Efficient deoxidation alloying process for high-quality medium-high carbon steel

Abstract

The invention discloses an efficient deoxidation alloying process for high-quality medium-high carbon steel. The deoxidation alloying process can effectively improve the casting success rate and the process full-flow casting rate of medium-high carbon steel, eliminates the defects of continuous casting nozzle formation, casting blank inclusion and the like caused by poor molten steel cleanliness and inclusion enrichment in the medium-high carbon steel casting process, improves the molten steel cleanliness and the casting blank quality, meets the use requirements of users for the medium-high carbon steel, and is suitable for industrial production. The production efficiency is effectively improved and the production cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and in particular relates to a high-efficiency deoxidation and alloying process for high-quality medium- and high-carbon steel. Background Art

[0002] Medium-high carbon steel is a series of specifications of high-value-added high-quality carbon structural steel with a carbon content of 0.45%-0.850%. It is mainly used to make steel wire ropes, prestressed steel wires, steel strands, medium-high strength fasteners, etc. through deep processing. As medium-high carbon steel for deep processing, it needs to have high cleanliness, high strength, high drawing properties and high toughness; to meet this requirement, the hard wire produced must have the characteristics of fine grains, uniform rod performance, and high dimensional accuracy. During the user's use, it must be drawn into Φ2.0mm-Φ5.0mm fine wires. In order to ensure the drawing quality and reduce the occurrence of wire breakage, calcium treatment must be carried out during the smelting process to achieve inclusion denaturation, and by changing the inclusion morphology, the inclusion plasticity is increased to meet user needs.

[0003] The main process route for smelting high-quality medium- and high-carbon steel is: KR molten iron pretreatment → converter smelting → LF furnace refining → small square billet full-process protection casting → steel rolling, and then handed over to users for deep processing.

[0004] Due to the requirements of silicon-manganese content in medium-high carbon steel, the manganese-silicon ratio in steel is low, and the fluidity of molten steel is relatively poor, but the pouring process requires the reduction of columnar crystals. Therefore, low superheat pouring must be achieved, and the pouring superheat is ≤25°C, and it is necessary to reduce the introduction of oxidized inclusions such as Al2O3 in the deoxidation alloying process to avoid the introduction of molten steel inclusions that affect the continuous casting castability and billet quality, so as to further improve the development and production efficiency of high-quality medium-high carbon steel. In order to improve the cleanliness, fluidity and deoxidation of molten steel, steel mills generally use conventional converter smelting endpoint control, silicon-manganese + silicon-calcium-barium alloying precipitation deoxidation in the steelmaking process, and LF refining diffusion deoxidation to assist in feeding silicon-calcium wire oxidation inclusion deformation treatment, so that the calcium content in molten steel reaches 0.001%-0.003%, so as to reduce the water mouth phenomenon caused by high melting point oxidized inclusions in the continuous casting pouring process. However, in the actual production process, there are still problems such as low cleanliness of molten steel, enrichment of high-melting-point inclusions that affect the castability and fluidity of molten steel, restricting the quality of ingots and the stability of deep processing for end customers, and reducing the high-quality development and production of medium and high-carbon steel in large batches.

[0005] In order to completely solve the problem that the oxide inclusions and high melting point oxides generated by the deoxidation and alloying of high-quality medium and high carbon steels affect the cleanliness of molten steel, the smoothness of continuous casting and the quality of ingots, the present invention aims to provide an efficient deoxidation and alloying process for high-quality medium and high carbon steels. Summary of the invention

[0006] The purpose of the present invention is to provide a high-efficiency deoxidation and alloying process for high-quality medium-high carbon steel.

[0007] The object of the present invention is achieved by a high-efficiency deoxidation and alloying process for high-quality medium-high carbon steel, which is achieved by the following steps: A. Carbon steel pulling in converter: 895kg / t 钢 and 15kg / t 钢 Add low-sulfur hot metal and refined scrap steel to the converter for smelting at a rate of 23-27kg / t 钢 、16-20kg / t 钢 Active lime and light-burned dolomite are added in the appropriate amount for slag making. The carbon content at the smelting end point is controlled to be ≥0.10%, the end point temperature is 1620~1690℃, and the oxygen content of the molten steel at the end point is ≤250PPm. B. Deoxidation and alloying: Before the smelting is completed and the steel is about to be tapped, the steel is deoxidized and alloyed at a rate of 1.0~1.2kg / t in the ladle. 钢 Add slag washing material and active lime in equal amounts, use the impact force and stirring function of molten steel during tapping to pre-deoxidize and slag wash the molten steel. When the tapping amount is greater than 1 / 4, add the steel ladle in the order of low aluminum silicon calcium barium-high carbon ferromanganese-ferrosilicon-low nitrogen carburizer deoxidation alloying. The corresponding addition amount is controlled according to the type and quantity of alloy required for each grade of medium and high carbon steel. The amount of low aluminum silicon calcium barium alloy is uniformly 1.2kg / t 钢 Add, and add all the above alloys when the amount of molten steel reaches 3 / 4; C. LF furnace refining: The molten steel is hoisted to the LF furnace for refining. The pure power refining time is ≥20min. The argon gas with a flow rate of 20NL / min is used for bottom blowing throughout the whole process. The 7~9 gear lower electrode is electrified to slag, and the reduction submerged arc operation is mainly carried out to fully purify the molten steel and fine-tune the molten steel composition and temperature. The oxygen content is ≤40ppm to meet the VD vacuum further degassing effect; the silicon calcium wire is cancelled, and the soft argon blowing time of the refining process is extended to ensure that the soft argon blowing time is 12-15 minutes / furnace; D. VD vacuum refining and deoxidation: VD vacuum refining is carried out with argon blowing throughout the process, with deep vacuum time ≥15min, and the outlet molten steel is controlled to have [O] ≤20ppm, [H] ≤1.3ppm, and [N] ≤40ppm.

[0008] The process of the present invention can effectively improve the success rate of medium-high carbon steel casting and the full flow casting success rate of the process, eliminate the occurrence of defects such as continuous casting water outlets and ingot inclusions caused by poor molten steel cleanliness and inclusion enrichment in the medium-high carbon steel casting process, improve the cleanliness of molten steel and the quality of ingots, meet users' requirements for the use of medium-high carbon steel, effectively improve production efficiency, and reduce production costs.

[0009] 1. The deoxidation alloying process of the present invention can effectively reduce the enrichment of high-melting-point Al2O3 inclusions, secondary oxidation inclusions, CaS and other inclusions in steel, which affect the cleanliness of molten steel and the fluidity and castability of continuous casting molten steel, ensure that the gas content of the steel grade is controlled at a low level, and effectively avoid the frequency of continuous casting water outlet drainage and operational safety hazards caused by inclusion enrichment, so as to improve the quality of molten steel and ingot, ensure the stable and smooth development and production of high-quality medium and high carbon steel, and effectively avoid customers' quality objections caused by raw material defects in the deep processing process.

[0010] 2. Through the application of the process of the present invention, the number of defective billets in the continuous casting process can be effectively reduced, and the billet yield rate can be increased by 0.3% on the original basis, which can effectively reduce the waste generated in the casting process. According to the market demand for medium and high carbon steel of 100,000 tons / year, the steel output can be effectively increased by 300 tons and the waste can be reduced by 300 tons. The price difference between scrap steel and qualified billets is 1,000 yuan / ton, which can generate benefits of 300,000 yuan / year. The consumption of tundishes and related refractory materials can be reduced by 20%, generating benefits of 100,000 yuan / year. There is a price difference of 1,470 yuan / ton between low-aluminum silicon calcium barium and ordinary silicon calcium barium. Calculated based on the addition amount of 1.1-1.15kg per ton of steel, the use of low-aluminum silicon calcium barium will increase the cost by 1.69 yuan / ton, and the cost will increase by 169,000 yuan based on 100,000 tons / year. Based on the above situation, the use of low-aluminum silicon calcium barium can ultimately reduce production by 231,000 yuan / year. DETAILED DESCRIPTION

[0011] The present invention is further described in detail below in conjunction with the embodiments, but the present invention is not limited in any way. Any changes or improvements made based on the teachings of the present invention fall within the protection scope of the present invention.

[0012] The invention discloses a high-efficiency deoxidation and alloying process for high-quality medium-high carbon steel, which is realized by the following steps: A. Carbon steel pulling in converter: 895kg / t 钢 and 15kg / t 钢 Add low-sulfur hot metal and refined scrap steel to the converter for smelting at a rate of 23-27kg / t 钢 、16-20kg / t 钢 Active lime and light-burned dolomite are added in the appropriate amount for slag making. The carbon content at the smelting end point is controlled to be ≥0.10%, the end point temperature is 1620~1690℃, and the oxygen content of the molten steel at the end point is ≤250PPm. B. Deoxidation and alloying: Before the smelting is completed and the steel is about to be tapped, the steel is deoxidized and alloyed at a rate of 1.0~1.2kg / t in the ladle. 钢Add slag washing material and active lime in equal amounts, use the impact force and stirring function of molten steel during tapping to pre-deoxidize and slag wash the molten steel. When the tapping amount is greater than 1 / 4, add the steel ladle in the order of low aluminum silicon calcium barium-high carbon ferromanganese-ferrosilicon-low nitrogen carburizer deoxidation alloying. The corresponding addition amount is controlled according to the type and quantity of alloy required for each grade of medium and high carbon steel. The amount of low aluminum silicon calcium barium alloy is uniformly 1.2kg / t 钢 Add, and add all the above alloys when the amount of molten steel reaches 3 / 4; C. LF furnace refining: The molten steel is hoisted to the LF furnace for refining. The pure power refining time is ≥20min. The argon gas with a flow rate of 20NL / min is used for bottom blowing throughout the whole process. The 7~9 gear lower electrode is electrified to slag, and the reduction submerged arc operation is mainly carried out to fully purify the molten steel and fine-tune the molten steel composition and temperature. The oxygen content is ≤40ppm to meet the VD vacuum further degassing effect; the silicon calcium wire is cancelled, and the soft argon blowing time of the refining process is extended to ensure that the soft argon blowing time is 12-15 minutes / furnace; D. VD vacuum refining and deoxidation: In view of the high-quality medium and high carbon steel's requirements for oxygen, hydrogen, nitrogen and other gases in molten steel, VD vacuum refining is adopted with argon blowing throughout the process. The deep vacuum time is maintained at 67Pa for ≥15min. The molten steel treatment cycle in the VD station is 40~45min to further remove the oxygen, hydrogen and other gas contents in the steel. The outgoing molten steel [O] ≤20ppm, [H] ≤1.3ppm, [N] ≤40ppm.

[0013] In step A, the chemical composition of the low-sulfur molten iron is: C 4.1~5.2wt%, Si 0.23~0.35wt%, Mn 0.15~0.25wt%, S ≤0.010wt%, P≤0.090wt%, and the temperature is ≥1320°C.

[0014] In step B, the chemical composition of the low aluminum silicon calcium barium is: Si 50-55wt%, P≤ 0.15wt%, S ≤0.25wt%, Ca9.0-13.0wt%, Ba11.0-14.0wt%, Al≤1.2wt%, and the proportion of particle size 10-70mm is ≥95%.

[0015] Example 1 The company smelts and produces 60 types of medium and high carbon steel, totaling 2,000 tons in 16 furnaces.

[0016] 1. Converter steelmaking: Converter steelmaking uses high-quality low-sulfur hot metal with refined scrap steel. The weight percentage of high-quality hot metal entering the converter is: C / 4.65wt%, Si / 0.27wt%, Mn / 0.18wt%, S / 0.008wt%, P / 0.089wt%. The temperature of the hot metal after pretreatment is 1320℃. Considering the requirements of smelting heat balance, terminal carbon pulling and terminal temperature steelmaking, the converter steelmaking is based on hot metal 890kg / t钢 + Scrap steel 16kg / t 钢 The cold material is added to the furnace to ensure the high-quality low-S hot metal KR pretreatment slag removal and S removal requirements, while taking into account the LF refining and VD non-overflow slag safety vacuum degassing requirements. The converter smelting is 25kg / t 钢 Active lime, 17kg / t 钢 Lightly burned dolomite is added for slag making to ensure that the smelting P removal rate meets the P control requirement of medium and high carbon steel at 0.012wt%. The auxiliary gun is used to determine the oxygen, carbon and temperature to assist in the control of the smelting end point. The final steel composition is achieved: C / 0.12%, P / 0.008%, O / 238ppm, and the steel tapping temperature is 1642℃, achieving the carbon extraction control target in converter smelting, effectively reducing the oxygen content in the molten steel, and reducing oxide inclusions in the steel at the source.

[0017] 2. Deoxidation and alloying of converter steel: Prior to steel tapping, 1.0~1.2kg / t of deoxidation and alloying should be added to the ladle in advance. 钢 The same amount of slag washing material (chemical composition mass ratio: Al2O321.4wt%, SiO26.9wt%, CaO 44.7wt%, Al 8.5wt%, MgO4.7wt%) and active lime are added for slag washing. The whole bottom blowing argon process is adopted in the steel tapping process, and the argon flow rate is controlled to 21NL / min. The molten steel is pre-deoxidized and slag washed by using the impact force and stirring function of the molten steel during steel tapping. When the amount of steel tapping is greater than 1 / 4, the steel ladle is added in the order of low aluminum silicon calcium barium-high carbon ferromanganese-ferrosilicon-low nitrogen carburizer deoxidation alloying. The corresponding amount of addition is controlled according to the type and quantity of alloys required for each grade of medium and high carbon steel. The amount of low aluminum silicon calcium barium alloy is uniformly added at 1.2kg / t steel. When the amount of molten steel reaches 3 / 4, all the above alloys and other materials are added to achieve one-time precipitation deoxidation, ensure the cleanliness and castability of the molten steel, and use the impact of molten steel and bottom blowing argon to ensure that the inclusions have sufficient floating time.

[0018] 3. LF ladle refining and deoxidation: After the steel is tapped and sampled at the argon station, the molten steel is hoisted to the LF furnace for refining. The pure power refining time is 21.5 minutes. The argon gas with a flow rate of 20NL / min is used for bottom blowing throughout the process to avoid excessive air intake during secondary oxidation. In combination with the temperature of the molten steel entering the station, the 7~9 gears are used to electrify the slag at the lower electrode, and the reduction submerged arc operation is mainly carried out. During the process, the slag is adjusted accordingly according to the slag condition in the ladle. If the slag condition is too thin or too black, add active lime / 3.2kg / t 钢Adjust the slag, otherwise add pre-melted refined slag for adjustment, lower the electrode twice, adjust the composition control and temperature, measure the temperature and determine the oxygen level before leaving the station, ensure the soft argon blowing time is 13.5 minutes / furnace, promote the effective floating of inclusions, improve the cleanliness and fluidity of the molten steel; the weight percentage of the molten steel leaving the station is: C / 0.60wt%, Si / 0.23wt%, Mn / 0.61wt%, S / 0.010wt%, P / 0.013wt%; the oxygen content is 39.4ppm, which meets the requirements of VD vacuum further degassing.

[0019] 4. VD vacuum refining and deoxidation: The molten steel with qualified LF outgoing composition and temperature is transported to the VD station by crane. The ladle automatic bottom blowing docking technology is adopted, and argon is blown throughout the process to cooperate with vacuum refining and degassing. The deep vacuum time is maintained at 67Pa for 18 minutes. The treatment cycle of the molten steel in the VD station is 42.3 minutes to further remove the oxygen, hydrogen and other gas contents in the steel. The outgoing molten steel has [O] 19.5ppm, [H] 1.27ppm, and [N] 31ppm, which meets the further degassing requirements and is ready for continuous casting at the outgoing station.

[0020] 5. Continuous casting of 7 streams started normally, achieving full flow at one time and normal continuous casting of 16 furnaces to complete the planned stop pouring. The casting time was 10 hours and 43 minutes. During the casting process, the electromagnetic stirring of the crystallizer and the automatic control of the liquid level had a 100% operating integrity rate. The inner wall of the water inlet channel was checked for smoothness, without CaS and Al2O3 enrichment, and was smooth without foreign matter and non-metallic cold steel attachment.

[0021] Example 2 A total of 26 furnaces with a total output of 3,000 tons are used to smelt and produce 60 types of medium and high carbon steel.

[0022] 1. Converter steelmaking: Converter steelmaking uses high-quality low-sulfur hot metal with refined scrap steel. The weight percentage of high-quality hot metal entering the converter is: C / 4.82wt%, Si / 0.31wt%, Mn / 0.22wt%, S / 0.01wt%, P / 0.078wt%. The temperature of the hot metal after pretreatment is 1326℃. Considering the requirements of smelting heat balance, terminal carbon pulling and terminal temperature steelmaking, the converter steelmaking is based on hot metal 892kg / t 钢 + Scrap steel 17kg / t 钢 The cold material is added to the furnace to ensure the high-quality low-S hot metal KR pretreatment slag removal and S removal requirements, while taking into account the LF refining and VD non-overflow slag safety vacuum degassing requirements. The converter smelting is 26kg / t 钢 Active lime, 18kg / t 钢Lightly burned dolomite is added for slag making to ensure that the smelting P removal rate meets the P control requirement of medium and high carbon steel at 0.011wt%. The auxiliary gun is used to determine the oxygen, carbon and temperature at the end of the smelting to assist in the control. The final steel composition is achieved: C / 0.13%, P / 0.006%, O / 227ppm, and the steel tapping temperature is 1639℃, achieving the carbon pulling control target in converter smelting, effectively reducing the oxygen content in the molten steel, and reducing oxide inclusions in the steel at the source.

[0023] 2. Deoxidation and alloying of converter steel: Prior to steel tapping, 1.0~1.2kg / t of deoxidation and alloying should be added to the ladle in advance. 钢 The same amount of slag washing material (chemical composition mass ratio: Al2O321.4wt%, SiO26.9wt%, CaO 44.7wt%, Al 8.5wt%, MgO4.7wt%) and active lime are added for slag washing. The whole bottom blowing argon process is adopted in the steel tapping process, and the argon flow rate is controlled to 21NL / min. The molten steel is pre-deoxidized and slag washed by using the impact force and stirring function of the molten steel during steel tapping. When the amount of steel tapping is greater than 1 / 4, the steel ladle is added in the order of low aluminum silicon calcium barium-high carbon ferromanganese-ferrosilicon-low nitrogen carburizer deoxidation alloying. The corresponding amount of addition is controlled according to the type and quantity of alloys required for each grade of medium and high carbon steel. The amount of low aluminum silicon calcium barium alloy is uniformly added at 1.2kg / t steel. When the amount of molten steel reaches 3 / 4, all the above alloys and other materials are added to achieve one-time precipitation deoxidation, ensure the cleanliness and castability of the molten steel, and use the impact of molten steel and bottom blowing argon to ensure that the inclusions have sufficient floating time.

[0024] 3. LF ladle refining and deoxidation: After the steel is tapped and sampled at the argon station, the molten steel is hoisted to the LF furnace for refining. The pure electric refining time is 20.3 minutes. The argon gas with a flow rate of 20NL / min is used for bottom blowing throughout the process to avoid excessive air intake during secondary oxidation. According to the temperature of the molten steel entering the station, the 7~9 gears are used to electrify the slag at the lower electrode, and the reduction submerged arc operation is mainly carried out. During the process, the slag is adjusted accordingly according to the slag condition in the ladle. If the slag condition is too thin or too black, add active lime / 3.2kg / t 钢 Adjust the slag, otherwise add pre-melted refined slag for adjustment, lower the electrode 3 times, adjust the composition control and temperature, measure the temperature and oxygen level before leaving the station, ensure the soft argon blowing time is 13 minutes / furnace, promote the effective floating of inclusions, improve the cleanliness and fluidity of the molten steel; the weight percentage of the molten steel leaving the station is: C / 0.62wt%, Si / 0.27wt%, Mn / 0.64wt%, S / 0.008wt%, P / 0.012wt%; the oxygen content is 37.8ppm, which meets the requirements of VD vacuum further degassing.

[0025] 4. VD vacuum refining and deoxidation: The molten steel with qualified LF outgoing composition and temperature is transported to the VD station by crane. The ladle automatic bottom blowing docking technology is adopted, and argon is blown throughout the process to cooperate with vacuum refining and degassing. The deep vacuum time is maintained at 67Pa for 17 minutes. The treatment cycle of the molten steel in the VD station is 41 minutes to further remove the oxygen, hydrogen and other gas contents in the steel. The outgoing molten steel has [O] 18.9ppm, [H] 1.25ppm, and [N] 35ppm, which meets the further degassing requirements and is ready for continuous casting at the outgoing station.

[0026] 5. Continuous casting of 7 streams started normally, achieving one-time full flow and normal continuous casting of 26 furnaces to complete the planned stop pouring, and the casting time was 17 hours and 52 minutes; the electromagnetic stirring of the crystallizer and the automatic control of the liquid level during the casting process had a 100% operating integrity rate; the inner wall of the water inlet channel was checked for smoothness, without CaS and Al2O3 enrichment, and smooth without foreign matter and non-metallic cold steel attachment.

[0027] Example 3 A total of 28 furnaces with a total output of 3,500 tons were used to smelt and produce 65 types of medium and high carbon steel.

[0028] 1. 120t converter steelmaking: converter smelting uses high-quality low-sulfur hot metal with refined scrap steel. The weight percentage of high-quality hot metal entering the converter is: C / 4.79wt%, Si / 0.35wt%, Mn / 0.21wt%, S / 0.007wt%, P / 0.082wt%; the temperature of the hot metal after pretreatment is 1324℃; considering the requirements of smelting heat balance, terminal carbon pulling and terminal temperature steelmaking, the converter smelting is based on hot metal 887kg / t 钢 + Scrap steel 19kg / t 钢 The cold material is added to the furnace to ensure the high-quality low-S hot metal KR pretreatment slag removal and S removal requirements, while taking into account the LF refining and VD non-overflow slag safety vacuum degassing requirements. The converter smelting is 25kg / t 钢 Active lime, 19kg / t 钢 Lightly burned dolomite is added for slag making to ensure that the smelting P removal rate meets the P control requirement of medium and high carbon steel at 0.010wt%. The auxiliary gun is used to determine the oxygen, carbon and temperature to assist in the control of the smelting end point. The final steel composition is achieved: C / 0.12%, P / 0.010%, O / 235ppm, and the steel tapping temperature is 1642℃, achieving the carbon extraction control target in converter smelting, effectively reducing the oxygen content in the molten steel, and reducing oxide inclusions in the steel at the source.

[0029] 2. Deoxidation and alloying of converter steel: Prior to steel tapping, 1.0~1.2kg / t of deoxidation and alloying should be added to the ladle in advance. 钢The same amount of slag washing material (chemical composition mass ratio: Al2O321.4wt%, SiO26.9wt%, CaO 44.7wt%, Al 8.5wt%, MgO4.7wt%) and active lime are added for slag washing. The whole bottom blowing argon process is adopted in the steel tapping process, and the argon flow rate is controlled to 21NL / min. The molten steel is pre-deoxidized and slag washed by using the impact force and stirring function of the molten steel during steel tapping. When the amount of steel tapping is greater than 1 / 4, the steel ladle is added in the order of low aluminum silicon calcium barium-high carbon ferromanganese-ferrosilicon-low nitrogen carburizer deoxidation alloying. The corresponding amount of addition is controlled according to the type and quantity of alloys required for each grade of medium and high carbon steel. The amount of low aluminum silicon calcium barium alloy is uniformly added at 1.2kg / t steel. When the amount of molten steel reaches 3 / 4, all the above alloys and other materials are added to achieve one-time precipitation deoxidation, ensure the cleanliness and castability of the molten steel, and use the impact of molten steel and bottom blowing argon to ensure that the inclusions have sufficient floating time.

[0030] 3. LF ladle refining and deoxidation: After the steel is tapped and sampled at the argon station, the molten steel is hoisted to the LF furnace for refining. The pure power refining time is 21 minutes. The argon gas with a flow rate of 20NL / min is used for bottom blowing throughout the process to avoid excessive air intake during secondary oxidation. In combination with the temperature of the molten steel entering the station, the 7~9 gears are used to electrify the slag at the lower electrode, and the reduction submerged arc operation is mainly carried out. During the process, the slag is adjusted accordingly according to the slag condition in the ladle. If the slag condition is too thin or too black, add active lime / 3.2kg / t 钢 Adjust the slag, otherwise add pre-melted refined slag for adjustment, lower the electrode 3 times, adjust the composition control and temperature, measure the temperature and oxygen level before leaving the station, ensure the soft argon blowing time is 12.5 minutes / furnace, promote the effective floating of inclusions, improve the cleanliness and fluidity of the molten steel; the weight percentage of the molten steel leaving the station is: C / 0.66wt%, Si / 0.24wt%, Mn / 0.64wt%, S / 0.007wt%, P / 0.012wt%; the oxygen content is 36.9ppm, which meets the requirements of VD vacuum further degassing.

[0031] 4. VD vacuum refining and deoxidation: The molten steel with qualified LF outgoing composition and temperature is transported to the VD station by crane. The ladle automatic bottom blowing docking technology is adopted, and argon is blown throughout the process to cooperate with vacuum refining and degassing. The deep vacuum time is maintained at 67Pa for 15.7min. The treatment cycle of the molten steel in the VD station is 39.7min to further remove the oxygen, hydrogen and other gas contents in the steel. The outgoing molten steel has [O] 17.8ppm, [H] 1.27ppm, and [N] 36ppm, which meets the further degassing requirements and is poured for continuous casting at the outgoing station.

[0032] 5. Continuous casting of 7 streams started normally, achieving one-time full flow and normal continuous casting of 28 furnaces to complete the planned stop pouring, and the casting time was 18 hours and 57 minutes; the electromagnetic stirring of the crystallizer and the automatic liquid level control had a 100% operating integrity rate during the casting process; the inner wall of the water inlet channel was checked for smoothness, without CaS and Al2O3 enrichment, and smooth without foreign matter and non-metallic cold steel attachment.

[0033] Comparative Example 1 According to the traditional method, 16 furnaces with a total of 2,000 tons of 60 types of medium and high carbon steel were smelted and produced. The specific method is as follows: 1. 60 steel smelting endpoint control: C / 0.056%, oxygen content 453ppm, steel tapping temperature 1632℃; 2. Steelmaking deoxidation and alloying: conventionally add high carbon ferromanganese, ferrosilicon and carburizer, add 150kg / furnace of silicon calcium and barium to strengthen deoxidation and alloying and inclusion deformation treatment. After LF refining and cleaning treatment, wire feeding and soft blowing, the steelmaking temperature and composition requirements are met and continuous casting protection pouring is carried out.

[0034] 3. The continuous casting of 7 streams was started normally, but the phenomenon of multi-stream water junction appeared in the second furnace. The overheat of the tundish was 28~32℃, and the problem could not be effectively improved even when the stopper was fully opened. Oxygen drainage was adopted for pouring, and there was unprotected bare pouring during the process. The diameter of 7 stream was greatly expanded due to improper drainage, which made it difficult to control the flow with the stopper. The bare pouring speed was too fast, 3.5 m / min, causing leakage and blocking, and less stream pouring.

[0035] 4. After the less-flow of this group of steel was poured to the 4th furnace, the fluidity of the molten steel still deteriorated and the water gate was formed, so only 4 furnaces were poured and the pouring was stopped, which was 12 furnaces short of the target 16 furnaces.

[0036] 5. Stop the machine and check the water inlet channel. There are inclusions such as high melting point Al2O3 and CaS enriched and blocked the water inlet channel, which is caused by cooling blockage of non-metallic cold steel.

[0037] Comparative Example 2 According to the traditional method, 26 furnaces of 3,000 tons of 60 types of medium and high carbon steel are produced. The specific method is as follows: 1. 60 steel smelting endpoint control: C / 0.06%, oxygen content 437ppm, steel tapping temperature 1624℃; 2. Steelmaking deoxidation and alloying: conventionally add high carbon ferromanganese, ferrosilicon and carburizer, add 150kg / furnace of silicon calcium barium to strengthen deoxidation alloying and inclusion deformation treatment. After LF refining and cleaning treatment and silicon calcium wire feeding and soft blowing, the steelmaking temperature composition requirements are met and continuous casting protection pouring is carried out.

[0038] 3. After pouring the medium-high carbon steel 60 steel ladle, there is no self-flow, the drainage is open for pouring for 25 minutes, and the initial pouring of the middle ladle is normal; 4. In the middle of the first furnace, the 1st and 7th streams had water clogging phenomenon, which was alleviated by the secondary drainage pouring. Intermittent water clogging appeared in other streams. The conventional silicon calcium barium deoxidation method was reduced, and the casting speed was maintained at a low level for 12 furnaces to be shut down unplanned, which was 14 furnaces short of the target 26 furnaces. Off-line inspection showed that the water nozzle had high melting point Al2O3 and CaS and other inclusions were enriched and blocked the water nozzle channel, which was caused by the cooling blockage of non-metallic cold steel.

[0039] Comparative Example 3 According to the traditional method, a total of 29 furnaces of 60 / 65 high carbon steel (the first 10 furnaces are 65 steel, and the 11th to 29th furnaces are 60 steel) totaling 3,500 tons are produced. The specific method is as follows: 1. 65 steel smelting endpoint control: C / 0.05%, oxygen content 486ppm, steel tapping temperature 1637℃; 2. Steelmaking deoxidation and alloying: conventionally add high carbon ferromanganese, ferrosilicon and carburizer, add 150kg / furnace of silicon calcium barium to strengthen deoxidation alloying and inclusion deformation treatment. After LF refining and cleaning treatment and silicon calcium wire feeding and soft blowing, the steelmaking temperature composition requirements are met and continuous casting protection pouring is carried out.

[0040] 3. The first batch of 65 steel was poured: in the middle stage of pouring, streams 1 to 7 all experienced water knots and reduced pulling speed. There was no improvement when switching to the full-open flow control mode with manual plugging rods. There was some improvement after oxygen drainage was adopted. Subsequently, continuous pouring was maintained until the 9th batch, and water knots still occurred. Stream 6 stopped pouring due to drainage failure. The machine was shut down after pouring 10 batches of steel due to insufficient flow, which was 19 batches short of the target of 29 batches.

[0041] 4. Stop the machine and check the water inlet channel. There are inclusions such as high melting point Al2O3 and CaS enriched and blocked the water inlet channel, which is caused by cooling blockage of non-metallic cold steel.

Claims

1. A high-efficiency deoxidation and alloying process for high-quality medium-high carbon steel, characterized in that: To do this, follow these steps: A. Carbon steel pulling in converter: 895kg / t 钢 and 15kg / t 钢 Add low-sulfur hot metal and refined scrap steel to the converter for smelting at a rate of 23-27kg / t 钢 、16-20kg / t 钢 Active lime and light-burned dolomite are added in the appropriate amount for slag making. The carbon content at the smelting end point is controlled to be ≥0.10%, the end point temperature is 1620~1690℃, and the oxygen content of the molten steel at the end point is ≤250PPm. B. Deoxidation and alloying: Before the smelting is completed and the steel is about to be tapped, the steel is deoxidized and alloyed at a rate of 1.0~1.2kg / t in the ladle. 钢 Add slag washing material and active lime in equal amounts, use the impact force and stirring function of molten steel during tapping to pre-deoxidize and slag wash the molten steel. When the tapping amount is greater than 1 / 4, add the steel ladle in the order of low aluminum silicon calcium barium-high carbon ferromanganese-ferrosilicon-low nitrogen carburizer deoxidation alloying. The corresponding addition amount is controlled according to the type and quantity of alloy required for each grade of medium and high carbon steel. The amount of low aluminum silicon calcium barium alloy is uniformly 1.2kg / t 钢 Add, and add all the above alloys when the amount of molten steel reaches 3 / 4; C. LF furnace refining: The molten steel is hoisted to the LF furnace for refining. The pure power refining time is ≥20min. The argon gas with a flow rate of 20NL / min is used for bottom blowing throughout the whole process. The 7~9 gear lower electrode is electrified to slag, and the reduction submerged arc operation is mainly carried out to fully purify the molten steel and fine-tune the molten steel composition and temperature. The oxygen content is ≤40ppm to meet the VD vacuum further degassing effect; the silicon calcium wire is cancelled, and the soft argon blowing time of the refining process is extended to ensure that the soft argon blowing time is 12-15 minutes / furnace; D. VD vacuum refining and deoxidation: VD vacuum refining is carried out with argon blowing throughout the process, with deep vacuum time ≥15min, and the outlet molten steel is controlled to have [O] ≤20ppm, [H] ≤1.3ppm, and [N] ≤40ppm.

2. The high-efficiency deoxidation and alloying process for high-quality medium-high carbon steel according to claim 1 is characterized in that: In step A, the chemical composition of the low-sulfur molten iron is: C 4.1~5.2wt%, Si 0.23~0.35wt%, Mn 0.15~0.25wt%, S ≤0.010wt%, P≤0.090wt%, and the temperature is ≥1320°C.

3. The high-efficiency deoxidation and alloying process for high-quality medium-high carbon steel according to claim 1 is characterized in that: In step B, the chemical composition of the low aluminum silicon calcium barium is: Si 50-55wt%, P≤0.15wt%, S ≤0.25wt%, Ca9.0-13.0wt%, Ba11.0-14.0wt%, Al≤1.2wt%, and the proportion of particle size 10-70mm is ≥95%.