A short process forging process of a Ti5331 medium-strength high-toughness titanium alloy in a full beta phase region

Abstract

This invention relates to the field of titanium alloy forging technology, specifically disclosing a short-process forging technology for Ti5331 medium-strength, high-toughness titanium alloy in the full β-phase region. The process involves forging a Ti5331 titanium alloy ingot at 1100℃-1200℃, followed by forging deformation at 30℃-50℃ below the phase transformation temperature, then recrystallization homogenization heating and multiple continuous reflow forging at 30℃-50℃ above the phase transformation temperature, and finally, finished product forging at 30℃-50℃ above the phase transformation temperature. This invention offers advantages such as fewer forging passes and a shorter forging cycle, significantly reducing the forging cost of Ti5331 titanium alloy bars.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy forging technology, specifically to a short-process forging process for Ti5331 medium-strength and high-toughness titanium alloy in the full β-phase region. Background Technology

[0002] Titanium alloys are widely used in aerospace, marine engineering, shipbuilding, and weaponry due to their excellent specific strength, plastic deformation capacity, large-section hardenability, and corrosion resistance. Especially in the aerospace field, titanium alloys have become the preferred material for manufacturing key components such as the main load-bearing frame of the fuselage and landing gear systems, and their usage percentage has become one of the important technical indicators for evaluating the advancement of modern aircraft. With the breakthrough progress in my country's aerospace equipment research and manufacturing capabilities, the concept of low-cost design throughout the entire life cycle, while ensuring high structural reliability, has been integrated into the design process from its inception. Modern aircraft design generally requires comprehensive cost control, which places even more stringent cost control requirements on the titanium alloy manufacturing process, as a major structural material.

[0003] Ti5331 titanium alloy, as a new generation of low-cost, high-performance titanium alloy independently developed in my country, maintains high strength while possessing comprehensive performance advantages such as high toughness, high damage tolerance, and ultra-long fatigue life. Its wide forging process window (supporting multiple combinations of two-phase forging + quasi-β heat treatment, two-phase forging + two-phase heat treatment, quasi-β forging + two-phase heat treatment, etc.) can meet the customized needs of different structural parts. However, the Ti5331 titanium alloy finished bars currently used in the aerospace field still use the traditional two-phase forging process. This process requires simultaneously achieving the dual goals of β grain homogenization and α phase equiaxation, resulting in a lengthy processing cycle. Furthermore, the two-phase deformation process significantly increases the risk of forging cracks and grinding losses, which to some extent restricts the achievement of material preparation efficiency and cost control goals. Summary of the Invention

[0004] To address the shortcomings of existing technologies in tapping the low-cost potential of Ti5331 titanium alloys, this invention provides a short-process forging process for Ti5331 medium-strength and high-toughness titanium alloys in the full β-phase region. This process produces Ti5331 titanium alloy bars with uniform microstructure and excellent comprehensive properties in the Φ150mm-Φ500mm specification through a small number of single-phase region forging passes, thereby fully releasing the low-cost manufacturing potential of this new titanium alloy.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A short-process forging process for Ti5331 medium-strength and high-toughness titanium alloy in the full β-phase region is characterized by forging Ti5331 titanium alloy ingots at 1100℃-1200℃, followed by forging deformation at 30℃-50℃ below the phase transformation temperature, then recrystallization homogenization heating and multi-fire continuous reflow forging at 30℃-50℃ above the phase transformation temperature, and finally finished product forging at 30℃-50℃ above the phase transformation temperature.

[0007] Furthermore, the aforementioned short-process forging process for the entire β-phase region of Ti5331 titanium alloy is achieved through the following steps:

[0008] Step 1) Heat the Ti5331 titanium alloy ingot to 1100℃-1200℃ for a single-pass upsetting and drawing forging, with the total forging ratio controlled at 5.0-10.0, to obtain the forged billet after upsetting;

[0009] Step 2) Heat the forged billet after the initial forging to 30-50°C below the phase transformation temperature for one-time upsetting or drawing forging, with the total forging ratio controlled at 5.0-10.0. Then, quickly heat the billet to 30-50°C above the phase transformation temperature for recrystallization and homogenization heating treatment, and quickly remove it from the furnace after heating.

[0010] Step 3) The forged billet obtained in Step 2) is subjected to multiple continuous forging in a furnace at a temperature 30℃-50℃ above the phase transformation point. The single-fire forging ratio for upsetting and drawing is controlled at 3.0-6.0, and the single-fire forging ratio for drawing is controlled at 1.5-2.0. The total forging ratio for this step is controlled at 15.0-30.0, resulting in a forged billet with an octagonal or hexagonal cross-section. (This step specifically controls the cumulative forging ratio. The dimensions of the upsetting and drawing billet and the finished product are affected. For example, if the billet after forging in Step 2 is a 600mm square, and the finished product after Step 3 is a 520mm octagonal (corresponding to a Φ500mm finished bar), if the straight...) If the billet is drawn from a 600mm square to a 520mm octagon, the pure drawing forging ratio is only 1.6. Therefore, several upsetting operations are needed, with each upsetting operation having a forging ratio of 3.0~6.0, ensuring a total forging ratio of 15.0~30.0. If the billet after forging in step 2 is a 600mm square, and the finished product after step 3 is a 170mm octagon (corresponding to a Φ150mm finished bar), directly drawing from the 600mm square to the 170mm octagon can achieve a drawing forging ratio of over 15.0, eliminating the need for upsetting operations. The forging ratio per drawing operation should be controlled at 1.5-2.0.

[0011] Step 4) Heat the forging billet obtained in Step 3) to 30℃-50℃ above the phase transformation temperature for finished product rounding forging, with the forging ratio controlled at 1.1-1.3, to obtain finished bar stock.

[0012] Furthermore, the heating and holding coefficient in steps 1) and 4) above is controlled to be 0.7-0.9 min / mm; the heating and holding coefficient in step 2) during forging at 30℃-50℃ below the phase transformation point temperature is controlled to be 0.7-0.9 min / mm, and the heating and holding coefficient for recrystallization homogenization at 30℃-50℃ above the phase transformation point is controlled to be 0.6-0.8 min / mm; the holding coefficient for hot material returning to the furnace in step 3) is controlled to be 0.3-0.5 min / mm.

[0013] Furthermore, the final forging temperature after each step from 1) to 4) is not lower than 750℃, and air cooling is used after each step.

[0014] Furthermore, in steps 1) to 3) above, after each air cooling to room temperature, the surface cracks of the billet need to be polished, and the polished area needs to be smoothly transitioned, with a width-to-depth ratio of not less than 8:1.

[0015] Furthermore, in step 2) above, the cross-sectional dimensions of the billet after forging at 30℃-50℃ below the phase transformation temperature are square or flat, but the minimum cross-sectional thickness does not exceed 600mm.

[0016] Furthermore, the specific choice between upset forging and drawing forging at temperatures 30℃-50℃ below the phase transformation point in step 2) above needs to be determined based on the cross-sectional dimensions of the finished bar. Specifically, if upset forging in step 2) would cause the pure drawing forging ratio in step 3) to exceed 30, then pure drawing forging is selected; if upset forging in step 2) would not cause the pure drawing forging ratio in step 3) to exceed 30, then upset forging is selected.

[0017] Furthermore, the specific method for the multi-fire continuous reflow forging in step 3) above—whether to use pure drawing forging or upset drawing forging + pure drawing forging—must ensure that the cumulative forging ratio in step 3) is 15.0-30.0. Specifically, if the cumulative forging ratio of pure drawing forging alone in step 3) is 15.0-30.0, then pure drawing forging should be performed directly; if the cumulative forging ratio of pure drawing forging alone in step 3) is less than 15.0-30.0, then appropriate upset drawing forging should be performed first, followed by pure drawing forging.

[0018] The working principle of this invention is as follows:

[0019] The mechanical properties of titanium alloys are generally closely related to the size of the β grains and the morphology and distribution of the α phase. In the traditional forging process of titanium alloy bars, to simultaneously ensure a good balance of comprehensive mechanical properties such as strength, plasticity, and toughness, a "high-low" or "high-low-high-low" process route is typically adopted. This involves first subjecting the titanium alloy ingot to multiple upsetting and drawing forgings above the phase transformation point to break down and refine the as-cast grains. Regardless of whether "high" or "high-low-high" forging is used, the billet is heated to the two-phase region and subjected to multiple upsetting and drawing forgings before finishing to break down and refine the α phase, thereby improving the alloy's plasticity. This application focuses on the characteristics of Ti5331 titanium alloy. Through extensive experiments, it explores the correlation between the mechanical properties of Ti5331 titanium alloy and the size of its β-grain and morphology of the α-phase. It was found that when the β-grain size of Ti5331 titanium alloy is refined to a certain extent, the alloy still exhibits good strength-plasticity-toughness matching even without two-phase forging. Further research revealed that when the deformed Ti5331 titanium alloy is heated at 30-50°C above its phase transformation point, the Ti5331 alloy rapidly recrystallizes. Furthermore, prolonged heating at 30-50°C above the phase transformation point significantly increases the size of the β-grain in the Ti5331 alloy. Simultaneously, forging at 30-50°C above the phase transformation point involves the entire β-phase region, and this temperature range is not too close to the phase transformation point. Therefore, the forging process is less prone to cracking of the billet and less likely to result in cross-phase forging, thus reducing the uniformity of the forged microstructure. Based on the above research conclusions, this application innovatively explores a full β-phase region forging method for large-size Ti5331 titanium alloy bars. First, the Ti5331 titanium alloy ingot is subjected to high-temperature large deformation at a temperature above 1100℃ to initially break up the as-cast crystals and improve the hot working plasticity of the alloy. Then, a "low-high" deformation recrystallization process is used, and parameters such as the cross-sectional thickness of the recrystallized billet, the recrystallization heating temperature, and the holding time are strictly controlled to achieve the first rapid refinement and homogenization of the microstructure. After the recrystallization homogenization is completed, the residual heat of the alloy recrystallization is fully utilized to continue multi-fire continuous forging in a temperature range of 30~50℃ above the phase transformation point. At the same time, the cumulative forging ratio of the billet in this temperature range is strictly controlled. Through continuous cyclic dynamic recrystallization and static recrystallization, the β-structure of the billet is rapidly refined to a range with matching comprehensive mechanical properties.

[0020] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0021] 1. The Ti5331 titanium alloy rods prepared by this invention are obtained by forging in the entire β phase region, without the need for additional two-phase region forging to break and refine the α phase. At the same time, the heating temperature and cumulative forging ratio of the β phase region are strictly controlled. The finished rods are forged in only 3 heats from cold material. Compared with the traditional process of forging rods in the two-phase region, it has the advantages of fewer forging heats and shorter forging cycle, which greatly reduces the forging cost of Ti5331 titanium alloy rods.

[0022] 2. Titanium alloys have a single-phase microstructure consisting entirely of bcc-structured β phases. When forged in the pure β-phase region, the alloy exhibits good hot working plasticity and is less prone to cracking during forging. The forging process of this invention is primarily completed in the single-phase region, minimizing cracking and eliminating the need for intermediate cooling and grinding. This makes it particularly suitable for continuous remelting forging. Compared to conventional two-phase forging processes that require cooling and grinding afterward, this patented technology can reduce heating energy consumption by over 50% and increase the forging yield by over 3%.

[0023] 3. The elongation process of the Ti5331 titanium alloy prepared by this invention is carried out in the β phase region. Each heating and forging process is accompanied by static recrystallization and dynamic recrystallization. The deformed structure disappears in large quantities during repeated recrystallization. The resulting finished bar has very small anisotropy in mechanical properties and excellent uniformity in mechanical properties. Attached Figure Description

[0024] Figure 1 This is a low-magnification microstructure image of the Φ500mm bar prepared in Example 1 of the present invention;

[0025] Figure 2 Microstructure (200X) of the Φ500mm bar prepared in Example 1 of this invention.

[0026] Figure 3 This is a low-magnification microstructure image of the Φ150mm bar prepared in Example 2 of the present invention;

[0027] Figure 4 The image shows the microstructure (200X) of the Φ150mm bar prepared in Example 2 of this invention. Detailed Implementation

[0028] The present invention will be described in detail below with reference to embodiments, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more definite definition of the scope of protection of the present invention. Any identical or similar solutions without departing from the concept of the present invention should fall within the scope of protection of the present invention. Furthermore, any parts not detailed herein are described in accordance with conventional methods in the art. In the following text: "Φ" refers to the diameter of a blank with a circular cross-section; T β This is the phase transition temperature.

[0029] Example 1 (Forging method for Φ500mm bar):

[0030] Material: Ti5331 titanium alloy ingot; Phase transformation temperature T β Temperature: 910℃; Ingot dimensions: Φ780×2100mm; Ingot weight: 4.5 tons. Forging was performed using a 45MN high-speed forging mill. The specific forging process is as follows:

[0031] S1: Heat the Ti5331 titanium alloy ingot to 1100-1200℃ for a single-fire upsetting and drawing forging. The heating and holding coefficient is controlled at 0.7-0.9 min / mm, and the total forging ratio is controlled between 5.0-10.0 to obtain the forged billet. After forging, air cool to room temperature. Then grind the surface cracks of the billet, and make the grinding area smooth. The width-to-depth ratio of the grinding area is not less than 8:1.

[0032] S2: Heat the forged billet after the initial forging to the phase transformation temperature T. β The billet is forged in a single upsetting and drawing process at 30-50℃, with the heating and holding coefficient controlled at 0.8-0.9 min / mm. The total forging ratio of the upsetting and drawing process is controlled at 5.0-6.0. The billet is forged into a flat square with a minimum cross-section of no more than 600mm. Then, the billet after the two-phase forging is completed is rapidly heated to the phase transformation point temperature T. β The material is subjected to recrystallization homogenization treatment at 30-50℃, with the recrystallization homogenization holding coefficient controlled at 0.6-0.8 min / mm. After heating, the material is quickly removed from the furnace and forged according to the requirements of step S3.

[0033] S3: The forged billet after recrystallization homogenization treatment is first heated at the phase transformation temperature T. β The forging process involves one heat treatment with two upsetting and two drawing operations at 30-50℃, with the upsetting and drawing forging ratio controlled between 5.0 and 6.0. Subsequently, the hot material is returned to the furnace twice to 30-50℃ above the phase transformation point temperature and then subjected to two heat treatments of pure drawing forging. The heat preservation coefficient of the hot material returned to the furnace for each heat treatment is controlled between 0.3 and 0.5 min / mm, and the drawing forging ratio for each heat treatment is controlled between 1.5 and 2.0. The forging billet is then forged into an octagonal forging billet with a cross-section of 530mm. After forging, the billet is air-cooled to room temperature. Then, the surface cracks of the billet are ground, and the ground area is smoothly transitioned with a width-to-depth ratio of not less than 8:1.

[0034] S4: After the single-phase region forging is completed, heat the forging billet to the phase transformation point temperature T. β The finished product is rolled and forged at 30-50℃, with the heating and holding coefficient controlled at 0.7-0.9 min / mm and the forging ratio controlled between 1.1 and 1.3 to obtain a Φ500×4700mm finished bar. After forging, it is air-cooled to room temperature.

[0035] Figure 1 The image shows a low-magnification microstructure of a Φ500mm Ti5331 titanium alloy bar prepared using the process described in Example 1. It can be seen that the low-magnification microstructure of the bar consists of uniform recrystallized grains with no obvious flow lines or metallurgical defects. Figure 2 The images show the microstructure of the corresponding bars at the edge, R / 2 section, and core. It can be seen that the microstructure is very uniform from the edge to the core. Table 1 shows the mechanical properties of the corresponding bars, indicating that the longitudinal and transverse mechanical properties differ little, and the overall performance is excellent.

[0036] Example 2 (Forging method for Φ150mm bar):

[0037] Material: Ti5331 titanium alloy ingot; Phase transformation temperature T β Temperature: 910℃; Ingot dimensions: Φ780×1160mm; Ingot weight: 2.5 tons. Forging was performed using a 45MN high-speed forging mill. The specific forging process is as follows:

[0038] S1: Heat the Ti5331 titanium alloy ingot to 1100-1200℃ for a single-fire upsetting and drawing forging. The heating and holding coefficient is controlled at 0.7-0.9 min / mm, and the total forging ratio is controlled between 5.0-10.0 to obtain the forged billet. After forging, air cool to room temperature. Then grind the surface cracks of the billet, and make the grinding area smooth. The width-to-depth ratio of the grinding area is not less than 8:1.

[0039] S2: Heat the forged billet after the initial forging to the phase transformation temperature T. β The billet is forged in a single upsetting and drawing process at 30-50℃, with the heating and holding coefficient controlled at 0.8-0.9 min / mm. The total forging ratio of the upsetting and drawing process is controlled at 5.0-6.0. The billet is forged into a flat square with a minimum cross-section of no more than 600mm. Then, the billet after the two-phase forging is completed is rapidly heated to the phase transformation point temperature T. β The material is subjected to recrystallization homogenization treatment at 30-50℃, with the recrystallization homogenization holding coefficient controlled at 0.6-0.8 min / mm. After heating, the material is quickly removed from the furnace and forged according to the requirements of step S3.

[0040] S3: The forged billet after recrystallization homogenization treatment is first heated at the phase transformation temperature T. β The phase transition point temperature T is obtained by firing five consecutive times at 30-50℃. β The above forging is carried out at 30-50℃ with pure drawing. After each forging, the hot material is returned to the furnace to the phase transformation point temperature T. β The temperature is 30-50℃. The heat preservation coefficient of the hot material is controlled at 0.3-0.5 min / mm for each forging. The drawing and forging ratio is controlled between 1.5 and 2.0 for each forging. After drawing in the first and second forgings, the material is cut into two equal parts. After forging in the fourth forging, the material is cut into three equal parts. The forging billet is forged into 12 octagonal forging billets with a cross-section of 170mm. After forging, the billet is air-cooled to room temperature. Then, the surface cracks of the billet are polished. The polished area is rounded and the width-to-depth ratio of the polishing is not less than 8:1.

[0041] S4: After the single-phase region forging is completed, heat the forging billet to the phase transformation point temperature T. β The finished product is rolled and forged at 30-50℃, with the heating and holding coefficient controlled at 0.7-0.9 min / mm and the forging ratio controlled between 1.1 and 1.3, to obtain 12 finished bars with a diameter of 150×2450mm. After forging, the bars are air-cooled to room temperature.

[0042] Figure 3 The image shows a low-magnification microstructure of a Φ150mm Ti5331 titanium alloy bar prepared using the process described in Example 2. It can be seen that the low-magnification microstructure of the bar consists of uniform recrystallized grains with no obvious flow lines or metallurgical defects. Figure 4 The images show the microstructure of the corresponding bars at the edge, R / 2 section, and core. It can be seen that the microstructure is very uniform from the edge to the core. Table 1 shows the mechanical properties of the corresponding bars, indicating that the longitudinal and transverse mechanical properties differ little, and the overall performance is excellent.

[0043] Table 1:

[0044] .

Claims

1. A short process forging process in the full β phase region of a Ti5331 medium-strength high-ductility titanium alloy, characterized in that, This can be achieved through the following steps: Step 1) Heat the Ti5331 titanium alloy ingot to 1100℃-1200℃ for a single-pass upsetting and drawing forging, with the total forging ratio controlled at 5.0-10.0, to obtain the forged billet after upsetting; Step 2) Heat the forged billet after the initial forging to 30-50°C below the phase transformation temperature for one-time upsetting or drawing forging, with the total forging ratio controlled at 5.0-10.

0. Then, quickly heat the billet to 30-50°C above the phase transformation temperature for recrystallization and homogenization heating treatment, and quickly remove it from the furnace after heating. Step 3) The forged billet obtained in Step 2) is subjected to multi-fire continuous reflow forging at a temperature 30℃-50℃ above the phase transformation point. Specifically, the multi-fire continuous reflow forging employs either pure drawing forging or upset drawing forging + pure drawing forging. The single-fire forging ratio for upset drawing forging is controlled at 3.0-6.0, and the single-fire forging ratio for drawing forging is controlled at 1.5-2.

0. The total forging ratio in this step is controlled at 15.0-30.0, resulting in an octagonal or decaangular cross-section. The hexagonal forging billet; the specific choice between pure drawing forging and upset drawing forging + drawing forging in the above-mentioned multi-fire continuous remelting forging process must be ensured to maintain a total forging ratio of 15.0-30.

0. Specifically, if the cumulative forging ratio of pure drawing forging in step 3) is 15.0-30.0, then pure drawing forging should be performed directly; if the cumulative forging ratio of pure drawing forging in step 3) is less than 15.0-30.0, then upset drawing forging should be performed first, followed by pure drawing forging. Step 4) Heat the forging billet obtained in Step 3) to 30℃-50℃ above the phase transformation temperature for finished product rounding forging, with the forging ratio controlled at 1.1-1.3, to obtain finished bar stock.

2. The Ti5331 titanium alloy full beta phase field short process forging process according to claim 1, characterized in that, The heating and heat preservation coefficients in steps 1) and 4) above are controlled at 0.7-0.9 min / mm; the heating and heat preservation coefficients in step 2) during forging at 30℃-50℃ below the phase transformation point temperature are controlled at 0.7-0.9 min / mm, and the heating and heat preservation coefficients for recrystallization homogenization at 30℃-50℃ above the phase transformation point are controlled at 0.6-0.8 min / mm; the heat preservation coefficients in step 3) during hot material return to the furnace are controlled at 0.3-0.5 min / mm.

3. The short-process forging process for Ti5331 titanium alloy in the full β-phase region according to claim 1, characterized in that, After each step from 1) to 4) above, the final forging temperature shall not be lower than 750℃, and air cooling shall be used after each step of forging.

4. The short-process forging process for Ti5331 titanium alloy in the full β-phase region according to claim 2 or 3, characterized in that, In steps 1) to 3) above, after each air cooling to room temperature, the surface cracks of the billet need to be polished, and the polished area needs to be smoothed out. The width-to-depth ratio of the polishing area should not be less than 8:

1.

5. The short-process forging process for Ti5331 titanium alloy in the full β-phase region according to claim 4, characterized in that, In step 2) above, the cross-sectional dimensions of the billet after forging at 30℃-50℃ below the phase transformation temperature are square or flat, but the minimum cross-sectional thickness does not exceed 600mm.

6. The short-process forging process for Ti5331 titanium alloy in the full β-phase region according to claim 1, characterized in that, In step 2) above, the specific choice between upsetting and drawing forging at temperatures 30℃-50℃ below the phase transformation point depends on the cross-sectional dimensions of the finished bar. Specifically, if upsetting in step 2) would cause the pure drawing forging ratio in step 3) to exceed 30, then pure drawing forging is chosen; if upsetting in step 2) would not cause the pure drawing forging ratio in step 3) to exceed 30, then upsetting forging is chosen.

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