Bessemer steel cost seven pounds a ton to make and sold for forty
For most of history steel was precious, made in small batches by skilled hands over days. Then in the 1850s the Bessemer converter turned pig iron into steel in about half an hour, burning the iron's own impurities for heat. Early converters produced it for £7 a ton while buyers still paid around £40.
The difference between iron and steel is a pinch of carbon. Cast iron, with too much, is hard and brittle; pure iron is weak; but iron holding under 1 percent carbon becomes strong, workable steel. Steelmaking is largely the art of removing excess carbon and impurities such as sulfur and phosphorus, then adding elements like manganese or chromium for specific qualities.
Early methods took patience. China described co-fusion, blending wrought and cast iron, as early as the 6th century AD, and Shen Kuo recorded two methods during an inspection tour in 1075. In Europe, cementation meant packing Swedish wrought iron bars with charcoal in a stone box for up to a week, producing blister steel. Benjamin Huntsman improved quality in 1740 by melting broken blister steel in small crucibles of about 20 kilograms each, at the cost of extra coke and hours of firing. European travellers in the 17th century even described Japanese smiths using a continuous blowing technique that may have resembled Bessemer's.
Today two routes dominate. Basic oxygen steelmaking, developed by Robert Durrer in 1948, refines Bessemer's idea by blowing pure oxygen instead of air through molten pig iron; a furnace can convert 350 tons in under 40 minutes, where an old open hearth needed 10 to 12 hours, and in 2013 it supplied 70 percent of world output. Electric arc furnaces melt scrap or directly reduced iron and turn out a batch roughly every 40 to 50 minutes. Afterwards, ladle treatments fine-tune the chemistry, and over 95 percent of steel is solidified by continuous casting into slabs, blooms and billets before rolling.
The price is carbon. Producing a ton of steel releases about 1.8 tons of carbon dioxide, and as of 2021 the industry accounted for roughly 11 percent of global carbon dioxide emissions, mostly because coal supplies the carbon that pulls oxygen from iron ore in blast furnaces. Alternatives are emerging. Reducing ore with hydrogen made from renewable electricity avoids fossil fuels but adds an estimated 20 to 30 percent to costs, while the HIsarna process skips an intermediate step and trims emissions by about a fifth.
Source: Steelmaking
