The present study was carried out to examine the tensile strength, creep rupture strength and cyclic creep rupture strength of dissimilar metal welded joint. To prepare test pieces, 2 1/4 Cr-1 Mo steel and 18 Cr-8 Ni-Cb steel or 18 Cr-8 Ni-Ti steel plates were welded with Inconel, 50 Ni-10 Cr-2 Mo, 25 Cr-20 Ni, 19 Cr-8 Ni-1 Mo and 16 Cr-8 Ni-2 Mo electrodes. These various dissimilar welded joints were tested as welded and after post heat treatment at 650°C for 3 hours and at 720°C for 1 hour. The results are summarized as follows: 1) The specimen welded with 50 Ni-10 Cr-2 Mo electrode fractures at the weld metal or 21/4 Cr-1 Mo base metal, but those specimens welded with other electrodes fracture at 214 Cr-1 Mo base metal in the tensile test at room temperature and 600°C. 2) Creep rupture strength of an as-welded specimen is higher than that of a post heat treated specimen in a shorter time test at 600°C, but in a longer time test, the creep rupture strength of a post heat treated specimen is higher than that of the as welded specimen. 3) Creep rupture strength of 720°C×1 h post heat treated specimen with Inconel is the highest of all other specimens in long time tests. 4) When temperature and load cycle are imposed in a creep rupture test, the rupture strength of an as-welded specimen is higher than the ordinary creep rupture strength, but the rupture strength of 720°C×1 h post heat treated specimen is lower than the ordinary creep rupture strength.
Thermodynamic method proposed in the previous paper to deal with the transformation of steel has been developed for three-components iron alloys. An equation has been derived as to the effect of a third element on the Ms temperature of an iron-carbon alloy, and the results are compared with the experimental ones. Calculation is also made of the equation to derive the carbonequivalent for hardenability and crack-sensitivity in the weld heat-affected zone on the basis of Ms temperature, and comparisons are made between calculated and empirical equations. The change in Ms temperature of an Fe-Ni-C alloy calculated by the present method is in good agreement with the experimental value. The effects of other alloying elements on Ms temperature and the coefficient in the equation of carbon equivalent for weldability can be calculated in reasonable agreement with experimental values.
The effects of anode voltage, welding current, beam diameter, welding speed and thickness of specimen on the characteristics of bead section (such as, penetration, width and penetration-to-width ratio) were studied with the 1.5 kW NRIM electron-beam welding equipment for type 304 stainless steel, low carbon steel, aluminium, brass, zirconium and titanium. The following conclusions were obtained: (1) An increase of anode voltage or welding current increased the penetration greatly and the width slightly. An increase of beam diameter greatly reduced the penetration but increased the width. An increase of welding speed coordinately reduced both the penetration and width. (2) New parameters were introduced to correlate satisfactorily the effects of anode voltage (V), welding current (I), welding speed (ν) and beam diameter (φ) on penetration (ρ) and width (ω) in bead welding; that is: ρ=κa×Ε1.7×Ι1/ν0.4×1/φ0.8 ω=κb×Ε0.1×Ι0.2/ν0.5×φ0.6 (φ<8mm) ρ/ω=κc×Ε1.6×Ι0.8×ν0.1×1/φ1.4 where, ka, kb, and kc arc constants which depend on the material. (3) An electron-beam was shown to cause a deep and wedge-shaped penetration in various materials, provided a sufficient weld heat input which exceeds a critical value is used for a given beam diameter. (4) The effect of plate thickness on bead characteristics for a given welding condition is slight only for metals of poorer heat conductivity and comparatively high welding speeds.
Chemical compositions, porosities and mechanical properties of electron-beam welds were studied of ractive and refractory metals, aluminium alloy, stainless steel and carbon steel by comparing with controlled atmosphere TIG welds and the following conclusions were obtained : (1) The contents of oxygen and nitrogen in titanium and zirconivm were changed neither by electron-beam welding (EBW) nor by TIG. By EBW, contents of carbon and oxygen in sintered niobium sheets, that of carbon in a sintered tantalum sheet and that of nitrogen in a type 304 stainless steel plate were considerably reduced. (2) X-ray radiographs of both EBW and TIG welds in sintered niobium, molybdenum and tungsten sheets showed usually many porosities in weld metal near the fusion line, while porosityfree welds were obtiand in vacuum melted sheets. Repeated electron-beam bead welding in sintered sheets was very effective in eliminating porosities in weld metals. (3) An element of which the partial pressure at melting point of a base metal is higher than about 10-2mmHg is likely to be vaporized during EBW in a vacuum of (1-5) × 10-5mmHg. (4) Subsize V-charpy impact values of commercially pure titanium, zirconium and Zircaloy-2 plates were generally far greater in EBW welds than in TIG welds. (5) Brittle behavior of arc welds of molybdenm sheets was not improved by EBW, probably because of grain coarsening in weld zone. (6) The joint efficiency of EBW, welds of a 1 mm thick 24 S aluminum alloy sheet was about 87% and much greater than 50 to 70% in TIG welds, owing to the very narrow width of weld metal and heat-affected zone. (7) The joint efficiency of EBW weld of a 6 mm thick 17-7 PH plate was 100% and was greater than 95% in TIG weld.