The creep rupture strength of TIG-welded Hastelloy X cylinders under internal pressure was remarkable lower than that of non-welded cylinders. In order to improve this strength, tests were performed on the cylinders welded by using various filler wires and welding procedures. The creep rupture strength of these cylinders were, to some extent, improved by using filler wires of Incoloy 800 or Hastelloy X with small boron content. Although the life of cylinders were comparable with that of cylinders without weld joint, several fine cracks were observed on the weld mteal and some of them were penetrated into the wall of the cylinders. The high creep rupture ductility of the weld metal was essential to achieve high reliablity in welded components served at elevated temperatures. The final target of the improvement in creep rupture ductility was discussed.
The correlation between occurrence of weld defects and welding parameters in high-current sub-mnerged-arc welding was studied over the range of 500 to 2000 amp, 25 to 50 volt and 25 to 250 cm/min, and a deep penetration multi-electrode submerged-arc welding process was developed. Main results obtained were as follows; (1) Solidification cracks, undercutting and overlapping were apt to occur in the weld bead made by the buried arc at high-current and low-voltage. (2) To prevent such cracks and undercutting it was effective to improve the solidification mode of weld metal by using a multi-electrode submerged-arc system suitably spacing the electrodes. (3) To prevent such overlapping it was necessary to select adequate groove geometry. (4) The multi-electrode submerged-arc welding process, which was characterized by the buried leading arc and the trailing arc operating as hot-top was able to provide a sound weld bead with deep penetration.
In order to avoid cold cracking in steel welds, a proper selection of welding conditions of heat input, preheat and interpass temperature is required corresponding with the interested plate, joint geometry and consumable. Although cooling rate at 300°C or time to cool 100°C etc. have been considered as the parameters which may be used to estimate the avoidance of cracking, the thermal factor calculated by means of welding thermal cycle and diffusivity coefficient for hydrogen should be more directly concerned as a parameter. From this point of view this paper firstly describes the estimation of the correlation between welding thermal cycles and welding conditions, and then, the effect of welding conditions on the thermal factors both for single root-pass weld by the y-slit test specimen and for the final pass of welds by large size multipass butt joint test specimen. It is found from the investigation that the estimated welding thermal cycles show a coincidence with directly obtained ones and the value of heat transfer coefficient (α) of 7×10-4 cal/cm2⋅ sec⋅ °C is applicable to the temperature range of 300°C through 90°C for single root pass welding. It is also found that the thermal factor is significantly influenced by heat transfer coefficient, and that the thermal factor in multipass butt welding shows the minimum value at the plate thickness of about 100 mm.
This paper describes the wledability for diffusion welding of stainless steel to mild steel. For this purpose, the joint tensile strength and microstructures were investigated. And the effect of insert materials was also examined. The results obtained are as follows. (1) The joint strength depends on the welding temperature and the surface roughness remarkably. The relation between the strength and the surface roughness for the dissimilar joint of stainless steel to mild steel has the same tendency as that of the similar joint between the mild steels. (2) When the joint is welded at about 800°C, chromium carbide is formed at the stainless steel near the joint interface due to carbon migration. If the welding temperature is higher than the sensitizing temperature range, chromium carbide precipitated zone along the joint interface is not formed. (3) To avoid the formation of chromium carbide precipitated zone and decarburized zone due to carbon migration, the insert material, nickel is effective. (4) To increase the weldability of the joint, which surface has been roughly treated, the insert material, silver is useful, when the welding temperature is high.
This paper describes the effects of the pulsation of welding current on the TIG welding arc sound by using a transistor-controlled power source. The arc behavior is observed by using a high-speed movie camera and an oscillograph. Based on the examinations, it is found that the contraction and expansion of arc form is synchronized with the chage of welding current. Therefore, it is possible to estimate the welding arc sound source as a pulsating sphere for sine wave current.
The important factors which affect the result of electromagnetic welding will be i) inductance of coil, ii) clearance between outer tube and core bar, iii) tapered angle of core bar, iv) thickness of core; if a tube is used as a core, v) hardness of outer tube. Each of those factors was examined on some joints made of industrial pure aluminum. The main part of the welding equipment was the capacitor of capacitance of 1, 000μF and proof voltage of 5 kV. The result of welding was expressed by the ratio of welded length to interfacial length along the circumferencial direction. The results could be summerized as follows: (1) The optimum result of welding was obtained by the coil inudctance of about 3μH. (2) The most suitable clearance was 3mm. (3) For the joint of straight core, two welds were obtained near the ends of the coil. They moved to inner sites of coil as the tapered angle increased up to 8 degree. (4) The successful welding result was obtained for tube to tube joint, when the thickness of core tube exceeded about 6mm. (5) The softer the outer tube, the more easily the welding was performed, if the energy input was constant.
The modified implant test was newly proposed in this paper as the suitable method for evaluating the sensitivity of the reheat cracking which has occasionally occurred in the welded zone of high strength steels. It was confirmed from the experimental results of the commercial high strength steels that the reheat cracking sensitivity could be compared by the critical value of the initial restraint stress obtained from the modified implant test. And the T-1 type high strength steel which contained both chromium and molybdenum was more sensitive to the reheat cracking than the chromium free high strength steel. The critical value of the initial restraint stress was determined by two factors; the critical value of the restraint stress after the post weld heat treatment and the stress relaxation characterestics. The reheat cracking sensitivity of the synthetic Ni-Cr-Mo steels were examined. As the results, the addition of nickel increased the reheat cracking sensitivity of the Cr-Mo steels only when its content exceeded 1.5%.
Austenitic stainless steel weld metal was studied concerning the toughness at cryogenic temperature and the hot cracking during welding. The results are as follows: (1) By the stress relief heat treatment (SRT) the weld metals containing more than 4% of delta-ferrite are severely embrittled at -196°C. The toughness of fully austenitic weld metal through SRT was decreased with carbon increasing. (2) The numbers of inclusions of 0.5 to less than 1.0 μ size, which are mostly detrimental to the toughness at -196°C, in the weld metal by (Ar+15% C02) shielding gas are about ten times more than one by Ar shielding gas. (3) Fully austenitic stainless steel can attain a highly improved hot cracking resistance, almost equal to that of 304, by limiting the segregation of P, S, and Si at grain boundary on solidification.
The effect of oxygen on the transformation of low carbon ferritic weld metal prepared by the MIG welding process has been investigated by means of dilatometry and microstructural observations. The Continuous-Cooling-Transformation (CCT) diagrams for the Si-Mn, Si-Mn-Ti and Si-Mn-Ti-B weld metal austenitized at 1350°C show that the region of ferrite formation was shifted to the faster cooling rate at high oxygen levels, and higher oxygen weld metals transformed from the austenite at significantly higher temperature. These observations suggest that the non-metallic inclusions promote the ferrite formation in weld metal. At sufficiently high oxygen levels the primary ferrite and the side plate ferrite were formed predomi-nantly at the higher temperature range, and the coarse grained ferrite structures were formed. The bainitic structures were apt to form at the low oxygen levels. The notch toughness of the weld metal, therefore, was low at both low and high oxygen levels, and was high at the intermediate oxygen levels because of fine acicular ferrite structures. The inclusion volume fractions in the high oxygen weld metal were larger than in the low oxygen weld metal, and these non-metallic inclusions act as the nucleants for ferrite. In the Si-Mn-Ti-B weld metals the grain boundary segregation of boron suppresses the formation of the primary ferrite at the austenite grain boundary and it leads to the uniform microstructure. The notch toughness of Si-Mn-Ti-B weld metal, therefore, was affected largely by the oxygen levels. On the other hand, the Si-Mn weld metals made primary ferrite formation more likely, and the notch toughness of these depended less on the oxygen content even if the cooling rate is significantly high. It is concluded that the effect of oxygen on the notch toughness of the weld metal can be understood by the transformation characteristics.
One of the greate advantages of the diffusion welding is that large movement of material does not occur at bonding surface which is usually seen in the case of the friction welding and the explosive welding. This means the easiness of the geometical control at the weld section, because the large deformation is not caused at this section. So, in this paper, considering the merit mentioned above, the diffusion welding process was applied to fabricate FRM (Fiber Reinforced Metals). To produce the FRM, the uniform distribution of the reinforcing fibers and the perfect consolidation between the matrix and the fibers are necessary. To sastisfy these conditions, the combined process of the filament winding method and diffusion welding was studied. In this case, SiC fibers were used as reinforcing fibers and A6061 aluminum alloy foils were used as the matrix metal. After fabrication of the FRM by this process, various tests were conducted on this material The results are summarized as follows. 1) The fabrication of the FRM by the combined process of the filament winding method and diffusion welding is applicable. The fibers in this material can be arranged uniformly. 2) The fabricated FRM consisting of the SiC fibers and A6061 aluminum alloy exhibits the maximum strength greater than 200 kg/mm2, which is nearly equal to the theoretical value derived from the rule of mixture. And the strength-to-weight ratio of this material is twice as high as that of the highest strength alloys such as the maraging steel. 3) Ultrasonic testing using reflector plate in the water is applicable for the nondestructive testing of the FRM plate.
The effect of water pressure on formation of porosity in underwater gravity welding were investigated within the range of 0 to 6 kgf/cm2 (gauge). The ilmenite type, high titanium oxide type and iron powder iron oxide type electrodes of 4 mm in diameter and SM41 steel base metals of 6 and 9 mm in thickness are used. Main results are summerized as follows: (1) The porosity is formed in weld metal, when water pressure is over about 0.5 kgf/cm2. The porosity increases with an increasing of water pressure. (2) The porosity (A type) in weld metal obtained under water-pressure of 0.5 to 3 kgf/cm2 is caused by the concentrated hydrogen in front of the solidification front. (3) The porosity (B type) is observed in weld metal obtained under water-pressure of 3 to 6 kgf/cm2 and the special solidification lines are often generated around porosity. The porosity is caused by bubble formed in molten metal, which is catched by the progressing solidification front. (4) The special solidification line is formed by a repetition of growth of bubble at the progressing solidification front and escape of bubble from there. (5) Changes of porosity shape and porosity formation mechanism with water pressure are caused by concentration of hydrogen in molten metal, which is greatly increased with water pressure.
In the previous paper, the authors have proposed a new test (the so called BNP test) to evaluate the susceptibility of bond to hot straining embrittlement. In this paper, effects of welding conditions on the degree of the embrittlement have been investigated by using the BNP test. The test have been carried out on the bond in HT80, A533 and SM50 steels. Main results can be summarized as follows. (1) The degree of hot straining embrittlement of bond (ΔTrs) is markedly dependent on heat input. Generally speaking, ΔTrs increases with heat input. (2) Preheat and interpass temperatures have a considerable effect on the transition temperature (Trs) as shown in Fig.9. (3) In the case of SM50 and base metal of HT80, annealing has a beneficial effect, but in the case of bond in A533 and HT80 steels, it is not always advantageous.