From the standpoint of geometrical shapes, the relation between the fatigue strength at the toe of weld and the inclination of a weld line to the direction of principal stress was investigated. Two plates, which differed in thickness from each other, were butt-welded, and then specimens were cut out of them, changing the angle between the long axis of specimen and the weld line. In addition, the simulated specimens made of the same steel, which had a fillet with a flnak angle of 45 degrees were prepared. Plain bending fatigue tests were then carried out on these specimens. Test results show that the fatigue limit does not increase monotonously, as the weld line changes from transverse to longitudinal to the long axis of the specimen, as often described, but takes a minimum value in about the middle direction, and the type of fracture changes afterwards. To make clear these differences, careful check is made of fatigue strength values reported in the literatures concerned and then, such tendencies as mentioned above are studied.
In the previous paper, authors have reported that the hydrogen diffusion phenomena in the steel were explanable comparatively well by Fick's law. The present experimental study was undertaken primarily to obtain an improved understanding of the behavior of hydrogen in various structures of steels. Discal specimens for the measurement of the hydrogen occlusion were prepared from a commercial steel S55C. The specimen diameter was 30 mm and its thickness was changed up to 16 mm, as indicated in the previous paper. The carbon content in the steel may affect the hydrogen occlusion. So the structures of the specimens, used in this experiment, were obtained by the heat treatment of the same kind of steel. Hydrogen was charged into the specimen by the cathodically charging method in 5% H2SO4 solution (current density; 0.2 Amp/cm2). Data which were obtained on the effect of the structures were studied using Fick's law, under the assumption that the materials were homogeneous on the average. The apparent diffusion coefficient, D, was computed from: D⋅t/L2=0.05 in which L represents the thickness of the specimens and t represents the period in which the hydrogen content of the specimen increases up to 1/2-maximum or equilibrium hydrogen content of the specimen from the start of the cathodic evolution. Solubility of hydrogen (i.e. equilibrium hydrogen content) in various structures was affected by the condition of the distribution of ferrite and cementite in the steel. The ferrite+pearlite structure showed a maximum solubility of hydrogen, on the other hand, the troostite structure showed a minumum. Moreover, the martensite structure showed the least. As to the diffusion coefficient of hydrogen, a maximum value was found in the ferrite+pearlite structure and a minumum one in the martensite structure.
A study has been made of the weldability of Al-Zn-Mg alloys. The experiments were carried out on the aging characteristics, tensile properties and weld-crack susceptibility of MIG-spot welds. Tensile properties were evaluated by the tensile-shear and the cross-tension test, and weld-crack susceptibility was evaluated by the slit-type weld-cracking and the restrained weld-cracking tests. The tensile-shear strengths of MIG-spot welds made with 5356 filler and AIZnMgZr filler were 500 kg/spot and 600 kg/spot respectively in 60 days after welding. Cross-tension strength decreased with aging after welding, while tensile-shear strength increased. According to the restrained weld-cracking test, crack susceptibility of MIG-spot welds in AI-Zn-Mg alloy was almost equal to that of 5052 alloy. However, crack susceptibility of Al-Zn-Mg alloy containing small amount of zirconium was almost equal. to that of 5083 alloy. Weld-crack susceptibility of AlMg alloy (upper sheet)-AlZnMg alloy (lower sheet) combination showed the tendency of smaller susceptibility than AlZnMg-AlZnMg combination.
When the weld molten metal solidifies, it forms a conspicuous cellular structure. Up to this time, the primary structure has been observed macroscopically. Then anthers investigate it microscopically using a special etching reagent that is a saturated solution of picric acid added with a surface active agent. On the other hand a temperature cooling curve is plotted of the weld deposit metal using the Fe-W thermocouple, and the relation studied between the cooling velocity and the primary structure. The results are summarized as follows; (1) The weld molten metal does not cool smoothly, because it is disturbed by the arc. (2) The cellular structure in the weld deposit metal grows in the direction of heat flow. But under, microscopy, each cell grows straight. (3) In proportion as the cellular structure grows, it also grows fat in radial direction and forms a counter cone. (4) It is not the cooling velocity but the mass of the weld deposit metal that controls the grain size of the primary structure. (5) In proportion as the cellular structure grows, it is transformed into a cellular dendrite, and a free dendrite is formed at last.
The viscosity of the fused salt systems NaCl-LiCl and KCl-NaCl-LiCl have been investigated as functions of both temperature and molar compositions by the damped oscillation method with platinum disc. The isotherms of viscosity against molar compositions were determined over extended temperature ranges for these system and the activation energy for viscous flow was calculated according to Eyring's theory. The isotherms of viscosity of fused NaCl-LiCl system showed negative deviation from additivity of molar compositions and increased with an increasing NaCl content in the liquid mixture. The activation energy showed negative deviation from additivity. In the KCl-NaCl-LiCl system, the isotherms of viscosity decreased with an increasing LiCl in the mixture and increased slightly with increasing KCl or NaCI. In the 20 mol% KCl-NaCl-LiCl and the 40 mol% KCI-NaCI-LiCl systems, the activation energy showed positive deviations and a maximum value was found for each system. These deviations are caused by the interaction between different types of ion pairs in the liquid mixture.
The paper explains the reason why the wire tip takes a pencil-like form for the wire of low heat conductivity from the standpoint of the anode heating on the cylindrical wire surface. It explains also the reason why the pencil like-forming tendency is increased when the wire is preheated by .Joule's loss. It is explained that the pencil-like forming of the solid part at the wire tip allows an easy detachment of the molten droplet and results in a lower temperature of the droplet arriving at the base metal. From the above mentioned idea, the following characteristics observed in MIG are welding are explained. For aluminum wire the heat content of the droplet increases as the current is increased until it reaches a nearly constant value in spray transfer range. The temperature is as high as the boiling point in spray transfer. The increase of the temperature is due to the quick heating of the droplet. For steel wire the heat content increases and reaches a maximum and then decreases as the current is increased under a constant wire extension The decrease of the heat content is related to the pencil forming. For any given current the heat content is smaller for longer wire extension because the pencil forming tendency is stronger. The decrease of the current corresponding to the maximum heat content above mentioned for longer wire extension is also attributed to the same cause. Lesnewich reports that the critical current in globular to spray transition decreases as the wire extension is increased. The reason is explained by the pencil forming. Salter reports that the melting speed is increased with decreasing of atmospheric pressure. The potential gradient of the arc column decreases in lower pressure and the arc foot climbs up along the wire. Therefore the pencil forming is increased and results in a decrease of the droplet temperature and an increase of the melting speed, because the equivalent anode melting voltage VmA=VA+VW+VT is presumed to be independent of the pressure which is not so much different from the atmospheric pressure.
In this report, we intend to describe the specific corrosive media and heat treatment in which sulphide corrosion is most likely to occur on 5% Cr-1/2% Mo alloy steel. The conclusions from our research are as follows; 1. The embrittlement due to sulphide corrosion is proportional to the volume of hydrogen absorbed from corrosive media. 2. Absorbed hydrogen and weight loss by corrosive media can be decreased fairly by addition of the TEPP 3. The embrittlement due to immersion in corrosive media shows apparent change in reduction of ductility, but in this case the tensile strength does not drop. The embrittlement can be undone by aging.