Technical Paper


Christoph Wöhrmeyer1 , Simon Gao1 , Scot Graddick1 , Chris Parr1 Makoto Iiyama2, Patrick Gehre3 1 Imerys Aluminates, Putaux, Paris-La Defense, France, 2 ABSTRACT

This article investigates the effect of addition of a Calcium Magnesium Aluminate material (MagArmour) to Magnesia-Carbon (MgO-C) bricks. MagArmour consists of grains in which microcrystalline MA-spinel phases are embedded in a matrix of calcium aluminates. Applied as binder in steel ladle castables it has proven already its positive effect on wear resistance in many steel plants due to the associated change in microstructure. The effect of MagArmour addition to MgO-C bricks in comparison to the addition of pure spinel has been investigated in the first part of this study. The MagArmour-doped MgO-C brick showed the lowest attack by slag. Following this positive result several trials in different steel plants have been conducted and results from post-mortem analyses are discussed in the second part of this paper. All ladle trials had in common that during operations a slag coating was formed on the surface of the MagArmour- containing bricks that reduced the wear rate of the bricks and gave a better protection of the carbon in the brick against oxidation. A lower wear rate was achieved, even when reducing the amount of anti-oxidants in the bricks.

1: Introduction

MgO-C is first choice refractory material for the slag line of steel ladles as it exhibits excellent slag penetration resistance due to the non-wetting property of carbon with slag, thermal shock resistance, high thermal

November 2018 Issue , Fabien Simonin1 , Christos Aneziris3 Presenting author, Consultant, Tokyo, Japan 3 Technische Universität Bergakademie Freiberg, Institute of Ceramic, Glass & Construction Materials, Freiberg, Germany

conductivity, low thermal expansion and high toughness [1]. However, poor oxidation resistance as well as low strength at high temperatures are known to limit service life of MgO-C refractories. Many researches dealt with the corrosion of MgO-C, which are summarized by Lee and Zhang [2]. In a first reaction step, FeO from the slag and/ or surrounding oxygen oxidize the carbon component. Hence, in a second reaction step, slag penetration as well as corrosion of MgO will increase. Additionally, reduction of MgO by contact with C at high temperatures will promote MgO-corrosion as well. Gaseous Mg reacts with oxygen forming a dense secondary MgO- layer at the refractory-slag-interface, which will reduce slag infiltration in turn. Furthermore, by reduction of FeO to Fe no eutectic oxide compounds will be formed. The resulting CO gas from oxidation of carbon creates an excess pressure at the refractory-slag-interface, which will promote corrosion resistance as well.

The addition of Al2O3 to MgO-C leads to AMC-bricks with excellent

properties like high thermal conductivity, thermal shock resistance and slag attack resistance [3]. Improved performance of AMC compared to conventional high alumina and doloma refractories has also been proven in ladle application [4]. These excellent properties are resulting from reaction between periclase and alumina to form spinel (MgAl2

O4 ). Spinel is widely

used as refractory material due to its high refractoriness, thermal shock resistance and high resistance against slag penetration and corrosion [5]. With increasing alumina content in MgO-C, slag penetration decreases due to (a) formation of spinel, (b) formation of carbide and nitride phases which

ENGINEER THE REFRACTORIES 15 , Goutam Bhattacharya1 ,

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