Under the condition that the base metal to be welded is easily distorted, cracking seldom occurs. As to welding crack in high tensile steel plates, a lot of researchers have studied and presented the results of their studies, in which not a few researchers have done the restraint cracking test, such as U-type or slant Y-type. In this research, a restraint cracking test was done as follows, first of all, special butt welding of high tensile steel plates (Fig. 2) was made by manual arc welding process with coated electrode, NOW process or submerged arc welding process, secondly the profile of butt groove, which seemed to be most suitable, was chosen for each process, and thirdly for heating, "A Process for Local Heating at Constant Maximum Temperature with Gas Flames" published before was used. In these tests, the following investigations were made, such as prevention of welding crack at welded parts of high tensile steel and the relation between welding cracks and preheating or post heating. According to the results of experiments, the authors recognized the following facts: 1. In case of butt welding of high tensile steel plates, Wel-Ten 80C, a crack rarely occurs. But if the. butt welding is made in central part of Fig. 2, crackings are likely to occur. 2. In these tests, welding was done after preheating by the above mentioned process. There are instances where cloy preheating at 120°C could prevent cracking at the welded part. But when the temperature of preheating was 120°C and the interlayer temperature was kept at 200°C, in any method of welding, cracking was fully prevented. 3. After welding by the various processes, post heating at 700°C was done by this heating method. By this post heating, the welded part with single-layer was softened and therefore cracking was prevented. But a small crack in crater was recognized in case of submerged arc welding process. Besides in case of multi-layer welding, if the interlayer temperature was kept at 200°C and post heating was done only after deposition of final weld, there was.no danger of cracking at all.
We described the fundamental mechanism of penetration and the influence of some welding conditions on the penetration of base metal in previous reports 1 and 2. This paper describes the influence of electrical conductance of molten slag on the penetration using some different fluxes. Fig. 2 shows the temperature characteristics of conductance of fluxes I, II and III used in our present investigation, flux es II being the same one as used in reports 1 and 2. Flux I has high conductivity even at low temperature, and flux III has conductivity only at higher temperature than flux II. The experimental results are as follows; Though the penetration for flux III shows the same tendency as flux II, which is already described in report 2, it is remarkable that the penetration for flux III is deeper in spite of the deeper steeping of wire in molten slag pool. This is contrary apparently to the conclusion obtained in report 2, where the deeper steeping of wire corresponds to poorer penetration in overcurrent range. We presume that the higher penetraion for flux III is due to the higher working temperature of molten slag. It maybe intresting to cmpare; the welding phenomena of flux III with that of arc welding, regarding the arc atmosphere as molten slag which has conducti ity only in high temperature range. Using flux I, the wire feed speed should be reduced to keep certain welding conditions. The steeping length of wire is naturally very shallow and the welding current from the wire flows out mainly in the upper zone of slag pool as shown in Figs. 10 and 11, and results in a poor penetration of base metal. When shallow slag depth is used, the penetration is naturally improved as shown in Fig. 14.
A basic investigation in brazing was made of the migration or the penetration of molten copper into solid cobalt and of the structure of copper-cobalt interface in the temperature range 1100°-1300°C for the reaction time from 0 to 30 min. The principal mechanism of the migration of molten copper into solid cobalt was shown to be volume diffusion. Initial rate of the penertation of molten copper into cobalt is 0.4-1.1×10-3 mm/min. The thickness of Cu-penetrated layer ranged from 5.4 to 50.4μ and it increase in proportion to the square root of the reaction time. The obtained value of the penetration-rateconstant is 2.57.3×10-3 mm/min1/2 and from the temperature dependence of the rate-constant the value of the activation energy for the penetration, 23.5 Kcal/mole was obtained. In copper-cobalt interface, a cobalt dendrite layer which had been crystallized on the copper side of the interface during solidification was recognizedand on the opposite side of this interface, a thicker copper-enriched cobalt solid solution.
Control of weld cracking is one of the most important problems in welding steel constructions. Two of the authors proposed the use of a new cracking parameter Pw to determine the successful welding procedure to avoid weld cracking for a given chemical compostion of steel used, the amount of diffusible hydrogen in weld metal and the intensity of restraint of the weldments. In the present report, research is focused on the practical use of the above proposals. For this work, firstly, the relations of welding procedures in terms of welding heat input, preheating conditions, plate thickness and others versus cooling time of welds are studied theoretically and experimentally.
This paper deals with the generation of plasma flame by a coaxial. tubular electrode. The coaxial tubular electrode consists of outer and inner tubes, of which cross-sectional areas are nearly the same. The inner tubular electrode is coaxially inserted into the outer tubular electrode with spacing of the insulator as shown in Fig. 2. Some experiments about the generation of plasme flame by the electrode and its application were performed. The experimental results are as follows. 1) The coaxial tubular electrode made of carbon was able to maintain stably the plasma flame in water as well as in atmosphere, in spite of the flow of gas. And the dissipation of electrode was a little, so that this type electrode became a kind of non-consumable plasma torch. 2) When the electrode was made of mild steel, the plasma flame could be easily maintained both in water and in atmosphere, by using of ilumenite and manganese dioxide as the chief ingredients of insulator between two tubular electrodes. Besides, it was possible to ignite the plasma flame in water by the mixing of small amount of electrolyte such as sodium chloride. 3) Under the condition of oxygen flow and mild steel electrode, the plasma flame was ejected very stably in water and in atmosphere. Moreover, the mild steel was oxidized and burned, so that the heat of plasma flame was stronger due to the addition of combustion heat. 4) A concrete board could be easily pierced by the plasma flame in atmosphere, in water or in salt water. In this case, the mild steel electrode and the oxygen flow were used for the generation of plasma flame. Thus the coaxial tubular electrode may be called very useful for applications to the field of ocean development.
Laminated plates of two to sixteen layers were made of 2.5% nickel steel and mild steel by hot rolling. Their impact values were examined on the specimens notched on plate side and plate surface, and the following results were obtained. (a) The order of the impact values of the laminated plate is; Three layers plate with mild steel surface>two layers plate> three layers plate with nickel steel surface. (b) Laminated plate notched on plate surface has a larger impact value than one notched on plate side. (c) Four to sixteen layers laminated plates show smaller impact values as compared with a three layers plate with mild steel surface.
Dispersing mechanism of oxide inclusions is studied by investigating the behavior of oxide film inserted artificially at the interface of specimens in the upset butt welding process. Applying the concept obtained in the study of flash welding, the authors presume that good mechanical properties can be obtained, if the oxide film which may exist always in the interface, is dispersed by adopting adequate welding conditions. It is obtained that if the temperature of the weld interface is above a certain value, welded joints with good mechanical properties are obtained under rapid heating and cooling as in this experiment. By using the model test pieces with oxide film artificially inserted in the interface, it is made clear that a certain maximum temperature in upset butt welding process is necessary for the dispersion of the oxide film. See Figs.10, 11. Above mentioned critical maximum temperature is measured to be about 1370°C which coincides with the melting point of FeO. Accordingly the mechanism of the dispersion of the oxide film is understood as follows. As the coupling force between Fe and O becomes weak in liquid state of oxide, O can diffuse easily from the oxide film layer in the interface, giving many fine oxide particles in the neighborhood and no trace of oxide film in the interface. It must be noticed that dispersion takes place at temperatures below the melting point of steel. The dispersion has little relation to applied mechanical pressure or the deformation of the test pieces. See Figs.13, 14.