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Nucleation of Graphite in Cast Irons
( Carl R . Loper ) 한국주조공학회 1997 한국주조공학회지 Vol.17 No.4
The current understanding of the mechanism of inoculation of the eutectic in commercial Fe-C-Si alloys using either silicon containing alloys or graphite has been discussed. The mechanism whereby inclusion formation within a cast iron melt is essential for inoculation effectiveness in ferro silicon inoculation has been reviewed. The role of graphitic inoculants has been presented, including the results of recent research that confirms the inoculating capability of graphite and demonstrates those factors which must be considered in evaluating inoculation effectiveness. Fading of inoculation, both ferro silicon and graphite, and the mechanism whereby this occurs, has also been discussed.
On the Mechanism of the Formation of Widmanstatten Graphite in Flake Graphite Cast Irons
Jr Carl R.Loper,Park, Junyoung 대한금속재료학회 2003 METALS AND MATERIALS International Vol.9 No.4
The mechanism whereby Widmanstatten graphite develops during the solidification of flake graphite cast irons has been found to involve the preferential segregation and a complex interaction of specific elements at the surface of the graphite flake during solidification and the development of the plate like appendages in the solid austenite adjacent to the graphite flake. The literature has suggested that lead, calcium and hydrogen may bc causal to the formation of Widmanstatten graphite. hut has the interaction of these elements has not been effectively documented. While the formation of this degraded graphite is often attributed to the presence of a sufficient amount of lead alone, it has been observed that Widmansatten graphite develops only in conjunction with a combination of factors operative at the graphite-austenite intertace. Commercial flake graphite cast irons may exhibit Widmanstatten graphite as a function of lead and calcium content in the iron, moisture content in the molding media, solidification cooling rate and the rate of cooling immediately after solidification, etc. Lead contamination of cast irons was also observed to increase the chilling tendency of the iron. The detrimental effects of lead can be counteracted by the presence of rare earths in the iron, where rare eanh elements react with lead to form stable. high melting point compounds.
유수안,Yew, S. A. 대한금속재료학회(대한금속학회) 1969 대한금속·재료학회지 Vol.6 No.4
灰鑄鐵의 初晶 dendrite를 볼 수 있는 方法을 發展시킴으로서 灰鑄鐵의 機械的性質과 初晶 dendrite, 共晶 cell, 共晶組織, 黑鉛等과의 關係를 硏究하였다. 方向性이 좋고 稠密한 初晶 dendrite가 잘 發達한 共晶 組織을 同伴하는 것이 方向性이 없고 稠密치 못한 dendrite가 未發達한 共晶組織을 同伴할 때 보담 機械的性質이 優秀하다. 初晶 dendrite는 그 凝固機構에 따라 Type I, Type II, Type III로 分類한다. Type I dendrite는 그 凝固過程에서 充分한 發達을 할 수 있으므로서 잘 發達한 共晶組織을 同伴하고 Type II dendrite는 凝固過程이 억압됨으로서 잘 發達하지 못한 共晶組織을 同伴하고 또 Type III dendrite는 高溫에서 凝固가 進行되어 오히려 發達할 機會를 갖지 못한 未發達된 共晶組織을 同伴한다. 灰鑄鐵의 黑鉛組織도 發達, 未發達, kish등 3種類로 分類할 것을 提案한다. Developing method of sample treatment for proeutectic dendrites, study a relationship between proeutectic dendrites, eutectic cell structures, eutectic structures, graphite structures and mechanical properties of gray cast iron. Hightly oriented and compact proeutectic dendrites with well developed eutectic structures have higher mechanical properties than random dendrites with underdeveloped eutectic structures. Proeutectic dendrite structures be classified according to the solidification mechanism, as Type I, II, and III. Type I dendrites associate well developed eutectic structures due to enough chance to develope during the solidification. Type II dendrites associate underdeveloped eutectic structures due to suppression of the solidification reaction. Type III dendrites associate underdeveloped eutectic structures due to lack of chance to develope at higher temperature solidification. Graphite structures of gray cast iron have proposed to be classified as developed, underdeveloped and kish graphite.
백종승,강춘식,Loper, C. R.,Perepezko, J. H. 대한금속재료학회(대한금속학회) 1982 대한금속·재료학회지 Vol.20 No.11
熔融狀態의 合金을 急冷(10^6℃/sec)方法을 利用하여 凝固시킬때 자주 觀察되는 非平衡狀態의 獨特한 顯微鑛組織은 高度의 過冷却現象이 結晶質의 核生成過程에서 關係되였음을 나타낸다. 따라서 過冷却現象이 高速凝固過程에 미치는 基本過程을 硏究하기 爲한 Model approach로 徐冷條件 (10∼30℃/min)에서도 高度의 過冷却現象 (0.3∼0.4 Tm)을 얻을 수 있는 Droplet Emulsion Technique이 低融點金屬에 導入되었다. Droplet Emulsion Technique의 應用은 高度의 過冷却狀態에서 작은 droplet를 (10∼20μ)을 빠른 速度로 凝固시켰을때, 急冷方法을 使用했을 때와 같은 準平衡相들의 形成이 可能함을 보여 줄 뿐만 아니라 이러한 準平衡相들의 核生成過程을 組織的으로 檢討할 수 있는 初期 固溶體를 觸媒로 한 非均一核生成實驗을 可能케 해 주었다. 이러한 實驗結果에 따라 金屬粉末裝置에 高速凝固方法이 應用된다면 粒子精製(grain refinement) 效果뿐만 아니라 核生成過程에서 顯微鏡組織의 發達을 調節함으로써 顯微鏡組織의 形態變形이 可能하여 優秀한 物理的性質을 갖인 새로운 金屬材料의 開發이 可能함이 밝혀졌다. 더 나가서, droplet方法에 依한 液體金屬의 過冷却實驗은 高速凝固過程 뿐 아니라 在來式 鑄物方法에서 일어나는 凝固過程을 糾明하는데에도 基凝的인 資料가 된다고 믿어 진다. A droplet emulsion technique which allows a deep undercooling (0.3-0.4Tm) at slow cooling rate (10-30℃/min) has been applied as a model approach to study the basic solidification mechanisms associated with rapid solidification processing. When a liquid metal is undercooled substantially, the crystal growth following nucleation will be rapid regardless of the cooling rate. Often, the usual solidification reactions can be suppressed at high undercooling by the formation of metastable solid solutions, intermediate phases and in some cases amorphous solids. The kinetic phase selection mechanism has been examined by a controlled nucleation catalysis experiment in which the primary solid solution is established as one type of suitable catalytic site for the generation of metastable phases during nucleation. Phase selection promoted by undercooling and known nucleation catalysis reactions provides numerous possibilities for nucleation controlled structure modification. This indicates that rapid solidification powder processing not only has a valuable potential for grain refinement, but also has extensive possibilities for microstructural modification.