Oxide Stability Analysis and Characterization in a Galvannealed Dual-Phase Steel Exhibiting Coating Defects

Abstract

complex . selective well the thermodynamic stability of the oxide. Wagner’s theory of oxidation enables prediction of the mechanism of oxidation for binary oxide systems 9 . The defects can be present after pickling and fluxing, causing wettability issues during the process. Coating defects may also form or be further exacerbated by the galvannealing operation. For this work, oxidation mechanism predictions were performed using Wagner’s theory of oxidation. In the present study a 0.07C-1.9Mn-0.2Si-0.3Cr galvannealed dual-phase steel which exhibited streaking defects in the coating was analyzed. Light optical metallography (LOM) and scanning electron microscopy (SEM) were performed to characterize defects within the galvannealed coating. Static spectra reactions 13 . Since Si solubility is extremely low in zeta phase, nucleation of zeta, as well as growth, would be influenced by the Si content in the steel. In the investigated steel, Si levels are low and Mn levels are high, resulting in a Mn rich defect, with some Si content. The Mn rich, Si containing oxides present on the surface could also influence zeta phase nucleation during galvanizing and subsequent intermetallic galvannealing reactions.