Downward method for eliminating defects in the core of a cast

Abstract

The application provides a method for eliminating the core defects of a casting blank by pressing, and belongs to the technical field of continuous casting, and comprises the following steps: taking the position at which the solidification make-up channel is closed at the end of the solidification of the central region of the casting blank as the solidification critical zone of the casting blank; performing first heavy pressing on the casting blank before the solidification critical zone of the casting blank along the drawing direction of the casting blank, and performing second heavy pressing on the casting blank after the solidification critical zone of the casting blank, so as to eliminate the core defects of the casting blank. The application can solve the problem that the existing method for eliminating the core defects of a casting blank by pressing cannot achieve the effect of completely and effectively eliminating the internal defects of the casting blank.

Description

Technical Field

[0001] This invention relates to the field of continuous casting processing technology, and more specifically, to a method for eliminating core defects in cast billets. Background Technology

[0002] Internal quality of cast billets constitutes a major category of billet quality, among which porosity, shrinkage cavities, and segregation in the central region are the most significant defects affecting billet quality. Porosity, shrinkage cavities, and segregation generally occur together. The common method used to address internal quality issues in cast billets is the reduction technique.

[0003] Currently, there are three types of reduction techniques: light reduction, a combination of light and heavy reduction, and single-roll heavy reduction. Light reduction effectively controls center segregation, but its effect on porosity and shrinkage cavities is not ideal. The combination of light and heavy reduction uses multiple light reduction points in the front part of the two-phase zone to address segregation. After the feeding channel is completely closed, heavy reduction using one or two rolls is applied to "weld" the shrinkage cavity and simultaneously reduce porosity. This method prioritizes preventing or controlling the occurrence of reduction cracks and then welds the shrinkage cavity after it forms; however, it cannot completely eliminate the shrinkage cavity. Single-roll heavy reduction applies sufficient reduction before the feeding channel is closed, making the billet center dense and preventing later shrinkage cavities. It can eliminate center shrinkage cavities and effectively suppress center segregation, but later V-shaped segregation will appear and continue to develop.

[0004] In summary, the existing pressing methods for eliminating core defects in cast billets each have their own advantages and disadvantages, as well as the main core defects they address. Their process guiding principles are not entirely the same, but none of them can achieve the effect of completely and effectively eliminating internal defects in cast billets. Summary of the Invention

[0005] In view of the above problems, the purpose of this invention is to provide a pressing method for eliminating core defects in cast billets, so as to solve the problem that the pressing method for eliminating core defects in cast billets in the prior art cannot achieve the effect of completely and effectively eliminating internal defects in cast billets.

[0006] This invention provides a pressing method for eliminating core defects in cast billets, comprising the following steps:

[0007] The central region of the billet at the point where the solidification feeding channel closes at the end of solidification is taken as the solidification critical region of the billet.

[0008] Along the casting direction of the billet, before the solidification critical region of the billet, the billet is subjected to a first heavy pressure, and after the solidification critical region of the billet, the billet is subjected to a second heavy pressure to eliminate core defects of the billet.

[0009] Furthermore, a preferred approach is to define the solidification critical region of the billet as the location where the central region of the billet closes the solidification feeding channel at the end of solidification.

[0010] The starting position of the solidification critical domain of the billet is defined as the location where the solidification feeding channel in the central region of the billet shows a tendency to close at the end of solidification.

[0011] The position where the solidification feeding channel is completely closed at the end of the solidification period in the central region of the billet is taken as the end position of the solidification critical domain of the billet.

[0012] Furthermore, a preferred embodiment is that defining the central region of the billet at the point where the solidification feeding channel closes at the end of solidification as the solidification critical region of the billet includes:

[0013] Obtain the initial position where shrinkage cavities begin to form in the central region of the billet, and set the initial position as the position where the solidification feeding channel in the central region of the billet closes at the end of solidification.

[0014] The central region of the billet at the point where the solidification feeding channel closes at the end of solidification is taken as the solidification critical region of the billet.

[0015] Furthermore, a preferred embodiment is that defining the central region of the billet at the point where the solidification feeding channel closes at the end of solidification as the solidification critical region of the billet includes:

[0016] The region with a central solid fraction of 0.7 to 0.73 in the billet is defined as the position where the solidification feeding channel closes at the end of solidification in the central region of the billet.

[0017] The central region of the billet at the point where the solidification feeding channel closes at the end of solidification is taken as the solidification critical region of the billet.

[0018] Furthermore, a preferred approach is to apply the first heavy pressure to the billet using a sufficient amount of single-roller heavy pressure during the first heavy pressure process.

[0019] Furthermore, a preferred embodiment is that the compression amount under the first heavy pressure is 10 to 40 mm.

[0020] Furthermore, a preferred embodiment is that, during the second heavy pressing process on the billet, the billet is subjected to the second heavy pressing by a single roller or multiple rollers.

[0021] Furthermore, in a preferred embodiment, when the billet is subjected to a second heavy pressing by a single roller, the pressing amount of the pressing roller is 5 to 15 mm.

[0022] In addition, a preferred embodiment is to apply a second heavy pressure to the billet using 2 to 3 pairs of pressure rollers, wherein the pressure reduction of each pressure roller is 5 to 15 mm during the second heavy pressure.

[0023] Furthermore, in a preferred embodiment, the pressing method eliminates core defects in the billet, including shrinkage cavities, center segregation, and V-shaped segregation.

[0024] As can be seen from the above technical solution, the pressing method for eliminating core defects in cast billets provided by this invention takes the central region of the cast billet at the point where the solidification feeding channel closes at the end of solidification as the solidification critical region of the cast billet; then, along the casting direction, before the solidification critical region of the cast billet, a first heavy pressing is applied to the cast billet, which can prevent the occurrence of shrinkage cavities and the aggravation of center segregation by heavy pressing before the shrinkage channel closes; after the solidification critical region of the cast billet, a second heavy pressing is applied to the cast billet, which can suppress the occurrence of later V-shaped segregation by heavy pressing after the shrinkage channel closes. By adopting the idea of ​​suppressing the occurrence of later defects before defects occur, rather than the idea of ​​mitigating them after defects occur, it can fundamentally maximize the elimination of defects; and further improve the density of the central structure, thereby comprehensively eliminating internal quality defects in the cast billet, so as to achieve the best quality improvement effect with the least equipment cost.

[0025] To achieve the foregoing and related objectives, one or more aspects of the invention include the features that will be described in detail below. The following description and accompanying drawings illustrate certain exemplary aspects of the invention. However, these aspects indicate only a few of the various ways in which the principles of the invention can be used. Furthermore, the invention is intended to encompass all such aspects and their equivalents. Attached Figure Description

[0026] Other objects and results of the invention will become more apparent and readily understood with reference to the following description taken in conjunction with the accompanying drawings. In the drawings:

[0027] Figure 1 A flowchart of a pressing method for eliminating core defects in a cast billet according to an embodiment of the present invention;

[0028] Figure 2 This is a low-magnification view of the cast billet without pressure reduction according to Embodiment 1 of the present invention;

[0029] Figure 3 This is a low-magnification view of the billet after a 15mm reduction due to the combination of light and heavy pressure according to Embodiment 1 of the present invention;

[0030] Figure 4 This is a low-magnification view of a billet that has been rolled down 15 mm before the solidification critical region according to Embodiment 1 of the present invention.

[0031] Figure 5 This is a low-magnification view of a cast billet that was pressed down 15 mm before the solidification critical region and then pressed down 7 mm after the solidification critical region, according to Embodiment 1 of the present invention. Detailed Implementation

[0032] In the following description, numerous specific details are set forth for illustrative purposes and to provide a thorough understanding of one or more embodiments. However, it will be apparent that these embodiments may also be implemented without these specific details.

[0033] In view of the problem that the pressing method for eliminating core defects in the cast billet mentioned above cannot achieve the effect of completely and effectively eliminating internal defects in the cast billet, a pressing method for eliminating core defects in the cast billet is proposed.

[0034] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0035] To illustrate the pressing method for eliminating core defects in cast billets provided by this invention, Figure 1 A flow chart of a pressing method for eliminating core defects in a cast billet according to an embodiment of the present invention is shown; Figure 2 This shows a low-magnification view of the cast billet without pressure reduction according to Embodiment 1 of the present invention; Figure 3 This is a low-magnification view of the billet under a 15mm reduction by a combination of light and heavy pressure according to Embodiment 1 of the present invention; Figure 4 This is a low-magnification view of a cast billet that has been pressed down 15 mm before the solidification critical region according to Embodiment 1 of the present invention. Figure 5 This is a low-magnification view of a cast billet that has been pressed down 15 mm before the solidification critical region and then pressed down 7 mm after the solidification critical region, according to Embodiment 1 of the present invention.

[0036] like Figures 1 to 5 As shown in the figure, the pressing method for eliminating core defects in cast billets provided by the present invention includes the following steps:

[0037] Step S1: The central region of the billet at the point where the solidification feeding channel closes at the end of solidification is taken as the critical solidification region of the billet.

[0038] Step S2: Along the billet pulling direction, before the billet reaches the solidification critical region, apply the first heavy pressure to the billet, and after the billet reaches the solidification critical region, apply the second heavy pressure to the billet to eliminate core defects in the billet.

[0039] During the later stages of solidification in the central region of the billet, as the feeding channels of the molten steel close, shrinkage cavities form and porosity intensifies. This is accompanied by a sharp increase in central porosity and shrinkage cavities, along with the occurrence and rapid increase of abnormal segregation. Segregation worsens continuously after the feeding channels close, shrinkage cavities form rapidly, and porosity persists throughout the solidification process, ultimately resulting in central shrinkage cavities, porosity, and segregation (with visible V-shaped segregation accompanying the porosity). Currently available light reduction techniques, combined light and heavy reduction techniques, and single-roll heavy reduction techniques cannot comprehensively solve the defects such as shrinkage cavities, central segregation, and V-shaped segregation in the core of the billet.

[0040] This invention addresses the shortcomings of existing pressing techniques by suppressing defects in the billet core before they appear, rather than eliminating them only after they have occurred. It introduces the solidification critical domain of the billet and sets the timing and method of pressing. Specifically, a sufficient amount of heavy pressing is applied before the shrinkage channel closes to prevent shrinkage cavities and the exacerbation of center segregation. Then, after the shrinkage channel closes, another heavy pressing is applied to suppress later V-shaped segregation and further improve the density of the central structure. This comprehensively solves the quality defects inside the billet, achieving optimal quality improvement with minimal equipment cost.

[0041] In a preferred embodiment of the present invention, the central region of the billet at the point where the solidification feeding channel closes at the end of solidification is defined as the critical solidification region of the billet.

[0042] The starting point of the solidification critical region of the billet is defined as the location where the solidification feeding channel in the central region of the billet shows a tendency to close at the end of solidification.

[0043] The point where the solidification feeding channel is completely closed at the end of the solidification process in the central region of the billet is taken as the end point of the solidification critical region of the billet.

[0044] Specifically, for specific steel grades and working conditions, the solidification critical domain of the billet can be determined, corresponding to the state of the solidification feeding channel in the central region of the billet during the later stage of solidification. The beginning of the solidification critical domain corresponds to the feeding channel showing a closing trend, and the end of the solidification critical domain corresponds to the feeding channel being completely closed, thus determining the beginning and end of the solidification critical domain. Since the closing position of the feeding channel fluctuates to a certain extent, this invention defines it as the solidification critical domain.

[0045] As a preferred embodiment of the present invention, the solidification critical region of the billet is defined as the location where the solidification feeding channel closes at the end of solidification.

[0046] Obtain the initial position where shrinkage cavities begin to form in the central region of the billet, and set the initial position to the position where the solidification feeding channel in the central region of the billet closes at the end of solidification.

[0047] The central region of the billet at the point where the solidification feeding channel closes at the end of solidification is taken as the critical solidification region of the billet.

[0048] Specifically, the initial position where shrinkage cavities begin to form in the central region of the billet can be obtained through a shrinkage cavity model or a shrinkage cavity formation judgment formula. For example, a shrinkage cavity formation judgment formula currently in use can be adopted:

[0049] G m T m =Pcri; where G is the temperature gradient to be determined, in °C / m; T is the cooling rate to be determined, in °C / s; m and n are constants, and Pcri is the critical position for the formation of shrinkage cavity in the billet. When the exponential product of G and T begins to be less than Pcri, the shrinkage cavity is fully formed. All the above data can be obtained by those skilled in the art through process parameter setting or calculation. Since this is prior art, it will not be elaborated here. In the technical solution of this invention, as long as the initial position where the shrinkage cavity begins to form in the central region of the billet can be obtained, the specific method is not particularly limited. The initial position for the formation of the shrinkage cavity is set as the position where the solidification feeding channel in the central region of the billet closes at the end of solidification. Then, the position where the solidification feeding channel in the central region of the billet closes at the end of solidification is taken as the solidification critical domain of the billet, thereby obtaining the solidification critical domain of the billet defined in the technical solution of this invention.

[0050] As a preferred embodiment of the present invention, the solidification critical region of the billet is defined as the location where the solidification feeding channel closes at the end of solidification.

[0051] The region with a central solid fraction of 0.7 to 0.73 in the billet is defined as the central region of the billet at the point where the solidification feeding channel closes at the end of solidification.

[0052] The central region of the billet at the point where the solidification feeding channel closes at the end of solidification is taken as the critical solidification region of the billet.

[0053] Specifically, in a preferred embodiment of the present invention, another way to obtain the solidification critical region is through experimental verification. First, a sufficient number of experimental data of various steel grades under specific working conditions are verified to obtain the region of central solid fraction corresponding to the position where the solidification feeding channel closes at the end of solidification, which is 0.7 to 0.73. Therefore, the region of central solid fraction of the billet of 0.7 to 0.73 can be set as the position of the central region of the billet where the solidification feeding channel closes at the end of solidification; then, the position of the central region of the billet where the solidification feeding channel closes at the end of solidification can be taken as the solidification critical region of the billet.

[0054] As a preferred embodiment of the present invention, the amount of compression under the second heavy pressure is less than the amount of compression under the first heavy pressure.

[0055] Specifically, the amount of pressure applied under the second heavy pressure is preferably less than the amount of pressure applied under the first heavy pressure. Of course, in practical applications, the amount of pressure applied under the second heavy pressure can also be greater than or equal to the amount of pressure applied under the first heavy pressure. This invention does not impose any particular limitation on this.

[0056] In a preferred embodiment of the present invention, during the first heavy pressing of the billet, the billet is subjected to a sufficient amount of single-roll heavy pressing. Performing a sufficient heavy pressing before the shrinkage cavity channel closes avoids the occurrence of shrinkage cavities and the exacerbation of center segregation.

[0057] As a preferred embodiment of the present invention, the compression amount under the first heavy pressure is 10-40 mm. This is a preferred embodiment. In practical applications, the compression amount under the first heavy pressure can be set slightly according to the actual situation. For example, the compression amount can be 9.5 mm, 9.6 mm, 40.1 mm, 40.5 mm, etc.

[0058] In a preferred embodiment of the present invention, during the second pressing of the billet, the billet is subjected to the second pressing using a single roll or multiple rolls. After the solidification critical region, the single-roll or multi-roll pressing suppresses the occurrence of later V-shaped segregation and also suppresses the increase of segregation. Multiple rolls refer to more than one pair of pressing rolls, such as two pairs, three pairs, four pairs, etc.

[0059] As a preferred embodiment of the present invention, when the billet is subjected to a second heavy pressing by a single roller, the pressing amount of the pressing roller is 5 to 15 mm.

[0060] As a preferred embodiment of the present invention, the billet is subjected to a second heavy pressing by 2 to 3 pairs of pressing rollers, and the pressing amount of each pressing roller is 5 to 15 mm during the second heavy pressing.

[0061] The above-described second heavy pressure method is a preferred embodiment of the present invention. In practical applications, appropriate selections can be made according to actual conditions. Therefore, the present invention does not impose any particular limitations on this.

[0062] As a preferred embodiment of the present invention, the pressing method eliminates core defects in the cast billet, including shrinkage cavities, center segregation, and V-shaped segregation.

[0063] The pressing method provided by this invention is mainly used, but not limited to, to eliminate defects such as shrinkage cavities, center segregation, and V-shaped segregation in the core of the billet.

[0064] To better illustrate the pressing method for eliminating core defects in cast billets provided by this invention, the following example is provided:

[0065] Example 1

[0066] Taking a 180X180mm square billet from a steel plant as an example, the steel grade is 82B, the billet casting speed is 1.45m / min, and the superheat is 45℃.

[0067] Low magnification results of the unpressurized billet, such as Figure 2 As shown, from Figure 2 As can be seen, there are severe central shrinkage cavities and V-shaped segregation bands at the center of the billet.

[0068] The central region of the billet at the point where the solidification feeding channel closes at the end of solidification is defined as the solidification critical region of the billet, and the billet is treated using the following three pressing methods.

[0069] The billet was pressed using a traditional light-heavy combination pressing method, specifically as follows: Before the solidification critical zone, two straightening machines were used to press the billet down by 1 mm and 5 mm respectively; after the solidification critical zone, a single straightening machine was used to press down by 9 mm. The total combined light-heavy pressing was 15 mm. The low-magnification result is shown below. Figure 3 As shown, from Figure 3 As can be seen from the data, when the billet is subjected to heavy pressure after the solidification critical region, shrinkage cavities have already begun to form, and the effect of welding to improve shrinkage cavities is not ideal.

[0070] Using a single-roller for heavy pressing, a sufficient amount of pressing is performed on a tension leveler before the solidification critical region of the cast billet. The single-roller pressing amount is 15mm, and the low-magnification result is as follows: Figure 4 As shown, from Figure 4 As can be seen, applying heavy pressure before shrinkage cavities form can prevent the occurrence of shrinkage cavities in the later stages, thus basically eliminating shrinkage cavities. However, there will be shallow V-shaped segregation bands, which is the reason why V-shaped segregation will gradually develop in the later stages.

[0071] Before the solidification critical region of the billet, a full reduction is applied using a tension leveler, with a single roll applying a 15mm reduction. After the solidification critical region of the billet, a relatively small reduction is applied using a tension leveler, with a reduction of 7mm, for a total reduction of 22mm. Figure 5 To display the results at a low magnification, from Figure 5 As can be seen, the central shrinkage cavity and V-shaped segregation band have been well resolved.

[0072] By comparing the effects of the above specific embodiments, it can be seen that the pressing method provided by the present invention requires fewer tension leveling machines compared to the traditional light and heavy combination method. Compared to single-roll heavy pressing, it requires more tension leveling machines, but it is more comprehensive and effective in eliminating defects in the core of the cast billet.

[0073] It should be noted that this embodiment is merely a detailed description of the pressing method for eliminating core defects in cast billets provided by the present invention in practical applications, and does not limit the technical solution provided by the present invention.

[0074] As can be seen from the above specific embodiments, the pressing method for eliminating core defects in cast billets provided by the present invention takes the position where the central region of the cast billet closes the solidification feeding channel at the end of solidification as the solidification critical region of the cast billet; then, along the casting direction, before the solidification critical region of the cast billet, a first heavy pressing is applied to the cast billet, which can avoid the occurrence of shrinkage cavities and the aggravation of center segregation by heavy pressing before the shrinkage channel is closed; after the solidification critical region of the cast billet, a second heavy pressing is applied to the cast billet, which can suppress the occurrence of later V-shaped segregation by heavy pressing after the shrinkage channel is closed. By adopting the idea of ​​suppressing the occurrence of later defects before defects occur, rather than the idea of ​​mitigating them after defects occur, the elimination of defects can be maximized from the root. Furthermore, it can further improve the density of the central structure, thereby completely eliminating internal quality defects in the cast billet, so as to achieve the best quality improvement effect with the least equipment cost.

[0075] The pressing method for eliminating core defects in cast billets according to the present invention has been described above by way of example with reference to the accompanying drawings. However, those skilled in the art should understand that various modifications can be made to the pressing method for eliminating core defects in cast billets according to the present invention without departing from the scope of the invention. Therefore, the scope of protection of the present invention should be determined by the contents of the appended claims.

Claims

1. A method for eliminating core defects in cast billets, characterized in that, Includes the following steps: The solidification critical region of the billet is defined as the position where the solidification feeding channel closes at the end of solidification; wherein, the position where the solidification feeding channel shows a tendency to close at the end of solidification is defined as the starting position of the solidification critical region of the billet. The position where the solidification feeding channel is completely closed at the end of the solidification period in the central region of the billet is taken as the end position of the solidification critical domain of the billet. Alternatively, the initial position where shrinkage cavities begin to form in the central region of the billet can be obtained, and the initial position can be set as the position where the solidification feeding channel in the central region of the billet closes at the end of solidification. The central region of the billet at the point where the solidification feeding channel closes at the end of solidification is taken as the solidification critical region of the billet. Alternatively, the region with a central solid fraction of 0.7 to 0.73 in the billet can be defined as the location where the solidification feeding channel closes at the end of solidification in the central region of the billet. The central region of the billet at the point where the solidification feeding channel closes at the end of solidification is taken as the solidification critical region of the billet. Along the casting direction of the billet, before the solidification critical region of the billet, the billet is subjected to a first heavy pressure, and after the solidification critical region of the billet, the billet is subjected to a second heavy pressure to eliminate core defects of the billet.

2. The pressing method for eliminating core defects in cast billets according to claim 1, characterized in that, During the first heavy pressure application to the cast billet The billet is subjected to the first heavy pressing by applying sufficient single-roller pressure.

3. The pressing method for eliminating core defects in cast billets according to claim 2, characterized in that, The initial compression under heavy pressure is 10-40 mm.

4. The pressing method for eliminating core defects in cast billets according to claim 1, characterized in that, During the second heavy pressure application to the cast billet The billet is subjected to a second heavy pressure using a single or multiple rollers.

5. The pressing method for eliminating core defects in cast billets according to claim 4, characterized in that, When the billet is subjected to a second heavy pressing by a single roller, the pressing amount of the roller is 5~15mm.

6. The pressing method for eliminating core defects in cast billets according to claim 4, characterized in that, The billet is subjected to a second heavy pressing by 2 to 3 pairs of pressing rollers. During the second heavy pressing, the pressing amount of each pressing roller is 5 to 15 mm.

7. The pressing method for eliminating core defects in cast billets according to claim 1, characterized in that, The pressing method eliminates core defects in the billet, including shrinkage cavities, center segregation, and V-shaped segregation.

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