One of the problems relating to fatigue strength of a welded joint containing a weld defect is the evaluation of propagation life of a fatigue crack initiated from the defect. In this paper propagation behaviors of fatigue cracks from a through-thickness notch and from a deliberately introduced internal weld defect in 100mm thick transverse joint of A533B class 1 steel were examined, and the propagation rates were analyzed. It was observed that the propagation rate from an internal weld defect was higher than that from a throughthickness notch at a given stress intensity range. These results were discussed by comparing with the propagation rate given in ASME Code Sec. XI.
80kg/mm2 high strength thick plate steels come into extensive use. In many application, welded structures are used under such a stress condition that tension and bending are superimposed, and danger of brittle fracture initiation at weld fusion line becomes greater all the more. So, the brittle fracture intiation characteristics of the welded joints, both manual arc welded and submerged arc welded made of 80 kg/mm2 high strength steel with a plate thickness of 50 mm were investigated using the wide plate tension test specimens with an angular distortion. The main results are summarized as follows: (1) The joints welded with a heat input of 45-50 kJ/cm does not cause low stress fracture in the temperature range above 0°C if it is free from weld defects, even under such a stress field condition that bending stress is almost twice as much as tension stress. The fracture stress is almost equal with ultimate tensile strength of round bar uniaxial tension specimens. (2) In the manual arc welded joints annealed for stress relief, crack initiates at a weld toe and propagates to the weld fusion line and developes to low stress fracture at -15°C under the same stress condition. An annealing for stress relief for welded joints of the 80kg/mm2 high strength steel cannot be recommended. (3) The submerged arc welded joints offer higher elongation than the manual arc welded joints, and even if it is of a cross welded type shows ductile fracture. In mannual arc welded joints, elongation of specimens as welded is higher than that of annealed specimens for stress relief and becomes lower in cross welded specimens. (4) Even in a specimen as welded the repair weld zone enhances the risk of low stress fracture. The quantitative investigation into this problem is to be made sometimes in the future. (5) The strain behavior of a specimen with angular distortion varies depending on the amount of angular distortion and the end restraint condition. Therefore comparison of its test result with those of actual structures in terms of the amount of angular distortion only is not advisable. Prediction of fracture for actual structures is possible, by comparing the stress condition of the structures with taking into account bending moment working on the weld zone estimated from the measured values of strain.
The study was made to determine the available electrode diameter in the region where good bead and good penetration coexist when the one pass welding is performed for the fillet welds in the flat position and in the horizontal position of the lay down welding. The results are summarized as follows: (1) The maximum available electrode diameter is 8 mm in use of the electrode with acidic covering and 9 mm in use of the electrode with basic covering for fillet weld in the flat position, and is 8 mm in use of the electrode with acidic covering and with basic covering for fillet weld in the horizontal position. (2) The maximum range of arc current is obtained by using the electrode diameter of 7 mm for fillet weld in the flat position and by using the electrode diameter of 6 mm for fillet weld in the horizontal position for both the electrodes with acidic covering and with basic covering. (3) The rate of blowhole increases with increasing of electrode diameter, and decreases with increasing of arc current for a constant electrode diameter. (4) The tensile strength, the elongation and the absorbed energy of deposited metal decreases with increasing of electrode diameter. (5) For the fillet weld in the flat position, the electrode diameter is recommended to be 5-8 mm with acidic covering and 5-9 mm with basic covering. For the fillet weld in the horizontal position, the electrode diameter is recommended to be 5-7 mm with acidic covering and 5-8 mm with basic covering.
In this paper, effects of several factors such as kind of wire, groove angle, intensity of restraint, weld heat input and welding position on the incubation time for cracking in the self-shielded arc welding are discussed. The new method preventing weld cracking by depositing the succeeding passes within the incubation time for crack initiation without preheating has been established. The new method can be successfully applied for steel structures of building, in which weld length is generally short.
Following phenomena were experienced on the welding with plate thickness 100 mm to 200 mm. (1) The weld cracking increases with an increases of the plate thickness (number of welded layer). (2) Weld cracking occurs several days after welding. In order to assure above phenomena and study the preventive method of the weld cracking, the weld cracking test was carried out and the weld cracking phenomena were observed. The main results obtained are as follows. (1) It is clarified that weld cracking increases with an in crease of the thickness of welded plate, and the initiating position of weld cracking lies just under the surface bead. (2) Incubation period of weld cracking is 4 days after welding. (3) Weld cracking is prevented with lower temperature postheating for 0.5 hr at 300°C in case of local gas heating for a 2 1/4 Cr-lMo steel. (4) It is clarified that above phenomena are based on the distribution of hydrogen in thick weldment which is reported by authors in the previous reportt.
Monitoring elements during welding for mild steel and aluminium alloy in spot welding are proposed, which can utilize in evaluating the tensile shear strength of the spot welds and the nugget dimension, by employing the same statistical analysis as 1st report. Monitoring elements selected are electrode movement, voltage between electrodes and voltage between sheets. The results obtained are as follows: (1) For the mild steel, the peak value of voltage between electrodes can be used properly as the element of monitor under the suitable welding conditions. (2) For the aluminium alloy, the peak value of electrode movement can be used properly as the element of monitor under the suitable welding conditions.
In this paper, a new method controlling a steady reverse-side bead appearance in the Narrow-Gap One-Side Arc Welding Process by measuring the shunt-current of a coated rod inserted in the I-butt groove is described. It is proved that the shunt-current wave shape shown in a recorded paper corresponds well to the configuration of a reverse-side bead, and relation between shunt-current wave shape and behaviour of molten Wool was established. The conclusions are summarized as follows. (1) Shunt-current wave shape corresponds well to the configuration of reverse-side bead. (2) Relative distance (d) between arc point (location of wire) and a head line of a molten pool corresponds well to the state of reverse-side bead. (3) Development of a system controlling the state of reverse-side bead by picking up several factors as mentioned above is expected.
It is important to make clear how the carbides in austenitic stainless steels behave during heat treatment and especially during welding, because in these steels the behaviour of carbides heavily affects the corrosion resisting property and the other mechanical. properties. It is main purpose to investigate fully the behaviour of carbides in stabilized austenitic stainless steels in the case of both time and temperature varying simultaneously such as weld thermal cycles. On the other hand, knife line attack phenomenon neighbouring region to weld interface is the serious problem for these steels. Though this phenomenon is explained to be related to the behaviour of carbides in these steels, the detail in the mechanism of this phenomenon is yet unclear. Therefore, it is also the purpose of this study to make clear the mechanism and the cause of knife line attack. In this report, it was carried out to investigate the influence of welding conditions and heat treatment conditions after welding on knife line attack and then to examine the change of corrosion resisting property in HAZ electrochemically. The experimental results obtained in this study are as follows; (1) Corosion rate at attacked region was little influenced by welding heat inputs, whereas much influenced by sensitizing time at 650°C. (2) The corrosion rate increased with sensitizing time up to 50 h. However, in the case of sensitizing time being over 50 h, the corrosion rate decreased with sensitizing time. (3) Corrosion resisting property in HAZ was closely related to the anodic current density at 900 mV (vs S.C.E.) which was, the corrosion potential in Huey test.
The effect of Ni on transformation behaviour in synthetic weld heat-affected zone of steel was investigated using simplified steels made of pure metals and graphite. Ni element displaced the SH-CCT diagram for each transformation region to a longer time and to a lower reaction temperature. Each critical cooling time Cz', Cf', Cp' and Ce' obtained from SH-CCT diagram for welding increased with Ni content. Morphologies of ferrite, pearlite and Zwischenstufengefuge (Zw) were strongly influenced by Ni. The morphology of ferrite formation was more liable to develop sideplate and needlelike ferrite than massive ferrite by the addition of Ni. The fine colony pearlite and degenerate pearlite precipitated more easily than lamellar pearlite. The volume of pearlite did not decreased with Ni content. It seems that these steel did not contain other elements except C and Ni. Zw precipitated easily in long cooling time. The effect of Ni on the hardness of martensite was a little. Ni element rasied the hardenability curves in synthetic weld heat-affected zone of steels.