Effect of Filler on the Microstructural Behavior of Dissimilar MIG Weldments for High Pressure Vessel Applications

Microstructural properties are significantly affected due to structural integrity issues. In present work an attempt has been made to study the effect of S4-C504 filler metal on the microstructural properties of API X70 and SA 516 structural steel dissimilar weld fabricated by metal inert gas welding process (MIG). Microstructure of SA 516 is basically a blend of ferrite and pearlite with grain boundary ferrite films dispersed in ferrite matrix. HAZ microstructure on API X70 side shows the partially unmixed region with some inclusions of ferrite embedded across the grain boundaries. SA516 and APIX70 weld region typically exhibit grain boundary ferrite, widmanstaten-ferrite and bainite as fine needle like structure in the fusion zone of weld metal.