JP3158921B2 - Refractories for furnaces using silicon chloride gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a refractory used in a furnace using silicon chloride gas, such as a furnace for continuous siliconizing of a steel strip.

[0002]

2. Description of the Related Art Silicon steel sheets have excellent soft magnetic properties and are therefore widely used as core materials for transformers and motors. As for the silicon steel sheet, the iron loss decreases as the Si content increases,
It is known that when the content of Si is about 6.5 wt%, magnetostriction becomes 0, and excellent magnetic characteristics are exhibited, such as a peak in the maximum magnetic permeability. As a method for industrially producing such a high silicon steel sheet, there is known a production method using a gas siliconizing method as disclosed in JP-A-62-227078. According to 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 a silicon chloride gas (SiCl ₄ ) to infiltrate the Si, and then the Si has a thickness A series of processes in which a diffusion heat treatment for diffusing in a direction is performed and a coil is wound into a coil after cooling is formed into a continuous line, and a high silicon steel strip can be efficiently manufactured.

[0003]

The siliconizing furnace in which the above siliconizing treatment is performed is operated at a furnace temperature of 1200 ° C. or more for a long time, and the silicon chloride gas contained in the atmosphere gas is extremely low. It is a highly reactive and highly corrosive gas.
For this reason, it is thought that sufficient consideration must be given to the selection of furnace materials (furnace refractories) for the siliconizing furnace, in terms of durability. Conventionally, furnace materials have been studied from such a viewpoint. Few reports. However, according to the study of the present inventors,
The surface of the furnace material in the siliconizing furnace is deteriorated and embrittled in a relatively short time due to erosion by the silicon chloride gas contained in the atmospheric gas, and a part of the furnace material falls off from the ceiling or wall of the furnace. Was found to occur. Some of the furnace material thus dropped adheres to the surface of the steel sheet, significantly impairing the surface properties of the product steel sheet, and the dropped furnace material builds up on the rolls in the furnace, resulting in continuous furnace operation. It will hinder you. The present invention has been made in view of such conventional problems,
An object of the present invention is to provide a refractory which does not cause deterioration or embrittlement for a long period of time as a refractory for a furnace in which silicon chloride gas is used.

[0004]

The present inventors conducted experiments and studies on the relationship between the material of the refractory and the degree of damage to the refractory due to silicon chloride gas. The degree of the total content of silicon oxide, silicon nitride and silicon oxynitride contained in the refractory, furthermore, the content of alkali metal, Mg, C
a, Ti, Fe, Cr and Zr are closely related to the content of each oxide, specifically, one of silicon oxide, silicon nitride and silicon oxynitride or By making the total content of two or more types equal to or more than a predetermined value,
Excellent damage resistance to silicon chloride gas is obtained,
Further, in addition to this, the total content of alkali metals is kept low, and more preferably, Mg, Ca, Ti, F
It has been found that particularly excellent damage resistance can be obtained by suppressing the total content of each oxide of e, Cr and Zr to be low.

[0005] The present invention has been made based on such knowledge, and the characteristic configuration thereof is as follows. (1) One or more selected from silicon oxide, silicon nitride and silicon oxynitride in total of 35
wt% or more and total alkali metal content
A refractory for a furnace using silicon chloride gas , wherein the amount is 0.05 wt% or less . (2) In the refractory of the above (1), Mg, Ca, T
The total content of each oxide of i, Fe, Cr and Zr is 1.
Use of silicon chloride gas characterized by being 0 wt% or less
Furnace refractories.

[0006]

The present inventors have prepared refractories made of various materials, and have prepared these refractories in an atmosphere containing silicon chloride gas (SiC
l ₄ concentration: about 15 vol%, furnace temperature: about 1200 ° C.)
Was placed in a furnace for 3 months, and changes in appearance, weight, etc. of each refractory were examined. The results are shown in Table 1 together with the total content of silicon oxide (silica), silicon nitride (silicon nitride) and silicon oxynitride (silicon oxynitride) contained in each refractory.

From the results of the experiment shown in Table 1, it is found that a refractory containing a large amount of any of silicon oxide, silicon nitride and silicon oxynitride is most stable against silicon chloride gas, It has been found that refractories made of silicon carbide have a high degree of damage. Then, as an evaluation of the damage resistance of the refractory to silicon chloride gas, alteration of the surface of the refractory,
Investigate the state of embrittlement, and finally use cases and silicon oxides, which become unusable due to a warped state or hair crack
The relationship with the total content of silicon nitride and silicon oxynitride was examined.

As a result, a refractory material having a total content of silicon oxide, silicon nitride and silicon oxynitride of less than 35% by weight is degraded and embrittled on the surface, and is in a state in which a warp state or a hair crack is generated. In addition, cracking and spalling were remarkable. FIG. 3 schematically shows such a state of damage to the refractory surface layer. In such a state in which the refractory material is in a warped state or a hair crack occurs, there is a problem that the furnace material surface layer comes off. On the other hand, in the case of the refractory having a total content of silicon oxide, silicon nitride and silicon oxynitride of 35 wt% or more, some cracks were found, but the refractory material of the furnace material surface layer portion There was no deterioration or embrittlement leading to falling off, and it could be judged that it could be used almost continuously. For this reason, in the present invention, the total content of silicon oxide, silicon nitride and silicon oxynitride contained in the refractory is 35 wt.
% Or more.

Next, paying attention to the content of alkali metal often contained in general refractories, the total content of silicon oxide, nitride and oxynitride is constant and the content of alkali metal is variously changed. Refractory materials were prepared, and each refractory material was placed in a furnace having the same atmosphere as described above for three months, and the weight loss rate of the refractory material was examined. As a result, there is a close relationship between the content of the alkali metal in the refractory and the weight reduction rate of the refractory, and the weight reduction rate rapidly increases when the total content of the alkali metals exceeds 0.05 wt%. I understood. Therefore, in the present invention,
The total content of alkali metals contained in the product is 0.05w
t% or less.

Further, focusing on the content of each oxide of Mg, Ca, Ti, Fe, Cr and Zr, which are often contained in the refractory together with the alkali metal, the total of oxides, nitrides and oxynitrides of silicon is considered. Various refractories in which the content and the total content of alkali metals are constant and the total content of oxides such as Mg and Ca are different from each other, and each refractory is placed in a furnace having the same atmosphere as above for 3 months. Then, the weight loss rate of the refractory was examined. As a result, there is a close relationship between the total content of the above oxides such as Mg and Ca and the weight loss rate. When the total content of these oxides exceeds 1.0 wt%, the weight loss rate may increase. understood. For this reason, in the present invention, Mg, Ca, Ti, Fe, Cr and Z contained in the refractory are preferable conditions.
The total content of each oxide of r was specified to be 1.0 wt% or less.

[0011]

[Table 1]

[0012]

EXAMPLES Refractories having various component compositions (50 mm ×
50 mm × 50 mm), and these were installed in the siliconized zone of the continuous production line for high silicon steel strips shown in FIG. 1, and this siliconized zone was subjected to a SiCl ₄ concentration of 15 vol% in the atmosphere and a furnace temperature of: After continuous operation at 1200 ° C. for three months, the damage status of each refractory was examined. The results are shown in Tables 2 and 3 together with the component composition of each refractory.

In Tables 2 and 3, 5-No.
Reference numeral 10 is an example of the present invention in which the total content of alkali metals was 0.05 wt% or less. These refractories were discolored on the surface thereof, had low reactivity with the gas in the furnace, and could be used continuously. . No. 11-No. No. 20 has a total content of alkali metals of 0.05 wt% or less, Mg, Ca, Ti,
The total content of each oxide of Fe, Cr and Zr is set to 1.0 w
an invention example in which t% or less, these refractories surface hardly react with the furnace gas which changes color, showing the most excellent durability. On the other hand, no. 21-N
o. It was found that the surface of the refractory of Comparative Example 24 became brittle due to the reaction with the furnace gas, and could not withstand long-term use.

FIG. 2 is a microscopic enlarged photograph of the cross section of the surface of the refractory after three months of use in the present embodiment. Photo (a) shows the refractory of the comparative example (No. 22) in which the surface is altered and embrittled. The refractory (No. 15) of the example of the present invention in which the surface layer is not altered is shown in FIG. The refractory of the comparative example (No. 22) shown in the photograph (a) contains a large amount of Al ₂ O ₃ component, and therefore chlorine gas is contained in the refractory as shown in the schematic diagram of FIG. It is presumed that Al reacts with the Al ₂ O ₃ component to gasify through Al, and as a result, the refractory structure is destroyed and the aggregate falls off. Therefore, it is considered that the main damage of the refractory is caused by the following reaction. 2Al ₂ O ₃ + 3SiCl ₄ → 4AlCl ₃ ↑ + 3SiO ₂ On the other hand, the refractory of the present invention example (No.
15) A refractory according to claim 2 of the present application, wherein the refractory contains an alkali metal, Fe, Cr, Mg, Ti, Zn.
And the total content of oxides of Ca and Ca is small, so that the products in the matrix portion constituting the refractory are also light and damage is small.

[0015]

[Table 2]

[0016]

[Table 3]

[0017]

The refractory of the present invention described above does not cause deterioration or embrittlement over a long period of time when used as a furnace material of a furnace using silicon chloride gas, and has excellent durability. Is shown. For this reason, in a continuous production line of high silicon steel strip by the gas siliconization method, the quality of the product steel strip may be impaired due to the drop of the surface layer of the furnace material, and the dropped furnace material may build up on the roll in the furnace. Therefore, a high-quality steel strip of good quality can be stably manufactured for a long period of time.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a continuous production line for high silicon steel strip by a siliconizing treatment method.

FIG. 2 is an enlarged microscopic photograph showing a structure of a cross section of a surface layer of a refractory used as a furnace material in Examples.

FIG. 3 is an explanatory view schematically showing a damage state of a refractory surface layer due to a reaction with silicon chloride gas.

(56) References JP-A-1-282148 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 35/00-35/599

Claims (2)

(57) [Claims] 1. A composition containing at least 35% by weight of at least one selected from oxides of silicon, nitrides of silicon and oxynitrides of silicon in combination with alkali metals.
A refractory for a furnace using silicon chloride gas , having a total content of 0.05 wt% or less . 2. Mg, Ca, Ti, Fe, Cr and Zr
2. The refractory for a furnace using silicon chloride gas according to claim 1, wherein the total content of each oxide is 1.0 wt% or less. 3.