The wear of refractories in slide gate plates depends on the grade of steel, operating conditions of casting, bore diameter, and quality of refractories. The wear of slide plates is summarized as the following :

1. Bore diameter increase.
2. Corrosion in the sliding surface.
3. Decarburization.
4. Radial crack formation

Bore diameter increase:

Chemical corrosion and hot abrasion are the main causes of bore enlargement. The bore of the plate erodes by steel flow and corrodes chemically by reactions. The steel flow attacks the edge of the bore of the slide plates and causes wear. During casting the refractory of the plate reacts with the elements dissolved in liquid steel to create low–melting-point compounds. If the refractory is made of Al2O3-C, it becomes corroded due to oxidation of carbon in refractory with dissolved oxygen in liquid steel.

Corrosion in the sliding surface:

The corrosion of sliding surface is the cause of roughening this part of the plate and often leads to peeling and break out of the grains. Due to this corrosion mechanism, metal tongues are frequently pulled in between the plates, which occurs due to frequent opening and closing of the plates. Each time of sliding the plates, the steel is lasting on the sliding area with its ferro-static pressure. With continuing corrosion, steel film can remain on the plates, leading to the formation of metal tongues within the plates.

Decarburization:

Decarburization, as it is found in carbon- or rather pitch-containing plate refractory, is caused by the oxidation of carbon in the presence of oxygen in air. When a plate refractory is exposed to the molten steel flow, carbon on the hot face dissolves into molten steel and a decarburized layer is formed at the surface.The friction between the plates during sliding increases when the lubricating carbon constituents are oxidized between the plates happens during tapping steel containing high oxygen ppm. The plates corrode faster, wear is increased and therefore the service life of tar-impregnated plates become limited.

Radial crack formation:

The formation of radial cracks is very common in all types of plates and it is caused by thermomechanical stress generated during service. The formation of crack and its widening is reduced by encasing the plates in steel casing. The stress is mainly generated due to severe thermal shock. At the first stream of the steel flow through the plate bore, the area around the bore instantly heated up to above 1600 C while the outside of the plate remains in room temperature. The area around outside of the plate is stressed beyond its structural limits and sustains radial cracks centering from its bore, Chemically bonded carbon-added Al2O3-C or Al2O3-C-ZrO2 plates show very small crack formation compared to tar-impregnated fired alumina plates due to higher thermal conductivity and very high hot strength, which results in superior thermal shock resistance.