Preparation method of high-sensitivity flaw detection Ti180 titanium alloy large-size bar

Abstract

The invention discloses a preparation method of a high-sensitivity flaw detection Ti180 titanium alloy large-size bar, which comprises the following steps: carrying out two-heating-number blooming forging on a Ti180 titanium alloy cast ingot to obtain a forging stock I; the forging stock I is subjected to three-heating-number high-low-high circulating forging at the temperature of 50-100 DEG C above the phase transformation point, 30-80 DEG C below the phase transformation point and 30-80 DEG C above the phase transformation point, and a forging stock II is obtained; the forging stock II is subjected to two-heating-number forging at the temperature of 30-80 DEG C below the phase transformation point and at the temperature of 30-80 DEG C above the phase transformation point, and a forging stock III is obtained; the forging stock III is subjected to one-heating-number forging, and a forging stock IV is obtained; and the forging stock IV is subjected to two-heating-number forging, and the large-specification bar is obtained. The method disclosed by the invention can be used for producing and preparing the high-temperature titanium alloy large-size bar, the prepared bar is subjected to ultrasonic flaw detection, the uniformity of results at different positions is good and reaches phi 1.2-6dB or above, and the alpha + beta state structure uniformity of the produced titanium alloy bar is good.

Description

Technical Field

[0001] The present invention belongs to the technical field of titanium alloy material preparation methods, and relates to a method for preparing large-sized Ti180 titanium alloy bars with high-sensitivity flaw detection. Background Art

[0002] Ti180 titanium alloy, with a nominal composition of Ti-6Al-2Sn-4Zr-6Mo, is a high-Mo content high-temperature titanium alloy developed by the United States in the 1960s. Its service temperature is around 450°C. This alloy has high strength, high temperature resistance, and excellent corrosion resistance, and is widely used in the aerospace field. It is also called a heat-resistant titanium alloy or a heat-resistant titanium alloy. The thermal strength and high specific strength of high-temperature titanium alloys are sufficient to meet the requirements of high-performance engines. Therefore, high-temperature titanium alloys have become one of the main structural materials for contemporary aircraft and engines, which can greatly reduce the weight of aircraft and improve structural efficiency, such as aircraft engine components, rocket thrusters, etc. These equipments require not only instantaneous strength from room temperature to relatively high temperatures, but also high-temperature creep resistance, creep strength, and tissue stability.

[0003] At present, most of the Ti180 titanium alloy bars are bars with a diameter of Φ210mm and below. For large-sized bars with a diameter of Φ210mm~Φ400mm, due to the large deformation resistance of Ti180 titanium alloy itself, the tissue and property uniformity of large-sized Ti180 titanium alloy are poor, and the overall forging yield is low. The traditional forging process follows the route of ingot blooming in the single-phase region → forging in the two-phase region → finished product forming. Not only are there many upsetting and drawing heat treatments, but also the processing flow is long, the ultrasonic flaw detection uniformity is insufficient, and it is only applicable to bars with a diameter of Φ210mm and below.

[0004] In view of this, the present invention proposes a method for preparing large-sized Ti180 titanium alloy bars with high-sensitivity flaw detection to overcome the defects of the prior art. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing large-sized Ti180 titanium alloy bars with high-sensitivity flaw detection, which solves the problems of low yield, poor tissue uniformity, and insufficient ultrasonic flaw detection uniformity in the prior art when preparing large-sized high-temperature titanium alloy bars (Φ210mm~Φ400mm).

[0006] The technical solution adopted by the present invention is that the method for preparing large-sized Ti180 titanium alloy bars with high-sensitivity flaw detection is specifically implemented according to the following steps: Step 1, ingot blooming forging: Forge the Ti180 titanium alloy ingot at 150°C~300°C above the phase transformation point and 100°C~150°C above the phase transformation point for 2 heat treatments to obtain forging blank I; Step 2: High-low-high cyclic forging: The forging blank I is forged three times at temperatures 50°C to 100°C above the phase transformation point, 30°C to 80°C below the phase transformation point, and 30°C to 80°C above the phase transformation point respectively to obtain the forging blank II; Step 3: Secondary low-high cyclic forging: The forging blank II is forged two times at temperatures 30°C to 80°C below the phase transformation point and 30°C to 80°C above the phase transformation point respectively to obtain the forging blank III; Step 4: Intermediate blank forging: The forging blank III is forged once at a temperature 30°C to 80°C below the phase transformation point to obtain the forging blank IV; Step 5: Finished product forging: The forging blank IV is forged two times at a temperature 30°C to 80°C below the phase transformation point to obtain large-sized bars.

[0007] The features of the present invention also lie in: Step 1 is specifically as follows: The ingot is heated to a temperature 150°C to 300°C above the phase transformation point and then held, with a heating coefficient of 0.55 to 0.85, and forged for the first time. Then it is returned to the furnace and held at a temperature 100°C to 150°C above the phase transformation point for 30 min to 150 min, and forged for the second time. The final forging temperatures are not lower than 800°C and 700°C respectively. After forging, the blank is cooled in the air to obtain the forging blank I.

[0008] In Step 1, the specific process of the two-time forging is as follows: For the first time, upsetting and reverse drawing are carried out using a quick forging machine. When upsetting, the forging ratio is controlled between 1.20 and 1.65; when reverse drawing, the deformation amount is controlled between 5% and 45%. For the second time, upsetting and drawing are carried out using a quick forging machine. When upsetting, the forging ratio is controlled between 1.30 and 1.60; when drawing, the deformation amount is controlled between 10% and 40%.

[0009] Step 2 is specifically as follows: The first-time forging: The forging blank I is held at a temperature 50°C to 100°C above the phase transformation point, with a heating coefficient of 0.60 to 0.95, and forged. Then it is returned to the furnace and held at a temperature 50°C to 100°C above the phase transformation point for 30 min to 150 min, and forged again. The final forging temperature is not lower than 700°C. After forging, the blank is cooled in the air; The second-time forging: It is held at a temperature 30°C to 80°C below the phase transformation point, with a heating coefficient of 0.65 to 0.95, and forged. Then it is returned to the furnace and held at a temperature 30°C to 80°C below the phase transformation point for 30 min to 150 min, and forged again. The final forging temperature is not lower than 700°C; The third-time forging: It is returned to the furnace at a temperature 30°C to 80°C above the phase transformation point, with a heating coefficient of 0.35 to 0.55, and upsetting and drawing are carried out. After forging, the blank is cooled in the air to obtain the forging blank II.

[0010] In Step 2, the specific process of the three-time forging is as follows: For the two forging processes in the first heat forging: Upsetting and drawing out are carried out using a quick forging machine. When upsetting, the forging ratio is controlled between 1.40 and 1.75. When drawing out, the drawing out rate is 70 mm / s to 120 mm / s, and the deformation amount is controlled between 20% and 40%. For the two forging processes in the second heat forging: Upsetting and drawing out are carried out using a quick forging machine. When upsetting, the forging ratio is controlled between 1.15 and 1.60, the drawing out deformation amount is 10% to 30%, and the drawing out rate is 20 mm / s to 60 mm / s. In the third heat forging: When upsetting, the forging ratio is controlled between 1.20 and 1.60, the drawing out rate is 30 mm / s to 80 mm / s, and the drawing out deformation amount is controlled between 5% and 15%.

[0011] Step 3 is specifically as follows: For the first heat forging: The forging billet II is kept warm at 30°C to 80°C below the phase transformation point, the heating coefficient is 0.65 to 0.95, forging is carried out, and then it is forged again in the furnace. The reheating holding time is 30 min to 150 min, and it is air-cooled after forging. For the second heat forging: It is kept warm at 30°C to 80°C above the phase transformation point, the heating coefficient is 0.35 to 0.55, and the billet is cooled in the air after forging to obtain the forging billet III.

[0012] In step 3, the specific process of the two heat forging is as follows: For the two forging processes in the first heat forging: Upsetting and drawing out are carried out. When upsetting, the forging ratio is controlled between 1.20 and 1.50, the drawing out rate is 30 mm / s to 60 mm / s, and the deformation amount is controlled between 20% and 40%. For the second heat forging: Upsetting and drawing out are carried out. When upsetting, the forging ratio is controlled between 1.30 and 1.70, the drawing out rate is 30 mm / s to 60 mm / s, and the drawing out deformation amount is controlled between 10% and 25%.

[0013] Step 4 is specifically as follows: The forging billet III is kept warm at 30°C to 80°C below the phase transformation point, the heating coefficient is 0.60 to 0.90, upsetting and drawing out are carried out. When upsetting, the forging ratio is controlled between 1.30 and 1.50, the drawing out rate is 30 mm / s to 50 mm / s, and the drawing out deformation amount is controlled between 15% and 30%. Then it is forged again in the furnace 4 times, the reheating holding time is 30 min to 150 min. After continuous reheating, drawing out is carried out using a quick forging machine, the drawing out rate is 30 mm / s to 50 mm / s, the drawing out deformation amount is controlled between 15% and 35%, the final forging temperature is not lower than 700°C, and the billet is cooled in the air after forging to obtain the forging billet IV.

[0014] Step 5 is specifically as follows: The first forging: Heat the forging blank Ⅳ to 30℃ - 80℃ below the phase transformation point for heat preservation, with a heating coefficient of 0.65 - 1.0. Conduct multi-step continuous back-forging elongation, with an elongation rate of 30mm / s - 50mm / s, and control the elongation deformation amount within 20% - 30%. Then conduct 2 times of back-forging, with a back-forging heat preservation time of 30min - 150min, and air-cool after forging; The second forging: Heat preservation at 30℃ - 80℃ below the phase transformation point, with a heating coefficient of 0.65 - 1.15. Conduct multi-step continuous back-forging elongation, with an elongation rate of 30mm / s - 50mm / s, and control the elongation deformation amount within 10% - 20%. Then conduct 1 time of hot material back-forging, and the back-forging heat preservation time is 30 - 150min for all. The final forging temperature is not lower than 650℃, and air-cool after forging, then the large-sized Ti180 titanium alloy bar is obtained.

[0015] The beneficial effects of the present invention are: Compared with the traditional preparation method, the preparation method of the present invention adopts the way of two high-low-high cycle forgings to fully refine the structure. At the same time, the deformation amount of a single forging is reasonably distributed, avoiding serious surface defects caused by the extreme temperature sensitivity of high-temperature titanium alloy. The method of the present invention can be used for the production and preparation of large-sized bars (Φ210mm - Φ400mm) of high-temperature titanium alloy. Moreover, the large-sized titanium alloy bars prepared are subjected to ultrasonic flaw detection, and the results at different positions have good uniformity, all reaching above Φ1.2 - 6dB, and the α + β state structure of the produced titanium alloy bars has good uniformity. In addition, the method of the present invention adopts a large amount of hot material back-forging, reducing the number of cold material heating times, reducing the high-temperature oxidation material loss of repeated material heating, and saving production costs. Description of the Drawings

[0016] Figure 1 It is a macrostructure diagram of the Φ230-sized bar prepared in Example 1; Figure 2 is a macrostructure diagram of the Φ230-sized bar prepared in Example 1 after burning in air; Figure 3 is a microstructure diagram of the Φ230-sized bar prepared in Example 1; Figure 4 It is an ultrasonic flaw detection diagram of the Φ230-sized bar prepared in Example 1; Figure 5 It is a macrostructure diagram of the Φ350-sized bar prepared in Example 2; Figure 6 It is a macrostructure diagram of the Φ350-sized bar prepared in Example 2 after burning in air; Figure 7 is a microstructure diagram of the Φ350-sized bar prepared in Example 2; Figure 8 It is an ultrasonic flaw detection diagram of the Φ350-sized bar prepared in Example 2. Detailed Embodiments

[0017] The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0018] The preparation method of high-sensitivity flaw detection Ti180 titanium alloy large-sized bars of the present invention uses Ti180 titanium alloy ingots with a weight of 3 to 5 tons and a specification of Φ700 - Φ740 mm. The chemical composition of the ingots meets the requirements of AMS 4981, and includes five steps: cogging forging → high-low-high cyclic forging → secondary low-high cyclic forging → intermediate billet forging → finished product forging, which are specifically implemented according to the following steps: Step 1, cogging forging: The ingot is forged in 2 heating passes, specifically: The ingot is heated to 150°C - 300°C above the phase transformation point and then held. The heating coefficient is 0.55 - 0.85, and the first heating pass forging is carried out. Specifically: a quick forging machine is used for upsetting and reverse drawing to fully break the β grains. When upsetting, the forging ratio is controlled between 1.20 and 1.65, and when reverse drawing, the deformation amount is controlled between 5% and 45%. Then it is returned to the furnace and held at 100°C - 150°C above the phase transformation point for 30 min - 150 min, and the second heating pass forging is carried out. Specifically: a quick forging machine is used for upsetting and drawing. When upsetting, the forging ratio is controlled between 1.30 and 1.60, and when drawing, the deformation amount is controlled between 10% and 40%.

[0019] The final forging temperatures of the 2 heating passes are not lower than 800°C and 700°C respectively. After forging, the billet is cooled in the air to obtain forging billet I; Step 2, high-low-high cyclic forging: The forging billet I obtained in Step 1 is forged in 3 heating passes, specifically: The first heating pass forging: The forging billet I is held at 50°C - 100°C above the phase transformation point. The heating coefficient is 0.60 - 0.95, and forging is carried out. Then it is returned to the furnace and held at 50°C - 100°C above the phase transformation point for 30 min - 150 min, and then forging is carried out again. The two forging processes are specifically: a quick forging machine is used for upsetting and drawing. When upsetting, the forging ratio is controlled between 1.40 and 1.75, when drawing, the drawing rate is 70 mm / s - 120 mm / s, the deformation amount is controlled between 20% and 40%, the final forging temperature is not lower than 700°C, and after forging, the billet is cooled in the air; The second heating pass forging: It is held at 30°C - 80°C below the phase transformation point. The heating coefficient is 0.65 - 0.95, and forging is carried out. Then it is returned to the furnace and held at 30°C - 80°C below the phase transformation point for 30 min - 150 min, and then forging is carried out again. The two forging processes are specifically: a quick forging machine is used for upsetting and drawing. When upsetting, the forging ratio is controlled between 1.15 and 1.60, the drawing deformation amount is 10% - 30%, the drawing rate is 20 mm / s - 60 mm / s, and the final forging temperature is not lower than 700°C; The 3rd forging: Reheat to 30°C - 80°C above the phase transformation point, with a heating coefficient of 0.35 - 0.55. Upsetting and drawing out are carried out. When upsetting, the forging ratio is controlled at 1.20 - 1.60, the drawing out rate is 30 mm / s - 80 mm / s, and the drawing out deformation is controlled at 5% - 15%. After forging, the billet is cooled in air to obtain the forged billet II. Step 3: Secondary low-high cycle forging: The forged billet II obtained in Step 2 is forged in 2 heats, specifically: The 1st heat forging: Keep the forged billet II at a temperature of 30°C - 80°C below the phase transformation point, with a heating coefficient of 0.65 - 0.95. Forging is carried out, and then it is reheated for forging once. The reheating holding time is 30 min - 150 min. The two forging processes are specifically: Upsetting and drawing out are carried out. When upsetting, the forging ratio is controlled at 1.20 - 1.50, the drawing out rate is 30 mm / s - 60 mm / s, and the deformation is controlled at 20% - 40%. After forging, it is air-cooled.

[0020] The 2nd heat forging: Keep it at a temperature of 30°C - 80°C above the phase transformation point, with a heating coefficient of 0.35 - 0.55. Upsetting and drawing out are carried out. When upsetting, the forging ratio is controlled at 1.30 - 1.70, the drawing out rate is 30 mm / s - 60 mm / s, and the drawing out deformation is controlled between 10% - 25%. After forging, the billet is cooled in air to obtain the forged billet III.

[0021] Step 4: Intermediate billet forging: The forged billet III obtained in Step 3 is forged in 1 heat, specifically: Keep the forged billet III at a temperature of 30°C - 80°C below the phase transformation point, with a heating coefficient of 0.60 - 0.90. Upsetting and drawing out are carried out. When upsetting, the forging ratio is controlled at 1.30 - 1.50, the drawing out rate is 30 mm / s - 50 mm / s, and the drawing out deformation is controlled at 15% - 30%. Then it is reheated for forging 4 times, and the reheating holding time is 30 min - 150 min. After continuous reheating, drawing out is carried out using a quick forging machine, the drawing out rate is 30 mm / s - 50 mm / s, and the drawing out deformation is controlled at 15% - 35%. The final forging temperature is not lower than 700°C. After forging, the billet is cooled in air to obtain the forged billet IV.

[0022] Step 5: Finished product forging: The forged billet IV obtained in Step 4 is forged in 2 heats, specifically: The 1st heat forging: Heat the forged billet IV to a temperature of 30°C - 80°C below the phase transformation point and keep it warm, with a heating coefficient of 0.65 - 1.0. Multi-step continuous reheating and drawing out are carried out, the drawing out rate is 30 mm / s - 50 mm / s, and the drawing out deformation is controlled at 20% - 30%. Then it is reheated for forging 2 times, and the reheating holding time is 30 min - 150 min. After forging, it is air-cooled; The second forging: Insulate at a temperature 30°C to 80°C below the phase transition point, with a heating coefficient of 0.65 to 1.15. Conduct multi-step continuous remelting and drawing out, with a drawing out rate of 30 mm / s to 50 mm / s, and the drawing out deformation amount controlled within 10% to 20%. Then conduct hot material remelting once, with the remelting insulation time all being 30 to 150 min. The final forging temperature is not lower than 650°C, and after forging, air cooling is carried out, thus obtaining large-sized Ti180 titanium alloy bars with high sensitivity flaw detection.

[0023] In order to further verify the efficacy of the preparation method of the present invention, the following specific examples were carried out: Example 1: The Ti180 titanium alloy bars with a specification of Φ230 mm were prepared in this example: Select a 5-ton Ti180 titanium alloy ingot with a specification of Φ720 mm, whose chemical composition meets the requirements of AMS 4981. The specific preparation steps are as follows: Step 1: Conduct 2-fire forging using a quick forging machine: The heating temperature is 1170°C. After insulating for 450 min to 600 min, upsetting and drawing out are carried out. When upsetting, the forging ratio is controlled at 1.5, and when drawing out, the deformation amount is controlled at 30%. After remelting to 1080°C and insulating for 30 min to 150 min, upsetting and drawing out are carried out again. When upsetting, the forging ratio is controlled at 1.4, and when drawing out, the deformation amount is controlled at 35%. The forging specification after forging is octagonal 630×L, and the final forging temperature is controlled above 700°C. After forging, air cooling is used for cooling to obtain forging blank I; Step 2: High-low-high cycle forging is divided into 3-fire forging in total: In the first fire, heat forging blank I to 1050°C, insulate for 480 min to 660 min, and use a quick forging machine to carry out upsetting and drawing out. When upsetting, the forging ratio is controlled at 1.5, and when drawing out, the deformation amount is controlled at 30%. Then remelt to 1050°C and insulate for 60 min to 120 min, and use a quick forging machine to carry out upsetting and drawing out. When upsetting, the forging ratio is controlled at 1.5, and when drawing out, the deformation amount is controlled at 31%. After forging, air cooling is carried out; In the second fire, heat to 925°C, insulate for 530 min to 650 min, and then carry out upsetting and drawing out. When upsetting, the forging ratio is controlled at 1.45, and when drawing out, the deformation amount is controlled at 30%. Then remelt to 925°C and insulate for 60 min to 120 min, and use a quick forging machine to carry out upsetting and drawing out. When upsetting, the forging ratio is controlled at 1.4, and when drawing out, the deformation amount is controlled at 20%. After forging, air cooling is carried out; In the third fire, heat to 1020°C, insulate for 240 min to 360 min, and then carry out upsetting and drawing out. When upsetting, the forging ratio is controlled at 1.45, and when drawing out, the deformation amount is controlled at 5%. After forging, air cooling is used for cooling to obtain forging blank II; Step 3: The secondary low-high cycle forging is divided into two forging heats. In the first heat, the forging blank II is heated to 915°C and held for 540 min to 720 min. Upsetting and drawing are carried out using a quick forging machine. When upsetting, the forging ratio is controlled at 1.5, and when drawing, the deformation amount is controlled at 25%. After returning to the furnace at 915°C and holding for 30 min to 150 min, upsetting and drawing are carried out again. When upsetting, the forging ratio is controlled at 1.3, and when drawing, the deformation amount is controlled at 30%. After forging, it is air-cooled. In the second heat, the heating temperature is 995°C, and it is held for 240 min to 360 min. Upsetting and drawing are carried out using a quick forging machine. When upsetting, the forging ratio is controlled at 1.6, and when drawing, the deformation amount is controlled at 15%. After forging, it is air-cooled to obtain the forging blank III. Step 4: Intermediate blank forging: The forging blank III is heated to 915°C for multi-step continuous furnace-return forging, and the furnace-return holding time between steps is 30 min to 150 min. Among them, in step 1, upsetting and drawing are carried out. When upsetting, the forging ratio is controlled at 1.3, and the drawing deformation amount is controlled at 20%. In step 2, drawing is carried out, and the drawing deformation amount is controlled at 15%. In steps 3 to 4, the drawing deformation amount is 30%. After forging, it is air-cooled to obtain the forging blank IV. Step 5: The finished product forging is completed in two heats. In the first heat, the forging blank IV is heated to 915°C and held for 300 min to 480 min. Multi-step continuous furnace-return forging is carried out using a quick forging machine. The furnace-return holding time between steps is 30 min to 150 min, and the drawing deformation amount is controlled at 25%. In the second heat, it is heated to 915°C and held for 200 min to 380 min. Multi-step continuous furnace-return forging is carried out using a quick forging machine. The furnace-return holding time is 30 min to 150 min, and the drawing deformation amount is controlled at 15%. After forging, the forging blank V is obtained, and then the forging blank V is machined to the target size through machining, that is, the Ti180 titanium alloy bar of Φ230mm specification is obtained.

[0024] Result analysis: I. For the Φ230mm bar prepared in this example, a 25mm thick specimen piece is taken and subjected to air cooling treatment at 900°C / 1h, air cooling + 593°C / 8h, and then the mechanical properties are tested. The results are shown in Tables 1 to 2: Table 1 Tensile property test results

[0025] Table 2 Creep property test results

[0026] It can be seen from the test results in Tables 1 to 2 that the room temperature tensile, high temperature tensile, and creep properties of the Φ230mm bar prepared by the method of the present invention all meet the requirements and have sufficient margins.

[0027] II. Macro and micro structure analysis The macro and micro structures of the bar prepared in this example are observed: As shown Figure 1 in the figure, it is the macrostructure diagram of the bar prepared in this embodiment. It can be seen that there are no cracks, inclusions, segregation, shrinkage cavities, pores or other metallurgical defects in the macrostructure, and there are no obvious clearly visible grains to the naked eye, all of which are uniform blurred grains.

[0028] As shown in Figure 2, it is the macrostructure diagram of the bar prepared in this embodiment after air burning. Among them, Figures a - d are the macrostructure diagrams after 4 different air - burning heat treatments (T β - 30°C / 60min → T β + 15°C / 30min, AC, T β + 30°C / 120min, AC, T β + 45°C / 120min, AC, T β + 60°C / 120min, AC) respectively. It can be seen that the grain sizes are 0.2 - 0.4mm, 0.2 - 0.6mm, 0.2 - 0.6mm, 0.4 - 0.8mm respectively, the average β - grain size does not exceed 1mm, and the tissue uniformity is good, without fine - grain rings or distinct stratified tissues with distinct thicknesses.

[0029] As shown in Figure 3, it is the microstructure diagram of the bar prepared in this embodiment at high magnification. Among them, Figures a - c are the microstructure diagrams at high magnification of the edge transverse, R / 2 transverse and core transverse respectively. It can be seen that the high - magnification microstructures at different positions are all tissues processed in the α + β phase region. There are equiaxed primary α - phases on the transformed β matrix, and there is no continuous α - network on the original β grain boundaries, and the tissue uniformity at different positions is relatively good.

[0030] III. Analysis of Ultrasonic Flaw Detection Results As shown Figure 4 in the figure, it is the ultrasonic flaw detection diagram of the bar prepared in this embodiment. It can be seen that the flaw detection results are uniform, meeting the requirements above Φ0.8 - 9dB.

[0031] Example 2: The Ti180 titanium alloy bar with a Φ350 specification is prepared in this example: A 4 - ton Ti180 titanium alloy ingot with a Φ720mm specification is selected, and its ingot chemical composition meets the requirements of AMS 4981. The specific preparation steps are as follows: Step 1: Forging is carried out in 2 heats using a quick forging machine. The heating temperature is 1170°C. After holding for 450min - 600min, upsetting and drawing are carried out. When upsetting, the forging ratio is controlled at 1.5, and when drawing, the deformation amount is controlled at 30%. After returning to the furnace and holding at 1080°C for 30min - 150min, upsetting and drawing are carried out again. When upsetting, the forging ratio is controlled at 1.4, and when drawing, the deformation amount is controlled at 35%. The forged specification is octagonal 630×L, and the final forging temperature is controlled above 700°C. After forging, air cooling is used for cooling to obtain forging blank I; Step 2: The high-low-high cyclic forging is divided into 3 forging heats. In the first heat, the forging blank I is heated to 1050°C and held for 480 min to 660 min. Upsetting and drawing are carried out using a quick forging machine. When upsetting, the forging ratio is controlled at 1.5, and when drawing, the deformation amount is controlled at 30%. Then it is returned to the furnace at 1050°C and held for 60 min to 120 min. Upsetting and drawing are carried out using a quick forging machine. When upsetting, the forging ratio is controlled at 1.5, and when drawing, the deformation amount is controlled at 31%. After forging, it is air-cooled. In the second heat, it is heated to 925°C and held for 530 min to 710 min, then upsetting and drawing are carried out. When upsetting, the forging ratio is controlled at 1.45, and when drawing, the deformation amount is controlled at 30%. Then it is returned to the furnace at 925°C and held for 60 min to 120 min. Upsetting and drawing are carried out using a quick forging machine. When upsetting, the forging ratio is controlled at 1.4, and when drawing, the deformation amount is controlled at 20%. After forging, it is air-cooled. In the third heat, it is heated to 1020°C and held for 240 min to 360 min, then upsetting and drawing are carried out again. When upsetting, the forging ratio is controlled at 1.45, and when drawing, the deformation amount is controlled at 5%. After forging, it is cooled by water cooling to obtain the forging blank II. Step 3: The secondary low-high cyclic forging is divided into 2 forging heats. In the first heat, the forging blank II is heated to 915°C and held for 540 min to 720 min. Upsetting and drawing are carried out using a quick forging machine. When upsetting, the forging ratio is controlled at 1.5, and when drawing, the deformation amount is controlled at 25%. After returning to the furnace at 915°C and holding for 30 min to 150 min, upsetting and drawing are carried out again. When upsetting, the forging ratio is controlled at 1.3, and when drawing, the deformation amount is controlled at 30%. After forging, it is air-cooled. In the second heat, the heating temperature is 995°C and held for 240 min to 360 min. Upsetting and drawing are carried out using a quick forging machine. When upsetting, the forging ratio is controlled at 1.6, and when drawing, the deformation amount is controlled at 15%. After forging, it is air-cooled to obtain the forging blank III. Step 4: Intermediate blank forging: The forging blank III is heated to 915°C for multi-step continuous furnace-return forging, and the furnace-return holding time between steps is 60 min to 150 min. Among them, in step 1, upsetting and drawing are carried out. When upsetting, the forging ratio is controlled at 1.3, and when drawing, the deformation amount is controlled at 20%. In step 2, drawing is carried out, and the drawing deformation amount is controlled at 15%. In steps 3 - 4, the drawing deformation amount is 30%. After forging, it is air-cooled to obtain the forging blank IV. Step 5: The finished product forging is completed in 2 heats. In the first heat, the forging blank IV is heated to 915°C and held for 330 min to 510 min. Multi-step continuous furnace-return forging is carried out using a quick forging machine. The furnace-return holding time between steps is 60 min to 150 min, and the drawing deformation amount is controlled at 25%. In the second heat, it is heated to 915°C and held for 240 min to 420 min. Multi-step continuous furnace-return forging is carried out using a quick forging machine. The furnace-return holding time is 60 min to 150 min, and the drawing deformation amount is controlled at 15%. After forging, the forging blank V is obtained, and then the forging blank V is machined to the target size through machining, that is, a Ti180 titanium alloy bar with a specification of Φ350 mm is obtained.

[0032] Result analysis: 1. For the 70-mm-thick specimen slices taken from the Φ350-mm bars prepared in Example 2, after air-cooling heat treatment at 910°C for 1.5 h followed by air cooling at 593°C for 8 h, the mechanical properties were tested, and the results are shown in Tables 3 to 4: Table 3 Tensile property test results

[0033] Table 4 Creep property test results

[0034] It can be seen from the test results in Tables 3 to 4 that the room-temperature tensile, high-temperature tensile, and creep properties of the Φ350-mm bars prepared by the method of the present invention all meet the requirements and have sufficient margins.

[0035] 2. Macro and micro structure analysis The macro and micro structures of the bars prepared in this example were observed: As Figure 5 shown, it is the macrostructure diagram of the bars prepared in this example. It can be seen that there are no cracks, inclusions, segregation, shrinkage cavities, pores or other metallurgical defects in the macrostructure, and there are no obvious clearly visible grains to the naked eye, and they are all uniform blurred grains.

[0036] As Figure 6 shown, it is the macrostructure diagram of the bars prepared in this example after burning in air. It can be seen that after the bars prepared are heat-treated by burning in air, the tissue uniformity is good, and there are no fine crystal rings or clearly stratified tissues with distinct thicknesses.

[0037] As shown in Figure 7, it is the microstructure diagram of the bars prepared in this example. Among them, Figures a-c are the microstructure diagrams of the edge transverse, R / 2 transverse, and core transverse parts respectively. It can be seen that the microstructures at different positions are all tissues processed in the α+β phase region. The primary α phase is equiaxed on the transformed β matrix, and there is no continuous α network on the original β grain boundary, and the tissue uniformity at different positions is relatively good.

[0038] 3. Analysis of ultrasonic flaw detection results As Figure 8 shown, it is the ultrasonic flaw detection diagram of the bars prepared in this example. It can be seen that the ultrasonic flaw detection results are uniform, meeting the requirements of Φ1.2 - 6 dB or above.

[0039] In summary, for the large-sized bars prepared by the method of the present invention, there are no obvious metallurgical defects in the macrostructure, the structure is uniform, showing blurred grains; the microstructure is uniform equiaxed structure. After heat treatment at 900°C ± 10°C for 1 - 2 h, followed by air cooling at 593°C for 8 h and then air cooling, the mechanical properties were tested, and all meet the standard requirements.

[0040] Example 3: This example is basically the same as Example 1, except that the process parameters in Steps 4 and 5 are different. Specifically: Step 4, Intermediate billet forging: Heat the forging billet III to 915 °C and perform multi-step continuous reheating forging. The reheating and heat preservation time between steps is 30 min to 150 min. Among them, in Step 1, upsetting and drawing out are carried out. The upsetting forging ratio is controlled at 1.5, and the drawing out deformation is controlled at 30%; in Step 2, drawing out is carried out, and the drawing out deformation is controlled at 35%; in Steps 3-4, the drawing out deformation is 20%. After forging, air cooling is carried out to obtain the forging billet IV; Step 5, Finish forging is completed in 2 heating times: In the first heating time, heat the forging billet IV to 915 °C, with a heat preservation time of 300 min to 480 min. Use a quick forging machine to perform multi-step continuous reheating forging. The reheating and heat preservation time between steps is 30 min to 150 min, and the drawing out deformation is controlled at 20%; in the second heating, heat to 915 °C, with a heat preservation time of 200 min to 380 min. Use a quick forging machine to perform multi-step continuous reheating forging. The reheating and heat preservation time is 30 min to 150 min, and the drawing out deformation is controlled at 20%. After forging, the forging billet V is obtained, and then the forging billet V is machined to the target size through machining, that is, a Ti180 titanium alloy bar with a specification of Φ230 mm is obtained.

[0041] Example 4: This example is basically the same as Example 1, except that the process parameter in Step 1 is different. Step 1 is specifically as follows: Step 1, Use a quick forging machine to perform forging in 2 heating times: The heating temperature is 1170 °C. After heat preservation for 450 min to 600 min, upsetting and drawing out are carried out. The upsetting forging ratio is controlled at 1.6, and the drawing out deformation is controlled at 40%. After reheating to 1080 °C and heat preservation for 30 min to 150 min, upsetting and drawing out are carried out again. The upsetting forging ratio is controlled at 1.45, and the drawing out deformation is controlled at 25%. The final forging specification is octagonal 630×L, and the final forging temperature is controlled above 700 °C. After forging, air cooling is used for cooling to obtain the forging billet I.

[0042] Example 5: This example is basically the same as Example 2, except that the process parameters in Steps 4 and 5 are different. Specifically: Step 4, Intermediate billet forging: Heat the forging billet III to 915 °C and perform multi-step continuous reheating forging. The reheating and heat preservation time between steps is 30 min to 150 min. Among them, in Step 1, upsetting and drawing out are carried out. The upsetting forging ratio is controlled at 1.35, and the drawing out deformation is controlled at 20%; in Step 2, drawing out is carried out, and the drawing out deformation is controlled at 15%; in Steps 3-4, the drawing out deformation is 20%. After forging, air cooling is carried out to obtain the forging billet IV; Step 5: The finished product forging is completed in 2 heating processes. In the first heating process, the forging blank Ⅳ is heated to 915°C and held for 300 min to 480 min. Then, multi-step continuous reheating forging is carried out using a quick forging machine, and the reheating holding time between steps is 30 min to 150 min. The drawing reduction is controlled at 30%. In the second heating process, it is heated to 915°C and held for 200 min to 380 min. Then, multi-step continuous reheating forging is carried out using a quick forging machine, the reheating holding time is 30 min to 150 min, and the drawing reduction is controlled at 10%. After forging, the forging blank Ⅴ is obtained. Then, the forging blank Ⅴ is machined to the target size, and thus the Ti180 titanium alloy bar with a specification of Φ230 mm is obtained.

[0043] Example 6: This example is basically the same as Example 2, except that the process parameters in Step 1 are different. Step 1 is specifically as follows: Step 1: Two-pass forging is carried out using a quick forging machine. The heating temperature is 1170°C. After holding for 450 min to 600 min, upsetting and drawing are carried out. When upsetting, the forging ratio is controlled at 1.5, and when drawing, the reduction is controlled at 15%. After reheating to 1080°C and holding for 30 min to 150 min, upsetting and drawing are carried out again. When upsetting, the forging ratio is controlled at 1.6, and when drawing, the reduction is controlled at 25%. The final forging specification is octagonal 630×L, and the final forging temperature is controlled above 700°C. After forging, air cooling is used for cooling to obtain the forging blank Ⅰ.

Claims

1. Preparation method of large-size bar of high-sensitivity flaw-detecting Ti180 titanium alloy, characterized in that, The implementation is specifically carried out according to the following steps: Step 1, bloom forging: Forge the Ti180 titanium alloy ingot at 150°C to 300°C above the phase transformation point and 100°C to 150°C above the phase transformation point for 2 heats to obtain bloom I; Step 2, high-low-high cyclic forging: Forge bloom I at 50°C to 100°C above the phase transformation point, 30°C to 80°C below the phase transformation point, and 30°C to 80°C above the phase transformation point for 3 heats to obtain bloom II; Step 3, secondary low-high cyclic forging: Forge bloom II at 30°C to 80°C below the phase transformation point and 30°C to 80°C above the phase transformation point for 2 heats to obtain bloom III; Step 4, intermediate billet forging: Forge bloom III at 30°C to 80°C below the phase transformation point for 1 heat to obtain bloom IV; Step 5, finished product forging: Forge bloom IV at 30°C to 80°C below the phase transformation point for 2 heats to obtain large-sized bars.

2. The preparation method of a large-sized bar of high-sensitivity flaw-detecting Ti180 titanium alloy according to claim 1, wherein, Specifically, Step 1 is as follows: Heat the ingot to 150°C to 300°C above the phase transformation point and hold, with a heating coefficient of 0.55 to 0.85, conduct the first heat forging, then return to the furnace and hold at 100°C to 150°C above the phase transformation point for 30 min to 150 min, conduct the second heat forging, and the final forging temperature is not lower than 800°C and 700°C respectively. After forging, cool the billet in the air to obtain bloom I.

3. The preparation method of the large-sized bar of high-sensitivity flaw-detecting Ti180 titanium alloy according to claim 2, wherein, In Step 1, the specific process of the 2-heat forging is as follows: For the first heat, use a quick forging machine for upsetting and reverse drawing. When upsetting, the forging ratio is controlled between 1.20 and 1.65; when reverse drawing, the deformation amount is controlled between 5% and 45%. For the second heat, use a quick forging machine for upsetting and drawing. When upsetting, the forging ratio is controlled between 1.30 and 1.60; when drawing, the deformation amount is controlled between 10% and 40%.

4. The preparation method of the large-sized bar of high-sensitivity flaw-detecting Ti180 titanium alloy according to claim 1, characterized in that, Specifically, Step 2 is as follows: The first heat forging: Hold bloom I at 50°C to 100°C above the phase transformation point, with a heating coefficient of 0.60 to 0.95, conduct forging, then return to the furnace and hold at 50°C to 100°C above the phase transformation point for 30 min to 150 min, and then conduct forging again. The final forging temperature is not lower than 700°C. After forging, cool the billet in the air; The second heat forging: Hold at 30°C to 80°C below the phase transformation point, with a heating coefficient of 0.65 to 0.95, conduct forging, then return to the furnace and hold at 30°C to 80°C below the phase transformation point for 30 min to 150 min, and then conduct forging again. The final forging temperature is not lower than 700°C; The third heat forging: Return to the furnace at 30°C to 80°C above the phase transformation point, with a heating coefficient of 0.35 to 0.55, conduct upsetting and drawing, and after forging, cool the billet in the air to obtain bloom II.

5. The preparation method of a large-sized bar of high-sensitivity flaw-detecting Ti180 titanium alloy according to claim 4, characterized in that, In Step 2, the specific process of the 3-heat forging is as follows: For both forging processes of the first heat forging: Use a quick forging machine for upsetting and drawing. When upsetting, the forging ratio is controlled between 1.40 and 1.75; when drawing, the drawing rate is 70 mm / s to 120 mm / s, and the deformation amount is controlled between 20% and 40%; For the two forging processes in the second forging heat: Upsetting and drawing out are carried out using a quick forging machine. When upsetting, the forging ratio is controlled between 1.15 and 1.60, the drawing out deformation is 10% - 30%, and the drawing out rate is 20 mm / s - 60 mm / s; In the third forging heat: When upsetting, the forging ratio is controlled between 1.20 and 1.60, the drawing out rate is 30 mm / s - 80 mm / s, and the drawing out deformation is controlled between 5% and 15%.

6. The preparation method of a large-sized bar of high-sensitivity flaw-detecting Ti180 titanium alloy according to claim 1, characterized in that, Step 3 is specifically as follows: The first forging heat: The forging blank II is held at a temperature 30°C - 80°C below the phase transformation point, with a heating coefficient of 0.65 - 0.95, forged, then subjected to 1 time of re-forging in the furnace, the re-forging holding time is 30 min - 150 min, and air-cooled after forging; The second forging heat: It is held at a temperature 30°C - 80°C above the phase transformation point, with a heating coefficient of 0.35 - 0.

55. After forging, the blank is cooled in the air to obtain the forging blank III.

7. The preparation method of the large-sized bar of high-sensitivity flaw detection Ti180 titanium alloy according to claim 6, characterized in that, In step 3, the specific process of the two-forging-heat forging is as follows: For the two forging processes in the first forging heat: Upsetting and drawing out are carried out. When upsetting, the forging ratio is controlled between 1.20 and 1.50, the drawing out rate is 30 mm / s - 60 mm / s, and the deformation is controlled between 20% and 40%; The second forging heat: Upsetting and drawing out are carried out. When upsetting, the forging ratio is controlled between 1.30 and 1.70, the drawing out rate is 30 mm / s - 60 mm / s, and the drawing out deformation is controlled between 10% and 25%.

8. The preparation method of a large-sized bar of high-sensitivity flaw-detecting Ti180 titanium alloy according to claim 1, characterized in that, Step 4 is specifically as follows: The forging blank III is held at a temperature 30°C - 80°C below the phase transformation point, with a heating coefficient of 0.60 - 0.

90. Upsetting and drawing out are carried out. When upsetting, the forging ratio is controlled between 1.30 and 1.50, the drawing out rate is 30 mm / s - 50 mm / s, and the drawing out deformation is controlled between 15% and 30%; then 4 times of re-forging in the furnace are carried out, the re-forging holding time is 30 min - 150 min. After continuous re-forging, drawing out is carried out using a quick forging machine, the drawing out rate is 30 mm / s - 50 mm / s, the drawing out deformation is controlled between 15% and 35%, the final forging temperature is not lower than 700°C, and the blank is cooled in the air after forging to obtain the forging blank IV.

9. The preparation method of the large-sized bar of high-sensitivity flaw-detecting Ti180 titanium alloy according to claim 1, characterized in that, Step 5 is specifically as follows: The first forging heat: The forging blank IV is heated to a temperature 30°C - 80°C below the phase transformation point and held, with a heating coefficient of 0.65 - 1.

0. Multi-step continuous re-forging drawing out is carried out, the drawing out rate is 30 mm / s - 50 mm / s, the drawing out deformation is controlled between 20% and 30%, then 2 times of re-forging in the furnace are carried out, the re-forging holding time is 30 min - 150 min, and air-cooled after forging; The second forging heat: It is held at a temperature 30°C - 80°C below the phase transformation point, with a heating coefficient of 0.65 - 1.

15. Multi-step continuous re-forging drawing out is carried out, the drawing out rate is 30 mm / s - 50 mm / s, the drawing out deformation is controlled between 10% and 20%, then hot material re-forging in the furnace is carried out 1 time, the re-forging holding time is 30 - 150 min for all, the final forging temperature is not lower than 650°C, and air-cooled after forging, thus obtaining the large-sized Ti180 titanium alloy bar.

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