A methodology to investigate the wear of blast furnace hearth carbon refractory lining

In this work it is presented a methodology applied by Companhia Siderurgica Nacional (CSN, Brazil) in order to assess its blast furnace 3 carbon refractory hearth lining conditions. The aim of the investigation was the gathering of critical data base for blast furnace refractories life cycle follow up and eventual repair decision taking. The sample drilling locations were chosen around the tap holes and hearth bottom areas. The advancing drilling depths were based on local temperature profiles. The isotherm limit of 5008C was elected as a control parameter to assess the critical carbon refractory condition. The guidelines for sampling and testing as well as the results obtained through the physical and chemical characterizations of the cored samples are presented. The condition of the refractory lining is discussed under the light of the different known wear mechanisms of blast furnace hearth carbon refractories. It is a well-known fact that the refractory hearth lining is a critical feature in the realm of the life expectancy of a blast furnace. In this sense, invasive procedures were undertaken in order to assess the carbon refractory hearth lining conditions of CSNs blast furnace 3, afterproducing28 million tons ofpigironin11 years of campaign. The guidelines used for the sampling and the information put together by the investigation, conducted on cored specimens, were important for a global understanding of carbon refractories hearth lining wear phenomenology, as well as for the setup refractories selection guidelines and possible repair programs. Historically everysteel millwants toincreaseits blast furnace productivity. The first step commonly taken in this direction consists in the increase of the processing temperature. As a consequence the molten pig iron temperature increases, resulting immediately in an overall increase in the refractory lining wear. This was particularly critical for the crucible lining based on carbon refractories. In order to counterbalance the increased wear, the use of microstructure engineered improved graphite-based carbon refractories (higher thermal conductivity,