A method for manufacturing a furnace bottom plate for a ring-shaped annealing furnace

Abstract

This invention relates to a method for manufacturing a furnace bottom plate for an annular annealing furnace, comprising the following steps: S1, steel smelting; S2, ingot casting: casting into flat ingots and slow cooling to room temperature; S3, rolling: rolling the flat ingots into square plates and allowing them to cool naturally after rolling; S4, water jet cutting: cutting the outer circle of the square plate and removing excess edges and corners; S5, boss welding: welding the pre-processed ring to the center of the furnace bottom plate; S6, heat treatment; S7, machining to complete the furnace bottom plate manufacturing. This invention utilizes a dual refining process combining an electric arc furnace and an AOD furnace, using a large amount of recycled scrap and inexpensive medium-carbon Cr iron and high-carbon Mn, which reduces manufacturing costs while ensuring the chemical composition of the materials. The rolling process eliminates internal porosity defects in the steel ingots, resulting in a denser structure and improved service life of the furnace bottom plate. High-pressure water jet cutting avoids quality defects such as cracks and decarburization caused by oxygen cutting on the outer circle, ensuring the quality of the furnace bottom plate.

Description

Technical Field

[0001] This invention relates to the field of industrial furnace thermal equipment manufacturing, specifically to a method for manufacturing a furnace bottom plate for an annular annealing furnace. Background Technology

[0002] The bottom plate in an annular annealing furnace is used to support silicon steel coils during high-temperature annealing. It has a disc structure with a 10-20mm boss on each of the top and bottom surfaces. The material is heat-resistant steel 0Cr23Ni13 (chemical composition: C≤0.08%, Si≤1.0%, Mn≤2.0%, P≤0.035%, S≤0.030%, Ni12.0-15.0%, Cr22.0-24.0%). The annealing process involves cycling from room temperature to high temperature, holding at that temperature, and then back to room temperature, with a maximum temperature of 1200℃ and an annealing cycle of 150 hours. Because the bottom plate is subjected to alternating compressive and tensile loads, cracks develop after several cycles, eventually leading to failure and scrapping due to crack propagation. Therefore, improving the internal quality and microstructure of the bottom plate is crucial to enhancing its performance and extending its service life, thereby reducing the production cost of heat treatment for silicon steel coils.

[0003] Currently, furnace bottom plates are manufactured using casting, forging, and rolling processes. Patent ZL200720088599.4 discloses a novel annealed furnace bottom plate with a plum blossom-shaped edge, made of ZG0Cr23Ni13. Due to its special structure, it is mostly manufactured using casting, with an average product lifespan of about 6-8 months. Patent ZL201510719184.1 discloses a high-temperature annealed furnace bottom plate and its manufacturing method. The bottom plate is circular, made of 0Cr23Ni13, and forged. The manufacturing process is as follows: medium-frequency furnace smelting → LF furnace refining → die casting → electroslag remelting → forging → heat treatment → machining. This process results in low levels of harmful element S and non-metallic inclusions in the steel, effectively preventing the generation of thermal fatigue cracks during use. Furthermore, forging improves its microstructure, resulting in a denser microstructure and extended service life. However, this process involves smelting, die casting, and electroslag remelting, resulting in high manufacturing costs. In addition, the riser end of the electroslag ingot is difficult to saw off, and inclusions are often rolled into the product during forging, affecting its service life.

[0004] Therefore, in order to reduce the heat treatment cost of cold-rolled grain-oriented silicon steel coils, it is necessary to improve the internal quality of the furnace bottom plate and extend its service life, and at the same time reduce the manufacturing cost of the furnace bottom plate. Therefore, it is essential to find a manufacturing method for the furnace bottom plate. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for manufacturing a bottom plate of an annular annealing furnace, which can not only ensure the internal quality of the bottom plate and extend its service life, but also reduce the manufacturing cost of the bottom plate, thereby reducing the heat treatment cost of silicon steel coils.

[0006] The specific solution of the present invention is as follows: a method for manufacturing a bottom plate for an annular annealing furnace, comprising the following steps: The objective of this invention is achieved through the following measures: a method for manufacturing a bottom plate for an annular annealing furnace, the process flow of which is: steel smelting → die casting → rolling → water jet cutting of the outer circle → boss welding → heat treatment → machining.

[0007] The specific steps described above are as follows: S1. Steel smelting: A dual refining process using an electric arc furnace and an AOD furnace is adopted.

[0008] The electric arc furnace melting process involves placing recycled waste furnace bottom plates, 0Cr23Ni13 return material, medium carbon ferrochrome, high carbon ferromanganese, nickel plates, ferrosilicon, and scrap steel into the electric arc furnace in a certain quantity and melting them together. The steel composition is controlled as follows: C: 0.30~0.50%, Si: 0.25~0.35%, Mn: 1.20~1.60%, Ni: 12.50~13.50%, Cr: 22.50~23.50%, P≤0.030%, and the tapping temperature is 1620~1670℃.

[0009] The AOD furnace oxidation and reduction refining process involves: adding the molten steel to the AOD furnace at a temperature of 1540-1600℃; blowing in an argon-oxygen mixture with the O2:Ar ratio continuously varying from 2:1 to 1:3, gradually reducing the flow rate until C ≤ 0.06%; adding a reduction mixture for refining and stirring with pure argon; the reduction mixture consists of 7-10 kg / ton of active lime, 1-2 kg / ton of fluorite, and 1.0-1.5 kg / ton of aluminum powder; sampling and analysis, adjusting the chemical composition of the molten steel based on the analysis results, specifically: C ≤ 0.08%; S ≤ 0.025%; Si, Mn, Cr, and Ni controlled according to the midline of the chemical composition; tapping temperature of 1555-1565℃; and soft blowing for 8-10 minutes to allow inclusions to float to the surface.

[0010] S2. Ingot casting: Cast into 6.0t flat ingots at a casting temperature of 1460~1470℃. The casting time for the ingot body is 6.0~8.0min, and the casting time for the riser is 4.0~6.0min. After casting, the mold is cooled for 3~4 hours, then demolded and placed in a slow cooling pit to cool to room temperature.

[0011] S3. Rolling: The flat ingots obtained in S2 are rolled using a reversible rolling mill with an initial rolling temperature of 1150℃ and a final rolling temperature of 850℃. The ingots are rolled into square plates according to the thickness of the furnace bottom plate blanks and then naturally cooled.

[0012] S4. Waterjet cutting: Cut the outer circle of the above square plate with a high-pressure waterjet cutting machine to remove excess edges and corners. The outer circle diameter is based on the blank size of the furnace bottom plate.

[0013] S5. Boss welding: Weld the pre-processed ring to the center of the furnace bottom plate. The ring material is 0Cr23Ni13 with a thickness of 10-20mm and a diameter according to the drawing dimensions. Welding method: CO2 gas shielded welding.

[0014] S6. Heat treatment: Place the furnace bottom plate blank after step S5 into the heating furnace, heat it to 850℃ at a heating rate of ≤60℃ / h, hold it for 3-4 hours, then heat it to 1050℃ at a heating rate of ≤100℃ / h, hold it for 5 hours, remove it from the furnace and quench it with water at ≤32℃, and start stirring until it cools to room temperature to complete the heat treatment.

[0015] S7. Machining the furnace bottom plate blank after step S6 to complete the furnace bottom plate production.

[0016] Furthermore, in step S2, the weight of the flat ingot is 6.0t, and the specifications of the flat ingot are: cross-sectional dimensions: 500×400×1430mm, width: 1200mm.

[0017] Furthermore, in step S3, the rolling heating regime is as follows: the temperature is increased to 600℃ at a heating rate of ≤60℃ / h and held for 3 hours, then increased to 850℃ at a heating rate of ≤80℃ / h and held for 3 hours, and then increased to 1210℃ at the fastest speed and held for 4 hours.

[0018] The present invention has the following beneficial effects: 1. The present invention adopts a dual refining process of electric arc furnace and AOD furnace, and uses a large amount of recycled waste and inexpensive medium carbon Cr iron and high carbon Mn, which can reduce manufacturing costs and at the same time ensure the chemical composition of the materials. 2. By employing a rolling process, this invention can eliminate internal porosity defects in steel ingots, resulting in a denser structure and improved service life of the furnace bottom plate. 3. The outer circle is cut with a high-pressure water jet to avoid quality defects such as cracks and decarburization caused by oxygen cutting, thus ensuring the quality of the furnace bottom plate. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the bottom plate of the annular annealing furnace of the present invention. Detailed Implementation

[0020] Example 1 This embodiment describes a furnace bottom plate used by a company for an annular annealing furnace, with the structure as follows: Figure 1 As shown, the weight is 3.79t, the material is 0Cr23Ni13, and the chemical composition is: C≤0.08%, Si≤1.0%, Mn≤2.0%, P≤0.035%, S≤0.030%, Ni12.5-13.5%, Cr22.0-24.0%. The manufacturing process is as follows: steel smelting → ingot casting → rolling → waterjet cutting of the outer circle → boss welding → heat treatment → machining. The specific steps described above are as follows: S1. Steel smelting: A dual refining process using an electric arc furnace and an AOD furnace is adopted.

[0021] The electric arc furnace melting process involves placing recycled waste furnace bottom plates, 0Cr23Ni13 return material, medium carbon ferrochrome, high carbon ferromanganese, nickel plates, ferrosilicon, and scrap steel into the electric arc furnace in a certain quantity and melting them together. The steel composition is controlled as follows: C: 0.30~0.50%, Si: 0.25~0.35%, Mn: 1.20~1.60%, Ni: 12.50~13.50%, Cr: 22.50~23.50%, P≤0.030%, and the tapping temperature is 1620℃.

[0022] The AOD furnace oxidation and reduction refining process involves: adding the molten steel to the AOD furnace at a temperature of 1540℃; blowing in an argon-oxygen mixture, with the O2:Ar ratio continuously varying from 2:1 to 1:3, gradually decreasing the flow rate until C ≤ 0.06%; adding a reduction mixture for reduction and stirring with pure argon; the reduction mixture consists of 7-10 kg / ton of active lime, 1-2 kg / ton of fluorite, and 1.0-1.5 kg / ton of aluminum powder; sampling and analysis, adjusting the chemical composition of the molten steel based on the analysis results, specifically: C ≤ 0.08%; S ≤ 0.025%; Si, Mn, Cr, and Ni controlled according to the chemical composition midline; and tapping at a temperature of 1555℃; and soft blowing for 8-10 minutes to allow inclusions to float to the surface.

[0023] S2. Ingot casting: Cast into 6.0t flat ingots. Flat ingot specifications: cross-sectional dimensions: 500×400×1430mm, width: 1200mm; casting temperature: 1460℃; casting time for the ingot body: 6.0min; casting time for the riser: 4.0~6.0min; after casting, the mold is cooled for 3 hours, then demolded and placed in a slow cooling pit to cool to room temperature.

[0024] S3. Rolling: The flat ingot obtained in S2 is rolled using a reversible rolling mill. The initial rolling temperature is 1150℃, and the final rolling temperature is 850℃. The rolling heating regime is as follows: heat to 600℃ at a heating rate of ≤60℃ / h and hold for 3 hours; heat to 850℃ at a heating rate of ≤80℃ / h and hold for 3 hours; then heat to 1210℃ at the fastest speed and hold for 4 hours. Figure 1 The finished size of the furnace bottom plate is to roll the flat ingot into a square plate of 1940×1940×200mm, and then let it cool naturally after rolling.

[0025] S4. High-pressure water jet cutting: Cut the outer circle of the above square plate with a high-pressure water jet cutting machine to remove excess edges and corners. The outer circle diameter is 1920mm.

[0026] S5. Boss welding: The pre-processed ring is welded to the center of the furnace bottom plate. The ring material is 0Cr23Ni13, the thickness is 20mm, and the diameter is 340mm. The welding method is CO2 gas shielded welding.

[0027] S6. Heat treatment: Place the furnace bottom plate blank after step S5 into the heating furnace, heat it to 850℃ at a heating rate of ≤60℃ / h, hold it at that temperature for 3 hours, then heat it to 1050℃ at a heating rate of ≤100℃ / h, hold it at that temperature for 5 hours, remove it from the furnace and quench it in water at 32℃, and start stirring until it cools to room temperature to complete the heat treatment.

[0028] S7. Machining the furnace bottom plate blank after step S6 to achieve... Figure 1 The dimensions were determined to complete the fabrication of the furnace bottom plate.

[0029] Example 2 This embodiment describes a furnace bottom plate used by a company for an annular annealing furnace; the structure is shown in the attached diagram. Figure 1 As shown, the weight is 3.79t, the material is 0Cr23Ni13, and the chemical composition is: C≤0.08%, Si≤1.0%, Mn≤2.0%, P≤0.035%, S≤0.030%, Ni12.5-13.5%, Cr22.0-24.0%. The manufacturing process is as follows: steel smelting → ingot casting → rolling → waterjet cutting of the outer circle → boss welding → heat treatment → machining.

[0030] The above steps are explained as follows: S1. Steel smelting: A dual refining process using an electric arc furnace and an AOD furnace is adopted.

[0031] The electric arc furnace melting process involves placing recycled waste furnace bottom plates, 0Cr23Ni13 return material, medium carbon ferrochrome, high carbon ferromanganese, nickel plates, ferrosilicon, and scrap steel into the electric arc furnace in a certain quantity and melting them together. The steel composition is controlled as follows: C: 0.30~0.50%, Si: 0.25~0.35%, Mn: 1.20~1.60%, Ni: 12.50~13.50%, Cr: 22.50~23.50%, P≤0.030%, and the tapping temperature is 1670℃.

[0032] The AOD furnace oxidation and reduction refining process involves: adding the molten steel to the AOD furnace at a temperature of 1540℃; blowing in an argon-oxygen mixture, with the O2:Ar ratio continuously varying from 2:1 to 1:3, gradually decreasing the flow rate until C ≤ 0.06%; adding a reduction mixture for reduction, and stirring with pure argon; the reduction mixture consists of 7-10 kg / ton of active lime, 1-2 kg / ton of fluorite, and 1.0-1.5 kg / ton of aluminum powder; sampling and analysis, adjusting the chemical composition of the molten steel based on the analysis results, specifically: C ≤ 0.08%; S ≤ 0.025%; Si, Mn, Cr, and Ni controlled according to the chemical composition midline; and tapping at a temperature of 1565℃; and soft blowing for 8-10 minutes to allow inclusions to float to the surface.

[0033] S2. Ingot casting: Cast into 6.0t flat ingots. Flat ingot specifications: cross-sectional dimensions: 500×400×1430mm, width: 1200mm; casting temperature: 1470℃; casting time for the ingot body: 8.0min; casting time for the riser: 4.0~6.0min; after casting, the mold is cooled for 4 hours, then demolded and placed in a slow cooling pit to cool to room temperature.

[0034] S3. Rolling: The flat ingot obtained in S2 is rolled using a reversible rolling mill. The initial rolling temperature is 1150℃, and the final rolling temperature is 850℃. The rolling heating regime is as follows: heat to 600℃ at a heating rate of ≤60℃ / h and hold for 3 hours; heat to 850℃ at a heating rate of ≤80℃ / h and hold for 3 hours; then heat to 1210℃ at the fastest speed and hold for 4 hours. Figure 1 The finished size of the furnace bottom plate is to roll the flat ingot into a square plate of 1940×1940×200mm, and then let it cool naturally after rolling.

[0035] S4. High-pressure water jet cutting: Cut the outer circle of the above square plate with a high-pressure water jet cutting machine to remove excess edges and corners. The outer circle diameter is 1920mm.

[0036] S5. Boss welding: The pre-processed ring is welded to the center of the furnace bottom plate. The ring material is 0Cr23Ni13, the thickness is 20mm, and the diameter is 340mm. The welding method is CO2 gas shielded welding.

[0037] S6. Heat treatment: Place the furnace bottom plate blank after step S5 into the heating furnace, heat it to 850℃ at a heating rate of ≤60℃ / h, hold it at that temperature for 3 hours, then heat it to 1050℃ at a heating rate of ≤100℃ / h, hold it at that temperature for 5 hours, remove it from the furnace and quench it in water at 32℃, and start stirring until it cools to room temperature to complete the heat treatment.

[0038] S7. Machining the furnace bottom plate blank after step S6 to achieve... Figure 1 The dimensions were determined to complete the fabrication of the furnace bottom plate.

Claims

1. A method of manufacturing a furnace floor for a ring-type annealing furnace, characterized by: Includes the following steps: S1. Steelmaking: A dual refining process using an electric arc furnace and an AOD furnace is employed. Electric arc furnace melting: Recycled scrap furnace bottom plates, 0Cr23Ni13 return material, medium-carbon ferrochrome, high-carbon ferromanganese, nickel plates, ferrosilicon, and scrap steel are added to the electric arc furnace in specific quantities and melted together. The steel composition is controlled as follows: C: 0.30~0.50%, Si: 0.25~0.35%, Mn: 1.20~1.60%, Ni: 12.50~13.50%, Cr: 22.50~23.50%, P≤0.030%, with a tapping temperature of 1620~1670℃. AOD furnace oxidation and reduction refining: Molten steel is added to the AOD furnace at a temperature of 1540℃. 1600℃; Introduce an argon-oxygen mixture, with the O2:Ar ratio continuously varying from 2:1 to 1:3, gradually reducing the gas flow until C ≤ 0.06%, at which point blowing stops; Add a reducing mixture for reduction and stir with pure argon. The reducing mixture consists of: 7-10 kg / ton of active lime, 1-2 kg / ton of fluorite, and 1.0-1.5 kg / ton of aluminum powder; Sample and analyze, adjusting the chemical composition of the molten steel based on the analysis results. Specific components: C ≤ 0.08%; S ≤ 0.025%; Si, Mn, Cr, and Ni are controlled according to the midline of the chemical composition. Tap-out temperature: 1555-1565℃; Soft blowing, with a blowing time controlled at 8-10 minutes, to allow inclusions to float sufficiently. S2. Ingot casting: Cast into flat ingots at a casting temperature of 1460~1470℃, casting time for the ingot body is 6.0~8.0min, and casting time for the riser is 4.0~6.0min; after casting, cool the mold for 3~4 hours, then demold and slowly cool to room temperature. S3. Rolling: The flat ingot is rolled into a square plate using a reversible rolling mill, according to the thickness of the furnace bottom plate blank, and then naturally cooled after rolling. S4. Cutting: Cut the outer circle of the square plate and remove excess edges and corners; S5. Boss welding: Weld the pre-processed ring to the center of the furnace bottom plate; S6. Heat treatment: Place the furnace bottom plate blank into the heating furnace and heat it to 850℃ at a heating rate of ≤60℃ / h. After holding it at that temperature for 3-4 hours, heat it to 1050℃ at a heating rate of ≤100℃ / h. After holding it at that temperature for 5 hours, remove it from the furnace and quench it in water at ≤32℃. Start stirring and continue cooling until it cools to room temperature to complete the heat treatment. S7. Machining to complete the production of the furnace bottom plate.

2. A method of manufacturing a furnace floor for a ring furnace as claimed in claim 1, characterized in that: Step S4 involves using a high-pressure water jet cutting machine to cut the outer circle.

3. A method of manufacturing a furnace floor for a ring furnace as defined in claim 1, characterized in that: In step S5, the ring material is 0Cr23Ni13, the thickness is 10-20mm, the diameter is according to the drawing size, and the welding method is CO2 gas shielded welding.

4. A method for manufacturing a bottom plate for an annular annealing furnace according to claim 1, characterized in that: Weight of the flat ingot in step S2: 6.0t, flat ingot specifications: cross-sectional dimensions: 500×400×1430mm, width: 1200mm.

5. A method for manufacturing a furnace bottom plate for an annular annealing furnace according to claim 1, characterized in that: The rolling heating process in step S3 is as follows: the temperature is increased to 600℃ at a heating rate of ≤60℃ / h and held for 3 hours, then increased to 850℃ at a heating rate of ≤80℃ / h and held for 3 hours, and then increased to 1210℃ at the fastest speed and held for 4 hours.

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