A processing method for high entropy alloy bolts for aerospace

Abstract

The present invention belongs to the technical field of aerospace fastener processing, and specifically relates to a processing method for a high entropy alloy bolt for aerospace, which specifically includes the following steps: (1) blanking; (2) grinding; (3) hot upsetting; (4) first sandblasting; (5) first heat treatment; (6) second sandblasting; (7) turning; (8) thread rolling: using warm rolling; (9) second heat treatment: secondary aging heat treatment after warm thread rolling; (10) cold extrusion; (11) cleaning. The present invention provides a method for preparing high-strength bolts using high-entropy alloy materials, wherein high-entropy alloy materials are selected as raw materials for parts, the high-entropy alloy materials are solid solutions, have good plasticity, and the heads are formed once by hot upsetting, which greatly reduces the processing cycle, and successfully prepares ultra-high-strength bolts with room temperature tensile strength greater than 1900MPa.

Description

Technical Field

[0001] The invention relates to a method for processing a high-entropy alloy bolt for aerospace, and belongs to the technical field of aerospace fastener processing. Background Art

[0002] Among the standard parts in the aviation and aerospace industries, high-strength bolts are fasteners used for assembly under harsh working conditions such as high strength requirements, high vacuum, and high pressure. At present, the grades of high-strength bolts are 1100-1025MPa, 1300-1500MPa, etc. The bolts with the highest strength grade are high-strength bolts made of MP159 material, and the room temperature tensile strength can reach 1795MPa. Bolts with room temperature tensile strength exceeding 1795MPa have not yet appeared in the existing technology. Due to the limitations of material properties and process methods, the yield of MP159 high-strength bolts is low. Therefore, it is necessary to develop an ultra-high strength bolt with a high yield to replace MP159 bolts. In 2004, some scholars proposed the concept of high-entropy alloys. Due to the high entropy effect and cocktail effect, high-entropy alloys show unique material properties. Shenyang Aerospace University has prepared high-entropy alloy raw materials, and the tensile strength of the raw materials can reach 1600MPa. However, there is no record in the existing literature on how to ensure that the room temperature tensile strength of aerospace fasteners made of high entropy alloys does not decrease or is even higher than the tensile strength of the raw materials.

[0003] Therefore, how to use high-entropy alloys to prepare high-strength bolts so that their room temperature tensile strength is better than that of existing high-strength bolts, or even to prepare ultra-high-strength bolts to replace MP159 bolts, is a technical problem that technicians in this field need to solve. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a method for processing a high entropy alloy bolt for aerospace.

[0005] The technical solution of the present invention to solve the above technical problems is as follows:

[0006] A method for processing a high entropy alloy bolt for aerospace, specifically comprising the following steps:

[0007] (1) Cutting: Cut the blank according to the size of the drawing;

[0008] (2) Grinding: Grinding the outer diameter of the blank after cutting;

[0009] (3) Hot upsetting: Place the ground blank into a hot upsetting die to hot upset the bolt head;

[0010] (4) First sandblasting: dry sandblasting after hot upsetting to make the surface clean;

[0011] (5) First heat treatment;

[0012] (6) Second sandblasting: remove the oxide scale on the workpiece surface after cooling after the first heat treatment;

[0013] (7) Turning: Turn the thread rolling diameter and bolt head to meet the requirements of the drawing;

[0014] (8) Thread rolling: warm rolling method is adopted;

[0015] (9) Second heat treatment: Secondary heat treatment is carried out after warm wire rolling;

[0016] (10) Cold extrusion: The arc R at the connection between the cold extruded support surface and the rod;

[0017] (11) Cleaning.

[0018] On the basis of the above technical solution, the present invention can also make the following improvements:

[0019] Furthermore, in step (1), the blank is a high entropy alloy material, and the high entropy alloy includes the following components: C≤0.02%, Cr 12%~18%, Co 21%~23%, Mo 1%~2%, Nb 1%~2%, W 2%~3%, Si≤1%, O≤0.005%, N≤0.01%, S≤0.01%, P≤0.01%, and the remainder Ni.

[0020] Furthermore, in step (8), the thread rolling temperature is 200° C. to 300° C. and is kept warm for 1 second to 5 seconds.

[0021] The beneficial effect of adopting the above further technical scheme is: the present invention controls the warm rolling temperature to be 200℃~300℃. If the warm rolling temperature is too low, during the rolling process, the surface grains will be broken and the grains will be refined. The fine grains will increase the surface area of ​​the grain boundaries. A large number of dislocations will be introduced during the rolling process. The dislocations will interact with the grain boundaries and the dislocations will accumulate with each other, which will hinder the continued movement of the dislocations and make it difficult for the dislocations to slip. The metal will undergo work hardening. Although the strength of the threaded part can be improved, the plasticity will be reduced. The deformation to meet the thread size will exceed the plasticity of the material, resulting in folding and cracking of the thread tips, causing the thread continuity to be unqualified. If the warm rolling temperature is too high, combined with the deformation heat released during the thread rolling process, a higher temperature will be formed on the thread surface, an oxide layer will appear on the surface, and the surface quality of the thread will be affected. Although the high temperature can make the plasticity good and is conducive to thread forming, the high temperature promotes the recovery of the surface dislocations, reduces the number of dislocations, and weakens the thread strength. Therefore, only the bolts prepared within the warm rolling temperature range of the present invention can meet the requirements.

[0022] Furthermore, in step (5), the first heat treatment is an aging treatment at a temperature of 700° C. and a time of 360 min.

[0023] Furthermore, in step (9), the second heat treatment is a low-temperature aging treatment at a temperature of 500° C. for a time of 120 to 180 min.

[0024] Furthermore, in step (10), the cold extrusion load is 250-400 kgf and the time is 2 s.

[0025] Furthermore, in step (1), the turning speed is 800 to 1000 rpm, and the feed rate is 0.05 mm per revolution.

[0026] Furthermore, in step (2), grinding is performed using a centerless grinder.

[0027] Furthermore, in step (3), the hot upsetting temperature is 920-1020°C, and the holding time is 2s.

[0028] Furthermore, in step (3), the material of the hot upsetting die is cemented carbide YG15, the hot upsetting current is 60A to 100A, the heating time is 5s to 15s, and the insulation time is 2s.

[0029] Furthermore, in step (3), the hot upsetting forming processing equipment is an open fixed press, the equipment model is YC1-250, and the maximum load is 250T.

[0030] The beneficial effect of adopting the above-mentioned further technical scheme is: the present invention adopts hot upsetting forming to save materials, has high production efficiency, and controls the hot upsetting temperature, so as to achieve a balance between the beautiful appearance of the bolt head and the strength of the head rod connection. If the hot upsetting temperature is low, the bolt head will not be fully formed; if the hot upsetting temperature is high, due to high-frequency heating, it will inevitably affect the strength of the head rod connection. When the strength of the head rod connection is low enough to make up for the difference caused by the small stress area of ​​the thread bottom, it will cause the bolt head to break and fail the tensile test. The present invention ensures the strength of the bolt head rod connection by controlling the hot upsetting temperature, and the prepared bolt head has a full and beautiful shape.

[0031] The beneficial effects of the present invention are as follows: the present invention provides a method for preparing high-strength bolts using high-entropy alloy materials, selecting high-entropy alloy materials as raw materials for parts, the high-entropy alloy materials are solid solutions, and have good plasticity. The head is formed in one step by hot upsetting, which greatly reduces the processing cycle, and successfully prepares ultra-high-strength bolts with room temperature tensile strength greater than 1900MPa. The present invention adopts hot upsetting forming, which saves materials and has high production efficiency. The strength of the bolt head rod connection is guaranteed by controlling the hot upsetting temperature. In the bolt processing process of the present invention, the sequence of heat treatment, warm thread rolling, and heat treatment is adopted, combined with cold extrusion parameter control, and the balance point of the strength of the bolt head rod connection and the strength of the thread is found. The hardness of the finished bolt after processing is about 50 to 53HRC, and it has high room temperature tensile strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the room temperature tensile stress-strain curve of Example 1. DETAILED DESCRIPTION

[0033] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0034] Example 1

[0035] A method for processing a high entropy alloy bolt for aerospace, specifically comprising the following steps:

[0036] (1) Material preparation and cutting: Cut the high entropy alloy billet according to the size of the drawing, with a turning speed of 800 rpm and a feed of 0.05 mm per revolution;

[0037] (2) Grinding: The outer diameter of the blank is ground using a centerless grinder;

[0038] (3) Hot upsetting: Place the ground blank into the hot upsetting die, hot upsetting the bolt head, the hot upsetting temperature is 970°C, and the blank is kept warm for 2 seconds;

[0039] (4) First sandblasting: dry sandblasting after hot upsetting to make the surface clean;

[0040] (5) The first heat treatment is an aging treatment process with an aging temperature of 700°C in an air furnace, with the temperature rising with the furnace, a holding time of 330 minutes, and air cooling;

[0041] (6) Second sandblasting: remove the oxide scale on the workpiece surface after cooling after the first heat treatment;

[0042] (7) Turning: Turn the thread rolling diameter and bolt head to meet the requirements of the drawing;

[0043] (8) Thread rolling: warm rolling method is adopted, the temperature is 250℃, and the temperature is kept for 3s;

[0044] (9) Second heat treatment: After warm wire rolling, secondary aging heat treatment is carried out at a temperature of 500°C in an air furnace. The steel is put into the furnace when it reaches the temperature, kept at the temperature for 120 minutes, and then air-cooled.

[0045] (10) Cold extrusion: The arc R at the connection between the support surface and the rod is cold extruded. The cold extrusion load is 250 kgf and the time is 2 s.

[0046] (11) Cleaning.

[0047] In this embodiment, the hot upsetting forming processing equipment is an open fixed press, the equipment model is YC1-250, and the maximum load is 250T.

[0048] The M10 hexagonal head bolt prepared by the above processing method in this embodiment has a room temperature tensile strength of 1914 MPa, and the fracture in the room temperature tensile test occurs at the threaded portion, and the product is qualified.

[0049] See also Figure 1 is the tensile stress-strain curve of the M10 hexagonal head bolt at room temperature in this embodiment. Figure 1 It can be seen from the results that the room temperature tensile strength of this embodiment reaches 1914MPa, which is better than that of comparative examples 1-11.

[0050] Example 2

[0051] The difference from Example 1 is that in step (1) of this embodiment, the turning speed is 900 rpm, the hot upsetting temperature in step (3) is 920°C, the aging holding time in step (5) is 360 min, the rolling temperature in the warm rolling process in step (8) is 200°C, the holding time is 5 s, the low-temperature aging time in step (9) is 150 min, and the cold extrusion load in step (10) is 325 kgf. The rest is the same as in Example 1.

[0052] The M10 hexagon head bolt prepared by the above processing method in this embodiment has a room temperature tensile strength of 1909 MPa, and the fracture in the room temperature tensile test occurs at the threaded portion, and the product is qualified.

[0053] Example 3

[0054] Different from Example 1, in step (1) of this embodiment, the turning speed is 1000 rpm, the hot upsetting temperature in step (3) is 1020°C, the aging holding time in step (5) is 300 min, the rolling temperature in the warm rolling process in step (8) is 300°C, the blank holding time is 1 s, the holding time in step (9) is 180 min, and the cold extrusion load in step (10) is 400 kgf. The rest is the same as in Example 1.

[0055] The M10 hexagon head bolt prepared by the above processing method in this embodiment has a room temperature tensile strength of 1905 MPa, and the fracture in the room temperature tensile test occurs at the threaded portion, and the product is qualified.

[0056] Comparative Example 1

[0057] Different from Example 1, this comparative example does not perform a secondary aging heat treatment process after the warm thread rolling process in step (8), that is, this comparative example does not perform the process operation of step (9) of Example 1, and the other steps are the same as Example 1.

[0058] When the bolts prepared by the processing method of this comparative example were subjected to a room temperature tensile test, the bolts broke off at the head rod connection and the product was unqualified. Although this comparative example adopts a warm thread rolling process, which has a positive effect on the strength of the bolts, the room temperature tensile strength of comparative example 1 is 1686MPa, which meets the strength requirements of high-strength bolts. However, since comparative example 1 lacks a subsequent heat treatment process compared to example 1, its tensile strength is lower than that of example 1. Because when comparative example 1 is thread rolled after the first aging heat treatment, the strength of the threaded part is high enough due to the superposition of aging strengthening and deformation strengthening, and the strength of the threaded part is higher than the strength of the head rod joint. Therefore, when stretched at room temperature, the bolt breaks at the low-strength head rod joint, indicating that the bolt after the warm thread rolling process needs to be subjected to a second heat treatment to make the bolt as a whole have sufficient strength.

[0059] The second aging heat treatment temperature of the present invention is 500°C. On the one hand, it can weaken the partial deformation strengthening effect caused by thread rolling and slightly reduce the strength of the thread part. On the other hand, the secondary strengthening phase r" is precipitated in this temperature range. At the temperature of the first aging heat treatment, the supersaturated solid solution in the threaded part has been fully precipitated to form the r' phase. During the second aging heat treatment, the precipitated phase r" is less, so the secondary aging heat treatment has little effect on the strengthening effect of this part. The head rod joint part is affected by the hot upsetting structure. Under the first aging heat treatment, the precipitated phase r' is limited, and the strength is lower than that of the threaded part. At the temperature of the second aging heat treatment, Although it is in a supersaturated solid solution, it can continue to precipitate a relatively larger secondary strengthening phase r than the threaded part. Therefore, after the secondary aging heat treatment, the strength of the hot upsetting affected area such as the head and the head-rod junction is increased more than the threaded part. Combined with the cold extrusion process, the R angle is extruded and the deformation strengthening further increases the R angle strength under the head, that is, the strength of the head-rod junction, so that the strength of the bolt head-rod junction is higher than the strength of the threaded part. When the room temperature tensile test is carried out, the bolt breaks at the threaded part with low strength, indicating that after being processed by the processing method of the present invention, the strength of the head-rod junction of the bolt is significantly improved, so that the tensile strength of the bolt is improved.

[0060] Comparative Example 2

[0061] Different from Example 1, in order to improve the strength of the head rod joint, this comparative example adopts a lower hot upsetting temperature, that is, the hot upsetting forming parameters of step (3) of this comparative example are different from those of Example 1, the hot upsetting temperature is 900°C, and the heating and holding time are the same.

[0062] The bolt head produced by the processing method of this comparative example is not fully formed and the head size is unqualified.

[0063] Comparative Example 3

[0064] Different from Example 1, in order to achieve a full head forming, this comparative example adopts a higher hot upsetting temperature, that is, the hot upsetting forming parameters of this comparative example and step (3) of Example 1 are different, the hot upsetting temperature is 1040°C, and the heating and holding time are the same.

[0065] The bolt head prepared by the processing method of this comparative example is well formed, the head size is qualified, the head rod joint is broken under room temperature tensile stress, and the room temperature tensile strength is 1704MPa. Although it meets the requirements of high-strength bolts, it is far lower than Example 1 and is unqualified. This is because the hot upsetting temperature is too high, which seriously reduces the strength of the joint between the bolt polished rod and the head rod. Although there are subsequent secondary heat treatment and cold extrusion processes to improve the strength of the joint between the bolt polished rod and the head rod, it cannot make up for the strength drop caused by the excessively high hot upsetting temperature. It can be seen that even if the warm rolling process and the secondary heat treatment process are combined to improve the strength of the bolt head rod joint, it is still necessary to cooperate with the adjustment of the hot upsetting temperature range to achieve a better effect, so that the room temperature tensile strength of the bolt is higher than 1900MPa.

[0066] Comparative Example 4

[0067] The difference from Example 1 is that the temperature of the first aging heat treatment in step (5) of this comparative example is 650° C. and the holding time is 360 min. The rest is the same as Example 1.

[0068] The M10 hexagonal head bolt prepared by the above processing method in this comparative example has a room temperature tensile strength of 1838 MPa because it is not at the optimal aging temperature. The fracture in the room temperature tensile test occurs at the threaded portion, and the strength is lower than 1900 MPa.

[0069] Comparative Example 5

[0070] The difference from Example 1 is that the temperature of the first aging heat treatment in step (5) of this comparative example is 750° C. and the holding time is 360 min. The rest is the same as Example 1.

[0071] The M10 hexagonal head bolt prepared by the above processing method in this comparative example has a room temperature tensile strength of 1824 MPa because it is not the optimal aging temperature. The fracture in the room temperature tensile test occurs at the threaded portion, and the strength is lower than 1900 MPa.

[0072] Comparative Example 6

[0073] The difference from Example 1 is that the thread rolling temperature in step (8) of this comparative example is 175°C, and the rest is the same as Example 1.

[0074] The M10 hexagonal head bolt prepared by the above processing method in this comparative example has a fold of 152μm at the thread tip, which does not meet the standard requirement of ≤150μm, and the product is unqualified. This is caused by the low thread rolling temperature.

[0075] Comparative Example 7

[0076] The difference from Example 1 is that the thread rolling temperature in step (8) of this comparative example is 325°C, and the rest is the same as Example 1.

[0077] The M10 hexagonal head bolt prepared by the above processing method in this comparative example has a slightly higher warm rolling temperature, which affects the strength of the threaded part. The room temperature tensile strength is 1886MPa. The fracture in the room temperature tensile test occurs at the threaded part, and the strength is lower than 1900MPa.

[0078] Comparative Example 8

[0079] The difference from Example 1 is that the temperature of the second low-temperature aging heat treatment in step (9) of this comparative example is 480° C. and the holding time is 120 min. The rest is the same as Example 1.

[0080] The M10 hexagon head bolt prepared by the above processing method of this comparative example has a low-temperature aging temperature of 480°C, while the optimal temperature for precipitation of the low-temperature strengthening phase is 500°C, which is not the optimal aging temperature, affecting the precipitation of the strengthening phase. The room temperature tensile strength is 1818MPa, and the fracture in the room temperature tensile test occurs at the threaded portion, with a strength lower than 1900MPa.

[0081] Comparative Example 9

[0082] The difference from Example 1 is that in step (9) of this comparative example, the low-temperature aging temperature is 520° C. and the holding time is 180 min. The rest is the same as Example 1.

[0083] The M10 hexagon head bolt prepared by the above processing method of this comparative example has a low-temperature aging temperature of 520°C and an optimal temperature for precipitation of the low-temperature strengthening phase of 500°C, which is not the optimal aging temperature and affects the precipitation of the strengthening phase. The room temperature tensile strength is 1803MPa, and the fracture in the room temperature tensile test occurs at the threaded portion, with a strength lower than 1900MPa.

[0084] Comparative Example 10

[0085] The difference from Example 1 is that the cold extrusion load in step (10) of this comparative example is 200 kgf and the time is 2 s. The rest is the same as Example 1.

[0086] When the bolts prepared by the processing method of this comparative example were subjected to room temperature tensile test, the bolts broke off from the head rod connection, and the product was unqualified. Although the thread strength of the warm thread rolling process adopted in this comparative example is high enough, the strength of the head rod joint is low, and the head rod joint breaks. The room temperature tensile strength is 1878MPa, which is lower than that of Example 1, indicating that the warm thread rolling process needs to be combined with cold extrusion parameter control to find the balance point between the strength of the bolt head rod joint and the strength of the thread, so as to achieve high strength of the bolt as a whole.

[0087] Comparative Example 11

[0088] Different from Example 1, the cold extrusion load of step (10) of this comparative example is 450 kgf and the time is 2 s. The rest is the same as Example 1.

[0089] The bolts prepared by the processing method of this comparative example are unqualified because the cold extrusion force is too large and the R angle is severely deformed, which does not meet the process size requirements.

[0090] The room temperature tensile test results and bolt head size inspection results of the embodiment and the comparative example are compared in Table 1:

[0091] Table 1 Room temperature tensile test results and bolt head size inspection results

[0092]

[0093] Comparative Example 3 was hot-forged at 1040°C, and the room temperature tensile strength was 1704MPa, indicating that high hot upsetting temperature will reduce the connection strength. Comparative Example 6 was warm-rolled at 175°C, at which time the plasticity of the threaded part did not meet the requirements of dimensional deformation, the thread tips were folded, and the continuity was unqualified. Comparative Example 7 was warm-rolled at 325°C, and the room temperature tensile strength was 1886MPa, which was lower than 1914MPa, indicating that the excessively high warm rolling temperature weakened the threaded connection strength. By comparing Examples 1-3 and Comparative Examples 1-11, it was found that only when the hot upsetting temperature, rolling temperature, secondary heat treatment temperature, and cold extrusion load were controlled within the range specified by the present invention, and the processes cooperated with each other, could a high strength of 1900MPa be achieved.

[0094] 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for processing high entropy alloy bolts for aerospace, characterized in that: The specific steps include: (1) Cutting: Cut the blank according to the size of the drawing; (2) Grinding: Grinding the outer diameter of the blank after cutting; (3) Hot upsetting: Place the ground blank into a hot upsetting die to hot upset the bolt head; (4) First sandblasting: dry sandblasting after hot upsetting to make the surface clean; (5) First heat treatment; (6) Second sandblasting: remove the oxide scale on the workpiece surface after cooling after the first heat treatment; (7) Turning: Turn the thread rolling diameter and bolt head to meet the requirements of the drawing; (8) Thread rolling: warm rolling method is adopted; (9) Second heat treatment: Secondary heat treatment is carried out after warm wire rolling; (10) Cold extrusion: The arc R at the connection between the cold extruded support surface and the rod; (11) Cleaning; In step (1), the blank is a high entropy alloy material, and the high entropy alloy includes the following components: C≤0.02%, Cr 12%-18%, Co 21%-23%, Mo 1%-2%, Nb 1%-2%, W 2%-3%, Si≤1%, O≤0.005%, N≤0.01%, S≤0.01%, P≤0.01%, and the remainder Ni; In step (8), the thread rolling temperature is 200°C to 300°C and is kept at this temperature for 1s to 5s; In step (5), the first heat treatment is an aging treatment at a temperature of 700°C for a time of 300 to 360 minutes; In step (9), the second heat treatment is a low-temperature aging treatment at a temperature of 500° C. for a time of 120 to 180 min; In step (10), the cold extrusion load is 250-400 kgf and the time is 2 s; In step (1), the turning speed is 800 to 1000 rpm, and the feed rate is 0.05 mm per revolution. In step (2), grinding is performed using a centerless grinder. In step (3), the hot upsetting temperature is 920-1020°C and the holding time is 2s; In step (3), the material of the hot upsetting die is cemented carbide YG15, the hot upsetting current is 60A to 100A, the heating time is 5s to 15s, and the heat preservation time is 2s; In step (3), the hot upsetting forming processing equipment is an open fixed press with a maximum load of 250T.

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