Preparation method for forging TC4 titanium alloy bar with short process and low cost

Abstract

The invention discloses a short-process low-cost preparation method for forging a TC4 titanium alloy bar. The short-process low-cost preparation method comprises the following steps: (1) cogging and forging a beta-phase region; (2) performing drawing-out thermal deformation on an alpha + beta region; (3) static quasi-beta annealing water quenching treatment; (4) carrying out thermal deformation in a near alpha + beta region; and (5) alpha + beta area small-deformation multi-tempering drawing-out finish forging forming is carried out. The method has the advantages that the requirements of uniform orientation distribution, sufficient grain refinement, process simplification and convenient operation in the short-process low-cost TC4 titanium alloy manufacturing bar are met, the structure uniformity of the large bar is improved, the obtaining of a homogeneous fine structure is facilitated, the requirement of nondestructive testing of the flaw detection clutter level is met, and the product quality is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of nonferrous metal processing technology, and in particular relates to a method for preparing a TC4 titanium alloy bar by forging with a short process and low cost. Background Art

[0002] Due to its advantages such as high tensile strength, good toughness, corrosion resistance, and ability to withstand high mechanical stress, TC4 titanium alloy is widely used in aerospace, biomedicine, and chemical industries. However, titanium alloy itself has poor plasticity and high temperature sensitivity, resulting in a narrow processing window and high processing difficulty. After the ingot is opened, multiple free forging and grinding are required, which is costly, has a long processing cycle, and has a large material loss, resulting in high overall cost.

[0003] In order to overcome the above defects, technicians began to explore short-process and low-cost forging methods for TC4 titanium alloy large bars. At present, most of them are formed by upsetting and drawing the blanks above the phase transformation temperature, and repeatedly drawing and stretching with small deformation and multiple tempering in the two-phase region to obtain fine structure and better performance indicators of the bars. The number of grinding times of forgings is reduced by 3 to 4 times during the forging process, and the comprehensive yield rate is increased by 3 to 5%, which greatly reduces the comprehensive cost of processing large titanium alloy bars. However, this existing process is usually unable to effectively suppress the influence of the heredity of the initial structure on the secondary α phase morphology of the large bar, and it is difficult to obtain a homogeneous fine structure, resulting in uneven performance of TC4 titanium alloy large bars and difficulty in meeting the noise level standards for non-destructive testing. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem that the existing TC4 titanium alloy large bars have uneven performance and cannot meet the noise level of non-destructive testing. It provides a short-process and low-cost preparation method for forging TC4 titanium alloy bars, which can improve the structural uniformity of large bars while simplifying the process and facilitating operation, and is more conducive to obtaining homogeneous fine structure, meeting the requirements of non-destructive testing noise level, and improving product quality.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A method for preparing TC4 titanium alloy bars by forging with a short process and low cost, comprising the following steps: (1) β phase region blank forging: Heat the TC4 titanium alloy ingot to 100-200℃ above the β phase transformation temperature, keep it warm for 8-12 hours, and then use a fast forging machine to stretch, return to the furnace for warming, and upset it once each. The total forging ratio is controlled at 2.5-3.5, the final forging temperature is ≥900℃, and air cooling is performed after forging. (2) Thermal deformation of α+β zone: The air-cooled billet is heated to 30-40°C below the β-transformation temperature, kept warm for 6-10 hours, and then subjected to one drawing forging cycle on a high-speed forging machine, with the forging ratio controlled at 1.2-1.5 and the final forging temperature ≥800°C. (3) Static quasi-β annealing water quenching treatment: Then the blank is directly returned to the furnace for annealing heat treatment. The heat treatment temperature is 15-30°C above the β phase transformation temperature. After holding for 90-150 minutes, it is quickly water quenched. The blank temperature is ≤400°C. After water cooling, the blank surface is ground. (4) Thermal deformation near α+β region: The annealed billet is heated to 30-40°C below the β-transformation temperature, kept at this temperature for 360-420 minutes, and then subjected to upsetting, returning to the furnace for holding, and drawing on a high-speed forging machine, with a total forging ratio of 2.5-3.5. After forging, the hot material is returned to the furnace; (5) Small deformation in the α+β zone, multiple tempering, drawing and final forging: Finally, the blank is heated at 40-50°C below the β phase transformation temperature, and then subjected to 3-5 rounds of drawing and forging, with a forging ratio of 1.2-1.5 for each round. After each round of forging, the blank is returned to the furnace and kept warm for 60-120 minutes. After repeated drawing, the formed bar is obtained.

[0006] Furthermore, in the step (1), the TC4 titanium alloy ingot has a specification of φ600-φ900 mm and a weight of 1200-2000 kg, and the forging blank is air-cooled to below 400° C. after being upsetting and deformed.

[0007] Furthermore, in the step (1), the forging ratio of each fire is controlled within a range of 1.3 to 1.8, and the total forging ratio is controlled within a range of 2.5 to 3.5.

[0008] Furthermore, in the step (2), the holding time after heating during the forging process is 360 to 420 minutes.

[0009] Furthermore, in the step (2), the forging speed during the drawing process is ≤20 mm / s, and the total forging time is less than 7 min.

[0010] Furthermore, in the step (4), the forging speed of the upsetting process is ≤10 mm / s, and the total forging time is less than 10 min.

[0011] Furthermore, in the step (4), upsetting deformation is performed on a fast forging machine with a forging ratio of 1.4 to 1.8, and the steel is returned to the furnace in a hot state after forging. After heating and holding at the original temperature for 60 to 120 minutes, stretching forging is performed with a forging ratio of 1.2 to 1.5, and the steel is returned to the furnace in a hot state after forging.

[0012] Furthermore, in the step (4), the heating temperature during the upsetting and forging process is 25 to 35°C below the phase transition point temperature, and the final forging temperature is ≥750°C.

[0013] Furthermore, in the step (5), the drawing forging anvil is preheated to 300°C, the forging ratio of each fire in the drawing deformation process is 1.3 to 1.5, and the anvil is returned to the furnace for heating after each fire forging, and kept warm for 60 to 120 minutes, and the heating temperature is 35 to 45°C below the phase transition point temperature.

[0014] Compared with the prior art, the advantages of the technical solution of the present invention are: (1) The present invention makes full use of the microstructure evolution mechanism of titanium alloy under high temperature deformation. After blanking and upsetting forging in the single-phase zone, it is air-cooled, then heated and subjected to one-time α+β zone drawing and forging, and then hot-remelted to β zone for annealing and water quenching, which can quickly break the grains. (2) The present invention adopts the upsetting deformation near the α+β region, which can effectively inhibit the interference of the initial tissue heredity on the secondary α phase morphology during subsequent processing, and at the same time inhibit the recovery of the deformed structure and the β recrystallization process during the β heat treatment water quenching process, thereby achieving the overlap of the (α+β / β) phase transformation and recrystallization process, increasing the nucleation points of recrystallized grains and β grains, shortening the grain growth time, and refining the grains; (3) The present invention adopts multiple fires in the α+β region below the phase transition temperature and repeated stretching deformation combined with hot reheating in each fire, which fully refines the grain size through continuous dynamic recrystallization and α phase spheroidization behavior, thereby promoting microstructure homogenization; (4) The method of the present invention ultimately produces a short-process, low-cost TC4 titanium alloy large bar with a fine-grained structure composed of equiaxed primary α phase, fine-lamellar secondary α phase and β transformation phase. The internal structure of the bar is uniform and fine, which meets the requirement of low noise level in non-destructive testing of the bar and can meet the demand for uniform structure and low noise level in the manufacture of aviation titanium alloy load-bearing components. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a 200x microstructure image of the rod prepared in Example 1 of the present invention; Figure 2 This is a 500x microstructure image of the rod prepared in Example 1 of the present invention; Figure 3 This is a 200x microstructure diagram of the rod prepared in Example 2 of the present invention; Figure 4 This is a 500x microstructure image of the rod prepared in Example 2 of the present invention; Figure 5 This is a 200x microstructure image of the rod prepared in Example 3 of the present invention; Figure 6This is a 500x microstructure image of the rod prepared in Example 3 of the present invention; Figure 7 This is a table of transverse mechanical properties of the TC4 titanium alloy φ300mm bar prepared in Example 1; Figure 8 This is a scanning diagram of the ultrasonic flaw detection curve of the rod φ1.2mm flat bottom hole test block in Example 1; Figure 9 This is a table of transverse mechanical properties of the TC4 titanium alloy φ300mm bar prepared in Example 2; Figure 10 This is a scanning diagram of the ultrasonic flaw detection curve of the rod φ1.2mm flat bottom hole test block in Example 2; Figure 11 This is the transverse mechanical properties table of the TC4 titanium alloy φ300mm bar prepared in Example 3; Figure 12 This is a scanning diagram of the ultrasonic flaw detection curve of the rod φ1.2mm flat-bottom hole test block in Example 3. DETAILED DESCRIPTION Example 1

[0016] To make the present invention more clear, a short-process and low-cost forging method for preparing TC4 titanium alloy bars of the present invention is further described below in conjunction with the accompanying drawings. The specific embodiments described here are only used to explain the present invention and are not used to limit the present invention.

[0017] This embodiment provides a short-process and low-cost method for preparing TC4 titanium alloy bars by forging, which is characterized by: (1) A 700-diameter TC4 titanium alloy ingot weighing 1500 kg and having a phase transition temperature of 995°C was used. The ingot was heated to 1150°C in a resistance furnace and kept warm for 480 minutes. Then, it was stretched once in the β phase region using a 4500-ton high-speed forging machine. The final forging temperature was not less than 900°C, and the forging ratio was controlled at 1.2-1.5. After forging, the ingot was returned to the furnace in a hot state and heated at 1150°C. After holding for 60-120 minutes, it was upset on a 4500-ton high-speed forging machine. The final forging temperature was not less than 900°C, and the forging ratio was controlled at 1.2-1.5. The ingot was air-cooled to 400°C to obtain a forging blank with a cross-sectional diameter of 600-680 mm.

[0018] (2) Using a resistance furnace, heat the forging blank obtained in step (1) to 955°C, keep it warm for 400 minutes, and perform stretch forging once on a 4500-ton fast forging machine. The final forging temperature is not less than 850°C, and the forging ratio is controlled at 1.3 to 1.6.

[0019] (3) The hot forging blank treated in step (2) is directly returned to the furnace and subjected to β annealing heat treatment at 1015°C. After holding for 120 minutes, the blank is rapidly water-quenched. The forging blank is cooled to below 400°C and then subjected to surface grinding treatment.

[0020] (4) The billet obtained in step (3) is heated to 965°C and kept at this temperature for 400 min. It is subjected to one round of upsetting forging on a 4500-ton high-speed forging machine with a forging ratio of 1.2 to 1.8. The forging billet is returned to the furnace and heated to 965°C and kept at this temperature for 60 to 120 min. It is then subjected to one round of drawing forging with a forging ratio of 1.3 to 1.6. The hot material is returned to the furnace for heating treatment.

[0021] (5) The billet obtained in step (4) is heated to 955°C, kept at this temperature for 60-120 minutes, and then drawn into a φ320 black bar in four consecutive fires. After each fire, the billet is returned to the hot state and kept at this temperature for 60-120 minutes. The billet forging ratio is controlled at 1.3-1.5 in each fire.

[0022] The properties of the TC4 titanium alloy φ300mm bar prepared in Example 1 are as follows: Figure 7 As shown in Table 1, the level of flaw detection clutter is as follows Figure 8 The microstructure of the rod prepared in Example 1 was analyzed and the following results were obtained: Figure 1 and Figure 2 The microstructure images are shown at 200 times and 500 times.

[0023] Nondestructive testing: 1.2mm flat-bottom hole test blocks were inspected, and no single discontinuous flat-bottom hole defect exceeding 1.2mm or multiple discontinuous defects were found. No bottom wave reduction or forward shift was found, conforming to Class A1 and meeting Class A acceptance requirements. The noise level was 1.2mm / 12dB. Example 2

[0024] This embodiment provides a short-process and low-cost method for preparing TC4 titanium alloy bars by forging, which is characterized by: (1) A TC4 titanium alloy ingot of Φ800 with a weight of 1400 kg and a phase transition temperature of 985°C was used. The ingot was heated to 1150°C in a resistance furnace and kept warm for 600 min. Then, it was stretched once in the β phase region using a 4500-ton high-speed forging machine. The final forging temperature was not less than 900°C, and the forging ratio was controlled at 1.2-1.5. After forging, the ingot was returned to the furnace in a hot state and heated at 1150°C. After holding for 60-120 min, it was upset on a 4500-ton high-speed forging machine. The final forging temperature was not less than 900°C, and the forging ratio was controlled at 1.2-1.5. The ingot was air-cooled to 400°C to obtain a forging blank with a cross-sectional diameter of 600-680 mm.

[0025] (2) Using a resistance furnace, heat the forging blank obtained in step 1) to 940°C and keep it at this temperature for 420 min. Then, perform a drawing forging on a 4500-ton high-speed forging machine. The final forging temperature is not less than 850°C, and the forging ratio is controlled at 1.3 to 1.5.

[0026] (3) The hot forging blank treated in step (2) is directly returned to the furnace and subjected to β annealing heat treatment at 1010°C. After holding the heat for 120 minutes, the blank is rapidly water-quenched. The forging blank is cooled to below 400°C and then subjected to surface grinding treatment.

[0027] (4) The billet obtained in step (3) is heated to 950°C and kept at this temperature for 400 min. It is subjected to one round of upsetting forging on a 4500-ton high-speed forging machine and then returned to the furnace with a forging ratio of 1.4 to 1.8. The forged billet is returned to the furnace and kept at 950°C for 60 to 120 min, and then subjected to one round of drawing forging with a forging ratio controlled at 1.2 to 1.5. After forging, it is returned to the furnace for heating.

[0028] (5) The billet obtained in step (4) is returned to the furnace and heated to 940°C. The billet is drawn into a φ320 bar in four consecutive fires. The forging ratio of the billet is controlled at 1.2 to 1.5 in each fire. After each fire, the billet is returned to the furnace and kept warm for 60 to 120 minutes.

[0029] The properties of the TC4 titanium alloy φ300mm bar prepared in Example 2 are as follows: Figure 9 As shown in Table 2, the level of flaw detection clutter is as follows Figure 10 The microstructure of the rod prepared in Example 2 was analyzed and the following results were obtained: Figure 3 and Figure 4 The microstructure images are shown at 200 times and 500 times.

[0030] Nondestructive testing: Φ1.2mm flat-bottom hole test blocks were inspected, and no single discontinuous flat-bottom hole defect exceeding Φ1.2mm or multiple discontinuous defects were found. The grade met A1, satisfying the A-level acceptance requirements. The noise level was Φ1.2mm -12dB. Example 3

[0031] This embodiment provides a short-process and low-cost method for preparing TC4 titanium alloy bars by forging, which is characterized by: (1) A TC4 titanium alloy ingot of Φ760 in size with a weight of 1450 kg and a phase transition temperature of 990 °C was used. The ingot was heated to 1150 °C in a resistance furnace and kept warm for 540 min. Then, it was stretched once in the β phase region using a 4500-ton high-speed forging machine. The final forging temperature was not less than 900 °C, and the forging ratio was controlled at 1.2-1.5. After forging, the ingot was returned to the furnace in a hot state and heated and kept warm at 1150 °C for 60-120 min. It was then upset on a 4500-ton high-speed forging machine. The final forging temperature was not less than 900 °C, and the forging ratio was controlled at 1.2-1.5. The ingot was air-cooled to 400 °C to obtain a forging blank with a cross-sectional diameter of 600-680 mm.

[0032] (2) Using a resistance furnace, heat the forging blank obtained in step (1) to 950°C, keep it at this temperature for 8 hours, and perform a drawing forging on a 4500-ton high-speed forging machine. The final forging temperature is not less than 850°C, and the forging ratio is controlled at 1.3 to 1.5.

[0033] (3) The hot forging blank treated in step (2) is directly returned to the furnace and subjected to β annealing heat treatment at 1010°C. After holding for 120 minutes, it is rapidly water-quenched. The forging blank is cooled to below 400°C and then subjected to surface grinding treatment.

[0034] (4) The billet obtained in step (3) is heated to 960°C and kept warm for 400 min. It is subjected to one round of upsetting forging on a 4500-ton high-speed forging machine with a forging ratio of 1.3 to 1.5. The forged billet is returned to the furnace for heating and holding for 60 to 120 min, and then subjected to one round of drawing forging with a forging ratio controlled at 1.3 to 1.6. After forging, the billet is returned to the furnace for heating.

[0035] (5) The billet obtained in step (4) is heated to 950°C and drawn into a φ320 black bar in four consecutive fires. The forging ratio of the billet is controlled at 1.2 to 1.5 in each fire, and the billet is returned to the hot state and kept warm for 60 to 120 minutes after each fire.

[0036] The properties of the TC4 titanium alloy φ300mm bar prepared in Example 3 are as follows: Figure 11 As shown in Table 3, the level of flaw detection clutter is as follows Figure 12 The microstructure of the rod prepared in Example 3 was analyzed and the following results were obtained: Figure 5 and Figure 6 The microstructure images are shown at 200 times and 500 times.

[0037] Nondestructive testing: Φ1.2mm flat-bottom hole test blocks were inspected, and no single discontinuous flat-bottom hole defect exceeding Φ1.2mm or multiple discontinuous defects were found. The grade met A1, satisfying the A-level acceptance requirements. The noise level was Φ1.2mm -12dB.

[0038] In addition to the above embodiments, the present invention may also have other implementations. Any technical solution formed by equivalent replacement or equivalent transformation falls within the scope of protection required by the present invention.

Claims

1. A method for preparing TC4 titanium alloy bars by short-process and low-cost forging, characterized by: (1) β phase region blank forging: Heat the TC4 titanium alloy ingot to 100-200℃ above the β phase transformation temperature, keep it warm for 8-12 hours, and then use a fast forging machine to stretch, return to the furnace for warming, and upset it once each. The total forging ratio is controlled at 2.5-3.5, the final forging temperature is ≥900℃, and air cooling is performed after forging. (2) Thermal deformation of α+β zone: The air-cooled billet is heated to 30-40°C below the β-transformation temperature, kept warm for 6-10 hours, and then subjected to one drawing forging cycle on a high-speed forging machine, with the forging ratio controlled at 1.2-1.5 and the final forging temperature ≥800°C. (3) Static quasi-β annealing water quenching treatment: Then the blank is directly returned to the furnace for annealing heat treatment. The heat treatment temperature is 15-30°C above the β phase transformation temperature. After holding for 90-150 minutes, it is quickly water quenched. The blank temperature is ≤400°C. After water cooling, the blank surface is ground. (4) Thermal deformation near α+β region: The annealed billet is heated to 30-40°C below the β-transformation temperature, kept at this temperature for 360-420 minutes, and then subjected to upsetting, returning to the furnace for holding, and drawing on a high-speed forging machine, with a total forging ratio of 2.5-3.

5. After forging, the hot material is returned to the furnace; (5) Small deformation in the α+β zone, multiple tempering, drawing and final forging: Finally, the blank is heated at 40-50°C below the β phase transformation temperature, and then subjected to 3-5 rounds of drawing and forging, with a forging ratio of 1.2-1.5 for each round. After each round of forging, the blank is returned to the furnace and kept warm for 60-120 minutes. After repeated drawing, the formed bar is obtained.

2. The method for preparing a short-process, low-cost forged TC4 titanium alloy bar according to claim 1, characterized in that: In the step (1), the TC4 titanium alloy ingot has a size of φ600-φ900 mm and a weight of 1200-2000 kg, and the forging blank is air-cooled to below 400° C. after being upsetting and deformed.

3. The method for preparing a short-process, low-cost forged TC4 titanium alloy bar according to claim 1, characterized in that: In the step (1), the forging ratio of each fire is controlled within a range of 1.3 to 1.8, and the total forging ratio is controlled within a range of 2.5 to 3.

5.

4. The method for preparing a short-process, low-cost forged TC4 titanium alloy bar according to claim 1, characterized in that: In the step (2), the holding time after heating during the forging process is 360 to 420 minutes.

5. The method for preparing TC4 titanium alloy bars by short-process and low-cost forging according to claim 1, characterized in that: In the step (2), the forging speed during the drawing process is ≤20 mm / s, and the total forging time is less than 7 minutes.

6. The method for preparing a short-process, low-cost forged TC4 titanium alloy bar according to claim 1, characterized in that: In the step (4), the forging speed of the upsetting process is ≤10 mm / s, and the total forging time is less than 10 min.

7. The method for preparing a short-process, low-cost forged TC4 titanium alloy bar according to claim 1, characterized in that: In the step (4), upsetting deformation is performed on a fast forging machine with a forging ratio of 1.4 to 1.8, and the steel is returned to the furnace in a hot state after forging. After heating and holding at the original temperature for 60 to 120 minutes, stretching forging is performed with a forging ratio of 1.2 to 1.5, and the steel is returned to the furnace in a hot state after forging.

8. The method for preparing TC4 titanium alloy bars by short-process and low-cost forging according to claim 1, characterized in that: In the step (4), the heating temperature during the upsetting and drawing forging process is 25 to 35°C below the phase transition point temperature, and the final forging temperature is ≥750°C.

9. The method for preparing a short-process, low-cost forged TC4 titanium alloy bar according to claim 1, characterized in that: In the step (5), the drawing forging anvil is preheated to 300°C, the forging ratio of each fire in the drawing deformation process is 1.3-1.5, and the anvil is returned to the furnace for heating after each fire forging, and the temperature is kept for 60-120 minutes. The heating temperature is 35-45°C below the phase transition point temperature.

Images