JP2000256719A - Steelmaking method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steelmaking method, with which converter slag after executing decarburizing treatment is left in the converter and the slag can efficiently be reused to converter dephosphorizing treatment in the following charge, continuously executing the dephosphorizing treatment, tapping, recharging and decarburizing treatment in the same converter. SOLUTION: Firstly in the converter 1, the dephosphorizing treatment is mainly executed, and thereafter the molten steel in the converter is tapped into a molten steel receiving ladle 2 and successively, after tapping the molten steel, the dephosphorized slag in the converter is tapped into a slag tapping pot 3 and the molten steel tapped into the molten steel receiving ladle is charged into the converter again, and the decarburize-refining is mainly executed. Then, after tapping the decarburized molten steel, the decarburized slag is left in the converter and auxiliary material containing one or more kinds among fluorite, Al ash and boron oxide are charged into the residual decarburized slag and used for the dephosphorize-refining in the following charge.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention utilizes a converter type furnace to continuously perform dephosphorization refining, tapping, recharging, and decarburization refining. C in slag
The present invention relates to a steelmaking method for efficiently reusing aO, iron, and Mn.

[0002]

2. Description of the Related Art In recent years, as the quality requirements (particularly low phosphorus and low sulfuration) regarding steel materials have become severe, various steel making methods for producing low phosphorus steel at lower cost have been proposed.
In particular, in the low temperature region where thermodynamics are advantageous for dephosphorization, hot metal pretreatment is performed in which hot metal dephosphorization is performed with high efficiency in advance, and then decarburization is performed. From the viewpoint of reducing fixed costs through process consolidation, converter-type hot metal pretreatment in which dephosphorization is performed in a converter is becoming popular.

On the other hand, from the viewpoint of reducing the cost of the dephosphorizing refining agent in the hot metal pretreatment and reducing the amount of generated slag, the dephosphorizing refining agent for the converter slag still having the dephosphorizing ability in the hot metal pretreatment stage. Is actively being reused. As a method of reusing the decarburized slag in the converter type hot metal pretreatment, two converter type furnaces each having a top-bottom blowing function as shown in JP-A-62-290815 are dedicated to dephosphorization. There is a method in which a converter and a furnace for exclusive use of decarburization are used, and the converter slag after the decarburization treatment is once discharged out of the system, and is charged as a dephosphorizing scouring agent into the dephosphorization furnace. According to this method, the converter slag once discharged into the pan is charged into the converter again. (A) The sensible heat loss of the converter slag is large, and it takes time to raise the temperature of the converter slag in the dephosphorization reaction refining. As a result, slag formation is eventually caused and sufficient dephosphorization reaction efficiency cannot be obtained. (B) In the case of hot reuse, a container for safely transporting the converter slag and a work process such as gradual cooling of the converter slag and crushing for putting it in the converter charging container are required. That time is also required. (C) Since two furnaces, one dedicated to dephosphorization and the other dedicated to decarburization, are required, there are great restrictions on equipment. There is a problem.

[0004] In order to improve the slagging in the dephosphorization and refining of the decarburized slag to be reused, Japanese Patent Laid-Open Publication No. 5-156338 discloses a method of receiving decarburized slag with fluorite charged in a slag pot. A method is disclosed in which the fluorite is reused after being melted and mixed in the decarburized slag. However, it is described that, even in this method, if the fluorine concentration in the decarburized slag is less than 10%, the slag has a high melting point, resulting in poor slag formation. It is presumed that the temperature of the slag at the time of recycling is low, and it takes time to raise the temperature of the slag.

[0005]

In order to solve the above-mentioned problems, the present inventors have studied a system for performing dephosphorization refining and decarburization refining in the same furnace. The molten metal from the blast furnace is charged into a converter, and then dephosphorized and refined.After dephosphorization and refining, the molten metal and slag are discharged respectively, and then the molten metal after dephosphorized and refined is returned to the same converter. Charge and decarburize and refine. The molten steel after the decarburization refining is discharged from the converter, but the decarburized slag is left in the furnace and used for dephosphorization blowing of the next charge. In this method, since the decarburized slag can be used for the next charge while remaining in the converter furnace, the slag sensible heat loss is small, and slag treatment equipment is not required.

[0006] When the decarburized slag is reused for dephosphorization refining while remaining in the furnace, it is most efficient if the slag can be reused in a molten state because sensible heat loss is small and reactivity is good. However, if the converter slag is left in the furnace in a molten state, the converter slag and the hot metal react rapidly when the next charge of the hot metal is charged, and the hot metal may blow out from the converter. for that reason,
When reusing converter slag, it is necessary that the converter slag left in the furnace be in a solidified state at the time of charging the hot metal for the next charge.

In order to solve this problem, it is conceivable to solidify the converter slag with a coolant such as limestone and then charge the hot metal of the next charge to perform the converter dephosphorization. However, in this method, phenomena such as slopping and a decrease in dephosphorized lime efficiency occur, and it is necessary to increase the use of lime to prevent such a phenomenon. There was a problem that it could not be enjoyed.

A first object of the present invention is to provide a steelmaking method in which dephosphorization, tapping, recharging, and decarburization are continuously performed in the same converter. An object of the present invention is to provide a steelmaking method that can be efficiently reused in a converter dephosphorization treatment of a next charge, which is left inside.

Mn in the hot metal is burned and oxidized during the decarburization refining and moves into the decarburized slag. If the oxidation of Mn can be suppressed to improve the Mn yield in decarburization refining, the amount of Mn added as an alloy can be reduced.

A second object of the present invention is to provide a steelmaking method in which dephosphorization, tapping, recharging, and decarburization are continuously performed in the same converter, wherein the steelmaking with a high Mn yield after decarburization is performed. It provides the law.

[0011]

That is, the gist of the present invention is as follows. First, in a converter, first, dephosphorization is mainly performed first, and then the molten metal in the converter is discharged to a receiving pan. Then, after the molten metal is discharged, the dephosphorized slag in the converter is discharged into a waste pan, the molten metal discharged into the receiving pan is charged into the converter again, mainly decarburization refining, and after decarburization, After discharging
The decarburized slag is left in the converter, and the remaining decarburized slag is charged with an auxiliary material containing at least one of fluorite, Al ash, and boron oxide, and is used for dephosphorization refining of the next charge. This is a characteristic steelmaking method.

The present inventors have conducted various tests and researches to achieve the first object. As a result, it was found that the slopping and the decrease in dephosphorized lime efficiency when the decarburized slag was reused for dephosphorization while remaining in the furnace were due to insufficient slag slag formation in dephosphorization and refining. .
That is, the melting point of the converter slag after the decarburization treatment is 1600 to 1700.
° C, and slag having such a composition is further added with limestone or the like to lower the temperature. Therefore, the slag after solidification is in a dense state with a low bubble rate, and the molten metal temperature is 13 ° C.
It does not dissolve sufficiently during dephosphorization refining at about 00 ° C.

According to the research results of the present inventors, it is possible to prevent slopping and improve the efficiency of dephosphorized lime by improving the slag conversion rate of the converter slag to be reused. And for that purpose, it was found that it is effective to add fluorite, Al ash, and boron oxide to the slag.

In the test and research conducted by the present inventors, slagification was satisfactory even when the fluorine concentration in the converter slag was about 5%. In the present invention, the converter slag is in a solidified state by reusing the converter slag without discharging and remaining in the converter furnace,
Since the converter can be subjected to the dephosphorization treatment of the next charge at a high temperature, the converter slag can be heated in a short time. That is, the effect can be exhibited even if the amount of the fluorite to be introduced is small.
In the invention disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 5-156338, the reason why the slagging failure occurs when the fluorine concentration is less than 10% is that the converter slag is once discharged out of the furnace and cooled, so that the temperature of the converter slag is reduced. It is presumed that, when subjected to the dephosphorization treatment, it took time to heat the converter slag.

The same effect as fluorite can also be obtained by adding Al ash or boron oxide.

The gist of the present invention is that, secondly, in the converter, first, dephosphorization and refining are first performed, and then the molten metal in the converter is discharged to a receiving pan, and then the molten metal is discharged. The dephosphorized slag in the furnace is discharged to a waste pan, and the molten metal discharged to the receiving pan is charged into the converter again, mainly performing decarburization refining, and at the end of the decarburization refining, fluorite, Al It is characterized by adding auxiliary materials containing at least one of ash and boron oxide, discharging the molten steel after decarburization, leaving the decarburized slag in the converter, and using it for dephosphorization refining of the next charge. Steelmaking method.

In order to achieve the second object of improving the molten steel [Mn] in addition to the first object, as described above, at the end of decarburization blowing, the fluorite, Al ash, and boron oxide are used. Among them, the auxiliary materials including one or more types are introduced. Of the added auxiliary materials, fluorite and Al ash can be realized by reducing the iron oxide and the Mn oxide in the converter slag to improve the Mn yield. Furthermore, in the second invention, since the auxiliary material charged in the last stage of the blowing is contained in the converter slag, the recycled slag is quickly melted in a short time in the subsequent converter dephosphorization treatment of the next charge. , It is possible to improve the dephosphorization efficiency,
The first object can be achieved at the same time.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, after decarburization blowing is completed, auxiliary materials containing at least one of fluorite, Al ash, and boron oxide are added to the residual slag in the converter to remove the decarburized slag. It is possible to lower the melting point of the coal slag and improve the slag conversion rate of the recycled slag during the dephosphorization treatment of the next charge. Therefore, the dephosphorization lime efficiency can be improved.
Particularly, since CaF ₂ contained in fluorite has an effect of reducing the concentration of Mn oxide in slag,
By introducing fluorite at the end of decarburization blowing, it is possible to reduce the Mn oxide in the slag and improve the yield.

If the amount of fluorite is increased, the liquid phase ratio of the recycled slag in the dephosphorization temperature range is improved, which is effective for improving the slagging ratio during dephosphorization blowing. Since the use has a bad effect on the converter refractory, it is desirable that the input amount of the fluorite be kept to a minimum necessary amount according to the blowing conditions.

Since the same effect as fluorite can be expected with Al ash and boron oxide in terms of improving the slagging rate, a slagging agent of Al ash and boron oxide can be used instead of fluorite. Good. This is because the melting point of the main component Al ₂ O ₃ or boron oxide in the aluminum ash can be reduced by adding it to the converter slag.

The amount of fluorite added is preferably about 5% of the amount of residual slag in the furnace. If the addition amount is too small, it does not contribute to slagging, and if it is too large, the refractory will be eroded. The amount of Al ash added is about 10% of the amount of residual slag in the furnace. If the amount is too small, it does not contribute to slagging, and if the amount is too large, it has an effect on the P removal ability.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below based on embodiments. FIG. 1 shows a converter refining process according to the present invention. Reference numeral 1 denotes a converter, and the hot metal that has been tapped from the blast furnace is subjected to desulfurization treatment as required, and then the converter 1
Is subjected to a dephosphorization treatment. In the dephosphorization treatment, a recycled slag according to the present invention, which will be described later, is used as a refining agent, and a medium solvent such as quicklime, fluorite, iron ore, or the like is added as needed to perform the dephosphorization treatment.

After the dephosphorization treatment, the hot metal is discharged to a hot-water receiving pan No. 2 and the converter dephosphorization slag is discharged to a discharge pan No. 3 and then charged again into the converter 1 to be decarbonized. Is performed. At the time of the decarburization treatment, a medium solvent such as quick lime, limestone, dolomite, Mn ore, iron ore, or the like is added as necessary, and the decarburization treatment is performed until the component range according to the purpose is reached.

An example in which the operation shown in FIG. 1 is performed will be described below.

[Example 1] In a 250-ton top-bottom blow converter, after the decarburization treatment was completed, molten steel was discharged, and slag 8 was left in the furnace. CaF ₂ was reduced to about 10% of the remaining slag in the furnace. In the case of the present invention in which fluorite was charged, and then a coolant for solidifying the slag was added, in the case of the comparative example in which only the coolant for solidifying the slag was added, for each of the comparative examples, The subsequent slag analysis was performed to determine the slag conversion rate and the dephosphorization lime efficiency. An outline of the process flow is shown in FIG. 1, and the results are shown in Table 1. The dephosphorization refining conditions and the like were the values shown in Table 1. Further, the slagging rate and the dephosphorization lime efficiency are respectively calculated by the following equations. Slagification ratio = actual basicity of slag after dephosphorization / calculated basicity of slag after dephosphorization Dephosphorized lime efficiency = phosphorus concentration in slag after dephosphorization / lime concentration in slag after dephosphorization

[0026]

[Table 1]

As shown in Table 1, in the case of the present invention in which fluorite was added to the decarburized slag and then solidified, the slagification ratio of the slag after the dephosphorization refining was about 1.4 as compared with the comparative example. The dephosphorization lime efficiency has increased about twice. No slopping was observed in the test charge.

[Example 2] In the case of the present invention in which fluorite was charged so that CaF ₂ became about 10% of the slag in the furnace at the end of decarburization refining in a 250-t top-bottom blower, Mn of molten steel for each of comparative examples where
The concentrations were compared. An outline of the process flow is shown in FIG.
Table 2 shows the results.

[0029]

[Table 2]

As shown in Table 2, the Mn concentration in the molten steel is increased by 0.02 to 0.03% as compared with the comparative example.

[0031]

As described above, according to the present invention, it is possible to recycle slag while utilizing the sensible heat of decarburized slag, reduce the rate of occurrence of slopping, and recycle decarbonized slag. It is possible to improve the rate of slag formation during dephosphorization blowing, and to reduce lime used for preventing slopping and assisting dephosphorization efficiency. In addition, by adding fluorite or the like at the end of decarburization blowing, in addition to the above effects, Mn oxide in slag is reduced, and molten steel [Mn] is added.
Can be improved.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a refining process according to the present invention.

FIG. 2 is a diagram showing a process flow of the first embodiment.

FIG. 3 is a diagram illustrating a process flow according to a second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Converter 2 Hot pot 3 Slag pot 4 Hot metal pot 5 Steel hot pot 6 Blowing lance 7 Melt 8 Slag

Continued on the front page (72) Inventor Kunihiko Watanabe 1 Kimitsu, Kimitsu, Nippon Steel Corporation Kimitsu Works F-term (reference) 4K002 AC05 AC09 AE01 BD04 4K014 AA03 AB00 AB02 AB16 AB21 AD00

Claims (2)

[Claims] In a converter, first, dephosphorization and refining are mainly performed, and thereafter, the molten metal in the converter is discharged to a receiving pan, and then, the dephosphorized slag in the converter is discharged to a waste pan. And
The molten metal discharged into the receiving pan is charged again into the converter, mainly decarburized and refined, and after the decarbonized molten steel is discharged, the decarburized slag is left in the converter, and the remaining decarbonized slag is left. Fluorite, Al
Add auxiliary material containing at least one of ash and boron oxide,
A steelmaking method characterized by being used for dephosphorization refining of the next charge. 2. In the converter, first, dephosphorization and refining are mainly performed first, and then, the molten metal in the converter is discharged to a receiving pan, and then the dephosphorized slag in the converter is discharged to a waste pan. The molten metal discharged and discharged into the hot pot was charged again into the converter, and mainly decarburized and refined. At the end of the decarburized refining, fluorite and A
Adds an auxiliary material containing at least one of ash and boron oxide, discharges molten steel after decarburization, leaves decarburized slag in the converter, and uses it for dephosphorization and refining of the next charge. And steel making method.