الفهرس 
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Abstract
High carbon – high chromium cold work tool steel type D3 containig 2%C and 12% Cr were commonly used for manufacturing stamping. The inoculation of this type of tool steel containing 0, 0.03%,0.04% and 0.05% Nb were casted in an induction furnace at 16000C. Thermomechanical treatment including stress relief, forging, annealing, hardening, and tempering processes were carried out. Examination via optical microscope, X – ray diffraction, hardness test, tensile strength, elongation, dimensional wear coefficient and wear rate has been investigated. Furthermore the fracture surfaces were examined using SEM microscope. The results revealed that microalloying addition of niobium improves the mechanical and wear properties of D3 tool steel.
The tool steel containing both Nb and Cr carbides exhibited a higher hardness strength, 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 tool steel structure. The microstructure observation revealed that, the tool steel containing both Nb, and Cr exhibited fine and uniformly distributed in the tool steel containing Cr only. As niobium content increases, the improvement of the mechanical properties and wear resistance were increased.
At the same time, an attempt has been made in this work to study the effect of thermomchanical trearment process on the microstructure, mechanical and wear resistance properties of D3 tool steel. More refinement and homogeneous distribution of carbides were observed after forging and annealing which improves the mechanical properties and wear resistance. Martensite formation after hardening increases the hardness, tensile strength, but lowering toughness and wear resistance which can be improved by tempering treatment process.
On conclusion grade D tool steel (with 0.05% Nb) has the highest hardness, tensile strength, elongation, toughness, and wear resistance and hence will tensile the stamping tool life. This is related to the finest structure, uniform distribution of carbides, and the highest Nb carbides in the matrix. Furacture feature indicating that, Nb addition and tempering process can load to changing the model of fracture from cleavage to quasi – cleavage mode.
High carbon – high chromium cold work tool steel type D3 containig 2%C and 12% Cr were commonly used for manufacturing stamping. The inoculation of this type of tool steel containing 0, 0.03%,0.04% and 0.05% Nb were casted in an induction furnace at 16000C. Thermomechanical treatment including stress relief, forging, annealing, hardening, and tempering processes were carried out. Examination via optical microscope, X – ray diffraction, hardness test, tensile strength, elongation, dimensional wear coefficient and wear rate has been investigated. Furthermore the fracture surfaces were examined using SEM microscope. The results revealed that microalloying addition of niobium improves the mechanical and wear properties of D3 tool steel.
The tool steel containing both Nb and Cr carbides exhibited a higher hardness strength, 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 tool steel structure. The microstructure observation revealed that, the tool steel containing both Nb, and Cr exhibited fine and uniformly distributed in the tool steel containing Cr only. As niobium content increases, the improvement of the mechanical properties and wear resistance were increased.
At the same time, an attempt has been made in this work to study the effect of thermomchanical trearment process on the microstructure, mechanical and wear resistance properties of D3 tool steel. More refinement and homogeneous distribution of carbides were observed after forging and annealing which improves the mechanical properties and wear resistance. Martensite formation after hardening increases the hardness, tensile strength, but lowering toughness and wear resistance which can be improved by tempering treatment process.
On conclusion grade D tool steel (with 0.05% Nb) has the highest hardness, tensile strength, elongation, toughness, and wear resistance and hence will tensile the stamping tool life. This is related to the finest structure, uniform distribution of carbides, and the highest Nb carbides in the matrix. Furacture feature indicating that, Nb addition and tempering process can load to changing the model of fracture from cleavage to quasi – cleavage mode.