JPH0478686B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a steel manufacturing method in which a large amount of solid iron-containing cold material such as cold pig iron or scrap is melted and then oxygen-blown in a converter. be.

(Prior technology) In general converter refining, hot metal supplied from a blast furnace is used as the main raw material, a relatively small amount of scrap is added to it, and a slag-forming agent and a high flow rate of oxygen are supplied to produce oxygen. It is common to perform blowing. In this conventional case,
Due to heat source constraints, the amount of scrap in the total raw material charge is at most 35%, and it cannot be said that this method allows for the use of a large amount of scrap.

Regarding this point, conventionally, as a steelmaking method in which a large amount of iron-containing cold material, mostly scrap or cold pig iron, is used for refining in a converter, an oxygen top blowing device as proposed in Japanese Patent Publication No. 60-34605 has been proposed. An oxygen top-bottom blowing converter furnace equipped with a carbon material introduction nozzle installed at the bottom of the furnace is used to refine 10 to 30% excess molten steel per heat from scrap, and the excess molten steel is used for the next heat. Some types of hot water are left in the furnace as a seed hot water for charging and refining scrap in the next heat.

However, this method uses the same converter for melting and refining, and then sequentially uses the remaining molten steel as a seed metal. As a result, the sulfur content in the large amounts of coal or coke used in the carbonaceous material is absorbed into the molten steel. enter.

There is a wide range of temperature changes from scrap melting to decarburization refining, and the high temperatures during the tapping stage result in a short refractory life.

Since the refining is carried out almost continuously from melting to the end of blowing, it takes a long time, and therefore more pyrolyzed hydrogen from propane, etc. used to protect (cool) the bottom blowing tuyere is absorbed into the molten steel.

It is said that there is a drawback.

As a means to solve these drawbacks,
No. 60-174812 is proposed. This method attempts to eliminate the above drawbacks by performing the process of melting the iron-containing cold material using seed water and the process of refining the melted material in separate converters. Two types of converters are used, and one converter (converter exclusively for melting) in which the seed metal exists is filled with iron-containing cold material,
The basic feature is to obtain high carbon molten iron by supplying carbonaceous material and oxygen, and then oxygen blowing this molten iron in another converter (a converter exclusively for refining) to obtain molten steel with the required composition. Specifically, the iron-containing cold material, carbonaceous material, and oxygen are supplied to a melting-only converter in the presence of seed water, the iron-containing cold material is melted to obtain high-carbon molten iron, and the melting-only converter is tilted. A part of the molten iron is extracted into a ladle, and the remaining molten iron is left as a seed liquid in the melting converter, where iron-containing cold material, carbon material, and oxygen are again supplied to melt the iron-containing cold material and create a high carbon content. Obtaining molten iron, repeating the operation of tilting the melting converter again and extracting a portion of the molten iron into the ladle, and finally removing the entire amount of high carbon molten iron in the melting converter. By discharging into a ladle different from the ladle, the amount of high carbon molten iron required for smelting and seeding is obtained.

Next, if there is molten slag generated in the melting converter, it is discharged.

The high carbon molten iron discharged into the ladle is then charged into a separate converter exclusively for refining, where it is oxygen blown and refined using conventional steelmaking methods to produce molten steel with the desired composition. It is refluxed to an empty melting converter as a seed water at the start of operation.

(Problems to be solved by the invention) As described above, the method proposed in JP-A-60-174812 is
High-carbon molten iron is produced in an amount equal to the total amount of seed metal at the start of the next heat operation in the converter exclusively for melting and the amount required in the converter exclusively for refining in the next process, and is returned to the converter exclusively for melting and refined. In order to supply the melt to the dedicated converter, the converter dedicated to melting must be tilted multiple times (specifically, three times), which poses a problem that the melting processing time becomes longer.

Furthermore, when starting the operation of the next heat, the molten iron temporarily stored in the ladle must be charged into the converter exclusively for melting as a seed metal, further prolonging the melting process time.

Furthermore, since the molten slag generated in the melting converter is discharged, there is no molten slag at the beginning of melting the iron-containing cold material in the next heat, and iron dust is not scattered until melting progresses and molten slag is formed. There is a problem that the yield of molten iron is severely reduced.

The present invention provides a converter steel manufacturing method that improves melting efficiency by shortening the melting treatment time, and also improves the yield of molten iron by preventing scattering of iron dust.

(Means for Solving the Problems) The present invention melts the iron-containing cold material by supplying iron-containing cold material, carbon material, oxygen, and slag-forming material to a melting-only converter in which seed water and molten slag exist. In the converter steelmaking method, which obtains high carbon molten iron and uses this molten iron as raw material to oxygen blow in another converter exclusively for refining to obtain molten steel with the required composition, the required refining amount in the converter exclusively for refining and the converter exclusively for melting are determined. Obtain high carbon molten iron in the total amount of required seed molten metal in the furnace,
The required refining amount of high carbon molten iron from the converter exclusively for melting in the converter exclusively for refining is subjected to oxygen refining by tapping once, while the remaining amount of seed metal of the high carbon molten iron is left in the converter exclusively for melting. In addition to being used as a seed water for melting the iron-containing cold material, all or part of the molten slag present in the converter exclusively for melting from which the above-mentioned total amount of high-carbon molten iron was obtained is left in the converter exclusively for melting to melt the iron-containing cold material. This is a converter steel manufacturing method characterized by using molten slag to prevent iron dust from scattering during cold material melting.

High carbon molten iron in the present invention refers to carbon content 2
% or more of molten iron.

According to the method of the present invention, the required amount of high-carbon molten iron in the refining converter can be obtained by tapping the iron once, that is, by performing only one tilting operation of the melting converter in which excess melt has been melted. The remaining amount of seed hot water of carbon molten iron is left in the melting converter and used as seed hot water for melting iron-containing cold materials. This eliminates the need for two or more tilt furnace operations, and eliminates the need to charge molten iron from a ladle into a converter dedicated to melting, which is required as a seed metal at the start of the next melting heat. The time is reduced and the dissolution efficiency is improved.

Further, according to the present invention, a ladle for storing seed hot water is also unnecessary, and the manufacturing cost of high carbon molten iron can be reduced.

Furthermore, according to the present invention, during the melting operation of the ferrous cold material, molten slag is always present from the initial stage of melting to prevent the scattering of iron dust during the melting of the ferrous cold material. Compared to the method proposed in JP-A No. 60-34605, the amount of iron dust scattered during the iron-containing cold material melting process is significantly reduced, and the yield of molten iron can be improved.

Although the invention disclosed in Japanese Patent Publication No. 60-34605 is different from the method of using two types of converters with different functions, which is the object of the present invention, Table 1 of the examples shows The process of supplying scrap, carbonaceous material, and oxygen into an oxygen top-bottom blowing converter is repeated twice to obtain high carbon molten iron, and the converter is tilted to place a portion of the molten iron into a ladle for the next heat. In addition to tapping as a seed hot water, scrap, carbonaceous material, and oxygen are newly supplied to the converter where the remaining molten iron remains to melt the scrap, and then oxygen blowing is performed to make molten steel with the required components and the entire amount is tapped. However, a method is disclosed in which the molten iron in the ladle is charged as seed water into the converter after tapping,
In addition to tapping the steel, a tilting furnace operation is required to tap the seed tap.
Two tilt furnace operations are required, and the molten iron in the ladle must be charged into the converter at the start of the next heat operation.
Similar to No. 2, it has the disadvantage that the scrap melting and refining treatment time, especially the melting treatment time, is long.

Furthermore, Table 2 of the Examples in the same publication shows a method in which the seed metal is left in the furnace, and this method has the same number of tilting furnaces as the present invention; Since the entire amount including the oxidized steel is refined into steel, there is a drawback that the amount of oxygen used is large and the steel manufacturing cost is high. Therefore, Japanese Patent Publication No. 60-34605 and the present invention are different.

Furthermore, according to JP-A No. 59-23808, it has a process dedicated to melting the seed metal called a repeat cycle, and a process for refining it into molten steel called a production cycle, and the two seed metals obtained by the above repeat cycle and tapped. ,1
It is proposed that one be subjected to the next repeat cycle and the other to the manufacturing cycle. and,
In this case, it is shown that the seed water is poured over iron-containing cold materials such as scrap. In contrast, the method of the present invention requires the seed metal to remain in the converter exclusively for melting, does not have the so-called production cycle of refining iron-containing cold material into molten steel all at once, etc.
This is fundamentally different from No. 59-23808.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a process diagram showing an embodiment of the present invention. Reference numeral 1 denotes a converter exclusively for melting, which has, for example, an oxygen top blowing lance 2 and a tuyere 3 at the bottom of the furnace, in which carbonaceous materials such as coal and coke are blown together with a non-oxidizing carrier gas (for example, nitrogen gas). , an oxygen top-bottom blowing converter configured to be able to blow oxygen and a non-oxidizing gas (for example, LPG) for cooling. 4
is another converter exclusively for refining, for example, it has an oxygen top-blowing lance 5 and a tuyere 6 for blowing an inert gas for stirring molten iron, such as carbon dioxide, into the bottom of the furnace. It is a furnace.

A seed bath 7 (a part of the high carbon molten iron obtained by melting the scrap described later is left in the furnace) and a molten slag 12 (a part of the high carbon molten iron obtained by melting the scrap described later) shown in FIG. All or part of the generated molten slag remains in the furnace)
Scrap 8 and limestone 13 as a slag material are charged into the converter 1, and carbon material and oxygen are supplied from the tuyere 3, and oxygen is supplied from the lance 2 to prevent the scattering of iron dust from the molten slag 12. The scrap 8 is carbonized and melted while being prevented. When the scrap 8 is melted, new scrap and limestone are charged into the furnace, and the same process of carburization and melting is carried out multiple times, for example twice,
As shown in FIG. 1b, high-carbon molten iron, for example, 3.5% carbon content, is obtained in the total amount of the seed metal and the amount required in the subsequent converter 4 exclusively for refining.

Next, as shown in Fig. 1c, the melting converter 1 is operated to reduce the amount of iron dust scattered from the required amount (total amount of scrap charged in multiple batches) in the refining converter 4. At the same time, the remaining amount of high carbon molten iron is left in the melting converter 1 and used as a seed molten metal for scrap carburization in the next heat. Use as 7.

Next, as shown in Fig. 1d, after erecting the converter 1 for melting, all of the molten slag is left in the converter 1 for melting without removing the slag by tilting furnace operation, and the molten slag is left in the converter 1 for scrap in the next heat. Alternatively, the melting converter 1 can be used as the molten slag 12 to prevent iron dust from scattering during melting, or the melting converter 1 can be operated from the upright position shown in Fig. 1 d in the opposite direction to that used when tapping the melt, as shown in Fig. 1 e. A part of the molten slag is poured into the ladle 14, and the remaining part is left in the melting converter 1, and the melting converter 1 is erected as shown in Fig. It is used as molten slag 12 to prevent iron dust from scattering.

FIG. 2 shows the relationship between the amount of molten slag at the start of melting of the iron-containing cold material, that is, the amount of initial molten slag, and the amount of iron dust scattered during the melting process, based on research conducted by the present inventors. More information on carbon content
29 tons of scrap and 1 ton of limestone were charged into the melting converter 1 in the presence of 84 tons of 3.5% molten iron and 0 to 4 tons of molten slag. Supplied from top blowing lance 2,
The above-mentioned scrap was first melted, and then 58 tons of scrap and 2 tons of limestone were additionally charged into the converter 1, which had been completely melted, and the coal was similarly fed from the bottom tuyere 3.
Supplying oxygen from the bottom tuyere 3 and top blowing lance 2,
The above-mentioned additionally charged scrap was melted, and 29 tons of scrap and 1 ton of limestone were additionally charged into the converter 1, which had been completely melted, and in the same way, coal was introduced from the bottom tuyere 3 and oxygen was transferred from the bottom tuyere. The initial molten slag amount is 0 to 4 tons when the additionally charged scrap is carburized and melted to obtain molten iron with a carbon content of 3.5%, and the iron from the three melting steps described above. It shows the relationship with the amount of dust scattering.

Figure 2 shows that when molten slag is present at the start of melting, the amount of iron dust scattered is significantly reduced compared to when it is not present, and it is clear that molten slag has the function of preventing iron dust from scattering. It is. It is also clear that under these investigation conditions, the initial amount of molten slag is preferably 1.5 tons or more.

In Fig. 1, the high carbon molten iron obtained in the ladle 9 is transferred to a converter dedicated to refining, as shown in Fig. 1g.
While stirring the molten iron by introducing carbon dioxide gas through the tuyere 6, oxygen is supplied from the top blowing lance 5 to perform decarburization and refine into molten steel with the required composition.
Steel is tapped into a ladle 10 as shown in Figure h.

If the sulfur content of the carbon material used in the melting converter 1 is high and the sulfur content of the molten iron discharged into the ladle 9 is high, the molten iron in the ladle 9 will have a high sulfur content as shown in Figure 1i. It is also possible to add a desulfurizing agent and perform the desulfurization treatment by stirring, for example, with an impeller 11, and then supply the desulfurized molten iron to the converter 4 exclusively for refining.

In addition, as the refining converter 4, an oxygen top-blowing converter,
An oxygen bottom blowing converter, an oxygen top and bottom blowing converter, etc. can be used.

Construction examples of the present invention and conventional examples will be described below.

First, to explain the construction example, the total amount of seed hot water is 84 tons, and the required amount for converter 4 for refining is 116 tons.
FIG. 3 shows an example of the operation pattern of the melting converter 1 shown in FIG. 1 when obtaining 200 tons of molten iron with a carbon content of 3.5%. For more information, see Molten iron with 3.5% carbon content
84 tons of molten slag, 29 tons of scrap and 1 ton of limestone were charged into the converter 1 in the presence of 2 tons of molten slag.
(Figure), coal is supplied from the bottom tuyere 3 and oxygen is supplied from the tuyere 3 and lance 2 to melt the scrap, and then the converter 1 is exposed to molten iron and molten slag without tapping or slag. 58 tons of scrap and 2 tons of limestone were additionally charged into the furnace (Fig. 3), and in the same way, coal was supplied from the bottom tuyere 3 and oxygen was supplied from the tuyere 3 and lance 2 to melt the scrap. Furthermore, 30.7 tons of scrap and 1 ton of limestone were additionally charged into the converter 1 in the presence of molten iron and molten slag without tapping or slag (Fig. 3), and the coal was similarly charged into the bottom tuyere 3 of the furnace.
Oxygen was then supplied from the tuyere 3 and the lance 2 to carburize and melt the scrap to obtain 200 tons of molten iron and 10 tons of molten slag with a carbon content of 3.5%.

Next, the converter 1 is tilted to discharge the required amount of 116 tons of hot water into the ladle 9 in the refining converter 4, and the remaining amount of seed hot water is
84 tons were left in the converter 1, and then the converter 1 was stood up and tilted to discharge the 8 tons of molten slag that had increased during the melting process into the ladle 14, and the remaining 2 tons of molten slag was removed. The melting heat cycle was completed by leaving it in the converter 1 as it was.

The dissolution heat cycle time was 66 minutes.
The amount of scattered iron dust during the melting heat cycle was 1.7 tons, and the iron loss rate due to the dust [amount of scattered iron dust/(amount of seed metal + total amount of scrap charged)%] was 0.8%.

Next, to explain the conventional example, the total amount of seed hot water is 84 tons, and the required amount for converter 4 for refining is 116 tons.
In obtaining 200 tons of molten iron with a carbon content of 3.5%,
29 tons of scrap and 1 ton of limestone were charged into the converter 1 in the presence of 84 tons of molten iron with a carbon content of 3.5%,
Coal was supplied from the bottom tuyere 3 and oxygen was supplied from the tuyere 3 and lance 2 to melt the scrap, and then a portion of the obtained molten iron, 29 tons, was tapped into a ladle for storing seed hot water. Next, 58 tons of scrap and 2 tons of limestone were additionally charged into the converter 1 in the presence of molten iron and molten slag, and similarly, coal was supplied from the bottom tuyere 3 and oxygen was supplied from the tuyere 3 and lance 2, respectively. Then, a part of the obtained molten iron, 55 tons, was tapped into a seed hot water storage ladle to secure a total amount of 84 tons of seed hot water in the seed hot water storage ladle. 34 tons of scrap and 1 ton of limestone were additionally charged into the converter 1 in the presence of molten iron and molten slag, and similarly, coal was supplied from the bottom tuyere 3 and oxygen was supplied from the tuyere 3 and lance 2, respectively. The scrap was carburized and melted to obtain 116 tons of molten iron and 8 tons of molten slag with a carbon content of 3.5%.

Next, the entire amount of 116 tons of molten iron obtained in the converter 1 is tapped into a ladle for transfer to the converter 4 exclusively for refining, and the entire amount of 8 tons of slag generated during the melting process in the converter 1 is used for slag. The melt was discharged into a ladle, and then 84 tons of molten iron was charged into the converter 1 from the seed hot water storage ladle to complete the melting heat cycle.

The melt heat cycle time is 81 minutes. The amount of scattered iron dust during the above melting heat cycle was 5 tons, and the iron loss rate due to the above dust was [amount of scattered iron dust / (amount of seed metal + total amount of scrap charged)]%.
is 2.5%.

(Effects of the Invention) As detailed above, according to the converter steel manufacturing method of the present invention, melting efficiency and molten iron yield can be improved, and molten iron manufacturing cost can be reduced.

[Brief explanation of drawings]

Figure 1 is a process diagram showing the steelmaking method of the present invention, Figure 2 is a diagram showing the relationship between the initial amount of molten slag and the amount of iron dust scattered, and Figure 3 is an example of the operation pattern of the steelmaking method of the present invention. FIG. 1... Converter exclusively for melting, 2, 5... Top blowing lance,
3, 6... Tuyere at the hearth bottom, 4... Converter for refining, 7
... seed water, 8 ... scrap, 9, 10 ... ladle, 11 ... impeller, 12 ... molten slag,
13...Limestone.

Claims (1)

[Claims] 1. Feed iron-containing cold material, carbon material, oxygen, and slag-forming material to a melting-only converter containing seed hot water and molten slag, melt the iron-containing cold material to obtain high-carbon molten iron, and use this molten iron as raw material to produce other materials. In the converter steelmaking method in which molten steel with the required composition is obtained by oxygen blowing in a converter exclusively for refining, high-carbon molten iron is produced in the total amount of the required amount of refining in the converter exclusively for refining and the amount of seed metal required in the converter exclusively for melting. The required refining amount of high carbon molten iron from the melting converter to the refining converter is subjected to oxygen refining by tapping once, while the remaining amount of seed metal of the high carbon molten iron is sent to the melting converter. All or part of the molten slag existing in the melting converter from which the above-mentioned total amount of high carbon molten iron was obtained is left in the melting converter. A converter steel manufacturing method characterized in that the molten slag is used as molten slag to prevent scattering of iron dust during melting of the iron-containing cold material.