The crack sensitivity of underwater welded joints of mild steel in various thickness was experimentally investigated by CTS and Y-groove cracking tests in shallow water, using coated electrodes.
From these experiments the following results were obtained:
1) Cracks in heat affected zone of CTS and Y-groove cracking test specimens increased with decrease of plate thickness.
2) Cooling rate and maximum hardness of welds of CTS and Y-groove cracking test specimens increased with decrease of plate thickness.
3) The reason of increase of cooling rate of underwater welds with decrease of plate thickness was explained by a calculation by a considering heat transfer coefficient from surface of welds into water.
4) Diffusible hydrogen content of underwater deposited metals was about 41.5-43.7 cc/100 g.

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From the standpoint of welding application, effects of cooling characteristic on metallurgical and mechanical properties of weld metals were examined in underwater wet plasma welding (melt run in flat position) in pressurized city water.
The test welding were carried out at ambient water pressure from 0.04 kgf/cm² to 30 kgf/cm² using 19 mm thick JIS-SM41A steel plate as the base metal, and, the welding conditions were employed under which the weld metal having an excellent appearance and being free from blow-hole was produced by melt run.
The main results obtained in this study are summarized as follows.
(1) Cooling below 800°C at each water pressure is rapid in comparison with that in air. And, cooling time tends to reduce up to 10 kgf/cm² in ambient water pressure, while it has increasing tendency over that water pressure.
(2) Effect of arc current on cooling characteristic is stronger than that of plasma gas flow rate.
(3) Structure of weld metal becomes clearly different with the increase in water pressure up to 10 kgf/cm², however, it is difficult to distinguish the difference between them at above that water pressure.
(4) Hardness of weld metals have an increasing tendency up to 10 kgf/cm², however, no difference in them is recognized at above that water pressure. Meanwhile, maximum hardness of HAZ is more than Hv 300 at each water pressure.

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This paper reports our study of the mechanical properties of austenitic stainless steel SUS3 04 of friction welded joint at elevated temperature.
Tension test and creep rupture test were carried out from room temperature to 700°C fatigue test was carried out at 600°C.
Main experimental results are as follows;
(1) Tensile strength of friction welded joint shows almost equal to that of base metal, but reduction of area and elongation of friction welded joint are reduced a little.
(2) Creep rupture stress of friction welded joint shows slightly smaller value compared with that of base metal, and this difference increases with testing temperature.
(3) Fatigue stress of friction welded joint is close to that of base metal at testing condition of 600°C and 1.0 × 10⁷ cycle. Coaxing effect is observed at friction welded joint.

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Nucleation and growth of a blow hole during the solidification of molten metal were discussed in the light of the newly proposed 'solidification theory' by the author.
The results obtained were as follows:
(1) The gas evolves through the protruding gas bubble surface, and its volumetric velocity per unit area w as compared with the solidification speed v determines the direction of growth of the blow hole inside wall. In the case of v/w=2, the resulting blow hole is cylindrical.
(2) It was deduced that the nucleation of a gas bubble occurs in the solute enriched zone on the solidifying interface, and that the blow hole enlarges rapidly to the thickness of the zone and then grows according to v/w in the bulk molten metal.
(3) Starting from the spherical bubble nucleus, various blow hole contours may be formed according to the variou values of v/w. In case that solidification angle ψ is smaller than liquid phase angle θ, the blow hole becomes a little shorter.
(4) 'Bubbling type' blow hole contour was reproduced well by means of the new theory.
(5) It was considered that the diameter of the cylindrical blow hole can not exceed a certain maximum value depending on the surface tension and density of the liquid concerned.

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Creep tests on circumferentially TIG-welded Hastelloy x cylinders were carried out under internal pressure for the investigation of structural behavior of welded components in high temperature enviror. ment. The creep rupture strength of TIG-welded cylinders was much lower than that of non-welded cylinders, while such reduction was not found in uniaxial creep tests on TIG-welded bars. It was deduced that the reduction was due to the low ductility (ranging from 1 to 5 %) of the weld metal to which enhanced creep was induced by the adjacent base metal whose creep strain rate was much higher than that of the weld metal. Therefore, uniaxial creep tests on bar specimens is not sufficient for proper assessment of the creep rupture strength of welded components. Both creep strain rate and creep ductility should be concerned for the assessment. Creep tests by using components such as cylinder under internalpressure are recommendable for the confirmation of creep strength of welded structures and components.

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This paper presents some experimental data concerning the effects of SUS308L stainless steel filler and/or A5183 aluminum alloy filler on 0.2 % carbon sintered steel welds and SUS304L stainless sintered steel welds by electron beam maintaining heat input per unit length constant. As the results, we can clearly observe that porosity formation was reduced owing to the deoxydizing action of chromium or aluminum at the welded joint. In addition, it was found that use of low welding speed was important in attaining porosityfree welds even if the filler metal was used.
In case of SUS304L stainless sintered steel weld, the porosity formation was not reduced by aluminum alloy filler metal and the necklace crack, a kind of cold shuts, were observed under the special welding condition. X-ray micro-analyser was used to detect chromium and nickel trace which were contained in SUS308L stainless steel filler at the fused area of sintered steel.

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The development of three wires submerged arc welding techniques was carried out to produce line-pipes in the large diameter and heavy-wall-thickness from 20 to 50 mm by UOE process. Some con-siderations on the polarity or the phase of the transformer connections, the stream of a molten metal, the deposition rate and the flux consumption were studied to clarify the following.
(1) A leading arc is directly occurred at a base metal and shows the gouging action. An arc voltage fluctuation of a leading arc is most stable in three wires. The molten metal is pushed out backward by a plasma and a magnetic force around a leading arc. The middle arc makes the stream of a molten metal slow down due to the collision against a leading stream, and the stream is changed to the transverse direction of bead to extend the bead width. An arc voltage fluctuation of middle arc is larger than others. An action of trail arc is to form a good bead appearance without an undercut. An arc voltage fluctuation of trail arc exists between a leading and a middle one.
(2) The fluctuation of an arc voltage and the deflection angle of DC leading arc in a transformer con-nection of DC-AC-AC are bigger than those of the AC-AC-AC connection. A leading arc in the Scott connection between a leading and a middle wire is apt to incline toward a middle arc and encourages the backward stream of a molten metal, so that the bead toe results the wavy shape. A leading arc in the reverse V connection between a leading and a middle arc is apt to incline forward to relieve the back-ward stream of a molten metal, so that this connection is suited to be applied to a high current and/or a high heat input welding. (3) A deposition rate of wire is proportional to the sum of three wire's current, and independent on the kind of fluxes. A cross sectional area and a flux consumption are directly proportional to the heat input.

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In copper brazing of iron to chromium, cobalt and nickel, the dissolution and deposit of base metal takes place at both base metal-molten filler metal interfaces owing to the narrow joint clearance and the deposited phases of solid solution consisting of both base metals grow at those interfaces with heating time at a constant brazing temperature.
In case of chromium, cobalt and nickel, the deposited phases are (α-Fe, Cr), (γ-Fe, α-Co) and γ(γ-Fe, Ni) respectively. This phenomenon should be observed in the dissimilar brazing where both base metals dissolve into the molten filler metal within a few percent and form a solid solution over a wide con-stituent range at a brazing temperature.

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There are many metallurgical and dynamical factors which influence initiation of cold cracking at weld joints. However, when welding conditions are specified, the initiation of cold cracking may be predicted by the stress and strain induced at a point where the initiation is expected. In this respect, the stress and strain are the important information to prevent cold cracking from the dynamical point of view.
When a welded joint is simple such as of one dimensional constraint state, the restraint stress of a weld joint can be estimated with a fairly good accuracy by the conventional concept of restraint intensity. On the other hand, restraint stresses and strains of two dimensional constraint state are produced by not only shrinkage of weld metal but also thermal deformation of the plate. In this reason, it is difficult to predict them simply from the geometric configuration of a joint without considering this thermal deformation.
In this paper, thermal elastic-plastic behaviors in a slit type welded joint is idealized and an analytical calculation method for the stresses and strains is developed. And, it is shown that the restraint stresses and strains in any size of slit joints can be calculated simply by this method.

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The effects of welding parameters on the penetration in submerged-arc welding were investigated for the purpose of regulating weld bead dimensions.
Main results obtained as follows.
1) In case of the open arc, the penetration depth can be regulated in a wide range by controlling welding current and welding speed, and the width by controlling arc voltage and welding speed.
2) In case of the buried arc, on the other hand, the penetration depth can be regulated freely by controlling welding current and welding speed, while the range of regulating the width is rather narrow in the wide range of welding parameters.

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