JPH07291716A - Basic refractory - Google Patents

Abstract

PURPOSE:To provide a basic refractory improved in corrosion resistance by making the structure dense. CONSTITUTION:This basic refractory is formed by adding 0.5-10wt.% titanium oxide into 100wt.% blended material composed of one or more kind of a magnesia clinker, a chromium ore, an electrofused magnesite-chrome clinker and chromium oxide and having (9:1) to (2:8) chemical composition ratio of (MgO:Cr2 O3), kneading, molding and burning.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molten metal container, and more particularly to a basic refractory lining for a molten metal vacuum processing container.

[0002]

2. Description of the Related Art Conventionally, in a steelmaking process, degassing treatment is carried out in a vacuum treatment container such as RH or DH equipment in order to remove impurities in molten steel.

As the lining material for these vacuum processing vessels, a magnesia / chromic refractory, which is a stable material under vacuum, is usually used, and a calcined magnesia / refractory material having excellent wear resistance against molten steel flow is used. It can be said that chrome refractories are suitable.

Further, the magnesia-chrome refractory is a refractory having excellent corrosion resistance due to a chemical reaction with slag or molten steel.

The magnesia / chromic refractory material can be roughly classified into direct bond and ribbond, depending on its raw material composition.

The former uses a high-purity synthetic magnesia clinker as a magnesia source and natural chrome ore as a chromium source. A suitable binder is added to these compounds and press-molded to obtain a temperature of 1600 ° C. It is manufactured by firing at the above high temperature.

On the other hand, the latter is obtained in the same manner as the former, using a low-impurity electromelting clinker obtained by previously melting magnesia clinker and chrome ore in an electric furnace, cooling and crushing.

A material having an intermediate property between the two,
That is, there are some which use a mixture of magnesia clinker, chrome ore, and electrofused magcro, which is called semi-ribbon.

By the way, one of the factors affecting the corrosion resistance of refractory materials is porosity. Since the melting loss of the refractory material progresses due to the chemical reaction between the refractory material and the slag or molten steel, the melting loss increases due to the penetration of the slag into the pores of the refractory material. Therefore, the smaller the porosity, the more this phenomenon can be suppressed, resulting in high corrosion resistance.

In the case of magnesia / chromic refractory, various means for ensuring low porosity, for example, chromium oxide powder is added to promote sintering (Japanese Patent Publication No. 57-5742).
No. 8, etc.), and metal chromium or the like is mixed and densified by volume expansion during firing (Japanese Patent Publication No. 44-18738, etc.).

[0011]

However, the aforementioned Japanese Patent Publication No. 57-57428 and Japanese Patent Publication No. 44-187.
Even the refractory obtained by the method of Japanese Patent No. 38, etc. has an apparent porosity of about 10% and the structure is not sufficiently densified.

An object of the present invention is to provide a refractory material having a denser structure and improved corrosion resistance as compared with refractory materials obtained by the conventional method.

[0013]

The present invention comprises at least one of magnesia clinker, chromium ore, electrofused magcro clinker and chromium oxide, and has a chemical composition ratio of MgO: Cr ₂ O ₃ of 9: 1 to 2. : Titanium oxide is added in an amount of 0.5 to 10% by weight with respect to 100% by weight of the mixture of 8: 8, and the mixture is kneaded, molded, and fired.

[0014]

The magnesia clinker may be either an electromelted product or a sintered product, and it is desirable that the magnesia clinker has a purity of 90% or more in order to prevent deterioration of corrosion resistance due to impurities.

The chromium ore preferably has a chromium oxide content of 30% or more in order to prevent deterioration of corrosion resistance due to impurities and to exert the effect of improving corrosion resistance due to chromium oxide.

It is desirable that the electrofused magcro clinker has a purity of 90% or more in order to prevent deterioration of corrosion resistance due to impurities.

Chromium oxide preferably has a purity of 90% or more in order to prevent deterioration of corrosion resistance due to impurities.

As the titanium oxide crystal, either rutile type or anatase type can be used, and it is preferable that the titanium oxide crystal has a purity of 90% or more in order to prevent deterioration of corrosion resistance due to impurities.

The added titanium oxide exhibits the effect by reacting as follows in the firing step in manufacturing the refractory.

The titanium oxide added to Magukuro compositions formulated reacts with constituents of the refractory during firing of the _{refractory, 2MgO · TiO 2, MgO ·} TiO 2, MgO ·
2TiO ₂ is generated, a liquid phase sintering reaction occurs at 1600 ° C. or higher, and titanium oxide forms a solid solution in MgO or Cr ₂ O ₃ to form lattice defects, which promotes volume diffusion and magnesia. Densify the structure of chrome refractories.

[0021] In this way, the densification of the structure suppresses the intrusion of slag, molten steel, etc. into the refractory, and the durability of the magnesia / chromium refractory can be enhanced.

The firing is preferably performed at a temperature of 1600 ° C. or higher in order to exert the effect of adding titanium oxide.

The amount of titanium oxide added is set to 0.5 to 10% by weight, if the amount is less than 0.5% by weight, the effect of densifying the structure is insufficient, and if it exceeds 10% by weight, 2Mg is added.
O · TiO _2, the amount of _{MgO · TiO 2, MgO · 2TiO} 2 is too much, because the corrosion resistance decreases.

The same effect can be obtained by using any one of the direct bonding, the ribboned and the semi-ribboned maguro compositions containing titanium oxide.

[0025]

[Examples] Table 1 shows examples of magnesia-chromic refractories for vacuum processing vessels.

The magnesia / chromium refractory molded body is made of three kinds of materials having the chemical composition shown in Table 1, that is, direct bond (DB), ribboned (RB) and semi-ribboned (SRB), and contains a predetermined amount of titanium oxide. Was added.

A 450 × 150 × 150 mm magnesia / chromium refractory molding was fired at 1750 ° C. for 5 hours.

The corrosion resistance test was carried out by the rotary erosion method, test conditions: 1650 ° C. × 3 hours, slag composition: Al ₂ O ₃ = 17.
% By weight, CaO = 50% by weight, SiO ₂ = 16% by weight,
CaF ₂ = 17% by weight, and the erosion amount of the comparative example of the same kind to which titanium oxide was not added is shown as 100.

The magnesia / chromium refractory moldings for comparison with the present invention were made of direct bond (DB), ribboned (RB), and semi-ribboned (SRB) having the chemical compositions shown in Table 1 at 1750. It was baked at ℃ × 5 hours, and the above-mentioned corrosion resistance test was conducted. The results are also shown in Table 1.

[0030]

[Table 1]

In the evaluation of the examples, compared with the comparative examples, those in which the apparent porosity was decreased, the strength was improved, the air permeability was decreased, and the corrosion resistance was improved at the same time were evaluated as ◯, and the other samples were evaluated as x.

As is clear from the comparison among DB, SRB, and RB, the refractory material of the present invention has a significantly reduced porosity and air permeability and a significantly improved strength and corrosion resistance as compared with the comparative example. It is understood that there is.

[0033]

According to the present invention, the following effects can be obtained.

As compared with the refractory obtained by the conventional method for improving the texture of a basic refractory, it is possible to improve the texture very uniformly and effectively, thereby obtaining a basic refractory having high corrosion resistance. This is extremely effective for extending the life of refractory linings in molten metal containers, improving productivity, and reducing costs.

Claims (1)

[Claims] 1. A blend of 100 parts by weight of at least one of magnesia clinker, chromium ore, electrofused magcro clinker and chromium oxide, and a chemical composition ratio of MgO: Cr ₂ O ₃ of 9: 1 to 2: 8. %, Titanium oxide is added in an amount of 0.5 to 10% by weight, and the mixture is kneaded, molded and fired, and a basic refractory material.