Method for producing green ultra-low-nitrogen bearing steel by ecological electric furnace and ultra-low-nitrogen bearing steel thereof

Abstract

The present application belongs to the technical field of metal material preparation, and particularly relates to a method for producing green ultra-low-nitrogen bearing steel by an ecological electric furnace and the ultra-low-nitrogen bearing steel thereof. The method for producing green ultra-low-nitrogen bearing steel GCr15-LN by an ecological electric furnace and the ultra-low-nitrogen bearing steel thereof adopt the production of high-carbon chromium bearing steel GCr15-LN by "ECOARC ecological electric furnace smelting + LF furnace refining + RH vacuum treatment + continuous casting + rolling", effectively control the nitrogen content of the steel, and ensure the performance requirements of the high-carbon chromium bearing steel, and have the characteristics of ultra-low-nitrogen and long service life. The present application smelts by using scrap steel, reduces carbon emissions, and realizes stable production of low-cost ultra-low-nitrogen green bearing steel.

Description

Technical Field

[0001] This invention belongs to the field of metal material preparation technology, and in particular relates to a method for producing green ultra-low nitrogen bearing steel using an eco-friendly electric furnace and the ultra-low nitrogen bearing steel thereof. Background Technology

[0002] Recently, the steel industry has increasingly emphasized the development of electric arc furnace (EAF) steelmaking, and the demand for steel materials is growing daily, such as green automotive steel and green bearing steel. However, due to the limitations of EAF technology, the nitrogen content of EAF steel remains high, failing to meet the low nitrogen content requirements of green steel and thus restricting its development. Therefore, to produce low-nitrogen green steel using EAF technology, a dual-process of EAF and converter must be adopted. This process utilizes the intense carbon-oxygen reaction in the converter to remove nitrogen, thereby achieving stable production of low-nitrogen green steel. However, for existing EAF plants or converter plants to develop EAF steel, it is necessary to invest in the construction of supporting converter or EAF equipment, resulting in a significant increase in investment. Therefore, it is urgent to solve the problem of ultra-low nitrogen control in EAF steel to create conditions for the production of low-nitrogen green steel.

[0003] Chinese patent application number 202210474754.5 discloses a "high-yield, low-nitrogen, low-oxygen electroslag bearing steel forging manufacturing process." The process includes consumable electrodes, electroslag ingots, forging, and forging flaw detection. During production, the total oxygen content of the consumable electrodes is controlled to be below 10 ppm and the nitrogen content below 40 ppm. A continuous deoxidation process is then used to extract the ingots into an electroslag remelting furnace to produce 6-meter-long (280mm × 325mm) electroslag square ingots. Finally, the desired forgings are produced through forging. This process features continuous deoxidation and high forging utilization. Using converter continuous casting billets as consumable electrodes, continuous deoxidation, and ingot extraction to produce electroslag ingots with a length-to-diameter ratio of 18:1, followed by rapid forging into bearing steel forgings, the electroslag ingot utilization rate reaches over 99% during the forging process. The oxygen content of the bearing steel forgings is ≤15 ppm and the nitrogen content is ≤40 ppm. Furthermore, it effectively reduces production consumption, improves the quality of electroslag ingots, and meets the requirements of high-end users. However, the nitrogen content of the product is still too high.

[0004] Chinese patent application No. 202210474754.5 discloses a low-nitrogen, high-carbon chromium bearing steel and its production method. The production method includes the following steps: Step S1: Controlling the [P] content in the molten iron entering the furnace to ≤0.135%, the [S] content to 0.013%-0.030%, and the scrap steel weight percentage to ≤20%; employing a single-stage carbon extraction and tapping process; Step S2: Inert gas is blown into the ladle from the bottom; silicon carbide is added to create foam slag in the early stage of LF refining for the first deoxidation of the slag; aluminum granules are added in the middle stage of LF refining for the second deoxidation of the slag, while aluminum wire is fed in to achieve an aluminum content of 0.02%-0.04% in the steel; Step S3: Controlling the vacuum degree of the molten steel to ≤100Pa, and the RH vacuum treatment time to not less than 30 minutes; Step S4: Continuously casting the molten steel after RH vacuum refining in Step S3 into the product under air-isolated conditions. This invention can effectively control the nitrogen content of the prepared high-carbon chromium bearing steel to ≤0.0030%. However, this invention only uses scrap steel with a weight percentage of ≤20%, resulting in high smelting costs. Summary of the Invention

[0005] The purpose of this invention is to provide a production method for green ultra-low nitrogen bearing steel GCr15-LN using an eco-friendly electric furnace, and the resulting ultra-low nitrogen bearing steel. This method employs an "ECOARC eco-friendly electric furnace smelting + LF furnace refining + RH vacuum treatment + continuous casting + rolling" process to produce high-carbon chromium bearing steel GCr15-LN. This invention effectively controls the nitrogen content of the steel and ensures the performance requirements of high-carbon chromium bearing steel, while also exhibiting the characteristics of ultra-low nitrogen and long service life. It achieves stable production of ultra-low nitrogen green bearing steel while reducing carbon emissions. To achieve the above objectives, this invention adopts the following technical solution:

[0006] A method for producing green ultra-low nitrogen bearing steel using an eco-friendly electric furnace specifically includes the following steps:

[0007] 1) Eco-friendly electric arc furnace smelting: Scrap steel is used as the furnace charge. The scrap steel used is high-quality scrap steel free of impurities, with a 100% proportion and a carbon content ≥2.50%. Oxygen blowing assists melting, utilizing carbon monoxide bubbles generated by the carbon-oxygen reaction for denitrification, reducing the nitrogen content of the molten steel. Low-nitrogen carbon powder is injected to create foamy slag, ensuring effective submerged arcing and reducing nitrogen absorption at the electrodes. High-power current is used to melt the scrap steel, with a tapping temperature of 1635–1650℃. Aluminum deoxidation is not performed during tapping; instead, a silicon deoxidation process is used, adding 2–3 kg / t of ferrosilicon. After deoxidation, alloying is carried out, and 2–5 kg / t of limestone is added to the bottom of the ladle. The carbon dioxide gas generated by the heated limestone reaction forms a protective gas layer on the molten steel, reducing nitrogen absorption during tapping.

[0008] 2) LF Refining: LF refining uses lime, fluorite, calcium carbide, and silicon carbide for aluminum-free slag formation. After the ladle is in place, argon gas is started at 300-500 NL / min, and 3-5 kg / t of lime and fluorite are added. The argon gas flow is adjusted to 150-250 NL / min, and slag formation begins. Large-scale argon gas stirring during heating is not allowed to prevent nitrogen buildup. 0.5-1 kg / t of calcium carbide is added simultaneously with each heating and slag formation. This maintains a reducing atmosphere near the electrodes to prevent nitrogen buildup and reacts with nitrogen in the molten steel to generate calcium cyanamide (CaCN2) for denitrification. Silicon carbide is also added to promote deoxidation of the slag system, achieving white slag refining. Temperature and composition are adjusted during the refining process. Once the requirements are met, slag removal is performed on the LF ladle to remove the high-basicity slag. 5-6 kg / t of lime and 4-6 kg / t of silica sand are added again to control the binary basicity R at 0.9-1.2.

[0009] 3) RH Refining: After LF refining, the molten steel enters the RH chamber for vacuum denitrification treatment. The RH inlet temperature is generally 1630-1650℃. The RH chamber adopts a high vacuum denitrification mode. After the pump is turned on for 2 minutes, the vacuum degree reaches below 100Pa and is circulated for more than 25 minutes. At the same time, calcium carbide is added to the vacuum chamber through the vacuum hopper for further denitrification and deoxidation reactions, further reducing the nitrogen content.

[0010] 4) Continuous casting: Continuous casting strictly implements the protective casting process. The long nozzle is sealed with argon gas, and the tundish uses an integral nozzle to ensure the sealing effect. The tundish opening tonnage is controlled to be greater than 25t and the ladle remaining tonnage is guaranteed to be greater than 5t. Slag discharge is not allowed. The tundish superheat is 20℃~40℃. The casting process maintains a constant casting speed of 0.4~1.2m / min. The liquid level fluctuation in the crystallizer is ≤±3mm. The billet is hot-charged or stacked for cooling.

[0011] 5) Heating and rolling: Heating is carried out using a regenerative walking beam furnace. The specific heating process is as shown in Table 1. The furnace exit temperature is 1190~1210℃.

[0012] Table 1 Heating Time and Temperature

[0013] 390mm×480mm 1200～1250 ≥5.5 ≥10 1190～1210 210mm×210mm 1200～1230 ≥2.5 ≥4 1190～1210

[0014] Large bars are rolled using a 1150BD roughing mill and finished using 800 and 650 finishing mills. For large bars with a diameter of Ф85~300mm, the initial temperature after rolling is ≥550℃, the final temperature is ≤200℃, and the holding time is ≥48h. Small bars smaller than Ф85mm are rolled using a 24-stand Danieli finishing mill, equipped with a sizing mill. Rolled steel should be slowly cooled promptly. Small bars undergo a stacking cooling process.

[0015] The ultra-low nitrogen bearing steel produced by the method of producing green ultra-low nitrogen bearing steel in an ecological electric furnace has the following chemical composition by weight percentage: C: 0.90%~1.10%, Si: 0.10%~0.50%, Mn: 0.20%~0.60%, P≤0.020%, S≤0.010%, Cr: 1.30%~1.80%, Mo≤0.08%, Al≤0.005%, Cu≤0.25%, Ni≤0.20%, O≤0.0006%, N≤0.0030%, Ti≤0.0015%, Ca≤0.0005%, Pb≤0.002%, Sb≤0.005%, Sn≤0.03%, As≤0.04%, with the balance being iron and unavoidable impurities.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] This invention employs an "ECOARC eco-friendly electric furnace smelting + LF furnace refining + RH vacuum treatment + continuous casting + rolling" process to produce high-carbon chromium bearing steel GCr15-LN. This effectively controls the nitrogen content of the steel and ensures the performance requirements of high-carbon chromium bearing steel, while also exhibiting ultra-low nitrogen and long service life characteristics. This invention utilizes scrap steel for smelting entirely, reducing carbon emissions while achieving stable production of low-cost, ultra-low nitrogen green bearing steel. Detailed Implementation

[0018] The specific implementation of the present invention will be further described below with reference to the embodiments.

[0019] Example 1:

[0020] 1) Eco-friendly electric arc furnace smelting: Scrap steel is used as the furnace charge. The scrap steel used is high-quality scrap steel free of impurities, with a 100% proportion and a carbon content of 2.60%. Oxygen blowing is used for melting, and carbon monoxide bubbles generated by the carbon-oxygen reaction are used for denitrification, reducing the nitrogen content of the molten steel. Low-nitrogen carbon powder is injected to create foamy slag, ensuring a good submerged arc effect and reducing nitrogen absorption at the electrodes. High-power current is used to melt the scrap steel, with a tapping temperature of 1640℃. Aluminum deoxidation is not performed during tapping; instead, a silicon deoxidation process is used, adding 2.5 kg / t of ferrosilicon. After deoxidation, alloying is carried out, and 4 kg / t of limestone is added to the bottom of the ladle. The carbon dioxide gas generated by the heated limestone reaction forms a protective gas layer on the molten steel, reducing nitrogen absorption during tapping.

[0021] 2) LF Refining: LF refining uses active lime, fluorite, calcium carbide, and silicon carbide for aluminum-free slag formation. After the ladle is in place, argon gas is started at 380 NL / min, and 4.5 kg / t steel of lime and 4.5 kg / t steel of fluorite are added. The argon gas flow is then adjusted to 180 NL / min, and heating begins to form slag. Large-scale argon gas stirring during heating is not allowed to prevent nitrogen buildup. 1 kg / t steel of calcium carbide is added during each heating and slag formation process. This maintains a reducing atmosphere near the electrodes to prevent nitrogen buildup and allows calcium carbide to react with nitrogen in the molten steel to form calcium cyanamide (CaCN2) for denitrification. Silicon carbide is also added to promote deoxidation of the slag system, achieving white slag refining. Temperature and composition are adjusted during the refining process. Once the requirements are met, the LF ladle is skimmed to remove the high-basicity slag. 5.5 kg / t steel of lime and 5 kg / t steel of silica sand are added again, maintaining the binary basicity R at 1.1. The composition of the LF ladle at the station is shown in Table 2.

[0022] Table 2 Chemical composition of LF off-site steel in the example

[0023]

[0024] 3) RH Refining: After LF refining, the molten steel enters the RH (Refining and Drying) system for vacuum denitrification. The RH inlet temperature is 1650℃, and the RH system uses a high-vacuum denitrification mode. After the pump is started for 2 minutes, the vacuum degree reaches 70Pa and is circulated for 28 minutes. At the same time, 1 kg / t of calcium carbide is added to the vacuum chamber through the vacuum hopper for further denitrification and deoxidation reactions, further reducing the nitrogen content. The composition of the RH system after leaving the station is shown in Table 3.

[0025] Table 3 Chemical composition of RH off-site steel in the example

[0026]

[0027] 4) Continuous casting: The continuous casting process strictly implements the protective casting process. The long nozzle is sealed with argon gas, and the tundish uses an integral nozzle to ensure the sealing effect. The tundish initial casting tonnage is 30t, and the ladle has 5.3t remaining with no slag. The tundish superheat is 35℃. The casting speed is 0.45m / min. The liquid level fluctuation in the crystallizer is ±3mm. The billet is hot-charged or stacked for cooling.

[0028] 5) Heating and rolling: The billet is 210mm×210mm in size. Heating is carried out in a regenerative walking beam furnace at a heating temperature of 1225℃, a soaking time of 160min, and a total heating time of 287min. The furnace exit temperature is 1195℃.

[0029] The rolling process utilizes a medium-length bar finishing mill to produce steel with a diameter of Ф60mm. After rolling, the steel is rapidly collected and then slowly cooled.

[0030] 6) Product quality is shown in Table 4.

[0031] Table 4 Chemical composition of the finished product in Example 1

[0032]

[0033] Example 2:

[0034] 1) Eco-friendly electric arc furnace smelting: Scrap steel is used as the furnace charge. The scrap steel used is high-quality scrap steel free of impurities, with a 100% proportion and a carbon content of 2.70%. Oxygen blowing is used for melting, and carbon monoxide bubbles generated by the carbon-oxygen reaction are used for denitrification, reducing the nitrogen content of the molten steel. Low-nitrogen carbon powder is injected to create foamy slag, ensuring a good submerged arc effect and reducing nitrogen absorption at the electrodes. High-power current is used to melt the scrap steel, with a tapping temperature of 1645℃. Aluminum deoxidation is not performed during tapping; instead, a silicon deoxidation process is used, adding 2.6 kg / t of ferrosilicon. After deoxidation, alloying is carried out, and 3 kg / t of limestone is added to the bottom of the ladle. The carbon dioxide gas generated by the heated limestone reaction forms a protective gas layer on the molten steel, reducing nitrogen absorption during tapping.

[0035] 2) LF Refining: LF refining uses active lime, fluorite, calcium carbide, and silicon carbide for aluminum-free slag formation. After the ladle is in place, argon gas is started at 450 NL / min, and 3.8 kg / t steel of lime and 3.8 kg / t steel of fluorite are added. The argon gas flow is then adjusted to 220 NL / min, and heating begins for slag formation. Large-scale argon gas stirring during heating is not permitted to prevent nitrogen buildup. 0.9 kg / t steel of calcium carbide is added simultaneously with each heating and slag formation process. This maintains a reducing atmosphere near the electrodes to prevent nitrogen buildup and allows calcium carbide to react with nitrogen in the molten steel to form calcium cyanamide (CaCN2) for denitrification. Silicon carbide is also added to promote deoxidation of the slag system, achieving a white slag refining effect. Temperature and composition are adjusted during the refining process. Once the requirements are met, the LF slag is removed, and high-basicity slag is cleaned off. 5.8 kg / t steel of lime and 5.5 kg / t steel of silica sand are added again, maintaining the binary basicity R at 1.0. The composition of the LF slag before leaving the station is shown in Table 5.

[0036] Table 5 Chemical composition of LF steel leaving the station in Example 2

[0037]

[0038]

[0039] 3) RH Refining: After LF refining, the molten steel enters the RH (Refining and Drying) system for vacuum denitrification. The RH inlet temperature is 1640℃. The RH system uses a high-vacuum denitrification mode. After the pump is started for 2 minutes, the vacuum degree reaches 80Pa and is circulated for 26 minutes. At the same time, 1 kg / t of calcium carbide is added to the vacuum chamber through the vacuum hopper for further denitrification and deoxidation reactions, further reducing the nitrogen content. The composition of the RH system leaving the station is shown in Table 6.

[0040] Table 6 Chemical composition of RH off-site steel in Example 2

[0041]

[0042] 4) Continuous casting: The continuous casting process strictly implements the protective casting process. The long nozzle is sealed with argon gas, and the tundish uses an integral nozzle to ensure the sealing effect. The tundish initial casting tonnage is 35t, and the ladle casting tonnage is 6t with no slag added. The tundish superheat is 28℃. The casting speed is 0.45m / min. The liquid level fluctuation in the crystallizer is ±2mm. The billet is hot-charged or stacked for cooling.

[0043] 5) Heating and rolling: The billet of 390mm×480mm is heated in a regenerative walking beam furnace at a heating temperature of 1240℃, a soaking time of 330min, and a total heating time of 630min. The furnace exit temperature is 1200℃.

[0044] The rolling process utilizes a medium-length bar finishing mill to produce steel with a diameter of Ф160mm. The rolled steel is then slowly cooled, with an initial temperature of 550℃ and an exit temperature of 180℃, followed by a holding time of 50 hours.

[0045] 6) Product quality is shown in Table 7.

[0046] Table 7 Chemical composition of the finished product in Example 2

[0047]

[0048] Example 3:

[0049] 1) Eco-friendly electric arc furnace smelting: Scrap steel is used as the furnace charge. The scrap steel used is high-quality scrap steel free of impurities, with a 100% proportion and a carbon content of 2.70%. Oxygen blowing is used for melting, and carbon monoxide bubbles generated by the carbon-oxygen reaction are used for denitrification, reducing the nitrogen content of the molten steel. Low-nitrogen carbon powder is injected to create foamy slag, ensuring a good submerged arc effect and reducing nitrogen absorption at the electrodes. High-power current is used to melt the scrap steel, with a tapping temperature of 1648℃. Aluminum deoxidation is not performed during tapping; instead, a silicon deoxidation process is used, adding 2.7 kg / t of ferrosilicon. After deoxidation, alloying is carried out, and 4.5 kg / t of limestone is added to the bottom of the ladle. The carbon dioxide gas generated by the heated limestone forms a protective gas layer on the molten steel, reducing nitrogen absorption during tapping.

[0050] 2) LF Refining: LF refining uses active lime, fluorite, calcium carbide, and silicon carbide for aluminum-free slag formation. After the ladle is in place, argon gas is started at 360 NL / min, and 4.8 kg / t steel of lime and 3.5 kg / t steel of fluorite are added. The argon gas flow is then adjusted to 200 NL / min, and heating begins to form slag. Large-scale argon gas stirring during heating is not allowed to prevent nitrogen accumulation. 1 kg / t steel of calcium carbide is added during each heating and slag formation process. This maintains a reducing atmosphere near the electrodes to prevent nitrogen accumulation and allows calcium carbide to react with nitrogen in the molten steel to form calcium cyanamide (CaCN2) for denitrification. Silicon carbide is also added to promote deoxidation of the slag system, achieving white slag refining. Temperature and composition are adjusted during the refining process. Once the requirements are met, the LF system undergoes slag removal to clean out the high-basicity slag. 5.2 kg / t steel of lime and 4.5 kg / t steel of silica sand are then added again, maintaining the binary basicity R at 1.2. The composition of the LF system at the station is shown in Table 8.

[0051] Table 8 Chemical composition of LF steel leaving the station in Example 3

[0052]

[0053] 3) RH Refining: After LF refining, the molten steel enters the RH (Refining and Drying) system for vacuum denitrification. The RH inlet temperature is 1640℃. The RH system uses a high-vacuum denitrification mode. After the pump is started for 2 minutes, the vacuum degree reaches 90Pa and is circulated for 30 minutes. At the same time, 1 kg / t of calcium carbide is added to the vacuum chamber through the vacuum hopper for further denitrification and deoxidation reactions, further reducing the nitrogen content. The composition of the RH system after leaving the station is shown in Table 9.

[0054] Table 9 Chemical composition of RH off-site steel in Example 3

[0055]

[0056] 4) Continuous casting: The continuous casting process strictly implements the protective casting process. The long nozzle is sealed with argon gas, and the tundish uses an integral nozzle to ensure the sealing effect. The tundish initial casting tonnage is 30t, and the ladle casting tonnage is 4t with no slag added. The tundish superheat is 25℃; the casting speed is 0.90m / min; the liquid level fluctuation in the crystallizer is ±3mm; the billet is hot-charged or stacked for cooling.

[0057] 5) Heating and rolling: The billet is 210mm×210mm. Heating is carried out in a regenerative walking beam furnace at a heating temperature of 1228℃, a soaking time of 165min, and a total heating time of 290min. The furnace exit temperature is 1200℃.

[0058] The rolling process uses a small bar finishing mill to roll steel with a diameter of Ф80mm. After rolling, the steel is stacked and cooled slowly. 6) Product quality is shown in Table 10.

[0059] Table 10 Chemical composition of the finished product in Example 3

[0060]

Claims

1. A method for producing green ultra-low nitrogen bearing steel using an eco-friendly electric furnace, characterized in that, Specifically, the methods and steps are as follows: 1) Ecological electric furnace smelting: 100% scrap steel is used as furnace charge, with a carbon content of ≥2.50%, oxygen blowing to assist melting, and a tapping temperature of 1635~1650℃. During the tapping process, aluminum deoxidation is not carried out, but silicon deoxidation is used, with 2~3kg / t of ferrosilicon added. After deoxidation, alloying is carried out, and 2~5kg / t of limestone is added to the bottom of the ladle. 2) LF refining: After the ladle is in place, start the argon gas at 300-500 NL / min, add 3-5 kg / t of lime and 3-5 kg / t of fluorite, adjust the argon gas to 150-250 NL / min, and start heating and slag formation. Add 0.5-1 kg / t of calcium carbide each time the heating and slag formation is carried out. After the LF slag removal operation, add lime and quartz sand again to control the binary basicity R at 0.9-1.

2. 3) RH refining: The RH inlet temperature is 1630~1650℃. After the pump is turned on for 2 minutes, the vacuum degree reaches below 100Pa and is circulated for more than 25 minutes. At the same time, calcium carbide is added into the vacuum chamber through the vacuum hopper to carry out further denitrification and deoxygenation reaction. 4) Continuous casting: Continuous casting strictly adheres to the protective casting process; 5) Heating and rolling: furnace exit temperature 1190~1210℃.

2. The method for producing green ultra-low nitrogen bearing steel in an eco-friendly electric furnace according to claim 1, characterized in that, The superheat of the tundish in continuous casting is 20℃~40℃; the casting process maintains a constant casting speed of 0.4~1.2m / min; and the liquid level fluctuation in the crystallizer is ≤±3mm.

3. The method for producing green ultra-low nitrogen bearing steel in an eco-friendly electric furnace according to claim 1, characterized in that, In the hot rolling step, for a billet of 390mm×480mm, the high-temperature diffusion temperature is 1200~1250℃, the high-temperature diffusion time is ≥5.5h, and the total heating time is ≥10h; For a 210mm×210mm billet, the high-temperature diffusion temperature is 1200~1230℃, the high-temperature diffusion time is ≥2.5 h, and the total heating time is ≥4h.

4. The method for producing green ultra-low nitrogen bearing steel in an eco-friendly electric furnace according to claim 1, characterized in that, For steel bars with a production specification range of Ф85~300mm, the insulation treatment requires an initial temperature of ≥550℃, an exit temperature of ≤200℃, and an insulation time of ≥48h; for small bars smaller than Ф85mm, a stacking cooling process is performed.

5. The method for producing green ultra-low nitrogen bearing steel in an eco-friendly electric furnace according to claim 1, characterized in that, The chemical composition of the steel, by weight percentage, is as follows: C: 0.90%~1.10%, Si: 0.10%~0.50%, Mn: 0.20%~0.60%, P≤0.020%, S≤0.010%, Cr: 1.30%~1.80%, Mo≤0.08%, Al≤0.005%, Cu≤0.25%, Ni≤0.20%, O≤0.0006%, N≤0.0030%, Ti≤0.0015%, Ca≤0.0005%, Pb≤0.002%, Sb≤0.005%, Sn≤0.03%, As≤0.04%, with the balance being iron and unavoidable impurities.

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