CN111604483A - Ultra-high-speed thin slab continuous casting mold flux for medium-carbon low-alloy steel - Google Patents

Abstract

The invention discloses an ultra-high-speed thin slab continuous casting mold powder suitable for casting medium _- carbon low-alloy steel. , Al ₂ O ₃ : 5-7%, MgO: 4-7%, Na ₂ O: 5-8%, K ₂ O: 0-1%, CaF ₂ : 8-10%, Fe ₂ O ₃ : 0 ~1%, Li ₂ O: 1-2%, C: 8-10%, and the balance is unavoidable impurities. Its basicity (CaO/SiO ₂ ) is 1.5 to 1.7, its melting point is 1090 to 1110°C, and its viscosity at 1300°C is 0.01 to 0.03 Pa·s. In the present invention, the basicity is appropriately increased and the protection is reduced by adjusting the components of the ultra-high-speed thin slab continuous casting mold flux for medium-carbon low-alloy steel, especially by adjusting the contents of CaO, SiO ₂ , Li ₂ O and elemental carbon. The viscosity, melting point and transition temperature of the slag can be improved, and the melting speed can be increased, so as to effectively reduce the incidence of cracks and slag inclusions during the pouring process. Enhancement provides protection.

Description

Ultra-high-speed thin slab continuous casting mold flux for medium-carbon low-alloy steel

technical field

The invention relates to the technical field of iron and steel metallurgy, in particular to metallurgical auxiliary materials for continuous casting, and more particularly to a continuous casting mold powder suitable for ultra-high-speed thin slabs used in the continuous casting process of medium-carbon low-alloy steel.

Background technique

Continuous casting mold flux is a silicate-based functional material containing various fluxes and framework materials. With the continuous improvement of continuous casting speed and the use of electromagnetic braking equipment, the environment and metallurgical behavior of the mold flux in the mold have changed greatly, especially the melting uniformity and lubricating performance are difficult to guarantee. In addition, due to the complex structure of the funnel-shaped mold, the crack susceptibility of the continuous casting slab is becoming more and more prominent, which requires the optimization of the performance of the mold flux in terms of controlling heat transfer and ensuring the uniform growth of the primary shell. In addition, with the increase of the pulling speed, the renewal speed of the molten steel at the liquid level of the mold is accelerated, which creates conditions for the reaction of the steel slag and the adsorption of inclusions in the mold slag from the dynamic point of view, which has an adverse effect on the stability of the mold slag during use. . It is necessary to make the mold slag have excellent lubricating performance and have a strong ability to control heat transfer to ensure that the shell and the mold wall have less friction and can grow evenly to avoid cracks. Performance presents new and more complex technical requirements.

Electromagnetic braking can not only affect the flow field of molten steel in the mold, but also have a great impact on the temperature field in the mold, which in turn affects a series of behaviors such as melting, crystallization, inflow, and lubrication of mold slag.

Compared with the medium-thick slab and the square billet molds, the shell surface temperature of the thin slab varies greatly in different positions. In addition, with the increase of the pulling speed, the consumption of mold slag per unit time increases, and the vibration frequency increases accordingly, which makes the inflow of mold slag into the mold more difficult. At the same time, the molten steel flow rate in the mold and the turbulence of the meniscus are intensified, and the molten mold slag on the liquid surface is easy to be involved in the molten steel, resulting in breakout and quality accidents of the cast slab. The introduction of electromagnetic braking equipment will effectively reduce the flow speed of molten steel in the mold, reduce the fluctuation of the liquid level of the mold, and then reduce the probability of slag entrainment in the mold. However, the electromagnetic braking also greatly changes the temperature field in the mold, which leads to a decrease in the uniformity of the melting and inflow of the mold slag, which endangers the quality of the continuous casting billet and increases the incidence of cracks and slag inclusions. Therefore, it is necessary to systematically study the properties of mold flux at different drawing speeds (especially high drawing speeds), and comprehensively evaluate the applicability of mold flux in the process of ultra-high drawing speed thin slab continuous casting under electromagnetic braking.

The liquidus temperature of medium carbon low alloy steel is around 1530℃. With the decrease of temperature, the solidification mode of this steel is L→L+δ→L+γ→γ. In this solidification mode, a typical peritectic reaction occurs, namely L+δ→γ, which belongs to peritectic steel category. Since ferrite δ is a body-centered cubic structure and austenite γ is a face-centered cubic structure, the density of austenite is higher than that of ferrite. Therefore, when the peritectic reaction occurs, the volume of the casting billet will shrink sharply, and the crack sensitivity of this steel is high, and surface cracks are prone to occur, especially when the pulling speed is high. At this time, if the mold flux does not flow uniformly and the temperature control ability is weak, the shell is very likely to cause longitudinal cracks on the surface. Therefore, the mold powder for casting this steel should have certain lubricating properties and control heat transfer ability.

To sum up, on the basis of the original continuous casting flux for medium carbon and low alloy steel with conventional drawing speed, an ultra-high drawing speed thin slab continuous casting flux for medium carbon low alloy steel under electromagnetic braking conditions should be designed. , to further improve its lubricating performance and control heat transfer ability, and reduce longitudinal cracks on the surface of the slab.

SUMMARY OF THE INVENTION

The purpose of the present invention is to invent an ultra-high-speed thin slab continuous casting mold flux for medium-carbon low-alloy steel under the condition of electromagnetic braking, which can be used under the condition of high drawing speed, electromagnetic braking equipment and large-section funnel-shaped mold. It ensures a sufficient thickness of the liquid slag layer, improves its lubricating ability, improves heat transfer, reduces the incidence of cracks and slag inclusions in the slab, and provides a guarantee for stable and efficient production.

In order to achieve the above-mentioned purpose, the ultra-high-speed thin slab continuous casting mold powder for medium-carbon low-alloy steel designed by the present invention has the following chemical composition percentages: CaO: 31-33%, SiO ₂ : 19-22%, Al ₂ O ₃ : 5-7%, MgO: 4-7%, Na ₂ O: 5-8%, K ₂ O: 0-1%, CaF ₂ : 8-10%, Fe ₂ O ₃ : 0-1% , Li ₂ O: 1-2%, C: 8-10%, and the remainder is inevitable impurities.

1. Further, the preferred chemical composition percentages of the mold slag are: CaO: 31.8-32.5%, SiO ₂ : 20.1-20.7%, Al ₂ O ₃ : 5.8-6.3%, MgO: 5.3-5.8%, Na ₂ O: 6.1-6.5%, K ₂ O: 0.1-0.3%, CaF ₂ : 9.4-9.9%, Fe ₂ O ₃ : 0.4-0.6%, Li ₂ O: 1.1-1.3%, C: 9.1-9.5%, The balance is unavoidable impurities.

Further, the basicity of the mold flux is preferably controlled in the range of 1.4 to 1.8, the melting point of the mold flux is preferably controlled in the range of 1090 to 1110°C, and the viscosity of the mold flux at 1300°C is preferably controlled in the range of 0.01 to 0.03Pa. s range.

The mechanism of action of various chemical components in the ultra-high-speed thin-slab continuous casting mold flux for medium-carbon low-alloy steel of the present invention and the limiting reasons are as follows:

CaO: It is one of the main components of mold slag, which is related to the crystallization temperature and belongs to the oxide outside the network. Therefore, increasing the content of CaO in the mold slag can significantly reduce the viscosity of the slag and absorb oxide inclusions in the steel, especially Al ₂ O ₃ and TiO ₂ . In the present invention, since the basicity of the mold slag is controlled to be 1.5-1.7, and the mold slag has good crystallization performance, the present invention controls the CaO weight percentage in the range of 31-33%, preferably in the range of 31.8-32.5% .

SiO ₂ : It is a network former. Increasing the content of SiO ₂ in the mold slag can significantly increase the viscosity of the slag, and at the same time, the mold slag can form a glass phase, which is easy to lubricate the casting billet. But if it is too high, it is pointed out in the patent CN101954464 that a chain-like structure [SiO ₃ ] _n will be formed, which will make the viscosity of the mold flux too high and the lubricating effect reduced; Lubrication needs. In the present invention, since the basicity of the mold slag is controlled to be 1.5-1.7, and the mold slag has a certain lubricating performance, the SiO ₂ content in the present invention is controlled in the range of 19-22%, preferably 20.1-20.7%.

Al ₂ O ₃ : The addition of Al ₂ O ₃ to the slag increases the viscosity of the slag, but it lowers the freezing point of the slag, thereby improving mold lubrication. However, when a large amount of slag enters the slag, it is easy to form mayenite (2CaO·Al ₂ O ₃ ·SiO ₂ ) and nepheline (Na ₂ O·Al ₂ O ₃ ·2SiO ₂ ) with high melting point, which deteriorates the lubricating effect. In the present invention, in order to maintain a low viscosity and at the same time ensure that the mold powder has a certain lubricating performance, the content of Al ₂ O ₃ in the present invention is controlled in the range of 5-7%, preferably in the range of 5.8-6.3%.

MgO: In high-speed continuous casting, MgO is the preferred component of mold flux, which can significantly reduce the viscosity and melting point of mold flux. The addition of MgO can increase the fluidity of the mold slag and increase the slag consumption while maintaining the same viscosity and softening point. However, if the dosage is too high, the melting performance of the mold slag will be deteriorated. In the present invention, in order to improve the fluidity of the medium carbon low alloy steel, the MgO content is controlled in the range of 4-7%, preferably in the range of 5.3-5.8%.

Na ₂ O: It belongs to the external network _oxide , which can destroy the silicate network structure, and plays the role _{of reducing} the melting point and viscosity in the mold _slag . ), which is detrimental to the lubrication of the mold, and its addition amount should be limited. In the present invention, in order to ensure that the mold powder has a certain lubricating performance, the content of Na ₂ O is controlled in the range of 5-8%, preferably in the range of 6.1-6.5%.

CaF ₂ : Increasing the content within the range of <10% has a great effect on reducing the viscosity of the mold powder, and the effect is not obvious if it is increased further. Adding a large amount will cause precipitation of high melting point substances such as spar (3CaO·SiO ₂ ·CaF ₂ ), thereby destroying the glassiness of the slag and deteriorating the lubrication conditions. In addition, F ^- too high will erode the nozzle. In the present invention, in order to make the mold powder have suitable viscosity and certain glass properties, the CaF ₂ content is controlled in the range of 8-10%, preferably in the range of 9.4-9.9%.

Li ₂ O: It is a strong flux, even if the content of Li ₂ O in the slag is low, it has a great influence on the melting temperature. Micro addition of Li ₂ O (Li ₂ O < 2%) improves the degree of vitrification of the mold powder and reduces the crystallization rate, but excessive addition of Li 2 O (Li ₂ O > 4%) will cause a large amount of yellow feldspar instead. The precipitation of crystals greatly reduces the degree of vitrification. Therefore, an appropriate amount of Li ₂ O can be added to obtain a mold powder with low melting point, low viscosity and good glassiness, and the appropriate amount is Li ₂ O<2%. In the present invention, in order to appropriately lower the melting point and transition temperature of the mold powder and improve the lubricating performance of the mold powder, the Li ₂ O content is controlled in the range of 1-2%, preferably 1.1-1.3%.

C: In the physical and chemical properties of mold slag, carbonaceous elements mainly play the role of adjusting the melting rate. At present, the method of compound carbon mixing is generally used in the production of mold slag. In order to obtain a higher melting rate, the content of carbon Generally controlled within 10%. In the present invention, in order to have a liquid slag layer of sufficient thickness after the mold slag is added to the mold, the melting speed of the mold slag should be further increased, so that it can flow into the gap between the mold and the slab better. In order to improve the lubricating performance, but also to ensure that the mold flux can flow in uniformly and stably, the C content is controlled in the range of 8-10%, preferably in the range of 9.1-9.5%.

Alkalinity: an important indicator that reflects the ability of mold slag to absorb inclusions in molten steel, and also reflects the advantages and disadvantages of mold slag lubricating performance. If the alkalinity is too large, the ability to absorb inclusions is also large, but its crystallization temperature increases, which is not conducive to heat transfer and lubricating performance; if the alkalinity is too small, the viscosity of the mold slag is high, and the lubricating effect is reduced. In the present invention, in order to keep the viscosity of the mold slag within a reasonable range and at the same time to ensure that the mold slag has certain lubricating and heat transfer properties, the basicity of the mold slag is controlled within the range of 1.5-1.7.

Melting point: too low, it is easy to cause slag entrainment, slag inclusion, forming billet defects, and at the same time increase the slag consumption, which is not conducive to the molding of the billet; too high is easy to solidify and crystallize, resulting in poor lubricity. By adjusting the content of each component, the present invention controls the melting point of the mold slag at 1090-1110° C., which can ensure that the mold slag forms a liquid slag layer of sufficient thickness in the mold, so that the casting slab can be lubricated throughout the mold.

Viscosity (1300℃): It is one of the main physical and chemical properties of mold slag, which represents the relative viscous force between molecular layers when the mold slag is melted. It is also one of the important parameters of the apparent lubricating performance of mold slag. When the viscosity is too high, the fluidity of the mold slag becomes poor, and the lubricating effect is reduced; if the viscosity is too low, the slag consumption will increase, the casting billet will be difficult to form, and it is easy to cause slag entrainment and slag inclusion. According to the special process conditions of high drawing speed and thin slab, the present invention controls the viscosity of the medium carbon low alloy steel mold flux to 0.01-0.03 Pa·s, which can effectively prevent slag entrainment and ensure good lubrication.

In order to adapt to the special environment of high drawing speed, thin slab and electromagnetic braking, the mold flux of the present invention needs to increase the thickness of the liquid slag layer on the original basis, improve the lubricating performance of the mold flux, and simultaneously Lower the melting point and increase the melting range. Therefore, as mentioned above, the content of Li ₂ O in the slag should be appropriately increased to reduce the melting point and improve the lubricating performance of the mold slag; at the same time, the carbon ratio should be appropriately adjusted to increase the melting speed and increase the thickness of the liquid slag layer after the mold slag is added to the mold. , so as to meet the demand for mold flux performance in the above-mentioned special cases.

Description of drawings

The accompanying drawings described herein are used to provide further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the attached image:

1A and 1B illustrate a schematic structural diagram of a crystallizer in an embodiment of the present invention;

2A to 2B illustrate the comparison diagrams of the surface sticking slag of the thin slab to which the mold flux according to the embodiment of the present invention is applied and the thin slab to which the mold flux according to the embodiment of the present invention is not applied;

3A to 3B illustrate comparison diagrams of surface cracks of a thin slab to which mold flux according to an embodiment of the present invention is applied and a thin slab to which mold flux according to an embodiment of the present invention is not applied;

4A and 4B illustrate comparative photographs of red-hot slab slag sticking of thin slabs to which mold flux according to an embodiment of the present invention is applied and a thin slab to which no mold flux according to embodiments of the present invention is applied.

Description of reference numbers:

Detailed ways

The ultra-high-speed thin slab continuous casting mold flux for medium-carbon low-alloy steel of the present invention will be further described in detail below with reference to specific embodiments.

[The mold powder according to the embodiment of the present invention]

Table 1 lists the chemical composition weight percentages of Examples 1-4 of the ultra-high-speed thin slab continuous casting mold flux for medium-carbon low-alloy steel of the present invention (the balance is inevitable impurities).

The preparation method is as follows: the raw materials containing the above-mentioned components are mixed in proportion and then ground into powder of less than 200 meshes, and the carbonaceous material of the designed content is added to make the properties and components meet the design requirements. After being melted at high temperature, it can be pulverized and slag formed to obtain the ultra-high-speed thin slab continuous casting mold for medium-carbon low-alloy steel listed in Table 1.

The above-mentioned ultra-high-speed thin slab continuous casting mold flux for medium-carbon low-alloy steel was tested, and it was melted and quenched by water. Observing and analyzing the surface of the cast slab, it was found that the slag inclusion and longitudinal cracks on the surface of the slab were significantly improved. At the same time, due to the obvious improvement of the lubricating performance of the mold slag in the meniscus and the area below the mold, cold teeth and bonding occurred. phenomenon has been significantly reduced.

Table 1:

Examples 1-4 in Table 1 above will be described in detail below.

Example 1

The preparation method of the mold powder according to the embodiment of the present invention is as follows: the raw materials containing the above-mentioned components are mixed in proportion and then ground into powder of less than 200 meshes, and the carbonaceous material of the designed content is added to make its performance and composition meet the design requirements. After being melted at a high temperature, crushed and slag-forming can obtain the ultra-high-speed thin slab continuous casting mold slag for medium-carbon low-alloy steel in the first row listed in Table 1.

Specifically, the ultra-high-speed thin slab continuous casting mold flux for medium-carbon low-alloy steel includes the following components: CaO: 31.0%, SiO ₂ : 19.0%, Al ₂ O ₃ : 5.0%, MgO: 4.0% , Na ₂ O: 5.0%, K ₂ O: 0.3%, CaF ₂ : 8.0%, Fe ₂ O ₃ : 0.5%, Li ₂ O: 1.0%, C: 8.0%, and the balance is inevitable impurities.

The binary basicity (CaO/SiO2 mass percentage) of the ultra-high-speed thin slab continuous casting mold flux for medium-carbon low-alloy steel is 1.63, and the physical indicators are as follows: melting point 1090°C, viscosity (1300°C): 0.010Pa·s .

The mold slag prepared with the above components and indicators is used on GRADE50 steel grade with 8 heats of steel, with a section of 1272 × 70 mm and a pulling speed of about 5.0 m/min. The quality is observed, and the rolling conditions are tracked. The results are as follows:

The situation in the mold: the mold slag melts evenly in the mold, and the reaction is relatively active. There is no large slag bar during use. The heat flow density curve is relatively stable, the loose side and the fixed side are 1800～2000kW/m ² , the heat flow density of the narrow side is 1300～1500kW/m ² , the qualified rate of the cast slab surface is 99.5%, the qualified rate of rolled steel is 100%, and no sticking alarm occurs. And breakout phenomenon, to meet the ultra-high-speed thin slab continuous casting production of medium-carbon low-alloy steel performance requirements of mold slag.

The following will describe in detail the properties of the mold flux prepared by using the above-mentioned components and indicators with reference to FIGS. 2A to 4B .

FIG. 2A and FIG. 2B are schematic diagrams of ultra-high-drawing-speed thin slabs continuously cast by using the mold flux in the prior art. As shown in FIG. 2A and FIG. 2B , it can be seen that there is a lot of sticky slag on the surface of the thin slab, such as the part circled by the black solid line in FIG. 2A .

In contrast, FIGS. 2A and 2B are schematic views of ultra-high-speed thin slabs continuously cast after applying the mold flux according to an embodiment of the present invention. As shown in Fig. 2A and Fig. 2B, it can be seen that the surface of the thin slab is smooth and substantially free of sticky slag.

FIG. 3A and FIG. 3B are schematic diagrams of ultra-high-speed thin slabs continuously cast by using the mold flux in the prior art. As shown in FIG. 3A , it can be seen that the thin slab has many cracks, such as the part circled by the solid white line in FIG. 3A .

In contrast, FIGS. 3A and 3B are schematic views of ultra-high-speed thin slabs continuously cast after applying the mold flux according to an embodiment of the present invention. As shown in FIGS. 3A and 3B , it can be seen that the surface of the thin slab is smooth and substantially free of cracks.

FIG. 4A is a photo of a red-hot slab of an ultra-high-speed thin slab continuously cast by using the mold flux of the prior art. As shown in Figure 4A, sticky slag can be seen on the red-hot slab of the thin slab.

In contrast, FIG. 4B is a red-hot slab photograph of an ultra-high-drawing-speed thin slab continuously cast after applying the mold flux according to an embodiment of the present invention. As shown in Figure 4B, it can be seen that the red-hot slab surface of the thin slab is smooth and free of sticky slag. Specifically, the slag sticking on the surface of the red-hot slab proves that the melting is not good, resulting in the sticking of unmelted mold slag on the surface of the continuous caster. The smooth surface of the slab proves that the optimized mold flux according to the embodiment of the present invention has a good use effect.

Example 2

The preparation method of the mold flux according to the embodiment 2 of the present invention is the same as that of the embodiment 1, so the detailed description thereof is omitted.

Specifically, the ultra-high-speed thin slab continuous casting mold flux for medium-carbon low-alloy steel includes the following components: CaO: 33.0%, SiO ₂ : 22.0%, Al ₂ O ₃ : 7.0%, MgO: 7.0% , Na ₂ O: 8.0%, K ₂ O: 1.0%, CaF ₂ : 10.0%, Fe ₂ O ₃ : 1.0%, Li ₂ O: 2.0%, C: 10.0%, and the remainder is inevitable impurities.

The binary basicity (CaO/SiO2 mass percentage) of the ultra-high-speed thin slab continuous casting mold flux for medium-carbon low-alloy steel is 1.50, and the physical indicators are as follows: melting point 1110°C, viscosity (1300°C): 0.030Pa·s .

The mold slag prepared with the above-mentioned components and indicators uses 6 heats of steel on the S320X steel grade, with a section of 1548×72mm and a pulling speed of about 5.0m/min. The quality is observed, and the rolling conditions are tracked. The results are as follows:

The situation in the mold: the mold slag melts evenly in the mold, the reaction is relatively active, no large slag bars appear in use, the thickness of the liquid slag layer is 8-10mm, the slag consumption is 0.26kg/t, and it has been relatively stable. The heat flow density curve is relatively stable, the loose side and the fixed side are 1800-2000kW/m ² , the narrow side heat flow density is 1300-1500kW/m2, the qualified rate of the cast slab surface is 99.6%, and the qualified rate of rolled steel is 100%. The phenomenon of steel breakout meets the requirements for mold flux performance of medium-carbon low-alloy steel produced by ultra-high-speed thin slab continuous casting.

Example 3

The preparation method of the mold flux according to the embodiment 3 of the present invention is the same as that of the embodiment 1, so the detailed description thereof is omitted.

Specifically, the ultra-high-speed thin slab continuous casting mold flux for medium-carbon low-alloy steel includes the following components: CaO: 31.8%, SiO ₂ : 20.1%, Al ₂ O ₃ : 5.8%, MgO: 5.3% , Na ₂ O: 6.1%, K ₂ O: 0.1%, CaF ₂ : 9.4%, Fe ₂ O ₃ : 0.4%, Li ₂ O: 1.1%, C: 9.1%, the balance is inevitable impurities.

The binary basicity (CaO/SiO2 mass percentage) of the ultra-high-speed thin slab continuous casting mold flux for medium-carbon low-alloy steel is 1.58, and the physical indicators are as follows: melting point 1100°C, viscosity (1300°C): 0.020Pa·s .

The mold slag prepared with the above-mentioned components and indicators uses 8 heats of steel on S350X steel, with a section of 1547 × 72 mm and a pulling speed of about 5.0 m/min. The quality is observed, and the rolling conditions are tracked. The results are as follows:

The situation in the mold: the mold slag melts evenly in the mold, and the reaction is relatively active. There is no large slag bar in use. The thickness of the liquid slag layer is 8-10mm, and the slag consumption is 0.27kg/t, and it has been relatively stable. The heat flow density curve is relatively stable, the loose side and the fixed side are 1800~2000kW/m2, the narrow side heat flow density is 1400~1600kW/m2, the qualified rate of the casting billet surface is 99.6%, the qualified rate of rolling is 100%, and no bonding alarm or leakage occurs. The steel phenomenon meets the requirements for the performance of the mold flux for the production of medium-carbon low-alloy steel by ultra-high-speed thin slab continuous casting.

Example 4

The preparation method of the mold flux according to the embodiment 4 of the present invention is the same as that of the embodiment 1, so the detailed description thereof is omitted.

Specifically, the ultra-high-speed thin slab continuous casting mold flux for medium-carbon low-alloy steel includes the following components: CaO: 32.5%, SiO ₂ : 20.7%, Al ₂ O ₃ : 6.3%, MgO: 5.8% , Na ₂ O: 6.5%, K ₂ O: 0.3%, CaF ₂ : 9.9%, Fe ₂ O ₃ : 0.6%, Li ₂ O: 1.3%, C: 9.5%, the balance is inevitable impurities.

The binary basicity (CaO/SiO2 mass percentage) of the ultra-high-speed thin slab continuous casting mold flux for medium-carbon low-alloy steel is 1.57, and the physical indicators are as follows: melting point 1105°C, viscosity (1300°C): 0.025Pa·s .

The mold slag prepared with the above-mentioned components and indicators uses 7 heats of steel on S350X steel, with a cross section of 1547×720 mm and a pulling speed of about 5.0 m/min. The quality is observed, and the rolling conditions are tracked. The results are as follows:

The situation in the mold: the mold slag melts evenly in the mold, and the reaction is relatively active. There is no large slag bar during use. The heat flow density curve is relatively stable, the loose side and fixed side are 1400～1600kW/m ² , the heat flow density on the narrow side is 1800～2000kW/m2, the qualified rate of the cast slab surface is 99.6%, and the qualified rate of rolled steel is 100%. The phenomenon of steel breakout meets the requirements for mold flux performance of medium-carbon low-alloy steel produced by ultra-high-speed thin slab continuous casting.

The mold powder according to the embodiment of the present invention solves the technical problem caused by the contradiction between lubrication and control of heat transfer. The advantages of the mold powder according to the embodiment of the present invention are that, first, it can balance the two Contradictory, the effect of high lubrication - high alkalinity (high alkalinity can ensure a decrease in heat transfer) is achieved. Second, according to the characteristics of the steel grade, the lubrication/heat control can be adjusted moderately incline under different steel grades to meet the needs of ultra-high pulling speed.

Although the present invention has been described above with reference to the exemplary embodiments, the above-mentioned embodiments are only intended to illustrate the technical concept and characteristics of the present invention, and cannot limit the protection scope of the present invention. Any equivalent variations or modifications made according to the spirit of the present invention shall be included within the protection scope of the present invention.

Claims (5)

1. The utility model provides a medium carbon low alloy steel is with super high pulling speed sheet billet continuous casting covering slag which characterized in that: the covering slag comprises the following chemical components in percentage by weight: CaO: 31 to 33% of SiO₂：19～22％，Al₂O₃：5～7％，MgO：4～7％，Na₂O：5～8％，K₂O：0～1％，CaF₂：8～10％，Fe₂O₃：0～1％，Li₂O: 1-2%, C: 8-10% and the balance of inevitable impurities.

2. The medium carbon low alloy steel ultra-high pulling speed thin slab continuous casting mold flux according to claim 1, characterized in that: the preferable chemical components of the casting powder are as follows: CaO: 31.8 to 32.5% of SiO₂：20.1～20.7％，Al₂O₃：5.8～6.3％，MgO：5.3～5.8％，Na₂O：6.1～6.5％，K₂O：0.1～0.3％，CaF₂：9.4～9.9％，Fe₂O₃：0.4～0.6％，Li₂O: 1.1-1.3%, C: 9.1 to 9.5 percent, and the balance of inevitable impurities.

3. The ultra-high drawing speed film for medium carbon low alloy steel according to claim 1The slab continuous casting covering slag is characterized in that: in the mold flux: basicity (CaO/SiO) of the mold flux₂) The temperature is controlled within the range of 1.5-1.7.

4. The medium carbon low alloy steel ultra-high pulling speed thin slab continuous casting mold flux according to claim 1, characterized in that: the melting point is 1090-1110 ℃, and the viscosity is 0.01-0.03 Pa.s at 1300 ℃.

5. The mold flux for continuous casting of ultra-high drawing speed thin slabs for medium carbon low alloy steel according to claim 1 or 2, wherein the continuous casting drawing speed of the ultra-high drawing speed thin slabs for medium carbon low alloy steel is 5.0m/min to 6.5 m/min.

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