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Divya, M.
- In-situ Weld Repair of Cracked Shrouds of Turbine and Characterization of The Weld Joint
Authors
1 Materials Joining Section, Materials Technology Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamilnadu, IN
Source
Indian Welding Journal, Vol 44, No 1 (2011), Pagination: 49-57Abstract
Cracked shrouds of the 3rd stage of a Low Pressure turbine was in-situ repaired by removing the cracked pieces of the shroud and welding new shroud pieces to the existing shroud. The shroud material was made of AISI414 martensitic stainless steel (SS), and the repair welding was carried out using ER 410NiMo filler wire. The tenon heads of the blades, which were removed for carrying out the in-situ repair, were also built-up by weld deposition. The repair welds were subjected to in-situ two-stage post weld heat treatment (PWHT) as required for the 414 SS material and the 410NiMo weld metal. For prior to simulation of the constraints of actual in-situ repair, a mock-up piece was made using the same blade material, welding consumable, welding procedure and PWHT as were to be used for the actual repair. After successful completion of the repair, the mock-up piece as well as separate weld pads prepared using the shroud material and ER 410NiMo consumable were subjected to detailed microstructural characterization and mechanical properties testing to generate data on the properties of the repair weld now in service. The paper discusses the details of the in-situ repair and results of the characterization of the weld joints. Results confirm the repair weld has adequate strength and ductility. The turbine with repair welded shrouds has been performing satisfactorily since 2008.
Keywords
Repair welding, Turbine Shroud, PWHT, Supermartensitic Stainless Steels.
- Study on Effect of Weld Cooling Rate on Fusion Zone Microstructure and Solidification Cracks in 316L Austenitic Stainless Steel
Authors
1 Department of Mechanical Engineering, SSN College of Engineering, Kalavakkam - 603 110, IN
2 Metallurgy and Materials Group, IGCAR, Kalpakkam - 603 102, IN
Source
Indian Welding Journal, Vol 52, No 1 (2019), Pagination: 56-63Abstract
A study on effect of cooling rate on mode of solidification and microstructure was carried out on austenitic stainless steel welds. A tube and plug of 316L stainless steel was joined using Gas Tungsten Arc Welding (GTAW) and laser welding processes. The welds were characterized using optical and Scanning Electron Microscope (SEM). The results indicate that cooling rate of the weld has significant effect on solidification mode, microstructure and solidification cracking. 316L weld joints prepared using GTAW process shows duplex microstructure of vermicular ferrite and austenite in the fusion zone. Whereas, the fusion zone of laser joint shows only single phase austenite microstructure. From these observations, it is clearly understood that the changes observed in the fusion zone microstructures of GTAW and laser welds are due to change in the mode of solidification as a result of change in the weld cooling rates. The predicted mode of solidification for GTA welds for 316L composition used in this study was Austenite-Ferrite (AF) and it was also confirmed through the microstructural observations. In laser joint, the weld has solidified in fully austenitic mode which deviates from the mode of solidification predicted by the conventional constitutional diagrams and hence modified weldability diagram was used. From this investigation, it was also found that the rapid solidification during laser welding is not completely partition less because segregation of sulphur was found using Scanning Electron Microscope – Energy Dispersive Spectroscope (SEM-EDS) along the dendrite boundaries of laser welds. High cooling rate during weld solidification which influences fully austenitic mode of solidification and micro segregation of impurities along the grain boundaries contribute to solidification cracking of welds in laser joints.
Keywords
Solidification Mode, Solidification Cracking, Cooling Rate, Energy Dispersive Spectroscopy, Laser Welding, Gas Tungsten Arc Welding.References
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- A Novel Approach for Welding SS 304B4 using Standard Austenitic Consumables with Low Cracking Tendency
Authors
1 Materials Joining Section, Metallurgy & Materials Group Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, IN
Source
Indian Welding Journal, Vol 55, No 1 (2022), Pagination: 48-53Abstract
304B4 SS is an austenitic stainless steel used for neutron shielding applications that contains ~1.3 wt.% of boron in the form of Cr B 2 borides distributed in the matrix. Though weldability of this steel is reported to be good because of backfilling of cracks by eutectic liquid formed during solidification, welding using standard E309 electrode during fabrication of components revealed high cracking tendency. This was attributed to base metal dilution in weld metal which alters the microchemistry of a portion of weld metal such that insufficient eutectic liquid is formed to heal the cracks. In order to overcome the cracking issue due to base metal dilution, an additional step of buttering was done using E309 on sides of 304B4 SS plates prior to welding. The concept of buttering was introduced because cracking tendency in the butter layer would be less in spite of significant base metal dilution due to less restraint present while buttering. Thickness of buttering layer is optimized such that at least 2-3 mm of undiluted E309 is deposited at the outermost edge to be joined. Welding is carried out on the buttered edges using E309 and subsequently specimens were suitably extracted for varestraint test from the weld joint. Spot varestraint test carried out at the “butter layer–weld” interface showed very low susceptibility for liquation cracking than direct joint tested at “base metal-weld” interface in earlier study. This is attributed to negligible dilution in the weld metal from the butter layer during actual joining when significant restraint is present.Keywords
Borated stainless steel; Hot cracking; Varestraint test; Dilution.References
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- Divya M and Albert S K (2018); Weldability Study on SS 304B4 Joined using Boron Containing Austenitic Stainless Steel Consumable, Journal of Welding and Joining, 36(6),pp. 60-70.