Effect of heat input and role of nitrogen on the phase evolution of 2205 duplex stainless steel weldment

Duplex stainless steels have excellent mechanical properties and corrosion resistance due to their austenitic/ferritic microstructure in equal phase fractions. This optimal phase ratio changes as a result of welding in the different zones of the weldment. The evolution of the austenite fraction in the heat affected zone is governed by the nitrogen diffusion during solid-state ferrite-to-austenite transformation, but no loss of nitrogen could be measured in the investigated heat input range. In the weld metal, significant nitrogen loss can be measured from the molten pool, if no filler material or nitrogen containing shielding gas is being used. In our paper, these two different mechanisms and their effect on the austenite fractions are investigated. A Johnson-Mehl-Avrami-Kolmogorov equations parameters predicting the austenite phase evolution has been determined. With the equations help, the austenite volume fraction of the heat affected zone can easily and accurately be predicted after welding in the industrially applicable arc energy range.