Presidente Shinagawa Refratários do Brasil Ltda. Gustavo PADILHA

Eiji ISHIHARA

Metal bath stirring by inert gas blowing from the furnace bottom, so called bottom gas blowing, is one of the technologies introduced in the evolutionary process of EAF steelmaking. Various metallurgical benefits, such as reduction of energy consumption, shortening of refining time or improvement of steel yield, were confirmed by trial operations of bottom gas blowing at many EAF facilities. Due to accompanied problems, such as service life of gas purging plug refractory, overall cost of bottom gas blowing system or complexity in purging plug replacement, practical application of bottom gas blowing was limited in the initial stage. However, in association with improvement in the service life of the purging plug or optimizations in bottom gas blowing operation, bottom gas blowing has been commonly used, especially in the stainless or special steel making EAF in which the effects of the introduction of the bottom gas blowing system have been relatively large. It is prospected that, in association with progress of activity toward realization of carbon neutrality, further development or innovation in EAF bottom gas blowing technologies will be necessitated so as to respond to arising EAF steelmaking requirements.

Shigeru KOMORI, Kiyoyuki KOMATSUBARA, Shinsuke SUETAKE

Refractory materials used in the reheating furnace are outlined in this article, along with review of heat insulation technologies used for ceramic fiber products in the reheating furnace. By applying gunning plastic refractory and dry-gunning repair plastic refractory, marked labor saving is expected in refractory relining and maintenance work. Service life extension of refractories relined on the skid post and skid beam has been achieved by application of newly developed chemical bond castable refractory, which is characterized by improved thermal spalling resistance and erosion resistance to FeO. Marked heat loss reduction was realized by application of the developed ceramic fiber products with superior thermal properties and sufficient erosion resistance to FeO. Further development or optimization, such as optimization in applied technologies for reheating furnace operational conditions as well as developing heat insulation products combined with refractory and CF product, will be challenged.

Yuga YAMAMOTO, Tatsuya KAGEYAMA

Long heating time induced changes of taphole mix properties in which aluminum nitride was substituted for ferro silicon nitride were investigated. It was affirmed that marked weight loss and change to a loosened porous structure, both of which have been observed in ferro silicon nitride containing taphole mix sample specimens after long heat treatment time, were suppressed in aluminum nitride containing taphole mix sample specimens after long-time heat treatment time. Ferro silicon nitride is decomposed by long heating time accompanied with emission of decomposed nitrogen gas out of the system, which causes structure deterioration of the taphole mix body. It is inferred that aluminum nitride functions as a reducing agent of CO gas coming from outside of the system associated with C precipitation in the taphole mix body, with which slag resistance of taphole mix is secured even after long heating time. It was expected that, by substituting aluminum nitride for ferro silicon nitride, the slag resistance of “mushroom” in blast furnace tap hole would be improved, resulting in sustention of proper “depth” parameter as well as improvement of taphole inner wall protection.

Naohide HAMAMOTO, Hiroki BABA, Takayuki MATSUNAGA, Toshio HORIUCHI

Although basic materials for slide valve (SV) plates used for corrosive steel grades have high corrosion resistance, they are vulnerable to repeated cycles of heating and cooling. Therefore, in many cases they are replaced after one charge of use. Therefore, we have developed new, high-durability basic material SVR-FB7 and SVR-FB8, that can be used repeatedly, by improving the weak points of basic materials. The newly developed materials have been used for multiple charges as ladle plates in steelworks with good results.

Wei LIN, Hironobu MIURA, Takayuki MATSUNAGA, Toshio HORIUCHI

In actual use, the CaO-ZrO2-C (CZ-C) inner lining of the submerged entry nozzles (SENs) is abnormally damaged, and microscopic observation of the microstructure may show a large amount of ZrC formation and significant microstructural deterioration. In the present study, we considered it necessary to find conditions under which the ZrC formation reaction can be suppressed even at low CO partial pressures, and examined the effects of adding Al2O3 and MgO components. In the heating test in Ar atmosphere, the amount of ZrC formation was significantly smaller in the Spinel (5 %) added specimens and especially (Spinel+Al2O3) (5 % each) added specimens than in the conventional materials. EPMA analysis showed that the conventional material exhibited a microstructure with isolated ZrC between CZ grains, whereas a low-melting phase of the Al2O3-CaO system was formed in both of the aforementioned specimens. This is due to the coating of CZ, ZrO2 and ZrC grains, as well as the densification of the overall microstructure. On the other hand, in the molten steel-dipping test, both specimens maintained high alumina adhesion resistance, as well as the conventional material.

Junya ITO, Satoshi YAMASAKI

In the initial phase of continuous steel casting, exothermic starter mold powders are often used to stabilize the casting operation and improve steel quality. This exothermic starter powder is designed to offer superior lubrication in the mold and improved thermal insulation on the surface of molten steel. However, a conventional exothermic starter powder will not necessarily solve the issues specific to steel grades, such as cracking on medium carbon and peritectic steel and carbon pick-up on ultra-low carbon steel. Additionally, it is undesirable to mix a low viscosity starter powder with a ultra-high viscosity running powder because of the large differences in their properties. New starter powders have been developed to solve the issues for each casting condition. The newly developed high basicity exothermic starter powder for medium carbon steel is expected to reduce steel strand surface cracks during the unstable condition during startup. Also the newly developed exothermic starter powder for ultra-low carbon steel was designed to be carbon-free and iron oxide-free to reduce carbon pick-up. Finally, a new ultra-high viscosity exothermic starter powder was developed to match with ultra-high viscosity running powder for better compatibility.

Kenji SUZUKI, Tsuneyuki IIKUNI, Minoru TANAKA, Atsushi MATONO

 Shortening of blast furnace troughs and runners refractory online repair maintenance operation period, which is periodically conducted usually with on-site castable refractory relining, is strongly required along with the reduction of labor. Thus, large-sized precast blocks are developed and applied for refractory repairing maintenance of the iron runner. As a result, marked shortening of overall operation period was achieved along with significant labor reduction. Specifically, working hours in the iron runner maintenance operation were reduced to one-fifth (1/5) associated with shortening of overall maintenance period to one-fourth (1/4). Furthermore, by applying a chemical-bonded castable refractory, which is our company’s original refractory, characterized by superior mechanical strength at high temperature for precast blocks, the durability of the iron runner refractories was improved by roughly 1.8 times, which contributes to the prolongation of periodical iron runner maintenance interval.

Daisuke MIYAMOTO, Eiji ISHIHARA

Toward achieving carbon neutrality, Shinagawa Refractories Co., Ltd. will take on the challenge of reducing CO2 gas emissions from fuel combustion and electricity consumption in our business activities by 50 % by 2030 compared to the fiscal 2013 level. Most magnesia-chrome bricks, which are representative of basic refractories for steelmaking furnaces and various kilns, are “burned” bricks, approximately 90 % of which are fired at high temperatures in the case of our production plant. In contrast, the magnesiachrome bricks SINTEX are originally unfired bricks, so the fuel used in the manufacturing process is about 1/9 of that of burned bricks, and their application is directly linked to a reduction in environmental impact. Although SINTEX has been used in the past as a suspended ceiling material for open hearth furnaces and as a lining material for nonferrous smelting furnaces, its production volume is not large at present. Therefore, we have developed a new product, SINTEX-3, to expand the range of its application. Laboratory evaluations of SINTEX-3, assuming the operating conditions in RH lower vessels where magnesia-chrome bricks are used, showed that it has thermal spalling resistance and FeO-slag corrosion resistance equivalent to those of the regular direct bonded product, S-DIR-6-5.

Yoshihiro TODA

Since the operational condition of the CGL metal pot varies according to type of zinc-based alloy to be galvanized on the steel strip, refractory products best suited for each operational condition have been developed. In the CGL operation for Galvalume steel strip, in which, due to the severest operational conditions, incidents caused by clogging of the molten metal circulating channel with reactant derived from the Al component in zinc-based alloy or by metal leakage from initiated cracks occasionally take place, high metal pot durability, especially its inductor block, is required. By applying newly developed castable refractories (CST-A6125，CST-S530), which are characterized by minimized reactivity with the Al component in zinc-based metal as well as by improved spalling resistance, to the metal pot inductor block, satisfactory performance has been achieved.

Yusuke KISHIGAWA, Takashi NEMOTO, Hiroyuki TERADA

Since ceramic fiber products are essential for global environment protection application uses such as energy saving or reduction of CO2 gas emission, it is prospected that demand will increase more and more. When nonfibrous particles (shots), which are subordinately generated in the fiberization process of ceramic fiber, drop off from fiber blanket products, they cause surface defects on steel plates processed in surface treatment facilities. In order to prevent such problems, minimization of shot content in fiber blanket products is required. In this article, a new AF product, “FIBERMAX 1600SF”, with markedly reduced shot content is introduced.

Masahiro YOSHIKAWA, Masaki KOSAKA, Toshifumi FUJIWARA, Kensuke TSUGAWA

Fine ceramics with excellent corrosion resistance, heat resistance, and rigidity are increasingly used in semiconductor and flat panel display (FPD) manufacturing equipment to achieve finer and more integrated designs and to improve product processing capacity. This report outlines the material properties and application examples of our Fine Ceramics used in this equipment field.