KR101356916B1 - Hot metal decarburization method for stainless steel - Google Patents

Abstract

The present invention provides a method for producing stainless steel using the molten iron produced in the blast furnace, the molten iron preliminary treatment step of delineating the molten iron; A converter decarburization step of decarburizing the molten iron in a converter, wherein the alloy iron is introduced into the molten iron in the converter decarburization step, and the input speed of the alloy iron is 20 kg / min · ton-steel to 30 kg / min · ton-steel It relates to a molten iron decarburization method for producing phosphorous stainless steel.

Description

HOT METAL DECARBURIZATION METHOD FOR STAINLESS STEEL}

The present invention relates to a molten iron decarburization method for manufacturing stainless steel for manufacturing stainless steel using molten iron produced in a blast furnace, and more particularly, for the production of stainless steel that can effectively inject ferrochrome without lowering the decarburization efficiency of the molten iron. It relates to a molten iron decarburization method.

In general, stainless steel dissolves scrap in an electric furnace and performs crude decarburization in argon oxygen decarburization (AOD) followed by fine decarburization in vacuum oxygen decarburization (VOD). In the LT (Ladle treatment), continuous casting is performed after controlling the composition of molten steel. In general, scrap containing indispensable elements of stainless steel such as chromium is dissolved in an electric furnace and then subjected to a decarburization process in a refining furnace such as AOD and / or VOD.

However, the method of manufacturing stainless steel using molten iron of blast furnace is considerably advantageous in terms of cost compared to the method of manufacturing scrap raw material, which is highly dependent on scrap and raw material prices. There is a trend to use the manufacturing method used.

In order to manufacture stainless steel using the molten iron of the blast furnace, a decarburization process is performed after a preliminary treatment for removing impurities such as silicon, phosphorus or sulfur from the molten iron from the blast furnace. In addition, steel mills that manufacture molten iron using carbon steel blast furnaces also have decarburization converters in most cases, so decarburization of stainless steel may also be advantageous. Especially in the case of using blast furnace molten iron, it is necessary to efficiently perform dephosphorization by preliminary treatment of molten iron before the decarburization process. It can be called a process. In addition, the molten iron having undergone the delineation process is decarburized, and ferrochrome is added in the process of decarburizing the molten iron in order to control the content of chromium and iron in the molten iron. At this time, ferrochrome can lower the decarburization efficiency, which is a problem.

An object of the present invention devised to solve the above-mentioned problems is to provide a method of shortening the decarburization time by optimizing the input method of ferrochrome introduced into the chromium source when decarburizing molten iron in the converter.

In addition, another object of the present invention is to prepare a stainless steel using molten iron in order to optimize the input speed of the ferrochrome introduced into the converter to increase the oxygen efficiency used during decarburization, molten iron for manufacturing a stainless steel that can shorten the decarburization time To provide a decarburization method.

According to a feature of the present invention for achieving the object as described above, the present invention is a method for producing stainless steel using the molten iron produced in the blast furnace, the molten iron preliminary treatment step of delineating the molten iron; A converter decarburization step of decarburizing the molten iron in a converter, wherein the alloy iron is introduced into the molten iron in the converter decarburization step, and the input speed of the alloy iron is 20 kg / min · ton-steel to 30 kg / min · ton-steel Molten iron decarburization method for production of phosphorus stainless steel.

The iron alloy may include ferro-chrome (FeCr).

The feed rate of the ferrochrome may be 20kg / min-ton-steel to 27kg / min-ton-steel.

While the ferrochrome is introduced in the converter decarburization step, the average decarburization rate of the molten iron according to Equation 1 below may be more than 0.3 wt% / min to less than 0.7 wt% / min.

(Equation 1) Average decarburization rate = removal amount of carbon in molten iron while ferrochrome is injected / time when ferrochrome is injected

In the converter decarburization step, the average decarburization rate of the molten iron may be 0.05 wt% / min to 0.055 wt% / min while the ferrochrome is added.

In the converter decarburization step, oxygen or oxygen / inert gas may be blown to the upper and lower odors of the converter.

According to the present invention as described above, it is possible to provide a method of shortening the decarburization time by optimizing the method of ferrochrome introduced into the chromium source when decarburizing molten iron in the converter.

In addition, according to the present invention, in order to manufacture stainless steel using molten iron, the molten iron decarburization method for manufacturing stainless steel, which can increase the oxygen efficiency used for decarburization and shorten the decarburization time by optimizing the input speed of ferrochrome introduced into the converter. Can be provided.

1 is a flow chart showing a molten iron decarburization method for producing stainless steel according to a preferred embodiment of the present invention.
Figure 2 is a view schematically showing a state that the molten iron in the converter decarburization step according to the present embodiment.
3 is a graph showing the decarbonation efficiency versus decarburization time in the converter decarburization step.
Figure 4 schematically shows the temperature of the molten steel and ferrochrome and the chromium concentration gradient in the ferrochrome input period.
5 is a graph comparing the decarburization rate with respect to decarburization time of Comparative Example 1 and Example 1. FIG.
6 is a graph comparing carbon content with respect to decarburization time of Comparative Example 1 and Example 1. FIG.

The details of other embodiments are included in the detailed description and drawings.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments described below, but may be embodied in various forms. In the following description, it is assumed that a part is connected to another part, But also includes a case in which other elements are electrically connected to each other in the middle thereof. In the drawings, parts not relating to the present invention are omitted for clarity of description, and like parts are denoted by the same reference numerals throughout the specification.

Hereinafter, the present invention will be described with reference to the accompanying drawings.

1 is a flowchart illustrating a molten iron decarburization method for manufacturing stainless steel according to a preferred embodiment of the present invention.

The molten iron decarburization method for manufacturing stainless steel according to a preferred embodiment of the present invention is a method of manufacturing stainless steel using molten iron prepared in a blast furnace, and a molten iron preliminary treatment step (S1) of delineating the molten iron; A converter decarburization step (S2) for decarburizing the molten iron in a converter; and including the ferroalloy into the molten iron in the converter decarburization step (S2), but the input speed of the alloy iron is 20 kg / min · ton-steel to 30 kg. / min.ton-steel.

The molten iron used to manufacture the stainless steel is used in the blast furnace, the molten iron contains a plurality of impurities, so that the molten iron before refining in a refining furnace such as VOD, the molten iron preliminary treatment step (S1) and converter decarburization Step S2 may be passed. At this time, in the molten iron preliminary treatment step (S1), with the delineation, desulfurization and desulfurization may be carried out, in the converter decarburization step (S2) may be provided with molten iron in the converter, and then decarburization.

2 is a view schematically showing the appearance of the molten iron in the converter decarburization step according to the present embodiment.

Referring to FIG. 2, in the converter decarburization step, the molten iron s may be decarburized in the converter 100. The inner wall of the converter 100 may be made of a refractory 110, the outlet 120 is provided on one side of the converter 100, it is possible to discharge the molten iron (s) of the converter decarburization step is completed. The upper portion of the converter 100 is provided with a lance 130 to blow the gas to the top of the converter 100, the lower portion of the converter 100 is provided with an air hole 140 is provided of the converter 100 The gas can be blown with low odor. For example, the gas blown into the upper and lower odor of the converter 100 may include oxygen or oxygen / inert gas. The molten iron (s) may be decarburized by oxygen or oxygen / inert gas blown into the upper and lower odors of the converter 100. The molten iron (s) may be injected into the molten iron (s) in the converter decarburization step in order to implement a suitable composition for producing stainless steel. For example, the ferro-alloy may include ferro-chrome (FeCr) 150.

3 is a graph showing the decarbonation efficiency versus decarburization time in the converter decarburization step, and FIG. 4 is a diagram schematically showing a temperature of molten steel and ferrochrome and a chromium concentration gradient in a ferrochrome input section.

Referring to FIG. 3, the molten iron produced in the blast furnace is dephosphorized or desulfurized in the molten iron preliminary treatment step and charged into the converter, and decarburized by oxygen blown through the deodorization or deodorization in the converter decarburization step. In this case, in the converter decarburization step, the ferrochrome may be introduced into the converter as a chromium (Cr) source to realize the composition of stainless steel, and the introduction of the ferrochrome lowers the efficiency of decarburization of the molten iron. Hereinafter, the molten iron before adding the ferrochrome is called the Fe molten iron, while the ferrochrome is injected into the molten iron is called a ferrochrome injection section, and the molten iron after the ferrochrome injection period is called a Cr molten iron.

While demelting molten iron by a large flow of oxygen in the converter, it can be seen that the decarbonation efficiency is greatly reduced in the ferrochrome input section when ferrochrome is introduced into the molten iron. Here, the decarbonation efficiency can be expressed by the following equation.

Deoxygenation efficiency = (the amount of oxygen used for decarburization) / (total amount of oxygen blown into the converter during decarburization) * 100

In the Fe molten iron phase, which is the initial stage of decarburizing the molten iron, the deoxygenation efficiency is maintained at about 60% or more, and the deoxygenation efficiency is drastically decreased from the time when the ferrochrome is injected, and the decarbonization efficiency is less than about 30% at the ferrochrome input section. Is maintained. After the ferrochrome addition is completed, the decarbonation efficiency in the Cr melting step is lower than that of the Fe melting step, but recovers to about 50% or more in the ferrochrome injection section. Therefore, while deferring molten iron in the converter, deoxygenation efficiency is drastically lowered during ferrochrome injection, which can be found through the Hily equation indicating equilibrium between temperature, carbon, and chromium.

(Hilti)

In the Hilti's formula, [% Cr] is the concentration of chromium, [% C] is the concentration of carbon, Pco is the partial pressure of CO gas, and T is the temperature. Referring to Hilti's equation, the equilibrium carbon concentration ([% C] of Hilti's equation) in the case of injecting ferrochrome while blowing oxygen into the converter can be calculated as follows.

Since ferrochrome is introduced at room temperature, the temperature is 25 ° C, and the component is composed of Fe-60% to 70% Cr-8% C-2% Si. The degree of misuse of the molten iron into which the ferrochrome is introduced is about 1600 ° C, and the molten iron is composed of Fe-0% to 20% Cr-1% to 2% C, and 1 atm of Po ₂ which is the partial pressure of oxygen blown into the converter. As calculated using Hilti's equation, the temperature and chromium concentration gradient of the molten iron and the ferrochrome could be obtained.

Referring to FIG. 4, when ferrochrome is introduced into the molten iron, a region having a high concentration of chromium (Cr) (eg, 40%) and a low temperature (eg, 1000 ° C.) is generated around the ferrochrome. At this time, the equilibrium carbon concentration is calculated as about 48% by the Hilti equation. In other words, when the carbon concentration is 48% or more, chromium does not oxidize and carbon and oxygen react to decarburize. In practice, the molten iron has a carbon concentration of up to 8% and has a low value, so that the oxygen blown into the converter reacts with chromium supplied by ferrochrome to oxidize chromium rather than decarburize to produce chromium oxide. Therefore, when ferrochrome is injected into molten iron at a high temperature while blowing oxygen, a large amount of chromium oxide is generated on the molten iron surface. Such chromium oxide covers the molten iron surface and also prevents the oxygen blown into the molten iron from diffusing into the molten iron. In addition, this lowers the concentration of oxygen in the molten iron, thereby rapidly reducing the amount of oxygen used for decarburization.

The present invention is to solve such a problem, in the process of decarburizing molten iron in the converter while blowing oxygen, when the ferrochrome is added to increase the decarburization efficiency of oxygen and also in the converter to reduce the decarburization time The molten iron decarburization method for manufacturing can be provided. In the converter decarburization step, the ferrochrome input section, which is the time to inject ferrochrome into the molten iron, is reduced, and the Cr charter step, which is the time point after the ferrochrome input, is relatively increased. In other words, the Cr molten iron phase contains chromium in the molten iron, whereas the decarbonization efficiency is relatively higher than that of the ferrochrome injection section. Can be.

In general, temperature and carbon concentration may be considered when ferrochrome is added in the process of decarburizing molten iron. In the case of temperature, the temperature rises due to the heat generated by the decarburization, while the temperature decreases due to the addition of ferrochrome having a low temperature, thereby achieving equilibrium with each other. In addition, in the case of carbon concentration, the carbon concentration is reduced by decarburization, but the carbon concentration is increased by the carbon contained in the ferrochrome, which is kept constant in the ferrochrome input section while maintaining equilibrium with each other.

On the other hand, in the present invention, the temperature and carbon concentration are not kept constant in the ferrochrome input section, the temperature may decrease and the carbon concentration may increase. That is, the ferrochrome input section was shortened by increasing the input speed of ferrochrome in the ferrochrome input section. As described above, the decarbonation efficiency can be increased by shortening the ferrochrome input period, and the carbon concentration is not constant and increases, which is advantageous in terms of decarburization rate. On the other hand, when the molten iron temperature is excessively reduced, the molten iron may be solidified, so it is necessary to consider this when increasing the ferrochrome input rate. Therefore, the ferrochrome is introduced into the molten iron, but the injection speed of the ferrochrome may be 20kg / min-ton-steel to 30kg / min-ton-steel.

The unit of the input speed of the ferrochrome is [kg / min-ton-steel], which means the amount of ferrochrome per minute per 1 ton of molten iron provided in the converter. If the input speed of the ferrochrome is less than 20kg / min-ton-steel, the ferrochrome input section is not shortened sufficiently to deoxygenation efficiency is reduced, the input speed of the ferrochrome exceeds 30kg / min-ton-steel In the case of the ferrochrome input section is shortened, but because the low-temperature ferrochrome is collectively introduced into the molten iron, the molten iron is solidified by excessively lowering the temperature of the molten iron, causing a problem of decarburization efficiency.

Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are only a preferred embodiment of the present invention, and the scope of the present invention is not limited by the following examples.

Delineation was carried out using the molten iron produced in the blast furnace, and then the molten iron was decarburized by blowing oxygen into the molten iron in the converter. In the process of decarburizing the molten iron, ferrochrome (FeCr) was introduced into the molten iron. In this case, as shown in Table 1 below, while adding the ferrochrome by varying the carbon content and the temperature of the molten iron as in Comparative Examples and Examples, the ferrochrome input rate and the ferrochrome input section , The average decarburization rate of the molten iron and the time taken for the carbon content of the molten iron to reach 0.3wt%.

Ferrochrome Loading Speed
(kg / minton-steel) Ferrochrome input time
(min) Average decarburization rate at ferrochrome input section
(wt% / min) Time required for molten iron up to 0.3wt%
(min) Comparative Example 1 12 30 0.07 52 Comparative Example 2 35 11 0.03 65 Example 1 22 18 0.05 45 Example 2 27 15 0.05 43 Example 3 20 20 0.055 46

Table 1 shows the ferrochrome loading rate (kg / min-ton-steel) and ferrochrome loading time (min), average decarburization speed (in the ferrochrome loading section in Comparative Examples 1 and 2 and Examples 1, 2 and 3, respectively) wt% / min) and the time (min) for the carbon content in the molten iron to reach 0.3wt%. At this time, in Comparative Examples 1 and 2 and Examples 1, 2 and 3, the time point at which the ferrochrome was introduced from the molten iron was the same.

5 is a graph comparing the decarburization rate with respect to the decarburization time of Comparative Example 1 and Example 1, Figure 6 is a graph comparing the carbon content with respect to the decarburization time of Comparative Example 1 and Example 1.

In Figure 5, Comparative Example 1 is when the ferrochrome injection rate for 12 minutes at a ferrochrome loading rate of 12kg / min-ton-steel, Example 1 is a ferrochrome loading rate to 22kg / min-ton-steel This is when ferrochrome was added for 18 minutes. The decarburization rate can be obtained by the following equation.

Decarburization rate = d (wt% C) / dt = removal of carbon from molten iron / hour

In both of Comparative Example 1 and Example 1, the decarburization rate was drastically reduced in the ferrochrome input section into which ferrochrome was input, and as the ferrochrome was continuously added, the decarburization rate was also continuously decreased. After the ferrochrome addition is finished, it can be seen that the decarburization rate is increased again quickly. In the case of Example 1 having a shorter ferrochrome input section than Comparative Example 1, the decarburization rate was lower in the ferrochrome input section of Example 1 than in Comparative Example 1 (region 1), but the ferrochrome input section of Example 1 After this, the decarburization rate was recovered quickly and the decarburization rate was faster than that of Comparative Example 1 (region 2). That is, the region 1 is a region in which the comparative example 1 is faster in decarburization rate than in Example 1, and the region 2 is an region in which Example 1 is relatively faster in decarburization rate than in Comparative Example 1. Comparing the difference between the area ratios of the area 1 and the area 2, it can be seen that the area 2 is larger than the area 1. That is, in some sections, the decarburization rate may be relatively lower than that of Comparative Example 1, but in terms of overall decarburization efficiency, it was confirmed that Example 1 is more superior to Comparative Example 1.

In Example 1, after the addition of ferrochrome is completed (after about 30 min), the chromium oxide disappears from the molten iron surface, and thus the oxygen blown from the upper liquor is easily diffused into the molten iron. Is done. In addition, as the reaction proceeds, the carbon content in the molten iron decreases (after about 37 min), and thus the decarburization rate decreases. Also in Comparative Example 1, the decarburization rate increased rapidly after the completion of the ferrochrome addition (after about 40 minutes). On the other hand, in FIG. 5, in the case of Comparative Example 1, the decarburization rate was not decreased after the ferrochrome input period, but this is because decarburization proceeded less than that of Example 1 for 50 minutes shown in FIG. 5. That is, when the decarburization rate is shown in excess of 50 min in FIG. 5, the decarburization rate also decreases in Comparative Example 1. FIG.

In FIG. 6, the carbon contents of Comparative Example 1 and Example 1 were confirmed, and quantitative comparison of the decarburization rate difference is possible through the change of the carbon content. In the ferrochrome loading section, the carbon content of Example 1 is rapidly increased compared to Comparative Example 1, but after the ferrochrome addition of Example 1 is completed, the carbon content of Example 1 is rapidly decreased compared to Comparative Example 1. That is, after the ferrochrome addition of Example 1 was finished, the decarburization rate of Example 1 was faster, and finally the carbon content of Example 1 was confirmed to decrease much faster than Comparative Example 1.

In addition, referring to Table 1, it can be seen that the injection speed of the ferrochrome is preferably 20kg / min-ton-steel to 27kg / min-ton-steel. When the ferrochrome loading rate is less than 20kg / min-ton-steel, the ferrochrome loading section is not shortened sufficiently to reduce the deoxygenation efficiency, the ferrochrome loading speed is 27kg / min-ton-steel Due to the ferrochrome addition, the temperature of the molten iron is excessively lowered, and the chromium oxide is excessively formed on the surface of the molten iron to prevent the reaction of the oxygen blown from the top and carbon in the molten iron. In addition, the average decarburization rate of the molten iron according to the following formula 1 during the ferrochrome may be more than 0.3wt% / min to less than 0.7wt% / min.

(Equation 1) Average decarburization rate = removal amount of carbon in molten iron while ferrochrome is injected / time when ferrochrome is injected

When the average decarburization rate of the molten iron is 0.3wt% / min or less while the ferrochrome is injected, the decarburization time is increased as in Comparative Example 2, and thus the ferrochrome input section, which is a region in which the decarburization efficiency is low, is long. It lowers decarburization efficiency. On the other hand, if the average decarburization rate of the molten iron while the ferrochrome is added is 0.7wt% / min or more, as in Comparative Example 1 the ferrochrome injection rate is too fast, so the temperature of the molten iron is too excessively lowered and thus the decarburization rate Can be reduced.

In addition, it is preferable that the average decarburization rate of the molten iron while the ferrochrome is added is 0.05wt% / min to 0.055wt% / min. When the average decarburization rate of the molten iron is 0.05wt% / min as in Examples 1 and 2, the decarburization time is 45min and 43min until the molten iron carbon content is 0.3wt%, and the average decarburization of the molten iron is as in Example 3. When the rate is 0.055wt% / min, it was confirmed that the time required to decarburize until the molten iron carbon content was 0.3wt% was 46min. This is, in Comparative Examples 1 and 2, respectively, the time required to decarburize until the molten iron carbon content is 0.3wt% is 52min and 65min, whereas the average decarburization rate of the molten iron, which is the case of Examples 1 to 3, is 0.05wt% / min. In the case of 0.055 wt% / min, it can be seen that decarburization can be efficiently performed.

It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the foregoing detailed description, and all changes or modifications derived from the meaning and scope of the claims and the equivalents thereof are included in the scope of the present invention Should be interpreted.

100: converter 110: refractory
120: outlet 130: lance
140: air hole 150: ferrochrome

Claims (6)

In the method of manufacturing stainless steel using the molten iron produced in the blast furnace,
A molten iron preliminary treatment step of removing the molten iron;
A converter decarburization step of decarburizing the molten iron in a converter;
Ferrochrome (FeCr) is introduced into the molten iron in the converter decarburization step, but the input speed of the ferrochrome is 20kg / min · ton-steel to 27kg / min · ton-steel. delete delete 3. The method of claim 2,
The molten iron decarburization method for manufacturing stainless steel, characterized in that the average decarburization rate of the molten iron according to the formula 1 during the ferrochrome in the converter decarburization step is more than 0.3wt% / min to less than 0.7wt% / min.
(Description 1) Average decarburization rate = removal amount of carbon in molten iron while ferrochrome is injected / time when ferrochrome is injected 5. The method of claim 4,
The molten iron decarburization method for producing stainless steel, characterized in that the average decarburization rate of the molten iron while the ferrochrome is added in the converter decarburization step is 0.05wt% / min to 0.055wt% / min. The method of claim 1,
In the converter decarburization step, the molten iron decarburization method for producing stainless steel, characterized in that the blowing up and low odor of the converter blowing oxygen or oxygen / inert gas.

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