JP2016079444A - Dephosphorizing method for hot pig iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dephosphorizing method for hot pig iron, in a refining step, even in the case blowing is performed in a short time, capable of sufficiently and efficiently performing dephosphorizing to hot pig iron.SOLUTION: Provided is a method where, using an upper base blowing converter 1, a refining agent 3 including lime, iron oxide and calcium ferrite is added to the inside of the converter, and the dephosphorizing treatment to the hot pig iron 4 is performed, the calcium ferrite containing NaO. By melting the calcium ferrite whose melting point has been reduced by the incorporation of the NaO before the start of blowing, even if the blowing time is short, the dephosphorizing treatment can be efficiently performed.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a hot metal dephosphorization method using an upper bottom blowing converter, and more particularly to a dephosphorization method that can efficiently remove phosphorus even in a refining process with a short blowing time.

  The refining process in steelmaking is a process of purifying pig iron containing impurities from a blast furnace and adjusting it to a predetermined component. Among impurities contained in pig iron, phosphorus is an element that greatly affects product performance. In recent years, along with an increase in demand for low phosphorus steel having a low phosphorus content, it has become an issue in the refining process to efficiently perform a dephosphorization process for reducing the concentration of phosphorus contained in products.

  As a hot metal dephosphorization method, there is known a method of adding a refining agent containing calcium ferrite to hot metal charged in an upper-bottom converter. Calcium ferrite is a compound that improves the melting property of CaO by previously melting or sintering CaO and iron oxide at a high temperature. Since calcium ferrite has a lower melting point than CaO (quick lime), it promotes slag formation and promotes dephosphorylation in the dephosphorization process. A hot metal dephosphorization method using calcium ferrite is disclosed in, for example, Patent Documents 1 and 2.

Patent Document 3 describes that Na ₂ O contributes to dephosphorization, and describes a method for producing a refining agent containing Na ₂ O.

JP 2013-163844 A JP 2013-064167 A JP 2012-12680 A

  However, ordinary calcium ferrite used in the dephosphorization treatment in Patent Documents 1 and 2 has a melting point of around 1400 ° C., which is higher than 1200 to 1350 ° C., which is the temperature of the hot metal in the converter. Therefore, it becomes possible to melt and melt only in a state in which oxygen gas is blown from the lance and Si, C, Fe, etc. in the molten iron are oxidized and used as a heating source, so that the blowing time is short. In this case, it is conceivable that the blowing is completed in a state where the calcium ferrite is not sufficiently melted and the dephosphorization process is not efficiently performed.

  In Patent Document 2, the blowing time is about 10 minutes, and after 35% of the total blowing time has elapsed, calcium ferrite starts to be added, and the addition is completed until 80% of the total blowing time has elapsed. It is described to do. However, for example, when blowing is performed in a short time within 4 minutes, the method of Patent Document 2 is insufficient in melting of calcium ferrite, and there is a concern that the dephosphorization effect is lowered.

Further, Patent Document 3 does not describe a dephosphorization method using a refining agent containing Na ₂ O.

  An object of the present invention is to provide a hot metal dephosphorization method that can perform hot metal dephosphorization sufficiently efficiently even when blowing in a short time in the refining process.

In order to solve the above problem, the present invention is a method for performing dephosphorization treatment of hot metal by adding a refining agent containing quicklime, iron oxide, and calcium ferrite to the furnace using an upper bottom blowing converter. The method for dephosphorizing hot metal is characterized in that the calcium ferrite contains Na ₂ O.

  The refining agent is preferably charged into the furnace before the hot metal is charged. In that case, the blowing time may be within 4 minutes. Moreover, the charging basicity when adding the calcium ferrite into the furnace is 1.5 to 1.8, and the CaO mass in the calcium ferrite with respect to the total CaO mass contained in the refining agent supplied to the converter Is preferably 20% or more.

According to the present invention, calcium ferrite having a lower melting point due to containing Na ₂ O is charged before the hot metal is charged and melted in advance using the stirring force at the time of hot metal charging. Thus, even if the blowing time is short, dephosphorization can be performed efficiently.

It is explanatory drawing which shows the outline of the refining process using the top bottom blowing converter concerning this invention. It is a graph which shows the result of the self-flux test of calcium ferrite. It is a graph which shows the melting rate for every hour of calcium ferrite.

  Embodiments of the present invention will be described below.

  As the refining furnace used in the steelmaking refining process, a converter is usually used. In the steelmaking process using the converter method, molten steel and scrap are charged as main raw materials to produce molten steel. FIG. 1 shows an outline of a refining process using an upper bottom blowing converter.

First, as shown in FIG. 1A, the scrap 2 is charged into the converter 1. In the present embodiment, simultaneously with the loading of scrap 2, turning on the refining agent 3 comprising calcium ferrite containing Na 2 _O in the furnace. The ratio of Na ₂ O in calcium ferrite is, for example, 0.3 to 5.0% by mass, preferably 1 to 3% by mass. The higher the Na ₂ O content, the lower the melting point of calcium ferrite. However, if too much, the quality of the slag after refining will be hindered, and the slag cannot be used as a product. If it is less than 1%, the effect of lowering the melting point of calcium ferrite becomes small. The particle diameter of calcium ferrite can be 1 to 50 mm, preferably about 5 to 35 mm, which is usually commercially available.

The basicity of charging when adding calcium ferrite into the furnace is about 1.5 to 1.8, preferably around 1.7, and the total mass of CaO contained in the refining agent 3 fed into the converter. The total amount of CaO in the calcium ferrite is preferably 20% or more. The charge basicity refers to “the total amount of CaO contained in the secondary raw material (refining agent) supplied into the converter” as a molecule, and “SiO ₂ contained in the secondary raw material supplied into the converter”. Si mass of total "and" included in the main raw material (molten iron and scrap) is a number of the ratio which is calculated the sum of the SiO ₂ mass "in the case of the oxidized to the total SiO ₂ as a denominator.

  After the scrap 2 and the refining agent 3 are charged, the hot metal 4 is charged into the furnace (FIG. 1 (b)), and then blown by blowing oxygen from the lance 11 into the hot metal 4 (FIG. 1 (c)). ).

By blowing, by reacting with phosphorus (P) is the oxygen in the hot metal _4, is generated P 2 _{O 5,} react with P 2 _{O 5} is CaO, 3CaO · _{P 2} is a stable compound in the slag O ₅ is produced. However, CaO has a high melting point, and as such, does not melt at the hot metal temperature during refining. Therefore, in the present invention, calcium ferrite containing Na ₂ O is used so that the melting point is lowered earlier, CaO melts at the hot metal temperature, and the compound 4CaO · P ₂ O ₅ is easily generated.

In this embodiment, by introducing the refining agent 3 before charging the hot metal 4, the melting time of the calcium ferrite can be ensured by utilizing the stirring force at the time of charging the hot metal 4. As a result, all of the calcium ferrite can be melted during the blowing, and as soon as the blowing is started and P ₂ O ₅ is generated, the CaO and P ₂ O ₅ melted from the Na ₂ O-containing calcium ferrite are produced. Reacts to produce 4CaO · P ₂ O ₅ , so that dephosphorization using calcium ferrite can be performed efficiently. Alternatively, only the calcium ferrite containing Na ₂ O among the refining agents may be charged before the molten iron 4 is charged, and other substances of the refining agent may be charged at the time of blowing.

Calcium ferrite is a compound that improves the melting property of CaO as described above, and it is well known that CaO is easily melted by using calcium ferrite during refining and exhibits a dephosphorization effect. By using calcium ferrite containing ₂ O, the melting point is further lowered and the dephosphorization effect can be enhanced.

A self-flux test was conducted to examine the difference in melting point of calcium ferrite depending on the presence or absence of Na ₂ O. Table 1 shows component ratios of conventional calcium ferrite and Na ₂ O-containing calcium ferrite containing 2% Na ₂ O as an example of the present invention.

FIG. 2 shows the results of the self-fluxing test. The conventional calcium ferrite containing no Na ₂ O had a melting temperature of 1370 ° C., but the melting point was lowered by containing 2% Na ₂ O, It was found that the temperature was below the hot metal temperature. That is, if the content of Na ₂ O is 2%, the melting temperature of calcium ferrite becomes lower than the hot metal temperature, and the melting time of calcium ferrite can be ensured by utilizing the stirring force at the time of hot metal charging. it can.

Next, a normal product of calcium ferrite (CF) not containing Na 2 _O, by introducing the calcium ferrite containing Na 2 _O shown in Table 1 the rolling furnace was investigated molten state.

FIG. 3 shows the time-dependent melting rates of calcium ferrite not containing Na ₂ O and Na ₂ O-containing calcium ferrite. The ambient temperature is 1350 ° C. The normal product of calcium ferrite took longer to melt than calcium ferrite containing Na ₂ O, and the melt rate was as low as about 1/4 in 4 minutes. Further, even in the case of calcium ferrite containing Na ₂ O, only about half was melted in 4 minutes, and it was found that a time of 7 minutes was required to make the melting rate 100%. That is, when using calcium ferrite containing Na ₂ O in a short blowing time of dephosphorization, usually within 4 minutes, it is necessary to ensure a melting time of 7 minutes.

Since Na ₂ O-containing calcium ferrite has a low melting point, it can be melted in the furnace using the stirring force at the time of hot metal charging even if it is added before the start of blowing. Therefore, Na ₂ O-containing calcium ferrite is charged before the hot metal is charged, and the melting rate can be improved to 100% by securing the insufficient melting time by using the stirring force at the time of hot metal charging. . That is, by introducing a refining agent containing Na ₂ O-containing calcium ferrite before the start of blowing, even if the blowing time is within 4 minutes, the dephosphorization process is efficiently performed until the blowing is completed. be able to.

  As a form of refining that performs dephosphorization, after dephosphorization, decarburization is performed in another furnace, and after dephosphorization, called the MURC (Multi Refining Converter) method, the converter is tilted. There are cases where slag with high phosphorus concentration is discharged and then decarburization is continued in the same furnace. The present invention can be applied to any case, but in particular, in the MURC method, the blowing time during dephosphorization is usually as short as 4 minutes or less. Even in such a case, the present invention is efficient. Dephosphorization can be performed.

  As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to this example. It is obvious for those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea described in the claims. It is understood that it belongs to.

Using two types of calcium ferrite shown in Table 1, that is, conventional calcium ferrite and Na ₂ O-containing calcium ferrite containing 2% Na ₂ O as an example of the present invention, dephosphorization treatment in a converter is performed. went. The blowing time was 3 to 4 minutes, the charging basicity was 1.8, and the amount of calcium ferrite used was 10 kg / t. In the inventive example, Na ₂ O-containing calcium ferrite was added 3 minutes before the start of blowing, and the conventional example was added at the start of blowing.

  As a result, the dephosphorization rate of 50% in the conventional example was improved to 70% in the example of the present invention.

  INDUSTRIAL APPLICABILITY The present invention can be applied to a dephosphorization processing method in which steel-containing scrap and molten iron are charged into a smelting furnace and blown in a steelmaking process to melt the molten steel.

1 Converter 2 Scrap 3 Refining agent 4 Hot metal 11 Lance

Claims (4)

A refining agent containing quicklime, iron oxide, and calcium ferrite is added to the furnace using a top-bottom blow converter, and the hot metal is dephosphorized.
The method for dephosphorizing hot metal, wherein the calcium ferrite contains Na ₂ O.   2. The hot metal dephosphorization method according to claim 1, wherein the refining agent is put into the furnace before the hot metal is charged.   3. The hot metal dephosphorization method according to claim 2, wherein the blowing time is within 4 minutes.   The charging basicity when adding the calcium ferrite to the furnace is 1.5 to 1.8, and the total CaO mass in the calcium ferrite with respect to the total CaO mass contained in the refining agent supplied to the converter The hot metal dephosphorization method according to any one of claims 1 to 3, wherein the hot metal content is 20% or more.

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