GAS INJECTION NOZZLE REFRACTORY AND GAS INJECTION NOZZLE

Abstract

A gas injection nozzle refractory with one or more gas injection small metal tubes buried therein has improved durability. The gas injection nozzle refractory includes a MgO-C central refractory with a small metal tube buried therein, and a MgO-C peripheral refractory surrounding the central refractory. The central refractory on a plane of the gas injection nozzle refractory has an external shape of a circle with a radius in the range of R+10 to R+150 mm concentric with a virtual circle with a minimum radius surrounding all buried small metal tubes, R mm being a radius of the virtual circle.

Claims

1. A gas injection nozzle refractory with at least one gas injection small metal tube buried in a carbon-containing refractory, the gas injection nozzle comprising: a central refractory with the at least one small metal tube buried therein, the central refractory being a MgO-C refractory with a carbon content in the range of 40% to 80% by mass, a metal Al content in the range of 3% to 8% by mass, and a mass ratio of a metal Si content to the metal Al content in the range of 0.30 to 1.0, and a peripheral refractory surrounding the central refractory, the peripheral refractory being a MgO-C refractory with a carbon content in the range of 10% to 25% by mass, wherein the central refractory on a plane of the gas injection nozzle refractory has an external shape of a circle with a radius in the range of R+10 to R+150 mm concentric with a virtual circle with a minimum radius surrounding the at least one buried small metal tube, R mm being a radius of the virtual circle.

2. The gas injection nozzle refractory according to claim 1, wherein the external shape is a circle with a radius in the range of R+40 to R+70 mm concentric with the virtual circle.

3. The gas injection nozzle refractory according to claim 1, wherein the metal Al content is in the range of 5% to 7% by mass.

4. The gas injection nozzle refractory according to claim 1, wherein the metal Al content is in the range of 5% to 7% by mass, and the mass ratio of the metal Si content to the metal Al content is in the range of 0.30 to 0.45.

5. A gas injection nozzle comprising the gas injection nozzle refractory according to claim 1.

6. The gas injection nozzle refractory according to claim 2, wherein the metal Al content is in the range of 5% to 7% by mass.

7. The gas injection nozzle refractory according to claim 2, wherein the metal Al content is in the range of 5% to 7% by mass, and the mass ratio of the metal Si content to the metal Al content is in the range of 0.30 to 0.45.

8. A gas injection nozzle comprising the gas injection nozzle refractory according to claim 2.

9. A gas injection nozzle comprising the gas injection nozzle refractory according to claim 3.

10. A gas injection nozzle comprising the gas injection nozzle refractory according to claim 4.

11. A gas injection nozzle comprising the gas injection nozzle refractory according to claim 6.

12. A gas injection nozzle comprising the gas injection nozzle refractory according to claim 7.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1 is a plan view of a gas injection nozzle refractory 10 according to an embodiment.

DETAILED DESCRIPTION

[0034] A gas injection nozzle refractory according to the disclosed embodiments is a gas injection nozzle refractory 10 with one or more small gas injection metal tubes 20 buried in a carbon-containing refractory. The gas injection nozzle refractory 10 includes a central refractory 12 with the small metal tubes 20 buried therein and a peripheral refractory 14 surrounding the central refractory 12.

[0035] As described above, the main cause of the wear of MHP tuyeres is thermal shock. In particular, the neighboring portion of the small metal tubes 20 of the MHP tuyere is cooled by the gas flowing through the small metal tubes 20 and therefore has high thermal stress. It is effective to increase the C content of a MgO-C refractory to reduce thermal shock or thermal stress. A MgO-C refractory with an increased C content, however, is easily dissolved in molten steel and has lower abrasion resistance and erosion resistance. The present inventors have found in this respect that the neighboring portion of the small metal tubes 20 with an increased C content is cooled by the gas flowing through the small metal tubes 20 due to its high thermal conductivity, a slag or metal mushroom is consequently formed on the working surface side, and the mushroom protects the refractory surface from molten steel and effectively reduces wear due to abrasion or erosion.

[0036] Thus, in the disclosed embodiments, the gas injection nozzle refractory 10 is composed of the central refractory 12 with the small metal tubes 20 buried therein and the peripheral refractory 14 surrounding the central refractory 12, and the central refractory 12 is composed of a MgO-C refractory with a high C content. In converters producing various steel grades, however, a mushroom often shrinks or disappears, for example, during continuous production of high-temperature tapping steel. In this case, molten steel comes into contact with the central portion of the tuyere. Measures to prevent the increase in wear rate even in such cases were studied. As a result, it was found that the addition of 3% or more by mass of metal Al, which is usually 1.5% or less by mass (2.5% or less by mass at a maximum) as an antioxidant, and the addition of metal Si at a mass ratio of the metal Si to the metal Al in the range of 0.30 to 1.0 to prevent slaking can significantly improve the resistance to molten steel of the MgO-C refractory and also prevent slaking.

[0037] To produce the above effects, the central refractory 12 composed of the MgO-C refractory with the high C content needs to have a predetermined size (external shape) described below.

[0038] FIG. 1 is a plan view of a gas injection nozzle refractory 10 according to an embodiment. As illustrated in FIG. 1, the central refractory 12 on a plane (working surface) of the gas injection nozzle refractory 10 has an external shape of a circle 18 with a radius in the range of R+10 to R+150 mm concentric with a virtual circle 16 with a minimum radius surrounding all the buried small metal tubes 20, R (mm) being the radius of the virtual circle 16. In other words, in FIG. 1, the circle 18 forming the external shape of the central refractory 12 has a radius of R+r, wherein r ranges from 10 to 150 mm. When the circle 18 forming the external shape of the central refractory 12 has a radius of less than R+10 mm, the small metal tubes 20 are too close to the boundary between the peripheral refractory 14 and the central refractory 12, and the small metal tubes 20 may be deformed when the refractory is formed. Thus, the circle 18 forming the external shape of the central refractory 12 needs to have a radius of R+10 mm or more. The circle 18 forming the external shape of the central refractory 12 preferably has a radius of R+40 mm or more. When the circle 18 forming the external shape of the central refractory 12 has a radius of more than R+150 mm, however, a portion not covered with the mushroom is formed on the working surface of the central refractory 12 and is damaged when coming into contact with molten steel. Thus, the circle 18 forming the external shape of the central refractory 12 needs to have a radius of R+150 mm or less. The circle 18 forming the external shape of the central refractory 12 preferably has a radius of R+70 mm or less. In other words, in FIG. 1, the circle 18 forming the external shape of the central refractory 12 preferably has a radius of R+r, wherein r ranges from 40 to 70 mm. The plane of the gas injection nozzle refractory 10 herein refers to a surface of the gas injection nozzle refractory 10 that is perpendicular to the axes of the small metal tubes 20.

[0039] The MgO-C refractory constituting the central refractory 12 has a carbon content in the range of 40% to 80% by mass. A MgO-C refractory with a carbon content of less than 40% by mass has insufficient thermal shock resistance. A MgO-C refractory with a carbon content of more than 80% by mass has low resistance to molten steel and low reliability. Thus, the MgO-C refractory constituting the central refractory 12 needs to have a carbon content in the range of 40% to 80% by mass.

[0040] The MgO-C refractory constituting the central refractory 12 has a metal Al content in the range of 3% to 8% by mass. A MgO-C refractory with a metal Al content of less than 3% by mass has low resistance to molten steel. These effects do not change even if the metal Al content of the MgO-C refractory exceeds 8% by mass. Thus, the MgO-C refractory constituting the central refractory 12 needs to have a metal Al content in the range of 3% to 8% by mass in terms of cost and safety.

[0041] The mass ratio of the metal Si content to the metal Al content of the MgO-C refractory ranges from 0.30 to 1.0. When the mass ratio of the metal Si content to the metal Al content of the MgO-C refractory is less than 0.30, the MgO-C refractory has low slaking resistance. When the mass ratio of the metal Si content to the metal Al content of the MgO-C refractory exceeds 1.0, the resistance to molten steel decreases. Thus, the mass ratio of the metal Si content to the metal Al content of the MgO-C refractory constituting the central refractory 12 needs to range from 0.30 to 1.0. Metal Si is oxidized to SiO.sub.2 when the refractory is exposed to air for extended periods, for example, due to an accidental shutdown of the equipment. When Si becomes SiO.sub.2, the strength of the refractory is decreased due to a low-melting-point substance formed between SiO.sub.2 and MgO or Al.sub.2O.sub.3. Thus, the metal Si content is preferably decreased, provided that slaking resistance is exhibited. The mass ratio of the metal Si content to the metal Al content of the MgO-C refractory preferably ranges from 0.30 to 0.45. A MgO-C refractory with a metal Al content in the range of 5% to 7% by mass can have further improved resistance to molten steel.

[0042] The MgO-C refractory constituting the peripheral refractory 14 has a carbon content in the range of 10% to 25% by mass. A MgO-C refractory with a carbon content of less than 10% by mass increases damage due to thermal shock. Thus, the MgO-C refractory constituting the peripheral refractory 14 needs to have a carbon content of 10% or more by mass. The MgO-C refractory constituting the peripheral refractory 14 preferably has a carbon content of 15% or more by mass. A MgO-C refractory with a carbon content of more than 25% by mass, however, has low abrasion resistance or erosion resistance and cannot have satisfactory durability. Thus, the MgO-C refractory constituting the peripheral refractory 14 needs to have a carbon content of 25% or less by mass.

[0043] The small metal tubes 20 may be made of any material and are preferably made of a metallic material with a melting point of 1300° C. or more. Examples of the metallic material with a melting point of 1300° C. or more include metallic materials (metallic elements and alloys) containing one or more of iron, chromium, cobalt, and nickel. A metallic material typically used for the small metal tubes 20 may be stainless steel (ferritic, martensitic, or austenitic), plain steel, or heat-resistant steel. The small metal tubes 20 preferably have an inner diameter in the range of 1 to 4 mm. It may be difficult to supply sufficient gas for stirring molten metal in the furnace through the small metal tubes 20 with an inner diameter of less than 1 mm. On the other hand, molten metal may flow into and block the small metal tubes 20 with an inner diameter of more than 4 mm. The small metal tubes 20 have a wall thickness in the range of approximately 1 to 2 mm.

[0044] The number of the small metal tubes 20 to be buried in the carbon-containing refractory is not particularly limited and is appropriately determined according to the required gas injection rate and the area of the operating portion. In furnaces that require a high flow rate, such as converters, approximately 60 to 250 of the small metal tubes 20 are buried. For a low gas injection rate in electric arc furnaces, ladles, and the like, one to tens of the small metal tubes 20 are buried.

[0045] Next, a method for producing a gas injection nozzle refractory according to the disclosed embodiments is described below. The carbon-containing refractories (the central refractory 12 and the peripheral refractory 14), which are composed mainly of an aggregate, a carbon source, metal Al, and metal Si, may contain other additive materials and binders.

[0046] The aggregate in the carbon-containing refractories may be magnesia, alumina, dolomite, zirconia, chromia, or spinel (alumina-magnesia or chromia-magnesia). In the disclosed embodiments, magnesia is used as a main aggregate from the perspective of resistance to molten metal and molten slag.

[0047] The carbon source in the carbon-containing refractories is not particularly limited and may be flake graphite, expanded graphite, earthy graphite, calcined anthracite, petroleum pitch, or carbon black. The amount of the carbon source to be added is determined according to the carbon contents of the central refractory 12 and the peripheral refractory 14. Examples of the additive materials other than the aggregate, the carbon source, metal Al, and metal Si include metal species, such as Al-Mg alloys, and carbides, such as SiC and B.sub.4C. One or more of these may be used. The amounts of these additive materials are typically 3.0% or less by mass.

[0048] The raw materials of the carbon-containing refractories typically include a binder. The binder may be a typical binder for shaped refractories, such as phenolic resin or liquid pitch. The amount of the binder ranges from approximately 1% to 5% by mass (with respect to 100% of each refractory excluding the binder).

[0049] The gas injection nozzle refractory 10 according to the disclosed embodiments may be produced by a known method. Although one exemplary production method is described below, the disclosed embodiments are not limited to this method. First, the refractory raw materials of the central refractory 12 and the refractory raw materials of the peripheral refractory 14 are independently mixed in a mixer to prepare mixtures. After the small metal tubes 20 are placed at predetermined positions in the mixture for the central refractory 12, the mixture is shaped by uniaxial pressing to produce the central refractory 12 with the small metal tubes 20 buried therein. The central refractory 12 is then surrounded with and integrated by isostatic pressing (CIP) with the mixture for the peripheral refractory 14 to form a base material for the gas injection nozzle refractory 10. The base material is subjected to a predetermined heat treatment, such as drying, by a routine method. If necessary, the external shape may be appropriately adjusted.

[0050] A compression molding method for the central refractory 12 may be a multi-stage compression molding method including first pressing a small amount of the mixture in a frame, placing the small metal tubes 20 at predetermined positions on the mixture, charging the frame with a predetermined amount of the mixture, pressing the mixture, and repeatedly performing the placing, charging, and pressing, or a single compression molding method including pressing the whole amount of the mixture only once while holding each end of the small metal tubes 20 such that the small metal tubes 20 move with the mixture while pressing. The small metal tubes 20 may be joined to a gas reservoir portion by welding after the formation of the central refractory 12, after the molding of the base material, or after the heat treatment of the base material, or by placing the small metal tubes 20 with the top surface plate of the gas reservoir portion welded in advance in the mixture for the central refractory 12 when the central refractory 12 is molded. The raw materials of the carbon-containing refractories may be kneaded by any method, for example, by a kneading means used as a kneading apparatus for shaped refractories, such as a high-speed mixer, a tire mixer (Corner mixer), or an Eirich mixer. The mixture may be molded by a uniaxial molding machine, such as a hydraulic press or a friction press, or a pressing machine used for the molding of a refractory, such as isostatic pressing (CIP). The molded carbon-containing refractories may be dried at a temperature in the range of 180° C. to 350° C. for approximately 5 to 30 hours.

EXAMPLES

Example 1

[0051] The following are evaluation results of the resistance to molten steel of a MgO-C refractory used as a central refractory in a gas injection nozzle refractory according to the disclosed embodiments. Tables 1 and 2 list the raw material composition of refractory samples. Refractory samples 30 mm square and 160 mm in length (samples according to the disclosed embodiments and comparative samples) were prepared from the raw material compositions listed in Tables 1 and 2. These refractory samples were immersed in molten steel (SS400) in a high-frequency eccentric furnace at 1650° C. for 30 minutes, and the remaining thickness was measured. The amount of wear was determined from the difference between the thickness before the test and the thickness after the test.

[0052] To evaluate slaking resistance, 25 mm×25 mm×25 mm refractory samples (samples according to the disclosed embodiments and comparative samples) were prepared from the raw material compositions listed in Tables 1 and 2. After heat treatment at 1000° C. for 3 hours in coke breeze and treatment in a steam atmosphere at 100° C. for 3 hours, these refractory samples were checked for cracks. The presence of cracks was judged by visual inspection. Tables 1 and 2 also show these results. A comparison between Examples 3 to 5 and Comparative Example 9 shows that the samples according to the disclosed embodiments (MgO-C refractories that satisfy the conditions for a central refractory according to the disclosed embodiments) had significantly improved resistance to molten steel by the addition of metal Al. It was confirmed that the samples according to the disclosed embodiments also had high slaking resistance and had no crack as in the refractory (Comparative Example 1) normally used for tuyere refractories.

TABLE-US-00001 TABLE 1 Number of sample according to disclosed embodiments 1 2 3 4 5 6 7 8 9 10 Raw MgO 30 30 30 30 30 30 60 50 20 20 material Dolomite components Spinel (Al.sub.2O.sub.3—MgO) of refractory Flake graphite 70 70 70 70 70 70 40 50 80 80 (mass %) Expanded graphite Calcined anthracite Phenolic resin *1 3 3 3 3 3 3 3 3 3 3 Metal Al *1 3.0 5.0 5.5 6.0 6.5 7.0 5.0 5.0 5.0 6.0 Metal Si *1 1.5 3.0 3.3 3.6 3.9 4.2 4.0 1.6 1.6 2.0 Metal Si/Metal Al 0.50 0.60 0.60 0.60 0.60 0.60 0.80 0.32 0.32 0.33 (mass ratio) Resistance Wear (mm) 1.7 1.6 1.4 1.2 1.5 1.0 1.6 1.4 1.9 1.8 to molten steel Slaking Presence of crack No No No No No No No No No No resistance *1 With respect to 100% of refractory excluding the component

TABLE-US-00002 TABLE 2 Comparative sample No. 1 2 3 4 5 6 7 8 9 Raw MgO 80 80 30 30 30 30 10 60 30 material Dolomite components Spinel (Al.sub.2O.sub.3—MgO) of refractory Flake graphite 20 20 70 70 70 70 90 40 70 (mass %) Expanded graphite Calcined anthracite Phenolic resin *1 3 3 3 3 3 3 3 3 3 Metal Al *1 0 3.0 5.0 4.5 4.5 3.0 6.0 0 0 Metal Si *1 0 0.5 1.0 0 1.0 0 1.5 0 0 Metal Si/Metal Al — 0.17 0.20 0 0.22 0 0.25 — — (mass ratio) Resistance Wear (mm) 1.1 1.5 1.3 1.6 1.7 1.2 1.4 4.5 10.7 to molten steel Slaking Presence of crack No Yes Yes Yes Yes Yes Yes No No resistance *1 With respect to 100% of refractory excluding the component

Example 2

[0053] As illustrated in FIG. 1, a gas injection nozzle refractory with 81 concentric small metal tubes was produced. Tables 3 to 6 list the production conditions for gas injection nozzle refractories.

[0054] On a plane of the gas injection nozzle refractories, a virtual circle with a minimum radius surrounding all the buried small metal tubes had a radius R of 50 mm. The radius R+r of the central refractory was altered in the range of r=5 to 200 mm.

[0055] The small metal tubes buried in the carbon-containing refractory are plain steel or small stainless steel (SUS304) tubes with an outer diameter of 3.5 mm and an inner diameter of 2.0 mm.

[0056] Refractory raw materials were mixed at ratios listed in Tables 3 to 6 and were kneaded in a mixer. The small metal tubes were placed in the mixture for the central refractory. The central refractory was molded by uniaxial pressing. The central refractory was surrounded with the mixture for the peripheral refractory, and the base material was formed by CIP. The base material was then dried by a routine method to obtain a product.

[0057] The prepared gas injection nozzle refractories according to the examples and comparative examples were used for furnace bottom bricks around a bottom blowing tuyere of a 250-ton converter. After 2500 charges, the wear rate (mm/h) was determined from the remaining thickness of the refractory, and the wear rate ratio (index) was calculated relative to the wear rate of Comparative Example 1, which was set to “1”. Slaking resistance was determined by visual inspection for cracks one week after use.

[0058] Tables 3 to 6 also show these results. Tables 3 to 6 show that in an actual converter that receives large thermal shocks the gas injection nozzle refractories according to the examples had a lower wear rate and higher durability than the gas injection nozzle refractories according to the comparative examples. No crack was formed as in ordinary Comparative Example 1, showing that the addition of metal Al had no adverse effects on slaking resistance. Among the examples, the gas injection nozzle refractories with a central refractory radius in the range of R+40 to R+70 mm had particularly high durability. In Comparative Example 18, the amount of added metal Al was increased. Although Comparative Example 18 had almost the same wear rate and slaking resistance as the examples, the gas injection nozzle refractory is expensive due to the large amount of added metal Al and may generate ammonia, which poses a safety problem.

TABLE-US-00003 TABLE 3 Example No. 1 2 3 4 5 6 7 8 9 10 Raw MgO 50 50 50 50 50 40 30 25 30 30 material Dolomite 5 components Spinel (Al.sub.2O.sub.3—MgO) 10 of central Flake graphite 40 40 50 48 48 50 70 70 70 70 refractory Expanded graphite 2 (a) (mass %) Calcined anthracite 2 Phenolic resin *1 3 3 3 3 3 3 3 3 3 3 Metal Al *1 3.5 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 6.0 Metal Si *1 1.5 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.5 2.6 Metal Si/Metal Al 0.43 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.50 0.43 (mass ratio) Raw MgO 80 80 80 80 80 80 80 80 80 80 material Flake graphite 20 20 20 20 20 20 20 20 20 20 components Expanded graphite of peripheral Phenolic resin *1 3 3 3 3 3 3 3 3 3 3 refractory (b) (mass %) Number of Material plain steel — — 81 81 81 — — — — — small metal Material SUS304 126 126 — — — 81 126 168 126 126 tubes (—) r (mm) 50 50 50 50 50 60 60 70 60 60 Wear rate ratio 0.65 0.54 0.57 0.56 0.58 0.57 0.55 0.59 0.57 0.54 (vs. Comparative example 1) Slaking resistance No No No No No No No No No No (presence of crack) *1 With respect to 100% of refractory excluding the component

TABLE-US-00004 TABLE 4 Example No. 11 12 13 14 15 16 17 18 19 20 Raw MgO 30 20 50 50 50 50 50 50 40 50 material Dolomite components Spinel (Al.sub.2O.sub.3—MgO) of central refractory Flake graphite 70 80 50 50 50 50 50 50 60 50 (a) (mass %) Expanded graphite Calcined anthracite Phenolic 3 3 3 3 3 3 3 3 3 3 resin *1 Metal Al *1 7.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 Metal Si *1 3.6 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 5.0 Metal Si/Metal Al 0.51 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 1.00 (mass ratio) Raw MgO 80 80 80 80 80 88 85 75 80 80 material Flake graphite 20 20 20 20 20 10 15 25 20 20 components Expanded graphite 2 of peripheral Phenolic resin *1 3 3 3 3 3 3 3 3 3 3 refractory r(b) (mass %) Number of Material plain steel — — — — — — — — — — small metal Material SUS304 81 81 126 81 81 126 126 126 126 126 tubes (—) r (mm) 40 40 10 100 150 10 10 10 40 10 Wear rate ratio 0.55 0.59 0.58 0.54 0.58 0.59 0.57 0.57 0.58 0.59 (vs. Comparative example 1) Slaking resistance No No No No No No No No No No (presence of crack) *1 With respect to 100% of refractory excluding the component

TABLE-US-00005 TABLE 5 Comparative example No. 1 2 3 4 5 6 7 8 9 10 Raw MgO 80 80 75 10 10 80 10 80 80 80 material Dolomite components of Spinel (Al.sub.2O.sub.3—MgO) central Flake graphite 20 20 20 85 90 20 85 20 20 20 refractory Expanded graphite 5 5 (a) (mass %) Calcined anthracite 5 Phenolic resin *1 3 3 3 3 3 3 3 3 3 3 Metal Al *1 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Metal Si *1 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 Metal Si/Metal Al 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 0.50 (mass ratio) Raw MgO 80 80 80 80 80 80 80 93 91 65 material Flake graphite 20 20 20 20 20 20 20 7 7 35 components of Expanded graphite 2 peripheral Phenolic resin *1 3 3 3 3 3 3 3 3 3 3 refractory (b) (mass %) Number of Material plain steel 81 — — — 126 126 126 — — — small metal Material SUS304 — 81 126 126 — — — 126 126 126 tubes (—) r (mm) 50 50 50 8 8 180 200 50 50 50 Wear rate ratio 1.00 0.98 0.95 1.41 1.50 1.22 1.43 1.38 1.25 1.18 (vs. Comparative example 1) Slaking resistance No No No No No No No No No No (presence of crack) *1 With respect to 100% of refractory excluding the component

TABLE-US-00006 TABLE 6 Comparative example No. 11 12 13 14 15 16 17 18 19 20 Raw MgO 50 50 50 10 50 50 50 30 30 30 material Dolomite components Spinel (Al.sub.2O.sub.3—MgO) of central Flake graphite 50 50 50 90 50 50 50 70 70 70 refractory Expanded graphite (a) (mass %) Calcined anthracite Phenolic resin *1 3 3 3 3 3 3 3 3 3 3 Metal Al *1 1.5 1.5 1.5 1.5 1.5 1.5 3.0 8.5 4.0 5.0 Metal Si *1 0.75 0.75 0.75 0.75 0.75 0.75 0.80 4.80 5.00 6.00 Metal Si/Metal Al 0.50 0.50 0.50 0.50 0.50 0.50 0.27 0.56 1.25 1.20 (mass ratio) Raw MgO 70 70 70 70 95 80 80 80 80 80 material Flake graphite 30 30 30 30 5 20 20 20 20 20 components Expanded graphite of peripheral Phenolic resin *1 3 3 3 3 3 3 3 3 3 3 refractory (b) (mass %) Number of Material plain steel — — — — — — — — — — small metal Material SUS304 126 126 126 126 126 126 126 126 126 126 tubes (—) r (mm) 50 160 5 50 50 50 50 50 50 50 Wear rate ratio 0.90 1.07 1.06 1.40 1.27 1.42 0.95 0.66 1.10 1.07 (vs. Comparative example 1) Slaking resistance No No No No No No Yes No No No (presence of crack) *1 With respect to 100% of refractory excluding the component