Forging process for improving flaw detection level of Ti2AlNb-based alloy large-size bar

Abstract

The invention provides a forging process for improving the flaw detection level of a Ti2AlNb-based alloy large-size bar, which comprises the following steps: 1) cogging and forging a cast ingot: heating to 1150-1200 DEG C to complete forging not lower than three-upsetting and three-drawing, and adopting a process of upsetting and drawing and long-time tempering for multiple times; (2) single-phase region forging is conducted, specifically, heating is conducted to 10-40 DEG C above the beta phase transformation point, forging not lower than four-upsetting and four-drawing is completed, and the multiple upsetting and drawing and short-time tempering technology is adopted; (3) low-temperature upsetting and drawing forging: heating to 80-30 DEG C below the beta phase transformation point to complete one-upsetting and one-drawing forging for 2-4 times, and (4) finished bar forging: heating to 80-30 DEG C below the beta phase transformation point to complete drawing forging. The Ti2AlNb-based alloy large-size bar prepared by the process is uniform in structure, good in flaw detection level, high in yield, short in production period and suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of titanium-based intermetallic compound processing, specifically involving a forging process to improve the flaw detection level of large-size Ti2AlNb-based alloy bars. Background Technology

[0002] Ti2AlNb-based alloys, as high-temperature lightweight structural materials with great application prospects, possess high specific strength, excellent thermal strength, and oxidation resistance. Their long-term service temperature can reach 750℃, breaking the thermal barrier temperature of traditional titanium alloys and potentially replacing nickel-based high-temperature alloys widely used in the aerospace field. However, compared to traditional titanium alloys, Ti2AlNb-based alloys have higher deformation resistance and lower specific heat capacity, leading to easy temperature rise during deformation in the two-phase region. Simultaneously, their intrinsic brittleness makes them prone to cracking during deformation in the two-phase region. Furthermore, the alloy has a high phase transformation point and is less prone to dynamic recrystallization during deformation in the β single-phase region, making β grain refinement difficult. For these reasons, it is difficult to improve the microstructure uniformity and flaw detection level of Ti2AlNb-based alloy bars, especially large-diameter bars, which greatly limits their practical engineering applications.

[0003] Currently, existing processes are insufficient for optimizing the microstructure uniformity and flaw detection level of Ti2AlNb-based alloy bars. The patent "Large-size Ti2AlNb Bars and Their Forging Methods and Applications" (Patent No.: CN202011560242.8) uses a three-dimensional reversal method to fully deform the core of the bar. However, this method easily leads to excessive cumulative differences in deformation between the core and edges, resulting in deterioration of microstructure uniformity. Furthermore, the beginning and end of the original ingot are easily confused during bar preparation, which does not meet the requirements for ingot head and tail calibration for military products. The patent "A Preparation Process for Large-Size Ti2AlNb-Based Alloy Bars with High Uniformity and Low Loss" (Patent No.: CN202210370245.8) uses a multiple upsetting and drawing process below the β phase region, which easily leads to coarsening of the α2 / O phase, similarly hindering microstructure uniformity control. In addition, this process involves numerous firings and a long production cycle, which is detrimental to improving production efficiency and cost control. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a forging process for improving the flaw detection level of large-diameter Ti2AlNb-based alloy bars. This method produces large-diameter bars that meet relevant technical requirements, exhibit good microstructure uniformity, and achieve a significantly higher flaw detection level than traditional processes. It is applicable to current flaw detection requirements for low impurity in Ti2AlNb forgings. The specific technical solution is as follows: A forging process for improving the flaw detection level of large-size Ti2AlNb-based alloy bars includes the following steps: Step 1): Forging the blank; The Ti2AlNb-based alloy ingot is heated to 1150~1200℃ and subjected to no less than three upsetting-drawing cycles of forging. The upsetting deformation is no less than 50%, the final forging temperature is no less than 850℃, and the ingot is air-cooled after forging. Step 2): Single-phase forging; Heat the billet to 10-40°C above the β phase transformation point, complete no less than four upsetting-drawing cycle forgings, with upsetting deformation not less than 50%, final forging temperature not less than 850°C, and air cooling after forging; Step 3): Low-temperature upsetting and forging; The billet is forged in 2 to 4 upsetting and drawing processes at 80 to 30°C below the β phase transformation point. The upsetting deformation is required to be no less than 40%, and the final forging temperature is no less than 750°C. After forging, the billet is air-cooled. Step 4): Forging of finished bar stock; The billet is heated to 80-30°C below the β phase transformation point to prepare the finished bar of the target size. The final forging temperature is not lower than 750°C. After forging, it is air-cooled and then machined to obtain the finished bar.

[0005] The preferred embodiment of the forging process for improving the flaw detection level of large-size Ti2AlNb-based alloy bars is as follows: In step 1), the Ti2AlNb-based alloy ingot is heated to 1150~1200℃, and the total holding time at the heating temperature is required to be no less than 15 hours. The deformation adopts a multiple "deformation + long tempering" process. This process can destroy the coarse as-cast structure of the alloy while fully promoting element diffusion through deformation-induced distortion, which is beneficial to improving the uniformity of the alloy structure.

[0006] The preferred embodiment of the forging process for improving the flaw detection level of large-size Ti2AlNb-based alloy bars is as follows: In step 2), the β single-phase region forging employs a multiple "deformation + short-time tempering" process. The tempering holding time is 15-30 minutes, and the tempering temperature is reduced by 5-15°C each time. Furthermore, the final deformation involves at least two consecutive upsetting and two drawing operations. Tempering promotes the static recrystallization of the alloy, fully refining the β grains, while controlling the tempering time and temperature inhibits the growth of recrystallized grains.

[0007] The preferred embodiment of the forging process for improving the flaw detection level of large-size Ti2AlNb-based alloy bars is as follows: In step 3), the bar billet is upsetting and drawing using a shaft upsetting and side upsetting method, with an upsetting deformation rate not exceeding 0.02 s. -1 The drawing process is carried out in multiple stages, with each stage involving a deformation of less than 25%. Excessive deformation during drawing can easily cause external surface cracks or internal core cracks in the bar. Selecting an appropriate deformation amount can effectively improve the surface quality of the forged bar and enhance the bar's flaw detection capabilities.

[0008] The preferred embodiment of the forging process for improving the flaw detection level of large-size Ti2AlNb-based alloy bars is as follows: In step 4), the elongation deformation of the finished product is required to be less than 25%, and the single elongation deformation should not be too large, so as to avoid cracks in the bar and reduce its flaw detection level. At the same time, it can reduce the amount of machining and grinding and improve the yield.

[0009] The preferred embodiment of the forging process for improving the flaw detection level of large-size Ti2AlNb-based alloy bars is that the Ti2AlNb alloy bars prepared by this process have a diameter of 300~400mm, and the content of the axial primary α2 / O phase is uniformly distributed in the high-magnification microstructure. Manual half-path ultrasonic flaw detection is performed along the diameter direction using a Φ2.0 flat-bottom hole, and the clutter level is lower than -9dB.

[0010] Compared with the prior art, the present invention has the following advantages and beneficial effects: The ingot forging process employs multiple upsetting and drawing processes followed by long-term tempering, which can simultaneously achieve homogenization. The large deformation forging method breaks up the as-cast structure and causes significant distortion within the alloy, effectively promoting element diffusion and facilitating the control of structural uniformity.

[0011] Single-phase forging employs a multi-stage upsetting and drawing process followed by short-time tempering, which promotes static recrystallization of the alloy and further refines the β grains. Furthermore, progressively decreasing the tempering temperature helps suppress rapid β grain growth.

[0012] Strict control of the single-drawing deformation during two-phase forging and finished bar forging can effectively avoid damage such as cracks in the bars, improve the surface quality of the bars, reduce machining losses, and increase the yield.

[0013] 4) Ti2AlNb alloy rods with diameters of 300~400mm prepared using this process have uniform distribution of axial α2 / O phases in high magnification microstructure, and the clutter level of manual half-path flaw detection using a Φ2.0 flat-bottom hole along the diameter direction is less than -9dB.

[0014] The large-size Ti2AlNb-based alloy bars prepared using this patented process exhibit good microstructure uniformity, low levels of flaw detection noise, high yield, and short production cycle, making them suitable for industrial production. Attached Figure Description

[0015] Figure 1 This is a high-magnification microstructure photograph of the Ti2AlNb alloy rod in Example 1; Figure 2 This is a high-magnification microstructure photograph of the Ti2AlNb alloy rod in Example 2. Detailed Implementation

[0016] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Those skilled in the art can make appropriate adjustments without departing from the spirit of the invention. The following embodiments illustrate the present invention in more detail, but do not limit the present invention in any way. The specific preparation process of the bar material is as follows: Example 1

[0017] The ingot dimensions of the Ti2AlNb-based alloy are Ф345×1475mm, and the chemical composition is Ti-22.3Al-24.2Nb-0.51Mo. The alloy's T... β The phase transformation point is 1060℃. The specific forging process for the bar stock is as follows: Step 1): Heat the ingot to 1160℃ using a resistance wire heating furnace. The total holding time for this heat treatment is 20 hours, completing a total of five upsetting and five drawing forging processes. The specific operation is as follows: Heat the ingot to 1160℃ and hold for 6 hours, then remove it from the furnace and shape it to Ф460×820, with a final forging temperature of 890℃; return the hot material to the furnace and hold for 2 hours, upsetting to ФD×370 with a deformation of 55% at an upsetting reduction rate of 60mm / s, drawing it to a square shape of 420×L, then turning it into an octagonal shape of 450×814, with a final forging temperature of 900℃; return the hot material to the furnace and hold for 3 hours, upsetting to an octagonal shape of D×365 with a deformation of 55% at an upsetting reduction rate of 60mm / s, then drawing it to a square shape of 420×L, then turning it into an octagonal shape of 450×814, and finally forging... The temperature was 915℃; the hot material was returned to the furnace and held for 3 hours, then upset to an octagonal D×365 with a deformation of 55%, an upsetting rate of 60mm / s, drawn to a square 420×L, and then turned into an octagonal 450×814, with a final forging temperature of 910℃; the hot material was returned to the furnace and held for 3 hours, then upset to an octagonal D×365 with a deformation of 55%, an upsetting rate of 60mm / s, drawn to a square 420×L, and then turned into an octagonal 450×814, with a final forging temperature of 905℃; the hot material was returned to the furnace and held for 3 hours, then upset to an octagonal D×365 with a deformation of 55%, an upsetting rate of 60mm / s, drawn to a square 420×L, and then turned into an octagonal 430×890, with a final forging temperature of 920℃, and then air-cooled after forging; Step 2): Heat the billet to 1100℃ using a resistance wire heating furnace. This furnace operation involves four upsetting and four drawing operations. Specifically: The billet is heated to 1100℃ and held for 350 minutes. It is then upset to an octagonal D×400 with a deformation of 55%, at an upsetting rate of 60mm / s. It is then drawn to an octagonal 420×L, and finally octagonalized to 450×814, with a final forging temperature of 880℃. The hot billet is then returned to the furnace for reheating to 1090℃ and held for 15 minutes. It is then upset to an octagonal D×365 with a deformation of 55%, at an upsetting rate of 60mm / s. It is then drawn to an octagonal 420×L, and finally octagonalized to 450×814, with a final forging temperature of 875℃. Finally, the hot billet is returned to the furnace for reheating to 1080℃ and held for 15 minutes. n, upset to octagonal D×365, deformation 55%, upset reduction rate 60mm / s, drawn to square 420×L, turned octagonal to 450×814, upset to octagonal D×365, deformation 55%, upset reduction rate 60mm / s, drawn to square 420×L, turned octagonal to 430×890, final forging temperature 865℃, air cooled after forging; Step 3): Heat the billet to 1000℃ using a resistance wire heating furnace, hold for 360 minutes, and then remove it from the furnace for one upsetting and one drawing forging. The specific operation is as follows: upsetting to an octagonal D×535, deformation amount 40%, upsetting reduction rate 0.018s. -1 Pour the forging material into an octagonal shape to 500×L, then into an octagonal shape to 450×814. The final forging temperature is 825℃, and the forging is then air-cooled. Step 4): Repeat step 3), with the final forging temperature at 805℃; Step 5): Repeat step 3), with the final forging temperature at 815℃; Step 6): Repeat step 3), with the final forging temperature at 805℃; Step 7): Heat the billet to 1000℃ using a resistance wire heating furnace, hold it at that temperature for 360 minutes, and then remove it from the furnace for drawing and forging of the finished bar. The specific operation is as follows: draw it to an octagonal 410×L, roll it to Φ410×L, with the drawing deformation amount between 15% and 20%, and then machine it to obtain a Φ400 bar.

[0018] Conclusion: The microstructure of the bar prepared in Example 1 is a two-phase processed microstructure. The isometric α² / O content is uniformly distributed in the high-magnification microstructure. The clutter level during manual half-path acoustic testing along the diameter direction using a Φ2.0 flat-bottom hole is -12 dB. The Ti₂AlNb-based alloy bar prepared in this example exhibits excellent room-temperature and high-temperature tensile properties after solution treatment and aging, as shown in Table 1. Table 1. Room temperature and high temperature tensile properties of Ti2AlNb alloy rods prepared in Example 1

[0019] Example 2

[0020] The ingot size for the Ti2AlNb-based alloy casting is Ф345×1450mm, with a chemical composition of Ti-21.8Al-24.5Nb-0.52Mo. The alloy's T... β The phase transformation point is 1055℃. The specific forging process for preparing bars from ingots is as follows: Step 1): Heat the ingot to 1160℃ using a resistance wire heating furnace. The total holding time for this heating cycle is 17 hours, completing four upsetting and four drawing operations. The specific operation is as follows: Heat the ingot to 1160℃ and hold for 6 hours, then remove it from the furnace and shape it to Ф455×820, with a final forging temperature of 885℃; return the hot material to the furnace and hold for 2 hours, upsetting to ФD×370 with a deformation of 55% and an upsetting pressing rate of 55mm / s, drawing it to a square shape of 420×L, then to an octagonal shape of 450×797, with a final forging temperature of 920℃; return the hot material to the furnace and hold for 3 hours, upsetting to an octagonal shape of D×360 with a deformation of 55%, then to an upsetting pressing rate of 55mm / s. The forging speed is 55 mm / s, drawn to a square shape of 420×L, then turned into an octagonal shape of 450×797, with a final forging temperature of 910℃; the hot material is returned to the furnace and held for 3 hours, then upset to an octagonal shape of D×365 with a deformation of 55%, the upset speed is 55 mm / s, drawn to a square shape of 420×L, then turned into an octagonal shape of 450×814, with a final forging temperature of 900℃; the hot material is returned to the furnace and held for 3 hours, then upset to an octagonal shape of D×360 with a deformation of 55%, the upset speed is 55 mm / s, drawn to a square shape of 420×L, then turned into an octagonal shape of 430×873, with a final forging temperature of 905℃, and then air-cooled after forging; Step 2): Heat the billet to 1080℃ using a resistance wire heating furnace. This process involves three upsetting and three drawing operations. Specifically: heat the billet to 1080℃ and hold for 350 minutes; upset to an octagonal D×390 with a deformation of 55% at an upsetting rate of 55mm / s; then draw to a square length of 420×L. The forging process involves re-forging the material to 450×797 in an octagonal shape, with a final forging temperature of 895℃. The hot material is then returned to the furnace for reheating to 1070℃ and held for 20 minutes. The material is then upset to 360 mm with a deformation of 55% and an upsetting rate of 55 mm / s. It is then drawn to a square shape of 420×L, re-forged to 450×797 in an octagonal shape, upset to an octagonal shape of D×360 with a deformation of 55% and an upsetting rate of 55 mm / s. It is then drawn to a square shape of 420×L, re-forged to 430×873 in an octagonal shape, with a final forging temperature of 855℃. The material is then air-cooled after forging. Step 3): Heat the billet to 980℃ using a resistance wire heating furnace, hold for 360 minutes, and then remove it from the furnace for one upsetting and one drawing forging. The specific operation is as follows: upsetting to an octagonal D×480, deformation amount 40%, upsetting reduction rate 0.015s. -1 The forging process involves drawing the material to a square shape of 420×L, then turning it into an octagonal shape to 450×797. The final forging temperature is 785℃, followed by air cooling.

[0021] Step 4): Repeat step 3), with the final forging temperature at 792℃; Step 5): Heat the billet to 980℃ using a resistance wire heating furnace, hold for 360 minutes, and then remove it from the furnace for drawing and forging of the finished bar. The specific operation is as follows: draw to 410×L octagon, draw to 380×L octagon, draw to 350×L octagon, draw to 320×L octagon, roll to Φ315×L, control the deformation amount of each drawing to 15%~20%, and then machine to obtain a Φ300mm bar.

[0022] Conclusion: The microstructure of the bar prepared in Example 2 is a two-phase processed microstructure. At high magnification, isometric α2 / O particles are uniformly distributed. The clutter level during manual full-path flaw detection using a Φ1.2 flat-bottom hole along the diameter direction is -9 dB. The Ti2AlNb-based alloy bar prepared in this example exhibits excellent room-temperature and high-temperature tensile properties after solution treatment and aging, as shown in Table 2. Table 2. Room temperature and high temperature tensile properties of the Ti2AlNb-based alloy rods prepared in Example 2

[0023] Matters not covered in this invention are common knowledge.

[0024] The above describes some implementation examples of the present invention, which are quite specific. Within the scope of the technical concept of the present invention, various modifications can be made to the technical solution of the present invention. These modifications all fall within the protection scope of the present invention.

Claims

1. A forging process for improving the flaw detection level of large-size Ti2AlNb-based alloy bars, characterized in that, Includes the following steps: Step 1): Forging the blank; The Ti2AlNb-based alloy ingot is heated to 1150~1200℃ and subjected to no less than three upsetting-drawing cycles of forging. The upsetting deformation is no less than 50%, the final forging temperature is no less than 850℃, and the ingot is air-cooled after forging. Step 2): Single-phase forging; Heat the billet to 10-40°C above the β phase transformation point, complete no less than four upsetting-drawing cycle forgings, with upsetting deformation not less than 50%, final forging temperature not less than 850°C, and air cooling after forging; Step 3): Low-temperature upsetting and forging; The billet is subjected to 2 to 4 upsetting and drawing forging processes at 80 to 30°C below the β phase transformation point. The upsetting deformation is not less than 40%, the final forging temperature is not less than 750°C, and the billet is air-cooled after forging. Step 4): Forging of finished bar stock; The billet is heated to 80~30℃ below the β phase transformation point, and then drawn and forged to the target size bar. The final forging temperature is not lower than 750℃. After forging, it is air-cooled and then machined to obtain the finished bar.

2. A forging process for improving the flaw detection level of large-size Ti2AlNb alloy bars according to claim 1, characterized in that: In step 1), the total holding time of the Ti2AlNb alloy ingot at 1150~1200℃ is not less than 15h, and the forging process adopts multiple "upsetting and drawing + long tempering" processes, with each tempering time not less than 3h.

3. A forging process for improving the flaw detection level of large-size Ti2AlNb alloy bars according to claim 1, characterized in that: In step 2), the β single-phase region forging adopts a multiple "upsetting and drawing + short-time tempering" process. The holding time for each tempering is 15~30 minutes, and the tempering temperature is reduced by 5~15℃ each time. The last deformation involves at least two consecutive upsetting-drawing cycles.

4. A forging process for improving the flaw detection level of large-size Ti2AlNb-based alloy bars according to claim 1, characterized in that: In step 3), the two-phase region forging is performed using a shaft upsetting and side-drawing method, with an upsetting deformation rate not exceeding 0.02 s. -1 The elongation is completed in multiple stages, with the deformation amount of each elongation being less than 25%.

5. A forging process for improving the flaw detection level of large-size Ti2AlNb-based alloy bars according to claim 1, characterized in that: In step 4), the single drawing deformation of the finished product is less than 25%.

6. A forging process for improving the flaw detection level of large-size Ti2AlNb-based alloy bars according to claim 1, characterized in that: The Ti2AlNb-based alloy rods prepared by this process have a diameter of 300~400mm. The isometric α2 / O phase is evenly distributed in the high-magnification structure of the forged state. When manual half-path ultrasonic testing is performed along the diameter direction using a Φ2.0 flat-bottom hole, the clutter level is below -9dB.

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