Characterization of Hot-Dip Aluminized C45 Carbon Steel before and after Cyclic Heating in Air

Abstract

An experimental study has been carried out on the surface characteristics of hot-dip aluminized (HDA) C45 carbon steel. The coated specimens were also tested thrice by cycling heat between the ambient temperature and 700°C inside an electrical resistance furnace. Both the as-coated and the oxidized samples were analyzed by scanning electron microscopy, energy dispersive spectrometry, and elemental mapping. Microstructural features and other important characteristics (compositional changes, chemical elemental distributions, growth of the intermetallic phases, the formation of micro-voids, etc.) were investigated. Under the high temperature tested conditions, the HDA coated C45 carbon steel close-to-surface top-layer almost entirely converted to iron-aluminum intermetallics, with Fe to Al atomic ratios of 1 to 2 corresponding to the phases FeAl and FeAl₂. However, the innermost intermetallic phase (FeAl) formed between the finger-like structure and the steel substrate appeared quite compact and sound (without voids, micro-crack, and internal iron oxide scale), which is a convincing sign and an experimental proof of a high chemical and mechanical stability of such type of surface coatings. The results confirm that even inexpensive carbon steel, if properly aluminized, can provide sufficient protection against excessive oxide scale formation in the air at high temperatures.