KR0128138B1 - Method for producing molten metal - Google Patents

Abstract

In preparing a hot steel using hot metal and scrap as major material in furnace, the hot steel which has low phosphorus content and high carbon content can provided by means of controling effectively composition of a slag within furnace and a hot steel by changing input method of sintered ore or iron ore. Burnt dolomite less than 2% by weight and caustic lime less than 1% by weight with respect to those of the previous step is introduced in furnace with 30% of slag raised in previous step remained, and slag is coated on wall of the furnace. Then, scrap and hot metal of low manganese content with the concentration less than 0.2% by weight are added and the hot metal in the furnace is kneaded by introducing oxygen. Concurrently, caustic lime of 3-4.5% by weight relative to the total added amount is all at once added and sintered ore of 3-3.5% by weight relative to the total added amount is input divisionally from time to complete the addition of caustic lime to 80% time point of total kneading duration, by which melt steel is prepared with not more than 0.02% by weight of phosphorus content.

Description

Manufacturing method of low carbon high molten steel

The present invention relates to a method for manufacturing low-lin (P) high-carbon molten steel, more specifically, in the converter operation mainly using molten iron and scrap iron, by changing the input method of sintered or iron ore as an auxiliary raw material, the slag and molten iron in the furnace during efficient drilling It relates to a method for producing high carbon molten steel having a phosphorus content of 0.02% by weight or less through control. In general, a conventional converter is charged with the main raw material (hot metal) and scrap metal (scrap) into the converter, and at the same time, the raw material is calcined lime (main component is calcium oxide, CaO), iron ore or sintered ore (main component is iron oxide), Forming (mainly calcium fluoride, CaF ₂ ), etc., by adding impurities such as carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), titanium (Ti), etc. A series of operations to remove them by oxidative refining are collectively referred to.

The molten steel obtained through such converter operation usually requires a phosphorus content of 0.02% by weight or less. Thus, in order to obtain molten steel having a phosphorus content of 0.02% or less, conventionally, carbon in molten iron (collectively referred to as molten iron and molten steel) had to be decarburized from about 4.5 wt% to about 0.04 wt%. However, when applying the converter operation method as described above to the steel material to be produced high carbon steel containing 0.10% by weight or more, there are the following problems.

At the end of the blow, the perforation yield of molten iron decreases, which leads to an increase in the slag content, the dissolved oxygen in the lumen along with the melting loss of the furnace refractory. In addition, the molten steel produced in this way must put various ferroalloys to meet the desired molten steel composition during the tapping. At this time, the ferroalloy is reacted with dissolved oxygen in molten steel to produce oxide, and this oxide becomes a non-metallic inclusion, which leads to deterioration of the quality of molten steel and clogs various nozzles during the post-secondary refining and continuous casting process. This causes a deterioration in productivity as well as workability, and causes a variety of defects in products. On the other hand, in order to efficiently remove phosphorus in molten iron at less than 0.02% by weight, the converter industry has elements such as carbon, silicon, and manganese in molten iron, calcium oxide (CaO), magnesium oxide (MgO), and silicon oxide (SiO2) in slag. Control of oxide concentrations such as manganese oxide (MnO) and iron oxide (FeO) is important.

The chemical reactions are as follows.

Where K is the equilibrium constant of the reaction formula, ai is the activity of the i component in the molten iron and slag, T means the absolute temperature, K depends only on the temperature. From the above formulas (1) and (2), it is preferable to satisfy the following conditions for effectively removing phosphorus [P] in molten steel to 0.02% by weight or less, that is, to lower ap.

First, the slag and molten iron temperature are controlled to low levels.

Second, it increases the basicity (calcium oxide weight% / silicon oxide weight%) in the slag.

Third, keep the dissolved oxygen in molten iron high.

Fourth, increase the oxygen potential of the slag (Oxygen Potential).

Fifth, the element with strong affinity with oxygen in molten iron is managed as low as possible. In order to achieve these conditions, low-carbon high-carbon steels should be selected as one of the most important technologies.However, high carbon and manganese concentrations in the molten iron under the converter operating conditions are not enough to produce quicklime, resulting in low bases. it's difficult. Therefore, it is necessary to improve the dephosphorization effect by maintaining the dephosphorization reaction product in a stable state while maintaining the slag and molten iron temperature by controlling the input amount and the method of quicklime and sintered ore. In addition, manganese in molten iron has a higher affinity with oxygen than iron, carbon, and phosphorus, and thus reacts preferentially during the delinquency reaction, and simultaneously causes redox reactions depending on the atmosphere in the furnace during the blowing process. In other words, manganese exhibits ridge phenomena in the order of oxidation at the beginning of the blowing, reduction at the middle, and oxidation at the end. At this time, manganese oxide in slag is increased by carbon monoxide (CO gas), which is a reducing gas generated in the furnace, and phosphorus compound is reduced as iron oxide content in slag decreases. The fact is generally known. Therefore, the availability of molten steel with a phosphorous content of 0.02% or less also depends on how to effectively suppress the above phenomenon in the high carbon region (carbon content of 0.70% or less) at the end of the blow. However, since carbon and phosphorus in molten iron are advanced by mutually opposed metallurgical reaction characteristics, there are many difficulties in manufacturing a high carbon steel satisfying a phosphorus concentration of 0.02% by weight or less.

Therefore, the present inventors have conducted research and experiments to produce molten steel having a phosphorous content of 0.02% or less even in the high carbon region at the end of the blowdown period. As a solution, the present inventors have focused on the following three methods and proposed the present invention. .

First, the effect of the presence or absence of light dolomite in the slag coating on the converter furnace wall before the blowing operation,

Second, the method of conducting the converter operation using the molten iron having a low manganese content as the main raw material,

Third, the present invention focuses on a method of efficiently controlling molten iron and slag components by appropriate input of sintered ore as an auxiliary raw material during drilling.

The present invention is based on the conventional molten iron containing not only the low manganese molten iron but also manganese content of about 0.27-0.40% by weight, and the constituent behavior of manganese by adjusting the input method of sintered ore as an auxiliary material, that is, the timing of injection and the amount of injection With the proper control of the slag, through the effective control of the slag, the chemically labile phosphorus compound in the high carbon region (carbon content below 0.80%) is maintained as a stable phosphorus compound in the slag, so that the low manganese molten iron containing 0.02% or less phosphorus It is an object of the present invention to provide a method for producing low carbon steel molten.

(Configuration and Contents of the Invention)

In the present invention, the slag of the slag of the previous operation, 30% of the slag of the previous operation, less than 2% by weight and 1% by weight of light bovine dolomite and quicklime of less than 1% by weight, respectively, and tilted to coat the slag on the furnace wall and scrap iron and molten iron After charging, the pure oxygen is blown out to purify the furnace vessel, the quicklime is added at the same time, and the sintered ore is added to produce low-lining (P) high carbon molten steel, wherein the molten iron is Mn: 0.2 wt% or less. Low manganese solution; At the same time as the start of the blow-in, a total of 3-4.5 wt% of quicklime was added to the total loading; The present invention relates to a method for producing low-drain high carbon steel using low manganese molten iron by dividing sintered ore into 3-3.5 wt% based on the total amount of charge from the completion of the batch injection of the quicklime to the 80% of the total blowing time. In addition, the present invention, after the addition of 2% by weight or less and 1% by weight of light bovine dolomite and quicklime, respectively, to the converter leaving 30% of the slag of the previous operation, and then tilted to coat the slag on the furnace wall and In the method of preparing molten iron (P) high carbon molten steel by charging molten iron, and then pure oxygen is fed to purge furnace vessels, and simultaneously charged with quicklime and sintered ore, wherein the molten iron is Mn: 0.27-0.40 Molten iron in the range of weight percent; At the same time as the start of the blow-in, a total of 3-4.5 wt% of quicklime was added to the total loading; The present invention relates to a method of manufacturing high carbon molten steel which is reduced by dividing sintered ore into 2-3.5 wt% based on the total amount of charge from the completion of the batch injection of quicklime to 70% of the total blowing time.

Hereinafter, the present invention will be described in more detail.

In general, the converter operation of low-carbon molten steel consists of (preparation stage preparation stage)-> (main raw material loading stage)-> (treatment work)-> (leave).

In the preparation stage of the blowdown operation, 30% of the total slag of the previous operating group is left in weight percent, and the total loading amount of light dolomite (Burnt dolomite, CaO, MgO) in order to prevent the erosion of the converter refractory (the weight of scrap iron combined with molten iron) 2% or less and quicklime 1% or less with respect to the total loading amount, and the slag is coated on the furnace wall by repeatedly tilting the furnace body about 4 times. Subsequently, in the charging phase of main raw materials, scrap metal and molten iron are charged into the furnace, and the furnace is run twice, followed by blowing with oxygen, and in the drilling operation stage, when the internal molten iron is ignited by Songsan, the raw material, which is an auxiliary raw material, is immediately followed. In this case, about 0.1% of fluorspar is added together with quicklime. And sintered ore which is a subsidiary material is also thrown in. In general, in the converter operation, it is necessary to estimate carbon content in molten iron by adjusting sublance at a time of about 90% of blowing time, and to adjust the target molten steel temperature by measuring the bath temperature to add an appropriate amount of sintered ore. Conversion work is completed. After finishing the blow, tap and drop, and add deoxidizer, ferroalloy, and charcoal for adjusting molten steel composition.

In the present invention, after inserting the scrap metal and molten iron as the main raw material in the furnace, when the incineration vessel is ignited by starting the production in the drilling operation stage, the input amount is 3-4.5% by weight relative to the total charge when the raw lime is added It is preferable to inject as, for the following reason.

When the amount of quicklime is less than 3% by weight, the slag control during the blowing is effective in effectively surpassing the temperature rise and excessive erosion of the converter refractory. When the amount of the quicklime exceeds 4.5% by weight, the slag conversion rate of the input quicklime is lowered and the problem is in terms of securing the heat source. Because you are holding. In the present invention, however, the method of adding sintered ore varies according to the manganese content in the molten iron after the quick injection of quicklime in the above-described dosage range. First, in the case of using a low-manganese molten iron having a manganese content of 0.2% by weight or less, the sintered ore is divided into 3-.35% by weight with respect to the total electric pressure from 80% of the total blowing time after the quick injection of quicklime in the above input range. It is preferable to inject. In the case of using low manganese molten iron, if the total input amount of the sintered ore is less than 3%, it causes excessive temperature rise during the drilling, and there is a disadvantage in controlling the composition of the slag. It is effective in removing slag and controlling slag in molten iron, but it is problematic in terms of securing a heat source. The sintered ore injected into the total input range is added 1-1.5 wt% based on the total loading at the time of completion of the quicklime injection, and subsequently 0.13-0.16 wt% per minute with respect to the total loading until 80% of the total blowing time. It is more preferable to divide evenly into. In other words, in the case of using low manganese molten iron, when sintered ore is added at 1% by weight to the total loading after the quicklime-lime injection, the metallurgical characteristics of the furnace are impaired due to disadvantages in the initial slag conversion rate or the lack of oxygen source, and at least 1.5% by weight. This is because it is disadvantageous for slag control due to low temperature, which is detrimental to the Tallinn reaction during the blowing. Thereafter, since 80% of the blowing time is a reducing atmosphere in which decarburization proceeds vigorously during the blowing, when the amount of sintered ore is less than 0.13% by weight per minute, the phosphorus compound generated in the slag appears, and at a low temperature of 0.16% by weight or more, This is because there is a problem in controlling the target temperature of the blowing endpoint.

On the other hand, in the case of using a conventional molten iron containing about 0.27 to 0.4% by weight manganese it is necessary to change the input method of the sintered ore. That is, in order to manufacture a low carbon high carbon steel containing less than 0.02% by weight of phosphorus in the slag chemically unstable molten iron in the high carbon region as a stable phosphorus compound in the slag while using a conventional molten iron as described above range It is preferable to separately add 2-3.5% by weight of sintered ore based on the total amount of loading from the batch of quicklime to 70% of the total blowing time. This is because in the case of using a conventional molten iron, if the total input amount of the sintered ore during the blow is less than 2%, excessive temperature rise occurs during the blow, and there is a disadvantage in that the slag composition control is disadvantageous. In addition, in the case of using a conventional molten iron, the sintered ore input in such a total input range is inputted with 1-2 wt% of the total loading at the time when the batch of quicklime is completed, and then for the total loading by 70% of the time for blowing. More preferably, 0.16-0.20 wt% per minute is continuously divided equally. That is, unlike the case of using the low manganese molten iron, when the sintered ore is added at 2% by weight or more relative to the total loading after the quicklime-lime batch injection, it is disadvantageous for slag control due to low temperature and is detrimental to the delineation reaction during the blowing. Thereafter, since the decarburizing process proceeds vigorously up to 70% of the time of blowing, when the molten iron is used, when the input amount of sintered ore is less than 0.16 wt% per minute, the phosphorus compound generated in the slag appears, 0.20 If the weight% or more, there is a problem in controlling the target temperature of the blowing point due to the low temperature.

The sintered ore in accordance with the present invention can be used in a typical converter operation, the composition of the typical sintered ore is shown in Table 1.

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

Example 1

Leave 3 tons of the total slag (about 10 tons) in the previous operation, and add 100 tons of the total charged amount (the combined weight of yongsan and scrap iron) to 2 tonnes of hard borosilicate and 1 ton of quicklime: The slag was coated on the furnace wall by repeated tilting. Subsequently, more than 80% of the low manganese molten iron containing less than 20% by weight of scrap metal as a main raw material and the components shown in Table 2 was loaded into the converter.

Then, after stirring the furnace body twice, the molten iron is ignited while transmitting pure oxygen, and briquettes are started. At the same time, quicklime is added and sintered ore is added. The molten steel was pulled out after the prediction and the temperature measurement were completed, and the deoxidizer, the ferroalloy, and the charcoal ash were added.

In the case of the quicklime and sintered ore, in Comparative Example (1), which is a conventional method as in FIG. 1, 3.5 tons of quicklime are added as soon as the furnace line is ignited, and then sintered ore is 750 at 30% of the start of blow. ㎏ was added, and then divided into equally divided doses up to 80% time point of the total blowing time by 250kg at 1 minute intervals.

In the case of Inventive Example (1), which is the method of the present invention, immediately after the furnace vessel is ignited, 4.5 tons of quicklime are added all at once, and then 1500 kg of sintered ore is added immediately thereafter, and then 130 kg is blown at the interval of 1 minute. Evenly divided into 80% time point, and in the case of Inventive Example (2), after the quicklime was added as in the case of Inventive Example (1), immediately followed by 1000 kg of sintered ore, and then 1 minute 160 kg at intervals were added evenly continuously until 80% of the time of the entire blowing time. In this case, the flow rate, main lance height, quicklime and sintered ore input timing are as shown in FIG.

When the slag and molten iron sample are collected by the above method, the slag and the molten iron sample are collected by using a sub lance at 2.5 minute intervals, and the carbon concentration according to the blowing time of molten iron is shown in FIG. 3 (a), and the manganese concentration (b). Phosphorus concentration is shown in (c), the molten iron temperature according to the blowing time is shown in FIG. 4 (a), the basicity of slag is shown in (b), and the content of iron oxide in the slag is shown in (c).

Figure 3 shows the changes over time of the carbon, manganese and phosphorus content of the major components of molten iron. Looking at the time-dependent change of each component in the molten iron of each embodiment from FIG. 3, first, carbon exhibits similar behavior, but manganese is all changing while drawing an S curve.

Looking at the manganese content change here, the abdominal manganese phenomenon (bumping phenomenon) during the blowing period (1, 2) is weaker than the fertilizer example (1) in the present invention, the amount of manganese is less. In particular, the present invention suggests that the sintered ore formed by introducing the manganese ridge phenomenon earlier than the comparative example (1) has a sensitive effect on the reaction between molten iron and slag, and promotes slag formation of the sintered ore.

As a result, as clearly confirmed in the behavior of phosphorus, the comparative example (1) shows the behavior of an S curve similar to that of manganese, but the inventive examples (1 and 2) show continuous Tallin behavior with blowing time.

As such, it can be seen that it is important to efficiently control the behavior of manganese in molten iron in order to induce an effective Tallinn reaction in the converter operation.

In order to prove the above effect, it is FIG. 4 that the temperature change in the converter and the time course of the slag over time were investigated.

First, when comparing Comparative Example (1) and Examples (1, 2) of the present invention, by injecting sintered ore during blowing early, the molten iron is kept low while maintaining the basicity and iron oxide content of slag at the same time. It can be seen that it is effective for Tallinn.

On the other hand, when comparing Comparative Example (1) and Examples (1, 2) of the present invention, the molten iron temperature during the blowing was low since the amount of quicklime input in the beginning of the blowing was many of the Examples (1,2) of the present invention. In addition, the amount of sintered ore input of the comparative example was rather increased in the blowing period, and the same tendency was observed temporarily. However, after 8 minutes of the blowing time, the molten iron temperature of the present invention was lowered again.

Because of this phenomenon, the slag basicity is high, and the iron oxide content is increased, and this action induces an effective delineation reaction, thereby obtaining a stable change of phosphorus as shown in FIG. 3 (c).

As shown by the dotted lines in FIG. 3 based on FIGS. 3 and 4 above, when the carbon content is 0.70% or less (after 13.5 minutes of blowing time), it can be confirmed that molten steel of 0.02% or less of phosphorous content can be produced. Can be.

Therefore, the present invention was able to derive the above results by deriving the proper input point and amount of sintered ore during the blowing operation using the low manganese molten iron in the present invention. First, it is possible to control the manganese during the low blowing. Second, the iron oxide content of the slag and slag rate of the added quicklime can be kept high, and third, the slag temperature can be controlled low.

Example 2

Except for using the molten iron containing the components shown in Table 3, the molten steel was tapped out by the same method as in Example 1 to terminate the blow of molten iron.

In the case of Comparative Example (2), which is a conventional method for the input of quicklime and sintered ore, 3.5 tons of quicklime are added in a batch as soon as the furnace line is ignited, and then the sintered ore is sintered between 30% and 80% of the start of blowing. -3 split was added.

In the case of Inventive Example (3), 4.5 tons of quicklime was collectively administered immediately after the furnace vessel was complexed, and then sintered ore was continuously equally added to 70% of the total blowing time. In this case, the pine flow rate, main lance height, quicklime and sintered ore input timing are as shown in FIG.

At the time of blowing in the same manner as above, the slag and molten iron samples are collected using the sub lance over the entire blowing time, and the carbon concentration according to the blowing time is shown in FIG. 6 (a), and the manganese concentration is shown in FIG. b), the phosphorus concentration is shown in FIG. 6 (c), the molten iron temperature according to the blowing time is shown in FIG. 6 (a), the iron oxide content in the slag is shown in FIG. 6 (b), and the basicity of the slag is It is shown in 6 (c).

The molten steel sample was collected at the end point of the blowing and the operation results for carbon, manganese, and phosphorus in the molten steel in the high carbon region were compared and the results are shown in FIGS.

6 and 7 show the behavior of molten iron and slag performed in Comparative Example (3) and Inventive Example (3) during drilling, and FIGS. 8 to 10 show correlations between carbon, manganese and phosphorus in molten steel at the point of drilling. It is shown.

FIG. 6 shows changes over time for carbon, manganese, and phosphorus in molten iron by the method of Inventive Example (3) and Comparative Example (3), but there is no significant difference in the case of carbon, but manganese and phosphorus The case shows a low value. In the case of Inventive Example (3), this is a result of continuously and equally inputting a sintered ore, which is an oxygen source, from the beginning of blowing.

That is, in Comparative Example (3), the abdominal manganese phenomenon was remarkable from about 3 minutes of blowing time, while Inventive Example (3) was decreasing. This effect is advantageous for the Tallinn reaction. In the slag and molten iron dephosphorization reaction, manganese can thus be controlled to less than 0.02% of phosphorus content in the case of the invention example (3) within about 60% of the blowing time, that is, in the region of 1% by weight of carbon.

When the component behavior of molten iron during the blowing as shown in FIG. 6 is compared through the change of the molten iron temperature and the slag behavior during the blowing in FIG. 7, the sintered ore as an auxiliary material in the case of Inventive Example (3) was compared with Comparative Example (3). As the oxidation degree of slag increases according to the proper supply, the phosphorus compound fished during the blowing is stably present in the slag, and the phosphorus compound produced during the blowing process keeps the furnace temperature lower and the iron oxide content and the basicity of the slag are kept high. By providing the opportunity, it was possible to produce molten steel having a carbon content of 1% by weight while maintaining a phosphorous content of 0.02% by weight or less.

8 shows the correlation between the carbon content of molten steel and manganese at the termination point of the molten steel. As the carbon content in the molten steel increases, the manganese increases, and the manganese content of the same carbon content is higher than that of Comparative Example (3). The case is low. This reflects the result of the enhanced splitting effect of the sintered ore into which manganese oxide is produced, which is produced by the initial removal of oxygen gas by reaction with manganese in molten iron. Due to this effect, in the case of Inventive Example (3), the manganese content of the blowdown and the end point is lower than 0.20% by weight as shown in FIG. 9, compared to the comparative example (3). Provide conditions that can be lowered.

On the other hand, as shown in FIG. 9, as shown in FIG. 10 by the control of stable manganese content of 0.20 wt% or less, in the case of Inventive Example (3), 0.02 wt% or less even in the high carbon region of 0.10 to 0.70 wt%. It has been demonstrated that molten steel having a phosphorus content of can be produced.

Therefore, all the silicon in the molten iron is oxidized to slag at the beginning of the blow, and carbon is discharged out of the converter as carbon monoxide (CO). Manganese is somewhat different depending on the atmosphere in the furnace, but is oxidized and remains in the slag. Therefore, the effective control of molten steel depends on how this series of processes is controlled.

1 is a graph showing the input amount of sintered ore according to the blowing time of the present invention method and the conventional method when using a low manganese molten iron

Figure 2 is a schematic diagram showing the flow rate, main lance height, quicklime and sintered ore time according to the blowing time of the present invention and the conventional method when using the low manganese molten iron

3 and 4 are graphs showing carbon, manganese, phosphorus concentration, molten iron temperature, slag basicity, and iron oxide content in slag according to the blowing time of the invention and comparative examples, respectively, when using low manganese molten iron.

Figure 5 is a schematic converter operation method for the invention example and the comparative example when using a conventional molten iron

FIG. 6 is a graph showing the component behavior of molten iron during blowing for the invention example and the comparative example when using ordinary molten iron

7 is a graph showing the molten iron temperature and the slag behavior during the blowing for the invention and comparative examples when using a conventional molten iron

8 is a graph showing the correlation between the carbon content in the molten steel and the manganese content at the time of completion of blowing for the invention example and the comparative example when using a conventional molten iron

9 is a graph showing the correlation between the manganese content and the phosphorus content in molten steel at the time of completion of blowing for the invention example and the comparative example when using ordinary molten iron

10 is a graph showing the correlation between the carbon content and the phosphorus content in molten steel at the time of completion of blowing for the invention example and the comparative example when using conventional molten iron

As described above, the present invention can maintain a high slag rate of molten iron and slag and the slag oxidized slag during the drilling, while deriving the appropriate starting point and amount of sintered or iron ore during the drilling, and lower the slag temperature during the drilling As a result, it can increase the activity of calcium oxide, making it possible to produce high carbon steels with phosphorus content of 0.02% by weight or less, as well as improving the yield of molten steel, extending the life of converter refractory, carburizing agent, ferroalloy, aluminum It is effective in reducing the amount of oil used, improving the cleanliness of molten steel, improving productivity due to smoke, and improving the quality of molten steel and products.

Claims (1)

In the converter which left 30% of the slag of the previous operation, less than 2% by weight of light bovine dolomite and less than 1% by weight of quicklime were added to the total loading, and then the slag was coated on the furnace wall, and the slag and molten iron were applied. In the method of charging, and then delivering pure oxygen to blow the molten iron in the furnace, and simultaneously administer quicklime, and injecting sintered ore into low-lining (P) high-carbon molten steel, The molten iron is a low manganese molten iron with an Mn concentration of 0.2% by weight or less; At the same time as the start of the blowing, a batch of 3-4.5 wt% quicklime was added to the total loading; From the completion of the batch injection of quicklime to 80% of the total blowing time, 3-4.5% by weight of the sintered ore is equally divided in the total loading amount. After the addition, the remaining sintered ore until the 80% time point of the total blowing time, the method of producing a low carbon steel molten steel, characterized in that it comprises continuously and equally added at a rate of 0.13-0.16% by weight per minute.