Weldability of two kinds of molybdenum, electron beam melted molybdenum (EB-Mo) and powder metallurgy molybdenum (P/M-Mo), were evaluated by the tensile tests of specimens with fusion bead introduced by electron beam welder of accelerating voltage of 50kV and 150kV. Test material was sheet and plate of thickness 1mm and 5mm. EB-Mo exhibited good fusion weldability in comparison with P/M-Mo. The followings are the main results obtained:
1) EB-Mo showed the joint strength of 66kg/mm2 at room temperature in 1mm thick stress relieved sheet, whereas, P/M-Mo showed at most 32kg/mm2 with fully intercrystalline fracture surface.
2) Primary cause of the poor weldability in P/M-Mo in the occurrence of voids in weld metal, especially in the portion close to the boundary between parent and weld metal.
3) Secondary cause for the better joint strength in EB-Mo may be due to the scavenging effect of zirconium, which is added as a doping material in amount of 30 to 50ppm in order to enhance the softening resistance to annealing. Zirconium may, in combination with carbon which is another dopant, react with oxygen and nitrogen in the molten molybdenum and therefore suppress the grain boundary embrittlement due to segregation of oxygen and nitrogen.
4) Test results with 5mm thick P/M-Mo were poorer than 1mm P/M-Mo. EB-Mo did not show the dependence of weldability on the thickness of the sheet or plate.
