A method for preparing layered ultra-fine grain microstructure titanium alloy rod by temperature-controlled multi-pass V-shaped groove rolling

Abstract

The application relates to a method for preparing layered ultra-fine-grain microstructure titanium alloy rods by temperature-controlled multi-pass V-shaped groove rolling, which comprises the following steps: heating an initial titanium alloy rod blank to an S1 temperature and keeping the temperature for T1 minutes; after the keeping temperature of the rod blank ends, the outer surface of the rod is wrapped with asbestos yarn to prevent temperature drop, then the rod is quickly transported to a rolling mill to complete the first-pass groove rolling; the rod is rotated by 90 degrees along the axial direction to complete the second-pass rolling; the rolled rod is returned to the furnace to be heated to an S2 temperature and kept for T2 minutes; after the keeping temperature of the rod ends, the rod is quickly moved to the rolling mill to complete the third-pass rolling; the rod is rotated by 90 degrees along the axial direction to complete the fourth-pass rolling; the rolled rod is returned to the furnace to be heated to an S3 temperature and kept for T3 minutes; after the keeping temperature of the rod ends, the outer surface of the rod continues to be wrapped with asbestos yarn, the rod is quickly moved to the rolling mill to complete the fifth-pass rolling; and the rod is rotated by 90 degrees along the axial direction to complete the sixth-pass rolling. The method can be used for preparing titanium alloy rods with multi-layer ultra-fine-grain microstructure, the high-temperature strength, plasticity and impact toughness of the titanium alloy rods are significantly improved, and the titanium alloy rods have wide application prospects in the field of aerospace fasteners.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy material preparation technology, specifically relating to a method for preparing layered ultrafine-grained titanium alloy rods by temperature-controlled multi-pass V-groove rolling. Background Technology

[0002] Titanium alloys possess advantages such as high strength, low density, low thermal conductivity, and low elastic modulus, and have been widely used in recent years for manufacturing fastener components in aerospace, defense, and other fields. Currently, titanium alloy fastener blanks are mainly prefabricated through processes such as free forging, rolling, or extrusion, and then cold-headed or warm-headed to form the fasteners. These conventional processes are relatively mature, and the fasteners exhibit stable mechanical properties at room temperature, making them widely used in industry.

[0003] However, some titanium alloy fasteners need to operate under high temperature and high pressure for extended periods. This harsh service environment can cause changes in the internal microstructure of the fasteners, potentially leading to defects such as high-temperature creep, microcracks, and localized grain coarsening. Ultimately, this weakens the high-temperature mechanical properties of the fasteners and shortens their service life. This is the main challenge faced by domestically produced titanium alloy fasteners operating under high temperature and high pressure, and it is also a technical problem that urgently needs to be solved. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing layered ultrafine-grained titanium alloy bars using temperature-controlled multi-pass V-groove rolling. This method can produce titanium alloy billets with layered structures and ultrafine grains, exhibiting stable microstructure and excellent mechanical properties under high temperature and high pressure conditions. The V-groove rolling upper and lower roll structure proposed in this invention is as follows: Figure 1 As shown.

[0005] The technical problem solved by this invention is achieved through the following technical solution:

[0006] A method for preparing layered ultrafine-grained titanium alloy bars using temperature-controlled multi-pass V-groove rolling, characterized in that the method comprises the following steps:

[0007] S1. Heat the initial titanium alloy billet to the S1 temperature and hold it at the T1 minute. Wrap the outer surface with asbestos yarn and ensure that the initial titanium alloy billet transfer time does not exceed 30 seconds. Ensure that the initial rolling temperature is not lower than S1-10℃.

[0008] S2. Preheat the die to 300°C with a flame to ensure the initial rolling temperature of the first pass is not lower than S1-10°C, and complete the first pass of V-groove rolling. Rotate the bar 90° axially and perform the second pass of groove rolling. After completion, return it to the furnace for reheating to S2 temperature and hold for T2 minutes. Wrap the outer surface with asbestos yarn and ensure that the bar transfer time does not exceed 30 seconds, and ensure that the initial rolling temperature of the third pass is not lower than S2-30°C. Preheat the die to 300°C with a flame to complete the third pass of V-groove rolling. Rotate the bar 90° axially and perform the fourth pass of groove rolling. After completion, return the bar to the furnace for further reheating to S3 temperature and hold for T3 minutes. Wrap the outer surface with asbestos yarn and ensure that the bar transfer time does not exceed 30 seconds. Preheat the die to 300°C with a flame to ensure that the initial rolling temperature of the fifth pass is not lower than S2-50°C. Rotate the bar 90° axially and perform the sixth pass of groove rolling. After groove rolling, air cool the bar to room temperature.

[0009] Where: S1∈[T] β +20℃, T β +100℃],S2∈[T β -100℃, T β -30℃],S3∈[T β -200℃, T β -150℃], T1=5+0.4*D0, T2=3+0.4*D2, T3=1+0.4*D4, T β D is the phase transformation temperature of the titanium alloy, and D0, D2, and D4 are the initial diameter of the titanium alloy billet, the diameter after the second pass, and the diameter after the fourth pass, respectively.

[0010] Furthermore, before the first, second, third, fourth, fifth, and sixth rolling passes begin, glass lubricant is applied to the upper and lower grooved rolls.

[0011] Furthermore, after the second, fourth, and sixth rolling passes are completed, high-pressure air guns are used to clean the adhering substances on the surfaces of the upper and lower rolls.

[0012] Moreover, the initial cross-sectional diameter of the titanium alloy billet does not exceed 40 mm.

[0013] Furthermore, in the first V-groove rolling pass, the upper and lower roll speeds are 0.3 rad / sec, the bar feed rate is 10 mm / sec, and the radial compression deformation is controlled within 10%–15%; in the second V-groove rolling pass, the upper and lower roll speeds are 0.3 rad / sec, the bar feed rate is 10 mm / sec, and the radial compression deformation is controlled within 10%–15%; and in the third V-groove rolling pass, the upper and lower roll speeds are 0.35 rad / sec, the bar feed rate is 12 mm / sec, and the radial compression deformation is controlled within 10%–15%. The fourth V-groove rolling pass has an upper and lower roll speed of 0.35 rad / sec, a bar feed rate of 12 mm / sec, and radial compression deformation controlled at 10%–15%. The fifth V-groove rolling pass has an upper and lower roll speed of 0.45 rad / min, a bar feed rate of 15 mm / sec, and radial compression deformation controlled at 10%–15%. The sixth V-groove rolling pass has an upper and lower roll speed of 0.45 rad / min, a bar feed rate of 15 mm / sec, and radial compression deformation controlled at 10%–15%.

[0014] Moreover, the rotational speed and bar rolling direction of the upper and lower groove rolls are kept consistent during the first to sixth passes of V-groove rolling.

[0015] The advantages and beneficial effects of this invention are as follows:

[0016] 1. The present invention relates to a method for preparing layered ultrafine-grained titanium alloy bars by temperature-controlled multi-pass V-groove rolling. On the one hand, by using a multi-pass V-groove rolling process, the cumulative plastic deformation within the material is increased, which can effectively break down and refine the grains to the nanoscale (100nm~500nm). At the same time, by utilizing the deformation characteristics of V-groove rolling, different material flow rates are achieved at the microscale, resulting in a layered structure. In addition, by combining the bar size and the evolution law of material structure, the deformation temperature of each pass can be controlled to suppress grain growth and ensure an ultrafine-grained structure.

[0017] 2. The method for preparing layered ultrafine-grained titanium alloy bars using temperature-controlled multi-pass V-groove rolling of this invention, compared with conventional extrusion and rolling processes, produces bars with a finer grain structure, reaching the nanoscale (100nm~500nm). The deformation characteristics of this invention allow for internal material stratification, resulting in a layered microstructure. Furthermore, this invention involves rolling from high to low temperatures with sufficient air cooling time between passes, eliminating the need for subsequent solution treatment and aging heat treatment. Additionally, the ultrafine-grained layered structure obtained by this invention is less prone to creep, grain coarsening, and second-phase precipitation during high-temperature service. Therefore, the high-temperature strength, plasticity, and impact toughness of the bars prepared by this invention are significantly superior to those prepared by conventional processes. Moreover, this invention also offers the following advantages: reduced preparation steps and passes, reduced load, improved equipment forming capacity, reduced energy consumption, cost savings, and improved product performance. Attached Figure Description

[0018] Figure 1 This is a model of the upper and lower rolls of the V-groove rolling mill of the present invention.

[0019] Figure 2 This is a flowchart of the present invention;

[0020] Figure 3 This is a comparison diagram of the preparation process of this invention with that of conventional extrusion or rolling;

[0021] Figure 4 This is a microstructure diagram of the titanium alloy in Example 1 of the present invention;

[0022] Figure 5 This is a microstructure diagram of the titanium alloy in Example 2 of the present invention;

[0023] Figure 6 This is a microstructure diagram of the titanium alloy in Example 3 of the present invention. Detailed Implementation

[0024] The present invention will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0025] A method for preparing layered ultrafine-grained titanium alloy bars by temperature-controlled multi-pass V-groove rolling specifically includes the following steps:

[0026] (1) The titanium alloy billets used in this invention are all forged structures, and the billet surface is required to be free of cracks, with uniform internal structure, no segregation and inclusion defects, and an initial diameter not exceeding 40 mm.

[0027] (2) Heat the initial titanium alloy billet to temperature S1 and hold it for T1 minutes. The temperature S1 is 20℃ to 100℃ higher than the alpha→beta phase transformation temperature of the material. T1 is the holding time of the billet, calculated according to T1=5+0.4*D0. After the holding time is completed, wrap the outer surface of the billet with asbestos yarn and quickly move it to the rolling mill. Ensure that the transfer time does not exceed 30s to ensure that the initial rolling temperature is not lower than S1-10℃. The preheating temperature of the upper and lower rolls of the groove roll is 300℃ and glass lubricant is applied. The rotation speed of the upper and lower rolls is 0.3rad / sec, the feed rate of the billet is 10mm / sec, and the radial compression deformation is controlled at 10%~15%. The first pass of V-groove rolling is completed.

[0028] (3) After the bar is rotated 90° along the axial direction, the second V-groove rolling begins. The roll speed and bar feed rate are consistent with the first pass. The radial compression deformation of the second pass is 10% to 15%, and the second V-groove rolling is completed.

[0029] (4) After the second pass of V-groove rolling is completed, the bar is immediately returned to the furnace. The bar is heated to the S2 temperature and held for T2 minutes. The S2 temperature is 100℃ to 30℃ lower than the alpha→beta phase transformation temperature of the material. T2 is the holding time of the bar, calculated according to T2=3+0.4*D2.

[0030] (5) Use a high-pressure air gun to clean the adhering substances on the surface of the upper and lower rolls;

[0031] (6) After the heat preservation is completed, wrap the outer surface of the bar with asbestos yarn and quickly move it to the rolling mill. Ensure that the transfer time does not exceed 30s to ensure that the initial rolling temperature is not lower than S1-10℃. The upper and lower rolls of the groove rolling mill are preheated to 300℃ and coated with glass lubricant. The upper and lower roll speed is 0.35rad / sec, the bar feed rate is 12mm / sec, and the radial compression deformation is controlled at 10% to 15%. The third pass of V-groove rolling is completed.

[0032] (7) After the bar is rotated 90° along the axial direction, the fourth pass of V-groove rolling begins. The roll speed and bar feed rate are consistent with the third pass. The radial compression deformation of the fourth pass is 10% to 15%, and the fourth pass of V-groove rolling is completed.

[0033] (8) After the fourth pass of V-groove rolling is completed, the bar is immediately returned to the furnace. The bar is heated to the S3 temperature and held for T3 minutes. The S3 temperature is 200℃~150℃ lower than the alpha→beta phase transformation temperature of the material. T3 is the holding time of the bar, calculated according to T2=1+0.4*D4.

[0034] (9) Use a high-pressure air gun to clean the adhering substances on the surface of the upper and lower rolls;

[0035] (10) After the heat preservation is completed, wrap the outer surface of the bar with asbestos yarn and quickly move it to the rolling mill. Ensure that the transfer time does not exceed 30s to ensure that the initial rolling temperature is not lower than S1-10℃. The hot preheating temperature of the upper and lower rolls of the groove roll is 300℃, and glass lubricant is applied. The upper and lower roll speed is 0.45rad / sec, the bar feed rate is 15mm / sec, and the radial compression deformation is controlled at 10% to 15%. The fifth pass of V-groove rolling is completed.

[0036] (11) After the bar is rotated 90° along the axial direction, the sixth V-groove rolling begins. The roll speed and bar feed rate are consistent with the fifth pass. The radial compression deformation of the sixth pass is 10% to 15%, and the sixth V-groove rolling is completed.

[0037] (12) After rolling, the bar stock is air-cooled to room temperature;

[0038] (13) Use a high-pressure air gun to clean the surface of the upper and lower rolls.

[0039] Example 1: Preparation of TC4 layered ultrafine crystal rods

[0040] The chemical composition (%, by mass fraction) of TC4 titanium alloy is as follows: Aluminum (Al) 6.2, Vanadium (V) 4.0, Iron (Fe) 0.3, Carbon (C) 0.10, Nitrogen (N) 0.05, Hydrogen (H) 0.015, Oxygen (O) 0.02, with the remainder being titanium. The phase transformation temperature of TC4 is T. β =990℃. The initial bar billet diameter was 40mm. After multiple passes of V-groove rolling, the microstructure was as follows: Figure 4 As shown, the material exhibits a distinct layered structure, with defect concentration areas between the layers. During high-temperature service deformation, cracks easily initiate and propagate in these defect areas. However, the propagation path is rugged and uneven, thus the material is less prone to fracture failure, resulting in good high-temperature performance. The specific multi-pass V-groove rolling process is as follows... Figure 2 As shown in Table 1, the mechanical properties of the rolled bars are as follows.

[0041] Table 1 Mechanical properties of the rods prepared according to the present invention at room temperature (20℃) and high temperature (550℃)

[0042] Test temperature (°C) Yield strength (MPa) Tensile strength (MPa) Impact toughness (J) 20 906 1013 14.18 550 473 535 111

[0043] Example 2: Preparation of Ti55531 layered ultrafine crystal rods

[0044] The chemical composition (%, mass fraction) of Ti55531 titanium alloy is as follows: aluminum 5.3, molybdenum 5.2, vanadium 5.2, chromium 2.65, zirconium 1.02, with the remainder being titanium. The phase transformation temperature T of Ti55531 is... β=850℃. Belongs to a high-strength, high-toughness near-β titanium alloy. The initial billet diameter is 40mm. After multiple passes of V-groove rolling, the microstructure is as follows: Figure 5 As shown in the figure, the material exhibits a distinct layered structure, with defect concentration areas between the layers. During high-temperature service deformation, cracks easily initiate and propagate in these defect areas. However, the propagation path is rugged and uneven, thus the material is less prone to fracture failure, resulting in good high-temperature performance. The mechanical properties of the rolled bar are shown in Table 2.

[0045] Table 2 Mechanical properties of the rods prepared according to the present invention at room temperature (20℃) and high temperature (550℃)

[0046] Test temperature (°C) Yield strength (MPa) Tensile strength (MPa) Impact toughness (J) 20 1121 1221 15.58 550 589 643 117.5

[0047] Example 3: Preparation of Ti6554 layered ultrafine crystal rods

[0048] The chemical composition (%, by mass) of Ti6554 titanium alloy is as follows: chromium 5.7, molybdenum 4.7, vanadium 4.8, aluminum 3.9, iron 0.08, silicon 0.028, carbon 0.025, with the remainder being titanium. The phase transformation temperature T of Ti6554 is... β =820℃, belonging to a high-strength and high-toughness near-β titanium alloy. The initial billet diameter is 40mm, and after multiple passes of V-groove rolling, the microstructure is as follows: Figure 6 As shown in the figure, the material exhibits a distinct layered structure, with defect concentration areas between the layers. During high-temperature service deformation, cracks easily initiate and propagate in these defect areas. However, the propagation path is rugged and uneven, thus the material is less prone to fracture failure, resulting in good high-temperature performance. The mechanical properties of the V-groove rolled bars are shown in Table 3.

[0049] Table 3 Mechanical properties of the rods prepared according to the present invention at room temperature (20℃) and high temperature (550℃)

[0050] Test temperature (°C) Yield strength (MPa) Tensile strength (MPa) Impact toughness (J) 20 1103 1243 17.72 550 600 673 116

[0051] Although embodiments and drawings of the present invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A method for preparing layered ultrafine-grained titanium alloy bars using temperature-controlled multi-pass V-groove rolling, characterized in that: The steps of the method are as follows: S1. Heat the initial titanium alloy billet to the S1 temperature and hold it at the T1 minute. Wrap the outer surface with asbestos yarn and ensure that the initial titanium alloy billet transfer time does not exceed 30 seconds. Ensure that the initial rolling temperature is not lower than S1-10℃. S2. Preheat the upper and lower grooved rolls with flame to 300℃ to ensure that the initial rolling temperature of the first pass is not lower than S1-10℃, and complete the first pass of V-groove rolling; then, perform the second pass of V-groove rolling, and after completion, return the billet to the furnace for reheating to S2 temperature and hold for T2 minutes; wrap the outer surface with asbestos yarn, and ensure that the billet transfer time does not exceed 30 seconds, and ensure that the initial rolling temperature of the third pass is not lower than S2-30℃, preheat the upper and lower grooved rolls with flame to 300℃, and complete the third pass of V-groove rolling; then, perform the fourth pass of V-groove rolling, and after completion, return the billet to the furnace for continued reheating to S3 temperature and hold for T3 minutes; wrap the outer surface with asbestos yarn, and ensure that the billet transfer time does not exceed 30 seconds, preheat the upper and lower grooved rolls with flame to 300℃, and ensure that the initial rolling temperature of the fifth pass of V-groove rolling is not lower than S2-50℃; then, perform the sixth pass of V-groove rolling, and after the groove rolling is completed, air cool the billet to room temperature; Where: S1∈[T] β +20℃, T β +100℃], S2∈[T β -100℃, T β -30℃], S3∈[T β -200℃, T β [-150℃], T1=5+0.4 D0, T2 = 3 + 0.4 D2, T3 = 1 + 0.4 D4, T β D is the phase transformation temperature of the titanium alloy, and D0, D2, and D4 are the initial diameter of the titanium alloy billet, the diameter after the second V-groove rolling, and the diameter after the fourth V-groove rolling, respectively.

2. The method for preparing layered ultrafine-grained titanium alloy bars by temperature-controlled multi-pass V-groove rolling according to claim 1, characterized in that: Before the first, second, third, fourth, fifth and sixth passes of V-groove rolling begin, glass lubricant is applied to the upper and lower grooved rollers.

3. The method for preparing layered ultrafine-grained titanium alloy bars by temperature-controlled multi-pass V-groove rolling according to claim 1, characterized in that: After the second, fourth and sixth passes of V-groove rolling are completed, high-pressure air guns are used to clean the adhering substances on the surfaces of the upper and lower groove rolls.

4. The method for preparing layered ultrafine-grained titanium alloy bars by temperature-controlled multi-pass V-groove rolling according to claim 1, characterized in that: The initial diameter of the titanium alloy billet cross section does not exceed 40 mm.

5. The method for preparing layered ultrafine-grained titanium alloy bars by temperature-controlled multi-pass V-groove rolling according to claim 1, characterized in that: The first pass of the V-groove rolling mill has an upper and lower groove roll speed of 0.3 rad / sec, a bar feed rate of 10 mm / sec, and radial compression deformation controlled at 10%~15%. The second pass of the V-groove rolling mill also has an upper and lower groove roll speed of 0.3 rad / sec, a bar feed rate of 10 mm / sec, and radial compression deformation controlled at 10%~15%. The third pass of the V-groove rolling mill has an upper and lower groove roll speed of 0.35 rad / sec, a bar feed rate of 12 mm / sec, and radial compression deformation controlled at 10%~15%. The fourth pass of the V-groove rolling mill has an upper and lower groove roll speed of 0.35 rad / sec, a bar feed rate of 12 mm / sec, and radial compression deformation controlled at 10%~15%. The fifth pass of the V-groove rolling mill has an upper and lower groove roll speed of 0.45 rad / sec. The bar feed rate is 15 mm / sec, and the radial compression deformation is controlled at 10%~15%. For the sixth pass of V-groove rolling, the upper and lower groove rolls rotate at 0.45 rad / min, the bar feed rate is 15 mm / sec, and the radial compression deformation is controlled at 10%~15%.

6. The method for preparing layered ultrafine-grained titanium alloy bars by temperature-controlled multi-pass V-groove rolling according to claim 1, characterized in that: The rotational speed and bar rolling direction of the upper and lower grooved rolls are kept consistent during the first to sixth passes of V-groove rolling.

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