Weldability of Molybdenum and Its Alloy Sheet (Report II) : Ductility of EB and GTA Welds(Materials, Metallurgy, Weldability)

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The ductility of the welds in electron-beam welding in high vacuum and GTA welding in pure and air mixed argon atmospheres has been examined for electron-beam melted pure molybdenum (EB-Mo) and TZM alloy by using bending test. The main conclusions were as follows ; (1) GTA and EB welds of EB-Mo became much brittle in comparison with base metal. Ductile-to-brittle transition temperature on transverse bend was 60℃ for EB welds and 180℃ for GTA welds in as-welded condition in comparison with that of base metal of -75℃. (2) The transition temperature of EB Mo welds was much lower on longitudinal bend than that on transverse bend by 100-150℃ for GTA and EB welds. (3) Low welding heat input was effective to weld bend ductility. Therefore, EB welds is generally superior to GTA welds. However, extreme low welding heat input gave a detrimental effect to weld bend ductility in EB welds. There is, therefore, an optimum condition for welding heat input in EB welds in order to obtain the welds having the best ductility. (4) Air gas mixed into argon welding atmosphere remarkably increased the transition temperature of GTA welds. Therefore, purity of argon welding atmosphere should be kept as pure as possible. (5) Post heat treatment of stress relieving was beneficial to weld bend ductility of the welds. (6) Rough surface of weld bead was detrimental to bend ductility of the welds.
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