Titanium alloy billet forging method for ship with low anisotropy

Abstract

The application provides a low-anisotropy titanium alloy blank forging method for ships, which comprises the following steps: S1, open-die forging; S2, high-temperature forging; S3, fine-grain forging; S4, low-temperature forging; and S5, forming forging. The low-anisotropy titanium alloy blank forging method for ships according to the application effectively improves the uniformity of the structure, reduces the axial and radial structural differences, and obtains a forged blank with uniform structure, wherein the titanium alloy plate prepared from the forged blank has low anisotropy and good comprehensive performance, and the technical indexes meet the requirements of relevant standards.

Description

Technical Field

[0001] This invention relates to the field of titanium and titanium alloy hot deformation forming technology, and in particular to a method for forging low anisotropy titanium alloy billets for ships. Background Technology

[0002] Titanium alloys possess excellent properties such as high specific strength, corrosion resistance, non-magnetic properties, sound transmission, and impact resistance, making them ideal materials for marine applications. They are widely used in pressure hulls, ship structures, pipelines, valves and fittings, power drive systems, heat exchangers, coolers / condensers, and sonar domes. Classified by titanium alloy grade, marine titanium alloys are primarily near-alpha alloys, such as TA5, TA23, TA24, and TA31. In recent years, with the continuous upgrading of marine engineering and equipment, higher requirements have been placed on the billet size, microstructure uniformity, and anisotropy of titanium alloy base materials.

[0003] Currently, vacuum arc remelting is the most commonly used smelting method for titanium alloys. The ingots formed by this method have a typical "tri-crystal zone", which makes the microstructures along the axial and radial directions of the ingots significantly different. The microstructures need to be broken down and refined by multiple forging and upsetting processes to improve the uniformity of the microstructure and the anisotropy of the billet.

[0004] However, since titanium alloys are close-packed hexagonal metals, which have few slip systems and poor plasticity, they are prone to forming texture and non-uniform structure during plastic deformation, resulting in anisotropy in structure and properties. Moreover, this non-uniformity and anisotropy has a hereditary effect and is not easily improved by cold and hot working deformation processes after forging. To address this, those skilled in the art have improved its anisotropy through various means. For example, Chinese patents with application numbers CN201810463298.8, CN201810604759.9, CN202010125203.9, and CN202110481468.7 disclose methods to improve the anisotropy of titanium alloys by adding boron to titanium alloy powder, reversing rolling, heat treatment, and pulsed current. Another example is Chinese patent with application number CN202210923225.9, which discloses a forging preparation method for a small inner diameter Ti2AlNb ring with high fracture toughness and low anisotropy. However, there is little mention of preparation methods for titanium alloy forgings for ships with low anisotropy and high uniformity. Therefore, in order to meet the increasingly sophisticated applications in equipment and marine engineering, it is of great practical significance to invent a titanium alloy billet forging method with low anisotropy and universal applicability to near-α titanium alloys commonly used in ships. Summary of the Invention

[0005] This invention designs a forging method for low anisotropy titanium alloy billets for ships, in order to overcome the technical problem that there are significant differences in the microstructure along the axial and radial directions in titanium alloy ingots obtained by vacuum consumable melting, resulting in poor microstructure uniformity and large anisotropy differences in the billets.

[0006] To address the above problems, this invention discloses a forging method for low-anisotropy titanium alloy billets for marine applications, comprising the following steps:

[0007] S1, Initial Forging: The titanium alloy ingot is subjected to one-time initial forging at a temperature above the phase transformation point (T). β +(100~250)℃, the heat preservation coefficient is 0.8~1.0min / mm, the final forging temperature is not lower than 850℃, and after forging, the surface oxidation and defects are removed by grinding and polishing to obtain the first forging billet;

[0008] S2, High-Temperature Forging: The first forging billet undergoes a single high-temperature forging process, with the forging temperature above the phase transformation point (T). β +(50~150)℃, heat preservation coefficient 0.8~1.0min / mm, final forging temperature not lower than 850℃, after forging, grinding and polishing are performed to remove surface oxidation and defects to obtain the second forging billet;

[0009] S3, Fine Grain Forging:

[0010] The first stage begins below the phase transition point T. β The second forging billet is forged in one pass at a temperature of -(10~30)℃, with a holding coefficient of 0.6~0.8min / mm, and the final forging temperature is not lower than 800℃;

[0011] The second stage, and then above the phase transition point T β The forging process is carried out at +(20~50)℃ in a single forging, with a holding coefficient of 0.8~1.0min / mm, and the final forging temperature is not lower than 850℃;

[0012] The third forging billet is obtained by grinding and polishing between the two forging processes to remove surface oxidation and defects;

[0013] S4, Low-temperature forging:

[0014] The first stage begins below the phase transition point T. β The third forging billet is forged in one pass at a temperature of -(10~30)℃, with a holding coefficient of 0.6~0.8min / mm and a final forging temperature of not less than 800℃.

[0015] The second stage, then below the phase transition point T β The forging process is carried out in one pass at (20~50)℃, with a holding coefficient of 0.6~0.8min / mm, and the final forging temperature is not lower than 800℃;

[0016] The fourth forging billet is obtained by grinding and polishing between the two forging processes to remove surface oxidation and defects;

[0017] S5, Forming Forging: The fourth forging billet is formed by forming forging at a temperature below the phase transformation point T. β -(30~50)℃, the heat preservation coefficient is 0.6~0.8min / mm, and the final forging temperature is not lower than 800℃.

[0018] Furthermore, during the billet forging process, the billet is first upset 2 to 3 times, and then diagonally drawn into a 16-square shape. Each upset is reversed, and the forging ratio for each upset is 1.2 to 1.8, with a total forging ratio of not less than 3.

[0019] Furthermore, during the high-temperature forging process, the first forging billet undergoes 2 to 3 upsetting and drawing processes, and then the material is widened into a flat square with a width-to-thickness ratio of 1.5 to 2.0. The direction is reversed each time the billet is widened, and the forging ratio of each upsetting and drawing process is 1.2 to 1.8, with a total forging ratio of not less than 4.

[0020] Furthermore, during the first stage of fine-grain forging, the second forging billet undergoes 2 to 3 upsetting and drawing processes, with each upsetting and drawing process involving a reversal of direction. The forging ratio for each upsetting and drawing process is 1.2 to 1.8, and the total forging ratio is not less than 4.

[0021] Furthermore, in the second stage of fine-grain forging, the forging billet undergoes 2 to 3 upsetting and drawing processes, with each upsetting and drawing process involving a reversal of direction. The forging ratio for each upsetting and drawing process is 1.2 to 1.8, and the total forging ratio is not less than 3.

[0022] Furthermore, in the first stage of low-temperature forging, the third forging billet is first upset 2 to 3 times, and then diagonally drawn into a 16-square shape. Each upset is reversed, and the forging ratio of each upset is 1.2 to 1.8, with a total forging ratio of not less than 4.

[0023] Furthermore, in the second stage of low-temperature forging, the billet is first upset 1 to 2 times, with the direction being reversed each time, and then pre-formed. The forging ratio for each upset is 1.2 to 1.8, and the total forging ratio is not less than 4.

[0024] Furthermore, during the forming and forging process, the total forging ratio is 1.2 to 1.8, and the deformation is controlled at 30% to 50%.

[0025] Furthermore, the low anisotropy forging method for marine titanium alloy billets is used for forging near-α titanium alloys.

[0026] Furthermore, the near-α titanium alloy is one of TA5, TA23, TA24 or TA31.

[0027] The forging method for low anisotropy titanium alloy billets for ships described in this invention has the following advantages:

[0028] First, the titanium alloy forging billet prepared has uniform axial and radial microstructure with small differences, which results in low anisotropy and good comprehensive performance of the plate rolled from the forging billet prepared by the present invention.

[0029] Second, the forging method developed is not only universally applicable to near-α titanium alloys used in ships, but also has good reference value for the promotion of other types of titanium alloys;

[0030] Third, it adopts conventional forging production methods, which are highly adaptable to the process, do not require the addition of new equipment, and are simple to operate, enabling mass production. Attached Figure Description

[0031] Figure 1 Metallographic images of the cross-sectional microstructure of the TA5 titanium alloy forging billet in different directions according to Embodiment 1 of the present invention;

[0032] Figure 2 Metallographic images of the cross-sectional microstructure of the TA23 titanium alloy forging billet in different directions according to Embodiment 2 of the present invention;

[0033] Figure 3 Metallographic images of the cross-sectional microstructure of the TA24 titanium alloy forging billet in different directions according to Embodiment 3 of the present invention;

[0034] Figure 4 The images show the cross-sectional microstructure of the TA31 titanium alloy forging billet in different directions according to Embodiment 4 of the present invention. Detailed Implementation

[0035] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0036] A method for forging low-anisotropic titanium alloy billets for marine applications includes the following steps:

[0037] S1, Initial Forging: The titanium alloy ingot is subjected to one-time initial forging at a temperature above the phase transformation point (T). β +(100~250)℃, the heat preservation coefficient is 0.8~1.0min / mm, the final forging temperature is not lower than 850℃, and after forging, the surface oxidation and defects are removed by grinding and polishing to obtain the first forging billet;

[0038] S2, High-Temperature Forging: The first forging billet undergoes a single high-temperature forging process, with the forging temperature above the phase transformation point (T). β +(50~150)℃, heat preservation coefficient 0.8~1.0min / mm, final forging temperature not lower than 850℃, after forging, grinding and polishing are performed to remove surface oxidation and defects to obtain the second forging billet;

[0039] S3, Fine Grain Forging:

[0040] The first stage begins below the phase transition point T. β The second forging billet is forged in one pass at a temperature of -(10~30)℃, with a holding coefficient of 0.6~0.8min / mm, and the final forging temperature is not lower than 800℃;

[0041] The second stage, and then above the phase transition point T β The forging process is carried out at +(20~50)℃ in a single forging, with a holding coefficient of 0.8~1.0min / mm, and the final forging temperature is not lower than 850℃;

[0042] The third forging blank is obtained by grinding and polishing between the two forging processes to remove surface oxidation and defects;

[0043] S4, Low-temperature forging:

[0044] The first stage begins below the phase transition point T. β The third forging billet is forged in one pass at a temperature of -(10~30)℃, with a holding coefficient of 0.6~0.8min / mm and a final forging temperature of not less than 800℃.

[0045] The second stage, then below the phase transition point T β The forging process is carried out in one pass at (20~50)℃, with a holding coefficient of 0.6~0.8min / mm, and the final forging temperature is not lower than 800℃.

[0046] The fourth forging billet is obtained by grinding and polishing between the two forging processes to remove surface oxidation and defects;

[0047] S5, Forming Forging: The fourth forging billet is formed by forming forging at a temperature below the phase transformation point (T). β -(30~50)℃, the heat preservation coefficient is 0.6~0.8min / mm, and the final forging temperature is not lower than 800℃.

[0048] Preferably, during the billet forging process, the billet is first upset 2 to 3 times, and then diagonally drawn into a 16-square shape. Each upset is reversed, and the forging ratio of each upset is 1.2 to 1.8, with a total forging ratio of not less than 3.

[0049] Preferably, during the high-temperature forging process, the first forging billet is first upset and drawn 2 to 3 times, and then the material is widened into a flat square with a width-to-thickness ratio of 1.5 to 2.0. The direction is reversed each time it is upset and drawn, and the forging ratio of each upset and drawn widening is 1.2 to 1.8, with a total forging ratio of not less than 4.

[0050] Preferably, in the first stage of fine-grain forging, the second forging billet is upset 2 to 3 times, with the direction being reversed each time. The forging ratio for each upset is 1.2 to 1.8, and the total forging ratio is not less than 4.

[0051] Preferably, in the second stage of fine-grain forging, the forging billet is upset 2 to 3 times, and the direction is reversed in each upset. The forging ratio of each upset is 1.2 to 1.8, and the total forging ratio is not less than 3.

[0052] Preferably, in the first stage of low-temperature forging, the third forging billet is first upset 2 to 3 times, and then diagonally drawn into a sixteen-square shape. Each upset is reversed, and the forging ratio of each upset is 1.2 to 1.8, with a total forging ratio of not less than 4.

[0053] Preferably, in the second stage of low-temperature forging, the forging billet is first upset 1 to 2 times, with the direction being reversed each time, and then pre-formed. The forging ratio for each upset is 1.2 to 1.8, and the total forging ratio is not less than 4.

[0054] Preferably, during the forming and forging process, the total forging ratio is 1.2 to 1.8, and the deformation is controlled at 30% to 50%.

[0055] As some embodiments of the present invention, the low anisotropy forging method for marine titanium alloy billets can be used for forging near-α titanium alloys, as well as for forging other titanium alloys.

[0056] Preferably, the low anisotropy forging method for marine titanium alloy billets is used for forging near-α titanium alloys.

[0057] As some embodiments of the present invention, the near-α titanium alloy is one of TA5, TA23, TA24, and TA31.

[0058] As some embodiments of the present invention, the forging method for low anisotropy titanium alloy billets for ships can be used for forging titanium alloy billets for ships, or for forging titanium alloy billets for other purposes.

[0059] Based on the phase transformation point of the alloy, this invention, through the rational design of forging cycles and the "high-low-high-low" cyclic deformation temperature, adopts a forging method that combines various deformation methods such as reversing upsetting, diagonal drawing, and flattening, effectively improving the uniformity of the microstructure, reducing the difference between axial and radial microstructures, and obtaining a uniform microstructure in the forged billet. Furthermore, the titanium alloy plate prepared from the forged billet has low anisotropy, good comprehensive performance, and all technical indicators meet the relevant standard requirements.

[0060] The following specific embodiments illustrate the forging method for low anisotropy titanium alloy billets for ships according to the present invention:

[0061] Example 1

[0062] The phase transformation point of the TA5 titanium alloy for shipbuilding with a diameter of φ600mm was measured to be 995℃.

[0063] S1, Initial Forging: One-time initial forging, initial forging temperature is 1170℃, holding coefficient is 1.0min / mm, the titanium alloy ingot is first upset twice, then diagonally drawn into a sixteen-square shape, each upset is reversed, the forging ratio of the first upset is 1.2, the forging ratio of other upsets is 1.6, the total forging ratio is 3.5, the final forging temperature is 893℃, after forging is completed, grinding and polishing are performed to remove surface oxidation and defects to obtain the first forging billet;

[0064] S2, High-temperature forging: The first forging billet is subjected to one high-temperature forging at a temperature of 1050℃ and a holding coefficient of 1.0 min / mm. The first forging billet is first upset twice and then widened into a flat square shape. The direction is reversed in each upset. The forging ratio of the flat square is 1.2, and the forging ratio of each other upset is 1.6, with a total forging ratio of 3.5. The final forging temperature is not lower than 872℃. After forging, the surface oxidation and defects are removed by grinding and polishing to obtain the second forging billet.

[0065] S3, Fine Grain Forging:

[0066] In the first stage, the second forging billet is forged once at 980℃ with a holding coefficient of 0.8 min / mm. The second forging billet is then upsetting and drawing twice, with the direction being reversed each time. The forging ratio for each upsetting and drawing is 1.6, the total forging ratio is 4.6, and the final forging temperature is 824℃.

[0067] In the second stage, a single forging is carried out at 1020℃ with a holding coefficient of 1.0 min / mm. The upsetting and drawing are performed twice, with the direction reversed each time. The forging ratio for each upsetting and drawing is 1.6, the total forging ratio is 4.6, and the final forging temperature is 861℃.

[0068] The third forging blank is obtained by grinding and polishing between the two forging processes to remove surface oxidation and defects;

[0069] S4, Low-temperature forging:

[0070] In the first stage, the third forging billet is forged in one heat at 980℃ below the phase transformation point with a holding coefficient of 0.8 min / mm. The third forging billet is first upsetting and drawing twice, and then diagonally drawn into a sixteen-square shape. The direction is reversed in each upsetting and drawing. The forging ratio of each upsetting and drawing is 1.6, the total forging ratio is 4.6, and the final forging temperature is 825℃.

[0071] In the second stage, the forging after the first stage of low-temperature forging is forged in one heat at 960℃ below the phase transformation point, with a holding coefficient of 0.8 min / mm. The forging billet is first upsetting and drawing twice, with the direction being reversed each time, and then pre-forming is performed. The forging ratio for each upsetting and drawing is 1.6, the forging ratio for pre-forming is 1.5, the total forging ratio is 4.4, and the final forging temperature is 805℃.

[0072] The fourth forging billet is obtained by grinding and polishing between the two forging processes to remove surface oxidation and defects;

[0073] S5, Forming Forging: The fourth forging billet is formed and forged at a temperature of 950℃, a holding coefficient of 0.8min / mm, a total forging ratio of 1.7, a deformation amount controlled at 41%, and a final forging temperature of 810℃.

[0074] Samples were taken from the forged billet for metallographic analysis, and the results are shown below. Figure 1 .

[0075] The forged billet was rolled in two passes to obtain a 14mm thick sheet. The properties of the finished sheet are shown in Table 1 below:

[0076] Table 1. Plate properties obtained using TA5 forging billets

[0077]

[0078]

[0079] Example 2

[0080] The TA23 titanium alloy for marine applications with a diameter of φ600mm was forged, and the measured phase transformation point was 950℃.

[0081] S1, Initial Forging: One-time initial forging, initial forging temperature is 1150℃, holding coefficient is 0.8min / mm, the titanium alloy ingot is first upset twice, then diagonally drawn into a 16-square shape, each upset is reversed, the forging ratio of the first upset is 1.2, the forging ratio of other upsets is 1.6, the total forging ratio is 3.5, the final forging temperature is 888℃, after forging is completed, grinding and polishing are performed to remove surface oxidation and defects to obtain the first forging billet;

[0082] S2, High-temperature forging: The first forging billet is subjected to one high-temperature forging at a temperature of 1020℃ and a holding coefficient of 0.8min / mm. The first forging billet is first upset twice and then widened into a flat square shape. The direction is reversed in each upset. The forging ratio of the flat square is 1.4, and the forging ratio of each other upset is 1.6, with a total forging ratio of 4.1. The final forging temperature is not lower than 863℃. After forging, the surface oxidation and defects are removed by grinding and polishing to obtain the second forging billet.

[0083] S3, Fine Grain Forging:

[0084] In the first stage, the second forging billet is forged once at 930℃ with a holding coefficient of 0.6 min / mm. The second forging billet is then upsetting and drawing twice, with the direction being reversed each time. The forging ratio for each upsetting and drawing is 1.6, the total forging ratio is 4.6, and the final forging temperature is 817℃.

[0085] In the second stage, a single forging process is carried out at 980℃ with a holding coefficient of 0.8 min / mm. The upsetting and drawing are performed twice, with the direction reversed each time. The forging ratio for each upsetting and drawing is 1.6, the total forging ratio is 4.6, and the final forging temperature is 873℃.

[0086] The third forging blank is obtained by grinding and polishing between the two forging processes to remove surface oxidation and defects;

[0087] S4, Low-temperature forging:

[0088] In the first stage, the third forging billet is forged once at 930℃ below the phase transformation point, with a holding coefficient of 0.6 min / mm. The third forging billet is first upsetting and drawing twice, and then diagonally drawn into a sixteen-square shape. The direction is reversed each time it is upsetting and drawing. The forging ratio of each upsetting and drawing is 1.6, the total forging ratio is 4.6, and the final forging temperature is 835℃.

[0089] In the second stage, the forging after the first stage of low-temperature forging is forged in one heat at 920℃ below the phase transformation point, with a holding coefficient of 0.6 min / mm. The forging billet is first upsetting and drawing twice, with the direction being reversed each time, and then pre-forming is performed. The forging ratio for each upsetting and drawing is 1.6, the forging ratio for pre-forming is 1.7, the total forging ratio is 4.9, and the final forging temperature is 803℃.

[0090] The fourth forging billet is obtained by grinding and polishing between the two forging processes to remove surface oxidation and defects;

[0091] S5, Forming Forging: The fourth forging billet is formed and forged at a temperature of 920℃, a holding coefficient of 0.6min / mm, a total forging ratio of 1.6, a deformation amount controlled at 38%, and a final forging temperature of 808℃.

[0092] Samples were taken from the forged billet for metallographic analysis, and the results are shown below. Figure 2 .

[0093] The forged billet was rolled twice to obtain a 10mm thick plate. The properties of the finished plate are shown in Table 2 below:

[0094] Table 2. Plate properties obtained using TA23 forging billets

[0095]

[0096] Example 3

[0097] The TA24 titanium alloy for marine applications with a diameter of φ600mm was forged, and the measured phase transformation point was 955℃.

[0098] S1, Initial Forging: One-time initial forging, initial forging temperature is 1150℃, holding coefficient is 0.8min / mm, the titanium alloy ingot is first upset twice, then diagonally drawn into a sixteen-square shape, each upset is reversed, the forging ratio of the first upset is 1.2, the forging ratio of other upsets is 1.7, the total forging ratio is 4.4, the final forging temperature is 878℃, after forging is completed, grinding and polishing are performed to remove surface oxidation and defects to obtain the first forging billet;

[0099] S2, High-temperature forging: The first forging billet is subjected to one high-temperature forging at a temperature of 1020℃ and a holding coefficient of 0.8min / mm. The first forging billet is first upset twice and then widened into a flat square shape. The direction is reversed in each upset. The forging ratio of the flat square is 1.3, and the forging ratio of each other upset is 1.7, with a total forging ratio of 4.8. The final forging temperature is not lower than 866℃. After forging, the surface oxidation and defects are removed by grinding and polishing to obtain the second forging billet.

[0100] S3, Fine Grain Forging:

[0101] In the first stage, the second forging billet is forged once at 940℃ with a holding coefficient of 0.6 min / mm. The second forging billet is then upsetting and drawing twice, with the direction being reversed each time. The forging ratio for each upsetting and drawing is 1.7, the total forging ratio is 6.3, and the final forging temperature is 826℃.

[0102] In the second stage, a single forging is carried out at 980℃ with a holding coefficient of 0.8 min / mm. The upsetting and drawing are performed twice, with the direction reversed each time. The forging ratio for each upsetting and drawing is 1.7, the total forging ratio is 6.3, and the final forging temperature is 875℃.

[0103] The third forging blank is obtained by grinding and polishing between the two forging processes to remove surface oxidation and defects;

[0104] S4, Low-temperature forging:

[0105] In the first stage, the third forging billet is forged once at 940℃ below the phase transformation point, with a holding coefficient of 0.6 min / mm. The third forging billet is first upsetting and drawing twice, and then diagonally drawn into a sixteen-square shape. The direction is reversed each time it is upsetting and drawing. The forging ratio of each upsetting and drawing is 1.7, the total forging ratio is 6.3, and the final forging temperature is 855℃.

[0106] In the second stage, the forging after the first stage of low-temperature forging is carried out in one heat at 930℃ below the phase transformation point, with a holding coefficient of 0.6 min / mm. The forging billet is first upsetting and drawing twice, with the direction being reversed each time, and then pre-forming is carried out. The forging ratio of each upsetting and drawing is 1.7, the forging ratio of pre-forming is 1.8, the total forging ratio is 6.7, and the final forging temperature is 811℃.

[0107] The fourth forging billet is obtained by grinding and polishing between the two forging processes to remove surface oxidation and defects;

[0108] S5, Forming Forging: The fourth forging billet is formed and forged at a temperature of 920℃, a holding coefficient of 0.6min / mm, a total forging ratio of 1.8, a deformation amount controlled at 44%, and a final forging temperature of 812℃.

[0109] Samples were taken from the forged billet for metallographic analysis, and the results are shown below. Figure 3 .

[0110] The forged billet was rolled twice to obtain a 25mm thick plate. The properties of the finished plate are shown in Table 3 below:

[0111] Table 3. Plate properties obtained using TA24 forging billets

[0112]

[0113]

[0114] Example 4

[0115] The TA31 titanium alloy for marine applications with a diameter of φ600mm was forged, and the measured phase transformation point was 990℃.

[0116] S1, Initial Forging: One-time initial forging, initial forging temperature is 1150℃, holding coefficient is 1.0min / mm, the titanium alloy ingot is first upset twice, and then diagonally drawn into a sixteen-square shape. The direction is reversed in each upset. The forging ratio of the first upset is 1.3, the forging ratio of the other upsets is 1.6, the total forging ratio is 3.8, and the final forging temperature is 865℃. After forging, the surface oxidation and defects are removed by grinding and polishing to obtain the first forging billet.

[0117] S2, High-temperature forging: The first forging billet is subjected to one high-temperature forging at a temperature of 1050℃ and a holding coefficient of 1.0 min / mm. The first forging billet is first upset twice and then widened into a flat square shape. The direction is reversed in each upset. The forging ratio of the flat square is 1.3, and the forging ratio of each other upset is 1.6, with a total forging ratio of 3.8. The final forging temperature is not lower than 856℃. After forging, the surface oxidation and defects are removed by grinding and polishing to obtain the second forging billet.

[0118] S3, Fine Grain Forging:

[0119] In the first stage, the second forging billet is forged once at 980℃ with a holding coefficient of 0.8 min / mm. The second forging billet is then upsetting and drawing twice, with the direction being reversed each time. The forging ratio for each upsetting and drawing is 1.6, the total forging ratio is 4.6, and the final forging temperature is 836℃.

[0120] In the second stage, a single forging is carried out at 1020℃ with a holding coefficient of 1.0 min / mm. The upsetting and drawing are performed twice, with the direction reversed each time. The forging ratio for each upsetting and drawing is 1.6, the total forging ratio is 4.6, and the final forging temperature is 862℃.

[0121] The third forging blank is obtained by grinding and polishing between the two forging processes to remove surface oxidation and defects;

[0122] S4, Low-temperature forging:

[0123] In the first stage, the third forging billet is forged once at 980℃ below the phase transformation point, with a holding coefficient of 0.8 min / mm. The third forging billet is first upsetting and drawing twice, and then diagonally drawn into a sixteen-square shape. The direction is reversed in each upsetting and drawing. The forging ratio of each upsetting and drawing is 1.6, the total forging ratio is 4.6, and the final forging temperature is 857℃.

[0124] In the second stage, the forging after the first stage of low-temperature forging is forged in one heat at 970℃ below the phase transformation point, with a holding coefficient of 0.8 min / mm. The forging billet is first upsetting and drawing twice, with the direction being reversed each time, and then pre-forming is performed. The forging ratio for each upsetting and drawing is 1.6, the forging ratio for pre-forming is 1.7, the total forging ratio is 4.9, and the final forging temperature is 806℃.

[0125] The fourth forging billet is obtained by grinding and polishing between the two forging processes to remove surface oxidation and defects;

[0126] S5, Forming Forging: The fourth forging billet is formed and forged at a temperature of 960℃, a holding coefficient of 0.8min / mm, a total forging ratio of 1.5, a deformation amount controlled at 33%, and a final forging temperature of 802℃.

[0127] Samples were taken from the forged billet for metallographic analysis, and the results are shown below. Figure 4 .

[0128] The forged billet was rolled in two passes to obtain a 25mm thick sheet. The properties of the finished sheet are shown in Table 4 below.

[0129]

[0130] Depend on Figures 1-4 As shown in Tables 1-4, the near-α titanium alloys for ships obtained in Examples 1, 2, 3, and 4 of this invention have uniform axial and radial cross-sectional structures with small anisotropic differences. Furthermore, the medium-thick plates rolled from the billets prepared by this invention exhibit low anisotropy, meet standard requirements in both transverse and longitudinal directions, and have a large performance margin.

[0131] In summary, the forging method for low anisotropy titanium alloy billets for ships described in this invention has the following advantages:

[0132] First, the titanium alloy forging billet prepared has uniform axial and radial microstructure with small differences, which results in low anisotropy and good comprehensive performance of the plate rolled from the forging billet prepared by the present invention.

[0133] Second, the forging method developed is not only universally applicable to near-α titanium alloys used in ships, but also has good reference value for the promotion of other types of titanium alloys;

[0134] Third, it adopts conventional forging production methods, which are highly adaptable to the process, do not require the addition of new equipment, and are simple to operate, enabling mass production.

[0135] While the present invention has been disclosed above, it is not limited thereto. In the description of this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for forging low-anisotropic titanium alloy billets for marine applications, characterized in that, Including the following steps: S1, Initial Forging: The titanium alloy ingot is subjected to one-time initial forging at a temperature above the phase transformation point (T). β +(100~250)℃, heat preservation coefficient is 0.8~1.0min / mm, final forging temperature is not lower than 850℃, after forging, grinding and polishing are performed to remove surface oxidation and defects to obtain the first forging billet; during the billet forging process, the billet is first upset and drawn 2~3 times, and then drawn diagonally into a sixteen-square shape. The direction is changed each time it is upset and drawn. The forging ratio of each upset and drawn is 1.2~1.8, and the total forging ratio is not lower than 3; S2, High-Temperature Forging: The first forging billet undergoes a single high-temperature forging process, with the forging temperature above the phase transformation point (T). β +(50~150)℃, heat preservation coefficient 0.8~1.0min / mm, final forging temperature not lower than 850℃, after forging, grinding and polishing are performed to remove surface oxidation and defects to obtain the second forging billet; during the high temperature forging process, the first forging billet is first upset and drawn 2~3 times, and then widened into a flat square with a width-to-thickness ratio of 1.5~2.

0. The direction is reversed each time it is upset and drawn, and the forging ratio of each upset and drawn widening is 1.2~1.8, and the total forging ratio is not lower than 4; S3, Fine Grain Forging: The first stage begins below the phase transition point T. β The second forging billet is forged in one pass at -(10~30)℃, with a holding coefficient of 0.6~0.8 min / mm, and the final forging temperature is not lower than 800℃; during the fine grain forging process in the first stage, the second forging billet is upsetting and drawing 2~3 times, with the direction being reversed each time, and the forging ratio of each upsetting and drawing is 1.2~1.8, with a total forging ratio of not less than 4; The second stage, and then above the phase transition point T β The forging process is carried out at +(20~50)℃ in one pass, with a holding coefficient of 0.8~1.0 min / mm and a final forging temperature of not less than 850℃; in the second stage of fine grain forging, the second forging billet is upsetting and drawing 2~3 times, with each upsetting and drawing being reversed, and the forging ratio of each upsetting and drawing being 1.2~1.8, with a total forging ratio of not less than 3; Between the two firing cycles, grinding and polishing are performed to remove surface oxidation and defects; S4, Low-temperature forging: The first stage begins below the phase transition point T. β The fine-grained forging billet is forged in one pass at -(10~30)℃, with a holding coefficient of 0.6~0.8 min / mm and a final forging temperature of not less than 800℃; in the first stage of low-temperature forging, the billet is first upset and drawn 2~3 times, and then diagonally drawn into a sixteen-square shape. The direction is reversed each time it is upset and drawn. The forging ratio of each upset and drawing is 1.2~1.8, and the total forging ratio is not less than 4. The second stage, then below the phase transition point T β - (20~50)℃ for one-time forging, with a holding coefficient of 0.6~0.8min / mm, and a final forging temperature of not less than 800℃; in the second stage of low-temperature forging, the forging billet is first upset and drawn 1~2 times, with the direction changed each time, and then pre-formed, with an upset forging ratio of 1.2~1.8 each time, and a total forging ratio of not less than 4; Between the two firing cycles, grinding and polishing are performed to remove surface oxidation and defects; S5, Forming Forging: Forming forging is performed on the forged billet after low-temperature forging. The forming forging temperature is below the phase transformation point T. β -30~50℃, heat preservation coefficient is 0.6~0.8min / mm, final forging temperature is not lower than 800℃; during the forming forging process, the total forging ratio is 1.2~1.8, and the deformation is controlled at 30%~50%; The low anisotropy forging method for marine titanium alloy billets is used for forging near-α titanium alloys.

2. The forging method for low anisotropy titanium alloy billets for ships according to claim 1, characterized in that, The near-α titanium alloy is one of TA5, TA23, TA24 or TA31.

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