JPH10102120A - Steelmaking method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steelmaking method of a high manganese steel at a low cost. SOLUTION: The steelmaking method is treated in the following process order. The first process: Manganese ore, lime and fluorspar are added into molten iron 2 in a ladle 1 and stirred to execute desulfurization, desiliconization and the rising treatment of manganese concn. The second process: The molten iron after the first process is charged into a converter type dephosphorizing furnace 7 and dephosphorizing slag-making agent containing at least the former two kinds among decarburizing furnace slag 8 produced in the following third process, manganese ore, lime and fluorspar, are added and the oxygen is blown to execute the dephosphorization and the rising treatment of manganese concn. while holding the temp. to <=1450 deg.C. The third process: the molten iron after the second process is charged into a converter type decarburizing furnace 12, and the slag-making agent and the manganese ore are added and the oxygen is blown to execute the decarburization and the rising treatment of manganese concn. Since smelting reduction is executed by adding the manganese ore in each process, the manganese concn. at the finishing pt. in the decarburizing furnace can be risen. Therefore, since the manganese ferro-alloy added at the time of tapping the steel can be saved, the high manganese steel can be produced in the low producing cost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for reducing manganese by adding manganese ore as an inexpensive manganese source using a process of sequentially subjecting hot metal to desiliconization, desulfurization, dephosphorization, and decarburization. And a steelmaking method for inexpensively melting high manganese steel.

[0002]

2. Description of the Related Art In recent years, as demands for quality stabilization and cost reduction of thick steel materials have increased, a steelmaking method for melting high manganese steel, which is a major steel type among these steel materials, at the lowest possible cost. Is desired.

[0003] At present, the following method is generally used when melting high manganese steel. That is, first, in converter blowing using dephosphorized hot metal (hereinafter, also referred to as dephosphorized pig iron blowing), manganese ore is added to perform smelting reduction to increase the manganese concentration at the end of blowing. Next, at the time of tapping after blowing, expensive manganese alloy iron is added to adjust the shortage to the product standard concentration.

According to this method, manganese oxide in manganese ore is reduced by carbon in molten steel to increase the manganese concentration in molten steel when a decarburization reaction occurs in dephosphorization pig iron blowing.

In consideration of the temperature drop due to the addition of manganese ore, the amount of manganese ore that can be added is determined in a calorific balance by the hot metal temperature and carbon concentration before the dephosphorization pig iron blowing, the molten steel temperature and the carbon concentration at the end of blowing. It is determined. For this reason, the amount of addition is limited, and the amount of manganese ore that can be added is limited to about 15 to 20 kg / t.

The present inventors have disclosed in Japanese Patent Application Laid-Open No. 1-142009 a method in which the total amount of manganese ore added in a steelmaking process can be greatly increased to about 40 ° / t. This method uses two vertically blown converters disclosed by the present inventors in Japanese Patent Application Laid-Open No. 62-290815,
After performing dephosphorization and desiliconization in a dephosphorization furnace, the treated hot metal is converted into the other converter (hereinafter, decarburization furnace).
Based on the method of decarburization and finish dephosphorization in
Manganese ore is added during each treatment of the dephosphorization furnace and the decarburization furnace.

In this method, since the dephosphorization treatment is performed prior to the decarburization treatment, the dephosphorization load in the decarburization furnace is light, a small amount of slag forming agent is required, and a small amount of decarburization furnace slag is generated. Becomes Moreover, since the generated decarburization furnace slag has a low concentration of P2O5 and still has a dephosphorizing ability, a sufficient dephosphorizing effect can be obtained even when reused as a substitute for quicklime-based slag-making agent in the dephosphorization treatment. . By this reuse, the effect of reducing the slag-making agent can be obtained in both the dephosphorization furnace and the decarburization furnace, so that the use amount of the slag-making agent can be reduced throughout the steelmaking process.

According to the above-mentioned method, it is possible to more effectively increase the manganese concentration in molten steel by adding manganese ore in a total of about 40 ° / t in a dephosphorization furnace and a decarburization furnace.

[0009] However, the manganese concentration at the end of the decarburization furnace achievable by the above method is about 1.1% by weight, and high-manganese steel having a manganese standard concentration of 1.2 to 1.5% by weight or more is inexpensive. In order to melt
Further, it is necessary to increase the amount of added manganese ore.

As described above, about 40 kg / t is the upper limit of the amount of added manganese ore in the conventional method, and if it is desired to add more, naturally, the heat source corresponding to the increased amount of added manganese ore is required. Must be provided. It is conceivable to add a carbon material such as coke and burn it as a heat source, but in this case, the carbon source also contains a considerable amount of sulfur, so the sulfur concentration in the hot metal also increases. However, problems such as poor heat transfer efficiency and long processing time occur.

Further, the silicon concentration in the hot metal is high (for example,
(0.3 to 0.5% by weight or more), it is necessary to increase the amount of the slag-making agent added in the dephosphorization furnace treatment. This is because the amount of SiO2 generated by the oxidation of silicon in the hot metal increases, so the amount of lime-based slag-making agent that is a CaO source is increased to increase the basicity of the generated slag (CaO / SiO2, weight ratio). Is required to be maintained at a certain value or more to secure the dephosphorizing ability of the slag. Further, the amount of dephosphorization slag generated in the dephosphorization treatment is increased, and not only the original effect of saving the slag-making agent is reduced, but also the loss of manganese due to disposal of the generated dephosphorization slag increases. Therefore, even if manganese ore is added in the dephosphorization furnace, the effect of increasing the manganese concentration in the hot metal is reduced.

The present inventors have disclosed in JP-A-6-271920 a method in which the concentration of silicon in hot metal is reduced to an appropriate level in advance before the dephosphorization treatment, and the manganese concentration is increased together with desulfurization. The method is as follows.

[0013] Oxidation of silicon is an exothermic reaction. When the concentration of silicon in the hot metal is high, the amount of heat generated during the desiliconization process is also large, so the amount of the desiliconizing agent added must be increased in accordance with the silicon concentration in the hot metal. Even if it does not become calorie disadvantageous. In addition, by using manganese ore as a desiliconizing agent, it becomes possible to increase the manganese concentration in the hot metal during the desiliconization treatment.

In addition, CaO and manganese ore
By adding CaF2, desulfurization reaction proceeds simultaneously with desiliconization and manganese concentration increase. This is because the addition of fluorite (CaF ₂ ) improves the slagging properties of desiliconized slag compared to conventional hot metal desiliconization treatment by adding only manganese ore or basic oxide sources such as manganese ore and quicklime. Therefore, the smelting reduction of the manganese ore proceeds effectively, the MnO concentration in the final desiliconized slag can be reduced to 2 to 3% by weight or less, and the slag basicity can be set higher than before ( For example, 2.0 or more).

Therefore, by using this method, that is, the hot metal desulfurization step before the dephosphorization treatment, the silicon concentration in the hot metal can be reduced to an appropriate level without providing a new treatment step for desiliconization. Manganese concentration can be increased.

[0016]

In order to produce a high manganese steel having a manganese concentration as described above at a lower cost, it is necessary to further increase the amount of inexpensive manganese ore used. For that purpose, how to increase the amount of manganese ore added during the steelmaking process and raise the manganese concentration at the end point of the decarburization furnace to a high manganese steel level by the smelting reduction are issues.

The present invention has been made to solve the above problems. An object of the present invention is to add inexpensive manganese ore as a manganese source, raise the manganese concentration in hot metal or molten steel to the highest possible concentration during hot metal processing and decarburization processing, and add expensive manganese ore during tapping in a decarburization furnace. It is an object of the present invention to provide a steelmaking method capable of producing high-manganese steel at low cost by saving a large amount of manganese alloy iron.

[0018]

The gist of the present invention resides in the following steel making method.

Converter type 2 with ladle and up-down blowing function
A steelmaking method in which the following first to third steps are performed using a base furnace.

First, a hot metal is charged into a ladle, manganese ore, quicklime and fluorite are added to the hot metal and stirred to perform desulfurization, desiliconization, and manganese concentration increasing treatment.
Process.

The desulfurized and desiliconized manganese-enriched hot metal obtained in the first step is charged into a converter type dephosphorizing furnace, and the decarburizing furnace slag, manganese ore, quicklime and fluorite generated in the third step At least decarburizing furnace slag and dephosphorizing slag containing manganese ore are added and oxygen gas is blown upward while stirring the bottom gas to maintain the hot metal temperature at 1450 ° C or less, and the dephosphorization and manganese concentration increase. The second step of performing the processing.

The dephosphorized manganese-enriched hot metal obtained in the second step is charged into a converter type decarburization furnace, a slag-making agent and manganese ore are added, and oxygen gas is added while stirring the bottom blow gas. The third step of performing decarburization and manganese concentration increasing treatment by blowing.

Regarding the combination of components constituting the dephosphorizing slag agent in the second step, decarburizing furnace slag and manganese ore are essential, and the following four types (a) to (d) are available. It is possible.

(A) Decarburizing furnace slag and manganese ore (b) Decarburizing furnace slag, manganese ore and quicklime (c) Decarburizing furnace slag, manganese ore and fluorite (d) Decarburizing furnace slag, manganese ore, quicklime And fluorite The present inventors have found that the concentration of silicon in hot metal is high (for example, 0.3 to
0.5% by weight or more).
When the high manganese steel is smelted by the method disclosed in Japanese Patent Publication No. 09-27, at the same time, by performing the pre-siliconization of the method described in Japanese Patent Application Laid-Open No. 6-271920, the manganese concentration in the hot metal after the dephosphorization treatment is significantly increased. We found that the effect was obtained. This will be described with reference to FIG.

FIG. 1 shows the relationship between the amount of the dephosphorizing slag agent added in the dephosphorization treatment in the second step and the manganese yield after the dephosphorization treatment and the silicon concentration in the hot metal before the dephosphorization treatment. It is. As shown in the figure, when the silicon concentration in the hot metal is high, the amount of slag in the dephosphorization furnace increases, and the manganese yield decreases. When the initial silicon concentration in the hot metal is high, the amount of dephosphorization slag increases, and at the same time, the oxidation loss of manganese in the hot metal increases.

However, if the silicon concentration is properly adjusted in advance, it is possible to desiliconize and increase the manganese concentration during hot metal desulfurization before the dephosphorization treatment, and as shown in FIG. 1, the manganese yield after the dephosphorization treatment is improved. , An increase in manganese concentration is achieved. In addition, pre-siliconization reduces the amount of dephosphorization slag and improves manganese yield, enabling effective smelting reduction of manganese ore. The synergistic effect that the ascending effect also increases is obtained.

[0027] For this reason, the total amount of manganese ore that can be added through the steelmaking process can be further increased, and the manganese concentration at the end of the decarburization furnace can be effectively increased.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION The method of the present invention comprises a first step of performing hot metal desulfurization on hot metal discharged from a blast furnace, for example.
A second step of performing a dephosphorization process using one vertical blowing converter type furnace and a third step of performing a decarburizing process using another vertical blowing converter type furnace Is done. Then, in all three steps, manganese ore is added to gradually increase the manganese concentration in the hot metal, and the manganese concentration in the molten steel after the third step is increased as much as possible.

In the method of the present invention, between the preceding and following steps,
A chain relationship is established in which the amount of slag in the post-process is reduced by the treatment in the pre-process, and the manganese concentration is effectively increased with the reduction in the amount of slag in each process.

An example of the method of the present invention will be described in the order of steps with reference to FIG. FIG. 2 is a schematic flow chart showing the method of the present invention. 2A shows the first step, FIG. 2B shows the second step, and FIG. 2C shows the third step.

In the addition in the first step, at least manganese ore is added first. A preferred example of the method is as follows. As shown in FIG. 2 (a), first, manganese ore 3 is added to hot metal 2 in ladle 1 and stirred using impeller stirring device 4 to perform desiliconization and manganese concentration increasing treatment. Thereafter, desulfurization and manganese concentration increasing treatment are further performed by adding quicklime and fluorite and stirring in the same manner, and the hot metal 2 is desulfurized and desiliconized manganese-enriched hot metal (desulfurized hot metal 6).

In the above stirring, a gas bubbling stirring method, a powder injection method and the like may be applied in addition to the impeller stirring method.

The purpose of the desiliconization treatment is as follows.
An object of the present invention is to reduce the amount of slag forming agent added in accordance with the concentration of silicon in the hot metal during the dephosphorization treatment in the process, to suppress the amount of slag, and to maintain a high manganese yield during smelting reduction of manganese ore. Conventional hot metal desiliconization is carried out by adding an iron oxide source such as iron ore, but in this case, manganese in the hot metal is also oxidized at the same time, and is not suitable for producing high manganese steel. Therefore, in the method of the present invention, manganese ore is used as a desiliconizing agent. The manganese ore may be a ferromanganese ore. The method of adding manganese ore not only eliminates manganese loss occurring simultaneously with desiliconization by iron oxide, but also increases the manganese concentration in the hot metal.

First, manganese ore is added to the hot metal and stirred, and manganese oxide in the ore is used as an oxidizing agent to oxidize silicon in the hot metal according to the following formula (1) to perform desiliconization and manganese concentration increasing treatment.

2 (MnO) + [Si] = 2 [Mn] + (SiO ₂ ) (1) The main components of oxides constituting slag after desiliconization are dissolved from manganese ore. MnO and SiO2 formed by oxidation of silicon. In binary slag of MnO-SiO2,
MnO is stably present in the slag, and the reduction reaction does not proceed to some extent.

Therefore, quick lime is added to the slag for the purpose of promoting the reduction reaction and desulfurization reaction of MnO in the slag after the desiliconization. Quicklime is a source of CaO to slag, and the presence of CaO in the slag increases the activity of MnO.
The reduction reaction of nO further proceeds. The desulfurization reaction proceeds according to the following equation (2).

Ca ²⁺ + S ²⁻ = CaS (2) At this time, fluorite (CaF ₂ ) is added. When CaF ₂ is present in the slag, the melting point of the slag is lowered and the fluidity is improved, so that manganese ore is melted into the slag, and MnO in the slag is
The reduction reaction and desulfurization reaction are promoted.

The most important point in the first step is how efficiently the desiliconization reaction and desulfurization reaction by smelting reduction of manganese ore proceed. That is, in order for the reduction reaction and desulfurization reaction of MnO 2 in slag to proceed smoothly, it is important that the slag always maintain a state of good fluidity in the liquid phase. Formed after the addition of manganese ore
MnO—SiO ₂ slag is a liquid phase, and based on this slag, it is good to consider the order of addition so that CaO, which has a high melting point, is gradually dissolved. Therefore, manganese ore is added to hot metal in advance, and quick lime is added after the formation of liquid phase slag.

On the other hand, the order of adding the fluorite may be as follows. Since fluorite is a slag-making accelerator for slag, it may be added in any order, but it is desirable to add it at the same time as the addition of quicklime or prior to the addition of quicklime. The best addition is with the manganese ore initially.

The addition of manganese ore may be carried out collectively, but by dividing or adding continuously, high-melting-point manganese ore which remains unreacted on the hot metal is reduced,
The formation of the liquid phase slag and the reduction reaction of MnO in the slag can be caused more efficiently.

As in the case of manganese ore, quick lime may be added at once, but more preferably divided or continuously added. This is to avoid the increase in melting point due to CaO saturation of liquid phase slag by reducing the amount of quicklime that remains undissolved on the hot metal. When increasing the basicity of slag to a high range of 2.0 or more, continuous addition is desirable.

Since fluorite plays a role as a slag-making accelerator, the addition thereof may be all at once, divided or continuous. What is important is that the lime is added simultaneously with or in advance of the quicklime as described above to prevent the slag from having a high melting point.

In the second step, as shown in FIG. 2 (b), the desulfurized and demanganese-enriched hot metal (desulfurized hot metal 6) obtained in the first step is charged into a dephosphorizing furnace 7. And manganese ore 3
Further, a dephosphorizing slag agent composed of the decarburizing furnace slag 8 generated in the third step described later and, if necessary, a dephosphorizing slag agent to which at least one of quick lime and fluorite is added are added. Next,
Oxygen gas is blown upward from the top blowing lance 10 while stirring with the bottom blown gas 9 to remove phosphorus and increase the manganese concentration while maintaining the hot metal temperature at 1450 ° C. or lower, thereby obtaining dephosphorized hot metal 11. As the dephosphorizing furnace 7, one vertical blowing converter type furnace is used.

At present, an iron oxide source such as iron ore is generally used as a refining agent at the time of the dephosphorization treatment. However, in the method of the present invention, manganese ore is used as a part of the slag-making agent. This means that even if iron ore, which is an oxidizing agent for the dephosphorization reaction, is replaced with manganese ore, the same dephosphorization efficiency as when iron ore is used can be obtained, as well as the temperature change during treatment and the amount of decarburization that occurs at the same time. Because there is no big difference. Thereby, manganese oxide, which is an oxidizing agent, is reduced, and the manganese concentration in the hot metal increases.

Since the decarburizing furnace slag contains CaO, it becomes an alternative source of quick lime, and since it has been melted once during the decarburization treatment, the slagging property at the time of reuse is very good. This is a great advantage. When only quicklime is used as a CaO source, it takes time to make slag slag because separate slag-making agents such as quicklime and manganese ore gradually fuse. Due to the excellent slagging properties of the decarburization furnace slag, the dephosphorization reaction proceeds rapidly, and at the same time, the advantageous effect of rapidly progressing the smelting reduction of the added manganese ore is exhibited.

Fluorite may be added to improve the slagging properties of the dephosphorized slag and promote the dephosphorization reaction and the manganese ore smelting reduction reaction. The specific effect in that case is the same as that in the case of the first step.

The processing temperature is adjusted to 1450 ° C. or less. If the temperature of the hot metal exceeds 1450 ° C., the decarburization reaction proceeds preferentially, and the reduction reaction of iron oxide and manganese oxide in the slag proceeds too much, so that the dephosphorization reaction does not proceed. On the other hand, if the treatment temperature is extremely low, the fluidity of the slag decreases, so that the hot metal is suspended in the slag as granular iron and is discarded with the slag as it is, causing loss of iron. Further, when the processing temperature is low, there is no room for the amount of heat in the third step, so that there is a problem that the amount of manganese ore added is restricted. Therefore, it is desirable that the processing temperature in the second step be 1450 ° C. or lower and as high as possible.

Items to be noted in the second step are as follows.
For efficient desulfurization and manganese ore smelting reduction of desulfurized desiliconized manganese-enriched hot metal that has passed through the process, the amount of dephosphorizing slag is controlled to an appropriate level by reducing the amount of slag-making agent added. That is. The silicon concentration in the hot metal before the dephosphorization treatment, that is, after the end of the first step, has a large effect on the amount of dephosphorized slag.

If the silicon concentration in the hot metal before the dephosphorization treatment is excessively low, the following problems (a) to (c) occur.

(A) Since the amount of SiO2 produced by desiliconization is small, slag slag formation is slow, and the progress of the dephosphorization reaction is also delayed.

(B) Since the Si oxidation reaction is an exothermic reaction,
The amount of heat generated during the dephosphorization treatment becomes insufficient due to a decrease in the amount of heat generated during oxidation.

(C) Since the decarburization reaction starts to occur, the heat generation due to the decarburization reaction in the third step is reduced due to the decrease in the carbon concentration in the hot metal, and the amount of manganese ore that can be added is reduced. Does not provide a sufficient effect of increasing the manganese concentration.

Therefore, before the dephosphorization treatment, that is, after the completion of the first step, the silicon concentration in the hot metal has an appropriate range, preferably 0.10 to 0.30% by weight, more preferably 0.15% by weight.
~ 0.25% by weight. That is, adjusting the silicon concentration in the hot metal in the first step to the above-described appropriate range provides an effective dephosphorization treatment in the second step.

In the third step, as shown in FIG. 2C, the dephosphorized manganese-enriched hot metal (dephosphorized hot metal 11) obtained in the second step is charged into a decarburizing furnace 12, and While adding the slag and the manganese ore 3 and stirring with the bottom blow gas 9, oxygen gas is blown upward from the top blow lance 10 to perform decarburization and manganese concentration increasing treatment. As the decarburization furnace 12, another one of a vertical blow converter type furnace different from the dephosphorization furnace 7 is used. Examples of the slag-making agent include quicklime and dolomite, which are the same as those used in ordinary converter blowing.

A desirable addition method and order of the slag-making agent and the manganese ore are preferably a method in which the slag-making agent and the manganese ore are charged from an addition hopper on the furnace to a furnace port, and the manganese ore is preferably added first. The reason why the manganese ore is added first is to prevent sintering of the manganese ore and the slag-making agent and to efficiently react with the hot metal.

This step is basically the same as the decarburization refining in a normal vertical blowing converter, but since the dephosphorization treatment is performed in advance in the preceding step, the amount of the slag-making agent to be added should be reduced. Is possible. Therefore, manganese ore is added in a state where the amount of slag is small, and effective smelting reduction and increase of manganese concentration in molten steel at the end point of blowing are achieved.

Other desirable conditions in the method of the present invention are as follows.

The range of the particle size of the additive is 1 for manganese ore.
Approximately 50mm, quick lime approximately 1-10mm, fluorite and decarburization slag approximately 1-50mm. The range of slag basicity is about 1.5 to 2.5 in a ladle and a dephosphorization furnace, and about 3.5 to 5.0 in a decarburization furnace.

Desirable addition ranges are about 5 to 15 kg / t for manganese ore in the first step, about 5 to 15 kg / t for quicklime,
Fluorite is about 2-6 kg / t. Similarly, the decarburization furnace slag in the second step is about 15 to 25 kg / t, manganese ore is about 3 to 15 kg / t, quicklime is about 10 to 20 kg / t, and fluorite is about 5 to 15 kg / t.
Similarly, the slag-making agent in the third step is about 10 to 20 kg / t, and the manganese ore is about 10 to 20 kg / t.

The gas for bottom blow stirring is Ar, N ₂ , C
O, CO _{2 and the} like are good, and the desirable range of the flow rate is 0.1 to 0.
It is about 3 Nm / min · t.

The structure of the upper blowing lance is preferably a Laval nozzle having 3 to 8 holes outward.

[0062]

【Example】

<Comparative Example> Hot metal desulfurization step: A 250-ton blast furnace hot metal (temperature 1350 ° C) was treated by a method of performing impeller stirring in a ladle. After stirring at an impeller rotation speed of 100 rpm, 1
From 10 min to 3 min, 10 kg / t of quicklime having a particle size of 10 mm or less and 2 kg / t of fluorite having a particle size of 50 mm or less are continuously added to the hot metal from a hopper, and the stirring state is continued. After 15 minutes from the start of impeller stirring Finished.

Hot metal dephosphorization step: Then, desulfurized hot metal 250 ton
Into a top-blowing converter type dephosphorization furnace, and 25 kg / t of decarburization slag generated in another decarburization furnace, 10 kg of quicklime having a particle size of 10 mm or less.
t, 8 kg / t of fluorite having a particle size of 50 mm or less, and 15 kg / t of manganese ore having a particle size of 50 mm or less were added, and a dephosphorization treatment was performed under the conditions shown in Table 1 for 13 minutes.

[0064]

[Table 1]

Decarburization Step Further, dephosphorized hot metal is poured into a decarburization furnace, and calcined lime 8 kg / t, dolomite 6 kg / t, fluorite 1 kg / t having a particle size of 50 mm or less, and particle size 1 kg / t.
Decarburization blowing was performed for 16 minutes by adding 20 kg / t of manganese ore of 50 mm or less. The manganese concentration in the molten steel at the end of blowing was 1.04% by weight. Table 2 shows the chemical compositions of the hot metal and molten steel.

[0066]

[Table 2]

<Examples of the present invention> First step: A blast furnace hot metal of 250 tons (temperature 1350 ° C) was treated by a method of impeller stirring in a ladle. After the impeller stirring was started at a rotation speed of 100 rpm, 15 kg / t of manganese ore having a particle size of 50 mm or less was continuously added to the hot metal from a hopper over 1 to 3 minutes. Further, after the start of stirring, from 3 minutes to 6 minutes, quicklime with a particle size of 10 mm or less 15 kg / t
And 5 kg / t of fluorite having a particle size of 50 mm or less was continuously added from another hopper. After continuing the stirring state, from the start of stirring
After 15 minutes, the desulfurization and manganese enrichment treatment was completed.

Second step (dephosphorization treatment without addition of quick lime): Then, 250 tons of desulfurized and desiliconized manganese-enriched hot metal was poured into a dephosphorization furnace, and the decarburization furnace slag generated in the decarburization furnace, 25 kg / t, Diameter
15 kg / t of manganese ore having a particle size of 50 mm or less and 8 kg / t of fluorite having a particle size of 50 mm or less were added, and the dephosphorized manganese enrichment treatment was performed under the same conditions as in Table 1.

Third step: The dephosphorized manganese-enriched hot metal was further poured into another decarburization furnace, and decarburization and manganese concentration increasing blowing were performed under the same conditions as in the decarburization step of the comparative example. Table 3
Figure 3 shows the chemical compositions of hot metal and molten steel.

[0070]

[Table 3]

As shown in Table 3, after the first step, the manganese concentration in the hot metal increased to 0.93% by weight, and the desulfurization treatment was able to be achieved to the same extent as the comparative example. Thereafter, the manganese concentration increased to 1.12% by weight in the hot metal after the second step and to 1.50% by weight in the molten steel after the third step.

In the first step, the silicon concentration in the hot metal was set to 0.20
Due to the reduction to% by weight, in the second step, dephosphorization proceeded to the same extent as the comparative example without adding quicklime. Thus, in the method of the present invention, it is also possible to reduce the amount of quicklime added in the dephosphorization step.

[0073]

According to the method of the present invention, in three steps of desulfurization, dephosphorization and decarburization of hot metal, manganese ore is added and smelted and reduced, thereby making it possible to process the hot metal in a stepwise and effective manner. The manganese concentration can be increased to increase the manganese concentration at the end point of the decarburization furnace. According to the increase in manganese concentration at the end of the decarburization furnace, the amount of expensive manganese alloy iron added during tapping of the decarburization furnace can be reduced, so high-manganese steel can be manufactured at low cost. is there. Furthermore, by desiliconizing to an appropriate level before the dephosphorization treatment, the amount of the slag-making agent added during the dephosphorization treatment can be reduced.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of a dephosphorization slag agent added in a dephosphorization treatment in a second step and the manganese yield after the dephosphorization treatment and the silicon concentration in the hot metal before the dephosphorization treatment.

FIG. 2 is a schematic flow chart showing the method of the present invention. (a)
Represents a first step, (b) represents a second step, and (c) represents a third step.

[Explanation of symbols]

1: ladle, 2: hot metal, 3: manganese ore, 4:
Impeller stirrer, 6: desulfurized hot metal, 7: dephosphorization furnace, 8: decarburization furnace slag, 9: bottom blown gas, 10: lance,
11: Dephosphorized hot metal, 12: Decarburizing furnace, 13: Slag making agent

Claims (1)

[Claims] 1. A converter type 2 equipped with a ladle and a vertical blowing function
A steelmaking method characterized by performing the following first to third steps using a base furnace. A first step of charging hot metal into a ladle, adding manganese ore, quicklime and fluorite to the hot metal and stirring to perform desulfurization, desiliconization, and manganese concentration increasing treatment. The desulfurized and desiliconized manganese-enriched hot metal obtained in the first step is charged into a converter type dephosphorizing furnace, and at least decarburizing furnace slag, manganese ore, quicklime and fluorite generated in the third step are removed. Dephosphorizing slag containing slag and manganese ore are added, and oxygen gas is blown upward while stirring the bottom gas to carry out dephosphorization and manganese concentration increase while maintaining the hot metal temperature at 1450 ° C or less. Second step. The dephosphorized manganese-enriched hot metal obtained in the second step is charged into a converter type decarburizing furnace, a slag-making agent and manganese ore are added, and oxygen gas is blown upward while stirring the bottom blow gas. , A third step of performing decarburization and manganese concentration increasing treatment.