Interaction of Al2O3-rich slag with MgO-C refractories during VOD refining-MgO and spinel layer formation at the slag/refractory interface

Abstract The interaction mechanisms between a pitch-bonded MgO–C refractory and an Al 2 O 3 rich (∼15 wt%) stainless steelmaking slag were investigated by rotating finger tests in a vacuum induction furnace. A porous MgO layer (instead of a dense MgO layer) was observed at the hot face of the MgO–C bricks. This implies that under the present low oxygen pressure conditions, the oxygen supply from the slag is insufficient to meet the demand of reoxidising the entire amount of Mg vapor generated from the MgO–C reaction to form a fully dense MgO layer. A Mg(Al,Cr) 2 O 4 spinel layer with zoning was found at the slag/brick interface in the top slag zone specimen of Test 3 (CHS3). Based on the thermodynamic analyses with and experimental data, a mechanism of Mg(Al,Cr) 2 O 4 spinel formation is proposed. Initially, hot face periclase grains take up Cr 2 O 3 , and to a much lesser extent, Al 2 O 3 from the slag. The further diffusion of Cr 2 O 3 and Al 2 O 3 from the slag establishes a spinel layer of three distinct compositions of the type MgAl 2(1− x ) Cr 2 x O 4 , with x decreasing when moving from the interior to the exterior spinel layer. Due to the low oxygen pressures, the thermodynamically less stable, dissolved Cr 2 O 3 in the hot face periclase decomposes and forms chromium-rich metal droplets.