Mild steel was welded in CO2 atmospheres at pressures between 1 and 6 Kg/cm2 abs. using an electrode wire of 1.6 mm diameter, commercially available for CO2 arc welding, in order to study the effect of ambient gas pressure on the characteristics of an arc, the mode of metal transfer, the geometry, composition and hardness of weld beads and so on. The results obtained are summarized as follows: (1) In welding under a shorting-arc condition at 22.5V, 250A, (a) the maximum arc voltage increases and the duration of short circuiting becomes longer with an increasing ambient gas pressure; (b) the ambient gas pressure has no significant influence on the melting rate of an electrode wire and the chemical composition of weld metals; (c) the hardness of weld metals increases with an increasing ambient gas pressure; and (d) the reinforcement of welds increases with an increasing ambient gas pressure. (2) In welding under a droplet transfer condition at 35V, 350A, (a) the melting rate of an electrode wire increases with an increase in the ambient gas pressure; (b) the arc voltage during welding under high pressure atmospheres appears in waves at intervals of some 25Hz, accompanied with many small fluctuations in a wave; (c) the ambient gas pressure has no significant influence on the chemical composition of weld metals; (d) the hardness of weld metals decreases with an increasing ambient gas pressure; and (e) the reinforcement and penetration depth of weld metals increase with an increasing ambient gas pressure. (3) In welding with 4 mm arc length under a droplet transfer condition at 350A, (a) manganese and silicon contents of weld metals decrease with an increasing ambient gas pressure; (b) the arc voltage during welding under high pressure atmospheres appears in waves in the same manner 35V, 350A; and (c) the hardness of weld metals decreases with an increase of the ambient gas pressure; (4) No porosity was observed in the weld metals made in the pressurized CO2 atmospheres.
Underwater welding by gravity arc welding process is investigated by using coated electrodes of six types and SM41 steel plate of 6 mm thickness as base metal. And it is ascertained that this process may be put to practical use. Main results are summarized as follows: (1) Sound weld can be obtained easily by any unskilled welding operator using any type electrode except low hydrogen one, due to stable arc. Especially appearances of beads obtaind using high titanium oxide type and lime titania type electrode are good. (2) The proper range of combinations of welding current and diameter of electrode for the high titanium oxide type is relatively wider than that for the ilmenite and the iron powder iron oxide type. (3) Weld metal has the same tensile strength as base metal. (4) Weld metal has an impact value of 40 - 50% of that of base metal. (5) Cooling rate at 500°C at bond is about 140°C/sec in water and 18°C/sec in air, the former being about 8 times higher than the latter.
In this report, the relationship between the heat treatment conditions and the behavior of ThO2 particles in solid matrix is discussed to get fundamental informations on the solid state bonding of TD nickel. The results obtained from this study are summarized as follows: (1) ThO2 particles begin to grow at a temperature near the melting point of matrix nickel and the agglomerating process of the particles takes place as the first step of the growth. The particles agglomerated and grown have the same crystal structures as those of ThO2 particles and the volume fractions of these particles don't change after growth. (2) The features mentioned above are not explained by the ordinary growth mechanisms of oxide particles, so the authors propose a different mechanism of growth based on the self-diffusion process of matrix atom, the adhesion process among ThO2 particles and the decrease of interfacial energy among the matrix and ThO2 particles (3) It is confirmed that the dispersion hardening effects of ThO2 particles decrease as ThO2 particles grow larger than 900 A in the mean diameter. (4) Fig. 17 and Fig. 18 show the time temperature regions where dispersion hardening effects are retained. In case of the solid state bonding, if the bonding conditions satisfy these regions, the dispersion hardening effects of ThO2 particles are expected to be preserved at bonding interface.
The fatigue notch sensitivity of steel has been reported to be raised by welding, though lowered value has also been appeared in another investigation. The present study was therefore undertaken in attempt to resolve the apparently paradoxical behavior. Considering the mean size of carbide, L', and its mean spacing, 2L, to be the main structural factors which influence the fatigue strength of steels, the authors has previously showed correlation between microstructure and fatigue behavior of quenched and tempered steels with and without notch. On this basis, the effect of microstructural change caused by welding on notched fatigue strength of welded steel was investigated. It is found that the notch sensitivity can be raised or lowered according to the metallurgical change at welded part. That is for a given steel with lowere value of Lb (Suffix b refers to base metal), the fatigue notch sensitivity is generally raised by welding. On the other hand, the notch sensitivity of welded part is not so affected by welding in case the value of Lb is small such as high strength steels. Moreover, it is expected to be lower notch sensitivity of welded part if Lw (Suffix w refers to weld part) is larger than Lb.
As described in the last reports, it was shown that a vertical butt welding of thick cast iron plates by electloslag process was succeeded using our new method with a cored wire and a hollow graphite nozzle. However, it is necessary to more improve the crack resistance of weld metals to apply to higher restraint welds, such as a repair welding of large hollow defects in a heavy cast frame of a machine tool. The present paper shows that the application of the transformation superplasticity by retarding martensite transformation is more effective for a prevension of weld metal cracking due to high thermal stress. A dilatation test and a restraint test under synthetic weld thermal cycles, determination of GGT diagrams, and hardness measurements are conducted on many cast iron specimens with various alloying elements. As these results, it is known that the weld metal compositions of cast iron in a range of 0.1 - 1 % Mo and 0.5-3 Ni are suitable to prevent weld cracking due to high restraint.