Introduction
A588 Grade A weathering steel is a commonly used construction material due to its ability to withstand harsh weather conditions. However, one of its major drawbacks is its susceptibility to high temperature oxidation, which can lead to a reduction in its mechanical properties and possibly, its structural integrity. As such, there is a need to study the oxidation behavior of A588 Grade A weathering steel at elevated temperatures to provide insights into its performance in such conditions. This study aims to investigate the high temperature oxidation behavior of A588 Grade A weathering steel through various characterization techniques.
Experimental Procedure
A588 Grade A weathering steel samples were subjected to high temperature oxidation by heating them in a furnace at 600°C for various durations of 1, 2, 4, 6, and 8 hours. The samples were coated with graphite to prevent the formation of scale on their surfaces during oxidation. The mass change due to oxidation was recorded using a high-precision balance, and the thickness of the oxide scale formed on the surface of the samples was measured using a digital micrometer. The microstructure of the samples was analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), while X-ray diffraction (XRD) analysis was used to identify the phases present in the oxide scale.
Results and Discussion
Mass change measurements showed that A588 Grade A weathering steel experienced mass loss due to oxidation at 600°C. The rate of mass loss increased with oxidation time, indicating that the oxidation kinetics were time-dependent. The thickness of the oxide scale formed on the steel samples increased with oxidation time as well, and it was found to consist mainly of Fe2O3 and Fe3O4 phases. SEM-EDS analysis revealed that the oxide scale had a porous structure, with the formation of voids due to the detachment of oxide particles from the surface of the sample during oxidation. Additionally, the analysis showed that oxygen penetration into the interior of the steel sample occurred during oxidation, which led to the formation of a subsurface oxide layer.
The high temperature oxidation behavior of A588 Grade A weathering steel is largely influenced by the following factors:
1. Oxygen diffusion
During oxidation, oxygen diffuses through the oxide scale formed on the surface of the sample to react with the steel substrate. The rate of oxygen diffusion is influenced by the thickness and porosity of the oxide scale, which, in turn, are influenced by the oxidation time and temperature.
2. Subsurface oxidation
The formation of a subsurface oxide layer is a function of the oxygen diffusion rate and the availability of oxidizable elements in the steel substrate. The subsurface oxidation can lead to the development of oxide-induced cracks and the embrittlement of the steel substrate.
3. Scale adherence
The adherence of the oxide scale to the surface of the sample is influenced by the chemical composition and morphology of the oxide scale. A poor adherence of the oxide scale can lead to its detachment from the steel substrate and the exposure of the unoxidized steel to further oxidation.
Conclusion
The high temperature oxidation behavior of A588 Grade A weathering steel was investigated through mass change measurements, oxide scale thickness measurements, SEM-EDS analysis, and XRD analysis. It was found that the oxidation kinetics were time-dependent, and the thickness of the oxide scale formed increased with oxidation time. The oxide scale consisted mainly of Fe2O3 and Fe3O4 phases and exhibited a porous structure. Oxygen penetration into the interior of the steel sample occurred during oxidation, which led to the formation of a subsurface oxide layer. The high temperature oxidation behavior of A588 Grade A weathering steel is influenced by factors such as oxygen diffusion, subsurface oxidation, and scale adherence. These factors should be taken into consideration when designing structures that are expected to withstand high temperature environments. Potential future work could include investigating the effects of alloying elements on the high temperature oxidation behavior of A588 Grade A weathering steel.
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