Berichte aus dem Produktionstechnischen Zentrum Berlin / Investigation of the Metallurgical and Thermo-Mechanical Factors Influencing Centreline Solidification Cracking by Laser Beam and Hybrid Welding.

The objective of the present thesis is to make advancements in understanding solidification crack formation in laser beam and laser-hybrid welding. Focus was laid on the investigation of the metallurgical and thermo-mechanical influencing factors. The factors affecting centreline crack formation are investigated with the aim of finding conditions for hot crack resistant welds. The main emphasis is placed on the impact of structural design and the associated stiffness conditions of the structure to be welded on the hot cracking resistance of various materials such as pipeline steels and a variety of stainless steels. This thesis provides a critical assessment of the current hot cracking tests for the evaluation of centerline solidification cracking during laser beam and laser hybrid welding. The self-restraint and externally-loaded hot cracking tests, IRC- and CTW-test respectively, were successfully applied in conjunction with laser beam welding. Both tests enabled the assessment of centreline solidification cracks based on measurable critical parameters.