S32750 duplex stainless steel samples with different initial microstructures obtained by solid solution heat treatment (SHT) were cold rolled with the thickness reduction of 80% and subsequently annealed at 1050℃. The distribution of phase boundary and grain boundary character for the as-processed samples was investigated by SEM-EBSD and XRD techniques. Furthermore, the effect of microstructure on mechanical properties and intergranular corrosion resistance was analyzed by means of tensile testing, nano-indentation and double loop electrochemical potential reactivation (DL-EPR) method. The results show that the fine-grained microstructure with the areal ratio of α to γ about 1, the highest fraction of phase boundaries out of the total interfaces (grain boundaries +phase boundaries), and the least grain clustering within the respective α and γ phases was obtained in the sample previously treated by high temperature SHT and subsequent cold rolling and annealing. As a result, the sample exhibits excellent mechanical properties. After the cold-rolled and annealed samples are sensitized at 750℃ for 4 h, the σ phase precipitates readily along the α grain boundary. The sample previously treated by high temperature SHT and subsequent cold rolling and annealing also possess better intergranular corrosion resistance due to the relatively small amount of α grain boundary and high population of phase boundaries meeting K-S orientation relationship between α and γ. Therefore, the strength and intergranular corrosion resistance might be improved simultaneously by controlling and designing interface character distribution via appropriate thermal mechanical treatment in duplex stainless steel.
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