Preparation method of Ti35 titanium alloy strip

Abstract

The invention discloses a preparation method of a Ti35 titanium alloy strip, which comprises the following steps of: 1, heating a Ti35 titanium alloy plate blank to be below a phase transformation point, carrying out multi-heating-number hot rolling, annealing, and then, carrying out air cooling to obtain a hot-rolled plate blank; secondly, after shot blasting, acid pickling and surface coping are conducted on the hot-rolled plate blank, first cold rolling and vacuum annealing are conducted, and a cold-rolled blank is obtained; thirdly, the cold-rolled blank is subjected to second cold rolling, and a titanium alloy strip coiled material is obtained; and fourthly, the titanium alloy strip coiled material is subjected to recrystallization annealing, and the high-plasticity titanium alloy strip is obtained. According to the method, the preparation technology of multi-heating-number hot rolling, multi-heating-number cold rolling and recrystallization annealing is adopted, the synchronism and uniformity of flowing of metal on the surface and in the titanium alloy material can be guaranteed, then grain distribution and size of the Ti35 titanium alloy strip are uniform, strength and plasticity are improved at the same time, the preparation and use requirements of the wound gasket are met, and the service life of the wound gasket is prolonged. The method is suitable for the technical field of titanium alloy material processing.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy material processing, and in particular relates to a method for preparing a Ti35 titanium alloy strip. Background Art

[0002] The spiral wound gasket has the ability to self-regulate the thermal cycle and vibration of pressure vessel equipment and pipelines due to its excellent resilience, and is suitable for occasions with uneven loads and periodic changes in the bonding force with temperature and pressure; the spiral wound gasket is a static seal at the flange connection of valves, pumps, heat exchangers, towers, manholes, hand holes, and is widely used in the fields of petrochemicals, machinery, electricity, metallurgy, shipbuilding, medicine, atomic energy, and aerospace. The Ti-Ta alloy with 6% Ta added is an excellent new material for nuclear spent fuel reprocessing equipment. It has the characteristics of resistance to nitric acid corrosion, low density, high specific strength, and excellent process performance, and can be used to prepare spiral wound gaskets.

[0003] However, the presence of Ta in Ti35 titanium alloy makes the alloy structure and properties very sensitive to process factors. The actual process execution, processing control and product heat treatment have a great influence on the final product performance and quality.

[0004] Therefore, there is an urgent need to develop Ti35 alloy strips that can meet the strength and plasticity requirements of wound gaskets for spent fuel reprocessing. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies in the above-mentioned prior art and provide a method for preparing a Ti35 titanium alloy strip. The preparation method adopts a preparation process of multiple hot rolling + multiple cold rolling + recrystallization annealing, which can ensure the synchronization and uniformity of the metal flow on the surface and inside of the titanium alloy material, thereby ensuring the uniformity of the grain distribution and size of the Ti35 titanium alloy strip, taking into account both strength and plasticity while improving, meeting the preparation and use requirements of the winding pad, and solving the problem that the Ti35 alloy strip in the prior art cannot meet the strength and plasticity indicators of the winding pad.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing a Ti35 titanium alloy strip, characterized in that the method comprises the following steps: Step 1: heating the Ti35 titanium alloy slab to below the phase transition point, performing multiple hot rolling, annealing, and air cooling to obtain a hot-rolled slab; Step 2: Shot blasting, pickling, and surface grinding are performed on the hot-rolled slab obtained in step 1, and first cold rolling and vacuum annealing are performed in sequence to obtain a cold-rolled billet; Step 3, performing a second cold rolling on the cold-rolled billet obtained in step 2 to obtain a titanium alloy strip coil; Step 4: Perform recrystallization annealing on the titanium alloy strip coil obtained in step 3 to obtain a high-plasticity titanium alloy strip.

[0007] The invention fully removes the oxide film and defects on the surface of the hot-rolled slab by shot blasting, pickling and surface grinding, thereby reducing stress concentration.

[0008] The above-mentioned method for preparing a Ti35 titanium alloy strip is characterized in that the mass percentage of Ta element in the Ti35 titanium alloy slab described in step 1 is 5.5%~6.5%.

[0009] The above-mentioned method for preparing a Ti35 titanium alloy strip is characterized in that the multi-fire hot rolling system in step 1 is: heating to 10°C to 70°C below the phase transition point and then rolling; the phase transition point is the temperature point where the α phase transforms to the β phase, and the unit is °C; the insulation time t1 is calculated by the following formula: ; Wherein, t1 is the insulation time, in min; a is 1, in min / mm; H is the thickness of the Ti35 titanium alloy slab described in step 1, in mm.

[0010] The present invention controls the temperature and the holding time according to the thickness of the hot-rolled slab, so that the slab can be fully heated, the machinability of the slab is improved, and the rolling resistance is reduced.

[0011] The above-mentioned method for preparing a Ti35 titanium alloy strip is characterized in that the annealing temperature in step one is 680°C~720°C.

[0012] The present invention controls the annealing temperature to be 680° C. to 720° C., thereby eliminating the work hardening of the titanium alloy during the rolling process, reducing the rolling resistance, and facilitating subsequent rolling.

[0013] The above-mentioned method for preparing a Ti35 titanium alloy strip is characterized in that the first cold rolling in step 2 is carried out using a reversible cold rolling mill, and the first cold rolling system is: multiple cold rolling treatments with a cumulative deformation of no more than 60% are performed, and the temperature is raised to 680°C~720°C between two cold rolling treatments for intermediate vacuum annealing treatment; the deformation amount of each pass of the first cold rolling is 2%~8%.

[0014] The above-mentioned method for preparing a Ti35 titanium alloy strip is characterized in that the temperature of the vacuum annealing in step 2 is 680°C~720°C, and pickling and degreasing are performed after the vacuum annealing.

[0015] The above-mentioned method for preparing a Ti35 titanium alloy strip is characterized in that the second cold rolling in step three is carried out using a twenty-roll cold rolling mill, and the deformation amount of each pass is 10% to 20%.

[0016] The present invention adopts a reversible cold rolling mill to perform the first cold rolling on the hot-rolled slab. The reversible cold rolling mill can improve the rolling efficiency and reach the working range of the twenty-roll cold rolling mill after a small number of rolling passes, which is convenient for subsequent rolling by the twenty-roll cold rolling mill. At this time, the hot-rolled slab is thicker, and the rolling resistance can be reduced by controlling the deformation to a smaller 2%~8%, and the strength and toughness of the hot-rolled slab can be made more uniform and stable, and the internal structural defects can be reduced; then, a high-precision, high-quality titanium alloy strip coil is obtained by adopting a twenty-roll cold rolling mill for the second cold rolling. At this time, the thickness of the slab after the first cold rolling is reduced, which can meet the rolling requirements of the twenty-roll cold rolling mill, and after the deformation of each pass is increased to 10%~20%, the actual deformation resistance is still small, which can effectively shorten the rolling cycle, thereby reducing the service life of the twenty-roll cold rolling mill and reducing equipment loss.

[0017] The above-mentioned method for preparing a Ti35 titanium alloy strip is characterized in that an intermediate vacuum annealing is performed during the second cold rolling process in step 3, the temperature of the intermediate vacuum annealing is 680° C. to 720° C., and the time t2 of the intermediate vacuum annealing is calculated by the following formula: ; Among them, t2 is the time of intermediate vacuum annealing, in min; the value of b is 2, in min / mm; R is the radius of the titanium alloy strip coil described in step 3, in mm.

[0018] The above-mentioned method for preparing Ti35 titanium alloy strip is characterized in that degreasing and pre-shearing are performed before the recrystallization annealing in step 4, and the system of the recrystallization annealing is: evacuating to a vacuum degree of no more than 5.0×10 -2 Pa, then the temperature is raised to 550°C~610°C for recrystallization annealing; the holding time t3 is calculated by the following formula: ; Among them, t3 is the insulation time, the unit is min; the value of c is 2, the unit is min / mm; R is the radius of the titanium alloy strip coil described in step three, the unit is mm.

[0019] The present invention can refine the structure of the Ti35 titanium alloy strip by adopting the above-mentioned multiple annealing system, forming equiaxed α grains with a grain size of 3.04μm~5.53μm, and effectively improve the elongation after fracture to 30%; the pre-shearing refers to removing the irregular edges generated during the rolling process to achieve the target size of the finished product.

[0020] The present invention controls the vacuum annealing time and the recrystallization annealing holding time according to the thickness of the titanium alloy strip coil, so as to avoid the titanium alloy strip coil not being heated thoroughly due to too short a holding time, which affects the performance of the titanium alloy strip coil and subsequent rolling, and can also avoid the problems of overburning, thickening of the oxide layer and increased loss of the titanium alloy strip coil due to too long a holding time; at the same time, the holding time of the heat treatment can be calculated according to a formula, which improves the versatility of the preparation method, and can directly obtain the holding time by measuring the material size, avoiding the need for multiple tests for materials with different thicknesses, and facilitating large-scale promotion.

[0021] The above-mentioned method for preparing a Ti35 titanium alloy strip is characterized in that the tensile strength Rm of the super-plastic titanium alloy strip described in step 4 is not less than 350 MPa, the yield strength is not less than 250 MPa, the elongation after fracture A is not less than 28%, and the thickness of the super-plastic titanium alloy strip is 0.1 mm~0.3 mm.

[0022] Compared with the prior art, the present invention has the following advantages: 1. The present invention adopts a preparation process of multiple hot rolling + multiple cold rolling + recrystallization annealing, which can ensure the synchronization and uniformity of metal flow on the surface and inside of the titanium alloy material, thereby improving the uniformity of grain distribution and size of the Ti35 titanium alloy strip, taking into account both strength and plasticity while improving to meet the preparation and use requirements of the winding pad, thereby extending the service life of the winding pad and greatly reducing the operation and maintenance costs of the equipment; the elongation and strength of the Ti35 titanium alloy strip prepared by this method can meet the preparation requirements of the corrugated pipe, so that its application conditions are expanded; compared with a single hot rolling or cold rolling processing method, the present invention adopts a combination of multiple hot rolling and two cold rolling processes, which can greatly shorten the production process of the strip coil and obtain a Ti35 titanium alloy strip with high surface quality and dimensional accuracy.

[0023] 2. The present invention strictly designs and controls the processing parameters and annealing system of hot rolling and cold rolling of Ti35 alloy slab according to the use conditions, so as to obtain a Ti35 alloy winding pad strip coil with good strength and plasticity matching.

[0024] 3. The present invention adopts Ti35 titanium alloy slab with a Ta element mass percentage of 5.5% to 6.5% as raw material. Ta element and Ti element can form an infinite solid solution, which greatly enhances the corrosion resistance of titanium alloy in oxidizing media. Compared with traditional pure titanium materials, it can effectively improve the corrosion resistance to concentrated nitric acid.

[0025] 4. The Ti35 titanium alloy strip with a thickness of 0.1 mm to 0.3 mm prepared by the present invention has the characteristics of uniform structure, refined recrystallized grains, good matching of strength and plasticity, and excellent corrosion resistance.

[0026] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The present invention is a flow chart of the preparation method.

[0028] Figure 2 This is a corrosion rate diagram of a cold-rolled sheet blank with a thickness of 2 mm in step 2 of Example 1 of the present invention.

[0029] Figure 3 This is the metallographic structure diagram of the high-ductility titanium alloy strip obtained in Example 1 of the present invention.

[0030] Figure 4 This is the metallographic structure diagram of the high-ductility titanium alloy strip obtained in Example 2 of the present invention.

[0031] Figure 5 This is the metallographic structure diagram of the high-ductility titanium alloy strip obtained in Example 3 of the present invention. DETAILED DESCRIPTION

[0032] Example 1 like Figure 1 As shown, the method of this embodiment includes the following steps: Step 1, heating a Ti35 titanium alloy slab with a thickness of 204 mm to 860°C and keeping it for 220 minutes, then performing three-time hot rolling, then heating to 700°C for annealing, and air cooling to obtain a hot-rolled slab with a thickness of 4 mm; the mass percentage of Ta element in the Ti35 titanium alloy slab is 6.2%; the system of the three-time hot rolling is: after the first hot rolling is completed, the temperature of the Ti35 titanium alloy slab is not less than 700°C, and the total deformation is 55%~90%, after the second and third hot rolling are completed, the temperature of the Ti35 titanium alloy slab is not less than 400°C, and the total deformation is 20%~85%, and the Ti35 titanium alloy slab is reversed before the second hot rolling, and the larger size slab is divided after the first hot rolling is completed; Step 2: Shot blasting, pickling, and surface grinding are performed on the hot-rolled slab obtained in step 1, and then a six-roller reversible cold rolling mill is used for the first cold rolling to obtain a cold-rolled sheet material with a thickness of 2 mm, and the temperature is raised to 700° C. for vacuum annealing, and then pickling and degreasing are performed, and the surface quality is checked. If there are surface defects, grinding is continued, and if the plate surface grinding amount is large, pickling is continued to obtain a cold-rolled billet; the grinding is performed along the rolling direction, and the deformation amount of each pass of the first cold rolling is 2% to 8%; Step 3: The cold-rolled billet obtained in step 2 is subjected to a second cold rolling process using a twenty-roll cold rolling mill to obtain a titanium alloy strip coil having a thickness of 0.2 mm and a radius of 45 mm; the deformation amount of each pass of the second cold rolling process is 10% to 20%; Step 4: Degrease and pre-shear the titanium alloy strip obtained in step 3, and evacuate the strip to a vacuum degree of no more than 5.0×10 -2 Pa, the temperature was raised to 550°C and maintained for 90 min, recrystallization annealing was performed, and then flattening and straightening treatment was performed to obtain a strong-plastic titanium alloy strip with a thickness of 0.2 mm.

[0033] The corrosion rate test was conducted on the cold-rolled sheet blank with a thickness of 2 mm obtained in step 2 of this embodiment. The results are as follows: Figure 2 As shown in the figure, the corrosion rate of the cold-rolled sheet blanks is not higher than 0.03 mm / a, and the corrosion rate decreases with the increase of corrosion time; the corrosion rate test includes the following four corrosion conditions: (1) The temperature is 108°C and the corrosive medium is a simulated dissolving liquid (configured according to the actual service environment of the wound gasket). The HNO3 concentration in the simulated dissolving liquid is 6 mol / L, the V element concentration is 1.70 g / L, the Ce element concentration is 2.09 g / L, the Ru element concentration is 2.24 g / L, and the Cr element concentration is 0.125 g / L; (2) The temperature is 108°C and the corrosive medium is a nitric acid solution of 6 mol / L; (3) The temperature is 111°C and the corrosive medium is a nitric acid solution of 7.5 mol / L; (4) The temperature is 112°C and the corrosive medium is a nitric acid solution of 8 mol / L.

[0034] The microstructure of the high-ductility titanium alloy strip obtained in this embodiment is analyzed. Figure 3 As shown, the grains of the super-plastic titanium alloy strip are all α equiaxed crystals with a particle size range of 10μm~25μm; after testing, the tensile strength of the super-plastic titanium alloy strip is 438MPa, the yield strength is 366MPa, the elongation after fracture A is 31.0%, and the Vickers hardness HV is 182.

[0035] Example 2 The difference between this embodiment and embodiment 1 is that: the system of the first cold rolling in step 2 is: two cold rolling treatments with a cumulative deformation amount not greater than 60% are performed, and an intermediate vacuum annealing is performed between the two cold rolling treatments, the temperature of the intermediate vacuum annealing is 700°C, and the holding time of the intermediate vacuum annealing is 15 minutes; the temperature of the recrystallization annealing in step 4 is 610°C.

[0036] In this embodiment, by adding intermediate vacuum annealing during the first cold rolling process in step 2, internal stress can be reduced, so that the grains can recover.

[0037] The microstructure of the high-ductility titanium alloy strip obtained in this embodiment is analyzed. Figure 4As shown, the grains of the super-plastic titanium alloy strip are all α equiaxed crystals with a particle size range of 10μm~25μm; after testing, the tensile strength of the super-plastic titanium alloy strip is 420MPa, the yield strength is 349MPa, the elongation after fracture A is 32%, and the Vickers hardness HV is 180.5.

[0038] Example 3 The difference between this embodiment and embodiment 1 is that the annealing temperature in step one and the vacuum annealing temperature in step two are both 680°C; in step three, an intermediate vacuum annealing is performed at a temperature of 680°C for 90 minutes during the second cold rolling process, 4 rolling passes are performed per fire, the cumulative deformation per fire is not higher than 55%, and the deformation per pass is 10% to 20%; the temperature of the recrystallization annealing in step four is 600°C.

[0039] The microstructure of the high-ductility titanium alloy strip obtained in this embodiment is analyzed. Figure 5 As shown, the grains of the super-plastic titanium alloy strip are all α equiaxed crystals with a particle size range of 10μm~25μm; after testing, the tensile strength of the super-plastic titanium alloy strip is 436MPa, the yield strength is 364MPa, the elongation after fracture A is 31.5%, and the Vickers hardness HV is 183.

[0040] Example 4 The difference between this embodiment and embodiment 3 is that: in step one, a Ti35 titanium alloy slab with a thickness of 204 mm is heated to 880°C and kept for 254 min, and then hot-rolled three times, and the mass percentage of Ta element in the Ti35 titanium alloy slab is 5.5%; the annealing temperature in step one, the vacuum annealing temperature in step two, and the intermediate vacuum annealing temperature in step three are all 720°C.

[0041] After testing, the thickness of the high-plastic titanium alloy strip is 0.15mm, the tensile strength is 416MPa, the yield strength is 338MPa, the elongation after fracture A is 33.5%, and the Vickers hardness HV is 176.

[0042] Example 5 The difference between this embodiment and embodiment 4 is that in step 1, a Ti35 titanium alloy slab with a thickness of 204 mm is heated to 820° C. and kept for 214 min before being hot-rolled three times, and the mass percentage of Ta element in the Ti35 titanium alloy slab is 6.5%.

[0043] After testing, the thickness of the high-plastic titanium alloy strip is 0.3mm, the tensile strength is 420MPa, the yield strength is 342MPa, the elongation after fracture A is 30.5%, and the Vickers hardness HV is 193.

[0044] 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 still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a Ti35 titanium alloy strip, characterized in that: The method comprises the following steps: Step 1: heating the Ti35 titanium alloy slab to below the phase transition point, performing multiple hot rolling, annealing, and air cooling to obtain a hot-rolled slab; Step 2: Shot blasting, pickling, and surface grinding are performed on the hot-rolled slab obtained in step 1, followed by first cold rolling and vacuum annealing to obtain a cold-rolled billet; Step 3, performing a second cold rolling on the cold-rolled billet obtained in step 2 to obtain a titanium alloy strip coil; Step 4: Perform recrystallization annealing on the titanium alloy strip coil obtained in step 3 to obtain a high-plasticity titanium alloy strip.

2. The method for preparing a Ti35 titanium alloy strip according to claim 1, characterized in that: The mass percentage of Ta element in the Ti35 titanium alloy slab described in step 1 is 5.5% to 6.5%.

3. The method for preparing a Ti35 titanium alloy strip according to claim 1, characterized in that: The system of the multi-pass hot rolling in step 1 is: heating to 10°C to 70°C below the phase transition point and then rolling; the phase transition point is the temperature point where the α phase transforms to the β phase, and the unit is °C; the holding time t1 is calculated by the following formula: ； Wherein, t1 is the insulation time, in min; a is 1, in min / mm; H is the thickness of the Ti35 titanium alloy slab described in step 1, in mm.

4. The method for preparing a Ti35 titanium alloy strip according to claim 1, characterized in that: The annealing temperature in step 1 is 680°C to 720°C.

5. The method for preparing a Ti35 titanium alloy strip according to claim 1, characterized in that: In step 2, the first cold rolling is performed using a reversible cold rolling mill, and the first cold rolling system is as follows: multiple cold rolling treatments with a cumulative deformation of no more than 60% are performed, and the temperature is raised to 680°C~720°C for intermediate vacuum annealing between two cold rolling treatments; the deformation of each pass of the first cold rolling is 2%~8%.

6. The method for preparing a Ti35 titanium alloy strip according to claim 1, characterized in that: The temperature of the vacuum annealing in step 2 is 680°C to 720°C, and pickling and degreasing are performed after the vacuum annealing.

7. The method for preparing a Ti35 titanium alloy strip according to claim 1, characterized in that: In step 3, the second cold rolling is carried out using a twenty-roll cold rolling mill, and the deformation amount of each pass is 10% to 20%.

8. The method for preparing a Ti35 titanium alloy strip according to claim 1, characterized in that: In step 3, intermediate vacuum annealing is performed during the second cold rolling process. The temperature of the intermediate vacuum annealing is 680° C. to 720° C. The time t2 of the intermediate vacuum annealing is calculated by the following formula: ； Among them, t2 is the time of intermediate vacuum annealing, in min; the value of b is 2, in min / mm; R is the radius of the titanium alloy strip coil described in step 3, in mm.

9. The method for preparing a Ti35 titanium alloy strip according to claim 1, characterized in that: Degreasing and pre-shearing are performed before the recrystallization annealing in step 4. The system of the recrystallization annealing is: evacuating to a vacuum degree of no more than 5.0×10 -2 Pa, then the temperature is raised to 550°C~610°C for recrystallization annealing; the holding time t3 is calculated by the following formula: ； Among them, t3 is the insulation time, the unit is min; the value of c is 2, the unit is min / mm; R is the radius of the titanium alloy strip coil described in step three, the unit is mm.

10. The method for preparing a Ti35 titanium alloy strip according to claim 1, characterized in that: The tensile strength Rm of the super-plastic titanium alloy strip described in step 4 is not less than 350 MPa, the yield strength is not less than 250 MPa, the elongation after fracture A is not less than 28%, and the thickness of the super-plastic titanium alloy strip is 0.1 mm~0.3 mm.

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