Investigation on the multi-pass gas tungsten arc welded Bi-metallic combination between nickel-based superalloy and Ti-s
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The present study addressed the weldability of Hastelloy C-276 and Type 321 austenitic stainless steel (ASS) dissimilar combination used for manufacturing of high-temperature equipments in nuclear power plants. Investigation of the microstructural evolutions across the different welding passes and their subsequent effect on the mechanical properties and corrosion resistance would be helpful in better understanding and pave way for the frequent application of such dissimilar joints in the industrial applications. The problem of segregation associated with the multi-pass gas tungsten arc welding process was also investigated systematically. The fusion zone microstructures exhibited a transition from columnar to an equiaxed dendritic structure with varying passes. The topologically closed packed (TCP) phases (such as P and l) were observed in the fusion zone as well as at the weld interface of Hastelloy C-276. Polarization test was performed to evaluate the corrosion resistance and results indicated that the Cr and Mo depleted zones formed around the TCP phases might be responsible for decreased Epit value for fusion zone. The novelty of this work is to explore the possibilities of substitution of an expensive Hastelloy C-276 with a cost-effective Ti-stabilized Type 321 ASS.
I. INTRODUCTION
Dissimilar joining of materials has been frequently used in many industrial applications such as chemical, petrochemical industries, aerospace, and nuclear industries due to the economical benefits and sometimes to satisfy the service necessities.1 Hastelloy C-276 is a solid solution strengthened nickel-based superalloy which offers better combination of mechanical properties as well as corrosion resistance and has been extensively used as a suitable candidate material for high-temperature equipments used in nuclear power plants.2 However, Hastelloy C-276 being an expensive alloy could be replaced with an inexpensive material in less severe environmental conditions and consequently cut down material costs. For such purpose, Type 321 is a stabilized ASS grade (presence of Ti avoids sensitization) used as a tubing material to fabricate tubes in steam gas reformers and would be a good alternative for Hastelloy C-276.3 Therefore, it seems very important to explore the dissimilar combination of Hastelloy C-276 and Type 321 ASS, which are unavoidable in many high temperature applications and has not been studied till now. Joining of dissimilar metals is relatively challenging as compared to similar welding of metals due to differences Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.235
in chemical, physical, and thermal properties.1 Conventionally, gas tungsten arc welding (GTAW) is a widely used fusion welding technique. This technique is widely used in industrial applications on account of its low cost and high efficiency. However, due to the higher heat input associated with fusion welding methods, metallurgical problems such as micro-fissuring, sol
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