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고알루미늄 (高) 내열주철에서의 (耐熱鑄鐵) 흑연구상화와 (黑鉛球狀化) 내산화성에 (耐酸化性) 관한 연구
김동규,나형용 ( D . K . Kim,H . Y . La ) 한국주조공학회 1981 한국주조공학회지 Vol.1 No.2
N/A Graphite spheroidization and scaling resistance of cast iron containing 5-10% Al were investigated. It is impossible to obtain spheroidal graphite in cast iron containing Al with 8 % and over, but possible to obtain spheroidal graphite even in cast iron with an Al content of about 10 % by increasing Si contant. In the scaling test carried out under the heating condition of 950℃ in air for total of 50 hours, the scaling resistance of cast iron containing Al with 8 % and over was remarkably superior, and also spheroidal graphite cast iron was superior to flake graphite cast iron. The scale became thinner more compacts and more protective with increasing Al content.
고 Si 구상흑연주철의 조직과 기계적성질에 미치는 Si 과 Mo 의 영향
김종연,나형용 ( Jong Yeon Kim,Hyung Yong Ra ) 한국주조공학회 1990 한국주조공학회지 Vol.10 No.3
N/A Spheroidal graphite cast irons which are Fe-3%C-(4-6)%Si-(0-0.5)%Mo were studied to improve not only heat resistance but also mechanical properties. With increasing Mo content, the graphitization was decreased and carbide volume fraction was increased. The graphite spheroidization ratio was not decreased in Fe-3%C-6%Si-Mo system cast iron with increasing Mo content, but that was decreased in Fe-3%C-4%Si-Mo system and Fe-3%C-5%Si-Mo system cast irons. Hardness was increased with the Si and Mo contents. At constant Si content, tensile strength was increased with increasing Mo content, but that was decreased at 6%Si. In the experiment of oxidation, weight gain was decreased as the Si and/or Mo content increased, but increased at 1.5%Mo content.
김형수,나형용 ( H . S . Kim,H . Y . Ra ) 한국주조공학회 1982 한국주조공학회지 Vol.2 No.3
N/A In this study, the influenced of graphite shape on the boriding of cast iron and boride structure was investigated. Gray cast iron, ferritic and pearlitic ductile cast iron were borided at 750,850,900 and 950 ℃ for 1,3 and 5 hours by powder pack method with the mixture of B₄C_9 Na₂B₄O_7, KBF₄and Shc. The boride layer was consisted of FeB(little), Fe₂B (main) and graphite. Some possibility of the existence of unknown Fe-B-C compound in the boride layer was suggested. And precipitates in the diffusion zone was Fe₃(B,C). The concentration of Si and precipitation of Fe₃(B,C) in the α layer raised the hardness of this Zone. The depth and hardness of boride layer increased with the increase of treating temperature and tim. But high temperature (over 950℃) caused pore at graphite position and long treating time (5hrs) sometimes caused formation of graphite layer beneath the boride layer. So, for the practical application of borided cast iron, treating in short time and at low temperature was recommended. And for ductile cast iron, ferritizing or pearlitizing heat treatment was seemmed to be possible at the same time with boriding. The graphite in the boride layer was deeply concerned with the qualitx and characteristics of the boride layer. And it greatly influenced on the shape of the boride phase, structure of the boride layer. Generally speaking, the existance of graphite restrained the growth of the boride phase. But the boundary between the graphite and the matrix acted as the shortcut of boron diffusion. So, for gray cast iron, the graphite layed length-wise led the formation of boride layer.
가스분무한 Al-8wt.%Fe 합금분말의 급속응고과정에 대한 수치해석
김성균,최회진,나형용 ( Seong Gyoon Kim,Hoi Jin Choi,Hyung Yong Ra ) 한국주조공학회 1993 한국주조공학회지 Vol.13 No.5
N/A A numerical analysis on the microstructural evolutions of microcellular and cellular α -aluminum phase in the gas-atomized Al-8wt. pct droplets was represented. The 2-dimensional non-Newtonian heat transfer and the dendritic growth theory in the undercooled melt were combined under the assumptions of a point nucleation on droplet surface and the macroscopically smooth solid-liquid interface enveloping the cell tips. It reproduced the main characteristic features of the reported microstructures quite well. It predicted a considerable volume fraction of segregation-free region in a droplet smaller than l0㎛ if an initial undercooling larger than 100K is given. The volume fractions of the microcellular region(g_A) and the sum of the microcellular and cellular region(g_a) were predicted as functions of the heat transfer coefficient, h and initial undercooling, ΔT. It was shown that g_A and g_a, in the typical gas-atomization processes with h=0.1-1.0W/㎠K, are dominated by ΔT and h, respectively, but for h larger than 4.0W/㎠K, a fully microcellular structure can be obtained irrespective of the initial undercooling.
주철분말의 소결조직에 (燒結組織) 미치는 산화철 (酸化鐵) 첨가의 효과
김형수,김철범,나형용 ( Hyung Soo Kim,Chul Bohm Kim,Hyung Yong Ra ) 한국주조공학회 1990 한국주조공학회지 Vol.10 No.2
N/A The microstructures of sintered products of Fe₂O₃or Fe₃O₄-Oxide added cast iron powder was investigated. And the effects of particle size distribution was investigated too. As the result, the structures of sintered products did not related to the species of Fe-Oxide. Th porosity of sintered products was decreased in size and spherodized with increasing sintering temperature, decreasing Fe-Oxide quantity. Fe-Oxide itself did not hinder sintering of cast iron powder particularly, therefore sintering could be occurred without termination of reduction of it. And the sintered products of finer particle size distribution had finer and more spherodized porosity, and had minimized the deviation of size and shape of porosity.
김동익,김동규,나형용 ( Dong Ik Kim,Dong Kyu Kim,Hyong Yong Ra ) 한국주조공학회 1984 한국주조공학회지 Vol.4 No.3
The transformation plenomena of γ phase which is formed by heating the ferritic malleable cast iron above Al transformation temperature, and the effects of heating temperature on the hardness were investigated. The results are summarized as follows; 1. By heating the ferritic malleable cast iron above 740℃ α phase surrounded the graphite particle transformed into γ phase. The volume fraction of γ phase is increased linearly with holding time in α + γ region and rapidly with increasing the heating temperature. 2. When the specimens are heated between 740℃-860℃, the grain boundary of ferrite prevent the growth of γ phase. Therefore the interface of γ and α are obserbed along the former ferrite grainboundary. But above that heating temperature the tendency of preventation is weaken, so the interface between γ and α phase are formed irregularly. 3. Having same volume fraction of γ phase, the hardness of specimen are increased with increasing the heating temperature.
과 공정주철에서 흑연의 형상에 미치는 Mischmetal Hydride 첨가의 영향
이호종,김관휴,나형용 ( Ho Jong Lee,Kwan Hyu Kim,Hyung Yong Ra ) 한국주조공학회 1988 한국주조공학회지 Vol.8 No.2
N/A The effects of mischmetal hydride 0.5wt% addition on the graphite morphology according to the various S contents and holding times were investigated. The results obtained in this work were as follows. 1. Giving a short time after the MmH₂addition, nodular graphites were formed by means of many bubbles remained in the melt. 2. The more S was given in the melt, the less the surface tension of the melt became. So the remained gas bubbles in the case of high S Content were decreased both number and size, and irregular nodular graphites were formed. 3. Mischmetal sulfides remained in the melt acted as heterogeneous nuclei not for the graphite precipitation but for the gas bubble formation. The remained gas bubbles in the melt operated as the site of the graphite precipitation.
주철분말의 소결성에 (燒結性) 미치는 산화철 (酸化鐵) 첨가의 효과
김형수,김철범,나형용 ( Hyung Soo Kim,Chul Bohm Kim,Hyung Young Ra ) 한국주조공학회 1990 한국주조공학회지 Vol.10 No.1
N/A In order to lower the cabon content of sintered products below the solubility of austenite, Fe-oxide was added to cast iron powder of which matrix was pearlite. And the effects of it on some sintering properties and mechanical properties were investigated. Roughly speaking, the linear shrinkage, density, and tensile strendth of sintered properties increased as the sintering temperature became higher, the size distribution of powder became finer, and the amount of Fe-oxide added became less. The maximum tensile strength of sintered products was 78㎏f/㎟ more or less, of which carbon content was 1.4% and sintering temperature was 1180℃.
구리봉의 연속주조금형에 사용된 아세틸렌 화염 도형의 최적화
김재욱,김영태,오규환,나형용 ( Jae Uk Kim,Young Tae Kim,Kyu Hwan Oh,Hyung Yong Ra ) 한국주조공학회 1996 한국주조공학회지 Vol.16 No.2
N/A In copper continuous casting, the soot, which is the incomplete pyrolitic product of acetylene, has been used as a mold coat. In this work, under constant acetylene pressure, the characteristics of soot and the optimum condition of sooting were investigated with different acetylene and oxygen flow rate. The soot particles deposited on the mold surface had mainly spherical shape and their sizes were about 20㎚. After reaction with melt, their shapes were changed into polygonal type due to the graphitization. With increasing oxygen flow rate up to 0.6ℓ/min, the amount of residues of soot after heat treatment were kept nearly constant. But the amount of residues increased rapidly with further increasing oxygen flow rate. Degree of graphitization was maximum at 0.4ℓ/min and 5ℓ/min of oxygen and acetylene flow rate, respectively.