A method for preventing shear cracking during titanium alloy swaging

Abstract

The application discloses a method for preventing shear cracking in the process of titanium alloy forging and drawing, which comprises the following steps: step one, heating titanium alloy ingot with a height-diameter ratio of not more than 2.5 to above the phase transition point, and performing first-time forging to obtain a forging blank with a size of a1*b1*l1; step two, heating the forging blank to 20-40 DEG C below the phase transition point, and performing final-time forging to obtain a forging piece with a size of a2*b2*l2, wherein the method for the final-time forging is as follows: adjusting the opening width k of the drawing die to the width a2 of the forging piece, loading the forging blank into the drawing die along the length direction, and performing slow pressing or impact deformation through the upper anvil. The method can effectively improve the uniformity of the material, avoid shear deformation cracking in the process of forging and drawing, and is suitable for the technical field of metal material processing.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing technology, and in particular relates to a method for preventing shear cracking during the forging and drawing process of titanium alloys. Background Technology

[0002] Metallic materials play a vital role in engineering construction and scientific research, and are widely used in aerospace, construction, transportation, energy, and other fields. Forging is a key process in the plastic forming of metallic materials. By applying pressure, it causes plastic deformation of metal billets, thereby obtaining forged billets with excellent mechanical properties and specific shapes. Forging can eliminate defects generated during the smelting process, optimize the microstructure, and improve the strength and toughness of metal components to meet design requirements. Forged products are widely used in machinery and equipment, as well as in the defense industry. Forging drawing is a core process in the plastic forming of metals. It achieves axial extension by reducing the cross-sectional area of ​​the billet and is widely used in the initial forming stage of metal billets, slabs, and forgings.

[0003] However, current forging and drawing methods for metal materials generally employ a segmented, "rolling out" approach using flat anvils, either by rotating the anvil 90° or using a spiral drawing motion. This method is inefficient, especially with materials exhibiting good ductility. Drawing longer billets requires reversing the direction of the drawing process, and prolonged drawing time can lead to material cooling, necessitating reheating. This method demands high operator skill; improper control can easily cause shear deformation and cracking of the billet, requiring grinding before the next forging, increasing processing steps and reducing production efficiency. Furthermore, differences in deformation at the shearing point and within the segmented sections of the billet result in uneven microstructure. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method to prevent shear cracking during the forging and drawing process of titanium alloys. This method, by adjusting the forging process and combining it with the use of a drawing die for the final heat treatment, can effectively improve the uniformity of the material and solve the problems of shear deformation cracking and uneven microstructure in titanium alloy billets during the forging and drawing process.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preventing shear cracking during the forging and drawing process of titanium alloys, characterized in that the method includes the following steps: Step 1: Heat a titanium alloy ingot with a height-to-diameter ratio of no more than 2.5 to above the phase transformation point and hold it at that temperature. Then, perform the first forging to obtain a forging blank with dimensions of a1×b1×l1, where a1 is the width of the forging blank, b1 is the height of the forging blank, and l1 is the length of the forging blank. The units of a1, b1, and l1 are all mm. Step 2: Heat the forging billet obtained in Step 1 to 20℃~40℃ below the phase transformation point and hold it therefore for the final forging to obtain a forging with dimensions a2×b2×l2, where a2=a1+(4mm~8mm), where a2 is the width of the forging, b2 is the height of the forging, and l2 is the length of the forging. The units of a2, b2, and l2 are all mm. The method of the final forging is as follows: adjust the opening width k of the drawing die to a2, load the forging billet into the drawing die along the length direction, and slowly press or impact deform it through the upper anvil.

[0006] Existing conventional forging drawing processes use flat anvils with limited width, which easily leads to shear deformation during the drawing process, causing problems such as cracking of forgings, low production efficiency, and uneven deformation. This invention uses a drawing die with adjustable opening width to replace the lower anvil for final heat forging. Combined with the titanium alloy forging process, this work together to avoid shear cracking during titanium alloy drawing, thus improving the production efficiency and quality of titanium alloy forging billets.

[0007] This invention controls the final forging temperature to be 20°C to 40°C below the phase transformation point. At this temperature, the titanium alloy is in a two-phase region with a relatively high proportion of β phase (usually above 60%). The β phase has a body-centered cubic structure with many slip systems and excellent plastic deformation capacity, which is beneficial for upsetting and drawing operations with large deformation, reducing deformation resistance and reducing the risk of cracking. At the same time, although the α phase (close-packed hexagonal structure) has slightly poor plasticity, it can effectively hinder the growth of β grains. The uniformly distributed α phase particles are like "nails" anchored on the β grain boundaries, preventing the β grains from coarsening rapidly during high-temperature deformation and heat preservation.

[0008] The above-mentioned method for preventing shear cracking during the forging and drawing process of titanium alloys is characterized in that b1 in step one is not greater than 2.5 times a1.

[0009] This invention controls the height and width of the forging blank to prevent excessive deformation from dimension b1 to b2 during deformation in the drawing die, which would result in an excessively large drawing length and make it difficult to achieve the desired drawing length.

[0010] The above-mentioned method for preventing shear cracking during the forging and drawing process of titanium alloy is characterized in that, in step one, the titanium alloy ingot is heated to 150°C~250°C above the phase transformation point and held at that temperature.

[0011] The above-mentioned method for preventing shear cracking during the forging and drawing process of titanium alloy is characterized in that the holding time t in step one is D / 2+(20min~40min), where t is the holding time in min; and D is the diameter of the titanium alloy ingot in step one in mm.

[0012] The above-mentioned method for preventing shear cracking during the forging and drawing process of titanium alloy is characterized in that the drawing die in step two includes a base with a groove, a movable baffle embedded in the groove, and an adjustable baffle set at the top of the base. A movable column is provided in the groove, and a spring is provided on the outer sleeve of the movable column. A second hole matching the movable column is opened at the bottom end of the movable baffle.

[0013] The above-mentioned method for preventing shear cracking during the forging and drawing process of titanium alloy is characterized in that the adjustable baffle is provided with a plurality of through holes, the base is provided with a first hole corresponding to the through holes, and has a fixing rod inserted into the through holes and the first hole.

[0014] The above-mentioned method for preventing shear cracking during the drawing and elongation process of titanium alloy forging is characterized in that the forging pressure of the final hot forging in step two is not less than 1.25 times the drawing and elongation deformation force of the final hot forging, wherein the drawing and elongation deformation force is calculated according to the following formula: ; ; Where P is the elongation deformation force, and the unit is N; The deformation condition coefficient is 1 for a flat anvil and 1.25 for a shaped anvil; m is a coefficient. 1 is the tensile strength of the forging billet at the deformation temperature, in MPa; A is the width of the forging billet, in mm; L is the contact length between the anvil and the forging billet, in mm; f is the coefficient of friction, taken as 0.5; h is the height of the forging billet pressed down each time, in mm.

[0015] Since the design forging pressure of existing forging machines far exceeds the forging pressure required by the forging material, this invention ensures that sufficient deformation is achieved when b1 is no more than 2.5 times a1 by controlling the forging pressure required for deformation to be higher than that of traditional forging methods and controlling the ratio of forging pressure to elongation deformation force. The invention also uses the above formula to estimate the forging machine and the reduction amount to determine whether the forging billet can be elongated.

[0016] Compared with the prior art, the present invention has the following advantages: 1. This invention improves the production efficiency and quality of titanium alloy forgings by adjusting the forging process and using a drawing die instead of the lower anvil in conventional forging drawing for the final heat forging. This avoids shear deformation during the forging drawing process, which can cause cracking of the forging billet, thereby reducing production efficiency and causing uneven deformation.

[0017] 2. This invention has unique advantages for alloys with poor forging plasticity. By setting the stress state of the forging billet to biaxial compressive stress and uniaxial tensile stress, which is different from the conventional uniaxial compressive stress and biaxial tensile stress state, it can effectively realize the deformation of materials that are difficult to deform and easy to crack, prevent the forging billet from shear deformation and cracking during the forging process, and improve the yield.

[0018] 3. This invention improves equipment utilization by increasing the forging pressure of titanium alloy during the forging and drawing process, achieves full deformation of titanium alloy through large deformation, improves the uniformity of titanium alloy forging billet structure, and refines the forging billet structure.

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the elongation mold of the present invention.

[0021] Figure 2 This is a schematic diagram of the internal structure of the drawing die of the present invention.

[0022] Figure 3 This is a photograph of the forging prepared in Example 1.

[0023] Figure 4 This is a metallographic diagram of the forging head prepared in Example 1.

[0024] Figure 5 The image shows the metallographic structure of the forging prepared in Example 1 at one-third of its length from the head.

[0025] Figure 6 The image shows the metallographic structure of the forging prepared in Example 1 at 2 / 3 of its length from the head.

[0026] Figure 7 This is a metallographic diagram of the tail section of the forging prepared in Example 1.

[0027] Figure 8 This is a photograph of the forging prepared in Example 2.

[0028] Figure 9 This is a photograph of the forging and drawing process in Comparative Example 1.

[0029] Figure 10 This is a photograph of the forging prepared in Comparative Example 1.

[0030] Figure 11 This is a metallographic diagram of the forging head prepared in Example 3.

[0031] Figure 12 The image shows the metallographic structure of the forging prepared in Example 3 at half the length from the head.

[0032] Figure 13 This is a metallographic diagram of the tail section of the forging prepared in Example 3.

[0033] Explanation of reference numerals in the attached figures: 1—Base; 1-1—Slot; 1-2—Modible column; 1-3—First hole; 2—Modible baffle; 2-1—Second hole; 3—Adjustable baffle; 3-1—Through hole; 4—Fixed rod. Detailed Implementation

[0034] Example 1 This embodiment uses a TC4 titanium alloy ingot with dimensions of Φ160mm×300mm and a phase transformation temperature of 995℃, and includes the following steps: Step 1: Heat the TC4 titanium alloy ingot to 1145℃ and hold for 120 minutes for the first forging to obtain a forging billet with dimensions of 90mm×150mm×447mm. The first forging process is as follows: upset from Φ160mm×300mm to Φ226mm×150mm, drawn to 150mm×150mm×268mm, upset to 200mm×200mm×150mm, drawn to 150mm×150mm×268mm, upset to 200mm×200mm×150mm, drawn to 90mm×150mm×447mm. Step 2: Heat the forging billet obtained in Step 1 to 955℃ and hold for 80 minutes. Then... Figure 1 and Figure 2 The opening width k of the drawing die is adjusted to 95mm. The forging billet is placed into the drawing die along the length direction for slow pressing deformation to obtain a forging with dimensions of 95mm×93mm×686mm. The required drawing deformation force when the forging billet is heated to 955℃ is calculated to be no less than 713 tons. A forging press with a forging pressure of 1250T is selected for slow pressing deformation. The specific process of loading the forging billet into the drawing die is as follows: the adjustable baffle 3 is moved to adjust the opening width k to 95mm. At this time, several through holes 3-1 of the adjustable baffle 3 correspond to several first holes 1-3 of the base 1. The fixing rod 4 is inserted into the through hole 3-1, so that the two ends of the fixing rod 4 are respectively located in the first hole 1-3 and the through hole 3-1, so that the adjustable baffle 3 is fixed in the horizontal direction. The movable baffle 2 is embedded into the groove 1-1 of the base 1. Then the forging billet is placed between the adjustable baffle 3 and the movable baffle 2 along the length direction. The movable baffle 2 and the forging billet are pressed down by the upper anvil to slowly deform the forging billet. A movable column 1-2 is provided in the groove 1-1. A spring is fitted around the movable column 1-2. A second hole 2-1 matching the movable column 1-2 is opened at the bottom of the movable baffle 2. During the pressing down of the upper anvil, the movable column 1-2 is inserted into the second hole 2-1 of the movable baffle 2. When the upper anvil is lifted, the movable baffle 2 is lifted under the action of the spring, maintaining the synchronous movement of the upper anvil and the movable baffle 2, so that the forging billet is always restricted by the adjustable baffle 3 and the movable baffle 2.

[0035] A physical image of the forging prepared in this embodiment is shown below. Figure 3 As shown, the macroscopic surface of the forging is smooth without cracks or defects, without shear deformation or cracking, and the deformation is uniform with no uneven deformation locations found.

[0036] In this embodiment, samples were taken from the head, one-third of the length from the head, two-thirds of the length from the head, and the tail of the forging, respectively, for metallographic observation. Figures 4-7 As shown, after forging in the two-phase region, the typical microstructure is a bimodal microstructure, consisting of equiaxed primary α phase + β transformed matrix (fine lamellar α + residual β). The bar microstructure is uniform, without continuously distributed grain boundary structures, and no microcrack defects were found.

[0037] Example 2 This embodiment uses a Ti5553 titanium alloy ingot with dimensions of Φ120mm×300mm prepared by powder metallurgy. The phase transformation temperature of the Ti5553 titanium alloy ingot is 980℃. The process includes the following steps: Step 1: Heat the Ti5553 titanium alloy ingot to 1230℃ and hold for 85 minutes to perform the first forging, obtaining a first forging billet with dimensions of 60mm×90mm×628mm; the dimensional changes during the first forging process are as follows: from Φ90mm×300mm upset to Φ140mm×220mm, with a drawing length of 80mm×80mm×528mm; upset to 110mm×110mm×279mm, with a drawing length of 80mm×80mm×528mm; upset to 110mm×110mm×279mm, with a drawing length of 60mm×90mm×628mm. Step 2: Heat the first forging billet obtained in Step 1 to 960℃ and hold for 80 minutes. Then, as follows... Figure 1 and Figure 2 The opening width k of the drawing die is adjusted to 65mm. The first forging billet is inserted into the drawing die along the length direction for slow pressing deformation to obtain a forging with dimensions of 65mm×63mm×828mm. The required drawing deformation force when the forging billet is heated to 960℃ is calculated to be no less than 415 tons. A forging press with a forging pressure of 630T is selected for slow pressing deformation. The specific process of loading the forging billet into the drawing die is as follows: the adjustable baffle 3 is moved to adjust the opening width k to 95mm. At this time, several through holes 3-1 of the adjustable baffle 3 correspond to several first holes 1-3 of the base 1. The fixing rod 4 is inserted into the through hole 3-1, so that the two ends of the fixing rod 4 are respectively located in the first hole 1-3 and the through hole 3-1, so that the adjustable baffle 3 is fixed in the horizontal direction. The movable baffle 2 is embedded into the groove 1-1 of the base 1. Then the forging billet is placed between the adjustable baffle 3 and the movable baffle 2 along the length direction. The movable baffle 2 and the forging billet are pressed down by the upper anvil to slowly deform the forging billet. A movable column 1-2 is provided in the groove 1-1. A spring is fitted around the movable column 1-2. A second hole 2-1 matching the movable column 1-2 is opened at the bottom of the movable baffle 2. During the pressing down of the upper anvil, the movable column 1-2 is inserted into the second hole 2-1 of the movable baffle 2. When the upper anvil is lifted, the movable baffle 2 is lifted under the action of the spring, maintaining the synchronous movement of the upper anvil and the movable baffle 2, so that the forging billet is always restricted by the adjustable baffle 3 and the movable baffle 2.

[0038] A physical image of the forging prepared in this embodiment is shown below. Figure 8 As shown, the macroscopic surface of the forging is smooth without cracks or defects, without shear deformation or cracking, and the deformation is uniform with no uneven deformation locations found.

[0039] Comparative Example 1 The difference between this comparative example and Example 2 is that in step two, the first forging billet is heated to 960°C and held for 80 minutes, using the following method... Figure 9 The conventional shearing and drawing forging method shown involves drawing the forging on a flat anvil at a 90° angle for the final heat forging, resulting in a forging with dimensions of 65mm × 63mm × 828mm.

[0040] A physical image of the forging prepared in this comparative example is shown below. Figure 10 As shown, compared with the forging prepared in Example 2, the surface of this forging has obvious cracks. It can be seen that the method of the present invention can effectively prevent shear deformation and surface cracking during the forging and drawing process.

[0041] Example 3 This embodiment uses a Ti150 titanium alloy ingot with dimensions of Φ160mm×300mm and a phase transformation temperature of 1050℃, and includes the following steps: Step 1: Heat the Ti150 titanium alloy ingot to 1250℃ and hold for 120 minutes to perform the first forging, obtaining a forging billet with dimensions of 90mm×150mm×447mm; the first forging process is as follows: upset from Φ160mm×300mm to Φ226mm×150mm, drawn to 150mm×150mm×268mm, upset to 200mm×200mm×150mm, drawn to 150mm×150mm×268mm, upset to 200mm×200mm×150mm, drawn to 90mm×150mm×447mm; Step 2: Heat the forging billet obtained in Step 1 to 1020℃ and hold for 80 minutes. Then... Figure 1 and Figure 2 The opening width k of the drawing die is adjusted to 95mm. The forging billet is loaded into the drawing die along the length direction for slow pressing deformation to obtain a forging with dimensions of 95mm×93mm×686mm. The required drawing deformation force when the forging billet is heated to 1020℃ is calculated to be no less than 67 tons. A forging press with a forging pressure of 630T is selected for slow pressing deformation. The specific process of loading the forging billet into the drawing die is as follows: the adjustable baffle 3 is moved so that the opening width k is adjusted to 95mm. At this time, several through holes 3-1 of the adjustable baffle 3 correspond to several first holes 1-3 of the base 1. The fixing rod 4 is inserted into the through hole 3-1 so that the two ends of the fixing rod 4 are respectively located in the first hole 1-3 and the through hole 3-1. The adjustable baffle 3 is fixed in the horizontal direction. The movable baffle 2 is embedded into the groove 1-1 of the base 1. Then the forging billet is placed between the adjustable baffle 3 and the movable baffle 2 along the length direction. The movable baffle 2 and the forging billet are pressed down by the upper anvil to slowly deform the forging billet. A movable column 1-2 is provided in the groove 1-1, and a spring is fitted over the movable column 1-2. The bottom end of the movable baffle 2 has a second hole 2-1 that matches the movable column 1-2. During the downward pressing of the upper anvil, the movable column 1-2 is inserted into the second hole 2-1 of the movable baffle 2, and the spring is compressed. When the upper anvil is lifted, the movable baffle 2 is lifted under the action of the spring, maintaining the synchronous movement of the upper anvil and the movable baffle 2, so that the forging billet is always restricted by the adjustable baffle 3 and the movable baffle 2.

[0042] Samples were taken from the head, halfway point, and tail of the forging obtained in this embodiment for metallographic observation. Figures 11-13 As shown, after forging in the two-phase region, the typical microstructure is a bimorphic microstructure, consisting of an equiaxed primary α phase and a β-transformed matrix. The bar microstructure is uniform, without continuously distributed grain boundary structures, and no microcrack defects were found.

[0043] Example 4 The difference between this embodiment and embodiment 3 is that: in step two, the opening width k of the drawing die is adjusted to 98mm, and the upper anvil is used to impact and deform the forging billet.

[0044] The forging prepared in this embodiment has a smooth macroscopic surface without cracks or defects, no shear deformation or cracking, and uniform deformation with no uneven deformation locations found.

[0045] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preventing shear cracking during the forging and drawing process of titanium alloys, characterized in that, The method includes the following steps: Step 1: Heat a titanium alloy ingot with a height-to-diameter ratio of no more than 2.5 to above the phase transformation point and hold it at that temperature. Then, perform the first forging to obtain a forging blank with dimensions of a1×b1×l1, where a1 is the width of the forging blank, b1 is the height of the forging blank, and l1 is the length of the forging blank. The units of a1, b1, and l1 are all mm. Step 2: Heat the forging billet obtained in Step 1 to 20℃~40℃ below the phase transformation point and hold it therefore for the final forging to obtain a forging with dimensions a2×b2×l2, where a2=a1+(4mm~8mm), a2 is the width of the forging, b2 is the height of the forging, and l2 is the length of the forging. The units of a2, b2, and l2 are all mm. The method of the final forging is as follows: adjust the opening width k of the drawing die to a2, load the forging billet into the drawing die along the length direction, and slowly press or impact deform it through the upper anvil. The elongation mold includes a base (1) with a groove (1-1), a movable baffle (2) embedded in the groove (1-1), and an adjustable baffle (3) set at the top of the base (1). A movable column (1-2) is provided in the groove (1-1), and a spring is provided on the outer sleeve of the movable column (1-2). A second hole (2-1) matching the movable column (1-2) is opened at the bottom of the movable baffle (2).

2. The method for preventing shear cracking during the forging and drawing process of titanium alloys according to claim 1, characterized in that, In step one, b1 is no greater than 2.5 times a1.

3. The method for preventing shear cracking during the forging and drawing process of titanium alloys according to claim 1, characterized in that, The titanium alloy ingot mentioned in step one is heated to 150℃~250℃ above the phase transformation point and held at that temperature.

4. The method for preventing shear cracking during the forging and drawing process of titanium alloys according to claim 1, characterized in that, The heat preservation time t mentioned in step one is D / 2+(20min~40min), where t is the heat preservation time in minutes; and D is the diameter of the titanium alloy ingot mentioned in step one in mm.

5. The method for preventing shear cracking during the forging and drawing process of titanium alloys according to claim 1, characterized in that, The adjustable baffle (3) has several through holes (3-1), and the base (1) has a first hole (1-3) corresponding to the through holes (3-1), and has a fixing rod (4) inserted into the through holes (3-1) and the first hole (1-3).

6. The method for preventing shear cracking during the forging and drawing process of titanium alloys according to claim 1, characterized in that, In step two, the forging pressure of the final forging is not less than 1.25 times the elongation deformation force of the final forging, and the elongation deformation force is calculated according to the following formula: ； ； Where P is the elongation deformation force in N; is the deformation condition coefficient, which is 1 for a flat anvil and 1.25 for a shaped anvil; m is a coefficient; is the tensile strength of the forging billet at the deformation temperature in MPa; A is the width of the forging billet in mm; L is the contact length between the upper anvil and the forging billet in mm; f is the friction coefficient, which is 0.5; and h is the height of the forging billet pressed down each time in mm.

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