A preparation method of a billet for H08A welding steel wire rod

Abstract

The invention discloses a preparation method for a billet of H08A welding steel wire rod. The preparation method includes process steps such as molten steel smelting, deoxidation alloying, LF furnace refining and continuous casting pouring. By optimizing the parameters of each process step, the castability of H08A molten steel is greatly improved, the incremental production of billets cast in a single ladle of H08A steel grade is realized, the number of continuous casting heats in a single ladle is broken through, and the ability to mass-produce billets of H08A welding steel wire rod is achieved. After the macroetching of the billets produced by the method of the invention, the rating of subcutaneous bubble defects is reduced from grade 1.0 to grade 0.5, no non-metallic inclusions are seen in the macrostructure, the chemical composition of the billets is uniform, the tissue state is good, the quality of the billets is excellent, and the through-train process mechanical properties are stable after rolling the rolled steel into wire rods with a specification of Ф6.5mm.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel smelting, and particularly relates to a method for preparing a billet of H08A welding steel wire rod. Background Art

[0002] H08A welding steel is a commonly used welding steel, mainly used for producing welding electrodes. Its main uses determine that the steel must have characteristics such as uniform composition, good structure, and stable performance. H08A welding steel belongs to the typical low-carbon, low-silicon, low-sulfur, and low-phosphorus series of steel grades. Therefore, the composition control of H08A steel grade is relatively strict. Due to the relatively high S and P contents in blast furnace hot metal during production, the desulfurization efficiency of hot metal pretreatment is low and the treatment time is long, which affects the subsequent production rhythm. The carbon content at the end of converter smelting is controlled relatively low, and the temperature is controlled relatively high. The molten steel at the end is severely over-oxidized. During the tapping process, a core aluminum deoxidizer needs to be added for deoxidation, which will bring two adverse effects: if the deoxidation is poor, the oxygen content in the molten steel is relatively high, and a large number of subcutaneous bubbles and surface pores will be generated in the cast billet cast from it, seriously affecting the product quality during rolling and the use of subsequent products; if the deoxidation is excessive, a large number of aluminum-containing inclusions will be generated in the molten steel. During the continuous casting process, high-melting-point inclusions (Al2O3) adhere to the nozzle to form nodules, which are likely to block the tundish nozzle. The blockage of the tundish nozzle forces the continuous casting drawing speed to be reduced, resulting in lack of flow or even stopping of casting, which not only affects production efficiency and increases production costs, but more seriously, during the treatment process, open casting and drainage with an oxygen lance are required, thus bringing many quality problems. Summary of the Invention

[0003] In view of the above problems, the purpose of the present invention is to provide a method for preparing a billet of H08A welding steel wire rod.

[0004] The purpose of the present invention is achieved as follows. A method for preparing a billet of H08A welding steel wire rod is realized according to the following steps:

[0005] A. Molten steel smelting: The pre-desulfurized hot metal and low-sulfur refined scrap steel are respectively added to a 120-ton LD top-bottom combined blowing converter for top-bottom combined blowing smelting according to the ratios of 840 - 890 kg / t 钢 and 160 - 200 kg / t 钢 . Low-sulfur active lime is added for slag making. Argon is blown from the bottom throughout the smelting process, and the working pressure of the bottom lance > 0.3 MPa. The smelting end temperature is controlled at 1630 ± 15 °C, the end carbon content is controlled at 0.05 - 0.06 wt%, the oxygen content of the molten steel at the end is controlled ≤ 600 ppm, P ≤ 0.015 wt%, and S ≤ 0.020 wt%. The S ≤ 0.020% and P ≤ 0.080% of the pre-desulfurized hot metal;

[0006] B. Deoxidation alloying: Tapping the molten steel. When the amount of molten steel in the ladle is 1 / 4 - 1 / 3, add the following substances to the ladle in the following deoxidation alloying sequence: calcium silicate barium alloy → medium-carbon ferromanganese → aluminum ferromanganese. Add the following substances in the following amounts: Add calcium silicate barium alloy in an amount of 0.38 kg / t 钢 with the following mass ratio: Ba 12%, Ca 9%, Si 50%, and the rest is Fe and inevitable impurities; add medium-carbon ferromanganese in an amount of 3.71 kg / t 钢 with the following mass ratio: Fe 20%, Mn 78%, C 2%; then add aluminum ferromanganese in an amount of 3.79 kg / t 钢 with the following mass ratio: Fe 50%, Al 20%, Mn 30%; if the oxygen activity of the molten steel is too high, supplement an appropriate amount of ferrosilicon aluminum to adjust and ensure that the oxygen activity of the molten steel at the argon blowing station is controlled between 25 - 50 ppm. Add the above alloys before the ladle steel amount reaches 2 / 3 - 3 / 4. Use a slide baffle to block the slag to ensure that the thickness of the ladle slag layer ≤ 60 mm and the tapping time ≥ 3.0 minutes; after tapping, lift the molten steel to the argon station for refining treatment;

[0007] C. LF furnace refining: Immediately connect the bottom argon blowing after lifting the molten steel to the LF furnace. The argon blowing volume is 350 - 450 L / min. Blow through the porous plug and stir for 1 min. Melt the crust on the surface of the molten steel and then carry out slag melting operation: Add 300 - 500 kg of lime. The argon blowing volume is 150 - 250 L / min to make the liquid surface wriggle. After the lower electrode is energized for slag melting for 5 - 8 minutes, the argon blowing volume is 200 - 300 L / min. Measure the temperature, determine the oxygen content, and take samples of the molten steel. If the oxygen activity of the molten steel is greater than 45 ppm, supplement 20 - 80 kg / heat of calcium silicate barium to deoxidize the molten steel; Observe the fluidity and color of the slag. If the slag sample is too thin and the color is too dark, supplement low-silicon deoxidizer and lime to adjust the slag. Otherwise, add pre-melted refining slag to adjust the slag. Then adjust the argon blowing volume to 150 - 250 L / min and then energize the lower electrode to heat until the chemical composition is qualified. The number of times of energizing the lower electrode during the refining process ≤ 2 times; Coarse adjustment of the composition is controlled according to the limit or lower limit value in the internal control composition of the finished steel. After the analysis results come out, carry out fine adjustment of the composition. After the composition is qualified, feed 100 - 300 m / heat of calcium-ferrite wire. The argon blowing volume during wire feeding is 30 - 50 L / min, and the wire feeding speed is 2.5 - 3.5 m / s. After wire feeding, the argon blowing volume is 50 - 80 L / min for soft blowing, and the soft blowing time ≥ 3 min; After the argon blowing is completed, lift the molten steel to the casting station;

[0008] D. Continuous casting: At the tundish temperature of 1561 - 1566 °C, the drawing speed is 2.1 - 2.2 m / min, the water pressure in the mold is 1.14 MPa, the water volume is 149 - 151 m 3 / h, the secondary cooling adopts the full water cooling mode, and the specific water volume is 1.9 - 2.1 L / kg 钢 The water volume of the foot rolls is 23 - 25 m 3 / h, the water volume in the first stage of secondary cooling is 17 - 19 m 3 / h, the water volume in the second stage of secondary cooling is 7 - 9 m 3 / h, the water volume in the third stage of secondary cooling is 6 - 7 m 3 Under the condition of / h, the molten steel after being processed in step C is continuously cast into a billet of 165 mm × 165 mm by an R9m7 machine with 7 - strand small billet continuous caster. Finally, after inspecting and cleaning the billet, it is sent to the rolling wire rod production line.

[0009] In the present invention, by controlling the S and P contents of blast furnace hot metal, hot metal pretreatment is carried out by injecting calcium - based desulfurizer through a lance for hot metal desulfurization. In the steel - making converter, the smelting process, end - point temperature and end - point carbon content are controlled. During the tapping process, a slide damper is used to block slag to ensure that the thickness of the ladle slag layer is ≤ 60 mm; for deoxidation alloying operation, calcium - silicon - barium alloy (Ba12Ca9Si50) is used for preliminary deoxidation, and ferromanganese - aluminum (FeAl20Mn30) is used for final deoxidation. If the oxygen activity of the molten steel is on the high side, an appropriate amount of ferrosilicon - aluminum is added for adjustment to ensure that the oxygen activity of the molten steel at the argon - blowing station is controlled between 25 - 50 ppm. The LF furnace refining treatment technology reduces or avoids the increase of oxygen activity caused by the molten steel absorbing oxygen by reasonably controlling the bottom - blowing argon flow rate and blowing time; the composition of the refining slag is controlled according to the slag color to maintain a reducing atmosphere in the furnace; the rough adjustment of the composition is controlled according to the limit value or lower limit value in the internal control composition of the finished steel. After the analysis results come out, the composition is finely adjusted. After the composition is qualified, 100 - 300 m / ladle of calcium - iron wire (calcium treatment) is fed to improve the castability of the molten steel. For the scientific and reasonable continuous casting pouring process technology, the stopper tundish is used for starting pouring operation, and a typical casting speed control process system is implemented. The whole process from the ladle to the tundish to the mold is protected by casting, and a carbon - free tundish covering agent and a special protective slag for low - carbon steel are used to prevent carbon increase; the liquid level in the mold is automatically controlled (radioactive source detection + stopper closed - loop control) to stably maintain the liquid level in the mold 80 mm ± 3 mm from the upper mouth of the copper tube, preventing slag inclusion caused by large liquid - level fluctuations. The cooling water in the mold is controlled by constant pressure and constant flow rate, and the water volume is 145 - 150 m 3 / h; the vibration form of the mold: four - link semi - leaf - spring electric non - sine vibration, and the vibration frequency changes according to F = 145 + 25*Vc (unit: times / min, Vc is the casting speed); the secondary cooling of the continuous caster adopts a full - water cooling mode and is controlled in four sections by partition. The water volume distribution ratio (%) of each section: the water volume of the full - roll is 41 - 43, the water volume of the first stage is 30 - 32, the water volume of the second stage is 13 - 14, and the water volume of the third stage is 11 - 13. Through the above - mentioned multi - process integrated technology innovation, a billet of H08A welding steel wire rod with uniform chemical composition, good tissue state and excellent quality is prepared.

[0010] The beneficial effects of the present invention are as follows:

[0011] 1. The blowing desulfurization treatment time of the method of the present invention is shortened by 2 - 4 minutes, and the desulfurization rate is increased to more than 50% (the desulfurization rate is increased by more than 10% compared with the current process).

[0012] 2. The method of the present invention has greatly improved the double hit rate of carbon and temperature in converter tapping, with better pre-deoxidation and deep deoxidation effects. The oxygen activity control in the argon blowing station is stable (oxygen activity: 28 ppm - 45 ppm), the temperature control in the refining furnace is stable, and the qualified rate of platform temperature is 100%.

[0013] 3. The method of the present invention has greatly improved the castability of H08A molten steel. The single-batch casting of H08A steel has achieved increased production, and the number of continuous casting heats per single ladle has achieved a breakthrough, with the ability to mass-produce high-quality H08A welded steel wire rod billets.

[0014] 4. After the macroetching of the billets produced by the method of the present invention, the rating of subcutaneous bubble defects has decreased from grade 1.0 to grade 0.5, and no non-metallic inclusions are visible in the macroetching.

[0015] 5. The billets produced by the method of the present invention have uniform chemical compositions, good tissue states, excellent billet qualities (except for a very small number of subcutaneous bubbles and surface pores in the first billet of the starting furnace, no subcutaneous bubbles and surface pores are found in the remaining billets), and stable through-train mechanical properties after rolling the Ф6.5mm wire rods.

[0016] 6. The preparation method of the H08A welded steel wire rod billets of the present invention has been verified by multiple on-site productions, is practically feasible in terms of process and technology, and has achieved good results. Moreover, the H08A steel is one of the raw material varieties with the largest usage in the welding industry, and has good prospects for popularization and application. Specific Embodiments

[0017] The following further illustrates the present invention with reference to embodiments, but the present invention is not limited in any way. Any transformation or replacement based on the teachings of the present invention falls within the protection scope of the present invention.

[0018] A preparation method of H08A welded steel wire rod billets of the present invention is realized according to the following steps:

[0019] A. Molten steel smelting: The pre-desulfurized hot metal and low-sulfur refined scrap steel are respectively added to a 120-ton LD top-bottom combined blowing converter at a ratio of 840 - 890 kg / t 钢 and 160 - 200 kg / t 钢 for top-bottom combined blowing smelting. Low-sulfur active lime is added for slag making. Argon is blown from the bottom throughout the smelting process, and the working pressure of the bottom lance > 0.3 MPa; the smelting end temperature is controlled at 1630 ± 15 °C, the end carbon content is controlled at 0.05 - 0.06 wt%, the end molten steel oxygen content is controlled ≤ 600 ppm, P ≤ 0.015 wt%, S ≤ 0.020 wt%; the S ≤ 0.020% and P ≤ 0.080% of the pre-desulfurized hot metal.

[0020] B. Deoxidation alloying: Tapping the molten steel. When the amount of molten steel in the ladle is 1 / 4 - 1 / 3, add the following substances to the ladle in the following deoxidation alloying sequence: calcium silicate barium alloy → medium-carbon ferromanganese → aluminum ferromanganese. Add the following substances in the following amounts: Add calcium silicate barium alloy for preliminary deoxidation in an amount of 0.38 kg / t 钢 with the following mass ratio: Ba 12%, Ca 9%, Si 50%, and the rest is Fe and inevitable impurities; add medium-carbon ferromanganese in an amount of 3.71 kg / t 钢 with the following mass ratio: Fe 20%, Mn 78%, C 2%; then add aluminum ferromanganese in an amount of 3.79 kg / t 钢 with the following mass ratio for final deoxidation: Fe 50%, Al 20%, Mn 30%; if the oxygen activity of the molten steel is too high, supplement an appropriate amount of ferrosilicon aluminum to adjust and ensure that the oxygen activity of the molten steel at the argon blowing station is controlled between 25 - 50 ppm. Add the above alloys before the amount of molten steel in the ladle reaches 2 / 3 - 3 / 4. Use a slide baffle to block the slag and ensure that the thickness of the ladle slag layer ≤ 60 mm, and the tapping time ≥ 3.0 minutes; after tapping, lift the molten steel to the argon station for refining treatment;

[0021] C. LF furnace refining: Immediately connect the bottom argon blowing after lifting the molten steel to the LF furnace. The argon blowing volume is 350 - 450 L / min. Blow through the porous plug and stir for 1 min, melt the crust on the surface of the molten steel and then carry out slag melting operation: Add 300 - 500 kg of lime, and the argon blowing volume is 150 - 250 L / min to make the liquid surface wriggle. After the lower electrode is energized for slag melting for 5 - 8 minutes, the argon blowing volume is 200 - 300 L / min. Measure the temperature, determine the oxygen content, and take samples of the molten steel. If the oxygen activity of the molten steel is greater than 45 ppm, supplement 20 - 80 kg / heat of calcium silicate barium to deoxidize the molten steel; Observe the fluidity and color of the slag. If the slag sample is too thin and the color is too dark, supplement low-silicon deoxidizer and lime to adjust the slag. Otherwise, add pre-melted refining slag to adjust the slag, and then adjust the argon blowing volume to 150 - 250 L / min and then energize the lower electrode to heat until the chemical composition is qualified. The number of times the lower electrode is used during the refining process ≤ 2 times; Coarse adjustment of the composition is controlled according to the limit or lower limit value in the internal control composition of the finished steel. After the analysis results come out, carry out fine adjustment of the composition. After the composition is qualified, feed 100 - 300 m / heat of calcium-ferrite wire. The argon blowing volume during wire feeding is 30 - 50 L / min, and the wire feeding speed is 2.5 - 3.5 m / s. After wire feeding, the argon blowing volume is 50 - 80 L / min for soft blowing, and the soft blowing time ≥ 3 min; After the argon blowing is completed, lift the molten steel to the casting station;

[0022] D. Continuous casting: At the tundish temperature of 1561 - 1566 °C, the drawing speed is 2.1 - 2.2 m / min, the water pressure in the mold is 1.14 MPa, the water volume is 149 - 151 m 3 / h, the secondary cooling adopts the full water cooling mode, and the specific water volume is 1.9 - 2.1 L / kg 钢 , and the water volume of the dummy bar is 23 - 25 m3 / h, the water volume in the first stage of secondary cooling is 17 - 19 m 3 / h, the water volume in the second stage of secondary cooling is 7 - 9 m 3 / h, the water volume in the third stage of secondary cooling is 6 - 7 m 3 / h, under the condition, the molten steel after being processed in step C is continuously cast into a billet of 165 mm × 165 mm by using an R9m7 machine with 7 - strand small billet continuous caster. Finally, after the billet is inspected and cleaned, it is sent to the rolling wire rod production line.

[0023] In step A, before steel smelting, the blast furnace hot metal is pre - desulfurized by injecting a calcium oxide - based desulfurizer into the hot metal through a lance. The calcium oxide - based desulfurizer contains the following components by mass ratio: CaO: 72 wt%, CaC2: 8 wt%, CaF2: 5.0 wt%, Al2O3: 2 wt%, and the balance is inevitable impurities. The temperature of the blast furnace hot metal is 1365 °C, and the composition is Si 0.25 wt%, P 0.074 wt%, S 0.029 wt%, and the rest are inevitable impurities.

[0024] In step A, for the low - sulfur active lime slag making, S ≤ 0.10% and the activity ≥ 300 mL.

[0025] In step A, during the smelting process, the oxygen lance blows oxygen in a constant - pressure variable - lance operation mode. Before and during the oxygen supply, the working oxygen pressure is controlled at 0.70 - 0.80 MPa, and the working lance position is 1.2 m. When the oxygen lance automatically descends to a lance position of 2.6 m, oxygen blowing starts automatically. Within 0 - 30 s, the oxygen flow rate rises from 0% of the normal oxygen supply flow rate to 60%, and this flow rate is maintained for 30 s. Then, from 60 - 90 s, it gradually rises to the normal oxygen supply flow rate. During blowing, according to the slag melting situation, by adjusting the lance position and slag materials, the slag melting and splashing are controlled. When the slag returns to dryness, the lance position can be appropriately increased or a small amount of slag melting agent can be added to adjust the slag; in the later stage of oxygen supply, the working oxygen pressure is 0.80 - 0.90 MPa, and the flow rate is 25000 - 30000 m 3 / h.

[0026] In step A, the bottom - blowing gas supply intensity is controlled in a "strong - medium - strong" mode respectively in the pre - middle - late stages of the carbon - oxygen reaction during the smelting process. In the early stage, the bottom - blowing argon gas supply volume is 400 - 500 Nm 3 / h, in the middle stage, the supply volume is 300 - 400 Nm 3 / h, in the later stage, the supply volume is 600 Nm 3 / h; control the smelting end - point temperature at 1630 ± 15 °C, control the end - point carbon content at 0.05 - 0.06 wt%, control the end - point molten steel oxygen content ≤ 600 ppm, P ≤ 0.015 wt%, S ≤ 0.020 wt%;

[0027] In step D, the distance between the mold liquid level and the upper mouth of the copper tube is 80 mm ± 3 mm, and the immersion depth of the nozzle is 90 - 100 mm.

[0028] In step D, before the first heat is tapped and during the tapping process, the argon pipe should be placed into the tundish to remove air. The tundish is tapped using a stopper rod. An immersion nozzle is put on the upper nozzle of the tundish, and the height of the tundish is reduced. The immersion nozzle is inserted more than 100 mm into the upper opening of the mold. When the molten steel in the tundish reaches more than 15 t, the stopper rod is manually controlled to inject molten steel into the mold. The rising speed of the molten steel injected into the mold before casting should be slow, and the seeding time is controlled between 20 and 40 seconds. Starting control: When the liquid level is 170 - 200 mm from the upper opening of the mold, the mold vibration is started. At this time, the secondary cooling water is automatically opened and supplied at the minimum flow rate. The starting casting speed is 0.8 - 1.0 m / min and is maintained for 20 - 40 seconds. After ensuring that the dummy bar head pulls the billet head out of the lower opening of the mold, the casting speed is gradually increased to the normal casting speed within 1 - 2 minutes. The molten steel level in the mold rises slowly and remains stable when it is 80 - 100 mm from the upper opening of the mold.

[0029] In step D, when the tundish temperature > 1557 °C, the casting speed is 2.1 - 2.2 m / min; when the tundish temperature < 1543 °C, the casting speed is 2.6 - 2.7 m / min.

[0030] Full protection casting is adopted from the ladle to the tundish to the mold to prevent the molten steel from being exposed. A carbon-free tundish covering agent and a special protective slag for low-carbon steel are used to prevent carbon increase. The material of the tundish nozzle is aluminum-carbon. The protective slag is added automatically. The immersion nozzle is inserted 90 - 120 mm into the liquid level of the mold. The liquid level of the mold is automatically controlled (radioactive source detection + stopper rod closed-loop control) to keep the liquid level of the mold 80 mm ± 3 mm from the upper opening of the copper tube to prevent large liquid level fluctuations from causing slag inclusions. The steel passing amount of the mold copper tube ≤ 2500 tons, and the appropriate mold taper is ensured to improve the heat transfer effect. The slag from the ladle is removed or slag is discharged once every 5 continuous heats to prevent slag from entering the mold. The cooling water of the mold is controlled with constant pressure and constant flow rate, the water pressure ≥ 1.0 MPa, and the water volume is 145 - 150 m 3 / h; The vibration form of the mold: Four-link semi-leaf spring electric non-sinusoidal vibration, and the vibration frequency changes according to F = 145 + 25 * Vc (unit: times / min, Vc is the casting speed); The secondary cooling of the continuous caster adopts a full water cooling mode. The pressure of the secondary cooling water ≥ 1.0 MPa, the inlet water temperature ≤ 40 °C, the outlet water temperature ≤ 50 °C, and the specific water volume is 1.9 - 2.1 L / kg 钢 , and it is controlled in four sections. The water volume distribution ratio of each section: the water volume of the foot rolls is 41 - 43%, the water volume of the first section is 30 - 32%, the water volume of the second section is 13 - 14%, and the water volume of the third section is 11 - 13%.

[0031] The chemical composition of the H08A welding steel by weight is: C ≤ 0.08 wt%, Si ≤ 0.03 wt%, Mn 0.47 - 0.63 wt%, S ≤ 0.020 wt%, P ≤ 0.020 wt%, O 0.0025 - 0.0045 wt%, V ≤ 0.07 wt%, As ≤ 0.015 wt%, Mo ≤ 0.20 wt%, and the balance is Fe and unavoidable impurities.

[0032] Example 1

[0033] 1. Hot metal pretreatment: The calcium oxide-based desulfurizer is sprayed into the 1365 °C blast furnace hot metal with a composition of Si 0.25 wt%, P 0.074 wt%, S 0.029 wt%, and the balance being unavoidable impurities by a lance for hot metal pre-desulfurization. The pretreatment cycle is 38 minutes. After treatment, the Si content in the hot metal is 0.23 wt%, P is 0.062 wt%, and S is 0.013 wt% (desulfurization rate: 55.2%). The calcium oxide-based desulfurizer consists of lime powder, calcium carbide, and fluorite, and contains the following components by mass ratio: CaO: 72 wt%, CaC2: 8 wt%, CaF2: 5.0 wt%, Al2O3: 2 wt%, and the balance is unavoidable impurities.

[0034] 2. Converter smelting and deoxidation alloying: Charge scrap steel at a ratio of 170 kg / t 钢 into the 120-ton LD top-bottom combined blowing converter with the following mass ratio of scrap steel: C 0.20 wt%, Si 0.38 wt%, Mn 1.31 wt%, P 0.030 wt%, S 0.018 wt%, and the balance being Fe and unavoidable impurities; then charge hot metal at a ratio of 870 kg / t 钢 into the 120-ton LD top-bottom combined blowing converter and smelt the hot metal treated in step 1. During the process, the top blowing adopts a constant pressure and variable lance operation mode. When the oxygen lance automatically descends to a lance position of 2.6 m, oxygen blowing starts automatically. The working oxygen pressure is 0.78 MPa, and the oxygen flow rate rises to 60% of the normal oxygen supply flow rate (about 16500 Nm 3 / h) within 30 s and blows at this flow rate for 30 s, then gradually rises to the normal oxygen supply flow rate of 27000 Nm 3 / h in 90 s. During the blowing process, control slag melting and splashing by adjusting the lance position and slag materials. After blowing for 9 min, adjust the working oxygen pressure to 0.86 MPa. Argon is blown from the bottom throughout the smelting process. The working pressure of the bottom lance is 0.45 MPa, and the bottom blowing gas supply intensity is controlled in the "strong - medium - strong" mode respectively in the pre-, middle-, and post-stages of the carbon-oxygen reaction during the smelting process. The argon gas supply volume in the early stage is 480 Nm 3 / h, in the middle stage is 350 Nm 3 / h, and in the later stage is 600 Nm 3 / h, tapping temperature is 1620°C, final C content is 0.06 wt%, dissolved oxygen content in the molten steel at the end is 499 ppm, P is 0.011 wt%, S is 0.017 wt%. During tapping, a slide gate baffle is used to prevent slag from flowing into the ladle. The thickness of the slag layer in the ladle is 57 mm, tapping time is 3.5 minutes, and the steel stream is relatively round. During tapping, 50 kg / furnace of calcium silicate-barium alloy is added for deoxidation, desulfurization and modification of inclusions, then 500 kg / furnace of medium-carbon ferromanganese and 500 kg / furnace of aluminum ferromanganese are added for deep deoxidation. The dissolved oxygen content in the molten steel is 40 ppm, C is 0.06 wt%, Si is 0.01 wt%, Mn is 0.49 wt%, P is 0.009 wt%, S is 0.014 wt%.

[0035] 3. LF furnace refining treatment: The molten steel obtained in step 2 is lifted to the LF furnace and immediately the bottom argon blowing is turned on. The argon blowing rate is 150 L / min to make the liquid surface wriggle. 500 kg of lime is added, the lower electrode is energized to melt the slag, and after 6 minutes of argon blowing, the temperature, dissolved oxygen are measured and samples are taken. The temperature is 1589°C, the dissolved oxygen content is 43 ppm. Depending on the slag condition, 150 kg of lime is added to adjust the slag. The argon blowing rate is 250 L / min, the lower electrode is energized to raise the temperature and melt the slag. After 8 minutes, the temperature, dissolved oxygen are measured and samples are taken. The temperature is 1622°C, the dissolved oxygen content is 38 ppm, C is 0.06 wt%, Si is 0.01 wt%, Mn is 0.49 wt%, P is 0.010 wt%, S is 0.018 wt%. During the refining process, the lower electrode is used 2 times. The chemical composition is qualified. The calcium-iron wire (calcium treatment) with a feeding speed of 2.5 m / s and a length of 150 m / furnace is fed in to improve the castability of the molten steel.

[0036] 4. Continuous casting: The molten steel treated in step 3 is lifted to the continuous casting platform and the temperature is measured as 1608°C. The temperature of the molten steel in the tundish is 1563°C, the casting speed is 2.1 m / min, the distance from the liquid level in the mold to the upper mouth of the copper tube is 83 mm, the insertion depth of the nozzle is 98 mm, the water pressure in the mold is 1.14 MPa, and the water volume is 151 m 3 / h. The secondary cooling adopts the full water cooling mode, and the specific water volume is 2.1 L / kg 钢 , the water volume of the supporting rolls is 24 m 3 / h, the water volume of the first stage of secondary cooling is 18 m 3 / h, the water volume of the second stage of secondary cooling is 8 m 3 / h, the water volume of the third stage of secondary cooling is 7 m 3 / h. Under the conditions, the molten steel treated in step 3 is continuously cast into billets with a size of 165 mm×165 mm by an R9m7 machine with 7 strands of small billet continuous caster. Finally, after inspection and cleaning of the billets, they are sent to the rolling wire rod production line.

[0037] The castability of the H08A molten steel smelted in this example is greatly improved. There is no phenomenon of tundish nozzle clogging during the casting process. The chemical composition of the produced billets is uniform, and there are no subcutaneous bubbles and surface pores in the billet quality.

[0038] After inspecting and cleaning the continuous casting billet, it is sent to the wire rod production line of the rolling mill and rolled into wire rods with a specification of Ф6.5mm. The obtained wire rods have a tensile strength Rm of 360 MPa and an elongation A of 44%.

[0039] Example 2

[0040] 1. Hot metal pretreatment: The calcium oxide-based desulfurizer is sprayed into the hot metal of a blast furnace at 1378 °C with a composition of Si 0.25 wt%, P 0.059 wt%, S 0.025 wt%, and the rest being inevitable impurities by a lance for hot metal pre-desulfurization. The pretreatment cycle is 36 minutes. After treatment, the Si in the hot metal is 0.21 wt%, P is 0.055 wt%, and S is 0.013 wt% (desulfurization rate 48%). The calcium oxide-based desulfurizer is composed of lime powder, calcium carbide, and fluorite, and contains the following components by mass ratio: CaO: 72 wt%, CaC2: 8 wt%, CaF2: 5.0 wt%, Al2O3: 2 wt%, and the balance being inevitable impurities.

[0041] 2. Converter smelting and deoxidation alloying: Scrap steel is charged at a ratio of 190 kg / t of steel. In a 120-ton LD top-bottom combined blowing converter, the following scrap steel with the following mass ratio is added: C 0.24 wt%, Si 0.44 wt%, Mn 1.42 wt%, P 0.033 wt%, S 0.020 wt%, and the rest being Fe and inevitable impurities; then, according to the charging ratio of 860 kg / t 钢 of hot metal, the hot metal treated in step 1 is added to the 120-ton LD top-bottom combined blowing converter for smelting. During the process, the top blowing adopts a constant pressure and variable lance operation mode. When the oxygen lance automatically descends to a lance position of 2.6 m, oxygen blowing starts automatically. The working oxygen pressure is 0.78 MPa, and the oxygen flow rate rises to 60% of the normal oxygen supply flow rate (about 16500 Nm 3 / h) within 30 s and blows at this flow rate for 30 s, and then gradually rises to the normal oxygen supply flow rate of 27000 Nm 3 / h in 90 s. During the blowing process, the slag melting and splashing are controlled by adjusting the lance position and slag materials. After blowing for 9 min, the working oxygen pressure is adjusted to 0.86 MPa. Argon is blown from the bottom throughout the smelting process. The working pressure of the bottom lance is 0.45 MPa, and the bottom blowing gas supply intensity is controlled in the "strong-medium-strong" mode respectively in the pre-middle-late stages of the carbon-oxygen reaction during the smelting process. The bottom blowing argon gas supply volume in the early stage is 450 Nm 3 / h, the supply volume in the middle stage is 380 Nm 3 / h, and the supply volume in the later stage is 600 Nm 3 / h, the tapping temperature is 1630 °C, the C content at the end is 0.06 wt%, the dissolved oxygen content in the molten steel at the end is 484 ppm, P is 0.010 wt%, S is 0.012 wt%. During tapping, a slide gate baffle is used to block the slag. The thickness of the ladle slag layer is 50 mm, the tapping time is 3.5 minutes, and the steel stream is relatively round. During tapping, 50 kg / furnace of calcium silicate barium alloy is added for deoxidation, desulfurization and modification treatment of inclusions respectively, and then 500 kg / furnace of medium-carbon ferromanganese and 500 kg / furnace of aluminum ferromanganese are added for deep deoxidation. The dissolved oxygen content in the molten steel is 44 ppm, C is 0.06 wt%, Si is 0.01 wt%, Mn is 0.50 wt%, P is 0.011 wt%, S is 0.013 wt%.

[0042] 3. LF furnace refining treatment: The molten steel obtained in step 2 is lifted to the LF furnace and immediately the bottom argon blowing is turned on. The argon blowing rate is 200 L / min to make the liquid surface wriggle. 400 kg of lime is added. The lower electrode is energized to melt the slag. After argon blowing for 5 minutes, the temperature, dissolved oxygen and sampling are measured. The temperature is 1585 °C, the dissolved oxygen content is 41 ppm. Depending on the slag condition, 100 kg of lime is added to adjust the slag. The argon blowing rate is 300 L / min. After the lower electrode is energized to raise the temperature and melt the slag for 6 minutes, the temperature, dissolved oxygen and sampling are measured. The temperature is 1620 °C, the dissolved oxygen content is 35 ppm, C is 0.06 wt%, Si is 0.01 wt%, Mn is 0.52 wt%, P is 0.014 wt%, S is 0.013 wt%. During the refining process, the lower electrode is used 2 times. The chemical composition is qualified. The calcium-iron wire (calcium treatment) of 150 m / furnace is fed at a wire feeding speed of 2.5 m / s to improve the castability of the molten steel.

[0043] 4. Continuous casting: The molten steel treated in step 3 is lifted to the continuous casting platform and the temperature is measured at 1598 °C. When the molten steel temperature in the tundish is 1549 °C, the drawing speed is 2.3 m / min, the distance between the liquid surface of the mold and the upper mouth of the copper tube is 82 mm, the insertion depth of the nozzle is 96 mm, the water pressure of the mold is 1.14 MPa, and the water volume is 150 m 3 / h. The secondary cooling adopts the full water cooling mode, and the specific water volume is 1.9 L / kg 钢 , the water volume of the dummy bar is 23 m 3 / h, the water volume of the first stage of secondary cooling is 18 m 3 / h, the water volume of the second stage of secondary cooling is 7 m 3 / h, the water volume of the third stage of secondary cooling is 6 m 3 / h. Under the conditions, the molten steel treated in step 3 is continuously cast into billets of 165 mm × 165 mm by an R9m7 machine with 7 strands of small billet continuous caster. Finally, the billets are inspected, cleaned and sent to the rolling wire rod production line.

[0044] The castability of the H08A molten steel smelted in this example is greatly improved. There is no phenomenon of tundish nozzle clogging during the casting process. The chemical composition of the produced billets is uniform. After the macroetching of the billets, there are no subcutaneous bubbles and surface pores.

[0045] After inspecting and cleaning the continuous casting billet, it is sent to the wire rod production line of the rolling mill and rolled into wire rods with a specification of Ф6.5mm. The obtained wire rods have a tensile strength Rm of 370 MPa and an elongation A of 43%.

[0046] Example 3

[0047] 1. Hot metal pretreatment: Inject the calcium oxide-based desulfurizer into the hot metal of a blast furnace at 1365°C with a composition of Si 0.28wt%, P 0.064wt%, S 0.027wt%, and the rest being inevitable impurities through a lance for hot metal pre-desulfurization. The pretreatment cycle is 39 minutes. After treatment, the Si in the hot metal is 0.24wt%, P is 0.057wt%, and S is 0.013wt% (desulfurization rate: 51.8%). The calcium oxide-based desulfurizer is composed of lime powder, calcium carbide, and fluorite, containing the following components by mass ratio: CaO: 72wt%, CaC2: 8wt%, CaF2: 5.0wt%, Al2O3: 2wt%, and the balance being inevitable impurities.

[0048] 2. Converter smelting and deoxidation alloying: Charge the scrap steel according to the ratio of 180 kg / t 钢 into the 120-ton LD top-bottom combined blowing converter. The scrap steel added has the following mass ratio: C 0.23wt%, Si 0.42wt%, Mn 1.50wt%, P 0.026wt%, S 0.023wt%, and the rest being Fe and inevitable impurities; then charge the hot metal according to the ratio of 865 kg / t 钢 and smelt the hot metal treated in step 1 in the 120-ton LD top-bottom combined blowing converter. During the process, the top blowing adopts a constant pressure and variable lance operation mode. When the oxygen lance automatically descends to a lance position of 2.6 m, the oxygen is automatically blown. The working oxygen pressure is 0.78 MPa, and the oxygen flow rate rises to 60% of the normal oxygen supply flow rate (about 16500 Nm 3 / h) within 30 s and blows at this flow rate for 30 s, and then gradually rises to the normal oxygen supply flow rate of 27000 Nm 3 / h in 90 s. During the blowing process, control the slag melting and splashing by adjusting the lance position and slag materials. After blowing for 9 min, adjust the working oxygen pressure to 0.86 MPa. Argon is blown from the bottom throughout the smelting process. The working pressure of the bottom lance is 0.45 MPa, and the bottom blowing gas supply intensity is controlled in the "strong-medium-strong" mode respectively in the pre-middle-late stages of the carbon-oxygen reaction during the smelting process. The argon gas supply volume in the early stage is 470 Nm 3 / h, the supply volume in the middle stage is 320 Nm 3 / h, and the supply volume in the later stage is 600 Nm 3 / h, the tapping temperature is 1635°C, the C content at the end is 0.05 wt%, the oxygen content in the molten steel at the end is 507 ppm, P is 0.011 wt%, S is 0.014 wt%. During tapping, a slide gate baffle is used to prevent slagging. The thickness of the ladle slag layer is 55 mm, the tapping time is 3.5 minutes, and the steel stream is relatively round. During tapping, 50 kg / furnace of calcium-silicon-barium alloy is added for deoxidation, desulfurization and modification treatment of inclusions respectively, and then 500 kg / furnace of medium-carbon ferromanganese and 500 kg / furnace of aluminum-manganese ferromanganese are added for deep deoxidation. The oxygen content in the molten steel is 42 ppm, C is 0.05 wt%, Si is 0.01 wt%, Mn is 0.51 wt%, P is 0.014 wt%, S is 0.014 wt%.

[0049] 3. LF furnace refining treatment: After lifting the molten steel obtained in step 2 to the LF furnace, the bottom blowing argon is immediately turned on. The blowing rate is 250 L / min to make the liquid surface wriggle. 350 kg of lime is added, the lower electrode is energized to melt the slag, and after blowing argon for 7 minutes, the temperature, oxygen content are measured and samples are taken. The temperature is 1588°C, the oxygen content is 39 ppm. Depending on the slag condition, 150 kg of lime is added to adjust the slag. The blowing rate is 300 L / min. After the lower electrode is energized to raise the temperature and melt the slag for 6 minutes, the temperature, oxygen content are measured and samples are taken. The temperature is 1615°C, the oxygen content is 37 ppm, C is 0.05 wt%, Si is 0.01 wt%, Mn is 0.51 wt%, P is 0.014 wt%, S is 0.015 wt%. During the refining process, the lower electrode is used 2 times, and the chemical composition is qualified. The calcium-iron wire (calcium treatment) of 150 m / furnace is fed at a feeding speed of 2.5 m / s to improve the castability of the molten steel.

[0050] 4. Continuous casting: The molten steel treated in step 3 is lifted to the continuous casting platform for temperature measurement at 1593°C. When the molten steel temperature in the tundish is 1541°C, the casting speed is 2.6 m / min, the distance between the liquid level in the mold and the upper mouth of the copper tube is 82 mm, the insertion depth of the nozzle is 96 mm, the water pressure in the mold is 1.14 MPa, and the water volume is 150 m 3 / h. The secondary cooling adopts the full water cooling mode, and the specific water volume is 1.9 L / kg 钢 , the water volume of the dummy bar is 25 m 3 / h, the water volume of the first stage of secondary cooling is 19 m 3 / h, the water volume of the second stage of secondary cooling is 9 m 3 / h, the water volume of the third stage of secondary cooling is 7 m 3 / h. Under the conditions, the molten steel treated in step 3 is continuously cast into billets of 165 mm×165 mm by an R9m7 machine 7-strand small billet continuous caster. Finally, after the billets are inspected and cleaned, they are sent to the rolling wire rod production line.

[0051] The castability of the H08A molten steel smelted in this example is greatly improved. There is no phenomenon of tundish nozzle clogging during the casting process. The chemical composition of the produced billets is uniform, and there are no subcutaneous bubbles and surface pores after the billets are pickled by macroetching.

[0052] After inspecting and cleaning the continuous casting billet, it is sent to the wire rod production line of the rolling mill and rolled into wire rods with a specification of Ф6.5mm. The obtained wire rods have a tensile strength Rm of 355 MPa and an elongation rate A of 45%.

[0053] Comparative Example 1

[0054] 1. Hot metal pretreatment: In hot metal from a blast furnace at a temperature of 1385°C, with a composition of Si 0.43wt%, P 0.067wt%, S 0.028wt%, and the rest being inevitable impurities, a calcium oxide-based desulfurizer with the following mass ratio is injected by a lance: CaO: 72wt%, CaC2: 8wt%, CaF2: 5.0wt%, Al2O3: 2wt%, and the balance being inevitable impurities, for desulfurization. The pretreatment cycle is 37 minutes. After treatment, the sulfur content in the hot metal is Si 0.35wt%, P 0.060wt%, S 0.015wt% (desulfurization rate 46.4%).

[0055] 2. Converter smelting and deoxidation alloying: Charge scrap steel at a ratio of 164 kg / t 钢 into the converter. In a 120-ton LD top-bottom combined blowing converter, add scrap steel with the following mass ratio: C 0.22wt%, Si 0.49wt%, Mn 1.48wt%, P 0.028wt%, S 0.021wt%, and the rest being Fe and inevitable impurities; then charge hot metal at a ratio of 873 kg / t 钢 into the converter. Add the hot metal treated in Step 1 to the 120-ton LD top-bottom combined blowing converter for smelting. During the smelting process, the top blowing adopts a constant pressure and variable lance operation mode. When the oxygen lance automatically descends to a lance position of 2.6 m, oxygen blowing is automatically started. The working oxygen pressure is 0.78 MPa, and the oxygen flow rate rises to 62% of the normal oxygen supply flow rate (about 16800 m 3 / h) within 30 s and blows for 30 s at this flow rate, and then gradually rises to the normal oxygen supply flow rate of 27000 Nm 3 / h in 90 s. During the blowing process, control slag melting and splashing by adjusting the lance position and slag materials. After blowing for 10 min, adjust the working oxygen pressure to 0.86 MPa. Argon is blown from the bottom throughout the smelting process. The working pressure of the bottom lance is 0.45 MPa. The bottom blowing gas supply intensity is controlled in the "strong-medium-strong" mode respectively before, during, and after the carbon-oxygen reaction in the smelting process. The bottom blowing argon gas supply volume in the early stage is 400 Nm 3 / h, the supply volume in the middle stage is 300 Nm 3 / h, and the supply volume in the later stage is 600 Nm 3 / h, the tapping temperature is 1632°C, the C content at the end is 0.04 wt%, the oxygen content of the molten steel at the end is 592 ppm, P is 0.008 wt%, S is 0.020 wt%. During tapping, a slide damper is used to block the slag, the thickness of the ladle slag layer is 60 mm, the tapping time is 3.3 minutes, and the molten steel flow is relatively round. During tapping, 50 kg / furnace of calcium silicate barium alloy is added for deoxidation, desulfurization and modification treatment of inclusions respectively, then 802 kg / furnace of medium-carbon ferromanganese and 230 kg / furnace of core aluminum are added for deep deoxidation. The oxygen content of the molten steel is 66 ppm, C is 0.06 wt%, Si is 0.02 wt%, Mn is 0.51 wt%, P is 0.008 wt%, and S is 0.016 wt%.

[0056] 3. LF furnace refining: After lifting the molten steel from step 3 to the LF furnace, the bottom argon blowing is immediately turned on, and the argon blowing rate is 150 - 250 L / min to make the liquid surface wriggle. 340 kg of lime is added, the lower electrode is energized to melt the slag, and after blowing argon for 5 minutes, the temperature, oxygen content are measured and samples are taken. The temperature is 1591°C and the oxygen content is 68 ppm. Depending on the furnace slag situation, 100 kg of refining slag is added to melt the slag, and 20 kg of calcium silicate barium and 50 kg of core aluminum are added to deoxidize the molten steel. The argon blowing rate is 200 L / min. After the lower electrode is energized to raise the temperature and melt the slag for 7 minutes, the temperature, oxygen content are measured and samples are taken. The temperature is 1598°C, the oxygen content is 18 ppm, C is 0.06 wt%, Si is 0.01 wt%, Mn is 0.51 wt%, P is 0.009 wt%, S is 0.014 wt%. During the refining process, the lower electrode is used 2 times, the chemical composition is qualified, and the calcium-ferrite wire (calcium treatment) is fed into the furnace at a feeding speed of 2.5 m / s for 100 m / furnace.

[0057] 4. Continuous casting: The molten steel treated in step 3 is lifted to the continuous casting platform for temperature measurement at 1594°C, the molten steel temperature in the tundish is 1550°C, and the casting speed is 2.3 m / min. However, during the casting process, the phenomenon of multi-stream flocculent flow and nozzle clogging occurs in all 7 strands, and the casting speed is reduced to 0.5 - 1.2 m / min. For continuous casting furnaces, depending on the coverage of the tundish liquid surface, carbon-free covering agent is supplemented to prevent the molten steel from being exposed and to prevent the formation of a crust on the tundish molten steel surface. The tundish nozzle material is aluminum-carbon; the mold powder used is a special slag for low-carbon steel; the mold liquid level is automatically controlled, the distance between the mold liquid level and the upper mouth of the copper tube is 80 mm, and the insertion depth of the nozzle is 92 mm; the mold water pressure is 1.14 MPa and the water volume is 149 m 3 / h, the secondary cooling adopts a full-water cooling mode, and the specific water volume is 1.9 L / kg 钢 , the water volume of the foot rolls is 23 m 3 / h, the water volume of the first stage of secondary cooling is 18 m 3 / h, the water volume of the second stage of secondary cooling is 8 m 3 / h, the water volume of the third stage of secondary cooling is 7 m 3 / h.

[0058] In Comparative Example 1, due to the relatively low control of the carbon content at the end of the converter, the oxygen content at the end was relatively high. During the tapping process of the converter, ferritic aluminum was used for primary deep deoxidation, but the degree of deoxidation was incomplete (the oxygen content of the molten steel at the argon blowing station was 66 ppm higher). Refining was carried out with additional ferritic aluminum for deoxidation, resulting in over-strong deoxidation of the molten steel (the oxygen content after refining was 18 ppm). After the acid-soluble aluminum in the molten steel was oxidized during transportation and casting, Al2O3 or compounds mainly composed of Al2O3 were formed. These have a high melting point and a sharp-angled shape, increasing the viscosity of the molten steel and affecting the castability of the molten steel. The Al2O3 inclusions in the steel reacted with the refractory material on the inner wall of the nozzle to form complex compounds and deposited on the inner wall, causing nozzle nodulation and blockage, resulting in difficult pouring and flocculent flow and nozzle blockage in multiple casting streams.

[0059] After low-power pickling of the H08A billet smelted in Comparative Example 1, the rating of the center crack defect was 0.5 level, and the rating of the non-metallic inclusion defect was 0.5 level.

[0060] Comparative Example 2

[0061] 1. Hot metal pretreatment: In a 1379 °C blast furnace hot metal with a composition of Si 0.32 wt%, P 0.078 wt%, S 0.022 wt%, and the rest being inevitable impurities, a magnesium-calcium composite desulfurizer with the following mass ratio was injected by a lance: CaO + MgO: 82 wt%, CaF2: 9.3 wt%, SiO2: 1.4 wt%, and the rest being inevitable impurities for desulfurization. The treatment cycle was 42 minutes. After treatment, the sulfur content in the hot metal was Si 0.28 wt%, P 0.073 wt%, S 0.019 wt% (desulfurization rate 13.6%).

[0062] 2. Steelmaking converter control technology and deoxidation alloying: Scrap steel was charged at a ratio of 188 kg / t of steel. In a 120-ton LD top-bottom combined blowing converter, scrap steel with the following mass ratio was added: C 0.25 wt%, Si 0.50 wt%, Mn 1.38 wt%, P 0.030 wt%, S 10.020 wt%, and the rest being Fe and inevitable impurities; then, according to the charging ratio of 842 kg / t 钢 of hot metal, the hot metal treated in Step 1 was added to the 120-ton LD top-bottom combined blowing converter for smelting. During the process, the top blowing adopted a constant pressure and variable lance operation mode. When the oxygen lance automatically lowered to a lance position of 2.6 m, oxygen blowing was automatically started. The working oxygen pressure was 0.78 MPa. The oxygen flow rate increased from 60% of the normal oxygen supply flow rate (16500 Nm 3 / h) within 30 s and was maintained at this flow rate for 30 s, and then gradually increased to the normal oxygen supply flow rate of 27000 Nm 3 / h. During the blowing process, the lance position and slag materials are adjusted to control slag formation and splashing. After 10 minutes of blowing, the working oxygen pressure is adjusted to 0.86 MPa. Argon is bottom-blown throughout the smelting process, with the bottom lance working pressure > 0.3 MPa. The bottom-blowing gas supply intensity is controlled in the "strong-medium-strong" mode respectively in the early, middle, and late stages of the carbon-oxygen reaction during the smelting process. The gas supply volume of bottom-blowing argon in the early stage is 450 Nm 3 / h, the gas supply volume in the middle stage is 300 Nm 3 / h, and the gas supply volume in the late stage is 600 Nm 3 / h. The tapping temperature is 1610 °C, the C content at the end point is 0.05 wt%, the dissolved oxygen content in the molten steel at the end point is 569 ppm, P is 0.006 wt%, S is 0.019 wt%. During the tapping process, a slide plate baffle is used to block the slag, the slag layer thickness in the ladle is 55 mm, the tapping time is 3.7 minutes, and the molten steel flow is relatively round. During the tapping process, 50 kg / furnace of calcium-silicon-barium alloy is added for deoxidation, desulfurization, and modification treatment of inclusions, and then 850 kg / furnace of medium-carbon ferromanganese and 220 kg / furnace of core aluminum are added for deep deoxidation. The dissolved oxygen content in the molten steel is 68 ppm, C is 0.08 wt%, Si is 0.02 wt%, Mn is 0.50 wt%, P is 0.010 wt%, S is 0.020 wt%.

[0063] 3. LF furnace refining treatment: After the molten steel in step C is lifted to the LF furnace, bottom-blowing argon is immediately turned on, and the argon blowing volume is 250 L / min to make the liquid surface wriggle. 484 kg of lime is added, the lower electrode is energized to melt the slag, and after blowing argon for 7 minutes, the temperature, dissolved oxygen, and sampling are carried out. The temperature is 1582 °C, the dissolved oxygen content is 66 ppm. Depending on the furnace slag situation, 270 kg of refining slag is added to melt the slag, and 30 kg of core aluminum is added to deoxidize the molten steel. The argon blowing volume is 250 L / min. After the lower electrode is energized to raise the temperature and melt the slag for 6 minutes, the temperature, dissolved oxygen, and sampling are carried out. The temperature is 1599 °C, the dissolved oxygen content is 48 ppm, C is 0.08 wt%, Si is 0.02 wt%, Mn is 0.52 wt%, P is 0.010 wt%, S is 0.020 wt%. The number of times the lower electrode is used during the refining process is 2 times, and the chemical composition is qualified. The calcium-iron wire (calcium treatment) is fed into the furnace at a feeding speed of 2.5 m / s for 150 m / furnace to improve the castability of the molten steel.

[0064] 4. Continuous casting: The molten steel treated in step 3 is lifted to the continuous casting platform for temperature measurement at 1592 °C, the tundish temperature range is 1562 °C, and the casting speed is 2.3 m / min; for continuous casting furnaces, carbon-free covering agent is added according to the covering situation of the tundish liquid surface to prevent the molten steel from being exposed and to prevent the formation of a crust on the tundish molten steel surface. The material of the tundish nozzle is aluminum-carbon; the mold powder used for the mold is a special slag for low-carbon steel; the slag in the ladle is discharged in time to prevent the slag from being involved in the mold; the mold liquid level is automatically controlled, the distance between the mold liquid level and the upper mouth of the copper tube is 83 mm, and the insertion depth of the nozzle is 95 mm; the water volume in the mold is 150 m 3 / h, and the secondary cooling adopts the full-water cooling mode, with a specific water volume of 2.0 L / kg钢 , the water volume of the bottom roll is 24 m 3 / h, the water volume of the first stage of secondary cooling is 19 m 3 / h, the water volume of the second stage of secondary cooling is 8 m 3 / h, the water volume of the third stage of secondary cooling is 7 m 3 / h.

[0065] In Comparative Example 2, the pretreatment period of hot metal is relatively long (42 min), and the desulfurization rate is relatively low. During the tapping process, the deep deoxidation degree of adding ferrosilicon aluminum is incomplete, and the oxygen content of the molten steel in the argon blowing station is relatively high at 68 ppm. In the refining station, ferrosilicon aluminum is added for supplementary deoxidation, and the oxygen content after refining is 48 ppm. The superheat of the continuous casting is relatively high (about 39 °C) and the casting speed of 2.3 m / min exceeds the specified casting speed (the specified casting speed is 2.1 - 2.2 m / min). The cast slabs cast have subcutaneous bubbles and surface pores to varying degrees. After the macroetching of the cast slabs, the defect rating of subcutaneous bubbles is 1.5, the defect rating of shrinkage cavity is 0.5, and the defect rating of center crack is 0.5.

Claims

1. A method for preparing a billet of wire rod for H08A welding, characterized in that It is realized according to the following steps: A. Molten steel smelting: The pre-desulfurized hot metal and low-sulfur refined scrap steel are added to a 120-ton LD top-bottom combined blowing converter at a ratio of 840 - 890 kg / t 钢 and 160 - 200 kg / t 钢 respectively for top-bottom combined blowing smelting. Low-sulfur active lime is added for slag formation. Argon is blown from the bottom throughout the smelting process, and the working pressure of the bottom lance > 0.3 MPa. Control the smelting end temperature at 1630 ± 15 °C, control the end carbon content at 0.05 - 0.06 wt%, control the oxygen content of the molten steel at the end ≤ 600 ppm, P ≤ 0.015 wt%, and S ≤ 0.020 wt%. The S ≤ 0.020% and P ≤ 0.080% of the pre-desulfurized hot metal; B. Deoxidation alloying: Tapping the molten steel. When the amount of molten steel in the ladle is 1 / 4 - 1 / 3, add the following substances to the ladle in the following deoxidation alloying sequence: calcium silicate barium alloy → medium-carbon ferromanganese → aluminum ferromanganese. Add the following substances in the amounts as follows: Add calcium silicate barium alloy with the following mass ratio for preliminary deoxidation at a rate of 0.38 kg / t: Ba 12%, Ca 9%, Si 50%, and the rest is Fe and inevitable impurities; add medium-carbon ferromanganese with the following mass ratio at a rate of 3.71 kg / t: Fe 20%, Mn 78%, C 2%; then add aluminum ferromanganese with the following mass ratio for final deoxidation at a rate of 3.79 kg / t: Fe 50%, Al 20%, Mn 30%; if the oxygen activity of the molten steel is on the high side, supplement an appropriate amount of ferrosilicon aluminum for adjustment to ensure that the oxygen activity of the molten steel at the argon blowing station is controlled between 25 - 50 ppm. Add the above alloys before the amount of molten steel in the ladle reaches 2 / 3 - 3 / 4. Use a slide baffle to prevent slag, ensuring that the thickness of the slag layer in the ladle ≤ 60 mm and the tapping time ≥ 3.0 minutes; after tapping, lift the molten steel to the argon station for refining treatment; 钢 Add calcium silicate barium alloy with the following mass ratio for preliminary deoxidation at a rate of 0.38 kg / t: Ba 12%, Ca 9%, Si 50%, and the rest is Fe and inevitable impurities; add medium-carbon ferromanganese with the following mass ratio at a rate of 3.71 kg / t: Fe 20%, Mn 78%, C 2%; then add aluminum ferromanganese with the following mass ratio for final deoxidation at a rate of 3.79 kg / t: Fe 50%, Al 20%, Mn 30%; if the oxygen activity of the molten steel is on the high side, supplement an appropriate amount of ferrosilicon aluminum for adjustment to ensure that the oxygen activity of the molten steel at the argon blowing station is controlled between 25 - 50 ppm. Add the above alloys before the amount of molten steel in the ladle reaches 2 / 3 - 3 / 4. Use a slide baffle to prevent slag, ensuring that the thickness of the slag layer in the ladle ≤ 60 mm and the tapping time ≥ 3.0 minutes; after tapping, lift the molten steel to the argon station for refining treatment; 钢 Add medium-carbon ferromanganese with the following mass ratio at a rate of 3.71 kg / t: Fe 20%, Mn 78%, C 2%; then add aluminum ferromanganese with the following mass ratio for final deoxidation at a rate of 3.79 kg / t: Fe 50%, Al 20%, Mn 30%; if the oxygen activity of the molten steel is on the high side, supplement an appropriate amount of ferrosilicon aluminum for adjustment to ensure that the oxygen activity of the molten steel at the argon blowing station is controlled between 25 - 50 ppm. Add the above alloys before the amount of molten steel in the ladle reaches 2 / 3 - 3 / 4. Use a slide baffle to prevent slag, ensuring that the thickness of the slag layer in the ladle ≤ 60 mm and the tapping time ≥ 3.0 minutes; after tapping, lift the molten steel to the argon station for refining treatment; 钢 Add aluminum ferromanganese with the following mass ratio for final deoxidation at a rate of 3.79 kg / t: Fe 50%, Al 20%, Mn 30%; if the oxygen activity of the molten steel is on the high side, supplement an appropriate amount of ferrosilicon aluminum for adjustment to ensure that the oxygen activity of the molten steel at the argon blowing station is controlled between 25 - 50 ppm. Add the above alloys before the amount of molten steel in the ladle reaches 2 / 3 - 3 / 4. Use a slide baffle to prevent slag, ensuring that the thickness of the slag layer in the ladle ≤ 60 mm and the tapping time ≥ 3.0 minutes; after tapping, lift the molten steel to the argon station for refining treatment; C. LF furnace refining: After the molten steel is lifted to the LF furnace, the bottom blowing argon is immediately turned on. The argon blowing volume is 350 - 450 L / min. The porous plug is blown through and stirred for 1 minute. The crust on the surface of the molten steel is melted, and then the slag-making operation is carried out: 300 - 500 kg of lime is added. The argon blowing volume is 150 - 250 L / min to make the liquid surface wriggle. After the lower electrode is energized for slag melting for 5 - 8 minutes, the argon blowing volume is 200 - 300 L / min. The temperature, dissolved oxygen and sampling of the molten steel are measured. If the oxygen activity of the molten steel is greater than 45 ppm, 20 - 80 kg / heat of calcium-silicon-barium is added to deoxidize the molten steel; Observe the fluidity and color of the slag. If the slag sample is too thin and the color is too black, low-silicon deoxidizer and lime are added to adjust the slag. Otherwise, pre-melted refining slag is added to adjust the slag. Then the argon blowing volume is adjusted to 150 - 250 L / min, and the lower electrode is energized to heat until the chemical composition is qualified. The number of times of the lower electrode during the refining process ≤ 2 times; The rough adjustment of the composition is controlled according to the limit or lower limit value in the internal control composition of the finished steel. After the analysis results come out, the composition is finely adjusted. After the composition is qualified, 100 - 300 m / heat of calcium-iron wire is fed. The argon blowing volume during the wire feeding process is 30 - 50 L / min, and the wire feeding speed is 2.5 - 3.5 m / s. After wire feeding, the argon blowing volume is soft blown at 50 - 80 L / min, and the soft blowing time ≥ 3 min; After the argon blowing is completed, the molten steel is lifted to the casting station; D. Continuous casting and pouring: At an intermediate ladle temperature of 1561 - 1566 °C, a casting speed of 2.1 - 2.2 m / min, a mold water pressure of 1.14 MPa, and a water volume of 149 - 151 m 3 / h, the secondary cooling adopts a full water cooling mode, with a specific water volume of 1.9 - 2.1 L / kg 钢 , with a water volume of 23 - 25 m 3 / h for the bottom rolls, 17 - 19 m 3 / h for the first stage of secondary cooling, 7 - 9 m 3 / h for the second stage of secondary cooling, and 6 - 7 m 3 / h for the third stage of secondary cooling. Under these conditions, a R9m7 machine with 7 strands of small billet continuous caster is used to continuously cast the molten steel processed in step C into billets of 165 mm × 165 mm. Finally, after inspecting and cleaning the billets, they are sent to the rolling wire rod production line.

2. The preparation method of the H08A welding steel wire rod billet according to claim 1, characterized in that In step A, before steel smelting, the blast furnace hot metal is pre-desulfurized by spraying a calcium oxide-based desulfurizer into the hot metal by a spray gun. The calcium oxide-based desulfurizer contains the following components by mass ratio: CaO 72 wt%, CaC2 8 wt%, CaF2 5.0 wt%, Al2O3 2 wt%, and the balance is inevitable impurities. The temperature of the blast furnace hot metal is 1365 °C, and the composition is Si 0.25 wt%, P 0.074 wt%, S 0.029 wt%, and the rest is Fe, C and inevitable impurities.

3. The preparation method of the H08A welding steel wire rod billet according to claim 1, characterized in that, In step A, for the low-sulfur active lime slag-making, S ≤ 0.10% and the activity ≥ 300 mL.

4. The preparation method of the H08A steel wire rod billet for welding according to claim 1, characterized in that, In step A, the oxygen lance in the smelting process blows oxygen in a constant-pressure variable-lance operation mode. Before and during oxygen supply, the working oxygen pressure is controlled at 0.70 - 0.80 MPa, and the working lance position is 1.2 m. When the oxygen lance automatically lowers to a lance position of 2.6 m, oxygen blowing starts automatically. Within 0 - 30 s, the oxygen flow rate rises from 0% of the normal oxygen supply flow rate to 60%, and this flow rate is maintained for 30 s. Then, it gradually rises to the normal oxygen supply flow rate within 60 - 90 s. During blowing, according to the slag melting situation, by adjusting the lance position and slag materials, slag melting and splashing are controlled. When the furnace slag becomes dry, the lance position can be appropriately increased or a small amount of slag melting agent can be added to adjust the furnace slag. In the later stage of oxygen supply, the working oxygen pressure is 0.80 - 0.90 MPa, and the flow rate is 25000 - 30000 m 3 / h.

5. The preparation method of the H08A welding steel wire rod billet according to claim 1, characterized in that, In step A, the bottom blowing gas supply intensity is controlled in the "strong-medium-strong" mode respectively before, during and after the carbon-oxygen reaction in the smelting process. The bottom blowing argon gas supply volume in the early stage is 400 - 500 Nm 3 / h, the supply volume in the middle stage is 300 - 400 Nm 3 / h, and the supply volume in the later stage is 600 Nm 3 / h; control the smelting end temperature to be 1630 ± 15 °C, control the end carbon content to be 0.05 - 0.06 wt%, control the molten steel oxygen content at the end ≤ 600 ppm, P ≤ 0.015 wt%, and S ≤ 0.020 wt%.

6. The preparation method of the billet of the H08A steel wire rod for welding according to claim 1, characterized in that, In step D, the distance between the liquid level of the mold and the upper mouth of the copper tube is 80 mm ± 3 mm, and the insertion depth of the nozzle is 90 - 100 mm.

7. The preparation method of the H08A welding steel wire rod billet according to claim 1, characterized in that, In step D, before the first furnace starts casting and during the casting process, the argon pipe should be placed in the tundish to remove air. The tundish is opened for casting by using a stopper rod. An immersion nozzle is sleeved on the upper nozzle of the tundish to reduce the height of the tundish. The immersion nozzle is inserted into the upper mouth of the mold by more than 100 mm. When the molten steel in the tundish reaches more than 15 t, the stopper rod is manually controlled to inject molten steel into the mold. The rising speed of the molten steel injected into the mold before continuous casting should be slow. The emergence time is controlled between 20 - 40 seconds; Starting control: When the liquid level is 170 - 200 mm from the upper mouth of the mold, the mold vibration is started. At this time, the secondary cooling water is automatically opened and supplied at the minimum flow rate; The starting casting speed is 0.8 - 1.0 m / min and is maintained for 20 - 40 seconds. After ensuring that the dummy bar head pulls the billet head out of the lower mouth of the mold, the casting speed is gradually increased to the normal casting speed in 1 - 2 minutes. The liquid level of the molten steel in the mold rises slowly and remains stable when it is 80 - 100 mm from the upper mouth of the mold.

8. The preparation method of the H08A welding steel wire rod billet according to claim 1, characterized in that, In step D, when the tundish temperature > 1557 °C, the casting speed is 2.1 - 2.2 m / min; when the tundish temperature < 1543 °C, the casting speed is 2.6 - 2.7 m / min.

9. The preparation method of the H08A welding steel wire rod billet according to claim 1, characterized in that The chemical composition of the H08A welding steel is by weight: C ≤ 0.08 wt%, Si ≤ 0.03 wt%, Mn 0.47 - 0.63 wt%, S ≤ 0.020 wt%, P ≤ 0.020 wt%, O 0.0025 - 0.0045 wt%, V ≤ 0.07 wt%, As ≤ 0.015 wt%, Mo ≤ 0.20 wt%, and the balance is Fe and unavoidable impurities.