Method for increasing number of continuous drawing furnaces of sulfur-containing gear steel
阅读说明：本技术 一种提高含硫齿轮钢连拉炉数的方法 (Method for increasing number of continuous drawing furnaces of sulfur-containing gear steel ) 是由 肖步庆 李瑞生 杨之俊 师艳秋 王建飞 李阳 王晓栋 于 2021-08-04 设计创作，主要内容包括：本发明公开了一种提高含硫齿轮钢连拉炉数的方法,包括转炉冶炼、LF精炼、RH精炼和连铸工序；(1)转炉冶炼终点C≥0.06%,P≤0.015%,出钢温度1640±10℃；出钢时向钢水中加入铝块和合成渣,使钢中氧含量≤50ppm；(2)LF精炼目标渣成分：TFe≤0.6%,CaO：54～56%,SiO-(2)：13～15%,Al-(2)O-(3)：21～23%,MgO：6～8%；成渣后采用补加石灰和碳化硅的方法保持白渣；出站前加入钙线；(3)RH精炼：真空处理完成后,加入硫线,软吹氩≥15min后钢水出站；(4)连铸：采用浸入式水口。本发明提供的方法浇次平均连拉炉数达到15炉,生产的齿轮钢低倍评级达到2.0级。(The invention discloses a method for increasing the number of continuous drawing furnaces of sulfur-containing gear steel, which comprises the working procedures of converter smelting, LF refining, RH refining and continuous casting; (1) the smelting end point C of the converter is more than or equal to 0.06 percent, the P is less than or equal to 0.015 percent, and the tapping temperature is 1640 +/-10 ℃; adding aluminum blocks and synthetic slag into molten steel during tapping to ensure that the oxygen content in the steel is less than or equal to 50 ppm; (2) LF refining target slag composition: TFe is less than or equal to 0.6 percent, CaO: 54-56% of SiO 2 ：13～15%，Al 2 O 3 : 21-23%, MgO: 6-8%; after slagging, maintaining white slag by adopting a method of supplementing lime and silicon carbide; adding a calcium wire before leaving the station; (3) RH refining: completion of vacuum treatmentThen, adding a sulfur wire, and discharging the molten steel after soft argon blowing is more than or equal to 15 min; (4) continuous casting: a submerged entry nozzle is used. The average number of continuous drawing furnaces of the casting times of the method provided by the invention reaches 15 furnaces, and the low-power rating of the produced gear steel reaches 2.0 grades.)
1. The method for increasing the number of the sulfur-containing gear steel continuous drawing furnaces is characterized by comprising the working procedures of converter smelting, LF refining, RH refining and continuous casting, and comprises the following specific steps:
(1) smelting in a converter: the smelting end point C of the converter is more than or equal to 0.06 percent, the P is less than or equal to 0.015 percent, and the tapping temperature is controlled to 1640 +/-10 ℃; adding 0.7-1.5 kg/t of aluminum blocks and synthetic slag into molten steel during tapping to ensure that the oxygen content in the steel is less than or equal to 50 ppm;
(2) LF refining: refining the target slag component: TFe is less than or equal to 0.6 percent, CaO: 54-56% of SiO2：13～15%，Al2O3: 21-23%, MgO: 6-8%; after slagging, maintaining white slag by adopting a method of supplementing lime and silicon carbide; adding a calcium wire before leaving the station;
(3) RH refining: after the vacuum treatment is finished, adding a sulfur wire, and discharging the molten steel after soft argon blowing is more than or equal to 15 min;
(4) continuous casting: a submerged entry nozzle is used.
2. The method for increasing the number of continuous drawing furnaces for sulfur-containing pinion steel according to claim 1, wherein the converter step of step (1) comprises the following synthetic slag components: CaO: 40 to 55 percent of SiO2≤10%，Al2O3：25～45%，MgO≤10%。
3. The method for increasing the number of continuous drawing furnaces for the sulfur-containing gear steel according to claim 1, wherein in the converter process of the step (1), the tapping time is 3.5-6 min, and the ladle argon blowing time is more than 3 min; and the clearance of the tapped ladle is controlled to be 300-600 mm.
4. The method for increasing the number of the sulfur-containing pinion steel continuous drawing furnaces according to claim 1, wherein in the step (2), in the LF refining process, the furnace cover is well sealed, and the opening of the air door is adjusted, wherein in the early stage of the LF refining, the opening of the air door for side suction in the refining is controlled to be 70-90%, and in the middle and later stages of the refining, the opening of the air door is controlled to be 20-40%, so that the micro-positive pressure state is kept in the furnace.
5. The method for increasing the continuous drawing furnace number of the sulfur-containing gear steel according to claim 1, wherein in the step (2) of the LF refining process, the lime is added in an amount of 9 to 11 kg/t steel, and the silicon carbide is added in an amount of 0.15 to 0.3 kg/t steel.
6. The method for increasing the number of continuous drawing furnaces for sulfur-containing gear steel according to claim 1, wherein in the step (2), the LF refining process is performed, and the addition amount of calcium wires is controlled to be 0.3-0.4 kg/ton steel; the calcium wire is a cored wire.
7. The method for increasing the number of continuous drawing furnaces for sulfur-containing gear steel according to claim 1, wherein in the step (3) RH refining process, the amount of sulfur added is controlled to be 0.2-0.26 kg/ton steel; the sulfur wire is a cored wire.
8. The method for increasing the number of furnaces for continuously drawing the sulfur-containing pinion steel as claimed in claim 1, wherein the step (4) of continuously casting is performed by using an aluminum-zirconium-carbon submerged entry nozzle having an inner diameter of 32 mm.
9. The method for increasing the number of the sulfur-containing gear steel continuous drawing furnaces according to claim 1, characterized in that in the step (4), the continuous casting process adopts full-protection casting, a new sealing gasket is replaced in each furnace at a joint between a ladle sliding nozzle and a long nozzle and is protected by argon, the flow of the argon is 60-70L/min, and the liquid level of the tundish molten steel is protected by a multifunctional covering agent; the baking temperature of the tundish is 1000-1100 ℃.
10. The method for increasing the number of continuous drawing furnaces for sulfur-containing pinion steel according to claim 9, wherein the multifunctional covering agent in the step (4) is composed of the following components: CaO is less than or equal to 2 percent, H2O≤2.5%, Fe2O3≤2%,SiO2≥90%，Al2O3≤2%，MgO≤2%。
Technical Field
The invention belongs to the technical field of metallurgy, and particularly relates to a method for increasing the number of continuous drawing furnaces of sulfur-containing gear steel.
Background
The free-cutting gear steel is the most widely used steel for manufacturing transmission gears and gear shaft materials of various engineering machinery, automobiles, agricultural vehicles and the like in China at present. The alloy has the requirements of excellent obdurability, high surface hardness, specific hardenability, narrow hardenability bandwidth, high purity, high crystal agglomeration degree, avoidance of mixed crystals and good surface quality, and can improve the wear resistance, bending strength, bending fatigue strength, fatigue life, pitting and peeling resistance, scratching resistance, scratch resistance and the like of the gear. Therefore, it is one of the most demanding steel grades in all steel production.
Because the smelting components of the free-cutting gear steel have high aluminum and sulfur contents and easily generate high-melting-point inclusions, the viscosity of molten steel is higher, the fluidity is poorer, and the problem of water gap blockage often occurs in the pouring process of the steel. The plug is mainly Al2O3Is a mixture of a glass phase and metallic iron. Al (Al)2O3Solid particles exist in molten steel, a layer of molten glass is generated on the inner wall of the nozzle due to high temperature, and solid Al exists when the molten steel flows through the nozzle2O3 Gradually deposit on the spout wall. Therefore, if the inner diameter of the submerged nozzle is optimized, the deposit of the inclusions can be effectively reduced and the production is facilitatedThe influence of (c).
Particularly, when a small square billet with a section of less than or equal to 200mm x 200mm is used for production, the stopper rod is easy to rise, the water gap is blocked and the plug is easy to flow, even the plug is shut down by accident, the normal production rhythm of a steel mill is disturbed, and the production cost is high. At present, in domestic special steel enterprises with small square billets with the cross sections of less than or equal to 200mm and 200mm, the number of continuous casting furnaces of gear steel is usually not more than 10.
As mentioned above, in order to normally produce free-cutting gear steel by using small square billets with the section of less than or equal to 200mm and prevent plug rods from rising and water gap from being blocked to cause flow loss, a technology specially suitable for producing the free-cutting gear steel by using a small-section square billet continuous casting machine needs to be developed.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a method for increasing the number of continuous drawing furnaces of sulfur-containing gear steel.
In order to achieve the purpose, the technical scheme provided by the invention is as follows:
the method for increasing the number of the sulfur-containing gear steel continuous drawing furnaces comprises the working procedures of converter smelting, LF refining, RH refining and continuous casting, and specifically comprises the following steps:
(1) smelting in a converter: the smelting end point C of the converter is more than or equal to 0.06 percent, the P is less than or equal to 0.015 percent, and the tapping temperature is controlled to 1640 +/-10 ℃; adding 0.7-1.5 kg/t of aluminum blocks and synthetic slag into molten steel during tapping to ensure that the oxygen content in the steel is less than or equal to 50 ppm;
(2) LF refining: refining the target slag component: TFe is less than or equal to 0.6 percent, CaO: 54-56% of SiO2：13～15%，Al2O3: 21-23%, MgO: 6-8%; after slagging, maintaining white slag by adopting a method of supplementing lime and silicon carbide; adding a calcium wire before leaving the station;
(3) RH refining: after the vacuum treatment is finished, adding a sulfur wire, and discharging the molten steel after soft argon blowing is more than or equal to 15 min;
(4) continuous casting: a submerged entry nozzle is used. In the step (1) of converter smelting, the synthetic slag comprises the following components: CaO: 40 to 55 percent of SiO2≤10%，Al2O3：25～45%，MgO≤10%。
The synthetic slag in the step (1) of the invention comprises the following components: CaO: 40 to 55 percent of SiO2≤10%，Al2O3：25～45%，MgO≤10%。
In the converter process in the step (1), tapping time is 3.5-6 min, and ladle argon blowing time is more than 3 min; and the clearance of the tapped ladle is controlled to be 300-600 mm.
In the step (1) of converter smelting, the slag discharge amount is controlled to be less than or equal to 4 kg/ton steel in the tapping process.
In the LF refining process in the step (2), the adding amount of lime is 9-11 kg/t steel, and the adding amount of silicon carbide is 0.15-0.3 kg/t steel.
In the step (2) of the LF refining process, the furnace cover is well sealed, the opening of the air door is adjusted, the opening of the air door sucked at the refining side is controlled to be 70-90% in the early stage of the LF refining, and the opening of the air door is controlled to be 20-40% in the middle and later stages of the refining, so that the micro-positive pressure state is kept in the furnace.
In the step (2) of the LF refining process, the heat storage of the steel ladle is more than 2 times in the refining process, so that the refractory material of the steel ladle can absorb heat fully.
In the step (2) of the LF refining process, the 1 st furnace outlet temperature is 1680-1700 ℃, and the continuous casting furnace secondary outlet temperature is 1638-1648 ℃.
In the LF refining process in the step (2), the adding amount of calcium wires is controlled to be 0.3-0.4 kg/ton steel; the calcium wire is a cored wire.
In the LF refining process in the step (2), sulfur in the molten steel is less than or equal to 0.005wt% before the calcium wire is added.
In the RH refining process in the step (3), the adding amount of sulfur wires is controlled to be 0.2-0.26 kg per ton of steel; the sulfur wire is a cored wire.
In the RH refining process in the step (3), the exposed diameter of the slag surface is less than or equal to 100mm during soft blowing, and the pressure of soft argon blowing is 0.25-0.50 MPa.
In the RH refining process in the step (3), the first furnace outlet temperature is 1616-1631 ℃, and the continuous casting furnace outlet temperature is 1573-1583 ℃.
In the step (4) of the continuous casting process, an aluminum-zirconium-carbon submerged nozzle with the inner diameter of 32mm is adopted.
In the step (4) of the continuous casting process, the whole-process protection casting is adopted in the casting process, a new sealing gasket is replaced in each furnace at the joint between the ladle sliding nozzle and the long nozzle and is protected by argon, the flow of the argon is 60-70L/min, and the liquid level of the tundish molten steel is protected by a multifunctional covering agent; before baking the tundish, sealing a gap between the ladle cover and the ladle body by using the asbestos felt and the refractory clay, and tightly covering a stopper hole on the ladle cover by using the asbestos felt to ensure that the baking temperature of the tundish reaches 1000-1100 ℃.
The multifunctional covering agent in the step (4) of the invention comprises the following components: CaO is less than or equal to 2 percent, H2O≤2.5%, Fe2O3≤2%,SiO2≥90%，Al2O3≤2%，MgO≤2%。
In the step (4) of the continuous casting process, the ladle is operated by using the steel scrap, and the steel scrap of each furnace is 1-2 tons.
In the continuous casting process in the step (4), the section of the casting blank is less than or equal to 200mm and 200 mm.
The invention has the beneficial effects that:
according to the invention, through adjusting parameters of smelting processes such as converter smelting, LF and RH refining, billet continuous casting and the like, stable casting of the free-cutting gear steel in the casting process is realized, rising of a stopper rod and water gap blockage are avoided, the number of continuous drawing furnaces is increased, and stable production is realized.
The average number of continuous drawing furnaces of the casting times of the method provided by the invention reaches 15 furnaces, and the low-power rating of the produced gear steel reaches 2.0 grades.
The method provided by the invention is suitable for a small square billet continuous casting machine with the section less than or equal to 200mm x 200mm, solves the problems of stopper rod rising, water gap blockage, even flow stoppage, accident stop and the like existing for a long time in the process of producing the free-cutting gear steel, increases the average continuous drawing furnace number of casting times from 10 furnaces to 15 furnaces, improves the qualified rate of casting blanks and the yield of molten steel, and has wide application prospect.
Drawings
FIG. 1 is a view showing a structure of a submerged entry nozzle having an inner diameter of 32 mm.
Detailed Description
The invention is described in further detail below with reference to the figures and specific examples.
Example 1
The method for increasing the number of the sulfur-containing gear steel continuous drawing furnaces comprises the following steps:
(1) smelting in a converter: and C, converter smelting end point C: 0.08%, P: 0.012 percent, the tapping temperature is 1636 ℃, 100kg of aluminum blocks and 400kg of synthetic slag (the synthetic slag comprises 48 percent of CaO and SiO) are added when tapping 1/32：9%，Al2O3: 36%, MgO: 7%); the oxygen content in the steel was 35 ppm; tapping time is 4min15s, ladle argon blowing time is 4min30s, and alloy materials on the surface of a slag layer do not lump; the clearance of a steel ladle tapping from the converter is 350mm, and the slag discharging amount is 3 kg/ton steel;
(2) LF refining: the whole process is operated by micro positive pressure, the opening of the air door of the refining side suction at the early stage is controlled at 72%, and the opening of the air door at the middle and later stages is controlled at 31%; 7.5 kg of lime is added in the heating process per t of steel, the total addition of silicon carbide is 0.21kg per t, and the refining final slag components are as follows: TFe 0.58%, CaO 54%, SiO2 14.42%， Al2O323 percent and 8.0 percent of MgO; the ladle is subjected to heat storage for 2 times in the refining process, so that the ladle refractory material can fully absorb heat; 0.004wt% of sulfur before the tapping, 0.32 kg of calcium wires per t of steel were fed, and the tapping temperature was 1638 ℃;
(3) RH refining: RH refining vacuum degree of 36Pa, pure degassing time of 21min23 s; after the vacuum treatment is finished, 0.23 kg of sulfur wires per t of steel are added, molten steel is discharged after soft argon blowing is carried out for 16min, the molten steel in a steel ladle is slightly moved during soft argon blowing, the exposed diameter of a slag surface is 90mm, the pressure of the soft argon blowing is 0.35MPa, and the discharging temperature is controlled at 1578 ℃;
(4) continuous casting: in the pouring process, full-process protection pouring is adopted, a new sealing gasket is replaced in each furnace at the joint between the ladle sliding water gap and the long water gap and is protected by argon, the argon flow is 65L/min, and the submerged nozzle is a special aluminum-zirconium-carbon submerged nozzle with the inner diameter of 32mm, as shown in figure 1; the liquid level of the tundish molten steel is protected by a multifunctional covering agent, and the multifunctional covering agent comprises the following components: CaO: 1.9%, H2O：2.5%, Fe2O3：1.9%,SiO2：90%，Al2O3: 1.7%, MgO: 2 percent; before baking the tundish, sealing a gap between the tundish cover and the tundish body by using an asbestos felt and refractory clay, and tightly covering a stopper hole on the tundish cover by using the asbestos felt, wherein the baking temperature of the tundish is 1030 ℃; continuous casting process casting blank section200mm*200mm。
By adopting the production method, the number of continuous drawing furnaces of the free-cutting gear steel can be stabilized at 15, the liquid level of the crystallizer steel is kept stable, the opening degree of the stopper rod is stable, and the low-power rating of the obtained free-cutting gear steel reaches 2.0 level.
Example 2
(1) Smelting in a converter: and C, converter smelting end point C: 0.09%, P: 0.013%, the tapping temperature was 1631 ℃, and 120kg of aluminum blocks and 400kg of synthetic slag (the synthetic slag components: CaO: 42%, SiO) were added during tapping 1/32：10%，Al2O3: 40%, MgO: 8%); the oxygen content in the steel is 40 ppm; tapping time is 4min21s, ladle argon blowing time is 3min26s, and alloy materials on the surface of a slag layer do not lump; the clearance of a steel ladle tapped from the converter is 300 mm; the slag amount is 3.5 kg/ton steel;
(2) LF refining: the whole process is operated by micro positive pressure, and the opening degree of an air door for refining side suction at the early stage is controlled at 80 percent; the opening degree of the air door in the middle and later periods is controlled to be 26 percent; adding 9.8 kg of lime per t of steel in the heating process, wherein the total addition of silicon carbide is 0.3 kg per t, and refining the final slag components: TFe 0.56%, CaO 54.8%, SiO2 15%，Al2O322.6 percent of MgO and 7.04 percent of MgO, and the ladle stores heat for 2 times in the refining process, so that the refractory material of the ladle absorbs heat fully; 0.002wt% of sulfur before the tapping, 0.34 kg of calcium wires per ton of steel before the tapping, and 1639 ℃ of tapping temperature;
(3) RH refining: RH refining vacuum degree of 37Pa, pure degassing time of 18min35 s; after the vacuum treatment is finished, 0.22 kg of sulfur wires per t of steel is added, molten steel is discharged after soft argon blowing is carried out for 8min, the molten steel in a steel ladle is slightly moved during the soft argon blowing, the exposed diameter of a slag surface is 90mm, the pressure of the soft argon blowing is 0.31MPa, and the discharge temperature is controlled at 1580 ℃;
(4) continuous casting: in the pouring process, full-process protection pouring is adopted, a new sealing gasket is replaced in each furnace at the joint between the ladle sliding water gap and the long water gap and is protected by argon, the argon flow is 62L/min, and the submerged nozzle is a special aluminum-zirconium-carbon submerged nozzle with the inner diameter of 32mm, as shown in figure 1; the liquid level of the tundish molten steel is protected by a multifunctional covering agent, and the multifunctional covering agent comprises the following components: CaO: 1.8%, H2O：2.3%, Fe2O3：1.7%,SiO2：90.5%，Al2O3: 1.8%, MgO: 1.9 percent. Baking tundishSealing a gap between the ladle cover and the ladle body by using asbestos felt and refractory clay, tightly covering a stopper hole on the ladle cover by using the asbestos felt, and baking the tundish at 1060 ℃; and in the continuous casting process, the section of a casting blank is 200mm by 200 mm.
By adopting the production method, the number of continuous drawing furnaces of the free-cutting gear steel can be stabilized at 15, the liquid level of the crystallizer steel is kept stable, the opening degree of the stopper rod is stable, and the low-power rating of the obtained free-cutting gear steel reaches 2.0 level.
Example 3
(1) Smelting in a converter: and C, converter smelting end point C: 0.10%, P: 0.014%, the tapping temperature was 1633 ℃, and 150kg of aluminum blocks and 400kg of synthetic slag (the synthetic slag components are CaO: 55%, SiO) were added during tapping 1/32：3%，Al2O3: 32%, MgO: 10%); the oxygen content in the steel is 26 ppm; tapping time is 5min13s, ladle argon blowing time is 3min20s, and alloy materials on the surface of a slag layer do not lump; the clearance of a steel ladle tapping from the converter is 400mm, and the slag discharging amount is 2 kg/ton steel;
(2) LF refining: the whole process is operated under micro-positive pressure, and the opening degree of an air door for refining side suction at the early stage is controlled to be 85 percent; the opening degree of the air door in the middle and later periods is controlled at 38 percent; 10.2 kg of lime is added in the heating process per t of steel, the total addition of silicon carbide is 0.30 kg per t, and the refining final slag components are as follows: TFe 0.5%, CaO 55.5%, SiO2 13%， Al2O323 percent and MgO 8.0 percent; the ladle is subjected to heat storage for 2 times in the refining process, so that the ladle refractory material can fully absorb heat; 0.003wt% sulfur before tapping, 0.33 kg of calcium wires per t of steel were fed, and the tapping temperature was 1639 ℃;
(3) RH refining: RH refining vacuum degree 39Pa, pure degassing time 18min43 s; after the vacuum treatment is finished, 0.21kg of sulfur wires per t of steel is added, molten steel is discharged after soft argon blowing is carried out for 6min, the molten steel in a steel ladle is slightly moved during the soft argon blowing, the exposed diameter of a slag surface is 60mm, the pressure of the soft argon blowing is 0.30MPa, and the discharge temperature is controlled at 1573 ℃;
(4) continuous casting: in the pouring process, full-process protection pouring is adopted, a new sealing gasket is replaced in each furnace at the joint between the ladle sliding water gap and the long water gap and is protected by argon, the argon flow is 60L/min, and the submerged nozzle is a special aluminum-zirconium-carbon submerged nozzle with the inner diameter of 32mm, as shown in figure 1; the liquid level of the tundish molten steel is protected by a multifunctional covering agent, and the multifunctional covering agent comprises the following components: CaO: 1.8%，H2O：2.2%, Fe2O3：1.8%,SiO2：90.6%，Al2O3: 1.9%, MgO: 1.7 percent. Before baking the tundish, sealing a gap between the tundish cover and the tundish body by using an asbestos felt and refractory clay, and tightly covering a stopper hole on the tundish cover by using the asbestos felt, wherein the baking temperature of the tundish is 1040 ℃; and in the continuous casting process, the section of a casting blank is 200mm by 200 mm.
By adopting the production method, the number of continuous drawing furnaces of the free-cutting gear steel can be stabilized at 15, the liquid level of the crystallizer steel is kept stable, the opening degree of the stopper rod is stable, and the low-power rating of the obtained free-cutting gear steel reaches 2.0 level.
Example 4
(1) Smelting in a converter: and C, converter smelting end point C: 0.09%, P: 0.010 percent, the tapping temperature is 1638 ℃, and 120kg of aluminum blocks and 450kg of synthetic slag (the synthetic slag comprises 50 percent of CaO and SiO) are added when tapping 1/32：10%，Al2O3: 31%, MgO: 9%); the oxygen content in the steel was 42 ppm; tapping time is 4min46s, ladle argon blowing time is 5min12s, and alloy materials on the surface of a slag layer do not lump; the clearance of a steel ladle tapping from the converter is 400mm, and the slag discharging amount is 2 kg/ton steel;
(2) LF refining: the whole process is operated by micro positive pressure, and the opening degree of an air door for refining side suction at the early stage is controlled at 76%; the opening degree of the air door at the middle and later periods is controlled to be 35 percent, so that the reducing atmosphere is kept in the furnace; adding 9.8 kg of lime per t of steel in the heating process, wherein the total addition amount of silicon carbide is 0.21 kg; refining the final slag components: TFe 0.6%, CaO 54.4%, SiO2 14.3%， Al2O322.7 percent of MgO, 8.0 percent of MgO; the ladle is subjected to heat storage for 2 times in the refining process, so that the ladle refractory material can fully absorb heat; 0.002wt% of sulfur before leaving the station, 0.30 kg of calcium wires per ton of steel were fed, and the temperature of leaving the station was 1639 ℃;
(3) RH refining: RH refining vacuum degree of 55Pa, pure degassing time of 20min12 s; after the vacuum treatment is finished, 0.26kg of sulfur wires per t of steel is added, molten steel is discharged after soft argon blowing is carried out for 17min, the molten steel in a steel ladle is slightly moved during soft argon blowing, the exposed diameter of a slag surface is 80mm, the pressure of the soft argon blowing is 0.31MPa, and the discharge temperature is 1583 ℃;
(4) continuous casting: the whole-course protection pouring is adopted in the pouring process, a new sealing gasket is replaced in each furnace at the joint between the ladle sliding nozzle and the long nozzle and is protected by argon, and the argon flow is 63L/min, the submerged nozzle is a special aluminum zirconium carbon submerged nozzle with the inner diameter of 32mm, as shown in figure 1; the liquid level of the tundish molten steel is protected by a multifunctional covering agent, and the multifunctional covering agent comprises the following components: CaO: 1.7%, H2O： 2.5%, Fe2O3：2%,SiO2：90.1%，Al2O3: 1.8%, MgO: 1.9 percent. Before baking the tundish, sealing a gap between the tundish cover and the tundish body by using an asbestos felt and refractory clay, and tightly covering a stopper hole on the tundish cover by using the asbestos felt, wherein the baking temperature of the tundish is 1010 ℃; and in the continuous casting process, the section of a casting blank is 200mm by 200 mm.
By adopting the production method, the number of continuous drawing furnaces of the free-cutting gear steel can be stabilized at 15, the liquid level of the crystallizer steel is kept stable, the opening degree of the stopper rod is stable, and the low-power rating of the obtained free-cutting gear steel reaches 2.0 level.
Example 5
(1) Smelting in a converter: and C, converter smelting end point C: 0.07%, P: 0.009%, 1638% of tapping temperature, adding 130kg of aluminum blocks and 400kg of synthetic slag (the synthetic slag comprises 40% of CaO, 8% of SiO2, 45% of Al2O3 and 7% of MgO) when tapping 1/3; the oxygen content in the steel was 41 ppm; tapping time is 5min15s, ladle argon blowing time is 5min10s, and alloy materials on the surface of a slag layer do not lump; the clearance of a steel ladle tapping from the converter is 300mm, and the slag discharging amount is 2.8 kg/ton steel;
(2) LF refining: the whole process is operated by micro positive pressure, the opening of the air door of the refining side suction at the early stage is controlled at 82%, and the opening of the air door at the middle and later stages is controlled at 20%; 9.7 kg of lime is added in the heating process per t of steel, and the total addition of silicon carbide is 0.21kg per t; refining the final slag components: TFe 0.6%, CaO 56%, SiO2 14.5%， Al2O321 percent and 7.9 percent of MgO. The ladle is subjected to heat storage for 2 times in the refining process, so that the ladle refractory material can fully absorb heat; 0.003wt% of sulfur before leaving the station, 0.33 kg of calcium wires per t of steel were fed, and the leaving temperature was 1648 ℃;
(3) RH refining: RH refining vacuum degree of 35Pa, pure degassing time of 21min22 s; after the vacuum treatment is finished, 0.26kg of sulfur wires per t of steel is added, molten steel is discharged after soft argon blowing is carried out for 16min, the molten steel in a steel ladle is slightly moved during the soft argon blowing, the exposed diameter of a slag surface is 80mm, the pressure of the soft argon blowing is 0.30MPa, and the discharge temperature is controlled at 1577 ℃;
(4) continuous casting: the whole process is adopted in the pouring processProtection pouring, namely replacing a new sealing gasket in each furnace at the joint between the ladle sliding water gap and the long water gap and protecting the sealing gasket by using argon, wherein the argon flow is 66L/min, and the submerged nozzle is a special aluminum-zirconium-carbon submerged nozzle with the inner diameter of 32mm, as shown in figure 1; the liquid level of the tundish molten steel is protected by a multifunctional covering agent, and the multifunctional covering agent comprises the following components: CaO: 2%, H2O: 2.4% of Fe2O3：1.8%,SiO2：90.3%，Al2O3: 1.9%, MgO: 1.6 percent. Before baking the tundish, sealing a gap between the tundish cover and the tundish body by using an asbestos felt and refractory clay, and tightly covering a stopper hole on the tundish cover by using the asbestos felt, wherein the baking temperature of the tundish is 1060 ℃; and in the continuous casting process, the section of a casting blank is 200mm by 200 mm.
By adopting the production method, the number of continuous drawing furnaces of the free-cutting gear steel can be stabilized at 15, the liquid level of the crystallizer steel is kept stable, the opening degree of the stopper rod is stable, and the low-power rating of the obtained free-cutting gear steel reaches 2.0 level.
Example 6
(1) Smelting in a converter: and C, converter smelting end point C: 0.08%, P: 0.015 percent, the tapping temperature is 1636 ℃, and 110kg of aluminum blocks and 400kg of synthetic slag (the components of the synthetic slag comprise 55 percent of CaO and SiO) are added when tapping 1/32：10%，Al2O3: 25%, MgO: 10%); the oxygen content in the steel was 38 ppm; tapping time is 5min30s, ladle argon blowing time is 4min40s, and alloy materials on the surface of a slag layer do not lump; the clearance of a steel ladle tapped from the converter is 350mm, and the slag discharging amount is 3.5 kg/ton steel;
(2) LF refining: the whole process is operated by micro positive pressure, and the opening degree of an air door for refining side suction at the early stage is controlled at 80 percent; the opening degree of the air door in the middle and later periods is controlled at 40 percent; 10.3 kg of lime is added in the heating process per t of steel, the total addition of silicon carbide is 0.21kg per t, and the refining final slag components are as follows: TFe 0.6%, CaO 55.9%, SiO2 14.8%， Al2O322.7 percent and 6 percent of MgO; the ladle is subjected to heat storage for 2 times in the refining process, so that the ladle refractory material can fully absorb heat; 0.002wt% of sulfur before tapping, 0.37 kg of calcium wires per t of steel were fed, and the tapping temperature was 1639 ℃;
(3) RH refining: RH refining vacuum degree of 77Pa, pure degassing time of 20min20 s; after the vacuum treatment is finished, 0.25 kg of sulfur wires per t of steel is added, molten steel is discharged after soft argon blowing is carried out for 15min, the molten steel in a steel ladle is slightly moved during the soft argon blowing, the exposed diameter of a slag surface is 90mm, the pressure of the soft argon blowing is 0.30MPa, and the discharge temperature is controlled at 1582 ℃;
(4) continuous casting: in the pouring process, full-process protection pouring is adopted, a new sealing gasket is replaced in each furnace at the joint between the ladle sliding water gap and the long water gap and is protected by argon, the argon flow is 70L/min, and the submerged nozzle is a special aluminum-zirconium-carbon submerged nozzle with the inner diameter of 32mm, as shown in figure 1; the liquid level of the tundish molten steel is protected by a multifunctional covering agent, and the multifunctional covering agent comprises the following components: CaO: 1.6%, H2O：2.5%, Fe2O3：1.9%,SiO2：90.2%，Al2O3: 2%, MgO: 1.8 percent. Before baking the tundish, sealing a gap between the tundish cover and the tundish body by using asbestos felt and refractory clay, and tightly covering a stopper hole on the tundish cover by using the asbestos felt, wherein the baking temperature of the tundish is 1065 ℃; and in the continuous casting process, the section of a casting blank is 200mm by 200 mm.
By adopting the production method, the number of continuous drawing furnaces of the free-cutting gear steel can be stabilized at 15, the liquid level of the crystallizer steel is kept stable, the opening degree of the stopper rod is stable, and the low-power rating of the obtained free-cutting gear steel reaches 2.0 level.
Example 7
(1) Smelting in a converter: and C, converter smelting end point C: 0.10%, P: 0.009%, 1633 deg.C, adding 200kg of aluminum block and 400kg of synthetic slag (the synthetic slag comprises CaO 48%, SiO) during tapping 1/32：7%，Al2O3: 38%, MgO: 7%); oxygen content in steel 33 ppm; tapping time is 4min and 10s, ladle argon blowing time is 5min and 13s, and alloy materials on the surface of a slag layer do not lump; the clearance of a steel ladle tapped from the converter is 350mm, and the slag discharging amount is 3.5 kg/ton steel;
(2) LF refining: the whole process is operated under micro-positive pressure, and the opening degree of an air door for refining side suction at the early stage is controlled at 70 percent; the opening degree of the air door in the middle and later periods is controlled at 22 percent; adding 9.6 kg of lime per t of steel in the heating process, wherein the total addition of silicon carbide is 0.14 kg per t, and refining the final slag components: TFe0.57%, CaO 54.9%, SiO215%，Al2O322.8 percent of MgO and 6.73 percent of MgO, and the ladle stores heat for 2 times in the refining process, so that the refractory material of the ladle absorbs heat fully; 0.004wt% of sulfur before the tapping, 0.38 kg of calcium wires per t of steel were fed, and the tapping temperature was 1648 ℃;
(3) RH refining: RH refining vacuum degree of 33Pa, pure degassing time of 20min15 s; after the vacuum treatment is finished, 0.22 kg of sulfur wires per t of steel is added, molten steel is discharged after soft argon blowing is carried out for 18min, the molten steel in a steel ladle is slightly moved during the soft argon blowing, the exposed diameter of a slag surface is 100mm, the pressure of the soft argon blowing is 0.46MPa, and the discharging temperature is controlled to be 1576 ℃;
(4) continuous casting: in the pouring process, full-process protection pouring is adopted, a new sealing gasket is replaced in each furnace at the joint between the ladle sliding water gap and the long water gap and is protected by argon, the argon flow is 67L/min, and the submerged nozzle is a special aluminum-zirconium-carbon submerged nozzle with the inner diameter of 32mm, as shown in figure 1; the liquid level of the tundish molten steel is protected by a multifunctional covering agent, and the multifunctional covering agent comprises the following components: CaO: 1.7%, H2O: 2.2% of Fe2O3：1.8%，SiO2 90.5%，Al2O31.8%, MgO: 2 percent. Before baking the tundish, sealing a gap between the tundish cover and the tundish body by using an asbestos felt and refractory clay, tightly covering a stopper hole on the tundish cover by using the asbestos felt, and baking the tundish at 1080 ℃; and in the continuous casting process, the section of a casting blank is 200mm by 200 mm.
By adopting the production method, the number of continuous drawing furnaces of the free-cutting gear steel can be stabilized at 15, the liquid level of the crystallizer steel is kept stable, the opening degree of the stopper rod is stable, and the low-power rating of the obtained free-cutting gear steel reaches 2.0 level.
Example 8
(1) Smelting in a converter: and C, converter smelting end point C: 0.07%, P: 0.011 percent, the tapping temperature is 1646 ℃, and 150kg of aluminum blocks and 400kg of synthetic slag (the components of the synthetic slag comprise 49 percent of CaO and SiO) are added when the steel is tapped 1/32：6%，Al2O3: 39%, MgO: 6%); the oxygen content in the steel is 30 ppm; tapping time is 5min30s, ladle argon blowing time is 4min30s, and alloy materials on the surface of a slag layer do not lump; the clearance of a steel ladle tapped from the converter is 350mm, and the slag discharging amount is 3.5 kg/ton steel;
(2) LF refining: the whole process is operated under micro-positive pressure, and the opening degree of an air door for refining side suction at the early stage is controlled at 90 percent; the opening degree of the air door in the middle and later periods is controlled at 36 percent; 10kg of lime is added in the heating process per t of steel, the total addition of silicon carbide is 0.14 kg per t, and the refining final slag components are as follows: TFe 0.53%, CaO 54.7%, SiO2 14.4%，Al2O322.5 percent and 7.87 percent of MgO. The ladle is subjected to heat storage for 2 times in the refining process, so that the refractory material of the ladle can fully absorb heat(ii) a 0.004wt% of sulfur before the tapping, 0.35 kg of calcium wires per t of steel were fed, and the tapping temperature was 1645 ℃;
(3) RH refining: RH refining vacuum degree of 29Pa, pure degassing time of 19min16 s; after the vacuum treatment is finished, 0.25 kg of sulfur wires per t of steel is added, molten steel is discharged after soft argon blowing is carried out for 20min, the molten steel in a steel ladle is slightly moved during the soft argon blowing, the exposed diameter of a slag surface is 60mm, the pressure of the soft argon blowing is 0.25MPa, and the discharge temperature is controlled at 1577 ℃;
(4) continuous casting: in the pouring process, full-process protection pouring is adopted, a new sealing gasket is replaced in each furnace at the joint between the ladle sliding water gap and the long water gap and is protected by argon, the argon flow is 60L/min, and the submerged nozzle is a special aluminum-zirconium-carbon submerged nozzle with the inner diameter of 32mm, as shown in figure 1; the liquid level of the tundish molten steel is protected by a multifunctional covering agent, and the multifunctional covering agent comprises the following components: CaO: 1.8%, H2O：2.4%, Fe2O3：1.9%,SiO2：90.2%，Al2O3: 1.9%, MgO: 1.8 percent. Before baking the tundish, sealing a gap between the ladle cover and the ladle body by using asbestos felt and refractory clay, and tightly covering a stopper hole on the ladle cover by using the asbestos felt, wherein the baking temperature of the tundish is 1070 ℃; and in the continuous casting process, the section of a casting blank is 200mm by 200 mm.
By adopting the production method, the number of continuous drawing furnaces of the free-cutting gear steel can be stabilized at 15, the liquid level of the crystallizer steel is kept stable, the opening degree of the stopper rod is stable, and the low-power rating of the obtained free-cutting gear steel reaches 2.0 level.
Although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that: modifications and equivalents may be made thereto without departing from the spirit and scope of the invention and it is intended to cover in the claims the invention as defined in the appended claims.