A method of producing TA6 titanium alloy bar for preventing rolling cracking

Abstract

A method for preparing TA6 titanium alloy bars to prevent rolling cracking includes the following steps: Step S1: Bar preparation: TA6 sponge titanium is smelted twice, then forged at 1130~1180℃ for three to five times at 940~1010℃ to obtain TA6 bar billets with a diameter of φ60~80; Step S2: The TA6 bar billets are heated to 980℃ and held for 60 minutes; Step S3: The TA6 bar billets are rolled in four passes: The first rolling pass yields a bar with a flat elliptical hole shape of 65~75mm wide and 30~32.5mm high; the second rolling pass yields a bar with a square hole shape of 35~36mm wide and 35~36mm high; the third rolling pass yields a bar with a flat elliptical hole shape of 50~55mm wide and 25~28mm high; the fourth rolling pass yields a black bar with a round hole shape of φ27~38mm. Compared with existing technologies, this invention uses a short-process rolling technology to prepare φ25~35mm TA6 bars with no surface cracks, which improves the rolling efficiency of alloy bars and saves production costs.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy manufacturing technology, and in particular to a method for preparing TA6 titanium alloy bars that prevent rolling cracking. Background Technology

[0002] TA6 bar stock is an α-type titanium alloy with strong resistance to hot working deformation. However, during the rolling process, longitudinally extending cracks are highly susceptible to appearing on the bar surface. The cracks are caused by the low slip system / plane of α-type titanium alloy, leading to difficulty in deformation and poor toughness. Furthermore, the faster cooling at the edges during hot working creates a mismatch between the low-temperature deformation at the edges and the high-temperature deformation in the center, resulting in longitudinally extending cracks on the alloy surface. Current industrial solutions for longitudinal cracks in TA6 alloy rolling involve increasing the turning allowance. However, this method significantly increases production costs, especially for small-diameter bars. Calculations show that for bars with a diameter of φ25~φ35mm, every 1mm increase in turning allowance on one side increases machining loss by approximately 8%, resulting in a substantial decrease in overall yield.

[0003] Existing technologies for preventing rolling cracks in TA6 titanium alloy bars are limited. Among them, patent announcement number CN104525567B, entitled "A Rolling Method for TA7 Titanium Alloy Sheets," discloses a method that involves: 1. Preparing a composite sheet and then subjecting it to a first heat treatment (1130-1150℃); 2. Separating the TA7 titanium alloy slab and then performing a first heat treatment to obtain a first semi-finished slab; 3. Cutting; 4. Performing a second heat treatment (≥950℃) on the second semi-finished slab; 5. Rolling; 6. Cutting; 7. Performing a third heat treatment (≥950℃) on the fourth semi-finished slab; 8. Performing a third heat treatment on the fourth semi-finished slab to obtain the TA7 titanium alloy sheet. This method avoids edge chipping and cracking of the rolled sheet after reversal through a three-heat rolling process, but the process is complex and involves multiple heat treatments, thus increasing production costs.

[0004] Chinese patent CN114226457B discloses a rolling method for Ti60 high-temperature titanium alloy plates. This method involves four rolling passes. The first and second passes use near-β temperature heating and consistent rolling direction, reducing surface cracking during large deformation rolling. The third pass, a reversing roll, also uses near-β temperature heating and reduces the total deformation rate. After the third pass, a cladding and stacking rolling process is employed, reducing chipping and cracking issues caused by the strong processing texture of Ti60 titanium alloy (a near-α titanium alloy) and the narrow hot working window of high-temperature titanium alloys, which are common in conventional reversing rolls. This improves the yield and production efficiency. However, this method involves multiple rolling passes and the cladding and stacking rolling process, significantly increasing process complexity and cost. Summary of the Invention

[0005] In view of this, it is necessary to provide a simple and low-cost method for preparing TA6 titanium alloy bars that prevents rolling cracks.

[0006] A method for preparing TA6 titanium alloy bars to prevent rolling cracking includes the following steps: Step S1: Billet preparation: TA6 sponge titanium is smelted twice, and then forged at 1130~1180℃ for three to five times at 940~1010℃ to obtain TA6 billets with a diameter of φ60~80. Step S2: Heat the TA6 billet to 980℃ and hold for 60 minutes; Step S3: Perform four rolling passes on the TA6 billet: the first rolling pass yields a flat oval-shaped bar with a width of 65-75mm and a height of 30-32.5mm; the second rolling pass yields a square-shaped bar with a width of 35-36mm and a height of 35-36mm; the third rolling pass yields a flat oval-shaped bar with a width of 50-55mm and a height of 25-28mm; and the fourth rolling pass yields a black bar with a round hole diameter of φ27-38mm.

[0007] In the above-mentioned method for preparing TA6 titanium alloy bars to prevent rolling cracks, preferably, in step S3, the deformation amount of the first rolling pass is 9~32%.

[0008] In the above-mentioned method for preparing TA6 titanium alloy bars to prevent rolling cracks, preferably, in step S3, the deformation amount of the second rolling pass is 15~32%.

[0009] In the above-mentioned method for preparing TA6 titanium alloy bars to prevent rolling cracks, preferably, in step S3, the deformation amount of the third rolling pass is 5~24%.

[0010] In the above-mentioned method for preparing TA6 titanium alloy bars to prevent rolling cracks, preferably, in step S3, the deformation amount of the fourth rolling pass is 13~35%.

[0011] In the above-mentioned method for preparing TA6 titanium alloy bars to prevent rolling cracks, preferably, the method further includes the following steps: Step S4: Peel and flatten the TA6 black bar stock to a finished size of φ32mm.

[0012] Beneficial Effects: Compared with existing technologies, the method for preparing TA6 titanium alloy bars to prevent rolling cracks in this invention addresses the causes of longitudinal cracks in TA6 alloy by optimizing the rolling pass. After preparing the billet, only one heat treatment is required: heating the TA6 billet to 980℃, holding for 60 minutes, and then performing four rolling passes to obtain crack-free TA6 titanium alloy bars. This short-process rolling technology produces φ25~35mm TA6 bars with no surface cracks, improving the rolling efficiency of alloy bars and saving production costs. Simultaneously, compared with other rolling passes, machining losses are reduced, and the product yield can be increased by at least 8%. The tensile strength of the TA6 bars reaches 780MPa, and the elongation after fracture reaches 20%, fully meeting the technical requirements for TA6 bars. Attached Figure Description

[0013] Figure 1 This is a process flow diagram of the method for preparing TA6 titanium alloy bars to prevent rolling cracking according to the present invention.

[0014] Figure 2 This is a diagram showing the changes in the bar shape during the rolling process of the TA6 titanium alloy bar of the present invention. Implementation

[0015] The present invention will be described in detail below with reference to specific embodiments.

[0016] A method for preparing TA6 titanium alloy bars to prevent rolling cracking includes the following steps: Step S1: Billet preparation: TA6 sponge titanium is smelted twice, and then forged at 1130~1180℃ for three to five times at 940~1010℃ to obtain TA6 billets with a diameter of φ60~80. The smelting of TA6 sponge titanium in this invention is a conventional smelting method, which will not be repeated here. After the sponge titanium is smelted into ingots, it is then subjected to billet cutting and forging to obtain TA6 bar billets.

[0017] Step S2: Heat the TA6 billet to 980℃ and hold for 60 minutes; Step S3: Perform four rolling passes on the TA6 billet: First rolling pass, to obtain a flat oval die with a width of 65~75mm and a height of 30~32.5mm → Second rolling pass, to obtain a square die with a width of 35~36mm and a height of 35~36mm → Third rolling pass, to obtain a flat oval die with a width of 50~55mm and a height of 25~28mm → Fourth rolling pass, to obtain a black bar with a diameter of φ27~38mm.

[0018] In a preferred embodiment, in step S3, the deformation amount of the first rolling pass is 9~32%.

[0019] In a preferred embodiment, in step S3, the deformation amount of the second rolling pass is 15-32%.

[0020] In a preferred embodiment, in step S3, the deformation amount of the third rolling pass is 5-24%.

[0021] In a preferred embodiment, in step S3, the deformation amount of the fourth rolling pass is 13-35%.

[0022] Black bar stock with a diameter of φ27~38mm is peeled, flattened, and polished to a diameter of 32mm to become TA6 titanium alloy bar stock.

[0023] In a preferred embodiment, in step S3, the horizontal portion of the flat elliptical hole occupies one-tenth of the major axis.

[0024] Example 1 Sponge titanium is smelted twice, then forged at 1130-1180℃ for three to five passes at 940-1010℃ to obtain TA6 billets with a diameter of φ60-80. The TA6 billets are then heated to 980℃ and held for 60 minutes. The TA6 billets are then rolled in four passes: the first pass produces a flat oval hole 65mm wide and 30mm high; the second pass produces a square hole 350mm wide and 35mm high; the third pass produces a flat oval hole 50mm wide and 25mm high; and the fourth pass produces a black-skinned bar with a diameter of 35mm. The surface of the black-skinned bar is as follows... Figure 1 As shown, no obvious cracks appeared. The black-skinned rod was then peeled, flattened, and polished to a finished thickness of 32mm. After room temperature mechanical property testing, the TA6 titanium alloy rod of this invention exhibited a tensile strength of 780MPa, an elongation of 20%, and a machining loss of 17%.

[0025] Example 2 Sponge titanium is smelted twice, then forged at 1130-1180℃ for three to five passes at 940-1010℃ to obtain TA6 billets with a diameter of 60-80 mm. The TA6 billets are then heated to 980℃ and held for 60 minutes. The TA6 billets are then rolled in six passes: the first pass produces a flat oval hole 65 mm wide and 30 mm high; the second pass produces a square hole 45 mm wide and 45 mm high; the third pass produces a flat oval hole 55 mm wide and 27 mm high; the fourth pass produces a square hole 37 mm wide and 37 mm high; the fifth pass produces a flat oval hole 50 mm wide and 25 mm high; and the sixth pass produces a black-skinned bar with a diameter of 35 mm. The surface of this black-skinned bar is as follows: Figure 2As shown, the longitudinal cracks are quite obvious. The black bar was then peeled, flattened, and ground to a finished thickness of 32mm. After room temperature mechanical property testing, the bar had a tensile strength of 789MPa, an elongation of 17%, and a machining loss of 25%, which is approximately 8% lower than the four-pass rolling yield of Example 1.

[0026] With all other processes being equal, six-pass rolling is the second-best rolling method. Other passes result in more pronounced rolling cracks or lower yields after grinding. Compared to six-pass rolling, the four-pass rolling method of this invention achieves an 8% higher yield than six-pass rolling. Machining losses are also lower.

[0027] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Those skilled in the art will understand that implementing all or part of the above-described embodiments and making equivalent changes in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A method of producing TA6 titanium alloy bar for prevention of rolling cracking, characterized by: Includes the following steps: Step S1: Billet preparation: TA6 sponge titanium is smelted twice, and then forged at 1130~1180℃ for three to five times at 940~1010℃ to obtain TA6 billets with a diameter of φ60~80mm. Step S2: Heat the TA6 billet to 980℃ and hold for 60 minutes; Step S3: Perform four rolling passes on the TA6 billet: the first rolling pass yields a flat elliptical die with a width of 65-75mm and a height of 30-32.5mm; the second rolling pass yields a square die with a width of 35-36mm and a height of 35-36mm; the third rolling pass yields a flat elliptical die with a width of 50-55mm and a height of 25-28mm; and the fourth rolling pass yields a black-skinned billet with a round die of φ27-38mm. The deformation amount of the first rolling pass is 9-32%; the deformation amount of the second rolling pass is 15-32%; the deformation amount of the third rolling pass is 5-24%; and the deformation amount of the fourth rolling pass is 13-35%.

2. The method of claim 1, wherein the TA6 titanium alloy bar is produced by the steps of: The preparation method of TA6 titanium alloy bars to prevent rolling cracks also includes the following steps: ​ Step S4: Peel and flatten the TA6 black bar stock to a finished size of φ32mm.

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