Effect of thermal aging on corrosion behavior of duplex stainless steels

Abstract

Despite their exceptional mechanical and corrosion properties, duplex stainless steels (DSS) have not found widespread use in high-temperature applications due to concerns over thermal aging and embrittlement at elevated operational temperatures (> 300 °C). The present study investigated the effect of thermal aging time on the electrochemical properties of lean and standard grade DSS that are exposed to a range of pressurized water reactors containing LiOH and H3BO3. The results indicated that the electrolyte chemistry plays a significant role in the corrosion behavior of the DSS alloys. Corrosion resistance decreased with thermal aging time for all DSS alloys; however, standard grade DSS (2205 and 2209-w) alloys showed better corrosion resistance than lean grades (2003, 2101, 2101-w). The presence of dissolved oxygen in the electrolytes resulted in a significant increase in corrosion rate for the DSS alloys, but it did not affect the general trend of corrosion rates with aging time. All DSS alloys became vulnerable to pitting corrosion due to chloride addition, but the pitting resistance decreased with increasing thermal aging time. Increased boron B content resulted in degradation of corrosion resistance of the DSS alloys, while minor changes in pH did not show a significant change in corrosion resistance. Mechanical and metallurgical characterization coupled with electrochemical characterization of the DSS alloys gave a comprehensive insight into the effects of thermal aging on the electrochemical response of the DSS. Graphical abstract

Exploring the Impact of Cooling Rate on Microstructural Features, Mechanical Properties, and Corrosion Resistance of a Novel Nb-Stabilized Super Duplex Stainless Steel in Shielded Metal Arc Welding

“…The growth and higher diffusion range of CrN and Cr 2 N, as well as the increase in the diffusion range due to the cooling in the ferritic phase, would allow the formation of the sigma phase due to the migration of Cr and Mo to zones of higher energy forming intermetallic phases such as Chi and Z phase. The transformation kinetics during prolonged cooling times would allow the transformation of Chi, Z, Cr 2 N, and CrN phases to the sigma phase [60]. This effect was corroborated by X-ray diffraction and CALPHAD CCT simulation results, which indicate the presence of the sigma phase in the air-cooled alloy.…”

In-Situ Analysis of Corrosion Products in Molten Salt: X-ray Absorption Reveals Both Ionic and Metallic Species

“…First, molten alkali halides become corrosive in the presence of impurities. Second, in the presence of corrosion and fission products, the salts might change their thermophysical and thermochemical properties, leading to suboptimal reactor operation conditions, stress-corrosion cracking, , or undesired plating on metal parts. − To understand and mitigate changes in the salt during operation, detailed information about the concentration of corrosion and fission products is necessary and should be measured in situ. Electrochemical techniques are proposed for that task.…”

In-situ analysis of corrosion products in molten salt: concurrent X-ray absorption and electrochemistry reveal both ionic and metallic species

“…First, molten alkali halides become corrosive in the presence of impurities. Second, in the presence of corrosion and fission products, the salts might change their thermophysical and thermochemical properties, leading to stress-corrosion cracking [3,4], undesired plating on metal parts [5,6], or changes in the salt ther-mophysical properties. To mitigate changes in the salt during operation, the redox potential of the salt should be monitored and controlled [7].…”