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Master's Thesis (Kaiwen Zhang).pdf (4.93 MB)

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Experimental and Computational Investigation of Temper Bead Welding and Dissimilar Metal Welding for Nuclear Structures Repair

Zhang, kaiwen
http://rave.ohiolink.edu/etdc/view?acc_num=osu1469036863

Abstract Details

2016, Master of Science, Ohio State University, Welding Engineering.
Structural materials in nuclear power plants are exposed to harsh service conditions and are susceptible to environmental degradation over extended period of time. There are several weldability challenges in the component replacement and repair such as the formation of brittle martensitic microstructure in low alloy ferritic steel and the solidification/hot cracking when cladding nickel filler metal on cast stainless steels. The overarching goal of the present research is to establish the quantitative knowledge of heat transfer, molten metal flow, mixing and dilution, and microstructure evolution during arc welding process. In particular, the tempering of weld heat-affected zone (HAZ) and the weld metal dilution in dissimilar metal weld are studied. In temper bead welding, the heat input from welding is purposefully utilized to temper the hard microstructure for improving toughness. In the present research, the effect of linear heat input on HAZ tempering was studied by a combination of experimental testing and numerical modeling. Temper bead welding experiments were performed on SA-533 Grade B Class 1 (P-No. 3) steel with filler metal 309L by cold wire Gas Tungsten Arc Welding (GTAW). Three different linear heat inputs were used while the power ratio was kept constant. The HAZ microstructure was characterized by scanning electron microscope (SEM) and the extent of tempering in HAZ was quantified using mircro-hardness mapping and thermo-mechanical simulation in Gleeble®. The extent of tempering is found to be a strong function of the peak temperature and to a much lesser extent is affected by time. 2-D and 3-D weld heat transfer models, using the double-ellipsoidal heat flux equation, were developed in Abaqus, a commercial finite element analysis code, to calculate temperature evolution. The peak temperatures experienced in the substrate’s HAZ were correlated to the hardness distribution. The results indicate that the linear heat input can have a significant influence on the extent of tempering in temper bead welding. For the dissimilar metal weld study, high quality and repeatable experimental data was generated by a series of autogenous spot welds (i.e., no filler metal) which were made on base plates of austenitic stainless steel 304L and nickel alloy 690 using GTAW. Two heats of stainless steel 304L were used: one with low sulfur content and the other with high sulfur content. The 304L plates were butt welded together with alloy 690 plates in two shielding gases: pure argon and a mixture of argon and helium. The temperature profiles in the weldment were measured by carefully-placed surface and bottom mounted type K and type C thermocouples. Micro-hardness mapping and chemical analysis using Energy-Dispersive X-ray Spectroscopy (EDS) in SEM were used to examine the property and composition inhomogeneity in the weld metal. 2-D and 3-D weld pool models were developed based on ANSYS Fluent, a commercial computational fluid dynamics code, to understand the transport of chemical elements in the dissimilar metal weld pool. Existing constitutive equations of viscosity and surface tension in the literature were used in the weld pool models. The molten metal fluid flow exhibits a strong outward flow driven by the Marangoni shear stress, resulting in a wide and shallow pool. The hardness distribution and chemical composition is relatively uniform in the dissimilar weld metal, indicating an extensive mixing in the molten pool. The predicted temperature by the 3-D weld pool model shows reasonable correlations with experimental data, indicating its potential in capturing the weld pool transport physics. In summary, the present research constitutes a significant step toward an improved understanding of the two important weldability issues for the repairing of nuclear structures. First, for temper bead welding, it is shown that the extent of tempering for SA-533 HAZ is a strong function of peak temperature. Therefore, the linear heat input has an important effect on HAZ tempering and is also an important parameter that should be considered and controlled in addition to the power ratio for welding procedure development. Future work for temper bead welding includes measuring the Charpy toughness of the tempered HAZ. Second, weld metal dilution in a dissimilar metal weld of stainless steel and nickel alloy is crucial for studying solidification cracking. Experimental data has been generated that can be used to validate future molten pool physics model to understand the molten metal flow and mixing of chemical alloying elements.
Wei Zhang (Advisor)
David Phillips (Committee Member)
97 p.
Engineering
Temper Bead Welding and Dissimilar Metal Welding

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Citations

  • Zhang, K. (2016). Experimental and Computational Investigation of Temper Bead Welding and Dissimilar Metal Welding for Nuclear Structures Repair [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1469036863

    APA Style (7th edition)

  • Zhang, kaiwen. Experimental and Computational Investigation of Temper Bead Welding and Dissimilar Metal Welding for Nuclear Structures Repair . 2016. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1469036863.

    MLA Style (8th edition)

  • Zhang, kaiwen. "Experimental and Computational Investigation of Temper Bead Welding and Dissimilar Metal Welding for Nuclear Structures Repair ." Master's thesis, Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1469036863

    Chicago Manual of Style (17th edition)

osu1469036863
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