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Melt treatment methods that involve the addition of small amounts of surface-active or/and inoculating elements have permitted the development of improved high speed steels (HSSs) with greater carbide control. In this work, addition of powdered W and WC into the melt was used to improve the as cast microstructure of AISI M2 HSS and, as consequence, its properties after full heat treatment. Under the action of inoculants, there was a refinement of the primary grains of the matrix and a transition from a columnar dendritic mode of solidification (typically found in uninoculated AISI M2) to a predominantly equiaxed morphology in the inoculated steels. SEM and EDS confirmed that the inoculation favoured the formation of the M 6 C eutectic at the expense of the M 2 C and MC variants, which prevailed in the as cast microstructure of the uninoculated steel. The relationship between microstructure and the properties is discussed.