Oxygen in weld metal is one of the causes of porosity during solidification and afect the mecha-nical properties of weld metal forming oxide inclusions in the solidified weld metal. In theprevious reports, the authors investigated the shapes, compositions and formation process of oxide inclusions in mild steel weld metals. In this report, oxygen contents in mild steel weld metals, deoxidation ability of coating fluxes and slag-metal interactions during weld process are investigated.
Oxygen content in weld metal is afected mainly by the chemical compositions of coating flux, because the composition of core wire is almost difinite. The author proposes the value of 'deoxidation tendency' (R₁-1/2R₂-A) calculated from the contents of deoxidizers, organic matters andoxidizers in coating flux. The relation between deoxidation tendency of flux and [O] in weld metal is as follows: on the cases of the same coating type electrodes using Fe-Mn as deoxidizer, the results are stand in a curve and on the case of basic type (low hydrogen type) electrodes using Fe-Mn, Fe-Si and Fe-Mn-Fe-Si as deoxidizer, the results are stand in a curve. These results prove the utility of 'deoxidation ten-dency'. It is shown that, the reaction of Mn-deoxidation (onthe cases of every type of electrode) and Si-deoxidation (on the case of bafic types electrodeonly) are seemed a rapid one and organic matters act as deoxidizer equal to Fe-Mn or Fe-Si.
On the other hand, oxygen content in molten metal is affected the composition of slag. Relation between [O] in weld metal and (FeO) in slag shows two lines, one is on the case of basic type (lowhydragen type) and the other is on the acidic types (several types except low hydrogen). These results show that, reaction of (FeO)=[Fe]+[O] is a rapid one during weld process. Distribution of Mn between weld metal and slag shows two lines, on the cases of acidic and basic types. It is shown that the reaction of (FeO)+[Mn]=[Fe]+ (MnO) is a rapid one during weld process. But distribution of Si between weld metal and slag is not shows a line on the case of acidic type and is showd a line on basic type. From these results, it is, shown that the reaction of 2(FeO)+[Si]=2[Fe]+(SiO₂) is a rapid one only on the case of basic type electrode.

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The arc length was rapidly changed in progress of welding. Thereby, the self-regulation of arc was investigated by means of the high speed motion pictures. Then effects of characteristic of welder, current value and arc length upon the self-regulation were studied.

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For three usual mild steels of tensile strengths 35, 42 and 49 kg/mm² and two high tensile steels of tensile strengths 51 and 54kg/mm², differed from the steels in the former reports 1-4, the non-notch bending test and tensile test were performed. Then the results of these tests were considered relating to the continuous cooling transformation diagram of each steel. The summary is as follows;
(1) According to the non-notch bending tests of the steels as received, the steel which has a higher tensile strength, has generally the larger absorbed energy. All angles bended by impact and slow bending were 180°, and the every specimen was not fractured.
(2) For the steels KS (49kg/mm²), YD (51kg/mm²) and YE (54kg/mm²), the bended angle becomes smaller in cases of specimens cooled with shorter cooling time than about C_f. For the steel SS (42kg/mm²), the bended angle becomes smaller below about C_p' critical cooling time (about 2 sec) already.
(3) Comparison of the cooling times at which the bended angle, the reduction of area and the elongation begin to lower is generally as follows. That of bended angle is shortest, that of reduction of area is intermediate and that of elongation is longest.
(4) It was understood from the relation between the chemical anlyses and results of the non-notch bending tests on steels that the carbon content is desired to be lower to than about 0.13%.

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On stellite surfacing by Oxy-acetylene flame, in order to obtain a uniform hardness distribution on stellite bead, some factors should be considered. Carbon content of stellite.bead is one of these factors, and influence the hardness greatly. Carbon content is a function of gas mixing ratio, O2/C2H2. So, gas mixing ratio should be well controlled.
On this view point, the relation between hardness and gas mixing ratio, O₂/C₂H₂, was studied. The results were as follows ;
(1) Marked increase in hardness of stellite bead was obtained by slight in crease in carbon content.
(2) A certain relation between gas mixing ratio and carbon content was observed.

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In our yard the stack cutting has been widely used in hull construction, especially in cutting structural members of identical pattern in cargo-oil tank compartment ordinarily up to 1/2 in. in thickness. For the success of this process the elimination of gap between stacked plates is most essntial. The authors investigated the effects of the gap on the cutting action and smoothness of the cut surface. In addition, the effectiveness of acetylene and propane gases which are commonly used for preheating were compared. The results showed that a gap located near the top or the bottom of the stack is permissible for securing a good surface if it does not exceed 0.2mm or so in extent. However, a gap located near the middle is detrimental even if it amounts to 0.2mm or less. It was also found that the cutting action by using propane is generally less active than that using acetylene, but in some cases of stack cutting the former is equivalent to or even higher than the latter.
In actual practice C-clamps and hydraulic clamping devices are used for the elimination of gaps. Motor-driven rail gided straight-line cutting machines and shape-cutting machines equiped with magnetic tracer and steel template are fully employed for obtaining accurate and smooth contour of cuts.
The use of stack ctting is largely a matter of economics. As compared with the ordinary cutting, the expense for gas consumption is slightly higher, but labour hours in marking, material handling and cutting are considerably less, and consequently the total cost may be reduced to a great extent.

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Welding conditions of 2 1/4Cr-lMo steel have been repored in previous report. This steel has been used at high temperature and high pressure as parts of steam boiler.
The study herein introduced was carried out to clarify the effect of post heat treatments on the creep rupture strength of 2 1/4 Cr-1Mo steel welded joints. Test pieces were prepared from welded joint and base metal which were treated with various post heat conditions. Creep rupture test was carried out at 600°C and 550°C by the multiple type rupture tester with six stations.
The results were summarised as follows :
(1) Specimens of welded joint, post heated at 680°C, 720°C and 760°C, fractured at base metal in creep rupture and tensile tests, however specimens, post-heated at 920°C, fractured at welded metal.
(2) Specimen, post-heated at 720°C for 1hour, showed the best creep rupture properties among the welded joints.
(3) Creep rupture strength of base metal decreased by post-heat treatments, but the decreasing at 720°C is less than it at 760°C.

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Experiments have been carried out by the authors to dissolve the coherent mechanism of lead on iron and steel surfaces called "lead homogen lining" in the practice. The conclusions which are introduced from experiment are as follows. For the purpose of deposition, metallic salts have to be used as a flux. The necessary properties of metallic salts used as a flux are following ;
(1) By its action, molten lead wets steel surface at acute contact angle.
(2) It prevents the oxidation of molten lead.
(3) As soon as the flux spread on steel surface, the component in it was reduced to metal electro-chemically. The metal which was reduced in the flux deposited on steel surface.
(4) Its metal easily alloys with iron under the temperature of 300°C.
In consequence, deposited metal from flux alloys with iron and lead cohere to new alloy layer turning out on steel surface. If lead wets iron surface and flux prevents oxidation alone, lead merely unites to steel surface mechanically.

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