Masayuki Inuzuka

Electrical conductivity of plasma-sprayed titanium oxide (rutile) coatings

Abstract Plasma spraying has been used to prepare n-type polycrystalline TiO2 coatings on SUS304 steel substrates. The influence of plasma spray process on the phases (corundum type Ti2O3, monoclinic Ti3O5, triclinic magneli phases, and tetragonal rutile) formed and the relation between deoxidation and the electrical conductivity of plasma-sprayed TiO2 coatings have been studied. The amount of oxygen loss in the plasma-sprayed TiO2 coatings is influenced greatly by the addition of hydrogen in the plasma gas. Accordingly, the electrical conductivity of TiO2 coatings increases with decreasing oxygen during plasma spraying. The amount of reduced TiO2 coating increases with a drop in pressure of the plasma spray atmosphere and an increase in the quantity of hydrogen. The amounte of Ti2O3 and Ti3O5 phases formed by plasma spraying increase with the deoxidation of TiO2 coatings.

Development of Friction Spot Joining

This paper describes the fundamental procedure and joint properties of Friction Spot Joining (FSJ), a new spot welding method for aluminium and other light metal alloys. The process uses frictional heat between a joining tool and work piece as the heat source, and produces a solid phase joining by causing plastic flow of the material. Technological essences of the process including the joining tool, a prototypic FSJ equipment, and process parameters were first fundamentally established. Consequently, based on those results, FSJ systems for practical use have been produced. Furthermore, various properties of the friction spot joint including metallurgical structure, hardness distribution, and tensile strength were investigated.

All-position continuous electron beam welding of horizontally fixed heavy-section pipes. Study of all-position electron beam welding of large-diameter pipeline joints (2nd Report)

The application of all-position electron beam welding has been previously investigated as a means of substantially increasing the speed of on-site welding of large-diameter, heavy-section steel pipes used in natural gas pipelines. In this context, the results of an investigation to determine the relationship between the welding conditions and the weld bead shape during full-penetration welding experiments of 19 mm thick API 5L-X65 pipes in eight typical welding positions by the method of the electron gun being fixed and the pipe rotated have also been reported. Despite showing that the weld bead shape tends to vary depending on the welding position, the experimental results indicate good scope available for all-position electron beam welding through the range of welding conditions being appropriately determined in each welding position case. Based on these results, this paper describes an investigation of all-position continuous electron beam welding of circumferential pipe joints through the sample pipes being horizontally fixed and the electron gun being positioned inside the pipe parts and rotated in the vertical plane. The paper also examines the effects on weld bead quality of poor groove accuracy (gap width, mismatch) as a problem likely to affect electron beam welding.

Mechanical Properties and Fracture Toughness of Aluminum Vessels by Friction Stir Welding

Mechanical properties and fracture toughness in friction stir welded joint of vessels of structural aluminum alloy type A5083-O are investigated. Welded joint from 25 mm-thick plate is fabricated by one-side one-pass friction stir. Charpy impact energy and critical crack-tip opening displacement (CTOD) in friction stir weld are much higher than those of base metal or heat-affected zone, whereas mechanical properties such as stress-strain curve and Vickers hardness do not have a conspicuous difference. Effects of microstructure on crack initiation and propagation are studied in order to clarify the difference of fracture toughness between stir zone and base metal. Both tensile test and bending test show that the fine-grained microstructure in stir zone induces to increase ductile crack initiation and propagation resistance by analyzing fracture resistance curves and diameter of dimples in fracture surface. It is found that high fracture toughness value in stir zone is affected fine-grained microstructure by friction stirring.Copyright

Effects of impurity elements on solidification cracking in electron beam welding of pipeline steel. Study of all‐position electron beam welding of large diameter pipeline joints (3rd report)

Introduction The first report and the second report in this series describe fundamental investigations into the application of all-position electron beam welding for on-site production of natural gas pipeline joints, considering selection of suitable electron beam welding conditions for API 5LX65 steel pipes with a plate thickness of 19 mm and an outside diameter of 762 mm and showing that all-position continuous electron beam welding can be successfully performed over the pipe circumference as a whole with assurance of a sound bead shape. Sivry et al, however, report the occurrence of longitudinal cracking at the weld metal centre as an important problem facing electron beam welding of steel pipelines. The solidification pattern of the molten metal strongly affects the occurrence of longitudinal cracking. In addressing this problem, Arata et al report that the phenomenon of solidification delay having some specific period progresses in the plate thickness direction without the solidification interface during electron beam welding having any constant shape. Tsukamoto et al also consider the factors affecting the occurrence of solidification delay and show it to be due to secondary melting of weld metal accumulating inside the beam keyhole. Tamura et al, Shida et al >9 and Tanaka et al ° further show that the phenomenon of solidification delay occurring over the plate thickness behind the molten pool induces longitudinal cracking with the same sinkhole morphology as that found in castings. To prevent longitudinal cracking, it is shown to be effective to avoid the beam focusing conditions of upfocusing (where the focal point is located above the plate surface), since such conditions lead to the penetration cross sectional shape bulging at the centre and a large volume of weld metal stagnating inside. During allposition welding of horizontally fixed pipes of the type treated in the present report, however, it is never possible from the perspective of optimising the weld bead shape as described in the previous reports, to adopt suitable beam focusing conditions for longitudinal cracking prevention. That is to say, to prevent underfills on the back bead in for example the overhead position, it is necessary to use a welding beam with upfocusing, which amplifies the possibility of longitudinal cracking. As a viable method for stable prevention of longitudinal cracking under such constraints, consideration has been given to optimisation of the chemical composition of the work material being welded, most particularly to a reduction of the impurity elements. A handful of previous papers examine the relationship between hot cracking and material components during electron beam welding of austenitic stainless steel. Uratani et al examine the relationship between impurity components and hot cracking during electron beam welding of heavy-gauge 304 and 316 stainless steel plates and report that hot cracking can be prevented through the (P + S) content being kept under 0.045%. Nakao et al report the experimental results of a study intended to improve the hot-cracking susceptibility of fully austenitised SUS316 steel by the addition of rare earth metal. For ferritic steels, Shida et al 3 investigate the tendency of weld cracking to occur in a large number of commercial steel grades and reinforcing weld metals, reporting that melting and solidification phenomena are more likely to be disturbed and longitudinal cracking to occur more readily with increasing C and O concentrations in the steel material. Matsuda et al also state that, to prevent hot cracking in the nailhead zone in heavy-gauge carbon steel and Cr-Mo steel plates, it is necessary to keep the (P + S) content under 0.03%. Within the context of these data, the present research study describes a quantitative investigation of the relationship between the welding conditions, hot cracking (longitudinal cracking) and a number of impurity elements contained in a sample low-C steel pipe material for pipeline applications, its purpose being to clarify the raw material constitution effective for prevention of cracking during all-position electron beam welding.

Relationship between welding position and proper welding parameters in all position electron beam welding. Study on all position electron beam welding of large diameter pipeline joints (1st Report)

The use of natural gas, as an environmentally friendly clean energy source, has been increasing and trends for the construction of large diameter (more than 500 mm) high-pressure gas line pipes for the conveyance of natural gas over long distances have finally begun in our country.* Shielded metal arc welding was initially employed for pipeline on-site construction welding, but highly efficient fabrication employing automatic MAG welding using multiple torches has been attempted in recent years. However, there is an inevitable restriction in welding fabrication efficiency with arc welding in its present form. For example, for welding high-pressure large diameter pipe of calibre 750 A and wall thickness approximately 20 mm, more than 1 hr or so of arc time is said to be required even using the latest MAG welding techniques. Consequently, there is a firm requirement for a substantial improvement of welding efficiency by means of innovative new techniques in order to construct large scale pipeline networks in the future. Consequently, the authors decided to carry out a fundamental investigation into the feasibility of the application of electron beam welding to high-speed, single pass welding fabrication of thick plate for on-site welding of such pipelines. If single pass root bead (uranami) welding became practicable using electron beam techniques, it would be feasible to reduce the welding time to several minutes for high-pressure large diameter pipe described above. Already there is a report* on the application of electron beam welding to natural gas pipelines. This concerned ocean floor pipeline construction by the TOTAL Co. However, in this case, the pipes were perpendicularly supported and welding was carried out in the horizontal position using an electron beam gun travelling around the outer pipe circumference. As an investigation into the application of local vacuum type electron beam welding to pipeline joints, Kita and others have reported on circumferential welding using a small electron beam gun installed within a pipe. For the investigation described in this paper, the electron beam gun was fixed either in a flat or a vertical position and circumferential welding was carried out while the pipes were rotated. In this regard, the investigation by the authors concerned a circumferential weld line within the vertical surface of the pipes fixed together horizontally and continuously welded throughout all positions at a pipeline construction site. For this type of welding, Kuroda introduced a method for approximately 10 mm thick line steel pipes such that a small electron beam gun travels around outside the pipe. However, there is no detailed report available concerning the procedural conditions. In addition, Mori has reported the fundamental results of an investigation for the application of the same type of welding to thin-walled, stainless steel pipes, but the application to large diameter thick-walled steel line pipes is difficult. As described above, it is hard to say that there has been a sufficiently detailed investigation from the aspect of the procedural conditions, under present day circumstances, concerning the application of electron beam welding to natural gas pipeline on-site construction. Accordingly, electron beam welding trials were carried out for high tensile strength steel pipes of wall thickness 19 mm and calibre 750 A for a pipeline in a number of typical welding positions with the primary aim of verifying the feasibility of all position electron beam welding of thick walled large diameter pipes. The results of the investigation into the relationship between the welding parameters and the weld bead formation for each welding position are reported.