H. Wegmann et M. Holthaus, 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, STAHL EISEN, 118(11), 1998, pp. 121
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.