In order to define the change of mechanical property owing to stress relief heat treatment, HT60 base metal and welded joint were subjected to S.R. treatment with or without restraint jig which induced tensile residual stress. Tensile test and impact test were carried out using specimens which had been machined out from test assembly after S.R. treatment. Results indicate the following findings, 1. Tensile and yield strengths of base metal showed small drop due to S.R. treatment at 600°C. But impact property did not show any change. 2. Impact property of heat affected zone indicated a tendency to be improved by S.R. treatment, especially when temperature was 600°C. 3. The existence of residual stress did not show any effect on the change in impact property of weld bonded region owing to S.R. treatment. 4. Effect of cooling rate in S.R. treatment on impact property of weld bonded region was not recognized in the region between 50°C/hr and 250°C/hr.
Regarding covered arc electrode, hitherto various studies and developments have been made for the improvement of the welding efficiency. In these studies, using the multiple composed covered electrode, that is, metal wire and metal pipe lapped and flux coating layer provided respectively (see Fig.1), the characteristics of welding arc were investigated. This new type of the electrode was available for 3 kinds of wire connecting methods, as shown in Fig.2, and comparison was carried out between them. The results showed that by double source type in which the current in either side of core wire or core pipe became comparatively high, the melting rate was increased. As the respective current densities became equal, the melting rate was decreased and became about equal to the melting rate of single source type (see Fig.9). Using this welding electrode, specially when the current was supplied to the core wire only, the melting rate was most increased and it was found that thermal efficiency was also increased.
A fundamental theory for the analysis of residual welding stresses and deformations based on the inherent strain distributed along the welded joint is presented. The first part of this paper deals with a general solution to a two-dimensional inherent stress problem which is a special case of the inherent stress theory presented by the author in a previous work. In the welded structures, the inherent strain is commonly created within the narrow strip-like region which encloses a welded joint. Therefore, the analysis of residual stress due to welding can be simplified using a model in which the inherent strain is assumed to be distributed on a line. In this case, the characteristics of the idealized inherent strain may be expressed by the intensity of the distribution. The concept of the inherent shrinkage of welded joint is introduced through the longitudinal and transverse components of this intensity of the inherent strain. The second part is concerned with the analogy between the two-dimensional inherent stress problem and the inherent deflection problem of a plate. A general solution to the inherent deflection of an elastic plate is directly obtained from this analogy by introducing the inherent curvature corresponding to the inherent strain. The inherent welding deformation is therefore defined as the combination of the inherent shrinkage and the inherent warping. In this paper, the inherent welding deformation is represented by six basic components, i.e. longitudinal shrinkage, transverse shrinkage, staggering; longitudinal warping, transverse warping and twisting. They are schematically illustrated in Fig.7. In the last part, an example of the inherent strain distribution along a butt welded joint is presented. This was recalculated by the author from the theoretical results of thermo-elastoplastic analysis of transient welding stress carried out by Prof. I. Tsuji of Kyushu University.
Japan Material Testing Reactor (JMTR) was constructed at Oarai Research Establishment of Japan Atomic Energy Research Institute. The reactor went critical in March, 1968. Plans are being made at present to install in-pile loops to perform irradiation tests. The first loop is OWL-1. The stainless steel SUS 43 (AISI 347) is used as the material of the in-pile tube: the tube is 5 meters long, 60.2 mm in outside diameter, with wall th kness 5.2 mm. Therefore welded joints are necessary to fabricate the loop. Since the welded joints are within the reactor, sufficient strength and rigorous accuracy are required for the joints. Electron-beam welding was first considered, where the safety must be assured. In this paper are described the results of tests on electron-beam welded joint specimens and joint-less specimens, including the tensile test, cyclic-pressure test, micro-tensile test and bending fatigue test. The strengths of the different specimens are compared, followed by some discussions. The following conclusions have been drawn: 1). The statical strength of electron-beam welded joint specimens is equivalent to that of the TIG welded joint specimens and of joint-less specimens. 2). The fatigue strength of electron-beam welded joint specimens is lower than that of the TIG welded joint specimens and joint-less specimens; there is some inadequacy in the electron-beam welding.
A basic investigation in brazing was undertaken to study of the dissolution of iron base metal in copper brazing filler metal. Cylinders of iron material were immersed in molten copper and then rotated under dynamic conditions of peripheral velocities from 18.3 to 58.6 cm/sec in the temperature range 1200°-1400°C, exposure times ranging from 40 to 480 sec. Rapid dissolving of the base metal in molten copper occurred and excess dissolved base metal was crystallized within the copper and on the iron-copper interface during solidification. The rate of dissolution of solid iron in molten copper increased with an increasing temperature and rotational speed. A modified first-order kinetic equation based on a mass was used to determine the solution rate constants. These varied from 0.68 to 2.90 × 10-2cm/sec depending on the temperature and the rotational speed, and increased in proportion to 0.60-0.71 powers of peripheral velocities. The activation energy for dissolution of solid iron in molten copper was estimated to be about 15.3 Kcal/mol. The dependence of the solution rate constant on temperature and peripheral velocity and of initial solution rate (the obtained values ranged from 2.88 × 10-3 to 3.70 × 10-2 g/cm2-sec) on temperature led to the results: the dissolution of solid iron in molten copper is diffusion-controlled, but at higher temperature and higher velocity there is a change in the behaviour of the dissolution, which was reviewed on the basis of effective boundary layer adjacent to the solid metal surface.
In plasma arc welding, an important role is played by the current density of the arc. The current density, however, is decreased greatly if the so-called series arc starts in parallel with the main arc. In this paper, the factors which predominate series arcing are experimentally investigated. Results are summarized as follows: (1) When the nozzle end of the plasma torch is covered with oxide film or is in oxidizing atmosphere, the cathode spot of series arc is easily formed with the help of oxide film, resulting in the great reduction of current capacity Ic. For example, if there is a sufficient quantity of oxide film on the nozzle end, Ic falls by half. But the series arc itself has the cathodic cleaning action of oxide film, so that by repeating the series arcing of short time (about 1 second) in an inert gas atmosphere, Ic increases according to the extent of oxide elimination, up to the value obtained without oxide film. (2) In case that the nozzle end is cleaned and is in an inert gas atmosphere, the series arc is started by the temperature rise of the nozzle exit up to its melting point, at every nozzle diameter. This means that if the temperature of the exit rises up to the melting point, the cathode spot is formed very easily. As a matter of course, after the series arc is started, the nozzle exit is melted or burnt off by the cathode energy of this arc. With increase of the nozzle diameter dn, however, Ic increases roughly in proportional to dn and not to the sectional area of the nozzle. (3) When some kind of metals of low melting point like solder is present at the end of the nozzle, the series arc starts very easily and consequently Ic decreases remarkably, for example, by half. (4) With use of tungsten for the nozzle duct, Ic is considerably lowered than with a copper nozzle. This can be considered to be caused by the easiness of the temperature rise of the tungsten nozzle, up to the extent at which hot cathode is formed, due to its low thermal conductivity. (5) With increase of working gas flow rate Q in the range relevant to plasma arc welding, Ic increases considerably, in spite of the remarkable rise of arc voltage with Q. This can be attributed to the fall of the nozzle temperature caused by increasing Q.