Large-thickness high‑toughness s355NLO steel plate for wind power and production method therefor

Abstract

The present invention relates to the technical field of iron and steel metallurgy, and in particular to a large-thickness high-toughness S355NLO steel plate for wind power and a production method therefor. The chemical composition of the steel plate, in terms of mass percentage, is 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≤50 ppm; H≤2 ppm; and the balance of Fe and inevitable impurities. In the present invention, by means of peritectic composition design, secondary cooling and dynamic reduction processes during continuous casting are optimized, and center segregation is reduced; the microstructure at the center is improved by means of rough rolling breakdown and heavy reduction; penetration into the center of the thick plate is improved by means of an intensive controlled rolling process, ensuring the impact toughness at -40°C at the center; and highly homogeneous microstructure control of the thick plate is achieved by means of high-efficiency heat treatment technology.

Description

Large-thickness high-toughness s355nlo wind power steel plate and production method thereof TECHNICAL FIELD

[0001] The present application relates to the technical field of steel metallurgy, in particular to a large-thickness high-toughness S355NLO wind power steel plate and a production method thereof. BACKGROUND

[0002] With the gradual development of clean energy, wind power, as a representative of clean energy, has been widely applied and promoted. Large-thickness, high-toughness wind power steel, as a basic material for wind power generation, has gradually attracted attention from the industry. Due to the extreme service environment of the ocean and construction needs, special technical requirements of high toughness and easy welding are put forward for large-thickness wind power steel. However, for large-thickness wind power steel, due to the plate thickness effect, there are certain differences in the near-surface, 1 / 4 position and core performance, which have certain influence on the cold deformation processing and welding performance of the product. For wind power steel below 80mm in thickness, the performance and strength difference in the thickness direction is relatively small, but for 80mm-120mm or more thick plates, the thickness difference brings certain challenges to the application and promotion of the product.

[0003] Patent 1 is a super-thickness S355NLO steel plate for offshore oil storage ship and a production method thereof (Chinese patent application number 2022111208188), the product thickness is 170-200mm, produced by die casting method, adopting controlled rolling and controlled cooling process and twice normalizing process, the product performance meets the requirements of offshore oil storage ship manufacturing, the-40℃ impact performance of the near-surface and 1 / 2 position of the plate thickness is excellent; patent 2 is a 420MPa grade high-toughness wind power steel plate and a preparation method thereof (Chinese patent application number 2022117098162), adopting low-carbon micro-alloying composition design, using TMCP controlled rolling and controlled cooling process, reducing the overall process cost, the product has good mechanical properties, and the impact toughness of the 1 / 4 position is excellent; patent 3 is a normalized special thick 420Mpa grade wind power steel with good low-temperature impact toughness and a manufacturing method thereof (Chinese patent application number 202410118280X), mainly adopting controlled rolling and controlled cooling + normalizing heat treatment process, producing >150-200mm thick plates, the product impact of 1 / 4 position-50℃ is ≥241J.

[0004] The above patents propose different design and process ideas for the production of large-thickness, high-toughness wind power steel, patent 1 is produced by mold casting and twice normalizing, the yield is low, the cost is higher than the ordinary level, and the impact temperature is-40 DEG C; patent 2 is produced by TMCP process, adopts low-carbon process composition design, the impact is 1 / 4 position, and the core impact performance is not mentioned; patent 3 is thick plate produced by normalizing process, and the core impact performance is not mentioned, therefore, developing a large-thickness, high-toughness S355NLO wind power steel plate has important guiding significance for the high-quality development of the wind power industry. SUMMARY

[0005] The present application aims at the above technical problems, overcomes the defects of the prior art, and provides a large-thickness, high-toughness S355NLO wind power steel plate and a production method thereof, which reduces center segregation by peritectic composition design, optimization of continuous casting secondary cooling and dynamic reduction process, improves core organization by roughing and large reduction, improves core penetration of thick plate by adopting strong controlled rolling process, ensures-40 DEG C impact of the core, and realizes high-uniform thick plate organization control by efficient heat treatment technology.

[0006] In a first aspect, the present application provides a large-thickness, high-toughness S355NLO wind power steel plate, which has a chemical composition and mass percentage of: 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 is Fe and inevitable impurities.

[0007] Further, the thickness of the steel plate is 80-120mm, and the mechanical properties meet: ReH≥325Mpa; Rm: 470-620Mpa, A≥22%, yield ratio≤0.87%;-40 DEG C transverse impact value: near surface≥200J, plate thickness 1 / 2 and 1 / 4≥200J, reduction of area≥40%, 5% aging strain impact value≥150J.

[0008] In a second aspect, the present application further provides a production method suitable for the large-thickness, high-toughness S355NLO wind power steel plate of any one of the first aspect, which specifically includes a smelting process, a roughing and blooming 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 is a near-surface metallographic diagram of the thick, high-toughness S355NLO wind power steel plate in Embodiment 2 of the present invention;

[0019] Figure 2 is a metallographic diagram 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 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] Table 2. Mechanical property data of steel plates in Examples 1 and 2

[0035] 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.

2. The thick, high-toughness S355NLO wind power steel plate according to claim 1, characterized in that, 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.

3. The method for producing thick, high-toughness S355NLO wind power steel plate as described in claim 1 or 2, characterized in that, This includes smelting processes, rough rolling processes, rolling processes, and heat treatment processes.

4. The production method according to claim 3, characterized in that, The smelting process specifically includes: using 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%; producing white slag in the LF refining furnace and controlling the sulfur content to below 0.002%; using 460mm billets for continuous casting, employing a weak cooling regime, and controlling the dynamic reduction to 10-15mm.

5. The production method according to claim 3, characterized in that, 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℃, and single-pass reduction ≥ 30mm.

6. The production method according to claim 3, characterized in that, 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 passes of roughing ≥35%; finishing 5-7 passes, with reduction rate of the first pass of finishing ≥12%, second-stage rolling temperature of 800-820℃, and controlled cooling temperature of 700-740℃.

7. The production method according to claim 3, characterized in that, 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℃.

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%, B≤0.0005%.

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