JPH02268953A - Nozzle for continuous casting machine and refractory for nozzle thereof - Google Patents

Abstract

PURPOSE:To prevent the development of breakage in a nozzle and collapse and crack in a refractory and to operate safely casting, etc., by containing the specific quantity of mesophase carbon powder, etc., in the nozzle, slit-shape submerged nozzle and refractory for nozzle in a continuous casting machine. CONSTITUTION:The nozzle contains 1-30% mesophase carbon powder and the balance alumina series raw material and/or zirconia series raw material as aggregate and silicon carbide and graphite powder as fine grain. The slit-shape submerged nozzle for twin belt type continuous casting machine contains 3-15% mesophase carbon powder and the balance of the same material as the above aggregate. The refractory for nozzle contains 1-30% mesophase carbon, which has <=50mum diameter of mesophase grain obtd. by executing heat treatment to pitch at 300-500 deg.C, >=50% mesophase content and <=30% volatile matter content, and the balance of the same material as the above aggregate. All of the above materials are decided under consideration of balance to the strength, spalling resistance and erosion resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to various nozzles for continuous casting machines and refractories for the nozzles.

[Prior Art] Examples of nozzles for continuous casting machines include sliding nozzles or sliding plates, long nozzles, and immersion nozzles that control the flow rate between the ladle and the tundish, and between the tundish and the mold.

These nozzles are required to have spalling resistance, corrosion resistance, and airtightness in order to be able to perform stable pouring/injection of molten metal and casting, and to obtain good quality.

For this reason, composites of oxides and non-oxides (including carbon) are widely used as materials.

For example, alumina-carbon materials are used for sliding nozzles or sliding plates, and alumina-graphite materials or zirconia-graphite materials are used for long nozzles or immersion nozzles. This is a combination of alumina, which has excellent corrosion resistance against molten steel, carbon (graphite), which has excellent corrosion resistance against slag, and carbon (graphite), which has high thermal conductivity and excellent spalling resistance.

Furthermore, such nozzles must have high mechanical strength to withstand large mechanical loads and shocks generated by molten steel flow and AAM braking during operation.

In conventional technology, methods for improving such mechanical strength include adding a large amount of resin used as a binder, adding fine-grained ultrafine aggregate to make the structure dense, aluminum, A method of adding a metal such as silicon to exhibit metal-induced bonding during the firing process of refractories, and a method of increasing the molding pressure of refractories to make the structure denser have been developed.

[Problems to be Solved by the Invention] However, when the strength of the nozzle is improved by such a method, the elastic modulus of the material is improved to the same extent or more than the improvement in strength. An increase in elastic modulus means a decrease in spalling resistance. For a nozzle for a continuous casting machine, the most important thing is a balance between strength, spalling resistance, and corrosion resistance, and sacrificing spalling resistance in order to increase strength is not desirable in actual use.

For example, a slit-like immersion nozzle of a twin-belt continuous casting machine that directly produces a metal ribbon with a thickness of several mm to several + lllIm close to the final cross-sectional shape from molten metal such as molten steel, which has been attracting attention recently, will be described.

In a twin-belt continuous casting machine, in order to generate and grow a well-shaped solidified shell in a wide, thin casting area formed by a pair of belts and short sides, it is necessary to uniformly supply molten metal to the casting area. It is necessary to.

Therefore, as a suitable immersion nozzle for this purpose, a so-called slit-shaped immersion nozzle with widths of several hundred meters spaced at intervals of several meters is used.

FIGS. 1 and 2 show a state in which a slit-shaped immersion nozzle (hereinafter simply referred to as a slit nozzle) is immersed in the molten metal in the casting region.

That is, this slit nozzle S has a cylindrical body 16 having an elongated rectangular cross section, and the bottom thereof is open to form a spout 17. Further, a head plate 19 having an opening 21 for molten metal inflow is attached to the upper part of the cylinder 16. The molten metal that has flowed into the cylinder 16 through the molten metal inflow opening 21 spreads over a long rectangular cross section within the cylinder 16 and flows out from the spout 17 into the casting region.

In the figure, 3a and 3b are belts, 4 is a short piece mold, 6 is molten metal, 7 is a casting area, and 20 is a molten metal surface.

Therefore, the slit nozzle comes into contact with the molten metal and becomes high in temperature, and especially at the start of casting, the molten metal flows into the empty slit nozzle, causing the nozzle inner wall temperature to rise rapidly. Therefore, the slit nozzle is required to have not only heat resistance but also thermal shock resistance.

Moreover, the inside of the slit nozzle may become negative pressure. That is, the flow rate of the molten metal in the slit nozzle is usually adjusted by a stopper provided within the tundish or a sliding nozzle provided between the tundish and the injection nozzle. If some abnormality occurs during casting, if the supply of molten metal to the slit nozzle is abruptly stopped, the inside of the slit nozzle becomes empty and becomes negative and positive.

The wall thickness of the slit nozzle is usually as thin as a few to a few inches, and the bending strength is relatively low.Therefore, there is a risk that the wide main wall of the slit nozzle will collapse under external pressure and the molten metal will flow out. If molten metal spills out, the casting operation must be stopped immediately and surrounding equipment will be damaged. Furthermore, it can cause a steam explosion when it comes into contact with cooling water, which is extremely dangerous.

Note that in order to increase the strength, it is possible to increase the wall thickness of the slit nozzle. However, since the slit nozzle is inserted into a narrow mold, the distance between the inner surface of the mold (belt surface) and the outer surface of the slit nozzle is narrow, making it impossible to increase the wall thickness sufficiently.

[Means for Solving the Problems] The features of the present invention for solving the problems described above are as follows:
A nozzle for a continuous casting machine, characterized in that the mesophase carbon powder is contained in an amount of 1 to 30%, and the remainder contains an alumina-based raw material and/or a zirconia-based raw material as an aggregate, and silicon carbide and graphite powder as fine particles; Contains 3 to 15% carbon powder, and the remainder contains alumina-based raw materials and/or zirconia-based raw materials as aggregate, and silicon carbide and graphite powder as fine particles for continuous casting machines such as twin belt type. A slit-shaped immersion nozzle, and a mesophase obtained by heat-treating the pitch at 300 to 500°C, with a particle size of 50 μm or less and a mesophase content of 50% or more,
Mesophase carbon with a volatile content of 30% or less
The refractory for a nozzle of a continuous casting machine is characterized in that the remaining 30% contains an alumina-based raw material and/or a zirconia-based raw material as an aggregate, and silicon carbide and graphite powder as fine particles.

The composition of the mesophase carbon powder in the present invention is obtained by heat-treating the pitch at 300 to 500°C, and contains mesophase and volatile matter as main components, and may contain residual pitch.

[Function] The present inventors investigated various carbon materials in an attempt to solve the above-mentioned problems and found that a certain type of mesophase carbon is effective.

Carbon materials can be broadly classified into easily graphitizable carbon such as coke and non-graphitizable carbon such as resin carbide (char). These two are called soft carbon and hard carbon, respectively, due to their elastic characteristics.

The present inventors focused on the carbonaceous mesophase that is observed in the softened and molten state that occurs during coke formation. When petroleum-based or coal-based pitch is heated, free carbon and hydrocarbons aggregate in a certain alignment, producing liquid crystals with optical anisotropy. This is a sphere with a size of several microns to several tens of microns called a micro mesophase. When this is heated further, the tiny globules coalesce to form a mass called bulk mesophase. Furthermore, bulk mesophase becomes coke through carbonization, and the present inventors focused on the fact that micromesophase develops a strong bonding effect during the process of coalescing into bulk mesophase, and used this as a strength-imparting agent for refractories. An attempt was made to do so.

As a result, it was found that micro mesophase is effective in improving strength, and at the same time, it is possible to prevent a decrease in spalling resistance by suppressing an increase in elastic modulus.

The content of the invention will be described in detail below.

First, it is necessary to use a micro mesophase that has not yet coalesced into a bulk mesophase by heating. For this purpose, the heat treatment temperature is 300-500℃.
The sphere size was set to 50 microns or less in order to define the stage before the mesophase coalescence progresses and the sphere size increases. Excessive heat treatment
In this case, coalescence of mesophases progresses and bulk mesophase is already generated, and the binding effect of the bulk mesophase generation process is not sufficiently exhibited at the stage of use in refractories.

If mesophase is insufficiently generated and the mesophase content is low, volatile matter due to pitch will increase, forming pores when firing the refractory and weakening the structure. More than 50%, volatile content is 3
It is desirable to use mesophase carbon with a content of 0% or less.

The mesophase carbon referred to here is a liquid crystal with optical anisotropy when hot, but becomes solid when cooled to room temperature, and can be used as particles of aggregated mesophase spheres.

The aggregate particle size can be arbitrarily selected from several microns to several thousand microns.

The present inventors have applied mesophase carbon to various continuous casting refractories, and the effects are as follows: (1) A strong bonding effect is produced due to the coalescence of mesophase spheres, softening and melting, and void-filling effect due to heating during firing of the refractories. and form strong carbon bonds. Strength improvement effects can be seen even when added in small amounts.

■ Due to the bonding form using soft carbon, the increase in elastic modulus is small compared to conventional methods. Therefore, it is effective in improving spalling resistance.

■ A small amount is effective, but if used in excess, there are problems such as carbon's inherent low wear resistance and dissolution into molten steel, so a range of 1 to 30%, preferably 3 to 15%, is appropriate. .

Next, the reasons for each limitation of the mesophase carbon powder will be explained in detail together with the data shown in FIGS. 5 to 10.

■ Reason for containing 1 to 30% mesophase carbon powder An immersion nozzle made by kneading a mixture of 35% scaly graphite powder, 58% alumina particles, 5% silicon carbide particles, and 2% silicon particles with phenol resin, molding, and firing. FIG. 5 shows the hot bending strength and FIG. 6 shows the melting loss index when part of the scaly graphite powder is replaced with mesophase carbon. From Figure 5, mesophase carbon is only 1
% addition has an effect of improving strength, and even addition of 30% or more shows high strength. However, as shown in FIG. 6, addition of 10% or more increases melting loss. Particularly when the addition amount is 30 or more, the melting loss is extremely large. Therefore, the content is 1~
It was set to 30%.

In Figure 4, the erosion index is the reduction rate of the slag-metal interface when 2.5 kg of electrolytic iron + 62.5 g of slag (GaO/5i02.2) is immersed in molten steel at 1600°C for 20 minutes. % of the sample was set as 100 and indexed. The larger the number, the greater the melting loss.

■ Reason for containing 3 to 15% mesophase carbon powder in the case of slit nozzles As mentioned in Hikari, the wall thickness of slit nozzles is several mm.
- Because it is thin, about 10 mm, it must have high strength, and melting loss must be minimized. In FIG. 5, even if the amount of mesophase carbon added is 1%, the strength is improved, but it is small, and in order to apply it to a slit nozzle, it is preferable to add 3% or more. Furthermore, as shown in FIG. 6, the addition of mesophase carbon tends to increase the melting loss. The amount of melting loss increases by 2% when adding 10% mesophase carbon, by 5% when adding 15%, by about 10% when adding 20% or more, and by more than 20% when adding 30% or more. If the casting nozzle is 3
Addition up to 0% is acceptable, but in the case of a slit nozzle, addition of 15% or less is preferable. For the above reasons, in the case of the slit nozzle, the content of mesophase carbon was set to 3 to 15%.

■ Reason for treating pitch at 300 to 500°C 10% mesophase carbon, which is heat-treated at a different temperature for raw pitch, is added to a mixture consisting of 25% scaly graphite powder, 58% alumina particles, 5% silicon carbide particles, and 2% silicon particles. Figure 7 shows the hot strength of the material for the immersion nozzle. If the heat treatment temperature is less than 300°C, the mesophase will not be sufficiently generated, resulting in low strength. If the heat treatment temperature is 500°C or higher, the mesophases will coalesce, forming bulk mesophase, resulting in low strength. The heat treatment temperature of raw material pitch is 300-5
00°C is preferred.

■ Reason for setting the mesophase particle system to 50 Bm or less For an immersion nozzle in which 10% mesophase carbon with different mesophase particle sizes is added to a metal distribution consisting of 25% scaly graphite powder, 58% alumina particles, 5% silicon carbide fine particles, and 2% silicon fine particles. Figure 8 shows the hot strength of the material. If the coalescence of the mesophases progresses and the mesophase particle size exceeds 50 μm, the strength development during the mesophase coalescence process will decrease and no strength will be obtained. Therefore, the mesophase particle size is preferably 50 μm or less.

■ Reasons for setting the mesophase content to 50% or more Immersion in which 10% mesophase carbon with different mesophase contents was added to a mixture consisting of 25% scaly graphite powder, 58% alumina particles, 5% silicon carbide fine particles, and 2% silicon fine particles. The hot strength and apparent porosity of the nozzle material are shown in FIG. 9. If the mesophase content is less than 50%, the apparent porosity is high and the strength is not sufficiently developed.

The mesophase content is preferably 50% or more.

■ Reason for keeping the volatile content below 30% 10% mesophase carbon with different volatile content is added to a mixture consisting of 25% scaly graphite powder, 58% alumina particles, 5% silicon carbide particles, and 2% silicon particles. Figure 10 shows the hot strength and apparent porosity of the material for the immersion nozzle. When the content of volatile matter exceeds 30%, the porosity appears to be high and the strength is not sufficiently developed. The volatile content is preferably 30% or less.

■ Why the remainder was made of alumina-based raw materials and/or zirconia-based raw materials for the aggregate, and silicon carbide and graphite powder for the fine particles The characteristics of continuous casting nozzle refractories include high strength, corrosion resistance to molten steel, wear resistance, and corrosion resistance to slag. ,
Examples include spalling resistance against temperature changes and oxidation resistance. To cope with this, alumina and zirconia, which have high strength and excellent corrosion resistance, are used as aggregates. In addition, graphite has low thermal expansion and high thermal conductivity, so it has excellent spalling resistance and high corrosion resistance against slag, and silicon carbide has the effect of suppressing oxidation of graphite and bonded carbon.

[Example] Example 1 A case will be described as an example in which a slit nozzle immersed in molten steel in a belt mold of a belt type continuous casting machine for manufacturing a wide thin steel slab is used.

FIG. 3 is a detailed view of the slit nozzle. As shown in the drawings, a molten steel inflow opening 21 is provided in the top plate 19 of the slit nozzle, and the inflow opening passes through the sliding nozzle. Slit nozzle body 16
is formed into a thin box shape with a wide main wall 22 and narrow side walls 23. The injection nozzle of this example was manufactured using a blend of refractory raw materials shown in Table 1 and a phenolic resin as a binder.

In addition, the slit size of the slit nozzle is 450m wide.
m, length 1050mm, thickness 30n+m, wall thickness 10m
It is m.

Steel slag was cast using the above slit nozzle, and the occurrence of cracks and cracks in the slit nozzle was investigated. The amount of molten steel injected was 20 tons, and the injection rate was 4 tons/mi.
n, the injection time was about 5 minutes.

Figure 4 shows the results of examining the length of cracks that had occurred on the nozzle surface after oiling. Comparative Example 1 is an alumina-graphite immersion nozzle made using a conventional method. Comparative Example 2 uses a large amount of metal silicon to improve strength.6 Strength is as follows:
However, it can be seen that the elastic modulus is improved more than that, and the spalling resistance is significantly reduced.

In Examples 1 to 5 (the present invention), natural phosphorous graphite was placed on mesophase carbon! In the present invention, which uses tA, despite the improvement in strength, the elastic modulus increases only slightly, and the spalling resistance improves. That is, almost no cracks are observed. Also,
Comparative Example 3 is a case in which mesophase carbon is used in an amount exceeding the range of the present invention, and as shown in Figure 5, the occurrence of cracks is equivalent to that of the material within the range of the present invention, but the corrosion resistance decreases, and after the test Looking at the cross section of the nozzle, it is approximately 2. Melting loss of Oa++s was observed. The shape is limited, such as the immersion nozzle used in belt-type continuous casting machines, and the wall thickness is 10 mm to 15 mm.
In the case of about 11111, it is practically undesirable that the corrosion resistance decreases.

Example 2 Example of Alumina-Carbon Sliding Nozzle Plate A molding compound was prepared by adding a phenol resin to the refractory raw material compound shown in Table 2 as a binder. The desired sliding nozzle plate was obtained through the steps of molding, firing, pitch impregnation, and firing. This was used as an example product, and its characteristics are shown in the lower column of Table 2 in comparison with a comparative example.

Furthermore, the lifespan of each sliding nozzle plate when applied to actual operations was investigated. The results are also shown in the lower column of Table 1. For each test, 20 sets were used, and the number of times of charging up to the usage limit standard at each place of use was measured, and this was defined as the service life.

As is clear from Table 2, in the case of the sliding nozzle plate according to the example of the present invention, the hot strength and spalling resistance are greatly improved compared to the comparative example, and the life is also extended in the actual furnace test. confirmed.

Example 3 Example of alumina-carbon submerged nozzle A molding compound was prepared by adding a phenol resin to the refractory raw material compound shown in Table 3 as a binder. It was subjected to an isostatic press->drying-firing process to obtain an immersion nozzle. Its characteristics are shown together with comparative examples.

Comparative Example 1 is an alumina carbon immersion nozzle made using a conventional method. Comparative Example 2 uses a large amount of metal silicon to improve strength. Although the strength is improved, the elastic modulus is further improved and the spalling resistance is significantly reduced. The examples use mesophase carbon within the scope of the present invention. In the examples, although the strength was improved, the elastic modulus was only slightly increased, and the spalling resistance was improved. Comparative Example 3 is a case where mesophase carbon was used in an amount exceeding the range of the present invention, but the corrosion resistance was significantly lowered.

For refractories such as immersion nozzles where spalling resistance is important, it is possible to
Improving strength is very effective in practice.

[Effects of the Invention] As explained above, the present invention provides a continuous casting nozzle and a refractory for the nozzle that have high strength and a well-balanced spalling resistance and corrosion resistance. Even when applied to a slit nozzle, it prevents the refractory from collapsing or cracking when internal pressure such as negative pressure or positive pressure is applied to the inside of the nozzle, and prevents leakage due to damage to the injection nozzle. This has the remarkable effect of allowing operations such as molten metal injection, pouring, and casting to be carried out safely.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the slit nozzle and the twin belt immersed in the pool of water, Fig. 2 is a sectional view taken along the line A-A in Fig. 1, and Fig. 3 is the immersion nozzle used in the embodiment of the present invention. Detailed perspective view, Figure 4 is a graph showing the occurrence of cracks in the nozzle, Figure 5
The figure is a graph showing the relationship between the amount of mesophase carbon added and the hot bending strength. Figure 6 is a graph showing the relationship between the amount of mesophase added and the melting index. Figure 7 is the graph showing the relationship between the heat treatment temperature of pitch and the hot bending strength. Figure 8 is a graph showing the relationship between mesophase grain size and hot bending strength.
The figure is a graph showing the relationship between mesophase content, hot bending strength and apparent porosity, and FIG. 10 is a graph showing the relationship between volatile content, hot bending strength and apparent porosity. 3a, 3b... Belt 6... Molten metal 16... Nozzle cylinder 19... Top plate 21... Molten metal inflow opening 23... Nozzle body side wall 4... Short side mold 7 ... Casting area 17 ... Pour hole 20 ... Molten water level 22 ... Nozzle main wall and other 4 people 16: Nozzle cylinder body 17: Pour hole 19: @ plate 22: Nozzle main wall Nozzle cylinder body Pouring hole Spout plate Opening for molten metal inflow Nozzle Main wall Nozzle body side wall Fig. Mesophase carbon addition it (%) Fig. Mesophase carbon addition amount (%) Fig. Pinch heat treatment temperature (°C) Fig. Figure 3 Mesophase content (%) Figure 3 Volatile content (%)

Claims (1)

[Claims] 1. Continuous casting characterized by containing 1 to 30% of mesophase carbon powder, and the remainder containing alumina-based raw materials and/or zirconia-based raw materials as aggregate, and silicon carbide and graphite powder as fine particles. Machine nozzle 2 For a twin-belt type continuous casting machine characterized by containing 3 to 15% mesophase carbon powder, the balance containing alumina-based raw materials and/or zirconia-based raw materials as aggregate, and silicon carbide and graphite powder as fine particles. Slit-shaped immersion nozzle 3 Mesophase carbon obtained by heat treating pitch at 300 to 500°C, with a mesophase particle size of 50 μm or less, a mesophase content of 50% or more, and a volatile content of 30% or less, with 1 to 30% of the balance being aggregate. A refractory for a nozzle of a continuous casting machine, characterized by containing an alumina-based raw material and/or a zirconia-based raw material as fine particles, and silicon carbide and graphite powder as fine particles.