Preparation method of TC4 alloy blade forging with high impact resistance

Abstract

The application belongs to the technical field of hot working of metal materials, and discloses a preparation method of TC4 alloy blade forgings with high impact resistance, which comprises the following steps: firstly, TC4 alloy ingots are heated to 1050-1150 DEG C, and then forged after heat penetration for 10-60 hours, with a total forging ratio of greater than or equal to 3.5 and air cooling; secondly, upsetting and reversing elongation are performed at 20-50 DEG C above the beta phase transition point, with a forging ratio of greater than or equal to 4 and water cooling; thirdly, 2-4 times of finish forging is performed at 10-30 DEG C below the beta phase transition point to obtain a rod with a diameter of 50-150 mm; and finally, the rod is die forged into TC4 alloy blade forgings at the same temperature. The TC4 alloy blade forgings obtained by the method have excellent impact resistance, with an impact energy of greater than or equal to 55 J, an impact toughness of greater than or equal to 70 J / cm2, and an impact bending toughness of greater than or equal to 7.0 kgf.m / cm2, which is significantly higher than the performance standard of conventional TC4 blade forgings.

Description

Technical Field

[0001] This invention relates to the field of hot working technology of metal materials, and specifically to a method for preparing TC4 alloy blade forgings with high impact resistance. Background Technology

[0002] TC4 titanium alloy is widely used in aerospace, energy and power fields due to its excellent specific strength, corrosion resistance and high temperature performance, and occupies an important position in key load-bearing components such as aero-engine blades.

[0003] Blade forgings are subjected to complex aerodynamic loads, centrifugal loads, and impact loads from foreign objects during operation, placing extremely high demands on their impact resistance. However, the performance of traditional TC4 blade forgings under impact loads remains significantly inadequate. According to industry statistics, the impact energy of conventional TC4 blade forgings is generally only around 32 J, the impact toughness is about 40 J / cm², and the impact bending toughness is about 1.5 kgf·m / cm². This is insufficient to meet the fracture resistance requirements of aero-engine blades under high-speed impact conditions. In existing forging processes, multi-fire, multi-stage forging schemes are usually adopted to improve microstructure uniformity, but the following problems often exist: First, insufficient cooling control after forging the β-phase region leads to grain coarsening or α-phase precipitation; second, there is a lack of extreme α-phase control technology for blade impact resistance, especially a systematic process scheme that precisely controls the residual equiaxed α-phase content below 20% during forging while simultaneously ensuring the precision of multi-fire forging. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing TC4 alloy blade forgings with high impact resistance, using the following technical solution: A method for preparing a high-impact-resistant TC4 alloy blade forging includes the following steps: Step 1: Forging the billet; First, the TC4 alloy ingot is placed in a heating furnace and heated to a temperature range of 1050℃~1150℃. This temperature range covers the β phase region of the TC4 alloy, ensuring that the ingot is fully homogenized. After the ingot is thoroughly heated at this temperature, it is held at this temperature for 10h~60h to ensure a uniform internal temperature field and eliminate compositional segregation. After the heat preservation is completed, the ingot is taken out of the furnace for free forging. The forging method can be a combination of upsetting and drawing deformation, and the total forging ratio of this process should be controlled to be ≥3.5. After forging, the billet is placed in the air to cool naturally, and a rough billet with a preliminary fine structure is obtained. Step 2: β-phase region reversing upsetting and water cooling; The billet after roughing is reheated to a temperature 20°C to 50°C above the β phase transformation point of TC4 alloy. At this temperature, the billet structure is completely transformed into β single phase. Subsequently, the billet undergoes at least one upsetting and reversible drawing forging process; reversible drawing refers to rotating the billet around its axis by a certain angle after each drawing deformation before performing the next drawing, with the preferred rotation angle being 90°±10°; reversible drawing can make the internal structure of the billet flow more uniform and promote the breakage of coarse β grains; the total forging ratio of this process is controlled to be ≥4 to ensure sufficient deformation energy accumulation; after forging, the billet must be immediately immersed in water to cool to room temperature.

[0005] Step 3: Temperature-controlled precision forging in the two-phase region; The intermediate billet, after being rapidly cooled by water, is heated to a temperature range of 10°C to 30°C below the β-phase transformation point of TC4 alloy. Deformation at this temperature allows for the utilization of the good plasticity of the β-phase and effective control over the morphology and distribution of the α-phase. The heated billet is precision forged in 2 to 4 passes on a precision forging machine to finally obtain precision forged bars with a diameter of Φ50mm to 150mm; After the process is completed, the microstructure of the precision forged bar is inspected. The low-magnification microstructure of the bar shows a uniform fuzzy crystal morphology, that is, the grain boundaries are not obvious, the grains are fine and uniformly distributed; under high magnification, the volume fraction of the residual equiaxed or deformed α phase is strictly controlled between 5% and 20%.

[0006] Step 4: Two-phase region die forging; The above-mentioned precision forged bar is reheated to a temperature range of 10°C to 30°C below the β phase transformation point of TC4 alloy, which is consistent with the temperature range of the precision forging process. Then, it is pre-forged and final forged on a die forging machine to finally obtain TC4 alloy blade forgings.

[0007] The preferred embodiment of the method for preparing a high-impact-resistant TC4 alloy blade forging is that, before each forging pass, the heating coefficient η of the billet is controlled within the range of 0.2 min / mm to 0.5 min / mm. The preferred embodiment of the method for preparing a high-impact-resistant TC4 alloy blade forging is that the transfer time from the time the billet exits the furnace to the start of forging in each heat treatment shall not exceed 40 seconds. The preferred embodiment of the method for preparing a high-impact-resistant TC4 alloy blade forging is that, during each forging process, the decrease in the final forging temperature compared to the initial forging temperature of that forging process shall not exceed 100°C.

[0008] The preferred embodiment of the method for preparing a high-impact-resistant TC4 alloy blade forging is as follows: In step 2, the reversing drawing refers to rotating the billet 90°±10° around its axis after each drawing process before performing the next drawing.

[0009] The preferred embodiment of the method for preparing a high-impact-resistant TC4 alloy blade forging is as follows: In step 2, the delay time for immediate water cooling after forging is within 15 seconds; here, "immediately" means that the time interval from the end of the last hammer blow or the last press stroke to the billet entering the cooling water tank does not exceed 15 seconds; the purpose of rapid water cooling is to freeze the deformed β grain structure in a refined state, suppress the premature precipitation and growth of the α phase during the cooling process, and lay the foundation for obtaining a low-content equiaxed α phase structure in subsequent processes.

[0010] The preferred embodiment of the method for preparing a high-impact-resistant TC4 alloy blade forging is that, in step 3, the volume fraction of the residual equiaxed or deformed α phase in the high-magnification microstructure of the precision forging bar is strictly controlled at 5% to 20%. This microstructure with ultra-low equiaxed α phase content is the key microscopic basis for the subsequent die forging to obtain excellent impact resistance.

[0011] The preferred embodiment of the method for preparing a high-impact-resistant TC4 alloy blade forging is that the TC4 alloy blade forging has an impact energy ≥ 55 J and an impact toughness ≥ 70 J / cm². 2 Impact bending toughness ≥7.0 kgf·m / cm 2 .

[0012] Beneficial effects

[0013] 1. Precise microstructure control and superior performance: Through a multi-stage, temperature-range-specific forging process involving "large deformation in the β-phase region + near-β deformation in the two-phase region," combined with strictly controlled heating coefficients, transfer times, and final forging temperature differences, the grains were effectively refined, resulting in a uniform, fuzzy-grained microstructure. The volume fraction of equiaxed or deformed α-phase was strictly controlled to below 5%–20%. This optimized microstructure is the fundamental reason for the material's high toughness.

[0014] 2. Significantly Improved Impact Resistance: The TC4 alloy blade forgings prepared by this invention exhibit impact energy ≥55J, impact toughness ≥70J / cm², and impact bending toughness ≥7.0kgf·m / cm², all far exceeding the performance standards of conventional TC4 blade forgings (impact energy ≥32J, impact toughness ≥40J / cm², impact bending toughness ≥1.5kgf·m / cm²). Compared with existing technologies, this invention achieves extreme optimization of the impact resistance of blade forgings through multi-stage firing and precise control of the α-phase within a narrow window.

[0015] 3. Stable and reliable process: This invention precisely defines the heating temperature, holding time, deformation amount and cooling method for each stage. The process window is clear and the parameters are highly repeatable, which is conducive to achieving high-quality mass production and stability, and meets the stringent requirements of the aviation, aerospace and other fields for the consistency of key load-bearing components. Attached Figure Description

[0016] Figure 1 This is a low-magnification microstructure of the Ф50mm precision forged bar obtained in Example 1; Figure 2 The image shows the metallographic structure of the blade forging obtained in Example 1. Figure 3 This is a low-magnification microstructure image of the Ф150mm precision forged bar obtained in Example 2; Figure 4 The image shows the metallographic structure of the blade forging obtained in Example 2. Detailed Implementation

[0017] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Those skilled in the art can make appropriate adjustments without departing from the spirit of the invention. The following embodiments illustrate the present invention in more detail, but do not limit the present invention in any way.

[0018] Example 1

[0019] This embodiment provides a method for preparing a Φ50mm precision forged bar and its corresponding TC4 alloy blade forging, including the following steps: Step 1: Forging the billet; TC4 alloy ingots with chemical composition conforming to GB / T 3620 standard were selected, placed in a heating furnace, and heated to 1100℃. After the ingots were thoroughly heated, they were held at this temperature for 15 hours. After the holding period, the ingots were removed from the furnace and subjected to upsetting and drawing forging. The upsetting deformation was 60%, and the total upsetting and drawing forging ratio was 4.5. After forging, the billet was air-cooled to room temperature to obtain the blank.

[0020] Step 2: β-phase region reversing upsetting and water cooling; The billet is heated to 50°C above the β phase transformation point of TC4 alloy, and the heating coefficient is controlled at η=0.3min / mm. After the billet is taken out of the furnace, it is transferred to the forging equipment within 40s for upsetting and reversing drawing forging. After each drawing, the billet is rotated 90° around the axis before the next drawing. The total forging ratio of this process is 4. After the forging is completed, the billet is immediately put into the cooling water tank. The delay time from the completion of the final forging to the water entry is controlled within 12s. After water cooling to room temperature, the intermediate billet is obtained.

[0021] Step 3: Precision forging of the two-phase region into a bar; The intermediate billet is heated to 10°C below the β phase transformation point, and the heating coefficient is still controlled at η=0.3min / mm. It is then precision forged in two passes on a precision forging machine to finally obtain a precision forged bar with a diameter of Ф50mm.

[0022] Step 4: Two-phase region die forging; The precision-forged bar is reheated to 10°C below the β phase transformation point, and then pre-forged and final-forged on a die forging machine to form a TC4 alloy blade forging.

[0023] Throughout the forging process, the transfer time from the billet exiting the furnace to the start of forging in each forging cycle does not exceed 40 seconds, and the drop in final forging temperature compared to initial forging temperature in each forging cycle is controlled within 100℃.

[0024] Conclusion: Figure 1 , Figure 2 As shown, the Φ50mm bar prepared by the method of this invention has a uniform fuzzy crystal structure at low magnification and a two-phase deformed structure at high magnification, wherein the volume fraction of equiaxed or deformed α phase is approximately 8%. Samples of the obtained blade forgings were taken for impact performance testing. Charpy impact tests were conducted according to GB / T 229 standard, and impact toughness and impact bending toughness tests were performed according to the corresponding standards. The test results are shown in Table 1: Table 1

[0025] The above data shows that the TC4 alloy blade forgings obtained in this embodiment have impact energy, impact toughness and impact bending toughness that far exceed conventional standards, demonstrating excellent impact resistance.

[0026] Example 2

[0027] This embodiment provides a method for preparing a Φ150mm precision forged bar and its corresponding TC4 alloy blade forging; including the following steps: Step 1: Forging the billet; The TC4 alloy ingot was heated to 1100℃, held at that temperature for 20 hours after being fully heated, and then forged. The total forging ratio of upsetting and drawing was 5, and the ingot was air-cooled after forging.

[0028] Step 2: β-phase region reversing upsetting and water cooling; The billet is heated to 30°C above the β phase transformation point of TC4 alloy; the heating coefficient is controlled at η=0.35min / mm. After the billet is taken out of the furnace, it is transferred to the forging equipment within 40s for upsetting and reversing drawing forging. After each drawing, the billet is rotated 90° around the axis before the next drawing. The total forging ratio of this process is 4.5. After the forging is completed, the billet is immediately put into the cooling water tank. The delay time from the completion of the final forging to the water entry is controlled within 14s. After water cooling to room temperature, the intermediate billet is obtained.

[0029] Step 3: Precision forging of the two-phase region into a bar; The intermediate billet is heated to 30°C below the β phase transformation point, with a heating coefficient η=0.35min / mm, and then precision forged in 4 passes on a precision forging machine to obtain a Ф150mm precision forged bar.

[0030] Step 4: Two-phase region die forging; The precision forged bar is heated to 30°C below the β phase transformation point, and then pre-forged and final-forged on a die forging machine to form a TC4 alloy blade forging.

[0031] Throughout the forging process, the time for transferring the product from the furnace shall not exceed 40 seconds, and the final forging temperature shall not decrease by more than 100°C compared to the initial forging temperature.

[0032] Conclusion: Figure 3 , Figure 4 As shown, the Φ150mm bar prepared by the method of this invention has a uniform fuzzy crystal structure at low magnification and a two-phase deformed structure at high magnification, wherein the volume fraction of equiaxed or deformed α phase is approximately 15%. Samples of the obtained blade forgings were taken for impact performance testing. Charpy impact tests were conducted according to GB / T 229 standard, and impact toughness and impact bending toughness tests were performed according to the corresponding standards. The test results are shown in Table 2. Table 2

[0033] The above results show that even for large-sized precision forged bars with a diameter of 150mm, the technical solution of this invention can still stably obtain excellent impact resistance, indicating that the process of this invention has good dimensional adaptability and process stability.

Claims

1. A method for preparing a high-impact-resistant TC4 alloy blade forging, characterized in that, The specific steps are as follows: Step 1: Forging the billet; TC4 alloy ingots are heated to 1050℃~1150℃, and after being thoroughly heated, they are held at that temperature for 10h~60h before being taken out of the furnace for forging. The total forging ratio is controlled to be ≥3.

5. After forging, the ingots are air-cooled to obtain the blanks. Step 2: β-phase region reversing upsetting and forging; The billet is heated to 20°C to 50°C above the β phase transformation point of TC4 alloy, and subjected to at least one upsetting and reversing drawing forging. The total forging ratio of this step is controlled to be ≥4. After forging, it is immediately water-cooled to obtain an intermediate billet. Step 3: Precision forging of the two-phase region into a bar; The intermediate billet is heated to 10°C to 30°C below the β-phase transformation point of TC4 alloy, and then precision forged in 2 to 4 passes on a precision forging machine to obtain precision forged bars with a diameter of Ф50mm to 150mm. The low-magnification structure of the obtained bars is a uniform fuzzy grain boundary structure, and the volume fraction of the residual equiaxed or deformed α-phase in the high-magnification structure is strictly controlled at 5% to 20%. Step 4: Two-phase region die forging; The precision forged bar is heated to 10°C to 30°C below the β phase transformation point of TC4 alloy, and pre-forged and final forged on a die forging machine to form a TC4 alloy blade forging. Furthermore, during the entire forging process, the heating coefficient η before each forging is controlled to be 0.2 min / mm to 0.5 min / mm, the transfer time from the billet exiting the furnace to the start of forging does not exceed 40 seconds, and the decrease in the final forging temperature of this forging compared to the initial forging temperature does not exceed 100℃.

2. The method for preparing a high-impact-resistant TC4 alloy blade forging according to claim 1, characterized in that: In step 2, the reversing drawing refers to rotating the billet 90°±10° around its axis after each drawing process before performing the next drawing.

3. The method for preparing a high-impact-resistant TC4 alloy blade forging according to claim 1, characterized in that: In step 2, the delay time for immediate water cooling after forging is within 15 seconds.

4. The method for preparing a high-impact-resistant TC4 alloy blade forging according to claim 1, characterized in that: The impact energy of the TC4 alloy blade forging is ≥55J, and the impact toughness is ≥70J / cm. 2 Impact bending toughness ≥7.0 kgf·m / cm 2 .

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