A method for preparing ultra-high-strength titanium alloy forgings

Abstract

The present invention discloses a method for preparing ultra-high-strength titanium alloy forgings, which comprises: 1. subjecting an ingot of ultra-high-strength titanium alloy to blanking, upsetting and forging to obtain a blank; 2. subjecting the blank to multiple-fire forging above the phase transition point; 3. subjecting the blank, after multiple-fire forging, to forming forging below the phase transition point to obtain a titanium alloy forging; and 4. subjecting the titanium alloy forging to solid solution aging treatment. The present invention achieves structural uniformity and performance matching through high-temperature, large-deformation forging processing and reduced forging fires, combined with (α+β) zone solid solution and aging treatment processes, so that the titanium alloy forgings achieve good strength-toughness matching, significantly reduce forging cycles and costs, and enhance process controllability, meeting the needs of high-load-bearing forgings in aviation.

Description

Technical Field

[0001] The present invention belongs to the technical field of titanium alloy materials, and in particular relates to a method for preparing an ultra-high-strength titanium alloy forging. Background Art

[0002] High strength and toughness titanium alloy refers to the room temperature strength greater than 1100MPa after heat treatment and the fracture toughness is 55MPa.m 1 / 2 The above titanium alloys represent a key area of development and application. These alloys include heat-treated, hardened martensitic α+β titanium alloys, near-β titanium alloys, and metastable β titanium alloys. These alloys are primarily used to replace high-strength steel and high-strength steel components in aircraft structures, reducing structural weight.

[0003] Entering the 21st century, aerospace vehicles are developing towards high speed, and with the establishment of material damage-safety design concepts and damage tolerance design criteria, high-strength titanium alloys are developing in two directions: one is the pursuit of high-strength and damage-tolerant titanium alloys with higher fracture toughness, and the other is the pursuit of ultra-high-strength titanium alloys with higher strength.

[0004] Foreign countries attach great importance to the research of ultra-high-strength titanium alloys with higher strength levels that can be used for large aviation structural parts. Its representative alloys are Ti-5553 (Ti-5Al-5Mo-5V-3Cr, USA) and VST-55531 (Ti-5Al-5Mo-5V-3Cr-1Zr, Russia), which are improved designs based on VT22 alloy. The alloys have achieved tensile strengths of 1250 to 1400 MPa to meet the high strength and high fracture toughness requirements of the new generation of large jet aircraft under more severe application conditions. China closely follows the forefront of international research and has developed ultra-high-strength titanium alloys with different strength levels of 1300 MPa to 1600 MPa.

[0005] When it comes to high-strength and high-toughness titanium alloys, strength and toughness are two diametrically opposed characteristics, with toughness typically decreasing as strength increases. While increasing alloy strength through alloying is relatively straightforward, simultaneously achieving high toughness is not. The microstructure of a titanium alloy significantly influences its mechanical properties, with slight changes in the microstructure often leading to significant differences in alloy performance. Achieving a well-balanced balance of strength, ductility, and toughness through microstructure optimization is a key technical challenge in the research of ultra-high-strength titanium alloys. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the shortcomings of the above-mentioned existing technologies and provide a method for preparing ultra-high-strength titanium alloy forgings. By adopting high-temperature, large-deformation forging processing and reducing the number of forging fires, combined with (α+β) zone solid solution and aging treatment processes, the present invention achieves structural uniformity and performance matching, resulting in titanium alloy forgings with excellent strength-toughness matching, thus solving the difficult problem of ultra-high-strength titanium alloys in achieving both high strength and high toughness.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing ultra-high strength titanium alloy forgings, characterized in that the method comprises the following steps:

[0008] Step 1: The ultra-high strength titanium alloy ingot is subjected to blanking, upsetting and forging to obtain a forging blank;

[0009] Step 2: reforging the forging blank obtained in step 1 above the phase transformation point with multiple fires;

[0010] Step 3: forming and forging the forging blank after multiple forgings in step 2 below the phase transition point to obtain a titanium alloy forging;

[0011] Step 4: subjecting the titanium alloy forging obtained in step 3 to solid solution aging treatment.

[0012] The above-mentioned method for preparing ultra-high-strength titanium alloy forgings is characterized in that the ultra-high-strength titanium alloy in step 1 is a titanium alloy with a tensile strength greater than 1450 MPa.

[0013] The above-mentioned method for preparing ultra-high-strength titanium alloy forgings is characterized in that the temperature of the blanking upsetting forging in step one is 1100°C to 1150°C, and the holding time t1 is 0.8D1, where D1 is the cross-sectional diameter or thickness of the ingot of ultra-high-strength titanium alloy, the unit is mm, the unit of t1 is min, and the blanking upsetting forging adopts a three-upsetting and three-drawing forging process, and the deformation of the upsetting and drawing passes is 50%.

[0014] The above-mentioned method for preparing ultra-high-strength titanium alloy forgings is characterized in that the multi-fire forging in step 2 is 3 to 4 fires, the temperature is 940°C to 1050°C, and the holding time t2 = 0.6D2, where D2 is the cross-sectional diameter or thickness of the forging blank, the unit is mm, and the unit of t2 is min. The multi-fire forging adopts a three-upsetting and three-drawing forging-tempering-two-upsetting and two-drawing forging process, the deformation of the upsetting and drawing passes is 50%, and the tempering time t0 = 0.3D0, where D0 is the cross-sectional diameter or thickness of the forging blank to be tempered, the unit is mm, and the unit of t0 is min.

[0015] The above-mentioned method for preparing ultra-high-strength titanium alloy forgings is characterized in that the temperature of the forming forging in step three is 790℃~800℃, and the holding time t3=0.6D3, where D3 is the cross-sectional diameter or thickness of the forging blank after multiple fire forgings, the unit is mm, the unit of t3 is min, and the deformation amount is not less than 50%.

[0016] The above-mentioned method for preparing ultra-high-strength titanium alloy forgings is characterized in that the solid solution and aging treatment in step 4 is (α+β) zone solid solution and aging treatment.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] 1. The present invention first adopts high-temperature large-deformation forging processing and strictly controls the holding time to prevent abnormal grain growth. The excellent deformation coordination ability of the body-centered cubic β phase of titanium alloy is utilized to make the forging blank structure uniform. Then, a high deformation temperature is adopted and the number of forging fires is reduced, so that the β grain size is significantly larger than that of the conventional process. Subsequently, large deformation is performed below the phase transformation point to crush the β grains, reducing the adverse effect of the β grain boundary traces remaining in the structure on the performance due to the existence of the grain boundary soft zone, achieving structural uniformity and performance matching, so that the titanium alloy forgings obtain good strength and toughness matching, meeting the needs of high-load-bearing forgings in aviation.

[0019] 2. The present invention adopts (α+β) zone solid solution and aging treatment process, so that the titanium alloy forgings obtain fine primary α and mutually staggered secondary α lamellar structure, achieving excellent strength and toughness matching of the titanium alloy forgings.

[0020] 3. The forging number of the present invention is greatly reduced, and the total forging number of fires from ingot to finished forging is only 5 to 6, which significantly reduces the forging cycle and cost and enhances the process controllability.

[0021] The technical solution of the present invention is further described in detail below through examples. DETAILED DESCRIPTION

[0022] Example 1

[0023] This embodiment includes the following steps:

[0024] Step 1: A Φ510 mm diameter Ti1500 ultra-high strength titanium alloy ingot is kept at 1150°C for 408 minutes and then subjected to blanking, upsetting and drawing forging. The deformation amount of the upsetting and drawing passes is 50%, and after three upsetting and three drawing deformations, a 450 mm diameter bar is prepared.

[0025] Step 2: The 450mm bar obtained in step 1 is subjected to multiple heat forging above the phase transformation point. The specific process is as follows:

[0026] (1) One-fire forging: After holding at 1050℃ for 270min, upsetting and drawing are performed. The deformation of upsetting and drawing is 50%. After three upsetting and three drawing, tempering and holding are performed for 135min. Then, two upsetting and two drawing are performed to obtain 450mm bar.

[0027] (2) Two-fire forging: After holding at 1000℃ for 270min, upsetting and drawing are performed, with the deformation of upsetting and drawing being 50%. After three upsetting and three drawing, tempering and holding are performed for 135min, and then two upsetting and two drawing are performed to obtain □450mm bars;

[0028] (3) Three-fire forging: After holding at 960℃ for 270min, upsetting and drawing are performed. The deformation of upsetting and drawing is 50%. After three upsetting and drawing, tempering and holding are performed for 135min. Then, two upsetting and two drawing are performed to obtain 450mm bars and sawing.

[0029] (4) Four-fire forging: After holding at 940℃ for 270min, upsetting and drawing are performed, with the deformation of upsetting and drawing being 50%. After three upsetting and three drawing, tempering and holding are performed for 135min, and then two upsetting and two drawing are performed to obtain 240mm bars and sawing.

[0030] Step 3: The forging blank after multiple-fire forging in Step 2 is kept at 800° C. for 144 minutes and then stretched and deformed for forming forging to obtain a titanium alloy forging rod with a diameter of Φ150 mm;

[0031] Step 4: subjecting the titanium alloy forged rod obtained in step 3 to a solution treatment at 770°C / 1h, AC and an aging treatment at 510°C / 4h, AC.

[0032] After testing, the performance of the titanium alloy forging rod of this embodiment after solution aging treatment reaches: tensile strength Rm = 1510MPa, elongation A = 8%, fracture toughness K IC =49.5MPa.m 1 / 2 , with good strength-plasticity-toughness matching.

[0033] Example 2

[0034] This embodiment includes the following steps:

[0035] Step 1: A 610 mm diameter Ti1500 ultra-high strength titanium alloy ingot is kept at 1100°C for 488 minutes and then subjected to blanking, upsetting and drawing forging. The deformation amount of the upsetting and drawing passes is 50%. After three upsetting and three drawing passes, a 640 mm diameter bar is prepared.

[0036] Step 2: The 640mm bar obtained in step 1 is subjected to multiple heat forging above the phase transformation point. The specific process is as follows:

[0037] (1) One-fire forging: After holding at 1050℃ for 384min, upsetting and drawing are performed, with the deformation of upsetting and drawing being 50%. After three upsetting and three drawing, tempering and holding are performed for 192min, and then two upsetting and two drawing are performed to obtain 640mm bar.

[0038] (2) Two-fire forging: After holding at 970℃ for 384min, upsetting and drawing are performed, with the deformation of upsetting and drawing being 50%. After three upsetting and three drawing, tempering and holding are performed for 192min, and then two upsetting and two drawing are performed to obtain 640mm bar.

[0039] (3) Three-fire forging: After holding at 940℃ for 384min, upsetting and drawing are performed. The deformation of upsetting and drawing is 50%. After three upsetting and drawing, tempering and holding are performed for 192min. Then, two upsetting and two drawing are performed to obtain 440mm bars and sawing.

[0040] Step 3: The forging blank after multiple-fire forging in step 2 is kept at 790° C. for 264 minutes and then stretched and deformed for forming forging to obtain a titanium alloy forging rod with a diameter of Φ250 mm;

[0041] Step 4: subjecting the titanium alloy forged rod obtained in step 3 to a solution treatment at 770°C / 1h, AC and an aging treatment at 510°C / 4h, AC.

[0042] After testing, the performance of the titanium alloy forging rod of this embodiment after solution aging treatment reaches: tensile strength Rm = 1476MPa, elongation A = 10%, fracture toughness K IC =58.5MPa.m 1 / 2 , with good strength-plasticity-toughness matching.

[0043] Example 3

[0044] This embodiment includes the following steps:

[0045] Step 1: A Ti1500 ultra-high-strength titanium alloy ingot with a diameter of 610 mm is kept at 1080°C for 488 minutes and then subjected to blanking, upsetting and drawing forging. The deformation amount of the upsetting and drawing passes is 50%, and after three upsetting and three drawing deformations, a 640 mm bar is prepared;

[0046] Step 2: The 640mm bar obtained in step 1 is subjected to multiple heat forging above the phase transformation point. The specific process is as follows:

[0047] (1) One-fire forging: After holding at 990℃ for 384min, upsetting and drawing are performed, with the deformation of upsetting and drawing being 50%. After three upsetting and three drawing, tempering and holding are performed for 192min, and then two upsetting and two drawing are performed to obtain 640mm bar.

[0048] (2) Two-fire forging: After holding at 970℃ for 384min, upsetting and drawing are performed, with the deformation of upsetting and drawing being 50%. After three upsetting and drawing, tempering and holding are performed for 192min, and then two upsetting and two drawing are performed to obtain 640mm bars and sawing;

[0049] (3) Three-fire forging: After holding at 940℃ for 384min, upsetting and drawing are performed. The deformation of upsetting and drawing is 50%. After three upsetting and drawing, tempering and holding are performed for 192min. Then, two upsetting and two drawing are performed to obtain 440mm bars and sawing.

[0050] Step 3: The forging blank after multiple-fire forging in Step 2 is kept at 795° C. for 264 minutes and then stretched and deformed for forming forging to obtain a titanium alloy forging rod with a diameter of Φ200 mm;

[0051] Step 4: subjecting the titanium alloy forged rod obtained in step 3 to a solution treatment at 770°C / 1h, AC and an aging treatment at 510°C / 4h, AC.

[0052] After testing, the performance of the titanium alloy forging rod of this embodiment after solution aging treatment reaches: tensile strength Rm = 1495MPa, elongation A = 9.5%, fracture toughness K IC =56.5MPa.m 1 / 2 , with good strength-plasticity-toughness matching.

[0053] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent variation made to the above embodiment based on the essence of the invention technology shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing ultra-high strength titanium alloy forgings, characterized in that: The method comprises the following steps: Step 1: Performing open-cut upsetting and forging of an ultra-high-strength titanium alloy ingot to obtain a forged billet; the ultra-high-strength titanium alloy is a titanium alloy having a tensile strength greater than 1450 MPa; the temperature of the open-cut upsetting and forging is 1100°C to 1150°C; the holding time of the open-cut upsetting and forging is t1=0.8D1, where D1 is the cross-sectional diameter or thickness of the ultra-high-strength titanium alloy ingot in mm and t1 is in min, and the open-cut upsetting and forging adopts a three-upsetting and three-drawing forging process, and the deformation of the upsetting and drawing passes is 50%; Step 2: The forging blank obtained in step 1 is subjected to multi-fire forging above the phase transformation point; the multi-fire forging is 3 to 4 fires, the temperature is 940°C to 1050°C; each fire forging adopts a three-upsetting and three-drawing forging-tempering-two-upsetting and two-drawing forging process, and the deformation of the upsetting and drawing passes is 50%; Step 3: forming and forging the forging blank after multiple forgings in Step 2 below the phase transition point with a deformation of not less than 50% to obtain a titanium alloy forging; the forming and forging temperature is 790° C. to 800° C.; Step 4: subjecting the titanium alloy forging obtained in step 3 to (α+β) zone solid solution and aging treatment.

2. The method for preparing an ultra-high strength titanium alloy forging according to claim 1, characterized in that: In step 2, the holding time for each forging change is t2=0.6D2, where D2 is the cross-sectional diameter or thickness of the forging blank, in mm, and t2 is in min. The tempering time is t0=0.3D0, where D0 is the cross-sectional diameter or thickness of the forging blank to be tempered, in mm, and t0 is in min.

3. The method for preparing an ultra-high strength titanium alloy forging according to claim 1, characterized in that: The holding time of the forming forging in step 3 is t3=0.6D3, where D3 is the cross-sectional diameter or thickness of the forging blank after multiple fire forgings, in mm, and t3 is in min.