JPH02282412A - Method for dephosphorizing molten iron - Google Patents

Abstract

PURPOSE:To improve Mn yield without deteriorating ability of dephosphorization and developing the operational trouble by adding small aggregative material, in which powdery Mn ore, powdery carbonaceous material and powdery slag- making agent are mixed, as Mn-containing material at the time of executing the dephosphorizing treatment to the molten iron. CONSTITUTION:At the time of executing the dephosphorizing treatment in the molten iron, the Mn-containing material is added and the dephosphorizing treatment is executed at the same time, the Mn concn. in the molten iron is raised. As this Mn-containing material, the small aggregative material of pellet- state, briquette-state, etc., in which the Mn ore powder, powdery carbonaceous material of coke, coal, etc., and powdery slag making agent of lime, lime stone, etc., are mixed is used. The molten iron to be treated is desirable to be subjected to predesiliconizing treatment to <=0.30wt.% Si content. By this method, Mn can be reduced and transferred into the molten iron from charged Mn source with high yield.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention simultaneously increases the [Mn]'lHr degree in the hot metal during dephosphorization (hereinafter referred to as "deP#") treatment of hot metal. This article relates to a method for dephosphorizing hot metal to make it more advantageous to produce high-Mn-concentration steel.

<Prior art and its issues> Conventionally, dephosphorization of hot metal was generally performed together with decarburization, etc. in the converter blowing process, but in this case, in order to increase the dephosphorization efficiency, it was necessary to produce CaO, etc. There is a problem in that a large amount of slag agent has to be used, which leads to an increase in the manufacturing cost of steel.In addition, the amount of slag by-product of converter blowing increases, which makes it necessary to dispose of and recycle it. It was necessary to prepare the expenses. In addition, the removal of P in the normal converter blowing process
In the treatment, even if the amount of sludge forming agent was unnecessarily increased, there was a limit to the effect of improving the P removal rate.

Therefore, recently, a method has become popular in which the charged molten iron is dephosphorized as a "molten iron pretreatment" before the molten iron is charged into a converter and decarburized by blowing.

On the other hand, in converter refining of steel, great attention is paid to the concentration of [Mnl] in molten iron. This is because Mn is known to be extremely useful as an element for improving the strength of steel, and high Mn
This is because the demand for steel is also on the rise. By the way, in the production of high Mn steel, conventionally Mn was added to the molten steel after converter refining.
The method used was to adjust the composition by adding ferromanganese containing 70 to 80% n, but since ferromanganese is produced by reducing Mn ore in an electric furnace, it is expensive, especially in Japan where electricity costs are high. This was one of the reasons for the increase in costs.

However, as mentioned above, with the recent development of hot metal dephosphorization treatment technology, the burden of dephosphorization in the converter has been reduced, and a method of blowing with the amount of slag minimized, ie "slag minimum blowing" has been developed. It became possible to reduce the amount of ferromanganese used by increasing the [Mnl tM degree in steel] by adding Mn ore directly to the converter and reducing it.

However, in the above method, M
The maximum amount of N ore blended is 15 to 20 kg/m, and the degree of increase in Mnl in steel is 0.7 to 0.8%.
It was not more than that.

Of course, carbonaceous material such as coke is added to the converter as a heat source, and M
One possibility is to increase the amount of n ore added, but
This method involves picking up S in the carbonaceous material [
New problems were pointed out, such as an increase in S] and a decrease in Mn yield due to an increase in the amount of slag due to the ash content of the carbonaceous material.

Therefore, indium ore is added during hot metal dephosphorization treatment, and
While proceeding with the reduction of Mn ore, [Mnl] in the molten iron was also reduced.
A method was proposed to increase the degree of
No. 8-84913, JP-A-61-153222).

Among these, the proposal as Japanese Patent Application Laid-open No. 58-84913,
A refining agent for hot metal treatment containing Mn oxide and iron oxide: 10 to 70%, calcium oxide: 20 to 70%, and one or both of calcium fluoride and calcium chloride at 1 to 40% is disclosed, On the other hand, a proposal in JP-A No. 61-153222 proposes that when hot metal after Si-removal treatment is subjected to deP treatment in the presence of a deP agent and oxygen, Mn-containing ore is introduced into the deP treatment system, and then dephosphorization is performed. A low-resolution method consisting of injecting a desulfurization agent into the molten iron to advance the desulfurization reaction without forcibly discharging the P slag, and also allowing the Mn component in the Mn-containing ore to remain in the hot metal, followed by refining. P/Low S/High M
This invention discloses a method for manufacturing n-steel.

However, even with these means, if you try to further increase the Mnl concentration in molten iron by increasing the amount of Mn ore (Mn-containing material) charged (especially when the amount of Mn ore charged exceeds 5 kg), In addition to lowering the manganese yield, problems such as deterioration of the hot metal removal rate and operational troubles due to slopping were also observed. This decrease in manganese yield is due to the fact that when the amount of Mn ore (Mn-containing substance) added increases, the melting of the Mn ore itself slows down, and the reduction of MnO by [c] in the molten iron does not proceed quickly. It is considered that In addition, the dephosphorization rate of hot metal deteriorates because the Mn oxide concentration increases due to the addition of a large amount of Mn ore, which reduces the dephosphorization ability of slag, and because the melting point of slag increases, which worsens slag formation. It is caused by

Furthermore, the reason why troubles such as slopping are likely to occur is that Mn due to °[C] in molten iron is
It is assumed that this is because slag with a high MnO content is generated because the reduction of the ore does not proceed quickly, resulting in significant slag foaming.

Therefore, in order to stably produce high Mn# at a low cost, it is absolutely necessary to establish a hot metal dephosphorization method that can solve the above problems.

Therefore, the purpose of the present invention is to add a Mn-containing substance during hot metal dephosphorization treatment to increase [Mnl '114 degrees in the molten iron at the same time as dephosphorization, which may lead to operational troubles such as deterioration of dephosphorization ability and slopping. The aim was to develop a means to effectively improve the Mn yield without causing any problems.

Means for Solving the Problems> In order to achieve the above object, the present inventors first investigated the basic causes of the above-mentioned disadvantages caused when Mn-containing substances such as Mn ore are added during hot metal dephosphorization treatment. After consideration, the following points were confirmed.

That is, MnFL stone has Mn oxide as its main component and also mainly contains Sing and A1□O1 as gangue.
Its melting point is as high as 1700°C or higher. Therefore, in order to reduce Mn ore, it is necessary to dissolve it in slag.

However, when a large amount of Mn ore is added during deP treatment, as the Mn ore dissolves into the deP slag (composed of quicklime, fluorite, etc.), the concentration of Mn oxide in the slag increases, and the melting point of the slag sharply increases. rise to

Note that if Mn oxide is reduced quickly, the increase in Mn oxide concentration will be suppressed and the above-mentioned problem will not occur, but in reality, the reduction rate is not fast enough, so the above-mentioned problem can be avoided. is difficult.

On the other hand, since the hot metal film P is formed at a relatively low temperature of 1250 to 1350°C, the solubility of Mn oxide is insufficient, and the Mn ore cannot be fully dissolved, so the slag becomes a semi-molten state.

For this reason, the reduction of Mn oxide becomes slow and the Mn yield decreases, and the P ratio of the hot metal film also deteriorates.

Furthermore, slag with a high Mn oxide content is highly prone to forming. Therefore, if a high MnO slag that is prone to forming is generated due to the above-mentioned phenomenon, it will lead to troubles such as slopping. It is known that spraying and adding powdered carbonaceous material such as coke powder is effective in suppressing foaming, but this is because MnO is reduced by the carbonaceous material and its concentration decreases. This is thought to be due to the dispersion of powdered carbonaceous material in the slag, which changes the state to a state where it is easier for the generated gas to be extracted.

For this reason, the inventors of the present invention have studied various solutions to the above-mentioned disadvantages based on the above-mentioned confirmation items. When trying to improve the [Mn] concentration in hot metal by adding
When "a mixture of powdered Mn ore, powdered carbonaceous material, and powdered slag-forming agent and agglomerated into a pellet shape, briquette shape, etc." is used as a Mn-containing substance, a) Mn ore and slag-forming agent The reaction with the slag occurs quickly and slag formation is promoted.

b) Mn ore is quickly reduced by the blended carbonaceous material.

c) Rapid reduction of Mn ore reduces the Mn oxide concentration in the slag, and the P ratio of the hot metal film does not deteriorate.

d) A state in which the powdered carbonaceous material is dispersed in the molten slag is quickly realized, and slag foaming is effectively suppressed.

Due to the effects of
] It will be possible to achieve a dramatic improvement of 74 degrees.
We have come to the conclusion that

The present invention has been made based on the above findings, and is based on the above findings.
Quicklime is added to the hot metal injected into the deP treatment furnace.

When performing hot metal film P treatment by adding slag forming agents such as fluorite and converter slag and oxidizing agents such as iron ore and gaseous oxygen, Mn ore powder, carbonaceous material powder and slag forming agent powder are mixed and formed. By introducing a small nodule refining agent into the process, the [Mn] concentration in hot metal can be effectively increased without adversely affecting the P removal rate or without operational troubles such as slopping. have.

In this case, the hot metal to be treated has si, & content of 0.30%.
If you use products that have been preliminarily desiliconized to the following (hereinafter, % representing the component ratio is weight %), the amount of dephosphorizing franks such as quicklime and fluorite can be reduced, and the amount of slag can be reduced. As the Mn content decreases and the Mn yield further improves, the P removal treatment becomes even more advantageous.

That is, in the present invention, when adding a Mn-containing substance during P treatment of hot metal film to increase the [Mn] concentration in the hot metal at the same time as the deP treatment, “powdered Mn ore, coke, etc.” are used as the Mn-containing substance. The basic idea is to use a mixture of powdered carbonaceous materials such as coal and powdered slag-forming agents such as quicklime and limestone, which are formed into small agglomerates in the form of pellets or briquettes.
The formulation of the refining agent for forming small agglomerates may be carried out using the following conditions as a guide.

First, it is desirable that the amount of powdered carbon material be in the stoichiometric amount necessary to reduce Mn oxides and iron oxides in Mn ore.
The amount necessary for the heat source may be further increased and blended.

In addition, the powdery slag agent has a ratio of CaO content to Sin content in small nodules (pellets, briquettes, etc.) of 0.5 to
It is desirable to mix it so that it becomes 2.0.

This is due to the dephosphorization treatment temperature (1
This is to promote slag formation of Mn ore at a temperature of 250 to 1350°C). Outside this range, slag formation and reduction of Mn ore will be delayed, and as a result, there is a strong possibility that Mn yield will deteriorate.

Incidentally, the particle size of the Mn ore powder, charcoal material powder, and slag-forming agent powder that constitute the refining agent is preferably 0.5*wh or less (if it is larger than this, it is difficult to form agglomerates), and It is desirable that the size of the baby clumps is 50 cranes or less. This is because if the size of the nodule refining agent is larger than 50 fins, the dissolution reaction will be delayed, which is not preferable.

Note that it is effective to add a suitable binder (for example, bentonite, etc.) when agglomerating the refining agent. In order to ensure reduction time for the Mn ore, it is appropriate to charge the agglomeration refining agent into the deP treatment furnace before the middle stage of refining.

Moreover, there is no problem in carrying out the dephosphorization treatment in any of a torpedo, a ladle, a converter, etc.

Next, the present invention will be explained in more detail with reference to Examples.

<Example> A 2-ton test hot metal processing furnace (converter) was prepared, and a Mnn ore-added hot metal removal method test was conducted using this.

The test was conducted when carbonaceous Mn ore pellets (powdered Mn ore, powdered coke, and powdered limestone were mixed in a predetermined amount and mixed into small nodules in the form of pellets) were charged as the Mn-containing substance. The results were compared with the case in which bulk Mn ore was charged, and the Mn yield, dephosphorization rate, and slopping conditions of both cases were compared.

Although the experiment was conducted many times with various amounts of Mn ore added, only typical examples will be described below.

First, Table 1 shows the Si-free/S-free hot metal used, Mn1
12: Shows the composition of stone, coke and converter slag.

Table 1 (Note) Values indicate "weight percentage (%)".

Furthermore, Table 2 shows the usage amounts of each raw material and fuel charged into the converter.

In Table 2, "Case 1" and "Case 2" respectively refer to carbonaceous-incorporated Mn ore pellets (A) with the composition shown in Table 3.
This is an example of the present invention using and (U), and - way “Case 3
” is a conventional example using massive Mn ore.

The composition of the carbon-filled Mn ore pellets is such that the ratio of CaO content to Si0g content in the pellet is approximately 1.0 for type (A), and approximately 1.6 for type (I). The amount of limestone was considered so that Furthermore, bentonite was used as a binder during pellet granulation. The particle size of each blended raw material in Table 3 is all 1
It was less than 00 mesh.

Table 3 Table 3 shows the composition ratio of the carbonaceous-equipped Mn ore pellets as described above, but it should be noted that each of the above-mentioned carbonaceous-equipped Kn ore pellets was granulated using a disc-type pelletizer. It is manufactured by drying pellets at 200℃ for 2 hours.
I selected and used 25 cranes.

By the way, in all cases 1 to 3, Mn ore is used.

The total amount of coke and each sludge-forming agent used was the same, and the slag-forming agent composition was determined so that the basicity of the slag (Ca O / Si Oz) was approximately 3.
I set it to be. And the amount of coke is
The amount was increased by 20% of the amount required to reduce all the Mn and Fe oxides in the added Mn ore.

Now, the hot metal film P treatment was carried out by pouring the de-S hot metal into a preliminary treatment furnace (converter), and then immediately before the start of the treatment, by charging the entire amount of the charge shown in Table 2. Note that the molten metal temperature at the start of blowing was 1300°C.

During the treatment, the amount of oxygen supplied from the top blowing lance was kept constant at 2.0Nrrr/min, and the argon gas was supplied from the bottom blowing tuyere at 1.0Nrrr/min.
It was blown in at a flow rate of Nrd 1 minute. And during the process,
Metal and slag samples were taken and analyzed.

Figures 1 and 2 show the changes in the [Mn] and [P] concentrations in the metal in cases 1 and 3 of this process.
Shown in the figure. In addition, the end point [C] density is 4.0 for both image processing.
%, and the molten metal temperature was 1320°C.

From the comparison between Figures 1 and 2, it is clear that the use of carbonaceous Mn ore pellets promotes the smelting reduction reaction of Mn ore, and as a result, the [Mn] in the metal increases and the dephosphorization reaction also occurs quickly. It can be seen that the degree of CP]tffi is decreasing as the temperature progresses. In addition, when using massive Mn ore (Case 3), the Mn yield was 45% and the P removal rate was 75%, whereas when using carbon-filled Mnt stone pellets (Case 1), the Mn yield was 45% and the P removal rate was 75%.
), it was confirmed that the Mn yield was improved to 65% and the P removal rate was improved to 85%.

Furthermore, Figure 3 shows the results of measuring the slag layer thickness during blowing, and it also shows that severe slopping occurred when massive Mn ore was used (Case 3). In contrast, when using carbonaceous interior pellets (case l
) was able to complete the process with almost no slopping.

Although the specific results of Case 2 have been omitted, it has been confirmed that almost the same good results as in Case 1 can be obtained in this case as well.

On the other hand, Fig. 4 shows that pellets with various combinations of slag-forming agents (limestone, quicklime, dolomite, etc.) were made, and the carbonaceous interior Mn
The results of a study on the appropriate proportion of slag-forming agents in ore pellets are shown. It goes without saying that in each of these tests, the total blending amount of the sludge-forming agent, including the lump-like sludge-forming agent, was kept constant.

From the results shown in Figure 4, it is concluded that "it is preferable to adjust the Cab/5tot ratio of the slag forming agent added to the pellets to 0.5 to 2.0 in order to ensure a high Mn yield." However, this is because the rMn yield particularly depends on the quality of slag formation of Mn ore at a low temperature range of 1250 to 1350°C, and when the CaO/SiOz ratio is 0.
This is presumed to be due to the fact that if the value is outside the range of 5 to 2.0, the slag formation and reduction of Mn ore will be delayed, resulting in a worsening of the Mn yield.

<Summary of Effects> As explained above, according to the present invention, it is possible to remove P without causing operational troubles in hot metal membrane P treatment.
It is possible to reduce and transfer Mn from the input Mn source to the hot metal with a high yield without deteriorating the Mn ratio, and the Mn in the hot metal [Mn
n] concentration can be stably and greatly improved, and the refining cost of high-Mn steel can be significantly reduced, which brings about extremely useful effects industrially.

[Brief explanation of drawings]

Figure 1 shows the [Mn concentration and [P] f in the metal during hot metal film P treatment when carbonaceous Mn ore pellets are introduced.
It is a graph showing the transition of one degree. FIG. 2 is a graph showing changes in [Mn 111 degrees and CC] S degrees in the metal during blowing when bulk Mn ore is introduced. FIG. 3 is a graph showing the measurement results of the slag layer thickness during the P removal process. Figure 4 shows the sludge-forming agent Cab/Sin added to the pellets.
, is a graph showing the relationship between the ratio and the Mn yield.

Claims (2)

[Claims] (1) When performing hot metal dephosphorization by adding a slag-forming agent and an oxidizing agent to the hot metal injected into the dephosphorization furnace, Mn ore powder, carbonaceous powder, and slag-forming agent powder are mixed and formed into small pieces. A hot metal dephosphorization method characterized by increasing [Mn] in hot metal by melting and reducing Mn ore at the same time as dephosphorization by adding a nodule refining agent. (2) The method for dephosphorizing hot metal according to claim 1, wherein the hot metal to be treated has been subjected to preliminary desiliconization treatment to reduce the Si content to 0.30% by weight or less.