A Clean Smelting and Inclusion Control Process for Steel for High-Strength Circular Link Chains

Abstract

This invention relates to the field of iron and steel metallurgy technology and discloses a clean smelting and inclusion control process for high-strength round link chain steel. The process includes S1 hot metal pretreatment, S2 converter smelting, S3 LF refining, S4 VD / RH vacuum refining, S5 continuous casting, S6 subsequent quality control, and S7 process monitoring and adjustment. Through clean smelting and precise inclusion control throughout the entire process, the total oxygen content of the high-strength round link chain steel is ≤25ppm, hydrogen content ≤2.0ppm, and sulfur content ≤0.008%; the A / B class inclusion level is ≤1.5, the D class inclusion level is ≤1.0, and there are no large inclusions larger than 50μm. The cleanliness of the molten steel meets the performance requirements for subsequent drawing, welding, and heat treatment, ensuring fatigue resistance and fracture toughness during chain use and reducing the risk of fracture induced by inclusions.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, specifically to a clean smelting and inclusion control process for high-strength circular link chain steel. Background Technology

[0002] High-strength circular link chains are widely used in harsh working conditions such as mining, hoisting, and logistics, where they must withstand alternating loads and impacts. Their fatigue resistance and fracture toughness directly determine their safety in use. Current technologies lack a comprehensive cleanliness and inclusion control design throughout the smelting and continuous casting processes for circular link chain steel. Problems such as incomplete desulfurization during hot metal pretreatment, over-oxidation during converter blowing, insufficient deoxidation during refining slag formation, and poor adaptability of calcium treatment parameters lead to high total oxygen, hydrogen, and sulfur content in the molten steel, exceeding the limits for A / B and D class inclusions, and easily forming large Al2O3 inclusions larger than 50μm. Simultaneously, insufficient crystallizer protection and improper secondary cooling water distribution during continuous casting cause secondary oxidation of the molten steel and inclusion aggregation. These inclusions become stress concentration sources, inducing cracks during chain drawing, welding, and service, significantly reducing fatigue resistance, and ultimately leading to chain breakage and failure, making it difficult to meet the stringent requirements of high-strength circular link chains. Summary of the Invention

[0003] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a clean smelting and inclusion control process for high-strength circular link chain steel. It has the advantages of clean smelting throughout the entire process and precise inclusion control, solving the problem of the lack of a synergistic control design for cleanliness and inclusions throughout the smelting and continuous casting process of circular link chain steel.

[0004] (II) Technical Solution To achieve the above-mentioned goals of clean smelting and precise inclusion control throughout the entire process, this invention provides the following technical solution: a clean smelting and inclusion control process for high-strength circular link chain steel, comprising the following steps: S1 hot metal pretreatment, S2 converter smelting, S3 LF refining, S4 VD / RH vacuum refining, S5 continuous casting, S6 subsequent quality control, and S7 process monitoring and adjustment. The S1 hot metal pretreatment includes S101 desulfurization pretreatment, S102 pretreatment control, and S103 slag removal and purification. The S2 converter smelting process includes S201 charging system, S202 blowing control, S203 endpoint control and S204 slag blocking and tapping. The S3 LF refining process includes S301 slag formation and deoxidation, S302 argon blowing and stirring, S303 composition fine-tuning, S304 slag formation control and S305 calcium treatment optimization. The S4 VD / RH vacuum refining process includes S401 vacuum treatment, S402 soft blowing purification, S403 steel purity control and S404 temperature and superheat control. The S5 continuous casting process includes S501 crystallizer protection, S502 crystallizer process, S503 secondary cooling water supply, S504 casting speed control, and S505 billet quality control.

[0005] Preferably, the S101 desulfurization pretreatment adopts KR mechanical stirring desulfurization, and the desulfurizing agent is a high-activity lime-fluorite mixture (85%-90% lime + 10%-15% fluorite), with an addition amount of 8-12 kg / t of molten iron (10 kg / t optimized and expanded based on material basis). S102 pretreatment control: stirring speed 120-150r / min, stirring time 15-25min, to ensure that the [S] content of the molten iron after desulfurization is ≤0.008% (material basis ≤0.010%, optimized and tightened); the temperature of the molten iron after pretreatment is controlled at 1280-1320℃ to avoid the temperature being too low and affecting the fluidity of subsequent smelting; S103 Slag Removal and Purification: The slag removal rate after desulfurization is ≥95%. After slag removal, the surface of the molten iron is covered with a heat-insulating agent to prevent secondary oxidation. Molten iron must not be transported in an exposed state before entering the converter.

[0006] Preferably, the S201 loading procedure is as follows: molten iron ratio 78%-85% (material base 80%-82% optimized and expanded), and the scrap steel is selected as low phosphorus, low sulfur, and rust-free scrap steel to avoid introducing harmful impurities and foreign inclusions; S202 blowing control: oxygen supply intensity 3.0-3.8m 3 / (t・min), bottom-blown argon stirring throughout, argon flow rate 0.8-1.5m³ / min. 3 / (min・furnace), to ensure the molten steel is stirred evenly; S203 endpoint control: endpoint carbon [C] ≥ 0.05% (material basis ≥ 0.06% optimized and expanded), endpoint phosphorus [P] ≤ 0.010% (material basis ≤ 0.012% optimized and tightened), endpoint temperature 1620-1660℃ (material basis 1630-1650℃ optimized and expanded), to avoid over-oxidation leading to increased oxygen content; S204 Slag-Blocking Steelmaking: Adopts a double slag-blocking process (slag-blocking ball + slag-blocking cone), with slag discharge of ≤5kg / t steel (material basis ≤8kg / t optimized tightening). During the steelmaking process, 3-5kg / t of pre-melted refining slag is added with the flow to advance slag formation and deoxidation.

[0007] Preferably, the S301 slag deoxidation involves adding CaO-Al2O3-SiO2 refining slag (CaO 50%-55%, Al2O3 25%-30%, SiO2≤15%) during the initial refining stage, with the basicity controlled at 3.0-4.5 (based on a material standard of 3.5-4.0, optimized and expanded); Al particle diffusion deoxidation is employed, added in batches, with a total addition of 0.8-1.2 kg / t steel to ensure sufficient deoxidation of the molten steel; S302 Argon Stirring: Argon stirring throughout the process, with argon flow rate adjusted in stages: 0.3-0.5 m³ / h during the heating phase. 3 / h, refining period 0.2-0.4m 3 / h, soft blowing period 0.1-0.2m 3 / h, total argon blowing time ≥35-50min (material basis ≥40min, optimized and expanded), to promote the flotation of inclusions.

[0008] Preferably, the S303 composition fine-tuning involves precisely adjusting the C, Mn, and Cr elements according to the target composition, with a composition deviation of ≤ ±0.01%; and residual elements (Sb, As, Sn) ≤ 0.03%, to avoid the cumulative effect of elements on the cleanliness of molten steel. S304 slag formation control: rapid slag formation time ≤30min (material basis ≤25min, optimized and expanded), slag thickness controlled at 80-120mm, to ensure full slag-steel reaction and adsorption of Al2O3 inclusions in steel; S305 calcium treatment optimization: Calcium wire (CaSi wire, Ca content 28%-32%) is fed at the end of refining, with a feeding speed of 2.5-4.0 m / s. The feeding amount is adjusted according to the acid-soluble aluminum content of the molten steel: when [Al]s=0.020-0.030%, the feeding amount is 0.8-1.2 kg / t; when [Al]s=0.030-0.055%, the feeding amount is 1.2-1.6 kg / t, modifying Al2O3 inclusions into low-melting-point calcium aluminate.

[0009] Preferably, the S401 vacuum treatment involves: evacuating the VD furnace to 0.3-0.5 torr (0.5 torr is the baseline for material selection, optimized and expanded), and maintaining the vacuum for ≥8-15 minutes (≥10 minutes is the baseline for material selection, optimized and expanded); and maintaining the vacuum in the RH furnace to ≤0.3 torr, with a cycle time ≥12-18 minutes, to promote the removal of hydrogen, nitrogen, and inclusions. S402 soft-blowing purification: After vacuum rupture, the soft-blowing argon time is ≥10-20 min (≥12 min for material-specific applications, optimized and expanded), with an argon flow rate of 0.1-0.2 m³ / min. 3 / h, to avoid secondary oxidation of molten steel and ensure that inclusions float to the surface.

[0010] Preferably, the purity of the S403 molten steel is controlled as follows: after vacuum treatment, the [H] content of the molten steel is ≤2.0ppm and the [O] content is ≤25ppm; 1-2 furnaces of molten steel are taken for large-sample electrolysis after each casting, and the total amount of inclusions is ≤50mg / 10kg of steel. S404 Temperature and Superheat Control: After vacuum treatment, the molten steel temperature is 1560-1590℃, and the superheat of the tundish is controlled at 20-45℃ (the material base is 20-35℃, which is optimized and expanded). The temperature of the first casting furnace is ≤45℃, and the temperature of the continuous casting furnace is ≤40℃.

[0011] Preferably, the S501 crystallizer protection adopts an integral nozzle + immersion nozzle (immersion depth 80-130mm, material base 80-120mm optimized expansion), and the tundish covering agent is a low carbon steel special covering agent, with an addition amount of 0.8-1.2kg / t steel, to prevent secondary oxidation of molten steel; S502 crystallizer process: The protective slag for the crystallizer is selected from a low melting point and low viscosity slag system (melting point 1100-1150℃, viscosity 0.8-1.2Pa・s), and the liquid level fluctuation in the crystallizer is controlled to be ≤±3mm; the electromagnetic stirring parameters of the crystallizer are: current 200-300A (based on material 250A, optimized and expanded), frequency 2.0-3.5Hz (based on material 2.5-3Hz, optimized and expanded), to promote the flotation of inclusions and uniform composition; S503 secondary cooling water distribution: A weak cooling water distribution system is adopted, with a secondary cooling water volume of 0.4-0.9 L / kg steel (0.45-0.8 L / kg for material basis, optimized and expanded), adjusted according to the billet cross-section: 0.4-0.6 L / kg for cross-section ≤150mm, and 0.6-0.9 L / kg for cross-section >150mm, to avoid excessively rapid cooling leading to the accumulation of inclusions; S504 casting speed control: Casting speed 2.0-2.8m / min (material base 2.3-2.7m / min optimized and expanded), dynamically adjusted according to the superheat of the ladle: casting speed 2.4-2.8m / min when superheat is 20-30℃, casting speed 2.0-2.4m / min when superheat is 30-45℃, to ensure uniform solidification; S505 billet quality control: The continuous casting billet adopts a light reduction process with a reduction of 3-8mm; 2-3 billets are taken from each casting for low magnification inspection, with central porosity ≤1.5 grade, central segregation ≤1.0 grade, and no obvious inclusions.

[0012] Preferably, the subsequent quality control step S6 is as follows: Billet cleaning: The surface cleaning depth of the continuously cast billet is ≥2mm, removing surface oxide scale, cracks and inclusions. The surface finish Ra after cleaning is ≤1.6μm. Pre-rolling treatment: Before the billet enters the furnace, it is shot blasted to remove residual inclusions and oxide scale from the surface; the heating furnace is protected by inert gas or a weak oxidizing atmosphere, the heating temperature is 1150-1200℃, and the holding time is 2-4h to avoid high-temperature oxidation. Inclusion detection: Take 3-5 samples from each batch of finished wire rod for metallographic inclusion rating and large particle inclusion scanning detection to ensure that the inclusion level meets the process target; for unqualified batches, the smelting and continuous casting process parameters need to be traced and the subsequent process adjusted.

[0013] Preferably, the S7 process monitoring and adjustment steps are as follows: For each casting, record the key parameters of molten iron pretreatment, converter, LF refining, VD / RH and continuous casting, and establish a database corresponding to "process-cleanliness". If excessive inclusions are detected (A / B class > 1.5 or D class > 1.0), prioritize adjusting the LF refining slag alkalinity (±0.5) or calcium treatment feed rate (±0.2 kg / t); if total oxygen > 25 ppm, extend the VD / RH vacuum holding time (+2-3 min) or soft blowing time (+3-5 min). Monthly statistics are compiled on inclusion detection data, steel purity indicators, and chain usage quality feedback. The deoxidation process, calcium treatment parameters, and continuous casting cooling process are optimized to continuously improve process stability.

[0014] (III) Beneficial Effects Compared with the prior art, the present invention provides a clean smelting and inclusion control process for steel for high-strength circular links, which has the following beneficial effects: 1. The clean smelting and inclusion control process of the steel used for this high-strength round link chain, through clean smelting and precise inclusion control throughout the entire process, ensures that the total oxygen content of the high-strength round link chain steel is ≤25ppm, the hydrogen content is ≤2.0ppm, and the sulfur content is ≤0.008%; the A / B class inclusion level is ≤1.5, the D class inclusion level is ≤1.0, and there are no large inclusions larger than 50μm; the cleanliness of the molten steel meets the performance requirements of subsequent drawing, welding and heat treatment, ensuring the fatigue resistance and fracture toughness of the chain during use, and reducing the risk of fracture induced by inclusions.

[0015] 2. The clean smelting and inclusion control process for the steel used in this high-strength circular link chain significantly improves the cleanliness of the molten steel: through the synergistic process of KR mechanical stirring for deep desulfurization of molten iron, double-slag tapping in the converter, LF refining for high-basicity slag formation and Al particle diffusion deoxidation, and VD / RH vacuum degassing, the total oxygen content of the molten steel is ≤25ppm, hydrogen content is ≤2.0ppm, and sulfur content is ≤0.008%, effectively reducing the impact of gases and harmful impurities on the purity of the molten steel and laying the foundation for subsequent processing performance.

[0016] 3. The clean smelting and inclusion control process of the steel used for this high-strength circular link chain achieves precise and controllable inclusions: the LF refining calcium treatment parameters are optimized to modify hard and brittle Al2O3 inclusions into low-melting-point calcium aluminate. Combined with continuous casting electromagnetic stirring and weak cooling water distribution, the inclusion level of A / B type is ≤1.5 and the inclusion level of D type is ≤1.0, with no large inclusions larger than 50μm, completely solving the problem of inclusion-induced cracks in traditional processes.

[0017] 4. The clean smelting and inclusion control process of the steel used for this high-strength circular link chain ensures the performance of the chain: the synergistic effect of improved cleanliness and inclusion control significantly enhances the chain's fatigue resistance and fracture toughness, reduces the risk of fracture caused by stress concentration due to inclusions during service, and meets the requirements of drawing, welding and heat treatment for the material's plasticity and toughness, ensuring the chain's stability under alternating loads and harsh working conditions.

[0018] 5. The clean smelting and inclusion control process for the steel used in this high-strength circular link chain enhances the stability of the production process: through full-process parameter monitoring, inclusion detection, and dynamic feedback mechanisms, a "process-cleanliness-inclusion" linkage database is established, which can accurately adjust desulfurization, deoxidation, calcium treatment, and continuous casting parameters, reduce batch quality fluctuations, improve product qualification rate, and reduce rework and scrap costs caused by excessive inclusions. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] This solution provides a technical approach, specifically a clean smelting and inclusion control process for high-strength circular link chain steel, comprising the following steps: S1 Hot metal pretreatment process steps: S101 Desulfurization Pretreatment: KR mechanical stirring desulfurization is adopted, and the desulfurizing agent is a high-activity lime-fluorite mixture (85%-90% lime + 10%-15% fluorite), with an addition amount of 8-12 kg / t molten iron (10 kg / t for material basis optimization and expansion). S102 pretreatment control: stirring speed 120-150r / min, stirring time 15-25min, to ensure that the [S] content of the molten iron after desulfurization is ≤0.008% (material basis ≤0.010%, optimized and tightened); the temperature of the molten iron after pretreatment is controlled at 1280-1320℃ to avoid the temperature being too low and affecting the fluidity of subsequent smelting; S103 Slag Removal and Purification: The slag removal rate after desulfurization is ≥95%. After slag removal, the surface of the molten iron is covered with a heat-insulating agent to prevent secondary oxidation. Molten iron must not be transported in an exposed state before entering the converter. S2 converter smelting process steps: S201 loading system: molten iron ratio 78%-85% (material base 80%-82% optimized and expanded), scrap steel should be low phosphorus, low sulfur and rust-free scrap steel to avoid introducing harmful impurities and foreign inclusions; S202 blowing control: oxygen supply intensity 3.0-3.8m 3 / (t・min), bottom-blown argon stirring throughout, argon flow rate 0.8-1.5m³ / min. 3 / (min・furnace), to ensure the molten steel is stirred evenly; S203 endpoint control: endpoint carbon [C] ≥ 0.05% (material basis ≥ 0.06% optimized and expanded), endpoint phosphorus [P] ≤ 0.010% (material basis ≤ 0.012% optimized and tightened), endpoint temperature 1620-1660℃ (material basis 1630-1650℃ optimized and expanded), to avoid over-oxidation leading to increased oxygen content; S204 Slag-Blocking Steelmaking: Adopts a double slag-blocking process (slag-blocking ball + slag-blocking cone), with slag discharge ≤5kg / t steel (material basis ≤8kg / t optimized tightening). During the steelmaking process, 3-5kg / t steel of pre-melted refining slag is added with the flow to advance slag formation and deoxidation. S3 LF refining process steps: S301 Slag Deoxidation: In the initial stage of refining, add CaO-Al2O3-SiO2 system refining slag (CaO 50%-55%, Al2O3 25%-30%, SiO2≤15%), and control the basicity at 3.0-4.5 (based on material 3.5-4.0, optimized and expanded); use Al particle diffusion deoxidation, added in batches, with a total addition of 0.8-1.2 kg / t steel to ensure sufficient deoxidation of molten steel; S302 Argon Stirring: Argon stirring throughout the process, with argon flow rate adjusted in stages: 0.3-0.5 m³ / h during the heating phase. 3 / h, refining period 0.2-0.4m 3 / h, soft blowing period 0.1-0.2m 3 / h, total argon blowing time ≥35-50min (material basis ≥40min optimization and expansion), to promote the flotation of inclusions; S303 composition fine-tuning: C, Mn, and Cr elements are precisely adjusted according to the target composition, with a composition deviation of ≤ ±0.01%; residual elements (Sb, As, Sn) ≤ 0.03%, avoiding the cumulative effect of elements on the cleanliness of molten steel; S304 slag formation control: rapid slag formation time ≤30min (material basis ≤25min, optimized and expanded), slag thickness controlled at 80-120mm, to ensure full slag-steel reaction and adsorption of Al2O3 inclusions in steel; S305 calcium treatment optimization: Calcium wire (CaSi wire, Ca content 28%-32%) is fed at the end of refining, with a feeding speed of 2.5-4.0 m / s. The feeding amount is adjusted according to the acid-soluble aluminum content of the molten steel: when [Al]s = 0.020-0.030%, the feeding amount is 0.8-1.2 kg / t; when [Al]s = 0.030-0.055%, the feeding amount is 1.2-1.6 kg / t, modifying Al2O3 inclusions into low-melting-point calcium aluminate. S4 VD / RH vacuum refining process steps: S401 Vacuum Treatment: VD furnace is evacuated to 0.3-0.5 torr (0.5 torr is the basic material standard, optimized and expanded), and the vacuum holding time is ≥8-15 min (≥10 min is the basic material standard, optimized and expanded); RH furnace vacuum degree ≤0.3 torr, cycle time ≥12-18 min, to promote the removal of hydrogen, nitrogen and inclusions; S402 soft-blowing purification: After vacuum rupture, the soft-blowing argon time is ≥10-20 min (≥12 min for material-specific applications, optimized and expanded), with an argon flow rate of 0.1-0.2 m³ / min. 3 / h, to avoid secondary oxidation of molten steel and ensure that inclusions float to the surface; S403 steel purity control: After vacuum treatment, the [H] in the molten steel is ≤2.0ppm and [O] is ≤25ppm; 1-2 heats of molten steel are taken from each casting for large-sample electrolysis, and the total amount of inclusions is ≤50mg / 10kg steel; S404 Temperature and Superheat Control: After vacuum treatment, the molten steel temperature is 1560-1590℃, and the superheat of the tundish is controlled at 20-45℃ (the material base is 20-35℃, which is optimized and expanded). The opening furnace temperature is ≤45℃, and the continuous casting furnace temperature is ≤40℃. S5 continuous casting process steps: S501 crystallizer protection: adopts integral nozzle + submersible nozzle (submersion depth 80-130mm, material base 80-120mm optimized expansion), the tundish covering agent is a special covering agent for low carbon steel, added at 0.8-1.2kg / t steel to prevent secondary oxidation of molten steel; S502 crystallizer process: The protective slag for the crystallizer is selected from a low melting point and low viscosity slag system (melting point 1100-1150℃, viscosity 0.8-1.2Pa・s), and the liquid level fluctuation in the crystallizer is controlled to be ≤±3mm; the electromagnetic stirring parameters of the crystallizer are: current 200-300A (based on material 250A, optimized and expanded), frequency 2.0-3.5Hz (based on material 2.5-3Hz, optimized and expanded), to promote the flotation of inclusions and uniform composition; S503 secondary cooling water distribution: A weak cooling water distribution system is adopted, with a secondary cooling water volume of 0.4-0.9 L / kg steel (0.45-0.8 L / kg for material basis, optimized and expanded), adjusted according to the billet cross-section: 0.4-0.6 L / kg for cross-section ≤150mm, and 0.6-0.9 L / kg for cross-section >150mm, to avoid excessively rapid cooling leading to the accumulation of inclusions; S504 casting speed control: Casting speed 2.0-2.8m / min (material base 2.3-2.7m / min optimized and expanded), dynamically adjusted according to the superheat of the ladle: casting speed 2.4-2.8m / min when superheat is 20-30℃, casting speed 2.0-2.4m / min when superheat is 30-45℃, to ensure uniform solidification; S505 billet quality control: The continuous casting billet adopts a light reduction process with a reduction of 3-8mm; 2-3 billets are taken from each casting for low magnification inspection, with central porosity ≤1.5 grade, central segregation ≤1.0 grade, and no obvious inclusions. S6 Subsequent Quality Control Steps: Billet cleaning: The surface cleaning depth of the continuously cast billet is ≥2mm, removing surface oxide scale, cracks and inclusions. The surface finish Ra after cleaning is ≤1.6μm. Pre-rolling treatment: Before the billet enters the furnace, it is shot blasted to remove residual inclusions and oxide scale from the surface; the heating furnace is protected by inert gas or a weak oxidizing atmosphere, the heating temperature is 1150-1200℃, and the holding time is 2-4h to avoid high-temperature oxidation. Inclusion detection: Take 3-5 samples from each batch of finished wire rod for metallographic inclusion rating and large particle inclusion scanning detection to ensure that the inclusion level meets the process target; for unqualified batches, the smelting and continuous casting process parameters need to be traced and the subsequent process adjusted. S7 Process Monitoring and Adjustment Steps: For each casting, record the key parameters of molten iron pretreatment, converter, LF refining, VD / RH and continuous casting, and establish a database corresponding to "process-cleanliness". If excessive inclusions are detected (A / B class > 1.5 or D class > 1.0), prioritize adjusting the LF refining slag alkalinity (±0.5) or calcium treatment feed rate (±0.2 kg / t); if total oxygen > 25 ppm, extend the VD / RH vacuum holding time (+2-3 min) or soft blowing time (+3-5 min). Monthly statistics are compiled on inclusion detection data, molten steel purity indicators, and chain usage quality feedback. The deoxidation process, calcium treatment parameters, and continuous casting cooling process are optimized to continuously improve process stability. Process objectives: Through clean smelting throughout the entire process and precise inclusion control, the total oxygen content of the high-strength round link chain steel is ≤25ppm, hydrogen content is ≤2.0ppm, and sulfur content is ≤0.008%; the inclusion level of Class A / B is ≤1.5, the inclusion level of Class D is ≤1.0, and there are no large inclusions larger than 50μm; the cleanliness of the molten steel meets the performance requirements of subsequent drawing, welding and heat treatment, ensuring the fatigue resistance and fracture toughness of the chain during use, and reducing the risk of fracture induced by inclusions; Furthermore, this process significantly improves the cleanliness of molten steel: through the synergistic process of KR mechanical stirring for deep desulfurization of molten iron, double-slag tapping in the converter, LF refining for high-basicity slag formation and Al particle diffusion deoxidation, and VD / RH vacuum degassing, the total oxygen content of molten steel is ≤25ppm, hydrogen content is ≤2.0ppm, and sulfur content is ≤0.008%, effectively reducing the impact of gases and harmful impurities on the purity of molten steel and laying the foundation for subsequent processing performance; Furthermore, this process achieves precise and controllable inclusions: by optimizing the LF refining calcium treatment parameters, hard and brittle Al2O3 inclusions are modified into low-melting-point calcium aluminate, and by combining continuous casting electromagnetic stirring with weak cooling water distribution, the level of A / B type inclusions is ≤1.5 and the level of D type inclusions is ≤1.0, with no large inclusions larger than 50μm, thus completely solving the problem of inclusion-induced cracks in traditional processes; Furthermore, this process ensures the performance of the chain: the synergistic effect of improved cleanliness and inclusion control significantly enhances the chain's fatigue resistance and fracture toughness, reduces the risk of fracture caused by stress concentration due to inclusions during service, and meets the requirements of drawing, welding and heat treatment for material plasticity and toughness, ensuring the chain's stability under alternating loads and harsh working conditions. Furthermore, this process enhances the stability of the production process: through full-process parameter monitoring, inclusion detection, and dynamic feedback mechanisms, a "process-cleanliness-inclusion" linkage database is established, which can accurately adjust desulfurization, deoxidation, calcium treatment, and continuous casting parameters, reduce batch quality fluctuations, improve product qualification rate, and reduce rework and scrap costs caused by excessive inclusions.

[0021] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A clean smelting and inclusion control process for steel used in high-strength circular link chains, comprising the following steps: S1 hot metal pretreatment, S2 converter smelting, S3 LF refining, S4 VD / RH vacuum refining, S5 continuous casting, S6 subsequent quality control, and S7 process monitoring and adjustment. The process is characterized by: The S1 molten iron pretreatment process includes S101 desulfurization pretreatment, S102 pretreatment control and S103 slag removal and purification. The S2 converter smelting process includes S201 charging system, S202 blowing control, S203 endpoint control and S204 slag blocking and tapping. The S3 LF refining process includes S301 slag formation and deoxidation, S302 argon blowing and stirring, S303 composition fine-tuning, S304 slag formation control and S305 calcium treatment optimization. The S4 VD / RH vacuum refining process includes S401 vacuum treatment, S402 soft blowing purification, S403 steel purity control and S404 temperature and superheat control. The S5 continuous casting process includes S501 crystallizer protection, S502 crystallizer process, S503 secondary cooling water supply, S504 casting speed control, and S505 billet quality control.

2. The clean smelting and inclusion control process for high-strength circular link chain steel according to claim 1, characterized in that: The S101 desulfurization pretreatment adopts KR mechanical stirring desulfurization, and the desulfurizing agent is a high-activity lime-fluorite mixture (85%-90% lime + 10%-15% fluorite), with an addition amount of 8-12 kg / t of molten iron (10 kg / t for material basis optimization and expansion). S102 pretreatment control: stirring speed 120-150r / min, stirring time 15-25min, to ensure that the [S] content of the molten iron after desulfurization is ≤0.008% (material basis ≤0.010%, optimized and tightened); the temperature of the molten iron after pretreatment is controlled at 1280-1320℃ to avoid the temperature being too low and affecting the fluidity of subsequent smelting; S103 Slag Removal and Purification: The slag removal rate after desulfurization is ≥95%. After slag removal, the surface of the molten iron is covered with a heat-insulating agent to prevent secondary oxidation. Molten iron must not be transported in an exposed state before entering the converter.

3. The clean smelting and inclusion control process for high-strength circular link chain steel according to claim 1, characterized in that: The S201 loading procedure is as follows: molten iron ratio 78%-85% (material base 80%-82% optimized and expanded), and low phosphorus, low sulfur, and rust-free scrap steel is selected to avoid introducing harmful impurities and foreign inclusions. S202 blowing control: oxygen supply intensity 3.0-3.8m 3 / (t・min), bottom-blown argon stirring throughout, argon flow rate 0.8-1.5m³ / min. 3 / (min・furnace), to ensure the molten steel is stirred evenly; S203 endpoint control: endpoint carbon [C] ≥ 0.05% (material basis ≥ 0.06% optimized and expanded), endpoint phosphorus [P] ≤ 0.010% (material basis ≤ 0.012% optimized and tightened), endpoint temperature 1620-1660℃ (material basis 1630-1650℃ optimized and expanded), to avoid over-oxidation leading to increased oxygen content; S204 Slag-Blocking Steelmaking: Adopts a double slag-blocking process (slag-blocking ball + slag-blocking cone), with slag discharge of ≤5kg / t steel (material basis ≤8kg / t optimized tightening). During the steelmaking process, 3-5kg / t of pre-melted refining slag is added with the flow to advance slag formation and deoxidation.

4. The clean smelting and inclusion control process for high-strength circular link chain steel according to claim 1, characterized in that: The S301 slag deoxidation process involves adding CaO-Al2O3-SiO2 refining slag (CaO 50%-55%, Al2O3 25%-30%, SiO2 ≤ 15%) during the initial refining stage, with the basicity controlled at 3.0-4.5 (based on a material baseline of 3.5-4.0, optimized and expanded); Al particle diffusion deoxidation is employed, added in batches, with a total addition of 0.8-1.2 kg / t steel to ensure sufficient deoxidation of the molten steel. S302 Argon Stirring: Argon stirring throughout the process, with argon flow rate adjusted in stages: 0.3-0.5 m³ / h during the heating phase. 3 / h, refining period 0.2-0.4m 3 / h, soft blowing period 0.1-0.2m 3 / h, total argon blowing time ≥35-50min (material basis ≥40min, optimized and expanded), to promote the flotation of inclusions.

5. The clean smelting and inclusion control process for high-strength circular link chain steel according to claim 1, characterized in that: The S303 composition fine-tuning involves precisely adjusting the C, Mn, and Cr elements according to the target composition, with a composition deviation of ≤ ±0.01%; residual elements (Sb, As, Sn) ≤ 0.03%, avoiding the cumulative effect of elements on the cleanliness of molten steel. S304 slag formation control: rapid slag formation time ≤30min (material basis ≤25min, optimized and expanded), slag thickness controlled at 80-120mm, to ensure full slag-steel reaction and adsorption of Al2O3 inclusions in steel; S305 calcium treatment optimization: Calcium wire (CaSi wire, Ca content 28%-32%) is fed at the end of refining, with a feeding speed of 2.5-4.0 m / s. The feeding amount is adjusted according to the acid-soluble aluminum content of the molten steel: when [Al]s=0.020-0.030%, the feeding amount is 0.8-1.2 kg / t; when [Al]s=0.030-0.055%, the feeding amount is 1.2-1.6 kg / t, modifying Al2O3 inclusions into low-melting-point calcium aluminate.

6. The clean smelting and inclusion control process for high-strength circular link chain steel according to claim 1, characterized in that: The S401 vacuum treatment involves: evacuating the VD furnace to 0.3-0.5 torr (0.5 torr is the baseline for materials, which can be optimized and expanded), and holding the vacuum for ≥8-15 minutes (≥10 minutes is the baseline for materials, which can be optimized and expanded); and evacuating the RH furnace to ≤0.3 torr, with a cycle time ≥12-18 minutes to promote the removal of hydrogen, nitrogen, and inclusions. S402 soft-blowing purification: After vacuum rupture, the soft-blowing argon time is ≥10-20 min (≥12 min for material-specific applications, optimized and expanded), with an argon flow rate of 0.1-0.2 m³ / min. 3 / h, to avoid secondary oxidation of molten steel and ensure that inclusions float to the surface.

7. The clean smelting and inclusion control process for high-strength circular link chain steel according to claim 1, characterized in that: The purity control of the S403 molten steel is as follows: after vacuum treatment, the [H] content of the molten steel is ≤2.0ppm and the [O] content is ≤25ppm; 1-2 heats of molten steel are taken for large-sample electrolysis after each casting, and the total amount of inclusions is ≤50mg / 10kg of steel. S404 Temperature and Superheat Control: After vacuum treatment, the molten steel temperature is 1560-1590℃, and the superheat of the tundish is controlled at 20-45℃ (the material base is 20-35℃, which is optimized and expanded). The temperature of the first casting furnace is ≤45℃, and the temperature of the continuous casting furnace is ≤40℃.

8. The clean smelting and inclusion control process for high-strength circular link chain steel according to claim 1, characterized in that: The S501 crystallizer protection adopts an integral nozzle + immersion nozzle (immersion depth 80-130mm, material base 80-120mm optimized expansion), and the tundish covering agent is a special covering agent for low carbon steel, with an addition amount of 0.8-1.2kg / t steel to prevent secondary oxidation of molten steel; S502 crystallizer process: The protective slag for the crystallizer is selected from a low melting point and low viscosity slag system (melting point 1100-1150℃, viscosity 0.8-1.2Pa・s), and the liquid level fluctuation in the crystallizer is controlled to be ≤±3mm; the electromagnetic stirring parameters of the crystallizer are: current 200-300A (based on material 250A, optimized and expanded), frequency 2.0-3.5Hz (based on material 2.5-3Hz, optimized and expanded), to promote the flotation of inclusions and uniform composition; S503 secondary cooling water distribution: A weak cooling water distribution system is adopted, with a secondary cooling water volume of 0.4-0.9 L / kg steel (0.45-0.8 L / kg for material basis, optimized and expanded), adjusted according to the billet cross-section: 0.4-0.6 L / kg for cross-section ≤150mm, and 0.6-0.9 L / kg for cross-section >150mm, to avoid excessively rapid cooling leading to the accumulation of inclusions; S504 casting speed control: Casting speed 2.0-2.8m / min (material base 2.3-2.7m / min optimized and expanded), dynamically adjusted according to the superheat of the ladle: casting speed 2.4-2.8m / min when superheat is 20-30℃, casting speed 2.0-2.4m / min when superheat is 30-45℃, to ensure uniform solidification; S505 billet quality control: The continuous casting billet adopts a light reduction process with a reduction of 3-8mm; 2-3 billets are taken from each casting for low magnification inspection, with central porosity ≤1.5 grade, central segregation ≤1.0 grade, and no obvious inclusions.

9. The clean smelting and inclusion control process for high-strength circular link chain steel according to claim 1, characterized in that: The subsequent quality control steps of S6 are as follows: Billet cleaning: The surface cleaning depth of the continuously cast billet is ≥2mm, removing surface oxide scale, cracks and inclusions. The surface finish Ra after cleaning is ≤1.6μm. Pre-rolling treatment: Before the billet enters the furnace, it is shot blasted to remove residual inclusions and oxide scale from the surface; the heating furnace is protected by inert gas or a weak oxidizing atmosphere, the heating temperature is 1150-1200℃, and the holding time is 2-4h to avoid high-temperature oxidation. Inclusion detection: Take 3-5 samples from each batch of finished wire rod for metallographic inclusion rating and large particle inclusion scanning detection to ensure that the inclusion level meets the process target; for unqualified batches, the smelting and continuous casting process parameters need to be traced and the subsequent process adjusted.

10. The clean smelting and inclusion control process for high-strength circular link chain steel according to claim 1, characterized in that: The S7 process monitoring and adjustment steps are as follows: For each casting, record key parameters for molten iron pretreatment, converter, LF refining, VD / RH, and continuous casting, and establish a database corresponding to "process-cleanliness". If excessive inclusions are detected (A / B class > 1.5 or D class > 1.0), prioritize adjusting the LF refining slag alkalinity (±0.5) or calcium treatment feed rate (±0.2 kg / t); if total oxygen > 25 ppm, extend the VD / RH vacuum holding time (+2-3 min) or soft blowing time (+3-5 min). Monthly statistics are compiled on inclusion detection data, steel purity indicators, and chain usage quality feedback. The deoxidation process, calcium treatment parameters, and continuous casting cooling process are optimized to continuously improve process stability.