Properties of Laser Welded SAF 2205 Duplex Stainless Steel Sheet

Abstract

High rate welding methods for sheet material can offer significant cost reduction for mass production application in comparison with more conventional arc processes. Therefore, in this research, laser welds in SAF 2205 duplex stainless steel (DSS) sheets welded using different welding speeds were investigated. Metallography, texture measurements and mechanical testing were carried out on the weld joints. The corrosion properties were not evaluated. The base material was characterised by a bamboo-like morphology and a ferrite volume fraction of 53 %. For all welding speeds, the ferrite level in the weld zone was higher than 85 % and the austenite showed an acicular morphology. Whereas in the base material a clear element partitioning existed between ferrite and austenite, no partitioning was observed in the welded zone. This is due to the very high cooling rates, which limit the amount of diffusion that can take place. Electron backscattering diffraction revealed that the texture of the cold rolled material was destroyed by the welding process. While the hardness of the base material was about 265 HV, the maximal hardness in the fusion zone exceeded 310 HV and increased with an increase of the welding speed. Yield and tensile stength were however not dramatically influenced. On the other hand, the formability properties were deteriorated by an increase of the welding speed. This behaviour can also be observed on the fracture surfaces of tensile specimens. The tensile tests on the welded sheet resulted in ductile fracture surfaces, but an easier void formation was observed in the laser welds. However, it has to be pointed out that formability of the laser welded DSS sheets is acceptable when a lower welding speed is used. This is also confirmed by the crack propagation observed during the Erichsen test. Therefore, the laser welding can be used as a joining operation for DSS sheet materials providing the corrosion requirements are fulfilled.