Forging method of ti5331 titanium alloy large-size bar

Abstract

This invention discloses a forging method for large-size Ti5331 titanium alloy bars, specifically implemented according to the following steps: A 2-5 ton Ti5331 titanium alloy large-size ingot is subjected to 1-2 forging passes to obtain intermediate forging billet A; intermediate forging billet A is subjected to 2-4 forging passes from below to above the phase transformation point in a single or multiple cycle forging to obtain intermediate forging billet B; intermediate forging billet B is subjected to 2-5 forging passes below the phase transformation point in upsetting or drawing forging to obtain intermediate forging billet C; intermediate forging billet C is subjected to 1-3 forging passes to obtain the finished bar. By controlling the forging temperature and forging deformation method, the produced large-size Ti5331 alloy bars exhibit a uniform and fine microstructure at low magnification and sufficient equiaxed microstructure at high magnification. This forging method can reduce the grain size of the titanium alloy billet material and improve the uniformity of the microstructure. The bar preparation requires fewer forging passes, has a shorter process, consumes less energy, and can meet the requirements of large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy processing technology, specifically relating to a forging method for large-diameter Ti5331 titanium alloy bars. Background Technology

[0002] As nuclear reactors develop towards new directions such as fusion-fission hybridization, miniaturization of marine power reactors, and modularization, the reliability of nuclear reactor units and components, as well as the rational selection and utilization of structural materials, also face requirements such as high strength, corrosion resistance, lightweight, and low activity.

[0003] Titanium alloys, due to their superior high specific strength, excellent resistance to seawater corrosion, and excellent neutron radiation attenuation properties, are gradually replacing traditional low-carbon stainless steel and are increasingly being used in the shells of small and medium-power nuclear reactors. Ti5331 titanium alloy is a near-alpha type titanium alloy with excellent comprehensive properties, with a nominal composition of Ti-5Al-3V-3Zr-1Cr. This alloy possesses excellent mechanical properties, corrosion resistance, and radiation resistance, and has broad application prospects in the field of nuclear reactor shell materials.

[0004] Ti5331 alloy can be used to manufacture large nuclear reactor components. Due to the large size of these components and their need for long-term operation under strong radiation and high chemical activity, ensuring reliability during service requires the preparation of large-diameter Ti5331 titanium alloy bars with uniform microstructure. These bars will serve as the raw material for subsequent processing to produce qualified forgings. However, this process is challenging because Ti5331 is a novel titanium alloy with no traditional processing methods to follow. Furthermore, the increased size of the bars presents significant difficulties in grain refinement and microstructure control. Summary of the Invention

[0005] The purpose of this invention is to provide a forging method for large-size Ti5331 titanium alloy bars, which can produce large-size alloy bars with uniform and fine microstructure and dimensions of Φ300mm to Φ500mm.

[0006] The technical solution adopted in this invention is a forging method for large-size Ti5331 titanium alloy bars, specifically as follows:

[0007] Step 1: Perform 1-2 forging processes on large-scale Ti5331 titanium alloy ingots of 2-6 tons to obtain intermediate forging billet A with a cuboid structure of 690mm-780mm in length and 530mm-780mm in width;

[0008] Step 2: Perform 2 to 4 cycles of single or multiple cycles of forging from the lower to the upper phase transformation point on the intermediate forging billet A to obtain a cuboid intermediate forging billet B with a length of 600 mm to 700 mm and a width of 500 mm to 570 mm.

[0009] Step 3: Perform upsetting or drawing forging at the phase transformation point on the intermediate forging billet B for 2 to 5 heats to obtain an octagonal intermediate forging billet C with a diameter of 520 mm to 540 mm.

[0010] Step 4: Perform 1 to 3 forging processes on the intermediate forging billet C to obtain finished bars with dimensions of Φ300mm to Φ510mm.

[0011] The invention is further characterized by:

[0012] Step 1 is as follows: A high-speed forging mill is used to saw 2-6 ton Ti5331 titanium alloy ingots with a diameter of Φ610mm~Φ890mm, resulting in a single ingot weight of 1400-3100kg. After sawing, the ingots are held at 1170℃ for 450-540 minutes. After exiting the furnace, they are repeatedly upsetting and drawing forging, with a cumulative forging ratio of 3.0-5.1. They are then held at 1080℃ and forged again, with a cumulative forging ratio of 3.3-5.0. One to two more forging cycles are then performed, with each cycle starting at a temperature 50℃-200℃ above the β phase transformation point and ending at a temperature 20℃-150℃ below the β phase transformation point. Each cycle involves 2-3 upsetting and drawing operations, resulting in an intermediate forging billet A with a rectangular structure of 690mm-780mm in length and 530mm-780mm in width.

[0013] In step 1, the forging ratio per firing is controlled between 3.0 and 6.0.

[0014] In step 2, during the single or multiple cycles of forging of the intermediate forging billet A from below to above the phase transformation point in 2 to 4 heats, low-high heating and repeated upsetting are used for 2 to 4 heats. In the two-phase zone forging, the initial forging temperature of each heat below the phase transformation point is 40℃ to 100℃ below the β phase transformation point, and the final forging temperature is 100℃ to 200℃ below the β phase transformation point. In the single-phase zone forging, the initial forging temperature of each heat is 30℃ to 80℃ above the β phase transformation point, and the final forging temperature is 50℃ to 100℃ below the β phase transformation point.

[0015] In step 2, the forging ratio for each firing is controlled between 1.5 and 3.0.

[0016] The parameters for upsetting or drawing forging at the phase transformation point in step 3 (2-5 heats) are as follows: the initial forging temperature for each heat is 30℃ to 100℃ below the β phase transformation point, and the final forging temperature is 100℃ to 250℃ below the β phase transformation point.

[0017] In step 3, the forging ratio per firing is controlled between 1.2 and 8.

[0018] Step 4 is as follows: The intermediate forging billet C is forged in 1 to 3 passes using a high-speed forging machine. The initial forging temperature of each forging is 50°C to 100°C below the β phase transformation point, and the final forging temperature is 100°C to 200°C below the phase transformation point.

[0019] In step 4, the cumulative forging ratio is controlled between 1.2 and 3.

[0020] The beneficial effects of this invention are:

[0021] This invention discloses a forging method for large-size Ti5531 titanium alloy bars. By controlling the forging temperature and deformation method, the produced large-size Ti5531 alloy bars exhibit a uniform and fine microstructure at low magnification and a fully equiaxed microstructure at high magnification. This forging method reduces the grain size of the titanium alloy billet and improves the uniformity of the microstructure. The bar preparation process requires fewer forging passes, is shorter, consumes less energy, and can meet the requirements of large-scale industrial production. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of temperature changes during the forging process of Ti5331 titanium alloy bars in this invention.

[0023] Figure 2 This is a schematic diagram of the Ti5331 titanium alloy bar used in this invention;

[0024] Figure 3(a) is a low-magnification microstructure diagram of the head of a bar in Embodiment 1 of the present invention;

[0025] Figure 3(b) is a low-magnification microstructure diagram of the tail section of a bar according to Embodiment 1 of the present invention;

[0026] Figure 4(a) is a high-magnification microstructure diagram of the head D / 4 of a bar in Embodiment 1 of the present invention;

[0027] Figure 4(b) is a high-magnification microstructure diagram of the tail section D / 4 of a bar according to Embodiment 1 of the present invention;

[0028] Figure 5(a) is a low-magnification microstructure diagram of the head of the bar in Embodiment 2 of the present invention;

[0029] Figure 5(b) is a low-magnification microstructure diagram of the tail section of the bar in Embodiment 2 of the present invention;

[0030] Figure 6(a) is a high-magnification microstructure diagram of the head D / 4 of the bar in Embodiment 2 of the present invention;

[0031] Figure 6(b) is a high-magnification microstructure diagram of the tail section (D / 4) of the bar in Embodiment 2 of the present invention;

[0032] Figure 7(a) is a low-magnification microstructure diagram of the head of the bar in Embodiment 3 of the present invention;

[0033] Figure 7(b) is a low-magnification microstructure diagram of the tail section of the bar in Embodiment 3 of the present invention;

[0034] Figure 8(a) is a high-magnification microstructure diagram of the head D / 4 of the bar in Embodiment 3 of the present invention;

[0035] Figure 8(b) is a high-magnification microstructure diagram of the tail section (D / 4) of the bar in Embodiment 3 of the present invention. Detailed Implementation

[0036] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0037] The forging method for large-diameter Ti5331 titanium alloy bars of the present invention is as follows:

[0038] Step 1: Perform 1-2 forging passes on large-sized Ti5331 titanium alloy ingots of 2-6 tons to obtain intermediate forging billet A with a rectangular structure of 690mm-780mm in length and 530mm-780mm in width. Specifically, the 2-6 ton Ti5331 titanium alloy ingots with a diameter of Φ610mm-Φ890mm are sawn using a high-speed forging mill, resulting in a single weight of 1400-3100kg. After sawing, the ingots are held at 1170℃ for 450-540 minutes, and then repeatedly upsetting and... The forging process involves drawing the billet, with a cumulative forging ratio of 3.0 to 5.1. The billet is then held at 1080℃ and forged again, with a cumulative forging ratio of 3.3 to 5.0. The billet is then forged 1 to 2 more times, with the initial forging temperature of each forging being 50℃ to 200℃ above the β phase transformation point and the final forging temperature being 20℃ to 150℃ below the β phase transformation point. Each forging process involves 2 to 3 upsetting and drawing operations, with the forging ratio controlled between 3 and 6. This process yields an intermediate forging billet A with a rectangular structure that is 690mm to 780mm long and 530mm to 780mm wide.

[0039] Step 2: Perform 2-4 cycles of forging on the intermediate forging billet A, either single or multiple cycles, from below the phase transformation point to above the phase transformation point. Use low-to-high heating and repeated upsetting for 2-4 cycles. For two-phase forging, the initial forging temperature for each cycle below the phase transformation point is 40℃-100℃ below the β phase transformation point, and the final forging temperature is 100℃-200℃ below the β phase transformation point. For single-phase forging, the initial forging temperature for each cycle is 30℃-80℃ above the β phase transformation point, and the final forging temperature is 50℃-100℃ below the β phase transformation point. The forging ratio for each cycle is controlled between 1.5 and 3.0. This yields a rectangular intermediate forging billet B with a length of 600mm-700mm and a width of 500mm-570mm.

[0040] Step 3: Perform upsetting or drawing forging on the intermediate forging billet B at the phase transformation point for 2 to 5 passes. The parameters are as follows: the initial forging temperature for each pass is 30℃ to 100℃ below the β phase transformation point, and the final forging temperature is 100℃ to 250℃ below the β phase transformation point. The forging ratio for each pass is controlled between 1.2 and 8, resulting in an octagonal intermediate forging billet C with a diameter of 520mm to 540mm.

[0041] Step 4: Perform 1-3 forging passes on the intermediate forging billet C. The specific process is as follows: Use a high-speed forging machine to perform 1-3 forging passes on the intermediate forging billet C. The initial forging temperature of each forging pass is 50℃-100℃ below the β phase transformation point, and the final forging temperature is 100℃-200℃ below the phase transformation point. The cumulative forging ratio is controlled between 1.2 and 3 to obtain finished bars with dimensions of Φ300mm-Φ510mm.

[0042] The present invention discloses a forging method for large-diameter Ti5331 titanium alloy bars, wherein the temperature change is as follows: Figure 1 As shown, large-scale Ti5331 titanium alloy ingots of 2-5 tons are forged in 1-2 forging cycles, and the selected bar stock is as follows. Figure 2 As shown, by adjusting the deformation amount and mode of the β phase, the large grains in the as-cast state are fully broken up. The forged billet after initial forging undergoes 2-4 cycles of single or multiple forging cycles between the phase transformation point and the phase transformation point, resulting in rapid, thorough, and uniform refinement of the forged billet's microstructure. Subsequently, the intermediate billet undergoes continuous reflow forging during forging, ensuring consistent forging temperatures at all stages of the process, and continuous cross-section transformation forging ensures uniform deformation and thorough microstructural breakage throughout the material. During the final forging of the intermediate billet, strict control of the forging temperature, deformation rate, and deformation amount is employed to shape the material into a round bar, ensuring compliance with dimensional deviations.

[0043] Example 1

[0044] The forging method for large-diameter Ti5331 titanium alloy bars of the present invention is implemented according to the following steps:

[0045] Step 1: Using a high-speed forging machine, a 4-ton Ti5331 titanium alloy ingot with a diameter of 690mm is sawn to a weight of 2100kg. After sawing, the ingot is held at 1170℃ for 450min. After exiting the furnace, it is forged by repeated upsetting and drawing, with a cumulative forging ratio of 3.02. Then, it is held at 1080℃ and forged again, with a cumulative forging ratio of 3.32. Then, it is forged again in one heat. The initial forging temperature of each heat is 100℃ above the β phase transformation point, and the final forging temperature is 20℃ below the β phase transformation point. Each heat is forged to complete 2 upsetting and drawing, with a forging ratio of 5 per heat. The resulting intermediate forging billet A has a square cross section with a side length of 780mm.

[0046] Step 2: Perform two cycles of forging on the intermediate forging billet A, either single or multiple cycles, from below the phase transformation point to above the phase transformation point. Use low-high heating and repeated upsetting and drawing. For the two-phase zone forging, the initial forging temperature for each cycle below the phase transformation point is 50°C below the β phase transformation point, and the final forging temperature is 120°C below the β phase transformation point, with a forging ratio of 1.67 per cycle. For the single-phase zone forging, the initial forging temperature for each cycle is 50°C above the β phase transformation point, and the final forging temperature is 90°C below the β phase transformation point, with a forging ratio of 1.78 per cycle. This yields a rectangular intermediate forging billet B with a length of 700mm and a width of 570mm.

[0047] Step 3: Perform upsetting or drawing forging of the intermediate forging billet B in two passes at the phase transformation point. The parameters are as follows: the initial forging temperature of each pass is 70°C below the β phase transformation point, and the final forging temperature is 130°C below the β phase transformation point. The first forging ratio is 7.8, and the second forging ratio is 7.3, to obtain a 530mm octagonal intermediate forging billet C.

[0048] Step 4: Use a high-speed forging mill to perform one-time forming forging on the intermediate forging billet C. The initial forging temperature of each forming forging is 60℃ below the β phase transformation point, and the final forging temperature is 160℃ below the phase transformation point. The cumulative forging ratio is 1.5, and a finished bar with a size of Φ510mm is obtained.

[0049] The microstructure of the large-diameter Ti5331 titanium alloy bars processed according to this embodiment is shown in Figures 3(a), 3(b), 4(a), and 4(b).

[0050] The microstructure of the large-diameter Ti5331 titanium alloy bars processed in this embodiment is shown in Figures 3(a), 3(b), 4(a), and 4(b).

[0051] As shown in Figures 3(a) and 3(b), the low-magnification microstructure of the Ti5331 titanium alloy bar processed in this embodiment is uniformly blurred.

[0052] As shown in Figures 4(a) and 4(b), the Ti5331 titanium alloy processed in this embodiment has good primary phase isoaxialization, sufficient microstructure fragmentation, and uniform distribution.

[0053] Example 2

[0054] The forging method for large-diameter Ti5331 titanium alloy bars of the present invention is implemented according to the following steps:

[0055] Step 1: Using a high-speed forging machine, a 3-ton Ti5331 titanium alloy ingot with a diameter of 610mm was sawn to a weight of 1400kg. After sawing, the ingot was held at 1170℃ for 450min. After being taken out of the furnace, it was forged by repeated upsetting and drawing, with a cumulative forging ratio of 3.48. Then, it was held at 1080℃ and forged again, with a cumulative forging ratio of 4.22. Two forging cycles were performed again, with the initial forging temperature of each cycle being 150℃ above the β phase transformation point and the final forging temperature being 30℃ below the β phase transformation point. Each forging cycle completed two upsetting and drawing cycles, with a forging ratio of 4.21 per cycle. The resulting intermediate forging billet A had a square cross section with a side length of 690mm.

[0056] Step 2: Perform two-cycle forging of the intermediate forging billet A, either single-cycle or multi-cycle, between the phase transformation point and the phase transformation point. Use low-high heating and repeated upsetting for the two-cycle forging. In the two-phase forging, the initial forging temperature for each cycle below the phase transformation point is 60°C below the β phase transformation point, and the final forging temperature is 110°C below the β phase transformation point, with a forging ratio of 1.86 per cycle. In the single-phase forging, the initial forging temperature for each cycle is 40°C above the β phase transformation point, and the final forging temperature is 80°C below the β phase transformation point, with a forging ratio of 1.92 per cycle. This yields a rectangular intermediate forging billet B with a length of 610mm and a width of 500mm.

[0057] Step 3: Perform upsetting or drawing forging on the intermediate forging billet B in two passes at the phase transformation point. The parameters are as follows: the initial forging temperature for each pass is 65°C below the β phase transformation point, and the final forging temperature is 150°C below the β phase transformation point. The forging ratio for the first pass is 7.4, and the ratio for the second pass is 7.1, resulting in an octagonal intermediate forging billet C with a diameter of 530 mm.

[0058] Step 4: Use a high-speed forging machine to perform one-time forming forging on the intermediate forging billet C. The initial forging temperature of each forming forging is 60℃ below the β phase transformation point, and the final forging temperature is 120℃ below the phase transformation point. The cumulative forging ratio is 1.5, and a finished bar with a size of Φ510mm is obtained.

[0059] The microstructure of the large-diameter Ti5331 titanium alloy bars processed in this embodiment is shown in Figures 5(a), 5(b), 6(a), and 6(b).

[0060] As shown in Figures 5(a) and 5(b), the Ti5331 titanium alloy rod processed in this embodiment has a uniform and blurred low-magnification microstructure.

[0061] As shown in Figures 6(a) and 6(b), the Ti5331 titanium alloy processed in this embodiment has a good degree of equiaxed primary phase, sufficient fragmentation, and uniform distribution.

[0062] Example 3

[0063] The forging method for large-diameter Ti5331 titanium alloy bars of the present invention is implemented according to the following steps:

[0064] Step 1: Using a high-speed forging machine, a 6-ton Ti5331 titanium alloy ingot with a diameter of 890mm was sawn to a weight of 3100kg. After sawing, the ingot was held at 1170℃ for 540min. After being taken out of the furnace, it was forged by repeated upsetting and drawing, with a cumulative forging ratio of 5.06. Then, it was held at 1080℃ and forged again, with a cumulative forging ratio of 4.98. Then, it was forged again in one heat. The initial forging temperature of each heat was 150℃ above the β phase transformation point, and the final forging temperature was 30℃ below the β phase transformation point. Each heat was forged to complete 3 upsetting and drawing, and the forging ratio of each heat was controlled at 4.02, resulting in an intermediate forging billet A with a rectangular structure of 700mm in length and 530mm in width.

[0065] Step 2: Perform two-cycle forging of the intermediate forging billet A, either single-cycle or multi-cycle, between the phase transformation point and the phase transformation point. Use low-high heating and repeated upsetting for the two-cycle forging. In the two-phase forging, the initial forging temperature for each cycle below the phase transformation point is 50°C below the β phase transformation point, and the final forging temperature is 160°C below the β phase transformation point, with a forging ratio of 2.83 per cycle. In the single-phase forging, the initial forging temperature for each cycle is 40°C above the β phase transformation point, and the final forging temperature is 50°C below the β phase transformation point; the forging ratio per cycle is 2.57. This yields a rectangular intermediate forging billet B with a length of 700mm and a width of 530mm.

[0066] Step 3: Perform upsetting or drawing forging on the intermediate forging billet B in two passes at the phase transformation point. The parameters are as follows: the initial forging temperature for each pass is 60°C below the β phase transformation point, and the final forging temperature for each pass is 120°C below the β phase transformation point; the forging ratio for the first pass is 7.6, and the ratio for the second pass is 7.9, to obtain an octagonal intermediate forging billet C with a diameter of 530mm.

[0067] Step 4: Use a high-speed forging machine to perform one-time forming forging on the intermediate forging billet C. The initial forging temperature of each forming forging is 50℃ below the β phase transformation point, and the final forging temperature is 160℃ below the phase transformation point. The cumulative forging ratio is controlled between 1.5 to obtain a finished bar with a size of Φ510mm.

[0068] As shown in Figures 7(a) and 7(b), the low-magnification microstructure of the Ti5331 titanium alloy bar processed in this embodiment is uniformly blurred.

[0069] As shown in Figures 8(a) and 8(b), the Ti5331 titanium alloy processed in this embodiment has a good degree of equiaxed primary phase, sufficient fragmentation, and uniform distribution.

[0070] Through the above-described method, the forging method for large-size Ti5531 titanium alloy bars of this invention, by controlling the forging temperature and forging deformation, produces large-size Ti5531 alloy bars with a uniform and fine microstructure at low magnification and a fully equiaxed microstructure at high magnification. This forging method can reduce the grain size of the titanium alloy billet and improve the uniformity of the microstructure. The bar preparation requires fewer forging passes, has a shorter process, consumes less energy, and can meet the requirements of large-scale industrial production.

Claims

1. A forging method for Ti5331 titanium alloy large-size bar, characterized by, Specifically: Step 1, 2-6 tons of Ti5331 titanium alloy large-size ingot is subjected to 1-2 times of open-die forging, to obtain a rectangular structure intermediate forging blank A with a length of 690mm-780mm and a width of 530mm-780mm; Step 2, the intermediate forging blank A is subjected to 2-4 times of single-cycle or multi-cycle forging at the phase transition point, to obtain a rectangular intermediate forging blank B with a length of 600mm-700mm and a width of 500mm-570mm; Step 3, the intermediate forging blank B is subjected to 2-5 times of upsetting or elongating forging at the phase transition point, to obtain an octagonal intermediate forging blank C with a length of 520mm-540mm; Step 4, the intermediate forging blank C is subjected to 1-3 times of forming forging, to obtain a finished product rod with a size of Φ300mm-Φ510mm; Step 1, the specific process is as follows: the 2-6 tons of Ti5331 titanium alloy ingot with a size of Φ610mm-Φ890mm is sawed into a single weight of 1400-3100kg, the sawed ingot is heated at 1170℃ for 450-540min, and then is subjected to repeated upsetting and elongating forging, with a cumulative forging ratio of 3.0-5.1, and then is continuously heated at 1080℃ and continuously forged, with a cumulative forging ratio of 3.3-5.0; then is subjected to 1-2 times of forging, with a starting forging temperature of 50-200℃ above the β phase transition point and a final forging temperature of 20-150℃ below the β phase transition point, and 2-3 times of upsetting and elongating are performed in each time of forging, to obtain a rectangular structure intermediate forging blank A with a length of 690mm-780mm and a width of 530mm-780mm; The forging ratio of each time of forging in step 1 is controlled to be 3-6; In step 2, the intermediate forging blank A is subjected to 2-4 times of single-cycle or multi-cycle forging at the phase transition point, and low-high heating and repeated upsetting and elongating forging are adopted for 2-4 times of forging, with a starting forging temperature of 40-100℃ below the β phase transition point and a final forging temperature of 100-200℃ below the β phase transition point in the two-phase zone forging, and a starting forging temperature of 30-80℃ above the β phase transition point and a final forging temperature of 50-100℃ below the β phase transition point in the single-phase zone forging; The forging ratio of each time of forging in step 2 is controlled to be 1.5-3.0; In step 3, the parameters of the 2-5 times of upsetting or elongating forging at the phase transition point are as follows: the starting forging temperature of each time of forging is 30-100℃ below the β phase transition point, and the final forging temperature is 100-250℃ below the β phase transition point; The forging ratio of each time of forging in step 3 is controlled to be 1.2-8; Step 4, the specific process is as follows: the intermediate forging blank C is subjected to 1-3 times of forming forging by using a fast forging machine, with a starting forging temperature of 50-100℃ below the β phase transition point and a final forging temperature of 100-200℃ below the phase transition point in each time of forming forging, to obtain a finished product rod with a size of Φ300mm-Φ510mm; The cumulative forging ratio in step 4 is controlled to be 1.2-3.

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