モリブデンの電子ビーム溶接継手の延性を改善するための最適炭素量

抄録

The effects of carbon on the strength and ductility of the electron-beam-welded joints of powdermetallurgy molybdenum were investigated systematically. Carbon addition of 0.0015 to 0.0093 wt.% was performed by a series of pre-or postweld carburizing. The materials were electron-beam-welded by a meltrun technique. Tensile tests were performed at temperatures -100 to 20°C with a strain rate of 1.2×10^-3 s^-1. The fracture surfaces were observed by a scanning electron microscopy. The fracture mode, crack generation and propagation characteristics and distribution of precipitates were examined.
At relatively low temperatures, the optimum carbon content to improve the ductility was 0.0015 to 0.0093 wt.% for the preweld heat-treated molybdenum, whilst 0.0015 wt.% for the postweld heat-treated one. Particularly, the preweld carburized specimen with more than 0.0030 wt.% carbon showed a ductility as high as the base metal with an equivalent carbon content. At relatively high temperatures, on the other hand, the ductility of the welded joint was wholly lower than that of the base metal. However, degradation in the ductility was the least for the preweld carburized specimen with 0.0093 wt.% carbon.