Influence of ceramic coating of MgO on oxidation behavior and descaling ability of low alloy steel

A high temperature MgO protective coating used onto 20Cr2Ni4A low Alloy steel was prepared by a slurry-spraying technique. The effects of coatings on high temperature oxidation behavior of the steel and the descaling ability of scale were invested. Metallurgical microscopy was used to characterize the surface topography of the samples. SEM and EDX were used to study the structure and element distribution of the oxide scale. The experimental results show the coating could enhance oxidation resistance of the steel effectively at 1100–1250 °C. The metal losses of coated samples are diminished by about 65% when compared with the uncoated samples. The Mg-Fe spinel layer, formed at the outer layer of the scale, can decrease the cation diffusion velocity throughout the scale during oxidation. Si-rich layer, which is existed at the interface of scale and substrate, strongly adhered to the steel, resulted in bad descaling ability, is also reduced by the coating. Cr-rich layer formed between Si-rich layer and the outer scale of the coated sample is thicker than that of uncoated sample. The proposed mechanism of oxidation resistant MgO coating is discussed.