Pitting Corrosion of Steel Induced by Al2O3 Inclusions

Abstract

To study the effect of Al2O3 inclusions on pitting corrosion in steel, our researchers utilized industrial pure iron as the raw material with the addition of a proper amount of pure aluminum powder to form Al2O3 inclusions. Corrosion experiments were performed by exposing the samples to a 6% FeCl3 solution at room temperature (25 °C) for different lengths of time. Microscopic corrosion morphology was observed by scanning electron microscope (SEM), and the size change of the inclusions was quantitatively analyzed with Image Pro Plus. The experimental results showed that pitting corrosion arose preferentially around the Al2O3 inclusions, and that pitting corrosion initiated at the junction of the Al2O3 inclusions. The steel matrix dissolved and micro-cracks occurred as the Al2O3 inclusions that were buried shallowly below the surface of the steel matrix promoted corrosion of the steel matrix. As corrosion progressed, the shallowly buried Al2O3 inclusions began to appear on the surface, and the small, shallow inclusions fell off and formed micro pits. Furthermore, the clustered distribution of alumina inclusions had a greater effect on pitting initiation than the alumina inclusions distributed alone.

Keywords

• Al2O3 inclusions
• pitting corrosion
• initiation
• steel