A welding rod for welding duplex stainless steel and a method for manufacturing the same

Abstract

This invention relates to the field of welding electrodes for duplex stainless steel, specifically to a welding electrode for duplex stainless steel and its preparation method. When residual stress at the weld seam of 2209 duplex stainless steel is eliminated through high-temperature heat treatment, the mechanical properties and corrosion resistance of the weld seam significantly decrease. To address the above technical problem, this invention provides a welding electrode for duplex stainless steel that effectively slows down the phase transformation rate during high-temperature heat treatment, avoids excessive austenite formation, and maintains the balance of the duplex structure. The electrode coating composition specifically includes lanthanum hexaboride and Ti-6Al-4V alloy, which have grain-refining effects and simultaneously inhibit the precipitation of harmful intermetallic phases. This effectively suppresses the precipitation of harmful phases such as the σ phase during weld heat treatment, ensures the solid solubility of chromium and molybdenum, and allows the weld seam to retain excellent comprehensive properties after high-temperature treatment.

Description

Technical Field

[0001] This invention relates to the field of duplex stainless steel technology, specifically to a welding electrode for welding duplex stainless steel and its preparation method. Background Technology

[0002] In the field of stainless steel materials, duplex stainless steel has attracted much attention due to its unique microstructure and excellent comprehensive properties. Among them, 2205 duplex stainless steel, as a typical representative, exhibits excellent corrosion resistance and high strength with its chemical composition of approximately 22% chromium, 5% nickel, 3% molybdenum, and approximately 0.15% nitrogen. The advantages of this stainless steel mainly stem from its balanced austenitic and ferrite two-phase structure, as well as the strengthening effect of nitrogen in the solid solution state. The austenitic phase provides good toughness and corrosion resistance, while the ferrite phase enhances the material's strength and resistance to stress corrosion cracking.

[0003] However, in practical applications, the welding process of 2205 duplex stainless steel has become a technical challenge. To ensure the quality of the weld, ER2209 welding rods with a composition similar to that of the base metal are usually selected. Although this type of welding rod can ensure the consistency of chemical composition between the weld and the base metal to a certain extent, the residual stress generated during the welding process and the subsequent heat treatment steps have an adverse effect on the microstructure and properties of the weld.

[0004] Specifically, after welding, the weld area often retains significant internal stress, which needs to be eliminated through heat treatment. However, during heat treatment, the balance between austenite and ferrite in the weld is easily disrupted, leading to the precipitation of harmful phases such as the σ phase, χ phase, and carbides. The precipitation of these harmful phases not only alters the microstructure of the weld but also causes an imbalance in the ratio of austenite to ferrite, thereby severely affecting the mechanical properties and corrosion resistance of the weld.

[0005] The presence of σ and χ phases reduces the toughness and plasticity of the weld, increasing its brittleness. Meanwhile, carbide precipitation consumes alloying elements such as chromium and nickel in the weld, leading to a decrease in corrosion resistance. Therefore, effectively preventing the precipitation of harmful phases during heat treatment and maintaining the balance between austenite and ferrite in the weld while ensuring welding efficiency and quality has become a pressing technical problem. Summary of the Invention

[0006] A problem with existing technologies is that when residual stress at the weld seam of 2205 duplex stainless steel is eliminated through heat treatment, the tensile strength and corrosion resistance of the weld seam decrease significantly. To address this problem, this invention provides a welding electrode for welding duplex stainless steel, comprising a core and a coating, wherein the coating accounts for 38-42% of the total electrode mass. The coating includes a binder and flux, with the mass ratio of binder to flux powder being 1:4-5. The core is made of low-carbon stainless steel, and the flux contains lanthanum hexaboride, Mg-Y-RE-Zr alloy, and titanium alloy powder, wherein the titanium alloy powder is of the Ti-6Al-4V alloy grade.

[0007] Preferably, the flux comprises the following components in parts by weight:

[0008]

[0009]

[0010] Preferably, the flux comprises the following components in parts by weight:

[0011]

[0012] Preferably, the Mg-Y-RE-Zr alloy is designated as WE43 alloy.

[0013] Preferably, the average particle size of each component in the flux is 10-100 mesh.

[0014] Preferably, the binder is potassium sodium silicate.

[0015] Preferably, the potassium-sodium water glass has a modulus of 2.5-3.5 and a potassium-sodium ratio of 3:1.

[0016] Preferably, the low-carbon stainless steel is 308L stainless steel.

[0017] The physicochemical analysis of each component in the flux is as follows:

[0018] Marble powder (CaCO3): decomposes into CaO and CO2 at high temperatures. CaO acts as an alkaline slag-forming agent for desulfurization and dephosphorization; CO2 provides a protective gas to prevent atmospheric pollution of the molten pool.

[0019] Calcium fluoride (CaF2) and barium fluoride (BaF2): lower the melting point of slag, improve fluidity, stabilize the electric arc, reduce hydrogen absorption, and prevent porosity.

[0020] Calcium oxide (CaO): Enhances the alkaline environment, further desulfurizes and dephosphorizes, and purifies the molten pool.

[0021] Rutile (TiO2): Stabilizes the electric arc, improves slag coverage, promotes oxygen control, and optimizes alloy transition.

[0022] Mica powder: increases the viscosity of molten slag, assists in slag formation, and may provide elements such as potassium and aluminum.

[0023] Chromium powder: Ensures the chromium content of duplex stainless steel, maintaining its corrosion resistance and duplex structure.

[0024] Manganese powder: deoxidizes, binds sulfur to reduce hot cracking, and stabilizes austenite.

[0025] Ferromolybdenum alloy powder: improves resistance to pitting and crevice corrosion and stabilizes ferrite.

[0026] Ferrochromium nitride powder: provides nitrogen, promotes austenite formation, and inhibits σ phase precipitation.

[0027] Lanthanum hexaboride (LaB6): It refines grains and cleans grain boundaries, reducing crack initiation and improving toughness; it reduces the precipitation of harmful phases (such as σ phase) and maintains corrosion resistance; rare earth elements can refine grains, boron inhibits grain boundary migration and purifies the molten pool, and boron pins grain boundaries by forming borides, slowing down atomic diffusion and reducing the driving force of phase transformation; lanthanum purifies grain boundaries, reduces impurity segregation, and stabilizes the microstructure. Excess boron may form brittle borides (such as Fe2B), so the amount added needs to be controlled.

[0028] Ti-6Al-4V alloy: avoids intergranular corrosion, improves high-temperature stability, and ensures proper austenite formation during cooling; during heat treatment, titanium preferentially combines with carbon / nitrogen to form Ti(C,N), reducing chromium carbide precipitation, maintaining the chromium content in the matrix, stabilizing the two-phase ratio, and vanadium refines the grains, inhibiting high-temperature grain coarsening. Although vanadium can improve hardness, it may also reduce corrosion resistance, so the addition of Ti-6Al-4V alloy must be strictly controlled.

[0029] Mg-Y-RE-Zr alloy: Magnesium and yttrium provide efficient deoxidation and desulfurization, rare earth elements spheroidize inclusions and reduce stress concentration; zirconium forms ZrC / ZrN, pinning grain boundaries; strong deoxidizing and desulfurizing agent, rare earth elements refine grains, zirconium forms stable precipitates. Although rare earth elements (RE) can improve corrosion resistance, during heat treatment, zirconium preferentially combines with carbon / nitrogen to form Zr(C,N), reducing chromium carbide precipitation, maintaining the chromium content in the matrix, and stabilizing the dual-phase ratio, excessive addition may lead to inhomogeneity of the weld structure, thus affecting the overall corrosion resistance. The amount of Mg-Y-RE-Zr alloy added should be reasonably controlled.

[0030] The present invention has the following beneficial effects:

[0031] This invention achieves grain refinement, phase stabilization, and grain boundary purification by rationally adjusting the composition of the welding electrode. This effectively slows down the phase transformation rate during high-temperature heat treatment, avoids excessive austenite formation, and maintains the balance of the two-phase structure. Grain refinement and clean grain boundaries reduce the risk of brittle fracture. At the same time, it effectively inhibits the precipitation of harmful phases such as the σ phase, ensures the solid solubility of chromium and molybdenum, and thus maintains corrosion resistance. These synergistic effects enable the weld to still have excellent comprehensive performance after high-temperature treatment. Detailed implementation method:

[0032] The present invention will be described in detail below with reference to embodiments. However, it should be understood that the following embodiments are merely illustrative examples of implementation of the present invention and are not intended to limit the scope of the invention. Unless otherwise specified, all raw materials used in the following embodiments of the present invention are purchased externally.

[0033] In the following embodiments of the present invention, the average particle size of each component of the flux is 50 mesh.

[0034] The binder used in the following embodiments of the present invention is potassium sodium water glass with a modulus of 2.5-3.5 and a potassium-sodium ratio of 3:1.

[0035] The purity of the chromium powder, ferromolybdenum alloy powder, and manganese powder in the following embodiments of the present invention is ≥99.9%.

[0036] Example 1

[0037] A welding electrode for welding duplex stainless steel comprises a core and a coating, wherein the coating comprises 38% of the total mass of the electrode. The coating includes a binder and a flux, with the mass ratio of binder to flux powder being 1:4. The core is made of 308L stainless steel, and the welding wire has a diameter of Ф3.2mm. The flux, by mass, has the following composition:

[0038]

[0039] The preparation method of the welding electrodes for duplex stainless steel mentioned above is as follows:

[0040] (1) Mix the flux and binder evenly according to the formula to obtain a uniform material;

[0041] (2) Using a pressure coating device, at 10MPa, the uniform material obtained in step (1) is combined with a 308L stainless steel core, so that the coating is uniformly wrapped on the outer surface of the core, thus obtaining the product.

[0042] Example 2

[0043] A welding electrode for welding duplex stainless steel comprises a core and a coating, wherein the coating comprises 40% of the total mass of the electrode. The coating includes a binder and a flux, with a binder to flux powder mass ratio of 1:4.3. The core is made of 308L stainless steel, and the welding wire has a diameter of Ф3.2mm. The flux, by mass, has the following composition:

[0044]

[0045] The preparation method of the welding electrodes for duplex stainless steel mentioned above is as follows:

[0046] (1) Mix the flux and binder evenly according to the formula to obtain a uniform material;

[0047] (2) Using a pressure coating device, at 12MPa, the uniform material obtained in step (1) is combined with a 308L stainless steel core, so that the coating is uniformly wrapped on the outer surface of the core, thus obtaining the product.

[0048] Example 3

[0049] A welding electrode for welding duplex stainless steel comprises a core and a coating, wherein the coating accounts for 42% of the total mass of the electrode. The coating includes a binder and a flux, with the mass ratio of binder to flux powder being 1:5. The core is made of 308L stainless steel, and the welding wire has a diameter of Ф3.2mm. The flux, by mass, has the following composition:

[0050]

[0051]

[0052] The preparation method of the welding electrodes for duplex stainless steel mentioned above is as follows:

[0053] (1) Mix the flux and binder evenly according to the formula to obtain a uniform material;

[0054] (2) Using a pressure coating device, at 15MPa, the uniform material obtained in step (1) is combined with a 308L stainless steel core, so that the coating is uniformly wrapped on the outer surface of the core, thus obtaining the product.

[0055] Comparative Example 1 is the same as Example 2, except that lanthanum hexaboride was not added in Comparative Example 1.

[0056] Comparative Example 2 is the same as Example 2, except that Ti-6Al-4V alloy was not added in Comparative Example 2.

[0057] Comparative Example 3 is the same as Example 2, except that WE43 alloy was not added in Comparative Example 3.

[0058] Comparative Example 4 is the same as Example 2, except that the mass fraction of WE43 alloy in the flux in Comparative Example 4 is 5 parts.

[0059] Comparative Example 5 is the same as Example 2, except that the mass fraction of lanthanum hexaboride in the flux in Comparative Example 5 is 3 parts.

[0060] Comparative Example 6 uses ER2209 duplex stainless steel welding wire with a wire specification of Ф3.2mm.

[0061] Performance testing

[0062] The welding process conditions are shown in Table 1:

[0063] Table 1

[0064]

[0065] The welding electrodes obtained in Examples 1-3 and Comparative Examples 1-6 of this invention were used to weld UNSS32205 base material. After welding, the mechanical properties of the weld metal were tested, and the specific test results are shown in Table 2.

[0066] Mechanical properties of the weld cladding metal: tested according to the tensile test method in ASTM E8 / E8M "Metallic materials, tensile testing method".

[0067] Table 2

[0068] Test Items Tensile strength (MPa) Elongation (%) Example 1 855 27.0 Example 2 868 26.2 Example 3 857 27.2 Comparative Example 1 833 29.1 Comparative Example 2 837 28.9 Comparative Example 3 829 29.2 Comparative Example 4 846 27.9 Comparative Example 5 852 27.3 Comparative Example 6 830 29.0

[0069] The welds obtained in Examples 1-3 and Comparative Examples 1-6 were then subjected to heat treatment, and the heat treatment process is as follows:

[0070] (1) Place the welded sample in an annealing furnace and heat it from room temperature to 350°C for 1 hour.

[0071] (2) The welding sample is then heated from 350℃ to 690℃ for 1.5 hours.

[0072] (3) Keep the welding sample at 690℃ for 1 hour.

[0073] (4) Turn off the power to the annealing furnace, open the furnace door, and allow the welded samples to cool naturally to room temperature. Then, the mechanical properties of the weld metal were tested, and the results are shown in Table 3.

[0074] Table 3

[0075] Test Items Tensile strength (MPa) Elongation (%) Example 1 840 28.5 Example 2 847 27.9 Example 3 836 28.7 Comparative Example 1 808 31.6 Comparative Example 2 812 31.4 Comparative Example 3 804 31.7 Comparative Example 4 821 30.4 Comparative Example 5 827 29.8 Comparative Example 6 763 35.0

[0076] Intergranular corrosion tests were conducted on the heat-treated weld cladding metal according to standard GB / T4334.5-2020 "Stainless Steel Corrosion Test Methods Part 5: Sulfuric Acid-Copper Sulfate Corrosion Test". The corrosion time was 20 hours. After the test, the samples were removed, cleaned, and the sample surface was observed with a low-magnification magnifying glass. The test results showed that the welds formed in Examples 1-3 did not show cracks on the surface after the intergranular corrosion test, indicating that the welds have strong resistance to intergranular corrosion. The welds obtained in Comparative Examples 4-5 did not show cracks on the surface, while the welds obtained in Comparative Examples 1-3 and 6 all showed microcracks on the surface.

[0077] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A welding electrode for welding duplex stainless steel, characterized in that, The electrode comprises a core and a coating, wherein the coating accounts for 38-42% of the total mass of the electrode. The coating includes a binder and a flux, wherein the mass ratio of the binder to the flux powder is 1:4-5. The core is made of low-carbon stainless steel, and the flux contains lanthanum hexaboride, Mg-Y-RE-Zr alloy, and titanium alloy powder. The titanium alloy powder is of the grade Ti-6Al-4V alloy. The flux, by weight, comprises the following components: 5-10 parts marble powder 5-10 parts of calcium fluoride powder Barium fluoride powder 3-8 3-8 parts of calcium oxide powder; 10-15 parts rutile powder; 5-8 parts mica powder; 22-25 parts chromium powder; 1-3 parts iron powder; 3-7 parts manganese powder; 10-15 parts of ferromolybdenum alloy powder; 3-5 parts of chromium nitride powder; Lanthanum hexaboride 0.5-2 parts; 1-5 parts of Ti-6Al-4V alloy; 1-3 parts of Mg-Y-RE-Zr alloy.

2. The welding electrode for welding duplex stainless steel according to claim 1, characterized in that, The flux, by weight, comprises the following components: 8 parts marble powder 6 parts calcium fluoride powder Barium fluoride powder 5 5 parts calcium oxide powder; 12 parts rutile powder; 6 parts mica powder; 23 parts chromium powder; 1.5 parts iron powder; 5 parts manganese powder; 13 parts of ferromolybdenum alloy powder; 3 parts of chromium nitride powder; 1 part of lanthanum hexaboride; Three parts of Ti-6Al-4V alloy; Two parts of Mg-Y-RE-Zr alloy.

3. A welding electrode for welding duplex stainless steel according to claim 1 or 2, characterized in that, The alloy grade of Mg-Y-RE-Zr is WE43 alloy.

4. The welding electrode for welding duplex stainless steel according to claim 1, characterized in that, The average particle size of each component in the flux is 10-100 mesh.

5. The welding electrode for welding duplex stainless steel according to claim 1, characterized in that, The binder is potassium sodium silicate.

6. The welding electrode for welding duplex stainless steel according to claim 5, characterized in that, The potassium-sodium water glass has a modulus of 2.5-3.5 and a potassium-to-sodium ratio of 3:

1.

7. The welding electrode for welding duplex stainless steel according to claim 1, characterized in that, The low-carbon stainless steel is 308L stainless steel.

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