Manufacturing process of NO7718 nickel base alloy nut for nuclear equipment

Abstract

The invention discloses a manufacturing process of an NO7718 nickel base alloy nut for nuclear equipment. The manufacturing process comprises the steps of material preparation, hot forging, shot blasting, solid solution heat treatment, physical and chemical detection, finish machining, precipitation hardening heat treatment and detection packaging. The hot forging near-net forming technology is adopted, the shape of the nut blank is directly obtained through plastic deformation, the cutting allowance of machining is greatly reduced, a large number of raw materials are prevented from becoming sweeps, the material utilization rate is remarkably increased, and the raw material cost is effectively reduced; by accurately controlling the initial forging temperature, the final forging temperature and the cooling speed of hot forging as well as subsequent solution treatment and precipitation hardening treatment, grains can be refined, and the precipitation form and distribution of a strengthening phase can be controlled, so that the microstructure of the material is optimized, and the material obtains more excellent comprehensive mechanical properties such as higher strength, plasticity and toughness cooperation; and the harsh working condition requirements of nuclear equipment can be better met. The process provided by the invention ensures the stability and consistency of product performance.

Description

Technical Field

[0001] This invention relates to the field of metal material processing technology, specifically to a manufacturing process for NO7718 nickel-based alloy nuts used in nuclear equipment. Background Technology

[0002] Nickel-based alloys, especially NO7718 alloy, are widely used in high-end equipment manufacturing fields such as aviation, aerospace, and nuclear power due to their excellent high-temperature strength, creep resistance, fatigue resistance, and good corrosion resistance. In nuclear equipment, nuts used in critical components such as valves and pipe connections need to withstand high temperatures, high pressures, and intense radiation environments, thus requiring extremely high comprehensive performance of the materials.

[0003] Currently, the traditional method for manufacturing NO7718 nickel-based alloy nuts mainly involves machining. However, NO7718 alloy is a typical difficult-to-machine material, with machinability far lower than that of ordinary steels such as 45# steel. This leads to a series of problems during machining, including severe tool wear, low machining efficiency, high production costs, and long production cycles. More importantly, a large amount of raw material becomes waste during machining, resulting in low material utilization and failing to meet the requirements of green manufacturing and cost reduction. Furthermore, simple machining cannot improve the original microstructure of the material, making it difficult to fully realize its potential mechanical properties.

[0004] In order to reduce the processing cost of NO7718 nickel-based alloy nuts, shorten the production cycle, achieve large-scale mass production, and at the same time optimize their microstructure and mechanical properties, it is urgent to develop a manufacturing process specifically for NO7718 nickel-based alloy nuts used in nuclear equipment. Summary of the Invention

[0005] The purpose of this invention is to provide a manufacturing process for NO7718 nickel-based alloy nuts for nuclear equipment, so as to solve the problems mentioned in the background art.

[0006] The manufacturing process for NO7718 nickel-based alloy nuts for nuclear equipment provided by this invention includes the following steps: (1) Material preparation: Prepare NO7718 nickel-based alloy bars with chemical composition meeting the requirements; the chemical composition of the NO7718 nickel-based alloy by weight percentage is: C≤0.08, Si≤0.35, Mn≤0.35, P≤0.015, S≤0.015, Cr:17.0~21.0, Mo:2.80~3.30, Ni:50.0~55.0, Cu≤0.3, Ti:0.65~1.15, Al:0.20~0.80, Co≤1.0, B≤0.006, Nb+Ta:4.75~5.5, with the balance being Fe; (2) Hot forging: The NO7718 nickel-based alloy bar is heated at an initial forging temperature of 1100-1120℃ and held for 10 minutes, and then multi-station die forging is performed. During the forging process, the length-to-diameter ratio of the material is 1.3-1.8, the final forging temperature is ≥960℃, and the forging is immediately water-cooled to obtain the forging. (3) Shot blasting: to remove oxide scale from the surface of forgings; (4) Solution heat treatment: Hold the shot-blasted forgings at 924-1010℃ for 1 hour, and then cool them with water; (5) Physical and chemical testing: Test the mechanical properties of the forgings to ensure that its tensile strength Rm≥1275MPa, yield strength Rp0.2≥1034MPa, elongation after fracture A≥12%, reduction of area Z≥15%, and hardness≥331HB; (6) Finishing: Machining the qualified forgings to form semi-finished nuts; (7) Precipitation hardening heat treatment: The semi-finished nut after fine machining is heated to 718℃±14℃ and held for 8 hours in a vacuum furnace. Then it is cooled to 621℃±14℃ at a rate of 55℃±20℃ / hour and held for 8 hours. After that, it is cooled to below 150℃ and then air-cooled. The total heat treatment time is 18 to 20 hours to obtain the finished nut. (8) Inspection and packaging: Non-destructive testing and finished product inspection are carried out on the finished nuts, and they are cleaned and packaged.

[0007] Preferably, in step (2), an ultra-high frequency induction heating furnace is used to heat the NO7718 nickel-based alloy bar.

[0008] Preferably, in step (2), the multi-station die forging process includes material positioning, ball pressing, pre-forming, and finishing.

[0009] Preferably, in step (4), the solution heat treatment is carried out in a mesh belt heat treatment furnace.

[0010] Preferably, in step (8), the non-destructive testing is liquid permeation testing.

[0011] The present invention also provides a nut for nuclear equipment, which is manufactured by the manufacturing process described in any one of claims 1 to 5.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention adopts hot forging near-net-shape forming technology, which directly obtains the shape of the nut blank through plastic deformation, greatly reduces the cutting allowance of machining, avoids a large amount of raw materials becoming waste, significantly improves material utilization, and effectively reduces raw material costs.

[0013] 2. By precisely controlling the initial forging temperature, final forging temperature, and cooling rate of hot forging, as well as subsequent solution treatment and precipitation hardening treatment, this invention can refine grains, control the precipitation morphology and distribution of strengthening phases, thereby optimizing the microstructure of the material and enabling it to obtain superior comprehensive mechanical properties, such as a higher combination of strength, plasticity, and toughness, to better meet the stringent operating requirements of nuclear equipment.

[0014] 3. The hot forging process of this invention is suitable for automated and continuous production, and compared with the machining of individual parts, the production efficiency is increased by orders of magnitude. At the same time, due to the reduction in machining time and tool consumption, the overall production cost is effectively reduced, laying the foundation for the large-scale mass production of NO7718 nickel-based alloy nuts.

[0015] 4. The process parameters provided by this invention have a clear range and a clear operation process. In particular, the key heat treatment and forging parameters have been optimized and limited, which ensures the stability and consistency of product performance and is suitable for industrial promotion and application. Attached Figure Description

[0016] Figure 1 This is a process flow diagram of the manufacturing process of the NO7718 nickel-based alloy nut for nuclear equipment according to the present invention; Figure 2 This is a schematic diagram of the precipitation hardening heat treatment curve in this invention; Figure 3 This is a metallographic diagram of the nut product in Embodiment 1 of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Please see Figure 1 and 2 The manufacturing process for NO7718 nickel-based alloy nuts for nuclear equipment provided by this invention includes the following steps: (1) Material preparation: Prepare NO7718 nickel-based alloy bars with chemical composition meeting the requirements; the chemical composition of the NO7718 nickel-based alloy by weight percentage is: C≤0.08, Si≤0.35, Mn≤0.35, P≤0.015, S≤0.015, Cr:17.0~21.0, Mo:2.80~3.30, Ni:50.0~55.0, Cu≤0.3, Ti:0.65~1.15, Al:0.20~0.80, Co≤1.0, B≤0.006, Nb+Ta:4.75~5.5, with the balance being Fe; (2) Hot forging: NO7718 nickel-based alloy bar is placed in an ultra-high frequency induction heating furnace, heated at an initial forging temperature of 1100-1120℃ and held for 10 minutes, and then multi-station die forging is carried out. The specific route is material positioning, ball pressing, pre-forming and finishing. The length-to-diameter ratio of the material during forging is 1.3-1.8, the final forging temperature is ≥960℃, and the forging is immediately water-cooled after forging to obtain the forging. (3) Shot blasting: to remove oxide scale from the surface of forgings; (4) Solution heat treatment: Place the shot-blasted forgings in a mesh belt heat treatment furnace and hold them at 924-1010℃ for 1 hour, then cool them with water; (5) Physical and chemical testing: Test the mechanical properties of the forgings to ensure that its tensile strength Rm≥1275MPa, yield strength Rp0.2≥1034MPa, elongation after fracture A≥12%, reduction of area Z≥15%, and hardness≥331HB; (6) Finishing: Machining the qualified forgings, including turning the outer circle and end face, drilling and tapping, to form a nut semi-finished product; (7) Precipitation hardening heat treatment: The semi-finished nut after fine machining is heated to 718℃±14℃ and held for 8 hours in a vacuum furnace. Then it is cooled to 621℃±14℃ at a rate of 55℃±20℃ / hour and held for 8 hours. After that, it is cooled to below 150℃ and then air-cooled. The total heat treatment time is 18 to 20 hours to obtain the finished nut. (8) Inspection and packaging: The finished nuts are subjected to liquid penetration test according to relevant requirements. The size and appearance of the finished products are inspected according to the standards and drawings. They are cleaned and dried with cleaning agent and packaged as required.

[0019] Example 1 Manufacturing number: 2024-1-8 Ordering Unit: CNNC Suzhou Valve Technology Industry Co., Ltd. (Nuclear Power Explosion Valve Project) Product Specifications: 1 3 / 4"-10UNC-2B The NO7718 nickel-based alloy is manufactured using the above-described process of this invention. The chemical composition of the NO7718 nickel-based alloy, by weight percentage, is: C=0.04, Si=0.19, Mn=0.08, P=0.011, S=0.001, Cr=18.76, Mo=3.04, Ni=53.2, Cu=0.06, Ti=0.90, Al=0.51, Co=0.32, B=0.005, Nb+Ta=5.07, with the balance being Fe. The initial forging temperature for hot forging is 1170℃; the length-to-diameter ratio of the material is 1.5; the solution heat treatment temperature is 980℃; during precipitation hardening heat treatment, the alloy is first heated to 720℃ and held for 8 hours, then cooled to 630℃ at a rate of 65℃ / hour and held for 8 hours, followed by cooling to 100℃ and air cooling. The total heat treatment time is 19 hours.

[0020] Performance test results: tensile strength Rm = 1276 MPa, yield strength Rp0.2 = 1123 MPa, elongation after fracture A = 20.5%, reduction of area Z = 27%, hardness 441 HB. All performance indicators meet and exceed the requirements of nuclear power standards.

[0021] Example 2 Manufacturing number: 2024-11-91 Ordering Unit: Dalian Dagao Valve Co., Ltd. (Haiyang Unit 5 PV64 Main Steam Isolation Valve Nuclear Power Project) Product Specifications: M56 The NO7718 nickel-based alloy is manufactured using the above-described process of this invention. The chemical composition of the NO7718 nickel-based alloy, by weight percentage, is: C=0.029, Si=0.079, Mn=0.019, P=0.003, S=0.006, Cr=17.59, Mo=291, Ni=52.55, Cu=0.08, Ti=0.91, Al=0.51, Co=0.37, B=0.003, Nb+Ta=5.18, with the balance being Fe. The initial forging temperature for hot forging is 1150℃. The length-to-diameter ratio of the material is 1.45. The solution heat treatment temperature is 980℃. During precipitation hardening heat treatment, the alloy is first heated to 720℃ and held for 8 hours, then cooled to 625℃ at a rate of 60℃ / hour and held for 8 hours, followed by cooling to 110℃ and air cooling. The total heat treatment time is 18.5 hours.

[0022] The performance test results are as follows: tensile strength Rm = 1277 MPa, yield strength Rp0.2 = 1102 MPa, elongation after fracture A = 19%, reduction of area Z = 22.3%, and hardness 396 HB. The product performance is excellent and fully meets the project's technical requirements.

[0023] The above embodiments demonstrate that the process of the present invention is stable and reliable, and the NO7718 nickel-based alloy nut produced has excellent mechanical properties and is fully applicable to nuclear equipment.

Claims

1. A manufacturing process for NO7718 nickel-based alloy nuts for nuclear equipment, characterized in that, Includes the following steps: (1) Material preparation: Prepare NO7718 nickel-based alloy bars with chemical composition meeting the requirements; the chemical composition of the NO7718 nickel-based alloy by weight percentage is: C≤0.08, Si≤0.35, Mn≤0.35, P≤0.015, S≤0.015, Cr:17.0~21.0, Mo:2.80~3.30, Ni:50.0~55.0, Cu≤0.3, Ti:0.65~1.15, Al:0.20~0.80, Co≤1.0, B≤0.006, Nb+Ta:4.75~5.5, with the balance being Fe; (2) Hot forging: The NO7718 nickel-based alloy bar is heated at an initial forging temperature of 1100-1120℃ and held for 10 minutes, and then multi-station die forging is performed. During the forging process, the length-to-diameter ratio of the material is 1.3-1.8, the final forging temperature is ≥960℃, and the forging is immediately water-cooled to obtain the forging. (3) Shot blasting: to remove oxide scale from the surface of forgings; (4) Solution heat treatment: Hold the shot-blasted forgings at 924-1010℃ for 1 hour, and then cool them with water; (5) Physical and chemical testing: Test the mechanical properties of the forgings to ensure that its tensile strength Rm≥1275MPa, yield strength Rp0.2≥1034MPa, elongation after fracture A≥12%, reduction of area Z≥15%, and hardness≥331HB; (6) Finishing: Machining the qualified forgings to form semi-finished nuts; (7) Precipitation hardening heat treatment: The semi-finished nut after fine machining is heated to 718℃±14℃ and held for 8 hours in a vacuum furnace. Then it is cooled to 621℃±14℃ at a rate of 55℃±20℃ / hour and held for 8 hours. After that, it is cooled to below 150℃ and then air-cooled. The total heat treatment time is 18 to 20 hours to obtain the finished nut. (8) Inspection and packaging: Non-destructive testing and finished product inspection are carried out on the finished nuts, and they are cleaned and packaged.

2. The manufacturing process of the NO7718 nickel-based alloy nut for nuclear equipment according to claim 1, characterized in that: In step (2), an ultra-high frequency induction heating furnace is used to heat the NO7718 nickel-based alloy bar.

3. The manufacturing process of the NO7718 nickel-based alloy nut for nuclear equipment according to claim 1, characterized in that: In step (2), the multi-station die forging process includes material positioning, ball pressing, pre-forming, and finishing.

4. The manufacturing process of the NO7718 nickel-based alloy nut for nuclear equipment according to claim 1, characterized in that: In step (4), the solution heat treatment is carried out in a mesh belt heat treatment furnace.

5. The manufacturing process of the NO7718 nickel-based alloy nut for nuclear equipment according to claim 1, characterized in that: In step (8), the non-destructive testing is liquid permeation testing.

6. A nut for nuclear equipment, characterized in that, The nut is manufactured using the manufacturing process described in any one of claims 1 to 5.

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