Steel EH420 for ultrahigh-strength offshore wind power pipe pile and production method of steel EH420

Abstract

The invention discloses ultrahigh-strength steel EH420 for an offshore wind power pipe pile and a production method of the ultrahigh-strength steel EH420. The technological process comprises the steps of converter smelting, refining, continuous casting, heating and rolling, cooling, normalizing and checking and warehousing. The steel comprises the following chemical components in percentage by mass: 0.10%-0.12% of C, 0.10%-0.30% of Si, 1.45%-1.53% of Mn, less than or equal to 0.012% of P, less than or equal to 0.003% of S, 0.035%-0.045% of Nb, 0.05%-0.06% of V, 0.010%-0.018% of Ti, 0.03%-0.05% of Al, 0.30%-0.38% of Ni, 0.15%-0.19% of Cr, 0%-0.08% of Mo, 0.18%-0.25% of Cu and less than or equal to 0.008% of N. The production of the normalized 420-grade steel plate is realized by adding Cr, Cu, V and other alloy strengthening elements and by optimizing the rolling process and the normalizing process. The yield strength of the produced steel plate is larger than or equal to 420 MPa, the tensile strength is larger than or equal to 530 MPa, the low-temperature impact toughness (-40 DEG C, Akv) of the 1 / 4 thickness and the core of the steel plate is larger than or equal to 150 J, and the steel plate has excellent welding performance.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology and relates to an ultra-high strength offshore wind power pipe pile steel EH420 and its production method. Background Technology

[0002] Larger offshore wind power equipment is currently an effective way to reduce the cost per kilowatt-hour. As wind turbines become increasingly larger, lightweight and high-strength concrete piles must be considered. The current trend is to use higher-grade steel to replace lower-grade steel, achieving weight reduction and cost savings. DH420 / EH420 must replace DH36 / EH36 as soon as possible, and future development may move towards even higher steel grades.

[0003] Due to the limitations of the ferrite + pearlite structure after normalizing, it is relatively difficult to achieve a strength level of 420 after normalizing, and existing technologies have made many explorations to address this issue. The chemical composition disclosed in Chinese Patent CN109321847B, "A High-Input Weldable EH420 Grade Marine Engineering Thick Steel Plate and Its Preparation Method," is as follows: C=0.05~0.12%, Si=0.1~0.3%, Mn=1.0~1.7%, P=0.001~0.01%, S=0.001~0.005%, Nb=0.01~0.04%, Ti=0.005~0.025%, Cu=0.2~0.5%, Ni=0.2~0.5%, N=0.001~0.006%, O=0.001~0.005%, Al=0.005~0.025%, Mg=0.0005~0.005%, Ca=0.0005~0.005%. This patent imposes strict control over the oxygen content in the steel, and also has high requirements for the quantity and size of Al-Mg-Ti-Ca-Mn-OS composite inclusions. The smelting process is difficult to control, and the stability is poor. Improper control of inclusions can negatively impact the internal quality of the steel plate, hindering mass production, and limiting the maximum produced size to 60mm. CN111057956B, "Production Method of EH420 Grade 150~200mm Extra-Thick Steel Plate," discloses the following chemical composition: C=0.10%~0.14%, Si=0.20%~0.50%, Mn=1.00%~1.45%, P≤0.015%, S≤0.005%, Nb=0.030~0.080%, V=0.001~0.050%, Al=0.01%~0. The alloy composition is 0.05%, Ti=0.005~0.020%, Cr=0.15~0.35%, Cu=0.10~0.50%, Ni=0.01~0.8%. It has a high Nb, Cr, Cu, Ni and other alloy components, resulting in a high alloy cost. The rolling red-hot temperature is below 450℃. It is delivered using TMCP. Compared with the normalizing process, the TMCP process results in poor uniformity of steel plate properties and higher stress, which is not conducive to the use of the next process. Summary of the Invention

[0004] The purpose of this invention is to provide an ultra-high strength offshore wind power pipe pile steel EH420 and its production method. The produced steel plate has a yield strength ≥420MPa, a tensile strength ≥530MPa, a low-temperature impact toughness of -40℃ at 1 / 4 thickness and core, Akv ≥150J, and excellent welding performance.

[0005] This invention is achieved through the following technical solution: EH420, an ultra-high strength steel for offshore wind turbine pipe piles, has the following chemical composition by mass percentage: C = 0.10%~0.12%, Si = 0.10%~0.30%, Mn = 1.45%~1.53%, P ≤ 0.012%, S ≤ 0.003%, Nb = 0.035%~0.045%, V = 0.05%~0.06%, Ti = 0.010%~0.018%, Al = 0.03%~0.05%, Ni = 0.30%~0. 0.38%, Cr=0.15%~0.19%, Mo=0%~0.08%, Cu=0.18%~0.25%, N≤0.008%, the remainder being Fe and unavoidable impurities; the steel plate is delivered in normalized condition, the thickness of the continuously cast billet is 350~450mm, the thickness of the finished product is 80~100mm, the yield strength of the steel plate is ≥420MPa, the tensile strength is ≥530MPa, the low-temperature impact toughness of the steel plate at 1 / 4 thickness and core is -40℃, Akv≥150J.

[0006] A production method for EH420 steel for ultra-high strength offshore wind turbine piles includes a process flow of converter smelting, refining, continuous casting, hot rolling, cooling, normalizing, inspection and warehousing. Key process steps include: (1) Smelting: The converter is used for smelting, and the top and bottom are combined for blowing; the LF furnace and VD or RH furnace are used for vacuum treatment to control O≤15ppm, H≤1.5ppm, S≤30ppm; (2) Continuous casting: Thick-gauge continuous casting billets are used, with thicknesses of 350mm / 400mm / 450mm and widths between 2070 and 2500mm. Continuous casting adopts low superheat control of 6~15℃, light reduction + large reduction technology, secondary cooling electromagnetic stirring, and low-magnification segregation control below national standard C class 1.0. (3) Heating: The steel billet is hot-charged into the furnace, heated at 1190~1230℃, for 320~500min; (4) Rolling: The two-stage controlled rolling process with two stands is adopted. The roughing stage is rolling in the recrystallization zone and adopts the large reduction technology. The single reduction of the last three passes is ≥40mm. The finishing stage is rolling in the non-recrystallization zone and the thickness is 120~150mm. The finishing rolling adopts low temperature and cumulative large reduction. The starting temperature of the finishing rolling is less than or equal to 840℃ and the cumulative reduction rate of the finishing rolling is ≥70%. After rolling, it is cooled by MULPIC and the final cooling temperature is 700~720℃. (5) Normalizing: The normalizing temperature is 890±10℃, the furnace time is 1.8~2.4 times the plate thickness mm×min / mm; the heating rate is 1.5~2.0min / mm, and the holding time is 40~60min. The grains are further refined through normalizing treatment.

[0007] Invention principle: This invention improves the strength and toughness of steel plates by controlling the rolling process to refine the austenite grains and introducing processing strain, which is then combined with subsequent normalizing heat treatment to obtain a refined ferrite structure.

[0008] The innovative aspects and beneficial effects of this invention are as follows: (1) Use 350 / 400 / 450mm continuous casting billets to ensure that the compression ratio from billet to steel plate is >4. In the roughing stage, roll in the recrystallization zone and use large reduction technology to ensure that the single reduction in the last three passes is ≥40mm. Large reduction breaks the original grains through strong plastic deformation, promotes dynamic recrystallization, and forms fine and uniform equiaxed grains. In the finishing stage, roll in the non-recrystallization zone with a thickness of 120~150mm. The finishing rolling adopts low temperature and cumulative large reduction. The starting temperature of finishing rolling is less than or equal to 840℃. With a cumulative reduction rate of ≥70% in the finishing rolling process, precipitation and grain elongation induced by cumulative strain are achieved, forming a fine ferrite / pearlite microstructure, which improves the mechanical properties of the steel plate. At the same time, sufficient cumulative reduction ensures effective deformation of the core, thereby guaranteeing core deformation penetration and improving core impact performance. Subsequently, by optimizing the normalizing process, ensuring the initial heating rate, and appropriately extending the normalizing holding time, the grains are further refined and the microstructure is homogenized, resulting in a fine and uniform microstructure, which further improves the strength and toughness of the steel plate. (2) The present invention adopts the normalizing process to produce steel for wind power pipe piles with a thickness of 80-100mm. The yield strength is ≥420MPa, the tensile strength is ≥530MPa, the low temperature impact toughness of the steel plate at 1 / 4 thickness and core is -40℃, Akv is ≥150J, Z-direction performance is >50%, and all mechanical properties are good. (3) It adopts a low carbon equivalent composition, with a carbon equivalent CEV ≤ 0.45%, and has excellent welding performance; (4) Ultra-high strength EH420 replaces ordinary high strength EH36, which can effectively reduce welds, shorten the processing cycle of the next process, and improve production efficiency. At the same time, the reduction of welds can also improve the fatigue life of pipe piles and extend service life, which fully meets the strength and quality requirements of offshore wind turbines as they develop towards larger size and deeper sea areas. Attached Figure Description

[0009] Figure 1 Metallographic structure diagram of a 1 / 4 thickness steel plate in Example 1.

[0010] Figure 2 This is a metallographic diagram of the core of the steel plate in Example 1. Detailed Implementation

[0011] Example 1: Production of 85mm thick wind turbine steel sheet weighing 22.7 tons The continuously cast billet size is 350mm × 2270mm × 4050mm, and the finished steel plate size is 85mm × 3180mm × L (length). The chemical composition of the steel (mass percentage) is C=0.11%, Si=0.22%, Mn=1.46%, P=0.010%, S=0.001%, Al=0.03%, Nb=0.040%, V=0.056%, Ti=0.012%, Cr=0.16%, Cu=0.2%, Ni=0.36%, Mo=0.01%, Ceq=0.44%, with the remainder being Fe and unavoidable impurities; the process steps include: (1) Smelting: The converter is used for smelting and top and bottom combined blowing is used; the LF furnace and RH furnace are used for vacuum treatment to reduce the content of harmful gases such as O and H and S. The O content is 12ppm, the H content is 1.3ppm and the S content is 10ppm. (2) Continuous casting: Thick-gauge continuous casting billet is used, with a superheat of 6-14℃, a casting speed of 0.65m / min, a light reduction + a large reduction of 17mm, a low magnification center segregation of C class 1.0, and good internal quality; the billet thickness is 350mm and the width is 2270mm, ensuring that the compression ratio from the continuous casting billet to the steel plate is 4.12; (3) Heating: The steel billet is hot-charged into the furnace, the furnace exit temperature is 1230℃, and the heating time is 340min; (4) Rolling: The two-stage controlled rolling process with two stands is adopted. In the roughing stage, the roughing opening temperature is 1170℃, the reduction of the last three passes of roughing is 42 / 41 / 41, the thickness after waiting for the temperature is 140mm, and the finishing rolling begins. The finishing rolling opening temperature is 838℃, the finishing rolling temperature is 813℃, the cumulative reduction rate of finishing rolling is 75%, and after rolling, it is water cooled by MULPIC, and the final cooling temperature is 702℃. (5) Normalizing: Normalizing temperature 896℃, furnace time 203min, heating rate 1.74min / mm, holding time 55min.

[0012] Example 2: Production of 95mm thick wind turbine steel plates weighing 20.5 tons each The continuously cast billet size is 450mm × 2270mm × 2845mm, and the finished steel plate size is 95mm × 2500mm × L (length). The chemical composition of the steel (mass percentage) is C=0.12%, Si=0.21%, Mn=1.51%, P=0.009%, S=0.0011%, Al=0.032%, Nb=0.044%, V=0.055%, Ti=0.013%, Cr=0.16%, Cu=0.18%, Ni=0.37%, Mo=0.01%, Ceq=0.45%, with the remainder being Fe and unavoidable impurities; the process steps include: (1) Smelting: The converter is used for smelting and top and bottom combined blowing is used; the LF furnace and VD furnace are used for vacuum treatment to reduce the content of harmful gases such as O and H and S. The O content is 10ppm, the H content is 1.1ppm and the S content is 13ppm. (2) Continuous casting: Thick-gauge continuous casting billet is used, with a superheat of 6-12℃, a casting speed of 0.45m / min, a light reduction + a large reduction of 23mm, a low magnification center segregation of C class 1.0, and good internal quality; the billet thickness is 450mm and the width is 2270mm, ensuring that the compression ratio from the continuous casting billet to the steel plate is 4.73; (3) Heating: The steel billet is cold-charged into the furnace, the furnace outlet temperature is 1225℃, and the heating time is 488min; (4) Rolling: The two-stage controlled rolling process with two stands is adopted. In the roughing stage, the roughing opening temperature is 1160℃, the reduction of the last three passes of roughing is 45 / 42 / 43, the thickness after waiting for the temperature is 150mm, and the finishing rolling begins. The finishing rolling opening temperature is 835℃, the finishing rolling temperature is 812℃, the cumulative reduction rate of finishing rolling is 73%, and after rolling, it is water cooled by MULPIC, and the final cooling temperature is 705℃. (5) Normalizing: Normalizing temperature 898℃, furnace time 225min, heating rate 1.84min / mm, holding time 50min.

[0013] Example 3: Production of 90mm thick wind turbine steel plate weighing 22.9 tons The continuously cast billet size is 450mm × 2500mm × 2885mm, and the finished steel plate size is 90mm × 2950mm × L (length). The chemical composition of the steel (mass percentage) is C=0.11%, Si=0.22%, Mn=1.53%, P=0.008%, S=0.0013%, Al=0.034%, Nb=0.043%, V=0.054%, Ti=0.012%, Cr=0.16%, Cu=0.19%, Ni=0.34%, Mo=0.01%, Ceq=0.445%, with the remainder being Fe and unavoidable impurities; the process steps include: (1) Smelting: The converter is used for smelting and top and bottom combined blowing is used; the LF furnace and VD furnace are used for vacuum treatment to reduce the content of harmful gases such as O and H and S. The O content is 9ppm, the H content is 1.0ppm and the S content is 13ppm. (2) Continuous casting: Thick-gauge continuous casting billets are used, with a superheat of 7-14℃, a casting speed of 0.45m / min, a light reduction + a large reduction of 23mm, a low magnification center segregation of C class 1.0, and good internal quality; the billet thickness is 450mm and the width is 2500mm, ensuring that the compression ratio from the continuous casting billet to the steel plate is 5.0; (3) Heating: The steel billet is cold-charged into the furnace, and the furnace outlet temperature is 1228℃, with a heating time of 465min; (4) Rolling: The two-stage controlled rolling process with two stands is adopted. In the roughing stage, the roughing opening temperature is 1162℃, the reduction of the last three passes of roughing is 46 / 41 / 43, the thickness after waiting for the temperature is 145mm, and the finishing rolling begins. The finishing rolling opening temperature is 838℃, the finishing rolling temperature is 810℃, the cumulative reduction rate of finishing rolling is ≥73%, and after rolling, it is water cooled by MULPIC, and the final cooling temperature is 703℃. (5) Normalizing: Normalizing temperature 896℃, furnace time 215min, heating rate 1.86min / mm, holding time 48min.

[0014] Table 1 Performance test results of steel produced in each embodiment .

[0015] As shown in Table 1, all indicators of the embodiments meet the requirements of GB / T712 for marine engineering steel. The impact energy at -40℃ is excellent, with the 1 / 4 thickness consistently maintaining above 220J, and the core impact energy consistently above 170J. Therefore, the steel plate of this invention possesses excellent mechanical properties and is fully suitable for the requirements of large-scale and deep-sea development in offshore wind power.

Claims

1. A type of ultra-high strength offshore wind power pipe pile steel EH420, characterized in that: The chemical composition of the steel, by mass percentage, is C=0.10%~0.12%, Si=0.10%~0.30%, Mn=1.45%~1.53%, P≤0.012%, S≤0.003%, Nb=0.035%~0.045%, V=0.05%~0.06%, Ti=0.010%~0.018%, Al=0.03%~0.05%, Ni=0.30%~0.38%, Cr=0.15%~0.19%, Mo=0%~0.08%, Cu=0.18%~0.25%, N≤0.008%, with the remainder being Fe and unavoidable impurities. The steel plates are delivered in normalized condition. The thickness of the continuously cast billet is 350-450mm, and the thickness of the finished product is 80-100mm. The yield strength of the steel plate is ≥420MPa, the tensile strength is ≥530MPa, and the low-temperature impact toughness of the steel plate at 1 / 4 thickness and core is -40℃, Akv ≥150J.

2. A production method for EH420 steel for ultra-high strength offshore wind turbine piles, the process flow including converter smelting, refining, continuous casting, heating and rolling, cooling, normalizing, inspection and warehousing, characterized in that... Key process steps include: (1) Smelting: The converter is used for smelting, and the top and bottom are combined for blowing; the LF furnace and VD or RH furnace are used for vacuum treatment to control O≤15ppm, H≤1.5ppm, S≤30ppm; (2) Continuous casting: Thick-gauge continuous casting billets are used, with thicknesses of 350mm / 400mm / 450mm and widths between 2070 and 2500mm. Continuous casting adopts low superheat control of 6~15℃, light reduction + large reduction technology, secondary cooling electromagnetic stirring, and low-magnification segregation control below national standard C class 1.

0. (3) Heating: The steel billet is hot-charged into the furnace, heated at 1190~1230℃, for 320~500min; (4) Rolling: The two-stage controlled rolling process with two stands is adopted. The roughing stage is rolling in the recrystallization zone and adopts the large reduction technology. The single reduction of the last three passes is ≥40mm. The finishing stage is rolling in the non-recrystallization zone and the thickness is 120~150mm. The finishing rolling adopts low temperature and cumulative large reduction. The starting temperature of the finishing rolling is less than or equal to 840℃ and the cumulative reduction rate of the finishing rolling is ≥70%. After rolling, it is cooled by MULPIC and the final cooling temperature is 700~720℃. (5) Normalizing: The normalizing temperature is 890±10℃, the furnace time is 1.8~2.4 times the plate thickness mm×min / mm; the heating rate is 1.5~2.0min / mm, and the holding time is 40~60min. The grains are further refined through normalizing treatment.

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