Use of Thermodynamic Calculations in Predicting the Corrosion Behavior of Refractories for Steelmaking

Abstract

Refractories are non-metallic materials used to line many industrial furnaces for the high temperature production of other materials such as metals, glass, cement, and petrochemicals. Decreased service life of refractories is caused by damage arising from, for example, deformation at high temperature, thermal shock, mechanical abrasion, and chemical corrosion. Among these factors, chemical attack by molten steel or slag is often the most critical. To determine chemical corrosion mechanisms and to compare corrosion behavior of different refractories, several test methods(rotary corrosion test, crucible test, high frequency induction furnace test, et al.) have evolved. However, many of these tests are expensive and time consuming, and in some cases, they are conducted just to re-establish information already known and generally available in existing phase diagrams. In the present study, the utilization of thermodynamic calculations is proposed to predict the corrosion behavior of refractories for steelmaking (especially, RH process and continuous casting process). At part 1, we proposed the effective equilibrium reaction zone model to predict the complex industrial RH process using thermodynamic calculations. In this approach, all phases within the "effective" reaction zone located at a reaction interface are assumed to reach equilibrium. The results of the model were used to clarify the decarburization behavior observed during the RH process. According to the model predictions, the RH slag contains a high FetO level during the first 15min of the RH process. During the Al addition, the reducible components in the slag including FetO, SiO2, MnO and CrOX are reduced by Al. After the Al addition, the RH slag becomes a CaO-Al2O3 slag containing some MgO. Five slag compositions were selected to simulate the major slag composition changes in the RH vessel during the degassing process

a typical ladle slag, two FeO-rich slags and two CaO-Al2O3 slags. The corrosion behavior of two comon refractories, i.e. magnesia-carbon and magnesia-chromite refractories, in contact with various RH slags were experimentally and thermodynamically investigate. Compared to the plant test, the predicted reactions were in good agreement with the observations. At part II, we investigated the influence of liquid inclusion(MnO-SiO2-FeO-MnS) in high oxygen steels on the corrosion of various refractories used for continuous casting stopper materials. In order to understand the complex chemical reactions between the inclusion and refractories, thermodynamic calculations using the Factsage thermodynamic software were also performed. The refractories with small amount of C partially reduced the inclusion, and the remaining liquid inclusion penetrated into the refractory easily to induce a noticeable chemical corrosion. On the other hand, the refractories containing high amount of C reduced a large quantity of the liquid inclusion to metallic Mn-Fe-Si and remained only a small amount of MnO-SiO2 of which composition was largely shifted toward SiO2 rich side. As a result, the corrosion of refractories containing high C by liquid inclusion could be significantly reduced. Among the various refractories, ZrO2-C showed the highest corrosion resistance against liquid MnO-SiO2-FeO-MnS inclusion. In real plant test, ZrO2-C(13 wt %) refractory showed an excellent corrosion resistance against high oxygen steels containing liquid MnO-SiO2-FeO-MnS inclusion, which improved the continuous casting of high oxygen steels.