Initial High-Temperature Oxidation Behavior of Fe–Mn Binaries in Air: The Kinetics and Mechanism of Oxidation

Abstract

High-temperature oxidation of steels can be relatively fast when exposed to air. Consequently, elucidating the effect of different parameters on the oxidation mechanism and kinetics is challenging. In this study, short-time oxidation was investigated to determine the oxidation mechanism, the affecting parameters, and the linear-to-parabolic growth transition of different Fe–Mn alloys in various oxygen partial pressures (10–30 kPa) and gas flow rates (26.6 and 53.3 sccm) in a temperature range of 950–1150 °C. Oxidation kinetics was investigated using a thermogravimetric analyzer (TGA) under controlled atmosphere. Linear oxide growth was observed within the first 20 minutes of oxidation. The linear rate constant was significantly increased by increasing the oxygen partial pressure or the flow rate of the oxidizing gas. The morphology of the oxide layer was determined by scanning electron microscopy (SEM). The crystal structure of the oxides formed was followed by in-situ X-ray diffraction (XRD), confirming that the growing layer consists of wustite mainly, which upon slow cooling to room temperature, transformed into magnetite. Energy-dispersive X-ray spectroscopy (EDS) showed that the atomic ratio of Fe+Mn to O was ~ 1.03:1 in the oxide scale, corresponding to Fe(Mn)O formation. Based on the characterization and a model for linear growth kinetics, it is concluded that the oxidation rate is controlled by the diffusion of oxidizing molecules through the gas layer to the sample’s surface. The findings led to a better understanding of initial oxidation behavior and provided a pathway for improved insight into the high-temperature oxidation behavior for more complex alloys.

Predicting the Parabolic Growth Rate Constant for High-Temperature Oxidation of Steels Using Machine Learning Models

“…( 1)) was chosen to describe the high-temperature oxidation kinetics where 𝛥𝑚 is the mass gain in g, 𝐴 is the specimen surface area in cm 2 , 𝑡 is time in s, and 𝑘 𝑝 is parabolic oxidation constant in g 2 cm −4 s −1 . Parabolic growth rate constants, 𝑘 𝑝 , were collected directly from published reports [3, where they were obtained from the mass gain results provided by Thermogravimetric analysis (TGA). The steps to get the parabolic growth rate constant are typically the same and begin with plotting the mass gain data on a squared mass gain vs. time plot.…”

“…Hence, developing the capability of predicting the oxidation behavior of steels in a variety of conditions is highly desirable. Although analytical [1][2][3] and numerical [4][5][6][7][8] simulations have significantly improved the high-temperature oxidation investigations, they are usually applicable for specific material compositions or a given oxidizing condition such as exposure time and gas mixture composition.…”