KR101320362B1 - Pre-treating method of pig iron for manufacturing of extra low phosphorous steel - Google Patents

Abstract

The present invention relates to a method for preliminary treatment of molten steel for preliminary molten steel using a Tallinn converter when manufacturing ultra-low grade steel, and completely excludes slag of a converter previously operated in a Tallinn reactor during molten iron preliminary treatment. A first step of injecting, and a second step of charging molten iron into the Tallinn converter after the quicklime injecting; and after charging the molten iron, injecting oxygen through the lance from the upper part of the Tallinn Furnace to blow the molten iron. A third step of drilling the molten iron while dividing the quicklime and the sub-materials into the molten iron over a plurality of stages during the drilling, and the fourth step of putting in the silicon generating source when starting the molten molten iron in the molten iron The present invention provides a method of preliminary treatment of molten steel.

Description

PRE-TREATING METHOD OF PIG IRON FOR MANUFACTURING OF EXTRA LOW PHOSPHOROUS STEEL}

The present invention relates to a molten iron preliminary treatment method of ultra-low steel, and more particularly, to a molten steel preliminary treatment method for preliminary molten steel using a Tallinn converter when manufacturing ultra-low steel.

The steelmaking process that uses iron ore as a raw material to produce steel as final product starts with a steelmaking process that dissolves iron ore in the blast furnace. A molten steel is prepared by performing a pretreatment process such as desulfurization on a molten iron which is an iron ore-dissolved form. The molten steel thus prepared is subjected to a first refining process for removing impurities and a second refining process for finely adjusting the components in the first refined molten steel. After the secondary refining is completed, the molten steel is moved to a continuous casting process, and a semi-finished product such as slab, bloom, billet, etc. is formed through a continuous casting process. The semi-finished product thus formed is manufactured into a desired final product such as a rolling coil and a heavy plate through a final molding process such as rolling.

The charcoal is subjected to a preliminary treatment before the primary refining, ie, decarburization and deoxidation, and the preliminary treatment of the charcoal refers to desulfurization and talline processes to remove sulfur and phosphorus components of the charcoal as needed. The preliminary treatment of the molten iron may be performed in a mechanical stirrer, or may be performed in a Tallinn converter in the manufacture of ultra low temperature steel. After the pretreatment is completed, the molten iron is transferred to the converter process for subsequent refining.

As described above, when manufacturing the ultra-low steel, the phosphorus component in the molten iron is controlled to a reference value by using a Tallinn converter, and the related art is related to Korean Patent No. 0449234 (Registration Date: 2004.9.8., Name: Pole Manufacturing method of low-lining steel).

The present invention to control the content of the phosphorus component in the Tallinn converter in a range suitable for the production of ultra-low steel, while providing a molten iron pre-treatment method for securing the molten iron temperature can be carried out without additional heat source in the subsequent process. It is for.

The technical problems to be achieved by the present invention are not limited to the technical problems mentioned above.

The molten iron preliminary treatment method of the present invention for achieving the above object is a first step of completely excluding the slag of the converter previously operated in the Tallinn converter during the molten iron preliminary treatment and injecting quicklime, and after the quicklime input, The second step of charging the molten iron into the Tallinn converter, and after the molten iron is charged, the molten iron is blown by blowing oxygen through the lance from the upper part of the Tallinn converter, while the quicklime and the raw materials into the molten iron during the drilling It may include a third step of blowing the molten iron while divided into a plurality of stages, and a fourth step of inputting the silicon generating source when starting the molten iron is blown out.

Specifically, in the first step and the third step, the amount of quicklime can be adjusted according to the silicon content in the molten iron.

In the third step, the quicklime may be dividedly injected at the time when the blowing is 10%, 40%, 70% respectively.

In the third step, when the total weight of the quicklime is added to 100%, 50% of the total weight of quicklime is added at the time when the blowdown is 10%, and 30% of the total weight of the quicklime is added when the blowdown is 40%. In addition, 20% of the total weight of quicklime may be added at the time when the blowdown progresses 70%.

In the third step, the secondary raw material includes a sintered ore and MgO-based powder, and the sintered ore is inputted at a time point when the blowing progresses 10% and dividedly input at a predetermined time interval until the end of the blowing, the MgO-based powder is 40% blowing 50% of the total weight of the MgO-based powder may be added at the time when the progress is advanced, and 50% of the total weight of the MgO-based powder may be added at the time when the blowdown proceeds to 70%.

In the third step, the blowing may be performed by adjusting the flow rate of the oxygen blown through the lance and the distance between the lance and the upper end of the molten iron during the blowing.

The silicon generation source may be silica powder.

In the fourth step, the molten iron in the molten iron (P) is controlled in the range of 0.03% by weight or less, the temperature of the molten iron can be maintained at 1400 ℃ or more.

As described above, the present invention allows the decarburization converter to be carried out without the addition of an additional heat source in the subsequent process while maintaining the molten iron temperature while controlling the content of the phosphorus component in the dephosphorization furnace in the range suitable for the preparation of the ultra low steel. Therefore, the use of expensive ferrosilicon used as a heat source during the decarburization converter process is unnecessary, thereby reducing the manufacturing cost. In addition, it is possible to improve the slag goods efficiency by the quicklime and secondary raw materials used in molten iron delineation by promoting the slag goods in the delineation converter.

1 is a conceptual diagram briefly showing a molten iron preliminary treatment process of the steelmaking process according to the present invention.
Figure 2 is a flow chart showing in order the method of molten iron preliminary treatment of ultra-low steel according to an embodiment of the present invention.
3 is a view schematically showing a method of manufacturing ultra low strength steel according to the present invention.
4 is a graph showing the relationship between the equilibrium constant and the temperature of the Tallinn reaction.
Figure 5 is a graph showing the amount of ferrosilicon required according to the discharge temperature in the molten iron in the molten iron process.
6 is a view showing the lance height (L) and the molten iron height (L0) according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same components are denoted by the same reference symbols whenever possible. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

1 is a conceptual diagram briefly showing a molten iron preliminary treatment process of the steelmaking process according to the present invention.

Referring to the drawings, generally used for preliminary treatment of molten steel in the manufacture of ultra-low steel, the Tallinn converter 10 receives the molten iron (M) in the form of dissolved iron ore to adjust the content of phosphorus (P) in the molten iron. It is used to accomplish the task. When the molten iron (M) is charged in the Tallinn converter 10 as described above, the tilted Tallinn converter 10 is erected upright, and then a lance 20 capable of blowing gas from the upper part is inserted into the converter 10. . Oxygen gas is blown into the upper portion of the molten iron M through a lance disposed above the molten iron M to remove phosphorus (P) components present in the molten iron M. In this case, a lower odor opening may be installed in the lower part of the Tallinn converter 10 to inject gas. That is, in the upper part of the Tallinn converter 10, gas is blown into the upper part of the molten iron through the lance 20, and in the lower part of the converter 10, that is, in the bottom of the charged molten iron M, argon gas passes through the gas deodorizing tuyere. The molten iron M is stirred so as to be blown into the molten iron to promote the delineation reaction in the molten iron M. While stirring the molten iron through the gas blowing in the molten iron (M) in the upper portion can be added to the secondary material through the hopper and the like to facilitate the dephosphorization reaction in the molten iron (M). As described above, slag is formed on the upper part of the molten iron (M) dephosphorized due to the addition of oxygen and argon gas and the subsidiary materials, and the molten iron (M) is tapped into the tap hole 11 for the subsequent process and transferred to the decarburization converter, which is a subsequent process. Let's go.

The preliminary treatment of the molten iron using the Tallinn converter is used when the required content of phosphorus in the molten iron is low to produce high grade steel such as an oil transportation pipe (API steel). After controlling phosphorus to the required level in the dephosphorization converter, it is transferred to the decarburization converter. In the decarburization converter, dephosphorization molten iron is received and oxygen is blown into the molten steel to produce decarburization.

Figure 2 is a flow chart showing in order the method of molten iron preliminary treatment of ultra-low steel according to an embodiment of the present invention.

Referring to FIG. 2, in the present invention, the slag in the Tallinn converter (hereinafter referred to as a 'converter') that has been completed last time is completely excused, and the quicklime is put upright into the converter (S10). Generally, after finishing the operation in the converter, the slag is coated on the wall of the furnace by injecting light dolomite 3-4 times, leaving about 10% of the slag operated last time. This is carried out to protect the furnace wall, and after the furnace wall is coated, the molten iron is charged again, and a large amount of quicklime is added to the upper portion of the molten iron to perform the delineation process. In this case, there is a disadvantage that P ₂ O ₅ in the slag coated on the wall of the furnace body acts as an unstable factor of Tallinn in the next operation. Therefore, in the present invention, after coating the furnace wall surface with the slag and the light dolomite left after the last operation in this way, the slag is completely discharged to the outside of the furnace body. After the converter is established and the quicklime is introduced into the converter, the quicklime powder is adhered to the surface of the wall surface of the furnace body first coated with slag so that the second coating is carried out.

In this way, when the lime is added to the furnace wall and coated, the slag may be prevented by reacting with the molten iron during the decontamination of the converter, which will be described later, and preventing the slope, and the protection effect of the furnace body wall may also be improved.

After the quicklime is introduced into the converter as described above, the molten iron is charged into the converter (S20). When the molten iron is introduced into the converter, slag goods begin to react with the quicklime.

After charging the molten iron in the converter, the lance is lowered from the upper part of the converter, and the oxygen gas is blown into the upper part of the molten iron through the lance and blown while splitting the quicklime and the subsidiary materials (S30).

In general, as shown in FIG. 3, the molten iron that has undergone the desulfurization process during ultra low lean steel production is transferred to the Tallinn converter 10, and the demolition process is performed separately from the Tallinn converter 10 to be discharged to the tap hole 11. The molten iron is transferred to the decarburization converter 30. In the decarburization converter 30, the decarburization process is performed by blowing oxygen of high pressure through the upper lance 40 into the charged molten iron. At this time, the dephosphorization process is carried out by charging the molten iron into the converter and calculating the amount of quicklime and subsidiary materials necessary for dephosphorization at the top, and then introducing the molten iron into the molten iron through the hopper at once. In addition, by continuously blowing oxygen through the upper lance 20, the molten iron and the quicklime, the subsidiary material and the oxygen reacts in combination to remove the phosphorus component in the molten iron. However, when the dephosphorization process is carried out as described above, a large amount of quicklime and by-products injected into the upper part of the molten iron may not react with the molten iron and may not remain as slag (S). In addition, since slag volume increases rapidly due to active reaction with molten iron at the beginning of quicklime and auxiliary raw materials, the gas generated from molten iron cannot accumulate through the slag layer and is accumulated at a time. Pinging may occur.

In addition, as shown in Figure 4, the equilibrium constant of the Tallinn reaction as a function of only the temperature it can be seen that the Tallinn reaction decreases as the temperature increases. Therefore, in general, when producing cryogenic steel, delineation operation is carried out with the molten iron temperature in the converter being in the range of 1300 ° C. After the demolition of the molten iron at such a temperature is transferred to the decarburization converter 40, which is a subsequent process, the molten iron temperature must be raised to 1680 ° C for decarburization. However, in order to heat up the molten iron which is 1300 ° C to 1680 ° C, an additional heat source, ie, ferrosilicon (Fe-Si), was inevitably lacked due to insufficient heating power by blowing high pressure oxygen from the decarburization converter 30. However, ferrosilicon is an expensive material, as shown in FIG. 5, when the molten iron is drawn out at 1300 ° C., the required amount of ferrosilicon reaches 1200 kg, which acted as a factor to increase the unit cost. Referring to FIG. 5, when the temperature of the molten iron is maintained at 1400 ° C., it is possible to carry out the decarburization converter blow, which is a subsequent process without the addition of additional ferrosilicon.

Therefore, in the present invention, while controlling the content of phosphorus in the molten iron to 0.03% by weight or less suitable for the production of ultra-low steel while maintaining the temperature of the molten iron at 1400 ℃, or more than 1400 ℃ at the time of drawing out a plurality of quicklimes and raw materials during the drilling Split through the steps. In addition, the blowing is performed while adjusting the flow rate of the oxygen blown through the lance and the distance between the lance and the upper end of the molten iron during the blowing operation.

In detail, first, the quicklime that is introduced into the furnace before charging the molten iron is introduced to promote the slag goods of the protection wall of the furnace before charging the molten iron. It can be prevented from dropping greatly, and it can help to reduce the phosphorus content in the molten iron during the drilling. In addition, the quicklime can be divided into three stages during the blow. In this case, the injection time may be separately inputted at the time when the injection proceeds 10%, 40%, 70% after the start of the blow.

In the present invention, when the quicklime is added after the start of the blow, 50% of the quicklime weight to be injected at the time of the blow is 10%, and the total weight of the quicklime to be added at the time of the blowdown is 40%. The quicklime can be split and purchased by adding 30% and adding 20% of the total weight of quicklime to be blown at the time of the 70% blowdown.

The reason for splitting the quicklime is to keep the temperature of the molten iron at 1400 ° C. or higher during the blowing process so that the quicklime and the molten iron react actively. In other words, if all of the quicklime is injected at the beginning of the blow, all of the quicklime does not react with the molten iron and some remain unreacted, so that the slag goods become inactive and the risk of slopes increases due to sudden slag volume increase. do.

According to an embodiment of the present invention, when the quicklime is divided into the quicklime, the molten iron reacts first by the quicklime which was first introduced into the converter before the blowdown. Will accelerate the reaction. After that, the quicklime is added once more at the time of blowing 40%, which is the point at which the quicklime reacts with the molten iron to promote slag goods, and finally, the quicklime is added at the 70% point of blowing to complete the dephosphorization reaction in the charter. As such, the slag material may be promoted through split lime injection while maintaining the temperature of the molten iron at a temperature higher than 1400 ° C.

In the present invention, quicklime may not be added during the blowing due to the silicon (Si) content in the molten iron.

In general, in order to perform demolition of the molten iron, it is necessary to lower the silicon content of the molten iron to a predetermined amount or less to dephosphorize it. That is, since the reaction of Scheme 1 below takes precedence over the reaction of Scheme 2, when the auxiliary material for dephosphorization is added to the molten iron, the reaction of Scheme 1 occurs, and then the reaction of Scheme 2 occurs.

Scheme 1

Si + O ₂ = SiO ₂

Scheme 2

_{2P + 5FeO = (P 2 O} 5) + 5Fe

Since silicon among the components in the molten iron is removed by reacting with oxygen first due to the difference in oxygen affinity, the silicon in the molten iron is mostly slag before dephosphorization to be below a certain level (typically 0.03% by weight or less). Therefore, the amount of quicklime to be added should be adjusted according to the silicon content in the charcoal. In this way, considering that the desulfurization reaction occurs before dephosphorization, the deliming reaction can be completed, but the amount of quicklime that can cause dephosphorization reaction after desulfurization should be added. Therefore, if the silicon content in the molten iron is below a certain level, it is possible to adjust the level enough to complete the desulfurization reaction and dephosphorization reaction only with the quicklime which is added before the blow without the quicklime during the blowing.

The reason why the quicklime is input in the talline process is that it is necessary to control the basicity of the charcoal in order to tallize the charcoal from the converter. The basicity in molten iron is calculated as CaO (wt%) / SiO ₂ (wt%), and quicklime is added according to the content of silicon (Si) contained in the molten iron to meet the basicity targeted for ultra-low steel production.

In other words, if the amount of silicon in the molten iron is high, the amount of quicklime (CaO) to be injected into the molten iron should be added during the drilling, but if the amount of silicon in the molten iron is very small, it is put into the converter before the drilling. The quicklime lime alone can reach the target level of the molten iron, so no additional quicklime is required during the drilling.

For example, when the target basicity of the molten iron during the production of ultra low strength steel is 2.5, the amount of quicklime input before and during the drilling may be determined as shown in Table 1 below.

Silicon content in charging charter
(weight%) Quicklime (ton) Input before blowing Input amount during blow 0.15 or less One - 0.15-0.20 1.5 - 0.20-0.25 2.5 - 0.26-0.30 3 0.5 0.31-0.35 3 1.5 0.36-0.40 3 2.5 0.41-0.45 3 3 0.46-0.50 3 4

 Table 1 is an example showing a case in which the target basicity of the molten iron is 2.5 as described above. In this case, when the silicon content in the molten iron is 0.25 or less, quick lime does not need to be added during the drilling. If the silicon content in the molten iron exceeds 0.25, the amount of quicklime injected is adjusted according to the silicon content in the molten iron. For example, referring to Table 1, when the molten iron basicity is 2.5, if 0.30% by weight of silicon in the charging molten iron is charged, the molten iron is charged into the converter after 3 tons of quicklime is charged into the converter before charging. . After that, while injecting oxygen into the converter, a total of 0.5 tons of quicklime is added at 10%, 40%, and 70% of the blown time. At 10% point of time, 0.25 tons, 50% of 0.5 tons are added. At 40% point of time, 0.15 tons, 30% of 0.5 ton, is added. To finish the quicklime split input.

In addition, in the present invention it is possible to divide the sub-material into the molten iron during the converter blow. At this time, the subsidiary material includes sintered advertising MgO-based powder. Specifically, in the case of sintered ore, the sintered ore input is started at the time when the blowing is 10% progressed, and the total weight of the sintered ore is continuously added at a predetermined time interval until the end of the blowing.

The reason why the sintered ore is continuously divided and injected is because the molten iron and the reaction are maximized, but this level is continuously maintained to minimize the unreacted sintered ore. If the sintered ore is injected at the time of starting the blow, not only the molten iron temperature is lowered but also the reaction with the molten iron explodes only at the start of the blow, and the reaction force decreases in the future, resulting in a greater amount of unreacted sintered ore Because.

In the present invention, in the case of MgO-based powder, which can be added MgO-based powder as an auxiliary raw material, 50% of the total weight of MgO-based powder is added at 40% of blowing time, and the remaining 50% is added at 70% of blowing time. . The reason why the MgO-based powder is divided into two portions is because the molten iron and the reaction are maximized when the above-described injection is performed, but the unreacted MgO-based powder can be minimized by continuously maintaining this level. If the MgO-based powder is added at the time of starting the blow, not only the molten iron temperature is lowered, but also the molten iron and the reaction exploded only at the start of the blow, and the reaction force decreases in the future, so that the amount of unreacted MgO-based powder is divided. This is because a large amount occurs than if.

Thus, the quicklime and the splitting method of the subsidiary materials are briefly shown in Table 2 below.

division Before blowing 10% point 40% of points 70% of points quicklime Input 50% of total weight 30% of total weight 20% of total weight Sintered ore none Input start Continue input until the end of the training at regular intervals MgO Powder none none 50% of total weight 50% of total weight

In addition, in order to secure the temperature of the molten iron which is the object of the present invention and stable control of the phosphorus in the molten iron, it is necessary to appropriately adjust the flow rate of the oxygen blown at the time of blowing and the distance between the lance and the upper side of the molten iron injecting oxygen.

Specifically, taking into account the timing of the input of quicklime or by-products and the promotion of slag goods, during the initial stage of the drilling, while maintaining a narrow gap between the lance and the upper surface of the molten iron, the flow rate of the oxygen to be blown is increased by hard blowing. At the end of the drilling period, the weight of quicklime or by-products in the molten iron is reduced compared to the initial stage, and accordingly, the slag goods are also reduced compared to the initial stage. Soft Blowing is performed by reducing the initial blow rate.

When it is described in detail with respect to the first in the case of strong pine acid it is preferable to perform from the start point of the blow to 60% of the point of progression. At this time, the flow rate of the oxygen blown may be adjusted as shown in Table 3 according to the content of silicon in the molten iron.

Silicon in molten iron
(weight%)
Calculation Silicon
Standard (% by weight)
Required amount of oxygen per target molten iron temperature (Nm ³ / Heat) Target temperature 1350 ℃ Target temperature 1400 ℃ ~ 0.15 0.15 3,900 3,500 0.16-0.20 0.20 4,000 3,500 0.21-0.25 0.25 4,100 3,500 0.26-0.30 0.30 4,100 3,500 0.31-0.35 0.35 4,200 3,600 0.36-0.40 0.40 4,200 3,600 0.41-0.45 0.45 4,200 3,600 0.46-0.50 0.50 4,200 3,600

As shown in Table 3, the reason why the total amount of oxygen blown in the molten iron is controlled by the silicon in the molten iron is because the silicon in the molten iron is first reacted with oxygen to de-silify and slag to remove the phosphorus in the molten iron. Since the dephosphorization reaction is started, oxygen is required to complete the dephosphorization reaction to the target amount while completing the desulfurization.

In addition, in the present invention, when the oxygen is blown, the strong acid from the start of the blow to the middle of the blow, but the weak feed in the latter blow will be described in detail.

First, from the start of the blow to the 60% point of blow, hard blowing is performed by increasing the flow rate of the blown oxygen while maintaining a narrow gap between the lance and the upper surface of the molten iron. Specifically, the flow rate of oxygen blown during strong acid (Nm ³ / h) may be adjusted according to the total oxygen blown amount of Table 3. In this case, it is preferable that the ratio of the total length L of the lance that injects oxygen into the converter from the height of the molten iron, which is the distance from the bottom of the converter to the upper end of the molten iron, is 0.16. Definitions of L and L0 in the present invention are shown in FIG.

In addition, from 60% of the time of blowing to the end of the blowing, while keeping the gap between the lance and the upper surface of the molten iron narrower than that of the strong pine acid reduced the flow rate of oxygen blown (Soft Blowing). Specifically, the flow rate of oxygen blown during the drug delivery (Nm ³ / hour) may be adjusted according to the total amount of oxygen blown in Table 3. In this case, the ratio of the total length L of the lance that injects oxygen into the converter is 0.07 compared to the height of the molten iron, which is the distance from the bottom of the converter to the upper end of the molten iron.

Referring to FIG. 6, the larger the ratio of the total length L of the lance to the molten iron height L0, the closer the lance is to the upper end of the molten iron, and the smaller the ratio of the total length L of the lance to the molten iron height L0 is smaller. This means that the lance is far from the top end of the charter. The lance is inserted into the converter while moving up and down in the lance lowering device fixed at the top of the converter. Therefore, assuming the same molten iron height, the longer the total length of the lance is closer to the top of the molten iron, the shorter the total length of the lance means that the lance is further away from the top of the molten iron.

In the present invention, argon gas may be blown through a low odor vent provided under the converter. At this time, the blowing of the argon gas is to agitate the molten iron to increase the chance of contact with quicklime or by-products and oxygen to promote the reaction. The argon flow rate lowered in the present invention may be 2400 Nm ³ / hour.

The phosphorus (P) content in the molten iron blown by the method described above is preferably controlled to 0.03% by weight or less. This is the content required to produce the ultra-low steel, in the present invention, the phosphorus content in the molten iron is controlled to 0.03% by weight or less and at the same time it is preferable that the molten iron temperature is maintained at 1400 ℃ or more at the time of starting.

The reason for maintaining such a temperature is that, as described above, the molten iron temperature must be maintained at 1400 ° C. or higher so that the process temperature of 1680 ° C. can be taken with only the blown oxygen in the decarburization converter, which is a post-lining process, without adding an additional heat source (ferrosilicon). Because.

Finally, when the drilling is finished, the molten iron is to be taken out through the tapping hole. At this time, the silicon generating source is put in and out (S40). The molten iron blown by the embodiment of the present invention is wired through the tapping hole of the converter, wherein the silicon in the molten iron is almost 0% by weight. Therefore, when the molten iron is transferred to the decarburization converter, which is a post-lining process, the basicity required for the decarburization process must be controlled, but the basicity cannot be controlled because there is no silicon in the molten iron. Therefore, in the subsequent decarburization process, the silicon generating source is input to be able to meet the target basicity, and then the starting line is performed. At this time, the silicon generation source is preferably silica powder.

Thus, in the present invention, while stably controlling the phosphorus in the molten iron during the delineation process to 0.03% by weight or less, while maintaining the temperature of the molten iron at 1400 ℃ or more in the dephosphorization process it can prevent the addition of additional ferrosilicon in the decarburization converter, a subsequent process. This has a great effect on the process cost reduction. In addition, it is possible to improve the slag goods efficiency by the quicklime and secondary raw materials used in molten iron delineation by promoting the slag goods in the delineation converter.

The molten iron preliminary treatment method of the ultra-low steel is not limited to the configuration and operation of the embodiments described above. The above embodiments may be configured such that various modifications may be made by selectively combining all or part of the embodiments.

10: Tallinn Electric Road 11: Exit
20: Lance (Tallinn) 30: Decarburization Furnace
40: Lance (decarburization) M: Molten steel
S: slag

Claims (8)

A first step of completely excluding slag of the converter previously operated in the Tallinn converter and injecting quicklime during the molten iron preliminary treatment;
A second step of charging molten iron into the Tallinn converter after the quicklime input;
After charging the molten iron, the molten iron is blown by blowing oxygen through the lance from the upper part of the Tallinn converter, and the molten iron is blown while split lime is injected into the molten iron in multiple stages during the drilling. step; And
And a fourth step of inputting a silicon generating source when drawing out the molten iron which has been blown out above.
In the third step,
The secondary raw material includes a sintered ore and MgO-based powder, and the sintered ore starts to be injected at the time when the blowing is 10% and is divided into a predetermined time interval until the end of the blowing, MgO-based powder is MgO-based powder at the time when the blowing is 40% A method of preliminary treatment of molten steel of ultra low-lining steel in which 50% of the total weight is added and 50% of the total weight of the MgO-based powder is added at the time when the blowing is 70%.
The method according to claim 1,
In the first step and the third step,
The molten iron preliminary treatment method for controlling the input amount of quicklime according to the silicon content in the molten iron.
The method according to claim 1,
In the third step,
The quicklime is molten preliminary treatment method of ultra-low steel is divided into the injection at the time 10%, 40%, 70% of the blow.
The method according to claim 1,
In the third step,
When the total weight of the quicklime is 100%, 50% of the total weight of quicklime is added at the time when the blowdown progresses 10%, and 30% of the total weight of the quicklime is added when the blowdown proceeds 40%, and the blowdown is 70%. The method of preliminary treatment of molten steel of 20% of the total weight of quicklime at the time of advanced stage.
delete The method according to claim 1,
In the third step,
The method of preliminary treatment of molten steel of ultra-low steel is carried out by adjusting the flow rate of the oxygen blown through the lance during the blowing and the distance between the lance and the upper end of the molten iron.
The method according to claim 1,
The silicon generation source is a method for preliminary treatment of molten steel of ultra low steel which is a silica powder.
The method according to claim 1,
In the fourth step, the molten iron in the molten iron (P) is controlled in the range of 0.03% by weight or less, the temperature of the molten iron is drawn to the molten iron pre-treatment method is maintained at 1400 ℃ or more.

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