Joining of thick section steels using hybrid laser welding

A recently completed project called Economical and Safe Laser Hybrid Welding of Structural Steel (HYBLAS) has developed the use of hybrid laser welding for thicker section steels up to 690 MPa yield strength. 1 The full project involved several European organisations, was part funded by the European Research Fund for Coal and Steel (ERFCS) and was led by Corus RD&T. This paper presents an outline of those parts of the project which relate to those developments which resulted in being able to laser hybrid weld, in a single pass, up to 25 m plate thickness using 20 kW of laser power at speeds of similar to 1 m min(-1). Multipass and dual sided welding techniques have also been developed up to 30 mm plate thickness and fillet welds up to 20 mm steel thickness. The project examined the weldability of steels from 180-690 MPa and operational windows for defect free welding were defined. In addition various NDE methods were studied for their efficiency in regard to the defect types which can occur in laser hybrid welds. The fracture and mechanical properties of the joints were shown to be perfectly acceptable for all structural uses and an extensive fatigue testing programme demonstrated that the fatigue behaviour of the welded joints exceeded conventional welding expectations. Finally full scale industrial components were manufactured, inspected and tested to demonstrate that the anticipated fatigue benefits were obtained.