Welding rod for welding duplex stainless steel and preparation method thereof

Abstract

The invention relates to the technical field of welding rods for duplex stainless steel welding, in particular to a welding rod for duplex stainless steel welding and a preparation method thereof. When the residual stress at the welding seam of the 2209 duplex stainless steel is eliminated through high-temperature heat treatment, the mechanical property and the corrosion resistance of the welding seam can be obviously reduced. In order to solve the technical problems, the invention provides the welding rod for welding the duplex stainless steel, the phase change rate during high-temperature heat treatment is effectively slowed down, excessive austenite is prevented from being generated, and the balance of a duplex structure is kept; lanthanum hexaboride, Ti-6Al-4V alloy and other components which have the grain refinement effect and meanwhile can inhibit precipitation of harmful phases among metals are specially added into components of the welding rod coating, precipitation of the harmful phases such as sigma and the like in the weld joint heat treatment process is effectively inhibited, the solid solubility of chromium and molybdenum is ensured, and a weld joint still has excellent comprehensive performance after high-temperature treatment.

Description

Technical Field

[0001] The invention relates to the technical field of duplex stainless steel, and in particular to a welding rod for duplex stainless steel welding and a preparation method thereof. Background Art

[0002] In the field of stainless steel materials, duplex stainless steel has attracted much attention due to its unique microstructure and excellent comprehensive performance. Among them, 2205 duplex stainless steel, as a typical representative, has shown excellent corrosion resistance and high strength with its chemical composition of about 22% chromium, 5% nickel, 3% molybdenum and about 0.15% nitrogen. The advantages of this stainless steel mainly come from its structural design of austenite and ferrite phase balance, and the strengthening effect of nitrogen on the material in the solid solution state. The austenite phase provides good toughness and corrosion resistance, while the ferrite phase enhances the strength and resistance to stress corrosion cracking of the material.

[0003] However, in practical applications, the welding process of 2205 duplex stainless steel has become a technical difficulty. In order to ensure the quality of the weld, ER2209 welding rods with a composition similar to that of the parent material are usually used for welding. Although this welding rod can ensure the consistency of the chemical composition of the weld and the parent material 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 performance of the weld.

[0004] Specifically, after welding, large internal stress often remains in the weld area, which needs to be eliminated through heat treatment. However, during the heat treatment process, the balance between austenite and ferrite in the weld is easily broken, resulting in the precipitation of harmful phases such as σ phase, χ phase and carbide. The precipitation of these harmful phases not only changes the microstructure of the weld, but also causes an imbalance in the ratio of austenite and ferrite, which seriously affects the mechanical properties and corrosion resistance of the weld.

[0005] The appearance of σ phase and χ phase will reduce the toughness and plasticity of the weld and increase the brittleness of the material; while the precipitation of carbides will consume alloy elements such as chromium and nickel in the weld, resulting in a decrease in the corrosion resistance of the weld. Therefore, how to effectively avoid the precipitation of harmful phases during heat treatment and maintain the two-phase balance of austenite and ferrite in the weld while ensuring welding efficiency and quality has become a technical problem that needs to be solved urgently. Summary of the invention

[0006] The problem in the prior art is that when the residual stress at the weld of 2205 duplex stainless steel is eliminated by heat treatment, the tensile strength and corrosion resistance of the weld will be significantly reduced. In view of the above technical problems, the present invention provides a welding rod for duplex stainless steel welding, which comprises a flux core and a coating, the coating accounts for 38-42% of the total mass of the welding rod, the coating comprises a binder and a flux, the mass ratio of the binder to the flux powder is 1:4-5, the flux core is low-carbon stainless steel, and lanthanum hexaboride, Mg-Y-RE-Zr alloy and titanium alloy powder are added to the flux, and the grade of the titanium alloy powder is Ti-6Al-4V alloy.

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

[0008]

[0009]

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

[0011]

[0012] Preferably, the grade of the Mg-Y-RE-Zr alloy is 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 water glass.

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

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

[0017] The physical and chemical analysis of each component in the flux is as follows:

[0018] Marble powder (CaCO 3 ): Decomposed into CaO and CO at high temperature 2 , CaO is used as alkaline slagging agent for desulfurization and dephosphorization; CO 2 Provide protective gas to prevent atmospheric contamination of the molten pool.

[0019] Calcium fluoride (CaF 2 ) and barium fluoride (BaF 2 ): Reduce the melting point of slag, improve fluidity, stabilize the arc, reduce hydrogen absorption and prevent porosity.

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

[0021] Rutile (TiO 2 ): Stabilize the arc, improve slag coverage, promote oxygen control, and optimize alloy transition.

[0022] Mica powder: increases slag viscosity, assists slag making, and may provide elements such as potassium and aluminum.

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

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

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

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

[0027] Lanthanum hexaboride (LaB 6 ): Fine grain strengthening and clean grain boundaries reduce crack initiation and improve toughness; reduce harmful phase precipitation (such as σ phase) and maintain corrosion resistance; rare earth elements can refine grains, boron inhibits grain boundary migration, purifies the molten pool, and boron pins grain boundaries by forming borides, slows down atomic diffusion, and reduces the driving force of phase transformation; lanthanum purifies grain boundaries, reduces impurity segregation, and stabilizes the microstructure. Excessive B may form brittle borides (such as Fe 2 B), the amount of addition needs to be controlled.

[0028] Ti-6Al-4V alloy: avoids intergranular corrosion, improves high-temperature stability, and ensures that austenite is formed in an appropriate amount during cooling; during heat treatment, titanium preferentially combines with carbon / nitrogen to form Ti(C,N), reduces the precipitation of chromium carbides, maintains the chromium content of the matrix, stabilizes the dual-phase ratio, and vanadium refines the grains and inhibits high-temperature grain coarsening. Although vanadium can increase hardness, it may also reduce corrosion resistance. The addition of Ti-6Al-4V alloy must be strictly controlled.

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

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

[0031] The present invention achieves the effects of grain refinement, stabilization of precipitation phase and purification of grain boundaries by reasonably adjusting the composition of the welding rod, effectively slowing down the phase transformation rate during high-temperature heat treatment, avoiding excessive austenite formation, and maintaining the balance of the two-phase structure; grain refinement and clean grain boundaries reduce the risk of brittle fracture; at the same time, the precipitation of harmful phases such as σ phase is effectively suppressed, ensuring the solid solubility of chromium and molybdenum, thereby maintaining corrosion resistance. These synergistic effects enable the weld to still have excellent comprehensive performance after high-temperature treatment. DETAILED DESCRIPTION

[0032] The present invention is described in detail below in conjunction with the examples. However, it should be understood that the following examples are only illustrative of the embodiments of the present invention, rather than limiting the scope of the present invention. The raw materials in the following examples of the present invention are purchased from outside unless otherwise specified.

[0033] The average particle size of each component of the flux in the following examples of the present invention is 50 mesh.

[0034] The binder 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 rod for duplex stainless steel welding, which consists of a flux core and a coating, the coating accounts for 38% of the total mass of the welding rod, the coating includes a binder and a flux, the mass ratio of the binder to the flux powder is 1:4, the flux core is 308L stainless steel, the welding wire specification is Ф3.2mm, and the flux, in terms of mass fractions, has the following composition:

[0038]

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

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

[0041] (2) Compounding the uniform material obtained in step (1) with a 308L stainless steel core by a pressure coating device at 10 MPa, so that the coating is evenly wrapped around the outer surface of the core.

[0042] Example 2

[0043] A welding rod for duplex stainless steel welding, which consists of a flux core and a coating, the coating accounts for 40% of the total mass of the welding rod, the coating includes a binder and a flux, the mass ratio of the binder to the flux powder is 1:4.3, the flux core is 308L stainless steel, the welding wire specification is Ф3.2mm, and the flux, in terms of mass fractions, has the following composition:

[0044]

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

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

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

[0048] Example 3

[0049] A welding rod for duplex stainless steel welding, which consists of a flux core and a coating, the coating accounts for 42% of the total mass of the welding rod, the coating includes a binder and a flux, the mass ratio of the binder to the flux powder is 1:5, the flux core is 308L stainless steel, the welding wire specification is Ф3.2mm, and the flux, in terms of mass fraction, has the following composition:

[0050]

[0051]

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

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

[0054] (2) Compounding the uniform material obtained in step (1) with a 308L stainless steel core by a pressure coating device at 15 MPa, so that the coating is evenly wrapped around the outer surface of the core.

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

[0056] Comparative Example 2 is the same as Example 2, except that no Ti-6Al-4V alloy is added in Comparative Example 2.

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

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

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

[0060] Comparative Example 6 is ER2209 duplex stainless steel welding wire, and the welding wire specification is Ф3.2mm.

[0061] Performance Testing

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

[0063] Table 1

[0064]

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

[0066] Mechanical properties of cladding metal at weld: tested according to the tensile test method in ASTM E8 / E8M "Tensile Test Methods for Metallic Materials" standard.

[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] Then, the welds obtained in Examples 1-3 and Comparative Examples 1-6 were heat treated, and the heat treatment process was as follows:

[0070] (1) Place the welding 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°C to 690°C for 1.5 hours;

[0072] (3) Keep the welded specimen at 690°C for 1 h.

[0073] (4) Turn off the power of the annealing furnace, open the furnace door, and let the welded sample cool naturally to room temperature. Then, the mechanical properties of the cladding metal at the weld were tested. The test 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 carried out on the weld cladding metals after heat treatment according to the standard GB / T4334.5-2020 "Stainless Steel Corrosion Test Method Part 5: Sulfuric Acid-Copper Sulfate Corrosion Test". The corrosion time was 20 hours. After the test, the samples were taken out and cleaned. The surface of the sample was observed with a low-power magnifying glass. The test results showed that no cracks appeared on the surface of the welds formed in Examples 1-3 after the intergranular corrosion test, indicating that the welds have strong resistance to intergranular corrosion. No cracks appeared on the surfaces of the welds obtained in Comparative Examples 4-5, while microcracks appeared on the surfaces of the welds obtained in Comparative Examples 1-3 and 6, respectively.

[0077] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A welding rod for duplex stainless steel welding, characterized in that: The invention comprises a flux core and a flux coating, wherein the flux coating accounts for 38-42% of the total mass of the electrode, the flux coating comprises a binder and a flux, the mass ratio of the binder to the flux powder is 1:4-5, the flux core is low-carbon stainless steel, lanthanum hexaboride, Mg-Y-RE-Zr alloy and titanium alloy powder are added to the flux, and the grade of the titanium alloy powder is Ti-6Al-4V alloy.

2. A welding rod for duplex stainless steel welding according to claim 1, characterized in that: The flux comprises the following components in parts by mass: 5-10 parts marble powder Calcium fluoride powder 5-10 parts Barium fluoride powder 3-8 powder 3-8 parts of calcium oxide powder; 10-15 parts of rutile powder; 5-8 parts of mica powder; 22-25 parts of chromium powder; 1-3 parts of iron powder; 3-7 parts of manganese powder; 10-15 parts of ferromolybdenum alloy powder; 3-5 parts of ferrochrome nitride powder; 0.5-2 parts of lanthanum hexaboride; Ti-6Al-4V alloy 1-5 parts; 1-3 parts of Mg-Y-RE-Zr alloy.

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

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

5. A welding rod for duplex stainless steel welding according to claim 1, characterized in that: The average particle size of each component in the flux is 10-100 meshes.

6. A welding rod for duplex stainless steel welding according to claim 1, characterized in that: The binder is potassium sodium water glass.

7. A welding rod for duplex stainless steel welding according to claim 6, characterized in that: The modulus of the potassium-sodium water glass is 2.5-3.5, and the potassium-sodium ratio is 3:

1.

8. The welding rod for duplex stainless steel welding according to claim 1, characterized in that: The low carbon stainless steel is 308L stainless steel.

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