JP2002363632A - Method for producing low n steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively suppress the cost of electric power as much as possibly on steel making using an electric furnace, and to produce low N steel which has not been produced heretofore. SOLUTION: An iron raw material and a carbonaceous material are charged to an electric furnace 10, and are dissolved to produce a high carbon molten metal 12 having a C content of >=1 wt.%. Further, the produced high carbon molten metal 12 is temporarily stored in a storage furnace 16, and the high carbon molten metal 12 from the storage furnace 16 and scrap are charged to an electric furnace 18, and they are mixed and dissolved to make steel. Further, on the steel making, the feed of oxygen is performed to decarburize the molten steel, and, in accordance with the exhaust of gaseous CO generated on the decarburization, N in the steel is denitrified as gaseous N2 , so that the content of N in the molten steel is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing low N steel.

[0002]

2. Description of the Related Art
As a method for producing molten steel, iron ore and coke are charged into a blast furnace, which are smelted and reduced at a high temperature, and the resulting hot metal having a high C content is transferred to a converter, where it is blown with oxygen to remove it. A so-called blast furnace-converter process in which steel is produced by making charcoal to obtain molten steel, and an electric furnace process in which scrap is melted and made using an electric furnace are widely used. Here, in the electric furnace process, scrap obtained from a scrap car or the like and slag making material such as quicklime are charged into an electric furnace represented by an arc furnace, and electric power is supplied to the electric furnace to melt the scrap.

[0003] In the former blast furnace-converter process, since iron ore is used as a starting material (iron raw material), in addition to the problem that a large amount of energy is required for iron ore reduction in hot metal production, equipment is required. There is a problem that the cost is large and the equipment cost, maintenance cost, and running cost are high. In addition, in the case of this method, the blast furnace operation is a continuous operation, and the hot metal is continuously output from the blast furnace.Therefore, it is substantially necessary to produce only the required amount of hot metal and make steel using it when necessary. There was a problem that it could not be done.

On the other hand, in the latter electric furnace process, scrap is generally used as an iron raw material.
Compared to the case of using iron ore, energy consumption is reduced by the amount of reduction heat for melting, and equipment is relatively simple. Therefore, it has the advantages of low equipment cost, maintenance cost, running cost, and basically Since it is a batch production, there is an advantage that the required amount of molten steel can be produced when necessary according to economic fluctuations.

[0005] In this electric furnace steelmaking operation, the electric power cost accounts for a large proportion of the steel production cost.
In this case, it is possible to reduce the required power cost by performing the electric furnace operation at night when the power cost is low, and this is actually performed. However, it is difficult to always operate the electric furnace only at night, and the fact is that the electric furnace must be operated during the daytime when power costs are high.

[0006] In addition, the following problems have conventionally occurred in electric furnace steelmaking. In electric furnace steelmaking, N as an impurity component enters a molten steel in a large amount, and it is difficult to remove N in electric furnace steelmaking. Therefore, N is compared with steel produced in an electric furnace. There was a problem that many targets were included.

[0007]

SUMMARY OF THE INVENTION The method for producing a low-nitride steel of the present invention has been devised to solve such a problem. According to the first aspect of the present invention, an iron furnace and a carbon material are charged and melted in an electric furnace to produce a high-carbon molten metal having a C content of 1% by weight or more, and the produced high-carbon molten metal is produced. Is temporarily stored in a storage furnace, the high-carbon molten metal and scrap from the storage furnace are charged into an electric furnace for steelmaking, mixed and melted to make steel, and oxygen is supplied during the steelmaking to supply molten steel. It is characterized by performing decarburization, denitrifying molten steel with the discharge of CO gas generated during the decarburization to the outside of the system, and reducing the N of the molten steel.

In a second aspect of the present invention, in the first aspect, the C content in the high-carbon molten metal is set to 2% or more, and the high-carbon molten metal is mixed with the scrap in steel making in the electric furnace. Characterized by being charged at a rate of 30% by weight or more with respect to

A third aspect of the present invention is characterized in that, in any one of the first and second aspects, the low N steel is N: 0.0080% by weight or less.

[0010]

As described above, according to the present invention, an electric furnace is charged with an iron raw material and a carbon material such as breeze or coal and has a C content of 1% or more (1% by weight: the same applies hereinafter). A high-carbon molten metal is manufactured, temporarily stored in a storage furnace, and the high-carbon molten metal and scrap discharged from the storage furnace are charged into an electric furnace for steelmaking, mixed, melted, and made into steel. It was done.

According to the present invention, a high-carbon molten metal can be produced by an electric furnace at night when the electric power cost is low. Steelmaking in an electric furnace can be performed using molten metal.

In this case, since the high-carbon molten metal and the scrap are mixed and melted at the time of steel making in the electric furnace, the latent heat of the high-carbon molten metal, specifically, the heat energy of the high-carbon molten metal and the heat energy during decarburization are obtained. The heat of reaction at the time of CO gas generation can be effectively utilized, so that steel making in an electric furnace can be performed with a small amount of energy.

On the other hand, the high-carbon molten metal can be produced at night when the electric power cost is low, so that the electric power cost required for producing the molten steel can be reduced. This is possible because, in the present invention, the production of high carbon molten metal using an electric furnace, the storage of high carbon molten metal using a storage furnace,
This is because steel is manufactured through each process of steel making in an electric furnace using a high-carbon molten metal.

Here, the reason why the C content is defined as 1% or more as a high-carbon molten metal is as follows: when the C content is less than 1%, the high-carbon molten metal is transferred from the electric furnace to the storage furnace and fixed there. This is because it is virtually impossible to save time.

The melting point of the high-carbon molten metal varies depending on the amount of C contained therein, and the higher the C content, the lower the melting point of the high-carbon molten metal and the harder it becomes. And the time which can be stored in a storage furnace becomes long according to this. In this case, the storage time (storage time including the handling time such as transfer from the electric furnace to the storage furnace or from the storage furnace to the electric furnace) is 1
It takes more than an hour, and according to the study of the present inventors, it has been found that a storage of 1 hour or more is possible with a C content of 1% or more. It is for this reason that the C content is defined as 1% or more in the present invention.

In the present invention, since the high-carbon molten metal is melted and manufactured in an electric furnace, the temperature control of the high-carbon molten metal is easy, and more specifically, the high-carbon molten metal can be discharged at a high temperature. There is. For example, when tapping hot metal that is a high-carbon molten metal from a blast furnace, the tapping temperature is 1300 to 135.
Although it is about 0 ° C., when the high-carbon molten metal is discharged from the electric furnace according to the present invention, it can be discharged at a high temperature of about 1500 ° C. By discharging the high-carbon molten metal at such a high temperature, the time that can be stored in the subsequent storage furnace can be lengthened.

The present invention relates to the production of high-carbon molten metal using an electric furnace, storage in a storage furnace, and the production time and production amount of molten steel in each process of steelmaking in an electric furnace using high-carbon molten metal. There is a feature that can be easily controlled according to the conditions.

In the present invention, oxygen is supplied during steel making using an electric furnace to decarburize the molten steel, and N in the steel is reduced by discharging CO gas generated during the decarburization to the outside of the system. It is characterized in that it is denitrified as N ₂ gas to reduce the N content of the molten steel.

In the present invention, high carbon molten metal and scrap are mixed and melted in an electric furnace to produce steel, so that a large amount of C is contained in the molten steel, and oxygen is supplied there to decarbonize the steel. As a result, C in the molten steel can be reduced to a required level, and at the same time, N in the molten steel can be discharged out of the system, whereby a low-N steel with a small N content can be obtained.

That is, N which cannot be obtained by conventional electric furnace steelmaking
It becomes possible to produce low-level low-N steel. Here, the amount of N ₂ gas discharged from the steel to the outside of the system is the amount of CO
It depends on the amount of gas, and the greater the amount of CO gas generated, the greater the amount of denitrification. That is, the N of the steel is reduced accordingly.

The amount of CO gas generated in this case is determined by the amount of C contained in the high-carbon molten metal and the amount of the high-carbon molten metal charged into the electric furnace for steelmaking. In this sense, in the present invention, the C content of the high-carbon molten metal is set to 2% or more, and the charging amount to the electric furnace for steelmaking is set to 30% or more with respect to the total amount including the scrap. Desirable (claim 2).

Furthermore, the present invention is particularly suitable when applied to the production of low N steel having an N content of 0.0080% or less (claim 3).

[0023]

Embodiments of the present invention will be described below with reference to the drawings. Arc furnace (electric furnace) 10 shown in FIG.
A scrap as an iron raw material and a carbonaceous material (breeze, coal, etc.) were charged into the furnace, and these were arc-melted to obtain a C content of 1%.
% (Preferably 2% or more) of the high-carbon molten metal 12 is produced. The production of the high-carbon molten metal 12 by the arc furnace 10 can be performed at night when the power cost is low.

Next, the high-carbon molten metal 12 thus obtained is poured into a ladle 14 and, as shown in FIG. 1 (II), is supplied to a storage furnace 16, preferably a larger capacity than the arc furnace 10. It is transferred into the storage furnace 16 and stored there. As the storage furnace 16, for example, the high-carbon molten metal 1 from the arc furnace 10 is used.
It is possible to use one having a capacity capable of storing 2 to 8 charges.

During storage by the storage furnace 16, the temperature of the storage furnace 16 can be maintained by a burner or the like, if necessary.
Here, the heat retention is an operation of supplementing the heat radiation from the storage furnace 16 by adding external energy.

Since the arc furnace 10 is used as a furnace in the production of the high carbon molten metal 12, the tapping temperature can be easily controlled. Specifically, the tapping temperature can be as high as about 1500 ° C. By setting the tapping temperature to a high temperature in this way, the time that can be stored in the next storage furnace 16 can be lengthened.

When storing the high-carbon molten metal 12 in the storage furnace 16, the high-carbon molten metal 12 from the arc furnace 10 is simultaneously stored for a plurality of charges. Then, a part of the hot water is taken out of the storage furnace 16, and the hot water is supplied through a ladle 22 to the hot water in FIG.
A separate arc furnace (electric furnace) 1 as shown in I)
8 and the scrap 20 are charged together to perform mixing and dissolution. At this time, the high carbon molten metal 1 from the storage furnace 16 received by the ladle 22 at a stage where the melting of the scrap 20 is less than 30%
2 is preferably charged into the arc furnace 18. The amount of the high-carbon molten metal 12 to be charged is desirably 30% or more based on the total amount combined with the scrap 20.

In the mixing and melting in the arc furnace 18, arc heat is generated by the supplied electric power, and the mixing and melting are performed. At an appropriate point in the mixing and dissolution, as shown in FIG. 2, a lance pipe 24 is inserted deep into the steel bath, and oxygen is blown into the steel bath through the lance pipe 24 to promote decarburization of the molten metal.

The mixing and melting by the arc furnace 18, that is, the steel making process, is usually performed during the daytime when the electric power cost is high. In the steel making process, however, the high carbon molten metal 12 itself has a large amount of thermal energy. In addition, since the heat of reaction of CO generated during decarburization can be effectively used, less external energy is required. That is, mixed melting and steel making can be performed with little energy.

FIG. 3 shows a high carbon molten metal 1 from an arc furnace 10 having a capacity of about 80 t with respect to a storage furnace 16 having a furnace storage amount of 700 t.
2 is a graph showing the storable time when stored (under no heat) under the following conditions in relation to the C content.

<Conditions> Storage furnace shape: φ7 m × length 9 m Refractory thickness: 880 mm Furnace heat dissipation: 15.1 Gcal / day Temperature of molten steel charged in furnace: 1500 ° C. Storage amount in furnace: 700 t Specific heat: 0.2 Mcal / t ・ ℃

Here, the melting point of the high-carbon molten metal 12 changes with the C content. The higher the C content, the lower the melting point and the harder it becomes. This relationship is shown below.

[0033]

The above results show that, considering the required handling time before and after the storage, the C content in the high-carbon molten metal 12 is set to 1% or more, so that the molten metal can be stored in the storage furnace 16 for a substantially effective time. Indicates that it is possible.

As described above, when the high-carbon molten metal 12 and the scrap 20 are mixed and melted in the arc furnace 18 to produce steel, oxygen is supplied through the lance pipe 24 to supply the molten steel C.
And decarburization, the N in the molten steel is also discharged out of the system as N ₂ gas. That is, denitrification from molten steel is performed. The amount of denitrification at that time depends on the amount of generated CO gas. The following shows this point based on actual steelmaking results.

Here, a high-carbon molten metal of C: 4% is produced in the arc furnace 10 and stored in the storage furnace 16, and the high-carbon molten metal from the storage furnace 16 is added to the total amount of the molten metal and the scrap. Arc furnace 18 for steel making at a rate of 40%, 70%
, And mixed and dissolved. At that time, O ₂ was blown through a lance pipe 24 to perform decarburization and denitrification, thereby producing a low-N steel.

Table 1 and FIG. 4 show the operating conditions and the relationship between the amount of generated CO gas and the amount of N in the steel in comparison with the conventional process. However, in FIG. 4, the generated CO gas amount shows only the amount generated from the high carbon molten metal charged in the electric furnace. Here, the conventional process simply means the arc furnace 1
In step 8, the scrap is melted together with the slag-making agent to produce steel. However, in FIG. 4, the generated CO gas amount shows only the amount generated from the high-carbon molten metal charged in the electric furnace.

[0038]

[Table 1]

As described above, by mixing and melting a high-carbon molten metal and scrap in an electric furnace to produce steel, a large amount of CO gas is generated at that time, and accordingly, N In particular, when the high carbon molten metal is blended as much as 70%, the N in the steel is reduced to 0.004% or less, and the low N steel which cannot be obtained by the conventional electric furnace steelmaking is reduced. You can see that it is obtained.

The results also show that N in steel is dramatically reduced by generating CO gas of 50 Nm ³ / t or more during steelmaking. In other words, by adjusting the C amount of the high carbon molten metal and the charging amount to the electric furnace so as to generate the CO gas at such an amount, the molten steel can be drastically reduced in N2.
You can see that it can be converted.

Although the embodiments of the present invention have been described in detail above, this is merely an example, and the present invention can be implemented in variously modified forms without departing from the gist thereof.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a method for producing a low-N steel according to the present invention.

FIG. 2 is a diagram illustrating a process following FIG. 1;

FIG. 3 is a diagram showing a relationship between a carbon concentration of a high-carbon molten metal and a storable time during storage in the storage furnace of FIG. 1;

FIG. 4 is a diagram showing the relationship between the amount of CO gas generated during steelmaking using an electric furnace and the amount of N in molten steel.

[Explanation of symbols]

 10, 18 Arc furnace (electric furnace) 12 High carbon molten metal 16 Storage furnace 20 Scrap 24 Lance pipe

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Atsushi Hattori 39 Motomoto-cho, Tokai City, Aichi Prefecture F-term in the Chita Plant of Daido Steel Co., Ltd. (Reference) 4K012 CA04 CA05 CA09 4K013 AA01 BA02 CA04 CA11 CA15 CD02 CF12 FA02 4K014 CA03 CB01 CC01 CD18

Claims (3)

[Claims] An iron furnace and a carbon material are charged and melted in an electric furnace to produce a high-carbon molten metal having a C content of 1% by weight or more, and the produced high-carbon molten metal is temporarily stored in a storage furnace. Storing,
The high-carbon molten metal and the scrap from the storage furnace are charged into an electric furnace for steelmaking, mixed and melted to make steel, and oxygen is supplied during the steelmaking to decarbonize the molten steel,
A method for producing low-N steel, comprising: denitrifying molten steel with the discharge of CO gas generated during the decarburization to the outside of the system to reduce the N of the molten steel. 2. The high-carbon molten metal according to claim 1, wherein the C content in the high-carbon molten metal is 2% or more, and the high-carbon molten metal is used in steelmaking in the electric furnace at a weight of 30% with respect to the total amount of the scrap. %. A method for producing low-N steel, characterized by charging at a rate of at least%. 3. The method for producing a low N steel according to claim 1, wherein the low N steel is N: 0.0080% by weight or less.