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podcast transcript
Steel has been known and used by humans for over 2,000 years. It gradually became important to mankind, and eventually became a central material of modern society.
They built railroads, bridges, battleships, skyscrapers, automobiles, and countless everyday tools.
However, steel was not discovered all at once. It has been improved over centuries through trial and error and scientific innovation.
Learn more about steel and how it changed the world in this episode of Everything Everywhere Daily.
Unlike other discoveries or inventions, there is no specific person, place, or time to which steel can be traced. The only thing we can be sure of is that the discovery was made in ancient times and was almost certainly accidental.
True iron smelting, achieved by heating iron ore over charcoal hot enough to reduce it to a spongy mass of metal called a bloom, appeared in Anatolia and the eastern Mediterranean around 1200 BC.
The bloomery process produces wrought iron, which is nearly pure iron and therefore soft. Harder, higher-carbon materials may also be accidentally included whenever conditions are right.
A higher quality material was steel.
Early metalworkers learned that they could significantly harden iron through a process now known as carburizing. This involved a repetitive cycle of heating the metal over charcoal and pounding it with a hammer to gradually infuse carbon into the metal’s surface. This breakthrough represents the first intentional method for producing steel.
As early as 300 BC, metallurgists on the Indian subcontinent took the lead in making crucible steel, also known as wootz. This elaborate process involved sealing iron, charcoal, and organic materials inside clay crucibles.
When heated, the iron absorbs a precise concentration of carbon, creating high-carbon steel, famous for its unique striped appearance that gives it exceptional hardness and luster.
Exported to Persia, Arabia, and the Roman world, wootz later became the raw material for blades known in the West as Damascus steel. Famous for its surface pattern of flowing water and its ability to maintain razor blades, it has puzzled European metallurgists for centuries.
Damascus steel swords became the subject of legend and were said to be sharper, stronger, and capable of cutting even small blades in two. In fact, its reputation probably stems from the high quality crucible steel used, combined with expert Middle Eastern forging techniques, to produce blades that are truly superior, if not supernatural.
In East Asia, Chinese blacksmiths produced cast iron by 500 BC, centuries before their European counterparts, due to the higher furnace temperatures they achieved. They also pioneered the decarburization technique of deliberately removing carbon from cast iron by prolonged heating in air, which produced a form of steel called “white iron.”
Blacksmiths in China and later Japan developed techniques to create complex composite blades by folding and welding steels of various carbon levels.
Perhaps representing the pinnacle of pre-industrial metallurgy, Japan’s Tamahagane steel was produced by smelting iron sand in charcoal ovens. This refined process involved folding the steel and applying a strategic clay coating for differential hardening before quenching.
During the Middle Ages, steel production in Europe was more of an art than a science. The jointing process, widely practiced in the 16th and 17th centuries, involved packing wrought iron rods with charcoal powder in stone boxes and heating them for days at a time.
Carbon slowly diffused inward from the surface of the iron, creating what is called cellular steel, which can be identified by the surface with bubbles formed as carbon bubbles are released. Blister steel is hard but uneven and has a carbon-rich shell and a softer core.
This is basically what steel looked like in the 18th century. Although it has been known for almost 2,000 years, its production was very irregular, difficult to work with, and it was only used for specialty items such as swords.
A major leap forward in steel production occurred in the 1740s when Benjamin Huntsman, a clockmaker from Sheffield, England, became frustrated with the inconsistent spring steel available for his clock mechanisms and began secretly experimenting with a new approach.
He melted crude steel in sealed clay crucibles heated to temperatures much higher than those previously achieved in English furnaces, and discovered that when the molten metal cooled, it formed completely homogeneous ingots of uniform composition.
It was harder, more durable, and more consistent than any steel previously made. This single innovation helped Sheffield become the steel capital of the world for over 100 years. Huntsman’s process spread slowly, in part because he tried to keep it secret, but it eventually transformed the manufacture of cutlery, tools, and springs throughout European industry.
The great contribution of the 18th century to steel was indirect. Steel changed the fuel that powered the blast furnace. Before Abraham Darby’s experiments at Coalbrookdale in 1709, iron smelting depended entirely on charcoal and required enormous quantities of wood.
Darby succeeded in commercially smelting iron in a coke oven, creating a virtually unlimited supply of fuel compared to charcoal. Coke is coal that has been partially burned to remove sulfur and other impurities. Coke-fueled furnaces could be built much larger and run hotter, producing previously unimaginable quantities of cast iron.
New processes for pooling and rolling iron made wrought iron cheap enough to build bridges, and by the early 19th century iron was being used for a variety of structural purposes. The steel itself was still expensive, limited to cutting tools, springs, and special applications.
Throughout the 18th and 19th centuries, industry craved something better than wrought iron. The problem was that steel was still too expensive to mass produce.
The answer came in the 1850s. Henry Bessemer, an English inventor with no formal metallurgical training, discovered in 1856 that blowing cold air into a bath of molten pig iron produced a spectacular combustion. This means that the excess carbon, silicon and manganese in the iron burned in a shower of sparks, converting the pig iron into steel in less than 20 minutes without any additional fuel. The latent heat of the chartered ship was sufficient.
The impact of the Bessemer process on steel production cannot be overstated. Steel that previously took days to produce in small quantities can now be produced in tons in minutes.
The price of steel rail in Britain fell by about 90% between 1870 and 1900. Railroads expanded exponentially throughout North America and Europe. Structural steel made skyscrapers possible.
Chicago’s Home Insurance Building, the first true steel-frame building, was constructed in 1885. Completed in 1883, the Brooklyn Bridge used steel wire for its cables, a choice that made Bessemer’s era of steel engineering internationally famous.
However, the Bessemer process had its limitations. It could not handle the high phosphorus iron ore common across most of continental Europe.
The Gilchrist-Thomas process, patented in 1878, solved this problem by lining the Bessemer converter with dolomite, similar to limestone, which absorbed the phosphorus in the slag. This allowed Europe’s vast iron ore reserves to be exploited for steel manufacturing.
Meanwhile, the Siemens-Martin open furnace developed in the 1860s offered an alternative. This means it is a slower process that allows for the use of scrap and pig iron and allows more control over its composition, making it better suited to consistent steel production. In 1900, hearth blast furnaces produced more steel than Bessemer converters.
In the first half of the 20th century, steel became a crucial material for industrial civilization. It was central to two world wars, the building of modern cities, and the rise of mass-market manufacturing.
Metallurgists in the late 19th and early 20th centuries discovered that adding small amounts of other elements, including chromium, nickel, manganese, vanadium, and tungsten, changed the properties of steel in very specific ways.
In 1913, Harry Brearley made an accidental discovery in Sheffield while researching corrosion-resistant steel for gun barrels. He discovered that alloys with high chromium content were resistant to rust, a discovery that established an entirely new category of stainless steel.
Additionally, the advent of tungsten carbide steel changed industrial manufacturing. This innovation made it possible to machine other metallic materials at speeds once thought impossible.
The two world wars led to a tremendous expansion in steel production capacity and accelerated the development of special grades, including armor plate steel, high-temperature steel for turbine blades, spring steel for artillery, and bearing steel for machinery.
The United States became the world’s largest steel producer, and Pittsburgh, with its proximity to coal and Great Lakes iron ore, became an iconic center for industrial steel manufacturing. By 1945, the United States produced about half of the world’s steel.
The post-war period saw the most important process innovations since the Bessemer process. The basic oxygen steelmaking process (BOS) was developed at the Linz-Donawitz steel mill in Austria in the early 1950s. This method blows pure oxygen into molten iron from above rather than from the air.
Because pure oxygen reacts much more violently than air, the BOS converter can process 300 tons of steel in one hour with better temperature control and less nitrogen absorption than the Bessemer converter allowed. BOS furnaces proliferated worldwide in the 1960s and 1970s and remain the dominant method of steelmaking today.
At the same time, electric furnaces, which use huge graphite electrodes to melt scrap metal, have matured from a special tool for alloy steel to a mainstream production method.
Electric arc furnaces did not require blast furnaces or coke plants. All it needed was scrap and electricity. This allowed a new type of producer, the mini-mill, to enter the market with much lower capital requirements than integrated steel mills.
In the 1970s, Nucor Corporation championed minimills in the United States. Initially utilizing scrap to produce low-grade rebar, the company eventually transitioned into higher value products. These developments were supported by advances in continuous casting, a process that increased consistency and productivity across the industry by pouring steel into moving strands rather than separate ingots.
The period from the 1980s to the 2000s was characterized by the globalization of the steel industry and the proliferation of specialty grades engineered for specific applications.
However, the most important changes of this era were geographical rather than technological. After investing heavily in production capacity starting in 1990, China overtook the United States to become the world’s number one steel producer in 1996, and overtook Japan in 2000.
By 2020, China’s production accounted for more than half of global steel production, producing about 1.06 billion tons of the 1.9 billion tons of global steel production.
These changes reshaped global trade, lowered prices, caused mass closures of traditional steel mills in Europe and North America, and shifted the center of gravity of the industry.
What is surprising about the history of steel is that it is not a story that ends with one invention. This is a chain of thousands of improvements stretching from ancient accidental steel to modern AI-controlled factories.
It was believed that each era mastered steel only for the next era to discover better methods of making steel. Steel helped build the modern world, and despite competition from aluminum, composites, and ceramics, it remains one of the most adaptable and essential materials humans have ever created.
