Innovative use of the unreacted shrinking core model to predict oxide scale formation during high-temperature processing of steel alloys

Abstract

© 2026 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.High-temperature oxidation is a major challenge in steel thermomechanical processing, as oxide scale formation reduces performance, increases production costs, and accelerates material degradation. The rate of oxidation is strongly influenced by temperature, and alloy composition, with temperature-dependent behaviors often governed by the formation and stability of protective oxide layers. Classical oxidation models, such as parabolic and linear rate laws, are limited because they assume planar geometries and single-limiting step mechanisms, making them unsuitable for multi-step oxidation or for comparing alloys with distinct oxide compositions. In this study, the Unreacted Shrinking Core Model (USCM) was, for the first time, applied to describe the oxidation rate of four distinct steel alloys (AISI 1045, 1095, 4340, and D6) oxidized between 900 °C and 1200 °C. The model was fitted to experimental data, supported by SEM, EBSD, and XRD characterization. Results show that scale diffusion and mixed diffusion–reaction mechanisms govern oxidation in AISI 1045, 1095, and 4340, while AISI D6 oxidation is primarily surface-reaction controlled due to its high chromium content. Among the alloys, AISI D6 exhibited the highest oxidation resistance, following a reaction-controlled oxidation rate mechanism, while AISI 1095 also showed improved resistance at 900–1000 °C attributed to its high carbon content. The USCM successfully quantified metal-to-oxide conversion as a function of temperature and time, enabling the determination of Arrhenius parameters for reaction rate and diffusivity, which can be extrapolated to different geometries. This geometry-flexible framework makes the USCM highly relevant for optimizing processing parameters such as working temperature, time and alloy composition in industrial applications.

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