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.
  • 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.

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