Bend Transition Temperature of Arc-Cast Molybdenum and Molybdenum - 0.5-Percent-Titanium Sheet in Worked, Recrystallized, and Welded Conditions

An investigation was conducted to determine the effects of welding on the ductile-to-brittle transition temperature of carbon-deoxidized arc-cast molybdenum and molybdenum - 0.5-percent-titanium sheet of two nominal thicknesses, 0.020 and 0.040 inch. Both materials, when annealed at 2000 deg or 2400 deg F to give recrystallized structures, gave fine grain structures about 3500 grainssq mm. These materials had ductile-to-brittle bend transition temperatures 90 deg bend over a 4 T radius punch descending at a rate of 12 inmin of 0 deg to 40 deg F as compared with -ll0 deg to 5 deg for the materials in the fibrous, as-worked condition. When the specimens were arc welded in a helium atmosphere with a nonconsumable tungsten electrode, the transition temperatures of both materials varied from 140 deg to 350 deg F. The grain size in the fusion zone of the welded specimens was large 2 to 5 grains across a 40-mil l.02-mm specimen. Specimens annealed in a vacuum at 3500 deg F to yield grain sizes equivalent to those found in the fusion zones of welds had transition temperatures of 350 deg F and above. Chemical analyses indicated no pickup of interstitial impurities during either welding or vacuum annealing, and it was concluded that the loss of room-temperature ductility in the welds and in the annealed material was primarily associated with the massive grain structures. Metallographic study revealed fewer grain-boundary precipitates in the welded specimens than in those annealed at 3500 deg F, probably because the faster cooling rate of the welded metal had left less time for precipitation to occur.