Steel
Steel is a metal made up of iron and carbon. The steel industry was never big until Andrew Carnegie found a way to manufacture steel at a much lower cost. He adopted the "Bessmer Process," which uses molten pig iron to add in the carbon. This process is much cheaper than other methods and can be done on a massive scale. This process was invented by Henry Besmer of Britain. Before this process, Britain would import wrought iron from Sweden and then add carbon to it, this process was extensive and expensive.