A large-sized seawater corrosion-resistant high-aluminum steel continuous casting billet and its production method

Abstract

A large-sized seawater corrosion-resistant high-aluminum steel continuous casting billet and its production method belong to the field of metallurgical technology. Its chemical composition and mass content are as follows: C: 0.07 - 0.11%, Si: 0.22 - 0.26%, Mn: 0.65 - 0.70%, P ≤ 0.015%, S ≤ 0.003%, Cr: 1.30 - 1.50%, Mo: 0.17 - 0.19%, Al: 0.80 - 1.00%, Ni ≤ 0.10%, Cu ≤ 0.10%, O ≤ 8 ppm, N ≤ 50 ppm, H ≤ 1.2 ppm, and the balance is Fe and inevitable impurities. Its production method includes BOF converter, LF refining, VD vacuum treatment, and continuous casting process; before entering VD, the slag is first poured out, and then aluminum ingots are added at 8.0 - 10.0 kg / t and then vacuum degassing treatment is carried out. The diameter of the high-aluminum steel continuous casting billet produced by the present invention is up to 600 mm at most, and it has good performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgy, and particularly relates to a large-sized seawater corrosion-resistant high-aluminum steel continuous casting billet and a production method thereof. Background Art

[0002] When aluminum is added to steel as an alloying element, it can refine the grains and improve the toughness of the steel at low temperatures. In high-aluminum steel, the Al element can form a dense Al2O3 film between the matrix surface and the air, and at the same time, the Al dissolved in the matrix will increase the electrode potential of the matrix, greatly improving the corrosion resistance of the steel. The steel has excellent properties such as corrosion resistance, wear resistance, heat resistance, low magnetic permeability, high precision dimensions after processing, high strength, low quality, and good ductility, and is widely used in fields such as ships, military, aerospace, machinery manufacturing, automobiles, and chemicals.

[0003] Research shows that in high-aluminum steel 10CrMoAl, micro-alloying elements such as Cr, Mo, and Al can be enriched on the surface of the rust layer, playing a role in protecting the matrix. At the same time, there are various compounds of Al and Mo in the 10CrMoAl material, which can also play a role in isolating the matrix from the corrosion environment. A firm and dense chromium oxide can be formed on the surface of the high-aluminum steel 10CrMoAl, playing a role in protecting the material. At the same time, most of the Cr in the 10CrMoAl steel is well dissolved in the matrix, which can significantly increase the electrode potential of the steel, reduce the electrochemical corrosion caused by different electrode potentials, and thus increase the seawater corrosion resistance of the 10CrMoAl steel.

[0004] In 10CrMoAl steel, due to the high Al content, which far exceeds the range of conventional deoxidation and grain refinement, the molten steel has the characteristics of high viscosity and poor fluidity. Moreover, Al is chemically active and easily reacts with oxygen and nitrogen in the air. There are the following several difficulties in the production process: 1. It is easy to occur oxidation reactions, generating Al2O3 inclusions and AlN inclusions, resulting in the clogging of the tundish nozzle during the continuous casting process. 2. Due to the high Al content, it is easy to make the mold powder denature, affecting the surface and internal quality of the continuous casting billet, and having high requirements for the composition and performance of the mold powder. 3. Al has a low melting point, a small specific gravity, is easy to oxidize, and is not easy to add, resulting in unstable yield and great difficulty in controlling the composition. If the method of adjusting the Al content is improper, not only will the aluminum loss be large, increasing the production cost, but also the reaction products will deposit on the nozzle, causing flocculent flow during the continuous casting process and even interrupting the casting sequence.

[0005] The currently published patent CN105463299A uses an electric furnace as the primary melting furnace to produce high-quality high-aluminum steel, and adds aluminum blocks during the evacuation process in the VD process to adjust the Al content. Using an electric furnace for production results in high power consumption, large electrode consumption, and a tight production rhythm, causing certain resource waste. Adding aluminum blocks during the evacuation process in the VD process leads to large fluctuations in the recovery rate of Al. At the same time, the added aluminum blocks react with SiO2 in the refining slag to form Al2O3, and the inclusions do not float up sufficiently in the later stage, potentially affecting the purity of the molten steel. The Al2O3 formed by the reaction is prone to cause continuous casting flocculation during the continuous casting process, affecting product quality and production smoothness. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a large-sized continuously cast billet of high-aluminum steel resistant to seawater corrosion and its production method, which can ensure a relatively high purity of molten steel, a relatively high aluminum recovery rate and a relatively low temperature loss during the VD process. The continuously cast billet of high-aluminum steel with a maximum diameter of 600 mm produced has good properties.

[0007] To achieve the above invention purpose, the technical solution adopted by the present invention is:

[0008] A large-sized continuously cast billet of high-aluminum steel resistant to seawater corrosion, its chemical composition and mass percentage are: C: 0.07 - 0.11%, Si: 0.22 - 0.26%, Mn: 0.65 - 0.70%, P ≤ 0.015%, S ≤ 0.003%, Cr: 1.30 - 1.50%, Mo: 0.17 - 0.19%, Al: 0.80 - 1.00%, Ni ≤ 0.10%, Cu ≤ 0.10%, O ≤ 8 ppm, N ≤ 50 ppm, H ≤ 1.2 ppm, and the balance is Fe and unavoidable impurities; the diameter of the continuously cast billet is 500 - 600 mm.

[0009] The production method of the above large-sized continuously cast billet of high-aluminum steel resistant to seawater corrosion includes BOF converter, LF refining, VD vacuum treatment, and continuous casting processes;

[0010] (1) BOF converter process: After the previous furnace smelting is completed, steel slag is left in the converter furnace, and nitrogen is blown from the bottom for slag splashing to protect the furnace. The converter is blown for 3 - 5 minutes to pour out the pre-stage slag, and slag materials are added for secondary slag formation and smelting. During the tapping process, slagging is prohibited to ensure that the P content in the LF refining reaches ≤ 0.012%. After tapping, aluminum wire is fed to ensure that the Al content in the LF refining reaches 0.020 - 0.040%;

[0011] (2) LF refining process: The CaO / Al2O3 in the refining slag system is 1.7 - 1.9;

[0012] (3) VD Vacuum Treatment Process: Before entering VD, slag is first poured out, and the weight of the poured slag is controlled to be 1 / 2 - 1 / 3 of the total slag weight. Then, aluminum ingots are added at 8.0 - 10.0 kg / t to adjust the Al content in the molten steel. After adding the aluminum ingots, the cover is immediately closed for VD vacuum degassing treatment;

[0013] (4) Continuous Casting Process: During continuous casting, the whole process is protected by argon sealing for pouring. A special protective slag for low-carbon high-aluminum steel is used, and the continuous casting billets are slowly cooled after being taken off the production line.

[0014] Furthermore, in the BOF converter process, the weight ratio of hot metal to scrap is: 85 - 95% hot metal, 5 - 15% scrap; after the previous furnace smelting is completed, 2 - 5 t of molten steel and slag are left in the converter furnace.

[0015] Furthermore, in the LF refining process, aluminum pellets and silicon carbide are used for diffusion deoxidation during refining to ensure that the [O] content in the molten steel is ≤ 8 ppm, the refining time is ≥ 50 min, and the white slag holding time is ≥ 20 min.

[0016] Furthermore, in the LF refining process, the refining slag system contains the following components by weight: CaO ≥ 55%, SiO2 ≤ 6.3%, Al2O3: 30 - 32%, TFe + MnO ≤ 0.5%, MgO ≤ 6%, TiO2 ≤ 0.20%; the basicity R of the refining slag system is ≥ 9.

[0017] Furthermore, in the VD vacuum treatment process, the vacuum holding time is controlled at 8 - 10 min, the soft blowing time is ≥ 15 min, and the argon gas flow rate during soft blowing is ≤ 10 L / min.

[0018] Furthermore, in the continuous casting process, the drawing speed is constant at 0.24 - 0.26 m / min, the water flow rate of the mold is 4500 - 5000 L / min·strand, the specific water ratio is 0.11 - 0.13 L / kg, the electromagnetic stirring intensity of the mold is 100 - 130 A, and the electromagnetic stirring intensity at the end is 150 - 180 A.

[0019] Furthermore, in the continuous casting process, the composition and weight content of the special protective slag for low-carbon high-aluminum steel are: CaO: 21.5 - 25%, SiO2: 36 - 39%, MgO: 4.5 - 5%, Al2O3: 2.5 - 3%, Fe2O3: 2.3 - 3%, Na2O: 8.8 - 10%, F: 7.5 - 9%, C: 12 - 13%; melting point: 950 - 980 °C, viscosity: 0.3 - 0.4 Pa·s / 1300 °C.

[0020] The beneficial effects of adopting the above technical solutions are as follows: The present invention optimizes the composition of 10CrMoAl. By increasing the contents of Cr, Mn, and Al and reducing the content of Mo, while ensuring the properties of the finished material, the usage amount of precious alloy Mo is reduced, resources are rationally utilized, and the production cost is lowered. The present invention uses a converter as the primary melting furnace to produce high-aluminum steel with low P and low S, which is of great production difficulty and high technical requirements. Before VD vacuum treatment and after slag pouring, aluminum ingots are added to adjust the Al content, enabling a high Al yield (≥95%) and a low temperature loss (1.5 - 1.8 °C / min) during the VD process, ensuring the floating of inclusions such as Al2O3 during VD vacuum treatment and slag washing and stirring processes, and ensuring the purity of the molten steel. The continuous casting process parameters are optimized to ensure good product quality.

[0021] The 10CrMoAl finished product produced by the present invention has low P and S contents, which can improve the mechanical properties of the material. At the same time, the diameter of the continuous casting billet of the high-aluminum steel resistant to seawater corrosion produced can reach up to It can be used to produce seamless pipes for conveying water in large-scale coastal natural gas and petrochemical plants or large-scale valve flanges. Specific embodiments

[0022] The present invention will be further described in detail below in conjunction with specific embodiments.

[0023] The diameter of the large-scale continuous casting billet of high-aluminum steel resistant to seawater corrosion of the present invention is 500 - 600 mm, and its chemical composition and mass percentage content are as follows: C: 0.07 - 0.11%, Si: 0.22 - 0.26%, Mn: 0.65 - 0.70%, P ≤ 0.015%, S ≤ 0.003%, Cr: 1.30 - 1.50%, Mo: 0.17 - 0.19%, Al: 0.80 - 1.00%, Ni ≤ 0.10%, Cu ≤ 0.10%, O ≤ 8 ppm, N ≤ 50 ppm, H ≤ 1.2 ppm, and the balance is Fe and inevitable impurities.

[0024] The production method of the above large-scale continuous casting billet of high-aluminum steel resistant to seawater corrosion includes BOF converter, LF refining, VD vacuum treatment, and continuous casting processes. The steps of each process are as follows:

[0025] (1) BOF converter process: High-quality low-P hot metal is used, with requirements of P ≤ 0.120%, S ≤ 0.030%, Si 0.30 - 0.80%, and temperature 1300 - 1450°C. After the previous furnace smelting is completed, 2 - 5 t of molten steel and slag are left in the converter furnace, and nitrogen is blown from the bottom for slag splashing to protect the furnace. The slag splashing time is 3 - 5 min. The ratio of hot metal to scrap in the converter is: hot metal amount 85 - 95%, scrap amount 5 - 15%, and high-quality scrap is used. Before smelting, the converter slag near the converter mouth and furnace cap is cleaned up. If splashing occurs during the blowing process, the residual converter slag on the furnace cap must be cleaned up twice to ensure that the furnace cap is clean without residue before tapping. The converter needs to pour out the early slag after blowing for 3 - 5 min, add slag materials for secondary slag making and smelting. During the tapping process, slagging is strictly prohibited to ensure that the P content in LF refining reaches ≤ 0.012%, and the finished product P content must be strictly controlled at ≤ 0.015%. During the tapping process, steel core aluminum, alloys, and slag materials are added in sequence. A small amount of molten steel is left in the furnace, and slagging is strictly prohibited. After tapping, aluminum wire is fed to ensure that the Al content in LF refining reaches 0.020 - 0.040%.

[0026] (2) LF refining process: After LF is in place, the ladle is opened with two permeable bricks to ensure good fluidity of the refining slag. The LF refining time ≥ 50 min, and the white slag holding time ≥ 20 min. Aluminum pellets and silicon carbide are used for diffusion deoxidation during the LF process to improve the reducibility of the slag, reduce the oxygen partial pressure in the furnace gas, and reduce secondary oxidation during the LF process. Since the Al2O3 content in the refining slag system reaches about 30%, when the CaO / Al2O3 in the slag system is controlled at 1.7 - 1.9, the melting point of the refining slag is lower, and the ability to desulfurize and adsorb inclusions is stronger. The tendency of molten steel reoxidation caused by SiO2 can be effectively inhibited.

[0027] Therefore, the control range of the refining slag system in the present invention is: CaO ≥ 55%, SiO2 ≤ 6.3%, Al2O3: 30 - 32%, TFe + MnO ≤ 0.5%, MgO ≤ 6%, TiO2 ≤ 0.20%, alkalinity R ≥ 9, and CaO / Al2O3 is controlled at 1.7 - 1.9, which can ensure good deoxidation and desulfurization effects, as well as good inclusion adsorption effects, and control a high purity of molten steel.

[0028] (3) VD vacuum treatment process: Before entering VD, the slag is first poured out, and the amount of poured slag is controlled at 1 / 2 - 1 / 3 of the total slag amount. Then, 8.0 - 10.0 kg / t of aluminum ingots are added to adjust the Al content in the molten steel. After adding the aluminum ingots, the cover is immediately closed for VD vacuum degassing treatment. The high vacuum holding time of VD is controlled at 8 - 10 min, which can ensure good degassing effects, a high recovery rate of aluminum ingots, and sufficient floating and removal of inclusions, and can also achieve energy-saving effects; after VD treatment, the soft blowing time ≥ 15 min, and the argon flow rate during soft blowing ≤ 10 L / min to promote the floating of inclusions and avoid secondary oxidation caused by excessive liquid surface fluctuation during soft blowing.

[0029] Since aluminum pellets and silicon carbide are continuously used for diffusion deoxidation during the LF refining process, the [O] content in the molten steel is ≤8 ppm at this time, and the oxygen content is relatively low. After adding aluminum ingots, they will not react with Al in large quantities. Therefore, less Al2O3 is generated in the molten steel. At the same time, a large amount of slag is poured before entering VD, ensuring that the total slag volume during VD treatment is small and the total oxygen content in the slag is low, which can effectively improve the recovery rate of Al after adding aluminum ingots and ensure that the recovery rate of Al in the added aluminum ingots is ≥95%. At the same time, the VD vacuum treatment and slag washing and stirring processes can effectively promote the floating of inclusions such as Al2O3 in the molten steel and ensure the purity of the molten steel.

[0030] In addition, during the melting and homogenization of aluminum ingots, an aluminothermic reaction will occur. During the normal VD vacuum treatment process, the temperature drop is 2.0 - 2.5 °C / min, while during the VD vacuum treatment process after adding aluminum ingots at 8.0 - 10.0 kg / t, the temperature drop is 1.5 - 1.8 °C / min, which can make up for part of the heat loss during VD vacuum treatment, that is, it can reduce the LF ladle temperature by 10 - 20 °C, achieving the purpose of reducing power consumption, reducing electrode consumption, saving energy, and controlling costs.

[0031] (4) Continuous casting process: The entire continuous casting process is protected by argon sealing during pouring to minimize secondary oxidation during pouring. Ensure that the ladle is self-opened without burning oxygen to control the purity of the molten steel. The casting speed is constant at 0.24 - 0.26 m / min, the water flow rate in the mold is 4500 - 5000 L / min·strand, the specific water ratio is 0.11 - 0.13 L / kg, the electromagnetic stirring intensity in the mold is 100 - 130 A, the electromagnetic stirring intensity at the end is 150 - 180 A, and a through-type nozzle is used. After cutting the head and tail billets, the overall billet yield is ≥96%. A special protective slag for low-carbon high-aluminum steel is used. Since the Al content in the molten steel is relatively high, it is easy to cause the denaturation of the protective slag, resulting in slag grooves and slag rings on the surface of the billet. The continuous casting billets are slowly cooled offline, and the surface inspection and cleaning of the billets should be strengthened after leaving the slow-cooling pit;

[0032] The component composition and weight content of the special protective slag for low-carbon high-aluminum steel are: CaO: 21.5 - 25%, SiO2: 36 - 39%, MgO: 4.5 - 5%, Al2O3: 2.5 - 3%, Fe2O3: 2.3 - 3%, Na2O: 8.8 - 10%, F: 7.5 - 9%, C: 12 - 13%; melting point: 950 - 980 °C, viscosity: 0.3 - 0.4 Pa·s / 1300 °C.

[0033] Examples 1 - 8: The chemical compositions and contents of the large-sized seawater corrosion-resistant high-aluminum steel continuous casting billets in each example are shown in Tables 1 and 2, the parameter controls of each process in each example are shown in Tables 3 - 8, and the observed results under the low-power microscope and the detection results of non-metallic inclusion grades of the continuous casting billets obtained in each example are shown in Tables 9 and 10 respectively.

[0034] Table 1: Chemical Compositions and Contents of High-Aluminum Steel Continuous Casting Billets in Each Example (wt%)

[0035]

[0036] In Table 1, the balance is Fe and unavoidable impurities.

[0037] Table 2: Gas Content of High-Aluminum Steel Continuous Casting Billets in Each Example (ppm)

[0038] Example O N H 1 8.0 38.6 0.9 2 7.7 41.9 1.0 3 7.4 40.2 0.9 4 8.0 46.2 1.2 5 7.6 38.1 1.0 6 8.0 35.4 1.1 7 7.8 44.3 0.9 8 7.1 49.8 1.0

[0039] Table 3: BOF Converter Process Parameter Control in Each Example

[0040]

[0041] Table 4: LF Refining Process Parameter Control in Each Example

[0042]

[0043] Table 5: Composition and Content of Refining Slag System in Each Example (wt%)

[0044]

[0045]

[0046] Table 6: VD Vacuum Treatment Process Parameter Control in Each Example

[0047]

[0048] Table 7: Continuous Casting Process Parameter Control in Each Example

[0049]

[0050] Table 8: Composition and Properties of Special Powder for Low-Carbon High-Aluminum Steel Continuous Casting in Each Example

[0051]

[0052]

[0053] Table 9: Observation Results of Macrostructure of Continuous Casting Billets in Each Example

[0054] Example Central porosity (grade) Other defects 1 1.0 None 2 1.0 None 3 1.0 None 4 1.0 None 5 1.0 None 6 1.0 None 7 1.0 None 8 1.0 None

[0055] Table 10: Non-Metallic Inclusion Grades in Each Example

[0056]

Claims

1. A continuously cast slab of large-sized seawater corrosion-resistant high-aluminum steel, characterized in that, The chemical composition and mass percentage of the high-aluminum steel are as follows: C: 0.07 - 0.11%, Si: 0.22 - 0.26%, Mn: 0.66 - 0.70%, P ≤ 0.015%, S ≤ 0.003%, Cr: 1.30 - 1.50%, Mo: 0.17 - 0.19%, Al: 0.80 - 1.00%, Ni: 0.01 - 0.10%, Cu: 0.01 - 0.10%, O ≤ 8 ppm, N ≤ 50 ppm, H ≤ 1.2 ppm, and the balance is Fe and unavoidable impurities; The production method of the high-aluminum steel continuous casting billet includes BOF converter, LF refining, VD vacuum treatment, and continuous casting processes; (1) BOF converter process: After the previous furnace smelting is completed, steel slag is left in the converter furnace, and nitrogen is blown at the bottom for slag splashing to protect the furnace. The converter is blown for 3 - 5 minutes to pour out the previous slag, and slag materials are added for secondary slag making and smelting. Slag falling is prohibited during the tapping process to ensure that the P content in LF refining reaches ≤ 0.012%. After tapping, aluminum wire is fed to ensure that the Al content in LF refining reaches 0.020 - 0.040%; (2) LF refining process: In the refining slag system, CaO / Al2O3 is 1.7 - 1.

9. During the refining process, aluminum pellets and silicon carbide are used for diffusion deoxidation to ensure that the [O] content in the molten steel is ≤ 8 ppm. The refining time is ≥ 50 minutes, and the white slag holding time is ≥ 20 minutes; (3) VD vacuum treatment process: Before entering VD, slag is first poured out, and the weight of the poured slag is controlled to be 1 / 2 - 1 / 3 of the total slag weight. Then, aluminum ingots are added at 8.0 - 10.0 kg / t to adjust the Al content in the molten steel. Immediately after adding the aluminum ingots, the cover is closed for VD vacuum degassing treatment; (4) Continuous casting process: During the continuous casting process, the whole process is protected by argon sealing for pouring, and a special protective slag for low-carbon high-aluminum steel is used. The continuous casting billet is slowly cooled after being taken off the production line.

2. The continuously cast slab of large-sized seawater corrosion-resistant high-aluminum steel according to claim 1, wherein The diameter of the continuous casting billet is 500 - 600 mm.

3. The production method of large-sized seawater corrosion-resistant high-aluminum steel continuous casting billets according to claim 1 or 2, characterized in that, It includes BOF converter, LF refining, VD vacuum treatment, and continuous casting processes; (1) BOF converter process: After the previous furnace smelting is completed, steel slag is left in the converter furnace, and nitrogen is blown at the bottom for slag splashing to protect the furnace. The converter is blown for 3 - 5 minutes to pour out the previous slag, and slag materials are added for secondary slag making and smelting. Slag falling is prohibited during the tapping process to ensure that the P content in LF refining reaches ≤ 0.012%. After tapping, aluminum wire is fed to ensure that the Al content in LF refining reaches 0.020 - 0.040%; (2) LF refining process: In the refining slag system, CaO / Al2O3 is 1.7 - 1.

9. During the refining process, aluminum pellets and silicon carbide are used for diffusion deoxidation to ensure that the [O] content in the molten steel is ≤ 8 ppm. The refining time is ≥ 50 minutes, and the white slag holding time is ≥ 20 minutes; (3) VD vacuum treatment process: Before entering VD, slag is first poured out, and the weight of the poured slag is controlled to be 1 / 2 - 1 / 3 of the total slag weight. Then, aluminum ingots are added at 8.0 - 10.0 kg / t to adjust the Al content in the molten steel. Immediately after adding the aluminum ingots, the cover is closed for VD vacuum degassing treatment; (4) Continuous casting process: During the continuous casting process, the whole process is protected by argon sealing for pouring, and a special protective slag for low-carbon high-aluminum steel is used. The continuous casting billet is slowly cooled after being taken off the production line.

4. The production method of the large-size seawater corrosion-resistant high-aluminum steel continuous casting billet according to claim 3, characterized in that, In the BOF converter process, the weight ratio of hot metal to scrap is: 85 - 95% hot metal and 5 - 15% scrap; after the previous furnace smelting is completed, 2 - 5 t of molten steel and slag are left in the converter furnace.

5. The production method of the large-sized seawater corrosion-resistant high-aluminum steel continuous casting billet according to claim 4, characterized in that, In the LF refining process, the refining slag system contains components with the following weight contents: CaO ≥ 55%, SiO2 ≤ 6.3%, Al2O3: 30 - 32%, TFe + MnO ≤ 0.5%, MgO ≤ 6%, TiO2 ≤ 0.20%; the basicity R of the refining slag system ≥ 9.

6. The production method of the large-sized seawater corrosion-resistant high-aluminum steel continuous casting billet according to claim 5, characterized in that, In the VD vacuum treatment process, the vacuum holding time is controlled at 8 - 10 min, the soft blowing time ≥ 15 min, and the argon gas flow rate during soft blowing ≤ 10 L / min.

7. The production method of the large-sized seawater corrosion-resistant high-aluminum steel continuous casting billet according to claim 6, characterized in that In the continuous casting process, the casting speed is constant at 0.24 - 0.26 m / min, the water flow rate of the mold is 4500 - 5000 L / min per strand, the specific water consumption is 0.11 - 0.13 L / kg, the electromagnetic stirring intensity of the mold is 100 - 130 A, and the electromagnetic stirring intensity at the end is 150 - 180 A.

8. The production method of the large-sized seawater corrosion-resistant high-aluminum steel continuous casting billet according to any one of claims 3-7, characterized in that, In the continuous casting process, the composition and weight content of the special protective slag for low-carbon high-aluminum steel are: CaO: 21.5 - 25%, SiO2: 36 - 39%, MgO: 4.5 - 5%, Al2O3: 2.5 - 3%, Fe2O3: 2.3 - 3%, Na2O: 8.8 - 10%, F: 7.5 - 9%, C: 12 - 13%; melting point: 950 - 980 °C, viscosity: 0.3 - 0.4 Pa·s / 1300 °C.

Images