The main aim of this work was to study the behavior of the secondary hardening of AISI M3:2 high speed steel named Sinter 23?? produced by powder metallurgy process of hot isostatic pressing (HIP). The M3:2 high speed steel Sinter 23?? was submitted to heat treatment of hardening with austenitizing temperatures of 1140 ??C, 1160 ??C, 1180 ??C and 1200 ??C and tempering at 540 ??C, 560 ??C and finally 580 ??C. The effectiveness and response of the heat treatment was determined using hardness tests (Vickers and Rockwell C hardness) and had its property of secondary hardness evaluated. The results showed that the secondary hardening peak of Sinter 23?? high speed steel (tempering temperature at which maximum hardness is attained) is at 540 ??C for the lower austenitization temperatures of 1140 ??C and 1160 ??C, and it is at 560 ??C for the higher austenitizing/quenching temperatures of 1180 ??C and 1200??C.