Héroult Electric Arc Furnace

Bessemer and open-hearth steelmaking both start from molten pig iron and burn impurities out of it — so both need a blast furnace upstream, coke, ore, and a whole ironmaking works. The electric arc furnace needs none of that. It strikes an arc between carbon electrodes and a bath of cold scrap steel, and the arc's heat alone melts it. The charge can be any steel at all, the heat comes from electricity rather than from burning fuel in contact with the metal, and because no combustion gases touch the bath the chemistry can be controlled far more precisely. Paul Héroult put the first commercial furnace to work around 1900. It is the reason steel became genuinely recyclable, and today it makes a large share of the world's steel from scrap.