Preparation method of near-beta ultrahigh-strength titanium alloy high-uniformity tissue bar

Abstract

The invention discloses a preparation method of a near-beta ultrahigh-strength titanium alloy high-uniformity structure bar. The preparation method specifically comprises the following steps: preparing a bar blank; the bar blank is heated, a two-roller reversible rolling mill is adopted, rolling is carried out according to the processes of square hole pattern primary rolling, oval hole pattern transition rolling and round hole pattern finish rolling, air cooling is carried out after rolling, and an intermediate blank bar with the uniform and fine structure is obtained; the rolled intermediate billet bar is heated, a broaching machine is adopted for hot drawing and diameter reducing, and a bar with the uniform and fine structure is obtained; and the bar is subjected to roller type hot straightening, scalping and polishing, and the high-uniform-structure alloy bar with the specification range of phi 6.0 mm to phi 20.0 mm is obtained. According to the high-uniform-structure bar prepared through the method, after solid solution aging, the tensile strength is larger than or equal to 1550 MPa, and the percentage elongation after fracture is larger than or equal to 10.5%.

Description

Technical Field

[0001] This invention belongs to the field of high-strength titanium alloy processing technology, specifically relating to a method for preparing near-β ultra-high-strength titanium alloy bars with highly uniform microstructure. Background Technology

[0002] With the rapid development of the aerospace industry, ultra-high strength titanium alloys have emerged. Ultra-high strength titanium alloys refer to alloys with a tensile strength exceeding 1400 MPa at room temperature. Currently, these ultra-high strength titanium alloy types include β alloys and near-β alloys. The high-strength and high-toughness titanium alloys currently in use are mainly TB3, TB8, and TB9. Newly developed 1300MPa~1500MPa grade titanium alloys are still in the development stage and have not yet been truly applied.

[0003] For near-β titanium alloys, where precipitation strengthening is the dominant mechanism, controlling the uniformity of the microstructure is crucial for ensuring the stability of the material's mechanical properties. However, this type of alloy faces a significant challenge in the hot deformation process for producing bars and wires: the significant temperature rise during hot deformation often leads to obvious overheating in the core. Core overheating disrupts the normal nucleation and growth of precipitates, resulting in significant differences between the core and edge microstructures in terms of grain size, precipitate morphology, and distribution. Ultimately, it is impossible to obtain high-quality bars and wires with consistent core and edge microstructures and uniform properties. Therefore, to address this core issue, it is urgent to achieve precise control of the temperature rise during hot deformation by optimizing hot deformation process parameters, improving heating and cooling methods, and microalloying the alloy composition. This will solve the core overheating problem and ensure the uniformity of the microstructure in near-β titanium alloy bars and wires. Furthermore, the coarse β grains have a strong heritability; even subsequent solution aging heat treatment cannot improve the microstructure uniformity, leading to a deterioration in the consistency of the alloy's strength, plasticity, and toughness, especially for T... β Near-β high-strength titanium alloys with a temperature range of ≤850℃ have an extremely narrow hot deformation temperature range, making it very difficult to effectively control the process temperature. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing near-β ultra-high strength titanium alloy bars with highly uniform microstructure, which solves the problem of temperature control during the hot deformation process of near-β ultra-high strength titanium alloys.

[0005] The technical solution adopted in this invention is a method for preparing near-β ultra-high strength titanium alloy rods with highly uniform microstructure, which is implemented according to the following steps: Step 1, billet preparation; Step 2: Heat the billet from Step 1 and roll it using a two-roll reversible rolling mill, following the process of square pass initial rolling, elliptical pass transition rolling, and circular pass finishing rolling. After rolling, air cool it to obtain a uniform and fine-structured intermediate billet. Step 3: Heat the intermediate billet rolled in Step 2 and use a broaching machine to hot draw and reduce its diameter to obtain a bar with a uniform and fine structure. Step 4: The bar obtained in Step 3 is subjected to roller hot straightening, peeling and polishing to obtain the finished bar.

[0006] The invention is further characterized in that, Step 1 specifically involves: A Ti-5Al-3Mo-3V-6Cr-3Zr-1Nb titanium alloy was selected. Its chemical composition, by mass percentage, is as follows: Al: 4.5%~5.5%, Mo: 2.5%~3.5%, V: 2.5%~3.5%, Cr: 5.5%~6.5%, Zr: 2.5%~3.5%, Nb: 0.5%~1.5%, O: ≤0.10%, with the balance being Ti. The sum of the mass percentages of these components is 100%. The above composition was melted to obtain a titanium alloy ingot. The titanium alloy ingot was then forged using a high-low-high forging process to obtain billets. The billet specifications are Φ95mm~Φ100mm.

[0007] In step 2, the heating temperature is 700℃~760℃, the deformation of each rolling pass is controlled at 10%~15%, and the final rolling temperature is 650℃~750℃.

[0008] In step 3, the heating temperature is 680℃~750℃, the deformation per pass is ≤10%, and the total deformation is 50%~75%.

[0009] In step 4, the hot straightening temperature is 650~700℃. The finished bar specifications are Φ6.0mm~Φ20mm.

[0010] The beneficial effects of this invention are: (1) The method of the present invention refines the billet structure by controlling the temperature rise during the low-temperature rolling process, and rationally designs the drawing temperature and deformation amount, thereby achieving high uniformity of the edge and core structure of the bar wire and significantly improving the consistency of the structure. (2) The finished bar material obtained by the above method has good edge-center consistency and reasonable solution aging of the sample, and can obtain a bar material with high uniformity, ultra-high strength and high plasticity. (3) The specifications of the rods prepared by this invention range from Φ6.0mm to Φ20.0mm, and can be applied to titanium alloy rods for ultra-high strength fasteners, structural parts, etc., with broad application prospects. Attached Figure Description

[0011] Figure 1 This is a flowchart illustrating the preparation process of the near-β ultra-high strength titanium alloy high-uniformity microstructure bar of the present invention; Figure 2This is a micrograph of the cross-section of a Φ18.5mm titanium alloy bar obtained in Example 1 of this invention; Figure 3 This is a micrograph of the cross-section of a Φ16.5mm titanium alloy bar obtained in Example 2 of this invention; Figure 4 This is a micrograph of the cross-section of a Φ12.5mm titanium alloy bar obtained in Example 3 of this invention. Detailed Implementation

[0012] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0013] The present invention relates to a method for preparing near-β ultra-high strength titanium alloy rods with highly uniform microstructure, such as... Figure 1 As shown, please follow these steps: Step 1, Billet Preparation The Ti-5Al-3Mo-3V-6Cr-3Zr-1Nb titanium alloy was selected. Its chemical composition by mass percentage is as follows: Al: 4.5%~5.5%, Mo: 2.5%~3.5%, V: 2.5%~3.5%, Cr: 5.5%~6.5%, Zr: 2.5%~3.5%, Nb: 0.5%~1.5%, O: ≤0.10%, with the balance being Ti. The sum of the mass percentages of the above components is 100%. The above components are smelted to obtain a titanium alloy ingot; this alloy ingot is then forged using high and low forging techniques to obtain billet blanks with dimensions of Φ95mm~Φ100mm, with 100% removal of oxide scale and surface defects. The transverse and longitudinal microstructure is a uniform and fine hot-deformed two-phase region microstructure. The high-low-high forging process involves: first, high-temperature forging of titanium alloy ingots, followed by low-temperature refining forging, and finally high-temperature re-homogenization forging. Through the process of high-temperature forging to break coarse grains, low-temperature refining of dispersed phases, and high-temperature re-homogenization recrystallization, coarse dendrites and defects in the ingot can be eliminated, ultimately obtaining a uniform and fine equiaxed structure, avoiding performance fluctuations caused by microstructure inheritance, and improving the stability of the forging structure.

[0014] Step 2, Heating and Rolling: The billet from Step 1 is heated in a walking beam or box-type resistance heating furnace at a temperature of 700℃~760℃. A two-roll reversible rolling mill is used to roll the billet through a process of square pass initial rolling, elliptical pass transition rolling, and circular pass finishing rolling. The deformation per rolling pass is controlled at 10%~15%, and the final rolling temperature is 650℃~750℃. After rolling, the billet is air-cooled to obtain a uniform and fine-grained intermediate billet. The use of a square-elliptical-round hole system can make the metal flow of the bar more uniform in each pass, promote dynamic recrystallization, refine the microstructure, suppress the formation of strong texture, and improve the anisotropy of the bar.

[0015] Step 3, Heating and Drawing The intermediate billet bar rolled in step 2 is heated in a tubular resistance heating furnace at a temperature of 680℃~750℃, and then hot-drawn to reduce its diameter using a broaching bed. The deformation per pass is ≤10%, and the total deformation is 50%~75%, resulting in a bar with a uniform and fine structure. The hot drawing process avoids the coarsening caused by rolling by properly controlling the temperature rise during hot deformation. Dynamic recrystallization can break down the post-rolling microstructure, refine the grains, and improve the strength and plasticity of the bar.

[0016] Step 4, Finishing of finished bar stock The bar obtained in step 3 is subjected to roller hot straightening at a temperature of 650~700℃, and then peeled and polished to a finished bar of Φ6.0mm~Φ20mm.

[0017] The present invention provides a method for preparing near-β ultra-high strength titanium alloy bars with highly uniform microstructure, which solves the problem of difficult temperature control during the hot deformation process of near-β ultra-high strength titanium alloys and can obtain bars with uniform and fine microstructure.

[0018] Example 1 The present invention provides a method for preparing near-β ultra-high strength titanium alloy rods with highly uniform microstructure, specifically comprising: Step 1, Billet Preparation The selected Ti-5Al-3Mo-3V-6Cr-3Zr-1Nb titanium alloy has the following elements: Al 4.5%~5.5%, Mo 2.5%~3.5%, V 2.5%~3.5%, Cr 5.5%~6.5%, Zr 2.5%~3.5%, Nb 0.5%~1.5%, and O ≤0.10%.

[0019] The above components are smelted to obtain a titanium alloy ingot; the alloy ingot is then forged at high and low speeds to obtain a billet with a size of Φ95mm~Φ100mm, and the transverse and longitudinal structures are uniform and fine hot-deformed two-phase regions.

[0020] Step 2, Heating and Rolling The bar billet from step 1 is heated in a walking beam or box resistance heating furnace at a temperature of 720℃. A two-roll reversible rolling mill with a square-elliptical-round die system is used, and the final rolling temperature is 718℃. After rolling, it is air-cooled to obtain a Φ33mm intermediate billet with a uniform and fine microstructure. Step 3, Heating and Drawing The billet rolled in step 2 is heated in a tubular resistance heating furnace at a temperature of 720℃, with a deformation of 8% per pass, and hot-drawn to Φ19.5mm, with a hot drawing deformation of 65.1%.

[0021] Step 4, Straightening and finishing of finished bars After the bar obtained in step 3 is hot-straightened by roller at a temperature of 660℃, it is peeled and polished to obtain a Φ18.5mm bar of Ti-5Al-3Mo-3V-6Cr-3Zr-1Nb alloy.

[0022] Example 2 The present invention provides a method for preparing near-β ultra-high strength titanium alloy rods with highly uniform microstructure, specifically comprising: Step 1, Billet Preparation A titanium alloy of Ti-5Al-3Mo-3V-6Cr-3Zr-1Nb was selected, containing 4.5%~5.5% Al, 2.5%~3.5% Mo, 2.5%~3.5% V, 5.5%~6.5% Cr, 2.5%~3.5% Zr, 0.5%~1.5% Nb, and ≤0.10% O. The above composition was smelted to obtain a titanium alloy ingot. This ingot was then forged using high-low-high forging techniques to obtain a billet with a diameter of Φ95mm~Φ100mm, exhibiting a uniform and fine two-phase microstructure in both the transverse and longitudinal directions.

[0023] Step 2, Heating and Rolling The bar billet from step 1 is heated in a walking beam or box resistance heating furnace at a temperature of 720℃. A two-roll reversible rolling mill with a square-elliptical-round die system is used. The final rolling temperature is 725℃. After rolling, it is air-cooled to obtain a Φ33mm intermediate billet with a uniform and fine microstructure. Step 3, Heating and Drawing The billet rolled in step 2 is heated in a tubular resistance heating furnace at a temperature of 720℃, with a deformation of 8% per pass, and hot-drawn to Φ17.5mm, with a hot drawing deformation of 71.9%.

[0024] Step 4, Straightening and finishing of finished bars After the bar obtained in step 3 is hot-straightened by roller at a temperature of 660℃, it is peeled and polished to obtain a Φ16.5mm bar of Ti-5Al-3Mo-3V-6Cr-3Zr-1Nb alloy.

[0025] Example 3 The present invention provides a method for preparing near-β ultra-high strength titanium alloy rods with highly uniform microstructure, specifically comprising: Step 1, Billet Preparation A titanium alloy of Ti-5Al-3Mo-3V-6Cr-3Zr-1Nb was selected, containing 4.5%~5.5% Al, 2.5%~3.5% Mo, 2.5%~3.5% V, 5.5%~6.5% Cr, 2.5%~3.5% Zr, 0.5%~1.5% Nb, and ≤0.10% O. The above composition was smelted to obtain a titanium alloy ingot. This ingot was then forged using high-low-high forging techniques to obtain a billet with a diameter of Φ95mm~Φ100mm, exhibiting a uniform and fine two-phase microstructure in both the transverse and longitudinal directions.

[0026] Step 2, Heating and Rolling The bar billet from step 1 is heated in a walking beam or box-type resistance heating furnace at a temperature of 720°C using a two-roll reversible rolling mill with a square-elliptical-round die system. The final rolling temperature is 725°C, followed by air cooling to obtain a Φ50mm intermediate billet. A second rolling process is then performed, with a heating temperature of 710°C using a reversible rolling mill with a square-elliptical-round die system. The final rolling temperature is 715°C, followed by air cooling to obtain a Φ26mm intermediate billet. Step 3, Heating and Drawing The billet rolled in step 2 is heated in a tubular resistance heating furnace at a temperature of 720°C, with a deformation of 8% per pass, and hot-drawn to Φ13.5 mm, with a hot drawing deformation of 69.6%.

[0027] Step 4, Straightening and finishing of finished bars After the bar obtained in step 3 is hot-straightened by roller at a temperature of 660℃, it is peeled and polished to obtain a Φ12.5mm bar of Ti-5Al-3Mo-3V-6Cr-3Zr-1Nb alloy.

[0028] Example 5 Figure 2 The high-magnification microstructure of the cross-section of the Φ18.5mm rod of Ti-5Al-3Mo-3V-6Cr-3Zr-1Nb alloy obtained in Example 1 of this invention is a two-phase microstructure with no coarse grains and overheating, and is fine and uniform. Figure 3 The high-magnification microstructure of the cross-section of the Φ16.5mm rod of Ti-5Al-3Mo-3V-6Cr-3Zr-1Nb alloy obtained in Example 2 of this invention is a two-phase microstructure with no coarse grains and overheating, and is fine and uniform. Figure 4 The cross-sectional high-magnification microstructure of a Φ12.5mm rod of Ti-5Al-3Mo-3V-6Cr-3Zr-1Nb alloy obtained in Example 3 of this invention is a two-phase microstructure with no coarse grains and overheating, and is fine and uniform.

[0029] Example 6 According to GB / T 228.1 Metallic Materials: Tensile Testing - Room Temperature Tensile Test, the Φ18.5mm titanium alloy bars prepared in Example 1, the Φ16.5mm titanium alloy bars prepared in Example 2, and the Φ12.5mm titanium alloy bars prepared in Example 3 of this invention were subjected to room temperature tensile performance tests after solution treatment and aging. The results are shown in Table 1. The high-uniformity structure bars prepared in the examples of this invention have a tensile strength ≥1500MPa and an elongation after fracture ≥10%.

[0030] Table 1. Tensile property test results of the bars prepared according to the embodiments of the present invention.

[0031] This invention addresses the challenge of temperature control during the hot deformation process of near-β type ultra-high strength titanium alloys. It employs heated rolling to prepare the billet, replacing the rolling process with a hot drawing process for bars. By designing a reasonable deformation temperature and deformation amount, bars with uniform and fine microstructure at the edges and center are obtained. Highly uniform alloy bars with a microstructure ranging from Φ6.0mm to Φ20.0mm are then produced through roller hot straightening, peeling, and polishing. The highly uniform bars prepared using this method, after solution treatment and aging, exhibit a tensile strength ≥1550MPa and an elongation at break ≥10.5%.

[0032] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention.

[0033] It should be understood that the present invention is not limited to the content already described above, and various modifications and changes can be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for preparing near-β ultra-high strength titanium alloy rods with highly uniform microstructure, characterized in that, The specific steps are as follows: Step 1, billet preparation; Step 2: Heat the billet from Step 1 and roll it using a two-roll reversible rolling mill, following the process of square pass initial rolling, elliptical pass transition rolling, and circular pass finishing rolling. After rolling, air cool it to obtain a uniform and fine-structured intermediate billet. Step 3: Heat the intermediate billet rolled in Step 2 and use a broaching machine to hot draw and reduce its diameter to obtain a bar with a uniform and fine structure. Step 4: The bar obtained in Step 3 is subjected to roller hot straightening, peeling and polishing to obtain the finished bar.

2. The method for preparing near-β ultra-high strength titanium alloy high-uniformity microstructure rods as described in claim 1, characterized in that, In step 1, specifically: A Ti-5Al-3Mo-3V-6Cr-3Zr-1Nb titanium alloy was selected. Its chemical composition by mass percentage was: Al: 4.5%~5.5%, Mo: 2.5%~3.5%, V: 2.5%~3.5%, Cr: 5.5%~6.5%, Zr: 2.5%~3.5%, Nb: 0.5%~1.5%, O: ≤0.10%, with the balance being Ti. The sum of the mass percentages of the above components was 100%. The above components were melted to obtain a titanium alloy ingot. The titanium alloy ingot was then forged using a high-low-high forging process to obtain a billet.

3. The method for preparing near-β ultra-high strength titanium alloy high-uniformity microstructure rods as described in claim 2, characterized in that, The billet specifications are Φ95mm~Φ100mm.

4. The method for preparing near-β ultra-high strength titanium alloy high-uniformity microstructure rods as described in claim 1, characterized in that, In step 2, the heating temperature is 700℃~760℃, the deformation of each rolling pass is controlled at 10%~15%, and the final rolling temperature is 650℃~750℃.

5. The method for preparing near-β ultra-high strength titanium alloy high-uniformity microstructure rods as described in claim 1, characterized in that, In step 3, the heating temperature is 680℃~750℃, the deformation per pass is ≤10%, and the total deformation is 50%~75%.

6. The method for preparing near-β ultra-high strength titanium alloy high-uniformity microstructure rods as described in claim 1, characterized in that, In step 4, the hot straightening temperature is 650~700℃.

7. The method for preparing near-β ultra-high strength titanium alloy high-uniformity microstructure rods as described in claim 1, characterized in that, The finished bar stock has a specification of Φ6.0mm~Φ20mm.

8. The near-β ultra-high strength titanium alloy high-uniformity microstructure rod prepared by the preparation method of any one of claims 1-7.

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