JP2001164313A - Method for reforming slag in ladle refining furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reforming method of slag, by which the powdering of reducing slag produced in a ladle refining furnace can be avoided. SOLUTION: A material containing >=25% MgO, in terms of the dry weight ratio is added into the slag in the ladle refining furnace and melted, and the ratio of MgO contained in the slag after completing the casting is made to 10-50 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reforming slag in a ladle refining furnace, and more particularly to a ladle refining furnace for preventing slag (reduced slag) generated in a ladle refining furnace from being powdered. Slag reforming method.

[0002]

2. Description of the Related Art With the improvement of ladle refining technology (secondary refining technology) in steelmaking, part of refining performed in a converter or an electric furnace, namely, component adjustment, decarburization, desulfurization, temperature adjustment, Ladle refining furnaces can now take over the functions of removing impurities and homogenizing molten steel. As a result, with the current steelmaking technology, the efficiency of refining can be improved by freely combining each method, and the production of ultra-low sulfur steel and ultra-low carbon steel, which was difficult in the past, can be performed easily. It is becoming possible.

[0003] In particular, in the case of blast furnace converter refining or electric furnace refining for special steel, desulfurization, temperature adjustment, homogenization of molten steel, etc.
In the past, the functions of the refining furnaces of converters and electric furnaces were completely transferred to ladle refining furnaces.In the converter and electric furnace refining furnaces, we focused on melting and decarburizing raw materials. The content of refining itself is changing, for example, by simplifying and speeding up operations.

[0004] Similarly, ladle refining furnaces have come to have various configurations, such as installing a degassing function and installing equipment for blowing pure oxygen.

[0005] In the ladle refining furnace, various additives are added according to the purpose. In both the converter method and the electric furnace method, the main reaction of refining is performed under a reducing atmosphere, and the main additive is advanced with quicklime. In addition, depending on the contents of the operation, fluorite is added for accelerating the dissolution of quicklime, and aluminum dross is added for heat compensation and slag reforming. Further, since the slag becomes basic, a material containing MgO enough to saturate the MgO in the slag, such as dolomite, is added for the purpose of reducing the erosion of the basic refractory in the ladle refining furnace. .

[0006] Although it depends on the refining temperature and the type of steel, the content of MgO in this case is generally targeted at about 8%, which is the slag saturation concentration. What occurs in this state is ladle refining slag, so-called reduction slag.

[0007] Incidentally, the amount of the additive added varies depending on the purpose, but in the case of a converter operation, there are frequent cases in which the target of sulfur reduction of the target steel type is less than 0.010% and aims at around 0.003%. Therefore, the input amount of lime increases, and as a result, the CaO concentration exceeds 50%, and the simple basicity (CaO) /
In some cases, the operation is performed with (SiO ₂ ) of 4.0 or more.

[0008]

However, in general, C
When the aO concentration exceeds 45% or (CaO) / (Si
O ₂₎ is reduced slag as Kosu 2.0 is easily formed 2CaO-SiO ₂ or 3CaO-SiO ₂ as a mineral composition after solidification, these minerals causing the powdering phenomenon of the reducing slag I have.

[0009] Reduction slag ladle refining furnace, to powdering during the cooling process or cooling after a few days, minerals typified by 2CaO-SiO ₂ is, in the structure at the low temperature from the crystal structure at high temperature It is said to be due to the structural expansion during metamorphosis. Further, Cause 3CaO-SiO ₂ with much CaO is powdering is, CaO and 2CaO upon cooling, is separated into SiO _2, as a result, CaO itself issued unreacted CaO and crystals also becomes hydrated lime to absorb moisture It is said that it is.

On the other hand, for example, in an oxide slag containing a large amount of metal oxides such as FeO and MnO, these metal oxides enter the crystal nuclei and hinder the powdering, or the metal oxides themselves become CaO-SiO2. _Since it forms a different mineral composition by forming a compound with ₂ , it is possible to suppress the phenomenon of slag powdering.

However, in a ladle refining furnace for reduction refining, this reaction cannot be expected because the ratio of metal oxides is low. The tendency of powdering is a very common phenomenon in the operation of a blast furnace system with high CaO, but in recent years,
Ladle smelting furnaces have also begun to spread in the ordinary steel electric furnace system, and since reduction smelting is performed, pulverization occurs similarly, although the speed varies depending on the size.

Recently, there has been a great interest in utilizing slag due to environmental problems, and blast furnace slag, which is stable in quality, is 100% reused.

On the other hand, steelmaking slag is generally said to be around 80% by recycling, including in-house reuse. Among them, the converter slag discharged from the converter is
In order to prevent adverse effects such as volume expansion associated with the hydroxylation reaction of residual quicklime, it is used for roadbed materials and landfills after aging treatment. The oxidized slag discharged from the electric furnace is used for roadbed materials and landfills without any pretreatment. However, it can be said that the reason why the utilization rate of steelmaking slag is lower than that of blast furnace slag is that reduced slag that powders is used.However, the expansion of use for these applications is based on the condition that the slag itself can maintain a predetermined shape state. Become.

The powdered slag is used for the purpose of promoting the compaction effect of the roadbed material by mixing with other slag by utilizing the solidification phenomenon by the hydration reaction of the CaO or CaO-SiO ₂ system contained therein. There are cases where it is used as a raw material for cement, as a raw material for cement, and as a material for treating hot metal in steelworks. At present, it is often discarded.

However, these are subject to many restrictions due to environmental problems and the like, and at the same time, the use of roadbed materials is also reduced as the use of construction waste materials is progressing due to the recent strengthening of the recycling law. Even in light of this trend, the field for actively using powdered slag will be limited in the future.

Another application of the powdered slag is in the field of soil improvement such as sludge solidification. However, since the slag processing work, storage of stock, and mixing with other materials are troublesome, reduction is required. It is unlikely that the slag will be expanded in the future as a mass processing field.

The present invention has been made in view of the above-mentioned problems of the conventional reduced slag, and has as its object to provide a slag reforming method for preventing powdered reduced slag generated in a ladle refining furnace. .

[0018]

In order to achieve the above object, a method for reforming slag in a ladle refining furnace according to the present invention comprises a slag in a ladle refining furnace containing 25% or more of MgO by dry weight ratio. The material is added and dissolved, and the ratio of MgO contained in the slag after completion of casting is set to 10% to 50% by weight.

According to the slag reforming method of the present invention, about 8% of M is added in advance to prevent erosion of refractories such as a ladle.
By further increasing the ratio of gO, CaO-MgO-SiO ₂ -based melvinite 3CaO-MgO-2SiO, which is commonly used as a rock component, while preventing refractory damage, which is a concern due to an increase in the content of other acidic components. _2, Akerumanaito 2CaO-MgO-2SiO _2, is to close the reducing slag components such as Monte celite CaO-MgO-SiO _2. MgO is a major basic component along with CaO, but by using it for refining mainly of a desulfurization reaction, it can replace CaO and reduce its ratio. If the weight ratio of MgO contained in the slag is less than 10%, there is no effect of preventing slag powdering, and if it exceeds 50%, unreacted free MgO is crystallized, and this is the MgO powder. The melting point may be extremely high, or the melting point may be extremely high, which may hinder the operation.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a slag reforming method for a ladle refining furnace according to the present invention will be described with reference to the drawings.

In order to reduce or prevent the reduction slag from being powdered in the ladle refining furnace (secondary refining furnace), the composition of the slag is changed from an easily pulverized mineral to a hardly pulverized mineral. It needs to be transformed. On the other hand, if the refining function, which is the purpose of the ladle refining furnace, is inhibited, the refining itself becomes meaningless. Here, in order to satisfy this conflicting function, a material containing a large amount of MgO is added to the molten slag in the ladle refining furnace for slag reforming.

Specifically, a material containing 25% or more of MgO by dry weight ratio is added to slag dissolved in a ladle refining furnace,
It is added alone or in combination with a material containing SiO ₂ or Al ₂ O ₃ and dissolved, and the ratio of MgO contained in the slag after final casting is adjusted to 10% to 50% by weight.

In this case, from the viewpoint of maintaining the refining function by the ladle refining furnace, CaO contained in the slag is added in a weight ratio of 15%.
%, 15% or more by weight of SiO ₂ and 5% or more by weight of Al ₂ O ₃ .

Thus, a typical component of the slag after the final casting is CaO—MgO—SiO ₂ shown in FIG.
On the system ternary phase diagram, MgO is 10% to 50% by weight, C
aO a weight ratio of 15% or more, the range of SiO ₂ weight ratio of 15% or more.

Further, in addition to the above, four components in the slag,
That is, CaO, MgO, SiO _Two, A1_TwoO_ThreeBut heavy
In a quantitative ratio, (CaO + MgO) / (SiO_Two+ A1_TwoO_Three) = 1.0
-2.5 (hereinafter, referred to as “component condition A”)
It is desirable that

By the way, the most appropriate method for adding the material containing MgO is a method of melting by energization in the course of refining in a ladle refining furnace. After mixing and dissolving the steelmaking slag discharged into the slag in the ladle refining furnace after the method of dissolving and dissolving the normal ladle refining, the remaining heat or part of the existing slag by the slag Is held in a semi-molten state until the end of casting, and when the casting is finished and the slag is turned over, there is a method of mixing and melting in the noro pot using the falling energy. The added MgO-containing material does not necessarily need to be completely melted. For example, when a MgO-based brick described later is charged, the unmelted portion is dispersed in the slag structure because the melting point of the fine particles is high. Although a state may occur, the present invention does not exclude such a state.

The reason that MgO is used as a main component for reforming slag is that the ratio of MgO added to about 8% to prevent erosion of refractories such as a ladle refining furnace is further increased. By doing so, it is possible to prevent damage to the refractory, which is a concern due to an increase in the content of other acidic components, and to reduce the general C content as a rock component.
aO-MgO-SiO ₂ Melvinite 3CaO-
MgO-2SiO _2, Akerumanaito 2CaO-MgO
-2SiO _2, Monte Celite CaO-MgO-SiO ₂
Is to bring the slag closer to the component. Furthermore, for another purpose, MgO is a major basic component along with CaO, but by using it for refining mainly of desulfurization reaction, it may substitute for CaO and reduce its ratio. .

[0028] The ratio of MgO contained in the slag after completion of casting is 10% to 50% by weight, and more preferably 15% to 50% from the viewpoint of preventing slag from being powdered. If the ratio of MgO is less than 10% by weight, the effect of preventing slag powdering is not obtained, and if it exceeds 50%, unreacted free MgO is crystallized, which is the powdered MgO. It is determined by the occurrence of a phenomenon or an extremely high melting point that hinders the operation. In addition, CaO is 15% or more as a basic component of refining from the viewpoint of securing basicity, and the upper limit depends on component condition A. Also,
SiO ₂ is set to 15% or more for constituting a rock component, and the upper limit depends on the component condition A. Further, since A1 ₂ O ₃ has a high effect of lowering the melting temperature of slag, the content is set to 5% or more.

By the way, the form of ladle refining can be roughly classified as follows:
Ladle refining of blast furnace system and ladle refining of ordinary steel electric furnace system can be roughly classified. Hereinafter, each will be described.

Ladle Refining in Blast Furnace System Ladle refining in blast furnace system is various. However, the basics of refining are to adjust the distribution of impurities in molten steel to molten slag, especially the distribution ratio of sulfur and oxygen, by vigorous stirring and increasing the basicity of slag,
Since the slag volume is forcibly increased by increasing the slag volume, refining itself cannot be realized if an attempt is made to reform slag from the beginning of refining. Therefore, after the molten steel component reaches the target value, it is most appropriate to aim at the floating slag on the surface of the molten steel involved in refining and to add a material containing MgO to reform the slag.

At this time, in the production of high-grade steel, the impurity elements are transferred and trapped in the slag, but the contact between the slag and the molten steel is not suppressed as much as possible with respect to sulfur and oxygen, which easily return to the molten steel when the basicity decreases. And the phenomenon that returns to the original occurs.
For this reason, in order to reduce the amount of the molten steel stirring gas and to suppress the slag dance, it is necessary to consider the adjustment of the amount of electricity to be supplied. Also,
Deoxidation products and nonmetallic inclusions suspended and separated from molten steel may be difficult to be trapped due to the change in slag composition.In addition, inclusions may increase due to the input MgO-containing material. It is necessary to pay attention to what is done.

The slag in the ladle refining furnace after the casting is completed in such a state, the lower part of the additive material in contact with the molten steel or the existing slag is in a molten state, and the upper part that comes into contact with the outside air is the additional material. Some of the material is dissolved or present in its entirety glowing. The slag in the ladle refining furnace is discharged to a slag pan for slag receiving set up at a predetermined location in the factory. Mix and react. Since the additive is already preheated sufficiently, the reaction proceeds quickly.
However, the particle size of the added material, the composition of the components, the method of spraying, etc. depend on the operating conditions of the steelmaking plant, that is, the casting time, the heat retention state of the ladle refining furnace, the characteristics of the steel type, etc. It will take any value and composition from body to particle body.

In the case of ladle refining of ordinary steel electric furnace system Unlike the blast furnace system ladle refining, in the case of ordinary steel in which the quality of the steel is regulated, in particular, in the case of ordinary steel in which components such as phosphorus and sulfur are not as strict as in the blast furnace system, Refining with less addition. However, even in this state, since the generated slag has a property of powdering, slag reforming is necessary as in the case of ladle refining in a blast furnace system. At this time, if the operation of reducing the absolute amount of the quick lime to be charged and simply lowering the basicity can prevent the slag from powdering itself, the desulfurization reaction depending on CaO is considerably restricted, and an appropriate slag In the ladle refining operation, which becomes stable only when there is a sufficient amount, the efficiency of the power supply decreases, the position control between the molten metal surface and the electrode becomes unstable, the heating rate decreases, etc., causing the entire operation to be delayed. Become.

Here, the amount of slag is secured, and
An MgO-based additive that can utilize its characteristics becomes important. High concentration
The capacity of the desulfurization reaction of MgO in the region is not fully understood.
However, in the concentration range of slag that has been practically used
Has been empirically determined to be around 60% of quicklime. Real truth
In the embodiment, the amount of CaO is reduced, and
Because it is in the component area far beyond the business area,
Simple basicity (CaO / SiO _Two) Then 1
An operation that cuts off always occurs. Therefore, slag base
Because the degree of MgO is positively increased, simple salt
Management by basis is not appropriate and comes from added materials
Control with component condition A, taking into account each oxide element
And expects MgO to replace lime
You. The lower limit of the ratio of the component condition A is set to 1 because 1
At full load, the absolute basicity of the slag is not maintained,
In addition to disturbing the ladle refractory,
The damage of the iron will progress, which will shorten the life of the ladle refining furnace.
It is. The upper limit of the ratio of the component condition A is set to 2.5.
This is for the purpose of preventing the slag powdering phenomenon.

The operation of the embodiment will be described below with reference to the case of ladle refining of a common steel electric furnace system.

[Example 1] (Addition of MgO-based brick debris) After tapping the bottom of the furnace from an electric furnace, crushed MgO-based brick debris was separately added as an additive to slag in a pot. Then, the same ladle refining operation was performed as usual, and the powdered state of the generated slag was observed.

(Observation results) Changes in sulfur of the product: The sulfur content at the time of tapping is 0.036% by weight, and the sulfur content at the end of refining is 0.1%.
At 033% by weight, desulfurization is progressing due to the effect of MgO. Powdering: Does not occur at all. Normal smelting slag is 8
The powder was powdered at around 00 ° C., but the slag to which the MgO-based brick waste was added had no powdering phenomenon at all. Slug condition:
Undissolved magnesia grains were found in the solidified slag. However, since it exists in the state of high-purity MgO brick waste, it does not become precipitated MgO that is easily powdered, and there was no phenomenon of powdering. Use: After cooling, the slag has relatively high hardness, has excellent shape stability even after crushing, and does not powder, so it has been confirmed that it can be used for concrete aggregate.

[Example 2] (Addition of nonferrous refining slag containing MgO) After steel bottom tapping was performed from an electric furnace, the slag in the pan was added as an additive.
As a non-ferrous refining slag containing MgO, slag (SiO ₂ : 53% by weight, M
gO: 33% by weight) alone, and the same ladle refining operation as usual was performed to observe the powdered state of the generated slag.

(Observation results) Changes in the sulfur content of the product: the sulfur content at the time of tapping is 0.033% by weight.
At 036% by weight, there is no desulfurization effect of MgO. For this reason,
If a desulfurization effect needs to be exerted, slag (SiO ₂ : 53% by weight, M
gO: 33% by weight) alone is not appropriate,
It is necessary to use other MgO-based additives in combination. Powdering: Does not occur at all. Normal refining slag powders at around 800 ° C. during cooling, but slag to which MgO-based slag is added has no powdering phenomenon at all. Further, the compositional, and has a rock structure near Monte celite on the diagram states CaO-SiO ₂ -MgO system ternary. Use: After cooling, the slag has relatively high hardness, has excellent shape stability even after crushing, and does not powder, so it has been confirmed that it can be used for concrete aggregate.

The embodiments of the present invention have been described above.
As a material containing O at a dry weight ratio of 25% or more, serpentine, olivine rock, pyroxene, olivine sand and the like can be used in addition to the above.

[0041]

According to the slag reforming method of the ladle refining furnace of the present invention, by increasing the MgO component in the reduced slag, refractory damage which may be caused by an increase in the mixing of other acidic components is prevented. While preventing, general CaO-Mg as a rock component
O-SiO ₂ Melvinite 3CaO-MgO-2
SiO ₂ , Akermanite 2CaO-MgO-2Si
The reduced slag can be brought close to components such as O ₂ and Montecellite CaO—MgO—SiO ₂ , thereby preventing the reduced slag from being powdered, stabilizing its shape characteristics, and the effective use range of the reduced slag. Can be significantly increased. Furthermore, by utilizing MgO for refining mainly using a desulfurization reaction, it is possible to substitute for CaO and reduce its ratio.

[Brief description of the drawings]

FIG. 1 is a ternary phase diagram of a CaO—MgO—SiO ₂ system.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G012 JL03 JM04 4K001 AA10 DA05 EA04 GA18 KA07 4K012 AA01 4K013 CF01 FA05

Claims (1)

[Claims] A slag in a ladle refining furnace is added with a material containing MgO in a dry weight ratio of 25% or more and melted, and the ratio of MgO contained in the slag after casting is reduced to 10% by weight.
%. A method for reforming slag in a ladle refining furnace, wherein the slag is set to 50% to 50%.