A Novel Approach to Characterizing the Corrosion Resistance of Super Duplex Stainless Steel Welds

• Published in: Corrosion (Houston, Tex.) Tex.), 2002-12, Vol.58 (12), p.1039-1048
• Main Authors: Turnbull, A., Francis, P.E., Ryan, M.P., Orkney, L.P., Griffiths, A.J., Hawkins, B.
• Format: Article
• Language: English
• Subjects: Activation; Applied sciences; Corrosion; Corrosion mechanisms; Corrosion resistance; Corrosion resistant alloys; Corrosion resistant steels; Depletion; Duplex stainless steels; Electrochemistry; Exact sciences and technology; Heat; Heat affected zone; Heat treatment; Joining, thermal cutting: metallurgical aspects; Localized corrosion; Metals; Metals. Metallurgy; Methods; Sigma phase; Stainless steel; Weld metal; Welded joints; Welded pipes; Welding
• ISSN: 0010-9312; 1938-159X
• DOI: 10.5006/1.3280793

ABSTRACTWelding can reduce the resistance of steels to corrosion and environment-assisted cracking by altering the material composition and microstructure, modifying the mechanical properties, introducing residual stress, and creating physical defects. Appropriate testing is conducted to ensure that the welding procedures are satisfactory for the application but a welder may deviate from the specified welding procedure and produce a poor quality weldment. Physical defects, such as porosity, slag inclusions, and lack of fusion, can be detected using methods such as radiography and ultrasonics, but the rapid identification of a weld with poor corrosion resistance relative to the parent plate is more of a challenge. To address this, the application of electrochemical techniques to both carbon steel and super duplex stainless steel (DSS) welds is being investigated, although only the results for the latter are reported herein. Welding of super DSS requires a greater degree of control compared to carbon steels, and poor welding practice can result in a severe loss of corrosion resistance. If the heat input during welding is too high, sigma-phase (Fe-Cr-Mo intermetallic) precipitates rich in chromium and molybdenum may be formed. The material surrounding the precipitates is depleted in chromium and molybdenum and is therefore potentially more susceptible to localized corrosion. The volume of the depleted zone and the associated minimum alloy content will depend on the volume of the sigma phase, the temperature at which precipitation has occurred and the temperature-time relationship. At higher temperatures (e.g., 1,000°C),