Diffusional evolution of σ-phase to resolve a long-standing dissimilar material joining issue in supercritical boiler

ABSTRACT

To restore sustainable growth in thermal power plant operation in view of energy efficiency perspective vis-à-vis an environment-friendly technological advancement, we hereby successfully develop a novel technological route of joining dissimilar steels in a supercritical boiler using GTAW process with Nickel-based filler containing chromium. In its most fundamental conceptualisation, the diffusion of chromium from the molten weld pool to adjacent heat-affected zone (HAZ) results in an evolution of σ-phase (in a region of 52 µm width), which, in turn, arrests grain boundary sliding at boiler operation temperature so as to resist failure. This phenomenon is judiciously established in this work by performing one of the most critical tasks of ascertaining tensile properties at the service temperature of the supercritical boiler followed by necessary characterisation of the weldment. This is further substantiated with an error-function-based analytical diffusion treatment. The high-temperature tensile failure through the base metal region (not through HAZ) with significant property (UTS = 332 MPa, %Elongation = 21) eventually indicates towards a hundred percent joint efficiency, thereby envisaging a sustainable techno-scientific advancement aided by diffusional evolution of σ-phase.

KEYWORDS:

• Supercritical boiler
• dissimilar material joining
• Ni-based filler wire
• Cr diffusion
• σ-phase evolution
• 100% joint efficiency

Acknowledgements

The authors are thankful to the Director, National Institute of Technology Durgapur, India, for necessary administrative support.

Disclosure statement

No potential conflict of interest was reported by the author(s).