EVALUATION OF THE SUSCEPTIBILITY TO INTERGRANULAR ATTACK OF 2205 DUPLEX STAINLESS STEEL BY DL-EPR METHOD

Abstract

Duplex stainless steels (DSS), consisted of ferrite and austenite, are widely used in oil, chemical, petrochemical, nuclear and marine industries because of their attractive combination of higher mechanical strength and corrosion resistance in various aggressive environments. However, precipitations of detrimental phases, such as chromium carbides, nitrides, intermetallic phases (χ, σ )i n- evitably occur when manufacturing conditions and welding procedure heat these duplex stainless steels to temperature ranging from 300 to 1000 , which results in a reduction in corrosion properties due to the presence of chromium-depleted zones around these precipitates. In this paper, the microstructure evolution of 2205 DSS was studied qualitatively at 800 by using Thermo-Calc coupled with optical microscope. The double-loop electrochemical potentiokinetic reactivation (DL-EPR) was optimized through studying the influences caused by four factors (scan rate, temperature, the concentration of the electrolyte and the surface finish). Then the susceptibility to intergranular attack (IGA) of 2205 DSS was tested by optimized DL-EPR. The results indicated that σ phase will be precipitated in the ferrite phase when 2205 DSS aged at 800 , and the volume fraction would increase with the aging time increasing. The optimized DL-EPR test can evaluate the susceptibility to IGA of 2205 DSS both quantitatively and qualitatively, which is proved by the morphologies of the sample after DL-EPR test.