A method for improving the aging efficiency of B2 / L21 phase strengthened ferritic steel

Abstract

This invention discloses a method for improving the aging efficiency of B2 / L21 phase-strengthened ferritic steel, relating to the field of heat treatment and external field control technology for metallic materials. The method includes: selecting high-purity raw materials and preparing ferritic-based alloy ingots using a dual process of vacuum induction melting and electroslag remelting; obtaining a workpiece with a supersaturated solid solution matrix through homogenization treatment, hot rolling deformation, and solution treatment; subsequently placing the solution-treated workpiece in a vacuum or inert gas protective environment, and applying a DC electric field during the aging process to accelerate diffusion; utilizing the directional "electron wind" generated by high-density current to increase the diffusion rate of solute atoms, shortening the aging period; simultaneously utilizing the electromigration effect to impart additional migration driving force to hydrogen atoms and matrix atoms, forcing interstitial hydrogen atoms to rapidly overflow to the surface and driving matrix atoms to fill microscopic pores and crack defects. This process breaks through the efficiency bottleneck of traditional heat treatment relying on a single thermal field to drive diffusion, achieving efficient microstructure optimization and hydrogen removal strengthening of high-performance iron-based alloys.

Description

Technical Field

[0001] This invention belongs to the field of high-performance metal material processing technology, and specifically relates to an efficient processing and strengthening method that significantly shortens the aging time of strengthened ferritic steel by accelerating diffusion through a DC electric field, and synergistically achieves micro-damage healing and elimination of hydrogen embrittlement risk. Background Technology

[0002] With increasingly stringent requirements for lightweight, high-strength, and high-temperature resistant structural materials in aerospace, deep-sea exploration, and advanced energy equipment, the development of high-performance ferrite-based alloys has become a key focus in materials science. 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 capabilities, significantly improving the service performance of ferrite-based alloys in high-temperature environments. B2 and L21 phase-strengthened ferrite steels are considered highly promising high-temperature structural materials due to their excellent high-temperature strength and low coefficient of thermal expansion. In traditional heat treatment processes, obtaining a high volume fraction of B2 / L21 dual-phase precipitation structure often requires extremely long aging periods, relying on a single thermal activation drive. This inefficient production method not only greatly increases energy consumption and preparation costs, but also easily leads to non-uniform coarsening of the reinforcing phase due to prolonged exposure to high temperatures, which severely restricts the large-scale industrial application of this type of material.

[0003] Furthermore, during the smelting, forming, and machining processes of metallic materials, microscopic defects such as micron / nano-scale vacancy clusters, micropores, and microcracks inevitably arise within the material. These defects not only weaken the structural integrity of the matrix but also become natural trapping points for hydrogen atoms. When the interstitial hydrogen atom concentration within the material is high, the accumulation of hydrogen at these defects generates enormous intramolecular pressure and weakens interatomic bonding forces, leading to severe hydrogen embrittlement and the risk of delayed fracture. Traditional hydrogen removal processes suffer from extremely slow diffusion kinetics at low temperatures, making it difficult to completely eliminate deep hydrogen accumulation and completely lacking the ability to close physical micro-damage, resulting in significant safety hazards for components during service.

[0004] In summary, achieving a significant increase in atomic diffusion rate to substantially improve aging efficiency without significantly increasing processing temperature is the core challenge currently faced. Existing traditional heat treatment processes struggle to achieve efficient precipitation of strengthening phases and healing of microscopic damage in a short period. Therefore, this invention introduces a DC electric field during the aging process, utilizing the electron wind effect to provide a non-thermal driving force. Through a single process, it achieves: 1. Overcoming diffusion lag to shorten the aging cycle; 2. Forcing rapid hydrogen atom escape to suppress hydrogen embrittlement; 3. Inducing directional atomic migration to fill microscopic defects. This method provides a novel technical route for the efficient and reliable preparation of high-performance B2 / L21 strengthened ferritic steel. Summary of the Invention

[0005] This invention discloses a method for improving the aging efficiency of B2 / L21 phase-strengthened ferritic steel. Addressing the technical challenges of extremely long processing cycles, low production efficiency, and susceptibility to hydrogen embrittlement cracking in high-alloy ferritic steels due to the sluggish diffusion kinetics of solute atoms during aging, this invention achieves non-thermodynamic control of atomic diffusion behavior by introducing a DC electric field. The method specifically includes the following steps: a) Selecting high-purity raw materials with a purity of not less than 99.9 wt.%, and using a dual process of vacuum induction melting + electroslag remelting to obtain ferrite-based alloy ingots; b) Homogenizing the ferrite-based alloy ingots to eliminate dendritic segregation; c) Hot-rolling the homogenized sample to obtain a billet close to the final shape for use; d) Solution-treating the hot-rolled alloy, followed by rapid cooling to obtain a supersaturated solid solution ferrite matrix; e) Electric field-assisted aging treatment: placing the solution-treated workpiece in a vacuum or inert gas protective environment, and applying a DC electric field to accelerate diffusion during the aging process: utilizing the directional "electron wind" generated by high-density current to enhance the diffusion rate of solute atoms and shorten the aging period. Synergistic hydrogen removal and repair: Simultaneously utilizing the electromigration effect to impart additional migration driving force to hydrogen atoms and matrix atoms, forcing interstitial hydrogen atoms to rapidly overflow to the surface, and driving matrix atoms to fill microscopic pores and crack defects. f. Cooling to room temperature: Cut off the DC electric field and cool the workpiece with the furnace or in a controlled manner to room temperature.

[0006] In one specific embodiment, the composition of the ferrite-based alloy in step a is Fe-(10-13wt.%)Cr-(2-5wt.%)Al-(12-20wt.%)Co-(12-15wt.%)Ni-(1-2wt.%)Mo-(0.1-2wt.%)Ti, and the small-size defects include micropores or microcracks with sizes ranging from 1 nm to 10 μm and enriched interstitial hydrogen atoms;

[0007] In one specific embodiment, in step b, the homogenization treatment temperature is 1000-1400℃ and the time is 6-24 hours, preferably 6-12 hours.

[0008] In one specific embodiment, in step c, the hot rolling starting temperature is 950-1150℃, the ending temperature is 800-900℃, and the total deformation is 50-85%.

[0009] In one specific embodiment, in step d, the solution treatment temperature is 800-1000℃, the time is 1-3 hours, and the cooling method is air cooling;

[0010] In one specific embodiment, in step e, the aging treatment temperature is 500-700℃, preferably 550-700℃, and the aging time is 1-10 hours, preferably 2-6 hours. During the aging treatment, a DC electric field with a current density of 10-40 A / mm² is applied to the workpiece, while the preset temperature of the heating furnace is set to be 30-200℃ lower than the target aging temperature. This allows the actual temperature of the workpiece to rise to and stabilize within the aging temperature range under the supplementary Joule heat generated by the DC electric field. The aging treatment is carried out in a vacuum or high-purity argon protective atmosphere, wherein the vacuum level of the vacuum environment is not lower than 1.0 × 10⁻⁶. -3 Pa.

[0011] In one specific embodiment, the aging time is shortened by no less than 60% compared to an aging process without an applied electric field, under the same composition and heat treatment temperature conditions.

[0012] The innovation of this invention lies not only in achieving kinetic reconstruction and multi-effect synergistic repair of the Co diffusion-suppressing system through a "DC electric field-diffusion kinetics enhancement mechanism," but also in the thermodynamic-kinetic synergistic design of the alloy system itself. Specifically, the designed ferrite-based alloy must simultaneously satisfy the following conditions:

[0013] (1) The matrix structure is stable within the electric field treatment temperature range of 550-700℃, without harmful phase transformation or significant grain growth, so as to ensure that the intrinsic mechanical properties of the material do not degrade.

[0014] (2) The material contains a high concentration of hydrogen atoms and diffusible healable defects (such as micropores and microcracks) with sizes ranging from 1 nm to 10 μm, which provide the material basis and healing object for electric field-accelerated diffusion.

[0015] (3) Hydrogen atoms have a high diffusion activation energy in the matrix, but under the action of an external DC electric field, they can generate directional electromigration, which increases the effective diffusion coefficient by more than an order of magnitude, thereby enabling the rapid escape of hydrogen and preventing hydrogen embrittlement.

[0016] This method establishes a synergistic optimization path of "defect characteristics - electric field parameters - period reduction" by comprehensively reconstructing diffusion dynamics through the electric field. It successfully and significantly shortens the aging time while simultaneously improving microstructure strengthening and defect repair. This method enables the efficient preparation of high-volume-fraction B2 / L21 phase-strengthened ferritic steel under low-cost conditions, demonstrating significant technological advancement and engineering application value.

[0017] Advantages of this invention:

[0018] 1. Significantly improves diffusion kinetic efficiency and shortens aging cycle: This invention introduces a DC electric field during the aging process, utilizing the "electron wind" generated by high-density current to break the induced diffusion lag effect, thereby achieving enhanced external field control of atomic migration behavior. Without increasing the aging temperature, it significantly accelerates solute atom diffusion, shortening the original aging cycle of 120-600 hours and greatly improving the overall heat treatment efficiency.

[0019] 2. Achieving Synergistic Unity of Tissue Strengthening and In-situ Defect Repair: While rapidly constructing a B2 / L21 biphase strengthened structure, this invention utilizes the directional driving effect of an electric field to guide matrix atoms to physically fill micro- and nano-scale pores and cracks, and forces interstitial hydrogen atoms with a high concentration inside to migrate rapidly to the surface and overflow. This integrated regulation of "strengthening-repair-hydrogen removal" significantly improves the structural integrity and overall strength and toughness of the matrix while eliminating the risk of hydrogen embrittlement.

[0020] 3. Reduce overall preparation cost and improve engineering application feasibility: Due to the significantly shortened aging cycle and the elimination of the need to increase the heat treatment temperature, this invention effectively reduces energy consumption and manufacturing costs while improving the efficiency of microstructure regulation, and significantly enhances the engineering application potential of B2 / L21 phase-strengthened ferritic steel in key load-bearing components of aerospace and energy equipment. Attached Figure Description

[0021] Figure 1 This is a process flow diagram of the present invention.

[0022] Figure 2 This is a schematic diagram of the SEM morphology of the B2 precipitate phase after aging with a DC electric field according to the present invention. Detailed Implementation

[0023] Example 1:

[0024] High-purity raw materials with a purity of not less than 99.9 wt.% were selected, and a ferritic alloy ingot with the composition of Fe-10 wt.% Cr-2 wt.% Al-12 wt.% Co-12 wt.% Ni-1 wt.% Mo-0.5 wt.% Ti was obtained using a dual process of vacuum induction melting and electroslag remelting. The ferritic alloy ingot was homogenized at 1200℃ for 12 hours to reduce the influence of dendrite segregation. Subsequently, the homogenized material was heated to 1000℃ for hot rolling, with a final rolling temperature of 800℃ and a total deformation of 60%, followed by air cooling to room temperature. The hot-worked material was then solution-treated at 800℃ and held for 2 hours. Aging treatment was performed at 550℃, with a DC electric field applied throughout the aging process. The surface-cleaned workpiece was then placed in a vacuum chamber with a vacuum degree of 5.0 × 10⁻⁻⁻⁻⁶. 4 In a Pa heating furnace, the preset temperature was set to 350℃. Copper electrodes were connected to both ends of the workpiece, and a DC electric field with a current density of 15 A / mm² was applied for aging for 6 hours. With the supplementary Joule heating effect of the current, the actual temperature of the workpiece rose to and stabilized at approximately 550℃. After treatment, the power was cut off, and the workpiece was cooled in the furnace. Compared to the case without an applied electric field, under the obtained B2 / L21 phase precipitation volume fraction, the aging time was reduced by approximately 65%, and the internal defects of the resulting alloy were reduced by approximately 65%.

[0025] Example 2:

[0026] High-purity raw materials with a purity of not less than 99.9 wt.% were selected, and a ferritic alloy ingot with the composition of Fe-11.5 wt.%, Cr-3.5 wt.%, Al-14 wt.%, Co-13.5 wt.%, Ni-1.5 wt.%, Mo-0.6 wt.%, and Ti was obtained using a dual process of vacuum induction melting and electroslag remelting. The ferritic alloy ingot was homogenized at 1250℃ for 8 hours to reduce the influence of dendrite segregation. Subsequently, the homogenized material was heated to 1050℃ for hot rolling, with a final rolling temperature of 850℃ and a total deformation of 70%, followed by air cooling to room temperature. The hot-worked material was then solution-treated at 850℃ and held for 1.5 hours. Aging treatment was performed at 625℃, with a DC electric field applied throughout the aging process. The surface-cleaned workpiece was then placed in a vacuum chamber with a vacuum degree of 1.0 × 10⁻⁻⁻⁻⁶. 4 In a Pa heating furnace, the preset temperature was set to 400℃. Copper electrodes were connected to both ends of the workpiece, and a DC electric field with a current density of 22A / mm² was applied for aging for 5 hours. Under the supplementary effect of Joule heating, the actual temperature of the workpiece rose to and stabilized at around 625℃. After the treatment, the power was cut off and the workpiece was cooled with the furnace. Compared with the case without an electric field, under the condition of obtaining the B2 / L21 phase precipitation volume fraction, the aging time was reduced by more than 70%, and the internal defects of the resulting alloy were reduced by about 70%.

[0027] Example 3:

[0028] High-purity raw materials with a purity of not less than 99.9 wt.% were selected, and a ferritic alloy ingot with the composition of Fe-13 wt.% Cr-5 wt.% Al-16 wt.% Co-15 wt.% Ni-2 wt.% Mo-0.8 wt.% Ti was obtained using a dual process of vacuum induction melting and electroslag remelting. The ferritic alloy ingot was homogenized at 1300℃ for 6 hours to reduce the influence of dendrite segregation. Subsequently, the homogenized material was heated to 1100℃ for hot rolling, with a final rolling temperature of 900℃ and a total deformation of 80%, followed by air cooling to room temperature. The hot-worked material was then solution-treated at 900℃ and held for 1 hour. Aging treatment was performed at 650℃, with a DC electric field applied throughout the aging process. The surface-cleaned workpiece was then placed in a vacuum chamber with a vacuum degree of 4.0 × 10⁻⁻⁻⁻⁶. 4 In a Pa heating furnace, the preset temperature was set to 430℃. Copper electrodes were connected to both ends of the workpiece, and a DC electric field with a current density of 28 A / mm² was applied for aging for 4 hours. Under the supplementary effect of Joule heating, the actual temperature of the workpiece rose to and stabilized at around 650℃. After the treatment, the power was cut off and the workpiece was cooled with the furnace. Compared with the workpiece without an electric field, under the condition of obtaining the B2 / L21 phase precipitation volume fraction, the aging time was reduced by about 75%, and the internal defects of the resulting alloy were reduced by about 75%.

[0029] Example 4:

[0030] High-purity raw materials with a purity of not less than 99.9 wt.% were selected, and a ferritic alloy ingot with the composition of Fe-12 wt.% Cr-4 wt.% Al-20 wt.% Co-14 wt.% Ni-1.8 wt.% Mo-1 wt.% Ti was obtained using a dual process of vacuum induction melting and electroslag remelting. The ferritic alloy ingot was homogenized at 1280℃ for 10 hours to reduce the influence of dendrite segregation. Subsequently, the homogenized material was heated to 1080℃ for hot rolling, with a final rolling temperature of 850℃ and a total deformation of 75%, followed by air cooling to room temperature. The hot-worked material was then solution-treated at 1000℃ and held for 2 hours. Aging treatment was performed at 700℃, with a DC electric field applied throughout the aging process. The surface-cleaned workpiece was then placed in a vacuum chamber with a vacuum degree of 2.0 × 10⁻⁶. -4 The workpiece was placed in a heating furnace with a rated temperature of 480°C. Copper electrodes were connected to both ends of the workpiece, and a DC electric field with a current density of 35 A / mm² was applied. The aging time was 3 hours. Under the supplementary effect of Joule heating, the actual temperature of the workpiece rose to and stabilized at around 700°C. After the treatment, the power was cut off and the workpiece was cooled in the furnace. Compared with the workpiece without an electric field, under the condition of obtaining the B2 / L21 phase precipitation volume fraction, the aging time was reduced by more than 75%, and the internal defects of the resulting alloy were reduced by about 80%.

Claims

1. A method for improving the aging efficiency of B2 / L21 phase-strengthened ferritic steel, characterized in that, The method specifically includes the following steps; a. Alloy smelting: 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. Homogenization: The ferrite-based alloy ingot is homogenized to eliminate dendritic segregation; c. Hot rolling: The homogenized sample is hot rolled to obtain a ferrite structure with refined grains and a billet that is close to the final shape for use. d. Solution treatment: The hot-rolled alloy is subjected to solution treatment, followed by rapid cooling to obtain a supersaturated ferrite matrix. e. Electric field-assisted aging treatment: The solution-treated workpiece is placed in a vacuum or inert gas protective environment, and a DC electric field is applied during the aging process to accelerate diffusion: the directional "electron wind" generated by high-density current is used to enhance the diffusion rate of solute atoms, shortening the aging period. Synergistic hydrogen removal and repair: The electromigration effect is used simultaneously to give hydrogen atoms and matrix atoms additional migration driving force, forcing interstitial hydrogen atoms to quickly overflow to the surface and driving matrix atoms to fill microscopic pores and crack defects. 2.f. Cooling to room temperature: Cut off the DC electric field and cool the workpiece to room temperature with the furnace.

3. According to the method of claim 1, the composition of the ferrite-based alloy in step a is Fe-(10-13wt.%)Cr-(2-5wt.%)Al-(12-20wt.%)Co-(12-15wt.%)Ni-(1-2wt.%)Mo-(0.1-2wt.%)Ti, and the small-size defects include micropores or microcracks with sizes ranging from 1 nm to 10 μm and enriched interstitial hydrogen atoms.

4. The method according to claim 1, characterized in that... The homogenization process in step b is carried out at a temperature of 1000-1400℃ for 6-24 hours, preferably 6-12 hours.

5. The method according to claim 1, characterized in that... The starting temperature of hot rolling in step c is 950-1150℃, the ending temperature is 800-900℃, and the total deformation is 50-85%.

6. The method according to claim 1, characterized in that... The solution treatment in step d is performed at a temperature of 800-1000℃ for 1-3 hours, and is cooled by air cooling.

7. The method according to claim 1, characterized in that, The aging treatment temperature in step e is 500-700℃, preferably 550-700℃, and the aging time is 1-10 hours, preferably 2-6 hours. During the aging treatment, a DC electric field with a current density of 10-40 A / mm² is applied to the workpiece, and the preset temperature of the heating furnace is set to be lower than the target aging treatment temperature, so that the actual temperature of the workpiece rises to and stabilizes within the aging temperature range under the supplementary Joule heat generated by the DC electric field. The aging treatment is carried out in a vacuum or high-purity argon protective atmosphere, wherein the vacuum degree of the vacuum environment is not less than 1.0×10⁻³ Pa.

8. The method according to claim 1, characterized in that, Under the same composition and heat treatment temperature conditions, the aging time is shortened by no less than 60% compared to the aging process without an applied electric field.

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