レーザ溶接部におけるHAZ割れに影響を及ぼす諸因子 : Inconel 718鋳造合金の溶接性に関する研究(第4報)

概要

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The factors affecting HAZ crack susceptibility were investigated for castalloy 718. The materials used were laboratory-cast alloy 718 plates with three levels of grain size. The alloys were heat-treated at 1368 K×5.4 ks or 1378 K×10.8 ks before welding. Welding was conducted by a CO_2 laser apparatus with a variation of laser power and welding speed. Crack susceptibility in HAZ was evaluated by a bead-on-plate test. The penetrated shape in the laser weld was classified into types of a wine cup-like Type W and nail head-like Type N. Type W and Type N were observed at the condition of lower and higher welding speed, respectively. Welding defects such as porosity, underfill and microcracking were seen in the laser welds as well. Most of the HAZ cracking occurred on grain boundaries in HAZ adjacent neck region of Type N weld metal. The fractographic investigation clearly suggested that the HAZ cracking is produced by the presence of a liquid film along grain boundaries. According to the crack test, it wasfound that the HAZ cracking susceptibility decreases with decreasing the grain size or homogenization heat treatment, and with increasing a radius of curvature in the neck zone. These results suggested that the HAZ cracking susceptibility can be improved by the control of penetrated shape to be Type W, a decrease in grain size and a appropriate heat treatment.
社団法人溶接学会の論文
2001-05-05