• Transactions of Materials Processing
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• v.29 no.6
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• pp.307-315
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• 2020

The cemented carbide and stainless steel were bonded using a hot-vacuum brazing method to analyze the bonding interface. Since it is suitable for the hot vacuum brazing, nickel metal was used as a binder among the main components of the cemented carbide, and a new cemented carbide material was developed by adjusting the alloy composition. The paste, which is one of the important factors affecting the hot vacuum brazing bonding, was able to improve brazing adhesion by mixing solder as Ni powder and a binder as an organic compound at an appropriate ratio. Division of the stainless steel yielded a dense brazing result. This study elucidated the interfacial characteristics of wear-resistant parts by bonding stainless steel and cemented carbide via hot vacuum brazing.

• Korean Journal of Materials Research
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• v.27 no.8
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• pp.431-437
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• 2017

This study investigated the surface pit corrosion of SS420J2 stainless steel accompanied by intergranular crack. To reveal the causes of surface pits and cracks, OM, SEM, and TEM analyses of the microstructures of the utilized SS420J2 were performed, as was simulated heat treatment. The intergranular cracks were found to have been induced by a grain boundary carbide of $(Cr,Fe)_{23}C_6$, which was identified by SEM/EDS and TEM diffraction analyses. The mechanism of grain boundary sensitization occurred at the position of the carbide, followed by its occurrence at the Cr depleted zone. The grain boundary carbide of $(Cr,Fe)_{23}C_6$ type precipitated during air cooling condition after a $1038^{\circ}C$ solid solution treatment. The carbide precipitate formation also accelerated at the band structure formed by cold working. Therefore, using manufacturing processes of cooling and cold working, it is difficult to protect SS420J2 stainless steel against surface pit corrosion. Several counter plans to fight pit corrosion by sensitization were suggested, involving alloying and manufacturing processes.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.2
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• pp.74-79
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• 2010

The synthesis and reactivities of molybdenum carbide crystallites were examined in this study. Especially, the effect of synthesis conditions were scrutinized on the preparation of molybdenum carbide crystallites. In order to perform this purpose, various characterization techniques such as BET surface area and oxygen uptake measurements were employed for the synthesized molybdenum carbide crystallites. First of all, the molybdenum carbide crystallites were synthesized using molybdenum oxide crystallites and methane gas or methane-hydrogen mixture. The experimental results showed that BET surface areas ranged from $7.4m^2/g$ to $31m^2/g$ and oxygen uptake values varied from $8.1{\mu}mol/g$ to $24.3{\mu}mol/g$. The Mo compounds were found to be active for ammonia decomposition reaction. Even though there are some molybdenum carbide crystallites that were exceeded by Pt/$Al_2O_3$ crystallite, the steady state reactivities for other molybdenum carbide crystallites were comparable to or even higher than that determined for the Pt/$Al_2O_3$ crystallite. These results implied that molybdenum carbide crystallites could be one of the promising crystallites that might be substitutes for Pt-like noble metal crystallites in the petroleum processes.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.48-50
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• 2005

Advanced hard materials based on diamond are in common use. In this study our main goal was employed to analyze, the mechanisms for the rich phases and chromium carbide, interface of a diamond grits brazed to a Ni-based brazing filler metal matrix. When Ni-7Cr-3Fe-3B-4Si (wt. %) was utilized as the brazing alloy, an isothermal holding resulted in the various products(Ni-rich/Cr-rich domains, carbide). According to these results, the chemical compounds and chromium carbides products is considered to play an important role in brazing temperature and time. Especially chromium carbide has an influence on brazing junction properties.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1091-1092
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• 2006

Silicon nitride - silicon carbide composite was developed by using an abrasive SiC powders as a raw material. The composites were prepared by mixing abrasive SiC powder with silicon, pressing and sintering at $1400^{\circ}C$ under nitrogen atmosphere in atmosphere controlled vacuum furnace. The proportion of silicon in the initial mixtures varied from 20 to 50 wt%. After sintering, crystalline phases and microstructure were characterized. All composites consisted of ${\alpha}-Si_3N_4$ and ${\beta}-Si_3N_4$ as the bonding phases in SiC matrix. Their physical and mechanical properties were also determined. It was found that the density of the obtained composites increased with an increase in the $Si_3N_4$ content formed in the reaction.

• Journal of Mechanical Science and Technology
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• v.15 no.12
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• pp.1676-1682
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• 2001

This work deals with the electrical conductivity of dielectric and cobalts percentage on output parameters such as metal removal rate and surface roughness value of sintered carbides cut by wire-electrical discharge machining (WEDM). To obtain a precise workpiece with good quality, some extra repetitive finish cuts along the rough cutting contour are necessary, Experimental results show that increases of cobalt amount in carbides affects the metal removal rate and worsens the surface quality as a greater quantity of solidified metal deposits on the eroded surface. Lower electrical conductivity of the dielectric results in a higher metal removal rare as the gap between wire electrode and workpiece reduced. Especially, the surface characteristics of rough-cut workpiece and wire electrode were analyzed too. To obtain a good surface equality without crack, 4 finish-cuts were necessary reducing fille electrical energy and the offset value.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.8
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• pp.100-105
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• 1999

This work analyses the effects of electrical conductivities of dielectric and cobalt amount on output parameters such as metal removal rate and the surface roughness value of cemented carbides cut by wire electrical discharge machining(W-EDM). Especially, the cracking behaviour of W-EDM machined surface and optimal machining condition of three kinds of cemented carbides, which have different chemical composition of tungsten carbide and cobalt are also tested. Experimental result shows that increases in cobalt content and electrical conductivity of the dielectric affect the metal removal rate and substantially worsen the final surface quality as a greater quantity of solidified metal deposits on the eroded surface.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.547-550
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• 2008

Precipitation characteristics of the Fe-36Ni based high strength Invar alloy for power transmission wire was investigated in this study. High strength can be obtained in this alloy through precipitation hardening and strain hardening by cold working. $FactSage{(R)}$ in this study, revealing that equilibrium phases which can be formed are two kind of MC-type precipitates and MoC carbide. The latter stoichiometric carbide was expected to be formed at relatively lower temperature $770^{\circ}C$. High strength above 1000MPa and 40% of elongation were obtained at room temperature in both cases.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.185-188
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• 2002

An abrasive vitreous bonded solid mass having a vitrified abrasive structure comprising diamond grains which are held by an in inorganic bonding agent, the vitrified diamond wheel is impregnated with a composition which comprises a thermosetting synthetic resin and a surfactant. The vitrified diamond wheel is manufactured by preparing the composition including the resin and the surfactant, impregnating the abrasive structure with the composition, and curing the composition. The diamond wheel newly developed showed excellent performance in grinding carbide.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.887-888
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• 2006

The present study describes the wear and mechanical behaviour of carbide composites in cyclic loading applications (blanking of sheet metal). Adhesive wear as well as fatigue endurance were tested, complemented by XRD studies. It was found that the blanking performance of a carbide composite is controlled by its resistance to adhesion wear and fatigue sensitivity. XRD studies revealed that fatigue damage is preceded by plastic strain in both phases of the composites