Division Director-Overseas Business　 Heiki MIKI

Yukimasa IWAMOTO, Junya ITO, Jim GILMORE, Masanori OKADA

In continuous casting of steel, improving the insulation property of the mold powder is effective to reduce gas bubble and inclusion defects on low carbon and ultra-low carbon steel grades. Similarly, increased insulation value can reduce surface cracking of cast slab on medium carbon and peritectic grades. Fine type mold powder has inherently higher heat insulation property than granulated type, and therefore provides better steel quality. Here we see by increasing the insulation property of granules by the addition of exothermic, metal raw materials, that it is possible to improve steel quality compared to steel produced with fine type powders

Masafumi FUJII, Masafumi NISHIMURA

In order to improve the durability of the impact zone precast block in teeming ladle, castable refractory material of which the cast body is highly densified by minimizing water content was developed. By optimizing particle size distribution and applying high-performance dispersant, an impact zone precast block that can be fabricated with 2.5 % water content was developed. In comparison with conventional material, highly densified precast block exhibits markedly improved mechanical strength at 1000℃ in association with well improved durability in actual operational application.

Yukio AI, Tsuneyuki IIKUNI, Kenji SUZUKI, Satoi KANATANI

A corrosion test for evaluating the influences of SiO2 content and preheating history on the corrosion rate of SiC-Al2O3-C castable refractory for main trough in blast furnace was carried out. It was clarified that, in accordance with an increase of SiO2 content, the corrosion rate of the castable refractory specimen was accelerated with a tendency, preheating for such reduction in the corrosion resistance to become more prominent. It was also understood through chemical analysis that the C content in a specimen is lowered by firing with marked dependency on the coexisting SiO2 content. The reduction of the C content caused by firing can be attributed to oxidization of C by SiO2 component, which is expressed with the following chemical equation. SiO2(s) + C(s) = SiO(g) + CO(g) 　By combining the above two experiment results, it is inferred that the accelerated corrosion of castable refractory specimens with a preheating history was caused by the reduction of the C component of which the existence is effective for securing corrosion resistance. Taking into account the time-series wearing situation of the main trough castable refractories in an actual blast furnace operation that, after gradual wear-off of the hot face refractories over a relatively lengthy time period, the back portion of refractory is exposed to molten metal and slag as the hot face. It can be predicted that, due to oxidation of the C component by SiO2 until surfacing at the hot face, the corrosion resistance of newly surfaced refractory has been reduced to some extent. It was concluded that minimizing the SiO2 content in castable refractories is important to improve or stabilize the corrosion rate. 

Koichi IGABO, Kentaro HIRAYAMA, Yuto MIYATA

Since one of the typical refractory damage patterns observed in secondary refining facilities is erosion, suficient erosion resistance is consequently required for magnesia chrome bricks commonly used in secondary refining facilities. Taking into account actual operational circumstances, erosion resistance especially under thermally deteriorated condition A is thought to be more important. A semi-rebonded magnesia chrome brick of which the erosion resistance was improved to have sufficient durability to thermal fluctuations in actual secondary refining operation by means of enhancing the brick’s binding structure is introduced in this report. 

Wei LIN, Naohide HAMAMOTO, Hiroki BABA, Takayuki MATSUNAGA

Al2O3-C containing metal Al is widely used for the slide valve plates in the continuous casting of steel. However, this material has some aspects that need to be further improved. For example, it sometimes lacks corrosion resistance in the case of casting Ca-treated steel. In this research, we developed metal chromium (Cr)-added Al2O3-C, as a new material for the plates. Ladle plates made of this material were trialed in a steel mill for the casting of Ca-treated steel and ordinary steel. They showed less damage and longer service life than the conventional material plates. This is considered to be because Cr played roles in hindering the reduction reaction of fine Al2O3 grains by carbon in the material matrix and inhibiting the penetration of molten steel and slag due to Cr increasing the viscosity of molten steel and slag. By basic investigation, it was found that Cr carbides and nitrides were formed in the new material during the firing and this material showed smaller microstructural deterioration after reaction with molten steel and smaller corrosion after reaction with molten slag than the conventional material.

Isolite Insulating Products Co., Ltd.　 Koki HORIBA, Kentaro UEMICHI, Yasuo SHIRAISHI

With the amendment of the Industrial Safety and Health Act‚ in which refractory ceramic fiber (hereinafter abbreviated as ＂RCF＂) is classified as one of the Group-2 substances specified in the Ordinance on Prevention of Hazards due to Specified Chemical Substances‚ substitution of alkaline earth silicate wool (hereinafter abbreviated as ＂AES＂)‚ which is exempted from the regulations for RCF‚ has been promoted. In order to satisfy the increasing requirements for AES products applicable at elevated temperatures‚ AES products with higher temperature grade are being developed. AES products with various temperature grades are compared in this report.

Eiji ISHIHARA

Ladle refining using porous plugs is currently the most common method for improving steel quality and reducing steel production cost. Porous plugs are directly installed in the bottom part of a ladle steel shell which allow purge gas to pass through for the purpose of stirring the molten steel. They occupy the full depth of the ladle bottom lining. This makes it difficult to exterminate all the risks of molten steel leakage even if various precautions for preventing excess use of the porous plug are taken, which have been incorporated from practical experience. Porous plug with ＂PKG＂ safety device for protection from molten steel leakage is the safest plug that surely reduces the risk of molten steel leakage in case it is used beyond the limit of its serviceable life. The basic constitution of the porous plug with the PKG device and the principle for preventing molten steel leakage are described in this report.

Kanae NISHIO, Hiroyasu NIITSUMA

The role of the submerged entry nozzle is very important because of the great influence of molten metal flow in the mold on stable continuous casting operation as well as on the qualities of cast products. Especially, the molten steel stream discharged from the outlet of the submerged entry nozzle greatly influences molten metal flow in mold. New outlet design, DiA type outlet, was developed to lower the velocity of the molten steel stream running out of the outlet. The details of the submerged entry nozzle with DiA type outlet are introduced in this report. 

Hidekuni NISHIGUCHI, Ryuta YAMADA, Koji ASAKAWA

In order to prevent internal coke oven gas leakage out of the thin gaps between the coal charging hole frames and the charging hole lids on the top of coke oven, the gaps are filled with a slurry that is prepared by mixing sealing powders with water. Due to inadequate preparation of the slurry, operational problems such as insufficient sealing, drainage failure, or malfunction during pressure-feeding operation of the slurry, are sporadically observed. The novel slurry-type sealing compound XX-12-W-1 was developed to eliminate these problems. Unlike conventional powder type sealing products, which require on-site slurry preparation, XX-12-W-1 is produced completely in our manufacturing plant, from mixing to container packaging. It can be used without the burdensome on-site preparation. Since this novel slurry-type sealing compound is produced under precise quality control, it’s less likely to cause the above-mentioned problems mainly caused by inadequate on-site slurry preparation. Especially, the sealing capability was significantly improved compared to conventional products, XX-12-W-1 remarkably reduces operational problems caused by insufficient sealing capability of sealing compounds.