A smelting method for controlling wind power pin shaft class D inclusions

Abstract

The present application relates to the technical field of steel metallurgy, and particularly provides a smelting method for controlling D-type inclusions of a wind power pin shaft. The present application stabilizes the whole-process slag components, ensures that the slag system has good adsorption inclusion capacity, makes the inclusions float as much as possible in the refining process, further removes the inclusions and improves their harmfulness through vacuum treatment and precise calcium treatment, improves the cleanliness of the molten steel while ensuring good castability of the molten steel, and stabilizes the product quality.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, specifically to a smelting method for controlling type D inclusions in wind turbine pin shafts. Background Technology

[0002] Currently, as the service environment of wind turbine shaft products becomes increasingly harsh and quality requirements become more stringent, shafts are required to possess excellent fatigue life, impact toughness, and mechanical stability. Type D inclusions, as spherical oxide-type non-metallic inclusions, disrupt the continuity and density of the steel matrix. Under stress, they easily become stress concentration points, inducing crack initiation and propagation, severely reducing the fatigue performance and impact resistance of the shaft, and even causing major equipment failures such as shaft fracture. Therefore, controlling this type of inclusion is a core requirement for ensuring the long-term reliable operation of wind power equipment. If the grade of Class D spherical oxide inclusions is too high, it will significantly affect the properties of the steel. For example, in the forging and heat treatment process of 40Cr steel, Class D inclusions are difficult to deform with the matrix and may also hinder grain refinement, resulting in anisotropy of the mechanical properties of the steel.

[0003] The traditional smelting process for 40Cr steel typically involves converter smelting → LF refining → VD / RH vacuum treatment. During this process, Class D inclusions originate from a variety of sources, including impurities in the raw materials, Al2O3 and other products generated during deoxidation, erosion and flaking of the furnace lining and refractory materials, and oxides produced by secondary oxidation of the molten steel during casting. Furthermore, the traditional process has several drawbacks. For instance, the alloys used during deoxidation tend to generate fine oxide particles that are difficult to float; the poor slag fluidity of LF refining hinders the aggregation and growth of inclusions, preventing them from floating to the slag; and surface fluctuations during continuous casting can cause slag entrapment and secondary oxidation, resulting in Class D inclusions remaining in the steel.

[0004] Strictly controlling the level of harmful inclusions such as Class D inclusions to a low level (such as below Class 1.0) has become a key technical direction for improving the quality of 40Cr wind turbine pin shafts and adapting to the needs of high-power wind turbine units. It is also an important way to reduce the operation and maintenance costs of wind power equipment. Summary of the Invention

[0005] To address the shortcomings of traditional smelting processes, the technical problem this invention aims to solve is to provide a smelting method for controlling Class D inclusions in wind turbine pin shafts. This method stabilizes the slag composition throughout the entire process, ensures the slag system has a good ability to adsorb inclusions, and allows inclusions to float as much as possible during refining. Through vacuum treatment and precise calcium treatment, inclusions are further removed and their harmfulness is reduced. While ensuring good castability of molten steel, the cleanliness of molten steel is improved, and product quality is stabilized.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A smelting method for controlling type D inclusions in wind turbine pin shafts, comprising the following steps: S1. Pre-deoxidation is performed when steel flow is observed during tapping from the electric furnace; S2. Add lime, synthetic slag and aluminum blocks during the steelmaking process; S3. After tapping, the steel is transferred to the LF refining furnace for refining. After the S4 and LF refining furnaces are smelted, the molten steel is transferred to the VD furnace for smelting without slag removal and is then subjected to vacuum treatment. S5. After breaking the void, feed in aluminum wire and calcium wire.

[0007] Preferably, in step S1, 0.4-0.6 kg / ton of silicon carbide and 0.2-0.4 kg / ton of aluminum ingot are added to the steel stream when the steel is tapped from the electric furnace for pre-deoxidation.

[0008] Preferably, in step S2, when the steel is tapped to 1 / 4-1 / 3, 3-5 kg ​​of lime per ton of steel, 5-7 kg of synthetic slag per ton of steel, and 0.6-0.8 kg of aluminum blocks per ton of steel are added from the silo, and the aluminum content of the tapped steel is controlled at 0.030% to 0.050%.

[0009] Preferably, in step S3, the refining process includes: molten steel entering the LF refining furnace and being powered to form slag, using submerged arc operation and soft argon blowing control; no slag is added throughout the refining process; slag fluidity is well controlled; silicon carbide and / or carbon powder are used for diffusion deoxidation; white slag is maintained for 12-18 minutes before power is cut off; after stirring, a first molten steel sample is taken for analysis; based on the analysis results of the first molten steel sample, an alloy is added, wherein the aluminum content after the alloy is added is 0.030%-0.035%. In this invention, the alloy is added after the first sample is taken out, and then multiple subsequent sampling analyses are performed.

[0010] Preferably, in step S3, the CaO content in the final refining slag is 46-50%, and the Al2O3 content is 26-30%.

[0011] Preferably, in step S4, after the smelting in the LF refining furnace is completed, the molten steel is transferred to the VD furnace for smelting without slag removal, the vacuum treatment time is 30 minutes, and the argon flow rate is controlled at 20-40 NL / min.

[0012] Preferably, in step S5, after breaking the void, a finished product sample is taken for analysis and a covering agent is added to the surface of the molten steel.

[0013] More preferably, aluminum wire is fed in after the steel and aluminum are refined and the void is broken, and the amount of aluminum wire fed in is X + (0.005% to 0.015%), where X refers to the target lower limit of finished aluminum.

[0014] Preferably, after feeding aluminum wire for 3-5 minutes, 0.2-0.5 m / ton of steel calcium wire is fed in for calcium treatment. Argon gas is adjusted for soft blowing. During soft blowing, the argon gas flow rate is controlled so that the surface of the molten steel moves slightly. The soft blowing time is controlled at 15-30 minutes.

[0015] The finished product prepared by this invention meets the requirement of 100% pass rate for Class D inclusions <1.0.

[0016] Compared with the prior art, the main advantages of the present invention are: 1. This invention reduces the initial inclusion content of molten steel by pre-deoxidizing during the steel tapping process.

[0017] 2. This invention achieves stable control of the slag system throughout the entire process, allowing inclusions to float to the surface as much as possible during the refining process.

[0018] 3. This invention further removes inclusions and reduces their harmfulness through precise calcium treatment, thereby improving the cleanliness of molten steel and stabilizing product quality. Detailed Implementation

[0019] Example 1 A smelting method for controlling type D inclusions in wind turbine pin shafts includes the following steps: S1. Add 50 kg of silicon carbide and 40 kg of aluminum ingot to the steel stream during tapping from the electric arc furnace for pre-deoxidation; the composition of the tapped steel is C: 0.156%, P: 0.007%; S2. When the steel has been tapped to 1 / 3 capacity, add 400 kg of lime, 600 kg of synthetic slag, and 80 kg of aluminum blocks to the silo. The aluminum content of the tapped steel will be 0.045%. S3. After tapping, the steel is transferred to the LF refining furnace. The molten steel enters the LF furnace for slag formation under electric current, using submerged arc operation and soft argon blowing control. No additional slag is added during the refining process. The slag fluidity is well controlled. Silicon carbide (150 kg) is used for diffusion deoxidation. After maintaining the white slag for 15 minutes, the power is turned off. After stirring, the first molten steel sample is taken for analysis. Based on the analysis results of the first molten steel sample (the aluminum content in the first molten steel sample analysis result is 0.023%), alloys are added. The aluminum content of the second molten steel sample is 0.036%, and the aluminum content of the third molten steel sample is 0.033%. At the end of the refining process, the CaO content in the slag is 48%, and the Al2O3 content is 27%. After the S4 and LF refining furnaces are smelted, the molten steel is transferred to the VD furnace for smelting without removing the slag. The vacuum treatment time is 30 minutes and the argon flow rate is controlled at 20 NL / min. S5. After breaking the void, take a sample of the finished product for analysis and add 120kg of alkaline covering agent to the surface of the molten steel. After breaking the void, feed aluminum wire with an aluminum content of 0.025% (the target lower limit of aluminum content in the finished product is 0.020%). The actual aluminum content is 0.025%. After feeding the aluminum wire, feed 30m of calcium wire for calcium treatment after an interval of 3 minutes. Adjust the argon gas for soft blowing. During soft blowing, the argon gas flow rate should be controlled so that it moves slightly on the surface of the molten steel. The soft blowing time is 25min.

[0020] The results of the spectral analysis are as follows: After pre-deoxidation, the aluminum content in the molten steel was determined to be 0.045% by spectral analysis. The aluminum content in the refined steel was determined to be 0.033% by spectral analysis. The finished product's aluminum content in the molten steel was determined to be 0.025% by spectral analysis, and the inclusions were rated as Class D, grade 0.5.

[0021] Comparative Example 1 This comparative example is the same as Example 1, except that in step S1, the amount of aluminum ingot added is 0.2 kg / ton of steel; in step S2, the amount of aluminum block added is 1.8 kg / ton of steel, and the aluminum content control point at the tapped steel is 0.075%; in step S3, 100 kg of lime is added after refining, and no aluminum wire is added during the entire refining process, with the CaO content at the refining endpoint being 49% and the Al2O3 content being 29%; in step S4, after the LF refining furnace smelting is completed, a slag removal operation is performed, removing 1 / 3 of the total slag; in step S5, no aluminum wire is fed in.

[0022] The results of the spectral analysis are as follows: After pre-deoxidation, the aluminum content in the molten steel was determined to be 0.070% by spectral analysis. After refining, the aluminum content in the molten steel was determined to be 0.050% using spectral analysis. The finished product's aluminum content in the molten steel was determined to be 0.030% by spectral analysis, and the inclusions were rated as Class D, grade 1.5.

Claims

1. A smelting method for controlling type D inclusions in wind turbine pin shafts, characterized in that, Includes the following steps: S1. When tapping steel from the electric furnace, add 0.4-0.6 kg / ton of silicon carbide and 0.2-0.4 kg / ton of aluminum ingot to the steel stream for pre-deoxidation; S2. When the steel is tapped to 1 / 4-1 / 3 capacity, add 3-5 kg ​​of lime per ton of steel, 5-7 kg of synthetic slag per ton of steel, and 0.6-0.8 kg of aluminum blocks per ton of steel to the silo. The aluminum content at the tapped steel should be controlled at 0.030% to 0.050%. S3. After tapping, the steel is transferred to the LF refining furnace for refining. After the S4 and LF refining furnaces are smelted, the molten steel is transferred to the VD furnace for smelting without slag removal and is then subjected to vacuum treatment. S5. After breaking the void, feed in aluminum wire and calcium wire; The aluminum wire feed rate is X + (0.005% to 0.015%), where X refers to the target lower limit of finished aluminum. After feeding aluminum wire for 3-5 minutes, feed 0.2-0.5m / ton of steel-calcium wire for calcium treatment.

2. The smelting method according to claim 1, characterized in that, In step S3, the refining process includes: molten steel is fed into the LF refining furnace and slag is formed by power supply; submerged arc operation and soft argon blowing control are adopted; no slag is added during the entire refining process; silicon carbide and / or carbon powder are used for diffusion deoxidation; white slag is maintained for 12-18 minutes and then the power is cut off; after stirring, the first molten steel sample is taken for analysis; based on the analysis results of the first molten steel sample, an alloy is added; after the alloy is added, the aluminum content is 0.030%-0.035%.

3. The smelting method according to claim 1, characterized in that, In step S3, the CaO content in the final refining slag is 46-50%, and the Al2O3 content is 26-30%.

4. The smelting method according to claim 1, characterized in that, In step S4, after the smelting in the LF refining furnace is completed, the molten steel is transferred to the VD furnace for smelting without slag removal. The vacuum treatment time is 30 minutes, and the argon flow rate is controlled at 20-40 NL / min.

5. The smelting method according to claim 1, characterized in that, In step S5, after breaking the void, a finished product sample is taken for analysis and a covering agent is added to the surface of the molten steel.

6. The smelting method according to claim 1, characterized in that, After feeding in the calcium thread, adjust the argon gas and perform soft argon blowing, with the soft argon blowing time controlled at 15-30 minutes.