Annealing method of TA18 titanium alloy fine grain cold-rolled pipe

Abstract

The invention discloses an annealing method of a TA18 titanium alloy fine grain cold-rolled pipe. The method comprises the following steps: 1, measuring the contents of four elements of Al, V, Fe and O on a TA18 extruded pipe blank; and secondly, multi-pass cold rolling is conducted on the TA18 extruded pipe blank, the deformation rate of single-pass cold rolling is 50% or above, annealing is conducted on the TA18 extruded pipe blank obtained after each-pass cold rolling is conducted, and the TA18 titanium alloy fine grain cold-rolled pipe is obtained. According to the method, the annealing temperature is quantitatively determined through formula calculation on the basis of the TA18 pipe element content and the single-pass cold rolling deformation rate epsilon, comprehensive matching of fine grains and plasticity of the TA18 pipe is achieved, the microscopic structure of the pipe is effectively refined, the production efficiency of the TA18 titanium alloy fine grain cold-rolled pipe is improved, efficient quantitative determination of the TA18 fine grain pipe annealing system is achieved, and the production cost is reduced. The method is suitable for precise control over the mass production performance of the high-performance small-caliber TA18 titanium alloy pipe for aviation.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium alloy processing, and in particular relates to an annealing method for a TA18 titanium alloy fine-grained cold-rolled tube. Background Art

[0002] The strengthening methods of metal materials mainly include solid solution strengthening, grain refinement strengthening, deformation strengthening and precipitation strengthening. TA18 (Ti-3Al-2.5V) is a near-α-type titanium alloy with a β-phase content of less than 5%. It is impossible to achieve strength improvement through solid solution strengthening and precipitation strengthening. Therefore, the strength of conventional TA18 cold-rolled pipes is only about 650MPa. The analysis of the in-service aviation TA18 oil pipes that meet the foreign AMS 4946 standard Level I found that the average size of the α grains in the pipes does not exceed 2μm, and the pipes have the characteristics of high intragranular dislocation density and a large proportion of small-angle grain boundaries. The above results show that the in-service aviation TA18 oil pipes of Level I use an incompletely recrystallized annealing process to retain the effect of work hardening, while superimposing the effect of grain refinement strengthening, and finally obtain a 900MPa-grade TA18 titanium alloy pipe. In recent years, domestic research on import substitution of TA18 tubes for key core of aircraft has made considerable progress, but the annealing process for this product still adopts the traditional empirical trial and error mode, without much consideration of the intermediate annealing system that combines the rollability and fine-grained structure of TA18, nor has a suitable finished product annealing system been developed for 900MPa grade TA18 tubes.

[0003] The alloy that has undergone large cold deformation (ε≥50%) has the basis for strength improvement and grain crushing and refinement brought by work hardening, but its plastic deformation capacity has been basically exhausted, and it is urgently needed to anneal to improve plasticity for subsequent forming. The annealing process is composed of three stages: recovery, recrystallization and grain growth. The recovery stage can basically eliminate the internal stress of the alloy, but the microstructure and mechanical properties do not change much; recrystallization is the process of new nuclei generation and growth in the area with a high degree of intracrystalline distortion. The number and size of recrystallized grains determine the degree of grain refinement of the organization, which can greatly change the mechanical properties of the alloy. The degree of recrystallization grain refinement depends on the degree of alloy distortion, holding time, nucleation rate N and grain growth rate G: the subcrystal nucleation theory shows that the nucleation rate N is positively correlated with the degree of deformation, that is, the more complete the cold deformation and the higher the degree of distortion, the higher the activation energy of alloy recrystallization, the faster the nucleation rate increases, and the finer the grains after recrystallization; the Avrami equation shows that the nucleation rate N during isothermal recrystallization decays exponentially with time, that is, the extension of the holding time at the recrystallization temperature leads to a sharp decrease in new nuclei and coarsening of the grains; increasing the annealing temperature significantly accelerates the grain growth rate G and coarsens the grains, resulting in a significant decrease in alloy strength and a significant increase in plasticity.

[0004] It can be seen that the heat treatment goal of TA18 titanium alloy fine-grained cold-rolled pipe is to consider the influence of dynamic factors, i.e., the degree of cold deformation of the alloy and the constant temperature time in the recrystallization temperature zone on the number of nuclei, combined with the influence of thermodynamic factors, i.e., the temperature rise on the degree of grain growth, and obtain an annealing system that effectively improves the rollability of the alloy by controlling the recrystallized grain size, thereby achieving a strengthening effect of both tube deformation and fine grains. The single-pass cold rolling deformation rate of the pipe is a reflection of the degree of cold deformation of the alloy. The annealing holding time depends on the pipe specifications and furnace loading, while the annealing temperature is jointly affected by the alloy phase transition point and the degree of cold deformation. Since the phase transition point of titanium alloy is closely related to the fluctuation of the chemical composition of the alloy, the annealing system of TA18 titanium alloy pipe is essentially determined by the alloy element content, the single-pass cold rolling deformation rate and the pipe specifications.

[0005] At present, the intermediate pass and finished product annealing of domestic TA18 pipes still rely on production experience. The wide range of temperature selection leads to differences in the performance of pipe batches, and the annealing system is not comprehensively considered to quantify the influencing factors of various aspects. The invention patent CN118023300A uses 650℃~750℃ to carry out intermediate recrystallization annealing for TA18 pipes. This temperature is the conventional annealing temperature of medium-strength titanium alloys in the industry. After annealing in this temperature zone, the TA18 pipe has been completely recrystallized to form an equiaxed structure with a grain size of about 10μm or more. The invention patent CN117548520A selects an annealing temperature of (T / 2+320×ε)℃ for cold-rolled pipes with a deformation rate of more than 70% in a single pass, and obtains TA18 pipes with a strength of 690MPa. Although this method preliminarily introduces the influence of alloy phase transformation point and deformation rate on annealing temperature, it does not consider the influence of alloy elements, and cannot effectively achieve the refinement of alloy grains and the improvement of strength. The tube annealing temperature involved in step 6 of invention patent CN117358778A is 600°C to 750°C. This temperature range is wide and has poor performance orientation. The high recrystallization temperature easily forms coarse grains and cannot be used to guide the preparation of TA18 small-diameter tubes with excellent comprehensive performance for aerospace use.

[0006] In summary, at present, there is no quantitative annealing method for intermediate and finished products of TA18 titanium alloy fine-grained cold-rolled tubes above 900MPa in China. Therefore, it is urgent to abandon the traditional trial-and-error annealing experience mode and develop a computational annealing method that controls the comprehensive performance of TA18 high-performance cold-rolled tubes by multiple factors such as chemical composition and deformation degree, so as to achieve precise control of the mass production performance of high-performance small-diameter titanium alloy tubes for aviation. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide an annealing method for TA18 titanium alloy fine-grained cold-rolled pipes in view of the deficiencies of the above-mentioned prior art. The method is based on the element content of the TA18 pipe and the single-pass cold rolling deformation rate, and quantitatively determines the annealing temperature through formula calculation, thereby achieving a comprehensive match between the fine grain and plasticity of the TA18 pipe, effectively refining the microstructure of the pipe, and improving the production efficiency of the TA18 titanium alloy fine-grained cold-rolled pipes, solving the problem of high-quality TA18 cold-rolled pipe annealing relying on experience and poor performance batch stability in the prior art.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for annealing a TA18 titanium alloy fine-grained cold-rolled tube, characterized in that the method comprises the following steps:

[0009] Step 1: Determine the contents of Al, V, Fe and O in the TA18 extruded tube;

[0010] Step 2, the TA18 extruded tube is subjected to multiple cold rolling passes, and the single cold rolling deformation rate during the multiple cold rolling process is more than 50%, and the TA18 extruded tube is annealed after each cold rolling, and the annealing temperature T = 647.4 + 16.1 × Al% -9.8 × V% -11.55 × Fe% + 140 × O% -155 × ε, wherein the annealing temperature T is in ° C, Al%, V%, Fe%, O% are respectively the mass percentages of the four elements Al, V, Fe, and O in the TA18 extruded tube measured in step 1, ε is the single cold rolling deformation rate, and a TA18 titanium alloy fine-grained cold-rolled tube is obtained.

[0011] The above-mentioned annealing method for TA18 titanium alloy fine-grain cold-rolled tube is characterized in that the contents of the four elements Al, V, Fe and O in step one are determined according to GB / T 4698 "Chemical Analysis Methods for Sponge Titanium, Titanium and Titanium Alloys".

[0012] The above-mentioned annealing method of a TA18 titanium alloy fine-grained cold-rolled tube is characterized in that the number of multiple cold rolling passes in step 2 is 1 to 3 passes. The annealing heat treatment method of the present invention is suitable for short-process TA18 titanium alloy fine-grained cold-rolled tubes with fewer cold rolling passes, and avoids the reduction of the tube yield and finished product rate due to the excessive cold rolling passes.

[0013] The above-mentioned annealing method of a TA18 titanium alloy fine-grained cold-rolled tube is characterized in that the annealing system of the TA18 extruded tube after each cold rolling in step 2 is: after keeping at the annealing temperature for 1 hour, furnace cooling to below 450°C at a rate of 1.2°C±0.2°C / min. By controlling the furnace cooling rate of the annealing process, the temperature is concentrated in the initial stage of the recrystallization temperature zone, and the grain size is effectively controlled to be uniform.

[0014] The above-mentioned annealing method of TA18 titanium alloy fine-grained cold-rolled tube is characterized in that the average diameter of the planar grains of the TA18 titanium alloy fine-grained cold-rolled tube in step 2 is No more than 3μm. This grain size meets the requirements of GB / T 6394-2017 "Method for Determination of Average Grain Size of Metals".

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] 1. The present invention abandons the traditional concept of relying on production experience to formulate TA18 heat treatment process, and incorporates alloy composition, single-pass cold rolling deformation rate and holding time into the consideration range of TA18 cold-rolled pipe annealing system. Based on the element content of TA18 pipe and single-pass cold rolling deformation rate, the annealing temperature is quantitatively determined by formula calculation, which realizes the comprehensive matching of TA18 pipe fine grain and plasticity, and is suitable for TA18 titanium alloy fine grain cold-rolled pipes above 900MPa.

[0017] 2. The annealing method of the present invention realizes the efficient quantitative determination of the annealing system of TA18 fine-grained tubes. It combines the influence of heat treatment kinetic factors on the number of nuclei and the influence of thermodynamic factors on the degree of grain growth to ensure that the tube annealing process is in the early stage of recrystallization annealing and that there is sufficient nucleation and trace growth, so that the tube can be completely stress-relieved while the grain size is uniform and small, effectively refines the microstructure of the tube, and improves the production efficiency of TA18 titanium alloy fine-grained cold-rolled tubes. It is suitable for the precise control of the mass production performance of high-performance small-diameter TA18 titanium alloy tubes for aviation, and helps to promote the localization process of high-performance TA18 titanium alloy tubes in the field of aviation oil pipes.

[0018] 3. The annealing method of TA18 titanium alloy fine-grained cold-rolled tube developed by the present invention breaks the barrier between the intermediate pass and finished product annealing in conventional production, and completes the correlation and unification between the two. It is suitable for the intermediate pass annealing and finished product annealing of TA18 fine-grained tubes with a large degree of cold deformation (≥50%).

[0019] 4. The annealing method of the present invention avoids the pipe annealing experiment required for conventional production, eliminates the dependence on vacuum annealing furnaces and related special equipment, and has no restrictions on the pipe loading method, which significantly improves the universality of the annealing method of the present invention.

[0020] 5. The annealing method of the present invention effectively reduces the degreasing, pickling, vacuuming and other processes related to rolling and annealing, greatly simplifies the production process of TA18 fine-grained cold-rolled pipes, and greatly improves the production efficiency of TA18 pipes.

[0021] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the metallographic structure diagram of the TA18 titanium alloy fine-grained cold-rolled tube obtained in Example 1 of the present invention.

[0023] Figure 2 This is the metallographic structure diagram of the TA18 titanium alloy fine-grained cold-rolled tube obtained in Example 2 of the present invention.

[0024] Figure 3 This is the metallographic structure diagram of the TA18 titanium alloy fine-grained cold-rolled tube obtained in Example 3 of the present invention. DETAILED DESCRIPTION

[0025] Example 1

[0026] This embodiment includes the following steps:

[0027] Step 1: According to GB / T 4698 "Chemical Analysis Methods for Titanium Sponge, Titanium and Titanium Alloys", the contents of Al, V, Fe and O in TA18 extruded tube with an outer diameter of 24.5 mm × wall thickness of 3.9 mm were determined. The results were: Al 3.17%, V 2.68%, Fe 0.026%, O 0.034%;

[0028] Step 2, the TA18 extruded tube with the same outer diameter × wall thickness of Ф24.5mm×3.9mm as in step 1 is subjected to one cold rolling, and the single cold rolling deformation rate during one cold rolling process is 69%. According to the formula, the annealing temperature T=647.4+16.1×Al%-9.8×V%-11.55×Fe%+140×O%-155×ε, wherein Al%, V%, Fe%, and O% are respectively the mass percentages of the four elements Al, V, Fe, and O in the TA18 extruded tube measured in step 1, and ε is the single cold rolling deformation rate. The annealing temperature after each cold rolling is calculated to be 570°C. The TA18 extruded tube after each cold rolling is heated to 570°C with the furnace and kept warm for 1h for annealing, and is furnace cooled to below 450°C at a rate of 1.2°C±0.2°C / min to obtain a TA18 titanium alloy fine-grained cold-rolled tube.

[0029] Figure 1 The metallographic structure diagram of the TA18 titanium alloy fine-grained cold-rolled tube obtained in this embodiment is shown in FIG. Figure 1 It can be seen that the average diameter of the plane grains of the TA18 titanium alloy fine-grained cold-rolled tube is Not more than 3μm.

[0030] Example 2

[0031] This embodiment includes the following steps:

[0032] Step 1: According to GB / T 4698 "Chemical Analysis Methods for Titanium Sponge, Titanium and Titanium Alloys", the contents of Al, V, Fe and O in TA18 extruded tube with an outer diameter of 24.5 mm × wall thickness of 3.75 mm were determined. The results were: Al 3.31%, V 2.78%, Fe 0.20%, O 0.102%;

[0033] Step 2: The TA18 extruded tube with the same outer diameter × wall thickness of Ф24.5mm×3.75mm as in step 1 is cold rolled for 2 passes, and the first cold rolling deformation rate in the 2 cold rolling processes is 61%, and the second cold rolling deformation rate is 68%. According to the formula, the annealing temperature T=647.4+16.1×Al%-9.8×V%-11.55×Fe%+140×O%-155×ε, wherein Al%, V%, Fe%, and O% are respectively the mass percentages of the four elements Al, V, Fe, and O in the TA18 extruded tube determined in step 1. The annealing temperature after the first cold rolling is 590°C, and the annealing temperature after the second cold rolling is 580°C. Therefore, the TA18 extruded tube billet after the first cold rolling is heated to 590°C with the furnace and kept for 1h for annealing, and then cooled to below 450°C at a rate of 1.2°C / min and taken out of the furnace. The TA18 extruded tube billet after the second cold rolling is heated to 580°C with the furnace and kept for 1h for annealing, and then cooled to below 450°C at a rate of 1.2°C±0.2°C / min and taken out of the furnace to obtain TA18 titanium alloy fine-grained cold-rolled tube.

[0034] Figure 2 The metallographic structure diagram of the TA18 titanium alloy fine-grained cold-rolled tube obtained in this embodiment is shown in FIG. Figure 2 It can be seen that the average diameter of the plane grains of the TA18 titanium alloy fine-grained cold-rolled tube is Not more than 3μm.

[0035] Example 3

[0036] Step 1: According to GB / T 4698 "Chemical Analysis Methods for Titanium Sponge, Titanium and Titanium Alloys", the contents of Al, V, Fe and O in TA18 extruded tube with an outer diameter of 16 mm × wall thickness of 3 mm were determined. The results were: Al 2.98%, V 2.61%, Fe 0.16%, O 0.12%;

[0037] Step 2: Perform three cold rolling on the TA18 extruded tube with the same outer diameter × wall thickness of Ф16mm×3mm as in step 1, and the first cold rolling deformation rate during the three cold rolling processes is 70%, the second cold rolling deformation rate is 69%, and the third cold rolling deformation rate is 75%. According to the formula, annealing temperature T=647.4+16.1×Al%-9.8×V%-11.55×Fe%+140×O%-155×ε, wherein Al%, V%, Fe%, and O% are respectively the mass percentages of the four elements Al, V, Fe, and O in the TA18 extruded tube measured in step 1, and ε is the single-pass cold rolling deformation rate. The temperature after the first cold rolling is calculated. The annealing temperature is 576°C, the annealing temperature after the second cold rolling is 577°C, and the annealing temperature after the third cold rolling is 568°C. Therefore, the TA18 extruded tube billet after the first cold rolling is heated to 576°C with the furnace for insulation, and is furnace cooled to below 450°C at 1.2°C±0.2°C / min and taken out of the furnace. The TA18 extruded tube billet after the second cold rolling is heated to 577°C with the furnace for insulation, and is furnace cooled to below 450°C at 1.2°C±0.2°C / min and taken out of the furnace. The TA18 extruded tube billet after the third cold rolling is heated to 568°C with the furnace for insulation, and is furnace cooled to below 450°C at 1.2°C±0.2°C / min and taken out of the furnace to obtain TA18 titanium alloy fine-grained cold-rolled tube.

[0038] Figure 3 The metallographic structure diagram of the TA18 titanium alloy fine-grained cold-rolled tube obtained in this embodiment is shown in FIG. Figure 3 It can be seen that the average diameter of the plane grains of the TA18 titanium alloy fine-grained cold-rolled tube is Not more than 3μm.

[0039] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. An annealing method for TA18 titanium alloy fine-grained cold-rolled tube, characterized in that: The method comprises the following steps: Step 1: Determine the contents of Al, V, Fe and O in the TA18 extruded tube; Step 2, the TA18 extruded tube is subjected to multiple cold rolling passes, and the single cold rolling deformation rate during the multiple cold rolling process is more than 50%, and the TA18 extruded tube is annealed after each cold rolling, and the annealing temperature T = 647.4 + 16.1 × Al% -9.8 × V% -11.55 × Fe% + 140 × O% -155 × ε, wherein the annealing temperature T is in ° C, Al%, V%, Fe%, O% are respectively the mass percentages of the four elements Al, V, Fe, and O in the TA18 extruded tube measured in step 1, ε is the single cold rolling deformation rate, and a TA18 titanium alloy fine-grained cold-rolled tube is obtained.

2. The annealing method of a TA18 titanium alloy fine-grained cold-rolled tube according to claim 1, characterized in that: The contents of the four elements Al, V, Fe and O described in step 1 are determined according to GB / T 4698 "Chemical Analysis Methods for Sponge Titanium, Titanium and Titanium Alloys".

3. The annealing method of a TA18 titanium alloy fine-grained cold-rolled tube according to claim 1, characterized in that: The number of the multiple cold rolling passes in step 2 is 1 to 3 passes.

4. The annealing method of a TA18 titanium alloy fine-grained cold-rolled tube according to claim 1, characterized in that: The annealing system of the TA18 extruded tube billet after each cold rolling in step 2 is: after keeping at the annealing temperature for 1 hour, furnace cooling to below 450°C at a rate of 1.2°C±0.2°C / min and taking out of the furnace.

5. The annealing method of a TA18 titanium alloy fine-grained cold-rolled tube according to claim 1, characterized in that: The average diameter of the planar grains of the TA18 titanium alloy fine-grained cold-rolled tube in step 2 is The diameter d does not exceed 3μm.

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