Fe-C-Al系 鑄鐵의 機械的 性質에 관한 硏究

羅亨用,金東奎 동아대학교 공과대학 부설 한국자원개발연구소 1985 硏究報告 Vol.9 No.1

For the purpose of investigating the effect of microstructural constituents on the mechanical properties of Fe-C-Al cast iron, the tensile properties, changes in hardness and variation of primary austenite dendrite morphology were investigated. The results obtained from this experiment are summarized as follows. Tensile strength appeared to be increased with increasing the directionality of primary austenite, the maximum tensile strength was obtained for the specimen containing 3% C and 4.4% Al. With increasing the Al content the tensile strength was shown to be increased at the constant carbon content but decreasing tendency of the tensile strength was shown over the carbon content of 4%. Tensile strength was increased with increasing the carbon content at all Al level. At same tensile strength, hardness was decreased with increasig the Al content. The factors controlling the tensile strength and hardness appeared to the primary austenite and pearlite in the matrix, respectively.

탈흑연주철분의 입도분포에 따른 분말특성과 소결에 관한 연구

나형용 대한금속재료학회(대한금속학회) 1981 대한금속·재료학회지 Vol.19 No.8

Cast iron powder is prepared by pulverization of gay cast iron swarf (grade GC20) with conventional hammer mill. After degraphitization is carried out by extracting the free graphite flakes from the powder, the characteristics of green compacts and sintered products are studied. The results obtained are as follows; 1) The compactability of degraphitized cast iron powder is superior. When compacted between 8-l0ton/㎠ pressure, the green density of compact gets up to about 90% of its parent iron density. 2) The sintered density and green density of compacts are increased with increasing compacting pressure. 3) The strength of sintered product is increased with raising the compacting pressure and with increased sintering temperature and time. The tensile strength of the product compacted with 8ton/㎠ pressure and sintered at 1150℃, 90min in N₂+3H₂atmosphere, goes up to 42.3㎏/㎟, twice of the tensile strength of its parent iron.

회주철의 공정응고에 대한 고찰

나형용 대한금속재료학회(대한금속학회) 1972 대한금속·재료학회지 Vol.11 No.2

灰鑄鐵의 응고조직은 대체로 共晶溫度에서의 凝固樣相이나 또는 熔鐵의 性狀에 따라 결정된다. 이들은 그 熔鐵의 화학조성 뿐만 아니라 原料鑄鐵의 조직이나 혹은 용해조건 등의 변화에 따라 다르게 된다. 따라서 본 실험에서는 原料鑄鐵의 조직이나 용해조건이 共晶凝固現象에 미치는 영향을 살펴보았다. 1) 熔鐵의 過熱度가 커지거나, 保持時間이 길어지면 原料鑄鐵의 조직이 어느 것이던지 共晶開始溫度가 낮아졌다. 2) 白鑄鐵의 용해시 過熱度가 커질수록 灰鑄鐵의 경우에 비하여, 同一 冷却條件下에서도 過冷이 심하였다. 3) 白鑄鐵의 가열시 分解生成된 temper-carbon과 灰鑄鐵의 片狀黑鉛은 서로 다른 熔解過程을 밟는다. The eutectic structure of gray iron is determined by the manner in which solidification takes place through the eutectic temperature and by the status of iron melts which depends not only on the composition, metallographic structure of cast irons but their melting conditions. The main purpose of the present investigation was to study the effects of metallographic structures and the melting conditions of cast iron on solidification at a given composition and results obtained are as follows : 1) The higher temperature and the longer holding time were applied in melting of iron, the lower eutectic temperature were observed. 2) The white iron remelted at high temperature gave rise to the more degree of supercooling, compared with the gray iron with the same composition and in the same cooling rate. 3) Differences in melting of the flake graphite in gray iron and of the temper-carbon decomposed from white iron have been discussed.

흑연형태 (黑鉛形態) 에 따른 주철의 Melting Morphology 에 관한 연구

나형용,임창희 대한금속재료학회(대한금속학회) 1982 대한금속·재료학회지 Vol.20 No.12

Many studies on the solidification process of cast iron were reported, but the studios on the melting morphology of cast iron are rare. Therefore, in this work the melting has been done by rapid melting method and melting morphology has been examined, according to graphite shape in cast iron. The main results are summarized as follows: 1. In white cast iron of Fe-C-Si system, melt appears first along the interface between temper carbon and austenite matrix, after the minute temper carbon which was decomposed from Fe₃C diffuses to austenite to eutectic composition. 2. In either hypo or hyper-eutectic gray cast iron, it is observed that the melt appears first at the boundary of eutectic cell. In case of the eutectic gray cast iron, the vicinity of all graphites melts at the same time. 3. In rapidly heated and water quenched specimen of hypereutectic gray cast iron, the crystallization of fine graphites near kish graphite leads to the conclusion that kish graphite does not dissolve easily. 4. In case of nodular cast iron, the boundary between austenite shell and austenite matrix melts first and nodular graphite dissolves very slowly.

구상흑연주철의 용해거동에 미치는 가열속도 및 인의 영향에 관한 연구

나형용,임창희 대한금속재료학회(대한금속학회) 1984 대한금속·재료학회지 Vol.22 No.11

Many studies have been done to explain the effect of grain boundaries in austenite shell on the growth of spheroidal graphite . But, its effect on the melting procedure of spheroidal graphite cast iron is unknown. Therefore, in this work, melting procedure of spheroidal graphite cast iron and the role of grain boundaries in austenite shell on melting of spheroidal graphite have been studied, by changing the condition of melting and the content of phosphor. The main results are summarized as follows. 1. Steadite melts under the eutectic temperature. Therefore, the melting phenomena of spheroidal graphite cast iron is changed by the existence of steadite. 2. In spheroidal graphite cast iron containing little phospher, melt appears first at the outer region of austenite shell in which Si is condensed, regardless of heating rate. In this case, grain boundaries in austenite shell give little effect on the melting procedure of spheroidal graphite. 3. In spheroidal graphite cast iron containing phosphor above 0.3%, melt appears first along the interface between spheroidal graphite and austenite shell, at low heating rate. It seems to be caused by moving of liquid phase to spheroidal graphite along grain boundaries in austenite shell. But, at high heating rate, melting proceeds with remaining austenite shell around spheroidal graphite.

Cu-Pb 합금의 응고조직에 미치는 진동의 영향

나형용,이대훈 대한금속재료학회(대한금속학회) 1980 대한금속·재료학회지 Vol.18 No.4

Cu-Pb 합금에 있어서 結晶粒 微細化, Pb의 重力 偏析, Pb-Leakage 및 硬度등에 미치는 振動의 影響을 조사하기 위하여 凝固中의 Cu-Pb 합금에 60CPS의 振動을 加하였다. 徐冷 凝固組織에서는 Pb의 含量이 10%, 20%, 30%로 증가함에 따라 單位 面積當 結晶粒數의 比가 2.78, 2.54, 1.36배로 되었으며, 急冷 凝固組織에서는 그 比가 24.80, 4.37, 1.90배로 되었다. 卽, 振動은 急冷 凝固인 경우에 結晶粒 微細化 效果가 크게 나타났다. 徐冷 凝固의 경우 振動에 依해서 Pb의 重力 偏析의 程度를 減小, 또는 除去시킬 수 있으며, 硬度를 增加시킬 수 있다. Cu-20%Pb 합금에서는 振動은 Dendrite가 晶出하기 시작하는 凝固 初期(1010℃∼980℃)에 結晶粒 微細化 效果를 크게 한다. To examine the influences of vibration and the duration of vibration on the grain refinement, gravity segregation of lead, leakage of lead and hardness, the 60 cps vibration was given to the melt of Cu-Pb alloy during solidification. Results obtained from this study can be summarized as follows ; (1) As the content of lead increases from 10% to 20%, 30%, the ratio of the number of grains per unit area decreases from 2.78 to 2.54, 1.36 in the slowly-cooled structure, and the ratio decreases from 24.80 to 4.37, 1.90 in the rapidly-coolded structure, i.e. the vibration has an effect on the grain refinement in case of low Pb alloy, especially in the rapidly-cooled structure. (2) In case of slow-cooling, the vibration can suppress or eliminate the amount of gravity segregation of lead, and can increase the hardness. (3) The influence on the grain refinement occurs only in the period from 1010℃ to 980℃ during which the dendrites begin to form in Cu-20%Pb alloy.

평면 고-액계면상에 존재하는 Perturbation의 morpohology 변화에 대한 이론적 고찰

나형용,김성균 대한금속재료학회(대한금속학회) 1984 대한금속·재료학회지 Vol.22 No.5

By using the quasi-steady state solution of the diffusion equation, we discussed the time evolution of a perturbation on the flat solid-liquid interface during solidification of dilute binary alloy or pure materials and the interaction between solute diffusion effect and interface curvature effect. As the results, we showed that the perturbation is propagated to the lateral directions with cell spacing, λ_s (=2π√(3D)_o) irrespective of its initial morphology and at this spacing, the interaction between diffusion and curvature effect reached equilibrium state. Also, appling these results to the secondary arm branching of dendrite, we showed that the branching mechanism can be expressed by the perturbation propagation process.

WO3 의 환원에 따른 입자의 Morphology 변화에 관한 연구

나형용,장재규 대한금속재료학회(대한금속학회) 1983 대한금속·재료학회지 Vol.21 No.5

Morphological changes of intermediate tungstic oxide particles, prepared by reducing WO₃with hydrogen and a mixture of hydrogen and nitrogen over the temperature range from 800℃ to 1000℃, were studied using scanning electron microscope. Two different morphologies of W_(18)O_(49), bundles of needle crystals and short pole-type particles, were obtained at 800℃, whereas W_(18)O_(49), obtained at 900℃ and above, consisted of pale-type particles and fine whiskers. The growth of W_(18)O_(49) particles was faster in the length than the width with increasing reduction temperature. The size and morphologies of W_(18)O_(49) particles were greatly influenced by those of WO₃particles. Transformation of W_(18)O_(49) to WO₂and WO₂to α-W was accompanied by the rounding of W_(18)O_(49) particles and the recrystallization of α-W in spherical shape respectively. Extremely fine α-W powder was obtained by reduction of WO₃powder at 500℃ for 4 hrs in hydrogen followed by immediate reduction at 650℃ for 1 hr.

급속응고된 Fe-C 2 원계 합금의 응고조직 및 열처리 조직에 관한 연구

나형용,김동익 대한금속재료학회(대한금속학회) 1988 대한금속·재료학회지 Vol.26 No.12

The rapidly solidified structures of Fe-C binary alloy containing 3.8-4.5 wt%C made by using the melt spinner and gas atomizer was analyzed and how the solidified structure of it, of which consolidation temperature is expected to be 700-1000 ˚C, changed was considered. As a result of experiment, the solidified structure consist of the eutectic structure of austenite and cementite, the size of which was within sevaral ㎛, and at the last solidified part, the austenite dendrite was observed. In the solidified structures by using the melt spinner, any meta-stable phase was not observed, but in the powder under the 25㎛ solidified by using the gas atomizer, there much observed meta-stable ε-phase. The microhardness of it showed the initial value of 550-900MVH(㎏/㎟) and even though after annealing. The high value of 700-800MVH(㎏/㎟) was also measured. So, it is possible that these metarials have practical use.

Acute Renal Cortical Necrosis Caused by Tampon

Chi-Yong Ahn · Na-Ra Yoon · Dae-Woong Kang · Kyung-Hee Park · Hyong-Sun Kim · Jong-Hoon Chung · Hyun-Lee Kim 조선대학교 의학연구원 2007 The Medical Journal of Chosun University Vol.32 No.2

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