JP5148963B2 - Continuous casting nozzle - Google Patents

Description

  The present invention relates to a technique for preventing damage to a continuous casting nozzle made of a tubular refractory structure having an inner hole through which molten metal such as molten steel passes in the axial direction. In the present invention, “tubular” means that the cross section in the direction perpendicular to the axial direction is not limited to a circular shape but includes an ellipse, a polygon, and the like.

  Continuous casting nozzles such as long nozzles that discharge molten steel from a ladle into a tundish and immersion nozzles that inject molten metal from a tundish into a continuous casting mold have an inner hole through which the molten steel passes in the vicinity of the center in the axial direction. It is composed of a tubular refractory structure, and when the molten steel passes through the inner hole, a temperature gradient is generated on the inner hole side and the outer peripheral side. In particular, when the molten steel starts to be discharged and passed, the inner hole side or the outer peripheral side is rapidly heated, and this phenomenon becomes remarkable.

  Such a temperature gradient causes stress distortion inside the refractory regardless of whether the refractory constituting the tubular refractory structure is a single layer or a plurality of layers, and cracks in the outer peripheral surface portion, etc. This is one of the causes of destruction, and the greater the temperature gradient, the higher the risk.

  As countermeasures against destruction caused by such thermal stress, conventionally, a refractory constituting a continuous casting nozzle (tubular refractory structure) contains a large amount of graphite, or fused silica having a small thermal expansion amount. In general, it is possible to prevent thermal stress failure by increasing the thermal conductivity, lowering the expansion, and lowering the elastic modulus of the refractory by adding them. However, on the other hand, increasing the amount of graphite or fused silica has a detrimental effect of reducing the durability due to a decrease in corrosion resistance, wear resistance, etc., due to a decrease in oxidation resistance and an increase in reactivity with molten steel components. So far, the refractory material with excellent thermal shock resistance has been used as the basic part of the tubular refractory structure. Damage to each part, for example, by installing a highly wear-resistant material with the minimum necessary thickness and installing a material with excellent corrosion resistance on the part that is affected by chemical erosion with slag, etc., immersed in molten steel The lifetime of the continuous casting nozzle has been extended by arranging appropriate materials according to the shape in a mosaic pattern.

However, in recent years, there has been a growing demand for continuous casting nozzles with high durability, stable casting, and improved cleanliness of molten steel. In response to these demands, the inner hole side of continuous casting nozzles in particular. As for, refractories on the outer peripheral side are being further reduced in carbon and functionality. Recently, materials that do not contain graphite at all, and materials that contain basic components that are excellent in wear resistance, erosion resistance, or adhesion prevention of inclusions such as alumina on the inner surface are applied to the inner hole side. It is not uncommon, and there is a tendency to increase the application of immersion nozzles and the like in which a refractory layer containing a CaO component, an MgO component, and a ZrO ₂ component is provided on the inner hole side.

However, the direction of technology related to the material of the inner-hole-side refractory layer related to high durability and stabilization is, as described above, low carbonization (high Al ₂ O ₃ component content), basicity, etc. Therefore, high thermal expansion is accompanied. Therefore, when these materials are installed on the inner hole side as the reinforcing layer of the outer refractory layer, the outer refractory layer is a heat generated by the temperature difference in the radial direction of the tubular refractory structure, particularly in the initial stage of casting. In addition to the thermal stress resulting from the difference in expansion, the inner hole side refractory layer having a large thermal expansibility is subject to a crack (radial compressive stress) from the inner hole side refractory layer. As a result, cracks or breaks in the vertical direction or the horizontal direction are likely to occur in the outer peripheral refractory layer.

  On the other hand, for example, in Patent Document 1, in order to prevent destruction due to thermal stress while aiming at high corrosion resistance and the like, a refractory layer having high thermal expansion and corrosion resistance not containing carbon is provided only on the inner hole side. In addition, a carbon-containing refractory layer with excellent spalling resistance is provided on the outer peripheral side to form a two-layer structure, and at least 80% or more of the contact surface between the refractory layers of this two-layer structure is made of polypropylene or nylon. A casting nozzle is disclosed which is separated by a separation layer formed by setting a combustible material such as the like at the time of molding and burning it off.

  However, in the casting nozzle of Patent Document 1, less than 20% of the contact surface between the refractory layers is bonded. Even if it is a slight adhesion portion, the cracking stress is transmitted from the inner hole side refractory layer to the outer periphery side refractory layer through this adhesion portion, so that it becomes the starting point of the cracking phenomenon. Further, when the bonded portion is 0%, there arises a basic problem that the inner hole side refractory layer cannot be held as a structure. Furthermore, the molten steel easily enters the separation layer, and when subjected to temperature changes, cracks occur in the refractory due to solidification shrinkage of the molten steel and expansion of the steel during heating, and the inner hole side refractory layer is on the outer peripheral side. There is a problem of peeling off because it is not bonded to the refractory layer.

  On the other hand, in Patent Document 2, a CaO nozzle containing 70 wt% or more of CaO and having an apparent porosity of 50% or less is incorporated in an immersion nozzle for the purpose of suppressing the adhesion of inclusions, and between this CaO nozzle and the base material nozzle. It is disclosed that a gap corresponding to the thermal expansion amount of the CaO nozzle is provided. Further, it is also disclosed that a CaO nozzle is fixed by packing a thin ceramic fiber or a small amount of mortar between the end of the CaO nozzle and the base material nozzle as necessary.

  However, a gap corresponding to the thermal expansion allowance of the CaO nozzle is provided between the inner hole side CaO nozzle (inner hole side refractory layer) and the outer peripheral side base material nozzle (outer peripheral side refractory layer). In the structure, it is described that it is preferable to provide a gap of 3% or more of the outer diameter of the CaO nozzle during preheating in paragraph 0022 of Patent Document 2, although it is possible to suppress the splitting phenomenon of the outer peripheral base metal nozzle due to the highly expanded CaO nozzle. It is considered that the inner hole side CaO nozzle and the outer peripheral side base material nozzle are not in close contact with each other (the thermal expansion coefficient of the CaO-based material is almost only CaO at about 1500 ° C.). The material with the highest coefficient of thermal expansion is about 2% or less.) If the CaO nozzle and the base material nozzle are not in close contact with each other during hot use, that is, when the nozzle is used, there is a risk that the internal nozzle will be displaced or dropped due to the compressive stress received during use. Also, since molten steel easily enters the gap between the CaO nozzle and the nozzle base material, the risk of damaging the CaO nozzle and the nozzle base material on the outer peripheral side due to solidification shrinkage of the molten steel and thermal expansion of the steel when subjected to temperature changes Accompanying sex.

  Thus, when the design of the joint part between the inner hole side refractory layer and the outer peripheral side refractory layer, such as the separation layer of Patent Document 1 and the gap of Patent Document 2, is too wide, the molten steel to the joint part There is a risk of peeling or damage to the inner refractory layer due to intrusion and damage to the outer refractory layer. If it is too narrow, vertical cracks may occur in the axial direction of the tubular refractory structure due to the tensile stress acting in the circumferential direction on the outer refractory layer due to thermal expansion of the inner refractory layer, Cracking damage (breaking in a direction having an angle with respect to the axial direction, so-called folding, etc.) is likely to occur.

Thus, in the case of a tubular refractory structure having a two-layer structure in which the inner hole side refractory layer is built in the outer peripheral side refractory layer, the outer peripheral side refractory layer is affected by the stress from the inner hole side refractory layer. The joint structure design has become a very important technology because it is strongly received, but there are few detailed joint designs and other measures for preventing damage to the tubular refractory structure.
JP 60-152362 A Japanese Patent Laid-Open No. 7-232249

  A problem to be solved by the present invention is a continuous casting nozzle comprising a tubular refractory structure having a two-layer structure of an inner hole side refractory layer and an outer periphery side refractory layer. Is to prevent damage.

  In order to solve the above-mentioned problems, the present inventor mainly deals with stress having two different directivities, namely stress mainly in the circumferential direction and stress mainly in the axial direction. We paid attention to the fact that each element has different damage forms.

  The thermal expansion of the refractory increases with increasing temperature, except for some zirconia. Therefore, in the continuous casting nozzle made of the tubular refractory structure targeted by the present invention, the inner hole side is at a higher temperature than the outer peripheral side, so that the inner hole can be formed even when the inner hole side is made of the same uniform material. The thermal expansion on the side becomes larger than the thermal expansion on the outer peripheral side. This tendency becomes more conspicuous when a layer composed of a plurality of different refractory layers and a layer of a material having a relatively higher thermal expansion coefficient than the outer peripheral side is installed on the inner hole side.

  The stress in the circumferential direction is caused by the high temperature on the inner hole side, and the outer peripheral side is compressed in the radial direction due to thermal expansion, which is converted into the tensile stress in the circumferential direction on the outer peripheral side, which mainly causes longitudinal cracks in the axial direction. Let

  On the other hand, the tubular refractory structure expands in the axial direction as the temperature of the inner hole rises due to the passage of molten steel, etc., but the thermal expansion coefficient of the inner hole side refractory layer is higher than that of the outer refractory layer. When it is larger than the expansion coefficient, a strong compressive stress is generated in the inner hole side refractory layer in the axial direction. The compressive stress acts on the outer peripheral refractory layer as an axial shear stress, which is converted into a tensile stress inside the outer peripheral refractory layer to tear the outer peripheral refractory layer in the axial direction. That is, the axial stress mainly causes lateral cracks such as lateral cracks, cracks, and folds. Conventionally, these axial compressive stresses, tensile stresses, transverse cracks and the like are hardly discussed.

  As described in the background section above, in recent years, the application of continuous casting nozzles with an inner-hole-side refractory layer having higher thermal expansion than the outer-side refractory layer has been promoted. In addition to the thermal stress associated with the temperature difference inside the material, the outer peripheral refractory layer has a tensile stress in the circumferential direction and an axial direction associated with the thermal expansion of the highly thermally expansible inner refractory layer as described above. Both shear stresses will be prominently received. For this reason, when the inner hole side has a layer having a higher thermal expansion than the outer peripheral side, the difference in the strain amount of each refractory layer caused by these stresses induces destruction, which is notable. Become. Note that the circumferential refractory layer is affected by the tensile stress in the circumferential direction and the shearing stress in the axial direction, and cracks in the oblique direction also occur.

  The present inventor can reduce the tensile stress in the circumferential direction and the shear stress in the axial direction by satisfying the following conditions in the continuous casting nozzle composed of the tubular refractory structure as described above. It has been found that damage can be prevented.

(Condition 1)
To suppress the compressive stress on the outer refractory layer by the inner hole refractory layer. That is, the inner hole side refractory is so formed that the tensile stress in the circumferential direction that occurs inside the outer peripheral refractory layer during preheating and casting and mainly causes vertical cracking is less than the fracture strength of the outer peripheral refractory layer. Provide a space layer with an appropriate thickness between the physical layer and the outer refractory layer.

(Condition 2)
In order to keep the inner hole side refractory layer in the outer periphery side refractory layer and prevent intrusion of molten steel into the space layer of the above condition 1 during the casting, the inner hole side refractory layer and the outer periphery Make sure that there is no space between the side refractory layers.

(Condition 3)
By slipping between the inner hole side refractory layer and the outer periphery side refractory layer with a shear stress of not more than the breaking (tensile) strength of each refractory layer, and shifting relative to the axial direction, To relieve the axial shear stress generated in the refractory layer.

Each of these conditions brings about the following effects.
(Condition 1)
The thermal expansion of the inner hole side refractory layer is absorbed by the space layer, the radial compressive stress exerted on the outer peripheral side refractory layer by the inner hole side refractory layer is suppressed, and the radial compressive stress is reduced to the outer peripheral side refractory layer. The outer peripheral refractory layer is caused by the tensile stress in the circumferential direction that is generated by the conversion inside and less than the fracture (tensile) strength of the outer refractory layer, and is caused by the tensile stress in the peripheral direction generated inside the outer refractory layer. Is prevented from breaking in the vertical direction.

(Condition 2)
The inner hole side refractory layer is in close contact with the outer hole side refractory layer without any gap between the inner hole side refractory layer and the inner hole side refractory layer is evenly distributed with the outer side refractory layer. Placed and fixed in the proper position. By such arrangement and fixation, a part of the inner hole side refractory layer locally contacts a part of the outer peripheral side refractory layer due to vibration or other causes caused by passage of molten steel at the time of casting, and the local Concentration of compressive stress is prevented. Furthermore, the penetration | invasion between refractory layers, such as molten steel which causes a push crack etc. of a tubular refractory structure, is prevented.

(Condition 3)
A sudden temperature change is applied during preheating or casting, and uneven and localized distribution of compressive stress occurs at the contact surface (boundary part) between the inner and outer refractory layers. Even if there is a factor that increases the frictional resistance such as irregularities on the contact surface between the inner refractory layer and the outer refractory layer, The inner hole side refractory layer has an outer side refractory layer by having a lubrication function capable of sliding with a shear stress less than the fracture (tensile) strength of the outer peripheral side refractory layer between the outer layer refractory layer and the outer refractory layer. It becomes possible to expand and contract smoothly in the axial direction independently of the layer. By separating the behavior of the inner hole side refractory layer and the outer periphery side refractory layer in this way, the axial tensile stress generated inside the outer periphery side refractory layer causes the outer peripheral side refractory layer to break (tensile). The strength is suppressed to less than the strength, and the lateral destruction of the outer peripheral refractory layer due to the axial tensile stress generated inside the outer peripheral refractory layer is prevented.

  Here, regarding the above condition 1, as described in the background art section, it has been disclosed that a space is conventionally provided between refractory layers. However, the conditions 2 and 3 have not been disclosed or suggested so far.

  That is, the present invention is configured so as to satisfy all of the above conditions 1 to 3, specifically, a tubular refractory structure having an inner hole through which molten metal passes in the axial direction, A part or all of the region of the tubular refractory structure includes an inner hole side refractory layer facing the inner hole and an outer peripheral side refractory layer positioned on the outer peripheral side of the inner hole side refractory layer, In the continuous casting nozzle in which the thermal expansion coefficient of the hole side refractory layer is larger than the thermal expansion coefficient of the outer peripheral side refractory layer, each refractory layer is interposed between the inner hole side refractory layer and the outer peripheral side refractory layer. The refractory layers having a solid lubricating function that allows the refractory layers to slide relative to each other under a shear stress not exceeding the fracture strength of the refractory layer, and the refractory layers are in close contact with each other between the heat of the inner hole of the molten metal temperature level. Therefore, the stress generated on the outer refractory layer due to thermal expansion of the inner refractory layer is reduced. And it is characterized in that it provided a space layer having a thickness of at normal temperature required to be less than the fracture strength of the peripheral side refractory layer.

  In the present invention, instead of providing a space layer between the inner hole side refractory layer and the outer periphery side refractory layer, the compressibility that is the same as that of the space layer and the same solid lubricating function as that of the lubrication layer is provided. A compressible lubricating layer may be provided. Specifically, between the inner hole side refractory layer and the outer peripheral side refractory layer, the solids that can slide with each other at a shear stress or less not exceeding the breaking strength of each refractory layer. Retractable lubrication that combines the lubrication function and the contractibility required to reduce the stress generated on the outer refractory layer by thermal expansion of the inner refractory layer to less than the fracture strength of the outer refractory layer Provide a layer.

  Further, the space between the inner hole side refractory layer and the outer periphery side refractory layer may be constituted only by a region provided with the above-described lubrication layer and space layer, or a region provided with the above-described contractible lubricant layer. Alternatively, these regions may be combined.

  According to the present invention, damage and destruction of the tubular refractory structure constituting the continuous casting nozzle can be prevented. In particular, when there is no lubrication layer and the inner hole side refractory layer and the outer peripheral side refractory layer are integrally bonded and molded, or a simple space layer called a void joint is formed on the inner hole side refractory layer and the outer peripheral side. It can be solved when it is formed between the refractory layer or when the inner hole side refractory layer is bonded to the outer periphery side refractory layer with mortar mainly composed of refractory aggregate. It is also possible to prevent damage and destruction due to lateral cracks and cracks.

  First, conditions 1 to 3 will be described in detail.

  Considering the temperature distribution during preheating and casting of the continuous casting nozzle, the thickness t (mm) at room temperature of the space layer for satisfying the above conditions 1 and 2 can be expressed by the following equation (1). .

(D / 2) × (Δα / 100−σ / E) <t <(D / 2) × α / 100 (1)
Here, α is the thermal expansion coefficient (linear expansion coefficient) (%) according to the measurement / evaluation method according to JIS R 2207 in the non-oxidizing atmosphere of the inner-hole-side refractory layer at 1500 ° C., and Δα is 1500 ° C. Difference in thermal expansion (%) between the inner hole side refractory layer and the outer peripheral side refractory layer, D is the outer diameter (mm) of the inner hole side refractory layer, and σ is the outer peripheral refractory layer patent No. 3459029 The tensile strength (MPa) by the measuring method of E, E represents the compression elastic modulus (MPa) of the inner hole side refractory layer.

  The above-mentioned “compression elastic modulus E” is obtained by compressing a test piece of, for example, φ30 × H100 mm at a room temperature within a range of a crosshead moving speed of 0.001 to 0.01 mm / sec using a material testing machine. P (N) and displacement can be measured and calculated by the following equation (a). Alternatively, a strain gauge is affixed to the side surface of the test piece, and the measured value of the strain gauge obtained by compressing the test piece using the same material testing machine as described above is used. Can also be calculated.

E =-((P1-P2) / S) / ((L1-L2) / L1) (a)
Here, S is the cross-sectional area (m ² ) of the test piece before compression, L1 is the height (m) of the test piece before compression, L2 is the height (m) of the test piece after compression, and P1 is the initial load. (N) and P2 represent load values (N) in the applied state.

  The upper limit value of the thickness t of the space layer defined by the above formula (1) is the thermal expansion allowance (change in radial direction length) of the inner hole side refractory layer at about 1500 ° C. corresponding to the temperature during continuous casting. Equal to the value.

  The lower limit value of the thickness t of the space layer can be derived from the following relational expressions (b) and (c). That is, the left side of the formula (b) shows the generated stress value when the inner hole side refractory layer is distorted. In the formula (b), the generated stress value indicates the tensile strength value of the outer refractory layer. Indicates a condition not exceeded. On the other hand, the strain ε of the inner hole side refractory layer can be expressed by the formula (c) from the difference in thermal expansion between the inner hole side refractory layer and the outer peripheral side refractory layer at 1500 ° C.

  E · ε <σ (b)

ε = ((D / 2) × Δα / 100−t) / (D / 2) (c)
Here, ε is the strain of the inner hole side refractory layer.

  The lower limit value of the thickness t of the space layer defined by the above formula (1) can be obtained from the formula (b) and the formula (c) as the following formula (d).

  (D / 2) × (Δα / 100−σ / E) <t (d)

  When a contractible lubricating layer is installed instead of the space layer, the contractible allowance tg (mm) represented by the following equation (3) for satisfying the above conditions 1 and 2 is It can be expressed by the following formula (4) based on the same idea as the thickness.

tg = W × K / 100 (3)
K: Shrinkage ratio (%) of the shrinkable lubricating layer
(Measured value of the sample after 1000 ° C reduction firing at normal temperature or 1000 ° C hot)
W: A gap (mm) between the inner hole side refractory layer and the outer peripheral side refractory layer at room temperature
(W is basically the initial thickness of the contractible lubricating layer, but includes the case where space coexists.)

  (D / 2) × (Δα / 100−σ / E) <tg <(D / 2) × α / 100 (4)

  Next, in order to satisfy the above condition 3, in the present invention, a lubricating layer is provided between the inner hole side refractory layer and the outer peripheral side refractory layer. In other words, this lubrication layer allows relative “slip” between the inner hole side refractory layer and the outer periphery side refractory layer, and the axial thermal expansion difference of each refractory layer. To alleviate stress generated inside the tubular refractory structure and prevent destruction of the refractory.

  More specifically, the inner-hole-side refractory layer that expands in the axial direction and expands in the axial direction due to the presence of the lubricating layer is the outer peripheral-side refractory layer whose elongation margin is smaller than that of the inner-hole-side refractory layer. Can extend in the axial direction independently. That is, without generating a tensile stress exceeding the fracture (tensile) strength of the outer refractory layer on the outer refractory layer, while reducing the compressive stress inside the inner refractory layer, Generation of axial tensile stress can be remarkably suppressed.

Furthermore, the present inventor used the compressive shear strength sh at 1500 ° C. between each refractory layer existing through the lubricating layer and cracking of the outer refractory layer as an index representing the degree of the lubricating function required for the lubricating layer. As a result of experimental investigation of the relationship with the phenomenon, it has been found that when the compression shear strength Sh (MPa) satisfies the following formula (2), no cracking phenomenon occurs in the outer refractory layer. In other words, this compressive shear strength Sh (MPa) represents the slip characteristic through the lubricating layer between the inner hole side refractory layer and the outer peripheral side refractory layer at a hot temperature of 1500 ° C.
0 <Sh ≦ 1.5 (2)

  As represented by the above formula (2), slip occurs between the inner hole side refractory layer and the outer peripheral side refractory layer with a compressive shear stress of 1.5 MPa or less at 1500 ° C. in the hot state. By providing a lubrication layer with a solid lubrication mechanism, the inner-hole refractory layer can easily expand and contract in the axial direction due to temperature changes during preheating, casting, etc., so axial stress is relieved. In addition, local stress concentration is less likely to occur in the outer refractory layer, and the outer refractory layer can be substantially free from breakage.

  This hot compressive shear strength Sh (MPa) is, for example, as shown in FIG. 6, a tubular refractory having a structure in which an outer refractory layer 1 is provided with an inner refractory layer via a lubricating layer 3. Using the structural sample, heat the entire sample up to 1500 ° C. in the furnace until the temperature stabilizes, and in this state, move only the inner hole side refractory layer 2 with the crosshead H. It compresses in the range of 0.001-0.01 mm / sec, the maximum load P (N) and displacement are measured, and it can obtain | require by following Formula (e).

Sh = P / A (e)
Here, A represents the area (m ² ) of the contact portion between the inner hole side refractory layer and the outer peripheral side refractory layer.

  In the measurement of the compressive shear strength, the shape of the sample is not particularly limited, and it can be cut out from the product (actual shape) or can be produced exclusively. Note that the measurement error tends to decrease as the area A of the contact portion increases, but the maximum load also increases, so the height of the sample may be within about 100 mm. The measurement atmosphere is preferably a non-oxidizing atmosphere, but by applying an antioxidant to the surface of the sample, measurement in an oxidizing atmosphere is possible.

  Next, a specific configuration and manufacturing method of the continuous casting nozzle of the present invention will be described.

  FIG. 1 shows an example of a continuous casting nozzle according to the present invention, in which (a) is a sectional view of the entire nozzle, and (b) to (f) are between an outer refractory layer and an inner hole refractory layer. It is an expanded sectional view showing an example of composition.

  The continuous casting nozzle shown in FIG. 1 is composed of a tubular refractory structure in which an inner hole side refractory layer 2 is housed in a part of the outer peripheral side refractory layer 1. In the example of FIGS. 1B to 1E, the lubricating layer 3 and the space layer 4 are installed between the outer peripheral side refractory layer 1 and the inner hole side refractory layer 2, and the example of FIG. Then, the contractible lubricating layer 5 is provided.

  As described above, the lubricating layer 3 is a solid in which the refractory layers 1 and 2 can slide relative to each other under a shear stress not exceeding the fracture strength of the outer refractory layer 1 and the inner hole refractory layer 2. Has a lubricating function.

  More specifically, the lubricating layer 3 is a refractory layer partly or entirely made of a material having a lubricating function, and the axial direction (longitudinal direction) of the refractory layers 1 and 2 is sheared. It is a layer having a function of causing “sliding” and “displacement (shearing)” regardless of whether it is plastic deformation or elastic deformation inside or outside its surface against stress.

  Such a lubricating layer has a layered or flat shape such as scaly graphite, boron nitride, talc, mica, etc., and itself has a fire resistance mainly composed of a raw material having a solid lubricating function (solid lubricating raw material). It is preferable to use a material.

  In order to stably maintain the solid lubricating function even at high temperatures, these solid lubricating raw materials have a smaller coefficient of friction, more uniform temperature distribution of the tubular refractory structure, that is, the generated stress. For suppression or the like, it is preferable that the thermal conductivity is high. In this respect, a graphite raw material is particularly preferable. Specifically, earthy graphite, scaly graphite, expanded graphite, artificial graphite, carbon black, crystallized carbon black and the like having a carbon purity of 80% or more can be used. In particular, scaly graphite having a purity of 90% or more is most preferable because it has higher thermal conductivity and higher lubricity. Boron nitride powder, talc, mica, etc. can also be used as the lubricating aggregate.

  These solid lubricating raw materials can be used by mixing one kind or plural kinds at an arbitrary ratio. Although the content ratio of these solid lubricating raw materials is preferably high, in order to stably maintain or improve the solid lubricating property of the surface even in a close contact state at a high temperature as a lubricating layer, it is 70% by mass or more. 90 mass% or more is more preferable. When the solid lubricating material is less than 70% by mass, the hot lubricity is not sufficient, and the lubricity satisfying the above formula (2) may not be obtained.

  The balance other than the solid lubricating raw material can contain one or more of binder components, metal powders, metal oxides, and the like.

  As binder components, organic binders such as acrylic resin, vinyl acetate resin, phenol resin, pitch, and tar can be used. Silicate solution such as water glass, colloidal binder containing metal components, aluminum phosphate In addition, it is possible to use a binder containing an inorganic component such as a metal alcoholate or an inorganic component, or a combination with an organic binder.

  However, in order not to lower the lubricating performance of the constituent raw materials, the amount of these binders should be kept to the minimum necessary.If there are many raw materials having a lubricating function, a lubricating layer can be formed even without the binder component. (For example, even with scaly graphite alone, shape retention and the like can be obtained by entanglement of raw material grains by press molding under certain conditions.)

  In order to install the lubricating layer on the tubular refractory structure, it is sufficient that the binder component undergoes a heat treatment or a drying treatment to an extent necessary for imparting shape retention to the lubricating layer. For example, heat treatment at about 1000 ° C. may be performed together with the refractory structure. Therefore, these binder components in the lubricating layer vary depending on conditions such as the temperature during the heat treatment in which they vary for each binder, but when the lubricating layer is heat treated at a low temperature, it is in the raw material stage in the cured state. When the components are substantially maintained and heat-treated at a high temperature, some or all of them are present as compounds such as carbon centering on amorphous carbon, metal carbides and metal oxides.

In order to improve the corrosion resistance and oxidation resistance performance of the lubricating layer portion, a metal oxide powder such as Al ₂ O ₃ , MgO, and SiO ₂ or a metal powder composed of one or more of Al, Mg, Si, Ti, and B components is used. Can be added. The metal powder improves the oxidation resistance and the holding strength of the inner hole side refractory layer by the outer peripheral side refractory layer after casting, but excessive addition is not preferable because it reduces the lubrication performance, and is less than 10% by mass. Is preferable.

  In order to form a lubricating layer between the inner hole side refractory layer and the outer peripheral side refractory layer of the tubular refractory structure, a powder raw material containing 70% by mass or more of a solid lubricating raw material is mixed with a binder component in advance. After forming the refractory layer constituting each refractory layer of the tubular refractory structure, the sheet-like lubrication layer is formed into a pipe shape to form the outer peripheral side refractory layer and the inner hole side refractory layer. It is possible to adopt a method of arranging them in between and simultaneously pressing them to form them integrally and heat-treating them.

  Further, when forming a refractory that constitutes each refractory layer of the tubular refractory structure without forming a soil in which a powder raw material containing 70 mass% or more of a solid lubricating raw material is mixed with a binder component into a sheet shape, It is also possible to use a method of filling between the outer periphery side refractory layer and the inner hole side refractory layer while being earthen and simultaneously pressurizing and integrally forming and heat-treating.

  In addition to the above, the inner hole side refractory layer, the outer periphery side refractory layer, and the lubrication layer are separately molded, and each layer that has undergone firing and processing is fixed with an adhesive such as mortar while forming a space. It is also possible to form a tubular refractory structure by, for example.

  The thickness of the lubrication layer is unevenness due to filling properties during molding of the inner hole side refractory layer or outer periphery side refractory layer (unevenness caused by the degree of dimensional change due to compression depending on the part) and in each refractory layer In view of the influence of unevenness due to the shape of the raw material, the thickness is preferably 0.3 mm or more.

  However, the lubrication layer may be in a product state (final form after all manufacturing processes) due to, for example, processing for forming radial through holes in the manufacturing process of nozzles for continuous casting or a structure by intentional design. ) May be open to the outside on the surface in contact with the molten steel. If it is too wide, it may cause the penetration of the molten steel or the destruction of the outer refractory layer due to the expansion of the penetrated steel. Therefore, it should be the minimum necessary thickness. Further, within the limited outer diameter and inner diameter of the tubular refractory structure, if the thickness of the lubricating layer is increased, the thickness of the inner hole side refractory layer and the outer peripheral side refractory layer must be reduced. For this reason, it is possible to suppress deterioration in durability due to erosion and wear of the inner hole side refractory layer, reduction in strength (section modulus) of the outer peripheral side refractory layer as a structure, and deterioration of the lubricating layer itself due to oxidation, etc. In view of the above, the radial thickness of the lubricating layer is preferably 3 mm or less.

  Here, when there is a large difference in elongation allowance due to thermal expansion between the inner hole side refractory layer and the outer peripheral side refractory layer, when these axial ends are fixed, stress concentrates in the vicinity of the fixed portion and the tubular refractory The risk of destruction of the structure (especially the outer refractory layer) is increased. Therefore, the inner hole side refractory layer and the outer peripheral side refractory layer are structured such that they are not firmly fixed to each other at least at one axial end, and the inner hole side refractory layer having a large thermal expansion margin is heated. It is preferable that the outer peripheral refractory layer having a small expansion is made to have a structure that does not cause or relaxes the stress compressing in the axial direction.

  Specifically, as shown in FIG. 1, when the inner hole side refractory layer is in an unconstrained state, when one end portion comes into contact with the tissue continuous with the outer peripheral side refractory layer, the other end portion ( Here, there is a structure in which a space (or a contractible material capable of obtaining a contractible allowance corresponding to the space) is installed in the upper end portion, or the following structure as shown in FIG.

(1) The outer peripheral refractory layer 1 having a small elongation allowance due to thermal expansion is not placed on the axial extension line of at least one end of the inner-hole refractory layer 1 having a large elongation allowance due to thermal expansion (FIG. 2 (a ))

(2) When the outer circumferential side refractory layer 1 having a small elongation allowance due to thermal expansion is also installed on the axial extension line of the inner-hole refractory layer 1 having a large elongation allowance due to thermal expansion, it is stretched between the two. A space 6 corresponding to the difference in cost is provided (FIG. 2B). This space 6 is preferably provided at a site where molten steel is difficult to enter.

(3) In the structure of (2) above, instead of the space 6, a refractory 7 having a contractible capacity sufficient to obtain a contraction allowance corresponding to a difference in elongation allowance between the refractory layers 1 and 2 is provided. Install (FIG. 2C).

  Also, as shown in FIG. 3, one end of each refractory layer 1, 2 in the axial direction is fixed (hereinafter, this end is referred to as "fixed side end"), and the other ends are mutually connected. When not firmly fixed (hereinafter, this end portion is referred to as “open side end portion”), the inner diameter of the outer peripheral side refractory layer 1 having a small elongation margin due to thermal expansion and the inner hole side refractory having a large elongation margin due to thermal expansion. The outer diameter of the layer 2 means that the diameter increases from the fixed side end toward the open side end or is linear (in the direction parallel to the axial direction), and the inner hole side refractory has a large expansion allowance due to thermal expansion. It is preferable that the elongation due to the thermal expansion of the physical layer 2 does not cause the tensile stress to be generated in the outer peripheral refractory layer 1 whose elongation is due to the thermal expansion.

  Next, the spatial layer 4 shown in FIG. 1 will be described in detail.

  The space layer 4 is installed so as to have a thickness that satisfies the above formula (1) at room temperature. Specifically, as shown in FIGS. 1B to 1D, the product state of the tubular refractory structure is shown. Between the lubricating layer 3 and the outer refractory layer 1, between the lubricating layer 3 and the inner hole refractory layer 2, or between both sides of the lubricating layer 3 or between the lubricating layers 3. It only has to exist in a form. When a plurality of space layers 4 are provided as shown in FIG. 1D, the total thickness of these space layers satisfies the above formula (1).

  As a method for forming such a space layer, the following method can be employed.

(1) When the above-described sheet-like lubricating layer is formed into a pipe shape and disposed between the outer peripheral refractory layer and the inner hole refractory layer and integrally molded at the same time, A flammable or volatile substance that disappears at the temperature of the firing step (up to about 1000 ° C.) on the surface of the pipe-shaped lubrication layer or the inner-hole-side refractory layer or outer-periphery-side refractory layer (for example, paper or paraffin) The sheet of organic material) is pasted and formed to a thickness satisfying the above formula (1), and then the combustible or volatile substance is eliminated by the heat treatment step of the tubular refractory structure, and lubrication is performed. Forming a layer and a space layer;

(2) When forming the lubricating layer integrally as a soil without pipe-like shape, between the lubricating layer and the inner hole side refractory layer or between the lubricating layer and the outer peripheral side refractory layer as described above. A sheet-like flammable or volatile substance is arranged and molded, and then the flammable or volatile substance is eliminated by a heat treatment step of the tubular refractory structure to form a lubricating layer and a space layer.

(3) In the method of forming the tubular refractory structure by separately forming the inner hole side refractory layer, the outer peripheral side refractory layer and the lubricating layer, and combining the fired and processed layers, the lubricating layer as described above And a flammable or volatile substance in the form of a sheet or liquid or powder between the inner hole side refractory layer or the lubrication layer and the outer peripheral side refractory layer, and arranged by a method such as coating, In the heat treatment process of the tubular refractory structure, the flammable or volatile substance is eliminated to form a space layer. That is, the outer peripheral side refractory layer, the inner hole side refractory layer, and the lubrication layer are prepared as separate “parts” and assembled together with the material forming the space layer with mortar or adhesive.

  It should be noted that the disappearing material for forming the space layer may be eliminated by preheating before use as a product of the tubular refractory structure instead of disappearing by the heat treatment step in the production of the tubular refractory structure. Is possible. In this case, it is preferable that the thermal stress disappears at a temperature of about 800 ° C. or less, more preferably about 500 ° C. or less.

  Next, the contractible lubricating layer 5 shown in FIG.

  The compressible lubricating layer 5 has a solid lubricating function that allows the refractory layers 1 and 2 to slide relative to each other under a shear stress not exceeding the fracture strength of the refractory layers 1 and 2, and the inner hole side between the heat. Combined with the contractibility required to make the stress generated on the outer refractory layer 1 due to the thermal expansion of the refractory layer 2 less than the fracture strength of the outer refractory layer 1, its resistance at 1000 ° C. The reduction allowance satisfies the above formula (4). That is, the contractible lubricating layer 5 has the functions of both the lubricating layer 3 and the space layer 4 described above, and the inner hole side is heated between 1000 ° C. and higher, including when the molten steel passes through about 1500 ° C. While maintaining the adhesion between the refractory layer and the outer refractory layer, it is possible to obtain a function that does not generate stress exceeding the breaking strength of the outer refractory layer.

  In order to form such a contractible lubricating layer, first, polyethylene powder that disappears by heat treatment is added to a powder raw material containing 70% by mass or more of the same solid lubricating raw material as used in forming the lubricating layer described above. Add the required amount of organic powder such as polypropylene and mix. Next, a binder is added to this mixed powder with a mixer, and kneading-granulating-sizing is performed to obtain granular secondary particles. Then, the soil composed of the secondary particles is filled and molded between the inner hole side refractory layer and the outer peripheral side refractory layer at the time of forming the tubular refractory structure, and then a predetermined heat treatment is performed. As a result, the above-mentioned organic powder disappears, and the air phase of the disappeared portion is dispersed inside and presents the compressibility that satisfies the above formula (4) and the lubrication that satisfies the above formula (2). A contractible lubricating layer having properties is obtained.

  The heat treatment temperature in this case may be a temperature set according to each specific product, but it is necessary to be at least the temperature at which the above-mentioned organic powder disappears. Further, by adjusting the blending amount of the organic powder, the volume ratio of the air phase in the contractible lubricating layer can be adjusted, whereby the contractible lubricating layer can satisfy the above formula (4). It can be adjusted to have a contractibility (contractable allowance tg).

  The contractible allowance tg in the above formula (4) can be obtained by measuring the contractible ratio K of the contractible lubricating layer as shown in the above formula (3).

  In order to measure the shrinkable ratio K, a compressible lubricating layer formed in a sheet shape with a predetermined molding pressure in advance using a material testing machine capable of controlling the temperature and atmosphere is, for example, φ20 × 50 mmL. Affixed to the end face of the refractory piece, put a refractory test piece (same refractory piece) of φ20 × 50mmL on the surface of the sheet-like shrinkable lubricant layer, and put the shrinkable lubricant layer into the refractory piece A test specimen for measurement sandwiched in between is prepared. Then, the thickness tg0 (mm) of the initial contractible lubricating layer is measured in an unweighted state.

  After holding this test piece at room temperature or a predetermined temperature (1000 ° C.), it is compressed from above and below in the range of a crosshead moving speed of 0.001 to 0.01 mm / sec to obtain a predetermined pressure (the shape of the tubular structure, each layer The test piece displacement amount h1 (mm) is measured when the pressure is increased to the appropriate value depending on the thermal expansion characteristics of the test piece.

  In order to measure the blank value at the same load and the same temperature of the refractory piece of the same material, pressurization is performed under the same conditions without sandwiching the compressible lubricating layer, and the displacement h2 (mm) is measured.

  The contractible ratio K (%) of the contractible lubricating layer is obtained by the following formula (e).

  K = (h1-h2) / tg0 × 100 (e)

[Example A]
In a long nozzle A (an outer diameter of 300 mm, an inner diameter of 210 mm, and a length of 1200 mm) having a flange portion as shown in FIG. 4, the outer peripheral refractory layer 1 is made of Al ₂ O ₃ —C material (Al ₂ O ₃ = 69 mass%). , Carbon = 31 mass%, and thermal expansion coefficient α = 0.65% at 1500 ° C., and the inner hole side refractory layer 2 is highly resistant to corrosion and has a large thermal expansion coefficient (MgO = 77%, FC = 23%, thermal expansion coefficient α at 1500 ° C. = 1.1%), and the inner hole side refractory layer 2 having a thickness of 15 mm is provided on the inner surface of the long nozzle on the entire inner surface in the axial direction. .

As the lubricating layer, a graphite sheet (0.4 mm thickness, 99% by mass of carbon component) is prepared, and several types of combustible sheets (0.2 mm, 0.5 mm, 0.7 mm, 1. 0 mm, 1.2 mm, and 1.3 mm) were attached, and each sheet was processed into a cylindrical shape. The graphite sheet and the flammable sheet processed into a cylindrical shape are mixed with the Al ₂ O ₃ —C outer periphery refractory layer of the earth mold and the MgO—C inner hole side refractory yes in the rubber mold for molding. After inserting between soils, it was molded by CIP (Cold Isostatic Pressing = cold isostatic pressing), and after heat treatment, a space layer having a thickness corresponding to the thickness of each combustible sheet was formed.

  For comparison, only a combustible sheet having the same thickness as that described above was provided in the same manner without providing a graphite sheet, and a space layer having the same thickness was formed after molding and heat treatment.

  Here, in the long nozzle A of this embodiment, the thermal expansion coefficient α of the inner hole side refractory layer 2 at 1500 ° C. is 1.1%, and the outer peripheral side refractory layer 1 and inner hole side refractory resistance at 1500 ° C. Thermal expansion coefficient difference Δα = 0.45% with the physical layer 2, outer diameter D = 240 mm of the inner hole side refractory layer 2, tensile strength σ = 5 (MPa) of the outer peripheral side refractory layer 1, inner hole side refractory Since the compression elastic modulus E at room temperature of the physical layer 2 is 3.0 GPa, the range of the thickness t of the space layer shown in the above formula (1) is 0.3 to 1.3 mm. That is, in the long nozzle A of the present embodiment, the refractory layers 1 and 2 are in close contact with each other when the temperature of the inner hole is 1500 ° C. or higher, and the thickness becomes zero, and the thermal expansion of the inner hole side refractory layer 2 The thickness at normal temperature required to make the stress generated on the outer refractory layer 3 less than the fracture strength of the outer refractory layer 2 is in the range of 0.3 to 1.3 mm. It is the range of the space layer of the present invention.

  For each of the long nozzles of Examples and Comparative Examples produced in this way, using a test apparatus schematically shown in FIG. 5, molten iron at 1500 ° C. was injected into the long nozzle A of each example, and thermal shock was applied. Later, the long nozzle A was lifted from the hot metal, cooled to room temperature, and then subjected to a similar pouring test to investigate the durability of the inner hole side refractory layer and the presence or absence of cracks in the outer peripheral side refractory layer.

  Further, the compression shear strength Sh at a hot temperature of 1500 ° C. was measured with a sample having a height of 100 mm cut out from these long nozzles by the method described above with reference to FIG. This compressive shear strength Sh serves as an indicator for determining whether or not the lubricating layer can provide a solid lubricating function that allows each refractory layer to slide relative to each other under a shear stress that does not exceed the fracture strength of each refractory layer. Thus, satisfying the above formula (2), that is, 0 <Sh ≦ 1.5 is the range of the shear stress of the present invention in this example.

  The results are shown in Table 1.

  In Table 1, Examples 1 to 5 have both the thickness of the space layer and the compressive shear strength Sh within the scope of the present invention, and good results were obtained without occurrence of cracks in the three pouring tests.

  On the other hand, in Comparative Example 1, the space thickness is 1.4 mm and the inner hole side refractory layer is not in close contact with the outer peripheral side refractory layer, and there was no problem in the first use, but in the second casting test The metal that had entered the joints led to a defect. Moreover, in Comparative Examples 2-7, although the thickness of the appropriate space layer was ensured, the crack accompanying a horizontal crack generate | occur | produced. This is because, as indicated by a compressive shear strength value of 1.8 MPa or more, the inner hole side refractory layer cannot freely expand and contract, and the frictional force between the inner hole side refractory layer and the outer peripheral side refractory layer is locally increased. It is thought that it occurred because it became large.

  Moreover, when Examples 1-5 which installed the graphite sheet as a lubrication layer and Comparative Examples 2-6 which did not install the graphite sheet by the thickness of the same space layer, compression shear strength Sh is set by installation of a graphite sheet. In Examples 1 to 5, a sufficient solid lubrication function is obtained by installing the graphite sheet.

  On the other hand, in Comparative Example 8 in which a graphite sheet is installed as a lubricating layer but does not satisfy the condition of the above formula (2), the inner hole side refractory, which is considered to be the influence of the hot metal that has entered the space layer in the second casting. The defect phenomenon of the material layer occurred. The measured value of the compressive shear strength Sh of Comparative Example 8 was zero, but this was outside the scope of the present invention because the thickness of the space layer was too large, and the inner hole side refractory layer and the outer periphery were hot at 1500 ° C. It is estimated that this is because the side refractory layer is not in close contact.

  In Comparative Example 9, since the thickness of the space layer was too small, the compressive shear strength Sh was 1.7 MPa even in the presence of the lubricating layer, and vertical cracks occurred in the outer refractory layer after the first casting.

  A test similar to the above was performed on a cylindrical refractory having an outer diameter of 130 mm and an inner diameter of 80 mm. The same result was obtained, and the validity of the present invention could be confirmed.

[Example B]
For the purpose of investigating the relationship between the graphite content and the compressive shear strength Sh in the lubricating layer, a 0.4 mm thick graphite sheet was formed at the ratios shown in Examples 6 to 10 and Comparative Example 10 in Table 2.

  Similar to Example A, these graphite sheets were arranged between the outer peripheral side refractory layer and the inner hole side refractory layer of the same long nozzle, and were simultaneously formed so that the thickness of the space layer was 0.6 mm. . Thereafter, the compression shear strength Sh was measured using a sample cut out at a height of 100 mm from the fired long nozzle.

  In Examples 6 to 10, the compression shear strength Sh was within 1.5 MPa within the range of the present invention, and a good solid lubricating function was obtained. On the other hand, Comparative Example 10 uses a graphite sheet with the graphite amount reduced to 65% by mass, and the flexibility to make the graphite sheet cylindrical at the time of cylindrical processing at the molding stage is not sufficient. , Cracks easily occur, and as a result, the compressive shear strength Sh exceeded 1.5 MPa, which was outside the scope of the present invention.

[Example C]
In this example, a contractible lubricating layer having the functions of the lubricating layer and the space layer described above was installed.

First, scaly graphite exhibiting solid lubricity, organic powder (polypropylene powder) that disappears by heat treatment to form a space, refractory powder (Al ₂ O ₃ powder), and metal powder (Al -Mg alloy powder), a raw material composed of a phenol resin as a binder that imparts shape retention and bonding strength from room temperature to high temperature range is blended in the proportions shown in Table 3, and kneaded and granulated with a high speed mixer Then, secondary particles (hereinafter referred to as “contractable secondary particles”) were obtained.

  The shrinkable ratio after reduction firing of the contractible secondary particles calculated from the specific gravity of each raw material particle is 20% in the calculation because the volume ratio of the organic powder under the closest packing is 60 vol%. is there.

  Measure the shrinkable ratio K of the sample that was molded into a sheet shape under the same molding pressure (about 50 MPa) as the conditions for molding the contractible secondary particles for the actual product, using the above formula (e). It was found to be 18% based on the value, and a contractible rate almost the same as the target value (20%) set by calculation was obtained.

  The thickness of the shrinkable secondary particles having a shrinkage ratio of 18% is set between the outer periphery side refractory layer and the inner hole side refractory layer using a double cylinder. It arranged so that it might be set to 3 mm, and it integrally formed by CIP. And the molded object was dried and heat-processed in reducing environment.

  In this way, a continuous casting nozzle having a 3 mm contractible lubricating layer having both lubricity and contractibility between the outer peripheral side refractory layer and the inner hole side refractory layer was obtained. That is, the contractible allowance tg of this contractible lubricating layer satisfied the above formula (4), and the continuous casting nozzle provided with this contractible lubricating layer satisfied the above formula (2).

  When the obtained continuous casting nozzle was subjected to three pouring tests in the same manner as in Example A, problems such as cracks, peeling, and metal intrusion did not occur and good results were obtained.

An example of the nozzle for continuous casting of this invention is shown, (a) is the whole sectional drawing, (b)-(f) shows the structural example between an outer peripheral side refractory layer and an inner-hole side refractory layer. It is an expanded sectional view. It is sectional drawing which shows the preferable example of arrangement | positioning with the outer peripheral side refractory layer and inner-hole side refractory layer in this invention. It is sectional drawing which shows the other preferable example of arrangement | positioning with the outer peripheral side refractory layer and inner-hole side refractory layer in this invention. It is sectional drawing which shows the Example of the nozzle for continuous casting of this invention. It is a schematic diagram which shows the pouring test apparatus by the nozzle for continuous casting (long nozzle). It is a schematic diagram which shows the apparatus which measures the compressive shear strength between an inner-hole side refractory layer and an outer peripheral side refractory layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Outer peripheral side refractory layer 2 Inner hole side refractory layer 3 Lubrication layer 4 Spatial layer 5 Retractable lubrication layer 6 Space 7 Refractory which has contractibility

Claims (8)

It consists of a tubular refractory structure having an inner hole through which molten metal passes in the axial direction, and a part or all of the region of the tubular refractory structure has an inner hole-side refractory layer facing the inner hole and the inner hole. In a continuous casting nozzle comprising an outer peripheral refractory layer located on the outer peripheral side of the side refractory layer, the thermal expansion coefficient of the inner hole side refractory layer being larger than the thermal expansion coefficient of the outer peripheral side refractory layer,
Lubrication having a solid lubrication function between the inner hole side refractory layer and the outer peripheral side refractory layer so that the refractory layers can slide relative to each other under a shear stress not exceeding the breaking strength of the refractory layers. A continuous casting nozzle, characterized in that a layer and a space layer having a thickness t (mm) at room temperature satisfying the following formula (1) are provided.
(D / 2) × (Δα / 100−σ / E) <t <(D / 2) × α / 100 (1)
α: Thermal expansion coefficient of inner-hole refractory layer at 1500 ° C (%)
Δα: Difference in thermal expansion coefficient (%) between the inner hole side refractory layer and the outer peripheral side refractory layer at 1500 ° C.
D: Outer diameter of inner hole side refractory layer (mm)
σ: Tensile strength of outer refractory layer (MPa)
E: Compression elastic modulus (MPa) of the inner hole side refractory layer The nozzle for continuous casting according to claim 1 , wherein the compressive shear strength Sh (MPa) between the inner hole side refractory layer and the outer peripheral side refractory layer at 1500 ° C satisfies the following formula (2).
0 <Sh ≦ 1.5 (2) The lubricating layer contains at least 70% by mass in total of at least one selected from the group consisting of graphite, boron nitride, talc and mica, and the balance is selected from the group consisting of binder component, metal powder and metal oxide powder The nozzle for continuous casting according to claim 1 or 2 comprising the above and inevitable components. It consists of a tubular refractory structure having an inner hole through which molten metal passes in the axial direction, and a part or all of the region of the tubular refractory structure has an inner hole-side refractory layer facing the inner hole and the inner hole. In a continuous casting nozzle comprising an outer peripheral refractory layer located on the outer peripheral side of the side refractory layer, the thermal expansion coefficient of the inner hole side refractory layer being larger than the thermal expansion coefficient of the outer peripheral side refractory layer,
A solid lubricating function that allows the refractory layers to slide relative to each other under a shear stress that does not exceed the breaking strength of the refractory layers between the inner hole side refractory layers and the outer periphery side refractory layers ; A compressible lubricating layer having compressibility is provided , and the contractible allowance tg (mm) of the compressible lubricating layer represented by the following formula (3) satisfies the following formula (4). A nozzle for continuous casting.
tg = W × K / 100 (3)
K: Shrinkage ratio (%) of the shrinkable lubricating layer
(Measured value of the sample after 1000 ° C reduction firing at normal temperature or 1000 ° C hot)
W: A gap (mm) between the inner hole side refractory layer and the outer peripheral side refractory layer at room temperature
(D / 2) × (Δα / 100−σ / E) <tg <(D / 2) × α / 100 (4)
α: Thermal expansion coefficient of inner-hole refractory layer at 1500 ° C (%)
Δα: Thermal expansion coefficient difference (%) between the outer refractory layer and the inner hole refractory layer at 1500 ° C.
D: Outer diameter of inner hole side refractory layer (mm)
σ: Tensile strength of outer refractory layer (MPa)
E: Compression elastic modulus (MPa) of the inner hole side refractory layer 5. For continuous casting according to claim 4 , wherein the compressive shear strength Sh (MPa) between the inner hole side refractory layer and the outer peripheral side refractory layer at 1500 ° C. satisfies the following formula (2). nozzle.
0 <Sh ≦ 1.5 (2) The contractible lubricating layer contains at least 70% by mass in total of at least one selected from the group consisting of graphite, boron nitride, talc and mica, and the balance is selected from the group of binder component, metal powder and metal oxide powder The nozzle for continuous casting according to claim 4 or 5 , comprising at least one of the above and inevitable components. At least one axial end of the inner bore-side refractory layer, for continuous casting according to any one of claims 1 to 6 in the axial direction is a non-constrained state with respect to the outer circumference side refractory layer nozzle. One end in the axial direction of the outer peripheral side refractory layer and the inner hole side refractory layer is fixed, and the other end is not fixed to each other, the inner diameter of the outer peripheral side refractory layer and the inner hole side refractory continuous casting nozzle according outer diameter, to claim 7, which is formed in parallel from said one end to, or axially diameter increases toward the other end of the layer.

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