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Steel
*** Shopping-Tip: Steel
{{otheruses}}
Image:Steel wire rope.png right|thumb|The old steel cable of a colliery winding tower
'''Steel''' is a
metal alloy whose major component is
iron, with
carbon being the primary alloying material. Carbon acts as a hardening agent, preventing iron atoms, which are naturally arranged in a
crystal lattice, from sliding past one another (
dislocation). Varying the amount of carbon and its distribution in the alloy controls qualities such as the
hardness,
elasticity,
ductility, and
tensile strength of the resulting steel. Steel with increased carbon content can be made harder and stronger than iron, but is also more
brittle. One classical definition is that steels are iron–carbon alloys with up to 2.1 percent
carbon by weight; alloys with higher carbon content than this are known as
cast iron.
Currently there are several classes of steels in which carbon is replaced with other alloying materials, and carbon, if present, is undesired. A more recent definition is that steels are iron-based alloys that can be
plasticity (physics) plastically formed (pounded, rolled, etc.).
Iron and steel
{{Template:Steels}}
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Iron, like most metals, is not found in the
Earth's
crust in a native state. Iron can be found in the crust only in combination with
oxygen or
sulfur. Typically Fe
2O
3—the form of
iron oxide (rust) found as the
mineral hematite, and FeS
2—
Pyrite (fools gold). Iron oxide is a soft
sandstone-like material with limited uses on its own. Iron is extracted from
ore by removing the oxygen by combining it with a preferred chemical partner such as carbon. This process, known as
smelting, was first applied to metals with lower
melting points.
Copper melts at just over 1000
Celsius °C, while
tin melts around 250
Celsius °C. Both temperatures could be reached with ancient methods that have been used for at least 6000 years (since the
Bronze Age). Since the oxidation rate itself increases rapidly beyond 800 °C, it is important that smelting take place in a fairly oxygen-free environment. Unlike copper and tin, liquid iron dissolves carbon quite readily, so that smelting results in an alloy containing too much carbon to be called steel.
Image:Phase diag iron carbon-color temp.png phase diagram.html" title="Meaning of thumb thumb|right|250px|Iron-carbon [[phase diagram, showing the conditions necessary to form different phases..html" title="Meaning of right|250px|Iron-carbon [[phase diagram">thumb|right|250px|Iron-carbon [[phase diagram, showing the conditions necessary to form different phases.">right|250px|Iron-carbon [[phase diagram">thumb|right|250px|Iron-carbon [[phase diagram, showing the conditions necessary to form different phases.
Even in the narrow range of concentrations that make up steel, mixtures of carbon and iron can form into a number of different structures, or
allotropes, with very different properties; understanding these is essential to making quality steel. At room temperature, the most stable form of iron is the
body-centered cubic structure '''
Ferrite (iron) ferrite''' or '''α-iron''', a fairly soft metallic material that can dissolve only a small concentration of carbon (no more than 0.021 wt% at 910 °C). Above 910 °C ferrite undergoes a
phase transition from
body-centered cubic to a
face-centered cubic configuration, called '''
austenite''' or '''γ-iron''', which is similarly soft and metallic but can dissolve considerably more carbon (as much as 2.04 wt% carbon at 1146°C). As carbon-rich austenite cools, the mixture attempts to revert to the ferrite phase, resulting in an excess of carbon. One way for carbon to leave the austenite is for
cementite to
precipitate out of the mix, leaving behind iron that is pure enough to take the form of ferrite, and resulting in a cementite-ferrite mixture. Cementite is a stochiometric phase with the chemical formula of Fe
3C. Cementite forms in regions of higher carbon content while other areas revert to ferrite around it. Self-reinforcing patterns often emerge during this process, leading to a patterned layering known as
pearlite due to its
pearl-like appearance, or the similar but less beautiful
bainite.
Perhaps the most important allotrope is
martensite, a chemically
metastable substance with about four to five times the strength of ferrite. A minimum of 0.4 wt% of carbon is needed in order to form Martensite. When the Austenite is quenched to form Martensite the carbon is "frozen" in place when the cell structure changes from FCC to BCC. The carbon atom are much too large to fit in the interstatial vaccancies and thus distort the cell structure into a Body Centered Tetragonal (BCT) structure. Martensite and Austenite have an identical chemical composition. As such, it requires extremely little thermal
activation energy to form.
The heat treatment process for most steels involves heating the alloy until austenite forms, then '''
quenching''' the hot metal in
water or
oil, cooling it so rapidly that the transformation to ferrite or pearlite does not have time to take place. The transformation into martensite, by contrast, occurs almost immediately, due to a lower activation energy.
Martensite has a lower density than austenite, so that the transformation between them results in a change of volume. In this case, expansion occurs. Internal stresses from this expansion generally take the form of
physical compression compression on the crystals of martensite and
tension (mechanics) tension on the remaining ferrite, with a fair amount of
shear on both constituents. If quenching is done improperly, these internal stresses can cause a part to shatter as it cools; at the very least, they cause internal
work hardening and other microscopic imperfections. It is common for quench cracks to form when water quenched, although they may not always be visible.
At this point, if its carbon content is high enough to produce a significant concentration of martensite, and is extremely hard but very brittle. Often, steel undergoes further heat treatment at a lower temperature to destroy some of the martensite (by allowing enough time for cementite, etc., to form) and help settle the internal stresses and defects. This softens the steel, producing a more ductile and fracture-resistant metal. Because time is so critical to the end result, this process is known as '''
tempering''', source of the term '''tempered steel'''.
Other materials are often added to the iron-carbon mixture to tailor the resulting properties.
Nickel and
manganese in steel add to its tensile strength and make austenite more chemically stable,
chromium increases the hardness and melting temperature, and
vanadium also increases the
hardness while reducing the effects of
metal fatigue. Large amounts of chromium and nickel (often 18% and 8%, respectively) are added to
stainless steel so that a hard
passivation oxide forms on the metal surface to inhibit corrosion.
Tungsten interferes with the formation of cementite, allowing martensite to form with slower quench rates, resulting in ''
high speed steel''. On the other hand
sulfur,
nitrogen, and
phosphorus make steel more brittle, so these commonly found elements must be removed from the ore during processing.
When iron is smelted from its ore by commercial processes, it contains more carbon than is desirable. To become steel, it must be melted and reprocessed to remove the correct amount of carbon, at which point other elements can be added. Once this liquid is cast into ingots, it usually must be "worked" at high temperature to remove any cracks or poorly mixed regions from the solidification process, and to produce shapes such as plate, sheet, wire, etc. It is then heat-treated to produce a desirable crystal structure, and often "cold worked" to produce the final shape. In modern steelmaking these processes are often combined, with ore going in one end of the
assembly line and finished steel coming out the other. These can be streamlined by a deft control of the interaction between
work hardening and
tempering.
History of iron and steelmaking
Iron was in limited use long before it became possible to smelt it. The first signs of iron use come from
Ancient Egypt and
Sumer, where around
4000 BC small items, such as the tips of spears and ornaments, were being fashioned from iron recovered from
meteorites (see
Iron#History Iron: History). About 6% of
meteorites are composed of an iron-
nickel alloy, and iron recovered from meteorite falls allowed ancient peoples to manufacture small numbers of iron artifacts.
Meteoric iron was also fashioned into tools in precontact
North America. Beginning around the year
1000, the
Thule people of
Greenland began making
harpoons and other edged tools from pieces of the
Cape York meteorite. These artifacts were also used as trade goods with other Arctic peoples: tools made from the Cape York meteorite have been found in archaeological sites more than 1000 miles (1600 km) away. When the
United States American polar explorer
Robert Peary shipped the largest piece of the meteorite to the
American Museum of Natural History in
New York City in
1897, it still weighed over 33
tons.
The name for iron in several ancient languages means "sky metal" or something similar. In distant antiquity, iron was regarded as a precious metal, suitable for royal ornaments.
The Iron Age
Image:Axe of iron from Swedish Iron Age, found at Gotland, Sweden.jpg thumb|right|250px|Iron axehead from Swedish Iron Age, found at Gotland, Sweden. Beginning between
3000 BC to
2000 BC increasing numbers of
smelting smelted iron objects (distinguishable from meteoric iron by their lack of
nickel) appear in
Anatolia,
Egypt and
Mesopotamia (see
Iron#History Iron: History). The oldest known samples of iron that appear to have been smelted from
iron oxides are small lumps found at copper-smelting sites on the
Sinai Peninsula, dated to about 3000 BC. Some iron oxides are effective fluxes for copper smelting; it is possible that small amounts of metallic iron were made as a by-product of copper and bronze production throughout the Bronze Age.
In
Anatolia, smelted iron was occasionally used for ornamental weapons: an iron-bladed dagger with a bronze hilt has been recovered from a
Hattic tomb dating from
2500 BC. Also, the
Egyptian ruler
Tutankhamun died in
1323 BC and was buried with an iron dagger with a golden hilt. An
Ancient Egyptian sword bearing the name of
pharaoh Merneptah as well as a
battle axe with an iron blade and gold-decorated bronze haft were both found in the excavation of
Ugarit (see
Ugarit). The early
Hittites are known to have
bartered iron for
silver, at a rate of 40 times the iron's weight, with
Assyria.
Iron did not, however, replace bronze as the chief metal used for weapons and tools for several centuries, despite some attempts. Working iron required more fuel and significantly more labor than working bronze, and the quality of iron produced by early smiths may have been inferior to bronze as a material for tools. Then, between
1200 BC 1200 and
1000 BC, iron tools and weapons displaced bronze ones throughout the near east. This process appears to have begun in the
Hittite Empire around
1300 BC, or in
Cyprus and southern
Greece, where iron artifacts dominate the archaeological record after
1050 BC.
Mesopotamia was fully into the Iron Age by
900 BC, central Europe by
800 BC. The reason for this sudden adoption of iron remains a topic of debate among archaeologists. One prominent theory is that warfare and mass migrations beginning around 1200 BC disrupted the regional tin trade, forcing a switch from bronze to iron.
Egypt, on the other hand, did not experience such a rapid transition from the bronze to iron ages: although Egyptian smiths did produce iron artifacts, bronze remained in widespread use there until after Egypt's conquest by
Assyria in
663 BC.
Iron smelting at this time was based on the
bloomery, a furnace where
bellows were used to force air through a pile of iron ore and burning
charcoal. The
carbon monoxide produced by the charcoal reduced the iron oxides to metallic iron, but the bloomery was not hot enough to melt the iron. Instead, the iron collected in the bottom of the furnace as a spongy mass, or '''''bloom''''', whose pores were filled with ash and slag. The bloom then had to be reheated to soften the iron and melt the slag, and then repeatedly beaten and folded to force the molten slag out of it. The result of this time-consuming and laborious process was
wrought iron, a malleable but fairly soft alloy containing little carbon.
Wrought iron can be '''''
carburization carburized''''' into a mild steel by holding it in a charcoal fire for prolonged periods of time. By the beginning of the Iron Age, smiths had discovered that iron that was repeatedly reforged produced a higher quality of metal. Quench-hardening was also known by this time. The oldest quench-hardened steel artifact is a knife found on
Cyprus at a site dated to
1100 BC.
Developments in China
Archaeologists and historians debate whether bloomery-based ironworking ever spread to China from the West. Around
500 BC, however, metalworkers in the southern state of
state of Wu Wu developed an iron smelting technology that would not be practiced in Europe until late medieval times. In Wu, iron smelters achieved a temperature of 1130°C, hot enough to be considered a
blast furnace. At this temperature, iron combines with 4.3% carbon and melts. As a liquid, iron can be
casting cast into
molds, a method far less laborious than individually forging each piece of iron from a bloom.
Cast iron is rather brittle and unsuitable for striking implements. It can, however, be '''''decarburized''''' to steel or wrought iron by heating it in air for several days. In China, these ironworking methods spread northward, and by
300 BC, iron was the material of choice throughout China for most tools and weapons. A mass grave in
Hebei province, dated to the early third century BC, contains several soldiers buried with their weapons and other equipment. The artifacts recovered from this grave are variously made of wrought iron, cast iron, malleabilized cast iron, and quench-hardened steel, with only a few, probably ornamental, bronze weapons.
During the
Han Dynasty (
202 BC–
220 AD 220), Chinese ironworking achieved a scale and sophistication not reached in the West until the eighteenth century. In the first century, the Han government established ironworking as a state monopoly and built a series of large blast furnaces in
Henan province, each capable of producing several tons of iron per day. By this time, Chinese metallurgists had discovered how to '''''
puddling furnace puddle''''' molten pig iron, stirring it in the open air until it lost its carbon and became wrought iron. (In
Chinese language Chinese, the process was called ''chao'', literally,
stir frying.)
Also during this time, Chinese metallurgists had found that wrought iron and cast iron could be melted together to yield an alloy of intermediate carbon content, that is, steel. According to legend, the sword of
Liu Bang, the first Han emperor, was made in this fashion. Some texts of the era mention "harmonizing the hard and the soft" in the context of ironworking; the phrase may refer to this process.
India
Perhaps as early as
300 BC, although certainly by
200 AD 200, high quality steel was being produced in southern
India by what Europeans would later call the
crucible steel crucible technique. In this system, high-purity wrought iron, charcoal, and glass were mixed in crucibles and heated until the iron melted and absorbed the carbon. The resulting high-carbon steel, called پولاد ('''''pulâd''''') in
Persian language Persian and '''''
wootz steel wootz''''' by later Europeans, was exported throughout much of Asia. A solid pillar of rust-resistant steel forged in 4th century AD and now standing for many centuries next to the Qutab Minar in Delhi is a testimony of the steel manufacturing skills of Indian artisans. The famous Damascus sword was made of steel imported from India.
Middle East
By the
9th century, smiths in the
Abbasid caliphate had developed techniques for forging wootz to produce steel blades of unusual flexibility and sharpness (
Damascus steel). The secret of forging this kind of steel was lost, even in the Middle East, by around 1600, and only recently have metallurgists found methods for reproducing its properties.
[http://www.tms.org/pubs/journals/JOM/9809/Verhoeven-9809.html Recent research] has established strong evidence supporting the theory that the distinct surface patterns on these blades result from a carbide-banding phenomenon produced by the microsegregation of minor amounts of carbide-forming elements present in the wootz ingots from which the blades were forged. Further, it is likely that wootz Damascus blades with damascene patterns may have been produced only from wootz ingots supplied from those regions of India having appropriate impurity-containing ore deposits.
Ironworking in medieval Europe
The middle ages in Europe saw the construction of progressively larger bloomeries. By the 8th century, smiths in northern
Spain had developed a style that become known as a
Catalan forge, a furnace about 1 meter (3 feet) tall, capable of smelting up to 150 kg (350 lb) of iron in each batch. In succeeding centuries, smiths in the
Frankish empire and later the
Holy Roman Empire scaled up this basic design, increasing the height of the flue to as tall as 5 meters (16 feet) and smelting as much as 350 kg (750 lb) of iron in each batch. These larger furnaces required more draft than could be provided by human power, and forging the large blooms that resulted was also beyond the capabilities of a single man. To this end,
waterwheels were employed to power the bellows and hammers.
Eventually, the scaling up of the bloomery reached a point where the furnace was hot enough to produce cast iron. Although the brittle cast iron may initially have been a nuisance to the smith, as it was too brittle to be forged, the spread of
cannons to Europe in the 1300s provided an application for iron casting, cast iron cannonballs.
The oldest known blast furnace in Europe was constructed at Lapphyttan in
Sweden, sometime between 1150 and 1350. Other early European blast furnaces were built throughout the
Rhine valley: blast furnaces were in operation near
Liège (city) Liège (a city in modern-day
Belgium) in the 1340s, and at
Massevaux in
France by
1409.
The first English blast furnace was not built until
1496, when
Henry VII of England Henry VII commissioned a new ironworks at Newbridge, in a part of
Sussex known as the
Weald. Despite this late start, the production of English iron foundries rapidly grew, in no small part due to foreign craftsmen hired by Henry to bring the craft of iron casting to England. In
1543,
William Levett, a Wealden ironmaster, and
Peter Baude, a
France French craftsman in
Henry VIII of England Henry VIII's employ, cast the Weald's first one-piece iron cannon. English iron cannons gained a reputation for being superior to, and less expensive than, the bronze cannons made elsewhere in Europe, and at least initially, efforts to copy them outside the Weald failed. The superiority of English cannons over Spanish ones has been credited as one factor in England's
1588 defeat of the
Spanish Armada.
In
1619,
Jan Andries Moerbeck, a
United Netherlands Dutch ironmaster, began importing Wealden iron ore for comparison to the ore available on the Continent. One difference he observed was that the English ore contained some calcareous material, and soon after, Dutch ironmasters introduced the use of limestone as a flux in the blast furnace. This practice improved the separation of slag from the cast iron and improved the quality of Continental cast iron.
Ironworking in early modern Europe
Image:Puddling furnace.jpg thumb|right|250px|Schematic drawing of a puddling furnace.
Also by the early 1600s, ironworkers in western Europe had found a means (called '''''cementation''''') to carburize wrought iron without individually forging each piece. Wrought iron bars and charcoal were packed into stone boxes, then held at a red heat for up to a week. During this time, carbon diffused into the iron, producing a product called '''''cement steel''''' or '''''blister steel'''''.
For many years the best steels could be produced by buying expensive iron ore from
Sweden. Although it was not understood at the time, Swedish ore had very low phosphorus content compared to most ores (notably those in England), which allowed for a finer and stronger crystal structure. Sales of Swedish ore generated considerable trade income, and local development helped the country become the industrialised nation it remains to this day.
By the 18th century,
deforestation in western Europe was making ironworking and its charcoal-hungry processes increasingly expensive. In
1709 Abraham Darby began smelting iron using
coke (fuel) coke, a refined
coal product, in place of charcoal at his
ironworks at
Coalbrookdale in
England. Although coke could be produced less expensively than charcoal, coke-fired iron was initially of inferior quality compared to charcoal-fired iron. It was not until the
1750s, when Darby's son refined the coking process to reduce the amount of sulfur in the coke that coke-fired furnaces became widespread.
Another 18th-century European development was the reinvention of the
puddling furnace. In particular, the form of coal-fired puddling furnace developed by the British engineer
Henry Cort in
1784 made it possible to convert cast iron into wrought iron in large batches, finally rendering the ancient bloomery obsolete. Wrought iron produced using this method became a major metal in the English midlands' emerging
toy industry. The combination of the blast furnace and the puddling furnace allowed iron to be produced at either end of the carbon spectrum, depending on the user's needs.
As for alloys of intermediate carbon content (that is, steel),
crucible steel was rediscovered in the 1740s by
Benjamin Huntsman in
Handsworth, South Yorkshire Handsworth in
England. In his process, wrought iron and cast iron were heated in small ceramic crucibles, melting together to form steel. While producing steel superior to cement steel, the crucible steel process remained relatively expensive in both time and fuel, and could not be used in any sort of modern industrial scale. The strong steels produced were however in high demand for specialty products such as
cutlery and weapons.
Sheffield's
Abbeydale Industrial Hamlet has preserved a waterwheel powered, scythe-making works dating from Huntsman's times. It is still operated for the public, several times per year, using crucible steel made on the Abbeydale site. An improvement on crucible steel was the
Cementation process.
Industrial steelmaking
image:Bessemer converter.jpg right|thumb|250px|Schematic drawing of a Bessemer converter
The problem of mass-producing steel was solved in
1855 by
Henry Bessemer, with the introduction of the
Bessemer process Bessemer converter at his steelworks in
Sheffield,
England. (An early converter can still be seen at the city's
Kelham Island Museum). In the Bessemer process, molten pig iron from the blast furnace was charged into a large crucible, and then air was blown through the molten iron from below, igniting the dissolved carbon from the
coke (fuel) coke. As the carbon burned off, the melting point of the mixture increased, but the heat from the burning carbon provided the extra energy needed to keep the mixture molten. After the carbon content in the melt had dropped to the desired level, the air draft was cut off: a typical Bessemer converter could convert a 25-ton batch of pig iron to steel in half an hour.
In
1867, the
Germany German-
United Kingdom British engineer
Carl Wilhelm Siemens Sir William Siemens introduced an improved puddling furnace – the
Siemens regenerative furnace regenerative furnace – that used brick
heat exchangers to preheat the incoming air and conserve fuel. The next year
Pierre Martin Pierre and
Émile Martin, French ironmasters who had licensed Siemens' furnace design, developed a method for measuring the carbon content of molten iron. Thus, the decarburization could be stopped at the steel stage rather than proceeding all the way to wrought iron. This
open hearth furnace open-hearth process coexisted in industrial practice with the Bessemer process for many years, but eventually proved more economical and displaced it. Reasons for this include its ability to
recycling recycle scrap metal in addition to fresh pig iron, its greater scalability (up to hundreds of tons per batch, compared to tens of tons for the Bessemer process), and the more precise
quality control it permitted.
Image:molten_steel_1942.jpg thumb|280px|A huge vat of molten steel being poured into an open hearth furnace at the Jones and Laughlin Steel Company, Pittsburgh, May 1942.
Initially, only ores low in phosphorus and sulfur could be used for quality steelmaking; ores rich in those elements yielded brittle metals little better than cast iron. This problem was solved in
1878 by
Percy Carlyle Gilchrist and his cousin
Sidney Gilchrist Thomas at the ironworks at
Blaenavon in
Wales. Their modified Bessemer process used a converter lined with
limestone or
dolomite, and additional lime was added to the molten metal as a
Flux_(metallurgy) flux. This added
base (chemistry) basic material removed phosphorus and sulfur from the steel as insoluble calcium or magnesium phosphates and sulfates. This development expanded the range of iron ores that could be used to make steel, especially in
France and
Germany, where high-phosphorus ores abounded.
Finally, the
Basic oxygen steelmaking basic oxygen process was introduced at the Voest-Alpine works in 1952; a modification of the basic Bessemer process, it lances oxygen from above the steel (instead of bubbling air from below), reducing the amount of nitrogen uptake into the steel. The basic oxygen process is used in all modern steelworks; the last Bessemer converter in the U.S. was retired in 1968. Furthermore, the last three decades have seen a massive increase in the mini-mill business, where scrap steel only is melted with an
electric arc furnace. These mills only produced bar products at first, but have since expanded into flat and heavy products, once the exclusive domain of the integrated steelworks.
These developments increased the availability and decreased the price of steel; 22 thousand tonnes were produced in 1867, 500 thousand in 1870, 1 million in 1880 and 28 million by 1900. In 2005, total world crude steel production was 1,107.2 million metric tons (mmt) [http://www.worldsteel.org/pictures/storyfiles/Crude%20Steel%20Dec%2005.pdf]. The [http://www.worldsteel.org top three steel-producing countries] were China (349.4 mmt), Japan (112.5 mmt) and the United States (93.9 mmt) (see chart below).
Image:IISI TopSteel2005.png thumb|centre|600px
The widespread availability of inexpensive steel powered the
industrial revolution and modern society as we know it. It also led to the introduction of newer "niche" steels (such as
stainless steel), all of them dependent on the wide availability of inexpensive iron and steel and the ability to alloy it at will.
Steel is currently the most recycled material in the world, the industry estimates that of new metal produced each year some 42.3% is recycled material. All steel that is available is currently recycled, the long service life of steel in applications such as construction means that there is a vast 'store' of steel in use that is recycled as it becomes available. New metal derived from raw materials is necessary to make up demand.
Uses of steel
{{expand}}
Types of steel
Alloy steels were known from antiquity, being
nickel-rich iron from
meteorites hot-worked into useful products. In a modern sense, alloy steels have been made since the invention of furnaces capable of melting iron, into which other metals could be thrown and mixed.
*
Carbon steel
*
Damascus steel, which was famous in ancient times for its durability and ability to hold an edge, was created from a number of different materials (some only in traces), essentially a complicated alloy with iron as main component.
*
Stainless steels and
surgical stainless steels contain a minimum of 10.5%
chromium, often combined with
nickel, to resist
corrosion (
rust). Some stainless steels are nonmagnetic.
*
Tool steels
*
HSLA Steel (High Strength, Low Alloy)
* Advanced High Strength Steels
**
Maraging steel
*Ferrous
superalloys
Though not an alloy, there exists also
hot-dip_galvanizing galvanized steel, which is steel that has gone through the chemical process of being hot-dipped or electroplated in zinc for protection against rust. Finished steel is steel that can be sold without further work or treatment.
Production methods
*
Crucible technique or
Puddling furnace puddling - the original steel making technique, developed in
India as
wootz steel wootz, used in the
Middle East as
Damascus steel and independently redeveloped in
Sheffield by Benjamin Huntsman in 1740, and Pavel Anosov in
Russia in 1837.
*
Bessemer process, the first commercial-scale steel production process
*
Open hearth furnace
*
Basic oxygen steelmaking
*
Electric arc furnace a form of secondary steelmaking from scrap, though the process can also use direct-reduced iron
References
-
Essays on geology, history, and people
-
Early iron in China, Korea, and Japan
-
Precursors of the blast furnace
-
Early progress in the melting of iron
-
Steel City founders
See also
*
Steel producers
External links
{{commons|Steel}}
{{wiktionary}}
-
Extensive '''picture gallery''' about all methods of making and shaping of iron and steel in North America and Europe. In German and English.
-
Exhibition of Persian Steel
-
International Iron & Steel Institute (IISI)
-
Steel Alloys and Their Classification
-
steeluniversity.org
-
Quenched & Tempered Steel Alloys
-
Quench hardening of steel
-
CIMsteel Integration Standards (CIS/2)
-
Steel in 20th-century architecture
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