Method for preventing shear cracking in titanium alloy forging and drawing-out process

Abstract

The invention discloses a method for preventing shear cracking in a titanium alloy forging and drawing-out process, which comprises the following steps of: 1, heating a titanium alloy cast ingot with the height-diameter ratio of not more than 2.5 to be above a phase transformation point, preserving heat, and carrying out first heating number forging to obtain a forging stock with the size of a1 * b1 * l1; and secondly, the forging stock is heated to be 20-40 DEG C below the phase transformation point, heat preservation is conducted, final heating number forging is conducted, a forge piece with the size being a2 * b2 * l2 is obtained, and the final heating number forging method comprises the steps that the opening width k of a drawing-out die is adjusted to be the width a2 of the forge piece, the forging stock is loaded into the drawing-out die in the length direction, and slow pressing or impact deformation is conducted through an upper anvil. According to the method, the forging technology is adjusted, final heating number forging is conducted by combining the drawing-out die, the uniformity of the material can be effectively improved, shear deformation and cracking in the forging and drawing-out process are avoided, and the method is suitable for the technical field of metal material machining.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material processing, and in particular relates to a method for preventing shear cracking from occurring during the forging and drawing process of a titanium alloy. Background Art

[0002] Metal materials play an important 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 metal materials. By applying pressure, the metal blank is plastically deformed to obtain a forging blank with excellent mechanical properties and a specific shape. Forging can eliminate defects produced in the metal smelting process, optimize the microstructure, and enhance the strength and toughness of metal components to meet design requirements. Forged products are widely used in mechanical equipment, defense industry and other fields. Forging stretching is the core process of metal plastic forming. It achieves axial extension by reducing the cross-sectional area of ​​the blank. It is widely used in the initial forming stage of metal bars, slabs and forging blanks.

[0003] However, the current forging and stretching of metal materials generally adopts a "rolling dough"-style stretching method in which the upper and lower flat anvils are used to stretch the material in sections, that is, stretching by turning 90° on the flat anvil or stretching in a spiral manner. This method has low stretching efficiency, especially when it comes to materials with good width extension. When stretching long billets, it is necessary to reverse the stretching direction, and the long stretching time can easily cause the material to cool down and need to be returned to the furnace for heating. This method has high technical requirements for the operator, and improper control can easily cause the billet to shear deformation and form cracks. It needs to be polished before the next forging, which increases the processing steps and reduces production efficiency. At the same time, the deformation differences at the shearing position of the billet and inside the billet segments can lead to uneven microstructure. Summary of the Invention

[0004] The present invention aims to overcome the shortcomings of the prior art by providing a method for preventing shear cracking during the forging and drawing process of titanium alloys. By adjusting the forging process and combining it with the use of a drawing die for the final forging pass, this method effectively improves material uniformity and addresses the issues of shear deformation, cracking, and structural inhomogeneity that can occur in titanium alloy billets during the forging and drawing process.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a method for preventing shear cracking during the forging and drawing process of titanium alloy, characterized in that the method comprises the following steps: Step 1: heating a titanium alloy ingot having an aspect ratio of not more than 2.5 to a temperature above the phase transition point and holding the temperature, and performing a first forging to obtain a forging blank having 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, and the units of a1, b1, and l1 are all mm; Step 2: Heat the forging blank obtained in step 1 to 20°C~40°C below the phase transformation point and keep it warm, and perform final fire forging to obtain a forging with dimensions of a2×b2×l2, and a2=a1+(4mm~8mm), wherein a2 is the width of the forging, b2 is the height of the forging, l2 is the length of the forging, and the units of a2, b2, and l2 are all mm; the method for the final fire forging is: adjust the opening width k of the drawing die to a2, load the forging blank into the drawing die along the length direction, and perform slow pressing or impact deformation through the upper anvil.

[0006] The upper and lower anvils used in the existing conventional forging and drawing are flat anvil heads and the anvil width is limited, which can easily lead to shear deformation during the forging and drawing process, causing problems such as cracking of the forgings, low production efficiency and uneven deformation; the present invention adopts a drawing die with adjustable opening width to replace the lower anvil for final fire forging, combined with the titanium alloy forging process, which jointly avoids shear cracking during titanium alloy drawing and improves the production efficiency and quality of titanium alloy forging billets.

[0007] The present invention controls the temperature of the final fire forging to be 20°C~40°C below the phase transformation point. At this time, the titanium alloy is in a two-phase region, the proportion of the β phase is relatively high (usually above 60%), and the β phase has a body-centered cubic structure, multiple slip systems, and excellent plastic deformation ability, which is conducive to performing large deformation upsetting operations, reducing deformation resistance and reducing the risk of cracking; at the same time, although the existing α phase (close-packed hexagonal structure) has slightly poor plasticity, it can effectively hinder the growth of β grains. The evenly distributed α phase particles are nailed to the β grain boundaries like "nails", preventing the β grains from rapid coarsening during high-temperature deformation and heat preservation.

[0008] The above-mentioned method for preventing shear cracking during the forging and drawing process of titanium alloy is characterized in that b1 in step 1 is not greater than 2.5 times a1.

[0009] The present invention controls the height and width of the forging blank to prevent excessive deformation from size b1 to size b2 during deformation in the drawing die due to excessive height of the forging blank, thereby causing the material to be drawn too long and difficult to draw.

[0010] The above-mentioned method for preventing shear cracking during the forging and drawing process of titanium alloy is characterized in that the titanium alloy ingot is heated to 150°C to 250°C above the phase transition point and kept warm in step 1.

[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), wherein t is the holding time in min; 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 2 includes a base with a groove, a movable baffle embedded in the groove, and an adjustable baffle arranged at the top of the base, a movable column is arranged in the groove, a spring is arranged on the outer sleeve of the movable column, and 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 a plurality of through holes are opened on the adjustable baffle, a first hole corresponding to the through holes is provided on the base, and a fixing rod is inserted into the through hole and the first hole.

[0014] The above-mentioned method for preventing shear cracking during the forging and drawing process of titanium alloy is characterized in that the forging pressure of the final fire forging in step 2 is not less than 1.25 times the drawing deformation force of the final fire forging, and the drawing deformation force is calculated according to the following formula: ; ; Wherein, P is the tensile deformation force, in N; is the deformation condition coefficient, which is 1 if the upper anvil is a flat anvil and 1.25 if the upper anvil is a profile anvil; m is the coefficient; is the tensile strength of the forging blank at the deformation temperature, in MPa; A is the width of the forging blank, in mm; L is the contact length between the upper anvil and the forging blank, in mm; f is the friction coefficient, which is 0.5; h is the height to which the forging blank is pressed down each time, in mm.

[0015] Since the design forging pressure of existing forging equipment far exceeds the forging pressure required for the forged material, the present invention controls the forging pressure required for deformation to be higher than that of traditional forging methods, and controls the ratio of forging pressure to drawing deformation force, thereby ensuring that sufficient deformation is achieved when b1 is not greater than 2.5 times a1. The forging machine and the amount of reduction are estimated through the above formula to determine whether drawing of the forging blank can be achieved.

[0016] Compared with the prior art, the present invention has the following advantages: 1. The present invention adjusts the forging process and uses a drawing die to replace the lower anvil in conventional forging drawing for final fire forging, thereby avoiding shear deformation during the forging drawing process that causes cracking of the forging blank, thereby reducing production efficiency and causing uneven deformation, thereby improving the production efficiency and quality of titanium alloy forgings.

[0017] 2. The present invention has unique advantages for alloys with poor forging plasticity. By setting the stress state of the forging blank to two-way compressive stress and one-way tensile stress, which is different from the conventional one-way compressive stress and two-way tensile stress state, it can effectively achieve the deformation of materials that are difficult to deform and easy to crack, prevent the forging blank from shear deformation and cracking during the forging process, and improve the yield rate.

[0018] 3. The present invention improves the forging pressure of the titanium alloy during the forging and drawing process to improve the equipment utilization rate, achieves sufficient deformation of the titanium alloy through large deformation, improves the uniformity of the titanium alloy forging blank structure, and refines the forging blank structure.

[0019] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of the drawing die of the present invention.

[0021] Figure 2 Schematic diagram of the internal structure of the drawing die of the present invention.

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

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

[0024] Figure 5 This is the metallographic structure diagram of the forging prepared in Example 1 at 1 / 3 of the length from the head.

[0025] Figure 6 This is the metallographic structure diagram of the forging prepared in Example 1 at 2 / 3 of the length from the head.

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

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

[0028] Figure 9 This is a real picture of the forging and stretching in comparative example 1.

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

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

[0031] Figure 12 This is the metallographic structure diagram of the forging prepared in Example 3 at 1 / 2 the length from the head.

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

[0033] Description of reference numerals: 1—base; 1-1—slot; 1-2—movable column; 1-3—first hole; 2—movable baffle; 2-1—second hole; 3—adjustable baffle; 3-1—through hole; 4—fixing rod. DETAILED DESCRIPTION

[0034] Example 1 This embodiment uses a TC4 titanium alloy ingot with a size of Φ160mm×300mm, and the phase transition temperature of the TC4 titanium alloy ingot is 995°C, and includes the following steps: Step 1: heating the TC4 titanium alloy ingot to 1145° C. and holding for 120 min, and performing the first fire forging to obtain a forging blank with a size of 90 mm × 150 mm × 447 mm; the first fire forging process is as follows: upsetting from Φ160 mm × 300 mm to Φ226 mm × 150 mm, drawing to 150 mm × 150 mm × 268 mm, upsetting to 200 mm × 200 mm × 150 mm, drawing to 150 mm × 150 mm × 268 mm, upsetting to 200 mm × 200 mm × 150 mm, and drawing to 90 mm × 150 mm × 447 mm; Step 2: Heat the forging blank obtained in step 1 to 955℃ and keep it for 80min. Figure 1 and Figure 2 The opening width k of the drawing die shown is adjusted to 95 mm. The forging blank is loaded into the drawing die along the length direction and subjected to slow compression deformation to obtain a forging with dimensions of 95 mm × 93 mm × 686 mm. When the forging blank is heated to 955°C, the required drawing deformation force is calculated to be no less than 713 tons. A forging press with a forging force of 1250 T is used for the slow compression deformation. The specific process of loading the forging blank into the drawing die is as follows: the adjustable baffle 3 is moved so that the opening width k is adjusted to 95 mm, at which time the plurality of through holes 3-1 of the adjustable baffle 3 correspond to the plurality of 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 inserted into the groove 1-1 of the base 1, and then the forging blank is placed between the adjustable baffle 3 and the movable baffle 2 along the length direction, and the movable baffle 2 and the forging blank are pressed downward by the upper anvil to slowly deform the forging blank; 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 provided at the bottom end of the movable baffle 2; when the upper anvil is pressed down, 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 blank is always restricted by the adjustable baffle 3 and the movable baffle 2.

[0035] The actual picture of the forging prepared in this embodiment is as follows Figure 3 As shown, the macroscopic surface of the forging is smooth without crack defects, no shear deformation cracking, uniform deformation and no uneven deformation locations are found.

[0036] The forging obtained in this embodiment was sampled at the head, 1 / 3 of the length from the head, 2 / 3 of the length from the head, and the tail, and the metallographic structure was observed. Figures 4 to 7 As shown in the figure, the typical structure after forging in the two-phase region is a dual-state structure, which is composed of equiaxed primary α phase + β transformation matrix (fine lamellar α + residual β). The rod structure is uniform, without continuously distributed grain boundary structure, and no microcrack defects are found.

[0037] Example 2 This embodiment uses a Ti5553 titanium alloy ingot made by powder metallurgy with a size of Φ120mm×300mm. The phase transition temperature of the Ti5553 titanium alloy ingot is 980°C. The following steps are included: Step 1: heating the Ti5553 titanium alloy ingot to 1230° C. and holding for 85 min, and performing the first fire forging to obtain a first forging blank with a size of 60 mm × 90 mm × 628 mm; the size changes during the first fire forging process are: from Φ90 mm × 300 mm to Φ140 mm × 220 mm during upsetting, and then stretched to 80 mm × 80 mm × 528 mm; the upsetting is 110 mm × 110 mm × 279 mm, and then stretched to 80 mm × 80 mm × 528 mm; the upsetting is 110 mm × 110 mm × 279 mm, and then stretched to 60 mm × 90 mm × 628 mm; Step 2: Heat the first forging blank obtained in step 1 to 960℃ and keep it for 80min. Figure 1 and Figure 2 The opening width k of the drawing die shown is adjusted to 65 mm. The first forging blank is loaded into the drawing die along its length and subjected to slow compression deformation to obtain a forging having dimensions of 65 mm × 63 mm × 828 mm. When the forging blank is heated to 960°C, the required drawing deformation force is calculated to be no less than 415 tons. A forging press with a forging force of 630 T is selected for the slow compression deformation. The specific process of loading the forging blank into the drawing die is as follows: the adjustable baffle 3 is moved so that the opening width k is adjusted to 95 mm, at which time the plurality of through holes 3-1 of the adjustable baffle 3 correspond to the plurality of 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 inserted into the groove 1-1 of the base 1, and then the forging blank is placed between the adjustable baffle 3 and the movable baffle 2 along the length direction, and the movable baffle 2 and the forging blank are pressed downward by the upper anvil to slowly deform the forging blank; 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 provided at the bottom end of the movable baffle 2; when the upper anvil is pressed down, 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 blank is always restricted by the adjustable baffle 3 and the movable baffle 2.

[0038] The actual picture of the forging prepared in this embodiment is as follows Figure 8 As shown, the macroscopic surface of the forging is smooth without crack defects, no shear deformation cracking, uniform deformation and no uneven deformation locations are found.

[0039] Comparative Example 1 The difference between this comparative example and Example 2 is that in step 2, the first forging blank is heated to 960°C and kept warm for 80 minutes. Figure 9 The conventional shear-drawing forging method shown, i.e., drawing with a 90° turn on a flat anvil for final fire forging, obtains a forging with a size of 65 mm × 63 mm × 828 mm.

[0040] The actual picture of the forging prepared in this comparative example is as follows Figure 10 As shown, compared with the forging prepared in Example 2, there are obvious cracks on the surface of the forging. This shows 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 a size of Φ160mm×300mm, and the phase transition temperature of the Ti150 titanium alloy ingot is 1050°C, and includes the following steps: Step 1: heating the Ti150 titanium alloy ingot to 1250° C. and holding for 120 min, and performing the first fire forging to obtain a forging blank with a size of 90 mm × 150 mm × 447 mm; the first fire forging process is as follows: upsetting from Φ160 mm × 300 mm to Φ226 mm × 150 mm, drawing to 150 mm × 150 mm × 268 mm, upsetting to 200 mm × 200 mm × 150 mm, drawing to 150 mm × 150 mm × 268 mm, upsetting to 200 mm × 200 mm × 150 mm, and drawing to 90 mm × 150 mm × 447 mm; Step 2: Heat the forging blank obtained in step 1 to 1020℃ and keep it warm for 80min. Figure 1 and Figure 2 The opening width k of the drawing die shown is adjusted to 95 mm. The forging blank is loaded into the drawing die along the length direction and subjected to slow compression deformation to obtain a forging with dimensions of 95 mm × 93 mm × 686 mm. When the forging blank is heated to 1020°C, the required drawing deformation force is calculated to be no less than 67 tons. A forging press with a forging force of 630 T is selected for the slow compression deformation. The specific process of loading the forging blank into the drawing die is as follows: the adjustable baffle 3 is moved so that the opening width k is adjusted to 95 mm, at which time the plurality of through holes 3-1 of the adjustable baffle 3 correspond to the plurality of 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, and the adjustable baffle 3 is fixed in the horizontal direction; the movable baffle 2 is inserted into the groove 1-1 of the base 1, and then the forging blank is placed between the adjustable baffle 3 and the movable baffle 2 along the length direction, and the movable baffle 2 and the forging blank are pressed downward by the upper anvil to slowly deform the forging blank; 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 provided at the bottom end of the movable baffle 2; when the upper anvil is pressed down, 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 blank is always restricted by the adjustable baffle 3 and the movable baffle 2.

[0042] The head, 1 / 2 and tail of the forging obtained in this embodiment were sampled and the metallographic structure was observed. Figures 11 to 13 As shown in the figure, after forging in the two-phase region, the typical structure is a dual-state structure, which is composed of equiaxed primary α phase + β transformation matrix. The rod structure is uniform, there is no continuously distributed grain boundary structure, and no microcrack defects are found.

[0043] Example 4 The difference between this embodiment and embodiment 3 is that in step 2, the opening width k of the drawing die is adjusted to 98 mm, and the upper anvil is used to perform impact deformation on the forging blank.

[0044] The macroscopic surface of the forging prepared in this embodiment is smooth and free of crack defects, no shear deformation or cracking, and the deformation is uniform with no uneven deformation locations found.

[0045] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural transformation made to the above embodiment based on the technical essence of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preventing shear cracking during forging and drawing of titanium alloy, characterized in that: The method comprises the following steps: Step 1: heating a titanium alloy ingot having an aspect ratio of not more than 2.5 to a temperature above the phase transition point and holding the temperature, and performing a first forging to obtain a forging blank having 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, and the units of a1, b1, and l1 are all mm; Step 2: Heat the forging blank obtained in step 1 to 20°C~40°C below the phase transformation point and keep it warm, and perform final fire forging to obtain a forging with dimensions of a2×b2×l2, and a2=a1+(4mm~8mm), wherein a2 is the width of the forging, b2 is the height of the forging, l2 is the length of the forging, and the units of a2, b2, and l2 are all mm; the method for the final fire forging is: adjust the opening width k of the drawing die to a2, load the forging blank into the drawing die along the length direction, and perform slow pressing or impact deformation through the upper anvil.

2. The method for preventing shear cracking during forging and drawing of titanium alloy according to claim 1, characterized in that: In step 1, b1 is not greater than 2.5 times a1.

3. The method for preventing shear cracking during forging and drawing of titanium alloy according to claim 1, characterized in that: The titanium alloy ingot in step 1 is heated to 150° C. to 250° C. above the phase transition point and kept warm.

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

5. The method for preventing shear cracking during forging and drawing of titanium alloy according to claim 1, characterized in that: The drawing die in step 2 comprises a base (1) having a groove (1-1), a movable baffle (2) embedded in the groove (1-1), and an adjustable baffle (3) arranged at the top of the base (1); a movable column (1-2) is arranged in the groove (1-1), a spring is provided on the outer sleeve of the movable column (1-2), and a second hole (2-1) matching the movable column (1-2) is opened at the bottom end of the movable baffle (2).

6. The method for preventing shear cracking during forging and drawing of titanium alloy according to claim 5, characterized in that: The adjustable baffle (3) is provided with a plurality of through holes (3-1), the base (1) is provided with first holes (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 holes (1-3).

7. The method for preventing shear cracking during forging and drawing of titanium alloy according to claim 1, characterized in that: The forging pressure of the final fire forging in step 2 is not less than 1.25 times the drawing deformation force of the final fire forging, and the drawing deformation force is calculated according to the following formula: ； ； Among them, P is the pulling deformation force, in N; is the deformation condition coefficient, which is 1 if the upper anvil is a flat anvil and 1.25 if the upper anvil is a profile anvil; m is the coefficient; is the tensile strength of the forging blank at the deformation temperature, in MPa; A is the width of the forging blank, in mm; L is the contact length between the upper anvil and the forging blank, in mm; f is the friction coefficient, which is 0.5; h is the height to which the forging blank is pressed down each time, in mm.

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