Chi Phase after Short-term Aging and Corrosion Behavior in 2205 Duplex Stainless Steel

摘要

Correlation between pitting corrosion behavior and chi (χ)phase formed after a short-term aging (5,10 and 15 min)at 850 ℃ of 2205 duplex stainless steel (DSS)was investigated using potentiodynamic polarization tests,optical microscopy,and scanning electron microscopy equipped with energy-dispersive spectrum system.Re-sults showed that after aging for 5 min,theχphase initially precipitated at ferrite grain boundaries,developed and then became linked with prolonging aging time.Theχphase was rich in Cr and Mo,resulting in formation of deple-ted zones nearby.Theχphase could reduce corrosion resistance of DSS and slightly influence its stability,but the specimens still displayed the capacity for repassivation.Some lines of evidence showed that stable pitting corrosion initiated at the boundaries of precipitates.Theχphase was selectively corroded during the first stage of corrosion and then the depleted zones nearby were attacked.In addition,the grain size and volume of precipitates also affected pit nucleation and progress,and suitable size and distribution ofχphase could aggravate pit initiation at precipi-tate boundaries.Theχphase with considerably low volume fraction and small size was not sensitive position for pit initiation.