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MBF 20으로 브레이징한 STS304 콤팩트 열교환기 접합부의 미세조직에 미치는 가열속도의 영향
김준태(Jun-Tae Kim),허회준(Hoe-jun Heo),김현준(Hyeon-Jun Kim),강정윤(Chung-Yun Kang) 대한용접·접합학회 2016 대한용접·접합학회지 Vol.34 No.2
Effect of heating rate on microstructure of brazed joints with STS 304 Printed Circuit Heat Exchanger (PCHE),which was manufactured as large-scale(1170(L) × 520(W) × 100(T), mm), have been studied to compare bonding phenomenon. The specimens using MBF 20 was bonded at 1080℃ for 1hr with 0.38℃/min and 20℃/min heating rate, respectively. In case of a heating rate of 20℃/min, overflow of filler metal was observed at the edge of a brazed joints showing the height of filler metal was decreased from 100㎛ to 68㎛. At the center of the joints, CrB and high Ni contents of γ-Ni was existed. For the joints brazed at a heating rate of 0.38℃/min, the height of filler was decreased from 100㎛ to 86㎛ showing the overflow of filler was not appeared. At the center of the joints, only γ-Ni was detected gradating the Ni contents from center. This phenomenon was driven from a diffusion amount of Boron in filler metal. With a fast heating rate 20℃/min, diffusion amount of B was so small that liquid state of filler metal and base metal were reacted. But, for a slow heating rate 0.38℃/min, solid state of filler metal due to low diffusion amount of B reacted with base metal as a solid diffusion bonding.
Cu foam / Cu plate 간 고상확산접합부의 인장성질에 미치는 접합압력과 유지시간의 영향
김상호 ( Sang-ho Kim ),허회준 ( Hoe-jun Heo ),윤태진 ( Tae-jin Yoon ),강정윤 ( Chung-yun Kang ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.12
Open cell Cu foam, which has been widely utilized in various industries because of its high thermal conductivity, lightweight and large surface area, was successfully joined with Cu plate by diffusion bonding. To prevent excessive deformation of the Cu foam during bonding process, the bonding pressure should be lower than 500 kPa at 800 ℃ for 60 min and bonding pressure should be lowered with increasing holding time. The bonding strength was evaluated by tensile tests. The tensile load of joints increased with the bonding pressure and holding time. In the case of higher bonding pressure or time, the bonded length at the interface was usually longer than the cross-sectional length of the foam, so fracture occurred at the foam. For the same reason, base metal (foam) fracture mainly occurred at the node-plate junction rather than in the strut-plate junction because the bonded surface area of the node was relatively larger than that of the strut. †(Received May 4, 2016; Accepted June 2, 2016)
Fe-3%C-16%(Ni+Mn+Cu) 주철에서 상변태에 미치는 Cu 조성비의 영향
박기덕 ( Gi Deok Park ),허회준 ( Hoe Jun Heo ),나혜성 ( He Sung Na ),강정윤 ( Chung Yun Kang ) 대한금속재료학회 ( 구 대한금속학회 ) 2012 대한금속·재료학회지 Vol.50 No.6
The purpose of this research was to develop a low Ni austenitic cast iron through replacing Ni by Cu and Mn because they are cheaper than Ni. The effect of the Cu content (6-12 wt%) on the microstructure characteristics was investigated in Fe-3%C-16%(Ni+Cu+Mn) cast iron. Contrary to general effect of the Cu on cast iron, the result of the microstructure analysis indicated that bainite and cementite were formed in high Cu content (>8 wt%Cu). A crystallized Cu-solution (Cu-Mn) phase and MnS in the Cu-solution were formed. The quantity of those phases increased as the Cu content increased. Consequently, the high Cu content in the composition ratio (Ni+Cu+Mn=16%) caused the formation of Cu-Mn/MnS and those phases decreased the effect of Cu and Mn on austenite formation. For this reason, bainite and cementite were formed in high Cu content.