지르칼로이-4 박판의 레이저 용접성과 용접부 미세조직에 관한 연구 = A Study on the Laser Weldability and Welds Microstructure of Zircaloy-4 Sheets

다국어 초록 (Multilingual Abstract)

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.