The microstructure of high-speed steels consists of a martensitic matrix with a dispersion of two sets of carbides. These carbides are usually known as primary and secondary carbides.

The role of the primary carbides has been reported to be of no importance in strengthening the steels, due to their large size and large interparticle spacing.

However, Secondary Carbide known as Hardening Carbide is the main reason for the improved strength and wear resistance.

Hardness depends primarily on the precipitation of the secondary hardening carbide and secondarily on martensitic strengthening. ■