Tensile and impact specimens to two kinds of project steels were tested to determine the effect of rolled plate thickness on the mechanical properties and notch toughness. These steel plates, containing the thickness, 12, 20, 25, 35, 50, 65 and 80 mm, were rolled from two different charges. One of them has the chemical compositions of the mild steel, C class of ABS (tested in both as rolled and normalized conditions) and the auther has those of high tensile steel (fabricated after quenching and tempering process).
To estimate the effect of plate thickness on mechanical properties, the full thickness tension specimen of JIS classification and micro tension specimen were used, and also, to evaluate the notch toughness affected by thickness the standard and full thickness V notched Charpy specimens and Van der Veen specimens of full thickness were used.
As a result, the conclustions were summarized as follows;
(1) It was recognized that there was, at least, one "transition thickness" for the notch toughness of steel rolled out in the range of thickness from 12 mm to 80 mm. The "transition thickness" depended upon the kind of steel.
(2) In the case of mild steel, any significant effect of thickness was not obtained on the mechanical properties. On the contrary, the roll finish thickness has influence on the notch toughness. In the range of thickness exceeding 50 mm, the toughness was remarkably lowered, in consequence, in order to apply this range of steel plate to actual steel constructions, further devices would be needed in heat treatment and determing of steel compositions. However, the notch toughness of mild steel plate, 50 mm thick, corresponded to that of plate, . 35 mm thick, when the plate was normalized after rolling.
(3) In the quenched and tempered steel (high tensile steel) whose thickness exceeds 25 mm, the steel quality and heat tratment process should be determined very cautiously to improve their emechanical properties and notch toughness. The notch toughness of this quenched and temperfd high tensile steel, in spite of the decrease of the tohghess as the increase of thickness, whose thickness exceeds 35 mm, corresponded to that of the normalized mild steel.

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Vanadium is a very weak deoxidizer being intermediate between chrominm and silicon. In this report vanadium was used as a single deoxizer in the straight lime electrodes. As a core rod extra low carbon steel was used. The weld metals have been attained by usual hand welding.
Inclusions located on the weld metals was extroated with carbon evaporated film, and investigated by means of the elecron microscope. The deoxidation products were proved to be vanadium oxide (V₂O₃). The form of oxide inclusions are usually angalar shaped particles, but vanadium carbides take the form of circular shaped film.

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In case of bead deposited on a plate of carbon steels or high tensile steels (low alloy steels) at room temperatures, with submerged arc welding process, the cooling time from 800°C to 500°C near fusion line "S sec" is presented strictly by the following experimental formula,
S=(60El/v)^{(2.48-0.055t)}/1.84×(10^9-0.228t){1+2/π tan^-1(t-12/3)}
where E: arc voltage, Volt
I: welding current, Amp.
v: proceeding rate of bead, cm/min
t: plate thickness, mm.
The diagram calculatedy this strict formula is shown in Fig. 13. Next the simple formula is as follows,
S=(60El/v)^1.7/1.18×10⁶{1+2/π tan^-1(t-12/3)}
The nomograph of this simple formula is shown Fig. 10. For obtaining the rough values, this nomograph of the simple formula can be used practically. Moreover, the author mentioned for submerged arc welding process that the cooling time from 800°C to 500°C near fusion line has close relation with the maximum hardness affected zone by welding.

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1. Cooling times in case of manual arc welding process with covered electrodes, generally, are remarkably smaller than those of three welding processes, namely, submerged arc welding process, C.S. arc welding process and argon arc welding process.
2. A cooling time in case of C.S. arc welding process is nearly equal to those of argon arc welding process, if the same arc energies per unit bead length and the same thickness of base plate are adopted in both cases.
3. Cooling times in case of submerged arc welding process differ slightly from those of C.S. arc welding process or argon arc welding process, and the differences are due to plate thickness and arc energy per unit bead length.
4. The cooling time S is proportional to J=(60EI/v)ⁿ, and the value of n changes according to the plate thickness generally, and decreases with increase of the plate thickness. This tendency was confirmed experimentally and theoritically.

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Carbon dio ide and oxygen, each of which is compressed and charged into two separate cylinder added intentionally enough free water (1 litre), were prepared. Dew points of flowing gases from these cylinders were continuously measured by a photoelectric tube type dew-pointmeter. It was recognized that the relations between dew point of flowing gas and pressure of residual gas in each cylinder are the same as the cases of carbon dioxide out of the specification of JIS and an ordinary oxygen reported previously. And these relations are discussed. The results of calculation about these relations agreed with the results of measurement of actual gases.
From the results of the calculation, it was deduced that a elevation of temperature of a cylinder, an increment of pressure of flowing gas considerably and a drop of temperature of flowing gas slightly elevate a dew point of flowing gas.
Hydrogen content of weld deposited by the carbon dioxide-Sekiguchi's filler wire-arc welding, i. e., CO₂-O₂ arc welding using carbon dioxide and oxygen in two separate cylinders with free water increases as the pressure in the cylinder decreases and temperature of supplied gas increases.

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To investgate the difference in crack sensitivity, the Crack-Starter Impact Bend Test was applied to fourteen steels consisting of two high tensile, and ten mild steels, namely four killed, three semi-killed, and three rimmed steels.
The high tensile steels showed the best result, being followed by in the order of killed, semi-killed and rimmed steels.
The 2kg-m/cm² transition temperature in this test was found to have linear corelation with the 15 ft-lb transition temperature in standard V Charpy test. And the fracture of Charpy test specimen at the temperature of 2kg-m/cm² transition in this test showed larger crystallinity than 85 percent.
Particulars were given on initiation and propagation of crack in some steels and fractures of twice blow test were observed.

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