CN108526423A - A kind of method, control method and device of slab quality improving casting process solidification middle and later periods solid-liquid two-phase region mobility - Google Patents

Abstract

The invention discloses 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, a method and a device for controlling the quality of a slab, and belongs to the technical field of metallurgical continuous casting. The present invention applies intermittent exciting force to the surface of the slab shell at the solidification end of the continuous casting slab, and utilizes the positive thixotropy of the solid-liquid two-phase metal to improve the feeding ability of the semi-solidified molten steel in the middle and late stages of solidification and improve the internal structure of the slab Loose; In addition, intermittent exciting force is applied to the surface of the billet shell at the end of continuous casting slab solidification and the middle part of continuous casting slab solidification; During the cooling process, the dendrite head growing at the solidification front promotes the growth of equiaxed crystals; and the exciting force striking the surface of the billet shell at the end of the solidification of the continuous casting billet can improve the feeding ability of the semi-solidified molten steel in the middle and late stages of solidification, and improve The internal structure of the slab is loose, which improves the quality of the slab.

Description

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, casting billet quality control method and device

technical field

The invention relates to the technical field of metallurgical continuous casting, and more specifically relates to 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 a method for controlling the quality of the slab during the continuous casting solidification process.

Background technique

The specific process of continuous casting is that the molten steel continuously passes through the water-cooled crystallizer, condenses into a hard shell, and then is continuously pulled out from the outlet below the crystallizer, cooled by spraying water, and then cut into billets after being completely solidified. During continuous casting of iron and steel, due to the increase in the solid phase ratio in the two-phase region in the middle and late stages of the solidification process, the viscosity of molten steel increases and the fluidity becomes poor. It is difficult to supplement the cavity formed at the end of solidification due to volume shrinkage when molten steel solidifies. Then the loosening of coagulated tissue is formed. Since the solidification shrinkage rate of steel is significantly greater 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 central porosity at the solidification end of the billet. In order to solve the above problems, many patents and technologies have been formed in this area for a long time. These patents and technologies are mainly divided into three categories: one is the solidification end electromagnetic stirring technology, the other is the solidification end pressing or casting rolling technology, and the last one is It is based on mechanical vibration molding casting technology. These three types of technologies have been used in modern steel casting production, but the existing technology is difficult to effectively improve the loose structure of the slab, which deteriorates the properties 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 porosity and composition segregation in the central area of the slab, the external field force stirring technology typical of electromagnetic stirring is widely used. However, due to the continuous application of constant or alternating electromagnetic force to the liquid metal by electromagnetic stirring, while brushing off the dendrite head of the columnar crystal to become the central equiaxed crystal nucleus, it also makes the liquid metal and the dendrite at the solidification front continue to move relative to each other. As a result, the solute elements are continuously transferred to the liquid metal, causing serious macroscopic negative segregation inside the slab in the area where the external field force acts, such as the white and bright band of the slab in continuous casting steel. There is an urgent need to overcome this technical problem.

After retrieval, relevant similar technologies have been published. For example: a continuous casting bloom soft reduction process based on terminal electromagnetic stirring (publication number: CN103121092A; publication date: 2013.05.29), this technology is installed in the secondary cooling zone after the terminal electromagnetic stirring device, air cooling before straightening zone, to ensure that the liquid phase between the columnar crystals has been completely solidified when the light reduction and straightening are carried out simultaneously, and this technology can improve the internal quality of the steel. In addition, a high-quality cord steel bloom continuous casting dynamic soft reduction process (public number: CN101648263A; public date: 2010.02.17), in the continuous casting light reduction area, through the change of the solid phase ratio fs in the center of the billet Control the reduction amount, and give the relationship between the reduction amount of the light reduction frame and the solid phase ratio in the center of the slab; it can reduce the center segregation of the cord steel slab, and improve the center porosity and center shrinkage of the cord steel slab hole. In addition, a method for improving the quality of continuous casting slabs and a vibrating support roller device (publication number CN1586767A; publication date 2005.03.02), through which the vibrating support rollers closely attached to the outer wall of the continuous casting slab shell are kept rotating synchronously with the surface of the continuous casting slab At the same time, under the drive of the vibration source, the vibration is perpendicular to the thickness direction of the slab or parallel to the direction of the slab, and the vibration is transmitted to the solidification shell with the liquid core through contact; The equiaxed crystal ratio in the center of the continuous casting slab can significantly improve the shrinkage cavity and porosity in the center of the continuous casting slab, reduce segregation and effectively avoid the rolling cracks caused by the light reduction at the end of solidification.

Contents of the invention

1. The technical problem to be solved by the invention

The purpose of the present invention is to improve the loose structure of the slab, and then improve 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 solidification of the continuous casting process. The intermittent exciting force is applied to the surface of the billet shell at the end of the solidification of the continuous casting billet, and the positive thixotropy of the solid-liquid two-phase metal is used. Improve the feeding 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 device for controlling the quality of the slab during the continuous casting solidification process. Intermittent exciting forces are respectively applied to the surface of the slab shell at the solidification end and the solidification middle section of the continuous casting slab to strike the slab shell at the solidification middle section of the continuous casting slab The exciting force on the surface can regularly interrupt the dendrite heads growing at the solidification front during the cooling process, making the process of transforming columnar crystals into equiaxed crystals and promoting the growth of equiaxed crystals; The exciting force on the surface of the slab shell utilizes the positive thixotropy of the solid-liquid two-phase metal to improve the feeding ability of the semi-solidified molten steel in the middle and late stages of solidification, thereby improving the quality of the slab.

2. Technical solution

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

A method of improving the fluidity of the solid-liquid two-phase region in the middle and later stages of continuous casting process of the present invention, the intermittent exciting force is applied to the shell surface at the solidification end of the continuous casting slab, wherein the casting slab at the solidification end of the continuous casting slab is horizontal The metal liquid phase ratio of the section is b ₁ , and 25%≥b ₁ >0.

Preferably, the time interval for applying the exciting force on the shell surface at the solidification end is t ₁ , where t ₁ =0.0167˜2s.

Preferably, the range of impact energy applied by the exciting force on the surface of the shell at the solidification end is W ₁ , where W ₁ =15-1500J.

Preferably, the impact energy of the exciting force applied to the shell surface at the solidification end of the continuous casting slab is W ₁ ,

The value range of a ₁ is 0.2～1.0J/mm ³ ,

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

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 the slab during the continuous casting solidification process of the present invention, respectively applies intermittent exciting force to the surface of the slab shell at the end of the solidification of the continuous casting slab and the surface of the middle section of the solidification of the continuous casting slab; and the slab at the solidification end of the continuous casting slab The time interval of applying the exciting force on the surface of the shell is shorter than the time interval of applying the exciting force on the surface of the shell in the middle of the solidification of the continuous casting slab; the liquid phase ratio of the cross-section of the slab at the end of the solidification of the continuous casting slab is b ₁ , and 25%≥ b ₁ >0; the metal liquid phase ratio of the cross-section of the slab in the solidification middle section of the continuous casting slab is b ₂ , and 75%≥b ₂ >25%.

Preferably, the time interval for applying the exciting force to the shell surface at the end of solidification is t ₁ , t ₁ =0.0167～2s, or/and the time interval for applying the exciting force to the shell surface in the middle stage of solidification is t ₂ , t ₂ = 1-30s.

Preferably, the impact energy range of the exciting force applied to the shell surface at the solidification end is W ₁ , W ₁ =15-1500J; or/and the impact energy range of the exciting force applied to the shell surface at the middle stage of solidification is W ₂ , W ₂ = 10 ~ 800J.

Preferably, the impact energy of the exciting force applied to the shell surface at the solidification end of the continuous casting slab is W ₁ ,

The value range of a ₁ is 0.2～1.0J/mm ³ ,

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

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 slab shell in the solidified middle section of the continuous casting slab is W ₂ ,

The value range of a ₂ is 0.2～2.6J/mm ³ ,

_b2 is the metal liquid phase ratio/% of the transverse section of the slab at the point where the exciting force is applied in the middle stage of 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 for applying the exciting force to the shell surface in the middle solidification section is t ₂ ,

t ₂ =ε×b ₂ ^τ ×S

The value range of ε is 0.4～0.8s/mm ² ;

_b2 is the metal solid phase rate/% in the transverse section of the continuous casting slab at the action position;

τ ranges from 1.4 to 2.0;

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

A control device for casting slab quality in the continuous casting solidification process of the present invention is provided with a terminal excitation force applying device at the position where the metal liquid phase ratio of the continuous casting slab is 25% ≥ _{b 1} >0, and the continuous casting slab The middle section of the excitation force application device is installed at the position where the metal liquid phase rate is 75%≥b ₂ >25%, and the end excitation force application device and the middle section of the excitation force application device are respectively used to apply intermittent the exciting force.

3. Beneficial effect

Compared with the existing known technology, the technical solution provided by the invention has the following remarkable effects:

(1) A method of improving the fluidity of the solid-liquid two-phase region in the middle and later stages of continuous casting process of the present invention, applying intermittent exciting force to the shell surface at the solidification end of the continuous casting slab, and the casting at the solidification end of the continuous casting slab The metal liquid phase ratio of the billet cross section is 0-25%. The exciting force is transmitted to the core of the billet through the billet shell, so that the semi-solidified molten steel is under the action of shear stress, and the viscosity is reduced and the fluidity is improved due to the positive thixotropy. Under the conditions of high pressure head of molten steel and vacuum suction of solidification shrinkage, the feeding capacity of semi-solidified molten steel is enhanced, so that the positive thixotropy of solid-liquid two-phase metals can be used to improve the fluidity of semi-solidified molten steel and improve the fluidity of semi-solidified molten steel in the middle and late stages of solidification. Feeding ability, improving the looseness of the internal structure of the slab, and improving the quality of the slab;

(2) A method of improving the fluidity of the solid-liquid two-phase region in the middle and later stages of the continuous casting process of the present invention, the time interval for applying the exciting force on the surface of the billet shell at the end of the solidification is t ₁ =0.0167～2s, during continuous casting production , apply continuous and rapid exciting vibration to the outer surface of the solidification end slab, so that the exciting force is transmitted to the core of the slab, so that the semi-solidified molten steel under the action of shear stress, due to the positive thixotropy, makes the viscosity drop and flow The property is improved, and the feeding ability of semi-solidified molten steel is enhanced, thereby effectively improving the looseness of the internal structure of the slab and improving the quality of the slab;

(3) In a method for controlling the quality of the slab during the continuous casting solidification process of the present invention, an intermittent exciting force is respectively applied to the surface of the slab shell at the end of the continuous casting slab solidification and the solidification middle section, and strikes at the solidification middle section of the continuous casting slab. The exciting force on the surface of the billet shell can regularly interrupt the dendrite heads growing at the solidification front during the cooling process, promote the growth of equiaxed crystals without negative segregation; Vibration force, using the positive thixotropy of solid-liquid two-phase metals, improves the feeding ability of semi-solidified molten steel in the middle and late solidification, improves the production of equiaxed crystals and improves the feeding ability of semi-solidified molten steel in the middle and late solidification, and improves casting The internal structure of the slab is loose, which improves the quality of the slab;

(4) A method for controlling the quality of slab in the continuous casting solidification process of the present invention, the liquid phase rate of the slab at the cross section of the slab cross section at the application point where the intermittent exciting force is applied to the surface of the slab shell in the solidification middle section is 25% ~85%, so that the solidified shell can withstand the shock and vibration force, and at the same time, the dendrite head growing at the solidification front can be interrupted, and the growth of equiaxed crystals can be promoted.

Description of drawings

Fig. 1 is a schematic diagram of a control device for improving the fluidity of the solid-liquid two-phase region in the middle and later stages of solidification in the continuous casting process of the present invention;

Fig. 2 is the topography schematic diagram of the microstructure of the round billet of embodiment 1;

Fig. 3 is the schematic diagram of the morphology of the round billet microstructure of Comparative Example 1;

Fig. 4 is the structural schematic diagram of the control device of slab quality in a kind of continuous casting solidification process of embodiment 2;

Fig. 5 is a schematic structural view of a control device for billet quality in a continuous casting solidification process of embodiment 3;

FIG. 6 is a schematic view of the microstructure of the round billet in Example 2.

Explanation of the labels in the schematic diagram:

100, continuous casting slab; 110, unsolidified molten steel; 120, solidified slab shell; 101, casting slab concave arc side; 102, casting slab convex arc side;

210. Terminal excitation force application device; 220. Middle section excitation force application device;

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

Detailed ways

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

The structures, proportions, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification, for those who are familiar with this technology to understand and read, and are not used to limit the conditions for the implementation of the present invention. Therefore, Without technical substantive significance, any modification of structure, change of proportional relationship or adjustment of size shall still fall within the technology disclosed in the present invention without affecting the effect and purpose of the present invention. within the scope of the content. At the same time, terms such as "upper", "lower", "left", "right", and "middle" quoted in this specification are only for the convenience of description and are not used to limit the scope of implementation. The change or adjustment of the relative relationship shall also be regarded as the implementable scope of the present invention without substantive change of the technical content.

A method for improving the fluidity of the solid-liquid two-phase region in the middle and later stages of continuous casting process of the present invention, the exterior of the continuous casting slab 100 is a solidified slab shell 120, and the inside of the solidified slab shell 120 is an unsolidified molten steel 110, and the continuous casting slab 100 Intermittent excitation force is applied to the surface of the slab shell at the solidification end, wherein the metal liquid phase ratio of the cross-section of the slab at the solidification end of the continuous casting slab 100 is b ₁ , and 25%≥b ₁ >0, that is, the excitation force at the solidification end Applied before the end point of solidification to the interval of metal liquid phase ratio of 25%; that is, a terminal excitation force application device 210 is provided at the position where the metal liquid phase ratio of the continuous casting billet 100 is 25% ≥ _{b 1} >0, and the terminal excitation force The force applying device 210 is used to apply an intermittent exciting force to the shell surface at the solidification end, and the direction of the exciting force applied by the end exciting force applying device 210 is perpendicular to the shell surface. That is to say, the excitation force is required to act on the surface of the slab with a metal liquid phase ratio not greater than 25% in the cross-section of the slab, so that the excitation energy can effectively act on the mushy area at the end of solidification and improve the fluidity of the semi-solidified molten steel ; When acting on the surface of the slab with a metal liquid phase ratio greater than 25% in the cross-section of the slab, the affected area will be transmitted forward along the solidified part of the slab, which will cause negative segregation in the affected area due to continuous vibration, and at the same time due to the vibration applied The position is too far forward, so that the vibration effect is difficult to affect the solidification end at the back, and the effect of improving the central structure of the slab cannot be achieved. It is worth noting here that the exciting force applied here is completely different from the vibration, as detailed below:

(1) The action mode of the exciting force is completely different from that of the vibration. The intermittent exciting force is a one-way single-shot hitting or knocking on the surface of the billet shell at the end of the solidification, and the billet itself will not have relative displacement; while the vibration It is the reciprocating shaking of the slab, the slab itself may produce relative displacement, and the vibration exerts a reciprocating force on the surface of the slab shell, so there is an essential difference between the intermittent exciting force and the vibration;

(2) The mechanism of action is completely different, because the exciting force and vibration act in completely different ways, and at the same time, the mechanism of action of the two on the billet is completely the same; the intermittent exciting force is applied to the surface of the billet shell in the middle of solidification. The solidified slab shell 120 is transmitted to the core of the cast slab in an instant, so that the semi-solidified molten steel is under the action of shear stress, and the viscosity decreases and the fluidity increases due to the positive thixotropy, which improves the fluidity of the semi-solidified molten steel and improves the semi-solidified molten steel. The feeding ability in the middle and late stages of solidification; and the vibration is to use the inertial force to feed and improve the loosening of the metal solidification structure. The vibration will additionally increase the external field force and cause the continuous relative displacement between the molten steel and the dendrites at the solidification front, and promote The solute elements in the steel transfer to the liquid phase of the steel, resulting in negative segregation of the slab.

It is worth noting that: the striking speed of the exciting force is too fast or too slow, which will make the transmission of the striking effect of the exciting force poor. The time interval for applying the exciting force on the surface of the shell at the solidification end is t ₁ , where t ₁ =0.0167-2s, so that the exciting force of rapid impact can be applied on the surface of the shell at the solidification end. The time interval for applying the exciting force on the surface of the billet shell at the solidification end is t ₁ , t ₁ =0.0167～2s. At the end of solidification, the thickness of the billet shell is different due to the size of the billet. In order to effectively transmit the vibration to the billet For the core, the time interval for applying the exciting force is 0.0167~2s, which can have a good impact effect of the exciting force, and the exciting force is transmitted to the core of the slab through the slab shell, so that the semi-solidified molten steel can withstand the shear stress. Under the influence of positive thixotropy, the viscosity decreases and the fluidity increases, thereby improving the feeding ability of semi-solidified molten steel.

In addition, the range of impact energy exerted by the excitation force on the surface of the shell at the end of solidification in the present invention is W ₁ , where W ₁ =15-1500J. The detailed description is: describe in detail that the impact energy range of the external force is related to the action position (metal liquid phase ratio) and the section of the slab, and the impact energy of the exciting force applied to the surface of the slab shell at the end of the solidification of the continuous casting slab 100 is W ₁ , The value range of a ₁ is 0.2～1.0J/mm ³ , b ₁ is the metal liquid phase ratio/% of the transverse section of the slab at the point where the exciting force is applied at the end of solidification; the value range of C ₁ is 2.7～3.3; S is Cross-sectional area of the slab/mm ² ; the lower the liquid phase ratio of the metal in the slab and the larger the cross-section, the greater the impact energy of the external force; the excitation force of the appropriate impact energy on the surface of the solidification end slab shell can make the semi-solidified Under the action of shear stress, the viscosity of molten steel decreases and its fluidity increases, thereby improving the feeding capacity of semi-solidified molten steel.

When the impact energy of the exciting force of the present invention is less than 15 joules, the fluidity of the slab cannot be effectively improved, and it is difficult to effectively improve the feeding ability of the semi-solidified molten steel in the middle and later stages of solidification; if the impact energy of the exciting force is greater than 1500 joules, then It is easy to cause problems with the surface quality of the slab. In addition, this patent also 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 method includes electromagnetic drive, motor drive, fluid drive, etc.

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

(1) The principle of applying external field force technology with electromagnetic stirring as a typical example is: the dendrites at 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 magnetic field force. However, at the end of the solidification of the slab, the temperature of the molten steel is close to the solidus line, and the solidus ratio gradually increases, the fluidity of the molten steel deteriorates, and the feeding ability is weak, so it is difficult to improve the loose structure of the slab. In practice, it is almost impossible to find There are no stable and effective cases.

(2) The main working principle of the solidification end pressing or casting and rolling technology is to apply a certain intensity of pressure to the solidified billet shell 120 of the cast slab to squeeze the semi-solidified molten steel out of the solidification cavity and squeeze the void area of solidification shrinkage, Reduce the porosity of the slab. However, this technology has the following disadvantages: it needs to add a huge light reduction device, it is difficult to eliminate the central porosity formed at the end of solidification when the reduction is small, and some crack-sensitive steel types are prone to cracks at the front of the slab solidification when the reduction is large , the location of the solidification end point is difficult to locate, and it is only applicable to rectangular billets and many other problems.

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

However, it is difficult to effectively improve the loose structure of the slab by the existing technology, which deteriorates various properties of the steel. However, the present invention applies an exciting force at the position where the metal liquid phase ratio of the slab cross section at the solidification end of the continuous casting slab 100 is 0-25%. Under the action of shear stress, due to the positive thixotropy, the viscosity decreases and the fluidity increases. Under the conditions of high pressure head of molten steel and vacuum suction of solidification shrinkage, the feeding capacity of semi-solidified molten steel is enhanced, thus utilizing the positive contact of solid-liquid two-phase metal Denaturation, improve the fluidity of semi-solidified molten steel, improve the feeding capacity 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.

Example 1

In this embodiment, a 5-strand round billet continuous casting machine in a certain factory is used. During the continuous casting process of round billets with different cross-sections, different time intervals and exciting force application devices are used at a certain position on the billet surface, and compression is used according to a certain time interval. The air drive provides an exciting force with a certain impact energy. In each case, a pouring test is carried out continuously. After casting, a low-magnification sample of the slab is taken, and the porosity is rated to determine the degree of porosity and take the average value. The specific parameters of the embodiment And the results are shown in Table 1.

In this embodiment, the excitation force is applied at the force application point, wherein the metal liquid phase ratio of the billet cross section at the force application point is 23%, 15%, 15% and 11% respectively, and one pouring test is carried out for each experimental condition. After casting, a low magnification sample of the slab was taken, 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 ratio of 23% at the application point is shown in Fig. 2 .

Comparative example 1

The basic content of this comparative example is the same as that of Example 1, except that no exciting force is applied to the surface of the continuous casting slab 100 during the continuous casting process. After casting, a low magnification sample of the slab was taken, 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 tissue of Comparative Example 1 is shown in FIG. 3 .

Table 1

Through the analysis of comparative example 1 and embodiment 1, it can be found that Fig. 2 is a schematic diagram of the morphology of the billet microstructure of embodiment 1; Fig. 3 is a schematic diagram of the morphology of the billet microstructure of comparative example 1; Crystal region 310 , equiaxed crystal region 320 and central porous hole 330 . By comparison, it is found that the equiaxed grain region 320 of the cast slab after using this patent is compared with the equiaxed grain region 320 of the cast slab that does not use this patent and is not applied to the external field force, the metal liquid phase ratio is 23%, 15%, 15% %, 11%; the time intervals are: 0.022, 0.037, 0.0625, 0.1s respectively; the magnitude of the impact energy is provided respectively: 35, 40, 60, 200/J; the center looseness rating test obtains the above center looseness, and the center looseness rating All are less than 0.5; while the central loose rating of Comparative Example 1 is 1.0. Embodiment 1 When the exciting force hits the slab shell on the surface of the slab, an intermittent exciting force is applied to the surface of the slab shell at the solidification end of the continuous casting slab 100, and the liquid metal phase of the slab cross section at the solidification end of the continuous casting slab 100 The ratio is 0-25%. The exciting force is transmitted to the core of the casting slab through the slab shell, so that the semi-solidified molten steel is under the action of shear stress, and the viscosity decreases and the fluidity increases due to the positive thixotropy. Under the condition of shrinking vacuum suction, the feeding ability of semi-solidified molten steel is enhanced, so that the positive thixotropy of solid-liquid two-phase metals can be used to improve the fluidity of semi-solidified molten steel, improve the feeding ability of semi-solidified molten steel in the middle and late solidification, and improve casting The inner structure of the slab is loose, which improves the quality of the slab.

Example 2

The basic content of this embodiment is the same as that of Embodiment 1, the difference is that intermittent exciting forces are respectively applied to the solidification end of the continuous casting slab 100 and the shell surface of the solidification middle section of the continuous casting slab 100; and the solidification end of the continuous casting slab 100 The time interval of applying the exciting force on the shell surface of the continuous casting slab 100 is less than the time interval of applying the exciting force on the surface of the slab shell in the solidification middle section of the continuous casting slab 100; wherein the metal liquid phase ratio of the slab cross section at the solidification end of the continuous casting slab 100 is b ₁ , And 25%≥b ₁ >0; the metal liquid phase ratio of the cross-section of the continuous casting slab 100 in the middle of solidification is b ₂ , and 75%≥b ₂ >25%. That is, a terminal excitation force application device 210 is provided at the position where the metal liquid phase rate of the continuous casting slab 100 is 25%≥b ₁ >0, and the terminal excitation force application device 210 is used to apply intermittent The exciting force applied by the terminal exciting force applying device 210 is applied at a time interval of 0.0167-2s, and the impact energy applied by the vibration force is in the range of 15-1500J. At the position where the metal liquid phase rate of the continuous casting slab 100 is 75%≥b ₂ >25%, a middle section exciting force applying device 220 is provided, and the middle section exciting force applying device 220 is used to apply intermittent The exciting force (as shown in FIG. 4 ), the time interval for applying the exciting force of the middle stage exciting force applying device 220 is 1-30 seconds; the range of impact energy applied by the exciting force is 10-800J.

It is worth noting here that it has been explained in Example 1 that the exciting force applied at the end of solidification is completely different from the vibration, and here again it is explained that the exciting force applied at the middle stage of solidification is completely different from the vibration. The specific description is as follows:

(1) The action mode of the exciting force is completely different from that of the vibration. The intermittent exciting force is a one-way single-shot hitting or knocking on the surface of the billet shell at the end of the solidification, and the billet itself will not have relative displacement; while the vibration It is the reciprocating shaking of the slab, the slab itself may produce relative displacement, and the vibration exerts a reciprocating force on the surface of the slab shell, so there is an essential difference between the intermittent exciting force and the vibration;

(2) The mechanism of action is completely different. Due to the completely different modes of action between the exciting force and the vibration, when the exciting force hits the slab shell on the surface of the slab, it can interrupt the dendrite head growing at the solidification front during the cooling process, prompting the The columnar crystals are converted into equiaxed crystals, and at the same time, the continuous relative displacement between the liquid steel and the dendrites at the solidification front caused by the external force is not increased, which inhibits the transfer of solute elements in the steel to the liquid phase of the steel; while the vibration is the use of inertial force It can feed shrinkage and improve the looseness of metal solidification structure. Vibration will additionally increase external force and cause continuous relative displacement between molten steel and dendrites at the solidification front, and promote the transfer of solute elements in steel to the liquid phase of steel, resulting in casting The generation of billet negative segregation.

Moreover, due to the differences in the location of the excitation force applied to the surface of the shell at the end of solidification and the middle section of solidification, the magnitude of the impact energy and the time interval, the mechanism of the excitation force applied at the end of solidification and the middle section of solidification is also completely different.

The continuous casting slab 100 of the present invention includes a casting slab concave arc side 101 and a casting slab convex arc side 102, and an intermittent exciting force is applied to the surface of the solidified slab shell 120 of the continuous casting slab 100, and at the point where the exciting force is applied The liquid phase ratio of the metal in the cross section of the slab is 25% to 85%. This is because when the metal liquid phase rate is higher than 85%, the strength of the solidified billet shell is not enough, and it does not have the conditions to withstand the external force of effectively breaking the dendrite head; Vibration has been unable to increase the equiaxed crystal ratio of the slab. Exciting force is applied on the concave arc side 101 or the convex arc side 102 of the continuous casting slab 100; Exciting force.

The time interval between the application of the excitation force in the middle stage of solidification is 1-30 seconds. This is because when the time is less than 1 second, the effect of the external force is close to continuous action, resulting in continuous relative displacement between the molten steel and the dendrites at the solidification front, resulting in constant solute elements. Transferring to the liquid metal, it is easy to produce negative segregation, and the breaking effect is also reduced due to the lack of time for the growth of dendrites; when the time is greater than 30 seconds, the length of dendrite growth is too long, the number of broken dendrite heads is small, and the inhibitory effect on columnar crystals is not enough. The time interval is related to the thickness of the billet shell at the action point. When the billet shell is thin, the dendrite grows faster, and the excitation interval should be shorter. Specifically, it can be expressed by the following relationship: the time interval for applying the excitation force to the shell shell surface in the middle of solidification is t ₂ , t ₂ =ε×b ₂ ^τ ×S, the value range of ε is 0.4～0.8s/mm ² ; b ₂ is the metal solid phase rate/% in the transverse section of continuous casting slab 100 at the action position; the value range of τ is 1.4～2.0; S is the sectional area of the slab/mm ² .

The range of impact energy applied by the exciting force in the middle stage of solidification is 10-800J. The specific value is related to factors such as the thickness of the slab shell (metal liquid phase ratio), and can be specifically expressed by the following relationship: the impact energy of the exciting force applied to the surface of the slab shell in the middle of the solidification of the continuous casting slab 100 is W ₂ , The value range of a ₂ is 0.2～2.6J/mm ³ , b ₂ is the metal liquid phase ratio/% of the transverse section of the slab at the point where the exciting force is applied in the middle stage of solidification; the value range of C ₂ is 1.8～2.4; S is Cross-sectional area of billet/mm ² .

Along the length direction of the liquidus line of the continuous casting slab 100, on the surface of the solidified slab shell 120 of the solidified middle section of the continuous casting slab 100, at least one set of middle section exciting force applying device 220 is arranged, and the middle section exciting force applying device 220 is used to provide To apply the excitation force, the concave arc side 101 of the cast slab in this embodiment is provided with a middle section of the excitation force application device 220, and the terminal excitation force application device 210 and the middle section of the excitation force application device 220 are arranged on the same side of the continuous casting slab 100. side, the terminal excitation force application device 210 and the middle section excitation force application device 220 of this embodiment are arranged on the concave arc side 101 of the billet. That is, the single-side excitation force applied at a position of the liquid metal phase ratio of the continuous casting slab 100 or the simultaneous application of the excitation force at the corresponding position on both sides is a group of excitation forces; The applied multiple excitation forces are multiple sets of excitation forces. At the same time, along the length direction of the liquidus line of the continuous casting slab 100 , multiple application points of the exciting force can be set on the surface of the solidified slab shell 120 of the continuous casting slab 100 .

In this example, a 5-strand round slab continuous casting machine is used in a certain factory. The diameter of the slab is 380mm. Different time intervals and exciting force application devices are used on the surface of the slab, and the liquid phase rate at the solidification end of the continuous casting slab 100: 23%. Exciting force is applied at the position, the time interval of the exciting force at this position is 0.022s, and the impact energy at the end of solidification is 35J; The work is 20J. After casting, take a low-magnification sample of the slab, detect the equiaxed crystal ratio, perform porosity rating, determine the porosity degree and take the average value. The specific parameters and results of Example 2 are shown in Table 2. The schematic diagram of the low-magnification structure As shown in Figure 6.

Comparative example 2

The basic content of this Comparative Example 2 is the same as that of Example 2, except that no other measures are applied in the continuous casting process. After casting, a low-magnification sample of the slab was taken, the equiaxed crystal ratio was detected, and the porosity rating was performed to determine the porosity degree and take the average value. The specific parameters and results of Comparative Example 2 are shown in Table 2.

Example 3

The basic content of this embodiment is the same as that of Embodiment 2, except that the diameter of the slab is 380mm, and the middle section of the solidified middle section of the continuous casting slab 100 is provided with a middle section exciting force applying device 220 correspondingly on both sides, and the middle section of the exciting force on both sides The direction of the exciting force applied by the applicator 220 is collinear, and the direction of the applied force of the middle section of the exciting force applied device 220 passes through the geometric center of the cross-section of the continuous casting slab 100. This embodiment is a round slab, and the exciting force is large in the striking direction Through the center of the cross-section of the slab; that is, at the position of a force application point on the surface of both sides of the slab, the same impact energy is used to symmetrically impact and apply the exciting force. In this embodiment, the concave arc side 101 and The same exciting force is simultaneously applied to the corresponding positions on both sides of the billet convex arc side 102 (as shown in FIG. 5 ).

In addition, the application position, time interval and impact energy of the excitation force at the solidification end and the solidification middle section of the continuous casting slab 100 are different. After casting, a low-magnification sample of the slab was taken, and the equiaxed grain rate was detected, and the porosity rating was performed to determine the porosity degree and take the average value. The specific parameters and results of the embodiment are shown in Table 2.

Table 2

It can be found from Table 2 that after the intermittent exciting force is applied to the surface of the slab shell at the end of the solidification of the continuous casting slab 100 and the solidification middle section of the continuous casting slab 100, the equiaxed grain ratios of Example 2 and Example 3 are respectively increased to 55 % or more, and the central porosity rating is 0, and no negative segregation occurs when the quality of the slab is improved. Compared with Comparative Example 1, the quality of Example 2 and Example 3 is greatly improved.

In addition, comparing Figure 3 and Figure 6, after intermittent excitation force is applied to the surface of the slab shell at the solidification end and solidification middle section of the continuous casting slab, not only the proportion of the equiaxed grain 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 slab shell at the solidification end of the continuous casting slab and the solidification middle section respectively, and the exciting force striking the surface of the slab shell at the solidification middle section of the continuous casting slab 100 can regularly interrupt the cooling process The dendrite head growing at the solidification front makes the columnar crystals transform into equiaxed crystals, which promotes the growth of equiaxed crystals; The positive thixotropy of liquid two-phase metal can improve the feeding ability of semi-solidified molten steel in the middle and late solidification, improve the production of equiaxed crystals and at the same time improve the feeding ability of semi-solidified molten steel in the middle and late solidification, and improve the loose internal structure of the slab. Improve the quality of the billet; in the middle of the solidification of the billet 100, the exciting force generating system is used to hit the shell of the billet surface with an external force of a certain intensity at a certain position and at a certain time interval, so that the exciting force passes through the billet. The shell is transmitted to the solidification front of the slab, periodically breaks the dendrite heads growing at the solidification front, and provides crystal nuclei for the subsequent formation of central equiaxed crystals while inhibiting the growth of columnar crystals.

The present invention has been described in detail above with reference to specific exemplary embodiments. However, it should be understood that various modifications and changes can be made without departing from the scope of the present invention as defined in the appended claims. The detailed description and drawings are to be regarded as illustrative only and not restrictive, and any such modifications and variations, if any, are intended to fall within the scope of the invention as described herein. In addition, the background art is intended to illustrate the research and development status and significance of the present technology, and is not intended to limit the present invention or the application and the application field of the present invention.

Claims (10)

1. a kind of method improving casting process solidification middle and later periods solid-liquid two-phase region mobility, it is characterised in that：In continuous casting billet (100) the green shell surface of solidification end applies intermittent exciting force, wherein the strand cross section of continuous casting billet (100) solidification end Metal liquid fraction is b₁, and 25% >=b₁>0。

2. a kind of method improving casting process solidification middle and later periods solid-liquid two-phase region mobility according to claim 1, It is characterized in that：The time interval that the exciting force on solidification end green shell surface applies is t₁, t₁=0.0167~2s.

3. a kind of method improving casting process solidification middle and later periods solid-liquid two-phase region mobility according to claim 1, It is characterized in that：The impact energy ranging from W that the exciting force on solidification end green shell surface applies₁, W₁=15~1500J.

4. solidifying middle and later periods solid-liquid two-phase region mobility according to a kind of casting process that improves of claim 1-3 any one of them Method, it is characterised in that：The impact energy for applying exciting force on the green shell surface of continuous casting billet (100) solidification end is W₁, W₁=a₁× (1-b)^C×S^1.5,

a₁Value range is 0.2~1.0J/mm³,

b₁For metal liquid fraction/% of the strand lateral cross section of solidification end exciting force point of application position；

C₁Value range is 2.7~3.3；

S is casting blank section area/mm²。

5. the control method of slab quality during a kind of continuous casting and solidifying, it is characterised in that：In continuous casting billet (100) solidification end and The green shell surface in continuous casting billet (100) solidification stage casing applies intermittent exciting force respectively；And the base of continuous casting billet (100) solidification end The time interval that shell surface applies exciting force was less than between the time of green shell surface application exciting force in continuous casting billet (100) solidification stage casing Every；Wherein the strand cross section metal liquid fraction of continuous casting billet (100) solidification end is b₁, and 25% >=b₁>0；Continuous casting billet (100) The strand cross section metal liquid fraction for solidifying stage casing is b₂, and 75% >=b₂>25%.

6. the control method of slab quality during a kind of continuous casting and solidifying according to claim 5, it is characterised in that：Solidification The time interval that the green shell surface of end applies exciting force is t₁, t₁=0.0167~2s, or/and solidify the green shell surface in stage casing The time interval for applying exciting force is t₂, t₂=1-30s.

7. the control method of slab quality during a kind of continuous casting and solidifying according to claim 5, it is characterised in that：Solidification The green shell surface of end applies the impact energy ranging from W of exciting force₁, W₁=15~1500J；Or/and the green shell surface in solidification stage casing Apply the impact energy ranging from W of exciting force₂, W₂=10~800J.

8. the control method of slab quality during a kind of continuous casting and solidifying according to claim 5, it is characterised in that：Even The impact energy that the green shell surface of strand (100) solidification end applies exciting force is W₁

a₁Value range is 0.2~1.0J/mm³,

b₁For metal liquid fraction/% of the strand lateral cross section of solidification end exciting force point of application position；

C₁Value range is 2.7~3.3；

S is casting blank section area/mm²。

9. the control method of slab quality during a kind of continuous casting and solidifying according to claim 5, it is characterised in that：Even The green shell surface that strand (100) solidifies stage casing applies the impact energy of exciting force as W₂,

a₂Value range is 0.2~2.6J/mm³,

b₂For metal liquid fraction/% of the strand lateral cross section of solidification stage casing exciting force point of application position；

C₂Value range is 1.8~2.4；

S is casting blank section area/mm²。

10. the control device of slab quality during a kind of continuous casting and solidifying, it is characterised in that：In continuous casting billet (100) metal liquid phase Rate is 25% >=b₁>End exciting force bringing device (210) is provided at 0 position, and in continuous casting billet (100) metal liquid fraction For 75% >=b₂>Stage casing exciting force bringing device (220), end exciting force bringing device (210) are provided at 25% position It is respectively used to stage casing exciting force bringing device (220) for applying intermittent exciting force to green shell surface.