JPH0283250A - Production of carbon-containing calcined refractory - Google Patents

Abstract

PURPOSE:To obtain a refractory useful as an inner lining material for molten metal container, showing oxidation preventing function even at low temperature by blending an oxide mixture containing specific amounts of carbon and chromium oxide, molding and calcining in an oxidizing atmosphere. CONSTITUTION:A mixture comprising 3-30wt.% carbon (e.g., natural graphite, artificial graphite and pitch coke), 0.1-20wt.%, preferably 0.0-10wt.% chromium oxide (<=0.05mm particle size) and the rest of oxide such as silica rock, agalmatolite, sintered alumina or electrofused magnesia, molded and heat-treated at >=1,2500 deg.C in an oxidizing atmosphere to give carbon-containing calcined refractory.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application: The present invention relates to a method for producing a carbon-containing fired refractory used as a lining material for molten metal containers.

Prior Art: Carbon-containing refractories are often used as lining materials for molten metal containers such as hot metal pots, molten steel pots, pig iron mixers, and converters.

Carbon is very difficult to wet with slag and has excellent thermal shock resistance, and by combining it with refractory raw materials such as alumina or magnesia, a highly durable refractory can be obtained. However, carbon has the disadvantage that it disappears by oxidation, and the oxidized decarburized structure becomes brittle, and erosion due to penetration of slag etc. progresses rapidly.

In order to suppress the oxidation of the contained carbon, which causes this, for example, Japanese Patent Application Laid-Open No. 54-47712, Japanese Patent Application Laid-Open No. 54-1639
Various means for suppressing oxidation are disclosed in JP-A No. 13, JP-A-59-12823, and JP-A-59-110713, but these oxidation suppressing means can be summarized into the following four points. In other words, (1) adding carbides and nitrides such as silicon carbide, boron carbide, silicon nitrogen, and boron nitride, (2) adding easily oxidizable substances such as aluminum, and (3) adding low-carbon materials such as borosilicate glass. (4) Applying borosilicate glass, etc. to the brick surface.

However, in the case of (1), the added carbide or nitride oxidizes itself to form a glass coating or to densify the brick, thereby achieving an oxidation-suppressing effect; however, the slag resistance of the resulting glass layer The corrosion resistance is extremely small and the corrosion resistance deteriorates. Furthermore, if the aggregate is a basic substance such as MgO5CaO, it will chemically react with these substances, producing low melting point substances and reducing slag resistance.
It was limited to combinations with acidic or neutral aggregates such as 3-quality and zircon-based aggregates.

In the case of (2), whether the oxidation suppressing effect of the refractory itself is obtained or the prevention of the formation of the decarburized layer, which reduces the size of the decarburized layer, is insufficient, and in addition, the decarburized layer becomes Al2O3 and reacts with other aggregates. However, a decrease in slag resistance is observed.

In the case of (3), a glass film is formed and the oxidation suppressing effect is increased, or low melting point substances are easily melted and washed away by contact with slag, and are not suitable for areas where slag conditions are severe.

(4) When applying borosilicate glass, etc. to the brick surface,
Although it does have an antioxidant effect, it has the disadvantage that once the surface coating is eroded, the effect cannot be obtained again.

In order to solve these problems, an attempt has been made to suppress oxidation by adding chromium oxide to prevent a decrease in durability (Japanese Patent Application Laid-Open No. 62-56351). However, in this case as well, although the antioxidant effect was expressed in a relatively high temperature range of 1300'C or higher, it did not contribute to the antioxidant effect in the most important low temperature range of carbon-containing refractories.

Problems to be solved: Including the addition of chromium oxide seen in the conventional technology, the above 130
As a means for preventing oxidation in a high temperature range of 0° C. or higher, the purpose is achieved by adding metals such as aluminum and silicon.

However, 1000 to 120 is common to carbon-containing refractories.
It was not possible to achieve a significant effect in preventing oxidation in the low temperature range of use below 0'C.

Means for Solving the Problems: The present invention solves the above-mentioned problems, and by elucidating the mechanism of action of chromium oxide in detail, it has been made to exhibit an antioxidant function even in a low temperature range.

The effect of adding chromium oxide disclosed in JP-A No. 62-56351 theoretically occurs in the reaction form shown in FIG. That is, it is based on the fact that a dense layer of Si02 is formed in a high temperature region near the operating surface. Figure 2 shows the reaction form when chromium oxide is not added.The major difference between Figures 1 and 2 is the rate of CO generation, and the presence of chromium oxide greatly increases the rate of CO generation. So, 5i
02 is formed in a short time and exhibits an antioxidant effect.

Furthermore, in order for the reaction shown in Figure 1 to occur, it is necessary for carbon to be oxidized to CO in advance, and according to detailed research by the present inventors, the weight loss rate determined by the thermobalance shown in Figure 3 is It was found that the temperature changed rapidly at temperatures above about 1250°C. In the method described in JP-A-62-56351, carbon is oxidized by oxygen in molten steel or oxygen injected for hot metal pretreatment, and reacts with chromium, resulting in carbon being deposited in bricks near the working surface. A dense layer of 5i02 was formed to prevent oxidation caused by external factors.

The present inventors focused on this mechanism, and the
By firing at a temperature of 250° C. or higher, the anti-oxidation function is maintained over the entire temperature range, solving the problem that conventional bricks of this type oxidize at low temperatures and reduce their durability.

Structure and operation of the invention: The present invention has excellent both oxidation resistance and corrosion resistance by adding chromium oxide within a certain range to a refractory raw material containing carbon and firing it under specific conditions. A carbon-containing fired refractory having good thermal shock resistance is obtained.

That is, in producing a carbon-containing fired refractory, the present invention involves kneading and shaping a mixture consisting of 3 to 30 wt% carbon, 0.1 to 20 wt% chromium oxide, and the balance being an oxide; and firing in an oxidizing atmosphere. Producing carbon-containing fired refractories; summary of the method.

In addition, carbides and nitrides of 3 to 20 w [%]
It may also be blended with.

The carbon used in the present invention includes natural graphite, artificial graphite, pitch coke, etc., which are used in combination with ordinary refractories. This carbon is blended in an amount of 3 to 30 wt%, and if it is less than 3 wt%, the effect of carbon addition cannot be obtained, resulting in insufficient slag resistance and thermal shock resistance. If it exceeds 30 wt%, the strength and wear resistance of the refractory will decrease. Other refractory raw materials include silica, fused silica, waxite, chamotte, anglesite, kyanite, sillimanite, synthetic mullite, clay shale, bauxite, sintered alumina,
Al 203-Si02 materials such as fused alumina, fused magnesia, sintered magnesia, synthetic spinel, synthetic calcia, zircon, zirconia materials, etc. can be used alone or in combination of two or more.

The chromium oxide that exhibits the characteristics in the present invention has a particle size of 0.05 mm or less in an amount of 0.1 to 20 wt%, preferably 0.5 to 20 wt%.
Add 10 wt%. The reason for setting the particle size to 0.05 a or less is to improve the reaction rate and also to fill the voids in the refractory structure. If the amount added is less than 0.1 wt%, it is difficult to uniformly disperse chromium oxide and the effect of addition is difficult to stabilize. On the other hand, if it exceeds 20 wt%, the fine powder portion of the refractory raw material as a whole becomes too large, which tends to cause cracks and decreases resistance to slag.

In addition, as an oxidation suppressing material, 20 wt% or less of carbides such as silicon carbide and boron carbide, or nitrides such as silicon nitride and boron nitride, or 10 wt% or less of AI, Si,
A metal such as Mg or an alloy thereof may also be used in combination.

A mixture of these materials is kneaded using, for example, a phenol resin as a binder, molded into a predetermined shape, and then dried.

Furthermore, heat treatment is performed in an oxidizing atmosphere at 1250°C or higher,
It is used as a fired brick.

The carbon-containing fired refractory obtained by the method of the present invention completely prevents carbon oxidation at low temperatures during use, and can be used as lining bricks in required parts of hot metal ladle, molten steel ladle, pig iron mixer, converter, etc. However, it shows excellent durability.

Examples: Using fire-resistant raw materials with the chemical components shown in Table 1, and according to the blending ratios shown in Table 2, the present invention examples (1 to 6) and comparative examples (!7 to 10) containing carbon or chromium oxide Blends with blending ratios outside the range of the present invention examples) and conventional examples (11 to 13) were obtained. This mixture was kneaded using a phenol resin as a binder and molded into a template shape using a friction press.

Then, it was dried by passing through a tunnel drying oven at 150°C and fired at 1300°C in an oxidizing atmosphere.
~13 were created.

The physical property values and characteristic values of each of these samples were measured, and the first
It is also shown in the table. Physical properties were determined by the refractory test method based on JIS. Characteristic values were determined by the following method.

a. For the thickness of the oxidized decarburized layer, a 5 x 5 x 56 In cube was cut out as a specimen, heated at 1400'C for 16 hours, then sliced into each part to measure the thickness of the decarburized layer, and the average of each part was calculated. .

b For corrosion resistance, cut out a specimen of an appropriate size,
Using 100% slag with basicity 3 by rotary erosion method, 1
Tested at 500°C for 5 hours. The degree of erosion was expressed as a ratio, with the erosion occurring in the conventional example being taken as 100. The smaller this value is, the richer the corrosion resistance is.

c Regarding heat-resistant spalling property, one side of the above-mentioned template-shaped specimen was heated to 1400°C, held for 30 minutes, and then taken out. This operation was repeated five times and the heated surface was visually observed. Those with no cracks were evaluated as ◎, those with fine cracks were evaluated as ○, and those with large cracks accompanied by peeling were evaluated as ×.

As is clear from the above test results, the present invention examples, K1 to 6, which have a specific amount of chromium oxide added and are fired at a constant temperature range, have improved properties compared to the comparative or conventional examples. Remarkably recognized.

Effects of the invention: The carbon-containing fired refractory obtained by the method of the present invention effectively prevents carbon oxidation, which has conventionally been a problem at low temperatures.
Approximately 30% improvement in durability was observed in actual furnace tests. Furthermore, it increases operational stability and contributes to the creation of refractories that can withstand use under harsh conditions without using special raw materials, so it has great industrial applicability.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the reaction form of the components depending on the working surface temperature of a carbon-containing refractory to which chromium oxide is added, Fig. 2 is an explanatory diagram showing the same reaction form when no chromium oxide is added, Fig. 3 is a diagram showing the weight reduction rate of carbon-containing refractories measured on a thermobalance. Applicant: Harima Firebrick Co., Ltd.

Claims (1)

[Claims] 1. 3 to 30 wt% carbon, 0.1 to 20 wt% chromium oxide
1. A method for producing a carbon-containing fired refractory, comprising: kneading and molding a mixture in which the balance is an oxide; and firing the molded body in an oxidizing atmosphere. 2 The compound to be kneaded and molded contains 3 to 30 wt% carbon,
2. The method for producing a carbon-containing fired refractory according to claim 1, wherein the chromium oxide is 0.1 to 20 wt%, the carbide and/or nitride is 3 to 20 wt%, and the balance is an oxide.