Microtexture evolution of sigma phase in an aged fine-grained 2205 duplex stainless steel

Duplex stainless steels were developed using the synergic effect of the ferritic and austenitic phases on the mechanical and corrosion properties when they form a microstructure. Due to the large number of alloying elements added in these materials, precipitation of deleterious phases may occur when they are subjected to certain thermal cycles. The objective of this work was to evaluate the microtexture aspects of sigma (σ) phase precipitation in a cold rolled 2205 duplex stainless steel with fine grains, after isothermal ageing at 850 °C for different times. The microtextures of ferrite and austenite were also assessed and used to correlate with the crystallographic aspects of sigma phase precipitation and growth. In the initial moments of σ-phase precipitation, its orientation distribution function (ODF) was similar to the ones found for ferrite. For longer ageing periods, the σ-phase microtexture showed its main components to be (111)[1¯1¯2] and near to the known copper component (Euler angles) of austenite. The results indicate a severe dependence of σ-phase texture from the ones of ferrite, being decomposed, and on the secondary austenite formed in the eutectoid reaction. In addition, this work shows that an initial low crystallographically coherent interface between ferrite and austenite enhances σ-phase precipitation and deviates it from the Nenno orientation relationship.