Production process of high-cleanliness ultra-low-carbon steel

Abstract

This invention belongs to the field of iron and steel metallurgy technology, specifically a production process for high-purity ultra-low carbon steel. It employs a dual RH+VOD control system. After RH decarburization treatment, the molten steel is fed into a VOD furnace. Once the VOD reaches the required vacuum level, hydrogen is blown onto the slag surface using a top lance. Simultaneously, gas is blown through bottom permeable bricks. Bottom hydrogen blowing deoxidizes the molten steel, while top hydrogen blowing onto the slag surface deoxidizes the slag and modifies it. After breaking up the voids, alloying is performed without using deoxidizing alloys. This invention offers high safety, effectively treating gas emissions; top hydrogen blowing reduces slag oxidizability, minimizing secondary oxidation of the molten steel; it increases Fe recovery from the slag and reduces iron loss; low-oxygen conditions improve alloy yield and reduce alloy oxidation consumption; favorable kinetic conditions facilitate efficient flotation of inclusions in the molten steel; and significantly improves the cleanliness of the molten steel, contributing to improved mechanical properties and lightweighting of automobiles.

Description

Technical Field

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

[0002] In the production of ultra-low carbon steel, some scholars have proposed hydrogen blowing deoxidation in the refining steps of AOD, RH, and RH+VD. This clean deoxidation method avoids the formation of oxide inclusions. However, due to oxygen diffusion at the slag-steel interface, when the oxygen content is below the slag / steel oxygen content equilibrium point, oxygen is transferred from the steel to the slag, achieving diffusion deoxidation. Conversely, when the oxygen content is above the slag / steel oxygen content equilibrium point, oxygen is transferred from the slag to the steel, resulting in secondary oxidation. While hydrogen blowing deoxidation can reduce the oxygen content to a low level, unstable control of the oxygen content in the slag can lead to poor final oxygen content control. Currently, when using top slag modifiers, there are still some problems that cannot be avoided with existing technologies.

[0003] (1) When the top slag is pre-deoxidized using a pre-deoxidizing agent, if the amount added is too small, it will not be able to pre-deoxidize the slag efficiently. If the amount added is too large, it will not only affect the fluidity and other properties of the refining slag, but also cause Al2O3 to diffuse into the molten steel.

[0004] (2) The process of adding modifiers to the surface of ladle slag after tapping may generate smoke and dust, which may pollute the environment.

[0005] (3) Inaccurate calculation of the amount of modifier added will lead to large fluctuations in the total iron content of the ladle top slag;

[0006] (4) After the RH immersion tube is lowered, the slag layer is thick, and it is difficult to mix after adding the top slag modifier. Overblowing at the bottom may expose the molten steel. Insufficient bottom blowing flow rate results in poor mixing effect.

[0007] (5) Excessive FeO content in slag will increase iron loss. Summary of the Invention

[0008] To address the problems existing in the prior art, the main objective of this invention is to propose a production process for high-purity ultra-low carbon steel.

[0009] To address the aforementioned technical problems, according to one aspect of the present invention, the present invention provides the following technical solution:

[0010] A production process for high-purity ultra-low carbon steel involves dual control of RH and VOD. The molten steel is decarburized by RH and then fed into the VOD furnace. Once the VOD reaches the required vacuum level, hydrogen is blown onto the slag surface through the top lance. At the same time, air is blown through the bottom permeable bricks. Bottom hydrogen blowing deoxidizes the molten steel, while top hydrogen blowing on the slag surface deoxidizes the steel slag and modifies the top slag. After breaking the void, alloying is carried out without using deoxidizing alloys.

[0011] As a preferred embodiment of the production process for high-purity ultra-low carbon steel described in this invention, the production process specifically includes: KR pretreatment, converter smelting, RH, VOD, and continuous casting.

[0012] As a preferred embodiment of the production process for high-purity ultra-low carbon steel described in this invention, the following is specified: KR pretreatment is used for desulfurization of molten iron, requiring the [S] content in the molten iron after treatment to be ≤50×10⁻⁶. -6 .

[0013] As a preferred embodiment of the production process for high-purity ultra-low carbon steel described in this invention, the following features are specified: the scrap steel ratio in the converter smelting is controlled to be ≤22%; the FeO content at the end of the blowing process is 22wt%; the converter endpoint temperature is controlled at 1690~1710℃, and the endpoint [C] content is controlled at (320~480)×10⁻⁶. -6 The endpoint [P] content is ≤90×10 -6 The endpoint [S] content is ≤55×10 -6 The endpoint [O] content is ≥480×10 -6 Carbon-free steel ladles are used for tapping; 0.8–3.5 kg / t of steel is added during tapping. 钢 Lime.

[0014] As a preferred embodiment of the production process for high-purity ultra-low carbon steel described in this invention, the ladle car is driven to the RH station, and vacuuming and circulation are initiated; a five-stage / four-stage vacuum pump is used to evacuate to 5-15 kPa and maintain the vacuum level; forced decarburization begins with the lower oxygen lance, and the oxygen blowing intensity is 1200-4200 NL / t. 钢 The oxygen blowing rate is 5–18 min; after decarbonization, the third-stage pump, second-stage pump, and first-stage pump are started sequentially after a 1-minute interval. After starting the first-stage pump, the vacuum level in the vacuum chamber is maintained at ≤67 Pa, and natural decarbonization is carried out for 5–20 min. After decarbonization, the vacuum chamber is broken open and the product leaves the station. The requirement for leaving the station is that the [C] content is ≤15×10⁻⁶. -6 The required temperature for molten steel is 1662–1688℃.

[0015] As a preferred embodiment of the production process for high-purity ultra-low carbon steel described in this invention, the RH is directly sent to the VOD station without the addition of top slag modifier after leaving the station.

[0016] As a preferred embodiment of the production process for high-purity ultra-low carbon steel described in this invention, the process involves: after entering the VOD station, the ladle is covered and vacuum treatment begins. When the vacuum level reaches 1500–3500 Pa, the top lance is lowered above the slag surface, and a hydrogen-inert gas mixture with a hydrogen content of 10–50% is injected at an intensity of 1500–4500 NL / t. 钢The blowing rate is 10% to 50%, and the blowing time is 8 to 20 minutes. Simultaneously, a hydrogen-inert gas mixture with a hydrogen content of 10% to 50% 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 1200 to 6000 NL / t. 钢 The blowing rate is 1 / min, and the blowing time is 8–30 min. When the blowing rate reaches 50%, the vacuum degree is further reduced. When the hydrogen blowing ends, the vacuum degree of the vacuum chamber is adjusted to ≤67 Pa. Argon is blown into the molten steel using bottom-blowing permeable bricks to assist in degassing. The total gas supply intensity is 1200–4500 NL / t. 钢 The blowing rate is 5-15 min; the VOD outlet temperature of the molten steel is required to be 1585-1630℃, and the [C] content of the molten steel is ≤15×10⁻⁶. -6 [O] content ≤15×10 -6 [P] content ≤90×10 -6 [N] content ≤30×10 -6 [H] content ≤ 3 × 10 -6 [S] content ≤50×10 -6 .

[0017] As a preferred embodiment of the production process for high-purity ultra-low carbon steel described in this invention, the required amount of alloy to be added is calculated based on the composition of the VOD-exported molten steel; 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 required to be controlled at 1570-1595℃, and the [C] content in the molten steel is ≤15×10⁻⁶. -6 [Si] content ≤ 55 × 10 -6 The [Mn] content is in the range of (900-1300)×10 -6 [P] content ≤90×10 -6 [S] content ≤50×10 -6 [Ti] content ≤110×10 -6 [Als] content ≤15×10 -6 [O] content ≤15×10 -6 [N] content ≤30×10 -6 [H] content ≤ 3 × 10 -6 .

[0018] As a preferred embodiment of the production process for high-purity ultra-low carbon steel 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 1554 and 1570°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 .

[0019] The beneficial effects of this invention are as follows:

[0020] This invention proposes a production process for high-purity ultra-low carbon steel. Through dual RH+VOD control, the molten steel undergoes RH decarburization treatment before being fed into the VOD furnace. Once the VOD reaches the required vacuum level, hydrogen is blown onto the slag surface using a top lance, while simultaneously blowing gas through bottom permeable bricks. Bottom hydrogen blowing deoxidizes the molten steel, while top hydrogen blowing onto the slag surface deoxidizes the slag and modifies it. After breaking up the voids, alloying is performed without using deoxidizing alloys. This invention offers high safety, effectively controlling gas emissions; top hydrogen blowing reduces slag oxidizability, minimizing secondary oxidation of the molten steel; it increases Fe recovery from the slag and reduces iron loss; low-oxygen conditions improve alloy yield and reduce alloy oxidation consumption; favorable kinetic conditions facilitate efficient flotation of inclusions in the molten steel; and significantly improves the cleanliness of the molten steel, contributing to enhanced mechanical properties and lightweighting of automobiles. Detailed Implementation

[0021] 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.

[0022] This invention provides a production process for high-purity ultra-low carbon steel. It is a method for pre-deoxidation without using deoxidizing alloys such as aluminum particles or pre-melted slag. This clean top slag pre-deoxidation process reduces iron loss and increases iron recovery from the slag, and is combined with a clean deoxidation process to produce high-purity ultra-low carbon steel. The combination of efficient steel deoxidation using reducing gas and top slag pre-deoxidation not only achieves efficient steel deoxidation but also increases iron recovery from the slag. The gas injection improves the slag kinetics, which is conducive to the deoxidation reaction. The reduction product is pollution-free H2O gas, which also effectively reduces the oxidizing properties of the slag and avoids secondary oxidation of the steel. VOD has degassing capabilities to remove residual H and N.

[0023] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0024] Example 1

[0025] This embodiment describes a production process for high-purity IF steel, including the following steps:

[0026] (1) KR pretreatment is used for desulfurization of molten iron, and the [S] content in the molten iron after treatment is required to be 46×10⁻⁶. -6 .

[0027] (2) The scrap ratio in the converter smelting is controlled at 15%; the FeO content at the end of the blowing process is 24wt%; the final converter temperature is controlled at 1703℃; the molten steel volume is 198t; and the final [C] content is controlled at 340×10⁻⁶. -6 The endpoint [P] content was 86 × 10⁻⁶. -6 The endpoint [S] content was 48 × 10⁻⁶. -6 The endpoint [O] content was 688 × 10⁻⁶. -6 The steel is tapped using a carbon-free steel ladle; 436 kg of lime is added during tapping.

[0028] (3) Drive the ladle car to the RH station, the temperature is measured to be 1688℃, and the oxygen content is measured to be 662×10. -6 Start vacuuming and activate circulation; use a five-stage / four-stage vacuum pump to evacuate to 10 kPa and maintain the vacuum level, then lower the oxygen lance to begin forced decarburization, with an oxygen blowing intensity of 1500 NL / t. 钢 The oxygen blowing rate was 13 min; after decarburization, the third-stage pump, second-stage pump, and first-stage pump were started sequentially at 1-min intervals. After starting the first-stage pump, the vacuum level in the vacuum chamber was maintained at 67 Pa for 10 min for natural decarburization; after decarburization, the vacuum chamber was broken out of the station, and the [C] content at the exit was 13 × 10⁻⁶ Pa. -6 The [O] content is 506 × 10⁻⁶. -6 The top slag FeO content is 27wt%, and the molten steel temperature is 1665℃.

[0029] (4) After leaving the RH station, no top slag modifier is added; the slag is directly sent to the VOD station. Upon entering the VOD station, the ladle is covered and vacuum treatment begins. When the vacuum reaches 3000 Pa, the top lance is lowered above the slag surface, and a hydrogen-argon mixture with a hydrogen content of 30% is injected at an intensity of 2200 NL / t. 钢 The blowing rate is 1800 NL / t, with a blowing time of 12 minutes. Simultaneously, a hydrogen-argon mixture (30% hydrogen) is blown in through the bottom permeable brick, providing a total gas supply of 1800 NL / t. 钢 The blowing rate is 1000 NL / min, and the blowing time is 20 min. When the blowing rate reaches 50%, the vacuum degree is further reduced. When the hydrogen blowing ends, the vacuum degree of the vacuum chamber is adjusted to 67 Pa. Argon is blown into the molten steel to assist in degassing using bottom-blowing permeable bricks. The total gas supply intensity is 2000 NL / t. 钢 / min, blowing time 12min; VOD outlet molten steel temperature 1610℃, molten steel [C] content 13×10 -6 The [O] content is 9×10 -6 [P] content 88×10 -6 [N] content 28×10 -6 [H] content 2.5×10 -6 [S] content 45×10 -6The required amount of alloy to be added is calculated based on the composition of the molten steel produced by VOD; 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 1588℃, 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 932 × 10⁻⁶. -6 The [P] content is 88 × 10⁻⁶. -6 The [S] content is 45×10 -6 The [Ti] content is 102×10 -6 The [Als] content is 12 × 10⁻⁶. -6 The [O] content is 13 × 10⁻⁶. -6 The [N] content is 24 × 10⁻⁶. -6 The [H] content is 2.2 × 10⁻⁶. -6 .

[0030] (5) Protective casting measures are adopted in continuous casting to strictly prevent secondary oxidation of molten steel and control the tundish temperature at 1556-1568℃; 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 .

[0031] Samples were taken from the cast billet prepared in Example 1, and inclusions were detected using the ASPEX inclusion automatic scanning system. The number density of inclusions larger than 1 μm was found to be 4 inclusions / mm. 2 The average size of the inclusions is 1.5 μm.

[0032] Example 2

[0033] This embodiment describes a production process for high-purity IF steel, including the following steps:

[0034] (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 .

[0035] (2) The scrap ratio in the converter smelting is controlled at 21%; the FeO content at the end of the blowing process is 21wt%; the converter final temperature is required to be controlled at 1698℃; the molten steel volume is 122t; and the final [C] content is controlled at 330×10⁻⁶. -6 The endpoint [P] content was 85 × 10⁻⁶. -6 The endpoint [S] content was 47 × 10⁻⁶. -6 The endpoint [O] content was 697 × 10⁻⁶. -6 The steel is tapped using a carbon-free steel ladle; 313 kg of lime is added during tapping.

[0036] (3) Drive the ladle car to the RH station, the temperature is measured to be 1679℃, and the oxygen content is measured to be 661×10. -6 The vacuum process begins with the circulation activated; a five-stage / four-stage vacuum pump is used to evacuate to 8 kPa and maintain the vacuum level. Forced decarbonization begins with the lower oxygen lance, and the oxygen supply intensity is 1600 NL / t. 钢 The oxygen blowing rate was 12 min; after decarburization, the third-stage pump, second-stage pump, and first-stage pump were started sequentially at 1-min intervals. After starting the first-stage pump, the vacuum level in the vacuum chamber was maintained at 67 Pa for 11 min for natural decarburization; after decarburization, the vacuum chamber was broken out of the station, and the [C] content at the exit was 11 × 10⁻⁶ Pa. -6 The [O] content is 403 × 10⁻⁶. -6 The temperature of the molten steel was 1663℃.

[0037] (4) After leaving the RH station, no top slag modifier is added; the slag is directly sent to the VOD station. Upon entering the VOD station, the ladle is covered and vacuum treatment begins. When the vacuum reaches 2800 Pa, the top lance is lowered above the slag surface, and a hydrogen-argon mixture with a hydrogen content of 20% is injected at an intensity of 1800 NL / t. 钢 The blowing rate is 14 min, and a hydrogen-argon mixture with a hydrogen content of 20% is blown in through the bottom permeable brick, with a total gas supply intensity of 2400 NL / t. 钢 The blowing rate was 100 NL / min, and the blowing time was 24 min. When the blowing rate reached 50%, the vacuum degree was further reduced. When the hydrogen blowing ended, the vacuum degree of the vacuum chamber was adjusted to 67 Pa. Argon was blown into the molten steel to assist in degassing using bottom-blowing permeable bricks. The total gas supply intensity was 2100 NL / t. 钢 / min, blowing time 9min; VOD outlet molten steel temperature 1629℃, molten steel [C] content 14×10 -6 The [O] content is 12 × 10⁻⁶. -6 [P] content 89×10 -6 [N] content 26×10 -6 [H] content 2×10 -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 VOD. After adding the alloy, soft blowing for 6 minutes is performed to ensure uniform composition of the molten steel. After alloying, the temperature of the molten steel is required to be controlled at 1591℃, and the [C] content in the molten steel is required to be 12×10⁻⁶. -6 The [Si] content is 50 × 10⁻⁶. -6 The [Mn] content is 1013×10 -6 The [P] content is 88 × 10⁻⁶. -6 The [S] content is 33 × 10⁻⁶. -6 The [Ti] content is 95 × 10⁻⁶. -6 The [Als] content is 10 × 10 -6The [O] content is 14 × 10⁻⁶. -6 The [N] content is 27 × 10⁻⁶. -6 The [H] content is 2×10 -6 .

[0038] (5) Protective casting measures are adopted in continuous casting to strictly prevent secondary oxidation of molten steel and control the tundish temperature at 1554-1569℃; 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 .

[0039] Samples were taken from the cast billet prepared in Example 2, and inclusions were detected using the ASPEX inclusion automatic scanning system. The number density of inclusions larger than 1 μm was found to be 4.3 inclusions / mm. 2 The average size of the inclusions is 1.8 μm.

[0040] Comparative Example 1

[0041] This comparative example illustrates a production process for IF steel, including the following steps:

[0042] (1) KR pretreatment is used for desulfurization of molten iron, and the [S] content in the molten iron after treatment is required to be 43×10⁻⁶. -6 .

[0043] (2) The scrap ratio in the converter smelting process is controlled at 21%; the FeO content at the end of the blowing process is 24wt%; the final converter temperature is controlled at 1699℃; the steel volume is 205t; and the final [C] content is controlled at 312×10⁻⁶. -6 The endpoint [P] content was 86 × 10⁻⁶. -6 The endpoint [S] content was 47 × 10⁻⁶. -6 The endpoint [O] content was 714 × 10⁻⁶. -6 The steel is tapped using a carbon-free steel ladle; 496 kg of lime is added during tapping.

[0044] (3) Drive the ladle car to the RH station, the temperature is measured to be 1679℃, and the oxygen content is measured to be 682×10. -6 Start vacuuming and activate circulation; use a five-stage / four-stage vacuum pump to evacuate to 10 kPa and maintain the vacuum level, then lower the oxygen lance to begin forced decarburization, with an oxygen blowing intensity of 2200 NL / t. 钢The oxygen blowing rate was 11 min / min; after decarburization, 182 kg of aluminum-containing top slag modifier was added, and then the third-stage pump, second-stage pump, and first-stage pump were started sequentially at 1-min intervals. After starting the first-stage pump, the vacuum degree of the vacuum chamber was maintained at 67 Pa for 6 min for natural decarburization; after decarburization, deoxidizer was added according to the oxygen determination results, and after 3 min of circulation, alloy was added according to the test results for alloying. After adjusting the alloy composition, the mixture was circulated for 6 min before being discharged from the station; the RH discharge temperature of the molten steel was 1594℃, and the [C] content in the molten steel was 14×10⁻⁶. -6 The [Si] content is 54 × 10⁻⁶. -6 The [Mn] content is 1011×10 -6 The [P] content is 88 × 10⁻⁶. -6 The [S] content is 47 × 10⁻⁶. -6 The [Ti] content is 106 × 10⁻⁶. -6 The [Als] content was 29 × 10⁻⁶. -6 The [O] content is 23 × 10⁻⁶. -6 The [N] content is 25 × 10⁻⁶. -6 The [H] content is 2×10 -6 .

[0045] (5) Protective casting measures are adopted in continuous casting to strictly prevent secondary oxidation of molten steel and control the tundish temperature at 1558-1569℃; 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 .

[0046] Samples were taken from the cast billet prepared in Comparative 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 10.3 inclusions / mm. 2 The average size of the inclusions is 4.1 μm.

[0047] Comparative Example 2

[0048] This comparative example illustrates a production process for IF steel using RH+VOD, including the following steps:

[0049] (1) KR pretreatment is used for desulfurization of molten iron, and the [S] content in the molten iron after treatment is required to be 43×10⁻⁶. -6 .

[0050] (2) The scrap ratio in the converter smelting is controlled at 18%; the FeO content at the end of the blowing process is 20wt%; the converter final temperature is required to be controlled at 1701℃; the molten steel volume is 125t; and the final [C] content is controlled at 341×10⁻⁶. -6 The endpoint [P] content was 86 × 10⁻⁶. -6The endpoint [S] content was 45 × 10⁻⁶. -6 The endpoint [O] content was 693 × 10⁻⁶. -6 The steel is tapped using a carbon-free steel ladle; 288 kg of lime is added during tapping.

[0051] (3) Drive the ladle car to the RH station, the temperature is measured to be 1683℃, and the oxygen content is measured to be 671×10. -6 The vacuum process begins with the circulation activated; a five-stage / four-stage vacuum pump is used to evacuate to 10 kPa and maintain the vacuum level. Forced decarburization begins with the lower oxygen lance, and the oxygen supply intensity is 1800 NL / t. 钢 The oxygen blowing rate was 13 min; after decarburization, the third-stage pump, second-stage pump, and first-stage pump were started sequentially at 1-minute intervals. After starting the first-stage pump, the vacuum level in the vacuum chamber was maintained at 67 Pa for 13 min for natural decarburization; after decarburization, the vacuum chamber was emptied and the product exited the station with a [C] content of 13 × 10⁻⁶. -6 The [O] content is 413 × 10⁻⁶. -6 The temperature of the molten steel was 1663℃.

[0052] (4) After leaving the RH station, the steel ladle is directly sent to the VOD station. After entering the VOD station, the ladle is covered and vacuum treatment begins. When the vacuum degree reaches 3000Pa, the top gun is lowered above the slag surface, and a hydrogen-argon mixture with a hydrogen content of 10% is injected at an intensity of 1200NL / t. 钢 The blowing rate is 10% / min, and the blowing time is 6min; at the same time, a hydrogen-argon mixture with a hydrogen content of 10% is blown in through the bottom permeable brick, with a total gas supply intensity of 1600NL / t. 钢 The blowing speed was 17 min; the vacuum level was further reduced at the end of top blowing, and the vacuum level in the vacuum chamber was adjusted to 67 Pa at the end of hydrogen blowing. Argon was blown into the molten steel using bottom blowing permeable bricks to assist in degassing, with a total gas supply intensity of 2100 NL / t. 钢 / min, blowing time 10min; VOD outlet molten steel temperature 1618℃, molten steel [C] content 13×10 -6 The [O] content is 25 × 10⁻⁶. -6 [P] content 88×10 -6 [N] content 25×10 -6 [H] content 3×10 -6 [S] content 43×10 -6 The required amount of alloy to be added is calculated based on the composition of the molten steel produced by VOD; after adding the alloy, soft blowing for 6 minutes ensures uniform composition of the molten steel; the temperature of the molten steel after alloying is 1591℃, and the [C] content in the molten steel is 15×10⁻⁶. -6 The [Si] content is 54 × 10⁻⁶. -6 The [Mn] content is 1094 × 10⁻⁶. -6 The [P] content is 85×10-6 The [S] content is 44 × 10⁻⁶. -6 The [Ti] content is 102×10 -6 The [Als] content was 13 × 10⁻⁶. -6 The [O] content is 28 × 10⁻⁶. -6 The [N] content is 27 × 10⁻⁶. -6 The [H] content is 3×10 -6 .

[0053] (5) Protective casting measures are adopted in continuous casting to strictly prevent secondary oxidation of molten steel and control the tundish temperature at 1557-1566℃; 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 .

[0054] Samples were taken from the cast billet prepared in Comparative Example 2, and inclusions were detected using the ASPEX inclusion automatic scanning system. The number density of inclusions larger than 1 μm was found to be 6.3 inclusions / mm. 2 The average size of the inclusions is 3.5 μm.

[0055] This invention employs a dual RH+VOD control system. After RH decarburization treatment, the molten steel is fed into a VOD furnace. Once the required vacuum level is reached, hydrogen is blown onto the slag surface using a top lance. Simultaneously, gas is blown through the bottom permeable bricks. Bottom hydrogen blowing deoxidizes the molten steel, while top hydrogen blowing onto the slag surface deoxidizes the steel slag and simultaneously modifies it. After breaking up the voids, alloying is performed without using deoxidizing alloys. This invention offers high safety and effective gas emission control. Top hydrogen blowing reduces slag oxidizability, minimizing secondary oxidation of the molten steel. It also increases Fe recovery from the slag and reduces iron loss. Low-oxygen conditions improve alloy yield and reduce alloy oxidation consumption. Favorable kinetic conditions facilitate efficient flotation of inclusions in the molten steel. The significantly improved cleanliness of the molten steel contributes to enhanced mechanical properties and lightweighting of automobiles.

[0056] 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 production process for high-purity ultra-low carbon steel, characterized in that, Through RH+VOD dual control, the molten steel is decarburized by RH and then sent to the VOD furnace. After the VOD reaches the vacuum requirement, the top gun blows hydrogen to the slag surface. At the same time, air is blown through the bottom permeable brick. Bottom hydrogen blowing deoxidizes the molten steel, and top hydrogen blowing on the slag surface deoxidizes the steel slag and modifies the top slag. After breaking the void, alloying is carried out. No deoxidizing alloy is used in the process. The production process specifically includes: KR pretreatment, converter smelting, RH, VOD, and continuous casting; Drive the ladle car to the RH station and begin vacuuming and circulation; use a five-stage or four-stage vacuum pump to evacuate to 5~15 kPa and maintain the vacuum level, then lower the oxygen lance to begin forced decarburization, with an oxygen blowing intensity of 1200~4200 NL / t. 钢 The oxygen blowing rate is 5-18 min; after decarburization, the third-stage pump, second-stage pump, and first-stage pump are started sequentially after a 1-minute interval. After starting the first-stage pump, the vacuum level in the vacuum chamber is maintained at ≤67 Pa, and natural decarburization is carried out for 5-20 min. After decarburization, the vacuum chamber is broken and the product leaves the station. The requirement for leaving the station is that the [C] content is ≤15×10⁻⁶ Pa. -6 The required molten steel temperature is 1662~1688℃. After leaving the RH station, no top slag modifier is added; the steel is directly sent to the VOD station. After entering the VOD station, the ladle is covered and vacuum treatment begins. When the vacuum degree reaches 1500~3500Pa, the top lance is lowered above the slag surface, and a hydrogen-inert gas mixture with a hydrogen content of 10~50% is injected at an intensity of 1500~4500NL / t. 钢 The blowing rate is 1000 NL / min, and the blowing time is 8-20 min; at the same time, a hydrogen-inert gas mixture with a hydrogen content of 10-50% is blown in through the bottom permeable brick, and bottom blowing is carried out through multiple bottom blowing holes, with a total gas supply intensity of 1200-6000 NL / t. 钢 The blowing rate is 1200-4500 NL / t, with a blowing time of 8-30 minutes. When the blowing rate reaches 50%, the vacuum level is further reduced. When hydrogen blowing ends, the vacuum level in the vacuum chamber is adjusted to ≤67 Pa. Argon is blown into the molten steel using bottom-blowing permeable bricks to assist in degassing. 钢 / min, blowing time is 5~15min; VOD outlet requirements: molten steel temperature is 1585~1630℃, molten steel [C] content ≤15×10 -6 [O] content ≤15×10 -6 [P] content ≤90×10 -6 [N] content ≤30×10 -6 [H] content ≤ 3 × 10 -6 [S] content ≤50×10 -6 .

2. The production process for high-purity ultra-low carbon steel according to claim 1, characterized in that, KR pretreatment is used for desulfurization of molten iron, requiring the [S] content in the molten iron after treatment to be ≤50×10⁻⁶. -6 .

3. The production process for high-purity ultra-low carbon steel according to claim 1, characterized in that, The scrap steel ratio in the converter smelting process should be controlled to be ≤22%; the FeO content at the end of the blowing process should be ≤25wt%; the final temperature of the converter should be controlled at 1690~1710℃, and the final [C] content should be controlled at (320~480)×10⁻⁶. -6 The endpoint [P] content is ≤90×10 -6 The endpoint [S] content is ≤55×10 -6 The endpoint [O] content is ≥480×10 -6 Carbon-free steel ladles are used for tapping; 0.8~3.5 kg / t of steel is added during tapping. 钢 Lime.

4. The production process for high-purity ultra-low carbon steel 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 VOD. 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 should be controlled at 1570-1595℃, and the [C] content in the molten steel should be ≤15×10⁻⁶. -6 [Si] content ≤ 55 × 10 -6 The [Mn] content is 900×10 -6 -1300×10 -6 [P] content ≤90×10 -6 [S] content ≤50×10 -6 [Ti] content ≤110×10 -6 [Als] content ≤15×10 -6 [O] content ≤15×10 -6 [N] content ≤30×10 -6 [H] content ≤ 3 × 10 -6 .

5. The production process for high-purity ultra-low carbon steel according to claim 1, characterized in that, Continuous casting employs protective casting measures to strictly prevent secondary oxidation of molten steel and control the tundish temperature at 1554~1570℃; the crystallizer covering agent is an ultra-low carbon covering agent, and protective casting is carried out throughout the continuous casting process, requiring oxygen increase of less than 3ppm and nitrogen increase of less than 3ppm.