JPH02225369A - Highly corrosion resistant brick for ladle - Google Patents

Abstract

PURPOSE:To improve corrosion resistance of a brick without impairing spalling resistance by blending Al2IO3, etc., with an electromelting Al2O3 contained in prescribed ratio and used as aggregate in the brick containing Al2O3 as a main component. CONSTITUTION:The highly corrosion resistant brick for ladle is formed by blending Al2O3 used as a main component with 25-75wt.% electromelting Al2O3 used as aggregate part of the above-mentioned Al2O3. In the above-mentioned brick, reaction of slag with fine powder and aggregate, production of low melt ing complex and outflow of low melting product are prevented by replacing bauxite by electromelting Al2O3. Consequently, slag resistance, corrosion resis tance and spalling resistance of the brick are improved.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is directed to secondary steelmaking, particularly to improving slag resistance, spalling resistance and wear resistance used as work bricks for ladle finishing. This invention relates to highly corrosion-resistant bricks for use in ladles with excellent properties.

(Prior art) Conventionally, a ladle has been used only as a container for transporting from a converter to an ingot or a continuous casting machine, and its internal structure is as shown in the longitudinal cross-sectional view of Fig. 4, where the bottom of the ladle (3) There are flooring bricks (21) surrounded by hearth stamps (1), and -S wall bricks (21) on the side walls.
22), slag line part bricks (23), freeboard part (24), and other bricks (2) are arranged, and these bricks (
For 2), either chirolith brick or chamotte brick is generally used. In addition, the code|symbol (4) is a tapping hole.

And the temperature control time in this seed ladle (3) is also 10 minutes ~
It was a short 60 minutes.

However, for example, when receiving steel such as high oxygen steel, the melting rate of the brick (2) in the ladle (3) is high, and therefore the general wall part (22) has a high alumina burden. Zone drying was carried out by constructing bricks and magnesia carbon bricks for the slag line part (23).

(Problems to be Solved by the Invention) Steel products have recently become of higher quality, and the quality requirements from users have also become stricter.

For this reason, the manufacturing process has changed from converter → ingot making and continuous casting to converter → ladle casting → ingot making and continuous casting.

That is, in the past, the ladle (3) only served as a transport container for the ingot making and continuous casting processes, but recently it has come to serve two functions: a refining container and a transport container.

However, although refining in the ladle (3) involves arc heating, stirring of molten steel, vacuum treatment, etc., the bricks placed in the ladle (3) are affected by various factors.

Incidentally, arc heating forms a hot spot in the freeboard part (24), and the brick (2) in that part tends to melt locally, and the temperature of the slag during refining is higher than that of molten steel. Therefore, the capacity loss of the bricks (2) in the slag line part (23) is also large. Stirring the molten steel in the ladle (3) causes a large amount of wear due to the wear of the molten steel on the -m wall (22) and the removal of the slag layer attached to the wall.

Furthermore, during vacuum processing, slag and molten steel splashes are scattered during degassing during refining, which can cause damage to the freeboard area (24
) and melt and damage the freeboard portion (24).

Therefore, in the past, the bricks (2) of the freeboard part (24) and the slag line part (23) were made of magnesia-carbon bamboo in consideration of slag resistance.

On the other hand, the brick (2) of the -fm wall part (22) is required to have slag resistance, and it is also necessary to consider spalling resistance. If it is applied to the wall (22), spalling will occur, and as a result, the rate of erosion will increase.

On the other hand, when high-alumina bricks are used, their corrosion resistance is poor, and as with magnesia-carbon bamboo bricks, the rate of erosion is high (which limits the life of the ladle (3)).

Based on the above facts, 1 of the bricks (2) of the general wall part (22)
Bricks used in a real pot to understand the injury mechanism (AI2
0+; 76wt%, S+Oz; 14wt%
, C; unfired bricks with a composition of 5 wt%) were collected, the working surface was cut, gF polished, and the part was observed under a microscope. As a result, the facts shown in Figure 1 were discovered. That is, as shown in the cross-sectional view of the same figure, about 31111 pieces of slag S adheres to the working side M of the original brick, and about 3III11 pieces of slag S adheres to the original brick side, and about 3III11 pieces of slag S is deposited inside the altered layer C1 of about 5111 m. Coal seam T
exists.

In the adhered slag S layer, CaO and AIzCh were more concentrated than in the furnace slag from the operating surface M toward the raw brick, and voids were observed in the slag S layer, altered layer C, and matrix within the decarburized layer circle. .

If the damage mechanism of brick (2) is estimated based on such observation results, the following can be considered.

■ Graphite in the matrix disappears due to the reaction of C→l/202→CO due to air permeation from the back side of the raw brick.

■ Relaxation of the matrix structure and generation of voids as graphite disappears.

■ Infiltration of slag into the relaxed parts of the matrix tissue.

■As a result of the reaction between slag, fine powder, and aggregate, a low-melting complex compound is produced.

■Low melting material flows out.

As described above, there has been a desire to develop a brick with high corrosion resistance and spalling resistance suitable for general walls of this type of ladle.

The present invention was invented in view of the above-mentioned viewpoints, and an object of the present invention is to provide a highly corrosion-resistant brick for ladle use that has high durability, corrosion resistance, and spalling resistance.

(Means for Solving the Problems) The present invention provides a ladle brick for achieving the above-mentioned object, in which electrified A1. A composition containing 25 to 75 wt% of O.

(Function) The present invention provides a ladle brick having the composition as described above, and the reason is as follows.

To prevent tissue relaxation due to graphite oxidation, graphite-free use,
The use of antioxidants and lower porosity are expected, but the purpose of using graphite in this type of brick is to improve the spalling resistance, and if the use of graphite is stopped, the resistance will decrease. Spalling performance deteriorates.

It is difficult to ensure this spalling resistance by other means, so the use of graphite is unavoidable.

As the above-mentioned antioxidant, various metals such as Si
, Fe-5i, and AI are conceivable, but since all of these metals react with oxygen and produce low-melting compounds, their usage is limited.

Lowering the porosity can reduce air intrusion, but on the other hand, spalling resistance deteriorates.

However, if the amount of graphite used is increased in order to improve the durable poling property, the amount of CO generated will increase, and the matrix will not only be loosened, but it will also be difficult to reduce the porosity during brick production.

Therefore, we specifically investigated the used bricks again and found the following.

That is, slag is attached to the surface of the brick, and small particles of spinel exist within the slag, and CaO・6^+zo
There are many needle-like crystals of s(cAi).

On the other hand, almost no infiltration of slag into the matrix within the brick was observed, and it is thought that the aggregate was in direct contact with the slag on the operating surface, precipitating CA&.

Under these circumstances, it was thought that if the aggregate was strengthened, the corrosion resistance would be the same as above.

Therefore, the bauxite was converted to 1lltlA to electrofused AIzOa.
When we focused on this, we found that slag resistance improved.

However, when bauxite is replaced with fused AhOs,
It was found that the Young's modulus of the brick increases, and as a result, the brick becomes more susceptible to spalling, and conversely, its durability deteriorates.

In view of this fact, we examined the optimal substitution rate when replacing bauxite with electrofused A1□O8, and found the following.

That is, the substitution rate (%) of Denfu A1□03 is A; OlB;
15, C; 25, D: 50, E; 75, F; 90, G
I made 7 types of bricks and melted them! 0
．． When the relationship between the substitution rate of slag and the erosion index and Young's modulus of slag was investigated, the results shown in the graphs of FIGS. 2 and 3 were obtained.

As is clear from Figure 2, it appears that when the substitution rate is less than 25%, the melt resistance is not improved, and as for the elastic modulus, as shown in Figure 3, when the substitution rate is 75% or more, the resistance is not improved. There was a problem that spalling deteriorated and it could not be put to practical use.In the end, based on the knowledge that the optimum substitution rate for electrofused Alto3 is 25 to 75%, this range was selected.

(Example) Examples of the present invention will be described below. In this example, material D with a substitution rate of 50% of electrofused ALzO+ was used as a brick in a container steel pot among the seven types of bricks (2). and 2 of 100% G material
Each type was fully stretched on the shell wall (22), and an actual pot test was conducted, and each type was dismantled and repaired using 80 charges, and the erosion index was investigated when the erosion index of the conventional base brick was set at 100. As a result, the following results were obtained: Base brick - 1 - - - wt00 Inventive brick - 80 Comparative material -90.

When the bricks used were observed, it was found that the bricks of the present invention had severe damage to the joints and had cracks parallel to the working surface of the cut surface.

It has been found that when the substitution rate is 75% or more, the spalling resistance deteriorates and there are problems in using it in steeple formations.

Therefore, in order to satisfy iV tN resistance and spalling resistance, it is desirable that the substitution rate of fused ALzOs be 25 to 75%.

(Effect of the invention) The ladle brick of the present invention has A1□0. In the brick whose main constituent is
The composition contains wL%, so the spalling resistance is...
Corrosion resistance can be improved without sacrificing slag resistance, corrosion resistance, and spalling resistance, as reaction between slag, fine powder, and aggregate, generation of low-melting composite compounds, and outflow of low-melting substances can be prevented. It is highly practical for this type of brick, as it has improved properties.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a single-shell wall brick observed under the 81i microscope, Figure 2
The figure is a graph showing the relationship between electric melting AIzO3 substitution rate and erosion index, and Figure 3 is electric melting A1□0. A graph showing the relationship between the substitution ratio and Young's modulus, and FIG. 4 is a longitudinal cross-sectional view of a commonly used ladle. The names of the codes are as follows. (1) - hearth bottom stamp, - (2) - brick, (21) - bedside brick, (22) - wt'G wall brick, (23) - slag line part brick, freeboard part brick, (3) Ladle, (4) Hole, altered layer, brick working surface, slag layer, decarburized layer.

Claims (1)

[Claims] A highly corrosion-resistant brick for ladle use, characterized in that, in a brick containing Al_2O_3 as a main component, 25 to 75 wt% of fused Al_2O_3 is blended in the aggregate.