Heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power and manufacturing method therefor

Abstract

The present invention provides a heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power and a manufacturing method therefor. The steel plate is composed of the following chemical components in percentage by mass: C: 0.12%-0.15%, Si: 0.15%-0.35%, Mn: 1.30%-1.50%, P≤0.015%, S≤0.005%,Nb: 0.015%-0.030%, V: 0.015%-0.030%, Ti: 0.005%-0.020%, and Al: 0.005%-0.030%, with the balance being Fe and unavoidable impurities. The manufacturing method comprises the steps of smelting, refining, continuous casting, heating, rolling and the like. Low-C high-Mn and Nb+V+Ti composite microalloying is used to significantly inhibit the growth of austenite grains; and a normalizing rolling process is used, so that the process flow is short, the cost is low, and the production line adaptability is strong.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Chinese Patent Application No. 202311075355.2, titled "HEAVY-GAUGE, FATIGUE-RESISTANT, EASY-TO-WELD, AND HIGH-STRENGTH STEEL PLATE FOR WIND POWER AND MANUFACTURING METHOD THEREFOR", filed on August 24, 2023, which is incorporated herein by reference.TECHNICAL FIELD

[0002] The present invention relates to the field of iron and steel metallurgy, and specifically to a heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power and manufacturing method therefor.BACKGROUND

[0003] Currently, with prominent energy shortages and environmental issues, the energy-saving and emission-reduction benefits of wind power have attracted much attention. Wind energy resources are renewable clean energy, representing a new energy source that is pollution-free, renewable, and has broad prospects. Wind energy offers many benefits for environmental protection, including eliminating local air pollution and reducing water resource consumption, but the most significant is its contribution to carbon dioxide emission reduction. It is currently one of the most effective ways for humanity to contribute to addressing global climate change.

[0004] Steel for wind turbine towers primarily uses low-alloy steel, requiring good strength and toughness, fatigue resistance, and excellent weldability. Currently, wind power is trending toward larger scales; offshore wind turbines have single-unit capacities exceeding 16MW, with tower heights over 100 meters. Key stress-bearing parts such as the tower base and foundation ring are often welded from thick high-strength steel plates, demanding extremely high strength and toughness from the steel, making production challenging. As the thickness of high-strength steel plates increases, their mechanical properties degrade significantly, with poor microstructural uniformity and large performance fluctuations in the center.

[0005] Existing technologies often employ costly offline normalizing processes for production, and lack indicators for weldability and fatigue performance, resulting in poor process adaptability.

[0006] Patent document 202210210565.7 discloses "A Production Method for 80~100mm Thick Steel Plate for Wind Power." This patent produces steel plates with good mechanical properties through appropriate smelting, continuous casting, heating, rolling, and controlled cooling processes, without requiring heat treatment, thus offering lower process costs. However, this patent does not study the weldability of the steel plate and lacks key data such as fatigue strength at weld joints.

[0007] Patent document CN107619997A discloses "Super-thick steel plate for wind power and production method thereof." This patent can produce 220-440mm thick steel plates for wind power through reasonable composition design combined with methods like electroslag remelting. This method has advantages such as large product thickness but offers lower strength grades and lacks research data on welding, especially post-weld fatigue strength.

[0008] Patent document CN114277315A discloses "Thick-specification normalizing process anti-fatigue wind power steel plate and preparation method thereof." This patent uses low-carbon micro-niobium technology while adding Cu, Ni, and Mo to improve the steel plate's strength and low-temperature impact performance. However, the process flow described in this invention is lengthy, lacks impact toughness data at extremely low temperatures (-60°C), and has low post-weld fatigue strength.SUMMARY

[0009] An object of this invention is to provide a heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power and manufacturing method therefor. This manufacturing method features low cost and strong production line adaptability, with the steel plate's mechanical properties, as well as post-weld mechanical and fatigue performance, all meeting application requirements.

[0010] To achieve the above object, the present invention provides the following technical solutions.

[0011] In one aspect, a heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power is provided, the steel plate has the following chemical composition by mass percentage: C: 0.12%-0.15%, Si: 0.15%-0.35%, Mn: 1.30%-1.50%, P≤0.015%, S≤0.005%, Nb: 0.015%-0.030%, V: 0.015%-0.030%, Ti: 0.005%-0.020%, Al: 0.005%-0.030%, with the remainder being Fe and unavoidable impurities.

[0012] Further, the steel plate has a thickness of 70mm-90mm, the base metal of the steel plate has a yield strength of ≥420MPa, a tensile strength of ≥540MPa, an elongation A≥40%, a -60°C core impact energy of ≥200J, and a CEV (carbon equivalent value) of ≤0.41; the steel plate is capable of achieving welding under a high-heat input condition of ≥30kJ / cm; after welding, the steel plate has a tensile strength of ≥540MPa at a welded joint, a -60°C core impact energy of ≥120J in a heat-affected zone, a fatigue limit stress of ≥400MPa at the welded joint under conditions of a stress ratio of 0.5 and 5×10 7< cycles.

[0013] In another aspect, a manufacturing method for the above heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power is provided, including the following steps: smelting, performed using a converter; refining, comprising LF refining and RH refining, yielding a thick slab with a thickness ≥300mm after RH refining; continuous casting, wherein the thick slab is cast using a continuous casting mold, and a billet after casting is subjected to slow cooling to obtain a continuous casting slab; heating, wherein the continuous casting slab is heated using a cold-charging method; and rolling, comprising rough rolling and finish rolling, wherein rough rolling is first performed, an intermediate slab is cooled after rough rolling via a MULPIC water cooling unit, then the slab is conveyed to a finishing mill for finish rolling, followed by straightening in a leveler to obtain a finished steel plate.

[0014] Further, in the smelting step of the manufacturing method, the converter uses pull carbon once and single-slag process for smelting, with a final slag basicity R being controlled between 3.2-4.2; a red clean ladle with ladle temperature of ≥800°C is employed, with a tapping time of ≥3 minutes, and high-sensitivity slag blocking is used during tapping, followed by deoxidization with aluminum-manganese-iron at 1.7kg / t-3.2kg / t steel; low-carbon low-phosphorus silicon-manganese, ferrosilicon, ferroniobium, and ferrovanadium are added in batches, and synthetic slag and pre-fused slag are added along a steel flow during tapping, with a ratio of the synthetic slag to the pre-fused slag of 2:1.

[0015] Further, during the LF refining process of the manufacturing method, argon bottom blowing stirring is maintained throughout, aluminum granules and aluminum slag are used for deoxidization, and lime is added for slag formation, with a final slag basicity of ≥2.7; fine-tuning composition is performed with silicon-manganese, ferrosilicon, ferroniobium, and ferrovanadium alloys; a Ti composition is adjusted with Ti wire and ferrotitanium; a Al composition is adjusted with aluminum wire, and a LF refining treatment time is controlled to be ≥40min; after LF refining is completed, RH refining is performed, with a RH refining time ≥45min, and after RH refining treatment, CaAl wire of 85m-160m is fed, then soft blowing is performed for over 9 minutes, obtaining a thick slab after RH refining treatment, with a thickness of the thick slab ≥300mm; and preferably, the thickness of the thick slab is 300mm.

[0016] Further, in the continuous casting step of the manufacturing method, a continuous caster casting speed is controlled at 0.8m / min-1.1m / min, peritectic steel mold powder is used, a mold oscillation mode is non-sinusoidal oscillation mode; secondary cooling water and dynamic soft reduction are controlled according to peritectic steel; after being flame-cut and divided, the thick slab enters a third cooling machine for water cooling, achieving shallow surface quenching of the slab, with an upper and lower water flow difference being controlled to 15%~30% during quenching, and a surface temperature of the thick slab is controlled to be ≤600°C, and surface cooling water is blown off after γ-α transformation is completed on the surface; the thick slab undergoes self-tempering using residual heat, with a self-tempering time of ≥120min, and after self-tempering is completed, the slab is placed in a pit for slow cooling, with a slow cooling time not less than 56 hours.

[0017] Further, in the heating step of the manufacturing method, a slab charging temperature is ≤350°C, a soaking zone temperature of a heating furnace is controlled at 1180°C-1260°C, and a discharging temperature is controlled at 1170°C-1250°C; a heating rate is 9min / cm-11.5min / cm; and preferably, the soaking zone temperature of the heating furnace is 1250°C, the discharging temperature is 1200°C, and the heating rate is 10min / cm.

[0018] Further, in the rolling step of the manufacturing method, rough rolling adopts a high reduction mode, and the rough rolling stage is completed using either a 4+1 pass or 6+1 pass rolling modes based on a target steel plate thickness, where the +1 pass is a dummy pass; a rolling pass reduction rate is controlled to increase progressively, with a first pass reduction rate ≥6%, and in both the 4+1 pass and 6+1 pass rolling modes, the reduction rate of a final pass is ≥20%, with the pass reduction rate increasing progressively by 3% to 8%.

[0019] Further, when a 90mm steel plat is produced using a 300mm-thick slab, 4+1 pass rough rolling is adopted, with the first pass reduction rate of 7%, the 4th pass reduction rate of 27.5%, and progressive increments of 5%, 7%, and 8.5% respectively.

[0020] Further, in the rolling step of the manufacturing method, finish rolling adopts a normalizing rolling mode, and 6+1 pass finish rolling is adopted, where the +1 pass is a dummy pass, and the reduction rate decreases progressively; when the finished thickness is 60mm-80mm, the first pass reduction rate is ≥12%, when the finished thickness is 80mm-90mm, the first pass reduction rate is ≥14%, with the reduction rate decreasing pass by pass by 0.5% to 4%; and preferably, when producing a 90mm steel plate using a 300mm-thick slab, a 6+1 pass finish rolling is adopted, with the first pass reduction rate of 16.5%, the reduction rate decreasing pass by pass by 1.0% to 3.5%, and the reduction rate at the 6th pass being 5.8%.

[0021] Analysis shows that in the heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power and manufacturing method therefor of the present invention, low-C high-Mn and Nb+V+Ti composite microalloying is used to form submicron-scale precipitates such as Ti(C, N), V(C, N) so as to significantly inhibit the growth of austenite grains and provide a microstructural foundation for subsequent rolling; the Cottrell and Snoek atmospheres formed by the composite nano-carbides Nb\Ti(C, N) generated during the finish rolling stage can markedly hinder dislocation movement and pin grain boundaries, suppressing austenite grain growth, meanwhile, due to the addition of microalloying elements Nb, V and Ti, the upper limit of the non-recrystallization temperature is increased, so that the rolling process window is expanded and the probability of mixed grains during two-phase zone rolling is reduced, which benefits the enhancement of strength and toughness. The slab three-cooling equipment quenching process is adopted to achieve shallow surface quenching of the slab, forming a uniform-thickness shell on the surface, enabling rapid slab cooling and defect-free slab surface preparation, followed by utilizing the slab's residual heat self-tempering effect to refine the surface grains of the cast slab. Rough rolling employs a gradually increasing reduction rate mode, while finish rolling uses a gradually decreasing reduction rate mode, fully refining grains and ensuring rolling penetration. The MULPIC cooling of the intermediate slab before finish rolling can reduce the intermediate slab's waiting time, while the normalizing effect can maximally preserve the dynamic recrystallization grain refinement achieved during the rough rolling stage. The normalized rolling process is used to produce thick-gauge steel plates for wind power, achieving in-line normalizing treatment during rolling, eliminating the offline normalizing process. The process flow is short, costs are low, production line adaptability is strong, and it has broad prospects for promotion.BRIEF DESCRIPTION OF DRAWINGS

[0022] The drawings, which form a part of this application, are provided to further illustrate the present invention. The illustrative embodiments and their descriptions are used to explain the present invention and do not constitute an undue limitation thereof. Among them: Figure 1 is a welding pass diagram of the steel plate according to Example 1 of the present invention.DESCRIPTION OF EMBODIMENTS

[0023] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments. The examples are provided to explain the present invention and not to limit it. In fact, it will be apparent to those skilled in the art that modifications and variations can be made to the present invention without departing from its scope or spirit. For example, features shown or described as part of one embodiment can be used in another embodiment to yield a further embodiment. Therefore, it is intended that the present invention cover such modifications and variations as fall within the scope of the appended claims and their equivalents.

[0024] According to embodiments of the present invention, a heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power is provided. The steel plate has the following chemical composition by mass percentage: C: 0.12%-0.15%, Si: 0.15%-0.35%, Mn: 1.30%-1.50%, P≤0.015%, S≤0.005%,Nb: 0.015%-0.030%, V: 0.015%-0.030%, Ti: 0.005%-0.020%, Al: 0.005%-0.030%, with the remainder being Fe and unavoidable impurities.

[0025] Carbon: C atoms in steel can produce significant interstitial solid solution strengthening, markedly increasing the strength and hardness of steel, making it the most economical and effective strengthening method in steel materials. However, when the content of C exceeds 0.15%, it leads to an increase in carbides in the steel, causing a significant decline in properties such as toughness and elongation, while also worsening weldability. Therefore, the C content in this invention is controlled between 0.12%-0.15%.

[0026] Silicon: Si can be used as a deoxidizing element during smelting, enhancing the oxidation resistance of the steel. Simultaneously, Si dissolved in the steel can cause lattice distortion, increasing the strength of the ferrite structure. However, a silicon content exceeding 0.35% may embrittle the ferrite structure in the steel, reducing its plasticity and toughness. Therefore, the silicon content in the present invention is controlled between 0.15% and 0.35%.

[0027] Manganese: Mn can lower the γ-α phase transformation temperature of steel, refine the pearlite lamellae in steel, and increase the strength of pearlite in low-carbon steel without significantly reducing ductility. Mn can also control the content of oxides and sulfides during smelting, making the steel structure uniform and refined, thereby improving the strength and toughness of the steel. However, a Mn content exceeding 1.50% tends to cause rolling cracking and worsen the weldability of the steel. Therefore, the manganese content in the present invention is controlled between 1.30% and 1.50%.

[0028] Phosphorus: P is an element prone to segregation in steel, making the steel susceptible to cold brittleness. Additionally, phosphorus easily causes welding cracks in welds. To ensure sufficient toughness in the weld metal, the P content in this invention is controlled below 0.015%.

[0029] Sulfur: S is a harmful element; sulfur easily combines with manganese to form MnS inclusions, which deform during the rolling process, reducing the impact toughness of the steel. S increases the hot brittleness of the weld metal, making welds prone to hot cracks and porosity. Therefore, the S content in this invention is controlled below 0.005%.

[0030] Niobium: Nb can promote grain refinement, improving the strength and toughness of the steel. Meanwhile, Nb in the steel combines with C, N to form nano-sized Nb(C, N), which can produce a significant strengthening effect and improve the mechanical properties of the welding heat-affected zone. However, if the niobium content exceeds 0.03%, it will deteriorate weldability and reduce cold deformation capability. Therefore, the niobium content in this invention is controlled between 0.015-0.030%.

[0031] Vanadium: V can form a continuous solid solution with Fe, significantly narrowing the austenite phase region, while also refining ferrite grains, producing a notable grain refinement strengthening effect. V and C, N have a strong affinity and exist in the steel as VC and VN precipitates, which can produce a significant precipitation strengthening effect. V is a scarce resource, and its usage should be minimized as much as possible. Therefore, the V content in this invention is controlled between 0.015-0.030%.

[0032] Titanium: Ti serves as an effective deoxidizing element in steel, combining with carbon in the steel to form stable TiC, which prevents the growth and coarsening of steel grains and improves the low-temperature impact toughness of the steel. However, if the Ti content exceeds 0.02%, the content and size of titanium carbide particles increase, reducing the strength and toughness of the steel. Therefore, the Ti content in this invention is controlled between 0.005% and 0.020%.

[0033] Aluminum: Al is a strong deoxidizing element that also refines grains and improves the toughness of steel. Controlling the Al content can enhance the purity and fatigue strength of the steel. However, if the Al content exceeds 0.030%, it leads to an increase in alumina-based inclusions in the steel, deteriorating its mechanical properties. Therefore, the Al content in this invention is controlled between 0.005% and 0.030%.

[0034] The design philosophy of this invention is as follows: Using low-C high-Mn and Nb+V+Ti composite microalloying, submicron-scale precipitates such as Ti(C, N), V(C, N) are formed, which significantly inhibit the growth of austenite grains and provide a microstructural foundation for subsequent rolling; the Cottrell and Snoek atmospheres formed by the composite nano-carbides Nb\Ti(C, N) generated during the finish rolling stage can markedly hinder dislocation movement and pin grain boundaries, suppressing austenite grain growth, meanwhile, due to the addition of microalloying elements Nb, V and Ti, the upper limit of the non-recrystallization temperature is increased, so that the rolling process window is expanded and the probability of mixed grains during two-phase zone rolling is reduced, which benefits the enhancement of strength and toughness.

[0035] The non-recrystallization zone refers to when high-strength low-alloy steel contains alloy elements like Nb, its recrystallization temperature increases, generally reaching around 950°C; therefore, the range from above 700°C where ordinary carbon steel undergoes recrystallization to 950°C where no recrystallization occurs is called the non-recrystallization zone. During hot rolling of steel, deformation-induced austenite undergoes recrystallization, especially dynamic recrystallization, which can refine austenite grains (recrystallization-controlled rolling), forming equiaxed austenite grains. Microalloy precipitates such as V(C, N) can form extensively in austenite, serving as nucleation sites for polygonal ferrite. In the rolling stage within the non-recrystallization zone, austenite grains are significantly elongated; at this stage, the Cottrell and Snoek atmospheres formed by Nb\Ti(C, N) composite nano-carbides markedly hinder dislocation movement and pin grain boundaries, inhibiting austenite grain growth, thereby increasing ferrite nucleation sites and rates during phase transformation, refining grains, and enhancing the fine-grain strengthening effect. During subsequent cooling of the steel plate, Nb\Ti(C, N) composite nano-carbides continue to precipitate dispersedly or interphase, obstructing dislocation motion and producing precipitation strengthening effects.

[0036] The present invention also discloses a manufacturing method for the above heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power, comprising the following steps: S1: Smelting

[0037] Smelting is carried out using a converter, with the converter employing high-quality lime and dolomite. During the smelting process, high lance position and feeding timing are controlled, and slag materials are fully added 3 minutes before the endpoint. The converter uses the pull carbon once and single-slag process for smelting, with the final slag basicity R being controlled between 3.2-4.2 (e.g., 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2), achieving early slag formation initially and good slagging during the process. A red clean ladle is used, with ladle temperature of ≥800°C and tapping time of ≥3 minutes. High-sensitivity slag blocking is employed during tapping to prevent significant slag carryover. Deoxidation and alloying: Use aluminum-manganese-iron at 1.7 kg / t to 3.2 kg / t steel (e.g., 1.7 kg / t, 1.9 kg / t, 2.0 kg / t, 2.2 kg / t, 2.4 kg / t, 2.6 kg / t, 2.8 kg / t, 3.0 kg / t, 3.2 kg / t) for deoxidation. When the molten steel reaches one-quarter of the tap, add low-carbon low-phosphorus silicon-manganese, ferrosilicon, ferroniobium, and ferrovanadium in batches, completing the addition by three-quarters of the tap. During tapping, add synthetic slag and pre-fused slag along the steel stream, with the ratio of synthetic slag to pre-fused slag (by mass) at 2:1 (e.g., 300 kg synthetic slag + 150 kg pre-fused slag).S2: Refining

[0038] Refining includes LF refining and RH refining. During LF refining, argon bottom blowing is used for stirring throughout the process, and molten steel must not be exposed to prevent secondary oxidation. Aluminum granules and aluminum slag are used for deoxidation during smelting, with argon gas in weak stirring mode during deoxidation. Lime is added for slag formation, and the top slag before leaving the station must be yellow-white or white slag, with such slag maintained for ≥13 minutes, and final slag basicity ≥2.7. Alloys such as silicon-manganese, ferrosilicon, ferroniobium, and ferrovanadium are used for fine-tuning composition; Ti wire or ferroitianium adjusts Ti content; aluminum wire adjusts Al content. Control LF refining treatment time ≥40min.

[0039] After LF refining is completed, RH refining is performed. During RH refining treatment, avoid chemical heating, ensure pure degassing time ≥5 minutes. Control RH refining time ≥45 min. After RH refining treatment is completed, feed CaAl wire of 85m-160m (e.g., 85m, 90m, 95m, 100m, 105m, 110m, 115m, 120m, 125m, 130m, 135m, 140m, 145m, 150m, 155m, 160m) for calcium treatment of inclusions, then soft blow for ≥9 minutes. After RH refining treatment, a thick slab is obtained, with thickness ≥300 mm. Preferably, the thick slab thickness is 300 mm.S3: Continuous casting

[0040] Produce the thick slab obtained in step S2 using a continuous casting mold, with the caster's casting speed at 0.8m / min to 1.1m / min, employing peritectic steel mold powder, and the mold oscillation mode set to non-sinusoidal oscillation. Secondary cooling water and dynamic soft reduction are controlled according to peritectic steel standards. After flame cutting, the thick slab enters the tertiary cooling machine for water cooling, where the equipment operates at maximum water flow and valve opening to achieve shallow surface quenching of the slab. Since the upper nozzle flow can retain the steel plate and the lower nozzle flow descends into the collection pipe, during quenching, the lower water flow is controlled to be greater than the upper flow, with a difference of 15%-30% between them. Control the thick slab surface temperature to ≤600°C; after the surface completes the γ-α transformation, blow off the surface cooling water. The thick slab utilizes residual heat for self-tempering, with a self-tempering time ≥120min. After self-tempering is complete, it enters a pit for slow cooling, with a slow cooling time not less than 56 hours, resulting in a continuous casting slab after casting is finished. By adopting the slab tertiary cooling equipment quenching process, shallow surface quenching of the slab is achieved, forming a uniform shell thickness on the surface, enabling rapid cooling of the slab and defect-free surface preparation. Subsequently, the slab's residual heat self-tempering effect refines the grain structure of the casting surface layer.S4: Heating

[0041] Continuous casting billets are heated by cold charging, with slab charging temperature ≤350°C. Due to the low-alloy, low CEV design of this steel grade of the present invention (low CEV is a relative concept, typically below 0.45 is considered low CEV), heating steel with low temperature is required to prevent grain coarsening. The soaking zone temperature of the heating furnace is controlled to 1180°C-1260°C (e.g., 1180°C, 1190°C, 1200°C, 1210°C, 1220°C, 1230°C, 1240°C, 1250°C, 1260°C), the discharging temperature is controlled to 1170°C-1250°C (e.g., 1170°C, 1180°C, 1190°C, 1200°C, 1210°C, 1220°C, 1230°C, 1240°C, 1250°C), the heating rate is controlled at 9min / cm-11.5min / cm (e.g., 9min / cm, 9.3min / cm, 9.5min / cm, 9.8min / cm, 10min / cm, 10.3min / cm, 10.5min / cm, 10.8min / cm, 11min / cm, 11.3min / cm, 11.5min / cm). The above heating speed and temperature can homogenize the original austenite structure in the billet, fully dissolve alloy elements such as Nb, V, Ti in the steel, providing a basis for subsequent precipitation of microalloy carbides in the steel. Preferably, the soaking zone temperature of the heating furnace is 1250°C, the discharging temperature is 1200°C, and the heating rate is 10min / cm.S5: Rolling

[0042] Rolling includes rough rolling and finish rolling. First, rough rolling is performed. The intermediate slab after rough rolling is cooled by the MULPIC water cooling unit, and then transported to the finish rolling mill for finish rolling, followed by straightening in a leveler to obtain the finished steel plate.

[0043] The steel plate is rough rolled using a high reduction mode. The intermediate slab after rough rolling is sent to the MULPIC water cooling unit for cooling, during which no rolling process is carried out. The intermediate slab is controlled to undergo reciprocating water cooling in the water cooling unit until its surface temperature reaches ≤830°C to generate a surface quenched zone of sufficient thickness.

[0044] In the rough rolling stage, 4+1 or 6+1 passes are selected based on the target steel plate thickness, where the +1 pass is a dummy pass without any rolling force applied. In terms of deformation, the reduction rate per pass is controlled to increase progressively. The reduction rate of the first pass ≥6%, the reduction rate of the final pass in both 4+1 and 6+1 rolling mode should be ≥20%. The reduction rate per pass increases progressively by 3% to 8% (e.g., 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%). The temperature during rough rolling is within the recrystallization zone, and the progressively increasing reduction rate can fully break down austenite grains, promote complete recrystallization of the core structure, and significantly refine the austenite grains. Preferably, when producing a 90mm steel plate using a 300mm thick slab, 4+1 pass rough rolling is adopted, with the first pass reduction rate of 7%, the 4th pass reduction rate of 27.5%, and progressive increments of 5%, 7%, and 8.5% respectively.

[0045] The specific process for finish rolling is shown in Table 1. During the finish rolling stage, the core of the intermediate slab is in the low-temperature non-recrystallization zone. The residual heat from the slab core causes surface re-austenitization to achieve a normalizing effect. The finish rolling stage adopts a mode of progressively decreasing reduction rates. Based on the finished thickness, the passes are controlled in a 6+1 mode, where the +1 pass is a dummy pass. When the finished thickness is 60mm-80mm, the reduction rate of the first pass is ≥12%, when the finished thickness is 80mm-90mm, the reduction rate of the first pass is ≥14%, and the reduction rate decreases pass by pass by 0.5% to 4%. The progressively decreasing reduction rates in the finish rolling stage ensures penetration effects during high-temperature core rolling and improves the uniformity of the core structure. Simultaneously, the nano-sized particles of NbC, TiC, and V(C, N) precipitated during finish rolling pin austenite grain boundaries, inhibiting abnormal grain growth. Preferably, when producing a 90mm steel plate using a 300mm-thick slab, 6+1 pass finish rolling is adopted, the first pass reduction rate is 16.5%, with the reduction rate decreasing by 1.0%-3.5% per pass, and the pass deformation (reduction rate) at the 6th pass can still reach 5.8%. After rolling, the steel plate enters the leveler for 1 or 3 passes of leveling to flatten the head and tail shape of the plate and improve the yield rate. The finish rolling adopts a normalizing rolling process, achieving normalizing treatment of the steel plate during rolling, eliminating the offline normalizing process, resulting in a short process flow, low cost, and strong adaptability of the production line. Rough rolling uses a gradually increasing reduction rate mode, while finish rolling uses a gradually decreasing reduction rate mode, fully refining the grains and ensuring rolling penetration effect. MULPIC cooling of the intermediate slab before finish rolling can reduce the waiting time of the intermediate slab, while the normalizing effect can maximally preserve the dynamic recrystallization grain refinement effect from the rough rolling stage. Table 1: Finish rolling temperature and pass reduction rateThickness specification / mmWidth specification / mmIntermediate slab thickness / finished thicknessFinish rolling start temperature / °CFinish rolling finish temperature / °CFirst pass reductionPass reduction decreasing rate>60-70≥1500-31002.2840820≥12%0.5%-4%>3100-4100860820≥12%>70-80≥1500-31001.8830810≥12%0.5%-4%>3100-4100850810≥12%>80-90≥1500-33001.6830810≥14%0.5%-4%

[0046] The high-thickness steel plate for wind power with a thickness of 70mm-90mm rolled using the above method has the characteristics of high strength and toughness, and low-temperature resistance. The base metal of the steel plate has the yield strength of ≥420MPa, the tensile strength of ≥540MPa, the elongation A≥40%, the -60°C core impact energy ≥200J, CEV≤0.41.

[0047] The steel plate can achieve welding under high-heat input conditions of ≥30kJ / cm. The steel plate does not require preheating before welding. The welding process uses gas-shielded welding or submerged arc welding, employing a single-sided V-groove, with welding inter-pass temperature control ≤180°C. The number of welding passes is determined based on the steel plate thickness. After welding, the tensile strength at the welded joint is ≥540MPa, the - 60°C core impact energy in the heat-affected zone is ≥120J, and the fatigue limit stress at the welded joint under conditions of a stress ratio of 0.5 and 5×10 7< cycles is ≥400MPa, fully meeting the requirements for high-heat input welding.Example 1:

[0048] The heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power of Example 1 had the following chemical composition: C: 0.13%, Si: 0.30%, Mn: 1.41%, P: 0.010%, S: 0.003%, Nb: 0.025%, V: 0.027%, Ti: 0.017%, Al: 0.023%, with the remainder being Fe and unavoidable impurities. The thickness of said steel plate was 80mm, the base metal of said steel plate had yield strength of 457MPa, tensile strength of 562MPa, elongation A of 43%, average -60°C core impact energy of 217J, and CEV of 0.37. After automated welding with a heat input of 30kJ / cm, the tensile strength at the welded joint was 552MPa, the -60°C core impact energy in the heat-affected zone was ≥120J, and the fatigue limit stress at the welded joint under conditions of a stress ratio of 0.5 and 5×10 7< cycles was 414MPa, fully meeting the requirements for high-heat input welding.

[0049] The manufacturing method for the above heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power includes the following steps: molten iron underwent converter smelting, LF refining, and RH degassing refining, followed by continuous casting, a 300mm thick continuous casting billet was used, and the billet was slowly cooled after continuous casting was completed. In the converter smelting process, the converter stage adopted pull carbon once and single-slag process smelting, with the final slag basicity controlled at R=3.5; LF refining final slag basicity was 2.7, holding time was 15 minutes, and during RH refining treatment, 115m of CaAl wire was fed, then soft blow was performed for 10 minutes, RH refining time was 48min; the continuous casting process executed a 300mm billet shape, with a casting speed of 0.9m / min, and surface shallow-layer quenching was performed on the slab during the three cooling stages, controlling the upper and lower water flow difference as 22.37% during quenching, the slab surface temperature at 602°C, then the slab utilized residual heat for self-tempering, with self-tempering time being 132min, and after self-tempering completion, it was placed in a pit for slow cooling, with a slow cooling time of 60 hours.

[0050] The billet was heated and rolled to obtain an 80mm thick high-strength steel plate for wind power. During the heating process, the billet soaking zone temperature was 1195°C, the discharging temperature was 1189°C, and the heating rate was 10min / cm; the rough rolling stage of the steel plate adopted 4+1 passes, controlling the pass reduction rate to gradually increase, with the first pass reduction rate at 6.7%, the 4th pass reduction rate at 23.90%, achieving a stepwise increase in rolling deformation, with an increment of 4.8%-6.6%. The finish rolling stage required 6+1 passes, using a pass reduction rate that decreases pass by pass, with the first pass reduction rate at 16.5%, the 6th pass reduction rate at 10.8%, the reduction rate decreased pass by pass, with a pass decrement of 0.5%-1.8%, the deformation rate of each rolling pass was shown in Table 2. Table 2: Rolling Pass Deformation Rate (%) in Example 1PassMill entry / mmMill exit / mmReduction rate / %Pass reduction rate increment / decrement / %Deformation temperature / °CRough rolling1300279.96.7% / 11852279.9247.7111.50%4.80%11813247.71204.8617.30%5.80%11784204.86155.923.90%6.60%11695dummy pass1165Finish rolling1156.00155.7416.50% / 8362155.74132.8514.70%1.80%8323132.85115.0513.40%1.30%8304115.05101.0112.20%1.20%8295101.0189.7011.20%1.00%827689.7080.1010.70%0.50%8247dummy pass821

[0051] The steel plate prepared by the above method, after being welded using submerged arc welding (SAW), the tensile strength at the welded joint was 552MPa, the -60°C core impact energy at the core of the weld fusion metal zone was 176J, the comprehensive mechanical properties at the weld were excellent. The axial loading fatigue limit strength at 5×10 7< cycles was 414MPa, the welded process was shown in Figure 1 and Table 3, and the mechanical properties were shown in Table 4. Table 3: Submerged Arc Welding Parameters of Steel Plate in Example 1Welding methodSubmerged arc welding / SAWWelding equipment and modelDC-100 automated welding systemWelding heat input30kJ / cmCurrent / A550±20Voltage / V34±2Welding speed / cm / min38±2Preheat temperature / °C100-200Inter-pass temperature / °C100-200 Table 4: Post-Weld Mechanical and Fatigue Properties of Steel Plate in Example 1 Tensile property-60°C Impact energy / JAxial loading fatigue limit strength at 5×10 7< cycles (stress ratio 0.5) / MPaTensile strength / MPaFracture zoneSampling location123Mean value562Base metal area outside the fusion lineHeat-affected zone in the core of steel plate202154171176414 Example 2:

[0052] The heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power of Example 2 had the following chemical composition: C: 0.14%, Si: 0.32%, Mn: 1.45%, P: 0.007%, S: 0.001%, Nb: 0.029%, V: 0.030%, Ti: 0.015%, Al: 0.025%, with the remainder being Fe and unavoidable impurities. The thickness of said steel plate was 90mm, the base metal of said steel plate had yield strength of 443MPa, tensile strength of 562MPa, elongation A of 40.2%, average -60°C core impact energy of 183J, and CEV of 0.39. After automated welding with a heat input of 30kJ / cm, the tensile strength at the welded joint was 552MPa, the -60°C core impact energy in the heat-affected zone was ≥120J, and the fatigue limit stress at the welded joint under conditions of a stress ratio of 0.5 and 5×10 7< cycles was ≥400MPa, fully meeting the requirements for high-heat input welding.

[0053] The manufacturing method for the above heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power includes the following steps: molten iron underwent converter smelting, LF refining, and RH degassing refining, followed by continuous casting, a 300mm thick continuous casting billet was used, and the billet was slowly cooled after continuous casting was completed. In the converter smelting process, the converter stage adopted pull carbon once and single-slag process smelting, with the final slag basicity controlled at R=3.5; LF refining final slag basicity was 2.7, holding time was 17 minutes, and during RH refining treatment, 132m of CaAl wire was fed, then soft blow was performed for 9 minutes, RH refining time was 50min; the continuous casting process executed a 300mm billet shape, with a casting speed of 0.9m / min, and surface shallow-layer quenching was performed on the slab during the three cooling stages, controlling the upper and lower water flow difference as 20.17% during quenching, the slab surface temperature at 587°C, then the slab utilized residual heat for self-tempering, with self-tempering time being 150min, and after self-tempering completion, it was placed in a pit for slow cooling, with a slow cooling time of 62 hours.

[0054] The billet was heated and rolled to obtain a 90mm thick high-strength steel plate for wind power. During the heating process, the billet soaking zone temperature was 1200°C, the discharging temperature was 1187°C, and the heating rate was 10min / cm; the rough rolling stage of the steel plate adopted 4+1 passes, controlling the pass reduction rate to gradually increase, with the first pass reduction rate at 7.0%, the 4th pass reduction rate at 27.5%, achieving a stepwise increase in rolling deformation, with an increment of 5.0%-8.5%. The finish rolling stage required 6+1 passes, using a pass reduction rate that decreases pass by pass, with the first pass reduction rate at 16.5%, the 6th pass reduction rate at 5.8%, the reduction rate decreased pass by pass, with a pass decrement of 1.0%-3.5%, the deformation rate of each rolling pass was shown in Table 5. Table 5: Rolling Pass Deformation Rate (%) in Example 2PassMill entry / mmMill exit / mmReduction rate / %Pass reduction rate increment / decrement / %Deformation temperature / °CRough rolling13002797.0% / 11832279245.5212.00%5.0%11803245.52198.8719.00%7.0%11754198.87144.1827.50%8.5%11715dummy pass1167Finish rolling1144.18143.9416.50% / 8402143.94125.2313.00%3.50%8363125.23112.0810.50%2.50%8324112.08102.558.50%2.00%8285102.5595.586.80%1.70%825695.5890.045.80%1.00%8237dummy pass821

[0055] The steel plate prepared by the above method, after being welded using submerged arc welding (SAW) with the same welding equipment and parameters as in Example 1, the tensile strength at the welded joint was 546MPa, the -60°C core impact energy at the core of the weld fusion metal zone was 157J, the comprehensive mechanical properties at the weld were excellent. The axial loading fatigue limit strength at 5×10 7< cycles was 420MPa, the mechanical properties were shown in Table 6. Table 6: Post-Weld Mechanical and Fatigue Properties of Steel Plate in Example 2Tensile property-60°C Impact energy / JAxial loading fatigue limit strength at 5×10 7< cycles (stress ratio 0.5) / MPaTensile strength / MPaFracture zoneSampling location123Mean value546Base metal area outside the fusion lineHeat-affected zone in the core of steel plate151154166157420 Comparative Example 1

[0056] A heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power of comparative Example 1 had the following chemical composition: C: 0.14%, Si: 0.30%, Mn: 1.40%, P: 0.008%, S: 0.003%, Nb: 0.027%, V: 0.026%, Ti: 0.020%, Al: 0.018%, with the remainder being Fe and unavoidable impurities. The thickness of said steel plate was 80mm.

[0057] The manufacturing method for the above steel plate includes the following steps: The implementation processes for smelting, refining, continuous casting, and heating were consistent with Example 1.

[0058] During the rolling process, the rough rolling stage of the steel plate was completed using 4+1 passes, with the pass reduction rate controlled to vary according to mill conditions. The first pass reduction rate was approximately 8%, and the final pass reduction rate was approximately 20%, with the rolling deformation dynamically adjusted based on slab spreading conditions and mill status. The finish rolling stage required 6+1 passes, with the first pass reduction rate approximately 10% and the sixth pass reduction rate 8%. Similar to rough rolling, the reduction rate was dynamically adjusted according to slab spreading conditions and mill status.

[0059] The steel plate prepared by the aforementioned method, after being welded by submerged arc welding (SAW), the base metal of said steel plate had a yield strength of 392MPa, a tensile strength of 530MPa , an elongation A of 31%, a -60°C core impact energy average of ≤80J, and a CEV of 0.38; using the same equipment as in Examples 1 and 2, after automatic welding with a line input of 30kJ / cm, the tensile strength at the welded joint was 522 MPa, the core impact energy at -60°C in the heat-affected zone was ≤30J, indicating poor impact toughness, and the fatigue limit stress at the welded joint under a stress ratio of 0.5 and 5×10 7< cycles was approximately 260MPa, which cannot meet the requirements for high heat input welding.

[0060] The upper and lower limits of the process parameters (such as rolling deformation, holding time, etc.) as well as the interval values of the present invention, can all achieve this method, and examples are not listed one by one here.

[0061] Content not detailed in the present invention can be implemented using conventional technical knowledge in the field.

[0062] From the above description, it can be seen that the embodiments of the present invention achieve the following technical effects: The heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power and manufacturing method therefor, innovates in chemical composition design, slab cooling process, and rolling process, mainly including the following: 1) low-C high-Mn and Nb+V+Ti composite microalloying is used to form submicron-scale precipitates such as Ti(C, N), V(C, N) so as to significantly inhibit the growth of austenite grains and provide a microstructural foundation for subsequent rolling; the Cottrell and Snoek atmospheres formed by the composite nano-carbides Nb\Ti(C, N) generated during the finish rolling stage can markedly hinder dislocation movement and pin grain boundaries, suppressing austenite grain growth, meanwhile, due to the addition of microalloying elements Nb, V and Ti, the upper limit of the non-recrystallization temperature is increased, so that the rolling process window is expanded and the probability of mixed grains during two-phase zone rolling is reduced, which benefits the enhancement of strength and toughness. 2) A slab three-cooling equipment quenching process is adopted to achieve shallow surface quenching of the slab, forming a uniform-thickness shell on the surface, enabling rapid slab cooling and defect-free slab surface preparation, followed by utilizing the slab's residual heat self-tempering effect to refine the surface grains of the cast slab. 3) Rough rolling employs a gradually increasing reduction rate mode, and finish rolling employs a gradually decreasing reduction rate mode, fully refining grains and ensuring rolling penetration effect, where MULPIC cooling of the intermediate slab before finish rolling can reduce the waiting time of the intermediate slab, while the normalizing effect can maximally preserve the dynamic recrystallization grain refinement effect from the rough rolling stage. 4) A normalizing rolling process is utilized to produce thick-gauge steel plates for wind power, achieving normalizing treatment of the steel plate during the rolling process, eliminating the offline normalizing step, resulting in a short process flow, low cost, strong production line adaptability, and broad prospects for promotion.

[0063] The above descriptions are merely preferred embodiments of the present invention and are not intended to limit the invention. For those skilled in the art, various modifications and changes can be made to the present invention. Any amendments, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Examples

example 1

[0048]The heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power of Example 1 had the following chemical composition: C: 0.13%, Si: 0.30%, Mn: 1.41%, P: 0.010%, S: 0.003%, Nb: 0.025%, V: 0.027%, Ti: 0.017%, Al: 0.023%, with the remainder being Fe and unavoidable impurities. The thickness of said steel plate was 80mm, the base metal of said steel plate had yield strength of 457MPa, tensile strength of 562MPa, elongation A of 43%, average -60°C core impact energy of 217J, and CEV of 0.37. After automated welding with a heat input of 30kJ / cm, the tensile strength at the welded joint was 552MPa, the -60°C core impact energy in the heat-affected zone was ≥120J, and the fatigue limit stress at the welded joint under conditions of a stress ratio of 0.5 and 5×10 7< cycles was 414MPa, fully meeting the requirements for high-heat input welding.

[0049]The manufacturing method for the above heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel...

example 2

[0052]The heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power of Example 2 had the following chemical composition: C: 0.14%, Si: 0.32%, Mn: 1.45%, P: 0.007%, S: 0.001%, Nb: 0.029%, V: 0.030%, Ti: 0.015%, Al: 0.025%, with the remainder being Fe and unavoidable impurities. The thickness of said steel plate was 90mm, the base metal of said steel plate had yield strength of 443MPa, tensile strength of 562MPa, elongation A of 40.2%, average -60°C core impact energy of 183J, and CEV of 0.39. After automated welding with a heat input of 30kJ / cm, the tensile strength at the welded joint was 552MPa, the -60°C core impact energy in the heat-affected zone was ≥120J, and the fatigue limit stress at the welded joint under conditions of a stress ratio of 0.5 and 5×10 7< cycles was ≥400MPa, fully meeting the requirements for high-heat input welding.

[0053]The manufacturing method for the above heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength st...

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Chinese Patent Application No. 202311075355.2, titled "HEAVY-GAUGE, FATIGUE-RESISTANT, EASY-TO-WELD, AND HIGH-STRENGTH STEEL PLATE FOR WIND POWER AND MANUFACTURING METHOD THEREFOR", filed on August 24, 2023, which is incorporated herein by reference.TECHNICAL FIELD

[0002] The present invention relates to the field of iron and steel metallurgy, and specifically to a heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power and manufacturing method therefor.BACKGROUND

[0003] Currently, with prominent energy shortages and environmental issues, the energy-saving and emission-reduction benefits of wind power have attracted much attention. Wind energy resources are renewable clean energy, representing a new energy source that is pollution-free, renewable, and has broad prospects. Wind energy offers many benefits for environmental protection, including eliminating local air pollution and reducing water resource consumption, but the most significant is its contribution to carbon dioxide emission reduction. It is currently one of the most effective ways for humanity to contribute to addressing global climate change.

[0004] Steel for wind turbine towers primarily uses low-alloy steel, requiring good strength and toughness, fatigue resistance, and excellent weldability. Currently, wind power is trending toward larger scales; offshore wind turbines have single-unit capacities exceeding 16MW, with tower heights over 100 meters. Key stress-bearing parts such as the tower base and foundation ring are often welded from thick high-strength steel plates, demanding extremely high strength and toughness from the steel, making production challenging. As the thickness of high-strength steel plates increases, their mechanical properties degrade significantly, with poor microstructural uniformity and large performance fluctuations in the center.

[0005] Existing technologies often employ costly offline normalizing processes for production, and lack indicators for weldability and fatigue performance, resulting in poor process adaptability.

[0006] Patent document 202210210565.7 discloses "A Production Method for 80~100mm Thick Steel Plate for Wind Power." This patent produces steel plates with good mechanical properties through appropriate smelting, continuous casting, heating, rolling, and controlled cooling processes, without requiring heat treatment, thus offering lower process costs. However, this patent does not study the weldability of the steel plate and lacks key data such as fatigue strength at weld joints.

[0007] Patent document CN107619997A discloses "Super-thick steel plate for wind power and production method thereof." This patent can produce 220-440mm thick steel plates for wind power through reasonable composition design combined with methods like electroslag remelting. This method has advantages such as large product thickness but offers lower strength grades and lacks research data on welding, especially post-weld fatigue strength.

[0008] Patent document CN114277315A discloses "Thick-specification normalizing process anti-fatigue wind power steel plate and preparation method thereof." This patent uses low-carbon micro-niobium technology while adding Cu, Ni, and Mo to improve the steel plate's strength and low-temperature impact performance. However, the process flow described in this invention is lengthy, lacks impact toughness data at extremely low temperatures (-60°C), and has low post-weld fatigue strength.SUMMARY

[0009] An object of this invention is to provide a heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power and manufacturing method therefor. This manufacturing method features low cost and strong production line adaptability, with the steel plate's mechanical properties, as well as post-weld mechanical and fatigue performance, all meeting application requirements.

[0010] To achieve the above object, the present invention provides the following technical solutions.

[0011] In one aspect, a heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power is provided, the steel plate has the following chemical composition by mass percentage: C: 0.12%-0.15%, Si: 0.15%-0.35%, Mn: 1.30%-1.50%, P≤0.015%, S≤0.005%, Nb: 0.015%-0.030%, V: 0.015%-0.030%, Ti: 0.005%-0.020%, Al: 0.005%-0.030%, with the remainder being Fe and unavoidable impurities.

[0012] Further, the steel plate has a thickness of 70mm-90mm, the base metal of the steel plate has a yield strength of ≥420MPa, a tensile strength of ≥540MPa, an elongation A≥40%, a -60°C core impact energy of ≥200J, and a CEV (carbon equivalent value) of ≤0.41; the steel plate is capable of achieving welding under a high-heat input condition of ≥30kJ / cm; after welding, the steel plate has a tensile strength of ≥540MPa at a welded joint, a -60°C core impact energy of ≥120J in a heat-affected zone, a fatigue limit stress of ≥400MPa at the welded joint under conditions of a stress ratio of 0.5 and 5×10 7< cycles.

[0013] In another aspect, a manufacturing method for the above heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power is provided, including the following steps: smelting, performed using a converter; refining, comprising LF refining and RH refining, yielding a thick slab with a thickness ≥300mm after RH refining; continuous casting, wherein the thick slab is cast using a continuous casting mold, and a billet after casting is subjected to slow cooling to obtain a continuous casting slab; heating, wherein the continuous casting slab is heated using a cold-charging method; and rolling, comprising rough rolling and finish rolling, wherein rough rolling is first performed, an intermediate slab is cooled after rough rolling via a MULPIC water cooling unit, then the slab is conveyed to a finishing mill for finish rolling, followed by straightening in a leveler to obtain a finished steel plate.

[0014] Further, in the smelting step of the manufacturing method, the converter uses pull carbon once and single-slag process for smelting, with a final slag basicity R being controlled between 3.2-4.2; a red clean ladle with ladle temperature of ≥800°C is employed, with a tapping time of ≥3 minutes, and high-sensitivity slag blocking is used during tapping, followed by deoxidization with aluminum-manganese-iron at 1.7kg / t-3.2kg / t steel; low-carbon low-phosphorus silicon-manganese, ferrosilicon, ferroniobium, and ferrovanadium are added in batches, and synthetic slag and pre-fused slag are added along a steel flow during tapping, with a ratio of the synthetic slag to the pre-fused slag of 2:1.

[0015] Further, during the LF refining process of the manufacturing method, argon bottom blowing stirring is maintained throughout, aluminum granules and aluminum slag are used for deoxidization, and lime is added for slag formation, with a final slag basicity of ≥2.7; fine-tuning composition is performed with silicon-manganese, ferrosilicon, ferroniobium, and ferrovanadium alloys; a Ti composition is adjusted with Ti wire and ferrotitanium; a Al composition is adjusted with aluminum wire, and a LF refining treatment time is controlled to be ≥40min; after LF refining is completed, RH refining is performed, with a RH refining time ≥45min, and after RH refining treatment, CaAl wire of 85m-160m is fed, then soft blowing is performed for over 9 minutes, obtaining a thick slab after RH refining treatment, with a thickness of the thick slab ≥300mm; and preferably, the thickness of the thick slab is 300mm.

[0016] Further, in the continuous casting step of the manufacturing method, a continuous caster casting speed is controlled at 0.8m / min-1.1m / min, peritectic steel mold powder is used, a mold oscillation mode is non-sinusoidal oscillation mode; secondary cooling water and dynamic soft reduction are controlled according to peritectic steel; after being flame-cut and divided, the thick slab enters a third cooling machine for water cooling, achieving shallow surface quenching of the slab, with an upper and lower water flow difference being controlled to 15%~30% during quenching, and a surface temperature of the thick slab is controlled to be ≤600°C, and surface cooling water is blown off after γ-α transformation is completed on the surface; the thick slab undergoes self-tempering using residual heat, with a self-tempering time of ≥120min, and after self-tempering is completed, the slab is placed in a pit for slow cooling, with a slow cooling time not less than 56 hours.

[0017] Further, in the heating step of the manufacturing method, a slab charging temperature is ≤350°C, a soaking zone temperature of a heating furnace is controlled at 1180°C-1260°C, and a discharging temperature is controlled at 1170°C-1250°C; a heating rate is 9min / cm-11.5min / cm; and preferably, the soaking zone temperature of the heating furnace is 1250°C, the discharging temperature is 1200°C, and the heating rate is 10min / cm.

[0018] Further, in the rolling step of the manufacturing method, rough rolling adopts a high reduction mode, and the rough rolling stage is completed using either a 4+1 pass or 6+1 pass rolling modes based on a target steel plate thickness, where the +1 pass is a dummy pass; a rolling pass reduction rate is controlled to increase progressively, with a first pass reduction rate ≥6%, and in both the 4+1 pass and 6+1 pass rolling modes, the reduction rate of a final pass is ≥20%, with the pass reduction rate increasing progressively by 3% to 8%.

[0019] Further, when a 90mm steel plat is produced using a 300mm-thick slab, 4+1 pass rough rolling is adopted, with the first pass reduction rate of 7%, the 4th pass reduction rate of 27.5%, and progressive increments of 5%, 7%, and 8.5% respectively.

[0020] Further, in the rolling step of the manufacturing method, finish rolling adopts a normalizing rolling mode, and 6+1 pass finish rolling is adopted, where the +1 pass is a dummy pass, and the reduction rate decreases progressively; when the finished thickness is 60mm-80mm, the first pass reduction rate is ≥12%, when the finished thickness is 80mm-90mm, the first pass reduction rate is ≥14%, with the reduction rate decreasing pass by pass by 0.5% to 4%; and preferably, when producing a 90mm steel plate using a 300mm-thick slab, a 6+1 pass finish rolling is adopted, with the first pass reduction rate of 16.5%, the reduction rate decreasing pass by pass by 1.0% to 3.5%, and the reduction rate at the 6th pass being 5.8%.

[0021] Analysis shows that in the heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power and manufacturing method therefor of the present invention, low-C high-Mn and Nb+V+Ti composite microalloying is used to form submicron-scale precipitates such as Ti(C, N), V(C, N) so as to significantly inhibit the growth of austenite grains and provide a microstructural foundation for subsequent rolling; the Cottrell and Snoek atmospheres formed by the composite nano-carbides Nb\Ti(C, N) generated during the finish rolling stage can markedly hinder dislocation movement and pin grain boundaries, suppressing austenite grain growth, meanwhile, due to the addition of microalloying elements Nb, V and Ti, the upper limit of the non-recrystallization temperature is increased, so that the rolling process window is expanded and the probability of mixed grains during two-phase zone rolling is reduced, which benefits the enhancement of strength and toughness. The slab three-cooling equipment quenching process is adopted to achieve shallow surface quenching of the slab, forming a uniform-thickness shell on the surface, enabling rapid slab cooling and defect-free slab surface preparation, followed by utilizing the slab's residual heat self-tempering effect to refine the surface grains of the cast slab. Rough rolling employs a gradually increasing reduction rate mode, while finish rolling uses a gradually decreasing reduction rate mode, fully refining grains and ensuring rolling penetration. The MULPIC cooling of the intermediate slab before finish rolling can reduce the intermediate slab's waiting time, while the normalizing effect can maximally preserve the dynamic recrystallization grain refinement achieved during the rough rolling stage. The normalized rolling process is used to produce thick-gauge steel plates for wind power, achieving in-line normalizing treatment during rolling, eliminating the offline normalizing process. The process flow is short, costs are low, production line adaptability is strong, and it has broad prospects for promotion.BRIEF DESCRIPTION OF DRAWINGS

[0022] The drawings, which form a part of this application, are provided to further illustrate the present invention. The illustrative embodiments and their descriptions are used to explain the present invention and do not constitute an undue limitation thereof. Among them: Figure 1 is a welding pass diagram of the steel plate according to Example 1 of the present invention.DESCRIPTION OF EMBODIMENTS

[0023] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments. The examples are provided to explain the present invention and not to limit it. In fact, it will be apparent to those skilled in the art that modifications and variations can be made to the present invention without departing from its scope or spirit. For example, features shown or described as part of one embodiment can be used in another embodiment to yield a further embodiment. Therefore, it is intended that the present invention cover such modifications and variations as fall within the scope of the appended claims and their equivalents.

[0024] According to embodiments of the present invention, a heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power is provided. The steel plate has the following chemical composition by mass percentage: C: 0.12%-0.15%, Si: 0.15%-0.35%, Mn: 1.30%-1.50%, P≤0.015%, S≤0.005%,Nb: 0.015%-0.030%, V: 0.015%-0.030%, Ti: 0.005%-0.020%, Al: 0.005%-0.030%, with the remainder being Fe and unavoidable impurities.

[0025] Carbon: C atoms in steel can produce significant interstitial solid solution strengthening, markedly increasing the strength and hardness of steel, making it the most economical and effective strengthening method in steel materials. However, when the content of C exceeds 0.15%, it leads to an increase in carbides in the steel, causing a significant decline in properties such as toughness and elongation, while also worsening weldability. Therefore, the C content in this invention is controlled between 0.12%-0.15%.

[0026] Silicon: Si can be used as a deoxidizing element during smelting, enhancing the oxidation resistance of the steel. Simultaneously, Si dissolved in the steel can cause lattice distortion, increasing the strength of the ferrite structure. However, a silicon content exceeding 0.35% may embrittle the ferrite structure in the steel, reducing its plasticity and toughness. Therefore, the silicon content in the present invention is controlled between 0.15% and 0.35%.

[0027] Manganese: Mn can lower the γ-α phase transformation temperature of steel, refine the pearlite lamellae in steel, and increase the strength of pearlite in low-carbon steel without significantly reducing ductility. Mn can also control the content of oxides and sulfides during smelting, making the steel structure uniform and refined, thereby improving the strength and toughness of the steel. However, a Mn content exceeding 1.50% tends to cause rolling cracking and worsen the weldability of the steel. Therefore, the manganese content in the present invention is controlled between 1.30% and 1.50%.

[0028] Phosphorus: P is an element prone to segregation in steel, making the steel susceptible to cold brittleness. Additionally, phosphorus easily causes welding cracks in welds. To ensure sufficient toughness in the weld metal, the P content in this invention is controlled below 0.015%.

[0029] Sulfur: S is a harmful element; sulfur easily combines with manganese to form MnS inclusions, which deform during the rolling process, reducing the impact toughness of the steel. S increases the hot brittleness of the weld metal, making welds prone to hot cracks and porosity. Therefore, the S content in this invention is controlled below 0.005%.

[0030] Niobium: Nb can promote grain refinement, improving the strength and toughness of the steel. Meanwhile, Nb in the steel combines with C, N to form nano-sized Nb(C, N), which can produce a significant strengthening effect and improve the mechanical properties of the welding heat-affected zone. However, if the niobium content exceeds 0.03%, it will deteriorate weldability and reduce cold deformation capability. Therefore, the niobium content in this invention is controlled between 0.015-0.030%.

[0031] Vanadium: V can form a continuous solid solution with Fe, significantly narrowing the austenite phase region, while also refining ferrite grains, producing a notable grain refinement strengthening effect. V and C, N have a strong affinity and exist in the steel as VC and VN precipitates, which can produce a significant precipitation strengthening effect. V is a scarce resource, and its usage should be minimized as much as possible. Therefore, the V content in this invention is controlled between 0.015-0.030%.

[0032] Titanium: Ti serves as an effective deoxidizing element in steel, combining with carbon in the steel to form stable TiC, which prevents the growth and coarsening of steel grains and improves the low-temperature impact toughness of the steel. However, if the Ti content exceeds 0.02%, the content and size of titanium carbide particles increase, reducing the strength and toughness of the steel. Therefore, the Ti content in this invention is controlled between 0.005% and 0.020%.

[0033] Aluminum: Al is a strong deoxidizing element that also refines grains and improves the toughness of steel. Controlling the Al content can enhance the purity and fatigue strength of the steel. However, if the Al content exceeds 0.030%, it leads to an increase in alumina-based inclusions in the steel, deteriorating its mechanical properties. Therefore, the Al content in this invention is controlled between 0.005% and 0.030%.

[0034] The design philosophy of this invention is as follows: Using low-C high-Mn and Nb+V+Ti composite microalloying, submicron-scale precipitates such as Ti(C, N), V(C, N) are formed, which significantly inhibit the growth of austenite grains and provide a microstructural foundation for subsequent rolling; the Cottrell and Snoek atmospheres formed by the composite nano-carbides Nb\Ti(C, N) generated during the finish rolling stage can markedly hinder dislocation movement and pin grain boundaries, suppressing austenite grain growth, meanwhile, due to the addition of microalloying elements Nb, V and Ti, the upper limit of the non-recrystallization temperature is increased, so that the rolling process window is expanded and the probability of mixed grains during two-phase zone rolling is reduced, which benefits the enhancement of strength and toughness.

[0035] The non-recrystallization zone refers to when high-strength low-alloy steel contains alloy elements like Nb, its recrystallization temperature increases, generally reaching around 950°C; therefore, the range from above 700°C where ordinary carbon steel undergoes recrystallization to 950°C where no recrystallization occurs is called the non-recrystallization zone. During hot rolling of steel, deformation-induced austenite undergoes recrystallization, especially dynamic recrystallization, which can refine austenite grains (recrystallization-controlled rolling), forming equiaxed austenite grains. Microalloy precipitates such as V(C, N) can form extensively in austenite, serving as nucleation sites for polygonal ferrite. In the rolling stage within the non-recrystallization zone, austenite grains are significantly elongated; at this stage, the Cottrell and Snoek atmospheres formed by Nb\Ti(C, N) composite nano-carbides markedly hinder dislocation movement and pin grain boundaries, inhibiting austenite grain growth, thereby increasing ferrite nucleation sites and rates during phase transformation, refining grains, and enhancing the fine-grain strengthening effect. During subsequent cooling of the steel plate, Nb\Ti(C, N) composite nano-carbides continue to precipitate dispersedly or interphase, obstructing dislocation motion and producing precipitation strengthening effects.

[0036] The present invention also discloses a manufacturing method for the above heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power, comprising the following steps: S1: Smelting

[0037] Smelting is carried out using a converter, with the converter employing high-quality lime and dolomite. During the smelting process, high lance position and feeding timing are controlled, and slag materials are fully added 3 minutes before the endpoint. The converter uses the pull carbon once and single-slag process for smelting, with the final slag basicity R being controlled between 3.2-4.2 (e.g., 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2), achieving early slag formation initially and good slagging during the process. A red clean ladle is used, with ladle temperature of ≥800°C and tapping time of ≥3 minutes. High-sensitivity slag blocking is employed during tapping to prevent significant slag carryover. Deoxidation and alloying: Use aluminum-manganese-iron at 1.7 kg / t to 3.2 kg / t steel (e.g., 1.7 kg / t, 1.9 kg / t, 2.0 kg / t, 2.2 kg / t, 2.4 kg / t, 2.6 kg / t, 2.8 kg / t, 3.0 kg / t, 3.2 kg / t) for deoxidation. When the molten steel reaches one-quarter of the tap, add low-carbon low-phosphorus silicon-manganese, ferrosilicon, ferroniobium, and ferrovanadium in batches, completing the addition by three-quarters of the tap. During tapping, add synthetic slag and pre-fused slag along the steel stream, with the ratio of synthetic slag to pre-fused slag (by mass) at 2:1 (e.g., 300 kg synthetic slag + 150 kg pre-fused slag).S2: Refining

[0038] Refining includes LF refining and RH refining. During LF refining, argon bottom blowing is used for stirring throughout the process, and molten steel must not be exposed to prevent secondary oxidation. Aluminum granules and aluminum slag are used for deoxidation during smelting, with argon gas in weak stirring mode during deoxidation. Lime is added for slag formation, and the top slag before leaving the station must be yellow-white or white slag, with such slag maintained for ≥13 minutes, and final slag basicity ≥2.7. Alloys such as silicon-manganese, ferrosilicon, ferroniobium, and ferrovanadium are used for fine-tuning composition; Ti wire or ferroitianium adjusts Ti content; aluminum wire adjusts Al content. Control LF refining treatment time ≥40min.

[0039] After LF refining is completed, RH refining is performed. During RH refining treatment, avoid chemical heating, ensure pure degassing time ≥5 minutes. Control RH refining time ≥45 min. After RH refining treatment is completed, feed CaAl wire of 85m-160m (e.g., 85m, 90m, 95m, 100m, 105m, 110m, 115m, 120m, 125m, 130m, 135m, 140m, 145m, 150m, 155m, 160m) for calcium treatment of inclusions, then soft blow for ≥9 minutes. After RH refining treatment, a thick slab is obtained, with thickness ≥300 mm. Preferably, the thick slab thickness is 300 mm.S3: Continuous casting

[0040] Produce the thick slab obtained in step S2 using a continuous casting mold, with the caster's casting speed at 0.8m / min to 1.1m / min, employing peritectic steel mold powder, and the mold oscillation mode set to non-sinusoidal oscillation. Secondary cooling water and dynamic soft reduction are controlled according to peritectic steel standards. After flame cutting, the thick slab enters the tertiary cooling machine for water cooling, where the equipment operates at maximum water flow and valve opening to achieve shallow surface quenching of the slab. Since the upper nozzle flow can retain the steel plate and the lower nozzle flow descends into the collection pipe, during quenching, the lower water flow is controlled to be greater than the upper flow, with a difference of 15%-30% between them. Control the thick slab surface temperature to ≤600°C; after the surface completes the γ-α transformation, blow off the surface cooling water. The thick slab utilizes residual heat for self-tempering, with a self-tempering time ≥120min. After self-tempering is complete, it enters a pit for slow cooling, with a slow cooling time not less than 56 hours, resulting in a continuous casting slab after casting is finished. By adopting the slab tertiary cooling equipment quenching process, shallow surface quenching of the slab is achieved, forming a uniform shell thickness on the surface, enabling rapid cooling of the slab and defect-free surface preparation. Subsequently, the slab's residual heat self-tempering effect refines the grain structure of the casting surface layer.S4: Heating

[0041] Continuous casting billets are heated by cold charging, with slab charging temperature ≤350°C. Due to the low-alloy, low CEV design of this steel grade of the present invention (low CEV is a relative concept, typically below 0.45 is considered low CEV), heating steel with low temperature is required to prevent grain coarsening. The soaking zone temperature of the heating furnace is controlled to 1180°C-1260°C (e.g., 1180°C, 1190°C, 1200°C, 1210°C, 1220°C, 1230°C, 1240°C, 1250°C, 1260°C), the discharging temperature is controlled to 1170°C-1250°C (e.g., 1170°C, 1180°C, 1190°C, 1200°C, 1210°C, 1220°C, 1230°C, 1240°C, 1250°C), the heating rate is controlled at 9min / cm-11.5min / cm (e.g., 9min / cm, 9.3min / cm, 9.5min / cm, 9.8min / cm, 10min / cm, 10.3min / cm, 10.5min / cm, 10.8min / cm, 11min / cm, 11.3min / cm, 11.5min / cm). The above heating speed and temperature can homogenize the original austenite structure in the billet, fully dissolve alloy elements such as Nb, V, Ti in the steel, providing a basis for subsequent precipitation of microalloy carbides in the steel. Preferably, the soaking zone temperature of the heating furnace is 1250°C, the discharging temperature is 1200°C, and the heating rate is 10min / cm.S5: Rolling

[0042] Rolling includes rough rolling and finish rolling. First, rough rolling is performed. The intermediate slab after rough rolling is cooled by the MULPIC water cooling unit, and then transported to the finish rolling mill for finish rolling, followed by straightening in a leveler to obtain the finished steel plate.

[0043] The steel plate is rough rolled using a high reduction mode. The intermediate slab after rough rolling is sent to the MULPIC water cooling unit for cooling, during which no rolling process is carried out. The intermediate slab is controlled to undergo reciprocating water cooling in the water cooling unit until its surface temperature reaches ≤830°C to generate a surface quenched zone of sufficient thickness.

[0044] In the rough rolling stage, 4+1 or 6+1 passes are selected based on the target steel plate thickness, where the +1 pass is a dummy pass without any rolling force applied. In terms of deformation, the reduction rate per pass is controlled to increase progressively. The reduction rate of the first pass ≥6%, the reduction rate of the final pass in both 4+1 and 6+1 rolling mode should be ≥20%. The reduction rate per pass increases progressively by 3% to 8% (e.g., 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%). The temperature during rough rolling is within the recrystallization zone, and the progressively increasing reduction rate can fully break down austenite grains, promote complete recrystallization of the core structure, and significantly refine the austenite grains. Preferably, when producing a 90mm steel plate using a 300mm thick slab, 4+1 pass rough rolling is adopted, with the first pass reduction rate of 7%, the 4th pass reduction rate of 27.5%, and progressive increments of 5%, 7%, and 8.5% respectively.

[0045] The specific process for finish rolling is shown in Table 1. During the finish rolling stage, the core of the intermediate slab is in the low-temperature non-recrystallization zone. The residual heat from the slab core causes surface re-austenitization to achieve a normalizing effect. The finish rolling stage adopts a mode of progressively decreasing reduction rates. Based on the finished thickness, the passes are controlled in a 6+1 mode, where the +1 pass is a dummy pass. When the finished thickness is 60mm-80mm, the reduction rate of the first pass is ≥12%, when the finished thickness is 80mm-90mm, the reduction rate of the first pass is ≥14%, and the reduction rate decreases pass by pass by 0.5% to 4%. The progressively decreasing reduction rates in the finish rolling stage ensures penetration effects during high-temperature core rolling and improves the uniformity of the core structure. Simultaneously, the nano-sized particles of NbC, TiC, and V(C, N) precipitated during finish rolling pin austenite grain boundaries, inhibiting abnormal grain growth. Preferably, when producing a 90mm steel plate using a 300mm-thick slab, 6+1 pass finish rolling is adopted, the first pass reduction rate is 16.5%, with the reduction rate decreasing by 1.0%-3.5% per pass, and the pass deformation (reduction rate) at the 6th pass can still reach 5.8%. After rolling, the steel plate enters the leveler for 1 or 3 passes of leveling to flatten the head and tail shape of the plate and improve the yield rate. The finish rolling adopts a normalizing rolling process, achieving normalizing treatment of the steel plate during rolling, eliminating the offline normalizing process, resulting in a short process flow, low cost, and strong adaptability of the production line. Rough rolling uses a gradually increasing reduction rate mode, while finish rolling uses a gradually decreasing reduction rate mode, fully refining the grains and ensuring rolling penetration effect. MULPIC cooling of the intermediate slab before finish rolling can reduce the waiting time of the intermediate slab, while the normalizing effect can maximally preserve the dynamic recrystallization grain refinement effect from the rough rolling stage. Table 1: Finish rolling temperature and pass reduction rateThickness specification / mmWidth specification / mmIntermediate slab thickness / finished thicknessFinish rolling start temperature / °CFinish rolling finish temperature / °CFirst pass reductionPass reduction decreasing rate>60-70≥1500-31002.2840820≥12%0.5%-4%>3100-4100860820≥12%>70-80≥1500-31001.8830810≥12%0.5%-4%>3100-4100850810≥12%>80-90≥1500-33001.6830810≥14%0.5%-4%

[0046] The high-thickness steel plate for wind power with a thickness of 70mm-90mm rolled using the above method has the characteristics of high strength and toughness, and low-temperature resistance. The base metal of the steel plate has the yield strength of ≥420MPa, the tensile strength of ≥540MPa, the elongation A≥40%, the -60°C core impact energy ≥200J, CEV≤0.41.

[0047] The steel plate can achieve welding under high-heat input conditions of ≥30kJ / cm. The steel plate does not require preheating before welding. The welding process uses gas-shielded welding or submerged arc welding, employing a single-sided V-groove, with welding inter-pass temperature control ≤180°C. The number of welding passes is determined based on the steel plate thickness. After welding, the tensile strength at the welded joint is ≥540MPa, the - 60°C core impact energy in the heat-affected zone is ≥120J, and the fatigue limit stress at the welded joint under conditions of a stress ratio of 0.5 and 5×10 7< cycles is ≥400MPa, fully meeting the requirements for high-heat input welding.Example 1:

[0048] The heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power of Example 1 had the following chemical composition: C: 0.13%, Si: 0.30%, Mn: 1.41%, P: 0.010%, S: 0.003%, Nb: 0.025%, V: 0.027%, Ti: 0.017%, Al: 0.023%, with the remainder being Fe and unavoidable impurities. The thickness of said steel plate was 80mm, the base metal of said steel plate had yield strength of 457MPa, tensile strength of 562MPa, elongation A of 43%, average -60°C core impact energy of 217J, and CEV of 0.37. After automated welding with a heat input of 30kJ / cm, the tensile strength at the welded joint was 552MPa, the -60°C core impact energy in the heat-affected zone was ≥120J, and the fatigue limit stress at the welded joint under conditions of a stress ratio of 0.5 and 5×10 7< cycles was 414MPa, fully meeting the requirements for high-heat input welding.

[0049] The manufacturing method for the above heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power includes the following steps: molten iron underwent converter smelting, LF refining, and RH degassing refining, followed by continuous casting, a 300mm thick continuous casting billet was used, and the billet was slowly cooled after continuous casting was completed. In the converter smelting process, the converter stage adopted pull carbon once and single-slag process smelting, with the final slag basicity controlled at R=3.5; LF refining final slag basicity was 2.7, holding time was 15 minutes, and during RH refining treatment, 115m of CaAl wire was fed, then soft blow was performed for 10 minutes, RH refining time was 48min; the continuous casting process executed a 300mm billet shape, with a casting speed of 0.9m / min, and surface shallow-layer quenching was performed on the slab during the three cooling stages, controlling the upper and lower water flow difference as 22.37% during quenching, the slab surface temperature at 602°C, then the slab utilized residual heat for self-tempering, with self-tempering time being 132min, and after self-tempering completion, it was placed in a pit for slow cooling, with a slow cooling time of 60 hours.

[0050] The billet was heated and rolled to obtain an 80mm thick high-strength steel plate for wind power. During the heating process, the billet soaking zone temperature was 1195°C, the discharging temperature was 1189°C, and the heating rate was 10min / cm; the rough rolling stage of the steel plate adopted 4+1 passes, controlling the pass reduction rate to gradually increase, with the first pass reduction rate at 6.7%, the 4th pass reduction rate at 23.90%, achieving a stepwise increase in rolling deformation, with an increment of 4.8%-6.6%. The finish rolling stage required 6+1 passes, using a pass reduction rate that decreases pass by pass, with the first pass reduction rate at 16.5%, the 6th pass reduction rate at 10.8%, the reduction rate decreased pass by pass, with a pass decrement of 0.5%-1.8%, the deformation rate of each rolling pass was shown in Table 2. Table 2: Rolling Pass Deformation Rate (%) in Example 1PassMill entry / mmMill exit / mmReduction rate / %Pass reduction rate increment / decrement / %Deformation temperature / °CRough rolling1300279.96.7% / 11852279.9247.7111.50%4.80%11813247.71204.8617.30%5.80%11784204.86155.923.90%6.60%11695dummy pass1165Finish rolling1156.00155.7416.50% / 8362155.74132.8514.70%1.80%8323132.85115.0513.40%1.30%8304115.05101.0112.20%1.20%8295101.0189.7011.20%1.00%827689.7080.1010.70%0.50%8247dummy pass821

[0051] The steel plate prepared by the above method, after being welded using submerged arc welding (SAW), the tensile strength at the welded joint was 552MPa, the -60°C core impact energy at the core of the weld fusion metal zone was 176J, the comprehensive mechanical properties at the weld were excellent. The axial loading fatigue limit strength at 5×10 7< cycles was 414MPa, the welded process was shown in Figure 1 and Table 3, and the mechanical properties were shown in Table 4. Table 3: Submerged Arc Welding Parameters of Steel Plate in Example 1Welding methodSubmerged arc welding / SAWWelding equipment and modelDC-100 automated welding systemWelding heat input30kJ / cmCurrent / A550±20Voltage / V34±2Welding speed / cm / min38±2Preheat temperature / °C100-200Inter-pass temperature / °C100-200 Table 4: Post-Weld Mechanical and Fatigue Properties of Steel Plate in Example 1 Tensile property-60°C Impact energy / JAxial loading fatigue limit strength at 5×10 7< cycles (stress ratio 0.5) / MPaTensile strength / MPaFracture zoneSampling location123Mean value562Base metal area outside the fusion lineHeat-affected zone in the core of steel plate202154171176414 Example 2:

[0052] The heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power of Example 2 had the following chemical composition: C: 0.14%, Si: 0.32%, Mn: 1.45%, P: 0.007%, S: 0.001%, Nb: 0.029%, V: 0.030%, Ti: 0.015%, Al: 0.025%, with the remainder being Fe and unavoidable impurities. The thickness of said steel plate was 90mm, the base metal of said steel plate had yield strength of 443MPa, tensile strength of 562MPa, elongation A of 40.2%, average -60°C core impact energy of 183J, and CEV of 0.39. After automated welding with a heat input of 30kJ / cm, the tensile strength at the welded joint was 552MPa, the -60°C core impact energy in the heat-affected zone was ≥120J, and the fatigue limit stress at the welded joint under conditions of a stress ratio of 0.5 and 5×10 7< cycles was ≥400MPa, fully meeting the requirements for high-heat input welding.

[0053] The manufacturing method for the above heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power includes the following steps: molten iron underwent converter smelting, LF refining, and RH degassing refining, followed by continuous casting, a 300mm thick continuous casting billet was used, and the billet was slowly cooled after continuous casting was completed. In the converter smelting process, the converter stage adopted pull carbon once and single-slag process smelting, with the final slag basicity controlled at R=3.5; LF refining final slag basicity was 2.7, holding time was 17 minutes, and during RH refining treatment, 132m of CaAl wire was fed, then soft blow was performed for 9 minutes, RH refining time was 50min; the continuous casting process executed a 300mm billet shape, with a casting speed of 0.9m / min, and surface shallow-layer quenching was performed on the slab during the three cooling stages, controlling the upper and lower water flow difference as 20.17% during quenching, the slab surface temperature at 587°C, then the slab utilized residual heat for self-tempering, with self-tempering time being 150min, and after self-tempering completion, it was placed in a pit for slow cooling, with a slow cooling time of 62 hours.

[0054] The billet was heated and rolled to obtain a 90mm thick high-strength steel plate for wind power. During the heating process, the billet soaking zone temperature was 1200°C, the discharging temperature was 1187°C, and the heating rate was 10min / cm; the rough rolling stage of the steel plate adopted 4+1 passes, controlling the pass reduction rate to gradually increase, with the first pass reduction rate at 7.0%, the 4th pass reduction rate at 27.5%, achieving a stepwise increase in rolling deformation, with an increment of 5.0%-8.5%. The finish rolling stage required 6+1 passes, using a pass reduction rate that decreases pass by pass, with the first pass reduction rate at 16.5%, the 6th pass reduction rate at 5.8%, the reduction rate decreased pass by pass, with a pass decrement of 1.0%-3.5%, the deformation rate of each rolling pass was shown in Table 5. Table 5: Rolling Pass Deformation Rate (%) in Example 2PassMill entry / mmMill exit / mmReduction rate / %Pass reduction rate increment / decrement / %Deformation temperature / °CRough rolling13002797.0% / 11832279245.5212.00%5.0%11803245.52198.8719.00%7.0%11754198.87144.1827.50%8.5%11715dummy pass1167Finish rolling1144.18143.9416.50% / 8402143.94125.2313.00%3.50%8363125.23112.0810.50%2.50%8324112.08102.558.50%2.00%8285102.5595.586.80%1.70%825695.5890.045.80%1.00%8237dummy pass821

[0055] The steel plate prepared by the above method, after being welded using submerged arc welding (SAW) with the same welding equipment and parameters as in Example 1, the tensile strength at the welded joint was 546MPa, the -60°C core impact energy at the core of the weld fusion metal zone was 157J, the comprehensive mechanical properties at the weld were excellent. The axial loading fatigue limit strength at 5×10 7< cycles was 420MPa, the mechanical properties were shown in Table 6. Table 6: Post-Weld Mechanical and Fatigue Properties of Steel Plate in Example 2Tensile property-60°C Impact energy / JAxial loading fatigue limit strength at 5×10 7< cycles (stress ratio 0.5) / MPaTensile strength / MPaFracture zoneSampling location123Mean value546Base metal area outside the fusion lineHeat-affected zone in the core of steel plate151154166157420 Comparative Example 1

[0056] A heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power of comparative Example 1 had the following chemical composition: C: 0.14%, Si: 0.30%, Mn: 1.40%, P: 0.008%, S: 0.003%, Nb: 0.027%, V: 0.026%, Ti: 0.020%, Al: 0.018%, with the remainder being Fe and unavoidable impurities. The thickness of said steel plate was 80mm.

[0057] The manufacturing method for the above steel plate includes the following steps: The implementation processes for smelting, refining, continuous casting, and heating were consistent with Example 1.

[0058] During the rolling process, the rough rolling stage of the steel plate was completed using 4+1 passes, with the pass reduction rate controlled to vary according to mill conditions. The first pass reduction rate was approximately 8%, and the final pass reduction rate was approximately 20%, with the rolling deformation dynamically adjusted based on slab spreading conditions and mill status. The finish rolling stage required 6+1 passes, with the first pass reduction rate approximately 10% and the sixth pass reduction rate 8%. Similar to rough rolling, the reduction rate was dynamically adjusted according to slab spreading conditions and mill status.

[0059] The steel plate prepared by the aforementioned method, after being welded by submerged arc welding (SAW), the base metal of said steel plate had a yield strength of 392MPa, a tensile strength of 530MPa , an elongation A of 31%, a -60°C core impact energy average of ≤80J, and a CEV of 0.38; using the same equipment as in Examples 1 and 2, after automatic welding with a line input of 30kJ / cm, the tensile strength at the welded joint was 522 MPa, the core impact energy at -60°C in the heat-affected zone was ≤30J, indicating poor impact toughness, and the fatigue limit stress at the welded joint under a stress ratio of 0.5 and 5×10 7< cycles was approximately 260MPa, which cannot meet the requirements for high heat input welding.

[0060] The upper and lower limits of the process parameters (such as rolling deformation, holding time, etc.) as well as the interval values of the present invention, can all achieve this method, and examples are not listed one by one here.

[0061] Content not detailed in the present invention can be implemented using conventional technical knowledge in the field.

[0062] From the above description, it can be seen that the embodiments of the present invention achieve the following technical effects: The heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power and manufacturing method therefor, innovates in chemical composition design, slab cooling process, and rolling process, mainly including the following: 1) low-C high-Mn and Nb+V+Ti composite microalloying is used to form submicron-scale precipitates such as Ti(C, N), V(C, N) so as to significantly inhibit the growth of austenite grains and provide a microstructural foundation for subsequent rolling; the Cottrell and Snoek atmospheres formed by the composite nano-carbides Nb\Ti(C, N) generated during the finish rolling stage can markedly hinder dislocation movement and pin grain boundaries, suppressing austenite grain growth, meanwhile, due to the addition of microalloying elements Nb, V and Ti, the upper limit of the non-recrystallization temperature is increased, so that the rolling process window is expanded and the probability of mixed grains during two-phase zone rolling is reduced, which benefits the enhancement of strength and toughness. 2) A slab three-cooling equipment quenching process is adopted to achieve shallow surface quenching of the slab, forming a uniform-thickness shell on the surface, enabling rapid slab cooling and defect-free slab surface preparation, followed by utilizing the slab's residual heat self-tempering effect to refine the surface grains of the cast slab. 3) Rough rolling employs a gradually increasing reduction rate mode, and finish rolling employs a gradually decreasing reduction rate mode, fully refining grains and ensuring rolling penetration effect, where MULPIC cooling of the intermediate slab before finish rolling can reduce the waiting time of the intermediate slab, while the normalizing effect can maximally preserve the dynamic recrystallization grain refinement effect from the rough rolling stage. 4) A normalizing rolling process is utilized to produce thick-gauge steel plates for wind power, achieving normalizing treatment of the steel plate during the rolling process, eliminating the offline normalizing step, resulting in a short process flow, low cost, strong production line adaptability, and broad prospects for promotion.

[0063] The above descriptions are merely preferred embodiments of the present invention and are not intended to limit the invention. For those skilled in the art, various modifications and changes can be made to the present invention. Any amendments, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Examples

example 1

[0048]The heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power of Example 1 had the following chemical composition: C: 0.13%, Si: 0.30%, Mn: 1.41%, P: 0.010%, S: 0.003%, Nb: 0.025%, V: 0.027%, Ti: 0.017%, Al: 0.023%, with the remainder being Fe and unavoidable impurities. The thickness of said steel plate was 80mm, the base metal of said steel plate had yield strength of 457MPa, tensile strength of 562MPa, elongation A of 43%, average -60°C core impact energy of 217J, and CEV of 0.37. After automated welding with a heat input of 30kJ / cm, the tensile strength at the welded joint was 552MPa, the -60°C core impact energy in the heat-affected zone was ≥120J, and the fatigue limit stress at the welded joint under conditions of a stress ratio of 0.5 and 5×10 7< cycles was 414MPa, fully meeting the requirements for high-heat input welding.

[0049]The manufacturing method for the above heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel...

example 2

[0052]The heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power of Example 2 had the following chemical composition: C: 0.14%, Si: 0.32%, Mn: 1.45%, P: 0.007%, S: 0.001%, Nb: 0.029%, V: 0.030%, Ti: 0.015%, Al: 0.025%, with the remainder being Fe and unavoidable impurities. The thickness of said steel plate was 90mm, the base metal of said steel plate had yield strength of 443MPa, tensile strength of 562MPa, elongation A of 40.2%, average -60°C core impact energy of 183J, and CEV of 0.39. After automated welding with a heat input of 30kJ / cm, the tensile strength at the welded joint was 552MPa, the -60°C core impact energy in the heat-affected zone was ≥120J, and the fatigue limit stress at the welded joint under conditions of a stress ratio of 0.5 and 5×10 7< cycles was ≥400MPa, fully meeting the requirements for high-heat input welding.

[0053]The manufacturing method for the above heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength st...

Claims

1. A heavy-gauge, fatigue-resistant, easy-to-weld, high-strength steel plate for wind power, wherein: the steel plate has the following chemical composition by mass percentage: C: 0.12%-0.15%, Si: 0.15%-0.35%, Mn: 1.30%-1.50%, P≤0.015% , S≤0.005%,Nb: 0.015%-0.030%, V: 0.015%-0.030%, Ti: 0.005%-0.020%, Al: 0.005%-0.030%, with the remainder being Fe and unavoidable impurities.

2. The heavy-gauge, fatigue-resistant, easy-to-weld, high-strength steel plate for wind power according to claim 1, wherein: the steel plate has a thickness of 70mm-90mm, the base metal of the steel plate has a yield strength of ≥420MPa, a tensile strength of ≥540MPa, A≥40%, a -60°C core impact energy of ≥200J, and a CEV of ≤0.41; and the steel plate is capable of achieving welding under a high-heat input condition of ≥30kJ / cm; after welding, the steel plate has a tensile strength of ≥540MPa at welded joint, a - 60°C core impact energy of ≥120J in heat-affected zone, and a fatigue limit stress of ≥400MPa at welded joint under conditions of stress ratio of 0.5 and 5×107 cycles.

3. A manufacturing method for the heavy-gauge, fatigue-resistant, easy-to-weld, and high-strength steel plate for wind power according to any one of claims 1-2, comprising the following steps: smelting, performed using a converter; refining, comprising LF refining and RH refining, yielding a thick slab with a thickness ≥300mm after RH refining; continuous casting, wherein the thick slab is cast using a continuous casting mold, and a billet after casting is subjected to slow cooling to obtain a continuous casting slab; heating, wherein the continuous casting slab is heated using a cold-charging method; and rolling, comprising rough rolling and finish rolling, wherein rough rolling is first performed, an intermediate slab is cooled after rough rolling via a MULPIC water cooling unit, then the slab is conveyed to a finishing mill for finish rolling, followed by straightening in a leveler to obtain a finished steel plate.

4. The manufacturing method according to claim 3, wherein: in the smelting step, the converter uses pull carbon once and single-slag process for smelting, with a final slag basicity R being controlled between 3.2-4.2; a red clean ladle with ladle temperature ≥800°C is employed, with a tapping time of ≥3 minutes, and high-sensitivity slag blocking is used during tapping, followed by deoxidization with aluminum-manganese-iron at 1.7kg / t-3.2kg / t steel; low-carbon low-phosphorus silicon-manganese, ferrosilicon, ferroniobium, and ferrovanadium are added in batches, and synthetic slag and pre-fused slag are added along a steel flow during tapping, with a ratio of the synthetic slag to the pre-fused slag of 2:1.

5. The manufacturing method according to claim 3, wherein: during the LF refining process, argon bottom blowing stirring is maintained throughout, aluminum granules and aluminum slag are used for deoxidization, and lime is added for slag formation, with a final slag basicity of ≥2.7; fine-tuning composition is performed with silicon-manganese, ferrosilicon, ferroniobium, and ferrovanadium alloys; a Ti composition is adjusted with Ti wire and ferrotitanium; a Al composition is adjusted with aluminum wire, and a LF refining treatment time is controlled to be ≥40min; and after LF refining is completed, RH refining is performed, with a RH refining time ≥45min, and after RH refining treatment, CaAl wire of 85m-160m is fed, then soft blowing is performed for over 9 minutes, obtaining a thick slab after RH refining treatment, with a thickness of the thick slab ≥300mm; and preferably, the thickness of the thick slab is 300mm.

6. The manufacturing method according to claim 3, wherein in the continuous casting step: a continuous caster casting speed is controlled at 0.8m / min-1.1m / min, peritectic steel mold powder is used, a mold oscillation mode is non-sinusoidal oscillation mode, secondary cooling water and dynamic soft reduction are controlled according to peritectic steel, after being flame-cut and divided, the thick slab enters a third cooling machine for water cooling, achieving shallow surface quenching of the slab, with an upper and lower water flow difference being controlled to 15%~30% during quenching, and a surface temperature of the thick slab is controlled to be ≤600°C, and surface cooling water is blown off after γ-α transformation is completed on the surface; the thick slab undergoes self-tempering using residual heat, with a self-tempering time of ≥120min, and after self-tempering is completed, the slab is placed in a pit for slow cooling, with a slow cooling time not less than 56 hours.

7. The manufacturing method according to claim 3, wherein in the heating step: a slab charging temperature is ≤350°C, a soaking zone temperature of a heating furnace is controlled at 1180°C-1260°C, and a discharging temperature is 1170°C-1250°C, a heating rate is 9min / cm-11.5min / cm; and preferably, the soaking zone temperature of the heating furnace is 1250°C, the discharging temperature is 1200°C, and the heating rate is 10min / cm.

8. The manufacturing method according to claim 3, wherein in the rolling step: rough rolling adopts a high reduction mode, and the rough rolling stage is completed using either a 4+1 pass or 6+1 pass rolling modes based on a target steel plate thickness, where the +1 pass is a dummy pass; a rolling pass reduction rate is controlled to increase progressively, with a first pass reduction rate ≥6%, and in both the 4+1 pass and 6+1 pass rolling modes, the reduction rate of a final pass is ≥20%, with the pass reduction rate increasing progressively by 3% to 8%.

9. The manufacturing method according to claim 8, wherein: when a 90mm steel plat is produced using a 300mm-thick slab, 4+1 pass rough rolling is adopted, with the first pass reduction rate of 7%, the 4th pass reduction rate of 27.5%, and progressive increments of 5%, 7%, and 8.5% respectively.

10. The manufacturing method according to claim 3, wherein in the rolling step: finish rolling adopts a normalizing rolling mode, and 6+1 pass finish rolling is adopted, where the +1 pass is a dummy pass, and the reduction rate decreases progressively; when the finished thickness is 60mm-80mm, the first pass reduction rate is ≥12%, when the finished thickness is 80mm-90mm, the first pass reduction rate is ≥14%, with the reduction rate decreasing pass by pass by 0.5% to 4%; and preferably, when producing a 90mm steel plate using a 300mm-thick slab, a 6+1 pass finish rolling is adopted, with the first pass reduction rate of 16.5%, the reduction rate decreasing pass by pass by 1.0% to 3.5%, and the reduction rate at the 6th pass being 5.8%.

Images