US-12617728-B2 - CaO—ZrO2 composition, method for producing CaO—ZrO2 composition, and CaO—ZrO2-containing refractory material and casting nozzle

Abstract

Provided is a ZrO 2 —CaO—C based refractory material which is capable of maintaining high adhesion resistance over a long period of time, while exhibiting significant slaking resistance, and suppressing self-fluxing, i.e., exhibiting corrosion-erosion resistance. The refractory material comprises a CaO—ZrO 2 composition containing a CaO component in an amount of 40% by mass to 60% by mass, wherein a mass ratio of the CaO component to a ZrO 2 component is 0.67 to 1.5, and wherein the CaO—ZrO 2 composition includes a eutectic microstructure of CaO crystals and CaZrO 3 crystals, wherein a width of each of the CaO crystals observable in a cross-sectional microstructure is 50 μm or less.

Inventors

• Ling Li
• Katsumi Morikawa
• Akinari Sasaki
• Shigefumi MATSUMOTO

Assignees

• KROSAKIHARIMA CORPORATION

Dates

Publication Date

20260505

Application Date

20201023

Priority Date

20191031

Claims (5)

1. 1 . A CaO—ZrO 2 composition containing a CaO component in an amount of 40% by mass to 60% by mass, wherein a mass ratio of the CaO component to a ZrO 2 component is 0.67 to 1.5, and wherein the CaO—ZrO 2 composition includes a eutectic microstructure of CaO crystals and CaZrO 3 crystals, wherein a width of each of the CaO crystals observable in a cross-sectional microstructure is 50 μm or less.
2. 2 . The CaO—ZrO 2 composition as claimed in claim 1 , wherein the width of each of the CaO crystals is 20 μm or less.
3. 3 . The CaO—ZrO 2 composition as claimed in claim 1 , wherein a CaCO 3 film having a thickness of 0.1 μm to 5 μm is formed on a surface of the CaO—ZrO 2 composition, such that it continuously lies over surfaces of the CaO crystals and the CaZrO 3 crystals.
4. 4 . A method of producing the CaO—ZrO 2 composition as claimed in claim 1 , comprising the steps of: heating a CaO raw material and a ZrO 2 raw material to a molten state at a temperature equal to or greater than that of a liquidus line for a composition of a CaO component and a ZrO 2 component; and cooling the CaO raw material and the ZrO 2 raw material from the molten state to a temperature of a solidus line for the composition at a cooling rate of 10° C./sec or more.
5. 5 . The method as claimed in claim 4 , wherein: the CaO raw material is one or more selected from the group consisting of quicklime, and CaO compounds each of which becomes CaO, except for unavoidable impurities, at a temperature during melting, the CaO raw material having a size of 10 mm or less; and the ZrO 2 raw material is one or more selected from the group consisting of: CaO-stabilized ZrO 2 , CaO-partially stabilized ZrO 2 , and unstabilized ZrO 2 , the ZrO 2 raw material having a size of 10 mm or less.

Description

TECHNICAL FIELD The present invention relates to: a CaO—ZrO2 composition (CaO—ZrO2 composite) having a special composition and structure; a production method for the CaO—ZrO2 composition; a refractory material capable of suppressing alumina adhesion thereto occurring during continuous casting of steel, particularly, aluminum killed steel or the like, and reducing harmful inclusions; and a casting nozzle (hereinafter also referred to simply as “nozzle”) using the refractory material. BACKGROUND ART Alumina-based inclusions in molten steel are apt to be deposited on the surface of a refractory material through physical contact of the refractory material with the molten steel and/or chemical interaction therebetween, wherein the resulting deposited substance will grow and become large inclusions, and the large inclusions will be incorporated into slabs together with molten steel, causing defects in slab and deterioration in slab quality. Moreover, if alumina-based inclusions in molten steel are deposited on, e.g., an inner bore of a casting nozzle such as an immersion nozzle or a discharge port of the casting nozzle having a great influence on a molten steel flow in a casting mold, and thereby an initial shape of the inner bore or the discharge port gradually changes, it is likely that the molten steel becomes failing to uniformly flow in the casting mold, and, due to the so-called “biased flow”, mold powder, gas bubbles and others are entrained into slabs, causing deterioration in slab quality. In recent years, the need for higher quality of steel and higher durability of a casting nozzle has been increasing more and more. From a viewpoint of this situation, various measures for material have been attempted to prevent alumina adhesion to a refractory material of the casting nozzle and minimize the wear amount of the refractory material and the adhesion thereto, in addition to improvements in nozzle structure. In order to improve the ability to form a compound having a melting point equal to or less than a molten steel temperature, there is a technique of incorporating CaO in the refractory material of the nozzle. When CaO is incorporated in a nozzle material, alumina precipitated from molten steel reacts with CaO in the nozzle material to form a reaction product having a melting point significantly lower than that of alumina. Since this reaction product is a low-melting-point substance, it has a low viscosity, and is easily eluted by the molten steel flow to suppress the adhesion to an inner wall of the nozzle. This reduces a situation where alumina grows on the inner wall, causing clogging of the nozzle. In order to improve the resistance to the adhesion (adhesion resistance), various techniques for increasing the amount of CaO in a refractory material to provide a composition consisting mainly of CaO component or a CaO—MgO component have been attempted. A core component of such techniques is to allow CaO which reacts with alumina inclusions to be present at the highest possible content to give high self-fluxing (self-melting) ability to a contact surface of the refractory material with molten steel, thereby suppressing the adhesion to the inner bore surface of the nozzle, and further causing alumina to flow down and float as a low-melting-point compound so as to remove the alumina. As a CaO-based refractory material, a refractory material containing a dolomite composition as a CaO source is disclosed in e.g., the below-mentioned Patent Document 1. Such a CaO-based refractory material contains free CaO, i.e., CaO in a form that is not a compound or a solid solution, in a large amount. When coming into contact with water in the air or directly with water, free CaO easily forms calcium hydroxide (Ca(OH)2) (undergoes a so-called slaking (hydration) phenomenon). When CaO-containing particles are slaked (hydrated), volume expansion during the hydration of Ca(OH)2 causes not only transgranular fracture but also fracture of the microstructure of the refractory material, leading to difficulty in maintaining the shape of the refractory material as a structural body, in many cases. Such a technique of simply increasing the amount of free CaO causes a serious problem not only in production, but also during storage, transportation and use (when used for casting of steel). Since CaO (lime) has a large thermal expansion, a refractory material containing a large amount of CaO is more likely to undergo fracture or the like, due to thermal shock or static stress caused by the large thermal expansion, in addition to slaking. In order to solve the problems with slaking of such free CaO, the present inventors invented a refractory material in which the surface of CaO is coated with carbonate or the like, as shown in, e.g., the below-mentioned Patent Document 2. Although the technique described in the Patent Document 2 can provide a significant improvement against fracture, etc., due to slaking and thermal expansion, a problem w