A rare earth magnesium composite type ultra-high strength steel wire for additive manufacturing and a preparation method thereof

Abstract

The application belongs to the technical field of metal material processing, and particularly relates to a rare earth magnesium composite type ultra-high strength steel wire for additive manufacturing and a preparation method thereof. In view of the problems of high alloy element burning loss rate, grain coarsening and interlayer crack of traditional low alloy ultra-high strength steel in the electric arc additive process, through magnesium-yttrium compounding, the nanoscale Mg-Y precipitated phase and Y2O3 inclusions formed under high cooling speed in the electric arc additive process can improve the strength of the accumulated body and refine the grains. The low-frequency pulse arc is matched with the dendrite growth rate, and the gradient heat treatment is combined to eliminate the residual stress. The tensile strength of the structural part prepared by the electric arc additive process reaches more than 1650 MPa, the elongation is higher than 8%, the impact energy at-40 DEG C is more than 50 J, and the oxygen and hydrogen element contents are lower than 20 ppm and 1.5 ppm respectively. The application is suitable for the fields of aerospace high-strength load-bearing parts and marine corrosion-resistant structural parts, and can significantly improve the performance of the additive manufacturing metal material.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing technology, specifically relating to a rare earth magnesium composite additive manufacturing ultra-high strength steel wire and its preparation method. Background Technology

[0002] In recent years, wire arc additive manufacturing (WAAM) technology has been rapidly adopted in aerospace, shipbuilding, and other fields due to its high efficiency, low cost, and ability to form large-size components. Compared with traditional forging and casting processes, WAAM achieves near-net-shape forming through layer-by-layer deposition, reducing material waste and shortening production cycles. However, the high heat input, rapid melting and solidification, and multiple thermal cycles inherent in this process place higher demands on wire composition design. While existing commercially available wires (such as ER100S-G and ER120S) can meet conventional welding requirements, they are prone to problems such as uncontrolled elemental burn-off, insufficient interlayer bonding strength, and crack sensitivity in WAAM, severely restricting the performance improvement of ultra-high-strength steel components.

[0003] Ultra-high strength steel is a type of alloy steel used to manufacture structural components that withstand high stress. It typically has a yield strength greater than 1180 MPa and a tensile strength greater than 1380 MPa. This type of steel generally possesses sufficient toughness, high specific strength and yield strength ratio, as well as good weldability and formability.

[0004] Low-alloy ultra-high strength steel generally contains 0.3-0.5% carbon (C), and the total content of alloying elements is less than 5%. In order to ensure the hardenability of the steel, improve the tempering stability of martensite and inhibit the growth of austenite grains, and refine the microstructure of the steel, it usually contains Ni, Cr, Si, Mn, Mo, V, etc. When traditional low-alloy ultra-high strength steel is directly used in WAAM, there are the following problems: (1) Uncontrollable element burn-off. The high temperature of the electric arc causes the burn-off rate of easily oxidized elements such as Mn and Si to be as high as 15% or more, causing the composition to deviate from the design value and severely weakening the strength. (2) Deterioration of the microstructure. Multiple thermal cycles cause grain coarsening (average size not less than 50 μm) and carbide aggregation, resulting in a serious decrease in impact toughness. (3) High crack sensitivity. The residual stress generated by rapid cooling during WAAM and hydrogen-induced cracking work together to make the scrap rate of components high.

[0005] Currently, the development of wires for WAAM mainly revolves around composition pre-compensation, microalloying, and process adaptation, but there are still significant shortcomings: (1) Limitations of composition pre-compensation strategies. Traditional MIG welding wires compensate for welding burn-off by increasing the Mn and Si content, but the multiple cladding of WAAM causes element burn-off to have a cumulative effect. Studies have shown that the burn-off rate of Mn in WAAM increases exponentially with the number of layers, and the burn-off rate in the later stages of printing can reach more than 40%, resulting in a significant composition gradient. Excessive Mn / Si will promote the formation of δ-ferrite and deteriorate low-temperature toughness. (2) Bottlenecks in microalloying technology. Existing research attempts to refine grains by adding microalloying elements such as Ti, B, and Nb, but this faces challenges in WAAM. Ti has a high affinity for O, and the high temperature in the arc region results in Ti utilization of less than 20%. The rapid solidification of WAAM causes NbC to accumulate between dendrites, leading to microsegregation and reduced toughness. (3) The potential of rare earth elements has not been fully utilized. Rare earth element Y (yellow) has been successfully used to suppress solidification cracks in aluminum alloy WAAM due to its strong deoxidizing, sulfide modification, and grain boundary purification effects. However, introducing Y into steel can lead to the formation of high-melting-point inclusions such as Y₂O₃ and Y₂S₃ with O and S. Excessive addition (greater than 0.1%) can cause inclusion size coarsening (not less than 5 μm), becoming a crack initiation point. Furthermore, Y has a low boiling point and is easily evaporated at the high temperatures of an electric arc, requiring precise control of the protective gas composition to minimize losses. Summary of the Invention

[0006] To address the aforementioned technical problems, this application provides the following technical solution:

[0007] This invention addresses the problems of uncontrollable elemental burn-off, insufficient interlayer bonding strength, and high crack sensitivity in ultra-high-strength steel during arc additive manufacturing by introducing a synergistic microalloying system of magnesium and yttrium. This invention provides a method for preparing rare-earth magnesium composite ultra-high-strength steel wire for additive manufacturing, comprising the following steps:

[0008] S11: For vacuum levels below 10 -2 Under the conditions of Pa, iron, nickel, chromium, yttrium, and master alloy are heated to above 1750℃, completely melted, and held at that temperature for 20-40 min for refining to remove gases from the molten metal; the ingot contains the following components by weight percentage: C: 0.18%-0.25%, Cr: 0.80%-1.20%, Ni: 3.80%-4.50%, Si: 1.60%-2.20%, Mo: 0.35%-0.60%, Mn: 0.25%-0.85%, Mg: 0.002%-0.005%, Y: 0.02%-0.08%, Nb: 0.02%-0.06%, Ti: 0.01%-0.04%, S≤0.005%, P≤0.006%, with the balance being Fe; wherein the mass ratio of Mg to Y is 1:10-40;

[0009] S12: The ingot is used as an electrode for vacuum arc remelting to obtain the rare earth magnesium composite additive manufacturing ultra-high strength steel wire.

[0010] Preferably, the intermediate alloy comprises a ferromolybdenum alloy and a nickel-magnesium alloy.

[0011] Preferably, the heating method is to use an electromagnetic induction furnace with a power of 700-800kW. Electromagnetic induction furnaces offer rapid heating, high thermal efficiency, and precise temperature control, enabling rapid and uniform melting of metals, reducing element loss and component segregation, improving alloy purity and microstructure uniformity, while also providing high production efficiency, energy saving, environmental protection, and safe operation.

[0012] Preferably, during vacuum arc remelting, the current is 14-16 kA and the voltage is 40-50 V. Vacuum arc remelting can stably maintain the molten pool morphology and melting rate, effectively remove inclusions and harmful gases, reduce alloy element burn-off, make the ingot structure dense and uniform, reduce segregation and porosity, and improve the purity and mechanical properties of the alloy.

[0013] This invention also provides a rare earth magnesium composite additive manufacturing ultra-high strength steel wire, comprising the following components by weight percentage: C: 0.18%-0.25%, Cr: 0.80%-1.20%, Ni: 3.80%-4.50%, Si: 1.60%-2.20%, Mo: 0.35%-0.60%, Mn: 0.25%-0.85%, Mg: 0.002%-0.005%, Y: 0.02%-0.08%, Nb: 0.02%-0.06%, Ti: 0.01%-0.04%, S≤0.005%, P≤0.006%, with the balance being Fe;

[0014] In the composition of the rare-earth magnesium composite additive manufacturing ultra-high strength steel wire, the mass ratio of Mg to Y is 1:10-40. The introduction of Mg and Y, through Mg / Y coupling strengthening, allows Mg and Y to form Mg-Y nano-precipitates, further enhancing strength through the Orowan mechanism.

[0015] Preferably, the diameter of the rare earth magnesium composite additive manufacturing ultra-high strength steel wire is 1.2-2.0 mm.

[0016] Preferably, the size of the inclusions in the rare earth magnesium composite additive manufacturing ultra-high strength steel wire is no greater than 10 μm.

[0017] Furthermore, the inclusions are Y2O3, and the Y2O3 inclusions are spherically distributed (length-to-diameter ratio not greater than 1.5). This can significantly reduce the tearing and stress concentration of the matrix caused by the inclusions, improve the toughness and fatigue performance of the steel, improve the formability of additive manufacturing, reduce defects such as cracks and porosity, and ensure the uniformity of the component structure.

[0018] The present invention also provides an electric arc additive manufacturing method, including an electric arc additive manufacturing method and a heat treatment method for the above-mentioned rare earth magnesium composite additive manufacturing ultra-high strength steel wire and the accumulated body.

[0019] During the aforementioned arc additive manufacturing, a pulsed arc mode is used, with a current of 180-240 A, a voltage of 22-28 V, a wire feed speed of 4-6 m / min, an interlayer temperature control of 80-150℃, and protection by a protective gas. The single-layer deposition thickness is 1.5-3.0 mm, and the overlap rate between paths is 40-60%.

[0020] The raw materials for the arc additive manufacturing process contain the following components: C: 0.18%-0.25%, Cr: 0.80%-1.20%, Ni: 3.80%-4.50%, Si: 1.60%-2.20%, Mo: 0.35%-0.60%, Mn: 0.25%-0.85%, Mg: 0.002%-0.005%, Y: 0.02%-0.08%, Nb: 0.02%-0.06%, Ti: 0.01%-0.04%, S≤0.005%, P≤0.006%, with the balance being Fe;

[0021] In the composition of the rare earth magnesium composite additive manufacturing ultra-high strength steel wire, the mass ratio of Mg to Y is 1:10-40; the heat treatment method of the accumulation body includes step solution treatment and aging treatment.

[0022] Preferably, the raw materials for the electric arc additive manufacturing are selected from pure iron, nickel plate (model N2), ferromolybdenum alloy (FeMo70), high-purity chromium, nickel-magnesium alloy (NiMg20), and yttrium plate.

[0023] Preferably, the protective gas is a mixture of argon and helium (with a purity of not less than 99.99%); the volume ratio of argon to helium is 98:1-3.

[0024] Preferably, the step-by-step solution treatment method is as follows: heat to 900-920℃ at a rate of 10-15℃ / min, hold at that temperature for 1-2 h, and cool to room temperature (25±5℃).

[0025] Preferably, the aging treatment method is as follows: heating to 480-520℃ at a rate of 5-8℃ / min, holding at that temperature for 4-6 hours, and then water cooling to promote the uniform distribution of the Mg-Y composite precipitate phase.

[0026] Preferably, before the stepped solution treatment, a low-temperature stress-relief annealing is performed, the steps of which are: heating to 350-400℃ at 8-12℃ / min and holding for 0.5-1 h to eliminate residual stress in the deposited state.

[0027] The technical solution of the present invention has the following advantages compared with the prior art:

[0028] Based on the traditional low-alloy ultra-high strength steel composition system, this invention develops low-alloy ultra-high strength steel wire and preparation process suitable for WAAM through a three-in-one design of composition pre-compensation + Mg-Y synergistic strengthening + process adaptation.

[0029] Based on the dispersed spherical NbC nanoprecipitates in steel, Mg and Y are introduced to strengthen the steel through Mg / Y coupling. Mg (0.002%-0.005%) and Y (0.02%-0.08%) form Mg-Y nanoprecipitates, which further enhance strength through the Orowan mechanism. At the same time, NbC and Y2O3 inclusions pin grain boundaries to inhibit grain coarsening and achieve grain refinement, thereby improving toughness. A dynamic burn-off compensation mechanism is utilized, dynamically adjusting the Mn / Si content in the wire according to the number of WAAM layers to offset the cumulative burn-off effect.

[0030] Simultaneously, utilizing hydrogen trap engineering, Y combines with H to form a stable YH2 phase, controlling the H content to no more than 1.5 ppm. Employing a low-frequency pulse mode (frequency 80-120 Hz, duty cycle 40%-60%), the molten pool oscillation frequency is matched with the dendrite growth rate, resulting in a uniform, fine-grained microstructure. Using the ultra-high-strength steel wire and additive manufacturing process developed in this technology, the Mn and Si burn-off rates in the packing are controlled to within 8%, and the Y element recovery rate reaches over 85%. The tensile strength of the WAAM component reaches over 1650 MPa, and the elongation reaches 8%. Attached Figure Description

[0031] Figure 1 This is a scanning electron microscope (SEM) image of the presence of yttrium in ultra-high strength steel in Example 1.

[0032] Figure 2 The presence of elements Fe(a), Y(b), S(c) and O(d) in the matrix in the alloy of Example 1 is shown.

[0033] Figure 3 The image shows the characterization of the nano-precipitated phases under a scanning electron microscope after the steel sample in Example 1 was corroded.

[0034] Figure 4 This is a microstructure characterization image of the steel sample after corrosion in Example 1, obtained under a scanning electron microscope.

[0035] Figure 5 for Figure 4 Elemental analysis data at positions A and B of the steel sample after corrosion in Example 1, where wt% is the mass fraction and σ is the analysis error.

[0036] Figure 6 The occurrence states of elements Nb(a), Y(b), O(c) and S(d) in the alloy of Example 1 are shown. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0038] Example 1:

[0039] 1. Preparation of filament

[0040] Calculate and weigh the metal and intermediate alloy raw materials, and the specific composition is shown in Table 1.

[0041] The master alloy ingot was smelted using a dual process of vacuum induction melting and vacuum arc remelting (VIM-VAR).

[0042] The first step, vacuum induction melting (VIM), is performed at a vacuum level below 10. -2 Under the condition of Pa, pure iron, nickel plate (model N2), ferromolybdenum alloy (FeMo70), high-purity chromium, nickel-magnesium alloy (NiMg20), and yttrium plate are added as raw materials and intermediate alloys, and the mixture is processed in a medium-frequency (5000 Hz) electromagnetic induction furnace (rated power 750). The raw material is first preheated at 30% of the rated power for 1.5 hours, and then heated to 1750℃ at the rated power to melt the raw material. The final alloy element composition can be precisely controlled as follows: C: 0.20%, Cr: 1.01%, Ni: 4.21%, Si: 1.86%, Mo: 0.45%, Mn: 0.62%, Mg: 0.003%, Y: 0.06% (mass ratio of Mg to Y is 1:20), Nb: 0.03%, Ti: 0.03%, S: 0.002%, P: 0.003%. This process effectively removes gases (such as H2 and N2) and some volatile impurities from the molten steel. The alloy elements added under the action of the electromagnetic field can be fully homogenized. Then, the molten steel is poured, and after solidification, a cylindrical ingot (consumable electrode) is formed.

[0043] The next step involves vacuum arc remelting (VAR) processing, using the ingot obtained from the first step of VIM as the arc remelting electrode, i.e., at a vacuum level below 10. -1A current of 15 kA and a voltage of 45 V are applied to Pa. The high-current electric arc is used to partially melt the steel and then drip it into a water-cooled copper crucible for rapid solidification. After melting, the ingot is cooled in a vacuum. The dripping in a vacuum can further remove residual gaseous elements in the molten steel, and inclusions in the molten steel can float to the surface or be decomposed by the electric arc. Rapid cooling in a water-cooled copper crucible can eliminate defects such as shrinkage cavities and segregation, and finally obtain an alloy ingot with uniform composition and dense structure.

[0044] The key control points are: oxygen (O) ≤ 15 ppm, nitrogen (N) ≤ 50 ppm, and hydrogen (H) ≤ 2 ppm; the master alloy ingot is hot-rolled into Φ8 mm bars, and then cold-drawn into Φ1.6 mm wires with a surface roughness Ra ≤ 1.6 μm.

[0045] Table 1. Composition of Raw Materials for Vacuum Induction Melting

[0046]

[0047] 2. Arc Additive Manufacturing Process

[0048] The Fronius TPS 5000 welding machine was used, equipped with an ABB six-axis robot. The shielding gas was a mixture of Ar and 2% He, with a purity ≥ 99.999% and a flow rate of 20 L / min. The current was 200 A, the voltage was 26 V, the wire feed speed was 6 m / min, the interlayer temperature was ≤150℃, and the path overlap rate was 40%-50%. A reciprocating scanning path was used, and the deposition direction was rotated 90° after every 5 layers to eliminate anisotropy. An infrared thermometer was used to monitor the melt pool temperature in real time.

[0049] 3. Post-heat treatment process

[0050] (1) Stress relief annealing: Low temperature annealing was carried out immediately after deposition. The heating rate was 10℃ / min, the temperature was 350℃×1 h, and the cooling method was furnace cooling to 150℃ followed by air cooling. The residual stress was reduced from 500 MPa to no more than 200 MPa.

[0051] (2) Solution treatment: Stepwise heating solution treatment. First stage: Heat to 650℃ at 15℃ / min and hold for 30 min to eliminate microsegregation. Second stage: Heat to 920℃ at 10℃ / min and hold for 2 h to achieve complete austenitization. Forced air cooling to room temperature (25℃, cooling rate 50℃ / s).

[0052] (3) Aging treatment: Two-stage aging strengthening is adopted, with a heating rate of 10℃ / min. The first stage is 480℃×4 h to promote the precipitation of Mg3Y phase (volume fraction ≥15%). The second stage is 520℃×2 h to promote the precipitation of dispersed spherical nano-precipitates (NbC) with a size of less than 10 nm. The cooling method is water cooling to room temperature (25℃) to obtain rare earth magnesium composite additive manufacturing ultra-high strength steel wire.

[0053] Example 2:

[0054] 1. Preparation of filament

[0055] Weigh the same raw materials as in Example 1, and smelt the master alloy ingot using the same vacuum induction melting + vacuum arc remelting (VIM-VAR) dual process as in Example 1. The key control points are oxygen (O) ≤ 15 ppm, nitrogen (N) ≤ 50 ppm, and hydrogen (H) ≤ 2 ppm. The master alloy ingot is hot rolled into Φ8 mm bars, and then cold drawn into Φ2.0 mm wires with a surface roughness Ra ≤ 1.6 μm.

[0056] 2. Arc Additive Manufacturing Process

[0057] The Fronius TPS 5000 welding machine was used, equipped with an ABB six-axis robot. The shielding gas was a mixture of Ar and 2% He with a purity ≥99.999% and a flow rate of 20 L / min. The current was 200 A, the voltage was 26 V, the wire feed speed was 6 m / min, the interpass temperature was 120℃, and the path overlap rate was 45%. A reciprocating scanning path was used, rotating the deposition direction by 90° after every 5 layers to eliminate anisotropy. Before the next layer of metal began deposition, an infrared thermometer was used to monitor the surface molten pool temperature of the previous metal weld bead in real time.

[0058] 3. Post-heat treatment process

[0059] (1) Stress-relief annealing. Low-temperature annealing was performed immediately after deposition. The heating rate was 10℃ / min, the temperature was 350℃×1 h, and the cooling method was furnace cooling to 150℃ followed by air cooling. The residual stress was reduced from 500 MPa to no more than 200 MPa.

[0060] (2) Solution treatment. Stepwise heating solution treatment: First stage: heating to 650℃ at 15℃ / min and holding for 30 min to eliminate microsegregation; Second stage: heating to 920℃ at 10℃ / min and holding for 2 h to achieve complete austenitization; Cooling method: forced air cooling (cooling rate 50℃ / s).

[0061] (3) Aging treatment. Two-stage aging strengthening: first stage: 480℃×4 h, mainly to promote the precipitation of Mg3Y phase, with a volume fraction ≥15%); second stage: 520℃×2 h, to promote the dispersion of NbC nano-precipitated phase with a size of less than 10 nm. The cooling method is water cooling to room temperature to obtain rare earth magnesium composite additive manufacturing ultra-high strength steel wire.

[0062] Comparative Example 1:

[0063] 1. Preparation of filament

[0064] Calculate and weigh the metal and intermediate alloy raw materials, and the specific composition is shown in Table 1.

[0065] The master alloy ingot is smelted using a dual process of vacuum induction melting and vacuum arc remelting (VIM-VAR); the first step, vacuum induction melting (VIM), is carried out at a vacuum level below 10. -2 Under the condition of Pa, pure iron, nickel plate (model N2), ferromolybdenum alloy (FeMo70), high-purity chromium, nickel-magnesium alloy (NiMg20), and yttrium plate are added as raw materials and intermediate alloys. The raw materials are preheated for about 1.5 minutes at 30% of the rated power in a medium-frequency (5000 Hz) electromagnetic induction furnace (rated power 750 KW). h, then the power is increased to the rated power and heated to 1750℃ to melt the raw materials. The final alloy element composition can be precisely controlled as follows: C: 0.20%, Cr: 1.01%, Ni: 4.21%, Si: 1.86%, Mo: 0.45%, Mn: 0.62%, Nb: 0.03%, Ti: 0.03%, S: 0.002%, P: 0.003%. This effectively removes gases (such as H2 and N2) and some volatile impurities from the molten steel. Under the action of the electromagnetic field, the added alloy elements can be fully homogenized. Subsequently, the molten steel is poured, and after solidification, a cylindrical ingot (consumable electrode) is formed. The next step is to perform a vacuum consumable remelting (VAR) process, using the ingot obtained from the VIM process as the consumable electrode, i.e., at a vacuum degree below 10... -1 A current of 15 kA and a voltage of 45 V are applied under a Pa environment. The high-current electric arc is used to partially melt the steel and then drip it into a water-cooled copper crucible for rapid solidification. After melting, the ingot is cooled in a vacuum. The dripping in a vacuum can further remove residual gaseous elements in the molten steel, and inclusions in the molten steel can float to the surface or be decomposed by the electric arc. Rapid cooling in a water-cooled copper crucible can eliminate defects such as shrinkage cavities and segregation, and finally obtain an alloy ingot with uniform composition and dense structure.

[0066] The key control points are: oxygen (O) not greater than 15 ppm, nitrogen (N) not greater than 50 ppm, and hydrogen (H) not greater than 2 ppm; the master alloy ingot is hot rolled into Φ8 mm bar, and then cold drawn into Φ1.6 mm wire, with a surface roughness Ra≤1.6 μm.

[0067] 2. Arc Additive Manufacturing Process

[0068] The Fronius TPS 5000 welding machine, equipped with an ABB six-axis robot, was used. The shielding gas was a mixture of Ar and 2% He, with a purity ≥99.999% and a flow rate of 20 L / min. The current was 200 A, the voltage was 26 V, the wire feed speed was 6 m / min, the interpass temperature was ≤150℃, and the path overlap rate was 40%-50%. A reciprocating scanning path was used, rotating the deposition direction by 90° after every 5 layers to eliminate anisotropy. Before the next layer of metal began deposition, an infrared thermometer was used to monitor the surface temperature of the previous metal weld bead in real time.

[0069] 3. Post-heat treatment process

[0070] (1) Stress relief annealing: Low temperature annealing was carried out immediately after deposition. The heating rate was 10℃ / min, the holding time was 350℃×1 h, and the cooling method was furnace cooling to 150℃ followed by air cooling. The residual stress was reduced from 500 MPa to no more than 200 MPa.

[0071] (2) Solution treatment; Step-by-step temperature rise solution, first stage: rise to 650℃ at 15℃ / min, hold for 30 min to eliminate micro segregation; second stage: rise to 920℃ at 10℃ / min, hold for 2 h to achieve complete austenitization; forced air cooling to room temperature (25℃, cooling rate 50℃ / s).

[0072] Effect evaluation:

[0073] To fully evaluate the effectiveness of the examples of the present invention, a series of performance tests were conducted on the workpieces printed with rare earth magnesium composite additive manufacturing ultra-high strength steel wire obtained in Examples 1 and 2, including tensile testing (GB / T 228.1-2021), impact testing (GB / T 229-2020), and salt spray corrosion testing (GB / T 10125-2021). The test results are shown in Table 2.

[0074] Table 2 Performance Evaluation Test Results

[0075]

[0076] The rare earth magnesium composite additive manufacturing ultra-high strength steel wire obtained in Example 1 was used to prepare an ultra-high strength support stack, which has a tensile strength of 1690 MPa, an elongation of 8.5%, an impact energy of 58 J at -40℃, and a crack rate of 1.2%.

[0077] In Example 2, the rare-earth magnesium composite additive manufacturing ultra-high strength steel wire obtained was used to prepare ultra-high strength structural components with a yield strength of 1620 MPa and a stress corrosion threshold value (KISCC) of not less than 35 MPa·m. 1 / 2 No pitting corrosion was observed after 2000 hours of salt spray testing.

[0078] In Comparative Example 1, the ultra-high strength steel without added magnesium rare earth elements has a tensile strength of 1520 MPa and an impact absorption energy of only 41 J.

[0079] The differences mentioned above are due to the fact that Examples 1 and 2 utilize Mg / Y coupling for strengthening. Mg (0.002%-0.005%) and Y (0.02%-0.08%) form Mg-Y nanoprecipitates, enhancing strength through the Orowan mechanism. Simultaneously, Y₂O₃ inclusions pin grain boundaries, inhibiting grain coarsening. A dynamic burn-off compensation mechanism is employed, dynamically adjusting the Mn / Si content in the filament based on the number of WAAM layers to offset the cumulative burn-off effect. Furthermore, hydrogen trapping engineering is used, where Y combines with H to form a stable YH₂ phase, controlling the H content to no more than 1.5 ppm, reducing the risk of hydrogen embrittlement. A low-frequency pulse mode (frequency 80-120 Hz, duty cycle 40%-60%) is employed, matching the molten pool oscillation frequency with the dendrite growth rate to obtain a uniform, fine-grained microstructure.

[0080] To verify the technical effect of the present invention, the microstructure of the sample prepared in Example 1 was characterized (corresponding to...). Figure 1 The testing method is as follows: Metallographic samples were cut from the specimen and polished sequentially with 400, 800, and 1200 grit sandpaper. Subsequently, the steel sample was etched with a 4 vol% (volume fraction) nitric acid alcohol solution for approximately 15 seconds, then cleaned and dried. Microstructure characterization and analysis were performed under a TESCAN MIRA scanning electron microscope. The results showed that diffusely distributed spherical NbC precipitates existed in the steel, with a size less than 10 nm. Figure 3 As shown, yttrium mainly exists as micron-sized yttrium oxide (Y₂O₃) second-phase particles, such as... Figure 5 As shown; and niobium-titanium carbonitrides can precipitate with yttrium oxide as the core, forming a second phase with a unique "core-shell" structure, such as Figure 6 As shown.

[0081] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing ultra-high strength steel wire for rare earth magnesium composite additive manufacturing, characterized in that, Includes the following steps: S11: For vacuum levels below 10 -2 Under the condition of Pa, iron, nickel, chromium, yttrium, and master alloy are heated to above 1750℃, melted, held at the temperature for 20-40 min for refining, and then cast to obtain an ingot; the ingot contains the following components by weight percentage: C: 0.18%-0.25%, Cr: 0.80%-1.20%, Ni: 3.80%-4.50%, Si: 1.60%-2.20%, Mo: 0.35%-0.60%, Mn: 0.25%-0.85%, Mg: 0.002%-0.005%, Y: 0.02%-0.08%, Nb: 0.02%-0.06%, Ti: 0.01%-0.04%, S≤0.005%, P≤0.006%, with the balance being Fe; wherein the mass ratio of Mg to Y is 1:10-40; S12: The ingot is used as an electrode for vacuum arc remelting, controlling oxygen (O) ≤ 15 ppm, nitrogen (N) ≤ 50 ppm, and hydrogen (H) ≤ 2 ppm. It is then hot-rolled into a bar and cold-drawn into a wire with a diameter of 1.2-2.0 mm to obtain the rare earth magnesium composite additive manufacturing ultra-high strength steel wire.

2. The preparation method according to claim 1, characterized in that, The intermediate alloy includes ferromolybdenum alloy and nickel-magnesium alloy.

3. The preparation method according to claim 1, characterized in that, The heating method is to use an electromagnetic induction furnace with a power of 700-800kW for heating.

4. The preparation method according to claim 1, characterized in that, During the vacuum self-consuming arc remelting process, the current is 14-16kA and the voltage is 40-50V.

5. A rare earth magnesium composite additive manufacturing ultra-high strength steel wire prepared by the preparation method according to any one of claims 1-4.

6. The rare earth magnesium composite additive manufacturing ultra-high strength steel wire as described in claim 5, characterized in that, The size of the inclusions in the rare earth magnesium composite additive manufacturing ultra-high strength steel wire is no greater than 10 μm; the inclusions are Y2O3, and the Y2O3 inclusions are spherically distributed.

7. An electric arc additive manufacturing method, characterized in that, The method includes an electric arc additive manufacturing process and a heat treatment method for the rare earth magnesium composite additive manufacturing ultra-high strength steel wire as described in claim 5 or 6; the electric arc additive manufacturing process uses a pulsed electric arc, the thickness of a single layer deposition is 1.5-3.0 mm, and the overlap rate between paths is 40-60%; the heat treatment method for the accumulated body includes a stepped solution treatment and an aging treatment.

8. The electric arc additive manufacturing method as described in claim 7, characterized in that, The conditions for the pulsed electric arc are: current 180-240 A, voltage 22-28 V, wire feed speed 4-6 m / min, and interlayer temperature 80-150℃.

9. The electric arc additive manufacturing method as described in claim 7, characterized in that, The stepwise solution treatment method is as follows: heat to 640-660℃ at a rate of 12-18℃ / min, hold for 25-35 min, then heat to 900-940℃ at a rate of 8-12℃ / min, hold for 110-130 min, and cool to 20-30℃; the aging treatment method is as follows: heat to 480℃ at a rate of 5-8℃ / min, hold for 3-5 h, then heat to 520℃, hold for 1-3 h, and water cool to 20-30℃.

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