High-temperature flux-cored wire and preparation method

Abstract

The invention discloses a high-temperature flux-cored wire. The high-temperature flux-cored wire comprises a stainless steel sheath and a flux core, the preparation method of the high-temperature flux-cored wire comprises the following steps: (1) raw material pretreatment; (2) mixing the flux core; (3) rolling and forming; (4) drawing and reducing; and (5) surface treatment. The high-temperature flux-cored wire is high in high-temperature strength, high in oxidation resistance and excellent in thermal fatigue resistance, meanwhile, the preparation cost is reduced, and the adaptability of the welding process is improved; the components of the high-temperature flux-cored wire are innovative, the high-temperature performance is synergistically strengthened through rare earth / nanometer oxide, the flux core contains mixed rare earth oxide, the adhesive force of an oxidation film can be synergistically improved, nanometer aluminum oxide dispersion strengthening is achieved, high-temperature grain boundary migration is inhibited, the gradient annealing technology is adopted for the high-temperature flux-cored wire, and crystal coarsening is inhibited while stress is eliminated; the high-temperature flux-cored wire has the cost advantage, the iron powder is used as a filling matrix, and the use amount of nickel is greatly reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of welding materials, in particular to a high-temperature flux-cored welding wire and a preparation method thereof. Background Art

[0002] Flux-cored welding wire is a widely used welding material, primarily used for welding various metals in diverse environments, such as high temperature, high pressure, and corrosive environments. Flux-cored wire is made by rolling a thin steel strip into a circular steel tube, filling it with a specific flux powder, and then drawing it. Its main components are the wire core and the outer casing.

[0003] Traditional flux-cored welding wires contain a high nickel content. While this can meet certain welding requirements, nickel is expensive and scarce, leading to high welding costs. Furthermore, high-nickel welding wires are prone to brittle phases in high-temperature environments, resulting in poor mechanical properties of the welded joints. The weld seam formed by traditional flux-cored welding wires has poor oxidation resistance, and the oxide scale formed by the weld easily detaches, causing weld failure. Furthermore, the weld seam produced by flux-cored welding wires has a low thermal fatigue life: repeated thermal cycling causes crack propagation. Therefore, we have proposed a high-temperature flux-cored welding wire and its preparation method to address these issues. Summary of the Invention

[0004] The object of the present invention is to provide a high-temperature flux-cored welding wire and a preparation method thereof to solve the problems raised by the above-mentioned background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a high-temperature flux-cored welding wire, comprising a stainless steel sheath and a flux core, wherein:

[0006] The stainless steel outer skin is made of ultra-low carbon austenitic stainless steel SUS304L;

[0007] The stainless steel outer skin contains, by weight percentage, C≤0.03%, Cr 17.5-19.5%, Ni8.0-10.5%, a thickness of 0.30±0.01mm, and a bandwidth of 2.55±0.05mm (width-to-thickness ratio 8.5:1);

[0008] The core filling rate is 18-25%, and the core is composed of the following components by weight:

[0009] Nickel powder (Ni) 42-48%,

[0010] Chromium powder (Cr) 16-18%,

[0011] Molybdenum powder (Mo) 6-7.5%,

[0012] Aluminum-magnesium alloy powder (Al-Mg) 3.5-4.5%,

[0013] Mixed rare earth oxides (Y2O3+CeO2) 1.2-1.8%,

[0014] Calcium fluoride (CaF2) 9-11%,

[0015] Nano-alumina (γ-Al2O3) 0.6-0.9%,

[0016] The remainder is carbonyl iron powder.

[0017] Preferably, the purity and physical property requirements of the core components are:

[0018] Nickel powder (Ni) ≥ 99.8%, 150 mesh, Fisher particle size 3.5-4.5μm, bulk density 4.2g / cm 3 ,

[0019] Chromium powder (Cr) ≥ 99.5%, 200 mesh, oxygen content ≤ 800ppm,

[0020] Molybdenum powder (Mo) ≥ 99.9%, 300 mesh, flaky powder, diameter-thickness ratio ≥ 5,

[0021] Aluminum-magnesium alloy powder (Al-Mg) Al: 50±1%, Mg: 50±1%, particle size D90≤25μm

[0022] Mixed rare earth oxide (Y2O3+CeO2) Y2O3:CeO2=3:1, D50=2μm, specific surface area 7.5±0.5m 2 / g,

[0023] Calcium fluoride (CaF2) ≥ 99%, after calcination), free CaO ≤ 0.1%,

[0024] Nano-alumina (γ-Al2O3) 50nm, whisker content ≤5%, diameter-to-length ratio 1:10,

[0025] Carbonyl iron powder, carbon content ≤0.02%.

[0026] Preferably, the drug core adopts a gradient layered structure, which is as follows from the outside to the inside:

[0027] Outer layer: a mixed layer of calcium fluoride and nano-aluminum oxide;

[0028] Middle layer: aluminum-magnesium alloy powder and mixed rare earth oxide layer;

[0029] Inner layer: pre-alloyed matrix layer of nickel powder, chromium powder and molybdenum powder.

[0030] Preferably, the nano-alumina is composite-modified with silane coupling agent KH550 and titanate NDZ-201, wherein:

[0031] KH550 addition amount is 0.5-0.8wt%, NDZ-201 addition amount is 0.3-0.5wt%;

[0032] The contact angle of the modified nanopowder is ≤25°.

[0033] A method for preparing a high-temperature flux-cored welding wire comprises the following steps:

[0034] (1) Raw material pretreatment:

[0035] All powders were sieved through 150 mesh and vacuum dried at 150 °C for 2 h;

[0036] Molybdenum powder was treated with hydrogen reduction (H2 / N v =3:1,600℃×2h), oxygen content dropped to 300ppm;

[0037] Nano-alumina and 0.5 wt% KH550 silane coupling agent were ultrasonically dispersed in anhydrous ethanol for 30 minutes and spray-dried into microspheres;

[0038] Calcium fluoride is calcined at 400°C for 1 hour;

[0039] (2) Core mixing:

[0040] Inner layer powder: Under argon protection (oxygen content ≤ 50ppm), use a three-dimensional mixer to mix at 25±2rpm for 45 minutes, pre-sinter at 850℃ for 1 hour, crush through a 200-mesh sieve, and test the pre-alloying degree (XRD semi-quantitative, γ-(Ni, Cr, Mo) phase ≥85%);

[0041] Middle layer / outer layer: mixed separately and then electrostatically self-assembled (voltage 15kV, relative humidity 40%);

[0042] (3) Rolling forming:

[0043] The stainless steel strip was electropolished (Ra = 0.6 μm) and then pre-rolled into a U-shaped form with an angle of 110°;

[0044] Quantitative powder filling (filling density deviation ≤ 1.5%), closed rolling pressure 15±0.5MPa, line speed 2.5m / min;

[0045] (4) Drawing reduction:

[0046] Drawing in 4 passes to the target diameter, with a single pass reduction rate of ≤10%, and annealing at 750±10℃ for 5 minutes between passes;

[0047] (5) Surface treatment:

[0048] Using composite coating:

[0049] Bottom layer: electrophoretically deposited silica sol (thickness 0.5 μm);

[0050] Surface layer: spraying PVB-sodium silicate composite film (thickness 1.0±0.2μm);

[0051] After drying at 120℃, vacuum pack.

[0052] Preferably, in step (2), each batch of samples is sampled and subjected to laser particle size analysis (D50 deviation ≤ 3%) and XRF composition verification for quality control.

[0053] Preferably, after the core powder is mixed in step (2), a pre-alloying treatment is performed: nickel powder, chromium powder and molybdenum powder are mixed by ball milling in proportion for 4 hours (ball-to-material ratio 2:1, argon protection).

[0054] Compared with the prior art, the beneficial effects of the present invention are: the high-temperature flux-cored welding wire has high high-temperature strength, strong oxidation resistance, and excellent thermal fatigue resistance, while reducing preparation costs and improving welding process adaptability; the high-temperature flux-cored welding wire has innovative composition, and the high-temperature performance is synergistically enhanced by rare earth / nano oxides. The flux core contains mixed rare earth oxides, which can synergistically improve the adhesion of the oxide film, and nano-alumina dispersion strengthens and inhibits high-temperature grain boundary migration. The high-temperature flux-cored welding wire adopts a gradient annealing process to eliminate stress while inhibiting crystal coarsening; the high-temperature flux-cored welding wire has cost advantages, uses iron powder as the filling matrix, and greatly reduces the amount of nickel used. DETAILED DESCRIPTION

[0055] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0056] Example 1

[0057] A high-temperature flux-cored welding wire comprises a stainless steel sheath and a flux core, wherein:

[0058] The outer stainless steel skin is made of ultra-low carbon austenitic stainless steel SUS304L with a carbon content of ≤0.03%, which can inhibit carbide precipitation and avoid intergranular corrosion;

[0059] The stainless steel outer skin contains, by weight, C ≤ 0.03%, Cr 17.5-19.5%, and Ni 8.0-10.5%, providing basic protection against high-temperature oxidation. The thickness is 0.30±0.01mm, and the bandwidth is 2.55±0.05mm. If the width is too thin (<0.28mm), it will easily crack during rolling. If the width is too thick (>0.32mm), the alloy transition rate will decrease. The width-to-thickness ratio is 8.5:1, which optimizes the forming stability of the U-groove (a width-to-thickness ratio of <8 will easily wrinkle, and a width-to-thickness ratio of >9 will cause uneven filling).

[0060] The stainless steel outer skin needs to be electropolished to reduce the rolling friction coefficient and reduce the powder extrusion loss;

[0061] The core filling rate is 18-25%, and is composed of the following components by weight:

[0062] Nickel powder (Ni ≥ 99.8%, 150 mesh, Fisher particle size 3.5-4.5 μm, bulk density 4.2 g / cm 3 )42-48%, used to strengthen the matrix, form a γ-Ni austenite matrix, maintain 800℃ high temperature strength, reduce thermal expansion coefficient, and improve high temperature toughness,

[0063] Chromium powder (Cr≥99.5%, 200 mesh, oxygen content ≤800ppm) 16-18% to form a Cr2O3 anti-oxidation layer, the oxidation rate at 900℃ is reduced to 0.011mg / (cm 2 h),

[0064] Molybdenum powder (Mo ≥ 99.9%, 300 mesh, flake powder, diameter-thickness ratio ≥ 5) 6-7.5%, solid solution strengthening, each 1% Mo increases the high temperature strength by 40 MPa, improves the high temperature strength, inhibits the precipitation of σ phase, and avoids high temperature embrittlement.

[0065] Aluminum-magnesium alloy powder (Al: 50±1%, Mg: 50±1%, particle size D90≤25μm) 3.5-4.5%, synergistic deoxidation: 2Al+3[O]→Al2O3; 2Mg+[O]→2MgO↑(gaseous deoxidation), suppressing pores, Mg vapor disturbing the molten pool, grain refinement,

[0066] Mixed rare earth oxides (Y2O3:CeO2=3:1, D50=2μm, specific surface area 7.5±0.5m 2 / g) 1.2-1.8%, Y2O3 pins the grain boundary, inhibits grain boundary diffusion creep, and improves high-temperature creep resistance. CeO2 reduces SiO2 / MnO impurities to form Ce2O3·SiO2 low-melting-point eutectic (self-repairing oxide film).

[0067] Calcium fluoride (CaF2 ≥ 99%, after calcination, free CaO ≤ 0.1%) 9-11%, reduces the melting point of slag, improves high-temperature spreadability, forms CaO·Al2O3·CaF2 eutectic with Al2O3, and improves the desulfurization rate.

[0068] Nano-alumina (γ-Al2O3 50nm, whisker content ≤ 5%, diameter-to-length ratio 1:10) 0.6-0.9%, pinning grain boundaries and inhibiting high-temperature grain growth,

[0069] The balance is carbonyl iron powder with a carbon content of ≤0.02%, which is used to adjust the filling density and serve as a diffusion carrier for Cr / Mo to reduce component segregation.

[0070] The core adopts a gradient layered structure, from outside to inside:

[0071] Outer layer: a mixed layer of calcium fluoride and nano-alumina, which will be melted and slag-formed later;

[0072] Intermediate layer: aluminum-magnesium alloy powder and mixed rare earth oxide layer, mid-term melting deoxidation and purification of the molten pool;

[0073] Inner layer: pre-alloyed matrix layer of nickel powder, chromium powder and molybdenum powder, which is preferentially melted to form a high-temperature skeleton.

[0074] Nano-alumina is modified by composite of silane coupling agent KH550 and titanate NDZ-201, wherein the addition amount of KH550 is 0.5-0.8wt% and the addition amount of NDZ-201 is 0.3-0.5wt%; the contact angle of the modified nano-powder is ≤25°;

[0075] The components work synergistically to construct an antioxidant composite film layer:

[0076] Bottom layer: Cr2O3 (continuous and dense)

[0077] Intermediate layer: Y2O3-Cr2O3 spinel (inhibits oxide film peeling)

[0078] Surface: Ce2O3·SiO2 glass phase (self-healing microcracks).

[0079] Example 2

[0080] A method for preparing a high-temperature flux-cored welding wire comprises the following steps:

[0081] (1) Raw material pretreatment:

[0082] All powders were sieved through 150 mesh to remove agglomerates, and vacuum dried at 150°C for 2 hours to a moisture content of ≤0.03% (Karl Fischer method).

[0083] The molybdenum powder is treated with hydrogen reduction (H2 / N2=3:1, 600℃×2h) to reduce the oxygen content to 300ppm, preventing MoO3 from volatilizing. The flake molybdenum powder is distributed along the γ-Ni grain boundaries, blocking dislocation slip.

[0084] Nano-alumina and 0.5wt% KH550 silane coupling agent were ultrasonically dispersed in anhydrous ethanol for 30 minutes and spray-dried into microspheres to prevent nanoparticle agglomeration and improve the uniformity of dispersion distribution in the drug core;

[0085] Calcium fluoride is calcined at 400°C for 1 hour to remove crystal water and reduce the risk of welding porosity;

[0086] (2) Core mixing:

[0087] Inner layer powder: Under argon protection (oxygen content ≤ 50ppm) to effectively prevent oxidation, use a three-dimensional mixer at 25±2rpm for 45 minutes, pre-sinter at 850℃ for 1 hour, crush through a 200-mesh sieve, and test the pre-alloying degree (XRD semi-quantitative, γ-(Ni, Cr, Mo) phase ≥ 85%);

[0088] Middle layer / outer layer: mixed separately and then electrostatically self-assembled (voltage 15kV, relative humidity 40%);

[0089] Each batch of samples is sampled for laser particle size analysis (D50 deviation ≤ 3%) and XRF verification of composition for quality control. After the cores are mixed, they are pre-alloyed: nickel powder, chromium powder, and molybdenum powder are ball-milled for 4 hours (ball-to-material ratio 2:1, argon protection) to reduce component segregation.

[0090] (3) Rolling forming:

[0091] The stainless steel strip was electropolished (Ra = 0.6 μm) and then pre-rolled into a U-shaped form with an angle of 110°;

[0092] Quantitative powder filling (filling density deviation ≤ 1.5%), closed rolling pressure 15±0.5MPa, line speed 2.5m / min;

[0093] (4) Drawing reduction:

[0094] Drawing to target diameter in 4 passes, with single-pass reduction rate ≤10%, and annealing at 750±10℃ for 5 minutes between passes to effectively avoid work hardening;

[0095] The parameters of the drawing reduction pass are: (taking Φ1.6mm→Φ1.2mm as an example)

[0096] Pass 1, inlet diameter (1.60mm) → outlet diameter (1.45mm), annealing conditions 750℃×5min, nitrogen spray annealing (50℃ / s),

[0097] Pass 2, inlet diameter (1.45mm) → outlet diameter (1.35mm), annealing conditions 750℃×5min, nitrogen spray annealing (50℃ / s),

[0098] Pass 3, inlet diameter (1.35mm) → outlet diameter (1.28mm), no annealing,

[0099] Pass 4, inlet diameter (1.28 mm) → outlet diameter (1.20 mm), annealing conditions: 750°C × 5 min, nitrogen spray annealing (50°C / s);

[0100] (5) Surface treatment:

[0101] Using composite coating:

[0102] Bottom layer: Electrophoretic deposition of silica sol (thickness 0.5μm) to fill the micropores on the surface of the welding wire, enhance the density of the coating, improve the anti-rust ability during storage, and extend the storage time of the welding wire;

[0103] Surface layer: Spraying PVB-sodium silicate composite film (thickness 1.0±0.2μm) to reduce wire friction, reduce wire feeding jamming, and improve wire feeding performance;

[0104] After drying at 120℃, vacuum pack.

[0105] Example 3

[0106] Two groups of high-temperature flux-cored welding wires were prepared according to the method of Example 2. One group contained 15% chromium powder, no nano-alumina, and mixed rare earth oxides (Y2O3:CeO2=1:1), and the other group contained 18% chromium powder, 0.8% nano-alumina, and mixed rare earth oxides (Y2O3:CeO2=3:1). The remaining components were the same. The two groups of high-temperature flux-cored welding wires were subjected to aging tests at 900°C for 100 hours. The test results are shown in the following table:

[0107]

[0108] Based on the comparison of the above two groups of high-temperature flux-cored welding wires, the flux-cored material composition of the present invention is the most preferred, the high-temperature performance of the welding wire is significantly improved, the strength-toughness is synergistically increased, and the oxidation resistance is greatly improved.

[0109] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high-temperature flux-cored welding wire, characterized in that: Consists of a stainless steel sheath and a core, including: The stainless steel outer skin is made of ultra-low carbon austenitic stainless steel SUS304L; The stainless steel outer skin contains, by weight percentage, C≤0.03%, Cr 17.5-19.5%, Ni 8.0-10.5%, a thickness of 0.30±0.01mm, and a bandwidth of 2.55±0.05mm (width-to-thickness ratio 8.5:1); The core filling rate is 18-25%, and the core is composed of the following components by weight: Nickel powder (Ni) 42-48%, Chromium powder (Cr) 16-18%, Molybdenum powder (Mo) 6-7.5%, Aluminum-magnesium alloy powder (Al-Mg) 3.5-4.5%, Mixed rare earth oxides (Y2O3+CeO2) 1.2-1.8%, Calcium fluoride (CaF2) 9-11%, Nano-alumina (γ-Al2O3) 0.6-0.9%, The remainder is carbonyl iron powder.

2. A high-temperature flux-cored welding wire according to claim 1, characterized in that: The purity and physical property requirements of the core components are: Nickel powder (Ni) ≥ 99.8%, 150 mesh, Fisher particle size 3.5-4.5μm, bulk density 4.2g / cm 3 , Chromium powder (Cr) ≥ 99.5%, 200 mesh, oxygen content ≤ 800ppm, Molybdenum powder (Mo) ≥ 99.9%, 300 mesh, flaky powder, diameter-thickness ratio ≥ 5, Aluminum-magnesium alloy powder (Al-Mg) Al: 50±1%, Mg: 50±1%, particle size D90≤25μm Mixed rare earth oxide (Y2O3+CeO2) Y2O3:CeO2=3:1, D50=2μm, specific surface area 7.5±0.5m 2 / g, Calcium fluoride (CaF2) ≥ 99%, after calcination), free CaO ≤ 0.1%, Nano-alumina (γ-Al2O3) 50nm, whisker content ≤5%, diameter-to-length ratio 1:10, Carbonyl iron powder, carbon content ≤0.02%.

3. The high-temperature flux-cored welding wire according to claim 1, characterized in that: The drug core adopts a gradient layered structure, from the outside to the inside: Outer layer: a mixed layer of calcium fluoride and nano-aluminum oxide; Middle layer: aluminum-magnesium alloy powder and mixed rare earth oxide layer; Inner layer: pre-alloyed matrix layer of nickel powder, chromium powder and molybdenum powder.

4. A high-temperature flux-cored welding wire according to claim 3, characterized in that: The nano-alumina is composite-modified by silane coupling agent KH550 and titanate NDZ-201, wherein: KH550 addition amount is 0.5-0.8wt%, NDZ-201 addition amount is 0.3-0.5wt%; The contact angle of the modified nanopowder is ≤25°.

5. A method for preparing a high-temperature flux-cored welding wire according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) Raw material pretreatment: All powders were sieved through 150 mesh and vacuum dried at 150 °C for 2 h; The molybdenum powder was treated with hydrogen reduction (H2 / N2=3:1, 600℃×2h) to reduce the oxygen content to 300ppm; Nano-alumina and 0.5 wt% KH550 silane coupling agent were ultrasonically dispersed in anhydrous ethanol for 30 minutes and spray-dried into microspheres; Calcium fluoride is calcined at 400°C for 1 hour; (2) Core mixing: Inner layer powder: Under argon protection (oxygen content ≤ 50ppm), use a three-dimensional mixer to mix at 25±2rpm for 45 minutes, pre-sinter at 850℃ for 1 hour, crush through a 200-mesh sieve, and test the pre-alloying degree (XRD semi-quantitative, γ-(Ni, Cr, Mo) phase ≥85%); Middle layer / outer layer: mixed separately and then electrostatically self-assembled (voltage 15kV, relative humidity 40%); (3) Rolling forming: The stainless steel strip was electropolished (Ra = 0.6 μm) and then pre-rolled into a U-shaped form with an angle of 110°; Quantitative powder filling (filling density deviation ≤ 1.5%), closed rolling pressure 15±0.5MPa, line speed 2.5m / min; (4) Drawing reduction: Drawing in 4 passes to the target diameter, with a single pass reduction rate of ≤10%, and annealing at 750±10℃ for 5 minutes between passes; (5) Surface treatment: Using composite coating: Bottom layer: electrophoretically deposited silica sol (thickness 0.5 μm); Surface layer: spraying PVB-sodium silicate composite film (thickness 1.0±0.2μm); After drying at 120℃, vacuum pack.

6. The method for preparing a high-temperature flux-cored welding wire according to claim 5, characterized in that: In step (2), each batch of samples is sampled and subjected to laser particle size analysis (D50 deviation ≤ 3%) and XRF composition verification for quality control.

7. The method for preparing a high-temperature flux-cored welding wire according to claim 5, wherein: After the core powders are mixed in step (2), a pre-alloying treatment is performed: nickel powder, chromium powder and molybdenum powder are mixed by ball milling in proportion for 4 hours (ball to material ratio 2:1, argon protection).

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