CA1139792A - Wear lining structure of a converter - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The invention relates to a wear lining structure of a converter. According to the invention, unburned carbon-bonded bricks comprising 3-40 weight % of a carbonaceous material, 1-10 weight % aluminum, and magnesite clinker for the residual part, are used for at least part of the wear lining in order to enable the wear lining structure of a converter to stand various severe thermal load conditions imposed on the wear lining refractories in a B.O.F. steel making process operated in various forms, such as an oxygen top-blown process, as oxygen bottom-blown process, and com-binations thereof, and the like, thereby to provide the wear lining structure of a converter capable of standing a long-range use even under the said severe thermal load con-ditions.

Description

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1 B~CKGROUND OF THE INVENTION

The invention relates to a wear lining structure of a converter~ Generally, burned magnesite-dolomite bricks including synthetic magIIesite-dolomite clinker are commonly used as the wear lining materials of a converker~
In addition to the use of the said furnace member, the application of hot gunning repair methods, slag control, slag coating, etc. has remarkably lengthened the useful life of the converter wear lining.
However, with the recent aggravatlon of the energy situation and resource problem, a further reduction of the steel production cost has become desirable in the Japanese steel industry.
In fact, the B.O.F. steel making process is now ~i`
operated in a variety of forms, such as by an oxygen top-blown mcthod, an oxygen bottom-blown method, combina~ions thereof, and the like. As a result, the thermal load con-ditions of the converter have been diversified whereby the converter wear lining refractories are now subjected to a much severer burden.
In view of the aforementioned circumstances, the invention has been accomplished with the object of de-veloping a refractory material having such properties as to ma];e them capable of being used under the severe con-ditions mentioned above for a long period of time when used in a converter wear lining.
It is commonly known that carbon has excellent properties as a refractory material, for example, good ~ .

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1 spalling resistance, slag corrosion resistance, slag permeation resistance and the like. Thus, unburned tar-dolornite bricks have been used in the past. However, such bricks had a disadvantage in that the texture was deteriorated due to the reaction between Ca~ in the dolomite and carbon during the use under high temper-aturè 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 tardolomite bricks have 1~ been replaced by tar-permeated burned magnesite-dolomite brlcks.
However, since the carbon content sustained by tar permeation is not sufficient to util.ize the properties of carbon satisfactorily, the disadvantages of the burned bricks have not yet been funda~
mentally obviated.
Unburned carbon-ma~nesia bricks (U.S. Patent No, 3667974, ~.K. Patent No. 1233646 and Canadian Patent ~o, 896629) have been e~tensivel~ used in an electric~arc furnace~ particu-larly as br.icks for the ceiling and hot spots~ with success~
However, the said ~ricks have been regarded as unsuitable for use in a converter since they involve the r;sk o~ receiving a shock when scraps are thrown in due to their relatively low crushing strength and present the phenomenon of decarbonizatlon when brought into contact ~ith molten steel, ~.
In order to improve the quality of unburned carbon-magnesia brickslp vari:ous developments have been accomplished~
For example, silicon was added with the object of improvin~ the oxidization resistance; the hot strength was increased by solving v~rious problems involved :in the pressing processr and as in U.S.
Patent 4,216pQ2~ wherein the carbon content was increased sub-stantially to more than 55~ thereby making it possible to have

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1 full use of the properties o:E carbon, and also various difficult-ies involved in the pressing process were improvedO Howe~er, the said carbon-bonding material used for carbon-magnesia brick~
were not such as to simultaneously exhibit both oxidi.zation resistance and modulus or rupture characteristics.
SUMMARY OF THE INVENTION
In order to develop carbon-bonded bricks capable o~
simultaneously improving the modulus of rupture and oxidization resistance values of the bonded bricks, the inventors of the ~resent invention conducted experiments on various additives.
As a result, it has been found tha-t metal additives, particularly aluminum, have a highly pronounced effect of increasing both the said properties simultaneously, 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 aluminum-containing unburned carbon-magnesia bricks.
The invention relates to the wear lining structure ~ i .

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1 of a converter characterized in that the converter wear lining, in part thereo~ at least, consists of unburned carbon-bonded bricks comprising 3-40 weight % o~ a carbonaceous material 1-10 weight % alurllinum and/or less than 6 weight % silicon~ the residual part being magllesite clinker~

DE~AI~ED DESCP~IP~ION OF T~ INVENTION

~he ~mburned carbon-bonded bricks according to the invention will be described in detail hereinunder.
The amount o~ carbonaceous material contained ~n the bricks is 3--40 weigh~ %, preferably 5-30 weigh-t %.
The range of the carbonaceous material content is so limited for the following reasons: If the content is less tha~ 3 weight %, it is impossible to make full use o~ the e~fect of resistance to spalling, slagr corrosion, slag permeation and -the like 9 while if the content is in excess of 40 weight ~, resistance to both shocks of scraps thrown in and the wearing effect o~ molten steel - is reduced.
Al~ninum is added to the brick material for the following reasons. Aluminum added to and mixed with the nnaterial prevents a bond be-tween the carbon and -the oxygen ~rom outside by bonding with the carbon (A14C3) remaining in a s-tructurally unstable cond:ition in the bonding material (resinous pitch, thermosetting phenolic resin, etc.) in a high temperature range, thereby making it possible to prevent ~ecarbonization from bonding mate-rial, ~rea-tly increase the rate of residual carbon in the ~P
.

~Li39'7~32 1 bonded part and display -the effect of carbon-magllesia brick.
Simultaneously, alumin~n reduces -the volume o~ each pore by cubical expansiol1 at the -time when it iS -turned into carbide in reaction to carbonaceous materi.als. Thus, the brick texture is CompQCt ed an~.~ the strength is in-creased -thereby making it difficult~ especially in top layer, for slag and molten steel to corrode bricks.
As described hereinabove~ the addition of aluminum has the effect of concur~rently irnproving both the proper--ties of the modulus of rupture anf~ oxidization resi.sta.nce of the carbon-bonded bricks.
In the bricks accordin~ -to the i~lvention conta:lning

3-40 weight ~ of carbonaceous material capable of display-ing the said excellent properties, a suitable content of aluminum is l-lC weight %, and preferably 1-6 weight ~0 If the aluminum content is less than 1 weight ~0, ~
the addition is not only insufficient to appreciably im-prove the proper-ties but also renders it impossible to make full use of the high effect o~ the carbonaceous material due to impossibility of increasing the carbon content in the bricks, while if in excess of 10 weigrht %, the re-frac-tory property is impairefl.
~ he properties of the bricks according to the in-vention can be greatly enhanced by adding silicon to the material, if necessaryO
~ o be more precise, the aluminum added to the brick material profluces carbide in combination with carbon under the heating conditions of the converter, and if the said il ~35~'7.92 .
l carbide is brought into contact with water at high tem-peratures, the following reaction proceeds Al4C3 ~ 12 H20 ~ 3CH4 -~ 4Al(OH)3 whereby the brick texture is liable to be deteriorated with the growth of cracks and even collapsed. If silicon has been added hydration of the carbide is prevented with success. The amount of silicon is less than 6 weight ~, and preferably 1-4 weight %. If the amount is in excess of 6 weight %, the refractory property of the bricks is ~0 undesirably impaired.
It is preferable that the addii-ion o~ silicon is increased in conformity with that of aluminum. The par-ticularly suitable ratio of addition is 0.2-1.0 weight %
silicon to l weight % aluminum.
The addition of silicon makes it possible to remark-ably improve the resistance of carbon to oxidization in collaboration with aluminum in addition to the effect of preventin~ hydration of the carbides. Therefore, the ob-ject is distinctly different from tha~ of the conventional case wherein silicon is independently added in order to pre-vent oxidization.
An example of the method for producing unburned carbon-bonded bricks according to the invention will be described in detail hereinunder.
Magnesite clinker and carbonaceous materials are used as re~ractories. The magnesite clinker comprises burned magnesite, sea-water magnesite clinker or electro-fused magnesite, while the carbonaceous material comprises plumbago, artificial graphite, electrode waste, petroleum .-6~

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coke, foundry coke, carbon black or pitch cokeO
These refractories are subjected to particle size control and then kneaded with such bonding materials as will produce carbon when heated, such as tarr pitch, resin and the like.
The kneaded mixture is pressed and heated ~ccording 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 a wear lining over the entire bottom, barrel and cone of a converter. A good result is obtainable even if the wear lining is employed only on the charging side and/or trunnion side of the converter, which is subjected to heavy wear.
Furthermore, since the cause and degree of wear i~-differs 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 carbon-bonded bric]cs containing 3-30 ~ of a carbonaceous material and more than 2 % of a metal powder for the bottom, bath and the charging side of the barrel; bricks containing 5-35 ~ of a carbonaceous material and more than 1 ~ of a metal powder ~or the tap side of the barrel and the trunnion side, and bricks containing 10-40 ~ of a 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 in~ention compared with con-1 ~entional buxned bricks arè as follows:
(1) Due to high spalling resistance, the bricks are safe from spalling evcn when the ~urnace body is rapidly heated or cooled by scraps thrown into it.
(2) The bricks are scarcely corroded since they do not react to slagO
When compared with ordinary unburned carbon bonded bricks containing no metal powder J the bricks according ~o the present invention have the following properties:
(3) The texture is more compact and has a greater strength.

(4) The texture is less de-~eriorated due to decarbonization, since it is scarceIy oxidized.
(S) Permeation o the slag into the brick texture is pre-vented, and the bric]cs show high resistance to shocks of -i scraps and weaxing 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 un-burned bricks. Mixtures accordin~ to the mixin~ ratio as shown in Table 1 were prepared, pressed and then heat treated at 300C for 4 hours to obtain the examples.
Comparative Example 4 is a burned magnesite-dolo-mite bric]c containing a synthetic magnesite-dolomite clinker ~.~.3g'7~

1 and permeated with tar. The chemical composition thereof is shown in Table 1.
The examples were subjected to measurements of various physical property values; the modulus of rupture values were determined and the examples subjected to the spalling and slag tests.
Furthermore, the bricks thus-obtained were used as the wear linin~ of the trunnion walls of a 300-ton con-verter 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 a heating element of silicon;carbide at 1~00C 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 1750C for 5 hours with slag throWn into it. Then, the example was cut to measure the wear dimensions and the thickness of the decarbonized layer.
(3) Actual Furnace Test The trunnion walls o~ a 300-ton converter made by _9_ 7~

1 A Company were wear-lined with the respective examples.
A~ter 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 o~ wear.
The wear ratios were computed with the wear ratio of Ex~nple 3 set at 1.

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1 As is apparent from the above table 1, each o~
the examples accordin~ to the invention showed better re-sults than any o~ the comparative examples did in all re-spects in the modulus of rupture test, spalling test, the slag test and the actual furnace test.
Exampl~ 7 Unburned carbonaceous bricks of the mixin~ ratio as shown in Table 2 were applied to a 300-ton converter made by A Company as the wear lining of the bottom, bath and barrel ~trunnion wall) thereo.
The wear speed until the back lining was exposed was compared with that oE the convent.ional products under the same conditions to obtain the result as shown in Table 2.

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1 As ls apparent from the said results, the wear lining composPd of 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 inven-tion has a longer useful life than that of the converter wear lining o the ordinary unburned carbon-bonded bricks containîng no metal powder, to say nothing of the conven-tional burned magnesite-dolomite bricks containing synthetic magnesite-dol~mite clinker.

~0

Claims (7)

What is claimed is:

1. A wear lining structure of a converter characterized in that at least part of the wear liner is composed of un-burned carbon-bonded bricks comprising 3-40 weight % of a carbonaceous material, 1-10 weight % of aluminum, and the residual portion being essentially magnesite clinker.

2. A wear lining structure of a converter as defined in claim 1 wherein the carbonaceous material is present in an amount of 5-30 weight %.

3. A wear lining structure of a converter as defined in claim 1 wherein the aluminum is present in an amount of 1-6 weight %.

a A wear lining structure of a converter characterized in that at least part of the wear liner is composed of un-burned carbon-bonded bricks comprising 3-40 weight % of a carbonaceous material, 1-10 weight % aluminum, less than 6 weight % silicon, and the remainder being essentially mag-nesite clinker.

5. A wear lining structure of a converter as defined in claim 4 wherein the carbonaceous material is present in an amount of 5-30 weight %.

6. A wear lining structure of a converter as defined in claim 4 wherein the aluminum is present in an amount of 1-6 weight %.

7. A wear lining structure of a converter as defined in claim 4 wherein the silicon is present in an amount of 1-4 weight %.