• Korean Journal of Materials Research
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• v.12 no.5
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• pp.414-422
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• 2002

Three different multi-component white cast irons alloyed with Cr, V, Mo and W were prepared in order to study their as-cast and solidification structures. Three combinations of the alloying elements were selected so as to obtain the different types of carbides and matrix structures : 3%C-10%Cr-5%Mo-5%W(alloy No.1), 3%C-10%V-5% Mo-5%W(alloy No. 2) and 3%C-17%Cr-3% V(alloy No.3). The as-cast microstructures were investigated with optical and scanning electron microscopes. There existed two different types of carbides, $M_7C_3$ carbide with rod-like morphology and $M_6C$ carbide with fishbone-like one, and matrix in the alloy No. 1. The alloy No. 2 consisted of MC carbide with chunky and flaky type and needle-like $M_2C$ carbide, and matrix. The chunky type referred to primary MC carbide and the flaky one to eutectic MC carbide. The morphology of the alloy No. 3 represented a typical hypo-eutectic high chromium white cast iron composed of rod-like $M_7C_3$ carbide which is very sensitive to heat flow direction and matrix. To clarify the solidification sequence, each iron(50g) was remelted at 1723K in an alumina crucible using a silicon carbide resistance furnace under argon atmosphere. The molten iron was cooled at the rate of 10K/min and quenched into water at several temperatures during thermal analysis. The solidification structures of the specimen were found to consist of austenite dendrite(${\gamma}$), $ ({\gamma}+ M_7C_3)$ eutectic and $({\gamma}+ M_6C)$ eutectic in the alloy No. 1, proeutectic MC, austenite dendrite(${\gamma}$), (${\gamma}$+MC) eutectic and $({\gamma}+ M_2C)$ eutectic in the alloy No. 2, and proeutectic $M_7C_3$ and $ ({\gamma}+ M_7C_3)$ eutectic in the alloy No 3. respectively.

• 한국기계연구소 소보
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• s.20
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• pp.57-63
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• 1990

The morphologies of MC carbides (M stands for metal) and creep-rupture properties in directionally solidified Rene 80 having standard and Hf-modified chemistries were studied. It was found that Hf depressed the melting point, $\gamma$- $\gamma$’ eutectic temperature and $\gamma$’ solvus of nickel-base superalloy Rene 80, but did not depress MC carbide forming temperature. The morphologies of MC carbides depended upon solidification sequence, which led to blocky type in the early stage and script type in the late stage of solidification. Creep failure occurs through the crack initiation at the transverse components of longitudinal grain boundaries or interdendritic carbides in directionally solidified superalloys. It could be concluded MC carbide morphologies played an important role in creep properties of DS superalloys, that is, Hf additions increased the creep ductilities and lives of Rene 80.

• Korean Journal of Materials Research
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• v.13 no.6
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• pp.381-388
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• 2003

Directional solidification experiments were carried out at 0.5-150 $\mu\textrm{m}$/s in the Co-base superalloy ECY 768. As increasing solidification rate, the dendrite length increased and it reached the maximum at 150 $\mu\textrm{m}$/s, where the tip temperature is close to the liquidus. The liquidus and eutectic temperatures could be estimated by comparing the dendrite lengths and the temperature gradients at the solid/liquid interface and those were estimated as $1424.6^{\circ}C$ and $1343^{\circ}C$ respectively. Between the dendrites just below final freezing temperature, MC carbide and $M_{23}$$C_{6}$ carbide were found. It was confirmed that the script or blocky shape was Ta or W-rich MC carbide, and the lamellar shape was Cr-rich eutectic carbide. The solid/liquid interface morphology clearly showed that the Cr-rich eutectic carbide formed just after the script type MC carbide.

• Journal of Korea Foundry Society
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• v.20 no.5
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• pp.323-329
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• 2000

The HSS consists of hard carbide and matrix of martensite, and so its characteristics of wear resistance, fracture resistance, and surface roughness are good. This study was undertaken to investigate the influence of Nb and V and manufacturing conditions on microstructural behaviors and characteristics in the HSS cylindrical specimens(90 $mm^{O.D.}$ ${\times}$ 60 $mm^{I.D.}$ ${\times}$ 50 $mm^H$) manufactured using VCC(Vertical Centrifugal Casting). In the specimen of Fe-2C-6Cr-1.5W-3Mo-4V alloy, the amount of MC carbide was increased and $M_7C_3$ carbide was decreased with the increase of V and Nb contents. The primary VC carbide was formed and followed by the rod-type eutectic MC carbide was formed in the cell boundary in 9%V added specimen. MC carbide was increased, and $M_7C_3$ carbide was decreased with the addition of Nb content. In the specimen containing more than 3%Nb, primary NbC carbide was formed within the cell of matrix. With increase in rpm, cell and carbides became fine, and amount of carbide $M_7C_3$ was decreased due to increase in cooling rate.

• Korean Journal of Materials Research
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• v.11 no.6
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• pp.472-476
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• 2001

Type and three-dimensional morphology of carbides precipitated in the X(X= 1.70, 1.92, 2.21, 2.50, 2.86)%C-5%Cr-5%V-5%Mo-5%W-5%Co multi-component white cast iron were investigated using an optical microscope and SEM. The types of carbides precipitated were MC, M$_2$C and M$_{7}$C$_{3}$. Morphology of the MC carbide took three forms, that it petal-like, nodular and coral-like. MC carbide seemed to change its morphology from petal-like through nodular, and finally to coral-like with an increase in carbon content. M7C carbide was classified into lamellar and plate-like type. The lamellar M$_2$C arbide precipitated in the iron with low molybdenum and tungsten contents, and higher contents of both elements in the iron were needed to form the plate-like M$_2$C carbide. The morphology of M$_{7}$C$_{3}$ was rod-like similar to that observed in high chromium white cast iron. However, cobalt does not affect the type and morphology of precipitated carbides.des.

• Korean Journal of Materials Research
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• v.30 no.12
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• pp.678-686
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• 2020

Microstructural characteristics of directionally solidified René 80 superalloy are investigated with optical microscope and scanning electron microscope; solidification velocity is found to change from 25 to 200 μm/s under the condition of constant thermal gradient (G) and constant alloy composition (Co). Based on differential scanning calorimetry (DSC) measurement, γ phase (1,322 ℃), MC carbide (1,278 ℃), γ/γ' eutectic phase (1,202 ℃), and γ' precipitate (1,136 ℃) are formed sequentially during cooling process. The size of the MC carbide and γ/γ' eutectic phases gradually decrease with increasing solidification velocity, whereas the area fractions of MC carbide and γ/γ' eutectic phase are nearly constant as a function of solidification velocity. It is estimated that the area fractions of MC carbide and γ/γ' eutectic phase are determined not by the solidification velocity but by the alloy composition. Microstructural characteristics of René 80 superalloy after solid solution heat-treatment and primary aging heat-treatment are such that the size and the area fraction of γ' precipitate are nearly constant with solidification velocity and the area fraction of γ/γ' eutectic phase decreases from 1.7 % to 0.955 %, which is also constant regardless of the solidification velocity. However, the size of carbide solely decreases with increasing solidification velocity, which influences the tensile properties at room temperature.

• Journal of the Korean institute of surface engineering
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• v.25 no.1
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• pp.8-15
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• 1992

To investigate the effects of substrate on transverse-rupture strength(TRS) and bonding strength between substrate and TiC layer coated by CVD, two kinds of substrate (substrate A: WC-9.5wt% Co-MC＊[low C], substrate B: WC -6wt% Co-MC＊[high C]) were studied in terms of Cobalt and C contents respectively. For preparation of test samples the coating parameters of deposition time, deposition temperature and deposition pressure were varied. The results show that the carbon contents in substrates have greater effects on the TRS of the CVD TiC coated cemented carbide than Co contents in substrates. ＊MC:TiC+TaC

• Korean Journal of Metals and Materials
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• v.48 no.7
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• pp.589-597
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• 2010

In the present study, the effect of variation in alloying elements on the carbide formation behavior during casting and homogenization treatment of M2 high speed steels was investigated. M2 high speed steels of various compositions were produced by vacuum induction melting. Contents of C, Cr, W, Mo, and V were varied from the basic composition of 0.8C, 0.3Si, 0.2Mn, 4.0Cr, 6.0W, 5.0Mo, and 2.0V in weight percent. Homogenization treatment at $1150^{\circ}C$ for 1.5 hr followed by furnace cooling was performed on the ingots. Area fraction and chemical compositions of eutectic carbide in as-cast and homogenized ingots were analyzed. Area fraction of eutectic carbide appeared to be higher in the ingots with higher contents of alloying elements the area fraction of eutectic carbide also appeared to be higher on the surface regions than in the center regions of ingots. As a result of the homogenization treatment, $M_2C$ carbide, which was the primary eutectic carbide in the as-cast ingots, decomposed into thermodynamically stable carbides, MC and $M_6C$. The latter carbide was found to be the main one after homogenization. Fine carbides uniformly distributed in the matrix was found to be MC type carbide and coarsened by homogenization.

• Journal of Korea Foundry Society
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• v.33 no.5
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• pp.193-203
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• 2013

The Ni-base superalloy CM247LC was directionally solidified (DS) using the Bridgman-type furnace to understand the effect of the chill plate on the microstructural evolution, such as dendrite arm spacing, microporosity, and MC-type carbide. The DS process was also modeled by the PROCAST to predict the solidification rate, thermal gradient, and resultant cooling rate in the entire length of the DS specimen. Due to the quenching effects of chill plate, four distinct areas were found to form in the specimen, in which the solidification rate was changed, during DS at a given withdrawal rate of 0.083 mm/s. Among the microstructural features investigated, the dendrite arm spacings and average size of the MC-type carbide near the chill plate were found to be influenced by the quenching effect of the chill plate. However, no significant influence was found on the size and volume fraction of microporosity, and the volume fraction of the MC-type carbide. The relationship between the microstructural features and the solidification variables was also analyzed and discussed on the basis of a combination of experimental and modeling results.

• Journal of the Korean institute of surface engineering
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• v.24 no.1
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• pp.8-8
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• 1991

To investigate the effects of substrate on transverse-rupture strength(TRS) and bonding strength between substrate and TiC layer coated by CVD, two kinds of substrate (substrate A:WC-9.5wt%Co-MC*[low C], substrate B: WC-6wt% Co-MC*[high C] were studied in terms of Cobalt and C contents respectively. For preparation of test samples the coating parameters of deposition time, deposition temperature and deposition pressure were varied. The result show that the carbon contents in substrates have greater effects on the TRS of the CVD TiC coated cemented carbide than Co contents in substrates.