High-purity steel for wind power main shaft bearing as well as preparation method and application of high-purity steel

Abstract

The invention relates to the technical field of metallurgical steel, and discloses high-purity steel for a wind power main shaft bearing and a preparation method and application thereof.The preparation method comprises the steps that molten iron and scrap steel are mixed according to the preset molten iron hot charging ratio and then smelted into molten steel in an electric furnace, and aluminum blocks, silicon-manganese alloy, ferromanganese, high-carbon ferrochrome, a carburant and slag are sequentially added during tapping; aluminum wires, carbon powder and silicon carbide are sequentially added for deoxidation, and foaming white slag is made through a CaO-SiO2-Al2O3 ternary slag system; soft blowing: adding an aluminum wire after vacuum breaking, and adding a silicon-calcium wire to carry out inclusion modification treatment; and the cast steel is crystallized and solidified through electric pulses, and a continuous casting billet is obtained. The inclusions in the steel prepared by the method disclosed by the invention are as follows: B fineness is less than or equal to 1.0 grade, B roughness is less than or equal to 0.5, D fineness is less than or equal to 1.0 grade, D roughness is less than or equal to 0.5 grade, DS is less than or equal to 1.0 grade, C-type inclusions are 0 grade, and the purity of the steel is ensured to meet the requirements of the steel for the wind power main shaft bearing.

Description

Technical Field

[0001] The present invention relates to the technical field of metallurgical steel materials, and in particular to a high-purity steel for a wind turbine main shaft bearing, and a preparation method and application thereof. Background Art

[0002] Wind turbine main shaft bearings are key components of wind turbine generators, supporting the impeller and main shaft in the wind turbine to ensure its normal operation. Due to the harsh operating environment and complex operating conditions of wind turbines, the service life of wind turbines is required to be 25 years. Therefore, the requirements for the materials of wind turbine parts are relatively high, especially the requirements for the raw materials of wind turbine main shaft bearings. The flaw detection of the wind turbine main shaft bearing raceway area must meet the requirements that there must be no flat-bottom hole equivalent defects exceeding φ0.5, and the requirements for non-metallic inclusions are particularly high, B fine ≤1.0 level, B coarse ≤0.5 level, D fine ≤1.0 level, D coarse ≤0.5 level, DS ≤1.0 level, and C inclusions are level 0. At present, the steel for wind turbine main shaft bearings is mainly produced by electroslag remelting steel. With the cost reduction of the wind power industry, the industry urgently needs a more cost-effective raw material manufacturing method.

[0003] For example, the Chinese patent with application number CN201610084238.6 discloses a smelting process for steel for wind turbine main shaft and steel for wind turbine main shaft, including arc furnace dissolution and impurity removal process, ladle refining furnace refining process, vacuum furnace impurity removal process and casting annealing slow cooling process. The smelting process steps of steel for wind turbine main shaft are simple, the steel structure is more uniform, fine and dense, and the comprehensive performance of steel is excellent; it also discloses a steel for wind turbine main shaft made by the above smelting process, the fluctuation range of element composition of the steel for wind turbine main shaft is narrow, which is conducive to simplifying the subsequent processing of steel ingots, and the mechanical properties of steel are more stable. However, the above technical scheme only regulates the performance of steel by the composition and content of molten steel, and it is still difficult to reduce and control the generation of inclusions in the preparation process, which will affect the purity of the prepared steel.

[0004] Currently, no effective solution has been proposed for the problems in the related technologies. Summary of the invention

[0005] In view of the problems in the related technology, the present invention proposes a high-purity steel for a wind turbine main shaft bearing and a preparation method and application thereof, so as to overcome the above-mentioned technical problems existing in the existing related technology.

[0006] To this end, the specific technical solution adopted by the present invention is as follows:

[0007] According to one aspect of the present invention, a method for preparing high-purity steel for a wind turbine main shaft bearing is provided, comprising the following steps:

[0008] S1. Smelting: According to the preset hot-charging ratio of molten iron, molten iron and scrap steel are mixed and smelted into molten steel in an electric furnace, and aluminum blocks, silicon-manganese alloy, ferromanganese, high-carbon ferrochrome, carburizer and slag are added in sequence when tapping the steel;

[0009] S2, LF refining: the smelted steel ladle is hoisted to the LF refining furnace, aluminum wire, carbon powder and silicon carbide are added in sequence for deoxidation, and the CaO-SiO2-Al2O3≤ element slag system is used to make foamed white slag to obtain refined molten steel;

[0010] S3, VD vacuum degassing: soft blowing for a preset time at a preset vacuum degree, and adding aluminum wire after breaking the air, adding silicon calcium wire to perform inclusion modification treatment to obtain casting molten steel;

[0011] S4. Continuous casting: The molten steel is crystallized and solidified by electric pulses to obtain a continuous casting billet.

[0012] In the present invention, the smelting step realizes the preliminary control of the composition of the molten steel, the preliminary deoxidation and the formation of a protective slag layer by sequentially adding aluminum blocks, silicon-manganese alloy, ferromanganese, high-carbon ferrochrome, a carburizer and slag, wherein the aluminum blocks are preliminarily deoxidized, the silicon-manganese alloy and ferromanganese adjust the silicon-manganese composition, the high-carbon ferrochrome and the carburizer adjust the chromium and carbon contents respectively, and the slag forms a protective slag layer to reduce the secondary oxidation of the molten steel; the LF refining step performs multi-stage deep deoxidation by adding aluminum wire, carbon powder and silicon carbide, and utilizes the CaO-SiO2-Al2O3 ternary slag system The foamed white slag is formed, which realizes deep deoxidation and removal of inclusions. The slag / steel interface area is increased by slag adjustment in the middle stage of refining, which effectively absorbs and removes inclusions. The VD vacuum degassing step is under high vacuum and soft blowing stirring conditions. This step promotes the escape of dissolved gases (such as hydrogen and nitrogen) and the floating of inclusions. After breaking the air, aluminum wire is added to adjust the Al content, and the chain Al2O3 inclusions are converted into spherical CaAlO inclusions by adding silicon-calcium wire, thereby realizing gas removal, further deoxidation and optimization of inclusion morphology.

[0013] Preferably, the preset molten iron hot charging ratio is determined according to a multi-objective optimization algorithm in combination with smelting parameters of molten iron and scrap steel, comprising the following steps:

[0014] S11. Obtain historical smelting data and determine key features that affect the hot charging ratio, wherein the key features include the composition and temperature of molten iron, the composition of scrap steel, preheating temperature and addition amount;

[0015] S12, minimizing energy consumption and maximizing production efficiency as optimization goals, and constructing a multi-objective function based on the optimization goals;

[0016] The expression of energy consumption function is:

[0017] E=a1·T iron +a2·Tscrap +a3·W scrap +a4·R hot_metal +b

[0018] The expression of production efficiency function is:

[0019] P=C1·C iron +c2·C scrap +c3·W xcrap+ c4·R hot_metal +d

[0020] The expression of the multi-objective function is:

[0021] min(w1·E-w2·P)

[0022] Where, E represents the energy consumption function, P represents the production efficiency function, a1 represents the influence coefficient of molten iron temperature on energy consumption, a2 represents the influence coefficient of scrap steel preheating temperature on energy consumption, a3 represents the influence coefficient of scrap steel addition on energy consumption, a4 represents the influence coefficient of molten iron hot charging ratio on energy consumption, b represents the bias constant of the energy consumption function, c1 represents the influence coefficient of molten iron composition on production efficiency, c2 represents the influence coefficient of scrap steel composition on production efficiency, c3 represents the influence coefficient of scrap steel addition on production efficiency, c4 represents the influence coefficient of molten iron hot charging ratio on production efficiency, d represents the bias constant of the production efficiency function, w1 represents the weight of energy consumption, w2 represents the weight of production efficiency, C represents the bias constant of the production efficiency function, iron Indicates the composition of molten iron, T iron Indicates the temperature of molten iron, C scrap Indicates the scrap steel composition, T scrap Indicates the scrap preheating temperature, W scrap Indicates the amount of scrap steel added, R hot_metal Indicates the hot iron charging ratio;

[0023] S13, taking the key features as input variables, building a hot charging ratio optimization model based on the multi-objective function and the input variables, and taking the range threshold of the hot charging ratio as a constraint condition;

[0024] The expression of the hot charging ratio optimization model is:

[0025]

[0026] Subject to R min ≤R hot_metal ≤R max

[0027] In the formula, X represents the set of input variables, R min , R max They represent the minimum and maximum values ​​of the hot-charging ratio of molten iron respectively;

[0028] S14, based on the multi-objective optimization algorithm, solving the hot charging ratio optimization model to obtain the optimal hot charging ratio of molten iron that meets the constraint conditions, specifically comprising the following steps:

[0029] S141, setting the population size, number of iterations, crossover and mutation probabilities, and randomly generating a preset number of initial solutions to form an initial population;

[0030] S142, evaluate each individual in the initial population, calculate its objective function value and constraint conditions, and select excellent individuals for crossover and mutation based on the evaluation results to generate a new population;

[0031] S143. Determine whether the preset number of iterations is met. If not, re-evaluate each individual in the initial population. If so, select a solution in the Pareto optimal solution set as the optimal molten iron hot charging ratio based on production demand.

[0032] Preferably, in step S1, hot charging technology of molten iron is used for smelting in the electric furnace; the tapping end point includes: the end point carbon is controlled at 0.15-0.25%, P≤0.010%, the end point oxygen of the electric furnace is ≤200ppm, and the tapping temperature is ≥1610°C.

[0033] By controlling the final carbon content at a relatively high level of 0.15-0.25%, the reducing effect of carbon is used to effectively inhibit the activity of oxygen in the molten steel and significantly reduce the formation of oxide inclusions; the final oxygen content of the electric furnace is controlled at ≤200ppm, which further improves the purity of the molten steel and creates favorable conditions for subsequent refining; stable control of the final carbon and oxygen content of steelmaking improves the stability of the entire production process and the consistency of product quality; high iron water hot charging ratio (≥79%) and high steelmaking temperature (≥1610℃) not only achieve energy conservation and emission reduction, but also improve production efficiency; low-oxygen and low-phosphorus (P≤0.010%) molten steel creates favorable conditions for subsequent processes, making deep purification and composition adjustment more efficient.

[0034] Preferably, the step of sequentially adding aluminum blocks, silicon-manganese alloy, ferromanganese, high carbon ferrochrome, carburizer and slag during steel tapping comprises: when the electric furnace is tapped to 1 / 4-1 / 3, adding aluminum blocks for pre-deoxidation, then adding silicon-manganese alloy, ferromanganese, high carbon ferrochrome, carburizer, and finally adding top slag, and the above alloys and slag are added before the steel is tapped to 3 / 4; wherein the amount of aluminum blocks added is 1.0-1.3 kg / ton of steel, the amount of top slag added is 8-1 kg / ton of steel; the silicon-manganese alloy is FeMn 68 Si 18 , ferromanganese is FeMn 78 C 2.0 , high carbon ferrochrome is FeCr 67 C 10Ti3, Ti content in high carbon ferrochrome is ≤0.03%; the recarburizer is FC95.

[0035] On the one hand, in order to prevent cold steel from being generated at the bottom of the ladle during the steel-making process, which affects the refining effect and the ladle from opening automatically when the continuous casting starts, and to prevent easily oxidized alloys such as silicon manganese from being oxidized under high oxygen potential to generate SiMnO-type low-melting-point inclusions, the timing, rhythm and sequence of charging during electric furnace steel-making are specified; on the other hand, in order to slag and deoxidize as early as possible, Al precipitation is added during the steel-making process of the electric furnace for deoxidation and top slag is formed. In order to reduce TiC and TiN inclusions brought by Ti in the alloy, low titanium alloy (Ti≤0.030%) is used.

[0036] Preferably, in step S2, aluminum wire is fed once according to the aluminum content in the molten steel, and the aluminum content in the steel during the refining process is 0.02-0.04wt%; the amount of carbon powder added is 0.4-0.5Kg / ton of steel, the amount of silicon carbide added is ≤2.0Kg / ton of steel, the total content of FeO and MnO in the refining slag is ≤1.0wt%, and the Si content in silicon carbide is 70; the slag basicity is controlled at 4-6 in the early stage of refining, and 1Kg / ton of wollastonite is added in the middle stage of refining to adjust the slag, and the slag basicity is controlled to 2-4. Argon stirring is used throughout the refining process to ensure that the inclusions are fully floated, and the reducing atmosphere is maintained throughout the smelting process to prevent secondary oxidation of the molten steel; the Al content in the refined steel is controlled between 0.015-0.025% to reduce the loss of Al in the VD process.

[0037] In order to ensure the effect of refining and removing inclusions, the CaO-SiO2-Al2O3 ternary slag system is used. In the early stage, high-basicity slag of 4-6 is used to remove sulfur in steel, and the sulfur in molten steel reaches below 0.005%. The lower the sulfur content in steel, the lower the sulfur segregation to form sulfides when the continuous casting molten steel solidifies. In order to ensure rapid deoxidation and remove oxidized inclusions in steel, the Al content in the steel during the refining process is controlled at 0.02-0.04%, and Al is added in place at one time when entering the station. On the one hand, it ensures that the deoxidation product is formed as soon as possible and has sufficient time to float to the slag. On the other hand, the Al content in the molten steel is controlled not to exceed 0.04%, reducing the steel slag reaction in the VD process. The Al in the steel reacts with the oxide in the slag to produce Al2O3 inclusions. In order to reduce the formation of inclusions in steel, precipitation deoxidation is no longer used in the whole refining process, but carbon powder and silicon carbide are used for slag surface deoxidation, and FeO+MnO in the refining slag is ≤1.0% to ensure sufficient deoxidation; the refining process effectively absorbs inclusions in the steel by making foamed white slag; 1Kg of wollastonite / ton of steel is used to adjust the slag in the middle of refining, and the slag basicity is controlled to 2-4 to improve the fluidity of the refining slag and the adsorption effect on inclusions. In order to ensure the basicity of the slag and control the content of SiO2 in the slag, the amount of silicon carbide does not exceed 2.0Kg / ton.

[0038] Preferably, in step S3, the amount of silicon-calcium wire added is 0.08-0.2 kg / ton of steel, the Ca content in the silicon-calcium wire is 28%, the Si content is 60%, and the Al2O3 chain inclusions are transformed into CaAlO spherical inclusions through inclusion modification treatment, and the Ca:Al value in the CaAlO spherical inclusions is less than 1. VD vacuum, while ensuring effective dehydrogenation effect, minimizes argon stirring and high vacuum holding time, and the high vacuum holding time is controlled at 12-20 minutes to reduce slag mixing and reduce inclusions in steel.

[0039] By precisely controlling the amount of silicon-calcium wire added (0.08-0.2Kg / ton of steel), the morphology and composition of inclusions are finely controlled, and Al2O3 chain inclusions are transformed into CaAlO spherical inclusions, which not only improves the morphology of inclusions, but also optimizes their impact on steel properties; ensuring that the Ca:Al value in the spherical inclusions after deformation is less than 1, preventing the formation of low-melting-point high-calcium calcium-aluminate inclusions.

[0040] Preferably, in step S4, the continuous casting process adopts long water inlet argon protection, integral submerged water inlet, and the tundish adopts special covering agent and crystallizer protective slag to achieve protective casting, the superheat is controlled at 20-30°C, the pulling speed is 0.25-0.40m / min, and the ratio of CaO / Al2O3 of the tundish covering agent is 1.2-1.8.

[0041] According to another aspect of the present invention, a high-purity steel for a wind turbine main shaft bearing is provided. The high-purity steel for a wind turbine main shaft bearing is composed of the following raw materials in percentage by mass:

[0042] C: 0.44-0.51%, Si: 0.20-0.40%, Mn: 0.70-0.90%, P≤0.015%, S≤0.005%, Cr: 1.20-1.40%, Ni: 0.40-0.70%, Mo: 0.30-0.40%, Cu≤0.20%, Al: 0.020-0.040%, V: 0.05-0.10%, Ti≤0.0030%, Ca≤0.0010%, As≤0.010%, Pb≤0.0020%, Sn≤0.0050%, Sb≤0.0030%, Bi≤0.0030%, O≤0.0010%, H≤0.00015%, the rest are Fe and unavoidable impurities.

[0043] Specifically, C is an important alloying element in steel, which enhances the strength and hardness of steel by forming carbides and martensite structures; Si, as a deoxidizer, improves the yield strength of steel and improves high-temperature performance; Mn can refine the grains and improve the solid solution strengthening effect of steel; Cr forms stable carbides, enhances the corrosion resistance and high-temperature strength of steel; Ni can refine the grains and improve the impact resistance of steel; Mo forms stable carbides, inhibits tempering softening, and improves the high-temperature strength of steel; V forms fine carbides, hinders grain growth, and improves the fatigue resistance of steel; Al is a strong deoxidizer that can effectively remove oxygen from steel; low oxygen content reduces oxide inclusions, and low hydrogen content avoids hydrogen embrittlement.

[0044] According to another aspect of the present invention, there is provided an application of the above-mentioned high-purity steel for wind turbine main shaft bearings in wind power generation load-bearing components or wind turbine main shafts.

[0045] The beneficial effects of the present invention are:

[0046] (1) The present invention uses high-quality molten iron as raw material, removes P and inclusions and harmful elements through electric furnace smelting, and controls the carbon, oxygen and P of the steel; uses special refining slag for refining outside the ladle furnace, and performs slag adjustment treatment in the middle stage of refining to effectively remove inclusions in the molten steel; VD vacuum degassing and hydrogen removal, and the whole process of casting and continuous casting round billet production is protected to obtain high-purity steel; the inclusions in the steel reach B fine ≤ 1.0 level, B coarse ≤ 0.5, D fine ≤ 1.0 level, D coarse ≤ 0.5 level, DS ≤ 1.0 level, and C inclusions are 0 level, ensuring that the purity of the steel meets the requirements for wind turbine main shaft bearing steel.

[0047] (2) The present invention can determine the optimal molten iron hot charging ratio by combining the smelting parameters of molten iron and scrap steel through a multi-objective optimization algorithm, thereby achieving precise control of the molten iron hot charging ratio, reducing energy consumption, lowering production costs, and reducing environmental pollution. The optimized hot charging ratio helps to increase the smelting speed and shorten the production cycle, thereby improving the overall production efficiency and effectively balancing cost control, smelting efficiency and steel liquid purity.

[0048] (3) The present invention adopts a precisely controlled weak calcium treatment process in the VD vacuum degassing stage to optimize the morphology and composition of inclusions, transform Al2O3 chain inclusions into CaAlO spherical inclusions, and effectively prevent the formation of low-melting-point high-calcium calcium aluminate inclusions by controlling the Ca:Al ratio to be less than 1, thereby significantly improving the mechanical properties, fatigue strength and high-temperature performance of the steel, and providing higher-quality and more reliable steel for high-demand components such as wind turbine main shaft bearings. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0050] Figure 1 The present invention is a flowchart of a method for preparing high-purity steel for a wind turbine main shaft bearing according to an embodiment of the present invention.

[0051] Figure 2 This is a low-magnification picture of the round billet prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0052] To further illustrate each embodiment, the present invention provides drawings, which are part of the disclosure of the present invention and are mainly used to illustrate the embodiments and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these contents, ordinary technicians in the field should be able to understand other possible implementations and advantages of the present invention. The components in the figures are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0053] According to an embodiment of the present invention, a high-purity steel for a wind turbine main shaft bearing and a preparation method and application thereof are provided.

[0054] Example 1

[0055] A high-purity steel for a wind turbine main shaft bearing, the high-purity steel for a wind turbine main shaft bearing is composed of the following raw materials in percentage by mass:

[0056] C: 0.44%, Si: 0.22%, Mn: 0.72%, P: 0.009%, S: 0.002%, Cr: 1.22%, Ni: 0.42%, Mo: 0.31%, Cu: 0.02%, Al: 0.028%, V: 0.06%, Ti: 0.0019%, Ca: 0.0004%, As: 0.007%, Pb: 0.0012%, Sn: 0.0015%, Sb: 0.0010%, Bi: 0.0009%, O: 0.0007%, H: 0.00009%, and the rest are Fe and unavoidable impurities.

[0057] like Figure 1 As shown, the method for preparing high-purity steel for wind turbine main shaft bearings comprises the following steps:

[0058] S1. Smelting: According to the preset hot-charging ratio of molten iron, molten iron and scrap steel are mixed and smelted into molten steel (about 100 tons) in an electric furnace. The electric furnace adopts hot-charging technology of molten iron, and the preset hot-charging ratio of molten iron is 83%. The carbon of EAF steel tapping end point is 0.15%, P: 0.010%, the oxygen of electric furnace end point is 153ppm, the tapping temperature is 1619℃, and eccentric furnace bottom is used for tapping to prevent slag from falling during tapping. When the electric steel is tapped, aluminum blocks are added for pre-deoxidation when 1 / 4-1 / 3 of the steel is tapped from the electric furnace. The amount of aluminum blocks added is 1.2Kg per ton of steel, and the amount of aluminum blocks added is 120Kg. After the aluminum blocks are added, silicon manganese alloy (FeMn 68 Si 18 ) 78 C 2.0 ), high carbon ferrochrome (FeCr 67 C 10 Ti3, Ti≤0.030%), carburizer, and finally add top slag. 9.12Kg of top slag is added per ton of steel, and a total of 912Kg is added. The above alloys and slag are guaranteed to be added before 3 / 4 of the steel is tapped.

[0059] S2, LF refining: refining outside the furnace adopts double-permeable brick ladle smelting. After the ladle slag is slaged, the Al wire is fed once according to the Al content in the steel. The Al content in the LF refining process is controlled at 0.020-0.040wt%. Carbon powder and silicon carbide are used for deoxidation in other smelting processes. The amount of silicon carbide is 1.8Kg / ton, and the FeO+MnO in the refining slag is 0.46% to ensure sufficient deoxidation; the refining process effectively adsorbs inclusions in the steel by making foamed white slag, and adopts CaO-SiO2-Al2O3 ternary slag system. The slag basicity is controlled at 4.9 in the early stage of refining. In the middle stage of refining, 1.0Kg / ton of wollastonite (a total of 100Kg) is used to adjust the slag, and the slag basicity is controlled to 2.7; the fluidity of the refining slag and the adsorption effect on inclusions. Argon gas stirring is used throughout the refining process to ensure that the inclusions are fully floated, and the reducing atmosphere is maintained throughout the process to prevent secondary oxidation of the molten steel. The Al content in the refined steel is 0.023%.

[0060] S3, VD vacuum degassing: the ultimate vacuum degree is 35Pa, and the ultimate vacuum holding time is 21min. Vacuum degree ≤67Pa soft blowing for 4min, feed Al wire once after breaking the air, and adjust the Al content in the steel to the target value. After feeding Al wire, 3min interval, weak calcium treatment is carried out, and 0.1Kg silicon calcium wire is fed per ton of steel for inclusion modification treatment, using sulfides and oxides in steel to effectively pass through modification, float and remove during the soft blowing process, soft blowing for 22min after VD.

[0061] S4. Continuous casting: The continuous casting process adopts long water inlet argon protection, integral submerged water inlet, special covering agent and crystallizer protective slag measures in the tundish to achieve protective casting, control the superheat at 23°C, the pulling speed at 0.39m / min, the ratio of CaO / Al2O3 in the tundish covering agent is 1.35, and continuous casting is carried out into continuous casting round billets.

[0062] Example 2

[0063] A high-purity steel for a wind turbine main shaft bearing, the high-purity steel for a wind turbine main shaft bearing is composed of the following raw materials in percentage by mass:

[0064] C: 0.48%, Si: 0.28%, Mn: 0.80%, P: 0.007%, S: 0.003%, Cr: 1.31%, Ni: 0.67%, Mo: 0.40%, Cu: 0.03%, Al: 0.025%, V: 0.07%, Ti: 0.0017%, Ca: 0.0005%, As: 0.006%, Pb: 0.0011%, Sn: 0.0025%, Sb: 0.0014%, Bi: 0.0008%, O: 0.0008%, H: 0.0001%, and the rest are Fe and unavoidable impurities.

[0065] The method for preparing high-purity steel for wind turbine main shaft bearings comprises the following steps:

[0066] S1. Smelting: According to the preset hot-charging ratio of molten iron, molten iron and scrap steel are mixed and smelted into molten steel (about 100 tons) in an electric furnace. The electric furnace adopts hot-charging technology of molten iron, and the preset hot-charging ratio of molten iron is 80%. The carbon of EAF steel tapping end point is 0.20%, P: 0.010%, the oxygen of electric furnace end point is 135ppm, the tapping temperature is 1625℃, and eccentric furnace bottom is used for tapping to prevent slag from falling during tapping. When the electric steel is tapped, aluminum blocks are added for pre-deoxidation when 1 / 4-1 / 3 of the steel is tapped from the electric furnace. The amount of aluminum blocks added is 1.1Kg per ton of steel, and the amount of aluminum blocks added is 110Kg. After the aluminum blocks are added, silicon manganese alloy (FeMn 68 Si 18 ) 78 C 2.0 ), high carbon ferrochrome (FeCr 67 C 10 Ti3, Ti≤0.030%), carburizer, and finally add top slag. 9.12Kg of top slag is added per ton of steel, and a total of 912Kg is added. The above alloys and slag are guaranteed to be added before 3 / 4 of the steel is tapped.

[0067] S2, LF refining: refining outside the furnace adopts double-permeable brick ladle smelting. After the ladle slag is slaged, the Al wire is fed once according to the Al content in the steel. The Al content in the LF refining process is controlled at 0.020-0.040wt%. Carbon powder and silicon carbide are used for deoxidation in other smelting processes. The amount of silicon carbide is 1.8Kg / ton, and the FeO+MnO in the refining slag is 0.50% to ensure sufficient deoxidation; the refining process effectively adsorbs inclusions in the steel by making foamed white slag, and adopts CaO-SiO2-Al2O3 ternary slag system. The slag basicity is controlled at 4.9 in the early stage of refining. In the middle stage of refining, 1.0Kg / ton of wollastonite (a total of 100Kg) is used to adjust the slag, and the slag basicity is controlled to 3.0; the fluidity of the refining slag and the adsorption effect on inclusions. Argon stirring is used throughout the refining process to ensure that the inclusions are fully floated, and the reducing atmosphere is maintained throughout the process to prevent secondary oxidation of the molten steel. The Al content in the refined steel is 0.016%.

[0068] S3, VD vacuum degassing: the ultimate vacuum degree is 42Pa, and the ultimate vacuum holding time is 18min. The vacuum degree is ≤67Pa and soft blowing is performed for 3min. After breaking the air, Al wire is fed once to adjust the Al content in the steel to the target value. After feeding Al wire, weak calcium treatment is performed at an interval of 3min. 0.1Kg silicon calcium wire is fed per ton of steel for inclusion modification treatment. The sulfides and oxides in the steel are effectively modified and floated up and removed during the soft blowing process. The soft blowing time after VD is 22min.

[0069] S4, continuous casting: the continuous casting process adopts long nozzle argon protection, integral immersion nozzle, special covering agent and mold protection slag measures for the tundish to achieve protective casting, control the superheat at 28 ° C, the pulling speed is 0.27m / min, the ratio of CaO / Al2O3 of the tundish covering agent is 1.2, and the continuous casting is carried out into a continuous casting round billet (such as Figure 2 shown).

[0070] Example 3

[0071] A high-purity steel for a wind turbine main shaft bearing, the high-purity steel for a wind turbine main shaft bearing is composed of the following raw materials in percentage by mass:

[0072] C: 0.47%, Si: 0.30%, Mn: 0.75%, P: 0.008%, S: 0.001%, Cr: 1.26%, Ni: 0.50%, Mo: 0.35%, Cu: 0.03%, Al: 0.027%, V: 0.07%, Ti: 0.0019%, Ca: 0.0003%, As: 0.006%, Pb: 0.0012%, Sn: 0.0022%, Sb: 0.00019%, Bi: 0.0011%, O: 0.0007%, H: 0.00011%, and the rest are Fe and unavoidable impurities.

[0073] The method for preparing high-purity steel for wind turbine main shaft bearings comprises the following steps:

[0074] S1. Smelting: According to the preset hot-charging ratio of molten iron, molten iron and scrap steel are mixed and smelted into molten steel (about 100 tons) in an electric furnace. The electric furnace adopts hot-charging technology of molten iron, and the preset hot-charging ratio of molten iron is 82%. The carbon of EAF steel tapping end point is 0.21%, P: 0.010%, the oxygen of electric furnace end point is 123ppm, the tapping temperature is 1627℃, and eccentric furnace bottom is used for tapping to prevent slag from falling during tapping. When the electric steel is tapped, aluminum blocks are added for pre-deoxidation when 1 / 4-1 / 3 of the steel is tapped from the electric furnace. The amount of aluminum blocks added is 1.1Kg per ton of steel, and the amount of aluminum blocks added is 110Kg. After the aluminum blocks are added, silicon manganese alloy (FeMn 68 Si 18 ) 78 C 2.0 ), high carbon ferrochrome (FeCr 67 C 10 Ti3, Ti≤0.030%), carburizer, and finally add top slag. 9.11Kg of top slag is added per ton of steel, and a total of 911Kg is added. The above alloys and slag are guaranteed to be added before 3 / 4 of the steel is tapped.

[0075] S2, LF refining: refining outside the furnace adopts double-permeable brick ladle smelting. After the ladle slag is slaged, the Al wire is fed once according to the Al content in the steel. The Al content in the LF refining process is controlled at 0.020-0.040wt%. Carbon powder and silicon carbide are used for deoxidation in other smelting processes. The amount of silicon carbide is 1.8Kg / ton, and the FeO+MnO in the refining slag is 0.46% to ensure sufficient deoxidation; the refining process effectively adsorbs inclusions in the steel by making foamed white slag, and adopts CaO-SiO2-Al2O3 ternary slag system. The slag basicity is controlled at 5.2 in the early stage of refining. In the middle stage of refining, 1.0Kg / ton of wollastonite (a total of 100Kg) is used to adjust the slag, and the slag basicity is controlled to 3.1; the fluidity of the refining slag and the adsorption effect on inclusions. Argon gas stirring is used throughout the refining process to ensure that the inclusions are fully floated, and the reducing atmosphere is maintained throughout the process to prevent secondary oxidation of the molten steel. The Al content in the refined steel is 0.021%.

[0076] S3, VD vacuum degassing: the ultimate vacuum degree is 47Pa, and the ultimate vacuum holding time is 21min. Vacuum degree ≤67Pa soft blowing for 3min, feed Al wire once after breaking the air, and adjust the Al content in the steel to the target value. After feeding Al wire, 3min interval, weak calcium treatment is carried out, and 0.1Kg silicon calcium wire is fed per ton of steel for inclusion modification treatment, using sulfides and oxides in steel to effectively pass through modification, float and remove during the soft blowing process, and the soft blowing time after VD is 22min.

[0077] S4. Continuous casting: The continuous casting process adopts long water inlet argon protection, integral submerged water inlet, special covering agent and crystallizer protective slag measures in the tundish to achieve protective casting, control the superheat at 25°C, the pulling speed at 0.27m / min, the ratio of CaO / Al2O3 in the tundish covering agent is 1.32, and continuous casting is carried out into continuous casting round billets.

[0078] Example 4

[0079] A high-purity steel for a wind turbine main shaft bearing, the high-purity steel for a wind turbine main shaft bearing is composed of the following raw materials in percentage by mass:

[0080] C: 0.50%, Si: 0.38%, Mn: 0.88%, P: 0.010%, S: 0.003%, Cr: 1.37%, Ni: 0.51%, Mo: 0.37%, Cu: 0.03%, Al: 0.027%, V: 0.09%, Ti: 0.0021%, Ca: 0.0003%, As: 0.010%, Pb: 0.0015%, Sn: 0.0010%, Sb: 0.0008%, Bi: 0.0011%, O: 0.0006%, H: 0.00007%, and the rest are Fe and unavoidable impurities.

[0081] The method for preparing high-purity steel for wind turbine main shaft bearings comprises the following steps:

[0082] S1. Smelting: According to the preset hot-charging ratio of molten iron, molten iron and scrap steel are mixed and smelted into molten steel (about 100 tons) in an electric furnace. The electric furnace adopts hot-charging technology of molten iron, and the preset hot-charging ratio of molten iron is 79%. The carbon of EAF steel tapping end point is 0.25%, P: 0.010%, the oxygen of electric furnace end point is 200ppm, the tapping temperature is 1660℃, and eccentric furnace bottom is used for tapping to prevent slag from falling during tapping. When the electric steel is tapped to 1 / 4-1 / 3, aluminum blocks are added for pre-deoxidation. The amount of aluminum blocks added is 1.3Kg per ton of steel, and the amount of aluminum blocks added is 130Kg. After the aluminum blocks are added, silicon manganese alloy (FeMn 68 Si 18 ) 78 C 2.0 ), high carbon ferrochrome (FeCr 67 C 10 Ti3, Ti≤0.030%), carburizer, and finally add top slag, 1.2Kg of top slag is added per ton of steel, and a total of 120Kg is added. The above alloys and slag are guaranteed to be added before 3 / 4 of the steel is tapped.

[0083] S2, LF refining: refining outside the furnace adopts double-permeable brick ladle smelting. After the ladle slag is slaged, the Al wire is fed once according to the Al content in the steel. The Al content in the LF refining process is controlled at 0.020-0.040wt%. Carbon powder and silicon carbide are used for deoxidation in other smelting processes. The amount of silicon carbide is 2.0Kg / ton, and the FeO+MnO in the refining slag is 1.0% to ensure sufficient deoxidation; the refining process effectively adsorbs inclusions in the steel by making foamed white slag, and adopts CaO-SiO2-Al2O3 ternary slag system. The slag basicity is controlled at 5 in the early stage of refining. In the middle stage of refining, 1.0Kg / ton of wollastonite (a total of 100Kg) is used to adjust the slag, and the slag basicity is controlled to 2; the fluidity of the refining slag and the adsorption effect on inclusions. Argon gas stirring is used throughout the refining process to ensure that the inclusions are fully floated, and the reducing atmosphere is maintained throughout the process to prevent secondary oxidation of the molten steel. The Al content in the refined steel is 0.025%.

[0084] S3, VD vacuum degassing: the ultimate vacuum degree is 50Pa, and the ultimate vacuum holding time is 12min. Vacuum degree ≤67Pa soft blowing for 4min, feed Al wire once after breaking the air, and adjust the Al content in the steel to the target value. After feeding Al wire, 3min interval, weak calcium treatment is carried out, and 0.08Kg silicon calcium wire is fed per ton of steel for inclusion modification treatment, using sulfides and oxides in steel to effectively pass through modification, float and remove during the soft blowing process, and the soft blowing time after VD is 40min.

[0085] S4. Continuous casting: The continuous casting process adopts long water inlet argon protection, integral submerged water inlet, special covering agent and crystallizer protective slag measures in the tundish to achieve protective casting, control the superheat at 30°C, the pulling speed at 0.25m / min, the ratio of CaO / Al2O3 in the tundish covering agent is 1.8, and continuous casting is carried out into continuous casting round billets.

[0086] Example 5

[0087] A method for determining an optimal molten iron hot charging ratio based on a multi-objective optimization algorithm combined with smelting parameters of molten iron and scrap steel comprises the following steps:

[0088] S11. Obtain historical smelting data and determine key features that affect the hot charging ratio, wherein the key features include the composition and temperature of molten iron, the composition of scrap steel, preheating temperature and addition amount;

[0089] Specifically, the smelting data includes:

[0090] 1) Molten iron data:

[0091] Composition: the main element content in molten iron, such as carbon (C), silicon (Si), sulfur (S), phosphorus (P), etc.

[0092] Temperature: The smelting temperature of molten iron, which has an important influence on the subsequent smelting process and hot charging ratio.

[0093] 2) Scrap data:

[0094] Composition: The content of various elements in scrap steel, including the above-mentioned molten iron component elements.

[0095] Preheating temperature: The preheating temperature of scrap steel before adding it to the smelting furnace, which affects the melting and smelting efficiency of the scrap steel.

[0096] Addition amount: The amount of scrap steel added, which is crucial to the hot charging ratio and composition control during the smelting process.

[0097] In addition, the smelting data in this embodiment may also include smelting time, energy consumption during the smelting process, quality data of the steel after smelting (such as mechanical properties, metallographic structure, etc.), production rate or output during the smelting process, operating status and performance indicators of the smelting equipment, etc.

[0098] These data usually need to be collected from production records, quality inspection reports, equipment maintenance logs, etc. By analyzing these data, the key features that affect the hot charging ratio can be identified and provide input for subsequent optimization models.

[0099] S12, minimizing energy consumption and maximizing production efficiency as optimization goals, and constructing a multi-objective function based on the optimization goals;

[0100] In this embodiment, the construction of energy consumption, production efficiency and multi-objective functions includes: firstly, recording C iron (molten iron composition), T iron (molten iron temperature), C scrap (Scrap Steel Composition), T scrap (Scrap preheating temperature), W scrap (amount of scrap steel added), R hot_metal The initial value of (hot iron charging ratio) and the corresponding energy consumption and production efficiency data can then be obtained by using linear or nonlinear regression methods to fit the relationship between variables and energy consumption and production efficiency to obtain mathematical expressions. Finally, the smelting thermodynamics and kinetics models are used to verify the rationality of the function through simulation calculations, and the parameters (i.e., a1, a2, a3, a4, b, c1, c2, c3, c4, d, w1, w2) are optimized to obtain expressions of energy consumption function, production efficiency function and multi-objective function.

[0101] The expression of energy consumption function is:

[0102] E=a1·T iron +a2·T scrap +a3·W scrap +a4·R hot_metal +b

[0103] The expression of production efficiency function is:

[0104] P=c1·C iron +c2·C scrap +c3·W scrap +C4·R hot_metal +d

[0105] The expression of the multi-objective function is:

[0106] min(w1·E-w2·P)

[0107] Where E represents the energy consumption function;

[0108] P represents the production efficiency function;

[0109] a1 represents the influence coefficient of molten iron temperature on energy consumption, which reflects the influence of molten iron temperature increasing by 1°C on energy consumption, and the value range is 0.8-1.5 (kWh / °C), and is preferably 1.2 in this embodiment;

[0110] a2 represents the influence coefficient of scrap steel preheating temperature on energy consumption, which reflects the influence of scrap steel preheating temperature increasing by 1°C on energy consumption, and the value range is 0.5-1.2 (kWh / °C), and is preferably 0.8 in this embodiment;

[0111] a2 represents the influence coefficient of the amount of scrap steel added on energy consumption, which reflects the influence of each increase of 1 kg of scrap steel added on energy consumption, and the value range is 0.05-0.2 (kWh / kg), and is preferably 0.1 in this embodiment;

[0112] a4 represents the influence coefficient of hot charging ratio of molten iron on energy consumption, which reflects the linear relationship between the change of hot charging ratio and energy consumption, and the value range is -0.2 to -0.1 (kWh / %), and in this embodiment, it is preferably -0.15;

[0113] b represents the bias constant of the energy consumption function, and its value range is 50 to 150 (kWh / t), and is preferably 100 in this embodiment;

[0114] c1 represents the influence coefficient of molten iron composition on production efficiency, which reflects the contribution of molten iron composition change to production efficiency, and the value range is 10-50 (t / unit composition change). "t / unit composition change" means the amount (ton) of production efficiency (output) change corresponding to each unit change of a certain composition (such as a 1% increase in carbon content). In this embodiment, it is preferably 30;

[0115] c2 represents the influence coefficient of scrap steel composition on production efficiency, which reflects the influence of scrap steel composition on production efficiency, and the value range is -20 to -5 (t / unit composition change), and in this embodiment, it is preferably -10;

[0116] c3 represents the coefficient of influence of the amount of scrap steel added on the production efficiency, which reflects the influence of each increase of 1 kg of scrap steel added on the production efficiency, and the value range is 0.01-0.05 (t / kg), and is preferably 0.03 in this embodiment;

[0117] c4 represents the influence coefficient of the hot charging ratio of molten iron on the production efficiency, which reflects the linear relationship between the hot charging ratio of molten iron and the production efficiency, and the value range is 0.1-0.5 (t / %), and is preferably 0.3 in this embodiment;

[0118] d represents the bias constant of the production efficiency function, and its value range is 10 to 50 (t / h), and is preferably 20 in this embodiment;

[0119] w1 represents the weight of energy consumption, which reflects the importance of energy consumption in the comprehensive goal, and has a value range of 0.4 to 0.6, and is preferably 0.5 in this embodiment;

[0120] w2 represents the weight of production efficiency, which reflects the importance of production efficiency in the comprehensive goal, and the value range is 0.4-0.6, and the preferred value in this embodiment is 0.5;

[0121] C iron Indicates the composition of molten iron;

[0122] T iron Indicates the temperature of molten iron;

[0123] C scrap Indicates the composition of scrap steel;

[0124] T scrap Indicates the scrap preheating temperature;

[0125] W scrap Indicates the amount of scrap steel added;

[0126] R hot_metal represents the hot charging ratio of molten iron. In this embodiment, the value of the hot charging ratio of molten iron is usually between 75% and 90%;

[0127] In addition, in this embodiment, the composition of molten iron and scrap steel is not a single value, but contains multiple components (such as carbon, silicon, sulfur, phosphorus and other elements). It is necessary to characterize these components and quantify them into usable numerical variables so as to be included in the calculation of the function. The following is a detailed description of the processing method and calculation method:

[0128] The composition of molten iron and scrap steel is a multi-dimensional vector, which can be quantified into a single value or weighted value for function calculation by the following method:

[0129] 1) Use key components as characteristic variables: Among the components of molten iron and scrap steel, select components that have a significant impact on production efficiency as representative variables (such as carbon, silicon, sulfur, phosphorus, etc.). Introduce each key component into the function separately, or weight them according to importance to form a comprehensive characteristic value.

[0130] For example:

[0131] Characteristic value of molten iron composition: C iron =k1·C C +k2·C si +k3·C S +k4·C P ;

[0132] Scrap steel composition characteristic value: C scrap =m1·C C +m2·C Si +m3·C S +m4·C P ;

[0133] In the formula, C C , C Si , C S , C P Respectively represent the mass fractions (%) of carbon, silicon, sulfur and phosphorus in molten iron;

[0134] k1, k2, k3, and k4 represent the influence coefficients of carbon, silicon, sulfur, and phosphorus in the molten iron composition, respectively, reflecting the degree of influence of each component on the target (carbon contributes greatly to the thermal enthalpy of molten iron and has a significant impact on production efficiency; silicon releases heat through oxidation reaction and has a certain contribution to thermal balance and efficiency; an increase in sulfur content will significantly reduce production efficiency and have a greater negative impact; an increase in phosphorus content will increase energy consumption, and the negative impact is small but cannot be ignored). In this embodiment, the values ​​of k1, k2, k3, and k4 are preferably 0.8, 0.5, -0.8, and -0.4, respectively;

[0135] m1, m2, m3, and m4 respectively represent the influence coefficients of carbon, silicon, sulfur, and phosphorus in the scrap steel composition (the contribution of carbon in scrap steel to production efficiency is limited, but it still needs to be taken into account; the silicon content contributes to the enthalpy balance in scrap steel to a certain extent, but is lower than the silicon in molten iron; the sulfur content in scrap steel is low, and its negative impact on production efficiency is smaller than the sulfur content in molten iron; the phosphorus content in scrap steel has a relatively small negative impact on smelting, which is mainly reflected in the adjustment of secondary smelting process). In this embodiment, the values ​​of m1, m2, m3, and m4 are 0.4, 0.3, -0.3, and -0.2, respectively.

[0136] 2) Use the weighted mass fraction method to calculate the total composition effect: For the composition of molten iron and scrap steel, their mass fractions can be directly weighted to quantify their combined impact:

[0137] Comprehensive composition of molten iron:

[0138]

[0139] Comprehensive composition value of scrap steel:

[0140]

[0141] In the formula, C iron，i represents the mass fraction of the i-th element in molten iron, C scrap，j represents the mass fraction of the jth element in the scrap steel, ω i represents the weight of the i-th element in the molten iron, ω j represents the weight of the jth element in the scrap steel;

[0142] S13, taking the key features as input variables, building a hot charging ratio optimization model based on the multi-objective function and the input variables, and taking the range threshold of the hot charging ratio as a constraint condition;

[0143] The expression of the hot charging ratio optimization model is:

[0144]

[0145] subjeCt to R min ≤R hot_metal ≤R max

[0146] In the formula, X represents the set of input variables, R min , R max They represent the minimum and maximum values ​​of the hot-charging ratio of molten iron respectively;

[0147] S14, based on the multi-objective optimization algorithm, solving the hot charging ratio optimization model to obtain the optimal hot charging ratio of molten iron that meets the constraint conditions, specifically comprising the following steps:

[0148] S141, setting the population size, number of iterations, crossover and mutation probabilities, and randomly generating a preset number of initial solutions to form an initial population;

[0149] S142, evaluate each individual in the initial population, calculate its objective function value and constraint conditions, and select excellent individuals for crossover and mutation based on the evaluation results to generate a new population;

[0150] In the process of optimizing the hot iron charging ratio based on the multi-objective optimization algorithm, each individual in the initial population represents a possible hot iron charging ratio configuration scheme. In order to gradually approach the optimal solution, it is necessary to evaluate these individuals and select individuals with excellent performance for crossover and mutation to generate a new population. This process is explained in detail below:

[0151] 1) Individual Assessment

[0152] Objective function calculation: Each individual consists of a set of input variables and heat loading ratio. The objective function value of the individual is calculated by substituting these inputs into the previously defined objective function. In this invention, we want to minimize energy consumption and maximize production efficiency.

[0153] Constraint check: In addition to the objective function value, it is also necessary to check whether the individual meets the constraints. Only those individuals who meet the constraints and perform well in the objective function can be considered "excellent individuals".

[0154] 2) Select outstanding individuals

[0155] After the evaluation, some selection mechanism is used to select outstanding individuals. Common selection methods are:

[0156] Roulette Wheel Selection: Select individuals with higher probability based on their fitness (objective function value).

[0157] Tournament Selection: Randomly select some individuals from the population and pick the best performing ones.

[0158] The selection of excellent individuals is to ensure the quality of the next generation of population, that is, to give better-performing solutions more opportunities to pass on their excellent genes in subsequent iterations.

[0159] 3) Crossover and Mutation

[0160] Crossover: The selected excellent individuals will be paired up for crossover operation to generate new individuals. Crossover operation usually simulates gene recombination in biological genetics, such as exchanging certain variable values ​​between individuals, so as to generate offspring that may be more excellent. Common crossover methods include:

[0161] Single-point crossover: swapping the variables of two individuals at a random point.

[0162] Multi-point crossover: variables are exchanged at multiple points.

[0163] Mutation: The mutation operation simulates random mutations in nature and introduces small-scale random changes in certain variables of individuals. This can prevent the algorithm from falling into a local optimal solution and increase the diversity of the population. A common mutation method is to randomly change a small range of values ​​of an input variable (such as molten iron temperature or scrap steel addition).

[0164] 4) Generate new population

[0165] After crossover and mutation, a new population is generated. The individuals in the new population may perform better than the previous population because they inherit the excellent characteristics of the excellent individuals of the previous generation and introduce new possibilities through mutation.

[0166] This process is usually carried out iteratively, and each new population generated goes through the same evaluation, selection, crossover and mutation steps as the previous one, constantly approaching the optimal solution.

[0167] S143. Determine whether the preset number of iterations is met. If not, re-evaluate each individual in the initial population. If so, select a solution in the Pareto optimal solution set as the optimal molten iron hot charging ratio based on production demand.

[0168] In addition, in the present invention, the method for determining the optimal molten iron hot charging ratio in Example 5 can be used to determine the molten iron hot charging ratio in the above-mentioned Examples 1-4.

[0169] Comparative Example 1

[0170] S1, smelting: molten iron and scrap steel are mixed and smelted into molten steel (about 100 tons, the composition of molten steel is the same as that of Example 1) in an electric furnace, wherein the electric furnace adopts molten iron hot charging technology, and the molten iron hot charging ratio is ≥70%. The EAF steel tapping control endpoint ensures that the endpoint carbon is controlled at 0.15%, P: 0.010%, the electric furnace endpoint oxygen is set at 153ppm, the steel tapping temperature is 1619℃, and an eccentric furnace bottom is used for steel tapping to prevent slag from falling during steel tapping. The electric steel is alloyed, and aluminum blocks are added for pre-deoxidation when the electric furnace taps 1 / 4-1 / 3 of the steel. 1.2Kg of aluminum blocks are added per ton of steel, and the amount of aluminum blocks added is 120Kg. After the steel is tapped and the aluminum blocks are added, silicon manganese alloy (FeMn 68 Si 18 ) 78 C 2.0 ), high carbon ferrochrome (FeCr 67 C 10 Ti3, Ti≤0.030%), carburizer, and finally add top slag. 9.12Kg of top slag is added per ton of steel, and a total of 912Kg is added. The above alloys and slag are guaranteed to be added before 3 / 4 of the steel is tapped.

[0171] S2, LF refining: Double-permeable brick ladle smelting is used for refining outside the furnace. After the ladle is slag-melted, the Al wire is fed once according to the Al content in the steel. The Al content in the LF refining process is controlled at 0.020-0.040wt%. Carbon powder and silicon carbide are used for deoxidation in other smelting processes. The amount of silicon carbide is 1.8Kg / ton, and the FeO+MnO in the refining slag is 0.46% to ensure sufficient deoxidation. Argon stirring is used throughout the refining process to ensure that the inclusions float fully, and the reducing atmosphere is maintained throughout the smelting process to prevent secondary oxidation of the molten steel. The Al content in the refined steel is 0.023%.

[0172] S3, VD vacuum degassing: the ultimate vacuum degree is 35Pa, and the ultimate vacuum holding time is 21min. Vacuum degree ≤67Pa soft blowing for 20min, feed Al wire once after breaking the air, and adjust the Al content in the steel to the target value. After feeding Al wire, 3min interval, weak calcium treatment is carried out, and 0.5Kg silicon calcium wire is fed per ton of steel for inclusion modification treatment, using sulfides and oxides in steel to effectively pass through modification, float and remove during the soft blowing process, soft blowing for 22min after VD.

[0173] S4. Continuous casting: The continuous casting process adopts long water inlet argon protection, integral submerged water inlet, special covering agent and crystallizer protective slag measures in the tundish to achieve protective casting, control the superheat at 23°C, the pulling speed at 0.39m / min, the ratio of CaO / Al2O3 in the tundish covering agent is 1.35, and the continuous casting billet is obtained.

[0174] Comparative Example 2

[0175] S1, smelting: molten iron and scrap steel are mixed and smelted into molten steel (about 100 tons, the composition of molten steel is the same as that of Example 1) in an electric furnace, wherein the electric furnace adopts hot charging technology of molten iron, and the hot charging ratio of molten iron is ≥70%. EAF steel tapping ensures that the final carbon is controlled at 0.15%, P: 0.010%, the final oxygen of the electric furnace is 153ppm, the tapping temperature is 1649℃, and eccentric furnace bottom steel tapping is adopted to prevent slag from falling during steel tapping. The electric steel is alloyed, and aluminum blocks are added for pre-deoxidation when the electric furnace tapping reaches 1 / 4-1 / 3. The amount of aluminum blocks added per ton of steel is 1.2Kg, and the amount of aluminum blocks added is 120Kg. After the aluminum blocks are added, silicon manganese alloy (FeMn 68 Si 18 ) 78 C 2.0 ), high carbon ferrochrome (FeCr 67 C 10 Ti3, Ti≤0.030%), carburizer, and finally add top slag. 9.12Kg of top slag is added per ton of steel, and a total of 912Kg is added. The above alloys and slag are guaranteed to be added before 3 / 4 of the steel is tapped.

[0176] S2, LF refining: refining outside the furnace adopts double-permeable brick ladle smelting. After the ladle slag is slaged, the Al wire is fed once according to the Al content in the steel. The Al content in the LF refining process is controlled at 0.020-0.040wt%. Carbon powder and silicon carbide are used for deoxidation in other smelting processes. The amount of silicon carbide is 1.8Kg / ton. The FeO+MnO in the refining slag is 0.46% to ensure sufficient deoxidation; the refining process effectively adsorbs the inclusions in the steel by making foamed white slag, and the CaO-SiO2-Al2O3 ternary slag system is used. The slag basicity is controlled at 3.9 in the early stage of refining. In the middle stage of refining, 1.0Kg / ton of wollastonite (a total of 100Kg) is used to adjust the slag, and the slag basicity is controlled to 3.7; the fluidity of the refining slag and the adsorption effect on inclusions. Argon stirring is used throughout the refining process to ensure that the inclusions are fully floated, and the reducing atmosphere is maintained throughout the process to prevent secondary oxidation of the molten steel. The Al content in the refined steel is 0.023%.

[0177] S3, VD vacuum degassing: The ultimate vacuum degree is 35Pa, and the ultimate vacuum holding time is 21min. Vacuum degree ≤ 67Pa soft blowing for 25min, after breaking the air, feed Al wire once to adjust the Al content in the steel to the target value. The whole process of vacuum degassing is stirred with argon gas, and soft blowing is carried out for 22min after VD to ensure that non-metallic inclusions are fully floated and removed during the soft blowing process.

[0178] S4. Continuous casting: The continuous casting process adopts long water inlet argon protection, integral submerged water inlet, special covering agent and crystallizer protective slag measures in the tundish to achieve protective casting, control the superheat at 23°C, the pulling speed at 0.39m / min, the ratio of CaO / Al2O3 in the tundish covering agent is 1.35, and the continuous casting billet is obtained.

[0179] Performance Testing

[0180] The continuous casting slabs prepared in the examples and comparative examples were sampled, and non-metallic inclusions were detected according to GB / T10561-2023 standard. According to the morphology and distribution of non-metallic inclusions, the most commonly observed inclusions were divided into Class A (sulfide), Class B (alumina), Class C (silicate), Class D (spherical oxide) and Class Ds (large-particle spherical oxide). Furthermore, the morphology and size of the inclusions were subdivided into fine and coarse categories, where fine refers to inclusions that are relatively small and large in number, and coarse refers to inclusions that are relatively coarse in morphology or small in number. The test results are shown in Table 1.

[0181] Table 1 Non-metallic inclusion detection

[0182]

[0183] It can be seen from the above test results that the steel purity of the continuous casting billet prepared by the present invention is within 0.5 level for B coarse, within 1.0 level for B fine, within 0.5 level for D coarse, within 1.0 level for D fine, within 1.0 level for Ds, without C-type inclusions. The purity of the high-purity steel produced by the process of the present invention can reach the purity of the electroslag remelting process, and the inclusions in the steel can meet the requirements of steel for wind turbine main shaft bearings.

[0184] In summary, with the aid of the above technical scheme of the present invention, the present invention selects high-quality molten iron as raw material, removes P and inclusions and harmful elements through electric furnace smelting, and controls the carbon, oxygen and P of the steel; uses special refining slag for refining outside the ladle furnace, and performs slag adjustment treatment in the middle stage of refining to effectively remove inclusions in the molten steel; VD vacuum degassing and hydrogen removal, and the whole process is protected to produce continuous casting round billets to obtain high-purity steel; the inclusions in the steel reach B fine ≤1.0 level, B coarse ≤0.5, D fine ≤1.0 level, D coarse ≤0.5 level, DS ≤1.0 level, and C-type inclusions are 0 level, ensuring that the purity of the steel meets the requirements for wind turbine main shaft bearing steel.

[0185] In addition, the present invention can determine the optimal molten iron hot charging ratio through a multi-objective optimization algorithm combined with the smelting parameters of molten iron and scrap steel, thereby achieving precise control of the molten iron hot charging ratio, reducing energy consumption, reducing production costs, and reducing environmental pollution. The optimized hot charging ratio helps to increase the smelting speed, shorten the production cycle, thereby improving the overall production efficiency, and effectively taking into account the balance between cost control, smelting efficiency and molten steel purity.

[0186] In addition, the present invention adopts a precisely controlled weak calcium treatment process in the VD vacuum degassing stage to optimize the morphology and composition of inclusions, transform Al2O2 chain inclusions into CaAlO spherical inclusions, and effectively prevent the formation of low-melting-point high-calcium aluminate inclusions by controlling the Ca:Al ratio to be less than 1, thereby significantly improving the mechanical properties, fatigue strength and high-temperature performance of the steel, and providing higher-quality and more reliable steel for high-demand components such as wind turbine main shaft bearings.

[0187] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing high-purity steel for wind turbine main shaft bearings, characterized in that: The following steps are involved: S1. Smelting: According to the preset hot-charging ratio of molten iron, molten iron and scrap steel are mixed and smelted into molten steel in an electric furnace, and aluminum blocks, silicon-manganese alloy, ferromanganese, high-carbon ferrochrome, carburizer and slag are added in sequence when tapping the steel; S2, LF refining: the smelted steel ladle is hoisted to the LF refining furnace, aluminum wire, carbon powder and silicon carbide are added in sequence for deoxidation, and the CaO-SiO2-Al2O3 ternary slag system is used to make foamed white slag to obtain refined molten steel; S3, VD vacuum degassing: soft blowing for a preset time at a preset vacuum degree, and adding aluminum wire after breaking the air, adding silicon calcium wire to perform inclusion modification treatment to obtain casting molten steel; S4. Continuous casting: The molten steel is crystallized and solidified by electric pulses to obtain a continuous casting billet.

2. The method for preparing high-purity steel for wind turbine main shaft bearing according to claim 1, characterized in that: The preset molten iron hot charging ratio is determined according to a multi-objective optimization algorithm combined with smelting parameters of molten iron and scrap steel, and includes the following steps: Obtain historical smelting data to determine the key features that affect the hot charging ratio, including the composition and temperature of the molten iron, the composition of the scrap steel, the preheating temperature and the amount of addition; Minimizing energy consumption and maximizing production efficiency are the optimization goals, and a multi-objective function is constructed based on the optimization goals; Taking key features as input variables, a hot charging ratio optimization model is constructed based on multi-objective functions and input variables, and the range threshold of the hot charging ratio is used as a constraint condition; Based on the multi-objective optimization algorithm, the hot charging ratio optimization model is solved to obtain the optimal molten iron hot charging ratio that meets the constraints.

3. The method for preparing high-purity steel for wind turbine main shaft bearing according to claim 2, characterized in that: Solving the hot charging ratio optimization model based on the multi-objective optimization algorithm to obtain the optimal hot charging ratio of molten iron that meets the constraint conditions includes the following steps: Set the population size, number of iterations, crossover and mutation probabilities, and randomly generate a preset number of initial solutions to form the initial population; Evaluate each individual in the initial population, calculate its objective function value and constraints, and select excellent individuals for crossover and mutation based on the evaluation results to generate a new population; Determine whether the preset number of iterations is met. If not, re-evaluate each individual in the initial population. If so, select the solution in the Pareto optimal solution set as the optimal molten iron hot charging ratio based on production needs.

4. The method for preparing high-purity steel for wind turbine main shaft bearing according to claim 1, characterized in that: In step S1, hot charging technology of molten iron is adopted for smelting in the electric furnace; the tapping end point includes: the end point carbon is controlled at 0.15-0.25%, P≤0.010%, the end point oxygen of the electric furnace is ≤200ppm, and the tapping temperature is ≥1610℃.

5. The method for preparing high-purity steel for wind turbine main shaft bearing according to claim 1, characterized in that: The aluminum block, silicon-manganese alloy, ferromanganese, high carbon ferrochrome, carburizer and slag are added in sequence during steel tapping, including: When the electric furnace taps 1 / 4-1 / 3 of the steel, add aluminum blocks for pre-deoxidation, then add silicon-manganese alloy, ferromanganese, high carbon ferrochrome, carburizer, and finally add top slag. The above alloys and slag are added before the steel taps 3 / 4. Among them, the addition amount of aluminum block is 1.0-1.3Kg / ton of steel, the Ti content in high carbon ferrochrome is ≤0.03%, and the addition amount of top slag is 8-1Kg / ton of steel.

6. The method for preparing high-purity steel for wind turbine main shaft bearing according to claim 1, characterized in that: In step S2, aluminum wire is fed at one time according to the aluminum content in the molten steel, and the aluminum content in the steel during the refining process is 0.02-0.04wt%; The amount of carbon powder added is 0.4-0.5Kg / ton steel, the amount of silicon carbide added is ≤2.0Kg / ton steel, and the total content of FeO and MnO in the refined slag is ≤1.0wt%; In the early stage of refining, the slag basicity is controlled at 4-6. In the middle stage of refining, 1 kg / ton of wollastonite is added to adjust the slag, and the slag basicity is controlled at 2-4.

7. The method for preparing high-purity steel for wind turbine main shaft bearing according to claim 1, characterized in that: In step S3, the amount of calcium silicon wire added is 0.08-0.2 kg / ton of steel, and the Al2O3 chain inclusions are transformed into CaAlO spherical inclusions through inclusion modification treatment, and the Ca:Al value in the CaAlO spherical inclusions is less than 1.

8. The method for preparing high-purity steel for wind turbine main shaft bearing according to claim 1, characterized in that: In step S4, the continuous casting process adopts long nozzle argon protection, integral submerged nozzle, and the tundish adopts special covering agent and crystallizer protective slag to achieve protective casting, the superheat is controlled at 20-30°C, the pulling speed is 0.25-0.40m / min, and the ratio of CaO / Al2O3 of the tundish covering agent is 1.2-1.

8.

9. A high-purity steel for a wind turbine main shaft bearing, prepared based on the preparation method of a high-purity steel for a wind turbine main shaft bearing according to any one of claims 1 to 8, characterized in that: The high purity steel for wind turbine main shaft bearings is composed of the following raw materials in percentage by mass: C: 0.44-0.51%, Si: 0.20-0.40%, Mn: 0.70-0.90%, P≤0.015%, S≤0.005%, Cr: 1.20-1.40%, Ni: 0.40-0.70%, Mo: 0.30-0.40%, Cu≤0.20%, Al: 0.020-0.040%, V: 0.05-0.10%, Ti≤0.0030%, Ca≤0.0010%, As≤0.010%, Pb≤0.0020%, Sn≤0.0050%, Sb≤0.0030%, Bi≤0.0030%, O≤0.0010%, H≤0.00015%, the rest are Fe and unavoidable impurities.

10. Use of the high-purity steel prepared by the preparation method of high-purity steel for wind turbine main shaft bearings according to any one of claims 1 to 8 or the high-purity steel for wind turbine main shaft bearings according to claim 9 in wind power generation load-bearing components or wind turbine main shafts.

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