High-temperature Interactions of Alumina–Carbon Refractories with Molten Iron

Abstract

IntroductionRefractory degradation is a complex phenomenon involving chemical wear (corrosion) and physical/mechanical wear (erosion/abrasion). Refractory corrosion results in the recession of "hot face" (working surface) due to chemical reactions and molten metal penetration. 1) Alumina-carbon refractories are commonly used in steelmaking applications due to their excellent high-temperature strength and thermal shock resistance. [2][3][4][5] The corrosion resistance of Al 2 O 3 -C refractories is influenced by its reactions with liquid iron, which leads to the dissolution of refractory constituents into the melt. 6) Carbon in the form of graphite is used in refractories since it enhances corrosion resistance and thermal shock resistance. 7) However, the degradation of carbon-based refractories occurs through carbon depletion, resulting in decreased refractory resistance to chemical attack, increased carbon pickup by steel and extensive metal penetration within the refractory. 8) Material inhomogeneity and porosity can promote corrosion and allow corrosive agents to penetrate and cause erosive damage, resulting in severe degradation. 9) Iron oxide formed can react with alumina to form hercynite (FeO-Al 2 O 3 ), which builds up in the refractory over time, eventually causing uncontrolled expansion of saturated refractory and hot face spalling. 10) The corrosion of alumina-carbon refractories is primarily influenced by their chemical reactions with molten iron/steel, which proceed through a direct contact with the metal. The composition of the refractory, its physical texture, the nature of the bonding phases, and the characteristics of melt and reaction products are known to influence reaction kinetics. 11) Refractory-iron reactions lead to molten metal penetration; the penetration depth is believed to be influenced by the chemical composition of the refractory, metal and physical properties like porosity of the refractory. The penetration depth may range from a few microns to several millimetres depending upon these factors, and the quantity of molten metal. 1) Carbon is picked up by Fe resulting in carbon dissolution from the refractory and the alumina left behind tends to resist Fe penetration. The regions which experience carbon depletion are subsequently filled with molten iron, which contributes to the corrosion. In the liquid iron/alumina-graphite system, carbon transfer from graphite to liquid iron is a well known phenomena, while alumina is considered to be unreactive to iron at steelmaking temperatures (1 550°C). 12) The influence of wettability on carbon dissolution into molten iron suggests that the rate of dissolution is significantly affected by the contact area available for the carbon-transfer. 13) The depth of penetration of molten iron into the refractory and the strength of bonding between the metal and the refractory 804 © 2010 ISIJ ISIJ International, Vol. 50 (2010), No. 6, pp. 804-812 The interfacial behaviour of alumina/carbon refractories with liquid iron was investigated at 1 550°C, w...

Chemical Interactions in Al2O3^|^ndash;C/Fe System at 1823 K: Implications for Refractory Recycling

“…24 ) The balance of these refractories was made up of vir- 19,24) The lower alumina content in the reacted refractory also indicates that a small part of alumina has been reduced that led to the formation of Fe-Al alloy. 19) Higher metal penetration was observed in AS1-Fe sample as observed from the results of XRF analysis with increases in iron content.…”

Reduction Reactions in Al2O3–C–Fe and Al2O3–Fe2O3–C Systems at 1823 K

“…Total solid carbon concentration (excluding the solute carbon present in iron) in the substrate (set I) was determined to be 26.53%; the increase in the carbon level was attributed to the pyrolysis yield from the binder. 11) In the second set, Fe2O3 powder was mixed with C in the ratio 75:25 wt pct (blend II); which was then mixed with blend I in the ratio 30:70 wt pct. The C content in set II was estimated to be 32.6%; additional carbon was added in this system for the reduction of iron oxide and the in-situ generation of molten iron.…”

Carbothermic Reduction of Alumina at 1823 K in the Presence of Molten Steel: a Sessile Drop Investigation

“…The increase in the carbon level was attributed to the pyrolysis yield from the binder. 12) Sessile drop investigations on the Al2O3-C/molten steel system were carried out at 1 823 K in a laboratory scale, horizontal tube resistance furnace (Fig. 1).…”