JP2765458B2 - Magnesia-carbon refractories - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnesia-carbon refractory used for various molten metal containers such as converters, electric furnaces, ladles and the like.

[0002]

2. Description of the Related Art In recent years, magnesia-carbon brick has been widely used for refractory linings of molten metal containers such as converters, electric furnaces, ladles, and the like, as the operating temperature increases. The magnesia-carbon brick prevents the spalling of the brick by covering the ease of slag penetration of magnesia with the low slag wettability of the carbonaceous material. However, the basicity of slag (CaO / S
When the slag has a low iO ₂ ) and a high content of Al ₂ O _{3 in} the slag, the viscosity of the slag is extremely reduced, so that the slag penetrates into the magnesia-carbon brick, Increases erosion and spoils.

In order to cope with such slag, a magcalcia clinker or a dolomite clinker containing a CaO component which is effective in preventing slag penetration is used as a magnesia clinker.
Magnesia-carbon brick used in combination with the above (for example, JP-A-61-141663).

[0004]

When a molten metal container using such a material containing a CaO component is used intermittently, a phenomenon occurs in which the brick absorbs moisture, digests and collapses. The material containing the CaO component cannot be used at all, especially in the fine powder portion, which has a great influence on slag penetration, because it is intensely digested, and its effect is small when used only in coarse and medium grain portions.

[0005] Further, as a material containing another CaO component, C
aCO ₃ and Ca (OH) ₂ may be added,
At a temperature of 0 to 600 ° C., the slag becomes porous with the disappearance of CO ₂ and H ₂ O, so that the slag penetration preventing effect is hardly observed. Further, a method of adding chromium oxide to reduce spoiling due to slag infiltration and use of magcro brick are known. However, the chromium oxide component is a material that one does not want to use for environmental measures.

[0006]

Means for Solving the Problems The present inventors have studied the permeation of slag and also considered the corrosion resistance of refractories, and as a result, have arrived at the present invention focusing on lime nitrogen.
That is, the present invention relates to a carbonaceous material of 1 to 25% by weight,
-20% by weight or, in addition, 0.2 to 5% by weight of one or more of metal powders or alloy powders thereof selected from the group consisting of aluminum, silicon, magnesium, and calcium, and the balance Is a magnesia-carbon refractory made of a refractory material mainly composed of magnesia. The refractory of the present invention has a feature that it can be used in a form such as an unrefractory fixed refractory as well as an unfired fixed refractory.

The refractory material mainly composed of magnesia used in the present invention may be a known magnesia-based refractory material such as an electro-fused magnesia clinker, a sintered magnesia clinker, a natural magnesia clinker, or these materials alone or magnesia. -It can be used by mixing with alumina spinel clinker. These refractory materials contain 50 MgO.
It is preferable from the viewpoint of slag corrosion resistance that the content is not less than% by weight.

As the carbonaceous material, natural graphite, artificial graphite,
Petroleum coke, carbon black, etc. can be used,
From the viewpoint of corrosion resistance at high temperatures, graphite, which is also of high purity, is suitable. The amount of the carbonaceous material used is 1 to 25% by weight. If the carbonaceous material exceeds 25% by weight, the thermal conductivity of the brick will increase, causing problems such as red heat of the steel shell and temperature drop of the steel, and the problem of steel contamination due to carbon elution.
Conversely, if the amount of the carbonaceous material is less than 1% by weight, the effect of preventing the slag from penetrating the carbonaceous material is not obtained, and the spoiling resistance becomes extremely inferior.

The amount of lime nitrogen used in the present invention is 0.2 to 20% by weight of the refractory. Lime nitrogen usage is 0.2
If the amount is less than 20% by weight, a sufficient slag penetration inhibiting effect is not exhibited, and if it exceeds 20% by weight, the corrosion resistance is reduced. Lime nitrogen contains calcium cyanamide (CaCN ₂ ) as a main component, and may contain a small amount of carbon in the production method, but may be used without any problem. There is no restriction on the particle size used, but the effect is great when used in the fine powder portion.

Further, when the magnesia-carbon refractory of the present invention is used in a violent oxidizing atmosphere, aluminum, lime and nitrogen are used as antioxidants for carbonaceous materials and lime nitrogen.
Metal powders such as silicon, magnesium and calcium can also be added. These metal powders are added alone or as one kind of alloy or as a mixed powder of two or more kinds. Among them, silicon in particular not only functions as an antioxidant, but also has an effect of preventing digestion of CaO generated by oxidation of CaCN ₂ . The addition amount of these metals is desirably 0.2 to 5% by weight. If the amount is less than 0.2% by weight, the effect of addition is not exhibited. If the addition amount exceeds 5% by weight, the corrosion resistance and spoiling resistance of the refractory deteriorate. Not preferred.

In the method for producing a low-carbon magnesia-carbon refractory of the present invention, when used as a fixed refractory, the raw materials are weighed according to a conventional method, a binder is added, and the mixture is kneaded and press-molded. . This is used as it is or as a non-fired brick after heat treatment at a temperature of 600 ° C. or less. As the binder, any of phosphate-based, silicate-based inorganic binders, and organic binders such as phenol resin can be used.

[0012] The refractory is mainly used as a cast material, but may be used in other forms. In this case, too, a raw material, a binder, a dispersant, a plasticizer, a curing modifier, and the like are appropriately selected and mixed with water and other solvents as usual. Alumina cement as a binder,
Sodium silicate, phosphate and the like can be used. Non-aqueous use using an organic binder such as phenol resin is also possible.

[0013]

[Function] A low basicity slag with a basicity of 1 or less in a metal container operated at a high temperature. If the content of Al ₂ O ₃ in the slag is 15% by weight or more, the viscosity of the slag is extremely reduced, and the fire resistance is reduced. If the object is composed only of magnesia and a carbonaceous material, the penetration of slag cannot be sufficiently suppressed, so that the structural slag is likely to occur due to the penetration of slag. If the carbonaceous material content is increased to 25% by weight or more for the purpose of preventing this, the refractory becomes too high in heat conductivity, causing problems such as red heat of the steel shell and a decrease in the temperature of the steel, and contamination of steel due to elution of carbon. There is a problem and it cannot be used Since CaCN _2, which is a component of lime nitrogen used in the present invention, is a non-oxide containing no oxygen atom, its wettability to slag is small, and the effect of suppressing slag penetration is particularly large. Also, since CaCN ₂ is not digestible, it can be used not only as coarse and medium-sized refractories but also as fine powder, so that the effect of suppressing slag penetration is great. Further, even if CaCN ₂ is oxidized at a high temperature, the refractory hardly becomes porous because the O atoms make up a considerable portion of the portion from which the C and N atoms have been removed, and the CaO that is formed is hardly formed. Dissolves in the slag, exerting the effect of increasing the viscosity of the low-viscosity slag and suppressing penetration. As a result, structural spoiling is prevented as well as erosion is prevented.

[0014]

EXAMPLES Trial production was performed using materials and binders having the compositions shown in Table 1. Similarly, samples having the composition shown in Table 2 were prepared as comparative examples. The compositions in Tables 1 and 2 are all shown in parts by weight. The molding methods "P" in Tables 1 and 2 were obtained by kneading and press molding according to a conventional method, and "V" was obtained by adding water to the material and then casting it by vibration using a rod-shaped vibrator. It is. Similarly, "Dry" shown in the column of the heat treatment method in Tables 1 and 2 was obtained by drying at 150 ° C. for 24 hours, and “Heat” was obtained by heat treatment at 300 ° C. for 10 hours. Tables 1 and 2 also show the physical properties of the samples thus manufactured.

The spalling resistance test was performed by melting in an induction furnace.
A sample of 40 × 40 × 114 mm was immersed in hot metal at 1400 ° C., taken out after 3 minutes, cooled naturally, and observed for cracks. Those having no crack were further immersed for the second time or later, and the state of the crack at the time when the crack occurred was observed. The expression of the crack size is as follows: "fine" means that only a few cracks were observed on the surface, "small" means small cracks,
"Medium" indicates moderate cracks, and "Large" indicates large cracks.

The slag test was carried out at 1700-1800 ° C. for 3 hours using a rotary slag test furnace and a propane-oxygen burner. The slag was replaced every hour after reaching a predetermined temperature. Further, at the first and second hours after the holding, an operation of cooling to 1000 ° C. with an air blow and then raising the temperature again was added in order to easily generate spoiling. The results are shown in Tables 1 and 2. The slag composition was 25% Al ₂ O _{3 and} 31% SiO ₂
%, Fe ₂ O ₃ 9%, CaO 30%, MgO 5%, C /
S = about 1 was used. "None" in the results of Tables 1 and 2
Indicates that no cracks were found on the cut surface of the sample after the test, "Large" indicates that large cracks occurred, "Medium" indicates moderate cracks, and "Small" Indicates small cracks, and “fine” indicates only a few cracks. The thickness of the permeation layer was indicated by the thickness of the densified portion from the back of the operating surface to the inside of the brick.

[0017]

[Table 1]

[0018]

[Table 2]

The results of the slag test shown in Tables 1 and 2 also show the samples to which the lime nitrogen of the present invention was added (Examples 1 to 7).
In each case, the permeation thickness of the slag is very small as compared with the magnesia-carbon brick (Comparative Examples 1 and 2) and the magnesia-carbon based refractory (Comparative Example 3) added with spinel. As a result, almost no cracking was observed as seen from the structural spolling, and a result of little erosion was obtained. However, when the amounts of lime nitrogen and metal powder are too large (Comparative Examples 5 and 6), it can be seen that the amount of erosion increases even though slag penetration can be prevented to some extent.

Further, as can be seen from the results of the thermal sporling test, no cracks occurred in the sample of the present invention in the first test, and only small cracks were observed in the second and subsequent tests. On the other hand, in each of the comparative examples, a considerable crack was formed in the first or second test, and a large difference was generated between the refractory of the present invention and the refractory of the present invention.
It can be seen that the ring properties are also excellent.

[0021]

According to the present invention, a low carbonaceous magnesia car
By adding lime nitrogen and further metal powder to the bon-based refractory, as is apparent from the results of the examples, the penetration of slag into the refractory is prevented, and the refractory by structural spoiling is prevented. Damage can be minimized. Also, it has excellent heat-resistant spoiling properties and slag corrosion resistance.

Claims (2)

(57) [Claims] 1 to 25% by weight of carbonaceous material, 0.2% of lime nitrogen
A magnesia-carbon refractory comprising about 20% by weight, with the balance being a refractory material mainly composed of magnesia. 2. Carbonaceous material 1 to 25% by weight, lime nitrogen 0.2
~ 20% by weight, aluminum, silicon, magnesium,
Magnesia carbon containing 0.2 to 5% by weight of one or more metal powders or alloy powders thereof selected from the group of calcium, and the balance being a refractory material mainly composed of magnesia. Series refractories.