HRAES study of oxide scale formation by decarburization of non-oriented electrical steel sheets

Abstract

The oxide growth during the decarburization process of non-oriented silicon steel sheets alloyed with 0.5 and 1 mass% of aluminium was studied using high-resolution auger electron spectroscopy (HRAES), the chemical composition was characterized by X-ray photoelectron spectroscopy (XPS). The samples were annealed in a H 2–H 2O–N 2 gas mixture with different oxygen potential in the temperature range from 800 to 1050°C. We found that oxide scale was a mixture of FeO, Fe 3O 4 and SiO 2 and Fayalite (FeSi 2O 4). This oxide scale was porous. In the high Al alloyed sheets (2 mass% Si and 1 mass% Al) the oxide scale was a mixture of FeO, Fe 3O 4, and Al 2O 3 and also Hercynite (Fe Al 2O 4). In this case the oxide scale was compact. For thermodynamic calculations of Fayalite and Hercynite formation during the decarburization process the Gibbs energy minimization model (GPRO) was applied (Koroušić, Kovine zlitine tehnol 1994;28:609; Koroušić and Rosina, RadexRundsch 1994;1(2):523).