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지르칼로이-4 박판의 레이저 용접성과 용접부 미세조직에 관한 연구
고진현,황용화,이완규 한국기술교육대학교 2002 論文集 Vol.9 No.1
By using Nd:YAG laser system, the weld bead formation, laser weldability and weld microstructure of Zircaloy-4 sheets for nuclear fuel structural components were investigated by changing the laser parameters which affect the mechanical properties and microstructure. It was found that the optimum pluse energy and beam power for Zircaloy-4 thin sheets welding were 18J and 200W, whereas the pulse duration and travel speed were 7.5ms and 200mm/min, respectively. The optimum range of focal point to obtain deep weld penetration and narrow width was about 0.5 mm below the surface of the specimen to be welded for Zircaloy-4 sheets. The optimum flow rate of shielding gas was about 60-150ℓ/min. In the same conditions, the results showed that there were no big differences in the weld depth and width between the bead-on-plate and butt welds. The hardness value was measured across the weld zone. Hardness values showed 160-165HV of base metal, 170-210 HV of HAZ and 220-230 HV of the weld metal. The mechanical test results showed that laser beam welds were ductile. It was found that the laser beam welded zone comprised ofa mixed microstructure of martensitic α, nonparallel Widmansta¨tten plates and basketweave.
급속 응고 분말 야금으로 제조된 알루미늄 합금의 용접성에 대한 연구
고진현 한국기술교육대학교 1997 論文集 Vol.4 No.1
The weldability of aluminum alloys made by the rapid solidification powder metallurgy was investigated by the hot cracking susceptibility test and microstructural examination. In this study, the optimum welding conditions for gas metal arc welding and electron beam welding processes were also established to weld aluminum alloys made by powder metallurgy. The weld beads of aluminum alloys insufficiently degassed showed nonuniform shape of beads, undercut and porosity in the weldments, while those of fully degassed aluminum alloys showed uniform beads and little porosity in the weldment. Based on this study, it can be recommended that the hot cracking susceptibility of aluminum alloys made by powder metallurgy can be minimized by controlling the homogenization temperature and the degree of recrystallization, which produce the fine-grained microstructure.
구조용강재의 FCAW에 의한 용접부의 미세조직과 기계적 성질
고진현,이완규,황용화 한국기술교육대학교 2001 論文集 Vol.8 No.1
ABSTRACT SM490B structural and SM45C rolled steels were welded in the multilayers with three different heat inputs of 0.6, 0.9 and 1.2kJ/mm and three different shielding gas compositions of 100%CO2, 75%CO2 + 25%Ar and 50%CO2 + 50%Ar. Tensile strength of weldments increased slightly with increasing heat inputs from 0.6 to 0.9kJ/mm whereas that of weldments with heat input of 1.2 kJ/mm decreased. Hardness values of weld metal decreased with increasing heat inputs while Charpy impact values increased with increasing heat inputs. In multilayers of weld metal, the microstructure in the columnar zone of top bead of weld metal consisted of coarser grain boundary ferrite and thicker ferrite side plate, as well as polygonal ferrite with increasing heat inputs. Key words: heat input(입열량), microstructure(미세조직), shielding gas(보호가스), grain boundary ferrite(결정립계 페라이트), carbide(탄화물), hardness value(경도값), impact value(충격값), weld zone(용접부), heat affected zone(열영향부)
CrMoV 강 용접부의 주기적 열시효처리에 따른 미세조직 , 미세경도 및 인장강도 특성
김광수,고진현 한국열처리공학회 1999 熱處理工學會誌 Vol.12 No.4
An investigation of the CrMoV rotor steel weldment which experienced by cyclic thermal aging heat treatment and as-received condition was performed. This evaluation was carried out to confirm whether this type of weldment is appropriate for the service environment in terms of microstructural examinations, microhardness measurements and tensile tests. The cyclic thermal aging heat treatment, containing continuous heating and cooling thermal cycle was programmed to simulate the real rotor service condition. The heat treatment was perfomed for 40 cycles(5920hrs). The results indicated that the weldment was composed of 4 different regions such as heat affected zone of the base metal, butter weld(initial weld), full thickness weld(final weld) and the base metal. The double welding process was applied to eliminate the susceptibility of reheat cracking at heat affected zone of base metal. The grain refinement at the HAZ due to the welding process could reduce the possibility of cracking susceptibility, but its tensile properties was appeared to be low due to the weld metal in as-received condition. The benefit effect, grain refinement was extended with carbides coarsening during the cyclic thermal aging heat treatment. However the poor mechanical properties of the weldment was more degraded as undergoing the heat treatment.