High carbon – high chromium cold work tool steel type D3 containing 2%C and 12% Cr was commonly used for manufacturing stamping tools. This paper introduces an investigation for the effect of inoculation of this type of tool steel by niobium. Four grades of this tool steel containing 0, 0.03%, 0.04% and 0.05% Nb were casted in an induction furnace at 1600ºC. Different treatment processes including annealing, forging, stress relief, hardening, and tempering were carried out for the casted alloy. Examination via optical microscopy, X – ray diffraction, hardness test, tensile test, and dimensional wear coefficient and wear rate measurements has been investigated. Furthermore the fracture surfaces were examined using SEM microscope.
The tool steel containing both Nb carbides and Cr carbides exhibited a higher hardness, toughness, and wear resistance in comparison with tool steel containing only Cr carbides. On the other hand, the addition of Nb increased hardenability, and led to the refinement of the tool steel grain structure. The microstructure observation revealed that, the tool steel containing both Nb, and Cr exhibited fine and uniformly distributed metal carbides, while, the carbides were coarse and sparsely distributed in the tool steel containing Cr only. As niobium content increases, the improvement of the mechanical properties and wear resistance were observed.