A high-purity IF steel production process

Abstract

This invention belongs to the field of iron and steel metallurgical technology, specifically a high-purity IF steel production process. It employs a dual-control system of RH+VD (Reverse Hydrogenation and Vapor Deoxidation). RH is used for decarburization of the molten steel. After RH degassing, a top slag modifier is added, and the steel is then fed into a VD furnace for bottom-blown hydrogen deoxidation and alloying. No deoxidizing alloys are used during this process. This invention separates decarburization and deoxidation, avoiding the safety hazards caused by the coexistence of hydrogen and oxygen. It also utilizes stronger molten pool stirring for efficient pre-deoxidation of the top slag, while bottom-blown reducing gas deoxidation not only reduces oxygen content but also avoids the risk of secondary oxidation of the molten steel by the slag. Furthermore, the degassing capacity of the VD furnace removes residual hydrogen and nitrogen. This invention reduces safety hazards, improves the cleanliness of the molten steel, and increases alloy yield, thus achieving the production of high-purity IF steel.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, specifically a production process for high-purity IF steel. Background Technology

[0002] Interstitial interferometric (IF) steel is widely used in the automotive and home appliance industries. Related research shows that lightweighting of automobiles helps reduce carbon emissions; for every 100kg reduction in vehicle weight, carbon dioxide emissions are reduced by 12.5g / km. Simultaneously, the requirements for controlling non-metallic inclusions in steel are gradually increasing due to the demands of lightweighting. Currently, the commonly used process for producing IF steel both domestically and internationally is BOF / EAF-RH-CC, where decarburization (oxygen blowing) is performed in the RH stage, followed by deoxidation and alloying. The main deoxidation method currently used is aluminum deoxidation, with the main deoxidation products being Al2O3 inclusions and composite inclusions formed by their combination with Ti nitrides. Inclusions are removed by creating slag with high basicity, good fluidity, and low oxidizing properties. This production process is relatively mature, but some problems still exist that cannot be avoided with existing technologies.

[0003] (1) Nozzle blockage: Al2O3 may cause problems such as nodule formation and nozzle blockage in continuous casting submerged entry nozzles during steel production. Due to different requirements for rolled materials, some IF steel production cannot be carried out with calcium treatment to remove modified alumina inclusions. Currently, scholars have proposed a clean deoxidation method based on carbon-oxygen reaction. However, due to the extremely high carbon content requirements of this steel grade, the excess oxygen after decarburization in the RH stage cannot be efficiently removed in this way.

[0004] (2) High basicity slag erosion: High basicity slag, which is used to remove alumina inclusions, may have poor fluidity and cause serious erosion of furnace lining and refractory materials. In addition, high basicity slag has a high melting point, which increases the heat transfer consumption and may cause serious slag entrapment, resulting in large-sized inclusions and affecting the quality of cast billets.

[0005] (3) Rolled product quality: The Young's modulus of hard and brittle Al2O3 is larger than that of steel, which has a greater impact on the quality of rolled products and reduces the product yield. In addition, alumina inclusions may cause local stress concentration in the material, reduce the toughness and ductility of steel, and may also become the initiation point of fatigue cracks, reducing the fatigue life of steel.

[0006] To address the aforementioned issues, some scholars have proposed a method of pre-deoxygenation by injecting reducing gas H2 after RH decarbonization. However, this method still has some problems:

[0007] (1) After RH oxygen blowing decarbonization, combined hydrogen blowing is used. Under certain conditions, hydrogen and oxygen may coexist. When the oxygen concentration is higher than 4%, there is a safety hazard of explosion.

[0008] (2) The high oxidizing power of the top slag in RH may lead to oxygen transfer from the slag to the steel in the later stage, which will cause secondary oxidation of the molten steel and is not conducive to the control of the oxygen content of the molten steel. After RH decarburization, the kinetic conditions of the top slag upgrading slag are poor. Summary of the Invention

[0009] To address the problems existing in the prior art, the main objective of this invention is to propose a high-purity IF steel production process.

[0010] To address the aforementioned technical problems, according to one aspect of the present invention, the present invention provides the following technical solution:

[0011] A high-purity IF steel production process is achieved through RH+VD dual control. The RH furnace is used for decarburization of the molten steel. After the RH furnace is ventilated, a top slag modifier is added, and the steel is then fed into the VD furnace for bottom-blown hydrogen deoxidation and alloying. No deoxidizing alloys are used in the process.

[0012] As a preferred embodiment of the high-purity IF steel production process described in this invention, the production process specifically includes: KR pretreatment, converter smelting, RH, VD, and continuous casting.

[0013] As a preferred embodiment of the high-purity IF steel production process described in this invention, the following is specified: KR pretreatment is used for molten iron desulfurization, requiring the [S] content in the molten iron after treatment to be ≤40×10⁻⁶. -6 .

[0014] As a preferred embodiment of the high-purity IF steel production process described in this invention, the following are specified: the scrap steel ratio in the converter smelting is controlled to be ≤20%; the FeO content in the slag is maintained at ≥15wt% during the mid-blowing stage and ≤20wt% during the final blowing stage; the converter endpoint temperature is controlled at 1690~1710℃, and the endpoint [C] content is controlled at (300~450)×10 -6 The endpoint [P] content is ≤100×10 -6 The endpoint [S] content is ≤50×10 -6 The endpoint [O] content is ≥500×10 -6 Carbon-free steel ladles are used for tapping; 1-3 kg / t of steel is added during tapping. 钢 Lime.

[0015] As a preferred embodiment of the high-cleanliness IF steel production process described in this invention, the following steps are taken: the ladle car is driven to the RH station, the riser and downcomer of the RH vacuum device are immersed in the molten steel, and vacuuming begins with the circulation activated; a five-stage vacuum pump is used to evacuate to 40–60 kPa and maintain the vacuum for 3–5 minutes, then a four-stage pump is started to evacuate to 5–15 kPa and maintain the vacuum level; forced decarburization begins at the lower oxygen lance, with an oxygen supply intensity of 1200–4500 NL / t. 钢The oxygen blowing rate is 8-15 min; the third-stage pump, second-stage pump, and first-stage pump are turned on sequentially, maintaining each pump for 1 min after each stage is turned on. After turning on the last stage pump, the vacuum level in the vacuum chamber is ≤67 Pa, and the vacuum level is maintained for 6-12 min for natural decarburization; the vacuum chamber is then broken out of the station, and the [C] content is required to be ≤12×10⁻⁶ Pa. -6 The required temperature of the molten steel is 1665–1690℃.

[0016] As a preferred embodiment of the high-purity IF steel production process described in this invention, 0.4–1.5 kg / t of RH is added after the RH outlet. 钢 An aluminum-containing top slag modifier is used, with the top slag basicity controlled at 1-2 and FeO+MnO controlled at ≤10wt%; it is then fed into the VD station. Preferably, the aluminum-containing top slag modifier, by mass percentage, comprises: Al: 40%-50%, CaO: 5%-10%, and Al2O3: 40%-55%.

[0017] As a preferred embodiment of the high-cleanliness IF steel production process described in this invention, after entering the VD station, the ladle is covered and then a hydrogen-inert gas mixture with a hydrogen content of 10-50 vol% is blown in through the bottom permeable bricks. Multiple bottom blowing holes can be selected for bottom blowing, with a total gas supply intensity of 1000-6500 NL / t. 钢 The blowing rate is 10-35 min; at the start of blowing, the vacuum pump is simultaneously turned on to create a vacuum, and the vacuum level in the vacuum chamber is reduced to below 2 kPa; at the end of blowing, the vacuum level in the vacuum chamber is adjusted to ≤67 Pa, and argon is blown into the molten steel using bottom-blowing permeable bricks to assist in degassing, with a total argon intensity of 1000-3000 NL / t. 钢 / min, argon blowing time 6-10min; VD outlet requires molten steel temperature of 1600-1620℃, molten steel [C] content ≤12×10 -6 [O] content ≤10×10 -6 [P] content ≤110×10 -6 [N] content ≤20×10 -6 [H] content ≤ 2.5 × 10 -6 [S] content ≤35×10 -6 .

[0018] As a preferred embodiment of the high-purity IF steel production process described in this invention, the required amount of alloy to be added is calculated based on the composition of the molten steel from the VD (Vacuum Distillation) tapping process; after adding the alloy, soft blowing is performed for 5-10 minutes to ensure uniform composition of the molten steel; after alloying, the temperature of the molten steel is controlled at 1585-1605℃, and the [C] content in the molten steel is ≤15×10⁻⁶. -6 [Si] content ≤ 60 × 10 -6 The [Mn] content is (800~1200)×10 -6[P] content ≤110×10 -6 [S] content ≤40×10 -6 [Ti] content ≤120×10 -6 [Als] content ≤10×10 -6 [O] content ≤15×10 -6 [N] content ≤25×10 -6 [H] content ≤ 2.5 × 10 -6 .

[0019] As a preferred embodiment of the high-purity IF steel production process described in this invention, the following features are included: continuous casting employs protective casting measures to strictly prevent secondary oxidation of the molten steel, and the tundish temperature is controlled between 1552 and 1566°C; the crystallizer covering agent is an ultra-low carbon covering agent; protective casting is performed throughout the continuous casting process, and the oxygen increase during the process is required to be less than 3 × 10⁻⁶. -6 Nitrogen increase less than 3×10 -6 .

[0020] The beneficial effects of this invention are as follows:

[0021] This invention proposes a high-purity IF steel production process. Through dual control of RH+VD (Reverse Hydrogenation and Vapor Deoxidation), RH is used for decarburization of the molten steel. After RH degassing, a top slag modifier is added, and the steel is then fed into a VD furnace for bottom-blown hydrogen deoxidation and alloying. No deoxidizing alloys are used during this process. By separating decarburization and deoxidation, this invention avoids the safety hazards caused by the coexistence of hydrogen and oxygen. It also allows for efficient pre-deoxidation of the top slag through stronger molten pool stirring, while bottom-blown reducing gas deoxidation not only reduces the oxygen content but also avoids the risk of secondary oxidation of the molten steel by the slag. Furthermore, the degassing capacity of the VD furnace removes residual hydrogen and nitrogen. This invention reduces safety hazards, improves the cleanliness of the molten steel, and increases alloy yield, thus achieving the production of high-purity IF steel. Detailed Implementation

[0022] The technical solutions described below in conjunction with the embodiments will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the 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.

[0023] This invention provides a high-purity IF steel production process, which involves decarburization (forced deep decarburization by oxygen blowing and natural decarburization) only in the RH reactor; after leaving the RH reactor, top slag is modified and pre-deoxidized, followed by reducing gas pre-deoxidation in the VD reactor, and then removal of H, N and other gaseous elements under vacuum; this method avoids the presence of hydrogen and oxygen in the same reactor, reducing the risk of explosion due to excessive gas concentration; the top slag pre-deoxidation and modification after leaving the RH reactor, and the rapid and uniform slag composition through bottom blowing, prevent secondary oxidation of the steel by the slag; and the process can be improved by adding [missing information - likely a specific ingredient or process] to the VD reactor. Desulfurizing agents such as CaO and Mg reduce the desulfurization burden on the KR desulfurization station; H2O bubbles generated by hydrogen injection and bottom-blown argon effectively float inclusions and slag in the molten steel to the surface; all added alloys are used for alloying, reducing the amount of alloys used and saving energy and carbon emissions in the alloy production process; the cleanliness of the molten steel is significantly improved, which is beneficial to the improvement of the steel's mechanical properties; the reduced slag basicity improves the life of the furnace lining and refractory materials, reduces problems such as slag entrapment, and extends the life of the ladle; the improved cleanliness of the steel contributes to the lightweighting of automobiles.

[0024] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0025] Example 1

[0026] This embodiment describes a high-purity IF steel production process, including the following steps:

[0027] (1) KR pretreatment is used for desulfurization of molten iron, and the [S] content in the molten iron after treatment is required to be 40×10⁻⁶. -6 .

[0028] (2) The scrap ratio in the converter smelting is controlled at 18%; the FeO content in the slag is maintained at 15wt% during the middle stage of blowing and 18wt% during the end stage of blowing; the final converter temperature is controlled at 1699℃, the steel volume is 202t, and the final [C] content is controlled at 320×10⁻⁶. -6 The endpoint [P] content was 93 × 10⁻⁶. -6 The endpoint [S] content was 40 × 10⁻⁶. -6 The endpoint [O] content was 735 × 10⁻⁶. -6 The steel is tapped using a carbon-free steel ladle; 505 kg of lime is added during tapping.

[0029] (3) Drive the ladle car to the RH station, the temperature is measured to be 1688℃, and the oxygen content is measured to be 680×10. -6 The riser and downcomer of the RH vacuum unit are immersed in the molten steel, and vacuuming begins with the circulation activated. A five-stage vacuum pump is used to evacuate to 50 kPa, and a four-stage pump is started to continue evacuating to 10 kPa to maintain the vacuum level. Forced decarburization begins at the lower oxygen lance, with an oxygen supply intensity of 2200 NL / t. 钢The oxygen blowing rate was 11 min; the third-stage pump, second-stage pump, and first-stage pump were started sequentially, and each pump was maintained for 1 min after starting. After starting the last-stage pump, the vacuum degree in the vacuum chamber was 67 Pa, and the vacuum degree was maintained for 7 min for natural decarburization; the vacuum chamber was then broken out of the station, and the [C] content at the exit station was 7 × 10⁻⁶ Pa. -6 The [O] content is 452 × 10⁻⁶. -6 The temperature of the molten steel was 1671℃.

[0030] (4) After leaving the RH station, add 96 kg of aluminum-containing top slag modifier, and control the top slag CaO / Al2O3 at 1.5 and FeO+MnO at 10wt%; then send it to the VD station.

[0031] (5) After entering the VD station, the ladle is covered and a hydrogen-argon mixture with a hydrogen content of 30 vol% is blown in through the three bottom permeable bricks, with a total gas supply intensity of 5400 NL / t. 钢 The blowing rate was set at 20 min, with a blowing time of 20 min. Simultaneously, a vacuum pump was activated at the start of blowing to create a vacuum chamber, lowering the vacuum level to below 2 kPa. At the end of blowing, the vacuum level was adjusted to 60 Pa, and argon was blown into the molten steel using three bottom-blowing permeable bricks to assist in degassing, with a total argon intensity of 2400 NL / t. 钢 / min, argon blowing time 8min; VD outlet molten steel temperature 1619℃, molten steel [C] content 12×10 -6 The [O] content is 9×10 -6 [P] content 95×10 -6 [N] content 18×10 -6 [H] content 2×10 -6 [S] content 38×10 -6 The required amount of alloy to be added is calculated based on the composition of the molten steel produced by VD; after adding the alloy, soft blowing for 6 minutes ensures uniform composition of the molten steel; after alloying, the temperature of the molten steel is controlled at 1592℃, and the [C] content in the molten steel is 13×10⁻⁶. -6 The [Si] content is 52 × 10⁻⁶. -6 The [Mn] content is 952 × 10⁻⁶. -6 The [P] content is 85×10 -6 The [S] content is 32×10 -6 The [Ti] content is 110×10 -6 The [Als] content is 9×10 -6 The [O] content is 12 × 10⁻⁶. -6 The [N] content is 22 × 10⁻⁶. -6 The [H] content is 2×10 -6 .

[0032] (6) Protective casting measures are adopted in continuous casting to strictly prevent secondary oxidation of molten steel and control the tundish temperature at 1558-1566℃; ultra-low carbon covering agent is used for the crystallizer covering agent, and protective casting is carried out throughout the continuous casting process, requiring oxygen increase of less than 3×10⁻⁶ during the process. -6 Nitrogen increase less than 3×10 -6 .

[0033] Samples were taken from the cast billet prepared in Example 1, and inclusions in the samples were detected using the ASPEX inclusion automatic scanning system. The number density of inclusions larger than 1 μm was found to be 5.8 inclusions / mm. 2 The average size of the inclusions is 1.6 μm.

[0034] Example 2

[0035] This embodiment describes a high-purity IF steel production process, including the following steps:

[0036] (1) KR pretreatment is used for desulfurization of molten iron, and the [S] content in the molten iron after treatment is required to be 36×10⁻⁶. -6 .

[0037] (2) The scrap ratio in the converter smelting is controlled at 20%; the FeO content in the slag is maintained at 14wt% during the middle stage of blowing and 18wt% during the end stage of blowing; the final converter temperature is controlled at 1695℃, the molten steel volume is 152t, and the final [C] content is controlled at 344×10⁻⁶. -6 The endpoint [P] content was 92 × 10⁻⁶. -6 The endpoint [S] content was 44 × 10⁻⁶. -6 The endpoint [O] content was 766 × 10⁻⁶. -6 The steel is tapped using a carbon-free steel ladle; 380 kg of lime is added during tapping.

[0038] (3) Drive the ladle car to the RH station, the temperature is measured to be 1678℃, and the oxygen content is measured to be 686×10. -6 The riser and downcomer of the RH vacuum unit are immersed in the molten steel, and vacuuming begins with the circulation activated. A five-stage vacuum pump is used to evacuate to 45 kPa, and a four-stage pump is started to evacuate to 10 kPa to maintain the vacuum level. Forced decarburization begins at the lower oxygen lance, with an oxygen supply intensity of 1580 NL / t. 钢 The oxygen blowing rate is 14 min; the third-stage pump, second-stage pump, and first-stage pump are turned on sequentially, and each pump is maintained for 1 min after being turned on. After turning on the last-stage pump, the vacuum degree in the vacuum chamber is 67 Pa, and the vacuum degree is maintained for 8 min for natural decarburization; the vacuum chamber is then broken out of the station, and the required [C] content is 12 × 10⁻⁶ Pa. -6 The [O] content is 385 × 10⁻⁶. -6 The required temperature of the molten steel is 1667℃.

[0039] (4) After leaving the RH station, add 168 kg of aluminum-containing top slag modifier, control CaO / Al2O3 at 1.4, and FeO+MnO at 10wt%; then send it to the VD station.

[0040] (5) After entering the VD station, the ladle is covered and a hydrogen-argon mixture with a hydrogen content of 20 vol% is blown in through the two bottom permeable bricks, with a total gas supply intensity of 4400 NL / t. 钢 The blowing rate was 1 / min, and the blowing time was 23 min. At the start of blowing, the vacuum pump was simultaneously turned on to create a vacuum, lowering the vacuum level in the vacuum chamber to below 2 kPa. At the end of blowing, the vacuum level in the vacuum chamber was adjusted to 67 Pa, and argon was blown into the molten steel using two bottom-blowing permeable bricks to assist in degassing, with a total argon intensity of 2200 NL / t. 钢 / min, argon blowing time 9min; VD outlet molten steel temperature 1620℃, molten steel [C] content 12×10 -6 The [O] content is 10 × 10 -6 [P] content ≤ 96 × 10 -6 [N] content 19×10 -6 [H] content 2.5×10 -6 [S] content 41×10 -6 The required amount of alloy to be added is calculated based on the composition of the molten steel produced by VD; after adding the alloy, soft blowing for 6 minutes ensures uniform composition of the molten steel; after alloying, the temperature of the molten steel is controlled at 1597℃, and the [C] content in the molten steel is 14×10⁻⁶. -6 The [Si] content is 54 × 10⁻⁶. -6 The [Mn] content is 866 × 10⁻⁶. -6 The [P] content is 104 × 10⁻⁶. -6 The [S] content is 34 × 10⁻⁶. -6 The [Ti] content is 103 × 10⁻⁶. -6 The [Als] content is 8×10 -6 The [O] content is 14 × 10⁻⁶. -6 The [N] content is 24 × 10⁻⁶. -6 The [H] content is 2.5 × 10⁻⁶. -6 .

[0041] (6) Protective casting measures are adopted in continuous casting to strictly prevent secondary oxidation of molten steel and control the tundish temperature at 1555-1564℃; ultra-low carbon covering agent is used for the crystallizer covering agent, and protective casting is carried out throughout the continuous casting process, requiring oxygen increase of less than 3×10⁻⁶ during the process. -6 Nitrogen increase less than 3×10 -6 .

[0042] Samples were taken from the cast billet prepared in Example 2, and inclusions in the samples were detected using the ASPEX inclusion automatic scanning system. The number density of inclusions larger than 1 μm was found to be 6.6 inclusions / mm. 2 The average size of the inclusions is 2 μm.

[0043] Comparative Example 1

[0044] This comparative example illustrates a vacuum carburizing and deoxidizing process for IF steel (RH), comprising the following steps:

[0045] (1) KR pretreatment is used for desulfurization of molten iron, and the [S] content in the molten iron after treatment is required to be 42×10⁻⁶. -6 .

[0046] (2) The scrap ratio in the converter smelting is controlled at 19%; the FeO content in the slag is maintained at 17wt% during the middle stage of blowing and 22wt% at the end stage of blowing; the converter tapping temperature is 1708℃, the steel volume is 154t, and the final [C] content is controlled at 212×10⁻⁶. -6 The endpoint [P] content was 91 × 10⁻⁶. -6 The endpoint [S] content was 44 × 10⁻⁶. -6 The endpoint [O] content was 920 × 10⁻⁶. -6 The molten steel is not deoxidized before entering the ladle, and no alloying or carbonizing agents are added. 310 kg of lime is added when the steel is tapped.

[0047] (3) RH arrived at the station, the temperature was 1665℃, and the oxygen concentration was 894×10⁻⁶. -6 RH is evacuated and the circulating flow is turned on. The argon blowing intensity in the riser is 6500 NL / t. 钢 A five-stage vacuum pump was used to evacuate the steel to 50 kPa, and a fourth-stage pump was started to evacuate it to 10 kPa to maintain the vacuum. 83 kg of a recarburizing agent containing 92% carbon was added to the molten steel. After adding the recarburizing agent, the third-stage pump, second-stage pump, and first-stage pump were started sequentially, maintaining each pump for 1 minute. After starting the last stage pump, the vacuum in the vacuum chamber was brought to 67 Pa. The molten steel was circulated for 10 minutes for deep decarburization. After decarburization, the oxygen content was determined to be 220 × 10⁻⁶ kPa. -6 [C] content 29×10 -6 Add 38 kg of aluminum granules for deoxidation, and supplement with alloy according to the RH alloy content of the molten steel. After adding the alloy, soft blow for 6 minutes to ensure uniform composition of the molten steel. After alloying, the temperature of the molten steel is controlled at 1586℃, and the [C] content in the molten steel is 30 × 10⁻⁶. -6 The [Si] content is 52 × 10⁻⁶. -6 The [Mn] content is 912×10 -6 The [P] content is 93 × 10⁻⁶. -6 The [S] content is 45×10 -6The [Ti] content is 103 × 10⁻⁶. -6 The [Als] content is 210 × 10⁻⁶. -6 The [O] content is 23 × 10⁻⁶. -6 The [N] content is 27 × 10⁻⁶. -6 The [H] content is 2×10 -6 .

[0048] (6) Protective casting measures are adopted in continuous casting to strictly prevent secondary oxidation of molten steel and control the tundish temperature at 1557-1565℃; ultra-low carbon covering agent is used for the crystallizer, and protective casting is carried out throughout the continuous casting process, requiring oxygen increase of less than 3×10⁻⁶ during the process. -6 Nitrogen increase less than 3×10 -6 .

[0049] Samples were taken from the cast billet prepared in Comparative Example 1. Inclusions in the samples were detected using the ASPEX inclusion automatic scanning system. The number density of inclusions larger than 1 μm was found to be 13.4 inclusions / mm. 2 The average size of the inclusions is 4.8 μm.

[0050] Comparative Example 2

[0051] This comparative example illustrates a production process for IF steel using RH+VD, including the following steps:

[0052] (1) KR pretreatment is used for desulfurization of molten iron, and the [S] content in the molten iron after treatment is required to be 42×10⁻⁶. -6 .

[0053] (2) The scrap ratio in the converter smelting is controlled at 19%; the FeO content in the slag is maintained at 15wt% during the middle stage of blowing and 19wt% at the end stage of blowing; the final converter temperature is controlled at 1697℃, the steel volume is 206t, and the final [C] content is controlled at 314×10⁻⁶. -6 The endpoint [P] content was 95 × 10⁻⁶. -6 The endpoint [S] content was 45 × 10⁻⁶. -6 The endpoint [O] content was 802 × 10⁻⁶. -6 The steel is tapped using a carbon-free steel ladle; 553 kg of lime is added during tapping.

[0054] (3) Drive the ladle car to the RH station, the temperature is measured to be 1683℃, and the oxygen content is measured to be 731×10. -6 The riser and downcomer of the RH vacuum unit are immersed in the molten steel, and vacuuming begins with the circulation activated. A five-stage vacuum pump is used to evacuate to 50 kPa, and a four-stage pump is started to continue evacuating to 10 kPa to maintain the vacuum level. Forced decarburization begins at the lower oxygen lance, with an oxygen supply intensity of 1000 NL / t. 钢The oxygen blowing rate was 14 min; the third-stage pump, second-stage pump, and first-stage pump were started sequentially, and each pump was maintained for 1 min after starting. After starting the last-stage pump, the vacuum degree in the vacuum chamber was 80 Pa, and the vacuum degree was maintained for 5 min for natural decarburization; the vacuum chamber was then broken out of the station, and the [C] content at the exit station was 23 × 10⁻⁶ Pa. -6 The [O] content is 472 × 10⁻⁶. -6 The temperature of the molten steel was 1671℃.

[0055] (4) After leaving the RH station, add 124 kg of aluminum-containing top slag modifier, and control the top slag CaO / Al2O3 at 1.5 and FeO+MnO at 10wt%; send it to the VD station.

[0056] (5) After entering the VD station, the ladle is covered and then a hydrogen-argon mixture with a hydrogen content of 30 vol% is blown in through the three bottom permeable bricks, with a total gas supply intensity of 6900 NL / t. 钢 The blowing rate was 18 min, and the blowing time was 18 min. At the start of blowing, the vacuum pump was simultaneously activated to create a vacuum chamber, bringing the vacuum level to below 2 kPa. At the end of blowing, the vacuum level was adjusted to 67 Pa, and argon was blown into the molten steel using three bottom-blowing permeable bricks to assist in degassing, with a total argon intensity of 2700 NL / t. 钢 / min, argon blowing time 6min; VD outlet molten steel temperature 1608℃, molten steel [C] content 23×10 -6 The [O] content is 9×10 -6 [P] content 98×10 -6 [N] content 18×10 -6 [H] content 4.5 × 10 -6 [S] content 44×10 -6 The required amount of alloy to be added is calculated based on the composition of the molten steel produced by VD; after adding the alloy, soft blowing for 7 minutes ensures uniform composition of the molten steel; after alloying, the temperature of the molten steel is controlled at 1594℃, and the [C] content in the molten steel is 25×10⁻⁶. -6 The [Si] content is 55 × 10⁻⁶. -6 The [Mn] content is 954 × 10⁻⁶. -6 The [P] content is 98 × 10⁻⁶. -6 The [S] content is 44 × 10⁻⁶. -6 The [Ti] content is 113 × 10⁻⁶. -6 The [Als] content is 10 × 10 -6 The [O] content is 10 × 10 -6 The [N] content is 23 × 10⁻⁶. -6 The [H] content is 4×10 -6 .

[0057] (6) Protective casting measures are adopted in continuous casting to strictly prevent secondary oxidation of molten steel and control the tundish temperature at 1553-1564℃; ultra-low carbon covering agent is used for the crystallizer covering agent, and protective casting is carried out throughout the continuous casting process, requiring oxygen increase of less than 3×10⁻⁶ during the process. -6 Nitrogen increase less than 3×10 -6 .

[0058] Samples were taken from the cast billet prepared in Comparative Example 1. Inclusions in the samples were detected using the ASPEX inclusion automatic scanning system. The number density of inclusions larger than 1 μm was found to be 7.9 inclusions / mm. 2 The average size of the inclusions is 2.9 μm.

[0059] This invention employs a dual RH+VD control system. RH is used for decarburization of molten steel, followed by the addition of a top slag modifier after RH degassing, before the steel is fed into a VD furnace for bottom-blown hydrogen deoxidation and alloying. No deoxidizing alloys are used during this process. By separating decarburization and deoxidation, this invention avoids the safety hazards caused by the coexistence of hydrogen and oxygen. It also allows for efficient pre-deoxidation of the top slag through stronger molten pool stirring, while bottom-blown reducing gas deoxidation not only reduces oxygen content but also avoids the risk of secondary oxidation of the molten steel by the slag. Furthermore, the degassing capacity of the VD furnace removes residual hydrogen and nitrogen. This invention reduces safety hazards, improves the cleanliness of the molten steel, and increases alloy yield, achieving the production of high-cleanliness IF steel.

[0060] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A high-purity IF steel production process, characterized in that, include: KR pretreatment, converter smelting, RH, VD, continuous casting; KR pretreatment is used for desulfurization of molten iron, requiring the [S] content in the molten iron after treatment to be ≤40×10⁻⁶. -6 ; In converter smelting, the scrap steel ratio in the furnace should be controlled to be ≤20%; during the mid-blowing stage, the FeO content in the slag should be maintained at ≥15wt%, and at the end of the blowing stage, the FeO content in the slag should be ≤20wt%; the converter final temperature should be controlled at 1690~1710℃, and the final [C] content should be controlled at (300~450)×10 -6 The endpoint [P] content is ≤100×10 -6 The endpoint [S] content is ≤50×10 -6 The endpoint [O] content is ≥500×10 -6 Carbon-free steel ladles are used for tapping; 1~3 kg / t of steel is added during tapping. 钢 lime; Drive the ladle car to the RH station, immerse the riser and downcomer of the RH vacuum unit in the molten steel, and begin vacuuming and circulation. Use a five-stage vacuum pump to evacuate to 40-60 kPa and maintain for 3-5 minutes, then start a four-stage pump to evacuate to 5-15 kPa and maintain the vacuum level. Begin forced decarburization with the lower oxygen lance, supplying oxygen at a rate of 1200-4500 NL / t. 钢 The oxygen blowing rate is 8-15 min; the third-stage pump, second-stage pump, and first-stage pump are turned on sequentially, maintaining each pump for 1 min after each stage is turned on. After turning on the last stage pump, the vacuum level in the vacuum chamber is ≤67 Pa, and the vacuum level is maintained for 6-12 min for natural decarburization; the vacuum chamber is then broken out of the station, and the [C] content is required to be ≤12×10⁻⁶ Pa. -6 The required temperature of the molten steel is 1665~1690℃; After entering the VD station, the ladle is covered and then a hydrogen-inert gas mixture with a hydrogen content of 10-50 vol% is blown in through the bottom permeable bricks, with a total gas supply intensity of 1000-6500 NL / t. 钢 The blowing rate is 10-35 min, and the blowing time is 10-35 min. At the start of blowing, the vacuum pump is simultaneously turned on to create a vacuum, bringing the vacuum level in the vacuum chamber below 2 kPa. At the end of blowing, the vacuum level in the vacuum chamber is adjusted to ≤67 Pa, and argon is blown into the molten steel using bottom-blowing permeable bricks to assist in degassing. The total argon intensity is 1000-3000 NL / t. 钢 / min, argon blowing time 6~10min; VD outlet requires molten steel temperature of 1600~1620℃, molten steel [C] content ≤12×10 -6 [O] content ≤10×10 -6 [P] content ≤110×10 -6 [N] content ≤20×10 -6 [H] content ≤ 2.5 × 10 -6 [S] content ≤35×10 -6 ; Continuous casting employs protective casting measures to strictly prevent secondary oxidation of the molten steel, controlling the tundish temperature between 1552 and 1566℃; ultra-low carbon covering agents are used in the crystallizer, and protective casting is carried out throughout the continuous casting process, requiring oxygen increase to be less than 3 × 10⁻⁶. -6 Nitrogen increase less than 3×10 -6 .

2. The high-purity IF steel production process according to claim 1, characterized in that, Add 0.4~1.5 kg / t of RH after it leaves the station. 钢 The aluminum-containing top slag modifier is prepared with the top slag basicity controlled at 1~2 and the FeO+MnO controlled at ≤10wt% and sent to the VD station.

3. The high-purity IF steel production process according to claim 1, characterized in that, The required amount of alloy to be added is calculated based on the composition of the molten steel produced by VD (Volume Deposition). After adding the alloy, soft blowing for 5-10 minutes is performed to ensure uniform composition of the molten steel. After alloying, the temperature of the molten steel should be controlled at 1585-1605℃, and the [C] content in the molten steel should be ≤15×10⁻⁶. -6 [Si] content ≤ 60 × 10 -6 The [Mn] content is (800~1200)×10 -6 [P] content ≤110×10 -6 [S] content ≤40×10 -6 [Ti] content ≤120×10 -6 [Als] content ≤10×10 -6 [O] content ≤15×10 -6 [N] content ≤25×10 -6 [H] content ≤ 2.5 × 10 -6 .