Effect of Solution Annealing on Microstructure Evolution and Pitting Corrosion Resistance of SAF2906 Super Duplex Stainless Steel

The effect of solution annealing on the microstructure evolution and pitting corrosion resistance of SAF2906 super duplex stainless steel has been investigated. The samples are solution treated from 850 to 1100 °C for 30 min and then water quenched to room temperature. The results show that static recrystallization preferentially occurs within the δ ferrite phase at 900 °C, and the static recrystallization of the ferrite and austenite phases is completed at 1050 °C. When samples aere exposed to higher temperatures, the grain of the ferrite and austenite does not seem to coarsen. Inappropriate annealing at temperatures below 1050 °C inevitably lead to many secondary phases, which are characterized by transmission electron microscopy to be Cr2N and the σ phase. With an increase in the solution temperature, the σ phase dissolved into the matrix before Cr2N, and as the temperature reached 1050 °C, no secondary phases can be observed by scanning electron microscopy. The pitting corrosion resistance of the samples after solution annealing is determined by anodic polarization tests. The electrochemical results show that the σ phase and Cr2N decreased the pitting corrosion resistance and that the σ phase had a more significant effect on the corrosion resistance compared with Cr2N.