Metallurgical and mechanical attributes of gas metal arc welded high-strength low-alloy steel

The intention of this study is to explore the influences of welding settings upon the geometry, microstructure transformation, and tensile properties of the gas metal arc welded joints of weathering steel ASTM A606 type IV. The individual effect of the welding variables (welding speed, welding current, and wire feed speed) on the geometries of the weld bead and its tensile properties was explored. The characteristics of the microstructure and macrostructure with various welding technological parameters were also investigated. It is indicated that all the selected welding process parameters significantly affect the welding microstructural and macrostructural features of the welded joints as well as their tensile properties. The results imply that no major defects were observed based on the macrostructure examination. The fusion zone (FZ) changes ferrite and pearlite morphology, relying upon the cooling speed and duration time. The FZ exhibits acicular ferrite, Widmanstatten ferrite, and grain boundary ferrite, resulting in its inferior hardness to that of the coarse grain heat-affected zone (CGHAZ) and weld interface (WI). The adjustment of the welding process parameters bringing about the reduction of the welding heat input contributes to the production of acicular ferrite. The hardness of the weld metal steadily decreases from the heat-affected zone (HAZ) to the base metal (BM). The average tensile strength of the weld metal is 596 MPa, which is comparable to that of the BM. The fracture location is in BM, and the fracture behavior retains ductility. After that, models computing the correlations between welding parameters and welding quality indexes (failure energy of the welded joints, depth of the penetration and bottom reinforcement, and standard derivation of the failure energy) were established and analyzed. The optimal welding parameters were figured out using the desirability approach.