Continuous casting production method of large-piece-weight extra-thick plate blank for offshore wind power tower tube steel

Abstract

The invention discloses a continuous casting production method of a large-piece-weight extra-thick slab for offshore wind power tower tube steel. The continuous casting production method comprises the following process steps that a 473 mm * 2600 mm straight crystallizer continuous bending and continuous straightening arc-shaped extra-thick slab continuous casting machine is adopted to conduct continuous casting on molten steel to obtain a slab; in the continuous casting process, a metallurgical reduction and mechanical reduction cooperative reduction technology is adopted, a secondary cooling electric stirring technology and a straightening stress relaxation roller column technology are coupled, the internal quality of the large-piece-weight extra-thick plate blank for offshore wind power tower tube steel is improved, and the defects of center segregation, center looseness and middle cracks near an inner arc side triangular area of the large-piece-weight extra-thick plate blank are overcome; according to the method, the transverse cracks on the surface of the casting blank are effectively controlled in a secondary cooling mode combining overall weak cooling and local air cooling. The piece weight of the extra-thick plate blank industrially prepared through the method can reach 60 t, the effect is good after implementation, and the use requirement for efficiently preparing the high-quality and large-piece-weight extra-thick steel plate for the offshore wind power tower tube at low cost can be met.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel production, and relates to a continuous casting production method for large single-weight extra-thick slab for offshore wind power tower barrel steel. Background Art

[0002] Large single-weight extra-thick plates generally refer to finished steel plates with a single weight of more than 20 - 30t and a thickness > 100mm. The heaviest such steel plate can reach 200t. For extra-thick plates of certain special steel grades, due to equipment conditions or steel grade limitations, it is difficult to produce with conventional continuous casting billets. Especially when the reduction ratio is insufficient, the internal quality is also difficult to guarantee, and only a few enterprises have the production capacity for extra-thick plates. When producing high-performance large single-weight extra-thick steel plates with special performance requirements, conventional ingots or continuous casting billets always have several problems due to internal defects and rolling reduction ratio, etc., such as unstable and uneven performance, poor plastic toughness, non-compliance in flaw detection, etc.

[0003] With the continuous increase in the single-unit installed capacity of offshore wind power, the demand for extra-thick steel plates for wind power pipe piles is increasing continuously, and the requirements for the size and single weight of extra-thick steel plates are also getting higher and higher. In order to reduce the welds in the manufacturing process, it is required that the length of the steel plate is greater than 15m, the thickness of the steel plate is usually designed to be 60 - 120mm, and the single weight of most steel plates is more than 20t. If large single-weight extra-thick continuous casting slabs for wind power can be produced by using an extra-thick continuous casting machine to replace ingots for producing large single-weight extra-thick wind power steel plates, the quality is excellent, the cost advantage is obvious, and it can effectively improve the development level and competitiveness of the wind power industry. As an advantageous equipment for producing thick plates, the extra-thick slab continuous casting machine has been more and more widely promoted and applied globally, but the stable production technology for high-end extra-thick slabs is still the key research point for steel mills at present.

[0004] Currently, numerous patents have been published for continuous casting methods for heavy, extra-thick slabs used in offshore wind turbine tower steel. Chinese patent CN201210264473.3, "A Process for Manufacturing Heavy-Weight Thick Steel Plates for Offshore Wind Turbine Towers," describes a method for producing heavy-weight, thick steel plates for offshore wind turbine towers. Two or more continuously cast slabs are beveled and stacked together. These are then welded together using a combination of gas shielded welding, submerged arc welding, and vacuum electron beam welding to form heavy-weight continuous casting slabs. These slabs are then heated in a hearth furnace or soaking pit, rolled, and subjected to controlled cooling and heat treatment. The resulting heavy-weight steel plates, with a maximum unit weight of 40 tons, meet the requirement for reducing welds during tower fabrication. The method features a simple production process, a high yield rate, an ultrasonic flaw detection pass rate exceeding 98%, and excellent low-temperature toughness, Z-axis properties, and other performance characteristics. This method utilizes multiple slabs to increase the unit weight, but this method results in a long production cycle and high manufacturing costs. CN201210182419.4 "A method for producing large-thickness, large-weight, low-alloy, high-strength structural steel plates" uses electroslag remelting of large slabs. Through reasonable control of the rolling and heat treatment processes, it can achieve good isotropy, impact toughness, and Z-direction properties of large-thickness steel plates, while reducing production costs and significantly shortening delivery time. This method improves the internal quality of large slabs through electroslag remelting, increasing manufacturing costs. CN202410612393.5 "A method for producing large-weight, high-homogeneity mold steel ingots" uses a special mold casting method to cast the molten steel after soft argon blowing according to the low-segregation solidification technology studied, producing large-weight, high-homogeneity mold steel flat ingots with a unit weight of 45t to 50t. This method uses mold casting to produce large-weight steel ingots, which not only has a low yield rate but also low production efficiency. CN202010654392.9 "A heavy and extra-thick steel for offshore wind power and its production method" is produced by continuous casting process, and the thickness of the continuous casting billet is 300-400mm, the thickness of the finished product is 60-150mm, and the maximum unit weight of the finished product is 28t. The unit weight of this method is insufficient. CN202211502416.4 "A production method of heavy and extra-thick continuous casting slab for wind power" is cast in a 450mm straight arc-shaped extra-thick slab continuous casting machine, the superheat of the middle bag is controlled at 10-20℃, the pulling speed is 0.40-0.70m / min, the slab is lightly pressed down and the solidification end is heavily pressed down, the total reduction is ≥20mm, and the electric stirring frequency of the crystallizer is 5-10H Z The current is 400-650A, the maximum width reaches 2600mm, and the maximum unit weight is 38t. The product has excellent physical quality and can replace die-cast steel ingots to produce heavy and thick wind power steel plates, meeting the transition needs of clean energy development. However, the electric stirring of the crystallizer used in this method is difficult to effectively control the center segregation of large-section slabs. Summary of the Invention

[0005] The object of the present invention is to provide a continuous casting production method for large single - weight and extra - thick slab for offshore wind turbine tower steel, so as to solve at least one of the problems and defects mentioned in the above - mentioned background technology.

[0006] The technical solution of the present invention: A continuous casting production method for large single - weight and extra - thick slab for offshore wind turbine tower steel, characterized in that the chemical composition of the steel by mass percentage is C = 0.05 - 0.07, Si = 0.15 - 0.40, Mn = 1.40 - 1.60, P≤0.015, S≤0.005, Als = 0.015 - 0.050, Nb = 0.030 - 0.035, Ti = 0.012 - 0.020, Cr = 0.13 - 0.18, and the rest are Fe and residual elements; it includes the following technological steps: After continuous casting of the molten steel by a 473mm×2600mm straight mold continuous bending and continuous straightening arc - type extra - thick slab continuous caster, a continuous casting slab is obtained; During the continuous casting process, the reduction method is composed of flat - roll soft reduction and convex - roll heavy reduction. The flat - roll soft reduction part starts to reduce from when the central solid fraction is greater than or equal to 0.35 and ends when the central solid fraction is less than or equal to 0.95. The total reduction amount of the soft reduction is 13mm; The convex - roll heavy reduction part starts to reduce from when the solid fraction at the solidification end is greater than or equal to 0.8 and ends when the temperature difference between the surface and the core of the slab is below 500°C. The total reduction amount of the convex - roll heavy reduction part is 10mm; During the continuous casting process, the secondary cooling method is composed of overall weak cooling and local air cooling. The specific water ratio of the overall weak cooling part is 0.10 - 0.12L / kg. For the local air cooling part, the side water of the 5th to 7th segments is closed to increase the straightening temperature of the slab to be greater than or equal to 860°C; During the continuous casting process, the second - stage cooling electromagnetic stirring technology based on a double - segmented roll - type electromagnetic stirrer is adopted in the 4th segment of the arc - shaped sector; During the continuous casting process, the straightening stress relaxation roll - train technology is adopted in the continuous straightening stage.

[0007] Furthermore, the thickness of the continuous casting slab is 450mm, the width is 2600mm, the length is 6200 - 6800mm, and the single weight is 55 - 60t.

[0008] Furthermore, the basic roll gap from the entrance to the exit of the 8th to 9th segments in the continuous straightening area gradually increases, and the increase amplitude is 0.125mm per roll.

[0009] Furthermore, the casting speed is 0.47m / min.

[0010] Furthermore, the temperature difference between the surface and the core of the slab is greater than or equal to 500°C when the convex - roll heavy reduction ends.

[0011] Further, the single-pass reduction amount of the convex roll under heavy pressure is 10 mm.

[0012] Further, the height of the convex platform of the convex roll is 10 mm, and the width of the convex platform is 2,200 mm.

[0013] Further, the continuous casting production method of the large single-weight extra-thick slab for the steel of the offshore wind power tower barrel is characterized in that: a pair of double-segment roll electromagnetic stirrers are arranged at the inlet and outlet of the fourth segment respectively, and an alternating stirring mode is adopted, with a current intensity of 600 A / 600 A, a frequency of 6 Hz, 20 s in the forward direction, 2 s stop, and 20 s in the reverse direction.

[0014] The present invention has the following beneficial effects: By comprehensively applying measures such as extra-thick slab continuous casting technology, solidification end convex heavy reduction technology, and extra-thick slab secondary cooling technology, the central porosity, central segregation, and surface cracks of the large single-weight continuous casting slab for high-quality extra-thick offshore wind power tower barrel steel are reduced, providing conditions for preparing a low-compression ratio non-destructive inspection extra-thick slab. The extra-thick slab industrially prepared by the present method has good effects after implementation and can meet the use requirements of preparing high-quality extra-thick offshore wind power tower barrel steel at low cost and high efficiency. Specific embodiments Example 1

[0015] A continuous casting production method of a large single-weight extra-thick slab for the steel of an offshore wind power tower barrel, the mass percentage of the chemical components of the steel is C = 0.06, Si = 0.20, Mn = 1.45, P = 0.010, S = 0.003, Als = 0.025, Nb = 0.032, Ti = 0.013, Cr = 0.15, and the rest are Fe and residual elements; the method includes the following process steps: Continuous casting the molten steel in the tundish to obtain a continuous casting slab; During continuous casting, first perform flat roll light reduction, and then continuously perform convex roll heavy reduction; In this embodiment, a continuous casting slab of an offshore wind power tower barrel steel plate with a cross-sectional size of 450 mm × 2,600 mm is prepared by continuous casting, and the thickness of the rolled steel plate is 120 mm; The casting speed of the continuous caster is 0.47 m / min, and the casting speed is kept stable; The superheat of the molten steel in the tundish is 7 - 15 °C; Adopt convex roll heavy reduction at the solidification end, with a reduction rate of 0.025 mm / s and a total reduction amount of 23 mm; Among them, the range of the central solid fraction of the flat roll light reduction part is 0.35 - 0.95, and the total light reduction amount is 13 mm; The convex roll heavy reduction part starts to reduce from the solid fraction of 1.0 at the solidification end point and ends the reduction when the temperature difference between the surface and the core of the slab is less than or equal to 500 °C. The total reduction amount of the convex roll heavy reduction is 10 mm.

[0016] During the continuous casting process, the specific water volume of the overall weak cooling part of the secondary cooling is 0.12 L / kg. The edge water from the 5th to the 7th segment is closed to achieve local air cooling, and the straightening temperature at the edge of the continuous casting billet is 861 °C.

[0017] The basicity of the mold powder is 1.20, the viscosity is 0.13 Pa∙s at 1300 °C, the melting point is 1160 °C, and the melting rate is 37 s at 1350 °C.

[0018] The secondary cooling electromagnetic stirrer adopts an alternating stirring mode, with a current intensity of 450 A / 450 A, a frequency of 6 Hz, 20 s in the forward direction, a 2 s stop, and 20 s in the reverse direction.

[0019] During the continuous casting process, the straightening stress relaxation roll train technology is adopted in the continuous straightening stage. The basic roll gap gradually increases from the entrance to the exit of the 8th to the 9th segment in the continuous straightening area, with a magnification of 0.042 mm per roll.

[0020] The thickness of the continuous casting slab is 450 mm, the width is 2600 mm, the length is 6200 mm, and the single weight is 55 t.

[0021] After casting, the internal quality of the continuous casting billet for the offshore wind turbine tower steel is inspected by macro-examination (Macrostructure Defect Rating Diagram for Continuous Cast Steel Slabs, YB / T 4003-2016, the national standard of the People's Republic of China for the ferrous metallurgy industry). The inspection results show that the proportion of no center shrinkage porosity in the transverse macrostructure of the continuous casting billet is 100%, the proportion of the center porosity defect rating of 1.0 is 100%, the proportion of the center segregation ≤ C1.5 is 90%, the incidence rate of intermediate cracks is 30%, and there are no cracks on the surface of the continuous casting billet. Example 2

[0022] A continuous casting production method for large single-weight extra-thick slabs for offshore wind turbine tower steel, with the chemical composition of the steel in mass percentage: C = 0.06, Si = 0.21, Mn = 1.46, P = 0.010, S = 0.003, Als = 0.027, Nb = 0.033, Ti = 0.015, Cr = 0.16, and the rest are Fe and residual elements; including the following technological steps: Continuous casting of the tundish molten steel to obtain a continuous casting slab; During the continuous casting process, first perform flat roll soft reduction, and then continuously perform convex roll heavy reduction; In this example, a continuous casting slab for offshore wind turbine tower steel with a cross-sectional size of 450 mm × 2600 mm is prepared by continuous casting, and the thickness of the rolled steel plate is 150 mm; The casting speed of the continuous caster is 0.47 m / min and the casting speed is kept stable; The superheat of the tundish molten steel is 7 - 15 °C; Adopt convex roll heavy reduction at the solidification end, with a reduction rate of 0.025 mm / s and a total reduction of 23 mm; The central solid fraction range of the soft reduction part of the flat roll is 0.35 - 0.95, and the total amount of soft reduction is 13 mm. The heavy reduction part of the convex roll starts to reduce from the solid fraction of 1.0 at the solidification end point and ends the reduction when the temperature difference between the surface and the center of the slab is less than or equal to 500 °C. The total reduction amount of the heavy reduction of the convex roll is 10 mm.

[0023] During the continuous casting process, the specific water volume of the overall weak cooling part of the secondary cooling is 0.11 L / kg. The side water from the 5th to the 7th segment is closed to achieve local air cooling, and the straightening temperature at the slab edge is 865 °C.

[0024] The basicity of the mold powder is 1.20, the viscosity is 0.13 Pa∙s / 1300 °C, the melting point is 1160 °C, and the melting rate is 37 s / 1350 °C.

[0025] The secondary cooling electromagnetic stirrer adopts an alternating stirring mode, with a current intensity of 600 A / 600 A, a frequency of 6 Hz, 20 s in the forward direction, a 2 s stop, and 20 s in the reverse direction.

[0026] During the continuous casting process, the straightening stress relaxation roll train technology is adopted in the continuous straightening stage. The basic roll gap gradually increases from the entrance to the exit of the 8th to the 9th segment in the continuous straightening area, and the increase amplitude is 0.125 mm per roll.

[0027] The thickness of the continuous casting slab is 450 mm, the width is 2600 mm, the length is 6800 mm, and the single weight is 60 t.

[0028] After casting, the internal quality of the cast slab for the offshore wind turbine tower steel is subjected to macrostructure inspection (Macrostructure Defect Rating Diagram for Continuous Cast Steel Slabs, YB / T 4003 - 2016, the national standard of the People's Republic of China for the ferrous metallurgy industry). The inspection results show that the proportion of no central shrinkage porosity in the transverse macrostructure of the slab is 100%, the proportion of the macrostructure defect rating of central porosity being 1.0 grade is 100%, the proportion of central segregation ≤ C1.5 grade is 100%, the incidence rate of intermediate cracks is 0%, and there are no cracks on the slab surface.

Claims

1. A continuous casting production method for extra-thick slab with large single weight for steel used in offshore wind power tower barrels, characterized in that: The chemical composition of the steel is by mass percentage: C = 0.05 - 0.07, Si = 0.15 - 0.40, Mn = 1.40 - 1.60, P ≤ 0.015, S ≤ 0.005, Als = 0.015 - 0.050, Nb = 0.030 - 0.035, Ti = 0.012 - 0.020, Cr = 0.13 - 0.18, and the rest is Fe and residual elements; It includes the following process steps: After continuous casting of molten steel using a 473mm×2600mm straight mold continuous bending and continuous straightening arc-type extra-thick slab caster, a continuous casting slab is obtained; During the continuous casting process, the reduction method consists of flat roll soft reduction and convex roll heavy reduction. The flat roll soft reduction part starts to reduce after the central solid fraction is greater than or equal to 0.35 and ends when the central solid fraction is less than or equal to 0.

95. The total reduction amount of the soft reduction is 13mm; The convex roll heavy reduction part starts to reduce after the solid fraction at the solidification end point is greater than or equal to 0.8 and ends when the temperature difference between the surface and the core of the slab is below 500°C. The total reduction amount of the convex roll heavy reduction part is 10mm; During the continuous casting process, the secondary cooling method consists of overall weak cooling and local air cooling. The specific water volume of the overall weak cooling part is 0.10 - 0.12L / kg. For the local air cooling part, the edge water of the 5th to 7th segments is closed to increase the straightening temperature of the slab to be greater than or equal to 860°C; During the continuous casting process, a secondary cooling electromagnetic stirring technology based on a double-segmented roll electromagnetic stirrer is adopted in the 4th segment of the arc-shaped segment; During the continuous straightening stage of the continuous casting process, a straightening stress relaxation roll train technology is adopted.

2. The continuous casting production method of the large single-weight and extra-thick slab for the steel of the offshore wind power tower barrel according to claim 1, characterized in that The thickness of the continuous casting slab is 450mm, the width is 2600mm, the length is 6200 - 6800mm, and the single weight is 55 - 60t.

3. The continuous casting production method of the large single weight and extra thick slab for the steel of the offshore wind power tower barrel according to claim 1, characterized in that: From the entrance to the exit of the 8th to 9th segments in the continuous straightening area, the basic roll gap gradually increases, and the increase amplitude is 0.125mm per roll.

4. The continuous casting production method of a large single-weight and extra-thick slab for an offshore wind power tower barrel steel according to claim 1, characterized in that: The casting speed is 0.47m / min.

5. The continuous casting production method of the large single weight and extra thick slab for the steel of the offshore wind power tower barrel according to claim 1, characterized in that, When the convex roll heavy reduction ends, the temperature difference between the surface and the core of the slab is greater than or equal to 500°C.

6. The continuous casting production method of a large single-weight and extra-thick slab for steel used in offshore wind turbine towers according to claim 1, characterized in that: When the convex roll is under heavy reduction, the reduction amount per single segment is 10mm.

7. The continuous casting production method of a large single weight and extra thick slab for steel used in offshore wind turbine towers according to claim 1, characterized in that: The convex height of the convex roll is 10mm, and the convex width is 2200mm.

8. The continuous casting production method of large single weight and extra thick slab for steel used in offshore wind power tower barrels according to claim 1, characterized in that: At the entrance and exit of the 4th segment, a pair of double-segmented roll electromagnetic stirrers are respectively configured, and an alternating stirring mode is adopted, with a current intensity of 600A / 600A, a frequency of 6Hz, 20s forward and 2s stop and 20s reverse.