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맹완영,강영환 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.6
The optimized condition for preventing metal delivery tube from freezing up during atomization was evaluated by analyzing the experimental data of gas atomizations which were carried out on various conditions. The optimum condition was established by controlling the protrusion length and the temperature of metal delivery tube. It was observed that powder shape is affected by the collision of particles. The probability of collision among particles can be controlled by changing atomization variables such as protrusion length of metal delivery tube, nozzle slit size and the condition of atomizing chamber. So it is possible to control the powder shape by changing the atomizing variables. It was also shown that the average particle size decrease with increasing atomizing pressure.
가스분무법에 의해 급냉응고된 Al-Fe 합금분말의 응고조직
맹완영,남태운 ( Wan Young Maeng,Tae Woon Nam ) 한국주조공학회 1994 한국주조공학회지 Vol.14 No.2
N/A The Al-Fe alloy powders were rapidly solidified by gas atomization. Rapidly solidified Al-Fe alloy powders for ranges of composition from 0 to 8wt.%Fe have various microstructure, i.e., cellular, dendritic or two-zone structure. Some small particles(∼10㎛ or less) of Al-Fe alloy at concentrations between 0 and 8wt.%Fe are undercooled significantly prior to solidification and exhibit a two-zone structure in individual powder particles. X-ray diffraction patterns were obtained with Copper K(λ=1.5418Å) in diffractometer to study the extension of the solubility limit of Fe in Al. Lattice parameters were estimated from extrapolation by means of the Nelson-Riley function. The X-ray diffraction patterns for the alloy powders containing up to 4wt.%Fe do not show intensity peak of FeAl₃phase. And the diffraction angles for α Al are shifted up to 4wt.%Fe alloy powders. Thus 4wt.%Fe probably represents the limit of metastable solubility of Fe in Al solidified by gas atomization.
맹완영,백정하,오인상,남태운 ( W . Y . Maeng,J . H . Bac,I . S . Oh,T . W . Nam ) 한국열처리공학회 1994 熱處理工學會誌 Vol.7 No.2
In the molten state, magnesium alloys vigousey react with oxygen in the air, is protected from oxidation and burning by the addition of SF_b to CO₂atmosphere over the melt. The mechanical properties and metallographic examinatin have made of Mg-Al alloys containing 3, 6, 9% in the solution treated state and precipitated state, comparing mechanical properties obtained during unidirectional solidification with mechanical properties obtained during conventional casting. For a given solution treatment, a higher aluminum contents produce more or less fine grains in conventional casting. For a given artifical aging treatment, a higher aluminum contents produces much precitates at the grain boundary as well as within the grain in unidirectional solidification. As a result of this experiment, for a given heat treatment, the higher is aluminum contents the higher is the ultimate tensile strength, yield strength, hardness while the lower the elongation. Also the mechanical properties of unidirectional solidification is larger than that of conventional casting.
험프(Hump) 시편에 의한 Alloy 600의 응력부식 가속화
맹완영,김우철 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.5
CERTs (Constant elongation rate tests) using hump type specimens were carried out to investigate the effect of "stress state" in the specimens on the SCC (stress corrosion cracking) behavior of alloy 600 in simulated environment of nuclear power plant (360℃, 200 atm). SCC susceptibility was increased in the hump type specimens compared with usual tensile specimens. Micro-structural observation, hardness measurements and stress analysis around the bended area of hump type specimens were conducted to understand the increase of SCC susceptibility in the specimens. It is considered that the acceleration of SCC in the hump type specimens is attributed to the triaxial stress state and the consequent plastic constraint around bended area in the specimens. CERT using hump type specimen is useful to evaluate the stress corrosion susceptibility of various corrosion system in short testing period.
순수 분위기에서 터빈 강의 응력부식균열 거동에 미치는 환경 요소의 영향
孟完永,李珍炯,金宇哲,元昌煥 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.7
Slow Strain Rate Tests(SSRT) were carried out to investigate the effect of dissolved oxygen on stress corrosion cracking(SCC) susceptibility of 3.5NiCrMoV steels used in discs of low-pressure(LP) steam turbines in electric power generating plants. The influence of dissolved oxygen on cracking in water was studied; for this purpose, specimens were strained to fracture at 150℃ in water environments with various amounts of dissolved oxygen. Also Tests were conducted in aerated water at temperature of 50∼200℃ and at various strain rates (5×10^-8∼1×10^-5 s-1). The maximum elongation of the turbine steel decreased with decreasing strain rate, and with increasing temperature. Dissolved oxygen significantly affected the SCC susceptibility of turbine steel in water. The increase of the SCC susceptibility of the turbine steel in a higher dissolved oxygen environment is due to the non protectiveness of the oxide layer of the turbine steel surface and the increase of corrosion current.
Inconel 600, 900 및 Incoloy 800 의 산화거동 비교
맹완영,강영환,주기남,유우석 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.12
Spalled oxide particles and corrosion products released from the surface of steam generator materials cause various problems of accelerating stress corrosion cracking, denting, wastage, erosion of turbine, and decrease of thermal efficiency. Because the major part of exposed material surface in steam generator atmosphere is the surface of the steam generator tube, it is important to know the oxidation behavior of the tube material. The oxidation behavior of three kinds of Inconel alloys, i.e., Inconel 600, Inconel 690 and Incoloy 800 in air, pure water, and steam was studied and the oxide layers were analysed by SEM, EDX, X-ray diffractometer. And thermal diffusivities of Inconel alloys were measured by the laser flash method. Inconel 690 shows the best resistance to oxidation among the three alloys tested in static air, pure water, and steam. The good oxidation resistance of Inconel 690 is due to maintaining uniform Cr₂O₃ layer during the oxidation time. The thermal diffusivity decreases as the extent of oxidation increases. The thermal diffusivity of Inconel 600 oxidized at 500℃ for 3hours in static air decreases to 85% of that of non-oxidized specimen. The results of this study can be applied to the development of oxidation resistant materials of controlled Cr content. And the test data can be used as reference for the estimation of the amount of sludge, and as input data of steam generator design.
인코넬 합금의 열처리에 따른 입계 탄화물 석출 및 입계응력부식 거동
맹완영,남태운 ( Wan Young Maeng,Tae Woon Nam ) 한국열처리공학회 1997 熱處理工學會誌 Vol.10 No.4
Inconel alloys used as nuclear power plant components have experienced intergranular stress corrosion cracking problems inspite of their good corrosion characteristics. In order to investigate the effects of heat treatments on carbide precipitation and intergranular stress corrosion cracking(IGSCC) in Inconel alloys, DSC(Differential Scanning Calorimeter), TEM, EDXS and static potential corrosion tests were carried out. Thermal treatment at 750℃ for 15hours in Inconel alloys increased the density of intergranular carbide. The carbides are mainly Cr_7C₃ in Inconel 600, and Cr_(23)C_6 in Inconel 690. The Cr depletion around grain boundary is not crucial factor on IGSCC. The carbides in grain boundary play an important role as acting dislocation source, and as decreasing stress around growing crack.