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김순국,장창우,이준희,정찬회,서용권,강충길,Kim, Soon-Kook,Jang, Chang-Woo,Lee, Jun-Hee,Jung, Chan-Hoi,Seo, Yong-Gwon,Kang, Choong-Gil 한국재료학회 2006 한국재료학회지 Vol.16 No.8
In recent years, Magnesium (Mg) and its alloys have become a center of special interest in the automobile industry. Due to their high specific mechanical properties, they offer a significant weight saving potential in modern vehicle constructions. Most Mg alloys show very good machinability and processability, and even the most complicated die-casting parts can be easily produced. The die casting process is a fast production method capable of a high degree of automation for which certain Mg alloys are ideally suited. In this study, step-dies and flowability tests for AM50 were performed by die-casting process according to various combination of casting pressure and plunger velocity. We were discussed to velocity effect of forming conditions followed by results of microstructure, FESEM-EDX, hardness and tensile strength. Experimental results represented that the conditions of complete filling measured die-casting pressure 400 bar, 1st plunger velocity 1.0 m/s and 2nd plunger velocity 6.0 m/s. The increasing of 2nd plunger velocity 4.0 to 7.0 m/s decreased average grain size of $\alpha$ phase and pore. It was due to rapid filling of molten metal, increasing of cooling rate and pressure followed by increased 2nd plunger velocity. The pressure should maintain until complete solidification to make castings of good quality, however, the cracks were appeared at pressure 800bar over.
정찬회,김순국,이준희,이해우,장창우,Jung, Chan-Hoi,Kim, Soon-Kook,Lee, Jun-Hee,Lee, Hae-Woo,Jang, Chang-Woo 한국재료학회 2007 한국재료학회지 Vol.17 No.4
The effects of immersion time in the liquid nitrogen on the behavior of aluminum alloys used for the hydrogen storage tank of auto-mobile at cryogenic temperature were investigated. With increasing immersion time in the liquid nitrogen, the elongation of AI 5083 alloy at cryogenic temperature decreased because of non-uniform fracture of precipitates on the grain boundary, and the serration also occurred because of discontinuous slip due to rapid decreasing of the specific heat. The mechanical properties of AI 6061 alloy at cryogenic temperature were characterized by uniformed yield strength, tensile strength and elongation regardless of the immersion time in the liquid nitrogen. These mechanical properties of aluminum alloys at cryogenic temperature were interpreted by the strength of grain boundary and the slip deformation behavior.
정찬회,김순국,이준희,정세진,김익수,Jung, Chan-Hoi,Kim, Soon-Kook,Lee, Jun-Hee,Jeong, Se-Jin,Kim, Ik-Soo 한국재료학회 2007 한국재료학회지 Vol.17 No.1
The effects of immersion time in the liquid nitrogen and deformation-induced martensitic transformation on the behavior of austenite stainless steels used for the hydrogen storage tank of auto-mobile at cryogenic temperature were investigated. With increasing of immersion time in the liquid nitrogen, the tensile strength of all austenite stainless steels at cryogenic temperature was increased because the martensite transformation of unstable austenite. The restraint of crack generation ana transmission also increased the tensile strength by the active ${\alpha}'$ transformation. The elongation decreasing of 321 steel is not the mechanical deformation of austenite phase but the stress induced martensite phase during the tensile test.
RF 스퍼터링으로 증착된 하이드록시아파타이트 박막의 ESCA 분석
정찬회,이준희,김순국,김명한,유재근,김승언,Jung, Chan-Hoi,Lee, Jun-Hee,Kim, Soon-Kook,Kim, Myung-Han,Yu, Jae-Keun,Kim, Seung-Eon 한국재료학회 2006 한국재료학회지 Vol.16 No.4
RF sputtering process was applied to produce thin hydroxyapatite(HAp) films on Ti-6Al-4V alloy substrates. The effects of different heat treatment conditions on the chemical composites between HAp thin films and Ti-6Al-4V alloy substrates were studied. After deposition, the HAp thin films were heat treated for 1h at $400^{\circ}C,\;600^{\circ}C\;and\;800^{\circ}C$ under the atmosphere, and analyzed O/M, FESEM-EDX and ESCA, respectively. Experimental results represented that interface of HAp thin films and Ti-6Al-4V alloy substrates was composed Ti-OH, TiO, TiN, $Al_2O_3,\;V_2O_3,\;VO_2$. pyrophosphate and decreased carbide followed by the increase of heat treatment temperature.
스퀴즈 캐스팅에 의해 제조된 AC4C / Kaowool 복합재료의 마모특성
강현기,이준희,김순국 ( Hyun Ki Kang,Jun Hee Lee,Soon Kook Kim ) 한국주조공학회 1998 한국주조공학회지 Vol.18 No.1
N/A The wear characteristics and mechanism of AC4C/Kaowool composite both in lubricated and in dry condition were investigated by using Falex Pin and Vee Block Test Machine. Volume fractions of the Kaowool were 7, 10, 15, and 20 % and the applied pressures for fabricating of the specimen were 80, 90 and 100 MPa. Wear loss was higher in dry condition than in lubricated condition, regardless of the wear conditions(wear time and wear load). Increasing of the applied ram speed during squeeze casting, resulted in increased wear loss in lubricated condition but decreased in dry condition. It was found that the wear loss is greatly dependent on kaowool volume fraction, temperature of the wear surface, and length of the kaowool fiber, and the wear mechanism is abrasive and fatigue wear in lubricated condition, but abrasive and adhesion wear in dry condition. (Received December 17, 1997)
원자력간 현미경을 이용한 TRIP강 저항 점용접부의 미세조직 분석에 관한 연구
최철영,지창욱,남대근,장재호,김순국,박영도,Choi, Chul Young,Ji, ChangWook,Nam, Dae-Geun,Jang, Jaeho,Kim, Soon Kook,Park, Yeong-Do 대한용접접합학회 2013 대한용접·접합학회지 Vol.31 No.1
The spot welds of Transformation Induced Plasticity (TRIP) steels are prone to interfacial failure and narrow welding current range. Hard microstructures in weld metal and heat affected zone arenormally considered as one of the main reason to accelerate the interfacial failure mode. There fore, detailed observation of weld microstructure for TRIP steels should be made to ensure better weld quality. However, it is difficult to characterize the microstructure, which has similar color, size, and shape using the optical or electron microscopy. The atomic force microscope (AFM) can help to analyze microstructure by using different energy levels for different surface roughness. In this study, the microstructures of resistance spot welds for AHSS are analyzed by using AFM with measuring the differences in average surface roughness. It has been possible to identify the different phases and their topographic characteristics and to study their morphology using atomic force microscopy in resistance spot weld TRIP steels. The systematic topographic study for each region of weldments confirmed the presence of different microstructures with height of 350nm for martensite, 250nm for bainite, and 150nm for ferrite, respectively.
TMCP강의 용접 공정별 입열량에 따른 용접부 물성 평가 및 비교
최철영,지창욱,김형찬,남대근,김정돈,김순국,박영도,Choi, Chul Young,Ji, Chang Wook,Kim, Hyoung Chan,Nam, Dae-Geun,Kim, Joungdon,Kim, Soon Kook,Park, Yeong-Do 대한용접접합학회 2014 대한용접·접합학회지 Vol.32 No.1
This paper has an aim to evaluate microstructure and fracture toughness of TMCP steel weldment applied for off-shore wind tower with the focus on the effect of heat input on the weldment with various welding processes; FCAW(13kJ/cm and 30kJ/cm), SAW(62kJ/cm), and EGW(177kJ/cm). Based on experimental results developed from this study, it was found that the impact toughness of top side for TMCP steel weldments with heat input up to 62 kJ/cm satisfied the required minimum value except the EGW(177kJ/cm). The heat input and microstructure are the main factors of impact toughness. The heat input of 13kJ/cm on back side with low heat input increased the amount of grain boundary ferrite which has low impact toughness, and heat input of 177kJ/cm on top side is significant enough to produce the austenite grain growth. The compositions and sizes of inclusions which are the dominant factors for the formation of acicular ferrite were analyzed by OM and EDS. As the heat input increased, the inclusions also grew and a nucleation site decreased. The size of nonmetallic inclusions and the crack width was nearly similar, therefore the inclusions were related with the crack propagation.
페라이트계 및 오스테나이트계 스테인리스강과 IF강의 이종 접합부의 저항 점 용접성 평가
이진범 ( Jin Beom Lee ),김동철 ( Dong Cheol Kim ),남대근 ( Dae Geun Nam ),강남현 ( Nam Hyun Kang ),김순국 ( Soon Kook Kim ),유지훈 ( Ji Hun Yu ),임영목 ( Young Mok Rhym ),박영도 ( Yeong Do Park ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.1
The spot weldability of dissimilar metal joints between austenitic stainless steels (STS316)/IF steels and ferritic stainless steels (STS430)/IF steels was investigated. This study was aimed to determine the spot welding parameters for a dissimilar metal joint and to evaluate the dissimilar metal joint`s weldability, including its welding nugget shape, tensile-shear strength, hardness, and microstructure. The comparison of these results was described in terms of fracture behavior. Compared with the weld lobe of similar metal joints, dissimilar metal joints (STS430/IF) had reduced weld current range. However, the weld lobe of STS316/IF steel joint showed increased weld current range. This is because the dilution of chemical composition in the molten weld pool suppressed the heat input being caused by Joule heat with current flow through the samples. The microstructure of the fusion zone was fully martensite and mixture of ferrite and martensite for austenitic stainless steel/IF steel and ferritic stainless steel/IF steel combination, respectively. The experimental results showed that the shape of nugget was asymmetric, in which the fusion zone of the austenitic and ferritic stainless steel sheet was larger due to the higher bulk-resistance. The predicted microstructure by using the Schaeffler diagram was well matched with experimental results. After peel test, the fracture was initiated from heat affected zone of ferritic stainless steel sheet side, however the final fracture was propagated into the IF steel sheet side due to its lower strength.