JP6747520B2 - Refractories for furnaces using silicon chloride gas - Google Patents

Description

The present invention relates to a refractory material used in a furnace that uses silicon chloride gas, such as a continuous siliconizing furnace for steel strip.

Since the silicon steel sheet has excellent soft magnetic characteristics, it is widely used as a core material for transformers and motors. It is known that the silicon steel sheet exhibits excellent magnetic properties such that the iron loss decreases as the Si content increases, and the magnetostriction becomes 0 and the maximum magnetic permeability peaks when Si content is about 6.5 wt %. As a method for industrially manufacturing such a high-silicon steel sheet, for example, a manufacturing method by a gas immersion silicon method as disclosed in Patent Document 1 is known. In this manufacturing method, a steel strip having a relatively low Si content is heated and subjected to a siliconizing treatment in a non-oxidizing gas atmosphere containing silicon chloride gas (SiCl ₄ ) so that Si is infiltrated, and then the Si thickness is reduced. A high-silicon steel strip can be efficiently manufactured by performing a diffusion heat treatment for diffusing in a given direction, forming a continuous process of cooling and winding it into a coil, into a continuous line.

The continuous silicidation treatment furnace in which the silicidation treatment is performed as described above is operated at a temperature of 1200° C. or higher for a long time, and the silicon chloride gas (SiCl ₄ ) contained in the atmospheric gas is very reactive. It is a rich and highly corrosive gas. Therefore, there is a problem that the silicon chloride gas activated in the high temperature furnace reacts with the refractory material which is the furnace material of the continuous siliconizing treatment furnace, and deteriorates the refractory material.

As a refractory for a continuous siliconizing treatment furnace, it is known to apply the refractory described in Patent Documents 2 and 3, for example.

JP-A-62-227078 JP, 10-147856, A JP, 08-169750, A

On the other hand, there is a problem that iron chloride (gas) generated as a by-product during the production of the high silicon steel sheet permeates into the refractory material in the furnace and agglomerates or solidifies in the temperature decreasing portion near the furnace wall or the furnace floor. By depositing this aggregated and solidified iron chloride in the refractory, the reduction reaction with the oxide in the refractory proceeds, and the alteration or embrittlement of the refractory is promoted.

Further, when the refractory material in the furnace is exposed to the atmosphere for repair or the like, iron chloride deposited in the refractory material absorbs moisture in the atmosphere and expands. As a result, the refractory itself increases in volume and expands, so that the refractory on the furnace wall or the furnace floor bids inside the furnace, or the refractory cracks and collapses. Therefore, there is a problem that the life of the refractory is shortened and the update cycle is shortened.

When the refractory materials described in Patent Documents 2 and 3 are used, although alteration and embrittlement of the refractory material due to silicon chloride gas can be suppressed, alteration and embrittlement of the refractory material due to iron chloride can be prevented. It turns out that it is difficult to suppress the acceleration.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a refractory for a siliconizing treatment furnace that is less likely to be altered or embrittled and has a long life.

As a result of diligent studies, the present inventors have found that by using a refractory having a predetermined composition and a low porosity, the life of the refractory can be improved and the renewal cycle can be extended.

The present invention has been made on the basis of such findings and has the following gist.
[1] One kind or two or more kinds selected from oxides of silicon, nitrides of silicon and oxynitrides of silicon in total of 35 mass% or more and alkali metals in total of 0.05 mass% or less. A refractory for a siliconizing treatment furnace, which contains: and has a porosity of 25 vol% or less and a compressive strength of 5 MPa or more.
[2] The refractory for a siliconizing furnace according to [1], further containing 1.0 mass% or less of each oxide of Mg, Ca, Ti, Fe, Cr and Zr in total.
[3] Silicidation according to [1] or [2], which contains 90% by mass or more in total of one or more selected from oxides of silicon, nitrides of silicon and oxynitrides of silicon. Refractory for processing furnace.

According to the present invention, it is possible to provide a refractory for a siliconizing treatment furnace, which has little deterioration or brittleness and has a long life. Therefore, when the refractory material of the present invention is applied as a refractory material for a continuous siliconizing treatment furnace using silicon chloride gas, the refractory material does not undergo alteration or embrittlement over a long period of time and exhibits excellent durability. Therefore, in a continuous production line of high silicon steel sheet by the gas immersion silicon method, stable operation can be performed for a long period of time without deterioration of refractory materials.

FIG. 1 is a schematic diagram of a continuous siliconizing treatment facility for producing a high silicon steel sheet.

Refractory materials made of various materials were manufactured. These refractories, an atmosphere containing a silicon chloride gas (SiCl _4: about 15 vol%, furnace temperature: about 1200 ° C.) placed furnace 3 months in the examined changes in appearance, weight, volume, etc. of the refractory It was As a result, a refractory containing a large amount of one or more of oxides of silicon (silica), nitrides of silicon (silicon nitride) and oxynitrides of silicon (silicon oxynitride) can be used against silicon chloride gas. Was found to be the least damaged. On the other hand, it has been found that the refractory made of silicon carbide has a high degree of damage.

Next, in order to evaluate the damage resistance of the refractory to the silicon chloride gas, the state of alteration or embrittlement of the surface of the refractory is investigated, and the state of alteration or embrittlement and the oxide of silicon, the nitride of silicon, the acid of silicon is examined. The relationship with the total content of nitrides was examined.

As a result, a refractory having a total content of one kind or two kinds or more selected from oxides of silicon, nitrides of silicon, and oxynitrides of silicon of less than 35 mass% has a surface modified or embrittled. In this state, there were defects or hair cracks were generated, and cracks and spalling were remarkable. On the other hand, a refractory having a total content of one or two or more selected from oxides of silicon, nitrides of silicon, and oxynitrides of silicon of 35% by mass or more is partially cracked. Although some were generated, there was no alteration or embrittlement that would cause the surface layer of the furnace material to fall off, and it was judged that the reactor could be used almost continuously.

As described above, in the present invention, the content of silicon oxide, silicon nitride, and silicon oxynitride contained in the refractory material is the same as that of silicon oxide, silicon nitride, and silicon oxynitride. One kind or two or more kinds selected from are defined as 35 mass% or more in total. Preferably, 90% by mass or more in total of one or more selected from oxides of silicon, nitrides of silicon, and oxynitrides of silicon is selected. When the content is 90% by mass or more, alteration/brittleness is remarkably reduced, cracks are not generated, and good results are obtained.

In the present invention, the silicon oxide, silicon nitride, and silicon oxynitride contained in the refractory are preferably silicon nitride and fused silica, and particularly preferably fused silica.

In the present invention, the total content of alkali metals contained in the refractory material is specified to be 0.05 mass% or less. The alkali metal contained in the refractory contributes to the reactivity with the silicon chloride gas. If the content of the alkali metal exceeds 0.05% by mass, the reaction between the refractory and the silicon chloride gas proceeds, and the refractory surface may be cracked or defective.

In the present invention, the total content of each oxide of Mg, Ca, Ti, Fe, Cr and Zr contained in the refractory is preferably 1.0% by mass or less. The oxides such as Mg and Ca contained in the refractory also contribute to the reactivity with the silicon chloride gas. If the content of oxides such as Mg and Ca exceeds 1.0% by mass, the reaction between the refractory and silicon chloride gas may proceed, and the refractory surface may be cracked or defective.

The rest of the refractory other than the above is Al ₂ O ₃ and impurities, and may include metal oxides other than the above as impurities.

There is a problem that iron chloride (gas), which is generated as a by-product during the production of a high silicon steel sheet, permeates into the refractory material in the furnace and agglomerates or solidifies in the temperature lowering portion near the furnace wall or the furnace floor. By depositing this aggregated or solidified iron chloride in the refractory, the reduction reaction with the oxide in the refractory proceeds, and the alteration or embrittlement of the refractory is promoted. Further, when the refractory material in the furnace is exposed to the atmosphere for repair or the like, iron chloride deposited in the refractory material absorbs moisture in the atmosphere and expands. As a result, the refractory itself increases in volume and expands, so that the refractory on the furnace wall or the furnace floor bids inside the furnace, or the refractory cracks and collapses. Therefore, there is a problem that the life of the refractory is shortened and the update cycle is shortened.

The inventors of the present invention diligently studied the deterioration and embrittlement of refractory materials caused by such iron chloride. As a result, they have found that the refractory material can be prevented from being deteriorated or embrittled by setting the porosity of the refractory material to 25% by volume or less.

Iron chloride (solid) deposited in the refractory is more likely to be deposited in the refractory as the pores in the refractory are larger. The iron chloride deposited in the refractory expands when it comes into contact with the atmosphere, and pressure is applied to the refractory from the inside, which causes deterioration of the refractory. For this reason, it is desirable that the refractory should have few pores. By controlling the porosity to 25 vol% or less, it is possible to suppress the deposition of iron chloride in the refractory and prevent the refractory from deteriorating. Is possible. Therefore, in the present invention, by setting the porosity to 25% by volume or less, alteration or embrittlement of the refractory can be suppressed. As a result, long-term stable operation in a continuous production line for high silicon steel sheets can be realized.

In addition, refractory materials having different compositional compositions and different compressive strengths were prepared. These refractories were placed in a furnace containing iron chloride gas (FeCl ₂ concentration): about 15 vol%, furnace temperature: about 1200° C. for 1 week, and then expanded after being exposed to the atmosphere for 2 months. The change in state was investigated. As a result, it has been found that there is a close relationship between the compressive strength and the expanded state by iron chloride, and when the compressive strength is less than 5 MPa, the expanded state becomes large and collapses. Therefore, in the present invention, the compressive strength of the refractory material is set to 5 MPa or more. If the compressive strength is less than 5 MPa, iron chloride gas, which is a by-product, penetrates into the refractory and expands the refractory, causing the refractory to collapse and affecting the surface appearance. Preferably, the compressive strength is 20-200 MPa. The compressive strength is preferably 200 MPa or less.

Further, in the present invention, the method for measuring the porosity and the compressive strength is not particularly limited and may be determined by a conventional method. Further, it is also possible to use a resisting material having a porosity of 25% by volume or less and a compressive strength of 5 MPa or more.

Refractory materials (50 mm×50 mm×50 mm) having various component compositions were prepared, and these were installed in the siliconizing furnace of the continuous production line for high silicon steel sheets shown in FIG. After continuously operating the atmosphere of the siliconizing treatment furnace with the SiCl ₄ concentration: 15 vol% and the furnace temperature: 1200° C. for 3 months, the damage state of each refractory was examined. Table 1 shows the results of the component composition, porosity, compressive strength and damage condition of each refractory.

The state of damage was judged by surface observation and reactivity. For the surface observation, the appearance of the refractory was observed, and the deterioration was evaluated according to the following four stages: defect: cracking> discoloration> no change. Regarding reactivity, four stages of ◎◎, ◎, ○, × from the deterioration state (◎◎: No reaction, ◎: Almost no reaction, ○: Small reaction (degradation of refractory is recognized , The level at which continuous use is possible), x: the reaction is remarkable). For surface observation, discoloration and no change were passed, and reactivity was ◎◎, ◎ and ◯.

From the results in Table 1, all of the examples of the present invention were good results.

In No. 1 showing a good result in Example 1. Regarding 10, 19, and 31, the renewal period when used as a refractory for a siliconizing furnace was examined. As a result, No. When using Nos. 10 and 19, it was possible to extend the update cycle by 1.5 times when the update cycle of the conventional refractory material (refractory material of Patent Document 3) was set to 1. Furthermore, No. When 31 is used, it becomes possible to extend the update period three times as long as the conventional one.

Claims (3)

Silicon chloride gas containing 35% by mass or more and 97.5% or less of fused silica and 0.05% by mass or less of alkali metal in total, having a porosity of 25% by volume or less and a compressive strength of 5 MPa or more. Refractory for furnace used . The refractory for a silicon chloride gas-using furnace according to claim 1, further containing a total of 1.0 mass% or less of each oxide of Mg, Ca, Ti, Fe, Cr and Zr. The refractory material for a furnace using silicon chloride gas according to claim 1 or 2, which contains 90 mass% or more of fused silica.