Mechanical and microstructural characterization of dissimilar welded joints between S355J2 + N and S690QL steels using G69 and T46 filler wires

This study evaluates and compares the mechanical performance and microstructures of dissimilar welded joints made from S355J2 + N and S690QL steels, using G69 and T46 fillers. Tensile, Charpy V-notch (CVN) impact, and hardness tests were conducted, along with optical microscopy and scanning electron microscopy (SEM) for microstructural and fractographic analysis. Average ultimate tensile strengths reached 540 ± 2.5 MPa for T46 and 524 ± 2.5 MPa for G69 joints, with all specimens fracturing within the weaker base metal (S355J2 + N) that had an ultimate tensile strength of 479 MPa, indicating successful overmatching with joint integrity. Hardness examination showed a peak value of 282 ± 3 HV in the S690QL-HAZ, attributed to the formation of martensite laths and localized tempered martensite. The G69 filler wire exhibited higher energy absorption ( 94 ± 13 J at − 20 ∘ C ) compared to the T46 wire ( 67 ± 23 J ). The T46 weld zone showed a higher density of brittle cleavage facets, likely due to the presence of M-A constituents. Despite the variances, all tested specimens fulfilled the minimum impact toughness requirement of 27 J at − 20 ∘ C according to EN 10025-2 standard for S355J2 + N structural steel, demonstrating that both filler wires are appropriate for high-strength dissimilar steel applications under the investigated conditions.