Within the framework of an AiF (The German Federation of Industrial Research Associations) project, investigations were conducted into the solidification behaviour of various high-alloy austenitic steels in laser and laser-GMA hybrid welding. For comparison purposes, reference was made to pure gas metalarc welding tests. It was possible to raise the welding speeds in hybrid welding compared with the individual gas metal-arc (GMA) and laser welding processes. The central subjects of the investigations were the type of solidification and the connected hot cracking behaviour during welding. In this respect, particular attention was paid not only to the kinetic effects during solidification which may be caused by the high solidification rates in laser and hybrid welding but also to their consequences.
Microcrack formation during gas metal arc welding of high-strength fine-grained structural steel
(2014)
The recent development of high-performance-modified spray arc processes in gas metal arc welding due to modern digital control technology and inverter power sources enables a focused spray arc, which results in higher penetration depths and welding speed. However, microcracks occurred in the weld metal while approaching the process limits of the modified spray arc, represented by a 20-mm double layer DV-groove butt-weld. These cracks were detected in structural steel exhibiting a yield strength level of up to 960 MPa and are neither dependent on the used weld power source nor a consequence of the modified spray arc process itself. The metallographic and fractographic investigations of the rather exceptional fracture surface lead to the classification of the microcracks as hot cracks. The effects of certain welding parameters on the crack probability are clarified using a statistical design of experiment. However, these microcracks do not impact the design specification for toughness in the Charpy V-notch test (absorbed energy at -40 °C for the present material is 30 J).