KR101320031B1 - Mole flux for high oxygen steel and Continuous casting method using the same - Google Patents

Abstract

The present invention relates to a mold flux for continuous casting of high oxygen-containing steel to suppress the occurrence of foaming defects on the surface of the cast steel, and a continuous casting method of high oxygen-containing steel using the same, in particular the continuous cast of high oxygen-containing steel according to an embodiment of the present invention The crude mold flux is a continuous casting mold flux of steel containing a large amount of oxygen, and contains CaO and SiO ₂ as main components, less than 1 wt% of C, and Al as an exothermic component.

Description

Mold flux for continuous casting of high oxygen-containing steel and continuous casting method for high oxygen-containing steel using same

The present invention relates to a mold flux for continuous casting of high oxygen-containing steel, and a continuous casting method of high oxygen-containing steel using the same, and more particularly, a mold flux for continuous casting of high oxygen-containing steel that suppresses the occurrence of bubble defects on the surface of the cast steel and It relates to a continuous casting method of the used high oxygen-containing steel.

In general, the molten iron produced in the blast furnace in the steel production process is refined in the blast furnace and then produced into cast steel after the secondary refining process and continuous casting process. Currently, most of the cast steel produced in the continuous casting process is deoxidized steel with less than 2-3 ppm of free oxygen in molten steel. In the secondary refining process, it is common to deoxidize with ferroalloy to completely remove free oxygen of molten steel.

Recently, however, a technique for finely dispersing inclusions in cast steels has emerged by intentionally forming fine inclusions by reacting dissolved oxygen in the steel with a deoxidizer component while the molten steel is solidified into cast steels. Accordingly, a technique has been attempted to perform a continuous casting process while maintaining free oxygen in steel from tens to hundreds of ppm.

However, in the continuous casting process of the dissolved oxygen-containing molten steel, a large amount of high melting point compound is formed due to the reaction of the oxide and the mold flux determined during the continuous casting, and the fluidity of the mold slag is sharply deteriorated, resulting in breakout. Caused an accident. In addition, a large amount of gaseous defects occurred on the surface of the cast steel due to the generation of CO gas due to the reaction between the carbon component and the solid solution oxygen in the mold flux.

As a result, the process was applied to the mold flux from which all the carbon was removed during continuous casting of the steel containing the dissolved solid oxygen. However, as the melt rate of the mold plus was controlled irregularly during the operation operation, irregular heat transfer behavior appeared to deteriorate the surface quality of the cast steel. In addition, the removal of carbon in the mold flux encouraged aggregation between mold fluxes, thereby promoting mold flux solidification due to the reaction with the aforementioned high melting point compound.

In addition, due to the lack of heat retention of the mold flux due to the removal of carbon in the mold flux, the temperature of the molten steel surface in the mold is lowered and cooled to a temperature below the liquidus level, resulting in a Decel defect in which the molten steel surface is locally solidified. The slag rim grew excessively. In this case, overgrowth of the meniscus solidification shell was encouraged, and nonmetallic inclusions and gas bubbles in molten steel were easily collected in the initial solidification shell, adversely affecting operation and quality.

Therefore, in the related art, carbon is lowered in the mold flux during continuous casting, and alloy elements such as Ca-Si and Mg-Al are burned to ensure heat retention. However, in order to provide oxygen to the mold flux, separate iron oxide and manganese oxide were added. However, the total amount of iron oxide and manganese oxide could not be reduced, but remained in the mold flux, resulting in an increase in the viscosity to worsen the inflow into the mold. In addition, alloy elements which are exothermic components such as Ca-Si and Mg-Al are expensive, resulting in cost increase and limiting their use.

Japanese Laid-Open Patent No. 2007-130684

Embodiment of this invention provides the mold flux for continuous casting of high oxygen containing steel which can suppress generation | occurrence | production of foaming defect on the surface of a cast steel during continuous casting of high oxygen containing steel, and the continuous casting method of high oxygen containing steel using the same.

In particular, the mold flux for continuous casting of high-oxygen-containing steel that can suppress the occurrence of pinholes and blowholes, which are excellent in dequel suppression and gaseous defects in the surface of cast steels, and high oxygen-containing content Provide continuous casting of steel.

In addition, during the continuous casting operation, the flux between the fluxes does not occur, and the solid flux due to the reaction between the mold flux and the crystallized oxide does not occur. to provide.

In addition, there is provided a mold flux for continuous casting of high oxygen-containing steel and a continuous casting method of high oxygen-containing steel using the same can reduce the production cost.

Continuous casting mold flux of high oxygen-containing steel according to an embodiment of the present invention is a continuous casting mold flux of a steel containing a large amount of oxygen, containing CaO and SiO ₂ as a main component, C more than 0wt% to less than 1wt% It is characterized in that it contains Al as an exothermic component.

The content of Al is characterized in that 3 to 7wt%.

The ratio of CaO / SiO ₂ is characterized in that 0.8 to 1.1.

The mold flux is characterized in that containing 3 to 10wt% Al ₂ O ₃ .

The mold flux is characterized by containing more than 0wt% to 5wt% of MgO.

The mold flux is characterized in that the total content of Na ₂ O, Li ₂ O and F is 10 to 20wt%.

The mold flux is characterized in that the melting point is 1000 ~ 1250 ℃.

The viscosity of the mold flux is characterized in that 2.5 to 4.0 poise at 1300 ℃.

The mold flux is characterized in that it is produced in powder form.

The mold flux is characterized in that it does not contain iron oxide or manganese oxide for supplying oxygen.

Continuous casting method of high oxygen-containing steel according to an embodiment of the present invention is a method for continuous casting by injecting molten steel having a dissolved oxygen content of 200ppm or more into a mold, comprising the step of injecting a mold flux to the molten steel in the mold The mold flux contains CaO and SiO 2 as main components, contains C at more than 0 wt% to less than 1 wt%, and contains Al as an exothermic component.

The content of Al is characterized in that 3 to 7wt%.

The mold flux is characterized in that it does not contain iron oxide or manganese oxide for supplying oxygen.

According to an embodiment of the present invention, the present invention contains Al as an additional exothermic component in the mold flux added to the mold when continuously casting high oxygen-containing high oxygen-containing steel, thereby suppressing the creation of dekels. can do. In particular, it is excellent in the effect of dekel suppression, and it is possible to suppress the generation of pinholes and blow holes, which are gaseous defects in the surface of the cast steel.

In addition, by using Al, which has a high deoxidation efficiency and low cost as a heat generating component, compared to Ca-Si, Mg-Si, Ca-Al, etc., which is used as a conventional heat generating component, the surface tension is increased by deoxidizing the surface of the dissolved oxygen-containing steel. Can be. Thereby, while it is possible to suppress the bubble defects on the surface of the cast steel, it is possible to suppress the solidification phenomenon of the mold flux.

In addition, conventionally, iron oxide or manganese oxides such as Fe ₂ O 3 and FeO were separately added to provide oxygen in the mold flux during continuous casting, but according to the embodiment of the present invention, the total amount of the exothermic components added to the mold flux is high oxygen. As it reacts sufficiently with oxygen contained in a large amount of molten steel for the containing steel, all of the oxidized powder in the mold flux remains. Accordingly, it is possible to omit adding iron oxide or manganese oxide separately as in the conventional combustion casting.

In addition, production cost can be reduced by using inexpensive Al without using expensive alloying elements such as Ca-Si, Mg-Si, Ca-Al, and the like.

1 is a table showing the chemical components and physical properties of the present invention and comparative examples,
2 is a graph showing the results of the bubble defect index on the surface of the cast steel of the examples of the present invention and the comparative example.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It will be apparent to those skilled in the art that the present invention may be embodied in many 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, It is provided to let you know.

First, the mold flux for continuous casting of high oxygen-containing steel according to an embodiment of the present invention is a mold flux used for the combustion casting of molten steel having a dissolved oxygen content of 200 ppm or more, and contains Al as an exothermic component, and has basicity and melting. It consists of a component which adds a small amount of carbon while controlling a point and a viscosity appropriately.

Therefore, when the mold flux of the present invention is applied to continuous casting of solid-zone oxygen-containing molten steel, the amount of heat generated is higher than that of mixed alloy-based pyrogenic elements such as Ca-Si and Mg-Al, which have been used as conventional heating elements. It is very effective in decal suppression and cast surface quality improvement. In addition, Al has a very high deoxidation efficiency, which is used as a deoxidizer and a heating agent in the steelmaking process, and has a lower cost than mixed alloy iron such as Ca-Si and Mg-Al, which has been used as an exothermic component. By deoxidation, it is also possible to reduce surface foaming defects by increasing surface tension. In addition, since molten steel contains dissolved oxygen in molten steel, Al, which is an exothermic component added to the mold flux, is completely oxidized to leave no microoxides in the mold plus, thereby providing iron in the existing mold flux. The addition of a cargo or manganese oxide is possible.

Mold casting for continuous casting of high oxygen-containing steel according to an embodiment of the present invention having such a property is made of CaO and SiO ₂ as a main component to facilitate the adjustment of physical properties such as solidification temperature, viscosity and crystallization behavior during solidification The total content of CaO and SiO ₂ is 70 to 80 wt%, and the ratio of CaO / SiO ₂ is 0.8 to 1.1. The remaining components other than CaO and SiO ₂ are composed of components or impurities for forming physical properties of the mold flux. Preferably it contains less than 1 wt% of C, and 3 to 7 wt% of Al as the exothermic component.

The mold flux contains 3-10 wt% of Al ₂ O ₃ , contains less than 5 wt% of MgO, and contains Na ₂ O, Li ₂ O, and F, wherein Na ₂ O, Li ₂ O, and It is preferable that the sum of content of F is 10-20 wt%.

In addition, it is preferable that the melting point of the mold flux is 1000 to 1250 ° C, and the viscosity is 2.5 to 4.0 poise at 1300 ° C. In addition, the mold flux is preferably produced in powder form.

In addition, it is possible to omit adding iron oxide or manganese oxide, such as Fe ₂ O ₃ , FeO, to the mold flux separately.

Hereinafter, each component constituting the mold casting flux for continuous casting of high oxygen-containing steel according to an embodiment of the present invention, the reason for adding the same, and an appropriate content range thereof will be described.

1) CaO / SiO ₂ : 0.8 ~ 1.1

The reason for limiting the analogy value of CaO / SiO ₂ to 0.8 ~ 1.1 is that when the CaO / SiO ₂ value is less than 0.8, the viscosity of molten steel is excessively increased, thereby reducing the incorporation of the molten flux to the surface of the slab, thereby reducing the inflow rate. This is because an operation accident called binding break out is likely to occur.

In the case where the value of CaO / SiO ₂ exceeds 1.1, the high and the solidification temperature of the mold flux, it is impossible to maintain stably the unreacted mold flux layer upper surface of the mold during casting. This phenomenon is localized due to the intermittent exposure of molten steel during casting, which leads to a local increase in the amount of inclusions, leading to surface defects.

2) C: more than 0wt% to 1wt% or less

C generally serves to control the melt rate of the mold flux, to insulate the molten steel, and to increase the temperature of the meniscus portion of the cast to weaken the oscillation mark to reduce surface defects. In addition, C suppresses the aggregation phenomenon between the mold flux particles to improve the operability.

If the content of C exceeds 1 wt%, C reacts with the dissolved oxygen of the high oxygen-containing molten steel to form CO gas, and the upper limit of C is increased by 1 wt% as the CO gas increases the foaming surface defect of the cast steel. It is preferable to limit to.

3) Sum of Al: 3 ~ 7wt%

Al reacts with dissolved oxygen in molten steel to generate heat of oxidation to increase heat retention, prevent deckle defects that the molten steel surface solidifies, and raise the temperature of the meniscus of the cast steel to cause oscillation marks. mark) and at the same time reduce the surface defects of the cast steel. In addition, through the effective deoxidation effect through the reaction with the solid-zone oxygen on the molten steel surface, the surface tension of the molten steel surface is increased and Al ₂ O ₃ is formed at the same time. When the Al component range is less than 3%, sufficient exothermic ability and deoxidation power cannot be exhibited, and when Al exceeds 7%, excessive reaction with molten steel occurs, resulting in increased fume generation during operation and microoxidation. Due to the generation of Al, the viscosity rises, and the coagulation imbalance may occur due to the decrease in fluidity and the nonuniformity of consumption.

4) Al ₂ O ₃ : 3 ~ 10 wt%

Al ₂ O ₃ increases the viscosity of the mold flux and at the same time increases the solidification temperature. By adding the amount of unavoidable oxide contained in the molten slag by the oxidation reaction due to the addition of Al, Al ₂ O ₃ must be added in a reduced amount in conjunction. Al ₂ O ₃ is insufficient, the viscosity is a synergistic effect and the solidification temperature is less than 3wt% and was the lower limit value to 3wt%. If Al ₂ O ₃ exceeds 10wt%, the viscosity and solidification temperature becomes too high to reduce the melting flux to the cast surface, and the crystallization during solidification becomes unstable, making it difficult to control stable heat transfer to the mold. It is desirable to limit the upper limit to 10wt% because it increases the likelihood of product defects.

5) MgO: Below 5wt%

MgO increases the solidification temperature of the mold flux or controls physical properties such as crystallization characteristics during solidification. If the MgO exceeds 5 wt%, the solidification temperature becomes too high to reduce the incorporation of the molten flux to the surface of the cast, and the crystallization during solidification becomes unstable, making it difficult to control stable heat transfer from the mold, resulting in solidification imbalance of molten steel. As a result, product defects are more likely to occur, so the upper limit of the MgO content is preferably limited to 5 wt%.

6) Sum of Na ₂ O, Li ₂ O and F: 10 ~ 20 wt%

Na ₂ O, Li ₂ O and F as a network modifier (network modifier) serves to lower the viscosity and solidification temperature by cutting the structure of the silicate (Silicate). However, if the total amount of Na ₂ O, Li ₂ O and F exceeds 20wt%, the viscosity and solidification temperature are too low to increase the flow rate of the mold flux, but the oscillation mark is deepened and the melting of the immersion nozzle increases. It is preferable to limit the upper limit to 20wt%.

On the other hand, if the total amount of Na ₂ O, Li ₂ O, and F is less than 10 wt%, the viscosity and solidification temperature are too high to reduce the melting flux to the surface of the cast steel, and the possibility of operation accidents such as restrictive breakout due to the inflow decrease. Since it becomes large, it is preferable to limit a lower limit to 10 wt% or less.

7) Melting Point: 1000 ~ 1250 ℃

When the solidification temperature of the mold flux is lower than 1000 ° C., the flow rate between the solidification shell and the mold is increased to easily cause defects in mold flux inclusions in molten steel. In addition, when the solidification temperature is higher than 1250 ℃, the flow rate of the mold flux is reduced, but due to the increased frictional resistance in the mold, there is a high possibility of an operation accident such as a constraint breakout. Therefore, in order to control the appropriate consumption amount of the mold flux aimed at by this invention, it is preferable to limit the range of solidification temperature to 1000-1250 degreeC.

8) Viscosity: converted value at 1300 ℃ 2.5 ~ 4.0 poise

Viscosity is a physical property that greatly affects the inflow of mold flux. When the viscosity of the converted value is lower than 2.5 poise at 1300 ° C, the inflow is increased to easily cause defects in mold flux inclusions in molten steel. On the other hand, when the viscosity of the converted value is higher than 4.0 poise at 1300 ℃, the flow rate of the molten mold flux to the slab surface is reduced, but due to the increased frictional resistance in the mold, there is a high possibility of operation accidents such as restrictive breakout. Therefore, in order to control the appropriate consumption amount of the mold flux aimed at by this invention, it is preferable to limit the viscosity range of the mold flux to 2.5-4.0 poise by conversion value at 1300 degreeC.

9) Particle shape: Powder

In the present invention, the particle shape of the mold flux is preferably in the form of powder rather than granules in order to increase the reaction efficiency with high oxygen molten steel. This is because it is difficult to produce the Al component in a granular form, and the efficiency of the reaction with the molten steel surface is poor when producing the granular form, and the non-metallic oxide of Al remains in the mold flux.

10) iron oxide or manganese oxide: not added

Conventionally, iron oxide or manganese oxide, such as Fe 2 O 3 and FeO, was added separately to provide oxygen in the mold flux during continuous casting, but according to an embodiment of the present invention, an exothermic component such as Al added to the mold flux has a considerable deoxidizing power. Since the total amount of Al contained in the molten steel for high oxygen is sufficiently reacted with the oxygen, all of the Al is oxidized, so that the unoxidized component in the mold flux remains. Accordingly, it is possible to omit adding iron oxide or manganese oxide separately as in the conventional combustion casting.

The mold flux formed as described above is preferably used in a combustion casting process in which molten steel having a dissolved oxygen content of 200 ppm or more is injected into a mold and cast.

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

(Example)

In order to confirm the effect of the mold flux for continuous casting of the high oxygen-containing steel according to an embodiment of the present invention, the result was evaluated after performing a continuous casting test after manufacturing the mold flux.

Test conditions and test results of the Invention Examples and Comparative Examples are shown in FIG. 1.

As can be seen from Figure 1, four types of mold fluxes of the invention example and one comparative example were prepared. In Examples 1 to 4, the total content of Al was changed. While measuring physical properties such as viscosity, melting point and the like at a solidification temperature of 1300 ° C., a continuous casting test of 300 tons capacity of high oxygen molten steel was performed.

The composition of the high oxygen molten steel used in the continuous casting test is C: 0.002 to 0.003 wt%, Mn: 0.2 to 0.4 wt%, S: 0.02 wt% or less, P: 0.01 wt% or less, and ZrO ₂ sensor in a tundish The dissolved oxygen measured using was 300 ~ 400ppm. A slab with a mold size of 1300 mm x 250 mm was cast, and the bubble index in the surface of the cast piece was visually determined to determine the defect index. Here, the bubble defects refer to pin-holes and blow holes.

In the measurement of foaming defects, after cutting the second cast from the cast slab to 1300mm x 1000mm x 250mm, foaming defects of 0.5 cm or more in size were measured for the surface layer of the upper slab in the casting direction. The foamability index is shown in Figs. 1 and 2 by converting the number of foaming defects of the comparative example into 100, and indexing the foaming defects of the respective inventive examples and comparative examples.

As can be seen in the table of FIG. 1 and the graph of FIG. 2, Inventive Examples 1 to 3 are mold fluxes according to embodiments of the present invention, and the component content and physical properties in the mold fluxes fall within the limited ranges of the aforementioned components. The mold fluxes of Inventive Examples 1 to 3 were utilized for continuous casting of high oxygen-containing steels with dissolved oxygen of 300 to 400 ppm, and were determined to have a foam surface defect index of 10 or less even under severe conditions. The solidification phenomenon did not occur, indicating very good operability.

Inventive Example 4 is a data showing the effect on the addition of Al, which is the main component of the present invention, and is a mold flux deviating from the Al ratio range, viscosity and melting point limited for the preferred embodiment of the present invention. As a result, it can be seen that the slab surface bubble defect number (= defect index) is 38, which is 62% lower than the defect number 100 of the comparative example. However, the bubble surface defect index showed a somewhat higher value than Inventive Examples 1 to 3.

On the other hand, Comparative Example is a mold flux that is widely used in the production of general ultra low carbon steel without addition of Al, which is a main component of the present invention, and when the mold flux according to Comparative Example 1 is used for high oxygen molten steel, A large amount of foaming defects on the surface of the slab was more than 10 times that of the mold fluxes of Inventive Examples 1 to 3. This is because a high content of C in the mold flux and a component capable of deoxidizing the molten steel surface are not added, and thus, the CO gas-based bubbles generated due to low surface tension are attached to the meniscus, and thus a large amount of foaming defects is generated.

Although the present invention has been described with reference to the accompanying drawings and the preferred embodiments described above, the present invention is not limited thereto but is limited by the following claims. Accordingly, those skilled in the art will appreciate that various modifications and changes may be made thereto without departing from the spirit of the following claims.

Claims (13)

Mold casting for continuous casting of steel containing a large amount of oxygen,
It contains CaO and SiO2, contains C in excess of 0wt% to less than 1wt%, 3 to 7wt% of Al as an exothermic component,
The mold flux for continuous casting of high oxygen-containing steel that does not contain iron oxide or manganese oxide for supplying oxygen.
The method according to claim 1,
The mold flux is a mold flux for continuous casting of high oxygen-containing steel comprising 3 ~ 10wt% Al2O3, more than 0wt%-5wt% or less MgO and a total content of 10 ~ 20wt% Na2O, Li2O and F.
The method according to claim 1,
Mold casting flux for continuous casting of high oxygen-containing steel, the ratio of CaO / SiO 2 is 0.8 ~ 1.1.
The method according to claim 1,
The mold flux is a mold flux for continuous casting of high oxygen-containing steel containing Al ₂ O ₃ 3 ~ 10wt%.
The method according to claim 1,
The mold flux is a mold flux for continuous casting of high oxygen-containing steel containing MgO in more than 0wt% to 5wt%.
The method according to claim 1,
The mold flux is a mold flux for continuous casting of high oxygen-containing steel having a total content of Na ₂ O, Li ₂ O and F of 10 to 20wt%.
The method according to claim 1,
The mold flux has a melting point of 1000 ~ 1250 ℃,
The mold flux of the mold flux for continuous casting of high oxygen-containing steel is 2.5 ~ 4.0 poise at 1300 ℃.
delete The method according to claim 1,
The mold flux is a mold flux for continuous casting of high oxygen-containing steel is produced in powder form.
delete As a method of continuous casting by injecting molten steel having a dissolved oxygen content of 200ppm or more into a mold,
Injecting a mold flux into the molten steel in the mold;
The mold flux contains CaO and SiO 2, contains C more than 0wt% to less than 1wt%, 3 to 7wt% of Al as an exothermic component,
The mold flux is a continuous casting method of high oxygen-containing steel that does not contain iron oxide or manganese oxide for supplying oxygen. delete delete

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