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Crucible steel is
steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistan ...
made by melting
pig iron Pig iron, also known as crude iron, is an intermediate product of the iron industry in the production of steel which is obtained by smelting iron ore in a blast furnace. Pig iron has a high carbon content, typically 3.8–4.7%, along with ...
(
cast iron Cast iron is a class of iron– carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuri ...
),
iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...
, and sometimes
steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistan ...
, often along with
sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class ...
,
glass Glass is a non- crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenchin ...
,
ash Ash or ashes are the solid remnants of fires. Specifically, ''ash'' refers to all non-aqueous, non-gaseous residues that remain after something burns. In analytical chemistry, to analyse the mineral and metal content of chemical samples, ash ...
es, and other fluxes, in a
crucible A crucible is a ceramic or metal container in which metals or other substances may be melted or subjected to very high temperatures. While crucibles were historically usually made from clay, they can be made from any material that withstands te ...
. In ancient times steel and iron were impossible to melt using charcoal or coal fires, which could not produce temperatures high enough. However, pig iron, having a higher carbon content and thus a lower melting point, could be melted, and by soaking
wrought iron Wrought iron is an iron alloy with a very low carbon content (less than 0.08%) in contrast to that of cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag inclusions (up to 2% by weight), which give it a wood-like "grain" ...
or steel in the liquid pig-iron for a long time, the carbon content of the pig iron could be reduced as it slowly
diffused Molecular diffusion, often simply called diffusion, is the thermal motion of all (liquid or gas) particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size (mass) of ...
into the iron, turning both into steel. Crucible steel of this type was produced in South and Central Asia during the
medieval era In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire a ...
. This generally produced a very hard steel, but also a composite steel that was inhomogeneous, consisting of a very high-carbon steel (formerly the pig-iron) and a lower-carbon steel (formerly the wrought iron). This often resulted in an intricate pattern when the steel was forged, filed or polished, with possibly the most well-known examples coming from the
wootz steel Wootz steel, also known as Seric steel, is a crucible steel characterized by a pattern of bands and high carbon content. These bands are formed by sheets of microscopic carbides within a tempered martensite or pearlite matrix in higher carbon ...
used in Damascus swords. The steel was often much higher in carbon content (typically ranging in the area of 1.5 to 2.0%) and in quality (lacking impurities) in comparison with other methods of steel production of the time because of the use of fluxes. The steel was usually worked very little and at relatively low temperatures to avoid any decarburization, hot short crumbling, or excess
diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical ...
of carbon; just enough hammering to form the shape of a sword. With a carbon content close to that of cast iron, it usually required no
heat treatment Heat treating (or heat treatment) is a group of industrial process, industrial, thermal and metalworking, metalworking processes used to alter the physical property, physical, and sometimes chemical property, chemical, properties of a material. ...
after shaping other than air cooling to achieve the correct hardness, relying on composition alone. The higher-carbon steel provided a very hard edge, but the lower-carbon steel helped to increase the toughness, helping to decrease the chance of chipping, cracking, or breaking. In Europe, crucible steel was developed by Benjamin Huntsman in England in the 18th century. Huntsman used coke rather than coal or charcoal, achieving temperatures high enough to melt steel and dissolve iron. Huntsman's process differed from some of the wootz processes in that it used a longer time to melt the steel and to cool it down and thus allowed more time for the diffusion of carbon. Huntsman's process used iron and steel as raw materials, in the form of blister steel, rather than direct conversion from cast iron as in puddling or the later
Bessemer process The Bessemer process was the first inexpensive industrial process for the mass production of steel from molten pig iron before the development of the open hearth furnace. The key principle is removal of impurities from the iron by oxidation ...
. The ability to fully melt the steel removed any inhomogeneities in the steel, allowing the carbon to dissolve evenly into the liquid steel and negating the prior need for extensive blacksmithing in an attempt to achieve the same result. Similarly, it allowed steel to be
cast Cast may refer to: Music * Cast (band), an English alternative rock band * Cast (Mexican band), a progressive Mexican rock band * The Cast, a Scottish musical duo: Mairi Campbell and Dave Francis * ''Cast'', a 2012 album by Trespassers William ...
by pouring into molds. The use of fluxes allowed nearly complete extraction of impurities from the liquid, which could then simply float to the top for removal. This produced the first steel of modern quality, providing a means of efficiently changing excess wrought iron into useful steel. Huntsman's process greatly increased the European output of quality steel suitable for use in items like knives, tools, and machinery, helping to pave the way for the
Industrial Revolution The Industrial Revolution was the transition to new manufacturing processes in Great Britain, continental Europe, and the United States, that occurred during the period from around 1760 to about 1820–1840. This transition included going f ...
.


Methods of crucible steel production

Iron
alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductili ...
s are most broadly divided by their
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...
content:
cast iron Cast iron is a class of iron– carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuri ...
has 2–4% carbon impurities;
wrought iron Wrought iron is an iron alloy with a very low carbon content (less than 0.08%) in contrast to that of cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag inclusions (up to 2% by weight), which give it a wood-like "grain" ...
oxidizes away most of its carbon, to less than 0.1%. The much more valuable
steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistan ...
has a delicately intermediate carbon fraction, and its material properties range according to the carbon percentage: high carbon steel is stronger but more brittle than low carbon steel. Crucible steel sequesters the raw input materials from the heat source, allowing precise control of
carburization Carburising, carburizing (chiefly American English), or carburisation is a heat treatment process in which iron or steel absorbs carbon while the metal is heated in the presence of a carbon-bearing material, such as charcoal or carbon monoxide. ...
(raising) or
oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...
(lowering carbon content). Fluxes, such as
limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms w ...
, could be added to the crucible to remove or promote
sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...
,
silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...
, and other impurities, further altering its material qualities. Various methods were used to produce crucible steel. According to Islamic texts such as al-Tarsusi and
Abu Rayhan Biruni Abu Rayhan Muhammad ibn Ahmad al-Biruni (973 – after 1050) commonly known as al-Biruni, was a Khwarazmian Iranian in scholar and polymath during the Islamic Golden Age. He has been called variously the "founder of Indology", "Father of Co ...
, three methods are described for indirect production of steel.Feuerbach et al. 1997, 105 The medieval Islamic historian Abu Rayhan Biruni (c. 973–1050) provides the earliest reference of the production of
Damascus steel Damascus steel was the forged steel of the blades of swords smithed in the Near East from ingots of Wootz steel either imported from Southern India or made in production centres in Sri Lanka, or Khorasan, Iran. These swords are characterized by ...
.Feuerbach et al. 1998, 38 The first, and the most common, traditional method is solid state carburization of
wrought iron Wrought iron is an iron alloy with a very low carbon content (less than 0.08%) in contrast to that of cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag inclusions (up to 2% by weight), which give it a wood-like "grain" ...
. This is a
diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical ...
process in which wrought iron is packed in crucibles or a
hearth A hearth () is the place in a home where a fire is or was traditionally kept for home heating and for cooking, usually constituted by at least a horizontal hearthstone and often enclosed to varying degrees by any combination of reredos (a lo ...
with charcoal, then heated to promote diffusion of carbon into the iron to produce steel.Feuerbach et al. 1995, 12 Carburization is the basis for the wootz process of steel. The second method is the decarburization of
cast iron Cast iron is a class of iron– carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuri ...
by removing carbon from the cast iron. The third method uses wrought iron and cast iron. In this process, wrought iron and cast iron may be heated together in a crucible to produce steel by fusion. In regard to this method Abu Rayhan Biruni states: "this was the method used in Hearth". It is proposed that the Indian method refers to Wootz carburization method; i.e., the
Mysore Mysore (), officially Mysuru (), is a city in the southern part of the state of Karnataka, India. Mysore city is geographically located between 12° 18′ 26″ north latitude and 76° 38′ 59″ east longitude. It is located at an altitude o ...
or
Tamil Tamil may refer to: * Tamils, an ethnic group native to India and some other parts of Asia ** Sri Lankan Tamils, Tamil people native to Sri Lanka also called ilankai tamils **Tamil Malaysians, Tamil people native to Malaysia * Tamil language, na ...
processes.Srinivasan 1994, 56 Variations of co-fusion process have been found primarily in
Persia Iran, officially the Islamic Republic of Iran, and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkmeni ...
and Central Asia but have also been found in Hyderabad, IndiaFeuerbach et al. 1998, 39 called Deccani or Hyderabad process. For the carbon, a variety of organic materials are specified by the contemporary Islamic authorities, including pomegranate rinds, acorns, fruit skins like orange peel, leaves as well as the white of egg and shells. Slivers of wood are mentioned in some of the Indian sources, but significantly none of the sources mention charcoal.


Early history

Crucible steel is generally attributed to production centres in
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
and
Sri Lanka Sri Lanka (, ; si, ශ්‍රී ලංකා, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon and officially the Democratic Socialist Republic of Sri Lanka, is an ...
where it was produced using the so-called " wootz" process, and it is assumed that its appearance in other locations was due to long-distance trade.Feuerbach 2002, 13 Only recently it has become apparent that places in Central Asia like
Merv Merv ( tk, Merw, ', مرو; fa, مرو, ''Marv''), also known as the Merve Oasis, formerly known as Alexandria ( grc-gre, Ἀλεξάνδρεια), Antiochia in Margiana ( grc-gre, Ἀντιόχεια ἡ ἐν τῇ Μαργιανῇ) and ...
in Turkmenistan and Akhsiket in Uzbekistan were important centres of production of crucible steel.Ranganathan and Srinivasan 2004, 126 The Central Asian finds are all from excavations and date from the 8th to 12th centuries CE, while the Indian/Sri Lankan material is as early as 300 BCE. India's iron ore had trace vanadium and other alloying elements leading to increased hardenability in Indian crucible steel which was famous throughout the middle east for its ability to retain an edge. While crucible steel is more attributed to the Middle East in early times,
pattern welded Pattern welding is the practice in sword and knife making of forming a blade of several metal pieces of differing composition that are forge-welded together and twisted and manipulated to form a pattern. Often mistakenly called Damascus steel, ...
swords, incorporating high-carbon, and likely crucible steel, have been discovered in Europe, from the 3rd century CE, particularly in
Scandinavia Scandinavia; Sámi languages: /. ( ) is a subregion in Northern Europe, with strong historical, cultural, and linguistic ties between its constituent peoples. In English usage, ''Scandinavia'' most commonly refers to Denmark, Norway, and S ...
. Swords bearing the brand name:
Ulfberht The Ulfberht swords are a group of about 170 medieval swords found primarily in Northern Europe, dated to the 9th to 11th centuries, with blades inlaid with the inscription ''+VLFBERH+T or +VLFBERHT+''. The word "Ulfberht" is a Frankish pers ...
, and dating to a 200-year period from the 9th century to the early 11th century, are prime examples of the technique. It is speculated by many that the process of making these blades originated in the Middle East and subsequently had been traded during the
Volga Trade Route In the Middle Ages, the Volga trade route connected Northern Europe and Northwestern Russia with the Caspian Sea and the Sasanian Empire, via the Volga River. The Rus used this route to trade with Muslim countries on the southern shores of the ...
days. In the first centuries of the Islamic period, some scientific studies on swords and steel appeared. The best known of these are by
Jabir ibn Hayyan Abū Mūsā Jābir ibn Ḥayyān (Arabic: , variously called al-Ṣūfī, al-Azdī, al-Kūfī, or al-Ṭūsī), died 806−816, is the purported author of an enormous number and variety of works in Arabic, often called the Jabirian corpus. The ...
8th century,
al-Kindi Abū Yūsuf Yaʻqūb ibn ʼIsḥāq aṣ-Ṣabbāḥ al-Kindī (; ar, أبو يوسف يعقوب بن إسحاق الصبّاح الكندي; la, Alkindus; c. 801–873 AD) was an Arab Muslim philosopher, polymath, mathematician, physician ...
9th century,
Al-Biruni Abu Rayhan Muhammad ibn Ahmad al-Biruni (973 – after 1050) commonly known as al-Biruni, was a Khwarazmian Iranian in scholar and polymath during the Islamic Golden Age. He has been called variously the "founder of Indology", "Father of Co ...
in the early 11th century, al-Tarsusi in the late 12th century, and Fakhr-i-Mudabbir 13th century. Any of these contains far more information about Indian and damascene steels than appears in the entire surviving literature of
classical Greece Classical Greece was a period of around 200 years (the 5th and 4th centuries BC) in Ancient Greece,The "Classical Age" is "the modern designation of the period from about 500 B.C. to the death of Alexander the Great in 323 B.C." ( Thomas R. Marti ...
and
Rome , established_title = Founded , established_date = 753 BC , founder = King Romulus ( legendary) , image_map = Map of comune of Rome (metropolitan city of Capital Rome, region Lazio, Italy).svg , map_caption ...
.Bronson 1986, 19


South India and Sri Lanka

There are many ethnographic accounts of Indian crucible steel production; however, scientific investigations of the remains of crucible steel production have only been published for four regions: three in India and one in Sri Lanka.Feuerbach 2002, 164 Indian/Sri Lankan crucible steel is commonly referred to as wootz, which is generally agreed to be an English corruption of the word ''ukko'' (in the
Canarese Kannada (; ಕನ್ನಡ, ), originally romanised Canarese, is a Dravidian language spoken predominantly by the people of Karnataka in southwestern India, with minorities in all neighbouring states. It has around 47 million native s ...
language) or ''hookoo'' (in the
Telugu language Telugu (; , ) is a Dravidian languages, Dravidian language spoken by Telugu people predominantly living in the Indian states of Andhra Pradesh, Andhra Pradesh and Telangana, where it is also the official language. It is the most widely spoken ...
).Feuerbach 2002, 163 European accounts from the 17th century onwards have referred to the repute and manufacture of "wootz", a traditional crucible steel made specially in parts of southern India in the former provinces of
Golconda Fort (Telugu: గోల్కొండ, romanized: ''Gōlkōnḍa'') is a historic fortress and ruined city located in Hyderabad, Telangana, India. It was originally called Mankal. The fort was originally built by Kakatiya ruler Pratāparu ...
, Mysore and Salem. As yet the scale of excavations and surface surveys is too limited to link the literary accounts to archaeometallurgical evidence.Griffiths and Srinivasan 1997, 111 The proven sites of crucible steel production in south India, e.g. at Konasamudram and Gatihosahalli, date from at least the late medieval period, 16th century.Srinivasan 1994, 52 One of the earliest known potential sites, which shows some promising preliminary evidence that may be linked to
ferrous In chemistry, the adjective Ferrous indicates a compound that contains iron(II), meaning iron in its +2 oxidation state, possibly as the divalent cation Fe2+. It is opposed to " ferric" or iron(III), meaning iron in its +3 oxidation state, suc ...
crucible processes in
Kodumanal Kodumanal is a village located in the Erode district in the southern Indian state of Tamil Nadu. It was once a flourishing ancient trade city known as Kodumanam, as inscribed in ''Patittrupathu'' of Sangam Literature. The place is an important ...
, near Coimbatore in
Tamil Nadu Tamil Nadu (; , TN) is a state in southern India. It is the tenth largest Indian state by area and the sixth largest by population. Its capital and largest city is Chennai. Tamil Nadu is the home of the Tamil people, whose Tamil language ...
.Ranganathan and Srinivasan 2004, 117 The site is dated between the third century BCE and the third century CE.Craddock 2003, 245 By the seventeenth century the main centre of crucible steel production seems to have been in Hyderabad. The process was apparently quite different from that recorded elsewhere.Craddock 1995, 281 Wootz from Hyderabad or the Decanni process for making watered blades involved a co-fusion of two different kinds of iron: one was low in carbon and the other was a high-carbon steel or cast iron.Moshtagh Khorasani 2006, 108
Wootz steel Wootz steel, also known as Seric steel, is a crucible steel characterized by a pattern of bands and high carbon content. These bands are formed by sheets of microscopic carbides within a tempered martensite or pearlite matrix in higher carbon ...
was widely exported and traded throughout ancient Europe, China, the
Arab world The Arab world ( ar, اَلْعَالَمُ الْعَرَبِيُّ '), formally the Arab homeland ( '), also known as the Arab nation ( '), the Arabsphere, or the Arab states, refers to a vast group of countries, mainly located in Western A ...
, and became particularly famous in the Middle East, where it became known as Damascus steel.Srinivasan 1994Srinivasan & Griffiths Recent archaeological investigations have suggested that Sri Lanka also supported innovative technologies for iron and steel production in antiquity.Ranganathan and Srinivasan 2004, 125 The Sri Lankan system of crucible steel making was partially independent of the various Indian and Middle Eastern systems.Bronson 1986, 43 Their method was something similar to the method of carburization of wrought iron. The earliest confirmed crucible steel site is located in the knuckles range in the northern area of the Central Highlands of Sri Lanka dated to 6th–10th centuries CE.Feuerbach 2002, 168 In twelfth century the land of Serendib (Sri Lanka) seems to have been the main supplier of crucible steel, but over the centuries production slipped back, and by the nineteenth century just a small industry survived in the Balangoda district of the central southern highlands.Craddock 1995, 279 A series of excavations at Samanalawewa indicated the unexpected and previously unknown technology of west-facing
smelting Smelting is a process of applying heat to ore, to extract a base metal. It is a form of extractive metallurgy. It is used to extract many metals from their ores, including silver, iron, copper, and other base metals. Smelting uses heat and a c ...
sites, which are different types of steel production.Juleff 1998, 51 These furnaces were used for direct smelting to steel.Juleff 1998, 222 These are named "west facing" because they were located on the western sides of hilltops to use the prevailing wind in the smelting process.Juleff 1998, 80 Sri Lankan furnace steels were known and traded between the 9th and 11th centuries and earlier, but apparently not later.Juleff 1998, 221 These sites were dated to the 7th–11th centuries. The coincidence of this dating with the 9th century Islamic reference to Sarandib is of great importance. The crucible process existed in India at the same time that the west- facing technology was operating in Sri Lanka.Juleff 1998, 220 Excavations of the Yodhawewa (near Mannar) site (in 2018) have uncovered a lower half of a bottom spherical furnace and crucible fragments used to make crucible steel in Sri Lanka during the 7th-8th centuries AD. The crucible fragments uncovered at the site were similar to the elongated tube-shaped crucibles of Samanalawewa.


Central Asia

Central Asia has a rich history of crucible steel production, beginning during the late 1st millennium CE.Papakhristu and Rehren 2002, 69 From the sites in modern Uzbekistan and Merv in Turkmenistan, there is good archaeological evidence for the large scale production of crucible steel.Rehren and Papakhristu 2000, 55 They all belong in broad terms to the same early
medieval In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire a ...
period between the late 8th or early 9th and the late 12th century CE,Rehren and Papachristou 2003, 396 contemporary with the early
crusades The Crusades were a series of religious wars initiated, supported, and sometimes directed by the Latin Church in the medieval period. The best known of these Crusades are those to the Holy Land in the period between 1095 and 1291 that were ...
. The two most prominent crucible steel sites in eastern Uzbekistan carrying the Ferghana Process are Akhsiket and Pap in the
Ferghana Fergana ( uz, Fargʻona/Фарғона, ), or Ferghana, is a district-level city and the capital of Fergana Region in eastern Uzbekistan. Fergana is about 420 km east of Tashkent, about 75 km west of Andijan, and less than 20 km fr ...
Valley, whose position within the Great
Silk Road The Silk Road () was a network of Eurasian trade routes active from the second century BCE until the mid-15th century. Spanning over 6,400 kilometers (4,000 miles), it played a central role in facilitating economic, cultural, political, and rel ...
has been historically and archaeologically proved.Rehren and Papakhristu 2000, 58 The material evidence consists of large number of archaeological finds relating to steel making from 9th–12th centuries CE in the form of hundreds of thousands of fragments of crucibles, often with massive
slag Slag is a by-product of smelting ( pyrometallurgical) ores and used metals. Broadly, it can be classified as ferrous (by-products of processing iron and steel), ferroalloy (by-product of ferroalloy production) or non-ferrous/base metals (by-p ...
cakes. Archaeological work at Akhsiket, has identified that the crucible steel process was of the carburization of iron metal.Rehren and Papakhristu 2000 This process appears to be typical of and restricted to the Ferghana Valley in eastern Uzbekistan, and it is therefore called the Ferghana Process.Rehren and Papakhristu 2000, 67 This process lasted in that region for roughly four centuries.. Evidence of the production of crucible steel have been found in Merv, Turkmenistan, a major city on the 'Silk Road'. The Islamic scholar
al-Kindi Abū Yūsuf Yaʻqūb ibn ʼIsḥāq aṣ-Ṣabbāḥ al-Kindī (; ar, أبو يوسف يعقوب بن إسحاق الصبّاح الكندي; la, Alkindus; c. 801–873 AD) was an Arab Muslim philosopher, polymath, mathematician, physician ...
(801–866 CE) mentions that during the ninth century CE the region of Khorasan, the area to which the cities
Nishapur Nishapur or officially Romanized as Neyshabur ( fa, ;Or also "نیشاپور" which is closer to its original and historic meaning though it is less commonly used by modern native Persian speakers. In Persian poetry, the name of this city is wri ...
, Merv,
Herat Herāt (; Persian: ) is an oasis city and the third-largest city of Afghanistan. In 2020, it had an estimated population of 574,276, and serves as the capital of Herat Province, situated south of the Paropamisus Mountains (''Selseleh-ye Safē ...
and
Balkh ), named for its green-tiled ''Gonbad'' ( prs, گُنبَد, dome), in July 2001 , pushpin_map=Afghanistan#Bactria#West Asia , pushpin_relief=yes , pushpin_label_position=bottom , pushpin_mapsize=300 , pushpin_map_caption=Location in Afghanistan ...
belong, was a steel manufacturing centre.Feuerbach 2003, 258 Evidence from a metallurgical workshop at Merv, dated to the ninth- early tenth century CE, provides an illustration of the co-fusion method of steel production in crucibles, about 1000 years earlier than the distinctly different wootz process.Feuerbach 1997, 109 The crucible steel process at Merv might be seen as technologically related to what Bronson (1986, 43) calls Hyderabad process, a variation of the wootz process, after the location of the process documented by Voysey in the 1820s.Feuerbach 2003, 264


China

The production of crucible steel began in China around the first century BC, or possibly earlier. The Chinese developed a method of producing pig iron around 1200 BC, which they used to make
cast iron Cast iron is a class of iron– carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuri ...
. By the first century BC, they had developed puddling to produce
mild steel Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states: * no minimum content is specified or required for chromium, cobal ...
and a process of rapidly decarburizing molten cast-iron to make
wrought iron Wrought iron is an iron alloy with a very low carbon content (less than 0.08%) in contrast to that of cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag inclusions (up to 2% by weight), which give it a wood-like "grain" ...
by stirring it atop beds of
saltpeter Potassium nitrate is a chemical compound with the chemical formula . This alkali metal nitrate Salt (chemistry), salt is also known as Indian saltpetre (large deposits of which were historically mined in India). It is an ionic salt of potassium ...
(called the Heaton process, it was independently discovered by John Heaton in the 1860s). Around this time, the Chinese began producing crucible steel to convert excess quantities of cast iron and wrought iron into steel suitable for swords and weapons. In 1064,
Shen Kuo Shen Kuo (; 1031–1095) or Shen Gua, courtesy name Cunzhong (存中) and pseudonym Mengqi (now usually given as Mengxi) Weng (夢溪翁),Yao (2003), 544. was a Chinese polymathic scientist and statesman of the Song dynasty (960–1279). Shen wa ...
, in his book ''
Dream Pool Essays ''The Dream Pool Essays'' (or ''Dream Torrent Essays'') was an extensive book written by the Chinese polymath and statesman Shen Kuo (1031–1095), published in 1088 during the Song dynasty (960–1279) of China. Shen compiled this encycloped ...
'', gave the earliest written description of the patterns in the steel, the methods of sword production, and some of the reasoning behind it:
Ancient people use ''chi kang'', (combined steel), for the edge, and ''jou thieh'' (soft iron) for the back, otherwise it would often break. Too strong a weapon will cut and destroy its own edge; that is why it is advisable to use nothing but combined steel. As for the ''yu-chhang'' (fish intestines) effect, it is what is now called the 'snake-coiling' steel sword, or alternatively, the 'pine tree design'. If you cook a fish fully and remove its bones, the shape of its guts will be seen to be like the lines on a 'snake-coiling sword'.


Modern history


Early modern accounts

The first European references to crucible steel seem to be no earlier than the Post Medieval period.Craddock 2003, 251 European experiments with “
Damascus )), is an adjective which means "spacious". , motto = , image_flag = Flag of Damascus.svg , image_seal = Emblem of Damascus.svg , seal_type = Seal , map_caption = , ...
” steels go back to at least the sixteenth century, but it was not until the 1790s that laboratory researchers began to work with steels that were specifically known to be Indian/wootz.Needham 1958, 128 At this time, Europeans knew of India's ability to make crucible steel from reports brought back by travellers who had observed the process at several places in southern India. From the mid-17th century onwards, European travellers to the Indian subcontinent wrote numerous vivid eyewitness accounts of the production of steel there. These include accounts by
Jean-Baptiste Tavernier Jean-Baptiste Tavernier (1605–1689) was a 17th-century French gem merchant and traveler. Tavernier, a private individual and merchant traveling at his own expense, covered, by his own account, 60,000 leagues in making six voyages to Persia ...
in 1679,
Francis Buchanan Francis Buchanan (15 February 1762 – 15 June 1829), later known as Francis Hamilton but often referred to as Francis Buchanan-Hamilton, was a Scottish physician who made significant contributions as a geographer, zoologist, and botanist whil ...
in 1807, and H.W. Voysey in 1832.Ranganathan and Srinivasan 2004, 60 The 18th, 19th and early 20th century saw a heady period of European interest in trying to understand the nature and properties of wootz steel. Indian wootz engaged the attention of some of the best-known scientists.Ranganathan and Srinivasan 2004, 78 One was
Michael Faraday Michael Faraday (; 22 September 1791 – 25 August 1867) was an English scientist who contributed to the study of electromagnetism and electrochemistry. His main discoveries include the principles underlying electromagnetic inducti ...
who was fascinated by wootz steel. It was probably the investigations of George Pearson, reported at the Royal Society in 1795, which had the most far-reaching impact in terms of kindling interest in wootz amongst European scientists.Ranganathan and Srinivasan 2004, 79 He was the first of these scientists to publish his results and, incidentally, the first to use the word "wootz" in print.Bronson 1986, 30 Another investigator, David Mushet, was able to infer that wootz was made by fusion.Bronson 1986, 31 David Mushet patented his process in 1800.Needham 1958, 132 He made his report in 1805. As it happens, however, the first successful European process had been developed by Benjamin Huntsman some 50 years previously in the 1740s.Craddock 1995, 283


History of production in England

Benjamin Huntsman was a clockmaker in search of a better steel for clock springs. In Handsworth near
Sheffield Sheffield is a city in South Yorkshire, England, whose name derives from the River Sheaf which runs through it. The city serves as the administrative centre of the City of Sheffield. It is historically part of the West Riding of Yorkshire ...
, he began producing steel in 1740 after years of experimenting in secret. Huntsman's system used a coke-fired furnace capable of reaching 1,600 °C, into which up to twelve clay crucibles, each capable of holding about 15 kg of iron, were placed. When the crucibles or "pots" were white-hot, they were charged with lumps of blister steel, an
alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductili ...
of iron and
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...
produced by the
cementation process The cementation process is an obsolete technology for making steel by carburization of iron. Unlike modern steelmaking, it increased the amount of carbon in the iron. It was apparently developed before the 17th century. Derwentcote Steel Fur ...
, and a
flux Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ...
to help remove impurities. The pots were removed after about 3 hours in the furnace, impurities in the form of
slag Slag is a by-product of smelting ( pyrometallurgical) ores and used metals. Broadly, it can be classified as ferrous (by-products of processing iron and steel), ferroalloy (by-product of ferroalloy production) or non-ferrous/base metals (by-p ...
skimmed off, and the molten steel poured into moulds to end up as
cast Cast may refer to: Music * Cast (band), an English alternative rock band * Cast (Mexican band), a progressive Mexican rock band * The Cast, a Scottish musical duo: Mairi Campbell and Dave Francis * ''Cast'', a 2012 album by Trespassers William ...
ingot An ingot is a piece of relatively pure material, usually metal, that is cast into a shape suitable for further processing. In steelmaking, it is the first step among semi-finished casting products. Ingots usually require a second procedure of sha ...
s.Juleff 1998, 11 Complete melting of the steel produced a highly uniform crystal structure upon cooling, which gave the metal increased
tensile strength Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or F_\text within equations, is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials ...
and hardness in comparison with other steels being made at the time. Before the introduction of Huntsman's technique, Sheffield produced about 200 tonnes of steel per year from Swedish wrought iron (see
Oregrounds iron Oregrounds iron was a grade of iron that was regarded as the best grade available in 18th century England. The term was derived from the small Swedish city of Öregrund, the port from which the bar iron was shipped. It was produced using the W ...
). The introduction of Huntsman's technique changed this radically: one hundred years later the amount had risen to over 80,000 tonnes per year, or almost half of Europe's total production. Sheffield developed from a small township into one of Europe's leading industrial cities. The steel was produced in specialised workshops called 'crucible furnaces', which consisted of a workshop at ground level and a subterranean cellar. The furnace buildings varied in size and architectural style, growing in size towards the latter part of the 19th century as technological developments enabled multiple pots to be "fired" at once, using gas as a heating fuel. Each workshop had a series of standard features, such as rows of melting holes, teaming pits, roof vents, rows of shelving for the crucible pots and annealing furnaces to prepare each pot before firing. Ancillary rooms for weighing each charge and for the manufacture of the clay crucibles were either attached to the workshop, or located within the cellar complex. The steel, originally intended for making clock springs, was later used in other applications such as scissors, axes and swords. Sheffield's Abbeydale Industrial Hamlet operates for the public a
scythe A scythe ( ) is an agriculture, agricultural hand tool for mowing grass or Harvest, harvesting Crop, crops. It is historically used to cut down or reaping, reap edible grain, grains, before the process of threshing. The scythe has been largely ...
-making works, which dates from Huntsman's times and is powered by a
water wheel A water wheel is a machine for converting the energy of flowing or falling water into useful forms of power, often in a watermill. A water wheel consists of a wheel (usually constructed from wood or metal), with a number of blades or buckets ...
, using crucible steel made at the site.


Material properties

Previous to Huntsman, the most common method of producing steel was the manufacture of
shear steel The cementation process is an obsolete technology for making steel by carburization of iron. Unlike modern steelmaking, it increased the amount of carbon in the iron. It was apparently developed before the 17th century. Derwentcote Steel Fu ...
. In this method, blister steel produced by cementation was used, which consisted of a core of wrought iron surrounded by a shell of very high-carbon steel, typically ranging from 1.5 to 2.0% carbon. To help homogenize the steel, it was pounded into flat plates, which were stacked and forge welded together. This produced steel with alternating layers of steel and iron. The resulting
billet A billet is a living-quarters to which a soldier is assigned to sleep. Historically, a billet was a private dwelling that was required to accept the soldier. Soldiers are generally billeted in barracks or garrisons when not on combat duty, alth ...
could then be hammered flat, cut into plates, which were stacked and welded again, thinning and compounding the layers, and evening out the carbon more as it slowly diffused out of the high-carbon steel into the lower-carbon iron. However, the more the steel was heated and worked, the more it tended to decarburize, and this outward
diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical ...
occurs much faster than the inward diffusion between layers. Thus, further attempts to homogenize the steel resulted in a carbon content too low for use in items like springs, cutlery, swords, or tools. Therefore, steel intended for use in such items, especially tools, was still being made primarily by the slow and arduous
bloomery A bloomery is a type of metallurgical furnace once used widely for smelting iron from its oxides. The bloomery was the earliest form of smelter capable of smelting iron. Bloomeries produce a porous mass of iron and slag called a ''bloom' ...
process in very small amounts and at high cost, which, albeit better, had to be manually separated from the wrought iron and was still impossible to fully homogenize in the solid state. Huntsman's process was the first to produce a fully homogeneous steel. Unlike previous methods of steel production, the Huntsman process was the first to fully melt the steel, allowing the full diffusion of carbon throughout the liquid. With the use of fluxes it also allowed the removal of most impurities, producing the first steel of modern quality. Due to carbon's high
melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depen ...
(nearly triple that of steel) and its tendency to oxidize (burn) at high temperatures, it cannot usually be added directly to molten steel. However, by adding wrought iron or pig iron, allowing it to dissolve into the liquid, the carbon content could be carefully regulated (in a way similar to Asian crucible-steels but without the stark inhomogeneities indicative of those steels). Another benefit was that it allowed other elements to be alloyed with the steel. Huntsman was one of the first to begin experimenting with the addition of alloying agents like
manganese Manganese is a chemical element with the Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of ...
to help remove impurities such as oxygen from the steel. His process was later used by many others, such as Robert Hadfield and Robert Forester Mushet, to produce the first
alloy steel Alloy steel is steel that is alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to improve its mechanical properties. Alloy steels are broken down into two groups: low alloy steels and high alloy steels. The differe ...
s like mangalloy, high-speed steel, and
stainless steel Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's r ...
. Due to variations in the carbon content of the blister steel, the carbon steel produced could vary in carbon content between crucibles by as much as 0.18%, but on average produced a
eutectoid A eutectic system or eutectic mixture ( ) is a homogeneous mixture that has a melting point lower than those of the constituents. The lowest possible melting point over all of the mixing ratios of the constituents is called the ''eutectic tempe ...
steel containing ~ 0.79% carbon. Due to the quality and high hardenability of the steel, it was quickly adopted for the manufacture of tool steel, machine tools, cutlery, and many other items. Because no oxygen was blown through the steel, it exceeded Bessemer steel in both quality and hardenability, so Huntsman's process was used for manufacturing tool steel until better methods, utilizing an
electric arc An electric arc, or arc discharge, is an electrical breakdown of a gas that produces a prolonged electrical discharge. The current through a normally nonconductive medium such as air produces a plasma; the plasma may produce visible light. ...
, were developed in the early 20th century.''Tool Steels, 5th Edition'' By George Adam Roberts, Richard Kennedy, G. Krauss. ASM International, 1998, p. 4


19th and 20th century production

In another method, developed in the United States in the 1880s, iron and carbon were melted together directly to produce crucible steel. Throughout the 19th century and into the 1920s a large amount of crucible steel was directed into the production of cutting tools, where it was called ''tool steel''. The crucible process continued to be used for specialty steels, but is today obsolete. Similar quality steels are now made with an
electric arc furnace An electric arc furnace (EAF) is a furnace that heats material by means of an electric arc. Industrial arc furnaces range in size from small units of approximately one-tonne capacity (used in foundries for producing cast iron products) up to ...
. Some uses of ''tool steel'' were displaced, first by high-speed steel and later by materials such as
tungsten carbide Tungsten carbide (chemical formula: WC) is a chemical compound (specifically, a carbide) containing equal parts of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine gray powder, but it can be pressed and formed into ...
.


Crucible steel elsewhere

Another form of crucible steel was developed in 1837 by the Russian engineer Pavel Anosov. His technique relied less on the heating and cooling, and more on the
quenching In materials science, quenching is the rapid cooling of a workpiece in water, oil, polymer, air, or other fluids to obtain certain material properties. A type of heat treating, quenching prevents undesired low-temperature processes, such as ...
process of rapidly cooling the molten steel when the right crystal structure had formed within. He called his steel bulat; its secret died with him. In the United States crucible steel was pioneered by William Metcalf.


See also

*
Damascus steel Damascus steel was the forged steel of the blades of swords smithed in the Near East from ingots of Wootz steel either imported from Southern India or made in production centres in Sri Lanka, or Khorasan, Iran. These swords are characterized by ...
* Noric steel *
Pattern welding Pattern welding is the practice in sword and knife making of forming a blade of several metal pieces of differing composition that are forge welding, forge-welded together and twisted and manipulated to form a pattern. Often mistakenly called Dam ...


Notes


References

* Bronson, B., 1986. "The Making and Selling of Wootz, a Crucible Steel of India". ''Archeomaterials'' 1.1, 13–51. * Craddock, P.T., 1995. ''Early Metal Mining and Production''. Cambridge: Edinburgh University Press. * Craddock, P.T, 2003. "Cast Iron, Fined Iron, Crucible Steel: Liquid Iron in the Ancient World". In: P.T., Craddock, and J., Lang. (eds) ''Mining and Metal Production through the ages''. London: The British Museum Press, 231–257. * Feuerbach, A.M., 2002. "Crucible Steel in Central Asia: Production, Use, and Origins": a dissertation presented to the University of London. * Feuerbach, A., Griffiths, D. R. and Merkel, J.F., 1997. "Production of crucible steel by co-fusion: Archaeometallurgical evidence from the ninth- early tenth century at the site of Merv, Turkmenistan". In: J.R., Druzik, J.F., Merkel, J., Stewart and P.B., Vandiver (eds) ''Materials issues in art and archaeology V: symposium held 3–5 December 1996'', Boston, Massachusetts; Pittsburgh, Pa: Materials Research Society, 105–109. * Feuerbach, A., Griffiths, D., and Merkel, J.F., 1995. ''Analytical Investigation of Crucible Steel Production at Merv, Turkmenistan''. IAMS 19, 12–14. * Feuerbach, A.M., Griffiths, D.R. and Merkel, J.F., 1998. "An examination of crucible steel in the manufacture of Damascus steel, including evidence from Merv", Turkmenistan. ''Metallurgica Antiqua'' 8, 37–44. * Feuerbach, A.M., Griffiths, D.R., and Merkel, J.F., 2003. "Early Islamic Crucible Steel Production at Merv, Turkmenistan", In: P.T., Craddock, J., Lang (eds). ''Mining and Metal Production through the ages''. London: The British Museum Press, 258–266. * Freestone, I.C. and Tite, M. S. (eds) 1986. "Refractories in the Ancient and Preindustrial World", In: W.D., Kingery (ed.) and E., Lense (associated editor) ''High technology ceramics : past, present, and future ; the nature of innovation and change in ceramic technology''. Westerville, OH: American Ceramic Society, 35–63. * Juleff, G., 1998. ''Early Iron and Steel in Sri Lanka: a study of the Samanalawewa area''. Mainz am Rhein: von Zabern. * Moshtagh Khorasani, M., 2006. Arms and ''Armor from Iran, the Bronze Age to the End of the Qajar Period''. Tübingen: Legat. * Needham, J. 1958. "The development of iron and steel technology in China": second biennial Dickinson Memorial Lecture to the Newcomen Society, 1900–1995. Newcomen Society. * Papakhristu, O.A., and Rehren, Th., 2002. "Techniques and Technology of Ceramic Vessel Manufacture Crucibles for Wootz Smelting in Centural Asia". In: V., Kilikoglou, A., Hein, and Y., Maniatis (eds) ''Modern Trends in Scientific Studies on Ancient Ceramics, papers presented at the 5th European Meeting on Ancient Ceramics'', Athens 1999/ Oxford : Archaeopress, 69–74. * Ranganathan, S. and Srinivasan, Sh., 2004. ''India's Legendary Wootz steel, and advanced material of the ancient world''. Bangalore: National Institute of Advanced Studies: Indian Institute of Science. * Rehren, Th. and Papachristou, O., 2003. "Similar like White and Black: a Comparison of Steel-making Crucibles from Central Asia and the Indian subcontinent". In: Th., Stöllner et al. (eds) ''Man and mining : Mensch und Bergbau : studies in honour of Gerd Weisgerber on occasion of his 65th birthday''. Bochum : Deutsches Bergbau-Museum, 393–404. * Rehren, Th. and Papakhristu, O. 2000. "Cutting Edge Technology – the Ferghana Process of medieval crucible steel smelting". ''Metalla'' 7.2, 55–69 Srinivasan, Sh., 1994. "woots crucible steel: a newly discovered production site in south India". Institute of Archaeology, University College London, 5, 49–61. * Srinivasan, Sh., and Griffiths, D., 1997. Crucible Steel in South India-Preliminary Investigations on Crucibles from some newly identified sites. In: J.R., Druzik, J.F., Merkel, J., Stewart and P.B., Vandiver (eds) Materials issues in art and archaeology V: symposium held 3–5 December 1996, Boston, Massachusetts; Pittsburgh, Pa: Materials Research Society, 111–125. * Srinivasan, S. and Griffiths, D. ''South Indian wootz: evidence for high-carbon steel from crucibles from a newly identified site and preliminary comparisons with related finds''. Material Issues in Art and Archaeology-V, Materials Research Society Symposium Proceedings Series Vol. 462. * Srinivasan, S. & Ranganathan, S
''Wootz Steel: An Advanced Material of the Ancient World''. Bangalore: Indian Institute of Science.
* Wayman Michael L. ''The Ferrous Metallurgy of Early Clocks and Watches''. The British Museum 2000 *


External links


Merv, Turkmenistan





Making Steel by Hand: A 1949 British Pathe newsreel showing the production of crucible steel in Sheffield

Metalworking History Detailed from 9000 BC
{{DEFAULTSORT:Crucible Steel Steels Steelmaking Indian inventions Firing techniques