High-flaw-detection-level large-specification TC4 bar and preparation method thereof

Abstract

The invention discloses a high-flaw-detection-level large-specification TC4 bar and a preparation method thereof, belongs to the technical field of titanium alloys, and solves the problems that in the prior art, when a large-specification TC4 bar is prepared through an existing titanium alloy bar preparation method, overheating is likely to happen, and the structure is not uniform. The preparation method comprises the following steps: carrying out two-heating cogging forging on a cast ingot to obtain a blank; the blank is subjected to one-heating-number upsetting and drawing forging; performing beta heat treatment on the blank to obtain an intermediate blank; the intermediate blank is subjected to multi-heating-number upsetting and drawing forging; forging a flat square; and rolling and forging to obtain the high-flaw-detection-grade large-specification TC4 bar. The high-flaw-detection-level large-specification TC4 bar prepared through the method is good in uniformity and high in flaw detection level.

Description

Technical Field

[0001] The invention relates to the technical field of titanium alloys, and in particular to a large-size TC4 bar with a high flaw detection level and a preparation method thereof. Background Art

[0002] Titanium alloy has the advantages of high specific strength, light weight, corrosion resistance, excellent high temperature performance, good machinability, etc., and is an important material for lightweight applications. With the rapid development of titanium alloy parts towards lightweight, structural, reduced welds, overall forming, and increasing usage, there is gradually a demand for large-scale development of titanium alloy ingots and forgings.

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

[0004] In view of the above situation, the present invention aims to provide a large-size TC4 bar with high flaw detection level and a preparation method thereof, which is used to solve at least one of the following problems: the existing titanium alloy bar preparation method is prone to overheating and uneven structure when preparing large-size TC4 bars.

[0005] The purpose of the present invention is mainly achieved through the following technical solutions:

[0006] The present invention provides a method for preparing a large-size TC4 bar with a high flaw detection level, the preparation method comprising:

[0007] Step 1, subjecting the ingot to two-time forging to obtain a billet;

[0008] Step 2, subjecting the blank to a first-stage drawing forging;

[0009] Step 3, subjecting the blank to β heat treatment to obtain an intermediate blank;

[0010] Step 4, subjecting the intermediate billet to multi-fire drawing forging;

[0011] Step 5: Flat square forging;

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

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

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

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

[0016] The ingot is heated to 680-780°C and kept warm; the ingot is heated to 1080-1180°C and kept warm; upsetting and drawing are performed; the ingot is returned to the furnace, the temperature is lowered, and kept warm at 1050-1150°C; upsetting and drawing are performed; the ingot is rounded and water-cooled.

[0017] Furthermore, in step 1, the second fire forging step includes: heating the billet to 680-780°C and keeping it warm; heating the billet to 1020-1120°C and keeping it warm; performing upsetting and drawing; returning to the furnace, lowering the temperature, and keeping it warm at 970-1070°C; performing upsetting and drawing; rounding, and water cooling.

[0018] Furthermore, the specific steps of step 2 include: heating the blank to 680-780°C and keeping the temperature; heating the blank to T β -(15~65℃), keep warm; perform upsetting and pulling; return to the furnace, and β -(15~65℃) keep warm; perform upsetting and pulling; rounding and air cooling.

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

[0020] Furthermore, in step 4, each step of forging includes: heating the blank to 680-780°C and keeping the temperature; heating the blank to T β -(15~65℃), keep warm; perform upsetting and pulling; return to the furnace, and β -(15~65℃) keep warm; perform upsetting and pulling; pour in eight directions and air cool.

[0021] Further, in step 5, each step of flat square forging includes:

[0022] S51, heating the blank to 680-780° C. and keeping the temperature;

[0023] S52, heating the blank to T β -(15~65℃), keep warm;

[0024] S53, the horizontal anvil is widened and flattened until the height of the blank is H, and H and the diameter d4 of the blank meet the following relationship: H≥d4 / 2;

[0025] S54, rotating the blank 90° around the axis, and widening and flattening the blank with the horizontal anvil until the blank height is H;

[0026] S55, shaping, stretching in all directions, turning in all directions;

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

[0028] The present invention also provides a large-size TC4 bar with a high flaw detection level, which is prepared by the above-mentioned 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 can prepare large-size bars with high uniformity and high flaw detection level by combining two-fire blanking forging, one-fire drawing forging, β heat treatment, multi-fire drawing forging, and flat square drawing forging.

[0031] b) In the preparation method of the present invention, by controlling the precise preheating temperature, the tendency of grain growth can be reduced, which is helpful for the refinement of the alloy structure and can promote the alloy to reach the target heating temperature faster in the subsequent heating process.

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

[0033] d) The high-flaw detection level and large-size TC4 bar of the present invention has uniform structure and excellent mechanical properties. For example, the tensile strength of radial and chordal specimens of the high-flaw detection level and large-size TC4 bar of the present invention is ≥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 cross-sectional shrinkage is ≥26% (e.g., 26%-32%); and the uniformity is good, the maximum difference in tensile strength at different locations is 14MPa, and the maximum difference in yield strength at different locations is 18MPa.

[0034] e) The macrostructure of the high-level flaw detection large-size TC4 bar of the present invention has no cracks, folds, pores, segregation, metal or non-metal inclusions and other metallurgical defects visible to the naked eye. The flaw detection level is high and can reach A1 level.

[0035] Other features and advantages of the present invention will be described in the following description, and part of them will become obvious from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the contents particularly pointed out in the written description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0037] Figure 1 This is the low-magnification structure of the A end of Example 1;

[0038] Figure 2 This is a low-magnification structure of the B end of Example 1. DETAILED DESCRIPTION

[0039] Preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used to explain the principles of the present invention together with the embodiments of the present invention.

[0040] Large-sized TC4 (Ti-6Al-4V) titanium alloy bars are prone to deformation dead zones during forging, which will cause uneven deformation and uneven organization and performance. In addition, due to the low thermal conductivity of titanium alloy, the core of the forging is prone to overheating during the upsetting process, resulting in local uneven organization; the above problems are particularly obvious during the forging process of bars with a diameter of ≥400mm, and the problems will become more and more obvious as the specifications of titanium alloy bars continue to increase. Therefore, it is urgent to find a forging method for large-sized bars, so that the forged bar organization is fully broken while avoiding the uneven organization caused by local uneven deformation and overheating.

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

[0042] Step 1, subjecting the ingot to two-time forging to obtain a billet;

[0043] Step 2, subjecting the blank to a first-stage drawing forging;

[0044] Step 3, subjecting the blank to β heat treatment to obtain an intermediate blank;

[0045] Step 4, subjecting the intermediate billet to multi-fire drawing forging;

[0046] Step 5, two-fire flat square forging;

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

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

[0049] Specifically, in the above step 1, the ingot can be obtained after three VAR smeltings, and the composition of the ingot is uniform and has no segregation.

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

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

[0052] Specifically, in the above step 1, the step of first-time blank forging includes:

[0053] S101, heating the ingot to 680-780° C. and keeping the temperature;

[0054] S102, heating the ingot to 1080-1180° C. and keeping the temperature;

[0055] S103, performing upsetting and pulling;

[0056] S104, return to the furnace, lower the temperature, and keep it at 1050-1150°C;

[0057] S105, performing upsetting and pulling;

[0058] S106, rounding, water cooling.

[0059] Specifically, in the above S101, the ingot is heated to 680-780°C (for example, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C) and kept warm. This is because this temperature is the low temperature range in the lower part of the two-phase region. 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 faster in the subsequent heating process.

[0060] Specifically, in the above S102, the heating rate is controlled to be 1.5-2.5°C / min, and the heating is slow, which can ensure uniform heating of the ingot.

[0061] Specifically, in the above S101, 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, the above T1, T2 and T3 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 the above S103, in order to prevent forging cracking of the as-cast structure, the forging ratio is controlled to be 1.3-1.45.

[0065] Specifically, in the above S103, considering that too low final forging temperature may easily lead to cracking of the alloy during forging, the final forging temperature is controlled to be above 1050°C.

[0066] Specifically, in the above S104, the purpose of returning to the furnace is to replenish the temperature. Since forging deformation will generate processing waste heat, and the upsetting deformation before returning to the furnace controls the final forging temperature, the short-term heat preservation is controlled for 60 to 120 minutes (for example, 70 minutes, 80 minutes, 90 minutes, 100 minutes, and 110 minutes); the temperature is lowered during the temperature replenishment in order to refine the forging structure.

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

[0068] Specifically, in the above S106, in order to prevent the broken structure from growing, on the other hand, more nucleation points are created to promote the formation of recrystallized structure in the next fire, and water cooling after rounding is controlled.

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

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

[0071] S201, heating the blank to 680-780°C and keeping the temperature;

[0072] S202, heating the blank to 1020-1120° C. and keeping the temperature;

[0073] S203, performing upsetting and pulling;

[0074] S204, return to the furnace, lower the temperature, and keep it at 970-1070°C;

[0075] S205, performing upsetting and pulling;

[0076] S206, rounding, water cooling.

[0077] Specifically, in the above S201, the billet is heated to 680-780°C (for example, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C) and kept warm. This is because this temperature is the low temperature range in the lower part of the two-phase zone. 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 faster in the subsequent heating process.

[0078] Specifically, in the above S202, the heating rate is controlled to be 1.5-2.5°C / min, and the heating is slowly increased to ensure uniform heating of the blank.

[0079] Specifically, in the above S201, the diameter of the blank 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, the above T4, T5 and T6 satisfy the following relationship: T6≥(T4+T5+T6) / 2.

[0081] For example, the range of T4 is 180-240 min (for example, 190 min, 200 min, 210 min, 220 min, 230 min), the range of T5 is 130-210 min (for example, 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 (for example, 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 toughness of the alloy gradually increases during the drawing process of each fire, a gradual increase in the forging ratio will not cause forging cracking of the forged structure. Therefore, based on comprehensive considerations, the forging ratio is controlled to be 1.45-1.55.

[0083] Specifically, in the above S203, considering that too low final forging temperature may easily lead to alloy forging cracking, the final forging temperature is controlled to be above 900°C.

[0084] Specifically, in the above S204, the purpose of returning to the furnace is to replenish the temperature. Since forging deformation will generate processing waste heat, and the upsetting deformation before returning to the furnace controls the final forging temperature, therefore, the short-term heat preservation is controlled for 60 to 120 minutes (for example, 70 minutes, 80 minutes, 90 minutes, 100 minutes, 110 minutes); the temperature is lowered during the temperature replenishment in order to refine the forging structure.

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

[0086] Specifically, in the above S206, in order to prevent the broken structure from growing, on the other hand, more nucleation points are created to promote the formation of recrystallized structure in the next fire, and water cooling after rounding is controlled.

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

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

[0089] S21, heating the blank to 680-780°C and keeping the temperature;

[0090] S22, heat the blank to T β -(15~65℃), keep warm;

[0091] S23, performing upsetting and pulling;

[0092] S24, re-melting, in T β -(15~65℃) insulation;

[0093] S25, performing upsetting and pulling;

[0094] S26, rounding, air cooling.

[0095] Specifically, in the above S21, the billet is heated to 680-780°C (for example, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C) and kept warm. This is because this temperature is the low temperature range in the lower part of the two-phase zone. 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 faster in the subsequent heating process.

[0096] Specifically, in the above S22, the heating rate is controlled to be 1.5-2.5°C / min, and the heating is slowly increased to ensure uniform heating of the blank.

[0097] Specifically, in S22, T β represents the β phase transition point temperature. Specifically, the insulation temperature of S22 is 930-980°C, for example, 940°C, 950°C, 960°C, and 970°C.

[0098] Specifically, in the above S21, the diameter of the blank 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, the above T7, T8 and T9 satisfy the following relationship: T9≥(T7+T8+T9) / 2.

[0100] For example, the range of T7 is 180-240 min (for example, 190 min, 200 min, 210 min, 220 min, 230 min), the range of T8 is 100-150 min (for example, 110 min, 120 min, 130 min, 140 min), and the range of T9 is 360-480 min (for example, 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 the above S23, after the first two fires improve the structure, increasing the forging ratio of this fire will not cause forging cracking of the as-forged structure. Therefore, after comprehensive consideration, the forging ratio is controlled to be 1.5-1.7.

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

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

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

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

[0106] Specifically, the specific steps of the above step 3 include: heating the furnace to T β +(5~25℃), after reaching the temperature, load the billet into the furnace, keep warm for 90~240min, and air cool.

[0107] Specifically, in the above step 3, the blank may be coated with high temperature glass powder before loading into the furnace to reduce oxidation of the blank surface.

[0108] Specifically, the function of step 3 is to promote uniform tissue. β +(5~25℃) insulation, at this time, the growth rate of small-sized grains will be much faster than that of large-sized grains. After short-term insulation at this temperature, the grain size difference will be greatly reduced, that is, the structure will be more uniform.

[0109] Specifically, the insulation temperature of step 3 can be 1000-1020° C., for example, 1005° C., 1010° C., 1015° C. The insulation 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, 230 min.

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

[0111] Specifically, in the above step 4, the multi-fire drawing forging can be 5 to 7 times.

[0112] Specifically, in the above step 4, the step of forging each time includes:

[0113] S41, heating the blank to 680-780° C. and keeping the temperature;

[0114] S42, heating the blank to T β -(15~65℃), keep warm;

[0115] S43, performing upsetting and pulling;

[0116] S44, retraining, in T β -(15~65℃) insulation;

[0117] S45, performing upsetting and pulling;

[0118] S46, pour in all directions, air cooling.

[0119] Specifically, in the above S41, the billet is heated to 680-780°C (for example, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C) and kept warm. This is because this temperature is the low temperature range in the lower part of the two-phase zone. 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 faster in the subsequent heating process.

[0120] Specifically, in the above S42, the heating rate is controlled to be 1.5-2.5°C / min, and the heating is slowly increased to ensure uniform heating of the blank.

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

[0122] Specifically, in the above S41, 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 grain coarsening due to excessive holding time, control T10+T11+T12≤T7+T8+T9.

[0123] Specifically, T10+T11+T12=(0.5-0.8)d3, wherein 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 to 200 min (for example, 130 min, 140 min, 150 min, 160 min, 170 min, 180 min, 190 min), the range of T11 is 100 to 150 min (for example, 110 min, 120 min, 130 min, 140 min), and the range of T12 is 180 to 360 min (for example, 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 the above S43, after the microstructure is homogenized by β heat treatment, a slight increase in the forging ratio of this fire will not cause forging cracking of the as-forged microstructure. Therefore, after comprehensive consideration, the forging ratio is controlled to be 1.7 to 2.2.

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

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

[0128] Specifically, in the above S46, in order to prevent the edges and corners of the billet from cooling too quickly when it is taken out of the furnace, the billet is turned into eight squares after the first forging is completed.

[0129] Specifically, in the above S46, considering that too fast cooling rate will cause cracks on the alloy surface, slow cooling is required. Therefore, air cooling after the inversion is controlled.

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

[0131] Specifically, in the above step 4, the steps of forging each time are the same.

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

[0133] S51, heating the blank to 680-780° C. and keeping the temperature;

[0134] S52, heating the blank to T β -(15~65℃), keep warm;

[0135] S53, the horizontal anvil is widened and flattened until the height of the blank is H, and H and the diameter d4 of the blank meet the following relationship: H≥d4 / 2;

[0136] S54, rotating the blank 90° around the axis, and widening and flattening the blank with the horizontal anvil until the blank height is H;

[0137] S55, shaping, stretching in all directions, turning in all directions;

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

[0139] Specifically, in the above S52, the heating rate is controlled to be 1.5-2.5°C / min, and the heating is slowly increased to ensure uniform heating of the blank.

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

[0141] Specifically, in the above S51, 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 grain coarsening due to excessive holding time, control T13+T14+T15≤T7+T8+T9.

[0142] Specifically, T13+T14+T15=(0.5-0.8)d4, wherein 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 to 200 min (for example, 130 min, 140 min, 150 min, 160 min, 170 min, 180 min, 190 min), the range of T14 is 100 to 150 min (for example, 110 min, 120 min, 130 min, 140 min), and the range of T15 is 180 to 360 min (for example, 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 the above S53 and S54, when the anvil is widened and flattened, the billet is flattened axially and parallel to the anvil. Relying on the law of least resistance, this method has a large lateral deformation and can effectively improve the lateral structure. After the billet is rotated 90° around the axis and then flattened laterally, the lateral structure of the difficult-to-deform areas at both ends of the billet can be improved.

[0145] Specifically, in the above step 6, the rounding forging includes the following steps:

[0146] S61, heating the blank to 680-780° C. and keeping the temperature;

[0147] S62, heat the blank to T β -(15~65℃), keep warm;

[0148] S63, square inversion, octagonal inversion, and rounding to obtain large-size TC4 bars.

[0149] Specifically, in the above S61, the temperature is kept warm for 120 to 200 minutes (for example, 130 minutes, 140 minutes, 150 minutes, 160 minutes, 170 minutes, 180 minutes, or 190 minutes).

[0150] Specifically, in the above S62, the heating rate is controlled to be 1.5-2.5°C / min, and the heating is slowly increased to ensure uniform heating of the blank.

[0151] Specifically, in the above S62, the temperature is kept warm for 180 to 360 minutes (for example, 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, and 350 minutes).

[0152] Specifically, in order to make the forged structure uniform, the above step 6 further includes:

[0153] Step 7: Raise the temperature to 700-750°C, place in a warm furnace, and keep warm for 180-240 minutes.

[0154] Specifically, the preparation method of the present invention can be applied to large-sized TC4 bars, and the specification range of the obtained large-sized TC4 bars is

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

[0156] Specifically, the billet obtained after two-fire forging in step 1 and the billet processed in step 2 have a height-to-diameter ratio of 1.7 to 1.9. The billet has a larger diameter at this time, and the metal forging deformation zone is more widely distributed under the condition of a large height-to-diameter ratio.

[0157] Specifically, the aspect ratio of the blank after the processing in step 4 is 1.5 to 1.75. At this time, the diameter of the blank is relatively small, and a blank with a large aspect ratio is easy to fold. Therefore, a small aspect ratio is used.

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

[0159] The high-detection-level large-size TC4 rod of the present invention has uniform structure. According to the GJB1538A-2021 standard rating, the grain size can reach above level 3, the level difference of the grain size in different parts is below level 1, and the flaw detection level is high, which can reach level A1.

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

[0161] Example 1

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

[0163] The preparation method of this embodiment includes:

[0164] Ingot preparation: Mix the raw materials according to the mass fraction to obtain Al: 6%, V: 3.5%, Fe: 0.1%, O≤0.05%, N≤0.05%, C≤0.08%, H≤0.001%, and the balance is Ti and unavoidable impurities. TC4 ingot; three VAR smeltings are performed to obtain a TC4 ingot with uniform composition and no segregation.

[0165] Two-fire forging:

[0166] First fire: preheat at 780℃, keep warm for 180min, heat up to 1150℃ in 180min, keep warm for 360min → tap the surface, control the forging ratio to 1.4 and perform one upsetting and one pulling → return to the furnace, keep warm at 1130℃ for 90min, → control the forging ratio to 1.4 and perform one upsetting and one pulling → rounding to Water cooling → full grinding.

[0167] Second fire: preheat at 780℃, keep warm for 180min, heat up to 1080℃ in 180min, keep warm for 360min→control forging ratio 1.5 to perform upsetting and pulling→return to original furnace for 90min, cool down by 30℃→control forging ratio 1.5 to perform upsetting and pulling→roll to Water cooling → full grinding.

[0168] Third fire: preheat at 780℃, keep warm for 180min, heat up to 950℃ for 100min, keep warm for 360min→control forging ratio 1.65 for upsetting and pulling→return to original furnace and keep warm for 90min→control forging ratio 1.65 for upsetting→pulling and rolling to Air cooling → spot grinding → center sawing.

[0169] β heat treatment: Apply high temperature glass powder, directly heat to 1010℃, put into warm furnace, keep warm for 120min, and air cool.

[0170] The fourth to tenth fire: preheat at 780℃, keep warm for 120min, heat up to 950℃ in 100min, keep warm for 180min→control the forging ratio at 1.8 and perform one upsetting and one pulling→return to the original furnace for 90min→control the forging ratio at 1.8 and perform one upsetting and one pulling→turn in eight directions to 770×Lmm→spot grinding.

[0171] From the eleventh fire to the twelfth fire: preheat at 780℃, keep warm for 120min, heat up to 950℃ for 100min, keep warm for 180min→widen and flatten directly on horizontal anvil until the billet height is 450mm→rotate 90°on the horizontal anvil around the axis to widen and flatten until the billet height is 450mm→shape→draw it in four directions to 770×Lmm→turn it in eight directions to 770×Lmm→return to the original furnace and keep warm for 60min→continue to widen and flatten it on horizontal anvil until the billet height is 450mm→rotate 90°on the horizontal anvil around the axis to widen and flatten until the billet height is 450mm→shape→draw it in four directions to 770×Lmm→turn it in eight directions to 770×Lmm→spot grinding.

[0172] Thirteenth fire: preheat at 780℃, keep warm for 120min, heat to 950℃ in 100min, keep warm for 180min→turn into four sides→turn into eight sides→roll into a round shape

[0173] Heat treatment: directly raise the temperature to 700-750℃, put it into warm furnace, and keep it warm for 200min.

[0174] The large-size TC4 bar with high flaw detection level in this embodiment was flaw detected: the flaw detection result was A1 level.

[0175] The A end and B end of the high-level flaw detection large-size TC4 bar of this embodiment were sampled and tested respectively. Referring to the upper limit specification of GJB2218A-2018 standard, the mechanical properties test results of this embodiment are shown in Table 1 below. The tensile strength of radial and chordal specimens is ≥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 cross-sectional shrinkage is ≥26% (e.g. 26%-32%). The mechanical properties are excellent and the uniformity is good. The maximum difference in tensile strength at different locations is 14MPa, and the maximum difference in yield strength at different locations is 18MPa.

[0176] The macrostructures at both ends of the high-level flaw detection large-size TC4 bar of this embodiment are detected, such as Figure 1 The A-end is shown in low magnification. Figure 2 The macrostructure of the B end is shown. It can be seen that the TC4 rod of this embodiment has no cracks, folds, pores, segregation, metal or non-metal inclusions and other metallurgical defects visible to the naked eye.

[0177] The high-magnification structures at both ends of the high-level flaw detection large-size TC4 bar of this embodiment are detected, such as Figure 2 As shown, the rod structure is a processed structure in the α+β two-phase region, without a complete original β grain boundary, and an equiaxed α structure is distributed on the transformed β matrix.

[0178] Table 1 Performance test results of Example 1

[0179]

[0180] The inventor has conducted a lot of research during the research process, and now uses some solutions with poor performance as comparative examples.

[0181] Comparative Example 1

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

[0183] The overall steps of the preparation method of this comparative example are roughly the same as those of Example 1, except that:

[0184] No beta heat treatment was performed.

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

[0186] Comparative Example 2

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

[0188] The overall steps of the preparation method of this comparative example are roughly the same as those of Example 1, except that:

[0189] The flat square forging from the eleventh to the twelfth fire was not carried out.

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

[0191] Comparative Example 3

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

[0193] The overall steps of the preparation method of this comparative example are roughly the same as those of Example 1, except that:

[0194] The forging ratio gradient was not controlled, and the upsetting forging was performed with a constant forging ratio of 1.5;

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

[0196] Comparative Example 4

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

[0198] The overall steps of the preparation method of this comparative example are roughly the same as those of Example 1, except that:

[0199] Only the fourth to sixth fires were carried out from the fourth to tenth fires.

[0200] The flaw detection result of the large-size TC4 bar in this comparative example is that the middle of the bar meets the B level, the edge does not meet the B level, and the microstructure uniformity is poor.

[0201] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope 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 comprises: Step 1, subjecting the ingot to two-time forging to obtain a billet; Step 2, subjecting the blank to a first-stage drawing forging; Step 3, subjecting the blank to β heat treatment to obtain an intermediate blank; Step 4, subjecting the intermediate billet to multi-fire drawing forging; Step 5: Flat square forging; Step 6: Forging and tumbling to obtain large-size TC4 bars with high flaw detection level.

2. The preparation method according to claim 1, characterized in that: In the step 1, the forging ratio of the first fire forging is controlled to be smaller than the forging ratio of the second fire forging.

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

4. The preparation method according to claim 1, characterized in that: In step 1, the first heat forging step includes: The ingot is heated to 680-780°C and kept warm; the ingot is heated to 1080-1180°C and kept warm; upsetting and drawing are performed; the ingot is returned to the furnace, the temperature is lowered, and kept warm at 1050-1150°C; upsetting and drawing are performed; the ingot is rounded and water-cooled.

5. The preparation method according to claim 1, characterized in that: In step 1, the second-time blank forging step includes: heating the blank to 680-780° C. and keeping it warm; heating the blank to 1020-1120° C. and keeping it warm; performing upsetting and drawing; returning to the furnace, lowering the temperature, and keeping it warm at 970-1070° C.; performing upsetting and drawing; rounding, and water cooling.

6. The preparation method according to claim 1, characterized in that: The specific steps of step 2 include: heating the blank to 680-780°C and keeping the temperature; heating the blank to T β -(15~65℃), keep warm; perform upsetting and pulling; return to the furnace, and β -(15~65℃) keep warm; perform upsetting and pulling; rounding and air cooling.

7. The preparation method according to claim 1, characterized in that: The step 3 comprises: heating the furnace to T β +(5~25℃), after reaching the temperature, load the billet into the furnace, keep warm for 90~240min, and air cool.

8. The preparation method according to claim 1, characterized in that: In step 4, each step of forging includes: heating the blank to 680-780°C and keeping the temperature; heating the blank to T β -(15~65℃), keep warm; perform upsetting and pulling; return to the furnace, and β -(15~65℃) keep warm; perform upsetting and pulling; pour in eight directions and air cool.

9. The preparation method according to claim 1, characterized in that: In step 5, each flat square forging step includes: S51, heating the blank to 680-780° C. and keeping the temperature; S52, heating the blank to T β -(15~65℃), keep warm; S53, the horizontal anvil is widened and flattened until the height of the blank is H, and H and the diameter d4 of the blank meet the following relationship: H≥d4 / 2; S54, rotating the blank 90° around the axis, and widening and flattening the blank with the horizontal anvil until the blank height is H; S55, shaping, stretching in all directions, turning in all directions; S56, return to the original furnace and keep warm for 60 to 120 minutes, and repeat S53 to S55.

10. A large-size TC4 bar with high flaw detection level, characterized in that: The preparation method is described in any one of claims 1 to 9.

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