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용융 붕사욕 침지법에 의해 금형용 강에 형성된 VC coating 층의 밀착성과 내마모성에 관한 연구
남태운,이병권 한국열처리공학회 2000 熱處理工學會誌 Vol.13 No.2
A study on adhesion and wear resistance of VC(vanadium carbide) coating on die steels, STD11 and STD61, has been carried out. The VC coating on the die steels was made by immersing them in molten borax bath, a kind of TRD(thermo-reactive deposition and diffusion). Adhesion strength and wear resistance were investigated using scratch test, indentation test and plate-disc test(Ogoshi type) respectively. The influence of sliding distance on the amount of wear has been determined and dominant wear mechanisms has been characterized using optical microscopy, scanning electron microscopy and EDS spectroscopy. The critical adhesion strength(L_c) between VC coating layer and substrate(STD11) was increased to 60N(L_c) in the scratch test. In the case of STD61, the strength increased to 24N. The wear resistance of VC coated die steels was excellent because the diffusion layer formed just below the coating layer. The dominant wear mechanism was identified as adhesive wear for VC coating die steels which were worn by combination of cracking and plucking of VC fragments and disc.
고온 고압 수 환경에서 인코넬 600 의 부식 피로 균열 성장 거동
남태운,맹완영,강영환,Ohashi, S .,Ishihara, T . 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.10
It is important to predict the corrosion fatigue crack growth rate of Inconel 600 for the structural integrity of nuclear power plants. In order to evaluate the corrosion fatigue crack growth rate of Inconel 600 in various applied load types, 3 different types of cracking loads which simulate corrosion fatigue, SCC and mixed mechanism of corrosion fatigue and SCC were applied to CT type Inconel 600 specimens in high temperature water at 290℃ with 4ppm dissolved oxygen concentration. There was synergistic effect on corrosion fatigue crack growth rate when mixed mode of SCC and corrosion fatigue load is applied to Inconel 600 specimens in the environment. The measured crack growth rate of the specimen to which mixed load were applied wsa faster than the predicted crack growth rate based on the superposition model. The increase in the crack growth rate indicates that there is sysnersistic interaction of fracture process at the growing crack tip which experiences mixed load of SCC and corrosion fatigue. So it is necessary to account for the synergistic acceleration of corrosion fatigue crack growth to predict the life of structural components of Inconel 600 alloys in corrosive environments.
南泰運 전북대학교 공업기술연구소 1981 工學硏究 Vol.11 No.-
The degree of graphite spheroidization and the matrix structure were studied by changing the amount of aluminum addition in spheroidal graphite cast iron. For the purpose of assessing the effect of aluminum on graphite spheroidization, three different alloys such as hypo eutectic, eutectic and hyper eutectic alloys were prepared by varying the amount of silicon only, while carbon contents were maintained constant. The results obtained were as follows : 1. The graphite spheroidization was retarded beyond the critical amount of aluminum. The critical amount of aluminum showed to be varied for three different alloys, that is, 0.68% for hyper eutectic alloy, 0.22% for eutectic alloy and 0.01% for hypo eutectic alloy. 2. The retarding effect of aluminum on the graphite spheroidization decreased with increasing both silicon contents and cooling velocity. 3. An increasing amount of aluminum and silicon contents resulted in promoting the formation of ferrite structure in the matrix, while an increasing cooling velocity showed to retard the formation of ferrite structure in the matrix.
오스테나이트계 스테인리스강에 대한 질소 고용화 처리 및 그 효과
남태운,허정 한국열처리공학회 2000 熱處理工學會誌 Vol.13 No.5
As a case hardening process for stainless steels, nitriding is more preferred and widely used than carburizing which deterioates corrosion resistance severely. In order to add the nitrogen into the stainless steels, passive film on the surface must be removed effectively before nitriding. Conventional gas nitriding process is performed in the temperature range of 500 to 600℃ with NH₃ gas, which often leads to sensitization of stainless steels. In this study, we tried to activate passive film of austenitic stainless steels by heating at low pressure.(900℃, 5×10^(-2) Torr.) Nitriding was performed at the solution treatment temperature of 1100℃ with nitrogen molecules instead of NH₃gas. An attainable nitrogen content in a case depends on the nitrogen gas pressure at constant nitriding temperature. A case depth is proportional to the square not of solution time, which suggests that inward diffusion of nitrogen follows the Fick's 2nd law. Surface nitrogen atoms are dissolved as interstitial solutes, or precipitated in the form of MN, M₂N nitrides, which increase the case hardeness. Dissolved nitrogen in the case enhances the cavitation resistance of austenitic stainless steels dramatically.
고온 . 고압 환경하에서 정전위법에 의한 인코넬합금의 입계응력부식 저항성 평가
남태운,맹완영 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.8
Inconel alloys which have good high temperature mechanical properties and corrosion resistance have been used extensively as steam generator tube of nuclear power plants. There have been some reports on the intergranular stress corrosion cracking (IGSCC) failure problems in steam generator tubes of nuclear reactors. In order to evaluate the effects of heat treatment and composition on the IGSCC behavior of Inconel alloys in simulated nuclear reactor environment, four different specimens(Inconel 600 MA, 600TT, 690 MA and 690 TT) were prepared and tested by electrochemical method. Static potential tests for stressed C-ring type Inconel specimens were carried out in 10% NaOH solution at 300℃(75atm). It was found that IGSCC was initiated in Inconel 600 MA specimen, but the other three specimens were not cracked. Based on the gradients of corrosion current density of the four specimens as a function of test time, thermally treated alloys show better IGSCC resistance than mill-annealed alloys, and Inconel 690TT has better passivation characteristic than Inconel 600 MA. Inconel 690 TT shows clear periodic passivation that indicates good SCC resistance. The good IGSCC resistance of Inconel 690TT is due to periodic passivation characteristics of surface layer.
급속응고한 AZ91-Misch Metal 합금의 미세조직에 관한 연구
남태운,김정균,박훈모 한국주조공학회 1999 한국주조공학회지 Vol.19 No.4
The purpose of this study was to investigate the change of microstructure of the rapidly solidified ribbons with composition and cooling rate by melt spinning process. The microstructure of ribbons has been refined with increasing wheel speed. The RS ribbon contains three layers, i.e. columnar layer on the chill side, equiaxed grains and dendrite layer on the free side. As the content of misch metal(rare earth element, Ce, La, Nd, Pr) was increased, the microstructure of RS ribbon became finer than that of AZ91 RS ribbon. As misch metal was added, Al₂RE and A11lRE3 phase was formed. With increasing wheel speed and content of misch metal, the hardness was increased. This behavior of characteristics was related to refinement of grain size and the increased volume fraction of intermetallic compound phases. (Received June 19, 1999)
급냉응고 분말법에 의한 7091 Al 합금의 분말제조와 분말조직에 관한 연구
남태운,심언택 대한금속재료학회(대한금속학회) 1990 대한금속·재료학회지 Vol.28 No.10
7091 Al alloy is high strength aluminum alloy and application of this alloy enlarge in current industry system. The powder of rapidly solidified 7091 Al alloy was produced by rapidly solidification processing(RSP). In this study, it was investigated the structures of rapidly solidified 7091 Al alloys ; powder morphology, growth shape, microstructure, particle collisions, satellites, cooling rate. Particle shape was more spherical as decreasing powder diameter, and SDAS was more narrow as decreasing powder diameter, therefore cooling rate was more increased. The effect of powder collision affected on the powder structures and shapes.