LF furnace refining method for high purity spring steel

Abstract

The application discloses a LF furnace refining method of high-purity spring steel, which comprises the following steps: 1) KR desulfurization; 2) converter initial refining; 3) argon blowing; 4) LF refining: in the same pouring of continuous six furnaces, the first three furnaces are not slagged, and pre-melted slag is added when the argon blowing station finishes argon blowing; after the molten steel of the first three furnaces enters the refining furnace, synthetic refining slag is added, the slag basicity is controlled to be the first basicity, and a deoxidizing agent is added after electric slagging; the last three furnaces are not added with pre-melted slag; no slag material is added after the fourth furnace finishes converter tapping, and the remaining molten steel and slag material of the first furnace are turned into the fourth furnace; after the fourth furnace finishes refining, quartz sand is added to adjust the slag, the slag basicity is controlled to be the second basicity, the second basicity is lower than the first basicity, and the fifth furnace and the sixth furnace repeat the molten steel and slag turning operation of the fourth furnace; and 5) continuous casting. The two-stage basicity is adopted in the refining, the high-basicity rapid slagging is realized by turning the slag, the slag material is reused, and the cost is reduced; the quartz sand is used to rapidly adjust the slag in the later stage of the refining, the plastic transformation of inclusions is promoted, and the purity of the molten steel is improved.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, and in particular relates to an LF furnace refining method for high-purity spring steel. Background Technology

[0002] Spring steel, as an important mechanical engineering material, is widely used in automobiles, railways, and machinery manufacturing. Its performance directly affects the safety, reliability, and service life of mechanical equipment. High-cycle fatigue fracture is one of the most common failure modes of springs, and inclusions in the steel are a key factor in inducing high-cycle fatigue fracture.

[0003] Hard inclusions (such as Al2O3) have a large difference in elastic modulus from the matrix, which easily leads to stress concentration under alternating stress, becoming the starting point for fatigue crack initiation. The interfacial bonding strength between inclusions and the matrix is ​​weak, and under cyclic stress, interfacial debonding easily occurs, forming and propagating microcracks. In addition, large-sized inclusions and clustered inclusions can also significantly reduce the fatigue strength of the material.

[0004] A Chinese invention patent with publication number CN102312054A discloses a low-alkalinity slag refining process for an LF furnace. The main steps include: during the steelmaking and tapping process, bottom-blowing argon is performed on the ladle throughout the process, and ferrosilicon, calcium-barium silicon, and high-carbon ferromanganese are added to the ladle in sequence for deoxidation and alloying. Then, under the condition of argon flow rate of 30-50 NL / min, argon is blown on the molten steel for 2-3 minutes. Electrode slag is inserted and adjusted, and the molten steel is heated to 1580-1600℃. The slag basicity is controlled at 0.8-1.3. The molten steel is bottom-blown for 25-30 minutes under the condition of argon flow rate of 20-30 NL / min, and the slag composition is controlled to form composite inclusion particles with low melting point and good plastic deformation in the molten steel. These particles float rapidly, which is conducive to the effective removal of inclusions in the molten steel and significantly improves the cleanliness of the molten steel. The inclusions of type B and type D oxides are significantly reduced, which can meet the subsequent processing requirements of 70 high-carbon hard wire steel and 60Si2Mn spring steel. Although the aforementioned invention patent uses a low-alkalinity slag system to promote the plastic flotation of inclusions during the LF refining process, its alkalinity control is low throughout the entire LF refining process. The deoxidation and desulfurization capacity is poor in the early stage, and the low viscosity and good fluidity of the refining slag make it easy to cause slag entrapment. Moreover, the low-alkalinity slag throughout the nearly two-hour LF refining cycle causes severe corrosion damage to the refractory material, significantly reducing the ladle life and easily causing the refractory material to peel off and generate foreign large particles containing Al2O3 or MgO and other inclusions.

[0005] Therefore, the technical problem to be solved by this invention is how to design a technology that can reduce the content of inclusions to improve the fatigue resistance of spring steel. Summary of the Invention

[0006] The purpose of this invention is to provide an LF furnace refining method for high-purity spring steel, thereby reducing the inclusion content and improving the fatigue resistance of the spring steel.

[0007] To solve the above-mentioned technical problems, the present invention is mainly achieved through the following technical solutions:

[0008] In a first aspect, the present invention provides an LF furnace refining method for high-purity spring steel, comprising the following steps:

[0009] 1) KR desulfurization: Blast furnace molten iron enters the KR desulfurization station for deep desulfurization. Desulfurization is carried out by adding composite desulfurizing agent and stirring, and the [S] of the molten iron entering the furnace is controlled to be ≤0.005%;

[0010] 2) Converter primary refining: The double-slag method is used for blowing, and the final [C] of the converter is controlled to be ≥0.15%, [P] ≤0.012%, and [S] ≤0.008%; deoxidation and alloying are carried out during the tapping process;

[0011] 3) Argon blowing: After tapping, argon is blown at the argon blowing station, and the argon flow rate is controlled at 300~500L / min;

[0012] 4) LF Refining: In the same casting cycle of 6 consecutive heats, for the first 3 heats without slag turning, pre-melted slag is added at the end of argon blowing at the argon blowing station; after the first 3 heats of molten steel enter the LF refining furnace, synthetic refining slag is added, and the slag basicity is controlled to the first basicity. After slag is energized, deoxidizer is added for deoxidation; for the last 3 heats with slag turning, no pre-melted slag is added.

[0013] In the six consecutive heats, after the fourth heat of the converter is tapped, no slag is added. Instead, the remaining steel and slag from the first heat of the continuous casting are added. The argon flow rate is controlled at 100-150 L / min to carry out rapid slag formation and power supply to raise the temperature. Then, the argon flow rate is gradually reduced to 30-50 L / min for deoxidation, sampling and composition.

[0014] In the continuous 6 heats, after the 4th heat of refining is completed, quartz sand is added for slag adjustment, and the slag basicity is controlled to the second basicity, which is lower than the first basicity. After the quartz sand is fully melted, it is taken out of the station, and a covering agent is added for soft blowing argon operation, controlling the soft blowing argon flow rate to 3~8L / min, so that the molten steel has slight creep and is not exposed.

[0015] In the six consecutive heats, the steel and slag turning operations of the fourth heat were repeated in the fifth and sixth heats. The remaining steel and slag of the second heat were turned into the molten steel after the fifth heat was tapped, and the remaining steel and slag of the third heat were turned into the molten steel after the sixth heat was tapped.

[0016] 5) Continuous casting: After refining and soft blowing are completed, the molten steel is hoisted to the continuous casting process for pouring. The liquid level of the tundish crystallizer, as well as the long nozzle and submerged nozzle, are protected to prevent secondary oxidation of the molten steel. Residual steel is left at the end of the pouring.

[0017] In step 1) of this application, the mass fraction of S in the blast furnace hot iron is controlled below 0.005% after deep desulfurization treatment at the KR desulfurization station, which reduces the desulfurization pressure on the LF refining furnace.

[0018] In step 2) of this application, the primary smelting in the converter adopts the double-slag blowing method. Through mid-process slag dumping and secondary slag making, the separation and optimization of the dephosphorization and decarburization stages are achieved, and the C mass fraction at the converter endpoint is controlled to be ≥0.15%, P mass fraction ≤0.012%, and S mass fraction ≤0.008%. Deoxidation and alloying are carried out during the converter tapping process.

[0019] In step 3) of this application, after the steel is tapped, argon is blown at the argon blowing station, which can uniformly adjust the chemical composition and temperature of the molten steel, accelerate the chemical reaction, remove harmful gases and inclusions, and achieve the purpose of purifying the molten steel.

[0020] In step 4 of this application, the same casting batch contains approximately 6 to 15 heats of molten steel; the covering agent includes carbonized rice husks.

[0021] It should be noted that the high-purity spring steel prepared by this invention is all refined from the last three furnaces.

[0022] In a preferred embodiment, in step 1), the composite desulfurizing agent includes calcium oxide and calcium fluoride.

[0023] As a preferred implementation, in step 2), the converter tapping temperature is controlled to be ≥1620℃; high-purity or low-aluminum, low-titanium high-quality alloys can be selected during the tapping process. For example, the tapping process is deoxidized and alloyed by adding ferrosilicon and ferromanganese.

[0024] In this application, by controlling the converter tapping temperature above 1620℃, the fluidity of molten steel can be ensured while avoiding excessive energy consumption.

[0025] By adding ferrosilicon, ferromanganese, and ferrochrome during the tapping process, deoxidation and alloying are combined into the tapping process, which significantly shortens the smelting cycle, increases the converter operating rate, reduces the waste of expensive alloys, and lowers production costs. By rationally combining ferrosilicon, ferromanganese, and ferrochrome, the deoxidation products generated are easy to float into the slag layer, creating conditions for the subsequent removal of non-metallic inclusions.

[0026] As a preferred implementation, in step 2), the steel is tapped using a tapping port in the middle or early stage, combined with a sliding plate to block slag. Slag discharge from the large tapping port and the tapping port in the later stage are prohibited, thus controlling the slag discharge process.

[0027] In this application, the steel tapping is carried out in the middle and early stages with the use of a sliding plate to block slag, and the tapping of large tapping holes and tapping of slag in the later stages is prohibited, which can reduce the amount of slag carried during steel tapping; the converter slag has strong oxidizing properties, and by controlling the slag feeding process, the phosphorus return of molten steel can be reduced, the content of inclusions can be reduced, and the cleanliness of molten steel can be improved.

[0028] In a preferred embodiment, in step 4), the pre-melted slag includes pre-melted lime.

[0029] In this application, by adding pre-melted lime as pre-melted slag at the end of argon blowing at the argon blowing station, the high temperature of molten steel can be fully utilized to play the role of pre-melted lime.

[0030] In a preferred embodiment, in step 4), the deoxidizer includes silicon carbide.

[0031] In this application, high-purity silicon carbide is used, with a silicon carbide content ≥85%, alumina ≤1.5%, and titanium dioxide ≤0.1%.

[0032] As a preferred embodiment, in step 4), the alkalinity range of the first alkalinity is 1.6 to 1.8; and the alkalinity range of the second alkalinity is 0.9 to 1.1.

[0033] In this application, the refining process adopts a two-stage alkalinity, and the slag turning operation is conducive to achieving rapid slag formation with high alkalinity in the early stage.

[0034] As a preferred embodiment, in step 4), the basicity R of the synthetic refining slag is approximately 1.0, and the synthetic refining slag comprises [CaO] ≥ 45%, [SiO2] ≥ 45%, [MgO] ≤ 1.5%, [P2O5] ≤ 0.05%, [Al2O3] ≤ 0.5%, and [TiO2] ≤ 0.03%.

[0035] In a preferred embodiment, the particle size of the pre-melted slag and the quartz sand is 0.5~5mm.

[0036] As a preferred implementation, the LF refining cycle is ≥50 min and the soft blowing argon time is ≥25 min.

[0037] Compared with the prior art, the advantages and positive effects of the present invention are as follows: The LF furnace refining method for high-purity spring steel of the present invention includes KR desulfurization, converter primary refining, argon blowing, LF refining and continuous casting processes. KR stirring desulfurization is carried out by adding a composite desulfurizing agent, which has high and stable desulfurization efficiency; the converter primary refining process can significantly improve the dephosphorization efficiency by blowing through the double slag method; the LF refining process adopts a two-stage basicity, and the slag turning operation realizes rapid slag formation with high basicity in the early stage. The slag added by slag turning has strong deoxidation and desulfurization capabilities, good arc submersion effect, and high power supply and temperature raising efficiency. At the same time, the slag can be reused, reducing the power consumption of the refining process and the cost reduction effect of ladle erosion.

[0038] After achieving the target for temperature increase and composition in the later stage of refining, quartz sand is used for rapid slag adjustment to achieve low alkalinity throughout the later stage of refining and the soft blowing argon process. This promotes the plastic transformation of high-melting-point inclusions, making them easier to float and remove, thereby improving the purity of the molten steel and enhancing the fatigue resistance of spring steel. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] It should be noted that in the description of this invention, terms such as "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," which indicate directional or positional relationships, are based on directional or positional relationships and are used merely for ease of description. They do not indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0041] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0042] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0043] The following disclosure provides many different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0044] In a first aspect, embodiments of this disclosure provide an LF furnace refining method for high-purity spring steel, comprising the following steps:

[0045] 1) KR desulfurization: Blast furnace molten iron enters the KR desulfurization station for deep desulfurization. The desulfurization is carried out by adding composite desulfurizing agent and stirring, and the [S] of the molten iron entering the furnace is controlled to be ≤0.005%.

[0046] 2) Converter primary refining: The double slag method is used for blowing, and the converter endpoint [C] is controlled at ≥0.15%, [P] ≤0.012%, and [S] ≤0.008%; deoxidation and alloying are carried out during the tapping process.

[0047] 3) Argon blowing: After tapping, argon is blown at the argon blowing station, and the argon flow rate is controlled at 300~500L / min.

[0048] 4) LF Refining: In the same casting cycle of 6 consecutive heats, the first 3 heats without slag turning are pre-melted slag added at the end of argon blowing at the argon blowing station; after the first 3 heats of molten steel enter the LF refining furnace, synthetic refining slag is added, the slag basicity is controlled to the first basicity, and deoxidizer is added after slag turning by electricity for deoxidation; no pre-melted slag is added in the last 3 heats with slag turning.

[0049] In the continuous casting of 6 heats, after the fourth heat of the converter is tapped, no slag is added. Instead, the remaining steel and slag from the first heat of the continuous casting are added. The argon flow rate is controlled at 100-150 L / min to carry out rapid slag formation and power supply to raise the temperature. Then, the argon flow rate is gradually reduced to 30-50 L / min for deoxidation, sampling and composition.

[0050] In the continuous 6 heats, after the 4th heat of refining is completed, quartz sand is added for slag adjustment, and the slag basicity is controlled to the second basicity, which is lower than the first basicity. After the quartz sand is fully melted, it is discharged from the station, and a covering agent is added for soft blowing argon operation. The soft blowing argon flow rate is controlled to be 3~8L / min, and the molten steel is slightly creeping without being exposed.

[0051] In the six consecutive heats, the steel and slag turning operations of the fourth heat were repeated in the fifth and sixth heats. The remaining steel and slag from the second heat were turned into the molten steel after the fifth heat was tapped, and the remaining steel and slag from the third heat were turned into the molten steel after the sixth heat was tapped.

[0052] 5) Continuous casting: After refining and soft blowing are completed, the molten steel is hoisted to the continuous casting process for pouring. The liquid level of the tundish crystallizer, as well as the long nozzle and submerged nozzle, are protected to prevent secondary oxidation of the molten steel. Residual steel is left at the end of the pouring.

[0053] In a preferred embodiment, in step 1), the composite desulfurizing agent includes calcium oxide and calcium fluoride.

[0054] As a preferred implementation, in step 2), the converter tapping temperature is controlled to be ≥1620℃; the tapping process is carried out by adding ferrosilicon and ferromanganese for deoxidation and alloying.

[0055] As a preferred implementation, in step 2), the steel is tapped using a tapping port in the middle or early stage, combined with a sliding plate to block slag. Slag discharge from the large tapping port and the tapping port in the later stage are prohibited, thus controlling the slag discharge process.

[0056] In a preferred embodiment, in step 4), the pre-melted slag includes pre-melted lime.

[0057] As a preferred embodiment, in step 4), the deoxidizer includes silicon carbide.

[0058] As a preferred embodiment, in step 4), the alkalinity range of the first alkalinity is 1.6 to 1.8; and the alkalinity range of the second alkalinity is 0.9 to 1.1.

[0059] As a preferred embodiment, in step 4), the basicity of the synthetic refining slag is R≈1.0, and the synthetic refining slag includes [CaO]≥45%, [SiO2]≥45%, [MgO]≤1.5%, [P2O5]≤0.05%, [Al2O3]≤0.5%, and [TiO2]≤0.03%.

[0060] As a preferred embodiment, the particle size of the pre-melted slag and quartz sand is 0.5~5mm.

[0061] As a preferred implementation, the LF refining cycle is ≥50 min and the soft blowing argon time is ≥25 min.

[0062] Example 1: Refining of 55SiCr spring steel, 6 short casting cycles, with slag turning operation adopting the 3+3 mode. Specifically, heats 1, 2, and 3 are turned into heats 4, 5, and 6 respectively. Heats 1, 2, and 3 are heats without slag turning, while heats 4, 5, and 6 are heats with slag turning.

[0063] 1) The blast furnace molten iron is desulfurized using KR, with an S content of 0.003% and a temperature of 1285℃.

[0064] 2) The converter primary refining adopts the double-slag blowing method, controlling the C content at the converter endpoint to 0.17%, P content to 0.010%, and S content to 0.007%, with a converter tapping temperature of 1630℃. A tapping port in the early to mid-stage is used in conjunction with a sliding plate to prevent slag from falling during tapping, resulting in no slag runoff. The tapping time is 4 minutes and 45 seconds. 2075 kg of high-purity ferrosilicon, 917 kg of medium-carbon ferromanganese, and 1001 kg of low-titanium, high-carbon ferrochrome are used for deoxidation and alloying, along with 352 kg of low-nitrogen carbon raiser.

[0065] 3) After tapping, argon is blown for 35 seconds at the argon blowing station. The bottom blowing argon flow rate is 400L / min. For the first 3 heats without slag turning, 200kg of top slag lime is added. The lime particle size is 2mm. For the last 3 heats without slag turning, no top slag lime is added.

[0066] 4) After the first three heats of molten steel enter the LF refining furnace, 800 kg of synthetic refining slag (basicity 0.98) is added. After slag is smelted by electricity, silicon carbide deoxidation is used. The first basicity of the slag is R=1.63. The final slag composition of the first three heats includes CaO content 52%, SiO2 content 32%, MgO content 4.12%, P2O5 content 0.01%, Al2O3 content 1.95%, TiO2 content 0.22%, TFe content 1.12%, and MnO content 0.28%.

[0067] No slag is added after the first tapping of steel from the slag turning furnace. The inlet temperature of the LF refining furnace is 1470℃. After slag turning, power is supplied to raise the temperature. The argon gas flow rate is gradually reduced in the order of 150L / min-100L / min-50L / min-30L / min. The first power supply sampling time is 15min, and the sampling temperature is 1500℃.

[0068] 5) After casting, 160 kg of quartz sand (3 mm particle size) was added to the slag after the third heat. The slag was then energized and tapped. The second basicity of the slag was R = 1.10. The final slag composition after the third heat included 43% CaO, 39% SiO2, 3.45% MgO, 0.01% P2O5, 1.85% Al2O3, 0.20% TiO2, 3.20% TFe, and 1.15% MnO. The total energizing time was 45 min, the refining cycle was 65 min, the soft-blowing argon flow rate was 5 L / min, and the soft-blowing time was 28 min.

[0069] 6) Continuous casting: steel pouring, casting speed 1.00m / min, black liquid level operation throughout the tundish and crystallizer, argon seal flow rate at the nozzle 100L / min, leaving 4.5t of residual steel and slag.

[0070] Example 2: Refining of spring steel SWRH82B, 12 long casting cycles, with slag turning operation adopting a 3+3 mode. Specifically, heats 1, 2, and 3 are turned into heats 4, 5, and 6 respectively; heats 7, 8, and 9 are turned into heats 10, 11, and 12 respectively; heats 1, 2, 3, 7, 8, and 9 are heats without slag turning, while heats 4, 5, 6, 10, 11, and 12 are heats with slag turning.

[0071] 1) The blast furnace molten iron was desulfurized using KR, with a stirring time of 4.5 min. After desulfurization, the S content of the molten iron was 0.004%, and the temperature was 1272℃.

[0072] 2) The converter primary refining adopts the double-slag blowing method, controlling the C content at the converter endpoint to 0.16%, P content to 0.009%, and S content to 0.008%, with a tapping temperature of 1620℃. A tapping port in the middle to early stage is used in conjunction with a sliding plate to prevent slag from falling during tapping. There is no slag during the tapping process, and the tapping time is 4 minutes and 38 seconds. 344 kg of high-purity ferrosilicon and 652 kg of medium-carbon ferromanganese are used for deoxidation and alloying, along with 602 kg of carbon raiser.

[0073] 3) After tapping, blow argon for 37 seconds at the argon blowing station. The bottom blowing argon flow rate is 500L / min. Add 250kg of top slag lime (5mm particle size) to the furnace without slag turning. Do not add lime to the furnace with slag turning.

[0074] 4) After entering the LF refining furnace in the non-slag-turning furnace, 800 kg of synthetic refining slag (basicity 1.01) is added. After electrolytic slag formation, silicon carbide deoxidation is used, and the first basicity of the slag is R=1.8. The final slag composition of the non-slag-turning furnace includes CaO content 57%, SiO2 content 33%, MgO content 4.8%, P2O5 content 0.01%, Al2O3 content 2.05%, TiO2 content 0.18%, TFe content 0.67%, and MnO content 0.25%.

[0075] No slag is added after the first tapping of steel from the slag turning furnace. The temperature at the refining furnace entrance is 1485℃. After slag turning, power is supplied to raise the temperature. The argon gas flow rate is gradually reduced in the order of 150L / min-100L / min-50L / min-30L / min. The first power supply sampling time is 9 minutes, and the sampling temperature is 1505℃.

[0076] 5) 260 kg of quartz sand (5 mm particle size) is added during the second slag adjustment in the slag turning furnace. Power is supplied for slag treatment and steel tapping. The second basicity of the slag is R = 0.9. The final slag composition of the second slag turning furnace includes CaO 44%, SiO2 45%, MgO 4.92%, P2O5 0.01%, Al2O3 2.19%, TiO2 0.17%, TFe 1.26%, and MnO 1.61%. The total power supply time is 32 min, the refining cycle is 52 min, the soft blowing argon flow rate is 5 L / min, and the soft blowing time is 31 min.

[0077] 6) Continuous casting: steel pouring, casting speed 1.20m / min, black liquid level operation throughout the tundish and crystallizer, argon seal flow rate at the nozzle 110L / min, leaving 5.5t of residual steel and slag.

[0078] Example 3: Refining of carbon spring steel 70 steel, 8 short casting cycles, slag turning operation adopts 3+3 mode, specifically, heats 2, 3 and 4 are turned into heats 5, 6 and 7 respectively, heats 2, 3 and 4 are heats without slag turning, heats 5, 6 and 7 are heats with slag turning.

[0079] 1) The blast furnace molten iron is desulfurized using KR, with an S content of 0.005% and a temperature of 1260℃.

[0080] 2) The converter primary refining adopts the double-slag blowing method, controlling the C content at the converter endpoint to 0.15%, P content to 0.012%, and S content to 0.008%, with a converter tapping temperature of 1620℃. A tapping port in the early to mid-stage is used in conjunction with a sliding plate to prevent slag from falling during tapping, resulting in no slag runoff. The tapping time is 4 minutes and 20 seconds. 335 kg of high-purity ferrosilicon and 727 kg of medium-carbon ferromanganese are used for deoxidation and alloying, along with 455 kg of low-nitrogen carbon raiser.

[0081] 3) After tapping, blow argon for 35 seconds at the argon blowing station. The bottom blowing argon flow rate is 300L / min. For the first 3 heats without slag turning, add 230kg of top slag lime with a particle size of 0.5mm. Do not add top slag lime for the 5th, 6th and 7th heats with slag turning.

[0082] 4) After the first four heats of molten steel enter the LF refining furnace, 800 kg of synthetic refining slag (basicity 1.0) is added. After slag is energized, silicon carbide deoxidation is used. The first basicity of the slag is R=1.78. The final slag composition of the first three heats includes CaO content 51.3%, SiO2 content 28.8%, MgO content 6.88%, P2O5 content 0.02%, Al2O3 content 3.35%, TiO2 content 0.25%, TFe content 1.15%, and MnO content 0.29%.

[0083] No slag is added after the first tapping of steel from the slag turning furnace. The inlet temperature of the LF refining furnace is 1480℃. After slag turning, power is supplied to raise the temperature. The argon gas flow rate is gradually reduced in the order of 100L / min-80L / min-70L / min-50L / min. The first power supply sampling time is 15min, and the sampling temperature is 1520℃.

[0084] 5) During castings 5 / 6 / 7, 250 kg of quartz sand (0.5 mm particle size) is added to the slag. Slag is then fed into the furnace and tapped. The second basicity of the slag is R = 0.94. The final slag composition after castings 3 times includes: CaO 42.8%, SiO2 44.9%, MgO 4.6%, P2O5 0.01%, Al2O3 2.95%, TiO2 0.14%, TFe 2.20%, and MnO 1.01%. The total power-on time is 35 min, the refining cycle is 50 min, the soft-blowing argon flow rate is 5 L / min, and the soft-blowing time is 25 min.

[0085] 6) Continuous casting: steel pouring, casting speed 1.21m / min, black liquid level operation throughout the tundish and crystallizer, argon seal flow rate at the nozzle 100L / min, leaving 5.0t of residual steel and slag.

[0086] The non-metallic inclusions in Examples 1-3 were rated according to Method A of GB / T 10561. The results are shown in Table 1 below:

[0087]

[0088] The inclusion detection results of Examples 1, 2 and 3 all meet the standard requirements. The inclusions are small in size, few in number, and evenly distributed. The cleanliness of the steel is high and can meet the quality requirements of spring steel.

[0089] Therefore, compared with the prior art, the beneficial effects of the present invention are as follows: The LF furnace refining method for high-purity spring steel of the present invention includes KR desulfurization, converter primary refining, argon blowing, LF refining and continuous casting processes. KR stirring desulfurization is carried out by adding a composite desulfurizing agent, which has high and stable desulfurization efficiency; the converter primary refining process can significantly improve the dephosphorization efficiency by blowing through the double slag method; the LF refining process adopts a two-stage basicity, and the slag turning operation realizes rapid slag formation with high basicity in the early stage. The slag added by slag turning has strong deoxidation and desulfurization capabilities, good arc submersion effect, and high power supply and temperature raising efficiency. At the same time, the slag can be reused, reducing the cost of power consumption and ladle erosion in the refining process.

[0090] After achieving the target for temperature increase and composition in the later stage of refining, quartz sand is used for rapid slag adjustment to achieve low alkalinity throughout the later stage of refining and the soft blowing argon process. This promotes the plastic transformation of high-melting-point inclusions, making them easier to float and remove, thereby improving the purity of the molten steel and enhancing the fatigue resistance of spring steel.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for refining high-purity spring steel in an LF furnace, characterized in that, Includes the following steps: 1) KR desulfurization: Blast furnace molten iron enters the KR desulfurization station for deep desulfurization. Desulfurization is carried out by adding composite desulfurizing agent and stirring, and the [S] of the molten iron entering the furnace is controlled to be ≤0.005%; 2) Converter primary refining: The double-slag method is used for blowing, and the final [C] of the converter is controlled to be ≥0.15%, [P] ≤0.012%, and [S] ≤0.008%; deoxidation and alloying are carried out during the tapping process; 3) Argon blowing: After tapping, argon is blown at the argon blowing station, and the argon flow rate is controlled at 300~500L / min; 4) LF Refining: In the same casting cycle of 6 consecutive heats, for the first 3 heats without slag turning, pre-melted slag is added at the end of argon blowing at the argon blowing station; after the first 3 heats of molten steel enter the LF refining furnace, synthetic refining slag is added, and the slag basicity is controlled to the first basicity. After slag is energized, deoxidizer is added for deoxidation; for the last 3 heats with slag turning, no pre-melted slag is added. In the six consecutive heats, after the fourth heat of the converter is tapped, no slag is added. Instead, the remaining steel and slag from the first heat of the continuous casting are added. The argon flow rate is controlled at 100-150 L / min to carry out rapid slag formation and power supply to raise the temperature. Then, the argon flow rate is gradually reduced to 30-50 L / min for deoxidation, sampling and composition. In the continuous 6 heats, after the 4th heat of refining is completed, quartz sand is added for slag adjustment, and the slag basicity is controlled to the second basicity, which is lower than the first basicity. After the quartz sand is fully melted, it is taken out of the station, and a covering agent is added for soft blowing argon operation, controlling the soft blowing argon flow rate to 3~8L / min, so that the molten steel has slight creep and is not exposed. In the six consecutive heats, the steel and slag turning operations of the fourth heat were repeated in the fifth and sixth heats. The remaining steel and slag of the second heat were turned into the molten steel after the fifth heat was tapped, and the remaining steel and slag of the third heat were turned into the molten steel after the sixth heat was tapped. 5) Continuous casting: After refining and soft blowing are completed, the molten steel is hoisted to the continuous casting process for pouring. The liquid level of the tundish crystallizer, as well as the long nozzle and submerged nozzle, are protected to prevent secondary oxidation of the molten steel. Residual steel is left at the end of the pouring.

2. The LF furnace refining method for high-purity spring steel according to claim 1, characterized in that, In step 1), the composite desulfurizing agent includes calcium oxide and calcium fluoride.

3. The LF furnace refining method for high-purity spring steel according to claim 1, characterized in that, In step 2), the converter tapping temperature is controlled to be ≥1620℃; during the tapping process, deoxidation and alloying are carried out by adding ferrosilicon and ferromanganese.

4. The LF furnace refining method for high-purity spring steel according to claim 1, characterized in that, In step 2), when tapping steel, use the tapping port in the middle or early stage to cooperate with the sliding plate to stop the slag during tapping. It is forbidden to tap the slag from the large tapping port or the tapping port in the later stage. Control the slag dropping process.

5. The LF furnace refining method for high-purity spring steel according to claim 1, characterized in that, In step 4), the pre-melted slag includes pre-melted lime.

6. The LF furnace refining method for high-purity spring steel according to claim 1, characterized in that, In step 4), the deoxidizer includes silicon carbide.

7. The LF furnace refining method for high-purity spring steel according to claim 1, characterized in that, In step 4), the alkalinity range of the first alkalinity is 1.6 to 1.8; the alkalinity range of the second alkalinity is 0.9 to 1.

1.

8. The LF furnace refining method for high-purity spring steel according to claim 1, characterized in that, In step 4), the basicity of the synthetic refining slag is R≈1.0, and the synthetic refining slag includes [CaO]≥45%, [SiO2]≥45%, [MgO]≤1.5%, [P2O5]≤0.05%, [Al2O3]≤0.5%, and [TiO2]≤0.03%.

9. The LF furnace refining method for high-purity spring steel according to claim 1, characterized in that, The particle size of the pre-melted slag and the quartz sand is 0.5~5mm.

10. The LF furnace refining method for high-purity spring steel according to claim 1, characterized in that, LF refining cycle ≥ 50 min, soft blowing argon time ≥ 25 min.

Images