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. 2

  • Submerged Arc Welding in the Ar-N2 Mixture Gas Atmosphere

    pp. 211-216

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    DOI:10.2207/qjjws.9.211

    The influence of nitrogen partial pressure were investigated with submerged arc welding. Especially the effect on the oxygen and nitrogen content in weld metal and the absorbed energy by Charpy impact test of those metals by various nitrogen partial pressure were measured.
    The results obtained are summarized as follows.
    (1) The oxygen content in the weld metal does not change remarkably irrespective of nitrogen partial pressure increased.
    (2) The nitrogen content in the weld metal increased as the nitrogen partial pressure increased.
    (3) The silicon content in the weld metal increased slightly as the nitrogen partial pressure increased.
    (4) The manganese content in the weld metal was almost constant and decreased slightly by the fluxes compositions as the nitrogen partial pressure increased.
    (5) The absorbed energy of weld metal increased and decreased due to the flux compositions as the nitrogen partial pressure increased.
  • Current Distribution on Molten Pool in Stationary TIG Arc Welds of Ti Alloy

    pp. 216-222

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    DOI:10.2207/qjjws.9.216

    The estimation of the electric current distribution on the molten pool was tride by measurement of the electric potential distribution on the back of a thin plate (3.5 mm, Ti-6Al-4V), which is one of the base metals in which it is expected that the anode distributes over the wide range on the molten pool. Electric resistivity of this plate is nearly constant with change in temperature.
    The measurement was carried out in a stationary TIG arc with current of 150A and arc length of 3 mm, and in the stationary state of the heat flow (molten pool diameter: 9.5 mm) which is obtained by water-cooling of the back of the plate.
    The result was not a Gaussian and an equi-current distribution but an equi-current density distribution (OD:8 mm) or the current distribution for equipotential surface (OD:7 mm) in which the current value at the outside was higher than at the center.
    x

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  • Metallic Joining Technique of Insulated Copper Coil

    pp. 223-228

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    DOI:10.2207/qjjws.9.223

    A new barzing method was investigated in order to increase the strength of fusing joints of insulated copper wires. This process is a combination of fusing and brazing of brass terminal and insulated conner wires.
    The filler metal, the brass terminal and the wires were heated simultaneously by resistance heating, and they were bonded. The joint which was brazed at about 700°C using BCuP-5 (Cu-15%Ag-5%P) filler metal gave the best result. That joint fractured at the insulated copper wire (base metal) in tensile testing.
    A joint layer which consisted of mainly Cu, Ag, P and a little carbide was formed at the joint interface.
  • Perimeter Measurement by Dual Lines Scanning Method

    pp. 228-233

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    DOI:10.2207/qjjws.9.228

    The development of the high-speed algorithm, using dual lines scanning, called DLS, of perimeter measurement for the figures of binary image was described in the previous report. And also it was proved theoretically that the accuracy of the measurement with that algorithm increases by employing rectangular pixel of large vertical-horizontal ratio in the same report.
    At this time, the algorithm is implemented in the simple hardware and the measuring characteristics is evaluated for various shape of figures. The experimental results closely agree with the estimation by the computer simulation made beforehand.
    There are two ways for realizing rectangular pixel with large vertical-horizontal ratio in the present raster scanning video system, they are to increase the horizontal or to decrease the vertical resolution respectively. It is confirmed experimentally that the accuracy of measurement is improved even in latter case, in which the total resolution is decreased.
    As the results of experimental investigation, it can be substantiated that the DLS algorithm is practically effective for the perimeter measurement of figures.
  • Mechanical Properties of Mild Steel Weld Metals Produced in Pressurized Ar-CO2 Atmospheres

    pp. 233-238

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    DOI:10.2207/qjjws.9.233

    Mild steel sheets with V-groove were welded in pressurized Ar-CO2 gas mixture atmospheres up to 2.0 MPa, using a 1.6 mm diameter solid wire. The effect of ambient gas pressure and gas composition on the mechanical properties of weld metals were studied. The Vickers hardness and tensile properties of weld metals were varied with the ambient gas composition but did not depend on the ambient gas pressure. The Charpy V notch toughness of weld metal was changed markedly with CO2 partial pressure in the atmosphere, and showed a maximum at 0.1-0.2 MPa CO2 partial pressure which resulted in about 0.03% oxygen content of weld metal having a fine ferrite microstructure. This suggests that toughness is strongly influenced by the oxygen content of weld metal. Mechanical properties of pressurized steel weld metal can be controlled by CO2% in the welding atmosphere, because the oxygen content of weld metal is determined by CO2 partial pressure.
  • Contraction Process and RRC Test of Nodular Graphite Cast Iron Weldments

    pp. 239-245

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    DOI:10.2207/qjjws.9.239

    Measurements of contraction process and RRC tests during first-pass welding and cooling were undertaken for the spheroidal graphite cast iron weldments with using DFCNiFe type and D4301 type electrodes. The contraction of cast iron welded joint with using DFCNiFe type electrode was larger than that of with using D4301 one at higher temperature, however final contraction of both weldments were nearly same, about 0.37 mm.
    In the RRC test, the restraint stress of welded joint with DFCNiFe type electrode increased immediately after the start of welding to about 200 MPa, then decreased gradually, and increased again; finally all specimens fractured without showing saturation of restraint stress. But in case of using D4301 type electrode, inspite of lower restraint stress than that of the case of DFCNiFe, cracking in head cccurred at about 670K. The restraint stress at the cracking started was about 120MPa, and then the cracking propagated in the bead with decreasing of temperature of welded joint.
  • Effect of Electrode Potential and Structure on the Susceptibility to HESCC in Duplex Stainless Steels Analytical Evaluation of Hydrogen Embrittlement Type SCC and Its Mechanism in Duplex Stainless Steel Welds

    pp. 245-252

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    DOI:10.2207/qjjws.9.245

    In this paper the authors discussed the depedence of crack initiation properties on potential and the effect of microstructures on the crack initiation and propagation properties in duplex stainless steels. It was clear that at less noble potential crack initiation occured from ferritic phase near the tip of austenitic phase which was controled by HESCC in this region. On the other hand, at noble potential crack initiated from corrosion pets which was formed at the boundary of ferritic and austenitic phases. As the effect of potential on the time to failure with decreasing the potential the time to failure decreased greatly both in a single ferritic phase stainless steel and duplex stainless steels, but even at the potential of -1.5V vs SCE there were no failures to he observed in a single austentic phase stainless steel, which means that austenitic phase is unsusceptible to HESCC. Additionally, as the effecc of ferrite content on HESCC properties of duplex stainless steels, with decreasing ferrite content the threshold stress increased and crack growth rate decreased greatly, which means that austenitic phase has a keying effect on crack propagating through ferritic phase. At the region of ferrite content less than 45%, threshold stress was nearly as same as the tensile strength of the materials and crack could not propagate through austenitic phase because of the continuousness of the austenitic phase which will prevent crack propagating through ferritic phase. Therefore, ferrite content of 45% should be considered as a critical value for crack initiating and propagating in duplex stainless steels.
  • Effect of Ambient Temperature on Steel Weldability

    pp. 252-258

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    DOI:10.2207/qjjws.9.252

    It is well known that there are four main factors for cold cracking probability in a heat affected zone (HAZ), i.e., carbon equivalent, diffusible hydrogen content, welding thermal history and residual stress. Using these four factors, several criteria have been presented to avoid cold crack-ng. At low ambient temperaturel welding without prehaeting is sometimes preculded, because the surface of a welded plate might be frozen. On the other hand, high tensile strength modern steels have low carbon equivalent owing to such newly developed processes as thermomechanical control, which means that steeleweldability is much higher than that of the old days. And because of this tendency, reducing carbon equivalent, many opportunities will occur that welding, sometimes without preheating, is condicted at low ambient temperature. However, there are few research reports which examine the effect of ambient temperature on steel weldability. The authors examined the eqect of ambient temperature on cold cracking susceptibility. Temperatures chosen were 20°C, -10°C and -30°C. The Tekken test method was applied to steels, and five macro sections were machined from every tets piece to observe cold cracking in hte HAZ. From the experimental results, it is concluded that it must be considered as an additional independent factor for cold cracking susceptibility. To assess this effect, the modified carbon equivalent is introduced.
  • Effect of Grain Boundary Structure on Weld Decay of Austenitic Stainless Steel (Part 1)

    pp. 258-263

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    DOI:10.2207/qjjws.9.258

    Grain boundary carbide precipitation and corrosion in weld heat affected zone of a type 304 austenitic stainless steel were investigated using optical and scanning electron microscopy to discuss effects of grain boundary structure on precipitation and corrosion from a crystallographic viewpoint. In the grain boundary precipitation region, the frequency of grain boundary carbide precipitation had a maximum near the coarse grained region and decreased gradually with the distance from there to the unaffected base metal region. The frequency increased with weld heat input. Strauss test of 304 steel HAZ showed that all the cracked grain boundaries after bend test had carbide precipitates and that the frequency of cracked boundary was roughly proportional to the frequency of grain boundary precipitation. Electron channel-ling pattern analyses in scanning electron microscopy showed that grain boundaries with ordered atomic structures were hardly etched after 10% oxalic acid etching test. These facts have suggested that grain boundary precipitation and corrosion in stainless steel weld heat affected zone depend sensitively on crystallographic character of grain boundary.
  • Effect of Grain Boundary Structure on Weld Decay of Austenitic Stainles Steel (Part 2)

    pp. 264-269

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    DOI:10.2207/qjjws.9.264

    Grain boundary carbide precipitation in weld heat affected zone of type 304 and 304L, austenitic stainless steels was observed using transmission electron microscope to make clear the effects of grain boundary misorientation and structure on carbide precipitation at grain boundaries in stainless steel welds from a crystallographic viewpoint. Grain boundary carbides were detected in grain boundary precipitation region of the 304 steel weld heat affected zone. In that region, some grain boundaries had carbide precipitates, but some were precipitation-free. Kikuchi line analyses showed that grain boundaries with ordered atomic structures had no carbide precipitates. This tendency was valid in 304L steel weld, although grain boundary carbide precipitates were finer in 304L, steel than in 304 steel. These facts have suggested that grain boundary precipitation and corrosion in stainless steel weld heat affected zone depend sensitively on crystallographic character of grain boundary.
  • HAZ Toughness of High Silicon Containing Duplex Stainless Steel

    pp. 269-275

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    DOI:10.2207/qjjws.9.269

    The HAZ toughness was investigated in the high silicon containing duplex stainless steels from a metallurgical point of view. The increase of silicon content is effective for improving the corrosion resistance to nitric acid containing highly oxydizing ions. However, the effect of increasing in silicon content on the HAZ toughness of duplex stainless steels has been rarely clarified.
    The effects of nickel and nitrogen content as well as the ferrite ratio on the HAZ toughness were studied to obtain proper chemistry in 23%Cr-3.3%Si-Ni-N duplex stainless steels. The HAZ toughness was evaluated by using Charpy impact test specimens machined from GTA welded joints. It was clarified that there were two reasons for the HAZ embrittlement. One was the sigma phase precipitation in case of lower ferrite ratio. Another was the nitride precipitation in case of higher ferrite ratio. In the proper range of nickel and nitrogen content, the high HAZ toughness was obtained. The sigma phase precipitation was accelerated by the decrease of the ferrite ratio and the increase of the nickel content. The increasing in the silicon content accelerated the nitride precipitation in the HAZ. However the decrease of ferrite ratio could reduce the nitride precipitation in the HAZ even though in the 3.3% silicon containing duplex stainless steels. It was clarified it was important for the sound HAZ toughness to control the nickel and nitrogen content in the proper range.
  • Adhesive Strength Evaluation of Coating Layer by Modified Pin Test

    pp. 275-281

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    DOI:10.2207/qjjws.9.275

    To establish the adhesive strength evaluation method of thin coating layer with high adhesive strength, hard chrominum plating and (Al2O3+TiO2) spray coating were tested by newly proposed pin test method and their date were evaluated by stress singularity parameter (kcr).
  • Study of g value of Edge Crack Existing along Bond Line of Joint Composed of Dissimilar Materials

    pp. 282-287

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    DOI:10.2207/qjjws.9.282

    The energy release rate, g, used for estimating the joint strength of dissimilar material joints with defect has been investigated by means of a boundary element method (BEM). Size and material parameters of g value in both load and residual stress fields were derived. The main conclusions are as follows:
    1) In a thermal stress filed, the relation between g value and material properties is given by the following equation;
    For the case of Poisson's ratios of dissimilar materials being equal,
    g/EA{(αAB)T}2a=f(EB/EA, vA=vB)
    where E is Young's modulus. ν is Poissons' ratio. α is a coefficientof linear expansion.
    T is temperature difference. α is half length of crack.
    Suffix A and B mean materials A and B. For the case of νA being different from νB,
    g/EAAT)2α=g(EB/EA, νA, νB, αBA)
    2) When the height of specimen, h, is greater than the width of specimen, b, h, hardly affects g value in both load and residual stress fields.
    3) When b is greater than twice of h, g value is almost constant in both fields.
  • Root Failure Resulting from Toe Treatment of Non-Load-Carrying Cruciform Fillet Welded Joints

    pp. 288-294

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    DOI:10.2207/qjjws.9.288

    The smoothing of fillet toe results in improvement of fatigue strength, but at the same time it seems to develop a liability to root failure occurrence.
    The purpose of this study is to investigate the relation between root failure and stress concentration in toe smoothed non-load carrying type cruciform fillet welded joint and the effects of lack of joint penetration on fatigue strength of the fillet joint.
    Lack of joint penetration in the welds was deliberately introduced by a special method of putting a half cut core wire on the weld joint. After weldig, toes were TIC dressed. In fatigue tests, the maximum stress of fatigue cycle was fixed to yield, stress of the material (Max. stress=Yield stress (const.)=559MPa, Min. stress=variable).
    Main results obtained are summarized as follows:
    1) The root failure seems to be apt to occur if the elastic stress concentration factor at the TIG dressed toe is less than about 1.6 in the present tests.
    2) The difference in heights of lack of joint penetration, 0.92 mm and 1.64 mm, shows no significant effects on fatigue strength.
    3) The root failure occurs in general at a lower stress range than the stress range where a toe failure follows a root crack.
    4) The most important condition for preventing a root failure is to allow no lack of joint penetration (rib side) i.e. slit perpendicular to the loading direction.
  • A Judging Method of Advisability of Welding under Pulsating Loads

    pp. 294-298

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    DOI:10.2207/qjjws.9.294

    The authors have been carrying out a series of research for the prevention of hot cracks produced by welding on the steel structures in service condition from a mechanical point of view. The opening displacement of root gap, Δδ, which can be easily measured before welding, has been already proposed as the practical mechanical measure for deciding the initiation of the hot cracks.
    In this study, based on Δδ, a way which judges the advisability of welding under the pulsating loads is concretely shown with taking the bridge in service condtion an instance. Therefore, first, the various displacement, vibration and acceleration are measured at the weld joints of the bridge in the service condition. So, the wave of vibtation of Δδ in service condition is clarified and its amplitude and the number of oscillations are known. On the other hand, as one of powerful approach to prevention of hot cracks based on Δδ, it is considered that the critical value, Δδcr which is mechanical property of the welding electrode for the hot cracks, is made as big as possible. From this point of view, the new welding electrode was tried to be developed. As the results of weld cracking test, Δδcr, of the newly developed welding electrode could be made three or four times as big as that of commonly used welding electrodes. From this fact, the welding under the pulsating loads should be easy. In these considerations, a way based on Δδ which judges the advisability of welding under the pulsating loads is shown. Then, applying the judging method to the repair work on the bridges in service condition, its validity is concretely shown.
  • Nondestructive Evaluation of Residual Weld Stress and Mechanical Stress Relieving by Acoustoelasticity

    pp. 299-304

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    DOI:10.2207/qjjws.9.299

    Residual stress affects the failure of machines and structures by contributing to buckling and brittle fracture when those failures occur at low applied stress levels. In addition, residual stress may contribute to fatigue and corrosion cracking. For in-process and in-service failure prediction of the machine and structure, nondestructive methods for residual stress measurement are required. The research on nondestructive evaluation of residual stress using ultrasonci technique has attracted special interest recently. A few works have been reported on the ultrasonic measurement of residual weld stress. However, reports on nondestructive evaluation of stress relieving have apparently not been published to date.
    In the present study, ultrasonic stress measurement techniques are applied to mild steel plate welded by shielded metal arc welding and aluminum alloy plate heated by TIG arc. In addition, the effect of mechanical stress relief treatment is examined by the ultrasonic method. Most ultrasonic stress measurement techniques measure some combination of stresses, such as the sum or difference of principal stresses. In order to evaluate the effect of residual stresses on the failure of structures, stresses must be determined absolutely. In the present paper, the ultrasonic technique for measurement of absolute residual stresses is examined. The residual stress distributions are compared with those measured by stress-relaxation techniques which use electric strain gauges or contact balls. It is clarified that residual stresses measured by ultrasonic technique are very close to those by conventional stress-relaxation methods. Consequently, the residual stress can be measured nondestructively and absolutely by means of the ultrasonic method.
  • Microstructure and Hardening Mechanism of Nitrided Ni Binary Alloys

    pp. 304-311

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    DOI:10.2207/qjjws.9.304

    In order to investigate the hardening mechanism of Ni alloys by nitriding treatment, tentative Ni binary alloys of Ni-7wt%Ti, Ni-15wt%V, Ni-10wt%Nb and Ni-30wt%Cr were intrided by plasma ion nitriding (PIN) process under various conditions of nitriding temperature from 673 to 1073K and nitriding time at 10, 8ks in N2+H2 mixed gas atmosphere of 800Pa.
    Hardness of the nitrided layer was increased with decrease of nitriding temperature. From the X-ray diffraction analysis and transmission electron microscopy, it was considered that the hardening mechansim of Ni alloys by PIN process was due mainly to the lattice strain of the matrix of nitrided layer caused by dispersive precipitation of metastable nitrides of each alloying element. A lower hardness of the nitrided layer at higher nitriding temperature was owing to the decrease of lattice strain by coarsening of equilibrium nitride particles.
  • Effect of the Third Alloying Elements on Surface Hardening of Ni-7wt%Ti and Ni-20wt% Cr Binary Alloys by PIN Process

    pp. 311-317

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    DOI:10.2207/qjjws.9.311

    The effect of the third alloying elements of various intride fomer, such asl Ti, V, Nb, Ta, Cr, Mo or Al, on the surface hardening of Ni-7wt%Ti and Ni-20wt%Cr binary alloys has been investigated by PIN process under various conditions of nitriding temperature from 773 to 1073K and nitriding time at 10.8ks in N2+H2 mixed gas atmosphere of 800Pa.
    The hardness and the thickness of nitrided layer of Ni ternary alloys were lager than these of Ni binary alloys at the same nitriding conditions, and the PIN treated Ni alloys showed far better wear resistance than untreated alloys. Among the alloying elemtn, Nb and Cr were beneficial for increasing the hardness and the thickness of nitrided layer for Ni-7wt%Ti and also Ti and Ta were beneficial for Ni-20wt%Cr. The maximum surface hardness Hv800-900 was obtained for Ni-7wt%Ti acontaining Nb and Cr, and Ni-20wt %Cr containing Ti and Cr, at nitriding temperature of 873-973K.
    Transimission electron microscoyp and X-ray diffraction analysis revealed that the surface hardening of Ni ternary alloys was due to the mattix lattice strain in the nitrided layer. Moreover, the effect of the third alloying element was found to be the increase of the matrix lattice strain in the nitrided layer caused by a fine dispersion of nitride particles.

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