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용체화처리 및 시효처리가 17-4 석출경화형 스테인레스강 정밀주조품의 미세조직 및 기계적 성질에 미치는 영향
유성곤,이경환,나태엽 ( Sung Kon Yu,Kyong Whoan Lee,Tae Yeob Ra ) 한국주조공학회 1992 한국주조공학회지 Vol.12 No.5
N/A The effect of the solution & aging treatment on the tensile strength, yield strength, elongation, reduction of area, hardness was studied in the 17-4 PH stainless steel. SEM pictures were also taken in order to examine the fracture surfaces and precipitated particles. X-ray diffraction patterns for the heat treated samples were also observed. Mechanical properties of the heat treated samples were superior to those of as cast samples. Tensile strength, yield strength, hardeness decreased with the increase of aging temperature. On the other hand, elongation and reduction of area increased as the aging temperature increased.
이강래 ( Kang Rae Lee ),최경환 ( Kyeong Hwan Choe ),조규섭 ( Gue Serb Cho ),이경환 ( Kyong Whoan Lee ),김명호 ( Myung Ho Kim ),임경화 ( Kyung Hwa Rim ),김기영 ( Ki Young Kim ) 한국주조공학회 2004 한국주조공학회지 Vol.24 No.5
N/A Vibrational motions of the compaction table were investigated to select the optimal operation conditions of sand filling and compaction for the EPC process. Their modes were measured at the nine points of the table with changing the relative rotation angles between the two eccentric mass vibrators which were attached parallel beneath the table. Well-defined vibration modes were measured at the center of the table but those of left and right sides of the table were distorted regardless of rotational angle differences. The distortion of vibration modes at both sides of the table were caused by the moment generated by offset positions of two eccentric masses. It was found that the uniform vibration modes would be gathered by controlling the relative distances between the rotating axis and the center of gravity in the compaction system at the various conditions of vibration modes and rotational angle differences.
소실모형 주조시 알루미늄 합금 용탕의 수소 용해에 관한 연구
신승렬(Seung Ryoul Shin),최현진(Hyun Jin Choi),이경환(Kyong Whoan Lee),이진형(Zin Hyoung Lee) 한국주조공학회 2002 한국주조공학회지 Vol.22 No.4
N/A The hydrogen gas pick-up problem that can occur during Lost Foam Casting was investigated by reduced pressure test and practical Lost Foam Casting. The proper test pressure of reduced pressure test was determined by experiments not to use polystyrene and gas contents of the melt were calculated from density measurement results. There sults showed that the hydrogen pick-up increased with the increased amount of polystyrene that was replaced by melt. The hydrogen pick-up was larger in the case of no degassed melt than that of degassed melt. So the hydrogen pick-up depended on the initial hydrogen content of the melt and the contact time of the melt with the decomposed gas phase. The mold evacuation decreased the hydrogen pick-up and increased the flow length of melt during Lost Foam Casting. And the error of calculated hydrogen pick-up was calculated by numerical method.
마그네슘 합금의 소실모형주조 시 기포형성 특성에 관한 연구 -알루미늄 합금과 비교-
신승렬 ( Seung Ryoul Shin ),한상원 ( Sang Won Han ),이경환 ( Kyong Whoan Lee ) 한국주조공학회 2004 한국주조공학회지 Vol.24 No.3
N/A The pore formation characteristic of Mg alloy during Lost Foam Casting(LFC) was investigated with reduced pressure test and real casting, which was compared with the results of previous work for Al alloy. Cast Mg alloys in LFC had much lower porosities in comparison with those of Al alloys. Also, the proper pouring temperature gave the minimum porosity like AI alloy although it was higher than that of Al alloys due to the worse fluidity of Mg alloy. The pore formation mechanism of Mg alloy in LFC was similar to that of AI alloy but the critical temperature showing the different mechanism is higher than that of Al alloy as much as 30~50℃. The result that Mg alloy in LFC had the lower porosity comparing with Al alloy was due to the extra solubility of hydrogen gas although the solubility of Al alloy was easily exceeded by the external sources like pyrolyzed polystyrene products. The mold evacuation gave the lower porosity due to the removal of polystyrene pyrolysis products, and reduced shrinkage defects. Also, there was a proper evacuation pressure that gave a porosity of almost 0vol%. But much higher vacuum degree than this proper pressure caused the severe entrapment of polymer pyrolysis products that gave the large porosity.
논문 : 응고 ; 불안정 온도구배 하에서 MnBi/Bi공정합금을 일방향응고시 미세조직에 미치는 강화중력의 영향
양영기 ( Young Ki Yang ),황창모 ( Chang Mo Hwang ),강춘식 ( Choon Sik Kang ),이경환 ( Kyong Whoan Lee ) 대한금속재료학회 ( 구 대한금속학회 ) 1998 대한금속·재료학회지 Vol.36 No.7
MnBi Bi eutectic alloy was directionally solidified under enhanced gravity conditions, for a destabilizing thermal gradient, Growth rates were either 1.0cm/h or 1.2cm/h. The thermal gradient applied externally was fixed with 20K/cm under rotational conditions. The experiment shows that the formation of striations can be avoided at certain conditions of net accelerations. This result was discussed in view of the change of critical Rayleigh number, Rac2. To do this, we measured temperature fluctuations in the Bi-melt under similar conditions to growth experiments.
Bi-Mn 공정합금의 일방향응고시 미세조직에 미치는 강화중력의 영향
양영기,강춘식,이경환,황창모 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.4
The microstructure of eutectic MnBi/Bi alloy was investigated after unidirectional solidification under centrifuge process in Bridgman-Stockbarger furnace. Microstructure of the crystals with growth velocity 100 ㎜/h, 25 ㎜/h showed cellular structure and evenly dispersed second phase morphology of MnBi intermetallic compound. The second phase MnBi rod size was varied with acceleration in all growth condition. Numerical analysis was produced to expect fluid flow in rotating system using flow 3d. According to numerical analysis, the fluid flow increased with centrifugal acceleration under constant temperature condition and abrupt increase was expected near centrifugal force is 5G (G = 9.8 m/s: territorial acceleration).
Al-1 wt % Mg 합금의 일방향응고시 고/액 계면의 형상에 미치는 강화중력의 영향
양영기,강춘식,이진형,이경환,백홍구,윤우영,황장모 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.3
Al-1wt%Mg was unidirectionally solidified to investigate the effect of enhanced gravity on the planar interface morphology. Planar solid/liquid interface morphology became unstable with increasing centrifugal force up to 15G but stabilized again at 20G. Surface stabilization of this alloy with increasing centrifugal force can be explained by thermosolutal convection.