JP3239722B2 - Hot metal pretreatment 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 pretreatment method capable of simultaneously performing desulfurization, desiliconization and [Mn] rise of hot metal.

[0002]

2. Description of the Related Art High-manganese low-sulfur steel ([% Mn] = 0.4-2.0, [% S] = 0.005-
The following processing method is generally used when melting 0.015).

[0003] That is, after hot metal from a blast furnace is desiliconized with a gutter or a torpedo car at the time of tapping, pretreatment such as dephosphorization and desulfurization is performed in a torpedo car or a ladle. Alternatively, after performing desulfurization treatment in a torpedo car or ladle, preliminary treatment such as desiliconization and dephosphorization is performed in a converter or the like. Thereafter, decarburization is performed in the converter, and at the time of tapping from the converter, expensive manganese alloy iron such as metallic manganese and ferromanganese is added to adjust the manganese concentration in the molten steel.

[0004] According to the above method, when the concentration of Si in the hot metal is high and the desiliconization treatment is not performed before the dephosphorization treatment, the amount of SiO ₂ generated during the dephosphorization treatment increases, so that the dephosphorization ability is secured ( In order to maintain basicity), more lime-based slag-making agent was required, which increased steelmaking costs. Also, when the amount of the slag-making agent increases (the slag volume increases), the amount of manganese lost into the slag increases (the manganese yield decreases), and the amount of manganese alloy iron added during converter tapping increases accordingly. This has also been a factor in increasing steelmaking costs.

[0005] In order to reduce steelmaking costs, it is desired to maintain the [Si] concentration in the hot metal before the dephosphorization treatment at a low level. However, this control is difficult for blast furnace operation.

[0006] Even when the desiliconization treatment is performed before the dephosphorization treatment, sinter ore or scale is added as a desiliconization agent in a usual method. [Mn]) was also oxidized into the slag.

As a method for adjusting the [Si] concentration in the hot metal before the dephosphorization treatment to an appropriate level, there is a method disclosed in JP-A-6-271920. This is during the hot metal desulfurization, CaO while stirring the hot metal desulfurization by adding a flux (first refining agent) consisting of CaF ₂ and manganese minerals, during desiliconization and molten pig iron to increase the [Mn] And then adding a flux (second refining agent) containing CaO, Na ₂ CO _3, C, etc. as a main component, to carry out further desulfurization. The manganese mineral means manganese ore, iron manganese ore, manganese oxide and the like.

According to this method, at the time of desulfurization treatment, it is possible to simultaneously perform the desiliconization treatment to an appropriate level without increasing the number of treatment steps, so that the amount of slag-forming agent added (slag volume) during the dephosphorization treatment is reduced, Manganese yield improved.

Moreover, in this method, an inexpensive manganese mineral is used as a desiliconizing agent, so that the silicon generated during the desiliconization treatment is reduced.
The calorific value of oxidation can be effectively used for the smelting reduction of manganese minerals, and the [Mn] concentration in the hot metal can be increased at low cost. Therefore, saving of expensive manganese alloy iron added after the decarburization treatment was achieved.

Japanese Patent Publication No. Sho 60-27721 discloses a method of desiliconizing hot metal and increasing [Mn] using iron manganese ore with a slag basicity of 1.0 to 2.0. However, this method has a low basicity, and sometimes CaF ₂ is not added.
Poor slag-making properties and desulfurization properties.

[0011]

When the first refining agent is added in the method disclosed in JP-A-6-271920, a sufficient refining effect may not be obtained within the treatment time depending on the order of addition. That is, even when the amounts of CaO, CaF ₂ and manganese oxide are the same, when these are added together at the same time, or when CaO is added earlier, CaO and manganese oxide are high. Forming a melting point oxide,
When the fluidity of the slag decreases, the reduction of MnO ₂ (generation of SiO ₂ ) in the slag stagnates, and [Mn] rise and desiliconization do not effectively proceed.

Regarding the desulfurization effect in the method of JP-A-6-271920, although the desulfurization reaction proceeds only by adding the first refining agent, [% S] = 0.0
In order to desulfurize the hot metal to 10 or less, it was necessary to add a second refining agent for the purpose of increasing the slag basicity. Since the second refining agent is added, the treatment time is longer than that of ordinary hot metal desulfurization treatment, which may be disadvantageous in terms of dropping hot metal temperature, etc. Mareta.

In order to carry out a sufficient desulfurization treatment by adding only the first refining agent, it is necessary to increase the basicity of the slag as much as possible. However, as the CaO concentration in the slag increases, the melting point of the slag increases, Is reduced. As the fluidity decreases, the progress of the reduction reaction of MnO 2 in the slag stagnates, and the effects of desiliconization and [Mn] increase cannot be sufficiently obtained. When a large amount of MnO remains in the slag, the desulfurization reaction does not effectively proceed.

[0014] Therefore, it is desired that the addition of only the first refining agent efficiently achieves desiliconization and the rise of [Mn] in the hot metal and sufficiently promotes the desulfurization reaction. While maintaining a good condition
Enhancing slag basicity sufficiently remained as a further problem.

[0015]

The present invention method Means for Solving the Problems], upon the addition of CaO and CaF ₂ as minerals and Zokasu agent to manganese oxide main component with respect to molten iron by considering their order of addition, the slag Makes it possible to increase the basicity in a state where the fluidity of the powder is kept good.

The gist of the present invention resides in a pretreatment method for hot metal, characterized in that the hot metal is treated in the following steps:

A mineral containing manganese oxide as a main component is added to hot metal.

This manganese oxide and silicon in hot metal ([S
i)) to generate SiO ₂ by an oxidation-reduction reaction with i)).

A liquid phase slag containing SiO ₂ and MnO as main components is formed.

[0020] CaO and CaF ₂ are added as a slag-making agent,
Adjust the slag basicity (CaO / SiO ₂ ) and melting point.

Simultaneously with desulfurization, desiliconization and increase of manganese ([Mn]) in hot metal are carried out.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The operation of the embodiment of the method of the present invention and the change in the composition of slag will be described.

First, a mineral mainly composed of manganese oxide is added to hot metal. As this mineral, manganese ore and iron manganese ore can be used.

When manganese oxide is added to hot metal, [Si] and manganese oxide in the hot metal cause an oxidation-reduction reaction represented by the following formulas (1) and (2).

MnO + (1/2) [Si] = Mn + (1/2) SiO ₂ ... (1) MnO ₂ + [Si] = [Mn] + SiO ₂ ... (2) Result SiO ₂ is produced, the liquid phase slag (melting point of MnO-SiO ₂ system mainly composed of SiO ₂ and MnO fused with MnO 1,200 to 13
(A composition of about 00 ° C.). The added manganese oxide is sequentially dissolved in the liquid phase slag and comes to exist in the liquid phase slag as MnO, and the MnO in the slag reacts with the (Si) in the hot metal through the interface between the slag and the hot metal. go. As the formation of SiO ₂ and the dissolution of MnO proceed continuously, the liquid phase slag increases.

Next, CaO and CaF ₂ are added as slag-making agents to adjust the basicity (CaO / SiO ₂ ) and melting point of the slag.

When CaO is added, CaO is added to the liquid slag.
Dissolves, and the composition of the liquid phase slag changes to CaO-MnO-SiO ₂ system. The slag basicity (CaO / SiO ₂ ) increases with the increase of CaO in the slag. At this time, a preferable range of the basicity is 2.0 to 5.0.

MnO in slag due to increase in slag basicity
Activity is reduced, and the reduction reaction is promoted. Further, since the activity of Ca ^{2+ in} the slag increases, the desulfurization reaction represented by the following formula (3) is also promoted.

Ca ²⁺ + S ²⁻ = CaS (3) By adding CaF ₂ simultaneously with CaO, CaO or manganese oxide contains SiO ₂ and MnO as main components. It is possible to promote the dissolution in the MnO—SiO ₂ liquid slag. This is because the presence of CaF ₂ having a relatively low melting point (having a melting point of 1417 ° C.) in the slag lowers the melting point of the entire slag and expands the compositional liquid phase region at a constant temperature. At this time, the preferable range of the amount of CaF ₂ added is 1 to 15 kg per ton of slag.

The above action increases the fluidity of the slag and speeds up the mass transfer in the slag, thereby increasing the reaction rate of reduction and desulfurization of MnO. Finally slag MnO is reduced to equal to or less than that or about 2-3%, the slag composition is the CaO-SiO ₂ -CaF ₂ system.

As described above, the rise of [Mn] in the hot metal, desiliconization and desulfurization simultaneously and effectively proceed.

Here, MnO— containing SiO ₂ and MnO as main components is used.
The timing of supplying CaO to the liquid phase slag of the SiO ₂ system greatly affects the progress speed of the above-mentioned action. That is, when the supply of CaO is simultaneous with or shortly after the generation timing of the liquid phase slag of the MnO-SiO ₂ system, the slightly generated liquid phase slag is
MnO
Dissolution and reduction reaction stagnate. Then, a large amount of unreacted manganese oxide and CaO remain.

In order for the reduction reaction of MnO and further the desulfurization reaction to proceed smoothly, it is important to always maintain the existing state of the liquid phase slag. For this purpose, it is necessary to add manganese oxide, which is a source of the liquid phase slag, to the hot metal in advance and wait for the formation of the liquid phase slag before adding CaO and CaF ₂ .

The above will be further explained with reference to FIG. FIG.
FIG. _{2 is a} ternary phase diagram of CaO—SiO ₂ —MnO illustrating transition of slag composition during processing, comparing the method of the present invention with the conventional method. In the figure, white arrows show typical examples of changes in slag composition when manganese oxide, CaO and CaF ₂ are simultaneously added to hot metal. On the other hand, the black arrow shows a typical example of a change in slag composition when manganese oxide is added first, and then CaO and CaF ₂ are added.

As shown in the figure, the slag composition in the case of the white arrow indicates that CaO—
Transitions to the high melting point region of MnO system (melting point is over 1700 ℃).
However, the slag composition in the case of the black arrow is the initial composition of MnO
The MnO-SiO ₂ Henjo remained toward the SiO ₂ points from the point, melting point
Reach the low melting point range of 1200-1300 ° C. Thereafter, the temperature changes toward the CaO—SiO ₂ side as CaO dissolves, and during that time, the temperature also changes in the low melting point region.

The time for adding manganese oxide is preferably as early as possible during the treatment as long as sufficient stirring is obtained, and the addition is preferably completed until half of the treatment time has elapsed. . The addition method at this time may be any of batch, division and continuation.

The addition of manganese oxide may be carried out all at once, but by dividing or adding continuously, manganese oxide remaining unreacted on the hot metal is reduced, and liquid phase slag is formed and slag in the slag is reduced. It is possible to cause the MnO reduction reaction more efficiently.

When CaO and CaF ₂ are added in a divided or continuous manner during a certain period of the manganese oxide treatment, the addition of CaO and CaF ₂ may be performed after the manganese oxide addition period or during the addition period. Importantly, and SiO ₂ in front of the CaO addition of Mn
This is to form a liquid phase slag of MnO—SiO ₂ system containing O ₂ as a main component, and it is necessary to secure a period for forming the liquid phase slag. The addition method at this time is not limited to batch, division and continuation.

As in the case of adding manganese oxide, the addition of CaO may be carried out in a lump, but it is more preferable to add it separately or continuously. This is due to the reduction of CaO remaining undissolved on the hot metal, resulting in a decrease in the Ca of the liquid phase slag of the MnO-SiO ₂ system.
This is for avoiding a high melting point due to O 2 saturation. In particular, when CaO is added to finally raise the basicity of the slag to a high range of 2.0 or more, continuous addition is desirable.

Since CaF ₂ serves as a slag-making accelerator, it may be added all at once, but may be divided or continuously added. It is important to avoid the slag having a high melting point when CaO is added. In view of this point, it is desirable to add slag at the same time as or before CaO addition. When the temperature of the hot metal before the treatment is low, it is preferable to add the manganese oxide at the same time as the manganese oxide to be added first to promote the formation of liquid phase slag.

Further, the addition of CaO and CaF ₂ reduces the processing time.
It is recommended that the reaction be completed before 2/3 has elapsed, and that a reaction time be maintained until the end of processing.

The treatment time is preferably set mainly based on a balance between the degree of progress of each refining reaction and the drop in hot metal temperature or the convenience in the process. Each refining reaction generally proceeds if the processing time is 10 to 15 minutes, and is almost completed in 30 minutes. On the other hand, as the treatment time increases, the temperature of the hot metal decreases in proportion to the treatment time, so that the time and thermal burden on the subsequent steps increases, and the progress of each refining reaction starts to stagnate. Therefore, the desired processing time is 10-30 minutes,
More desirable is 15-20 minutes.

During the treatment, it is desirable to stir the hot metal and the slag.

The desired particle size of the added manganese mineral and slag-making agent should be selected in consideration of the effect on the refining effect and the workability of addition. The finer the particle size, the faster it dissolves in the slag and the greater the refining effect. On the other hand, if the particle size is too fine, it will cause problems such as dust generation at the time of addition. Conversely, if the particle size is excessively coarse, there is a concern that dissolution in the slag will be slow. Further, it depends on the type (melting point) of the slag-making agent, and the higher the melting point, the smaller the desired particle size. In particular, CaO has a high melting point of 2570 ° C,
A particle size as fine as possible is desired. Therefore, a specifically desirable particle size range is 1 mm or more for manganese oxide and CaF _2.
It is 50 mm or less and CaO is 1 mm or more and 10 mm or less.

It is preferable that the concentrations of manganese oxide in the manganese mineral and CaO or CaF ₂ in the slag-making agent are as high as possible. The impurities inevitably contained in the manganese mineral and the slag-making agent include Al ₂ O ₃ , MgO, SiO ₂ , P and S, and the total of these concentrations is desirably 5% or less. Similarly, iron oxides are included, which, like manganese oxide, cause a redox reaction with hot metal (Si) and act as a desiliconizing agent, so they are usually included in manganese minerals and slag-making agents. There is no particular harm as long as it is.

The slag-making agent may contain CaO or CaF ₂ alone as a main component, or may contain these as a main component at the same time.

The amounts of the manganese mineral and the slag-making agent are set according to the required desiliconization amount and desulfurization level.

First, the addition amount of the manganese mineral is set with respect to the required desiliconization amount. What works as a desiliconizer,
Manganese oxide and iron oxide in minerals. The reduction reaction of manganese oxide proceeds substantially according to the above equation (1), and iron oxide
It may be considered that Fe ₂ O ₃ undergoes a redox reaction with [Si] in the hot metal. Therefore, it is preferable to calculate the required addition amount based on the required desiliconization amount, the manganese and iron concentrations in the manganese mineral, and the stoichiometric balance of the oxidation-reduction reaction formula. The range of the normally assumed addition amount is 5 to 30 kg / t (kg / t: hot metal 1 to
Amount added per n. same as below. ).

The amount of CaO to be added is preferably determined based on the CaO concentration in the slag-making agent and the slag basicity for achieving the required desulfurization level. Usually, the range of the added amount is 5 to 5.
30 kg / t.

The addition amount of CaF ₂ is set according to the degree of slag-forming property required for slag, and is preferably determined from the addition amount of CaO and the hot metal temperature. Normally assumed hot metal temperature of 1350 ℃
Before and after, it is desirable that the ratio of the amount added to CaO be in the range of 1/5 to 1/2. The range of addition amount is 1 to 15 kg
/ t. If the temperature of the hot metal is lower than 1350 ° C. and there is a concern that the slag may be poorly formed, it is preferable to increase the amount of CaF ₂ added.

When the [Si] concentration in the hot metal is high and there is a thermal margin, both the manganese mineral and the slag-making agent are not limited to the above-mentioned amounts, and a larger amount may be added.

The method of adding manganese oxide and the slag-making agent is as follows.
Any of addition from a hopper and injection may be used, and can be selected depending on facility or operational convenience.

The desirable composition range of the liquid phase slag produced during the treatment using the method of the present invention is (CaO) = 0 to 30%,
(MnO) = 20-70% and (SiO ₂ ) = 30-50%. In the composition of this range, the melting point of CaO-MnO-SiO ₂ slag 1200
11300 ° C., and the presence of CaF ₂ further lowers its melting point to the aforementioned desirable range.

After changing the composition in this range, (MnO) further decreases due to the increase of (CaO), and the MnO in the slag finally reaches 2-3%, and even lower. Is desirable. At this time, the content of CaF ₂ in the slag is preferably about 5 to 30%.

It is desirable that the final slag basicity is set in consideration of the desulfurization effect. Desirable range is 2.0 ~
5.0. As the slag basicity increases, the effect of promoting the desulfurization reaction increases accordingly. On the other hand, as the slag basicity is increased, the cost of the slag-making agent and the temperature drop during the treatment are increased. Therefore, it is preferable to set the slag basicity according to the desulfurization level required in view of the balance between the two.

As is clear from the above, in the method of the present invention,
To increase the slag basicity to 2.0 or more,
Due to the large amount of CaO added, liquid phase slag composed mainly of SiO ₂ and MnO is generated by the prior addition of manganese oxide, and the reduction reaction of MnO in the slag is surely advanced to ensure the MnO in the slag. It is an essential addition condition to increase the slag basicity by continuing to add CaO after reducing it.

[0057]

【Example】

(Invention Example 1) Hot metal 18 having a composition shown in Table 1 at 1350 ° C.
Charge 0 ton into the ladle and rotate at 100rpm with impeller
With stirring.

In this state, one minute to two minutes after the start of the impeller rotation.
Over a period of minutes, the total amount of manganese ore shown in Table 1 was preceded and continuously added from the hopper. Next, over 3 to 4 minutes after the start of the impeller rotation, the total amount of CaO and CaF ₂ shown in Table 1 was simultaneously and continuously added.

Thereafter, the stirring by the rotation of the impeller was continued, and the processing was completed 15 minutes after the start of the rotation.

Table 1 shows the compositions of hot metal and slag after 15 minutes.

[0061]

[Table 1]

Comparative Example 1 1350 having the composition shown in Table 2
180 tons of hot metal at ℃ was charged into a ladle and stirred at a rotation speed of 100 rpm by an impeller.

In this state, the entire amount of manganese ore, CaO and CaF ₂ shown in Table 2 was simultaneously added from the hopper over 1 to 2 minutes after the start of the impeller rotation. Table 2 shows the compositions of hot metal and slag at the time when 15 minutes have passed.

[0064]

[Table 2]

As is clear from the comparison between Example 1 of the present invention and Comparative Example 1, even if manganese ore and the slag-making agent were added in the same amounts, desiliconization, desulfurization and [Mn] It can be seen that the effect of the increase in the refining is different, and the refining effect is increased by adding manganese ore in advance.

(Invention Example 2) 13 having the composition shown in Table 3
180 tons of hot metal at 50 ° C. were charged into a ladle and stirred at a rotation speed of 100 rpm by an impeller.

[0067]

[Table 3]

In this state, one minute to three minutes after the start of the rotation of the impeller.
Over a period of minutes, the total amount of manganese ore shown in Table 3 was preceded and continuously added from the hopper. Then, over the 3 minutes to 6 minutes after the start of the impeller rotation was continuously added the total amount of CaO and CaF ₂ are shown in Table 3 at the same time.

Thereafter, the stirring by the rotation of the impeller was continued, and the processing was completed 15 minutes after the start of the rotation.

Table 3 shows the compositions of hot metal and slag after 15 minutes.

The slag could be treated while maintaining a good slag condition, and as shown in Table 3, the slag basicity could be finally increased to 2.3. For this reason, a sufficient refining effect can be obtained.
Reached up to 0.003.

(Invention Example 3) 13 having the composition shown in Table 4
180 tons of hot metal at 50 ° C. were charged into a ladle and stirred at a rotation speed of 100 rpm by an impeller.

[0073]

[Table 4]

In this state, one minute to three minutes after the start of the impeller rotation.
Over a period of minutes, the total amount of manganese ore shown in Table 4 was preceded and continuously added from the hopper. Then, over the 3 minutes to 6 minutes after the start of the impeller rotation, and simultaneously continuously added the total amount of CaO and CaF ₂ are shown in Table 4.

Thereafter, the stirring by the rotation of the impeller was continued, and the processing was completed 15 minutes after the start of the rotation.

Table 4 shows the compositions of the hot metal and the slag after 15 minutes.

The slag could be treated while maintaining a good slag condition, and as shown in Table 4, the slag basicity could be finally increased to 4.0. For this reason, a sufficient refining effect can be obtained.
Reached up to 0.002.

The effect of the above-described embodiment of the present invention is that MnO—SiO ₂ containing SiO ₂ and MnO as main components by adding manganese oxide in advance.
Promotes the formation of liquid phase slag in the system, followed by CaO and CaF ₂
Is obtained because it becomes possible to increase the basicity of the slag and advance the smelting reaction while maintaining the molten state of the slag by adding slag.

[0079]

According to the method of the present invention, liquid phase slag and molten slag can always be formed by adding CaO and CaF ₂ after adding manganese oxide. As a result, desiliconization, desulfurization and [M
n] can be simultaneously achieved.

[Brief description of the drawings]

FIG. 1. CaO—SiO ₂ explaining the transition of slag composition during processing
FIG. 4 is a ternary phase diagram of -MnO.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C21C 1/00 C21C 1/02 C21C 1/04

Claims (1)

(57) [Claims] 1. A mineral containing manganese oxide as a main component is added to hot metal, and SiO ₂ is generated by a redox reaction with silicon ([Si]) in the hot metal, and the main component is SiO ₂ and MnO. After forming liquid phase slag, CaO and CaF ₂
A method for pre-treatment of hot metal characterized by carrying out desulfurization and raising manganese ([Mn]) in hot metal simultaneously with desulfurization by adjusting the basicity (CaO / SiO ₂ ) and melting point of slag by adding iron .