JP2001181725A - Method for modifying slag in refining of molten stainless steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a modifying method for slag in the refining of molten stainless steel, in which chromium oxide contained in the slag developed when performing the decarburize-refining of the molten stainless steel, is efficiently reduced and recovered into the molten stainless steel, and the powdering caused by the reduction and the expansion of the chromium contained in the slag is improved and the slag can be used as a resource. SOLUTION: In the modifying method for the slag at the refining of the molten stainless steel by using a refining furnace 10, the ratio of Al2O3 concentration to the basicity of the slag is regulated to >=10.

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 stainless steel smelting slag which recovers valuable metals from slag generated by refining molten stainless steel and suppresses natural expansion of the slag to recycle it.

[0002]

2. Description of the Related Art Conventionally, chromium (Cr) contained in molten iron is simultaneously oxidized when decarburization refining by blowing acid is performed using a refining furnace such as a top-bottom blow converter or a top blow converter. Generally, this chromium oxide (Cr ₂ O ₃ ) is contained in the produced slag in an amount of 10% by weight or more. Since chromium is expensive, chromium oxide contained in slag is reduced by adding alloy iron such as Fe-Si, and is recovered as chromium in molten stainless steel. But,
Since the reduction of chromium oxide is determined by the cost balance between the cost of using a reducing agent such as Fe-Si and the amount of chromium oxide remaining unreduced in the slag, the chromium concentration is about 0.6 to 5% by weight. Remains in the slag, and a part of the metal chromium is present. As a result, the amount of chromium loss increases, the amount of chromium alloy iron to be replenished increases, and the production cost of molten stainless steel increases. Further, the use of slag generated during the decarburization and refining of molten stainless steel is being promoted as a resource. However, it has the property of expanding and disintegrating (pulverizing) greatly, so there are restrictions when using it as a landfill material for civil engineering or a roadbed material,
There is a problem that it cannot be used.

As a countermeasure against this, Japanese Patent Laid-Open Publication No.
As described in Japanese Patent Publication No. 2
Carbon concentration in the atmosphere using a refining furnace such as
Decarburizing with blowing acid until it becomes about 0.2-0.3% by weight
After that, transfer the molten stainless steel to a vacuum ladle refining device.
Inert gas is blown from the bottom of the ladle to melt stainless steel.
Mix and stir steel and slag, and add chromic acid contained in the slag
Chromium yield by reducing oxides with carbon
It is done to raise the low carbon stainless steel molten steel
ing. In addition, a method of utilizing slag as a resource
And described in JP-A-8-104553.
Chromium oxide of slag produced by decarburization refining
After the reduction treatment, FeS or CaS
Addition of divalent sulfide such as
Slag. Further, JP-A-9-165238
And Japanese Patent Application Laid-Open No. 11-61219.
Slag generated during the production process of molten stainless steel
Boric acid (B_Two O _Five ) And add dicalcium silique
(2CaO.SiO)_Two Diffuses boric acid into solid solution
And α'2Ca0.SiO_Two (C_Two S) to γ2Ca
O ・ SiO_Two (C_Two Suppresses the phase transition to S) and causes expansion
To prevent powdering caused by the
No. 13, boric acid and phosphoric acid
(P _Two O_Five ) By adding the ingredients and making them form a solid solution,
Α'C of slag_Two S to γC _Two Suppress phase transition to S
That is being done.

[0004]

However, in the method described in Japanese Patent Application Laid-Open No. 52-147512, it takes a long time to reduce chromium oxide in slag and recover it in molten stainless steel. This leads to deterioration of the properties and wear of refractories such as ladles. In addition, there is a limit to the reduction of chromium oxide, the amount of chromium oxide remaining in the slag after refining is increased, and the use of ferrochrome and other ferroalloys increases, which increases the production cost. In addition, it is impossible to improve the slag disintegration property, so that there is a problem when used as a landfill material for civil engineering or a roadbed material. Also, Japanese Patent Laid-Open No. 9-1
No. 65238, JP-A-11-61219 and JP-A-8-18813, boric acid or boric acid and phosphoric acid are added to a slag to prepare 2C.
Although powdering caused by expansion of aO.SiO ₂ can be prevented,
Since a large amount of expensive boric acid is added, the processing cost increases. In addition, boron (B) or phosphoric acid is added to the slag, which leads to an increase in the amount of the slag, which is not preferable because there are economic and environmental problems including slag processing costs. Furthermore, since the chromium oxide remaining in the slag after refining cannot be reduced and recovered in the molten stainless steel, chromium loss is caused, the use of ferrochrome and other ferroalloys is increased, and the production cost of the molten stainless steel is reduced. There is a problem such as becoming high.

The present invention has been made in view of the above circumstances, and efficiently reduces chromium oxide contained in slag generated during decarburization and refining of molten stainless steel to recover the chromium oxide in the molten stainless steel. It is an object of the present invention to provide a method for reforming refined slag of molten stainless steel, which can reduce chromium contained in slag and improve pulverization due to expansion to make slag a resource.

[0006]

According to the present invention, there is provided a method for reforming slag of refined stainless steel according to the present invention, which comprises refining slag of molten stainless steel using a refining furnace. The concentration ratio of Al ₂ O ₃ to is set to 10 or more. By this method, slagification of slag is promoted and reduction of chromium oxide is facilitated, and dicalcium silicate (2CaO · SiO
₂ ) can be prevented from being generated, and collapse due to expansion of the slag itself can be eliminated. The basicity of the slag is
The ratio of CaO to SiO ₂ contained in the slag (Ca
O / SiO ₂ ).

Here, aluminum dross and / or
Alternatively, it is preferable to add metal Al. By this method, it is possible to promote the reduction of chromium oxide contained in the slag and reduce the total amount of chromium remaining in the slag,
2CaO · SiO ₂ generated at the same time can be suppressed.

Further, an Al ₂ O ₃ containing material may be added to the slag. 2CaO · S by inexpensive Al ₂ O ₃
The generation of iO ₂ can be suppressed, and the processing cost can be reduced.

Further, the total chromium content in the slag after the slag has been modified can be reduced to 0.5% by weight or less. Since the content of chromium is made equal to that of slag generated in a general steelmaking process, it can be recycled and used as a landfill material for civil engineering or a roadbed material.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention. First, the present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, the carbon concentration was 2 to 5 times.
Slag produced by performing decarburization smelting from molten iron by weight using a smelting furnace, and VOD (Vacuum Oxygen).
It was found that the characteristics of slag produced by secondary refining using vacuum such as one-foot large-diameter immersion tube and the like have large differences in characteristics. Furthermore, the secondary smelting slag that has undergone Al deoxidation has a smaller amount of chromium remaining in the slag, similarly to ordinary steel slag. In addition, the disintegration due to expansion is small and a lump is maintained. On the other hand, it was found that the secondary refining slag deoxidized with Si had a low chromium oxide reduction efficiency, a high amount of chromium remaining in the slag, and a large disintegration property due to expansion. Then, they focused on the fact that the reduction efficiency and slag properties of chromium oxide are greatly related to the method of deoxidation, and reached the present invention. This will be specifically described below. FIG. 1 is an overall view of an upper-bottom blow converter applied to a method for reforming stainless steel smelting slag according to an embodiment of the present invention, and FIG. 2 is CaO—Al ₂ O.
FIG. 4 is a _3- SiO ₂ phase diagram. As shown in FIG. 1, an upper-bottom blowing converter 1 which is an example of a smelting furnace used in a method for reforming a stainless steel smelting slag according to an embodiment of the present invention.
Reference numeral 0 denotes a furnace body 11, a lance 12 for blowing oxygen or an oxygen-containing gas obtained by mixing oxygen and argon gas into the furnace body 11 from above the furnace body 11, and an inert gas for stirring the inside of the furnace body 11. A nozzle 13 provided at the bottom to be blown and auxiliary materials such as quicklime, iron ore, dust and Fe-S
i, Fe-Cr, aluminum dross, chute 14 for adding ferrous alloys such as metal Al and storage hopper 15 and stainless steel for which decarburization and refining has been completed (hereinafter referred to as molten steel) for tapping into a ladle (not shown). A tap hole 16 is provided.

Next, a description will be given of a method of reforming a slag for smelting stainless steel using the upper-bottom blow converter 10. 150 tons of hot metal, which has been subjected to desulfurization, dephosphorization, etc. in advance, is charged into the top and bottom blown converter 10, and quicklime or Fe-Cr stored in the storage hopper 15 is added from the chute 14 into the furnace 11,
By lowering the lance 12 and spraying the oxygen-containing gas onto the hot metal, so-called decarburization for burning and removing carbon contained in the hot metal is performed, and at the same time, quicklime and Si and the like in the hot metal are oxidized. Slag is generated. Then, with the progress of decarburization, chromium (Cr) contained in the molten iron is also oxidized to 10 to 30% by weight of chromium oxide (Cr ₂ O).
₃ ) is formed and this chromium oxide migrates into the slag. The carbon concentration decreases to 0.1 to 1.0% by weight,
When the decarburization refining is completed and molten steel is melted, aluminum dross or metal Al is added (aluminum dross and metal A).
l may be added), and argon gas, which is an example of an inert gas, is blown into the furnace 11 from the nozzle 13,
The slag is stirred, and Cr ₂ O ₃ in the slag is reduced by a reaction represented by the following formula (1), and the reduced Cr is recovered in the molten steel. Cr ₂ O ₃ + 2Al → 2Cr + Al ₂ O ₃ ... (1) The addition amount of Al or metal Al contained in the aluminum dross is equal to or more than the stoichiometric amount consumed in the above equation (1). The amount of metal (metallic) Al in the slag after the modification is such that the residual total Cr concentration (total chromium content in the slag) obtained by converting all the metallic Cr and Cr ₂ O ₃ in the modified slag to Cr is reduced to 0. 0.5% by weight or less, which is equivalent to the slag generated during the smelting of ordinary molten steel.
It is possible to eliminate the influence of r ₂ O ₃ on the environment and to make the resources available. Further, when the amount of metal Al to be added is set to be equal to or more than the stoichiometric amount necessary for reducing the amount obtained by adding the amounts of Cr ₂ O ₃ and FeO and MnO in the slag,
Since the residual total Cr concentration can be more stably set to 0.5% by weight or less, a preferable result is obtained.

Further, the slag composition satisfies the following equation (2).
So, Al_Two O_Three Adjust the volume. For example, in the slag
Cr_Two O_Three And to reduce FeO, MnO, etc.
Generated from the amount of metallic Al_Two O_Three When there is a shortage
Aluminum dross or Al to match the shortage_Two O
_Three Is added. Al_Two O_Three / (CaO / SiO_Two ) ≧ 10 (2) The slag composition is adjusted using a top-bottom blow converter 10
By analyzing the slag generated during the smelting,_Two 
O_Three , CaO, SiO_Two , Al_Two O_Three , FeO, MnO
Operation in the past based on the amount of quicklime etc.
The total amount of slag can be determined from experience.
Calculation of lag basicity, amount of metal Al added and Al_Two O
_Three The amount is determined by general chemical equivalent calculation. Slag base
Degree (CaO / SiO_Two Al)_Two O_Three The concentration ratio of
When it is smaller than 10, as shown in FIG.
SiO_Two (Dicalcium silicate) generated area
Becomes α′2Ca0 · SiO after solidification_Two (C_Two 
S) to γ2CaO.SiO_Two (C_Two Phase transition to S)
It causes volume expansion and powders when the expansion becomes severe. Follow
And 2CaO ・ SiO_Two Production range and high CaO concentration range
Gelenite (2CaO Al_Two O_Three ・ SiO
_Two C of FIG. 2_Two AS), Ca_Three Al_Two O ₆ (FIG. 2
C_Three A) and the like, that is, Al with respect to basicity._Two O_Three No
Al in the slag so that the degree ratio becomes 10 or more_Two O_Three Including
By adjusting the weight, the expansion of the solidified slag
Landfill material for civil engineering that can sufficiently suppress collapse (pulverization)
And can be used as roadbed material. And Cr_Two 
O_Three And the total amount of residual chromium in metallic slag
Slurry whose disintegration due to expansion was suppressed to 0.5% by weight or less.
Is discharged from the top and bottom blown converter 10 and cooled to reduce the particle size.
After being crushed to about 5 to 70 mm,
It is transported as roadbed material and the like.

[0013]

Next, a description will be given of an embodiment of a method for reforming slag of smelted stainless steel. 150 tons of hot metal, which has been subjected to desulfurization and dephosphorization beforehand, is charged into a top-bottom blow converter (converter), and quick lime, iron ore, and Fe-Cr alloy iron are added from a chute to the converter. And from the lance 15000-2800
Decarburization refining was performed by blowing acid at a rate of 0 Nm ³ / hr until the carbon concentration became 0.3% by weight. Then, the basicity of the slag generated during the decarburization refining and the concentration of Al ₂ O ₃ were changed,
The quality of the reduction efficiency of the chromium oxide at that time, the quality of the chromium in the slag after the reduction, the expandability of the slag, and the comprehensive evaluation were investigated. Table 1 shows the results. In Example 1, the ratio of Al ₂ O ₃ to basicity was set to 10, and 1.0 times the stoichiometric amount required to reduce the total amount of Cr ₂ O ₃ , FeO and MnO in the slag. In this case, the metal Al is added, the chromium oxide reduction efficiency is good, the chromium concentration in the slag after reduction can be reduced to the same level as that of ordinary molten steel (（), and the slag expansibility can be reduced (○). Good (○) results were obtained for evaluation. In Example 2, the ratio of Al ₂ O ₃ to basicity was set to 12, and the C in the slag was
This is a case in which 1.2 times the stoichiometric amount of metal Al required to reduce the total amount of r ₂ O ₃ and FeO and MnO is added. The medium chromium concentration could be reduced (○) to the same level as ordinary molten steel, the slag expansibility could be reduced (○), and good results (○) were obtained as a comprehensive evaluation. Example 3 shows that A
The ratio of l ₂ O ₃ is set to 12 and the Cr ₂ O
₃ and a case where a metal Al of 1.0 times the stoichiometric amount required to reduce the total amount of FeO and MnO was added,
Good chromium oxide reduction efficiency, reduced chromium concentration in slag after reduction to the same level as ordinary molten steel (○), reduced slag expansibility (○), good overall evaluation (○) Was.

[0014]

[Table 1]

[0015] On the other hand, Comparative Example 1
Al_Two O_Three Ratio of 8 and the Cr in the slag_Two O
_Three Required to reduce the total amount of FeO and MnO
It is the case where 1.0 times the stoichiometric amount of metal Al is added,
Good chromium oxide reduction efficiency.
Although the metal concentration could be reduced (○) to the same level as ordinary molten steel,
O ・ SiO_Two Is generated and the slag expands significantly (×)
The result was bad (x) as the overall evaluation. Comparative example
2 is Al to basicity_Two O_Three The ratio of 8
Cr in slag _Two O_Three And total amount of FeO and MnO
0.6 times the stoichiometric amount of metal Al required to reduce
Is added, and the chromium oxide reduction efficiency is poor.
The chromium concentration in the slag after reduction is also high (x),
CaO ・ SiO_Two Is generated and the slag expands greatly.
(X), and a poor (x) result as the overall evaluation.

The embodiments of the present invention have been described above.
The present invention is not limited to the above-described embodiment, and all changes in conditions that do not depart from the gist are within the scope of the present invention. For example, AOD (Argon, Oxygen, De)
The present invention can be applied to slag that has been subjected to Si deoxidation in secondary refining such as slag or a ladle generated by decarburization refining with blowing acid in an electric furnace or the like. Further, the present invention can be applied to a smelting furnace such as a stainless steel smelting reduction furnace and a slag such as a slag processing furnace.

[0017]

Method of modifying a stainless molten steel refining slag of claims 1 to 4, wherein according to the present invention is the method for modifying a slag when smelting stainless molten steel using a refining furnace, Al ₂ O ₃ with respect to the slag basicity Since the concentration ratio is set to 10 or more, the recovery rate of chromium contained in the slag into the molten steel is increased by the metal Al as an Al ₂ O ₃ source to reduce the use amount of Fe-Cr alloy iron, etc. The production of dicalcium silicate (2CaO.SiO ₂ ) or the like is suppressed to reduce the slag disintegration, and can be used as resources such as roadbed materials and civil engineering landfill materials.

[0018] In particular, in the method for refining slag of molten stainless steel according to claim 2, since aluminum dross and / or metallic Al is added to the slag, the amount of chromium contained in the slag can be stably reduced, and at the same time, the slag is improved. It is possible to stably prevent the collapse of the slag, make it possible to use the slag as a resource, and reduce the processing cost by minimizing the amount of slag.

According to the method for modifying slag of refined stainless steel slag according to the _{third aspect of the} present invention, since the slag is added with an Al ₂ O ₃ -containing material, the slag processing cost can be reduced, and the slag can be prevented from collapsing and utilized as a cheap resource. be able to.

In the method for reforming slag of molten stainless steel according to claim 4, the total chromium content of the slag after the slag is modified to 0.5% by weight or less, so that it is generated in a general steelmaking process. The slag can be made equivalent to the slag to be used, there is no environmental restriction, the range of utilization as a resource is widened, and the added value of the slag can be increased.

[Brief description of the drawings]

FIG. 1 is an overall view of an upper-bottom blow converter applied to a method for reforming a slag of molten stainless steel according to an embodiment of the present invention.

FIG. 2 is a CaO—Al ₂ O ₃ —SiO ₂ system phase diagram.

[Explanation of symbols]

10: top and bottom blown converter, 11: furnace body, 12: lance, 1
3: nozzle, 14: chute, 15: storage hopper, 1
6: Steel tap

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Yoshito Mimura 1-1, Hibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture Inside Nippon Steel Corporation Yawata Works (72) Kenichiro Miyamoto Hibata, Tobata-ku, Kitakyushu-shi, Fukuoka No. 1-1, New Town F-term in Nippon Steel Corporation Yawata Works (reference) 4K001 AA08 AA10 BA13 HA03 4K002 AA03 AB02 AE01 AE06 4K013 AA02 BA02 DA03 DA05 DA08 EA05 EA19 FA06

Claims (4)

[Claims] 1. A slag reforming method for refining molten stainless steel using a refining furnace, wherein the concentration ratio of Al ₂ O ₃ to the basicity of the slag is 10 or more. Slag reforming method. 2. The method according to claim 1, further comprising adding aluminum dross and / or metal Al to said slag. 3. The method according to claim 1, wherein said slag is made of Al ₂ O _3.
A method for reforming slag for smelting stainless steel, comprising adding a content. 4. The method of reforming slag for smelting stainless steel according to claim 1, wherein the total chromium content of the slag after the slag has been modified is 0.5% by weight. A method for reforming slag for smelting stainless steel, comprising: