Abstract
Microstructural observation plus chemical and structural analysis of the real heat-affected zone (HAZ) of a TIG weld performed on a 2205 Duplex stainless steel were carried out, both in the as-welded state and after long ageing periods of time at 380 °C. The weld thermal cycle re-transforms the 50/50 austenite/ferrite duplex original microstructure into large ferritic grains and a combination of grain boundary Widmanstatten plates and small intragranular islands of austenite. Intensive precipitation of 0.5-1.0 µm long platelets identified as Fe-Cr-Mo carbonitrides was observed in the ferritic grains. These features were homogeneously dispersed in the central part of the ferritic grains and heterogeneously arranged along curved lines, the latter being possibly associated with previous ferritic or austenite/ferrite grain boundaries. Close to the fusion line the weld thermal cycle caused the onset of spinodal decomposition in the HAZ ferritic grains, characterized by a typical "mottling" contrast detected by transmission electron microscopy. After 5000 h at 380 °C the spinodal decomposition became more intense and gave rise to the homogeneous precipitation of particles identified as the G-phase.

Key words
duplex stainless steel, heat affected zone, spinodal decomposition, G-phase precipitation

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