Production method of high-chromium, high-aluminum and high-titanium-iron-nickel base alloy billet

Abstract

The invention relates to a production method of a high-chromium high-aluminum high-titanium-iron-nickel base alloy billet, which adopts a short flow process of electric furnace-AOD furnace-VOD furnace-LF refining furnace-continuous casting for smelting, and specifically comprises the following steps: continuous casting adopts vertical bending type casting, and specifically comprises the following steps: starting casting when the temperature of a rotary table steel ladle is lower than 1450 DEG C, controlling the superheat degree to be less than or equal to 35 DEG C, performing argon sealing on a continuous casting long steel nozzle, and performing continuous casting on the continuous casting long steel nozzle; argon is injected before tundish casting is started to well protect casting, the casting speed is 0.8-1.0 mm / s, EMS is started, and the electromagnetic stirring current is 600-1200 A; the wide surface of the cold mold water of the crystallizer I is 2900-3100L / min, and the narrow surface of the cold mold water of the crystallizer I is 320-360L / min; weak cooling is adopted for secondary cooling mold water, the steel billet is placed in a window to be rapidly air-cooled after being produced, and finally a continuous casting sheet billet is obtained. The molten steel is high in purity, nodulation and blockage are avoided during casting, and a casting blank is free of surface cracks.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical steel rolling technology, and particularly relates to a method for producing high-chromium, high-aluminum, and high-titanium iron-nickel-based alloy steel billets. Background Technology

[0002] High-chromium, high-aluminum, and high-titanium iron-nickel-based alloys are widely used in high-temperature fields such as energy and chemical engineering, heat exchangers, and water heater heating elements due to their excellent high-temperature strength, creep resistance, and corrosion resistance. However, the extremely high degree of alloying also presents significant challenges to their preparation. First, in the smelting process, aluminum and titanium, as highly reactive elements, readily react with oxygen, nitrogen, and refractory materials, leading to difficulties in controlling element loss, large compositional fluctuations, and the generation of large amounts of hard inclusions such as Al2O3 and Ti(C,N), severely affecting the purity of the molten steel. Second, during the casting process, these inclusions easily deposit on the inner wall of the continuous casting nozzle, causing fatal blockages and forcing production interruptions. Simultaneously, the complex solidification characteristics result in severe macroscopic segregation, surface longitudinal cracks, and subcutaneous crack defects in the cast billets, leading to extremely low yields and high costs. Existing blast furnace smelting and casting technologies are unable to overcome the aforementioned bottlenecks, which severely restricts the stabilization and low-cost industrial production of such high-performance alloys. There is an urgent need to develop entirely new composition designs and process flows to significantly improve the purity of molten steel, avoid blockage of casting nozzles in continuous casting, and ensure that the surface of the cast billet is free of cracks. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, this invention provides a method for producing high-chromium, high-aluminum, high-titanium iron-nickel-based alloy steel billets, which improves the purity of molten steel, prevents nodules and blockages during casting, and eliminates surface cracks in the billets.

[0004] To achieve the above objectives, the present invention employs the following technical solution: A method for producing high-chromium, high-aluminum, and high-titanium iron-nickel-based alloy steel billets, comprising a short-process smelting method using an electric furnace → AOD furnace → VOD furnace → LF refining furnace → continuous casting, the specific method including: 1) The steel billet is composed of the following chemical composition by weight percentage: C≤0.015%, Si≤0.30%, Mn≤1.50%, P≤0.03%, S≤0.001%, Cr: 19.0%~21.0%, Ni: 30.0%~35.0%, Ti: 0.20%~0.40%, Al: 0.20%~0.40%, Mo≤0.60%, Cu≤0.50%, N≤0.01%, with the balance being Fe and unavoidable impurities.

[0005] 2) Raw material smelting: Pure nickel, nickel materials, and high-carbon ferrochrome raw materials are processed through baking and other methods to obtain smelting raw materials that meet the requirements.

[0006] 3) Electric furnace smelting: Pure nickel, nickel material, and high-carbon ferrochrome are smelted into molten steel in an electric furnace to obtain a preliminary range of main components, especially to control trace elements to meet the expected range. The chemical composition of the molten steel after tapping from the electric furnace is as follows by weight percentage: C≤2.60%, Si≤0.60%, Mn≤1.5%, P≤0.035%, S≤0.080%, Cr: 14.0%~21.0%, Ni: 26.0%~32.0%, Cu≤0.50%, N≤0.06%; the balance is Fe and unavoidable impurities.

[0007] 4) AOD converter smelting: Molten steel from electric arc furnace smelting is added to the AOD furnace for smelting. During the oxygen blowing decarburization process in the AOD furnace, pure nickel and high-carbon ferrochrome are added for alloying. The oxygen flow rate is 1.5–2.5 L / min per ton of molten steel. After decarburization, 5.0–15.0 kg / ton of ferrosilicon, 10.0–15.0 kg / ton of fluorite, and 70–100 kg / ton of lime are added for reduction and slag formation. After tapping from the AOD furnace, slag is removed to remove steel slag. The ladle contains steel slag, and the slag thickness after ladle removal is ≤100mm. The chemical composition of the molten steel after tapping from the AOD furnace is as follows by weight percentage: C≤0.30%, Si≤0.30%, Mn≤1.5%, P≤0.03%, S≤0.020%, Cr: 19.0%~21.0%, Ni: 26.0%~35.0%, Mo≤0.60%, Cu≤0.50%, N≤0.03%, with the balance being Fe and unavoidable impurities.

[0008] 5) VOD Vacuum Refining Furnace: After slag removal from the ladle, the steel is hoisted to the VOD furnace for smelting. Vacuuming and oxygen blowing are performed in the VOD furnace for decarburization. Simultaneously, argon gas is blown from the bottom of the ladle for stirring, diluting the partial pressure of CO, thereby further reducing the partial pressure of CO in the molten steel and promoting the decarburization reaction. After decarburization, 1.0–3.0 kg / ton of fluorite and 20.0–25.0 kg / ton of lime are added for further slag formation, reduction, and desulfurization. After desulfurization, 8.0–10.0 kg / ton of aluminum ingots and 1.5–3 kg / ton of ferrosilicon are added for silicon-aluminum refining. The steel is deoxidized; then the composition is fine-tuned to approach the target value of the final composition; the chemical composition of the molten steel after VOD tapping is as follows by weight percentage: C≤0.015%, Si≤0.30%, Mn≤1.50%, P≤0.03%, S≤0.006%, Cr: 19.0%~21.0%, Ni: 28.0%~35.0%, Al: 0.20%~0.40%, Mo≤0.60%, Cu≤0.50%, N≤0.04%, with the balance being Fe and unavoidable impurities.

[0009] 6) After reduction in the VOD furnace, the ladle is hoisted to the LF furnace. In the LF furnace, 2.0-6.0 kg / ton of fluorite and 2.0-5.0 kg / ton of lime are added to form slag for further deep desulfurization. After desulfurization, pure nickel, low-carbon ferrochrome, and 300 series cold materials are added for alloying. After alloying, bottom-blown argon gas is used to stir and cause impurities to float to the surface, purifying the molten steel and cooling it. The argon gas flow rate is 1.5-2.5 L / min per ton of molten steel. The chemical composition of the molten steel after tapping from the LF furnace is as follows by weight percentage: C≤0.015%, Si≤0.30%, Mn≤1.50%, P≤0.03%, S≤0.001%, Cr: 19.0%-21.0%, Ni: 30.0%-35.0%, Al: 0.20%-0.40%, Mo≤0.60%, Cu≤0.50%, N≤0.01%, with the balance being Fe and unavoidable impurities.

[0010] 7) After the LF tapping, the ladle is moved to the CAS operation station for wire feeding. First, 3.0-4.0 kg / ton of high-calcium wire is fed, followed by 4.0-5.0 kg / ton of titanium wire. Weak blowing is performed every 2-4 minutes to perform final deoxidation and desulfurization, as well as to change the morphology and distribution of oxide and sulfide inclusions. After the wire feeding is completed, micro-stirring is performed for ≥15 min with a stirring flow rate <300 Nl / min. When the temperature is controlled at 1460-1475℃, the ladle is transferred to the continuous casting machine turntable.

[0011] 8) The continuous casting adopts vertical bending casting, specifically including: casting starts when the temperature of the turntable ladle is below 1450℃, controlling the superheat to ≤35℃, argon sealing of the continuous casting long steel nozzle, argon flushing before casting in the tundish to protect the pouring and avoid secondary oxidation, casting speed of 0.8~1.0m / min, EMS is turned on, electromagnetic stirring current is 600~1200A; the first cooling mold water flow rate in the crystallizer is 2900~3100L / min for the wide side and 320~360L / min for the narrow side; the second cooling mold water uses weak cooling, and the billet is placed in the window for rapid air cooling after production, finally obtaining the continuously cast slab.

[0012] Compared with existing technologies, the beneficial effects of this invention are: 1. This invention upgrades the production and smelting process and has environmental value. The smelting method of this invention adopts a short-process smelting process of electric furnace → AOD furnace → VOD furnace → LF refining furnace, which significantly reduces the C, S, and N content in high-chromium, high-aluminum, and high-titanium iron-nickel alloys compared with traditional blast furnace smelting. This reduces the C content of the billet to below 0.015%, the S content to below 0.0010%, and the N content to below 0.010%, improving the purity of the molten steel and controlling the inclusion level to below 1.0. At the same time, the short-process smelting process eliminates high-pollution smelting processes such as coking and sintering compared with blast furnaces, significantly reducing energy consumption and carbon emissions, making it more environmentally friendly and meeting the requirements of high-end equipment for green manufacturing and sustainable development.

[0013] 2. This invention overcomes key quality defects in high-aluminum, high-titanium, nickel-iron alloy steels, improving production efficiency. The continuous casting process employs a vertical bending casting method, with the ladle sealed with argon gas to prevent secondary oxidation. Through continuous casting protection, EMS is activated, and weak cooling and low casting speed are used, successfully resolving defects in high-aluminum, high-titanium, nickel-iron alloy steels such as casting blockage, longitudinal cracking of billets, and subcutaneous cracks. Furthermore, the vertical bending continuous casting process offers strong continuity, eliminating intermediate steps such as billet preparation, significantly shortening the production cycle and reducing production costs. Attached Figure Description

[0014] Figure 1 This is a process flow diagram of the present invention.

[0015] In the diagram: 1-Alloy iron, 2-Scrap steel, 3-Electric furnace, 4-AOD furnace, 5-VOD furnace, 6-LF refining furnace, 7-Waiting station, 8-Vertical bending casting machine, 9-Steel billet. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the specific implementation methods of this invention will be further described below in conjunction with the embodiments. The following embodiments are used to specifically illustrate the content of this invention. These embodiments are only general descriptions of the content of this invention and do not limit the content of this invention.

[0017] The specific chemical composition by weight percentage of the steel billet in this embodiment of the invention is shown in Table 1; the chemical composition of the molten steel after tapping from the electric furnace in this embodiment of the invention is shown in Table 2; the production process parameters of the AOD furnace in this embodiment of the invention are shown in Table 3; the production process parameters of the VOD furnace in this embodiment of the invention are shown in Table 4; the smelting process parameters of the LF furnace in this embodiment of the invention are shown in Table 5; the process parameters of the waiting station in this embodiment of the invention are shown in Table 6; the continuous casting production process of the steel billet in this embodiment of the invention is shown in Table 7; the secondary cooling water for continuous casting of the steel billet in this embodiment of the invention is shown in Table 8; and the inclusion grade parameters of the cast billet in this embodiment of the invention are shown in Table 9.

[0018] Table 1. Specific chemical composition (weight percentage) of steel billets in embodiments of the present invention. Table 2 Chemical composition (%) of molten steel after tapping from the electric furnace in the embodiments of the present invention Table 3. Production process parameters of AOD furnace in the embodiments of the present invention. Table 4. Production process parameters of VOD furnace in the embodiments of the present invention Table 5 Process parameters of the LF furnace in the embodiments of the present invention Table 6 Process parameters of the waiting station in the embodiment of the present invention Table 7. Continuous casting process of steel billets in embodiments of the present invention. Table 8. Secondary Cooling Water for Continuous Casting of Steel Billets in Embodiments of the Invention Table 9 Inclusion grades of billets in embodiments of the present invention

Claims

1. A method for producing a high-chromium, high-aluminum, high-titanium iron-nickel-based alloy steel billet, characterized in that, This method employs a short-process smelting method: electric furnace → AOD furnace → VOD furnace → LF refining furnace → continuous casting. Specific methods include: The continuous casting adopts a vertical bending casting method, specifically including: starting casting when the ladle temperature on the turntable is below 1450℃, controlling the superheat to ≤35℃, argon sealing the long steel nozzle of the continuous casting, argon flushing before casting from the tundish for protection, casting speed of 0.8~1.0m / min, EMS turned on, electromagnetic stirring current of 600~1200A; the wide side of the first cooling mold water in the crystallizer has a flow rate of 2900~3100L / min, and the narrow side has a flow rate of 320~360L / min; the second cooling mold water uses weak cooling.

2. The method for producing a high-chromium, high-aluminum, high-titanium iron-nickel-based alloy steel billet according to claim 1, characterized in that, The chemical composition of the molten steel after tapping from the electric furnace is as follows by weight percentage: C≤2.60%, Si≤0.60%, Mn≤1.5%, P≤0.035%, S≤0.080%, Cr: 14.0%~21.0%, Ni: 26.0%~32.0%, Cu≤0.50%, N≤0.06%; the balance is Fe and unavoidable impurities.

3. The method for producing a high-chromium, high-aluminum, high-titanium iron-nickel-based alloy steel billet according to claim 1, characterized in that, Alloying is carried out during the oxygen blowing decarburization process in the AOD furnace. The oxygen flow rate is 1.5-2.5 L / min per ton of molten steel. After decarburization, 5.0-15.0 kg / ton of ferrosilicon, 10.0-15.0 kg / ton of fluorite, and 70-100 kg / ton of lime are added for reduction and slag formation. The chemical composition of the molten steel after tapping from the AOD furnace is as follows by weight percentage: C≤0.30%, Si≤0.30%, Mn≤1.5%, P≤0.03%, S≤0.020%, Cr: 19.0%-21.0%, Ni: 26.0%-35.0%, Mo≤0.60%, Cu≤0.50%, N≤0.03%, with the balance being Fe and unavoidable impurities.

4. The method for producing a high-chromium, high-aluminum, high-titanium iron-nickel-based alloy steel billet according to claim 1, characterized in that, After smelting in the AOD furnace, the molten steel is subjected to oxygen blowing decarburization in the VOD furnace under vacuum. Simultaneously, argon gas is blown into the ladle for stirring at a flow rate of 1.5–2.5 L / min per ton of steel. After decarburization, 1.0–3.0 kg / ton of fluorite and 20.0–25.0 kg / ton of lime are added for further slag formation, reduction, and desulfurization. After desulfurization, 8.0–10.0 kg / ton of aluminum ingots and 1.5–3 kg / ton of ferrosilicon are added for silicon-aluminum composite deoxidation. Then, the composition is fine-tuned. The chemical composition of the molten steel after VOD tapping is as follows by weight percentage: C≤0.015%, Si≤0.30%, Mn≤1.50%, P≤0.03%, S≤0.006%, Cr: 19.0%~21.0%, Ni: 28.0%~35.0%, Al: 0.20%~0.40%, Mo≤0.60%, Cu≤0.50%, N≤0.04%, with the balance being Fe and unavoidable impurities.

5. The method for producing a high-chromium, high-aluminum, high-titanium iron-nickel-based alloy steel billet according to claim 1, characterized in that, After reduction in the VOD furnace, the ladle is hoisted to the LF furnace. In the LF furnace, 2.0–6.0 kg / ton of fluorite and 2.0–5.0 kg / ton of lime are added to create slag for further deep desulfurization. After desulfurization, alloying is carried out, followed by bottom-blowing argon stirring. The argon flow rate is 1.5–2.5 L / min per ton of molten steel. The chemical composition of the molten steel after tapping from the LF furnace is as follows (by weight percentage): C≤0.015%, Si≤0.30%, Mn≤1.50%, P≤0.03%, S≤0.001%, Cr: 19.0%–21.0%, Ni: 30.0%–35.0%, Al: 0.20%–0.40%, Mo≤0.60%, Cu≤0.50%, N≤0.01%, with the balance being Fe and unavoidable impurities.

6. The method for producing a high-chromium, high-aluminum, high-titanium iron-nickel-based alloy steel billet according to claim 1, characterized in that, After the LF steel is tapped, the ladle is moved to the waiting station for wire feeding. First, 3.0-4.0 kg / ton of high-calcium wire is fed, followed by 4.0-5.0 kg / ton of titanium wire. The ladle is then gently stirred with a gentle blowing motion every 3-4 minutes for a total stirring time of ≥15 minutes. When the temperature is controlled at 1460-1475℃, the ladle is transferred to the continuous casting machine turntable.

7. The method for producing a high-chromium, high-aluminum, high-titanium iron-nickel-based alloy steel billet according to claim 1, characterized in that, The steel billet is composed of the following chemical composition by weight percentage: C≤0.015%, Si≤0.30%, Mn≤1.50%, P≤0.03%, S≤0.001%, Cr: 19.0%~21.0%, Ni: 30.0%~35.0%, Ti: 0.20%~0.40%, Al: 0.20%~0.40%, Mo≤0.60%, Cu≤0.50%, N≤0.01%, with the balance being Fe and unavoidable impurities.

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