Still the Iron Age

Iron and Steel in the Modern World

Vaclav Smil

• Publisher: Butterworth-Heinemann
• Year: 2016
• ISBN:
  9780128042359
• Topic: Tecnología e ingeniería
• Subtopic: Ingeniería minera

Although the last two generations have seen an enormous amount of attention paid to advances in electronics, the fact remains that high-income, high-energy societies could thrive without microchips, etc., but, by contrast, could not exist without steel. Because of the importance of this material to comtemporary civilization, a comprehensive resource is needed for metallurgists, non-metallurgists, and anyone with a background in environmental studies, industry, manufacturing, and history, seeking a broader understanding of the history of iron and steel and its current and future impact on society. Given its coverage of the history of iron and steel from its genesis to slow pre-industrial progress, revolutionary advances during the 19th century, magnification of 19th century advances during the past five generations, patterns of modern steel production, the ubiquitous uses of the material, potential substitutions, advances in relative dematerialization, and appraisal of steel's possible futures, Still the Iron Age: Iron and Steel in the Modern World by world-renowned author Vaclav Smil meets that need.

• Incorporates an interdisciplinary discussion of the history and evolution of the iron- and steel-making industry and its impact on the development of the modern world
• Serves as a valuable contribution because of its unique perspective that compares steel to technological advances in other materials, perceived to be important
• Discusses how we can manufacture smarter rather than deny demand
• Explores future opportunities and new efforts for sustainable development in the industry

Chapter 1

Iron and Steel Before the Eighteenth Century

Slow Adoption, Artisanal Production, and Scaling-Up

Abstract

We can only guess at the beginnings of metal smelting in Neolithic societies. Were the minerals containing metals with low melting points accidentally present in or near fire pits used for heat of for searing meat, and did their melting attract the attention of people tending the fires? Did curiosity lead people to throw colored minerals into fires to see what will happen? Or did the discoveries of naturally occurring nuggets, crystals, or lumps of native metals (copper, gold, silver, lead, tin) lead to deliberate experimentation with minerals (metallic ores) that contained small particles of those elements? And once melting of some materials was discovered, were not attempts at their deliberate smelting almost inevitable? Craddock (1995) thinks that was almost certainly the case.

Keywords

Charcoal making; bloomery iron; smelting; premodern steel; blast furnaces

We can only guess at the beginnings of metal smelting in Neolithic societies. Were the minerals containing metals with low melting points accidentally present in or near fire pits used for heat or for searing meat, and did their melting attract the attention of people tending the fires? Did curiosity lead people to throw colored minerals into fires to see what will happen? Or did the discoveries of naturally occurring nuggets, crystals, or lumps of native metals (copper, gold, silver, lead, tin) lead to deliberate experimentation with minerals (metallic ores) that contained small particles of those elements? And once melting of some materials was discovered, were not attempts at their deliberate smelting almost inevitable? Craddock (1995) thinks that was almost certainly the case.

What we know for certain is that the earliest evidence of exploiting native metal—as beads of malachite and native copper in southeastern Turkey—goes as far back as 7250 BCE (Scott, 2002). Because copper often occurs with arsenic and the eutectic point (the lowest melting temperature) of Cu–As alloys is just 685°C, the first bronzes, encountered at the end of the 4th and the beginning of the 3rd millennium BCE in many settlements in Mesopotamia, were variants of this natural combination. Bronzes that eventually gave the name to the first metallic age were alloys of copper and tin (with the eutectic point at 910°C), and they were introduced throughout the region around 3500 BCE (De Ryck, Adriaens, & Adams, 2005).

While the protometal cultures (up to the 5th millennium BCE) were confined to Mesopotamia and southeast Turkey, the copper age (5th millennium BCE) extended into the Nile Valley, Southeastern Europe, and the steppes north of the Black Sea, cultures of the early bronze age (4th millennium BCE) occupied large parts of southern and eastern Europe and reached eastward to the Indus Valley, the middle bronze age (3rd millennium BCE) included nearly all Europe except for Scandinavia as well as parts of China, and the societies of the late bronze age (2nd millennium BCE) were found across Eurasia, from Portugal to Korea and from southern Siberia to India and Ethiopia (Chernykh, 2014).

But despite this lengthy smelting experience, the transition from the reliance on bronze to societies whose dominant metal was iron took typically many hundreds of years, in some cases an entire millennium. Again, the Middle Eastern civilizations pioneered the process, and again, the first manufactured iron objects were made from native iron: the oldest known iron artifacts are nine tubular Egyptian beads made from meteoritic iron (characterized by large crystal grain size and high nickel content), and reliably dated to about 3200 BCE (Rehren et al., 2013). The beads were discovered in 1911, and their shape was made by multiple cycles of rolling and annealing.

Perhaps the most surprising case of using meteoritic iron was discovered in 1818 when an English expedition, led by John Ross searching for the Northwest Passage, encountered the Inuit in northwest Greenland who had iron knives and iron spear points. The origin of these metal objects was puzzling, but eventually they were traced to iron flakes removed by hammer stones from meteorites of the Cape York fall (Wayman, 1988). Egyptian meteoritic beads predate the emergence of iron smelting by nearly 2000 years. Small iron objects are first documented from Mesopotamia of 2600–2500 BCE, but larger items and ceremonial weapons (the metal was still too rare to produce functional designs) became more common only after 1900 BCE; the metal was in everyday use after 1400 BCE and became widely affordable only after 1000 BCE.

Bloomery Iron

Smelting of iron followed the practices established for the production of color metals that had been going on in some parts of the Middle East for nearly 2000 years. Simple bowl-shaped hearths—shallow and usually clay- or stone-lined pits—were encircled by low circular clay walls. These walls were sometimes only knee high (Romans made most of their metal in furnaces no more than 1 m tall and less than half a meter of internal diameter), but in some parts of the Old World (including Central Africa) they eventually reached heights of more than 2 m (Van Noten & Raymaekers, 1988). Furnaces were filled with charcoal and crushed (and often roasted) iron ore, and relatively high temperatures were achieved by blowing in air through tuyères, narrow clay tubes inserted near the surface level (see Appendix B for definitions of some major technical terms associated with the production of iron and steel).

Tuyères were connected to leather bellows to force air into the hearth and to raise smelting temperature. Small bellows were operated by hand, larger ones by a man’s weight (using a treadle or a rocking bar), and the most powerful bellows were eventually powered by waterwheels. Temperature inside these charcoal-fueled furnaces usually did not reach more than 1100–1200°C (and often it was less than 900°C), high enough to reduce iron oxide and far from enough to melt the metal and produce liquid iron (pure Fe liquefies at 1535°C): the final product of this smelting was a bloom, a spongy mass made up of iron and iron-rich slag composed of nonmetallic impurities (Bayley, Dungworth, & Paynter, 2001). Hence the common name of these furnaces, bloomery, and of the product, bloomery iron.

Modern experiments demonstrated a relatively narrow range of conditions required for successful smelting (Tylecote, Austin, & Wraith, 1971). When the conditions inside the furnace are insufficiently reducing there is no metal produced, just iron-rich slag, but when they are too reducing slag becomes too viscous and cannot be easily separated from the metal. Intermediate conditions produce a good bloom; most of the slag comes from iron ore, about 30% originates from siliceous furnace lining, and less than 5% is fuel ash (Paynter, 2006). Blooms made in the smallest early furnaces weighed less than 1 kg, more typical medieval range was 5–15 kg, and the bloom mass increased to 30–50 kg (or even to more than 100 kg) only with the introduction of taller furnaces and waterwheel-powered bellows.

Bloomery iron contained typically between 0.3% C and 0.6% C, and in Europe it was the only ferrous material available in significant quantities during the antiquity and until the later medieval period. The iron produced by bloomeries was consolidated and shaped by subsequent smithing: repeated reheating and hammering of the bloom was required to produce a mass of wrought iron that contained just 0.04–0.08% C and that was ductile, malleable, and weldable. Wrought iron was used to make an increasing range of weapons and utilitarian and ornamental objects, ranging from arrowheads to bolts and axes (Ashkenazi, Golan, & Tal, 2013; Barrena, Gómez de Salazar, & Soria, 2008), and modern metallurgical examinations find small amount of slag trapped in these products.

Bloomeries supplied all of Europe’s iron during the continent’s first notable increase of demand for the metal that started in the eleventh century—with the introduction of iron mail, originally as small metal plaques, later as hand-forged and riveted knots—and expanded during the twelfth and thirteenth centuries. There was an increase in the production of hand weapons (ranging from knives to maces) and helmets, as well as agricultural and transportation tools and implements, with iron turned into plows, pitchforks, sickles, hoes, cart axles, hoops (for casks, wagons, and windmills), and horseshoes. The first documented use of powerful forge tilt hammers driven by waterwheels dates from 1135 in the famous Cistercian monastery of Clairvaux. More iron also went into construction as bolts, grills, bars, and clasps, and in the thirteenth century metal bands were used in Notre Dame de Paris. A century later the papal palace in Avignon consumed 12 t of the metal (Caron, 2013).

Bloomery smelting was practiced by virtually all Old World cultures, and thousands of these simple, temporary hearths (sometimes with parts of walls still intact) were excavated in regions ranging from both Sahelian and sub-Saharan Africa (Haaland & Shinnie, 1985) to nomadic societies on the steppes of Central Asia (Sasada & Chunag, 2014), and from coastal Sri Lanka (Juleff, 1996; 2009) to Scandinavia (Olsson, 2007; Svensson et al., 2009) and Korea, where the practice may have been transferred from what is now Russia’s Pacific coast region rather than from China where cast iron was dominant (Park & Rehren, 2011).

Most of the evidence of the earliest Euroasian iron smelting has been known for a long time, with numerous remains of simpler and lower structures (often called Corsican forges) and sturdier and taller furnaces (called Catalan forges) found from the Atlantic to the Urals. In contrast, new excavations of ancient bloomeries and new carbon datings have been changing our views on the development of iron metallurgy in Africa (Holl, 2009; Zangato & Holl, 2010). These findings indicate early smelting activities in regions ranging from the Middle Senegal Valley in the west to the Nile Valley in the east, and from Niger’s Eghazzer basin to the Great Lakes region of East Africa, with the many dates going to more than 2500 years before present and with inferred furnace temperatures of 1100–1450°C.

Persistence of this smelting technique is attested by the fact that the Spanish bloomeries at San Juan Capistrano (built during the 1790s) were the oldest ironworks in California, and operating bloomeries survived in parts of England into the eighteenth century; in parts of Spain and in southern France they were still present by the middle of the nineteenth century. Bloomery smelting was just the first step in obtaining useful metal: the ferrous sponge mixed with slag had to be processed by being repeatedly worked (wrought) by alternate heating and hammering (requiring as many as 30–50 cycles) in order to remove the interspersed impurities and to produce wrought iron that could be forged into weapons, horseshoes, colter tips, nails, and other small iron objects. For centuries all of this hot and hard labor was done everywhere manually, and only the adoption of larger waterwheels made it possible to build mechanized forges using heavier hammers. Even so, this traditional combination of bloomeries and forges had its obvious production limits.

Being small-scale batch operation—every heat was terminated in order to remove relatively small masses of the solid bloom—iron smelting in traditional low-rise bloomeries could never supply large-scale demand for the metal in an economic way, and labor-intensive (and also highly energy-intensive) forging added to the cost (further increased by substantial losses of iron during the forging process). Not surprisingly, with rising demand some European bloomeries, exemplified by medieval German and Austrian Stucköfen, became taller (Technisches Museum in Vienna has a fine model). These furnaces still produced small masses of metal (Stuck) whose removal required tearing the front wall of the structure, but because the smelting process lasted a bit longer and because waterwheel-driven bellows supplied more powerful blast and temperatures in lower parts of the furnace were higher, the resulting bloom was often a mixture of sponge iron and steel.

Blast Furnaces

Japan’s traditional tatara is the best known example of a furnace that could be both a bloomery producing a solid sponge iron and a blast furnace yielding liquid iron or steel (Hitachi Metals, 2014; Iida, 1980). Tatara furnaces were rather low and rectangular (height of just over 1 m, width of 1 m, and length of 3 m) and (since the late seventeenth century) the blast was delivered by cross-blowing bellows. Given the scarcity of Japanese iron ores, abundant iron sands were charged with charcoal and the furnaces were operated in two modes, as zuku-oshi (pig iron-pressing) and kera-oshi (steel pressing, which will be described in the following section). Pig iron production used akome iron sand (with high titanium content, as 5% or more of TiO₂) which was added after the charcoal charge; the furnace’s tuyères were placed low and at a low incline so the blast could penetrate the entirety of the furnace’s lower part; and, in order to achieve high temperatures needed to produce liquid iron, the heats lasted 4 days. The liquid metal was cast, or, after cooling, taken to a workshop for decarburization to produce sage-gane (low carbon steel) used to make a variety of everyday items.

Experiments with a replica of a 1.3-m tall tatara furnace built in Miyagi prefecture and charged with magnetite ore (rather than with iron sand) confirmed that it reaches very high smelting temperatures (in excess of 1500°C) during the last stage of its operation, and found increasing metal yield with higher metal content in the ore (Matsui, Terashima, & Takahashi, 2014). But even with the best available ore the yield was no higher than 62%, and with poorer ores more than half of iron present in charged iron sand could be lost in slag. Analysis of the produced metal showed carbon content of 0.15% and silicon content of 0.03%, with negligible amounts of Mn, P, S, Ti, and Cu, corresponding to low carbon steel.

But the first liquid iron was produced long before Japanese tatara became common. Unlike in Europe, where solid-state reduction of iron in bloomeries dominated the metal’s production until the late medieval period, there is only sparse and inconclusive evidence of bloomery smelting in ancient China, but plentiful evidence of producing liquid iron for casting. Chinese metallurgists, after centuries of experience with bronze castings, became the pioneers of liquid iron production during the Spring and Autumn Period (770–473 BCE), and smelting of relatively large quantities of liquid iron in fairly large furnaces is well documented during the Han dynasty (207 BCE–220 CE).

Chinese smelting took advantage of phosphorus-rich iron ores (with a lower melting point) and good refractory clays. The tallest refractory clay structures were just over 5 m high and they were often strengthened on the outside by vine cables or heavy timbers, were charged with nearly 1 tonne of iron ore, and the pro...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Preface and Acknowledgments
• Previous Works by The Author
• Chapter 1. Iron and Steel Before the Eighteenth Century: Slow Adoption, Artisanal Production, and Scaling-Up
• Chapter 2. Rise of Modern Ferrous Metallurgy, 1700–1850: Coke, Blast Furnaces, and Expensive Steel
• Chapter 3. Iron and Steel Before WW I, 1850–1914: The Age of Affordable Steel
• Chapter 4. A Century of Advances, 1914–2014: Changing Leadership in Iron and Steel Industry
• Chapter 5. Modern Ironmaking and Steelmaking: Furnaces, Processes, and Casting
• Chapter 6. Materials in Modern Iron and Steel Production: Ores, Coke, Fluxes, Scrap, and Other Inputs
• Chapter 7. Energy Costs and Environmental Impacts of Iron and Steel Production: Fuels, Electricity, Atmospheric Emissions, and Waste Streams
• Chapter 8. Ubiquitous Uses of Steel: Sectoral Consumption and the Quest for Quality
• Chapter 9. Looking Back: Advances, Flows and Stocks
• Chapter 10. Looking Ahead: The Future of Iron and Steel
• Appendix A. Units and Their Multiples and Submultiples
• Appendix B. Some Basic Terms
• Appendix C. Global and National Production of Pig Iron and Steel, 1800–2015
• Appendix D. Production of Crude Steel, 1900–2014 (All figures in Mt/year)
• References
• Index