A high-grade, large-size TC4 bar and its preparation method

Abstract

This invention discloses a high-flaw-detection-grade large-size TC4 bar and its preparation method, belonging to the field of titanium alloy technology. It solves the problems of overheating and uneven microstructure in existing titanium alloy bar preparation methods for large-size TC4 bars. The preparation method includes: forging an ingot in two stages to obtain a billet; forging the billet in one stage; performing a β-heat treatment on the billet to obtain an intermediate billet; forging the intermediate billet in multiple stages; flattening and square forging; and rounding forging to obtain the high-flaw-detection-grade large-size TC4 bar. The high-flaw-detection-grade large-size TC4 bar prepared by the method of this invention has good uniformity and a high flaw detection grade.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy technology, and in particular to a high-flaw-detection-level large-size TC4 bar and its preparation method. Background Technology

[0002] Titanium alloys possess advantages such as high specific strength, lightweight and corrosion resistance, excellent high-temperature performance, and good machinability, making them an important material for lightweight applications. With the rapid development of titanium alloy components towards lightweighting, structural design, reduced weld seams, and integral forming, and with increasing usage, there is a growing demand for larger titanium alloy ingots and forgings.

[0003] The following problems often exist in the forging of large-sized titanium alloy bars: (1) There are deformation dead zones in the forging process, which will cause uneven deformation and lead to uneven microstructure and properties; (2) Titanium alloy has a low thermal conductivity, and the core of the forging is prone to overheating during the upsetting process, resulting in uneven local microstructure. The typical microstructure caused by overheating is "annual ring" structure. The above two problems become more and more obvious as the size of the titanium alloy bar increases. In the existing technology, the preparation methods of titanium alloy bars are mostly for bars with a diameter of less than 400mm, which cannot meet the technical requirements of larger bars. Therefore, it is urgent to find a forging method for large-sized bars that can fully break the microstructure of the forged bar while avoiding uneven microstructure caused by uneven local deformation and overheating. Summary of the Invention

[0004] In view of the above, the present invention aims to provide a high-level flaw detection grade large-size TC4 bar and its preparation method, to solve at least one of the following problems: existing titanium alloy bar preparation methods are prone to overheating and uneven microstructure when preparing large-size TC4 bars.

[0005] The objective of this invention is mainly achieved through the following technical solutions:

[0006] This invention provides a method for preparing large-size TC4 bars with high flaw detection level, the method comprising:

[0007] Step 1: The ingot is forged in two stages to obtain the billet;

[0008] Step 2: Perform a single-fire upsetting and drawing forging on the billet;

[0009] Step 3: Perform β heat treatment on the billet to obtain an intermediate billet;

[0010] Step 4: Perform multi-stage upsetting and drawing forging on the intermediate billet;

[0011] Step 5: Flat square forging;

[0012] Step 6: Forging with a high flaw detection level to obtain large-size TC4 bars.

[0013] Furthermore, in step 1, the forging ratio of the first forging is controlled to be less than that of the second forging.

[0014] Furthermore, the forging ratio in step 2 is greater than the forging ratio in the second forging.

[0015] Furthermore, in step 1, the first forging process includes:

[0016] Heat the ingot to 680-780℃ and hold it; heat the ingot to 1080-1180℃ and hold it; perform one upsetting and one drawing; return it to the furnace, lower the temperature, and hold it at 1050-1150℃; perform one upsetting and one drawing; roll it into a ball and water cool it.

[0017] Furthermore, in step 1, the second forging process includes: heating the billet to 680-780°C and holding it at that temperature; heating the billet to 1020-1120°C and holding it at that temperature; performing one upsetting and one drawing; returning it to the furnace, lowering the temperature, and holding it at 970-1070°C; performing one upsetting and one drawing; rolling it into a ball and water cooling it.

[0018] Furthermore, step 2 specifically includes: heating the billet to 680–780°C and holding it at that temperature; heating the billet to T β - (15~65℃), keep warm; perform one upsetting and one drawing; return to the furnace, in T β - (15~65℃) Keep warm; perform one upsetting and one pulling; roll into a ball and air cool.

[0019] Furthermore, step 3 includes: heating the furnace to T. β + (5~25℃), after reaching the temperature, load the billet into the furnace, keep it at the temperature for 90~240 minutes, and then air cool.

[0020] Furthermore, in step 4, the steps for each forging and drawing process include: heating the billet to 680–780°C and holding it at that temperature; heating the billet to T… β - (15~65℃), keep warm; perform one upsetting and one drawing; return to the furnace, in T β - (15~65℃) Keep warm; perform one upsetting and one pulling; turn in eight directions and air cool.

[0021] Furthermore, in step 5, each step of the flat forging process includes:

[0022] S51. Heat the billet to 680-780℃ and hold it at that temperature;

[0023] S52. Heat the billet to T β - (15~65℃), heat preservation;

[0024] S53. The horizontal anvil is spread and flattened until the billet height is H. The relationship between H and the billet diameter d4 is as follows: H≥d4 / 2;

[0025] S54. Rotate the billet 90° around the axis and flatten it with the cross anvil until the billet height is H.

[0026] S55, reshaping, elongating the four sides, inverting the eight sides;

[0027] S56, return to the original furnace and keep warm for 60-120 minutes, then repeat S53-S55.

[0028] The present invention also provides a large-size TC4 bar with high flaw detection level, which is prepared by the above-described preparation method.

[0029] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0030] a) The method for preparing large-size TC4 bars with high flaw detection level of the present invention combines two-stage billet forging, one-stage upsetting and drawing forging, β heat treatment, multi-stage upsetting and drawing forging, and flat square upsetting and drawing forging to prepare large-size bars with high uniformity and high flaw detection level.

[0031] (b) By controlling the precise preheating temperature in the preparation method of the present invention, the tendency of grain growth can be reduced, which helps to refine the alloy structure and promotes the alloy to reach the target heating temperature more quickly in the subsequent heating process.

[0032] c) In the preparation method of the present invention, by precisely controlling the process parameters such as temperature, forging ratio, and holding time in different steps, forging cracks and overheating are avoided, ensuring that the microstructure of large-size TC4 bars is uniform and the mechanical properties are excellent.

[0033] d) The high-flaw-detection-grade large-size TC4 bars of the present invention have uniform microstructure and excellent mechanical properties. For example, the radial and tangential tensile strengths of the high-flaw-detection-grade large-size TC4 bars of the present invention are ≥900MPa (e.g., 904~918MPa), yield strength is ≥825MPa (e.g., 827~845MPa), elongation after fracture is ≥11% (e.g., 11%~13%), and reduction of area is ≥26% (e.g., 26%~32%). Furthermore, they exhibit good uniformity, with the maximum difference in tensile strength between different parts being 14MPa and the maximum difference in yield strength between different parts being 18MPa.

[0034] e) The high-flaw-detection-grade large-size TC4 bars of this invention exhibit no cracks, folds, pores, segregation, metallic or non-metallic inclusions, or other visually visible metallurgical defects in their low-magnification microstructure. The flaw detection grade is high, reaching A1 level.

[0035] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of what is particularly pointed out in the written description and the accompanying drawings. Attached Figure Description

[0036] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0037] Figure 1 The low-magnification tissue of end A in Example 1;

[0038] Figure 2 This is a low-magnification tissue of the B end of Example 1. Detailed Implementation

[0039] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of the present invention and, together with the embodiments of the present invention, serve to illustrate the principles of the present invention.

[0040] Large-diameter TC4 (Ti-6Al-4V) titanium alloy bars are prone to deformation dead zones during forging, leading to uneven deformation and resulting in inhomogeneous microstructure and properties. Furthermore, due to the low thermal conductivity of titanium alloys, the core of the forging is prone to overheating during upsetting, causing localized microstructure inhomogeneity. These problems are particularly pronounced in forging bars with a diameter ≥400mm, and become increasingly significant as the diameter of the titanium alloy bars continues to increase. Therefore, there is an urgent need to find a forging method for large-diameter bars that can fully break down the microstructure while avoiding uneven microstructure caused by localized deformation and overheating.

[0041] This invention provides a method for preparing large-size TC4 bars with high flaw detection level, comprising:

[0042] Step 1: The ingot is forged in two stages to obtain the billet;

[0043] Step 2: Perform a single-fire upsetting and drawing forging on the billet;

[0044] Step 3: Perform β heat treatment on the billet to obtain an intermediate billet;

[0045] Step 4: Perform multi-stage upsetting and drawing forging on the intermediate billet;

[0046] Step 5: Two-stage flat forging;

[0047] Step 6: Forging with a high flaw detection level to obtain large-size TC4 bars.

[0048] Specifically, in step 1 above, the composition of the ingot, by mass percentage, includes: Al: 5.5%–6.75%, V: 3.5%–4.5%, Fe: ≤0.3%, O ≤0.2%, N ≤0.05%, C ≤0.08%, H ≤0.001%, with the balance being Ti and unavoidable impurities.

[0049] Specifically, in step 1 above, the ingot can be obtained after three VAR melting processes, and the composition of the ingot is uniform and free of segregation.

[0050] Specifically, in step 1 above, considering that the alloy toughness gradually increases during the sequential forging process, in order to prevent cracking in the forging of the as-cast structure, the forging ratio of the first forging is controlled to be less than that of the second forging.

[0051] Specifically, the forging ratio in step 2 above is greater than the forging ratio in the second forging.

[0052] Specifically, in step 1 above, the first forging process includes:

[0053] S101. Heat the ingot to 680-780℃ and hold it at that temperature;

[0054] S102. Heat the ingot to 1080-1180℃ and hold it at that temperature;

[0055] S103, Perform one upsetting and one pulling;

[0056] S104, return to the furnace, lower the temperature, and keep warm at 1050~1150℃;

[0057] S105, Perform one upsetting and one pulling;

[0058] S106, rounded, water-cooled.

[0059] Specifically, in S101 above, the ingot is heated to 680-780℃ (e.g., 690℃, 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃) and held at this temperature. This is because this temperature is the low-temperature range in the lower part of the two-phase region. Holding and preheating within this temperature range can reduce the tendency of grain growth, help refine the alloy structure, and promote the alloy to reach the target heating temperature more quickly in the subsequent heating process.

[0060] Specifically, in S102 above, the heating rate is controlled at 1.5 to 2.5℃ / min, and the slow heating can ensure uniform heating of the ingot.

[0061] Specifically, in S101 above, the diameter of the ingot is d, and the holding time is T1; in S102, the heating time is T2; in S102, the holding time is T3; T1+T2+T3=(0.7~0.85)d, where the unit of d is mm, and the units of T1, T2 and T3 are all min.

[0062] Specifically, T1, T2, and T3 above satisfy the following relationship: T3≥(T1+T2+T3) / 2.

[0063] For example, the range of T1 is 180–240 min (e.g., 190 min, 200 min, 210 min, 220 min, 230 min), the range of T2 is 180–210 min (e.g., 190 min, 200 min, 210 min), and the range of T3 is 360–480 min (e.g., 370 min, 380 min, 390 min, 400 min, 410 min, 420 min, 430 min, 440 min, 450 min, 460 min, 470 min).

[0064] Specifically, in S103 above, in order to prevent forging cracks in the as-cast structure, the forging ratio is controlled to be 1.3 to 1.45.

[0065] Specifically, in S103 above, considering that a low final forging temperature can easily lead to cracking during the alloy forging process, the final forging temperature is controlled to be above 1050℃.

[0066] Specifically, in S104 above, the purpose of reheating is to replenish the temperature. Since forging deformation will generate residual heat from processing, and the final forging temperature is controlled by the upsetting deformation before reheating, the short-term holding time is controlled for 60 to 120 minutes (e.g., 70 minutes, 80 minutes, 90 minutes, 100 minutes, 110 minutes). The purpose of reducing the temperature during reheating is to refine the forging structure.

[0067] Specifically, in S105 above, in order to prevent forging cracks in the as-cast structure, the forging ratio is controlled to be 1.3 to 1.45.

[0068] Specifically, in S106 above, in order to prevent the broken tissue from growing, and on the other hand, to create more nucleation points, promote the secondary formation of recrystallized tissue under the heat, and control water cooling after rounding.

[0069] Specifically, in S106 above, considering that dense fine cracks are easily generated on the surface of the billet after water cooling, water cooling may also include full grinding to remove surface cracks.

[0070] Specifically, in step 1 above, the second forging process includes:

[0071] S201. Heat the billet to 680-780℃ and hold it at that temperature;

[0072] S202. Heat the billet to 1020-1120℃ and hold it at that temperature;

[0073] S203, Perform one upsetting and one pulling;

[0074] S204, return to the furnace, lower the temperature, and keep warm at 970-1070℃;

[0075] S205, Perform one upsetting and one pulling;

[0076] S206, rounded, water-cooled.

[0077] Specifically, in S201 above, the billet is heated to 680-780℃ (e.g., 690℃, 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃) and held at this temperature. This is because this temperature is the low-temperature range in the lower part of the two-phase region. Holding and preheating within this temperature range can reduce the tendency of grain growth, help refine the alloy structure, and promote the alloy to reach the target heating temperature more quickly in the subsequent heating process.

[0078] Specifically, in S202 above, the heating rate is controlled at 1.5 to 2.5℃ / min, and the slow heating ensures uniform heating of the billet.

[0079] Specifically, in S201 above, the diameter of the billet is d1 and the holding time is T4; in S202, the heating time is T5; in S202, the holding time is T6; T4+T5+T6=(0.7~0.85)d1, where the unit of d1 is mm, and the units of T4, T5 and T6 are all min.

[0080] Specifically, T4, T5, and T6 above satisfy the following relationship: T6≥(T4+T5+T6) / 2.

[0081] For example, the range of T4 is 180–240 min (e.g., 190 min, 200 min, 210 min, 220 min, 230 min), the range of T5 is 130–210 min (e.g., 140 min, 150 min, 160 min, 170 min, 180 min, 190 min, 200 min, 210 min), and the range of T6 is 360–480 min (e.g., 370 min, 380 min, 390 min, 400 min, 410 min, 420 min, 430 min, 440 min, 450 min, 460 min, 470 min).

[0082] Specifically, in the above S203, considering that the alloy toughness gradually increases during the sequential forging process, and that the forging ratio gradually increases without causing forging cracks in the forged structure, the forging ratio is controlled to be 1.45 to 1.55.

[0083] Specifically, in S203 above, considering that a low final forging temperature can easily lead to alloy forging cracks, the final forging temperature is controlled to be above 900℃.

[0084] Specifically, in the above S204, the purpose of reheating is to replenish the temperature. Since forging deformation will generate residual heat from processing, and the forging temperature is controlled by the upsetting deformation before reheating, the short-term holding time is controlled for 60-120 minutes (e.g., 70 minutes, 80 minutes, 90 minutes, 100 minutes, 110 minutes). The purpose of reducing the temperature during reheating is to refine the forging structure.

[0085] Specifically, in the above S205, in order to prevent forging cracks in the as-cast structure, the forging ratio is controlled to be 1.45 to 1.55.

[0086] Specifically, in S206 above, in order to prevent the broken structure from growing, and on the other hand, to create more nucleation points, promote the secondary formation of recrystallized structure under the heat, and control water cooling after rounding.

[0087] Specifically, in S206 above, considering that dense fine cracks are easily generated on the surface of the billet after water cooling, water cooling may also include full grinding to remove surface cracks.

[0088] Specifically, the steps in step 2 above include:

[0089] S21. Heat the billet to 680-780℃ and hold it at that temperature;

[0090] S22. Heat the billet to T β - (15~65℃), heat preservation;

[0091] S23. Perform one upsetting and one pulling operation;

[0092] S24, Remelted, in T β - (15~65℃) Heat preservation;

[0093] S25. Perform one upsetting and one pulling operation;

[0094] S26, rounded, air-cooled.

[0095] Specifically, in S21 above, the billet is heated to 680-780℃ (e.g., 690℃, 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃) and held at this temperature. This is because this temperature is the low-temperature range in the lower part of the two-phase region. Holding and preheating within this temperature range can reduce the tendency of grain growth, help refine the alloy structure, and promote the alloy to reach the target heating temperature more quickly in the subsequent heating process.

[0096] Specifically, in S22 above, the heating rate is controlled at 1.5 to 2.5℃ / min, and the slow heating ensures uniform heating of the billet.

[0097] Specifically, in S22, T β This represents the β phase transition temperature. Specifically, the holding temperature of S22 is 930–980℃, for example, 940℃, 950℃, 960℃, and 970℃.

[0098] Specifically, in S21 above, the diameter of the billet is d2 and the holding time is T7; in S22, the heating time is T8; in S22, the holding time is T9; T7+T8+T9=(0.6~0.8)d2, where the unit of d2 is mm, and the units of T7, T8 and T9 are all min.

[0099] Specifically, T7, T8 and T9 above satisfy the following relationship: T9≥(T7+T8+T9) / 2.

[0100] For example, the range of T7 is 180–240 min (e.g., 190 min, 200 min, 210 min, 220 min, 230 min), the range of T8 is 100–150 min (e.g., 110 min, 120 min, 130 min, 140 min), and the range of T9 is 360–480 min (e.g., 370 min, 380 min, 390 min, 400 min, 410 min, 420 min, 430 min, 440 min, 450 min, 460 min, 470 min).

[0101] Specifically, in S23 above, after the microstructure is improved by the first two heats, the increase in the forging ratio in this heat will not cause forging cracks in the forged microstructure. Therefore, taking all factors into consideration, the forging ratio is controlled to be 1.5 to 1.7.

[0102] Specifically, in S24 above, the purpose of returning the material to the furnace is to replenish the temperature. Since forging deformation will generate residual heat from processing, and the upsetting deformation before returning the material to the furnace controls the final forging temperature, the short-term holding time is controlled for 60 to 120 minutes (e.g., 70 minutes, 80 minutes, 90 minutes, 100 minutes, 110 minutes).

[0103] Specifically, in S25 above, in order to prevent forging cracks, the forging ratio is controlled to be 1.5 to 1.7.

[0104] Specifically, in S26 above, considering that excessively rapid cooling will cause cracks on the alloy surface, slow cooling is required. Therefore, air cooling is controlled after rounding.

[0105] Specifically, in S26 above, considering that forging residual cracks may appear on the surface of the billet after air cooling, spot grinding can also be included after air cooling to remove the residual cracks.

[0106] Specifically, step 3 above includes: heating the furnace to T. β + (5~25℃), after reaching the temperature, load the billet into the furnace, keep it at the temperature for 90~240 minutes, and then air cool.

[0107] Specifically, in step 3 above, the billet can be coated with high-temperature glass powder before loading into the furnace to reduce oxidation on the billet surface.

[0108] Specifically, step 3 above aims to promote tissue homogeneity. This step is performed at T... β + (5~25℃) heat preservation. At this time, the growth rate of small-sized grains will be much greater than that of large-sized grains. After a short period of heat preservation at this temperature, the difference in grain size will be greatly reduced, that is, the structure will be more uniform.

[0109] Specifically, the heat preservation temperature in step 3 above can be 1000–1020℃, for example, 1005℃, 1010℃, or 1015℃. The heat preservation time is 90–240 min, for example, 100 min, 110 min, 120 min, 130 min, 140 min, 150 min, 160 min, 170 min, 180 min, 190 min, 200 min, 210 min, 220 min, or 230 min.

[0110] Specifically, in step 3 above, considering that excessively rapid cooling will cause cracks on the alloy surface, slow cooling is required. Therefore, air cooling is performed after heat preservation.

[0111] Specifically, in step 4 above, the multi-stage forging process can be performed in 5 to 7 stages.

[0112] Specifically, in step 4 above, the steps for each forging and drawing process include:

[0113] S41. Heat the billet to 680-780℃ and hold it at that temperature;

[0114] S42. Heat the billet to T β - (15~65℃), heat preservation;

[0115] S43. Perform one upsetting and one pulling;

[0116] S44, Return to furnace, in T β - (15~65℃) Heat preservation;

[0117] S45. Perform one upsetting and one pulling operation;

[0118] S46, inverted octagon, air-cooled.

[0119] Specifically, in S41 above, the billet is heated to 680-780℃ (e.g., 690℃, 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃) and held at this temperature. This is because this temperature is the low-temperature range in the lower part of the two-phase region. Holding and preheating within this temperature range can reduce the tendency of grain growth, help refine the alloy structure, and promote the alloy to reach the target heating temperature more quickly in the subsequent heating process.

[0120] Specifically, in S42 above, the heating rate is controlled at 1.5 to 2.5℃ / min, and the slow heating ensures uniform heating of the billet.

[0121] Specifically, the insulation temperature of S42 is 930-980℃, for example 940℃, 950℃, 960℃, 970℃.

[0122] Specifically, in S41 above, the diameter of the billet is d3 and the holding time is T10; in S42, the heating time is T11; in S42, the holding time is T12; in order to avoid excessive holding time leading to grain coarsening, T10+T11+T12≤T7+T8+T9 is controlled.

[0123] Specifically, T10 + T11 + T12 = (0.5 ~ 0.8)d3, where the unit of d3 is mm, and the units of T10, T11 and T12 are all min.

[0124] For example, the range of T10 is 120–200 min (e.g., 130 min, 140 min, 150 min, 160 min, 170 min, 180 min, 190 min), the range of T11 is 100–150 min (e.g., 110 min, 120 min, 130 min, 140 min), and the range of T12 is 180–360 min (e.g., 190 min, 200 min, 210 min, 220 min, 230 min, 240 min, 250 min, 260 min, 270 min, 280 min, 290 min, 300 min, 310 min, 320 min, 330 min, 340 min, 350 min).

[0125] Specifically, in S43 above, after homogenizing the structure through β heat treatment, a slight increase in the forging ratio in this heat treatment will not cause forging cracks in the forged structure. Therefore, taking all factors into consideration, the forging ratio is controlled to be 1.7 to 2.2.

[0126] Specifically, in S44 above, the short-term heat preservation is controlled for 60 to 120 minutes (e.g., 70 minutes, 80 minutes, 90 minutes, 100 minutes, 110 minutes).

[0127] Specifically, in the above S45, in order to prevent forging cracks, the forging ratio is controlled to be 1.7 to 2.2.

[0128] Specifically, in S46 above, in order to prevent the edges of the billet from cooling down too quickly when it comes out of the furnace, the billet is turned into an octagon after the first forging.

[0129] Specifically, in S46 above, considering that excessively rapid cooling will cause cracks on the alloy surface, slow cooling is required. Therefore, air cooling is controlled after the inverted octagon.

[0130] Specifically, in S46 above, considering that a small number of fine cracks may be generated on the surface of the billet after air cooling, spot grinding can also be included after air cooling to remove the fine cracks.

[0131] Specifically, in step 4 above, the steps for each forging and drawing process are the same.

[0132] Specifically, in step 5 above, each step of the flat forging process includes:

[0133] S51. Heat the billet to 680-780℃ and hold it at that temperature;

[0134] S52. Heat the billet to T β - (15~65℃), heat preservation;

[0135] S53. The horizontal anvil is spread and flattened until the billet height is H. The relationship between H and the billet diameter d4 is as follows: H≥d4 / 2;

[0136] S54. Rotate the billet 90° around the axis and flatten it with the cross anvil until the billet height is H.

[0137] S55, reshaping, elongating the four sides, inverting the eight sides;

[0138] S56, return to the original furnace and keep warm for 60-120 minutes, then repeat S53-S55.

[0139] Specifically, in S52 above, the heating rate is controlled at 1.5 to 2.5℃ / min, and the slow heating ensures uniform heating of the billet.

[0140] Specifically, the insulation temperature of S52 is 930-980℃, for example 940℃, 950℃, 960℃, 970℃.

[0141] Specifically, in S51 above, the diameter of the billet is d4 and the holding time is T13; in S52, the heating time is T14; in S52, the holding time is T15; in order to avoid excessive holding time leading to grain coarsening, T13+T14+T15≤T7+T8+T9 is controlled.

[0142] Specifically, T13+T14+T15=(0.5~0.8)d4, where the unit of d4 is mm, and the units of T13, T14 and T15 are all min.

[0143] For example, the range of T13 is 120–200 min (e.g., 130 min, 140 min, 150 min, 160 min, 170 min, 180 min, 190 min), the range of T14 is 100–150 min (e.g., 110 min, 120 min, 130 min, 140 min), and the range of T15 is 180–360 min (e.g., 190 min, 200 min, 210 min, 220 min, 230 min, 240 min, 250 min, 260 min, 270 min, 280 min, 290 min, 300 min, 310 min, 320 min, 330 min, 340 min, 350 min).

[0144] Specifically, in S53 and S54 above, when the billet is widened and flattened by the anvil, the billet is flattened parallel to the anvil along the axial direction. Based on the law of least resistance, this method has a large lateral deformation, which can effectively improve the lateral structure. After the billet is rotated 90° around the axial direction, it is flattened laterally, which can improve the lateral structure of the difficult-to-deform areas at both ends of the billet.

[0145] Specifically, step 6 above, the round forging process includes the following steps:

[0146] S61. Heat the billet to 680-780℃ and hold it at that temperature;

[0147] S62. Heat the billet to T β - (15~65℃), heat preservation;

[0148] S63, bevel to square, bevel to octagon, and roll to round, to obtain large-size TC4 bar stock.

[0149] Specifically, in S61 above, the heat preservation time is 120-200 min (e.g., 130 min, 140 min, 150 min, 160 min, 170 min, 180 min, 190 min).

[0150] Specifically, in S62 above, the heating rate is controlled at 1.5 to 2.5℃ / min, and the slow heating ensures uniform heating of the billet.

[0151] Specifically, in S62 above, the heat preservation time is 180 to 360 minutes (e.g., 190 minutes, 200 minutes, 210 minutes, 220 minutes, 230 minutes, 240 minutes, 250 minutes, 260 minutes, 270 minutes, 280 minutes, 290 minutes, 300 minutes, 310 minutes, 320 minutes, 330 minutes, 340 minutes, 350 minutes).

[0152] Specifically, in order to homogenize the forged microstructure, step 6 above also includes:

[0153] Step 7: Heat to 700-750℃, fill the furnace at the set temperature, and hold for 180-240 minutes.

[0154] Specifically, the preparation method of this invention is applicable to large-size TC4 bars, and the resulting large-size TC4 bars have the following specifications:

[0155] Specifically, in step 1 above, the diameter of the ingot can reach 850mm or more.

[0156] Specifically, the height-to-diameter ratio of the billet obtained after two forging processes in step 1 and the billet processed in step 2 is 1.7 to 1.9. At this time, the billet diameter is relatively large, and the metal forging deformation zone is more widely distributed under the condition of large height-to-diameter ratio.

[0157] Specifically, the height-to-diameter ratio of the billet after step 4 is 1.5 to 1.75. At this point, the billet diameter is relatively small, and using a large height-to-diameter ratio makes the billet easier to fold. Therefore, a small height-to-diameter ratio is used.

[0158] The present invention also provides a large-size TC4 bar with high flaw detection level, which is prepared by the above-described preparation method.

[0159] The high-flaw-detection-level large-size TC4 bar of this invention has a uniform microstructure. According to the GJB1538A-2021 standard, the grain size can reach level 3 or above, and the difference in grain size level between different parts is less than level 1. Moreover, the flaw detection level is high, reaching level A1.

[0160] The advantages of precise control of process parameters of the present invention will be demonstrated below with specific embodiments and comparative examples.

[0161] Example 1

[0162] This embodiment provides a high-level flaw detection grade, large-size TC4 bar and its preparation method.

[0163] The preparation method of this embodiment includes:

[0164] Ingot preparation: Raw materials are mixed and distributed according to the following mass fractions to obtain Al: 6%, V: 3.5%, Fe: 0.1%, O≤0.05%, N≤0.05%, C≤0.08%, H≤0.001%, with the balance being Ti and unavoidable impurities. TC4 ingots; three VAR melting processes were performed to obtain TC4 ingots with uniform composition and no segregation.

[0165] Two-stage forging:

[0166] First heat: Preheat to 780℃, hold for 180 minutes, then increase to 1150℃ and hold for 360 minutes → gently tap the surface, control the forging ratio to 1.4 and perform one upsetting and one drawing → return to the furnace, hold at 1130℃ for 90 minutes → control the forging ratio to 1.4 and perform one upsetting and one drawing → roll into a round shape. Water cooling → full grinding.

[0167] Second heating: Preheat to 780℃, hold for 180 minutes, then increase to 1080℃ and hold for 360 minutes → control the forging ratio at 1.5 for one upsetting and one drawing → return to the original furnace for 90 minutes, cool down by 30℃ → control the forging ratio at 1.5 for one upsetting and one drawing → roll into a round shape. Water cooling → full grinding.

[0168] Third heat: Preheat to 780℃, hold for 180 minutes, increase to 950℃ after 100 minutes, hold for 360 minutes → control the forging ratio at 1.65 for one upsetting and one drawing → return to the original furnace for 90 minutes → control the forging ratio at 1.65 for one upsetting → draw and round to... Air cooling → spot grinding → center sawing.

[0169] β-Heat treatment: Coat with high-temperature glass powder, directly heat to 1010℃, load into the furnace at the set temperature, hold for 120 minutes, and air cool.

[0170] Fourth to tenth heats: Preheat to 780℃, hold for 120 minutes, increase to 950℃ in 100 minutes, hold for 180 minutes → control the forging ratio to 1.8 and perform one upsetting and one drawing → return to the original furnace for 90 minutes → control the forging ratio to 1.8 and perform one upsetting and one drawing → turn the octagon to 770×Lmm → spot grinding.

[0171] Eleventh to twelfth furnace: Preheat to 780℃, hold for 120 minutes, increase to 950℃ in 100 minutes, hold for 180 minutes → Directly widen and flatten the billet with the horizontal anvil until the billet height is 450mm → Rotate the horizontal anvil 90° around the axis to widen and flatten the billet height until the billet height is 450mm → Shaping → Lengthen the billet to 770×Lmm in a square shape → Turn the billet to 770×Lmm in an octagonal shape → Return to the original furnace for 60 minutes → Continue to widen and flatten the billet with the horizontal anvil until the billet height is 450mm → Rotate the horizontal anvil 90° around the axis to widen and flatten the billet to 450mm → Shaping → Lengthen the billet to 770×Lmm in a square shape → Turn the billet to 770×Lmm in an octagonal shape → Spot grinding.

[0172] Thirteenth step: Preheat to 780℃, hold for 120 minutes, increase to 950℃ after 100 minutes, hold for 180 minutes → shape into a square → shape into an octagon → roll into a round shape

[0173] Heat treatment: directly heat to 700-750℃, load into the furnace at the temperature, and hold for 200 minutes.

[0174] The high-level flaw detection of the large-diameter TC4 bar in this embodiment was tested: the flaw detection result was A1 grade.

[0175] Sampling and testing were conducted at ends A and B of the large-diameter TC4 bar with high flaw detection level in this embodiment. Referring to the upper limit specifications of GJB2218A-2018 standard, the mechanical property test results of this embodiment are shown in Table 1 below. The radial and tangential tensile strengths of the samples are ≥900MPa (e.g., 904~918MPa), the yield strength is ≥825MPa (e.g., 827~845MPa), the elongation after fracture is ≥11% (e.g., 11%~13%), and the reduction of area is ≥26% (e.g., 26%~32%). The mechanical properties are excellent and uniform; the maximum difference in tensile strength between different locations is 14MPa, and the maximum difference in yield strength between different locations is 18MPa.

[0176] The low-magnification microstructure at both ends of the large-diameter TC4 bar with high flaw detection level in this embodiment was inspected, such as... Figure 1 The image shows the low-magnification tissue at end A. Figure 2 The image shows the low-magnification microstructure at end B. It can be seen that the TC4 bar in this embodiment is free from cracks, folds, pores, segregation, metallic or non-metallic inclusions, and other visually visible metallurgical defects.

[0177] The high-magnification microstructure at both ends of the large-diameter TC4 bar with high flaw detection level in this embodiment was inspected, such as... Figure 2 As shown, the bar structure is a processed structure in the α+β two-phase region, without complete original β grain boundaries, and equiaxed α structure is distributed on the transformed β matrix.

[0178] Table 1 Performance test results of Example 1

[0179]

[0180] The inventors conducted extensive research during the research process, and some poorly performing solutions are now presented as comparative examples.

[0181] Comparative Example 1

[0182] This comparative example provides a large-size TC4 bar and its preparation method. The material of the TC4 bar in this comparative example is the same as that in Example 1, and will not be described again here.

[0183] The preparation method of this comparative example is generally the same as that of Example 1, except that:

[0184] No β heat treatment was performed.

[0185] The flaw detection result of the large-size TC4 bar in this comparative example is Grade A, and the microstructure uniformity is worse than that of Example 1.

[0186] Comparative Example 2

[0187] This comparative example provides a large-size TC4 bar and its preparation method. The material of the TC4 bar in this comparative example is the same as that in Example 1, and will not be described again here.

[0188] The preparation method of this comparative example is generally the same as that of Example 1, except that:

[0189] The flat forging process was not carried out in the eleventh to twelfth heats.

[0190] The flaw detection result of the large-size TC4 bar in this comparative example is grade B, indicating poor microstructure uniformity.

[0191] Comparative Example 3

[0192] This comparative example provides a large-size TC4 bar and its preparation method. The material of the TC4 bar in this comparative example is the same as that in Example 1, and will not be described again here.

[0193] The preparation method of this comparative example is generally the same as that of Example 1, except that:

[0194] No forging ratio gradient control was implemented; a constant forging ratio of 1.5 was used for upsetting and drawing forging.

[0195] The flaw detection result of the large-size TC4 bar in this comparative example is grade B, indicating poor microstructure uniformity.

[0196] Comparative Example 4

[0197] This comparative example provides a large-size TC4 bar and its preparation method. The material of the TC4 bar in this comparative example is the same as that in Example 1, and will not be described again here.

[0198] The preparation method of this comparative example is generally the same as that of Example 1, except that:

[0199] The fourth to tenth firings only involved the fourth to sixth firings.

[0200] The flaw detection results of the large-size TC4 bar in this comparative example show that the middle part of the bar meets the grade B standard, while the edge part does not meet the grade B standard, indicating poor microstructure uniformity.

[0201] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing large-size TC4 bars with high flaw detection level, characterized in that, The preparation method includes: Step 1: The ingot is forged in two stages to obtain the billet; Step 2: Perform a single-fire upsetting and drawing forging on the billet; Step 3: Perform β heat treatment on the billet to obtain an intermediate billet; Step 4: Perform multi-stage upsetting and drawing forging on the intermediate billet; Step 5: Flat square forging; Step 6: Forging with a high flaw detection level to obtain large-size TC4 bars; In step 1, the forging ratio of the first forging is controlled to be less than that of the second forging. In step 1, the first forging process includes: S101. Heat the ingot to 680~780℃ and hold it at that temperature; S102. Heat the ingot to 1080~1180℃ and hold it at that temperature; S103, Perform one upsetting and one pulling; S104, return to the furnace, lower the temperature, and keep warm at 1050~1150℃; S105, Perform one upsetting and one pulling; S106, rounded, water-cooled; In S103, the forging ratio is controlled at 1.3~1.45, and the final forging temperature is controlled at above 1050℃; In S105, the forging ratio is controlled at 1.3~1.45; In step 1, the second forging process includes: S201. Heat the billet to 680~780℃ and hold it at that temperature; S202. Heat the billet to 1020~1120℃ and hold it at that temperature; S203, Perform one upsetting and one pulling; S204, return to the furnace, lower the temperature, and keep warm at 970~1070℃; S205, Perform one upsetting and one pulling; S206, rounded, water-cooled; In S203, the forging ratio is controlled at 1.45~1.55; in S205, the forging ratio is controlled at 1.45~1.

55. In step 5, each step of the flat forging process includes: S51. Heat the billet to 680~780℃ and hold it at that temperature; S52. Heat the billet to T β - (15~65℃), heat preservation; S53. The horizontal anvil is spread and flattened until the billet height is H. The relationship between H and the billet diameter d4 is as follows: H≥d4 / 2; S54. Rotate the billet 90° around the axis and flatten it with the cross anvil until the billet height is H. S55, reshaping, elongating the four sides, inverting the eight sides; S56, return to the original furnace and keep warm for 60~120 minutes, repeat S53-S55; The size range of the large-diameter TC4 bars obtained is as follows: 550~800mm.

2. The preparation method according to claim 1, characterized in that, The forging ratio in step 2 is greater than the forging ratio in the second forging.

3. The preparation method according to claim 1, characterized in that, The specific steps of step 2 include: heating the billet to 680~780℃ and holding it at that temperature; heating the billet to T... β - (15~65℃), keep warm; perform one upsetting and one drawing; return to the furnace, in T β - (15~65℃) Insulate; perform one upsetting and one pulling; roll into a ball and air cool.

4. The preparation method according to claim 1, characterized in that, Step 3 includes: heating the furnace to T. β + (5~25℃), after reaching the temperature, load the billet into the furnace, keep it at the temperature for 90~240 minutes, and then air cool.

5. The preparation method according to claim 1, characterized in that, In step 4, the steps of each forging and drawing process include: heating the billet to 680~780℃ and holding it at that temperature; heating the billet to T... β - (15~65℃), keep warm; perform one upsetting and one drawing; return to the furnace, in T β - (15~65℃) Insulation; one upsetting and one pulling; turn to eight sides, air cooling.

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