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Investigating the Microstructure and Mechanical Properties of IN617 Nickel Base Superalloy Welding using SMAW and Keyhole GTAW Welding Processes

Latifi, Reza | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57284 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Pouranvari, Majid
  7. Abstract:
  8. The tungsten inert gas keyhole (K-TIG) welding process is an arc welding technique renowned for its ability to achieve full penetration welding of thick plates without the need for filler metal. This process is valued for its high production rate and cost-effectiveness. However, compared to conventional gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW), K-TIG involves higher input heat, which can influence the microstructural evolution and mechanical properties of the joint region. This study aims to investigate and compare the effects of K-TIG and SMAW welding processes on the microstructure and mechanical properties of thick plates made from the nickel-based superalloy IN617. The K-TIG welding process was conducted in both single-pass and double-pass modes, while the SMAW process involved multiple passes on 10 mm thick IN617 plates. In all three cases, the fusion zone exhibited a dendritic structure with the presence of titanium-rich carbides and molybdenum-rich carbides in the interdendritic regions. The dendrite spacing in the single-pass K-TIG mode was coarser due to the higher input heat and longer solidification time compared to the double-pass K-TIG and SMAW modes. No constitutional liquation was observed in the heat-affected zone of the K-TIG welds, likely due to the presence of micron-sized M23C6/M6C carbides and the lower heating rate associated with this welding process. The weld metal displayed lower hardness in all conditions compared to the base metal due to its coarser solidification structure. Evaluating the mechanical properties of the welds revealed that the SMAW weld metal exhibited higher strength but lower ductility and impact energy compared to the other processes. The investigations indicated an inverse relationship between the ductility and impact energy of the weld metal and its hardness, while the tensile strength of the weld metal correlated with its hardness. The decrease in hardness observed in the heat-affected zone could be attributed to the dissolution of carbides and limited grain growth. Additionally, the study examined the correlation between the material response in different regions of the weld metal, the heat-affected zone, and the base metal using the Small Punch test. The results were compared with the material behavior observed in tensile and impact tests. The correlation between the Small Punch test results and the impact, tensile, and hardness tests suggests that this test can accurately predict the outcomes obtained from these tests. However, a satisfactory correlation was not found between the results of the Small Punch test and the ductility obtained from the tensile test
  9. Keywords:
  10. Nickel-Base Superalloy ; Inconel 617 Superalloy ; Microstructure ; Mechanical Properties ; Gas Tungsten Arc Welding (GTAW) ; Tungsten Inert Gas (TIG)Welding ; Keyhole Gas Tungsten Welding ; Shielded Metal Arc Welding (SMAW)

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