JP6978677B2 - Refractory lining for secondary refractory equipment with decompression - Google Patents

Description

The present invention relates to refractory linings for secondary smelting equipment, and in particular, spinel-carbon suitable for lining of secondary smelting equipment with decompression such as a vacuum degassing tank used in the DH method, RH method, VOD method and the like. It is about quality bricks.

In recent years, the secondary smelting process has become more severe due to the improvement of steel quality and the shift of production items to high-grade steel, and the characteristics required for refractory linings for secondary smelting equipment have become higher. Secondary refractory processing under reduced pressure is an indispensable process for the production of high-grade steel, but at the same time, this process significantly increases the damage to refractories, so the development of refractories with better durability is required. There is.

Magnesia-carbon bricks are widely used as refractory linings for secondary refractory equipment with decompression such as RH and VOD, but their durability has reached a plateau and further improvement has been sought. The influence of the magnesia-carbon reaction is considered to be a factor that does not extend the service life.
MgO (solid) + C⇒Mg (gas) + CO (gas)
It goes without saying that this magnesia-carbon reaction is more likely to proceed at higher temperatures, but since Mg (gas) and CO (gas) generated in decompression vessels such as RH and VOD are discharged to the outside of the system by vacuuming, the reaction proceeds. Is significantly promoted. This reaction is a reaction in which the solid becomes a gas and disappears, and causes embrittlement of the structure of magnesia-carbon bricks, so that the effect on the durability is considered to be extremely large.

Several proposals have been made to suppress such magnesia-carbon reactions. For example, US Pat. Refractories are disclosed.

However, the spinel-carbonic brick of Patent Document 1 was found to have a tendency to crack or peel off during intermittent operation. Cracking and exfoliation were particularly pronounced in spinel-carbonic bricks with low carbon content. Further, when it is used in a part that is relatively strongly affected by cooling, such as a slag line of a VOD pot or a reflux pipe of an RH lower tank, cracks often occur. That is, among the spinel-carbon bricks of Patent Document 1, the spinel-carbon bricks having a medium to high carbon content are strong in intermittent operation and can be used relatively stably, but there are many carbon pickups and high-grade steel. There was also the problem that it was not suitable for manufacturing. Therefore, the current situation is that the development of spinel-carbon bricks that can be used stably even under intermittent operation and that can suppress carbon pickups as much as possible is desired.

Therefore, various proposals have been made to improve the spalling resistance of carbon-containing bricks. For example, Patent Document 2 discloses a carbon-containing brick characterized by containing expanded graphite as a carbonaceous material. Further, Patent Document 3 contains compressed and crushed expanded graphite, which comprises expanded graphite crushed after compression as a carbon material in carbon-containing bricks composed of 0.5 to 40% by weight of a carbon material. Brick is disclosed. In Patent Documents 2 and 3, basic refractory materials such as magnesia, dolomite, calcia, and magcarcia, neutral refractory materials such as alumina and spinel, other oxide refractory materials, and non-oxide refractory materials are described. It is disclosed that it can be used, and in particular, it can improve the spalling resistance of magnesia-carbon bricks. Since expanded graphite has excellent elasticity as an action effect of these carbon-containing bricks, carbon-containing bricks using expanded graphite expand the thermal expansion and contraction of refractory materials with a high coefficient of thermal expansion such as magnesia. It is disclosed that the absorption of graphite chemicals improves the spalling resistance.

Further, Patent Document 4 contains 1 to 70% by weight of a carbonaceous raw material containing 0.05 to 5% by weight of carbon fiber ^{and 0.1 to 10% by weight of a carbon material having a specific surface area of 10 to 200 m 2 / g.} A magnesia-carbon brick characterized by this is disclosed. The magnesia-carbon brick disclosed in Patent Document 4 uses carbon fiber instead of metallic fiber such as steel fiber and aluminum fiber, and also uses carbon raw material having a large specific surface area such as carbon black and expanded graphite. When used in combination, the bonding force of the matrix portion with carbon is increased, the contact points between the carbonaceous raw material in the matrix and the carbon fiber are increased, and the pull-out resistance of the carbon fiber is increased.

Japanese Unexamined Patent Publication No. 2016-060651 Japanese Unexamined Patent Publication No. 5-301772 Japanese Unexamined Patent Publication No. 8-81256 Japanese Unexamined Patent Publication No. 2004-196578

However, although Patent Documents 2 and 3 also disclose spinnel-carbon bricks, there is no example of application of expanded graphite or compressed or crushed expanded graphite to spinel-carbon bricks, but thermal expansion of spinel is not exemplified. Although the rate is very low compared to magnesia, it is considered to be the same effect as magnesia-carbon bricks, and sufficient consideration has been given to the application of expanded graphite, compressed and crushed expanded graphite to spinel-carbon bricks. It cannot be said that it is done.
Further, the magnesia-carbon brick disclosed in Patent Document 4 contains 0.05 to 5% by weight of carbon fiber, increases the contact point between the carbonaceous raw material and the carbon fiber in the matrix, and increases the contact point of the carbon fiber. It is intended to increase the pull-out resistance, that is, to suppress the elongation rather than the generation of cracks, not to suppress the generation of cracks.

Therefore, an object of the present invention is for secondary refractory equipment with decompression made of spinel-carbon brick, which has excellent durability, especially spalling resistance, can be used stably even under intermittent operation, and can suppress carbon pickup. It is to provide a lining refractory material.

The present inventors used a low carbon spinel-carbon material in a vacuum ladle slag line to confirm the damage status of spinel-carbon bricks used in a slag line of a secondary smelting facility with decompression treatment. The damage situation of bricks (carbon content 3% by mass) was investigated, and the following findings were newly obtained.

After use, the spinel-carbon brick had cracks extending at a position about 20 mm from the working surface, and a part of the cracks had peeled off. This exfoliation significantly increases the amount of damage to spinel-carbon bricks. The microstructure near the crack portion is observed in detail by the reflection micrograph near the crack portion in FIG. As shown in Fig. 1, it can be observed that a very thick neck is growing and developing with a bridge between the in contacting spinel aggregates, and the spinel-carbon brick is burned by receiving heat. It was confirmed that the conclusion was progressing. Sintering with the growth and development of this neck is a phenomenon not seen in difficult-to-sinterable magnesia-carbon bricks that are generally used as refractory linings for secondary refractory equipment with reduced pressure such as RH and VOD. This is a phenomenon peculiar to spinel-carbon bricks that uses spinel, which is rich in sinterability, as an aggregate. In addition, it was found that the above-mentioned neck growth did not occur when the distance between the aggregates was wide or where graphite was present between the aggregates.

When the ultrasonic transmission speed was measured using an ultrasonic flaw detector to qualitatively grasp the elastic modulus of the sintered surface layer, the transmission speed of the spinel-carbon material brick was higher than the transmission speed of the magnesia-carbon material brick. It was found to be extremely fast, especially on the working surface side of spinel-carbonic bricks, with significantly faster transmission speeds. In general, it is known that the transmission speed of ultrasonic waves transmitted through a substance increases as the elastic modulus of the substance increases. From these facts, it was found that the spinel-carbonaceous brick has a high elastic modulus due to the sintering of the spinel aggregates by heat reception, and cracks and peeling occur due to thermal shock.

In view of the microstructure observation results of the post-use bricks as described above, in order to suppress the sintering of spinel aggregates, a gap is arranged between the spinel aggregates to widen the distance between the aggregates, or carbon is used. It is considered effective to arrange a material that is inert to the spinel aggregate between the aggregates. Of these, arranging voids in the brick to increase the distance between spinel aggregates is synonymous with increasing the porosity of spinel-carbon bricks, which is not preferable in terms of corrosion resistance and is not practical. No. Therefore, we investigated a method for arranging materials that are inert to spinel. As disclosed in Patent Document 1, various carbon raw materials such as scaly graphite are used as carbon sources in spinel-carbonic bricks, but the present inventors have a larger volume than these carbon raw materials. It has been found that the use of a certain graphitic raw material more efficiently prevents the spinnel aggregates from coming into contact with each other, and suppresses sintering during heat reception and cracking due to the accompanying thermal shock. These findings have led to the completion of the present invention.

That is, the present invention relates to a refractory lining for secondary refractory equipment with reduced pressure, which is composed of spinel-carbon fiber containing 88 to 99.5% by mass of a spinel raw material and 0.5 to 12% by mass of a carbon raw material. Refractory lining for secondary refractory equipment with reduced pressure, characterized in that one or more graphitic raw materials with a ^{specific surface area in the range of 5 to 200 m 2} / g are used for some or all of the carbon raw materials. It is related to things.

Further, the refractory lining for secondary refining equipment of the present invention is characterized in that the graphitic raw material is expanded graphite.

Further, the refractory lining for secondary refining equipment of the present invention is characterized in that the graphitic raw material is graphene.

Further, in the lining lining structure of the secondary smelting equipment with decompression of the present invention, the refractory lining for the secondary smelting equipment with decompression is arranged at least in the slag line portion and the vicinity of the molten metal surface of the secondary smelting equipment. It is characterized by becoming.

According to the spinnel-carbonic bricks constituting the refractory lining for secondary refractory equipment with reduced pressure of the present invention, one or more kinds of graphite having a specific specific surface area in a part or all of the carbon raw material. By using raw materials, magnesia-spinel that is effective in suppressing carbon reaction-spinel that suppresses carbon pickup while maintaining the characteristics of carbon fiber and is less likely to crack or peel due to thermal shock under intermittent conditions- Carbon fiber can be obtained, and high durability of the refractory lining for secondary refining equipment can be achieved.

It is a reflection micrograph of the microstructure near the crack portion located about 20 mm from the working surface surface of the spinel-carbon brick after use.

The refractory lining for secondary refractory equipment (hereinafter, simply referred to as “refractory material for secondary refractory equipment”) with reduced pressure of the present invention is a spinel-carbon brick mainly composed of spinel and carbon. Here, the mass ratio of the spinel to the carbon raw material of the spinel-carbonic brick is in the range of 88 to 99.5% by mass for the spinel and 0.5 to 12% by mass for the carbon raw material. If the carbon raw material is less than 0.5% by mass, slag infiltration and thermal spalling of the spinel-carbonic brick become remarkable, which is not preferable. Further, if the carbon raw material exceeds 12% by mass, the influence of the carbon pickup becomes strong, and it is not preferable because it is strongly influenced by the steel type manufactured in the secondary refining equipment. From the viewpoint of suppressing carbon pickup and being applicable to a wider range of kilns, it is more preferable that the spinel is in the range of 90 to 99% by mass and the carbon raw material is in the range of 1 to 10% by mass.

The carbon raw material used for spinel-carbon bricks needs to be well dispersed in the spinel-carbon brick structure because it serves as an inhibitor that inhibits the sintering of spinel aggregates. Therefore, as a part or all of the carbon raw material used for the spinel-carbon bricks constituting the refractory lining for the secondary refractory of the present invention, the volume per unit mass is large, in other words, the volumetric graphite. Apply the raw material. The volume of the graphitic raw material can be evaluated by the specific surface area of the graphite raw material, and the graphite raw material having a specific surface area in the range of 5 to 200 m ² / g, preferably 7 to 150 m ² / g is used. Here, if the specific surface area of the graphitic raw material ^{is less than 5 m 2} / g, it is not preferable because sintering cannot be sufficiently inhibited, and if it ^{exceeds 200 m 2} / g, a dense molded product cannot be obtained. Not preferred.

Any graphite raw material having a specific surface area within this range can be applied, but expansion graphite or graphene having good crystallinity and a scaly shape is particularly preferable. The expanded graphite or graphene used in the present invention is not particularly limited by a manufacturing method or the like, and any known or conventional manufacturing method can be applied.

The spinel raw material used for spinel-carbonic brick is not particularly limited, and theoretical composition spinel, alumina-rich spinel, magnesia-rich spinel, etc. can be used, and naturally produced spinel or ferroalloy. You can also use slag during manufacturing. Further, as the spinel raw material, the electrolytic product tends to show higher corrosion resistance, but it is also possible to use a sintered product or the like in consideration of cost and the like.

Further, spinel constitutes a secondary refining facility for refractory lining of the present invention - alloys such as the carbonaceous bricks, metal Al, metals such as metal Si, Al-Mg, Fe- Si, B 4 Additives such as non-metals such as C, BN and SiC can be blended. When these additives are blended, the total blending amount thereof is in the range of 5% by mass or less, preferably 4% by mass or less, based on the total amount of the spinel raw material and the carbon raw material. If the total blending amount exceeds 5% by mass on the outer surface, the elastic modulus after heating becomes high and the spalling resistance is remarkably lowered, which is not preferable. When the temperature change is large and the spalling of spinel-carbonic brick becomes a problem, it is possible to suppress the increase in elastic modulus without adding these additives.

In producing the spinel-carbonic brick constituting the refractory lining for the secondary refractory of the present invention, the above-mentioned spinel raw material, carbon raw material and additives which are appropriate components are weighed in a predetermined amount and mixed as described later. Further, as the binder, an organic binder typified by furan resin, phenol resin, dextrin, and pulp waste liquid, which is carbonized after receiving heat and functions as a binder, can be used as in the case of a general carbon-containing refractory. When manufacturing long bricks used in DH, RH, etc., powdered phenolic resin can also be used as an auxiliary measure against corner chipping and breakage. In addition, powdered pitches can be added to improve hot properties. Inorganic binders such as sodium silicate, potassium silicate, bittern, and magnesium sulfate can also be used. These can be used alone or in admixture of two or more. The total blending amount of these binders is in the range of 0.3 to 7% by mass, preferably in the range of 0.5 to 5% by mass, based on the total amount of the spinel raw material and the carbon raw material. Is. If the total compounding amount is less than 0.3% by mass in the outer coating, the binder does not sufficiently spread to the raw material, and if it exceeds 7% by mass, lamination may occur during molding and the product yield may be extremely deteriorated. Not preferable because of.

The method of mixing the blended raw materials in the production of the spinel-carbonic brick constituting the refractory lining for the secondary refractory of the present invention is not particularly limited, and for example, the blended raw materials are collectively or divided. Then, it can be mixed and kneaded by a mixer or a kneader. Devices that can be used for kneading, which is a pretreatment process for press molding of bricks, include, for example, roller-type SWPs and Simpson mixers, blade-type high-speed mixers, pressurized high-speed mixers and henschel mixers for fixed-container types. Alternatively, a kneader called a pressurized kneader or a kneader such as a container-driven roller-type MKP, a wet pan, a Connor mixer, a blade-type Erich mixer, or a vortex mixer can be used. Further, the kneader or the mixer may be provided with a pressurizing or depressurizing device, a temperature control device (heating, cooling or heat retaining) or the like. The mixing or kneading time varies depending on the type of raw material, blending amount, type of binder, temperature (room temperature, raw material or binder), type and size of mixer or kneader, but is usually several minutes to several hours.

The kneaded product obtained as described above is called a vibration press or CIP, as well as a friction press, a screw press or a hydroscrew press which is an impact pressure press, a hydraulic press or a toggle press which is a static pressure press, and the like. It can be molded by the existing molding machine. These molding machines may be equipped with a vacuum degassing device, a temperature control device (heating, cooling, or heat retention). The molding pressure and the number of times of tightening by the press molding machine vary depending on the size of the brick to be molded, the type of raw material, the blending amount, the type of binder, the temperature (room temperature, raw material and binder), and the type and size of the molding machine. The molding pressure is usually 0.2 to 3.0 ton / cm ² , and the number of times of tightening can be one to several tens.

The spinel-carbon bricks constituting the refractory lining for secondary refractory equipment of the present invention can exhibit strength that can withstand construction by heat treatment after molding. A hot air circulation type dry heating furnace can be used for heating at about 500 ° C. or lower, and when heating at a higher temperature is required, electric heating type, gas heating type, oil heating type, etc. Batch type single kilns, such as shuttle kilns and carbell kilns, and continuous tunnel kilns are most suitable. Of course, any type of heating furnace can be used as long as the temperature can be sufficiently adjusted and homogeneous heating can be performed.

The shape of the spinel-carbonic brick constituting the refractory lining for the secondary refractory of the present invention is not particularly limited, and is not particularly limited, but is a rectangular shape such as a normal brick, a bee type, a fan shape, or a semi-universal shape. It can be made into various shapes such as those of a thing, and it is also possible to combine a plurality of shapes. Further, when viewed in a vertical cross section, it is possible to provide a lining along the iron skin for a can body with a taper by using a trapezoid or an irregular shape in addition to a rectangle.

In constructing the refractory lining for the secondary refining equipment of the present invention using the above spinel-carbon brick, various mortars such as magnesia and alumina can be used as the mortar to be applied to the back surface of the spinel-carbon brick. be. In addition, spinel-carbon brick joints can basically be constructed with empty joints. However, if construction is difficult due to factors such as distortion of the iron skin, various mortars such as magnesia and alumina can be used in the same manner as the mortar applied to the back surface of spinel-carbon bricks. In this case, the joint thickness can be about 0.5 to 4 mm, preferably about 2 mm. Further, when it is strongly affected by stress, it is possible to dispose cardboard or ceramic fiber to use it as an expansion / absorption allowance. Of course, the spinel-carbon bricks constituting the refractory lining for the secondary refractory of the present invention can be manually constructed in the same manner as general bricks.

The refractory lining for secondary refractory equipment of the present invention exhibits features not found in existing refractory under high temperature and reduced pressure. It is desirable to install it on the part of the area. For example, a large effect can be obtained by using the slag line of the VOD method or the vicinity of the molten metal surface of the side wall of the vacuum chamber of the DH method or the RH method in a portion where the damage due to the high temperature slag is significant. On the other hand, since it is possible to exhibit durability above the standard even in other parts, it is also possible to line the entire furnace body with the refractory lining for secondary refractory equipment of the present invention.

Example 1
The raw materials are blended at the blending ratios shown in Table 1 below, kneaded using an Erich mixer, and the obtained kneaded product is 2.5 tons / cm by a hydraulic press using a 230 × 200 mm mold. ^A molded product was obtained by molding at a pressure of 2, and then dried at 300 ° C. for 12 hours in a drying furnace to produce a spinel-carbon brick constituting the refractory lining for the secondary refractory of the present product. .. Further, by the same operation, a comparative refractory product was produced at the blending ratios shown in Table 2.

In the table,
"Theoretical composition spinel" _is, Al ₂ O 3: MgO 71.7: those of 28.3;
"Magnesia" is an electric fusion product having an MgO purity of 98% by mass;
The "phenolic resin" has a residual coal ratio of 25% by mass measured after a reduction heat treatment at 1000 ° C. The amount of residual coal was measured based on the fixed carbon measurement method in JIS K 6910 (phenol resin test method);
"Amount of carbon contained in brick (% by mass)" indicates the sum of the amount of residual carbon in the phenol resin of scaly graphite, expanded graphite, and graphene;

The "high temperature heating test: mass reduction rate (%)" was carried out using an electric furnace with an adjustable atmosphere in order to evaluate the degree of the magnesia-carbon reaction. Here, the present invention relates to a refractory lining for secondary refining equipment accompanied by depressurization, and should be evaluated under reduced pressure or vacuum, but under reduced pressure or vacuum, it should be evaluated. Mg (gas) is generated, Mg gas is deposited on the furnace wall as metallic Mg, and when the furnace lid is opened after processing, it may react with air and cause an explosion. The following test method was adopted. That is, the test temperature is set to 1800 ° C., an Ar atmosphere is created, and P (Mg) and P (CO) are lowered by blowing Ar, and the magnesia-carbon reaction is promoted in the same manner as the treatment under reduced pressure or vacuum. It is something that makes you. As described above, the magnesia-carbon reaction is a reaction in which solid magnesia and carbon react to form gaseous Mg and CO, and the sample in which the reaction occurs always accompanies mass loss, so this mass reduction rate (%) is used. Evaluated using. The smaller the value, the more the reaction was suppressed, and those with a mass reduction rate of more than 10% were judged to be unsuitable.

In the "hot metal immersion spalling test", a sample obtained by burying a brick having a shape of 40 x 40 x 230 mm in a coke breeze at 1000 ° C or 1500 ° C in advance and heat-treating it for 10 hours raises the sample to 1700 ° C. It was carried out by immersing in warm hot metal for 1 minute and then cooling with water for 15 seconds.
The intention of the heat treatment of bricks is that the heat treatment at 1000 ° C. for 10 hours removes the residual volatile matter in order to prevent explosion due to the residual volatile matter during the test, and the heat treatment at 1500 ° C. for 10 hours burns the spinel aggregate. It is to connect them to make an organization similar to the actual machine.
After the test, the sample was cut and the cross section was observed, and the number and thickness of cracks in the cross section were measured, and the degree and amount of cracks were evaluated on a 5-point scale. “⊚” indicates that no crack was observed in the sample, and “◯” indicates that the width of the crack in the sample was 1 mm or less. Further, the sample having a crack width exceeding 1 mm was evaluated as “□” or “Δ” depending on the number of cracks. Furthermore, "x" indicates that the bricks were broken during water cooling, and none of them was judged to be suitable for use;

The above evaluations were summarized and shown in 5 grades of ◎, ○, □, △, and × in order from the best one as the “comprehensive evaluation”. Particularly good ones were evaluated as "◎", and those that seemed to be usable without problems were evaluated as "○". “□”, “△”, and “×” were judged to have little or no improvement effect, to varying degrees.

From the results shown in Table 1, it can be seen that the product of the present invention obtained excellent results in both the high-temperature heating test and the hot metal immersion spalling test.
On the other hand, from the results shown in Table 2, it is considered that the magnesia-carbon bricks of Comparative Products 1 to 3 have a large mass reduction rate in the high temperature heating test and are strongly influenced by the magnesia-carbon reaction. .. Further, comparative 4-12 has a specific surface area, which respectively using flake graphite of ^{1.1m 2 /g,2.8m 2 /g,4.0m 2 / g} , the specific surface area is large scaly graphite Although the results of the hot metal immersion spalling test of the sample preheated at 1500 ° C. for 10 hours tend to be improved, it can be seen that the improvement effect is not sufficient as compared with the product of the present invention.

Example 2
The products 1, 3, 5 and 9 of the present invention and the comparative products 1, 4 and 13 were introduced into the vacuum ladle slag line of the actual machine, and a separate test was performed. After using 30 channels, they were collected and the damage rate (comparative product 1 was displayed as a melting rate index 100: the smaller the better), the degree of cracking, and the degree of carbon pickup were compared.
As shown in Table 3, compared to the magnesia-carbon bricks of Comparative Product 1, all of the products of the present invention have a lower damage rate, and cracks and cracks in the bricks after use and carbon pickup to molten steel are also improved, which is good. It was a result. The comparative product 13 was not much different from the product of the present invention in terms of the degree of cracking and durability, but was unsuitable due to the strong influence of the carbon pickup.

The refractory lining for secondary refractory equipment with reduced pressure of the present invention is used in a portion significantly damaged by high temperature slag, for example, near the slag line of the VOD method or the vicinity of the hot water surface of the side wall of the vacuum tank of the DH method or the RH method. This will give you a great effect. On the other hand, since it is possible to exhibit durability above the standard even in other parts, it is also possible to line the entire furnace body with the refractory material for secondary refractory equipment with reduced pressure of the present invention.

Claims (5)

A part of carbon raw material or a part of carbon raw material in a refractory lining for secondary refractory equipment with decompression composed of spinel-carbon fiber containing 88 to 99.5% by mass of spinel raw material and 0.5 to 12% by mass of carbon raw material. A refractory lining for secondary refractory equipment with reduced pressure, characterized in that one or more graphite raw materials having a specific surface area in ^{the range of 5 to 200 m 2 / g are used.} The refractory lining for secondary refining equipment with reduced pressure according to claim 1, wherein the graphitic raw material is expanded graphite. The refractory lining for secondary refractory equipment according to claim 1, wherein the graphitic raw material is graphene. Add one or more additives selected from the group consisting of metals, alloys and non-metals in a total amount of 5% by mass or less with respect to the total amount of spinel raw material and carbon raw material. The refractory lining for secondary refining equipment, which comprises the reduced pressure according to any one of claims 1 to 3. In the lining lining structure of the secondary smelting equipment with reduced pressure, the lining fireproof for the secondary smelting equipment with reduced pressure according to any one of claims 1 to 4 at least in the slag line portion and the vicinity of the molten metal surface of the secondary smelting equipment. A lining lining structure for secondary refractory equipment with reduced pressure, characterized by the arrangement of objects.

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