Evaluation of LF Slag Degradation and Its Impact on Ladle Lining

M. MOLINÉ ; A.TOMBA; P. GALLIANO

Santiago

Congreso; 16th Biennial Worldwide Congress on Refractories UNITECR 17; 2017

ALAFAR

MgO-C and Al2O3-MgO-Cbricks are widely used in working linings of steelmaking ladles. Due to theircarbon content, these materials are susceptible to be oxidized by air orcombustion atmospheres during its campaign. This risk is present after theladle leaves the continuous casting machine and before it receives the liquidsteel in the following heat. After ladle casting step is finished, a film of steelmakingladle furnace (LF) slag covers the refractory lining and remains partly adheredto it. This slag coating, which is mainly composed of CaO, SiO2, MgOand Al2O3, can have a beneficial effect on the liningproviding a barrier against refractory decarburization. As far as the ladle is cooleddown the remaining slag is solidified. In this stage several phases crystallizefrom the liquid state.  Further cooling downuntil room temperatures can led to additional phase transformations andreactions involving those crystallized phases. Some of these reactions can be stronglydeleterious for the materials integrity, leading to a rapid degradation andpulverization of the solid slag. Ambient degradation of steelmaking ladle slagshas been mainly attributed to the presence of phases that shows an expansivebehavior due to hydration and carbonation reactions with high volumevariations. Table 1 resumes main phases and reactions involved, together withtheir volumetric and mass variation. Slagweathering is conditioned by chemical, mineralogical and microstructuralproperties of the material, as well as by the thermal and atmosphericconditions during this process. [1,2]. Characterization studies of steelmakingslags and evaluation of their degradation pattern have been reported and have agreat value when looking for better alternatives for re-using or recyclingthese materials in different industrial processes. However, no studies has beendone on the evaluation of the degradation of these slags when they are coatingladle bricks under operation. And little is known about how do degradationaffects slag protective role against in service refractory lining decarburation.In this work, the degradation of an industrial steelmaking slag was studied byevaluating the evolution of its physical and chemical properties withincreasing weathering time. The aim of this work is to get knowledge about thedegradation mechanism of a steelmaking ladle slag under different conditions.This work is part of a research focused on the impact of the slag on thebehavior of steelmaking carbon-containing refractory bricks.