JPS5855504A - Manufacture for pig and steel - Google Patents

Abstract

PURPOSE:To practically use converter-slag as pig making-raw material and to reduce the cost in the process of manufacturing pig and steel, by the following method in which the phosphorus in moten pig enriched by utilizing converter- slag in pig making-process is removed, before the pig is charged into a converter. CONSTITUTION:For the molten pig tapped from a blast furnace, dephosphorizing treatment is carried out before the pig is charged into a converter, thereby it is able to controll the enriched phosphorus in the molten pig corresponding to the used amount of converter-slag. In order to dephosphorize the molten pig, desiliconizing treatment is achieved before the dephosphorization of the molten pig tapped from a blast furnace. This is essential to elevate the dephosphorizing efficiency. The desiliconizing treatment may be carried out on a casting bed, in a mixer or a ladle. Then, soda ash is preferred to caustic lime for dephosphorizing the molten pig, because amount of generated slag and the loss of Fe and Mn are decreased, and additionally the high efficiency for dephosphorizing and desiliconizing is obtained. Next, the dephosphorized molten pig is charged into the converter.

Description

Detailed Description of the Invention The present invention relates to a method for making iron and steel using t'h converter slag, and more specifically, it suppresses the enrichment of phosphorus in hot metal due to the circulating use of converter slag, and Concerning ironmaking and steelmaking methods that use slag.

Most of the phosphorus in the hot metal tapped from conventional blast furnaces is the reduced iron ore charged in the blast furnace, and its component concentration (hereinafter referred to as [P]) is between 0.080 and 0.08. 110%, and the phosphorus in this hot metal can be removed by melting high basicity slag using a large amount of quicklime solvent in converter refining, or by reducing the total amount of iron in the slag [hereinafter referred to as (T, Fe)]. It was dephosphorized by a method that increases the amount of phosphorus. According to these methods, 100 to 130 converter slags are generated per ton of steel, and since the (T, Fe) content is as high as 20 to 25%, a decrease in iron yield is unavoidable.

It is considered to recover iron by using the converter slag generated there as a raw material for ironmaking, but [P] increases depending on the amount of converter slag used, and the amount of solvent used in converter refining increases. Since there are many problems such as the inability to stably refine some steel types, the use of converter slag as a raw material for ironmaking has not been beneficial in terms of the overall ironmaking and steelmaking process.

Furthermore, a problem with the properties of converter slag is the presence of unsludged lime, which is collapsible, and for this reason, only a small portion of converter slag can be used as aggregate for assemblers, etc. However, most of it is discarded as landfill.

However, converter slag contains large amounts of quicklime and iron, and by using this in the ironmaking process, costs can be significantly reduced. For example, when converter slag is used in a blast furnace, there are advantages such as (1) adjusting the basicity of slag, (2) recovering iron content, and (3) increasing the manganese concentration in hot metal. When used, there are advantages such as (1) recovery of iron content, (2) increase in manganese concentration in hot metal, (3) reduction in the amount of lime powder used, and (4) reduction in the amount of coke powder used.

Therefore, if [P] enriched by using converter slag in the pig iron making process is removed in the final pig iron stage before charging into the converter, dephosphorization treatment that requires a large amount of quicklime solvent can be performed in converter refining. The problem can be resolved and the above-mentioned advantages can be utilized.

Zero Hatsu '3A was made based on certain knowledge,
The purpose of this project is to use converter slag, which was previously almost discarded, as a raw material for ironmaking, reduce the amount of iron ore and auxiliary materials used, and reduce costs in the ironmaking and steelmaking process.

The ironmaking and steelmaking method according to the present invention uses converter slag as a raw material for ironmaking, and in order to prevent phosphorus from accumulating in the hot metal due to the circulation of converter slag, the iron is tapped from the blast furnace. The method is characterized in that a part or all of the hot metal is subjected to dephosphorization treatment before the hot metal is charged into the converter. Then, a portion of the hot metal that has been subjected to dephosphorization treatment is combined with hot metal that has not been subjected to dephosphorization treatment, and then charged into a converter.

The present invention will be explained in detail below based on the drawings. The drawing is an explanatory diagram showing the principle of enrichment of CF3 when converter slag is used as a raw material for iron making. Let P be the amount of phosphorus contained in the ore raw materials, coke, etc. charged to the blast furnace L, and let the reduction efficiency of phosphorus in the blast furnace L be ηl (generally, most of the phosphorus is reduced in the blast furnace, so η1 is 1). Then, the amount of phosphorus contained in the hot metal tapped from the blast furnace becomes (P1×η1). Also, if the amount of phosphorus contained in the scrap charged to the converter 2 is P, then the total phosphorus amount #i (Pt + P + v+), and if the dephosphorization efficiency in the converter 2 is η2, the amount of phosphorus in the product is η,
x (Pt + P1×ηI), and the amount of terrestrial phosphorus in the converter is roughly expressed as (1−ηt) X (Pt×P□×η1). If the return rate for returning this converter slag to the blast furnace 1 is R, then the track of phosphorus returned to the blast furnace 1 is R×(1-η2
)X(P2+ p, Xη,), and the amount of phosphorus dumped is (1-R)
1).

Therefore, when the converter slag is returned to the blast furnace 1 at a return rate R, the amount of phosphorus charged into the blast furnace 1 is P, +RX(1-ηt)x(pt+P ,Xη1
), and the phosphor lid Vip 2 charged into the converter 2
+ηr (PI+RX (1-mu) ×(P, +P,
xη1)) That is, (P, 10P1xηI) 10RXη1×
(1-ηt) X (p, +P1xη1),'
By using converter slag as raw material for ironmaking, R×η1×
It will be enriched by (1-η2)X (PH+P, xη1).

If [P] enriched by using converter slag as a raw material for ironmaking is charged into the converter without being removed before charging, it will not be able to be used in the converter if it is normally blown. Since the dephosphorization ability of steel is limited, the phosphorus concentration level in the molten steel increases. Therefore, in order to prevent this, it becomes necessary to perform blowing such as the double slag method, which leads to a significant increase in refining costs.

The present invention avoids certain unreasonableness and suppresses enrichment of CF3 by dephosphorizing the hot metal tapped from the blast furnace before it is charged into the converter. , the above-mentioned converter slag will be returned to the ironmaking process. Next, the above-mentioned dephosphorization method will be explained.

Hot metal tapped from a blast furnace is first subjected to desiliconization treatment prior to dephosphorization treatment. This desiliconization treatment is essential to improve the efficiency of the desiliconization treatment, especially when the silicon concentration in the hot metal is 0.
．． A range of 10% or less is convenient for dephosphorization treatment. The location where this desiliconization treatment is performed is appropriately selected depending on the location of the dephosphorization treatment. For example, it may be a blast furnace casthouse, a pig iron mixer, or a ladle. The composition of the slag generated at this time is shown in Table 1. This slag is made of slag hemlock, V, S
The silica is removed by a cleaner and can be used as a sintering raw material as a silica source.

The hot metal that has been desiliconized in this way is subjected to dephosphorization treatment, which can be done either by quicklime or by soda ash, but for the reasons described below, soda ash is preferred. is more preferable.

The characteristics of quicklime-based dephosphorization treatment are (1) because it is treated at a high oxidation potential (
T, Fe) and high iron loss.

(2) Accompanied by manganese loss.

(3) Desulfurization progress is as low as about 50%, requiring desulfurization treatment again either before or after dephosphorization treatment.

On the other hand, the characteristics of treatment with soda ash are: (1) Because it is treated at t, oxidation potential, (T, Fe,) is low, and iron loss is small.

(2) No loss of manganese.

(3) The desulfurization phenomenon during dephosphorization proceeds extremely quickly, and the desulfurization rate can be maintained at over 90%.

Regarding dephosphorization treatment, soda ash treatment generates less slag, less iron loss and manganese loss, and can perform dephosphorization and desulfurization more efficiently. Furthermore, the composition of the dephosphorization slab is shown in Table 2, and this dephosphorization slag is excellent in that valuable metals can also be recovered.

The dephosphorized hot metal is then charged into a converter. In the converter, the dephosphorized hot metal is directly decarburized by slagless blowing, and untreated hot metal is used for further heat compensation. There is a method of increasing the silicon concentration in hot metal by combining it. According to the method of combining hot metal, it is also possible to adjust the phosphorus concentration in the hot metal by changing the ratio of the amount of combined metal depending on the phosphorus concentration level required by the steel type.

By immediately returning the converter slag to the ironmaking process and removing the fA enriched in the resulting melt with soda ash, quicklime, etc., the converter slag is utilized, and a large amount of waste is generated in the ironmaking process. This will realize a total system that increases the benefits of dephosphorization and slag recovery, and does not increase the amount of charged phosphorus in steelmaking.

Next, examples of the method of the present invention will be described. Table 3 shows a comparison of young fruit produced by the method of the present invention using the converter slag in the ironmaking process with that of the conventional method, and shows the composition of the taste slag. Compared to the conventional method, when using L1, i [P] is enriched to 0.200%, whereas with the method of the present invention, i [P] is enriched to 0.200%. If converter slag is used, [
P] was suppressed to a low concentration of 0.087% (lower than 0.105% when converter slag was not used), and the effect of the method of the present invention was sufficiently confirmed.

Table 4 shows the components of the converter slag used.

As detailed above, in the case of the present invention, converter slag is used in the pig iron making process, [P] enriched from K is removed by dephosphorization treatment at the pig iron stage before charging into the converter, Since the accumulation of [P] is prevented, converter slag, which was conventionally almost discarded, can be utilized, leading to a significant cost reduction in the iron and steel manufacturing process.

[Brief explanation of drawings]

The drawing is an explanatory diagram showing the principle of enrichment of CF3 when converter slag is used as a raw material for iron making. 1... Blast furnace 2... Converter patent Applicant: Sumitomo Metal Industries, Ltd. Agent: Valent, Buried soil: Noboru Kono

Claims (1)

[Claims] 1. In the ironmaking and steelmaking process that uses converter slag as a raw material for ironmaking, in order to prevent the accumulation of phosphorus in the hot metal due to the circulation of converter slag, some or all of the hot metal discharged from the blast furnace is On the other hand, a method for making iron and steel is characterized in that a dephosphorization treatment is carried out in the dark before the hot metal is charged into a converter.