• Journal of Welding and Joining
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• v.18 no.2
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• pp.184-184
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• 2000

In this study, the lap welding between austenitic stainless steel and carbon steel was carried out using arc spot welding process and weldability of welded specimens was estimated. From the tensile-shear strength test, micro Vickers hardness test, and microstructure observation, specimen of 6.5mm(hole of upper plate) showed the best results in terms of tensile-shear strength and nugget shape. And there was an unmixed zone in fusion boundary between the carbon steel base metal and bulk weld metal. This zone had very thin width with the hard microstructure. The shape of weld nugget in arc spot welding of dissimilar metal welds was predicted by searching thermal history of a weld joint through a three-dimensional finite element model. From the numerical analysis, predicted the shape of weld nugget showed good agreement with the experiment(Received August 24, 1999)

• Journal of Welding and Joining
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• v.33 no.1
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• pp.87-93
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• 2015

This study was performed to develop repair technology for J-Groove dissimilar metal weld of pressurizer heater sleeve in nuclear power plants. Pad, J-Groove automatic welding and mechanical machining equipments to develop repair technology using 'Half Nozzle Repair' were designed and manufactured. To obtain the optimum welding process parameters during Pad temperbead overlay welding, several welding experiments using Taguchi method were conducted. Weldability of Pad overlay weld specimens was estimated by PT/RT test, FE-SEM, EDS and Vickers hardness test. Also, J-Groove welding to adjust weld shape conditions requiring in ASME Code was carried out and its integrity of weld specimens was evaluated through PT/RT test and optical microscope. Consequently, it was revealed that Pad and J-Groove overlay welding for dissimilar metal weld of pressurizer heater sleeve could be possible to meet Code standard without weld defect.

• Journal of Welding and Joining
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• v.32 no.4
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• pp.26-33
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• 2014

The metallurgical and mechanical characteristics, toughness and corrosion resistance of dissimilar welds between super duplex stainless steel UNS S32750 and carbon steel ASTM A516Gr.70 have been evaluated. Three heat inputs of 21.12, 24.00, 26.88kJ/cm were employed to make joints of dissimilar metals with flux cored arc welding(FCAW). Based on microstructural examination, vermicular ferrite was formed in the first layer of weld at low heat input(21.12kJ/cm) and $Cr_{eq}/Ni_{eq}$ of 1.61 while acicular ferrite was formed in last layer of weld at high heat input(26.88kJ/cm) and $Cr_{eq}/Ni_{eq}$ of 1.72. Ferrite percentage in dissimilar welds was lowest in the first layer of weld regardless of heat inputs and it gradually increased in the second and third layers of weld. Heat affected zone showed higher hardness than the weld metal although reheated zone showed lower hardness than weld metal due to the formation of secondary austenite. Tensile strengths of dissimilar welds increased with heat input and there was 100MPa difference. The corrosion test by ferric chloride solution showed that carbon steel had poor corrosion resistance and pitting corrosion occurred in the first layer(root pass) of weld due to the presence of reheated zone where secondary austenite was formed. The salt spray test of carbon steel showed that the surface only corroded but the amount of weight loss was extremely low.

• Nuclear Engineering and Technology
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• v.44 no.6
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• pp.673-682
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• 2012

Three dimensional atom probe tomography (3D APT) is applied to characterize the dissimilar metal joint which was welded between the Ni-based alloy, Alloy 690 and the low alloy steel, A533 Gr. B, with Alloy 152 filler metal. While there is some difficulty in preparing the specimen for the analysis, the 3D APT has a truly quantitative analytical capability to characterize nanometer scale particles in metallic materials, thus its application to the microstructural analysis in multi-component metallic materials provides critical information on the mechanism of nanoscale microstructural evolution. In this study, the procedure for 3D APT specimen preparation was established, and those for dissimilar metal weld interface were prepared near the fusion boundary by a focused ion beam. The result of the analysis in this study showed the precipitation of chromium carbides near the fusion boundary between A533 Gr. B and Alloy 152.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.1
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• pp.97-101
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• 2010

PWSCC(Primary Stress Corrosion Cracking) in Alloy 82/182 butt welds is the problem affecting safety and integrity of nuclear power plant. PWSCC can be occurred in the area that is at high magnitude of tensile residual stress, such as Alloy 82/182 dissimilar metal welds in PZR(pressurizer) nozzles. There have been a number of incidents recently at the dissimilar metal welds in overseas nuclear power plants. Overlay weld is the one of the effective methods to decrease tensile residual stress of inside surface, which will result in preventing PWSCC. In this paper, overlay weld conditions on the purpose of preventing PWSCC was explained and the benefit of the overlay weld was confirmed performing finite element analysis.

• Journal of Welding and Joining
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• v.28 no.1
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• pp.100-106
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• 2010

In this paper crack propagation analyses in the dissimilar metal weldment of a nozzle were performed using a finite element alternating method (FEAM). A two-dimensional axisymmetric finite element nozzle model was prepared and welding simulation including the thermal heat transfer analysis and the thermal stress analysis was performed. Initial cracks were inserted at weld and heat affected zone in the finite element model which has welding residual stress distribution obtained from the welding simulation. To calculate crack propagation trajectories of these cracks, a new fatigue crack evaluation module was developed in addition to the previous FEAM program. With the new FEAM fatigue crack evaluation module, crack propagation trajectory and crack growth time were calculated automatically and effectively.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.8 no.1
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• pp.8-18
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• 2012

In early constructed nuclear power plants, Ni-based Alloys 82/182 had been widely used for dissimilar metal welds (DMW) as a weld filler metal. However, Alloys 82/182 have been proven to be susceptible to primary water stress corrosion cracking (PWSCC) in the nuclear primary water environment. The formation of crack due to PWSCC is also influenced by weld residual stresses. Thus, the accurate estimation of weld residual stresses of DMW is crucial to investigate the possibility of PWSCC and instability behaviors of crack due to PWSCC. In this context, the present paper investigates weld residual stresses of nuclear reactor piping nozzles based on 2-D axi-symmetric finite element analyses based on layer-based approach using maximum molten bead temperature. In particular, the effect of analysis parameters, i.e., a thickness of weld layer, an initial molten bead temperature, convection heat transfer coefficient, and geometric constraints on predicted weld residual stresses was investigated.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.85-87
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• 2008

DMWs are common feature of the PWR in the welded connections between carbon steel and stainless steel piping. The nickel-based weld metal, Alloy 82/182, is used for welding the dissimilar metals and is known to be susceptible to PWSCC. A round-robin program has been implemented to benchmark the numerical simulation of the transient temperature and weld residual stresses in the DMWs. To solve the round-robin problem related to Pressurizer Safety & Relief nozzle, the thermal elasto-plastic analysis is performed in the DMW by using the FEM. The welding includes both the DMW of the nozzle to safe-end and the SMW of the safe-end and piping. Major results of the analyses are discussed: The axial and circumferential residual stresses are found to be -88MPa(225MPa) and -38MPa(293MPa) on the inner surface of the DMW; where the values in parenthesis are the residual stresses after the DMW. Thermo-mechanical interaction by the SMW has a significant effect on the residual stress fields in the DMW.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.73-78
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• 2008

The paper presents the characteristics of mechanical properties within the heat affected zone (HAZ) of dissimilar metal weld between SA508 Gr.1a and F316 stainless steel (SS) with Alloy 82/182 filler metal. Tensile tests were performed using small-size specimens taken from the HAZ regions close to both fusion lines of weld, and the micro-structures were examined using optical microscope (OM) and transmission microscope (TEM). The results showed that significant gradients of the yield stress (YS), ultimate tensile stress (UTS), and elongations were observed within the HAZ of SA508 Gr.1a. This was attributed to the different microstructures within the HAZ. In the HAZ of F316 SS, however, the welding effect dominated the YS and elongation rather than UTS, and TEM micrographs conformed the strengthening in the HAZ of F316 SS was associated with a dislocation-induced strain hardening.

• Nuclear Engineering and Technology
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• v.44 no.5
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• pp.491-500
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• 2012

The dissimilar metal joints welded between Ni-based alloy, Alloy 690 and low alloy steel, A533 Gr. B with Alloy 152 filler metal were characterized by using optical microscope, scanning electron microscope, transmission electron microscope, secondary ion mass spectrometry and 3-dimensional atom probe tomography. It was found that in the weld root region, the weld was divided into several regions including unmixed zone in Ni-base alloy, fusion boundary, and heat-affected zone in the low alloy steel. The result of nanostructural and nanochemical analyses in this study showed the non-homogeneous distribution of elements with higher Fe but lower Mn, Ni and Cr in A533 Gr. B compared with Alloy 152, and the precipitation of carbides near the fusion boundary.