With the aim to study the mechanism of vertical welding in the light of "interfacial tension theory" hitherto reported, the authors have studied phenomena of a simplified vertical welding, using a fixed TIG torch against a vertically set mild steel plate. Following are the conclusions obtained by putting together the various facts, observed through the high speed cine-photography and the rapid blow technique applied to the steel plate in the course of welding, with the interfacial tension theory. 1) From the measurement of the penetration angles and bead angles at the edge of the penetration surface, the contact angle of the molten metal of mild steel was estimated approximately to be 60 degrees, assuming static equilibrium of molten metal drop, and this value conforms well to the observed configuration of the molten metal drop during welding. 2) Smooth weld bead with no undercut is generally obtainable when the molten metal drop is completely confined within the penetration surface, leaving no exposed metal surface. The authors discovered that the indirect melting action of the arc plays the most essential role in keeping the upper penetration angle large enough for the confinement of the metal drop. 3) Change of the type of the penetration and moving pattern of small floating particles on the molten pool seems to show that the arc coveres almost the whole surface of the molten pool at the start, forming a 'peripheral type' penetration, and later, the arc is limited to the central part of the pool resulting in 'Pa' type penetration (typical penetration of paraffin plate heated by a spot heat source.) At the final stage of welding, decreased upper penetration angle results in slipping of the molten metal drop into, and then out of, the penetration surface, leaving the exposed metal surface. 4) Three types of the exposed metal surface, from which the bulk of the molten metal was expelled, were observed in this experiment. 1st type surface is the 'slipping solidification' surface, and 2 nd is the one covered partially by small metal droplets and 3 rd is the one coverd completely by a thin film of the molten metal. Occurrence of either type of exposed surface depends on the strength of the indirect and direct melting action and blasting force of the plasma jet.
This paper deals with the effects of applied tensile stresses on the diffusion coefficient of hydrogen. In the present ivestigation, measurements were carried out for the hyrdogen flow through cylindrical steel tubes subjected to tensile stresses. Hydrogen was charged cathodically at the external surface of the tube, and hydrogen gas permeating at the internal surface was collected and measured by glycerin method. The experimental data were analyzed by using the Time-Lag method. The results obtained are summarized as follows; (1) Hydrogen diffusivity depends upon the applied tensile stress. The hydrogen diffusion coefficient in steel increases with an increase in the applied stress. (2) The solubility of hydrogen is 45 cc/100g Fe. (3) From this result, it is assumed that hydrogen diffusion process interacts with various defects within the matrix of metal.
As reported in the previous papers, the effect of electric field acting during bonding process on adhesive strength was examined and it became evident that in the case of epoxy adhesive and polyvinyl chloride (PVC), the adhesive strength was influenced by the D.C. electric field and referring to polyethylene (PE), the influence of the electric field on adhesive strength was not observed. In this paper, it is intended to investigate the phenomena above mentioned from the viewpoint of dielectric relaxation. The results are summarized as follows: (1) As to epoxy adhesive and PVC, the absorption currents were observed and as to PE, they were scarcely observed. The observed absorption currents are assumed to be due to the orientation of dipoles and accumlation of ions near metal surfaces. (2) The changing rate of charge that is calculated from absorption current as a function of time and that of adhesive strength resemble each other (3) It is assumed that the influence of electric field on adhesive strength is caused by the accumulation of ions ncar metal surfaces or the orientation of dipoles.
The fluctuation of the welding current caused by the fluctuation of the source voltage or the secondary impedance variation of the spot welder reflects upon the strength of weld, so from the stand point of heat control it is necessary to control the welding time for improvement of the tensile shear strength. For the above mentioned reason, we used both the ∫10 In dt=const. welding time control method and the welding current control method with feed-back loop (n 2). From the spot welding experiment of mild steel sheet of 1.6 mm to 3.2 mm thickness, the following results were obtained. (1) In comparison to the welding time and current setting methods without feed-back loop, these control methods could improve the consistency of the tensile shear strength at the decreased welding current to normal welding current, and could increase the reliability of the tensile shear strength. (2) By using both the ∫10 I2 dt=const. welding time control method and the welding current control method thod with feed-back loop, the tensile shear strength at the welding current about 40 percent less than normal welding current was kept nearly equal to the tensile shear strength of normal welding current specified by R.W.M.A. (3) The setting of the welding time and current in these control methods can be applied to the welding condition specified by R.W.M.A., and no particular difficulty of welding depending on the thickness of mild steel sheet to be welded was observed in the case of above mentioned control methods with feedback loop. (4) In the case of the ∫10 I2 dt=const. welding time control method, it was possible to obtain the tensile shear strengthat the welding condition of A class specified by R.W.M.A. even with a welding current about 30 percent less than normalwelding current. By way of example, the most suitable values of I2⋅t replaced ∫10 I2 dt=const. were in the following range plate.thickness 1.6 mm: (10-30)×108 (A2. cycle) plate thickness 2.3 mm: (40-60)×108 (A2. cycle)
In the creep rupture test, it has been reported that the probability of heat affected zone fracture increases with increasing rupture time. The authors aimed to study the behavior of weld heat affected zone of 2 1/4 Cr-1 Mo steel during creep rupture test. We used simulated heat affected zone specimens, one series of which was in accord with the coarse grained region (peak temperature 1350°C) and the other with the fine grained region (peak temperature 1000°C) of weld heat affected zone. The simulated specimens were post heat treated at various temperatures (690°C-760°C) and then exposed at 550°C for 5000 hours. The above specimens were rupture tested at 550°C. The results are summarized as follows. 1. The coarse grained specimens showed intergranular fracture independently of the application of post heat treatment as well as of long-time exposure treatment. On the other hand, most of fine grained specimens showed transgranular fracture. 2. The rupture strength was improved by post heat treatment. The optimum post heat treatment temperature was found to be about 725°C. In accordance with the deviation from the above optimum condition, rupture strength decreased. 3. The long-time exposure treatment at 550°C improved the rupture strength of coarse grained specimens. But for the fine grained specimens, it usually deteriorated the rupture strength. 4. The effects of post heat treatment and long-time exposure treatment were discussed on the basis of the effect of carbide precipitation on the formation of denuded zone around grain boundary and on matrix strengthening.