Abstract
In order to increase the performance of the preferred Ferritic 430 SS for manufacturing automobile and motor-cycle exhaust systems. The aluminizing coating on the surface of bare steel was applied by hot-dipping method in a molten pure aluminum. The high temperature oxidation of the aluminized steel was cyclically studied at 900 °C and 1000 °C in static air. The degradation of intermetallic layers during cyclic oxidation were analyzed by means of X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The crack perpendicular to the specimen surface rapidly propagated through the FeAl and Fe3Al layers due to a thermal expansion mismatch upon cooling to room temperature. The accumulation of voids generated crack at the interface between the aluminide layer and the steel substrate. Oxygen is allowed to penetrate into the aluminide layer crack, rapidly forming alumina oxide and closing the crack. Some of the aluminide layers peeled off due to this rapid growth. Thus, the protective Al2O3 layer degraded and later, the substrate was oxidized subsequently to form iron-rich oxide (Fe2O3) at 1000 °C.
Highlights
Ferritic 430 stainless steel (SS430) is widely used as an exhaust material in petrochemical, gasification and automotive application because it has a cheaper price than austenitic stainless steel
The inward diffusion of Al into steel substrate at temperatures above 900 °C forms the intermetallic compounds FeAl and Fe3Al [7]; this reduces the solubility of Cr to a lower level in the aluminide layer compared to in the metal substrate
Few studies have reported the combined effect of Cr concentrations on the oxidation resistance of Fe-Al based alloys at high temperatures based on long term cyclic oxidation, which relates to the resistance of the coating at high temperatures
Summary
Ferritic 430 stainless steel (SS430) is widely used as an exhaust material in petrochemical, gasification and automotive application because it has a cheaper price than austenitic stainless steel. For improving high-temperature oxidation resistance of the steel, several of coating processes; hot-dipping process is an effective and inexpensive method to modify on the surface of bare steel because its process is simpler and it provides a thick coating layer for reliable oxidation resistance [4 6]. Some studies report that the FeAl and Fe3Al alloys without Cr show a decrease in oxidation resistance at 1000 °C [8,9]. It is important to investigate the temperature dependence of the oxidation properties of aluminized coatings on steel with high concentrations of Cr. The formation of protective Al2O3 is expected to protect the steel substrate during high temperature service. Few studies have reported the combined effect of Cr concentrations on the oxidation resistance of Fe-Al based alloys at high temperatures based on long term cyclic oxidation, which relates to the resistance of the coating at high temperatures. The oxidation kinetics behavior was studied by the weight change of specimens every cycle
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