Studying and understanding the oxidation state of DC04 CRS metal surfaces from an industrial standpoint, using IRRAS, XPS analysis: effect of preparation and surface treatments

A comprehensive understanding of the surface chemistry and oxidation states of cold-rolled steel (CRS) DC04 grade is crucial for optimizing subsequent industrial processes, particularly preparation and surface treatments. Despite the widespread use of DC04 in industry, detailed studies on its surface chemistry after typical treatment remain limited. This study provides a descriptive assessment of the surface oxide formed on CRS DC04 substrates under various controlled treatments, focusing on the surface preparation and mimetic surface treatments. Surface preparation and mimetic treatments replicate the acid-base environment experienced by CRS DC04 surfaces in industrial context. Indeed, cleaning protocols and subsequent treatments were systematically varied in terms of pH and immersion time. While X-ray photoelectron spectroscopy (XPS) is widely referenced in the literature, it is not routinely available in industrial settings. Therefore, this study centers in infrared reflection absorption spectroscopy (IRRAS), a technique well-suited to the substrates and industrial constraints but scarcely reported for CRS DC04. By comparing IRRAS and XPS results, we demonstrate that IRRAS can reliably identify and monitor surface oxides, offering a practical alternative for industrial applications. This work establishes a reference dataset for the surface state of CRS DC04, providing essential groundwork for optimizing future surfaces treatments processes. XPS analysis revealed that alkaline cleaning (pH 10.5) produces a thin, mixed oxide/hydroxide layer dominated by Fe2O3 and FeOOH, with residual organic contaminants. IRRAS identified the presence and polymorphism of FeOOH (notably γ- and α-FeOOH), Fe2O3, Fe(OH)3, and FeCO₃, with their relative abundances strongly dependent on treatment parameters. Lower pH and longer treatment times increased oxide layer thickness and favored more oxidized species, but excessively thick layers may be fragile and less conducive to adhesion. These findings highlight the critical roles of both oxide composition and layer morphology in determining surface reactivity and adhesion potential. This work provides a detailed analysis of CRS surface species as a function of treatment conditions, offering valuable insights for the rational design of surface preparation protocols to enhance adhesion performance in steel-based assemblies.