The effects of mould flux residues on descaling of type 304 austenitic stainless steel were
investigated, for simulated slab reheating conditions and hydraulic descaling. Several industrial and laboratory mould flux compositions and dosages were tested, and all of these were found to improve descaling substantially. This effect was associated with the elimination of the subscale containing nickel enriched metal tendrils and chromite (spinel). This subscale is characteristic of reheated austenitic stainless steel which does not have mould flux residues. In the presence of mould flux residues the subscale is absent, and nickel is oxidised and incorporated in a nickel–iron–chromium spinel which is close to the steel/scale interface, but separated from the steel by a layer of chromium oxide and molten silicate.