On the formation of the spinel MgAl2O4 during steel deoxidation and its effect

Abstract

Samples with hook cracks were analyzed in order to find their origin. For that purpose, samples were analyzed by using optical and scanning electron microscopes. WDX-microanalyses performed in areas close to and into the crack detected the presence of a spinel, which showed a MgAl2O4 stoichiometry. In order to find the origin of this spinel, analyses of refractory and raw materials were performed. It was detected that material detached from the MgO/C lined ladles together with the Al-cone used as deoxidizer (with up to 14 wt. % Mg) enhances spinel formation. The steelmaking practice together with a stability diagram of MgO, MgO.Al2O3, Al2O3 drawn at 1863 K indicated that the spinel is formed with oxygen contents as low as 5 mass ppm, 0.13 mass ppm of Mg and 325 mass ppm of Al. It was found that formation of the spinel is reduced by avoiding the use of the aluminium- cone used as deoxidizer.