A thick, high-toughness S355NLO wind power steel plate and its production method

Abstract

This invention relates to the field of iron and steel metallurgy technology, and in particular to a thick, high-toughness S355NLO wind power steel plate and its production method. The chemical composition and mass percentage of the steel plate are as follows: 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, with the remainder being Fe and unavoidable impurities. This invention reduces center segregation by designing peritectic composition, optimizing continuous casting secondary cooling and dynamic reduction processes; improving core microstructure by rough rolling and large reduction; enhancing core penetration of thick plates by using strong controlled rolling process; ensuring -40℃ impact in the core; and achieving highly homogeneous thick plate microstructure control through efficient heat treatment technology.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, and in particular to a thick, high-toughness S355NLO wind power steel plate and its production method. Background Technology

[0002] With the gradual development of clean energy, wind power, as a representative of clean energy, is increasingly being widely applied and promoted. Thick, high-toughness wind power steel, as a fundamental material for wind power generation, is gradually gaining industry attention. Due to the extreme service environment and construction requirements of the ocean, special technical requirements for thick wind power steel, such as high toughness and ease of welding, are being placed on it. However, for thick wind power steel, due to the plate thickness effect, there are certain differences in performance near the surface, the 1 / 4 position, and the core, which affects the cold deformation processing and welding performance of the product. For wind power steel with a thickness of less than 80mm, the differences in performance and strength in the thickness direction are relatively small, but for plates thicker than 80mm-120mm, the differences in the thickness direction pose certain challenges to the application and promotion of the product.

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

[0004] The above patents all propose different design and process ideas for the production of thick, high-toughness wind power steel. Patent 1 uses ingot casting and double normalizing to produce thick steel plates, resulting in low yield and higher cost than ordinary steel plates, with an impact temperature of -40℃. Patent 2 uses the TMCP process and adopts a low-carbon process composition design, with an impact at 1 / 4 position, but does not mention the core impact performance. Patent 3 uses the normalizing process to produce thick plates, but also does not mention the core impact performance. Therefore, developing a thick, high-toughness S355NLO wind power steel plate is of great guiding significance for the high-quality development of the wind power industry. Summary of the Invention

[0005] This invention addresses the aforementioned technical problems and overcomes the shortcomings of existing technologies by providing a thick, high-toughness S355NLO wind power steel plate and its production method. It reduces center segregation through peritectic composition design, optimized continuous casting secondary cooling and dynamic reduction processes; improves core microstructure through rough rolling and large reduction; enhances core penetration in thick plates using a high-pressure controlled rolling process; ensures -40℃ impact resistance in the core; and achieves highly homogeneous thick plate microstructure control through efficient heat treatment technology.

[0006] In a first aspect, the present invention provides a thick, high-toughness S355NLO wind power steel plate, the chemical composition and mass percentage of which 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, with the remainder being Fe and unavoidable impurities.

[0007] Furthermore, the steel plate has a thickness of 80-120mm and its mechanical properties meet the following requirements: ReH≥325Mpa; Rm:470-620Mpa, A≥22%, yield strength ratio≤0.87%; transverse impact value at -40℃: near the surface ≥200J, at 1 / 2 and 1 / 4 of the plate thickness ≥200J, reduction of area ≥40%, and time-effect deformation impact value at 5% ≥150J.

[0008] Secondly, the present invention also provides a method for producing thick, high-toughness S355NLO wind power steel plates applicable to any of the embodiments in the first aspect, specifically including a smelting process, a rough rolling process, a rolling process, and a heat treatment process.

[0009] Furthermore, the smelting process specifically includes: adopting a top-and-bottom blown converter + LF refining + RH vacuum + continuous casting process; controlling the oxygen content of the converter tapped steel to ≤600ppm and the phosphorus content to below 0.010%; using the LF refining furnace to produce white slag, improving the purity of the molten steel, and controlling the sulfur content to below 0.002%; using 460mm billets for continuous casting, and adopting a weak cooling regime for continuous casting to ensure the uniformity of the solidification structure, with the dynamic reduction controlled at 10-15mm to improve center segregation.

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

[0011] Furthermore, the rolling process specifically includes: reheating the billet to 1200℃, with a total heating time of 9-14 min / cm, holding in the soaking zone for 30-45 min, a soaking temperature of 1180-1200℃, roughing 5-9 passes, intermediate billet thickness of 150-180 mm, and a total reduction rate of ≥35% for the last three passes of roughing; finishing 5-7 passes, with a reduction rate of ≥12% for the first pass of finishing, a second-stage rolling temperature of 800-820℃, a controlled cooling temperature of 700-740℃, and a large reduction per pass in the last three passes of roughing and the first pass of finishing 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℃, heating and holding time of 160-220min, controlled cooling after the steel plate is taken out of the furnace, controlled cooling temperature of 680-700℃, fan cooling on the cooling bed, and the offline temperature below 150℃.

[0013] Furthermore, 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%, B≤0.0005%.

[0014] The beneficial effects of this invention are:

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

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

[0017] (3) The wind power steel provided by the present invention has good market prospects as a basic material for offshore wind power. Moreover, 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. Attached Figure Description

[0018] Figure 1 This is a near-surface metallographic image of the thick, high-toughness S355NLO wind power steel plate in Embodiment 2 of the present invention;

[0019] Figure 2 This is a metallographic image of the 1 / 4 position of the thick, high-toughness S355NLO wind power steel plate in Embodiment 2 of the present invention;

[0020] Figure 3 This is a metallographic diagram of the core of the thick, high-toughness S355NLO wind power steel plate in Embodiment 2 of the present invention. Detailed Implementation

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

[0022] (1) The composition control of Example 1 is shown in Table 1. High steel purity and internal quality are ensured by smelting and continuous casting processes. The process of top and bottom blowing converter + LF refining + RH vacuum + continuous casting is adopted. The oxygen content of the steel produced by the converter is 550ppm and the phosphorus content is 0.008%. The white slag produced by the LF refining furnace has a sulfur content of 0.002%. 460mm billet is used for continuous casting. The peritectic steel weak cooling secondary cooling system is adopted. The dynamic reduction is controlled at 12mm. The main reduction sections are in the 5th and 6th sections 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 heat soaking section is kept for 45 min, the heat soaking temperature is 1090℃, the billet is rolled from 460mm to 370mm, the single pass reduction is about 30-32mm, and the core penetration is improved and the grains are refined by low temperature rolling and single pass large reduction.

[0024] (3) The rolling process: the steel plate is 100mm thick and 3200mm wide, heated to 1200℃, with a total heating time of 12min / cm, and the heat soaking section is kept at 38min with a heat soaking temperature of 1200℃. There are 7 rough rolling passes, the intermediate billet thickness is 165mm, and the total reduction rate of the last three rough rolling passes is 37%. There are 5 finishing rolling passes, the first finishing rolling pass has a reduction rate of 13%, the second stage starting rolling temperature is 810℃, the final rolling temperature is 813℃, and the controlled cooling temperature is 715℃.

[0025] (4) The heat treatment process: heat treatment temperature 880℃, heating + holding time 180min, controlled cooling after steel plate is taken out of the furnace, controlled cooling temperature 690℃, fan cooling on the cooling bed, and offline temperature 130℃.

[0026] (5) The mechanical properties of the 100mm thick S355NLO wind power steel in this embodiment are shown in Table 2. The CTOD characteristic values ​​of the base material at -10℃ are 1.115mm, 1.286mm, and 1.183mm, respectively. The steel plate was welded by submerged arc welding. The impact values ​​at -40℃ at different positions of the weld joint are as follows: 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 joint and heat-affected zone have excellent fracture toughness and impact performance.

[0027] Example 2 provides an S355NLO wind power steel plate and its production method. The steel plate has a thickness of 120mm, and its chemical composition and mass percentage are shown in Table 1.

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

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

[0030] (3) The rolling process: the steel plate is 120mm thick and 3200mm wide, heated to 1205℃, with a total heating time of 12min / cm, and the heat soaking section is kept at 40min with a heat soaking temperature of 1205℃. There are 7 rough rolling passes, the intermediate billet thickness is 185mm, and the total reduction rate of the last three rough rolling passes is 36%. There are 5 finishing rolling passes, the first finishing rolling pass has a reduction rate of 12%, the second stage starting rolling temperature is 808℃, the final rolling temperature is 810℃, and the controlled cooling temperature is 710℃.

[0031] (4) The heat treatment process: heat treatment temperature 875℃, heating and holding time 200min, controlled cooling after steel plate is taken out of the furnace, controlled cooling temperature 700℃, fan cooling on the cooling bed, and the offline temperature 145℃.

[0032] (5) The mechanical properties of the 120mm thick S355NLO wind power steel in this embodiment are shown in Table 2. The CTOD characteristic values ​​of the base material at -10℃ are 0.925mm, 0.981mm, and 0.926mm, respectively. The steel plate was welded by submerged arc welding. The impact values ​​at -40℃ at different positions of the weld joint are as follows: 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 performance and good fracture toughness.

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

[0034]

[0035] Table 2. Mechanical property data of steel plates in Examples 1 and 2

[0036]

[0037] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A thick, high-toughness S355NLO wind power steel plate, characterized in that, Its chemical composition and mass percentage are as follows: 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, with the remainder being Fe and unavoidable impurities; The production method of the thick, high-toughness S355NLO wind power steel plate includes smelting process, rough rolling process, rolling process and heat treatment process. The smelting process specifically includes: a top-and-bottom blown converter + LF refining + RH vacuum + continuous casting process; oxygen content in the converter tapping is controlled to ≤600ppm, and phosphorus content is controlled to below 0.010%; white slag is produced in the LF refining furnace, and sulfur content is controlled to below 0.002%; 460mm billets are used in continuous casting, and a weak cooling regime is adopted, with dynamic reduction controlled to 10-15mm; The rough rolling process specifically includes: billet stacking cooling time ≥ 72 hours, continuous furnace segmented heating, total heating time 12-16 min / cm, soaking zone holding temperature 40-50 min, soaking temperature 1080-1100℃, billet from 460mm to 370mm at 1100℃, single pass reduction ≥ 30mm. The rolling process specifically includes: reheating the billet to 1200℃, with a total heating time of 9-14 min / cm, holding in the soaking zone for 30-45 min, soaking temperature of 1180-1200℃, roughing 5-9 passes, intermediate billet thickness of 150-180 mm, and total reduction rate of the last three roughing passes ≥35%; finishing 5-7 passes, with a reduction rate of ≥12% in the first finishing pass, second-stage rolling temperature of 800-820℃, and controlled cooling temperature of 700-740℃; The heat treatment process specifically includes: heat treatment temperature of 870-890℃, heating and holding time of 160-220min, controlled cooling of steel plate after exiting the furnace, controlled cooling temperature of 680-700℃, fan cooling on cooling bed, and offline temperature below 150℃. The steel plate has a thickness of 80-120mm and meets the following mechanical properties: ReH≥325Mpa; Rm:470-620Mpa, A≥22%, yield strength ratio≤0.87%; transverse impact value at -40℃: near the surface ≥200J, at 1 / 2 and 1 / 4 of the plate thickness ≥200J, reduction of area ≥40%, and time-effect deformation impact value at 5% ≥150J.

2. The thick, high-toughness S355NLO wind power steel plate according to claim 1, 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%, B≤0.0005%.

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