Evaluation of Optimal Forging Temperature Range for an Industrial UNS S32750 SDSS Alloy Using SEM-EBSD Analysis

The deformation temperature of Super-Duplex Stainless Steels (SDSS) is a key factor defining the number of phases, their proportions, and their arrangement in space, with the main role for the hot plastic processing on the industrial scale. The main scope of the study was to determine the optimal forging temperature of UNS S32750 Super-Duplex Stainless Steel by means of the SEM-EBSD technique. The alloy was forged at different temperatures between 800 °C and 1300 °C, after which the most representative samples were analysed by SEM-EBSD. Microstructural characteristics as nature, distribution, morphology, and relative proportion of constituent phases, grain form, homogeneity, and dynamic recrystallization of the structure were analysed in relation to forging temperature. Primary phases as δ-Fe and γ-Fe were identified in all structural states of the steel, irrespective of the deformation temperature. Secondary phases σ-(Cr-Fe) and χ-(Fe-Cr-Mo), identified only under 1050 °C, have a strong negative effect on hot formability because they are fragile. The conclusion was that the optimal forging temperature range for the UNS S32750 steel is 1050-1300 °C because between these temperatures the structure is composed only of ferrite and austenite, without other harmful secondary alloy phases. Due to the dynamic recrystallization, the plasticity of the material also increases in this thermal range.