Oxidation phenomena that occur during high-temperature operations, such as hot rolling and annealing, generate oxide scale on the steel surface. These oxides may have different features depending on the chemical composition of the processed material, the oxidation temperature, and the oxidizing atmosphere. The presence of elements such as Chromium, Silicon, and Aluminum contributes to the formation of more adherent and compact scales compared to those composed only of Iron oxides. The factors influencing scale formation have been analysed, distinguishing between casting, primary, secondary, and tertiary scales.

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The characterization of surface oxides is firstly carried out through visual inspection and macrography, observing properties such as smoothness, uniformity, and cracks presence. Subsequently, a more accurate examination is conducted using advanced laboratory techniques, such as SEM, SEM-EDS, GDOES, XRD, EPMA and Raman spectroscopy, to understand the external and internal structure, chemical composition, and mechanical properties.

To achieve a product with a high surface quality, mandatory operations for removing surface oxide residues, such as descaling and pickling, have been described with respect to three main types of steel: carbon steel, stainless steel, and magnetic steel.

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Descaling is a surface treatment aimed at the partial removal of oxide scale and, additionally, by generating cracks on the surface layer. In fact, the descaling process facilitates the penetration of acids that are used in the subsequent pickling phase. Various factors influence this treatment: scale thickness and morphology, type of oxides and characteristics of the scale/steel interface. Descaling can be conducted using traditional techniques such as shot blasting, scale-breaker, brushing, tension leveler, or innovative methods like laser. The methodologies differ in their operating mechanism, mechanical action, and treatment efficiency in terms of weight loss and reduction of pickling times.

The total removal of surface scale is not guaranteed by descaling. Therefore, further surface treatment is required to achieve the necessary quality for subsequent steel processing stages or the final use of the semi-finished product.

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Pickling allows the chemical or electrochemical dissolution of surface oxide residues. Chemical pickling uses different acid solutions depending on the type of steel: sulfuric acid, hydrochloric acid, nitric/hydrofluoric acids, and ecological baths. The mechanisms of action and optimal operating conditions for each are indicated. Electrochemical pickling operates under the influence of an electric field and in the presence of an electrolyte. Possible configurations (grid to grid or face to face) and the differences between direct current and alternating current are illustrated.

Preliminary treatments, such as cleaning, and post-pickling treatments, such as washing, drying, and oiling, have been described to provide a comprehensive overview of treatments related to the removal of surface oxides.