Mechanical and Metallurgical Characterization of Dissimilar P92/SS304 L Welded Joints Under Varying Heat Treatment Regim

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TRODUCTION

RESEARCH on advanced ultrasupercritical power plants where the dissimilar welded joints (DWJs) are used for high-temperature application is progressing throughout the world. The dissimilar joining of creep-strength-enhanced ferritic steels to austenitic steel is required in practical conditions based on end application requirements. The making of the DWJ is more complex as compared to a similar joint (joining of two similar materials). The compositional gradient and microstructural changes produced during the dissimilar joining lead to variations in chemical and thermophysical properties across the welded joint. Sun and Han[1] studied a major weldability issue in martensitic/austenitic welded joints using Granjon implant and crack susceptibility testing using various filler compositions. The hot cracking and cold tendency were satisfactory for welded joints produced using the nickel-based filler metal. However, the welded joints produced with martensitic fillers were reported to be embrittled in nature.

CHANDAN PANDEY is with the Department of Mechanical Engineering, IIT Jodhpur, Karwar, Rajasthan 342037, India. Contact e-mail: [email protected] Manuscript submitted July 11, 2019.

METALLURGICAL AND MATERIALS TRANSACTIONS A

The major issue observed during the dissimilar joining of austenitic steel and martensitic steel is the formation of intermetallic compounds, C- and Cr-related diffusion problems, formation of C- and Cr-enriched or depleted regions, heterogeneity across the welded joints, and differences in the thermophysical properties. King et al.[2] studied the major weldability issues in martensitic and austenitic steel welded joint. Carbon migration near the fusion line, variation in the thermal expansion coefficient of the steels, and formation of the soft transaction zone in the heat-affected zone (HAZ) along the martensitic steel welded joint were also major issues being reported. Sˇohaj and Foret[3] reported the higher stability of martensitic steel as compared to austenitic steel in terms of potential carbon redistribution during long-term aging. The C-enriched and depleted regions were observed along the P91-182 buttering layer as a result of C migration. The effect of heterogeneity on mechanical properties was also studied. Pandey et al.[4] reported that the martensitic filler with martensitic plate mainly led to the formation of the unwanted delta ferrite in the weld fusion zone (WFZ) and heterogeneity across the welded joint. Karthick et al.[5] studied the effect of stainless steel fillers on mechanical behavior of the DWJ and observed the premature failure of the welded joint due to carbon and chromium migration at the fusion boundary and unwanted sigma phase formation. To overcome these problems, researchers are focusing on the use of nickel-based superalloy as a filler material. Kim et al.[6] reported that high-temperature nickel-based superalloy as a filler metal is quite helpful in retarding the local migration of C along the interface. In this manner, it

also stops the formation of localiz