Abstract
In this study, the influence of the dual-beam energy ratio on weld metal geometry, microstructural evolution, and mechanical performance was investigated for two duplex stainless steels: 2507 type super duplex, 2304 type lean duplex, and their combination. Butt joints in 5 mm thick sheets were produced using an IPG YLS-5000 fiber laser equipped with a twin-spot module, with a beam power ratio of 50:50 and 65:35. Weld cross-sections were analyzed using optical and scanning electron microscopy, phase fractions were quantified by
image analysis, and mechanical properties were assessed via Vickers hardness mapping and room-temperature tensile tests. A 65:35 split concentrated energy in the primary beam, narrowing the bead by up to 33 % and deepening penetration by up to 329 %, while accelerating cooling to refine ferrite dendrites, suppress coarse boundary austenite, and shift phase balance toward higher ferrite contents (up to +10 %). These microstructural changes moderated weld metal hardness, bringing 2507 type super duplex steel closer to base�metal levels, and promoted mixed�mode fracture with smaller, more uniform dimples in a combination of 2507 type super duplex and 2304 type lean duplex steels, exhibiting the highest toughness under primary beam dominance. The results demonstrate that precise control of beam power ratio enables tailored duplex weld microstructures and properties, offering a route to optimize joint performance in demanding applications.

Key words
dual beam laser welding, duplex stainless steel, austenite, ferrite

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