Enhanced Corrosion Resistance of an Alumina-forming Austenitic Steel Against Molten Al
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Enhanced Corrosion Resistance of an Alumina‑forming Austenitic Steel Against Molten Al C. C. Li, et al. [full author details at the end of the article] Received: 2 July 2020 / Revised: 20 September 2020 / Accepted: 30 September 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The development of corrosion resistant steel for molten Al has always attracted the interests from die casting industry for several decades. In this paper, we reported the enhanced corrosion resistance in 750 °C molten Al of an alumina-forming austenitic steel (AFA) via deliberately producing oxide layer after different high-temperature oxidation processes. The results showed that the corrosion resistance against molten Al of the AFA was improved significantly due to the presence of a stable, compact and continuous oxides barrier, in comparison with H13 tool steel as well as unoxidized AFA without Al2O3 film. Apparently, the non-wetting α-Al2O3 film, which was formed after high-temperature oxidation, effectively protected the substrate from inner-diffusion and penetration of the molten Al. These findings provide one of cost-effective ways to improve the corrosion resistance of steels against molten Al. Graphic Abstract
Keywords Corrosion resistance · Alumina-forming austenitic steel · Molten Al · Oxidation
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Oxidation of Metals
Introduction Die casting, which is one of rapid-developing industrial manufacturing methods, is largely expanded due to fast-growing demands of portable communication products (PCP). Many components of PCP with complex shape, high-dimensional accuracy, good surface finishing and superior mechanical properties have been manufactured by die-casting machines (DCM) [1, 2]. Consequently, cast molds used for DCM to handle the alloy melts with low melting point during casting, such as Al, Mg and Zn-based alloys, must be able to sustain severe abrasive and shocking conditions during repeated usage. These mold materials are usually made from hot-work tool steels not only because of their desired performance but also for being relatively low cost. Many previous researches showed that brittle Fe–Al intermetallic compounds were easily formed via reaction diffusion of molten Al and Fe, leading to shorten the service life of the mold and deteriorate the quality of Al alloy products [3, 4]. Up to date, surface coating has been one of the most practical ways to promote the corrosion resistance of steels in Al melts. In this way, some strong non-wetting nitrogen oxides were selected to spray on a surface of the workpiece to protect the workpiece materials from molten Al. However, this approach has high cost and is not suitable for workpieces with complex shapes. The corrosion resistance also can be improved via surface treatments such as nitriding and boronizing. In this case, N or B atoms diffuse into the surface of a workpiece at high temperatures to form hard and brittle nitrides or borides, respectively [5, 6]. However, these protective films have very low toughness and
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