GB2044242A - Wear lining structure of a converter - Google Patents

Abstract

The wear lining structure of a converter is constructed at least in part from unburned carbon-bonded bricks comprising 3-40 weight % carbonaceous material, 1-10 weight % aluminum, and magnesite clinker for the residual part in order to enable the wear lining structure to withstand various severe thermal load conditions imposed on wear lining refractories in the B.O.F. steel making process.

Description

SPECIFICATION Wear lining structure of a converter The invention relates to wear lining structure of a converter. Generally, burned magnesite-dolomite bricks including synthetic magnesite-dolomite clinker are commonly used as wear lining material of a converter. In addition to the use of the said furnace member, the application of hot gunning repair, slag control, slag coating, etc. has remarkably lengthened the useful life of the converter wear lining.

However, with the recent aggravation of the energy situation and resource problems, a further reduction of the steel production cost has come to be desired in the Japanese steel industry.

In fact, the B.O.F. steel making process is now operated in a variety of forms, such as oxygen topblown process, oxygen bottom-blown process, combination thereof, and the like. As a result, the thermal load conditions ofthe converter have been diversified whereby the converter wear lining refractories have come to be subjected to a severer burden.

In view of the aforementioned circumstances, the invention has been accomplished with the object of developing a refractory material having high properties capable of coping with the said circumstances thereby enabling to prolong the useful life of the converter wear lining.

It has commonly been known that carbon has high properties as a refractory material, for example, spalling resistance, slag corrosion resistance, slag permeation resistance and the like.

Thus, unburned tar-dolomite bricks were used in the past. However, such bricks had a disadvantage in that the texture was deteriorated due to reaction between CaO in dolomite and carbon during the use under high temperature conditions.

Since the amount of carbon to be added to tardolomite was necessarily limited, the properties of carbon could not be utilized satisfactorily.

In fact, the tar-dolomite bricks have been replaced by tar-permeated burned magnesite-dolomite bricks. However, since the carbon content sustained by tar permeation is not sufficient to enable to utilize the properties of carbon satisfactorily, the disadvantages of the burned bricks have not yet been fundamentally obviated.

Unburned carbon-magnesia bricks (Japanese Patent No.756495, U.S. Patent No.3667974, U.K.

Patent No. 1233646 and Canadian Patent No. 896629) have been extensively used in an electric-arc furnace, particularly as bricks for the ceiling and hot spots, with success. However, the said bricks have been regarded as unsuitable for use in a converter since they involve the risk of receiving a shock when scraps are thrown in due to their relatively low crushing strength and presentthe phenomenon of decarbonization when brought into contact with molten steel.

In order to improve the quality of unburned carbon-magnesia bricks, various developments have been accomplished, for example, Japanese Laying-Open Gazette No. SHO-53-6312 (dated 1978, 1,20) wherein silicon was added with the object of improving the oxidization resistance, Japanese Laying-Open Gazette No. SHO-54-11113 (dated 1979, 1,27) wherein hot strength was increased by solving various problems involved in the pressing process, and Japanese Patent Application No.

SHO-53-104292 (dated 1978,8,26, U.S. Application No. 13478 dated 1979,2, 21, Notice of Allowance issued on 1980, 1, 2) wherein the carbon content was increased substantially to more than 55% thereby enabling to make full use of the properties of carbon, and various difficulties involved in the pressing process were improved.

After all, however, the said carbon-bonding material used for carbon-magnesia bricks were not such that could display simultaneously both properties of oxidization resistance and modulus of rupture.

In order to develop carbon-bonded bricks capable of synchronously displaying a combined property of the modulus of rupture and oxidization resistance, the inventors of the present invention conducted experiments on various additives. As a result, it has been found that metal additives, particularly aluminium, have a high effect of increasing both the said properties synchronously, and the present invention has been accomplished as a result of tests to obtain the wear lining structure of a converter having a longer useful life by making use of aluminiumcontaining unburned carbon-magnesia bricks.

The invention relates to wear lining structure of a converter characterized in that the converter wear lining, in part thereof at least, consists of unburned carbon-bonded bricks comprising 3-40 weight% carbonaceous material, 1-10 weight % aluminium and/or less than 6 weight% silicon, the residual part being magnesite clinker.

The unburned carbon-bonded bricks according to the invention will be described in detail hereinunder.

The amount of carbonaceous material contained in the bricks is 3-40 weight%, preferably 5-30 weight %. The range of the carbonaceous material content is so limited for the following reasons. If the content is less than 3 weight %, it is impossible to make full use of the effect of resistance to spalling, slag corrosion, slag permeation and the like, whilst if the content is in excess of 40 weight %, resistance to both shocks of scraps thrown in and wearing effect of molten steel is reduced.

Aluminum is added to the brick material for the following reasons. Aluminum added to and mixed with the material prevents bond between carbon and oxygen from outside by bonding with carbon (AlAC3) remaining in a structurally unstable condition in the bonding material (resinous pitch, thermosetting phenolic resin, etc.) in a high temperature range thereby enabling to prevent decarbonization from bonding material, greatly increase the rate of residual carbon in the bonded part and display the effect of carbon-magnesia brick.

Synchronously, aluminum reduces the volume of each pore by cubical expansion at the time when it is turned into carbide in reaction to carbonaceous materials. Thus, the brick texture is compacted and the strength is increase thereby making it difficult, especially in top layer, for slag and molten steel to cor rode bricks.

As described hereinabove, the addition of aluminum has the effect of synchronously improving both properties of modulus of rupture and oxidization resistance of the carbon-bonded bricks.

In the bricks according to the invention containing 340 weight % carbonaceous material capable of displaying the said high properties, the suitable content of aluminum is 1-10 weight%, and preferably 1-6 weight%.

If the aluminum content is less than 1 weight%, the addition is not only effectless but also renders it impossible to make full use of the high effect of the carbonaceous material due to impossibility of increasing the carbon content in the bricks, whilst if in excess of 10 weight%, the refractoriness is impaired.

The properties of the bricks according to the invention can be redoubled by adding silicon to the material, if necessary.

To be more precise, aluminum added to the brick material produces carbide in combination with carbon under the heating conditions of the converter, and if the said carbide is brought into contact with water at high temperatures, the following reaction proceeds.

whereby the brick texture is liable to be deteriorated with growth of cracks and even collapsed. If silicon has been added, hydration of the carbide is prevented with success. The amount is less than 6 weight%, and preferably 14 weight %. If the amount is in excess of 6 weight %, the refractoriness of the bricks is unpreferably impaired.

It is preferable that the addition of silicon is increased in conformity with that of aluminum. The particularly suitable ratio of addition is 0.2-1.0 weight% silicon to 1 weight% aluminum.

The addition of silicon enables to remarkably improve the resistance of carbon to oxidization in collaboration with aluminum in addition to the effect of prevention of hydration of carbides. Therefore, the object is distinctly different from that of the conventional case wherein silicon was independently added in order to prevent oxidization.

An example of the method for producing unburned carbon-bonded bricks according to the invention will be described in detail herein under.

Magnesite clinker and carbonaceous material are used as refractories. The magnesite clinker comprises burned magnesite, sea-water magnesite clinker or electrofused magnesite, whilst the carbonaceous material comprises plumbago, artificial graphite, electrode waste, petroleum coke, foundry coke, carbon black or pitch coke.

These refractories are subjected to particle size control and then kneaded with such bonding materials as will produce carbon when heated, such as tar, pitch, resin and the like.

The kneaded mixture is pressed and heated according to the ordinary process to obtain finished products.

The most satisfactory result is obtainable if the unburned carbon-bonded bricks thus obtained are applied as wear lining to all over the bottom, barrel and cone of a converter. A good result is obtainable even by wear lining the charging side and/or trunnion side only which is subjected to heavy wear.

Furthermore, in view of the fact that the cause and degree of wear differ according to the respective parts of each converter, the useful life of the converter can be further prolonged by wear lining it with unburned carbon-bonded bricks having different contents of carbon and metal powders. To be more precise, it is preferable to use unburned carbonbonded bricks containing 3-30 % carbonaceous material and more than 2 % metal powder for the bottom, bath and the charging side of the barrel; bricks containing 5-35 % carbonaceous material and more than 1 % metal powder for the tap side of the barrel and the trunnion side; bricks containing 1040 % carbonaceous material and more than 3 % metal powder for the cone part, respectively.

The characteristic features of the unburned carbon-bonded bricks according to the invention compared with the conventional burned bricks are as follows.

(1) Due to high spalling resistance, the bricks are safe from spalling even when the furnace body is rapidly heated or cooled by scraps thrown thereinto.

(2) The bricks are scarcely corroded since they do not react to slag.

When compared with the ordinary unburned carbon-bonded bricks containing no metal powder, the bricks according to the invention have the following properties.

(3) The texture is more compact and has a greater strength.

(4) The texture is less deteriorated due to decarbonization since it is scarcely oxidized.

(5) Thus, permeation of slag into the brick texture is prevented, and the bricks show high resistance to shocks of scraps and wearing effect of molten steel.

The aforementioned characteristic features ensure a long-range useful life of the wear lining structure of a converter in which the bricks according to the invention are used.

The invention will now be described in more detail in reference to the following examples.

Examples 1-6 Examples 1-6 and Comparative Examples 1-3 are unburned bricks. Mixtures according to the mixing ratio as shown in Table 1 where prepared, pressed and then heat treated at 300 C for 4 hours to obtain the examples.

Comparative Sample4 is a burned magnesitedolomite brick containing synthetic magnesitedolomite clinker and permeated with tar. The chemical composition thereof is shown in Table 1.

The examples were subjected to measurement of physical property values and modulus of rupture as well as spalling test and slag test.

Furthermore, the bricks thus obtained were used as wear lining of the trunnion walls of a 300-ton converter made by A Company. The results were as shown in Table 1.

The spalling test, slag test and actual furnace test were conducted by the following methods.

(1) Spalling Test The examples placed in a carbon crucible were heated in an electric furnace using heating element of silicon carbide at 1400"C for 15 minutes, and then left to cool in the atmosphere for 15 minutes. After the said operation was repeated 5 times consecutively, the examples were cut to examine the growth of cracks.

(2) Slag Test Each example was formed into the shape of a cylinder. The said cylinder was rotated in the horizontal disposition and heated at 1750 C for 5 hours with slag thrown thereinto. Then, the example was cut to measure the wear dimensions and the thickness of the decarbonized layer.

(3) Actual Furnace Test The trunnion walls of a 300-ton converter made by A Company were wear lined with the respective examples. After the said converter was used until the back lining was exposed, the wear lining was disassembled and the examples were collected to compare the amount of wear. The wear ratios were computed with the wear ratio of Example 3 set at 1.

fable 1

Example 1 Example 2 Ok8nesite 80 clinker eo en Graphite 15 15 aluminum poevder 5 3 Silicon powder s: Resinous pitch(out) 2.5 2.5 x Thermosetting phenolic 3.5 3.5 resin (out) Apparent porosity 5.4 5.2 ts) Apparent speeifie 2.92 2.93 9 g :s gravity a. a Bulk specific 2.76 2.79 S gravity :2 i P. Crusbing strength 408 422 modulus of rupture at 115 86 1500 b (lcg/em2 ) Spelling Test Growth of cracks Nil Nil Melting lose =i measurement (ma) 19.5 20.5 n Es Deearbonized ) layer (mum) O O Wear ratio when used 1.2 1.2 in actual furnace

Comparative Example 3 Example 4 Example 5 Example 6 Example 1 ) 79 go 83 83 85 15 7 7 15 15 3 3 6 1 3 4 1 2.5 2.0 2.0 2.5 2.5 3.5 3.0 3.0 3.5 3.5 4.0 5.2 4.5 5.0 4.4 2.92 3.07 3.05 2.96 2.94 2.81 2.91 2.91 2.81 2.80 435 507 520 410 U1 180 loO 110 82 50 Nil Nil Nil Nil Nil 16.0 21.0 22.5 19.2 25.5 0 0 o o o 3.0 1.0 1.3 1.4 1.2 1.6

Comparative Comparative Comparative Example Example 2 Example 3 l] ple 4 68 68 Igloss 4.8 C 7 7 15 5i02 0.5 15 + t12 3 0.2 1 203 N o0 Fe203 0.3 2.0 2.5 es CaC 8.5 3.0 3.5 e MgO 85.7 4.3 6.3 1.0 3.07 2.91 3.23 2.95 2.73 3.20 530 380 1100 60 45 30 Nil Nil Big cracks 26.5 26.5 33.5 30 3.5 O 5.0 1.7 2.1 2.0 As is apparent from the above tabie 1, each of the examples according to the invention showed better results than any of the comparative examples did in all respects of the modulus of rupture, spalling test, slag test and actual furnace test.

Example 7 Unburned carbonaceous bricks of the mixing ratio as shown in Table 2 were applied to a 300-ton converter made by A Company as wear lining of the bottom, bath and barrel (trunnion wall) thereof.

The wear speed until the back lining was exposed was compared with that of the conventional products under the same conditions to obtain the result as shown in Table 2.

Table 2

Bottom of Dottos Bath Tniiinion Vlall Unburned Conventional Unburned Conventional Unburned Convontionsl material Carbonaceous Product A Carbonaceous Product B Carbonaceous Product C Item Brick A Brick B I ~ Brick C Maosito o o1ier 83 88 80 85 78 82 m Grallhit e 12 12 15 15 18 18 Aluainn Powder 3 3 2 Silicon ?oi-ider 2 2 2 tIgO 1.8 26.2 78.8 83.3 76.8 80.4 .o > F.(l 12.0 12.0 14.6 14.6 17.2 17.2 Piov Aparent porosity (8) 4.0 4.5 4.0 4.5 4.0 4.5 A:rparont sacific 3.CO 3.03 2.98 3.01 2.96 2.98 gravity Bulk 2.86 2.87 2.84 2.85 o spocific 2.88 2.89 H Specific 460 2 S of gravity Crusdng stren h k-'-- ow2 550 540 ':lear ratio 1.0 1.6 1.0 1.6 1.0 1.7 .2. Conventionul Products A, 9 and G are unbv.med carbonaceous bricks.

As is apparent from the said results, the wear lining constituted by the unburned carbon-bonded bricks according to the invention showed high durability with a smaller degree of spalling, wear by molten steel and corrosion by slag compared with the case of conventional products.

Thus, it has been substantiated that the wear lining structure of a converter according to the invention has a longer useful life than that of the converter wear lining of the ordinary unburned carbon-bonded bricks containing no metal powder, to say nothing of the conventional burned magnesite-dolomite bricks containing synthetic magnesite-dolomite clinker.

Claims (7)

1. Wear lining structure of a converter wherein at least a part of the wear lining is constructed from unburned carbon-bonded bricks comprising 340 weight% carbonaceous material, 1-10weight% aluminum, and magnesite clinker as the residual part.

2. Wear lining structure as claimed in claim 1, wherein the carbonaceous material is present in an amount of from 5-30 weight %.

3. Wear lining structure as claimed in claim 1 or 2, wherein the aluminum is present in an amount of from 1-6 weight %.

4. Wear lining structure as claimed in claim 1,2 or 3, comprising in addition less than 6 weight % silicon.

5. Wear lining structure as claimed in claim 4, wherein the silicon is present in an amount of from 14 weight %.

6. Wear lining structure of a converter, substantially as hereinbefore described.

7. Process for preparing unburned carbonbonded bricks, substantially as hereinbefore described.