JPH02267158A - Refractory for metallurgy - Google Patents

Abstract

PURPOSE:To obtain an MgO-CaO refractory for metallurgy having excellent corrosion resistance and digestion resistance by calcining a composition composed of an MgO-CaO refractory aggregate having a specific composition and a calcium compound having a specific melting point. CONSTITUTION:The objective refractory can be produced by calcining a composition composed of an MgO-CaO refractory aggregate having an MgO/CaO molar ratio of 100/0 to 60/40 and one or more kinds of calcium compounds having a melting point of <=1500 deg.C. The calcium compound is e.g. CaF2, CaCN2, CaCl2 or Ca(NO3)2 and its amount is preferably about 0.05-0.3 mol per 1mol of the MgO in the aggregate particle. The particle size of the compound is smaller the better. The calcination is carried out preferably by heat-treating the composition at a temperature near the melting point of the compounded calcium compound and then calcining at <=1800 deg.C or thereabout. A dense MgO-CaO metallurgical refractory having excellent corrosion resistance and digestion resistance can be produced by this process. When a carbon component is added to the clinker produced by the above heat-treatment, an MgO-CaO-C metallurgical refractory capable of suppressing the MgO-C reaction can be produced.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is directed to MgO-CaO system or MgO-CaO-C
Regarding metallurgical refractories of
The present invention relates to a metallurgical refractory that is enriched with aO and has excellent corrosion resistance and digestion resistance, and is used for lining a refining furnace.

(Prior Art) Magnesia-dolomite-based refractories have conventionally been used as linings for smelting furnaces, especially converters. However, in recent years, as operating conditions have become more severe and demands for steel cleaning have increased, there has been a desire to develop refractories with better corrosion resistance than before, and various proposals have been made.

For example, JP-A-58-74564 proposes a fired refractory in which finely divided CaO is added to MgO. This is fine CaO using MgO as a matrix.
By uniformly dispersing the slag, MgO imparts spalling resistance, and CaO increases the melting point of the slag, thereby preventing the slag from penetrating into the refractory. However, since this refractory contains fine CaO, it has poor digestion resistance and its structure is significantly weakened. Therefore, there was a problem that it was difficult to handle.

In addition, a refractory has been developed in which spalling resistance is imparted by generating MgO crystals of 100p or less in CaO clinker by sintering and at the same time forming microcranks. However, since this refractory usually contains a sintering aid to lower the temperature (1800 to 2500'C) during sintering, it is difficult to obtain stable corrosion resistance. Furthermore, the presence of the formed microcrystals results in an increase in the specific surface area of the CaO clinker, which is undesirable because it promotes the digestive action of CaO.

On the other hand, high-purity Mg0-C-based unfired bricks have been developed as refractories that fundamentally improve the disadvantages of the above-mentioned fired refractories and exhibit high corrosion resistance. Since this brick does not contain CaO, there is no need to worry about weakening of the structure due to CaO digestion, and it shows a revolutionary effect in normal converter operation. However, depending on the usage conditions, Mg0-C reaction may occur. This results in tissue deterioration. In particular, it has been found that when this brick is used in the melting of stainless steel, its corrosion resistance against low basicity slag is poor. Furthermore, in the case of slag containing CrzOs, the blended carbon is oxidized, so the brick structure is significantly weakened, and the corrosion resistance may be inferior to that of conventional fired MgO--CaO-based refractories.

Under these circumstances, recently unfired Mg0Ca
OC-based refractories have been developed.

Japanese Patent Publication No. 61-27349 states that the Fe2O3 content is 0.1% or less and the MgO/CaO ratio is 10/90 to 90/
It describes a refractory mainly containing electrofused MgO--CaO clinker having a composition of 10 and a particle size of 0.2 mm or more. The refractory includes a carbonaceous material as a second component. However, since this refractory uses electrofused gOCaO clinker, clinker production is difficult even when auxiliary agents such as Fe2O3 are added.
Since it is necessary to carry out the process at a temperature exceeding 000°C, the manufacturing cost is high. In addition, this clinker contains MgO and Ca.
The composition range in which O forms a solid solution is narrow (and the difference in melting point is large (MgO: 2800°C, cao: 2570'C)
Therefore, the fractional crystallization action works in the solidification process after electric melting,
Mg.

The formation and coarsening of Ca0 grains are likely to occur. Therefore, C
The recovery rate of clinker in which aO and MgO are uniformly dispersed is low, and this also increases the production cost, making it difficult to put it into practical use on an industrial scale.

(Problem to be solved by the invention) As mentioned above, MgO-CaO system or MgO-C
Although it is known that the corrosion resistance of a0C-based refractories is improved by uniformly dispersing CaO (CaO enrichment) in the microstructure, Ca
The current situation is that an optimal method for supplying CaO into refractories for O enrichment has not been found. In particular, with regard to bricks containing carbon, a low-cost and stable manufacturing method that enables CaO enrichment, which is also a means of suppressing the Mg0-C reaction, has not been established.

The current situation is that the oxide raw materials are MgO and Ca, both of which have high melting points.
This is due to the combination with O. The disadvantages of the CaO enrichment method for the conventional refractories are summarized below.

■Refined C, a In the method of adding O, the structure tends to become brittle due to poor digestion resistance.

■In the method of producing uniformly dispersed particles of CaO by sintering MgO and CaO, the amount of sintering aid added is increased in order to lower the clinker production temperature, but the corrosion resistance performance itself decreases accordingly. become.

■In the method using electrofused MgO-CaO clinker, Ca
Because it is difficult to obtain uniformly dispersed particles of O, the manufacturing cost is high;
Industrial practicality is low.

In addition, in any of these methods, MgO-CaO-C obtained by blending carbon content with MgO-CaO-based clinker
It is not possible to sufficiently enrich the refractory with CaO to suppress the M, 0-C reaction, and the conventional method lacks manufacturing stability.

The object of the present invention is to provide an MgO-CaO-based refractory that does not have the problems of the above-mentioned prior art and has excellent corrosion resistance and digestion resistance, and an MgO-CaO-C refractory that can suppress the Mg0-C reaction.
The purpose of the present invention is to provide refractories based on refractories.

(Means for solving the problem) As a result of various studies to achieve the above object, the present inventors have found that conventionally, in order to enrich CaO in a refractory matrix, high melting point Previously, CaO was supplied as it is or as a finely divided version of CaO, but instead of CaO,
The present invention was completed based on the discovery that CaO enrichment can be advantageously carried out at a relatively low temperature by supplying a calcium compound with a lower melting point than O to the surface of the aggregate.

Herein, the present invention provides that MgO/CaO has a molar ratio of ]0010
~60/40 MgO-CaO-based refractory aggregate, and 15
Mg obtained by firing a compound containing one or more calcium compounds having a melting point of 00'C or less
It is an OCaO-based metallurgical refractory.

In addition, from another aspect, the present invention provides an MgO-CaO refractory aggregate with a molar ratio of MgO/CaO of 10010 to 60/40, and one or more calcium compounds having a melting point of 1500°C or less. MgO-CaO-C metallurgical use, which is made by blending a carbon component into an MgO-CaO-based clinker obtained by heat-treating a compound containing the above at a temperature range of ±10% of the melting point of the calcium compound. It is refractory.

(Function) Next, the reason why the refractory composition is limited as described above in the present invention will be explained in detail.

In the refractory of the present invention, MgO/
An MgO-CaO clinker having a composition in which CaO is in a molar ratio of 10010 to 60/40 is used. That is, F'1go clinker alone or, for example, MgO-
By blending CaO clinker and CaO clinker, M
A blend having a gO/CaO ratio within the above range (ie, CaO content of 40 mol% or less of the total aggregate) is used as the bone phase. Ca in the MgO-CaO aggregate used
If the content of O exceeds 40 mol%, the corrosion resistance and hot strength as a smelting furnace lining material will decrease, which is not preferable. This has nothing to do with the quality of the sinterability of the CaO-based refractory itself. The particle size of the refractory aggregate particles is preferably 0.05 mm or more. Particle size 0.05
If particles smaller than mm are present, these fine particles will react with 5iO7 contained in the slag to produce a low melting point compound and weaken the matrix.

The metallurgical refractory according to the present invention has a temperature of 1500°C for the aggregate.
It is obtained by containing a calcium compound having the following melting point. Examples of this calcium compound include C
aFz (melting point: 1373°C), CaCNz (melting point: 1
300°C), CaCQz (74°C), and Ca(N.

3) 2 (same: 561°C). One or more of these may be blended into the aggregate. When such a relatively low melting point calcium compound is blended into aggregate and heat treated at a temperature near the melting point of the calcium compound, the blended calcium compound melts on the surface of the aggregate particles, and Ca ions are absorbed into the aggregate particles. It was confirmed that while diffusing inside, the reactive sites combined with Ca were gasified and released into the atmosphere, while excessive Ca ions coated the aggregate particle surfaces as CaO and were deposited. At this time, the distribution of Ca inside and on the surface of the aggregate particles is uniform, and therefore CaO enrichment can be performed at a lower temperature than conventionally.

In the case of a calcium compound whose melting point exceeds 1500° C., Ca ions cannot be quickly diffused into the oxide aggregate such as MgO. Therefore, the melting point is 25
CaO above 00°C is excluded. Also, Ca003
Compounds that thermally decompose at temperatures below 1500° C. under normal pressure, such as the following, cannot be used. Furthermore, metal Ca or Ca
The alloy is also difficult to handle due to its extremely high reactivity, and the oxides of components other than Ca (e.g. Si, Fe) contained in the alloy lower the melting point of the brick. Cannot be used due to problems with corrosion resistance.

The amount of calcium compound added to the refractory aggregate is preferably 0.05 to 0.3 mol per mol of MgO in the aggregate particles. If the amount is less than 0.05 mol, the amount of Ca ions diffused into the aggregate particles is insufficient, and the Mg0-C reaction in the Mg0CaO-C refractory, which is one of the effects associated with the addition of calcium compounds, is sufficiently suppressed. I can't. If the amount is more than 0.3 mol, the active CaO coating formed on the surface of the aggregate particles will be excessive, and the sinterability will be improved, but the digestion resistance will be significantly deteriorated.

The particle size of the calcium compound to be blended is changed depending on the particle size of the aggregate particles, which is the blended amount. If the particle size of the aggregate particles is d, the particle size is 1 mm or less in the case of 421 mm (coarse particles), and 0 in the case of 0.15 mm≦d<1 mm (medium particles).
．． 15mm or less, 0.05mm≦d<0.15mm
(Fine particles), a calcium compound of 0.05 mm or less is blended. That is, the blended calcium compound particles are always blended with a particle size lower than that of the aggregate particles. If the particle size of the Ca compound to be blended is the same as or larger than the aggregate particles, particle agglomerates mainly composed of CaO will be formed, resulting in the inconvenience of generation and segregation of polycrystalline Ca0 particles rich in activity. Furthermore, in order to uniformly enrich CaO in the aggregate, it is preferable that the calcium compound to be blended be in the form of a fine powder.

One of the metallurgical refractories according to the present invention is a compound obtained by adding a calcium compound having a melting point of 1500°C or less to the above-mentioned refractory aggregate, and, like conventional fired refractories, It can be obtained by adding a commonly used organic binder, molding and firing. In conventional MgO-CaO-based fired refractories, it is known that sized aggregates fired at 1800°C or lower form a dense structure, but in the case of the fired refractories of the present invention, By firing at a similar temperature, a refractory can be obtained in which an active CaO coating is formed on the surface of aggregate particles forming a dense structure.

Further, in order to further increase the densification of the structure, it is preferable to once maintain the temperature near the melting point of the blended calcium compound and then raise the temperature to the firing temperature and fire it. In this case as well, taking into account the good sinterability of the blended compound, 1800
Calcining at temperatures above 0.degree. C. is unnecessary.

Another refractory of the present invention is characterized in that the refractory aggregate has a melting point of 1500.
A MgO-CaO clinker is obtained by heat-treating a mixture of a calcium compound at ℃ or less, adding a commonly used organic binder, etc., and molding the mixture, and then adding a carbon component to this, and then adding a phenol resin, etc. by adding a customary binder.

Here, "heat treatment" refers to an operation of heating near the melting point of the calcium compound, which involves melting and decomposition of the calcium compound, diffusion of calcium ions, and coating with CaO.

The heat treatment temperature at this time is preferably +10% of the melting point of the blended calcium compound;
Heat treatment at a temperature exceeding 100% increases the rate of formation of a CaO coating, resulting in non-uniform CaO enrichment in the aggregate.

If the temperature is less than -10%, the heat treatment time becomes long and the efficiency is poor. The heat treatment temperature also changes depending on the size of the aggregate particles.

Graphite is exemplified as the above-mentioned "carbon component".

In addition, the term "large metallurgical materials" used in the present invention refers to refractories used as lining materials for metal refining equipment in general, and specifically refers to refractories used as lining materials for steelmaking converters. It is not limited to such specific uses.

Hereinafter, the present invention will be explained in detail with reference to Examples.

Example 111 - FIgo clinker and MgO-CaO clinker with particle size 2-0.05 mm as refractory aggregates and particle size 1
~0.1 mm of each low melting point calcium compound was blended in the proportions shown in Table 1. A polypropylene binder was added in an amount of 3.5% to 100 parts of this mixture, and the mixture was heated and kneaded. This was molded at 800 kg/cm2 into a shape of 100 mm in diameter and 100 mm in height, held at 1200°C for 2 hours, and then fired at 1600°C for 2 hours. In addition, as a comparative example, a refractory aggregate without a low melting point calcium compound was molded in the same manner, and then
It was baked at 0°C for 5 hours.

The CaO and MgO contents in each of the obtained refractories were examined.

Each refractory was also tested for hot strength and erosion resistance. Hot strength was measured by a three-point bending test method. The erodibility test was conducted by taking out the center of the obtained refractory and using it as a sample in a crucible with an inner diameter of 60 mm. In this crucible, c/s=1.2, FezOz
5% slag and 18-8 stainless steel (slag/metal ratio, 0.2) were placed and held at 1750°C for 60 minutes, and the depth of erosion at the slag-metal interface was determined. Comparative example N
Each amount of erosion was expressed as an index when the amount of erosion of o, 1 was set as 100. The results are shown in Table 1.

Table 1 MgO-CaO clinker with a purity of 99% is coarsely granulated (particle size 1
mm or more), medium grains (0,15≦particle size <1 mm), fine grains (
0.05≦particle size<0.15). In a mixture of clinkers of the same particle size in the proportions shown in Table 2,
100p for coarse grains, 100/JI11 for medium grains
, CaNz having a particle size of 50IIJ]n was added to the fine particles at a ratio of 10% to the contained MgO. A polypropylene binder was added to the mixture at a concentration of 5% by weight, and the mixture was placed in a stainless steel container and heat-treated at 1000°C. The obtained product is sized in the same particle size classification as each mixed clinker at the beginning,
The coarse grained material was designated as clinker (8), the medium grained material was designated as clinker (B), and the fine grained material was designated as clinker (C). By blending each of the heat-treated clinkers in the proportions shown in Table 2, further adding artificial graphite and an appropriate amount of phenol resin, heating and kneading and molding into the same shape as in Example 1,
An unfired MgO-Ca0-C brick having a composition of 75% Mg, 15% Ca, and 10% C was produced. In addition, in order to set the amount of CaO to 15%, medium-sized electrofused clinker was used. As a comparative example, the heat-treated clinker was not included, and the MgO
- CaO clinker and CaO electrofused clinker
It was manufactured by blending in the proportions shown in the table. For each of the obtained refractories, the amount of erosion was investigated in the same manner as in Example 1. The results are shown in Table 2.

As shown in Table 2, since CaO is enriched in the aggregate structure, it is an industrially useful refractory with excellent corrosion resistance and low manufacturing cost. Also, h.

As a Ca0-C-based unfired refractory, it is an excellent refractory that can suppress the Mg0-C reaction, which was a problem in conventional carbon-containing basic refractories.

Claims (2)

[Claims] (1) MgO/CaO molar ratio is 100/0 to 60/4
An MgO-CaO metallurgical refractory obtained by firing a blend containing an MgO-CaO-based refractory aggregate having a melting point of 1,500° C. or less and one or more calcium compounds having a melting point of 1,500° C. or less. (2) MgO/CaO molar ratio is 100/0 to 60/4
A mixture containing an MgO-CaO-based refractory aggregate having a temperature of 0.0 °C and one or more calcium compounds having a melting point of 1500°C or less is heat-treated in a temperature range of ±10% of the melting point of the calcium compound. MgO-
MgO made by blending carbon content with CaO-based clinker
-CaO-C based metallurgical refractory.