Sigma-Phase Formation in Weldments of Cast Super Duplex Stainless Steel [Formación de Fase Sigma en Uniones Soldadas de Acero Inoxidable Súper Dúplex Fundido]

This paper decribes the microstructural characteristics of weldments of cast super duplex stainless steel (J93404), being subjected to annealing processes to induce formation of sigma-phase at high temperatures. The influence of heating time at 1073 K, 1123 K and 1173 K upon precipitation of sigma in the heat affected zone, base metal and fusion zone of the weldments was analyzed. The experimental results revealed the formation of this intermetallic compound throughout decomposition of the ferritic phase into austenite and sigma. At earlier stages of the transformation the phase rapidly nucleates and growth along the ferrite-austenite grain boundaries, and then massively advances towards the bulk of the ferritic zone with greater effectiveness as temperature increases. The formation of sigma-phase in all weldments resembles the Johnson-Mehl-Avrami s mechanism stated for nucleation and growth.