KR20160141124A - Mold flux and method of continuous casting of steel using the same - Google Patents

Mold flux and method of continuous casting of steel using the same Download PDF

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Publication number
KR20160141124A
KR20160141124A KR1020150074863A KR20150074863A KR20160141124A KR 20160141124 A KR20160141124 A KR 20160141124A KR 1020150074863 A KR1020150074863 A KR 1020150074863A KR 20150074863 A KR20150074863 A KR 20150074863A KR 20160141124 A KR20160141124 A KR 20160141124A
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KR
South Korea
Prior art keywords
mold flux
mold
continuous casting
flux
present invention
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KR1020150074863A
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Korean (ko)
Inventor
조중욱
박정혁
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포항공과대학교 산학협력단
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Priority to KR1020150074863A priority Critical patent/KR20160141124A/en
Publication of KR20160141124A publication Critical patent/KR20160141124A/en

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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22DCASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/10Supplying or treating molten metal
    • B22D11/108Feeding additives, powders, or the like
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22DCASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/07Lubricating the moulds
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21CPROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04Removing impurities by adding a treating agent
    • C21C7/076Use of slags or fluxes as treating agents
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02PCLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00Technologies related to metal processing
    • Y02P10/20Process efficiency
    • Y02P10/21Process efficiency by recovering materials
    • Y02P10/242Slag reuse in metallurgical processes

Abstract

Since the mold flux according to an embodiment of the present invention does not contain a fluorine component having high reactivity with water vapor in the mold flux used for continuous casting, So that the lubrication function and the heat transfer control function can be stably maintained during operation and the break-out can be prevented.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold flux and a continuous casting method using the 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 worldwide since the 1960s, and is a widely used process because it has many advantages such as improved productivity and yield compared to the ingot casting process which has been performed before. In the continuous casting process, the quality and productivity of the cast steel are determined by controlling the solidification in the mold.

When the molten steel flows into the mold from the tundish serving as a buffer, through the immersion nozzle, solidification starts from the meniscus, which is the portion where the molten steel and the mold abut.

At this time, when the solidification cell formed by solidification comes into direct contact with the mold, the solidification cell can be ruptured due to the friction between the solidification cell and the mold. Therefore, a mold flux serving as a lubricant is injected between the mold wall and the solidification cell.

In the continuous casting process, the mold flux applied to the bath surface is dissolved in the sensible heat of the bath surface molten steel, then flows into the mold wall surface from the meniscus portion and is present as a slag film. A solid film is present near the mold wall surface, There is a liquid film. Such a mold flux controls the rate of heat transfer from the molten steel to the mold wall surface, and has a lubricating ability.

The heat transfer through the liquid film and the solid film consists of two paths, conduction and radiation, respectively, and there are five kinds of heat resistance related to the slag film including the interface thermal resistance.

If the total heat becomes larger than a certain amount in the initial solidification step in the mold, that is, in the solidification step near the meniscus, a cracking defect occurs on the surface portion, which deteriorates the quality of the final product, A breakout may occur in which the molten steel exits through a crack and explodes.

Also, during the solidification of the slag film of the mold flux, the crystal grains of the mold flux are excessively grown to have a size similar to the thickness of the solid phase film, or a secondary crystal phase is generated around the primary crystal phase, When the network structure is formed, the solid film can stick to the mold wall surface without flowing down in the casting direction. As a result, the overall effective viscosity of the slag film is increased, and the nonuniformity of the local heat transfer is also increased, so that cracks are generated on the surface of the cast steel, and breakout occurs, thereby deteriorating the quality and productivity of the continuous casting process .

In the conventional mold flux, CaO-SiO2-CaF2 was used as a basic component and Na2O, Al2O3, Li2O, B₂O₃ were appropriately added to adjust the physical properties such as crystallization temperature and liquid viscosity. Cuspidine (3CaO-2SiO₂-CaF2 ) As a main crystal phase.

It has been widely known that break-out accidents occur frequently due to seasonal factors, especially wet atmospheres in summer, when producing such steels by continuous casting using such conventional mold fluxes. Although the cause of this phenomenon has not yet been clarified, it has been clarified that the H 2 O in the wet atmospheric air is indirectly penetrated into the slag or via the molten steel and exists as an OH- group, thereby excessively promoting the crystallization behavior of the mold flux, It is presumed that the lubricating function is deteriorated and eventually breakout occurs. If breakout occurs during continuous casting operation, it must be suppressed as it is not only a direct repair cost but also an additional cost due to production disruption. In order to prevent the occurrence of breakout concentrated in the summer, measures are taken to measure the hydrogen concentration in the molten steel during continuous casting operation and to reprocess the molten steel without performing continuous casting operation when the molten steel is above a certain level (for example, 10 ppm or more) It is not possible to provide a solution to the problem.

Korean Patent Registration No. 10-0749027

The mold flux and the continuous casting method using the same according to an embodiment of the present invention are intended to solve the above-mentioned problems.

By using the mold flux not containing fluorine, it is possible to prevent the chemical components from being changed due to seasonal factors, thereby improving the lubricity in continuous casting of steel or metal and controlling the heat transfer and deteriorating the quality and productivity of the cast steel And a continuous casting method using the same.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide an apparatus and method for controlling the same.

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 crystallization start temperature independent of the magnitude of the partial pressure of water vapor in the atmospheric gas and does not contain a fluorine component.

The mold flux may be added in an amount of 3% or more and 10% or less of magnesium oxide (MgO).

The mold flux may be added in an amount of 10% or more and 30% or less of boron trioxide (B₂O₃).

A continuous casting method using a mold flux according to an embodiment of the present invention includes the steps of injecting a mold flux having a crystallization starting temperature independent of the magnitude of the steam partial pressure in the atmospheric gas and containing no fluorine component into the mold; And solidifying the mold flux.

The mold flux and the continuous casting method using the mold flux according to an embodiment of the present invention can prevent the occurrence of a component change and a physical property change due to the presence of a large amount of OH groups in the slag by using the mold flux not containing fluorine It is possible to maintain the distribution of the crystal phase inside the solid film in an ideal form at the inner wall of the mold, to prevent the solidification of the solid film, and to improve the lubricating ability between the solidification cell and the mold in the mold.

The effects of the present invention are not limited to those mentioned above, and other effects not mentioned can be clearly understood by those skilled in the art from the following description.

1 is a schematic view schematically showing metallurgical phenomena occurring in a mold in a continuous casting process,
Fig. 2 is a view schematically showing heat transfer in a mold in the continuous casting process of Fig. 1,
3 is a view showing a crystalline phase of a conventional mold flux,
FIG. 4 is a view showing a crystalline phase of a mold flux according to an embodiment of the present invention,
Fig. 5 is a diagram comparing the crystallization start temperature according to the partial pressure of steam in the atmospheric gas with respect to the mold flux of Fig. 4 and the mold flux of Fig. 3,
FIG. 6 is a view sequentially illustrating a continuous casting method using a mold flux according to an embodiment of the present invention.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings, wherein like or similar elements are denoted by the same reference numerals, and redundant description thereof will be omitted. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. It is to be noted that the accompanying drawings are only for the purpose of facilitating understanding of the present invention and should not be construed as limiting the scope of the present invention.

FIG. 4 is a view showing a crystalline phase of a mold flux according to an embodiment of the present invention, FIG. 5 is a graph showing the relationship between the crystallization start temperature according to the partial pressure of steam in the atmospheric gas with respect to the mold flux of FIG. 4 and the mold flux of FIG. FIG.

The mold flux has a crystallization initiation temperature independent of the magnitude of the steam partial pressure in the atmospheric gas, and does not contain a fluorine component. The crystalline phase to be formed in the solid-state film is suspended in a glass (G) of the remaining solid phase. 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 solid phase film has a specific crystal phase grown to a great extent, The effective viscosity increases sharply and the lubricating ability may deteriorate and may stick to the mold wall surface and the solid film may be torn by the vibration of the casting mold, resulting in local lack of lubrication and excessive heat transfer. As a result, various types of crack defects are generated in the cast steel, and breakout occurs in which the non-solidified molten steel inside the cracks is ejected and exploded. Thus, it is desirable to control nucleation of the crystalline phase.

In this embodiment, the process of crystal phase production and growth behavior is evaluated for a conventional mold flux A using a single hot thermocouple technique (SHTT) and a mold flux B according to an embodiment of the present invention.

Referring to Table 1, each mold flux is completely melted at 1350 degrees Celsius and then cooled to room temperature at a cooling rate of 20 degrees and 50 degrees per minute.

Chemical Composition (mass%) SiO2 CaO MgO Al₂O₃ Na2O F B₂O₃ CaO / SiO2 A 33.4 44.8 0.8 5.4 7.6 7.6 1.34 B 31.3 39.0 4.5 6.5 8.6 8.1 1.25

Thus, as shown in Fig. 5A, the conventional mold flux A has a crystallization starting temperature which is increased by at least 100 degrees relative to the second atmosphere D in the first atmosphere W, It can be seen that it is rapidly promoted. On the other hand, as shown in FIG. 5B, the mold flux B according to the embodiment of the present invention has the crystallization start temperature almost coincident with the first atmosphere W and the second atmosphere D It can be seen that the crystallization behavior is not affected by the partial pressure of steam in the atmospheric gas. Here, the first atmosphere (W) refers to the wetted atmosphere and the second atmosphere (D) refers to the dry atmosphere.

When the partial pressure of steam in the atmospheric gas is high, the OH-group increases in the slag according to the formula (1).

≪ Formula 1 >

Figure pat00001

The OH-group is then reacted with fluorine in the slag to produce hydrogen fluoride gas by the formula (2).

≪ Formula 1 >

Figure pat00002

As a result, the water vapor in the atmosphere removes the fluorine ions in the slag and increases the oxygen ions. As a result, the first primary crystal phase (C1), which is first formed in the mold flux, is changed from Cuspidine to 2Cao.SiO2, . In addition, the fraction of the crystalline phase in the solid film formed on the wall surface of the mold at the same position also increases sharply, so that the lubricating ability of the mold flux can be drastically reduced finally.

Therefore, the mold flux according to one embodiment of the present invention is formed so as not to contain a fluorine component, and magnesium oxide (MgO) is added in an amount of 3% or more and 10% or less to replace fluorine, Is added in an amount of 10% or more and 30% or less.

Accordingly, even when the OH group is present in the slag, no hydrogen fluoride (HF) gas is generated, and no change in the chemical composition of the slag or a change in the physical properties due to the change occurs. Further, by adding magnesium oxide and B 2 O 3, the viscosity of the liquid slag can be lowered and the liquid phase viscosity can be maintained.

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 a step (S100) of injecting a mold flux into a mold and a step (S200) of solidifying the mold flux.

The step (S100) of injecting the mold flux into the mold has a crystallization starting temperature independent of the magnitude of the partial pressure of steam in the atmosphere gas, and the mold flux not containing the fluorine component is supplied from the outside and melted outside the mold, .

The step of solidifying the mold flux (S200) increases the heat resistance of the mold flux, reduces the amount of heat, and solidifies the mold flux.

In this embodiment, magnesium oxide (MgO) is added in an amount of not less than 3% and not more than 10% to replace fluorine, and B₂O₃ is added in an amount of not less than 10% and not more than 30%. Accordingly, even when the OH group is present in the slag, no hydrogen fluoride (HF) gas is generated, and no change in the chemical composition of the slag or a change in the physical properties due to the change occurs. Further, by adding magnesium oxide and B 2 O 3, the viscosity of the liquid slag can be lowered and the liquid phase viscosity can be maintained.

The embodiments and the accompanying drawings described in the present specification are merely illustrative of some of the technical ideas included in the present invention. Therefore, it is to be understood that the embodiments disclosed herein are not for purposes of limiting the technical idea of the present invention, but are intended to be illustrative, and thus the scope of the technical idea of the present invention is not limited by these embodiments. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents. It should be interpreted.

C1: primary crystal phase
C ': first crystal phase
G: vitreous
W: First atmosphere
D: Second atmosphere

Claims (6)

  1. In the mold flux used for continuous casting,
    Wherein the mold flux has a crystallization initiation temperature independent of the magnitude of the partial pressure of steam in the atmospheric gas, and does not contain a fluorine component.
  2. The method according to claim 1,
    Wherein the mold flux is added in an amount of 3% or more and 10% or less of magnesium oxide (MgO).
  3. The method according to claim 1,
    Wherein the mold flux is doped with boron trioxide (B₂O₃) in an amount of 10% or more and 30% or less.
  4. Injecting a mold flux having a crystallization starting temperature independent of the magnitude of the steam partial pressure in the atmospheric gas and containing no fluorine component into the mold; And
    And then solidifying the mold flux.
  5. 5. The method of claim 4,
    Wherein the mold flux is added with magnesium oxide (MgO) in an amount of 3% or more and 10% or less.
  6. 5. The method of claim 4,
    Wherein the mold flux is added with boron trioxide (B₂O₃) in an amount of 10% or more and 30% or less.

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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100749027B1 (en) 2006-06-23 2007-08-07 주식회사 포스코 Continuous casting machine and method using molten mold flux

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100749027B1 (en) 2006-06-23 2007-08-07 주식회사 포스코 Continuous casting machine and method using molten mold flux

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