Effect of Austenite Reformation on Localized Corrosion Resistance of Hyper-Duplex Stainless Steel in Hot Chloride Solution
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The materiality of duplex stainless steels for deep-sea applications, where high corrosive conditions prevail, was studied in the present work. The effect of annealing temperature on the phase balance of the new hyper-duplex grade and subsequent variation in their corrosion resistance at hot chloride environments were estimated. ASTM A890 grade 7A samples were soaked at 1130 °C, 1160 °C, and 1190 °C and furnace-cooled till 1060 °C followed by water quenching. Electron microscope and optical micrograph images confirmed the decrease in austenite with the rise in solutionizing temperature; but on slow cooling, major austenite reformation takes place. Energy-dispersive spectroscopy (EDS) and line-scan methods were used to find out the distribution of constituent alloying elements. The migration of Cr and Mo to the austenite phase occurred as a result of the heat-treatment processes. Potentiodynamic polarization technique was conducted at different temperatures of 30 °C, 40 °C, 50 °C, and 60 °C on all heat-treated samples. At higher temperatures, corrosion resistance improved with an increase in austenite percentage. Optical images of the corroded samples showed the metastable pit growth with an increase in chloride medium temperature.
Keywordsduplex stainless steel corrosion NaCl annealing temperature austenite reformation PREN
The authors are much indebted to Peekay Steels Pvt Ltd for casting the required compositions and their prompt services after that. We are also obliged to Dr. M Ravi of NIIST CSIR Trivandrum for all the assistance and support bestowed on for EDS and SEM analysis.
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