A method for improving the surface quality of a titanium alloy seamless pipe

Abstract

The application discloses a method for improving the surface quality of a titanium alloy seamless pipe, optimizes the titanium alloy composition, adds 3-7% transition element Cu, improves the plasticity of the titanium alloy, adopts a reversing upsetting and diagonal line upsetting switching mode to obtain titanium alloy bars with uniform structure, and obtains a titanium alloy seamless pipe rough blank after machining of the bars, and a new type of glass lubricant is adopted to greatly improve the flowability of titanium alloy surface metal in the extrusion process, so that higher surface quality is obtained; main chemical components of the new type of glass lubricant include SiO2: 30-40%, NaAlO2: 20-25%, CaTiO3: 7-9%, B2O3: 7-9%, NaCl: 10-15% and MgSiO3: 8-12%. Through the above comprehensive preparation method, the surface quality of the titanium alloy seamless pipe is improved, and the mechanical properties of the seamless pipe are greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy processing, and particularly relates to a method for improving the surface quality of a titanium alloy seamless pipe. Background Art

[0002] Titanium alloy seamless pipes, combining excellent mechanical properties with corrosion resistance, have recently found widespread application in aerospace, ship power systems, heat exchangers for seawater desalination, water and oil pipelines for ships and offshore oil platforms, and pipe networks for island and reef municipal engineering projects. Existing processes for manufacturing titanium alloy seamless pipes primarily include extrusion and cross-cutting piercing-rolling. Compared to cross-cutting piercing, extrusion has been used the earliest and most mature in my country. Extrusion can produce profiles with diverse shapes and complex cross-sections, making it irreplaceable by other forming techniques. However, due to the high friction coefficient and poor fluidity of titanium alloy during extrusion, poor lubrication during hot extrusion can lead to adhesion to the extrusion die material, resulting in surface defects such as longitudinal scratches, pitting, bubbles, peeling, flash, and burrs. Commonly used lubricants include grease, glass lubricants, and metal cladding. Glass lubricants hold the greatest potential for development, but a suitable glass lubricant for industrial application remains elusive. Summary of the Invention

[0003] In order to solve the bottleneck problems existing in the above-mentioned existing technologies, the present invention changes the composition of titanium alloy to improve its own plasticity. On this basis, a new lubricant is used to improve the hot extrusion lubrication effect, so that the prepared seamless pipe has excellent mechanical properties and the surface quality of the seamless pipe is significantly improved. It can be used in important or key components such as hydraulic pipelines and fuel pipelines of aircraft.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides a method for improving the surface quality of a titanium alloy seamless tube, the method comprising the following steps:

[0005] ① Add the transition element Cu to the raw materials (such as first-grade and above titanium sponge, aluminum alloy or aluminum beans and aluminum foil, and corresponding grade metal stabilizing elements), with the mass content of Cu element being 3% to 7%, and mix the materials and press them into multiple electrode blocks. After welding the multiple electrode blocks, consumable electrodes are obtained. Adding the transition element Cu is mainly used to improve the plasticity of the alloy.

[0006] ② The consumable electrode obtained in step ① is melted 2 to 3 times in a vacuum consumable arc furnace to obtain a titanium alloy ingot.

[0007] ③ The titanium alloy ingot obtained in step ② is kept at 880℃ to 1100℃ for 4 to 5 hours, and then subjected to six fires of upsetting and rounding to form titanium alloy bars. The upsetting adopts a switching mode of xyz reversing upsetting and diagonal reversing upsetting; the xyz reversing upsetting adopts three upsetting and three drawing, and the diagonal reversing upsetting adopts four upsetting and four drawing, with a deformation of 40% to 50% per fire. After the first fire of xyz reversing upsetting, the second fire is subjected to diagonal reversing upsetting, and so on. That is, each xyz reversing upsetting is replaced by diagonal reversing upsetting, and the two upsetting modes are operated alternately. The last fire is drawn and rounded into bars. This forging method can significantly improve the structural uniformity of the forged bars, reduce Cu element segregation, and improve the subsequent extrusion pass rate and surface quality.

[0008] ④ The bar obtained in step ③ is subjected to at least two heats of fine forging. The fine forging bar is annealed at an annealing temperature of [T-(120-200)]°C for 1-2 hours, where T is the phase transition temperature in °C. After annealing and straightening, the bar is subjected to lathing and drilling to obtain a titanium alloy seamless tube rough billet.

[0009] ⑤ Heating the titanium alloy seamless tube blank obtained in step ④ to a temperature of [T-(50-80)]°C, where T is the phase transition temperature in degrees Celsius. Then, adding a small amount of water to a novel glass lubricant is applied to the inner and outer surfaces of the tube blank. The novel glass lubricant mainly comprises SiO2: 30%-40%, NaAlO2: 20%-25%, CaTiO3: 7%-9%, B2O3: 7%-9%, NaCl: 10%-15%, and MgSiO3: 8%-12%. The addition of magnesium metasilicate helps reduce the friction coefficient of the lubricant.

[0010] ⑥ The lubricated seamless tube obtained in step ⑤ is extruded using a horizontal extruder, and the resulting seamless tube is vacuum annealed and pickled at a temperature of [T-(150-400)]°C for 1-2 hours. Wherein, T is the phase transition temperature in °C.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] This invention optimizes the titanium alloy's composition, improving its plasticity. It employs a switching process between reversing and diagonal upsetting to produce titanium alloy bars with a uniform microstructure. Machining the bars yields seamless tube blanks. The use of a novel glass lubricant significantly improves the metal's fluidity during the extrusion process, resulting in superior surface quality. This comprehensive preparation method not only enhances the surface quality of titanium alloy seamless tubes, but also significantly improves their mechanical properties. DETAILED DESCRIPTION

[0013] The present invention will be further described below with reference to specific examples, but the present invention is not limited in any way. To avoid redundancy, the raw materials in the following examples are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0014] Example 1

[0015] A method for improving the surface quality of titanium alloy seamless pipes, producing TA18 titanium alloy seamless pipes with specifications of Φ48×12mm, the specific process is as follows:

[0016] ① The raw materials are mixed to press a plurality of electrode blocks, and the plurality of electrode blocks are welded to obtain a consumable electrode, and a transition element Cu is added; the mass content of the Cu element is 3%.

[0017] ② The consumable electrode obtained in step ① is melted twice in a vacuum consumable arc furnace to obtain a titanium alloy ingot; the ingot specification is Φ550mm.

[0018] ③ The titanium alloy ingot obtained in step ② is kept at 880℃ for 5h, and is subjected to 6 fire upsetting and rounding to form a titanium alloy bar (machining). The upsetting adopts the switching mode of xyz reversing upsetting and diagonal reversing upsetting; odd-numbered fire reversing upsetting (three upsetting and three drawing) → even-numbered fire diagonal upsetting (four upsetting and four drawing), and the last fire (sixth fire) upsetting forging (drawing and lengthening and rounding).

[0019] ④ The bar obtained in step ③ is subjected to no less than two rounds of fine forging. The fine forged bar (Φ150mm bar) is annealed (750℃ / 2h), and after annealing and straightening, it is polished and drilled to Φ130*Φ30mm to obtain a titanium alloy seamless pipe rough blank.

[0020] ⑤ Heat the titanium alloy seamless tube rough billet obtained in step ④ to 900° C.; then apply a glass lubricant to the inner and outer surfaces of the tube billet; the main chemical components of the new glass lubricant include SiO2: 38%, NaAlO2: 22%, CaTiO3: 8%, B2O3: 8%, NaCl: 13% and MgSiO3: 11%.

[0021] ⑥ The lubricated seamless tube obtained in step ⑤ is extruded using a horizontal extruder to obtain a Φ48×12mm seamless tube, which is then vacuum annealed and pickled; the annealing temperature is 700°C and the holding time is 2h.

[0022] The outer surface of the TA18 titanium alloy seamless tube prepared in Example 1 is smooth without any defects such as grooves, scratches and abrasions, and has a tensile strength of 800 kPa and an elongation of 24%.

[0023] Example 2

[0024] A method for improving the surface quality of titanium alloy seamless pipes, producing TA18 titanium alloy seamless pipes with specifications of Φ48×12mm, the specific process is as follows:

[0025] ① The raw materials are mixed to press a plurality of electrode blocks, and the plurality of electrode blocks are welded to obtain a consumable electrode, and a transition element Cu is added; the mass content of the Cu element is 7%.

[0026] ② The consumable electrode obtained in step ① is melted three times in a vacuum consumable arc furnace to obtain a titanium alloy ingot; the ingot specification is Φ550mm.

[0027] ③ The titanium alloy ingot obtained in step ② is kept at 1100℃ for 4h, and is subjected to 6 fire upsetting and rounding to form a titanium alloy bar (machining). The upsetting adopts the switching mode of xyz reversing upsetting and diagonal reversing upsetting; odd-numbered fire reversing upsetting (three upsetting and three drawing) → even-numbered fire diagonal upsetting (four upsetting and four drawing), and the last fire (sixth fire) upsetting forging (drawing and lengthening and rounding).

[0028] ④ The bar obtained in step ③ is subjected to no less than two rounds of fine forging. The fine forged bar (Φ150mm bar) is annealed (750℃ / 2h), and after annealing and straightening, it is polished and drilled to Φ130*Φ30mm to obtain a titanium alloy seamless pipe rough blank.

[0029] ⑤ Heat the titanium alloy seamless tube rough billet obtained in step ④ to 900°C, where T is the phase transition temperature; then apply a glass lubricant to the inner and outer surfaces of the tube billet; the main chemical components of the new glass lubricant include SiO2: 38%, NaAlO2: 25%, CaTiO3: 7%, B2O3: 8%, NaCl: 12% and MgSiO3: 10%.

[0030] ⑥ The lubricated seamless tube obtained in step ⑤ is extruded using a horizontal extruder to obtain a Φ48×12mm seamless tube, which is then vacuum annealed and pickled; the annealing temperature is 700°C and the holding time is 2h.

[0031] The outer surface of the TA18 titanium alloy seamless tube prepared in Example 2 is smooth without any defects such as grooves, scratches and abrasions, and has a tensile strength of 780 kPa and an elongation of 26%.

[0032] Anyone skilled in the art will be able to utilize the above-disclosed technical content to make many possible changes and modifications to the technical solution of the present invention, or to modify it into equivalent embodiments with equivalent changes, without departing from the scope of the technical solution of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention that do not depart from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for improving the surface quality of titanium alloy seamless pipe, characterized in that: The method comprises the following steps: ① The raw materials are mixed and pressed into a plurality of electrode blocks, and the plurality of electrode blocks are welded to obtain a consumable electrode, and a transition element Cu is added; the mass content of the Cu element is 3% to 7%; ② The consumable electrode obtained in step ① is melted 2 to 3 times in a vacuum consumable arc furnace to obtain a titanium alloy ingot; ③ The titanium alloy ingot obtained in step ② is kept at 880°C to 1100°C for 4 to 5 hours, and is subjected to 6 rounds of upsetting and rounding to form a titanium alloy bar. The upsetting adopts a switching mode of xyz reversing upsetting and diagonal reversing upsetting; The xyz reversing upsetting and drawing adopts three upsetting and three drawing, and the diagonal reversing upsetting and drawing adopts four upsetting and four drawing, and the deformation amount of each fire is 40% to 50%; The two upsetting modes are operated alternately, and each time the xyz reversing upsetting is replaced by the diagonal reversing upsetting; ④ The bar obtained in step ③ is subjected to at least two rounds of fine forging, the fine forged bar is annealed, and after annealing and straightening, it is subjected to lathing and drilling to obtain a titanium alloy seamless tube rough blank; The annealing temperature is T-(120-200)°C, and the holding time is 1-2h, where T is the phase transition point temperature; ⑤ heating the titanium alloy seamless tube blank obtained in step ④ to a temperature of T-(50-80)° C., where T is the phase transition temperature; and then applying glass lubricant to the inner and outer surfaces of the tube blank; The main chemical components of the glass lubricant include SiO2: 30% to 40%, NaAlO2: 20% to 25%, CaTiO3: 7% to 9%, B2O3: 7% to 9%, NaCl: 10% to 15% and MgSiO3: 8% to 12%; ⑥ The lubricated seamless tube obtained in step ⑤ is extruded by a horizontal extruder, and the obtained seamless tube is vacuum annealed and pickled; the annealing temperature is T-(350-500)°C, and the holding time is 1-2h.