Method for hot straightening of a cold-rolled titanium strip coil and resulting finished product

Abstract

The present application relates to the field of cold-rolled titanium strip coil straightening technology, and more particularly to a hot straightening method for cold-rolled titanium strip coil and the obtained finished product. The method comprises the following steps: after the strip head of the pre-processed cold-rolled titanium strip coil is welded with the strip tail of the upper cold-rolled titanium strip coil in the protective gas continuous annealing furnace, the cold-rolled titanium strip coil sequentially enters the preheating section, the process section and the cooling section in the protective gas continuous annealing furnace to complete the corresponding first preheating treatment, first process treatment and first cooling treatment respectively, and the annealed cold-rolled titanium strip coil is obtained; after the strip head of the annealed cold-rolled titanium strip coil is welded with the strip tail of the upper cold-rolled titanium strip coil in the protective gas continuous annealing furnace, the cold-rolled titanium strip coil sequentially enters the preheating section, the process section and the cooling section in the protective gas continuous annealing furnace to complete the corresponding second preheating treatment, second process treatment and second cooling treatment respectively, and the hot straightened cold-rolled titanium strip coil is obtained. The method can prepare the finished product cold-rolled titanium strip coil with improved strength, no residual stress and low plasticity loss.

Description

Technical Field

[0001] This invention relates to the field of cold-rolled titanium strip straightening technology, and in particular to a hot straightening method for cold-rolled titanium strip and the resulting finished product. Background Technology

[0002] Cold-rolled titanium strip coils are widely used in various fields such as energy, chemical industry, marine industry, and engineering. Cold-rolled titanium strip coils are products obtained by cold-rolling titanium strip coils followed by heat treatment. Common heat treatment methods include protective gas coil annealing (where the entire cold-rolled titanium strip coil is placed in an annealing furnace for annealing) and protective gas continuous annealing (where the cold-rolled titanium strip coil is unrolled and continuously fed into an annealing furnace for annealing). Because both of these annealing methods involve complete annealing, the cold-rolled titanium strip coil softens, resulting in a significant reduction in its strength, thus failing to meet customer requirements.

[0003] Currently, to improve the strength of cold-rolled titanium strip coils after full annealing (i.e., after heat treatment), the industry often uses cold straightening to treat the coils. This applies a slight degree of cold plastic deformation, increasing the dislocation density within the material and the resistance to dislocation movement. This increases the stress required for further deformation, thereby improving the strength of the cold-rolled titanium strip coils. Additionally, cold straightening can also straighten the cold-rolled titanium strip coils and improve their shape. However, cold straightening inevitably leads to work hardening, resulting in increased residual stress and a significant decrease in plasticity. Increased residual stress poses a risk of springback after prolonged storage, which is detrimental to subsequent processing and use. The significant decrease in plasticity weakens the material's deformability, affecting subsequent processing and use by customers.

[0004] Therefore, it is necessary to provide a hot straightening method for cold-rolled titanium strip coils and the resulting finished product to solve the problem that the cold straightening method used in the prior art causes an increase in residual stress and a significant decrease in plasticity of the cold-rolled titanium strip coils due to work hardening. Summary of the Invention

[0005] The purpose of this invention is to provide a method for hot straightening cold-rolled titanium strip coils and the resulting finished product. The specific technical solution is as follows:

[0006] In a first aspect, the present invention provides a method for hot straightening of cold-rolled titanium strip coils, comprising:

[0007] Step S1: After welding the head of the pretreated cold-rolled titanium strip coil to the tail of the previous cold-rolled titanium strip coil in the protective gas continuous annealing furnace, the cold-rolled titanium strip coil enters the preheating section, process section and cooling section of the protective gas continuous annealing furnace in sequence to complete the corresponding first preheating treatment, first process treatment and first cooling treatment, and obtain the annealed cold-rolled titanium strip coil.

[0008] In the first preheating treatment, the first process treatment, and the first cooling treatment, a first tension and a first running speed are applied to the cold-rolled titanium strip coil; the first tension is 3.0~4.0 N per square millimeter of the cross-sectional area of ​​the cold-rolled titanium strip coil; the first running speed is... m / min; the TV The value of 1 ranges from 2 to 4. TV 1 = Thickness of cold-rolled titanium strip coil × First running speed; d The value represents the thickness of the cold-rolled titanium strip coil, which is 0.3~1.0 mm; the first running speed is 2~5 m / min.

[0009] The first preheating treatment uses a preheating temperature of (400℃, 600℃) or (400℃, 1.2T). 再 ℃; T 再 The recrystallization temperature of the cold-rolled titanium strip coil;

[0010] The first process temperature used in the first process is 1.2T. 再 ~1.5T 再 ℃;

[0011] Step S2: After welding the end of the annealed cold-rolled titanium strip coil to the end of the previous cold-rolled titanium strip coil in the protective gas continuous annealing furnace, the coil is then sequentially introduced into the preheating section, process section and cooling section of the protective gas continuous annealing furnace to complete the corresponding second preheating treatment, second process treatment and second cooling treatment, so as to obtain the hot-straightened cold-rolled titanium strip coil.

[0012] In the second preheating treatment, the second processing treatment, and the second cooling treatment, a second tension and a second running speed are applied to the cold-rolled titanium strip coil; the second tension is 4.5~6.0 N per square millimeter of cross-sectional area of ​​the cold-rolled titanium strip coil; the second running speed is... m / min; the TV The value of 2 ranges from 5 to 8. TV 2 = thickness of cold-rolled titanium strip coil × second running speed; the value of the second running speed is 4~10m / min;

[0013] The second preheating temperature used in the second preheating treatment is T. 再 +10~T 再 +30℃;

[0014] The second process temperature used in the second process is T. 再 +10~T 再 +30℃.

[0015] Optionally, when the first preheating temperature is taken as the upper limit, it can be 600℃ and 1.2T. 再 The minimum value in ℃.

[0016] Optionally, the first cooling process employs a first cooling rate greater than 8°C / s.

[0017] Optionally, the second cooling process employs a second cooling rate greater than 10°C / s.

[0018] Optionally, the pretreatment includes degreasing the cold-rolled titanium strip coil.

[0019] Optionally, the hot straightening method for cold-rolled titanium strip coils further includes step S3: winding the hot-straightened cold-rolled titanium strip coils, removing them from the production line, and obtaining finished cold-rolled titanium strip coils.

[0020] Optionally, the T 再 The value range is 500~600℃.

[0021] In a second aspect, the present invention provides a finished cold-rolled titanium strip coil, which is prepared by the hot straightening method of the cold-rolled titanium strip coil.

[0022] Optionally, the flatness of the finished cold-rolled titanium strip coil after being stored for 30 days is ≤3mm.

[0023] Optionally, the thickness of the finished cold-rolled titanium strip coil is 0.3~1.0 mm.

[0024] The application of the technical solution of the present invention has at least the following beneficial effects:

[0025] The hot straightening method for cold-rolled titanium strip coils provided by this invention can produce finished cold-rolled titanium strip coils with increased strength, no residual stress, and very low plasticity loss, avoiding the risk of springback after prolonged storage. Specifically, in step S1, the cold-rolled titanium strip coil undergoes continuous annealing treatment, and appropriate temperature, tension, and running speed are controlled to allow the titanium strip coil material to undergo complete recovery annealing and recrystallization annealing processes. During recovery annealing, the high-density dislocations in localized locations caused by intense plastic deformation migrate and rearrange within the microstructure of the material, reducing the dislocation density, partially releasing lattice distortion energy, and forming subcrystalline structures that facilitate recrystallization nucleation. Macroscopically, this significantly eliminates residual stress while maintaining a essentially unchanged strength level and slightly recovering plasticity. During recrystallization annealing, new dislocation-free and distortion-free grains appear within the microstructure of the material (i.e., recrystallization). The material undergoes nucleation and growth, continuously engulfing the surrounding deformed grains, causing the deformed grains to completely disappear and the lattice distortion energy to be fully released. This results in significant softening of the material structure, a marked decrease in macroscopic material strength, and a significant increase in plasticity until complete recovery. Furthermore, in step S2, the cold-rolled titanium strip coil undergoes continuous annealing again, with appropriate temperature, tension, and running speed controlled. This allows the titanium strip coil material to undergo plastic deformation strengthening while simultaneously experiencing a certain degree of dynamic recovery. Microscopically, the plastic deformation caused by the hot straightening process leads to dislocation slippage and entanglement within the material, resulting in increased dislocation density, lattice distortion, and the generation of internal stress. While the high temperature of hot straightening causes dynamic recovery annealing to occur within the titanium strip coil material, this process allows entangled high-density dislocations to continue moving, maintaining a relatively low dislocation density. Simultaneously, lattice distortion energy is partially released, eliminating most of the internal stress. Furthermore, the relatively low temperature and fast running speed of the annealing process during hot straightening in step S2 prevent the material from undergoing recrystallization annealing and softening. Ultimately, macroscopically, this results in the titanium strip coil material exhibiting increased strength while effectively eliminating residual stress with almost no loss of plasticity. Therefore, this invention combines steps S1 and S2 to achieve two consecutive annealing processes for cold-rolled titanium strip coils. By combining appropriate temperature, tension, and belt speed control during the heating process, the cold-rolled titanium strip coil can undergo both plastic deformation strengthening and annealing stress relief processes simultaneously, resulting in a hot-straightened cold-rolled titanium strip coil. The plastic deformation strengthening process allows the cold-rolled titanium strip coil to achieve a certain strength increase without significant loss of plasticity, thus effectively reducing the degree of deformation required for subsequent cold working to improve straightness. Furthermore, stress relief produces cold-rolled titanium strip coils with almost no residual stress, avoiding the risk of springback after prolonged storage and effectively improving the performance consistency of the cold-rolled titanium strip coil over time, thereby achieving stable performance and stable use. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1:

[0028] A method for hot straightening cold-rolled titanium strip coils includes:

[0029] Step S1: After welding the head of the pretreated (i.e. degreasing) cold-rolled titanium strip coil to the tail of the previous cold-rolled titanium strip coil in the protective gas continuous annealing furnace, the cold-rolled titanium strip coil enters the preheating section, process section and cooling section of the protective gas continuous annealing furnace in sequence to complete the corresponding first preheating treatment, first process treatment and first cooling treatment, respectively, to obtain the annealed cold-rolled titanium strip coil.

[0030] In the first preheating treatment, the first process treatment, and the first cooling treatment, a first tension and a first running speed are applied to the cold-rolled titanium strip coil; the first tension is 3.0 N per square millimeter of the cross-sectional area of ​​the cold-rolled titanium strip coil; the first running speed is... m / min; the TV The value of 1 ranges from 2 to 4 (specifically, it takes the value 2). TV 1 = Thickness of cold-rolled titanium strip coil × First running speed; d The value indicates the thickness of the cold-rolled titanium strip coil, which is 0.5 mm; the first running speed is 2~5 m / min (specifically 4 m / min).

[0031] The first preheating treatment uses a preheating temperature of (400℃, 600℃) or (400℃, 1.2T). 再 ℃; T 再 The recrystallization temperature of the cold-rolled titanium strip coil is 520℃ in this embodiment; when the first preheating temperature is the upper limit, it is 600℃ and 1.2T. 再 The minimum value in ℃ is taken as 600℃;

[0032] The first process temperature used in the first process is 1.2T. 再 ~1.5T 再 ℃, which is 780℃ in this embodiment;

[0033] Step S2: After welding the end of the annealed cold-rolled titanium strip coil to the end of the previous cold-rolled titanium strip coil in the protective gas continuous annealing furnace, the coil is then sequentially introduced into the preheating section, process section and cooling section of the protective gas continuous annealing furnace to complete the corresponding second preheating treatment, second process treatment and second cooling treatment, so as to obtain the hot-straightened cold-rolled titanium strip coil.

[0034] In the second preheating treatment, the second processing treatment, and the second cooling treatment, a second tension and a second running speed are applied to the cold-rolled titanium strip coil; the second tension is 5.5 N per square millimeter of cross-sectional area of ​​the cold-rolled titanium strip coil; the second running speed is... m / min; the TV The value of 2 ranges from 5 to 8 (specifically, it is 5). TV 2 = Cold-rolled titanium strip thickness × Second running speed; The second running speed is 4~10m / min (specifically 10m / min).

[0035] The second preheating temperature used in the second preheating treatment is T. 再 +10~T 再 +30℃, which is 540℃ in this embodiment;

[0036] The second process temperature used in the second process is T. 再 +10~T 再 +30℃, which is 540℃ in this embodiment.

[0037] Step S3: The hot-straightened cold-rolled titanium strip is wound up and taken off the production line to obtain the finished cold-rolled titanium strip.

[0038] The first cooling process uses a first cooling rate greater than 8°C / s.

[0039] The second cooling process employs a second cooling rate greater than 10°C / s.

[0040] Comparative Example 1:

[0041] Unlike Example 1, step S2 is omitted. The cold-rolled titanium strip coil annealed in step S1 is taken off the production line in step S3 and then straightened using a conventional cold straightening process to obtain the finished cold-rolled titanium strip coil.

[0042] Comparative Example 2:

[0043] Unlike Example 1, step S2 is omitted, and the cold-rolled titanium strip coil annealed in step S1 is taken off the production line in step S3 to obtain the finished cold-rolled titanium strip coil.

[0044] Samples of the finished cold-rolled titanium strip coils obtained in Example 1 and Comparative Examples 1-2 were taken for longitudinal tensile strength R.m Longitudinal yield strength R p0.2 The longitudinal elongation (A50), cupping value, grain size, and flatness were tested. The test results are shown in Table 1. Among them, the longitudinal tensile strength R... m The test method is GB / T 228. Longitudinal yield strength R p0.2 The test method for longitudinal elongation (A50) is GB / T 228. The test method for cupping value is GB / T 4156. The test method for straightness is GB / T 3621.

[0045] Table 1 Test Results

[0046]

[0047] From the data in Table 1, we know that:

[0048] Compared to Example 1, Comparative Example 1 uses a process route of high-temperature low-tension annealing and cold straightening of the finished product, which can obtain a higher longitudinal yield strength R of the finished product. p0.2 While exhibiting relatively low flatness, the significant loss of plasticity leads to a decrease in cupping value and longitudinal elongation A50. Furthermore, the residual stress generated by cold straightening can cause springback in the finished product after prolonged storage, resulting in a deterioration in flatness.

[0049] Compared to Example 1, Comparative Example 2 employed a high-temperature, low-tension annealing process with no straightening of the finished product. Although the resulting product exhibited better plasticity (i.e., reduced plasticity loss and increased cupping value and longitudinal elongation A50), the lack of effective straightening resulted in a decrease in the longitudinal yield strength R of the finished product. p0.2 It is too low and the flatness is poor.

[0050] Compared to Comparative Examples 1 and 2, Example 1 employs a two-stage continuous annealing production method, consisting of high-temperature, low-tension annealing as defined in step S1 and low-temperature, high-tension hot straightening as defined in step S2. This means that the material's plasticity is restored through high-temperature annealing, and then the yield strength is increased and the straightness optimized without excessive loss of plasticity through hot straightening. The final product strength (i.e., longitudinal tensile strength R) is obtained as a result. m and longitudinal yield strength R p0.2 It is similar to Comparative Example 1, and has better plasticity, which is closer to Comparative Example 2. Furthermore, due to the almost absence of residual stress, it can maintain good flatness for a long time, such as the flatness still being 3mm after being left for 30 days.

[0051] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made using the present invention's specification under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for hot straightening cold-rolled titanium strip coils, characterized in that, include: Step S1: After welding the head of the pretreated cold-rolled titanium strip coil to the tail of the previous cold-rolled titanium strip coil in the protective gas continuous annealing furnace, the cold-rolled titanium strip coil enters the preheating section, process section and cooling section of the protective gas continuous annealing furnace in sequence to complete the corresponding first preheating treatment, first process treatment and first cooling treatment, and obtain the annealed cold-rolled titanium strip coil. In the first preheating treatment, the first process treatment, and the first cooling treatment, a first tension and a first running speed are applied to the cold-rolled titanium strip coil; the first tension is 3.0~4.0 N per square millimeter of the cross-sectional area of ​​the cold-rolled titanium strip coil; the first running speed is... m / min; the TV The value of 1 ranges from 2 to 4. TV 1 = Thickness of cold-rolled titanium strip coil × First running speed; d The value represents the thickness of the cold-rolled titanium strip coil, which is 0.3~1.0 mm; the first running speed is 2~5 m / min. The first preheating treatment uses a preheating temperature of (400℃, 600℃) or (400℃, 1.2T). 再 ℃; T 再 The recrystallization temperature of the cold-rolled titanium strip coil; The first process temperature used in the first process is 1.2T. 再 ~1.5T 再 ℃; Step S2: After welding the end of the annealed cold-rolled titanium strip coil to the end of the previous cold-rolled titanium strip coil in the protective gas continuous annealing furnace, the coil is then sequentially introduced into the preheating section, process section and cooling section of the protective gas continuous annealing furnace to complete the corresponding second preheating treatment, second process treatment and second cooling treatment, so as to obtain the hot-straightened cold-rolled titanium strip coil. In the second preheating treatment, the second processing treatment, and the second cooling treatment, a second tension and a second running speed are applied to the cold-rolled titanium strip coil; the second tension is 4.5~6.0 N per square millimeter of cross-sectional area of ​​the cold-rolled titanium strip coil; the second running speed is... m / min; the TV The value of 2 ranges from 5 to 8. TV 2 = thickness of cold-rolled titanium strip coil × second running speed; the value of the second running speed is 4~10m / min; The second preheating temperature used in the second preheating treatment is T. 再 +10~T 再 +30℃; The second process temperature used in the second process is T. 再 +10~T 再 +30℃.

2. The hot straightening method for cold-rolled titanium strip coils as described in claim 1, characterized in that, When the first preheating temperature is taken as the upper limit, 600℃ and 1.2T are used. 再 The minimum value in ℃.

3. The hot straightening method for cold-rolled titanium strip coils as described in claim 1, characterized in that, The first cooling process uses a first cooling rate greater than 8°C / s.

4. The hot straightening method for cold-rolled titanium strip coils as described in claim 1, characterized in that, The second cooling process employs a second cooling rate greater than 10°C / s.

5. The hot straightening method for cold-rolled titanium strip coils as described in claim 1, characterized in that, The pretreatment includes degreasing the cold-rolled titanium strip coil.

6. The hot straightening method for cold-rolled titanium strip coils as described in claim 1, characterized in that, It also includes step S3, which involves winding up the hot-straightened cold-rolled titanium strip and removing it from the production line to obtain the finished cold-rolled titanium strip.

7. The hot straightening method for cold-rolled titanium strip coils as described in claim 1, characterized in that, The T 再 The value range is 500~600℃.

8. A finished cold-rolled titanium strip coil, characterized in that, It is prepared by the hot straightening method of cold-rolled titanium strip coil as described in any one of claims 1 to 7.

9. The finished cold-rolled titanium strip coil as described in claim 8, characterized in that, The flatness of the finished cold-rolled titanium strip coil after being stored for 30 days is ≤3mm.

10. The finished cold-rolled titanium strip coil as described in claim 8, characterized in that, The thickness of the finished cold-rolled titanium strip coil is 0.3~1.0mm.

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