Experimental Analysis of T23–T91 Dissimilar Steel Joining in Supercritical Boiler by a Cost‐Effective Fusion Welding Route

Abstract

The critical aspect of joining T23 steel to T91 steel in a supercritical boiler is studied by a low‐cost gas tungsten arc welding (GTAW) process using an iron‐based filler wire (ER90S‐G). The hardness variation across the weldment does not reflect any drastic fall in hardness, thereby indicating an absence of “soft zone.” A significant joint strength (UTS = 318 MPa) together with a modest ductility (%Elongation = 6) is established by carrying out tensile test at boiler operation temperature (571 °C) and thereafter carrying out advanced characterization keeping all different regions of the weldment intact. During high‐temperature tensile deformation, Cr23C6 particles are found to be pushed along with grain boundary sliding and finally are clustered around the cavity formed thereby. The presence of Cr23C6 particles surrounding cavity promotes a cleavage mode of failure so as to negate a high ductility to be achieved. Yet, a modest ductility is still retained by virtue of soft α‐ferrite matrix promoting a concomitant dimple mode of failure. Furthermore, these Cr23C6 particles are also found to be responsible for an accumulation of dislocation loops around them, thereby providing quite significant high‐temperature strength with 88% joint efficiency.