Wear mechanism for blast furnace hearth refractory lining S. N. Silva 1 , F. Vernilli* 2 , S. M. Justus 3 , O. R. Marques 1 , A. Mazine 3 , J. B. Baldo 3 , E. Longo 3 and J. A. Varela 3 Over recent years, owing to the need to increase productivity, it has been necessary among other things to increase the hot metal temperature in the blast furnace hearth ; . As a result, refractory lining wear becomes more intense. While publications present a host of comparative tests for hearth refractories and their performance, hardly any information is available in such publications regarding reaction mechanisms and further deterioration of these materials. Based upon comparative laboratory test results using two carbon materials of different concepts, the various reaction mechanisms and enhanced refractory lining deterioration for the blast furnace hearth have been identified. From an understanding of these wear mechanisms acting upon the hearth lining, it has been decided to introduce some practical operating measures, with a view to extending the blast furnace campaign. Keywords: Wear mechanism, Hearth, Blast furnace Introduction It is of worldwide consensus that hearth refractory lining wear is the main culprit determining the end of the blast furnace campaign. 1 Over recent years, owing to the need to increase productivity, it has been necessary among other things to increase the hot metal temperature. As a result, refractory lining wear becomes more intense, for two reasons: 1 (i) liquid flowrate in the hearth rises substantially because of increased production; therefore, the wear process known as ‘elephant’s foot’ in the tap hole area is accelerated (ii) the high rate of pulverised coal injection (120– 200 kg t 21 hot metal) reduces deadman perme- ability while increasing its size. As a result, hot metal flow becomes more turbulent, thereby accelerating even further the lining wear while leading to ‘brittle zones’, which start inside the carbon refractory walls. While specialist publications present a host of comparative tests for hearth refractories and their performance, hardly any information is available in such publications on reaction mechanisms and further deterioration of these materials. It is necessary, there- fore, to understand the wear mechanisms of these refractories to extend the blast furnace campaign. Materials and methods Materials To assess the role of each different property for a carbon refractory, in view of the various blast furnace (BF) hearth requirements, two carbon refractories of different concepts were selected for the present study: (i) micropore carbon refractory, conventionally cured, anthracite based (80% anthracite), char- acterised by carbon particles with a low crystal- lisation degree and graphite particles (20%) bonded by an amorphous carbon matrix of high permeability and high ash content (ii) supermicropore carbon refractory, with double densification by means of pitch impregnation under vacuum and coking with SiC, Al 2 O 3 and silicon addition to the carbonaceous microstruc- ture, characterised by graphite particles (50%) with a high degree of crystallisation and carbon particles with a low degree of crystallisation (50% anthracite), bonded by an amorphous carbon matrix (tar) of low permeability and low ash content. Methods: comparative tests Oxidation resistance Oxidation resistance was measured by means of mass loss from a cubic test specimen of 40 mm edge submitted to five heating cycles at 1100uC under an air atmosphere, the specimens being air cooled to room temperature after each 3 h exposure. Ironmaking and Steelmaking irs1924.3d 23/8/05 12:51:30 The Charlesworth Group, Wakefield +44(0)1924 369598 - Rev 7.51n/W (Jan 20 2003) 1 Companhia Sideru ´ rgica Nacional (CSN), Rio de Janeiro, Brazil 2 Department of Materials Engineering, Faenquil, Sa ˜ o Paulo, Brazil 3 Multidisciplinary Centre for the Development of Ceramic Materials (CMDMC), UFSCar, Sa ˜ o Paulo, Brazil *Corresponding author, email vernilli@demar.faenquil.br ß 2005 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute Received 30 November 2004; accepted 17 June 2005 DOI 10.1179/174328105X48160 Ironmaking and Steelmaking 2005 VOL 32 NO 6 1