CN117564199A - Forging method for improving uniformity of mechanical properties of end part of titanium alloy bar - Google Patents
Forging method for improving uniformity of mechanical properties of end part of titanium alloy bar Download PDFInfo
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- CN117564199A CN117564199A CN202311565991.3A CN202311565991A CN117564199A CN 117564199 A CN117564199 A CN 117564199A CN 202311565991 A CN202311565991 A CN 202311565991A CN 117564199 A CN117564199 A CN 117564199A
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- 238000005242 forging Methods 0.000 title claims abstract description 164
- 229910001069 Ti alloy Inorganic materials 0.000 title claims abstract description 56
- 238000000034 method Methods 0.000 title claims abstract description 50
- 238000010438 heat treatment Methods 0.000 claims abstract description 48
- 230000008569 process Effects 0.000 claims abstract description 21
- 230000007704 transition Effects 0.000 claims abstract description 16
- 229910052751 metal Inorganic materials 0.000 claims abstract description 15
- 239000002184 metal Substances 0.000 claims abstract description 15
- 238000010304 firing Methods 0.000 claims abstract description 9
- VEMKTZHHVJILDY-UHFFFAOYSA-N resmethrin Chemical compound CC1(C)C(C=C(C)C)C1C(=O)OCC1=COC(CC=2C=CC=CC=2)=C1 VEMKTZHHVJILDY-UHFFFAOYSA-N 0.000 claims abstract description 7
- 238000001953 recrystallisation Methods 0.000 claims abstract description 5
- 238000003825 pressing Methods 0.000 claims description 20
- 238000004321 preservation Methods 0.000 claims description 18
- 238000005096 rolling process Methods 0.000 claims description 17
- 238000007599 discharging Methods 0.000 claims description 15
- 238000001816 cooling Methods 0.000 claims description 13
- 238000007493 shaping process Methods 0.000 claims description 11
- 230000002093 peripheral effect Effects 0.000 claims description 6
- 238000004513 sizing Methods 0.000 claims description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 5
- 238000007670 refining Methods 0.000 claims description 3
- 230000009466 transformation Effects 0.000 claims description 3
- 230000000694 effects Effects 0.000 abstract description 4
- 230000009467 reduction Effects 0.000 description 10
- 230000007797 corrosion Effects 0.000 description 9
- 238000005260 corrosion Methods 0.000 description 9
- 239000000956 alloy Substances 0.000 description 5
- 238000005520 cutting process Methods 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 238000009864 tensile test Methods 0.000 description 3
- 229910000831 Steel Inorganic materials 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000010276 construction Methods 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 238000003754 machining Methods 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 238000005070 sampling Methods 0.000 description 2
- 239000010959 steel Substances 0.000 description 2
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 238000012795 verification Methods 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
- B21J5/00—Methods for forging, hammering, or pressing; Special equipment or accessories therefor
- B21J5/002—Hybrid process, e.g. forging following casting
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
- B21J1/00—Preparing metal stock or similar ancillary operations prior, during or post forging, e.g. heating or cooling
- B21J1/06—Heating or cooling methods or arrangements specially adapted for performing forging or pressing operations
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
- B21J5/00—Methods for forging, hammering, or pressing; Special equipment or accessories therefor
- B21J5/06—Methods for forging, hammering, or pressing; Special equipment or accessories therefor for performing particular operations
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
- B21J5/00—Methods for forging, hammering, or pressing; Special equipment or accessories therefor
- B21J5/06—Methods for forging, hammering, or pressing; Special equipment or accessories therefor for performing particular operations
- B21J5/08—Upsetting
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Abstract
The invention discloses a forging method for improving the uniformity of mechanical properties of the end part of a titanium alloy bar, which adopts the process of cogging continuous round section forging, cross-fire reversing heating forging, alternate forging of edges during drawing, and U-shaped anvil forming forging; the dynamic recrystallization of an as-cast structure is quickened by utilizing the high-temperature continuous forging of the cogging firing time, the blank is controlled to be a circular section, and the circumferential deformation uniformity is improved; the cross-fire reversing forging below the phase transition point and above the phase transition point is adopted in the recrystallization fire, so that the influence of dead zones at the end parts on the uniformity of the structure is inhibited; and the metal enters into the two-phase region and is forged by the U-shaped anvil with combined forming fire at last in a mode of forging the edges alternately, so that the flow uniformity of the metal at the end part is improved. The forging method effectively solves the end effect problem caused by large dead zone of end forging and uneven metal flow due to the limitation of the free forging method of the large-specification titanium alloy bar, reduces the cutting-off amount of the end, and greatly improves the yield of the titanium alloy bar.
Description
Technical Field
The invention belongs to the technical field of nonferrous metal processing, and particularly relates to a forging method for improving uniformity of mechanical properties of ends of titanium alloy bars, which is mainly used for preparing finished TC4 titanium alloy bars with the specification of phi 200 mm-phi 300 mm.
Background
Titanium and titanium alloy materials are widely used in the aerospace field, such as for manufacturing aircraft structural members, engine parts, propellers, missiles, satellites and the like, because of their excellent comprehensive properties of low density, high specific strength, low thermal expansion coefficient, good corrosion resistance, high compatibility, easiness in welding and the like, are well known.
Wherein, when the titanium alloy is used for manufacturing aeroengine parts, the requirement on the uniformity of mechanical properties of the materials is more strict. At present, most titanium alloy materials applied to aeroengine parts are formed by die forging, and blanks selected by die forging are produced by free forging, and are generally cut and fed on a single long round rod according to the size of the parts. The metal flow is restrained by the mould when free forging is carried out, but the local contact with the hammer anvil is limited in flow due to friction force action, so that a deformation dead zone is formed, the characteristic causes the difference of the dead zone and a streamline zone after forging of a free forging product naturally, particularly the difference of an end zone contacted with the hammer anvil during upsetting, the deformation dead zone and the excessive rapid temperature drop superposition of a free end lead to insufficient end deformation and carry over of uneven tissues, and further the poor uniformity of mechanical properties of different positions of a blank is caused, and the characteristic is often called as the end effect of a free forging bar. This difference is acceptable for common constructions, but should be minimized or even eliminated for aero-engine constructions. Taking TC4 titanium alloy free forging bars with the common specification phi of 200 mm-phi 300mm as an example, the length-diameter ratio of the free forging bars is often more than 8, the length-diameter ratio (or height-diameter ratio) of an original blank for forging one bar is at most 2, and the titanium alloy is difficult to deform, repeated upsetting and drawing are often required to be combined, so that the end tissues and performances of the finally forged long bar show obvious non-uniformity compared with the middle part of the bar, a sample piece is sawed at the end of the bar according to the bar inspection specification, a group of tensile samples are annularly taken at the D/4 position of the sample piece for testing after heat treatment, the difference between the maximum value and the minimum value of room temperature tensile strength Rm can reach 30MPa, the difference between the maximum value and the minimum value of the elongation A after breaking can reach 15%, and the free forging bar cannot be directly used. The conventional solution to this problem is to increase the cut-out amount of the end portions while improving the overall uniformity of the core and edge portions of the bar, failing to form an effective method for improving the performance uniformity of the end portion region of the bar, resulting in a low yield.
In view of this, the present invention has been made.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides a forging method for improving the uniformity of mechanical properties of the end part of a titanium alloy bar, which is mainly used for solving the problem that the end effect of the bar after free forging of the existing titanium alloy causes poor uniformity of the structure properties of the end part of the bar after forging.
The invention aims at solving the problems by the following technical scheme:
a forging method for improving uniformity of mechanical properties of end parts of titanium alloy bars comprises the following steps:
step 1, cogging continuous round section forging
The cogging stage uses flat anvil upsetting and transverse drawing, continuous furnace return and temperature compensation forging, fully utilizes dynamic recrystallization at the high temperature stage to refine the cast structure, and maintains a round section after forging, so that the circumferential deformation of the blank is relatively uniform;
step 2, forging in a fire-crossing reversing mode
Heating under the transformation point, discharging, and upsetting the axial direction of the blank along the radial direction of the original ingot, wherein the metal at the original end part is distributed on the peripheral surface of the blank; then returning to the furnace, heating to a temperature above a phase transition point, preserving heat, further statically recrystallizing and refining a circumferential surface (an original end surface) with stored strain energy in the furnace, and axially upsetting and pulling a blank to be along the axial direction of an original ingot after discharging to realize end regression, so as to finish one round of reversing forging across fire, wherein the blank is square in section;
step 3, alternately forging the prismatic surface during drawing
The blank enters a two-phase region drawing forging stage, and the phenomenon of large difference of end metal flow resistance caused by different contact areas between edges and faces of the end part of the blank and an anvil in the drawing process is changed by carrying out a forging mode of alternately pressing edges and faces of opposite sides in sequence, so that the uniformity of end part deformation is improved;
step 4, forming and forging the U-shaped anvil
The forming fire adopts U-shaped anvil rounding forging, so that the circumferential constraint of the blank in the forging process is increased, and the difference of metal flow directions of the blank is further reduced.
Further, the cogging continuous round section forging in the step 1 is 2-firing continuous forging, and the specific process is as follows:
the heating temperature of the 1 st firing time is 1100-1200 ℃, the heating heat preservation coefficient is 0.65-0.85, and the total deformation of the flat anvil upsetting and the transverse drawing is 50-65%;
the heating temperature of the 2 nd heating time is 1030 ℃ to 1100 ℃ and the heat preservation time is 60min to 210min; the total deformation of the upsetting and the transverse drawing of the flat anvil is 45-55%.
Further, in the step 1, the continuous round section forging process of cogging uses upper and lower flat anvils, 2 upsetting times and 2 drawing times are total per fire, the axial direction of the blank is always along the original axial direction of the ingot, the blank is square section after the drawing is finished, the blank is transversely placed on the flat anvils to be rolled and forged into a round section, and air cooling is carried out after forging.
Further, the specific process of the cross-fire reversing forging in the step 2 is divided into the following two stages:
the first stage: heating to 30-50 ℃ below the phase transition point, wherein the heat preservation coefficient is 0.65-0.75, forging by using upper and lower flat anvils, radially pulling after upsetting for one time, setting the section to be square after forging, controlling the total forging ratio to be 1.7-2.5, changing the original end of the blank to the peripheral surface of the blank, and returning to the furnace after forging;
and a second stage: heating to 30-50 ℃ above the phase transition point, wherein the heat preservation coefficient is 0.4-0.5, selecting an upper flat anvil and a lower flat anvil after discharging, upsetting for one time, axially pulling out, forging to obtain an octagon-shaped cross section, wherein the forging ratio is 1.4-1.8, returning the axial direction of the blank to the original axial direction, and cooling by water after forging.
Further, the specific process of alternately forging the prismatic surface during the drawing in the step 3 is as follows:
heating the blank to 30-50 ℃ below the phase transition point, wherein the heat preservation coefficient is 0.65-0.75, forging by using upper and lower flat anvils, controlling the length-diameter ratio of the blank before beginning drawing to be 0.8-1.2, setting the section to be square, starting pressing down and drawing along the edge of the square section, controlling the rotation angle of the blank between every two times to be 45 degrees, respectively forging the edge and the surface in adjacent passes, carrying out small deformation on the edge of the first pass, marking the pressing down amount as (1), then carrying out the second pass by rotating 45 degrees, carrying out large deformation on the large surface, marking the pressing down amount as (2), carrying out the third pass by rotating 45 degrees, carrying out small deformation on the original edge, marking the pressing down amount as (3), and carrying out conventional flat anvil shaping according to the single pressing down amount which is less than or equal to (3), until the section is nearly circular.
Further, the pressing rate of each time is 30 mm/s-60 mm/s when the prismatic surface is alternately forged during the drawing in the step 3, and the feeding amount is 100 mm-200 mm.
Further, in the step 4, the length of the sizing area of the U-shaped anvil is 400-550 mm, the single-fire deformation is less than or equal to 15%, the U-shaped anvil is drawn out at a constant speed, and the U-shaped anvil is air-cooled after being forged to a finished product.
Further, the forging method is mainly used for preparing finished TC4 titanium alloy bars with the specification of phi 200 mm-phi 300mm, and is used for improving the uniformity of mechanical properties of the end parts of the finished TC4 titanium alloy bars, and of course, other brands of titanium alloy bars, such as TA15, TC17 and other titanium alloy bars for aeroengines, are also prepared, and detailed description is omitted.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a forging method, which comprises the following steps,
the round section forging, the fire reversing under the crossing phase change point and on the phase change point and the prismatic surface alternate forging are controlled to be performed sequentially, finally, the U-shaped anvil is utilized to restrict the end part to be self-widened, the deformation difference of the bar in all directions in the free forging process is effectively reduced, the mechanical property of the end part of the bar is finally obtained, the mechanical property is obviously improved, and the yield is greatly improved. According to practical verification, the method is used for preparing finished TC4 titanium alloy bars with the specification of phi 200 mm-phi 300mm, the tensile strength of the bars is extremely poor and the elongation value after fracture is extremely poor within 3% under the condition that the room temperature tensile test results of the bars meet the standard requirements, the requirements of the aero-engine on high-standard uniformity of mechanical properties of titanium alloy materials are completely met, and meanwhile, the forging method is also suitable for preparing the titanium alloy bars for the aero-engine such as TA15 and TC 17.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate principles of the invention and together with the description, serve to explain the principles of the invention.
In order to more clearly illustrate the embodiments of the invention or the technical solutions of the prior art, the drawings which are used in the description of the embodiments or the prior art will be briefly described, and it will be obvious to a person skilled in the art that other drawings can be obtained from these drawings without inventive effort.
FIG. 1 is a flow chart of a forging method for improving the uniformity of mechanical properties of an end portion of a titanium alloy bar according to the present invention;
FIG. 2 is a drawing of a low-power corrosion structure of the end of a TC4 titanium alloy bar with the specification of phi 300mm prepared in example 1 of the invention;
FIG. 3 is a diagram of a 200-fold corrosion structure at the end of a TC4 titanium alloy bar with a specification of phi 300mm prepared in example 1 of the present invention;
FIG. 4 is a diagram of a 500-fold corrosion structure at the end of a TC4 titanium alloy bar with a specification of phi 300mm prepared in example 1 of the present invention;
FIG. 5 is a drawing of a low-power corrosion structure of the end of a TC4 titanium alloy bar with the specification of phi 220mm prepared in example 2 of the invention;
FIG. 6 is a diagram of a 200-fold corrosion structure at the end of a TC4 titanium alloy bar with a specification of phi 220mm prepared in example 2 of the present invention;
FIG. 7 is a drawing showing a 500-fold corrosion structure of an end portion of a TC4 titanium alloy bar with a specification of phi 220mm prepared in example 2 of the present invention.
Detailed Description
Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, the same numbers in different drawings refer to the same or similar elements, unless otherwise indicated. The implementations described in the following exemplary examples do not represent all implementations consistent with the invention. Rather, they are merely examples of devices that are consistent with aspects of the invention that are set forth in the following claims.
The present invention will be described in further detail below with reference to the drawings and examples for better understanding of the technical solutions of the present invention to those skilled in the art.
Referring to fig. 1, the invention provides a forging method for improving uniformity of mechanical properties of an end part of a titanium alloy bar, which specifically comprises the following steps:
step 1, cogging continuous round section forging
The cogging stage uses flat anvil upsetting and transverse drawing, continuous furnace return and temperature compensation forging, fully utilizes dynamic recrystallization at the high temperature stage to refine the cast structure, and maintains a round section after forging, so that the circumferential deformation of the blank is relatively uniform.
Specifically, the cogging continuous round section forging is 2-fire continuous forging, and the specific process is as follows:
the heating temperature of the first firing time is 1100-1200 ℃, the heating heat preservation coefficient is 0.65-0.85, the total deformation of upsetting and transverse drawing of a flat anvil is 50-65%, the upsetting and drawing are round by rolling forging of a transverse anvil after being square cross section, 2 times of upsetting and 2 times of drawing are total, the axial direction of a blank is always along the original axial direction of an ingot, and the second firing is continued after the blank is returned to the furnace;
the heating temperature of the 2 nd heating time is 1030 ℃ to 1100 ℃ and the heat preservation time is 60min to 210min; the total deformation of the upsetting and the transverse drawing of the flat anvil is 45% -55%, the total deformation is 2 times of upsetting and 2 times of drawing, the upsetting and drawing are performed to form a square section, then the square section is rolled and forged into a round shape by the transverse anvil, the axial direction of the blank is always along the original axial direction of the ingot, and the blank is air-cooled to room temperature.
Step 2, forging in a fire-crossing reversing mode
Heating under the transformation point, discharging, and upsetting the axial direction of the blank along the radial direction of the original ingot, wherein the metal at the original end part is distributed on the peripheral surface of the blank; and then returning the next fire to heat the furnace to a temperature above the phase transition point for heat preservation, further statically recrystallizing and refining the circumferential surface with stored strain energy in the furnace, axially upsetting and pulling the blank to be along the axial direction of the original ingot after discharging, realizing end regression, and completing one round of fire-crossing reversing forging, wherein the blank is square in section in the process.
Specifically, the specific process of cross-fire reversing forging is divided into the following two stages:
the first stage: heating to 30-50 ℃ below the phase transition point, wherein the heat preservation coefficient is 0.65-0.75, forging by using upper and lower flat anvils, radially pulling after upsetting for one time, setting the section to be square after forging, controlling the total forging ratio to be 1.7-2.5, changing the original end of the blank to the peripheral surface of the blank, and returning to the furnace after forging;
and a second stage: heating to 30-50 ℃ above the phase transition point, wherein the heat preservation coefficient is 0.4-0.5, selecting an upper flat anvil and a lower flat anvil after discharging, upsetting for one time, axially pulling out, forging to obtain an octagon-shaped cross section, wherein the forging ratio is 1.4-1.8, returning the axial direction of the blank to the original axial direction, and cooling by water after forging.
Step 3, alternately forging the prismatic surface during drawing
The blank enters a two-phase region drawing forging stage, and the forging mode of alternately pressing the edges and the faces of the opposite sections in sequence is adopted, so that the phenomenon of large difference of end metal flow resistance caused by different contact areas of the edges and the faces of the end part of the blank and the anvil in the drawing process is changed, and the uniformity of end part deformation is improved.
Specifically, the specific process of alternately forging the prismatic surface during the drawing is as follows: heating the blank to 30-50 ℃ below the phase transition point, wherein the heat preservation coefficient is 0.65-0.75, forging by using upper and lower flat anvils, controlling the length-diameter ratio of the blank before beginning drawing to be 0.8-1.2, setting the section to be square, starting pressing down and drawing along the edge of the square section, controlling the rotation angle of the blank between every two times to be 45 degrees, respectively forging the edge and the surface in adjacent passes, carrying out small deformation on the edge of the first pass, marking the pressing down amount as (1), then carrying out the second pass by rotating 45 degrees, carrying out large deformation on the large surface, marking the pressing down amount as (2), carrying out the third pass by rotating 45 degrees, carrying out small deformation on the original edge, marking the pressing down amount as (3), carrying out conventional flat anvil shaping according to the single pressing down amount which is less than or equal to (3), and carrying out furnace returning temperature compensation when the forging temperature is lower than the set temperature in the midway. Meanwhile, the pressing rate is required to be 30-60 mm/s each time, and the feeding amount is required to be 100-200 mm.
Step 4, forming and forging the U-shaped anvil
The forming fire adopts U-shaped anvil rounding forging, so that the circumferential constraint of the blank in the forging process is increased, and the difference of metal flow directions of the blank is further reduced.
Specifically, when the U-shaped anvil is formed and forged, the length of a sizing area of the U-shaped anvil is 400-550 mm, the deformation amount of single fire is less than or equal to 15%, the U-shaped anvil is drawn out at a constant speed, and the U-shaped anvil is air-cooled after being forged to a finished product.
To further verify the efficacy of the forging method of the present invention, the inventors performed the following specific examples:
example 1 (preparation of TC4 titanium alloy bars with a gauge of Φ300 mm)
1) Continuous forging of cogging
Adopting TC4 titanium alloy cast ingot with specification phi 720mm, wherein the phase transition point of the cast ingot is 990 ℃, the heating temperature at the 1 st firing time is 1150 ℃, the heat preservation coefficient is 0.75, upsetting for 2 times and transversely drawing and forging for 2 times by using a flat anvil according to the total deformation of 55 percent to form square billets, and shaping the cross section into a round shape; and (3) returning to the furnace for heating for 2 times after forging, wherein the heating temperature is 1050 ℃, preserving heat for 120min, discharging and forging, upsetting for 2 times and transversely drawing and forging for 2 times according to 50% of the total deformation to form square billets, shaping the cross section into a round shape, and air cooling after finishing.
2) Cross-fire reversing forging
Heating the blank to 950 ℃ after charging, forging the blank by using an upper flat anvil and a lower flat anvil, upsetting the blank once and radially drawing the blank according to a total forging ratio of 2.0, wherein the section of the forged blank is square, and returning the forged blank to the original heating furnace; heating to 1020 ℃, preserving heat for 200min, upsetting and axially drawing by using upper and lower flat anvils according to a total forging ratio of 1.7 after discharging, wherein the section of the forged steel is regular octagon, and water cooling is carried out after forging for 3h.
3) Alternate forging of prismatic surface during drawing
Heating the blank to 940 ℃ after charging, forging by using upper and lower flat anvils, wherein the rolling speed is set to 40mm/s, rolling and drawing from an edge after feeding by 45 degrees, the rolling reduction is set to 80mm, drawing for the second pass after 45 degrees, the rolling reduction is set to 140mm, drawing for the third pass after 45 degrees, and the rolling reduction is set to 60mm; at the moment, the blank generates new edges, the rolling reduction rate is set to be 40mm/s, the rolling reduction is set to be 60mm, shaping is started, 4 times of furnace return and temperature compensation are completed, the blank is discharged after the temperature is kept for 60 minutes, shaping is continued until the cross section of the blank is approximately circular, at the moment, the nominal diameter of the blank is set to be 330mm, and air cooling is performed after forging.
4) Forging of U-shaped anvil finished product
Heating the blank to 940 ℃, preserving heat for 210min, discharging, setting the drawing speed to be 30mm/s, feeding to be 100mm, drawing the finished product by using a U-shaped anvil with the length of a sizing area of 450mm, enabling the target diameter of the finished product to reach 310mm, forging, cooling by air, and finally machining to prepare the TC4 titanium alloy finished bar with the specification of phi 300 mm.
Cutting a low-power sample piece from the end of a TC4 titanium alloy finished bar with the specification of phi 300mm, taking a metallographic sample on the low-power piece, observing a high-power structure by using a microscope, and evaluating the structure uniformity of the end of the bar, wherein the structure photo after corrosion is shown in figure 2; after standard heat treatment is carried out on the end part sampling sheet, the mechanical properties of the chord direction tensile sample are tested along 6 positions of the D/4 position of the sample sheet, and the results are shown in Table 1:
TABLE 1 Room temperature tensile Property of the ends of the rods of example 1 (Heat treatment System: 790 ℃ C./120 min, air-cooled)
From fig. 2 to 4, it can be seen that the end part of the bar with the typical specification of phi 300mm prepared by the embodiment of the invention is low-power and high-power uniform, and meanwhile, the detection data in table 1 show that the bar prepared by the forging method has the maximum tensile strength of only 10MPa and the maximum elongation value of only 3% after breaking while the room temperature tensile test result meets the standard requirement, thus obtaining the TC4 titanium alloy phi 300mm bar with good end part performance uniformity, and completely meeting the requirement of the aeroengine on the high standard of the mechanical property uniformity of the titanium alloy material.
Example 2 (preparation of TC4 titanium alloy rod with specification phi 220 mm)
1) Continuous forging of cogging
Adopting TC4 titanium alloy cast ingots with the specification of phi 820mm, wherein the phase transition point of the cast ingots is 995 ℃, the heating temperature of the 1 st firing is 1160 ℃, the heat preservation coefficient is 0.75, upsetting for 2 times and transversely drawing and forging for 2 times by using a flat anvil according to the total deformation of 60 percent to form square billets, and shaping the cross sections into circles; and (3) returning to the furnace for heating for 2 times after forging, wherein the heating temperature is 1080 ℃, preserving heat for 150min, discharging and forging, upsetting for 2 times and laterally drawing and forging for 2 times according to 52% of total deformation to form square billets, shaping the cross section into a round shape, and air cooling after finishing.
2) Cross-fire reversing forging
Heating the blank to 945 ℃ after charging, forging the blank by using an upper flat anvil and a lower flat anvil, upsetting the blank once according to a total forging ratio of 2.2, radially drawing the blank, forging the blank to form a square cross section, and returning the forged blank to the original heating furnace; heating to 1025 ℃, preserving heat for 240min, upsetting and axially drawing by using upper and lower flat anvils according to a total forging ratio of 1.8 after discharging, wherein the section of the forged steel is regular octagon, and water cooling is carried out after forging for 3h.
3) Alternate forging of prismatic surface during drawing
Heating the blank to 955 ℃ after charging, forging by using upper and lower flat anvils, wherein the rolling speed is set to 45mm/s, rolling and drawing from an edge after feeding by 45 degrees, the rolling reduction is set to 100mm, drawing for the second pass after 45 degrees, the rolling reduction is set to 150mm, drawing for the third pass after 45 degrees, and the rolling reduction is set to 50mm; at the moment, the blank generates new edges, the rolling reduction rate is set to be 50mm/s, the rolling reduction is set to be 60mm, shaping is started, 4 times of furnace return and temperature compensation are completed, the blank is discharged after the temperature is kept for 30 minutes, shaping is continued until the cross section of the blank is nearly circular, at the moment, the nominal diameter of the blank is set to be 250mm, and air cooling is performed after forging.
4) Forging of U-shaped anvil finished product
Heating the blank to 950 ℃ and preserving heat for 150min, discharging, setting the drawing speed to be 30mm/s, feeding the blank to be 100mm, drawing the blank by using a U-shaped anvil with the sizing area length of 450mm as a finished product, enabling the target diameter of the finished product to reach 230mm, forging, cooling by air, and finally machining to prepare the TC4 titanium alloy finished bar with the specification of phi 220 mm.
Cutting a low-power sample piece from the end of a TC4 titanium alloy finished bar with the specification of phi 220mm, taking a metallographic sample on the low-power piece, observing a high-power structure by using a microscope, and evaluating the structure uniformity of the end of the bar, wherein the structure photo after corrosion is shown in figure 5; after standard heat treatment is carried out on the end part sampling sheet, the mechanical properties of the tensile sample in the chord direction are tested along 4 positions at the D/4 position of the sample sheet, and the results are shown in Table 2:
TABLE 1 Room temperature tensile Property of the ends of the bars of example 2 (Heat treatment System: 790 ℃ C./120 min, air-cooled)
From fig. 5 to 7, it can be seen that the end part of the bar with phi 220mm typical specification prepared by the embodiment of the invention is low-power and high-power uniform, and meanwhile, the detection data in table 2 show that the bar prepared by the forging method has the maximum tensile strength of 7MPa and the maximum elongation value of 2% after fracture when the room temperature tensile test result meets the standard requirement, thus obtaining the TC4 titanium alloy phi 220mm bar with good end part performance uniformity, and completely meeting the requirement of the aeroengine on the high standard of the mechanical property uniformity of the titanium alloy material.
In summary, by adopting the forging method for improving the uniformity of the mechanical properties of the end part of the titanium alloy bar, the prepared bar end part has uniform high-low power structure, so that the more uniform mechanical properties are obtained, the end effect problem caused by large dead zone of end forging and uneven metal flow due to the limitation of the free forging method of the large-size titanium alloy bar is effectively solved, the cutting amount of the end part is reduced, and the yield of the titanium alloy bar is greatly improved.
The foregoing is only a specific embodiment of the invention to enable those skilled in the art to understand or practice the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention.
It will be understood that the invention is not limited to what has been described above and that various modifications and changes may be made without departing from the scope thereof. The scope of the invention is limited only by the appended claims.
Claims (8)
1. The forging method for improving the uniformity of the mechanical properties of the end part of the titanium alloy bar is characterized by comprising the following steps of:
step 1, cogging continuous round section forging
The cogging stage uses flat anvil upsetting and transverse drawing, continuous furnace return and temperature compensation forging, fully utilizes dynamic recrystallization at the high temperature stage to refine the cast structure, and maintains a round section after forging, so that the circumferential deformation of the blank is relatively uniform;
step 2, forging in a fire-crossing reversing mode
Heating under the transformation point, discharging, and upsetting the axial direction of the blank along the radial direction of the original ingot, wherein the metal at the original end part is distributed on the peripheral surface of the blank; returning to the furnace, heating to a temperature above a phase transition point, preserving heat, further statically recrystallizing and refining the circumferential surface with stored strain energy in the furnace, axially upsetting and pulling the blank to be along the axial direction of the original ingot after discharging, realizing end regression, and completing one round of fire-crossing reversing forging, wherein the blank is square in section in the process;
step 3, alternately forging the prismatic surface during drawing
The blank enters a two-phase region drawing forging stage, and the phenomenon of large difference of end metal flow resistance caused by different contact areas between edges and faces of the end part of the blank and an anvil in the drawing process is changed by carrying out a forging mode of alternately pressing edges and faces of opposite sides in sequence, so that the uniformity of end part deformation is improved;
step 4, forming and forging the U-shaped anvil
The forming fire adopts U-shaped anvil rounding forging, so that the circumferential constraint of the blank in the forging process is increased, and the difference of metal flow directions of the blank is further reduced.
2. The forging method for improving the uniformity of mechanical properties of the end part of the titanium alloy bar according to claim 1, wherein the continuous round section forging of the cogging in the step 1 is 2-firing continuous forging, and the specific process is as follows:
the heating temperature of the 1 st firing time is 1100-1200 ℃, the heating heat preservation coefficient is 0.65-0.85, and the total deformation of the flat anvil upsetting and the transverse drawing is 50-65%;
the heating temperature of the 2 nd heating time is 1030 ℃ to 1100 ℃ and the heat preservation time is 60min to 210min; the total deformation of the upsetting and the transverse drawing of the flat anvil is 45-55%.
3. The forging method for improving the uniformity of mechanical properties of the end part of the titanium alloy bar according to claim 2, wherein in the step 1, the continuous round section forging process of the cogging uses an upper flat anvil and a lower flat anvil, 2 upsetting times and 2 drawing times are used for each fire, the axial direction of the blank is always along the original axial direction of the ingot, the square section is formed after each fire drawing is finished, the blank is transversely placed on the flat anvil for rolling forging to form a round section, and air cooling is performed after forging.
4. The forging method for improving the uniformity of mechanical properties of the end part of the titanium alloy bar according to claim 1, wherein the specific process of cross-fire reversing forging in the step 2 is divided into the following two stages:
the first stage: heating to 30-50 ℃ below the phase transition point, wherein the heat preservation coefficient is 0.65-0.75, forging by using upper and lower flat anvils, radially pulling after upsetting for one time, setting the section to be square after forging, controlling the total forging ratio to be 1.7-2.5, changing the original end of the blank to the peripheral surface of the blank, and returning to the furnace after forging;
and a second stage: heating to 30-50 ℃ above the phase transition point, wherein the heat preservation coefficient is 0.4-0.5, selecting an upper flat anvil and a lower flat anvil after discharging, upsetting for one time, axially pulling out, forging to obtain an octagon-shaped cross section, wherein the forging ratio is 1.4-1.8, returning the axial direction of the blank to the original axial direction, and cooling by water after forging.
5. The forging method for improving the uniformity of mechanical properties of the end part of the titanium alloy bar according to claim 1, wherein the specific process of alternately forging the prismatic surface during the drawing in the step 3 is as follows:
heating the blank to 30-50 ℃ below the phase transition point, wherein the heat preservation coefficient is 0.65-0.75, forging by using upper and lower flat anvils, controlling the length-diameter ratio of the blank before beginning drawing to be 0.8-1.2, setting the section to be square, starting pressing down and drawing along the edge of the square section, controlling the rotation angle of the blank between every two times to be 45 degrees, respectively forging the edge and the surface in adjacent passes, carrying out small deformation on the edge of the first pass, marking the pressing down amount as (1), then carrying out the second pass by rotating 45 degrees, carrying out large deformation on the large surface, marking the pressing down amount as (2), carrying out the third pass by rotating 45 degrees, carrying out small deformation on the original edge, marking the pressing down amount as (3), and carrying out conventional flat anvil shaping according to the single pressing down amount which is less than or equal to (3), until the section is nearly circular.
6. The forging method for improving the uniformity of mechanical properties of the end part of a titanium alloy bar according to claim 5, wherein the rolling speed of each time of alternate forging of the prismatic surface during the drawing in the step 3 is 30mm/s to 60mm/s, and the feeding amount is 100mm to 200mm.
7. The forging method for improving the uniformity of mechanical properties of the end part of the titanium alloy bar according to claim 1, wherein in the step 4, the length of a sizing area of the U-shaped anvil is 400-550 mm, the single-fire deformation amount is less than or equal to 15%, the uniform drawing is performed, and the forging is performed to a finished product and then the finished product is air-cooled.
8. The forging method for improving the uniformity of mechanical properties of the end part of a titanium alloy bar according to any one of claims 1 to 7, wherein the forging method is mainly used for preparing a finished TC4 titanium alloy bar with the specification of phi 200mm to phi 300mm and is used for improving the uniformity of mechanical properties of the end part of the finished TC4 titanium alloy bar.
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