A method for multi-heat continuous casting of high-aluminum steel with high aluminum content

Abstract

The present application relates to a kind of methods for continuously casting ultra-high aluminum content high aluminum steel multi-furnace continuous casting, including the heating of barrier device and mould cover, the preparation of liquid protective liquid, the casting process in the molten steel surface is put barrier device and cover mould cover, inject liquid protective slag and control its flow rate etc.;By adding a layer of blocking layer with high thermal conductivity, high temperature resistance, oxidation resistance on the contact surface of protective slag and molten steel, reduce the contact area of molten steel and protective slag, inhibit the reaction ability of slag-steel;On this basis, directly add liquid protective slag into the mould, ensure that protective slag flows into the channel, stabilize the slag consumption of high aluminum steel during continuous casting production, while ensuring that protective slag has stable lubrication and heat transfer function, solve a series of problems such as strong slag-steel reaction, easy crystallization of protective slag, low slag consumption, easy sticking and leakage during continuous casting production of ultra-high aluminum content high aluminum steel, realize multi-furnace continuous casting of this kind of steel.

Description

Technical Field

[0001] This invention relates to the field of continuous casting technology, and in particular to a method for continuous casting of high-alumina steel with ultra-high aluminum content (Al≥4%) in multiple furnaces. Background Technology

[0002] Increasing the Al content in steel can significantly improve its performance, such as in aluminum-containing TRIP steel and TWIP steel, which are important materials for achieving lightweighting in automobiles. However, Al in molten steel is a reactive element. During the casting process using traditional CaO-SiO2-based protective slag, Al reacts with components such as SiO2 in the protective slag, causing changes in the composition and properties of the protective slag and disrupting the continuous casting process. Therefore, the increasing aluminum content in high-aluminum steel products poses a significant challenge to traditional continuous casting processes.

[0003] Based on the above issues, researchers have developed novel continuous casting mold fluxes for high-alumina steel, mainly including two categories: low-basicity CaO-SiO2-based mold fluxes and low-reactivity CaO-Al2O3-based mold fluxes. In practical applications, low-basicity CaO-SiO2-based mold fluxes can meet the requirements of continuous casting production of high-alumina steel (aluminum content less than 1%) with relatively low slag-steel reaction strength. However, in the production of steel grades with even higher aluminum content, low-reactivity CaO-Al2O3-based mold fluxes have shown greater potential.

[0004] A domestic plant conducted continuous casting production trials of high-alumina steel with an aluminum content of 4% using both low-basicity CaO-SiO2-based and low-reactivity CaO-Al2O3-based protective slags. Both trials resulted in difficulties in single-furnace casting. Therefore, optimizing the continuous casting process for ultra-high alumina steel (Al≥4%), further suppressing slag-steel reactions, and stabilizing the physicochemical properties of the protective slag to consistently obtain good billet quality and ensure smooth continuous casting operation are urgent problems to be solved.

[0005] Chinese patent application CN108213365A discloses a "non-reactive protective slag for high-alumina steel," with the following weight percentage composition: CaO: 26%–40%, Al₂O₃: 18%–28%, BaO: 14%–28%, Li₂O: 2%–10%, F: 6%–14%, MgO ≤2%, C: 2%–8%, with the remainder being unavoidable impurities, and the impurity content (Na₂O + K₂O + SiO₂) ≤2%. This protective slag is essentially free of components such as SiO₂, Na₂O, Fe₂O₃, and B₂O₃ that react with reactive elements such as Al and Ti in molten steel. After use, the composition and properties of the protective slag remain stable, ensuring the smooth operation of the high-alumina steel continuous casting process. However, this protective slag has excessively strong crystallization ability, with a crystallization rate reaching 100%; simultaneously, the Li₂O content is too high, making the protective slag expensive.

[0006] Chinese patent application CN114130972A discloses a "non-reactive protective slag for a fluorine-free high-alumina steel continuous casting crystallizer," comprising, by mass percentage: CaO: 20-35%, Al₂O₃: 15-35%, SiO₂: 1-10%, BaO: 7-15%, B₂O₃: 7-15%, Na₂O + Li₂O: 10-17%, C: 2-10%, MnO: 1-7%, and MgO: 1-7%, with the remainder being unavoidable impurities. The SiO₂, B₂O₃, and Na₂O in this protective slag still react with Al in the molten steel.

[0007] Chinese patent application CN106270429A discloses a "low-reactivity protective slag and its preparation method," which contains, by mass percentage: SiO2: 8±2%, CaO: 32-38%, Al2O3: 25-31%, MgO: 1-5%, Na2O: 6-10%, F: 4-8%, Li2O: 1-4%, BaO: 0-6%, B2O3: 1-4%, C: 1-5%, and unavoidable impurities. It limits the silica content in the protective slag to a stable range, reducing the slag-steel reactivity of the slag. However, the Na2O and B2O3 it contains still exhibit strong reactivity with Al in molten steel.

[0008] Chinese patent application CN102764866A discloses a "high Al2O3 content high-aluminum steel continuous casting protective slag". The chemical composition of the slag, by mass percentage, is: CaO: 5-20%, BaO: 5-20%, Al2O3: 20-50%, B2O3: 2-15%, SiO2 ≤ 7%, flux: CaF2: 6-13%, Na2O: 6-13%, Li2O: 1-4%, MnO: 2-6%, C: 3-10%. This protective slag exhibits good glass morphology and can significantly reduce the reaction between aluminum in the steel and SiO2 in the slag. However, the slag contains Na2O and B2O3, and these components still react with Al in the molten steel.

[0009] It is evident that the main method to address the problem of strong slag-steel reaction during continuous casting of high-alumina steel is to use a low-reactivity protective slag with CaO-Al2O3 as the slag base component. However, two problems remain unresolved with CaO-Al2O3-based protective slag: (1) CaO-Al2O3-based protective slag has strong crystallization properties, resulting in low slag consumption in practical applications and unstable surface quality of the produced billets; (2) CaO-Al2O3-based protective slag contains other flux components that are reactive with Al in the molten steel, such as Na2O and B2O3, which react with molten steel with high Al content, leading to changes in the composition and properties of the protective slag and affecting the smooth operation of the continuous casting process.

[0010] Chinese utility model patent CN205732868U discloses a "crystallizer cover plate device for casting liquid protective slag," comprising: a cover plate, at least two annular pipes, and an argon blowing pipe. The cover plate, with a steel pouring hole and a slag conveying hole, is positioned at the upper end of the crystallizer; the cover plate has a sandwich structure; the side of the cover plate closest to the steel is coated with a high-temperature radiation coating. At least two annular pipes are respectively embedded in the bottom outer edge of the steel pouring hole and the slag conveying hole; multiple through holes are formed at the bottom of the annular pipes; the argon blowing pipe is connected to the top of the annular pipes. This crystallizer cover plate device can isolate air, prevent secondary oxidation of the steel, improve the thermal insulation performance of the crystallizer, increase the meniscus steel temperature, reduce the depth of oscillation marks, avoid the formation of solidification hooks, reduce pinholes, and reduce slag adhesion on the meniscus, ultimately improving the quality of the cast billet.

[0011] Chinese utility model patent CN205341853U discloses a "conveying device for liquid protective slag in continuous casting". The slag conveying pipe includes: an inner pipe, a protective layer, and a heating element; the hollow cylindrical inner pipe is made of graphite; the protective layer wraps around the inner pipe; the heating element is located outside the protective layer. The conveying device includes: a slag conveying pipe, a slag storage container, and a throttling valve; the slag storage container is a hollow cylinder with one open end; a second protective layer wraps around the slag storage container; a second heating element is located outside the second protective layer; the slag inlet of the slag conveying pipe is connected and fixed to the closed end of the slag storage container; the slag outlet of the slag conveying pipe is located on the side of the submerged entry point of the crystallizer; the throttling valve is located at the slag inlet of the slag conveying pipe, acting as a flow stop. This conveying device allows the liquid protective slag to quickly and evenly cover the surface of the molten steel in the crystallizer and fill the gaps between the solidified billet shell and the crystallizer wall, effectively improving the surface quality of the cast billet.

[0012] Both of the above technical solutions involve directly adding liquid protective slag into the continuous casting mold. This technology has received more attention and is a new research and development direction. Summary of the Invention

[0013] This invention provides a method for continuous casting of ultra-high alumina steel with high aluminum content in multiple furnaces. A barrier layer with high thermal conductivity, high temperature resistance, and oxidation resistance is added to the contact surface between the protective slag and molten steel to reduce the contact area and suppress the slag-steel reaction. Based on this, liquid protective slag is directly added into the crystallizer, ensuring its flow into the slag channel and stabilizing the slag consumption during continuous casting of high-alumina steel. Simultaneously, the protective slag maintains stable lubrication and heat transfer functions. This method solves a series of problems encountered during the continuous casting of ultra-high alumina steel, such as strong slag-steel reaction, easy crystallization and slag strip formation of the protective slag, low slag consumption, and easy sticking and leakage of steel. This enables continuous casting of this type of steel in multiple furnaces.

[0014] To achieve the above objectives, the present invention employs the following technical solution:

[0015] A method for continuous casting of ultra-high alumina steel with high aluminum content in multiple furnaces includes the following steps:

[0016] 1) Heat the barrier device to 1300-1400℃ and set it aside; the barrier device is a rectangular plate with a positioning hole in the center, which can float on the surface of the molten steel in the crystallizer to block the contact between the molten steel and the protective slag.

[0017] 2) Heat the crystallizer cover to above 800℃ and set aside;

[0018] 3) Heat and melt the low-reactivity protective slag to a liquid state in a graphite crucible to prepare a liquid protective slag for later use;

[0019] 4) Fix the barrier device to the bottom of the tundish with molybdenum wire, and align the positioning hole of the barrier device with the submerged entry nozzle; after casting begins, when the continuous casting billet emerges and the molten steel level is stable, cut the molybdenum wire used to fix the barrier device, so that the barrier device slowly falls to the surface of the molten steel and is placed on the outside of the submerged entry nozzle.

[0020] 5) Place the crystallizer cover plate on top of the crystallizer, pass the other end of the liquid slag drainage pipe leading from the graphite crucible through the crystallizer cover plate and insert it into the crystallizer, open the valve on the liquid slag drainage pipe, and inject liquid protective slag into the barrier device above the crystallizer.

[0021] 6) Based on the slag consumption, control the flow rate of the liquid protective slag through the valve on the liquid slag diversion pipe until the entire casting process is completed.

[0022] Furthermore, the contact area between the barrier device and the upper surface of the molten steel accounts for 20% to 80% of the total area of ​​the upper surface of the molten steel.

[0023] Furthermore, the density of the barrier device is 4.0 g / cm³. 3 ~7.0g / cm 3 Thickness ≥ 20mm.

[0024] Furthermore, the barrier device consists of a barrier device body and a surface coating layer; the barrier device body is made of a high thermal conductivity and high temperature resistant material; the surface coating layer is made of one or more of the following materials: high thermal conductivity, high temperature resistant, and antioxidant.

[0025] Furthermore, the high thermal conductivity high-temperature resistant material includes one or more of 2050 high-temperature alloy, titanium, and corundum.

[0026] Furthermore, the material of the surface coating is molybdenum disilicide, hexagonal boron nitride, or titanium diboride.

[0027] Furthermore, the surface coating is applied using ion spraying or laser cladding.

[0028] Furthermore, the liquid protective slag is a CaO-SiO2-based protective slag or a CaO-Al2O3-based protective slag; wherein, the basicity of the CaO-SiO2-based protective slag is less than 0.7; and the mass content of SiO2 in the CaO-Al2O3-based protective slag is ≤10%.

[0029] Furthermore, the lower surface of the crystallizer cover is coated with a high-temperature radiation material.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] (1) Install a barrier device in the crystallizer to block the contact between slag and steel, thereby reducing the contact area between molten steel and protective slag, inhibiting the reaction between slag and steel, effectively alleviating the deformation of protective slag, and solving the problem of easy crystallization and precipitation of slag strips in protective slag.

[0032] (2) Liquid protective slag is directly added to the crystallizer with the barrier device installed, which avoids the problems of insufficient heat transfer and poor melting that may be caused by the solid protective slag (powder slag, granular slag, etc.) due to the installation of the barrier device.

[0033] (3) Adding a cover plate to the top of the crystallizer solved the problem of poor heat insulation effect of liquid protective slag;

[0034] (4) Adding liquid protective slag directly into the crystallizer ensures the flow of protective slag into the slag channel, stabilizes the slag consumption during continuous casting production, and ensures that the protective slag has stable lubrication and heat transfer functions, thus solving the problems of low slag consumption and easy sticking and leakage of steel during the continuous casting of ultra-high aluminum content steel. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the continuous casting process of high-alumina steel with ultra-high aluminum content as described in this invention.

[0036] In the diagram: 1. Crystallizer 2. Submerged entry nozzle 3. Barrier device 4. Graphite crucible 5. Liquid slag drainage pipe 6. Valve 7. Crystallizer cover 8. Molten steel 9. Solidified billet shell 10. Liquid protective slag Detailed Implementation

[0037] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0038] like Figure 1 As shown, in the method of continuous casting of high-alumina steel with ultra-high aluminum content in multiple furnaces according to the present invention, a device for preventing molten steel from contacting protective slag, namely the blocking device 3, is used. The blocking device 3 is placed on the surface of the molten steel 8 in the crystallizer 1. The contact area between the blocking device 3 and the upper surface of the molten steel 8 accounts for 20% to 80% of the total area of ​​the upper surface of the molten steel 8.

[0039] The material of the barrier device 3 body includes, but is not limited to, one or more of the following high thermal conductivity and high temperature resistance materials: 2050 high temperature alloy, titanium (Ti), corundum, etc.

[0040] The surface of the barrier device 3 is modified by spraying one or more of the following materials with high thermal conductivity, high temperature resistance and oxidation resistance using ion spraying or laser cladding. The materials used for modification include, but are not limited to, molybdenum disilicide (MoSi2), hexagonal boron nitride (HBN), titanium diboride (TiB2), etc.

[0041] The density of barrier device 3 is between 4.0 g / cm³. 3 ~7.0g / cm 3 Between them, they can float on the surface of molten steel to prevent the molten steel from coming into contact with the protective slag.

[0042] A positioning hole is provided in the middle of the barrier device 3, which can be used to restrict the horizontal movement of the barrier device 3 on the surface of molten steel by means of the immersion nozzle 2. In order to ensure that the barrier device 3 has sufficient impact resistance, the thickness of the barrier device 3 is required to be ≥20mm.

[0043] A crystallizer cover plate 7 is added to the upper edge of the crystallizer 1 to provide heat insulation and heat preservation for the traditional "three-layer structure" (liquid slag layer, sintering layer, and powder slag layer) protective slag.

[0044] The continuous casting protective slag is melted in a graphite crucible 4 using induction heating. The resulting liquid protective slag 10 is injected into the crystallizer 1 of the continuous casting machine through a liquid slag guide pipe 5. The liquid protective slag 10 includes, but is not limited to, CaO-SiO2-based protective slag or CaO-Al2O3-based protective slag; wherein, the basicity of the CaO-SiO2-based protective slag is less than 0.7; and the SiO2 mass content in the CaO-Al2O3-based protective slag is ≤10%.

[0045] The specific operation process of the method for continuous casting of ultra-high alumina steel with high aluminum content in multiple furnaces according to the present invention is as follows:

[0046] (1) Heat the crystallizer cover plate 7 to 800°C and the barrier device 3 to 1300-1400°C for later use.

[0047] (2) Heat and melt the protective slag in graphite crucible 4 until it is liquid, and set aside for use.

[0048] (3) Fix the barrier device 3 to the bottom of the intermediate tundish with molybdenum wire, and align the positioning hole in the center of the barrier device 3 with the immersion nozzle 2.

[0049] (4) The conventional continuous casting process is adopted for the casting operation. After the continuous casting billet emerges and the molten steel 8 liquid level is stable, the molybdenum wire used to fix the barrier device 3 is cut, so that the barrier device 3 slowly falls to the surface of the molten steel 8.

[0050] (5) Place the crystallizer cover plate 7 on top of the crystallizer 1, insert the liquid slag drainage pipe 5, and connect the other end of the liquid slag drainage pipe 5 to the graphite crucible 4.

[0051] (5) Open the valve 6 on the liquid slag drainage pipe 5 and inject liquid protective slag 10 into the barrier device 3 in the crystallizer 1.

[0052] (6) Control the flow rate of liquid protective slag 10 according to the slag consumption. If necessary, lift the crystallizer cover plate 7 above the crystallizer 1 and clean the slag strips that may exist in the slag channel.

[0053] The following embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0054]

Example

[0055] In this embodiment, a twin-strand slab continuous casting machine is used to continuously cast high-alumina steel with an Al content of 4.0 wt%. The weight of molten steel in a single ladle is 200 t, and the number of ladles is 3. The cross-sectional dimensions of the crystallizer 1 are 1100 mm × 230 mm, and the continuous casting speed is 1.0 m / min. In the twin-strand slab continuous casting machine, the first strand adopts the conventional casting process, and the second strand adopts the process method described in this invention.

[0056] like Figure 1 As shown, the relevant process parameters and operating procedures for flow 2 are as follows:

[0057] 1. Fabricate the barrier device 3; design it so that the contact area between the barrier device 3 and the upper surface of the molten steel 8 accounts for 65% of the total area of ​​the upper surface of the molten steel 8; the barrier device 3 is a rectangular plate with a central opening, with external dimensions of 1000mm × 170mm × 30mm, and the diameter of the positioning hole at the center is [missing information]. During casting, the barrier device 3 is positioned horizontally by fitting it around the immersion nozzle 2 through positioning holes. The frame of the barrier device 3 is made of 2050 high-temperature alloy and filled with corundum, with a volume ratio of 3:1 between the 2050 high-temperature alloy and corundum. The outer surface of the barrier device 3 is modified by ion spraying with molybdenum disilicide (MoSi2) powder, and the overall density of the barrier device 3 is 7.0 g / cm³. 3 .

[0058] 2. Fabrication of the crystallizer cover plate 7: A cover plate body with external dimensions of 1300mm × 400mm × 30mm is prepared using refractory material. The lower surface of the cover plate body is sprayed with a high-temperature radiant material. An aperture of [diameter missing] is made at a distance of 300mm on each side of the center point of the crystallizer cover plate 7. A circular hole is provided for inserting the liquid-slag drainage conduits 5 on both sides. A hole with a diameter of [missing information] is opened at the center of the crystallizer cover plate 7. The round hole is used for the immersion nozzle 2 to pass through.

[0059] 3. Heat the crystallizer cover plate 7 to 800°C and the barrier device 3 to 1400°C, and set aside for use.

[0060] 4. At a height of 500mm and a diameter of In the graphite crucible 4, the low-reactivity CaO-Al2O3-based protective slag (SiO2 mass content of 7%) is heated and melted to a liquid state for later use.

[0061] 5. Fix the barrier device 3 to the bottom of the tundish with molybdenum wire, and align the central positioning hole with the immersion nozzle 2.

[0062] 6. The conventional continuous casting start-up process is adopted for the start-up operation. After the continuous casting billet emerges and the molten steel 8 liquid level is stable, the molybdenum wire used to fix the blocking device 3 is cut, so that the blocking device 3 slowly falls to the surface of the molten steel 8 and is fitted on the outside of the submerged entry nozzle 2 through the positioning hole.

[0063] 7. Place the crystallizer cover plate 7 on top of the crystallizer 1, insert the liquid slag drainage pipe 5, and connect the other end of the liquid slag drainage pipe 5 to the graphite crucible 4.

[0064] 8. Open valve 6 on liquid slag drainage pipe 5 and inject liquid protective slag 10 into crystallizer 1.

[0065] 9. Control the flow rate of liquid protective slag 10 according to the slag consumption. Open the crystallizer cover 7 every 30 minutes to observe whether there are slag bars in the slag channel. If so, clean the slag bars. Inside the crystallizer 1, the molten steel 8 transfers heat with the water-cooled copper plate, causing the molten steel 8 to solidify into a solidified billet shell 9 of a certain thickness and sufficient strength. Then, under the vibration of the crystallizer 1 and the lubrication of the protective slag, the solidified billet shell 9 is continuously and safely pulled out of the crystallizer 1, realizing continuous casting.

[0066] In the continuous casting process of this embodiment, the leakage prediction system triggered five major alarms within 20 minutes after the start of casting for the first run. The casting process consumed only 5 kg of protective slag, and a large number of slag streaks appeared on the surface of the crystallizer. Casting was forced to stop after 20 minutes. However, the leakage prediction system did not trigger any alarms during the entire casting process for the second run, and the multi-heat continuous casting of three ladles of high-alumina steel was successfully completed.

[0067] As can be seen from the above comparison, the method of continuous casting of high-alumina steel with ultra-high aluminum content described in this invention can realize continuous casting of this type of steel in multiple furnaces, ensuring the smooth operation of continuous casting production.

[0068] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for continuous casting of ultra-high alumina content high-alumina steel in multiple furnaces, characterized in that, Includes the following steps: 1) Heat the barrier device to 1300–1400℃ for later use; the barrier device is a rectangular plate with a positioning hole in the center, capable of floating on the surface of the molten steel in the crystallizer, used to block the contact between the molten steel and the protective slag; the density of the barrier device is 4.0 g / cm³. 3 ~7.0g / cm 3 Thickness ≥ 20mm; The barrier device consists of a barrier device body and a surface coating; The barrier device body is made of a high thermal conductivity and high temperature resistant material; The surface coating material is one or more of the following: high thermal conductivity, high temperature resistant, and anti-oxidation material; 2) Heat the crystallizer cover to above 800℃ and set aside; 3) The low-reactivity protective slag is heated and melted to a liquid state in a graphite crucible to prepare a liquid protective slag for later use; the liquid protective slag is a CaO-SiO2-based protective slag or a CaO-Al2O3-based protective slag; wherein, the basicity of the CaO-SiO2-based protective slag is less than 0.7; and the SiO2 mass content in the CaO-Al2O3-based protective slag is ≤10%; 4) Fix the barrier device to the bottom of the tundish with molybdenum wire, and align the positioning hole of the barrier device with the submerged entry nozzle; after casting begins, when the continuous casting billet emerges and the molten steel level is stable, cut the molybdenum wire used to fix the barrier device, so that the barrier device slowly falls to the surface of the molten steel and is placed on the outside of the submerged entry nozzle. 5) Place the crystallizer cover plate on top of the crystallizer, pass the other end of the liquid slag drainage pipe leading from the graphite crucible through the crystallizer cover plate and insert it into the crystallizer, open the valve on the liquid slag drainage pipe, and inject liquid protective slag into the barrier device above the crystallizer. 6) Based on the slag consumption, control the flow rate of the liquid protective slag through the valve on the liquid slag diversion pipe until the entire casting process is completed.

2. The method for continuous casting of ultra-high alumina steel with high aluminum content in multiple furnaces according to claim 1, characterized in that, The contact area between the barrier device and the upper surface of the molten steel accounts for 20% to 80% of the total area of ​​the upper surface of the molten steel.

3. The method for continuous casting of ultra-high alumina steel with high aluminum content in multiple furnaces according to claim 1, characterized in that, The high thermal conductivity, high temperature resistant material includes one or more of high temperature alloys, titanium, and corundum.

4. The method for continuous casting of ultra-high alumina steel with high aluminum content in multiple furnaces according to claim 1, characterized in that, The material of the surface coating is molybdenum disilicide, hexagonal boron nitride, or titanium diboride.

5. The method for continuous casting of ultra-high alumina steel with high aluminum content in multiple furnaces according to claim 1, characterized in that, The surface coating is applied using either ion spraying or laser cladding.

6. The method for continuous casting of ultra-high alumina steel with high aluminum content in multiple furnaces according to claim 1, characterized in that, The lower surface of the crystallizer cover is coated with a high-temperature radiation material.

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