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Welds of the commercial Ni‐based alloys 602 CA, 699 XA, 601 and 690 were exposed under harsh metal dusting conditions. The pit formation was compared for as‐welded, brushed, ground, glass bead blasted, steel shot peened and dry cathodic pickled surfaces. Surface treatments were applied by industrial partners. When (stainless) steels were involved in the surface treatment, Fe contaminations acted as catalyst sites for pit initiation. A fast metal dusting attack was also observed on dry cathodic pickled samples. A beneficial effect was attributed to deformation of the sub‐surface zone, as it provides diffusion paths for oxide formers (by grinding and glass bead blasting). In the same region, formation of α‐Cr (BCC) precipitates was observed. The best performance was found for samples where the weld bead was fully flattened by grinding to P40 grit. In addition, it was demonstrated that on‐site slurry aluminization further enhances the resistance against metal dusting attack. [ABSTRACT FROM AUTHOR]

Metal dusting attack is a serious problem in processing industries using carbonaceous gases and high temperatures. Ni‐based alloy 699 XA was recently developed as an alloy for these types of environments with high resistance against metal dusting. In this study, different surface treatments of this chromium‐ and aluminum‐rich alloy are shown to have an important influence on the metal dusting onset behavior. It was found that surface treatments that are traditionally considered to be helpful for fatigue performance, for example, shot peening, and pickling were detrimental to the metal dusting performance of alloy 699 XA. Additionally, the shot peening surface treatment promoted Fe surface contamination, resulting in a negative impact on the metal dusting pitting resistance of the alloy. Deformation accompanied by apparent BCC α‐Cr precipitation in the bulk microstructure, but a comparison with cold‐rolled materials shows that the surface treatment dominates the metal dusting resistance. [ABSTRACT FROM AUTHOR]

Corrosion by metal dusting causes problems in various industries that process carbonaceous gases. Recently, the chromium‐ and aluminum‐rich Ni‐based Alloy 699 XA was introduced as a material with high resistance against metal dusting attacks. In this study, the metal dusting degradation of Alloy 699 XA and model alloys was investigated. In the model alloys, the aluminum, chromium, and iron contents were varied to analyze the role of each element systematically. Alloy 602 CA was included as a reference material. It was found that the alloys with the highest chromium and aluminum contents (30 and 2–3 wt%, respectively) showed the highest resistance against metal dusting. Also, the limited addition of iron enhanced the aluminum activity and thereby promoted the formation and maintenance of an aluminum‐rich oxide scale. This effect at low iron levels is contrary to the negative impact of iron at higher levels, which typically leads to an increased metal dusting susceptibility. Exposure tests were performed with two gas mixtures having similar compositions, but different carbon activities. It was found that both gases had a similar aggressiveness regarding metal dusting attacks. [ABSTRACT FROM AUTHOR]

Metal dusting is still an unresolved issue at high temperatures. Currently, two material‐related strategies to mitigate metal dusting are described in the literature. On the one hand, highly alloyed materials are used, which contain large amounts of protective oxide‐forming elements, such as Cr, Al, and Si. The second mitigation strategy is based on inhibiting the catalytic effect of Fe, Ni, and Co. These elements all strongly catalyze the formation of solid carbon from the gas phase. Combining the catalytic protection of Cu alloying for metal dusting with protection by a classical alumina/chromia barrier is a native feature that high‐entropy alloys (HEAs) can offer. In this study, the behavior of different equiatomic HEAs with and without Al and/or Cu are studied when exposed at 620°C in a highly aggressive metal‐dusting environment. [ABSTRACT FROM AUTHOR]

This article features the cover picture of the journal "Materials & Corrosion / Werkstoffe und Korrosion" for the March 2024 issue. The image shows electron backscatter diffraction (EBSD) images of steel shot peened Ni‐base alloy 699 XA after exposure to a carbon‐rich gas at high temperature. The images reveal the formation of α‐Cr (BCC) precipitates in the nearsurface zone. For more detailed information on the topic of metal dusting resistance of welds and the influence of surface treatment, readers are referred to a related article by Clara Schlereth, Emma Marie Hamilton White, Maren Lepple, Benedikt Nowak, Heike Hattendorf, and Mathias Christian Galetz in the same journal. [Extracted from the article]

B Cover: b Optical cross-sectional images of the cold rolled alloy 699XA ( =cold rolling level) and pits after metal dusting exposure: a) without etching, b) with etching to highlight grain boundaries and carburized zones. More detailed information can be found in: I Emma White, Clara Schlereth, Maren Lepple, Heike Hattendorf, Benedikt Nowak, Mathias C. Galetz i , Influence of surface treatment on the metal dusting behavior of Alloy 699 XA, I Materials and Corrosion i B 2023 b , I 74 i , 190. The top layer on all samples is galvanic Ni-plating for cross-sectional preparation [labeled in the b) 2% image] and is especially clear over the pits in the 2, 10 and 50% cold rolled samples. [Extracted from the article]