High temperature corrosion behaviour of aluminised FC 25 cast iron using pack cementation

Abstract

Purpose This study aims to apply the pack cementation to develop the Fe-Al layers on the surface of FC 25 cast iron in order to increase the high-temperature corrosion resistance of the alloy. Design/methodology/approach Pack cementation was applied on the surface of FC 25 cast iron at 1,050°C. The bare and aluminised alloys were subjected to the oxidation test in 20 per cent O2-N2 at 850 °C. Scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy and X-ray diffraction (XRD) were used for characterisation. Findings The layers of pack cementation consisted of Fe2Al5, FeAl2 and FeAl, and solid solution alloyed with Al. The oxidation kinetics of the bare cast iron was parabolic. Mass gain of the aluminised cast iron was significantly decreased compared with that of the bare cast iron. This was because of the protective alumina formation on the aluminised alloy surface. Al in the Fe–Al layer also tended to be homogenised during oxidation. Originality/value Even though the aluminising of alloys was extensively studied, the application of that process to the FC 25 cast iron grade was originally developed in this work. The significantly reduced mass gain of the aluminised FC 25 cast iron makes the studied alloy be promising for the use as a valve seat insert in an agricultural single-cylinder four-stroke engine, which might be run by using a relatively cheaper fuel, i.e. LPG, but as a consequence requires the higher oxidation resistance of the engine parts.