How much does adhered ladle slag protect MgO-C refractories from oxidation?

This study explores how much adhered ladle slag protects MgO-C refractories against environmental oxidation at high temperature, a major factor that shortens their lifetime as a working lining for certain industrial vessels such as steelmaking ladles. For this investigation, an ad hoc methodology was used to test the behaviour of refractory samples, both with and without a ladle slag layer, when subjected to oxidation by air at high temperature. Different types of refractories were also tested to evaluate the effect of critical compositional variables such as graphite content, the addition of an antioxidant, or organic binder type. Moreover, the impact of the environmental degradation of the slag on its protective role during a subsequent heat treatment is assessed. The experiments showed that a slag layer could be viable as a protective barrier for any of the MgO-C refractories studied, providing a maximum degree of protection of approximately 90 %. Although the slag's environmental degradation reduced its protective role, the oxidation level did not reach that of the unprotected refractory materials (which lost among 2.3 and 3.1 wt% of mass, depending on the refractory composition) even after 60 days of environmental exposure, when the protection degree was around15 – 30 %. In addition, the reduction of refractory permeability and a higher degree of interaction with the slag produced fewer protective barriers. • A new method used to quantify slag protection degree to MgO-C refractories oxidation. • Ambient slag degradation reduced the protection role but it remained after 60 days. • Better slag anchorage improved initial protection, but increased degradation over time. • The presence of Al and a higher graphite content reduced the initial slag protection. • Combining resin with a soft binder in the refractory improved the slag's protection.