A heat treatment method for GH350 alloy fasteners for aviation

Abstract

The application belongs to the technical field of aviation fastener processing, and particularly relates to a heat treatment method of GH350 alloy fastener for aviation, which comprises the following steps: after upsetting forming, two-step solid solution treatment and two-step aging treatment are sequentially performed; wherein the temperature of the first solid solution treatment is 1017-1023 DEG C, the holding time is 115-125 min, the temperature of the second solid solution treatment is 945-955 DEG C, and the holding time is 230-250 min; the temperature of the first aging treatment is 880-890 DEG C, the holding time is 50-70 min, the temperature of the second aging treatment is 750-770 DEG C, and the holding time is 230-250 min. The heat treatment process solves the problem of grain size exceeding the standard of GH350 bolt products, can control the bolt to meet the requirement of grain size being 2-6 levels under the condition of meeting other mechanical properties, and simultaneously improves the mechanical properties of the bolt product.

Description

Technical Field

[0001] This invention relates to a heat treatment method for GH350 alloy fasteners used in aviation, belonging to the field of aviation fastener processing technology. Background Technology

[0002] GH350 alloy is a nickel-based high-temperature alloy that has high strength at 700℃, as well as excellent corrosion resistance, good plasticity and toughness, making it suitable for manufacturing aerospace parts and military materials.

[0003] GH350 alloy is commonly used as turbofan disk bolts for turbofan engines in the aerospace field. The design operating temperature range of turbofan disk bolts is 560-580℃. According to the engine design requirements, the performance requirements for a certain type of turbofan disk bolt are as follows: room temperature tensile strength ≥1130Mpa, high temperature tensile strength ≥740Mpa at 750℃, stress endurance at 412Mpa at 750℃ ≥50h, and grain size requirement of 2-6.

[0004] Currently, GH350 bolts produced using conventional processing methods exhibit Grade 1 grains in their metallographic microstructure, which fails to meet the 2-6 grain size requirement for turbofan disk bolts. Therefore, it is necessary to optimize the heat treatment process to reduce the presence of Grade 1 grains, obtain a uniform microstructure, and simultaneously meet the room temperature strength and high-temperature mechanical properties requirements of GH350 alloy bolts, thus producing bolt products that meet engine requirements. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a heat treatment method for GH350 alloy fasteners used in aviation, reducing large grains (Grade 1) in GH350 bolts and achieving a dual improvement in room temperature strength and high-temperature mechanical properties of GH350 alloy bolts.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0007] A heat treatment method for GH350 alloy fasteners for aviation applications includes the following steps: after upsetting, two-step solution treatment and two-step aging treatment are performed sequentially; wherein, the temperature of the first solution treatment is 1017℃-1023℃, and the holding time is 115min-125min, and the temperature of the second solution treatment is 945℃-955℃, and the holding time is 230min-250min; the temperature of the first aging treatment is 880℃-890℃, and the holding time is 50min-70min, and the temperature of the second aging treatment is 750℃-770℃, and the holding time is 230min-250min.

[0008] Based on the above technical solution, the present invention can also be improved as follows:

[0009] Furthermore, during the heating process of the first solution treatment, the temperature is held at 800℃ for 40-50 minutes.

[0010] Furthermore, the first solution treatment is carried out in a vacuum furnace with a vacuum degree ranging from 0.133 Pa to 13.3 Pa. After the first solution treatment is held at a certain temperature, it is first cooled in argon gas for ≥30 min, and then air-cooled.

[0011] Furthermore, the temperature for the first solution treatment is 1020℃.

[0012] Furthermore, the secondary solution treatment is carried out in a vacuum furnace with a vacuum degree ranging from 0.133 Pa to 13.3 Pa. After the secondary solution treatment is held at a certain temperature, it is first cooled in argon gas for ≥30 min, and then air-cooled.

[0013] Furthermore, the temperature for the secondary solution treatment is 950℃.

[0014] Furthermore, the first aging treatment is carried out in a vacuum furnace with a vacuum degree ranging from 0.133 Pa to 13.3 Pa. After the first aging treatment is completed, it is first cooled in argon gas for ≥30 min, and then air-cooled.

[0015] Furthermore, the temperature for a single aging treatment is 885℃.

[0016] Furthermore, the secondary aging treatment is carried out in a vacuum furnace with a vacuum degree ranging from 0.133 Pa to 13.3 Pa. After the secondary aging treatment is completed, it is first cooled in argon gas for ≥30 min, and then air-cooled.

[0017] Furthermore, the temperature for the secondary aging treatment was 760℃, and the holding time was 240 minutes.

[0018] The beneficial effects of this invention are as follows:

[0019] This invention controls the grain size of GH350 alloy by lowering the solution treatment temperature, controlling the holding time and cooling method of the solution treatment, and adding a secondary solution treatment process, combined with two-step aging treatment. This allows the alloy to meet the requirements of grain size 2-6 while satisfying mechanical properties, resulting in bolt products that meet both mechanical properties and grain size requirements.

[0020] This invention utilizes an 800℃ heat preservation platform, combined with two solution treatments, to regulate grain size and ensure the product meets grain size requirements. The 800℃ heat preservation platform helps the GH350 alloy reach an overall equilibrium state, reducing localized grain coarsening. Combined with the subsequent two solution treatments and argon cooling for ≥30 minutes, rapid cooling prevents residual heat from causing grain coarsening, thus controlling the crystal structure to meet a grain size of 2-6. The two aging treatments aim to precipitate gradient strengthening phases through secondary aging. These strengthening phases hinder dislocation movement, improving the product's room temperature strength and high-temperature creep resistance. Attached Figure Description

[0021] Figure 1 Metallographic photograph of Example 1;

[0022] Figure 2 Metallographic photograph of Example 2;

[0023] Figure 3 Metallographic photograph of Example 3;

[0024] Figure 4 Metallographic photograph of Comparative Example 1;

[0025] Figure 5 This is a metallographic photograph of Comparative Example 2;

[0026] Figure 6 Metallographic photograph of Comparative Example 3;

[0027] Figure 7 Metallographic photograph of Comparative Example 4;

[0028] Figure 8 The metallographic photograph is for comparison example 5;

[0029] Figure 9 The metallographic photograph is for Comparative Example 6;

[0030] Figure 10 The metallographic photograph is for Comparative Example 7;

[0031] Figure 11 The metallographic photograph is for comparison example 8;

[0032] Figure 12 The metallographic photograph is for comparison example 9;

[0033] Figure 13 Metallographic photographs for comparison scale 10;

[0034] Figure 14 For comparison, a metallographic photograph;

[0035] Figure 15 This is a metallographic photograph of Comparative Example 12. Detailed Implementation

[0036] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0037] The purpose of this invention is to provide a heat treatment method for GH350 alloy fasteners used in aviation, which can solve the problem that the grain size of turbofan disk bolts made of GH350 alloy cannot meet the requirements. This invention reduces the solution treatment temperature and adds a secondary solution treatment process based on conventional processes, combined with a two-step aging treatment process, to obtain bolt products that simultaneously meet the requirements for mechanical properties and grain size.

[0038] The GH350 alloy of the present invention is composed of the following elements by mass fraction: Mn≤0.1%, W 1.8~2.3%, Si≤0.15%, Al 0.85~1.25%, P≤0.01%, C≤0.02%, O≤0.005%, Co 23.5~26.5%, N≤0.01%, Mo2.8~3.3%, Cr 14~17.5%, S≤0.01%, Ti 1.9~2.35%, Nb 0.9~1.3%, B≤0.03%, Cu≤0.02%, Zr≤0.1%, Ta 3.7~4.5%, Fe≤0.8%, with the balance being Ni.

[0039] Example 1

[0040] The heat treatment of bolts after hot upsetting the head includes the following steps:

[0041] (1) One solution treatment, the specific process is as follows: a solution treatment is carried out in a vacuum furnace, the vacuum degree is set to 4.5 Pa, the bolt is heated to 1020℃ with the furnace, and held at 1020℃ for 120 min. During the heating process, a heat preservation platform is set up, and the heat preservation is carried out at 800℃ for 45 min.

[0042] (2) After the heat preservation is completed, cool with high-purity argon gas for ≥30 min;

[0043] (3) Secondary solution treatment, the specific process is as follows: the secondary solution treatment is carried out in a vacuum furnace, the vacuum degree is set to 3.3 Pa, the bolts are heated to 950℃ with the furnace and held for 240 min;

[0044] (4) After the heat preservation is completed, cool with high-purity argon gas for ≥30 min;

[0045] (5) First aging treatment, the specific process is as follows: the bolts after the second solution treatment are aged in a vacuum furnace, the vacuum degree is set to 0.47Pa, the bolts are heated to 885℃ in the furnace for aging treatment, and the holding time is 60min;

[0046] (6) After the heat preservation is completed, cool with high-purity argon gas for ≥30 minutes. Then take out the bolt sample and let it cool naturally in the air to room temperature.

[0047] (7) Secondary aging treatment, the specific process is as follows: aging treatment is carried out in a vacuum furnace, the vacuum degree is set to 0.156Pa, the bolts are heated to 760℃ with the furnace for aging treatment, and the holding time is 240min;

[0048] (8) After the heat preservation is completed, cool with high-purity argon gas for ≥30 minutes. Then take out the sample and let it cool naturally in the air to room temperature.

[0049] Example 2

[0050] Unlike Example 1, in this example, the first solution temperature in step (1) is 1023℃, the holding time is 115 min, and the vacuum degree of the vacuum furnace is set to 4.1 Pa. In step (3), the second solution temperature is 945℃, the holding time is 230 min, and the vacuum degree of the vacuum furnace is set to 3 Pa. In step (5), the first aging temperature is 880℃, the holding time is 50 min, and the vacuum degree of the vacuum furnace is set to 0.16 Pa. In step (7), the second aging temperature is 750℃, the holding time is 230 min, and the vacuum degree of the vacuum furnace is set to 0.33 Pa; all other aspects are the same as in Example 1.

[0051] Example 3

[0052] Unlike Example 1, in this example, the first solution temperature in step (1) is 1017℃, the holding time is 125 min, and the vacuum degree of the vacuum furnace is set to 3.9 Pa. In step (3), the second solution temperature is 955℃, the holding time is 250 min, and the vacuum degree of the vacuum furnace is set to 2.8 Pa. In step (5), the first aging temperature is 890℃, the holding time is 70 min, and the vacuum degree of the vacuum furnace is set to 0.155 Pa. In step (7), the second aging temperature is 770℃, the holding time is 250 min, and the vacuum degree of the vacuum furnace is set to 0.88 Pa; all other aspects are the same as in Example 1.

[0053] Comparative Example 1

[0054] After the head is hot-forged, the bolt undergoes conventional heat treatment, specifically including the following steps:

[0055] (1) The solution treatment process is carried out in an air furnace, and the temperature is raised to 1030℃ and held for 120 min. After the sample is held for 120 min, it is air-cooled. In the heat treatment of this comparative example, the bolt is only subjected to solution treatment once.

[0056] (2) The aging process is as follows: the sample is placed in an air furnace at 885°C and aged for 60 minutes. After that, the sample is taken out and allowed to cool naturally to room temperature in the air.

[0057] (3) The secondary aging process is carried out in an air furnace. The sample is placed in the furnace at 760°C and aged for 240 minutes. After that, the sample is taken out and allowed to cool naturally to room temperature in the air.

[0058] Comparative Example 2

[0059] After the head is hot-forged, the bolt is heat-treated. The difference from Example 1 is that this comparative example only performs the first step of solution treatment, with a solution temperature of 1020℃ and a holding time of 120min. No second solution treatment is performed. The rest is the same as Example 1.

[0060] Comparative Example 3

[0061] The bolts after hot upsetting of the head are subjected to heat treatment. The difference from Example 1 is that the solution treatment temperature of this comparative example is 1030°C and the holding time is 120 min. The rest is the same as Example 1.

[0062] Comparative Example 4

[0063] The bolts after hot upsetting of the head are subjected to heat treatment. The difference from Example 1 is that the solution treatment temperature of this comparative example is 1010℃ and the holding time is 120min. The rest is the same as Example 1.

[0064] Comparative Example 5

[0065] The bolts after hot upsetting of the head are subjected to heat treatment. The difference from Example 1 is that the heat treatment time for the first solution treatment in this comparative example is 60 minutes, and the heat treatment time for the second solution treatment is 120 minutes. The rest is the same as in Example 1.

[0066] Comparative Example 6

[0067] The bolts after hot upsetting of the head are subjected to heat treatment. The difference from Example 1 is that the heat treatment time for the second solution treatment in this comparative example is 120 minutes, while the rest is the same as in Example 1.

[0068] Comparative Example 7

[0069] The bolts after hot upsetting of the head are subjected to heat treatment. The difference from Example 1 is that the heat treatment time for the first solution treatment in this comparative example is 180 min, and the heat treatment time for the second solution treatment is 120 min. The rest is the same as in Example 1.

[0070] Comparative Example 8

[0071] The bolts after hot upsetting of the head are subjected to heat treatment. The difference from Example 1 is that the heat treatment time for the first solution treatment in this comparative example is 240 min, and the heat treatment time for the second solution treatment is 120 min. The rest is the same as in Example 1.

[0072] Comparative Example 9

[0073] The bolts after hot upsetting of the head are subjected to heat treatment. The difference from Example 1 is that the heat treatment time for the first solution treatment in this comparative example is 60 minutes, while the rest is the same as in Example 1.

[0074] Comparative Example 10

[0075] The bolts after hot upsetting of the head are subjected to heat treatment. The difference from Example 1 is that the heat treatment time for the first solution treatment in this comparative example is 180 minutes, while the rest is the same as in Example 1.

[0076] Comparative Example 11

[0077] The bolts after hot upsetting of the head are subjected to heat treatment. The difference from Example 1 is that the solution treatment and heat preservation time in this comparative example is 240 minutes, while the rest is the same as in Example 1.

[0078] Comparative Example 12

[0079] The bolts after hot upsetting of the head are heat treated. The difference from Example 1 is that an 800°C heat treatment platform was not set up during the first solution treatment in this comparative example. Otherwise, it is the same as Example 1.

[0080] Optical metallographic observation and mechanical property measurement were performed on the products of the examples and comparative examples, and the results are shown in Table 1.

[0081] Table 1 Product Performance Data Table

[0082]

[0083] As can be seen from the data in the table above, the room temperature tensile strength of the bolts in Examples 1-3 of this invention is 1271 MPa-1299 MPa, which is higher than that of Comparative Examples 1-12; the creep rupture performance of the bolts in Examples 1-3 can reach 71h-72h, which is significantly better than that of Comparative Examples 1-12. Therefore, the heat treatment of the bolts in this invention significantly affects the product performance. In Comparative Examples 1-4, grade 7 and 8 fine grains were observed, which do not meet product requirements. In Comparative Examples 5-12, grade 1 and 0 large grains were observed (the presence or absence of grade 1 grains is indicated in parentheses after grain size in Table 1), which also do not meet product requirements. After heat treatment using the method of this invention, the grain size of the bolts in Examples 1-3 is grade 2-6, with no grade 1 grains, thus simultaneously meeting the requirements for mechanical properties and grain size, and conforming to product requirements.

[0084] According to the Hall-Petch formula: σ s =σ o + Kd -1 / 2 In the formula: σ s σ represents the yield strength of a material. o This represents the lattice friction required to generate a single dislocation, where K is a constant and d represents the average grain size.

[0085] According to the Hall-Petch formula, the yield strength of a material at room temperature is inversely proportional to the grain size; that is, the finer the grains, the higher the strength of the material. However, at high temperatures, grain boundary defects reduce the alloy strength, while coarse grains at high temperatures have higher creep limits and endurance strength. The operating temperature of GH350 turbofan disk bolts is 560℃-580℃. In this temperature range, grain boundary strengthening is dominant. Grade 1 coarse grains result in low grain boundary density, weakening the effect of hindering dislocation movement, which manifests as a decrease in alloy strength. Furthermore, a large number of small-angle grain boundaries (LAGBs) appear at the grain boundaries of Grade 1 large grains. These LABs accumulate at the grain boundaries, and when the bolt deforms, as deformation continues, stress concentration occurs at the intersection of the large grains and the surrounding small grains, initiating cracks and ultimately leading to part failure. The process of this invention, by controlling the holding temperature, holding time, and cooling method, and adding a secondary solution treatment process, can control the grain size of the GH350 alloy, allowing it to meet the requirements of grain size grades 2-6 while satisfying other mechanical properties.

[0086] Figures 1-3 The bolt grain size of Embodiments 1-3 of the present invention, grade 2-6, meets the product requirements. Figures 4-15 Present metallographic photographs of scales 1-12. Figure 4Comparative Example 1 uses a conventional process, meaning that during the heating process, there is no heat preservation platform at 800℃, no secondary solution treatment, and only a single solution treatment at 1030℃ / 120min. The product has a grain size of grade 7 or finer, indicating that the energy provided by the heat treatment in Comparative Example 1 is insufficient to grow the grains to grade 2-6. Figure 5 Comparative Example 2 underwent a single solution treatment at 1020℃ for 2 hours, resulting in a product with a grain size of grade 7 or finer. This indicates that a single solution heat treatment at 1020℃ does not provide sufficient energy to grow grains to grades 2-6. Figure 4 Compared to Comparative Example 1, which was heat-treated at 1030℃, Figure 5 The comparative example 2 shows that the grains are finer, indicating that when only one heat treatment is performed, the higher the temperature, the more favorable it is for atomic diffusion and grain boundary movement, and the more favorable it is for further grain growth. Figure 6 Comparative Example 3 is a metallographic model that has undergone two solution treatments at 1030℃ / 120min + 950℃ / 240min. The grain size is grade 1-8, indicating that the grain size has increased further after the two solution treatments. However, the grain structure is not uniform and there are abnormally grown grade 1 grains. Figure 7 Comparative Example 4 shows the metallographic structure after two solution treatments at 1010℃ / 120min + 950℃ / 240min. The grain size is 2-8, with the presence of 8-level small grains, indicating that the temperature needs to be increased or the holding time extended to provide energy to promote the growth of 8-level small grains. Combined with... Figure 6 It was found that raising the first heat treatment temperature to 1030℃ resulted in abnormally large grains. Therefore, controlling the first heat treatment temperature between 1010℃ and 1030℃ is beneficial for controlling the uniformity of grain size.

[0087] See Figures 8-14 The temperature for the first solution treatment was fixed at 1020℃, and the temperature for the second solution treatment was fixed at 950℃. The holding time for the two heat treatments was then determined. Figure 8 and Figure 12 It was found that even after a single solution treatment holding time of 60 min in Comparative Examples 5 and 9, 8-level small grains still existed. Therefore, the holding time for a single solution treatment should be no less than 60 min. Figures 8-11 As the holding time of the first solution treatment of comparative examples 5, 6, 7 and 8 was gradually extended from 60 min, 120 min, 180 min and 240 min, the grain size of the products was 3-8 (1), 5-6 (1), 2-7 and 2-6 (1), and the grains gradually grew. Figure 13 and Figure 14The holding time for the second solution treatment of Comparative Example 10-11 was 240 min, and the holding time for the first solution treatment was 180 min and 240 min respectively. The grain size of the product was 4-7 (1) and 1-7.5 grade, with abnormal grade 1 grains. Therefore, the first solution treatment time should not exceed 180 min. Figure 15 Comparative Example 12 did not set a heating platform at 800°C during the heating process of a single solution treatment; otherwise, it was the same as Example 1. It can be seen that... Figure 15 The presence of large, order-0 grains is evident in Table 1, which shows that the mechanical properties are inferior to those of the previous example. This is because the absence of a heating plateau at 800°C led to rapid grain growth in certain areas during the heating process. Dislocation pile-up at the junction of large and small order-0 grains easily resulted in crack formation, which eventually led to fracture and deteriorated mechanical properties.

[0088] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A heat treatment method for GH350 alloy fasteners used in aviation, characterized in that, Includes the following steps: After upsetting, two solution treatments and two aging treatments are performed sequentially. The first solution treatment is performed at a temperature of 1017℃-1023℃ for 115-125 minutes, and the second solution treatment is performed at a temperature of 945℃-955℃ for 230-250 minutes. The first aging treatment is performed at a temperature of 880℃-890℃ for 50-70 minutes, and the second aging treatment is performed at a temperature of 750℃-770℃ for 230-250 minutes. During the heating process of a single solution treatment, the temperature is maintained at 800℃ for 40-50 minutes; The first solution treatment is carried out in a vacuum furnace with a vacuum degree range of 0.133 Pa to 13.3 Pa. After the first solution treatment is held at a certain temperature, it is first cooled in argon for ≥30 min, and then air cooled. The secondary solution treatment was carried out in a vacuum furnace with a vacuum degree ranging from 0.133 Pa to 13.3 Pa. After the secondary solution treatment was held at the same temperature, the furnace was first cooled in argon for ≥30 min, and then air cooled.

2. The heat treatment method for GH350 alloy fasteners for aviation use according to claim 1, characterized in that, The temperature for the first solution treatment is 1020℃.

3. The heat treatment method for GH350 alloy fasteners for aviation use according to claim 1, characterized in that, The temperature for the secondary solution treatment is 950℃.

4. The heat treatment method for GH350 alloy fasteners for aviation use according to claim 1, characterized in that, The aging process is carried out in a vacuum furnace with a vacuum level of 0.133 Pa to 13.3 Pa. After the aging process is completed, the furnace is first cooled in argon gas for ≥30 min, and then air-cooled.

5. The heat treatment method for GH350 alloy fasteners for aviation use according to claim 4, characterized in that, The temperature for one aging treatment is 885℃.

6. The heat treatment method for GH350 alloy fasteners for aviation use according to claim 1, characterized in that, The secondary aging treatment was carried out in a vacuum furnace with a vacuum degree ranging from 0.133 Pa to 13.3 Pa. After the secondary aging treatment was completed, the furnace was first cooled in argon gas for ≥30 min, and then air-cooled.

7. The heat treatment method for GH350 alloy fasteners for aviation use according to claim 6, characterized in that, The temperature for the second aging treatment was 760℃, and the holding time was 240 minutes.

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