The history of ferrous metallurgy began far back in prehistory, most likely with the use of iron from meteorites. The smelting of iron in bloomeries began in the 12th century BC in India, Anatolia or the Caucasus. Iron use, in smelting and forging for tools, appeared in Sub-Saharan Africa by 1200 BC.[1] The use of cast iron was known in the 1st millennium BC. 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.
Meteoric iron
Willamette Meteorite, the sixth largest in the world, is an iron-nickel meteorite
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".[2] 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).[3] 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".[4]
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.[5] 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 artefacts.
Iron meteorites consist overwhelmingly of nickel-iron alloys. The metal taken from these meteorites is known as meteoric iron and was one of the earliest sources of usable iron available to man.
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 shaft 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 artefacts 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.
Iron Age
Near East
Mining areas of the ancient Middle East. Boxes colors: arsenic is in brown, copper in red, tin in grey, iron in reddish brown, gold in yellow, silver in white and lead in black. Yellow area stands for arsenic bronze, while grey area stands for tin bronze.
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.[6]
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).[7] 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.[8]
The traditional explanation of the rise of iron was that the Hittites of Anatolia had mastered iron technology during the Late Bronze Age.[9] 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.[10] One problem with it 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.[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.
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.
India
The Delhi iron pillar is an example of the iron extraction and processing methodologies of India. The iron pillar at Delhi has withstood corrosion for the last 1600 years.
Archaeological sites in India, such as Malhar, Dadupur, Raja Nala Ka Tila and Lahuradewa in present day Uttar Pradesh show iron implements in the period between 1800 BC - 1200 BC.[14] Early iron objects found in India can be dated to 1400 BC by employing the method of radio carbon dating. Spikes, knives, daggers, arrow-heads, bowls, spoons, saucepans, axes, chisels, tongs, door fittings etc. ranging from 600 BC to 200 BC have been discovered from several archaeological sites of India.[15] Some scholars believe that by the early 13th century BC, iron smelting was practiced on a bigger scale in India, suggesting that the date the technology's inception may be placed earlier.[14] In Southern India (present day Mysore) iron appeared as early as 11th to 12th centuries BC; these developments were too early for any significant close contact with the northwest of the country.[16]
The beginning of the 1st millennium BC saw extensive developments in iron metallurgy in India. Technological advancement and mastery of iron metallurgy was achieved during this period of peaceful settlements.[16] The coming years saw several advancements being made to the technology involved in metallurgy during the politically stable Maurya period.[17]
Greek historian Herodotus wrote the first western account of the use of iron in India.[15] The Indian mythological texts, the Upnishads, have mentions of weaving, pottery, and metallurgy as well.
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 a crucible and heated until the iron melted and absorbed the carbon.[19] Iron chain was used in Indian suspension bridges as early as the 4th century.[20]
Wootz steel was produced in India and Sri Lanka from around 300 BC. This early steel-making method employed the use of a wind furnace, blown by the monsoon winds.[19] Also known as Damascus steel, wootz is famous for its durability and ability to hold an edge. It was originally created from a number of different materials including various trace elements. It was essentially a complicated alloy with iron as its main component. Recent studies have suggested that carbon nanotubes were included in its structure, which might explain some of its legendary qualities, though given the technology available at that time, they were probably produced more by chance than by design.[21]
The iron pillar of Delhi, the capital city of India, is one of the world's foremost metallurgical curiosities, standing in the famous Qutb complex. The pillar—almost seven meters high and weighing more than six tonnes—was erected by Chandragupta II Vikramaditya.[22] The pillar is made up of 98% wrought iron of pure quality, and is a testament to the high level of skill achieved by ancient Indian iron smiths in the extraction and processing of iron. It has attracted the attention of archaeologists and metallurgists as it has withstood corrosion for the last 1600 years, despite harsh weather.
Historians of metallurgy hold that Indian iron smelters had acquired an advanced and precise knowledge about the production of iron and steel, and the related details including the thermo-mechanical aspects and heat treatment. The Indians developed wootz, which was popular in international markets. The Dutch carried wootz from South India to Europe, where it subsequently spread through mass production.[23]
Will Durant wrote in The Story of Civilization I: Our Oriental Heritage:
“
"Something has been said about the chemical excellence of cast iron in ancient India, and about the high industrial development of the Gupta times, when India was looked to, even by Imperial Rome, as the most skilled of the nations in such chemical industries as dyeing, tanning, soap-making, glass and cement... By the sixth century the Hindus were far ahead of Europe in industrial chemistry; they were masters of calcinations, distillation, sublimation, steaming, fixation, the production of light without heat, the mixing of anesthetic and soporific powders, and the preparation of metallic salts, compounds and alloys. The tempering of steel was brought in ancient India to a perfection unknown in Europe till our own times; King Porus is said to have selected, as a specially valuable gift from Alexander, not gold or silver, but thirty pounds of steel. The Moslems took much of this Hindu chemical science and industry to the Near East and Europe; the secret of manufacturing "Damascus" blades, for example, was taken by the Arabs from the Persians, and by the Persians from India."
”
Europe
Axe made of iron, dating from Swedish Iron Age, found at Gotland, Sweden.
Ironworking is first introduced to Central Europe in Hallstatt C (8th century BC). Throughout the 7th to 6th centuries, iron artefacts remain luxury items reserved for an elite. This changes dramatically shortly after 500 BC with the rise of the La Tène culture, from which time iron metallurgy also becomes common in Northern Europe and Britain. The spread of ironworking in Central and Western Europe is associated with Celtic expansion. By the 1st century BC, Noric steel was famous for its quality and sought-after by the Roman military.
China
The puddling process of smelting iron ore to make wrought iron from pig iron, with the right illustration displaying men working a blast furnace, from the Tiangong Kaiwu encyclopedia, 1637.
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 which could create cast iron.[24][25][26] 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.
An illustration of furnace bellows operated by waterwheels, from the Nong Shu, by Wang Zhen, 1313 AD, during the Yuan Dynasty in China.
During the Han Dynasty (202 BC–AD 220), Chinese ironworking achieved a scale and sophistication not reached in the West until the eighteenth century[citation needed]. 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.) By the 1st century BC, 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.[27][28][29] 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. Also, the ancient city of Wan (Nanyang) from the Han period forward was a major center of the iron and steel industry.[30] Along with their original methods of forging steel, the Chinese had also adopted the production methods of creating Wootz steel, an idea imported from India to China by the 5th century AD.[31] The Chinese during the ancient Han Dynasty were also the first to apply hydraulic power (ie. a waterwheel) in working the inflatable bellows of the blast furnace. This was recorded in the year 31 AD, an innovation of the engineer Du Shi, Prefect of Nanyang.[32] Although Du Shi was the first to apply water power to bellows in metallurgy, the first drawn and printed illustration of its operation with water power came in 1313 AD, in the Yuan Dynasty era text called the Nong Shu. In the 11th century, there is evidence of the production of steel in Song China using two techniques: a "berganesque" method that produced inferior, heterogeneous steel and a precursor to the modern Bessemer process that utilized partial decarbonization via repeated forging under a cold blast. By the 11th century, there was also a large amount of deforestation in China due to the iron industry's demands for charcoal. However, by this time the Chinese had figured out how to use bituminous coke to replace the use of charcoal, and with this switch in resources many acres of prime timberland in China were spared. This switch in resources from charcoal to coal was later used in Europe by the 17th century.
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