Hybrid Welding (Laser–Electric Arc MAG) of High Yield Point Steel S960QL

Abstract

The article discusses the effect of the hybrid-welding process (laser–electric arc MAG Metal Active Gas) on the structure and properties of butt joints (having various thicknesses, i.e., 5 mm and 7 mm) made of steel S960QL. Welding tests were performed in the flat position (PA) and in the horizontal position (PC). Joints made of steel S960QL in the above-presented configuration are present in elements of crane structures (e.g., telescopic crane jibs). The welding tests involved the use of the G Mn4Ni1.5CrMo solid electrode wire and the Ar+18% CO2 shielding gas mixture (M21) (used in the MAG method). Non-destructive visual and radiographic tests did not reveal the presence of any welding imperfections in the joints. The welded joints obtained in the tests represented quality level B in accordance with the requirements of the ISO 12932 standard. Microscopic metallographic tests revealed that the heat-affected zone (HAZ) contained the coarse-grained martensitic structure resulting from the effect of the complex welding thermal cycle on the microstructure of the joints. Destructive tests revealed that the joints were characterised by tensile strength similar to that of the base material. The hybrid welding (laser–MAG) of steel S960QL enabled the obtainment of joints characterised by favourable plastic properties and impact energy exceeding 27 J. The tests revealed the possibility of making hybrid-welded joints satisfying the quality-related requirements specified in the ISO 15614-14 standard.

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“…The main benefits of laser welding compared to arc welding are: (1) by adjusting the laser metal interaction, the dimension and melt pool geometry can be controlled, which would be difficult to achieve with an arc-welding method; (2) because of the high energy density in laser welding, a nominal heat-affected zone is created; (3) higher cooling and solidification levels compared to other fusion welding methods; and (4) localized and focused heating [10][11][12][13][14]. Furthermore, with gas tungsten arc welding (GTAW), managing the temperature ranges is not feasible as the temperature required to melt the aluminum will only wet the steel [15][16][17]. Traditional non-consumable techniques, such as GTAW or plasma, would not provide such control.…”