Processing method of Inconel 718 decagonal head bolt

Abstract

The invention relates to a machining method of an Inconel 718 decagonal head bolt, and belongs to the technical field of bolt machining and manufacturing. The machining method of the Inconel 718 decagonal head bolt comprises the following steps that a blank is subjected to aging treatment after being subjected to hot upsetting forming of the head of the bolt, and a heat treatment part is obtained; and then performing rough turning, finish turning and screw blank rod part grinding on the heat treatment part, performing R rolling on a transition arc part between the head part and the rod part, performing warm thread rolling on the screw blank rod part, and finally performing passivating treatment. According to the machining method of the Inconel 718 dodecagonal head bolt, the strength of a material can be improved through heat treatment, so that the problem that an internal metal flow line of a bolt workpiece is broken when a semi-finished bolt workpiece is subjected to finish turning machining and thread rolling machining is solved, and the strength, fatigue resistance and vibration resistance of the finished bolt workpiece are guaranteed.

Description

Technical Field

[0001] The invention relates to a method for processing an Inconel 718 twelve-angle head bolt, and belongs to the technical field of bolt processing and manufacturing. Background Art

[0002] Inconel 718 is the most widely used high-temperature alloy in aircraft engines. It is mainly used to manufacture various stationary and rotating parts in aviation and aerospace engines, such as disks, rings, casings, shafts, blades, fasteners, elastic elements, etc. Inconel 718 twelve-point head bolts are commonly used fasteners in engine combustion chambers, and are also representative products of high-temperature and high-strength fasteners. The twelve-point head of the Inconel 718 twelve-point head bolt has a complex structure and a twelve-point wrench structure. It is fully stressed during wrench tightening and the wrench is not easy to slip. At the same time, there is a flange at the bottom of the twelve-point head as a load-bearing part after installation. The structural diagram of the Inconel 718 twelve-point head bolt is as follows: Figure 1 As shown in the actual picture Figure 2 shown.

[0003] Since the working temperature of the engine combustion chamber is 650℃, the Inconel 718 twelve-point head bolts used in the combustion chamber are required to work continuously without failure in an environment of 650℃ to 800℃. Therefore, strict requirements are put forward for the mechanical properties of Inconel 718 twelve-point head bolts: high temperature resistance (above 900℃), vibration resistance (large vibration without failure under high-speed engine rotation), fatigue resistance (no maintenance and no failure under the maximum range of the aircraft). At the same time, strict requirements are also put forward for the raw materials used to manufacture Inconel 718 twelve-point head bolts. Inconel 718 materials that have been vacuum induction melted and remelted in a vacuum arc furnace must be selected.

[0004] Among them, the Inconel718 high-temperature alloy with a performance level of tensile strength Rm ≥ 1517MPa and yield strength Rp0.2 ≥ 1379MPa is the most difficult to process. Due to the high degree of alloying, its hot processing performance deteriorates and the hot deformation area is reduced, which increases the difficulty of hot forming. At the same time, due to the high strength and low plasticity of the material, the tensile strength Rm of the Inconel 718 material after heat treatment is ≥ 1600MPa, and the Rockwell hardness is 48 to 49.5HRC, which increases the difficulty of subsequent processing. The schematic diagram of the metal streamline at the transition arc between the head and the rod of the Inconel718 twelve-point head bolt is shown in the figure below. Figure 3 As shown in the figure, the metal flow line diagram of the threaded part of Inconel 718 twelve-point head bolt is as follows Figure 4As shown. Since the metal streamlines at the junction of the head and the rod of the Inconel 718 twelve-point head bolt are not allowed to be destroyed or cut off, the metal streamlines at the threaded part should be continuous and the density of the streamlines at the bottom of the thread teeth should be the largest to improve the fatigue resistance of the bolt, which puts more stringent requirements on the manufacturing and processing of the Inconel 718 twelve-point head bolt. The current method for processing the Inconel 718 twelve-point head bolt includes the following process flow: blanking → general turning → centerless grinding → lubrication → hot upsetting → decoating → sandblasting → heat treatment → sandblasting → numerical turning → deburring → labeling → penetrant flaw detection → surface treatment → final inspection → packaging and warehousing. Since the current process flow for processing the Inconel 718 twelve-point head bolt includes lubrication before hot upsetting and decoating after hot upsetting, the process flow is cumbersome. At the same time, the use of CNC lathes to turn threads will cause the metal streamlines at the threaded part of the Inconel 718 twelve-point head bolt to be destroyed or cut off, resulting in low fatigue and vibration resistance of the Inconel718 twelve-point head bolt. Summary of the invention

[0005] The object of the present invention is to provide a method for processing an Inconel 718 twelve-point head bolt, which can solve the problem that the fatigue resistance of the currently processed Inconel 718 twelve-point head bolt is relatively low.

[0006] In order to achieve the above purpose, the technical solution adopted by the processing method of Inconel 718 twelve-point head bolt of the present invention is:

[0007] A processing method for an Inconel 718 twelve-point head bolt comprises the following steps: performing hot upsetting of a bolt head on a blank and then performing aging treatment to obtain a heat-treated part; then performing rough turning, fine turning, and grinding of a screw blank shank on the heat-treated part, then performing R rolling on a transition arc portion between the head and the shank, then performing warm thread rolling on the screw blank shank, and finally performing passivation treatment to obtain an Inconel 718 twelve-point head bolt; the aging treatment comprises a first-stage heat treatment and a second-stage heat treatment performed sequentially, the temperature of the first-stage heat treatment is 718-720°C, and the temperature of the second-stage heat treatment is 612-614°C.

[0008] The processing method of the Inconel 718 twelve-angle head bolt of the present invention can improve the strength of the material by performing heat treatment after hot upsetting the bolt head of the blank, thereby avoiding the problem of the internal metal streamline of the bolt workpiece being broken when the semi-finished bolt workpiece is fine-turned and threaded, and can make the internal metal streamline of the semi-finished bolt workpiece evenly distributed, thereby ensuring the strength, fatigue resistance and vibration resistance of the finished bolt workpiece. The tensile strength of the Inconel718 twelve-angle head bolt processed by the present invention can reach 1600MPa, the shear strength can reach 930MPa, and the fatigue resistance is not less than 65,000 times, which meets the use requirements in the aerospace field.

[0009] Preferably, the first stage heat treatment time is 8 hours.

[0010] Preferably, the second stage heat treatment time is 8 hours.

[0011] Preferably, the cooling rate from the temperature corresponding to the first stage heat treatment to the temperature corresponding to the second stage heat treatment is (56°C±8°C) / h.

[0012] Preferably, the aging treatment includes a first stage heat treatment, a second stage heat treatment and a cooling treatment which are performed in sequence. The cooling treatment is achieved by gas quenching. The atmosphere used for gas quenching is argon gas with a gas pressure of 150-200 MPa.

[0013] Preferably, hot upsetting is to heat the bolt head of the blank to a specified temperature and keep it warm before upsetting; the diameter of the blank is 13.297-13.3 mm, the specified temperature is 880-920°C, the time required to heat to the specified temperature is 3-6 s, and the keeping time is 3-6 s; the diameter of the blank is 15.297-15.3 mm, the specified temperature is 890-920°C, the time required to heat to the specified temperature is 3-6 s, and the keeping time is 3-6 s; the diameter of the blank is 16.597-16.7 mm, the specified temperature is 900-920°C, the time required to heat to the specified temperature is 6-8 s, and the keeping time is 6-8 s.

[0014] Preferably, the warm thread rolling process is to first heat the screw blank rod and then perform the thread rolling process on the heated screw blank rod; the heating temperature is 180-200° C. and the heating time is 5-8 seconds.

[0015] Preferably, the passivation treatment method is as follows: the thread rolling workpiece is sequentially deoiled, washed with hot water, washed with water at room temperature, activated, washed with flowing water for the first time, passivated, washed with flowing water for the second time, neutralized, washed with flowing water for the third time, washed with hot pure water and dried.

[0016] Preferably, the passivation is to place the bolt workpiece after the first flowing cold water washing in dilute nitric acid and soak it at room temperature for 30 to 60 minutes. The dilute nitric acid is prepared by mixing concentrated nitric acid with a density of 1.42 g / mL and water. The mass concentration of the concentrated nitric acid is 68%, and the concentration of concentrated nitric acid in the dilute nitric acid is 380 to 390 g / L.

[0017] Preferably, the activation is to place the bolt workpiece after normal temperature water washing in hydrochloric acid with a concentration of 100-150g / L and soak it at room temperature for 0.5-2min; the water temperature used for normal temperature water washing, the first flowing water washing and the second flowing water washing is room temperature; the water temperature used for hot water washing and hot pure water washing is 60-80℃. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural diagram of the Inconel 718 twelve-point head bolt in the present invention;

[0019] Figure 2 This is a physical picture of the Inconel 718 twelve-point head bolt in the present invention;

[0020] Figure 3 The figure is a schematic diagram of metal streamlines at the transition arc between the head and the shank of the Inconel 718 twelve-point head bolt in the present invention;

[0021] Figure 4 It is a schematic diagram of metal flow lines at the threaded part of the Inconel 718 twelve-point head bolt in the present invention;

[0022] Figure 5 This is a schematic diagram of the structure of the blank processed in Example 1 of the present invention;

[0023] Figure 6 It is a schematic structural diagram of a semi-finished bolt workpiece processed in Example 1 of the present invention;

[0024] Figure 7 It is a schematic structural diagram of a rough-turned workpiece processed in Example 1 of the present invention;

[0025] Figure 8 It is a schematic structural diagram of a grinding workpiece processed in Example 1 of the present invention;

[0026] Fig. 9 It is a schematic structural diagram of the vibration marking member processed in Example 1 of the present invention;

[0027] Fig.10 It is a schematic structural diagram of a rolled R workpiece processed in Example 1 of the present invention;

[0028] Fig.11 It is a schematic structural diagram of a thread rolling workpiece processed in Example 1 of the present invention;

[0029] Fig.12 A physical photo of a finished bolt workpiece processed in Example 1 of the present invention;

[0030] Fig.13 This is a metallographic structure picture of the Inconel 718 twelve-point head bolt processed in Example 1 of the present invention;

[0031] Fig.14 This is a metallographic structure picture of the Inconel 718 twelve-point head bolt processed in Comparative Example 1 of the present invention;

[0032] Fig.15 This is a metallographic structure picture of the Inconel 718 twelve-point head bolt processed in Comparative Example 2 of the present invention;

[0033] Fig.16 This is a picture of the broken teeth of the thread rolling wheel after rolling in step (8) of comparative example 3 of the present invention;

[0034] Fig.17 This is a picture showing defects such as cracks and excessive folding at the threads of the Inconel 718 twelve-point head bolt processed in comparative example 3 of the present invention. DETAILED DESCRIPTION

[0035] The processing method of the Inconel 718 twelve-angle head bolt of the present invention is a pioneering invention. The processing method of the Inconel 718 twelve-angle head bolt of the present invention obtains the Inconel 718 twelve-angle head bolt by sequentially performing hot upsetting, heat treatment, turning, R rolling and thread rolling on the blank, thereby avoiding the problem of the internal metal streamline of the bolt workpiece being broken when the semi-finished bolt workpiece is finely turned and thread rolled, and can make the internal metal streamline of the semi-finished bolt workpiece evenly distributed, thereby ensuring the strength, fatigue resistance and vibration resistance of the finished bolt workpiece.

[0036] The process flow of the processing method of the Inconel 718 twelve-angle head bolt of the present invention is: blanking → general turning → centerless grinding → hot upsetting → sandblasting → heat treatment → sandblasting → general turning → number turning → general turning → deburring → marking → centerless grinding → R rolling → thread rolling → penetrant flaw detection → surface treatment → final inspection → packaging and warehousing. In the present invention, the head twelve-angle head is upset by hot upsetting forming, so that the transition arc part between the head and the rod of the finished bolt workpiece is a circular arc transition. At the same time, by controlling the heating temperature, heating time and insulation time during hot upsetting, it is ensured that the grain size of the bolt after hot upsetting fully meets the standard requirements, and the problem of overheating, overburning or poor grain size of the blank after hot upsetting is completely solved. The strength of the material can be improved, thereby avoiding the problem of the internal metal streamline of the bolt workpiece being broken when the semi-finished bolt workpiece is subjected to fine turning and thread rolling. The internal metal streamline of the semi-finished bolt workpiece can be evenly distributed, and the strength, fatigue resistance and vibration resistance of the finished bolt workpiece are ensured.

[0037] The technical solution of the present invention is described in detail below in conjunction with specific embodiments.

[0038] Example 1

[0039] The processing method of the Inconel 718 twelve-point head bolt of this embodiment takes the processing specification of the Inconel 718 twelve-point head bolt of .5-20UNJF-3A as an example, and specifically includes the following steps:

[0040] (1) Inconel 718 alloy bars that meet the standard AMS 5962 and are smelted by vacuum induction melting and vacuum arc furnace remelting are selected as the raw materials for processing Inconel 718 twelve-point head bolts. The diameter and length of the Inconel 718 alloy bars are calculated and determined according to the specifications and length of the processed Inconel 718 twelve-point head bolts. According to the length of a single Inconel 718 twelve-point head bolt, the Inconel 718 alloy bar is cut into a single bar using a sawing machine, and then the single bar is clamped on an ordinary hexagonal lathe using a three-jaw chuck. The two end faces of the single bar are turned until they are shiny, and then chamfered on the two end faces. Then, the outer diameter of the bar is ground using a CNC centerless grinder to ensure that the outer diameter size is consistent, and the following is obtained: Figure 5 The blank shown is suitable for hot upsetting processing.

[0041] (2) The blank (diameter 13.3 mm, upper deviation 0 mm, lower deviation -0.03 mm) was placed in a hot upsetting die and hot upsetting was performed on the blank using a 315-ton press. A twelve-point head of the bolt head was upset at one end of the blank, and then the oxide scale and oxidation color were removed by sandblasting to obtain the following: Figure 6The semi-finished bolt workpiece shown. During hot upsetting, the area of ​​the twelve-pointed head of the upsetting bolt head is first heated by a portable transistor induction heating device. After the heating temperature and time meet the requirements, the heated blank is immediately placed in the hot upsetting die for hot upsetting. The portable transistor induction heating device is used to heat the area of ​​the twelve-pointed head of the upsetting bolt head, which effectively controls the heating temperature, heating time (heating time refers to the time for heating the surface and core of the workpiece to a specified temperature, and the specified temperature is the heating temperature) and insulation time (insulation time refers to the time for maintaining the temperature after the workpiece reaches the specified heating temperature), so that the grain size of the bolt after hot upsetting is ≤5 levels and the microstructure has no overheating or overburning phenomenon, which completely solves the problem of overheating, overburning and poor grain size of the blank after hot upsetting. In this embodiment, the heating parameters during hot upsetting are shown in Table 1. The cooling time in Table 1 refers to the time interval between the completion of heating of the blank and the placement of the blank into the hot upsetting die for hot upsetting.

[0042] Table 1 Heating parameters during hot upsetting

[0043]

[0044]

[0045] Since the material of Inconel 718 twelve-point head bolts used in aerospace engines is high-temperature resistant Inconel 718 alloy material, this material cannot be cold-forged to complete the upsetting of the twelve-point head. At the same time, the bolt has a twelve-point flange face head. In order to obtain a good head shape, size and batch production stability, the twelve-point head is upset by hot upsetting. This not only achieves the purpose of forming the twelve-point flange face head of the bolt, but also ensures the integrity of the metal streamline at the transition arc between the bolt head and the rod, thereby indirectly improving the fatigue resistance of the bolt. The present invention adopts hot upsetting to form the twelve-point head of the bolt head. Since hot upsetting is to form the twelve-point head of the bolt head in a heated state, it can not only solve the problem that the cold upsetting method cannot achieve upsetting of the high-temperature resistant Inconel 718 alloy material, but also make the billet diameter close to the final product polished rod diameter, which can reduce the subsequent mechanical cutting amount, avoid the metal streamline at the r below the head being cut off due to excessive turning of the support surface and the rod during the factor turning, and ensure that the metal streamline at the transition arc between the bolt head and the rod is complete. In this embodiment, the metallographic method is used to detect the metal streamline from the head to the rod of the semi-finished bolt workpiece. The results show that the metal streamline from the head to the rod of the semi-finished bolt workpiece obtained in this embodiment is complete, and the metallographic structure has no overheating or overburning.

[0046] (3) The semi-finished bolt workpiece is subjected to aging treatment, and then the oxide scale and oxidation color are removed by sandblasting to obtain a heat-treated part. The aging treatment is to place the semi-finished bolt workpiece in the heating chamber of a horizontal vacuum gas quenching furnace, raise the temperature to 718°C, and keep it at this temperature for 8 hours, then cool it to 612°C at a rate of (56°C±8°C) / h, and keep it at this temperature for 8 hours. Finally, the semi-finished bolt workpiece is transferred to the cooling chamber of the horizontal vacuum gas quenching furnace for gas quenching cooling. The atmosphere in the cooling chamber is argon gas, and the argon gas pressure is 150-200MPa. The vacuum degree of the vacuum gas quenching furnace used for aging treatment is 1×10 -3 Pa, the leakage rate of the vacuum gas quenching furnace is 20μmHg / h.

[0047] Since the Inconel718 high-temperature alloy bar is a raw material blank in a cold-drawn state with material technical conditions of AMS5962, and is work-hardened by hot upsetting, the product needs to be heat treated to achieve the final performance, so that the product is strengthened by aging and reaches a precipitation hardening state to obtain comprehensive properties such as high strength and good plasticity. The present invention adopts a heat treatment process for aging treatment, and the role of aging treatment is to strengthen the high-temperature alloy structure and strength to obtain a suitable γ / γ' microstructure, which effectively solves the problem of tensile strength test of semi-finished bolt workpieces.

[0048] In the present invention, the heat treatment is advanced to before the rough turning process, which can improve the strength of the material, thereby avoiding the problem of the internal metal streamlines of the bolt workpiece being broken when the semi-finished bolt workpiece is subjected to fine turning and thread rolling. The internal metal streamlines of the semi-finished bolt workpiece can be evenly distributed, thereby ensuring the strength, fatigue resistance and vibration resistance of the finished bolt workpiece.

[0049] (4) Use a three-jaw chuck to clamp the heat-treated part on a common hexagonal lathe, and perform rough turning on the shape of the heat-treated part to obtain the following Figure 7 Rough turned part shown.

[0050] (5) The rough-turned workpiece is clamped on a CNC lathe using a three-jaw chuck, and the shape of the rough-turned workpiece is fine-turned to obtain a fine-turned workpiece; the screw blank rod of the fine-turned workpiece is ground using a CNC centerless grinder to make the screw blank rod diameter and the screw blank rod roughness meet the processing requirements before thread rolling, and the following is obtained: Figure 8 Grinding workpiece shown.

[0051] (6) The ground workpiece is clamped on the workbench of the vibration marking machine, and the vibration marking machine is used to vibrate and mark the identification mark on the end face of the twelve-pointed head of the ground workpiece to obtain the following Fig. 9 Vibrating marker shown.

[0052] (7) Place the vibration marker on the roller of a CNC rolling machine, and perform rolling processing on the transition arc between the head and the rod of the vibration marker to strengthen the bonding strength between the head and the rod, and obtain the following Fig.10 The R-rolled part shown. In the present invention, the transition arc portion between the head and the rod of the vibration marker is R-rolled, which achieves secondary strengthening of the portion, improves the fatigue resistance of the bolt, and solves the problem of easy fracture at the junction of the bolt head and the rod. The R-rolling machine is used to select a suitable R-rolling wheel to perform R-rolling on the transition arc portion between the head and the rod of the semi-finished bolt workpiece, which can improve the smoothness of the transition arc, enhance the density of the metal streamline at the transition arc portion between the head and the rod, and effectively improve the fatigue resistance of the Inconel 718 twelve-point head bolt.

[0053] (8) A CNC warm thread rolling machine of model MC-40FI(V) is used to perform warm thread rolling on the rod blank of the rolled R workpiece, and an external thread is rolled out on the rod blank to obtain the following: Fig.11 The thread rolling workpiece shown. The present invention adopts a processing technology of first aging treatment and then warm rolling. The rolling strengthening of the screw blank rod by warm rolling can improve the strength of the threaded part of the Inconel 718 twelve-point head bolt. The performance of the Inconel718 high-temperature alloy must meet the tensile strength Rm≥1517MPa and the yield strength Rp0.2≥1379MPa. It has a high hardness, the Rockwell hardness can reach 43~48HRC, the plasticity is poor, and the work hardening phenomenon of the material is serious. In order to avoid defects such as cracks and folds at the thread during the thread rolling process, the thread is processed by warm rolling in this embodiment. After heating, the strength of the material is reduced, the work hardening phenomenon is alleviated, the fluidity of the material is enhanced, and the thread is easy to form, which can effectively solve the problems of rolling wheel tooth collapse and poor thread quality during cold rolling. During the warm rolling process, the screw blank rod is first heated, and then the heated screw blank rod is subjected to thread rolling. During the warm rolling process, the heating temperature, heating time and screw blank rod diameter are key factors in manufacturing process control and need to be determined through process tests. In this embodiment, during the warm thread rolling process, the screw rod diameter and warm thread rolling parameters are shown in Table 2.

[0054] Table 2 Screw blank rod diameter and warm rolling parameters during thread rolling

[0055]

[0056]

[0057] (9) According to the requirements of ASTM E1417 "Standard Practice for Penetrant Testing", the fluorescent penetrant method (i.e., Type I) and the water washing method (i.e., Method A) are selected, and 100% fluorescent flaw detection is performed on the thread rolling parts using a level 3 sensitivity, and the defective thread rolling parts are sorted out and scrapped.

[0058] (10) The thread rolling workpiece that has passed the fluorescent flaw detection is passivated to form a dense passivation film on the surface of the finished bolt workpiece, thereby improving the corrosion resistance of the finished bolt workpiece, and obtaining the following Fig.12 The finished bolt workpiece is shown. The passivation treatment method is as follows: the thread rolling workpiece is sequentially subjected to degreasing, hot water washing, normal temperature water washing, activation, first flowing water washing, passivation, second flowing water washing, neutralization, third flowing water washing, hot pure water washing and drying. Among them, activation is to place the bolt workpiece after normal temperature water washing in hydrochloric acid with a concentration of 100g / L, and soak it at room temperature for 2min. During the activation process, the parts should be manually turned over 3 to 5 times, and attention should be paid to controlling the force when turning over to prevent bumps and scratches; passivation is to place the bolt workpiece after the first flowing cold water washing in dilute nitric acid (dilute nitric acid is prepared by mixing concentrated nitric acid with a density of 1.42g / mL and water, the mass concentration of concentrated nitric acid is 68%, and the amount of concentrated nitric acid is 380g / L), and soak it at room temperature for 30min. During the passivation process, the parts should be manually turned over 3 to 5 times to ensure that the surface of the workpiece can contact the passivation solution. Pay attention to controlling the force when turning over to prevent bumps and scratches; the water temperature used for normal temperature water washing, the first flowing water washing and the second flowing water washing is room temperature; the water temperature used for hot water washing and hot pure water washing is 60℃.

[0059] (11) According to the number of finished bolt workpieces obtained by passivation treatment, a certain number of bolts are randomly selected according to the standards and relevant technical requirements, and mechanical properties tests of tensile strength, shear strength, fatigue and Rockwell hardness are carried out on tension, fatigue and hardness testing machines. After the tests are qualified, a mechanical properties test qualification report is issued; finally, the finished bolt workpieces are packaged and stored.

[0060] Example 2

[0061] The processing method of the Inconel 718 twelve-point head bolt of this embodiment takes the Inconel 718 twelve-point head bolt with a processing specification of .5625-18UNJF-3A as an example, and specifically includes the following steps:

[0062] (1) Inconel 718 alloy bars that meet the standard AMS 5962 and are smelted by vacuum induction melting and vacuum arc furnace remelting are selected as the raw materials for processing Inconel 718 twelve-point head bolts. The diameter and length of the Inconel 718 alloy bars are calculated and determined according to the specifications and length of the processed Inconel 718 twelve-point head bolts. According to the length of a single Inconel 718 twelve-point head bolt, the Inconel 718 alloy bar is cut into a single bar using a sawing machine, and then the single bar is clamped on a common hexagonal lathe using a three-jaw chuck. The two end faces of the single bar are turned until they are shiny, and then chamfers are turned on the two end faces. Then, the outer diameter of the bar is ground using a CNC centerless grinder to ensure that the outer diameter size is consistent, and a blank suitable for hot upsetting processing is obtained.

[0063] (2) Place the blank (diameter 15.3 mm, upper deviation 0 mm, lower deviation -0.03 mm) into a hot upsetting die, and use a 315-ton press to perform hot upsetting on the blank. A twelve-point head of the bolt head is upset at one end of the blank, and then the oxide scale and oxidation color are removed by sandblasting to obtain a semi-finished bolt workpiece. During hot upsetting, a portable transistor induction heating device is first used to heat the area of ​​the twelve-point head of the upset bolt head. After the heating temperature and time meet the requirements, the heated blank is immediately placed in the hot upsetting die for hot upsetting. The heating parameters during hot upsetting are shown in Table 3. The cooling time in Table 3 refers to the time interval between the completion of heating of the blank and the start of hot upsetting when the blank is placed in the hot upsetting die.

[0064] Table 3 Heating parameters during hot upsetting

[0065]

[0066] (3) The semi-finished bolt workpiece is subjected to aging treatment, and then the oxide scale and oxidation color are removed by sandblasting to obtain a heat-treated part. The aging treatment is to place the semi-finished bolt workpiece in the heating chamber of a horizontal vacuum gas quenching furnace, raise the temperature to 718°C, and keep it at this temperature for 8 hours, then cool it to 612°C at a rate of (56°C±8°C) / h, and keep it at this temperature for 8 hours. Finally, the semi-finished bolt workpiece is transferred to the cooling chamber of the horizontal vacuum gas quenching furnace for gas quenching cooling. The atmosphere in the cooling chamber is argon gas, and the argon gas pressure is 150-200MPa. The vacuum degree of the vacuum gas quenching furnace used for aging treatment is 1×10 -3 Pa, the leakage rate of the vacuum gas quenching furnace is 20μmHg / h.

[0067] (4) The heat-treated part is clamped on a common hexagonal lathe using a three-jaw chuck, and the shape of the heat-treated part is rough-turned to obtain a rough-turned part.

[0068] (5) The rough-turned workpiece is clamped on a CNC lathe using a three-jaw chuck, and the rough-turned workpiece is fine-turned to obtain a fine-turned workpiece; the screw blank rod portion of the fine-turned workpiece is ground using a CNC centerless grinder to ensure that the screw blank rod diameter and the screw blank rod roughness meet the processing requirements before thread rolling, thereby obtaining a ground workpiece.

[0069] (6) The ground workpiece is clamped on a workbench of a vibration marking machine, and the vibration marking machine is used to vibration-mark the end face of the twelve-pointed head of the ground workpiece to obtain an identification mark to obtain a vibration marked part.

[0070] (7) The vibration marker is placed on the rolling wheel of a CNC rolling machine, and the transition arc portion between the head and the rod of the vibration marker is rolled to strengthen the bonding strength between the head and the rod, thereby obtaining a rolled part.

[0071] (8) A CNC warm thread rolling machine of model MC-40FI(V) is used to perform warm thread rolling on the rod portion of the R-rolled workpiece, and an external thread is rolled out at the rod portion of the screw blank to obtain a thread rolling workpiece. During the warm thread rolling process, the screw blank rod is first heated, and then the heated screw blank rod is subjected to thread rolling. During the warm thread rolling process, the heating temperature, heating time, and screw blank rod diameter are key factors in controlling the manufacturing process and need to be determined through process tests. In this embodiment, during the warm thread rolling process, the screw blank rod diameter and warm thread rolling parameters are shown in Table 4.

[0072] Table 4 Screw blank rod diameter and warm rolling parameters during thread rolling

[0073]

[0074] (9) According to the requirements of ASTM E1417 "Standard Practice for Penetrant Testing", the fluorescent penetrant method (i.e., Type I) and the water washing method (i.e., Method A) are selected, and 100% fluorescent flaw detection is performed on the thread rolling parts using a level 3 sensitivity, and the defective thread rolling parts are sorted out and scrapped.

[0075] (10) The thread rolling workpiece that has passed the fluorescent flaw detection is passivated to form a dense passivation film on the surface of the finished bolt workpiece, thereby improving the corrosion resistance of the finished bolt workpiece to obtain the finished bolt workpiece. The passivation treatment method is as follows: the thread rolling workpiece is sequentially degreased, washed with hot water, washed with water at room temperature, activated, washed with flowing water for the first time, passivated, washed with flowing water for the second time, neutralized, washed with flowing water for the third time, washed with hot pure water, and dried. Among them, activation is to place the bolt workpiece after normal temperature water washing in hydrochloric acid with a concentration of 120g / L, and soak it at room temperature for 1 minute. During the activation process, the parts should be manually turned over 3 to 5 times, and attention should be paid to controlling the force when turning over to prevent bumps and scratches; passivation is to place the bolt workpiece after the first flowing cold water washing in dilute nitric acid (dilute nitric acid is prepared by mixing concentrated nitric acid with a density of 1.42g / mL and water, the mass concentration of concentrated nitric acid is 68%, and the amount of concentrated nitric acid is 385g / L), and soak it at room temperature for 45 minutes. During the passivation process, the parts should be manually turned over 3 to 5 times to ensure that the surface of the workpiece can contact the passivation solution. Pay attention to controlling the force when turning over to prevent bumps and scratches; the water temperature used for normal temperature water washing, the first flowing water washing and the second flowing water washing is room temperature; the water temperature used for hot water washing and hot pure water washing is 70°C.

[0076] (11) According to the number of finished bolt workpieces obtained by passivation treatment, a certain number of bolts are randomly selected according to the standards and relevant technical requirements, and mechanical properties tests of tensile strength, shear strength, fatigue resistance and hardness are carried out on tension, fatigue and hardness testing machines. After the tests are qualified, a mechanical properties test qualification report is issued; finally, the finished bolt workpieces are packaged and stored.

[0077] Example 3

[0078] The processing method of the Inconel 718 twelve-point head bolt of this embodiment takes the Inconel 718 twelve-point head bolt with a processing specification of .625-18UNJF-3A as an example, and specifically includes the following steps:

[0079] (1) Inconel 718 alloy bars that meet the standard AMS 5962 and are smelted by vacuum induction melting and vacuum arc furnace remelting are selected as the raw materials for processing Inconel 718 twelve-point head bolts. The diameter and length of the Inconel 718 alloy bars are calculated and determined according to the specifications and length of the processed Inconel 718 twelve-point head bolts. According to the length of a single Inconel 718 twelve-point head bolt, the Inconel 718 alloy bar is cut into a single bar using a sawing machine, and then the single bar is clamped on a common hexagonal lathe using a three-jaw chuck. The two end faces of the single bar are turned until they are shiny, and then chamfers are turned on the two end faces. Then, the outer diameter of the bar is ground using a CNC centerless grinder to ensure that the outer diameter size is consistent, and a blank suitable for hot upsetting processing is obtained.

[0080] (2) The blank (diameter 16.7 mm, upper deviation 0 mm, lower deviation -0.03 mm) was placed in a hot upsetting die, and a 315-ton press was used to perform hot upsetting on the blank. A twelve-point head of the bolt head was upset at one end of the blank, and then the oxide scale and oxidation color were removed by sandblasting to obtain a semi-finished bolt workpiece. During hot upsetting, a portable transistor induction heating device was used to heat the area of ​​the twelve-point head of the upset bolt head. The heating parameters during hot upsetting are shown in Table 5.

[0081] Table 5 Heating parameters during hot upsetting

[0082]

[0083] (3) The semi-finished bolt workpiece is subjected to aging treatment, and then the oxide scale and oxidation color are removed by sandblasting to obtain a heat-treated part. The aging treatment is to place the semi-finished bolt workpiece in the heating chamber of a horizontal vacuum gas quenching furnace, raise the temperature to 718°C, and keep it at this temperature for 8 hours, then cool it to 612°C at a rate of (56°C±8°C) / h, and keep it at this temperature for 8 hours. Finally, the semi-finished bolt workpiece is transferred to the cooling chamber of the horizontal vacuum gas quenching furnace for gas quenching cooling. The atmosphere in the cooling chamber is argon gas, and the argon gas pressure is 150-200MPa. The vacuum degree of the vacuum gas quenching furnace used for aging treatment is 1×10 -3 Pa, the leakage rate of the vacuum gas quenching furnace is 20μmHg / h.

[0084] (4) The heat-treated part is clamped on a common hexagonal lathe using a three-jaw chuck, and the shape of the heat-treated part is rough-turned to obtain a rough-turned part.

[0085] (5) The rough-turned workpiece is clamped on a CNC lathe using a three-jaw chuck, and the rough-turned workpiece is fine-turned to obtain a fine-turned workpiece; the screw blank rod portion of the fine-turned workpiece is ground using a CNC centerless grinder to ensure that the screw blank rod diameter and the screw blank rod roughness meet the processing requirements before thread rolling, thereby obtaining a ground workpiece.

[0086] (6) The ground workpiece is clamped on a workbench of a vibration marking machine, and the vibration marking machine is used to vibration-mark the end face of the twelve-pointed head of the ground workpiece to obtain an identification mark to obtain a vibration marked part.

[0087] (7) The vibration marker is placed on the rolling wheel of a CNC rolling machine, and the transition arc portion between the head and the rod of the vibration marker is rolled to strengthen the bonding strength between the head and the rod, thereby obtaining a rolled part.

[0088] (8) A CNC warm thread rolling machine of model MC-40FI(V) is used to perform warm thread rolling on the rod portion of the R-rolled workpiece, and an external thread is rolled out at the rod portion of the screw blank to obtain a thread rolling workpiece. During the warm thread rolling process, the screw blank rod is first heated, and then the heated screw blank rod is subjected to thread rolling. During the warm thread rolling process, the heating temperature, heating time, and screw blank rod diameter are key factors in controlling the manufacturing process and need to be determined through process tests. In this embodiment, during the warm thread rolling process, the screw blank rod diameter and warm thread rolling parameters are shown in Table 6.

[0089] Table 6 Screw blank rod diameter and warm rolling parameters during thread rolling

[0090]

[0091] (9) According to the requirements of ASTM E1417 "Standard Practice for Penetrant Testing", the fluorescent penetrant method (i.e., Type I) and the water washing method (i.e., Method A) are selected, and 100% fluorescent flaw detection is performed on the thread rolling parts using a level 3 sensitivity, and the defective thread rolling parts are sorted out and scrapped.

[0092] (10) The thread rolling workpiece that has passed the fluorescent flaw detection is passivated to form a dense passivation film on the surface of the finished bolt workpiece, thereby improving the corrosion resistance of the finished bolt workpiece to obtain the finished bolt workpiece. The passivation treatment method is as follows: the thread rolling workpiece is sequentially degreased, washed with hot water, washed with water at room temperature, activated, washed with flowing water for the first time, passivated, washed with flowing water for the second time, neutralized, washed with flowing water for the third time, washed with hot pure water, and dried. Among them, activation is to place the bolt workpiece after normal temperature water washing in hydrochloric acid with a concentration of 150g / L, and soak it at room temperature for 0.5min. During the activation process, the parts should be manually turned over 3 to 5 times, and attention should be paid to controlling the force when turning over to prevent bumps and scratches; passivation is to place the bolt workpiece after the first flowing cold water washing in dilute nitric acid (dilute nitric acid is prepared by mixing concentrated nitric acid with a density of 1.42g / mL and water, the mass concentration of concentrated nitric acid is 68%, and the amount of concentrated nitric acid is 390g / L), and soak it at room temperature for 60min. During the passivation process, the parts should be manually turned over 3 to 5 times to ensure that the surface of the workpiece can contact the passivation solution. Pay attention to controlling the force when turning over to prevent bumps and scratches; the water temperature used for normal temperature water washing, the first flowing water washing and the second flowing water washing is room temperature; the water temperature used for hot water washing and hot pure water washing is 80℃.

[0093] (11) According to the number of finished bolt workpieces obtained by passivation treatment, a certain number of bolts are randomly selected according to the standards and relevant technical requirements, and mechanical properties tests of tensile strength, shear strength, fatigue resistance and hardness are carried out on tension, fatigue and hardness testing machines. After the tests are qualified, a mechanical properties test qualification report is issued; finally, the finished bolt workpieces are packaged and stored.

[0094] Example 4

[0095] The difference between the processing method of the Inconel 718 twelve-angle head bolt of the present embodiment and the processing method of the Inconel 718 twelve-angle head bolt of Example 1 is that the aging treatment in step (3) of the processing method of the Inconel 718 twelve-angle head bolt of the present embodiment is to place the semi-finished bolt workpiece in the heating chamber of a horizontal vacuum gas quenching furnace, heat it to 720°C, and keep it at this temperature for 8 hours, then cool it to 614°C at a rate of (56°C±8°C) / h, and keep it at this temperature for 8 hours, and finally, transfer the semi-finished bolt workpiece to the cooling chamber of the horizontal vacuum gas quenching furnace for gas quenching cooling, the atmosphere in the cooling chamber is argon, and the argon gas pressure is 150-200MPa.

[0096] Example 5

[0097] The difference between the processing method of the Inconel 718 twelve-angle head bolt of the present embodiment and the processing method of the Inconel 718 twelve-angle head bolt of Example 2 is that the aging treatment in step (3) of the processing method of the Inconel 718 twelve-angle head bolt of the present embodiment is to place the semi-finished bolt workpiece in the heating chamber of a horizontal vacuum gas quenching furnace, heat it to 720°C, and keep it at this temperature for 8 hours, then cool it to 614°C at a rate of (56°C±8°C) / h, and keep it at this temperature for 8 hours, and finally, transfer the semi-finished bolt workpiece to the cooling chamber of the horizontal vacuum gas quenching furnace for gas quenching cooling, the atmosphere in the cooling chamber is argon, and the argon gas pressure is 150-200MPa.

[0098] Example 6

[0099] The difference between the processing method of the Inconel 718 twelve-angle head bolt of the present embodiment and the processing method of the Inconel 718 twelve-angle head bolt of Example 3 is that the aging treatment in step (3) of the processing method of the Inconel 718 twelve-angle head bolt of the present embodiment is to place the semi-finished bolt workpiece in the heating chamber of a horizontal vacuum gas quenching furnace, heat it to 720°C, and keep it at this temperature for 8 hours, then cool it to 614°C at a rate of (56°C±8°C) / h, and keep it at this temperature for 8 hours, and finally, transfer the semi-finished bolt workpiece to the cooling chamber of the horizontal vacuum gas quenching furnace for gas quenching cooling, the atmosphere in the cooling chamber is argon, and the argon gas pressure is 150-200MPa.

[0100] Comparative Example 1

[0101] The difference between the processing method of the Inconel 718 twelve-angle head bolt of this comparative example and the processing method of the Inconel 718 twelve-angle head bolt of Example 1 is that the heat treatment in step (3) of the processing method of the Inconel 718 twelve-angle head bolt of this comparative example includes solution treatment and aging treatment performed in sequence, and the solution treatment is to place the semi-finished bolt workpiece in the heating chamber of a horizontal vacuum gas quenching furnace, heat it to 1000°C, and keep it at this temperature for 1h, and then transfer the semi-finished bolt workpiece to the cooling chamber of the horizontal vacuum gas quenching furnace for gas quenching cooling, and the atmosphere in the cooling chamber is argon gas, and the argon gas pressure is 150-200MPa. The aging treatment is the same as the aging treatment in Example 1.

[0102] Comparative Example 2

[0103] The difference between the processing method of the Inconel 718 twelve-angle head bolt of this comparative example and the processing method of the Inconel 718 twelve-angle head bolt of Example 1 is that in step (3) of the processing method of the Inconel 718 twelve-angle head bolt of this comparative example, the aging treatment is to place the semi-finished bolt workpiece in the heating chamber of a horizontal vacuum gas quenching furnace, heat it to 725°C, and keep it at this temperature for 8 hours, then cool it to 612°C at a rate of (56°C±8°C) / h, and keep it at this temperature for 8 hours, finally, transfer the semi-finished bolt workpiece to the cooling chamber of the horizontal vacuum gas quenching furnace for gas quenching cooling, the atmosphere in the cooling chamber is argon, and the argon gas pressure is 150-200MPa.

[0104] Comparative Example 3

[0105] The difference between the processing method of the Inconel 718 twelve-angle head bolt of this comparative example and the processing method of the Inconel 718 twelve-angle head bolt of Example 1 is that in step (3) of the processing method of the Inconel 718 twelve-angle head bolt of this comparative example, the aging treatment is to place the semi-finished bolt workpiece in the heating chamber of a horizontal vacuum gas quenching furnace, heat it to 710°C, and keep it at this temperature for 8 hours, then cool it to 612°C at a rate of (56°C±8°C) / h, and keep it at this temperature for 8 hours, finally, transfer the semi-finished bolt workpiece to the cooling chamber of the horizontal vacuum gas quenching furnace for gas quenching cooling, the atmosphere in the cooling chamber is argon, and the argon gas pressure is 150-200MPa.

[0106] Comparative Example 4

[0107] The difference between the processing method of the Inconel 718 twelve-angle head bolt of this comparative example and the processing method of the Inconel 718 twelve-angle head bolt of Example 1 is that in step (8) of the processing method of the Inconel 718 twelve-angle head bolt of this comparative example, the temperature of the shank blank is room temperature during the thread rolling process.

[0108] Comparative Example 5

[0109] The difference between the processing method of the Inconel 718 twelve-angle head bolt of this comparative example and the processing method of the Inconel 718 twelve-angle head bolt of Example 1 is that step (7) is omitted in the processing method of the Inconel 718 twelve-angle head bolt of this comparative example, that is, the vibration marker is not subjected to R rolling processing, but the vibration marker is directly subjected to thread rolling processing.

[0110] Comparative Example 6

[0111] The difference between the processing method of the Inconel 718 twelve-angle head bolt of this comparative example and the processing method of the Inconel 718 twelve-angle head bolt of Example 2 is that step (7) is omitted in the processing method of the Inconel 718 twelve-angle head bolt of this comparative example, that is, the vibration marker is not subjected to R rolling processing, but the vibration marker is directly subjected to thread rolling processing.

[0112] Comparative Example 7

[0113] The difference between the processing method of the Inconel 718 twelve-angle head bolt of this comparative example and the processing method of the Inconel 718 twelve-angle head bolt of Example 3 is that step (7) is omitted in the processing method of the Inconel 718 twelve-angle head bolt of this comparative example, that is, the vibration marker is not subjected to R rolling processing, but the vibration marker is directly subjected to thread rolling processing.

[0114] Experimental Example 1

[0115] In this experimental example, the metallographic structure and mechanical properties of Inconel 718 twelve-point head bolts processed in Example 1 and Comparative Examples 1-3 were tested. The metallographic structure pictures are shown in Figures 13-15 The mechanical properties test results are shown in Table 7. Among them, the tensile strength is tested according to the method in standard ASTM E8 / E8M-24, the yield strength is tested according to the method in standard ASTM E8 / E8M-24, and the Rockwell hardness is tested according to the method in standard NASM 1312-6. Three samples were selected for testing, and the average value of the test results was taken as the final test result.

[0116] Table 7 Mechanical properties test results of Inconel 718 twelve-point head bolts processed in Example 1 and Comparative Examples 1-3

[0117] Twelve-point head bolt Tensile strength Rm / MPa Yield strength Rp0.2 / MPa Shear strength / MPa Rockwell hardness / HRC Example 1 1676 1603 932 49.5 Comparative Example 1 1632 1571 928 47.5 Comparative Example 2 1626 1570 907 47.7 Comparative Example 3 1615 1552 910 47.0

[0118] From the metallographic organization pictures of the Inconel 718 twelve-angle bolts processed in Example 1 and Comparative Examples 1-3, it can be seen that the grain size of the Inconel 718 twelve-angle bolts processed in Comparative Example 1 is coarsened, there is no δ phase at the grain boundary and in the grain, there is notch sensitivity, and it is mainly used in products with high grain size requirements; the Inconel 718 twelve-angle bolts processed in Comparative Example 2 have less δ phase, which can improve the strength and impact properties of the material, and are mainly used in the direct aging heat treatment system of cold-drawn raw materials; the Inconel 718 twelve-angle bolts processed in Example 1 have δ phase at the grain boundary, which is conducive to eliminating notch sensitivity. In addition, when the same number of Inconel 718 twelve-angle bolts are prepared, the scrap rate of the Inconel 718 twelve-angle bolts processed in Example 1 and Comparative Examples 1-3 (the scrap rate refers to the percentage of bolts with cracks or other defects on the surface when 100 twelve-angle bolts are produced) is shown in Table 8.

[0119] Table 8 Scrap rate and batch quality stability of Inconel 718 twelve-point head bolts processed in Example 1 and Comparative Examples 1-3

[0120] Twelve-point head bolt Scrap rate Example 1 5％ Comparative Example 1 15％ Comparative Example 2 9％ Comparative Example 3 13％

[0121] It can be seen from Tables 7 and 8 that the mechanical properties of the Inconel 718 twelve-point head bolt processed in Example 1 are the best, and its processing quality stability is the best. Therefore, the heat treatment system in Example 1 is the optimal heat treatment system.

[0122] Experimental Example 2

[0123] This experimental example counts the service life of the thread rolling wheel in step (8) of the processing method of Inconel 718 twelve-point head bolts in Example 1 and Comparative Example 4, and counts the defects at the thread of the processed Inconel 718 twelve-point head bolts. The results show that in step (8) of Comparative Example 4, the thread rolling wheel will have a tooth breakage problem after rolling several or dozens of products, such as Fig.16 At the same time, the threads of the Inconel 718 twelve-point head bolt processed in Example 4 are prone to cracks, folding and other defects, such as Fig.17 shown.

[0124] Experimental Example 3

[0125] In this experimental example, the mechanical properties of the Inconel 718 twelve-point head bolts processed by Examples 1-3 and Comparative Examples 5-7 were tested, and the results are shown in Table 9. Among them, the tensile strength was tested according to the method in the standard ASTM E8 / E8M-24, the yield strength was tested according to the method in the standard ASTM E8 / E8M-24, the Rockwell hardness was tested according to the method in the standard NASM 1312-6, and the fatigue resistance was tested according to the method in the standard NASM1312-11.

[0126] Table 9 Mechanical properties of Inconel 718 twelve-point head bolts processed by Examples 1-3 and Comparative Examples 5-7

[0127] Twelve-point head bolt Tensile strength Rm / MPa Yield strength Rp0.2 / MPa Rockwell hardness / HRC Anti-fatigue performance Example 1 ≥1600 ≥1540 48～49.5 68,000 to 130,000 times Example 2 ≥1600 ≥1540 48～49.5 65,000 to 125,000 times Example 3 ≥1600 ≥1540 48～49.5 65,000 to 115,000 times Comparative Example 5 1542～1595 1500～1530 47.5～48.9 ≤46,000 times Comparative Example 6 1542～1590 1500～1525 47.5～48.9 ≤45,000 times Comparative Example 7 1542～1550 1500～1510 47.5～48.9 ≤43,000 times

[0128] As shown in Table 9, in the methods of Examples 1-3, the transition arc between the bolt head and the shank is subjected to R rolling, so the transition arc between the bolt head and the shank is strengthened, and the fatigue life is greatly improved, reaching the standard requirement of an average of not less than 65,000 times. In the methods of Comparative Examples 5-7, the transition arc between the bolt head and the shank is not subjected to R rolling, and the fatigue life is less than 50,000 times. Moreover, as the specification increases, the fatigue life decreases and fails to meet the standard requirement of an average of not less than 65,000 times.

[0129] Experimental Example 4

[0130] This experimental example evaluates the passivation treatment effect of different nitric acids. Three specifications of nitric acids are selected from the market. The numbers of the three specifications of nitric acids are 1, 2 and 3 respectively; the density of nitric acid No. 1 is 1.38g / mL, the purity grade is analytically pure, and the mass concentration is 68%; the density of nitric acid No. 2 is 1.42g / mL, the purity grade is analytically pure, and the mass concentration is 68%; the density of nitric acid No. 3 is 1.40g / mL, the purity grade is chemically pure, and the mass concentration is 68%. Then the three specifications of nitric acid are stirred and mixed with water to obtain a dilution with a mass fraction of 380g / mL, and then the thread rolling parts that have passed the fluorescent flaw detection are passivated according to the method in Example 1, Example 2 or Example 3, and then the finished bolt workpiece obtained by passivation is subjected to salt spray resistance test. The test standard is GJB715.1. During the experiment, the time when the bolt workpiece begins to corrode is recorded. The test results are shown in Table 10.

[0131] Table 10 Experimental results of salt spray resistance test of thread rolling parts treated with different nitric acid

[0132]

[0133]

[0134] Experimental Example 5

[0135] This experimental example statistically analyzed the scrap rate (the scrap rate refers to the percentage of bolts with cracks or other defects on the surface when producing 100 twelve-point head bolts) of the processing methods of each embodiment and comparative example, and the results are shown in Table 11.

[0136] Table 11 Scrap rate of processing methods of various embodiments and comparative examples

[0137] Processing methods Scrap rate Example 1 5％ Example 2 5％ Example 3 7％ Example 4 6％ Example 5 5％ Example 6 6％ Comparative Example 1 15％ Comparative Example 2 9％ Comparative Example 3 85％ Comparative Example 4 35％ Comparative Example 5 36％ Comparative Example 6 39％

[0138] In summary, through the control of the above key processes, the processing method of the present invention can effectively solve the problem that the tensile strength of Inconel 718 twelve-angle head bolts is unqualified and the fatigue test does not meet the standard requirements. At the same time, it also effectively solves the problems that the Inconel 718 twelve-angle head bolts are difficult to manufacture, the scrap rate is high, the production delivery cycle is long, the batch quality stability is poor, and the mechanical properties do not meet the standard requirements. The processing method of the Inconel 718 twelve-angle head bolt of the present invention can be processed by a general operator, and the processing efficiency is extremely high. It has the advantages of efficient production process and simple operation, and can ensure that the dimensional accuracy and form and position tolerance requirements of the Inconel 718 twelve-angle head bolts can be guaranteed, and the mechanical properties can meet the requirements specified in the standards. At the same time, the finished bolts processed by the present invention have high dimensional accuracy, form and position tolerance, and mechanical properties that can meet the standard design requirements, and are easy to measure. The size and form and position tolerance of the Inconel 718 twelve-angle head bolts can be measured using a vernier caliper, a micrometer, and a projector.

Claims

1. A method for processing Inconel 718 twelve-point head bolt, characterized in that: The following steps are involved: The blank is subjected to hot upsetting of the bolt head and then subjected to aging treatment to obtain a heat-treated part; the heat-treated part is then subjected to rough turning, fine turning, and grinding of the screw blank shank, and then the transition arc portion between the head and the shank is subjected to R rolling, and then the screw blank shank is subjected to warm thread rolling, and finally a passivation treatment is performed to obtain an Inconel 718 twelve-point head bolt; the aging treatment includes a first-stage heat treatment and a second-stage heat treatment performed sequentially, the temperature of the first-stage heat treatment is 718-720° C., and the temperature of the second-stage heat treatment is 612-614° C.

2. The method for processing the Inconel 718 twelve-point head bolt according to claim 1, characterized in that: The first stage heat treatment time is 8h.

3. The processing method of Inconel 718 twelve-point head bolt according to claim 1, characterized in that: The second stage heat treatment time is 8h.

4. The method for processing an Inconel 718 twelve-point head bolt according to claim 1, characterized in that: The cooling rate from the temperature corresponding to the first stage heat treatment to the temperature corresponding to the second stage heat treatment is (56°C±8°C) / h.

5. The method for processing an Inconel 718 twelve-point head bolt according to any one of claims 1 to 4, characterized in that: The second stage heat treatment is followed by a cooling treatment, wherein the cooling treatment is achieved by gas quenching, wherein the atmosphere used for the gas quenching is argon gas, and the gas pressure is 150-200 MPa.

6. The method for processing an Inconel 718 twelve-point head bolt according to any one of claims 1 to 4, characterized in that: Hot upsetting is to heat the bolt head of the blank to a specified temperature and keep it warm before upsetting; the diameter of the blank is 13.297-13.3 mm, the specified temperature is 880-920°C, the time required to heat to the specified temperature is 3-6 seconds, and the holding time is 3-6 seconds; or the diameter of the blank is 15.297-15.3 mm, the specified temperature is 890-920°C, the time required to heat to the specified temperature is 3-6 seconds, and the holding time is 3-6 seconds; or The diameter of the blank is 16.597-16.7 mm, the specified temperature is 900-920° C., the time required to heat to the specified temperature is 6-8 s, and the heat preservation time is 6-8 s.

7. The method for processing an Inconel 718 twelve-point head bolt according to any one of claims 1 to 4, characterized in that: The warm thread rolling process is to heat the screw blank rod first, and then perform the thread rolling process on the heated screw blank rod; the heating temperature is 180-200° C., and the time is 5-8 seconds.

8. The method for processing an Inconel 718 twelve-point head bolt according to any one of claims 1 to 4, characterized in that: The passivation treatment method is as follows: the thread rolling parts are sequentially degreased, washed with hot water, washed with water at room temperature, activated, washed with flowing water for the first time, passivated, washed with flowing water for the second time, neutralized, washed with flowing water for the third time, washed with hot pure water and dried.

9. The method for processing an Inconel 718 twelve-point head bolt according to claim 8, characterized in that: The passivation is to place the bolt workpiece after the first flowing cold water washing in dilute nitric acid and soak it at room temperature for 30 to 60 minutes. The dilute nitric acid is prepared by mixing concentrated nitric acid with a density of 1.42 g / mL and water. The amount of concentrated nitric acid used is 380 to 390 g / L.

10. The method for processing an Inconel 718 twelve-point head bolt according to claim 8, characterized in that: The activation is to place the bolt workpiece after normal temperature water washing in hydrochloric acid with a concentration of 100-150g / L and soak it at room temperature for 0.5-2min; the water temperature used for the first flowing water washing and the second flowing water washing is room temperature; the water temperature used for hot water washing and hot pure water washing is 60-80℃.

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