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겹치기 마찰교반접합된 Inconel 600/SS 400 합금의 미세조직과 기계적 특성 평가
송국현,Song, Kuk-Hyun,Nakata, Kazuhiro 한국재료학회 2012 한국재료학회지 Vol.22 No.3
The microstructures and mechanical properties of friction stir welded lap joints of Inconel 600 and SS 400 were evaluated; friction stir welding was carried out at a tool rotation speed of 200 rpm and welding speed of 100 mm/min. Electron back-scattering diffraction and transmission electron microscopy were introduced to analyze the grain boundary characteristics and the precipitates, respectively. Application of friction stir welding was notably effective at reducing the grain size of the stir zone. As a result, the reduced average grain size of Inconel 600 ranged from $20{\mu}m$ in the base material to $8.5{\mu}m$ in the stir zone. The joint interface between Inconel 600 and SS 400 showed a sound weld without voids and cracks, and MC carbides with a size of around 50 nm were partially formed at the Inconel 600 area of lap joint interface. However, the intermetallic compounds that lead to mechanical property degradation of the welds were not formed at the joint interface. Also, a hook, along the Inconel 600 alloy from SS 400, was formed at the advancing side, which directly brought about an increase in the peel strength. In this study, we systematically discussed the evolution of microstructures and mechanical properties of the friction stir lap joint between Inconel 600 and SS 400.
HIGH PERFORMANCE SOLVERS FOR SEMIDEFINITE PROGRAMS
Makoto Yamashita,Katsuki Fujisawa,Kazuhiro Kobayashi,Mituhiro Fukuda,Kazuhide Nakata,Maho Nakata 한국산업응용수학회 2011 한국산업응용수학회 학술대회 논문집 Vol.6 No.2
Semidefinite program (SDP) is one of important problems in mathematical optimization, since it covers many applications. To solve SDPs, we have developed SDPA (SemiDefinite Programming Algorithms) and its family. SDPARA can solve extremely large-scale SDPs in a short time by parallel computing, and SDPA-GMP can obtain highly accurate solutions of SDPs.
( Heung Il Park,Kazuhiro Nakata ) 한국주조공학회 1998 한국주조공학회지 Vol.18 No.4
회주철 모재의 표면에 감압 플라즈마 용사법으로 실리콘 분말을 피복시킨 후 CO₂레이저를 이용하는 표면 합금화로 고온 내스케일성이 향상된 표면 개질층을 제조하였다. 실리콘의 표면 합금층에는 응집상의 흑연(chunky graphite)이 Fe_5Si₃로 구성된 망상의 화합물 기지속에 정출하는 조직특성을 보였다. 대기 분위기에서 18.0ks동안 열중량측정(TG)한 결과 실리콘 표면 합금층의 무게 증가율은 회주철 모재에 비하여 923K에서는 약 1/3, 1098K에서는 약 1/10을 나타내었다. 그리고 1098K에서 18.0ks동안 유지시킨 주철모재 시편에서 원래의 모재표면을 기준으로 다공성의 외부스케일과 편상흑연을 따라 생성된 내부스케일로 구성된 두께 60-70㎛의 두꺼운 산화스케일이 생성되었으나, 실리콘의 표면 합금층에서는 두께 3∼5㎛의 치밀한 외부 산화스케일만이 생성되었다. 실리콘 합금층의 단면 미소경도값은 MHV 300∼1100으로 그 변동폭이 심하였으나, 진공분위기에서 열처리(1223K, 18.0ks)한 경우 미소경도값의 편차는 MHV 300∼500으로 개선되었다. N/A
송국현,Song, Kuk-Hyun,Nakata, Kazuhiro 한국재료학회 2011 한국재료학회지 Vol.21 No.7
This study was carried out to evaluate the microstructures and mechanical properties of a friction stir welded Ni based alloy. Inconel 600 (single phase type) alloy was selected as an experimental material. For this material, friction stir welding (FSW) was performed at a constant tool rotation speed of 400 rpm and a welding speed of 150~200 mm/min by a FSW machine, and argon shielding gas was utilized to prevent surface oxidation of the weld material. At all conditions, sound friction stir welds without any weld defects were obtained. The electron back-scattered diffraction (EBSD) method was used to analyze the grain boundary character distributions (GBCDs) of the welds. As a result, dynamic recrystallization was observed at all conditions. In addition, grain refinement was achieved in the stir zone, gradually accelerating from 19 ${\mu}m$ in average grain size of the base material to 5.5 ${\mu}m$ (150 mm/min) and 4.1 ${\mu}m$ (200 mm/min) in the stir zone with increasing welding speed. Grain refinement also led to enhancement of the mechanical properties: the 200 mm/min friction stir welded zone showed 25% higher microhardness and 15% higher tensile strength relative to the base material.
겹치기 마찰교반접합된 Invar 42/SS 400 합금의 미세조직과 기계적 특성 발달
송국현,Song, K.H.,Nakata, Kazuhiro 대한용접접합학회 2012 대한용접·접합학회지 Vol.30 No.5
This study was conducted to investigate the microstructure and mechanical properties of friction stir lap joints. Invar 42 and SS 400 were selected as the experimental materials, and friction stir welding was carried out at a tool rotation speed of 200 rpm and welding speed of 100 mm/min. The application of friction stir welding to Invar 42 effectively reduced the grain size in the stir zone; the average grain size of Invar 42 was reduced from $11.5{\mu}m$ in the base material to $6.4{\mu}m$ in the stir zone, which resulted in an improvement in the mechanical properties of the stir zone. The joint interface between Invar 42 and SS 400 showed a relatively sound weld without voids and cracks, and the intermetallic compounds with $L1_2$ type in lap jointed interface were partially formed with size of 100 nm. Moreover, the hook in the advancing side of Invar 42 was formed from SS 400, which contributed to maintenance of the tensile strength. The evolution of microstructures and mechanical properties of friction stir lap jointed Invar 42 and SS 400 are also discussed herein.