Cr7C3: A potential antioxidant for low carbon MgO-C refractories

Magnesia carbon (MgO-C) refractory, one of the most commonly used refractories in the steelmaking system, relies on graphite to improve the thermal shock resistance and slag corrosion resistance. The oxidation of graphite carbon in a MgO-C brick usually leads to the destruction of the carbon network in the brick, which causes the structure of the brick to become loose and easily eroded. At present, metal powders, carbides, and borides are used as antioxidants to prevent the oxidation of carbon in MgO-C bricks. The metal carbide Cr7C3 can be prepared from aluminum chromium slag through a simple synthetic process and at a low cost. In this work, we investigated the oxidation resistance of low carbon MgO-C refractories with different amounts of Cr7C3 powder (1, 2, 3, and 4 wt%). The refractories with 3 wt% Cr7C3 powder showed optimal resistance to oxidation. The microstructure indicated that oxygen reacts with Cr7C3 preferentially over carbon to form chromium oxide and magnesium chromium spinel, blocking the pores and hindering oxygen diffusion. Carbon arising from the reduction of carbon monoxide by Cr7C3 can act as a supplementary carbon source. The better oxidation resistance also contributed to the improvements in slag corrosion and thermal shock resistance of the refractories.