A method of precipitate free solution annealing of n08028 alloy after forging

Abstract

The present application belongs to the field of corrosion-resistant iron-nickel-based alloys. More particularly, it relates to a method for eliminating precipitated phases of N08028 alloy after forging without solid solution. The method comprises the steps of electrode preparation, crystallizer preparation, polishing the copper bottom plate of the bottom water tank using a polishing device, placing four arc initiators at the center of the carbon steel plate, filling argon into the crystallizer, preparing slag, controlling the steady-state melting rate during smelting, using fast forging + radial forging for forging, and directly water cooling after radial forging without solid solution, so that the total content of precipitated phase intermetallic compound phase, nitride phase and carbide phase is not more than 1.0%, and the content of sigma phase is not more than 0.2%.

Description

Technical Field

[0001] This invention belongs to the field of iron-nickel based corrosion-resistant alloys. More specifically, it relates to a method for eliminating N08028 alloy precipitates without solid solution after forging. Background Technology

[0002] N08028 alloy belongs to the Ni-Fe-Cr-Mo-Cu series of iron-nickel-based corrosion-resistant alloys. It exhibits excellent resistance to pitting corrosion, crevice corrosion, intergranular corrosion, and stress corrosion, and is commonly used in oil and gas well tubing. However, the high Cr and Mo content in N08028 alloy makes it prone to forming the intermetallic compound σ phase. This σ phase significantly reduces the room temperature impact toughness and creep rupture properties of the N08028 alloy, and also severely affects its resistance to H2S stress corrosion. Extensive research has shown that the precipitated phase in N08028 is a Cr- and Mo-rich phase, while the Ni content is much lower than the matrix, making it a typical σ phase. This phase reaches its precipitation peak at around 800℃, and completely dissolves after solution treatment at 1200℃. Therefore, in actual large-scale production, solution treatment at 1150-1200℃ after forging is generally considered to completely dissolve the precipitated phase, followed by immediate water cooling to address the σ phase issue. Summary of the Invention

[0003] The purpose of this invention is to provide a method for eliminating N08028 alloy precipitates without solution treatment after forging, thereby addressing the above-mentioned problems. The forged bars produced by this method, without solution treatment, have precipitates that satisfy the following requirements: the total content of intermetallic compound phases, nitride phases, and carbide phases does not exceed 1.0%, and the σ phase does not exceed 0.2%.

[0004] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0005] A method for eliminating N08028 alloy precipitates without solid solution after forging, characterized in that:

[0006] Step 1: Electrode preparation: The electrode size is (420-460)mm×(2700-3000)mm. It is sawed and polished before remelting and smelting.

[0007] Ensure that the electrode rod has flat ends and that the electrode surface is free from serious cracks, laps, burrs, scars, oxide scale, rust, oil, and other impurities.

[0008] Step 2: Crystallizer preparation: Use a 600-700mm crystallizer. Before use, clean the inner wall of the crystallizer to remove dust and foreign objects.

[0009] Ensure the inner wall of the crystallizer is dry and clean.

[0010] Step 3: Use polishing equipment to grind the copper base plate of the bottom water tank to remove surface adhering substances, and grind both sides of the 15-20mm thick carbon steel plate clean.

[0011] After polishing, the original metal color must be visible, and there must be no oxide scale present.

[0012] Step 4: Place four pieces of arc-starting agent in the center of the carbon steel plate. The arc-starting agent is 0.8-1.3% of the total slag around it, which facilitates the formation of a slag pool for arc starting.

[0013] Step 5: Fill the crystallizer with argon gas at a flow rate of 27-32 m³ / h. 3 Maintain the flow rate at 9-12 m³ / h for 8-15 minutes, then purge the air from the crystallizer and adjust the argon flow rate to 9-12 m³ / h. 3 / h, until the smelting is complete;

[0014] Step 6: Prepare slag material. Smelting is carried out using the electroslag furnace liquid slag arc initiation method. The slag system uses pre-melted quaternary slag. The slag system composition is: CaF2 50%-65%, Al2O3 15%-25%, CaO 8%-15%, MgO 8%-15%, and the slag amount is 150-220kg.

[0015] Step 7: Power on and start the arc. Use a 450-550mm graphite electrode to perform slag removal. The slag removal current is 1500-3500A and the voltage is 50-70V. Perform slag removal in a stepped upward mode. The slag removal time is controlled at 60-80 minutes. During the slag removal process, reduce the opening of the bottom water tank inlet valve and control the outlet water temperature to ≥40℃.

[0016] It is necessary to reduce heat loss and maintain slag temperature to ensure the quality of the bottom of the electroslag ingot.

[0017] Step 8: The steady-state melting rate of the smelting process is controlled at (0.65-0.75)D kg / h, where D is the diameter of the crystallizer in mm;

[0018] The steady-state melting rate during smelting is slightly lower than that of conventional stainless steel in order to reduce the segregation of Mo while also taking into account the surface quality of the electroslag ingot.

[0019] Step 9: Forging adopts fast forging + radial forging, high temperature homogenization, and after fast forging homogenization, billet is made. The billet size is determined according to the finished round bar size. Radial forging is formed in one heat; ensure the final forging temperature is ≥900℃.

[0020] The forging process takes into account the heating temperature and the number of deformation passes to ensure that the final forging temperature is within a certain range and to avoid the formation of precipitates.

[0021] Step 10: After radial forging, if no solution is found, directly water cool for ≥40 minutes.

[0022] After water cooling, samples were taken from both ends to test the precipitated phase.

[0023] This method uses an electroslag furnace liquid slag arc initiation method for smelting. The slag system uses pre-melted quaternary slag with the following composition: CaF2 50%-65%, Al2O3 15%-25%, CaO 8%-15%, MgO 8%-15%.

[0024] This method uses 450-550mm graphite electrodes for slag treatment, with a slag treatment current of 1500A-3500A, a voltage of 50V-70V, and a slag treatment time of 60-80min. During the slag treatment, the opening of the bottom water tank inlet valve is reduced to control the outlet water temperature to ≥40℃, thereby reducing heat loss and ensuring slag temperature, thus ensuring the quality of the bottom of the electroslag ingot.

[0025] The steady-state melting rate of this method is controlled at (0.65-0.75)D kg / h, where D is the diameter of the crystallizer in mm. The steady-state melting rate is lower than that of conventional stainless steel, in order to reduce the segregation of Mo and at the same time take into account the surface quality of the electroslag ingot.

[0026] Forging adopts fast forging + radial forging, high temperature homogenization, and after fast forging homogenization, billet is made. The billet size is determined according to the finished round steel size. Radial forging is formed in one heat. The forging process takes into account the heating temperature and deformation passes to ensure that the final forging temperature is ≥900℃ and avoid the generation of precipitates.

[0027] After forging, if no solid solution is found, directly water-cool the product for ≥40 minutes. After water cooling, samples are taken from both ends to test for precipitated phases.

[0028] The present invention has the following beneficial effects:

[0029] This invention employs a novel process route: rapid forging followed by radial forging, with direct water cooling after forging without solution treatment. The conventional process route is: rapid forging + solution treatment + water cooling. This invention eliminates the solution treatment step, ensuring that the total content of intermetallic compound phases, nitride phases, and carbide phases does not exceed 1.0%, and the σ phase does not exceed 0.2%.

[0030] The conventional process of rapid forging + solution treatment + water cooling is insufficient to solve the problem of precipitated phases, resulting in a certain percentage of defects. Attached Figure Description

[0031] To more clearly illustrate the specific embodiments of this application or the technical solutions in the prior art, the accompanying drawings used will be briefly described below.

[0032] Figure 1 The image is from the test in Example 1; Figure 2 The image is from the detection in Example 2; Figure 3 The image is from the detection in Example 3; Figure 4 This is a graph showing the detection results of Comparative Example 1; Figure 5 This is a graph from the detection of Comparative Example 2. Detailed Implementation

[0033] Example 1

[0034] A method for eliminating N08028 alloy precipitates without solid solution after forging, characterized in that:

[0035] Step 1: Electrode preparation: The electrode size is 420mm×3000mm. It is sawed and polished before remelting and smelting.

[0036] Step 2, Crystallizer Preparation: Use a 600mm crystallizer. Before use, clean the inner wall of the crystallizer to remove dust and foreign objects.

[0037] Step 3: Use polishing equipment to grind the copper base plate of the bottom water tank to remove surface adhering substances and grind both sides of the 20mm thick carbon steel plate clean.

[0038] Step 4: Place four pieces of arc-starting agent in the center of the carbon steel plate. The arc-starting agent is 0.8% of the total slag around it, which facilitates the formation of a slag pool for arc ignition.

[0039] Step 5: Fill the crystallizer with argon gas at a flow rate of 32 m³ / h. 3 Maintain the flow rate at 12 m³ / h for 8 minutes, then purge the air from the crystallizer and adjust the argon flow rate to 12 m³ / h. 3 / h, until the smelting is complete;

[0040] Step 6: Prepare slag material. Smelting is carried out using the electroslag furnace liquid slag arc initiation method. The slag system uses pre-melted quaternary slag with the following composition: CaF2 50%, Al2O3 25%, CaO 15%, MgO 10%, and slag quantity 220kg.

[0041] Step 7: Power on and start the arc. Use a 450mm graphite electrode to perform slag removal. The slag removal current is 1500A and the voltage is 70V. Perform slag removal in a stepped upward mode. The slag removal time is controlled at 80 minutes. During the slag removal process, reduce the opening of the bottom water tank inlet valve and control the outlet water temperature to 43℃.

[0042] Step 8: The steady-state melting rate of the smelting process is controlled at 0.65D kg / h, where D is the diameter of the crystallizer in mm;

[0043] Step 9: Forging adopts fast forging + radial forging, high temperature homogenization, and after fast forging homogenization, billet is made. The billet size is determined according to the finished round bar size. Radial forging is formed in one heat; ensure the final forging temperature is 910℃.

[0044] Step 10: After radial forging, do not solution-solidify; directly water-cool for 45 minutes.

[0045] Test results: The total content of intermetallic compound phase, nitride phase and carbide phase is less than 1%, and the σ phase does not exceed 0.2%.

[0046] Example 2

[0047] A method for eliminating N08028 alloy precipitates without solid solution after forging, characterized in that:

[0048] Step 1: Electrode preparation: The electrode size is 460mm×2700mm. It is sawed and polished before remelting and smelting.

[0049] Step 2, Crystallizer Preparation: Use a 700mm crystallizer. Before use, clean the inner wall of the crystallizer to remove dust and foreign objects.

[0050] Step 3: Use polishing equipment to grind the copper base plate of the bottom water tank to remove surface adhering substances and grind both sides of the 15mm thick carbon steel plate clean.

[0051] Step 4: Place four pieces of arc-starting agent in the center of the carbon steel plate. The arc-starting agent is 1.3% of the total slag around it, which facilitates the formation of a slag pool for arc ignition.

[0052] Step 5: Fill the crystallizer with argon gas at a flow rate of 27 m³ / h. 3 Maintain the flow rate at 9 m³ / h for 15 minutes, then purge the air from the crystallizer and adjust the argon flow rate to 9 m³ / h. 3 / h, until the smelting is complete;

[0053] Step 6: Prepare slag material. Smelting is carried out using the electroslag furnace liquid slag arc initiation method. The slag system uses pre-melted quaternary slag with the following composition: CaF2 65%, Al2O3 15%, CaO 12%, MgO 8%, and slag quantity 150kg.

[0054] Step 7: Power on and ignite the arc. Use a 550mm graphite electrode for slag formation. The slag formation current is 3500A and the voltage is 50V. Slag formation is carried out in a stepped upward mode. The slag formation time is controlled at 60 minutes. During the slag formation, reduce the opening of the bottom water tank inlet valve and control the outlet water temperature at 42℃. Step 8: Control the steady-state melting rate of smelting at 0.75D kg / h, where D is the diameter of the crystallizer in mm.

[0055] Step 9: Forging adopts fast forging + radial forging, high temperature homogenization, and after fast forging homogenization, billet is made. The billet size is determined according to the finished round bar size. Radial forging is formed in one heat; ensure the final forging temperature is 920℃.

[0056] Step 10: After radial forging, do not solution-solidify; directly water-cool for 48 minutes.

[0057] Test results: The total content of intermetallic compound phase, nitride phase and carbide phase is less than 0.95%, and the σ phase does not exceed 0.18%.

[0058] Example 3

[0059] A method for eliminating N08028 alloy precipitates without solid solution after forging, characterized in that:

[0060] Step 1: Electrode preparation: The electrode size is 450mm×2800mm. It is sawed and polished before remelting and smelting.

[0061] Step 2, Crystallizer Preparation: Use a 650mm crystallizer. Before use, clean the inner wall of the crystallizer to remove dust and foreign objects.

[0062] Step 3: Use polishing equipment to grind the copper base plate of the bottom water tank to remove surface adhering substances and grind both sides of the 18mm thick carbon steel plate clean.

[0063] Step 4: Place four pieces of arc-starting agent in the center of the carbon steel plate. The arc-starting agent is 1% of the total slag material around it, which facilitates the formation of a slag pool for arc starting.

[0064] Step 5: Fill the crystallizer with argon gas at a flow rate of 30 m³ / h. 3 Maintain the flow rate at 10 m³ / h for 10 minutes, then purge the air from the crystallizer and adjust the argon flow rate to 10 m³ / h. 3 / h, until the smelting is complete;

[0065] Step 6: Prepare slag material. Smelting is carried out using the electroslag furnace liquid slag arc initiation method. The slag system uses pre-melted quaternary slag with the following composition: CaF2 60%, Al2O3 20%, CaO 10%, MgO 10%, and slag quantity 190kg.

[0066] Step 7: Power on and start the arc. Use a 500mm graphite electrode to perform slag removal. The slag removal current is 3000A and the voltage is 60V. Perform slag removal in a stepped upward mode. The slag removal time is controlled within 70 minutes. During the slag removal process, reduce the opening of the bottom water tank inlet valve and control the outlet water temperature to 43℃.

[0067] Step 8: The steady-state melting rate of the smelting process is controlled at 0.7D kg / h, where D is the diameter of the crystallizer in mm;

[0068] Step 9: Forging adopts fast forging + radial forging, high temperature homogenization, and after fast forging homogenization, billet is made. The billet size is determined according to the finished round bar size. Radial forging is formed in one heat; ensure the final forging temperature is 925℃.

[0069] Step 10: After radial forging, do not solution-solidify; directly water-cool for 46 minutes.

[0070] Test results: The total content of intermetallic compound phase, nitride phase and carbide phase is less than 0.87%, and the σ phase does not exceed 0.16%.

[0071] Comparative Example 1

[0072] A method for eliminating N08028 alloy precipitates without solid solution after forging, characterized in that:

[0073] Step 1: Electrode preparation: The electrode size is 420mm×3000mm. It is sawed and polished before remelting and smelting.

[0074] Step 2, Crystallizer Preparation: Use a 900mm crystallizer. Before use, clean the inner wall of the crystallizer to remove dust and foreign objects.

[0075] Step 3: Use polishing equipment to grind the copper base plate of the bottom water tank to remove surface adhering substances and grind both sides of the 20mm thick carbon steel plate clean.

[0076] Step 4: Place four pieces of arc-starting agent in the center of the carbon steel plate. The arc-starting agent is 3% of the total slag material around it, which facilitates the formation of a slag pool for arc starting.

[0077] Step 5: Fill the crystallizer with argon gas at a flow rate of 40 m³ / h. 3 Maintain the flow rate at 6 m / h for 15 minutes, then purge the air from the crystallizer and adjust the argon flow rate to 6 m / h. 3 / h, until the smelting is complete;

[0078] Step 6: Prepare slag material. Smelting is carried out using the electroslag furnace liquid slag arc initiation method. The slag system uses pre-melted quaternary slag with the following composition: CaF2 30%, Al2O3 10%, CaO 30%, MgO 30%, and slag quantity 220kg.

[0079] Step 7: Power on and start the arc. Use a 450mm graphite electrode to perform slag removal. The slag removal current is 5500A and the voltage is 30V. Perform slag removal in a stepped upward mode. The slag removal time is controlled at 80 minutes. During the slag removal process, reduce the opening of the bottom water tank inlet valve and control the outlet water temperature to 36℃.

[0080] Step 8: The steady-state melting rate of the smelting process is controlled at 0.9D kg / h, where D is the diameter of the crystallizer in mm;

[0081] Step 9: Forging adopts fast forging + radial forging, high temperature homogenization, and after fast forging homogenization, billet is made. The billet size is determined according to the finished round bar size. Radial forging is formed in one heat; ensure the final forging temperature is 870℃.

[0082] Step 10: After radial forging, do not solution-solidify; directly water-cool for 25 minutes.

[0083] Test results: The total content of intermetallic compound phase, nitride phase, and carbide phase is approximately 2.3%, and the σ phase is approximately 0.6%. The problem of precipitated phases is difficult to resolve, and a certain proportion of samples are substandard.

[0084] Comparative Example 2

[0085] A method for eliminating N08028 alloy precipitates without solid solution after forging, characterized in that:

[0086] Step 1: Electrode preparation: The electrode size is 420mm×3000mm. It is sawed and polished before remelting and smelting.

[0087] Step 2, Crystallizer Preparation: Use a 600mm crystallizer. Before use, clean the inner wall of the crystallizer to remove dust and foreign objects.

[0088] Step 3: Use polishing equipment to grind the copper base plate of the bottom water tank to remove surface adhering substances and grind both sides of the 20mm thick carbon steel plate clean.

[0089] Step 4: Place four pieces of arc-starting agent in the center of the carbon steel plate. The arc-starting agent is 3.5% of the total slag around it, which facilitates the formation of a slag pool for arc starting.

[0090] Step 5: Fill the crystallizer with argon gas at a flow rate of 32 m³ / h. 3 Maintain the flow rate at 12 m³ / h for 8 minutes, then purge the air from the crystallizer and adjust the argon flow rate to 12 m³ / h. 3 / h, until the smelting is complete;

[0091] Step 6: Prepare slag material. Smelting is carried out using the electroslag furnace liquid slag arc initiation method. The slag system uses pre-melted quaternary slag with the following composition: CaF2 50%, Al2O3 25%, CaO 15%, MgO 10%, and slag quantity 100kg.

[0092] Step 7: Power on and start the arc. Use a 450mm graphite electrode to perform slag removal. The slag removal current is 1000A and the voltage is 70V. Perform slag removal in a stepped upward mode. The slag removal time is controlled at 80 minutes. During the slag removal process, reduce the opening of the bottom water tank inlet valve and control the outlet water temperature to 43℃.

[0093] Step 8: The steady-state melting rate of the smelting process is controlled at 0.65D kg / h, where D is the diameter of the crystallizer in mm;

[0094] Step 9: Forging adopts a fast forging + solution treatment + water cooling process, high temperature homogenization, and after fast forging homogenization, billet is made. The billet size is determined according to the finished round steel size, and radial forging is formed in one heat; ensure the final forging temperature is 865℃.

[0095] Step 10: After radial forging, perform solution treatment and then water cooling for 60 minutes.

[0096] Test results: The total content of intermetallic compound phase, nitride phase, and carbide phase is approximately 2.6%, and the σ phase is approximately 0.7%. The problem of precipitated phases is difficult to resolve, and a certain proportion of samples are substandard.

[0097] The embodiments described above are merely illustrative of several implementation methods of this application, designed to facilitate a detailed understanding of the technical solutions of this application. However, they should not be construed as limiting the scope of protection of the invention patent. The content illustrated in the embodiments should be understood as being used only to more clearly illustrate the present invention, and not as limiting the scope of the present invention. Any improvements and modifications made without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A method for eliminating N08028 alloy precipitates without solid solution treatment after forging, characterized in that: Step 1: Electrode preparation: The electrode size is (420-460)mm×(2700-3000)mm. It is sawed and polished before remelting and smelting. Step 2, Crystallizer Preparation: Use a 600-700mm crystallizer. Before use, clean the inner wall of the crystallizer to remove dust and foreign objects. Step 3: Use polishing equipment to grind the copper base plate of the bottom water tank to remove surface adhering substances, and grind both sides of the 15mm-20mm thick carbon steel plate clean. Step 4: Place four pieces of arc-starting agent in the center of the carbon steel plate. The arc-starting agent is 0.8-1.3% of the total slag around it, which facilitates the formation of a slag pool for arc starting. Step 5: Fill the crystallizer with argon gas at a flow rate of 27-32 m³ / h. 3 Maintain the flow rate at 9-12 m³ / h for 8-15 minutes, then purge the air from the crystallizer and adjust the argon flow rate to 9-12 m³ / h. 3 / h, until the smelting is complete; Step 6: Prepare slag material. Smelting is carried out using the electroslag furnace liquid slag arc initiation method. The slag system uses pre-melted quaternary slag with the following composition: CaF2 50-65%, Al2O3 15-25%, CaO 8-15%, MgO 8-15%, and slag amount 150-220kg. Step 7: Power on and start the arc. Use a 450-550mm graphite electrode to perform slag removal. The slag removal current is 1500-3500A and the voltage is 50-70V. Perform slag removal in a stepped upward mode. The slag removal time is controlled at 60-80 minutes. During the slag removal process, reduce the opening of the bottom water tank inlet valve and control the outlet water temperature to ≥40℃. Step 8: The steady-state melting rate of the smelting process is controlled at (0.65-0.75)D kg / h, where D is the diameter of the crystallizer in mm; Step 9: Forging adopts fast forging + radial forging, high temperature homogenization, and after fast forging homogenization, billet is made. The billet size is determined according to the finished round bar size. Radial forging is formed in one heat; ensure the final forging temperature is 910℃ or 925℃. Step 10: After radial forging, if no solution is found, directly water cool for ≥40 minutes.

2. The method for eliminating N08028 alloy precipitates after forging without solid solution treatment according to claim 1, characterized in that: The electrode dimensions are 420mm × 3000mm.

3. The method for eliminating N08028 alloy precipitates after forging without solid solution treatment according to claim 1, characterized in that: The crystallizer uses a 600mm specification.

4. The method for eliminating N08028 alloy precipitates after forging without solid solution treatment according to claim 1 or 2, characterized in that: Argon gas is introduced into the crystallizer at a flow rate of 32 m³ / h. 3 Maintain the flow rate at 12 m³ / h for 8 minutes, then purge the air from the crystallizer and adjust the argon flow rate to 12 m³ / h. 3 / h, until the smelting is complete.

5. The method for eliminating N08028 alloy precipitates after forging without solid solution treatment according to claim 1 or 2, characterized in that: Prepare the slag material and smelt it using the electroslag furnace liquid slag arc initiation method. The slag system uses pre-melted quaternary slag with the following composition: CaF 250%, Al2O3 25%, CaO 15%, MgO 10%, and slag quantity 220kg.

6. The method for eliminating N08028 alloy precipitates after forging without solid solution treatment according to claim 1 or 2, characterized in that: Step 7: Power on and start the arc. Use a 450mm graphite electrode to perform slag treatment. The slag treatment current is 1500A and the voltage is 70V. Perform slag treatment in a stepped upward mode. The slag treatment time is controlled at 80 minutes. During the slag treatment, reduce the opening of the bottom water tank inlet valve and control the outlet water temperature to 43℃.

7. The method for eliminating N08028 alloy precipitates after forging without solid solution treatment according to claim 1 or 2, characterized in that: Step 8: The steady-state melting rate of the smelting process is controlled at 0.7D kg / h, where D is the diameter of the crystallizer in mm.

8. The method for eliminating N08028 alloy precipitates after forging without solid solution treatment according to claim 1 or 2, characterized in that: Step 10: After radial forging, do not solution-solidify; directly water-cool for 45 minutes.

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