Director, Managing Executive Officer　　Keiji SAITO

JFE Bars & Shapes Corporation　　Yoshimi KOMATSU

This report has the following composition. The historical situation around the birth of EAF (Electric Arc Furnace) is to be mentioned firstly. Next, the history of the creative developments done for EAF by many pioneers and the technical explanations for good understanding are to be mentioned. Finally, the expected items of EAF industry and the importance of the connection among the surrounding industries are also to be tried to be mentioned.

Atsushi TORIGOE, Hisashi TOMIYA, Ryoma FUJIYOSHI and Hitoshi KUNII

We will explain the characteristics of our newly developed EAF refractories using typical examples. By applying sidewall refractories with high corrosion resistance, HIDEN and EBT tube, bottom blowing nozzle, slide gate valve for tapping, ABB type bottom electrode in DC furnace, and high slaking resistant bricks for back lining. Our customers can improve refractory performance and operation efficiency.

Shigefumi NISHIDA, Daisuke TANAKA and Kiyoyuki KOMATSUBARA

Recently, operating conditions of electric arc furnaces (EAFs) have become severe, not only because high quality steel is being produced but also because low grade steel scrap is utilized as a raw material. Development of monolithic refractories and precast blocks for EAFs have been progressing along with the change in operation. In this paper, features of our monolithic refractories and precast blocks for EAFs are comprehensively described.

Ryoma FUJIYOSHI，Atsuhisa IIDA, Atsushi TORIGOE and Hiroki YOSHIOKA

In this paper, the development of MgO-C bricks, designed for the basic oxygen furnace (BOF) taking into account the mechanical impact of scrap charge on the charging pad is described. In order to clarify the influence of scrap charging on the wear of the BOF charging pad accurately, a steel block dropping experiment was carried out, followed by industrial trials. According to the results of the experiment and industrial trials, it was verified that charging pad wear is a result of the linking of cracks, which were initiated and propagated by mechanical shock induced by scrap collision. Thus, it is concluded that the application of high fracture toughness MgO-C brick, which shows excellent crack propagation resistance, is effective.

Hisashi TOMIYA, Koichi IGABO and Koyo MURAKAMI

Application of semi-rebonded magnesia-chrome bricks for clean steel refining vessels as RH degasser and AOD is extending because of its superior corrosion resistance. We have an extensive lineup of semi-rebonded magnesia-chrome bricks as; material A with general versatility, material B with high spalling resistance and material C and D with excellent erosion resistance. While chemical compositions of these four materials are almost identical, unique characteristics such as spalling resistance and erosion resistance are given by adjustments of grain size distribution and/ or sinterability. Reduction of wear rate is possible by applying appropriate material corresponding to individual wear status.

Fumihiko MIZOBUCHI, Naohide HAMAMOTO and Koji MORIWAKI

MgO-C based materials are often used for the steel ladle and/or tundish slide gate plate treating corrosive steel due to its excellent corrosion resistance. Disadvantageously, the thermal spalling resistance of the materials is very poor. Although including low thermal expansion substances such as spinel improve the thermal spalling resistance, the corrosion resistance deteriorates if excessively large amount of spinel are added. Therefore, the influence of the grain size distribution of spinel was investigated. On the bases of the investigation, the corrosion resistance of high thermal spalling resistant MgO-C slide gate plate was successfully improved by utilizing coarse spinel aggregates.

Hiroyasu NIITSUMA, Michinori YOSHIKAWA, Hitoshi KUNII, Shinsuke INOUE, Koji MORIWAK and Makoto NAKAMURA

Cold-start ladle shrouds require very good thermal spalling resistance. Silica raw materials such as fused silica and zirconia mullite materials are widely used to them because of their low thermal expansion characteristics and improved thermal spalling resistance. However silica raw materials have poor wear resistance to tundish slag. We studied the application of non-silica alumina-carbon materials used in hot start practice that have superior wear resistance to cold-start ladle shrouds with carbon-free inner liners. Carbon-free material has low thermal conductivity and acts as a heat insulator to reduce the temperature difference between the inside and outside of the ladle shroud body. The result is reduction of thermal stress, especially at the start of casting. We confirmed the good effect by using FEM at actual casters with successful results.

Hiroyasu NIITSUMA, Koji MORIWAKI and Kanae NISHIO

Two new SEN structures which may prevent alumina adhesion around outlet ports were developed by CFD calculation in conjunction with a water model test. ＂The no well and home plate＂ shape can be expected to suppress alumina adhesion from the column to the lower part of the outlet port. ＂The trapezoidal vertical section port＂ shape can be expected to suppress adhesion at the upper part of the outlet port. Also, optimum SEN shape was calculated to improve heat supply to the meniscus near the mold narrow face. The new SEN, with an ideal outlet port angle and annular-step structure, obtained good results at an actual casting.

Yukimasa IWAMOTO

The basic characteristics of mold powder crystallization behavior were evaluated using differential thermal analysis (DTA). The crystallization properties of 75 different mold powders were measured by the process of heating solid glass and in the process of cooling the molten slag along with the melting points. Room temperature solid glass phase slag samples were used for the heating process, and liquid phase samples at 1300℃ were used for the cooling process. The lower viscosity mold powder showed lower recrystallization temperatures in the heating condition. The high basicity (CaO/SiO2 ratio) samples showed more crystallization behavior in both heating and cooling conditions as compared with lower basicity. The crystallization under the cooling condition has a large variation depending on the measurement condition. A correlation between the supercooling and the amount of exothermicity measured during crystallization was found. As the supercooling increased, the crystal growth increased.

Kazuya NAKABO and Shigefumi NISHIDA

Alumina-magnesia castable materials used mainly in steel ladles form spinel at high temperatures heated under free conditions results in large permanent linear change and the material texture becomes porous. The materials are used as a structure in actual use and are bi-axially restrained by the surrounding structural members. It is known that the textures and characteristics of the materials in actual use do not match the laboratory evaluations. This study investigated the influence of bi-axial restraint on the characteristics of alumina-magnesia castable refractories. The other castable material with high strength was cast to the surrounding area of the alumina-magnesia castable to prepare bi-axially restrained specimens. Densification of the specimen texture was observed after heating under restraint. The strength was greatly increased especially after heating at high temperature. This suggests that the difference in the strength between the working face and backside of actual ladles is significantly larger than the material evaluations carried out under non-restrained conditions.

Tsuneyuki IIKUNI, Daisuke TANAKA and Masatsugu KITAMURA

In this study, the susceptibility of properties of blast furnace trough slag line material including various types of carbonaceous materials to thermal cycle was investigated. Properties of slag line material changed throughout the thermal cycle according to progress of sintering characterized by mullite formation. However, the degree of sintering varied according to the kind of carbonaceous materials, that is, sintering of the castable containing pitch as a carbonaceous material progressed little. The corrosion resistance of the castable containing carbon black deteriorated after 5 thermal cycles. Increase of pore size was observed in the castable containing carbon black after 5 heats, which probably caused large slag penetration and poor corrosion resistance.

Kyohei YAMASHITA, Tsuyoshi SUWA, Koichi IGABO and Tamiatsu KOYAKE

The refractory lining for cement rotary kiln (furnace) is often damaged by mechanical spalling because it is mechanically stressed by both circumferential deformation and axial movement of the kiln shell repeatedly．Therefore, improving mechanical stress resistance is important for prolonging the service-life of the refractory lining．We evaluated not only the conventionally physical characteristics of cement rotary kiln refractories but also the thermos-mechanical characteristics. We report on some new evaluation methods and explain some refractory performance results for the cement rotary kiln.

Yoshimitsu MUKAIDA, Takahiro KAGO and Koji ASAKAWA

From reliability point of view, as a gas blowing plug for steel ladle used in secondary refining, the porous plug is widely used. In recent years, application of slit plugs, which through slits installed pre-casted blocks, has been broadening because of large gas flowability as well as excellent durability. High corrosion resistance is required of gas blowing plugs for steel ladles because the plugs are cleaned by oxygen gas blowing to recover gas flowability while in use. For the purpose of improving corrosion resistance, chromium oxide is added to slit plug. On the other hand, customers demand chromium-free products from an environmental point of view. Therefore, we used the technique of densification to develop a chromium-free slit plug, which shows the equivalent level of corrosion resistance to the conventional chromium oxide containing product.

Kenji YAMAMOTO and Atsushi TAKATA

A conventional slide gate valve system for the tundish can control molten steel flow and the submerged entry nozzle is exchangeable during casting. We have developed a new slide gate system (SGT system) that adds a unique function which changes the SEN port direction for generating a swirling flow in the mold during casting to the said conventional functions. The SGT system is expected to improve steel quality similar to electromagnetic stirrer and longer casting sequence and higher productivity.

Yoshihiro TODA, Koichiro MORI and Tsuyoshi SUWA

This report introduces newly developed unburned Al2O3-Cr2O3-MgO brick for the non-ferrous smelting facilities. The brick exhibits superior resistance against corrosion and infiltration compared to burned magnesia-chrome bricks, which have been widely applied to non-ferrous metal smelting facilities. By applying the newly developed unburned Al2O3-Cr2O3-MgO brick not only prolongation of service life of the facilities but also reduction of trouble resulted from brick wear are expected.

Shuhei ARIMA, Shinichi FUJINO and Shigeki UCHIDA

Application of the laser flash (LF) method in place of the stationary heat flow method which was standardized in JIS R 2251-3 for measuring the thermal conductivity of non-oxide refractory materials was studied. Evaluation of many types of non-oxide refractory materials confirmed that the LF method could replace the stationary heat flow method. In the future, the scope of the LF method for measuring the thermal conductivity of non-oxide refractory materials should be researched for standardization.

Atsushi MAKIYA and Kimiaki SASAKI

We have been proposing SNB, which is a composite ceramic consisting of silicon nitride (Si3N4) and boron nitride (h-BN), as a material for metal atomizing spray nozzles. SNB has superior thermal shock resistance which can be controlled by changing the amount of h-BN (BN) because of excellent thermal spalling resistance of BN. The thermal shock resistance of SNB was improved by using ultra-fine BN powder of 50nm in diameter instead of conventional BN powder. Thus, the amount of BN in the SNB could be reduced in terms of thermal shock resistance. Reduction in the amount of BN, in other words, increase in Si3N4, improves corrosion resistance. Thus, improvement in SNB corrosion resistance for metal atomizing spray nozzles without deterioration in thermal shock resistance is possible

Atsushi SUEYOSHI and Daisuke NEMOTO

The newly developed ISOLITE tapping products and coating products are made of unshaped fibrous thermal-insulation materials which are not subject to the RCF regulation. The onsite workability of the products was the same as the conventional products. It was shown that the thermal insulation characteristics were improved by changing from insulation castable materials to tapping products. We adjusted the heat shrinkage ratio of the coating products to almost equal that of base fibrous insulation matrixes to reduced detachment and peeling off. Coating on the heated face of fibrous blocks with ISOLITE significantly improves erosion resistance characteristics, resulting in longer service-life.