A continuous casting protective slag for lanthanum-containing ferrochrome-aluminum alloy and a preparation method thereof

Abstract

The application discloses a continuous casting protective slag for lanthanum-containing iron-chromium-aluminum alloy and a preparation method thereof, and mainly relates to the design of physical and chemical indexes of the protective slag and a production process. The preparation method of the protective slag comprises the following steps: water, ethanol and carbon powder are fully mixed according to a certain proportion, the carbon powder is fully dispersed into the slurry, and the remaining materials are added into the solution to be stirred and ball-milled to prepare slurry with a suitable concentration; and spray granulation is carried out according to a specific process to obtain a suitable particle size requirement, so as to ensure the gas permeability of the protective slag. Through the above method, a new CaO-free type protective slag can be obtained, the protective slag has the high-temperature characteristics of low melting point and excellent lubricity, meanwhile, the special preparation process controls the uniformity of each component in the protective slag, the good dispersibility of the carbon material and the suitable gas permeability, so that the lanthanum-containing iron-chromium-aluminum alloy can realize multi-furnace continuous casting.

Description

Technical Field

[0001] This invention relates to the fields of steelmaking and continuous casting, and in particular to a protective slag for continuous casting of lanthanum-containing iron-chromium-aluminum alloys and its preparation method. Background Technology

[0002] Lanthanum-containing iron-chromium-aluminum alloys can contain 3-7% Al and 0.05-0.08% La. These alloys are widely used in the electrothermal field due to their high cost-effectiveness, high heating efficiency, and ease of processing.

[0003] Al and rare earth elements in steel are easily oxidized. During continuous casting, they readily react violently with SiO2 in the protective slag, causing severe changes in the basicity, viscosity, and melting point of the protective slag. This leads to deterioration in the lubrication and heat transfer performance of the crystallizer, which in turn affects the smooth operation of the continuous casting process and the surface quality of the cast billet.

[0004] Currently, many metallurgical scholars at home and abroad have conducted extensive research on protective slags for high-alumina steel and high-rare-earth steel, mainly focusing on two aspects: one is the traditional CaO-SiO2 system reactive protective slag; the other is the novel CaO-Al2O3 system non-reactive protective slag. There are successful cases in high-alumina and high-rare-earth steels. For example, patent CN102233414A successfully applied a low-basicity (R=0.55-0.65) CaO-SiO2 system protective slag to the continuous casting production of high-alumina and high-manganese non-magnetic steel with an aluminum content of 2.0-2.5%; patent CN101612653A successfully applied a CaO-SiO2 system protective slag with a basicity R=0.917-0.333M to the continuous casting of high-alumina titanium rare-earth steel; patent CN110560649B proposed a CaO-Al2O3 system protective slag with cryolite (Na3AlF6) and Al2O3 as the main base materials, and used it in the continuous casting of high-alumina steel with an aluminum content of 0.5-3.5%, reducing the generation of billet cracks and meeting the requirements of high-alumina steel continuous casting. Patent CN114713782A proposes a CaO-SiO2-based pre-melted protective slag for casting stainless steel with a rare earth (Ce) content of 0.03-0.08%. However, this technology suffers from high basicity and low carbon content in the protective slag, making it difficult to control the slag ring problem caused by steel slag reaction. The protective slag involved in the aforementioned invention provides a good approach for continuous casting of high-alumina steel and high-rare earth steel, but its applicability is limited, and it cannot be used for continuous casting of iron-chromium-aluminum steel with a simultaneous aluminum content of 4-7% and a rare earth lanthanum content of 0.05-0.08%.

[0005] Practice has shown that when using CaO-SiO2 and CaO-Al2O3 system protective slags to cast lanthanum-containing iron-chromium-aluminum alloys, the physicochemical properties of the protective slag change drastically, resulting in increased slag strands, severe slag agglomeration, and disrupted continuous casting. Scanning electron microscopy and energy dispersive spectroscopy analysis of the slag strands revealed the presence of 2CaO·Al2O3·SiO2, LiAlO2, Ca4Si2F2O7, and CaF... 2、 The protective slag is composed of multiple phases, including 2CaO, Al2O3, SiO2, and La2O3, with significant aggregation of the La2O3 phase, which deteriorates the performance of the protective slag. Therefore, there is an urgent need to develop a new type of protective slag.

[0006] This invention provides a continuous casting protective slag for lanthanum-containing iron-chromium-aluminum alloys and its preparation method. This method effectively controls problems such as the deterioration of the protective slag caused by steel slag reaction, and realizes multi-furnace continuous casting of ultra-high aluminum and high rare earth alloy steel. Summary of the Invention

[0007] The purpose of this invention is to address the above-mentioned problems by providing a continuous casting protective slag for lanthanum-containing iron-chromium-aluminum alloys and its preparation method.

[0008] The objective of this invention is achieved as follows: a continuous casting protective slag for lanthanum-containing iron-chromium-aluminum alloys, wherein the effective component percentage content of the protective slag is as follows: BaO: 9~11%, SrO: 14~18%, SiO2: 40~45%, Na2O: 9~12%, F - : 3~6%, Li2O: 4~6%, B2O3: 5~7%, Al2O3: <1%, CaO: <0.5% and unavoidable impurities; (BaO+SrO) / SiO2=0.55-0.7, 24%≤Na2O+F - The content of Li₂O and B₂O₃ is ≤28%, the melting point is 600-800℃, the melting rate is 18-21s, the viscosity is 0.15-0.25Pa·s, and the heat flux density is 700-800kw / m³. 2 .

[0009] A method for preparing a continuous casting protective slag for lanthanum-containing iron-chromium-aluminum alloys includes the following steps: Step 1: First, add clean water to a high-speed pulping machine, ensuring the slag concentration is 48-51% in the later stages; the speed of the high-speed pulping machine is 120-140 rpm; Step 2: The raw materials and their weight percentages for the protective slag are as follows: borosilicate glass powder: 17-18%, sodium fluoride: 8.2-9%, quartz sand: 23.5-27%, barium carbonate: 10.5-12%, strontium carbonate: 19-20%, lithium carbonate: 9-10.2%, carbon powder: 5-7%, binder: 1.5%. -2.3%; Add ethanol to water to make the solution concentration reach 0.4-0.6%, stir for 5-10 minutes, add carbon powder to the above solution, stir for 10-15 minutes; Step 3: Mix the remaining raw materials and add them to the solution in Step 2, stir for 10-15 minutes and then ball mill for 30-40 minutes at a speed of 40-60 rpm; Step 4: Perform atomization granulation with an atomization pressure of 1.5-1.6 MPa and a nozzle diameter of 0.8-1.2 mm. The resulting protective slag should have a particle size of >95% within the range of 0.1-0.4 mm.

[0010] The raw material is borosilicate glass powder: SiO2: 58-62%, Na2O: 11-13%, B2O 3： 24-26%, Sodium fluoride: NaF > 90%, Quartz sand: SiO2 > 98%, Barium carbonate: BaCO3 > 98%, Strontium carbonate: SrCO3 > 98%; Lithium carbonate: Li2CO3 > 99%, Carbon powder: TC > 99%, Channel black is selected.

[0011] The beneficial effects of this invention are as follows: Through the above method, a continuous casting protective slag for lanthanum-containing iron-chromium-aluminum alloys and its preparation method are presented. This method innovatively proposes a CaO-free protective slag and, in conjunction with a unique production process, effectively controls the deterioration of the protective slag caused by steel slag reaction, thereby realizing multi-furnace continuous casting of ultra-high aluminum and high rare earth alloy steel. Detailed Implementation

[0012] This invention addresses the limitations of existing technologies in meeting the requirements of continuous casting of lanthanum-containing iron-chromium-aluminum alloys. It abandons the traditional research approaches of CaO-SiO2 and CaO-Al2O3 protective slag systems, and innovatively proposes a CaO-free protective slag by replacing CaO with BaO and SrO. This protective slag is less likely to combine with reacted substances to form high-melting-point precipitates, ensuring sufficient lubrication. Simultaneously, a unique production process controls the uniformity of components, good dispersion of carbon materials, and suitable permeability in the protective slag, ensuring uniform sintering and melting during its use. This facilitates smooth continuous casting. The technical solution of the invention is as follows.

[0013] 1. Physicochemical properties of protective slag: (1) The percentage content of effective components of protective slag is as follows: BaO: 9~11%, SrO: 14~18%, SiO2: 40~45%, Na2O: 9~12%, F - : 3~6%, Li2O: 4~6%, B2O3: 5~7%, Al2O3: <1%, CaO: <0.5% and unavoidable impurities.

[0014] (2) (BaO+SrO) / SiO2=0.55-0.7, 24%≤Na2O+F - +Li₂O+B₂O₃≤28%, melting point 600-800℃ (hot wire method), melting rate at 1350℃: 18-21s, viscosity at 1300℃: 0.15-0.25Pa·s, heat flux density: 700-800kw / m³ 2 .

[0015] (3) Preferred: (BaO+SrO) / SiO2=0.62, melting point is 718℃ (hot wire method), melting rate at 1350℃ is 18s, viscosity at 1300℃ is 0.18Pa.s, heat flux density is 710kw / m 2 .

[0016] The raw materials and their weight percentages of the protective slag are as follows: borosilicate glass powder: 17-18%, sodium fluoride: 8.2-9%, quartz sand: 23.5-27%, barium carbonate: 10.5-12%, strontium carbonate: 19-20%, lithium carbonate: 9-10.2%, carbon powder: 5-7%, and binder: 1.5-2.3%.

[0017] (4) Compared with traditional protective slag, this protective slag does not contain CaO, but uses BaO and SrO instead of CaO. The reason is that BaO and SrO can make the protective slag have a lower melting point and viscosity, which can inhibit the crystallization of the protective slag. Most importantly, BaO+SrO is not easy to react with steel slag products such as Al2O3 and rare earth oxides to form a high melting point phase, which can effectively control the problems of slag strips and agglomeration in the protective slag.

[0018] (5) The flux (Na2O+F) in this invention - The high proportion of (+Li2O+B2O3) is intended to give the protective slag liquid better resistance to denaturation.

[0019] 2. Raw materials and preparation method: According to the above requirements of physicochemical indicators, borosilicate glass powder, sodium fluoride, quartz sand and barium carbonate, strontium carbonate, lithium carbonate, carbon powder and binder are selected as raw materials to prepare the product. The specific technology is as follows: (1) Each raw material meets the following requirements: borosilicate glass powder: SiO2: 58-62%, Na2O: 11-13%, B2O 3：24-26%; Sodium fluoride: NaF > 90%; Quartz sand: SiO2 > 98%; Barium carbonate: BaCO3 > 98%; Strontium carbonate: SrCO3 > 98%; Lithium carbonate: Li2CO3 > 99%; Carbon powder: TC > 99%, using channel black.

[0020] (2) Calculate the required weight of each raw material based on the weight percentage of the constituent elements of the protective slag. Borosilicate glass powder: 17-18%, sodium fluoride: 8.2-9%, quartz sand: 23.5-27%, barium carbonate: 10.5-12%, strontium carbonate: 19-20%, lithium carbonate: 9-10.2%, carbon powder: 5-7%, binder: 1.5-2.3%.

[0021] (3) First, add clean water to the high-speed pulping machine. The amount of water added should ensure that the concentration of the pulp in the later stage is 48-51%.

[0022] (4) Add a certain amount of ethanol to the water and stir for 5-10 minutes until the concentration of ethanol in the aqueous solution reaches 0.4-0.6%. Add the carbon powder to the solution in small amounts several times and stir for 10-15 minutes. Adding ethanol can make the carbon powder better dispersed in the solution and make the carbonaceous material in the protective slag evenly distributed.

[0023] (5) Mix the remaining material with the binder and add it to the solution in the previous step. Stir for 10-15 minutes and then ball mill for 30-40 minutes.

[0024] (6) Next, atomization granulation is carried out. The atomization pressure is 1.5-1.6 MPa, and the nozzle diameter of the spray gun is 0.8-1.2 mm. Compared with traditional hollow protective slag, this patent has the characteristics of low slurry concentration, low atomization pressure and small nozzle diameter, which makes the particle size of the protective slag smaller (the proportion of particles with a diameter in the range of 0.1~0.4 mm is >95%), resulting in more suitable air permeability, which is conducive to reducing the slag streaks of the protective slag. Example 1

[0025] (1) The effective components of this protective slag are BaO: 10.21%, SrO: 15.83%, SiO2: 41.8%, Na2O: 10.34%, F - : 4.67%, Li2O: 4.62%, B2O3: 5.55%, Al2O3: 0.49%, CaO: 0.098%.

[0026] (2) (BaO+SrO) / SiO2=0.62, melting point is 718℃ (hot wire method), melting rate at 1350℃: 19s, viscosity at 1300℃ is 0.18Pa.s, heat flux density is 710kw / m 2 .

[0027] (3) The raw materials of this protective slag are prepared in the following weight percentages: borosilicate glass powder: 17.89%, sodium fluoride: 8.87%, quartz sand: 24.74%, barium carbonate: 11.36%, strontium carbonate: 19.92%, lithium carbonate: 9.72%, carbon powder: 5.5%, binder: 2%.

[0028] (4) Manufacturing process of protective slag: The preparation method of protective slag includes the following steps: Step 1: First, add clean water to the high-speed pulping machine. The amount of water added should ensure that the concentration of the slurry in the later stage is 50%, and the rotation speed is 130 rpm. Step 2: Add a certain mass of ethanol to the water and stir for 6 minutes until the concentration of ethanol in the aqueous solution reaches 0.5%. Add carbon powder to the above solution and stir for 12 minutes. Step 3: Mix the remaining material with the binder and add it to the solution in the previous step. Stir for 10 minutes and then ball mill for 30 minutes at a ball milling speed of 50 rpm. Step 4: Then perform atomization granulation. The atomization pressure is 1.55 MPa, the nozzle diameter of the spray gun is 0.9 mm, and the particle size of the obtained protective slag is in the range of 0.1~0.4 mm, accounting for 96.5%.

[0029] This embodiment is used for continuous casting of lanthanum-containing iron-chromium-aluminum steel, with a rare earth lanthanum content of 0.05% and an aluminum content of 5.5%. Example 2

[0030] (1) The effective components of this protective slag are BaO: 9.92%, SrO: 15.61%, SiO2: 42.59%, Na2O: 10.23%, F - : 4.57%, Li2O: 4.49%, B2O3: 5.62%, Al2O3: 0.50%, CaO: 0.098%.

[0031] (2) (BaO+SrO) / SiO2=0.60, melting point is 800℃ (hot wire method), melting rate at 1350℃: 19s, viscosity at 1300℃ is 0.22Pa.s, heat flux density is 731kw / m 2 .

[0032] (3) The raw materials of this protective slag are prepared in the following weight percentages: borosilicate glass powder: 18.00%, sodium fluoride: 8.72%, quartz sand: 25.32%, barium carbonate: 11.07%, strontium carbonate: 19.71%, lithium carbonate: 9.48%, carbon powder: 5.5%, binder: 2%.

[0033] (4) Manufacturing process of protective slag: The preparation method of protective slag includes the following steps: Step 1: First, add clean water to the high-speed pulping machine. The amount of water added should ensure that the concentration of the slurry in the later stage is 49%, and the rotation speed is 130 rpm. Step 2: Add a certain mass of ethanol to the water and stir for 10 minutes until the concentration of ethanol in the aqueous solution reaches 0.4%. Add carbon powder to the above solution and stir for 15 minutes. Step 3: Mix the remaining material with the binder and add it to the solution in the previous step. Stir for 10 minutes and then ball mill for 30 minutes at a speed of 50 rpm. Step 4: Then perform atomization granulation. The atomization pressure is 1.6 MPa, the nozzle diameter of the spray gun is 1.0 mm, and the particle size of the obtained protective slag is in the range of 0.1~0.4 mm, accounting for 95.8%.

[0034] This embodiment is used for continuous casting of lanthanum-containing iron-chromium-aluminum steel, with a rare earth lanthanum content of 0.04% and an aluminum content of 6.0%.

[0035] The above description is only a specific embodiment of the present invention, but the structural features protected by the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for preparing a continuous casting protective slag for lanthanum-containing iron-chromium-aluminum alloys, characterized in that: Includes the following steps: Step 1: First, add clean water to the high-speed pulper. The amount of water added should ensure that the concentration of the pulp in the later stage is 48-51%. The speed of the high-speed pulper is 120-140 rpm. Step 2: The raw materials and their weight percentages for preparing the protective slag are as follows: borosilicate glass powder: 17-18%, sodium fluoride: 8.2-9%, quartz sand: 23.5-27%, barium carbonate: 10.5-12%, strontium carbonate: 19-20%, lithium carbonate: 9-10.2%, carbon powder: 5-7%, binder: 1.5-2.3%; add ethanol to water to make the solution concentration reach 0.4-0.6%, stir for 5-10 minutes, add carbon powder to the above solution, and stir for 10-15 minutes; Step 3: Mix the remaining raw materials and add them to the solution from Step 2. Stir for 10-15 minutes and then ball mill for 30-40 minutes at a speed of 40-60 rpm. Step 4: Perform atomization granulation with an atomization pressure of 1.5-1.6 MPa and a nozzle diameter of 0.8-1.2 mm. The resulting protective slag should have a particle size of 0.1-0.4 mm accounting for >95%. The percentage content of effective components in the protective slag is as follows: BaO: 9~11%, SrO: 14~18%, SiO2: 40~45%, Na2O: 9~12%, F - : 3~6%, Li2O: 4~6%, B2O3: 5~7%, Al2O3: <1%, CaO: <0.5% and unavoidable impurities; (BaO+SrO) / SiO2=0.55-0.7, 24%≤Na2O+F - The content of Li₂O and B₂O₃ is ≤28%, the melting point is 600-800℃, the melting rate is 18-21s, the viscosity is 0.15-0.25Pa·s, and the heat flux density is 700-800kw / m³. 2 .

2. The method for preparing a continuous casting protective slag for lanthanum-containing iron-chromium-aluminum alloys according to claim 1, characterized in that: The raw material is borosilicate glass powder: SiO2: 58-62%, Na2O: 11-13%, B2O 3： 24-26%, Sodium fluoride: NaF > 90%, Quartz sand: SiO2 > 98%, Barium carbonate: BaCO3 > 98%, Strontium carbonate: SrCO3 > 98%; Lithium carbonate: Li2CO3 > 99%, Carbon powder: TC > 99%, Channel black is selected.