Refractory material and casting nozzle

Abstract

A refractory material contains: 40 mass % or more of MgO; 4 to 30 mass % of a free carbon component; and one or more of B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2 and TiO.sub.2, in a total amount of 0.3 to 3 mass %, with the remainder being at least one other type of additional refractory component. A void layer exists in an interface between a carbon-containing matrix microstructure residing at least on opposite sides of a maximum-size one of a plurality of MgO-containing particles in the refractory material, and the maximum-size MgO-containing particle. A sum of respective thicknesses of the void layer at two positions on the opposite sides is 0.2 to 3.0% of a ratio with respect to particle size of the maximum-size MgO-containing particle. An inorganic compound of MgO and the one or more of B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2 and TiO.sub.2 exists entirety or partially in a surface of each of the MgO-containing particles.

Claims

1. A refractory material containing, in terms of a chemical composition as measured after being subjected to a heat treatment in a non-oxidizing atmosphere at 1000° C.: MgO in an amount of 40 mass % or more; a free carbon component in an amount of 4 to 30 mass %; and one or more selected from the group consisting of B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2 and TiO.sub.2, in a total amount of 0.3 to 3 mass %, with the remainder being at least one other type of additional refractory component, wherein a void layer exists in an interface between a carbon-containing matrix microstructure residing at least on opposite sides of a maximum-size one of a plurality of MgO-containing particles in the refractory material, and the maximum-size MgO-containing particle, a sum of respective thicknesses of the void layer at two positions on the opposite sides being 0.2 to 3.0% in terms of a ratio with respect to a particle size of the maximum-size MgO-containing particle, and wherein an inorganic compound comprised of MgO and the one or more selected from the group consisting of B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2 and TiO.sub.2 exists in an entirety or a part of a surface of each of the plurality of MgO-containing particles.

2. The refractory material as recited in claim 1, wherein the additional refractory component consists of Al.sub.2O.sub.3, except for inevitable components originating from raw materials or resulting from manufacturing conditions, and wherein a mass ratio of Al.sub.2O.sub.3 to MgO (Al.sub.2O.sub.3/MgO) is 0 to 0.65.

3. The refractory material as recited in claim 1, wherein, in a state at room temperature after being subjected to the heat treatment in a non-oxidizing atmosphere at 1000° C., an amount of the refractory material except for the free carbon component is 100 mass %, a total amount of particles having a particle size of 0.1 mm or less among raw material particles is 5 to 45 mass %, and a maximum thermal expansion rate at temperatures of up to 1500° C. is 1.1% or less.

4. The refractory material as recited in claim 1, wherein an entire amount of the refractory material as measured after being subjected to a heat treatment in a non-oxidizing atmosphere at 600° C. before start of the heat treatment in a non-oxidizing atmosphere at 1000° C. is 100 mass %, the refractory material contains one or more metals selected from the group consisting of Al, Si and Mg, in a total amount of 0.5 to 6 mass %, and/or B.sub.4C in an amount of 0.5 to 1.5 mass %.

5. A casting nozzle which is partially or entirely formed of the refractory material as recited in claim 1.

6. A casting nozzle comprising the refractory material as recited in claim 1, wherein the refractory material is disposed to define a part or an entirety of a surface of the casting nozzle to be subjected to a contact with molten steel.

7. A casting nozzle comprising a plurality of layers comprised of: a first layer disposed to define a part or an entirety of a region of the casting nozzle to be subjected to a contact with molten steel, the first layer being composed of the refractory material as recited in claim 1; and one or more second layers arranged on a back side of the first layer, each of the one or more second layers having a composition different from that of the first layer, wherein adjacent ones of the plurality of layers are integrated together in direct contact relation to each other.

8. A casting nozzle which is partially or entirely formed of the refractory material as recited in claim 2.

9. A casting nozzle which is partially or entirely formed of the refractory material as recited in claim 3.

10. A casting nozzle which is partially or entirely formed of the refractory material as recited in claim 4.

11. A casting nozzle comprising the refractory material as recited in claim 2, wherein the refractory, material is disposed to define a part or an entirety of a surface of the casting nozzle to be subjected to a contact with molten steel.

12. A casting nozzle comprising the refractory material as recited in claim 3, wherein the refractory material is disposed to define a part or an entirety of a surface of the casting nozzle to be subjected to a contact with molten steel.

13. A casting nozzle comprising the refractory material as recited in claim 4, Wherein the refractory material is disposed to define a part or an entirety of a surface of the casting nozzle to be subjected to a contact with molten steel.

14. A casting nozzle comprising a plurality of layers comprised of: a first layer disposed to define a part or an entirety of a region of the casting nozzle to be subjected to a contact with molten steel, the first layer being composed of the refractory material as recited in claim 2; and one or more second layers arranged on a back side of the first layer, each of the one or more second layers having a composition different from that of the first layer, wherein adjacent ones of the plurality of layers are integrated together in direct contact relation to each other.

15. A casting nozzle comprising a plurality of layers comprised of: a first layer disposed to define a part or an entirety of a region of the casting nozzle to be subjected to a contact with molten steel, the first layer being composed of the refractory material as recited in claim 3; and one or more second layers arranged on a back side of the first layer, each of the one or more second layers having a composition different from that of the first layer, wherein adjacent ones of the plurality of layers are integrated together in direct contact relation to each other.

16. A casting nozzle comprising a plurality of layers comprised of: a first layer disposed to define a part or an entirety of a region of the casting nozzle to be subjected to a contact with molten steel, the first layer being composed of the refractory, material as recited in claim 4; and one or more second layers arranged on a back side of the first layer, each of the one or more second layers having a composition different from that of the first layer, wherein adjacent ones of the plurality, of layers are integrated together in direct contact relation to each other.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 illustrates one type of immersion nozzle (casting nozzle) using a refractory material of the present invention.

(2) FIG. 2 illustrates other types of immersion nozzles (casting nozzles) using the refractory material of the present invention.

(3) FIG. 3 illustrates one type of long nozzle (casting nozzle) using the refractory material of the present invention.

(4) FIG. 4 illustrates another type of long nozzle (casting nozzle) using the refractory material of the present invention.

(5) FIG. 5 illustrates one type of lower nozzle (casting nozzle) using the refractory material of the present invention.

(6) FIG. 6 illustrates one type of SN plate (casting nozzle) using the refractory material of the present invention.

(7) FIG. 7 illustrates an outline of an in-molten steel rotation test method.

(8) FIG. 8 illustrates a test piece for the in-molten steel rotation test, wherein FIG. 9(a) is a front view, and FIG. 9(b) is a top plan view.

(9) FIG. 9 illustrates an outline of an adhesion and wear speed measurement method in the in-molten steel rotation test.

(10) FIG. 10 is a conceptual diagram illustrating MgO-containing particles and the surrounding microstructure of a refractory material according to the present invention, wherein FIG. 10(a) illustrates a refractory microstructure in which a void layer is formed around an MgO-containing particle in such a manner that it has a geometrically similarly magnified shape with respect to a contour of the particle, wherein the particle is located in approximately concentric relation to the contour of the void layer (a typical example of the present invention), and FIG. 10(b) illustrates a refractory microstructure in which a void layer is formed around an MgO-containing particle in such a manner that it has a geometrically similarly magnified shape with respect to a contour of the particle, wherein the particle is located offset toward an inner wall surface defining the contour of the void layer, in one direction (an example of positional offset occurring during preparation of a sample for microscopic observation).

(11) FIG. 11 is a conceptual diagram illustrating MgO-containing particles and the surrounding microstructure of a conventional refractory material, wherein FIG. 11(a) illustrates a refractory microstructure in which a void layer is formed around an MgO-containing particle in such a manner that it partially has a geometrically similarly magnified shape with respect to a contour of the particle, wherein solids having a porous or densified (non-porous) body exist inside a part of the void layer (an example in which the void layer is formed by means of a coating made of a residual carbon-forming material such as pitch), and FIG. 11(b) illustrates a refractory microstructure in which a void layer is formed around an MgO-containing particle in such a manner that it has a discontinuous shape, instead of a geometrically similarly magnified shape with respect to a contour of the particle, i.e., it partially does not exist to form a contact region between the particle and a carbonaceous matrix (an example in which, when the void layer is formed by means of a coating made of a combustible material, the void layer is not fully formed due to missing of a part of the coating).

DESCRIPTION OF EMBODIMENTS

(12) A role of MgO-containing particles used in the present invention is to bring out an expansion lowering effect based on formation of an approximately continuous void layer around a surface of each of the particles, and improve erosion/corrosion resistance based on an MgO component. Examples of the MgO-containing particles typically include a particle-form magnesia-based raw material consisting primarily of naturally-produced or artificially-synthesized MgO. As the magnesia-based raw material, it is possible to use either one of fused magnesia and sintered magnesia. In either case, the purity of MgO is preferably 90 mass % or more. As the raw material for the MgO-containing particles, it is also possible to partially use a spinel-based raw material containing a theoretical spinel composition (MgO.Al.sub.2O.sub.3). However, as a prerequisite for bringing out the expansion lowering effect and the erosion/corrosion resistance improving effect based on MgO, it is necessary that the MgO-containing particles, i.e., an MgO source, are at least partially made of a magnesia-based raw material (periclase).

(13) The refractory material of the present invention contains one or more metal oxides (hereinafter referred to as “specific metal oxides”) selected from the group consisting of B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2 and TiO.sub.2. As a raw material therefor, it is possible to use one or more selected from oxides, hydroxides, colloidal substances, esters, metal alkoxides, etc., of B, P, Si and Ti, independently or in the form of a combination of two or more thereof. For example, as a suitable B.sub.2O.sub.3 source, it is possible to use boron oxide, tetraboric acid, metaboric acid, orthoboric acid, or borate ester. Alternatively, it is also possible to use borosilicate glass. As a P.sub.2O.sub.5 source, it is possible to use phosphoric acid, phosphoric ester, various phosphoric salts, such as aluminum phosphate and sodium phosphate, or phosphate hydrate. As a SiO.sub.2 source, it is possible to use orthosilicate, metasilicate, anhydrous silica powder, colloidal silica, a solution type of ethyl silicate or the like, silicate, or aluminosilicate, without causing deterioration in quality. As a TiO.sub.2 source, it is possible to use titanium oxide, titania hydrate, titanium compound, or colloidal dispersion.

(14) It is necessary to allow the one or more specific metal oxides selected from the group consisting of B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2 and TiO.sub.2 to be dispersed around each of the MgO-containing particles uniformly without segregation. For this purpose, it is desirable to adequately perform dispersion during kneading, and use as the raw materials, a fine powder having a particle size of 0.1 mm or less, or a liquid type.

(15) In the present invention, in addition to a carbon component, the MgO component, B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2 and TiO.sub.2, it is possible to contain at least one other type of additional refractory component. As the additional refractory component, an Al.sub.2O.sub.3 component is most preferable, for the aforementioned reason. As the additional refractory component other than Al.sub.2O.sub.3, it is possible to use an oxide component such as ZrO.sub.2, Y.sub.2O.sub.3, CaO or Cr.sub.2O.sub.3, and SiC. These may be added independently, or may be used in the form of a solid solution or a compound. As one example, it is possible to add one or more of various types of ZrO.sub.2-based raw materials (unstabilized zirconia, partially stabilized zirconia, fully stabilized zirconia, and alumina-zirconia), chromia, magnesia-chromia, and spinel. In this case, the expansion lowering effect can be developed by setting the content of the MgO component to at least 40 mass % or more. SiC is preferably added in an amount of 15 mass % or less.

(16) In the refractory material of the present invention, a natural raw material can be used as refractory particles, as mentioned above. In such a natural raw material for use as the refractory particles, and other refractory raw materials, impurities (an inevitable component other than effective components) originating from raw materials therefor or resulting from manufacturing conditions of the raw materials can be mixed (the inevitable component originating from raw materials or resulting from manufacturing conditions will hereinafter be referred to simply as “inevitable component”). Examples of the inevitable component include Fe.sub.2O.sub.3 and R.sub.2O (R═Na, K or Li). A content of the inevitable component is limited to about 3 mass % or less, preferably, about 2 mass % or less, more preferably, about 1 mass % or less. The content of the inevitable component can be adjusted to some extent, for example, by employing a technique of selecting each raw material whose effective components are high in purity, or a technique of enhancing cleaning or the like during a manufacturing process.

(17) As a carbon source, a carbon raw material serving as a binder (binder carbon) may be used. As the binder carbon, it is preferable to use a phenolic resin, pitch or tar, because they can leave residual carbon as a binding network, at a high rate after burning in a non-oxidizing atmosphere. In the present invention, in addition to the binder carbon raw material, a solid carbonaceous raw material except for the binder carbon raw material may be arbitrarily used. As the solid carbonaceous raw material except for the binder carbon raw material, it is possible to use a particle-form carbonaceous raw material such as graphite or carbon black, or a fiber-form carbonaceous raw material such as carbon fibers. However, it is necessary to add the above carbon source to a raw material mixture in such a manner that, in terms of a chemical composition as measured after the refractory material is subjected to a heat treatment in a non-oxidizing atmosphere at 1000° C., a ratio of a free carbon component to the refractory material is in the range of 4 to 30 mass %, while taking into account a rate of a loss of the binder carbon raw material (a rate after subtraction of a rate of residual carbon) and a rate of a loss of the solid carbonaceous raw material (a loss of impurities on heating, etc.), and others.

(18) The above raw materials are mixed so as to have the chemical composition defined in the appended claims. Then, a resulting mixture is subjected to kneading and shaping, and a resulting shaped body is subjected to a heart treatment under a non-oxidizing atmosphere at 800° C. or more.

(19) In order to uniformly disperse the oxide component such as B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2 and/or TiO.sub.2 around each of the MgO-containing particles, it is preferable to perform the kneading after preparing the oxide components such as B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2 and TiO.sub.2, in a liquid form or a fine powder form, and directly adding, to the MgO-containing particles, additives using the liquid or fine power-form oxide components independently or in the form of a combination of two or more of them.

(20) Various examples of a casting nozzle using the refractory material of the present invention will be described below.

(21) FIG. 1(a) illustrates one type of immersion nozzle (casting nozzle) in which a refractory material 20 of the present invention is disposed to defined a part of a region of the nozzle to be subjected to a contact with molten steel, in the form of a single layer having a surface to be subjected to a contact with molten steel, and a back surface. In FIG. 1(a), the refractory material 20 of the present invention may be additionally disposed to form a powder line portion 21. In this case, the resulting immersion nozzle (casting nozzle) is configured such that the refractory product 20 of the present invention is disposed to define an entirety of the region to be subjected to a contact with molten steel, in the form of a single layer having a surface to be subjected to a contact with molten steel, and a back surface. While FIG. 1(a) illustrates an example of a circular cylindrical-shaped type, a casting nozzle using the refractory material of the present invention is not limited to a particular shape, such a circular cylindrical shape. For example, the refractory material of the present invention can be used in immersion nozzles (casting nozzles) having various shapes, such as a flat shape, an elliptic shape or a funnel shape (a funnel shape having a diametrally enlarged upper portion), primarily used for thin slab casting, as illustrated in FIG. 1(b).

(22) FIG. 2(a) illustrates another type of immersion nozzle (casting nozzle) which comprising a plurality of layers comprised of: a first layer disposed to define a part (in this type, inner bore surface) of a region of the nozzle to be subjected to a contact with molten steel, wherein the first layer is composed of the refractory material 20 of the present invention; and a second layer (a powder line portion 21 or a nozzle body 22) disposed on a back side of the first layer, wherein the second layer has a composition different from that of the refractory material 20. The plurality of layers are integrated together in direct contact relation to each other. FIG. 2(b) illustrates yet another type in which, in addition to the part in FIG. 2(a), the refractory material 20 of the present invention is further used to define an inner peripheral surface and an outer peripheral surface of a discharge port, as the region to be subjected to a contact with molten steel, wherein a lower portion of the nozzle including a portion located immediately upstream of the discharge port is entirely formed of the refractory material 20 of the present invention. Alternatively, in the lower portion of the nozzle including the portion located immediately upstream of the discharge port, only a surface layer defining an inner peripheral surface to be subjected to a contact with molten steel may be formed of the refractory material 20 of the present invention, and the remaining region may be formed of a different refractory material, such as an alumina-graphite based refractory material.

(23) Specific examples of the refractory material (of the powder line portion 21 and the nozzle body 22) on the back side of the first layer, illustrated in FIG. 2, include: a refractory material comprising carbon and refractory particles comprised of one or more selected from the group consisting of Al.sub.2O.sub.3, SiO.sub.2, MgO and ZrO.sub.2 and compounds thereof; and a refractory material having a composition which falls within the range of that of the refractory material of the present invention but is different from that of the refractory material disposed to define a part or an entirety of the region to be subjected to a contact with molten steel.

(24) The above multi-layer casting nozzle may be produced by: partitioning a raw material mixture filling space in a target region inside a CIP molding mold, at a position radially distant from a molten steel contact surface (inner bore surface) by a given thickness; filling one sub-space on the side of the molten steel contact surface with a raw material mixture for the refractory material of the present invention, while filling the other sub-space on a back side thereof with a raw material mixtures, for example, for the refractory material comprising carbon and refractory particles composed of one or more selected from the group consisting of Al.sub.2O.sub.3, SiO.sub.2, MgO and ZrO.sub.2 and compounds thereof; removing a jig used for the partition, such as a partition plate; and then subjecting the mixtures to pressure forming.

(25) FIG. 3 illustrates one type of long nozzle in which the refractory material 20 of the present invention is disposed to define a part of a region to be subjected to a contact with molten steel.

(26) FIG. 4 and FIG. 5 illustrate, respectively, another type of long nozzle and one type of lower nozzle each of which comprising a plurality of layers comprised of: a first layer disposed to define a part of a region of the nozzle to be subjected to a contact with molten steel, wherein the first layer is composed of the refractory material 20 of the present invention; and a second layer (a nozzle body 22) disposed on a back side of the first layer, wherein the second layer has a composition different from that of the refractory material 20. The plurality of layers are integrated together in direct contact relation to each other. FIG. 6 illustrates one type of SN plate formed of the refractory material 20 of the present invention.

(27) For example, as illustrated in FIGS. 2(b) and 2(c), a CaO-based alumina adhesion-resisting refractory material 23 may be used to define a region to be subjected to a contact with molten steel, such as an inner bore surface of a casting nozzle, and the refractory material 20 of the present invention may be used for a portion on a back side thereof, and a part or an entirety of an intermediate layer of the nozzle. In this case, for example, the CaO-based refractory material and the MgO-based refractory material of the present invention are a basic material in common. This makes it possible to obtain an advantageous effect, for example, of being able to prevent lowering in melting point caused by a reaction, e.g., between the CaO-based refractory material and an Al.sub.2O.sub.3-based refractory material being in contact therewith, or damage or the like due to the lowering in melting point.

EXAMPLES

(28) A phenolic resin was added as a binder to each of a plurality of types of refractory raw materials (refractory particles) having respective compositions illustrated in Tables 1 to 9, and, after kneading, the resulting mixture was adjusted to have formability suitable for shaping. The mixture was formed into a desired shape by a CIP process, and the shaped body was subjected to a hardening-drying treatment at temperatures of up to 300° C. and then to a heat treatment in a non-oxidizing atmosphere at 1000° C. In the Examples, fused magnesia clinker particles and spinel fine powder were used as the Mg-containing particles.

(29) The obtained refractory material was subjected to analysis for chemical composition, microstructure observation, and an evaluation test. In the microstructure observation, a refractory microstructure was observed through a microscope after being subjected to impregnation with a resin and then mirror-finishing by mechanical polishing, and then an MS value was calculated in the aforementioned manner.

(30) The refractory material was evaluated in terms of thermal expansion rate, wear resistance (erosion/corrosion resistance), thermal shock resistance, and oxidation resistance.

(31) In the evaluation of thermal expansion rate, a thermal expansion rate at temperatures of up to 1500° C. was measured (according to JIS R 2207-3) to evaluate a maximum thermal expansion rate at temperatures of up to 1500° C.

(32) The evaluation of wear resistance (erosion/corrosion resistance) of the refractory material was performed by an in-molten steel rotation test using high-oxygen steel. The in-molten steel rotation test is a method for evaluating erosion/corrosion resistance against molten steel to be owned as one prerequisite by the refractory material of the present invention. As used in this specification, the term “wear” or “wear damage” is used as a concept generally expressing a state in which a sample after the test is dimensionally reduced, irrespective of whether a damaging mechanism is a loss caused by a chemical reaction (corrosion due to lowering in meting point, etc.) or a loss caused by a mechanical abrasive action, such as abrasion (so-called “erosion”).

(33) FIG. 7 schematically illustrates an in-molten steel rotation test method, and FIG. 8 illustrates a test piece for the in-molten steel rotation test, wherein FIG. 8(a) is a schematic front view, and FIG. 8(b) is a schematic top plan view.

(34) In the in-molten steel rotation test, a test piece 10 held at a lower portion of a holder 11 is immersed in molten steel 13 in a crucible 12. The test piece 10 is formed in a rectangular parallelepiped shape and the number of test pieces 10 is four. The holder 11 is formed in a square pillar shape, wherein the four test pieces 10 are fixed, respectively, to four side surfaces of the lower portion of the holder 11. The test pieces 10 are inserted, respectively, into four recesses provided in the square pillar-shaped holder 11, in such a manner that they can be pulled out therefrom after completion of the test. An upper portion of the holder 11 is connected to and held by a non-illustrated rotary shaft in a rotatable manner about a longitudinal axis thereof as a rotation axis.

(35) The holder 11 is made of a zirconia-carbon based refractory material and formed to have a square shape with a side of 40 mm, in horizontal cross-section, and a longitudinal length of 160 mm. Each of the test pieces 10 has a portion exposed from the holder 11. The exposed portion has a heightwise length of 20 mm, a widthwise length of 20 mm and a protruding length of 25 mm. The test piece 10 is attached to the holder at a position located upwardly away from a lower end thereof by 10 mm. The crucible 12 is made of a refractory material and formed in a cylindrical shape having an inner diameter of 130 mm and a depth of 190 mm. The holder 11 is immersed at a depth of 50 mm or more. The crucible 12 is placed inside a high-frequency induction furnace 14. Although not illustrated, an upper surface of the crucible can be closed by a cover.

(36) In the in-molten steel rotation test, after pre-heating the test pieces 10 by holding them just above the molten steel 13 for 5 minutes, the test pieces 10 are immersed in the molten steel 13 (high-oxygen steel, in-steel oxygen concentration: 100 to 150 ppm), and rotated at an average circumferential velocity of 1 m/sec at an outermost periphery of each of the test pieces 10. During the test, the temperature of the molten steel 13 is kept in the range of 1550 to 1600° C. After three hours, the test pieces 10 are pulled up, and, an adhesion/wear speed (μm/min) is measured.

(37) The measurement of the adhesion/wear speed is performed as follows. As shown in FIG. 9(b), each of the test pieces 10 after completion of the test is detached from the holder, and cut along a horizontal plane with respect to the rotation axis. Then, respective lengths at 6 positions of the cut surface are measured at 3 mm pitch in a direction from an edge 10a of the test piece 10 toward the rotation axis, and averaged. Respective lengths at the same positions of the test piece 10 before the test are also measured and averaged, as illustrated in FIG. 9(a). Then, the average value (mm) after the test is subtracted from the average value (mm) before the test, and the obtained value is divided by a test time of 180 minutes, to obtain the adhesion/wear speed (μm/min). In a furnace operation, the wear speed is essentially required to be 35 μm/min or less. Thus, the wear resistance (erosion/corrosion resistance) of the material was relatively evaluated by using the following criteria for the wear speed: Excellent (⊚): <0 to 5 μm/min, Good (∘): <5 to 20 μm/min, Acceptable (Δ): 21 to 35 μm/min, and NG (×): >36 μm/min.

(38) Next, an evaluation method for thermal shock resistance to be owned as one prerequisite by the refractory material of the present invention will be described. Thermal shock resistance of the refractory material was evaluated by a test designed to pre-heat a tubular-shaped sample (outer diameter/inner diameter (inner bore diameter)/height=130/55/300 mm) to a given temperature Ts° C., and, after holding a constant-temperature state at the given temperature for 1 hour, pouring hot metal at 1600° C. into an inner bore of the sample to thereby give thermal shock to the refractory material of the sample. That is, a maximum temperature difference (ΔT) is (1600−Ts) ° C. After the test, the sample was cut along a horizontal cross-section at 50 mm pitch to check the presence or absence of crack. A maximum value of ΔT at which no crack was observed was defined as an endurance limit temperature ΔT. The endurance limit temperature ΔT of thermal shock resistance to be owned as one prerequisite by the refractory material of the present invention, particularly, a continuous casting refractory material requiring thermal shock resistance is 800° C. or more. Thus, when the endurance limit temperature ΔT was 800° C. or more, the sample was evaluated as Good (∘), and when it was 800° C. or more, the sample was evaluated as Excellent (⊚). On the other hand, when the endurance limit temperature ΔT was 700° C. or less, the sample was evaluated as NG (×), and when it was 700 to 800° C., the sample was evaluated as Acceptable (Δ).

(39) In an SN plate, a lower nozzle, an upper nozzle, a steel making brick or the like which are generally used without coating of an anti-oxidant, a refractory material thereof needs to have oxidation resistance by itself. Therefore, there is a situation where it is desirable or necessary to provide an oxidation resistance enhancing function to an inside of a refractory microstructure. Oxidation resistance was evaluated by placing a sample (30 mm square) of the refractory material in an atmospheric atmosphere at 800° C. or 1400° C. Immediately after holding the temperature for 3 hours, the sample was taken out and, after being cooled, cut in a horizontal direction. Then, an average thickness of a decarburized layer was measured. When the thickness of the decarburized layer was less than 0.5 mm at the above two temperatures, the sample was evaluated as Excellent (⊚), and when it was less than 1 mm at the above two temperatures, the sample was evaluated as Good (∘). On the other hand, when the thickness of the decarburized layer was greater than 1 mm at the above two temperatures, the sample was evaluated as NG (×).

(40) Results of the evaluations are presented in Tables 1 to 9. Comprehensive evaluation in Tables 1 to 9 was determined as Good and indicated as (∘), when the following conditions were satisfied: the MS value was in the range of 0.2 to 3.0%; an inorganic compound comprised of MgO and one or more selected from the group consisting of B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2 and TiO.sub.2 existed in an entirety or a part of a surface of each of the plurality of MgO-containing particles; the maximum thermal expansion rate at temperatures of up to 1500° C. was 1.1% or less; the evaluation in the in-molten steel rotation test was (⊚) or (∘); the evaluation of thermal shock resistance was (⊚) or (∘): and the evaluation of oxidation resistance was (⊚) or (∘) (however, the evaluation of oxidation resistance is presented only in Table 9). On the other hand, when the above evaluations included (Δ) without (×), the sample was evaluated as Acceptable and indicated as (Δ), and when the above evaluations included (×), the sample was evaluated as NG and indicated as (×). When the comprehensive evaluation was (∘) or (Δ), the sample was determined to be OK (usable).

(41) TABLE-US-00001 TABLE 1 Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Refractory Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) Raw Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) Material Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 80 78 77 65 Fused magnesia −0.1 mm (mass %) 20 20 20 20 Alumina fine −0.1 mm (mass %) powder Spinel fine powder −0.1 mm (mass %) Graphite 0.1-1.0 mm (mass %) 0 2 3 15 Fine carbon −0.1 mm (mass %) Additive (*) Boron oxide (Mass % with respect to and in addition to total amount) Phosphrous (Mass % with respect to and in addition to total amount) pentaoxide Silicon oxide (Mass % with respect to and in addition to total amount) Titanium oxide (Mass % with respect to and in addition to total amount) Borosilicate glass (Mass % with respect to and in addition to total amount) {close oversize brace} 0 {close oversize brace} 0 {close oversize brace} 0 {close oversize brace} 0 Al—Si ally (Mass % with respect to and in addition to total amount) B.sub.4C (Mass % with respect to and in addition to total amount) Binder Phenolic resin (Solid content of resin, mass % with respect to and in 5 5 5 5 addition to total amount Particle Size Content of −0.1 mm Mass % 20 20 21 24 of Raw MgO-containing Material particles Comparative Comparative Example 5 Example 6 Refractory Raw Material Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 60 50 Fused magnesia −0.1 mm (mass %) 20 20 Alumina fine powder −0.1 mm (mass %) Spinel fine powder −0.1 mm (mass %) Graphite 0.1-1.0 mm (mass %) 20 30 Fine carbon −0.1 mm (mass %) Additive (*) Boron oxide (Mass % with respect to and in addition to total amount) Phosphrous pentaoxide (Mass % with respect to and in addition to total amount) Silicon oxide (Mass % with respect to and in addition to total amount) Titanium oxide (Mass % with respect to and in addition to total amount) {close oversize brace} 0 {close oversize brace} 0 Borosilicate glass (Mass % with respect to and in addition to total amount) Al—Si ally (Mass % with respect to and in addition to total amount) B.sub.4C (Mass % with respect to and in addition to total amount) Binder Phenolic resin (Solid content of resin, mass % with respect to and in 5 5 addition to total amount Particle Size of Raw Content of −0.1 mm MgO-containing Mass % 25 29 Material particles Comparative Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Surface Treatment of With/Without surface treatment Without Without Without Without MgO-containing Hydration treatment (Exposure to superheated steam at 250° C.) — — — — Particles Layer thickness, μm Carbonation treatment (After heating at 500° C. under vacuum, — — — — exposure to CO.sub.2 gas at room temperature) Layer thickness, μm Chemical Composition Free carbon component 2.4 4.4 5.4 17.1 (mass %) MgO 97.6 95.6 94.6 82.9 Al.sub.2O.sub.3 0.0 0.0 0.0 0.0 Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 0 0 0 0.0 Mass ratio (Al.sub.2O.sub.3/MgO) 0.0 0.0 0.0 0.0 State of Microstructure Void layer thickness rate betweeb maximum-diameter <0.2 <0.2 <0.2 <0.2 MgO-containing particle and carbonaceous matrix, MS value (%) Continuity of void layer — — — — Presence or absence of compound with oxide (*) on Absence Absence Absence Absence surface of MgO-containing particle Quality after Burning Maximum thermal expansion rate at temperature of up to 1.82 1.80 1.77 1.07 1500° C. Evaluation Result {circle around (1)} In-molten steel rotation test (wear resistance) ⊚ ⊚ ⊚ ⊚ {circle around (2)} (Endurance limit temperature ΔT ° C.(thermal shock X300 X400 X450 X650 resistance) {circle around (3)} Oxidation resistance — — — — Comprephensive Evaluation: ◯: Excellent, Δ: Good, X: NG X X X X Comparative Comparative Example 5 Example 6 Surface Treatment of With/Without surface treatment Without Without MgO-containing Hydration treatment (Exposure to superheated steam at 250° C.) Layer thickness, μm — — Particles Carbonation treatment (After heating at 500° C. under vacuum, exposure to CO.sub.2 gas at — — room temperature) Layer thickness, μm Chemical Composition Free carbon component 22.0 31.7 (mass %) MgO 78.0 68.3 Al.sub.2O.sub.3 0.0 0.0 Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 0.0 0.0 Mass ratio (Al.sub.2O.sub.3/MgO) 0.0 0.0 State of Microstructure Void layer thickness rate betweeb maximum-diameter MgO-containing particle and carbonaceous <0.2 <0.2 matrix, MS value (%) Continuity of void layer — — Presence or absence of compound with oxide (*) on surface of MgO-containing particle Absence Absence Quality after Burning Maximum thermal expansion rate at temperature of up to 0.85 0.65 1500° C. Evaluation Result {circle around (1)} In-molten steel rotation test (wear resistance) X X {circle around (2)} (Endurance limit temperature ΔT ° C.(thermal shock ◯1000 ◯1500 resistance) {circle around (3)} Oxidation resistance — — Comprephensive Evaluation: ◯: Excellent, Δ: Good, X: NG X X

(42) TABLE-US-00002 TABLE 2 Comparative Inventive Inventive Inventive Example 7 Example 1 Example 2 Example 3 Refractory Raw Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) Material Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 80 78 77 70 Fused magnesia −0.1 mm (mass %) 20 20 20 20 Alumina fine powder −0.1 mm (mass %) Spinel fine powder −0.1 mm (mass %) Graphite 0.1-1.0 mm (mass %) 0 2 3 10 Fine carbon −0.1 mm (mass %) Additive (*) Boron oxide (Mass % with respect to and in addition to total amount) 1 1 1 1 Phosphrous pentaoxide (Mass % with respect to and in addition to total amount) Silicon oxide (Mass % with respect to and in addition to total amount) Titanium oxide (Mass % with respect to and in addition to total amount) Borosilicate glass (Mass % with respect to and in addition to total amount) Binder Phenolic resin (Solid content of resin, mass % with respect to and in 5 5 5 5 addition to total amount Particle Size of Content of −0.1 mm Mass % 20 20 21 22 Raw Material MgO-containing particles Surface With/Without surface treatment With With With With Treatment Hydration treatment (Exposure to superheated steam at 250° C.) 10-15 10-15 10-15 10-15 of MgO- Layer thickness, μm containing Carbonation treatment (After heating at 500° C. under vacuum, — — — — Particles exposure to CO.sub.2 gas at room temperature) Layer thickness, μm Inventive Comparative Comparative Inventive Example 4 Example 8 Example 9 Example 5 Refractory Raw Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) Material Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 65 65 65 60 Fused magnesia −0.1 mm (mass %) 20 20 20 20 Alumina fine powder −0.1 mm (mass %) Spinel fine powder −0.1 mm (mass %) Graphite 0.1-1.0 mm (mass %) 15 15 15 20 Fine carbon −0.1 mm (mass %) Additive (*) Boron oxide (Mass % with respect to and in addition to total amount) 1 1 0 1 Phosphrous pentaoxide (Mass % with respect to and in addition to total amount) Silicon oxide (Mass % with respect to and in addition to total amount) Titanium oxide (Mass % with respect to and in addition to total amount) Borosilicate glass (Mass % with respect to and in addition to total amount) Binder Phenolic resin (Solid content of resin, mass % with respect to and in 5 5 5 5 addition to total amount Particle Size of Content of −0.1 mm Mass % 24 24 24 25 Raw Material MgO-containing particles Surface With/Without surface treatment With Without With With Treatment Hydration treatment (Exposure to superheated steam at 250° C.) 10-15 — 10-15 10-15 of MgO- Layer thickness, μm containing Carbonation treatment (After heating at 500° C.under vacuum, — — — — Particles exposure to CO.sub.2gas at room temperature) Layer thickness, μm Comparative Inventive Inventive Example Example 6 Example 7 10 Refractory Raw Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) Material Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 56 51 50 Fused magnesia −0.1 mm (mass %) 20 20 20 Alumina fine powder −0.1 mm (mass %) Spinel fine powder −0.1 mm (mass %) Graphite 0.1-1.0 mm (mass %) 24 29 30 Fine carbon −0.1 mm (mass %) Additive (*) Boron oxide (Mass % with respect to and in addition to total amount) 1 1 1 Phosphrous pentaoxide (Mass % with respect to and in addition to total amount) Silicon oxide (Mass % with respect to and in addition to total amount) Titanium oxide (Mass % with respect to and in addition to total amount) Borosilicate glass (Mass % with respect to and in addition to total amount) Binder Phenolic resin (Solid content of resin, mass % with respect to and in 5 5 5 addition to total amount Particle Size of Raw Content of Mass % 26 28 29 Material −0.1 mm MgO-containing particles Surface Treatment of With/Without surface treatment With With With MgO-containing Hydration treatment (Exposure to superheated steam at 250° C.) Layer thickness, μm 10-15 10-15 10-15 Particles Carbonation treatment (After heating at 500° C. under vacuum, exposure to — — — CO.sub.2gas at room temperature) Layer thickness, μm Comparative Inventive Inventive Inventive Example 7 Example 1 Example 2 Example 3 Chemical Composition Free carbon component 2 4 5 12 (mass %) MgO 96.6 94.7 93.7 87.0 Al.sub.2O.sub.3 0.0 0.0 0.0 0.0 Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 1.0 1.0 1.0 1.0 Mass ratio (Al.sub.2O.sub.3/MgO) 0.0 0.0 0.0 0.0 State of Microstructure Void layer thickness rate betweeb maximum-diameter MgO-containing <0.2 0.9 1.2 2.1 particle and carbonaceous matrix, MS value (%) Continuity of void layer Discontinuous Almost Almost Almost continuous continuous continuous Presence or absence of compound with oxide (*) on surface of MgO- Presence Presence Presence Presence containing particle Quality after Burning Maximum thermal expansion rate at temperatures of up to 1500° C. 1.55 1.10 1.07 0.80 Evaluation Result {circle around (1)}In-molten steel rotation test (wear resistance) ⊚ ⊚ ⊚ ◯ {circle around (2)}Endurance limit temperature ΔT ° C. (thermal shock X500 ◯800 ◯900 ◯1150 resistance) {circle around (3)}Oxidation resistance — — — — Comprephensive Evaluation: ◯: Excellent, Δ: Good, X: NG X ◯ ◯ ◯ Inventive Comparative Comparative Inventive Example 4 Example 8 Example 9 Example 5 Chemical Composition Free carbon component 17 17 17 22 (mass %) MgO 82.1 82.1 82.9 77.3 Al.sub.2O.sub.3 0.0 0.0 0.0 0.0 Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 1.0 1.0 0.0 1.0 Mass ratio (Al.sub.2O.sub.3/MgO) 0.0 0.0 0.0 0.0 State of Microstructure Void layer thickness rate betweeb maximum-diameter 2.4 <0.2 <0.2 2.5 MgO-containing particle and carbonaceous matrix, MS value (%) Continuity of void layer Almost Discontinuous Discontinuous Almost continuous continuous Presence or absence of compound with oxide (*) on surface of Presence Presence Absence Presence MgO-containing particle Quality alter Burning Maximum thermal expansion rate at temperatures of up to 1500° C. 0.64 1.11 1.03 0.55 Evaluation Result {circle around (1)}In-molten steel rotation test (wear resistance) ◯ ◯ ⊚ ◯ {circle around (2)}Endurance limit temperature ΔT ° C. (thermal shock ⊚1500 X700 X700 ⊚1500 resistance) {circle around (3)}Oxidation resistance — — — — Comprephensive Evaluation: ◯: Excellent, Δ: Good, X: NG ◯ X X ◯ Comparative Inventive Inventive Example Example 6 Example 7 10 Chemical Composition Free carbon component 26 30 31 (mass %) MgO 73.4 68.6 67.6 Al.sub.2O.sub.3 0.0 0.0 0.0 Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 1.0 1.0 1.0 Mass ratio (Al.sub.2O.sub.3/MgO) 0.0 0.0 0.0 State of Microstructure Void layer thickness rate betweeb maximum-diameter MgO-containing particle 2.6 2.7 2.7 and carbonaceous matrix, MS value (%) Continuity of void layer Almost Almost Almost continuous continuous continuous Presence or absence of compound with oxide (*) on surface of MgO-containing particle Presence Presence Presence Quality after Burning Maximum thermal expansion rate at temperatures of up to 1500° C. 0.42 0.32 0.29 Evaluation Result {circle around (1)}In-molten steel rotation test (wear resistance) ◯ Δ X {circle around (2)}Endurance limit temperature ΔT ° C.(thermal shock ⊚1500 ⊚1500 ⊚1500 resistance) {circle around (3)}Oxidation resistance — — — Comprephensive Evaluation: ◯: Excellent, Δ: Good. X: NG ◯ ◯ X

(43) TABLE-US-00003 TABLE 3 Comparative Inventive Inventive Inventive Example Example Example Example 9 4 8 9 Refractory Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) Raw Material Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 65 65 35 23 Fused magnesia −0.1 mm (mass %) 20 20 20 20 Alumina fine powder −0.1 mm (mass %) Spinel fine powder −0.1 mm (mass %) Fused Alumina Greater than 0.1 mm to 0.5 mm (mass %) 30 42 Stabilized zirconia Fused alumina-zirconia Greater than 0.1 mm to 0.5 mm (mass %) Silicon cabide Greater than 0.1 mm to 0.5 mm (mass %) Graphite 0.1-1.0 mm (mass %) 15 15 15 15 Fine carbon −0.1 mm (mass %) Additive (*) Boron oxide (Mass % with respect to and in addition 0 1 1 1 to total amount) Phosphrous (Mass % with respect to and in addition pentaoxide to total amount) Silicon oxide (Mass % with respect to and in addition to total amount) Titanium oxide (Mass % with respect to and in addition to total amount) Borosilicate glass (Mass % with respect to and in addition to total amount) Al (Mass % with respect to and in addition to total amount) Si (Mass % with respect to and in addition to total amount) Al—Si alloy (Mass % with respect to and in addition (Al:Si = 3:1) to total amount) B.sub.4C (Mass % with respect to and in addition to total amount) Binder Phenolic resin (Solid content of resin, mass % with 5 5 5 5 respect to and in addition to total amount) Particle Size Content of −1 mm raw %, >70% 100 100 100 100 of Raw materials Material Content of −0.1 mm %, 5-45% 24 24 24 24 MgO-containing particles Comparative Inventive Inventive Comparative Example Example Example Example 11 10 11 12 Refractory Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) Raw Material Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 20 35 23 20 Fused magnesia −0.1 mm (mass %) 20 20 20 20 Alumina fine powder −0.1 mm (mass %) Spinel fine powder −0.1 mm (mass %) Fused Alumina Greater than 0.1 mm to 0.5 mm (mass %) 45 Stabilized zirconia 30 42 45 Fused alumina-zirconia Greater than 0.1 mm to 0.5 mm (mass %) Silicon cabide Greater than 0.1 mm to 0.5 mm (mass %) Graphite 0.1-1.0 mm (mass %) 15 15 15 15 Fine carbon −0.1 mm (mass %) Additive (*) Boron oxide (Mass % with respect to and in addition 1 1 1 1 to total amount) Phosphrous (Mass % with respect to and in addition pentaoxide to total amount) Silicon oxide (Mass % with respect to and in addition to total amount) Titanium oxide (Mass % with respect to and in addition to total amount) Borosilicate glass (Mass % with respect to and in addition to total amount) Al (Mass % with respect to and in addition to total amount) Si (Mass % with respect to and in addition to total amount) Al—Si alloy (Mass % with respect to and in addition (Al:Si = 3:1) to total amount) B.sub.4C (Mass % with respect to and in addition to total amount) Binder Phenolic resin (Solid content of resin, mass % with 5 5 5 5 respect to and in addition to total amount) Particle Size Content of −1 mm raw %, >70% 100 100 100 of Raw materials Material Content of −0.1 mm %, 5-45% 24 24 24 24 MgO-containing particles Comparative Inventive Inventive Example Example Example 13 12 13 Refractory Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) Raw Material Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 20 23 23 Fused magnesia −0.1 mm (mass %) 20 20 20 Alumina fine powder −0.1 mm (mass %) Spinel fine powder −0.1 mm (mass %) Fused Alumina Greater than 0.1 mm to 0.5 mm (mass %) 30 Stabilized zirconia 45 Fused alumina-zirconia Greater than 0.1 mm to 0.5 mm (mass %) 42 Silicon cabide Greater than 0.1 mm to 0.5 mm (mass %) 42 Graphite 0.1-1.0 mm (mass %) 15 15 15 Fine carbon −0.1 mm (mass %) Additive (*) Boron oxide (Mass % with respect to and in addition 0 1 1 to total amount) Phosphrous (Mass % with respect to and in addition pentaoxide to total amount) Silicon oxide (Mass % with respect to and in addition to total amount) Titanium oxide (Mass % with respect to and in addition to total amount) Borosilicate glass (Mass % with respect to and in addition to total amount) Al (Mass % with respect to and in addition to total amount) Si (Mass % with respect to and in addition to total amount) Al—Si alloy (Mass % with respect to and in addition (Al:Si = 3:1) to total amount) B.sub.4C (Mass % with respect to and in addition to total amount) Binder Phenolic resin (Solid content of resin, mass % with 5 5 5 respect to and in addition to total amount) Particle Size Content of −1 mm raw %, >70% of Raw materials Material Content of −0.1 mm %, 5-45% 24 24 24 MgO-containing particles Comparative Inventive Inventive Inventive Example Example Example Example 9 4 8 9 Surface Treatment With/Without surface treatment With With With With of MgO-containing Hydration treatment (Exposure to superheated steam 10-15 10-15 10-15 10-15 Particles at 250° C.) Layer thickness, μm Carbonation treatment (After heating at 500° C. under — — — — vacuum, exposure to CO.sub.2 gas at room temperature) Layer thickness, μm Chemical Free carbon component 17.1 16.9 16.9 16.9 Composition MgO 82.9 82.1 53.1 41.5 (mass %) Al.sub.2O.sub.3 0.0 0.0 29.0 40.6 ZrO.sub.2 0.0 0.0 0.0 0.0 Y.sub.2O.sub.3 0.0 0.0 0.0 0.0 SiC Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 0.0 1.0 1.0 1.0 Mass ratio (Al.sub.2O.sub.3/MgO) 0.0 0.00 0.55 0.98 State of Void layer thickness rate betweeb maximum-diameter <0.2 2.4 2.0 1.8 Microstructure MgO-containing particle and carbonaceous matrix, MS value (%) Continuity of void layer Discontinuous Almost Almost Almost continuous continuous continuous Presence or absence of compound with oxide (*) on Absence Presence Presence Presence surface of MgO-containing particle Quality after Maximum thermal expansion rate at temperature of up 1.03 0.64 0.74 0.80 Burning to 1500° C. Evaluation Result {circle around (1)} In-molten steel rotation test (wear resistance) ⊚ ∘ ∘ ∘ {circle around (2)} Endurance limit temperature ΔT ° C. (thermal shock x700 ⊚1500 ∘1200 ∘1100 resistance) {circle around (3)} Oxidation resistance — — — — {circle around (4)} Erosion/corrosion resistance Δ Δ ∘ ∘ Comprehensive Evaluation: ∘: Excellent, Δ: Good, x: NG x ∘ ∘ ∘ Comparative Inventive Inventive Comparative Example Example Example Example 11 10 11 12 Surface Treatment With/Without surface treatment With With With With of MgO-containing Hydration treatment (Exposure to superheated steam 10-15 10-15 10-15 10-15 Particles at 250° C.) Layer thickness, μm Carbonation treatment (After heating at 500° C. under — — — — vacuum, exposure to CO.sub.2 gas at room temperature) Layer thickness, μm Chemical Free carbon component 16.9 16.9 16.9 16.9 Composition MgO 38.6 53.1 41.5 38.6 (mass %) Al.sub.2O.sub.3 43.5 0.0 0.0 0.0 ZrO.sub.2 0.0 26.7 37.3 40.0 Y.sub.2O.sub.3 0.0 2.3 3.2 3.5 SiC Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 1.0 1.0 1.0 1.0 Mass ratio (Al.sub.2O.sub.3/MgO) 1.13 0.00 0.00 0.00 State of Void layer thickness rate betweeb maximum-diameter 1.6 2.2 1.8 1.7 Microstructure MgO-containing particle and carbonaceous matrix, MS value (%) Continuity of void layer Almost Almost Almost Almost continuous continuous continuous continuous Presence or absence of compound with oxide (*) on Presence Presence Presence Presence surface of MgO-containing particle Quality after Maximum thermal expansion rate at temperature of 1.15 0.68 0.77 1.08 Burning up to 1500° C. Evaluation Result {circle around (1)} In-molten steel rotation test (wear resistance) ∘ ∘ ∘ ∘ {circle around (2)} Endurance limit temperature ΔT ° C. (thermal shock x700 ⊚1400 ∘1100 x700 resistance) {circle around (3)} Oxidation resistance — — — — {circle around (4)} Erosion/corrosion resistance ∘ ⊚ ⊚ ⊚ Comprehensive Evaluation: ∘: Excellent, Δ: Good, x: NG x ∘ ∘ x Comparative Inventive Inventive Example Example Example 13 12 13 Surface Treatment With/Without surface treatment With With With of MgO-containing Hydration treatment (Exposure to superheated steam 10-15 10-15 10-15 Particles at 250° C.) Layer thickness, μm Carbonation treatment (After heating at 500° C. under — — — vacuum, exposure to CO.sub.2 gas at room temperature) Layer thickness, μm Chemical Free carbon component 17.1 16.9 16.9 Composition MgO 39.0 41.5 41.5 (mass %) Al.sub.2O.sub.3 0.0 24.3 29.0 ZrO.sub.2 40.4 16.2 0.0 Y.sub.2O.sub.3 3.5 0.0 0.0 SiC 11.6 Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 0.0 1.0 1.0 Mass ratio (Al.sub.2O.sub.3/MgO) 0.00 0.59 0.70 State of Void layer thickness rate betweeb maximum-diameter <0.2 1.7 1.6 Microstructure MgO-containing particle and carbonaceous matrix, MS value (%) Continuity of void layer Discontinuous Almost Almost continuous continuous Presence or absence of compound with oxide (*) on Absence Presence Presence surface of MgO-containing particle Quality after Maximum thermal expansion rate at temperature of 1.15 0.68 0.86 Burning up to 1500° C. Evaluation Result {circle around (1)} In-molten steel rotation test (wear resistance) ∘ ∘ ∘ {circle around (2)} Endurance limit temperature ΔT ° C. (thermal shock x700 ⊚1500 ∘800 resistance) {circle around (3)} Oxidation resistance — — — {circle around (4)} Erosion/corrosion resistance ⊚ ⊚ ∘ Comprehensive Evaluation: ∘: Excellent, Δ: Good, x: NG x ∘ ∘

(44) TABLE-US-00004 TABLE 4 Comparative Comparative Inventive Inventive Example Example Example Example 9 14 14 15 Refractory Raw Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) Material Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 65 65 65 65 Fused magnesia −0.1 mm (mass %) 20 20 20 20 Alumina fine powder −0.1 mm (mass %) Spinel fine powder −0.1 mm (mass %) Graphite 0.1-1.0 mm (mass %) 15 15 15 15 Fine carbon −0.1 mm (mass %) Additive (*) Boron oxide (Mass % with respect to and in addition 0 0.2 0.3 0.5 to total amount) Phosphrous (Mass % with respect to and in addition pentaoxide to total amount) Silicon oxide (Mass % with respect to and in addition to total amount) Titanium oxide (Mass % with respect to and in addition to total amount) Borosilicate glass (Mass % with respect to and in addition to total amount) Binder Phenolic resin (Solid content of resin, mass % with 5 5 5 5 respect to and in addition to total amount) Particle Size of Content of −0.1 mm Mass % 24 24 24 24 Raw Material MgO-containing particles Surface With/Without surface treatment With With With With Treatment of Hydration treatment (Exposure to superheated steam at 250° C.) 10-15 10-15 10-15 10-15 MgO-containing Layer thickness, μm Particles Carbonation treatment (After heating at 500° C. under — — — — vacuum, exposure to CO.sub.2 gas at room temperature) Layer thickness, μm Inventive Inventive Inventive Comparative Example Example Example Example 4 16 17 15 Refractory Raw Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) Material Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 65 65 65 65 Fused magnesia −0.1 mm (mass %) 20 20 20 20 Alumina fine powder −0.1 mm (mass %) Spinel fine powder −0.1 mm (mass %) Graphite 0.1-1.0 mm (mass %) 15 15 15 15 Fine carbon −0.1 mm (mass %) Additive (*) Boron oxide (Mass % with respect to and in addition 1 2 3.2 3.3 to total amount) Phosphrous (Mass % with respect to and in addition pentaoxide to total amount) Silicon oxide (Mass % with respect to and in addition to total amount) Titanium oxide (Mass % with respect to and in addition to total amount) Borosilicate glass (Mass % with respect to and in addition to total amount) Binder Phenolic resin (Solid content of resin, mass % with 5 5 5 5 respect to and in addition to total amount) Particle Size of Content of −0.1 mm Mass % 24 24 24 24 Raw Material MgO-containing particles Surface With/Without surface treatment With With With With Treatment of Hydration treatment (Exposure to superheated steam at 250° C.) 10-15 10-15 10-15 10-15 MgO-containing Layer thickness, μm Particles Carbonation treatment (After heating at 500° C. under — — — — vacuum, exposure to CO.sub.2 gas at room temperature) Layer thickness, μm Comparative Comparative Inventive Inventive Example Example Example Example 9 14 14 15 Chemical Free carbon component 17.1 17.0 17.0 17.0 Composition MgO 82.9 82.8 82.7 82.5 (mass %) Al.sub.2O.sub.3 0.0 0.0 0.0 0.0 Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 0.0 0.19 0.3 0.5 Mass ratio (Al.sub.2O.sub.3/MgO) 0.0 0.0 0.0 0.0 State of Void layer thickness rate betweeb maximum-diameter <0.2 <0.2 0.4 1.2 Microstructure MgO-containing particle and carbonaceous matrix, MS value (%) Continuity of void layer Dis- Partially Almost Almost continuous continuous continuous continuous Presence or absence of compound with oxide (*) on surface Presence Presence Presence Presence of MgO-containing particle Quality after Maximum thermal expansion rate at temperature of up to 1.03 1.01 0.95 0.80 Burning 1500° C. Evaluation {circle around (1)} In-molten steel rotation test (wear resistance) ⊚ ∘ ∘ ∘ Result {circle around (2)} Endurance limit temperature ΔT ° C. (thermal shock x700 x700 ∘900 ∘1300 resistance) {circle around (3)} Oxidation resistance — — — — Comprehensive Evaluation: ∘: Excellent, Δ: Good, x: NG x x ∘ ∘ Inventive Inventive Inventive Comparative Example Example Example Example 4 16 17 15 Chemical Free carbon component 16.9 16.7 16.6 16.5 Composition MgO 82.1 81.3 80.4 80.3 (mass %) Al.sub.2O.sub.3 0.0 0.0 0.0 0.0 Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 1.0 1.9 3.0 3.1 Mass ratio (Al.sub.2O.sub.3/MgO) 0.0 0.0 0.0 0.0 State of Void layer thickness rate betweeb maximum-diameter 2.4 1.8 0.3 <0.2 Microstructure MgO-containing particle and carbonaceous matrix, MS value (%) Continuity of void layer Almost Almost Almost None continuous continuous continuous Presence or absence of compound with oxide (*) on surface Presence Presence Presence Presence of MgO-containing particle Quality after Maximum thermal expansion rate at temperature of up to 0.64 0.70 0.92 1.15 Burning 1500° C. Evaluation {circle around (1)} In-molten steel rotation test (wear resistance) ∘ ∘ ∘ ∘ Result {circle around (2)} Endurance limit temperature ΔT ° C. (thermal shock ⊚1500 ∘1500 ∘850 x700 resistance) {circle around (3)} Oxidation resistance — — — — Comprehensive Evaluation: ∘: Excellent, Δ: Good, x: NG ∘ ∘ ∘ x

(45) TABLE-US-00005 TABLE 5 Inventive Inventive Inventive Comparative Example Example Example Example 18 17 19 16 Refractory Raw Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) Material Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 65 65 65 65 Fused magnesia −0.1 mm (mass %) 20 20 20 20 Alumina fine powder −0.1 mm (mass %) Spinel fine powder −0.1 mm (mass %) Graphite 0.1-1.0 mm (mass %) 15 15 15 15 Fine carbon −0.1 mm (mass %) Additive (*) Boron oxide (Mass % with respect to and in addition 3.2 3.2 3.2 3.2 to total amount) Phosphrous pentaoxide (Mass % with respect to and in addition to total amount) Silicon oxide (Mass % with respect to and in addition to total amount) Titanium oxide (Mass % with respect to and in addition to total amount) Borosilicate glass (Mass % with respect to and in addition to total amount) Binder Phenolic resin (Solid content of resin, mass % with 5 5 5 5 respect to and in addition to total amount) Particle Size of Content of −0.1 mm Mass % 24 24 24 24 Raw Material MgO-containing particles Surface With/Without surface treatment With With With With Treatment of Hydration treatment (Exposure to superheated steam at 250° C.) 5-10 10-15 15-20 20-25 MgO-containing Layer thickness, μm Particles Carbonation treatment (After heating at 500° C. under — — — — vacuum, exposure to CO.sub.2 gas at room temperature) Layer thickness, μm Inventive Inventive Inventive Comparative Example Example Example Example 18 17 19 16 Chemical Free carbon component 16.6 16.6 16.6 16.6 Composition MgO 80.4 80.4 80.4 80.4 (mass %) Al.sub.2O.sub.3 0.0 0.0 0.0 0.0 Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 3.0 3.0 3.0 3.0 Mass ratio (Al.sub.2O.sub.3/MgO) 0.0 0.0 0.0 0.0 State of Void layer thickness rate betweeb maximum-diameter 0.2 0.3 3.0 3.2 Microstructure MgO-containing particle and carbonaceous matrix, MS value (%) Continuity of void layer Almost Almost Almost Almost continuous continuous continuous continuous Presence or absence of compound with oxide (*) on Presence Presence Presence Presence surface of MgO-containing particle Quality after Maximum thermal expansion rate at temperature of 1.00 0.92 0.54 0.52 Burning up to 1500° C. Evaluation Result {circle around (1)} In-molten steel rotation test (wear resistance) ∘ ∘ Δ x {circle around (2)} Endurance limit temperature ΔT ° C. (thermal shock ∘800 ∘850 ⊚1500 ⊚1500 resistance) {circle around (3)} Oxidation resistance — — — — Comprehensive Evaluation: ∘: Excellent, Δ: Good, x: NG ∘ ∘ ∘ x

(46) TABLE-US-00006 TABLE 6 Inventive Inventive Inventive Inventive Example Example Example Example 4 20 21 22 Refractory Raw Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) Material Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 65 65 65 65 Fused magnesia −0.1 mm (mass %) 20 20 20 20 Alumina fine powder −0.1 mm (mass %) Spinel fine powder −0.1 mm (mass %) Graphite 0.1-1.0 mm (mass %) 15 15 15 15 Fine carbon −0.1 mm (mass %) Additive (*) Boron oxide (Mass % with respect to and in addition 1 1 to total amount) Phosphrous (Mass % with respect to and in addition 1 pentaoxide to total amount) Silicon oxide (Mass % with respect to and in addition 1 to total amount) Titanium oxide (Mass % with respect to and in addition to total amount) Borosilicate glass (Mass % with respect to and in addition to total amount) Binder Phenolic resin (Solid content of resin, mass % with 5 5 5 5 respect to and in addition to total amount) Particle Size of Content of −0.1 mm Mass % 24 24 24 24 Raw Material MgO-containing particles Surface With/Without surface treatment With With With With Treatment of Hydration treatment (Exposure to superheated steam at 250° C.) 10-15 10-15 10-15 10-15 MgO-containing Layer thickness, μm Particles Carbonation treatment (After heating at 500° C. under — — — — vacuum, exposure to CO.sub.2 gas at room temperature) Layer thickness, μm Inventive Inventive Inventive Inventive Example Example Example Example 23 24 25 26 Refractory Raw Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) Material Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 65 65 65 65 Fused magnesia −0.1 mm (mass %) 20 20 20 20 Alumina fine powder −0.1 mm (mass %) Spinel fine powder −0.1 mm (mass %) Graphite 0.1-1.0 mm (mass %) 15 15 15 15 Fine carbon −0.1 mm (mass %) Additive (*) Boron oxide (Mass % with respect to and in addition 0.5 0.5 to total amount) Phosphrous (Mass % with respect to and in addition pentaoxide to total amount) Silicon oxide (Mass % with respect to and in addition 1 to total amount) Titanium oxide (Mass % with respect to and in addition 1 1 to total amount) Borosilicate glass (Mass % with respect to and in addition 1.5 to total amount) Binder Phenolic resin (Solid content of resin, mass % with 5 5 5 5 respect to and in addition to total amount) Particle Size of Content of −0.1 mm Mass % 24 24 24 24 Raw Material MgO-containing particles Surface With/Without surface treatment With With With With Treatment of Hydration treatment (Exposure to superheated steam at 250° C.) 10-15 10-15 10-15 10-15 MgO-containing Layer thickness, μm Particles Carbonation treatment (After heating at 500° C. under — — — — vacuum, exposure to CO.sub.2 gas at room temperature) Layer thickness, μm Inventive Inventive Inventive Inventive Example Example Example Example 4 20 21 22 Chemical Free carbon component 16.9 16.9 16.9 16.9 Composition MgO 82.1 82.1 82.1 82.1 (mass %) Al.sub.2O.sub.3 0.0 0.0 0.0 0.0 Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 1.0 1.0 1.0 1.0 Mass ratio (Al.sub.2O.sub.3/MgO) 0.0 0.0 0.0 0.0 State of Void layer thickness rate betweeb maximum-diameter 2.4 2.1 1.8 0.95 Microstructure MgO-containing particle and carbonaceous matrix, MS value (%) Continuity of void layer Almost Almost Almost Almost continuous continuous continuous continuous Presence or absence of compound with oxide (*) on surface Presence Presence Presence Presence of MgO-containing particle Quality after Maximum thermal expansion rate at temperature of up to 0.64 0.68 0.70 0.84 Burning 1500° C. Evaluation {circle around (1)} In-molten steel rotation test (wear resistance) ∘ ∘ ∘ ∘ Result {circle around (2)} Endurance limit temperature ΔT ° C. (thermal shock ⊚1500 ⊚1500 ⊚1500 ⊚1200 resistance) {circle around (3)} Oxidation resistance — — — — Comprehensive Evaluation: ∘: Excellent, Δ: Good, x: NG ∘ ∘ ∘ ∘ Inventive Inventive Inventive Inventive Example Example Example Example 23 24 25 26 Chemical Free carbon component 16.9 16.8 16.8 16.8 Composition MgO 82.1 81.7 81.7 81.7 (mass %) Al.sub.2O.sub.3 0.0 0.0 0.0 0.0 Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 1.0 1.4 1.4 1.4 Mass ratio (Al.sub.2O.sub.3/MgO) 0.0 0.0 0.0 0.0 State of Void layer thickness rate betweeb maximum-diameter 0.4 2.2 2.4 2.6 Microstructure MgO-containing particle and carbonaceous matrix, MS value (%) Continuity of void layer Almost Almost Almost Almost continuous continuous continuous continuous Presence or absence of compound with oxide (*) on surface Presence Presence Presence Presence of MgO-containing particle Quality after Maximum thermal expansion rate at temperature of up to 0.96 0.66 0.64 0.63 Burning 1500° C. Evaluation {circle around (1)} In-molten steel rotation test (wear resistance) ∘ ∘ ∘ ∘ Result {circle around (2)} Endurance limit temperature ΔT ° C. (thermal shock ∘850 ⊚1500 ⊚1500 ⊚1500 resistance) {circle around (3)} Oxidation resistance — — — — Comprehensive Evaluation: ∘: Excellent, Δ: Good, x: NG ∘ ∘ ∘ ∘

(47) TABLE-US-00007 TABLE 7 Inventive Inventive Inventive Inventive Example Example Example Example 3 27 28 29 Refractory Raw Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) Material Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 70 70 60 53 Fused magnesia −0.1 mm (mass %) 20 10 0 0 Alumina fine powder −0.1 mm (mass %) 10 30 10 Spinel fine powder −0.1 mm (mass %) 27 Graphite 0.1-1.0 mm (mass %) 10 10 10 10 Fine carbon −0.1 mm (mass %) Additive (*) Boron oxide (Mass % with respect to and in addition 1 1 1 1 to total amount) Phosphrous (Mass % with respect to and in addition pentaoxide to total amount) Silicon oxide (Mass % with respect to and in addition to total amount) Titanium oxide (Mass % with respect to and in addition to total amount) Borosilicate glass (Mass % with respect to and in addition to total amount) Binder Phenolic resin (Solid content of resin, mass % with 5 5 5 5 respect to and in addition to total amount) Particle Size of Content of −0.1 mm Mass % 22 11 0 31 Raw Material MgO-containing particles Surface With/Without surface treatment With With With With Treatment of Hydration treatment (Exposure to superheated steam at 250° C.) 10-15 10-15 10-15 10-15 MgO-containing Layer thickness, μm Particles Carbonation treatment (After heating at 500° C. under — — — — vacuum, exposure to CO.sub.2 gas at room temperature) Layer thickness, μm Inventive Inventive Example Example 30 31 Refractory Raw Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) Material Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 55 52 Fused magnesia −0.1 mm (mass %) 0 0 Alumina fine powder −0.1 mm (mass %) 35 38 Spinel fine powder −0.1 mm (mass %) Graphite 0.1-1.0 mm (mass %) 10 10 Fine carbon −0.1 mm (mass %) Additive (*) Boron oxide (Mass % with respect to and in addition 1 1 to total amount) Phosphrous (Mass % with respect to and in addition pentaoxide to total amount) Silicon oxide (Mass % with respect to and in addition to total amount) Titanium oxide (Mass % with respect to and in addition to total amount) Borosilicate glass (Mass % with respect to and in addition to total amount) Binder Phenolic resin (Solid content of resin, mass % with 5 5 respect to and in addition to total amount) Particle Size of Content of −0.1 mm Mass % 0 0 Raw Material MgO-containing particles Surface With/Without surface treatment With With Treatment of Hydration treatment (Exposure to superheated steam at 250° C.) 10-15 10-15 MgO-containing Layer thickness, μm Particles Carbonation treatment (After heating at 500° C. under — — vacuum, exposure to CO.sub.2 gas at room temperature) Layer thickness, μm Inventive Inventive Inventive Inventive Example Example Example Example 3 27 28 29 Chemical Free carbon component 12 12 12 12 Composition MgO 87.0 77.3 58.0 57.9 (mass %) Al.sub.2O.sub.3 0.0 9.7 29.0 29.0 Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 1.0 1.0 1.0 1.0 Mass ratio (Al.sub.2O.sub.3/MgO) 0.00 0.13 0.50 0.50 State of Void layer thickness rate betweeb maximum-diameter 2.1 2.1 2.1 2.1 Microstructure MgO-containing particle and carbonaceous matrix, MS value (%) Continuity of void layer Almost Almost Almost Almost continuous continuous continuous continuous Presence or absence of compound with oxide (*) on surface Presence Presence Presence Presence of MgO-containing particle Quality after Maximum thermal expansion rate at temperature of up to 0.80 0.85 0.98 0.98 Burning 1500° C. Evaluation {circle around (1)} In-molten steel rotation test (wear resistance) ∘ ∘ ∘ ⊚ Result {circle around (2)} Endurance limit temperature ΔT ° C. (thermal shock ∘1150 ∘1100 ∘850 ∘850 resistance) {circle around (3)} Oxidation resistance — — — — Comprehensive Evaluation: ∘: Excellent, Δ: Good, x: NG ∘ ∘ ∘ ∘ Inventive Inventive Example Example 30 31 Chemical Free carbon component 12 12 Composition MgO 51.5 49.1 (mass %) Al.sub.2O.sub.3 33.4 35.8 Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 1.0 1.0 Mass ratio (Al.sub.2O.sub.3/MgO) 0.65 0.73 State of Void layer thickness rate betweeb maximum-diameter 2.1 2.1 Microstructure MgO-containing particle and carbonaceous matrix, MS value (%) Continuity of void layer Almost Almost continuous continuous Presence or absence of compound with oxide (*) on surface Presence Presence of MgO-containing particle Quality after Maximum thermal expansion rate at temperature of up to 1.04 1.08 Burning 1500° C. Evaluation {circle around (1)} In-molten steel rotation test (wear resistance) ⊚ ⊚ Result {circle around (2)} Endurance limit temperature ΔT ° C. (thermal shock ∘800 Δ750 resistance) {circle around (3)} Oxidation resistance — — Comprehensive Evaluation: ∘: Excellent, Δ: Good, x: NG ∘ Δ

(48) TABLE-US-00008 TABLE 8 Inventive Inventive Inventive Inventive Inventive Example Example Example Example Example 32 33 3 34 35 Refractory Raw Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) Material Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 86 85 70 50 48 Fused magnesia −0.1 mm (mass %) 4 5 20 40 42 Alumina fine powder −0.1 mm (mass %) Spinel fine powder −0.1 mm (mass %) Graphite 0.1-1.0 mm (mass %) 10 10 10 10 10 Fine carbon −0.1 mm (mass %) Additive (*) Boron oxide (Mass % with respect to and in addition 1 1 1 1 1 to total amount) Phosphrous (Mass % with respect to and in addition pentaoxide to total amount) Silicon oxide (Mass % with respect to and in addition to total amount) Titanium oxide (Mass % with respect to and in addition to total amount) Borosilicate glass (Mass % with respect to and in addition to total amount) Binder Phenolic resin (Solid content of resin, mass % with 5 5 5 5 5 respect to and in addition to total amount) Particle Size of Content of −0.1 mm Mass % 4 5 22 45 47 Raw Material MgO-containing particles Surface With/Without surface treatment With With With With With Treatment of Hydration treatment (Exposure to superheated steam at 250° C.) 10-15 10-15 10-15 10-15 10-15 MgO-containing Layer thickness, μm Particles Carbonation treatment (After heating at 500° C. under — — — — — vacuum, exposure to CO.sub.2 gas at room temperature) Layer thickness, μm Inventive Inventive Inventive Inventive Inventive Example Example Example Example Example 32 33 3 34 35 Chemical Free carbon component 12 12 12 12 12 Composition MgO 87.0 86.9 87.0 87.0 87.0 (mass %) Al.sub.2O.sub.3 0.0 0.0 0.0 0.0 0.0 Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 1.0 1.0 1.0 1.0 1.0 Mass ratio (Al.sub.2O.sub.3/MgO) 0 0 0 0 0 State of Void layer thickness rate betweeb maximum-diameter 2.5 2.3 2.1 1.9 1.7 Microstructure MgO-containing particle and carbonaceous matrix, MS value (%) Continuity of void layer Almost Almost Almost Almost Presence of continuous continuous continuous continuous discontinuous portion (aggregated portion) Presence or absence of compound with oxide (*) on surface Presence Presence Presence Presence Presence of MgO-containing particle Quality after Maximum thermal expansion rate at temperature of up to 0.70 0.75 0.80 0.96 1.09 Burning 1500° C. Evaluation {circle around (1)} In-molten steel rotation test (wear resistance) Δ ∘ ∘ ∘ ∘ Result {circle around (2)} Endurance limit temperature ΔT ° C. (thermal shock ⊚1350 ⊚1200 ∘1150 ∘800 Δ750 resistance) {circle around (3)} Oxidation resistance — — — — — Comprehensive Evaluation: ∘: Excellent, Δ: Good, x: NG Δ ∘ ∘ ∘ Δ

(49) TABLE-US-00009 TABLE 9 Inventive Inventive Inventive Inventive Example Example Example Example 36 37 38 39 Refractory Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) 30 30 30 Raw Material Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) 22 22 22 Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 77 15 15 15 Fused magnesia −0.1 mm (mass %) 20 30 30 30 Alumina fine powder −0.1 mm (mass %) Spinel fine powder −0.1 mm (mass %) Graphite 0.1-1.0 mm (mass %) Fine carbon −0.1 mm (mass %) 3 3 3 3 Additive (*) Boron oxide (Mass % with respect to and in addition 1 1 1 1 to total amount) Phosphrous (Mass % with respect to and in addition pentaoxide to total amount) Silicon oxide (Mass % with respect to and in addition to total amount) Titanium oxide (Mass % with respect to and in addition to total amount) Borosilicate glass (Mass % with respect to and in addition to total amount) Al (Mass % with respect to and in addition to total amount) Si (Mass % with respect to and in addition to total amount) Al—Si alloy (Mass % with respect to and in addition 0 0.52 3.2 (Al:Si = 3:1) to total amount) Al—Mg alloy (Mass % with respect to and in addition (Al:Mg = 1:1) to total amount) B.sub.4C (Mass % with respect to and in addition to total amount) Binder Phenolic resin (Solid content of resin, mass % with 5 5 5 5 respect to and in addition to total amount) Particle Size Content of −0.1 mm Mass % 21 31 31 31 of Raw MgO-containing Material particles Surface With/Without surface treatment With With With With Treatment of Hydration treatment (Exposure to superheated steam at 250° C.) 10-15 10-15 10-15 10-15 MgO-containing Layer thickness, μm Particles Carbonation treatment (After heating at 500° C. under — — — — vacuum, exposure to CO.sub.2 gas at room temperature) Inventive Inventive Inventive Inventive Example Example Example Example 40 41 42 43 Refractory Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) 30 30 30 30 Raw Material Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) 22 22 22 22 Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 15 15 15 Fused magnesia −0.1 mm (mass %) 30 30 30 Alumina fine powder −0.1 mm (mass %) Spinel fine powder −0.1 mm (mass %) 45 Graphite 0.1-1.0 mm (mass %) Fine carbon −0.1 mm (mass %) 3 3 3 3 Additive (*) Boron oxide (Mass % with respect to and in addition 1 1 1 1 to total amount) Phosphrous (Mass % with respect to and in addition pentaoxide to total amount) Silicon oxide (Mass % with respect to and in addition to total amount) Titanium oxide (Mass % with respect to and in addition to total amount) Borosilicate glass (Mass % with respect to and in addition to total amount) Al (Mass % with respect to and in addition to total amount) Si (Mass % with respect to and in addition to total amount) Al—Si alloy (Mass % with respect to and in addition 3.2 3.2 3.2 6.6 (Al:Si = 3:1) to total amount) Al—Mg alloy (Mass % with respect to and in addition (Al:Mg = 1:1) to total amount) B.sub.4C (Mass % with respect to and in addition 0.5 1.6 1.6 to total amount) Binder Phenolic resin (Solid content of resin, mass % with 5 5 5 5 respect to and in addition to total amount) Particle Size Content of −0.1 mm Mass % 31 31 46 31 of Raw MgO-containing Material particles Surface With/Without surface treatment With With With With Treatment of Hydration treatment (Exposure to superheated steam at 250° C.) 10-15 10-15 10-15 10-15 MgO-containing Layer thickness, μm Particles Carbonation treatment (After heating at 500° C. under — — — — vacuum, exposure to CO.sub.2 gas at room temperature) Inventive Inventive Inventive Inventive Example Example Example Example 44 45 46 47 Refractory Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) 30 30 30 30 Raw Material Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) 22 22 22 22 Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 15 15 15 15 Fused magnesia −0.1 mm (mass %) 30 30 30 30 Alumina fine powder −0.1 mm (mass %) Spinel fine powder −0.1 mm (mass %) Graphite 0.1-1.0 mm (mass %) Fine carbon −0.1 mm (mass %) 3 3 3 3 Additive (*) Boron oxide (Mass % with respect to and in addition 1 1 1 1 to total amount) Phosphrous (Mass % with respect to and in addition pentaoxide to total amount) Silicon oxide (Mass % with respect to and in addition to total amount) Titanium oxide (Mass % with respect to and in addition to total amount) Borosilicate glass (Mass % with respect to and in addition to total amount) Al (Mass % with respect to and in addition 0.52 3.2 6.6 3.2 to total amount) Si (Mass % with respect to and in addition to total amount) Al—Si alloy (Mass % with respect to and in addition (Al:Si = 3:1) to total amount) Al—Mg alloy (Mass % with respect to and in addition (Al:Mg = 1:1) to total amount) B.sub.4C (Mass % with respect to and in addition 0.52 to total amount) Binder Phenolic resin (Solid content of resin, mass % with 5 5 5 5 respect to and in addition to total amount) Particle Size Content of −0.1 mm Mass % 31 31 31 31 of Raw MgO-containing Material particles Surface With/Without surface treatment With With With With Treatment of Hydration treatment (Exposure to superheated steam at 250° C.) 10-15 10-15 10-15 10-15 MgO-containing Layer thickness, μm Particles Carbonation treatment (After heating at 500° C. under — — — — vacuum, exposure to CO.sub.2 gas at room temperature) Inventive Inventive Inventive Inventive Example Example Example Example 48 49 50 51 Refractory Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) 30 30 30 30 Raw Material Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) 22 22 22 22 Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 15 15 15 15 Fused magnesia −0.1 mm (mass %) 30 30 30 30 Alumina fine powder −0.1 mm (mass %) Spinel fine powder −0.1 mm (mass %) Graphite 0.1-1.0 mm (mass %) Fine carbon −0.1 mm (mass %) 3 3 3 3 Additive (*) Boron oxide (Mass % with respect to and in addition 1 1 1 1 to total amount) Phosphrous (Mass % with respect to and in addition pentaoxide to total amount) Silicon oxide (Mass % with respect to and in addition to total amount) Titanium oxide (Mass % with respect to and in addition to total amount) Borosilicate glass (Mass % with respect to and in addition to total amount) Al (Mass % with respect to and in addition to total amount) Si (Mass % with respect to and in addition 0.52 3.2 6.6 3.2 to total amount) Al—Si alloy (Mass % with respect to and in addition (Al:Si = 3:1) to total amount) Al—Mg alloy (Mass % with respect to and in addition (Al:Mg = 1:1) to total amount) B.sub.4C (Mass % with respect to and in addition 0.52 to total amount) Binder Phenolic resin (Solid content of resin, mass % with 5 5 5 5 respect to and in addition to total amount) Particle Size Content of −0.1 mm Mass % 31 31 31 31 of Raw MgO-containing Material particles Surface With/Without surface treatment With With With With Treatment of Hydration treatment (Exposure to superheated steam at 250° C.) 10-15 10-15 10-15 10-15 MgO-containing Layer thickness, μm Particles Carbonation treatment (After heating at 500° C. under — — — — vacuum, exposure to CO.sub.2 gas at room temperature) Inventive Inventive Example Example 52 53 Refractory Fused magnesia Greater than 1.0 mm to 3.0 mm (mass %) 30 30 Raw Material Fused magnesia Greater than 0.5 mm to 1.0 mm (mass %) 22 22 Fused magnesia Greater than 0.1 mm to 0.5 mm (mass %) 15 15 Fused magnesia −0.1 mm (mass %) 30 30 Alumina fine powder −0.1 mm (mass %) Spinel fine powder −0.1 mm (mass %) Graphite 0.1-1.0 mm (mass %) Fine carbon −0.1 mm (mass %) 3 3 Additive (*) Boron oxide (Mass % with respect to and in addition 1 1 to total amount) Phosphrous (Mass % with respect to and in addition pentaoxide to total amount) Silicon oxide (Mass % with respect to and in addition to total amount) Titanium oxide (Mass % with respect to and in addition to total amount) Borosilicate glass (Mass % with respect to and in addition to total amount) Al (Mass % with respect to and in addition to total amount) Si (Mass % with respect to and in addition to total amount) Al—Si alloy (Mass % with respect to and in addition (Al:Si = 3:1) to total amount) Al—Mg alloy (Mass % with respect to and in addition (Al:Mg = 1:1) to total amount) 3.2 B.sub.4C (Mass % with respect to and in addition 1.6 to total amount) Binder Phenolic resin (Solid content of resin, mass % with 5 5 respect to and in addition to total amount) Particle Size Content of −0.1 mm Mass % 31 31 of Raw MgO-containing Material particles Surface With/Without surface treatment With With Treatment of Hydration treatment (Exposure to superheated steam at 250° C.) 10-15 15-20 MgO-containing Layer thickness, μm Particles Carbonation treatment (After heating at 500° C. under — — vacuum, exposure to CO.sub.2 gas at room temperature) Inventive Inventive Inventive Inventive Example Example Example Example 36 37 38 39 Chemical Free carbon component 5 5 5 5 Composition MgO 93.6 93.7 93.3 90.9 (mass %) Al.sub.2O.sub.3 0.0 0.0 0.0 0.0 Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 1.06 0.97 0.97 0.97 Mass ratio (Al.sub.2O.sub.3/MgO) 0 0 0 0 Al Si Al—Si alloy 0 0.5 3.0 (Al:Si = 3:1) Al—Mg alloy (Al:Mg = 1:1) B.sub.4C State of Void layer thickness rate betweeb maximum-diameter 1.2 1.4 1.4 1.4 Microstructure MgO-containing particle and carbonaceous matrix, MS value (%) Continuity of void layer Almost Almost Almost Almost continuous continuous continuous continuous Presence or absence of compound with oxide (*) on Presence Presence Presence Presence surface of MgO-containing particle Quality after Maximum thermal expansion rate at temperature of 1.05 0.95 0.96 1.02 Burning up to 1500° C. Evaluation {circle around (1)} In-molten steel rotation test (wear resistance) ⊚ ⊚ ⊚ ⊚ Result {circle around (2)} Endurance limit temperature ΔT ° C. (thermal shock ∘900 ∘1000 ∘950 ∘900 resistance) {circle around (3)} Oxidation resistance ∘ ∘ ⊚ ⊚ Comprehensive Evaluation: ∘: Excellent, Δ: Good, x: NG ∘ ∘ ∘ ∘ Inventive Inventive Inventive Inventive Example Example Example Example 40 41 42 43 Chemical Free carbon component 5 5 5 5 Composition MgO 90.5 89.6 59.2 88.1 (mass %) Al.sub.2O.sub.3 0.0 0.0 30.3 0.0 Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 0.97 0.97 0.97 0.97 Mass ratio (Al.sub.2O.sub.3/MgO) 0 0 0.5 0 Al Si Al—Si alloy 3.0 3.0 3.0 6.0 (Al:Si = 3:1) Al—Mg alloy (Al:Mg = 1:1) B.sub.4C 0.5 1.5 1.5 State of Void layer thickness rate betweeb maximum-diameter 1.3 1.1 1.2 1.0 Microstructure MgO-containing particle and carbonaceous matrix, MS value (%) Continuity of void layer Almost Almost Almost Almost continuous continuous continuous continuous Presence or absence of compound with oxide (*) on Presence Presence Presence Presence surface of MgO-containing particle Quality after Maximum thermal expansion rate at temperature of 1.03 1.08 1.08 1.10 Burning up to 1500° C. Evaluation {circle around (1)} In-molten steel rotation test (wear resistance) ⊚ ∘ ∘ ⊚ Result {circle around (2)} Endurance limit temperature ΔT ° C. (thermal shock ∘900 ∘800 ∘800 ∘800 resistance) {circle around (3)} Oxidation resistance ⊚ ⊚ ⊚ ⊚ Comprehensive Evaluation: ∘: Excellent, Δ: Good, x: NG ∘ ∘ ∘ ∘ Inventive Inventive Inventive Inventive Example Example Example Example 44 45 46 47 Chemical Free carbon component 5 5 5 5 Composition MgO 93.3 90.9 88.1 90.5 (mass %) Al.sub.2O.sub.3 0.0 0.0 0.0 0.0 Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 0.97 0.97 0.97 0.97 Mass ratio (Al.sub.2O.sub.3/MgO) 0 0 0 0 Al 0.5 3.0 6.0 3.0 Si Al—Si alloy (Al:Si = 3:1) Al—Mg alloy (Al:Mg = 1:1) B.sub.4C 0.5 State of Void layer thickness rate betweeb maximum-diameter 1.3 1.1 0.9 0.8 Microstructure MgO-containing particle and carbonaceous matrix, MS value (%) Continuity of void layer Almost Almost Almost Almost continuous continuous continuous continuous Presence or absence of compound with oxide (*) on Presence Presence Presence Presence surface of MgO-containing particle Quality after Maximum thermal expansion rate at temperature of 0.95 1.02 1.06 1.09 Burning up to 1500° C. Evaluation {circle around (1)} In-molten steel rotation test (wear resistance) ⊚ ⊚ ∘ ⊚ Result {circle around (2)} Endurance limit temperature ΔT ° C. (thermal shock ∘950 ∘900 ∘800 ∘850 resistance) {circle around (3)} Oxidation resistance ⊚ ⊚ ⊚ ⊚ Comprehensive Evaluation: ∘: Excellent, Δ: Good, x: NG ∘ ∘ ∘ ∘ Inventive Inventive Inventive Inventive Example Example Example Example 48 49 50 51 Chemical Free carbon component 5 5 5 5 Composition MgO 93.3 90.9 88.1 90.5 (mass %) Al.sub.2O.sub.3 0.0 0.0 0.0 0.0 Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 0.97 0.97 0.97 0.97 Mass ratio (Al.sub.2O.sub.3/MgO) 0 0 0 0 Al Si 0.5 3.0 6.0 3.0 Al—Si alloy (Al:Si = 3:1) Al—Mg alloy (Al:Mg = 1:1) B.sub.4C 0.5 State of Void layer thickness rate betweeb maximum-diameter 1.4 1.4 1.4 1.3 Microstructure MgO-containing particle and carbonaceous matrix, MS value (%) Continuity of void layer Almost Almost Almost Almost continuous continuous continuous continuous Presence or absence of compound with oxide (*) on Presence Presence Presence Presence surface of MgO-containing particle Quality after Maximum thermal expansion rate at temperature of 0.96 0.96 1.02 1.00 Burning up to 1500° C. Evaluation {circle around (1)} In-molten steel rotation test (wear resistance) ⊚ ∘ ∘ ∘ Result {circle around (2)} Endurance limit temperature ΔT ° C. (thermal shock ∘950 ∘900 ∘800 ∘800 resistance) {circle around (3)} Oxidation resistance ⊚ ⊚ ⊚ ⊚ Comprehensive Evaluation: ∘: Excellent, Δ: Good, x: NG ∘ ∘ ∘ ∘ Inventive Inventive Example Example 52 53 Chemical Free carbon component 5 5 Composition MgO 92.3 90.9 (mass %) Al.sub.2O.sub.3 0.0 0.0 Total of (B.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2, TiO.sub.2)(*) 0.97 0.97 Mass ratio (Al.sub.2O.sub.3/MgO) 0 0 Al Si Al—Si alloy (Al:Si = 3:1) Al—Mg alloy (Al:Mg = 1:1) 3.0 B.sub.4C 1.5 State of Void layer thickness rate betweeb maximum-diameter 0.8 0.5 Microstructure MgO-containing particle and carbonaceous matrix, MS value (%) Continuity of void layer Almost Almost continuous continuous Presence or absence of compound with oxide (*) on Presence Presence surface of MgO-containing particle Quality after Maximum thermal expansion rate at temperature of 1.05 1.09 Burning up to 1500° C. Evaluation {circle around (1)} In-molten steel rotation test (wear resistance) ∘ ⊚ Result {circle around (2)} Endurance limit temperature ΔT ° C. (thermal shock ∘850 ∘800 resistance) {circle around (3)} Oxidation resistance ⊚ ⊚ Comprehensive Evaluation: ∘: Excellent, Δ: Good, x: NG ∘ ∘

(50) Inventive Examples 1 to 7 and Comparative Examples 1 to 10 presented in Tables 1 and 2 are examples in which, regarding a group of refractory materials containing MgO as a primary component, i.e., using MgO-containing particles containing periclase as a primary component, an influence of the void layer thickness rate between the maximum-diameter MgO-containing particle and the carbonaceous matrix (MS value) was researched.

(51) In each of Inventive Examples 1 to 7 where the content of the free carbon component is 4 to 30 mass %; the MS value is 0.2 to 3.0%; and the content of B.sub.2O.sub.3 is 0.3 to 3 mass %, the maximum thermal expansion rate at temperatures of up to 1500° C. and the thermal shock resistance were good, and a good result could be also obtained in terms of the wear resistance.

(52) On the other hand, in each of Comparative Examples 1 to 4 where the MS value is less than 0.2%, it became impossible to obtain a good result in terms of the thermal shock resistance. In Comparative Examples 5 and 6, although the thermal shock resistance was enhanced because of a large content of graphite, the erosion/corrosion resistance deteriorated, so that the comprehensive evaluation was determined as (×). The increase of the content of graphite is a conventional technique for enhancing thermal shock resistance. A property of graphite having poor erosion/corrosion resistance (including chemical damage, mechanical damage such as abrasion, etc.) against molten steel is shown in the test result.

(53) Each of Comparative Examples 1 to 9 corresponds to at least one of: a refractory material in which the MgO-containing particles are not subjected to the surface treatment; a refractory material in which the content of B.sub.2O.sub.3 is not in the range of 0.3 to 3 mass % (no B.sub.2O.sub.3 is contained); and a refractory material in which the free carbon component is not in the range of 4 to 30 mass %.

(54) In Comparative Example 10 where the content of B.sub.2O.sub.3 is 1 mass %, and the content of the free carbon component is greater than 30 mass % although the MS value is 2.7%, the evaluation of the wear resistance was bad although the thermal shock resistance was excellent.

(55) Table 3 is an example in which an influence of the content of MgO and each component containing alumina, zirconia, alumina-zirconia and silicon carbide, as the additional refractory component, was researched.

(56) Inventive Examples where the content of MgO is 40 mass % or more, and the MS value is in the range of 0.2 to 3.0% show that excellent thermal shock resistance is exhibited in any combination with the components containing the above various refractory raw materials.

(57) In the example of Table 3, the erosion/corrosion resistance of each refractory material against molten slag during a casting operation was evaluated (circled 4: Evaluation of erosion/corrosion resistance in Table 3). In this test method, each of various refractory material samples (size: 20×20×160 mm) was immersed in molten steel at 1550° C. on which synthetic slag (C/S (mass ratio CaO/SiO.sub.2)=1.8) floated to have a thickness of about 30 mm, in such a manner to allow an interface between the molten slag and the molten steel to be located at a position away from a lower end of the sample by about 50 mm. After holding the immersed state for 60 minutes, the sample was pulled up, and, after being cooled to room temperature, the wear speed was calculated from a maximum dimensional change in a width direction before and after the immersion. When the wear speed was less than 25 μm/min, the sample was evaluated as Excellent (⊚), and, when it was 25 to 50 μm/min, the sample was evaluated as Good (∘). Further, when the wear speed was greater than 50 μm/min (but there was a remaining portion), the sample was evaluated as Acceptable (Δ), and, when there was no remaining portion, the sample was evaluated as NG (×). (⊚), (∘) and (Δ) were determined as usable (OK).

(58) This result shows that each of Inventive Examples and Comparative Examples in Table 3 is excellent in the thermal shock resistance, and therefore usable in casting operations giving large thermal shock. As regards the erosion/corrosion resistance, a refractory material using not only the MgO component but also a raw material containing the aforementioned various components exhibits better erosion/corrosion resistance. It is considered that this is due to influences of a relationship between the refractory composition and a composition, a degree of basicity or the like of slag, densification by a reaction between components within the refractory material, etc.

(59) FIG. 4 presents a result of research on an influence of the content of B.sub.2O.sub.3 in regard to a group of refractory materials in which the content of the free carbon component is 17 mass % (falling within the range of 4 to 30 mass %) and the MgO-containing particles is subjected to the surface treatment, in a group of refractory materials containing MgO as a primary component (a group of refractory materials using MgO-containing particles containing periclase as a primary component).

(60) In each of Inventive Examples where the content of B.sub.2O.sub.3 is in the range of 0.3 to 3 mass %, the MS value was 0.2 to 3.0%, and good results could be obtained in terms of all of the maximum thermal expansion rate at temperatures of up to 1500° C., the thermal shock resistance and the wear resistance.

(61) Differently, in Comparative Example 9 where no B.sub.2O.sub.3 is contained, and Comparative Example 14 where the content of B.sub.2O.sub.3 is 0.19 mass %, the MS value was less than 0.2%, and therefore it became impossible to obtain a good result in terms of the thermal shock resistance. Further, in Comparative Example 15 where the content of B.sub.2O.sub.3 is 3.1 mass %, it became impossible to obtain a good result in terms of the thermal shock resistance. This shows that, if the content of B.sub.2O.sub.3 is less than 0.3 mass %, a densification effect of the aforementioned MgO active layer becomes insufficient to cause difficulty in obtaining an MS value of 0.2% or more, and, if the content of B.sub.2O.sub.3 is greater than 3 mass %, a reaction product is excessively formed to cause disappearance of the void layer around each of the MgO-containing particles, resulting in failing to obtain the expansion lowering effect.

(62) Table 5 presents a result of research on a range of the MS value in regard to a group of refractory materials containing MgO as a primary component (a group of refractory materials using MgO-containing particles containing periclase as a primary component). In this research, samples were prepared by setting the content of B.sub.2O.sub.3 to 3 mass % (the maximum amount in the allocable range defined in the appended claims), and changing a level of the surface treatment for the MgO-containing particles.

(63) As seen in Table 5, in Inventive Example 18 where the MS value is 0.2% and Inventive Example 19 where the MS value is 3.0%, good results could been obtained in terms of all of the maximum thermal expansion rate at temperatures of up to 1500° C., the thermal shock resistance and the wear resistance. Differently, in Comparative Example 16 where the MS value is 3.2, although the maximum thermal expansion rate at temperatures of up to 1500° C. and the thermal shock resistance were good, large wear occurred, and therefore the comprehensive evaluation was determined as NG.

(64) Table 6 presents a result of research on, in a group of refractory materials containing MgO as a primary component (a group of refractory materials using MgO-containing particles containing periclase as a primary component), a refractory material using borosilicate glass as the B.sub.2O.sub.3 source, a refractory material using P.sub.2O.sub.5, SiO.sub.2 or TiO.sub.2 as a component (specific metal oxide) other than B.sub.2O.sub.3, and a refractory material using a combination of two or more specific metal oxides including B.sub.2O.sub.3. As the borosilicate glass, a type containing SiO.sub.2; 70 mass %, B.sub.2O.sub.3: 25 mass %, and RO (R=Na, K or Li): 5 mass %.

(65) In each of: Inventive Example 4 and Inventive Examples 20 to 23 where the specific metal oxides are added independently; Inventive Examples 24 and 25 where B.sub.2O.sub.3 is used in combination with the specific metal oxide other than B.sub.2O.sub.3; and Inventive Example 26 where silicate glass is used as the B.sub.2O.sub.3 source, good results could be obtained in terms of all of the maximum thermal expansion rate at temperatures of up to 1500° C., the thermal shock resistance and the wear resistance.

(66) Table 7 presents a result of research on an influence of the Al.sub.2O.sub.3 component.

(67) Inventive Examples 27, 28, 30 and 31 are examples in which a part of the MgO-containing particles is replaced with an alumina fine power as corundum. Observing these Inventive Examples on the basis of Inventive Example 3 where a mass ratio of (Al.sub.2O.sub.3/MgO) is 0, it is proven that the maximum thermal expansion rate at temperatures of up to 1500° C. becomes larger as the mass ratio is gradually increase to 0.13 (Inventive Example 27), 0.50 (Inventive Example 28) and 0.65 (Inventive Example 30). When the mass ratio is 0.65 (Inventive Example 30), the maximum thermal expansion rate at temperatures of up to 1500° C. increases to 1.04%, and when the mass ratio is 0.73 (Inventive Example 31), the maximum thermal expansion rate at temperatures of up to 1500° C. increases to 1.08% which is approximately close to the upper limit of the target value. Thus, the thermal shock resistance deteriorates to a level approximately equal to (Δ) although it falls with a usable range. The reason is as follows. Firstly, even if the thickness of the void layer around each of the MgO-containing particles is approximately the same, an absolute amount of the void layers (around the respective MgO-containing particles) becomes smaller along with an increase in amount of the alumina particles, because no void layer exists around each of the alumina particles. Secondly, a rigid skeletal structure formed with poor stress absorbing ability by the alumina particles becomes larger along with an increase in amount of the alumina particles. Thirdly, the alumina particles mixedly exist together with the MgO-containing particles in a fine particle fraction, and therefore a spinel formation reaction progresses with time.

(68) Further, in Inventive Example 29 where a part of the alumina source is replaced with spinal at the same mass ratio of (Al.sub.2O.sub.3/MgO) as that in Inventive Example 28 where the mass ratio increases to 0.50 by incorporating an alumina fine powder as corundum, a result equivalent to that in Inventive Example 28 could be obtained in each evaluation item.

(69) As is evident from the above results, the mass ratio of (Al.sub.2O.sub.3/MgO) is preferably set to 0.65 or less.

(70) Further, in view of a tendency of the erosion/corrosion resistance to be enhanced along with an increase in content of Al.sub.2O.sub.3, it can be assumed that, as long the mass ratio of (Al.sub.2O.sub.3/MgO) is in an adequate range, excellent erosion/corrosion resistance can be maintained without impairing soundness of the refractory microstructure and the expansion lowering effect, over a long period of timer of casting operation.

(71) Table 8 presents a result of research on an influence of a ratio of MgO-containing particles having a particle size of 0.1 mm or less to the entire MgO-containing particles. In Table 8, “ratio of MgO-containing particles having a particle size of −0.1 mm” means a ratio of a part of MgO-containing particles having a particle size of 0.1 mm or less, in a state at room temperature after the refractory material is subjected to the heat treatment in a non-oxidizing atmosphere at 1000° C., and on an assumption that an amount of the refractory material except for the free carbon component and boron oxide is 100 mass %. This applies to other Tables.

(72) In each of Inventive Examples 33 and 34 where a total amount of particles having a particle size of 0.1 mm or less among the MgO-containing particles is in the range of 5 to 45 mass %, good results could be obtained in terms of all of the maximum thermal expansion rate at temperatures of up to 1500° C., the thermal shock resistance and the wear resistance. On the other hand, in Inventive Example 32 where the content of particles having a particle size of 0.1 mm or less is 4 mass %, the wear resistance slightly deteriorates although it still falls within the usable range, and in Inventive Example 35 where the content is 47 mass %, the thermal shock resistance slightly deteriorates although it still falls within the usable range. The reason is considered as follows. Firstly, when the content of particles having a particle size of 0.1 mm or less among the MgO-containing particles is increased, a surface area of the particles in the refractory microstructure relatively increases, and thus the thickness of the void layer around each of the MgO-containing particles relatively decreases. Secondly, small particles can aggregate together as if they were one large particle having a void layer with a small thickness. These results show that, on the assumption that an amount of the refractory material except for the free carbon component is 100 mass %, the total amount of the particles having a particle size of 0.1 mm or less among the MgO-containing particles is preferably in the range of 5 to 45 mass %.

(73) Table 9 presents a result of research on an influence of addition of one or more metals or alloys selected from the group consisting of Al, Si and Mg, or addition of B.sub.4C, independently or in combination with one or more of the metals or alloys. As a test sample in Table 9, fine graphite (particle size: under 0.1 mm) was employed as particle-form carbon comprised of the free carbon components. The chemical composition of Al, Si, Mg or B.sub.4C in Table 9 is presented by mass %, on an assumption that an entire amount of the refractory material as measured after being subjected to a heat treatment in a non-oxidizing atmosphere at 600° C. before start of the heat treatment in a non-oxidizing atmosphere at 1000° C. is 100 mass %, and any other chemical component is presented by mass % as measured after the refractory material is subjected to a heat treatment in a non-oxidizing atmosphere at 1000° C.

(74) Inventive Examples 38, 39 and 43 correspond to a group of refractory materials comprising an Al—Si alloy containing metal Al and metal Si at a mass ratio of 3:1, and Inventive Examples 40 to 42 correspond to a group of refractory materials additionally using B.sub.4C in combination with the Al—Si alloy.

(75) Inventive Examples 44 to 46 correspond to a group of refractory materials containing only metal Al independently, and Inventive Example 47 corresponds to a refractory material using B.sub.4C in combination with the metal Al.

(76) Inventive Examples 48 to 50 correspond to a group of refractory materials containing only metal Si independently, and Inventive Example 51 corresponds to a refractory material using B.sub.4C in combination with the metal Si.

(77) Inventive Example 52 corresponds to a refractory material containing only B.sub.4C independently, and Inventive Example 53 corresponds to a refractory material comprising an Al—Mg alloy containing metal Al and metal Mg at a mass ratio of 1:1

(78) In Inventive Examples, respectively, using: Al—Si alloy; only metal Al; only metal Si; Al—Mg alloy; only B.sub.4C; B.sub.4C in combination with one or more of Al—Si alloy, metal Al and metal S, the oxidation resistance is excellent, as compared to Inventive Examples 36 and 37 where none of these alloys and the metals is contained. However, in Inventive examples using two or more of the alloys, the metals and B.sub.4C in combination, the thermal shock resistance is apt to slightly deteriorate. This shows that in view of the thermal shock resistance, it is desirable to avoid addition of a large amount of two or more of the metals, the alloys and B.sub.4C.

(79) In the above Inventive Examples, Al—Si alloy and Al—Mg alloy are used. Alternatively, a mixture of Al and Si or a mixture of Al and Mg may also be used to obtain the same effect.

LIST OF REFERENCE SIGNS

(80) 10: test piece 10a: edge 11: holder 12: crucible 13: molten steel 14: high-frequency induction furnace 20: refractory material of the present invention 21: power line portion (refractory material on back side) 22: nozzle body (refractory material on back side) 23: other refractory material for molten steel contact surface (e.g., CaO-based refractory material)