Composite magnesium reduction pot and method of production thereof

Abstract

A composite magnesium reduction pot and a production method thereof belong to the technical field of production of reduction pots used in magnesium metal smelting. Specifically, a large-diameter thick-wall seamless steel pipe with a diameter of 559mm to 1500mm, a thickness of 50mm to 120mm, a length of 2.8m to 8m and a material of 9%Cr steel is used as a base body, a high-temperature-resistant and corrosion-resistant alloy strengthening layer with a thickness of 1.0-3.5mm is formed on the outer surface of the base body by using an additive manufacturing technology laser cladding, a composite magnesium reduction pot body with the strengthening layer arranged on the outer surface of the base body is obtained, and the pot body is welded with a cooling water jacket at the top end, welded with a slag discharge cone and a water jacket at the tail to obtain a composite magnesium reduction pot. The product has good heat conduction performance and high-temperature oxidation resistance, good high-temperature durable strength, thermal stability and high-temperature creep resistance and other comprehensive performance.

Description

Technical Field

[0001] This invention belongs to the technical field of magnesium refining equipment, specifically a composite magnesium reduction tank and its production method. Background Technology

[0002] Currently, magnesium refining mainly uses reduction tanks made of centrifugal casting tubes made of ZG35Cr24Ni7SiN material. These centrifugal casting tubes have a high carbon content and are covered with a layer of cast quartz sand on their outer surface, thus exhibiting excellent resistance to high-temperature ablation. This advantage is also the reason why casting tubes have been used in the magnesium smelting industry.

[0003] However, due to the inherent defect of high surface roughness of the casting parts, the inner surface of the casting pipe becomes severely adhered during the magnesium smelting process, forcing the magnesium smelting unit to be taken offline every 20 days to clean the inner wall of the pipe parts, which affects production efficiency.

[0004] In addition, although the quartz sand on the outer wall of the pipe has high resistance to high temperature erosion, it also affects the thermal conductivity. Poor thermal conductivity reduces the heat utilization rate of the magnesium smelting unit, increases the energy consumption of production, increases the heating cost of magnesium reduction, and the manufacturing cost of the cast pipe is high.

[0005] In summary, the disadvantages of centrifugal casting pipes include: poor high-temperature strength, short service life, short cleaning cycle for slag buildup on the inner wall, increased maintenance and operating costs; and poor thermal conductivity, which hinders the development of high-efficiency and energy-saving technologies in the magnesium refining industry. Summary of the Invention

[0006] To address the challenge of achieving high-temperature strength, strong resistance to high-temperature oxidation, minimal slag buildup on the inner wall, low production energy consumption, long service life, and low-cost manufacturing of magnesium reduction tanks, the primary objective of this invention is to propose a composite magnesium reduction tank with strong comprehensive performance and high cost-effectiveness.

[0007] The technical solution to achieve the above objectives is as follows: a composite magnesium reduction tank, comprising a tank body open at both ends, a central tube installed inside the tank body, a top cooling water jacket welded to the top of the tank body, a magnesium vapor condensation and collection chamber connected to the top of the tank body inside the cooling water jacket, a slag discharge tail cone welded to the bottom of the tank body, a bottom cooling water jacket welded to the tail end of the slag discharge tail cone, an inlet and an outlet respectively provided on the top cooling water jacket and an exhaust port connecting the cavity between the top cooling water jacket and the magnesium vapor condensation and collection chamber; characterized in that: the tank body uses seamless steel pipe as the base, and an alloy reinforcement layer is additively manufactured on the outer surface of the tank body.

[0008] Furthermore, the alloy reinforcement layer is a nickel-based cobalt-based alloy powder layer, and the chemical composition of the nickel-based cobalt-based alloy powder layer by weight percentage is: chromium 50-60%, nickel 20-30%, cobalt 10-15%, carbon 0.1-0.15%, tungsten carbide 9-12%, and the remainder is iron.

[0009] High chromium content can increase the melting point of the cladding layer; nickel and cobalt enhance oxidation and ablation resistance, as well as improve the bonding strength between the cladding layer and the substrate; tungsten carbide can prevent coal powder ablation; and low carbon content is beneficial for increasing the melting point of the material. These components collectively increase the melting point of the cladding layer, improve ablation resistance, and provide good bonding properties.

[0010] Furthermore, the tank body is made of hot-rolled seamless steel pipe with 9% Cr steel.

[0011] The beneficial effects of this invention are:

[0012] This invention uses a hot-rolled seamless steel pipe with 9%Cr steel as the base of the reduction tank. On the one hand, it has sufficient high-temperature strength, and on the other hand, it ensures the airtightness of the gas inside the tank during magnesium refining and good thermal conductivity.

[0013] The inner wall roughness of the seamless tube of the present invention reaches 3.2μm at the rolling level, while the inner wall roughness of the centrifugally cast tube is higher than that of the sand casting level, reaching 64μm. The lower inner wall roughness of the present invention reduces the possibility of magnesium smelting adhering to the wall.

[0014] Because seamless tubes have low carbon content and no quartz sand on their outer surface, using them directly as magnesium smelting vessels would result in reduced surface ablation resistance and an unsatisfactory service life. Therefore, this invention additively manufactures a layer of nickel-based and cobalt-based alloy powder with high-temperature resistance on the outer surface of the seamless tube, ensuring its high-temperature resistance and high-temperature oxidation resistance to meet the harsh environmental conditions inside the magnesium reduction furnace.

[0015] The composite magnesium reduction vessel matrix is ​​formed using a hot-rolling process, resulting in a dense internal structure that improves the material's crystal structure, eliminates gaps, and significantly enhances the material's strength and toughness. The high-temperature strength performance of the composite magnesium reduction vessel is superior to that of centrifugally cast vessels.

[0016] Because of the uneven internal structure and coarse grains in the casting tank, and the presence of a layer of casting quartz sand on the surface which has a heat insulation effect, the cooling water temperature at the outlet of the composite magnesium reduction tank was higher than that at the outlet of the casting tank during the same furnace test, proving that the thermal conductivity of the composite magnesium reduction tank is significantly better than that of the casting tank.

[0017] The inner wall of the casting ladle is prone to slag buildup, which directly affects thermal conductivity and the amount of magnesium ore charged. Therefore, the casting ladle needs to be removed from the reduction furnace and its inner wall cleaned every 20 days on average, wasting a significant amount of manpower and energy and severely impacting production efficiency. Same-furnace tests have shown that the slag buildup on the inner surface of the rolling ladle is significantly better than that of the casting ladle, allowing it to remain uncleaned for up to 40 days.

[0018] In summary, the composite magnesium smelting vessel of the present invention has the advantages of high thermal conductivity, resistance to high-temperature ablation, and minimal adhesion to the inner wall.

[0019] Another object of the present invention is to provide a method for producing a composite magnesium reduction vessel, comprising the following steps:

[0020] S1. Manufacture hot-rolled large-diameter thick-walled seamless steel pipes with diameters of 559mm~1500mm, thicknesses of 50mm~120mm, lengths of 2.8m~8m, and material of 9%Cr steel.

[0021] S2. Additively manufacture a 1.0~3.5mm thick nickel-based cobalt-based alloy powder layer on the surface of hot-rolled large-diameter thick-walled seamless steel pipe;

[0022] S3. A central tube is installed inside the hot-rolled large-diameter thick-walled seamless steel pipe. A magnesium vapor condensation and collection chamber and a top cooling water jacket are set at the top of the hot-rolled large-diameter thick-walled seamless steel pipe. A slag discharge tail cone is welded to the bottom of the hot-rolled large-diameter thick-walled seamless steel pipe. A bottom cooling water jacket is welded to the tail end of the slag discharge tail cone.

[0023] The production method of the reduction vessel described in this invention is simple and reasonable, and the resulting product has good stability, high yield, and low manufacturing cost, meeting the design requirements.

[0024] Furthermore, the hot-rolled large-diameter thick-walled seamless steel pipe in step S1 is obtained by sequentially processing a 9%Cr steel continuous casting billet through the following processes: blanking, drilling a center hole, heating, skew rolling and piercing, sizing, heat treatment, physical and chemical testing, straightening, grinding, non-destructive testing, sawing, and polishing.

[0025] Skew rolling piercing is a method for producing seamless steel tubes under hot conditions. Skew rolling piercing has a fast production cycle and high yield. This invention uses 9%Cr steel continuously cast billets with a center hole, heats them to 1240℃, and performs skew rolling piercing to form the required seamless tube. Then, a combination of annealing, shot peening, straightening, sizing, and heat treatment is used to improve wall thickness uniformity and geometric dimensional accuracy, enhance the density of the microstructure, and improve the overall performance of the product.

[0026] Furthermore, the 9%Cr steel in step S1 is P9, P91, or P92 steel.

[0027] Furthermore, the nickel-based cobalt-based alloy powder layer mentioned in step S2 is applied to the surface of the hot-rolled large-diameter thick-walled seamless steel pipe using laser cladding or 3D printing processes. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the invention. Detailed Implementation

[0029] Example 1

[0030] like Figure 1As shown, this invention discloses a composite magnesium reduction tank. The structure of the magnesium reduction tank belongs to the prior art, and its structure is briefly described here. The magnesium reduction tank includes a tank body 1 with openings at both ends. A central tube 2 is installed inside the tank body 1. A top cooling water jacket 3 is welded to the top of the tank body 1. A magnesium vapor condensation and collection chamber 4 connected to the top of the tank body 1 is provided inside the top cooling water jacket 3. A slag discharge tail cone 5 is welded to the bottom of the tank body 1. A bottom cooling water jacket 6 is welded to the tail end of the slag discharge tail cone 5. The top cooling water jacket 4 and the bottom cooling water jacket 6 are respectively provided with a water inlet and a water outlet. An air extraction port 7 is also provided on the top cooling water jacket to connect the cavity between the top cooling water jacket and the magnesium vapor condensation and collection chamber 4.

[0031] As a further explanation of this embodiment, the tank body 1 uses a hot-rolled seamless steel pipe with a diameter of 559mm~1500mm, a thickness of 50mm~120mm, a length of 2.8m~8m, and a material of 9%Cr steel as the base. The outer surface of the tank body 1 is additively manufactured with an alloy reinforcement layer 8.

[0032] The production method of the above-mentioned composite magnesium reduction vessel is characterized by comprising the following steps:

[0033] S1. Clean the surface of the 9%Cr steel large-diameter thick-walled seamless pipe.

[0034] S2. A high-power solid-state laser is used to apply a synchronous powder feeding method to laser cladding alloy reinforcement layer on the substrate surface, with a single-pass powder feeding cladding thickness of 1.5 mm.

[0035] S3, Repeat step 2) to obtain the main body of the composite magnesium reduction tank with a 3mm thick alloy reinforcement layer on the surface;

[0036] S4. A central pipe 2 is installed inside the main body of the composite magnesium reduction tank. A magnesium vapor condensation and collection chamber 4 and a top cooling water jacket 3 are welded to the top of the hot-rolled large-diameter thick-walled seamless steel pipe. A slag discharge tail cone 5 is welded to the bottom of the hot-rolled large-diameter thick-walled seamless steel pipe. A bottom cooling water jacket 6 is welded to the tail end of the slag discharge tail cone 5.

[0037] The alloy reinforcement layer is a nickel-based cobalt-based alloy powder layer, and the chemical composition of the nickel-based cobalt-based alloy powder layer by weight percentage is: 50% chromium, 30% nickel, 10% cobalt, 0.15% carbon, 9% tungsten carbide, and the remainder is iron.

[0038] The specifications for the 9%Cr steel large-diameter thick-walled seamless tube are: outer diameter φ1016 mm, wall thickness 63.5 mm, and length 8 m. The specific manufacturing process is as follows:

[0039] 1) Select a 9%Cr steel round continuous casting billet with a diameter of φ760mm and a length of 4200±10mm, and drill a center hole in the billet along the axis.

[0040] 2) Place the 9%Cr steel round continuous casting billet with the center hole drilled into a ring furnace and heat it for 24 hours at 1240±10℃.

[0041] 3) After heating, the tube blank is pierced and hot rolled using an 800 piercing mill and a 960 rolling mill to obtain a rough tube.

[0042] Control the cold-rolled dimensional tolerances of the raw tubes: diameter tolerance: ±10mm; wall thickness tolerance: ±2mm; length tolerance: ±100mm.

[0043] 4) The rough tubes are annealed at 810℃ using a bogie furnace and held for 180 minutes. The temperature deviation during the holding period shall not exceed -10℃ to +10℃. The tubes are then air-cooled after being removed from the furnace.

[0044] 5) Use a shot blasting machine to shot blast the outer wall of the rough pipe to remove the oxide scale on the surface.

[0045] 6) Use 2500T pressure straightening to straighten the rough pipe. After straightening, the curvature is ≤4mm / m and the total curvature is ≤15mm.

[0046] 7) Use a saw to cut both ends of the rough pipe evenly. The recommended cutting length is ≤0.3 m.

[0047] 8) Use an internal grinding machine to polish the inner wall of the rough pipe.

[0048] 9) The inner diameter is determined by a medium-frequency heating sizing machine with an inner diameter specification of φ1025*67, a sizing length of 8.7m, and a dimensional tolerance of D±1mm.

[0049] 10) Normalize the rough tubes at 1050℃ and hold for 65 minutes. The temperature deviation during the holding period shall not exceed -10℃ to +10℃. Air cool after removal from the furnace.

[0050] 11) Temper the rough tubes at 760℃ for 130 minutes, with a temperature deviation of no more than -10℃ to +10℃ during the holding period; air cool after removal from the furnace.

[0051] 12) Take samples of the tempered raw tubes for testing, composition analysis, and physical properties testing.

[0052] 13) Use 2500T pressure straightening to straighten the rough pipe with heat. After straightening, the curvature is ≤2mm / m and the total curvature is ≤5mm.

[0053] 14) The base tube is obtained by grinding the inner and outer walls using an internal grinding machine and an external grinding machine. After grinding, there shall be no defects such as folds, cracks, scars, or unevenness.

[0054] 15) Perform manual and 100% PT+100% UT tests on the substrate tube.

[0055] 16) A high-power solid-state laser is used to perform laser cladding on the surface of the substrate tube using a synchronous powder feeding method. The cladding thickness is 1.5 mm for a single powder feeding; two cladding passes are performed to obtain a composite magnesium reduction tank with a 3 mm reinforcing layer on the outer surface of the substrate.

[0056] 17) Use a saw to cut the magnesium reduction tank to length according to the main body specifications.

[0057] 18) A central pipe 2 is installed in the composite magnesium reduction tank using a combination of manual and automatic submerged arc welding. A magnesium vapor condensation collection chamber 4 and a top cooling water jacket 3 are set at the top of the composite magnesium reduction tank. A slag discharge tail cone 5 is welded at the bottom of the composite magnesium reduction tank. A bottom cooling water jacket 6 is welded to the tail end of the slag discharge tail cone 5.

[0058] Example 2

[0059] The difference between Example 2 and Example 1 is as follows:

[0060] The specifications for 9%Cr steel large-diameter thick-walled seamless pipes are: manufacturing diameter 559mm, thickness 120mm, and length 2.8 meters.

[0061] The chemical composition by weight percentage of the nickel-based cobalt-based alloy powder layer is as follows: chromium 60%, nickel 20%, cobalt 10%, carbon 0.15%, tungsten carbide 9%, and the remainder is iron.

[0062] Example 3

[0063] The difference between Example 3 and Example 1 is as follows:

[0064] The specifications for 9%Cr steel large-diameter thick-walled seamless pipes are: diameter 1500mm, thickness 50mm, and length 5 meters.

[0065] The nickel-based cobalt-based alloy powder layer is applied to the surface of a hot-rolled large-diameter thick-walled seamless steel pipe using a 3D printing process. The thickness of the nickel-based cobalt-based alloy powder layer is 1.0 mm.

[0066] The chemical composition by weight percentage of the nickel-based cobalt-based alloy powder layer is as follows: 50% chromium, 20% nickel, 15% cobalt, 0.15% carbon, 12% tungsten carbide, and the remainder is iron.

[0067] The test parameters of the composite magnesium reduction vessel manufactured by the process of this invention and the reduction vessel manufactured by centrifugal casting tube in the prior art are as follows:

[0068]

Claims

1. A method for producing a composite magnesium reduction tank, the composite magnesium reduction tank comprising a tank body open at both ends, a central pipe installed inside the tank body, a top cooling water jacket welded to the top of the tank body, a magnesium vapor condensation collection chamber connected to the top of the tank body being provided inside the top cooling water jacket, a slag discharge tail cone welded to the bottom, a bottom cooling water jacket welded to the tail end of the slag discharge tail cone, an inlet and an outlet respectively provided on the top cooling water jacket, and an exhaust port connecting the cavity between the top cooling water jacket and the magnesium vapor condensation collection chamber being provided on the top cooling water jacket; Its features are: The tank body uses seamless steel pipe as the base, and an alloy reinforcement layer is additively manufactured on the outer surface of the tank body. The alloy reinforcement layer is a nickel-based cobalt-based alloy powder layer. The chemical composition of the nickel-based cobalt-based alloy powder layer by weight percentage is: chromium 50-60%, nickel 20-30%, cobalt 10-15%, carbon 0.1-0.15%, tungsten carbide 9-12%, and the remainder is iron. The production method of the composite magnesium reduction vessel includes the following steps: S1. Manufacture hot-rolled large-diameter thick-walled seamless steel pipes with diameters of 559mm to 1500mm, thicknesses of 50mm to 120mm, lengths of 2.8 meters to 8 meters, and material of 9%Cr steel; S2. Additively manufacture a 1.0~3.5mm thick nickel-based cobalt-based alloy powder layer on the surface of hot-rolled large-diameter thick-walled seamless steel pipe; S3. A central tube is installed inside the hot-rolled large-diameter thick-walled seamless steel pipe. A magnesium vapor condensation and collection chamber and a top cooling water jacket are set at the top of the hot-rolled large-diameter thick-walled seamless steel pipe. A slag discharge tail cone is welded to the bottom of the hot-rolled large-diameter thick-walled seamless steel pipe. A bottom cooling water jacket is welded to the tail end of the slag discharge tail cone.

2. The production method of a composite magnesium reduction vessel according to claim 1, characterized in that: The hot-rolled large-diameter thick-walled seamless steel pipe in step S1 is produced by sequentially processing a 9%Cr steel continuous casting billet through blanking, drilling a center hole, heating, and oblique rolling. The process involves drilling, sizing, heat treatment, physical and chemical testing, straightening, grinding, non-destructive testing, sawing, and polishing.

3. The production method of a composite magnesium reduction vessel according to claim 1, characterized in that: The 9%Cr steel in step S1 is P9, P91, or P92 steel.

4. The production method of a composite magnesium reduction vessel according to claim 1, characterized in that: The nickel-based cobalt-based alloy powder layer mentioned in step S2 is applied to the surface of a hot-rolled large-diameter thick-walled seamless steel pipe using laser cladding or 3D printing processes.

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