JPWO2019054222A1 - Refractories for siliconizing furnace - Google Patents

Abstract

An object of the present invention is to provide a refractory for a siliconization furnace that has little alteration and embrittlement and has a long life. One or two or more selected from silicon oxide, silicon nitride and silicon oxynitride are contained in a total of 35% by mass or more, and alkali metals in total containing 0.05% by mass or less. A refractory for a siliconization furnace having a porosity of 25% by volume or less and a compressive strength of 5 MPa or more.

Description

  The present invention relates to a refractory used in a furnace using silicon chloride gas, such as a continuous siliconization furnace for steel strip.

Silicon steel sheets are widely used as iron core materials for transformers and motors because they have excellent soft magnetic properties. It is known that the silicon steel sheet exhibits excellent magnetic properties such that the iron loss is reduced as the Si content is increased, and the magnetostriction becomes zero and the maximum magnetic permeability reaches a peak when Si 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 method as shown in Patent Document 1 is known. In this manufacturing method, a steel strip having a relatively low Si content is heated and immersed in a non-oxidizing gas atmosphere containing silicon chloride gas (SiCl ₄ ) to infiltrate Si. A series of processes in which a diffusion heat treatment for diffusing in the direction is performed and coiled after cooling is made into a continuous line, and a high silicon steel strip can be produced efficiently.

The continuous siliconization furnace in which the above-described siliconization treatment is performed is operated at a furnace temperature of 1200 ° C. or more for a long time, and silicon chloride gas (SiCl ₄ ) contained in the atmosphere gas is very reactive. It is a rich and highly corrosive gas. For this reason, there exists a problem that the silicon chloride gas activated in the high temperature furnace reacts with the refractory which is a furnace material of a continuous siliconization furnace, and degrades a refractory.

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

JP-A-62-227078 Japanese Patent Laid-Open No. 10-147856 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 a high silicon steel sheet penetrates into the refractory in the furnace and aggregates or solidifies at a temperature-decreasing portion near the furnace wall or the hearth. As the agglomerated and solidified iron chloride is deposited in the refractory, the reduction reaction with the oxide in the refractory proceeds, and the alteration and embrittlement of the refractory are promoted.

  Also, when the refractory in the furnace is exposed to the atmosphere for repair or the like, the iron chloride accumulated in the refractory absorbs moisture in the atmosphere and expands. As a result, since the volume of the refractory itself increases and expands, the refractory on the furnace wall and the hearth comes up inside the furnace, or the refractory is cracked and collapses. Therefore, there is a problem that the life of the refractory is shortened and the renewal cycle is shortened.

  When the refractories described in Patent Documents 2 and 3 are used, it is possible to suppress the alteration and embrittlement of the refractory caused by the silicon chloride gas, but the alteration and embrittlement of the refractory caused by iron chloride. It turned out to be difficult to suppress until promotion.

  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 siliconization furnace having little deterioration and embrittlement and a long life.

  As a result of intensive studies, the present inventors have found that by using a refractory having a predetermined component 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 knowledge and has the following gist.
[1] One or two or more selected from silicon oxide, silicon nitride, and silicon oxynitride in total 35% by mass or more and alkali metals in total 0.05% by mass or less A refractory for a siliconization furnace having a porosity of 25% by volume or less and a compressive strength of 5 MPa or more.
[2] The refractory for a siliconization furnace according to [1], further containing 1.0% by mass or less of each oxide of Mg, Ca, Ti, Fe, Cr, and Zr.
[3] The silicon immersion as set forth in [1] or [2], containing one or more selected from silicon oxide, silicon nitride and silicon oxynitride in a total of 90% by mass or more Refractory for processing furnace.

  According to the present invention, it is possible to provide a refractory for a siliconization furnace that has little deterioration and embrittlement and has a long life. Therefore, when the refractory material of the present invention is applied as a refractory material for a continuous siliconization furnace using silicon chloride gas, it does not cause deterioration or embrittlement over a long period of time and exhibits excellent durability. For this reason, in the continuous production line of the high silicon steel plate by a gas immersion method, the stable operation for a long period of time becomes possible, without producing deterioration of a refractory.

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

Refractories made of various materials were prepared. These refractories are placed in a furnace containing an atmosphere containing silicon chloride gas (SiCl ₄ : about 15 vol%, furnace temperature: about 1200 ° C.) for 3 months, and changes in the appearance, weight, volume, etc. of each refractory are examined. It was. As a result, a refractory containing one or more of silicon oxide (silica), silicon nitride (silicon nitride) and silicon oxynitride (silicon oxynitride) is more effective against silicon chloride gas. The least damage was found. In contrast, it has been found that refractories made of silicon carbide are highly damaged.

  Next, as an evaluation of the damage resistance of the refractory to silicon chloride gas, the surface of the refractory is examined for the state of alteration and embrittlement, and the state of alteration and embrittlement and the silicon oxide, silicon nitride, silicon acid The relationship with the total content of nitride was investigated.

  As a result, the surface of a refractory having a total content of one or more selected from silicon oxide, silicon nitride, and silicon oxynitride of less than 35% by mass is altered or embrittled. It was in a state with defects or a hair crack, and cracks and spalling were also remarkable. On the other hand, a refractory having a total content of one or more selected from silicon oxide, silicon nitride, and silicon oxynitride of 35% by mass or more is partially cracked. Although some were generated, it was judged that there was no alteration or embrittlement leading to the dropping of the surface layer of the furnace material, and it 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 is the same as that of silicon oxide, silicon nitride, and silicon oxynitride. 1 type or 2 types or more 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 silicon oxide, silicon nitride, and silicon oxynitride is contained. When the content is 90% by mass or more, alteration and embrittlement are 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 or fused silica, particularly preferably fused silica.

  In the present invention, the total content of alkali metals contained in the refractory is defined as 0.05% by mass or less. The alkali metal contained in the refractory contributes to the reactivity with the silicon chloride gas. When the content of the alkali metal exceeds 0.05% by mass, the reaction between the refractory and the silicon chloride gas proceeds, and there is a risk that the surface of the refractory will be cracked or defective.

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

The remainder other than the above in the refractory is Al ₂ O ₃ or impurities, and metal impurities other than the above may be included as impurities.

  There is a problem that iron chloride (gas) generated as a by-product during the production of the high silicon steel sheet penetrates into the refractory in the furnace and aggregates or solidifies at the temperature-decreasing portion near the furnace wall and the hearth. As this agglomerated or solidified iron chloride accumulates in the refractory, the reduction reaction with the oxide in the refractory proceeds, and the alteration and embrittlement of the refractory are promoted. Also, when the refractory in the furnace is exposed to the atmosphere for repair or the like, the iron chloride accumulated in the refractory absorbs moisture in the atmosphere and expands. As a result, since the volume of the refractory itself increases and expands, the refractory on the furnace wall and the hearth comes up inside the furnace, or the refractory is cracked and collapses. Therefore, there is a problem that the life of the refractory is shortened and the renewal cycle is shortened.

  The present inventors diligently investigated the alteration and embrittlement of refractories caused by iron chloride. As a result, it has been found that by setting the porosity of the refractory to 25% by volume or less, alteration and embrittlement of the refractory can be suppressed.

  The more iron chloride (solid) deposited in the refractory, the more the pores in the refractory, the more likely it will accumulate in the refractory. 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, causing deterioration of the refractory. For this reason, it is desirable that the number of pores in the refractory is small. By setting the porosity to 25% by volume or less, deposition of iron chloride in the refractory is suppressed and deterioration of the refractory is prevented. Is possible. Therefore, in the present invention, alteration of the refractory and embrittlement can be suppressed by setting the porosity to 25% by volume or less. As a result, long-term stable operation in a continuous production line for high silicon steel sheets can be realized.

Also, refractories having different component compositions and different compressive strengths were prepared. These refractories were placed in a furnace containing an iron chloride gas atmosphere (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 state change was examined. As a result, it was found that there is a close relationship between the compressive strength and the expanded state due to iron chloride, and when the compressive strength is less than 5 MPa, the expanded state increases and collapses. For this reason, in this invention, the compressive strength of a refractory shall be 5 Mpa or more. If the compressive strength is less than 5 MPa, the by-product iron chloride gas penetrates into the refractory and expands the refractory, causing the refractory to collapse and affecting the surface appearance. Preferably, the compressive strength is 20 to 200 MPa. The compressive strength is preferably 200 MPa or less.

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

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

  The damage situation was judged by surface observation and reactivity. The surface observation was performed by observing the appearance of the refractory, and evaluated in four stages, from the state of deterioration to defects> cracks> discoloration> no change. Regarding the reactivity, there are four stages of ◎◎, ◎, ○, × from the deterioration situation (◎◎: no reaction, ◎: little reaction, ○: little reaction (deterioration of refractory is observed) , Level that can be used continuously), ×: the reaction was remarkable). For surface observation, discoloration and no change were acceptable, and reactivity was acceptable for ◎◎, ◎ and ○.

  From the results of Table 1, all of the inventive examples were good results.

  No. 1 which showed a good result in Example 1. About 10, 19, and 31, the update period at the time of using as a refractory of a siliconization furnace was investigated. As a result, no. In the case of using 10 and 19, when the update cycle of the conventional refractory (refractory of Patent Document 3) is set to 1, the update cycle can be extended 1.5 times. Furthermore, no. When 31 was used, it became possible to extend the update cycle to three times that of the prior art.

Claims (3)

One or two or more selected from silicon oxide, silicon nitride and silicon oxynitride are contained in a total of 35% by mass or more, and alkali metals are contained in a total of 0.05% by mass or less. ,
A refractory for a siliconization furnace having a porosity of 25% by volume or less and a compressive strength of 5 MPa or more.   The refractory for a siliconization furnace according to claim 1, further comprising 1.0% by mass or less of Mg, Ca, Ti, Fe, Cr and Zr oxides in total.   The refractory for a siliconization furnace according to claim 1 or 2, containing one or more selected from silicon oxide, silicon nitride, and silicon oxynitride in a total of 90 mass% or more. .

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