A continuous casting and rolling method for preparing a super-large-caliber TA24 titanium alloy seamless pipe

Abstract

The application provides a continuous casting and rolling preparation method of a super-large caliber TA24 titanium alloy seamless pipe, which comprises the following steps: step one, preparing a hollow round ingot: proportioning prepared titanium alloy raw materials, and adopting an electron beam cold bed furnace to melt and prepare the hollow round ingot; step two, ingot heating: placing the hollow round ingot in a heating furnace for heating; step three, inclined rolling hole expanding: continuously rolling the heated hollow round ingot in an inclined rolling hole expander to obtain a mother pipe; step four, ingot secondary heating: conveying the mother pipe to a heating furnace for re-heating; and step five, rotary rolling hole expanding: conveying the heated mother pipe to a rotary rolling hole expander for rolling and forming, and heat treatment; through the continuous casting and rolling preparation method of the super-large caliber TA24 titanium alloy seamless pipe, the super-large caliber titanium alloy seamless pipe can be efficiently prepared and formed through continuous casting and rolling, the pipe production process is simplified, the pipe production cost is reduced, the pipe production cycle is shortened, the pipe production efficiency is improved, and the material utilization rate is improved.

Description

Technical Field

[0001] This invention relates to the field of metal machining, and more specifically, to a continuous casting and rolling method for preparing ultra-large diameter TA24 titanium alloy seamless tubes. Background Technology

[0002] Titanium alloys possess significant advantages such as high specific strength, excellent corrosion resistance, and non-magnetic properties. They are currently used as key materials in deep-sea equipment, significantly improving equipment safety, reliability, and service life. Based on the clear need for corrosion resistance and weight reduction, seamless titanium and titanium alloy pipes are being used in marine seawater piping systems and high-pressure air systems to replace existing copper-nickel alloys or steel materials. Currently, in-service marine seawater piping systems are using pure titanium or alloy pipes with a yield strength below 500 MPa in large quantities, with the largest diameter being only DN200. The manufacturing technology of relatively mature skew rolling piercing + cold rolling is widely adopted. However, with the increase in displacement of deep-sea equipment leading to increased pressure resistance, there is a clear demand for high-strength, ultra-large diameter, thin-walled (typically referring to an outer diameter of not less than 600 mm and a diameter-to-thickness wall thickness ≥ 35) seamless titanium alloy pipes.

[0003] The complete manufacturing process of ultra-large diameter thin-walled titanium alloy seamless tubes is described as follows: Round ingots are prepared using vacuum arc remelting, with material loss typically around 8-10% in the melting process; the round ingots are then freely forged or precision forged into billets and machined into smooth bars, with material loss typically around 15-25% in the forging process; thick-walled tube blanks are prepared using machining or skew rolling piercing methods, and then rolled into tube blanks using extrusion or forging methods, with material loss typically around 10-20% in the rolling process; finally, the tube blanks are heat-treated and machined into finished tubes, with material loss typically around 20-30% in the machining process. In general, the manufacturing process of ultra-large diameter thin-walled titanium alloy seamless tubes involves multiple steps such as ingot smelting, billet forging, tube blank rolling, and tube machining. This results in numerous manufacturing steps, high material loss, low production efficiency, and high costs, making it difficult to meet the needs of mass production for deep-sea equipment. Therefore, researching how to improve the efficiency of ultra-large diameter thin-walled titanium alloy seamless tube manufacturing and reduce manufacturing costs is an urgent problem to be solved.

[0004] Patent CN106493187A discloses a low-cost manufacturing method for large-diameter, thick-walled seamless titanium and its alloy tubes, primarily employing drawing expansion and cold rolling. However, the drawing expansion method is a cold forming method, more suitable for pure titanium or titanium alloys with strength grades below 400 MPa. Due to the low room temperature plasticity of titanium alloys, cold forming methods typically reduce the amount of deformation per pass to control cracking during the forming process. Therefore, the forming process requires multiple passes, with intermediate annealing between each pass. Therefore, there are problems such as high manufacturing costs and long processing cycles. However, the manufacturing method of large-diameter titanium and titanium alloy seamless tubes mentioned in patent CN111167862A mainly uses the skew rolling and piercing of titanium alloy forging billets to prepare tube blanks. The tube blanks are obtained by hot expansion using mandrels, and finally the finished tubes are machined. This method can solve the problem of high manufacturing costs to a certain extent. However, since the tube blanks need to be obtained by melting and forging first, and then the finished products need to be machined, the manufacturing process is discontinuous, the process is complicated, and there are problems such as long production cycles and low efficiency. Summary of the Invention

[0005] In view of this, the present invention aims to propose a continuous casting and rolling method for preparing ultra-large diameter TA24 titanium alloy seamless tubes, in order to solve the bottleneck problems in the existing seamless tube manufacturing process, such as discontinuous production process, multiple production steps, high cost, and long cycle time; thereby achieving efficient continuous casting and rolling preparation of ultra-large diameter titanium alloy seamless tubes, simplifying the tube production process, reducing the tube production cost, shortening the tube production cycle, improving the tube production efficiency, and increasing the utilization rate of materials.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] This invention relates to a continuous casting and rolling method for preparing ultra-large diameter TA24 titanium alloy seamless tubes, the method comprising the following steps:

[0008] Step 1: Preparation of hollow circular ingots: The raw materials of the prepared titanium alloy are proportioned, and hollow circular ingots are prepared by single melting in an electron beam cold hearth furnace.

[0009] Step 2, Ingot Heating: Place the hollow round ingot in a resistance heating furnace for initial heating;

[0010] Step 3, skew rolling expansion: The heated hollow round ingot is placed into a skew rolling expansion mill and subjected to continuous rolling deformation in at least one pass to obtain the mother tube;

[0011] Step 4, Secondary heating of ingots: The mother tube is transferred to a walking beam reheating furnace for heating;

[0012] Step 5, Rotary Rolling and Expanding: The heated mother tube is transferred to a rotary rolling and expanding mill for rolling and forming, and then subjected to heat treatment.

[0013] Furthermore, in step one, the outer diameter of the hollow round ingot prepared by a single melting process ranges from φ400mm to 610mm, the wall thickness ranges from φ50mm to 100mm, and the length ranges from 1500mm to 12000mm.

[0014] Furthermore, in step two, the temperature of placing the hollow round ingot in the resistance heating furnace needs to be controlled within the range of 30℃ to 50℃ above the α+β / α phase transformation point, and the heating time is 5h to 11h.

[0015] Furthermore, in step three, after the hollow round ingot is rolled by the skew rolling mill, the rolling deformation of the hollow round ingot ranges from 30% to 80%, and the final rolling temperature is ≥200℃ below the α+β / α phase transformation point.

[0016] Furthermore, in step four, the heating temperature of the mother tube in the walking beam reheating furnace is controlled within the range of 100℃ to 200℃ below the α+β / α phase transition point, and the heating is maintained for 3h to 6h.

[0017] Furthermore, step five includes:

[0018] Step S51: Spin rolling expansion: The heated mother tube is transferred to a spin rolling expansion mill for rolling and forming to obtain a finished tube that meets the surface quality and dimensional requirements;

[0019] Step S52: Annealing heat treatment to obtain medium-high strength TA24 titanium alloy seamless tubes.

[0020] Furthermore, the room temperature mechanical properties of medium-high strength TA24 titanium alloy seamless pipes show a tensile strength Rm≥750MPa.

[0021] Furthermore, the room temperature mechanical properties of medium-high strength TA24 titanium alloy seamless pipes show a yield strength Rp0.2 ≥ 600 MPa.

[0022] Furthermore, the room temperature mechanical properties of the medium-high strength TA24 titanium alloy seamless tubes have a break-end elongation A ≥ 13%.

[0023] Furthermore, the room temperature mechanical properties of medium-high strength TA24 titanium alloy seamless pipes include an impact energy KV2 ≥ 60 J.

[0024] Compared with existing technologies, the continuous casting and rolling method for preparing ultra-large diameter TA24 titanium alloy seamless tubes described in this invention has the following advantages:

[0025] The aforementioned preparation method enables the efficient continuous casting and rolling of ultra-large diameter titanium alloy seamless tubes. Compared with traditional processes, it eliminates multiple intermediate melting processes, multi-fire forging processes, and machining steps, effectively simplifying the tube production process, reducing production costs, shortening the production cycle, improving production efficiency, and increasing material utilization. This allows for efficient and continuous tube forming, effectively improving tube quality, enhancing dimensional accuracy, and ensuring the prepared tubes possess excellent room-temperature comprehensive mechanical properties. Attached Figure Description

[0026] The accompanying drawings, which constitute a part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0027] Figure 1 This is a schematic diagram of the metallographic structure of a φ680*15mm TA24 alloy seamless tube at 200 micrometers.

[0028] Figure 2 A schematic diagram of the metallographic structure of a φ680*15mm TA24 alloy seamless tube at 50 micrometers.

[0029] Figure 3 This is a schematic diagram of the metallographic structure of a φ760*20mm TA24 alloy seamless tube at 200 micrometers.

[0030] Figure 4 This is a schematic diagram of the metallographic structure of a φ760*20mm TA24 alloy seamless tube at 50 micrometers. Detailed Implementation

[0031] The inventive concepts of this disclosure will be described below using terminology commonly used by those skilled in the art to communicate the essence of their work to others skilled in the art. However, these inventive concepts may be embodied in many different forms and should not be construed as limited to the embodiments described herein.

[0032] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0033] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0034] In existing technologies, the preparation process of ultra-large diameter thin-walled titanium alloy seamless tubes includes multiple steps such as ingot smelting, bar forging, tube blank rolling, and tube machining. In addition, the preparation of large diameter titanium alloy seamless tubes mainly adopts drawing and expansion and cold rolling to manufacture large diameter titanium tubes, or mainly adopts titanium alloy forging billet skew rolling and piercing to prepare tube blanks, and the tube blanks are obtained by hot expansion using mandrels, and finally processed into finished tubes.

[0035] To address the bottlenecks in existing seamless tube manufacturing technologies, such as discontinuous processes, numerous production steps, high costs, and long cycles, this embodiment proposes a continuous casting and rolling method for preparing ultra-large diameter TA24 titanium alloy seamless tubes. The method includes the following steps:

[0036] Step 1: Preparation of hollow circular ingots: According to the target titanium alloy composition, the raw materials of the titanium alloy required for preparation are proportioned, and the EBCHM hollow circular ingots are prepared by single melting in an electron beam cold hearth furnace. Here, single melting means melting once, without multiple meltings. The main raw materials are composed of sponge titanium, aluminum-molybdenum alloy, sponge zirconium, and aluminum briquettes. Preferably, the proportions of each component in the raw materials are: sponge titanium 93%, aluminum-molybdenum alloy 2.77%, sponge zirconium 2.1%, and aluminum briquettes 2.13%.

[0037] Step 2, Ingot Heating: Place the large-diameter EBCHM hollow round ingot in the resistance heating furnace for initial heating, and keep the resistance heating furnace at the set heating temperature and the set heating time.

[0038] Step 3, skew rolling expansion: The heated EBCHM hollow round ingot is placed in a skew rolling expansion mill and subjected to continuous rolling deformation at least once to obtain a mother tube that meets the dimensional requirements. The mother tube that meets the dimensional requirements means that the rolled mother tube needs to meet the set requirements for the amount of rolling deformation, and the temperature at the end of the rolling process needs to be maintained within 200°C greater than or equal to the α+β / α phase transformation point.

[0039] Step 4, Secondary heating of ingots: The mother tube is quickly conveyed to the walking beam reheating furnace via roller conveyor for heating, and the heating temperature and heating time of the walking beam reheating furnace are maintained.

[0040] Step 5, Spin Rolling and Expanding: The heated mother tube is transferred to a spin rolling and expanding mill for rolling and forming, and then subjected to heat treatment;

[0041] In this embodiment, the heating principle of the resistance heating furnace is the same as that of the walking beam reheating furnace.

[0042] This process first utilizes an electron beam cold hearth furnace to prepare EBCHM hollow round ingots, which are then directly placed in a resistance heating furnace for uniform heating. Next, a skew rolling expansion process is used to obtain a mother tube that meets surface quality and dimensional requirements. Finally, the mother tube undergoes secondary heating and is expanded by rotary rolling to obtain the finished tube of the target specifications. This achieves a highly efficient, short-process manufacturing of ultra-large diameter thin-walled TA24 alloy seamless tubes from round ingots to seamless tubes. Furthermore, it enables efficient continuous casting and rolling of ultra-large diameter titanium alloy seamless tubes. Compared to traditional processes, this eliminates multiple intermediate melting processes, multi-forging processes, and machining steps, simplifying the tube production process, reducing production costs, shortening the production cycle, improving production efficiency, and increasing material utilization.

[0043] In step one, the outer diameter of the hollow round ingot prepared by a single melting process ranges from φ400mm to 610mm, the wall thickness ranges from φ50mm to 100mm, and the length ranges from 1500mm to 12000mm.

[0044] By molding and melting into hollow round ingots in one step, the process of seamless pipe manufacturing is effectively simplified, the continuity of pipe manufacturing is improved, the production cycle of pipes is reduced, and the production efficiency of pipes is increased.

[0045] In step two, the temperature of the hollow round ingot placed in the resistance heating furnace needs to be controlled within the range of 30℃ to 50℃ above the α+β / α phase transformation point, and the heating time is 5h to 11h.

[0046] In step three, after the hollow round ingot is rolled by the skew rolling mill, the rolling deformation of the hollow round ingot ranges from 30% to 80%, and the final rolling temperature is ≥200℃ below the α+β / α phase transformation point.

[0047] In step four, the heating temperature of the mother tube in the walking beam reheating furnace is controlled within the range of 100℃ to 200℃ below the α+β / α phase transformation point, and the heating is maintained for 3h to 6h. In this embodiment, the α+β / α phase transformation point refers to the phase transformation point when α+β→α is transformed. Controlling the heating temperature of the mother tube within the range of 100℃ to 200℃ below the α+β / α phase transformation point helps the mother tube to be fully heated and reduces the impact of excessively high or low temperatures on the spin-rolling expansion of the mother tube.

[0048] By reheating the mother tube in a walking beam furnace, the dimensional accuracy of the prepared tube is effectively improved, and the prepared tube has good comprehensive mechanical properties at room temperature.

[0049] Step five includes:

[0050] Step S51: Spin rolling expansion: The heated mother tube is transferred to a spin rolling expansion mill for rolling and forming to obtain a finished tube that meets the surface quality and dimensional requirements;

[0051] Step S52: Annealing heat treatment to obtain medium-high strength TA24 titanium alloy seamless tubes.

[0052] Among them, the room temperature mechanical properties of medium-high strength TA24 titanium alloy seamless pipes include tensile strength Rm≥750MPa; yield strength Rp0.2≥600MPa; elongation at break A≥13%; and impact energy KV2≥60J.

[0053] By using a rotary rolling mill in conjunction with the traditional drawing and expansion process, the low material utilization rate can be effectively avoided, thus improving the utilization rate of materials used in the tube manufacturing process and reducing production costs. Furthermore, by directly using an eccentric rolling expansion process to obtain the mother tube from an EBCHM hollow round ingot, followed by a second heating and rotary rolling expansion, the finished tube of the target specification is obtained. This eliminates the need for multiple forging processes and final machining of the tube blank, enabling efficient and short-process manufacturing of ultra-large diameter thin-walled TA24 alloy seamless tubes from round ingots. The finished tubes not only have high dimensional accuracy but also excellent room-temperature comprehensive mechanical properties: tensile strength Rm≥750MPa, yield strength Rp0.2≥600MPa, elongation at break A≥13%, and impact energy KV2≥60J. Therefore, this manufacturing method provides a new option for ultra-large diameter thin-walled titanium alloy seamless tubes and has broad application prospects.

[0054] Example 1:

[0055] Step 1: Using sponge titanium and master alloy as raw materials, a TA24 alloy hollow round ingot with a diameter of φ400mm (outer diameter) * φ80mm (wall thickness) * 2500mm (round ingot length) is obtained by one or more of AlMo alloy, sponge zirconium and aluminum briquettes after one continuous melting using high energy beam melting EBCHM.

[0056] Step 2: The TA24 alloy hollow round ingot is heated fully and evenly in a resistance heating furnace. The billet, i.e. the raw material, is heated with the furnace to a temperature range of 980℃~1000℃, and the holding time is ≥6h.

[0057] Step 3: After the hollow round ingot billet is directly skewed and expanded, a mother tube with a diameter of φ518mm (outer diameter) * φ40mm (wall thickness) * 5020mm (round ingot length) is obtained. The total rolling deformation of the mother tube is 50%.

[0058] Step 4: Perform secondary heating on the main tube at a temperature of 800℃~850℃ for 3 hours;

[0059] Step 5: After the mother tube is expanded by rotary rolling, an ultra-large diameter thin-walled TA24 alloy seamless tube with an outer diameter of φ680mm * φ15mm (wall thickness) * 9600mm is obtained; the tube undergoes ordinary annealing treatment, with an annealing temperature of 750℃~800℃ and a holding time of 90min. After the tube is removed from the furnace, it is air-cooled; the properties and microstructure of the finished seamless tube are shown in Table 1 and Table 2 respectively. Figure 2 .

[0060] Example 2:

[0061] Step 1: Using sponge titanium and master alloy as raw materials, a hollow round ingot of TA24 alloy with a diameter of φ600mm (outer diameter) * φ100mm (wall thickness) * 2500mm (round ingot length) is obtained by one continuous melting of EBCHM using high energy beam melting. In this embodiment, the master alloy includes any one or more of AlMo alloy, sponge zirconium and aluminum briquettes.

[0062] Step 2: The TA24 alloy hollow round ingot is heated fully and evenly in a resistance heating furnace. The billet, i.e. the raw material, is heated with the furnace to a temperature range of 980-1000℃ and held for ≥6 hours.

[0063] Step 3: After the hollow round ingot billet is directly skewed and expanded, a mother tube with a diameter of φ630mm (outer diameter) * φ45mm (wall thickness) * 9970mm (round ingot length) is obtained. The total rolling deformation of the mother tube is 70%.

[0064] Step 4: Perform secondary heating on the main tube at a temperature of 800℃~850℃ for 3 hours;

[0065] Step 5: After the mother tube is expanded by rotary rolling, an ultra-large diameter thin-walled TA24 alloy seamless tube with an outer diameter of φ762mm * φ20mm (wall thickness) * 17600mm (circular ingot length) is obtained. The tube undergoes ordinary annealing treatment, with an annealing temperature of 750℃~800℃ and a holding time of 90min. After the tube is removed from the furnace, it is air-cooled. The properties and microstructure of the finished seamless tube are shown in Table 1 and Table 2, respectively. Figure 2 .

[0066] Seamless TA24 titanium alloy tubes of different specifications prepared by the method described in this embodiment were compared with the technical indicators in the national military standard "GJB.9579-2018 Specification for Seamless Titanium and Titanium Alloy Tubes for Ships". Assuming the tube grade is TA24 titanium alloy, the performance of the seamless tubes prepared in this embodiment compared with the design indicators is shown in Table 1, based on improvements in yield strength, tensile strength, percentage elongation at break, and impact energy simulation calculations.

[0067] Table 1. Mechanical property results of TA24 alloy seamless tubing from the examples.

[0068]

[0069] As can be seen from Examples 1 and 2, combined with Table 1 and the accompanying drawings, the seamless pipes prepared by this method can meet the characteristics of ultra-large diameter thin-walled seamless pipes, and have good elongation at break, as well as greater impact resistance. Furthermore, the tensile strength and yield strength are higher than the design specifications. In addition, it can be seen that the larger the diameter, the greater the impact resistance of the seamless pipes prepared in this example, and the percentage of elongation at break will also be significantly improved.

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for manufacturing a seamless pipe of super large caliber TA24 titanium alloy by continuous casting and rolling, characterized in that, The method includes the following steps: Step 1: Preparation of hollow circular ingots: The raw materials of the prepared titanium alloy are proportioned, and hollow circular ingots are prepared by single melting in an electron beam cold hearth furnace. Step 2, Ingot Heating: Place the hollow round ingot in a resistance heating furnace for initial heating; Step 3, skew rolling expansion: The heated hollow round ingot is placed into a skew rolling expansion mill and subjected to continuous rolling deformation in at least one pass to obtain the mother tube; Step 4, Secondary heating of ingots: The mother tube is transferred to a walking beam reheating furnace for heating; Step 5, Spin Rolling and Expanding: The heated mother tube is transferred to a spin rolling and expanding mill for rolling and forming, and then subjected to heat treatment; In step four, the heating temperature of the mother tube in the walking beam reheating furnace is controlled within the range of 100℃~200℃ below the α+β / α phase transition point, and the heating is maintained for 3h~6h. Step five includes: Step S51: Spin rolling expansion: The heated mother tube is transferred to a spin rolling expansion mill for rolling and forming to obtain a finished tube that meets the surface quality and dimensional requirements; Step S52: Annealing heat treatment to obtain medium-high strength TA24 titanium alloy seamless tubes; The room temperature mechanical properties of medium-high strength TA24 titanium alloy seamless tubes have a tensile strength Rm≥750MPa; The room temperature mechanical properties of medium-high strength TA24 titanium alloy seamless tubes include a yield strength Rp0.2 ≥ 600 MPa. The room temperature mechanical properties of high-strength TA24 titanium alloy seamless tubes include an elongation at break (A) ≥ 13%. The room temperature mechanical properties of medium-high strength TA24 titanium alloy seamless pipes include an impact energy KV2≥60J.

2. A continuous casting and rolling process for producing a seamless pipe of super- heavy gauge TA24 titanium alloy as claimed in claim 1, wherein, In step one, the outer diameter of the hollow round ingot prepared by a single melting process ranges from φ400mm to 610mm, the wall thickness ranges from φ50mm to 100mm, and the length ranges from 1500mm to 12000mm.

3. A continuous casting and rolling process for producing a super large diameter TA24 titanium alloy seamless pipe as claimed in claim 1, wherein, In step two, the temperature of placing the hollow round ingot in the resistance heating furnace needs to be controlled within the range of 30℃~50℃ above the α+β / α phase transformation point, and the heating time is 5h~11h.

4. A continuous casting and rolling process for producing a super large diameter TA24 titanium alloy seamless pipe as claimed in claim 1, wherein, In step three, after the hollow round ingot is rolled by the skew rolling mill, the rolling deformation of the hollow round ingot ranges from 30% to 80%, and the final rolling temperature is ≥ 200℃ below the α+β / α phase transformation point.

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