A high-carbon alloy steel large-section rectangular billet based on multi-field synergy and its preparation method

Abstract

The present invention provides a high-carbon alloy steel large-section rectangular billet and preparation method based on multi-field synergy, belonging to the field of special steel continuous casting. The high-carbon alloy steel has a C content of 0.6-1.0% by mass, and the Cr and Mn content of the alloy is 0.5-1.1% by mass. The cross-section is 320-390 mm × 385-510 mm. A Gauss meter based on a low-frequency alternating mode is used to measure the magnetic induction intensity at the center of the crystallizer and the electromagnetic stirrer at the end of solidification. The stirring frequency is determined based on the relationship between the measured magnetic induction intensity and the electromagnetic torque. The electromagnetic stirrer at the end of solidification is positioned at a central solid phase ratio of 0.1-0.2, with a light reduction at a reduction position of 0.3-0.8 and a reduction of 12-20 mm, and a heavy reduction at a reduction position of 0.9-1 and above and a reduction of 10-12 mm. The present invention controls the composition uniformity and central density of the ingot through the synergistic effect of the electromagnetic field and the mechanical stress field.

Description

Technical Field

[0001] The present invention belongs to the field of special steel continuous casting, and in particular relates to a high-carbon alloy steel large-section rectangular billet based on multi-field synergy and a preparation method thereof. Background Art

[0002] Due to the high content and variety of carbon and alloying elements, high-carbon alloy steels exhibit severe centerline segregation and central density during the solidification process. Compared to small square billets (under 200mm×200mm), large rectangular billets exhibit even more severe centerline segregation and density due to the extended two-phase region and prolonged solidification time. This centerline segregation is difficult to completely eliminate during the subsequent heating furnace and rolling processes, and can be inherited into the rolled / forged material, forming carbides that severely impact the fatigue life and service performance of the resulting components. Furthermore, due to compression ratio limitations, this centerline density also limits the cross-sectional dimensions of large bars produced from these materials. Therefore, it is necessary to increase the density of large-section billets and reduce centerline segregation.

[0003] To improve the center segregation and density of large-section rectangular high-carbon alloy steel billets, existing technologies typically equip continuous square billet casters with a mold electromagnetic stirrer and an electromagnetic stirrer at the end of solidification, employing techniques such as light and heavy reduction at the end of solidification. While these technologies are effective for smaller square billets, they are inconsistent with larger rectangular billets, failing to improve center segregation and achieving a significant improvement in density, particularly center density. For example, Chinese invention patent No. 202311517739.5 discloses a reduction control method for improving macro- and semi-macrosegregation in high-carbon low-alloy steel. However, this method targets 200 mm × 240 mm high-carbon low-alloy steel and is not applicable to large rectangular billets. Heavy reduction technology is not involved, and there are no established rules for optimizing the process parameters for the mold and electromagnetic stirring at the end of solidification. Furthermore, the solidification heat transfer model used to calculate the center solid fraction of the billet has not been verified for accuracy. Another example is the Chinese invention patent with patent number 201811578543.6, which discloses a method for improving the internal quality of high-carbon steel large square billet continuous casting. It proposes a suitable pulling speed, secondary cooling water ratio and the ratio of water in the width and thickness directions, the surface temperature range of the billet in the width and thickness directions in the reduction interval, and sets electromagnetic stirring in front of the first reduction roller; the reduction interval is determined by the solid phase ratio calculated by the distance between the liquidus point and the solidus point, and the reduction of each reduction roller is determined in the reduction interval according to the solid phase ratio, the total reduction and the coefficient k. However, this patent uses light reduction to control the density of the center of the ingot. The looseness and shrinkage holes in the center of the ingot are formed after the center solid phase ratio is greater than 0.8 at the end of solidification. The light reduction range is between 0.2 and 0.8 of the center solid phase ratio, and the effect on the center looseness and control is limited. In addition, this patent does not involve heavy reduction technology and crystallizer electromagnetic stirring technology. This technology only uses low-magnification rating to improve the center segregation, looseness and shrinkage holes of the ingot, and does not conduct quantitative impact analysis on the cross-sectional center segregation index, longitudinal center line segregation index and center density. Summary of the Invention

[0004] An embodiment of the present invention provides a high-carbon alloy steel large-section rectangular billet and a preparation method based on multi-field collaboration to solve the problem that the existing high-carbon alloy steel large bar casting billets have central carbon segregation and central non-density, resulting in carbides and non-density in the center of the large bar, affecting the fatigue life of the manufactured parts and deteriorating the service performance, and thus the use of large-section rectangular billets limits the production of larger specifications of large bars.

[0005] In order to achieve the above objectives, the embodiments of the present invention adopt the following technical solutions:

[0006] In a first aspect, an embodiment of the present invention provides a method for preparing a large-section rectangular billet of high-carbon alloy steel based on multi-field synergy.

[0007] The high-carbon alloy steel has a C content of 0.6% to 1.0% by mass and contains at least alloying elements such as Mn and Cr, and the content by mass percentage of each element is less than 1.0%. In the continuous casting production process of large-section rectangular billets, strong crystallizer electromagnetic stirring with an optimal stirring frequency (central magnetic induction intensity greater than 500 Gs), strong alternating solidification end electromagnetic stirring (central magnetic induction intensity 800 Gs to 1000 Gs), large-reduction light reduction (12 to 20 mm) by multiple straightening machines, and heavy reduction (10 mm to 12 mm) by two straightening machines adjacent to the light reduction position are adopted to maximize the improvement of the center segregation of the billet and improve the center density. The center solid phase fraction of the billet calculated by the verified solidification heat transfer model determines the installation position of the electromagnetic stirring at the end of solidification (center solid phase fraction 0.1 to 0.2), the light reduction reduction position (center solid phase fraction 0.3 to 0.8), and the heavy reduction reduction position (center solid phase fraction 0.9 to 1), and is reasonably matched with the casting speed. This invention achieves stable improvements in the compositional uniformity and center density of large-section rectangular high-carbon alloy steel billets by precisely and rationally matching process parameters for electromagnetic stirring in the mold, electromagnetic stirring at the end of solidification, and light and heavy reduction. This allows for the independent metallurgical effects of the electromagnetic field (electromagnetic stirring in the mold and at the end of solidification) and the mechanical stress field (light and heavy reduction at the end of solidification), as well as a synergistic effect. The resulting large-section rectangular high-carbon alloy steel billets are comprehensively evaluated using low-magnification morphology and grading of cross-sectional and longitudinal sections, the central carbon segregation index of the cross section and the central carbon segregation index of the longitudinal section, and quantitative cross-sectional composition and center density. The center carbon segregation index of the billets is controlled within a range of 0.93 to 1.07, the cross-sectional carbon range is controlled below 0.03, and the center density is above 95%, enabling the production of larger bars using these billets.

[0008] Specifically, if Figure 1 As shown, the method for preparing a high-carbon alloy steel large-section rectangular billet based on multi-field synergy includes the following steps:

[0009] Step S1: electromagnetic stirrers are respectively installed at the crystallizer and the solidification end of the continuous casting machine, and 9 to 10 straightening machines are installed at the solidification end.

[0010] In this step, the 9 to 10 straightening machines set up all have the light pressure function, and the maximum pressure reduction of a single roller of the straightening machine implementing light pressure is not less than 5mm. Among them, 4 to 5 straightening machines have the heavy pressure function, and the heavy pressure straightening machines are flat rollers. The maximum pressure reduction of a single roller of the straightening machine implementing heavy pressure is not less than 10mm, and the maximum pressure is 2500KN.

[0011] Step S2, determine the optimal stirring frequency of the crystallizer electromagnetic stirrer; determine the setting position and optimal stirring frequency of the electromagnetic stirrer at the end of solidification; determine the pressing position and single roller pressing amount of the light pressing and heavy pressing of the tension and leveling machine at the end of solidification.

[0012] In this step, the center magnetic induction intensity of the crystallizer and the electromagnetic stirrer at the end of solidification is measured offline using a Gaussmeter with an alternating low-frequency mode; and when measuring the center magnetic induction intensity of the crystallizer electromagnetic stirrer, the probe of the Gaussmeter is inserted into the copper tube of the crystallizer for measurement; based on the measured center magnetic induction intensity and according to the calculation formula of the electromagnetic torque, the optimal stirring frequency of the electromagnetic stirrer of the crystallizer and the optimal stirring frequency of the electromagnetic stirrer at the end of solidification are determined;

[0013] The solidification heat transfer model verified by temperature measurement and nail shooting tests is used to calculate the solid phase fraction at the center of the ingot. The setting position of the electromagnetic stirrer at the end of solidification, the reduction position under light pressure and heavy pressure, and the single-roll reduction amount are determined according to the solid phase fraction at the center of the ingot.

[0014] In this step, the selection of the Gaussmeter is crucial for measuring the central magnetic induction intensity of the electromagnetic stirrer. Since the stirring frequency of the current crystallizer electromagnetic stirrer is less than 10Hz, which is a low frequency, and the magnetic field generated by the stirrer is an alternating magnetic field, the frequency range currently measured by conventional Gaussmeters is above 50Hz. Therefore, a Gaussmeter with low-frequency measurement capabilities and an alternating mode is required to accurately measure the magnetic induction intensity. Low frequency here refers to less than 10Hz.

[0015] A copper tube is required to measure the central magnetic induction intensity of the mold's electromagnetic stirrer. Since the mold contains a copper tube and the electromagnetic stirrer is placed outside it, the copper tube shields the magnetic field and creates a skin effect. Consequently, the lower the frequency, the greater the central magnetic induction intensity of the mold's electromagnetic stirrer. For electromagnetic stirring at the end of solidification, the shell shields the magnetic field, which is weaker than the copper tube. However, the actual stirring action of the molten steel is the electromagnetic force generated by the interaction between the alternating magnetic field and the moving molten steel. This electromagnetic force has a predetermined relationship with the magnetic induction intensity and the stirring frequency. Therefore, there is an optimal stirring frequency that maximizes the stirring force at different stirring currents.

[0016] Specifically, when the measured central magnetic induction intensity is used to calculate the optimal stirring frequency in this step, the optimal stirring frequency is determined by the following formula:

[0017] (1)

[0018] In formula (1), T is the electromagnetic torque, σ is the conductivity of the conductor, which is 1.4~2.0×10^6 S / m for molten steel; f is the stirring frequency; B is the measured magnetic induction intensity at the center of the stirrer; r1 is the equivalent radius of the liquid core, which is approximately 0.185m~0.231m for a section of 320~390mm×385~510mm; L is the effective length of the stirrer, which is approximately 0.4m~0.5m.

[0019] For the crystallizer and the electromagnetic stirrer at the end of solidification, the stirring current is positively correlated with the central magnetic induction intensity B, while the stirring frequency f is negatively correlated with the central magnetic induction intensity B and the stirring frequency f. A predetermined negative correlation exists between the two. The magnetic induction intensity at the center of the stirrer is measured using a Gaussmeter at different stirring currents and frequencies, and then fitted to obtain the relationship between the central magnetic induction intensity B and the frequency f. Therefore, due to the correlation between B and f in Equation (1), the electromagnetic torque T reaches its maximum value relative to the variable f. The frequency corresponding to the maximum electromagnetic torque T is the optimal stirring frequency.

[0020] Preferably, the gaussmeter is a Lakeshore 475DS gaussmeter. The central magnetic induction intensity of the crystallizer electromagnetic stirrer is 500-600 Gs, and the calculated optimal stirring frequency is 1.5 Hz-2.5 Hz, which is used as the optimal stirring frequency of the crystallizer electromagnetic stirrer. The central magnetic induction intensity of the solidification end stirrer is 800-1000 Gs, and the calculated optimal stirring frequency is 6-8 Hz, which is used as the optimal stirring frequency of the solidification end electromagnetic stirrer. The crystallizer electromagnetic stirrer adopts a continuous stirring mode, and the solidification end electromagnetic stirrer adopts an alternating mode. The time that the billet passes through the stirrer (the ratio of the effective stirrer length to the casting speed) must be greater than at least two stirring cycles.

[0021] At the same time, in this step, the setting position of the electromagnetic stirrer at the end of solidification, the pressing positions under light pressure and heavy pressure, and the single-roll pressing amount are determined according to the solid phase ratio at the center of the ingot, specifically including:

[0022] The solid phase ratio in the center of the ingot is 0.1~0.2, which is the location of the electromagnetic stirrer at the end of solidification;

[0023] After the electromagnetic stirrer at the end of solidification, when the solid phase ratio at the center of the ingot is 0.3-0.8, 4-5 straightening machines are set up for soft reduction; the total soft reduction is 12-20 mm; the single-roller reduction is determined according to the total soft reduction and the number of straightening machines;

[0024] Near the light pressure straightening machine, when the solid phase ratio at the center of the billet is 0.9-1, a straightening machine is set up for heavy pressure reduction. After the solid phase ratio at the center reaches 1, another straightening machine is set up for heavy pressure reduction, with a total weight reduction of 10-12 mm; the single-roll reduction amount is determined based on the total weight reduction amount. In this step, two straightening machines with heavy pressure are set up at the end of solidification. When the solid phase ratio at the center of the billet is 0.9-1, the single-roll heavy pressure is further improved to improve the center segregation and increase the center density. After the solid phase ratio at the center of the billet is 1, a straightening machine with heavy pressure is set up to eliminate the shrinkage cavity and looseness at the center of the billet. Through the cooperation of the two straightening machines with heavy pressure, the center segregation is improved and the center density of the billet is increased. Preferably, the straightening machine with heavy pressure uses flat rollers.

[0025] In a preferred embodiment, the relationship between the light reduction and heavy reduction and the center solid phase ratio of the ingot is: when the center solid phase ratio is in the range of 0.3~0.5, the single-roll reduction is 1~2mm; when the center solid phase ratio is in the range of 0.5~0.8, the single-roll reduction is 3~5mm; two drawing and straightening machines are configured under heavy pressure, and when the center solid phase ratio is in the range of 0.9~1, one drawing and straightening machine is configured and the single-roll reduction is 5mm~6mm. After the center solid phase ratio is 1, one drawing and straightening machine is configured and the single-roll reduction is 5mm~6mm, and the reduction in the heavy pressure stage after the center solid phase ratio is 1 is greater than the reduction in the heavy pressure stage of 0.9~1.

[0026] Step S3, after the continuous casting machine starts pouring, from the tundish to the crystallizer stage:

[0027] The molten high-carbon alloy steel flows from the tundish of a multi-stream large-section rectangular billet continuous casting machine into the crystallizer through an immersed nozzle.

[0028] In this step, the mass percentage of C in the high carbon alloy steel liquid is 0.6% to 1.0%, and the high carbon alloy steel liquid contains at least alloying elements such as Mn and Cr, and the mass percentage of the alloying elements is less than 1.0%.

[0029] Preferably, the multi-strand, large-section rectangular billet continuous casting machine is a fully curved, 5-strand, 5-machine continuous casting machine, with billet cross-sectional dimensions of 320-390 mm x 385-510 mm. Preferably, the continuous casting process parameters are: a casting speed of 0.39 m / min to 0.6 m / min, a weak cooling mode for the secondary cooling, and a water content of 0.12-0.2 L / kg.

[0030] Step S4, during the crystallizer to solidification end stage:

[0031] The crystallizer electromagnetic stirrer rotates and stirs the molten steel, and solidifies it in the secondary cooling zone through full water combined with mist cooling; at the setting position of the solidification end, the solidification end electromagnetic stirrer stirs the molten steel in the core pasty zone.

[0032] In this step, overheat is dissipated through electromagnetic stirring of the crystallizer, columnar crystals are broken, and central equiaxed crystals are increased; electromagnetic stirring at the end of solidification refines the central equiaxed crystals on the basis of the large central equiaxed crystals produced by electromagnetic stirring of the crystallizer to produce a fine and wide central equiaxed crystal zone, reduces the spacing between the secondary dendrite arms, controls the permeability of the mushy zone, and hinders the penetration of concentrated molten steel between the dendrites; based on the solidification conditions of the large proportion of fine and wide central equiaxed crystal zones and less concentrated molten steel penetrating between the dendrites obtained by the crystallizer and electromagnetic stirring technology at the end of solidification, light pressure at the end of solidification acts on the solidification front to compensate for shrinkage, promote the flow of concentrated molten steel between the dendrites, and thus improve the center segregation and center density of the ingot through the synergy of the stirring magnetic field and the stress field.

[0033] Step S5, from the end of solidification to the stage of casting:

[0034] The ingot containing the liquid core that is not completely solidified is bent and straightened by multiple straightening machines; according to the set light reduction position and the corresponding single-roll reduction, light reduction is implemented with the corresponding light reduction single-roll reduction at the straightening machine corresponding to the light reduction position; when approaching the end point of solidification, according to the set heavy reduction position and the corresponding single-roll reduction, heavy reduction is implemented with the corresponding heavy reduction single-roll reduction at the straightening machine corresponding to the heavy reduction position.

[0035] From the crystallizer to the final billet forming, the electromagnetic fields of the crystallizer electromagnetic stirrer and the electromagnetic stirrer at the end of solidification, and the mechanical stress fields under light pressure and heavy pressure from the end of solidification to the billet forming, achieve a multi-field synergistic effect, thereby reducing the central segregation of large-section rectangular billets and improving the central density.

[0036] Step S6, for the obtained high-carbon alloy steel large-section rectangular billet, performance evaluation is performed using parameters such as the cross-sectional and longitudinal low-magnification morphology and rating of the billet, the cross-sectional center carbon segregation index and the longitudinal line center carbon segregation index, the cross-sectional composition and the quantitative central density.

[0037] In a second aspect, an embodiment of the present invention further provides a large-section rectangular billet, which is prepared using the high-carbon alloy steel large-section rectangular billet and preparation method based on multi-field synergy as described above.

[0038] The solution of the embodiment of the present invention has the following beneficial effects:

[0039] The embodiments of the present invention provide a high-carbon alloy steel large-section rectangular billet and preparation method based on multi-field synergy, and address the problems existing in the current continuous casting production process of high-carbon alloy steel large-section rectangular billets in controlling the center segregation and center density of the billet. The methods include optimizing the rules for determining the process parameters of the crystallizer and electromagnetic stirring at the end of solidification, verifying the accuracy of the solidification heat transfer model, arranging the heavy reduction position at the end of solidification and the corresponding straightening rollers, and using process technology to quantitatively evaluate the center segregation and density of the billet. By independently exerting the metallurgical effects of the electromagnetic field (crystallizer and electromagnetic stirring at the end of solidification) and the mechanical stress field (light reduction and heavy reduction at the end of solidification), and fully exerting the synergistic effect, the center segregation and center density of the high-carbon alloy steel large-section rectangular billet are stably controlled to the greatest extent. The obtained high-carbon alloy steel large-section rectangular billet is comprehensively evaluated using low-magnification morphology and rating of the billet cross section and longitudinal section, the center carbon segregation index of the cross section and the center carbon segregation index of the longitudinal section, and the quantification of the cross-sectional composition and center density.

[0040] Of course, it is not necessary to achieve all of the advantages described above simultaneously in order to implement any product or method of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0042] Figure 1 Flowchart of a method for preparing a large-section rectangular billet of high-carbon alloy steel based on multi-field synergy in an embodiment of the present invention;

[0043] Figure 2 Schematic diagram of low-magnification sampling of the cross section of the ingot prepared in an embodiment of the present invention;

[0044] Figure 3 Schematic diagram of carbon segregation sampling in the cross section of the ingot prepared in an embodiment of the present invention;

[0045] Figure 4 Schematic diagram of carbon segregation sampling along the center line of a longitudinal section of a slab prepared in an embodiment of the present invention;

[0046] Figure 5 This is the OPA carbon composition distribution diagram of the cross section of the ingot prepared in Example 1 of the present invention;

[0047] Figure 6 This is the OPA density distribution diagram of the cross section of the ingot prepared in Example 1 of the present invention;

[0048] Figure 7 This is a distribution diagram of the inner and outer arc carbon segregation index of the cross section of the ingot prepared in Example 1 of the present invention;

[0049] Figure 8 This is a distribution diagram of the segregation index of the center line of the longitudinal section of the slab prepared in Example 1 of the present invention;

[0050] Figure 9 This is the OPA carbon composition distribution diagram of the cross section of the ingot prepared in Example 2 of the present invention;

[0051] Figure 10 This is the density distribution diagram of the OPA diagram of the cross section of the ingot prepared in Example 2 of the present invention;

[0052] Figure 11 This is a distribution diagram of the inner and outer arc carbon segregation index of the cross section of the ingot prepared in Example 2 of the present invention;

[0053] Figure 12 This is a carbon segregation index distribution diagram of the center line of the longitudinal section of the slab prepared in Example 2 of the present invention;

[0054] Figure 13 This is the OPA carbon composition distribution diagram of the cross section of the ingot prepared in Comparative Example 1 of the present invention;

[0055] Figure 14 This is the density distribution diagram of the cross-section OPA diagram of the ingot prepared in Comparative Example 1 of the present invention;

[0056] Figure 15 This is a distribution diagram of the inner and outer arc carbon segregation index of the cross section of the ingot prepared in Comparative Example 1 of the present invention;

[0057] Figure 16 This is a carbon segregation index distribution diagram of the center line of the longitudinal section of the slab prepared in Comparative Example 1 of the present invention;

[0058] Figure 17 This is the OPA carbon composition distribution diagram of the cross section of the ingot prepared in Comparative Example 1 of the present invention;

[0059] Figure 18 This is the OPA density distribution diagram of the cross section of the ingot prepared in Comparative Example 1 of the present invention;

[0060] Figure 19 This is a distribution diagram of the inner and outer arc carbon segregation index of the cross section of the ingot prepared in Comparative Example 1 of the present invention;

[0061] Figure 20 This is a carbon segregation index distribution diagram of the center line of the longitudinal section of the ingot prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0062] After discovering the above problems, the inventors of this application conducted a detailed study on the existing continuous casting process of large-section rectangular billets. The study found that the adopted crystallizer electromagnetic stirrer and solidification end electromagnetic stirrer, solidification end light pressure and heavy pressure and other technologies still have the following problems: electromagnetic stirring stirs the molten steel by generating electromagnetic force of electromagnetic induction with the molten steel, and the stirring force is the main parameter to measure the stirring capacity. Due to the shielding effect of the crystallizer copper tube and the solidified billet shell on the magnetic field and the skin effect, the stirring current and stirring frequency cannot directly reflect the stirring capacity. In order for the electromagnetic stirring and light and heavy pressure at the end of solidification to fully play their role, it is closely related to the installation position of the end electromagnetic stirring and the layout of the light and heavy pressure straightening machine. The reasonable matching of it with the pulling speed is a prerequisite. If the pulling speed is too high, the liquid core will become larger and solidify. The end point is prolonged, resulting in excessive stirring at the end of solidification, causing a white bright band, and a large amount of pressure at the front of the reduction position, which causes cracks and segregation to worsen. The pulling speed is low, the liquid core at the electromagnetic stirring position at the end of solidification is large, and there are few pressure-reduction and straightening machines in the light reduction area, which has poor effects on improving center segregation and density. The appropriate pulling speed is determined according to the solid phase ratio at the center of the billet, and the solid phase ratio at the center of the billet is calculated by the established solidification heat transfer model. The accuracy verification of the model is crucial to it, but there is currently no relevant accuracy verification model. The large square billet is pressed down with a convex roller, and there are concave surface and convex side deformations on the billet surface. It cannot be guaranteed that the cross-sectional size of the billet matches the rolling hole type. In addition, the surface cracks generated affect the surface quality of the billet.

[0063] It should be noted that the defects existing in the solutions in the above-mentioned prior art are the results obtained by the inventors after practice and careful research. Therefore, the discovery process of the above-mentioned problems and the solutions proposed in the embodiments of the present invention below for the above-mentioned problems should all be the contributions made by the inventors to the present invention in the process of the invention.

[0064] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations. It should be noted that the embodiments of the present invention and the features in the embodiments can also be combined with each other in the absence of conflict.

[0065] It should be noted that similar reference numerals and letters represent similar items in the following figures. Therefore, once an item is defined in one figure, it does not need to be further defined or explained in subsequent figures. In the description of the present invention, the terms "first," "second," "third," "fourth," etc. are used only to distinguish the description and are not to be understood as indicating or implying relative importance.

[0066] Based on the above in-depth analysis, the present invention provides a high-carbon alloy steel large-section rectangular billet and a preparation method based on multi-field synergy. The present invention is described in detail below through specific examples.

[0067] In Example 1, Example 2 and Comparative Examples 1 and 2, the main equipment parameters and technical configurations of the continuous casting machine are shown in Table 1.

[0068] Table 1 Main equipment parameters and technical configuration of casting machine

[0069]

[0070] In order to evaluate the macro, segregation and center density of the ingot, the sampling method of the ingot is as follows: Figures 2 to 4 As shown in the figure, the inner side refers to the inner arc of the ingot, and the outer side refers to the outer arc of the ingot. Low magnification was obtained using the hot pickling method; carbon composition was measured using the borehole carbon-sulfur analyzer method. The central carbon segregation index is the ratio of the central carbon content to the average carbon content at 12 points; and the carbon composition and density distribution of the ingot cross section were obtained using the metal in-situ analyzer OPA scanning analysis.

[0071] Example 1

[0072] This embodiment provides a multi-field coordinated high-carbon alloy steel large-section rectangular billet and a preparation method. The high-carbon alloy steel is B2-3, and the specific composition is shown in Table 2:

[0073] Table 2 Chemical composition of high carbon alloy steel B2-3 (wt%)

[0074]

[0075] like Figure 1 As shown, the preparation method includes:

[0076] Equipment determination:

[0077] Electromagnetic stirrers are installed in the crystallizer and at the end of solidification, and 9 straightening machines are set up at the end of solidification. All 9 straightening machines have light reduction function. The maximum reduction of a single roller of the straightening machine is not less than 5mm. Among them, 4 straightening machines have heavy reduction function. The heavy reduction straightening machines are flat rollers. The maximum reduction of a single roller of the straightening machine is not less than 10mm and the maximum pressure is 2500KN.

[0078] Determination of steel grade process technical parameters:

[0079] Offline measurements of the magnetic flux density at the center of the crystallizer and the electromagnetic stirrer at the end of solidification were conducted using a Lakeshore 475DS gaussmeter in alternating low-frequency mode and a TM801 gaussmeter in alternating mode, respectively, at different stirring currents and frequencies. Table 3 (only partial data) shows that the magnetic flux density at the center of the crystallizer and the end of solidification measured with the TM801 gaussmeter was approximately one-fold lower than that measured with the Lakeshore 475DS gaussmeter. Furthermore, the relationships between magnetic flux density, stirring current, and frequency did not conform to conventional estimates, making it difficult to optimize and determine the optimal stirring frequency.

[0080] Table 3 Magnetic induction intensity of the mold and electromagnetic stirrer at the end of solidification measured by different Gauss meters (Gs)

[0081]

[0082] Therefore, the electromagnetic stirrer set at the crystallizer and the end of solidification was measured offline using a Lakeshore 475DS Gauss meter. The electromagnetic stirring current of the crystallizer was 500 A, the stirring frequency was 2.5 Hz, and the central magnetic induction intensity was 500 Gs. The electromagnetic stirring current at the end of solidification was 600 A, the stirring frequency was 6 Hz, the stirring mode was alternating 10s-2s-10s, and the central magnetic induction intensity was 800 Gs.

[0083] The solidification heat transfer model verified by temperature measurement and nail shooting tests is then used to calculate the solid phase fraction at the center of the ingot; the setting position of the electromagnetic stirrer at the end of solidification, the pressing position under light pressure and heavy pressure, and the single-roller pressing amount are determined according to the solid phase fraction at the center of the ingot.

[0084] The solid phase ratio at the center of the ingot at the end of solidification is 0.12, and the electromagnetic stirring installation position is 14.3m.

[0085] Table 4 shows the corresponding solid phase ratio and reduction of the billet center for different drawing and straightening machines. The 2#~5# drawing and straightening machines have a light reduction when the solid phase ratio of the billet center is in the range of 0.33~0.7, and the total reduction is 12.5 mm. The 6#~7# drawing and straightening machines have a heavy reduction when the solid phase ratio of the billet center is in the range of 0.99~1, and the total reduction is 12 mm.

[0086] Table 4 Reduction amount of light and heavy pressure of different tension levelers

[0087]

[0088] Production preparation:

[0089] After the continuous casting machine is started, the molten steel with qualified smelting composition is cast through BOF→LF→VD. The submerged nozzle adopts a four-hole nozzle, the casting section is 325mm×380mm, the superheat of the tundish is 23℃, the pulling speed is 0.6m / min, and the secondary cooling water volume is 0.2L / Kg; the electromagnetic stirring current of the crystallizer is 500A, the stirring frequency is 2.5Hz, the magnetic induction intensity at the center of the stirrer is 500Gs, the electromagnetic stirring installation position at the end of solidification is 14.3m, the electromagnetic stirring current at the end of solidification is 600A, the stirring frequency is 6Hz, the stirring mode is alternating 10s-2s-10s, the magnetic induction intensity at the center of the stirrer is 800Gs, and the corresponding solid phase ratio at the center of the ingot is 0.12. The light reduction and heavy reduction operations are performed on the straightening machine as shown in Table 4.

[0090] The cross section of the ingot obtained in this embodiment was scanned and analyzed by the metal in-situ analyzer OPA to obtain the carbon composition distribution and density distribution of the cross section. Figure 5 and Figure 6 As shown in the figure, the carbon segregation index distribution of the inner and outer arc center lines and the longitudinal center line of the slab cross section is as follows: Figure 7 and Figure 8 As shown in the figure, the cross-section center of the ingot prepared in this embodiment has no shrinkage cavity, the central equiaxed crystal ratio is 47%, the longitudinal section center has no segregation line and shrinkage cavity, the inner arc surface of the ingot has no concave cracks, and the side has no convex deformation. Figure 5 and Figure 6 As shown in the OPA scan, the central area with high carbon content in the ingot of this embodiment is small, the corresponding carbon segregation index is 1.05-1.07, and the central density is 96.8%. Figure 7 and Figure 8 As shown, the carbon segregation index of the cross-section center of the ingot in this embodiment is 1.07, and the carbon segregation index of the longitudinal centerline is mainly distributed within the range of 0.93 to 1.07.

[0091] Example 2

[0092] This embodiment also provides a multi-field coordinated high-carbon alloy steel large-section rectangular billet and a preparation method.

[0093] The high carbon alloy steel used in this embodiment is B3, and the specific composition is shown in Table 5.

[0094] Table 5 Chemical composition of high carbon alloy steel B3 (wt%)

[0095]

[0096] The preparation method of this embodiment is basically the same as that of Example 1, except that:

[0097] During the equipment determination phase, 10 tension and leveling machines were installed;

[0098] The electromagnetic stirrer set in the crystallizer and at the end of solidification was measured offline using a Lakeshore 475DS Gauss meter. The electromagnetic stirring current of the crystallizer was 450A, the stirring frequency was 1.8Hz, and the magnetic induction intensity at the center of the stirrer was 520Gs. The electromagnetic stirring current at the end of solidification was 600A, the stirring frequency was 8Hz, the stirring mode was alternating 10s-5s-10s, and the magnetic induction intensity at the center of the stirrer was 830Gs.

[0099] The crystallizer electromagnetic stirring current was 450A, the stirring frequency was 1.8Hz, the magnetic induction intensity at the center of the stirrer was 520Gs, the solidification end electromagnetic stirring current was 600A, the stirring frequency was 8Hz, the stirring mode was alternating 10s-5s-10s, and the magnetic induction intensity at the center of the stirrer was 830Gs;

[0100] The corresponding solid phase ratio at the center of the ingot is 0.18, and the electromagnetic stirring installation position at the end of solidification is 16.4m;

[0101] The measured reduction positions and single-roll reduction amounts under light and heavy reduction of the 10 tension levelers are shown in Table 6.

[0102] Table 6 Reduction amount of light and heavy pressure of different tension levelers

[0103]

[0104] In the preparation stage, the molten steel with qualified composition is cast through BOF→LF→RH smelting. The submerged nozzle adopts a four-hole nozzle, the casting section is 390mm×510mm, the superheat of the ladle is 25℃, the pulling speed is 0.43m / min, the secondary cooling water volume is 0.12L / Kg, the electromagnetic stirring current of the crystallizer is 450A, the stirring frequency is 1.8Hz, the magnetic induction intensity at the center of the stirrer is 520Gs, the electromagnetic stirring installation position at the end of solidification is 16.4m, the electromagnetic stirring current at the end of solidification is 600A, the stirring frequency is 8Hz, the stirring mode is alternating 10s-5s-10s, the magnetic induction intensity at the center of the stirrer is 830Gs, and the light pressure and heavy pressure operations are performed on the straightening machine as shown in Table 6.

[0105] The cross section of the ingot obtained in this embodiment was scanned and analyzed by the metal in-situ analyzer OPA to obtain the carbon composition distribution and density distribution of the cross section. Figure 9 and Figure 10 As shown in the figure, the carbon segregation index distribution of the inner and outer arc center lines and the longitudinal center line of the slab cross section is as follows: Figure 11 and Figure 12 The cross-section center of the ingot prepared in this embodiment has no shrinkage cavity, the central equiaxed crystal ratio is 45%, the center of the longitudinal section has no segregation line and shrinkage cavity, the inner arc surface of the ingot has no concave cracks, and the side has no convex deformation. Figure 9 and Figure 10As shown in the OPA scan, the central area with high carbon content in the ingot of this embodiment is small, the corresponding carbon segregation index is 1.05-1.07, and the central density is 97.2%. Figure 11 and Figure 12 As shown, the carbon segregation index of the cross-section center of the ingot in this embodiment is 1.06, and the carbon segregation index of the longitudinal centerline is mainly distributed within 0.93~1.06.

[0106] Comparative Example 1

[0107] This comparative example 1 provides a multi-field coordinated method for preparing a large-section rectangular billet of high-homogeneity, high-density high-carbon alloy steel, wherein the high-carbon alloy steel is B2-3, and the molten steel with qualified composition is cast by BOF→LF→VD smelting. The submerged nozzle adopts a four-hole nozzle, the casting section is 325mm×380mm, the superheat of the ladle is 25°C, the pulling speed is 0.55m / min, the secondary cooling water volume is 0.2L / Kg, the electromagnetic stirring current of the crystallizer is 500A, the stirring frequency is 2.5Hz, the electromagnetic stirring installation position at the end of solidification is 14.3m, the electromagnetic stirring current at the end of solidification is 600A, the stirring frequency is 6Hz, the stirring mode is alternating 10s-2s-10s, and the corresponding solid phase ratio at the center of the billet is 0.22. Table 7 shows the reduction amounts of different straightening machines corresponding to different solid phase ratios at the center of the ingot. For the 2#~3# straightening machines, light reduction is performed when the solid phase ratio at the center of the ingot is in the range of 0.47~0.67, with a total reduction of 3.5 mm. For the 4#~7# straightening machines, heavy reduction is performed when the solid phase ratio at the center of the ingot is in the range of 1, with a total reduction of 17 mm.

[0108] Table 7 Reduction amount of light and heavy pressure of different tension levelers

[0109]

[0110] Compared with Example 1 and Example 2, the low drawing speed in Comparative Example 1 results in a small light reduction range, which is only for the 2#~3# drawing and leveling machines, with an effective reduction of 3.5mm. The 4#~7# drawing and leveling machines implement heavy reduction, but the single-roll reduction of the 4#~5# drawing and leveling machines near the light reduction area is only 3mm and 4mm. The cross-section of the ingot obtained in Comparative Example 1 was scanned and analyzed by the metal in-situ analyzer OPA to obtain the carbon composition distribution and density distribution of the cross section. Figure 13 and Figure 14 As shown in the figure, the carbon segregation index distribution of the inner and outer arc center lines and the longitudinal center line of the slab cross section is as follows: Figure 15 and Figure 16 The ingot prepared in Comparative Example 1 has a large shrinkage cavity in the center of the cross section, a central equiaxed crystal ratio of 32%, a serious segregation line and continuous shrinkage cavity in the center of the longitudinal section, no concave cracks on the inner arc surface of the ingot, and no convex deformation on the side. Figure 13 and Figure 14As shown, the OPA scan of the ingot in this embodiment shows a large area with high carbon content in the center, corresponding to a carbon segregation index of 1.1-1.18 and a center density of 92%. Figure 15 and Figure 16 As shown, the carbon segregation index of the cross-section center of the ingot in this embodiment is 1.18, and the carbon segregation index of the longitudinal centerline is mainly distributed within 0.91-1.28, and the carbon segregation index is above 1.1 in a large proportion.

[0111] Comparative Example 2

[0112] This comparative example 2 provides a multi-field coordinated method for preparing a large-section rectangular billet of high-homogeneity, high-density high-carbon alloy steel, wherein the high-carbon alloy steel is B2-3, and the molten steel with qualified composition is cast through BOF→LF→VD smelting. The submerged nozzle adopts a four-hole nozzle, the casting section is 325mm×380mm, the superheat of the ladle is 28°C, the pulling speed is 0.6m / min, the secondary cooling water volume is 0.2L / Kg, the electromagnetic stirring current of the crystallizer is 300A, the stirring frequency is 3Hz, the electromagnetic stirring installation position at the end of solidification is 14.3m, the electromagnetic stirring current at the end of solidification is 400A, the stirring frequency is 8Hz, the stirring mode is alternating 10s-2s-10s, and the corresponding solid phase ratio at the center of the billet is 0.25. Table 8 shows the reduction amounts of different straightening machines corresponding to different solid phase ratios at the center of the ingot. For straightening machines 2#~5, light reduction is performed when the solid phase ratio at the center of the ingot is in the range of 0.33~0.7, with a total reduction of 12.5 mm. For straightening machines 6#~7, heavy reduction is performed when the solid phase ratio at the center of the ingot is in the range of 0.99~1, with a total reduction of 12 mm.

[0113] Table 8 Reduction amount of light and heavy pressure of different tension levelers

[0114]

[0115] Compared with Example 1 and Example 2, the stirring current of the electromagnetic stirring of the crystallizer and the electromagnetic stirring at the end of solidification is smaller, and the stirring frequency is not the optimal frequency. The cross-section of the ingot obtained in this comparative example 2 is obtained by metal in-situ scanning to obtain the cross-section carbon composition distribution and density distribution as shown in FIG. Figure 17 and Figure 18 As shown in the figure, the carbon segregation index distribution of the inner and outer arc center lines and the longitudinal center line of the slab cross section is as follows: Figure 19 and Figure 20 The ingot prepared in Comparative Example 2 has a small shrinkage cavity in the center of the cross section, a central equiaxed crystal ratio of 43%, a light segregation line and discontinuous small shrinkage cavity in the center of the longitudinal section, no concave cracks on the inner arc surface of the ingot, and no convex deformation on the side. Figure 17 and Figure 18 As shown in the OPA scan, the high carbon content area in the center of the ingot in this embodiment is relatively small, with a corresponding carbon segregation index of 1.08-1.1 and a center density of 94%. Figure 19 and Figure 20 As shown, the carbon segregation index of the cross-section center of the ingot in Comparative Example 2 is 1.1, the carbon segregation index of the longitudinal centerline is mainly distributed within 0.92-1.2, and the carbon segregation index above 1.1 accounts for a small proportion.

[0116] From the corresponding carbon segregation index, cross-sectional carbon composition, and density results of Example 1 and Comparative Examples 1 and 2, it can be found that the continuous casting process of the embodiment significantly improves the cross-sectional center carbon segregation index, the longitudinal centerline carbon segregation index, and the cross-sectional center density of the ingot. In addition, compared with Comparative Examples 1 and 2, the equiaxed crystal ratio at the center of the ingot in the embodiment is increased from 43% and 32% to 47%, respectively, and the solidification structure is refined. By comparing the embodiment, Comparative Example 1, and Example 2, both Comparative Examples 1 and 2 also use crystallizer electromagnetic stirring, electromagnetic stirring at the end of solidification, light reduction, and heavy reduction technology. However, the electromagnetic field and mechanical stress field do not achieve synergistic control, and the improvement in the carbon segregation index and density at the center of the ingot is lower than that of the embodiment. In Comparative Example 1, although the same light and heavy reduction processes as in Example 1 were employed, the solidification endpoint was significantly reduced due to the reduction in the drawing speed from 0.6 m / min to 0.55 m / min. The appropriate light reduction range shifted from the 2#-5# drawing and leveling machines to the 2#-3# drawing and leveling machines, reducing the effective reduction from 12.5 mm to 3.5 mm. This slowed the flow of concentrated molten steel in the core mushy zone, significantly reducing the improvement in centerline segregation. The heavy reduction reduction decreased from 6 mm per roll in the 6#-7# drawing and leveling machines to 3 mm to 4 mm per roll in the 4#-5# drawing and leveling machines. After solidification, the pressure generated by a single heavy reduction roll of less than 5 mm only deformed the billet shell and failed to affect the core, thus failing to achieve the desired effect of heavy reduction. In Comparative Example 2, the pulling speed was 0.6 m / min, and the same light reduction and heavy reduction processes as in Example 1 were employed. Due to the low current in the mold and the electromagnetic stirring at the end of solidification, and the suboptimal stirring frequency, the low stirring force prevented the formation of a large proportion of central equiaxed crystals, and the ability to refine the secondary dendrite arms in the central equiaxed crystal region was weakened. However, due to the reasonable matching of the pulling speed with the electromagnetic stirring at the end of solidification, the light reduction, and the heavy reduction, the light and heavy reduction processes played their role, significantly improving the central segregation and density of the ingot compared to Comparative Example 1. This also demonstrates that, compared to electromagnetic stirring technology, light reduction and heavy reduction provide more significant improvements in the central segregation and density of large-section rectangular high-carbon alloy steel ingots.

[0117] It can be seen from the above technical solutions that the high-carbon alloy steel large-section rectangular billet and preparation method based on multi-field synergy provided in the embodiments of the present invention have the following beneficial effects:

[0118] (1) It can independently exert the metallurgical effects of the electromagnetic field (electromagnetic stirring of the crystallizer and the end of solidification) and the mechanical stress field (light pressure and heavy pressure at the end of solidification), and at the same time fully exert the synergistic effect of multiple fields to stably control the center segregation and center density of large-section rectangular billets of high-carbon alloy steel to the greatest extent, providing high-quality parent material for subsequent material processing (rolling or forging), and producing larger-sized rolled or forged materials;

[0119] (2) Taking into account the performance differences of different continuous casting machine technical equipment and the differences in the casting machine process design layout, a reproducible method for determining the continuous casting process parameters (casting speed, electromagnetic stirring of the crystallizer and the end of solidification, light pressure and heavy pressure) can be developed, which does not require a large number of comparative tests, improves efficiency, saves time and cost; the process flow of the present invention is simple and easy to implement, has low manufacturing cost, and can be applied in large-scale industrial production. At the same time, it is ensured that in the actual production process, the improvement of the center segregation and density of the steel with the same cross-section under similar equipment configuration is relatively small.

[0120] The above description is only a preferred embodiment of the present invention and an explanation of the technical principles used. It is not intended to limit the scope of the invention to be protected, but merely represents a preferred embodiment of the present invention. Those skilled in the art should understand that the scope of the invention involved in the present invention is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative work shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing a large-section rectangular billet of high-carbon alloy steel based on multi-field synergy, characterized in that: The steps include: Step S1, electromagnetic stirrers are respectively installed at the crystallizer and the solidification end of the continuous casting machine, and 9 to 10 tensioning and straightening machines are installed at the solidification end; Step S2, determining the optimal stirring frequency of the electromagnetic stirrer of the crystallizer; determining the setting position and optimal stirring frequency of the electromagnetic stirrer at the end of solidification; determining the pressing position and single-roll pressing amount of the light pressure and heavy pressure of the tension and leveling machine at the end of solidification; wherein, the heavy pressure tension and leveling machine includes two, setting one tension and leveling machine to perform heavy pressure when the center solid phase ratio is 0.9~1, and after the center solid phase ratio is 1, setting another tension and leveling machine to perform heavy pressure, and the total amount of heavy pressure is 10~12mm; wherein, The solid phase ratio in the center of the ingot is 0.1~0.2, which is the location of the electromagnetic stirrer at the end of solidification; After the electromagnetic stirrer at the end of solidification, when the solid phase ratio at the center of the ingot is 0.3~0.8, 4~5 tensioning and straightening machines are set for light reduction; the total amount of light reduction is 12~20mm; the single-roll reduction is determined according to the total amount of light reduction and the number of tensioning and straightening machines; and when determining the single-roll reduction, the relationship between the light reduction and heavy reduction and the solid phase ratio at the center of the ingot is: when the solid phase ratio at the center is in the range of 0.3~0.5, the single-roll reduction is 1~2mm; when the solid phase ratio at the center is in the range of 0.5~0.8, the single-roll reduction is 3~5mm; two tensioning and straightening machines are configured under heavy pressure, and when the solid phase ratio at the center is in the range of 0.9~1, one tensioning and straightening machine is configured and the single-roll reduction is 5mm~6mm. After the solid phase ratio at the center is 1, one tensioning and straightening machine is configured and the single-roll reduction is 5mm~6mm. Moreover, the reduction in the heavy reduction stage after the solid phase ratio at the center is 1 is greater than the reduction in the heavy reduction stage of 0.9~1. A heavy pressure pull-down leveler is set up near the light pressure pull-down leveler; Step S3, after the continuous casting machine starts casting, in the stage from the tundish to the crystallizer: the molten high-carbon alloy steel liquid flows from the tundish of the multi-stream large-section rectangular billet continuous casting machine into the crystallizer through the submerged nozzle; Step S4, from the crystallizer to the end of solidification: the crystallizer electromagnetic stirrer rotates and stirs the molten steel, and solidifies it in the secondary cooling zone through full water combined with mist cooling; at the set position of the solidification end, the solidification end electromagnetic stirrer stirs the molten steel in the core mushy zone; Step S5, from the end of solidification to the stage of casting forming: the casting containing the liquid core that is not completely solidified is bent and straightened by multiple straightening machines; according to the set light reduction position and the corresponding single-roll reduction amount, light reduction is performed at the straightening machine corresponding to the light reduction position with the corresponding light reduction single-roll reduction amount; when approaching the end of solidification, according to the set heavy reduction position and the corresponding single-roll reduction amount, heavy reduction is performed at the straightening machine corresponding to the heavy reduction position with the corresponding heavy reduction single-roll reduction amount; Step S6, for the obtained high-carbon alloy steel large-section rectangular billet, performance evaluation is performed by quantitatively measuring the cross-section and longitudinal section low-magnification morphology and rating, cross-section center carbon segregation index and longitudinal section center carbon segregation index, cross-section composition and center density.

2. The preparation method according to claim 1, characterized in that In step S1, the 9 to 10 straightening machines set up all have a light pressure function, and the maximum pressure reduction of a single roller of the straightening machine implementing light pressure is not less than 5 mm. Among them, 4 to 5 straightening machines have a heavy pressure function, and the heavy pressure straightening machines are flat rollers. The maximum pressure reduction of a single roller of the straightening machine implementing heavy pressure is not less than 10 mm, and the maximum pressure is 2500KN.

3. The preparation method according to claim 1, characterized in that The high carbon alloy steel contains C in a mass percentage of 0.6% to 1.0%; and contains at least Mn and Cr alloy elements, and the mass percentages of both elements are less than 1.0%.

4. The preparation method according to claim 1, characterized in that In step S2, the central magnetic induction intensity of the crystallizer and the electromagnetic stirrer at the end of solidification is measured offline using a Gaussmeter with an alternating low-frequency mode; and when measuring the central magnetic induction intensity of the crystallizer electromagnetic stirrer, the probe of the Gaussmeter is inserted into the copper tube of the crystallizer for measurement; based on the measured central magnetic induction intensity, the optimal stirring frequency of the crystallizer electromagnetic stirrer and the optimal stirring frequency of the solidification end electromagnetic stirrer are determined according to the calculation formula of the electromagnetic torque.

5. The preparation method according to claim 4, characterized in that When the optimal stirring frequency is calculated using the measured central magnetic induction intensity, the optimal frequency is determined by the following formula: （1） In formula (1), T is the electromagnetic torque, σ is the conductivity of the conductor; f is the stirring frequency; B is the measured magnetic induction intensity at the center of the stirrer; r1 is the equivalent radius of the liquid core; L is the effective length of the stirrer; The stirring frequency corresponding to the maximum value of the electromagnetic torque T is the optimal stirring frequency.

6. The preparation method according to claim 5, characterized in that σ for molten steel is 1.4~2.0×10^6 S / m; r1 for 320~390mm×385~510mm section ranges from 0.185m~0.231m; L value ranges from 0.4m~0.5m.

7. The preparation method according to claim 4, characterized in that In step S4, the solidification heat transfer model verified by temperature measurement and nail shooting tests is used to calculate the solid phase ratio at the center of the ingot; the setting position of the electromagnetic stirrer at the end of solidification, the pressing position under light pressure and heavy pressure, and the corresponding single-roll pressing amount are determined according to the solid phase ratio at the center of the ingot.

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