• 한국주조공학회지
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• 제37권5호
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• pp.139-147
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• 2017

Microstructural evolution of cast Hastelloy X during thermal exposure has been investigated. OM, SEM, and TEM microscopy were carried out on the as-cast, the standard heat treated, and the thermally exposed conditions. Tensile tests were also conducted to understand the effect of microstructural evolution on the degradation of tensile properties. Coarse $M_6C$ and fine $M_{23}C_6$ carbides were found in as-cast Hastelloy X with fine carbides on sub-boundary. Some of $M_{23}C_6$ carbide dissolved into the matrix during solution heat treatment and dislocation network formed at the interface between the carbide and the matrix due to the misfit strain. There was no significant microstructural difference between the exposed specimens at $400^{\circ}C$ and the solution heat treated specimen. A large amount of $M_{23}C_6$ carbides precipitated along and near grain boundaries and sub-boundaries after exposure at $650^{\circ}C$. Exposure at $870^{\circ}C$ of the alloy caused precipitation of $M_6C$ and ${\mu}$. The strength increased and the elongation decreased by thermal exposure at $650^{\circ}C$ and $870^{\circ}C$ because carbides interfere with the movement of the dislocation. It was found that the precipitation of carbide gave significant effects on the tensile properties of Hastelloy X.

• 대한금속재료학회지
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• 제47권7호
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• pp.406-415
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• 2009

A study was conducted on the effects of carbon, tungsten, and vanadium on the wear properties and surface roughness of four High Speed Steel (HSS) rolls manufactured by the centrifugal casting method. Hot-rolling simulation tests were carried out using a high-temperature wear tester capable of controlling speed, load, and temperature. HSS rolls contained a large amount (up to 25 vol.%) of carbides such as MC, $M_{2}C$, $M_{7}C_{3}$, and $M_{6}C$ carbides formed in the tempered martensite matrix. The matrix consisted mainly of lath tempered martensite when the carbon content in the matrix was small, and contained a considerable amount of plate tempered martensite when the carbon content increased. The high-temperature wear test results indicated that the wear properties and surface roughness of the rolls improved when the amount of hard MC carbides formed inside solidification cells increased. The rolls distribution was also homogeneous. The best wear properties and surface roughness were obtained from a roll where a large amount of MC carbides was homogeneously distributed in the lath tempered martensite matrix. The proper contents of carbon equivalent, tungsten equivalent, and vanadium were 2.0~2.3%, 9~10%, and 5~6%, respectively.

• 한국분말재료학회지
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• 제29권4호
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• pp.291-296
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• 2022

The green body of WC-Co cemented carbides containing polymeric binders such as paraffin, polyethylene glycol (PEG), and polyvinyl acetate (PVA) are prepared. The green density of the WC-Co cemented carbides increases with the addition of binders, with the exception of PVA, which is known to be a polar polymeric substance. The green strength of the WC-Co cemented carbides improves with the addition of paraffin and a mixture of PEG400 and PEG4000. In contrast, the green strength of the WC-Co does not increase when PEG400 and PEG4000 is added individually. The compressive strength of the green body increases to 14 MPa, and the machinability of the green body improves when more than 4-6 wt% paraffin and a mixture of PEG400 and PEG4000 is used. Simultaneously, the sintered density of WC-Co is as high as 99% relative density, similar to a low binder addition of 1-2 wt%.

• 한국정밀공학회지
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• 제20권9호
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• pp.55-62
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• 2003

This paper investigates the micro-cutting of cemented carbides using PCD (polycrystalline diamond) and PCBN (polycrystalline cubic boron nitride) cutting tools are performed with SEM direct observation method. The purpose of this study is to make clear the cutting mechanism of cemented carbides and the fracture of WC particles at the plastic deformation zone in orthogonal micro-cutting. And also to achieve systematic understanding, the effect of machining parameter on chip formation and machined surface was studied, including cutting speed, depth of cut and various tool rake angle. Summary of the results are shown below. (1) Three type of chip formation process have been proposed by the results of the direct observation in orthogonal micro-cutting of cemented carbide materials. (2) From the whole observation of chip formation, primary WC particles are crushed and/or fine grained in the shearing deformation zone. A part of them are observed to collide directly with a cutting edge of tool by following the micro-cutting. (3) Surface finish, surface morphology and surface integrity is good to obtain by cutting with PCD cutting tool compared with PCBN. (4) The machined surface has the best quality near the low cutting speed of 10${\mu}m$/sec with a cutting depth of 10 ${\mu}m$ using 0$^\circ$ rake angle and 3$^\circ$ flank angle in this condition, but it was found that excessively low speed, for example the extent of 1 ${\mu}m$/sec, is not good enough to select for various reason.

• 동력기계공학회지
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• 제20권3호
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• pp.11-16
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• 2016

The effect of carbides on the tensile properties in 0.5C-17Cr-0.5Ni martensitic stainless steel was studied. With the increase of austenitizing temperature, the volume fraction of residual carbide was decreased rapidly. In tempered specimens after quenching, the volume fraction of total carbide was decreased with the increase of austenitizing temperature. In tempered specimens after quenching, strength was decrease and elongation was increased with the increase of austenitizing temperature. Tensile strength was increase and elongation was decreased with the increase of volume fraction of residual and total carbides. With the increase of austenitizing temperature, the tensile properties of mod. 0.5C-17Cr-0.5Ni martensitic stainless was affected greatly by residual carbide than tempered carbide.

• 한국주조공학회지
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• 제15권3호
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• pp.242-251
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• 1995

Highly alloyed high speed tool steels(ASP steels) were rapidly solidified by melt spinning process, and the microstructures of melt spun tool steel ribbons were examined by optical microscopy and transmission electron microscopy with energy dispersive x-ray spectroscope. The microstructure of melt spun tool steel ribbon was found to be consisted of ${\delta}-ferrite$ cells surrounded by austenite and V-rich MC carbides. The size of ${\delta}-ferrite$ cells and intercellular MC carbides were about $0.4{\mu}m$ or less and 30nm or less, respectively. From the melt spun tool steel ribbons, only the MC type carbide phase was observed, instead of $M_2C$, $M_{23}C_6$ and $M_6C$ carbides which were generally observed in other rapidly solidified high speed steels. Such a change in type of carbide phase formed could be attributed to the increase in alloying content of vanadium and carbon. However, changes in microsturcture of melt spun tool steels with alloying content of cobalt, vanadium and carbon were not observed.

• 한국주조공학회지
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• 제35권6호
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• pp.178-184
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• 2015

Due to excellent abrasion resistance the high-chrome white irons are widely used in mining and mineral industries. Minor variation of carbon content in 28% chrome white iron resulted in difference in primarily solidified microstructure. Sub-eutectic (hypoeutectic) composition led to formation of primarily solidified dendrites. Formation of primarily solidified dendrites which were supersaturated with carbon and chrome also caused precipitation of fine secondary carbides that are different from relatively large plate type $M_7C_3$ carbides in the eutectic structure. Small portion of primarily solidified dendrite expected to contribute significantly to the improvement of abrasion resistance of the white iron because the dendrites provided mechanical support to carbides. The relative fraction of primary dendrite increased with reduction of carbon content from the eutectic composition. The increased fraction of primary dendrite increased hardness value of the white irons.

• Journal of Industrial and Engineering Chemistry
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• 제67권
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• pp.12-27
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• 2018

Supercapacitors (SCs) has gained an impressive concentration by the researchers due to its advantages such as high energy and power densities, long cyclic life, rapid charge-discharge rates, low maintenance and desirable safety. Hence it has been widely utilized in energy storage and conversion devices. Among the different components of SC, electrodes play a vital role in the performances of SCs. In this review, we present the recent advances in 2-D nanostructured metal nitrides, carbides, and phosphides based materials for SC electrodes. Finally, the electrochemical stability and designing approach for the future advancement of the electrode materials are also highlighted.

• Corrosion Science and Technology
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• 제20권6호
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• pp.361-366
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• 2021

Localized corrosion behavior of Ni-based Inconel 718 alloy was investigated by electrochemical anodic polarization techniques in NACE TM 0177 A solution of 5 wt% NaCl + 0.5 wt% acetic acid at room temperature. After the solution heat treated at 1080 ℃ for 2.5 h, Inconel 718 was age-hardened at 780 ℃ for 8 h. The microstructure of the alloy surface was investigated by optical microscopic or scanning electron microscopic technique. The austenitic phase with the presence of metal carbides was observed on the surface of Inconel 718. Metal-carbides such as Nb-Mo and Ti-carbide with diameters of approximately 10 and 3 ㎛, respectively, were formed in Inconel 718. Anodic polarization results revealed that localized corrosion was observed at the interface between austenitic phase of a substrate and metal carbides. Difference in electrochemical property between a metal carbide and an austenitic substrate could provide an initiation site for localized corrosion of Inconel 718 surface.

• 자원리싸이클링
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• 제13권5호
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• pp.45-50
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• 2004

탄화철을 합성하는 공정을 수소($H_2$) 환원과 $CO-H_2$ 혼합가스에 의한 탄화의 2단계 과정으로 나누어서 수행했다. 환원종료 후 미량의 암모니아 가스를 첨가하여 환원철의 표면을 개질한 후, 탄화시간 경과별 탄화상태를 C/S 분석기(Low C/S determinator), 뫼스바우어 분광 분석기(Mossbauer spectroscopy), XRD(X-ray diffraction patterns), SEM(Scanning electron microscopy), TEM(Transmission electron microscopy), XPS(Photoelectron spectroscopy), 및 라만분광기 (Raman spectroscopy)를 사용하여 조사하였다. 연구결과, 미량의 암모니아가스로 환원철 표면을 개질함으로써 탄화철의 분해 및 유리탄소의 석출을 방지할 수 있을 뿐만아니라 6.68wt% 이상 10wt% 까지 탄소가 과고용된 상태에서도 분해되거나 유리탄소를 석출하지 않고 안정상태를 유지하였다. 이러한 결과로부터 철(Fe)과 세멘타이트(cementite, $Fe_3C$)가 혼합되지 않고 고탄화철(SIC, super iron carbide)인 Fe5C2 상태의 안정한 단일상을 얻는데 성공하였다.