A method for forging a phase transformation-induced plasticity metastable β titanium alloy

Abstract

This application relates to a method for split forging a transformation-induced plasticity metastable β titanium alloy, comprising the following steps: split forging a transformation-induced plasticity metastable β titanium alloy ingot, repeatedly upsetting and drawing the ingot to a desired size; reforging the split ingot through multiple fires to produce an intermediate forging ingot; and forging the intermediate forging ingot through multiple fires to form a titanium alloy forging ingot with a rectangular cross-section. By rationally designing each step of the split forging process, increasing the deformation storage energy at specific stages, and introducing an appropriate amount of primary α phase, this method achieves both the goal of refining the final grain structure and improving its uniformity. This method not only overcomes the grain structure control challenges (such as coarse and uneven grains) often associated with transformation-induced plasticity metastable β titanium alloys due to the low stability of the β phase, but also offers the advantages of a simple process and a reduced number of forging fires.

Description

Technical Field

[0001] The invention relates to the technical field of titanium alloy blank forging, and in particular to a blank forging method of a phase transformation induced plasticity metastable β titanium alloy. Background Art

[0002] Among different types of titanium alloys, metastable β-titanium alloys achieve the highest strength levels. These alloys have been used in the aviation industry since the 1950s, primarily for critical, load-bearing components requiring high strength, such as lower anti-torsion arms, actuators, and wheel rods in aircraft landing gear. However, it is noteworthy that despite their high strength, the metastable β-titanium alloys currently used in the aviation industry generally exhibit very low work-hardening capacity and ductility. Improving the work-hardening capacity and ductility of metastable β-titanium alloys has long vexed titanium alloy researchers. However, the successful development of metastable β-titanium alloys exhibiting twin-induced plasticity and / or phase transformation-induced plasticity has provided a promising approach to addressing this issue. Currently, small-scale (<500 g) samples of these alloys prepared in the laboratory, when characterized by a uniform and fine grain structure, have been found to exhibit high work-hardening capacity and elongation after fracture exceeding 50%, demonstrating exceptionally high ductility. This is mainly due to the fact that a large number of deformation twins and / or stress-induced martensite phases can be generated during plastic deformation, causing the original grains to be continuously divided into smaller grains by twins and / or martensite, that is, dynamic grain refinement occurs, resulting in high work hardening ability and plasticity. However, it should be pointed out that metastable β titanium alloys with twin-induced plasticity effect and / or phase transformation-induced plasticity effect have very low β phase stability, and are prone to non-uniform recrystallization and abnormal grain growth during processing and forming, making their grain structure difficult to control.

[0003] For small-scale alloy ingots prepared in the laboratory, due to the limited casting defects and generally small grain size, a uniform, fine grain structure can be easily obtained after simple hot rolling, cold rolling, and solution heat treatment. However, alloy ingots prepared for actual engineering applications are usually tens of kilograms, and in some cases even tons of ingots are produced. In these cases, the ingots often contain highly uneven structures such as coarse equiaxed grains, columnar grains, and dendrites, as well as numerous casting defects such as shrinkage and shrinkage cavities. A uniform, fine grain structure can only be achieved through forging and multiple reforging. For large-scale ingots of metastable β titanium alloys with twin-induced plasticity and / or transformation-induced plasticity effects, given their very low β phase stability and the resulting difficulty in controlling the grain structure, a uniform, fine grain structure must be obtained through the rational design and meticulous control of each step of the forging process to ensure the generation of twins and / or transformation-induced plasticity, thereby achieving high work hardening ability and plasticity.

[0004] Based on this, the present invention provides a method for forging a phase transformation induced plasticity metastable β titanium alloy. Summary of the Invention

[0005] Taking into account the problems of non-uniform recrystallization and abnormal grain growth in the process of blank forging caused by the low stability of the β phase in phase induced plasticity metastable β titanium alloy, the present invention can refine the final grain structure and improve the uniformity of the grain structure by increasing the deformation storage energy and introducing an appropriate amount of primary α phase in a specific stage of the forging process. Therefore, the present invention team designed a reasonable blank forging method after a large number of experiments to obtain sufficient deformation storage energy and an appropriate amount of primary α phase at the appropriate stage, thereby solving the problem of controlling the grain structure of phase induced plasticity metastable β titanium alloy.

[0006] Specifically, the present invention provides a method for forging a phase transformation induced plasticity metastable β titanium alloy, comprising the following steps:

[0007] S1. Cogging forging: Cogging forging is performed on a transformation-induced plasticity metastable β titanium alloy ingot, and the ingot is repeatedly upset and drawn to a set size;

[0008] S2, intermediate forging: the blank is subjected to multiple forgings to obtain the intermediate forging blank;

[0009] S3. Final forging: The intermediate forging blank is subjected to multiple forging processes to form a titanium alloy forging blank having a rectangular cross section.

[0010] As a further illustration of the present application, the phase transformation induced plasticity metastable β titanium alloy ingot is a cylindrical Ti-12Mo-1Al alloy ingot obtained by vacuum consumable arc melting.

[0011] As a further explanation of the present application, the S1 blank forging is performed in one fire; the heating temperature is 190~200°C above the phase transformation point to reduce deformation resistance and fully bridge casting defects such as shrinkage and shrinkage cavities; the deformation amount of each upsetting or drawing is 40%~50% to fully break up coarse equiaxed crystals, columnar crystals, dendrites and other casting structures.

[0012] As a further explanation of the present application, the blank forging process of S1 includes two upsettings and two drawing operations, and the blank is chamfered after each drawing operation.

[0013] As a further explanation of this application, S2 specifically includes:

[0014] S21, subjecting the blank forged in step S1 to one heat reforging to obtain a primary intermediate forging blank; the heating temperature is 90-100° C. above the phase transformation point; the reforging method is two upsetting and two drawing, the forging ratio of each upsetting or drawing is greater than 2.0, and the blank is chamfered after each drawing;

[0015] S22, reforging the primary intermediate forging blank once to obtain a secondary intermediate forging blank; the heating temperature is 20-30° C. above the phase transformation point; the reforging method is two upsetting and two drawing, the forging ratio of each upsetting or drawing is greater than 2.0, and the blank is chamfered after each drawing;

[0016] S23, reforging the secondary intermediate forging billet once to obtain a tertiary intermediate forging billet; heating the billet to a temperature of 25° C. to 35° C. below the phase transformation point, introducing a primary α phase with a volume fraction of 10.4% to 12.8%; reforging the billet by two upsettings and two stretchings, with each upsetting or stretching having a deformation of 40% to 50% to ensure that the billet obtains sufficient deformation storage energy, and chamfering the billet after each stretching;

[0017] S24. The three-stage intermediate forging blank is subjected to two-stage reforging to obtain a four-stage intermediate forging blank; the heating temperature is 50-60°C below the phase transformation point to introduce a primary α phase with a volume fraction of 26.4%-28.9%; the reforging method is one upsetting and one drawing per fire, and the deformation amount of each upsetting or drawing is 40%-50% to ensure that the blank obtains sufficient deformation storage energy, and the blank is chamfered after each drawing.

[0018] As a further explanation of the present application, the S3 is specifically as follows: the intermediate forging blank obtained in step S2 is forged and formed, the heating temperature is 50~60°C below the phase transformation point, the forming method is continuous drawing, the drawing ratio is 2.4~2.5, and air cooling is adopted after forging to finally obtain a titanium alloy forging blank with a rectangular cross section and an aspect ratio of 1.5~2.0.

[0019] As a further illustration of the present application, the forging equipment is a 20MN fast forging machine, and the heating equipment is a resistance furnace with a temperature control accuracy within ±10°C.

[0020] As a further explanation of this application, the heating and holding time of cold materials is calculated based on the minimum cross-sectional size (mm) × 0.8 min / mm, and the returning and holding time of hot materials is calculated based on the minimum cross-sectional size (mm) × 0.4 min / mm.

[0021] Compared with the existing technology, this application has the following beneficial technical effects:

[0022] By rationally designing each step of the open forging process, increasing deformation storage energy at specific stages, and introducing an appropriate amount of primary α phase, this application achieves the goals of simultaneously refining the final grain structure and improving its uniformity. This not only overcomes the grain structure control challenges (such as coarse and uneven grains) often associated with transformation-induced plasticity metastable β-titanium alloys due to the low stability of the β phase, but also offers the advantages of a simple process and a reduced number of forging cycles. The open forging method provided in this application ensures that transformation-induced plasticity metastable β-titanium alloys can fully exploit their advantages of high work hardening capacity and high plasticity, thereby promoting their application in the aviation industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a microstructure image of the Ti-12Mo-1Al alloy forging in Example 1 of the present application after undergoing solution heat treatment at 770°C for 0.5h.

[0024] Figure 2 This is a microstructure image of the Ti-12Mo-1Al alloy forging blank after tensile deformation at room temperature after solution heat treatment at 770°C for 0.5h in Example 1 of the present application.

[0025] Figure 3 This is a microstructure image of the Ti-12Mo-1Al alloy forging in Example 1 of the present application after undergoing solution heat treatment at 930°C for 0.5h.

[0026] Figure 4 This is a microstructure picture of the Ti-12Mo-1Al alloy forging in Comparative Example 1 of the present application after undergoing solution heat treatment at 780°C for 0.5h.

[0027] Figure 5 This is a microstructure picture of the Ti-12Mo-1Al alloy forging in Comparative Example 2 of the present application after undergoing solution heat treatment at 765°C for 0.5h. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the implementation methods of this application clearer, the technical solutions in the implementation methods of this application will be clearly and completely described below in conjunction with the drawings in the implementation methods of this application. Example

[0029] A Ti-12Mo-1Al alloy ingot with a size of Φ108×258mm, obtained by vacuum consumable arc melting, was selected as the raw material. Its phase transition point was determined to be 805°C by metallographic analysis. A 20MN fast forging machine was used as the forging equipment, and a resistance furnace with a temperature control accuracy of within ±10°C was used as the heating equipment. The ingot was forged as follows:

[0030] S1. Blank forging:

[0031] The Ti-12Mo-1Al alloy ingot was forged at a heating temperature of 1000℃ and a holding time of 90min. The forging process included two upsetting and two drawing operations, with the deformation of each upsetting or drawing being 40%~50%. The ingot was chamfered after each drawing.

[0032] S2, intermediate forging:

[0033] The billet after the blanking forging in step S1 is subjected to a first heat reforging, with a heating temperature of 900° C. and a holding time of 85 minutes; the reforging method is two upsetting and two drawing, with the forging ratio of each upsetting or drawing being greater than 2.0, and the billet is chamfered after each drawing to obtain a primary intermediate forging billet with a size of 105×215 mm.

[0034] The primary intermediate forging billet is subjected to one heat reforging process, with a heating temperature of 830°C and a holding time of 85 minutes. The reforging process is performed by two upsetting processes and two drawing processes, with a forging ratio of each upsetting or drawing process being greater than 2.0. The billet is chamfered after each drawing process to obtain a secondary intermediate forging billet with a size of 105×215 mm.

[0035] The secondary intermediate forging billet was reforged once, with a heating temperature of 775℃ and a holding time of 85min. The volume fraction of the introduced primary α phase was ~10.5%; the reforging method was 2 upsetting and 2 drawing, with the deformation of each upsetting or drawing being 40%~50%. After each drawing, the billet was chamfered to obtain a tertiary intermediate forging billet with a size of □105×215mm.

[0036] The three-time intermediate forging billet was reforged twice with a heating temperature of 750°C and a holding time of 85 min. The volume fraction of the introduced primary α phase was ~27.1%. The reforging method was one upsetting and one drawing per fire. The deformation of each upsetting or drawing was 40%~50%. After each drawing, the billet was chamfered to obtain a four-time intermediate forging billet with a size of □105×215mm.

[0037] S3, Final Forging:

[0038] The four intermediate forging billets obtained in step S2 are forged and formed, with a heating temperature of 750°C and a holding time of 85 min. The forming method is continuous drawing with a drawing ratio of 2.4 to 2.5. After forging, air cooling is adopted to finally obtain a titanium alloy forging billet with a rectangular cross section and an aspect ratio of ~1.8.

[0039] Forging billet microstructure observation:

[0040] The sample was taken from the forging blank, heated to 770℃ for solution treatment, kept at this temperature for 0.5 hours and then quenched to room temperature. The microstructure of the sample is shown in the attached figure. Figure 1 As shown in the figure, the grain distribution is very uniform, with an average size of ~2μm and contains ellipsoidal primary α phase with a volume fraction of ~15.6%. After tensile deformation, its microstructure is shown in the attached figure. Figure 2 As shown in the figure, a large number of stress-induced α" martensite laths can be found in the β grains, and these martensite laths divide and refine the original β grains, indicating that the sample has exerted a phase transformation induced plasticity effect during the deformation process, thus having the advantages of high work hardening ability and high plasticity.

[0041] The sample was taken from the forging blank, heated to 930℃ for solution treatment, kept at this temperature for 0.5 hours and then quenched to room temperature. The microstructure of the sample is shown in the attached figure. Figure 3 As shown in the figure, the grain distribution is very uniform, and the average grain size is about 100 μm, indicating that the grain size of the forging billet can still be kept at a very small level after solution treatment at 125℃ above the phase transformation point.

[0042] Comparative Example 1:

[0043] Similarly, a Ti-12Mo-1Al alloy ingot with a size of Φ96×253mm, obtained through vacuum consumable arc melting, was selected as the raw material. Metallographic measurement showed that its phase transition point was 815°C. A 20MN fast forging machine was used as the forging equipment, and a resistance furnace with a temperature control accuracy of within ±10°C was used as the heating equipment. The ingot was forged as follows:

[0044] S1. Blank forging:

[0045] The Ti-12Mo-1Al alloy ingot was forged at a heating temperature of 1010℃ and a holding time of 90min. The forging process included two upsetting and two drawing operations, with the deformation of each upsetting or drawing being 40%~50%. The ingot was chamfered after each drawing.

[0046] S2, intermediate forging:

[0047] The billet after the blanking forging in step S1 is subjected to one heat reforging, with a heating temperature of 910° C. and a holding time of 85 minutes; the reforging method is two upsetting and two drawing, with the forging ratio of each upsetting or drawing being greater than 2.0, and the billet is chamfered after each drawing to obtain a primary intermediate forging billet with a size of 95×200 mm;

[0048] The primary intermediate forging billet is subjected to one heat reforging process, with a heating temperature of 840°C and a holding time of 85 minutes. The reforging process is performed by two upsetting processes and two drawing processes, with a forging ratio of each upsetting or drawing process being greater than 2.0. The billet is chamfered after each drawing process to obtain a secondary intermediate forging billet with a size of 95 × 200 mm.

[0049] The secondary intermediate forging billet was reforged once, with a heating temperature of 805℃ and a holding time of 85min. The volume fraction of the introduced primary α phase was ~1.63%; the reforging method was 2 upsetting and 2 drawing, with the deformation of each upsetting or drawing being 40%~50%. After each drawing, the billet was chamfered to obtain a tertiary intermediate forging billet with a size of □95×200mm.

[0050] The three-time intermediate forging billet was reforged twice with a heating temperature of 790°C and a holding time of 85 min. The volume fraction of the introduced primary α phase was ~6.98%. The reforging method was one upsetting and one drawing per fire. The deformation of each upsetting or drawing was 40%~50%. After each drawing, the billet was chamfered to obtain a four-time intermediate forging billet with a size of □95×200mm.

[0051] S3, Final Forging:

[0052] The four intermediate forging billets obtained in step S2 are forged and formed, with a heating temperature of 790°C and a holding time of 85 min. The forming method is continuous drawing with a drawing ratio of 2.4 to 2.5. After forging, air cooling is adopted to finally obtain a titanium alloy forging billet with a rectangular cross section and an aspect ratio of ~1.8.

[0053] Forging billet microstructure observation:

[0054] The sample was taken from the forging blank, heated to 780℃ for solution treatment, kept at this temperature for 0.5 hours and then quenched to room temperature. The microstructure of the sample is shown in the attached figure. Figure 4 As shown in the figure, it can be seen that the grain size distribution is very uneven.

[0055] Compared with Example 1, although the metastable β titanium alloy with the same composition is used and the forging steps are unchanged, the forging temperature and the corresponding primary α phase content when re-forging the secondary intermediate forging billet and the tertiary intermediate forging billet are not within the scope of protection of this patent application (25~35℃, 50~60℃ below the phase transformation point, primary α phase content of 10.4%~12.8%, 26.4%~28.9%), that is, the phenomenon of uneven grain size occurs.

[0056] Comparative Example 2:

[0057] Similarly, a Ti-12Mo-1Al alloy ingot with a size of Φ102×249mm, obtained through vacuum consumable arc melting, was selected as the raw material. Metallographic measurement showed that its phase transition point was 800°C. A 20MN fast forging machine was used as the forging equipment, and a resistance furnace with a temperature control accuracy of within ±10°C was used as the heating equipment. The ingot was forged as follows:

[0058] S1. Blank forging:

[0059] The Ti-12Mo-1Al alloy ingot was forged at a heating temperature of 995°C and a holding time of 90 min. The forging process included two upsetting and two drawing operations, with the deformation of each upsetting or drawing being 40% to 50%. The ingot was chamfered after each drawing operation.

[0060] S2, intermediate forging:

[0061] The billet after the blanking forging in step S1 is subjected to a first heat forging, with a heating temperature of 895° C. and a holding time of 85 minutes; the forging method is two upsetting and two drawing, with a forging ratio of each upsetting or drawing greater than 2.0, and the billet is chamfered after each drawing to obtain a primary intermediate forging billet with a size of 100×205 mm;

[0062] The primary intermediate forging billet is subjected to one heat reforging process, with a heating temperature of 825°C and a holding time of 85 minutes; the reforging process is performed by two upsetting processes and two drawing processes, with a forging ratio of each upsetting or drawing process being greater than 2.0, and the billet is chamfered after each drawing process to obtain a secondary intermediate forging billet with a size of □100×205mm;

[0063] The secondary intermediate forging billet was reforged once, with a heating temperature of 770℃ and a holding time of 85min. The volume fraction of the introduced primary α phase was ~12.5%; the reforging method was 2 upsetting and 2 drawing, with the deformation of each upsetting or drawing being 25%~30%. After each drawing, the billet was chamfered to obtain a tertiary intermediate forging billet with a size of □100×205mm.

[0064] The three-time intermediate forging billet was reforged twice with a heating temperature of 745°C and a holding time of 85 min. The volume fraction of the introduced primary α phase was ~28.8%. The reforging method was one upsetting and one drawing per fire. The deformation of each upsetting or drawing was 25%~30%. After each drawing, the billet was chamfered to obtain a four-time intermediate forging billet with a size of □100×205mm.

[0065] S3, Final Forging:

[0066] The four intermediate forging billets obtained in step S2 are forged and formed, with a heating temperature of 745°C and a holding time of 85 min. The forming method is continuous drawing with a drawing ratio of 2.4 to 2.5. After forging, air cooling is adopted to finally obtain a titanium alloy forging billet with a rectangular cross section and an aspect ratio of ~1.8.

[0067] Forging billet microstructure observation:

[0068] The sample was taken from the forging blank, heated to 765℃ for solution treatment, kept at this temperature for 0.5 hours and then quenched to room temperature. The microstructure of the sample is shown in the attached figure. Figure 5 As shown in the figure, it can be seen that the grain size distribution is also uneven.

[0069] Compared with Example 1, although the metastable β titanium alloy with the same composition is used and the forging steps are unchanged, the upsetting deformation when the secondary intermediate forging billet and the tertiary intermediate forging billet are changed in the forging process of Comparative Example 2 is not within the scope of protection of this patent application (40%~50%), that is, the phenomenon of uneven grain size occurs.

[0070] The foregoing description is intended only to provide specific embodiments of the present invention, which will enable those skilled in the art to understand and implement the present 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 present invention.

[0071] It should be understood that the present invention is not limited to the above description and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for forging a phase transformation induced plasticity metastable β titanium alloy, characterized in that: The following steps are involved: S1. Cogging forging: Cogging forging is performed on a transformation-induced plasticity metastable β titanium alloy ingot, and the ingot is repeatedly upset and drawn to a set size; wherein, the cogging forging is performed in one fire; the heating temperature is 190-200°C above the phase transformation point, and the deformation amount of each upsetting or drawing is 40%; S2. Intermediate forging: The billet after blanking is subjected to multiple forgings to obtain the intermediate forging billet, which specifically includes: S21, subjecting the blank forged in step S1 to one heat reforging to obtain a primary intermediate forging blank; the heating temperature is 90-100° C. above the phase transformation point; the reforging method is two upsetting and two drawing, the forging ratio of each upsetting or drawing is greater than 2.0, and the blank is chamfered after each drawing; S22, reforging the primary intermediate forging blank once to obtain a secondary intermediate forging blank; the heating temperature is 20-30° C. above the phase transformation point; the reforging method is two upsetting and two drawing, the forging ratio of each upsetting or drawing is greater than 2.0, and the blank is chamfered after each drawing; S23, reforging the secondary intermediate forging billet once to obtain a tertiary intermediate forging billet; heating the billet to a temperature of 25-35° C. below the phase transformation point, introducing a primary α phase with a volume fraction of 10.4%-12.8%; reforging the billet by two upsettings and two stretchings, with each upsetting or stretching having a deformation of 40%, and chamfering the billet after each stretching; S24, reforging the three-stage intermediate forging billet twice to obtain a four-stage intermediate forging billet; the heating temperature is 50-60°C below the phase transformation point to introduce a primary α phase with a volume fraction of 26.4%-28.9%; the reforging method is one upsetting and one drawing per fire, the deformation of each upsetting or drawing is 40%, and the billet is chamfered after each drawing; S3. Final forging: The intermediate forging blank is subjected to multi-fire forging forming to finally obtain a titanium alloy forging blank with a rectangular cross section. Specifically, the intermediate forging blank obtained in step S2 is forged and formed, the heating temperature is 50-60°C below the phase transformation point, the forming method is continuous drawing, the drawing ratio is 2.4-2.5, and air cooling is adopted after forging to finally obtain a titanium alloy forging blank with a rectangular cross section and an aspect ratio of 1.5-2.

0.

2. The method for forging a transformation-induced plasticity metastable β titanium alloy according to claim 1, characterized in that: The phase transformation induced plasticity metastable β titanium alloy ingot is a cylindrical Ti-12Mo-1Al alloy ingot obtained by vacuum consumable arc melting.

3. The method for forging a transformation-induced plasticity metastable β titanium alloy according to claim 1, characterized in that: The blank forging process of S1 includes two upsettings and two drawing operations, and the blank is chamfered after each drawing operation.

4. The method for forging a transformation-induced plasticity metastable β titanium alloy according to claim 1, wherein: The forging equipment is a 20MN fast forging machine, and the heating equipment is a resistance furnace with a temperature control accuracy within ±10℃.

5. The method for forging a transformation-induced plasticity metastable β titanium alloy according to claim 1, characterized in that: The heating and holding time of cold materials is calculated based on the minimum cross-sectional size (mm) × 0.8min / mm, and the returning and holding time of hot materials is calculated based on the minimum cross-sectional size (mm) × 0.4min / mm.

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