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High chromium cast irons show superior abrasion resistance due to their chromium carbides. Their abrasion resistance is improved by insert casting with cemented carbide. The effects of high-temperature exposure during insert casting on the microstructures of cemented carbide were investigated in this research. The high chromium cast iron (2.7%C27%Cr) and the cemented carbide round bars (WC13.7%Co) were prepared. The round bars were dipped in molten high chromium cast iron at 1596 K. The dipped round bars were pulled up after the elapse of 30180 s. Microstructures of dipped round bars were changed from homogeneous sinter structure to three-layer structure, cemented carbide, diffusion layer, and reaction layer. The thicknesses of the diffusion layer and the reaction layer were increased with increasing of dipping time. FE-EPMA analysis revealed that the diffusion layer was formed by the elution of Co from the cemented carbide and diffusion of Fe and Cr from the molten high chromium cast iron into the cemented carbide round bar. In addition, rectangular particles were randomly distributed in the diffusion layer. The equivalent circular diameter of the rectangular particle was increased with increasing dipping time. The Vickers hardness of the diffusion layer decreased about 30% relative to the cemented carbide but higher than that of high chromium cast irons. The inserted cemented carbide is thought to have contributed to improving abrasion resistance. It was suggested that thin diffusion layers are more effective for improving abrasion resistance.
High chromium cast irons show superior abrasion resistance due to their chromium carbides. Their abrasion resistance is improved by insert casting with cemented carbide. The effects of high-temperature exposure during insert casting on the microstructures of cemented carbide were investigated in this research. The high chromium cast iron (2.7%C27%Cr) and the cemented carbide round bars (WC13.7%Co) were prepared. The round bars were dipped in molten high chromium cast iron at 1596 K. The dipped round bars were pulled up after the elapse of 30180 s. Microstructures of dipped round bars were changed from homogeneous sinter structure to three-layer structure, cemented carbide, diffusion layer, and reaction layer. The thicknesses of the diffusion layer and the reaction layer were increased with increasing of dipping time. FE-EPMA analysis revealed that the diffusion layer was formed by the elution of Co from the cemented carbide and diffusion of Fe and Cr from the molten high chromium cast iron into the cemented carbide round bar. In addition, rectangular particles were randomly distributed in the diffusion layer. The equivalent circular diameter of the rectangular particle was increased with increasing dipping time. The Vickers hardness of the diffusion layer decreased about 30% relative to the cemented carbide but higher than that of high chromium cast irons. The inserted cemented carbide is thought to have contributed to improving abrasion resistance. It was suggested that thin diffusion layers are more effective for improving abrasion resistance.
When cemented carbide contacts molten cast iron during the insert casting process, the binder phase of the cemented carbide is thought to melt even if the molten temperature of the cast iron is lower than the solidus temperature of the cemented carbide (1593 K). It is important to understand the melting mechanism to clarify the interface formation mechanism, and subsequently control the interface structure. The purpose of this study is to clarify the interface formation mechanism from the microstructural change of cemented carbide dipped in molten cast iron. A round bar specimen made of cemented carbide was dipped in molten cast iron at 1473 to 1596 K, and pulled up after a predetermined time. Microstructure observation, elemental analysis, and hardness test were performed on the cross-section of the specimen. The specimen changed from a homogeneous sintered structure to a two-layer structure, the center side was a non-reacted layer that did not change, and the outer side was the transition layer where melting had occurred. The diffusion of Fe and C is thought to have decreased the solidus temperature of the binder phase significantly that the binder phase melted. The non-reacted layer radius could be expressed by the rate equation derived from the Nernst-Brunner equation. Structural changes were seen at the interface such as increased outer diameter of the cemented carbide round bar specimen, occurrence of shrinkage cavities in the transition layer, and characteristic concentration of Co at the boundary. These are thought to be due to liquid phase migration occurring in the molten binder phase and decreased WC solubility due to increase in Fe concentration.
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