HIST363: Global Perspectives on Industrialization

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 B.C.E. small items, such as the tips of spears and ornaments, were being fashioned from iron recovered from meteorites. About six percent of meteorites are composed of an iron-nickel alloy, and iron recovered from meteorite falls allowed ancient peoples to manufacture small numbers of iron artifacts.

Meteoric iron was also fashioned into tools in precontact North America. Beginning around the year 1000, the Thule people of Greenland began making harpoons and other edged tools from pieces of the Cape York meteorite. These artifacts were also used as trade goods with other Arctic peoples: tools made from the Cape York meteorite have been found in archaeological sites more than 1,000 miles (1,600 kilometers) 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.

The name for iron in several ancient languages means "sky metal" or something similar. In distant antiquity, iron was regarded as a precious metal, suitable for royal ornaments.

Presently iron is the most-recycled substance on the planet.

The Iron Age

Iron axehead from Swedish Iron Age, found at Gotland, Sweden

Beginning between 3000 B.C.E. to 2000 B.C.E., increasing numbers of smelted iron objects (distinguishable from meteoric iron by their lack of nickel) appear in Anatolia, Egypt, and Mesopotamia. The oldest known samples of iron that appear to have been smelted from iron oxides are small lumps found at copper-smelting sites on the Sinai Peninsula, dated to about 3000 B.C.E. Some iron oxides are effective fluxes for copper smelting; it is possible that small amounts of metallic iron were made as a by-product of copper and bronze production throughout the Bronze Age.

In Anatolia, smelted iron was occasionally used for ornamental weapons: an iron-bladed dagger with a bronze hilt has been recovered from a Hattic tomb dating from 2500 B.C.E. Also, the ancient Egyptian ruler Tutankhamun died in 1323 B.C.E. 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. The early Hittites are known to have bartered iron for silver, at a rate of 40 times the iron's weight, with Assyria.

Iron did not, however, replace bronze as the chief metal used for weapons and tools for several centuries, despite some attempts. Working iron required more fuel and significantly more labor than working bronze, and the quality of iron produced by early smiths may have been inferior to bronze as a material for tools. Then, between 1200 and 1000 B.C.E., iron tools and weapons displaced bronze ones throughout the near east. This process appears to have begun in the Hittite Empire around 1300 B.C.E., or in Cyprus and southern Greece, where iron artifacts dominate the archaeological record after 1050 B.C.E. Mesopotamia was fully into the Iron Age by 900 B.C.E., central Europe by 800 B.C.E. The reason for this sudden adoption of iron remains a topic of debate among archaeologists. One prominent theory is that warfare and mass migrations beginning around 1200 B.C.E. disrupted the regional tin trade, forcing a switch from bronze to iron. Egypt, on the other hand, did not experience such a rapid transition from the bronze to iron ages: although Egyptian smiths did produce iron artifacts, bronze remained in widespread use there until after Egypt's conquest by Assyria in 663 B.C.E.

Iron smelting at this time was based on the bloomery, a furnace where bellows were used to force air through a pile of iron ore and burning charcoal. The carbon monoxide produced by the charcoal reduced the iron oxides to metallic iron, but the bloomery was not hot enough to melt the iron. Instead, the iron collected in the bottom of the furnace as a spongy mass, or bloom, whose pores were filled with ash and slag. The bloom then had to be reheated to soften the iron and melt the slag, and then repeatedly beaten and folded to force the molten slag out of it. The result of this time-consuming and laborious process was wrought iron, a malleable but fairly soft alloy containing little carbon.

Wrought iron can be carburized into a mild steel by holding it in a charcoal fire for prolonged periods of time. By the beginning of the Iron Age, smiths had discovered that iron that was repeatedly reforged produced a higher quality of metal. Quench-hardening was also known by this time. The oldest quench-hardened steel artifact is a knife found on Cyprus at a site dated to 1100 B.C.E.

Developments in China

Archaeologists and historians debate whether bloomery-based ironworking ever spread to China from the Middle East. Around 500 B.C.E., 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 1,130 °C, hot enough to be considered a blast furnace. At this temperature, iron combines with 4.3 percent 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 B.C.E., 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 B.C.E., 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, 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.

Steelmaking in India and Sri Lanka

Perhaps as early as 300 B.C.E., although certainly by 200 C.E., 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.

Steelmaking in early modern Europe

In the early seventeenth 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.

Ironmaking in early modern Europe

From the sixteenth to the eighteenth century, most iron was made by a two-stage process involving a blast furnace and finery forge, using charcoal as fuel. Production was limited, however, by the supply of wood for making charcoal.

Schematic drawing of a puddling furnace

By the eighteenth century, deforestation in Western Europe was making ironworking and its charcoal-hungry processes increasingly expensive. In 1709 Abraham Darby began smelting iron using coke, a refined coal product, in place of charcoal at his ironworks at Coalbrookdale in England. Although coke could be produced less expensively than charcoal, coke-fired iron was initially of inferior quality compared to charcoal-fired iron. It was not until the 1750s, when Darby's son, also called Abraham, managed to start selling coke-smelted pig iron for the production of wrought iron in finery forges.

Another eighteenth century European development was the invention of the puddling furnace. In particular, the form of coal-fired puddling furnace developed by the British ironmaster Henry Cort in 1784 made it possible to convert cast iron into wrought iron in large batches (without charcoal), rendering the ancient finery forge obsolescent. Wrought iron produced using this method became a major raw material in the English midlands' iron manufacturing trades.

Industrial steelmaking

Schematic drawing of a Bessemer converter

The problem of mass-producing steel was solved in 1855 by Henry Bessemer, with the introduction of the Bessemer 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 nineteenth-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 nineteenth century. Stainless steel was only developed on the eve of World War I 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.

Steel is currently the most-recycled material in the world, the industry estimates that of new metal produced each year some 42.3 percent is recycled material. All steel that is available is currently recycled, the long service life of steel in applications such as construction means that there is a vast store of steel in use that is recycled as it becomes available. But new metal derived from raw materials is also necessary to make up demand.