A production process of ultra-low carbon steel by clean deoxidization

Abstract

The present application belongs to the technical field of steel metallurgy, and specifically relates to a production process of ultra-low carbon steel by a clean deoxidization method, which does not need to add deoxidizers at all, and the deoxidization product generated by hydrogen deoxidization is H2O, which is in a gaseous state at the steelmaking temperature, can be quickly removed from the molten steel, and can adsorb the generated inclusions after the formation of bubbles, thereby realizing secondary purification of the molten steel, and the number of titanium nitride inclusions in the steel is also significantly reduced; the hydrogen blown into the molten steel can be removed to the same level as the conventional smelting method under the joint action of bottom argon blowing and vacuum in the AOD refining furnace; and the alloy added into the molten steel is completely used for alloying, thereby directly reducing the overall energy consumption of steelmaking production and preventing excessive carbon dioxide emission; therefore, the smelting method of the ultra-low carbon steel based on the clean deoxidization method of hydrogen deoxidization can promote the green development process of the steelmaking process, and bring huge environmental and economic benefits.

Description

Technical Field

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

[0002] Problems in the current production of ultra-low carbon steel: (1) Inclusions and nozzle nodules: Ultra-low carbon steel is a typical aluminum deoxidized steel. After adding aluminum to the overoxidized molten steel, a large number of Al2O3 inclusions are formed while the oxygen content can be reduced to an extremely low level. Once oxide inclusions are formed, they need to be removed by means of soft blowing, steel slag adsorption, etc., but none of them can be completely purified. After the steelmaking process, Al2O3 inclusions eventually exist in granular, blocky and clustered forms. Some Al2O3 inclusions form composite inclusions with Ti, which are cubic in shape. The presence of these inclusions has a great negative effect on the rolling and forming of ultra-low carbon steel. In addition, aluminum-containing inclusions are prone to forming nozzle nodules, which affect the normal production process and increase energy consumption. (2) Carbon dioxide emission problem: Under the dual carbon background, the downstream steel industry is paying more and more attention to the carbon emissions of the steel production process. As the world's largest producer of crude steel, my country's steel industry accounts for about 15% of the total national emissions. Reactive metals require direct electrolytic production, so using aluminum directly for deoxidation in ultra-low carbon steel would result in significant energy consumption and increase the carbon emission burden on enterprises. It is evident that existing ultra-low carbon steel production processes suffer from the inability to completely remove Al2O3 inclusions generated during aluminum deoxidation, which easily leads to nodule formation in continuous casting submerged entry nozzles and results in substantial carbon dioxide emissions. Summary of the Invention

[0003] To address the problems existing in the prior art, the main objective of this invention is to propose a production process for ultra-low carbon steel using a clean deoxidation method.

[0004] To address the aforementioned technical problems, according to one aspect of the present invention, the present invention provides the following technical solution:

[0005] A clean deoxidation method for producing ultra-low carbon steel involves blowing hydrogen into an AOD furnace for deoxidation. By controlling the hydrogen blowing regime and the vacuum level in the vacuum chamber, the deoxidation process is stabilized and controlled. No deoxidizer needs to be added during the entire process, which significantly reduces inclusions in the molten steel and carbon emissions from the production process.

[0006] As a preferred embodiment of the ultra-low carbon steel production process using a clean deoxidation method described in this invention, the production process adopts the process route of KR stirring → converter smelting → AOD refining → alloying → continuous casting.

[0007] As a preferred embodiment of the ultra-low carbon steel production process using a clean deoxidation method described in this invention, wherein: KR stirring is used to pre-desulfurize the molten iron, requiring the [S] content in the molten iron after treatment to be ≤50×10⁻⁶. -6 .

[0008] As a preferred embodiment of the ultra-low carbon steel production process using a clean deoxidation method described in this invention, the following features are specified: High-quality low-P and low-S scrap steel is used in the converter smelting, with the scrap steel ratio in the furnace controlled to ≤25%; rapid slag formation is achieved in the initial stage of converter blowing, with a slag formation time ≤4 min; the FeO content in the slag is maintained at ≥10 wt% during the middle stage of blowing; the slag basicity is controlled at 3.0–3.6 in the final stage of blowing, with an FeO content ≤20 wt%; the converter final temperature is required to be controlled at 1690–1710℃, and the final [C] content is controlled at (300–450) × 10⁻⁶. -6 The endpoint [P] content is ≤130×10 -6 .

[0009] As a preferred embodiment of the ultra-low carbon steel production process using a clean deoxidation method described in this invention, the AOD refining process includes initial AOD decarburization, mid-term AOD deoxidation, and final AOD dehydrogenation.

[0010] As a preferred embodiment of the ultra-low carbon steel production process employing a clean deoxidation method as described in this invention, the process includes: Initial decarburization via AOD: After the molten steel arrives at the station, the vacuum pump is turned on to maintain the vacuum level at 5000–15000 Pa. Then, oxygen is blown into the molten steel using an oxygen lance for decarburization. The lance position is selected as 1000–1150 mm, and the oxygen supply intensity is determined by the carbon content of the molten steel, with a value of W. [C] / (250×10 -6 )m 3 / (min·t), oxygen blowing time is 12-18 min; bottom blowing argon flow rate is controlled at 1.2-1.6 m³ / (min·t). 3 / (min·t) ensures that the slag surface can be blown away, exposing the molten steel to oxygen; at the end of the blowing process, the temperature of the molten steel should be 1660~1680℃, and the [C] content should be ≤13×10 -6 .

[0011] As a preferred embodiment of the ultra-low carbon steel production process employing a clean deoxidation method as described in this invention, the process includes: AOD mid-term deoxidation: adjusting the vacuum chamber to 500–2000 Pa, and using bottom-blowing permeable bricks to blow an argon-hydrogen mixture with a hydrogen content of 10–35% into the molten steel, with a gas supply intensity of 1.2–2.5 m³ / min. 3 / (min·t), hydrogen blowing time is 15-35 min; at the end of hydrogen blowing, the temperature of the molten steel should be 1620-1640℃, and the [O] content should be ≤15×10 -6 .

[0012] As a preferred embodiment of the ultra-low carbon steel production process employing a clean deoxidation method as described in this invention, the process includes: AOD final-stage dehydrogenation: adjusting the vacuum chamber vacuum to <67 Pa, and using bottom-blowing permeable bricks to blow pure argon gas into the molten steel at a supply intensity of 1.0–1.8 m³ / s. 3 / (min·t), blowing time is 6-8min; the temperature at AOD outlet is required to be controlled at 1600-1615℃, and the [C] content in the molten steel is ≤15×10⁻⁶. -6 [P] content ≤130×10 -6 [O] content ≤15×10 -6 [N] content ≤30×10 -6 [H] content ≤ 4 × 10 -6 .

[0013] As a preferred embodiment of the ultra-low carbon steel production process using a clean deoxidation method described in this invention, the following steps are taken: during alloying, the amount of alloy to be added is calculated based on the AOD steel composition and the requirements of the finished steel product; after the alloy is added, soft blowing is performed for at least 5 minutes to ensure uniform steel composition; after alloying, the temperature is required to be controlled at 1580~1595℃, and the [C] content in the molten steel is ≤20×10⁻⁶. -6 [Si] content ≤250×10 -6 The [Mn] content is (500~1500)×10 -6 [P] content ≤130×10 -6 [S] content ≤50×10 -6 [O] content ≤18×10 -6 [N] content ≤35×10 -6 [H] content ≤ 4 × 10 -6 .

[0014] As a preferred embodiment of the ultra-low carbon steel production process using a clean deoxidation method described in this invention, the continuous casting adopts protective casting measures to strictly prevent secondary oxidation of the molten steel and controls the tundish temperature at 1558~1573℃.

[0015] The beneficial effects of this invention are as follows:

[0016] This invention proposes a clean deoxidation process for producing ultra-low carbon steel that eliminates the need for deoxidizers and prevents the formation of solid oxide inclusions. The deoxidation product, H2O, produced by hydrogen deoxidation is in a gaseous state at steelmaking temperatures and quickly floats to the surface of the molten steel. Furthermore, the bubbles adsorb existing inclusions, and their dispersion and upward movement achieve a secondary purification of the molten steel, significantly reducing the amount of titanium nitride inclusions. The hydrogen blown into the molten steel is removed to the same level as in conventional smelting methods under the combined action of bottom-blown argon and vacuum in the AOD refining furnace. Alloys added to the molten steel are entirely used for alloying; the deoxidation of aluminum is replaced by hydrogen, reducing the total amount of alloy used. This directly reduces the overall energy consumption of steelmaking and prevents excessive carbon dioxide emissions. Therefore, this clean deoxidation method for ultra-low carbon steel based on hydrogen deoxidation can promote the green development of the steelmaking process, bringing significant environmental and economic benefits. Detailed Implementation

[0017] 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.

[0018] This invention addresses the problem that Al2O3 inclusions generated during aluminum deoxidation in the production of ultra-low carbon steel cannot be completely removed, easily causing nodule formation in the immersion nozzle of continuous casting and resulting in high carbon dioxide emissions. It proposes a clean deoxidation process for ultra-low carbon steel production, in which hydrogen is blown into the AOD furnace for deoxidation. By controlling the hydrogen blowing regime and the vacuum level in the vacuum chamber, the deoxidation process is stabilized. No deoxidizing agent is required throughout the process, significantly reducing inclusions in the molten steel and carbon emissions during production, achieving clean deoxidation. The residual hydrogen content in the steel meets the steel quality requirements.

[0019] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0020] Example 1

[0021] This embodiment illustrates the industrial application of producing ultra-low carbon steel using a clean deoxidation method in a 200t converter.

[0022] (1) Pre-desulfurization of molten iron was performed using KR stirring. After treatment, the [S] content in the molten iron was 46×10⁻⁶. -6 .

[0023] (2) The converter uses high-quality scrap steel with low phosphorus and low sulfur content, with a scrap steel ratio of 20%. Rapid slag formation is achieved in the initial blowing stage, with a slag formation time of 4 minutes. During the middle blowing stage, the FeO content is maintained at approximately 15 wt%. In the final blowing stage, the slag basicity is controlled at 3.1, and the FeO content is 18 wt%. The converter's final temperature is 1695℃, and the final [C] content is controlled at 434 × 10⁻⁶. -6 The endpoint [P] content was 83 × 10⁻⁶. -6 .

[0024] (3) After the molten steel reaches the AOD station, the vacuum pump is turned on to maintain the vacuum at 10000Pa. Then, oxygen is blown into the molten steel to remove carburization using an oxygen lance. The lance position is selected as 1080mm, and the oxygen supply intensity is based on the carbon content of the molten steel, which is 434×10⁻⁶. -6 The value is 1.736m. 3 / (min·t), oxygen blowing time 17 minutes. Bottom blowing argon flow rate controlled at 1.5m³ / min·t. 3 / (min·t) ensures that the slag surface can be blown away, exposing the molten steel to oxygen. At the end of the blowing process, the temperature of the molten steel is 1668℃, and the [C] content is 12×10⁻⁶. -6 .

[0025] (4) Then, adjust the vacuum level of the vacuum chamber to 800 Pa, and use bottom-blowing permeable bricks to blow an argon-hydrogen mixture with a hydrogen content of 20% into the molten steel, with a gas supply intensity of 2.2 m. 3 / (min·t), hydrogen blowing time 29min. At the end of hydrogen blowing, the temperature of the molten steel was 1636℃, and the [O] content was 13×10⁻⁶ / (min·t). -6 .

[0026] (5) Adjust the vacuum level of the vacuum chamber to 13 Pa, and use the bottom-blowing permeable bricks to blow pure argon gas into the molten steel at a supply intensity of 1.6 m³ / s. 3 / (min·t), blowing time 7min. The temperature of AOD at the station outlet is controlled at 1609℃, and the [C] content in the molten steel is 11×10⁻⁶. -6 The [P] content is 86 × 10⁻⁶. -6 The [O] content is 12 × 10⁻⁶. -6 The [N] content is 20 × 10 -6 The [H] content is 4×10 -6 .

[0027] (6) Calculate the required amount of alloying agent to be added based on the steel composition and finished steel product requirements from AOD. After adding the alloy, perform soft blowing for 5 minutes to ensure uniform steel composition. After alloying, control the temperature at 1588℃, and the [C] content in the molten steel should be 14×10⁻⁶. -6 The [Si] content is 221 × 10⁻⁶. -6 The [Mn] content is 966 × 10⁻⁶. -6The [P] content is 86 × 10⁻⁶. -6 The [S] content is 35×10 -6 The [Al] content is 478 × 10⁻⁶. -6 The [Ti] content is 389 × 10⁻⁶. -6 The [O] content is 13 × 10⁻⁶. -6 [N] content 22×10 -6 The [H] content is 4×10 -6 .

[0028] (7) Continuous casting: Take protective casting measures to strictly prevent secondary oxidation of molten steel and control the temperature of the tundish at 1560~1565℃.

[0029] Example 2

[0030] This embodiment illustrates the industrial application of producing ultra-low carbon steel using a clean deoxidation method in a 150t converter.

[0031] (1) Pre-desulfurization of molten iron was performed using KR stirring. After treatment, the [S] content in the molten iron was 38×10⁻⁶. -6 .

[0032] (2) The converter uses high-quality scrap steel with low phosphorus and low sulfur content, with a scrap steel ratio of 15% in the furnace. Rapid slag formation is achieved in the initial blowing stage, with a slag formation time of 3.5 minutes. During the middle blowing stage, the FeO content is maintained at approximately 16%. In the final blowing stage, the slag basicity is controlled at 3.3, and the FeO content is 19%. The converter's final temperature is 1702℃, and the final [C] content is controlled at 359 × 10⁻⁶. -6 The endpoint [P] content was 72 × 10⁻⁶. -6 .

[0033] (3) After the molten steel reaches the AOD station, the vacuum pump is turned on to maintain the vacuum at 11300 Pa. Then, oxygen is blown into the molten steel to remove carburization using an oxygen lance. The lance position is selected as 1150 mm, and the oxygen supply intensity is based on the carbon content of the molten steel, which is 359 × 10⁻⁶. -6 The value is 1.436m. 3 / (min·t), oxygen blowing time 15 minutes. Bottom blowing argon flow rate controlled at 1.4 m³ / t. 3 / (min·t) ensures that the slag surface can be blown away, exposing the molten steel to oxygen. At the end of the blowing process, the temperature of the molten steel is 1676℃, and the [C] content is 10×10 -6 .

[0034] (4) Then, adjust the vacuum level of the vacuum chamber to 650 Pa, and use bottom-blowing permeable bricks to blow an argon-hydrogen mixture with a hydrogen content of 15% into the molten steel, with a gas supply intensity of 1.6 m. 3 / (min·t), hydrogen blowing time 20min. At the end of hydrogen blowing, the temperature of the molten steel was 1630℃, and the [O] content was 12×10⁻⁶ / (min·t).-6 .

[0035] (5) Adjust the vacuum level of the vacuum chamber to 13 Pa, and use the bottom-blowing permeable bricks to blow pure argon gas into the molten steel at a supply intensity of 1.4 m³ / s. 3 / (min·t), blowing time 8min. The temperature of AOD at the station is controlled at 1604℃, and the [C] content in the molten steel is 10×10. -6 The [P] content is 73 × 10⁻⁶. -6 The [O] content is 12 × 10⁻⁶. -6 The [N] content is 19 × 10⁻⁶. -6 The [H] content is 3×10 -6 .

[0036] (6) Calculate the required amount of alloying agent to be added based on the AOD steel composition and finished steel product requirements. After adding the alloy, gently blow the molten steel for 5 minutes to ensure uniform steel composition. After alloying, control the temperature at 1590℃, and the [C] content in the molten steel should be 11×10⁻⁶. -6 The [Si] content is 232 × 10⁻⁶. -6 The [Mn] content is 883 × 10⁻⁶. -6 The [P] content is 72 × 10⁻⁶. -6 The [S] content is 21 × 10⁻⁶. -6 The [Al] content is 382 × 10⁻⁶. -6 The [Ti] content is 411 × 10⁻⁶. -6 The [O] content is 13 × 10⁻⁶. -6 [N] content 24×10 -6 The [H] content is 3×10 -6 .

[0037] (7) Continuous casting: Take protective casting measures to strictly prevent secondary oxidation of molten steel and control the temperature of the tundish at 1558~1563℃.

[0038] Example 3

[0039] This embodiment illustrates the industrial application of producing ultra-low carbon steel using a clean deoxidation method in a 100t converter.

[0040] (1) Pre-desulfurization of molten iron was performed using KR stirring. After treatment, the [S] content in the molten iron was 43×10⁻⁶. -6 .

[0041] (2) The converter uses high-quality scrap steel with low phosphorus and low sulfur content, with a scrap steel ratio of 22%. Rapid slag formation is achieved in the initial blowing stage, with a slag formation time of 4 minutes. During the middle blowing stage, the FeO content is maintained at approximately 15%. In the final blowing stage, the slag basicity is controlled at 3.5, and the FeO content is 20%. The converter's final temperature is 1694℃, and the final [C] content is controlled at 380×10⁻⁶. -6The endpoint [P] content was 63 × 10⁻⁶. -6 .

[0042] (3) After the molten steel reaches the AOD station, the vacuum pump is turned on to maintain the vacuum at 6000 Pa. Then, oxygen is blown into the molten steel to remove carburization using an oxygen lance. The lance position is selected as 1080 mm, and the oxygen supply intensity is based on the carbon content of the molten steel, which is 380 × 10⁻⁶. -6 The value is 1.52m. 3 / (min·t), oxygen blowing time 18 minutes. Bottom blowing argon flow rate controlled at 1.6m³ / min·t. 3 / (min·t) ensures that the slag surface can be blown away, exposing the molten steel to oxygen. At the end of the blowing process, the temperature of the molten steel is 1662℃, and the [C] content is 9×10⁻⁶. -6 .

[0043] (4) Then, adjust the vacuum level of the vacuum chamber to 500 Pa, and use bottom-blowing permeable bricks to blow an argon-hydrogen mixture with a hydrogen content of 30% into the molten steel, with a gas supply intensity of 1.9 m. 3 / (min·t), hydrogen blowing time 32min. At the end of hydrogen blowing, the temperature of the molten steel was 1624℃, and the [O] content was 8×10⁻⁶. -6 .

[0044] (5) Adjust the vacuum level of the vacuum chamber to 10 Pa, and use the bottom-blowing permeable bricks to blow pure argon gas into the molten steel at a supply intensity of 1.2 m³ / s. 3 / (min·t), blowing time 8min. The temperature of AOD at the station outlet is controlled at 1602℃, and the [C] content in the molten steel is 9×10⁻⁶. -6 The [P] content is 61 × 10⁻⁶. -6 The [O] content is 8×10 -6 The [N] content is 27 × 10⁻⁶. -6 The [H] content is 4×10 -6 .

[0045] (6) Calculate the required amount of alloying agent to be added based on the AOD steel composition and finished steel product requirements. After adding the alloy, gently blow the molten steel for 5 minutes to ensure uniform steel composition. After alloying, control the temperature at 1580℃, and the [C] content in the molten steel should be 10×10⁻⁶. -6 The [Si] content is 244 × 10⁻⁶. -6 The [Mn] content is 890×10 -6 The [P] content is 63×10 -6 The [S] content is 30×10 -6 The [Al] content is 366 × 10⁻⁶. -6 The [Ti] content is 423 × 10⁻⁶. -6 The [O] content is 9×10 -6 [N] content 30×10-6 The [H] content is 4×10 -6 .

[0046] (7) Continuous casting: Take protective casting measures to strictly prevent secondary oxidation of molten steel and control the temperature of the tundish at 1558~1568℃.

[0047] As can be seen from the above embodiments, the present invention does not require the addition of deoxidizers, thus eliminating the formation of solid oxide inclusions. The deoxidation product generated by hydrogen deoxidation is H2O, which is in a gaseous state at steelmaking temperatures and quickly floats to the surface of the molten steel for removal. Moreover, the bubbles can adsorb the already formed inclusions after formation, and the diffusion and floating of the bubbles achieves a secondary purification effect on the molten steel, significantly reducing the amount of titanium nitride inclusions in the steel. The hydrogen blown into the molten steel can be removed to the same level as conventional smelting methods under the combined action of bottom-blown argon and vacuum in the AOD refining furnace. The alloys added to the molten steel are entirely used for alloying, and the deoxidation of aluminum is replaced by hydrogen, reducing the total amount of alloys used. This directly reduces the overall energy consumption of steelmaking production and prevents excessive carbon dioxide emissions. Therefore, the ultra-low carbon steel smelting method based on hydrogen deoxidation can promote the green development of the steelmaking process and bring huge environmental and economic benefits.

[0048] 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 ultra-low carbon steel using a clean deoxidation method, characterized in that, The production process adopts the following route: KR stirring → converter smelting → AOD refining → alloying → continuous casting. AOD refining includes initial AOD decarbonization, mid-stage AOD deoxidation, and final AOD dehydrogenation. Initial decarburization in AOD: After the molten steel arrives at the station, turn on the vacuum pump to maintain the vacuum level at 5000~15000Pa. Then, use an oxygen lance to blow oxygen into the molten steel for decarburization, with a blowing time of 12~18 minutes; the bottom-blowing argon flow rate is controlled at 1.2~1.6m³ / min. 3 / (min·t), at the end of blowing, the temperature of the molten steel should be 1660~1680℃, and the [C] content should be ≤13×10 -6 ; Mid-stage deoxidation in AOD: Adjust the vacuum level in the vacuum chamber to 500~2000Pa, and use bottom-blowing permeable bricks to blow an argon-hydrogen mixture with a hydrogen content of 10~15% into the molten steel, with a gas supply intensity of 1.2~2.5m. 3 / (min·t), the blowing time is 15~35min; at the end of the blowing, the temperature of the molten steel should be 1620~1640℃, and the [O] content should be ≤15×10 -6 ; Final dehydrogenation at the end of AOD: Adjust the vacuum level in the vacuum chamber to <67 Pa, and blow pure argon gas into the molten steel using bottom-blowing permeable bricks, with a gas supply intensity of 1.0~1.8 m³ / s. 3 / (min·t), blowing time is 6~8min; the temperature at AOD outlet is required to be controlled at 1600~1615℃, and the [C] content in the molten steel is ≤15×10 -6 [P] content ≤130×10 -6 [O] content ≤15×10 -6 [N] content ≤30×10 -6 [H] content ≤ 4 × 10 -6 ; Hydrogen is blown into the AOD furnace for deoxidation. By controlling the hydrogen blowing regime and the vacuum degree of the vacuum chamber, the deoxidation process can be stabilized and controlled. No deoxidizer needs to be added during the entire process, which significantly reduces inclusions in the molten steel and carbon emissions from the production process.

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

3. The ultra-low carbon steel production process using a clean deoxidation method according to claim 1, characterized in that, The converter smelting uses high-quality scrap steel with low phosphorus and low sulfur content, controlling the scrap steel ratio in the furnace to ≤25%; rapid slag formation is required in the initial stage of converter blowing, with a slag formation time ≤4 min; the FeO content in the slag is maintained at ≥10 wt% during the middle stage of blowing; the slag basicity is controlled at 3.0~3.6 and the FeO content ≤20 wt% at the end of blowing; the converter final temperature is required to be controlled at 1690~1710℃, and the final [C] content is controlled at (300~450)×10 -6 The endpoint [P] content is ≤130×10 -6 .

4. The ultra-low carbon steel production process using a clean deoxidation method according to claim 1, characterized in that, During alloying, the amount of alloy to be added is calculated based on the AOD steel composition and the requirements of the finished steel product. After the alloy is added, it is soft-blown for at least 5 minutes to ensure that the composition of the molten steel is uniform. After alloying is completed, the temperature is required to be controlled at 1580~1595℃.

5. The ultra-low carbon steel production process using a clean deoxidation method according to claim 1, characterized in that, Continuous casting employs protective casting measures, controlling the tundish temperature at 1558~1573℃.