KR102300854B1 - Mold flux and method of continuous casting of steel using the same - Google Patents

Abstract

The mold flux according to an embodiment of the present invention relates to a mold flux used in a continuous casting process of steel, and more particularly, it is applied during continuous casting of high-strength high-alloy steel containing a large amount of alloying elements such as Al, Ti, and Mn. It is related to the mold flux based on the 3CaO-2SiO₂-CaF₂ component system.
The mold flux according to the present invention has a crystalline phase in the form of Cuspidine (3CaO-2SiO₂-CaF₂) and a compound between CaO and B₂O₃ so that individual crystal grains are formed small and uniformly compared to the thickness of the slag film. The purpose of the present invention is to provide a mold flux composition and method that fundamentally blocks the occurrence of defects such as cracks on the surface of cast steel and accidents such as breakouts by preventing the sticking phenomenon of the solid film adhering to the surface and ensuring smooth lubrication.

Description

Mold flux and continuous casting method using same

The present invention relates to a mold flux and a continuous casting method using the same, and more particularly, to a mold flux used in a continuous casting process of steel and a continuous casting method using the same.

The continuous casting process of steel has been widely used since the 1960s, and has many advantages, such as productivity improvement and yield improvement, compared to the previous ingot casting process. In the continuous casting process, the quality and productivity of the cast is determined by the control of solidification in the mold.

When molten steel flows into the mold from the tundish, which acts as a kind of buffer, through the immersion nozzle, solidification starts from the meniscus, which is the area where the molten steel and the mold come into contact.

At this time, when the solidification cell formed due to solidification directly comes into contact with the mold, the solidification cell may rupture due to friction between the solidification cell and the mold.

In the continuous casting process, the mold flux applied to the molten steel is melted by the sensible heat of the molten steel and then flows into the mold wall from the meniscus and exists as a slag film. There is a liquid film on the side. Such mold flux controls the rate of heat transfer from the molten steel to the mold wall and has lubricating ability.

Heat transfer through the liquid film and the solid film consists of two paths, conduction and radiation, respectively, and there are five types of thermal resistance related to the slag film including interfacial thermal resistance.

In the initial solidification stage in the mold, that is, in the solidification stage near the meniscus, if the amount of heat is increased above a certain level, cracking defects occur in the surface area, which deteriorates the quality of the final product, A breakout may occur in which the molten steel escapes through a crack and explodes.

In addition, in the process of solidifying the slag film of the mold flux, the crystal grains of the mold flux grow too large to have a size similar to the thickness of the solid film, or secondary crystal phases are generated around the primary crystal phase to form the primary and secondary crystal phases. When this network structure is formed, the solid film may stick to the mold wall without flowing down in the casting direction. Accordingly, the overall effective viscosity of the slag film is increased, and since the non-uniformity of local heat transfer also increases, cracks occur on the surface of the cast steel and further breakouts occur, thereby reducing the quality and productivity of the continuous casting process. .

The conventional mold flux uses CaO-SiO₂-CaF₂ as a basic component, and Na₂O, Al₂O₃, Li₂O, B₂O₃, etc. are appropriately added to adjust physical properties such as crystallization temperature and liquidus viscosity, mainly Cuspidine (3CaO-2SiO₂-CaF₂ ) was formed as the main crystalline phase.

On the other hand, as the demand for high-strength steel with higher strength has increased in recent years, the necessity of manufacturing high-alloy steel containing a large amount of alloying elements such as Al, Mn, and Ti in steel has increased. When casting high alloy steel, alloy components such as SiO₂ and Al, which are the main components of the existing mold flux, react to change the chemical composition of the mold flux. There is a problem of deterioration. Accordingly, there are frequent attempts to develop a new component-based mold flux that does not contain SiO₂, that is, a CaO-Al₂O₃-CaF₂ component-based mold flux, and apply it to high-alloy steel casting. However, unlike the existing CaO-SiO₂-CaF₂ system, it is difficult to control the shape of the crystalline phase in the CaO-Al₂O₃-CaF₂ system, which often reduces the lubrication ability, which is the basic function of the mold flux.

Korean Patent Publication No. 10-0749027

A mold flux and a continuous casting method using the same according to an embodiment of the present invention have the following object in order to solve the above problems.

A mold flux capable of inhibiting the reaction with alloy components, thereby improving the stability of the chemical components of the mold flux, and stably controlling the size of the crystal phases present in the slag film, thereby improving the lubrication ability, and a continuous casting method using the same is in providing.

The problems to be solved of the present invention are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those of ordinary skill in the art from the following description.

The mold flux according to an embodiment of the present invention is a mold flux used for continuous casting, wherein the mold flux has a primary crystalline phase formed of Cuspidine (3CaO-2SiO ₂ -CaF).

The first crystal phase may include calcium oxide (CaO) and boron trioxide (B ₂ O ₃ ).

In the mold flux, silicon dioxide (SiO ₂ ) may be further added in an amount of 5 wt% or more and 15 wt% or less.

The mold flux may have a ratio of CaO-Al₂O₃ of 2 to 5.

The mold flux may maintain the diboron trioxide (B ₂ O ₃ ) in an amount of 10 wt% or more and 30 wt% or less.

inputting a mold flux in which the first crystalline phase is formed of Cuspidine (3CaO-2SiO₂-CaF₂) into the mold; and solidifying the mold flux.

The mold flux and the casting method using the same according to an embodiment of the present invention prevent sticking by maintaining the distribution of crystalline phases inside the solid film in an ideal shape, thereby effectively lowering the amount of heat transferred in the mold, and solidifying in the continuous casting mold It has the effect of improving the lubrication ability between the cell and the mold.

Furthermore, there is an effect that the cast steel surface is beautiful and there is no defect such as cracks, so that it is possible to produce a cast steel of excellent quality.

Effects of the present invention are not limited to those mentioned above, and other effects not mentioned will be clearly understood by those of ordinary skill in the art from the following description.

1 is a schematic diagram schematically illustrating a metallurgical phenomenon occurring in a mold in a continuous casting process;
Figure 2 is a diagram schematically illustrating heat transfer in a mold in the continuous casting process of Figure 1;
3 is a view showing the structure of a crystalline phase of a conventional mold flux,
4 is a view showing the structure of a crystalline phase of a mold flux according to an embodiment of the present invention;
5 is a view comparing the crystal grain size of the mold flux of FIG. 4 and the conventional mold flux;
6 is a flowchart sequentially illustrating a continuous casting method using a mold flux according to an embodiment of the present invention.

Hereinafter, a preferred embodiment according to the present invention will be described in detail with reference to the accompanying drawings, but the same or similar components, regardless of reference numerals, are assigned reference numerals and redundant description thereof will be omitted. In addition, in the description of the present invention, if it is determined that a detailed description of a related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted. In addition, it should be noted that the accompanying drawings are only for easy understanding of the spirit of the present invention and should not be construed as limiting the spirit of the present invention by the accompanying drawings.

4 is a view showing the structure of a crystalline phase of a mold flux according to an embodiment of the present invention, and FIG. 5 is a view comparing the crystal grain size of the mold flux of FIG. 4 and the conventional mold flux.

In the mold flux, the primary crystalline phase (C1) is formed of Cuspidine (3CaO-2SiO₂-CaF₂), and the primary crystalline phase (C1) contains calcium oxide (CaO) and boron trioxide (B₂O₃). Cuspidine is a sorosilicate mineral containing calcium, fluorine and hydroxyl groups. The crystalline phase formed in the solid film exists as a kind of suspended material in the remaining solid glass (G). The effective viscosity of the solid film is determined according to the size, shape, and volume fraction of the suspended material. As shown in FIG. 3 , the effective viscosity of the solid film rapidly increases when a specific crystalline phase grows coarsely. As a result, the lubricating ability may be reduced, the mold may stick to the mold wall, and the solid film may be torn by vibration of the mold, causing local insufficient lubrication and excessive heat transfer. Accordingly, various types of crack defects may occur in the cast steel, and a breakout may occur in which the unsolidified molten steel is ejected between the cracks and explodes. Therefore, it is desirable to control the nucleation of the crystal phase.

In this embodiment, the generation and growth behavior of crystalline phases with respect to the conventional mold flux (A) and the mold flux (B, C) according to an embodiment of the present invention using Differential Scanning Calorimetry (DSC) evaluate the process of

Referring to Table 1, each mold flux is completely melted at 1350°C and then cooled to 600°C at a cooling rate of 10°C per minute. After confirming the temperature at which the phase change was observed, the same mold flux in a separate high-temperature melting furnace cools the samples at the corresponding cooling rate, takes them out of the melting furnace at a temperature several tens of degrees lower than the temperature at which the phase change is confirmed, cools them quickly, and then X-rays the samples. Analyze using a diffractometer and scanning electron microscope.

Oxide
Sample CaO
(weight%) SiO₂
(weight%) Na ₂ O
(weight%) F
(weight%) B ₂ O ₃
(weight%) Li ₂ O
(weight%) Primary crystalline phase (C1) Secondary
crystalline phase (C2) A 44.6 3.2 17.9 21.9 7.8 4.5 CaF₂ CaO.₂Al₂O₃ B 44.2 10.5 10.5 10.4 18.7 5.7 Cuspidine 9CaO.3B₂O₃.CaF₂ C 50.5 14.1 5.7 11.0 12.8 5.8 Cuspidine CaO.B₂O₃

As described above, in the conventional mold flux (A), all of the firstly generated primary crystalline phases (C1) are CaF₂, and the secondary crystalline phases (C2) are CaO·2Al₂O₃. Since CaO-Al₂O₃-CaF₂ is the main component of the conventional mold flux (A), when CaF₂ is formed as the primary crystalline phase (C1), a compound between CaO and Al₂O₃ is formed from the remaining components to prevent rapid growth. can't Accordingly, as shown in FIG. 3 , it can be seen that the secondary crystal phase C2 is coarsely formed, and consequently, the lubrication function is deteriorated during the casting process and defects of the cast steel may occur.

In this embodiment, the mold flux is silicon dioxide (SiO ₂ ) is added in an amount of 5 wt% or more and 15 wt% or less. For example, when silicon dioxide is added up to 15% by weight, 15% by weight or less of silicon dioxide has low activity, which is an index of chemical activity, so that the reduction rate by alloying elements such as Al of alloy steel may be lowered.

In this embodiment, the mold flux has a CaO-Al₂O₃ ratio of 2 to 5. If the ratio of CaO-Al₂O₃ is low and the content of Al₂O₃ is high, the formation of a compound between CaO and Al₂O₃ cannot be prevented and coarse grains are formed. On the other hand, if the ratio of CaO-Al₂O₃ is high and the content of Al₂O₃ is low, the melting point of the mold flux is excessively increased, making it difficult to form a liquid slag film. Therefore, the ratio of CaO-Al₂O₃ is adjusted to prevent the formation of a compound crystal phase between CaO-Al₂O₃ and at the same time to easily form liquid slag.

In this embodiment, the mold flux _{maintains the content of B 2} O ₃ of 10 wt% or more and 30 wt% or less. Even if the primary crystalline phase (C1) is maintained with Cuspidine, there is a limit to the fraction of Cuspidine in the secondary crystalline phase (2) because the mold flux with _{CaO-Al 2} O ₃ -CaF _{2 as its main component has a small content of SiO₂.} . Accordingly, it is possible to add B ₂ O ₃ in the mold flux, B ₂ O ₃ is added when there is a secondary crystal phase (C2) to the crystal phase of Ca0 and B ₂ O ₃ and 9CaO and 3B ₂ O ₃ and CaF₂ be formed . Such a crystalline phase is fine and does not reduce the lubricating ability and prevents the formation of a compound crystalline phase between _{CaO-Al 2} O _{3 that reduces the lubricating ability.}

Meanwhile, FIG. 6 is a flowchart sequentially illustrating a continuous casting method using a mold flux according to an embodiment of the present invention.

A continuous casting method using a mold flux according to an embodiment of the present invention includes the step of injecting the mold flux into the mold (S100) and the step of solidifying the mold flux (S200).

In the step (S100) of injecting the mold flux into the mold, the primary crystalline phase (C1) is formed of Cuspidine (3CaO-2SiO₂-CaF₂), and the mold flux containing calcium oxide (CaO) and boron trioxide (B₂O₃) is applied to the outside. It is supplied from the mold, melted outside the mold, and then put into the mold.

In the solidifying of the mold flux ( S200 ), the thermal resistance of the mold flux is increased, the heat transfer amount is reduced, and the mold flux is solidified.

In this embodiment, the mold flux contains silicon dioxide (SiO₂) in an amount of 5 wt% or more and 15 wt% or less, a CaO-Al ₂ O ₃ ratio of 2 to 5, and a B ₂ O _{3 content} of 10 wt% It is maintained at a content of more than 30% by weight or less.

Specifically, when up to 15% by weight of silicon dioxide is added, silicon dioxide of 15% by weight or less has low activity, which is an index of chemical activity, so that the reduction rate by alloying elements such as Al of alloy steel may be lowered, and CaO-Al _{The ratio of CaO-Al 2} O ₃ is controlled to prevent the formation of a compound crystal phase between ₂ O ₃ and at the same time easily form liquid slag, and the crystalline phase is fine, so CaO does not reduce the lubrication ability and reduces the lubrication ability. -Prevent the formation of a compound crystal phase between _{Al 2} O _{3 .}

The embodiments described in this specification and the accompanying drawings are merely illustrative of some of the technical ideas included in the present invention. Therefore, since the embodiments disclosed in the present specification are for explanation rather than limitation of the technical spirit of the present invention, it is obvious that the scope of the technical spirit of the present invention is not limited by these embodiments. Modifications and specific embodiments that can be easily inferred by a person of ordinary skill in the art within the scope of the technical idea included in the specification and drawings of the present invention are included in the scope of the present invention. will have to be interpreted.

C1: primary crystalline phase
C2: secondary crystalline phase
G: vitreous
A: Conventional mold flux
B, C: mold flux according to an embodiment of the present invention

Claims (10)

delete In the mold flux used for continuous casting and the primary crystal phase is _{formed of Cuspidine (3CaO-2SiO 2 -CaF),}
The mold flux includes calcium oxide (CaO) and boron trioxide (B ₂ O ₃ ),
A mold flux comprising the boron trioxide (B ₂ O ₃ ) in an amount of 10% by weight or more and 30% by weight or less of the total weight of the mold flux. 3. The method of claim 2,
The mold flux is a mold flux in which silicon dioxide (SiO ₂ ) is further added in an amount of 5 wt% or more and 15 wt% or less. 3. The method of claim 2,
The mold flux is a mold flux having a CaO-Al ₂ O ₃ ratio of 2 to 5. delete inputting a mold flux in which the first crystal phase is _{formed of Cuspidine (3CaO-2SiO 2 -CaF) into the mold;} and
Including; solidifying the mold flux;
The mold flux includes calcium oxide (CaO) and boron trioxide (B ₂ O ₃ ),
A continuous casting method using a mold flux comprising 10 wt% or more and 30 wt% or less of the _{boron trioxide (B 2} O ₃ ) in the total weight of the mold flux. delete 7. The method of claim 6,
The mold flux is _{a continuous casting method using a mold flux in which silicon dioxide (SiO 2} ) is further added in an amount of 5 wt% or more and 15 wt% or less. 7. The method of claim 6,
The mold flux is a continuous casting method using a mold flux having a _{CaO-Al 2} O _{3 ratio of 2 to 5.} delete

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