A smelting process for efficiently and precisely controlling the B content in gear steel

Abstract

The invention discloses a smelting process for efficiently and accurately controlling the B content in gear steel. The process includes converter smelting, slag skimming after the furnace, LF refining, RH vacuum, continuous casting and other processes. Among them, low-carbon tapping in the converter process can increase the molten steel temperature, which is conducive to rapid slag formation; low-carbon tapping makes the molten steel in a peroxidized state, and the B element in the molten steel can be oxidized to B2O3 and enter the slag, further reducing the residual B element content in the converter tapping; no Al-based alloy is added during the tapping process to avoid reducing the B2O3 in the slag and entering the molten steel; slag skimming after the furnace is adopted during tapping, which can remove the B2O3 in the furnace slag, avoid being reduced and entering the molten steel during LF refining. At the same time, after removing the oxidized slag, the refining burden is reduced, and the purity of the molten steel is further improved; the tapping alloy does not have to use low-B alloy, reducing the alloy cost. This method can efficiently and accurately control the residual B content in the molten steel ≤ 1.5 ppm, significantly improving the purity of the molten steel and the product quality level.

Description

Technical Field

[0001] The present invention relates to a smelting process for controlling the B content in steel, and particularly to a smelting process for efficiently and accurately controlling the B content in gear steel. Background Art

[0002] Hardenability is an important performance index of gear steel. The narrower the hardenability bandwidth of gear steel is required, the better. This is mainly to ensure the core hardness of different gears and is conducive to controlling the heat treatment deformation of gears. Generally, for the steel used in high-grade automotive transmission gears, the hardenability bandwidth of different heats is required to be ≤4HRC. Therefore, improving and stabilizing the hardenability of steel has always been a research topic for special steel plants. The residual B element in gear steel has a great influence on hardenability. High-end gear steel has extremely strict requirements for both the purity of molten steel and the hardenability bandwidth. Reducing the content of residual B element in gear steel can effectively reduce the hardenability bandwidth. Relevant literature shows that when the B content ≤4ppm, the hardenability bandwidth ≤4HRC.

[0003] The main problems affecting the residual B content in gear steel produced by the converter process are as follows:

[0004] (1) Slag falling during converter tapping. In the converter oxygen-blowing smelting process, the B element in molten iron is oxidized to B2O3 and enters the slag. Since the converter tapping cannot adopt the operation of retaining steel, slag falling will inevitably occur due to the vortex effect with the steel flow at the end of tapping. The LF refining stage is the reduction period, and the B2O3 in the slag will undergo a reduction reaction and enter the molten steel again, resulting in an increase in the B element content in the molten steel.

[0005] (2) B element in alloys. The main elements in gear steel are C, Si, Mn, Cr, etc. Silicon-based, manganese-based, and chromium-based alloys need to be added to the molten steel for alloying. The B element content in different alloys varies greatly, but selecting low-B alloys will lead to a significant increase in alloy costs.

[0006] (3) Adding Al-based alloys during converter tapping. Due to its strong reducibility, the B2O3 in the slag is reduced and enters the molten steel, resulting in an increase in the B element content in the molten steel.

[0007] To solve the above problems, generally, electric furnace production is adopted, and the operations of retaining steel and retaining slag are carried out to reduce slag falling and prevent B increase. This method is not applicable to the converter process, and the operation of retaining steel is not conducive to efficient production and increases the production cost of enterprises; or low-B content alloys and raw and auxiliary materials are selected, but this will greatly increase the production cost; or by optimizing the slag system, reducing the reduction degree during the LF refining period, and reducing the reduction of B2O3 in the slag into the molten steel. By reducing the reduction degree, it is not conducive to the deep deoxidation operation of molten steel and is not conducive to improving the purity of molten steel.

[0008] CN114574750A Method for controlling boron content in narrow hardenability gear steel. By optimizing the types of alloys used, strictly prohibiting the addition of silicon manganese and high-carbon alloys, strictly controlling the boron content in alloys and raw and auxiliary materials, performing the operation of leaving steel and slag in electric furnace smelting, optimizing the boron content in ladle bricks and the deoxidation process of tapping in electric furnace, and performing the operation of leaving steel and slag in the tundish, etc., the boron content in narrow hardenability gear steel is reduced. This method mainly relies on operations such as leaving steel and slag in electric furnace and leaving steel in tundish, which is not conducive to efficient production and increases production costs; moreover, the operation of leaving steel cannot be achieved in converter smelting, so this method cannot be promoted and used in the converter process; in addition, strictly controlling the B content in alloys, raw and auxiliary materials, and ladle bricks in this scheme will greatly increase the raw material costs.

[0009] CN108950125A Method for reducing boron content in 20CrMnTiH gear steel. In the converter smelting stage of this method, low-carbon ferromanganese and medium-carbon ferromanganese alloys are used as manganese additives, and in the LF refining stage, a refining slag with an Al2O3 mass fraction of 20 - 25% is used for refining. By controlling the material formula and adjusting the composition of the refining slag system, and canceling the step of adding slag melting balls, the content of boron (B) element is reduced, the B content is controlled ≤2 ppm, and the hardenability of 20CrMnTiH gear steel is stabilized. Al2O3 can reduce the B element in the slag, making B enter the molten steel. In the present invention, the composition of the refining slag system is adjusted, and by reducing the Al2O3 content in the slag, the reduction amount of B element in the slag is reduced, realizing the reasonable control of B element in the steel. However, this scheme does not completely remove the B-containing slag, but only reduces the reduction degree of refining and the reduction amount of B in the slag. This method will lead to insufficient deoxidation of the molten steel and is not conducive to improving the purity of the molten steel.

[0010] CN113832294A Method for controlling B content in 20CrMnTiH gear steel. In this method, silicon manganese deoxidation is carried out during the tapping process of the converter, large-flow argon blowing is carried out on the small platform and then aluminum wire is fed, and the adjustment of alloying elements in LF is controlled according to the middle line of the specification, which well solves the problem that the high B content in 20CrMnTiH gear steel affects the hardenability. By optimizing the process steps, deoxidation process, feeding aluminum wire and adjusting alloying elements are carried out at appropriate times, which well reduces the B content in the gear steel. In the experiment, using the control method of this invention, the B content of the test furnace batches can be effectively controlled within 4 ppm. However, this invention patent does not effectively treat the slag of the converter tapping, and at the same time, the B content in the silicon manganese alloy is relatively high, which is easy to increase the B content in the molten steel and is not conducive to the production of ultra-low B content steel grades.

[0011] CN 114737021 A A method for controlling the boron content in steel. Adding Al blocks to the ladle for deoxidation in this method will reduce the B element in the slag into the molten steel, increasing the B content in the molten steel; the ferroalloys added in this method are selected as low-boron alloys, including low-carbon ferromanganese, metallic manganese, and low-boron low-carbon ferrochromium, which will further increase the production cost and is not conducive to large-scale promotion; this method controls the residual B in the molten steel to be above 2.8 ppm and cannot further reduce the residual B content in the molten steel.

[0012] CN 114908215 A A method for controlling the B content in gear steel. Adding aluminum pellets last when adding auxiliary materials during alloying in this method will reduce the B element in the slag into the molten steel, increasing the B content in the molten steel; the finished product B content in this method is controlled at 3.7 ppm, and the residual B content is still relatively high, and the residual B content in the molten steel cannot be further reduced. Summary of the Invention

[0013] Object of the Invention: The present invention aims to provide a smelting process for efficiently and accurately controlling and reducing the B content in gear steel, with the B element content in gear steel ≤ 1.5 ppm.

[0014] Technical Solution: The smelting process for efficiently and accurately controlling the residual B content in gear steel according to the present invention includes the following steps:

[0015] (1) Converter:

[0016] The C content at the end of converter tapping is 0.04 - 0.07%, and the tapping oxygen content is controlled at 300 - 800 ppm to create a relatively high oxidation atmosphere, fully oxidizing the B element in the molten steel into B2O3 and entering the slag to reduce the residual B element content in the molten steel; the tapping temperature is 1600 - 1660 °C. Observe the tapping situation in the converter at any time during the tapping process to avoid tapping with slag; when the molten steel tapping volume is 20 - 40 t, start adding alloys and lime, and the alloying at tapping reaches the lower limit of the steel grade composition to reduce the LF alloy addition amount; at the end of tapping, put the slag stopper into the molten steel and immediately tilt the furnace to lift the furnace; after tapping, stir with large argon gas to fully oxidize the B element brought in by the alloy into B2O3 and float it to the slag, and at the same time facilitate the floating of molten steel inclusions;

[0017] (2) Skimming:

[0018] Transfer the molten steel to the skimming process. After the slag surface is blown open, reduce the argon gas flow rate, tilt the ladle to remove the slag, and the exposed area of the molten steel after skimming ≥ 80%;

[0019] (3) LF refining:

[0020] After slag removal, the ladle of molten steel is lifted to the LF process. Al wire is fed through a wire feeder for precipitation deoxidation and Al alloying, rapidly reducing the oxygen content in the molten steel to a reduced level, and reducing the oxygen content in the molten steel to below 15 ppm. Alloy is added through a high-level bin to finely adjust the composition of the molten steel. Lime and refining slag are added, and electric power is supplied to heat up and melt the slag. A diffusion deoxidizer is added in the early stage of refining for diffusion deoxidation. After the slag turns white, the diffusion deoxidizer is added in small amounts and multiple batches to maintain the white slag.

[0021] Furthermore, in step (1), the addition of Al-based deoxidizer is prohibited during the tapping process to avoid the reduction reaction of B2O3 in the slag and its re-entry into the molten steel.

[0022] Furthermore, in step (1), the alloy is ferrosilicon manganese, low-carbon ferromanganese, high-carbon ferromanganese, low-carbon ferrochrome or ferrosilicon. The amount of lime added is 2 - 5 kg / t. The argon flow rate for large argon stirring after tapping is 200 - 500 L / min, and the stirring time is 3 - 6 min.

[0023] Furthermore, in step (2), the bottom blowing argon flow rate at the start of slag removal is 200 - 400 L / min. After breaking the slag, the argon flow rate is adjusted to 20 - 80 L / min. The diameter of the slag surface blown open is 10 - 40 cm, and the tilt angle of the ladle is 5 - 30°.

[0024] Furthermore, in step (3), the length of the Al wire fed during LF refining is between 50 - 300 m. The Al content controlled in the first LF analysis is 0.010 - 0.040 wt%. The diffusion deoxidizer includes high-purity silicon carbide powder, ferrosilicon powder and calcium carbide. The addition amount of lime is 4 - 6 kg / t, the refining slag is 2 - 5 kg / t, and the target composition of the slag system is R: 4 - 6, Al2O3 content: 20 - 30%, FeO + MnO ≤ 1%.

[0025] Furthermore, the residual B content in the gear steel is ≤ 1.5 ppm.

[0026] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: (1) This method can control the residual B content in gear steel at a low cost, efficiently and precisely to ≤1.5 ppm, significantly improve the purity of molten steel, enhance the quality level of special steel products, and increase added value; (2) The converter taps steel with low carbon drawing, controls the tapping oxygen content at 300 - 800 ppm, creates a relatively high oxidation atmosphere, can oxidize the B element in hot metal into B2O3 and enter the slag, further reducing the residual B element content in the converter tapping; (3) The converter taps steel with low carbon drawing, raises the tapping temperature, which is convenient for slag skimming after the furnace, and is also conducive to increasing the slag formation speed in refining; (4) Alloys are mainly added after the converter, so that the residual B element in the alloy is quickly oxidized by the molten steel and enters the slag, reducing the LF alloy consumption. The types of alloys are not restricted, and there is no need to specifically select low-B alloys, effectively reducing production costs; (5) No Al-based deoxidizer is added during the converter tapping to avoid reducing B2O3 in the slag back into the molten steel, further reducing the B element content in the molten steel; (6) The B element in the alloy added during the converter tapping process is oxidized into B2O3 and floats to the slag, and the B2O3 in the slag dropped at the end of tapping are removed by slag skimming after the furnace, avoiding the reduction of the B element in the slag back into the molten steel during LF refining, and minimizing the B element in the molten steel from the source; (7) After slag skimming after the furnace, the oxidized slag is removed, reducing the pressure of LF reduction and inclusion removal, and further improving the purity of molten steel; (8) The converter can produce molten steel to the maximum extent, increasing the output. Specific embodiments

[0027] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0028] Example 1

[0029] The smelting process for efficiently and precisely controlling the residual B content in gear steel according to the present invention includes the following steps:

[0030] Converter process

[0031] At the end of the converter tapping, C is 0.04%, the oxygen content before tapping is 754 ppm, creating a relatively high oxidation atmosphere to fully oxidize element B in the molten steel into B2O3 and make it enter the slag, reducing the content of residual B element in the molten steel; at the end of the converter tapping, the B content in the molten steel is 0.5 ppm, the tapping temperature is 1640 °C, and the P content is 0.015%. Observe the tapping situation in the converter at any time during the tapping process to avoid tapping with slag; when the tapping amount reaches the end stage, put the slag stopper cone into the molten steel through the slide rail car. When the slag stopper cone is submerged in the swirling molten steel during the descending process, quickly tilt the furnace to avoid excessive slag in the steel flow; when the tapping amount of the molten steel is 20 t, start adding ferrosilicon manganese alloy, high-carbon ferromanganese alloy, high-carbon ferrochrome alloy and 2 kg / t of lime. The alloying during tapping reaches the lower limit of the steel grade composition, reducing the LF alloy addition amount, and prohibiting the addition of Al-based deoxidizer. After the tapping is completed, adjust the bottom blowing argon flow rate to 250 L / min and stir for 3 min to fully oxidize the B element brought into the alloy into B2O3 and make it float to the slag, while also facilitating the floating of inclusions in the molten steel. After stirring, take a molten steel sample for composition analysis, B: 0.8 ppm, and then lift the ladle of molten steel to the slag skimming process.

[0032] Slag skimming station

[0033] After stirring, drive the ladle car to the slag skimming process. Control the bottom blowing argon flow rate at 300 L / min. After the slag surface is blown open, reduce the argon flow rate to 40 L / min to ensure that the diameter of the blown slag surface is 25 cm; the tilt angle of the ladle is 10°, which is conducive to skimming the slag. Skim the slag surface clean, and then transfer the ladle to the LF refining process after skimming the slag.

[0034] LF refining

[0035] Lift the ladle of molten steel to the LF process, feed 100 m of Al wire through the wire feeder for precipitation deoxidation to quickly reduce the oxygen content in the molten steel to 14 ppm, and the first analysis of Al in LF is 0.020%. Add ferrosilicon manganese alloy and low-carbon manganese alloy through the high-level bunker to fine-tune the molten steel composition, add 4.5 kg / t of lime and 2.5 kg / t of refining slag, and energize the lower electrode for 10 min to raise the temperature and melt the slag. Add 100 kg of high-purity silicon carbide powder, ferrosilicon powder, calcium carbide and other diffusion deoxidizers for diffusion deoxidation in the early stage of refining. After the slag turns white, add the diffusion deoxidizer in small amounts and multiple batches to maintain the white slag. The target R of the slag system is 4 - 6, the Al2O3 content is 20 - 30%, and FeO + MnO ≤ 1%.

[0036] RH vacuum · asZ

[0037] The RH vacuum degree ≤ 100 Pa, the vacuum holding time is 10 min. After breaking the vacuum, perform calcium treatment, feed 30 m of calcium wire per furnace, and then perform soft blowing operation. After 10 min of soft blowing, lift the ladle to continuous casting.

[0038] Continuous casting

[0039] During the continuous casting process, casting is protected throughout. The long nozzle of the tundish is sealed with argon, and the tundish is covered with a double layer of basic covering agent and carbonized rice husk. Before starting the casting in the tundish, argon is purged. The superheat is controlled at 30°C, the casting speed is 0.85 m / min, and the water flow rate in the mold is 150 m 3 / h. The secondary cooling water adopts the medium cooling mode, and the specific secondary cooling water volume is 0.25 L / kg.

[0040] The B content is analyzed for different processes as follows:

[0041] Process Converter End Point After Alloying First Sample in LF LF End Point Sample RH Ladle Sample Final Product Sample Content / ppm 0.5 0.8 1.2 1.3 1.4 1.5

[0042] The finished product composition is as follows:

[0043]

[0044] Example 2

[0045] Converter process

[0046] At the end of the converter tapping, C is 0.05%, the oxygen is determined to be 650 ppm before tapping, creating a relatively high oxidation atmosphere to fully oxidize the B element in the molten steel into B2O3 and enter the slag, reducing the residual B element content in the molten steel; the B content in the molten steel at the end of the converter tapping is 0.6 ppm, the tapping temperature is 1630°C, and the P content at tapping is 0.012%. During the tapping process, observe the tapping situation in the converter at any time to avoid tapping with slag; when the tapping volume reaches the end stage, the slag stopper is put into the molten steel through the slide rail car. When the slag stopper is submerged in the swirling molten steel during the descending process, immediately tilt the furnace to lift the furnace to avoid excessive slag in the steel flow; when the tapping volume of the molten steel is 30 t, start adding ferrosilicon manganese alloy, high-carbon ferromanganese alloy, high-carbon ferrochromium alloy and 2.5 kg / t of lime. The alloying during tapping reaches the lower limit of the steel grade composition, reducing the LF alloy addition amount, and prohibiting the addition of Al-based deoxidizer. After the tapping is completed, the bottom blowing argon gas flow rate is adjusted to 280 L / min and stirred for 4 min to fully oxidize the B element brought into the alloy into B2O3 and float it to the slag, while also facilitating the floating of inclusions in the molten steel. After stirring, take a sample of the molten steel for composition analysis, B: 0.9 ppm, and then lift the ladle of the molten steel to the slag skimming process.

[0047] Slag skimming station

[0048] After stirring, move the ladle car to the slag skimming process. Control the bottom blowing argon gas flow rate at 250 L / min. After the slag surface is blown open, reduce the argon gas flow rate to 60 L / min to ensure that the diameter of the blown-open slag surface is 30 cm; the tilting angle of the ladle is 15°, which is conducive to slag skimming. Skim the slag surface clean, and then transfer the ladle to the LF refining process after slag skimming.

[0049] LF refining

[0050] The molten steel ladle is transferred to the LF process. 150m of Al wire is fed through a wire feeder for precipitation deoxidation, rapidly reducing the oxygen content in the molten steel to 10ppm. The first analysis of Al in the LF is 0.025%. Silicon-manganese alloy and low-carbon manganese alloy are added through a high-level bin to fine-tune the composition of the molten steel. 5kg / t of lime and 3kg / t of refining slag are added. The lower electrode is energized for 12 minutes to raise the temperature and melt the slag. At the early stage of refining, 80kg of high-purity silicon carbide powder, ferrosilicon powder, calcium carbide and other diffusion deoxidizers are added for diffusion deoxidation. After the slag turns white, the diffusion deoxidizer is added in small amounts and multiple batches to maintain the white slag. The target slag system R: 4 - 6, Al2O3 content: 20 - 30%, FeO + MnO ≤ 1%.

[0051] RH vacuum

[0052] The RH vacuum degree ≤ 100Pa, the vacuum holding time is 12 minutes. After breaking the vacuum, calcium treatment is carried out, 40m of calcium wire is fed per furnace, and then soft blowing operation is carried out. After the soft blowing time of 12 minutes, the ladle is transferred to continuous casting.

[0053] Continuous casting

[0054] The whole process of continuous casting is carried out under protected casting. The long nozzle of the tundish is sealed with argon, and the tundish uses a double-layer covering of alkaline covering agent and carbonized rice husk. Argon is purged before the tundish is poured. The superheat is controlled at 25°C, the casting speed is 0.90m / min, and the water flow rate in the mold is 150m 3 / h. The secondary cooling adopts the medium cooling mode, and the secondary cooling water ratio is 0.25L / kg.

[0055] The analysis of B content in different processes is as follows:

[0056] Process Converter End Point After Alloying First Sample in LF LF End Point Sample RH Ladle Sample Final Product Sample Content / ppm 0.6 0.9 1.2 1.3 1.3 1.4

[0057] The finished product composition is as follows:

[0058] Composition C Si Mn S P Cr Al Ti B 0.21 0.25 1.04 0.008 0.010 1.13 0.018 0.05 0.00014

[0059] Example 3

[0060] Converter process

[0061] At the end of the converter tapping, C is 0.04%, the oxygen content before tapping is 737 ppm, creating a relatively high oxidation atmosphere to fully oxidize B element in the molten steel into B2O3 and enter the slag, reducing the content of residual B element in the molten steel; at the end of the converter tapping, the B content in the molten steel is 0.5 ppm, the tapping temperature is 1645 °C, and the P content is 0.011%. Observe the tapping situation in the converter at any time during the tapping process to avoid tapping with slag; when the tapping amount reaches the end stage, put the slag stopper cone into the molten steel through the slide rail car. When the slag stopper cone is submerged in the swirling molten steel during the descending process, quickly tilt the furnace to avoid excessive slag in the steel flow; when the tapping amount of the molten steel is 35 t, start adding silicomanganese alloy, high-carbon ferromanganese alloy, high-carbon ferrochrome alloy and 3.0 kg / t of lime. The alloying during tapping reaches the lower limit of the steel grade composition, reducing the LF alloy addition amount, and prohibiting the addition of Al-based deoxidizer. After the tapping is completed, adjust the bottom blowing argon flow rate to 300 L / min and stir for 5 min to fully oxidize the B element brought into the alloy into B2O3 and float it to the slag, while facilitating the floating of inclusions in the molten steel. After stirring, take a sample of the molten steel for composition analysis, B: 0.8 ppm, and then lift the ladle of the molten steel to the slag skimming process.

[0062] Slag skimming station

[0063] After stirring, drive the ladle car to the slag skimming process. Control the bottom blowing argon flow rate at 290 L / min. After the slag surface is blown open, reduce the argon flow rate to 70 L / min to ensure that the diameter of the blown slag surface is 35 cm; the tilt angle of the ladle is 13°, which is conducive to skimming the slag. Skim the slag surface clean, and then transfer the ladle to the LF refining process after skimming the slag.

[0064] LF refining

[0065] Lift the ladle of the molten steel to the LF process, feed 200 m of Al wire through the wire feeder for precipitation deoxidation to quickly reduce the oxygen content in the molten steel to 7 ppm, and the Al content in the first analysis of LF is 0.030%. Add silicomanganese alloy and low-carbon manganese alloy through the high-level bin to fine-tune the composition of the molten steel, add 6 kg / t of lime and 5 kg / t of refining slag, and energize the lower electrode for 15 min to heat up and melt the slag. Add 100 kg of high-purity silicon carbide powder, ferrosilicon powder, calcium carbide and other diffusion deoxidizers for diffusion deoxidation in the early stage of refining. After the slag turns white, add diffusion deoxidizers in small amounts and multiple batches to maintain the white slag. The target slag system R: 4 - 6, Al2O3 content: 20 - 30%, FeO + MnO ≤ 1%.

[0066] RH vacuum

[0067] The RH vacuum degree ≤ 100 Pa, the vacuum holding time is 14 min. After breaking the vacuum, perform calcium treatment, feed 50 m of calcium wire per furnace, and then perform soft blowing operation. After 14 min of soft blowing, lift the ladle to continuous casting.

[0068] Continuous casting

[0069] During the continuous casting process, casting is protected throughout. The long nozzle of the tundish is sealed with argon, and the middle tundish uses a double-layer covering of alkaline covering agent and carbonized rice husk. Argon is purged before the middle tundish is tapped. The superheat is controlled at 20°C, the casting speed is 0.90 m / min, and the water flow rate in the mold is 150 m 3 / h. The secondary cooling water adopts the medium-cooling mode, and the specific secondary cooling water volume is 0.25 L / kg.

[0070] The B content is analyzed for different processes as follows:

[0071] Process Converter End Point After Alloying First Sample in LF LF End Point Sample RH Ladle Sample Final Product Sample Content / ppm 0.5 0.8 1.3 1.3 1.4 1.5

[0072] The finished product composition is as follows:

[0073] Composition C Si Mn S P Cr Al Ti B 0.20 0.26 1.06 0.007 0.011 1.14 0.020 0.04 0.00015

Claims

1. A smelting process for efficiently and precisely controlling the residual B content in gear steel, characterized in that, The process includes the following steps: (1) Converter: At the end of tapping from the converter, the C content is 0.04 - 0.07%, the oxygen content during tapping is controlled at 300 - 800 ppm, the B element in the molten steel is fully oxidized to B2O3 and enters the slag, the tapping temperature is controlled at 1600 - 1660 °C. Subsequently, alloy and lime are added. When the alloying during tapping reaches the lower limit of the steel grade composition, the LF alloy addition amount is reduced; at the end of tapping, the slag stopper is put into the molten steel, and the furnace is promptly tilted up by rocking the furnace; after tapping, stirring is carried out with large argon flow, and the B element brought in by the alloy is fully oxidized to B2O3 and floats up to enter the slag; (2) Skimming: The molten steel is transferred to the skimming process. After the slag surface is blown open, the argon flow rate is reduced, the ladle is tilted to remove the slag, and the exposed area of the molten steel after skimming is ≥80%; (3) LF refining: After skimming is completed, the molten steel is lifted by the ladle to the LF process, and Al wire is fed for precipitation deoxidation and Al alloying, reducing the oxygen content in the molten steel to below 15 ppm; the composition of the molten steel is finely adjusted by adding alloy through the high-level bin, lime and refining slag are added, and the power is turned on to heat up and melt the slag. At the early stage of refining, a diffusion deoxidizer is added for diffusion deoxidation. After the slag turns white, the diffusion deoxidizer is added in small amounts and in multiple batches to maintain the white slag; The alloy described in step (1) is ferrosilicon manganese alloy, low-carbon ferromanganese, high-carbon ferromanganese, low-carbon ferrochrome or ferrosilicon alloy.

2. The smelting process for efficiently and precisely controlling the residual B content in gear steel according to claim 1, characterized in that, The amount of lime added in step (1) is 2 - 5 kg / t.

3. The smelting process for efficiently and precisely controlling the residual B content in gear steel according to claim 1, characterized in that, The argon flow rate for stirring with large argon after tapping in step (1) is 200 - 500 L / min, and the stirring time is 3 - 6 min.

4. The smelting process for efficiently and precisely controlling the residual B content in gear steel according to claim 1, characterized in that, The bottom-blowing argon flow rate at the start of skimming in step (2) is 200 - 400 L / min, and the argon flow rate is adjusted to 20 - 80 L / min after breaking the slag.

5. The smelting process for efficiently and precisely controlling the residual B content in gear steel according to claim 1, characterized in that, The diameter of the slag surface blown open in step (2) is 10 - 40 cm, and the tilting angle of the ladle is 5 - 30°.

6. The smelting process for efficiently and precisely controlling the residual B content in gear steel according to claim 1, characterized in that, The length of the Al wire fed during LF refining in step (3) is between 50 - 300 m, and the Al content controlled in the first analysis of LF is 0.010 - 0.040 wt%.

7. The smelting process for efficiently and precisely controlling the residual B content in gear steel according to claim 1, characterized in that, The diffusion deoxidizer described in step (3) includes high-purity silicon carbide powder, ferrosilicon powder and calcium carbide.

8. The smelting process for efficiently and precisely controlling the residual B content in gear steel according to claim 1, characterized in that, The addition amount of lime in step (3) is 4 - 6 kg / t, the refining slag is 2 - 5 kg / t, and the target composition of the slag system is R: 4 - 6, Al2O3 content: 20 - 30%, FeO + MnO ≤ 1%.

9. The smelting process for efficiently and precisely controlling the residual B content in gear steel according to claim 1, characterized in that, The residual B content in the said gear steel is ≤1.5 ppm.

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