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

QUARTERLY JOURNAL OF THE JAPAN WELDING SOCIETY Vol. 9 (1991), No. 3

  • Prediction of Welding Residual Stresses in T-and I-Joints Using Inherent Strains

    pp. 337-343

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    DOI:10.2207/qjjws.9.337

    A new method for prediction of welding residual stress was proposed. The prediction is realized by an elastic analysis using inherent strain as the source of residual stress. In this paper, the method is extended for the prediction of residual stresses in welded T- and I-joints.
    Inherent strains in T- and I-joints were calculated from residual stresses which were obtained by thermal elastoplastic analysis. It is found that the distributions of inherent strain in the flange side and web side near the weld part are the same provided that the widths of flange and web are not considerably different. The inherent strain distributions in the vicinities of two weld parts of I-joint are both the same as one in T-joint of the same geometrical sizes. Two simple formulae are presented to predict the width and magnitude of inherent strain distribution in T- and I-joints corresponding to the specified welding conditions.
    It is demonstrated that the proposed method predicts welding residual stresses accurately by an elastic analysis imposing the inherent strain in the same order as actual welding building-up procedure.
  • 平成3年度春季全国大会論文発表講演討論記録

    pp. 344-347

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    DOI:10.2207/qjjws.9.344

  • Effect of Molten Metal Behavior on Melting Process in Electron Beam Welding

    pp. 348-354

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    DOI:10.2207/qjjws.9.348

    This paper describes the effect of molten metal behavior on melting process and spiking phenomenon in electron beam welding. X-rays generated as a consequence of beam-metal interaction were detected at specific sites of 3 mm in length along penetration to clarify the melting process for various beam focussing conditions and welding speeds. Behavior of molten metal flow was also observed using high speed cinecamera simultaniously. JIS SM 50 A steel, Fe-10% Mn alloy and Fe-20% Mn alloy were used as base metals to investigate the effect of vapor pressure on melting process.
    Results obtained were as follows.
    (1) Spiking phenomenon was caused by an intermittent melting of base metal depending on the fluctuation in morphology of beam cavity.
    (2) Spiking was suppressed with an increase in Mn content involved in the base metal, since the beam cavity was stable and always clear of molten metal during welding by high pressure Mn vapor.
    (3) The front wall of the beam cavity was melted almost continuously for upper focussing condition, whereas it was melted intermittently for down focussing condition due to the periodical flow of the molten metal, resulting in more probable occurrence of acute spiking.
    (4) Spiking was more likely to occur with a decrease in the welding speed under the same penetration depth, since the electron beam could drill the bottom deeply for low welding speed.
    (5) The periodical flow was caused by natural vibration of the molten metal or high voltage power ripple depending on the amount of the molten metal around the beam cavity.
  • Wettability and Interaction of Silver-base Brazing Alloy Melts to Spheroidal Graphite Cast Iron

    pp. 354-359

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    DOI:10.2207/qjjws.9.354

    Wettability and interaction between ferritic spheroidal graphite cast iron and silver-base brazing alloy melts were studied to attain the higher interfacial strength and reliability of bonding. Wettability was estimated by sessile drop method. At 1023 K, the contact angles of molten Ag-Cu eutectic alloy melt were about 60° to the spheroidal graphite cast iron containing 13 vol.% graphite nodules, 150° to graphite substrate and 20° to Fe-Si-Mn alloy with the almost same composition as that of cast iron matrix, which satisfied the Cassie's equation for the wettability to composite materials. Although zinc lowered liquidus of brazing alloy below the eutectoid temperature of cast iron, it impaired the wettability. The addition of manganese to the alloy decreased the contact angle to about 60°. The thin Mn rich layer containing about 60% manganese appeared at the interface between brazing alloy and cast iron, which was identified as α-Mn by analytical electron microscope. The enrichment of manganese at the interface should improve the wettability.
  • Investigation of TIG Welding in Pressurized Helium Atmosphere

    pp. 359-365

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    DOI:10.2207/qjjws.9.359

    The effects of non-voltage load on the starting condition of arching in high pressure atmosphere (up to 3 MPa) of argon and helium were investigated. And the effects of an high pressure atmosphere (up to 3 MPa) on arc-voltage and bead formation were also investigated.
    The results are as follows:
    (1) The critical distance of arc starting between the electrode and the work decreased with increasing of the ambient helium pressure.
    (2) The ambient pressure affected the critical distance of arc starting much more in argon atmosphere than in helium.
    (3) No-load voltage at arc starting was constant in helium atmosphere between 0.1 MPa and 3 MPa pressure.
    (4) The arc voltage in helium atmosphere was higher than that in argon. And it was affected markedly by the ambient pressure.
    (5) The shape of welding arc in helium atmosphere was affected remarkably by the ambient pressure in comparison with that in argon.
    (6) The erosion of the electrode in helium atmosphere became larger above the ambient pressure of 0.5 MPa.
    (7) Good weld can be formed even in helium atmosphere of 3 MPa.
  • Study on Liquid Phase Diffusion Welding of Nickel Base Superalloy Used Ni-B System Alloyed Layer Formed on Bonding Surface with Sputtering

    pp. 365-372

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    DOI:10.2207/qjjws.9.365

    Liquid phase diffusion welding of Ni-base superalloy (IN738LC) was studied. In this study, the surface of IN738LC was cleaned by Ar ion bombardment and an alloyed layer (Ni-B alloy, Ni-Cr-Si-B alloy) was deposited on the bonding surface by sputtering.
    In this report, the effect of Ar ion bombardment on melting temperature of alloyed layer formed on base metal, penetration of alloyed layer into base metal and weldability, and the effect of composition of alloyed layer on melting temperature of alloyed layer, penetration of alloyed layer into base metal and weldability were investigated.
    The main results indicated that : (1) The penetration was increased by cleaning with Ar ion bombardment.(2) Penetration of Ni-Cr-Si-B alloyed layer was larger than penetration of Ni-B alloyed layer and melting temperature range of Ni-Cr-Si-B alloyed layer was larger than melting temperature range of Ni-B alloyed layer.
    (3) Pressure of welding used Ni-Cr-Si-B alloyed layer was lower than pressure of welding used Ni-B alloyed layer. (4) Weldability with cleaning was better than weldability without cleaning (5) Tensile strength of welded joint was the same as tensile strength of base metal, but elongation and reduction of area were lower than elongation and reduction of area of base metal. But mechanical property was improved by diffusion heat treatment.
  • Brazing of Commercial Pure Titanium with Zr-based Filler Metal

    pp. 372-379

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    DOI:10.2207/qjjws.9.372

    The work in this paper was designed to develop the brazing filler metal for commercial pure titanium (CPTi) from the viewpoint that the filler metal is composed of simpler alloy system having lower melting point and sufficient wettability comparing with Ti-based filler metals which have been developed so far. In this work, we investigated the Zr-based eutectic system filler metal and the wettability. The results of this work show that the Zr-47Cu filler metal allows brazing of CPTi below the α-β transfomation temperature and provides us with the joint possessing sufficient mechanical properties and corrosion resistance.
  • A Study of the Susceptilility for HESCC and It's Evaluation in Duplex Stainless Steel Weldaments

    pp. 379-385

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    DOI:10.2207/qjjws.9.379

    In this paper the authers discussed the effect of microstructure and residual stress on the susceptibility to HESCC in TIG and EBW duplex stainless steel weld metals. It was found that weld metal has a remarkable susceptibility to HESCC than base metal because of the ferrite content increasing in weld metal and the discontinuous precipitation of austenitic phase in ferritic phase in TIG and EBW weld metal, which results in the decreasing of keying effect of austenitic phase on crack propagation. Crack growth rate in EBW weld metal was found to be faster than that in TIG weld metal, although their threshold stresses were almost the same. In addition to that, the existence of residual stress increased the susceptibility to HESCC in welded joint, especially in the welded joint of cold worked material.
  • A Study of Criterion of HESCC Initiation and Prediction of Life Time in Duplex Stainless Steel

    pp. 386-391

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    DOI:10.2207/qjjws.9.386

    In this paper, HESCC initiation condition was studied and HESCC initiation life prediction was done by numerical analysis method. In the analysis, the HESCC initiation condition was found to be determined by the correlation between hydrostatic stress and hydrogen activity in ferritic phase near the tip of austenitic phase on specimen surface. But the relationship between hydrostatic stress and hydrogen activity at the crack initiation state was consitituted of two lines which had different inclination in log-log figure.
  • A Study of Mechanism of HESCC in Duplex Stainless Steel and It's Welds

    pp. 392-398

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    DOI:10.2207/qjjws.9.392

    In this paper, the mechanism for hydrogen embrittlement type stress corrosion cracking (HESCC) in duplex stainless steel and its weld metal was studied by using facet pit method. It was found that ferritic phase fractured in quasi-cleavage mode and austenitic phase in ductile mode. From the morphologies of facet pits formed on the fracture surfaces in ferritic phase, it was clarified that fracture planes in ferritic phase were mainly constituted of {100} plane in lower stress intensity region, and {110}, {112} plane in higher one. Consequently, the mechanism for HESCC in duplex stainless steel was explained by lattice decohesion at lower stress intensity and fracture on slip plane at higher stress intensity. From the view point of mechanism for HESCC, it was clear that the criterion for HESCC initiation mentioned in the former report (Report-3) was suitable for the lower stress intensity.
  • Influence of Microstructure in the Heat-Affected Zone on the Reheat Cracking Susceptibility of Cr-Mo steel

    pp. 398-404

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    DOI:10.2207/qjjws.9.398

    Influence of microstructure in the Heat-Affected Zone on the reheat cracking susceptibility of Cr -Mo steels (11/4Cr-1/2Mo steel, 21/4Cr-lMo steel and 5Cr-1/2Mo steel) were studied. Reheat crackingg tests on 3 type steels were carried out by means of three point bending method, constant-strain rate test on heating and constant-load test on heating. Influence of microstructure of synthetic HAZ at high temperature during the reheat treatment process was investigated by atomic absorption spectrometry, X-ray diffraction and scanning electron microscopic observation. The relation between the concentration of alloying elements in the precipitated carbides and their concentration in the matrix of synthetic HAZ were investigated. The effect of this relationship on the stress relaxation behavior was discussed. The results are summarized as follows.
    1) The reheat cracking susceptibility of Cr-Mo steels were very low. The reason why it is estimated that it had good stress relaxation behavior during reheat treatment process.
    2) The reheat cracking susceptibility of Bainitic structure specimens (Air Cooled) was the higher than that of Lath-martensitic structure specimens (Water Quenched) of 11/4Cr-1/2Mo steel and 21/4 Cr-lMo steel. But, it was not occured to reheat cracking on both specimens A.C and W.Q of 5Cr-1/ 2Mo steel.
    3) The difference of reheat cracking susceptibility could be explained by the stress relaxation behavior of specimens and change of the concentration of alloying elements in the matrix. Especially, change of Cr content during the reheat treatment process is effective.
  • Oxygen Absorption of Arc-Melted Pure Iron

    pp. 405-409

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    DOI:10.2207/qjjws.9.405

    The oxygen absorption behavior of arc melted pure iron has been investigated in a controlled atmosphere of Ar-O2 or Ar to elucidate the oxygen absorption mechanism of steel weld metal during arc welding process. As the arc current increases, the temperature of arc melted pure iron increases. The oxygen content of arc melted pure iron increased with an increasing arc melting time, and then had a constant value. The constant value of oxygen in arc melted pure iron agreed well with the oxygen solubility calculated from each molten iron temperature.
    It is considered that the results apply to weld metals during arc welding process. Therefore, above the 0.01 MPa of oxygen partial pressure, it is probably that the pure iron weld metals absorb oxygen corresponding to the oxygen solubility calculated from the average weld pool temperature.
  • Oxygen Absorption and Deoxidation of Arc-Melted Fe-Si Alloy

    pp. 410-415

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    DOI:10.2207/qjjws.9.410

    An investigation was made of silicon on the oxygen absorption and deoxidation in Ar-O2 or Ar atmosphere during arc melting process, to elucidate the oxygen absorption mechanism of steel weld metal during arc welding process. In Ar-O2 atmosphere, the amount of oxygen absorbed by Fe-Si alloy far exceeded the oxygen levels calculated from the molten Fe-Si alloys temperatures. After changing the atmosphere Ar-O2 to Ar, the oxygen content of arc melted Fe-Si alloy decreased toward the oxygen levels calculated from the Fe-Si alloys temperatures. The probable interpretation is that excessive amount of oxygen is present in Fe-Si alloy as the oxide due to the incomplete separation of reaction products. It is considered that the results apply to weld metals during arc welding process.
  • Influence of Delta-ferrite on Sensitization of the Austenitic Stainless Steel Weld Metal

    pp. 415-422

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    DOI:10.2207/qjjws.9.415

    Sensitization behavior of the delta-ferrite containing stainless steel weld metal was investigated using Type 304 and Type 308 alloys with the carbon content ranging from 0.04% to 0.09%, respective-ly. The weld metals heat treated at 923 K for times varying between 1 sec and 100 hr were tested for intergranular corrosion susceptibility in the acidified copper sulfate solution. The delta ferrite contain-ing weld metal with lower carbon content indicated rapidly healing of sensitization after the short heat treatment, whereas ones with higher carbon content than a critical value behaved as a fully austenitic steel regardless the existence of ferrite without showing the sign of rapid healing. SEM observation revealed that M23C6 precipitated preferentially at the ferrite-austenite boundary and also at the austenite-austenite boundaries although its amount at the latter boundaries was much less than the other in the both weld metals which indicated rapid healing of sensitization and behaved as a fully austenitic steel. A mathematical model is developed for the sensitization of the ferrite containing austenitic stainless steel weld metal. The degree of sensitization calculated using this model has shown a good agreement with the experimental corrosion test results. The calculation also demonstrated that for a given carbon content there exist the critical values for not only the total amount but the thickness of ferrite, above which the weld metal develop the rapid healing of sensitization.
  • Effect of Plastic Deformation on Fatigue Crack Closure Behavior in Low Yield Strength Material and Its Welded Joint

    pp. 423-429

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    DOI:10.2207/qjjws.9.423

    Crack closure behavior in fatigue crack propagation process was induced by plastic deformation near crack. In the paper, the effect of plastic deformation on fatigue crack closure in low strength material and its welded joint was studied.
    The results are as follows. Crack closure would be caused by plastic deformation near crack surface. Generally, crack opening ratio in high yield strength material is higher than that in low yield one. This tendency based on the degree of deformation near crack surface. In addition, in welded joint, crack propagation rate was higher than mother metal, though crack opening ratio showed almost 1 by the effect of residual stress. This could be explained by the effect of restrain for plastic deformation, which was induced by existence of compresive stress field ahead of crack.
  • Study of Residual Stress in the Vicinity of Interface Corner of Sprayed Coatings

    pp. 430-436

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    DOI:10.2207/qjjws.9.430

    This paper deals with the singularity of residual stress arising at the interface corner of sprayed substrates and the effects of specimen size, mechanical and physical properties on residual stress distributions using the theory of elasticity and a boundary element method (BEM).
    The residual stress distribution is not only defined by one singular term, then it is difficult to use a stress intensity factor as the parameter to define the strength of sprayed substrate.
    The residual stress distribution of test specimen satisfying following conditions are the same as that of sprayed substrate in a working field : The test specimen is composed of the substrate with the thickness being 4 times, and the length and the width being 8 times as large as a thickness of sprayed coating.
    The preheat temperature TB of substrate in order to make a residual stress zero is given by the temperature of sprayed coating and the ratio of linear thermal expansions of coating and substrate materials.
  • Estimation of the Cooling Time t8/5 and Thermal Factor of Weldments with Local Preheating

    pp. 436-441

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    DOI:10.2207/qjjws.9.436

    Preheating is performed to prevent cold cracking in steel constructions. Preheating produces a good effect on cooling times, which are t8/5 (cooling time from 800°C to 500°C) related to the maximum hardness at HAZ, or which are t200, t150, t100 (tθ : cooling time from the solidification to θ) connected with the thermal factor. In the welding field, a whole member can not be preheated uniformly, and then local preheating near the weld line is generally performed.
    This report deals with local preheating and welding procedures of a butt joint and a corner joint. Predicted values of cooling times have been compared with the experimental data. The predicted values have been obtained by theoretical formulae. The results are summarized as follows :
    (1) Relation between cooling time and thermal factor, (ΣD·Δt)100 has been investigated. The thermal factor is correlated most closely with cooling time t150.
    (2) The predicted values of cooling time t8/5 and thermal factor (ΣD·Δt)100 have given good agreement with the experimental values.
  • Effect of Continuous Postheating Time of Reduction of Preheating Temperature

    pp. 442-445

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    DOI:10.2207/qjjws.9.442

    Continuous postheating for 1-5 hours at same temperature as preheating was carried out on weld cracking test of 80 kgf/mm2 tension steel, and following result were obtained.
    (1) Continuous postheating was recognized to be very useful to reduce the preheating temperature to prevent weld cracking.
    (2) The preheating temperature was reduced to 80°C by 1 hour postheating from 150°C which is the temperature without any postheating, and to 60°C by 5 hour postheating.
  • Predicting Heating and Cooling Times due to Local Preheating

    pp. 446-451

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    DOI:10.2207/qjjws.9.446

    Preheating procedure is applied to prevent cold cracking in steel construction. Then local preheating near the weld line is generally applied, because preheating whole the construction can not be did simultaneously. In case of using electric heaters as means of fecal preheating, the temperature of their heaters can be controlled by sensor fitted on some distance from the weld line. So it is necessary to estimate the temperature on weld line by temperature on the position of sensor.
    In this report, we derive the theoretical formula that finds the temperature of the other position but weld line during preheating, and cooling temperature and time on the weld line can be estimated by using the calculated values. We compared experimental data under various welding conditions with calculated values.
  • Construction of 3-dimensional Image by Using A Characteristics of Secondary Electron Intensity with SEM and It's Application

    pp. 452-457

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    DOI:10.2207/qjjws.9.452

    Intensity of secondary electron induced by incident electron beam depends on a degree of inclina-tion of surface. In the present work, 3-dimensional image for fracture surface was tried to constitute by applying this secondary elecron property with improved type SEM equipment which had four secondary electron detectors to remove a image distortion caused by observating direction. As the results, we could obtain 3-dimensional image and measured direction depth of fracture surfaces by real time treatment with 32 bit personal computer. In the case, the calculation time for one fractograph analysis was about only 5 minutes.
  • Spot Welding of Iron-based and Cobalt-based Amorphous Alloy Foils (Report 2)

    pp. 457-464

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    DOI:10.2207/qjjws.9.457

    Further examinations and considerations were carried out for Foil S of Fe-Si-B alloy, Foil A of Fe-Co-Si-B alloy, Foil B of Fe-Ni-Mo-B alloy and Foil C of Co-Fe-Ni-Mo-Si-B alloy.
    Tensile shear strength of Foil B single spot-welded joints somewhat increased with the increase both in electrode force and in charging voltage, but fracture modes of these joints did not change so much. This result suggests that the increased electrode force could not suppress crystallization of Foil B weld nuggets.
    Tensile shear strength of Foil C single spot-welded joints did not vary so much; these joints were welded at various capacitances up to 700μF and both at a constant peak welding current of 1118 A and. at a higher electrode force of 83.1 N.
    Crystallization temperature Tx and melting temperature Tm of these foils were estimated through DSC in the course of heating. The order of the ratio Tx/Tm fairly relates to the order of spotweldability of these foils.
    Weld nuggets of Foil C produced by irradiating a defocused Nd-YAG laser beam pulse maintained the amorphous state, whereas weld nuggets of the other foils crystallized under the same condition.

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