Short-time low-fault-tolerant vacuum heat treatment method

Abstract

The present application provides a kind of short time low fault tolerance vacuum heat treatment method, comprising the following steps: S1: preparation test part, test part is placed into heating furnace;S2: according to the temperature of test part position test, judge the heating area of heating furnace;S3: the part to be heated is placed into the heating area obtained in S2;S4: according to the temperature of test part test, the position of the part to be heated is adjusted, after heat preservation for a period of time, cooling is carried out.The present application has beneficial effects: not only suitable for the aerospace fastener commonly used in time-dependent strengthening alloy as raw material, such as TB98, A286, etc., but also suitable for other heat treatable strengthening alloy as raw material parts.Through the accurate control of heat treatment process parameters, the part obtains excellent strength and plasticity.

Description

Technical Field

[0001] This invention belongs to the field of vacuum heat treatment technology, and in particular relates to a short-time, low-fault-tolerance vacuum heat treatment method. Background Technology

[0002] In the aerospace fastener industry, some products require a high degree of balance between strength and plasticity, necessitating special heat treatment methods to achieve the required performance. Common examples include A286 rivets and TB9 bolts.

[0003] To achieve a better strength-plasticity match, A286 rivets are typically subjected to a short-term heat treatment method, which involves holding the rivet at the aging temperature for a short time. This allows only a portion of the reinforcing phase to precipitate in the matrix, improving strength while retaining most of the plasticity of the solution-treated material.

[0004] Due to the inherent properties of β-titanium alloy, TB9 bolts may exhibit localized primary α-phase and ω-quenched phase when not fully dissolved. During low-temperature aging, the ω-aging phase is formed first. The ω-phase is a hard and brittle phase. Further aging or heating to a higher temperature allows the α-phase to nucleate, grow, and gradually "devour" the ω-phase. If the ω-phase is unevenly distributed or incompletely eliminated, it can lead to brittle fracture of the product sample upon tensile testing, resulting in a sharp decrease in strength and plasticity. To address this issue, we designed a short-time annealing process, which involves short-term holding above the ω-phase dissolution temperature. This eliminates the brittle phase without causing performance degradation due to excessively high temperatures, thus achieving stable performance.

[0005] The typical heat treatment processes described above share common control characteristics: short holding time and high temperature precision. The advantage of this heat treatment method is that it can achieve an ideal microstructure and the desired precipitates through short-time heat treatment, saving production costs and being energy-efficient and environmentally friendly. However, its disadvantages are also significant: the control range for time and temperature is very narrow, making it extremely easy to exceed tolerances and leading to a decrease in product performance. Due to the short holding time, the control requirements for the heat treatment process are very strict. For example, for A286 rivets, the holding temperature must be within ±5℃, and the time tolerance is only 1 minute. Exceeding this control range will significantly alter the performance of the part. For TB9 bolts, because the melting temperature range of the ω phase is relatively narrow, the requirements are even stricter. Low temperatures will not achieve the purpose of eliminating the ω phase, while high temperatures will significantly reduce the material strength; similarly, long holding times will also lead to a significant decrease in strength. Summary of the Invention

[0006] In view of this, the present invention aims to propose a short-time, low-fault-tolerance vacuum heat treatment method, which is applicable to, but not only to, aerospace fasteners commonly made of age-hardening alloys such as TB98 and A286, but also to other parts made of heat-treatable hardening alloys. Through precise control of the heat treatment process parameters, the parts achieve excellent strength and ductility.

[0007] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0008] A short-time, low-fault-tolerant vacuum heat treatment method includes the following steps:

[0009] S1: Prepare the test part and place it into the heating furnace;

[0010] S2: Determine the heating zone of the furnace based on the temperature measured at the location of the test part;

[0011] S3: Place the part to be heated into the heating area obtained in S2;

[0012] S4: Adjust the position of the part to be heated according to the test temperature of the part, keep it heated for a period of time, and then cool it down.

[0013] Further, the preparation of the test part in step S1 includes: drilling mounting holes in the part to be tested, and setting the temperature measuring component on the part to be tested through the mounting holes to obtain the test part.

[0014] The temperature sensing component is a load coupler, and the load coupler is a controller.

[0015] Furthermore, in step S1, the test parts are placed on each layer of the heating furnace;

[0016] Several test parts are set around and in the center of the heating furnace on each floor.

[0017] Furthermore, the number of test parts on the first floor of the heating furnace is at least three, and the test parts are actually set at the head and left and right sides of the first floor of the electric heating furnace.

[0018] Furthermore, step S2 also includes taking the temperature value that appears most frequently as the standard value;

[0019] If the temperature at the test point of the test part is within ±3℃ of the marked value, and the time difference in reaching the set temperature is within 1 minute, then the location of the test part is an effective heating zone.

[0020] If the temperature of the test parts on both sides differs from the standard value by more than 3°C, then the position of the test part at that point is invalid. The test parts on both sides should then be moved horizontally towards the center by 5-10cm, and step S2 should be repeated.

[0021] If the temperature of the test piece located in the middle of the heating furnace differs from the standard value by more than 3°C, then the test piece at that location is invalid, and the test area in the middle is cancelled.

[0022] Furthermore, step S4 includes taking the temperature value that appears most frequently as the standard value;

[0023] If the temperature of the test parts on both sides differs from the standard value by more than 3°C, then the position of the test parts at that point is invalid. The test parts on both sides should be moved horizontally towards the center by 5-10cm. The parts to be heated on both sides should be moved inward by 5-10cm at the same time.

[0024] The part to be heated moves the same distance as the test parts on both sides, and the part to be heated is placed within the area of ​​the test parts;

[0025] If the temperature at the test part in the middle differs from the standard value by more than 3°C, then the position of the test part at that point is invalid. Move the two test parts in the middle to the sides by 5-10 cm.

[0026] Furthermore, in step S4, when the temperature of all tested parts reaches the minimum temperature value for the specified heat preservation, the heat preservation time is calculated.

[0027] Furthermore, the temperature for heat preservation in step S4 is 695–715°C, and the heat preservation time is 15–30 min.

[0028] Furthermore, the cooling in step S4 includes cooling with argon gas.

[0029] Compared with existing technologies, the short-time, low-fault-tolerance vacuum heat treatment method described in this invention has the following advantages:

[0030] 1. The main method of this invention is to perform a short-time heat treatment of the alloy-processed parts for 10 to 25 minutes within a temperature range of 695 to 730°C. This results in a significantly lower number of γ′ phase precipitates compared to peak aging, thus strengthening the alloy while preserving its good plasticity in the solution-treated state, thereby achieving a balance between strength and plasticity.

[0031] 2. This invention addresses the issue of β-type heat-treatable titanium alloy parts precipitating the ω phase during heat treatment. Specific parameters are as follows: holding at 695–715°C for 10 minutes, followed by rapid cooling. Its main function is to eliminate the ω phase generated during solution treatment or low-temperature aging, reducing the risk of brittle fracture and significantly improving batch stability. Simultaneously, the short-term holding within a precise temperature range does not affect the original strength grade of the alloy. Attached Figure Description

[0032] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0033] Figure 1 This is a schematic diagram of the heating furnace described in an embodiment of the present invention. Detailed Implementation

[0034] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0035] The present invention will now be described in detail with reference to the embodiments.

[0036] 1. Short-time, low-fault-tolerance vacuum heat treatment process technology

[0037] This method primarily utilizes the phase changes in the alloy during heat treatment to precisely control the content of phases in the microstructure, thereby improving performance. Its main technical characteristics are a precise temperature control range and a relatively short heat treatment time.

[0038] (1) Short-term aging of precipitation-hardening stainless steel:

[0039] Taking A286 rivet products as an example, this type of product is strengthened through solution treatment and aging heat treatment. In the solution state, the alloy has a γ-austenite matrix. After aging, its microstructure consists of spherical Ni3(Al,Ti) type γ′ phases, TiN, and TiC uniformly dispersed on the γ-austenite matrix. There are trace amounts of M3B2 borides at the grain boundaries, and there may be a small amount of η and L phases near the grain boundaries. Among them, the γ′ strengthening phase has the greatest impact on the alloy properties. The quantity, size, and morphology of the γ′ phase have a great influence on the alloy properties. The γ′ phase begins to precipitate at around 650℃, and the precipitation is most abundant at 700-730℃. The usual heat treatment method is to aging at this temperature for at least 16-24 hours. After this, the amount of γ′ phase accounts for about 2% to 3% of the alloy weight, and the alloy strength reaches its peak.

[0040] The main method of this invention is to perform a short-time heat treatment of the alloy-processed parts for 10 to 25 minutes within a temperature range of 700 to 730°C. This results in a significantly lower number of γ′ phase precipitates compared to peak aging, thus strengthening the alloy while preserving its good plasticity in the solution-treated state, thereby achieving a balance between strength and plasticity.

[0041] Other precipitation-hardening stainless steel parts can be treated using the same heat treatment method to control the amount of strengthening phase precipitation, thereby achieving good overall performance.

[0042] (2) Short-time annealing of β-type titanium alloys:

[0043] Taking TB9 screws as an example, the microstructure after solution treatment is generally equiaxed β grains, with a small amount of primary α phase in some areas. After solution treatment and aging, the microstructure consists of a large number of secondary α phase particles uniformly dispersed within the β grain boundaries and grains. However, during low-temperature aging, the ω phase will form first. Only with continued aging or after high-temperature aging will the α phase nucleate, grow, and gradually "devour" the ω phase. If the ω phase is unevenly distributed or does not disappear completely, it will inevitably affect the performance instability of the final product. Therefore, at the same solution treatment temperature, the aging temperature also has a significant impact on the alloy properties. Within the standard recommended aging temperature range, aging at an appropriate temperature can achieve better overall performance.

[0044] This invention addresses the issue of β-type heat-treatable titanium alloy parts precipitating the ω phase during heat treatment. The specific parameters are as follows: holding at 695–715°C for 10 minutes, followed by rapid cooling. Its main function is to eliminate the ω phase generated during solution treatment or low-temperature aging, reducing the risk of brittle fracture and significantly improving batch stability. Simultaneously, the short holding time within a precise temperature range does not affect the original strength grade of the alloy.

[0045] The same applies to other β-type titanium alloy parts, but the control parameters need to be adjusted appropriately according to the different types of precipitated phases and alloy strength.

[0046] 2. Control methods for short-time, low-fault-tolerance vacuum heat treatment

[0047] Due to the characteristics of vacuum in short-time, low-tolerance vacuum heat treatment, precise control of temperature and time is required. Because of the thermal hysteresis in vacuum heat treatment, a discrepancy exists between the temperature displayed on the temperature controller and the actual heating temperature of the workpiece, which affects the actual effect of the short-time, low-tolerance vacuum heat treatment. Therefore, this invention further proposes key control points for this method to address this problem.

[0048] During short-time heat treatment, the parts must be placed at one of the nine temperature testing points in the furnace (as follows). Figure 1 All 9 points), and load couplers were installed at the nine locations to monitor the actual temperature at different locations and generate temperature / time curves. Product shear test specimens were used to verify the influence of furnace temperature uniformity on product performance dispersion and metallographic structure.

[0049] 1) Based on the results obtained from the load couple test, further specify the furnace loading position of the parts. For example, if the temperature dispersion of position 9 is large, it is necessary to clearly stipulate that parts are not allowed to be placed in this position, and can only be placed in other positions with smaller temperature dispersion.

[0050] 2) During the insulation process, the parts placed in positions 1-9 need to be connected to load couplers. When the temperature monitored by all load couplers reaches the minimum specified insulation temperature, the insulation time is calculated.

[0051] 3) It is stipulated that during the heat preservation process, the temperature tolerance shall not exceed 3℃ and the time tolerance shall not exceed 1min; if the temperature and time tolerance range is exceeded, the position points where the parts can be placed at the 9 load couple positions shall be further specified, or the area covered by the 9 load couples shall be further reduced until the measured position meets the temperature and time tolerance requirements.

[0052] Example 1:

[0053] Heat the A286120° countersunk rivet to (680~740)℃ and hold for 15~30 minutes. During the heating process, use a load coupler to monitor the temperature of the nine parts placed at the edge of the heating zone.

[0054] 1) Define the "Effective Heating Zone": Before mass production, the area where parts are placed is defined to ensure that the holding temperature and holding time of all parts during the heating process are within the same control level. The effective heating zone is mainly determined by the test results of the load couplers. Only when the temperature tolerance obtained from the tests of all 9 load couplers is within ±3℃, and the time tolerance to reach the set temperature is within 1 minute, can the area covered by these 9 load couplers be determined as the effective heating zone.

[0055] 2) When the temperature and time to reach the temperature measured by the load couple are not within the specified range, the measured "effective heating zone" needs to be further reduced by moving the position of the load couple. The direction of movement of the load couple is towards the interior and the center, and the distance of each movement is 5-10cm, until the effective heating zone required for verification is finally determined.

[0056] 3) When using a load couple to determine the effective heating zone, the measurement is performed by loading, which simulates the actual furnace loading environment in order to achieve precise control.

[0057] 4) During the short-time, low-tolerance vacuum heat treatment, the parts to be heated are evenly placed in the middle of the effective heating zone, and the parts placed in positions 1-9 are connected to load couplers. When the temperature monitored by all load couplers reaches the minimum temperature value of the specified heat preservation, the heat preservation time is calculated.

[0058] 5) When connecting the load couple, pre-drill small holes on the substrate of the test piece of the same batch of parts to be heated, and insert the load couple into the small holes to achieve the purpose of real-time monitoring.

[0059] When the temperatures monitored by all load couplers reach the minimum specified insulation temperature, the insulation time is calculated, and the temperature is cooled in argon gas after the insulation is completed.

[0060] Comparative Example 1:

[0061] The A286120° countersunk rivets from the same batch as in Example 1 were heated to (680~740)℃ and held for 60 minutes. The control method specified in this method was not used. The holding time was calculated only according to the temperature control instrument. After the holding time was completed, the rivets were cooled in argon gas.

[0062] Example 2:

[0063] The parts were heated to a temperature range of 695–715℃ and held for 5–15 minutes, then cooled with argon gas. Afterward, they were held at 480℃ for 11 hours and cooled with argon gas again. During the heating process, the temperature of nine parts positioned at the edge of the heating zone was monitored using load couplers. The holding time was calculated when all temperatures monitored by the load couplers reached the minimum specified holding temperature.

[0064] Comparative Example 2:

[0065] The parts were heated to 480℃ and held for 11 hours without using the control methods specified in this method. The holding time was calculated only based on the temperature control instrument readings, and the parts were cooled with argon gas.

[0066] To verify the effectiveness of the present invention, the heat treatment process of the above-described embodiments and comparative examples of the present invention was verified.

[0067]

[0068]

[0069]

[0070] Note: The data in the table are experimental results obtained from the same batch of fastener products, 10 heat treatments, with 3 test pieces randomly selected each time.

[0071] As can be seen from the above examples, the pass rate of the method of the present invention in Example 1 is 100%, while that in the comparative example is 63%, and the fluctuation and coefficient of variation of shear strength are significantly improved compared with Comparative Example 1; the pass rate of the method of the present invention in Example 2 is 100%, while that in the comparative example is 86%, and the fluctuation and coefficient of variation of shear strength are significantly improved compared with Comparative Example 2.

[0072] By comparison, it can be found that the strength of the present invention is more stable than that of conventional heat treatment, and the performance of the parts can be controlled within a small fluctuation range, which significantly improves the pass rate and batch stability of the parts.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A short-time, low-fault-tolerance vacuum heat treatment method, characterized in that: Includes the following steps: S1: Prepare the test part and place it into the heating furnace; S2: Determine the heating zone of the furnace based on the temperature measured at the location of the test part; S3: Place the part to be heated into the heating area obtained in S2; S4: Adjust the position of the part to be heated according to the test temperature of the part, keep it heated for a period of time, and then cool it down; The preparation of the test part in step S1 includes: drilling mounting holes in the part to be tested, and setting the temperature measuring component on the part to be tested through the mounting holes to obtain the test part; In step S1, the test parts are placed on each layer of the heating furnace; Several test parts are set around and in the center of the heating furnace on each floor; The number of test parts on each layer of the heating furnace shall be at least three, and the test parts shall be set in the middle and on the left and right sides of the layer of the electric heating furnace. Step S2 also includes taking the temperature value that appears most frequently as the standard value; If the temperature at the test point of the test part is within ±3℃ of the marked value, and the time difference in reaching the set temperature is within 1 minute, then the location of the test part is an effective heating zone. If the temperature difference between the test part and the standard value is greater than 3℃, the test part at that location is invalid. The test parts on both sides should then be moved horizontally towards the center by 5-10cm, and step S2 should be repeated. If the temperature difference between the test piece and the standard value is greater than 3°C for the test piece located in the middle of the heating furnace, then the test piece at that location is invalid and the test area in the middle is cancelled. Step S4 includes taking the temperature value that appears most frequently as the standard value; If the temperature difference between the test part and the standard value is greater than 3℃, the test part is invalid at that position. The test parts on both sides should be moved horizontally towards the center by 5-10cm. The parts to be heated on both sides should be moved inward by 5-10cm at the same time. The part to be heated moves the same distance as the test parts on both sides, and the part to be heated is placed within the area of ​​the test parts; If the temperature difference between the test part in the middle and the standard value is greater than 3℃, then the test part at that location is invalid. Move the test part in the middle to both sides by 5-10cm.

2. The short-time, low-fault-tolerance vacuum heat treatment method according to claim 1, characterized in that: In step S4, the holding time is calculated when the temperature of all tested parts reaches the minimum specified holding temperature.

3. The short-time, low-fault-tolerance vacuum heat treatment method according to claim 1, characterized in that: The temperature for heat preservation in step S4 is 695~715℃, and the heat preservation time is 15~30min.

4. The short-time, low-fault-tolerance vacuum heat treatment method according to claim 1, characterized in that: Cooling in step S4 includes cooling with argon gas.

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