Laser welding of high-strength structural steels with a yield strength up to 960 N/mm2 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 well as improved control systems that are on offer. The objective of research work jointly undertaken with SLV Duisburg GmbH was to test the laser weldability of several characteristic high-strength steels in plate thicknesses up to 10 mm. Provided for the research work were two thermomechanical controlled 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 yield 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 frequently displayed pore formation which, however, had no detectable influence on the mechanical properties. Satisfactory strength properties and a comparatively 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 region of the 8 mm and 10 mm welded joints of the water-quenched and tempered steels has so far been not quite satisfactory. Even if it is considered that the results were obtained on side-notched samples whose assessment is still uncertain due to a lack of adequate experience, the transition temperatures T27 at around -30 degrees C are less favourable than for conventional welded joints. Although sufficient for ambient temperatures, an improvement of the impact toughness in the weld region should be striven-for with a view to utilisation at lower temperatures and for safety-relevant components. The use of a suitable filler metal wire could have a positive effect on the impact toughness and on the resistance to porosity. Appropriate considerations have long been a topic of discussion and have meanwhile found expression in ongoing and planned cooperative programmes aimed at optimising the laser welding of heavier-gauge plates.