A method for accelerating the precipitation of B2 / L21 phase and efficiently preparing ferrite-based alloys

Abstract

The application discloses a kind of high-efficiency preparation methods for accelerating B2 / L21 phase rapid precipitation ferrite-based alloy, belong to alloy material technical field.The method includes: selecting high-purity raw materials, vacuum induction melting and electroslag remelting duplex process are used to obtain ferrite-based alloy ingot;After homogenization treatment, hot deformation and solid solution treatment, the sample is aged, and pulse current is applied in the aging process, the diffusion of solute atoms is accelerated to promote the rapid precipitation of B2 / L21 phase, thereby significantly shortening the aging time.The parameters of the pulse current are: voltage 10-150V, current density 15-35 A / cm², frequency 500-1000Hz, action time 0.5-2 hours.The application mainly utilizes the electronic wind effect of pulse current, reduces the diffusion energy barrier of solute atoms, accelerates the non-equilibrium diffusion process, and shortens the traditional aging treatment time by more than 50%.The process flow of the application is simple, and complex equipment modification is not needed, which reduces energy consumption and manufacturing cost while improving preparation efficiency, and is suitable for industrialized preparation of ferrite-based alloy and related high-temperature structural parts.

Description

Technical Field

[0001] This invention belongs to the field of high-performance iron-based alloy preparation technology, and specifically provides a method for efficiently preparing ferrite-based alloys by using pulsed current to accelerate the precipitation of B2 / L21 phase and shorten the aging time. Background Technology

[0002] The B2 phase (β′) is an intermetallic compound with an ordered body-centered cubic (BCC) structure, while the L21 phase is a Heusler phase with even higher order. By introducing a high volume fraction of coherent B2 and L21 phases into the ferrite matrix, a B2 / L21 phase co-strengthening microstructure is formed. The B2 phase provides basic precipitation strengthening, while the L21 phase exhibits higher thermal stability and ordered strengthening ability, significantly improving the service performance of ferrite-based alloys at high temperatures. These alloys, due to their excellent high-temperature strength, creep resistance, and oxidation resistance, are widely used in key hot-end components such as turbine disks and blades in aero-engines, as well as high-temperature structural components in supercritical generator sets. However, the complex preparation process and long heat treatment cycle of these alloys have become major bottlenecks restricting their large-scale engineering applications.

[0003] In recent years, many research teams have systematically studied the effects of Co on the microstructure and mechanical properties of ferrite-based alloys. Studies have shown that Co can achieve secondary solid solution in the B2 phase, forming a B2-(Ni, Co)Al precipitate, thereby further increasing the volume fraction and thermal stability of the B2 phase. Simultaneously, the introduction of Co promotes the formation of the L21 phase. As a more ordered Heusler phase, the L21 phase has lower interfacial energy, higher thermal stability, and stronger precipitation strengthening ability than the B2 phase. Research indicates that the synergistic precipitation of the B2 and L21 phases in the ferrite matrix produces a stronger strengthening effect: the B2 phase provides high-density fine precipitates, while the L21 phase provides higher microstructural stability at higher temperatures; their combined effect significantly improves the high-temperature creep resistance of the alloy. Furthermore, Co can further delay the coarsening behavior of the precipitates by reducing the overall diffusion rate of alloying elements.

[0004] However, while Co enhances high-temperature performance, it also introduces new processing challenges. Because Co significantly reduces the diffusion rate of alloying elements, the precipitation kinetics of the B2 and L21 phases are severely constrained. In traditional heat treatment processes, the precipitation of the B2 / L21 phases depends on a diffusion-type phase transformation process, where austenite (γ) is first transformed to ferrite (α) by controlling the temperature, and then the B2 / L21 phase precipitates from the supersaturated solid solution during aging. Due to the low diffusion coefficients of elements such as Ni, Al, and Co in the ferrite matrix, the kinetic characteristics of this process significantly extend the aging time. Under typical process parameters, to achieve a B2 / L21 phase volume fraction of over 30%, the aging time often reaches tens of hours, or even exceeds 120 hours, resulting in excessively high process costs and severely restricting the alloy preparation efficiency and industrial application.

[0005] To shorten heat treatment time, researchers have explored various process improvement strategies. For example, increasing the aging temperature can accelerate atomic diffusion, but excessively high temperatures can lead to coarsening of the B2 / L21 phase and a decrease in its volume fraction, thus weakening the strengthening effect. Other approaches have employed rapid heating rates or staged aging processes, but these have limited effectiveness and cannot fundamentally address the slow diffusion rate. Therefore, significantly shortening the aging time while maintaining a fine and dispersed distribution of the B2 / L21 phase has become a key technical challenge in this field.

[0006] In recent years, pulsed current treatment, as a non-equilibrium external field control method, has been applied to aluminum alloys, steel materials, and other fields. Studies have shown that low-density pulsed current can generate an electron wind effect, significantly reducing the diffusion barrier of solute atoms and accelerating the non-equilibrium diffusion process. However, the application of pulsed current to the aging process of B2 / L21 phase-strengthened ferrite-based alloys, thereby accelerating solute atom diffusion to promote the rapid precipitation of the B2 / L21 phase and significantly shortening the aging time, has not yet been reported. Summary of the Invention

[0007] This invention discloses an efficient method for preparing ferrite-based alloys using pulsed current to accelerate the rapid precipitation of the B2 / L21 phase, thereby solving the technical problems of excessively long aging time and low preparation efficiency required for B2 / L21 phase precipitation in existing technologies. The method of this invention specifically includes the following steps:

[0008] a. Select high-purity raw materials with a purity of not less than 99.9 wt.% and use a dual process of vacuum induction melting + electroslag remelting to obtain ferritic alloy ingots.

[0009] b. Homogenize the ferrite-based alloy ingot obtained in step a.

[0010] c. Hot-roll the homogenized sample to obtain a billet that is close to the final shape for use;

[0011] d. Perform solution treatment on the hot-rolled alloy;

[0012] e. The solution-treated sample is subjected to aging treatment, and a pulsed current is applied in the early stage of aging treatment or throughout the entire aging treatment process to accelerate the diffusion of solute atoms and promote the rapid precipitation of the B2 / L21 phase, thereby shortening the aging time.

[0013] f. Finally, ferrite-based alloy samples were obtained.

[0014] In one specific embodiment, the composition of the ferrite-based alloy in step a is Fe-(10-13wt.%)Cr-(2-5wt.%)Al-(10-20wt.%)Co-(10-15wt.%)Ni-(1-2wt.%)Mo-(0.1-1wt.%)Ti;

[0015] In one specific embodiment, the homogenization treatment in step b is performed at a temperature of 1000-1400°C for 1-24 hours, preferably 6-12 hours.

[0016] In one specific embodiment, the initial rolling temperature in step c is 950-1150℃, the final rolling temperature is 800-900℃, and the relative deformation during rolling is 50-80%, preferably 60-75%.

[0017] In one specific embodiment, the solution treatment in step d is performed at a temperature of 800-1000°C for 1-3 hours, and the cooling method is water cooling.

[0018] In one specific embodiment, the aging treatment in step e is performed at a temperature of 500-700℃, preferably 550-700℃, for a time of 1-12 hours. This reduces the aging treatment time by more than 50% compared to aging without the application of pulsed current. The parameters of the pulsed current are: voltage 10-150V, current density 15-35 A / cm², frequency 500-1000Hz, and duration 0.5-2 hours.

[0019] The innovation of this invention lies in the fact that the electron wind effect generated by the pulsed current lowers the diffusion barrier of solute atoms, increases the driving force of solid-state phase transition, and thus accelerates the non-equilibrium diffusion process of elements such as Ni, Al, and Co. During the aging treatment stage, this effect significantly increases the nucleation rate and growth rate of the B2 / L21 phase, enabling the B2 / L21 phase to precipitate and achieve the ideal volume fraction and distribution state in a shorter time. Compared with traditional aging treatments, this invention can shorten the aging time to tens of hours or even less than a few hours, greatly improving the preparation efficiency.

[0020] Advantages of this invention:

[0021] 1. Significantly shortens aging time and improves preparation efficiency: This invention applies pulsed current during the aging process, utilizing the electron wind effect to lower the diffusion barrier of solute atoms, accelerating the non-equilibrium diffusion process of elements such as Ni, Al, and Co, thereby promoting the rapid precipitation of the B2 / L21 phase. Compared with traditional aging treatments, this invention can shorten the aging time to tens of hours or even several hours, a reduction of more than 50%, significantly improving the alloy preparation efficiency.

[0022] 2. Reduced overall manufacturing costs and enhanced engineering application feasibility: Due to the significantly shortened aging cycle and the elimination of the need to increase heat treatment temperature, this invention effectively reduces energy consumption and manufacturing costs while improving microstructure regulation efficiency. Furthermore, this invention does not require complex modifications to existing heat treatment equipment; it only requires the introduction of a pulse current generator. The process is simple and easy to industrialize, thus significantly enhancing the engineering application potential of pulse current-assisted heat treatment technology in ferrite-based alloys and related high-temperature structural components.

[0023] 3. Maintaining excellent mechanical properties, suitable for high-temperature service scenarios: The ferritic-based alloy prepared by this invention exhibits uniform and dispersed B2 / L21 phase precipitation, maintaining a good coherent relationship with the matrix, significantly shortening the aging time without sacrificing the material's mechanical properties. The alloy possesses excellent high-temperature strength, creep resistance, and microstructural stability, making it suitable for high-temperature load-bearing components in high-end equipment fields such as aero-engines and gas turbines. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of the present invention.

[0025] Figure 2 This is a schematic diagram of the SEM morphology of the B2 / L21 precipitate phase after aging with pulsed current according to the present invention. Detailed Implementation

[0026] Example 1

[0027] High-purity raw materials with a purity of not less than 99.9 wt.% were selected, and a ferritic-based alloy ingot with the composition of Fe-10 wt.% Cr-3 wt.% Al-15 wt.% Co-12 wt.% Ni-2 wt.% Mo-0.5 wt.% Ti was obtained using a dual process of vacuum induction melting and electroslag remelting. The alloy ingot was homogenized at 1150℃ for 12 hours. The homogenized alloy was then heated to 1100℃ and held for 1.5 hours, followed by hot rolling at a final rolling temperature of 880℃ and a relative deformation of 60%. The hot-rolled alloy was solution-treated at 800℃ for 3 hours and then water-cooled. Subsequently, it was aged at 600℃, with a pulsed current applied for the first hour after the start of aging treatment, with parameters of: voltage 20V, current density 20 A / cm², and frequency 1000 Hz. The total aging time was 8 hours, representing a reduction in aging time of approximately 58%.

[0028] Example 2

[0029] High-purity raw materials with a purity of not less than 99.9 wt.% were selected, and a ferritic-based alloy ingot with the composition of Fe-13 wt.% Cr-4 wt.% Al-20 wt.% Co-14 wt.% Ni-1 wt.% Mo-0.8 wt.% Ti was obtained using a dual process of vacuum induction melting and electroslag remelting. The alloy ingot was homogenized at 1300℃ for 6 hours. The homogenized material was then heated to 1000℃ and held for 2 hours, followed by hot rolling at a final rolling temperature of 820℃ and a relative deformation of 67%. The hot-rolled alloy was solution-treated at 1000℃ for 1 hour and then water-cooled. It was then aged at 700℃ for 3 hours, with a pulsed current applied for the first 40 minutes after the start of aging treatment. The parameters were: voltage 15V, current density 15 A / cm², and frequency 800 Hz. Compared with the condition without pulsed current, the aging time was shortened by approximately 75% for the same precipitation level.

[0030] Example 3

[0031] In this example, a dual process of vacuum induction melting and electroslag remelting was used to obtain a ferritic-based alloy ingot with the composition of Fe-11wt.%Cr-2wt.%Al-10wt.%Co-13wt.%Ni-1.5wt.%Mo-1wt.%Ti. The alloy ingot was homogenized at 1250℃ for 10 hours. The homogenized alloy was then heated to 950℃ and held for 3 hours, followed by hot rolling at a final rolling temperature of 800℃ and a relative deformation of 70%. The hot-rolled alloy was solution-treated at 900℃ for 1.5 hours and then water-cooled. Subsequently, it was aged at 650℃, with a pulsed current applied for the first 50 minutes after the start of aging. The parameters were: voltage 18V, current density 18 A / cm², frequency 900 Hz, and a total aging time of 4 hours. Compared with the condition without pulsed current, the aging time was shortened by approximately 70% for the same precipitation level.

[0032] Example 4

[0033] High-purity raw materials with a purity of not less than 99.9 wt.% were selected, and a ferritic-based alloy ingot with the composition of Fe-12 wt.% Cr-3.5 wt.% Al-12 wt.% Co-11 wt.% Ni-1.3 wt.% Mo-0.6 wt.% Ti was obtained using a dual process of vacuum induction melting and electroslag remelting. The alloy ingot was homogenized at 1280℃ for 8 hours. The homogenized alloy was then heated to 1150℃ and held for 1 hour, followed by hot rolling at a final rolling temperature of 900℃ and a relative deformation of 75%. The hot-rolled alloy was solution-treated at 850℃ for 2 hours and then water-cooled. Subsequently, it was aged at 620℃ for 5 hours, with a pulsed current applied for the first 45 minutes after the start of aging treatment, with parameters of: voltage 22V, current density 22 A / cm², and frequency 950 Hz. The precipitated phases were uniformly distributed, and the aging time was shortened by approximately 67%.

Claims

1. A method for efficiently preparing ferrite-based alloys by accelerating the precipitation of the B2 / L21 phase, characterized in that, Includes the following steps: a. Select high-purity raw materials with a purity of not less than 99.9 wt.% and use a dual process of vacuum induction melting + electroslag remelting to obtain ferritic alloy ingots. b. Homogenize the ferrite-based alloy ingot obtained in step a. c. After homogenization, the sample is heated and then hot-rolled to obtain a billet that is close to the final shape for use. d. Perform solution treatment on the hot-rolled alloy; e. The solution-treated sample is subjected to aging treatment, and a pulsed current is applied during the aging treatment to accelerate the formation of the precipitated phase; f. Finally, ferrite-based alloy samples were obtained.

2. The preparation method according to claim 1, wherein the ferrite-based alloy has the following composition: Fe-(10-13wt.%)Cr-(2-5wt.%)Al-(10-20wt.%)Co-(10-15wt.%)Ni-(1-2wt.%)Mo-(0.1-1wt.%)Ti.

3. The preparation method according to claim 1, wherein the homogenization treatment is carried out at a temperature of 1000-1400℃ for 1-24 hours, preferably 6-12 hours.

4. The preparation method according to claim 1, wherein the initial rolling temperature is 950-1150℃, the final rolling temperature is 800-900℃, and the relative deformation during rolling is 50-80%, preferably 60-75%.

5. The preparation method according to claim 1, wherein the solution treatment temperature is 800-1000℃, the time is 1-3 hours, and the cooling method is water cooling.

6. The preparation method according to claim 1, wherein the aging treatment temperature is 500-700℃, preferably 550-700℃, and the time is 1-24 hours. The aging treatment time is shortened by more than 50% compared to aging treatment without applied pulse current; the parameters of the pulse current are: voltage 10-150V, current density 15-35 A / cm², frequency 500-1000Hz, and treatment time 0.5-2 hours.

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