. In 1856 Bessemer completed his vertical converter, and in 1860 he patented a tilting converter which could be tilted to receive molten iron from the furnace and also to pour out its load of liquid steel. The Bessemer converter made possible the high tonnage production of steel for ships, railroads, bridges , and large buildings in the mid-nineteenth century. However, the steel was brittle from the many impurities which remained, especially phosphorus and sulfur, and by the oxygen from the air blast. An English metallurgist, Robert F. Mushet, discovered in 1856 that adding an iron alloy (spiegeleisen) containing manganese would remove the oxygen. Around 1875, Sidney G. Thomas and Percy Gilchrist, two English chemists, discovered that by adding limestone to the converter they could remove the phosphorus and most of the sulfur.

In England, another new furnace was introduced in 1861 by two brothers, William and Frederick Siemans. This was the open-hearth furnace, also known as the regenerative open-hearth because the outgoing hot gases were used to preheat the incoming air. Pierre Émile Martin of France improved the process in 1864 by adding scrap steel to the molten iron to speed purification. During this period hardened alloy steels came into commercial use; Mushet made a high carbon steel in 1868 which gave tools longer life in France, a chromium steel alloy was produced in 1877 and a nickel steel alloy in 1888. An Englishman, Sir Robert Hadfield, discovered in 1882 how to harden manganese tool steel by heating it to a high temperature and then quenching it in water.

Around 1879, the electric furnace was developed by William Siemans. This furnace was used very little prior to 1910 because of the high electrical costs and the poor quality of electrodes used to produce the arc for melting.

The open-hearth furnace was the most popular method of steel production until the early 1950s. Pure oxygen became more economical to produce in large quantities and in 1954 the first basic oxygen process facility opened for production in the United States. Today, most of the world's steel is made by either a basic oxygen furnace or an electric furnace.


Raw materials

The ores used in making iron and steel are iron oxides, which are compounds of iron and oxygen. The major iron oxide ores are hematite, which is the most plentiful, limonite, also called brown ore, taconite, and magnetite, a black ore. Magnetite is named for its magnetic property and has the highest iron content. Taconite, named for the Taconic Mountains in the northeastern United States, is a low-grade, but important ore, which contains both magnetite and hematite.

Ironmaking furnaces require at least a 50% iron content ore for efficient operation. Also, the cost of shipping iron ores from the mine to the smelter can be greatly reduced if the unwanted rock and other impurities can be removed prior to shipment. This requires that the ores undergo several processes called "beneficiation." These processes include crushing, screening, tumbling, floatation, and magnetic separation. The refined ore is enriched to over 60% iron by these processes and is often formed into pellets before shipping. Taconite ore powder, after beneficiation, is mixed with coal dust and a binder and rolled into small balls in a drum pelletizer where it is then baked to hardness. About two tons of unwanted material is removed for each ton of taconite pellets shipped.

The three raw materials used in making pig iron (which is the raw material needed to make steel) are the processed iron ore, coke (residue left after heating coal in the absence of air, generally containing up to 90% carbon) and limestone (CaCO3) or burnt lime (CaO), which are added to the blast furnace at intervals, making the process continuous. The limestone or burnt lime is used as a fluxing material that forms a slag on top of the liquid metal. This has an oxidizing effect on the liquid metal underneath which helps to remove impurities. Approximately two tons of ore, one ton of coke, and a half ton of limestone are required to produce one ton of iron.

There are several basic elements which can be found in all commercial steels. Carbon is a very important element in steel since it allows the steel to be hardened by heat treatment. Only a small amount of carbon is needed to produce steel: up to 0.25% for low carbon steel, 0.25-0.50% for medium carbon steel, and 0.50-1.25% for high carbon steel. Steel can contain up to 2% carbon, but over that amount it is considered to be cast iron, in which the excess carbon forms graphite. The metal manganese is used in small amounts (0.03-1.0%) to remove unwanted oxygen and to control sulfur. Sulfur is difficult to remove from steel and the form it takes in steel (iron sulfide, FeS) allows the steel to become brittle, or hot-short, when forged or rolled at elevated temperatures. Sulfur content in commercial steels is usually kept below 0.05%. A small quantity of phosphorus (usually below 0.04%) is present, which tends to dissolve in the iron, slightly increasing the strength and hardness. Phosphorus in larger quantities reduces the ductility or formability of steel and can cause the material to crack when cold worked in a rolling mill, making it cold-short. Silicon is another element present in steel, usually between 0.5-0.3%. The silicon dissolves in the iron and increases the strength and toughness of the steel without greatly reducing ductility. The silicon also deoxidizes the molten steel through the formation of silicon dioxide (SiO2), which makes for stronger, less porous castings. Another element that plays an important part in the processing of steel is oxygen. Some large steel mills have installed their own oxygen plants, which are located near basic oxygen furnaces. Oxygen injected into the mix or furnace "charge" improves and speeds up steel production.

Steel can be given many different and useful properties by alloying the iron with other metals such as chromium, molybdenum, nickel, aluminum , cobalt, tungsten, vanadium, and titanium , and with nonmetals such as boron and silicon.


Manufacturing processes

Most steel is produced using one of four methods: Bessemer converters, open-hearth furnaces, basic oxygen furnaces, and electric furnaces. The basic oxygen process is the most efficient, while the Bessemer and open-hearth methods have become obsolete. Electric furnaces are used to produce high quality steels from selected steel scrap, lime, and mill scale (an iron oxide that forms on the surface of hot steel and falls off as black scale).

Until 1909, most steel made in the United States came from Bessemer converters. A Bessemer converter looks like a huge pear-shaped pot and can hold anywhere from 5-25 tons. It is balanced on axles so that its open top can be tilted one way to take a charge and the other way to pour out steel. After the converter is charged with hot metal, it is swung to the upright position. Air is then blown through holes in its bottom at a typical rate of 30,000 cubic feet per minute. Sparks and thick, brown smoke pour from the converter's mouth as the oxygen in the blow combines with the iron, silicon, and manganese to form slag. Then 30-ft (9-m) flames replace the smoke as the oxygen combines with the carbon fuel and burns. The whole process took less than 15 minutes. Unfortunately, the blowing air contained contaminants (such as nitrogen ) and also removed some desirable elements such as carbon and manganese. This was solved by adding the necessary elements back into the converter after the blow. Because of stricter air pollution regulations and more efficient processes, the Bessemer converter is no longer used.

From 1909 until the 1960s, the open-hearth process was the most popular method of steel production. Open-hearth furnaces got their name from a shallow area called a hearth that is exposed to a blast of flames that alternately sweeps across the hearth from one side for a period of time and then to the side of the furnace. To make a "heat," or one batch of steel, pig iron, limestone, and scrap steel, are initially "charged," or loaded, into the hearth. These materials are heated for about two hours at temperatures 2,700–3,000°F (1,482–1,649°C) until they begin to fuse. Then the furnace is charged with many tons of molten pig iron. Scrap is placed in the furnace with a charging machine which usually serves a series of open hearth furnaces in a single building. Other elements, such as fluxing agents, carbon (usually in the form of anthracite coal pellets), and alloying materials, are then added to improve the steel. These elements can be added either in the furnace charge, the melt or "bath," ladle, or the ingot molds to meet the desired chemical composition of the finished steel or to eliminate or counteract the effect of oxides or other impurities. Fluxing agents (primarily lime, added in the form of either limestone or burnt lime and supplemented by magnesia, MgO, and lime from the furnace bottom and sides) melt and combine with the impurities to form slag at the top of the melt which is poured off into a separate slag pot. Mill scale, a form of iron oxide (Fe3O4), is used to reduce carbon content. Aluminum ferrosilicon is added if the steel is to be "killed." A killed steel is one that has been deoxidized to prevent gas evolution in the ingot mold , making a more uniform steel. "Rimmed" steel is steel that has not been deoxidized and gas pockets and holes from free oxygen form in the center of the ingot while the rim near the surface of the ingot is free of defects. Rolling processes are used in later operations to remove these defects. Semikilled steels are a compromise between rimmed and killed steels and are mainly limited to steels to be rolled into sheet bar, plate, and structural sections. The quantity of deoxidizers used must be closely controlled to allow a limited evolution of gas from the carbon-oxygen reaction.

When the contents of the heat are acceptable and the temperature is right, the furnace is tapped and the molten metal is poured into a ladle. An open-hearth furnace is tapped through a hole in the furnace's bottom. A heat is refined into steel during an 8-12 hour time period. Oxygen released from the ore and additional injected oxygen combine with carbon in the molten pig iron to form carbon gases. These, along with any additional gases from the burned fuel, are used to heat incoming air and this is why the open-hearth process is sometimes called the regenerative open-hearth.

The basic oxygen converter resembles a Bessemer converter. It receives materials from the top and tips to pour off the finished steel into ladles. The main element is a water-cooled oxygen lance, which is placed into the top of the converter after it is charged with scrap steel, molten pig iron, and fluxing agents. The lance, lowered to within a few feet of the charge, directs high-purity oxygen at supersonic speeds into the molten metal. This burns out the impurities and also enables the making of steel with a minimum amount of nitrogen, which can make steel brittle. The oxidation of the carbon and impurities causes a violent rolling agitation which brings all the metal into contact with the oxygen stream. The furnace ladle is first tipped to remove slag and then rotated to pour molten steel into a ladle. The speed and efficiency of the oxygen process has had a significant impact on the steel industry. An oxygen converter can produce a heat of quality steel in 30-45 minutes. An open-hearth furnace without an oxygen lance requires as much as eight hours to produce steel of a similar quality. Recent advances in refractory "brick," the insulating ceramics that protect vessels from the hot steel, have allowed injection of oxygen from the bottom of a vessel without a large complicated lance. This allows for a much more efficient use of the oxygen and can lower the capital costs in constructing a basic oxygen facility, especially if the building and cranes of a retired open-hearth facility is used.

High-quality carbon and alloy steels, such as tool and stainless steels, are produced in electric arc furnaces. These furnaces can make 150-200 tons in a single heat in as little as 90 minutes. The charge is melted by the arcing between carbon electrodes and high quality scrap steel. Some of the electrodes can be 2 ft (0.6 m) in diameter and 24 ft (7.2 m) long. The entire electric furnace is tilted during a tapping operation in which molten steel flows into a waiting ladle. Electric furnaces are the most competitive where low-cost electricity is available and where very little coal or iron ore is found.

After the steel in the ladle has cooled to the desired temperature, the ladle is moved by a traveling crane to either a pouring platform for ingot production or to a continuous caster. Ingots may be square, rectangular, or round and weigh anywhere from a few hundred pounds to 40 tons. A small amount of steel is cast directly into the desired shape in molds of fine sand and fireclay. Small rail cars carrying a series of heavy cast iron ingot molds wait alongside the pouring platform. The steel is "teemed" or poured into the molds through a fire-clay nozzle in the bottom of the ladle. After the steel in the molds has solidified, the cars are pulled under a stripping crane. The crane's plunger holds down the ingot top as its jaws lift the mold from the glowing hot ingot. The ingots are then taken to soaking pits for further processing.

An underground soaking pit is used to heat the steel ingots to a uniform temperature throughout. The ingots must be the same temperature throughout so that they can be easily plastically deformed and to prevent damage to the heavy machinery of the mills. The jaws of the crane clamp onto the ingots and lower them into the open soaking pits. The roof of the pits is then closed and burning oil or gas heats the ingots to about 2,200°F (1,204°C). After "soaking" in the pits for several hours, the ingots are then lifted out by crane and transported by rail to the blooming and slabbing mills.

The mechanical working of steel, such as rolling, forging, hammering, or squeezing, improves it in several ways. Cavities and voids are closed, harmful concentrations of nonmetallic impurities are broken up and more evenly disbursed, and the grain structure is refined to produce a more homogeneous or uniform product. Some ingots are sent directly to a universal plate mill for immediate rolling of steel plates. Most ingots, however, are sent to semifinishing mills (also known as slabbing or blooming mills) for reduction and shaping into slabs, blooms, or billets. A slab is generally a large flat length of steel wider than a bloom, a bloom is a length of steel either square or rectangular with a cross-sectional area larger than 36 in (90 cm), and a billet is generally two to five inches square, although some billets can be round or rectangular. The exact sizes of slabs, blooms, and billets depend on the requirements of further processing.

In slabbing and blooming mills, the steel ingot is gradually squeezed between heavy rolls. To make billets, the steel is first shaped into blooms, then further reduced in a billet mill. Each time the ingot is forced through the rolls, it is further reduced in one dimension. Blooming mills can be classified as either two-high or three-high, depending on the number of rolls used. The two rolls of the two-high mill can be reversed so that the ingot is flattened and lengthened as it passes back and forth between the rolls. The top and bottom rolls of the three-high mill turn in one direction while the middle roll turns in the opposite direction. The ingot is flattened first between the bottom and middle rolls and ends up on a runout table. The table rises and the steel is then fed through the top and middle rolls. The continuous, or cross-country, mill is a third type of blooming mill. This mill has a series of two-high rolls. As many as 15 passes may be required to reduce an ingot 21 in2 (135 cm2) in cross section to a bloom 8 in2 (52 cm2) in cross section. The twoand three-high blooming mills roll the top and bottom of the steel in every pass. After one or two passes, mechanical manipulators on the runout table turn the steel to bring the side surfaces under the rolls for a more uniform material. After the steel is rolled, the uneven ends are sheared off, and the single long piece is cut into shorter lengths. The sheared off ends are reused as scrap. Most of the rolls used in these mills are horizontal, but there are also vertical rolls which squeeze the blooms or slabs from the sides. High-pressure water jets are used to remove mill scale which forms on the surface. Surface defects on the finished blooms and slabs are burned off, or scarfed, with an oxygen flame. The hot lengths of steel are moved from one station to another on a series of roller conveyors. The mill operations are automatically controlled by workers in an overhead glass-enclosed room called a "pulpit." The slabs, blooms, and billets are then taken to finishing mills where they are formed into special shapes and forms such as bars, beams, plates, and sheets. The steel is still not completely "finished" but it is closer to the form in which it will eventually be used in manufactured goods. Blooms and billets are finished into rails , wire rods, wires, bars, tubes, seamless pipe, and structural shapes such as I and H beams. Slabs are converted into plates, sheets, strips, and welded pipe.

After they are hot rolled, steel plates or shapes undergo further processing such as cleaning and pickling by chemicals to remove surface oxides, cold rolling to improve strength and surface finish, annealing (also known as stress relieving), and coating (galvanizing or aluminizing) for corrosion resistance.

Continuous or "strand" casting of steel eliminates the need to produce ingots and the use of soaking pits. In addition to costing less, continuously cast steels have more uniform compositions and properties than ingot cast steels. Continuous casting of steel produces an endless length of steel which is cut into long slabs or blooms that are ready for shaping in rolling mills. Molten steel is poured into the top of a continuous casting machine and is cooled by passing through a water-cooled mold. Pinch rolls draw the steel downward as it solidifies. Additional cooling is provided by water sprays along the travel path of the solidifying metal. The thickness of the steel "strand" is typically 10 in (25 cm) but new developments have reduced this thickness to 1 in (2.5 cm) or less. The thinner strand reduces the number of rolling operations required and improves the economy of the overall process. Some continuous cast machines bend the steel while it is still hot and flexible so that it comes out of the bottom in a horizontal position. Other machines cut the steel into sections while it is still in a vertical position. The continuous cast process has become the most economical method to produce large quantities of conventional steels. Small heats of alloy and specialty steels are still cast in ingots because the small size makes the continuous cast process impractical.

Some steel shapes are produced from powder. There are several chemical, electrochemical, and mechanical ways to make steel powder. One method involves improving the ore by magnetically separating the iron. A ball mill is then used to grind the ore into a powder that is then purified with hot hydrogen . This powder, under heat and pressure , is pressed into molds to form irregularly shaped objects; objects that would be hard to form any other way.


Quality control

To specify the various physical and mechanical properties of the finished product, various tests, both destructive and nondestructive, are performed. Metallurgical, hardness, hardenability, tension, ductility, compression, fatigue, impact, wear, corrosion, creep, machinability, radiography, magnetic particle, ultrasonic, and eddy current are some of the major tests that are performed by quality control personnel.

Metallurgical testing is used to determine the quality of steel by analyzing the microstructure of a sample under a microscope . A cross section of a sample is first highly polished and then examined at a magnification from 100-500 diameters. The microstructure of steel consists of grains of different compositions and sizes. Generally, a sample of steel with fine grains is tougher than one with large grains. Different characteristics are produced through alloying the steel with other substances. It is possible to determine grain size and the size, shape, and distribution of various phases and inclusions (nonmetallic material) which have a great effect on the mechanical properties of the metal. Some grains are made of ferrite, or pure metallic iron; graphite, a crystal form of carbon; pearlite, an alloy of iron of carbon; cementite, also called iron carbide, a hard compound of iron and carbon and other carbide-forming elements; austenite, a solid solution of carbon in gamma iron, a nonmagnetic form of iron; and martensite, an extremely hard constituent of steel produced by heat-treating. The sample can also be etched to make visible many structural characteristics of the metal or alloy by a preferential attack on the different constituents. The microstructure will reveal the mechanical and thermal treatment of the metal, and it may be possible to predict its expected behavior under a given set of conditions.

Hardness is not a fundamental property of a material, but is related to its elastic and plastic properties. The hardness value obtained in a particular test serves only as a comparison between materials or treatments. The test procedure and sample preparation are fairly simple and the results may be used in estimating other mechanical properties. Rockwell and Brinell are two popular hardness tests that are widely used for inspection and control. These tests are usually performed by impressing into the test specimen, which is resting on a rigid platform, an indenter of fixed and known geometry , under a known static load.

Hardenability is a property that determines the depth and distribution of hardness induced by quenching. The standardized test used is called the end-quench hardenability test, also known as the Jominy test. A 1-in (2.54 cm) round 4-in (10 cm) long sample is heated uniformly to the austenitizing temperature (this temperature depends on the material composition, ranging from 1,500–1,900°F [816–1,038°C]). The sample is removed from the furnace and placed on a fixture where a jet of water contacts the bottom face of the sample. After ten minutes on the fixture, the sample is removed and two flat parallel surfaces are ground on the sample. Rockwell hardness readings are taken along the ground surfaces at certain intervals from the quenched end. The results are expressed as a curve of hardness values versus distance from the quenched end. Plain carbon steels tend to be hard on the surface, near the quenched end, but remain relatively soft at the core, or further away from the quenched end. Alloyed steels, in general, have an increased depth of hardenability which is one of the main advantages of using alloyed steels.

Next to the hardness test, the tensile test is the most frequently performed test to determine certain mechanical properties. A specifically prepared tensile sample is placed in the heads of a testing machine and an axial load is placed on the sample through a hydraulic loading system. The tensile test is used to determine several important material properties such as yield strength, where the material starts to exhibit plastic or permanent deformation, and the ultimate tensile or breaking strength.

Ductility of a material is indicated by the amount of deformation that is possible until fracture and can be determined by measuring elongation and reduction in area of a tensile sample that has been tested to failure.

Compression tests are performed on small cylinders, blocks, or strips to determine the ability of a material to undergo large plastic deformations (a mechanical property also known as malleability) and its limits. Stress-strain relations determined from this testing are used to predict the pressures and forces arising in industrial forming operations such as rolling, forging, or extrusion. Samples are placed between anvils or pressure plates and are compressed (friction is also a factor to consider as the material slides sidewise over the anvils).

The fatigue test is used to determine the behavior of materials when subjected to repeated or fluctuating loads. It is used to simulate stress conditions developed in materials under service conditions. The fatigue potential, or endurance limit, is determined by counting the number of cycles of stress, applied first in one direction and then another, to which the metal can be subjected before it breaks. Fatigue tests can be used to study the material behavior under various types and ranges of fluctuating loads and also the effect of corrosion, surface conditions, temperature, size, and stress concentrations.

Impact tests are used to determine the behavior of materials when subjected to high rates of loading, usually in bending, tension, or torsion. The quantity measured is the energy absorbed in breaking the specimen in one blow, two such tests are called the Charpy and the Izod, which use notched bar specimens. A swinging pendulum of fixed weight raised to a standard height is used to strike the specimen. Some of the energy of the pendulum is used to rupture the specimen so that the pendulum rises to a lower height than the standard height. The weight of the pendulum times the difference in heights indicates the energy absorbed by the specimen, usually measured in foot-pounds.

Wear resistance is represented by few standardized tests because of its complex nature. One test is the "pin on disk" method, where a pin is moved against a disk of the test material. Usually, wear testing is application specific and the equipment is designed to simulate actual service conditions.

Corrosion involves the destruction of a material by chemical, electrochemical, or metallurgical interaction between the environment and the material. Various types of environmental exposure testing is done to simulate actual use conditions, such as salt bath immersion testing. Zinc coating, or galvanizing, is commonly applied to sheet and structural steel used for outdoor applications to protect against corrosion.

Creep tests are used to determine the continuing change in the deformation of a material at elevated temperatures when stressed below the yield strength. This is important in the design of parts exposed to elevated temperatures. Creep may be defined as a continuing slow plastic flow under constant load conditions. A creep test is a tension test run at a constant load and temperature. The percent elongation of the sample is measured over time.

Machinability is the ease with which a metal may be machined. Many factors are considered in arriving at machinability ratings. Some of the more important factors are the rate of metal removal, quality of the finished surface, and tool life. Machinability ratings are expressed as a percentage, in comparison with AISI 1112 steel, which is rated at 100%. Metals which are more difficult to machine have a rating of less than 100% while metals which machine easily have a rating more than 100%.

Radiography of metals involves the use of x rays or gamma rays. The short-wavelength electromagnetic rays are capable of going through large thickness of metal and are typically used to nondestructively test castings and welded joints for shrinkage voids and porosity.

Magnetic particle inspection (also called "Magnaflux") is a method of detecting cracks, tears, seams, inclusions, and similar discontinuities in iron and steel. This method will detect surface defects too fine to be seen by the naked eye and will also detect discontinuities just below the surface. The sample is magnetized and then covered with a fine iron powder. The presence of an imperfection is indicated by a pattern that assumes the approximate shape of the defect.

Ultrasonic testing utilizes sound waves above the audible range with a frequency of 1-5 million Hz (cycles per second). Ultrasonics allow for fast, reliable, nondestructive testing which employs electronically produced high-frequency sound waves to penetrate metals and other materials at speeds of several thousand feet per second. If there is a flaw in the path of the ultrasonic wave, part of the energy will be reflected and the signal received by a receiving transducer will be reduced. Ultrasonic inspection is used to detect and locate such defects as shrinkage voids, internal cracks, porosity, and large nonmetallic inclusions.

Eddy current inspection is used to inspect electrically conducting materials for defects and variations in composition. Eddy current testing involves placing a varying magnetic field (which is produced by connecting alternating current to a coil) near an electrically conducting sample. Eddy currents are induced in the sample which then produces a magnetic field of its own. A detection unit measures this new magnetic field and converts the signal into a voltage which can be read on a meter for comparison. Properties such as hardness, alloy composition, chemical purity, and heat treat condition influence the magnetic field and may be measured through the use of eddy current testing.


Byproducts/waste

There are a number of waste byproducts from the steel making process. Mine tailings from the ore beneficiation process are returned to the mining site. Growing vetches (a species of plant valuable for fodder), grasses , and trees on some of these barren landscapes has been a project of biologists and foresters. Gases that are given off from the coke ovens, blast furnaces, and steel furnaces are largely recovered for reuse. After use in iron and steelmaking, most slags are used for other purposes such as railroad ballast and road fill, an ingredient in cement or blocks, insulating material, or fertilizer.


The future

In the future there will be many new developments involving computer controls and automation that will improve economy and quality and lower energy consumption and pollution . More automation will also lead to more robots replacing humans in hazardous areas. Computers can be used to control several rolling mills operating as a continuous unit. The decreasing material thickness can be maintained automatically as it passes through the various mills to produce a more uniform final sheet. Continued research and development is ongoing to connect continuous casting machines with rolling mills to provide a single continuous process from molten metal to the final product. This will produce energy and cost savings because the material would not have to be reheated for processing, and result in a higher quality end product.

The use of 100% scrap in charging electric furnaces has cut the dependence on pig iron and ores, and has resulted in the development of more small steel mills, also called mini-mills, which can be located far from natural resources to serve wider geographical areas.

More net steel shapes will be formed using powder metallurgy as direct reduction processes produce steel powders directly from iron ore, bypassing the blast furnace and making difficult shapes easier to form.

See also Metal production; Metallurgy.

Resources

books

Hudson, Ray and Sadler, David. The International Steel Industry. Routledge, 1989.

Kalpakjian, Serope. Manufacturing Processes for Engineering Materials. 2nd ed. Addison-Wesley Publishing, 1991.

Walsh, Ronald A. McGraw-Hill Machining and MetalworkingHandbook. McGraw-Hill, Inc., 1994.

periodicals

ASM Publication. ASM Metals Handbook Vol. 1: Properties and Selection: Irons, Steels, and High Performance Alloys

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