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 ofthis type oftool steel by niobium. Four grades ofthis tool steel containing
0, 0.03%, 0.04% and 0.05% Nb were casted in an induction furnace at 1600°C. 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 ëomparison 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 microstructtre 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 ofthe mechanical properties and wear resistance were observed.
Fracture surface examination indicating that Nb addition and hardening followçd by tempering
process lead to changing the mode of fracture from cleavage to quasi — cleavage mode. The
highest wear resistance can be achieved by hardening followed by tempering of 0.05 % Nb tool
steel.