WO2019100809A1 - High strength and toughness filamentous grain pure titanium and preparation method therefor - Google Patents

Abstract

A high strength and toughness filamentous grain pure titanium, the micro-structure being formed of filamentous grains or filamentous grains mixed with equiaxed grains, the length ratio of the long axis of the filamentous grains to the short axis thereof being greater than 40, and the size of the short axis being 10 μm to 10 nm, the equiaxed grains being recrystallised ultra-fine grains. The preparation method comprises the following steps: (1) performing 1-2 equal channel angular extrusions to acquire titanium bar; (2) performing swaging of the titanium bar multiple times and then cutting to acquire titanium plate having a rectangular cross section; (3) cyclically performing annealing and multiple times of control rolling of the titanium plate; and (4) annealing to obtain the high strength and toughness filamentous grain pure titanium. The mechanical properties of the obtained pure titanium are equivalent to titanium alloy, and costs are reduced, avoiding complex processing and elements such as Al and V that are harmful to living organisms, being a biological implantable structural material suitable for joints, dentistry, and stents.

Description

High-strength toughness filamentous crystal pure titanium and preparation method thereof Technical field

The invention belongs to the field of biosurgical implantable structural materials, and particularly relates to a filamentous crystal pure titanium material with high toughness and energy and a preparation method thereof.

Background technique

Compared with titanium, such as Ti-xAl-yV, Ti-xAl-yNb, Ti-wSn-xNb-yTa-zPb and Ti-wZr-xNb-yTa-zPb, pure titanium not only has a better biological phase. Capacitive and corrosion-resistant, it also avoids the expensive cost of the alloy, complex processes and elements such as Al and V which are harmful to living organisms. It can be preferably used as a structural material for joints, dental and scaffold organisms. However, conventional pure titanium exhibits lower yield strength and wear resistance due to the lack of strengthening of alloying elements. For example, the standard GB/T 13810-2007 (ISO 5832-2 2012) specifies the yield strengths of TA1 (Grade 1) and TA2 (Grade 2) pure titanium of 170 MPa and 275 MPa, respectively, which is much lower than the 860 MPa of Ti-6Al-4V. . Therefore, the development of pure titanium with ultra-high strength and toughness is an urgent problem to be solved as a load-bearing structural material.

Although the ultrafine or nanocrystalline structure formed by severe plastic deformation can effectively improve the strength of the metal material, the lattice defects such as saturated dislocations and grain boundaries severely limit the subsequent plastic deformation ability, so that after the type of material yields Immediately breaks the failure. In addition, the use of large plastic deformation method at room temperature to refine the hexagonal structure of pure titanium has the problem of difficult deformation and easy cracking. Although the patent CN 103981472 B achieves grain refinement by equal channel angular extrusion in the form of copper wrapping, the process requires copper wrapping, multi-pass equal channel corner extrusion, and removal of the wrapped copper, which is extremely inefficient. It is not suitable for large-scale production. According to the mechanism of multi-mode grain strengthening and toughening, patent CN 102703756 B combined with high energy ball milling and spark plasma sintering process to prepare coarse-grain/fine-grain bimodal grain Ti-6Al-4V with better mechanical properties. However, this process step is complicated and the energy consumption is high. Even if it is popularized for the preparation of pure titanium, the limited toughness of the multimodal grain structure makes it difficult to make the strength of the pure titanium reach the strength of the alloy material. XLWu et al. (Heterogeneous Lamella Structure Unites Ultrafine-Grain Strength with Coarse-Grain Ductility. Proceedings of the national academy of sciences, 2015; 112: 14501-14505.) using non-uniform layered structural mechanics inconsistency toughening mechanism The pure titanium with superior toughness can be prepared by asynchronous rolling and subsequent annealing, but the tensile strength of the whole material is still lower than 700 MPa, and the block size is only 300 μm, which is difficult to be practical. The effect of ultrasonic impact treatment on the deformation behavior of the present pure titanium under uniaxial tension. Materials and design, 2017; 117: 371–381., based on the mechanism of fine-grain strengthening and gradient structure coupling toughening, use The high-energy shot peening method prepares a nano-gradient layer on the surface of pure titanium. However, since the thickness of the nano-gradient layer is too thin, the yield strength is only increased by 60 MPa and the plasticity is greatly reduced. In addition, the overall strength of the materials prepared by the surface mechanical nanometering method is not much improved, and the surface roughness is too large, which is not conducive to production and practical.

Up to now, the bottleneck of pure titanium in biomedical, aerospace, military equipment and other fields still lies in the low toughness. In the case that pure titanium obtained by fine-grain strengthening, multi-mode grain strengthening and toughening, gradient coupling strengthening and other related processes cannot achieve a large breakthrough in the comprehensive mechanical properties of toughness, it is necessary to explore a new type of toughening microscopic Structure and its industrial preparation method.

Summary of the invention

Aiming at the problem of low mechanical strength of pure titanium, it aims to provide a high-strength and tough filamentous grain pure titanium from the perspective of microstructure. The pure titanium has the same tough mechanical properties as the alloy titanium, and has better biocompatibility and corrosion resistance, avoiding the expensive cost of the alloy, the complicated process and the elements such as Al and V which are harmful to the living body. It is preferably used as a structural material for implants, dental and scaffold organisms. The invention also provides a preparation method of high-strength and tough filamentous crystal pure titanium.

The invention is achieved by the following technical solutions:

A high-strength and tough filamentous grain pure titanium, the microstructure consists of a mixture of filamentary grains and equiaxed grains, wherein the ratio of the major axis to the minor axis of the filamentous grains is greater than 40 and the minor axis size is 10 μm to 10 nm. The equiaxed grains are recrystallized ultrafine grains.

The volume fraction of the filamentous crystal grains is more than 80%, and the difference in orientation between the long axes of the filamentary crystal grains is less than 10°.

The equiaxed grains are equiaxed ultrafine grains formed by partial recrystallization of a severely plastically deformed structure by short-time annealing.

The preparation method of the high-strength tough filamentous crystal pure titanium as described above comprises the following steps:

(1) adjusting the grain orientation of pure titanium by 1-2 passes of equal channel angular pressing to obtain a titanium bar;

(2) further performing the multi-pass swaging of the titanium rod obtained in the step (1) and cutting to obtain a titanium plate having a rectangular cross section;

(3) annealing the titanium sheet material again - multi-pass control rolling;

(4) Annealing high-strength tough filamentous grains of pure titanium.

Step (1) The corner of the mold used for medium-channel corner extrusion is 120°.

In step (2), the amount of strain for each rotary forging is ≤1.4, and the cumulative strain for multi-pass swaging is ≥2.5.

The annealing in the step (3) is a reductive annealing at a temperature of 300 to 400 ° C, and each annealing time is 60 s to 1 h.

The multi-pass control rolling process in the step (3) is synchronous symmetrical rolling along the longitudinal direction of the sheet, that is, the size and speed of the upper and lower rolls are the same and the rolling speed is not higher than 50 mm/s.

Step (3) The temperature range of the multi-pass control rolling process is -196 to 400 ° C, the strain of a single pass is ≤ 0.1, and the cumulative strain of the multi-pass rolling between adjacent annealing is ≤ 0.5.

The annealing process in the step (4) is a partial recrystallization annealing at a critical recrystallization temperature, the temperature is 400 to 450 ° C, and the time is 30 to 600 s.

The textured orientation of the filamentary grains of the filamentary crystal pure titanium produced along the long axis direction is a crystallographic soft orientation, and the equiaxed grains are discretely distributed between the filamentary grains.

The reason why the filamentary grain pure titanium has high strength and toughness is that: (1) ultrafine/nano-sized filamentary grains and equiaxed grains have high-density grain boundaries, which can effectively improve the yield strength of the material; (2) The recovered or recrystallized grains have lower dislocation density relative to the severely plastically deformed grains, providing more lattice defect storage space for subsequent work hardening; (3) discretely distributed between the filamentary grains Submicron and/or nano equiaxed crystals can effectively alleviate the stress concentration along the grain boundary caused by the uncoordinated deformation between filamentous grains, broaden the spatial range along the grain boundary strain gradient, and promote structural strengthening and toughening; (4) Compared with the equiaxed ultrafine or nanocrystalline, the dislocations have a sufficiently long sliding path along the long axis direction of the filamentary grains, and the soft orientation texture in this direction facilitates the actuation of the slip system, prompting the material to occur. Uniform plastic deformation.

At present, there is no large bulk metal material whose microstructure is composed of filamentary grains in the scientific research and industrial fields. The reason is: (1) in the thermoplastic environment, the crystal grains are difficult to grow spontaneously in one direction; (2) the conventional severe plastic deformation method can change the shape of the parent metal grain, but the complex dislocation proliferation, quenching, and recombination process Grain refinement is evident and tends to form equiaxed dislocation structures or new grains. For example, the equal channel angular extrusion process has a circumferential confining pressure, but the large shear deformation at the corner causes the original grain to be broken and cannot be greatly elongated in one direction; the simple cumulative rolling process can be elongated. The lamellar grain structure, but the long diameter of these grains is relatively small; the drawing process does not have a large cumulative strain amount, and the aspect ratio of the formed crystal grains is also very small. Therefore, the preparation of the filamentary structure requires not only the accumulation of a sufficiently high plastic strain but also a suitable plastic deformation rate and path.

The purpose of a few passes of the equal channel corner extrusion step is to apply large strain to the bar and adjust the texture to reduce the angle between the grain slip system and the length direction of the rod, which is beneficial to the subsequent grain in the process of swaging. The length direction is elongated and deformed. The rotary forging process not only can apply uniform circumferential confining pressure, but the concentric unidirectional passage of variable diameter and the control single-pass strain are the key factors to ensure that the filamentary grains do not undergo equiaxed fracture. In order to avoid the fracture of the swaged bar grain due to excessive plastic strain and torsional shear stress, and further increase the aspect ratio of the filamentous grain, the pure titanium after multi-pass swaging is recycled and annealed. And control rolling.

The filamentary grain pure titanium prepared by the method has the mechanical characteristics of having excellent strength and plastic deformation ability, the tensile yield strength is greater than 770 MPa, the tensile strength is greater than 900 MPa, and the uniform tensile plasticity is greater than 5%. The elongation after break is greater than 10%.

The strain-variable algorithm of the swaging process is ε ₁ = ln(A ₀ /A), where A ₀ is the cross-sectional area of the pure titanium rod before swaging, and A is the cross-sectional area of the pure titanium rod after swaging.

The strain-variable algorithm for the rolling process is ε ₂ = Δh/h ₀ , where h ₀ is the thickness of the pure titanium sheet before rolling, and Δh is the reduction of the thickness of the pure titanium sheet after rolling relative to h ₀ .

Compared with the prior art, the present invention has the following advantages and beneficial effects:

1. Strictly controlled process steps and parameters to prepare a unique microstructure, which not only overcomes the easy fracture and fragmentation of elongated grains, but also avoids the large-scale recrystallization of the deformed structure and grows up;

2. The microstructure composed of micro/nanofilamentous grains and ultrafine equiaxed grains can simultaneously exhibit various strengthening and toughening mechanisms of fine grain strengthening, non-uniform structure coupling strengthening and toughening, and texture toughening. The pure titanium of the structure exhibits mechanical properties comparable to those of the alloy titanium;

3. The material prepared is practical, and the filamentary grain pure titanium overcomes the bottleneck of toughness and can replace the application of alloy titanium, especially for biosurgical implantable structural materials;

4. The preparation process is simple, the cost is low, the efficiency is high, and the production can be scaled.

DRAWINGS

The drawings are intended to provide a further understanding of the embodiments of the present invention, and are not intended to limit the embodiments of the invention. In the drawing:

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph showing the comparison of engineering stress-strain curves of the starting material, the pre-recrystallization pre-annealing material, and the filament-like grain materials obtained by different portions of recrystallization annealing conditions in Examples 1-3.

Figure 2 is a transmission electron micrograph (TEM) image of a cross section of a bar obtained after completion of multi-pass swaging in this Example 1.

3 is a three-dimensional metallographic diagram of the high-strength and tough filamentous crystal pure titanium prepared in Example 1, and it can be seen that the material is composed of ultrafine filamentary crystal grains.

4 is an electron backscatter diffraction (EBSD) gray scale image of a 500×100 μm ² region of high-strength tough filamentous crystal grains prepared in Example 1.

5 is an EBSD grayscale image of a 40×35 μm ² region of high-strength and tough filamentous crystal grains prepared in Example 1, and black arrows indicate recrystallization superfine crystals.

Fig. 6 is a graph showing the comparison of the engineering stress-strain curves of the filament-like crystal pure titanium prepared in Example 4 (broken line) and Example 1 (solid line).

Fig. 7 is a EBSD gray scale diagram of a portion of a high-strength tough filamentous grain pure titanium partial 40 × 35 μm ² prepared in Example 4.

Figure 8 is a graph showing the comparison of the engineering stress-strain curves of the filament-like crystal pure titanium prepared in Example 5 (broken line) and Example 1 (solid line).

Detailed ways

The present invention will be further described in detail below with reference to the embodiments and the accompanying drawings. As a limitation of the invention.

The raw material grade is TA2, the technical standard is in accordance with GB/T3620.1-2007, and the composition is shown in Table 1. The raw material is made into a standard tensile pattern. The engineering stress-strain curve obtained by quasi-static tensile test is shown by the dotted line in Figure 1. The yield strength is 280 MPa, the tensile strength is 430 MPa, the uniform elongation is 11.9%, and the elongation after fracture. It is 27%.

Table 1

Example 1

Raw material: pure titanium rod with a diameter of 32 mm.

Follow the specific steps below:

(1) Two-pass equal channel angular extrusion: The die with a channel diameter of 32 mm is selected, and the initial bar is subjected to the first pass equal channel angular extrusion. The extrusion die has a rotation angle of 120° and an extrusion temperature of 400 ° C. The bar is rotated 180° around the axis and placed in a mold for a second pass equal channel corner extrusion.

(2) Multi-pass swaging: the first pass swaging is to forge the 32mm diameter bar obtained in step (1) to a diameter of 24mm, the strain is about 0.58; the second pass swaging will swallow the diameter of 24mm bar To a diameter of 16 mm, the strain should be about 0.81; the third pass swallowing will forge a diameter of 16 mm bar to a diameter of 8 mm, and the strain should be about 1.39.

(3) The titanium rod having a diameter of 8 mm obtained in the step (2) was cut into a sheet having a cross section of 6.9 × 4 mm ² , and the longitudinal direction of the sheet was parallel to the longitudinal direction of the swaged bar.

(4) The sheet obtained in the step (3) was subjected to annealing in a vacuum furnace at a temperature of 350 ° C for a period of 600 s.

(5) Start the rolling mill, adjust the height of the rolls to be equal to 4 mm, adjust the speed of the upper and lower rolls to be equal to 50 mm/s or less.

(6) Multi-pass room temperature synchronous rolling: the height of the roll is lowered by 0.1 mm, and the plate is rolled twice; the plate is fed in the direction of feeding, and the plate is further rolled twice.

(7) Step (6) is repeated four more times, wherein the rolling direction is the length direction of the sheet and the strain of a single pass is less than 0.1.

(8) The pure titanium obtained in the step (7) is subjected to annealing in a vacuum furnace at a temperature of 350 ° C for 600 s.

(9) The steps (6) to (8) were repeated five times to obtain a pure titanium plate having a thickness of 1 mm.

(10) The pure titanium plate obtained in the foregoing step was subjected to partial recrystallization annealing in a vacuum furnace at a temperature of 450 ° C for 300 s.

The rolling process is room temperature rolling, in which the single pass rolling strain does not exceed 0.1, the cumulative plastic strain between adjacent annealings does not exceed 0.35, and the total cumulative plastic strain is 0.75.

Fig. 2 is a TEM microstructure of a cross section of a bar obtained after the multi-pass swaging of the step (2) in the present embodiment, and the grain profile is ultra-finely equiaxed.

Fig. 3 is a three-dimensional metallographic diagram of the high-strength and ductile grain-like pure titanium prepared in the present embodiment, and it can be seen that the material is composed of ultrafine filamentary grains.

Figure 4 is a EBSD grayscale image of a partial 500 x 100 ^m2 region of a pure titanium material prepared in this case. It can be seen that the body of the microstructure consists of elongated filamentary grains. The statistical results in this region show that the average length of the filamentous crystal grains is 166 μm, the average aspect ratio is 45.7, and the composition ratio of the filamentous crystal grains is 94%, and the orientation difference between the long axes of the filamentous crystal grains is smaller than 10°. Among them, the individual filamentous crystal grains have a length of 500 μm and an aspect ratio of more than 100.

Figure 5 is a EBSD grayscale image of a partial 40 x 35 μm ² region of pure titanium material prepared in this case. Black arrows indicate that the recrystallized ultrafine crystals are discretely distributed along the filamentary grains.

The thin solid line in Fig. 1 is the quasi-static tensile test engineering stress-strain curve of the filamentous grain pure titanium in the rolling direction after the completion of step (9) in the case, and the yield strength and tensile strength are 973.7 MPa and 1030.3, respectively. MPa, but the uniform elongation is only 2.1%, and the elongation after fracture is greater than 7%

The thick solid line in Fig. 1 is the quasi-static tensile test engineering stress-strain curve of the filamentous grain pure titanium prepared in the step (10) of the present case, the yield strength is 770.5 MPa, and the tensile strength is 909.7 MPa. The uniform elongation was 8.3%, and the elongation after break was greater than 15%.

Example 2

This example differs from Example 1 in that the partial recrystallization annealing temperature of the preparation step (10) is 400 ° C for 480 s.

The thin dotted line in Figure 1 is the quasi-static tensile test engineering stress-strain curve of the filamentous grain pure titanium prepared in this case along the rolling direction. The yield strength is as high as 838.2 MPa, with a very large work hardening rate and tensile strength. 964.8MPa, uniform plastic strain is 6.2%, elongation after fracture is greater than 12%.

The microstructure was similar to that of Example 1, but the degree of recovery and recrystallization ratio were reduced, and the composition ratio of filamentous crystal grains was about 99%.

Example 3

This example differs from Example 1 in that the partial recrystallization annealing temperature of the preparation step (10) is 475 ° C for 300 s.

The thick dashed line in Figure 1 is the quasi-static tensile test engineering stress-strain curve of the filamentous grain pure titanium prepared in this case along the rolling direction. Compared with Example 1, the yield strength of the filamentous structure prepared in this case was reduced by about 90 MPa, while the uniform plasticity was only increased by 1.7%, and the elongation after fracture was greater than 16%. The ratio of filamentous grain composition in the microstructure is reduced to 73%, which indicates that the filamentous grains have an important contribution to the toughness of the material.

Example 4

The difference between this embodiment and the embodiment 1 is that the initial diameter of the raw material is 20 mm; the diameter of the channel of the extrusion die used in the step (1) is 20 mm; and the first pass of the step (2) is obtained by the step (1) The 20mm diameter bar is swaged to a diameter of 16mm. The second pass swaged swages a 16mm diameter bar to a diameter of 8mm. The total cumulative plastic strain is only 1.833. The subsequent steps are identical to those of Embodiment 1.

Fig. 6 is a comparison diagram of the engineering stress-strain curves of the filament-like structural material obtained before and after partial recrystallization in Example 1 and Example 1. The yield strength and tensile strength of the filamentary grain material obtained before partial recrystallization annealing in this example were 740.8 MPa and 850.3 MPa, respectively. After partial recrystallization annealing, the uniform elongation increased to 10.8%, and the elongation after fracture was greater than 20%, but the yield strength and tensile strength were 587.2 MPa and 707.2 MPa, respectively, which were much lower than those obtained in Example 1 and Example 2.

Figure 7 is a EBSD grayscale image of a partial 40 x 35 μm ² region of a pure titanium material prepared in this case. A small amount of recrystallized ultrafine crystals have a discrete distribution, and most of the crystal grains are filamentous. However, the average minor axis size of the filamentary grains is much larger than that obtained in Example 1 and the distribution is extremely uneven, ranging from submicron spans to tens of micrometers.

Comparing the present embodiment with the first embodiment can show that the step (2) accumulating a sufficiently high plastic strain during the swaging process is favorable for forming uniform, fine filamentous crystal grains, and the size of the filamentous crystal grains seriously affects the material strength. Toughness properties, the smaller the diameter of the filamentary grains, the higher the material strength.

Example 5

The difference between this embodiment and the embodiment 1 is that the temperature of the controlled rolling process is the liquid nitrogen temperature, that is, -196 ° C; in order to avoid the formation of cracks during the severe plastic deformation process at low temperature, the step (6) to the step of the rolling process ( 8) Performed a total of 4 times with a total cumulative plastic strain of 50% and a final sheet thickness of 2 mm. The other steps and parameters are identical to those of the first embodiment.

Fig. 8 is a comparison diagram of the engineering stress-strain curves of the filament-like structural material obtained before and after partial recrystallization in Example (dashed line) and Example 1 (solid line). The yield strength of the filamentous structural material obtained before partial recrystallization annealing in this example was 981.7 MPa, which was comparable to that obtained in the room temperature rolling of Example 1, but showed significant work hardening and tensile strength of 1072.3 MPa in the subsequent deformation process, and uniformity. The elongation reached 3.4% and the elongation after break was greater than 7%. The wire-like structural material obtained by vacuum annealing at 450 ° C for 300 s has a yield strength of 808.6 MPa, a tensile strength of 939.9 MPa, a uniform elongation of 7.4%, and an elongation after fracture of more than 14%.

The low temperature and large cumulative plastic deformation induced twinning is the reason why the strength of the filamentous structural material obtained in the present embodiment is higher than that obtained in Example 1.

The yield strength, tensile strength, and elongation after elongation of the filamentary grain pure titanium prepared in the above examples are in accordance with the Chinese National Standard (GB), the International Standardization Organization (ISO), and the American Society for Testing and Materials (ASTM). The mechanical properties of pure titanium and titanium alloys for implantation were compared. The results are shown in Table 2.

Table 2

Note: The status bar in the table indicates the material supply status, including annealed state (A), cast state (W), cold worked state (CW), cold worked and partially recrystallized annealed state (CW+PRA); the table specifies the non-proportional extension strength (R _p0.2 ) refers to the strength corresponding to 0.2% plastic strain, that is, the yield strength described in this patent.

It can be seen from the table that the toughness of the filamentous crystal pure titanium provided by the present invention is much higher than that of the conventional surgical implanted pure titanium, and has the same properties as Ti-6Al-4V and Ti-6Al-7Nb. Quite mechanical properties.

The invention provides a high-strength and tough filamentous crystal pure titanium and a preparation method thereof, which are not limited to the application of biomedical surgical implantable structural materials. Any high-strength and tough filamentous crystal pure titanium provided by the invention and its preparation method in any field and industry are all covered by the patent.

The specific embodiments of the present invention have been described in detail with reference to the preferred embodiments of the present invention. All modifications, equivalent substitutions, improvements, etc., made within the spirit and scope of the invention are intended to be included within the scope of the invention.

Claims (9)

1. A high-strength and tough filamentous grain pure titanium characterized in that the microstructure is composed of filamentary crystal grains or filamentary crystal grains mixed with equiaxed grains, wherein the ratio of the length of the long axis to the minor axis of the filamentous crystal grains is greater than 40 and the minor axis size is 10 μm to 10 nm, and the equiaxed grains are recrystallized ultrafine crystals.
2. The high-strength tough filamentous grain pure titanium according to claim 1, wherein the volume fraction of the filamentary crystal grains is more than 80%, and the difference in orientation between the long axes of the filamentary crystal grains is less than 10°.
3. The method for preparing high-strength and tough filamentous crystal pure titanium according to any one of claims 1 to 2, comprising the steps of:

   (1) adjusting the grain orientation of pure titanium by 1-2 passes of equal channel angular pressing to obtain a titanium bar;

   (2) further performing the multi-pass swaging of the titanium rod obtained in the step (1) and cutting to obtain a titanium plate having a rectangular cross section;

   (3) annealing the titanium sheet material again - multi-pass control rolling;

   (4) Annealing high-strength tough filamentous grains of pure titanium.
4. The preparation method according to claim 3, wherein the step (1) of the mold for medium-channel corner extrusion has a rotation angle of 120°.
5. The preparation method according to claim 3, characterized in that the strain amount of each pass swaging in step (2) is ≤1.4, and the cumulative strain amount of multi-pass swaging is ≥2.5.
6. The preparation method according to claim 3, wherein the annealing in the step (3) is a reductive annealing at a temperature of 300 to 400 ° C, and each annealing time is 60 s to 1 h.
7. The preparation method according to claim 3, wherein the multi-pass controlled rolling process in the step (3) is synchronous symmetrical rolling along the longitudinal direction of the sheet, that is, the size and speed of the upper and lower rolls are the same and rolling The speed is not higher than 50mm/s.
8. The preparation method according to claim 3, wherein the step (3) multi-pass control rolling process has a temperature range of -196 to 400 ° C, a single pass strain ≤ 0.1, and two adjacent annealings The cumulative strain of the multi-pass rolling performed between ≤ 0.5.
9. The preparation method according to claim 3, wherein the annealing process in the step (4) is partial recrystallization annealing at a critical recrystallization temperature, the temperature is 400 to 450 ° C, and the time is 30 to 600 s.

Images