Electric furnace smelting process for reducing sulfur content of wind power steel 18CrNiMo7-6

Abstract

The invention belongs to the technical field of wind power steel, and particularly relates to an electric furnace smelting process for reducing the sulfur content of wind power steel 18CrNiMo7-6. The production process route comprises the steps of molten iron, scrap steel and nickel-containing pig iron, EAF electric furnace primary smelting, LF external refining, VD vacuum degassing, CC continuous casting, slow cooling (annealing) and inspection and warehousing. According to the electric furnace smelting process for reducing the sulfur content of the wind power steel 18CrNiMo7-6, the core technology is that nickel-containing pig iron is added into an electric furnace to replace electrolytic nickel or nickel plates and other materials with high value, the productivity is improved, and the production cost is reduced; meanwhile, the content of the S element at the end point is effectively controlled, the technological operation of electric furnace blowing is combined, slag overflowing in the VD vacuum process is effectively controlled by optimizing the smelting mode and controlling the proportion and usage amount of waste steel, nickel-containing pig iron and blast furnace molten iron, the product quality is improved, and the market application prospect is wide.

Description

Technical Field

[0001] This invention belongs to the field of wind power steel technology, specifically relating to an electric furnace smelting process for reducing the sulfur content of 18CrNiMo7-6 wind power steel. Background Technology

[0002] Wind power is a green energy source and the fastest-growing energy source in the world. my country is vigorously promoting the development of wind power. Wind turbine gears are one of the most critical components of wind turbines, requiring increasingly stringent flaw detection standards. For some products, the equivalent of flat-bottomed holes for flaw detection defects in functional areas has been increased to approximately Φ0.5mm. High purity of steel is also required. With the continuous advancement of clean steel smelting technology and the increasing demands for steel cleanliness, the requirements for sulfur content in steel are becoming more stringent. With the need for cost reduction and efficiency improvement, the rational use of nickel-containing alloys in conventional smelting processes urgently needs to be addressed. Simultaneously, scrap steel smelting also suffers from unstable trace element sulfur (S). Excessive S content in molten steel during smelting affects the smoothness of the smelting process and product quality due to fluctuations in slag-steel balance. Therefore, it is urgent to control the S content in the process and optimize and refine the smelting process requirements. For example, pipeline steel plates have stringent requirements for weldability and resistance to sulfur-induced and hydrogen-induced cracking; the sulfur content must be controlled at an extremely low level ([S] < 0.005%). In recent years, in particular, the demand for ultra-low sulfur steel (high-strength steel) with a sulfur content of less than 0.001% has been gradually increasing. The use of high-quality refining slag for deep desulfurization outside the ladle has become a focal point of research both domestically and internationally.

[0003] Previously, the sulfur content at the final stage of electric arc furnace refining was often too high. Conventional operations involved increasing the amount of lime (CaO) during the refining process to reduce the sulfur content in the molten steel. This led to a problem: it didn't account for high CaO / Al₂O₃ (basicity) ratios > 3, where the sulfur distribution coefficient (Ls) decreases with increasing CaO / Al₂O₃ ratio. This can be explained by two main factors: firstly, as the CaO / Al₂O₃ ratio increases, the sulfur capacity of the refining slag increases; secondly, as the CaO / Al₂O₃ ratio increases, the activity of Al₂O₃ in the slag decreases, leading to a decrease in oxygen activity under equilibrium conditions. As shown in the Ls calculation formula, the sulfur distribution ratio (Ls) increases. When the CaO / Al₂O₃ ratio is greater than 3, Ls decreases with increasing CaO / Al₂O₃ ratio. This is because as CaO increases, the viscosity of the slag increases, worsening the desulfurization kinetics and reducing the desulfurization effect, thus decreasing the Ls of the slag. A higher sulfur distribution ratio can be obtained when the CaO / Al2O3 ratio is between 2.5 and 3.

[0004] The effect of CaO content (mass fraction, %) on the sulfur distribution ratio Ls is as follows: as the CaO content increases, the sulfur distribution ratio Ls increases significantly; however, when the CaO content is greater than 60%, Ls decreases with further increases in CaO content. The reason for this is that when the CaO content is too high, solid particles precipitate in the slag, resulting in a heterogeneous phase in the slag, which leads to an increase in slag viscosity and a decrease in fluidity. Therefore, it affects the desulfurization kinetics and causes the sulfur distribution ratio to decrease.

[0005] After LF treatment, the refined slag exhibits high basicity and low oxidizing properties, with a basicity typically between 5 and 8, and an FeO mass fraction below 1%. Theoretically, as the FeO content in the slag decreases, the foaming index of the slag increases significantly. However, increasing the w(FeO) content in the slag cannot reduce its foaming properties, as this would not only decrease the slag-steel sulfur distribution ratio but also significantly increase the oxygen content and inclusions in the molten steel. When the ladle is fed into the VD furnace, the temperature of the refined slag is lower than at the end of LF treatment, resulting in relatively poor fluidity and increased foaming capacity. Before vacuuming, the bottom-blown argon has weak stirring ability, the slag-metal interface reaction is slow, and the slag surface fluctuates slightly. As the vacuum level in the VD furnace increases, the volume expansion of the blown argon becomes increasingly violent, and the volume of gas passing through the slag layer increases dramatically. If, within the allowable clearance of the ladle, the amount of gas entering and exiting the slag layer reaches equilibrium, then during vacuum refining in the VD furnace, slag foaming will cause the slag volume to expand dramatically, overflowing along the ladle and damaging equipment within the vacuum chamber. Simultaneously, it affects product quality because the reduced slag content hinders the adsorption of inclusions. The impact of high sulfur content on smelting processes and quality: (1) High S-values ​​cause a burden on the smelting process and increase smelting time; (2) High S affects the balance of steel slag, resulting in excessive inclusions and affecting product quality; (3) The reaction of high-strength steel slag is violent, and the slag overflows during the vacuum process, which can damage the equipment.

[0006] To achieve cost reduction and efficiency improvement, the use of nickel-containing alloys in the smelting process needs to be addressed; however, simply replacing materials will result in high sulfur content. Therefore, it is urgent to research an effective method to reduce sulfur content while simultaneously achieving cost reduction and efficiency improvement, thereby solving the current technical challenges and improving product quality. Summary of the Invention

[0007] In view of the shortcomings of the existing technology, the present invention aims to solve at least one of the above-mentioned technical problems to a certain extent. The present invention provides an electric furnace smelting process for reducing the sulfur content of 18CrNiMo7-6 steel for wind power. The core technology is that the electric furnace uses nickel-containing pig iron instead of electrolytic nickel to achieve cost reduction and efficiency improvement. At the same time, the sulfur content at the end point is controlled to be <0.0130% to improve product quality.

[0008] An electric arc furnace (EAF) smelting process for reducing the sulfur content of 18CrNiMo7-6 steel for wind power is described. The production process route is as follows: high-quality molten iron + a small amount of scrap steel + nickel-containing pig iron (ferronickel) → EAF electric arc furnace primary smelting → LF ladle refining → VD vacuum degassing → CC continuous casting → slow cooling (annealing) → inspection and warehousing. The key step is to control sulfur in the process: high-quality molten iron + a small amount of scrap steel + nickel-containing pig iron → EAF electric arc furnace primary smelting.

[0009] The objective of this invention is achieved through the following technical solution, the preparation steps of which include: Smelting, VD vacuum degassing, continuous casting, slow cooling, annealing, inspection and warehousing; smelting includes furnace charge selection, EAF electric furnace primary smelting, and LF ladle refining. I. Selection of furnace charge:

[0010] The furnace charge includes molten iron, nickel-containing pig iron and / or scrap steel; wherein the mass ratio of molten iron, nickel-containing pig iron and / or scrap steel is 88~96:10~18:12~32; 1. Scrap steel requirements: S content ≤ 0.030% (self-produced scrap steel, try not to use purchased scrap steel, pig iron, etc.).

[0011] Specifically, during electric arc furnace smelting, the iron-to-metal ratio is 80%–86%; the residual steel in the electric arc furnace is controlled at 20–30 tons.

[0012] 2. The nickel-containing pig iron has a FeNi content of 9.5% and a sulfur content of ≤0.30%; Specifically, the sulfur (S) content in nickel-containing pig iron ranges from 0.20% to 0.30%. 3. Control the sulfur content at the final stage of the electric furnace to be ≤0.020%. II. During the initial smelting process in the EAF electric furnace:

[0013] Oxygen lance blowing and total oxygen consumption requirements: oxygen consumption per ton of steel is 50~53m³. 3 / t, total smelting time is 45~52min, total oxygen consumption is 5200~5500m³ / t. 3 During the smelting process, the oxygen consumption during the oxidation period should be controlled to be ≤4800m³. 3 / t; Specifically, the electric furnace smelting operation requires a two-step process, with molten iron added in two stages. The first stage adds 42% to 52% of the total amount, and the second stage adds the remainder. Corresponding smelting stages: Charging stage: oxygen lance stops blowing; Melting stage: oxygen consumption reaches 300~400 mg / L. 3 ; During the final stage of melting: oxygen consumption reaches 1000~1203m 3 Oxidation period: Oxygen consumption reaches 4200~4800 m³ / h 3 Sampling and temperature measurement period: Oxygen consumption up to 4900~5200m³ 3During the tapping stage: oxygen consumption reaches 5200~5500 mg / L. 3 ; To control the iron oxide content in electric arc furnace slag, 8-10 kg of lime is added per ton of molten steel during alloying at the tapping point, with a target tapping temperature range of 1610-1650℃. Lime is added in batches during operation to achieve rapid phosphorus removal, creating conditions for carbon and sulfur removal in the later stages of smelting, thus meeting the initial smelting composition requirements for carbon, phosphorus, and sulfur.

[0014] 5. After smelting, take samples to test the sulfur content. If the sulfur content is greater than 0.015%, increase the smelting time by 5-10 minutes, and add 100-200 kg of lime per 100 tons of molten steel to form slag and reduce the sulfur content. Finally, control the sulfur content to ≤0.010%. Specifically, the final controlled range for sulfur content is 0.005% to 0.010%. LF external refining:

[0015] The molten steel after electric arc furnace smelting in step two is refined and heated in an LF refining furnace. After the submerged arc is stabilized, 0.080~0.140 kg / t of deoxidizer ferrosilicon powder or deoxidizer silicon carbide is added according to the quality of the molten steel to adjust the slag fluidity; the white slag retention time is ≥20 min. IV. VD Vacuum Degassing:

[0016] After refining in the LF furnace in step three, vacuum degassing is performed using a VD degassing device, with a vacuum degree ≤67pa and a holding time ≥15min; ensuring that [H] ≤1.2ppm and [O] ≤10ppm during vacuum breaking; soft blowing time is not less than 20 minutes, and no calcium wire is added; Specifically, the blowjob time should be controlled at 20-25 minutes; V. Continuous casting:

[0017] Following the VD vacuum degassing treatment in step four, a continuous casting machine was used for full-process protective casting, controlling the gas absorption of molten steel, with nitrogen increase ≤5ppm during continuous casting; electromagnetic stirring in the crystallizer, casting stirring, and end electromagnetic stirring were employed to maintain a constant casting speed, with the casting speed controlled ≤0.40m / min; the amount of molten steel remaining in the ladle was ≥6 tons, and the amount of molten steel remaining in the tundish was >4 tons, and finally, steel billets were obtained after continuous casting; the steel billets were annealed in the slow cooling pit for ≥36 hours.

[0018] Specifically, electromagnetic stirring in the crystallizer and electromagnetic stirring at the end are used. The electromagnetic stirring frequency in the crystallizer is 2Hz, the stirring frequency in the casting is 8Hz, and the electromagnetic stirring frequency at the end is 8Hz. Beneficial effects

[0019] Compared with existing technologies, the beneficial effects of this invention in smelting high-purity gear steel are reflected in the following: the current technical challenge lies in reducing sulfur content while achieving cost reduction and efficiency improvement, without affecting product performance and improving product quality. Addressing the shortcomings of existing technologies, this invention provides an electric arc furnace smelting process for reducing the sulfur content of 18CrNiMo7-6 wind power steel. The core technology lies in replacing high-value materials such as electrolytic nickel or nickel plates with nickel-containing pig iron in the electric arc furnace, thereby improving productivity and reducing production costs. Simultaneously, it effectively controls the sulfur content at the endpoint. Combined with the process operation control of electric arc furnace blowing, by optimizing the smelting method and controlling the proportions of scrap steel, nickel-containing pig iron, and blast furnace hot metal, it effectively controls slag overflow during the VD vacuum process, thus improving product quality. Detailed Implementation

[0020] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0021] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art.

[0022] Various improvements and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, which will be obvious to those skilled in the art.

[0023] Other embodiments derived from this specification will be apparent to those skilled in the art. The specification and embodiments are merely exemplary. Example 1:

[0024] I. Scrap Steel Charging Requirements: 6 tons of scrap steel with a sulfur content of S≤0.030%, and 10 tons of nickel-containing pig iron (FeNi 9.5%); totaling 16 tons of scrap steel and nickel-containing pig iron. 92 tons of blast furnace molten iron with a sulfur content of 0.024% are added through the chute, resulting in an iron-to-iron ratio of 85.2%, and 25 tons of residual steel from the electric arc furnace.

[0025] II. Primary Smelting in EAF Electric Furnace During the charging stage, the oxygen lance stops blowing, and the iron and water are added in two batches: 40 tons in the first batch and 52 tons in the second batch. Oxygen blowing for 5 minutes during the melting stage: oxygen consumption 360m³ 3 During the final stage of smelting (up to 10 minutes): oxygen consumption reached 1105 m³ / s. 3 Oxidation period: Oxygen consumption up to 4560m³ 3 Smelting to 38 minutes, sampling and temperature measurement period: oxygen consumption up to 5130m³3 Smelting to 46 minutes, during the tapping stage: oxygen consumption reaches 5240 mg / L. 3 The smelting time for the entire furnace was 46 minutes, and the oxygen content of the molten steel was measured at 423 ppm.

[0026] III. LF external refining: The molten steel after electric arc furnace smelting in step two is refined and heated in an LF refining furnace. After the submerged arc is stabilized, 0.080~0.140 kg / t of deoxidizer ferrosilicon powder or deoxidizer silicon carbide is added according to the quality of the molten steel to adjust the slag fluidity; the white slag retention time is ≥20 min. IV. VD Vacuum Degassing: After refining in the LF furnace in step three, vacuum degassing is performed using a VD degassing device, with a vacuum degree ≤67pa and a holding time ≥15min; ensuring that [H] ≤1.2ppm and [O] ≤10ppm during vacuum breaking; soft blowing time is 20-25 minutes, and no calcium wire is added; V. Continuous casting: Following the VD vacuum degassing treatment in step four, continuous casting is employed with full-process protective casting to control gas absorption in the molten steel, resulting in nitrogen increase of ≤5ppm during continuous casting. Electromagnetic stirring in the crystallizer and at the end of the casting process are used, with a crystallizer electromagnetic stirring frequency of 2Hz, a casting stirring frequency of 8Hz, and an end electromagnetic stirring frequency of 8Hz. A constant casting speed is maintained, controlled to ≤0.40m / min. The remaining molten steel in the ladle is ≥6 tons, and the remaining molten steel in the tundish is >4 tons. Finally, steel billets are obtained after continuous casting. The billets are then annealed in a slow cooling pit for ≥36 hours. Comparative Example 1:

[0027] I. Scrap steel charging requirements: 16 tons of scrap steel with a sulfur content of S≤0.020%, 95 tons of molten iron with an S content of 0.022% are added to the electric furnace through a chute, with an iron-to-iron ratio of 85.6%, and 28 tons of residual steel in the electric furnace.

[0028] II. Primary Smelting in EAF Electric Furnace During the charging stage, the oxygen lance stops blowing and the iron and water are added in two batches, 50 tons in the first batch and 45 tons in the second batch. Oxygen blowing for 5 minutes during the melting stage: oxygen consumption 400m³ 3 During the final stage of smelting (up to 10 minutes): oxygen consumption reached 1203m³. 3 Oxidation period: Oxygen consumption up to 4600m³ 3 Smelting to 38 minutes, sampling and temperature measurement period: oxygen consumption up to 5200m³ 3 Smelting for 45 minutes, during the tapping stage: oxygen consumption reaches 5300 mg / L. 3 The smelting time for the entire furnace was 45 minutes, and the oxygen content of the molten steel was measured at 506 ppm.

[0029] The initial material does not use nickel-containing pig iron. During the refining process, nickel plates (99% content, or can be replaced with 99% nickel briquettes) are added according to conventional operations; the remaining steps (steps three to five) are the same as in Example 1. Example 2:

[0030] I. Scrap Steel Charging Requirements: 18 tons of nickel-containing pig iron (FeNi 9.5%), totaling 18 tons. 93 tons of molten iron with a sulfur content of 0.012% from the blast furnace, added via chute, with an iron-to-iron ratio of 83.8%, and 28 tons of residual steel from the electric arc furnace.

[0031] II. Primary Smelting in EAF Electric Furnace During the charging stage, the oxygen lance stops blowing and molten iron is added twice: 48 tons the first time and 45 tons the second time. Oxygen blowing for 5 minutes during the melting stage: oxygen consumption 390m³ 3 ; During the final stage of smelting (up to 10 minutes): oxygen consumption reached 1189m³. 3 Oxidation period: Oxygen consumption up to 4605m³ 3 Smelting to 38 minutes, sampling and temperature measurement period: oxygen consumption up to 5080m³ 3 Smelting time up to 44 minutes; tapping stage: oxygen consumption up to 5189m³ 3 The smelting time for the entire furnace was 44 minutes, and the oxygen content of the molten steel was measured at 439 ppm.

[0032] The remaining steps (steps three to five) are the same as in Example 1. Comparative Example 2:

[0033] I. Scrap Steel Charging Requirements: 5 tons of scrap steel with a sulfur content of S≤0.012%, 10 tons of nickel-containing pig iron (FeNi 9.5%), totaling 15 tons. Blast furnace molten iron with an S content of 0.024% is added via a chute, resulting in an iron-to-metal ratio of 86.5%. 30 tons of residual steel from the electric arc furnace are also included. II. Primary Smelting in EAF Electric Furnace During the charging stage, the oxygen lance stops blowing and molten iron is added twice: 48 tons the first time and 48 tons the second time. Oxygen blowing for 5 minutes during the melting stage (oxygen consumption 340m³) 3 -- Smelting at the end of the melting process for 10 minutes (oxygen consumption up to 1160m³) 3 --Oxidation period (oxygen consumption up to 4736m) 3 Smelting to 38 minutes -- Sampling and temperature measurement period (oxygen consumption to 5105m) 3 Smelting to 42 minutes -- tapping stage (oxygen consumption to 5306m³) 3 The smelting time for the entire furnace was 42 minutes, and the oxygen content of the molten steel was measured at 500 ppm.

[0034] The remaining steps (steps three to five) are the same as in Example 1. Example 3:

[0035] I. Scrap Steel Charging Requirements: 2 tons of scrap steel with a sulfur content of S≤0.012%, 18 tons of nickel-containing pig iron (FeNi 9.5%), totaling 20 tons. 80 tons of molten iron with a sulfur content of 0.020% are added through the chute, with an iron-to-iron ratio of 80%, and 22 tons of residual steel from the electric arc furnace.

[0036] II. Primary Smelting in EAF Electric Furnace During the charging stage, the oxygen lance stops blowing, and the iron and water are added in two batches: 41 tons in the first batch and 39 tons in the second batch. Oxygen blowing for 5 minutes during the melting stage (oxygen consumption 310m³) 3 -- Smelting at the end of the melting process for 10 minutes (oxygen consumption up to 1100m³) 3 --Oxidation period (oxygen consumption up to 4900m) 3 Smelting to 38 minutes -- Sampling and temperature measurement period (oxygen consumption to 5200m) 3 Smelting to 52 minutes -- tapping stage (oxygen consumption to 5500m) 3 The smelting time for the entire furnace was 52 minutes, and the oxygen content of the molten steel was measured at 600 ppm.

[0037] The remaining steps (steps three to five) are the same as in Example 1. Comparative Example 3:

[0038] I. Scrap Steel Charging Requirements: 2 tons of scrap steel with a sulfur content of S≤0.012%, 18 tons of nickel-containing pig iron (FeNi 9.5%), totaling 20 tons. 84 tons of molten iron with a sulfur content of 0.020% are added through the chute, with an iron-to-iron ratio of 80.8%, and 26 tons of residual steel from the electric arc furnace.

[0039] II. Primary Smelting in EAF Electric Furnace During the charging phase, the oxygen lance stops blowing, and molten iron is added twice, once 41 tons and the second time 43 tons. Oxygen blowing for 5 minutes during the melting stage (oxygen consumption 320m³) 3 -- Smelting at the end of the melting process for 10 minutes (oxygen consumption to 1210m) 3 --Oxidation period (oxygen consumption up to 5000m) 3 Smelting to 38 minutes -- Sampling and temperature measurement period (oxygen consumption to 5250m) 3 Smelting to 48 minutes -- tapping stage (oxygen consumption to 5300m³) 3 The smelting time for the entire furnace was 48 minutes, and the oxygen content of the molten steel was measured at 300 ppm.

[0040] The remaining steps (steps three to five) are the same as in Example 1.

[0041] The indicators are shown in the table below: Table 1: Test data indicators for electric furnace slag samples: Sample furnace number CaO SiO2 Al2O3 MgO S FeO R Remark 189ZE-1 50.012 9.588 0.754 2.22 0.102 25.6984 5.2163 Example 1 155ZE-1 48.197 9.413 1.604 2.7 0.115 25.1774 5.1202 Comparative Example 1 196ZE-1 48.369 11.055 0.668 1.63 0.086 32.1011 4.3636 Example 2 198ZE-1 48.352 8.714 1.092 2.03 0.111 26.3844 5.5488 Comparative Example 2 202ZE-1 45.987 6.787 1.289 2.66 0.098 30.4275 6.7757 Example 3 206ZE-1 44.336 9.344 1.195 2.11 0.124 29.8607 4.745 Comparative Example 3 Table 2: Material Usage and S Content Sample furnace number oxygen consumption Smelting cycle / min Electric furnace endpoint S% Does the VD process overflow? Remark 189ZE-1 <![CDATA[5240Nm 3 ]]> 46 0.030 Severe overflow Example 1 155ZE-1 <![CDATA[5300Nm 3 ]]> 45 0.012 No overflow Comparative Example 1 196ZE-1 <![CDATA[5189Nm 3 ]]> 44 0.013 No overflow Example 2 198ZE-1 <![CDATA[5306Nm 3 ]]> 42 0.024 Less overflow Comparative Example 2 202ZE-1 <![CDATA[5500Nm 3 ]]> 52 0.013 No overflow Example 3 206ZE-1 <![CDATA[5300Nm 3 ]]> 48 0.0268 Less overflow Comparative Example 3 Table 3: Inclusion levels in Examples 1-3 Referring to Tables 1-3, a comparison between Example 1 and Comparative Example 1 shows that controlling the sulfur content at the electric furnace endpoint is crucial. In Example 1, the excessively high sulfur content at the electric furnace endpoint (0.030) resulted in severe slag overflow and adverse effects. Comparative Example 1 strictly controlled the sulfur content at the electric furnace endpoint, did not use nickel-containing pig iron, and added nickel plates during the refining process using conventional methods. Combined with the process improvements of this invention, it also achieved good technical results. Although Comparative Example 1 also achieved good results, it used nickel plates, which increased the material cost by 1000-2000 yuan per ton compared to nickel-containing pig iron. This significantly increased cost is not conducive to market application and is a technical problem that needs to be solved.

[0042] By comparing Example 2 and Comparative Example 2, it can be seen that the high sulfur content in the molten iron and the electric furnace endpoint in Comparative Example 2 has an adverse effect on the production process. Therefore, controlling the sulfur content in the molten iron is crucial.

[0043] Comparing Example 3 and Comparative Example 3, Comparative Example 3 suffered from adverse effects on the production process due to improper S content and electric furnace blowing operation. Specifically, the oxygen consumption in the early stage of Comparative Example 3 was excessively high, reaching ≥5000 mg / L during the oxidation period. 3 The process control of blowing is also crucial, as it has a significant impact on the results.

[0044] By controlling the raw material ratio and blowing method, and further controlling the sulfur content at the electric furnace endpoint, we can reduce costs and increase efficiency without affecting quality.

[0045] Note: The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Therefore, although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention. All technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. An electric furnace smelting process for reducing the sulfur content of 18CrNiMo7-6 steel for wind power, characterized in that, The process steps are: smelting, VD vacuum degassing, continuous casting, slow cooling, annealing, inspection and warehousing; among which smelting includes furnace charge selection, EAF electric furnace primary smelting, and LF ladle refining; Furnace charge selection: The furnace charge includes molten iron, nickel-containing pig iron, and / or scrap steel; the mass ratio of molten iron, nickel-containing pig iron, and / or scrap steel is 88~96:10~18:12~32; scrap steel requirements: sulfur content ≤0.030%; nickel-containing pig iron sulfur content ≤0.30%; the final sulfur content of the electric furnace should be controlled to ≤0.020%. During the primary refining process in an EAF electric arc furnace: Requirements for oxygen lance blowing and total oxygen consumption: 50-53 mg / ton of steel. 3 / t, total smelting time is 45~52min, total oxygen consumption is 5200~5500m³ / t. 3 During the smelting process, the oxygen consumption during the oxidation period should be controlled to be ≤4800m³. 3 / t; After smelting, samples are taken to test the sulfur content. If the sulfur content is greater than 0.015%, the smelting time is increased by 5 to 10 minutes, and 100 to 200 kg of lime is added per 100 tons of molten steel to form slag and reduce the sulfur content. The final sulfur content is controlled to be ≤0.010%. LF external refining: The molten steel after electric arc furnace smelting in step two is refined and heated in an LF refining furnace. After the submerged arc is stabilized, 0.080~0.140 kg / t of deoxidizer ferrosilicon powder or deoxidizer silicon carbide is added according to the quality of the molten steel to adjust the slag fluidity; the white slag retention time is ≥20 min. VD vacuum degassing: After the LF furnace refining in step three, vacuum degassing is performed using a VD degassing device, with a vacuum degree ≤67pa and a holding time ≥15min; ensuring that [H] ≤1.2ppm and [O] ≤10ppm during vacuum breaking; and the soft blowing time is not less than 20 minutes. Continuous casting: Following the VD vacuum degassing treatment in step four, a continuous casting machine was used for full-process protective casting, controlling the gas absorption of molten steel, with nitrogen increase ≤5ppm during continuous casting; electromagnetic stirring in the crystallizer, casting stirring, and end electromagnetic stirring were employed to maintain a constant casting speed, with the casting speed controlled ≤0.40m / min; the amount of molten steel remaining in the ladle was ≥6 tons, and the amount of molten steel remaining in the tundish was >4 tons, and finally, steel billets were obtained after continuous casting; the steel billets were annealed in the slow cooling pit for ≥36 hours.

2. The electric furnace smelting process for reducing the sulfur content of 18CrNiMo7-6 steel for wind power according to claim 1, characterized in that: Nickel-containing pig iron contains 9.5% FeNi, with a content range of 0.20% to 0.30%.

3. The electric furnace smelting process for reducing the sulfur content of 18CrNiMo7-6 steel for wind power according to claim 1, characterized in that: During electric arc furnace smelting, the iron-to-metal ratio is 80%–86%; the residual steel in the electric arc furnace is controlled at 20–30 tons.

4. The electric furnace smelting process for reducing the sulfur content of 18CrNiMo7-6 steel for wind power according to claim 1, characterized in that: During the initial smelting process in the EAF electric furnace, molten iron is added in two stages: the first stage adds 42% to 52% of the total amount, and the second stage adds the remainder.

5. The electric furnace smelting process for reducing the sulfur content of 18CrNiMo7-6 steel for wind power according to claim 1, characterized in that: During the primary smelting process in an EAF electric arc furnace, the corresponding smelting stages are as follows: Charging stage: oxygen lance blowing stops; Melting stage: oxygen consumption reaches 300~400 mg / m³. 3 ; During the final stage of melting: oxygen consumption reaches 1000~1203m 3 Oxidation period: Oxygen consumption reaches 4200~4800 m³ / h 3 Sampling and temperature measurement period: Oxygen consumption up to 4900~5200m³ 3 During the tapping stage: oxygen consumption reaches 5200~5500 mg / L. 3 .

6. The electric furnace smelting process for reducing the sulfur content of 18CrNiMo7-6 steel for wind power according to claim 1, characterized in that: During the initial smelting process in the EAF electric furnace, the final controlled sulfur content range is 0.005% to 0.010%.

7. The electric furnace smelting process for reducing the sulfur content of 18CrNiMo7-6 steel for wind power according to claim 1, characterized in that: VD vacuum degassing: The soft blowing time is controlled at 20-25 minutes.

8. The electric furnace smelting process for reducing the sulfur content of 18CrNiMo7-6 steel for wind power according to claim 1, characterized in that: During continuous casting, electromagnetic stirring in the crystallizer and electromagnetic stirring at the end are used. The frequency of electromagnetic stirring in the crystallizer is 2Hz, while the frequency of electromagnetic stirring in the casting and the frequency of electromagnetic stirring at the end are 8Hz.