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The influence of heat treatment on the microstructure of AISI M2 type high-speed steels modified with powder additions of W and TiB₂ was studied. The primary focus was on the effects of austenitizing temperatures on the prior austenite grain size and size distribution, volume fraction, and morphology of the eutectic carbides M₂C, M₆C, and MC, as well as the character of the secondary precipitation of carbides in the high-speed steels studied. It was shown that austenitizing significantly affects the changes in the chemical composition, morphology, size, and character of distribution of the eutectic carbides in the high-speed steels studied, as well as the volume fraction of retained austenite in the matrix and the prior austenite grain size. These changes in carbides seemed to be induced by a diffusion-induced redistribution of alloying elements between the steel matrix and the carbide phases due to their mutual interaction at high temperatures, which is accompanied by carbide decomposition, coagulation and dissolution and, as a consequence, saturation of the solid solution by alloying elements.