Near-final hole expansion forming method with axial constraint for nickel-based alloy special-shaped ring of nuclear island flow distribution skirt

Abstract

The present invention discloses a near-final hole expansion forming method with axial constraints for a special-shaped nickel-based alloy ring of a nuclear island flow distribution skirt. The blank is placed on a hole expansion inner die with grooves and limits, and the upper anvil is pressed down and the mandrel drives the blank to rotate for die forging constraint deformation, including: 690 nickel-based alloy steel ingot cutting treatment, at least two upsetting and two pulling to open the blank; forging hole expansion forming, the initial forging temperature is 1000-1220℃, and the final forging temperature is ≥850℃; each pressing amount is ≥12% of the current blank thickness, and after each pressing, the blank is rotated 18° counterclockwise for the second pressing, and the pressing and rotation are repeated until the target forging size, performance heat treatment, ultrasonic, size, non-destructive, microstructure and performance and intergranular corrosion detection, and the test is qualified. Compared with the ring rolling process, the present invention has higher production efficiency, realizes a three-dimensional compressive stress state in the forging deformation area, and improves the comprehensive mechanical properties of nickel-based alloy forging products.

Description

Technical Field

[0001] The invention relates to a near-final hole expansion forming method of a nickel-based alloy special-shaped ring with axial constraints for a nuclear island flow distribution skirt. Background Art

[0002] Large forgings refer to free forgings produced by forging hydraulic presses of more than 1,000 tons, which can be divided into large shaft parts, large pancake parts and large ring parts. As a key category of large forgings, large ring parts are widely used in important industrial fields such as aerospace, nuclear power, petrochemicals, transportation and deep sea. Their production capacity and technical level are important criteria for measuring a country's industrial development level and self-sufficiency in key technical equipment. With the continuous development of my country's economic level and the continuous enhancement of its comprehensive national strength, industrial production is also facing various severe challenges such as international and domestic competition. Therefore, improving the quality control level in the production process of large ring parts and ensuring the safety and reliability of large ring parts during use are of great importance to improving my country's industrial development level and international competitiveness.

[0003] The special-shaped nickel-based alloy rings of the nuclear island are key load-bearing components of the nuclear island core. They are installed in the pressure vessel, and the nuclear fuel assemblies are installed inside. The main functions are to provide positioning and support for the nuclear fuel assemblies, to provide reliable guidance for the control rod startup, power adjustment, and shutdown, to absorb the impact energy of the control rod when it falls, to reasonably distribute channels for the fluid medium, to shield neutrons and gamma rays to reduce radiation damage to the pressure vessel, to provide fixed support and guidance for neutron injection rate and temperature measurement, and to provide secondary safety protection for falling in the event of a core melt accident. Therefore, strict requirements are placed on its microstructure state and mechanical properties.

[0004] The production process of large rings in industry can be roughly divided into cutting, roughing, punching, and hole expansion. Among them, the hole expansion process is an important step to reduce the wall thickness of the blank and make the inner and outer diameters reach the final ring standard. Therefore, it is also an indispensable key link in the entire process. During the hole expansion process, the carbides and coarse dendritic cast structures inside the blank are broken, the internal grains are refined, the uniformity is improved, and defects such as looseness and voids are effectively reduced, so that the mechanical properties of the ring are significantly improved.

[0005] Commonly used hole expansion methods include radial and axial rolling (referred to as ring rolling), horse frame hole expansion and other processes. In the ring rolling process, the driving roller drives the ring to rotate, while the core roller performs radial rolling movement, so that the wall thickness of the ring is reduced, the inner and outer diameters are increased, and the upper and lower cone rollers feed the ring axially to reduce the height of the ring, and finally obtain the ring of the target size. The difficulty lies mainly in the control of various feed speeds during the rolling process, such as the driving roller speed, the core roller radial feed speed, the axial feed speed and the retreat speed of the cone roller. Only when various speed conditions match each other can the rolling process be finally completed, otherwise it is easy to cause various defects and dimensional errors in the ring, such as severe widening, taper, uneven wall thickness and height, pits and local flattening. At present, there is no systematic theoretical research on the radial and axial feed speeds. In addition, dynamic recrystallization occurs during the hot deformation of the ring blank, generating equiaxed recrystallized grains with a smaller average grain size, thereby refining the original cast structure and improving the comprehensive mechanical properties of the ring. However, in the ring rolling process, when setting the radial feed speed of the core roller, it is necessary to prevent the roller jamming and ring instability caused by too high radial feed speed, and the matching of radial and axial speeds must also be considered. Therefore, during the radial and axial rolling process, the billet undergoes continuous small deformation in the radial direction, and the deformation of the billet per unit time may not meet the critical deformation required for dynamic recrystallization of most grains, resulting in the final average grain size of the billet not being significantly refined compared to before hole expansion, but being greatly elongated along the circumferential direction.

[0006] However, the horse frame expansion technology is to rotate the ring blank to a certain angle by rotating the mandrel, and then perform a large amount of deformation by pressing down. Therefore, the critical deformation amount that triggers dynamic recrystallization of the material can be reached through a single pressing, thereby greatly refining the grains and improving the homogeneity of the material, so as to enhance the macro and micro mechanical properties of the nickel-based alloy rings. Summary of the invention

[0007] The purpose of the present invention is to provide a near-final hole expansion forming method with axial constraint for nickel-based alloy special-shaped rings of nuclear island flow distribution skirt, that is, a horse rack hole expansion method with axial constraint on material flow, which can form nickel-based alloy annular parts with various cross-sections. Due to the large local deformation (exceeding the critical strain required for dynamic recrystallization of the material), the grain structure is finer (≥6 levels) than that of traditional rolled rings.

[0008] To achieve the above object, the present invention adopts the following technical solution:

[0009] The present invention provides a near-final hole expansion forming method with axial constraint for a nickel-based alloy special-shaped ring of a nuclear island flow distribution skirt, wherein a blank is placed on a hole expansion inner die with a groove and a limit, an upper anvil is pressed downward, and a mandrel drives the blank to rotate for die forging constraint deformation, comprising the following steps:

[0010] Step 1: Prepare 690 nickel-based alloy steel ingot by using a vacuum induction furnace + electroslag remelting smelting method;

[0011] Step 2: Ingot cutting process, wherein the ingot head is removed by ≥6% and the ingot tail is removed by ≥9%;

[0012] Step 3: The steel ingot after cutting is subjected to at least two upsetting and two drawing processes, and the forging ratio of each area of ​​the forging is ≥5;

[0013] Step 4: Forging hole expansion forming, wherein the initial forging temperature of the forging is 1000-1220°C, and the final forging temperature is ≥850°C; the pressing amount each time is ≥12% of the current billet thickness, ensuring that the strain of the deformed material each time exceeds the critical deformation amount for dynamic recrystallization of 690 nickel-based alloy; after each pressing, the billet is rotated 18° in the counterclockwise direction, and then pressed for the second time, the pressing rate of the press is ≥5 mm / s, and the entire deformation process including the rotation and displacement of the billet is ≤12 minutes, and the pressing and rotation are repeated until the target forging size is reached;

[0014] Step 5: The special-shaped ring obtained in step 4 is subjected to rough machining before performance heat treatment;

[0015] Step 6: Performance heat treatment;

[0016] Step 7: Rough machining and ultrasonic testing after performance heat treatment;

[0017] Step 8: Size detection;

[0018] Step 9: Nondestructive testing;

[0019] Step 10: Microstructure and performance testing;

[0020] Step 11: Intergranular corrosion detection;

[0021] Step 12: After passing the above tests, the nuclear island flow distribution skirt nickel-based alloy special-shaped ring is obtained.

[0022] Preferably, in step 4, the hole expansion mold positioning structure adopts a horse frame hole expansion positioning structure, including a horse frame and a hole expansion mandrel with a profile sleeved thereon;

[0023] The profiled hole-expanding mandrel is provided with annular protrusions of different sizes;

[0024] The annular blank is sleeved on the horse frame, and its axial inner side contacts the reaming core rod with the profile surface, an upper reaming anvil is pressed on the axial outer side above it, and its radial outer side below it is fixed between the horse frames through a stopper.

[0025] Preferably, in step 4, the pressing process of the forging hole expansion forming includes: the annular protrusion on the hole expansion core rod limits the axial flow of the ring blank, and after the upper hole expansion anvil is pressed down to complete one deformation, the blank is rotated a certain angle to complete the second deformation, and this cycle is repeated to complete the ring hole expansion forming.

[0026] Preferably, in step 6, the process of the performance heat treatment is: (1000-1150)°C×(0.5-1.5) hours+water cooling+(705-725)°C×(5-6) hours+water cooling.

[0027] Preferably, in step 9, the nondestructive testing includes ultrasonic testing, liquid penetrant testing and visual testing of the forgings.

[0028] Preferably, in step 10, the process of microstructure and performance testing is: sampling at intervals of 120° along the circumference of the ring, with the number of samples taken along the axial direction being ≥10, and the grain size is graded, and at the same time, tensile and impact specimens are processed in accordance with the national military industry standard (GJB) for tensile and drop hammer tests.

[0029] Preferably, in step 11, the intergranular corrosion test is carried out on each sample according to GB / T 4334-2008E, the sample is subjected to sensitization treatment by keeping at 650°C for 2h, and the material is observed for intergranular corrosion tendency.

[0030] The present invention proposes placing the blank on a hole-expanding inner die with grooves and limits, with the upper anvil pressing down and the mandrel driving the blank to rotate. It is named "a new method of hole-expanding with axial constraints on material flow", which cleverly borrows the working principle of die forging constraint deformation, increases the volume of materials subjected to three-dimensional compressive stress during a single deformation process, and promotes the hot nickel-based alloy material to fill the boss cavity while expanding the hole to the target size. In addition, the blank is placed on a mandrel with axial constraints, and the specific size is designed according to the size of the ring. The deformation area of ​​the forging is always in a relatively closed space, and the deformed material area is mainly subjected to three-dimensional compressive stress, which improves the internal quality of the forging.

[0031] Compared with the prior art, the present invention has the following beneficial effects: compared with the radial and axial rolling (referred to as ring rolling) process, the present invention has higher production efficiency, can realize a three-dimensional compressive stress state in the deformation area of ​​the forging, is conducive to the forging of defects such as looseness inside the forging, has a larger single deformation amount, is conducive to triggering dynamic recrystallization, can further refine the grain size inside the ring, and improve the comprehensive mechanical properties of nickel-based alloy forging products. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 2 is a schematic diagram of the structure of the nickel-based alloy special-shaped ring of the flow distribution skirt of the mobile reactor nuclear island in the embodiment.

[0033] Figure 2 Schematic diagram of the structure of the expansion core rod with axial constraint protrusions in the embodiment.

[0034] Figure 3 It is a schematic diagram of the horse frame expansion structure with axial constraint deformation in the embodiment.

[0035] Figure 4 It is a schematic diagram of the process principle of the nickel-based alloy special-shaped ring of the flow distribution skirt of the mobile reactor nuclear island in the embodiment.

[0036] Figure 5 Schematic diagram of the hole expansion forming process in the embodiment.

[0037] Figure 6 1 and 2 are the microstructures of the nickel-based alloy ring before and after deformation in the embodiment; (a) the grain structure before hole expansion; (b) the grain structure after hole expansion.

[0038] Figure 7 These are nickel-based alloy rings with different cross-sectional shapes in the embodiments. DETAILED DESCRIPTION

[0039] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments. These embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0040] like Figure 1 As shown in the figure, the flow distribution skirt forging has a circle of raised small steps on the inner wall. The difficulty of its forming technology lies in the small raised inner wall. As the load-bearing component in the nuclear island pressure vessel, it is required to ensure the full streamline of the forged fiber and the grain size ≥ 6. It is difficult to use the traditional ring forging forming process (ring rolling, horse frame expansion, etc.) for manufacturing:

[0041] If the traditional forming process of equal-thickness annular forgings is adopted to envelop the convex part of the inner wall, the thickness of the forging needs to be greatly increased, the forming conditions are complex, the cutting allowance is large, the material utilization rate is low, the production cycle is long, and the cutting process will cut off the fiber streamline formed by forging, greatly weakening the service performance of the forging;

[0042] If the traditional horse rack expansion process is adopted, the blank will be subjected to compressive stress in the radial direction and tensile stress in the axial direction. The material will flow axially while flowing circumferentially. The radial dimension will grow slowly and the expansion efficiency will be relatively low, which is not conducive to the elimination of defects in the center of the blank. In addition, it is difficult to fill the small raised steps on the inner wall without additional constraints.

[0043] like Figure 2 and 3As shown, the horse frame expansion deformation structure adopted by the present invention is composed of a horse frame, an expansion mandrel with axial constraints and an upper expansion anvil. The expansion mandrel has an annular protrusion of a certain size for limiting the axial flow of the ring blank. After the upper expansion anvil is pressed down to complete the first deformation, the blank is rotated by a certain angle to complete the second deformation. This cycle can realize the ring forming. By setting the ring protrusion on the mandrel to limit the axial flow of the blank, the blank is subjected to three-dimensional pressure in the rolling deformation zone, which is conducive to the forging of defects such as looseness inside the forging, and can also further refine the grain size inside the forging, thereby improving the comprehensive mechanical properties.

[0044] The raised features on the mandrel can be adjusted according to actual conditions, and the specific parameters include the raised height H and the spacing width W. By adjusting the characteristic parameters, the forging process of different-sized special-shaped nickel-based alloy rings can be adapted to achieve the best forming effect. It can be seen that the axially restricted horse frame expansion process of the present invention has a strong organizational refinement ability, can reduce the internal defects of forgings, improve the radial growth efficiency of rings, and can form special-shaped rings with local raised features. The process is simple to operate and has the potential for industrial application.

[0045] Example 1

[0046] This embodiment provides a near-final hole expansion forming method with axial constraint for a nickel-based alloy shaped ring of a nuclear island flow distribution skirt. The nuclear island internal components have very strict requirements on the purity and grain size of the forgings. The flow distribution skirt is thermally manufactured and the performance test and evaluation are evaluated. The specific steps are as follows:

[0047] (1) 690 nickel-based alloy ingots are smelted by vacuum induction furnace + electroslag remelting;

[0048] (2) Ingot cutting process: removing ≥6% of the ingot head and ≥9% of the ingot tail;

[0049] (3) Ingot blanking process: To ensure that the metal on the entire cross section can be forged through and the internal structure of the forging is uniform, at least two upsetting and two drawing are performed, and the forging ratio of each area of ​​the forging is ≥5;

[0050] (4) The initial forging temperature of the forging is 1200±20℃, and the final forging temperature is ≥850℃; the amount of each pressing is ≥12% of the current billet thickness, ensuring that the strain of the deformed material each time exceeds the critical deformation amount for dynamic recrystallization of 690 nickel-based alloy; after each pressing, the billet is rotated 18° in the counterclockwise direction and then pressed for the second time. The pressing rate of the press is ≥5 mm / s, and the entire deformation process including the rotation and displacement of the billet is ≤12 minutes to prevent the temperature from decreasing and causing deformation and cracking of the ring. Positioning of the expansion die as follows Figure 4 As shown, the pressing process is as Figure 5 As shown, press down and rotate repeatedly until the target forging size is reached;

[0051] (5) Rough machining before performance heat treatment: The performance heat treatment shape of the special-shaped ring should be as close to the final delivery size as possible. Therefore, the forging needs to be rough machined before performance heat treatment. The machining size is generally the final delivery size plus a certain heat treatment allowance. At the same time, in order to avoid cracking during solution treatment caused by structures such as sharp corners and grooves;

[0052] (6) Performance heat treatment system: (1000-1150)℃×(0.5-1.5) hours + water cooling + (715±10)℃×(5-6) hours + water cooling;

[0053] (7) Rough machining and ultrasonic testing after performance heat treatment: After final machining, since some areas cannot be inspected ultrasonically, it is necessary to inspect them in advance at the stage closest to the final stage. Therefore, forgings need to be rough machined and ultrasonically tested before finished products are processed;

[0054] (8) Dimension inspection: CNC lathes, vertical lathes and other equipment are used for finished product processing to ensure that the dimensional accuracy and roughness meet the requirements. After the finished product is processed, the forgings are dimensionally inspected according to the requirements of the purchase drawings and technical specifications;

[0055] (9) Nondestructive testing: ultrasonic testing, liquid penetrant testing and visual testing of forgings shall be carried out according to the requirements of drawings and technical specifications;

[0056] (10) Microstructure and performance testing: Samples are taken every 120° along the circumference of the ring, and the number of samples along the axial direction is ≥10, and the grain size is rated; at the same time, tensile and impact specimens are processed according to GJB for tensile and drop hammer tests. Figure 6 Shown are photos of the grain structure in the center area of ​​the special-shaped ring before and after hole expansion.

[0057] (11) Intergranular corrosion test: Intergranular corrosion test was carried out on each sample according to GB / T 4334-2008E method. The samples were sensitized by keeping them at 650℃ for 2h to observe whether the materials had intergranular corrosion tendency, so as to prove whether the C element content of the raw materials and the heat treatment process were effectively controlled.

[0058] The "new method of expanding holes with axial constraints on material flow" proposed in this invention can form nickel-based alloy annular parts with various cross-sections. Due to the large local deformation (exceeding the critical strain required for dynamic recrystallization of the material), the grain structure is finer (≥6 levels) than that of traditional rolled rings. The cross-sectional shapes that can be formed are as follows: Figure 7 shown.

[0059] The above description of the embodiments is to facilitate the understanding and use of the present invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without having to go through creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the principles of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. Near-final hole expansion forming method with axial constraint for nickel-based alloy special-shaped ring of nuclear island flow distribution skirt. It is characterized in that The blank is placed on an inner die with grooves and limiters, the upper anvil presses down, and the mandrel drives the blank to rotate for forging and constrain deformation, including the following steps: Step 1: Prepare 690 nickel-based alloy steel ingot by using a vacuum induction furnace + electroslag remelting smelting method; Step 2: Ingot cutting process, in which the ingot head is removed by ≥6% and the ingot tail is removed by ≥9%; Step 3: The steel ingot after cutting is subjected to at least two upsetting and two drawing processes, and the forging ratio of each area of ​​the forging is ≥5; Step 4: Forging hole expansion forming, wherein the initial forging temperature of the forging is 1000~1220℃, and the final forging temperature is ≥850℃; the pressing amount each time is ≥12% of the current billet thickness, ensuring that the strain of the deformed material each time exceeds the critical deformation amount for dynamic recrystallization of 690 nickel-based alloy; after each pressing, the billet is rotated 18° in the counterclockwise direction, and then pressed for the second time, the pressing rate of the press is ≥5 mm / s, and the entire deformation process including the rotation and displacement of the billet is ≤12 minutes, and the pressing and rotation are repeated until the target forging size is reached; Step 5: The special-shaped ring obtained in step 4 is subjected to rough machining before performance heat treatment; Step 6: Performance heat treatment; the process of the performance heat treatment is: 1000-1150°C × 0.5-1.5 hours + water cooling + 705-725°C × 5-6 hours + water cooling; Step 7: Rough machining and ultrasonic testing after performance heat treatment; Step 8: Size detection; Step 9: Nondestructive testing; Step 10: Microstructure and performance testing; Step 11: Intergranular corrosion detection; Step 12: After passing the above tests, the nuclear island flow distribution skirt nickel-based alloy special-shaped ring is obtained.

2. According to the method for forming the near-final hole expansion of the nickel-based alloy special-shaped ring of the nuclear island flow distribution skirt with axial constraint according to claim 1, It is characterized in that In step 4, the hole expansion mold positioning structure adopts a horse frame hole expansion positioning structure, including a horse frame and a hole expansion core rod with a profile sleeved thereon; The profiled hole-expanding mandrel is provided with annular protrusions of different sizes; The annular blank is sleeved on the horse frame, and its axial inner side contacts the reaming mandrel with the profile surface, an upper reaming anvil is pressed on the axial outer side above it, and its lower side is fixed between the horse frames through a stopper.

3. According to claim 2, the near-final hole expansion forming method of the nickel-based alloy special-shaped ring of the nuclear island flow distribution skirt with axial constraint, It is characterized in that In step 4, the pressing process of the forging hole expansion forming includes: the annular protrusion on the hole expansion core rod limits the axial flow of the ring blank, and after the upper hole expansion anvil is pressed down to complete the first deformation, the blank is rotated a certain angle to complete the second deformation, and this cycle is repeated to complete the ring hole expansion forming.

4. According to claim 1, the near-final hole expansion forming method of the nickel-based alloy special-shaped ring of the nuclear island flow distribution skirt with axial constraint, It is characterized in that In step 9, the nondestructive testing includes ultrasonic testing, liquid penetrant testing and visual testing of the forgings.

5. According to claim 1, the near-final hole expansion forming method of the nickel-based alloy special-shaped ring of the nuclear island flow distribution skirt with axial constraint, It is characterized in that In step 10, the process of microstructure and performance testing is as follows: sampling is performed at intervals of 120° along the circumference of the ring, and the number of samples taken along the axial direction is ≥10, and the grain size is rated. At the same time, tensile and impact specimens are processed in accordance with national military industry standards for tensile and drop hammer tests.

6. According to claim 1, the near-final hole expansion forming method of the nickel-based alloy special-shaped ring of the nuclear island flow distribution skirt with axial constraint, It is characterized in that In step 11, the intergranular corrosion test is carried out on each sample according to GB / T 4334-2008 E. The sample is subjected to a sensitization treatment of being kept at 650° C. for 2 hours to observe whether the material has a tendency to intergranular corrosion.

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