... gas to the liquid steel. These stirring gases can cause erosion of the hearth refractories resulting in the regular maintenance requirement of the hearth refractories.
Slag line – The slag line of EAFs is the transitional area between the hearth and the side wall. This area is subjected to high temperatures due to the exposure to the electric arc, oxidation, and flame impingement from supplemental O2 injection, and most importantly to the slag attack from high temperature slags containing FeO, SiO2, and MnO. Refractory selection in the slag line is to be carefully coordinated with the expected slag chemistry. In case of EAFs producing C steels, there is generation of lime rich, FeO -SiO2 slags with a lime: silica ratio of plus 2:1. This demands basic refractories. In the slag line area of the EAFs generally Mag-C bricks or tar impregnated magnesite bricks are used. In EAFs for stainless steel production, a more neutral fused grain magnesite chrome brick can be used.
Slag line refractory design in EAFs is the combination of bricks and monolithic refractories. A very common design for the slag line is Mag-C bricks of 300 mm to 450 mm in thickness and with 10 % to 20 % of C content. The C phase of the brick is composed of graphite and a carbonaceous resin bond. These C materials have very good resistance to slag attack as well as a very good resistance to high temperatures. However, the C is susceptible to the oxidation and to protect the slag line refractories from oxidation metal powders such as aluminum, silicon, or magnesium are added. These metallic powders combine with C to form carbides which have higher oxidation resistance. The carbides also strengthen the refractory bricks. Strength is needed for resisting the erosive action of the liquid slag and the steel washing taking place the slag line zone of the furnace. Mag-C bricks in the slag line are additionally protected by the monolithic refractories. Initial installation of the monolithic refractories normally covers all or the part of the slag line bricks. However, because of the difficult operating conditions in this zone, the refractories corrode. Additional protection of the slag line is done by guniting with the MgO based guniting mix to build-up a protective layer on the slag line. The build-up activity of the slag line refractories is required to be carried out frequently depending upon the severity of the operating conditions.
Upper side wall – The upper side wall of the EAFs are lined with Mag-C bricks which are similar to the bricks of the slag line. The upper side wall is subjected to the arc flare (very high temperatures) and impingement by heavy scrap during the process of charging of the furnace. During the furnace tapping, when the furnace tilts, liquid steel and liquid slag is in contact with the upper sidewall on the tapping side of the furnace. Also, the upper side wall bricks are required (To be followed)