JP2000087125A - Method for dephosphorize-refining molten iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stable dephosphorize-refining method of molten iron while reducing a produced slag. SOLUTION: Following processes are provided. (a) Molten iron having <=0.2 wt.% Si content is charged into a converter. (b) A CaO component is charged by <=18 kg/ton with lime and the molten iron is refined with oxygen blowing. Further, it is desirable to substantically and continuously charge the lime at least for two min after starting the dephosphorize-refining. Furthermore, it is desirable to use a part of the CaO component with the lime as premelt flux.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dephosphorization refining method for producing steel by mainly dephosphorizing and refining blast furnace hot metal and then decarburizing and refining.

[0002]

2. Description of the Related Art In a conventional converter steelmaking method, dephosphorizing and decarburizing refining of molten iron in a blast furnace is performed in the same converter to perform a steelmaking operation. However, while the demands on the quality of steel materials have increased in recent years, with the expansion of continuous casting, and the spread of secondary refining of molten steel such as vacuum degassing and ladle refining, the tapping temperature in converters has increased, The dephosphorization capacity in the converter has been reduced. The reason for this is that the dephosphorization reaction proceeds disadvantageously as the temperature increases.

[0003] Accordingly, a steelmaking method has been developed in which hot metal is dephosphorized and refined in one converter to remove phosphorus (hereinafter, referred to as P) to some extent, and then decarburized and refined mainly in another converter. . As such a technique, Japanese Patent Application Laid-Open No. 2-200715, Japanese Patent Publication No. 2-14404, Japanese Patent Publication No.
No. 243 is proposed.

[0004] The applicant of the present application has also improved the conventional steelmaking method and charged hot metal dephosphorized and refined in one converter into another converter, where the steel was decarburized and refined. A steel making method has been developed (JP-A-6-41624).

[0005]

In the above steel making method, the steel is manufactured by sufficiently dephosphorizing and refining in one converter, and mainly decarburizing and refining the hot metal in another converter. Therefore, in decarburization refining, for example, the P
It must be refined to a standard value of 0.02% by weight or less, preferably about P content of about 0.015% by weight on average.
Furthermore, it is necessary to minimize the amount of slag generated by the dephosphorization refining and to reduce the amount of slag that is difficult to dump.

[0006] The outline of the dephosphorization refining of the hot metal will be described. The converter is charged with scrap, followed by hot metal and oxygen blowing. Usually, calcined lime is charged as a slag-making material at about 12 to 27 kg / ton at the start of blowing and at the beginning of blowing, and blowing is continued. At the end of blowing, raw dolomite is charged for slag coating, and coke and ogalite are added to calm the slag. Also, scale and iron ore are charged during refining to promote dephosphorization refining and increase iron yield.

However, conventionally, the amount of calcined lime charged is
The slag is charged so that the basicity of the slag is constant according to the content, and the P content after dephosphorization and refining is considered so as to be a predetermined target value. The higher the amount, the higher the P content after dephosphorization refining. This indicates that the calcined lime charged did not completely dissolve and there was an undissolved portion.

Further, slag generated by dephosphorization refining (hereinafter referred to as slag)
Approximately 40 kg per 1 ton of molten steel
And its component composition is, for example, Fe: 5wt
%, CaO: 52 wt%, SiO ₂ : 13 wt%, Ca
O / SiO ₂ : 4, P: 3 wt%. We want to reduce this slag amount as much as possible.

Therefore, as described above, the present invention provides a method of dephosphorizing and refining ordinary steel by dephosphorizing so as not to perform dephosphorizing refining again.
It is an object of the present invention to surely refine a standard content of 0.02 wt% or less, preferably about 0.015 wt% on average. Furthermore, the aim is to minimize the amount of slag generated by dephosphorization refining and to reduce the amount of slag that is difficult to dump.

[0010]

As a result of various studies on the above-mentioned problems, as a result of reducing the Si content of hot metal to 0.2% by weight or less and using premelt flux in addition to calcined lime as a slag-making material for dephosphorization refining. Then, the P content is made equal to or less than the P content of the ordinary crude steel component (so-called standard value or less, usually 0.02 wt.
% Or less), and the following invention has been made based on the finding that refining can be further promoted.

[0011] A first aspect of the present invention is a method for dephosphorizing and refining hot metal, comprising the following steps. (A) charging hot metal having a Si content of 0.20 wt% or less into a converter,
(B) A CaO component of 18 kg / ton or less is charged by calcined lime, followed by oxygen blowing and dephosphorization refining. When the Si content of the hot metal is 0.20% by weight or less, it is sufficiently dissolved when CaO (lime) is charged with a target of a predetermined basicity, so that the P content after the dephosphorization refining is at least the ordinary crude steel component. P
Since the refining can be performed to the content or less (so-called standard value or less, usually 0.02 wt% or less), there is no need for dephosphorization refining in decarburization refining, so that the refining work is promoted as a whole.

A second aspect of the present invention is a method for dephosphorizing molten iron, wherein the calcined lime is charged substantially continuously for at least 2 minutes after the start of dephosphorization refining. Since calcined lime has poor solubility, it is not charged all at once, and if it is continuously charged for at least two minutes in the initial stage of refining in which molten iron is oxidized, unmelted components can be reduced, and dephosphorizing refining is performed smoothly. be able to.

[0013] A third aspect of the present invention is a method for producing carbon by the calcined lime.
This is a method for dephosphorizing and refining hot metal, in which a part of the aO component is charged with a pre-melt flux. Since the pre-melt flux is melted in advance, uniform slag formation of the slag is promoted, so that the dephosphorization reaction is stably performed.

A fourth aspect of the present invention is a method for dephosphorizing hot metal, wherein the premelt flux is slag generated by decarburization refining. In the case of decarburizing and refining the dephosphorized hot metal by the refining method of the present invention, almost no dephosphorizing refining is performed.
It has a low content and has a dephosphorizing ability. Therefore, when this slag is used as a pre-melt flux, dephosphorization refining can be promoted, and slag that has been conventionally dumped can be effectively used.

According to a fifth aspect of the present invention, when the Si content of the hot metal exceeds 0.2 wt%, the hot metal is desiliconized to refine the Si content to 0.2 wt% or less. A method for dephosphorizing and refining hot metal, comprising dephosphorizing and refining the hot metal. If the Si content of the hot metal exceeds 0.2 wt%, it is desiliconized in advance, refines the Si content to 0.2 wt% or less, and then performs dephosphorizing refining of the hot metal with a small amount of CaO. Can be refined to a P content of 0.02 wt% or less.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An outline of a conventional dephosphorization refining in a converter for hot metal will be described below with reference to FIG. FIG. 7 shows the operation mode of dephosphorization refining in a converter of, for example, 340 ton of hot metal (acid supply amount, lance height, bottom blowing gas amount, charging time of slag-making material such as calcined lime, charging amount, and the like).

Following the charging of the scrap, after charging the hot metal,
Oxygen blowing is performed for about 13 minutes while charging calcined lime (4 to 6 ton / ch), fluorite (0.6 ton / ch), and possibly raw dolomite as a slag-making material. afterwards,
Rinse for about 3 minutes to separate hot metal and slag. After that, wait about 4 minutes to calm down the slag forming, and then tap out.

FIG. 1 shows the relationship between the Si content of the hot metal and the P content after the dephosphorization treatment in the dephosphorization refining in the 340 ton converter. In the following, the P content after the dephosphorization treatment was all refined with the target of 0.015 wt%. Conventionally, as shown in FIG. 1, the amount of CaO charged is increased along with the increase of the Si content, and refining is performed so that the P content after the dephosphorization treatment becomes 0.020 wt% based on the dephosphorization equilibrium theory.

When the Si content is 0.2 wt% or less, the P content after the dephosphorization treatment is stable at 0.020 wt% or less, but when the Si content is 0.2 wt% or more, the P content after the dephosphorization treatment is low. The P content varies between 0.014 wt% and 0.03 wt%. From this point, it can be seen that when the Si content increases, undissolved lime is generated even when the CaO charging amount is increased. Therefore, it is desirable to charge the charged lime substantially continuously for 2 minutes after the start of oxygen blowing in which oxidation of Si proceeds from the initial stage of refining.

Next, FIG. 2 shows the P content after the dephosphorization treatment when calcined lime was charged at 12 kg / ton and premelt flux was charged at 7 kg / ton. Slag generated by decarburization refining as premelt flux (component composition; T.Fe: 1
5-25 wt%, CaO: 40-50 wt%, Si
O ₂ : 8 to 15 wt%, P: 0.3 to 1.2 wt%).

The P content after the treatment is stable at 0.017 w
It is stable at t% or less. Premelt flux is Ca
It is presumed that the O component was dissolved in the slag, thereby promoting the dephosphorization reaction. As the pre-melt flux, for example, slag generated by decarburization refining can be used.

FIG. 3 shows the P content after the dephosphorization treatment when 12 kg / ton of calcined lime is continuously charged during the initial 2 minutes of refining and the premelt flux is charged at 7 kg / ton at the initial stage of refining. Is shown. The P content was more stably in the range of 0.014 to 0.16 wt%.

FIG. 4 summarizes the above results. FIG. 4 is summarized as follows. In the conventional method in which only calcined lime is charged, the P content after the dephosphorization refining varies greatly. Si content is 0.2wt
%, There is much more variation, and undissolved lime is generated.

When a part of the calcined lime is replaced with the pre-melt flux, the P content is stabilized at 0.017 wt% or less after the dephosphorization treatment. When the premelt flux and calcined lime are continuously charged at the initial stage of refining, the P content after the dephosphorization treatment is 0.017 to 0.01.
3 wt%, average 0.015 wt%.

FIG. 5 shows the efficiency of lime in the above three types of refining as actual basicity / calculated basicity. Here, the actual basicity is the basicity calculated from the slag amount and CaO wt% in the slag, and is an effective CaO content. The calculated basicity is a basicity calculated from the total CaO content charged.

From this figure, it can be seen that the Si content of the hot metal is 0.2 w
It was found that when the content exceeds t%, the efficiency of lime is inferior, and the efficiency of calcined lime increases when premelt flux is used together with calcined lime. Therefore, in the dephosphorization refining, refining is performed using hot metal having a Si content of 0.2 wt% or less. When the content of Si in the hot metal exceeds 0.2 wt%, preliminary desiliconization is performed in advance.

As a method of preliminary desiliconization, a hot metal ladle desiliconization method, blast furnace cast floor desiliconization, or oxygen blowing in a converter for dephosphorizing refining to remove silicon, and after removing generated slag, Subsequently, there is a method of performing dephosphorization refining, and any method can be used.

In the dephosphorization refining, the concentration of FeO in the slag is increased in order to promote the dephosphorization refining. For this reason, iron ore or mill scale is charged in the middle stage of blowing (see FIG. 7). However, if the slag FeO is too high,
Slag forming becomes large after the end of oxygen blowing. Therefore, it is desirable to perform the iron ore charging such that the iron ore charging has been completed 5 minutes before the oxygen blowing end time.

The effect of the present invention is also exerted in the decarburization refining using the dephosphorized hot metal. That is, in the case of decarburizing and refining the dephosphorized and refined hot metal, the amount of oxygen to be blown is increased because the purpose is mainly for decarburizing and refining. Since the P content of the hot metal is already below the standard value (0.02 wt%), slag-making materials such as calcined lime, which are conventionally used in large quantities, are generally charged except for the first charge in a series of blowing. do not do.

Therefore, the amount of slag generated in the furnace is 10 to
It is as small as 30 kg / ton. In addition, since slag remains in the furnace after tapping in principle, the amount of slag to be discharged is greatly reduced as compared with the conventional method. Further, in the present invention, there is no need to remove phosphorus in the decarburization refining. Therefore, in the present invention, manganese ore (for example, about 50% by weight of Mn, about 10% by weight or less of Fe, and about 10% by weight or less of SiO ₂ ) can be charged to increase the Mn content of the molten steel, thereby making it more economical. Steelmaking work becomes possible.

FIG. 6 shows an example in which decarburization refining is performed without charging calcined lime to produce steel. Example 1 shows a case in which Al was not added as a deoxidizing material in a converter after decarburization refining, and Examples 2 and 3 show a case in which Al was added as a deoxidizing material in a converter. In No. 4, Fe-Si is used as a deoxidizing material
(Ferrosilicon) is shown. The deoxidizer reduces Mn in the slag to improve the Mn yield. Each example is shown as an average of about 50 charge examples.

By performing the dephosphorization refining of the present invention,
Since the P content after the dephosphorization refining treatment can be surely refined to 0.02 wt% or less, and about 0.015 wt% on average, it is not necessary to perform dephosphorization refining again when decarburizing the hot metal. Therefore, without the need of charging lime, charging manganese ore to save expensive ferromanganese of steel,
Economical production of steel becomes possible.

[0033]

According to the present invention, the Si content is 0.2%.
Since the hot metal of not more than wt% is used, the amount of slag generated can be made lower than before. Also, the phosphorus (P) content of the hot metal is determined by the P content required for crude steel (specified value of steel components).
Refining is performed below, and other converters can mainly perform decarburization refining. Furthermore, in the present invention, by performing dephosphorization refining by using slag that is usually generated in refining in addition to calcined lime as premelt slag, the phosphorus content at the end point can be stably reduced as compared with the conventional method. .

Further, since it is not necessary to perform dephosphorization in a converter for decarburization refining, manganese ore is charged and Mn of molten steel is reduced.
The content can be increased, and a very economical steelmaking method can be realized. In addition, this steelmaking method has the effect of saving resources by recycling the generated slag. Therefore, the industrial effects of the present invention are remarkable.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the Si content of hot metal and the P content after dephosphorization refining.

FIG. 2 is a diagram showing the relationship with the P content after dephosphorization refining when a pre-melt flux is added in addition to calcined lime.

FIG. 3 is a view showing the P content after dephosphorization refining when calcined lime is continuously charged at the initial stage of refining and premelt flux is charged.

FIG. 4 is a diagram showing the P content after the dephosphorization refining treatment in various dephosphorization refining modes.

FIG. 5 is a view showing the Si content of hot metal and the dissolution efficiency of lime charged in various dephosphorization refining modes.

FIG. 6 is a view showing the results when dephosphorized hot metal of the present invention is decarburized and refined.

FIG. 7 is a diagram showing an outline of a conventional dephosphorization refining.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ichiro Kikuchi 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Satoshi Kodaira 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Sun (72) Inventor: Shigeru Inoue 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan F-term (reference) 4K014 AA01 AA03 AB01 AB03 AC16 AD00 AD23 AD25

Claims (5)

[Claims] 1. A method for dephosphorizing and refining hot metal, comprising the following steps: (A) The converter has a Si content of 0.20.
wt% or less of hot metal and (b) calcined lime
Ingredients are charged at 18 kg / ton or less and refined by oxygen blowing. 2. The method for dephosphorizing hot metal according to claim 1, wherein the calcined lime is charged substantially continuously for at least 2 minutes after the start of the dephosphorization refining. 3. The method for dephosphorizing and refining hot metal according to claim 1, wherein a part of the CaO component by the calcined lime is charged by a pre-melt flux. 4. The method for dephosphorizing hot metal according to claim 3, wherein the premelt flux is slag generated by decarburization refining. 5. If the Si content of the hot metal exceeds 0.2 wt%, the hot metal is desiliconized to refine the Si content to 0.2 wt% or less, and then the dephosphorizing refining of the hot metal is performed. The method for dephosphorizing and refining hot metal according to any one of claims 1 to 4, wherein: