R F Mushet's 'self-hardening' steel, 1868.
© Science Museum / Science & Society Picture Library
A piece of the original ingot of the steel made by the British metallurgist Robert Forester Mushet (1811-1891), which was the first to remain hard at the high temperatures produced when cutting metals. Mushet devised this new type of steel, which he named self-hardening steel, by adding a small amount of tungsten to the molten steel in the crucible. The steel hardened in the air, whereas previously the only way to make steel hard enough for machine tools had been to quench it, by rapid cooling in water. Self-hardening (or tungsten) steel machine tools could run much faster and were able to cut harder metals than had been posible previously. This resulted in a revolution in the design of machine tools and in the progres of industrial metalworking.