JPH10245617A - Steelmaking method using plural converters - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the productivity of a steel by using molten iron having <=0.3wt.% Si, refining P content of the molten iron to a standard value or lower of crude steel and shortening dephosphorize-refining time as less as possible, in the dephosphorization of molten iron in a converter. SOLUTION: (a) In one side of the converter, the molten iron having <=0.3wt.% silicon(Si) content is dephosphorized within a prescribed time and the phosphorus(P) content in the molten iron is refined to the P content (the component standard value of the steel) or lower needed to the crude steel. (b) The dephosphorized molten iron is charged into the other side of converter and slag-making agent is not substantially charged and the decarburization is mainly executed within a prescribed time. When Si content in the molten iron is >0.3wt.%, the Si content is preliminary refined into <=0.3wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to dephosphorization and refining of hot metal in one converter, and the dephosphorized and refined hot metal in one or more other converters within the dephosphorization and refining time in one converter. The present invention relates to a method for producing steel from hot metal with continuous and high productivity by performing decarburization refining.

[0002]

2. Description of the Related Art In a conventional converter steelmaking method, dephosphorizing and decarburizing refining of hot metal are performed in the same converter to perform steelmaking. However, while the demand for steel quality in recent years has increased, with the expansion of continuous casting, vacuum degassing, and secondary refining of molten steel such as 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] Therefore, a hot metal pretreatment method has been developed in which the hot metal charged into the converter is preliminarily treated, and in particular, the phosphorus (P) component is removed to some extent before the hot metal is charged into the converter. As one of the methods, dephosphorizing and refining hot metal in one converter etc.
A steelmaking method in which the dephosphorized hot metal is transferred to another converter to perform decarburization refining has been implemented.

As such a technique, Japanese Patent Publication No. 4-38810 is disclosed.
JP, JP-B2-14404, JP-B-61-2
There is a proposal of 3243 gazette. In addition, the inventor of the present application has also remodeled a conventional steelmaking plant, provided working floor openings in the working floor in front of each of a plurality of converters, and received molten metal obtained by dephosphorizing hot metal in one converter. A refining method has been developed in which a hot pot is received, and the hot pot is transported to another converter through the opening of the work floor, charged into the converter, and decarburized and refined therein (Japanese Patent Laid-Open No. Hei 6 (1994)). -41624).

[0005]

In the above steelmaking method, the hot metal is dephosphorized and refined in one converter and the like, and the hot water is immediately discharged in another converter and the like within at least the dephosphorization and refining time. Decarburization and refining are necessary for smooth steelmaking operations.

FIG. 11 shows an outline of dephosphorization refining in a 340 ton converter before the present invention. The dephosphorization and refining of the hot metal is performed at a low temperature (1250-1400 ° C.), and the slag FeO (5-10
%), The slag is formed,
Immediately after tapping, the slag flows out of the furnace port or a large amount of slag flows into the hot pot, so that the sedation time as shown in the figure required about 4 minutes. Therefore, the dephosphorization refining time was, for example, about 36 minutes on average.

On the other hand, the decarburization refining time of this dephosphorized hot metal in another converter is 29 minutes on average due to various improvements, and is 27 minutes without slag coating. Therefore, the decarburization smelting furnace has at least 7 minutes, up to 9 minutes idle time,
Therefore, the steel making efficiency was reduced accordingly. Reducing the 7 minute play time results in about a 20% increase in production. In addition, during this idle time, the temperature inside the decarburization refining furnace was lowered, bricks were worn, etc., and the converter life was shortened.

Accordingly, an object of the present invention is to reduce the dephosphorization refining time, eliminate idle time in the decarburization refining furnace, ensure a smooth steelmaking operation, and improve the steelmaking efficiency. In the above dephosphorizing refining, the P content of the molten steel is refined to the P content of the crude steel component (a so-called standard value, usually 0.02 wt% or less), and in the decarburizing refining, substantially no dephosphorizing refining is performed. The aim is to improve efficiency.

[0009]

As a result of various studies on the above-mentioned problems, the lower the Si content of the hot metal, the more the dephosphorization refining proceeds. Particularly, when the Si content is 0.3 wt% or less, the P content is usually reduced. P content of the crude steel component (so-called standard value, usually 0.1%).
(Less than 02 wt%), and found that the decarburization smelting can be achieved by substantially performing only decarburization smelting, and led to the following invention.

A first invention is a steel making method using a plurality of converters, comprising the following steps. (A) In one converter, the Si content of the hot metal is 0.3 wt.
% Of the hot metal is dephosphorized and refined within a predetermined time, and the P content of the hot metal is refined to the P content (specified component value of steel) required for the crude steel. The hot metal is charged into one or more other converters, and decarburization refining is mainly performed within the predetermined time without substantially charging slag-making material.

In the above invention, the P content of the hot metal is refined to the P content of the crude steel (specified value of the steel component) in the dephosphorization refining, so that in the decarburization refining, calcined lime for refining the P is refined. It is not necessary to insert a slag-making material, etc., and the decarburization refining is mainly performed, so that it can be extremely simplified and the refining time can be shortened. Further, when performing the dephosphorization refining, the Si content is set to 0.1.
Since the hot metal of 3 wt% or less is used, the amount of slag generated is small, and the slag calming time can be mainly eliminated. In addition, the waste time can be shortened and the dephosphorizing refining time can be shortened. Steelmaking efficiency can be improved.

According to a second aspect of the present invention, when the Si content of the hot metal exceeds 0.3% by weight, the Si content is set to 0.1% in advance.
This is a steel making method using a plurality of converters, which is characterized by preliminarily refining to 3 wt% or less.

[0013] Hot metal obtained from a blast furnace usually has a Si content of 0.3 wt% or less, but may exceed 0.3 wt% if the operation of the blast furnace becomes unstable. In this case, the pre-refining is performed to reduce the Si content of the hot metal to 0.3 wt% or less, and the time for dephosphorizing refining can be reduced as much as possible.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a converter (349 t)
On), dephosphorization refining as shown in FIG. 1 is performed. After charging the scrap, the hot metal from the blast furnace is charged, oxygen blowing is started, and refining is performed while charging calcined lime, fluorite, iron ore, and the like. When the oxygen blowing is completed, a rinse is performed and hot water is discharged.

The effect of the Si content of the hot metal on the dephosphorization refining of the hot metal in the above blowing will be described with reference to FIGS. FIG. 2 shows Ca added or added in the dephosphorization refining.
O amount and the hot metal basicity is calculated from the Si content of the _{(CaOwt% / SiO 2 wt%} , indicated as C / S in the figure) to indicate the relationship between the obtained basicity derived from the analysis of the slag. From this figure, it can be seen that the higher the Si content in the hot metal, the greater the dissociation of the calculated basicity (C / S) and the analytical basicity. CaO is not effectively acting on the dephosphorization reaction.

FIG. 3 shows the relationship between the Si content of the hot metal and the distribution ratio of _P (L _P = (P) / [P]) at substantially the same basicity. The lower Si content indicates that L _P is high. That is, it is presumed that the lower the Si content is, the more uniform slag is generated.

FIG. 4 shows the relationship between the refining time for refining P to 0.02 wt% or less and the Si content of the hot metal, for example. The lower the Si content, the shorter the refining time. FIG. 5 specifically shows the dephosphorization refining time when the Si content is 0.3 wt%.

FIG. 6 shows the relationship between the Si content of the hot metal and the P content after the dephosphorization refining process. The lower the Si content of the hot metal, the lower the P content after the dephosphorization refining treatment. Further, FIG. 7 shows that the lower the Si content of the hot metal, the higher the dephosphorization refining charge per day (charge / day), that is, the higher the productivity.

The dephosphorized hot metal that has been dephosphorized and refined is charged into another converter and decarburized and refined as shown in FIG. 8 to finally produce a predetermined steel. This decarburization refining is refining mainly by subjecting carbon in steel to oxygen blowing to obtain a target carbon content. In principle, slag-making materials such as calcined lime are not charged, but iron ore, scale, etc., which are iron sources, are charged.

Since the hot metal has already been sufficiently dephosphorized, manganese ore is charged during blowing to increase the Mn content of the molten steel and save expensive manganese alloys. However, if the P content of the dephosphorized hot metal is equal to or higher than the P content (specified component value of steel) required for crude steel, it does not exclude charging of slag-making material such as calcined lime. .

Further, in the above-mentioned decarburization refining, in order to maximize the life of the decarburization refining furnace, lightly-burned dolomite and / or raw dolomite can be added before charging the dephosphorized hot metal. Then, during the decarburization refining, it is sufficiently dissolved in the slag, and the MgO concentration is set to 10 wt% or more. Since such slag itself contains MgO up to the solubility limit, the slag has an effect of suppressing wear of the furnace body brick made of magnesium (MgO) brick and extending the life of the furnace body.

Further, after the molten steel is tapped, the furnace body is tilted so that the slag remaining in the furnace adheres to the brick in the furnace, so-called slag coating is performed. This slag coating greatly contributes to prolonging the life of the furnace, and the life of the furnace is about the same as that of the dephosphorizing smelting furnace. Therefore, not only the time cycle of the dephosphorization refining time and the decarburization refining time become the same, but also the furnace life of both furnaces becomes the same, and a smooth and consistent steelmaking operation becomes possible.

The decarburization refining time is about 29 minutes. As described above, the dephosphorization refining changes depending on the Si content of the hot metal. Therefore, in the present invention, the Si content of the hot metal is at least 0.1.
3 wt% or less. This is to reduce the time difference between the decarburization refining times as much as possible. When the Si content of the hot metal is 0.
It is more desirable that the content be 2 wt% or less. However, Si
If the content is less than 0.05% by weight, slag for dephosphorization refining is not generated, which is not desirable.

In the present invention, hot metal of 0.3 wt% or less is used, but there is no problem in steady blast furnace operation because Si is 0.3 wt% or less. However, in an unsteady operation (after the blast furnace is shut down), Si may exceed 0.3 wt%. In such a case, silicon removal is performed in advance using a hot metal pot or the like.

Further, in the present invention, two or more converters can be used. That is, as described above, the present invention can be practiced in at least two converters having substantially the same capacity. However, for example, a 340 ton dephosphorization refining furnace 1
And two 170-ton decarburization refining furnaces. In the decarburization refining, it is desirable to perform different refining depending on the C component of the crude steel. Therefore, the present invention can be implemented even if one or two or more decarburization refining furnaces are provided.

In the above description, the converter is a concept including not only a so-called oxygen top-blowing converter but also a converter type refining vessel such as a top-bottom blowing converter and a bottom-blowing converter. It goes without saying that it can be carried out in these various converters.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Low carbon steel (C: 0.1
wt% or less), medium carbon steel (C: 0.1-0.2wt)
%) And high carbon steel (C: 0.3 wt% or more)
FIGS. 9 and 10 show the changes in the component compositions in the above-mentioned dephosphorization refining and decarburization refining after zero charge production. Hot metal Si
The lower the content, the lower the P content after dephosphorization refining, and the lower the P content (standard value) required for ordinary crude steel,
In the decarburization refining, there was no need to perform dephosphorization at all. In addition, as described above, the dephosphorization refining time averaged 32.2 minutes,
The decarburization refining time was 29 minutes on average, and the dephosphorized and refined hot metal could be smoothly decarburized and refined, and steel could be continuously produced.

[0028]

According to the present invention, the Si content is 0.3%.
By dephosphorizing and refining hot metal of less than wt% and decarburizing and refining this hot metal, the dephosphorizing refining, which was longer than the conventional decarburizing refining time, can be shortened and approaching the decarburizing refining time including the slag coating time. Can be. Therefore, the so-called steel making time can be reduced by about 20% as a whole.

Further, in the decarburization refining, the need for dephosphorization is eliminated, so that inexpensive Mn ore can be used to the maximum and expensive manganese alloys can be saved, so that steel can be more economically produced than before. Can be manufactured. Further, since the life of the furnace body of the decarburizing smelting furnace is almost the same as that of the dephosphorizing smelting furnace, the furnace body can be repaired at the same time, and a smooth steelmaking operation can be performed. These effects are extremely large, the production efficiency is greatly improved, and the industrial effects are remarkable.

[Brief description of the drawings]

FIG. 1 is a diagram showing the entire dephosphorization refining process in the present invention.

FIG. 2 is a diagram showing the relationship between the blended basicity and the actual basicity in dephosphorization refining.

FIG. 3 is a diagram showing the relationship between the Si content and the distribution rate of phosphorus in dephosphorization refining.

FIG. 4 is a diagram showing a relationship between a Si content and a dephosphorization refining time in dephosphorization refining.

FIG. 5 is a diagram showing a dephosphorization refining time at a Si content of 0.3 wt%.

FIG. 6 is a graph showing the relationship between the Si content of hot metal and the phosphorus content after dephosphorization refining.

FIG. 7 is a diagram showing the Si content and the number of charges per day in dephosphorization refining.

FIG. 8 is a view showing all the steps of decarburization refining.

FIG. 9 shows that the dephosphorization refining of the present invention is carried out using a low carbon steel (C: 0.1 wt.
% Or less), medium carbon steel (C: 0.1 to 0.2 wt%), and a diagram showing a change in component composition when applied to high carbon steel.

[FIG. 10] The decarburization refining of the present invention is performed using low carbon steel (C: 0.1 w
t% or less), medium carbon steel (C: 0.1 to 0.2 wt%),
It is a figure which shows the change of a component composition at the time of applying to each of high carbon steel.

FIG. 11 is a view showing a dephosphorization refining process before the present invention.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Satoshi Kodaira 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Inside Nihon Kokan Co., Ltd. (72) Inventor Ichiro Kikuchi 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan (72) Inventor Manabu Arai, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Nihon Kokan Co., Ltd. (72) Hideei Tanaka 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Inside the corporation

Claims (2)

[Claims] 1. A steel making method using a plurality of converters, comprising the following steps. (A) In one converter, hot metal whose content of silicon (hereinafter, referred to as Si) in the hot metal is 0.3 wt% or less is dephosphorized and refined within a predetermined time, and the hot metal contains phosphorus (hereinafter, referred to as P). Refining the amount to below the P content required for crude steel (specification of steel components), and (b) charging the dephosphorized and refined hot metal into one or more other converters to substantially form Decarburization refining is mainly performed within the above-mentioned predetermined time without charging slag material. 2. A plurality of converters according to claim 1, wherein when the Si content of the hot metal exceeds 0.3 wt%, the pre-refining is performed in advance to reduce the Si content to 0.3 wt% or less. Use steel making method.