JPS5833289B2 - Method for producing industrial pure iron using a bottom blowing converter - Google Patents

Description

Detailed Description of the Invention The present invention relates to a method for producing industrial pure iron using a bottom blowing converter, and by reducing other impurities while producing ultra-low sulfur steel, it is possible to produce industrial pure iron. This is a method of manufacturing.

A conventional oxygen bottom-blown converter is equipped with a large number of concentric double-tube tuyeres at the bottom of the furnace, each consisting of a flow path for an oxidizing gas such as oxygen gas and a flow path for a protective gas for cooling the blades.

And the refining gas flow path (inner pipe) of those tuyeres
In order to remove impurities such as phosphorus and sulfur along with oxidizing gas, powdered slag-forming agent (limestone) is jetted out to perform oxidation and decarburization of molten iron.

Normally, in the case of a top-blown converter such as an LD converter, the desulfurization reaction proceeds at the interface between molten slag and molten iron in a nearly static state, using CaO dissolved in the slag as a desulfurization agent.

On the other hand, in a bottom-blown converter, powdered lime is supplied into the steel bath in an undissolved solid state from the bottom lining of the furnace, so CaO
The activity is considerably higher than in the case of melted materials such as the LD converter.

Moreover, the powdered lime adheres to the numerous gas bubbles that form directly above the siding, or enters and disperses into the bath, which has the advantage of significantly expanding the interfacial area for the desulfurization reaction. A bottom-blown converter is more advantageous than a blown converter.

In addition, when the S concentration in the hot metal is low, the diffusion of S in the bath becomes slow, which becomes the rate-limiting step in the desulfurization reaction.
It is known that the desulfurization rate decreases.

Therefore, in order to avoid this, it is necessary to stir the bath sufficiently, but in the case of a bottom-blowing converter, since there are many holes at the bottom of the furnace, the molten steel in the bath cannot be stirred. The strength is significantly greater than that of a top-blown lance, which is advantageous when viewed as a desulfurization vessel.

Therefore, the present invention is a method based on the above-mentioned knowledge, focusing on producing low sulfur steel using an oxygen bottom-blown converter.

However, in conventional refining using an oxygen bottom-blown converter,
Since burnt lime powder is usually supplied together with pure oxygen gas, even if it contains a lot of carbon or silicon, which is advantageous for desulfurization (
Even if it is in the hot metal stage), once it is generated,
aS was oxidized again by the oxidizing gas to produce CaO, making it virtually impossible to achieve extremely low sulfidation.

This can be considered as follows.

That is, in general, the desulfurization reaction in the converter is expressed by the following formula;
It is shown as % expression %.

From this, when the oxygen concentration 01 in molten steel or the 02 partial pressure at the location where these reactions occur is high, there is a drawback that S, which was removed as (CaS) in the slag, returns to CaO.

Therefore, the inventors identified a certain period during refining and performed strong desulfurization blowing at that time, creating conditions favorable for desulfurization with low oxygen partial pressure, promoting desulfurization, and continuing to strongly reduce the inside of the furnace. This enabled the production of low-sulfur steel while maintaining the atmosphere.

In short, this invention uses a bottom-blowing converter and performs desulfurization blowing at the early stage of refining when the hot metal is in the so-called molten metal state where the activity of S is high and is once made into low-sulfur pig iron.

After that, impurities such as carbon, silicon, phosphorus, and manganese are removed by oxidation, and blowing is continued to prevent the S that has been removed from returning to the molten steel. This is the manufacturing method.

The details of the configuration will be explained below along with examples.

The melting method according to the present invention is comprised of the following steps.

(b) The S content in the hot metal tapped from the blast furnace is reduced to 0.0% or less using an outside-furnace desulfurization device, and the temperature is set to 1200.
(b) Separating the desulfurization slag from the hot metal that has been desulfurized outside the furnace; (c) The hot metal treated in (0) is separated into a refining gas passage and a cooling gas passage at the bottom of the furnace. Steel beets are charged into a bottom blowing converter equipped with multiple concentric double tube tuyeres, and oxidizing gas such as oxygen is blown into them to produce steelmaking beets with a carbon concentration of 3.5% or more and a temperature of 1400°C or more. a) when the steelmaking heat shown in the above process is achieved,
A process in which CaO powder is injected together with an inert gas such as nitrogen or argon from the inner tube of the tuyere, and a hydrocarbon-based reducing gas is injected from the outer tube to reduce the S content to 0.002% or less. (e) After the process of (e)), a refining gas such as oxygen is blown into the inner pipe of the tuyere to cause decarburization, dephosphorization, demanganization, and desiliconization reactions.
At the same time, a process of injecting CaO powder from the inner tube of the tuyere to prevent resulfurization into the molten steel; (f) a process of finally tapping the steel; Next, each process will be described in detail.

First, in the process (a), 0.002%
This is a preliminary desulfurization step necessary to obtain the following S concentration,
Furthermore, if the temperature of the hot metal falls below 1200°C, it will interfere with the subsequent desulfurization in the bottom blowing converter, so the hot metal temperature needs to be at least 1200°C at the end of this process.

In the step (0), when the desulfurization slag is brought into the converter,
This step is necessary because there is a danger of resulfurization in the latter stages of refining.

The process ←→ is a step in which the temperature of the bath is raised to 1400° C. or higher in order to advantageously develop the desulfurization reaction of hot metal in the bottom blowing converter.

However, at this time, if the carbon concentration in the hot metal drops below 3.5%, the conditions for promoting desulfurization in a reducing atmosphere will weaken, which is even unfavorable, so the carbon concentration in the hot metal must be 3.5% or higher. No.

The above process) is a process of desulfurizing the hot metal in the bottom blowing converter by arranging the most favorable conditions for the desulfurization reaction, and unlike the conventional bottom blowing converter blowing method, burnt lime powder is In addition, a hydrocarbon-based protective gas is blown into the converter from the outer tube of the siding to create a strongly reducing atmosphere inside the converter.In this way, it is possible to reduce the S content in the hot metal to less than o, ooi%. It is possible to reliably desulfurize to at least 0.002% or less.

The process e) is a second blowing step for removing impurities other than S, carbon, silicon, manganese, and phosphorus contained in the hot metal to produce industrial pure iron.

What is important here is to prevent as much as possible the phenomenon in which S, once separated into the slag, resulfurizes into the molten iron due to the strongly oxidizing atmosphere in the furnace.

For this purpose, it is advantageous to continue blowing in the burnt lime powder even during this step (e).

The above step is a step of tapping the industrial pure iron produced in this way into a ladle.

In addition, after the start-up of the refining in (c) above, and before carrying out the desulfurization blowing referred to in (2), silicon is added to create favorable conditions for desulfurization, and then the desulfurization blowing in (2) is performed. It is thermodynamically more advantageous to increase the activity of S and promote the desulfurization reaction, especially when the Si concentration in the furnace is low before charging into the bottom blowing converter. MnO, Fe
Lower oxides such as O are generated and become slag, which inhibits the desulfurization reaction, but by adding Si, these are re-reduced and become advantageous to the desulfurization reaction, making the effect more pronounced.

In addition, inert gas such as Ar gas is injected into the tuyeres after the middle to final stage of refining (e), which involves blowing while suppressing resulfurization, and in the middle of the process (f) (e.g., tapping). Cleaning the steel bath by blowing it into the furnace before tapping is effective in reducing the H concentration to 0.0002% or less and the O concentration to 0.03% or less.

Examples of the present invention will be described below.

The converter used in this example is a 5-ton oxygen bottom-blown converter with 6 tuyeres and an oxygen feed rate of 2 using inner tubes.
The flow rate of propane gas blown from the outer pipe used for cooling the siding was 0.69 Nm'/min.

Example 1 First, 60 tons of blast furnace hot metal was held in a ladle, and 2.0 kg/kg of calcium carbide was added to the ladle and desulfurized using an impeller.

The hot metal after the outside-furnace desulfurization was dispensed into a 6.90 t hot metal ladle for a bottom blowing converter.

At this time, the temperature of the hot metal in the hot metal pot was 1330'C,
The components were 4.48%C, 0.88%Si, 0.41%M, 0.110%P, and 0.007%S.

Next, the slag on the bath surface of the hot metal pot was scraped out manually, and the desulfurized hot metal was charged into a bottom blowing converter and oxygen blown for 4 minutes and 30 seconds.

The oxygen delivery rate in this blower is 23Nm/min, and the flow rate of propane gas passed through the outer pipe for cooling the tuyere is 0.69N? 71
It was 3/min.

During this time, burnt lime powder was heated at 13 kp/l through the tuyere inner tube.

When we once collapsed the reactor and conducted temperature measurements and analysis, we found that the temperature was 149.
0'C, 3,88%C, 0,003%Si.

The results were 0.36%Mn, 10.071%P, and 0.008%S.

Next, Ar gas was applied at 23 Nm'/m1 from the tuyere inner tube.
n1 Also, propane gas is 0.69 Nm from the tuyere outer tube.
Desulfurization blowing was carried out for 2 minutes and 55 seconds while flowing at a flow rate of 1 min, and at the same time, burnt lime powder of 25 kg/l heat was blown from the tuyere inner tube.

When the furnace was collapsed and the temperature and bath composition of the steel bath were analyzed, the results were 1350°G, 3.81%C, 0,002%5i10
．． It was 36%Mn10.075%P10.001%S.

Thereafter, the blowing conditions as described above were continued, that is, the oxygen gas flow rate from the tuyere inner pipe was 23 Nm/m1n1, and the propane gas flow rate from the tuyere outer pipe was 0.69 Nrl/
Normal decarburization blowing was performed at min for 16 minutes OO seconds.

During this time, burnt lime powder with a heat of 40k19/l was blown into the tuyere tube.

When the furnace was collapsed and the temperature was measured and analyzed, it was found to be 1710℃ and 0.5℃.
008%C, 0,002%5i10, O35Mn, 0.
005%P10.0020%S, 0.072%0.

Finally, put 3 kg of M into the receiving ladle and tap the steel immediately.
The steel was poured from the ladle into a 6-ton wide mold at a temperature of 1600°C.

According to the check analysis of the steel ingot, o,oos%C,0,0
03%Si, 0.032%Mn.

0.007%P, 0.0020%S, 0.0014%N
10.0040%H, 0.03%0, 0.001%A7
Industrial pure iron was obtained.

Example 1 First, 60 tons of blast furnace hot metal was held in a ladle, and 1.8 kg of calcium carbide was added to the ladle and desulfurized using an impeller.

After the outside-furnace desulfurization, 6.8 liters of the hot metal was dispensed into a hot metal ladle for a bottom blowing converter.

At this time, the hot metal temperature in the hot metal pot was 1260'C, and the components were 4.45%C, 0.64%5i, 10.52%an, 0
．． It was 12% P and 0.009% S.

Next, the slag on the bath surface of the hot metal pot is scraped out by input, and then the hot metal is charged into the bottom blowing converter, and the slag is poured into the bottom blowing converter for 4 minutes and 5 minutes.
Oxygen blowing was performed for seconds.

The amount of burnt lime injected from the tuyere tube at this time was 13.7k.
g/l heat, the steel bath temperature was 1458°C, and the bath composition was 3.6%C, 0,003%Si, 0.35%Mn.
, 0.112%P10.009%S.

After this period, the metal Si
was added to the heat furnace at 6 kg/l.

Next, 23N of Ar gas was applied from the inner tube above the double tube tuyere.
mlmin, and 0.0% propane gas from the tuyere outer tube.
Blowing was carried out for 4 minutes and 5 seconds at a flow rate of 69 Nm37 min, during which time burnt lime powder at a heat of 25 kIi/l was blown from the tuyere inner tube.

When the furnace was immediately collapsed and the temperature and composition of the steel bath was analyzed, the temperature was 1345℃, 3.56%C10, 55%Si,
0.35%Mn.

It was 0.112% P and 0.001% S.

Thereafter, the blowing conditions described above were continued, that is, the oxygen gas flow rate from the tuyere inner pipe was 23 Nm'/m1n1, and the propane gas flow rate from the tuyere outer pipe was 0.69 Nm'/m1n1.
Normal decarburization blowing was performed at min. for 12 minutes and 19 seconds.

During this time, 40 kg/l heat of burnt lime powder was blown into the tuyere tube.

When the furnace was collapsed again and the temperature was measured and analyzed, it was found to be 1750℃.
, 0.009%C10,002%Si, 0.04%Mn
, 0.007% H8, 001% S, and 0.06% O.

Finally, put 3 kg of Al into the receiving ladle and tap the steel immediately.
The steel was poured from the ladle into a 6-ton wide mold at a temperature of 1620°C.

According to the check analysis of the steel ingot, o,oos%C,0,0
03%Si.

0.043%Mn, 0.009P, 0.0010
%810.0017%N, 0.00038%H, 0,0
Industrial pure iron of 2% o 10.002% Al was obtained.

Example 2 The converter used in this example was the same 5 oxygen bottom-blown converter as in Example I above.

After desulfurization treatment as described above, hot metal of 6.72 tons in weight, 1306°C in temperature, and 4 in composition was placed in the bottom blowing converter ladle.
．． 36%C10, 79%5i10.39%Mn10.1
Hot metal containing 26% P and 0.008% S was received.

After scraping and removing the slag on the surface of the hot metal pot bath, the desulfurized hot metal was charged into a bottom blowing converter and oxygen blown for 4 minutes and 05 seconds.

The oxygen supply rate in this blowing was 23 Nm'/min, and the flow rate of propane gas passed through the outer pipe for cooling the blade was 0.69 Nrr.
l/min.

During this time, 13 kg/l of burnt lime powder was heated and blown into the tuyere tube.

When we once collapsed the reactor and conducted temperature measurements and analysis, we found that 148.
0°C, 3.73%C10,003%Si.

The results were 0.22%Mn, 0.093%P10.008%S.

Next, Ar gas was applied at 23 N m”/
min 1 Also, from the tuyere outer pipe, propane gas is 0.69
While flowing at a flow rate of Nrrt/min, desulfurization blowing was carried out for 3 minutes and 12 seconds, and at the same time 25 kg was removed from the tuyere inner pipe.
/l heat of burnt lime powder was injected.

When the furnace was collapsed and the temperature and bath composition of the steel bath were analyzed, it was found to be 1342°C, 3.77%C, 0,003%Si.

The content was 0.22% Mn, 0.102% P, and 0.001% S.

Thereafter, decarburization blowing was performed for 15 minutes under the blowing conditions described above, that is, an oxygen gas flow rate of 23 Nm'/min from the tuyere inner tube and a propane gas flow rate of 0.69 Nm''/min from the tuyere outer tube. It took 18 seconds.

During this time, burnt lime powder at a heat rate of 27 ky/t was blown into the tuyere tube.

When we collapsed the furnace again and analyzed the bath temperature and bath composition, we found that 170
6℃, 0.010C, 0.002%Si, 0.043%
Mn, 0.006%P10.0018%810.074
%O.

After that, 20 N77L'/min of A was applied to the tuyere inner tube.
After flowing r gas and flowing Ar gas at a rate of 0.8 Nm'/min into the tuyere outer tube, the steel was blown for 3 minutes and then immediately tapped into a receiving ladle containing 3 kg of metal M. 6 from the pot
The mixture was poured into a top mold at a temperature of 1580°C.

According to the check analysis of the steel ingot, 0.006% C10
,002%5ls0.03%Mn10. OO6%P10
．． 0017%s1o, ooio%N10.0021%H
Industrial pure iron containing 10,017% and 0.0.001% Al was obtained.

In addition, in the above-mentioned example, a small furnace of 5 tons was used, so the heat loss was large, and the single piece material (
It was unnecessary to introduce silicon steel scrap, etc.) into the furnace.

However, in large furnaces exceeding 100 tons, it may be necessary to charge pieces of material from the viewpoint of heat balance, and in that case, pieces of material may be charged.

As explained above, according to the present invention, industrial pure iron can be produced relatively easily.

Claims (1)

[Claims] 1. From desulfurized hot metal with S: 0.010% or less, which is obtained by desulfurizing in advance outside the furnace and removing the desulfurization slag generated by the preliminary desulfurization, a refining gas passage and a protective gas are added to the bottom of the furnace. When melting industrial pure iron using a bottom-blown converter having a double-pipe siding consisting of a pipe passage, (a) the above-mentioned desulfurized hot metal is charged into the bottom-blowing converter, and oxygen, etc. oxidizing gas is injected to form a steelmaking heat with a C content of 3.5% or more and a temperature of 1400'C or more; Burnt lime was injected and reducing gas was injected from the protective gas passage for blowing to bring S to 0.002% or less, and (c) After that, burned lime powder was further injected from the refining gas passage. A method for producing pure iron for industrial use using a bottom-blowing converter, which consists of continuously injecting oxygen gas mixed with iron to perform oxidative decarburization blowing, and (2) subsequently tapping the steel. 2. From desulfurized hot metal with S: 0.010% or less, which is obtained by desulfurizing in advance outside the furnace and removing the desulfurization slag generated by the preliminary desulfurization, 2 consists of a refining gas passage and a protective gas passage at the bottom of the furnace. When melting industrial pure iron using a bottom-blown converter having heavy pipe linings, (a) the above-mentioned desulfurized hot metal is charged into the bottom-blowing converter, and oxidizing gas such as oxygen is injected through the linings. and blowing to form a steelmaking heat with a carbon content of 3.5% or more and a temperature of 1400°C or higher, (b) next, metal Si is introduced into the bath, (c) then the tuyere Powdered calcined lime was injected together with an inert gas from the refining gas passage, and reducing gas was injected from the protective gas passage for blowing to bring the S content to 0.002% or less. Production of industrial pure iron using a bottom blowing converter, which consists of continuously injecting oxygen gas mixed with burnt lime powder from the refining gas passage to carry out oxidation and decarburization blowing, and (e) then tapping the steel. Melting method. 3 Desulfurization is done in advance outside the furnace and the desulfurization slag generated by the preliminary desulfurization is removed.S: 0.010% or less desulfurized hot metal is made of desulfurized hot metal with a refining gas passage and a protective gas passage at the bottom of the furnace.2 When melting industrial pure iron using a bottom-blown converter having heavy pipe linings, the above-mentioned desulfurized hot metal is charged into the bottom-blowing converter, and oxidizing gas such as oxygen is injected through the linings. (b) Next, metal Si is introduced into the bath, (c) After that, the refining gas of the above-mentioned size is heated. Powdered burnt lime was injected together with inert gas from the passage, and reducing gas was injected from the protective gas passage for blowing to bring S to Q,002% or less. Oxidative and decarburizing blowing is carried out by continuously injecting oxygen gas mixed with burnt lime powder from the tuyere, (e) After that, inert gas is injected from the tuyere to degas oxygen gas, etc. A method for producing industrial pure iron using a bottom blowing converter, which comprises: