Large-thickness high-toughness S355NLO wind power steel plate and production method thereof

Abstract

The invention relates to the technical field of ferrous metallurgy, in particular to a large-thickness high-toughness S355NLO wind power steel plate and a production method thereof, and the steel plate comprises the following chemical components in percentage by mass: 0.09-0.12% of C, 0.10-0.40% of Si, 1.45-1.60% of Mn, less than or equal to 0.010% of P, less than or equal to 0.002% of S, 0.025-0.040% of Nb, 0.30-0.50% of Ni, 0.025-0.040% of Alt, 0.025-0.035% of V, 0.005-0.020% of Ti, 0.10-0.20% of Cu, less than or equal to 50ppm of N, less than or equal to 2ppm of H and the balance of Fe and inevitable impurities. Through peritectic component design, continuous casting secondary cooling and dynamic reduction processes are optimized, and center segregation is reduced; the core structure is improved by rough rolling cogging and under large pressure, the penetration of the core of the thick plate is improved by adopting a strong controlled rolling process, the impact of-40 DEG C of the core is ensured, and the high-homogeneity thick plate structure control is realized by adopting an efficient heat treatment technology.

Description

Technical Field

[0001] The invention relates to the technical field of iron and steel metallurgy, and in particular to a thick and high-toughness S355NLO wind power steel plate and a production method thereof. Background Art

[0002] With the gradual development of clean energy, wind power, as a representative of clean energy, has gradually been widely used and promoted. As the basic material for wind power generation, thick and high-toughness wind power steel has gradually received attention from the industry. Due to the extreme marine service environment and construction requirements, special technical requirements for high toughness and easy welding are put forward for thick wind power steel. However, for thick wind power steel, due to the plate thickness effect, there are certain differences in the performance near the surface, 1 / 4 position and core, which has a certain impact on the cold deformation processing and welding performance of the product. For wind power steel with a thickness of less than 80mm, the performance and strength differences in the thickness direction are relatively small, but for thick plates above 80mm-120mm, the differences in the thickness direction bring certain challenges to the application and promotion of the product.

[0003] Patent 1 is an ultra-thick S355NLO steel plate for offshore oil storage vessels and its production method (Chinese patent application number is 2022111208188). The product thickness is 170-200mm. It is produced by die casting, controlled rolling and controlled cooling process and two normalizing processes. The product performance meets the manufacturing requirements of offshore oil storage vessels. The plate thickness is close to the surface and the -40℃ impact performance at the 1 / 2 position is excellent; Patent 2 is a 420MPa grade high-toughness steel plate for wind power and its preparation method (Chinese patent application number is 202211709 8162), adopts low-carbon microalloying composition design, uses TMCP controlled rolling and controlled cooling process to reduce the overall process cost, the product has good mechanical properties, and the impact toughness at the 1 / 4 position is excellent; Patent 3 is a normalized extra-thick 420Mpa grade wind power steel with good low-temperature impact toughness and its manufacturing method (Chinese patent application number is 202410118280X), which mainly adopts controlled rolling and controlled cooling + normalizing heat treatment process to produce >150-200mm thick plates, and the impact of the product at the 1 / 4 position -50℃ is ≥241J.

[0004] The above patents have proposed different design and process ideas for the production of thick and high-toughness steel for wind power. Patent 1 produces thick steel plates by die casting and double normalizing, with a low yield rate, higher cost than the ordinary level, and an impact temperature of -40°C; Patent 2 is produced by TMCP process, adopts low-carbon process component design, the impact is at 1 / 4 position, and the core impact performance is not mentioned; Patent 3 produces thick plates by normalizing process, and the core impact performance is not mentioned. Therefore, the development of a thick and high-toughness S355NLO wind power steel plate has important guiding significance for the high-quality development of the wind power industry. Summary of the invention

[0005] In view of the above-mentioned technical problems, the present invention overcomes the shortcomings of the prior art and provides a thick and high-toughness S355NLO steel plate for wind power and a production method thereof. The peritectic composition design optimizes the continuous casting secondary cooling and dynamic pressing process to reduce center segregation. Rough rolling and large pressing are used to improve the core structure. A strong controlled rolling process is used to improve the core penetration of the thick plate to ensure the -40°C impact of the core. High-efficiency heat treatment technology is used to achieve high-homogeneity thick plate structure control.

[0006] In the first aspect, the present invention provides a thick and high-toughness S355NLO steel plate for wind power, whose chemical composition and mass percentage are: C: 0.09-0.12%, Si: 0.10-0.40%, Mn: 1.45-1.60%, P≤0.010%, S≤0.002%, Nb: 0.025-0.040%, Ni: 0.30-0.50%, Alt: 0.025-0.040%, V: 0.025-0.035%, Ti: 0.005-0.020%, Cu: 0.10-0.20%, N≤50ppm, H≤2ppm, and the rest are Fe and unavoidable impurities.

[0007] Furthermore, the thickness of the steel plate is 80-120 mm, and the mechanical properties meet the following requirements: ReH ≥ 325 MPa; Rm: 470-620 MPa, A ≥ 22%, yield strength ratio ≤ 0.87%; transverse impact value at -40°C: near surface ≥ 200 J, ≥ 200 J at 1 / 2 and 1 / 4 of the plate thickness, section shrinkage ≥ 40%, and 5% time-effect strain impact value ≥ 150 J.

[0008] In the second aspect, the present invention also provides a production method for the thick and high-toughness S355NLO wind power steel plate described in any scheme in the first aspect, which specifically includes a smelting process, a rough rolling process, a rolling process and a heat treatment process.

[0009] Furthermore, the smelting process specifically includes: adopting top and bottom combined blowing converter + LF refining + RH vacuum + continuous casting process; the oxygen of the converter steel is controlled to be ≤600ppm, and the phosphorus is controlled to be below 0.010%; the LF refining furnace produces white slag to improve the purity of the molten steel, and the sulfur is controlled to be below 0.002%; the continuous casting adopts 460mm billet, and the continuous casting cooling adopts a weak cooling system to ensure the uniformity of the solidification structure, and the dynamic reduction is controlled at 10-15mm to improve the center segregation.

[0010] Furthermore, the rough rolling process specifically includes: the billet cooling time is ≥72 hours, continuous furnace segmented heating is adopted, the total heating time is 12-16min / cm, the soaking section is kept warm for 40-50min, the soaking temperature is 1080-1100℃, the billet is opened from 460mm to 370mm at 1100℃, the single-pass reduction is ≥30mm, and high temperature and large reduction are used to improve the penetration of the core of the thick plate.

[0011] Furthermore, the rolling process specifically includes: reheating the open billet to 1200°C, with a total heating time of 9-14min / cm, keeping the soaking section warm for 30-45min, soaking temperature of 1180-1200°C, rough rolling for 5-9 passes, intermediate billet thickness of 150-180mm, and a total reduction rate of the last three passes of rough rolling ≥35%; finishing rolling for 5-7 passes, with a reduction rate of ≥12% in the first pass of finishing rolling, a second-stage rolling temperature of 800-820°C, a controlled cooling temperature of 700-740°C, and a large single-pass reduction in the last three passes of rough rolling and the first pass of finishing rolling to ensure improved penetration and segregation in the core of the thick plate.

[0012] Furthermore, the heat treatment process specifically includes: heat treatment temperature of 870-890°C, heating + holding time of 160-220min, controlled cooling of the steel plate after it comes out of the furnace, controlled cooling temperature of 680-700°C, fan cooling on the cooling bed, and offline temperature below 150°C.

[0013] Furthermore, in the smelting process, the composition of the molten iron is controlled to be: As≤0.03%, Sb≤0.010%, Sn≤0.020%, Pb≤0.010%, Bi≤0.010%, Ca≤0.0050%, and B≤0.0005%.

[0014] The beneficial effects of the present invention are:

[0015] (1) The thick and high-toughness S355NLO wind power steel plate and its production method provided by the present invention optimize the continuous casting secondary cooling and dynamic reduction process through peritectic composition design to reduce center segregation; use rough rolling and large reduction to improve the core structure, use strong controlled rolling process to improve the core penetration of the thick plate, ensure the -40℃ impact of the core, and use efficient heat treatment technology to achieve high-homogeneity thick plate structure control, and achieve stable production of thick normalized S355NLO wind power steel, meeting the extreme service environment and construction technology requirements of offshore wind power;

[0016] (2) The thick and high-toughness S355NLO wind power steel plate provided by the present invention realizes -40°C impact toughness ≥200J of the entire cross section near the surface of the steel plate + 1 / 2 of the plate thickness, yield strength ≥325Mpa, tensile strength: 470-620Mpa, elongation ≥22%, and yield strength ratio ≤0.87;

[0017] (3) The wind power steel provided by the present invention serves as the basic material for offshore wind power and has a good market prospect. In addition, the industry has an increasing demand for thick plates with large thickness, high toughness and easy welding. Therefore, the trial production and development of the present invention has important economic value and practical significance for the large-scale development of wind power. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a near-surface metallographic structure diagram of a thick and high-toughness S355NLO wind power steel plate in Example 2 of the present invention;

[0019] Figure 2 This is the metallographic structure diagram of the 1 / 4 position of the thick and high-toughness S355NLO wind power steel plate in Example 2 of the present invention;

[0020] Figure 3 This is the metallographic structure diagram of the core of the thick and high-toughness S355NLO wind power steel plate in Example 2 of the present invention. DETAILED DESCRIPTION

[0021] In Example 1, a S355NLO steel plate for wind power and a production method thereof are provided. The thickness of the steel plate is 100 mm, and its chemical composition and mass percentage are shown in Table 1.

[0022] (1) Example 1 The composition is controlled as shown in Table 1. The smelting and continuous casting processes are used to ensure high purity and internal quality of the molten steel. The top and bottom combined blowing converter + LF refining + RH vacuum + continuous casting process is adopted; the converter steel oxygen content is 550ppm, the phosphorus content is 0.008%, and the LF refining furnace produces white slag with a sulfur content of 0.002%; 460mm billet is used for continuous casting, and the weak cooling secondary cooling system of peritectic steel is adopted. The dynamic reduction is controlled at 12mm, and the main reduction sections are in sections 5 and 6 to improve the center segregation.

[0023] (2) The rough rolling process: the billet cooling time is ≥72 hours, continuous furnace segmented heating is adopted, the total heating time is 13 min / cm, the soaking section is kept warm for 45 min, the soaking temperature is 1090°C, the billet is opened from 460 mm to 370 mm, the single pass reduction is about 30-32 mm, and low temperature rolling and single pass large reduction are used to improve the core penetration and refine the grains.

[0024] (3) The rolling process is as follows: the thickness of the rolled steel plate is 100 mm, the width is 3200 mm, the steel plate is heated to 1200° C., the total heating time is 12 min / cm, the soaking section is kept warm for 38 min, the soaking temperature is 1200° C., the rough rolling is performed for 7 passes, the intermediate billet thickness is 165 mm, and the total reduction rate of the last three rough rolling passes is 37%; the finishing rolling is performed for 5 passes, the reduction rate of the first finishing rolling pass is 13%, the second stage start rolling temperature is 810° C., the final rolling temperature is 813° C., and the controlled cooling temperature is 715° C.

[0025] (4) The heat treatment process: the heat treatment temperature is 880°C, the heating + holding time is 180 minutes, the steel plate is cooled after leaving the furnace, the cooling temperature is 690°C, the cooling bed is cooled by a fan, and the offline temperature is 130°C.

[0026] (5) The mechanical properties of the 100 mm thick S355NLO wind power steel of this embodiment are shown in Table 2. The CTOD characteristic values ​​of the parent material welding at -10°C are 1.115 mm, 1.286 mm, and 1.183 mm, respectively. The steel plate is welded by submerged arc welding. The -40°C impact values ​​of the weld joints at different positions are: weld center WM: 108 / 104 / 108, fusion line FL: 199 / 206 / 211, fusion line FL+2mm: 235 / 237 / 232, fusion line FL+5mm: 266 / 261 / 267. The weld joints and heat-affected zones have excellent fracture toughness and impact properties.

[0027] In Example 2, a S355NLO steel plate for wind power and a production method thereof are provided. The thickness of the steel plate is 120 mm, and its chemical composition and mass percentage are shown in Table 1.

[0028] (1) Example 2 The composition is controlled as shown in Table 1. The smelting and continuous casting processes are used to ensure a high purity and internal quality of the molten steel. The top and bottom combined blowing converter + LF refining + RH vacuum + continuous casting process is adopted; the converter steel has an oxygen content of 530ppm and a phosphorus content of 0.009%. The LF refining furnace produces white slag with a sulfur content of 0.001%; ​​460mm billet is used for continuous casting, and a weak cooling secondary cooling system is adopted. The dynamic reduction is controlled at 13mm, and the main reduction sections are sections 5 and 6 to improve center segregation.

[0029] (2) The rough rolling process: the billet cooling time is ≥72 hours, continuous furnace heating is adopted, the total heating time is 13.5 min / cm, the soaking section is kept warm for 48 min, the soaking temperature is 1100°C, the billet is opened from 460 mm to 370 mm, the single-pass reduction is about 32 mm, and large reduction is used to improve the core penetration and refine the grains.

[0030] (3) The rolling process is as follows: the thickness of the rolled steel plate is 120 mm, the width is 3200 mm, the steel plate is heated to 1205° C., the total heating time is 12 min / cm, the soaking section is kept warm for 40 min, the soaking temperature is 1205° C., the rough rolling is performed for 7 passes, the intermediate billet thickness is 185 mm, and the total reduction rate of the last three rough rolling passes is 36%; the finishing rolling is performed for 5 passes, the reduction rate of the first finishing rolling pass is 12%, the second stage start rolling temperature is 808° C., the final rolling temperature is 810° C., and the controlled cooling temperature is 710° C.

[0031] (4) The heat treatment process: the heat treatment temperature is 875°C, the heating + holding time is 200 minutes, the steel plate is cooled after leaving the furnace, the cooling temperature is 700°C, the cooling bed is cooled by a fan, and the offline temperature is 145°C.

[0032] (5) The mechanical properties of the 120 mm thick S355NLO wind power steel of this embodiment are shown in Table 2. The CTOD characteristic values ​​of the parent material welding at -10°C are 0.925 mm, 0.981 mm, and 0.926 mm, respectively. The steel plate is welded by submerged arc welding. The -40°C impact values ​​of different positions of the weld joint are: weld center WM: 95 / 92 / 98, fusion line FL: 149 / 189 / 181, fusion line FL+2mm: 201 / 235 / 208, fusion line FL+5mm: 241 / 247 / 251. The weld joint and heat-affected zone have excellent impact properties and good fracture toughness.

[0033] Table 1 Chemical composition of steel plates of Examples 1 and 2 (wt%)

[0034]

[0035] Table 2 Mechanical properties of steel plates in Examples 1 and 2

[0036]

[0037] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A thick and high-toughness S355NLO steel plate for wind power, characterized in that: Its chemical composition and mass percentage are: C: 0.09-0.12%, Si: 0.10-0.40%, Mn: 1.45-1.60%, P≤0.010%, S≤0.002%, Nb: 0.025-0.040%, Ni: 0.30-0.50%, Alt: 0.025-0.040%, V: 0.025-0.035%, Ti: 0.005-0.020%, Cu: 0.10-0.20%, N≤50ppm, H≤2ppm, and the rest are Fe and unavoidable impurities.

2. The thick and high-toughness S355NLO wind power steel plate according to claim 1 is characterized in that: The thickness of the steel plate is 80-120mm, and the mechanical properties meet the following requirements: ReH≥325Mpa; Rm:470-620Mpa, A≥22%, yield strength ratio≤0.87%; transverse impact value at -40°C: near surface ≥200J, ≥200J at 1 / 2 and 1 / 4 of the plate thickness, section shrinkage ≥40%, and 5% time-effect strain impact value ≥150J.

3. The method for producing the thick and high-toughness S355NLO wind power steel plate as claimed in claim 1 or 2, characterized in that: It includes smelting process, rough rolling process, rolling process and heat treatment process.

4. The production method according to claim 3, characterized in that: The smelting process specifically includes: top and bottom combined blowing converter + LF refining + RH vacuum + continuous casting process; oxygen in converter steel is controlled to be ≤600ppm, and phosphorus is controlled to be below 0.010%; white slag is produced in LF refining furnace, and sulfur is controlled to be below 0.002%; 460mm billet is used for continuous casting, weak cooling system is used for cooling, and dynamic reduction is controlled to be 10-15mm.

5. The production method according to claim 3, characterized in that: The rough rolling process specifically includes: the billet cooling time is ≥72 hours, continuous furnace segmented heating is adopted, the total heating time is 12-16min / cm, the soaking section is kept warm for 40-50min, the soaking temperature is 1080-1100℃, the billet is opened from 460mm to 370mm at 1100℃, and the single-pass reduction is ≥30mm.

6. The production method according to claim 3, characterized in that: The rolling process specifically includes: reheating the open billet to 1200°C, with a total heating time of 9-14min / cm, keeping the temperature in the soaking section for 30-45min, the soaking temperature of 1180-1200°C, 5-9 rough rolling passes, the intermediate billet thickness of 150-180mm, and the total reduction rate of the last three rough rolling passes being ≥35%; 5-7 finishing rolling passes, with a reduction rate of ≥12% in the first finishing rolling pass, the second stage starting rolling temperature of 800-820°C, and the controlled cooling temperature of 700-740°C.

7. The production method according to claim 3, characterized in that: The heat treatment process specifically includes: heat treatment temperature of 870-890°C, heating + holding time of 160-220min, controlled cooling of the steel plate after it comes out of the furnace, controlled cooling temperature of 680-700°C, fan cooling on the cooling bed, and offline temperature below 150°C.

8. The production method according to claim 3, characterized in that: In the smelting process, the composition of the molten iron is controlled as follows: As≤0.03%, Sb≤0.010%, Sn≤0.020%, Pb≤0.010%, Bi≤0.010%, Ca≤0.0050%, and B≤0.0005%.

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