Microstructure and fatigue performance of butt-welded joints in advanced high-strength steels

This study presents a comparative analysis of the high-cycle fatigue behaviors of butt weld joints in advanced high-strength steels with different strength levels and weld bead geometry. Welded joints were made using a gas metal arc welding (GMAW) process on dual-phase steels (DP440 and DP590) and martensitic steel (MS) with tensile strengths of 440, 590, and 1500 MPa, respectively. The microstructures with the lowest hardness were found at the base metal, the sub-critical heat-affected zone (HAZ), and the fusion zone for DP440, DP590, and MS weldments, respectively. Fatigue failure of specimens without weld beads occurred at the points of lowest hardness, and fatigue life exhibited the order MS>DP590>DP440, similar to the order of lowest hardness values in each weldment. However, the introduction of high weld beads resulted in very short, similar fatigue lives for all welded joints and fracture occurred at weld toe due to the overwhelming stress concentration effect. A transition from geometry-governed fracture toward microstructure-governed fracture was investigated by varying weld bead heights.