JP2000234117A - Method for refining molten metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a refining method of molten metal, by which the suitable slag component enabling the prevention to the reoxidation of molten metal can be obtd. and the hitting ratio of the molten metal component can be raised. SOLUTION: When the molten metal is refined by adding reducing agent in a molten metal holding vessel, a jig for taking slag analyzing sample of a hollow body constituted with a member having at least one smooth and flat surface and slag quick cooling function, is dipped into the slag in the molten metal holding vessel and immediately pulled up at one or more times to take the sample for slag analysis. The quick analysis is executed and the adding quantity of reducing agent is adjusted so that the components in the slag and/or the molten metal become the target composition. The hollow body is a hollow square columnar body 1 and it is desirable to be constituted with a metal plate having >=3 mm thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for refining molten metal, and more particularly, to a method for adjusting the amount of a reducing agent to be introduced in the refining process of molten metal, particularly molten steel.

[0002]

2. Description of the Related Art Conventionally, in the refining of metals such as iron and steel, it is important to adjust the composition of slag in order to obtain a metal having a target composition at a high yield. Further, recently, in steel products, requirements for quality including high cleanliness of steel have become strict, and for this reason, there has been a strong demand for improvement in the appropriate ratio of components in steel. In order to meet such demands, it is important to adjust the amount of the reducing agent to be supplied so as to have a target slag composition and a target component in steel.

[0003] Conventionally, for example, the input amount of a reducing agent in the refining of molten steel depends on the decarburization efficiency and the amount of acid transported, and thus the amount of Fe contained in the slag is reduced.
It was determined by estimating the production amount of lower oxides such as O ₂ and Cr ₂ O ₃ . However, the reaction of the molten metal during refining changes subtly due to changes in the input raw material concentration, reaction temperature, or the amount of slag on the molten steel, and it is extremely difficult to accurately estimate the amount of lower oxides generated. Therefore, it was difficult to adjust the target slag composition or target steel component properly.

[0004] In order to know the amount of lower oxides in the slag in the refining process, it is preferable to perform slag analysis in the refining process. In short, it was extremely difficult to obtain slag analysis results during the refining operation. This was because, in particular, the time required for sample preparation for using the collected slag as an analysis sample was long.

Heretofore, glass bead X-ray fluorescence analysis, which can simultaneously analyze multiple elements with high accuracy, has been mainly used for slag analysis. In this method, a ground slag is melted by using a flux such as sodium borate, which is about 10 times as large as that of the slag, adjusted to a homogeneous glassy sample, and analyzed by X-ray fluorescence analysis. This method is characterized by high analysis accuracy with little influence of coexisting elements.However, it requires grinding, weighing, and melting operations for sample preparation. I needed it. The adjustment of the sample in the glass bead X-ray fluorescence analysis is defined in JIS M 8205.

[0006] For this reason, a briquetting method has been devised for the purpose of shortening the time required for sample preparation. Compared to the glass bead method, the time required for sample preparation is reduced because there is no weighing and melting work, but the analysis time is still 25 to
Needed 30min. Further, even if these slag analysis methods are automated, it is difficult to reduce the analysis time to 20 minutes or less, and there is a problem that the slag analysis results cannot be reflected in the refining work.

To solve such a problem, see, for example,
No. 79952 discloses that the composition of slag on molten steel was analyzed using a sample in which molten slag was poured into a metal frame placed on a metal plate with a smooth surface and cooled and solidified. Further, a method for refining molten steel in which a flux is added so that the concentration or basicity of AL ₂ O ₃ in slag becomes an optimum value is disclosed.

Japanese Patent Application Laid-Open No. H10-170411 discloses a sampler having a prismatic shape having a side length of 20 mm or more and having a smooth flat surface including a circle having a diameter of 10 mm or more on at least one side surface. A quick method of analyzing steel slag is to insert it into a steel slag layer, attach the slag to a flat surface, immediately pull it up, peel off the solidified slag, and subject the surface that was in contact with the flat surface to fluorescent X-ray analysis. It has been disclosed.

[0009]

SUMMARY OF THE INVENTION
In the technique described in JP-A-9-79952, solidification progresses before the molten slag collected from the smelting vessel is injected into the metal frame, and the analytical surface is significantly different from the average composition of the slag in the smelting process There was a problem of becoming a composition. Also,
The technique described in Japanese Patent Application Laid-Open No. 10-170411 has a problem that the size of the sampler is too small, and it is not possible to reliably collect slag that vibrates violently during the refining process. Using a sampler described in JP-A-10-170411, in order to reliably collect slag, the length is 500 m
m or more, which makes the sampler heavier and significantly reduces operability.

As described above, in the prior art, it is difficult to obtain a highly representative slag analysis value enough to accurately control the slag-metal reaction of molten steel, and it is difficult to sample the slag itself. There was a problem that it was difficult to apply to the actual refining of molten steel. The present invention advantageously solves the above-mentioned problems of the prior art, optimizes the amount of the reducing agent to be added, and makes it possible to obtain an appropriate slag component capable of preventing reoxidation of the molten metal. It is an object of the present invention to propose a method for refining molten metal capable of increasing the rate.

[0011]

In the slag analysis using the fluorescent X-ray analysis, in order to improve the analysis accuracy, the slag has a smooth and flat surface and an amorphous state having a composition at the time of melting. A sample that has been solidified (glass-like) is required. Since the analysis depth in fluorescent X-ray analysis is at most several μm,
The present inventors have come to the conclusion that rapid cooling is required only up to several μm in order to solidify the molten slag into a glassy state, and a jig having such a large cooling capacity is not required. As a result of further study, the present inventors have found that a jig for slag analysis sample collection for directly immersing in molten slag and attaching and solidifying the slag has a relatively thick slag quenching function. It has been found that a hollow body having a smooth and flat surface made of a thin metal plate is preferable. By using such a jig for slag analysis sample collection, it has been found that slag analysis can be performed online, and the slag composition can be adjusted according to the refining process.

The present invention has been made based on the above-mentioned findings and further studied. That is, the present invention, when refining the molten metal by adding a reducing agent in the molten metal holding vessel, at least once, immediately dipping the jig for slag analysis sample collection in the slag in the molten metal holding vessel Withdrawing, collecting a sample for slag analysis from the slag, quickly analyzing the slag, and adjusting the amount of the reducing agent added based on the analysis result so that the component in the slag and / or the molten metal has a target composition. In the present invention, the jig for slag analysis and sampling has at least one smooth and flat surface, and has a slag quenching function. It is preferable that the hollow body constituted by, furthermore, the hollow body,
It is preferable that the member which is a hollow prism and has the slag quenching function is a metal plate having a thickness of 3 mm or more.

Further, in the present invention, the refining is performed by using a metal
Refining using a slag reaction is preferable, and
The refining may be a refining utilizing a metal-slag reaction and further including an oxidation refining process. In the present invention,
Preferably, the target composition of the slag is determined by the concentration of the lower oxide.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION A molten metal roughly refined in a converter or the like is refined by secondary refining such as a VOD method and an LF method.
In this secondary refining, the molten metal transferred to a molten metal holding container such as a ladle is added with a flux as necessary in the molten metal holding container, and is finished by gas blowing, gas stirring, heating, vacuum processing, or the like. After refining such as decarburization, a reducing agent is further charged to reduce useful alloying elements, such as (Cr), (Si), (Mn), etc., present in the slag as oxides into the molten metal. Then, the components in the molten metal are adjusted, or slag is reformed in order to prevent the reoxidation of the molten metal.

Hereinafter, the present invention will be described by taking as an example a case where steel is used as the molten metal and the VOD method is used as the secondary refining, but it goes without saying that the present invention is not limited to this. The molten steel that has been roughly decarburized in a converter, an electric furnace, or the like is tapped into a ladle, which is a molten metal holding container, and subjected to VOD treatment. The VOD treatment is usually performed by blowing oxygen under reduced pressure,
In addition, rimded decarburization treatment that promotes the reaction between [C] and [O] in the steel by stirring Ar under high vacuum, and reducing flux such as ferrosilicon and other reducing agents, CaO, Al ₂ O ₃ , MgO, and SiO ₂ It consists of a reduction treatment or the like in which Ar is added and stirred under vacuum. In the present invention, slag is collected at least once before the refining and during the refining, particularly before the reduction treatment, and a rapid analysis is performed.

In the slag sampling according to the present invention, a jig for slag analysis and sampling preferably used is a hollow body having at least one smooth and flat surface and having a slag quenching function. Is preferred. The hollow body is more preferably a hollow prismatic body in terms of ease of manufacture. The member having the slag quenching function is preferably a metal plate having a thickness of 3 mm or more, particularly a steel plate having a thickness of 3 mm or more. If the thickness of the member is less than 3 mm, it will not melt or deform when immersed in the slag to obtain an analysis sample having a flat surface, and the slag cannot be rapidly cooled, thus lowering the analysis accuracy. In addition, even if the thickness of the member exceeds 5 mm, not only does not contribute to the improvement of the analysis accuracy, but also the weight of the jig increases and hinders handling, so that the thickness of the member is preferably 5 mm or less. Further, the width of the member is preferably adjusted so that the slag analysis sample has a smooth and flat surface having a size of 20 mm or more in diameter. A hollow body is formed using these members. The length of the hollow body is preferably 300 mm or more so that a slag analysis sample can be reliably collected even if the slag swings.

FIG. 1 shows an example of a jig for sampling a slag analysis sample using a hollow quadrangular prism. In FIG. 1, a hollow body (hollow quadrangular prism) 1 having a flat surface around it is attached to a paper tube 2 to facilitate handling. Mortar 3 is packed at the tip of this jig so that molten metal does not enter inside.
In the present invention, preferably using the above-mentioned slag analysis and sampling jig, immediately dipping the jig for slag analysis sample collection into the slag in the molten metal container, and pulling up the slag analysis sample from the slag, Perform a quick analysis.

A jig (hollow body) for slag analysis and collection is immersed in molten slag, and the molten slag is brought into contact with a smooth and flat surface of a hollow body constituting the slag analysis and collection jig.
Immediately, the slag is adhered and solidified on a smooth and flat surface, and the solidified slag is peeled off to obtain a slag analysis sample. Since the hollow body of this jig is formed of a member having a slag quenching function, the attached slag is quenched and solidified in a glass state in a state having a composition at the time of melting. The surface of the slag analysis sample which is in contact with the smooth and flat surface and rapidly cooled is used as the analysis surface for rapid analysis.

The contact between the jig for slag analysis sample collection and the molten slag is as short as possible, and it is to be pulled up immediately after immersion in the slag. The immersion of the slag analysis sample collecting jig into the molten slag is preferably about 1 second. Thereby, even if a hollow body is formed using a relatively thin member, the slag has a function of rapidly cooling the slag, and a slag analysis sample having a smooth and flat surface without deformation even when immersed in the slag. Can be collected.

The rapid analysis is performed by using X-ray fluorescence analysis.
In order to keep the analysis accuracy within 10% relative error, the smooth and flat surface of the jig for slag analysis sampling is preferably finished with a surface roughness Ra of 20 μm or less. Thereby, it is possible to reduce the variation of the incident angle of the incident X-ray. By using the jig for collecting the slag analysis sample described above, the adjustment time of the analysis sample can be significantly reduced, and the time from the collection of the slag to the time when the analysis result is obtained can be reduced to 5 minutes or less.

Based on the analysis results of the slag by the rapid analysis, the slag composition having an appropriate lower oxide content such as Total Fe, Cr ₂ O ₃ , MnO, etc., or [Si], [Al] So that the amount of alloy elements such as
Refining of molten metal is performed by adjusting the amount of reducing agent added. The desired slag composition or the amount of alloying elements such as [Si] and [Al] in the molten metal is appropriately set depending on the type of steel to be refined, the target composition, and the like. In the present invention, the molten metal is effective for both alloy steel and ordinary steel.

During the secondary refining process, a rapid analysis of the slag can confirm the deviation of the slag composition from a desired slag composition (particularly the amount of lower oxides), and adjust the amount of the reducing agent added during the refining. It becomes possible. The reducing agent to be added can be selected from ferrosilicon, aluminum ash, metallic Al, and the like according to the type of steel to be refined, the target composition, and the like. In the method for refining molten metal of the present invention, slag analysis can be carried out before and / or during refining as appropriate and composition of the slag can be easily controlled. Especially effective. Further, the refining method of the present invention,
Refining may utilize slag metal reaction, and may be refining including an oxidizing refining process. In the present invention, a slag analysis sampling probe is attached to a part of a lance for temperature measurement sampling, so that the timing during refining, which was conventionally difficult, can be performed.
Slug sampling becomes possible. From the viewpoint of the addition of the reducing agent, the slag analysis is preferably performed during refining immediately before the addition of the reducing agent, that is, during refining before the reduction treatment.

In the method for refining molten metal of the present invention, since the composition of slag is easily controlled, it is also easy to obtain a desired composition of molten metal (metal) through adjustment of slag composition. The analysis of the slag composition before addition makes it possible to accurately grasp the required addition amount of the reducing agent that has been conventionally estimated. For this reason, the reducing agent can be added without excess or shortage, and there is an effect that it avoids additional refining and leads to an improvement in the unit consumption of the reducing agent. Further, the amount of the reducing agent component dissolved in the molten steel can be easily estimated, and the appropriateness of the component in the molten steel can be improved. In addition, by optimizing the slag composition such as the reduction of Total Fe and MnO, it is possible to avoid product defects, avoid reoxidation of molten steel, etc., improve the predictive value of molten steel components, and in particular, optimize the amount of (Al) There is also an effect that nozzle clogging in continuous casting is prevented.

As described above, according to the present invention, steel is
Although VOD has been described as an example of the next refining, the present invention is not limited to this.

[0025]

EXAMPLES (Example 1) Cr-containing molten steel that had been roughly decarburized in a 175-t converter was transferred to a ladle and subjected to secondary refining by the VOD method.
06wt%, Si: 0.20 ~ 0.65wt%, Mn: 0.90 ~ 1.10wt%, C
r: 18.00 to 19.00 wt%, P: 0.04 wt% or less, S: 0.012
A molten steel containing wt% or less, Ni: 8.00 to 8.30 wt%, and O: 0.0080 wt% or less was obtained.

In the secondary refining by the VOD method, oxygen blowing is performed under reduced pressure, and Ar is stirred under a high vacuum to perform decarburization treatment.
Next, one or more of Al ₂ O ₃ flux, CaO flux, SiO ₂ flux, and MgO flux is adjusted and added as a flux, and the amount of ferrosilicon added as a reducing agent is adjusted. Then, a reduction treatment was performed. At this time, before the reduction treatment during the refining, a jig for slag analysis sample collection using a hollow quadrangular prism composed of a steel plate member having a thickness of 3 mm shown in FIG. 1 was immersed in molten slag for 1 second. Immediately, a sample was taken for analysis of the lifted slag.

The flat surface of the jig for collecting a slag analysis sample was a surface of 50 × 400 mm and Ra 10 μm. A slag release agent was applied on the flat surface to obtain a smooth surface. The analysis was rapid analysis using X-ray fluorescence analysis. Table 1 shows the results of slag analysis before reduction. Based on the results of the rapid analysis, a reducing agent (ferrosilicon) in an amount shown in Table 2 was added so as to obtain a desired slag composition and molten steel composition (standard Si amount). The desired slag composition is also shown in Table 1.
The slag composition after addition of the reducing agent was analyzed and is shown in Table 1. The same slag analysis sample was collected 50 times at the same sampling time, and this was used as an example of the present invention. Table 1 shows the average value and variation of each component of the slag for the 50 charges performed. Table 2 also shows the average value and variation of the amount of molten steel [Si].

Further, as a conventional example, ferrosilicon was added in an amount determined from the predicted oxidation amount of Cr and the standard Si value of the molten steel, and the secondary refining of the molten steel was performed for 50 charges.
As a result, the composition of the generated slag was analyzed, and the average value and the variation of 50 charges are shown in Table 1. Table 2 also shows the average value and variation of the amount of molten steel [Si]. Also,
The presence or absence of additional refining is also described.

The appropriate predictive values of the components of the molten steel in the conventional example and the present invention example were determined and are shown in Table 2. The component predictive value was the ratio of the component predictive charge number to the total charge number of each of the conventional example and the present invention example.

[0030]

[Table 1]

[0031]

[Table 2]

From Tables 1 and 2, it can be seen that the slag analysis is completed during the refining and the reducing agent can be added on the basis of the analysis, whereby the slag composition is within the desired slag composition range and the component predictive ratio is high. Further, no additional refining is required, and the amount of the added reducing agent is smaller than in the conventional example, so that the reducing unit consumption is reduced. On the other hand, in the conventional example, additional refining is often required,
The amount of the added reducing agent is large.

[0033]

According to the present invention, slag analysis during refining becomes possible, and the slag composition can be easily adjusted to a desired composition by adjusting the amount of the reducing agent added based on the slag analysis results. In addition, it is possible to increase the predictive value of the molten metal component, and to achieve remarkable industrial effects such as improvement of the unit consumption of the reducing agent, prevention of reoxidation of the molten metal, and reduction of product defects.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a jig for collecting a slag analysis sample.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hollow quadrangular prism 2 Paper tube 3 Mortar

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuki Nabeshima 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba F-term in the Chiba Works, Chiba Works (reference) 2G055 AA30 BA01 CA02 CA03 CA05 CA07 CA09 CA25 CA29 DA02 DA31 EA10 FA04 4K013 AA02 BA03 BA14 CE06 EA01 EA03 EA04 EA05 FA05

Claims (6)

[Claims] When smelting a molten metal by adding a reducing agent in a molten metal holding vessel, a jig for slag analysis sample collection is immersed in slag in the molten metal holding vessel at least once, and is immediately pulled up. A slag analysis sample is collected from the slag, rapidly analyzed, and based on the analysis result,
A method for refining molten metal, comprising adjusting the amount of the reducing agent to be added so that the components in the slag and / or the molten metal have a target composition. 2. The jig for slag analysis sample collection is a hollow body having at least one smooth and flat surface and a member having a slag quenching function. 2. The method for refining molten metal according to 1. 3. The method for refining molten metal according to claim 2, wherein the hollow body is a hollow prism, and the member having the slag quenching function is a metal plate having a thickness of 3 mm or more. . 4. The method for refining a molten metal according to claim 1, wherein the refining is refining utilizing a metal-slag reaction. 5. The method for refining a molten metal according to claim 1, wherein the refining is a refining utilizing a metal-slag reaction and further including an oxidizing refining process. 6. The method for refining a molten metal according to claim 1, wherein the target composition of the slag is a concentration of a lower oxide.