WO2020013662A1 - Magnesia-carbon basic castable for secondary refining furnace - Google Patents

Abstract

A magnesia-carbon basic castable for a secondary refining furnace is provided. The magnesia-carbon basic castable of the present invention comprises, as a basic composition, a main material comprising, in wt%, 87-91% of a magnesia clinker, 2-4% of crystalline graphite, 1-2% of graphite microparticles, 2-4% of a pitch powder, 4-5% of a silicon powder, and the balance of inevitable impurities, and comprises an additive comprising, on the basis of 100 parts by weight of the main material, 1-2 parts by weight of a silica ultrafine powder, 1-1.5 parts by weight of a B4C powder, 0.1-0.3 parts by weight of a carbon fiber, and 1-1.5 parts by weight of a metal fiber.

Description

Magnesia-carbon basic castable for secondary refinery

In the present invention, the molten steel after the primary refining in the Basic Oxygen Furnace or Electric Furnace process is finely adjusted to meet the properties of steel required by the final product. It relates to a basic castable that can be used in a snorkel of an RH plant for a secondary refinery.

RH is one of the secondary refining plants that finely adjusts the impurities in the molten steel that has been first refined from the converter. RH is connected to the lower part of the upper / lower basin and the lower part of the chamber which acts as a vacuum chamber, and it is a immersion tube that directly immerses the molten steel by direct immersion in the molten steel and guides the molten steel to the upper reflux tube. Consists of.

Refractories for RH facilities are typically MgO-C bricks and MgO-Cr2O3 bricks, and in particular, for refractory pipes, Al2O3-MgO castables are generally used in addition to the two types of bricks.

Refractory for immersion pipes of RH facilities exhibits the weakest service life compared to other parts due to direct contact with slag that floats on top of molten steel as well as hot molten steel. In particular, the RH immersion pipe has a thermal shock phenomenon of the refractory by sharply dropping the temperature below about 900 ℃ after 3 minutes at a high temperature of about 1,600 ~ 1,700 ℃ immediately after the operation, resulting in cracks and severe fall off of the refractory Sudden downtimes are the most frequent.

The most vulnerable material of the refractory for RH dip tube is Al2O3-MgO castable in the bottom of the dip tube brick.

1 is a diagram showing the process of using the RH immersion pipe for the secondary refinery, it can be divided into four problem areas.

As shown in Figure 1, when the brick construction and hardware assembly is completed, Al2O3-MgO castable construction is made. Indeterminate castables are cured approximately 24 hours, with the first problem occurring in this section. Indeterminate products are subject to occasional quality fluctuations each season. For example, due to delay in curing and lack of curing strength, damage to the construction body occurs after the removal of the bark (winter), and in the summer, the problem of deterioration of the fillability due to premature curing often occurs. In addition, due to the excessive material-moisture separation that occurs during construction, the robustness of the construction body is also significantly reduced. Figure 2 is a diagram showing the damage after curing of the Al2O3-MgO castable for the lower RH immersion tube.

Subsequently, the finished body after curing is subjected to a drying process after removing the outer shell as the next step. During drying, cracks in the outer surface of the construction are generated, and the propagation of cracks generated during drying continues to accelerate, increasing the thickness and length of the crack continuously. In this case, when the refractory is used in the operation, infiltration by slag in molten steel increases, and if such a phenomenon persists, a sudden operation may occur due to the dropping of the castable. 3 is a diagram showing a crack after drying of the Al 2 O 3 -MgO castable.

In the next process, the dried castable is heated in order to prevent sudden thermal shock before operation. Although the appearance of the Al2O3-MgO castable in the lower part of the immersion tube is good due to the construction, curing, and drying, cracks may occur in the refractory during heating. Cracks during heating are strongly influenced by the material composition of the refractory and can lead to very serious accidental shutdowns during operation by cracks generated. 4 is a photograph showing cracks during heating of the Al 2 O 3 -MgO castable.

Finally, the problem of cracking underneath the RH dip pipe during operation is the most significant and can result in significant losses for steel producers or refractory suppliers. Therefore, precautionary measures for the occurrence of cracks or repair of cracks during operation must be made. Al2O3-MgO castables in the lower part of the immersion tube are especially cracking during operation, causing crack propagation and propagation or acceleration. The dropping of the castable by this crack causes the accompanying dropout of the firebrick placed on the upper side, which causes a great adverse effect on the operation stability. In conclusion, the problem of cracking of the castable shown above must be solved, and the development of a new castable to overcome this problem is necessary. FIG. 5 is a photograph showing that the upper refractory brick is dropped due to dropping out during operation of the Al 2 O 3 -MgO castable.

(Prior art document)

(Patent Document 1) Korean Patent Publication No. 10-0590712

Therefore, the present invention has been devised to solve the above problems, there is little variation in the quality of the product with respect to the temperature change, high cracking resistance due to curing, drying and molten steel of high temperature, such as falling off due to cracking during operation It provides a very low risk of unexpected risks and improves corrosion resistance by molten steel and slag, enabling stable use of RH immersion pipes, and additionally reducing the use of repair materials, eliminating waste of workers, and greatly improving steelmaking productivity. It is an object to provide a magnesia-carbon basic castable for a refinery.

In addition, the subject of this invention is not limited to the content mentioned above. The problem of the present invention will be understood from the general contents of the present specification, those skilled in the art will have no difficulty understanding the additional problem of the present invention.

The present invention to achieve the above object,

By weight%, magnesia clinker: 87-91%, impression graphite: 2-4%, fine graphite: 1-2%, pitch powder: 2-4%, silicon powder: 4-5%, including residual unavoidable impurities Based on main raw materials to say,

With respect to 100 parts by weight of the main raw material, ultrafine silica powder: 1 to 2 parts by weight, B4C powder: 1 to 1.5 parts by weight, carbon fiber: 0.1 to 0.3 parts by weight and an additive containing 1 to 1.5 parts by weight of metal fibers Magnesia-carbon basic castable for secondary refinery.

The magnesia-carbon basic castable for secondary refining furnace of this invention contains 15-17 weight part of resol type phenol resins, and 1.5-2.55 weight part of ester-type hardeners with respect to 100 weight part of mixed materials of the said main raw material and an additive. It is preferable to be prepared by

In addition, the solution of the said subject does not enumerate all the characteristics of this invention. Various features of the present invention and the advantages and effects thereof may be understood in more detail with reference to the following specific embodiments.

As described above, the composition according to the embodiment of the present invention and the magnesia-carbon basic castable prepared therefrom are phenol resins and phenols with magnesia clinker, impression graphite, fine graphite, pitch powder, silicon powder and other additives as main ingredients. Used in combination of resin curing agents. Accordingly, it is possible to obtain a basic castable having increased corrosion resistance and thermal shock resistance, thereby increasing cracking resistance due to thermochemical erosion by molten steel and slag and rapid temperature change from high temperature to low temperature.

Therefore, it provides a low risk of accidental dropping due to cracking during RH immersion pipe operation.The stable use of RH immersion pipe reduces the use of repair materials, eliminates workforce waste, and greatly improves steelmaking productivity. It works.

1 is a diagram showing a step of using the RH immersion pipe for the secondary refinery.

Figure 2 is a diagram showing the damage after curing of the Al2O3-MgO castable for the lower RH immersion tube of FIG.

3 is a diagram illustrating a crack after drying of the Al 2 O 3 -MgO castable of FIG. 1.

4 is a photograph showing cracks during heating of the Al 2 O 3 -MgO castable of FIG. 1.

FIG. 5 is a photograph showing that the upper refractory brick is dropped due to dropping out during operation of the Al 2 O 3 -MgO castable.

Hereinafter, the magnesia-carbon basic castable for the secondary refining furnace which is one aspect of this invention is demonstrated in detail.

The magnesia-carbon basic castable for the secondary refining furnace of this invention is a weight%, magnesia clinker: 87-91%, impression graphite: 2-4%, fine graphite: 1-2%, pitch powder: 2- 4%, silicon powder: 4-5%, the main composition containing the remaining unavoidable impurities as a base composition, with respect to 100 parts by weight of the main raw material, ultra fine silica powder: 1-2 parts by weight, B4C powder: 1-1.5 weight Part, carbon fiber: 0.1 to 0.3 parts by weight and includes an additive containing 1 to 1.5 parts by weight of metal fibers.

In the present invention, the castable refractory includes a magnesia clinker as the main raw material composition.

In general, magnesia clinker is a basic main refractory raw material used for the purpose of improving the corrosion resistance to molten steel and slag, and is much higher than other raw materials in the temperature range of about 1,600 ° C or higher during secondary refining operations. Effect. In particular, in order to exhibit more improved corrosion resistance, it is effective to use an electrolytic magnesia material having a lower content of other components than a sintered magnesia containing a large amount of CaO and other impurities as MgO and other components.

In the present invention, the main raw material preferably comprises the magnesia clinker in the range of 87 to 91% by weight. If the magnesia clinker content is higher, the erosion resistance may be lowered if it is less than 87% by weight, and if it exceeds 91%, crack resistance may be lowered. Therefore, the content of magnesia clinker is preferably in the range of 87 to 91% by weight based on the weight of the main raw material.

Castable refractory material of the present invention includes the raw graphite, fine graphite and pitch powder in the basic composition.

As the impression graphite, fine graphite and pitch powder have high thermal conductivity and low thermal expansion characteristics at high temperature, it suppresses a large amount of cracks generated at high temperature thermal expansion of magnesia raw material having high thermal expansion characteristics, and permeability to high temperature molten steel and slag and Plays an important role in inhibiting chemical reaction erosion. In the present invention, the impression graphite, fine graphite or pitch powder may include at least one of them.

The impression graphite reduces the wettability and penetration of magnesia clinker, molten steel and slag, and improves crack resistance. Thus increasing the erosion resistance of the magnesia-carbon basic castable. At this time, the content of the impression graphite is preferably limited to 2 to 4% by weight, based on the weight of the main material itself. If the added amount of the impression graphite is less than 2%, the above-mentioned effect is not exhibited. If the addition amount of the graphite is more than 4%, the flowability of the magnesia-carbon basic castable kneaded with the binder decreases drastically, and it may be applied to the site to be installed. Because it can be impossible.

The particulate graphite powder is also used to express the same effect as impression graphite, and further helps to slightly improve the fluidity of the magnesia-carbon basic castable. The fine graphite powder is preferably included in an amount of 1 to 2% by weight based on the weight of the main raw material. If the particulate graphite powder is less than 1%, the erosion resistance and strength values may be reduced. If the fine graphite powder is more than 2%, the flowability of the magnesia-carbon basic castable may be slightly reduced.

The pitch powder is also used to express the same effect as the impression graphite and fine graphite, and in particular, improves the binding force in the low temperature region (200 ~ 250 ℃) of the main raw material and other additives of magnesia-carbon basic castable. In addition, after carbonization at high temperature, the crystallinity of carbon is high, which further improves the crack resistance of the castable to rapidly changing temperatures. Pitch powder is preferably contained in an amount of 2 to 4% by weight based on the weight of the main raw material. If the pitch powder content is less than 2%, the above effect cannot be obtained. If the pitch powder content is more than 4%, the flowability of the magnesia-carbon basic castable is greatly reduced, which may render it impossible to apply the inlet construction.

Castable refractory material of the present invention may include silicon (Si) powder in the raw material composition.

The silicon (Si) powder is an essential raw material to improve the oxidation resistance of the graphite, fine graphite and pitch powder by the oxygen at high temperature, and also plays an important role of improving the strength of the castable by reacting with carbon at a temperature of 1,200 ° C. or higher. Perform. The silicon powder is preferably contained in the range of 4 to 5% by weight based on the main raw material. If the content is less than 4%, it is difficult to improve the oxidation resistance of carbon. If the content is more than 5%, a large amount of gas phase "SiO" component is generated by reaction with high temperature oxygen, and the corrosion resistance of the castable is increased. It is because it can lower.

In addition, the castable refractory material of the present invention is an additive, with respect to 100 parts by weight of the main raw material, ultrafine silica powder: 1 to 2 parts by weight, B4C powder: 1 to 1.5 parts by weight, carbon fibers: 0.1 to 0.3 parts by weight and metal fibers It may include 1 to 1.5 parts by weight.

The ultrafine silica (SiO 2) powder significantly improves the flowability of the castable and the oxidation resistance of carbon at high temperatures. In particular, in the present invention, it is preferable to use ultrafine silica (SiO 2) powder having a ZrO ₂ content of 7.0% or less and a pH of 2-5 in its own weight%. These silica powders are produced by capturing and producing steam produced during the manufacture of Fused Zirconia using Zircon (ZiSiO4), and have a white color unlike general silica. When the silica powder is added to the castable, it exhibits dispersibility, flowability, strength, and the high temperature sintering inhibiting effect of the castable.

In the present invention, the ultrafine silica powder is preferably added in an amount of 1 to 2 parts by weight by extrapolation with respect to 100 parts by weight of the main raw material, and when less than 1 part by weight is added, the fluidity, dispersibility and high temperature oxidation resistance of the castable are insufficient. When added in excess of 2 parts by weight, the high temperature corrosion resistance of the castable may be reduced.

The B4C powder may inhibit or prevent high temperature oxidation of carbon. Therefore, it exhibits a great effect on improving the corrosion resistance of the castable through high temperature carbon oxidation. Therefore, in the present invention, the B4C powder is preferably limited to 1 to 1.5 parts by weight per 100 parts by weight of the main raw material, and the addition of less than 1 part by weight reduces the high temperature oxidation inhibitory effect of carbon, and when the addition of more than 1.5 parts by weight of Boron liquid phase at high temperature As a result, a large amount of cracking may occur due to the decrease in the high temperature thermal shock resistance of the castable.

The carbon fiber not only prevents cracking during drying of the graphite-containing amorphous refractory material after completion of construction, but also has the advantage of delaying or suppressing crack generation due to expansion and contraction of the refractory material at high temperature. Therefore, the carbon fiber in the present invention is preferably limited to 0.1 to 0.3 parts by weight per 100 parts by weight of the main raw material. If the amount is more than 0.3 parts by weight, the flowability of the castable is reduced, and if it is less than 0.1 parts by weight, the delay or suppression effect of crack generation due to expansion and contraction of the refractory may be reduced. .

The metal fiber may reduce the quality characteristics due to thermal corrosion at high temperatures of 1,600 ° C. or higher, but is stable without damage at temperatures of 1,500 ° C. or lower, and is not affected by structural stress of the RH immersion tube after curing and drying of the castable or during high temperature use. It shows the effect of suppressing or delaying the occurrence of cracks. The addition amount of the metal fiber is usually preferably added 1 to 1.5 parts by weight per 100 parts by weight of the main raw material. If the added amount is less than 1 part by weight, the above effect is reduced, because if it is more than 1.5 parts by weight, it may cause a decrease in fluidity of the castable and damage to the castable internally by high temperature thermal corrosion.

Furthermore, in the present invention, the magnesia-carbon basic castable consisting of the main raw material and the additive may add an organic binder as a fluid medium.

In this invention, the resol type phenol resin which is an organic binder is used. This resol type phenolic resin binder can be used stably mixed with the other additives, there is no harmful reaction, and also forms residual carbon (Fixed Carbon) at a high temperature to induce all carbon bonds of the amorphous refractory to a high temperature atmosphere Excellent strength of the refractory. Resol-based phenolic resin of the present invention is a resol-based phenolic resin that can be cured at room temperature, unlike the phenolic resin used in conventional magnesia-carbon brick.

In the present invention, the resol-based phenol resin addition amount is preferably mixed in the range of 15 to 17 parts by weight based on 100 parts by weight of the material in which the main raw material and the additive are mixed. If the amount of the resol-based phenolic resin is less than 15 parts by weight, the fluidity of the castable is reduced, and the workability is reduced. When the amount of the resol-based phenolic resin is more than 17 parts by weight, sedimentation of the magnesia clinker in the castable occurs due to the use of an excessive amount of binder. Can be significantly reduced.

On the other hand, in the present invention, it is preferable to use an ester curing agent as a curing agent added for the purpose of room temperature curing of the resol-based phenol resin. Unlike the magnesia-carbon brick which hardens at a high temperature, ester-based curing agents have a great advantage of causing hardening of the resol type phenolic resin at room temperature, and maintain a uniform shape without expansion or contraction of the magnesia-carbon castable. Do it.

In the present invention, it is preferable to limit the amount of the ester-based curing agent to the range of 1.5 to 2.55 parts by weight based on 100 parts by weight of the material mixed with the main raw material and the additive. If the amount of the ester-based curing agent is less than 1.5 parts by weight, curing of the castable occurs, but a large amount of pores are formed by expansion during drying or high temperature firing, thereby reducing the durability. This is because the time required for the construction of the castable is shortened, which may cause great inconvenience to the work.

Hereinafter, the present invention will be described in more detail with reference to Examples.

(Example 1)

To prepare a magnesia-carbon basic castable composition to which the main raw materials and additives as shown in Table 1 were added. At this time, evaluation was conducted to select an appropriate amount of the main raw material, and the amount of the other additives was fixed by fixing the minimum amount to secure the fluidity and physical properties in the magnesia-carbon basic castable and to prevent the oxidation of carbon. Was carried out.

After kneading by adding the organic binder to the composition consisting of the main raw material and the additive, a specimen for quality characteristics evaluation was produced. The prepared test specimens were dried at 250 ° C. for 24 hours, and then, as shown in Table 1 below, the fluidity and physical properties (porosity, cold bending strength, hot bending strength, and thermal shock resistance) of the specimens were evaluated.

Specifically, in order to prepare the specimens of the experimental examples, 17 parts by weight of the resol-based phenol resin and 2.34 parts by weight of the ester-based curing agent were added per 100 parts by weight of the mixed composition of the main raw material and the additive. Samples of the finished dough were sampled to evaluate their fluidity, 40 mm × 40 mm × 160 mm specimens for porosity and cold compressive strength measurements, 25 mm × 25 mm × 120 mm specimens for cold bending strength measurements, and thermal shock. For resistance evaluation, specimens of 60 mm × 60 mm × 60 mm size were prepared. The porosity and cold compressive strength were measured for 3 hours at 1,500 ℃ reducing atmosphere, and the strength of the cooled specimen was measured. The hot bending strength was measured at 1,450 ℃ reducing atmosphere for 1 hour and then the strength of the specimen was measured. Thermal shock resistance evaluation was carried out 30 times the process of maintaining the temperature in the furnace at 1,400 ℃, inserting the specimen inside the furnace, 30 minutes, then forced air injection and cooling for 30 minutes. In this case, the meaning of "O" of thermal shock resistance means that the final crack did not occur or the amount of generation is very small, based on the specimens repeatedly performed 30 times of the test process.

division		Experimental Example
		One	2	3	4	5	6
Main raw material (wt%)	Magnesia Clinker	92	90	88	89	87	87.5
	Impression	2	4	6	4	4	4
	Fine graphite	2	2	2	0	0	One
	Pitch Powder	0	0	0	2	4	2.5
	Si powder	4	4	4	5	5	5
Additive (part by weight)	Ultrafine Silica Powder	One	One	One	One	One	One
	B4C Powder	One	One	One	One	One	One
	Carbon fiber	0.1	0.1	0.1	0.1	0.1	0.1
	Metal fiber	1.2	1.2	1.2	1.2	1.2	1.2
Binder (parts by weight)	Resol type phenol resin	17
	Ester curing agent	2.34
Fluidity (mm)		152	146	101	148	136	147
Porosity (%)		26.9	27.6	29	30.2	33.6	30.2
Cold bending strength (kg / cm2)		27	30	34	38	32	38
Hot bending strength (kg / cm2)		53	52	43	32	22	34
Thermal shock resistance		X	△	-	△	△	O
		O: Good, X: Poor, △: Normal

As shown in Table 1, Experimental Examples 1 to 3 evaluated the quality characteristics according to the addition amount of the impression graphite. In general, when the addition amount of the impression graphite exceeds 6 parts by weight, as shown in Experiment 3, the fluidity of the castable showed a tendency to decrease rapidly. Experimental Example 3 measured only physical properties in the present invention according to the difficulty in the actual operation due to the reduced fluidity, and did not measure the thermal shock resistance.

Experimental Example 1 and Experimental Example 2 showed good fluidity, and Experimental Example 2 showed a tendency to slightly decrease the fluidity due to an increase in the amount of the added graphite compared to Experimental Example 1. In general, when the amount of graphite added was 2 to 4 parts by weight, good physical properties and fluidity were exhibited, but the thermal shock resistance was decreased when 2 parts by weight of graphite was added. It can be seen that the thermal conductivity of the magnesia clinker is reduced due to the lack of graphite content, and cracks are generated due to high thermal stress.

In Experimental Examples 4 to 5, 2 and 4 parts by weight of the pitch powder replacing fine graphite were added, respectively, and the quality of the metal silicon powder was changed to 5 parts by weight. As a result, when the pitch powder was added, the fluidity was similar to that of Experiment 2, but the cold compressive strength and the porosity were increased, and the hot bending strength was decreased. However, the results showed that the thermal shock resistance was significantly improved compared to the composition without the pitch powder. In particular, when using 1 part by weight of particulate graphite of the experimental example 6, 2.5 parts by weight of pitch powder showed a very good thermal shock resistance results.

(Example 2)

The amount of the composition added as the main raw material was fixed based on Experimental Example 6 of Example 1. And evaluation was performed as Table 2 in order to select the suitable addition amount of other additives.

Specimen preparation for quality characteristics evaluation was carried out in the same manner as in Example 1 and evaluated. In addition, the rate of erosion by molten steel and slag was carried out for a total of eight times for 30 minutes at a high temperature of 1,600 to 1,700 ° C.

division		Conventional example	Comparative example			Inventive Example
			One	2	3	One	2	3
Main raw material (wt%)	Alumina Clinker	86-91
	Magnesia Clinker	7-12	87.5	87.5	87.5	87.5	87.5	87.5
	Impression		4	4	4	4	4	4
	Fine graphite		One	One	One	One	One	One
	Pitch Powder		2.5	2.5	2.5	2.5	2.5	2.5
	Si powder		5	5	5	5	5	5
	Metal fiber	1 ~ 2
Additive (part by weight)	Ultrafine Silica Powder		2	2	3	One	2	2
	B4C Powder		2	1.5	1.5	1.5	One	1.5
	Carbon fiber		0.3	0.1	0.3	0.3	0.3	0.3
	Metal fiber		1.2	2	1.2	1.2	1.2	1.2
Fluid media	moisture	6.1 parts by weight
Binder (parts by weight)	Resol type phenol resin		17
	Ester curing agent		2.34
Fluidity (mm)		106	146	114	156	132	144	147
Porosity (%)		19.9	30	32	30.1	31.2	30.3	30.2
Cold bending strength (kg / cm2)		258	34	63	57	29	27	49
Hot bending strength (kg / cm2)		29	38	27	49	33	43	44
Erosion Rate (%)		100	81.7	110	118	85.6	83.6	80.2
Thermal shock resistance		X	X	O	△	△	△	O
		O: Good, X: Poor, △: Normal

As shown in Table 2, the prior art uses water as the flow medium. The fluidity is 106mm, which results in a very poor result compared to Comparative Examples 1 to 3 and Inventive Examples 1 to 3, and it can be seen that there is a disadvantage that the workload for the workers may be increased during the actual operation. Porosity was also very low compared to Comparative Examples 1 to 3 and Inventive Examples 1 to 3, the cold compressive strength was also very high. As a reason for this, the conventional example is made of alumina cement bonded material, and ceramic bonding is performed by sintering at high temperature. Therefore, very high cold compressive strength is shown compared with Comparative Examples 1-3 and Inventive Examples 1-3 which formed carbon bond. However, the low porosity and high cold compressive strength indicate that the brittleness of the ceramic-bonded castable is very high, so that the crack propagation amount and propagation rate are very large when cracks are generated. In this case, it can be expected that there is a high possibility of an outbreak caused by cracking during operation. Therefore, the thermal shock resistance showed a very low evaluation result compared to Comparative Examples 1 to 3 and Inventive Examples 1 to 3.

Comparative Example 1 was evaluated by increasing the B4C powder to 2 parts by weight. Other quality characteristics were good while thermal shock resistance was significantly lower. For this reason, it can be seen that a crack occurs when a sudden temperature change is caused by the liquefied boron in the castable.

In Comparative Example 2, the metal fibers were increased to 2 parts by weight, and evaluated. Similarly, the quality characteristics and thermal shock resistance were quite good, but the erosion rate was increased to 10% compared to the conventional example due to the corrosion at high temperature due to the increase in metal fiber.

Comparative Example 3 evaluated the ultrafine silica powder as 3 parts by weight. The fluidity due to the addition of ultrafine silica showed the highest value. In addition, the strength value was also increased, but the erosion rate due to the increased silica content was significantly reduced.

On the contrary, Inventive Examples 1 to 3 showed good overall quality characteristics.

Specifically, Inventive Example 1 was evaluated by 1 part by weight of the ultrafine silica powder, the hot bending strength was reduced compared to Inventive Example 2-3, but the thermal shock resistance is good, the erosion rate also showed a very good result compared to the conventional example.

Inventive Example 2-3 fixed 2 parts by weight of the ultrafine silica powder and 1.2 parts by weight of the metal fiber, changed the B4C powder to 1 part by weight and 1.5 parts by weight, and increased the carbon fiber to 0.3 parts by weight. Evaluation of using 0.3 parts by weight of carbon fiber did not cause a special crack during drying without significantly affecting the flowability of the castable compared to Comparative Example 1 using 0.1 parts by weight. When 1.5 parts by weight of B4C powder was added, the cold compressive strength was increased compared to 1 part by weight, and in particular, the thermal shock resistance was excellent.

As described above, in the case of Inventive Examples 1 to 3, which satisfies all of the ranges proposed by the present invention, it can be confirmed that the results have excellent erosion resistance and thermal shock resistance.

As described above, in the detailed description of the present invention has been described with respect to the preferred embodiment of the present invention, those skilled in the art to which the present invention pertains various modifications without departing from the scope of the present invention Of course it is possible. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the equivalents as well as the claims to be described later.

Claims (3)

1. By weight%, magnesia clinker: 87-91%, impression graphite: 2-4%, fine graphite: 1-2%, pitch powder: 2-4%, silicon powder: 4-5%, including residual unavoidable impurities Based on main raw materials to say,

   With respect to 100 parts by weight of the main raw material, ultrafine silica powder: 1 to 2 parts by weight, B4C powder: 1 to 1.5 parts by weight, carbon fiber: 0.1 to 0.3 parts by weight and an additive comprising a metal fiber 1 to 1.5 parts by weight Magnesia-carbon basic castable for secondary refinery.
2. The magnesia for secondary smelting furnace according to claim 1, wherein the magnesia for secondary smelting furnace is composed of 100 parts by weight of the mixed material of the main raw material and the additive, including resol-based phenolic resin: 15-17 parts by weight and ester-based curing agent: 1.5-2.55 parts by weight Carbon basic castable.
3. The magnesia-carbon basic castable according to claim 1, wherein the ultrafine silica powder has a ZrO ₂ content of 7.0% or less and a pH of 2-5 in its own weight%.

Images