KR19980014324A - Pre-processing method of charcoal using converter - Google Patents

Abstract

The present invention relates to a molten iron pre-treatment for removing impurities in advance in a molten iron step charged in a steel-making furnace; The object of the present invention is to provide a pretreatment method for removing [Si] [P] and the like in a molten iron using an existing converter without using a separate iron pre-treatment vessel.

In order to accomplish the above object, the present invention provides a method for pre-desulfurizing a molten iron discharged from a blast furnace, comprising the steps of preliminarily desulfurizing the molten iron discharged from the blast furnace as much as the target sulfur amount during the transfer to the converter, charging the molten preliminary desulfurized molten iron into the converter, Oxygen gas of 1700-1900 Nm < 3 > is blown in the range of 1.7-2.2, the molten iron is simultaneously tallied and degassed while the molten iron is at a temperature of 1300-1400 DEG C, and then the molten iron thus treated is degassed And a preliminary treatment method for a steel wire to be secondarily refined.

Description

Pre-processing method of charcoal using converter

[0001] The present invention relates to a preliminary ironing process for removing impurities beforehand in a preliminary ironing step to be charged in a steel making furnace, and more particularly, ] [P] and the like.

As the demand for high-grade steels becomes more stringent due to the advancement of the industrial environment, the quality improvement of high-quality steels is becoming an important issue. Conventionally, molten iron produced in a blast furnace is transported in a container called a ladle or torpedo, charged into a converter, and refined into a steel only in the converter. However, the manufacturing of high-clean steel is not only insufficient by converter refining but also is not efficient, so that a method of sharing a part of the refining function to the front and rear of the converter has been practically used.

Generally, about 0.1% of P is contained in the charcoal, and [P] in the charcoal is removed through the pretreatment, converter refining and secondary refining process to such an extent that the properties of the steel are not deteriorated. Thermodynamically, talline treatment is most preferable at a relatively low temperature (about 1320 ° C) in the molten steel treatment step, and it is necessary to inject oxygen for oxidative tallin. That is, the [P] reacted with the injected oxygen is removed by the slag according to the following equation with the quicklime introduced as the sub-raw material.

3 (CaO) +2 [P] +5 [O] = (3CaO.P2O5) (1)

4 (CaO) +2 [P] +5 [O] = (4CaO.P2O5) (2)

This chartered talline method has been studied by the preliminary tallin method for the manufacture of the zeolite steel, and a method of injecting the charcoal accounting flux or soda ash into the charcoal in the open ladle has been developed and put into practical use. However, in recent years, such molybdenum talline method has been extended to the refining of general steel, which contributes to reduction of manufacturing costs such as reduction of coarse aggregate in converter and reduction of Mn alloy iron by melting and reducing Mn ore.

On the other hand, [Si] in the charcoal is oxidized and removed by reacting with oxygen as follows.

2 (CaO) + [Si] +2 [O] = (2CaO.SiO2) (3)

Comparing the equilibrium constants of equations (1), (2) and (3) above, it is likely that the lower the molten iron temperature, the higher the [P] oxidation reaction may precede or coincide with the oxidation reaction of [Si]. As a result, the reaction at a low temperature enables efficient removal of [P] as well as simultaneous deprotection, which can reduce the burden of converter refining.

Recently, to cope with the increase in demand for high-grade steel, we developed a pre-treatment method of transfer-type iron wire that can be pre-processed more efficiently. By doing simultaneous demolition, Tallinn and Til sulfur, we reduce the refining load in the converter and reduce the cost of raw materials. Contributing.

In this way, the degassing of the molten iron and the talline are the most important factors by taking oxygen and removing the [Si] and [P] as oxides with slag by causing the oxidation reaction, and the reaction temperature is the most important factor. do. Conventional torpedo is originally intended to transport molten iron from a blast furnace to a steelmaking plant, and its shape is not suitable as a reaction vessel, which is very disadvantageous in terms of reaction efficiency. Also, in the case of open ladles, since the vessel is a carrier vessel, there is not enough space in the vessel itself, and when oxygen is taken in, oxygen and oxygen are not taken in at high speed because charcoal and slag are scattered, Lt; / RTI >

To solve these problems, many studies have been made on the preliminary treatment of molten iron using the most efficient converter as a reaction vessel, and some of them have been practically used. In KOBE steelmaking, we proposed a preheating process using H furnace. However, in the case of an induction furnace, the immersion lance for the addition of the additional raw material is applied because the agitation of the bath is insufficient, and as the subsidiary raw material, the massive quicklime, converter slag, Mn ore, mill scale, , And basically, it is aimed at talline and desulfurization aimed at the chartered ship. Also, in the process of transferring Tallin, the removal of [Si] remaining after the columnar degasification and the removal of a full-scale [P] began, and it takes about 9 minutes or more for talline (iron and steel, vol. 74, p991). In addition, in the case of Sumitomo Reis, a slag recycling process (SRP) using decarburized slag as a talline flux has been developed and applied. However, in the case of the above SRP, it is applied to the molten iron of [Si] ≤0.30%, which is assumed to be the main phase degassing or the toffee degassing. In the Tallin converter, the purpose of the talline and desulfurization of the molten iron is (iron and steel, vol. 76, p1809). In addition, in Nippon Steel, we have developed and applied the pre-treatment process (LD-ORP), which utilizes the inactive copper furnace. The characteristic of the LD-ORP is that it is intended for simultaneous degassing, talline, and desulfurization unlike the H and SRP described above, and does not undergo a pre-degassing process. In addition, Tallin furnace utilizes the upper and lower furnace furnace, which has a function to reduce powder by single pipe. However, the removal of the molten iron [P] is delayed by the preferential oxidation of Si depending on [Si] in the molten iron, taking about 10 minutes for talline and about 20 minutes for desulfurization as a whole And Kang, vol. 79, p597).

As described above, there is a problem in the reaction efficiency in the case of the preliminary treatment of the molten iron using the existing toe or open lays, and the time required for the talline in the case of the transfer charter preliminary treatment is not less than about 10 minutes, Some require preliminary cancellation. In some cases, a separate dipping lance is required in addition to the oxygen lance.

Therefore, unlike the conventional method, the present invention is capable of performing simultaneous talline and degassing treatment in the converter immediately after the pre-desulfurization treatment without preliminary degassing treatment of the molten iron, The present invention has been made in view of the above problems.

FIG. 1 is a schematic view for explaining a transfer charter pre-treatment process according to the present invention;

2 is a graph showing the change in [P] content in the molten iron before and after the molten iron pretreatment according to the present invention

FIG. 3 is a graph showing a change with time in the composition of the molten iron in the furnace during the preliminary ironing treatment according to the present invention

4 is a graph showing a change in temperature over time of the molten iron wire in the molten iron preliminary treatment according to the present invention

FIG. 5 is a graph showing the relationship between the slag basicity and the talline ratio in the molten iron wire in the molten iron pretreatment according to the present invention

According to an aspect of the present invention, there is provided a desulfurization apparatus including: a preliminary desulfurizing process of a charcoal discharged from a blast furnace to a converter by a target sulfur content during transfer;

The preliminarily desulfurized molten iron is charged into a converter and an additive is charged into the molten iron to inject oxygen gas of 1700-1900 Nm3 while controlling the basicity of the molten iron in the range of 1.7-2.2, Simultaneous talling and demarking of the molten iron in the process; And

And then decarburizing and secondarily refining the molten iron treated as described above by a conventional method.

Hereinafter, the present invention will be described in detail.

First, the preliminary desulfurizing process is performed so as to be suitable for the amount of sulfur in the course of the transfer, as shown in FIG. The preliminarily desulfurized molten iron is discharged to the charging ladle 3, discharges the desulfurization slag, and is charged into the tallin transfer furnace 4. The molten iron charged into the Tallinn transfer furnace 4 is charged with a certain amount of subsidiary raw material, and simultaneously performs deoxidation and degassing treatment while reducing the inert gas or nitrogen gas such as argon with oxygen. In this case, the additive may be added in an appropriate amount such that the basicity of the slag is in the range of 1.7-2.2. In general, the slag basicity can be adjusted by adding an appropriate amount of CaO according to the amount of SiO2 in the molten iron. The range of 3-4 Kg / ton-molten iron is suitable for the fluorite (CaF2) added to dissolve the burnt lime easily, and the sintered ore (iron ore) serving as the oxygen source in addition to the oxygen gas to be injected is 25 -35 Kg / ton-is preferably added as a molten iron. When the basicity of the slag is 1.7 or less, the talline ratio becomes poor. When the basicity of the slag is 2.2 or more, it is not preferable because the addition of additives such as burnt lime is excessive. In addition, it is preferable that the blowing of oxygen be carried out at a high speed in an amount of about 1700-1900 Nm < 3 >. Under the above-described conditions, the molten iron preheating temperature is preferably maintained at a low temperature, preferably about 1300-1400 ° C, for efficient talling. The simultaneous tallyne and decalcification treatment according to the present invention is preferably carried out for about 7 minutes.

After the talline process is completed at this predetermined level, the charcoal is repaired into another decarbonization furnace (6) through another charging ladle (5), and the furnace is decarburized by a small amount of slag operation to complete the refining in the converter. (7) to carry out ordinary secondary refining.

In this process, the preliminary treatment of the charcoal leads to the removal of the degassed and talline from the converter

Meanwhile, unlike the conventional pre-treatment process, the pre-treatment process of the molten iron according to the present invention has a disadvantage in that it can not be immediately taken out due to a severe boiling phenomenon after the preliminary treatment, In order to compensate, it is preferable to add an appropriate amount of coke to produce oxygen remaining in the hot bath after the pretreatment. In this case, since the specific gravity of the coke is lower than that of the slag, the slag may not penetrate into the slag and may not show a soothing effect of the slag. To inject the coke into the slag, the coke is added to increase the oxygen lance at the end of the coke. It is possible to penetrate into the slag by the oxygen residual pressure on the way. In addition, if the inert gas is lowered for about 3 minutes even after the completion of the blowing, the slag boiling phenomenon after the pretreatment can be prevented.

When the preliminary treatment is carried out in this way, the talline and degassing in the converter can be completed in about 7 minutes, and the preliminary treatment can be performed in a shorter time than the existing preliminary treatment.

Hereinafter, the present invention will be described in detail with reference to examples.

[Example]

The general chartered ship, which was discharged from Torpedo De-S (TDS) in the blast furnace, was desulfurized in the above TDS prior to Tallinn. [S] was about 0.03% in the charcoal discharged from the blast furnace, and about 0.006% after the TDS desulfurization. The desulfurized charcoal was charged to a Tallin furnace with a 300-ton class complex furnace (NK-CB) and the outlet lance was lowered to 2700 mm from the bath surface while the Ar or N 2 gas was reduced to about 0.1 Nm 3 / The additives and oxygen were removed under the same conditions as in Table 1, and the charging charcoal was simultaneously degassed and degassed for about 7 minutes.

[P] in the thus treated charcoal line and [P] in the pre-treatment line were measured, and the talline ratio results are shown in Table 1 below. Further, the talled molten iron was continuously decarburized in the decarburizing furnace, and the [P] in the decarburized refined molten steel was measured. The results are shown in FIG. When the oxygen lance was elevated after completion of the oxygen kneading for stable outlet, the molten iron treated as described above was supplied with a small amount of coke, followed by cooling down the Ar gas for about 3 minutes.

Example Dose (ton) Substrate input (ton) Transmission amount (Nm ³ ) [P] content in charcoal (%) CaO CaF ₂ Sintered ore Before processing After processing Tallinn Rate Inventory 1 280 4.1 1.1 9 1750 0.114 0.025 78 Inventory 2 310 4.1 1.3 9 1750 0.093 0.025 73 Inventory 3 320 4.5 1.3 9 1750 0.099 0.040 60 Honorable 4 310 4.5 1.3 9 1760 0.098 0.028 71 Inventory 5 310 5.6 1.2 9 1800 0.107 0.050 53 Inventory 6 310 6.0 1.2 9 1760 0.103 0.046 55 Honorable 7 310 6.8 1.2 9 1640 0.125 0.053 58 Honors 8 310 6.8 1.2 9 1870 0.104 0.026 75 Proposition 9 310 5.6 1.2 9 1770 0.093 0.035 62 Inventory 10 310 4 1.2 9 1810 0.098 0.018 84

As shown in Table 1 and FIG. 2, [P] in the charcoal was about 0.1%, but it was about 0.034% after the charcoal pretreatment using the converter, and the end point [P] It was found that a weakened steel can be easily produced at about 0.008%.

The results of the measurement are shown in FIG. 3. As shown in FIG. 3, [Si] [P] in the charcoal line was measured from the beginning of the blowing operation It can be seen that the equilibrium value is reached by completing the reaction within about 5 minutes after starting to remarkably decrease. This means that simultaneous degassing and tallin can be performed by injecting oxygen at high speed without a separate pretreatment step. Also, as shown in FIG. 3, in the charcoal [C], about 4% or more even after the completion of the degassing and the talline reaction indicates that there is no problem in the thermal mixing in the subsequent decarburization process.

As a result of the measurement of the temperature of the molten iron in the Tallinn converter, the temperature of the molten iron is lower than about 1400 ° C as shown in FIG. 4, indicating that the molten iron is maintained in a favorable state for the talline reaction.

On the other hand, to examine the effect of slag basicity on the talline ratio of the talline furnace, the talline ratio according to the slag basicity in each molten iron was measured and the result is shown in FIG. As shown in FIG. 5, it can be seen that the slag basicity exhibits a talline ratio of 70% or more at a slag basicity of about 1.7 or more. However, considering the basic level of lime and the like, it is preferable that the basicity should not exceed 2.2, so the basicity of the slag should be maintained in the range of about 1.7-2.2.

As described above, according to the present invention, it is possible to process the molten iron after the preliminary desulfurization treatment, the talline and the degassing treatment in a short time, and the subsequent decarburization time can be shortened from about 18 minutes to about 13 minutes It is possible to more easily perform the preliminary processing of the molten iron, which is advantageously applicable to extremely hard steel types.

Claims (4)

Performing a preliminary desulfurization treatment on the molten iron leaving the blast furnace by the target sulfur amount during the transfer to the converter; The preliminarily desulfurized molten iron is charged into a converter and an additive is charged into the molten iron to inject oxygen gas of 1700-1900 Nm3 while controlling the basicity of the molten iron in the range of 1.7-2.2, Simultaneous talling and demarking of the molten iron in the process; And And then decarburizing and secondary refining the molten iron treated in the above manner by a conventional method. The method as claimed in claim 1, wherein the addition of the sub-raw material comprises a fluorite (CaF2): 3-4 Kg / ton-charcoal, and an ore: 25-35 Kg / ton-charcoal The method according to claim 1, wherein the oxygen blowing is carried out for 7 minutes 4. A preheating method for molten iron according to any one of claims 1 to 3, characterized in that the coking is carried out at the same time that the oxygen blowing is completed,