JPH01312020A - Method for dephosphorizing molten iron by heating - Google Patents

Abstract

PURPOSE:To effectively heat molten iron and to secure high dephosphorization efficiency by adding a part of a dephosphorizing agent and a carbonaceous material to the molten iron in a top and bottom-blown converter, blowing O2 from the top at the same time to heat the molten iron, and then adding the remaining dephosphorizing agent. CONSTITUTION:A part of a dephosphorizing agent and a carbonaceous material such as coke are added to the molten iron in the early stage of dephosphorization, and the molten iron is ordinarily heated by top-blowing oxygen. When the heating stage is finished, the remaining dephosphorizing agent is added, and dephosphorization is carried out. As a result, a decrease in the [C] concn. after treatment (decreased to <=0.5wt.%) is not caused even when low-temp. crude molten iron is used, and effective heating is carried out. By this method, high dephosphorization efficiency is secured, and molten iron can be dephosphorized to the stage where sufficient scrap iron and Mn ore can be added to the obtained dephosphorized molten iron in the succeeding decarburization stage.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides a method for improving the dephosphorization rate of low-temperature hot metal (hereinafter referred to as deP), as well as ensuring a sufficient temperature of the hot metal after treatment. This relates to a temperature-programmed dephosphorization method.

<Conventional technology> In response to the increasing quality requirements for various steel materials in recent years, efforts have been made to produce low-P steel at low cost and to streamline costs as a total steel manufacturing system (reducing the total amount of slag-forming agent used, With the aim of reducing ferromanganese by melting and reducing manganese ore, hot metal dephosphorization treatment, which removes phosphor from hot metal before steelmaking, has been actively adopted.

The following methods are representative of the hot metal dephosphorization treatment methods that have been proposed so far.

(A) A method in which quicklime-based flux or soda ash is injected into the hot metal in the torpedo.

(B) A method in which quicklime-based flux is injected or blasted into the hot metal in the ladle.

(C) A method of blasting quicklime-based flux to hot metal in the blast furnace casthouse trough.

(D) Method of blowing using a converter and quicklime-based flux [Tetsu to Tsuna, (1981), 326B
page〕.

(E) Using an upper and lower blowing converter, the converter slag (decarburization (hereinafter referred to as
A method of blowing using the product (referred to as decarbonization) as the main component of a dephosphorizing agent [Japanese Patent Application No. 132517/1982].

However, it is generally known that performing such hot metal deP treatment causes a decrease in the temperature of the hot metal.

Moreover, for example, in a steelworks with a blast furnace of 2000 to 3000 m class, and where hot metal is handled by a small torpedo with a capacity of about 150 m or less, heat dissipation from blast furnace tapping to the next process is difficult. The drop in temperature of the hot metal was even more significant.

However, recently, the amount of ferroalloy (ferromanganese) added has been reduced by melting scrap in the next steelmaking process, increasing the amount of smelting reduction of manganese ore, etc. to increase the concentration at the end point of the converter. In this case, it is important that the supplied hot metal has a [CltN degree as high as possible and a temperature as high as possible. A drop in temperature had to be avoided at all costs.

However, as a method of increasing the hot metal temperature during hot metal deP, a small amount (about 5N rrr/) is added along with the addition of a deP agent.
It has also been considered and implemented to inject oxygen gas into the hot metal and burn part of the [Si] in the hot metal and the [C] into i8 I'. However, it was not possible to significantly increase the temperature of hot metal to the desired value.

Of course, it is possible to further raise the temperature of the hot metal by increasing the amount of oxygen gas injected, but in this case, there will be a lot of decarbonization, so when processing in a torpedo or ladle, it is difficult to supply oxygen and collect dust. There were limitations in terms of equipment, and it was not a method that could actually be adopted.

On the other hand, when using a top and bottom blowing converter for deP treatment as shown in (D) or (E) above, there is no problem with the oxygen supply or dust collection equipment, so the top blowing oxygen amount is For example, 1ON
n? / could be set to a large value such as above, which would increase the temperature of the hot metal, promote the formation of dephosphorizing agent into slag, and improve the dephosphorization rate, but in this case, In this case, decarbonization of the hot metal progresses excessively, and the [C] concentration in the hot metal after dephosphorous treatment decreases to, for example, 3.5% by weight or less, resulting in a lack of heat source in the next converter (decarbonizing furnace). There was a problem in that the amount of scrap used in the Nawate converter and the amount of manganese ore and iron ore that can be melted and reduced were reduced, resulting in a reduced cost reduction effect.

In addition, when performing the hot metal deP treatment shown in item (11) or (H) above, it is advantageous to deSi the hot metal coming out of the blast furnace in the blast furnace casthouse or torpedo in advance. In some cases, adding a desiliconizing agent mainly composed of iron oxide to perform the desiliconization treatment causes a drop in the temperature of the hot metal, and sometimes the temperature of the hot metal when poured into the converter (dephosphorization furnace) of a net making factory decreases. 1300
The temperature drops to below ℃, and in some cases, 1250℃.
Sometimes it decreased to below. As the temperature of the hot metal continues to decrease in this way, the temperature of the hot metal will rise significantly if only the usual supplementary oxygen injection of <5N%/j is performed during the deP treatment in the upper and lower blowing converters. Therefore, it was not possible to avoid the above-mentioned problem of poor slag formation of the P-removed slag, resulting in poor P-removal.

On the other hand, in this case, a method of adding carbonaceous materials such as coke in the converter (decarbonizing furnace) to compensate for the decrease in [01 min] during dephosphorization was considered, but if such a method is adopted, coke It is used in converters (decarbonization furnaces) that process hot metal whose P content has already been reduced by picking up S from the molten iron (usually the S content is about 0.5% by weight) and entering the hot metal. There was a problem in that the amount of slag forming agent was small and the slag's ability to remove S was low, leading to an increase in the [S]C degree of molten steel.

<Problem to be solved by the invention> Under these circumstances, the main purpose of the present invention is to
[S] DeP of low-temperature hot metal that would normally be difficult to remove by increasing the hot metal temperature to a high value (temperature after deP treatment of 1300 to 1400°C) without causing inconveniences such as It is an object of the present invention to provide a hot metal film P method that can effectively carry out the process and ensure a sufficient hot metal temperature after deP treatment.

Means for Solving the Problems> The present inventors have conducted research from various viewpoints to achieve the above object, and have obtained the following knowledge.

(a) The method proposed in the above-mentioned Japanese Patent Application No. 132517/1982 (one of the two upper and lower blowing converters is replaced by a dephosphorizing furnace,
The other is a carbon removal furnace, and a refining agent mainly composed of converter slag generated in the carbon removal furnace is added to the hot metal injected into the carbon removal furnace, and while bottom blowing gas is stirred, oxygen is blown into the hot metal. DeP obtained after performing P deP? 9) When pre-dephosphorizing hot metal by blowing it with a dephosphorizing agent in an upper and lower blowing converter, such as in the dephosphorization treatment process (method of decarbonizing and finishing dephosphorizing pig iron in a decarbonizing furnace) , 21, when blowing is performed by adding carbonaceous materials such as coke, unlike the case where carbonaceous materials are added to increase the temperature in the subsequent converter blowing (de-C furnace blowing), the carbonaceous materials S, which tends to enter the hot metal from the slag, is captured in the dephosphorization slag, which is sufficiently present, and even though the hot metal temperature is sufficiently increased by the combustion heat of the input carbonaceous material, the The concentration should not show any particular upward trend.

(bl However, if carbonaceous materials such as coke are added during hot metal dephosphorization blowing, the iron oxide content in the dephosphorization slag is reduced due to the presence of carbonaceous materials at the beginning of blowing, and the dephosphorization rate deteriorates. There was a problem, but this problem was solved by adding only a part of the dephosphorizing agent at the beginning of oxygen blowing after adding carbonaceous material, and then raising the temperature of the hot metal and finishing part of the dephosphorization. At that point, the amount of oxygen top blowing was reduced to the normal small amount in the ``Hot metal dephosphorization method using an upper and lower blowing converter'' shown in the above-mentioned Japanese Patent Application No. 132517/1984, etc., and the remainder of the dephosphorization agent was added. When the treatment is carried out for a predetermined period of time (approximately 10 to 15 minutes) in this state, the iron oxides (T, T,
Fe) is secured to a level that is advantageous to IThP, and good P removal progresses, so that it is sufficiently wiped out.

This invention was made based on the above knowledge, and [a dephosphorizing agent is added to hot metal poured into a converter type furnace having both upper and lower blowing functions, and oxygen gas is removed while stirring the bottom blowing gas.] In the method of dephosphorizing hot metal by top-blowing, first a part of the dephosphorizing agent and carbon material are added and oxygen is top-blown to heat the hot metal, and then the remaining dephosphorizing agent is added. This method is characterized by the fact that a sufficient temperature of the hot metal can be maintained after the deP treatment without causing problems such as a decrease in the deP removal rate or an increase in the concentration.

Note that the "converter-type furnace with both upper and lower blowing functions" referred to here is basically an LD converter, with Ar flowing from the bottom of the furnace.
, N, CO□, CO or 02 gas from 0.03 to 0
．． 3ON n? A typical example is a so-called "compound blowing converter" in which auxiliary stirring is provided by blowing in a certain amount of /mfn-.

In addition, although the dephosphorizing agent is not particularly specified, from the viewpoint of reducing slag and reducing the total cost of steelmaking,
"Converter slag-iron oxide-fluorite base" or "converter slag-iron oxide-fluorite base containing converter slag 2 with low p, o (e.g. 1% by weight or less)" generated in a decarbonizing furnace as shown in No. 1-132517 as a basic component "Converter slag - manganese ore - fluorite base 1 is good, and quicklime may be added to this. Of course, quicklime - iron oxide - fluorite base, which is usually used for dephosphorization of hot metal in a torpedo or ladle, is preferable. As mentioned above, it does not matter.

The amount of dephosphorization agent to be added is approximately 50 kg for those whose main component is converter slag, but depending on the basicity of the slag (Ca
It is preferable to set O/SiOz) to 2 or more, preferably 2.5 or more from the viewpoint of removing S. This is because when carrying out the method of the present invention, S enters into the hot metal from carbonaceous materials such as coke. What is trending is the above-mentioned tendency, but in order to avoid high [S] after P removal, S removal by P removal slag becomes important.

There are no particular restrictions on the shape, particle size, etc. of the dephosphorizing agent;
For example, there is no need to transform granular materials into powder.

Coke is commonly used as a carbon material, but the type is not particularly important as long as it can be used as a fuel. Of course, low S coke is preferable, but dephosphorization slag is used during dephosphorization treatment. Since S removal also progresses, a regular product with an S content of about 0.5% by weight is sufficient. However, when the S content of the carbonaceous material is high, as described above, it is preferable to adjust the basicity of the slag to 2.5 or more.

The amount of carbonaceous material added varies depending on the desired temperature increase level, but is preferably about 1 to 10 kg/coke, and may be about 15 kg/at most.

Next, details of the hot metal dephosphorization process according to the present invention will be explained along with its operation.

<Function> In the hot metal dephosphorization treatment according to the present invention, at the beginning 1υj, a
A portion of the P agent and carbonaceous material are added, and the hot metal is usually heated and raised in temperature by top-blown oxygen.

After the heating/temperature raising period ends, the remaining dephosphorization agent is added to enter the dephosphorization refining period.

FIG. 1 is a diagram illustrating an example of the above-mentioned method of the present invention, with the amounts of dephosphorization agent and carbon material added, and the amount of top-blown oxygen added.
Figure 2 similarly shows another example, but during the temperature rise period (
Since P dephosphorization continues during this period, the following steps will be taken:
The characteristics of the P phase and the de-P phase are described below.

Seika 2nd edition, temperature rise and de-P! ! If Jl is simply heated, it is sufficient to add scrap and coke and top-blow oxygen, but even in this case, if slag is not present, a) Spitting (less than 1 m diameter) will occur. granular iron scattering) increases.

b) Fe yield decreases due to increase in hume loss.

c)/8 [Si] in the pig iron is oxidized, and the resulting acidic SiC2 promotes the erosion of basic refractories.

d) Top-blown oxygen causes combustion of not only coke but also [C] in the hot metal, resulting in a decrease in [C] in the hot metal.

Such inconveniences may occur. Therefore, a cover slug is necessary.

When a part or most of the dephosphorization agent is added to form this cover slag, it is sufficiently turned into slag during the heating/temperature raising period, making the dephosphorization reaction advantageous in the next dephosphorization period.

The amount of top-blown oxygen for temperature raising and P'M removal may be the same level (2 to 4 N rrr/m1n4) as for carbon removal blowing for boat fishing.

However, in order to preferentially burn the carbonaceous powder in the slag rather than [C] in the hot metal, it is important to perform blowing as softly as possible. In addition, this makes it possible to
Secondary combustion (a phenomenon in which CO gas produced by combustion is further combusted into CO2 by top-blown oxygen) can also be expected. In addition,
This secondary combustion is more likely to occur at low temperatures, such as during dephosphorization of hot metal (
Moreover, since the temperature of the refractory in the furnace is lower than that during carbon-free main blowing or normal converter blowing, problems such as refractory melting and loss do not occur.

When performing the above soft plow, the design of the lance nozzle must be devised or the distance between the lance and the metal surface must be increased to reduce L/LO (L: metal bath indentation depth by O□ jet, Lo: metal bath depth). It is desirable to perform blowing so that the ratio of

The ratio of coke to top-blown oxygen at this time is determined by the stoichiometric amount of oxygen required to burn the coke.

However, it goes without saying that it is necessary to consider the amount of oxygen required for secondary combustion.

The time required for the temperature increase/P removal phase varies depending on the desired temperature increase level, but is usually about 2 to 6 minutes.

What is important during the dephosphorization phase is to pay attention to whether the slag formed during the temperature rise and dephosphorization phase is in a state in which the amount of iron oxide is reduced and is unfavorable for dephosphorization. It is a point. For this reason, it is desirable to add iron oxide or manganese ore to increase the oxidizing power of the slag during the aP period.

In addition, if the hot metal temperature before the temperature increase/deP phase is extremely low, for example, 1250℃ or less, the
Adding most of the agents is thermally difficult. Therefore, in order to deal with such a situation, it may be necessary to add about half of the dephosphorizing agent first and then add the remaining amount during the dephosphorizing period.

The amount of top-blown oxygen during the dephosphorization period may be as small as 0.5 N/ml.

Further, the time required for the de-P phase may normally be 5 to 15 minutes.

Here, when considering the P removal rate, the hot metal temperature is 140
It is important to keep the temperature below 0"C. This is because if the pig iron temperature exceeds 1400"C, iron oxide in the dephosphorized slag is reduced by [C] in the hot metal (T and Fe in the slag are 2% or more), dephosphorization will worsen.

Next, the present invention will be specifically explained with reference to Examples.

<Examples> Example 1 First, 160 tons of the hot metal shown in the upper row of Table 1, which had been subjected to de-S and Si-removal treatment in a torpedo, was poured into an upper and lower double blowing combined blowing converter used as a de-P furnace.

Since the hot metal temperature at this time was as low as 1250°C, the converter slag generated in the same type of carbon removal furnace was cooled and solidified and crushed into particles with a particle size of 30 fl or less: 25 kg/l,
Similar particle size iron ore: 5kg/and fluorite: 8ktr
At the same time, 6 kg of coke grains were added to Yazoe, and 3 Nn (7 m1 n-
Oxygen gas was blown upward for 2.5 minutes to raise the temperature of the hot metal.

In addition, the middle row of Table 1 shows the composition of hot metal after temperature rise.

Next, the distance between the lance and the hot water surface was set to 2m, and the
The amount was reduced to 0.5N rrr/m1nt, and blowing (deP treatment) was performed for 10 minutes. During this time, 5 kg/l of iron ore was added.

As a result, the slag formation of the dephosphorizing agent was good, and hot metal having the component composition and temperature shown in the lower row of Table 1 was obtained. Table 1 also shows that hot metal dephosphorization can be carried out with a small [S] amp at a good dephosphorization rate, and at a sufficiently high temperature of 1320°C.
It can be seen that hot metal can be secured.

The refining conditions of the deP furnace used were as follows.

Top-blowing 02 lance nozzle: 3-hole Laval.

Stirring gas blown into the bottom of the furnace: CO2 gas.

Stirring gas amount: 0. IN%/+n1n-t.

Example 2 Hot metal dephosphorization treatment was carried out under all the same conditions as in Example 1, except that manganese ore was used instead of iron ore as the dephosphorizing agent during the temperature rise/dephosphorization period.

Table 2 shows the component compositions and temperatures of the raw hot metal, the hot metal after heating, and the hot metal after dephosphorization used at this time.

As is clear from the results shown in Table 2, hot metal film P can be formed with a good P removal rate through this treatment.
The temperature of the hot metal was also sufficiently high at 1325℃, and the temperature of the hot metal [
It was confirmed that Mn] 4 degrees increased to 0.59% by weight.

It goes without saying that the desaturation of the dephosphorizing agent was achieved relatively well during the temperature rise/dephosphorization period.

Example 3 Hot metal whose temperature was as low as 1220°C due to problems in the upstream process was sent to us, so 160 tons of the hot metal was sent to the upper and lower double blowing combined blowing converter as in Example 1. Pour the iron and add the same converter slag as in Example 1: 10 kg/l
, 4 kg/l of fluorite and 79 kg/l of coke grains were added, the distance between the top blowing lance and the hot water level was 3 m, and the temperature was 3 N/l.
The temperature of the hot metal was raised by blowing oxygen gas upward for 4 minutes at an oxygen supply amount of m1nt.

After this, the distance between the top blowing lance and the hot water surface was set to 2 m,
Oxygen supply amount is 0.5N n? /min・t, converter slag: 15 kg/l, quicklime: 5 kg/l,
After adding 5 kg of iron ore and 4 kg/l of fluorite and performing blowing (deP treatment) for 8 minutes, 5 kg/l of iron ore was added and blowing was continued for another 2 minutes (deP treatment). treatment) was carried out.

Table 3 shows the composition and temperature of the raw hot metal, hot metal after heating, and hot metal after dephosphorization that were used at this time. Favorable results were obtained in terms of temperature and impurity contamination.

Table 3 Comparative Example 1 Dephosphorization agent (converter slag: 25 kg/l, iron ore: 1
Hot metal dephosphorization treatment was carried out under the same conditions as in Example 1, except that fluorite: 0 kg/l and fluorite: 8 kg/l) were added in bulk.

Table 4 shows the component compositions and temperatures of the raw hot metal, the hot metal after heating, and the hot metal after dephosphorization at this time.

As is clear from the results shown in Table 4, this method of adding the dephosphorizing agent all at once had a sufficient effect of raising the temperature of the hot metal and the dephosphorizing agent was well formed into slag, so the dephosphorizing effect was low. However, it can be seen that the P removal rate is slightly worse.

Comparative Example 2 Hot metal dephosphorization treatment was carried out under the same conditions as in Example 1 except that no coke was added.

As a result, the temperature of the hot metal rose and the dephosphorization agent was successfully turned into slag, but the [C] in the hot metal decreased to 3.4% by weight, and the heat source in the subsequent decarbonization furnace was insufficient, resulting in a reduction in scrap. Addition and dissolution could not be performed at all.

In addition, the raw material hot metal at this time, Noboru? Table 5 shows the composition and temperature of the hot metal after A and the hot metal after dephosphorization.

=19- Comparative Example 3 In this example, no coke was added or the temperature rising period was set.
DeP agent in the converter (converter slag: 25 kg/l, iron ore:
fluorite: 8 kg/l) was added, and the distance between the top blowing lance and the hot water surface: 2 m, the amount of oxygen supplied: 0.
DeP treatment was carried out at 5 N rrr/m1nt for 10 minutes, and the results shown in Table 6 were obtained. Note that the conditions other than those described above were the same as in Example 1.

As can be seen from Table 6 above, in this case, hot metal [
C] was not observed, but it was confirmed that the dephosphorization agent remained in slag for a long time without increasing the hot metal temperature, and the dephosphorization rate was also poor.

As explained above, according to the present invention, even if low-temperature raw hot metal is used, the [C]?M degree after treatment can be exceptionally reduced (reduction to 0.5% by weight or less ), thereby ensuring a good dephosphorization rate and producing dephosphorized pig iron that allows sufficient addition of scrap and manganese ore during the subsequent decarbonization process. This brings about extremely useful effects industrially, such as being able to provide a hot metal dephosphorization treatment method.

[Brief explanation of the drawing]

FIG. 1 illustrates an example of the method of the present invention, with the amounts of the dephosphorizing agent and carbonaceous material added, and the amount of top-blown oxygen added.

Claims (1)

[Claims] In a method of dephosphorizing hot metal by adding a dephosphorizing agent to hot metal poured into a converter-type furnace having both upper and lower blowing functions, and blowing oxygen gas upward while stirring the bottom blowing gas, first the dephosphorization is performed. A method for temperature elevation dephosphorization of hot metal, which comprises adding a part of a dephosphorizing agent and a carbonaceous material, heating the hot metal by blowing oxygen over the top, and then adding the remaining dephosphorizing agent.