Optimization of sigma phase precipitates with respect to the functional properties of duplex cast steel

The paper presents the results of examination concerning optimization of the \sigma phase precipitates with respect to the functional properties of ferritic-austenitic cast steel. The examined material comprised two grades of corrosion-resistant cast steel, namely GX2CrNiMoN25-6-3 and GX2CrNiMoCuN25-6-3-3, used for example in elements of systems of wet flue gas desulphurisation in power industry. The operating conditions in media heated up to 70 C and containing Cl- and SO4 ions and solid particles produce high erosive and corrosive wear. The work proposes an application of the \sigma phase as a component of precipitation strengthening mechanism in order to increase the functional properties of the material. Morphology and quantities of \sigma phase precipitates were determined, as well as its influence on the erosion and corrosion wear resistance. It was shown that annealing at 800 C or 900 C significantly improves tribological properties as compared with the supersaturated state, and the best erosion and corrosion wear resistance achieved due to the ferrite decomposition [...] was exhibited in the case of annealing at the temperature of 800 C for 3 hours.