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.

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造船用高張力鋼および軟鋼の切欠靱性に及ぼすガス切断の影響を調べるために,標準カーン引裂試験片の切欠を機械およびガス加工して遷移温度の測定を行った。その結果次の結論が得られた.
(1)ガス切断切欠は機械切欠に比べて遷移温度を著しく(30～60℃またはそれ以上)上昇させる.
(2)ガス切断は切欠試験片の最大荷重を19～25%減少させ切欠底部の変形能を1/7～1/2に減じ,さらに亀裂発生までの吸収エネルギーを2/3(高温)～1/7(低温)に減少させる.
(3)ガス切欠尖端の硬化は直線切断面の硬化に比べて著しく高い.
(4)ガス切欠は軟鋼でも高張力鋼でも極めて危険である.
(5)ガス切断による低炭素高張力鋼(C=0.14%)の切欠脆性は軟鋼リムド鋼と同程度で,高炭素高張力鋼(G=0.19%)の脆化はこれらよりはるかに著しい.
以上によりガス切断中のミスカットや火焔中断後の再出発による板縁えの切込みは切欠脆性の見地から極めて危険である.特に高張力鋼では注意を要する.

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本報告は筆者の一人が先きに発表した軟鋼丸棒,管などの実験結果にもとづき新たにレール用ガス圧接機を試作しこれにより種々実験されたもの瓦一部である.
まず最初に本機による50kgレールの接合要領を説明した後,これらの接合レールの強度試験として先づ曲げ試験を行い,その実用性を検討した.この判定には従来の破断荷重に重点を置く方法を改め,主として破断荷重と撓みを自動的に考慮する曲げ破断エネルギーにあることゝした,これにより本法の接手強度を求め,さらにその他の熔接法によるものゝ接手強度と比較したところ,ガス圧接法によるものは少くとも曲げ試験においてはおおよそフラッシュバット法と同等で,電弧,ガスなどによるものと比べ格段の信頼度を有することが明らかとなった.

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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.

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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.

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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.

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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.

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