JP3158895B2 - Converter refining method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently decarburizing while reducing the partial pressure of CO by hydrogen gas generated by blowing hydrocarbon gas while blowing, while obtaining a high yield of valuable metals. The present invention relates to a converter refining method for producing steel while proceeding and suppressing an increase in hydrogen concentration in molten iron.

[0002]

2. Description of the Related Art At present, the mainstream method employed for smelting carbon steel by a converter refining method is to use an upper-bottom blown converter and to use Ar, N ₂ , and CO ₂ through a furnace bottom tuyere. Gas mainly composed of O ₂ , O _2, etc. is referred to as molten iron or molten steel (hereinafter simply referred to as molten iron) 1
While stirring at a flow rate of less than 0.3 Nm ³ / min per ton and stirring the molten iron, oxygen is blown from the top blowing lance onto the molten iron.

[0003] In the converter refining of carbon steel, it is necessary to promote the decarburization reaction in a state where the iron content in the slag and the oxygen content in the molten iron are as small as possible, thereby improving the iron content yield, saving the deoxidizing agent, and reducing the furnace body erosion. It is desired from such a viewpoint. In addition, recently, there has been a demand for a method of further promoting decarburization in converter refining.

[0004] As a method for improving the decarburization efficiency, it is conceivable to blow Ar gas or steam during blowing to reduce the CO partial pressure in the furnace. These are methods generally used mainly at the time of decarburization and refining of stainless steel and high manganese steel, and the AOD method and the CLU method correspond thereto. In the AOD method, a mixed gas of Ar and O ₂ is blown from a plurality of tuyeres installed on a furnace wall near a furnace bottom, and the Ar gas is used, while in the CLU method, steam is blown from a converter bottom tuyere to generate gas. In this method, decarbonization is promoted by reducing the CO partial pressure in the furnace with H ₂ gas.

[0005] However, when the AOD method or the like is applied to carbon steel, there is a problem that the use of a large amount of Ar gas is not practical in terms of cost. When blowing unphosphorized blast furnace pig iron, it is necessary to reduce the Ar gas flow rate to about 0.2 Nm ³ / min or less per ton of molten iron in order to promote the dephosphorization reaction, but the Ar gas flow rate is too small. In that case, C
Not only is the effect of reducing the partial pressure of O small, but also there is a problem in operation, such as the tendency of tuyere clogging.

Japanese Unexamined Patent Publication No. 56-20112 discloses a method of melting a low-hydrogen steel top-bottom blow converter in which the blowing of a hydrocarbon-based nozzle coolant is stopped at the end of blowing, and the blowing is switched to mainly inert gas. It is shown. This falls into the category of a hydrogen reduction method by a so-called rinsing process.

[0007] Japanese Patent Application Laid-Open No. 145309/1985 discloses a method of refining a top or bottom blown converter using a recovery gas containing hydrogen gas, hydrocarbon gas or Ar gas as a refining gas. This aims to improve the Mn yield and the decarburization efficiency in the extremely low carbon region.

[0008] The Applicant has raised bottom blown converter refining method using a hydrocarbon gas to the bottom-blown gas in JP-A 5-78726 discloses (hereinafter referred to as low-P _CO blowing method) have been disclosed.
The hydrocarbon gas is easy to handle in actual operation, and is advantageous in cost. In addition, the hydrocarbon gas blown into the molten iron is decomposed to generate hydrogen gas of an original volume or more, so that the molten iron can be effectively stirred and, at the same time, has the effect of reducing the CO partial pressure. It is possible to efficiently advance the decarburization reaction. As a result, the following refining effects a) to c) can be achieved.

A) Effective dephosphorization and decarburization of blast furnace iron b) Acceleration of decarburization of dephosphorized iron under low iron content in slag and low oxygen content in molten iron c) Chromium in high chromium steel or high manganese steel Acceleration of decarburization under low loss or low manganese loss

[0010]

The low P _CO blowing method described above [0005], a large amount of hydrogen gas by blowing hydrocarbon bottom end of the blow is generated during the molten iron, the molten iron in hydrogen concentration by the solubility increases.

[0011] When the amount of hydrogen in the molten iron increases, there arises a problem in the quality of steel, such as generation of cracks caused by hydrogen. Further, in order to remove the increased hydrogen in the molten iron, it is necessary to perform a rinsing treatment by blowing an inert gas such as Ar after the completion of the blowing, but in this case, a drop in the tapping temperature and a process after the converter are required. Operational problems may occur, such as adverse effects on continuity.

An object of the present invention is to provide a feature of progress of high yield and high efficiency decarburization valuable metals included in the low P _CO blowing method, on it is possible to suppress an increase of the hydrogen concentration in the molten iron It is an object of the present invention to provide a bottom-blown converter refining method.

[0013]

The gist of the present invention is a converter refining method of the following (1) .

(1) In the last stage of the top and bottom blowing converter refining, hydrocarbon gas is blown into the molten iron from the tuyere below the molten iron bath, and the CO partial pressure is reduced by the hydrogen gas decomposed and generated from this gas. During decarburization refining, the flow rate of hydrocarbon gas is reduced, and the amount of inert gas equivalent to the reduced flow rate of hydrogen gas is added, and the gas is blown simultaneously with the hydrocarbon gas to suppress the increase in the hydrogen concentration in the molten iron. furnace smelting method der
Then, the gas flow rate is blown in as follows .

That is, the total flow rate of the hydrogen gas generated by the decomposition of the hydrocarbon gas and the inert gas blown at the same time as the hydrocarbon gas is 0.3 Nm ³ / min or more per ton of molten iron, and the flow rate of the hydrogen gas therein is 0.1 ton per ton of molten iron.
³ Nm ³ / min or less.

The above "end of blowing" means a period from the time when the carbon concentration in the molten iron reaches about 1% to the end of blowing (end point).

The present inventors replace the part of hydrocarbons blown down at the end of blowing with an inert gas, so that the effect of stirring the molten iron and the effect of reducing the partial pressure of CO in the furnace are not impaired. It has been found that it is possible to suppress an increase in the concentration of hydrogen.

[0018]

Refining behavior in the upper bottom blown converter when blown hydrocarbons bottom in [action] low P _CO blowing method is described as follows.

The supply of hydrocarbon gas for obtaining the effect of reducing the CO partial pressure in the furnace is started when the carbon concentration in the molten iron reaches 0.5 to 1.0%, and is continued for 3 to 5 minutes until the end of blowing. In the state where the carbon concentration in the molten iron is higher than 0.5%, even if the bottom blown gas is stirred at about 0.2 Nm ³ / min per ton of molten iron,
The iron content in the slag is not so high at about 5%, but when the carbon concentration in the molten iron is 0.5% or less, C
The amount of O gas generated decreases, and FeO is generated by the following reaction formula, so that the iron content in the slag increases.

[Fe] + [O] = (FeO) At this time, the hydrocarbon gas is generated by bottom blowing.
0.3 to 1.0 Nm ³ / min of hydrogen gas per ton of molten iron promotes decarburization. This is based on the principle that molten iron is stirred by hydrogen gas generated by the decomposition of hydrocarbon gas, and at the same time, the partial pressure of CO decreases. As a result, the following a) to
The effect of c) is achieved.

A) Decrease in iron content in slag b) Decrease in oxygen in molten iron c) Decrease in end-point carbon concentration However, if blowing is continued under the same gas injection conditions only for the purpose of reaching the end point, ie, the target carbon concentration, Then, the hydrogen gas decomposed and generated from the bottom blown hydrocarbon gas begins to dissolve in the molten iron with the lapse of the blowing time, and the hydrogen concentration in the molten iron starts to increase.

The hydrogen dissolved in the molten iron is removed by being contained in the CO gas bubbles generated by the decarburization reaction. However, the increase in the hydrogen concentration in the molten iron increases with the decrease in the carbon concentration in the molten iron. This is because the amount of generated CO gas decreases, the rate of removing hydrogen from molten iron decreases, and the rate of dissolution of hydrogen gas into molten iron increases. At the end of blowing, the concentration of hydrogen dissolved in the molten iron ranges from 5 to 12 ppm.

In order to suppress the increase in the hydrogen concentration in the molten iron,
Although it is preferable to reduce the bottom flow rate of the hydrocarbon gas, the effect of stirring the molten iron and reducing the partial pressure of CO is reduced, and the effects of the above a) to c) are impaired. Retention decreases.

At the end of blowing, when the carbon in the molten iron is reduced to about 1% or less, the flow rate of the bottom-blown hydrocarbon gas is reduced, and an inert gas equivalent to the reduced hydrogen gas flow rate is converted into the bottom-blown hydrocarbon gas. In addition, if supplied by bottom blowing, the effects of the above a) to c) can be obtained while maintaining the molten iron stirring and CO partial pressure reducing effects equivalent to those of only the hydrocarbon gas, and the hydrogen source in the molten iron can be reduced. Since it can be reduced, it is possible to suppress an increase in the hydrogen concentration in the molten iron. For this reason, a part of the bottom-blown hydrocarbon gas is replaced with an inert gas, and the flow rate of the inert gas is set to be equal to the hydrogen gas flow rate reduced by reducing the hydrocarbon gas flow rate.

The inert gas species is not particularly limited as long as it hardly contains hydrogen. For example, a gas such as Ar, He, or nitrogen is used. Apart from the problem of high gas prices,
He is particularly effective because He has a low density and a large flow rate that can be supplied even at the same tuyere pre-pressure. Nitrogen gas may be used for steel types that do not particularly dislike an increase in the nitrogen concentration in the molten iron, and this case is economically advantageous.

The supply of the inert gas may be started at the same time as the start of the bottom blowing of the hydrocarbon gas, or before or after the start. It is appropriate to appropriately change the target hydrogen concentration in the molten iron and the supply time of the hydrocarbon gas, and when the increase in the hydrogen concentration is relatively acceptable, the supply start time of the inert gas can be delayed.

There are desirable conditions for the hydrocarbon gas flow rate and the inert gas flow rate in the above case. That is, the total total flow rate of the hydrogen gas generated by the decomposition of the hydrocarbon gas and the inert gas blown at the same time as the hydrocarbon gas is 0.3 Nm ³ / min or more per ton of molten iron, and the flow rate of hydrogen gas in the ton is It is preferable that the pressure is not more than 0.3 Nm ³ / min.

The desirable upper limit of the total total flow rate is 1.0 Nm ³ / min per ton of molten iron, and the desirable lower limit of the hydrogen gas flow rate is 0.1 Nm ³ / min per ton of molten iron. Total total flow in the 0.3 Nm less than ³ / min per molten iron ton converter blowing normal upper base blowing and not much different, the effect of low P _CO can not be expected. On the other hand, even if it exceeds 1.0 Nm ³ / min, no further remarkable low _PCO effect can be obtained. If the flow rate of hydrogen gas is less than 0.1 Nm ³ / min per ton of molten iron, the required flow rate of inert gas is large relative to the total flow rate, which is disadvantageous in terms of cost. On the other hand, if it exceeds 0.3 Nm ³ / min, an increase in the hydrogen concentration in the molten iron becomes a problem.

It is desirable that the flow rate of the inert gas is appropriately set according to the limit value of the hydrogen concentration in the molten iron at the end point of the blowing. As described above, when the supply of the hydrocarbon gas is started when the carbon concentration in the molten iron reaches 0.5%, the supply time until the end of the blowing is about 3 to 5 minutes in normal blowing.
At this time, for example, if the flow rate of hydrogen gas generated by decomposition from hydrocarbon gas is 0.3 Nm ³ / min or less per ton of molten iron,
The concentration of hydrogen in the molten iron at the end of blowing also falls to about 5 ppm or less, and can be sufficiently reduced in the subsequent degassing step, so there is usually no problem. However, when the hydrogen gas flow rate becomes higher, the hydrogen concentration at the blowing end point is 5 pp.
m or more, it is desirable to supply the inert gas so that the hydrogen gas flow rate is 0.3 Nm ³ / min or less.

Since the decarburization reaction rate decreases with the progress of blowing, the rate of increase in the concentration of hydrogen in the molten iron increases with this. Therefore, it is also effective to increase the flow rate of the inert gas within the above range with the progress of blowing. It is.

The inert gas may be blown down by an independent system, or may be blown down by mixing it with a main blowing gas such as bottom blown oxygen or hydrocarbon. In each case,
It is desirable that the selection be made in accordance with the convenience of facilities and operation.

With respect to the tuyere when the inert gas is blown down by an independent system, a dedicated bottom blown tuyere may be installed, or a double or triple tube used for bottom blowing of the main blown gas. Any of the mouths may be used.

If a double or triple tube tuyere is used for bottom blowing of the main blowing gas, one or more systems will be switched to the replacement inert gas. Either the outer tube or the inner tube when using the double tube, or any of the inner tube, the middle tube and the outer tube when using the triple tube may be used. It is desirable to select so as not to cause problems such as clogging of the tuyere, tuyere and melting of refractory in the furnace bottom due to the balance with the kind of gas supplied at the same time.

[0034]

【Example】

(Test 1) 250 tons of hot metal having the composition shown in Table 1 were charged into an upper-bottom blowing converter having four triple-tube furnace bottom tuyeres, and CO ₂ supplied from an inner pipe, a middle pipe, and an outer pipe. The total flow rate of the gas was 0.2 Nm ³ / min per ton of molten iron, and the bottom was blown. While stirring the molten iron, 12 kg / t of quicklime, 3 kg / t of silica, and 10 kg / t of iron manganese ore were added as slag-making agents. 3.0 N per ton of molten iron from top blow lance with perforated Laval nozzle
Decarburization refining was started by blowing up m ³ / min oxygen.

[0035]

[Table 1]

As an experiment of the present invention, the carbon concentration in the molten iron was
When it reached 0.5%, the bottom blowing gas was changed from CO ₂ gas as follows. That is, when propane gas is supplied from the outer tube at 0.1 Nm ³ / min per ton of molten iron and oxygen is supplied from the middle tube at 0.1 Nm ³ / min per ton of molten iron, Ar gas at 0.4 Nm ³ / min per ton of molten iron is supplied from the inner tube. Thereafter, blowing was performed until the carbon concentration in the molten iron became 0.03%. At this time, the total total flow rate of the hydrogen gas flow and the Ar gas is 0.8 N
m ³ / min.

As an experiment of Comparative Example 1, the carbon concentration in the molten iron was
At the time when the concentration becomes 0.5%, propane gas is supplied from the outer tube and the inner tube at 0.1 Nm ³ / min per ton of molten iron, and oxygen is supplied from the middle tube at 0.1 Nm ³ / min per ton of molten iron, so that the carbon concentration in the molten iron is 0.03%. Blowing was carried out until.

As an experiment of Comparative Example 2, CO ₂ gas was supplied as a bottom-blown gas at 0.2 Nm ³ / min per ton of molten iron.
Blowing was performed until the carbon concentration in the molten iron became 0.03%.

FIG. 1 is a diagram showing the concept of the blowing pattern under each of the above conditions. The results are shown in Table 2.

[0040]

[Table 2]

As shown in Table 2, even at the same end point carbon concentration, the bottom blowing of propane and Ar (Example of the present invention) and the bottom blowing of propane without Ar (Comparative Example 1) gave CO as the bottom blowing gas. Comparative Example 2 using only _two gases
As compared with, oxygen activity in molten iron and iron content in slag decrease,
The Mn yield was improved.

The hydrogen concentration at the end point is naturally the lowest at 3.1 ppm in Comparative Example 2 using only CO ₂ gas. However, as is clear from the comparison between the present invention example and Comparative example 1, the present invention has a lower hydrogen concentration. In the example, the value was reduced from 9.0 ppm to 4.5 ppm, which was a value close to Comparative Example 2.

As described above, it is apparent that the method of the present invention can suppress an increase in the hydrogen concentration in the molten iron without impairing the characteristics of high yield of valuable metals and progress of highly efficient decarburization.

(Test 2) 250 tons of hot metal having the composition shown in Table 1 were charged into an upper-bottom blowing converter having four triple-tube furnace bottom tuyeres, and supplied from an inner pipe, a middle pipe, and an outer pipe. The total flow rate of CO ₂ gas is 0.2 Nm ³ / min per ton of molten iron, and the bottom is blown.
Decarburization refining was started by adding 3 kg / t of silica stone and 10 kg / t of iron-manganese ore, and blowing up oxygen at 3.0 Nm ³ / min per ton of molten iron from an upper blowing lance having a 4-hole Laval nozzle.

During the blowing, when the carbon concentration in the molten iron becomes 0.5% or less, blowing is performed by blowing bottom of propane and Ar, and the blowing is completed when the carbon concentration at the end point is in the range of 0.03 to 0.05%. did.

At this time, the total flow rate of the flow rate of hydrogen gas and the flow rate of Ar gas decomposed from the supplied propane is changed in the range of 0 to 1.0 Nm ³ / min per ton of molten iron in each blowing, and the blowing end point is changed. Oxygen activity in molten iron and T. in slag The relationship between the Fe and Mn yields and the (hydrogen + Ar) flow rate was investigated.

FIG. 2 shows the results of the above investigation. As shown in the figure, as the (hydrogen + Ar) flow rate increases, the oxygen activity in the molten iron and the T.O. Fe was reduced and Mn yield was improved. This improvement effect was remarkable when the flow rate of (hydrogen + Ar) was 0.3 Nm ³ / min or more per ton of molten iron.

(Test 3) Decarburization refining was started in the same manner as in Tests 1 and 2, and during the blowing, the carbon concentration in the molten iron was 0.5.
% Or less, propane and Ar are blown from the bottom to perform blowing, and the carbon concentration in the molten iron at the end point is 0.03 to 0.05%.
Ended blowing in the range.

At this time, the total amount of the flow rate of hydrogen gas and the flow rate of Ar generated by decomposition from the supplied propane is made constant at 1.0 Nm ³ / min per ton of molten iron in each blowing, and the flow rate of hydrogen gas is set to 0 ton per molten ton. The relationship between the end point hydrogen concentration and the hydrogen gas flow rate was investigated by changing the flow rate within the range of 1.0 Nm ³ / min.

FIG. 3 shows the result. As shown
When a part of propane was replaced with Ar and the hydrogen gas flow rate was reduced, the hydrogen concentration in the molten iron was also reduced, and the hydrogen gas flow rate was within 5 ppm or less in the range of 0.3 Nm ³ / min per ton of molten iron.

[0051]

According to the method of the present invention, the effect of stirring the molten iron of the hydrogen gas decomposed and generated from the bottom-blown hydrocarbon gas and reducing the partial pressure of CO is ensured, and the decarburization is efficiently performed at a high yield of valuable metals. The reaction can be promoted and the increase in the hydrogen concentration in the molten iron due to the dissolution of hydrogen gas can be suppressed.

[Brief description of the drawings]

FIG. 1 is a view showing the concept of a blowing pattern.

FIG. 2 shows oxygen activity in molten iron at the end of blowing and T.O. It is a figure which shows the relationship between Fe and Mn yield and (hydrogen + Ar) flow rate.

FIG. 3 is a diagram showing a relationship between a hydrogen concentration and a hydrogen gas flow rate at a blowing end point.

Claims (1)

(57) [Claims] At the end of blowing in the upper and bottom blower converter refining, hydrocarbon gas is blown into the molten iron from the tuyere below the surface of the molten iron bath, and the CO partial pressure is reduced by hydrogen gas decomposed and generated from the gas to remove the gas. A converter that reduces the hydrogen concentration in the molten iron by reducing the hydrocarbon gas flow rate during coal refining and adding an inert gas equivalent to the reduced hydrogen gas flow rate and simultaneously blowing it with the hydrocarbon gas. A refining method, wherein the total flow rate of hydrogen gas generated by the decomposition of a hydrocarbon gas and an inert gas blown at the same time as the hydrocarbon gas is 0.3 Nm ³ / min or more per ton of molten iron, and the hydrogen gas contained therein A converter refining method characterized in that the flow rate is 0.3 Nm ³ / min or less per ton of molten iron.