JPH06287622A - Blowing method of converter - Google Patents

Abstract

PURPOSE:To stabilize (Total.Fe) in slag during oxygen-blowing in a converter to the low content, to enable blowing without slopping and, at the same time, to enable melting of an extra low carbon steel which can not be melted in the conventional converter, by improving stirring in a furnace. CONSTITUTION:In the converter arranged with a side blowing nozzle 3 at the side wall part of the furnace body in contact with molten iron 5 in the converter main body 1 and a bottom blowing nozzle 4 at the furnace bottom part and blowing stirring gas into the molten iron 5 from the side blowing nozzle 3 and the bottom blowing nozzle 4 at the same time, the stirring gas of >=0.1Nm<3>/ min.ton from the side blowing nozzle 3 and >=0.06Nm<3>/min.ton from the bottom blowing nozzle 4 is blown into the molten iron to efficiently stir both of the molten iron 5 and the slag 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a converter blowing method which is an improved method for stirring molten iron and slag in a converter.

[0002]

2. Description of the Related Art In a pure oxygen top-blown converter, the molten iron and slag in the furnace are agitated by the stirring force of only the top-blown oxygen jet, and therefore the molten iron and slag in the furnace are not sufficiently agitated. In addition to insufficient removal of impurities such as carbon, phosphorus, and sulfur, the slag is overheated and the iron concentration in the slag (hereinafter referred to as (Total.Fe)) is increased to promote furnace wear and It was deteriorating the yield of iron and ferroalloy.

In recent years, 0.15 to 0.25 Nm ³ from the bottom of the furnace has been blown at the same time as the top blowing of pure oxygen. The so-called compound blowing was started, in which a stirring gas of /min.ton was blown. By this composite blowing, stirring of molten iron and slag was improved and overheating of slag was almost eliminated. However, although (Total.Fe) is slightly lower than that of the top blowing converter, it is usually 15 to 2
At 0% by weight (hereinafter referred to as "%"), there is not a sufficient decrease. In addition, in this composite blowing, decarburization refining has come to be performed by a method (rinsing treatment) in which an inert gas is introduced from a nozzle at the bottom of the furnace and stirred after acid blowing.

As a positive method for producing low carbon steel in a converter, there is a method disclosed in Japanese Patent Publication No. 56-2124. In Japanese Examined Patent Publication No. 56-2124, the hot metal after the dephosphorization treatment is used, and the blowing is performed in the converter without using the slag-making agent. During and / or after the blowing, the nitrogen gas is blown. Alternatively, a method of introducing an inert gas into molten iron and stirring it, that is, stirring slag having a high oxidizing power mainly with iron oxide and molten iron, and reacting carbon in molten iron with iron oxide in slag to decarburize Is the way. The following three methods are disclosed as stirring methods. They are (1) introducing gas from a plurality of nozzles arranged in the furnace bottom in the circumferential direction, (2) introducing gas from a plurality of nozzles on the furnace bottom and side walls, or from one of them (3 )
This is a method of introducing gas from an immersion nozzle that hangs down from the furnace opening into the furnace. In the method shown in (2), a plurality of nozzles are arranged in the circumferential direction at the bottom of the furnace, and a plurality of nozzles are arranged in the circumferential direction at the same height of the side wall. The required minimum gas flow rate of the furnace bottom nozzle, the side wall nozzle and furnace bottom nozzle arrangement method, the side wall nozzle installation height and the circumferential arrangement method are not shown. Further, not only is there no significant difference in the stirring methods among these three methods, but the reached carbon (hereinafter referred to as [C]) level here is 0.009%.

On the other hand, in the AOD method mainly used for decarburization and refining of stainless steel, 1 Nm ^{3 is obtained} from several tuyere installed on the side wall near the bottom of the furnace body. /min.ton or more oxygen gas,
A method of blowing a mixed gas of an inert gas into the molten iron in the furnace is adopted. As an example of melting ultra-low carbon steel, for example, there is a report at the 91st Special Steel Subcommittee of the Japan Iron and Steel Institute Joint Study Group, in which case the [C] level reached in molten iron is 0.00.
Although it has reached 1%, the initial [C] in molten iron is 1.3-
50 from 1.4% to [C] level 0.001%
It takes ~ 60 minutes and the decarburization rate is slow, so the required time is long.

In the iron bath type smelting reduction process,
A converter-type refining vessel with a horizontal blow nozzle as well as a bottom blow nozzle has been proposed, but the horizontal blow nozzle in the smelting reduction process is located at the slag bath position and is intended to strengthen the stirring of the slag. The technical field is essentially different from that of the present invention.

[0007]

The conventional converter blowing has the following two problems. (1) The (Total.Fe) value at the end of blowing is high and the blowing is unstable.

In order to remove phosphorus and sulfur impurities in the converter and to adjust the slag composition, a lime-based slag-forming agent is used in a normal converter operation. This slag-forming agent and the oxide generated in the furnace are melted to generate slag. Due to non-uniform molten state, non-uniform slag composition, or increase in (Total.Fe),
Slopping (melted slag flowing out from furnace opening during blowing) occurs. In order to stabilize the blowing, it is necessary to suppress sloping, and from this viewpoint, it is essential to reduce (Total.Fe) and make the slag composition uniform.

In Japanese Examined Patent Publication No. 56-2124, no slag-forming agent is used, and slag having a strong oxidizing power, that is, iron oxide is 5
Generating slag mainly composed of iron oxide, which is 0% or more, is a means for solving the problem, and naturally the (Total.Fe) value becomes high. Therefore, this is a book aimed at the operation using a lime-based slag forming agent. The invention is essentially different.

[0010] In the current converter composite blowing, blown stop molten iron [C] of general steel type [C] = 0.05%, (Tota
l.Fe) is 15 to 20% as shown in FIG. 3, and it cannot be said that it is sufficiently lowered. This is because the stirring force between the molten iron and the slag in the furnace is weak, the reaction between the molten iron and the slag does not proceed sufficiently, and the result (Total.Fe) is high. In addition, sloping cannot be prevented due to high (Total.Fe) and uneven slag composition due to weak stirring power in the furnace. (2) The lower limit of arrival [C] is high

Since the decarburization reaction in the low [C] region is controlled by the mass transfer of carbon and oxygen, it is necessary to sufficiently stir the molten iron and slag in the furnace in order to lower the reached [C] to a low level. is there. In Japanese Examined Patent Publication No. Sho 56-2124, the stirring gas flow rate is 0.057 Nm ³ At the operation of /min.ton, the reached [C] level is 0.009%, which is higher than the target level of the present inventors. Also, in the rinsing process of the composite converter (bottom blowing only),
Since the bath depth in the furnace is shallow, the gas stirring efficiency is not always good, and the arrival [C] is 0.006 to
It is about 0.01%, which is equivalent to the level of Japanese Patent Publication No. 56-2124.

In these methods, the stirring power in the furnace is still insufficient, and the [C] value reached to the level of the present inventors' target of ultra-low carbon steel ([C] ≦ 0.005%) is reached. Is not lowered. Therefore, vacuum degassing treatment such as RH is indispensable in order to produce ultra-low carbon steel, which has been in increasing demand as a steel sheet for automobiles.
In order to compensate for the temperature drop in the secondary refining, it is a factor of increasing the converter end point temperature.

By the way, when stirring the liquid in the container by blowing gas, side blowing is more effective for stirring the entire bath than bottom blowing. From the measurement results of the uniform mixing time in the water model experiment, Known from the past.

However, according to the experiments conducted by the present inventors, the molten iron is agitated only by the lateral blowing, but the slag is only pushed in the direction opposite to the nozzle, and the agitation of the slag becomes extremely insufficient. Was observed. That is, in the blowing of the converter, it was impossible to sufficiently stir both the molten iron and the slag by only lateral blowing.

Therefore, bottom blowing was added to side blowing to stir the slag and the molten iron-slag interface. Simultaneous side-blow and bottom-blow stirring improves the agitation of molten iron and slag compared to side-blow only. However, the total flow rate of the side-blown and bottom-blown stirring gas is
57 Nm ³ /min.ton), the stirring energy was weak and the stirring state until the molten iron and the slag were suspended could not be obtained. In order to improve the decarburization reaction rate by suspending molten iron and slag, as shown in FIG. 5 and FIG. 6, the lateral blowing gas flow rate is 0.1 Nm ³ /min.ton or more, and 0.06 Nm ³ at bottom blowing gas flow rate Although a stirring gas of more than /min.ton was required, the amount of these gases was
It was a small amount compared to the amount of bottom-blown gas in combined blowing.

Further, the same nozzle arrangement as in Japanese Examined Patent Publication No. Sho 56-2124, that is, a case where a plurality of nozzles are arranged in the circumferential direction at the bottom of the furnace and a plurality of nozzles are arranged in the circumferential direction at the same height of the side wall portion. Is that the agitation of molten iron due to multiple horizontal blows interferes with each other, and the agitation of molten iron deteriorates.Because the bottom blows arranged in the circumferential direction cause molten iron to rise up in the peripheral area of the furnace, the slag is at the center of the furnace. Gathered in some parts and could not sufficiently stir the slag. Therefore, as a result of further research by changing the nozzle arrangement, when the horizontal blowing nozzle was installed in a specific range in the circumferential direction of the furnace, and when the bottom blowing nozzle was installed in the center of the furnace bottom and the horizontal blowing nozzle It was found that the agitation efficiency was significantly improved when installed in a specific range in the circumferential direction. The present invention has been made based on the above findings, and an object thereof is to provide a method for efficiently stirring both molten iron and slag in a converter.

[0017]

[MEANS FOR SOLVING THE PROBLEMS] In a converter refining using a slag forming agent containing lime, a side-blow nozzle and a bottom-blow nozzle are provided in a side wall of a furnace body in contact with molten iron in a converter and a bottom blow nozzle in a bottom of the furnace. In order to blow the stirring gas into the molten iron at the same time from the side blowing nozzle and the bottom blowing nozzle to efficiently stir both the molten iron and the slag, and to put the molten iron and the slag in a suspended state, the stirring gas flow rate From the side-blow nozzle to 0.1 Nm ³ /min.ton or more, 0.06 Nm ³ from the bottom blowing nozzle /min.ton or more. At this time, in order to carry out the stirring more efficiently, it is effective to install the side-blowing nozzle and the bottom-blowing nozzle in the ranges shown below.

Even if the number of horizontal blowing nozzles is one or more than one, it is necessary to install all the horizontal blowing nozzles within a range of 120 degrees in the circumferential direction of the furnace.
The reason for this is that the effect of horizontal blowing is that it causes a large flow in the molten iron bath in the furnace to improve stirring, and if it is installed over 120 degrees, a plurality of flow patterns are generated,
This is because stirring of molten iron interferes with each other and the stirring deteriorates. It is effective to install the bottom blowing nozzle in the following two ranges.

One range is the bottom of the furnace, which includes the center of the bottom of the furnace and is separated from the position of the horizontal blowing nozzle in the range of 120 to 240 degrees in the circumferential direction of the furnace. The reason for limiting the installation position to the bottom of the furnace at a distance of 120 to 240 degrees in the circumferential direction of the furnace is that the slag that is about to be pushed in the opposite direction by the side blowing nozzle is pushed back by the bottom blowing nozzle, This is because it is evenly distributed in the interior. This is because when the bottom blowing nozzle is installed closer to the horizontal blowing nozzle than the above range, the above effect is not obtained and the slag is pushed toward the opposite side of the horizontal blowing nozzle and gathers. Further, the effect when installed in the center of the furnace is to prevent molten iron in the peripheral part of the furnace from rising due to stirring by the bottom blowing nozzle in the peripheral part of the furnace, which prevents slag from gathering in the central part of the furnace.

Another range is a range including the center of the bottom of the furnace, which is ± 20 degrees from the position of the side-blow nozzle in the circumferential direction of the furnace and is close to the side-blow nozzle. Install position ± in the circumferential direction of the furnace
The reason for limiting it to the bottom of the furnace at 20 degrees is that it is installed near it, and the interaction between the side-blown gas jet and the bottom-blown gas jet promotes the refinement of the stirring gas, and the reaction interfacial area between the gas and molten iron is increased. Is dramatically increased, and the degassing reaction rate is improved. This is because the interaction of the gas jets becomes weaker as the angle exceeds ± 20 degrees, and hence the degassing reaction rate cannot be expected to improve. The effect when installed in the center of the furnace is similar to the above effect.

When a plurality of side-blowing nozzles are installed, the bottom-blowing nozzles are installed on the bottom of the furnace at a distance of 120 to 240 degrees in the circumferential direction. 120 degrees to 240 with respect to the blowing nozzle
Is installed in the range of ± 20 degrees in the circumferential direction of the furnace, meaning that the bottom blowing nozzle is installed in the range of ± 20 degrees in the circumferential direction of the furnace. This means installing a bottom blowing nozzle.

The stirring condition in the furnace also depends on the installation height of the horizontal blowing nozzle. If the height of the iron bath in the furnace is H, the horizontal blowing nozzle should be installed at a height of 1/2 H or less. However, it is efficient. This is because the agitation of the molten iron is promoted by installing the side-blowing nozzle deep in the molten iron, and the slag is well agitated at the shallow installation position, but the agitation of the molten iron is insufficient.

[0023]

In the converter, [C] in molten iron and iron oxide in slag (hereinafter referred to as (FeO)) react according to the equation (1). FeO + C → Fe + CO (1)

However, according to the research conducted by the inventors, this reaction is rate-controlled by mass transfer between molten iron [C] and slag (FeO), and if the molten iron and slag are not sufficiently stirred, the reaction does not proceed and the molten iron [C] and (FeO) in the slag complete the blowing with a high concentration.

In the present invention, the stirring gas flow rate is 0.1 Nm ³ from the side blowing nozzle in the stirring method by simultaneous gas blowing from the side blowing nozzle and the bottom blowing nozzle. /min.ton or more, 0.06 Nm ³ from the bottom blowing nozzle /min.ton or more, the stirring of both molten iron and slag in the furnace is drastically improved, and molten iron and slag become in a suspended state, and the reaction of formula (1) proceeds well and reaches [ C] and (FeO) in the slag are the main components (Total.Fe), but they are significantly lower than in the conventional case. Further, since the level of (FeO) in the slag is stable at a low level, the slag is sufficiently stirred, and the slag composition is made uniform, stable operation with almost no sloping can be obtained.
On the other hand, there is an upper limit value for the gas flow rate, which is defined by the horizontal bubble arrival distance of the blown gas in the case of horizontal blowing and by blow-through in the case of bottom blowing.

[0026]

EXAMPLES The present invention will be described based on examples.

FIG. 1 shows the converter installation positions of the side-blowing nozzle and the bottom-blowing nozzle according to the present invention. The dephosphorized hot metal was charged into a 250 ton converter body 1, and first, acid was fed by an upper blowing lance 2 to decarburize and blow, and molten iron [C] = 0.02.
The acid transfer is terminated when the content reaches ˜0.04%. After the end of the acid feeding, with the nozzle arrangement according to the present invention, the inert gas is blown into the molten iron 5 from the gas introduction pipe 7 through the side blowing nozzle 3 and the bottom blowing nozzle 4, and a rinsing treatment is performed for 10 to 15 minutes. We tried to melt ultra-low carbon steel. The bath shape in the converter is H / D (H: bath height, D: bath diameter) of approximately 0.3,
Oxygen consumption is 3.5 Nm ^{3 with} constant oxygen flow rate during oxygen transfer. / mi
n.ton. For adjusting the composition of slag 6, a lime-based slag-forming agent was used, the amount of slag was 20 to 30 kg / ton, and the hot metal [C] at the start of blowing was about 4%. If a sloping phenomenon occurred during blowing, the inhibitor was charged. In FIG. 1, Case A is a case where the bottom blowing nozzle is installed in the center of the furnace bottom and the furnace bottom near the side blowing nozzle within a range of ± 20 degrees from the side blowing nozzle in the circumferential direction of the furnace. When the blowing nozzle is installed at the center of the bottom of the furnace and the lateral blowing nozzle is installed at the bottom of the furnace in the range of 120 to 240 degrees in the circumferential direction of the furnace, Case C is such that the bottom blowing nozzle is at the center of the bottom of the furnace. It shows the case where the nozzles are installed at the bottom of the furnace at 90 ° and 270 ° in the circumferential direction from the side-blow nozzle. At the same time, as a comparative example, FIG. 1 shows a case where two horizontal blowing nozzles are installed 180 degrees apart in the circumferential direction and two bottom blowing nozzles are installed side by side in the circumferential direction of the furnace. The gas flow rate and the height of the side-blow nozzle were set as follows.

Gas flow rate: 0.7 Nm ^{3 for the} horizontal blowing nozzle / mi
n.ton as standard, 0 to 1 Nm ³ /min.ton range, bottom blowing nozzle 0.2 Nm ³ /min.ton as standard, 0-
0.5 Nm ³ It was changed in the range of /min.ton. Side blow nozzle position: 1/4 when the height of molten iron bath is H
Using H as a standard, 1 / 2H and 3 / 4H were also performed.

FIG. 2 shows a side-blown and bottom-blown simultaneous stirring with a nozzle arrangement according to the present invention (Example), bottom blowing only (normal converter, conventional example), and two side-blown nozzles and a bottom-blown nozzle in a furnace. Fig. 7 shows the transition of molten iron [C] when the rinse treatment is performed by side-blown / bottom-blown simultaneous stirring (comparative example) installed side by side in the circumferential direction. In the example, the molten iron and the slag were sufficiently stirred, and as a result, the decarburization rate was high, and the [C] level reached in the treatment for about 10 minutes was 0.003% or less, which was extremely low carbon steel ([C] ≦ 0. 0.005%) has become possible. Further, in this case, the nozzle arrangements of the cases A and B are very effective. In the case of the conventional example, the influence of the stirring gas flow rate on the decarburization rate was small, and the reached [C] was also in the range of 0.006 to 0.01%, and it was impossible to melt the ultra-low carbon steel. . In the comparative example, although the reached [C] was lower than in the conventional example, stable melting of the ultra low carbon steel was impossible.

FIG. 3 shows the influence of each stirring method on (Total.Fe) during oxygen transfer in the converter. In the examples, the stirring of molten iron and slag is efficient, and the (Total.Fe) value is about half that of the conventional example, and the reduction effect is remarkable. On the other hand, in the comparative example, the improvement effect is small even though it is lower than the conventional example.

FIG. 4 shows the number of times the sloping inhibitor was added during the acid transfer in the converter in each stirring system. In the examples, since the level of (FeO) in the slag was stable at a low level, the slag was sufficiently stirred, and the slag composition was made uniform, it was almost unnecessary to add the slopping inhibitor.

Further, the effects of the stirring gas flow rate and the nozzle position on the decarburization rate, the reached [C] level in molten iron, and (Total.Fe) during the rinse treatment in the method of the present invention were investigated. Here, the decarburization rate during the rinse treatment was compared using the Kc defined by the equation (2) at the decarburization rate for 5 minutes from the start of the rinse treatment. Kc = ln (C ₀ / C _t ) / t (2) Kc: decarburization rate constant (1 / min), C ₀ : initial carbon concentration (ppm) C _t : carbon concentration after t minutes ( ppm), t: time (mi
n)

FIG. 5 shows a lateral blowing gas flow rate of 0.7 Nm ³ /min.t
The following shows the dependence of the bottom blown gas flow rate under constant conditions. Bottom blown gas flow rate is 0.06 Nm ³ /min.ton or more, decarburization rate = 0.4 to 0.6 / min, reaching [C] level in molten iron = 15 to 25 ppm, and (Total.Fe) =
It is 6 to 9% and depends on the gas flow rate of the bottom blown gas flow rate.

In FIG. 6, the bottom blowing gas flow rate is 0.2 Nm ³ /min.t
The following shows the dependence of the laterally blown gas flow rate under a constant condition. In this case, the lateral blowing gas flow rate is 0.1 Nm ³ /min.ton or more, the decarburization rate improves to 0.4 to 0.6 / min, and the [C] level reached in molten iron becomes 30 ppm or less,
(Total.Fe) is also 10% or less and depends on the gas flow rate.

FIG. 7 shows the influence of the installation height of the horizontal blowing nozzle. In this case, when the side-blowing nozzle is set to 1 / 2H or less, the stirring effect of the side-blowing becomes large, and the decarburizing rate,
The effect of improving the [C] level reached in molten iron and (Total.Fe) is large.

[0036]

According to the present invention, the lateral blowing nozzle and the bottom blowing nozzle make the lateral blowing gas amount about 1/10 of the AOD method.
The amount of bottom blown gas is about 1/3 of that of combined blowing, and the total amount of side blowing and bottom blowing is the same amount of stirring gas as combined blowing, and both the molten iron in the furnace and the slag are efficiently stirred, The reaction between [C] and (FeO) in the slag is promoted, and as a result, (Total.Fe) during converter oxygen transfer is stabilized at a low level, and blowing without sloping is possible, and stable operation is achieved. It is possible to improve the iron yield, and it is also possible to melt ultra-low carbon steel that could not be melted in the conventional converter, and it is possible to omit the secondary refining process such as RH.

[Brief description of drawings]

FIG. 1 is a diagram showing the installation positions of a side-blowing nozzle and a bottom-blowing nozzle showing an embodiment of the present invention together with the case of a comparative example.

FIG. 2 is a diagram showing decarburization rate and arrival [C] during rinse decarburization in the method of the present invention, together with the cases of the conventional example and the comparative example.

FIG. 3 is a diagram showing the effect of the method of the present invention on the reduction of (Total.Fe) during acid transfer, together with the cases of the conventional example and the comparative example.

FIG. 4 is a view showing the influence of the method of the present invention on the occurrence frequency of sloping during acid transfer, together with the cases of a conventional example and a comparative example.

FIG. 5 is a diagram showing the influence of a bottom-blowing gas flow rate on refining characteristics in side-blowing and bottom-blowing nozzle agitation in the method of the present invention.

FIG. 6 is a diagram showing the influence of a side-blowing gas flow rate on refining characteristics in side-blowing and bottom-blowing nozzle agitation in the method of the present invention.

FIG. 7 is a diagram showing the influence of the horizontal blowing nozzle height on the refining characteristics of the horizontal blowing and bottom blowing nozzle agitation in the method of the present invention.

[Explanation of symbols]

1: Converter main body, 2: Top blowing lance, 3: Side blowing nozzle,
4: bottom blowing nozzle, 5: molten iron, 6: slag, 7: gas introduction tube.

Claims (5)

[Claims] 1. In refining using a slag forming agent containing lime, one or more side blowing nozzles are provided in the side wall of the furnace body in contact with molten iron, and a bottom blowing nozzle is provided in the bottom of the furnace. And a converter blowing method in which a stirring gas is blown from the bottom blowing nozzle, wherein 0.1 Nm ^{3 is applied} from the side blowing nozzle. /min.ton
Above, and 0.06 Nm ³ from the bottom blowing nozzle /min.ton
A converter blowing method characterized by blowing the above stirring gas. 2. When the number of horizontal blowing nozzles is plural, all the horizontal blowing nozzles are installed within a range of 120 degrees in the circumferential direction of the furnace. Method. 3. The bottom blowing nozzle is installed only at the bottom of the furnace, which is distant from the position of the horizontal blowing nozzle including the center of the bottom of the furnace in the circumferential direction of the furnace by 120 to 240 degrees. The method described. 4. The method according to claim 1, wherein the bottom blowing nozzle is installed only at the bottom of the furnace within a range of ± 20 degrees in the circumferential direction of the furnace from the position of the lateral blowing nozzle including the center of the bottom of the furnace. 5. The method according to claim 1, wherein when the height of the iron bath in the furnace is H, the horizontal blowing nozzle is installed at a height of 1/2 H or less.