The resistance of an aluminide coating on a high-strength ASTM A29 steel subjected to a temperature of 850 °C

Abstract

An ASTM A29 steel was coated with aluminide by dipping in a molten Al bath at 700 °C for 16 s. The resistance of ASTM A29 steel to high-temperature oxidation drastically decreased upon oxidation at 850 °C for 12 h, whereas the oxidation resistance of the aluminised steel subjected to hot dipping was higher (by 25-fold). The external part of the aluminide layer, which consists of Fe2Al5, FeAl2, and FeAl(Cr, Si) phases scattered in the Fe2Al5 phase, was formed through the outward diffusion of Al and inward diffusion of Fe. The Fe2Al5 phase played an important role as a reservoir of Al atoms that form the alumina (Al2O3) scale, while Cr and Fe from the FeAl(Cr, Si) particles and accelerated the conversion of the metastable θ-Al2O3 phase to a stable α-Al2O3 phase. Consequently, the parabolic rate constants of aluminised steel decreased with extended oxidation time.