A corundum hydraulically hardening compound with addition of baddeleyite for steel ladle vacuum degassing vessels

Abstract

At present MKN corundum hydraulically hardening compound produced by Borovichi Refractory Combine to TU 14-8-359-80 is used for the outer lining of the nozzles of batch and circulating steel vacuum degassing vessels [I, 2].Wear of nozzle lining of this compound during serive is observed in areas in contact with slag and metal. The basic reasons for wear are penetration and attack of the lining by slag, penetration by metal, erosion action of the moving flows of metal and slag, and sharp thermal shocks at the start and end of vacuum degassing. To increase the life of the lining it is desirable to decrease its porosity and increase the strength and slag resistance.According to [3][4][5][6][7][8] one of the directions in improvement of corundum refractories is addition to the charge of zirconium dioxide. Taking this into consideration, addition of baddeleyite to MKN corundum hydraulically hardening compound to improve the above properties was tested.In conducting the investigations the following original materials were used: fused corundum powder to TU 14-8-384-81 produced by Kazakh Refractory Plant; type PB-2 baddeleyite powder to TU 14-8-393-82; high-alumina cement produced in the experimental Technology Section of All-Union Refractory:Institute meeting the requirments for type Talyum high-alumina cement to TU 6-03-339-78.The chemical analyses* of the original materials are shown in Table i.To obtain comparable results under the same conditions laboratory specimens of concretes were prepared** from corundum hydrauiicaily hardening compounds with additions of 6 and 16%% finely found baddeleyite and also from standard production MKN corundum compound.For all of the compounds s maximum grain size of the fused corundum was 7 mm. in preparation of the specimens the mixtures were moistened with 10% water. The moistened compounds were tamped in split metal molds and held in a humid atmospehre. The hardened specimens had the form of cubes with an edge length of 30 mm. Specimens in the form of 80 mm diameter 35 mm thick disks were prepared for determination of thermal conductivity.The compressive strengths of the specimens after hardening for 3 and 7 days had comparable values for the compound with addition of 6% baddeleyite and MKN compound (21.4 and 25.6 N/mm =, respectively, after 3 days and 30.9 and 26.9 N/mm: after 7 days). With an increase in baddeleyite content in the corundum compound to 16% the compressive strength of the specimens dropped to 17 N/mm 2 after 3 days and to 21N/mm = after 7 days of hardening.The hardened concrete specimens were fired in a batch kiln at 1600~ the service temperature of the lining. The properties of the fired specimens are given in Table 2. An analysis of this data showed that specimens of the corundum compound with addition of 6% baddeleyite possess the best combination of properties (lowest porosity, greatest strength, *The chemical analyses of the materials and the physicotechnical properties of the specimens were determined in the Laboratory for investigation of Refractory Propert...