# Evaluation of Factors Affecting the MgO-C Refractory Lining Degradation in a Basic Oxygen Furnace
## 4 Discussion  
Figure 2a,b demonstrates distinct trends in refractory thickness evolution over time in the studied areas. Figure 3 illustrates these changes in the BOF cross-section. Significant skull formation on the MgO-C lining occurred predominantly within the initial third of the campaign, up to approximately melt 6,000. After this period, skull development decreased. A resurgence in large skulls occurred around heat 12,000, coinciding with increased gunning refractory consumption. The most substantial loss in working lining thickness was observed between heats 14,739 and 16,400. Subsequently, the residual thickness of the gunning mix only increased to its final level due to the extensive use of gunning refractory. The wear of the MgO-C refractory lining in both trunnion ring zones (S3 and S9) is primarily influenced by slag additive consumption and overall oxygen consumption levels. Flux additives, like lime and dolomitic lime, were initially thought not to impact the refractory lining within trunnion ring wear because, based on [18; 19; 20], the durability of the MgO-C lining is positively affected by the addition of lime and dolomitic lime. However, statistical analysis revealed that excessive skulls on the refractory lining, caused by reduced slag viscosity due to lime and dolomitic lime, necessitated their removal with a 20-hole oxygen nozzle. This method, though effective, led to oxidation damage of the BOF lining. Oxygen had a similar statistical impact in both zones but differed operationally. In the S3 zone, wear occurred during skull removal, while in the S9 zone, oxygen from the blowing lane significantly wore down the lining. From a statistical point of view, the total oxygen consumption has a major influence on the wear of the BOF refractory lining in the slag line area (S3 zone); this fact is consistent with the literature [21; 24; 26]. However, the effect of oxygen in the form of metal oxides in the slag is more pronounced than that of blowing or free oxygen in the steel. From this, it can be concluded that the greater the amount of oxygen acting on the system, the more unfavorable it is for the development of the MgO-C lining thickness. In the S3 zone of the slag line area, dolomitic lime is of particular importance. In addition to its chemical influence, it has a mechanical effect on the refractory material. Dolomitic lime causes impact damage to the lining walls and, therefore, has a particular effect on the MgO-C in this area. The amount of dolomitic lime and lime added significantly affects the basicity of the slag and decreases the BOF slag viscosity. The greater the amount of dolomitic lime and lime added, the higher the slag basicity, which protects MgO-C lining, and lower the viscosity, which causes skull formation on the lining. However, the skull on the lining must be  
Figure 23: Comparison of gunning material (GM) consumption per heat in the most exposed areas of the BOF refractory lining and the total iron content of the BOF slag per heat during the analyzed campaign. removed, causing excessive oxidation of the BOF lining. The higher flux consumption also results in a higher mechanical wear rate of the MgO-C liner within the S3 zone, resulting in higher gunning refractory consumption. Thus, more flux additives result in a higher abrasive effect. In the S9 zone of the slag line area, the silicon in pig iron contributes to refractory wear by increasing BOF slag viscosity, thus clogging the refractory pores and cracks. This effect is temporary and can be mitigated by adding basic flux additives, eliminating the impact of silicon and its compounds. The largest consumption of gunning refractories occurred in the S3 zone of the slag line area. A total of 2326.343 tons of gunning mixes were used during the campaign, of which 44.83% was used in this area. The second most exposed area was the S9 zone in the trunnion ring area, where 16.79% of the total gunning mix was used for repair. The other monitored areas experienced minor wear during the campaign.