Laser-arc hybrid welding of 25 mm high strength steel sections

Abstract

This research delves into the underlying mechanisms of laser-arc hybrid welding (LAHW) for 25 mm-thick EH36 high-strength steel, examining the impact of varying groove widths on the welding process. Experimental results show that the groove width substantially influences weld formation, arc characteristics, and droplet transitions. Narrower grooves are prone to sidewall arc attraction, which increases the likelihood of arc interruptions and the deflection angles of droplets. A wider groove width promotes a more stable arc, more consistent droplet transitions, and enhanced weld formation. Microstructural analysis reveals that narrower grooves correlate with rapid cooling rates in the lower regions of the weld, resulting in a higher martensite content and increased hardness. Wider grooves are associated with slower cooling rates, a higher formation of bainite, and a less pronounced trend of hardness increase.

With a 4 mm groove width, the LAHW process, consisting of a double-layer and two passes, was successfully applied to achieve single-sided welding that resulted in a double-sided formation in the 25 mm-thick EH36 high-strength steel. The resulting weld is defect-free and predominantly composed of columnar crystals. Hardness testing shows a general increase in hardness values within the weld zone, with variations observed in the remelting zone of the two weld layers. Tensile tests show that the weld achieves a maximum tensile strength of 553 MPa, with all samples fracturing in the base metal and exhibiting ductile fracture characteristics. The tensile strength of the weld meets the requirements of the base metal, indicating good ductility and toughness. The average impact energy of the base material is 138.9 J, the average impact energy of the heat-affected zone is 97.6 J, and the average impact energy of the weld is 109.0 J.