With the demand for the increasingly large capacity of machines and equipment, structural dimensions are growing large, and design stress is becoming higher eventually. This naturally necessitates the use of high-strength steel possessing high tensile strength and high toughness. Although mild steel is generally adopted for welded structures, it needs an exceedingly large gauge to give sufficient strength and involves difficulties in building up welded structures. In this report an examination was conducted on the effects of intensity of restraint, restraint stress, and the groove shape influencing delayed cracks during manual are welding on 80 kg/mm2 high-strength steel. A summary of the results of this research is as follows. (1) It was clarified in single bevel groove and H-type restraint cracking tests that the values of critical intensity of restraint KCr for preventing weld cracks at various preheat temperatures were as follows: KCr≅1700 kg/mm.mm for 50°C preheating KCr≅1900 kg/mm.mm for 100°C preheating KCr≅2500 kg/mm.mm for 150°C preheating Regarding the parcentage of weld cracks in welds, the single bevel groove was nigher than the Y-slit groove in the above value, and materials of high carbon equivalent were also high in the abovo value. (2) Root crack-preventive preheat temperatures for the Y-slit groove (PHY) and single bevel groove (PHK) may be determined respectively by the following equations: PHy≅(1.33Pw-0.38)×103(°C) PHK≅(2.03Pw-0.55)×103(°C) PW=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B+H/60+/40×103
Effect of welding conditions on the mottling that appearing on radiograph of austenitic stainless steel weldments was investigated. the results may be summarized as follows. 1. the mottled appearance is related to the δ ferrite content in the weldment. The mottling is more pronounced when the δ ferrite content is low. It lose its contrast with an increase in content of the δ ferrite and it almost disappeared when the δ ferrite content come up to about 6%. 2. the mottling is more pronounced when travel velocity is lowered, accompanied by a decrease in 6 ferrite content in the weldment. 3. the mottling is more pronounced when a 25:20 filler metal is used instead of a 19:9 filler metal, accompanied by a decrease in δ ferrite content in the weldment. 4. the mottling is more pronounced with an increase in sulfur content in the weldment. 5. the results obtained in this investigation seem to suggest that low density grain boundary containing voids, microfisures or impurities may be important concerning the mechanism of the mottled appearance.
We have proposed the water curtain type underwater CO2 arc welding as a method of underwater welding. With this method we could make nozzle-to-work distance longer than 2-3 times compared with that for conventional underwater CO2 arc welding because of good shielding effects. But, in case of welding with solid wires, welding speed was limited up to 30 cm/min. For the purpose of solution to this trouble, we tried single pass butt welding on mild steel at 0.3 m underwater by using flux cored wires. Results obtained are as follows: 1) At high speed welding 120 cm/min as underwater welding, we succeeded to get good welds without blowholes and cracks. 2) The welds obtained from this method have excellent mechanical properties at bending test and tensile test. 3) Maximum hardness in welds was Hv 300. 4) This method had a weak point of poor visibility in the cause of melting of flux and slag into the water.
The purpose of this paper is to clarify the characteristic of simultaneous two-axis drawing nylon film and seek after the possibilities of welding bond, making use of the property of thermoplastics. Namely molecular chain oriented by simultaneous two-axis drawing is considered to be set at random by welding, which causes a great property change on both weld and heat affected zone, and thus the characteristic of simultaneous two-axis drawing nylon film can be considered to be done away with. The focus of the study, therefore, is to ob-tain the welding conditions without losing the characteristic of simultaneous two-axis drawing nylon film. Welding method used is heating plate welding and suitable conditions are established by studying the in-terrelation among heating plate shape, heating temperature, welding pressure and welding time. Specimen used was simultaneous two-axis drawing 6-nylon film, 0.025 mm in thickness. First, tensile strength and elongation were recorded from tension tests in machine direction (M.D.), transverse direction (T.D.), and a 45-degree angle direction, and microstructure was examined by X-ray diffraction. Specimen used in the tension test was JIS K6475 type-3 dumb-bell type. The suitable voltage for the desired heating temperature is obtained from A.C. 100 V regulated by slidac, and the temperature was measured from heating plate by thermocouple. Welding pressure was applied based on lever principle and was pricked up by compression load cell and then put into tensilon recorder. The pressure was applied quickly, and welding time was recorded just after necessary pressure being obtained. Both up and down sides of specimen surface were covered with 0.18 mm teflon film mixed with glass cloth to make me specimen stick to neither heating plate nor rubber plate. Specimen was preheated just before the experiment in the hot air circulating dryer at 50°C for 25hr. for the sake of getting better conditions. Bubbles born at welding time are thus avoided. Heating plate attached to the welding apparatus is made of copper, and 3 different types in shape are shown in fig. 1. Type I is for peeling the specimen, type 2 is for manufacturing the tensile specimen, type 3 is for inspecting the differences of joint efficiency resuting from the variouss hapes of heating plate. Changes of microstructure caused by influences described above were examined by studying the orientation changes obtained from comparison of diffraction degree of X-ray diffraction photographs taken on plain films, by penetration method. In case of 6-nylon, diffraction patterns of (200) (002) side are observed to be relatively strong. X-ray test conditions are as follows. Voltage:55 KV, electric current:10m A, distance between specimens :28 mm, irradiation time:2 hr, X-ray apparatus: SHIMAZU analysis type X-ray apparatus GX-1. The following conclusion can be made from the results of the present experiments. Welding of simultaneous two-axis drawing nylon film is possible without losing its characteristic, by choosing the proper welding conditions.
As described in the last report, it was known that electroslag welding of cast iron can be exected by use of a cored wire(Fe3C+Fe-Si) and a hollow graphite nozzle. This welding, however, has been somewhat unstable; as one reason for this instability may be mentioned the adoption of commercial flux for mild steel. Since the melting point of castiron is only slightly higher than that of the commercial flux, slag inclusion is liable to happen and the welding results tend to be poor. Thereupon, with mainly the aim to develop a welding flux that can produce a lower temperature fusible slag, several types of flux were prepared; the electroslag welding ofcast iron plates using them were investigated. Meanwhile, the performances of these fluxes were compared by measuring the physical properties, such as viscosity and electric resistance of welding slag. Furthermore, the dynamic behavior of the molten slag during welding was observed by X-ray inspection. Finally there were discribed the results of repair welding practically applied on defects of large machine tool tables using the flux E6 selected from the results in this study.
Nowadays a gas shielded arc welding, i.e.a semi-automatic welding, has been popularized in the metal work industry, but it has a disadvantage with respest to the wind resistance. Under windy condition the growth of defects, for example blow hole and crack, cannot be avoided. In order to eliminate this disadvantage of gas shiedled arc welding, research of the welding nozzle was planned and 3 types of welding nozzles, i.e.A, B and C types, were trial-manufactured. A shows an axial single-shielded nozzle, B an axial dual-shielded nozzle with inner and outer flows and C a wirling vortex shielded nozzle with axial and tangential flows. Experiments were carried out on the distribution ofshielding gas (CO2) velocity, the shape of gas jets and influence of gas flows on welds. Results of the experiments are summarizedas follows: (1) The distribution of the gas velocity in A type nozzel is indicated in a convergent solid pattern and B type bozzle is indicated in a semi-redial pattern. In the latter, the inner flow being a little and the outer flow much, the so-called "saddle type" distribution can certainly be gained. (2) On the shape of gas jet, it is observed that C type nozzle may have all patterns from a convergent solid to a complete radial pattern and this type is estimated to be better for practital welding under windy condition than the other nozzles used. (3) With A type nozzle we have no defects in the welds in the region of gas flow of 70 or 80 1/min concerning the spattering, the shape of bead and the air inclusion.
Effects of S, Mn and P on solidification crack in weld metals of plain crabon steels containing not more than 0.12% carbon and Fe-S-Mn ternary alloys have been investigated by Trans-Varestraint and Modified Trans-Varestraint tests. Further the relation between Mn and S contents to minimize the solidification crack susceptibility has been theoretically deduced, and this relation has been experimentally confirmed. Main conclusions obtained are as follows: 1) Both S and P promote the solidification crack. The effect of P, however, is negligible in comparison with that of S. 2) Mn is an effective element to prevent the detrimental effect of S. 3) Relation between Mn and S contents to minimize the solidification crack susceptibility has been theoretically deduced by combining the changing curve in composition and Fe-(Mn, Fe) S eutectic temperature. This relation is represented as follows; Mn3/S>6.7 This relation is confirmed by Trans-Varestraint test. Brittleness temperature range (BTR) in weld metal which satisfies the above relation is 30-40°C.