1855

Bessemer Process

Henry Bessemer (1813–1898)

In the Iron Age, the prevalent use of iron implements changed the world. However, an equally revolutionary shift occurred after English engineer Henry Bessemer developed a process to refine iron and produce steel commercially, first patented in 1855.

Where does steel come from? Start with iron. Dig iron ore out of the ground and transform it into iron in a blast furnace. It comes out as pig iron with a carbon content of 5 percent or so. Put pig iron into a basic oxygen furnace to form steel. Pure oxygen blasts in under pressure and burns off much of the carbon, leaving behind 0.1 percent carbon (mild steel) to 1.25 percent carbon (high-carbon steel). The carbon content, plus any alloying metals, plus the quenching process, determine the properties of the steel in use.

Steel is a remarkable material: dependably strong and resistant to fatigue, it is also workable and highly mutable—it can take a number of different forms. For example, if you heat up steel and quench (cool) it one way, it is more ductile. Quench it another way and it is much harder and more brittle. It is even possible to get both effects at the same time with case hardening. The outer shell is hard and therefore difficult to cut, while the interior is softer to combat the brittleness.

Then there are the alloys. Add a little chromium to steel and it won’t rust. Add extra carbon and it becomes much harder. Add tungsten or molybdenum and you get tool steels. Add vanadium and it holds up better to wear.

This combination of advantages explains why steel is so ubiquitous. Engineers use steel in car bodies and engines because of the combination of strength, cost, and durability. Engineers use steel in skyscrapers such as Burj Khalifa for the same reasons. Big bridges such as the Millau Viaduct, same thing. They reinforce concrete with steel to greatly improve its strength in tension. One place where steel isn’t found is where weight is a factor—aluminum or carbon fiber is used there. Or where strength and durability isn’t a big factor and cost is—plastic is used there.

SEE ALSO Concrete (1400 BCE), Plastic (1856), Hall-Héroult Process (1889), Nitrous Oxide Engine (1978), Millau Viaduct (2004), Burj Khalifa (2010).

White-hot steel pours like water from a 35-ton electric furnace, Allegheny Ludlum Steel Corp., Brackenridge, PA, circa 1941.