Authors: MEHMET EMİN ARIKAN, MUSTAFA DORUK
Abstract: Specimens taken from a hot rolled cylindrical duplex stainless steel (DSS) bar with 22% Cr and 5% Ni grade were solution annealed at 1050 °C and then sensitization heat treatments were conducted at 650 °C. A series of specimens with ageing times ranging from 100 to 31,622 min were held for sensitization treatment. The effects of isothermal ageing treatments on the microstructure and on the localized corrosion resistance of the DSS were investigated, through the double loop electrochemical potentiodynamic reactivation (DLEPR) and standard weight loss immersion acid tests. The degree of sensitization (DOS) is measured by determining the ratio of the maximum current generated by the reactivation (reverse) scan to that of the anodic (forward) scan, (I_r/I_a) \times 100. The solution annealed samples and those aged at 650 °C for 100 and 316 min were found to be unsensitized, whereas samples aged 10,000 and 31,622 min were heavily sensitized. Their microstructure is composed of primary ferrite and austenite, sigma, and secondary austenite. The increased degree of sensitization can be attributed to the higher contribution of chromium and molybdenum depleted areas resulting from the formation of the intermetallic phases.
Keywords: Duplex stainless steel, Sigma phase, Secondary austenite, Electrochemical potentiostatic reactivation
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