Method for eliminating surface color difference of cold-rolled titanium coil

Abstract

The invention discloses a method for eliminating surface chromatic aberration of a cold-rolled titanium coil, which comprises the following steps of: S1, at a rolling inlet, spraying a rolling lubricant to the surfaces of a roller and a strip through a partitioned cooling and lubricating system; s2, a fine grinding working roller is selected for rolling through a micro-tension system; s3, an asynchronous rolling mode is adopted for multi-pass rolling, and when 40%-50% of the total machining rate is achieved, the strip is turned over by 180 degrees once and then continues to be rolled; s4, the rolled titanium coil is subjected to intermediate annealing or finished product annealing after being subjected to oil removal; and S5, recrystallization bright continuous annealing is carried out under high-purity argon. According to the method, the rolling technology, the heat treatment system and the lubricating conditions are cooperatively regulated and controlled, so that the strip shape precision, the mechanical property and the surface quality are integrally and cooperatively improved, the cold-rolled titanium coiled strip with extremely high comprehensive quality can be stably produced, and the requirements of the high-precision fields such as aerospace and medical treatment are met.

Description

Technical Field

[0001] This invention relates to the field of precision rolling technology for titanium metal, and in particular to a method for eliminating color differences on the surface of cold-rolled titanium coils. Background Technology

[0002] Titanium, due to its excellent corrosion resistance, biocompatibility, and moderate strength, is widely used in chemical, medical, aerospace, and high-end consumer goods industries. High-precision cold-rolled titanium strip is a key material for manufacturing precision medical devices and high-end electronic product components. Multi-roll mills, with their strong rigidity and precise shape control capabilities, are core equipment for producing such products. During the cold rolling process, titanium strip often exhibits alternating light and dark stripes along the rolling direction, resulting in color differences. While this color difference has a relatively small impact on the material's mechanical properties, it severely damages the product's appearance consistency and surface quality, failing to meet the stringent surface aesthetic requirements of high-end applications. At its root, this color difference is a manifestation of the material's uneven microstructure on the surface in terms of macroscopic optical properties, and its main causes include: Crystallographic orientation (texture) inhomogeneity: Titanium has an HCP structure, and its plastic deformation exhibits strong anisotropy. During rolling, grains in different regions experience varying stress states (compressive stress, shear stress), resulting in differences in the slip system initiation sequence and grain rotation behavior. During cold rolling deformation, due to the uneven distribution of factors such as deformation, friction, and temperature, grains tend to move along specific crystal orientations (e.g., ...). <0001> Preferred orientation (i.e., texture) in the <10-10> direction. Grains with different orientations have different oxide film thicknesses (affected by the atomic density and surface energy of the crystal plane) and reflectivity to light, resulting in slight differences in the thickness of the oxide film formed subsequently, which in turn present different colors under illumination.

[0003] Uneven surface deformation and lubrication failure: In conventional rolling, the uneven distribution of friction coefficients between the rolls and the titanium strip surface leads to inconsistent metal flow and shear deformation. Poorly lubricated areas generate greater shear strain and deformation heat, exacerbating texture strengthening and surface roughness changes in these areas, becoming the origin points of color difference streaks.

[0004] Special characteristics of multi-roll mills: Although multi-roll mills have strong shape control capabilities, their roll system is complex. Improper setting of process parameters can exacerbate the unevenness of surface texture due to uneven deformation of multiple contact arc areas.

[0005] Existing technologies often employ subsequent polishing or acid pickling to address color differences, but these methods only provide temporary relief and cannot solve the root cause. Furthermore, they alter thickness dimensions, increase costs, and pollute the environment. Therefore, it is essential to precisely control deformation and lubrication during the rolling process to suppress the textural inhomogeneity that leads to color differences at its source.

[0006] In view of this, improvements should be made to the existing technology. Summary of the Invention

[0007] The main objective of this invention is to provide a method for eliminating color differences on the surface of cold-rolled titanium coils. By synergistically controlling the rolling process, heat treatment regime, and lubrication conditions, the method achieves an integrated and synergistic improvement in sheet shape accuracy, mechanical properties, and surface quality. This method can stably produce cold-rolled titanium coil strips with extremely high overall quality, meeting the needs of high-precision fields such as aerospace and medical.

[0008] According to one aspect of the present invention, a method for eliminating color difference on the surface of cold-rolled titanium coils is provided, comprising the following steps: S1. At the rolling inlet, rolling lubricant is sprayed onto the rolls and strip surface through a zoned cooling and lubrication system; S2. Select precision-ground work rolls and use a micro-tension system for rolling; S3. The asynchronous rolling mode is used for multi-pass rolling. When the total processing rate reaches 40-50%, the strip is flipped 180° once and rolling continues. S4. After degreasing the rolled titanium coil, perform intermediate annealing or finished product annealing. S5. Recrystallization bright continuous annealing is carried out under high-purity argon gas.

[0009] According to one embodiment of the present invention, in step S3, the asynchronous rolling mode includes controlling the ratio of the linear speeds of the upper and lower work rolls to 1.1:1 to 1.5:1, and the linear speed of the upper work roll to be 80 to 150 m / min.

[0010] According to one embodiment of the present invention, in step S4, the annealing process is carried out in the range of 20~50°C below the recrystallization temperature of pure titanium, with a annealing temperature ≤5×10⁻⁶. -3 The furnace is held under high vacuum conditions for 10-18 hours, and then cooled with the furnace.

[0011] According to one embodiment of the present invention, in step S5, the dew point of the high-purity argon gas is ≤-60℃.

[0012] According to one embodiment of the present invention, in step S5, the annealing temperature is 650~800℃, the strip travel speed is 3~6m / min, the annealing time is 5~15min, followed by rapid cooling, which includes gas quenching.

[0013] According to one embodiment of the present invention, in step S1, the kinematic viscosity of the rolling lubricant at 40°C is in the range of 20~25 cSt, and the oil film strength is >600N.

[0014] According to one embodiment of the present invention, in step S1, rolling lubricant is sprayed onto the surface of the roll and strip at a pressure of 0.5~1.0MPa and a constant temperature of 40℃±2℃.

[0015] According to one embodiment of the present invention, in step S2, the rolling process using a micro-tension regime includes selecting a finely ground work roll with a surface roughness Ra≤0.20μm, controlling the unit tension at 10~20% of the material yield strength, and the tension ratio between the inlet and outlet is 1:(1.10~1.25).

[0016] According to one embodiment of the present invention, in step S2, the last two passes of precision rolling are performed by replacing the work rolls with new work rolls, the surface roughness of which Ra ≤ 0.08 μm.

[0017] According to one embodiment of the present invention, in step S3, the first two rolling passes are only surface oil lubrication is performed without rolling deformation, and the deformation amount of the last two rolling passes is <8%.

[0018] According to an embodiment of the present invention, a method for eliminating surface color difference of cold-rolled titanium coils is proposed. By synergistically controlling the rolling process, heat treatment regime and lubrication conditions, the integrated and synergistic improvement of plate shape accuracy, mechanical properties and surface quality can be achieved. This method can stably produce cold-rolled titanium coil strips with extremely high comprehensive quality, meeting the needs of high-precision fields such as aerospace and medical. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some implementation examples of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A process flow diagram of a method for eliminating surface color difference of cold-rolled titanium coil according to an exemplary embodiment of the present invention is shown; Figure 2 A metallographic image is shown according to an exemplary embodiment of the present invention; Figure 3 A metallographic photograph is shown according to yet another exemplary embodiment of the present invention. Detailed Implementation

[0021] The following detailed description of the embodiments is intended to exemplify the principles of the present invention, but should not be construed as limiting the scope of the invention. The present invention can be implemented in many different forms and is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0022] These embodiments are provided to make this disclosure thorough and complete, and to fully express the scope of the invention to those skilled in the art. It should be noted that, unless otherwise specifically stated, the relative arrangement of components and steps, material composition, numerical expressions, and values ​​set forth in these embodiments should be interpreted as merely exemplary and not as limiting.

[0023] It should be noted that, in the description of this invention, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicating orientation or positional relationships, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0024] It should also be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention depending on the specific circumstances. When a specific device is described as being located between a first device and a second device, an intermediary device may or may not be present between the specific device and the first or second device.

[0025] All terms used in this invention have the same meaning as understood by one of ordinary skill in the art to which this disclosure pertains, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries should be interpreted as having meanings consistent with their meanings in the context of the relevant art, and not as idealized or highly formalized, unless expressly defined herein.

[0026] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0027] This invention provides a method for eliminating color difference on the surface of cold-rolled titanium coils, comprising the following steps: S1. At the rolling inlet, rolling lubricant is sprayed onto the rolls and strip surface through a zoned cooling and lubrication system; S2. Select precision-ground work rolls and use a micro-tension system for rolling; S3. The asynchronous rolling mode is used for multi-pass rolling. When the total processing rate reaches 40-50%, the strip is flipped 180° once and rolling continues. S4. After degreasing the rolled titanium coil, perform intermediate annealing or finished product annealing. S5. Recrystallization bright continuous annealing is carried out under high-purity argon gas.

[0028] In the method for eliminating surface color difference of cold-rolled titanium coils according to an embodiment of the present invention, by synergistically controlling the rolling process, heat treatment regime and lubrication conditions, the integrated synergistic improvement of plate shape accuracy, mechanical properties and surface quality can be achieved, and cold-rolled titanium coil strips with extremely high comprehensive quality can be stably produced to meet the needs of high-precision fields such as aerospace and medical.

[0029] This invention is applicable to cold-rolled pure titanium and titanium alloy coils with a thickness range of 0.5~1.5mm.

[0030] The thickness of the rolled strip base material is 2.5~6.0mm, and the width is 1500~2200mm.

[0031] In some specific embodiments, in step S3, the asynchronous rolling mode includes controlling the ratio of the linear speeds of the upper and lower work rolls to 1.1:1 to 1.5:1, with the upper work roll linear speed being 80 to 150 m / min. This high speed difference introduces strong shear strain within the rolling deformation zone.

[0032] Multi-pass rolling is employed, with the reduction rate per pass controlled at 8-20%. When the total processing rate reaches 40-50%, the strip is flipped 180° and rolling continues. This low reduction rate process reduces deformation heat and strain gradient per pass, while the flipping rolling alters the direction of shear stress, disrupting the original preferential initiation sequence of the slip system. The introduction of strong shear strain forces grains with different orientations to undergo a more complex multi-slip process, effectively dispersing and randomizing the texture, thus avoiding the banded aggregation of a single strong texture. After rolling, surface impurities are removed through degreasing and other processes to obtain a bright surface.

[0033] Based on the above embodiments, in step S4, the annealing regime for low-temperature stress-relief annealing is within the range of 20~50℃ below the recrystallization temperature of pure titanium, i.e., 450℃~500℃, ≤5×10 -3 The furnace is held under high vacuum conditions for 10-18 hours, and then cooled with the furnace.

[0034] Without recrystallization, atomic diffusion fully relaxes the non-uniform internal stress generated during rolling, allowing the grains that have stored distortion energy due to uneven deformation to fully recover (polygonalize), thus making the distortion energy state of the entire strip coil more uniform and releasing processing stress synchronously. This lays the foundation for obtaining a uniform recrystallized structure in the future. At the same time, it avoids the formation of new orientation inhomogeneities due to recrystallization texture.

[0035] In some specific embodiments, in step S5, the dew point of high-purity argon is ≤-60℃.

[0036] Based on the above embodiments, in step S5, the annealing temperature is 650~800℃, the strip travel speed is 3~6m / min, the annealing time is 5~15min, followed by rapid cooling, which includes gas quenching.

[0037] Bright annealing completes the recrystallization process in an extremely clean and uniform environment, ensuring that all grains nucleate and grow under conditions free from oxidation and pollution, forming a uniformly sized, randomly oriented equiaxed fine-grained structure, and generating an extremely thin oxide film of uniform thickness, fundamentally eliminating optical interference differences caused by uneven oxide film thickness.

[0038] In some specific embodiments, in step S1, the kinematic viscosity of the rolling lubricant at 40°C is in the range of 20~25 cSt, and the oil film strength is >600N.

[0039] Based on the above embodiments, in step S1, the rolling lubricant is sprayed onto the surface of the rolls and strip at a pressure of 0.5~1.0 MPa and a constant temperature of 40℃±2℃. The spraying of the rolling lubricant can form a uniform, stable and tough hydrodynamic lubricating film at the roll-strip interface, minimizing the variation of the friction coefficient, ensuring a high degree of uniformity in the shear strain distribution within the deformation zone, and providing a basis for uniform grain deformation.

[0040] In some specific embodiments, step S2, employing a micro-tension rolling process, includes selecting finely ground work rolls with a surface roughness Ra ≤ 0.20 μm, controlling the unit tension at 10-20% of the material's yield strength, and setting the inlet to outlet tension ratio to 1:(1.10-1.25). The low-roughness roll surface and high-precision micro-tension, combined with the lubrication in step S1, effectively suppress localized concentrated slippage caused by uneven surface friction and additional shear stress, promoting smoother rolling. Slip and Conical Surface<c+a> Multiple slip systems, such as slip, are activated more evenly in the width direction of the strip, avoiding the formation of strong textured strips.

[0041] Based on the above embodiments, in step S2, the last two precision rolling passes involve replacing the work rolls with new ones having a surface roughness Ra ≤ 0.08 μm. Using ultra-smooth roll surfaces, the strip surface is rolled into a uniform low-roughness state (target Ra 0.2~0.4 μm), eliminating microscopic defects and obtaining a uniform silvery-white metallic luster.

[0042] Based on the above embodiments, in step S3, the first two rolling passes only perform surface oil spraying lubrication and do not perform rolling deformation, and the deformation amount of the last two rolling passes is <8%.

[0043] The present application will be further described below through specific embodiments.

[0044] Example 1 1. Using hot-rolled, annealed, and pickled 6.0mm×2200mm×L material as raw material, roll to 1.5mm×2200mm×L. Use special high-viscosity cold rolling oil (viscosity 20cSt at 40℃, PB value 650N), and maintain the oil temperature at 38℃ through a constant temperature control system, and spray in sections at a pressure of 1.0MPa.

[0045] 2. The rolling process is shown in Table 1. The longitudinal yield strength of the base material after annealing is 210 MPa, and the longitudinal yield strength after rolling 1.5 mm is 715 MPa. After rolling, the material is degreased and dried.

[0046] 3. A 1.5mm × 2200mm × L titanium coil is laid in a 5×10... - The intermediate annealing was completed by holding the furnace at 500°C for 10 hours under a high vacuum of 3Pa, followed by furnace cooling.

[0047] 4. A titanium coil measuring 1.5 mm × 2200 mm × L was continuously bright annealed at a constant rate of 3 m / min at a temperature of 800 °C for 15 min, followed by rapid cooling, specifically gas quenching at an argon dew point of -60 °C. After bright annealing, a titanium coil with a bright, clean surface and no color difference was obtained, along with a uniform equiaxed microstructure with an average grain size of 46.9 μm.

[0048] like Figure 2 The image shown is a metallographic photograph of the structure obtained in Example 1.

[0049]

[0050] Example 2 1. Using 2.5mm×1500mm×L hot-rolled, annealed, and pickled material as raw material, roll to 0.5mm×1500mm×L. Use special high-viscosity cold rolling oil (viscosity 25cSt at 40℃, PB value 750N), and maintain the oil temperature at 42℃ through a constant temperature control system, and spray in sections at a pressure of 0.5MPa.

[0051] 2. The rolling process is shown in Table 2. The longitudinal yield strength of the base material after annealing is 211 MPa, and the longitudinal yield strength after rolling 0.5 mm is 692 MPa. After rolling, the material is degreased and dried.

[0052] 3. A 0.5mm × 1500mm × L titanium coil is cut into 4.5 × 10... - The intermediate annealing was completed by holding the furnace at 450°C for 18 hours under a high vacuum of ³Pa, followed by furnace cooling.

[0053] 4. A titanium coil measuring 0.5 mm × 1500 mm × L was continuously bright annealed at a constant rate of 6 m / min at a temperature of 650 °C for 3 min, followed by rapid cooling, which was performed by gas quenching at an argon dew point of -60 °C. After bright annealing, a titanium coil with a bright, clean surface and no color difference was obtained, along with a uniform equiaxed microstructure with an average grain size of 13.0 μm.

[0054] like Figure 3 The image shown is a metallographic photograph of the structure obtained in Example 2.

[0055]

[0056] The beneficial effects of this invention are: (1) Starting from the physical nature of crystal slip and texture evolution, asynchronous rolling and path optimization are used to actively promote the initiation of multiple slip systems, effectively break and randomize the deformation texture, and fundamentally avoid the formation of strong texture bands that lead to color difference.

[0057] (2) The innovative two-step heat treatment process of low-temperature long-term recovery annealing and bright recrystallization annealing first eliminates the uneven internal stress through recovery, and then achieves uniform recrystallization in an oxidation-free environment, thus doubly ensuring the consistency of surface grain orientation and oxidation state.

[0058] (3) The method of the present invention can completely eliminate the surface stripe color difference of cold rolled titanium strip, obtain a uniform and bright silver-white surface, significantly improve the product grade and added value, and save costs without subsequent mechanical or chemical polishing.

[0059] (4) This method is applicable to the production of cold-rolled strip of industrial pure titanium (such as TA1, TA2), with low requirements for rolling mill equipment and easy to realize industrial application.

[0060] The above are exemplary embodiments disclosed in this invention. The order of the disclosed embodiments is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. However, it should be noted that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the disclosed embodiments of this invention (including the claims) is limited to these examples. Various changes and modifications can be made without departing from the scope defined by the claims. The functions, steps, and / or actions of the methods according to the disclosed embodiments described herein do not need to be performed in any particular order. Furthermore, although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular.

[0061] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of the different aspects of the invention as described above exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for eliminating color difference on the surface of cold-rolled titanium coils, characterized in that, Includes the following steps: S1. At the rolling inlet, rolling lubricant is sprayed onto the rolls and strip surface through a zoned cooling and lubrication system; S2. Select precision-ground work rolls and use a micro-tension system for rolling; S3. The asynchronous rolling mode is used for multi-pass rolling. When the total processing rate reaches 40-50%, the strip is flipped 180° once and rolling continues. S4. After degreasing the rolled titanium coil, perform intermediate annealing or finished product annealing. S5. Recrystallization bright continuous annealing is carried out under high-purity argon gas.

2. The method for eliminating color difference on the surface of cold-rolled titanium coils according to claim 1, characterized in that, In step S3, the asynchronous rolling mode includes controlling the ratio of the linear speeds of the upper and lower work rolls to 1.1:1 to 1.5:1, and the linear speed of the upper work roll to be 80 to 150 m / min.

3. The method for eliminating color difference on the surface of cold-rolled titanium coils according to claim 1, characterized in that, In step S4, the annealing process is carried out within the range of 20~50℃ below the recrystallization temperature of pure titanium, with a final temperature of ≤5×10⁻⁶. -3 The furnace is held under high vacuum conditions for 10-18 hours, and then cooled with the furnace.

4. The method for eliminating color difference on the surface of cold-rolled titanium coils according to claim 1, characterized in that, In step S5, the dew point of the high-purity argon gas is ≤-60℃.

5. The method for eliminating color difference on the surface of cold-rolled titanium coils according to claim 4, characterized in that, In step S5, the annealing temperature is 650~800℃, the strip travel speed is 3~6m / min, the annealing time is 5~15min, followed by rapid cooling, which includes gas quenching.

6. The method for eliminating color difference on the surface of cold-rolled titanium coils according to claim 1, characterized in that, In step S1, the rolling lubricant has a kinematic viscosity range of 20~25 cSt at 40°C and an oil film strength >600 N.

7. The method for eliminating color difference on the surface of cold-rolled titanium coils according to claim 1, characterized in that, In step S1, the rolling lubricant is sprayed onto the surface of the rolls and strip at a pressure of 0.5~1.0MPa and a constant temperature of 40℃±2℃.

8. The method for eliminating surface color difference of cold-rolled titanium coils according to claim 1, characterized in that, In step S2, the rolling process using a micro-tension regime includes selecting a finely ground work roll with a surface roughness Ra≤0.20μm, controlling the unit tension at 10~20% of the material's yield strength, and setting the tension ratio between the inlet and outlet to 1:(1.10~1.25).

9. The method for eliminating color difference on the surface of cold-rolled titanium coils according to claim 8, characterized in that, In step S2, the last two passes of precision rolling are performed, and new work rolls are replaced. The surface roughness of the new work rolls is Ra≤0.08μm.

10. The method for eliminating color difference on the surface of cold-rolled titanium coils according to claim 1, characterized in that, In step S3, the first two rolling passes only involve surface oil spraying for lubrication and no rolling deformation is performed. The deformation amount in the last two rolling passes is less than 8%.

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