• Analytical Science and Technology
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• v.13 no.2
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• pp.200-207
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• 2000

The growth mechanisms of graphite spherulite both in the nodular cast iron and the high pressuretreated Ni-C alloy were investigated by SEM, HRTEM and EELS. The internal microstructure and lattice image of graphite spherulite extracted from Ni-C alloy were compared with those of graphite spherulite extracted from the nodular cast iron. The ratios of $sp^2$ and $sp^3$ bonding in the respective graphite spherulite measured by EELS, are compared each other. The graphite spherulite of Ni-C alloy had little internal defects and much $sp^3$ carbon species compared to that of the nodular cast iron. Present difference in microstructural features and bonding characters indicated that the graphite spheruites in the high pressuretreated Ni-C alloy grew by different mechanism compared with those in the nodular cast iron.

• Journal of Korea Foundry Society
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• v.43 no.6
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• pp.279-285
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• 2023

In order to predict the mechanical properties of ductile cast iron heat treated in an intercritical temperature range, samples machined from cast iron with a tensile strength of 450 MPa were heat-treated at various intercritical temperatures and air-cooled, after which a microstructural analysis and Brinell hardness test were conducted. As the heat treatment temperature was increased in the intercritical temperature range, the ferrite fraction in the ductile cast iron decreased and the pearlite fraction increased, whereas the nodularity and nodule count did not change considerably from the corresponding values in the as-cast condition. The Brinell hardness values of the heat-treated ductile cast iron increased gradually as the heat treatment temperature was increased. Based on the measured alloy composition, the fraction of each stable phase and the hardness model from the literature, the hardness of the ductile cast iron heat treated in the intercritical temperature range was calculated, showing values very similar to the measured hardness data. In order to check whether it is possible to predict the hardness of heat-treated ductile cast iron by using the phase fraction obtained from thermodynamic calculations, the volumes of graphite, ferrite, and austenite in the alloy were calculated for each temperature condition. Those volume fractions were then converted into areas of each phase for hardness prediction of the heat-treated ductile cast iron. The hardness values of the cast iron samples based on thermodynamic calculations and on the hardness prediction model were similar within an error range up to 27 compared to the measured hardness data.

• Analytical Science and Technology
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• v.6 no.2
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• pp.149-156
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• 1993

The formation of the graphite spherulites has been studied experimentally in the Ni-C liquid under high pressure and temperature. In the diamond-stable region the graphite spherulites were formed and grew stably. They were not the polycrystalline particles but the single crystals of the fullerene-type, respectively, grown spirally with much imperfection. And they were proved to be in a mixture state of carbon atoms with $sp^2$- and $sp^3$-bonding by an Auger electron spectroscope and a high resolution transmission electron microscope. As the pressure decreased from the diamond-stable region to the graphite-stable region, the shape of the graphite particles changed gradually from the sphere to the flaky shape. The formation of the graphite spherulites was attributed to the stable existence of the carbon atoms with $sp^3$ bonding in the diamond-stable region. The formation of the large fullerene-type graphite spherulites with much imperfection is well agreed with Kroto's prediction for growth of the giant fullerene.

• Journal of Korea Foundry Society
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• v.24 no.2
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• pp.101-107
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• 2004

회주철 및 구상흑연주철에 있어서 압탕방안 및 합금원소가 수축결함의 생성에 미치는 영향을 연구하였다. 두 종류의 압탕방안으로 실린더형상의 계단상시편을 제조하였으며 회주철의 경우 5조성(ISO 150, 200, 250, 300, 350), 구상흑연주철의 경우 6조성(SG 10, 20, 30, 40, 50, 60)을 사용하였다. 회주철 및 구상흑연주칠 공히, 1차 압탕방안의 경우 액상수축에 의한 1차수축결함이 후육부의 표면에 발생하였으며 수축결함의 내면은 매끄러웠다. 회주철의 경우 응고수축에 의한 2차수축결함은 생성되지 않았으나 구상흑연주철의 경우 모든 시편의 내부열점에 2차수축결함이 발생하였고 그 내면은 거칠었다. 2차압탕방안의 경우 회주철의 모든 시편에서는 1차 및 2차수축결함이 발생되지 않았다. 그러나 구상흑연주철의 경우 탄화물 생성원소가 첨가된 SG 40, 50 및 60의 3조성에서 2차수축결함이 열점에 생성되었다. 견고한 ���V주형을 사용하였기 때문에 주형벽이동으로 인한 표면팽창은 어느 경우에도 관찰되지 않았다.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1993.04a
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• pp.63-69
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• 1993

오스템퍼링 한 저합금구상흑연주철 은 일반의 구상흑연주철의 기지조직을 베이나이트로 함으로써 치수변화가 적고, 균열의 위험성이 없으며 또한 강도 및 인성이 좋은 특성을 지니고 있기 때문에 강에 필적할 만한 성질을 가진다는 것은 잘 알려져 있지만 주철은 주조한 그대로 사용한다는 개념이 강하여 지금까지 거의 공업적으로 이용되지 않았다. 그런데 최근 이 주철이 고응력을 받는 기계부붐에 적용되어 중형 및 대형의 gear wheel에 퍼얼라이트와 조질된 구상흑연주철 및 강을 대체하게되어 미국, 핀란드 및 영국 등에서는 자동차 후차축의 링 기어, 피니언 기어 및 크랭크축에 이르기까지 사용되기 시작하였고, 그 결과가 경제적으로도 은강품보다 오히려 유리하다고 보고되어 오늘날 자동차공업 부문에서도 맣은 주목을 모으고 있다.

• Journal of Korea Foundry Society
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• v.8 no.3
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• pp.322-328
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• 1988

3.9%C-2.0%Si-Fe 조성의 압분체(壓粉體)를 $1350^{\circ}$, Ar가스 분위기에서 50분간 용해한 용탕에 시판(市販) misch metal과 misch metal hydride인 MmH와 $MmH_2$를 각각 여러비율로 첨가(添加)한후 서냉(徐冷)및 급냉(急冷)한 시편의 흑연형상(黑鉛形狀)의 변화로부터 misch metal hydride의 구상화능(球狀化能)과 흑연구상화(黑鉛球狀化) 기구(機構) 로서의 기포설(氣泡說)의 타당성을 고찰한 결과 다음과 같은 결론을 얻었다. 1) Misch metal은 0.5% 이상, 그리고 misch metal hydride는 0.25% 이상 첨가한 때 구상흑연(球狀黑鉛)과 CV 흑연(黑鉛)이 나타났으며, misch metal hydride를 첨가한 때가 misch metal에 비하여 흑연립수(黑鉛粒數)가 더 많았다. 이와같이 misch metal hydride의 첨가량이 misch metal에 비하여 적었음에도 흑연립수(黑鉛粒數)가 더 많은 것을 보면 Mm으로부터 방출되는 다수(多數)의 수소기포(水素氣泡)가 구상흑연(球狀黑鉛)의 정출장소로 되는 것으로 해석되기 때문에 기포설(氣泡說)이 타당하다고 생각된다. 2) Misch metal 과 misch metal hydride의 첨가량(添加量)이 1.0%로 증가되면 두경우 모두 흑연립수(黑鉛粒數)가 감소하였다. 이는 용탕중에 개재된 수소기포(水素氣泡)의 실수율차이에 의한 잔류 수소기포수의 증가율둔화와 첨가량(添加量)의 증가에 따른 잔류 misch metal량의 상대적(相對的) 증가로 인한 다량의 잔류 misch metal이 응고과정에서 수소를 재흡수 용해하여 흑연입수를 결정하는 용탕중의 유효수소기포수(有效水素氣泡數)를 감소시켰기 때문으로 생각된다.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.1
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• pp.82-87
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• 2012

For different ferrite-pearlite matrix structure, contain more than 90% spheroidal ratio of graphite, GCD 45-3, GCD 50, GCD 60 series and 70%, 80%, 90% spheroidal ratio of graphite, GCD 40, GCD 45-1, GCD 45-2 series, this paper has carried out rotary bending fatigue test, estimated maximum and mean size of spheroidal graphite, investigated correlation. It was concluded as follows. (1) Fatigue limit in $10^7$cycles and numbers of spheroidal graphite per 1$mm^2$ was linear relation. (2) projection area of graphite can be used to predict fatigue limit of Ductile Cast Iron. The Statistical distribution of extreme values of projection area of defects may be used as a guideline for the control of inclusion size in the steelmaking processes.

• Journal of Korea Foundry Society
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• v.41 no.5
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• pp.411-418
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• 2021

In order to experimentally investigate the effect of Ni or Cu addition on microstructure and mechanical properties of high Si Solution Strengthened Ferritic Ductile cast Iron (SSF DI), a series of lab-scale sand casting experiment were conducted by changing initial concentration of Ni up to 3.0wt% or Cu up to 0.9wt% in the alloy. It was found that increase in Ni or Cu content in the alloy leads to increase in strength properties and hardness as well as decrease in ductility. The higher Ni or Cu content the SSF DI has, the higher fraction of pearlite was observed. At similar levels of Ni or Cu contents in the alloy, higher pearlite area fraction was observed in the Cu-containing SSF DI than that in the Ni-containing SSF DI. When the effect of the microstructure on the mechanical properties of Ni-containing SSF DI was considered, Ni-containing SSF DI was found to have excellent strength and hardness as well as good elongation when the pearlite fraction was controlled less than 10%. As the pearlite fraction in the Ni-containing SSF DI exceeds 10%, however, it shows drastic decrease in elongation. Meanwhile, gradual increase in strength and hardness, and decrease in elongation with respect to increase in pearlite fraction were observed in Cu-containing SSF DI. The different microstructure-mechanical property relationships between Ni-containing and Cu-containing SSF DI were due to the combined effect of the relatively weak pearlite stabilizing effect of Ni compared to that of Cu in high Si SSF DI, and matrix strengthening effect caused by the different amounts of those alloying elements required for similar pearlite fraction.

• Journal of Korea Foundry Society
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• v.42 no.4
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• pp.248-254
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• 2022

• Resources Recycling
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• v.9 no.1
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• pp.15-20
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• 2000

The effect of different kinds of steel scraps, the raw material in the manufacturing of nodular cast iron, on the microstructures and mechanical properties has been investigated Different grades were produced by changing the steel scraps. When nodular graphite cast iron was produced by using Zn rich steel scrap, such as galvanized steel sheet and auto body sheet, mechanical properties were deteriorated due to the decomposition of graphite, so close control must be maintained over this element. Tensile strength and hardness of nodular graphite cast iron which were manufactured by using Sb rich steel scrap were increased while elongation was decreased due to the increased amounts of pearlite within matrix. Mn and Cr contents in the structural steel sheet scrap or malleable iron scrap increased tensile strength and hardness of nodular graphite cast iron by facilitating the formation of pearlite.