Effect of Aging Time on Microstructure and Susceptibility to Intergranular Corrosion of UNS S32304 Duplex Stainless Steel

The effect of aging treatment time on the microstructure and intergranular corrosion resistance of UNS S32304 stainless steel with solid solution state and rolled state was investigated by optical microscopy, scanning electron microscopy and energy spectrometer. The sensitivity of intergranular corrosion of samples with different states after aging treatment for different time was evaluated by double-cycle potentiodynamic reactivation test and oxalic acid corrosion test. The results showed that no secondary phase was found in the solid solution sample after aging for 0.5 h, and secondary austenite was preferentially precipitated in ferrite in the rolled sample. After aging for 4 h, the spherical M₂₃C₆ and small granular secondary austenite precipitated at the phase boundary of the solid solution sample, while only serrated secondary austenite precipitated along the phase boundary of the rolled sample. With the aging time prolonging, the serrated secondary austenite of the two samples became wide and extended into ferrite, and when the aging treatment time was the same, the precipitation amount of the secondary phase in the rolled sample was more than that in the solid solution sample. In addition, prolonging the time would also increased the sensitization coefficient of intergranular corrosion of samples with solid solution state and rolling state, the latter's sensitization coefficient was larger than the former, and its corrosion resistance was not as good as the former.