Tailoring of oxide morphology and crystallinity on advanced high-strength steel surfaces prior hot-dip galvanizing

Annealing of advanced high-strength steel (AHSS) grades often results in surfaces being fully covered by oxides due to alloying elements which diffuse to the steel surface during annealing and which are oxidized there by residual oxygen from the furnace atmosphere. However, these surface oxides tend to significantly hamper the hot-dip galvanizability and are therefore repeatedly under investigation with respect to their morphology and chemical composition for an optimization of the overall galvanizing performance. In the present work two different kinds of AHSS grades are analysed in detail by scanning electron microscopy as well as by X-ray photoelectron spectroscopy and transmission electron microscopy to characterize the formed surface oxides, clearly revealing that it is not only the chemical composition of the oxides influencing their morphology and structure: the oxidation potential of the annealing atmosphere is found to have a significant impact on the surface oxide characteristics, namely the degree of crystallinity, as well. Consequently, these findings can be used to improve the galvanizability of a steel grade by changing the surface oxide morphology.