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

QUARTERLY JOURNAL OF THE JAPAN WELDING SOCIETY Vol. 39 (2021), No. 3

  • Stud Shape and Joint Strength for Low Carbon Steel Joints fabricated by Friction Stud Welding with Low Load Force Requirement

    pp. 141-150

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    DOI:10.2207/qjjws.39.141

    This paper describes the stud shape and joint strength of low carbon steel joints fabricated by friction stud welding with low load force requirement. To reduce the load force during the welding process, the stud side with the circular hole at the weld faying surface part was used. The outer diameter of a cylindrically shaped stud side had 12.0mm and that was welded to the circular solid bar with a diameter of 24.0mm as the work side. The joint was made with a friction speed of 27.5s-1, a friction pressure of 60MPa, and a forge pressure of 60MPa, which was determined as the low force condition for obtaining good joint in the previous study. When joints were made by a cylindrically shaped stud with a hole diameter of 6.0mm and its depth of 0.5mm, all joints at a friction time of 0.6s, i.e. the friction torque reached to the initial peak, had the same tensile strength as that of the base metal with the base metal fracture. All joints with flash from the initial weld interface had the fracture on the base metal, the bend ductility of over 15 degrees with no cracking at the initial weld interface through an impact shock bending test, and a high fatigue strength of the base metal. That is, the sound joint could be successfully achieved, and that could be obtained with the same friction stud welding condition of the circularly shaped solid stud. As a conclusion, the joining technique for the friction stud welding method with low load force requirement was proposed in accordance with using a cylindrically shaped stud that has the circular hole with the shallow depth at the weld faying surface part.
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  • Observation of Stability and Cleaning Action in AC-GTA under like Mars atmosphere

    pp. 151-157

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    DOI:10.2207/qjjws.39.151

    In 2010, Barack Obama, the former president of the United States, announced sending humans to the Red Planet in the 2030s. Outposts and habitats will be set up in the future by welding technique. In this study, effectiveness of previous AC-GTA welding was investigated in a like Mars atmosphere consisting only CO2 gas with pressure range from 600 to 1000Pa. In order to observe the AC-GTA phenomena, the arc appearances were filmed by a high-speed video camera. Furthermore, the arc voltage and the welding current waveforms were recorded to evaluate the AC-GTA stability. It was found that the cathode spots distribution area spreads and the AC-GTA stability decreases in the less pressure. In conclusion, the AC-GTA welding in the Mars atmosphere can be applicable by considering the ambient pressure and the EP time ratio.
  • Effect of aging treatment on fatigue behavior of Nb-added ferritic stainless steel type 429 welds in 3% NaCl solution

    pp. 158-162

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    DOI:10.2207/qjjws.39.158

    The effect of aging treatment on fatigue behavior of Nb-added ferritic stainless steel type 429 welds in 3% NaCl solution was investigated. Two filler metals with different chemical compositions, Filler I and II, had been used for the MIG butt welding of type 429. After aging treatment at 700℃ for 100 hours was applied to the smooth specimens of the welds, the fully reversed axial fatigue tests were performed in 3% NaCl solution. In the case of the welds with Filler I, there was almost no change in corrosion fatigue strength even after aging treatment. On the other hand, in the case of the welds with Filler II, the corrosion fatigue strength decreased after aging treatment. It was concluded that the combination of aging treatment and heat history of welding using Filler II caused the sensitization of the base metal of the welds and increased the sensitivity to the corrosive environment.
  • Simulation of Nucleation and Growth of Austenite in Duplex Stainless Steels

    pp. 163-170

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    DOI:10.2207/qjjws.39.163

    The microstructure of duplex stainless steels is formed by dendrite growth in the primary ferrite-phase and by subsequent solid-state transformation to the secondary austenite-phase. In this study, formation of austenite by solid-state transformation in duplex stainless steels was evaluated. The nucleation and initial growth of austenite was simulated by the software TC-PRISMA. The formation temperatures of austenite in previous works were corresponding to the calculation obtained by adjusting the interfacial energy. Moreover, the microstructure formation process both in grain boundary and intragranular was simulated using a multiphase field method (MICRESS software). The growth of austenite was assumed to be under paraequilibrium considering the diffusion control of nitrogen and its morphology was assumed to be an acicular growth. The microstructure morphologies were relatively similar to those obtained by the experiments. The simulation method in this study can analyze complex microstructural morphology as well as predict the composition distributions. This method is considered to be highly effective in designing duplex stainless steels and in evaluating the microstructure morphology in welding process.
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  • Analysis of Local Fracture Driving Force for a Micro-crack under Combined Stress Field in Plastic Zone

    pp. 171-179

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    DOI:10.2207/qjjws.39.171

    The critical Weibull stresses for brittle fracture of cracked specimens tested under different loading mode, that is mode I and mixed mode of I and II, estimated with an original Beremin model based on a linear fracture mechanics does not present the unique value. Local fracture driving force to control brittle fracture of a micro-crack in the material under large-scale yielding and combined loading conditions is analyzed based on nonlinear elastic-plastic energy release rate, Local-J of a unit cell containing a penny-shaped crack. Local-J is enlarged due to decrease in normal stress subjected to the horizontal direction with respect to a crack surface under the same normal stress, whereas such stress did not influence the linear elastic energy release rate. Also, the Local-J is significantly enlarged by shear stress acting on the crack plane. These results implied that the local fracture driving force Local-J should be taken into account for estimating the combined loading effect on brittle fracture resistance under large scale yielding condition.
  • Relationship between pitting corrosion resistance and Cr-depleted zone in duplex stainless steel weld metals

    pp. 180-189

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    DOI:10.2207/qjjws.39.180

    The microstructures, solute concentration distribution, and pitting corrosion resistance have been investigated in duplex stainless steel SUS329J1 weld metals with different nitrogen content (0.066, 0.142, and 0.207mass%). Ferrite content decreases and critical pitting potential shifts to the noble direction with increasing nitrogen content. For the weld metals with low nitrogen content (0.066 and 0.142mass%), not only CrN within the ferrite grains but also Cr2N along the ferrite/austenite interfaces is observed; in contrast, for the weld metal with high nitrogen content (0.207mass%), only CrN precipitates within the ferrite grains. Cs-TEM/EDS analyses revealed that Cr-depletion in the vicinity of Cr2N is deeper than that of CrN. Additionally, Cr-depletion decreases with increasing nitrogen content. Increment of nitrogen content promotes the nucleation and growth of austenite phase, which has high solubility limit of nitrogen, thereby decreasing nitrogen concentration in ferrite phase. Diffusion-controlled growth simulation of Cr-nitrides in ferrite phase indicated that Cr-depletion is suppressed by decrement of initial nitrogen concentration in ferrite phase. Hence, nitrogen addition improves pitting corrosion resistance owing to the suppression of Cr-depletion.
  • Influence of Material Adhered to Welding Tool in Consideration of Shape of Cutting Tools on Friction Stir Spot Welds

    pp. 190-199

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    DOI:10.2207/qjjws.39.190

    This paper investigates the influence of the presence or absence of material adhered to the tool in A5052/A6061 lap joints when friction stir spot welding tools with cutting edges and rake angles similar to a cutting tool are used. The main focus was the inflection of material flows by the behavior of the material adhered to the tool during the friction stir spot welding. The failure load of friction stir spot lap joints made using tools with adhered material was more than 1.5 times higher than those made using tools without adhered material in some welding conditions. At this time, it was clear that the ability of the tool to discharge chips did not change irrespective of whether or not there was adhered material. In addition, the material flows during friction stir spot welding, with or without adhered material, were the material flow made by the chips in the keyhole edge and the material flow made by the cutting edge of the tip of the probe in the keyhole corner. However, when tools with adhered material were used, the material flow in the keyhole corner produced not only a flow of welding material but also a flow of adhered material stirred inside the welding material. From the results, when these tools with adhered material are used, it is clear that the adhered material assists the flows inside of the welding material, and can improve the characteristics of friction stir spot welds.
  • Effect of Friction Stir Processing on Mechanical Properties of AA-TIG welded 9%Ni Steel

    pp. 200-208

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    DOI:10.2207/qjjws.39.200

  • Effect of paint baking thermal cycle on joint strength of spot welds

    pp. 209-217

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    DOI:10.2207/qjjws.39.209

    Advanced high strength steel sheet (AHSS) is widely used in the automotive body for weight reduction and the improvement of crash performance. Such a use requires higher joint strength of the resistance spot weld in AHSS. In laboratory tests, the joint strength of specimens is evaluated in as-welded condition. The effect of paint baking cycles is usually not considered, so the actual joint strength in the automotive body is not clear. In this study, we focus on the effect of the thermal cycle corresponding to paint baking treatment on the joint strength of spot welds. Two types of tensile test, shear tensile test and L-shaped peel tensile test were carried out. The material strength grades used in this test were from 270MPa to 980MPa. The weld nugget diameter was varied from three to five square root t in each material. A paint baking thermal cycles (170 degrees centigrade for 20 minutes) was applied to the welded joints before the tensile tests were carried out. The paint baking treatment doesn't cause change in shear strength of joints in any of the conditions (materials and nugget diameter). On the other hand, in case materials of 590MPa grade or higher are used, the paint baking treatment can cause an increase in peel strength of joint. Especially, the increase of joint strength by the paint baking treatment is most obvious in smaller nugget conditions. The results of this study suggest that the improvement in peel strength by paint baking treatment is caused by a tempering effect in the weld nugget. From these results, we concluded that the joint strength of paint baked specimen would be more practical data, representing the actual joint performance in automotive bodies.
  • Effect of the strength of steel sheets and wires on residual stress of thin steel sheet lap-fillet GMA weld joint

    pp. 218-231

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    DOI:10.2207/qjjws.39.218

    [in Japanese]

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