Research On Properties And Microstructure Of SEN For The Super Clean Steel Casting

In this study, MA, Al2O3 and MgO are used as main materials, phenol resin as binder, and H3BO3, B4C, BN, Si, Al and Mg-Al alloy as additives. Through the experiments at lab and steel mills, the properties of Al2O3-graphite materials were determined. And microstructure and phase of used and un-used materials were also determined by XRD, SEM and EDAX. The study indicates:(1) Good properties were gained when three materials were added with 5wt% phenol resin and the ratio of particles to powers was 6/4. CMOR of three materials dried at 110℃ for 5hr was greater than 40MPa and CMOR of three materials heat-treated at 1100℃ for 5hr was greater than 20MPa, which could meet the needs of strength for composite moulding with Al2O3-graphite materials and machining SEN.(2)During the carbon embed heat-treated process (1100℃×5h), boracic acid, boron carbide and boron nitride decomposed and oxidized, so boron oxide was generated. Magnesia-alumina spinel decomposed when boron oxide existed and corundum occurred. The reaction products of silicon powder were β- SiC and Si2N2O. Alumina from metallic aluminum reacted with magnesia or spinel in the sample and the spinel was regenerated. Aluminum nitride, product of metallic aluminum in the heat-treated process, reacted with alumina or magnesia in the samples and the A10N or MgAlON were generated. The additives had a remarkable influence on the properties of the materials. The additive of metallic aluminum can improve the physical properties of the materials.(3) The anti-alumina adhension property of materials could not be distinguished by the ordingary medium-frequency furnace Simulation test.(4) The test on-site showed that carbon-free submerged entry nozzle of magnesia-alumina materials had the perfect properties of thermal-shock resistance and slag-erosion resistance. Additionally, the carbon-free layer of the SEN showed the good properties of scour resistance, erosion resistance and anti-alumina adhesion. The average carbon pick-up was 1.1ppm when casting the ultra-low-carbon steel, while the average carbon pick-up with the normal alumina-graphite SEN was 3.8ppm. It was a remarkable improvement to the casting of ultra-low-carbon steel and this material could meet the demands of the production of the ultra-low-carbon steel and the super clean steel.