JP7107099B2 - Hot metal refining method - Google Patents

Description

The present invention relates to a method of refining molten iron, and more particularly to a method of refining that can reduce the P content of molten iron as much as possible.

Conventionally, many proposals have been made for pretreatment techniques and/or refining techniques that reduce impurities in hot metal as much as possible in order to produce high-quality steel that can be used in a variety of applications (see, for example, Patent Documents 1 to 7). .

When removing P from hot metal, the lower the temperature, the more efficiently it can be removed. Dephosphorization treatment is applied.

As a refining method for reducing the P content of hot metal as much as possible, Patent Document 2 discloses that after the dephosphorization treatment is completed, the refining is once suspended, the slag generated in the dephosphorization treatment is discharged (intermediate slag), and a new A method has been proposed in which a slag-forming material is added to the slag to form slag, and the subsequent decarburization treatment is continuously performed. According to the method of Patent Document 2, the P content of hot metal can be finally reduced to 0.015% or less, but in recent years, the demand for steel quality has become more severe than before, and a refining technology that meets this demand is required. there is

JP-A-05-026842 JP-A-07-018318 JP-A-09-959709 JP-A-2001-234221 JP 2005-092158 A JP 2008-138281 A Japanese Unexamined Patent Application Publication No. 2011-038176

In view of the above requirements for steel quality, the present invention provides a refining process that consists of a series of steps of dephosphorization, intermediate waste, and decarburization using a refining furnace after hot metal pretreatment. In addition to increasing the dephosphorization rate, the slag removal rate is increased at the time of intermediate slag removal, the amount of P in the refining furnace system (hot metal and slag) after intermediate removal is reduced as much as possible, and finally, the required level of low P content is achieved. It is an object of the present invention to provide a refining method for solving the problem.

The present inventors diligently studied methods for solving the above problems. As a result, when a solid oxygen source is added to the slag from above during the dephosphorization process, the T.D. The amount of Fe (FeO, Fe ₂ O ₃ , etc.) increases, (x) the liquid phase ratio of the slag increases, the reaction between the slag and the hot metal progresses, the dephosphorization rate improves, and (y ) It was found that a large amount of carbon dioxide gas is generated, the slag is in a foaming state, and the slag discharge rate at the time of intermediate slag discharge is improved.

The present invention was made based on the above findings, and the gist thereof is as follows.

(1) A refining method in which hot metal is refined through a series of dephosphorization, intermediate slag, and decarburization processes using a refining furnace. A method for refining hot metal, characterized by adding

(2) The method for refining molten iron according to (1) above, wherein the refining furnace is a top-bottom blown converter.

(3) The method for refining molten iron according to (1) or (2) above, wherein the molten iron is preliminarily dephosphorized in a separate refining vessel.

(4) _The above (1) to ( 3) The method for refining hot metal according to any one of the above items.

(5) The method for refining hot metal according to any one of (1) to (4) above, wherein the solid oxygen source is added in an amount of 4.0 kg/t-pig or more in terms of oxygen content.

(6) The method for refining hot metal according to any one of (1) to (5) above, wherein the solid oxygen source is in the form of particles having a sieving size of 5 mm or less.

(7) The method for refining hot metal according to any one of (1) to (6), wherein the solid oxygen source is sintered ore powder.

According to the present invention, since the dephosphorization rate in the dephosphorization step is improved and the slag removal rate in the intermediate slag removal is improved, finally molten steel with a required level of low P content can be obtained.

It is a figure which shows a series of refining processes. It is a figure which shows the relationship between the amount of FeO of slag, and the apparent density of slag.

The method of refining molten iron of the present invention (hereinafter sometimes referred to as the "refining method of the present invention") is a refining method in which molten iron is refined through a series of processes of dephosphorization, slag, and decarburization using a refining furnace. The method is characterized in that, during the dephosphorization process, a solid oxygen source in powder form is added to the slag from above.

The refining method of the present invention will be described below.

FIG. 1 shows a series of refining steps on which the refining method of the present invention is based. Molten iron is charged from a ladle 1 into a top-bottom blown converter 2 . After charging, a slag 4 for dephosphorization is prepared, and oxygen is blown into the molten iron and slag from the lance 2a to dephosphorize the molten iron while stirring the molten iron by blowing an inert gas from the nozzle 2b at the bottom of the furnace. .

After the dephosphorization treatment is completed, the produced dephosphorization slag 4a is discharged (intermediate slag), and then the dephosphorized molten iron is decarburized under normal conditions to obtain molten steel 6, which is tapped. Steel is tapped into the ladle 7 from the mouth 6a.

In this series of refining processes, the intermediate waste after dephosphorization treatment is an important process for discharging P concentrated in the dephosphorization slag out of the refining furnace system. If the dephosphorization slag is not sufficiently removed in the intermediate slag, P in an amount exceeding the permissible amount remains in the newly prepared slag for decarburization, and the remaining P migrates to the molten steel during the decarburization process. , the amount of P in the molten steel may not decrease to the desired level.

In the refining method of the present invention, in the dephosphorization process, a powdery solid oxygen source is added to the slag from above to increase the dephosphorization rate, increase the slag rate at the time of intermediate waste, and refining after the intermediate waste. The amount of P in the furnace system (hot metal and slag) is reduced as much as possible, and finally molten steel with a required level of low P amount is produced.

The smelting furnace may be a furnace capable of refining hot metal, but a furnace capable of continuously performing a series of processes of dephosphorization, slag removal, and decarburization, such as a converter, is preferable. . Above all, a top-bottom blown converter is preferable because it can efficiently perform the series of processes described above.

According to the refining method of the present invention, if ([hot metal P%]-[product P%])/[hot metal P%] is defined as the dephosphorization rate, a dephosphorization rate of 90% or more can be stably achieved. If the hot metal is preliminarily subjected to a preliminary dephosphorization treatment in another refining vessel (torpedo car, ladle, converter, etc.), the product P % can be further reduced.

In the refining method of the present invention, a solid oxygen source is added to the slag from above when the hot metal is dephosphorized. Addition of a solid oxygen source reduces the T.V. of the slag. The amount of Fe (FeO, Fe ₂ O ₃ , etc.) is increased, the dephosphorization rate is improved, and the slag removal rate is improved. This point is a feature of the refining method of the present invention.

The refining method of the present invention reduces the T.D. As a technique for increasing the amount of Fe, instead of oxidizing the hot metal, a powdery solid oxygen source is added to the slag from above. Since the solid oxygen source has a lower specific gravity than the hot metal, the powdery solid oxygen source is captured by the slag and blends with the slag, resulting in the T.V. of the slag. The amount of Fe increases.

Slag's T. When the amount of Fe (FeO, Fe ₂ O ₃ , etc.) increases, the liquid phase ratio of the slag increases, the dephosphorization reaction between the slag and the hot metal proceeds further, and the dephosphorization rate improves.

Also, T.I. When the amount of Fe increases, C in the hot metal reacts with FeO in the slag (FeO+C→Fe+CO, etc.) to generate a large amount of carbon dioxide gas, and the slag enters a foaming state. When the slag is in a foaming state, the slag dischargeability is improved, a large amount of slag can be discharged easily, and the intermediate slag rate is improved.

FIG. 2 shows the relationship between the amount of FeO in slag and the apparent density of slag. As the amount of FeO in the slag increases, the apparent density of the slag decreases. If the slag foaming state occurs excessively, it will cause operational troubles, but one of the features of the refining method of the present invention is to form a slag foaming state to some extent and increase the slag discharge rate during intermediate slag discharge. do.

The solid oxygen source contains 5% by mass or more of CaO and is a solid in which [CaO]/[ _SiO2 ] ([CaO]: mass% of CaO, [ _SiO2 ]: mass% of _SiO2 ) is 2.0 or less. Oxygen sources are preferred. Since this solid oxygen source has a low liquidus temperature and is trapped in the slag, the T.V. The amount of Fe can be effectively increased. The solid oxygen source is preferably powdery or granular with a sieving size of 5 mm or less from the viewpoint of compatibility with slag.

Specific examples of the solid oxygen source include sintered ore powder, dust pellets, iron ore, etc. Among them, sintered ore powder and dust pellets are preferable from the viewpoint of composition. Sintered ore powder is more preferable.

Sintered ore powder is sintered under a sieve of 5 mm or less generated during sintered ore production, with Fe: 50 mass% or more, CaO: 5 mass% or more, and CaO mass% / SiO ₂ mass% of 2.0 or less. Mineral dust is preferred. Compared to pure iron oxide (FeO), sintered ore powder contains CaO and the like and has a lower liquidus temperature (1369°C → 1290°C). . The amount of Fe can be effectively increased.

For example, when sintered ore powder is added to slag in an amount of 4.0 kg/t-pig or more in terms of oxygen content, the T.V. The amount of Fe can be 10% by mass or more.

Next, examples of the present invention will be described. The conditions in the examples are one example of conditions adopted for confirming the feasibility and effect of the present invention, and the present invention is based on this one example of conditions. It is not limited. Various conditions can be adopted in the present invention as long as the objects of the present invention are achieved without departing from the gist of the present invention.

(Example 1)
Using sintered ore powder and dust pellets having the composition and particle size shown in Table 1, the refining method of the present invention was carried out under the conditions shown in Table 2. The slag removal rate during intermediate slag removal is 60% or more. Table 2 also shows the dephosphorization rate (=([hot metal P %]−[product P %])/[hot metal P %]) as an evaluation index for dephosphorization by the refining method of the present invention. A case where the dephosphorization rate was 90% or more and less than 92% was evaluated as ◯, and a case where the dephosphorization rate was less than 90% was evaluated as Δ. In particular, when the dephosphorization rate was 92% or more, it was evaluated as ⊚.

When dust pellets are used, the evaluation is uncertain, but this is presumed to be influenced by the particle size of the dust pellets used, which has a wide range of particle sizes from 3 to 50 mm.

As described above, according to the present invention, the dephosphorization rate in the dephosphorization step is improved, and the slag removal rate in the intermediate slag removal step is improved. can be obtained. Therefore, the present invention has high applicability in the steel industry.

Reference Signs List 1, 7 ladle 2 top and bottom blown converter 2a lance 2b nozzle 3 hot metal 4, 5 slag 4a dephosphorization slag 6 molten steel 6a tapping port

Claims (4)

In a refining method in which hot metal is refined through a series of dephosphorization, intermediate slag, and decarburization processes using a refining furnace, a powdery solid oxygen source is added to the slag from above during the dephosphorization process. A method for refining hot metal,
The solid oxygen source is a sintered ore powder having a sieve size of 5 mm or less,
The solid oxygen source contains 5% by mass or more of CaO, and [CaO%]/[SiO ₂ %] is 2.0 or less.
A molten iron refining method characterized by: 2. The method for refining molten iron according to claim 1, wherein said refining furnace is a top and bottom blown converter. 3. The method of refining molten iron according to claim 1, wherein the molten iron is preliminarily dephosphorized in another refining vessel. The method for refining molten iron according to any one of claims 1 to 3 , characterized in that the solid oxygen source is added in an amount of 4.0 kg/t-pig or more in terms of oxygen content.

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