A number of grades of steel are called alloy steels and owe their properties to the alloy which is added to them. The principal one is tungsten steel, which is made by adding ferrotungsten (an alloy of tungsten and iron) to the metal while it is in the crucible. Tungsten steel is also called high-speed steel, because the tools made from it can be used at a higher speed than others.
Tungsten is also an alloying element in steel. Tungsten steel is noted for its strength and stability at high temperatures. Nozzles for rocket engines are made from tungsten steel. Tungsten is also a component of cathodes in electronic devices and of welding electrodes. Tungsten carbide, WC, is used in machine tools and metal-cutting dies. Various alloys are also used in electric circuitry.