JP2001254120A - Lining in rh furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lining structure in an RH furnace using dechromium brick excellent in erosion resistance to slag having low CaO/SiO2. SOLUTION: The brick having complex oxides of magnesia with rare earth metal oxides, such as yttria, latnia, is used for a circulating tube and a vessel bottom at the lower layer of the RH furnace, and an MgO-C brick is used for a side wall thereof. The complex oxide brick of the magnesia with the rare earth metal oxide can be formed from the blended material containing 80-99.8 wt.% magnesia raw material and 0.2-20 wt.% rare earth metal oxide raw material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combination configuration of a lining of an RH furnace used as a secondary smelting furnace for steel.

[0002]

2. Description of the Related Art An RH furnace is widely used for degassing as a secondary smelting furnace for steel. Magnesia-chrome brick (hereinafter referred to as "magcro brick") is often used as the refractory lining of the RH furnace. Magcro brick is a brick mainly composed of magnesia and chromite ore, and usually contains 10% or more of Cr ₂ O ₃ .

[0003] Then, spinel group minerals mainly the _{Cr 2 O 3 (MgR 2 O} 4; R = Cr, Fe, Al)
However, during the firing of the brick, it precipitates as a secondary spinel in the matrix and binds the aggregate mainly composed of magnesia, which provides the property of increasing the resistance of the matrix portion to slag infiltration.

However, when disposing of this magcro brick after use, a special treatment is required to prevent hexavalent chromium contained in the brick from being eluted into water, and the cost is increased accordingly. Have a problem.

[0005] For this reason, as a refractory material which has the same properties as magcro brick but has no problem in disposal, it is a substitute for magcro brick, for example, as disclosed in JP-A-9-30976.
No. 2 discloses low carbon MgO-C bricks, and Japanese Patent Publication No. 7-51458 discloses magnesia-spinel bricks (hereinafter referred to as mag spinel bricks).

[0006] The MgO-C brick is mainly composed of magnesia, and has slag infiltration that is hardly wetted by slag in a matrix portion, thereby strongly suppressing slag infiltration. However, since MgO-C bricks contain scale graphite in the matrix, the graphite causes carbon pickup to elute in the steel, and during refining of molten steel containing iron oxide, the graphite is oxidized by slag, and Has a problem that the wear of the brick increases due to the roughness.

Further, the mag spinel brick is a common spinel (MgAl ₂
O ₄ ) is a composition that does not contain chromium, and is considered to become the mainstream of dechromed bricks in the future. However, the common spinel has a particularly low Ca
Since the corrosion resistance to O / SiO ₂ slag is inferior, the mag spinel brick has a disadvantage that the matrix is preliminarily eroded and the durability is insufficient.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks of the conventional dechromed brick, and has a low CaO / S content.
Provided is a lining structure of an RH furnace having excellent corrosion resistance to iO ₂ slag.

[0009]

The applicant of the present application has previously disclosed in Japanese Patent Application No. 10-31195 a magnesia yttria brick containing 0.2 to 20% by weight of a rare earth oxide mainly composed of yttria. did. The present invention is
This composite oxide brick of magnesia and rare earth oxide was confirmed not to use Cr ₂ O ₃ and to have a durability equal to or higher than that of a conventional magcro brick, and came up with an application to an RH furnace. .

That is, the lining of the RH furnace according to the present invention uses a brick made of a composite oxide of magnesia and a rare earth oxide on the reflux tube and the bottom of the RH furnace lower layer, and a MgO-C brick on the side wall. The feature is in the point used.

The rare earth oxide is not limited to Y ₂ O ₃ , but La ₂ O ₃ and other rare earth oxides have similar chemical properties, and therefore, the same effect can be expected.

In the present invention, the magnesia-rare earth oxide composite oxide brick used for the reflux tube in the lower layer of the RH furnace and the tank bottom is a magnesia raw material of 80 to 99.8.
In general, it is possible to use a mixture containing 0.2% by weight of a rare earth oxide raw material and 0.2 to 20% by weight of a rare earth oxide raw material. Can be obtained in a similar manner to bricks. Rare earth oxide raw materials include Y ₂ O ₃ , La ₂
O ₃ or other rare earth oxides as a total amount,
A raw material containing 50% by weight or more is used. For example, a purified high-purity raw material or a mixture of rare earth oxides obtained from minerals such as xenotime and bastnaesite can be used. The magnesia raw material may be any material that is generally used as a raw material for MgO-C brick or magcro brick, and may be used without any particular limitation. The amount of the magnesia raw material is preferably from 80 to 99.8% by weight, and if it is less than 80% by weight, the corrosion resistance to slag is insufficient.

When investigating the structure of the magnesia-rare earth oxide composite oxide brick used in the present invention, the rare earth oxide is mainly present in the matrix portion in the structure. It is not sufficiently clear how this suppresses slag permeation and improves corrosion resistance, but rare earth oxides react with SiO ₂ in the slag to increase the melting point of the slag and suppress permeation. There is a mechanism to do this.

Further, MgO-C used for the side wall of the RH furnace
As the brick, MgO-C brick conventionally used in a converter, a ladle or an RH furnace can be used.

[0015] Magcro bricks conventionally used as furnace materials for secondary refining furnaces have one aspect that they are vulnerable to changes in temperature and atmosphere. This is because the iron content in the chromium ore, which is the raw material of the magcro brick, depends on changes in temperature and atmosphere.
This is because a so-called "bursting" in which the tissue is deteriorated with a change in volume occurs due to the repetition of the change between the valence positive ion and the trivalent positive ion. When exposed to a strong reducing atmosphere, Cr ₂ O ₃ itself, which is a main component, is reduced and volatilized as CrO gas, or remains in the structure as a Cr metal phase. This impairs corrosion resistance. Nevertheless, the reason why magcro brick is widely used as a large refractory furnace for secondary smelting furnaces is that, compared to conventional dechromed brick, for example, mag spinel brick, the corrosion resistance of magcro brick is so strong that it compensates for the above-mentioned disadvantages. It is.

On the other hand, the composite oxide brick with magnesia-rare earth oxide typified by magnesia yttria brick used in the present invention has a corrosion resistance equal to or higher than that of magcro brick and is contained in the brick. Since rare earth oxides are stable as oxides even at high temperatures,
Corrosion resistance does not deteriorate due to changes in temperature or atmosphere.

For example, a typical rare earth oxide, Y₂
O₃Are FeO, Fe₂O₃, Cr ₂O₃Oxide than
As stable as. Because of this, the atmosphere changes drastically
Kiln furnace for secondary refining, especially with deoxidizer such as Al in RH furnace
The bottom of the tank is easily exposed to the strong reducing atmosphere
Excellent durability in reflux and immersion tubes.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to examples.

[0019]

1 is a vertical sectional view of a lower tank of an RH furnace according to an embodiment of the present invention, and FIG. 2 is a plan view of FIG. 1 as viewed from above. And a bottom wall 4 forming a furnace bottom so as to surround the reflux tube 3 and a side wall 5 forming an upper wall from the bottom 4. Is connected to the intermediate tank by an upper flange portion 6. The recirculation tube 3 forms a cylinder formed by magnesia rear brick in two upper and lower stages. A casting material 8 is filled between the lower tube and the outer shell 7 of the reflux tube 3. A magnesia rear brick is lined on the bottom 4 of the lower tank at substantially the same level as the upper end surface of the upper brick of the reflux pipe 3. A MgO-C brick is lined on a side wall 5 above the bottom of the tank, and a perm brick 9 made of magnesia is lined around the outer periphery with a steel shell.

In use, molten steel is sucked up from one of the two reflux tubes, and the flow of molten steel discharged from one is generated.
The surface of the molten steel just contacts the side wall 5. Since slag with a low specific gravity is floating on the surface of the molten steel,
Will be chemically attacked by slag.

When the test was repeated using magnesia-it rear brick for the entire lower tank, it was found that the side wall 5 was damaged earlier than the reflux tube or the tank bottom. Therefore,
When the side wall 5 was combined with MgO-C brick having better slag infiltration resistance than magnesia yttria brick, the life of the entire furnace could be further extended.

That is, this side wall is formed of molten steel slag as C
_{aO-Al 2 O 3 -SiO 2} -FeO system of slag attack. As a result, the slag infiltrates the working surface of the magnesia yttria brick, generating structural spalls and causing damage. On the other hand, MgO-C bricks can suppress the penetration of slag by the scale-like graphite, so that structural spall hardly occurs. Thus, the overall furnace life can be extended over using magnesia yttria brick alone.

In the lower vessel of the RH furnace shown in FIGS. 1 and 2, the first embodiment uses a magnesia rear brick to separate the vessel bottom and the reflux tube from each other.
Wall lining with MgO-C brick, Comparative Example 1
All the lower tanks were lined with magnesia-it rear bricks and constructed, and the durability of each furnace was compared. The intermediate tank and dip tube were lined with magcro brick.

In the furnace of the embodiment of the present invention, the target 1000 charge was reached, but in the furnace of the comparative example, the remaining size of the brick near the sixth side wall became small at 850 charges, and the temperature of the steel shell increased. The use was discontinued.

After use, the inside of each furnace was inspected to examine the state of brick wear. As a result, in the furnace of the example, each part is evenly worn, whereas in the furnace of the comparative example, the wall is greatly worn and the tank bottom and the reflux pipe are little worn.

Then, the bricks on the side wall and the central part of the tank bottom were collected and cut, and the state of wear was investigated. As a result, in the side wall brick, in the example (MgO-C brick), the vicinity of the operating surface was hardly decarburized, and no slag infiltration was observed. The wear rate was about 0.25 mm / charge at the sixth side wall. On the other hand, in the comparative example furnace (magnesia yttria brick), the slag was infiltrated to a depth of about 30 mm from the working surface, and a crack parallel to the working surface was found on the back side of about 50 mm from the working surface. From this, it is considered that the side wall of the comparative example was mainly worn by structural spalling. The wear rate was about 0.39 mm /
It was a charge.

On the other hand, the brick at the center of the bottom of the tank had a slag infiltration thickness of about 5 mm and no evidence of structural spalling in both the example and the comparative example (both are magnesia rear bricks). The wear rate was about 0.2 for both furnaces.
It was 2 mm / charge.

[0028]

According to the present invention, by properly lining the lower tank of the RH furnace with the magnesium rear brick and the MgO-C brick, the durability can be improved as compared with the case where only the magnesium rear brick is used.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view of a lower tank of an RH furnace according to an embodiment of the present invention.

FIG. 2 is a plan view of FIG. 1 as viewed from above.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lower tank 2 Lower flange part 3 Recirculation pipe 4 Tank bottom 5 Side wall 6 Upper flange part 7 Iron shell 8 Casting material 9 Perm brick

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masahiko Uchida 3, Hikari, Kashima-shi, Ibaraki Sumitomo Metal Industries Co., Ltd. Steelworks Dept., Kashima Works F-term (reference) 4G030 AA07 AA11 AA12 AA13 BA26 GA09 4K013 CE01 CE09 CF18 CF19

Claims (2)

[Claims] 1. A lining of an RH furnace using a composite oxide brick of magnesia-rare earth oxide for a reflux tube and a tank bottom of a lower layer of the RH furnace and MgO-C brick for a side wall. 2. The magnesia-rare earth oxide composite oxide brick comprises a blend containing 80 to 99.8% by weight of a magnesia raw material and 0.2 to 20% by weight of a rare earth oxide raw material. 3. The lining of an RH furnace according to item 1.