H21 Steel is a hot work tool steel for oil or air setting to develop high hot quality, support of hardness, and warmth checking resistance. These are tungsten hot-work steels which are of different types, namely, H21 to H26 types. These steels have similar characteristics to that of high-speed steels.

Thermal shock resistance and toughness of these steels can be improved by reducing the carbon content.

This is mostly utilized in hot work gadgets, instruments for production of hollows, screws, bolts, stray pieces. Die casting tools, forming dies, die inserts, hot shear blades.