A processing method for improving uniformity of microstructure and performance of near-alpha titanium alloy forgings

Abstract

This application discloses a processing method for improving the uniformity of microstructure and properties of near-α type titanium alloy forgings, comprising the steps of: holding the titanium alloy forging at a set solution temperature; air-cooling the titanium alloy forging after it is removed from the furnace, wherein the air-cooling duration is positively correlated with the equivalent diameter D of the maximum cross-section of the titanium alloy forging; immediately after air-cooling, liquid-cooling the titanium alloy forging; and aging treatment of the titanium alloy forging after liquid-cooling. This application, based on the cooling characteristics of different parts of the near-α type titanium alloy thick-section forging, adopts a reasonable combination of different cooling methods for heat treatment. Specifically, it combines air-cooling for a corresponding duration based on the equivalent diameter D of the maximum cross-section of the titanium alloy forging with liquid-cooling, thereby achieving uniform microstructure and properties of the near-α type titanium alloy forging. This significantly improves the non-uniformity of the forging's microstructure and properties, ensures the service performance of the forging, and expands the application of near-α type titanium alloy materials in aero-engines. The process is low in difficulty and highly operable.

Description

Technical Field

[0001] This invention relates to the field of metal processing technology, and in particular, to a processing method for improving the uniformity of microstructure and properties of near-α type titanium alloy forgings. Background Technology

[0002] Near-alpha titanium alloys can typically be used at higher temperatures, meeting the requirements of aerospace vehicles for lightweight, high-temperature, and high-strength materials, making them a key material in the aerospace field. To achieve good performance matching, it is necessary to precisely control the grain size, primary alpha phase volume fraction, alpha lath size, and arrangement morphology of these titanium alloy forgings. The most important control method is solution treatment in the two-phase region, with solution temperature, holding time, and cooling rate being the main control parameters.

[0003] However, near-α type titanium alloys have poor thermal conductivity. For forgings with large cross-sectional dimensions, the cooling rate near the surface is much higher than that in the core, resulting in inhomogeneity in the microstructure. Mechanically, this manifests as higher strength near the surface and lower strength in the core. To ensure that the core strength meets the required specifications, these thick-section forgings are typically cooled by oil or even water during solution treatment, which further exacerbates the inhomogeneity of microstructure and properties in different parts of the forging, affecting its service performance.

[0004] Therefore, it is necessary to optimize the solution treatment process for near-α type titanium alloy thick section forgings to improve the uniformity of microstructure and mechanical properties. Summary of the Invention

[0005] This application provides a preferred embodiment of a processing method to improve the uniformity of microstructure and properties of near-α type titanium alloy forgings, thereby solving the technical problem that the non-uniformity of microstructure and properties in different parts of the existing near-α type titanium alloy thick section forgings affects their service performance.

[0006] The technical solution adopted in this application is as follows:

[0007] A processing method for improving the uniformity of microstructure and properties of near-α type titanium alloy forgings includes the following steps:

[0008] S1. Heat the titanium alloy forgings at the set solution treatment temperature;

[0009] S2. After exiting the furnace, the above-mentioned titanium alloy forgings are air-cooled for a duration of t. FAC It is positively correlated with the equivalent diameter D of the maximum cross section of the titanium alloy forging;

[0010] S3. Immediately after air cooling, liquid cooling is applied to the titanium alloy forgings;

[0011] S4. After liquid cooling, the titanium alloy forgings are subjected to aging treatment.

[0012] Furthermore, the titanium alloy forgings include near-α type titanium alloys such as TA15, TA32, TA33, TA37, and TA38, which have poor hardenability and high requirements for microstructure.

[0013] Furthermore, the equivalent diameter D of the maximum cross-section of the titanium alloy forging is 60-120 mm.

[0014] Furthermore, when the titanium alloy forging is kept at a set solution temperature of 1022℃~1028℃, the holding time is 2h.

[0015] Furthermore, the duration of air cooling (t) FAC The calculation formula is:

[0016] t FAC = (0.6~0.7)×D

[0017] In the formula, the air cooling time t FAC The unit is s, and the unit of D is mm.

[0018] Furthermore, the liquid cooling is either oil cooling or water cooling.

[0019] Furthermore, the timeliness processing specifically includes:

[0020] After being heated to 650℃ and held at that temperature for 4 hours, the product is then air-cooled after being removed from the oven.

[0021] Compared with the prior art, this application has the following advantages:

[0022] This invention provides a processing method to improve the uniformity of microstructure and properties of near-α titanium alloy forgings. This method acknowledges and fully utilizes the inherent characteristic of poor hardenability in near-α titanium alloys. Based on the cooling characteristics of different parts of the thick-section near-α titanium alloy forging, different cooling methods are rationally combined for heat treatment. Specifically, the method involves first applying air cooling for a corresponding duration based on the equivalent diameter D of the maximum cross-section of the titanium alloy forging, followed by liquid cooling. This rational combination of cooling methods can ensure uniform microstructure and properties of the near-α titanium alloy forging, significantly improving the unevenness of the forging's microstructure and properties, ensuring the service performance of the forging, and expanding the application of near-α titanium alloy materials in aero-engines. The process is relatively simple and highly operable, which will promote a deeper understanding of heat treatment processes among industry professionals and contribute to technological progress in the industry.

[0023] In addition to the purposes, features, and advantages described above, this application provides other purposes, features, and advantages. The application will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0024] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0025] Figure 1 This is a schematic diagram of the cross-sectional morphology of the impeller forging according to a preferred embodiment of this application.

[0026] Figure 2 (a) and Figure 2 (b) are schematic diagrams showing the comparison of the microstructure of the edge and core of the forging in Comparative Example 2.

[0027] Figure 3 (a) and Figure 3 (b) are schematic diagrams showing the comparison of the microstructure of the forging edge and core in Embodiment 2 of this application. Detailed Implementation

[0028] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0029] This invention provides a processing method for improving the uniformity of microstructure and properties of near-α titanium alloy forgings. It is applicable to near-α titanium alloys such as TA15, TA32, TA33, TA37 (Ti150), and TA38, which have poor hardenability and require high-quality microstructure. The maximum equivalent diameter D of the forging cross-section is between 60 and 120 mm (see...). Figure 1 ).

[0030] The present invention will be further described in detail below through embodiments.

[0031] Comparative Example 1:

[0032] S1. Impeller forgings were prepared using TA37 (Ti150) alloy and subjected to solution treatment at a temperature of 1028℃. After heat treatment, the forgings were held at the temperature for 2 hours. The maximum equivalent diameter of the forging section was about 60 mm, and the alloy β transformation temperature was 1042℃.

[0033] S2. After being taken out of the furnace, it is transferred to an oil quenching tank for oil cooling;

[0034] S3. Then, an aging treatment is carried out, which involves heating the product through at 650℃ and holding it at that temperature for 4 hours. After removing it from the furnace, it is then air-cooled.

[0035] Example 1:

[0036] S1. The impeller forging was prepared using the same TA37 (Ti150) alloy as Comparative Example 1, and then heat-treated at a solution temperature of 1028℃ for 2 hours.

[0037] S2. Immediately after exiting the oven, transfer the product to the fan cooling zone for air cooling for 36-40 seconds.

[0038] S3, then it is transferred to a water tank for water cooling;

[0039] S4. Then, an aging treatment is carried out, which involves heating the product through at 650℃ and holding it at that temperature for 4 hours. After removing it from the furnace, it is then air-cooled.

[0040] Comparative Example 2:

[0041] S1. Impeller forgings were prepared using TA37 (Ti150) alloy and subjected to solution treatment at a temperature of 1022℃. After heat treatment, the forgings were held at the temperature for 2 hours. The maximum cross-sectional equivalent diameter of the forgings was approximately 90 mm, and the alloy β transformation temperature was 1042℃.

[0042] S2. After being taken out of the furnace, it is transferred to an oil quenching tank for oil cooling;

[0043] S3. Then, an aging treatment is carried out, which involves heating the product through at 650℃ and holding it at that temperature for 4 hours. After removing it from the furnace, it is then air-cooled.

[0044] Example 2:

[0045] S1. The impeller forging was prepared using the same TA37 (Ti150) alloy as in Comparative Example 2. After being thoroughly heated at a solution temperature of 1022℃, it was held at that temperature for 2 hours.

[0046] S2. Immediately after exiting the oven, transfer the product to the fan cooling zone for air cooling for 55-60 seconds.

[0047] S3, then transferred to an oil quenching tank for oil cooling;

[0048] S4. Then, an aging treatment is carried out, which involves heating the product through at 650℃ and holding it at that temperature for 4 hours. After removing it from the furnace, it is then air-cooled.

[0049] Comparative Example 3:

[0050] S1. Impeller forgings were prepared using TA33 alloy and subjected to solution treatment at a temperature of 1028℃. After heat treatment, the forgings were held at the temperature for 2 hours. The maximum equivalent diameter of the forging section was approximately 120 mm, and the alloy β transformation temperature was 1045℃.

[0051] S2. After being taken out of the oven, transfer it to a water tank for water cooling;

[0052] S3. Then, an aging treatment is carried out, which involves heating the product through at 650℃ and holding it at that temperature for 4 hours. After removing it from the furnace, it is then air-cooled.

[0053] Example 3:

[0054] S1. The impeller forgings made of the same TA33 alloy as Comparative Example 3 were heat-through at a solution temperature of 1028℃ and then held at that temperature for 2 hours.

[0055] S2. Immediately after exiting the oven, transfer the product to the fan cooling zone for air cooling for 75-80 seconds.

[0056] S3, then it is transferred to a water tank for water cooling;

[0057] S4. Then, an aging treatment is carried out, which involves heating the product through at 650℃ and holding it at that temperature for 4 hours. After removing it from the furnace, it is then air-cooled.

[0058] Radial tensile specimens were taken from the edge and core of the forgings of each comparative example and embodiment to test their tensile properties. The results are shown in Table 1. It can be seen that the performance difference between the edge and core of the embodiment is smaller.

[0059] Table 1: Mechanical properties of the core of forgings in comparative examples and embodiments

[0060]

[0061] like Figure 2 (a) Figure 2 (b) Figure 3 (a) Figure 3 As shown in (b), the metallographic structure of the forgings at different locations of Example 2 and Comparative Example 2 is compared. It can be seen that, compared with Comparative Example 2, the microstructure difference between the edge and the core of the forging in Example 2 of this application is smaller and the microstructure properties are more uniform. This significantly improves the uneven microstructure properties of the forging and ensures the service performance of the forging.

[0062] During the cooling process after solution treatment of near-α type titanium alloys, the microstructure characteristics are determined by the cooling stage after the alloy is cooled to 100-120°C below the phase transformation point. The microstructure of titanium alloys is formed during the solid-state phase transformation process, and the main phase transformation temperature range of near-α type titanium alloys is in this stage. The cooling rate in this stage will affect the arrangement and size of α laths in the β transformation structure, which is a very important control parameter in the heat treatment process.

[0063] The cooling rate of the core of a forging decreases with the increase of the cross-sectional size, while the cooling rate near the surface of the forging is most significantly affected by the cooling medium. For a specific forging, there is an upper limit to the cooling rate of the core, which is related to the cooling medium, and thus the required cooling medium after solution treatment can be determined.

[0064] This application utilizes the temperature difference between the surface and core of the forging, employing different cooling methods in stages. Immediately after exiting the furnace, air cooling is used to lower the near-surface temperature to 100°C–120°C below the phase transformation point, while the core temperature decreases only slightly. Subsequently, oil or water cooling is used to lower the core temperature to 100°C–120°C below the phase transformation point at the desired cooling rate. To achieve even smaller performance differences, it is necessary to reduce the difference in microstructure between the edge and core; therefore, the temperature of both the edge and core needs to be 100°C below the phase transformation point.

[0065] The cooling rate should be kept as uniform as possible within the range of ~120℃. Titanium alloys have poor thermal conductivity, so the core temperature does not decrease significantly as the surface temperature decreases; therefore, a step-by-step cooling control method can be adopted.

[0066] This application uses simulation and experimental methods to determine the cooling process and cooling rate at different locations in the forging under different cooling methods, and then determines the air cooling time after exiting the furnace, finally obtaining the aforementioned air cooling time t. FAC The calculation formula.

[0067] In summary, this invention provides a combined cooling method to improve the uniformity of microstructure and properties of thick-section titanium alloy forgings, thereby solving problems such as the inhomogeneity of the microstructure of forging blanks and the performance deviations of different parts of the forging, and improving the consistency of forging blank quality.

[0068] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0069] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A processing method for improving the uniformity of microstructure and properties of near-α type titanium alloy forgings, characterized in that, Including the following steps: S1. Heat the titanium alloy forgings at the set solution treatment temperature; S2. After exiting the furnace, the above-mentioned titanium alloy forgings are air-cooled for a duration of t. FAC It is positively correlated with the equivalent diameter D of the maximum cross section of the titanium alloy forging; S3. Immediately after air cooling, liquid cooling is applied to the titanium alloy forgings; S4. After liquid cooling, the titanium alloy forgings are subjected to aging treatment. When the titanium alloy forging is kept at a set solution temperature of 1022℃~1028℃, the holding time is 2 h. Air cooling duration (t) FAC The calculation formula is: t FAC =(0.6~0.7)×D; In the formula, the air cooling time t FAC The unit is s, and the unit of D is mm; The timeliness processing specifically includes: After being heated to 650℃ and held at that temperature for 4 hours, the product is then air-cooled after being removed from the oven.

2. The processing method for improving the uniformity of microstructure and properties of near-α type titanium alloy forgings according to claim 1, characterized in that, The titanium alloy forgings mentioned include near-α type titanium alloys such as TA15, TA32, TA33, TA37, and TA38, which have poor hardenability and high requirements for microstructure.

3. The processing method for improving the uniformity of microstructure and properties of near-α type titanium alloy forgings according to claim 1, characterized in that, The maximum equivalent diameter D of the titanium alloy forging is 60~120mm.

4. The processing method for improving the uniformity of microstructure and properties of near-α type titanium alloy forgings according to claim 1, characterized in that, The liquid cooling is either oil cooling or water cooling.

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