Understanding the effect of weld parameters on the microstructures and mechanical properties in dissimilar steel welds

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Welding of dissimilar steel grades, such as stainless and medium carbon steel, is becoming increasingly challenging in petrochemical refineries, as well as in many mining and mineral processing operations. Problems encountered in dissimilar weld joints during in-service applications are associated with formation of brittle phases and undesired residual stresses that develop, resulting in cracks or failures in the component. Many of these problems can be largely tackled by tailoring the microstructure during the weld processing steps. It has been demonstrated in this work that welding process variables can have a direct impact on the resulting microstructure and that the properties of the material can be fine-tuned through a better understanding of the different microstructural mechanisms. Few different weld specimens of a stainless (SS 304) and a medium carbon (EN 8) steels were prepared by changing the weld parameters (current, voltage, speed) by tungsten inert gas (TIG) welding technique. The studies on the microstructural development were performed using the electron backscattered diffraction (EBSD) techniques. Large microstructural differences were brought out between these samples, especially in terms of the distribution of phases and fractions of grain boundary. The tensile strength measured for these welded joints had a strong bearing on the presence of low angle grain boundaries (LAGB). This brief study presents a systematic approach to establish microstructure-mechanical property relationship in dissimilar steel welded joints.