Director, Managing Executive Officer Eishi IIDA

Takayuki MATSUNAGA, Koji MORIWAKI and Masakazu IIDA

Refractories for continuous casting such as the submerged entry nozzle and gas-blowing upper nozzle considerably influence steel quality. In this article, a suitable submerged entry nozzle structure that allows desirable molten steel flow in the mold, and suitable properties of the gasblowing upper nozzle in terms of inclusion floating, improving seal-ability of gasket of ladle shroud are described. By improving these refractories for continuous casting, it is possible to improve steel quality as well as refractory durability.

Wei LIN and Yukio OHKAWA

The microstructures of the inner hot face of CaO-ZrO2-C (CZ-C) submerged entry nozzles used in actual continuous casting of Al-killed steel were investigated. It was observed that a thick Al2O3 clog deposit occurred on the Al2O3-C region of the nozzle inner hot face, whereas no clog deposit was found on the CZ-C region, which did not show any macro-corrosion either. The CZ- C inner hot face consisted of a surface layer (molten steel side) and a decarburized layer. There were mainly Al2O3-CaO phases forming the matrix, ZrO2-CaO grains and Al2O3-MgO grains in the surface layer. The decarburized layer revealed a microstructure where the initial carbon (graphite) had disappeared and Al2O3-CaO phases were distributed among the ZrO2-CaO grains. The two layers were all dense. The deposition inhibition action of the CZ-C may be a result from the surface layer being dense and having good wettability with the molten steel. The long lasting performance may be because the surface layer had a high apparent viscosity and thus was able to resist washing out of the molten steel flow.

Junya ITO, Shogo YAMASHITA, Yukimasa IWAMOTO and Daisuke KATAYAMA

Generally, high basicity mold powders (CaO/SiO2 = 1.1 - 1.4) have been used to cast medium and peritectic carbon steel. However, longitudinal surface cracking can still be an issue. Because softer heat removal in the mold meniscus area is required to prevent surface cracking, the crystallization properties of mold powder slags with higher basicity (>1.5) was investigated. A new very high basicity powder was developed using the results of our own unique slag film simulator. This new mold powder provides softer heat removal in the meniscus area. This new technology improved steel surface quality and provided sufficient solidified shell thickness when used in actual casting.

Naoko DOI, Masakazu IIDA and Yukio OHKAWA

MgO-C reaction, which spontaneously occurs at high temperature in low oxygen atmosphere, is one of the important wear factors of MgO-C bricks. In this paper, we will report the influence of porosity on MgO-C reaction. As a result of the experimental heating of porosity-varied specimens, it was verified that weight loss increased with increase in porosity and the reaction progressed from the surface toward the inside. According to the microstructure of the post-heated specimen, the reaction front, which is the boundary between reacted peripheral and unreacted inside, was clearly recognized. Thus, it is assumable that MgO-C reaction occurs only at the peripheral. Based on the experimental results, we constructed a “reaction front model” that describes the influence of the porosity of each brick on the migration speed of the reaction front. The results calculated by the model well-agreed with the previously published data and experimental results.

Michinori YOSHIKAWA, Tamiatsu KOYAKE and Masakazu IIDA

Several types of shaped refractories were evaluated in this report, which focuses on “R-curve”. R-curve is the plot of the stress intensity factor (KR), which indicates crack propagation resistance, as a function of crack growth length. As a result of comparison of R-curve between MgO-C brick and MgO-Spinel brick, MgO-Spinel brick showed larger KR than MgO-C brick in all regions, i.e., crack occurrence resistance and crack growth resistance of MgO-Spinel brick are larger than those of MgO-C brick. From the above results, it was found that MgO-Spinel brick has less crack occurrence and crack growth probabilities compared to MgO-C brick. When comparing the R-curve between two slide valve plate Al2O3-C materials, (Al2O3-C ① and Al2O3-C ②), KR at the crack initiation point is larger for Al2O3-C ②. Thus, the Al2O3-C ② is less likely to initiate cracking. According to the independently carried out spalling test result, Al2O3-C ② exhibited better spalling resistance than Al2O3-C ①. It is considered that the KR at the crack initiation point, that is, the crack occurrence resistance, is an effective index for Al2O3-C material. Also, the diameter of the frontal process zone for each material was estimated to be about 6 to 7 mm.

Tatsuya KAGEYAMA, Daisuke TANAKA and Akihito KAJITANI

We investigated the influence of the addition of Fe-Si3N4 on taphole mix focusing on change in characteristics caused by long heating time. β-SiC was generated from a decomposition reaction of Fe-Si3N4 in taphole mix after heating at 1500 ℃ for a long time. It was confirmed that this β-SiC didn’t reduce molten iron corrosion resistance of taphole mix better than SiC which was added as a raw material beforehand. The reason is inferred to be that Silicon oxynitride is also generated with β-SiC at the same time. Fe-Si3N4 has better molten iron resistance than SiC. The reason may be that the Nitrogen released continuously by the decomposition reaction of Fe-Si3N4 raises the pore internal pressure of the hot face and reduces corrosion by molten iron in addition to generating Silicon oxynitride.

Yoshihisa MORIMOTO and Kosuke YASUO

The influence of tapping temperature rise on the wear rate and properties of blast furnace main trough ML material was investigated. Compared with the results of the corrosion test carried out at 1500 ℃, the wear rate increased by about 2.9 times at 1550 ℃ and about 5.5 times at 1600 ℃. In addition, once exposed to high temperatures exceeding 1550 ℃, corrosion resistance was found to deteriorate. This is because at 1500 ℃ the function of SiC as a Free C antioxidant is retained, but the function of SiC as a Free C antioxidant is lost when temperatures exceed 1550 ℃. A highly porous structure is also a cause of corrosion resistance deterioration. SiO2 and Free C are dissipated outside the system as SiO(g) and CO(g) as the heating temperature rises. In the actual furnace, if there is high-temperature tapping exceeding 1550 ℃, the wear rate of the main trough ML castable becomes very large. The decreased corrosion resistance of part which is exposed to high temperature once remains, even if the tapping returns to normal temperature.

Yuto SUZUKI and Kiyoyuki KOMATSUBARA

Dry gunning materials are commonly used as an easy repairing method. They have been improved by changing the binder system mainly in order to improve durability. In this study, the effect of silicate and phosphate binders on the properties of gunning materials was investigated. As a result, we found that phosphate binder was able to provide high adhesive strength because of high melting characteristic and high reaction ability with chamotte aggregate.

Kazuya NAKABO, Naoko DOI, Shigefumi NISHIDA and Atsuhisa IIDA

Various materials are selected for the tundish for continual casting on the basis of the structure for the facility and the form of damage. The authors have developed some new products for the tundish, which different from the existing products in that they have high durability and high cost performance compatibly. Moreover, a lineup to support various construction methods has been prepared.

Tsuyoshi SUWA, Kyohei YAMASHITA, Yoshihiro TODA and Tamiatsu KOYAKE

Chrome-free brick ELK-85AX for the burning zone and spinel brick SP-8L-3 for the transition zone of the cement rotary kiln were developed. ELK-85AX has a high hot modulus of rupture through improved texture and high abrasion resistance. SP-8L-3 has good coating adhesion, stress relaxation and low thermal conductivity by optimization of raw material. It is expected that application of ELK-85AX for the burning zone and SP-8L-3 for the transition zone will permit the cement rotary kiln to operate stably.

Hidekuni NISHIGUCHI and Shigehumi NISHIDA

Two recent developments in coke oven refractories are introduced. In the first place, the development of a sole also referred to as hearth repair material is introduced. This material has excellent peeling resistance due to similar thermal expansion to that of a silica brick, as well as superior abrasion resistance due to high strength. In the second place, the recycling of refractory door blocks is introduced. Recycled materials added to the door block scarcely deteriorate the quality of the door block and the door block has successfully been used in service.

Kazuya NAKABO and Shigefumi NISHIDA

The long term stability of the newly developed materials has been improved by reducing shrinkage. Moreover, the product lineup can be used for various construction methods including casting, pumping, troweling and gunning.

Shohei KANEKO, Masayoshi KAKIHARA and Hisashi TOMIYA

The most important issue in refractories for the bottom-blowing tuyere of the converter is suppression of spalling and peeling wear. We have developed high-performance tuyere refractories in view of improving fracture toughness, and good results have been obtained by various customers. In this report, we introduce our latest tuyere refractories and their test results.

Shinya KUROSE, Atsushi SUEYOSHI and Shinsuke SUETAKE

ISOLITE developed and commercialized LTC-A, with has low thermal conductivity, high strength, and is excellent in processability and water resistance. LTC-A was compared with other microporous insulation materials. The modulus of rupture was found to be more than 5 times greater, and compressive strength more than 2 times greater than the other microporous insulation materials. Furthermore, it can be handled more easily, complex processing is possible, and it can be used for assembling that requires strength. Furthermore, since it is excellent in resistance to dew condensation and water vapor, it can be applied to sites where other microporous insulation materials have not been usable so far. Making use of the high strength and water resistance, it is beginning to be adopted to the linings of various industrial furnaces.

Shinya HARA and Takashi MAKIHARA

Akashi works, Ceratechno Co., Ltd. is the only works that can mass-produce resin taphole mix in the Shinagawa Group. This time, we developed a taphole mix with higher performance than ordinary taphole mix, and introduce actual stable high tapping ratio operation.