The process of transforming cast iron into a resistant type of steel free from chemical impurities is commonly known as the Bessemer process. It was invented by Sir Henry Bessemer, an English engineer and inventor, in 1856. The Bessemer process revolutionized steelmaking by allowing large-scale production of steel from molten pig iron, drastically reducing the cost and time required to produce high-quality steel. Although there were earlier attempts to remove impurities from iron, Bessemer's patent and innovations significantly advanced the steel industry.