As a means of obtaining deionization characteristies of the space between electrodes after the extinction of welding arc, we calculated the resiRfance of the space from the condenser discharge current. We find, the conductivity of the space remains so long that the arc can reignite even after the interval of half a cycle (1/100sec) at the welding conditions of the current 50A and open-circuit voltage 60V.
To investigate the effect of flame cutting on notch sensitivity of two high tensile and one mild ship steels, tests were performed with Kahn Test specimens of which the notches were machined or flame cut. The conclusions may be summarised as follows: (a) A flame cut notch raised transition temperatures by 30 to 60°C higher than that of machine-notched. (b) Flame-notched specimens showed 19 to 25% lower load carrying capacity than machine-notched, and very poor ductility at notch root when measured by lateral contraction, only 1/6 to 1/2 times that of machine-notched. The energies up to the maximum load in flame-notched specimens were only 2/3 to 1/7 times that of machine-notched, at higher and lower temperatures, respectively. (c) The hardening of base metal was considerably greater at the root of a flame-notch than at a straight flame-cut edge. (d) A flame-nothch is very dangerous in a mild steel as well as in a high tensile steel. (e) The notch sensitivity of tested high tensile steel with lower carbon content, 0.14%, was similar to that of a mild steel, while the high tensile steel with higher carbon content, 0.19%, was embrittled seriously by flame cutting. Thus, a miss cut in flame cutting or a notch which has been caused by flame interruption during cutting is considered very dangerous and should be carefully avoided from the standpoint of notchbrittle fracture. It is more so in high tensile steels.
This is to report a part of the results obtained with the new gas-pressure rail welder developed on the test data of mild steel rods, tubes, etc, which were earlier published by one of the authors. First, the welding procedure of 50 kg rails by this apparatus is explained. Then these welded rails are put to bending test to determine their strength and practicability. In the evaluationn of the test results, emphasis is shifted from the conventional breaking load to bending failure energy which naturally includes breaking load and deflection. The joint strength obtained by this method is compared with those of other methods with the results revealing that at least in the bending test, this is nearly as good as that of flash-butt process and by far superior to that of arc or gas welding.
An investigation on spot welding for galvanized steel sheets of 0.4, 0.6, 0.7 and 1.0mm thickness is reported in this paper. Tension shear and cross tension strengthes are tested, making one of four spot welding conditions i.e., current, time, pressure and spherical radius of electrode tip, variable and the other three constant, showing effects of these welding conditions by curves. Experiment on weld consistency, surface conditions and microscopic structures of the weld nugget are also explained. Zinc is not found in the weld nugget by spectrographic analysis.
When 0.15 percent carbon steel bars are flash-butt welded, the weld metal and heat affected zone show the widmanstätten structure and large grains. It is suitable that these parts are postheated (air cooling) at about 850°C with an electric furnace in order to change the widmanstatten structure to the annealed structure having good ductility. In the case of postheating with a flash-butt-welder, however, it is suitable that these parts are postheated at about 950°C for a short time.
The discontinuity-migration theory on hydrogen brittleness of steels has been published and supported by researchers. The purpose of this investigation is to reconsider this theory on hydrogen brittleness and, if possible, to establish the new theory. In this paper, authors report the results of a few experiments on hydrogen brittleness of mild steel. Hydrogen was charged in mild steel specimens by cathodic electrolysis method (5%H2SO4, 0.08-0.09A/cm2, carbon tube anode used). The volumes of hydrogen in specimens were regulated with change the charging hours and were measured using other specimens before mechanical tests. On mechanical tests, tensile test, V-notched slow bend test and V-notched charpy impact test were used. (1) In the case that the specimens were tested soon after charging; Yield strengths and maximum stresses on tensile test were almost same value, in spite that the volumes of hydrogen in specimens were different. But the elongation was remarkably decrease in accordance with increase of the volume of hydrogen in specimen. Energy of crack initiation and propagation on V-notched slow bend test were also remarkably decrease. The decrease of ductility on V-notched charpy impact test with increase the hydrogen in specimen was considerably remarkable, in spite that the test was carried out under very high speed and atomic hydrogen in specimen could not consider to migrate through the gap of Fe-atom. (2) In the case that specimens were aged up 4 days after charging before test; Ductility was remarkably recovered nearly equal to that of virgin specimen. From these experimental results and consideration, authors obtain the guiding-star of the new theory of hydrogen brittleness.
We have studied in this paper on the problem of effect of residual stress on the vibration of welded joints. For the sake of simplicity we have used the so-called "H-type constrained specimen" as shown in Fig. 1 which was made from structural plain cabon steel SS41 of 10mm thick. At first we examined the relief of residual stress due to vibration. Specimen, which was fixed at oneend, was vibrated at constant amplitude and constant frequency, and the residual stress was measuredafter 10, 102, 103, 104 and 105 numbers of vibration respectively. It was known'that the residual stress, initial value of which is about 14-18kg/mm2 in center bar of the specimen, decreased with the increase of numbers of vibration, and after 105 numbers of vibration it became about 50% of the initial value for the case of amplitude 10mm. The magnitude of relieaved stress increase with amplitude. The resultsof this experiment are shown in Figs.3, 4and 5. Nextly we have made the test of free damped vibration of the specimen which was fixed at one end. The frequency and logarithmic decrement of each specimen are shown in Table 3. It is known from this that the frequency decreases with increase of residual stress and the logarithmic decrement is vice versa. At last we have made the test of forced vibration at various number of frequency, and the amplitude of welded specimen was known to be lower than the specimen without weld at the resonance point.