China's Refractories

The causes, the formation process, and the prevention of submerged entry nozzle (SEN) clogging were introduced. The influence of electric field on the SEN clogging was focused on, including the basic theory and measurement of SEN charging, the preliminary research on SEN charging, the influence of molten steel on the wetting behavior of refractory materials in electric field, and the influence of electric field on the oxide inclusions in molten steel. Based on the influence of the hydrodynamics, chemistry and other factors on refractory materials, structure, inclusion particle transfer and adhesion, many anti-clogging researches have been carried out, such as optimizing process conditions, compositing anti-clogging inner lining materials, innovating SEN structure and applying physical fields, which solve the problem of SEN clogging to a certain extent. However, the problems of weak adaptability and superficial study on clogging mechanism are still prominent. The electric field control is a new technology to prevent clogging. Although it has achieved certain results in on-site continuous casting trials, some problems such as the method of applying electric field, the electric field parameters and the equipment still need to be gradually improved, and the surface characteristics of inclusions and SEN materials at high temperatures need to be further studied. It was pointed out that the combination of materials and applied electric field will become an important direction for SEN anti-clogging technology.

For the proper use of micropowders in castables, slurries and fired samples were prepared with two kinds of corundum-spinel micropowders (D and G). The effects of the solid content and disperser WSM-R1 on the rheological properties of the slurries were studied. The sintering properties and the slag corrosion resistance of the fired samples were also researched. The results show that: the slurries all show pseudoplastic rheological characteristics. With the same solid content, the slurry with micropowder G has higher initial viscosity than that with micropowder D. Disperser WSM-R1 significantly reduces the initial viscosity of the two slurries and plays a more obvious dispersing effect on the slurry with micropowder G. The fired sample with micropowder G has higher bulk density, lower apparent porosity and better corrosion resistance than that with micropowder D.

Periclase-spinel bricks were prepared using sintered magnesia, flotation magnesia, fused magnesium aluminate spinel and calcined Al₂O₃ fines as the starting materials and calcium lignosulfonate as the binder, mixing, shaping and firing at 1 650 ℃. Flotation magnesia particles were used to replace ordinary sintered magnesia particles and different amounts of calcined Al₂O₃ fines were extra-added (0%, 3% and 5%, by mass) to investigate their effects on the properties of periclase-spinel bricks. The results show that: the periclase-spinel bricks prepared with flotation magnesia particles have reduced apparent porosity and cold compressive strength, and enhanced bulk density, thermal shock resistance, hot strength and hot toughness. As the calcined Al₂O₃ fines addition increases, the apparent porosity and the cold compressive strength decrease, and the bulk density, the thermal shock resistance, the hot strength and the hot toughness are improved.

Considering the high melting point and high stability of SrO, it has potential applications in the field of the preparation of titanium alloys. To improve the hydration resistance, SrO samples with different ZrO₂ additions were fabricated after firing at 1 750 ℃ for 6 h. The phase, the microstructure, and the hydration resistance of the samples were researched. The results show that the sample with 33 mol% ZrO₂ addition possesses good hydration resistance with the mass gain after hydration for 13 days of less than 0.42 mass%. The SrO crucible with 33 mol% ZrO₂ addition does not react with TiNi alloy melt during melting, which provides a support for searching new refractories with good hydration resistance for induction melting titanium alloys.

β-SiAlON-SiC composites were prepared using SiC particles and fines, silicon powder, AlN powder, α-Al₂O₃ micropowder and flake graphite as starting materials. The influence of the graphite ( particle size of ≤45 and ≤300 μm, addition of 3.0%, 5.5%, 7.5%, and 10.0%, by mass) on the molten-alkali corrosion resistance was investigated. The results show that the molten-alkali resistance for the β-SiAlON-SiC sample with 7.5% of graphite (≤300 μm) is optimal, showing the lowest mass change rate after corrosion and the highest retention ratios of cold modulus of rupture and hot modulus of rupture.

β-SiAlON reticular porous ceramics (Si_6-ZAl_ZO_ZN_8-Z, Z=2) were prepared with α-Al₂O₃, AlN and Si as raw materials and Y₂O₃ as the sintering aid by the foam impregnation method. The influence of the Y₂O₃ addition (0, 3%, 6% and 9%, by mass) on the microstructure and the properties of the samples was studied. The results show that the Y₂O₃ addition is conductive to the sintering of samples and the growth of grains. The sample added with 6% Y₂O₃ has the optimal properties: the apparent porosity of 82.9%, the bulk density of 0.53 g · cm^-3, the cold compressive strength of 1.97 MPa, and the residual cold compressive strength of 1.68 MPa after oxidation, which can be used as porous ceramic filters.

In order to further improve the strength and the thermal shock resistance of Al₂O₃-C materials for steel ladle slide gates, the effects of four kinds of alumina micropowders (unimodal activated alumina micropowder 07RAL, unimodal activated alumina micropowder 15RA, bimodal activated alumina micropowder 22RABL, and calcined alumina micropowder 40CA) on the density, the strength and the thermal shock resistance of Al₂O₃-C materials were studied. The results show that the density, the strength and the thermal shock resistance of Al₂O₃-C materials can be improved with the introduction of activated alumina micropowders. Among them, the specimen with bimodal activated alumina micropowder shows the best comprehensive performance, especially the hot modulus of rupture. Its actual application results in steel mills show that the average service life of the Al₂O₃-C slide plates prolongs, and the problems of cast hole reaming, plate oxidation, roughening and cracking during the use of slide plates are obviously improved.

Al₂O₃-SiC-C castables were prepared using C@SiC composite powder modified by molten salts to replace ball pitch gradually. The effects of the C@SiC composite powder addition (0, 1%, 1.5%, and 2%, by mass) on the water requirement, the flow value, the physical properties, the thermal shock resistance, the oxidation resistance, and the corrosion resistance of castables were studied. The results show that with the C@SiC addition increasing, the amount of water added to the castable increases, but the apparent porosity of the samples after heat treatment first increases and then decreases, and the cold modulus of rupture increases significantly. After completely replacing the ball pitch, the cold modulus of rupture of the sample increases by 51.2%, and the residual strength ratio increases by 28.7%. In addition, the sample with 2% C@SiC has the best oxidation resistance, and the sample with 1.5% C@SiC composite powder has the smallest corrosion depth.

Fused magnesium aluminate spinel carbon materials were prepared using fused magnesium aluminate spinel and flake graphite as the main raw materials and phenolic resin as the binder. The effects of the Al-Si alloy addition (0, 2%, 4%, 6%, 8% and 10%, by mass) on the properties of fused magnesium aluminate spinel carbon materials were studied. The results show that fiber materials are generated in the samples with Al-Si alloy addition, which can significantly improve the cold and hot modulus of rupture, the cold elastic modulus, and the thermal shock resistance of the samples. When the addition of Al-Si alloy is 6%-8%, the comprehensive performance of the sample is the optimum.