Laser welding of high-strength structural steels with a yield strength up to 960 N/mm(2) and in plate thicknesses up to 10 mm

Objective. The laser welding of high-strength structural steels is gaining in importance thanks to ever less expensive and more efficient lasers as we ll as improved control systems that are on offer. The objective of research work jointly undertaken with SLV Duisburg GmbH was to test the laser welda bility of several characteristic high-strength steels in plate thicknesses up to 10 mm. Provided for the research work were two thermomechanical contr olled rolled steels with a minimum yield strength of 460 N/mm(2) and 700 N/ mm(2), as well as two water-quenched and tempered steels with a minimum yie ld strength of 690 N/mm(2) and 960 N/mm(2). The welding took place with the aid of a commercially available 6 kW CO2 laser. Summary, The research showed that all of the welded joints more or less fre quently displayed pore formation which, however, had no detectable influenc e on the mechanical properties. Satisfactory strength properties and a comp aratively good forming behaviour were found in the weld region of the 5 mm as well as 8 mm and 10 mm welded joints. The impact toughness in the weld r egion of the 8 mm and 10 mm welded joints of the water-quenched and tempere d steels has so far been not quite satisfactory. Even if it is considered t hat the results were obtained on side-notched samples whose assessment is s till uncertain due to a lack of adequate experience, the transition tempera tures T27 at around -30 degrees C are less favourable than for conventional welded joints. Although sufficient for ambient temperatures, an improvemen t of the impact toughness in the weld region should be striven-for with a v iew to utilisation at lower temperatures and for safety-relevant components . The use of a suitable filler metal wire could have a positive effect on t he impact toughness and on the resistance to porosity. Appropriate consider ations have long been a topic of discussion and have meanwhile found expres sion in ongoing and planned cooperative programmes aimed at optimising the laser welding of heavier-gauge plates.