MOLTEN STEEL TREATMENT DEVICE AND MOLTEN STEEL TREATMENT METHOD USING SAME

- POSCO

Provided is a molten steel treatment device and a molten steel treatment method using same. The molten steel treatment method may include: preparing slag on molten steel; contacting a first electrode to at least a portion of the slag and a second electrode to at least a portion of the molten steel; and polarizing the slag by applying a voltage to the first electrode and the second electrode, to easily remove inclusions and impurity elements in the molten steel by controlling basicity and oxidation degree of the slag without using separate additives.

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Description
TECHNICAL FIELD

The present disclosure relates to a molten steel treatment device and a molten steel treatment method using same, and more particularly, to a molten steel treatment device capable of: preventing reoxidation of molten steel by controlling an interface reaction between molten steel and slag; and controlling elements of the molten steel, and a molten steel treatment method using same.

BACKGROUND ART

A ladle refining process warms molten steel by using slag, prevents external impurities from being introduced into the molten steel, and performs a refining reaction for removing impurities in the molten steel through an interface reaction between the slag and the molten steel. The above-described slag is made of a compound oxide, and exists in the form of an ionic solution at an upper portion of the molten steel in case of a ladle refining condition. Main elements of the slag include a basic oxide such as CaO and MgO, an acid oxide such as SiO2 and Al2O3, and a neutral oxide such as FeO and MnO, and exist in ion states such as Ca2+, Mg2+, SiO4−, AlO4−, Fe2+/3+, Mn2+/3+, and O2− to maintain electrical neutrality.

Inclusions and impurity elements in the molten steel may be removed through an interface reaction between the slag and the molten steel during the ladle refining, and, for this, the basicity and oxidation degree of the slag may be controlled. Here, the basicity represents a ratio of a basic oxide content with respect to an acid oxide content, and high basicity is required for the ladle refining. Also, the oxidation degree of the slag represents a content of a neutral oxide such as FeO and MnO contained in the slag. Also, as the oxidation degree of the slag increases, the slag reacts with deoxidation elements in the molten steel to easily produce inclusions, which is called as reoxidation by the slag.

As described above, a method for increasing the basicity of the slag by inputting quicklime and decreasing the oxidation degree of the slag by inputting slag deoxidizer having main elements of aluminum and calcium carbonate to easily remove the inclusions and impurity elements in the molten steel by using the slag in the ladle refining. However, since production costs increases by using additives such as quicklime and slag deoxidizer, and particularly, in case of the slag deoxidizer, inclusions are generated due to the inputted aluminum, an alternative technology is required.

Also, Ca elements are inputted in forms of metallic Ca, Fe—Ca, and Ca—Si to prevent alumina inclusions in the molten steel from having a low melting point and being glomerate and MnS from being generated by sulfur (S) in the molten steel during casting. However, Ca has a limitation of high volatility and extremely low yield rate. Thus, although there is attempt for supplying Ca by inputting pulverized quicklime (CaO), the dissolution and dissociative reaction of quicklime are difficult, and, since a yield rate is also low, the elements of molten steel is hardly controlled.

PRIOR ART DOCUMENT

Japanese Laid-Open Patent No. 1994-128618A

DISCLOSURE OF THE INVENTION Technical Problem

The present disclosure provides a molten steel treatment device capable of: restricting reoxidation of molten steel by generating an interface reaction between slag and molten steel; and adjusting elements of the molten steel, and a molten steel treatment method using same.

Technical Solution

In accordance with an exemplary embodiment, a molten steel treatment device, which is used for ladle refining, includes: a power supply module comprising a first electrode, a second electrode, and an insulator provided between the first electrode and the second electrode to electrically separate the first electrode from the second electrode; and a power unit connected to the power supply module. Here, the first electrode has a plate shape having an area, the second electrode vertically extends while passing through the first electrode, and an insulator is provided between the first electrode and the second electrode.

An extension part, which has an area and is disposed in parallel to the first electrode, may be provided to a lower portion of the second electrode.

The first electrode may include a material having a specific gravity less than that of the slag provided on molten steel.

The first electrode may include graphite.

The second electrode may include a conductive refractory material containing Al2O3(MgO)—C.

The power supply module may be installed on a ladle cover so that the first electrode and a portion of the second electrode are inserted into a ladle.

In accordance with another exemplary embodiment, a molten steel treatment device, which is used for ladle refining, includes: a power supply module including a first electrode, a second electrode, and an insulator provided between the first electrode and the second electrode to electrically separate the first electrode from the second electrode; and a power unit connected to the power supply module. Here, each of the first electrode and the second electrode has a plate shape having an area, and the insulator has a length greater than a thickness of slag provided on the molten steel. The first electrode may include a material having a specific gravity less than that of the slag provided on molten steel.

The first electrode may include graphite.

The second electrode may include a conductive refractory material containing Al2O3(MgO)—C.

The power supply module may be installed on a ladle cover so that the first electrode and a portion of the second electrode are inserted into a ladle.

In accordance with another exemplary embodiment, a molten steel treatment method includes: preparing slag on molten steel; contacting a first electrode to at least a portion of the slag and a second electrode to at least a portion of the molten steel; and polarizing the slag by applying a voltage to the first electrode and the second electrode.

The first electrode may float on the slag, and at least a portion of the second electrode may be dipped into the molten steel.

In the polarizing of the slag, the first electrode may be connected to a positive electrode, and the second electrode may be connected to a negative electrode.

The first electrode may include graphite, and in the polarizing of the slag, oxygen ions in the slag may react with the first electrode and be removed in a form of a CO gas.

Ca elements in the slag may be reduced by being introduced into the molten steel.

The Ca elements may react with sulfur elements in the molten steel to produce CaS.

The CaS may be collected to the slag.

Advantageous Effects

In accordance with the exemplary embodiment, the inclusions and impurity elements in the molten steel may be easily removed by controlling the basicity and the oxidation degree of the slag without using separate additives. That is, as a current is supplied to the slag and the molten steel to induce the polarization phenomenon in the slag, the inclusions and impurity elements in the molten steel may be collected to the slag through the ion-exchange at the interface between the slag and the molten steel. Also, the elements of the molten steel may be adjusted by introducing a specific element of the slag into the molten steel even without using separate additives.

Also, the cleanliness of the molten steel may be prevented from being degraded due to the use of the additives, and the production costs may be prevented from increasing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating a molten steel treatment device in accordance with an exemplary embodiment.

FIG. 2 is a view illustrating a modified example of a power supply module.

FIGS. 3 and 4 are views illustrating a state in which the power supply module is installed in a ladle.

FIG. 5 is a view illustrating a slag polarization phenomenon generated in a process of treating molten steel in a molten steel treatment method in accordance with an exemplary embodiment.

FIG. 6 is a schematic view illustrating an interface reaction generated in the process of treating the molten steel in the molten steel treatment method in accordance with an exemplary embodiment.

FIG. 7 is a graph showing experimental results obtained by controlling a concentration of sulfur in molten steel in the molten steel treatment method in accordance with an exemplary embodiment.

 MODE FOR CARRYING OUT THE INVENTION

Hereinafter, specific embodiments will be described in more detail with reference to the accompanying drawings. The present invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. In the descriptions, the same elements are denoted with the same reference numerals. In the figures, the dimensions of layers and regions are exaggerated for clarity of illustration. Like reference numerals refer to like elements throughout.

FIG. 1 is a schematic view illustrating a molten steel treatment device in accordance with an exemplary embodiment, FIG. 2 is a view illustrating a modified example of a power supply module, and FIGS. 3 and 4 are views illustrating a state in which the power supply module is installed in a ladle.

Referring to FIG. 1, the molten steel treatment device in accordance with an exemplary embodiment may include: a power supply module 100 including a first electrode 110 having an area for covering at least a portion of a melting surface of molten steel and a second electrode 120 electrically separated from the first electrode 110 and vertically extending while passing through the first electrode 110 so that at least a portion there of is dipped into the molten steel; and a power unit 140 connected to the power supply module 100. Here, the power supply module 100 may be provided as one unit and include an insulator 130 disposed between the first electrode 110 and the second electrode 120 to electrically separate the first electrode 110 from the second electrode 120.

The power supply module 100 may be installed to float on an upper portion of the molten steel or installed to a structure such as a ladle cover. In the former case, as illustrate in FIG. 3, the power supply module 100 may be inserted to the upper portion of the molten steel so that the first electrode 110 floats in an upper portion of a slag and a portion of the second electrode 120 is dipped into the molten steel. In the latter case, as illustrated in FIG. 4, when the ladle 10, in which the molten steel is accommodated, is covered by the ladle cover 12 by connecting the power supply module 100 to the ladle cover 12, the first electrode 110 may be disposed on the upper portion of the slag, and a portion of the second electrode 120 may be dipped into the molten steel.

The first electrode 110 may extend in one direction to have an area. For example, the first electrode 110 may have a circular plate shape corresponding to the melting surface of the molten steel. Alternatively, the first electrode 110 may have various shapes. However, the first electrode 110 preferably has a shape corresponding to the melting surface of the molten steel in order to induce polarization over a wide area of the slag. Also, an insertion hole 112 for installing the second electrode may be defined in the first electrode 110. The insertion hole 112 may vertically pass through the first electrode 110. For example, the insertion hole 112 may be defined in a central portion of the first electrode 110. This is for forming a balance of the first electrode 110 at the upper portion of the molten steel or the upper portion of the slag to increase a contact surface with the slag when the first electrode 110 is installed.

The first electrode 110 may be installed so that a bottom surface thereof is contactable to a surface of the slag, to provide, e.g., a current to the slag. Accordingly, the first electrode 110 may be manufactured by using graphite, which has high electrical conductivity, is low in melting loss, and is not reacted with the slag. Here, when the power supply module 100 is inserted to the ladle 10 without being connected to an additional structure, since the first electrode 110 has to maintain a floating state at the upper portion of the slag, the first electrode 110 is preferably made of a material having a specific gravity less than that of the slag.

The second electrode 120 may have a bar shape vertically extending while passing through the first electrode 110. The second electrode 120, which is for supplying a power to the molten steel, may be made of a material, which has high electrical conductivity, is low in melting loss, and is not reacted with molten steel. Here, since the second electrode 120 is dipped into the molten steel, which is greater in temperature than the slag, the second electrode 120 is preferably made of a refractory material having electrical conductivity. For example, the second electrode 120 may be made of a material of Al2O3(MgO)—C.

The insulator 130 may be disposed between the first electrode 110 and the second electrode 120 to electrically separate the first electrode 110 from the second electrode 120. Here, the insulator 130 may have a hollow shape to accommodate the second electrode 120 therein and have opened upper and lower portions to expose the second electrode 120, thereby receiving a power and supplying the power to the molten steel.

When the power supply module 100 is installed in the ladle, the second electrode 120 may be disposed from the upper portion of the slag to the molten steel while the first electrode 110 floats at the upper portion of the slag. Accordingly, since the second electrode 120 is necessarily electrically separated from the first electrode 110 at least in an area in which the second electrode 120 passes through the slag, the insulator 130 preferably has a length H greater than at least a thickness of the slag.

However, an exemplary embodiment is not limited to the above-described structure of the power supply module 100. For example, the power supply module 100 may have various structures capable of supply a power to the slag and the molten steel. For example, referring to (a) of FIG. 2, the second electrode 120 may include an extension part 120a disposed in parallel to the first electrode 110 at a lower portion of the second electrode 120 to increase a contact area with the molten steel.

Alternatively, as illustrate in (b) of FIG. 2, the first electrode 110 and the second electrode 120, each of which has an area, may be vertically separated from each other. Here, the first electrode 110 and the second electrode 120 may have the same area as or an area similar to each other, and may be connected to each other by the insulator 130. Here, the insulator 130 preferably has a length, i.e., a spaced distance between the first electrode 110 and the second electrode 120, greater than the thickness of the slag. Also, a plurality of through holes 122 may be defined in the second electrode 120 to easily install the power supply module 100.

The power unit 140 may be electrically connected to the power supply module 100, i.e., the first electrode 110 and the second electrode 120, to provide a power such as a current or a voltage. The power unit 140 may be installed in the ladle in which the molten steel is accommodated or installed in a separate treatment place.

Also, each of the first electrode 110 and the second electrode 120 may be connected to the power unit 140 through a line. The line may be made of carbon steel or stainless steel covered by a heat dissipation sheath, and be stretchable so that the power supply module 100 is vertically movable according to variation of a molten steel amount in the ladle 10.

Hereinafter, a molten steel treatment method in accordance with an exemplary embodiment will be described.

FIG. 5 is a view illustrating a slag polarization phenomenon generated during treatment of molten steel as the molten steel treatment method in accordance with an exemplary embodiment, and FIG. 6 is a schematic view illustrating an interface reaction generated during the treatment of the molten steel as the molten steel treatment method in accordance with an exemplary embodiment.

An exemplary embodiment may be applied after converter refining before casting, e.g., during transferring molten steel after secondary refining. The exemplary embodiment may control an oxidation degree and basicity of the slag by applying a power to the slag for inducing polarization. Accordingly, inclusions and impurity elements in the molten steel may be picked-up and removed into the slag through ion-exchange at an interface between the slag and the molten steel, and elements of the molten steel may be adjusted by introducing components, which are necessary for adjustment of the elements of the molten steel, into the molten steel from the slag.

When the molten steel, which is completed in converter refining or secondary refining, is prepared, the power supply module 100 is installed in the ladle in which molten steel M is accommodated. Here, the first electrode 110 contacts a slag S formed at an upper portion of the molten steel M, and a portion of the second electrode 120, i.e., a lower portion thereof, is dipped into the molten steel M.

When the power supply module 100 is installed, each of the first electrode 110 and the second electrode 120 is connected to the power unit 140 through a line. Here, when the power unit 140 is installed in the ladle, a process of connecting the power supply module 100 and the power unit 140 may be omitted.

Thereafter, a power is applied to the power supply module 100 through the power unit 140. Here, the power, e.g., voltage, may be applied so that the first electrode 110 has a positive electrode (+) and the second electrode 120 has a negative electrode (−). That is, a surface of the slag, at which the first electrode 110 is disposed, has a positive electrode, and the molten steel, into which the second electrode 120 is dipped, has a negative electrode. Also, a surface of the molten steel, which contacts the slag, may be an interface between an electrode and an electrolyte.

Referring to FIGS. 5 and 6, when a voltage is applied from the power unit 140 to each of the first electrode 110 and the second electrode 120, ions, which are randomly distributed in the slag, move to the first electrode 110 and the second electrode 120 according to polarities. Electric charges, which are charged by the first electrode 110 and the second electrode 120, and ions, which move to satisfy electrical neutrality, are collected at an electrode interface, i.e., the interface between the slag and the molten steel. Accordingly, as negative ions are collected at an upper layer, at which the first electrode 110 is disposed, and positive ions are collected at a lower layer, at which the second electrode 120 is disposed, polarization is generated.

Here, MnO, CaO, and FeO, which are contained in the slag, may be ionized into Mn2+/3+, Ca2+, and Fe2+/3+ ions and free oxygen ions (O2−). The free oxygen ions (O2−) in the slag may move to the first electrode 110 containing graphite to generate an electrochemical reaction, thereby being removed in a form of a CO gas. Also, electrons separated from the free oxygen ions may be supplied to the molten steel through the power unit 140. Also, the Ca2+, Fe2+/3+, and Mn2+/3+ ions move toward the molten steel, into which the second electrode 120 is dipped, i.e., the interface between the slag and the molten steel. The Ca2+, Fe2+/3+, and Mn2+/3+ ions, which move to the interface between the slag and the molten steel, may be reduced and dissolved by electrons, which are supplied to the molten steel, and introduced into the molten steel in a form of Ca, Fe, and Mn.

Through the above-described reaction, MnO and FeO, which affect the oxidation degree of the slag, may be reduced to decrease the oxidation degree of the slag. Also, Ca2+, which affects the basicity of the slag, may be collected at the interface between the slag and the molten steel, to selectively increase the basicity at the lower layer of the slag, which contacts the molten steel. Accordingly, inclusions such as Al2O3 in the molten steel may be collected into the slag to reduce the inclusions in the molten steel.

Also, Ca elements, which are introduced to the molten steel, may react with sulfur elements in the molten steel to produce CaS. That is, the Ca elements, which are introduced from the slag to the molten steel, may serve as additives that are inputted to control the sulfur elements in the molten steel. The CaS, which is generated due to the introduction of the Ca elements, may be collected to the slag, and a concentration of the sulfur elements in the molten steel may decrease.

Hereinafter, an experimental example for verifying effects acquired by inducing the polarization of the slag will be described.

FIG. 7 is a graph showing an experimental result obtained by controlling a concentration of sulfur in the molten steel in a molten steel treatment method in accordance with an exemplary embodiment.

Firstly, an experiment for verifying a reaction generated by introducing the Ca element of the slag into the molten steel is performed.

In the experiment, molten silver containing about 4 ppm of Ca elements is used instead of the molten steel, and CaO—SiO2—Al2O3—MgO slag is used.

In an experimental example 1, 50 g of molten silver (Ag) and 25 g of slag having basicity of 1 are inserted into a melting pot, and maintained for five hours. Thereafter, a content of the Ca element in the molten silver is measured.

In an experimental example 2, 50 g of molten silver (Ag) and 25 g of slag having basicity of 3.2 are inserted into a melting pot, and a voltage of 5V is applied for five hours. Thereafter, the content of the Ca element in the molten silver is measured.

In an experimental example 3, 50 g of molten silver (Ag) and 25 g of slag having basicity of 3.2 are inserted into a melting pot, and a voltage of 10V is applied for five hours. Thereafter, the content of the Ca element in the molten silver is measured.

Results measured in the experimental examples are shown in table 1 below.

TABLE 1 Ag (g)/ Applied Slag (g) Basicity voltage (V) Ca [ppm] Ca [g] Experimental 50/25 1.0 0 9 0.00045 example 1 Experimental 50/25 3.2 5 100 0.005 example 2 Experimental 50/25 3.2 10 200 0.010 example 3

When the table 1 is reviewed, in case of the experimental example 1 without forming the polarization in the slag, it may be seen that a slight amount of Ca elements in the slag is introduced into the molten silver.

On the other hand, in case of the experimental examples 2 and 3 with forming the polarization in the slag by applying a voltage thereto, it may be seen that a quite great amount of Ca elements are introduced into the molten silver in consideration of an initial amount of Ca elements contained in the molten silver. Also, when a magnitude of a voltage applied to the slag is greater under the same condition, it may be seen that an introduced amount of Ca elements increases.

Secondly, an experiment for verifying an effect, in which Ca elements, which are introduced into the molten steel through the polarization of the slag, control sulfur elements in the molten steel, is performed.

The molten steel containing about 80 ppm of sulfur elements and the CaO—SiO2—Al2O3—MgO slag having basicity of 3.2 are inserted into a melting pot, and a power supply module is installed in the melting pot. Also, a power is maintained as it is without being applied to the power supply module at the beginning of the insertion, and then a voltage of 10V is applied during 220 minutes from a time when 175 minutes elapses (395 minutes after the insertion). Also, the concentration of the sulfur in the molten steel is measured for 500 minutes from the time when the molten steel and the slag are inserted into the melting pot, and the measured values are recorded in FIG. 7.

Referring to FIG. 7, the concentration of the sulfur in the molten steel gently decreases before a voltage is applied to the power supply module from the time when the molten steel and the slag are inserted into the melting pot. However, when a voltage is applied to the power supply module, the concentration of the sulfur in the molten steel sharply decreases, and then increases again when time when about 200 minutes elapses after the voltage is applied. Also, when the voltage applied to the power supply module is blocked, the concentration of the sulfur in the molten steel sharply increases again.

At the beginning of the insertion, as the Ca elements in the slag are introduced into the molten steel by an interface reaction between the molten steel and the slag, the concentration of the sulfur in the molten steel gently decreases. However, when the voltage is applied to the power supply module, Ca ions are collected to the interface between the slag and the molten steel due to the polarization of the slag. Due to this, the introduction amount of the Ca elements increases, and the concentration of the sulfur in the molten steel remarkably decreases. Also, when the voltage supplied to the power supply module is blocked, as the ions, which have moved around an electrode, randomly move again, re-sulfurization is generated, and the concentration of the sulfur in the molten steel remarkably increases.

Through the above-described experiments, it may be seen that inclusions and impurity materials in the molten steel may be removed, and element adjustment may be performed without inputting separate additives by controlling the oxidation degree and the basicity of the slag such that the slag is polarized by applying a voltage to the slag and the molten steel during the ladle refining.

Although embodiments have been described with reference to a number of illustrative embodiments thereof, the embodiments are not limited to the foregoing embodiments, and thus, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. Hence, the real protective scope of the present invention shall be determined by the technical scope of the accompanying claims.

INDUSTRIAL APPLICABILITY

The molten steel treatment device and the molten steel treatment method using same in accordance with an exemplary embodiment may easily remove the inclusions and impurity elements in the molten steel by controlling the basicity and oxidation degree of the slag without using separate additives. Thus, the degradation in the cleanliness of the molten steel due to usage of the additives may be prevented, and the increase in production costs due to purchase of the additives may be prevented.

Claims

1. A molten steel treatment device, which is used for ladle refining, comprising:

power supply module comprising a first electrode, a second electrode, and an insulator provided between the first electrode and the second electrode to electrically separate the first electrode from the second electrode; and
a power unit connected to the power supply module,
wherein the first electrode has a plate shape having an area,
the second electrode vertically extends while passing through the first electrode, and
an insulator is provided between the first electrode and the second electrode.

2. The molten steel treatment device of claim 1, wherein an extension part, which has an area and is disposed in parallel to the first electrode, is provided to a lower portion of the second electrode

an insulator is provided between the first electrode and the second electrode.

3. The molten steel treatment device of claim 2, wherein the first electrode comprises a material having a specific gravity less than that of the slag provided on molten steel.

4. The molten steel treatment device of claim 3, wherein the first electrode comprises graphite, and the second electrode comprises a conductive refractory material containing Al2O3(MgO)—C

an insulator is provided between the first electrode and the second electrode to space the first electrode from the second electrode.

5. The molten steel treatment device of claim 1, wherein the power supply module is installed on a ladle cover so that the first electrode and a portion of the second electrode are inserted into a ladle.

6. A molten steel treatment device, which is used for ladle refining, comprising:

a power supply module comprising a first electrode, a second electrode, and an insulator provided between the first electrode and the second electrode to electrically separate the first electrode from the second electrode; and
a power unit connected to the power supply module,
wherein each of the first electrode and the second electrode has a plate shape having an area, and
the insulator has a length greater than a thickness of slag provided on the molten steel.

7. The molten steel treatment device of claim 6, wherein the first electrode comprises a material having a specific gravity less than that of the slag provided on molten steel.

8. The molten steel treatment device of claim 7, wherein the second electrode comprises a conductive refractory material containing Al2O3(MgO)—C.

9. The molten steel treatment device of claim 6, wherein the power supply module is installed on a ladle cover so that the first electrode and a portion of the second electrode are inserted into a ladle.

10. A molten steel treatment method comprising:

preparing slag on molten steel;
contacting a first electrode to at least a portion of the slag and a second electrode to at least a portion of the molten steel; and
polarizing the slag by applying a voltage to the first electrode and the second electrode.

11. The molten steel treatment method of claim 10, wherein the first electrode floats on the slag, and at least a portion of the second electrode is dipped into the molten steel.

12. The molten steel treatment method of claim 11, wherein in the polarizing of the slag, the first electrode is connected to a positive electrode, and the second electrode is connected to a negative electrode.

13. The molten steel treatment method of claim 12, wherein the first electrode comprises graphite, and

in the polarizing of the slag, oxygen ions in the slag react with the first electrode and are removed in a form of a CO gas.

14. The molten steel treatment method of claim 13, wherein Ca elements in the slag are reduced by being introduced into the molten steel.

15. The molten steel treatment method of claim 14, wherein the Ca elements react with sulfur elements in the molten steel to produce CaS.

16. The molten steel treatment method of claim 15, wherein the CaS is collected to the slag.

Patent History
Publication number: 20190309380
Type: Application
Filed: Oct 30, 2017
Publication Date: Oct 10, 2019
Applicant: POSCO (Pohang-si)
Inventor: Wook KIM (Pohang-si)
Application Number: 16/345,522
Classifications
International Classification: C21C 7/00 (20060101); C21C 7/064 (20060101);