Fusion Boundary Region in Single and Multi-Pass Dissimilar Metal Welds

Abstract

Dissimilar metal welds between 2507 superduplex stainless steel and API X-52 carbon steel were joined using ER2594 via the gas metal arc welding process. Two joints were configured to be completed by single- and multipass welds to observe the effects of heat input and dilution on solidification across the fusion boundary region. Therefore, a dual etching technique was employed to reveal the microstructure across the interphase between the materials. The optical microscopy analysis shows the microstructural evolution of the weld metal from blocky austenite to Widmanstätten, as dilution promotes redistribution of elements across the fusion boundary region, as observed in the EDS analysis. However, the WRC-1992 diagram indicates that this occurs at dilutions above ~36%. On the other hand, the weld metal/API X-52 interphase comprises an unmixed zone that exhibits morphologies such as beach, bay, and island and is a function of the percentage of base metal in the weld metal, with rapid cooling due to the weld metal’s lower liquidus temperature. The tensile strength of both dissimilar welds is approximately equal and higher than that of the base metal, API X-52. The hardness distribution shows higher values in the weld metal/2507 of the multipass welding, reflecting the effect of heat input; however, it does not influence failure during the tensile test. This work analyzed and described the fusion boundary region in dissimilar welds for different joint designs and welding parameters.