QUARTERLY JOURNAL OF THE JAPAN WELDING SOCIETY
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PRINT ISSN: 0288-4771

QUARTERLY JOURNAL OF THE JAPAN WELDING SOCIETY Vol. 37 (2019), No. 4

  • Effect of Nitrogen on Weld Solidification Cracking Susceptibility of Fe-25%Cr-22%Ni-P-N Fully Austenitic Stainless Steels

    pp. 133-140

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    DOI:10.2207/qjjws.37.133

    The effect of nitrogen on weld solidification cracking susceptibility of Fe-25%Cr-22%Ni-P-N fully austenitic stainless steels was experimentally investigated. Maximum crack length in Trans-Varestraint test slightly increased with increasing nitrogen content. Moreover, nitrogen content also did not affect the cracking susceptibility in self-restraint type weld crack test. The observation of liquid Sn quenched microstructure revealed that the addition of nitrogen caused microstructural transition from cell to dendrite, decreasing microsegregation of chromium and phosphorus during solidification. We concluded that brittleness temperature range was not enlarged by nitrogen addition, because the increment related to microsegregation of nitrogen itself and the decrement related to the suppressed microsegregation of chromium and phosphorus canceled each other out.
  • Enhanced Idealized Explicit FEM for Predicting Welding Deformation in Complex Large-Scaled Structure and Application to the Real Structure

    pp. 141-151

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    DOI:10.2207/qjjws.37.141

    In the fabrication of steel structures, welding is widely utilized to join the materials. Due to the welding, distortions are inevitably generated, and these distortions may cause problems in accuracy or labor costs. In this research, to establish an analysis method which can predict the welding distortions in complex large-scale structures, we proposed a new analysis method based on the Idealized Explicit FEM. In the proposed method, an algebraic multigrid method was introduced to the Idealized Explicit FEM to achieve an efficient analysis in realistic structures. The proposed method was applied to the prediction of the welding distortion in the base structures of the construction machine. The number of welding passes was 28. The predicted and measured distortions were compared. As a result, it was demonstrated that the proposed method has a high analysis accuracy. The analysis finished within the realistic time within 35 hours. The influence of welding sequence on the deformation was also investigated by changing welding sequence. The result indicated that the welding sequence may have considerable effect on the welding distortion and is necessary to be investigated in advance of the production.
  • Effects of material strength levels and nugget sizes on fatigue behavior of resistance spot welded steel sheets

    pp. 152-161

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    DOI:10.2207/qjjws.37.152

    Tensile-shear test blanks were fabricated using high strength and low carbon steel sheets with three different strength levels by a resistance spot welding (RSW) procedure. The nugget sizes were changed by controlling the welding process parameters, resulting in the nugget sizes of 3√t, 4√t and 4.7√t, where t was the sheet thickness. Subsequently, tensile-shear static and fatigue tests were conducted to investigate the effects of strength levels of steels and nugget sizes on the mechanical properties of the welds. The tensile strength increased with increasing strength levels and nugget sizes. However, the fatigue strengths of the welds with the nugget sizes of 4√t and 4.7√t were nearly comparable irrespective of the strength levels of steels. That was because fatigue crack propagation life was dominant in the total fatigue life. In the welds with 3√t nugget size, the steel with higher strength level exhibited lower fatigue strength. It could be attributed to the lower bonding strength along the corona bond in the high strength steel.
  • EXPERIMENTAL STUDY ON DEFORMATION CAPACITY OF FIELD WELDING BEAM TO COLUMN JOINT WITH DIFFERENT BEAM END DETAILS

    pp. 162-172

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    DOI:10.2207/qjjws.37.162

    The purpose of this paper is to examine the influence of fracture toughness and non-welded part in submerged arc weld (SAW) on deformation capacity of pre-assembled H-shaped beam to column joint. For this purpose, higher toughness (about 60J) and lower toughness (about 20J) SAW joints were prepared. In addition, improved beam end scallop details, BS_P (billet insertion), BM (mini scallop), and BF_5 (height of fillet:5mm), were proposed. The rate of increase of strength and the deformation capacity of these four type details were examined by experiment. From the results of experiments, it is revealed that brittle fracture at beam end flange is likely to occur at small deformation when the field welding beam to column joint has BS (composite scallop) detail and non-welded part of low toughness SAW. On the other hand, using higher toughness SAW and shortening non-welded SAW parts delayed brittle fracture and raised deformation capacity. Moreover, using proposed improved beam end scallop details buffered stress at the bottom of scallop and improved deformation capacity. Therefore, the authors showed following the method for improving deformation capacity of field welding beam to column joints.
    1) Improving toughness of SAW
    2) Using proposed improved beam end scallop details
    3) Shortening the length of non-welded of SAW
  • Development of resistance spot welding technology applying multi-stage adaptive control for narrow pitch spot welding

    pp. 173-180

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    DOI:10.2207/qjjws.37.173

    Narrow pitch spot welding causes decrease in nugget diameter due to shunting to existing- welds under conventional resistance spot welding. This study aims to develop new resistance spot welding technology for ensuring required nugget diameter regardless of weld spacing. Adaptive control based on real-time feedback of heat quantity was applied for welding of mild steel sheets. However, expulsion occurred from steel sheet surface around the contact edge with electrode when weld spacing was shortened to 10mm. To solve this problem, a new adaptive control method was developed. The method includes 2-stage adaptive control, in which heat quantity is controlled independently in each stage to obtain proper nugget diameter. It is effective to set relatively low heat quantity compared to conventional method in the 1st stage to ensure current pass between steel sheets, and then to apply enough current-flow to obtain proper nugget diameter in the 2nd stage. This method can decrease shunt current flow to existing-welds, and excess increase in welding current and over-heating around contact edge with electrode was suppressed. Appropriate nugget diameter can be consequently ensured without expulsion from steel sheet surface even with 10mm weld spacing.
  • Influence of the magnesium content on cathode spot behavior in AC TIG welding of aluminum alloy

    pp. 181-186

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    DOI:10.2207/qjjws.37.181

    The influence of magnesium contents on cathode spot (CS) behavior in aluminum AC TIG welding was investigated by High-Speed Video Camera (HSVC) observation with the maximum frame rate of 500,000fps. The number of CS in A5052 case was larger than that in A1050, leading to the smaller average current per spot of 6.9A comparing with 16.7A in A1050. The larger current per spot is considered to cause the CS higher velocity. The average velocity of CS on liquid surface of A5052 was 110±37m/s far lower than that in A1050 case. The central area, where the CS did not exist, had a radius of 2.0mm and expanded over EP time. The existence of magnesium in A5052 led to the increase in the cathode spot number inside the weld pool. The predicted mechanism could be the more easy evaporation of magnesium than that of aluminum.
  • Optimization of Laser-Irradiating Conditions for Vertical Welding on Thick Steel Plate using Hot-Wire Laser-Welding Method

    pp. 187-192

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    DOI:10.2207/qjjws.37.187

    We investigated the effect of laser-irradiating conditions—specifically laser spot size, laser power density and laser weaving. Three laser spot widths of 10, 4 and 2mm were applied by changing the optical-lens and fiber-cable combination to investigate the effects of the laser power density and laser spot width. The weaving-irradiating method was applied with narrow laser widths of 4 and 2mm. The effects of the laser-irradiating condition were obtained based on high-speed imaging during welding and cross-sectional observation. Stable laser irradiation by a 10-mm laser spot width provided a lower power density than the critical value of 35W/mm2 and a lack of fusion. Weaving laser irradiation by a 4- or 2-mm laser spot width provided a higher power density, reduced the large lack of fusion and achieved a large penetration of base metal. The ratio between the laser beam-spot width and gap width (WL/WG ratio) affect the base-metal fusion significantly. A sound WL/WG ratio promoted base-metal fusion by providing a uniform and stable molten-pool temperature, whereas a small WL/WG ratio maintained a smaller fusion area because of the sudden temperature drop and temperature fluctuation of the molten pool.
  • Effect of frequency on self-induced fusion solidification bonding of aluminum by pressure controlled periodic motion

    pp. 193-199

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    DOI:10.2207/qjjws.37.193

    The joint of the self-induced fusion solidification bonding of aluminum is obtained by the isothermal fusion and the isothermal solidification by the reaction diffusion. The reaction diffusion between the dissimilar solid interfaces requires the fracture of the oxide film on the interface at the initial stage of the bonding process. The periodic motion of the interface promoted the fracture of the oxide film by the impact at the bonding interface. Increase of the frequency of the impact also will promote the fracture of the oxide film. The joint of the self-induced fusion solidification bonding under bonding pressure control was investigated with the periodic motion of the different frequency. The initial stage of the bonding process occurred in the short time by high frequency motion. Flash of the liquid from the interface occurred at the fixed impacts under a stable maximum pressure, regardless of the change of the frequency. High frequency motion reached the fixed number of the impact in the short time. However, middle frequency motion obtained the self-induced fusion solidification bond with maximum tensile strength, maximum bonding area ratio and maximum displacement of the bond. These results suggest that the deformation of the bonding interface promotes the self-induced fusion solidification bonding process.
  • Investigation of Standardizing for Evaluation Method of Transverse Varestraint Test

    pp. 200-207

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    DOI:10.2207/qjjws.37.200

    Varestraint test is one of the most-used methods to evaluate weld solidification cracking susceptibility. However, standard about the detailed test method and the evaluation method has not been clearly defined. Thus, it is required to standardize the methods of Varestraint test and the evaluation indexes in order to compare the results tested by each researcher.
    In this study, round-robin test of transverse-Varestraint test with GTAW was carried out under identical specimens and test conditions using five test machines to clarify the influence of test machine and human factor on the test result. Crack number and crack length were measured using a scanning electron microscope (SEM) and an optical microscope. 6 evaluators measured the crack number and the length.
    The maximum crack lengths measured by the evaluators were nearly the same. In contrast, there were big differences in the crack numbers and the total crack lengths. Thus, the influence of the human factor on the maximum crack length was relatively low and that on the crack number and the total crack length was high. This should be caused by different judgment depending on the evaluators for the crack opening and the propagated crack tip. Using SEM was an adequate measuring method for the crack length since the measurement using an optical microscope tended to cause false judgment of wrinkle as cracks. Maximum crack length must be appropriate evaluation index for solidification cracking susceptibility compared to the total crack length and the crack number.
  • Melting by Reflected Laser Beam during Vertical Welding via Hot-Wire Laser Welding

    pp. 208-214

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    DOI:10.2207/qjjws.37.208

    We investigated the melting of a base metal, molten pool growth, and joint creation during vertical welding via hot-wire-laser welding. Three laser-weaving conditions were investigated by changing the weaving frequency and waveform to study the effects of the irradiation duration near the groove surface. In addition, high-speed and cross-sectional imaging were performed to investigate the heating and melting processes on the groove surface during hot-wire laser welding. The irradiation duration near the groove surface in a cycle had a marked effect on the melting of the groove surface. The combination of a 5Hz laser frequency with an exponential waveform led to a longer duration near the groove surface during a cycle and realized improved fusion compared with the other combinations with a 15Hz laser frequency and a sine waveform. The laser beam reflected from the molten pool surface was the main source of heat for melting the groove surface. Hot-wire feeding provided a continuous and efficient supply of melted material and a stable heat input on the groove surface via the reflected laser beam.

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