JP2003147430A - Reducing agent for steelmaking, and steelmaking method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the oxides of alloying elements such as manganese oxide, chromium oxide and iron oxide in slag during oxygen blowing in the steelmaking refining process. SOLUTION: A reducing agent for steelmaking, consisting of formed bodies of a mixture prepared by mixing a carbon source with a deoxidizer containing metal for deoxidation, is added to slag during the blowing of gaseous oxygen, by which the iron oxide, manganese oxide and chromium oxide contained in the slag can be reduced. As to this reducing agent for steelmaking, the reduction of the above oxides can be promoted, e.g. by blending the carbon souse in such a way that the amount of oxygen with which carbon in the carbon source is combined at primary combustion is larger than the amount of oxygen with which the above metal for deoxidation is combined when completely oxidized, using one or more kinds among coal and plastics as the carbon source and also using one or more kinds among aluminum dross, metal aluminum, metallic silicon and ferrosilicon as the deoxidizer.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a reducing agent used for steel refining and a steelmaking method using the reducing agent.

[0002]

2. Description of the Related Art In order to manufacture a steel product from hot metal produced in a blast furnace or iron scrap in the market, it is necessary to go through a steel refining process. In this steelmaking refining process, oxidation refining using oxygen is performed in order to remove impurities contained in hot metal and iron scrap and to raise the metal temperature. or,
At the same time, the alloying components such as manganese and chromium, which are necessary for the material properties of steel products, are adjusted.

Conventionally, alloy components such as manganese and chromium have been adjusted with ferromanganese (Fe--Mn alloy) and ferrochromium (Fe--Cr alloy), etc., but in recent years, manganese ore, chromium ore, etc. In the steel refining process, the above oxide was added and reduced by the carbon contained in the hot metal, so that a steelmaking method in which alloy iron was saved was adopted. In particular, since manganese is an essential component of steel products, manganese ore is widely added.

However, in the steelmaking refining process of hot metal in the converter, it is necessary to remove carbon in the hot metal, which is one of the impurities, and oxygen blowing increases the oxidation degree of slag existing in the furnace. . As the degree of slag oxidation increases, manganese and chromium, which have a stronger affinity for oxygen than iron, are preferentially oxidized and migrate into the slag, reducing the reduction yield of manganese ore and chromium ore.

Therefore, in order to increase the concentration of these alloy components to a predetermined concentration by adding ore, a large amount of ore must be added, and as a result, not only the economical disadvantage due to the low reduction yield is caused. However, there is a problem that the refractory material in the furnace increases in wear due to the increase in the treatment time and the increase in the amount of slag due to the addition of a large amount of ore, and the long-term stable operation is not achieved due to this.

[0006]

Conventionally, as a method for recovering alloying elements such as manganese and chromium existing in the form of oxide in slag, ferrosilicon (Fe-Si alloy) etc. after completion of oxygen blowing. There is only a method of adding the deoxidizing metal of slag to the slag and reducing it, and during the oxygen blowing in the steelmaking refining process, that is, while performing the oxidative refining with oxygen, the alloy such as manganese and chromium in the slag. A method for actively recovering the element has not been proposed yet.

The method of adding the deoxidizing metal after completion of the oxygen blowing has a problem that the refining time is extended. In the conventional steelmaking method in a converter,
Carbonaceous materials such as high-purity graphite are added to the slag from the furnace opening during oxygen blowing, but this is to form the slag and stabilize the operation. However, nitrogen and sulfur contained in the carbonaceous material are limited to a small addition amount within the range that does not cause a problem in the composition of the steel material, and there is no method for positively recovering alloying elements such as manganese and chromium in slag. It is different. Also, there is a limit to reducing oxides such as chromium in slag with carbon materials alone,
It cannot be fully reduced.

The present invention has been made in view of such circumstances, and an object thereof is to oxidize alloying elements such as manganese oxide and chromium oxide in slag during oxygen blowing in a steelmaking refining process. It is an object of the present invention to provide a reducing agent for steelmaking and a steelmaking method capable of reducing a substance and an iron oxide.

[0009]

The reducing agent for steelmaking according to the first invention of the present application for solving the above-mentioned problems comprises a carbon source,
The reducing agent for steelmaking according to the second invention is characterized in that it is produced by mixing a deoxidizing agent containing a deoxidizing metal and molding the mixture. The amount of oxygen bound during the primary combustion of carbon of the carbon is larger than the amount of oxygen bound when the deoxidizing metal is completely oxidized, and is characterized in that the carbon source is blended. The steelmaking reducing agent according to the third invention is the reducing agent for steelmaking according to the first invention or the second invention, wherein the carbon source is at least one of coal and plastic, and the deoxidizing agent is aluminum dross, metal. It is one or more kinds of aluminum, metallic silicon, and ferrosilicon, and the reducing agent for steelmaking according to the fourth invention is the reducing agent for steelmaking according to the third invention, wherein the coal is
It is characterized by containing 4 mass% or more of volatile components.
The reducing agent for steelmaking according to the invention in the third invention is characterized in that, in the third invention, the plastic is a waste plastic material generated in a plastic manufacturing process or a plastic processing process, or a waste plastic generated after a plastic product is used. The steelmaking reducing agent according to the sixth invention is characterized in that, in the third invention, the aluminum dross contains 25 mass% or more of metallic aluminum.

In the steelmaking method according to the seventh invention, the reducing agent for steelmaking according to any one of the first invention to the sixth invention is added to the slag during the blowing of gaseous oxygen, and the steelmaking method is used. It is characterized by reducing one or more of iron oxide, manganese oxide and chromium oxide contained in the slag with a reducing agent.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic cross-sectional view of converter equipment used when carrying out the steelmaking method according to the present invention.

The hot metal 5 discharged from the blast furnace is received in a hot metal carrying container such as a hot metal ladle and subjected to preliminary treatments such as desiliconization, desulfurization and dephosphorization, and then charged into the converter 1. . In the converter 1, mainly in order to remove carbon in the hot metal 5, oxidative refining is carried out by feeding acid from the upper blowing lance 2. A bottom blowing nozzle 4 for stirring the molten pig iron 5 is installed in the converter 1 and has a structure in which an inert gas such as gaseous nitrogen or Ar is blown. Instead of the top blowing lance 2, a bottom blowing tuyere (not shown) similar to the bottom blowing nozzle 4 may be installed to feed acid from this bottom blowing tuyere, or an inert gas for stirring may be used. It is not always necessary to install the bottom blowing nozzle 4 for blowing.

In steel refining using such converter equipment, manganese ore is added to the converter 1 for the purpose of reducing the amount of ferromanganese used, and the manganese ore is reduced by the carbon in the hot metal 5. The amount of manganese ore added varies depending on the type of steel product that is finally manufactured,
2-15 kg per ton of hot metal (hereinafter referred to as "kg
"/ T").

By starting the blowing of oxygen from the upper blowing lance 2, the decarburization reaction of the hot metal 5 proceeds, and at the same time, iron oxide is also produced and the hot metal temperature rises. During this oxygen blowing,
From the early stage to the middle stage of blowing, manganese ore is continuously or intermittently added to the furnace to melt the manganese ore and promote reduction by carbon in the hot metal. Since the slag 6 is generated due to the SiO ₂ contained in the manganese ore by melting / reducing the manganese ore, in order to adjust the basicity (CaO / SiO ₂ ) of the slag 6, before adding the manganese ore Alternatively, a flux such as quick lime containing CaO as a main component is added during the addition.

By continuing the oxygen blowing in this way, the carbon concentration in the hot metal 5 gradually decreases, and at the same time, the reduction of the manganese ore proceeds and the manganese concentration in the hot metal 5 gradually increases. However, the middle to late stages of oxygen blowing
That is, in the region where the carbon concentration in the hot metal 5 is reduced to approximately 0.6 mass% or less, the decarburization rate becomes slow and the slag 6
And the manganese remains in the slag 6 in the form of MnO according to the degree of oxidation of the slag 6. In this case, the higher the degree of oxidation of the slag 6, the higher the MnO concentration in the slag 6. The oxidation degree of the slag 6 depends on the iron oxide concentration in the slag 6, and the higher the iron oxide concentration, the higher the slag oxidation degree.

Therefore, at the end of blowing, the upper blowing lance 2
The amount of acid to be fed from the slag 6 is reduced to preferentially cause the decarburization reaction and suppress the oxidation of manganese, but further, forcibly promoting the reduction of MnO in the slag 6, the raw material charging device 3 is used. The reducing agent 7 for steelmaking is added to the furnace via the above. The steelmaking reducing agent 7 is manufactured by mixing a carbon source and a deoxidizing agent containing a deoxidizing metal, and molding the mixture.

As the deoxidizing agent constituting the reducing agent 7 for steelmaking, the kind of steel to be produced, the economical efficiency, etc., from aluminum dross, metallic aluminum, metallic silicon, ferrosilicon, etc. which are generated during the smelting or melting of aluminum. In consideration of the above, the optimum one can be used. However, when the content of metallic aluminum in the aluminum dross is small, it is difficult to promote the reduction reaction, so at least 25
It is preferable to use aluminum dross containing mass% or more.

As a carbon source constituting the steelmaking reducing agent 7, carbonaceous materials such as coal, coke and graphite, and plastics can be used. In particular, coal contains a volatile component, and the volatile component stirs the slag 6 to accelerate the reduction reaction. Therefore, it is preferable to use coal among the carbonaceous materials. However, in this case, if the amount of volatile components is small, the stirring effect cannot be expected. Therefore, it is preferable to use coal containing 4 mass% or more of volatile components. As the plastic, basically any plastic can be used, but from the economical viewpoint, it is a plastic waste material generated in the plastic manufacturing process or the plastic processing process, or a waste plastic generated after the use of the plastic product. Is preferably used. As a matter of course, the carbonaceous material and the plastic may be mixed and used.

Most of the plastics have thermoplasticity, and when they are stirred and mixed with a deoxidizing agent, or when they are stirred and mixed with a deoxidizing agent while being heated, the plastic is semi-melted or melted and functions as a binder. When a plastic is used, a molded product can be produced without adding a special binder. From the viewpoint of treating plastic waste, it is preferable to use plastic as a carbon source. In this case, when the plastic compounding amount is 2 to 40 mass%, it is molded into a briquette,
When it exceeds 40 mass%, the composition can be molded by extrusion molding, so that the plastic content can be widely adjusted. In addition, when only carbonaceous material is blended as a carbon source and when the plastic content is 1 mass% or less, an organic or inorganic binder is required,
It is molded into a briquette with an appropriate blending amount. Even when carbonaceous materials are blended as the carbon source, the blending ratio of the carbon source is 1 to 9
It can be any value of 9 mass%.

The reducing agent for steelmaking 7 produced in this way
Is added during oxygen blowing, the reduction of the iron oxide in the slag 6 and MnO 2 by the deoxidizing metal which is a strong deoxidizing agent.
Reduction occurs. At the same time, the reduction of the slag 6 is further promoted by the carbon component in the carbon source. That is, direct reduction of iron oxides and MnO in the slag 6 by carbon in the carbon source and indirect reduction by CO gas generated by the primary combustion of carbon occur, and further gasification of the carbon source (CO The slag 6 is stirred by the gas and volatile components), and the reduction reaction by the deoxidizing metal is efficiently performed.

The gas generation due to this carbon source is extremely effective in reducing the oxides in the slag 6, and therefore,
From the viewpoint of accelerating the gasification reaction of the carbon source, the particle size of the carbonaceous material used as the carbon source is preferably as fine as possible, and it is particularly desirable to use the carbonaceous material having a particle diameter of 10 mm or less.

Further, the reduction efficiency can be enhanced by optimizing the reaction by the deoxidizing metal, that is, the association between the deoxidizing metal and oxygen, and the reaction by the carbon source, that is, the association between the carbon source and oxygen. Therefore, the carbon source is blended so that the calculated amount of oxygen bound to the carbon in the carbon source during the primary combustion is greater than the calculated amount of oxygen bound when the deoxidizing metal is completely oxidized. Preferably. In other words, the compounding ratio of the carbon source and the deoxidizing metal is determined so that the chemical equivalent of the carbon source to oxygen is larger than that of the deoxidizing metal. Here, the primary combustion is a reaction in which carbon reacts with oxygen and the like in the slag to generate CO gas.

The steelmaking reducing agent 7 is added in the latter half of oxygen blowing when the degree of oxidation of the slag 6 becomes high. By doing so, the peroxidation of the slag 6 can be suppressed, it is effective for the reduction reaction, the total manganese recovery can be increased, and the amount of the steelmaking reducing agent 7 used can be reduced. When the steelmaking reducing agent 7 is added at a time when the degree of oxidation of the slag 6 is low, it is burned uselessly and its effect is not exhibited.

The above explanation is for the case where the reducing agent for steelmaking of the present invention is used in the steelmaking refining process of carbon steel.
The reducing agent for steelmaking according to the present invention can be used also in the steelmaking refining process of high manganese steel or stainless steel having a manganese content of several mass% to several tens mass%. In the case of high manganese steel, high carbon ferromanganese is added to adjust the manganese content of the molten metal to a predetermined value, and then the reducing agent for steelmaking of the present invention can be used when deoxidizing by feeding acid. .
In addition, the method of using the reducing agent for steelmaking in the stainless steelmaking method is basically the same as the steelmaking refining process of carbon steel, except that the reduction target is chromium instead of manganese. A used in the steel refining process of stainless steel
In the OD furnace, the amount of oxygen fed for decarburization is reduced as the oxygen blowing progresses (the amount of carbon in the molten metal decreases). At that time, Ar is increased instead of gaseous oxygen. When the slag becomes a peroxidized state during smelting, a reducing agent for steelmaking is added to promote the reduction of chromium in the slag. In the AOD furnace, since the gaseous oxygen is diluted with a large amount of Ar and the deviation from the equilibrium in the reaction of carbon is easily controlled, it is possible to use a reducing agent for steelmaking having a large carbon source content.

Further, the present invention can be applied to any steel-making refining process involving acid feeding, without being limited to the above converter and AOD furnace. For example, an electric furnace, a burner melting furnace using oxygen or air, a reflux degassing process represented by RH performing blowing under vacuum, and a bath represented by VOD performing blowing under vacuum. The present invention can be applied to a surface degassing process or the like.

[0026]

Example 1 The hot metal tapped from the blast furnace was subjected to desiliconization treatment in the blast furnace casting bed and dephosphorization treatment in the converter, and then decarburization treatment in the converter. In the decarburization treatment step in this converter, a test with the addition of the steelmaking reducing agent according to the present invention and a test without it were carried out,
The effects of iron and manganese concentration in the slag after decarburization treatment and the effect on the manganese concentration in metal were compared and investigated.

In all the tests, the silicon concentration in the hot metal after desiliconization was lowered to 0.06 mass% and the phosphorus concentration in the hot metal after converter dephosphorization was lowered to 0.012 mass%. The hot metal after the dephosphorization treatment was once discharged from the converter to a ladle, and then charged into another converter to carry out oxidation refining for the purpose of decarburization.

The converter used had a capacity of 250 tons, and manganese ore was added to the converter as a manganese source in the initial stage of blowing. The manganese ore used had a manganese concentration of 48 mass%,
The SiO ₂ concentration is 4 mass% and is 1 as pure manganese.
0 kg / T manganese ore was added. At that time, in order to prevent the decrease of the slag basicity due to SiO ₂ supplied from the manganese ore, quicklime is added to adjust the slag basicity to 3.
Adjusted to 3.

[0029] Then, while stirring the hot metal by blowing a gaseous nitrogen or Ar of the converter bottom bottom blowing each per hot metal tons from the nozzle of the unit 0.12 nm ³ (hereinafter referred to as "Nm ³ /min.T"), the upper Oxygen was blown from the blowing lance. The acid transfer rate is
From blowing early to 11 minutes 3.1Nm ³ /min.T, since 11 minutes was 2.0Nm ³ /min.T. The end point of this decarburization treatment step was the point when the carbon concentration in the molten steel reached 0.05 mass%, and the molten steel temperature at that time was set to 1650 ° C.

The reducing agent for steelmaking used was a mixture of aluminum dross containing 50 mass% of metal aluminum and waste plastic, and the ratio of the amount of aluminum dross to the amount of waste plastic was 0.35. And was added 11 minutes after the start of blowing. 5kg / T, 10kg / T, 15kg / T, 20 per ton of hot metal
There were 4 levels of kg / T.

Table 1 shows the test conditions and test results in each test. As is clear from Table 1, the addition of a steelmaking reducing agent consisting of a deoxidizer and a plastic
It was possible to greatly reduce the iron oxide in the slag, that is, to greatly reduce the degree of oxidation of the slag. As a result, manganese oxide in the slag was also reduced, manganese loss was reduced, and the manganese concentration of the metal could be increased. Also, there is no pickup of phosphorus in the metal,
The amount of slag could be reduced, and, despite the increase in the amount of heat consumed in the reduction reaction, there was no decrease in the heat margin, and the treatment end temperature could be set to a predetermined value. In the remarks column of Table 1, examples of the present invention are shown for tests in which a reducing agent for steelmaking is added, and examples of conventional examples are shown for other tests.

[0032]

[Table 1]

Example 2 A stainless steel crude molten metal produced in an electric furnace was decarburized in an AOD furnace.
In this decarburization process, a test in which the reducing agent for steelmaking according to the present invention was added and a test in which it was not added were carried out, and the effects on the chromium concentration in the slag and the chromium concentration in the metal after treatment were compared and investigated. The AOD furnace used had a capacity of 120 tons, and the lower wall surface of the molten metal inside the furnace had a double tube tuyere capable of blowing gaseous oxygen and Ar.

In all the tests, the oxygen flow rate was 1.0 Nm ³ /min.T at the start of blowing, and the ratio of oxygen gas to Ar (oxygen / Ar) was about 3 to 2 as the blowing progressed. 1,
It was decreased in order of 1/2 and 1/3. The initial molten metal had a chromium concentration of 18.0 mass% and a nickel concentration of 7.0 mass.
%, Carbon concentration 1.4 mass%, silicon concentration 0.8 mass%
Met.

Ferrosilicon was used as the deoxidizing agent for the reducing agent used for steel making, and the levels of carbon were changed to two levels: waste plastic (A) and coal (B). The mass ratio of ferrosilicon in the reducing agent for steelmaking was fixed at 25 mass%. Further, quick lime was added to adjust the slag basicity to about 1.4 in order to prevent a decrease in the slag basicity due to SiO ₂ supplied from a reducing agent for steelmaking.

Blowing is carried out for 10 minutes to 1 minute before the end of blowing while adding a reducing agent for steelmaking,
Blowing was performed until the carbon concentration in the molten stainless steel reached 0.03 mass%. The temperature of the molten stainless steel at the end of blowing is 17
The target was 20 ° C.

Table 2 shows the test conditions and test results in each test. As is clear from Table 2, by adding a reducing agent for steelmaking composed of a deoxidizer and a plastic,
It was possible to reduce the chromium loss to the slag at the end of the treatment.

[0038]

[Table 2]

Further, for example, in the case of using a steelmaking reducing agent (ferrosilicon: 2.5 kg / T) of 10 kg / T at the time of blowing, the chromium concentration in the slag is reduced,
As the amount of slag-reducing ferrosilicon at the time of adjusting the final component could be reduced from 8 kg / T in the conventional example to 3 kg / T, by using the steelmaking reducing agent of the present invention, during blowing and blowing. The total amount of ferrosilicon used after smelting could be reduced compared to the conventional example. In the remarks column of Table 2, examples of the present invention are shown for tests in which a reducing agent for steelmaking is added, and examples of conventional examples are shown for other tests.

[0040]

According to the present invention, in the steel refining process, it becomes possible to reduce the oxides of iron and the alloying elements such as manganese oxide and chromium oxide in the slag during the blowing of oxygen. , Resource saving and energy saving are achieved and the amount of generated slag can be reduced, etc.
Industrially beneficial effects are brought about.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of converter equipment used when carrying out a steelmaking method according to the present invention.

[Explanation of symbols]

1 converter 2 Top blowing lance 3 Raw material charging device 4 bottom blowing nozzle 5 hot metal 6 slugs 7 Steelmaking reducing agent

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tomoo Izawa             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. F-term (reference) 4K013 EA19 EA28 EA30                 4K070 AB04 AC02 BB08 BC01

Claims (7)

[Claims] 1. A reducing agent for steelmaking, which is produced by mixing a carbon source and a deoxidizing agent containing a deoxidizing metal and molding the mixture. 2. The carbon source so that the amount of oxygen bound to the carbon in the carbon source during primary combustion is greater than the amount of oxygen bound to the deoxidizing metal when it is completely oxidized. The reducing agent for steelmaking according to claim 1, wherein: 3. The carbon source is at least one of coal and plastic, and the deoxidizer is one of aluminum dross, metallic aluminum, metallic silicon, and ferrosilicon.
It is 1 or more types, The reducing agent for steelmaking of Claim 1 or Claim 2 characterized by the above-mentioned. 4. The reducing agent for steel making according to claim 3, wherein the coal contains 4 mass% or more of a volatile component. 5. The reduction for steel manufacturing according to claim 3, wherein the plastic is a waste plastic material generated in a plastic manufacturing process or a plastic processing process, or a waste plastic generated after a plastic product is used. Agent. 6. The reducing agent for steel making according to claim 3, wherein the aluminum dross contains 25 mass% or more of metallic aluminum. 7. An iron contained in the slag by the reducing agent for steelmaking according to claim 1 added to the slag during the blowing of gaseous oxygen. A steelmaking method comprising reducing one or more of oxides, manganese oxides, and chromium oxides.