JPS6256101B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a long nozzle immersion nozzle and a short nozzle (hereinafter referred to as a short nozzle) used in continuous steel casting.
(simply referred to as a nozzle). This nozzle plays an important role in preventing oxidation of molten steel and disturbance of the flow of molten steel when transferring molten steel between a ladle and a tundish, between a tundish and a mold, or between a ladle and a ladle. Conventional nozzle materials are fused silica and alumina.
Carbon, zircon, and zirconia materials are mainly used, but each has advantages and disadvantages. For example, with fused siliceous steel, nozzle clogging is less likely to occur because there is less adhesion of alumina precipitated from molten steel.
There is a drawback that spalling resistance is reduced due to crystallization due to high temperatures during use. Alumina-carbonaceous nozzles have excellent corrosion resistance and spalling resistance, but are prone to nozzle clogging due to adhesion of alumina precipitated from molten steel. Furthermore, zircon and zirconia have excellent corrosion resistance, but are significantly inferior in spalling resistance. The lifespan of conventional nozzle materials is extremely short due to the above-mentioned drawbacks.Moreover, there is a recent trend toward multiple casting in which one nozzle is used for a long time, so related industries are using conventional nozzle materials. There is a strong desire to develop a high-performance nozzle material that can be used instead of other materials. As a result of repeated research to meet these demands, the present inventors first discovered a novel lime-carbon material as a nozzle material. This material has the following effects. First, carbon in the composition has low wettability to molten steel, which suppresses the penetration of molten steel, and also acts as a cushion material that absorbs the expansion and contraction of other composition raw materials, which improves the corrosion resistance and spalling resistance of the nozzle. Contribute to improvement. On the other hand, lime has low reactivity with carbon, which is a raw material used in combination, and is stable in a high-temperature reducing atmosphere, so the nozzle has excellent hot strength, corrosion resistance, etc. without deterioration of structural strength due to reduction reaction. . In addition, lime reacts with alumina precipitated from molten steel to become low melting point substances such as CaO.Al ₂ O ₃ and 3CaO.Al ₂ O ₃ and flows without stopping on the inner wall of the nozzle, which has the effect of preventing nozzle clogging. Furthermore, lime has the effect of adsorbing nonmetallic inclusions such as sulfur, phosphorus, and oxygen in the molten steel, thereby cleaning the molten steel passing through the nozzle. Since molten steel is generally cleaned in a container such as a ladle, there is a concern that non-metallic inclusions may be mixed in again in the subsequent path of the molten steel, but using a lime-carbon nozzle can eliminate this problem during the casting process. Since cleaning can be done even in the nozzle during the final process, this does not occur and contributes greatly to improving the quality of steel products. However, while the lime-carbonaceous nozzle has the above-mentioned excellent liquefaction effect, when the lime component comes into contact with water, it causes the so-called digestion phenomenon due to the reaction of CaO + H ₂ O → Ca (OH) ₂ . There is a disadvantage that the nozzle structure becomes weak due to the volumetric expansion. For this reason, the nozzle after manufacture must be carefully controlled to prevent it from coming into contact with moisture, and since this digestion phenomenon also occurs due to moisture in the air holes, it is especially important to keep the nozzle in place for long periods of time during hot and humid seasons such as summer. It was not possible to store it for a long time. The first aspect of the present invention is to provide a new lime-carbon nozzle as a nozzle material, and at the same time, in order to fully exhibit its excellent effects, boron carbide,
The purpose is to prevent digestion of the nozzle by adding boron nitride or boron, and its characteristics include 40 to 90 wt% lime and 10 to 60 wt% carbon.
% and one or more selected from boron carbide, boron nitride, and boron and 0.1 to 10 wt % of boron carbide, boron nitride, and boron. The figure shows a lime-carbon nozzle obtained by kneading, molding, and firing a mixture in which lime and carbon are kept at a constant ratio and boron, boron carbide, and boron nitride are added at varying amounts of 0 to 10 wt%. Digestion resistance was determined by weight increase rate under the same conditions as shown in the Examples below. The addition of boron carbide, which is a carbide of boron, to refractories has been known in Japanese Patent Application Laid-open Nos. 57705-1982 and 34664-1980. but,
Unlike the present invention, these are aimed at preventing oxidation of carbon-containing refractories, and since their purpose is different from the present invention, the target refractory is a different material that does not contain lime. Metals other than boron are also effective in preventing the digestion of lime-containing refractories, but boron carbide, boron nitride, and boron have a much more pronounced effect than these.
The detailed mechanism is not clear, but during firing of the nozzle, boron or boron compounds combine or decompose to form B ₂ O ₃ , which is used to coat lime and is added as boron carbide, boron nitride, or boron. This is thought to be caused by combining with carbon to form boron carbide, and since these have similar properties to carbon, they form a solid solution replacing carbon and cover the lime. As a result of further research by the present inventors, it was found that adding magnesia to the formulation of the first invention is more favorable in terms of resistance to digestion and prevention of nozzle clogging. The second invention was made based on this point, with 40 to 90 wt% lime and 10 to 60 wt% carbon.
%, magnesia 40wt% or less, one or more selected from boron carbide, boron nitride, and boron 0.1~
This is a method for manufacturing a continuous casting nozzle in which a compound containing 10 wt% is kneaded, molded, and fired in the usual manner. That is, as the particle size of lime becomes smaller, the contact area with air increases and it becomes easier to digest. Therefore, part of the lime is replaced with magnesia to reduce the fine particles of lime and improve the digestibility. For this reason, it is preferable to use magnesia mainly in the form of fine particles. Also, the reason why the addition of magnesia acts as a nozzle blockage prevention effect is that magnesia causes a reaction with the carbon component of MgO+C→Mg↑+CO↑ while the nozzle is in use, and the gas generated at this time covers the inner peripheral surface of the nozzle. It is presumed that this is because it prevents the adhesion of alumina precipitated from molten steel. Next, specific examples of the formulation used in the present invention and reasons for limiting the ratio will be explained. First, as lime, we mainly use electrofused or sintered lime clinker, and if it is a small amount, it will thermally decompose during nozzle firing or use and become CaO.
Ca compounds such as CaF ₂ , CaCO ₃ , Ca(CH) ₂ , Ca ₂ SO ₄ , CaCl ₂ may be used in combination with the lime clinker. The proportion of lime should be 40 to 90wt%; if it is less than 40wt%, the corrosion resistance as an aggregate will not be exhibited, and if it is less than 40wt%,
% or more, the spalling resistance is poor. Carbon can be used regardless of whether it is crystalline or amorphous, such as scaly graphite, earthy graphite, electrode scraps, coke, pitch, carbon black, brassy carbon,
Carbon fiber, etc. can be used. Its proportion should be 10 to 60 wt%, and if it is less than 10 wt%, carbon will not easily wet the molten steel and will not have the effect of improving spalling resistance. Oxidation resistance is poor at 60wt% or more. The content of one or more of boron carbide, boron nitride, and boron is 0.1 to 10 wt%. If it is less than 0.1wt%, the effect of the addition is not sufficient, and if it is more than 10wt%, a large amount of low melting point substances will be produced during use, resulting in a decrease in hot strength and corrosion resistance, and all of these additives are expensive. It is also unfavorable from an economic point of view. The magnesia source used in the second invention is magnesia clinker, magnesium hydroxide, magnesium carbonate, etc., and the proportion thereof is 40 wt% or less. If it exceeds 40 wt%, the proportions of lime and carbon, which are other ingredients, will be so small that the effects of these ingredients will not be obtained sufficiently, and the quality of the nozzle as a whole will deteriorate. In addition, there is no lower limit to the amount of magnesia added, but in order to obtain a sufficient effect,
5wt% or more is preferable. The effects of the present invention can be achieved within the limited proportions of the above compounds, but more preferable proportions include 45 to 70 wt% lime, 20 to 50 wt% carbon, 0 to 35 wt% magnesia, boron carbide, and nitride. One or more selected from boron and boron at 0.5 to 8 wt% or more. The present invention uses the above formulation, and during kneading, binders such as epoxy resins, polyacrylic resins, or tar, pitch, or polyvinyl alcohol are added to the exterior, similar to those used in conventional nozzle manufacturing. Add about 5 to 15 wt%. After kneading, the mixture is molded using a molding machine such as a rubber press, and then reduced and fired at about 1000 to 1400°C. The nozzle of the present invention obtained in this manner may contain acidic, neutral, or basic refractories other than the essential requirements, or known antioxidants, sintering agents, and Inhibitors and fibers may be added, and tar and fibers may be added after firing.
Impregnation treatment may be performed with carbon resin such as Pitch. As described above, the nozzle obtained by the present invention has excellent effects in cleaning steel, corrosion resistance, spalling resistance, and nozzle clogging prevention, and is therefore suitable for manufacturing clean steel and for multiple casting. This nozzle has sufficient performance to be used as a nozzle, and is extremely valuable in continuous casting equipment.Furthermore, even though this nozzle contains lime, it has no problem with digestion resistance, so it can be stored for a long time. However, there is no reduction in quality. The table shows Examples and Comparative Examples of the present invention, in which 10 wt% of tarpitz was added as a binder to the formulation shown in the table, and after kneading,
It is molded using a rubber press and then reduced and fired at 1000℃.

【table】

[Table] The physical property values shown at the bottom were measured as follows. (1) Porosity and bulk specific gravity: Based on JIS-R2205. (2) Erosion rate: A test piece cut into a size of 30 x 30 x 150 mm was immersed for 2 hours in 1600°C molten steel melted in a high frequency furnace, and its elution rate was determined using the following formula. Erosion rate (%) = Dimensions before immersion - Dimensions after immersion / Dimensions before immersion x 100 (3) Spalling resistance: Cut a test piece of 50 x 50 x 50 mm and heat it in an electric furnace at 1500℃ for 15 minutes. After heating,
The cycle of air cooling for 15 minutes was repeated 5 times, and the occurrence of cracks was observed. (4) Alumina deposition rate: melted in a high frequency induction furnace
Aluminum was added to molten steel at 1600°C, and the samples were immersed therein for 2 hours, and the state of adhesion of alumina precipitated from the molten steel was observed. (5) Digestion resistance: After being left in a constant temperature and humidity chamber set at a temperature of 30°C and a humidity of 90% for 48 hours, the weight increase rate was measured. The larger the value, the worse the digestion resistance. Further, the figure is a graph showing the relationship between the amount of each additive added and the weight increase rate.

[Brief explanation of the drawing]

The drawing is a graph showing the weight change rate measured to determine the digestion resistance of the nozzle manufactured according to the example.

Claims (1)

[Claims] 1. Knead, mold, and sinter a mixture consisting of 40 to 90 wt% lime, 10 to 60 wt% carbon, and 0.1 to 10 wt% of one or more selected from boron carbide, boron nitride, and boron. A method for manufacturing a continuous casting nozzle. 2 Lime 40-90wt%, Carbon 10-60wt%, Carbon 10
~ 60wt%, magnesia 40wt% or less, and one or more selected from boron carbide, boron nitride, and boron, 0.1 to 10wt% are kneaded, molded,
A method of manufacturing a continuous casting nozzle for firing.