A method for continuous annealing and scale removal of gas-protected cold-rolled titanium strip TA1

Abstract

The present application belongs to the technical field of titanium material processing, and particularly relates to a method for continuous annealing and scale removal of cold-rolled titanium TA1 strip without gas protection, comprising the following steps: degreasing-continuous annealing-pickling; continuous annealing: controlling the pressure of the annealing furnace to be 2-5 Pa, and continuously annealing the TA1 cold hard coil with a thickness of 0.3-2.8 mm in an air atmosphere with an oxygen content of not more than 5%; pickling: removing the surface scale of the titanium TA1 strip after continuous annealing by using a Na2SO4 electrolysis+HF / HNO3 mixed acid pickling composite process. According to the technical scheme, the continuous annealing production of the TA1 plate strip is completed in the air atmosphere under the conditions of micro-positive pressure control, an oxygen content of not more than 5% and a process speed of 20-63 m / min, and since there is no protective gas consumption, the energy consumption is reduced by more than 20% compared with the traditional process, so that the production efficiency is further improved and the production cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of titanium material processing technology, specifically relating to a method for continuous annealing and oxide scale removal of cold-rolled titanium strip TA1 without gas protection. Background Technology

[0002] Industrial pure titanium is widely used in chemical, aerospace, and medical fields due to its excellent corrosion resistance, high specific strength, and biocompatibility. Cold-rolled titanium strip requires annealing to eliminate work hardening and restore plasticity. Traditional titanium strip annealing processes typically require a vacuum or inert gas atmosphere to prevent high-temperature oxidation and hydrogen embrittlement. However, annealing equipment with a protective atmosphere requires significant investment and has high operating costs. Furthermore, existing annealing processes are relatively slow, significantly impacting production efficiency and thus limiting the reduction of titanium strip production costs and its large-scale application. Therefore, there is an urgent need to develop a method for continuous annealing and oxide scale removal of cold-rolled titanium strip that can be performed in an air atmosphere without gas protection, ensuring product quality while significantly reducing production costs.

[0003] CN108165822B discloses a method for preparing low-strength, easily formable TA2 cold-rolled titanium strip for welded pipes, comprising the following steps: raw material preparation, cold rolling, degreasing, continuous annealing, pickling, leveling, and obtaining the finished TA2 cold-rolled titanium strip for welded pipes after degreasing and sampling. The continuous annealing in this method needs to be carried out under argon protection, with an annealing temperature of 600~750℃ and an annealing holding time of 1~5 min. The titanium strip after continuous annealing is pickled with a mixed acid solution and then dried. The mixed acid solution is a mixture of hydrofluoric acid, nitric acid, and water, wherein the mass concentration of hydrofluoric acid is 1.5~3%, the mass concentration of nitric acid is 12~20%, and the remainder is water. This technical solution requires the preparation of TA2 cold-rolled titanium strip coils under an argon atmosphere.

[0004] CN114410900A discloses a continuous stress-relief annealing process for cold-rolled titanium strip. The cold-rolled titanium strip is TA1 titanium strip with a thickness of 0.3-0.8 mm. The process includes the following steps: preheating in an annealing furnace, feeding, cleaning, multi-zone synergistic stress-relief annealing, cooling, and winding. This process uses cold-rolling rollers for correction between annealing zones, thereby improving the hot straightening effect and improving the stress distribution within the material. An argon atmosphere is used. After cleaning, the cold-rolled titanium strip sequentially passes through the first, second, third, and fourth annealing zones in a continuous annealing furnace (the first annealing zone has an annealing temperature of 450-510℃ and a recrystallization holding time T of 5-8 min; the second...). The annealing temperature in the first annealing zone is 610–650℃, and the recrystallization holding time T is 3–6 min; the annealing temperature in the second annealing zone is 720–780℃, and the recrystallization holding time T is 4–8 min; the annealing temperature in the third annealing zone is 590–620℃, and the recrystallization holding time T is 3–6 min, with an annealing speed of 1.8–3.2 m / min. The cold-rolled titanium strip is then cooled to below 400℃ by argon purging (after argon purging, it undergoes ultrasonic treatment for 6–12 min using an ultrasonic impact device, with an ultrasonic vibration frequency of 8000–15000 Hz), followed by air purging to cool the cold-rolled titanium coil to below 80℃, and then rewound into a coil using a coiler. This technical solution requires the preparation of TA1 cold-rolled titanium strip coils under an argon atmosphere.

[0005] CN119530690A discloses a continuous annealing process for TA4 cold-rolled titanium strip coils, including the following steps: S1, surface degreasing: degreasing the TA4 cold-rolled coils to remove surface oil; S2, continuous annealing of the coils: a protective gas is introduced into a continuous annealing furnace, and the temperature is continuously raised to 520°C. At 650℃, the degreased TA4 titanium strip is wound into the furnace for continuous annealing. A winding machine continuously feeds the titanium strip at a set speed and tension. S3, Strip Cooling: The titanium strip is cooled in the continuous furnace cooling section, and the winding machine winds the strip. This process, involving surface degreasing, continuous annealing, and strip cooling, produces TA4 titanium strip coils and foldable screen mobile phone display back panels with stable mechanical properties, meeting usage standards. The tensile strength can be controlled between 650-750 MPa, and the yield strength can be controlled within 500 MPa. 650MPa, elongation A 50mm ≥16%, this technical solution requires the preparation of TA4 cold-rolled titanium strip coils in the presence of a protective gas.

[0006] CN119433400A discloses a continuous annealing process for cold-rolled titanium strip coils for deep drawing, comprising the following steps: S1: Preparation stage, degreasing and cleaning the titanium strip coil; S2: Heating the continuous annealing furnace to the required temperature, purging the furnace with high-purity argon gas and maintaining positive pressure inside; S3: The pretreated titanium strip is drawn into the continuous annealing furnace by a guide belt, passing through the preheating section, heating section, and cooling section at a specified speed, with the annealing temperature between 720 and 810°C; S4: Unloading and coiling. This technical solution uses a tension control device within the annealing furnace to suspend the titanium strip coil inside, reducing contact with the furnace wall and minimizing adhesion and pitting defects. Simultaneously, a first guide rail parallel to the furnace wall ensures stable movement of the titanium strip coil under the guidance of a correction device. An ultrasonic generator and vibration transmission device transmit ultrasonic vibration energy to the surface and interior of the titanium strip coil, promoting microstructural reorganization, reducing internal defects, and improving the material's deep-drawing capability. The ultrasonic vibration frequency and intensity are adjusted according to the material of the titanium strip coil and the annealing requirements. This method still requires annealing under argon protection. Summary of the Invention

[0007] To address the problems of existing technologies, such as the need for a protective atmosphere during titanium strip annealing, difficulty in removing oxide scale, high production costs, and low production efficiency, this invention provides a method for continuous annealing and oxide scale removal of cold-rolled titanium strip TA1 without gas protection. This technical solution employs a pickling process after continuous annealing using Na2SO4 electrolysis + mixed acid pickling (HNO3 + HF) to remove oxide scale, achieving high-quality annealing of titanium strip TA1 and subsequent oxide scale removal in an air atmosphere, thus obtaining mechanical properties and surface quality that meet user requirements.

[0008] To address the above problems, this invention provides a method for continuous annealing and oxide scale removal of cold-rolled titanium strip TA1 without gas protection, comprising the following steps: degreasing - continuous annealing - pickling;

[0009] Continuous annealing: The annealing furnace pressure is controlled at 2~5Pa, and TA1 cold-rolled coils with a thickness of 0.3~2.8mm are continuously annealed in an air atmosphere with an oxygen content of no more than 5%. Pickling: The oxide scale on the surface of the TA1 titanium strip after continuous annealing is removed by a composite process of Na2SO4 electrolysis + HF / HNO3 mixed acid pickling.

[0010] Based on the above technical solution, the TA1 cold-rolled coil is degreased after welding. The welding process specifically involves mechanically connecting the cold-rolled titanium strip TA1 to other steel grades, and using narrow lap welding for TA1 of the same grade.

[0011] Based on the above technical solution, the degreasing specifically involves using a NaOH solution with a concentration of 20~30g / L as the degreasing liquid to degrease the welded cold-rolled titanium strip TA1, with the degreasing liquid temperature being 60~80℃ and the electrical conductivity of the rinsing section being 10~50ms / cm.

[0012] Based on the above technical solution, the continuous annealing includes a radiation preheating section, a heating section and a heat preservation section, an air cooling section, and a water cooling section; Radiant preheating section: preheating from room temperature to 200-230℃ in 23-72 seconds; Heating and holding sections: Heating from 200-230℃ to annealing temperature of 830-870℃ for 35-110s, and then holding for 23-71s; Air-cooled section: Air-cooled temperature ≤230℃; Water-cooled section: outlet temperature < 80℃.

[0013] Based on the above technical solution, the continuous annealing process uses a speed of 20-63 m / min.

[0014] Based on the above technical solution, the pickling includes electrolytic treatment and mixed acid pickling, wherein the electrolytic treatment specifically involves: operating at 60~85℃ with a current of 5000~9000A and using a concentration of 1.0~1.2g / cm³. 3 The cold-rolled titanium strip TA1 after continuous annealing was electrolyzed with Na2SO4 solution for 42–133 seconds (to remove most of the surface oxide scale), and then pickled with mixed acid.

[0015] Based on the above technical solution, the mixed acid pickling includes a mixed acid stage I and a mixed acid stage II; Mixed acid stage I: A mixed acid solution of 100~150g / L HNO3 and 10~30g / L HF is used for a single pickling treatment at 40~60℃ for 17~53s. Mixed acid stage II: A mixed acid solution of 110~160g / L HNO3 and 15~35g / L HF is used for a second acid washing treatment at 40~60℃ for 17~53s. The metal ion concentration in the mixed acid I and mixed acid II sections is ≤25g / L.

[0016] Beneficial effects (1) The technical solution disclosed in this invention is a continuous annealing process for industrial pure titanium TA1 strip without gas protection, and uses Na2SO4 electrolysis + HF / HNO3 mixed acid pickling process to remove the surface oxide scale of industrial pure titanium TA1 strip after continuous annealing. This technical solution completes the continuous annealing production of TA1 strip in an air atmosphere under micro-positive pressure control and oxygen content not greater than 5%. Since there is no protective gas consumption, the energy consumption is reduced by more than 20% compared with the traditional process, thereby reducing the production cost.

[0017] (2) The technical solution disclosed in this invention can achieve a process speed of 20 to 63 m / min depending on the thickness, which breaks through the existing process speed of up to 20 m / min for continuous annealing in vacuum or protective atmosphere, thereby improving production efficiency.

[0018] (3) The mechanical properties and hydrogen content of the product obtained by the technical solution disclosed in this invention fully meet the standard requirements of users. The mechanical properties are: yield strength 140~310MPa, tensile strength ≥240MPa, elongation ≥30%; hydrogen content <120ppm. Detailed Implementation

[0019] To make the objectives and technical solutions of this invention clearer, the following embodiments are provided for further explanation. However, the scope of protection of this invention is not limited to these embodiments; the embodiments are merely for illustrative purposes. Those skilled in the art should understand that any changes or equivalent substitutions that do not depart from the concept of this invention are included within the scope of protection of this invention.

[0020] Unless otherwise specified, all reagents and raw materials used in this invention are obtained through purchase.

[0021] Examples 1-3 The processing of industrial pure titanium TA1 cold-rolled coils (0.3~2.8mm) of different thicknesses includes the following steps: Step 1, Degreasing: Degrease industrial pure titanium TA1 cold-rolled coils of different thicknesses using a sodium hydroxide solution with a concentration of 10~30g / L at 60~80℃ (the purpose of degreasing is to remove the rolling oil on the surface of the TA1 titanium strip after cold rolling). Then, rinse the degreased industrial pure titanium TA1 with rinsing water with a conductivity of 10~30ms / cm at 60~80℃. The specific degreasing and rinsing parameters are shown in Table 1.

[0022] Step 2, Continuous Annealing: Under an annealing furnace pressure of 2~5Pa, TA1 cold-rolled coils of different thicknesses are continuously annealed in an air atmosphere with an oxygen content of no more than 5%. The process speed is 20~63m / min. The continuous annealing includes a radiation preheating section, a heating section, a holding section, an air cooling section, and a water cooling section. Specifically, the radiation preheating section is: preheating from room temperature for 23~72s to 200~230℃. The heating and holding sections are: heating from 200~230℃ for 35~110s to the annealing temperature of 830~870℃ and holding for 23~71s. The air cooling temperature of the air cooling section is ≤230℃, and the outlet temperature of the water cooling section is <80℃. Specific continuous annealing parameters are shown in Table 2.

[0023] Step 3, Pickling: The surface oxide scale after TA1 annealing is removed using a Na2SO4 electrolysis + HF / HNO3 mixed acid pickling process. The specific electrolysis treatment is as follows: at 60~85℃ with a current of 5000~9000A, using a pickling solution with a concentration of 1.0~1.2 g / cm³. 3 The continuously annealed cold-rolled titanium strip TA1 was electrolyzed with Na2SO4 solution for 42–133 s (to remove most of the surface oxide scale), and then subjected to mixed acid pickling. The mixed acid pickling (twice) specifically involved: pickling the electrolyzed cold-rolled titanium strip TA1 with a mixture of 100–150 g / L HNO3 and 10–30 g / L HF at 40–60 °C for 17–53 s, and then pickling again at 40–60 °C with a mixture of 110–160 g / L HNO3 and 15–35 g / L HF for 17–53 s. The metal ion concentration in the mixed acid section was ≤25 g / L. The specific pickling parameters are shown in Table 3. Cold-rolled annealed products of different thicknesses were obtained, and the product indicators are shown in Table 4.

[0024] Table 1. Parameters related to degreasing and rinsing

[0025] Table 2 Parameters related to continuous annealing

[0026] Table 3 Pickling-related parameters

[0027] Table 4 Mechanical properties (transverse) and hydrogen content of cold-rolled products

[0028] The cold-rolled TA1 titanium strip coils prepared through Examples 1-3 have stable mechanical properties, fully meet the standard requirements of users, have good surface quality, and have a hydrogen content of <120ppm.

[0029] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for continuous annealing and oxide scale removal of cold-rolled titanium strip TA1 without gas protection, characterized in that, The steps include: degreasing, continuous annealing, and pickling. Continuous annealing: The annealing furnace pressure is controlled at 2~5Pa, and TA1 cold-rolled coils with a thickness of 0.3~2.8mm are continuously annealed in an air atmosphere with an oxygen content of no more than 5%. Pickling: The oxide scale on the surface of the TA1 titanium strip after continuous annealing is removed by a composite process of Na2SO4 electrolysis + HF / HNO3 mixed acid pickling. The continuous annealing includes a radiation preheating section, a heating section and a heat preservation section, an air cooling section, and a water cooling section; Radiant preheating section: preheating from room temperature to 200-230℃ in 23-72 seconds; Heating and holding sections: Heating from 200-230℃ for 35-110s to annealing temperature of 830-870℃ and holding for 23-71s; Air-cooled section: Air-cooled temperature ≤230℃; Water-cooled section: outlet temperature < 80℃; The continuous annealing process uses a speed of 20–63 m / min.

2. The method according to claim 1, characterized in that, The degreasing process specifically involves using a 20-30 g / L NaOH solution as the degreasing liquid to degrease the welded cold-rolled titanium strip TA1. The temperature of the degreasing liquid is 60-80°C, and the conductivity of the rinsing section is 10-50 ms / cm.

3. The method according to claim 1, characterized in that, The pickling process includes electrolytic treatment and mixed acid pickling. Electrolytic treatment: at 60~85℃ with a current of 5000~9000A, using a concentration of 1.0~1.2g / cm³. 3 The cold-rolled titanium strip TA1 after continuous annealing was electrolyzed with Na2SO4 solution for 42–133 s, and then pickled with mixed acid.

4. The method according to claim 3, characterized in that, The mixed acid pickling includes a mixed acid stage I and a mixed acid stage II; Mixed acid stage I: A mixed acid solution of 100~150g / L HNO3 and 10~30g / L HF is used for a single pickling treatment at 40~60℃ for 17~53s. Mixed acid stage II: A mixed acid solution of 110~160g / L HNO3 and 15~35g / L HF is used for a second acid washing treatment at 40~60℃ for 17~53s.

5. The method according to claim 4, characterized in that, The metal ion concentration in the mixed acid I and mixed acid II sections is ≤25g / L.

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