Chemical, mechanical, non-destructive and corrosive properties were investigated of welded joints of 1 mm thick niobium and tantalum sheets, which were either electron-beam welded in a high vacuum or TIG welded in a controlled welding chamber filled with one-atmosphere argon gas containing an impurity gas of air, nitrogen, oxygen or hydrogen. The following conclusions were obtained ; (1) Contents of carbon and oxygen in the weld metal of sintered niobium base metal (C : 180 ppm, 0 : 60 ppm) were not changed by TIG welding, while they were reduced considerably by electronbeam welding. Content of nitrogen in the weld metal of electron-beam melted base metal (N: 85 ppm) was increased by TIG welding. (2) The heat affected zone and weld metal in both niobium and tantalum specimens showed very coarse grains in microstructure. A rapid cooling was slightly effective in preventing grain coarsening. (3) The hardness of weld metal in the electron-beam melted niobium specimen was greater when TIG welded in 99.99% argon atmosphere than when electron-beam welded, probably because of nitrogen absorption from argon atmosphere. Air contents over 103 ppm in argon atmosphere hardened and embrittled niobium weld metal. The TIG weld metal in sintered tantalum specimen was hardened and embrittled by air contents greater than 200 to 500 ppm and 103 ppm, respectively. Repeated bead welding more than twice with electron-beam softened the sintered niobium weld metal. Fracture in tensile test of sintered tantalum welded joints with TIG and electron-beam occurred only in weld metal, while fracture in welded joints of niobium, sintered or electron-beam melted, occurred in HAZ or base metal. (4) The sintered tantalum specimens used in the present study showed no porosity both with TIG and electron-beam welding. The electron-beam melted niobium specimen showed no porosity witn both welding methods. However, the sintered niobium specimens showed pbrosities with electron-beam welding, while far less porosities with TIG welding.
The metal transferring characteristics of welding electrode play a significant role in evaluating the so-called workability of the electrode. They have various meanings including the behaviour of metal droplets which leave the electrode tip and are transferred to molten pool. Although the size of droplets depends upon the distance from electrode tip to molten pool, the average size of droplet when the distance is too large to make the contact transfer, may be a constant value characteristic of the electrode. Authors devised a new method to catch such flying droplets by means of directly quenching them in water, during arc discharging between a carbon and a coated electrode. Droplets are sifted through standard sieves, the weight of specified number of droplets in each lot is measured and averaged, and then the particle diameter assumed as a solid sphere is calculated. Obtained diagram, which is showing the relation between the integrated weight percentage of each lot and calculated particle size, is the most clear-cut representation of transferring characteristic of droplets peculiar to each kind of welding electrode and welding condition. On this curve, the particle diameter at 50% is designated as d 50 as a criterion of the droplets size, and it seems to be a very convenient measure to analyze the meanings of workability. In this report, various factors influencing the result were tested, and a standard method was established.
Applying the same method for evaluating the metal transferring characteristics of welding electrode as described in the first report, authors studied on the various factors influencing the metal droplet size from electrode, and the following results were obtained. (1) The size of droplet depends upon the welding current used, rod diameter and the coating thicknesses. It is considered that the existance of the protective sheath at the tip of electrode and its shape are the decisive factor. (2) The droplet size of high iron oxide type electrode is considerably affected by carbon content of core wire ; the larger the amount of carbon the finer the droplet size. This is presumably due to growth of CO gas bubble in the droplet and its bursting out. (3) The so-called "Burning" phenomenon in the end part of an electrode may be understood as a transition of spray to drop type metal transferring characteristics, which is proved by the measurement of droplet size. (4) The relation between the various items of socalled electrode workability and metal transferring characteristics were discussed ; and it was shown that d50, mean droplet size as defined in the 1st report, may be chosen as the most important independent variable for assesing workabillity.
On the complete welded joint of the welded plate girder, the fatigue strength of a straight joint was compared with the shift joint. These two types were compared in the executed bridge (The Urayamagawabashi ; composite beam). The effect of scallop and the filling up method of scallop were investigated. Principal points in the results of these studis are as follows : It is confirmed that the straight joint is never inferior to the shift one. The fatigue strength is fairly improved by filling up their scallops, but the best method of filling up has not been found and the joint witout scallops is ideal. It is more than 3 year since the Urayamagawabashi opened to traffic, and no damage has been found at all.
The present study was carried out to make clear the C migration in dissimilar metal welded joint at high temperature. To prepare test pieces, C steel and 2 1/4 Cr-1 Mo steel plates were welded with eight kinds of ferritic electrodes, 1/2 Mo, Cr-Mo Cr-Mo-V etc. and eight kinds of ferritic steel plates were welded with two kinds of sustenitic electrodes and 2 1/4 Cr-1 Mo steel was welded with Inconel electrode. These dissimilar welded joint specimens were heated at 500-800°C for 1-3, 000 h and then observed microscopically. The results are summerized as follows : (1) C in lower Cr steel migrated to higher Cr steel and carbides precipitated in higher Cr steel along fusion line. At higher temperatures, the ferrite grains coarsened in decarburized zone. (2) C migration was promoted with increase of Cr content in higher Cr steel and addition of V. (3) C migration was reduced with increase of Cr content in lower Cr steel and addition of V. (4) In the welded joints of Cr-Mo weld metals to C steel, the width of carbides precipitated zone increased with increase of Cr content in Cr-Mo weld metals up to 3 Cr-1 Mo steel and decrease with the increass of Cr content more than 3 Cr-1 Mo steel. The distribution density of carbides increased with the increase of Cr content in Cr-Mo weld metals. (5) The extent of C migration with 25 Cr-20 Ni weld metal was slightly more than 16 Cr-8 Ni-2 Mo weld metal. The extent of C migration with Inconel weld metal was less than those with 16 Cr-8 Ni-2 Mo and 25 Cr-20 Ni weld metals.
This report describes properties of deposit metal for making submerged-arc wdlding with domestic bonded fluxes for mild steel and high tensile steels up to 60 kg/mm2. It is shown that impact test results at low temperature with bonded fluxes are far superior to ones with fused fluxes. (1) Filler wire contained one percent manganese is better than the others to weld mild steel. Impact values with deposit metal are 6 kg-m/cm2 at -70°C with 650°C one hour stress relief. Then those values are 21 kg-m/cm2 as weld and 30 kg-m/cm2 stress relief at room temprature to use bonded fluxes for mild steel. (2) With high tensile steels, mechanical properties are good according to combination of filler wires and bonded fluxes to obtain chemical component of deposit metal Mn-Mo type to 55 kg/mm2, and Mn-Ni-Mo type to 60 kg/mm2. And the effect of manganese deoxidizing from bonded flux is remerkable.