JPH01305849A - Magnesia-carbon brick - Google Patents

Abstract

PURPOSE:To obtain a magnesia.carbon brick having improved mechanical strength and wear resistance without deteriorating thermal shock resistance by blending starting material for magnesia with carbon fibers. CONSTITUTION:Carbon fibers are added to starting material for magnesia by 0.1-50wt.% (inner percentage) of the amt. of the starting material to obtain a magnesia.carbon brick. Sintered magnesia clinker, electromelted magnesia clinker or other magnesia clinker may be used as the starting material for magnesia. When the corrosion resistance of the brick is improved, starting material contg. >=90% magnesium oxide is preferably used. The carbon fibers may be carbonaceous or graphitic carbon fibers obtd. by heat-treating synthetic resin fibers typified by commercially available polyacrylonitrile fibers or pitch fibers at a high temp. The pref. diameter of the carbon fibers is 2-50mum.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to magnesia carbon bricks, and in particular,
This invention relates to a magnesia carbon brick that has improved mechanical strength and abrasion resistance without reducing thermal shock resistance.

[Conventional technology and its issues]

Magnesia carbon bricks have become widely used as refractories for steelmaking in recent years because of their excellent corrosion resistance and thermal shock resistance. However, magnesia carbon bricks have disadvantages in terms of increasing mechanical strength and wear resistance due to the disadvantage that carbon disappears in an oxidizing atmosphere and the properties of graphite, which is the main carbon source. For example, damage is severe in areas that are subject to mechanical shock and wear due to the input of scrap and hot metal, such as the charging side wall of a converter, which is one of the causes of shortening the life of the furnace body. .

Therefore, in order to increase the mechanical strength and wear resistance of magnesia carbon bricks, it has been proposed to add metal powders such as aluminum, silicon, magnesium, and calcium, but as long as graphite is used as the main carbon source, It is not possible to achieve dramatic improvements in strength and wear resistance, and the metal additives may harden the bricks after heating, resulting in a decrease in thermal shock resistance.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a magnesia carbon brick that can improve mechanical strength and abrasion resistance without reducing thermal shock resistance. That is.

[Means to solve the problem]

As a result of intensive research, the present inventors deduced that the cause of disadvantageous mechanical strength and wear resistance of magnesia carbon bricks was the use of graphite as the main carbon source. The inventors have discovered that the above objects can be achieved by using carbon fibers with high mechanical strength as a carbon source, and have completed the present invention.

That is, in order to achieve the above object, the magnesia-carbon brick according to the present invention is characterized in that 0.1 to 50% by weight of carbon fiber is added to the magnesia raw material.

[Effect]

Carbon fiber has higher mechanical strength than flaky graphite and the like, and can obtain the same level of thermal shock resistance with a much smaller amount of use than flaky graphite.

In addition, carbon fiber has a high tensile strength in the longitudinal direction of the fiber, and does not have a layered structure like graphite scales, so there is almost no decrease in strength due to the addition of carbon fiber.On the contrary, it can be strengthened by reinforcing the binding material. is enhanced.

The F gnesia raw material used in the present invention is not particularly limited, and for example, one or more of sintered magnesia clinker, fused magnesia clinker, other magnesia clinkers, etc. can be used. . However, if we take into account the improvement of the corrosion resistance of bricks, it is preferable to use a material containing 90% or more of magnesium oxide (MgO).

The carbon fibers used in the present invention are not particularly limited, and include, for example, commercially available synthetic resin fibers such as polyacrylonitrile fibers, carbonaceous or graphite fibers obtained by heat-treating pinch fibers at high temperatures. Carbon fiber can be used. The fiber length of the carbon fiber is preferably 0.1 to 50+n, more preferably 0.5 to 20 m. If the fiber length of the carbon fiber is less than O3l mi, it is not preferable because the peeling prevention effect becomes poor, and if it exceeds 50 m, it becomes difficult to mix uniformly with the magnesia raw material, which is not preferable. It is particularly preferable that the carbon fiber has a fiber length of 0.5 to 20 fins, since a sufficient peeling prevention effect can be obtained and it can be easily mixed uniformly with the magnesia raw material. The diameter of the carbon fiber is preferably 2 to 50 μm. If the diameter of the carbon fiber is less than 2 μm, it is not preferable because the required strength cannot be obtained, and if it exceeds 50 μm, the flexibility becomes poor and the moldability of the brick is impaired, so it is not preferable.

It should be noted that within this range, there is no hindrance to mixing and using carbon fibers having different fiber lengths and diameters. The amount of carbon fiber added is preferably 0.1 to 50% by weight based on the magnesia raw material, and 0.5% by weight.
It is more preferable to set the content to 10% by weight. If the amount of carbon fiber added is less than 0.1% by weight, the effect of adding carbon fiber to improve strength and thermal shock resistance will be insufficient, which is undesirable, and if it exceeds 50% by weight, it will be difficult to mix uniformly with the magnesia raw material. Undesirable. It is particularly preferable that the amount of carbon fiber added is 0.5 to 10% by weight, since it can be easily and uniformly mixed with the magnesia raw material, and the effect of adding carbon fiber to improve strength and thermal shock resistance can be sufficiently obtained.

In addition, when the magnesia carbon brick according to the present invention is used in a particularly strongly oxidizing atmosphere, the carbon fibers and the bonding parts may be oxidized and wear and tear may be significantly increased. To prevent this, metal powders such as aluminum, silicon, magnesium, and calcium, magnesium
Total amount of one or more oxidation inhibitors such as aluminum, aluminum-silicon, magnesium-aluminum-calcium, magnesium-aluminum-silicon alloy powder, boron carbide (84C) powder, boron nitride (BN) powder, etc. It may be added in an amount of 0.2 to 30% by weight. If the total amount of these additives is less than 0.2% by weight, the anti-oxidation effect will not be sufficient, which is undesirable; if it exceeds 30% by weight, the volumetric expansion during carbonization or oxidation of the additives will increase, and the brick become porous,
This is not preferable as it may cause cracks.

Further, the procedure for manufacturing the magnesia carbon brick of the present invention is not particularly limited as long as it has the above-mentioned composition. For example, after adding and mixing carbon fiber to the magnesia raw material whose particle size has been adjusted, Add one or more selected organic binders such as liquid or powder pitch, tar, phenolic resin, etc.
After kneading and molding, the magnesia carbon brick is then heat-treated at a low temperature of 100 to 400°C to obtain an unfired product, or it is heat-treated at a high temperature of 400°C or higher in a reducing atmosphere to produce a fired product. Magnesia carbon bricks are obtained. Furthermore, the magnesia carbon brick as a fired product may be used after being impregnated with pinch, phenol resin, etc., if necessary.

〔Example〕

Examples of the present invention will be described below.

Sintered magnesia clinker with MgO purity of 98% by weight,
The mixture was mixed with carbon fiber as shown in Examples 1 to 5 in Table 1, kneaded in a roll pan using phenol resin as a binder, and then molded into a dish-shaped brick shape using a 500 mm hydraulic press. A magnesia carbon brick was obtained as an unfired product by heat treatment at 250° C. for 12 hours.

In addition, as a comparative example, sintered magnesia clinker with an MgO purity of 98% by weight and scaly graphite were used in Comparative Examples 1 to 4 in Table 1.
After mixing in a roll pan using phenol resin as a binder, it was formed into a dish-shaped brick shape using a 500-ton hydraulic press, and heat-treated at 250°C for 12 hours to form an unfired product. Obtained Magnesia Carbon Brick.

For each example and each comparative example, room temperature bending strength test, 1
A 400°C bending strength test, a thermal shock resistance test, and an oxidative wear test were conducted. These test conditions are as follows.

First, the room temperature bending strength test was performed by three-point bending with a span of 100 m.

In addition, the 1400° C. bending strength test was performed by holding the specimen buried in coke pleat at 1400° C. for 30 minutes, and then performing three-point bending with a span of 127.5 mm.

In the thermal shock resistance test, a brick was immersed in molten steel at 1,700°C for 3 minutes, taken out, and allowed to cool to room temperature in a carbon pleat.The operation was repeated, and the number of times until peeling occurred was counted.

In the oxidation wear test, 12 cubic specimens with 50 irises on each side were
The sample was rotated for 30 minutes at 2Or, p, m in a rotary furnace at 00°C, and the weight loss rate after cooling was measured.

The results of these tests are shown in Table 1.

As is clear from Table 1, the magnesia carbon bricks according to each example have significantly higher room temperature bending strength and 1400° C. bending strength than those to which conventional scaly graphite is added.

It also has far superior thermal shock resistance. That is, in Examples 2 to 4 in which 2% by weight of carbon fiber was added, 20% of scale graphite was added.
It is equivalent to or higher than Comparative Examples 2 to 4 in which carbon fiber is added in an amount of 0.5 weight %, and Example 1 in which carbon fiber is added in an amount of 0.5 weight % is superior to Comparative Example 1 in which scaly graphite is added in an amount of 10 weight %.

Furthermore, in Comparative Example 4 in which scale graphite and carbon fiber were used in combination, the effect of adding carbon fiber to Comparative Example 3 was not seen.

Furthermore, since each of the examples of the present invention contains less carbon than each of the comparative examples, it can be seen that they are significantly superior in oxidative wear resistance.

Furthermore, the bricks of Example 4 were used for the charging side wall of a 250-ton converter, and as a result of a practical test comparing them with a conventional product containing 20% graphite, the wear rate of the conventional product was 2.4 mm/ch. In contrast, in Example 4, it was 1.81■/ch.
It was confirmed that the durability was improved.

(The following is a blank space) [Effects of the Invention] As explained above, the magnesia carbon brick of the present invention uses carbon fiber with high mechanical strength as a carbon source instead of a carbon source having a layered structure such as scaly graphite. By doing so, it was possible to dramatically improve mechanical strength and I'iit abrasion resistance without reducing thermal shock resistance.

Claims (1)

[Claims] (1) A magnesia carbon brick characterized by adding 0.1 to 50% by weight of carbon fiber to the magnesia raw material.