1856: Englishman Henry Bessemer receives a U.S. patent for a new steel-making process that revolutionizes the industry.
The Bessemer converter was a squat, ugly, clay-lined crucible that simplified the problem of removing impurities -- excess manganese and carbon, mostly -- from pig iron through the process of oxidation. Once the impurities were removed, either as gas or as solid slag, the properties of the molten steel were bolstered using certain alloys, then poured into molds and given shape.
Depending on the size of the converter, as much as 30 tons of molten iron could be processed in one go. Air was blown into the converter through a number of small channels and forced through the liquid to remove the impurities.
The Bessemer process, which could take as little as 30 minutes to complete, resulted in better quality steel that could be mass-produced. This made steel a viable (read: cheaper) building material and it soon became the standard in heavy construction projects, like skyscrapers and bridges.
The first Bessemer steel mill in the United States opened outside of Detroit in 1855, a year before the U.S. patent was issued. As a Great Lakes port city, and given its proximity to the fertile iron-ore-producing fields in the upper Midwest, Detroit became an early steel-producing town.
Bessemer, meanwhile, moved his mill operations to Sheffield in England's industrial Midlands, which became the British equivalent of Germany's Essen, seat of the Krupp steel dynasty.
Bessemer wasn't alone in working on this process. In fact, an American, William Kelly, developed a similar oxidation technique a few years earlier. He held a patent but was forced through bankruptcy to eventually sell it to Bessemer.
The Bessemer process was used into the 1960s, when it was finally replaced by newer technologies, including the Linz-Donawitz process.
Source: Various
