Method for reducing anisotropy of continuous annealing alpha-phase titanium plate and titanium plate

Abstract

The invention discloses a method for reducing anisotropy of a continuous annealing alpha-phase titanium plate and the titanium plate. The method comprises the following steps that a pure titanium plate is subjected to primary annealing treatment, the heat preservation temperature ranges from 600 DEG C to 700 DEG C, and the heat preservation time ranges from 1 min to 3 min; primary acid pickling and cold rolling; the cold-rolled pure titanium plate is subjected to secondary annealing treatment, the heat preservation temperature ranges from 820 DEG C to 910 DEG C, the heat preservation time ranges from 1 min to 5 min, and then air cooling is conducted; and carrying out secondary pickling. The invention mainly aims to provide a method for improving the anisotropy of an alpha-phase titanium plate in a continuous annealing process so as to solve the problem that the performance difference of the alpha-phase titanium plate in different directions is obvious in the existing titanium plate processing technology. Compared with the prior art, the process is simple, cost is saved, and the method is suitable for continuous annealing equipment.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy material processing, and in particular relates to a method for reducing the anisotropy of a continuously annealed α-phase titanium plate. Background Art

[0002] Rolling and annealing are essential steps in the titanium plate processing process. Continuous annealing and hood annealing are two methods used in the plate production process. Continuous annealing offers advantages such as high production efficiency, superior product quality, and low cost. The type and distribution of the final texture after rolling and annealing significantly affect the plate's mechanical properties along the rolling direction (RD) and perpendicular to the rolling direction (TD), resulting in anisotropy that affects its usability. To mitigate the anisotropy of titanium plates, variations in the rolling and annealing processes are one approach. α-phase titanium is a close-packed hexagonal metal with a limited slip system and low symmetry, and its internal evolution mechanism is quite complex during processing. Deformation textures are easily generated during rolling and inherited during annealing. Furthermore, due to the existence of allotropes in titanium, phase transformations can also occur during annealing, affecting the material's texture and properties.

[0003] Currently, inventions for improving the anisotropy of titanium plates focus on the bell annealing process. These include: ① Reversing rolling, including reversing hot rolling and reversing cold rolling, combined with subsequent annealing, effectively improves the anisotropy of titanium plates and is a widely used method (CN106925612, CN111589859A, CN117600230A, CN118957466A). ② Adding alloying elements to control the phase composition of the titanium plates, combined with appropriate rolling and annealing processes, improves anisotropy (CN117418083A). ③ Flattening the titanium plates after annealing, by applying micro-deformation to improve the crystallographic texture and, in turn, anisotropy (CN102989768A, CN113265603A). ④ Controlling the phase transformation process through complex thermal cycling combined with a series of rolling processes allows for improved anisotropy through the manipulation of microstructure and texture through phase transformation. (CN11134731A, CN111394669A).

[0004] Among the above methods, reversing rolling is not conducive to high-efficiency mass production of titanium plates, and has low efficiency and high cost; the method of changing the phase composition of alloying elements will change the type of titanium plates; the flattening treatment after annealing has a small effect on the change of the organizational texture, and it is difficult to significantly improve the anisotropy; the method of controlling phase change and texture through complex rolling and thermal cycle processes requires a long annealing holding time and is not applicable to the faster continuous annealing process.

[0005] Therefore, there is an urgent need to provide a method for efficiently reducing the anisotropy of α-phase titanium plates that can be applied to a continuous annealing process. Summary of the Invention

[0006] The main purpose of the present invention is to provide a method for reducing the anisotropy of a continuously annealed α-phase titanium plate and a titanium plate in view of the problems and shortcomings of the prior art.

[0007] In order to solve the above technical problems, the technical solutions of the present invention are as follows: A method for reducing the anisotropy of a continuously annealed α-phase titanium plate comprises the following steps: The pure titanium plate is subjected to an annealing treatment, wherein the holding temperature is 600-700°C and the holding time is 1-3 minutes; Once pickled and cold rolled; The cold-rolled pure titanium plate is subjected to secondary annealing treatment, wherein the holding temperature is 820-910°C, the holding time is 1-5 minutes, and then air-cooled; Secondary pickling.

[0008] In the above solution, the heating rate in the primary annealing and the secondary annealing is 15-25°C / min.

[0009] In the above scheme, the pickling solution used in the pickling step is a mixture of hydrofluoric acid, nitric acid and water, and the pickling time is 5-15 minutes.

[0010] In the above scheme, the volume ratio of hydrofluoric acid, nitric acid and water is 1:5:11.

[0011] In the above scheme, in the cold rolling step, the rolling direction is unidirectional rolling, the rolling speed is 5-18 m / min, and the cold rolling reduction rate is ≥70%.

[0012] The titanium plate prepared by the method described above.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The main purpose of the present invention is to provide a method for improving the anisotropy of α-phase titanium plates during continuous annealing, so as to solve the problem of significant performance differences in different directions of α-phase titanium plates in existing titanium plate processing technology. The present invention only requires adjusting the continuous annealing process during the production of conventional titanium plates. Its characteristics and principle are that by adjusting the continuous annealing temperature, the industrial pure titanium plate undergoes an α→β→α phase transformation process in a short period of time, and the grain size and orientation distribution of the titanium plate can be effectively adjusted at the same time, thereby achieving the purpose of reducing anisotropy. Compared with the prior art, the process is simpler, saves costs, and is suitable for continuous annealing equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The orientation imaging diagram of the sample after annealing is shown in FIG1 (a), FIG1 (b), and FIG1 (c), respectively.

[0015] Figure 2 The orientation images of the samples after annealing are shown in Figure 2(a), Example 2(b), Example 1, and Example 3(c). DETAILED DESCRIPTION

[0016] The principles and features of the present invention are described below in conjunction with examples, which are only used to explain the present invention and are not intended to limit the scope of the present invention. In addition, it is worth noting that the raw materials involved in the present invention are all common commercially available products unless otherwise specified.

[0017] Example 1

[0018] This embodiment provides a method for reducing the anisotropy of a continuously annealed α-phase titanium plate, comprising the following steps: S101, performing an annealing treatment on the pure titanium plate, wherein the holding temperature is 600-700° C. and the holding time is 1-3 minutes.

[0019] The thickness of the pure titanium plate is 2.0 mm. This step can produce a primary annealed plate with a relatively coarse equiaxed structure and an average grain size of 15 μm.

[0020] S201, one pickling and cold rolling.

[0021] In the first pickling step, the pickling solution used is a mixture of hydrofluoric acid, nitric acid and water, and the pickling time is 5-15 minutes. The volume ratio of hydrofluoric acid, nitric acid and water is 1:5:11.

[0022] In the cold rolling step, the rolling direction is unidirectional rolling, the rolling speed is 5 m / min, the cold rolling reduction ratio is 75%, and a cold rolled sheet with a thickness of 0.5 mm is obtained.

[0023] S301, the cold-rolled pure titanium plate is subjected to a second annealing treatment to complete the α→β→α phase transformation process. The holding temperature is 880°C for 120 seconds, followed by air cooling. S401, secondary pickling.

[0024] The orientation imaging of the α-phase titanium plate obtained is shown in Figure 1 As shown in Figure b, it shows a uniform and fine equiaxed structure with an average grain size of approximately 9.1 μm and a relatively small proportion of pyramidal texture (32.4%). The difference in yield strength in the longitudinal and transverse directions is 44 MPa, as shown in Table 1.

[0025] Table 1 Mechanical properties of specimens (MPa)

[0026] Comparative Example 1 This comparative example is similar to Example 1, except that the secondary annealing temperature is 760°C. Figure 1 As shown in Figure a, after annealing at 760°C, the grain size is significantly larger, with an average grain size of approximately 15 μm. The pyramidal texture accounts for a high proportion (36.8%). The difference in yield strength between the longitudinal and transverse directions is 72 MPa. During annealing at 760°C, the material's phase transition temperature is not reached, and only recrystallization occurs, resulting in coarser grains.

[0027] Comparative Example 2 This comparative example is similar to Example 1, except that the secondary annealing temperature is 950°C. Figure 1 As shown in Figure c, while the grain sizes are relatively similar, with an average grain size of approximately 8.9 μm, the proportion of pyramidal texture increases (35.9%). The difference in yield strength between the longitudinal and transverse directions is 60 MPa. Annealing at 950°C reaches the material's phase transition temperature, resulting in finer grains. However, the higher temperature affects the nucleation and growth of grains with different orientations, leading to an increase in the proportion of pyramidal texture.

[0028] Example 2

[0029] This embodiment is similar to embodiment 1, except that the secondary annealing time is 90s. Figure 2 As shown in Figure a, grain size variation is minimal, with the pyramidal texture accounting for 33.7%. The difference in yield strength between the longitudinal and transverse directions is 56 MPa. After holding at 880°C for 90 seconds, the material reaches its phase transition temperature, resulting in fine grains. However, the holding time affects the growth of grains with different orientations, resulting in a slightly higher proportion of pyramidal texture.

[0030] Example 3

[0031] This embodiment is similar to embodiment 1, except that the secondary annealing time is 150s. Figure 2 As shown in Figure c, grain size differences are minimal, with the pyramidal texture accounting for 33.1%. The yield strength difference between the longitudinal and transverse directions is 45 MPa. After holding at 880°C for 150 seconds, the material reaches its phase transition temperature, resulting in fine grains. However, the holding time affects the growth of grains with different orientations, resulting in a slightly higher proportion of pyramidal texture.

[0032] Comparative Example 3 This comparative example is similar to Example 1, except that the primary annealing step (step 1) was omitted. This resulted in fine, uniform grains, but a high proportion of pyramidal texture (40.2%). Omission of the primary annealing step resulted in stronger initial grain orientation (hot-rolled sample) and uneven surface and center layers. This texture is inherited in subsequent processing steps, resulting in changes in the final texture.

[0033] It should be noted that those skilled in the art may make various modifications and improvements without departing from the scope of the present invention, and these modifications and improvements fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be based on the appended claims.

Claims

1. A method for reducing the anisotropy of a continuously annealed α-phase titanium plate, characterized in that: The steps include: The pure titanium plate is subjected to an annealing treatment, wherein the holding temperature is 600-700°C and the holding time is 1-3 minutes; Once pickled and cold rolled; The cold-rolled pure titanium plate is subjected to secondary annealing treatment, wherein the holding temperature is 820-910°C, the holding time is 1-5 minutes, and then air-cooled; Secondary pickling.

2. The method according to claim 1, wherein During the primary annealing and the secondary annealing, the heating rate is 15-25° C. / min.

3. The method according to claim 1, wherein The pickling solution used in the pickling step is a mixture of hydrofluoric acid, nitric acid and water, and the pickling time is 5-15 minutes.

4. The method according to claim 3, wherein The volume ratio of the hydrofluoric acid, nitric acid and water is 1:5:

11.

5. The method according to claim 1, wherein In the cold rolling step, the rolling direction is unidirectional rolling, the rolling speed is 5-18 m / min, and the cold rolling reduction rate is ≥70%.

6. A titanium plate prepared according to the method according to any one of claims 1 to 5.

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