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

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.Results showed that after aging for 5min,the χ phase initially precipitated at ferrite grain boundaries,developed and then became linked with prolonging aging time.The χ phase was rich in Cr and Mo,resulting in formation of depleted zones nearby.The χ phase 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.The χ phase 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 of χ phase could aggravate pit initiation at precipitate boundaries.The χ phase with considerably low volume fraction and small size was not sensitive position for pit initiation.

Effect of compression deformation on precipitation phase behavior of B-containing S31254 super austenitic stainless steel

Effects of compression deformation on the sigma-phase precipitation behavior of B-containing S31254 stainless steel after solution treatment were studied using the Gleeble compression test. The cold and hot processing characteristics of B-containing S31254 stainless steel were evaluated, and the results show that the speed of compression deformation increased the precipitation rate of the sigma phase, and the location of precipitation extended from the austenite grain boundary to the original hot rolling deformation area. During cold deformation at room temperature, the precipitation rate increased when the deformation reached at 40%. Deformation at 950℃ affected precipitation more obviously. At 1074 ℃, when the deformation reached 20%, the precipitated phases started increasing, and above this deformation range, precipitation began decreasing. Also, at 1074℃ the deformation accelerated the precipitation of sigma phase;but with deformation, there was a change in critical temperature for the sigma-phase excursion. The precipitation position of the sigma phase is strongly related to the area of the original hot rolling deformation. With an increase in the deformation amount, precipitates in this region appeared as coarse-grained, skeletal, and network-like features.

Effect of boron on dissolution and repairing behavior of passive film on S31254 super-austenitic stainless steel immersed in H_(2)SO_(4) solution

The impact of boron on the dissolution and repairing behavior of passive films formed on S31254 super-austenitic stainless steel(SASS)was investigated.SASS was immersed in 0.5 mol/L of H_(2)SO_(4) for 0,2,6,10,and 14 days to explore the evolution of the passive film.The electrochemical impedance spectroscope(EIS),the Mott–Schottky analysis,and X-ray photoelectron spectroscope were utilized to analyze the semiconductor properties and compositions of the passive films.EIS showed a decrease and consequent increase over 14 days;the same pattern was observed for Cr_(2)O_(3) and Cr/Fe.However,the defect density of the passive film exhibited a reverse trend.The variation in film thicknesses indicated that the passive films possessed dissolution and repairing behavior.SASS passive film had a double-layer structure;the outer layer was found to be rich in Fe3+and Cr(OH)3,but low on Mo6+,while the inner layer was rich in Cr_(2)O_(3) and low in Mo4+.The addition of boron increased the corrosion resistance and could promote the efficiency of the passive film repair,likely by promoting the migration of Mox+,which promoted the repairing of the passive film.