Double loop electrochemical potentiokinetic reactivation test optimization in checking of duplex stainless steel intergranular corrosion susceptibility

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Vol. 35; no. 11; pp. 3499 - 3513
• Main Authors: AMADOU, T, BRAHAM, C, SIDHOM, H
• Format: Journal Article
• Language: English
• Published: New York, NY Springer 01.11.2004; Springer Nature B.V
• Subjects: Applied sciences; Chromium; Corrosion; Corrosion tests; Electrolytes; Exact sciences and technology; Ferritic stainless steel; Metallurgy; Metals. Metallurgy; Scanning electron microscopy; Electron diffraction; Steel; Experimental study; Intergranular corrosion; Sulfuric acid; Hydrochloric acid; Corrosion resistance; Scanning tunneling microscopy; Potentiodynamic method; Precipitation; Corrosion; Corrosion test; Duplex stainless steel; Sensitization; Microstructure; Electrochemical reaction
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-004-0187-4

The double loop electrochemical potentiokinetic reactivation (DL-EPR) test using an electrolyte of 33 pct H^sub 2^SO^sub 4^ solution with 0.3 pct HCl, at room temperature and at a potential scan rate dE/dt of about 2.5 mV/s, was chosen to evaluate the sensitization of austeno-ferritic duplex stainless steels (DSS). Reproducible and optimal test responses and high test selectivity in detecting intergranular corrosion (IGC) susceptibility were verified for four DSS differing in their method of fabrication (cast or wrought) and their ferrite phase content (44 to 57 pct). The test was successfully used to analyze the interactions between precipitation, chromium depletion, and IGC sensitization of the UNS S31250 steel, which was aged between 6 minutes and 120 hours at temperatures varying from 500 °C to 900 °C. The eutectoid decomposition of the ferrite, at different aging temperatures, was investigated using various techniques. The chromium depletion was analyzed qualitatively by X-ray mapping in a scanning transmission electronic microscope (STEM) and quantitatively by analytical calculation based on the chromium diffusion in the ferrite. It was shown that the chromium content in the ferrite can decrease from 30 to 7.5 pct by weight during aging before total decomposition occurs. The interactions between precipitation and IGC sensitization during DSS aging were clearly shown by superimposing the time-temperature-start of precipitation (TTP) and time-temperature-sensitization (TTS) diagrams obtained from the DL-EPR tests performed for various levels of sensitization. [PUBLICATION ABSTRACT]