JPH111714A - Steelmaking method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To develop an economical refining method capable of stably reducing the amount of slag generated and applicable to more steel types. SOLUTION: (i) A first step of performing desiliconization or desulfurization desulfurization without charging Mn raw material by charging hot metal into a ladle and mechanically stirring with an impeller, A second step of charging the hot metal obtained in the step into the first refining vessel, blowing oxygen upward and dephosphorizing by introducing a slag-making agent, and (iii) the hot metal obtained in the second step After removing the slag, the third step of charging the second smelting vessel, blowing up oxygen, adding a slag-making agent, and decarburizing is sequentially performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steelmaking method for efficiently producing steel by sequentially performing desiliconization, dephosphorization, and decarburization of hot metal.

[0002]

2. Description of the Related Art In recent years, demands for stabilizing the quality of steel materials and reducing costs have increased, and the following various means have been proposed in order to reduce smelting costs.

[0003] First, as a method for more economically producing steel in the steelmaking process, Japanese Patent Application Laid-Open No. 1-142009 discloses that one of two refining vessels having a converter function is provided with a de-P furnace. A method of refining using another as a de-C furnace is disclosed.

[0004] Various desiliconization methods have been proposed to reduce the amount of slag and perform economic refining. JP
Japanese Unexamined Patent Publication No. Hei 5-5114 discloses a method in which a desiliconizing agent containing Fe ₂ O ₃ as a main component is blown into a molten iron with an inert gas at a depth of 2 m or more together with an inert gas. A method of injecting iron oxide and gaseous oxygen into a vehicle to desilicate is disclosed in
Japanese Patent Laid-Open No. 60-116707 discloses a method of adding iron oxide to a hot metal gutter in a blast furnace cast bed to desiliconize.
Japanese Patent Publication No. 08 proposes a desiliconization method including a method of placing a desiliconizing agent in a receiving iron container in advance and then dropping the hot metal. All of these are
It shows an example for removing Si, and many other known techniques as a desiliconization method are known.

[0005]

However, the problems of the above-mentioned conventional methods include the following.

[0006] For example, in the method of removing P and C using two converters disclosed in Japanese Patent Application Laid-Open No. 1-142009, the removal of C slag is used as a slag-making agent in a P removal furnace. Although there is an advantage that the amount can be suppressed to the minimum, when the hot metal [Si] is high, the amount of P is removed in order to keep CaO / SiO ₂ in the slag constant.
A large amount of slag-making agent was required in the furnace, and the slag-making agent had to be added.

[0007] When the desiliconization treatment is performed on the hot metal in advance, it is possible to reduce the amount of the slag-making agent used for de-P in the subsequent converter refining. The amount of lime was governed by the amount of quicklime determined by the Si concentration in the hot metal and the required basicity (= CaO / SiO ₂ ), and it was extremely difficult to further reduce the slag-making agent.

Here, the applicant of the present application has filed Japanese Patent Application No. 8-254367.
As a method for producing high Mn steel by combining de-silica treatment of hot metal, de-P, and de-C in combination, manganese is enriched at the time of de-silica and then de-P and de-C are performed. In addition, a method for raising manganese in both a de-P furnace and a de-C furnace has been proposed.

Further, there is a method in which manganese is enriched at the same time as desiliconization, followed by removal of P and C in two refining furnaces having a converter function, and addition of manganese in both of them to further increase the manganese concentration. Although it was possible to greatly reduce the amount of slag generated by using the de-C furnace slag in the de-P furnace and the de-silica effect, most of the manganese enriched during the de-silica was removed during the de-P refining or There has been a problem that it is oxidized and removed during the C-free refining. Similarly, the manganese enriched during the de-P refining is oxidized and removed during the de-C refining, so the economical benefits of this method can be obtained only for some steel types with a high C content and a high manganese steel. Was limited.

[0010] In view of the above-mentioned conventional problems, an object of the present invention is to develop an economical refining method that can stably reduce the amount of slag generated and that can be applied to more steel types. .

[0011]

Means for Solving the Problems As means for solving the above-mentioned problems, the present inventors have proposed a desiliconization method by impeller stirring and two refining vessels having a converter function (hereinafter referred to as a converter). Further investigations were made, focusing on the fact that the steelmaking process can be efficiently performed by using the P as a de-P furnace and the C-removal furnace, respectively.

In the above-mentioned prior application, when the Mn raw material is added in the desiliconization treatment, a considerable amount is oxidized and removed in the subsequent de-P and de-C treatment, and Mn: 1.0%
Regardless of the purpose of high Mn steel, if the amount of Mn is a normal level, the Mn raw material is not added at the time of desiliconization treatment, and is more efficiently added as needed at the time of decarbonization treatment. We knew that steelmaking would be possible at low cost, and completed the present invention.

[0013] Here, the present invention provides (i) a first step of desiliconization or desulfurization desulfurization without charging Mn raw material by charging hot metal into a ladle and mechanically stirring with an impeller. (Ii) charging the hot metal obtained in the first step into a first smelting vessel, blowing oxygen upward and introducing a slag-making agent to dephosphorize the second step, and (iii) the second step. After removing the slag of the hot metal obtained in the process, it is charged into a second smelting vessel, while blowing up oxygen and adding a slag-making agent, a third step of decarburizing is a steelmaking method comprising .

In an embodiment of the present invention, steelmaking slag may be charged as at least a part of the slag-making agent charged in the first step.

Further, the slag generated in the third step may be used as at least a part of the slag-making agent charged in the second step. Further, in the third step, a Mn raw material may be introduced as necessary.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The components of the present invention and the operation thereof will be described in detail below. The present invention comprises a first step using a ladle, a second step using a converter, and a third step also using a converter.

First step: According to the present invention, a desiliconizing agent containing iron oxide as a main component, such as iron ore, mill scale or sintered ore, is added to hot metal placed in a ladle after tapping from a blast furnace. Input. Further, the desiliconizing agent may be put in advance in another place. For example, when the hot metal is charged into the ladle after the desiliconizing agent is placed in the ladle, a certain degree of desiliconizing reaction proceeds during the charging, but the unreacted desiliconizing agent also remains. Even if impeller stirring is performed in this state, a good desiliconization effect can be obtained. It is desirable to remove slag from the blast furnace slag before the desiliconization treatment in order to avoid an increase in the sulfur concentration from the blast furnace slag, but it is not always necessary to remove the slag.

In the present invention, manganese oxide is not supplied during desiliconization. This is because when manganese oxide is charged, the manganese content increases with desiliconization as described in the above-mentioned prior application, Japanese Patent Application No. 8-254367. The manganese is increased during desiliconization because it is oxidized and removed in the process.
This is because it is not a good idea to use general steel, regardless of steel.

The reason why the mechanical stirring by the impeller is used is that the efficiency is higher than that of other injection desilking or blast furnace desilking. For example, desiliconization can be performed with a smaller unit of the desiliconizing agent than blast furnace desiliconization, and can be performed in a shorter time than injection desiliconization.

[0020] The amount of the desiliconizing agent varies depending on the target desiliconizing amount. That is, the Si level is increased from 0.4% to 0.2
When desiliconizing to%, oxygen is stoichiometrically
0.2 × 32/28 = 0.229% is required, but considering the desiliconization effective efficiency of oxygen of about 60%, 0.229 / 0.6 ×
1.4 = 0.38% oxygen is required. For example, considering iron ore having an oxygen content of 30%, 0.38% / 0.3 = 1.3
% = 13k / t.

The desilicater can be charged in a lump or in several batches.

In the desiliconization treatment, the impeller is immersed in hot metal and rotated. The desiliconizing agent placed above by this mechanical stirring is caught in the hot metal and reacts, and the desiliconization reaction proceeds. There is no particular limitation on the rotation speed and processing time of the impeller, but the reaction proceeds better with a higher rotation speed and a longer processing time. The structure of the impeller and the like are not particularly limited, and a normal structure may be used.

At this time, it is not necessary to add anything other than the desiliconizing agent only for the purpose of desiliconizing, but other additives may be added as necessary. For example, when desulfurization is performed simultaneously with desiliconization, the desulfurization agent may be added simultaneously or sequentially with the desiliconization agent. As a desulfurizing agent, a substance containing CaO may be charged, and the slag after treatment may be adjusted so that the basicity CaO / SiO ₂ becomes 0.8 to 10.0.

At this time, it is effective to add fluorite to promote slagging and to increase the reaction rate. In the slag
A CaF ₂ concentration of about 15 to 40% is desirable for accelerating desulfurization and improving the reaction rate, but from the viewpoint of preventing refractory material damage and reducing the amount of slag generated, it is desirable to set the CaF ₂ concentration to 15% or less. Often. It is advisable to determine the set value based on local conditions at that time.

In order to further advance desulfurization, it is effective to supplementally add either or both of soda ash and Al ash. Although there is no particular limitation on the input amount in this case, in consideration of economic efficiency, it is preferable that Al ash is 0.5 k / t or less and soda ash is 2.5 k / t or less. Further, if possible in terms of time, after the desiliconization reaction is completed, the impeller stirring is temporarily stopped to remove the required amount of slag, and when the process proceeds to the next desulfurization step, the slag composition can be easily adjusted, which is advantageous in some cases.

Further, as a method of accelerating the reaction, there is a method of introducing steelmaking slag. For example, when converter slag is added to hot metal, the converter slag itself contains iron oxide and thus contributes as a desiliconizing agent, and also contains CaO, which also contributes as a desulfurizing agent. In addition, there is also an advantage that the slag is quickly formed because it is once melted. For example, if the FeO concentration
When converter slag of 20% is input at 10k / t,
Since 2 k / t of FeO contributes as a desiliconizing agent, when the desiliconization amount is set from 0.4 to 0.2% as described above, there is an advantage that the amount of iron ore to be input can be reduced to 11 k / t. Furthermore, the amount of CaO to be added for the purpose of desulfurization can be reduced, and the amount of CaO / SiO ₂ in the treated slag can be reduced to zero if 0.8 or more can be secured. In particular, converter slag that has undergone hot metal desulfurization and hot metal desulfurization can perform desulfurization desulfurization while keeping the sulfur and phosphorus concentrations low. If this converter slag is the third step of the present invention, which is a de-C furnace slag, of course, it will be an excellent integrated process without any problem. For example, if there are two or more steel mills in the same steel mill and the other converter slag When the generation amount is extremely large, it is effective to bring the slag and use it. The steelmaking slag used at this time may be a converter slag as described above, or another slag such as a ladle slag remaining after casting.

According to the present invention, not only the simultaneous desiliconization and desulfurization effect can be expected by adding a basic substance at the time of desiliconization to maintain the CaO / SiO ₂ in the slag at 0.8 to 10.0, but also the conversion is improved. By using furnace slag or ladle slag as a desulfurizing agent, the amount of basic substances that should be added for desulfurization can be reduced, and the amount of slag generated in the entire steelmaking process can be further reduced, compared to conventional methods. It has become possible to produce steel in a very inexpensive manner.

Second step: Further, oxygen is blown upward in the de-P furnace, but slag generated in the de-C furnace in the third step described later is introduced as one of the slag-making agents, so that quicklime is added. Since the unit can be reduced, the amount of slag generated can be suppressed.

In the de-P furnace, if there is a thermal margin, manganese oxide may be added as needed. However, since a part of the manganese which has been raised by this is oxidized and removed in the de-C furnace,
It is advisable to feed only the minimum necessary in consideration of the yield. It is generally preferred that the manganese to be raised is raised in a de-C furnace because the manganese yield increases.

In the de-P furnace, oxygen is blown upward after adding a slag-making agent to perform de-P. When the addition of forming agent is slag basicity CaO / SiO ₂ after treatment is adjusted to 1.5 to 4.0. Addition of de-C slag to reduce the amount of slag-making agent added at this time has the advantage of reducing the amount of slag generated as a whole process,
Since it is slag once melted, it promotes slagging and removes slag.
There is also an effect that processing proceeds promptly.

In order to quickly perform the de-P treatment,
It is sufficient if the components after desiliconization are [C]> 3.5% and [Si]> 0.05%, but [Si] is most preferably about 0.10 to 0.30%. Further, the temperature at that time is preferably in the range of 1200 to 1500 ° C.

After removal of P, [Si] becomes a trace amount, but it is preferable that the temperature after the treatment is maintained at 1450 ° C. or less and [C]> 3.0% or more. At this time, the heat margin is basically iron ore,
It is often most effective to use iron oxide such as scale to increase the yield of steel output.However, for some steel types, such as medium-carbon high-manganese steel, iron manganese ore, which is a manganese oxide source, is used. In some cases, increasing manganese is economically advantageous.

Third step: In a decarbonizing furnace, oxygen is blown upward to mainly remove carbon. At this time, depending on the thermal margin and the target component,
It is preferable to add an appropriate amount of manganese oxide. However,
When the final C concentration in blowing is less than 0.05%, the manganese yield deteriorates. Therefore, the heat allowance contributes to the improvement of the tapping yield by introducing iron ore or scale, which is an iron oxide-based coolant. Desirable. In this step, the final removal P can be performed by adjusting the final C concentration of the blowing and the amount of the solvent used.

In the conventional method, for example, when desiliconization is performed by injection or when there is no desiliconization step itself, [Si] before the de-P furnace treatment tends to be high.
Since it was difficult to keep the CaO / SiO ₂ important for the performance high, the removal of P sometimes became poor as a result. As a result, in a de-C furnace, finishing de-P was often required. However, in the present invention, since [Si] before the de-P furnace treatment can be stably desiliconized to a target level, the removal of P in the de-P furnace becomes easy, and as a result, the de-C furnace is used. It is rare that finishing removal P is necessary.

In the de-C furnace, the slag basicity CaO / SiO ₂ is adjusted to 1.5 to
After adding the slag-making agent to keep it in the range of 10.0, oxygen is blown upward. The heat margin is iron oxide based iron ore, scale,
Alternatively, manganese oxide-based Mn ore and iron Mn ore may be added, but if [C] at the end of blowing is 0.05% or more, it is more economical to add a manganese oxide-based additive. Often advantageous.

[0036]

In this example, Conventional Examples 1 to 3, Comparative Example 1, and Inventive Examples 1 and 2 shown in Table 1 were conducted under the conditions summarized in Table 2. The results are also shown in Table 2.

[0037]

[Table 1]

[0038]

[Table 2]

As can be seen from the results shown in Table 2, Example 2 of the present invention using slag from a de-C furnace uses the least amount of the desiliconizing agent and slag-making agent, followed by Example 1 of the present invention.

In the example of the present invention, manganese is not added at the time of desiliconization and at the time of removal of P, but manganese is added in the de-C furnace. By adding manganese in a process with a high manganese yield, manganese can be efficiently yielded, and the [Mn] at the end of the decarbonizing furnace is reduced in Comparative Example 1 in which manganese is added in all processes (Japanese Patent Application No. (Equivalent to No. 8-254675), but the tortoise cost of steel making taking into account the tapping yield becomes worse in the order of Invention Example 2 → Invention Example 1 → Comparative Example 1 → Comparative Example 2. Further, the cost is worse in the order of Conventional Example 3 → Conventional Example 2 → Conventional Example 1 lower than Comparative Example 1.

[0041]

Industrial Applicability According to the present invention, comprehensive and efficient smelting of steel by performing desiliconization + desulfurization, desulfurization, and desulfurization in a series of processes has become possible. Since the Mn raw material is not charged during the desiliconization desulfurization accompanied by impeller stirring, the cost is low, and the substantial significance of the present invention is very large.

Claims (4)

[Claims] 1. (i) A first step of performing desiliconization or desulfurization desulfurization without charging Mn raw material by charging hot metal into a ladle and mechanically stirring with an impeller, The molten iron obtained in one step is charged into the first refining vessel, the oxygen is blown up, and the dephosphorization is performed by adding a slag-making agent, and (iii) the second step is obtained in the second step. A steelmaking method comprising a third step of removing molten iron slag, charging the molten iron into a second smelting vessel, blowing oxygen upward, adding a slag-making agent, and decarburizing. 2. The steelmaking method according to claim 1, wherein in the first step, an iron oxide-based desilicater is added. 3. The steelmaking method according to claim 1, wherein the slag generated in the third step is used as at least a part of the slag-making agent to be charged in the second step. 4. The steelmaking method according to claim 1, wherein a Mn raw material is charged in the third step.