# Evaluation of Factors Affecting the MgO-C Refractory Lining Degradation in a Basic Oxygen Furnace
## 1 Introduction
Penetration of BOF slag through cracks and pores into the MgO-C refractory results in degradation of the refractory's surface layer through the formation of a decarburized layer. Slag passes through this layer to a depth of approximately 5 mm; below this layer, the MgO-C refractory is mechanically degraded to a depth of approximately 10 mm [4]. The transition between the bonded working layer and the original unchanged refractory is sharp [5]. By crystallizing the solid phase, stresses are generated at the interface, leading to the formation of cracks and, upon temperature change, to peeling of the bonded layer and exposure of the bonded shard [6]. The filtered slag reacts with the MgO lining to form easy-to-melt magnesium silicate phases: mixed Ca and Mg silicates with melting points from 1320 \({}^{\circ}\)C to 1580 \({}^{\circ}\)C [4]. Penetration of the slag forms a zonal structure, which is the cause of delamination. The depth of the bonded layer and, thus, the formation of the zonal structure can be reduced by adding anti-wetting agents, such as carbon, SiC, or spinel particles [21]. The interaction of the three-phase MgO-C-slag-metal system and the formation of CO bubbles are the main causes of local corrosion and, hence, wear of the BOF refractory lining. Local corrosion is strongly influenced by the formation location and number of CO bubbles. The CO bubbles formed at the phase interface of the ternary MgO-C-slag-metal system inhibit the progress of local corrosion. Meanwhile, gas bubbles formed at the MgO-C--metal interface enhance the local corrosion process [33]. Equation (4) is the main reaction involved in the formation of carbon monoxide. The FeO in Equation (4) is produced by the reaction presented in Equation (5). Iron oxide (FeO) passes from the slag-metal phase interface to the slag-refractory phase interface, where it reacts with carbon to generate CO bubbles, according to Equation (4) [34]:  
\[\mathrm{(FeO)+C_{(s),refractory}\rightarrow[Fe]+\{CO\}} \tag{4}\]  
\[\mathrm{[O]+[Fe]\rightarrow(FeO)} \tag{5}\]  
An additional factor that affects the wear rate of the MgO-C refractory is the effect of the flow of molten slag and steel. The movement of the slag film is caused by intense swirling and turbulent flow due to high-intensity oxygen blowing; this is a significant factor causing local corrosion of the oxygen converter lining. The movement of the slag film accelerates the dissolution of the MgO-C refractory and acts as an abrasive on the BOF lining [21; 27; 35]. The factor determining the efficiency of the mass and heat transfer process in BOF slag is viscosity, primarily a function of temperature and the size and mobility of the anions present. Basic BOF slags have a very low viscosity at the temperatures of the steelmaking process, which increases significantly as the temperature decreases. BOF slags differ from other iron or steelmaking slags containing FeO due to their elevated FeO content and high CaO/SiO\({}_{2}\) ratio [36]. Only five studies in the literature address the viscosity of BOF slags or slags with compositions similar to BOF slags [37; 38; 39; 40; 41]. The viscosity of basic (BOF) slags is substantially increased by the addition of components with the ability to form large complexes (SiO\({}_{4}\)\({}^{-}\), Si\({}_{2}\)O\({}_{6}\)\({}^{-}\), PO\({}_{4}\)\({}^{3-}\)) and is decreased by the addition of ions with small dimensions (Ca\({}^{2+}\), F\({}^{1-}\), Na\({}^{1+}\)). The viscosity can be calculated according to various formulas [6; 21; 42], represented by Equations (6) and (7):  
\[\eta=A\cdot T^{\frac{B}{1+\lambda}} \tag{6}\]  
\[\eta=T^{\frac{B}{1+\lambda}} \tag{7}\]  
where \(\eta\) is viscosity in Pa.s\({}^{-1}\); T is temperature in K; A and B are coefficients. Dynamic mechanical loading of the MgO-C lining, which includes abrasion, impact, and vibration, occurs mainly during the charging of steel scrap into the oxygen converter. During the raw material feed, the refractory lining is most stressed in the impact area.