"Fus-arc Welding Machine" has been used for welding of boilers and other pressure vessels. In this report the process and results of investigations and experiments on its routine working are given. It can be summarized as follows : 1. Sulphur cracking is perfectly prevented by use of multi-pass welding method. 2. Mechanical properties of multi-pass welded deposit metal which is stress-relieved are as follows : Yield point, 35-40 kg/mm2 Ultimate strength, 45-50 kg/mm2 Elongation, 28-30% Reduction of area, 60-70% Impact value (Izod), 6-12kg-m From this it will be seen that this welded metal is suitable for pressure vessel welding. 3. Fatigue strength of joint specimens is equal to that of mother metal and fatigue strength of columnar structure is about 94% of that of mother metal. So the general opinion that columnar structure is weak for fatigue may be corrected. 4. When welding the end of longitudinal joint of cylindrical vessel, magnetic blow occurs but it does not disturb the working. 5. In the operation mentioned above, we have proper opposite strain, so we can keep the difference between the maximum and minimum diameter of any sections below 1% of designed diameter.
Charpy impact tests were carried out at various temperatures on the specimens of one-pass mild steel submarged-arc-welded metals in as-welded and annealed states. It was pointed out that the specimens annealed at 800°C. had higher impact values and lower transition temperatures than the others. This fact led the author to infer that large grains of dendritic structures have decisive influences upon brittle fracture. The photomicrographs of fractured edges and fracture facets showed the validity of the inference. Moreover, the X-ray back-reflection patterns of the brittle fractures were taken and the brittleness of these fractures were compared with each other in the light of the lattice distortions in them.
The authors reported in previous announcements about the change of properties in the heataffected zones. Generally, it is known that the weld metal made by low-hydrogen type electrode has the superior toughness comparing with the one made by ilmenite type electrode, and the transition temperature is lower, so possesses the excellent properties even at low temperatures. In this report the authors investigated the toughness at fusion-line of both low-hydrogen type and ilmenite type. As a result of investigation it is recognized that the excellent toughness of lowhydrogen type depends not the action of hydrogen but that of nitrogen and oxide-inclusion of low melting point. The position at which the crack initiates and develops is different according to the types of electrodes. As a result it was concluded that : 1) Low-hydrogen type shows the superior toughness at both weld metal and fusion line comparing with ilmenite type, and the reason of this difference is the low contents of nitrogen and oxygen. 2) Crack of low-hydrogen type weld metal develops in the heat-affected zone if notched to the fusion line, and that of ilmenite type does so if notchedin the direction of weld metal. 3) Increase of toughness after 600°C. heat-treatment is caused by the escape of hydrogen, but very slight. 4) The heat-affected zone at which the temperature rise during weld is estimated about 720°C (A1-transformation point) shows low toughness irrespective of the types of electordes, and this will de caused only by the effect of heat.
It is recognized that the impact-resistance of sharp-notched specimen decreases suddenly at the so-called "transition temperature". Below this temperature the fracture shows more brittle than shear one and at low temperatures the shear fracture vanishes. It is important to investigate the properties of welded part at low temperatures. The authors reported in the previous report that there are two brittle zones in the heat-affected zone both in killed and rimmed steels, after testing the distribution of impact resistance when a single bead was deposited on the surface of steel and observing the fracture with X-ray diffraction incthod and microscope. In this report the authors mainly deal with the low temperature brittleness of heat-affected zone of parent plate. Observation of the X-ray diffraction rings of the fractures as well as V-notch Charpy impact resistances are also given. As a result of experiments it has been concluded as follows : 1) Weld metal shows somewhat different pattern of the temperature-resistance curve as compared with that of heat-affected zone. In the temperature range above 60°C, the resistance is somewhat inferior, which is ascribed to the precipitation of nitride, but at lower temperatures it is superior to that of heat-affected zone, which may be the effect of low carbon content and small grain size. 2) The most brittle part in the heat-affected zone is the one which is affected by the temperature-increase reaching around A transformation point through heat of arc. 3) In the temperature range below 30°C, the influence of welding heat vanishes ; so there exists no differences in the impact resistance of parent plate, but the resistance of weld metal is good in this range.
It is the purpose of this research to investigate the effect of sulphur cracks upon the fatigue strength of welded joints. With the everincreasing need for the elevation of welding operation efficiency, maintenance of uniform weld and the reduction of man-hours, there has recently been made considerable application of automatic welding in the field of ship structure. However, when automatic welding was adopted for ship structure using indigenous rimmed steel, the authors were confronted with a particular problem of sulphur crack (fig 1), originating from the point of segregation of sulphur in the direction of solidification of weld metal. So the experiments were performed in order to investigate the fatigue strength of welded joints by varying the degree of sulphur crack. The specimens used in this experiment were prepared, as shown in fig. 2 and fig. 3, with a conventional Vee edge preparation perpendicular to the rolled direction. Table 4 summarizes the chemical composition of three kinds of steel, A, B, C, utilized in this research, while Table 3 shows the welding conditions used. The specimens were repeatedly stressed under purely alternating equal load using the Schenck Fatigue Testing Machine. Fig. 5 is a summary of fatigue test results for steel C, compiled from the results for parent metal (marked), perfect welded joints (Δ marked), and the welded joints containing slight sulphur crack. Fig. 4 is a summary of data for steel A and B, when the degree of sulphur crack is varied as follows; 0%, 30%, 50%, 70% and 90%.