P. Kallage
D. Herzog
A. Ostendorf
B. Boese
H. Haferkamp

Mechanical properties of laser MAG hybrid welded high strength steels

Welding in the World
Sonderheft
52
109-115
2008
Type: Zeitschriftenaufsatz (reviewed)
Abstract
In the crane and freight vehicle manufacturing industry, lightweight construction is a strong issue. A reduction of material thickness in booms of cranes or mobile concrete pumps leads to an increase of the number of segments possible and therefore to a longer reach and a higher payload. For these applications, a wide range of high strength fine grain steels for thick sheets has been developed. While these steels have excellent material properties with high yield strengths, special care has to be taken during welding. Therefore, the thermal cycle implemented by Laser MAG hybrid welding has to be fitted to the metallurgical needs of the steel. The energy input per unit length can be varied by the laser power, the arc current or by an additional inductive heating. An accurate setup of these parameters guaranties reliable steel constructions. Combined with the benefits of the Laser MAG hybrid welding process, higher productivity and better process stability, new lightweight constructions are realisable. In this paper, mechanical properties of hybrid welded high strength steels with 960 MPa and more will be shown. Thermomechanically rolled steel and quenched steel can be joined using laser hybrid welding. With the tested material thicknesses, the short cooling times do not resemble a problem. The heat input of the welding process can easily be fitted to the metallurgical needs of the welding process. All material specifications given in factory or European standards could be met. No special weld preparation was needed for hybrid welding of thicknesses up to 7 mm, as the welding process allows high gap tolerances. A quality laser nitrogen cut is sufficient. As laser hybrid welding has got a high welding speed and a low heat input compared to MAG or submerged arc welding, it has got high potential in automated welding of long crane booms. Due to the low heat input, weld distortion will be low, compared to conventional arc welding methods. Potential to increase welding speed is given using an additional energy source like inductors. Mechanical properties show no negative influence so far.