JPH07224311A - Structural body of gas blowing tuyere for steel making furnace - Google Patents

Abstract

PURPOSE:To provide the structural body of a tuyere which has a excellent thermal impact resistance and has a longer life. CONSTITUTION:This structural body of the gas blowing tuyere for a steel making furnace is inserted with a ceramic pipe 2 contg. 0 to 40% BN and 0 to 10% SiC and/or B4C and consisting of the balance substantially ZrB2 between a tuyere brick 3 and a metallic tuyere 1. As a result, the crack and damage of the tuyere brick by thermal stress and thermal impact are eliminated and the damage of the tuyere is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas blowing tuyere structure of a steelmaking furnace in a steelmaking process.
The present invention relates to a tuyere structure having a ceramic heat insulating layer provided between a tuyere brick and a metal tuyere tube for supplying gas.

[0002]

2. Description of the Related Art In the present steel manufacturing process, a converter is generally used in the smelting process. The most widely used converter type is a bottom blowing converter or a composite blowing converter having a top and bottom blowing function. Further, there are a VOD furnace having tuyere at the bottom of the furnace, and a metallurgical furnace having tuyere on the wall of the furnace for the purpose of melting scrap and secondary combustion.

As these tuyere, a single tube tuyere mainly made of metal, a double tube tuyere similarly composed of an inner tube and an outer tube,
There are three types of aggregate tuyere with many thin tubes on refractory. The metal type is often stainless steel. As a structure of the tuyere portion, as shown in FIG. 3 described later, a structure in which a stainless steel double pipe is directly inserted into a tuyere brick is generally used.

As the gas species blown from the tuyere, O ₂ gas is selected for the purpose of decarburizing the hot metal and is blown into the hot metal from the inner tube of the double pipe. At this time, hydrocarbons such as LPG are blown as a cooling gas from the outer pipe for the purpose of cooling the tuyere. This is because hydrocarbons such as LPG are thermally decomposed by an endothermic reaction and have excellent heat removal ability. Such LPG cooling is performed in order to prevent ignition and melting damage of the metal tuyere tube at the time of blowing O ₂ gas. However, at the same time, the tuyere bricks around the tuyere tube are also cooled, and are subject to thermal stress and thermal shock and wear.

On the other hand, N ₂ or Ar gas is selected for the purpose of improving the efficiency of the refining reaction by vigorous stirring of molten steel and promoting the decarburization reaction. Although the use of N ₂ gas is advantageous from the viewpoint of cost,
It is used together with Ar because it adversely affects the steel quality. When only such an inert gas is blown, the ignition and melting loss of the metal tuyere pipe does not occur, but as with the case of LPG blowing, the tuyere brick is subjected to heat removal due to gas cooling, so thermal stress and thermal shock Received and worn out.

Of the tuyere parts, the tuyere bricks, in particular, are the parts that are difficult to repair locally even after the operation of the furnace is once started after the construction of the furnace. Rate limiting.

Japanese Utility Model Publication No. 63-44449 discloses a bottom blowing nozzle made of a ceramic material for preventing ignition and melting damage of tuyere of a stainless steel tube by O ₂ gas. However, this invention is intended to prevent the pre-melting damage of the metal tuyere at the time of blowing O ₂ , and in order to extend the life of the tuyere, the wear of the tuyere brick must be further suppressed.

The wear mechanism of tuyere bricks is explained as follows.

In other brick parts, melting loss is the main cause of wear, whereas in the tuyere brick, heat spalling is the main cause. That is, in the tuyere brick, an extreme temperature gradient is generated in the tuyere brick due to the heat received from the molten steel and the removal of the tuyere cooling gas during the blowing, which causes thermal stress in the tuyere brick. Moreover, since batch refining is usually performed in the converter, this thermal stress is repeatedly generated by thermal shock.

When this thermal stress reaches the breaking stress of the brick or more, a crack is generated in the brick, and the crack develops by being repeatedly subjected to thermal shock, and the brick is separated and worn (thermal spalling damage). .

In the bottom blowing converter, the material of the tuyere bricks was initially calcined magdro bricks, but since the above-mentioned thermal spalling damage became a problem, refractory materials excellent in heat resistant spalling properties were aimed at, and MgO -C brick was selected.
At present, MgO-C bricks are used as the lining material in almost all composite blowing converters and bottom blowing converters.

[0012] MgO-C brick is a composite refractory material having resistance to thermal shock by blending carbon having excellent thermal conductivity with MgO. MgO as a tuyere brick
By using -C, the life of the tuyere was extended compared to conventional oxide refractories.

However, its life has not yet reached a satisfactory level, and various measures have been taken for further improvement. One direction was to increase the thermal conductivity and improve the thermal shock resistance. That is, it is a method of increasing the thermal conductivity and increasing the thermal shock resistance by increasing the amount of carbon blended in the MgO-C brick.

However, excessive blending of carbon leads to an increase in oxidation loss of carbon and reduces the oxidation resistance of MgO-C bricks. Furthermore, the oxidation resistance of carbon also deteriorates the corrosion resistance of MgO-C bricks to slag. Therefore,
The carbon content can only be increased up to 30%, which is not a fundamental solution.

It has been reported that thermal spraying of tuyere bricks was reduced by spraying ZrO ₂ on the outer circumference of the tuyere (iron and steel,
vol.70, 1984, S949). This is to reduce the thermal stress in the tuyere brick by reducing the thermal gradient generated in the tuyere brick by using the ZrO ₂ sprayed layer as the heat insulating layer, and to suppress the heat spalling.

According to this report, although the heat-insulated tuyere brick becomes high in temperature, the temperature change is halved and the wear rate of the tuyere brick is reduced by 7%. However, in the method of using such a thermal sprayed layer as the heat insulating layer, the following points are problems. That is, the applicable sprayed layer thickness is generally 2 to 300 μm.
Since it is about m, a sufficient effect cannot be obtained as a heat insulating layer. The thermal sprayed layer formed is an oxide, which is inferior in thermal shock resistance. Therefore, it is still insufficient as a technique for extending the life of tuyere bricks.

[0017]

SUMMARY OF THE INVENTION An object of the present invention is to prevent the occurrence of cracks in the tuyere brick body, which is a drawback of the conventional gas-blowing tuyere structure, to suppress wear and to stabilize the life of tuyere. It is to provide a tuyere structure that can be extended.

[0018]

The gist of the present invention resides in the following gas blown tuyere structure for a steelmaking furnace.

% Between the tuyere brick and the metal tuyere
In, BN: 0 to 40% SiC and / or B ₄ C: contains 0-10%, for steel furnaces, characterized in that the balance has been inserted into the ceramic tube consisting substantially ZrB ₂ Gas blown tuyere structure.

Materials having particularly excellent corrosion resistance and molten spalling resistance against molten steel include ZrB ₂ ceramics and ZrB ₂ ceramics.
Containing refractories are known. The present inventor evaluated the resistance to thermal shock of these ceramic materials by using R ″ (thermal shock fracture resistance coefficient) as an index.
It was found that the life of the tuyere structure can be effectively extended by inserting the ZrB ₂ containing material between the tuyere brick and the metal tuyere.

[0021]

1 is a view showing an example of a tuyere structure of the present invention. This example is for a furnace bottom tuyere, FIG. 1 (a) is a vertical sectional view, and FIG. 1 (b) is a plan view of only the tuyere structure viewed from the direction A.

As shown, the tuyere structure of this example is
It consists of a metallic double tube tuyere 1, a ZrB ₂ quality ceramics tube 2 and a tuyere brick 3. The ZrB ₂ quality ceramics tube 2 is inserted into the tuyere brick 3 and further to a ZrB ₂ quality ceramics tube 2. The metal double tube tuyere 1 is inserted.

This ZrB ₂ ceramic tube 2 is
BN: 0 to 40%, SiC and / or B ₄ C: 0 to 10%, the balance being a ceramic tube consisting essentially of ZrB ₂ (hereinafter referred to as ZrB ₂ ceramic tube), corrosion resistance to molten steel And a heat insulating pipe that acts as a heat insulating layer for the tuyere bricks 3, that is, a structural material that mitigates thermal shock when the metallic double pipe tuyere 1 is cooled. If the tuyere is made of metal, it may be a single tube or multiple tubes of three or more tubes, and the tuyere structure is the same. The metal material can be selected from stainless steel, copper, cast iron and the like.

The reason why the ZrB ₂ ceramic tube is limited to the above composition is as follows.

Since the ceramic tube itself is in contact with the metallic tuyere, when the tuyere is cooled, it is directly and repeatedly subjected to thermal stress and thermal shock.

Therefore, the ceramic tube must be made of a material having high resistance to thermal shock fracture.

Considering the application of the thermal shock fracture resistance coefficient R ″ as a means for quantitatively evaluating the resistance of the material to thermal shock, R ″ is expressed by the following equation (1).

[0028]

[Equation 1]

Here, S: fracture strength, μ: Poisson's ratio, K: thermal conductivity, E: Young's modulus, α: coefficient of thermal expansion,
ρ: density, C: specific heat.

That is, it can be seen that the thermal shock fracture resistance coefficient R ″ is improved by improving the fracture strength and thermal conductivity, and by lowering the Young's modulus and thermal expansion coefficient.

Table 1 shows the results of the evaluation of typical commercially available ceramics and ZrB ₂ -based ceramics using the formula (1).

[0032]

[Table 1]

From Table 1, R ″ of non-oxide ceramics such as SiC and Si ₃ N ₄ is MgO, Al ₂ O ₃ , PSZ (partially stabilized ZrO 2).
₂ ) Higher than that of oxide-based ceramics such as ₁ ) or more, indicating that these non-oxide-based ceramics have excellent resistance to thermal shock.

However, considering the physical properties of each material, Si
Since C and Si ₃ N ₄ are inferior in corrosion resistance to molten steel, it is difficult to apply them as heat insulating materials and thermal shock resistant materials. Al ₂ O ₃ has a low thermal shock temperature difference, and PSZ loses its stabilizing effect at high temperatures, resulting in a marked decrease in strength. Therefore, these are not realistic materials as well.

For the above reason, one of the materials of the ceramic tube used as the heat insulating layer in the tuyere structure of the present invention is substantially made of ZrB ₂ .

In this ZrB _two- quality ceramic,
B ₂ with 40% or less by weight of BN added, or 10% B ₄ C and / or SiC.
% Or less, and it is desirable that these are uniformly dispersed in the matrix of the ZrB ₂ component.

The reason why the BN, B ₄ C and / or SiC may be blended in the above range is as follows.

By adding BN, the heat-resistant spalling property is further improved as compared with the case of using ZrB ₂ alone. However, on the contrary, if the BN content exceeds 40%, the heat spalling property is excellent but the corrosion resistance is deteriorated.

SiC and B ₄ C act as a sintering aid for ZrB ₂ and increase the hot strength, but B ₄ C and / or SiC are not
If it exceeds%, a liquid phase containing B ₂ O ₃ or SiO ₂ as a main component is generated in the matrix portion of the ZrB ₂ component during hot use, resulting in a decrease in strength.

The ZrB ₂ quality ceramic tube is prepared by molding powders having the ZrB ₂ quality and the residual composition adjusted to the above composition, or raw material powders that can be the ZrB ₂ quality and the residual composition by sintering, and molding the powder. It can be manufactured by a method of firing in a reducing atmosphere or an inert atmosphere. If necessary, in order to further densify, hot pressing as a firing method,
A pressure sintering method such as HIP may be applied.

The material of the tuyere brick can be selected from materials commonly used as refractory for lining steelmaking furnaces such as alumina, magnesia, magcro, magdro, Al ₂ O ₃ -C and MgO-C.

The dimensions of the tuyere brick and the metallic double tube tuyere are:
Although it may be equivalent to the tuyere of the conventional structure, it is desirable that the length of the ZrB ₂ ceramics tube is equal to the length of the tuyere brick into which it is inserted. However, in recent large-scale furnaces, long bricks with a length of near 1500 mm may be used as furnace bottom tuyere bricks.Therefore, when a ZrB ₂ quality ceramics tube of this length is produced in one piece, it will be Warping may occur due to unevenness or the like. For this reason, if necessary
A method may be used in which a ZrB _two- quality ceramics tube is divided into a plurality of pieces to be manufactured, and when they are inserted into a tuyere brick, they are connected and fixed by MgO castable or the like. The diameter of the ZrB ₂ ceramics tube may be determined by the tuyere diameter.

The tuyere structure of the present invention is most effectively applied to the tuyere bottom tuyeres that are in direct contact with molten steel, mainly in composite blowing converters and bottom blowing converters, but scrap In a melting furnace or a furnace that performs refining after scrap melting, brick erosion due to the influence of slag is relatively small, but it can also be used as a structure for the tuyeres of furnace walls that are repeatedly subjected to thermal stress and thermal shock. it can.

[0044]

EXAMPLES A length of 280 mm and an outer diameter of 70 m were obtained according to the components and firing conditions shown in the following Inventive Examples 1 to 8 and Comparative Examples 1 to 3.
A dense ceramics tube with an inner diameter of 20 mm and an inside diameter of 20 mm was produced and inserted as a heat insulating layer in the tuyere bricks. These were applied to the bottom tuyeres of a 50 ton VOD furnace, and a test was conducted to compare the wear of the tuyere bricks. did.

FIG. 2 is a diagram showing the tuyere structure (furnace bottom tuyere) in which the ceramic tubes are inserted and the dimensions in the examples of the present invention and the comparative example. (a) is a longitudinal sectional view and (b) is a plan view of only the tuyere structure viewed from the direction A. Ceramic tube 8
Corresponds to the ZrB ₂ ceramic tube 2 in FIG.

As a concrete method, four bottom blown tuyere are provided, and three tuyere of them are used as the tuyere structure shown in FIG.
Each tuyere was a conventional tuyere (referred to as a conventional example) in which a heat insulating layer was not inserted. For the tuyere brick, MgO-C quality was used in all tuyere structures.

The tuyere was made of a stainless steel double tube, and O ₂ was selected as the gas blown from the inner tube and LPG was selected as the cooling gas from the outer tube. The test conditions are shown in Table 2.

[0048]

[Table 2]

Inventive Example 1 1 wt% of polyvinyl alcohol (hereinafter referred to as PVA) was added as a binder to a ZrB ₂ raw material powder and kneaded, and after CIP molding, the temperature was 1600 ° C. and the pressure was 1600 ° C.
Ceramic tube produced by hot pressing method under the condition of 500 kg / cm ² Inventive example 2: A raw material powder containing ZrB ₂ 95 wt% and BN ₅ wt% was prepared, and 1 wt% of PVA was added and kneaded to give an inventive example. Ceramic tube produced under the same conditions as in Example 1 of the present invention: Ceramic tube produced under the same conditions as those of Inventive Example 1 of the present invention by adjusting raw material powders having ZrB ₂ 60 wt% and BN 40 wt% as components Inventive Example 4: ZrB ₂ Ceramics tube prepared by adjusting raw material powder containing 98 wt% and SiC 2 wt% as components, CIP-molded, and then pressure-sintered in N ₂ atmosphere at 1700 ° C. Inventive Example 5: ZrB ₂ 90 wt%, SiC 10 wt% A ceramics tube prepared by adjusting the raw material powder to be produced under the same conditions as in the present invention example 4. Inventive example 6: A raw material powder containing ZrB ₂ 98 wt% and B ₄ C ₂ wt% as components was prepared and the same as in the present invention example 4. Ceramic tube produced under the conditions Inventive Example 7: Preparation of raw material powder containing 90 wt% ZrB _{2 and} 10 wt% B ₄ C Then, a ceramic tube produced under the same conditions as those of Inventive Example 4 Inventive Example 8: A raw material powder containing ZrB ₂ 90 wt%, SiC ₅ wt% and B ₄ C 5 wt% was prepared, and produced under the same conditions as Inventive Example 4. Comparative example 1: Al ₂ O ₃ powder was uniaxially molded into a predetermined shape, then CIP molded, and sintered under atmospheric pressure at 1500 ° C. under atmospheric pressure.
Al ₂ O ₃ ceramic tube Comparative Example 2: Zr containing 3 mol% Y ₂ O ₃ as a stabilizing material
Partially stabilized ZrO ₂ ceramics tube produced by using O ₂ as a raw material powder and shaping it into a predetermined shape, and then firing it at 1400 ° C. in the air atmosphere. Comparative Example 3: Uniaxial molding of SiC powder into a predetermined shape, followed by CIP molding. SiC ceramic tube manufactured by hot pressing under the conditions of 1700 ° C. in N ₂ atmosphere and pressure of 500 kg / cm ² Table 3 shows the physical properties of the ceramic tube materials of Inventive Examples 1 to 8 and Comparative Examples 1 to 3 and comparison. The wear rate of the tuyere brick after the test is shown. The wear rate of the conventional tuyere is 1.30 to 1.60 mm / c.
was h.

[0050]

[Table 3]

The tuyere wear rate was reduced to 0.74 to 0.80 mm / ch by using the tuyere structure of the present invention in which the ceramic tubes of Examples 1 to 8 of the present invention were inserted.

After the test, the tuyere bricks were collected and their cross sections were observed. In the conventional example, the working surface (molten steel contact surface)
A crack parallel to the working surface was found inside the brick of about 60 mm.

FIG. 3 is a view showing an example of a crack generated inside a tuyere brick of a conventional tuyere structure, in which (a) is a longitudinal sectional view,
(b) is a plan view of only the tuyere structure viewed from the A direction.

In Comparative Examples 1 and 2, cracks were also generated in the ceramic tube itself, and the ceramic tube was partially broken on the operating surface side. Figure 4
[Fig. 3] is a vertical cross-sectional view showing an example of cracks generated in the tuyere brick of the tuyere structure and the ceramic tube when the material of the ceramics tube is not proper, and (a) is Comparative Example 1, (b ) Is the case of Comparative Example 2.

In Comparative Example 3, the tuyere brick and the ceramic tube were not cracked and the wear rate was reduced, but an oxide layer of 4 to 6 mm was generated on the operating surface of the ceramic tube. The part was eroded by molten steel.

On the other hand, in Examples 1 to 8 of the present invention, no deteriorated layer was observed on the working surfaces of the tuyere brick and the ceramic tube, and almost no corrosion by molten steel was observed.

[0057]

EFFECTS OF THE INVENTION According to the present invention, by inserting a ZrB ₂ ceramics tube as a heat insulating layer between the tuyere brick and the metal tuyere, crack damage of the tuyere brick due to thermal stress or thermal shock It is possible to suppress wear of tuyere.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a tuyere structure of the present invention (furnace bottom tuyere). (a) is a longitudinal sectional view, and (b) is a plan view of only the tuyere structure viewed from the direction A.

FIG. 2 is a view showing a tuyere structure (furnace bottom tuyere) used in Examples of the present invention and Comparative Examples. (a) is a longitudinal sectional view and (b) is a plan view of only the tuyere structure viewed from the direction A.

FIG. 3 is a view showing a tuyere structure (furnace bottom tuyere) used in a conventional example. (a) is a longitudinal sectional view and (b) is a plan view of only the tuyere structure viewed from the direction A.

FIG. 4 is a vertical cross-sectional view showing an example of a situation after use of a tuyere structure used in a comparative example. (a) is comparative example 1, (b) is comparative example 2
Is the case.

[Explanation of symbols]

1: Metal double tube tuyeres 2: ZrB ₂ quality ceramic tube,
3: Tuyere brick, 4: Wear brick, 5: Permanent brick, 6: Iron crust, 7: Stainless steel double pipe tuyere, 8: Ceramics pipe

Claims (1)

[Claims] 1. A weight percentage between the tuyere brick and the metal tuyere.
In, BN: 0 to 40% SiC and / or B ₄ C: contains 0-10%, for steel furnaces, characterized in that the balance has been inserted into the ceramic tube consisting substantially ZrB ₂ Gas blown tuyere structure.