A method for improving cross-type segregation of a bloom casting blank

Abstract

The application discloses a method for improving cross-type segregation of a bloom, which avoids the aggregation of solute elements to intercrystalline and center by controlling parameters of a crystallizer electromagnetic stirring, dynamic soft reduction, superheat and drawing speed of a continuous casting production process, and improves the cross-type segregation of the bloom.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel metallurgy, and particularly relates to a method for improving cross-type segregation of bloom ingot. BACKGROUND

[0002] With the development of continuous casting technology, high-quality ingot has become the goal of today's continuous casting technology, which not only requires good ingot surface quality, but also puts forward higher requirements for the internal quality and homogenization of the ingot.

[0003] The segregation of continuous casting ingot is caused by the solidification characteristics of the ingot, which cannot be avoided in the continuous casting production process, but can be alleviated to the greatest extent by optimizing the continuous casting production process parameters. The cross-type segregation of the ingot can comprehensively reflect the overall segregation of the ingot. The electromagnetic stirring of the crystallizer controls the flow of molten steel by means of the electromagnetic force generated in the liquid core of the ingot, produces kinetic conditions for inhibiting the development of columnar crystals, promoting uniform composition and floating of inclusions, reduces the segregation degree of the ingot, and further improves the solidification structure of the ingot and improves the quality of the ingot. Light pressing can eliminate or reduce the internal voids formed by the shrinkage of the ingot, and the extrusion effect promotes the reverse flow of the steel liquid rich in solute elements along the drawing direction, so that the solute elements are redistributed in the steel liquid, and the solidification structure of the ingot is more uniform and dense, and the center segregation and center porosity are improved. Controlling the continuous casting production process parameters such as appropriate drawing speed, superheat degree, etc. is beneficial to improve the internal quality of the ingot. Therefore, for high-carbon steel bloom ingot, the cross-type segregation of the ingot is improved by controlling the light pressing, crystallizer electromagnetic stirring, superheat degree, drawing speed and other parameters of the continuous casting production process.

[0004] A method for improving the frame-type segregation of bloom continuous casting ingot is disclosed in Chinese patent No. 201910299087.X, which comprises the steps of using a continuous casting machine with a casting ingot section size of 400-500mm wide and 300-400mm thick for continuous casting production, wherein the continuous casting ingot drawing speed is 0.45-0.60m / min; the specific water quantity of the secondary cooling zone is 0.20-0.30L / kg; the crystallizer electromagnetic stirring is set at 500mm below the molten steel surface, the current intensity is 150-350A, and the frequency is 1.0-2.5Hz; the secondary cooling electromagnetic stirring is set at 5000-8000mm below the molten steel surface, the current intensity is 500-1000A, and the frequency is 5-8Hz. The method effectively improves the frame-type segregation of the bloom continuous casting ingot according to the process parameters of the continuous casting machine, the drawing speed, the position of the crystallizer electromagnetic stirring and the secondary cooling electromagnetic stirring.

[0005] A process method for controlling center carbon segregation of bearing steel casting blank is disclosed in Chinese patent No. 201911233884.4, which includes continuous casting tundish temperature control, continuous casting using submerged entry nozzle, protective casting, parameters of crystallizer electromagnetic stirring, parameters of solidification end electromagnetic stirring, and the stirring direction of crystallizer electromagnetic stirring and the stirring direction of solidification end electromagnetic stirring always keep opposite stirring, etc., which promotes the floating of molten steel inclusions, reduces the internal inclusions of the casting blank, improves the center equiaxed crystal rate of the casting blank, and reduces the center carbon segregation index of the casting blank.

[0006] A method for reducing segregation in continuous casting square billet pouring process for gear is disclosed in Chinese patent No. 202010209492.0, which heats the molten steel to a continuous casting molten steel superheat degree of 20-30℃ before the end of LF refining, uses a large amount of water for the first and second cold of continuous casting 150x150mm square billet, the water amount proportion of the roller section reaches 40%, the crystallizer electromagnetic stirring is closed, the end electromagnetic stirring uses a lower current, and the pouring is performed at a pulling speed of 2.00m / min. The present application can control the carbon difference on the diagonal line of the continuous casting square billet for gear from the surface to 3 / 8 diagonal line within the range of 0.015%, the center carbon segregation index is within 1.05, and the steel performance stability is improved. SUMMARY

[0007] To solve the above technical problems, the purpose of the present application is to provide a method for improving the cross-type segregation of large square billet casting blank, which controls the parameters of crystallizer electromagnetic stirring, dynamic soft reduction, superheat degree, and pulling speed of continuous casting production process, avoids the aggregation of solute elements to the intercrystalline and center, improves the cross-type segregation of large square billet casting blank, and solves the above problems.

[0008] To solve the above technical problems, the present application adopts the following technical solutions:

[0009] The present application is a method for improving the cross-type segregation of large square billet casting blank, which comprises:

[0010] The position of crystallizer electromagnetic stirring of continuous casting production process is 200mm below the crystallizer molten steel surface, the current is 300-600A, and the frequency is 1-3HZ;

[0011] The position of solidification end soft reduction is 15000-23000mm below the crystallizer molten steel surface, which is dynamically adjusted according to the pulling speed, superheat degree, etc. of continuous casting, and the reduction amount is 2-10mm;

[0012] The pulling speed of continuous casting production process is 0.5-0.7m / min, and constant speed operation is adopted;

[0013] The superheat degree of continuous casting production process adopts low superheat degree control, and the range is 20-30℃;

[0014] Adopt the protection casting technology, ensure the molten steel and air insulation, prevent the secondary oxidation of molten steel in long nozzle, tundish, submerged entry nozzle, control the nitrogen increase of casting machine less than 5ppm;

[0015] Ensure the suitable submerged entry nozzle insertion depth, the range is 110-130mm.

[0016] Further, the section size of the bloom casting blank is 280mm*380mm.

[0017] Further, every 15mm along the inner arc to the outer arc, along the left side to the right side of the cross section of the bloom casting blank, a sample is taken, the segregation element content in each sample is analyzed by chemical method, and the macro cross segregation of the casting blank is analyzed.

[0018] Further, the position of the crystallizer electromagnetic stirring of the continuous casting production process is 200mm below the crystallizer molten steel surface, the current is 500A, and the frequency is 2HZ.

[0019] Further, the position of the light press-down at the solidification end is 15000-23000mm below the crystallizer molten steel surface, is dynamically adjusted according to the casting speed, superheat and the like, and the press-down amount is 5mm.

[0020] Further, the casting speed of the continuous casting production process is 0.65m / min, and constant speed operation is adopted.

[0021] Further, the superheat temperature of the continuous casting production process is 26 DEG C.

[0022] Compared with the prior art, the beneficial technical effects of the present application are:

[0023] The present application aims at the continuous casting production process of the bloom casting blank, by controlling the parameters such as the crystallizer electromagnetic stirring, dynamic light press-down, superheat, casting speed and the like of the continuous casting production process, the effect of avoiding the aggregation of solute elements to intercrystalline and center, reducing the center equiaxed crystal rate, improving the cross-type segregation of the bloom casting blank, improving the internal quality of the casting blank, and providing strong guarantee for the subsequent rolling production process. The method control measure is accurate and effective, easy to implement, and has wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0024] The present application will be further described below in combination with the description of the drawings.

[0025] Figure 1 It is a cross-type segregation analysis point position schematic view.

[0026] Figure 2 It is the carbon segregation index of the casting blank along the inner arc to the outer arc direction.

[0027] Figure 3 It is the carbon segregation index of the casting blank along the left side to the right side direction. DETAILED DESCRIPTION

[0028] Example 1

[0029] A method for improving cross segregation of a bloom casting blank, comprising:

[0030] 1. The cross-sectional size of the bloom casting blank is 280mm x 380mm.

[0031] 2. The carbon content of the steel grade is 0.72%.

[0032] 3. The position of the electromagnetic stirring of the crystallizer of the continuous casting production process is 200mm below the steel liquid surface of the crystallizer, the current is 500A, and the frequency is 2HZ.

[0033] 4. The position of the light press-down at the solidification end is 15000-23000mm below the steel liquid surface of the crystallizer, which is dynamically adjusted according to the casting speed, superheat, etc., and the press-down amount is 5mm.

[0034] 5. The casting speed of the continuous casting production process is 0.65m / min, and constant speed operation is adopted.

[0035] 6. The superheat of the continuous casting production process adopts low superheat control, and the range is 26℃.

[0036] 7. The protective casting technology is adopted to ensure that the molten steel is isolated from the air and prevent the secondary oxidation of the molten steel in the long nozzle, tundish and submerged nozzle. The nitrogen content of the refining off-site is 37ppm, the nitrogen content of the casting blank is 40ppm, and the nitrogen increase of the casting machine is less than 5ppm, and the protective casting effect is good.

[0037] 8. The appropriate insertion depth of the submerged nozzle is ensured, and the range is 130mm.

[0038] 9. In the cross section of the bloom casting blank, one sample is taken every 15mm from the inner arc to the outer arc, a total of 17 points, and one sample is taken every 15mm from the left side to the right side, a total of 17 points, and the carbon content in each sample is analyzed by chemical method.

[0039] 10. The cross segregation analysis method is adopted to comprehensively analyze the segregation of the casting blank. The highest carbon segregation index of the casting blank center from the inner arc to the outer arc is 1.07, and the highest carbon segregation index of the casting blank center, 1 / 4 of the left and right sides from the left side to the right side is 1.05. The carbon segregation index from the inner arc to the outer arc is higher than that from the left side to the right side, and the overall carbon element distribution is uniform.

[0040] The above described embodiments are only to illustrate the preferred modes of the present application, and are not intended to limit the scope of the present application. Any modification and improvement made by those skilled in the art to the technical solutions of the present application without departing from the design spirit of the present application shall fall within the protection scope of the present application as defined by the claims.

Claims

1. A method for improving cross-shaped segregation in large square billet castings, characterized in that: include: The cross-sectional dimensions of the large square billet are 280mm × 380mm; The carbon content of the steel is 0.72%; In the continuous casting process, the electromagnetic stirrer of the crystallizer is positioned 200mm below the surface of the molten steel in the crystallizer, with a current of 500A and a frequency of 2HZ. The final pressure reduction position is 15000-23000mm below the molten steel surface in the crystallizer. It is dynamically adjusted according to the casting speed and superheat of the continuous casting process, and the reduction amount is 5mm. The continuous casting production process uses a casting speed of 0.65 m / min and constant casting speed operation. The superheat in the continuous casting process is controlled at a low temperature of 26℃. The protective casting technology is adopted to ensure that the molten steel is isolated from the air and to prevent secondary oxidation of the molten steel at the long nozzle, tundish, and submerged entry nozzle; the nitrogen content of the refined steel is 37 ppm, the nitrogen content of the billet is 40 ppm, and the nitrogen increase of the casting machine is less than 5 ppm, resulting in a good protective casting effect. Ensure the appropriate insertion depth of the submersible nozzle, within the range of 130mm; A sample was taken every 15 mm along the inner arc to the outer arc of the large square billet cross section, for a total of 17 points. A sample was also taken every 15 mm along the left to the right side, for a total of 17 points. The carbon content in each sample was analyzed by chemical method.

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