WO2019184729A1 - Method for improving fluidity of solid-liquid two-phase region in middle and late solidification stages of continuous casting process, and method and device for controlling quality of cast ingot - Google Patents

Abstract

A method for improving the fluidity of a solid-liquid two-phase region in middle and late solidification stages of a continuous casting process comprises applying intermittent excitation force to a surface of an ingot shell (120) at a solidified end of a continuously cast ingot (100), wherein intermittent excitation force can be further applied to the surface of the ingot shell at a solidified intermediate segment of the continuously cast ingot. Additionally, a method for controlling quality of a cast ingot in a solidification process of continuous casting and a device for controlling quality of a cast ingot in a solidification process of continuous casting are provided. Excitation force applied to a surface of an ingot shell at a solidified end of a continuously cast ingot improves shrinkage compensation of semi-solidified molten steel in intermediate and late solidification stages and reduces porosity of an internal structure of the cast ingot. Excitation force applied to the surface of an ingot shell at a solidified intermediate section of a continuously cast ingot breaks up dendritic crystal head growth at a solidification front edge during a cooling process in an even manner and promotes growth of equiaxed crystals.

Description

Method for improving fluidity of solid-liquid two-phase region in middle and late solidification of continuous casting process, control method and device for slab quality Technical field

The invention relates to the technical field of metallurgical continuous casting, and more particularly to a method for improving the fluidity of a solid-liquid two-phase region in the middle and late stages of solidification in a continuous casting process and a control method for the quality of a slab during continuous solidification.

Background technique

The specific process of continuous casting is that the molten steel continuously passes through the water-cooled crystallizer, and is solidified into a hard shell and then continuously pulled out from the outlet of the crystallizer, cooled by water spray, and completely solidified and then cut into a billet casting process. In the continuous casting of steel, due to the increase of the phase-to-solid ratio of the two-phase zone, the viscosity of the molten steel increases and the fluidity deteriorates. It is difficult to supplement the cavity formed by the volume shrinkage at the solidification end when the molten steel is solidified. This in turn forms the looseness of the solidified structure. Since the solidification shrinkage rate of steel is significantly larger than that of non-ferrous metals such as copper and aluminum, and the thermal conductivity is much lower than that of copper and aluminum, it is easier to form a center looseness at the solidified end of the slab. In order to solve the above problems, many patents and technologies have been formed in this respect for a long time. These patents and technologies are mainly divided into three categories: one is solidification end electromagnetic stirring technology, the other is solidification end pressing or casting and rolling technology, and the last one. It is a mechanical vibration molding casting technology. These three types of technologies have been used in modern steel casting production, but the existing processes are difficult to effectively improve the looseness of the slab, which deteriorates the performance of the steel.

In addition, in the continuous casting production process, in order to improve the solidification structure of the slab, increase the equiaxed crystal ratio, and reduce the looseness and composition segregation in the central portion of the slab, an external field stirring technique using electromagnetic stirring is widely used. However, due to the continuous application of constant or alternating electromagnetic force to the liquid metal, the electromagnetic stirring causes the dendrite of the columnar crystal to become the central equiaxed crystal nucleus, and also causes the liquid metal to continuously move relative to the dendrites of the solidification front. The solute element is continuously transferred into the liquid metal, causing severe macroscopic negative segregation inside the casting blank in the area where the continuous external field force acts, such as the white bright band of the casting blank in the continuous casting steel. There is an urgent need to overcome this technical problem.

Related technologies have been published through the search. For example: a continuous casting bloom soft reduction process based on the end electromagnetic stirring (publication number: CN103121092A; publication date: 2013.05.29), the technology is installed after the end electromagnetic stirring device is installed in the second cold zone, and the air cooling before straightening The zone ensures that the liquid phase between the columnar crystals has completely solidified while the light reduction and straightening are carried out simultaneously. This technique can improve the internal quality of the steel. In addition, a high-quality cord steel bloom continuous casting dynamic soft reduction process (publication number: CN101648263A; publication date: 2010.02.17), in the area of continuous casting light reduction, through the change of the solid phase rate fs of the casting blank Control the amount of reduction, and give the relationship between the reduction of the frame under soft reduction and the solid phase rate of the slab; it can reduce the center segregation of the cord steel slab and improve the center looseness and center shrinkage of the cord slab hole. In addition, a method for improving the quality of continuous casting slabs and a vibration supporting roller device (publication number CN1586767A; publication date 2005.03.02) are kept in synchronization with the surface of the continuous casting blank by a vibration supporting roller which is closely attached to the outer wall of the continuous casting shell At the same time, under the driving of the vibration source, the vibration is perpendicular to the thickness direction of the casting blank or parallel to the casting direction, and the vibration is transmitted to the solidified shell with the liquid core by contact; the technology is improved by the vibration supporting roller device. The equiaxed crystal ratio of the center of the continuous casting blank can significantly improve the shrinkage and porosity of the continuous casting billet, reduce segregation and effectively avoid the occurrence of rolling cracks caused by the soft pressing of the solidified end.

Summary of the invention

1. The technical problem to be solved by the invention

The object of the invention is to improve the problem of loose structure of the slab, thereby improving the quality of the slab;

Provided is a method for improving the fluidity of the solid-liquid two-phase region in the middle and late stages of solidification in the continuous casting process, applying intermittent exciting force on the surface of the solid shell at the solidification end of the continuous casting billet, and utilizing the positive thixotropy of the solid-liquid two-phase metal, Improve the shrinkage ability of semi-solidified molten steel in the middle and late stages of solidification, improve the looseness of the internal structure of the slab, and improve the quality of the slab;

Provided is a method and a device for controlling the quality of a slab in a continuous casting solidification process, in which an intermittent exciting force is applied to the solidified end of the continuous casting billet and the solidified middle section, respectively, to strike the shell of the solidified middle section of the continuous casting billet The exciting force of the surface can regularly interrupt the dendrite head growing in the solidification front during cooling, transforming the columnar crystal into equiaxed crystal, promoting the growth of equiaxed crystals; and striking the solidified end of the continuous casting billet. The exciting force on the surface of the shell is enhanced by the positive thixotropy of the solid-liquid two-phase metal to improve the shrinkage ability of the semi-solidified molten steel in the middle and late solidification stage, thereby improving the quality of the slab.

2. Technical solutions

In order to achieve the above object, the technical solution provided by the present invention is:

The invention discloses a method for improving the fluidity of the solid-liquid two-phase region in the middle and late stages of solidification in the continuous casting process, and applying intermittent exciting force on the surface of the solid shell at the solidification end of the continuous casting billet, wherein the casting blank of the solidified end of the continuous casting billet The cross-sectional metal liquid phase ratio is b ₁ and 25% ≥ b ₁ >0.

Preferably, the exciting force applied to the surface of the solidified end shell is applied at a time interval of t ₁ , t ₁ = 0.0167 to 2 s.

Preferably, the impact energy exerted by the exciting force on the surface of the solidified end shell is W ₁ , W ₁ = 15 to 1500 J.

Preferably, the impact energy of the exciting force applied to the surface of the shell of the solidified end of the continuous casting billet is W ₁ ,

The value of a ₁ ranges from 0.2 to 1.0 J/mm ³ .

b ₁ is the metal liquid phase ratio /% of the transverse section of the slab at the position of the solidification end exciting force application point;

C ₁ ranges from 2.7 to 3.3;

S is the cross-sectional area of the slab/mm ² .

The method for controlling the quality of a slab during continuous solidification in a continuous casting process, wherein intermittently exciting force is applied to the solidified end of the continuous casting billet and the solidified middle portion of the continuous casting billet; and the billet of the solidified end of the continuous casting billet The time interval at which the excitation force is applied to the surface of the shell is less than the time interval at which the excitation force is applied to the surface of the solid shell in the solidified section of the continuous casting billet; wherein the cross-section metal liquid phase of the billet at the solidified end of the continuous casting billet is b ₁ and 25% ≥ b ₁ >0; the cross-section metal liquid phase of the slab of the continuous solidification section is b ₂ , and 75% ≥ b ₂ > 25%.

Preferably, the time interval at which the exciting force is applied to the surface of the shell of the solidified end is t ₁ , t ₁ = 0.0167 to 2 s, or / and the time interval at which the exciting force is applied to the surface of the shell of the solidified middle section is t ₂ , t ₂ = 1-30s.

Preferably, the impact energy of the surface of the solidified end of the solid shell is excited by W ₁ , W ₁ = 15 to 1500 J; or / and the impact energy of the surface of the solidified middle portion is excited by W ₂ , W ₂ = 10 ~ 800J.

Preferably, the impact energy of the exciting force applied to the surface of the shell of the solidified end of the continuous casting billet is W ₁ ,

The value of a ₁ ranges from 0.2 to 1.0 J/mm ³ .

b ₁ is the metal liquid phase ratio /% of the transverse section of the slab at the position of the solidification end exciting force application point;

C ₁ ranges from 2.7 to 3.3;

S is the cross-sectional area of the slab/mm ² .

Preferably, the impact energy of the exciting force applied to the surface of the shell of the solidified middle section of the continuous casting billet is W ₂ ,

The value of a ₂ ranges from 0.2 to 2.6 J/mm ³ .

b ₂ is the metal liquid phase ratio /% of the transverse section of the slab at the position of the excitation force at the middle stage of the solidification;

C ₂ ranges from 1.8 to 2.4;

S is the cross-sectional area of the slab/mm ² .

Preferably, the time interval at which the exciting force is applied to the surface of the shell of the solidified middle section is t ₂ ,

t ₂ = ε × b ₂ ^τ × S

The value of ε ranges from 0.4 to 0.8 s/mm ² ;

b ₂ is the metal solid phase ratio /% in the transverse section of the continuous casting slab at the action position;

The value of τ ranges from 1.4 to 2.0;

S is the cross-sectional area of the slab/mm ² .

The control device for the quality of the slab in the continuous casting solidification process of the present invention is provided with a terminal exciting force applying device at a position where the metal liquid ratio of the continuous casting billet is 25% ≥ b ₁ > 0, and in the slab A medium-stage exciting force applying device is provided at a position where the metal liquid phase ratio is 75% ≥ b ₂ > 25%, and the end exciting force applying device and the middle-stage exciting force applying device are respectively used for applying intermittentness to the surface of the shell The exciting force.

3. Beneficial effects

Compared with the prior art, the technical solution provided by the invention has the following remarkable effects:

(1) A method for improving the fluidity of the solid-liquid two-phase region in the middle and late stages of solidification in the continuous casting process, applying intermittent exciting force to the surface of the solid shell at the solidification end of the continuous casting billet, and casting the solidified end of the continuous casting billet The liquid phase ratio of the cross section of the billet is 0 to 25%, and the exciting force is transmitted to the core of the slab through the shell, so that the semi-solidified molten steel is subjected to shear stress and the viscosity is lowered and the fluidity is improved due to the positive thixotropy. Under the conditions of molten steel high pressure head and solidification shrinkage vacuum suction, the semi-solidified steel water enrichment ability is enhanced, thereby utilizing the positive thixotropy of solid-liquid two-phase metal to improve the fluidity of semi-solidified molten steel and improve the semi-solidified molten steel in the middle and late stages of solidification. The ability to fill, improve the internal structure of the slab, and improve the quality of the slab;

(2) A method for improving the fluidity of the solid-liquid two-phase region in the middle and late stages of solidification in the continuous casting process, wherein the excitation force applied to the surface of the solidified end shell is applied at a time interval of t ₁ = 0.0167 to 2 s, during continuous casting production Continuous and rapid excitation is applied to the outer surface of the solidified end casting blank, so that the action of the exciting force is transmitted to the core of the casting blank, so that the semi-solidified molten steel is subjected to shear stress and the viscosity is decreased and flowed due to positive thixotropy. The improvement of the property, the semi-solidified steel water enrichment ability is enhanced, thereby effectively improving the internal structure looseness of the slab and improving the quality of the slab;

(3) A method for controlling the quality of a slab in a continuous casting solidification process according to the present invention, wherein an intermittent exciting force is applied to the solidified end of the continuous casting slab and the surface of the solidified intermediate portion to strike the solidified section of the continuous casting slab The exciting force on the surface of the shell can regularly interrupt the dendrite head growing in the solidification front during cooling, promote the growth of equiaxed crystals without negative segregation, and strike the surface of the billet shell at the end of the solidification of the continuous casting billet. The vibration force utilizes the positive thixotropy of the solid-liquid two-phase metal to improve the shrinkage ability of the semi-solidified molten steel in the middle and late solidification period, improve the production of equiaxed crystals, and improve the shrinkage ability of the semi-solidified molten steel in the middle and late solidification, and improve the casting. The internal structure of the billet is loose to improve the quality of the billet;

(4) A method for controlling the quality of a slab during continuous solidification in the solidification process of the present invention, wherein the metal liquid phase of the cross section of the slab at the point of application of the intermittent exciting force on the surface of the solidified middle section is 25% ～85%, so that the solidified shell can withstand the shocking force, the dendrite head growing at the solidification front can be broken, and the growth of equiaxed crystals can be promoted.

DRAWINGS

1 is a schematic view of a control device for improving the fluidity of a solid-liquid two-phase region in the middle and late stages of solidification in a continuous casting process according to the present invention;

2 is a schematic view showing the microstructure of the round blank of Example 1;

3 is a schematic view showing the microstructure of a round blank of Comparative Example 1;

4 is a schematic structural view of a control device for quality of a slab during continuous casting solidification in Embodiment 2;

Figure 5 is a schematic view showing the structure of a control device for the quality of a slab during continuous casting solidification in Embodiment 3;

Fig. 6 is a schematic view showing the morphology of the round billet microstructure of the second embodiment.

The label description in the schematic diagram:

100, continuous casting billet; 110, unsolidified molten steel; 120, solidified shell; 101, concave side of the casting blank; 102, convex arc side of the billet;

210, an end excitation force application device; 220, a middle excitation force application device;

310, columnar crystal region; 320, equiaxed crystal region, 330, central loose pores.

detailed description

In order to further understand the contents of the present invention, the present invention will be described in detail with reference to the accompanying drawings and embodiments.

The structures, the proportions, the sizes, and the like of the drawings are only used to clarify the contents disclosed in the specification for understanding and reading by those skilled in the art, and are not intended to limit the conditions that can be implemented by the present invention. Without technical significance, the modification of any structure, the change of the proportional relationship or the adjustment of the size should still fall within the technology disclosed by the present invention without affecting the effects and the achievable objectives of the present invention. The content can be covered. In the meantime, the terms "upper", "lower", "left", "right", "intermediate", etc., as used in this specification, are merely for convenience of description, and are not intended to limit the scope of implementation. Changes or adjustments in relative relationships are considered to be within the scope of the invention, without departing from the scope of the invention.

A method for improving the fluidity of the solid-liquid two-phase region in the middle and late stages of solidification in the continuous casting process, the outer portion of the continuous casting blank 100 is a solidified shell 120, and the inside of the solidified shell 120 is unsolidified molten steel 110 in the continuous casting blank 100. An intermittent exciting force is applied to the surface of the solid shell at the solidified end, wherein the cross-section metal liquid phase of the billet at the solidified end of the continuous casting billet 100 is b ₁ and 25% ≥ b ₁ >0, that is, the exciting force at the solidified end Applied to the interval before the solidification end point to 25% of the metal liquid phase; that is, at the position where the metal liquid phase ratio of the continuous casting blank 100 is 25% ≥ b ₁ > 0, the end exciting force applying device 210 is provided, and the terminal is excited. The force applying device 210 is for applying an intermittent exciting force to the surface of the solid shell at the solidified end, and the exciting force applying direction of the end exciting force applying device 210 is perpendicular to the surface of the shell. That is, the exciting force is required to act on the surface of the slab in which the liquid phase ratio of the metal in the cross section of the slab is not more than 25%, so that the excitation energy can effectively act on the mushy zone at the end of the solidification, thereby improving the fluidity of the semi-solidified molten steel. When the surface of the slab in which the metal liquid phase ratio is greater than 25% is applied in the cross section of the slab, the affected zone will be transmitted forward along the solidified body part of the slab, which will cause negative segregation of the affected zone due to continuous vibration and simultaneous application due to vibration. The position is too far forward, which makes it difficult for the vibration effect to affect the solidification end at the back, and the effect of improving the center structure of the slab is not improved. It is worth noting here that the exciting force applied here is completely different from the vibration, as follows:

(1) The excitation force is completely different from the vibration mode. The intermittent excitation force is a single stroke to hit or knock on the surface of the solid shell at the end of the solidification. The billet itself does not have relative displacement; It is the reciprocating sway of the slab, the slab itself may have a relative displacement, and the vibration exerts a reciprocating force on the surface of the slab shell, so the intermittent exciting force is substantially different from the vibration;

(2) The mechanism of action is completely different. Formally, the action of excitation force and vibration is completely different, and the mechanism of action of the two on the slab is exactly the same. The intermittent excitation force is applied to the surface of the shell in the middle section of solidification. Instantly transferred to the core of the slab by the solidified shell 120, so that under the action of shear stress, the semi-solidified molten steel is reduced in viscosity and fluidity due to positive thixotropy, improving the fluidity of the semi-solidified molten steel and improving the semi-solidified molten steel. The ability to compensate in the middle and late stages of solidification; and the vibration is to use the inertial force to compensate and improve the looseness of the solidification structure of the metal. The vibration will additionally increase the external field force and cause the continuous relative displacement between the molten steel and the solidification front dendrites. The solute element in the steel is transferred to the liquid phase of the steel, resulting in the generation of negative segregation of the slab.

It is worth noting that if the speed of the excitation force is too fast or too slow, the impact of the excitation force will be poorly transmitted. The exciting force applied to the surface of the solidified terminal shell of the present invention is applied at a time interval of t ₁ , t ₁ = 0.0167 to 2 s, so that a rapid striking exciting force can be applied to the surface of the solidified end shell. The time interval for applying the exciting force on the surface of the solidified end shell is t ₁ , t ₁ = 0.0167 ~ 2 s, and the thickness of the shell is different due to the size of the billet at the solidification end, so that the vibration effect is effectively transmitted to the billet In the core, the excitation force is applied at a time interval of 0.0167 to 2 s, which can exert a good striking force striking effect, and the exciting force is transmitted to the core of the slab through the shell, so that the semi-solidified molten steel acts as a shear stress. Next, the viscosity decreases and the fluidity is improved due to the positive thixotropy, thereby improving the shrinkage ability of the semi-solidified molten steel.

a ₁取值范围为0.2～1.0J/mm ³，b ₁为凝固末端激振力施力点位置的铸坯横向截面的金属液相率/％；C ₁取值范围为2.7～3.3；S为铸坯断面面积/mm ²；随着铸坯中金属液相率越低、断面越大外力的冲击功越大；在凝固末端坯壳表面的施加恰当冲击能的激振力，可以使半凝固钢水在剪切应力的作用下粘度下降和流动性提高，进而提高半凝固钢水补缩能力。 Further, the impact energy applied by the exciting force of the surface of the solidified end shell of the present invention is W ₁ and W ₁ = 15 to 1500 J. The detailed description is as follows: the impact energy range of the external force is described in detail with the action position (metal liquid phase rate) and the section of the slab, and the impact energy of the exciting force applied to the surface of the solid shell at the solidified end of the continuous casting blank 100 is W ₁ .

The value of a ₁ ranges from 0.2 to 1.0 J/mm ³ , and b ₁ is the metal liquid phase ratio/% of the transverse section of the slab at the position of the solidification end excitation force; C ₁ ranges from 2.7 to 3.3; S is The cross-sectional area of the billet/mm ² ; the lower the liquid phase ratio of the metal in the billet, the larger the cross-section, the greater the impact energy of the external force; the exciting force of the appropriate impact energy applied to the surface of the solid shell at the end of the solidification can make the semi-solidification The molten steel has a viscosity drop and fluidity under the action of shear stress, thereby improving the water-replenishing ability of the semi-solidified steel.

When the impact energy of the exciting force of the invention is less than 15 joules, the fluidity of the casting blank cannot be effectively improved, and it is difficult to effectively improve the feeding ability of the semi-solidified molten steel in the middle and late solidification; if the impact energy of the exciting force is greater than 1500 joules, then It is easy to cause surface quality problems of the slab. In addition, the patent further includes an excitation force generation system, which includes: an energy supply device, an excitation force application device, and an excitation parameter control device, wherein the excitation force generation mode includes electromagnetic drive, motor drive, fluid drive, and the like.

In addition, after long-term research and development, the technical research and development team found that the solidification end electromagnetic stirring technology, solidification end pressing or casting and rolling technology and mechanical vibration molding casting technology have the following problems:

(1) The principle of applying external field force as a typical example of electromagnetic stirring is that the dendrites of the solidification front are broken and broken by applying a magnetic field, and the two-phase semi-solidified molten steel in the mushy zone is stirred by the magnetic field force. However, at the solidification end of the slab, the temperature of the molten steel is close to the solidus line, and the solid ratio is gradually higher, the fluidity of the molten steel is deteriorated, the shrinkage ability is weak, and the looseness of the slab is difficult to improve, and the practical application is almost impossible. Not a stable and effective case.

(2) The main working principle of the solidification end pressing or casting and rolling technology is to squeeze the semi-solidified molten steel into the solidified cavity and squeeze the solidified shrinkage void region by applying a certain strength pressure to the solidified billet shell 120 of the cast billet. Reduce the looseness of the slab structure. However, this technique has the following disadvantages: it needs to increase the bulk of the light reduction device, the small amount of reduction is difficult to eliminate the center looseness formed by the solidification end, and the large reduction amount is easy for some crack-sensitive steels to crack at the solidification front of the slab. The solidification end position is difficult to position and is only suitable for many problems such as rectangular casting.

(3) Mechanical vibration molding casting technology has been reported only in small die casting ingots. The principle is to vibrate the liquid metal inside the mold through the vibration of the entire molding platform, and use the inertial force to compensate and improve. The problem of loose solidification of metal. However, this technology cannot be used in the continuous casting process. The main reasons are: 1. The continuous casting equipment is unlikely to vibrate as a whole; 2. Continuous casting is a dynamic continuous production process, and the static process of molding is very different. 3, compared to the small die casting ingot, the continuous casting slab has a large length.

However, the existing process is difficult to effectively improve the looseness of the slab structure, which deteriorates the properties of the steel. The present invention applies an exciting force at a position where the metal liquid phase of the cross section of the slab of the continuous casting billet 100 is 0 to 25%, and the exciting force is transmitted to the core of the slab through the shell, so that the semi-solidified steel is Under the action of shear stress, the viscosity decreases and the fluidity increases due to positive thixotropy. Under the conditions of molten steel high pressure head and solidification shrinkage vacuum suction, the semi-solidified steel water enrichment ability is enhanced, so that the positive contact of solid-liquid two-phase metal is utilized. Denaturation, improve the fluidity of semi-solidified molten steel, improve the shrinkage ability of semi-solidified molten steel in the middle and late solidification stage, improve the looseness of the internal structure of the slab, and improve the quality of the slab.

Example 1

In this embodiment, a 5-stream round billet continuous casting machine of a factory is used. In the continuous casting process of round billets with different cross-sections, different time intervals and exciting force applying devices are used at a certain position on the surface of the billet, and compression is used according to a certain time interval. The air drive provides the excitation force of a certain impact energy. In each case, the test of one casting is carried out continuously. After the casting is finished, the casting blank is taken at a low magnification, and the looseness rating is performed to determine the degree of looseness and average, and the specific parameters of the embodiment are given. And the results are shown in Table 1.

In this embodiment, an exciting force is applied at a point of application, wherein the metal liquid phase ratio of the cross section of the slab at the point of application is 23%, 15%, 15%, and 11%, respectively, and a test of one casting is performed for each experimental condition. After casting, the slab was taken at a low magnification, and the equiaxed crystal ratio and negative segregation of the slab were analyzed. The specific parameters and results of the examples are shown in Table 1. The schematic diagram of the morphology of the low-magnification structure with a metal liquid phase rate of 23% at the point of application is shown in Fig. 2.

Comparative example 1

The basic content of this comparative example is the same as that of Embodiment 1, except that no exciting force is applied to the surface of the continuous casting blank 100 during the continuous casting. After casting, the slab was taken at a low magnification, and the equiaxed crystal ratio and negative segregation of the slab were analyzed. The specific parameters and results of the examples are shown in Table 1. A schematic diagram of the morphology of the low-magnification structure of Comparative Example 1 is shown in FIG.

Table 1

It can be found from the analysis of Comparative Example 1 and Example 1, FIG. 2 is a schematic view showing the morphology of the microstructure of the slab of Example 1, and FIG. 3 is a schematic view showing the microstructure of the slab of Comparative Example 1; A crystal region 310, an equiaxed crystal region 320, and a central loose hole 330. In comparison, it was found that the equiaxed crystal region 320 of the slab after using the patent has a liquid phase ratio of 23%, 15%, 15 in the metal as compared with the equiaxed crystal region 320 of the slab which is not used in this patent and which does not use the external field force. %, 11%; time intervals are: 0.022, 0.037, 0.0625, 0.1s; respectively provide impact energy size: 35, 40, 60, 200 / J; central loose rating test to obtain the above-mentioned center loose situation, the center loose rating Both are less than 0.5; while the center looseness of Comparative Example 1 is 1.0. In the first embodiment, when the exciting force hits the blank shell on the surface of the slab, intermittent exciting force is applied to the surface of the solid shell at the solidified end of the continuous casting billet 100, and the slab cross-section metal liquid phase at the solidified end of the continuous casting billet 100 The rate is 0~25%, and the exciting force is transmitted to the core of the slab through the shell, so that the semi-solidified molten steel under the action of shear stress, the viscosity decreases and the fluidity is improved due to the positive thixotropy, and the high pressure head and solidification in the molten steel Under the condition of shrinking vacuum suction, the semi-solidified steel water enrichment ability is enhanced, thereby utilizing the positive thixotropy of the solid-liquid two-phase metal to improve the fluidity of the semi-solidified molten steel, improve the shrinkage ability of the semi-solidified molten steel in the middle and late solidification, and improve the casting. The internal structure of the billet is loose and the quality of the billet is improved.

Example 2

The basic content of the embodiment is the same as that of the first embodiment, except that an intermittent exciting force is applied to the solidified end of the continuous casting blank 100 and the solidified intermediate portion of the continuous casting blank 100; and the solidified end of the continuous casting blank 100 The time interval at which the exciting force is applied to the surface of the shell of the billet is less than the time interval at which the exciting force is applied to the surface of the shell of the solidified section of the continuous casting billet 100; wherein the cross-section metal liquid phase of the billet at the solidified end of the strand 100 is b ₁ , And 25% ≥ b ₁ >0; the cross-section metal liquid phase ratio of the slab of the continuous solidification section 100 is b ₂ , and 75% ≥ b ₂ > 25%. That is, the end exciting force applying means 210 is provided at a position where the metal liquid phase ratio of the continuous casting blank 100 is 25% ≥ b ₁ > 0, and the end exciting force applying means 210 is used to apply intermittentness to the surface of the solidified end. The exciting force is applied by the end exciting force applying device 210 at a time interval of 0.0167 to 2 s, and the impact energy applied by the vibration force is in the range of 15 to 1500 J. A middle-stage exciting force applying device 220 is disposed at a position where the metal liquid phase ratio of the continuous casting blank 100 is 75% ≥ b ₂ > 25%, and the middle-stage exciting force applying device 220 is used to apply intermittentness to the surface of the solidified middle portion of the blank. The exciting force (as shown in FIG. 4) is such that the exciting force applied by the middle-stage exciting force applying device 220 is applied in a time interval of 1 to 30 seconds; and the exciting energy applied by the exciting force is in the range of 10 to 800 J.

It should be noted here that the exciting force applied by the solidification end is completely different from the vibration in the first embodiment. Here again, the exciting force applied in the middle of the solidification is completely different from the vibration, and the details are as follows:

(1) The excitation force is completely different from the vibration mode. The intermittent excitation force is a single stroke to hit or knock on the surface of the solid shell at the end of the solidification. The billet itself does not have relative displacement; It is the reciprocating sway of the slab, the slab itself may have a relative displacement, and the vibration exerts a reciprocating force on the surface of the slab shell, so the intermittent exciting force is substantially different from the vibration;

(2) The action mechanism is completely different. Formally, the excitation force and the vibration action mode are completely different. When the excitation force hits the billet shell on the surface of the slab, it can interrupt the dendrite head growing in the solidification front during the cooling process, prompting The columnar crystals are transformed into equiaxed crystals, and the continuous relative displacement between the molten steel and the solidification front dendrites caused by the external field force is not additionally increased, and the transfer of the solute elements in the steel to the liquid phase of the steel is inhibited; and the vibration is the inertial force. It plays the role of supplementing and improving the looseness of the solidification structure of the metal. The vibration will additionally increase the external field force and cause the continuous relative displacement between the molten steel and the dendrites of the solidification front, and promote the transfer of the solute elements in the steel to the liquid phase of the steel, resulting in casting. Negative segregation of the billet.

Moreover, the action mechanism of applying the exciting force at the solidification end and the solidification middle section is completely different due to the difference in the position where the excitation force is applied to the surface of the solidification end and the solidification middle section, the magnitude of the impact energy, and the time interval.

The continuous casting blank 100 of the present invention comprises a slab concave side 101 and a slab convex side 102, and an intermittent exciting force is applied to the surface of the solidified shell 120 of the continuous casting slab 100, and the exciting force is applied at the point of application. The metal liquid phase of the cross section of the slab is 25% to 85%. This is because the solidified solid shell has a strength less than 85%, and does not have the external force to withstand the effective breaking of the dendritic head; when the metal liquid fraction is less than 25%, it is already at the end of solidification, continue Excitation has not been able to increase the equiaxed crystal ratio of the slab. Applying an exciting force to the slab concave side 101 of the continuous casting blank 100 or the slab convex arc side 102; or applying at the corresponding positions of the concave side 101 of the slab 100 and the convex side 102 of the slab Exciting force.

The time interval during which the excitation force is applied in the middle of solidification is 1-30 seconds. This is because the effect of the external force is close to the continuous action when the time is less than 1 second, resulting in a continuous relative displacement between the molten steel and the solidification front dendrites, resulting in constant solute elements. The transfer to the liquid metal tends to cause negative segregation, and the breaking effect is also reduced by the growth of the dendrites. When the time is longer than 30 seconds, the length of the dendrite growth is too long, the number of broken dendrites is small, and the inhibition effect on the columnar crystal is insufficient. The time interval is related to the thickness of the shell of the action point. When the shell is thin, the dendrite grows fast and the excitation interval is short. The specific relationship can be expressed by the following relationship: the time interval for applying the exciting force on the surface of the shell of the solidified middle section is t ₂ , t ₂ = ε × b ₂ ^τ × S, ε ranges from 0.4 to 0.8 s/mm ² ; b ₂ is the solid phase ratio/% of the metal in the transverse section of the continuous casting blank 100 at the action position; 1.4 to 2.0; S is the cross-sectional area of the slab/mm ² .

a ₂取值范围为0.2～2.6J/mm ³，b ₂为凝固中段激振力施力点位置的铸坯横向截面的金属液相率/％；C ₂取值范围为1.8～2.4；S为铸坯断面面积/mm ²。 The impact energy applied by the exciting force in the middle of solidification ranges from 10 to 800 J. The specific value is related to factors such as the thickness of the shell (metal liquid phase), and can be expressed by the following relationship: the impact energy of the exciting force applied to the surface of the shell of the solidified section of the continuous casting billet 100 is W ₂ .

The value of a ₂ ranges from 0.2 to 2.6 J/mm ³ , and b ₂ is the liquid phase ratio/% of the transverse section of the slab at the position of the excitation force at the middle of the solidification; the value of C ₂ ranges from 1.8 to 2.4; Casting section area / mm ² .

Along the longitudinal direction of the continuous casting billet 100, at least one set of the middle-stage exciting force applying means 220 is disposed on the surface of the solidified shell 120 of the solidified middle section of the continuous casting blank 100, and the middle-stage exciting force applying means 220 is used for the solidifying middle section The exciting force is applied. In the present embodiment, the concave arc side 101 of the casting blank is provided with one middle-stage exciting force applying device 220, and the end exciting force applying device 210 and the middle-stage exciting force applying device 220 are disposed in the same of the continuous casting blank 100. On the side, the end exciting force applying device 210 and the middle exciting force applying device 220 of the present embodiment are disposed on the concave arc side 101 of the slab. That is, the one-side exciting force applied at one metal liquid phase position of the continuous casting billet 100 or the corresponding position of the two side surfaces simultaneously apply the exciting force to one set of exciting force; at different metal liquid phase positions of the continuous casting blank 100 The multiple exciting forces applied are multiple sets of exciting forces. At the same time, a plurality of exciting force applying points may be provided on the surface of the solidified shell 120 of the continuous casting blank 100 along the longitudinal direction of the continuous casting billet 100.

In this embodiment, a 5-round round billet continuous casting machine of a factory is used, and the casting blank has a diameter of 380 mm, and a device for applying different time intervals and exciting force on the surface of the casting blank, and the solid solution end of the continuous casting billet 100 is 23%. The position is applied with an exciting force. The time interval of the exciting force at this position is 0.022 s, and the solidified end impact energy is 35 J. The liquid phase ratio of the solidified middle section of the continuous casting billet 100 is 75%, and the time interval is 3 s. The work is 20J. After the casting is finished, the casting blank is taken at a low magnification, the equiaxed crystal ratio is measured, the looseness rating is performed, the looseness is determined and averaged. The specific parameters and results of the example 2 are shown in Table 2, and the morphology of the low-fold structure is shown. As shown in Figure 6.

Comparative example 2

The basic content of this Comparative Example 2 is the same as that of Embodiment 2, except that no other measures are applied in the continuous casting process. After the casting is finished, the casting blank is taken at a low magnification, the equiaxed crystal ratio is measured, the looseness rating is performed, the degree of looseness is determined and averaged, and the specific parameters and results of Comparative Example 2 are shown in Table 2.

Example 3

The basic content of the embodiment is the same as that of the embodiment 2, except that the diameter of the slab is 380 mm, and the two sides of the solidification middle section of the continuous casting slab 100 are correspondingly provided with the middle-stage excitation force applying device 220, and the middle-stage excitation force on both sides The exciting force applying direction of the applying device 220 is collinear, and the biasing direction of the middle exciting force applying device 220 passes through the geometric center of the cross section of the continuous casting blank 100. In this embodiment, the round blank is used, and the exciting force is greatly struck. Through the center of the cross section of the slab; that is, at the position of one point of application of the two side surfaces of the slab, simultaneously applying the exciting force by the same impact work symmetrical impact, the present embodiment in the solidification of the continuous casting slab 100 in the middle section of the slab concave concave side 101 and The corresponding positions of the two sides of the convex arc side 102 of the slab are simultaneously applied with the same exciting force (as shown in FIG. 5).

Further, the application position, time interval, and magnitude of the impact energy of the solidification end and the solidification middle section of the continuous casting blank 100 are different. After the casting is finished, the slab is taken at a low magnification, the equiaxed crystal ratio is measured, the looseness rating is performed, the degree of looseness is determined and averaged, and the specific parameters and results of the examples are shown in Table 2.

Table 2

It can be seen from Table 2 that the equiaxed crystal ratios of Examples 2 and 3 were increased to 55, respectively, after the solidification end of the continuous casting billet 100 and the surface of the billet of the continuous casting billet 100 were intermittently excited. Above %, and the center looseness rating is 0, and no negative segregation occurs when the quality of the slab is improved. The quality of Example 2 and Example 3 was greatly improved compared to Comparative Example 1.

In addition, comparing FIG. 3 and FIG. 6, after the intermittent excitation force is applied to the solidification end of the continuous casting slab and the surface of the solidified middle section respectively, not only the proportion of the equiaxed crystal region 320 is enlarged, but also the internal structure of the slab is reduced. loose. This is because the intermittent exciting force is applied to the surface of the solidified end of the continuous casting billet and the solidified middle section, respectively, and the exciting force on the surface of the shell of the solidified section of the continuous casting billet 100 is struck, and the cooling process can be interrupted regularly. The dendrite head which grows in the solidification front, which converts the columnar crystal into an equiaxed crystal, promotes the growth of the equiaxed crystal; and strikes the exciting force against the surface of the shell at the solidified end of the continuous casting billet 100, using solid The positive thixotropy of liquid two-phase metal improves the shrinkage ability of semi-solidified molten steel in the middle and late solidification period, improves the production of equiaxed crystals, improves the shrinkage ability of semi-solidified molten steel in the middle and late solidification stage, and improves the internal structure looseness of the cast slab. Improve the quality of the slab; use the excitation force generation system to instantaneously hit the slab surface of the slab at a certain position in the solidification stage of the slab 100 at a certain position and at a certain time, with an external force of a certain strength, so that the exciting force passes through the slab The shell is transferred to the solidification front of the slab, periodically breaking the dendrite head growing at the solidification front, and suppressing the growth of the columnar crystal while providing the nucleus core for the subsequent formation of the central equiaxed crystal.

The invention has been described in detail above with reference to specific exemplary embodiments. It should be understood, however, that various modifications and changes can be made without departing from the scope of the invention as defined by the appended claims. The detailed description and drawings are to be regarded as illustrative and not restrictive In addition, the background art is intended to illustrate the state of the art and the meaning of the present invention, and is not intended to limit the invention or the application field of the present application and the present invention.

Claims (10)

A method for improving the fluidity of a solid-liquid two-phase region in the middle and late stages of solidification in a continuous casting process, characterized in that intermittent exciting force is applied to the surface of the solid shell at the solidification end of the continuous casting billet (100), wherein the continuous casting billet (100) The slab of the solidified end has a cross-section metal liquid phase ratio b ₁ and 25% ≥ b ₁ >0. A method for improving the fluidity of a solid-liquid two-phase region in the middle and late stages of solidification in a continuous casting process according to claim 1, wherein the time interval of the exciting force applied to the surface of the solidified end shell is t ₁ , t ₁ = 0.0167 ~ 2s. A method for improving fluidity of a solid-liquid two-phase region during solidification in a continuous casting process according to claim 1, wherein the impact energy of the surface of the solidified end shell is applied by W ₁ , W ₁ = 15 ~ 1500J. A method for improving fluidity of a solid-liquid two-phase region during solidification in a continuous casting process according to any one of claims 1 to 3, characterized in that the surface of the solid shell at the solidified end of the continuous casting billet (100) is excited. The impact energy of the vibration force is W ₁ , W ₁ = a ₁ × (1-b) ^C × S ^1.5 , The value of a ₁ ranges from 0.2 to 1.0 J/mm ³ . b ₁ is the metal liquid phase ratio /% of the transverse section of the slab at the position of the solidification end exciting force application point; C ₁ ranges from 2.7 to 3.3; S is the cross-sectional area of the slab/mm ² . A method for controlling the quality of a slab during continuous solidification, characterized in that an intermittent exciting force is applied to the solidified end of the continuous casting billet (100) and the surface of the solidified middle portion of the continuous casting billet (100); The time interval at which the exciting force is applied to the surface of the shell of the solidified end of the continuous casting billet (100) is less than the time interval at which the exciting force is applied to the surface of the shell of the solidified section of the continuous casting billet (100); wherein the solidified end of the continuous casting billet (100) The metal liquid phase ratio of the cross section of the slab is b ₁ , and 25% ≥ b ₁ >0; the cross-section metal liquid phase of the slab of the continuous casting slab (100) is b ₂ , and 75% ≥ b ₂ >25 %. The method for controlling the quality of a slab in a continuous casting solidification process according to claim 5, wherein the time interval at which the exciting force is applied to the surface of the solidified end is t ₁ , t ₁ = 0.0167 ～ 2 s, or / The time interval between the application of the exciting force to the surface of the shell of the solidified middle section is t ₂ , t ₂ =1 30 s. The method for controlling the quality of a slab in a continuous casting solidification process according to claim 5, wherein the impact energy of the surface of the solid shell at the end of the solidification is W ₁ , W ₁ = 15 to 1500 J; The impact energy of the exciting force applied to the surface of the shell of the solidified middle section is W ₂ , W ₂ = 10 to 800 J. A method for controlling the quality of a slab during continuous solidification in a continuous casting process according to claim 5, wherein the impact energy of the exciting force applied to the surface of the solidified end of the continuous casting billet (100) is W ₁

The value of a ₁ ranges from 0.2 to 1.0 J/mm ³ . b ₁ is the metal liquid phase ratio /% of the transverse section of the slab at the position of the solidification end exciting force application point; C ₁ ranges from 2.7 to 3.3; S is the cross-sectional area of the slab/mm ² . The method for controlling the quality of a slab during continuous solidification in a continuous casting process according to claim 5, wherein the impact energy of the exciting force applied to the surface of the solidified portion of the continuous casting billet (100) is W ₂ .

The value of a ₂ ranges from 0.2 to 2.6 J/mm ³ . b ₂ is the metal liquid phase ratio /% of the transverse section of the slab at the position of the excitation force at the middle stage of the solidification; C ₂ ranges from 1.8 to 2.4; S is the cross-sectional area of the slab/mm ² . A control device for the quality of a slab during continuous casting solidification, characterized in that an end exciting force applying device (210) is provided at a position where the metal liquid phase ratio of the continuous casting billet (100) is 25% ≥ b ₁ > 0 And a middle-stage exciting force applying device (220), an end exciting force applying device (210), and a middle segment are provided at a position where the molten metal (100) has a metal liquid phase ratio of 75% ≥ b ₂ > 25%. The vibration applying devices (220) are respectively used to apply an intermittent exciting force to the surface of the shell.

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