JP2000288697A - Refractory for continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a refractory for continuous casting which can integrally be formed and has excellent heat shock resistance at the using time and prevents the clogging of an immersion nozzle caused by the precipitation of Al2O3 without generating the crack at the firing time, by composing it of a specified wt. ratios of agalmatolite having specified grain diameter and carbon and the balance refractory oxide raw material. SOLUTION: This refractory is composed of 5-50 wt.% agalmatolite having <=150 μm grain diameter, <=7 wt.% carbon and the balance refractory oxide raw material. The refractory 3 is used for the inner hole part of an immersion nozzle body 1 and the lining of a spouting hole part, and in a part of the outer peripheral portion, a refractory 2 for powder line part is used. As the refractory oxide, alumine, zirconia, mullite, magnesia, etc., are used. For preventing the deposit of Al2O3 on the nozzle for casting, the effectiveness is obtained by using the material containing graphite as less as possible in a part of the nozzle. Further, in the case of using the agalmatolite, since the stress is released by hot-softening even when the thermal stress is loaded at the firing time, the crack is restrained and the heat shock resistance is drastically improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the use of a long nozzle used for pouring molten metal from a ladle to a tundish or the injection of molten metal from a tundish to a mold in continuous casting of metal such as steel. The present invention relates to prevention of blockage of an immersion nozzle or the like and prevention of adhesion of alumina (Al ₂ O ₃ ) of a long stopper.

[0002]

2. Description of the Related Art In continuous casting of steel, an immersion nozzle is used to inject molten steel from a tundish into a mold. FIG. 11 is a schematic view of a conventional immersion nozzle in which a powder line refractory 2 is provided on a main body 1 of the immersion nozzle. The purpose of using this immersion nozzle is to prevent the molten steel from coming into contact with the atmosphere, suppress the oxidation of the molten steel, prevent the molten steel from being scattered, and inject the molten steel in a rectified state. An object of the present invention is to prevent impurities such as floating slag and nonmetallic inclusions from being entrained in molten steel, to improve steel quality and at the same time to ensure operational stability.

[0003] One of the obstacles during the continuous casting operation is the obstruction of the immersion nozzle due to the adhesion of Al ₂ O ₃ precipitates to the inner wall of the immersion nozzle. If Al ₂ O ₃ precipitates on the inner wall of the immersion nozzle, casting conditions become unstable, and in severe cases, casting becomes impossible due to blockage of the nozzle inner hole, which is a major operational problem. In order to solve this problem, an inert gas is blown into the immersion nozzle, a material containing no carbon in the inner hole portion, or a ZrO ₂ -CaO-graphite material is used.

Matsui et al .: Refractory 49 (2) p64-7
3 (1997)}, generally used Al
₂ O ₃ - as compared to the graphite material, in the material which does not contain carbon, refractory - the molten steel gradient of Si interface than the molten steel side is very small, much smaller concentration gradient of carbon.
For this reason, if the temperature gradient is constant, the force F {see equation (1)} due to the interfacial tension gradient toward the refractory which Al ₂ O ₃ particles precipitated in the molten steel undergoes decreases. Since (dC / dx) in the equation (2) decreases, Al ₂ on the refractory wall surface
O ₃ deposition is greatly reduced.

F = (8πR ² K) / 3 (1) (where R is the particle radius and K is the interfacial tension gradient)

[0006] The interfacial tension gradient K is expressed by equation (2). K = [∂σ / ∂C] [dC / dx] + [∂σ / ∂T] [dT / dx] (2) (where σ is surface tension, C is concentration, T is temperature, x is displacement)

The use of a carbon-free material for the inner wall of the immersion nozzle and in the vicinity of the discharge hole is difficult because of the following problems.
It has the effect of controlling the adhesion of l ₂ O ₃ and preventing the clogging of the immersion nozzle.
It can be seen that since x) is reduced, there is an effect of preventing blockage.

Further, applying a material containing no carbon to the inner wall of the immersion nozzle is effective not only in preventing the clogging of the immersion nozzle but also in preventing the steel quality from deteriorating due to the elution of carbon into the steel.

Japanese Patent Application Laid-Open No. 8-57601 discloses a continuous casting in which a submerged nozzle body is formed of a refractory material containing carbon, and a portion through which molten steel passes and a portion in contact with the molten steel are covered with a refractory material containing no carbon. An application nozzle is disclosed.

In US Pat. No. 5,681,499, a refractory layer containing 10% by weight or less of carbon is disposed on the surface of a continuous casting nozzle, and graphite is oxidized and volatilized during preheating during use. This may form a layer containing no carbon.

Further, in Japanese Patent Application Laid-Open No. Hei 10-24351, 72 to 90% by weight of Al ₂ O _{3 and} 10 to ₂ % by weight of SiO ₂ are disclosed.
Al ₂ O ₃ -SiO ₂ system refractories consisting of 8% by weight is disclosed.

However, in the continuous casting nozzle described in Japanese Patent Application Laid-Open No. 8-57601, a joint made of a refractory mortar exists between the carbon-free material layer and the inner wall of the immersion nozzle. The discharge hole column may be broken due to the intrusion of the metal into the joint.

Further, in the continuous casting nozzle described in US Pat. No. 5,681,499, a graphite-containing refractory such as Al ₂ O ₃ -graphite material and carbon, which are usually used for a continuous casting nozzle body, are used. Since the difference between the thermal expansions of the materials containing no is very large, when the nozzle is actually used, there is a possibility that cracks may occur. Further, a raw material which promotes densification of a metal or the like is used for the purpose of making the thickness of the material layer containing no carbon constant, but the use of a metal causes an increase in elastic modulus and a decrease in thermal shock resistance. Further, the thermal shock resistance is greatly reduced by densification. Therefore, the possibility of cracking or breaking due to a decrease in thermal shock resistance of the nozzle due to these effects is very high. In addition, the rate of expansion and contraction due to heating is significantly different between the graphite-containing material and the material that does not contain carbon. Therefore, when a material that does not contain carbon is applied to the inner wall of the nozzle, the cracking rate in the firing process during manufacturing Is very high, which is a major manufacturing problem.

In the refractory described in Japanese Patent Application Laid-Open No. H10-24351, mullite is used to regulate the amount of Al ₂ O ₃ and to increase the amount of SiO ₂ for the purpose of improving thermal shock resistance. Since the fire resistance of mullite is SK37 or higher, the mullite is rigid in the operating temperature range, and thus the use of mullite has little effect of improving the thermal shock resistance. Therefore, it is considered that the thickness of the carbon-free material layer is preferably 10 mm. However, in the case where the nozzle is actually manufactured, the thickness of the carbon-free material layer in the vicinity of the discharge hole may be 10 mm or more. In addition, there is anxiety such as breakage or cracking during actual use.

Japanese Patent Application Laid-Open No. H10-166116 discloses a method using calcined limestone at 800 ° C. or higher to prevent cracking of refractories. There is a disadvantage that the softening property is lost.

[0016]

The problem to be solved by the present invention is that it can be integrally molded, has no cracks even when it is fired at the manufacturing stage, has a good manufacturing yield, and further has a problem in actual use. An object of the present invention is to provide a refractory for continuous casting which has excellent thermal shock resistance and is highly effective in preventing clogging of an immersion nozzle due to Al2O3 precipitation.

[0017]

According to the present invention, there is provided a method for producing a powder having a particle size of 150 μm.
This is a refractory for continuous casting comprising 5 to 50% by weight of rosacea having a particle size of m or less, 7% by weight or less of carbon, and the balance being a refractory oxide raw material.

[0018]

DETAILED DESCRIPTION OF THE INVENTION The present inventors have found that discussed with respect to Al ₂ O ₃ precipitation prevention of a continuous casting nozzle, by using a material which does not contain as much as possible the graphite part of the nozzle or the like, to prevent clogging It has been found that there is a great effect, and further, the use of rosacea suppresses the occurrence of cracks during firing and further significantly improves the thermal shock resistance. The continuous casting refractories, usually Al ₂ O ₃ - graphite, Al ₂ O ₃ -Si
O ₂ - graphite, ZrO ₂ - graphite material is used.
Graphite occupies most of the carbon content in these materials, and if graphite is removed, the amount of carbon is greatly reduced, which is sufficiently effective in preventing clogging.

However, the graphite-containing refractory and the non-graphite-containing material of the main body have significantly different shrinkage and expansion behavior upon heating. Therefore, a two-layer structure using a graphite-containing material for the main body and a graphite-free material for the inner wall is used. When a continuous casting nozzle having a structure is manufactured, cracks are likely to occur during firing.

Since graphite has a lower coefficient of thermal expansion than a refractory oxide raw material usually used as a refractory, a graphite-containing refractory has a much lower coefficient of thermal expansion than a material containing no graphite. Therefore, when placing the material which does not contain graphite inner wall of the nozzle for continuous casting, usually Al ₂ O ₃ is used in the body - of the nozzle cracking or breaking is generated by the difference in thermal expansion coefficient between the graphite material. As such, constituting at least a part of the nozzle with a material containing no graphite,
Significantly reduces thermal shock resistance.

When a metal is used as this material, the thermal shock resistance further decreases as the elastic modulus increases. Therefore, the use of metals should be avoided, but the addition of metals can be used within the scope of conventional techniques with minimal adverse effects.

However, since the thermal shock resistance is insufficient only by removing the metal, in the present invention, the uncalcined limestone is used. The coefficient of thermal expansion of the rosette is about 2% at 1000 ° C., which is a large value compared to graphite. However, the rosette has a property of softening and deforming at about 1000 ° C. or higher because of its low fire resistance. Due to this property, when the refractory of the present invention is simultaneously applied to the inner wall of the continuous casting nozzle for integral molding, the material is restricted by the material of the main body, so even if a thermal stress is applied to the material of the present invention during firing, the material is deformed by hot softening. However, cracks do not occur in both the main body and the refractory of the present invention in order to relieve the stress. Further, even in actual use, the stress is similarly relaxed due to deformation, so that there is a great effect in improving the thermal shock resistance.

In order to obtain the best effect of the present invention, it is preferable to use uncalcined rosacea, but it is also possible to use calcined materials at 800 ° C. or higher while suppressing the adverse effects.

When the refractory of the present invention is molded simultaneously with the main body at the same time, a method of filling each kneaded material into a predetermined position by using a core and a method of pre-forming the refractory portion of the present invention in advance For example, there is a method in which the base is formed by molding, and then the base is arranged at a predetermined position at the time of molding the main body and molded simultaneously and integrally.

In the present invention, the use amount of the rosacea is 5% by weight or more, but if it is less than 5% by weight, the contribution to the improvement of the thermal shock resistance is small and the production yield is deteriorated. If it is desired to further improve the thermal shock resistance and suppress the spalling occurrence rate to 0%, the content is desirably 10% by weight or more. In addition, rubble is usually used for continuous casting nozzles such as Al ₂ O ₃ and Z.
Since the corrosion resistance is inferior to rO ₂ , the use of rubble may be insufficient in erosion resistance depending on the use conditions depending on the use conditions.
Therefore, the use amount of the rosacea is preferably 50% by weight or less.

The raw material used for rosacea has a particle size of 150 μm.
If it exceeds m, the softening and deformation of the rosemite during heating is unlikely to occur, and conversely, the thermal shock resistance of the nozzle is significantly reduced due to the coefficient of thermal expansion of the rosemite. For this purpose, the particle size of the raw material used for the wax is preferably 150 μm or less. Further, the average particle size is desirably in the range of 30 μm to 100 μm. In a commercially available raw material, 150 μm
From the following, those up to 45 μm can be used.
The pyroxene used in the present invention is mainly composed of pyrophyllite, and pyroxene having a fire resistance of SK 29 to 32 is preferable. Then, SK26-29 sericite-based rubble can also be used. Although it is slightly inferior in hot softening property, SK33-36
Can also be used.

The refractory of the present invention has a carbon content of 7% by weight or less. Al that contains as little carbon as possible
To ₂ O ₃ precipitation prevention effect is large, when using a nozzle for continuous casting refractories of the present invention is usually not coated an antioxidant that is applied to the nozzle for the graphite-containing continuous casting inner wall of the nozzle In some cases. As a result, in the preheating stage performed before actual use, carbon is oxidized and disappears by volatilization, so that during use, the inner wall of the nozzle and the discharge port become a material that does not contain carbon, which greatly prevents nozzle clogging due to Al ₂ O ₃ precipitation. effective. In the present invention, the carbon content is
The content is 7% by weight or less, which is mainly carbon generated from an organic binder having a residual carbon such as a phenol resin used as a binder. . The same organic binder as that used for the material of the main body constituting the refractory for continuous casting is selected in order to improve the production yield.
Furthermore, if the carbon content is 5% by weight or less, the apparent porosity after oxidation can be kept small and within a certain range,
It can suppress the infiltration of molten steel during use and prevent exfoliation due to infiltration of molten steel. Further, the value of the apparent porosity after oxidation can be reduced to 18% or less. If the carbon content exceeds 7% by weight, the apparent porosity increases when the carbon disappears due to preheating, the base metal is easily infiltrated, and the material layer of the present invention may fall off.

In order to prevent clogging, it is desirable not to add graphite to the material of the present invention. However, since at least a part of the nozzle or the like is made of a material that does not contain graphite, thermal shock resistance is significantly reduced. Therefore, graphite can be added to a degree that does not adversely affect the blocking prevention effect. However, the amount of graphite to be added is limited to a range in which the total amount of carbon and binder carbon is 10% by weight or less.

As the refractory oxide used in the present invention, commercially available alumina, silica, zirconia, zircon, mullite, spinel, magnesia, and calcia are generally used regardless of whether they are electrofused products or sintered products. It is appropriately selected according to the above.

1 to 5 are schematic views showing a continuous casting nozzle according to the present invention. FIG. 1 shows an embodiment in which a refractory according to the present invention is applied to an inner hole portion and a discharge hole portion lining of a submerged nozzle body 1. 2 and 3 show a refractory immersion nozzle body 1 according to the present invention.
FIG. 4 shows an embodiment in which the refractory according to the present invention is applied to the inner hole of the long nozzle body, and FIG. 5 shows an embodiment in which the refractory according to the present invention is applied to the immersion nozzle body 1. This is an embodiment applied only to the section.

[0031]

EXAMPLES Example 1 Tables 1 and 2 show the results of examining the thermal shock resistance depending on the difference in the amount of rubble.

[0032]

[Table 1]

[0033]

[Table 2]

In the production, the raw materials shown in Tables 1 and 2 were mixed using pyrophyllite-based pyroxene which was not calcined, and an appropriate amount of carbon was adjusted so that the amount of carbon before oxidation became as shown in Tables 1 and 2. A phenolic resin is added and kneaded with an outer shell, and the core in such a manner that the material in Tables 1 and 2 is the inner wall and the main body is Al ₂ O ₃ -graphite material (hereinafter referred to as “AG material”). Is set in advance, and the potting clay is filled in the mold, and then the core is removed, and then simultaneously and simultaneously isostatically molded at a pressure of 1000 kg / cm ² and embedded in coke to a maximum temperature of 1000 ° C. Was carried out to produce a nozzle. The state of crack generation after firing was visually inspected by X-rays. To evaluate the yield after firing, 30 nozzles were manufactured and evaluated by the ratio of the number of nozzles having no abnormality (the larger the number, the better).

Further, a spalling test was performed using the manufactured nozzle. In the spalling test, the nozzle was preheated at a maximum temperature of 1000 ° C. for 90 minutes, allowed to cool for 5 minutes, then immersed in hot metal at 1600 ° C. for 1 hour, and then pulled out from the hot metal and allowed to cool. After completion of the test, cracks, cracks, and breaks were visually inspected. Ten tests were performed on one material, and the evaluation was made based on the number of cracks and the like that did not occur (the larger the number, the better the thermal shock resistance was. is there.). The thickness of the test material layer was 10 mm (allowable error +5 mm) at the inner hole and 25 mm near the discharge hole.

Further, an Al ₂ O ₃ adhesion test was performed to perform Al ₂ O ₃
The amount of adhesion and the state of infiltration of molten steel were investigated. In the test, molten steel was charged into a zirconia-graphite crucible, heated to 1600 ° C. in a high-frequency induction furnace, heated and melted, a sample was immersed in the molten steel, and then metal aluminum was charged into the molten steel. It was carried out by soaking for a time. The Al ₂ O ₃ adhesion state was evaluated by the thickness of the Al ₂ O ₃ adhesion layer (smaller numbers are better), and the molten steel infiltration state was evaluated by the thickness of the infiltration layer (smaller numbers were better). Further, the erosion rate was calculated from the dimensional change of the sample before and after the test, the ratio thereof was calculated and used as the erosion index in the evaluation of erosion (the smaller the number, the lower the erosion rate).

For the identification of the mineral phase, a commercially available X-ray diffractometer was used. The symbols of the mineral phases shown in the table are as follows. C
o: Corundum, Q: Quartz, M: Mullite, P: Recyclase, Z: ZrO ₂ (However, in this test, the ZrO ₂ raw material uses a partially stabilized ZrO ₂ raw material, so Z is marked. Has confirmed both ZrO ₂ (m) and ZrO ₂ (c).)

Table 3 shows No. No. 1 to No. 3 and No. 3
9 and No. 9 10 is a result of investigating a change in the yield after firing with a change in the use amount of the rosacea and a thermal shock resistance and a erosion state by a spall test. FIGS. 6 and 7 are graphs showing the results.

[0039]

[Table 3]

The quartz phase confirmed by X-ray diffraction was due to rubble, and was slightly confirmed even in those with a small amount of rubble. According to this, it can be seen that both the yield after baking and the thermal shock resistance are significantly improved when the amount of rosacea used is 5% by weight or more. Therefore, the amount of rosacea used is 5
% By weight or more is desirable. In addition, in the case of No. 5 in which the use amount of rubble was 55%. 11 shows that the erosion index is significantly increased. From this, it is understood that the use amount of the rosacea is desirably 50% by weight or less. No. 6 to No. 6 8 is the result of examining the type of oxidation-resistant raw material to be used, with the use amount of rubble being 30% by weight. Also in this case, the yield after firing is 100.
%, And the spall test was good without any cracks or the like. In comparison with this, no. 12 to No. 12 No. 14 has a very low yield after firing. As a result, in the case of using rubble as in the present invention, alumina, mullite, magnesia, zirconia, etc. can be used as a refractory aggregate.

In Table 4, No. No. 15 to No. 19 is the result of studying the particle size of the rosacea used.

[0042]

[Table 4]

As is apparent from these results, when using the waxite having a size of more than 150 μm and less than 500 μm, the spalling test results are poor, although there is a difference in the occurrence of the turtle, and the use of only the waxite having a size of 150 μm or less is performed. The results of the spalling test are good. From this result, it is desirable that the particle size of the raw material used is 150 μm or less.

No. 5 in Table 5 No. 20 to No. No. 24 is an example in which mullite was examined as a raw material for improving thermal shock resistance in addition to roesite. In this case, too, the yield after firing was low and the spalling test results were unfavorable.

[0045]

[Table 5]

In the refractory disclosed in Japanese Patent Application Laid-Open No. 10-24351, the use of mullite is said to be effective in improving the thermal shock resistance. However, in the present embodiment, the thickness of the carbon-free material is 25 mm at the maximum. It is considered that a crack occurred because of the above.

In Table 6, No. 4 and No. 4. 25 to No.
Reference numeral 28 is an evaluation of the state of infiltration of molten steel accompanying a change in the amount of carbon as a chemical component. Note that these carbons are carbons generated from the binder during firing. The state of infiltration was evaluated by the thickness of the infiltration layer of the molten steel. FIG. 10 is a graph showing the relationship between the amount of carbon before oxidation and the wet thickness.

[0048]

[Table 6]

According to the results, when the carbon content exceeds 7% by weight, the apparent porosity after oxidation increases greatly, and the thickness of the infiltration layer also greatly increases. No. 27 and N
o. In No. 28, some exfoliation was confirmed with the infiltration of the molten steel.
The same tendency is observed in the Al ₂ O ₃ adhesion test, and when the amount of carbon before oxidation is 10% by weight or more, the thickness of the deposited Al ₂ O ₃ greatly increases. If the carbon content is 7% by weight or less, the apparent porosity after oxidation is 18% or less, which is a range in which the infiltration of molten steel can be suppressed, so that refractories such as metals are densified. It is not necessary to use a raw material that increases the aging resistance and reduces the ripening resistance.

In Table 6, No. 4 and No. 4. No. 20 to No.
23 shows the results of tests on the amount of carbon before oxidation, the thickness of Al ₂ O ₃ adhered, and the apparent porosity after oxidation.

[0051]

[Table 7]

FIG. 8 is a graph showing the relationship between the amount of carbon before oxidation and the thickness of alumina adhered. The effect of preventing alumina adherence is satisfactory if the amount of carbon is 7% by weight or less. Therefore, the carbon content is preferably 7% by weight or less.

FIG. 9 is a graph showing the relationship between the amount of carbon before oxidation and the apparent porosity after oxidation. It can be seen that the apparent porosity after oxidation is desirably 18% or less.

Example 2 The material of No. 4 was lined in the discharge hole portion, and an immersion nozzle used for the liner portion was manufactured, and an actual machine test was conducted at a steel mill.
As a result, there was no crack or the like, and the device could be used for about 800 minutes. Furthermore, the amount of alumina adhered to the inner wall of the nozzle is very small, and the average thickness of deposited Al ₂ O _{3 on} the inner hole of the immersion nozzle after casting is as thin as 3 mm, and the molten steel surface during casting is stable. It was good. On the other hand, when the immersion nozzle using the same Al ₂ O ₃ -graphite material as the main body in the inner hole is used, there is no spalling such as cracks and cracks, and the melting of the powder line is also considered. However, since the discharge holes were blocked by the precipitation of Al ₂ O ₃ , replacement was required in about 400 minutes.
The average deposited thickness of ₂ O ₃ was about 40 mm.

[0055]

According to the present invention, cracks after firing are suppressed, and the thermal shock resistance is greatly improved by using rosacea in the carbon-free material used for the inner wall of the continuous casting nozzle. It has a great effect on suppressing alumina adhesion to the nozzle.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment in which the material of the present invention is applied to a immersion nozzle inner hole and a discharge hole lining.

FIG. 2 is a schematic view showing an embodiment in which the material of the present invention is applied only to the immersion nozzle discharge hole lining.

FIG. 3 is a schematic view showing an embodiment in which the material of the present invention is applied only to the immersion nozzle discharge hole lining.

FIG. 4 is a schematic view showing an embodiment in which the material of the present invention is applied to a long nozzle inner hole.

FIG. 5 is a schematic view showing an embodiment in which the material of the present invention is applied only to the inner hole of the immersion nozzle.

FIG. 6 is a graph showing a change in the post-firing yield with a change in the amount of use of rosacea.

FIG. 7 is a graph showing a result of a spall test according to a change in the amount of use of rubble.

FIG. 8 is a graph showing the relationship between the amount of carbon before oxidation and the thickness of alumina attachment.

FIG. 9 is a graph showing the relationship between the amount of carbon before oxidation and the apparent porosity after oxidation.

FIG. 10 is a graph showing the relationship between the amount of carbon before oxidation and the wet thickness.

FIG. 11 is a schematic view of a conventional immersion nozzle.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Main body, 2 Refractory for powder line parts, 3 Refractory of the present invention

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C04B 35/00 C04B 35/00 W (72) Inventor Koji Ogata 1-1-1, Higashihama-machi, Yawata-nishi-ku, Kitakyushu-shi, Fukuoka Prefecture No. Kurosaki Ceramics Co., Ltd. Technical Research Laboratory F-term (reference) 4E014 DA03 GA01 4G030 AA07 AA17 AA27 AA60 BA23 BA30 GA04 GA11 GA20 GA26 HA06 PA21

Claims (1)

[Claims] 1. A refractory for continuous casting comprising 5 to 50% by weight of rosacea having a particle size of 150 μm or less, 7% by weight or less of carbon, and a balance of a refractory oxide raw material.