History of ferrous metallurgy

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The history of ferrous metallurgy began far back in prehistory, most likely with the use of iron from meteors. The smelting of iron in bloomeries probably began in Anatolia or the Caucasus in the second millennium BC or the latter part of the preceding one. Cast iron was first produced in China about 550 BC, but not in Europe until early in the second millennium AD. During the medieval period, means were found in Europe of producing wrought iron from cast iron (in this context known as pig iron) using finery forges. For all these processes, charcoal was required as fuel.

Steel (with a smaller carbon content than pig iron but more than wrought iron) was first produced in antiquity. New methods of producing it by carburizing bars of iron in the cementation process were devised in the 17th century AD. In the Industrial Revolution, new methods of producing bar iron without charcoal were devised and these were later applied to produce steel. In the late 1850s, Henry Bessemer invented a new steelmaking process, involving blowing air through molten pig iron, to produce mild steel. This and other 19th century and later processes have led to wrought iron no longer being produced.

Contents 1 Meteoric iron 2 Bloomery iron 2.1 Eastern Mediterranean 2.1.1 Further reading 2.2 Developments in China 2.3 India and Sri Lanka 2.4 Africa 3 Medieval and early modern Europe 3.1 Powered bloomeries 3.2 The first blast furnaces in Europe 3.3 Osmond iron 3.4 Finery process 3.5 Steelmaking in early modern Europe 4 The transition to coke in England 4.1 Beginnings 4.2 Abraham Darby and his successors 4.3 New forge processes 5 Hot blast 6 Industrial steelmaking 7 References

[edit] Meteoric iron

Because meteorites fall from the sky, some linguists have conjectured that the English word iron (OE īsern), which has cognates in many northern and western European languages, derives from the Etruscan aisar which means "the gods".^[1] Even if this is not the case, the word is likely a loan into pre-Proto-Germanic from Celtic or Italic. Krahe compares Old Irish, Illyrian, Venetic and Messapic forms).^[2] The meteoric origin of iron in its first use by humans is also alluded to in the Quran : "and We sent down Iron in which has incredible strength and many benefits for mankind".^[3] 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.^[4] However, their use appears to be ceremonial, and iron was probably an expensive metal, perhaps more expensive than gold. 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.

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.

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 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.

[edit] Bloomery iron

[edit] Eastern Mediterranean

Ancient Greeks considered the Halybes to be "the inventors of iron".^{[citation needed]} The people of the Caucasian Isthmus, Khaldi people (or Khalib/Halyb and Halisones by Strabo) were one of the oldest west-Georgian tribes (4th to 2nd millennia BC). The word "Halybes" may refer to people in Anatolia or in the Caucasus, and it is also possible that by the time the Greeks knew of iron, it was associated with Chaldea, where it was produced in large quantities (but not where it was invented).^{[citation needed]}

About 1500 BC, increasing numbers of smelted iron objects (distinguishable from meteoric iron by the lack of nickel in the product) appear in Mesopotamia, Anatolia, and Egypt.^{[citation needed]}.^[5] In the Iliad, weaponry is mostly bronze, but iron bars are used for trade. An actual iron macehead was located at Troy in 1902.^{[citation needed]}. Some resources (see the reference What Caused the Iron Age? below) suggest that iron was being created then as a by-product of copper refining, as sponge iron, and was not reducible by the metallurgy of the time. By 1600 BC to 1200 BC, iron was used increasingly in the Middle East, but did not supplant the dominant use of bronze^{[citation needed]}.

During the Early Iron Age (12th to 10th centuries BCE) iron came to replace bronze as the dominant metal used for tools and weapons across the Eastern Mediterranean (the Levant, Cyprus, Greece, Crete, Anatolia, and Egypt).^[6] Although iron objects are known from the Bronze Age across the Eastern Mediterranean, they occur only sporadically and are statistically insignificant compared to the quantity of bronze objects during this time.^[7]

The traditional explanation of the rise of iron was that the Hittites of Anatolia had mastered iron technology during the Late Bronze Age.^[8] They maintained a monopoly on ironworking, which allowed them to establish their empire based on iron's superiority over bronze. The invasions of the Sea Peoples at the end of the Late Bronze Age that brought an end to the Hittite empire broke up the monopoly, spreading the technological knowledge throughout the Eastern Mediterranean as a result of their migrations. This theory is no longer held in the mainstream of scholarship as a result of two principle problems.^[9] The first is that there is no archaeological evidence that the Hittites held a monopoly on iron during the Bronze Age. While there are some iron objects from Bronze Age Anatolia, the number is comparable to iron objects found in Egypt and other places of the same time period, and only a small number of these objects are weapons.^[10] The second problem with the Hittite monopoly theory is that iron is not inherently superior to bronze. Three things have to be done to iron ore in order for its properties to be superior to bronze: it must be made steel by adding carbon, then hardened by quenching, and finally tempered to make it less brittle.^[11]

A more recent theory for the rise of iron has been that the collapse of the empires at the end of the Late Bronze Age disrupted the trade routes necessary for bronze production.^[12] Copper and, more importantly, tin were not widely available and needed to be transported over long distances. It is assumed that during the Early Iron Age this was not possible on a scale necessary to satisfy the needs of metalworkers. Since iron ore is more abundant naturally, metalworkers exploited this more universal metal. So, the rise of iron was the result of necessity due principally to the shortage of tin. The problem with this theory is that there is nothing archaeologically that would suggest a bronze or tin shortage in the Early Iron Age.^[13] Bronze objects are still abundant and these objects have the same percentage of tin as those from the Late Bronze Age.

Mesopotamia was fully into the Iron Age by 900 BC, central Europe by 800 BC. 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.

Concurrent with the transition from bronze to iron was the discovery of carburization, which was the process of adding carbon to the irons of the time. Iron was recovered as sponge iron, a mix of iron and slag with some carbon and/or carbide, which was then repeatedly hammered and folded over to free the mass of slag and oxidise out carbon content, so creating the product wrought iron. Wrought iron was very low in carbon content and was not easily hardened by quenching. The people of the Middle East found that a much harder product could be created by the long term heating of a wrought iron object in a bed of charcoal, which was then quenched in water or oil. The resulting product, which had a surface of steel, was harder and less brittle than the bronze it began to replace. 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.^{[citation needed]}

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.

[edit] Further reading

Pleiner, R. (2000) Iron in Archaeology. The European Bloomery Smelters, Praha, Archeologický Ústav Av Cr. Veldhuijzen, H.A. (2005) 'Technical Ceramics in Early Iron Smelting. The Role of Ceramics in the Early First Millennium Bc Iron Production at Tell Hammeh (Az-Zarqa), Jordan'. In: Prudêncio, I.Dias, I. and Waerenborgh, J.C. (Eds.) Understanding People through Their Pottery; Proceedings of the 7th European Meeting on Ancient Ceramics (Emac '03). Lisboa, Instituto Português de Arqueologia (IPA). Veldhuijzen, H.A. and Rehren, T. (2006) Iron Smelting Slag Formation at Tell Hammeh (Az-Zarqa), Jordan. In: Pérez-Arantegui, J. (Ed.) Proceedings of the 34th International Symposium on Archaeometry, Zaragoza, 3-7 May 2004. Zaragoza, Institución «Fernando el Católico» (C.S.I.C.) Excma. Diputación de Zaragoza.

[edit] Developments in China

Archaeologists and historians debate whether bloomery-based ironworking ever spread to China from the Middle East. Around 500 BC, however, metalworkers in the southern state of 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 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–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 puddle molten pig iron, stirring it in the open air until it lost its carbon and became wrought iron. (In 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.

[edit] India and Sri Lanka

Iron was used in India as early as 250 BC. The famous iron pillar in the Qutb complex in Delhi is made of very pure iron (98%) and has not rusted or eroded till this day. This is believed to have been made by welding together blooms of iron, indicating the spread of the technology described above.

Perhaps as early as 300 BC, although certainly by AD 200, high quality steel was being produced in southern India also by what Europeans would later call the 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. One of the earliest evidence of steel making comes to us from Samanalawewa area in Sri Lanka where thousands of sites were found.^[14]

[edit] Africa

Iron use, in smelting and forging for tools, appears in Subsaharan Africa by 1200 BC.^[15]

[edit] Medieval and early modern Europe

There was no fundamental change in the technology of iron production in Europe for many centuries. Iron continued to be made in bloomeries. However there were two separate developments in the Medieval period. One was the application of water power to the bloomery process. The other was the first European production in cast iron.

[edit] Powered bloomeries

Main article: bloomery

Sometime in the medieval period, water power was applied to the bloomery process. In England, the first clear documentary evidence for this is the accounts of a forge of the Bishop of Durham, near Bedburn in 1408,^[16] but that was certainly not the first such ironworks. In the Furness district of England, powered bloomeries were in use into the beginning of the 18th century, and near Garstang until about 1770.

The Catalan Forge was a variety of powered bloomery. Bloomeries with hot blast were used in upstate New York in the mid 19th century.

[edit] The first blast furnaces in Europe

Cast iron development lagged in Europe, as the smelters could only achieve temperatures of about 1000 C; or perhaps they did not want hotter temperatures, as they were seeking to produce blooms as a precursor of wrought iron, not cast iron. Through a good portion of the Middle Ages, in Western Europe, iron was thus still being made by the working of iron blooms into wrought iron. Some of the earliest casting of iron in Europe occurred in Sweden, in two sites, Lapphyttan and Vinarhyttan, between 1150 and 1350 CE. Some scholars have speculated the practice followed the Mongols across Russia to these sites, but there is no clear proof of this hypothesis, and it would certainly not explain the pre-mongol datings of many of these iron-production centres. In any event, by the late fourteenth century, a market for cast iron goods began to form, as a demand developed for cast iron cannonballs.

[edit] Osmond iron

Main article: osmond iron

Iron from furnaces such as Lapphyttan was refined into into wrought iron by the osmond process. The pig iron from the furnace was melted in front of a blast of air and the droplets caught on a staff (which was spun). This formed a ball of iron, known as an osmond. This was probably a traded commodity by c.1200.

[edit] Finery process

Main article: Finery forge

An alternative method of decarburising pig iron seems to have been devised in the region around Namur in the 15th century. This Walloon process spread by the end of that century to the Pay de Bray on the eastern boundary of Normandy before the end of that century, and to then to England, where it became the main method of making wrought iron by 1600. It was introduced to Sweden by Louis de Geer in the early 17th century and was used to make the oregrounds iron favoured by English steelmakers.

A variation on this was the German process. This became the main method of producing bar iron in Sweden.

[edit] Steelmaking in early modern Europe

Main article: cementation process

In the early 17th century, ironworkers in western Europe had found a means (called cementation) to carburize wrought iron. 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 (see cementation process). One of the earliest places where this was used in England was at Coalbrookdale, where Sir Basil Brooke had two cementation furnaces (recently excavated). For a time in the 1610s, he owned a patent on the process, but had to surrender this in 1619. He probably used Forest of Dean iron as his raw material, but it was soon found that oregrounds iron was more suitable.

Main article: crucible steel

The quality of the steel could be improved by faggoting, producing shear steel. However in the 1740s, Benjamin Huntsman found a means of melting blister steel, made by the cementation process in crucibles; this was cast usually as ingots as crucible steel. This is more homogeneous than blister steel.

[edit] The transition to coke in England

[edit] Beginnings

Early iron smelting used charcoal as both the heat source and the reducing agent. By the 18th century, the availability of wood for making charcoal was limiting the expansion of of iron production, so that England became increasingly dependent for a considerable part of the iron required by its industry, on Sweden (from the mid 17th century) and then from about 1725 also on Russia.^[17]

Smelting with coal (or its derivative coke) was a long sought objective. The production of pig iron with coke was probably achieved by Dud Dudley in the 1620s, and with a mixed fuel made from coal and wood again in the 1670s. However this was probably only a technological rather than a commercial success. Shadrach Fox may have smelted iron with coke at Coalbrookdale in Shropshire in the 1690s, but only to make cannon balls and other cast iron products such as shells. However, in the peace after the Nine Years War, there was no demand for these.^[18]

[edit] Abraham Darby and his successors

Main article: Abraham Darby I

In 1707, Abraham Darby patented a method of making cast iron pots. His pots were thinner and hence cheaper than those of his rivals. Needing a larger supply of pig iron he leased the blast furnace at Coalbrookdale in 1709. There, he made iron using coke, thus establishing the first successful business in Europe to do so. His products were all of cast iron, though his immediate successors attempted (with little commercial success) to fine this to bar iron.^[19]

bar iron thus continued normally to be made with charcoal pig iron until the mid 1750s. In 1755 Abraham Darby II (with partners) opened a new coke-using furnace at Horsehay in Shropshire, and this was followed by others. These supplied coke pig iron to finery forges of the traditonal kind for the production of bar iron. The reason for the delay remains controversial.^[20]

[edit] New forge processes

It was only after this that economically viable means of converting pig iron to bar iron began to be devised. A process known as potting and stamping was devised in the 1760s and improved in the 1770s, and seems to have been widely adopted in the West Midlands from about 1785. However, this was largely replaced by Henry Cort's puddling process, patented in 1784, but probably only made to work with grey pig iron in about 1790. These processes permitted the great expansion in the production of iron that constitutes the Industrial Revolution for the iron industry.^[21]

In the early 19th century, Hall discovered that the addition of iron oxide to the charge of the puddling furnace caused a violent reaction, in which the pig iron was decarburised, this became known as 'wet puddling'. It was also found possible to produce steel by stopping the puddling process before decarburisation was complete.

[edit] Hot blast

The efficiency of the blast furnace was improved by the change to hot blast, patented by James Beaumont Neilson in Scotland in 1828. This further reduced production costs. Within a few decades, the practice was to have a 'stove' as large as the furnace next to it into which the waste gas (containing CO) from the furnace was directed and burnt. The resultant heat was used to preheat the air blown into the furnace.^[22]

[edit] Industrial steelmaking

Apart from some production of puddled steel, English steel continued to be made by the cementation process, sometimes followed by remelting to produce crucible steel. These were batch-based processes whose raw material was bar iron, particualrly Swedish oregrounds iron. The problem of mass-producing cheap steel was solved in 1855 by Henry Bessemer, with the introduction of the 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. 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.

Finally, the 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.

Until these 19th century developments, steel was an expensive commodity and only used for a limited number of purposes where a particularly hard or flexible metal was needed, as in the cutting edges of tools and springs. The widespread availability of inexpensive steel powered the second industrial revolution and modern society as we know it. Mild steel ultimately replaced wrought iron for almost all purposes, and wrought iron is not now (or is hardly now) made. With minor exceptions, alloy steels only began to be made in the late 19th century. Stainless steel was only developed on the eve of the First World War and only began to come into widespread use in the 1920s. These alloy steels are all dependent on the wide availability of inexpensive iron and steel and the ability to alloy it at will.

[edit] References

1. ^ Benvéniste 1969 cit. dep; Rick Mc Callister and Silvia Mc Callister-Castillo (1999). Etruscan Glossary. Retrieved on 2006-06-19.
2. ^ Indogermanische Forschungen|IF]] 46:184f
3. ^ Quran 57:25 page:541. Template:Edition needed
4. ^ R. F. Tylecote, A Hisotry of Metallurgy (2nd edn, 1992), 3
5. ^ E. Photos, 'The Question of Meteoritic versus Smelted Nickel-Rich Iron: Archaeological Evidence and Experimental Results' World Archaeology Vol. 20, No. 3, Archaeometallurgy (Feb., 1989), pp. 403-421.
6. ^ Waldbaum, Jane C. From Bronze to Iron. Göteburg: Paul Astöms Förlag (1978): 56-8.
7. ^ Waldbaum 1978: 23.
8. ^ Muhly, James D. 'Metalworking/Mining in the Levant' pp. 174-83 in Near Eastern Archaeology ed. S. Richard Winona Lake, IN: Eisenbrauns (2003): 180.
9. ^ Muhly 2003: 180.
10. ^ Waldbaum 1978: 23.
11. ^ Waldbaum 1978: 69.
12. ^ Muhly 2003: 180.
13. ^ Muhly 2003:180.
14. ^ Juleff, 1996
15. ^ Duncan E. Miller and N.J. Van Der Merwe, 'Early Metal Working in Sub Saharan Africa' Journal of African History 35 (1994) 1-36; Minze Stuiver and N.J. Van Der Merwe, 'Radiocarbon Chronology of the Iron Age in Sub-Saharan Africa' Current Anthropology 1968.
16. ^ R. F. Tylecote, A History of Metallurgy, 76.
17. ^ P. W. King, 'The production and consumption of bar iron in early modern England and Wales' Economic History Review 58(1) (2005), 1-33.
18. ^ P. W. King, 'Dud Dudley's contribution to metallurgy' Historical Metallurgy 36(1) (2002), 43-53; P. W. King, 'Sir Clement Clerke and the adoption of coal in metallurgy' Trans. Newcomen Soc. 73(1) (2001-2), 33-52.
19. ^ A. Raistrick, A dynasty of Ironfounders (1953; 1989); N. Cox, 'Imagination and innovation of an industrial pioneer: The first Abraham Darby' Industrial Archaeology Review 12(2) (1990), 127-144.
20. ^ A. Raistrick, Dynasty; C. K. Hyde, Technological change and the British iron industry 1700-1870 (Princeton, 1977), 37-41; P. W. King, 'The Iron Trade in England and Wales 1500-1815' (Ph. D. thesis, Wolverhampton University, 2003), 128-41.
21. ^ G. R. Morton and N. Mutton, 'The transition to Cort's puddling process' Journal of Iron and Steel Institute 205(7) (1967), 722-8; R. A. Mott (ed. P. Singer), Henry Cort: The great finer: creator of puddled iron (1983); P. W. King, 'Iron Trade', 185-93.
22. ^ A. Birch, Economic History of the British Iron and Steel Industry , 181-9; C. K. Hyde, Technological Change and the British iron industry (Princeton 1977), 146-59.