Austenitic stainless steel welds have been the prime candidate material joints for superheaters and reheaters in advanced ultra-supercritical (AUSC) boilers among the diverse high-temperature alloys employed in power plant boilers.

The formation of the wide heat- affected zone (HAZ) in conventional fusion welding has led to the evolution of novel joining processes that form fine/narrow heat-affected zones. Among the novel joining methods, magnetically impelled arc butt (MIAB) welding is a unique thermo-mechanical welding technique for joining closed tubular structures with localized heating and melting, resulting in fine/narrow HAZ.

A systematic investigation was undertaken to analyse the microstructural characteristics of a high-temperature alloy, Super304H welded using MIAB welding.

The weldment showed a narrow HAZ adjacent to the faying surface of Super304H. Also, there was no significant change in hardness across the weld interface. A detailed microstructural evolution was characterised using optical and scanning electron microscopy (SEM).

The high temperature (at a strain rate 10-3 s-1 and temperatures of 600-700°C) and room temperature tensile tests were conducted to understand the effect of precipitates and gradient microstructure on the integrity of the weldment.

The creep strength of the weldment was evaluated at temperatures 600-700°C at different stress levels of 200-300 MPa. The high-temperature creep failure of the Super304H welds was analyzed by correlating the mechanical data with microstructural characteristics.

This article is shared by Abhijith S, G D Janaki Ramb, Murugaiyan Amirthalingam and Ravi Sankar Kottada