Laser and laser gas-metal-arc hybrid welding of 960 MPa direct-quenched structural steel in a butt joint configuration

Welding trials have been carried out using direct-quenched 960 MPa ultrahigh-strength steel utilizing several welding processes: gas-metal-arc, laser, and laser gas-metal-arc hybrid welding. Laser power sources like the CO2-laser and the fiber-delivered solid state laser were used. In the trials, butt joints with various groove geometries were used and the thickness of the base material was a constant 6 mm. Welding filler materials varied from matching Union X96 (ISO 14341: G 89 5 M Mn4Ni2.5CrMo) to undermatching Esab OK 12.50 (G3Si1). The diameter of the filler wire varied from 1 to 1.2 mm. The highest hardness value, over 400 HV, was reached on laser welds. According to the results, the strength of the joints corresponded to the nominal strength of base materials (tensile strength of 960 MPa), regardless of the welding method and welding filler material used. As a whole, the results of transverse bend testing were poor as expected, especially when the face side of welds was under tension. The standardized bend and also the used impact toughness tests (Charpy-V) are not the best methods to evaluate the ductility or the toughness of a weld in direct-quenched steels. However, relatively good impact toughness values were achieved to the fusion line of the welds both with the continuous laser and laser hybrid welding process, reaching 57 J with the laser welding and 49 J with the laser hybrid welding when the matching filler material was used.