460MPa-grade high-strength steel continuous casting large round billet as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of steel smelting and continuous casting, and particularly relates to a 460MPa-grade high-strength steel continuous casting large round billet and a preparation method and application thereof. The invention discloses a preparation method of a 460MPa-grade high-strength steel continuous casting large round billet. The preparation method comprises the following steps: (1) smelting to obtain molten steel meeting the standard; (2) the molten steel is subjected to continuous casting, the molten steel is crystallized in a crystallizer with the diameter phi being 800 mm, and a continuous casting blank is obtained; and (3) slowly cooling the continuous casting billet.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting and continuous casting, and specifically relates to a 460MPa grade high-strength steel continuous casting large round billet and a preparation method and application thereof. Background Art

[0002] With the demand for increasing wind turbine power and reducing the weight of wind towers, higher-strength wind turbine flanges are urgently needed to gradually replace low-strength wind turbine flanges.

[0003] Increasing the strength of wind turbine flanges can build wind turbines with higher power, while significantly reducing the thickness and weight of wind turbine flanges, and making them safer. The development of higher-strength steel for wind turbine tower flanges is an inevitable trend. With the demand for "carbon peak and carbon neutrality", my country has vigorously developed the wind power industry. At present, the annual demand for steel for wind turbine tower flanges in my country remains at 1 million tons / year, and is increasing year by year. Most of them are made of 355MPa-grade S355NL (Q355NE) steel. In recent years, some manufacturers have developed 420MPa-grade S420NL (Q420NE) steel. In order to meet the high-quality and rapid development of my country's wind power industry, it is necessary to develop higher-strength (460MPa-grade) steel for wind turbine tower flanges. Summary of the invention

[0004] In order to develop a 460MPa grade S460NL (Q460NE) high-strength steel continuous casting large round billet for large wind turbine tower flanges to meet the rapid demand for high-quality development of wind turbine power increase and wind turbine tower weight reduction, the present invention provides a 460MPa grade high-strength steel continuous casting large round billet and its preparation method and application.

[0005] Specifically, the present invention is achieved through the following technical solutions:

[0006] A method for preparing a 460MPa grade high-strength steel continuous casting large round billet, comprising:

[0007] (1) Smelting to obtain molten steel that meets the standards;

[0008] (2) continuously casting the molten steel, and crystallizing the molten steel in a φ800 mm crystallizer to obtain a continuously cast billet;

[0009] (3) Slowly cooling the continuously cast billet.

[0010] The above-mentioned method for preparing 460MPa grade high-strength steel continuous casting large round billet, in terms of weight percentage, the molten steel includes C0.17-0.19%, Si 0.30-0.60%, Mn 1.55-1.65%, P≤0.015%, S≤0.005%, Nb 0.03-0.06%, V 0.05-0.10%, Ti≤0.0050%, Cr≤0.30%, Ni≤0.8%, Cu≤0.10%, Mo≤0.10%, Al 0.018-0.033%, and the balance is Fe and unavoidable impurities.

[0011] In the above-mentioned method for preparing 460MPa grade high-strength steel continuous casting large round billet, the carbon equivalent CEV in the molten steel is controlled to be 0.44%≤CEV≤0.49%.

[0012] In the above-mentioned method for preparing 460MPa grade high-strength steel continuous casting large round billet, the contents of H, O and N in the molten steel are controlled as follows: H≤2ppm, O≤20ppm, N: 70-150ppm.

[0013] In the above-mentioned method for preparing 460MPa-grade high-strength steel continuous casting large round billets, three-stage electromagnetic stirring is set during the continuous casting process, and the stirring operation is limited as follows: the current of the crystallizer electromagnetic stirring is 210A-250A, the frequency is 2.4-2.8Hz, and the reversing time is 20-25s; the second cooling zone electromagnetic stirring is set at a position 10.5m-14.2m away from the meniscus, and the current of the second cooling zone electromagnetic stirring is 80-100A, the frequency is 1.8-2.0Hz, and the reversing time is 20-25s; the end electromagnetic stirring is set at 17.0m-18.5m away from the meniscus, and the current of the end electromagnetic stirring is 320-350A, the frequency is 1.0-1.2Hz, and the reversing time is 20-25s.

[0014] In the above-mentioned method for preparing the 460MPa grade high-strength steel continuous casting large round billet, during the continuous casting process, the superheat of the tundish is controlled to be 15°C-35°C.

[0015] In the above-mentioned method for preparing 460MPa grade high-strength steel continuous casting large round billet, the casting speed during the continuous casting process is 0.17-0.19m / min, and the secondary cooling water volume is controlled to be 0.12-0.14L / kg.

[0016] In the above-mentioned method for preparing the 460MPa grade high-strength steel continuous casting large round billet, the slow cooling time is ≥36h; and the surface temperature of the round billet should be ≤200°C when it comes out of the slow cooling pit.

[0017] On the other hand, the present invention also provides a 460MPa grade high-strength steel continuous casting large round billet, which is prepared by the above-mentioned preparation method.

[0018] In another aspect, the present invention further provides the use of the above-mentioned 460MPa grade high-strength steel continuous casting large round billet in the preparation of large wind power tower flanges.

[0019] The technical solution of the present invention has the following beneficial effects:

[0020] The 460MPa grade S460NL (Q460NE) steel continuous casting billet for the φ800mm wind turbine tower flange obtained according to the composition design and continuous casting process of the high-strength wind turbine flange steel of the present invention has excellent billet quality and is finally forged into a large-size wind turbine flange with high stability in room temperature mechanical properties and low temperature mechanical properties, which meets the industry standard of 460MPa grade wind turbine flanges in the wind power industry. DETAILED DESCRIPTION

[0021] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments. Except for the following contents, the process method of the present invention adopts conventional methods or devices in the art. Unless otherwise specified, the following terms have the meanings commonly understood by those skilled in the art.

[0022] When a numerical range is disclosed herein, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0023] 1. Composition system design of continuous casting large round billet

[0024] With the continuous improvement of wind turbine power and the increasing complexity of the service environment, higher requirements are placed on the strength and low-temperature toughness of the flanges of the key connecting parts of wind turbine towers. In order to develop higher-strength steel for wind turbine tower flanges, it is necessary to fully consider the micro-alloying of steel grades. The present invention fully considers the micro-alloying of Nb, V and N elements based on the performance improvement requirements.

[0025] The invention fully explores the influence law between the component system and the mechanical properties, and discloses a method for manufacturing a 460MPa grade S460NL (Q460NE) high-strength steel for a large wind power tower flange. The chemical composition of the steel by mass percentage is as follows: C 0.17-0.19%, Si 0.30-0.60%, Mn1.55-1.65%, P≤0.015%, S≤0.005%, Nb0.03-0.06%, V 0.05-0.10%, Ti≤0.0050%, Cr≤0.30%, Ni≤0.8%, Cu≤0.10%, Mo≤0.10%, Al 0.018~0.033%, carbon equivalent CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15 is controlled as 0.44%≤CEV≤0.49%, the contents of H, O and N in steel are controlled as: H≤2ppm, O≤20ppm, N:70-150ppm, the remainder is Fe and unavoidable impurities.

[0026] The present invention controls the composition of molten steel within the above range, thereby ensuring that the mechanical properties of the finished large-size wind turbine flange meet the mechanical property requirements of 460MPa-level high-strength wind turbine flanges.

[0027] 2. Quality control of continuous casting large round billets

[0028] Large wind turbine flanges are not allowed to be welded and must be forged as a whole. Therefore, large-section die-cast ingots or continuous casting billets are required for production. Large-section steel ingots (continuous casting billets) will inevitably form central defects such as central porosity and central shrinkage, as well as macro-segregation caused by selective crystallization. Such defects will cause the final finished flange to have varying degrees of looseness defects, resulting in a low flaw detection pass rate for the final large wind turbine flange. Severe macro-segregation will cause poor stability of mechanical properties and affect the service life. In order to solve this problem, it is necessary to develop a continuous casting process based on the characteristics of the steel grade and the cross-sectional features, effectively control the central shrinkage, central porosity and macro-segregation, so as to improve the flaw detection pass rate and mechanical property stability of large-size wind turbine flanges. The present invention has developed a dedicated continuous casting process for high-strength wind turbine flanges based on a thorough study of the characteristics of the steel grade.

[0029] The molten steel is crystallized in a φ800mm crystallizer, and three-stage electromagnetic stirring is set during the continuous casting process. The stirring operation is limited as follows: the current of the crystallizer electromagnetic stirring is 210A-250A, the frequency is 2.4-2.8Hz, and the reversing time is 20-25s; the second cooling zone electromagnetic stirring is set at a position 10.5m-14.2m away from the meniscus, and the current of the second cooling zone electromagnetic stirring is 80-100A, the frequency is 1.8-2.0Hz, and the reversing time is 20-25s; the end electromagnetic stirring is set at a position 17.0m-18.5m away from the meniscus, and the current of the end electromagnetic stirring is 320-350A, the frequency is 1.0-1.2Hz, and the reversing time is 20-25s. The present invention adopts a specific three-stage electromagnetic stirring, which can reduce the degree of carbon segregation in the process of transformation from columnar crystals to equiaxed crystals in the ingot compared to the traditional two-stage electromagnetic stirring, and can effectively expand the range of equiaxed crystals in the center of the ingot and reduce the center shrinkage cavity.

[0030] In order to reduce the central looseness and shrinkage of large-sized continuous casting billets, a lower superheat should be used as much as possible. At the same time, in order to ensure the smooth continuous casting process and avoid interruption of casting, the superheat should not be too low. Preferably, in the present invention, the superheat of the tundish is controlled to be 15℃-35℃ during the continuous casting process.

[0031] Since the drawing speed and the water ratio of the secondary cooling water have a great influence on the solidification structure, center quality and surface quality of the ingot, the drawing speed in the continuous casting process is 0.17-0.19m / min, and the water ratio of the secondary cooling water is controlled to 0.12-0.14L / kg. The center looseness, shrinkage cavity, center crack, middle crack, subcutaneous crack and subcutaneous bubble on the acid-leached low-magnification test piece of the round ingot cross section are evaluated according to YB / T 4149, and the rating chart implements YB / T 153, all ≤ Grade 2.

[0032] During the research process, the inventor discovered that direct air-cooling of the ingot resulted in internal stress concentration, which caused problems such as cracking during subsequent processing by users. Therefore, the continuous casting ingot cannot be directly air-cooled but needs to be slowly cooled.

[0033] In some preferred embodiments, the slow cooling time of the present invention is ≥36h; and the surface temperature of the round billet when leaving the slow cooling pit should be ≤200°C. Slow cooling of the billet according to the method of the present invention can diffuse and evenly distribute the segregation structure (distributed in the surface and core areas) in the billet.

[0034] The present invention fully explores the influence between the composition system and the mechanical properties. By innovating the composition system and the continuous casting process steps, the two work together to effectively improve the uniformity of the composition of the cross-section of the ingot, thereby reducing composition segregation and improving the center quality of the ingot.

[0035] The large-section continuous casting billet (continuous casting large round billet) prepared according to the method of the present invention has the following properties: the center crack level of the continuous casting billet is 0, the middle crack is 0, and the center looseness is ≤0.5; after forging into a finished wind power flange with a thickness of 230 mm, the yield strength is 390-410 MPa, the tensile strength is 530 MPa-560 MPa, and the -40°C V-notch impact energy is ≥80 J, which fully meets the industry standard of 460 MPa wind power flanges in the wind power industry.

[0036] Example

[0037] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods without specific conditions in the following examples are based on conventional methods and conditions.

[0038] Example 1

[0039] A 460MPa grade high-strength steel continuous casting large round billet for a large wind power tower flange is prepared by "converter smelting→LF refining→VD vacuum refining→φ800mm large round billet continuous casting→slow cooling". The chemical composition of the steel by mass percentage is as follows: C 0.18%, Si 0.38%, Mn 1.60%, P 0.0075%, S0.0017%, Nb 0.035%, V 0.06%, Ti0.0025%, Cr 0.05%, Ni 0.02%, Cu 0.01%, Mo 0.003%, Al 0.030%, carbon equivalent CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15 is 0.46%, and the contents of H, O and N in the steel are controlled as follows: H 0.5ppm, O 0.1ppm, and Ni 0.01ppm. 16ppm, N120ppm, the balance is Fe and inevitable impurities.

[0040] Φ800mm large round billet continuous casting is adopted, and the continuous casting process parameters are as follows: the superheat of the tundish is 25℃, the pulling speed is 0.18m / min, the secondary cooling water volume is 0.13L / kg, and a three-stage electromagnetic stirring is set in the continuous casting process, including crystallizer electromagnetic stirring, secondary cooling zone electromagnetic stirring set at a position 14.2m away from the meniscus, and terminal electromagnetic stirring set at a position 18.5m away from the meniscus. Among them, the current of the crystallizer electromagnetic stirring is controlled to 230A, the stirring frequency is controlled to 2.8Hz, and the reversing time is controlled to 25s; the current of the secondary cooling zone electromagnetic stirring is controlled to 100A, the stirring frequency is controlled to 1.8Hz, and the reversing time is controlled to 20s; the current of the terminal electromagnetic stirring is controlled to 350A, the stirring frequency is controlled to 1.0Hz, and the reversing time is controlled to 25s.

[0041] The continuous casting billet is cooled in the slow cooling pit for 50 hours, and the surface temperature of the round billet is 185℃ when it leaves the slow cooling pit.

[0042] The φ800mm wind tower flange 460MPa grade S460NL (Q460NE) steel continuous casting billet obtained by the above high-strength wind power flange steel composition design and continuous casting process has excellent billet quality, and the low-power quality is rated according to YB / T 4149: center crack level 0, center looseness ≤0.5, and middle crack 0. The final forged 230mm thick large-size wind power flange has a yield strength range of 390MPa-410MPa, a tensile strength of 530MPa-560MPa, and a -40℃ V-notch impact energy ≥80J, which meets user needs and industry standards, and the qualified rate of room temperature mechanical properties and low temperature mechanical properties reaches 100%.

[0043] Example 2

[0044] The S460NL steel for large wind turbine flanges is smelted by “electric converter smelting → LF refining → VD vacuum refining → φ800mm round billet continuous casting → slow cooling”. The chemical composition of the steel by mass percentage is as follows: C 0.18%, Si 0.52%, Mn 1.58%, P 0.0085%, S 0.0023%, Nb 0.04%, V 0.06%, Ti 0.0035%, Cr 0.08%, Ni 0.04%, Cu 0.02%, Mo 0.004%, Al 0.028%, carbon equivalent CEV = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15 is 0.48%, and the contents of H, O and N in the steel are controlled as follows: H 0.5ppm, O 15ppm, N 118ppm, the remainder is Fe and inevitable impurities.

[0045] Φ800mm large round billet continuous casting is adopted, and the continuous casting process parameters are as follows: the superheat of the tundish is 15℃, the pulling speed is 0.19m / min, the secondary cooling water volume is 0.14L / kg, and a three-stage electromagnetic stirring is set in the continuous casting process, including crystallizer electromagnetic stirring, secondary cooling zone electromagnetic stirring set at a position 14.2m away from the meniscus, and terminal electromagnetic stirring set at a position 18.5m away from the meniscus. Among them, the current of the crystallizer electromagnetic stirring is controlled to 230A, the stirring frequency is controlled to 2.8Hz, and the reversing time is controlled to 25s; the current of the secondary cooling zone electromagnetic stirring is controlled to 100A, the stirring frequency is controlled to 1.8Hz, and the reversing time is controlled to 20s; the current of the terminal electromagnetic stirring is controlled to 350A, the stirring frequency is controlled to 1.0Hz, and the reversing time is controlled to 25s.

[0046] The continuous casting billet is cooled in the slow cooling pit for 50 hours, and the surface temperature of the round billet is 185℃ when it leaves the slow cooling pit.

[0047] The φ800mm wind tower flange 460MPa grade S460NL (Q460NE) steel continuous casting billet obtained by the above high-strength wind power flange steel composition design and continuous casting process has excellent billet quality, and the low-power quality is rated according to YB / T 4149: center crack level 0, center looseness ≤0.5, and middle crack 0. The final forged 230mm thick large-size wind power flange has a yield strength range of 390MPa-410MPa, a tensile strength of 530MPa-560MPa, and a -40℃ V-notch impact energy ≥80J, which meets user needs and industry standards, and the qualified rate of room temperature mechanical properties and low temperature mechanical properties reaches 100%.

[0048] Comparative Example 1

[0049] A 460MPa grade high-strength steel continuous casting large round billet for a large wind power tower flange is prepared by "converter smelting→LF refining→VD vacuum refining→φ800mm large round billet continuous casting→slow cooling". The chemical composition of the steel by mass percentage is as follows: C 0.18%, Si 0.43%, Mn 1.62%, P 0.0075%, S0.0017%, Nb 0.035%, V 0.06%, Ti0.0025%, Cr 0.05%, Ni 0.02%, Cu 0.01%, Mo 0.003%, Al 0.030%, carbon equivalent CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15 is 0.46%, and the contents of H, O and N in the steel are controlled as follows: H 0.5ppm, O 0.1ppm, and Ni 0.01ppm. 17ppm, N120ppm, the remainder is Fe and inevitable impurities.

[0050] Φ800mm large round billet continuous casting is adopted, and the continuous casting process parameters are as follows: the superheat of the tundish is 25℃, the pulling speed is 0.20m / min, the secondary cooling water volume is 0.13L / kg, and a three-stage electromagnetic stirring is set in the continuous casting process, including crystallizer electromagnetic stirring, secondary cooling zone electromagnetic stirring set at a position 14.2m away from the meniscus, and terminal electromagnetic stirring set at a position 18.5m away from the meniscus. Among them, the current of the crystallizer electromagnetic stirring is controlled to 230A, the stirring frequency is controlled to 2.8Hz, and the reversing time is controlled to 25s; the current of the secondary cooling zone electromagnetic stirring is controlled to 100A, the stirring frequency is controlled to 1.8Hz, and the reversing time is controlled to 20s; the current of the terminal electromagnetic stirring is controlled to 350A, the stirring frequency is controlled to 1.0Hz, and the reversing time is controlled to 25s.

[0051] The continuous casting billet is cooled in the slow cooling pit for 50 hours, and the surface temperature of the round billet is 185℃ when it leaves the slow cooling pit.

[0052] The φ800mm wind power tower flange 460MPa grade S460NL (Q460NE) steel continuous casting billet obtained by the above high-strength wind power flange steel composition design and continuous casting process has a low-power quality rating according to YB / T 4149: center crack level 0.5, center looseness ≤1.0, and middle crack level 0. The final forged large-size wind power flange with a thickness of 230mm has a normal temperature mechanical property qualification rate of 90% and a low temperature mechanical property qualification rate of 88.2%.

[0053] Comparative Example 2

[0054] The S460NL steel for large wind turbine flanges is smelted by “electric converter smelting → LF refining → VD vacuum refining → φ800mm round billet continuous casting → air cooling”. The chemical composition of the steel by mass percentage is as follows: C 0.18%, Si 0.48%, Mn 1.60%, P 0.0085%, S 0.0020%, Nb 0.04%, V 0.06%, Ti 0.0035%, Cr 0.08%, Ni 0.04%, Cu 0.02%, Mo 0.004%, Al 0.028%, carbon equivalent CEV = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15 is 0.48%, and the contents of H, O and N in the steel are controlled as follows: H 0.5ppm, O 15ppm, N 118ppm, the remainder is Fe and inevitable impurities.

[0055] Φ800mm large round billet continuous casting is adopted, and the continuous casting process parameters are as follows: the superheat of the tundish is 15℃, the pulling speed is 0.19m / min, the secondary cooling water volume is 0.14L / kg, and a three-stage electromagnetic stirring is set in the continuous casting process, including crystallizer electromagnetic stirring, secondary cooling zone electromagnetic stirring set at a position 14.2m away from the meniscus, and terminal electromagnetic stirring set at a position 18.5m away from the meniscus. Among them, the current of the crystallizer electromagnetic stirring is controlled to 230A, the stirring frequency is controlled to 2.8Hz, and the reversing time is controlled to 25s; the current of the secondary cooling zone electromagnetic stirring is controlled to 100A, the stirring frequency is controlled to 1.8Hz, and the reversing time is controlled to 20s; the current of the terminal electromagnetic stirring is controlled to 350A, the stirring frequency is controlled to 1.0Hz, and the reversing time is controlled to 25s.

[0056] The continuous casting ingot is directly air-cooled.

[0057] The φ800mm wind tower flange 460MPa grade S460NL (Q460NE) steel continuous casting billet obtained by the above high-strength wind turbine flange composition design and continuous casting process was cracked during the sawing process by the user, resulting in a low yield of only 80%.

[0058] The present invention has been disclosed above with preferred embodiments, but those skilled in the art should understand that these embodiments are only used to describe the present invention and should not be understood as limiting the scope of the present invention. It should be noted that all changes and substitutions equivalent to these embodiments should be deemed to be included in the scope of the claims of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined in the claims.

Claims

1. A method for preparing a 460MPa grade high-strength steel continuous casting large round billet, characterized in that: include: (1) Smelting to obtain molten steel that meets the standards; (2) continuously casting the molten steel, and crystallizing the molten steel in a φ800 mm crystallizer to obtain a continuously cast billet; (3) Slowly cooling the continuously cast billet.

2. The preparation method according to claim 1, characterized in that: Measured by weight percentage, the molten steel includes C0.17-0.19%, Si 0.30-0.60%, Mn 1.55-1.65%, P≤0.015%, S≤0.005%, Nb 0.03-0.06%, V 0.05-0.10%, Ti≤0.0050%, Cr≤0.30%, Ni≤0.8%, Cu≤0.10%, Mo≤0.10%, Al 0.018-0.033%, and the balance is Fe and unavoidable impurities.

3. The preparation method according to claim 2, characterized in that: The carbon equivalent CEV in the molten steel is controlled to be 0.44%≤CEV≤0.49%.

4. The preparation method according to claim 2, characterized in that: The contents of H, O and N in the molten steel are controlled as follows: H≤2ppm, O≤20ppm, N: 70-150ppm.

5. The preparation method according to claim 1, characterized in that: During the continuous casting process, three-stage electromagnetic stirring is set, and the stirring operation is limited as follows: the current of the crystallizer electromagnetic stirring is 210A-250A, the frequency is 2.4-2.8Hz, and the switching time is 20-25s; the second cooling zone electromagnetic stirring is set at a distance of 10.5m-14.2m from the meniscus, and the current of the second cooling zone electromagnetic stirring is 80-100A, the frequency is 1.8-2.0Hz, and the switching time is 20-25s; the end electromagnetic stirring is set at a distance of 17.0m-18.5m from the meniscus, and the current of the end electromagnetic stirring is 320-350A, the frequency is 1.0-1.2Hz, and the switching time is 20-25s.

6. The preparation method according to claim 1, characterized in that: During the continuous casting process, the superheat of the tundish is controlled at 15℃-35℃.

7. The preparation method according to claim 1, characterized in that: The casting speed during continuous casting is 0.17-0.19 m / min, and the secondary cooling water volume is controlled at 0.12-0.14 L / kg.

8. The preparation method according to claim 1, characterized in that: The slow cooling time is ≥36h; and the surface temperature of the round billet should be ≤200°C when it comes out of the slow cooling pit.

9. A 460MPa grade high strength steel continuous casting large round billet, characterized in that: The preparation method is described in any one of claims 1 to 8.

10. Use of the 460MPa grade high strength steel continuous casting large round billet as claimed in claim 9 in the preparation of large wind power tower flanges.