ESSC & DUPLEX 2019

Super duplex stainless steels (SDSS) combine superior mechanical properties and high corrosion resistance, which makes them an attractive choice for demanding applications. The welding of SDSS, however, is more challenging than for standard and lean duplex stainless steels as the desired balanced ferrite fraction sometimes is conflicting with the more rapid formation of deleterious phases in SDSS. The relationship between process parameters, determining the welding thermal cycle, and the final microstructure is, therefore, of a great importance for reliable fabrication of welded SDSS structures. The present study was primarily aimed at investigating this relationship for root/single pass welding of type 2507 SDSS. Fourteen welds were produced using GMAW, GTAW, SAW, and SMAW with different joints geometries, plate thicknesses, and welding parameters. Thermal cycles were recorded using several thermocouples attached to the plates and thermocouples were also harpooned into the weld pool. Weld pool geometries and base metal dilution in the weld metal were determined for all welds. Ferrite fractions were measured using Feritscope and image analysis for all single pass welds. Results allowed the influence of dilution and cooling rate on the ferrite fraction to be determined. Kinetics of austenite formation was also modelled using computational thermodynamics (Thermo-Calc & DICTRA) to predict the ferrite fractions in the weld zone and calculated fractions were compared to experimental results. Furthermore, based on the results from the single pass welds, a geometrical approach was proposed to predict the dilution in multipass welds. Results will be discussed, and it is shown that the above approach can be used for prediction of the ferrite fraction of duplex stainless steel single- and multi-pass welds.