• Journal of Korea Foundry Society
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• v.7 no.3
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• pp.184-191
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• 1987

In this study the principles of melting phenomena of compacted vermicular graphite cast iron are discussed by considering the effects of the variation of phosphorus content and heating rate on the quenched microstructure of the specimens. In compacted vermicular graphite cast iron containing little phosphorus, the melting phenomena are found initially at the outer region of austenite shell and subsequently progressed with the diffusion of carbon through the austenite shell without regard to heating rate. But as the phosphorus content was increased over than 0.12wt.%, the melting phenomena initiated at the boundary of eutectic shell and progressed along the contact area between the melt and graphite tips at higher heating rate. At lower heating rate, the melt of steadite dissolved at the lower temperature than that of eutectic was moved toward the graphite through the austenite grain-boundary and promoted melting of graphite and matrix.

• 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.

• Journal of Korea Foundry Society
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• v.5 no.4
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• pp.243-257
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• 1985

Many authors have studied the solidification process of cast iron and the effect of grain boundaries in austenite shell on the growth of spheroidal graphite. But, the studies on the melting morphology of cast iron are rare and the effect of grain boundaries in austenite shell on the melting procedure of spheroidal graphite cast iron is unknown. Therefore, in this work, the melting procedure of cast iron and the role of grain boundaries in austenite shell on the melting of spheroidal graphite have been studied. The main results are summarized as follows. 1. In white cast iron containing silicon, melting initiates at the interface between austenite matrix and temper carbon which was decomposed from $Fe_3C$ during heating. 2. In gray cast iron, melting initiates at the boundary of eutectic cell where elements with low melting temperature are condensed. The dissolution of kish graphite is difficult. 3. In spheroidal graphite cast iron containing little phosphor, melting initiates at the outer region of austenite shell in which silicon is condensed. In this case, grain boundaries in austenite shell give little effect on the melting procedure of spheroidal graphite. 4. In spheroidal graphite cast iron containing phosphor above 0.3 wt%, its melting phenomena are changed with heating rate due to the existence of steadite. In this case, it can be concluded that liquid phase of steadite, which segregated on outer region of austenite shell, moves to spheroidal graphite-austenite interface along the grain boundaries in austenite shell.

• Journal of Welding and Joining
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• v.15 no.4
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• pp.78-89
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• 1997

This study has evaluated the weld metal solidification cracking behavior of several Ni base superalloys (Incoloy 825, Inconel 718 and Inconel 600). Austenitic stainless steels(304, 310S) were also included for comparison. In addition, a possible mechanism of solidification cracking in the fusion zone was suggested based on the extensive microstructural examinations with SEM, EDAX, TEM, SADP and AEM. The solidification cracking resistance of Ni base superalloys was found to be far inferior to that of austenitic stainless steels. The solidification cracking of Incoloy 825 and Inconel 718 was believel to be closely related with the Laves-austenite (Ti rich in 825 and Nb rich in 718) and MC-austenite eutectic phases formed along the grain boundaries during solidification. Cracking in Inconel 600 was always found along the grain boundaries which were enriched with Ti and P. Further, solidifidcation cracking resistance was dependent not only upon the type of love melting phases but also on the amount of the phases along the solidification grain boundaries.

• Corrosion Science and Technology
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• v.20 no.6
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• pp.367-372
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• 2021

The effect of carbon addition on the general corrosion behavior of high-chromium cast iron (HCCI) was studied by a scanning electron microscope with energy dispersive spectroscopy (SEM-EDS) or electron back-scattered diffraction (EBSD), or electrochemical polarization techniques in 0.1 mol dm^-3 H₂SO₄ + 0.05 mol dm^-3 HCl at room temperature. The addition of 2.1-2.8 wt% carbon to HCCI increased the fraction of eutectic austenite and eutectic carbide phases, while that of HCCI decreased the fraction of the primary austenitic phase. Potentiostatic polarization of the HCCI at -0.35 V_SSCE or 0.0 V_SSCE resulted in preferential general corrosion of the primary austenitic or eutectic austenitic phases, respectively. The decrease in corrosion current density and the shift in noble corrosion potential direction with increasing carbon content in the HCCI indicated that the fraction and the chemical composition of austenitic (primary and eutectic) and carbide phases were strongly related to the general corrosion behavior of the HCCI.

• Korean Journal of Materials Research
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• v.10 no.2
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• pp.144-147
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• 2000

10%C-5%Mo-5%W-10%Cr 및 10%C-5%Mo-5%W-10%V 백주철의 응고거동을 열분석을 통하여 연구하였다. 15Kg 용량의 고주파 유도옹해로에 선철, 고철, Fe-Mo, Fe-W, Fe-Cr, Fe-V 등을 장입시켜 용해시킨 후 슬래그를 제거시키고 $1550^{\circ}C$에서 Y블럭의 펩 주형에 주입하였다. 응고거동을 조사하기 위하여 50g을 Y블럭에서 채취한 뒤 알루미나 도가니에 넣어 재용해시킨 후 1$0^{\circ}C$/min의 냉각속도로 냉각시키면서 여섯 종류의 다른 온도에서 도중에 급냉시켜 응고조직을 광학현미경으로 관찰하였다. 10%C-5%Mo-5%W-10%Cr 백주철의 경우 초정 오스테나이트, 오스테나이트와 M(sub)7C(sob)3의 공정, 오스테나이트와 M(sub)6C의 공정으로, 10%C-5%Mo-5%W-10%V 백주철의 경우 초정 MC, 오스테나이트와 MC의 공정, 오스테나이트와 M(sub)2C의 공정으로 각각 순차적으로 정출하였다. 정출하였다.

• Journal of Welding and Joining
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• v.15 no.5
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• pp.46-55
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• 1997

This study has evaluated the liquation cracking behavior in the heat affected zone of several Ni base superalloys (Incoloy 825, Inconel 718 and Inconel 600). 304 and 310S austenitic stainless steels were also included for comparison. In addition, the mechanism of liquation cracking in the HAZ was postulated based on the extensive microstructural examinations with SEM, EDAX and TEM. The liquation cracking resistance of Ni base alloys was found to be far inferior to that of austenitic stainless steels. The liquation cracking of Incoloy 825 and Inconel 718 was believed to be closely related with the Laves-austenite(Ti rich in 825 and Nb rich in 718) and MC-austenitic eutectic phases formed along the grain boundaries by constitutional liquation and incipient melting under rapid welding thermal contraction. Further, liquation cracking resistance of the HAZ was dependent not only upon the type and amount of low melting phases but also on the grain size.

• Journal of Korea Foundry Society
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• v.37 no.2
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• pp.31-37
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• 2017

A new form of austenitic heat-resistant ductile iron was developed and its microstructures and elevated temperature properties were compared to those of Ductile Ni-Resist D5S. According to JMatPro calculations, it was predicted that Mo-rich carbides would be crystallized before the eutectic reaction starts in the developed alloy. At the austenite cell boundaries of the developed alloy, both Mo-rich carbides and Cr-rich carbides were found. In addition, Ni-silicides were found adjacent to Cr-rich carbides in D5S specimen and were identified as $Ni_2Si$. The developed alloy also had greater yield strength and lower tensile strength levels with less elongation due to the dissolution of Mo atoms into the austenite matrix and the precipitation of Mo-rich carbides. From the results of elevated temperature tensile tests and stress-rupture tests, it was found that the developed alloy had elevated temperature properties superior to those of D5S. This was due to the pinning effect of the dissolved Mo atoms in the austenite matrix.

• Journal of Korea Foundry Society
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• v.12 no.6
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• pp.450-457
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• 1992

The study aims to investigate the influence of alloying elements(V,Ti) and heat treatment on the mechanical properties in hypo-eutectic chromium cast iron. Before heat treatment, all of the specimen were fully annealed(950$^{\circ}C{\times}5Hr$) to homogenize their structures. The influence of heat treatment and alloying elements(V,Ti) on hardness, retained austenite volume, and charpy impact energy as well as tensile strength of the specimen was tested systematically. Retained austenite decreased with the increase of V and Ti, but incresed with the increase of number of cycles. The impact energy decreased, and hardness and tensile strength increased with the increase of alloying elements (V,Ti) and the decrease of the number of cycles. The hardness and tensile strength increased, but impact energy decreased with the increase of V and Ti elements and the temperature of destabillization heat treatment. After the destabillization heat treatment at the same temperature, the impact energy is increased, while hardness and tensile strength decreased as the increase of tempering temperature. Retained austenite increased with increase of destabilizatoin heat treatment temperature, while decrease with the increase of tempering temperature.

• Journal of Korea Foundry Society
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• v.16 no.2
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• pp.141-148
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• 1996

In high chromium cast iron, the control of matrix microstructure as well as carbide structure is important to the performance as a wear resistant material. In this study, 3.0% C-24.0% Cr white cast irons with various molybdenum contents(residual, 1.0%, 3.0% and 5.0%) were solidified conventionally and unidirectionally for studying their effects on the microstructure and hardness. In the conventional casting, two sets of castings were poured from each melt. One set of the castings consisted of cylindrical bars of 10 and 20mm by 155mm long. The second set of the castings was a cylindrical bar of 30mm by 200mm long. On the other hand, a pep-set mold set on the Cu plate was employed to make the solidification unidirectionally. X-ray diffraction method was used to observe retained austenite and carbides in the high chromium cast iron. The morphology of eutectic $M_7C_3$ carbides changed from needle-like type to nodular type with the increase of Mo content. And, the presence of $M_2C$ carbides was identified in the sample where Mo was added over 3.0 %. Primary and eutectic carbides appeared as rod type and corngrain type, respectively in the unidirectionally solidified samples which were cut to parallel to the solidification direction. In the EDX analysis, Cr concentration was higher in the primary and eutectic $M_7C_3$ carbides, Mo in the $M_2C$ carbides, and Fe in the matrix.