The corrosion properties and the mechanical properties of brazing alloy and brazed butt joints are equally important problems that have to be made clear. In brazing, the joints are jointed with different metals to a base metal. Consequently, the corrosion properties of a brazed joint become a very important thing. It is said that the corrosion properties of copper-phosphorus brazed joints are good. However, very little is definitely known about these properties through reasearch. In this study, the corrosion properties of a copper-phosphorus brazing alloy and a brazed joint with the same alloys are examined both in a normal chemical solution and in an ammonium sulfid gas atomosphere. The results obtained are as follows: 1) The corrosion in copper-hosphorus brazing alloys increases in proportion to the amount of phosphorus added to the brazing alloys. (in roome temperature) When oxygen (30cc/min.) is added to the corrosion atmosphere ((NH4)2S-Gas), the corrosion rate increased ten times. Also when the temperature of the test chamber is increased to 70°C the corrosion rate becomes five or seven times greater than the room temperature. Two cylindrical copper brazed butt joints, joined together by a copper-phsphorus brazing alloy, were placed in a test chamber atmosphere filled with (NH4)2S gas. The brazed joints were attached to the wall of the chamber and a weight (3Kg/mm2) was hung from the free side of the brazed joint. This lasted for a period of 100 days. At the end of the 100 days, it was found that the outlayer surfaces of the two cylindrical copper brazed butt joints, attached directly to the phosphorus brazing alloy, were beginning to corrode. 2) The corrosion rate of a copper-phosphours brazing alloy in a chemical solution of HNO3 is the fastest. After this solution the following chemical solutions in this order have the fastest corrosion rate, namely chemical solution of NH4OH; (NH4)2S; HCl and H2SO4. Aside from the corrosion effect of HCl and H2SO4 solution s an pitting corrosion was also observed on the brazing alloy surface. This pitting corrosion was found to be in the α-phase. 3) Two cylindrical copper brazed butt joints, joined together as above by a phosphorus brazing alloy, were placed in separate chemical solutions of HCI, NHO3 and NH4OH for 30 days. After 30 days the cylindrical joints were taken out of each of these solutions and the strength of each was tested by a tension test. It was found that the cylindrical brazed joint in the chemical solution of NH4OH was the weakest followed by joints in HCI and NHO3 chemical solutions respectively. The brazed joint was 1/3 dgree weaker than it was prior to placing in that solution.
Bead-on-plate welding was performed on thin sheets of 99.96%-, 1050- and 1100- aluminum. Then, the microsegreagation was investigated in the weld metal of these materials with the aid of electron probe microanalyser. Morevoer, distribution of dislocations and compounds in the weld mead were examined by means of electorn microscope. Main conclusions obtained are as follows: 1) Compounds of Al3Fe and AlFeSi were observed in the weld metal of 1050-aluminum. 2) It was observed that Fe segregated in boundaries of subgrains. This was due to the phenomenon that compounds mentioned in (1) were developed in subboundaries. 3) Content of compounds in boundaries of columnar grains was almost the same as in boundaries of subgrains. 4) Boundaries of subgrains observed in 99.96%-aluminum consisted of dislocations parallel to the growth direction and tangled dislocations. In this case compounds were not observed. 5) There existed compounds in boundaries of subgrains in the weld metal of commercially pure aluminum and dislocations tangled in the compounds. Besides, some boundaries consisted only of dislocations.
In order to study the mechanism of hot cracking in aluminum alloys, the characteristics of brittle range existing behind the molten pool are investigated experimentally by using special tension executed soon after the welding. As to the characteristics of brittle range in weld metal, length, temperature range and minimum quantity of deformation necessary for a real rupture are examined. It is observed in the tention test of the specimen that there is a region rupturing with a small quantity of deformation and it exists in weld bead behind molten pool. Furthermore, it is confirmed experimentally that length of brittle range along the welding direction depends on heat input, welding speed, kinds of material, but not tension velocity with the range of 0.5, 12 mm/sec and not quantity of deformation. Temperature range of brittle range is determined by cooling curve at a certain point in weld bead and the length of brittle range. By this method, it is clarified that this value depends on kinds of material, but not welding condition and tensile velocity. Minimum quantity of deformation necessary for cracking (Δl) with no influence on expansion or contraction of specimen due to welding heat is measured by the method as shown in Fig. 14. It is clarified by above method that minimum deformation (Δl) is influenced by welding condition, tensile velocity and kinds of material, and is a very small value of 0.05-0.01 mm for high velocity welding bead and 0.10-0.05 mm for low velocity.
In the submerged arc welding of HT-80 steels, it has been the subject of intensive study to increase the toughness of the weld metal without decreasing the strength of it for long years. The relationship between the composition of flux and the toughness of the weld metal has been studied in this investigation. In addition, in order to make clear the cause of embrittlement occurring in the weld metal by stress relief treatment, X-ray diffraction analysis and electron microscopic observation on carbides precipitated in the weld metal have been carried out. This paper shows that the combination of highly basic agglomerated flux and the wire containing adequate amounts of manganese and silicon can yield weld metal with high toughness and stress relief embrittlement can be prevented by the chemical composition of weld metal. The main results obtained are as follows; (1) In order to increase the toughness of the weld metal, it is effective to decrease oxygen in the weld metal and for it to increase the basicity of slag. (2) Particular range of manganese to silicon which yields highly tough weld metal exists only in the weld metal produced by highly basic flux. (3) Stress relief embrittlement may occur at temperatures from 350 to 300°C during cooling process. (4) The main reason of stress relief embrittlement is considered to be precipitation of complex molybdenum-carbides. (5) Stress relief embrittlement can be prevented by the selection of contents of C, Cr and Mo in the weld metal.
Conventional sewing process has been one of the hindrances in development of textile gathering materials as industrial materials. Synthetic fiber, most of which are of thermo-polymer, has made startling progress recently; hence there is a possibility that the conventional cutting and sewing processes are replaced with melt-cutting and welding processes. This report treats weldability and comments on microstructure and macroproperties of the weld achieved by ultrasonic welding method on flat woven cloth of 6-nylon as textile gathering materials, whose fineness was represented by 912 denier warps and 895 denier woofs, while density was 28 warps and 29 woofs per inch. In other words, (i) relationship between welding conditions (welding pressure, ultrasonic acting time) and strength of the weld; (ii) relationship between shape of the weld (shape of anvil) and welding joint strength; (iii) relationship between heat effect by X-ray diffraction and change in microstructure of the nylon woven cloth; and (iv) change in structure of woven cloth at the section of the weld, as observed by microscope are discussed in the report, and possibility of weld of textile gathering materials is looked for. The following summary can be made from the results of the present experiments. The possibility seems to have been found out to weld the nylon cloth, maintaining the properties as fiber and, obtaining necessary. The weld done with the type V anvil has stable structure and higher strength at the place of the weld.
A short-time creep rupture test has been carried out on the synthetic weld HAZ specimen in a 80 kg/mm2 high strength steel. An effect of weld thermal cycle is investigated and there is some discussion with the results of the fractographic study on the fracture surface. In this study, to observe the creep rupture tendency of specimens especially during heating, a tensile loading is started at the beginning of heating. First, rupture strength and creep time to rupture of the coarse-grained HAZ specimens of 1, 380°C peak temperature are both lowered with increasing testing temperature, while the elongation to failure is improved distinguishly. In comparison with the effect of cooling rate from 1, 380°C peak temperature, rupture strength and time to rupture are lowered in a rapid cooling than in a slow cooling. Second, the results on the effect of which varied the peak temperatures showed that rupture strength, time and elongation to rupture are increased remarkably with decreasing peak temperature. From the results of the effect of second thermal cycle after being 1, 380°C peak temperature, creep rupture properties of the reproduced HAZ are improved conspicuously in case of 900°C second peak temperature, but did not be affected in the least in case of 600°C. In the fractographic study, it was found that an intergranular brittle fracture was mainly observed when tested below 700°C, and on the other hand, an intergranular ductile fracture above it. However, the fracture surface is almost affected to the original austenite grain boundary produced by a first thermal cycle regardless of brittle or ductile fracture. According to the prolonged heating time, rupture stress was decreased markedly with increasing heating time in higher stress conditions, and when a heating time was increased extremely, some specimen was broken during heating before reaching to the fixed temperature.
In Report 1 of this study, the authors showed that grain growth during thermal cycles can be calculated using the grain growth equation during isothermal heating. It is considered that weld thermal cycles consist of heating cycle, isothermal holding and cooling cycle. Therefore, in this report, grain growth during these cycles under various conditions was examined using commercial-purity nickel. The effect of the initial grain size (the grain size before the thermal cycle) on grain growth during thermal cycles was also examined. It was found that the method to estimate the grain size during linear thermal cycles could be obtained, giving the level of initial grain size. Results obtained are as follows; 1) Grain growth during heating cycle, isothermal holding and cooling cycle under various conditions can be calculated using the method proposed in the Report 1 of this study. 2) Grain growth during various thermal cycles are as shown in Figs. 2, 4 and 6. 3) The effect of initial grain size on grain size after thermal cycles varies according to the condition of the thermal cycles, as shown in Fig. 10. 4) The effect of multiple thermal cycle on the grain size can be calculated as shown in Fig. 12. 5) If the condition of thermal cycle is given and the thermal cycle can be considered as a linear form at near the peak temperature, grain size after this thermal cycle can be obtained using Figs. 13, 14 and 15.