In this work, thermodynamical equilibria have been calculated for super hard high speed tool steel (HSS), AISI M41 composition belonging to the multicomponent system Fe–C–Cr–W–Mo–V–Co as well as for its three different variant containing niobium. Some temperature-concentration diagram for both class of alloys are presented and calculated quantities (melting and transformations, amount and composition of phases) are compared with experimental data. Effect of niobium and high cooling rate during electroslag remelting on the precipitated carbides were discussed. In this work, the effect of niobium on morphology of carbides secondary hardening temperature and wear rate of investigated HSSs were studied. This work aims to study the effect of niobium as alloying element on precipitated carbides type and shape, in addition to study the effect of precipitated carbides after full heat treatment on secondary hardening and wear resistance for investigated steels.