Abstract

Alumina-magnesia-carbon (AMC) refractories used in the steelmaking ladles support temperatures up to 1600-1700°C and are also exposed to the attack of melts (liquid metal and slag) and oxidant gases of the atmosphere. On the other hand, the high degradation of the bricks under real conditions in-service is difficult to reproduce at laboratory scale. For this reason, a combination of analytical methodologies is convenient to face the problem.

In this work, the corrosion of commercial AMC bricks by molten slag is studied by a combination of methodologies in order to achieve a deep understanding of the corrosion mechanisms and its relationship with refractory characteristics such as composition, microstructure and texture.

The dipping-test, which reproduces the relative movement between the slag and the refractory, is used together with the thermodynamic simulation of the system by a commercial software. Prismatic specimens extracted from the brick are subjected to the corrosion test at 1600°C during 30 min, and a sample speed of 25 rpm. A typical industrial slag is evaluated with a CaO/SiO2 ratio of 10.6. After the test, the sample wear is evaluated by dimensional variations, XRD, DTA/TGA, density and porosity measurements. Also, optical and SEM/EDS microscopies are employed. A previous characterization of the commercial bricks is performed by the same analytical techniques in order to use this information as reference. The thermodynamic simulation of slag-refractory system is carried out using FactSage 7.0 commercial package and the chemical composition of the slag and the brick. An iterative procedure is employed until the amount of equilibrium liquid is null. The specimen wear as well as the identification of the new phases formed at the slag-refractory interface (mainly different calcium aluminates and MgO.Al2O3 spinel) are used as indications of sample corrosion. Moreover, the equilibrium calculations brings good prediction with regard to the phases present at the slag-refractory interface, and the degree of corrosion wear taking into account number of steps from the iterative process, and the amount and viscosity of the equilibrium liquid, among others.

From these results, the main steps of the corrosion process (mechanisms) are inferred, as well as the relationship between chemical attack and AMC bricks characteristics (raw materials, periclase, graphite content, type of antioxidant, etc.).