Optimizing impact toughness in Q1100E steel welds via laser-arc hybrid welding energy ratio control

Joint brittleness and softening are a prominent challenge in the high-quality welding of Gigapascal-level high-strength steel, severely restricting its engineering application. This study employed laser-arc hybrid welding (LAHW) technique to achieve equal-strength matched joints of Q1100E steel under varying laser-to-arc energy ratios. The correlation between impact toughness and microstructure evolution of the welded joints were systematically studied, and the optimized mechanism of toughness was deeply revealed. The results show that the hybrid heat energy control significantly influences both the impact toughness and the proportion of high-angle grain boundaries (HAGBs). At a parameter set of 3800 W–330 A, the heat-affected zone (HAZ) and the weld metal (WM) exhibited impact absorbed energies of 27.1 J and 25.8 J at −40 °C, with HAGB fractions of 63.2% and 58.5%, respectively. Reducing the laser power to 2500 W while increasing the arc current to 351 A led to a notable decline in impact energy (16.75 J for HAZ and 17.11 J for WM), accompanied by decreased HAGB proportions (56.6% in HAZ and 49.0% in WM). Interestingly, under a low-laser high-arc condition (1500 W–372 A), the impact toughness increased to 24.9 J (HAZ) and 25.54 J (WM), with HAGB levels rising to 62.7% and 54.2%, respectively. Dynamic impact tests demonstrated that the prior austenite grain (PAG) coarsening cannot directly deteriorate the impact toughness. The quantity, morphology, and distribution of lath bainite, governed by the welding energy input, played a critical role in refining the lath martensite substructure. This refinement directly affected the HAGB density, which in turn determined the effective grain size governing toughness.