JP3355028B2 - Converter operation method to control slag coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slag coating control method for extending the refractory life of a converter, and more particularly to a coating control method for preventing slag coating from flowing out during blowing. is there.

[0002]

2. Description of the Related Art Generally, as a technique for extending the life of refractories in a converter by using slag, CaO,
A method is known in which the concentration of MgO is increased to suppress the elution of refractories. In addition, a method is well known in which a solidified material, brick waste, or the like is charged into slag after the completion of blowing, and then the slag is welded to the surface of the brick by spraying or tilting of the furnace (hereinafter, referred to as slag coating method). For the effect of suppressing refractory wear, the former suppresses chemical component dissolution,
The latter is mainly for suppressing heat spall by reducing the heat load on the refractory. Of the above methods, it is important to reduce the rapid wear in order to extend the life of the converter brick, because it is necessary to suppress the heat spall that is the cause,
Various improvements have been made to the slag coating method.

[0003] Although the life of converter refractories has been extended by the above-described method, even when the slag coating method is applied, the case where the coating layer is completely peeled off before tapping and the case where the coating layer remains remain. However, even if solidification material, brick waste, and the like were added, the effect corresponding to the input amount was not sufficiently achieved. As a method for solving the problem, Japanese Patent Application Laid-Open Nos. 61-157610 and 61-56223, a method in which a coating is applied and then forced cooling is performed, Japanese Patent Publication No. Sho 62-24490, Japanese Patent Publication No. Hei 2-292 is disclosed.
Japanese Patent Application Laid-Open No. 62-13407, Japanese Patent Application Laid-Open No. 61-5-5
No. 9364 discloses a technique for charging a solidified material and brick waste. Considering that forced cooling promotes solidification of the coating but causes thermal loss, an economical method is to specify the slag composition at the time of blowing, or to control the composition by adding solidified material and brick waste. Becomes

[0004] As for slag coating by controlling the composition, as disclosed in Japanese Patent Publication No. 24490/1987, the blowing slag composition is adjusted to CaO / SiO ₂ = 1.6 to 2.5 MgO / CaO ≧ 0. .25 SiO ₂ / (CaO + MgO + SiO ₂ ) ≧ 0.25, or as disclosed in Japanese Patent Publication No. 2-2922, (% Cr ₂ O ₃ ) is 30 to 50.
Weight percent or JP-A-3-68712
As disclosed in Japanese Unexamined Patent Publication, [C] ≧ 0.
1, basicity ≧ 2, T.I. It is known that Fe is defined as 5 to 15%.

[0005] As can be seen from the above disclosed examples, in the case of slag coating in ordinary steel refining, CaO, Si
The general idea is that it is determined by the combination of O ₂ , MgO, and FeO. However, in some cases, coating deposition can be performed by these methods.
Even if the conditions of O, SiO ₂ , MgO, and FeO are determined, slag coating may not be performed reliably.

[0006] Other than these components, components that have an effect on slag solidification and flow are disclosed in Japanese Patent Application Laid-Open No. 2-111810 as flow control for suppressing slag flowing out along with molten steel flow during tapping. In Al ₂ O
_It mentions the effect of ₃ . Here,% Al ₂ O ₃
Has an effect on the solidification limit of slag, but MgO
The effect of% Al ₂ O _{3 on} the amount of added slag is small, and T.P. Fe and CaO / SiO ₂ for M
It is disclosed that% Al ₂ O ₃ has substantially no effect if the added amount of gO is changed. However, this method is intended to prevent the slag in the converter from flowing out under the furnace due to entrainment due to the flow of molten steel at the time of tapping, so that it is only at a level that slightly reduces the fluidity. Therefore, it cannot be applied at all to maintain a slag coating which is directly exposed to molten steel flow for a long time such as during blowing.

[0007] In recent operations, the use of scrap such as canned waste and the reforming of slag have resulted in the% Al ₂ O _{3 in} slag.
Is higher than before, and past findings could not be simply applied.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is intended for coating a converter furnace bottom and / or a furnace wall even when Al ₂ O _{3 in} slag is high. We control outflow of slag coating layer during blowing,
We propose a converter operation method for controlling slag coating, which aims to extend the life of converter refractories by maintaining the protective effect of slag coating until tapping.

[0009]

Means for Solving the Problems The present inventors examined the cause of the difference between the case where the slag coating remained after the end of blowing and the case where the slag coating was eluted and peeled halfway, and found that the slag coating was coated. There is a strong correlation between the flow of the slag and the% Al ₂ O ₃ in the slag, and the optimal amount of the solidifying material to be applied for coating is% MgO or Cg.
It was found that it did not depend on aO / SiO ₂ or the like but changed by% Al ₂ O ₃ .

Based on this finding, the present inventors measured the apparent viscosity as an indicator of fluidity as shown in FIG. 1 and found that the apparent viscosity has a temperature that rapidly changes. It was found that the change was little affected by CaO, SiO ₂ and MgO, and that the addition of a small amount of Al ₂ O ₃ greatly affected the fluidity. In the research leading to the present invention, the slag outflow was more directly evaluated, and further, in the actual furnace, by changing the dolomite input amount in response to the change in% Al ₂ O ₃ , a good coating layer was obtained. That you can get.

[0011] Namely, the present invention provides a slag after the converter tapping allowed to remain on the rolling furnace, light burned mud thereto as dolomite
When adding a mite or raw dolomite to coat a converter bottom and / or a furnace wall, Al ₂ O in slag is used.
₃ is a converter operation method for controlling slag coating, characterized in that the amount of dolomite charged is determined by the following formula for 1 part by weight of slag of 2% or more.

W ≧ {K ₁ + K ₂ × (% Al ₂ O ₃ ) −K ₃ × (% Al ₂ O ₃ ) ² } / (100-I) where W: Dolomite input amount (parts by weight) I: Application Ignition loss of dolomite
_{(%) K 1 = 35,} K 2 = 7.5, a K ₃ = 0.2. Ignition loss is to ignite a dried sample at 1000 ° C. for 1 hour, cool, measure the weight, and determine the weight loss as the ignition loss. A sample dried at 105 to 110 ° C. until a constant weight becomes a platinum crucible or porcelain Measure in a crucible, about 100
It is ignited at 0 ° C. for 1 hour, allowed to cool in a desiccator, weighed, and the weight loss at that time is determined. This is repeated twice or more to obtain a weight loss value when the weight becomes constant.

The operating method according to the present invention can be applied to a converter operation for controlling slag coating in a bottom-blown or top-bottom-blown combined converter having a strong flow of molten steel. In the operation method according to the present invention, the measured value of each charge can be used as the slag composition at the time of tapping. In this converter operation method, the average slag composition under general blowing conditions in the target converter can be used as the slag composition at the time of tapping.

Further, in this converter operating method, it is preferable to use the average slag composition at the time of blowing of the same steel type as the slag composition at the time of tapping. In addition, the composition of slag at the time of tapping is the latest 50 to 10 in the target converter.
An average slag composition of 0 charge may be used. As the cold iron source, it is also possible to use can scrap and / or iron scrap partially containing slag generated from a steelmaking process after the converter step.

In the operation of the converter over a large number of charges, in controlling the dolomite input amount as described above,
If the number of charges in which the dolomite input amount is less than the above-mentioned management value is three or less consecutive charges and less than 30% of the cumulative number of charges in the past, the coating layer in the converter can be maintained.

[0016]

The present inventors have investigated the cause of the difference between the case where the slag coating remains until after the end of blowing and the case where the slag coating is eluted and peeled halfway, and found that the fluidity of the slag is% Al ₂ O. _It has been found that if the value of ₃ slightly changes, the value rapidly changes, and even if it increases by 1%, the case where the coating cannot be maintained under the normally used dolomite input condition when the Al ₂ O ₃ is low increases.

FIG. 1 shows an example in which apparent viscosity is measured as an index of fluidity. The viscosity of slag has a rapidly changing critical point of flow. Further, the critical temperature is Ca
It was found that, although affected by the amounts of O, SiO ₂ , and MgO, the effect was small, but greatly changed by the amount of% Al ₂ O ₃ . Tables 1 and 2 clearly show this.

[0018]

[Table 1]

[0019]

[Table 2]

% Al in actual furnace_Two O_Three The change of the screen
Due to the reuse of cold iron sources such as wraps, changes in steel grades,
Changes easily due to changes in slag composition conditions.
In operation, these changes cause the% Al in the slag_Two O_Three 
Tend to be higher than conventional levels. Conventionally% Al
_Two O_Three Is low, so the amount of solidified slag_Two O _Three 
Slag coating is relatively inexpensive
Fixed and adhered. However, as described above,% Al_Two 
O_Three % Al even under the condition where_Two O _Three change of
If the slag solidified material was introduced regardless of the
If the coating is not done reliably
Was.

In the study of the present invention, the most common dolomite is used as a solidifying material, and a good coating layer can be obtained by changing the dolomite input amount in accordance with the change in% Al ₂ O _3. I confirmed the fact. The state of the coating layer, with the introduction of the coating material, for receiving an effect on the degree of CaO and MgO is deposited on the slag coating,% Al ₂ O ₃
It was found that there was an optimum amount of coating material input corresponding to% Al ₂ O ₃ in the slag before the input of the coating material, without depending on the absolute value of the coating material. Based on this finding, the present inventors have further studied the most effective dolomite input amount, and have reached the present invention.

FIG. 2 shows the results of examining the residual state of% Al ₂ O ₃ and the coating in the slag when the amount of slag remaining before the solidification material is set to 3 tons in the actual furnace. Here, the residual state of the slag coating was determined by observing whether or not the slag coating layer performed before hot metal insertion was attached to the converter bottom when tapping was performed after one smelting. . Regardless of whether raw material dolomite is used or solid dolomite is used,% Al _{2 in} slag is used.
O ₃ changes the amount of the solidified material charged to improve the coating. The burning loss of raw dolomite and lightly burnt dolomite used this time were 46% and 3%, respectively. However, the difference in the amount of input that gives good adhesion of both coatings can be unified by the difference in burning loss. Thus, the relational expression of the dolomite input amount W of the present invention was obtained.

The method of controlling and managing the dolomite input amount is as follows. First, the composition of the target slag at the time of tapping is examined. Then, the above-mentioned slag composition% Al ₂ O
Substitute ₃ into the following formula, and put in the actual dolomite based on the result. W ≧ {K ₁ + K ₂ × (% Al ₂ O ₃ ) −K ₃ × (% Al ₂ O ₃ ) ² } / (100-I) where W: Dolomite input amount (parts by weight) I: Burning of applied dolomite Ignition loss
(%) K ₁ = 35, K ₂ = 7.5, K ₃ = 0.2 If a dolomite amount W that satisfies the above equation is supplied, the slag coating does not flow out and the effect as a protective film is maintained. However, if the dolomite input is insufficient,
Since the Al ₂ O ₃ concentration in the coating slag is high and the fluidity is high, it flows out during blowing.

There are the following means for determining the slag composition at the time of tapping. (A) Value for each charge: The blow-off slag composition estimated from the auxiliary material input amount and the blown oxygen amount in each charge, or the slag composition measured by sampling after blowing. (B) Values under general blowing conditions in the target converter: average slag composition based on past performance of the target converter, or slag composition based on the usage plan of the target converter. (C) The value at the time of blowing of the same steel type: average slag composition for each steel type refined in the target converter. (D) Average value of recent 50 to 100 charges: Average slag composition of recent 50 to 100 charges obtained in the target converter.

The slag composition determined by these means can be used. Dolomite, which is a solidifying material, is charged after tapping or after tapping and after removing a part of the slag. As the dolomite to be added as a solidifying material, general ones such as raw dolomite and lightly burned dolomite may be used.

As the iron source for blowing, it is not necessary that the entire amount be hot metal, and Al and / or Al such as ingots and slag partially generated from the steelmaking process after the converter step are mixed. It is also possible to use a cold iron source containing ₂ O ₃ . The amount of the cold iron source is not limited, but is desirably 15% or less. Further, in the coating control based on the dolomite input amount based on the present invention, it is most desirable to satisfy the control value in all the charges, since the effect is the largest. However, achieving this completely can be difficult in practical operations. In actual operation, even if some charges do not meet the management value of dolomite input, slag coating is almost maintained, and even if the coating is slightly peeled off, if the charge that does not satisfy the management value is 3 or less, fire resistance The effect on things is minor.

If the number of charges that do not satisfy the management value of the dolomite input amount based on the present invention is 3 or less consecutive charges and is less than 30% of the past cumulative number of charges, a refractory protection effect can be obtained. However, when the charge that does not satisfy the control value is continuous for 4 or more charges, or when the accumulated charge number is 30% or more, the coating is completely peeled off at that time, and the amount of damage to the refractory increases significantly. In practice, it is desirable that the number of charges below the management value of the dolomite input amount with respect to the past cumulative number of charges be less than 20%.

As a result, the coating can be stably maintained until tapping, so that thermal spalling of the refractory can be suppressed and the life of the converter can be extended.

[0029]

EXAMPLE In a 230 t pure oxygen bottom-blowing converter, as an example of the present invention, when the tapping temperature is 1580 ° C. to 1650 ° C., the dolomite input amount is controlled to the control value of the present invention in all charges ( Example 1) and a case in which the dolomite input amount satisfies the control value in a charge corresponding to 75% of the past cumulative number of charges, and the operation that does not satisfy the control value is 3 or less consecutive charges (Examples 2 and 3). ) Was adjusted. The average slag composition under similar operating conditions was used as the slag composition, and raw dolomite was used as the solidification material. 5% on average for iron sources
Cold iron source (can metal, slag mixed ingots, grain iron, etc.) and 9
5% hot metal was used.

As a comparative example, the past accumulated charge number of 5
In the case where the dolomite input amount is controlled to the control value in the charge corresponding to 0% (Comparative Example 1), the dolomite input amount is lower than the control value in the charge of less than 30% of the past cumulative number of charges, but does not satisfy the control value. Investigation was also made on the case where the charge was 5 or more consecutive charges (Comparative Example 2).

FIG. 3 shows the transition of the remaining brick thickness of the furnace bottom.
Curves 1, 2, and 3 show the cases of Examples 1, 2, and 3 of the present invention. Curves 4 and 5 are Comparative Examples 1 and 2. Curves 1, 2, 3
Is stable at a lower level than curves 4 and 5, and it can be seen that the wear of the refractory is suppressed. The tuyere wear rate was 0.76 mm / charge in Comparative Example 1, and 0.71 m in Comparative Example 2.
With respect to m / charge, in the present invention, it was 0.47 mm / charge in Example 1, 0.55 mm / charge in Example 2, and 0.54 mm / charge in Example 3. When the tapping was completed and the slag coating residue on the furnace bottom and furnace wall was observed before the next hot metal was charged, when the present invention was implemented, the joint between the multiple bricks being constructed was Was not visible and the coating remained sufficiently.
In contrast, in the case of Comparative Example 1, joints between the bricks are clearly recognized, and in the case of Comparative Example 2, not only when the charge below the control value continues but also over the subsequent several charges. Joints between the bricks were observed, and it was clear that the coating had disappeared during blowing and the bricks were directly exposed to the molten steel.

As described above, the% Al ₂ O in the slag at the time of tapping
Based on _{3 above} , the effect of managing the dolomite input was confirmed. In addition, 7
By controlling the dolomite input amount at the charge number of 0% or more based on the% Al ₂ O ₃ in the slag, and limiting the charge whose dolomite input amount is less than the control value to three or less continuous charges, the operation is performed. Although the life extension effect was weaker than the case where the dolomite input amount of all charges was controlled to a control value or more, a remarkable effect was confirmed.

[0033]

According to the present invention, in the operation of coating the converter bottom and / or the furnace wall, it is possible to suppress the outflow of the coating during the blowing and to greatly extend the life of the refractory. In addition, the cost of the converter operation can be reduced.

[Brief description of the drawings]

FIG. 1 is a graph showing an example of a relationship between apparent viscosity of slag and temperature.

FIG. 2 is a graph showing the relationship between% Al ₂ O ₃ and the amount of dolomite charged.

FIG. 3 is a graph showing transition of a remaining brick thickness with respect to a furnace charge number.

Continuing on the front page (72) Inventor Sumio Yamada 1 Kawasaki-cho, Chuo-ku, Chiba-shi Kawasaki Steel Corporation Chiba Works (72) Inventor Daichi Nakazawa 1 Kawasaki-cho, Chuo-ku Chiba-shi Kawasaki Steel Corporation Chiba Works (72) Inventor Yasuo Iida 1 Kawasaki-cho, Chuo-ku, Chiba-shi Kawasaki Steel Corporation Chiba Works (56) References JP-A-3-82705 (JP, A) JP-A-62-40307 (JP, A (58) Fields surveyed (Int. Cl. ⁷ , DB name) C21C 5/44

Claims (8)

(57) [Claims] Claims: 1. Slag remaining in a converter after tapping from a converter, into which raw dolomite or lightly burned
In adding the mite and coating the converter bottom and / or the furnace wall, the amount of dolomite to be added to 1 part by weight of slag containing 2% or more of Al ₂ O _{3 in} the slag is determined by the following formula. A converter operation method for controlling slag coating, comprising: W ≧ {K ₁ + K ₂ × (% Al ₂ O ₃ ) −K ₃ × (% Al ₂ O ₃ ) ² } / (100-I) where W: Dolomite input amount (parts by weight) I: Burning of applied dolomite K ₁ , K ₂ , K ₃ : constants K ₁ = 35, K ₂ = 7.5, K ₃ = 0.2 2. The method for operating a converter for controlling slag coating according to claim 1, wherein the converter is a bottom-blown or top-bottom-blown combined converter. 3. The converter operation method for controlling slag coating according to claim 1, wherein a measured value of each charge is used as a composition of slag at tapping. 4. The converter operation for controlling slag coating according to claim 1, wherein the average slag composition under general blowing conditions in the target converter is used as the slag composition at tapping. Method. 5. The converter operation method for controlling slag coating according to claim 1, wherein the average slag composition at the time of blowing of the same steel type is used as the slag composition at the time of tapping. 6. The converter operation method for controlling slag coating according to claim 1, wherein the average slag composition of the latest 50 to 100 charges in the target converter is used as the slag composition at tapping. 7. The slag coating according to claim 1, wherein as the cold iron source, can scrap and / or iron scrap containing a part of slag generated from a steelmaking process after the converter step are used. Converter operation method. 8. An operation over a large number of charges, wherein the charges having a dolomite input amount less than the control value are not more than three consecutive charges and less than 30% of the past cumulative number of charges. A converter operation method for controlling slag coating according to any one of the above.