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Abstract
On newly developed Febalance-18Cr-7Mn-3Mo-3W-0.4N-(0.03, 0.57)Ni (in wt%) lean duplex stainless steels, the microstructure, element partitioning behavior, and resistance to pitting corrosion were investigated. After solution treatments, the two alloys were found to have similar microstructures in terms of phase fraction and grain size, and have a precipitation-free matrix. The polarization tests revealed that the addition of Ni was beneficial to improve the resistance to pitting corrosion, which was confirmed by the rise in pitting and repassivation potentials. The uniform corrosion behavior and galvanic corrosion rate of the matrix were investigated to explain the improved pitting corrosion resistance of the Ni-added lean duplex stainless steel. As a result, it was found that the addition of Ni enhanced the resistance to uniform corrosion by reducing the galvanic corrosion rate between the ferrite and austenite phases in the lean duplex stainless steel; thus, the pit growth rate was decreased, leading to improvement of the resistance to pitting corrosion.
Highlights
Duplex stainless steels (DSSs) have a dual-phase structure composed of approximately equal amounts of ferrite (α) phase and austenite (γ)
Towas be 1:1, 1100 °C was determined for the solution treatment be 1:1, 1100 determined for the solution treatment for the Ni03 alloy. for
The present study strongly suggests that controlling the galvanic corrosion rate between the constituent phases for DSSs is helpful to improve the resistance to pitting corrosion, and one of the effective ways to achieve the favorable resistance to pitting corrosion for the LDSS would be the use of small amount of Ni
Summary
Duplex stainless steels (DSSs) have a dual-phase structure composed of approximately equal amounts of ferrite (α) phase and austenite (γ). DSSs are economically attractive because commercial DSSs commonly contain only 1–7 wt% Ni, which is less than the Ni content of FeCrNi-based γ-SS (8–24 wt%) [2,6,9,11]. These advantages of DSSs make them promising alternatives to γ-SSs, and demands for DSSs show a continuous increase in various industrial fields such as the on/off-shore oil and gas industry and chemical process industry [2,3,5,12–14]. Economic feasibility of DSSs can be further achieved by reducing the amount of expensive alloying elements, Ni. various lean-DSSs (LDSSs), in which Ni is replaced with other γ stabilizers, such as Mn and N, have been developed and investigated [1,14–18]. This author group has proposed new LDSSs [17,19], which comprise 16.5–19.5 wt% Cr, 2.5–3.5 wt% Mo, 1.0–3.5 wt%
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