A low-cost flux-cored welding wire for duplex stainless steel and its preparation method

Abstract

The present invention relates to the technical field of stainless steel flux-cored welding wires, and specifically to a low-cost flux-cored welding wire for duplex stainless steel and a preparation method thereof. Currently on the market, no stainless steel flux-cored welding wire for all-position welding of S32001 duplex stainless steel pipes has been developed. In response to the above technical problems, the present invention provides a low-cost flux-cored welding wire for duplex stainless steel. By studying and analyzing the composition of S32001 duplex stainless steel pipes and through a large number of experimental studies, a duplex stainless steel flux-cored welding wire all-position welding material that matches the S32001 duplex stainless steel pipes is developed. The material has a low Ni content, low cost, good welding stability, and the obtained weld has excellent comprehensive mechanical properties. This innovation has effectively promoted the widespread application of S32001 duplex stainless steel pipes in urban underground pipeline construction, demonstrating extremely high practical value.

Description

Technical Field

[0001] The invention relates to the technical field of stainless steel flux-cored welding wires, and in particular to a low-cost flux-cored welding wire for duplex stainless steel and a preparation method thereof. Background Art

[0002] Urban underground sewage pipeline systems are crucial infrastructure for ensuring urban ecological security and sustainable development. The performance of their pipes directly impacts the network's service life, maintenance costs, and environmental risks. Currently, ductile iron and PVC (polyvinyl chloride) are the primary mainstream pipe materials, but their performance limitations under complex operating conditions are becoming increasingly apparent. Duplex stainless steel, due to its comprehensive performance advantages, is becoming the preferred next-generation pipe material. The following analysis examines the differences between different pipe materials from the perspectives of technical limitations and market demand.

[0003] Ductile iron uses a graphite spheroidization process to improve its toughness, but it is still an iron-based material and has the following inherent defects:

[0004] Corrosion protection relies on external coatings: In sewage containing Cl⁻, H₂S, or acidic media (pH < 5), cement mortar or epoxy coatings are prone to peeling and pore corrosion, leading to rapid rust of the substrate (annual average corrosion rate > 0.1mm), posing a risk of leakage; high density and installation complexity: The density is as high as 7.3g / cm³, requiring heavy machinery for lifting; socket-type joints rely on rubber sealing rings, which are prone to relaxation and failure under long-term pressure, with a leakage rate as high as 5%-10%.

[0005] Although PVC pipes are lightweight and low-cost, their performance limitations severely restrict their application scenarios:

[0006] Insufficient mechanical properties: The elastic modulus is only 2-4GPa, and it is prone to buckling and deformation (deformation rate <5%) when buried at a depth greater than 3m or under dynamic loads (such as traffic vibration); it is significantly brittle at low temperatures (impact strength drops by 70% at -5°C), and cannot adapt to cold areas; narrow chemical tolerance: it is sensitive to hydrocarbons, ester organic solvents and concentrated sulfuric acid (concentration > 50%), and the pipe wall swelling rate reaches 8%-12% after contact, leading to structural failure; the upper limit of long-term use temperature is 60°C, and high-temperature sewage (> 70°C) will induce thermal creep.

[0007] Duplex stainless steel (DSS) offers significant advantages due to its two-phase (austenite + ferrite) microstructure:

[0008] Excellent corrosion resistance: High Cr (22%-25%), Mo (3%-4%), and N content maintains passivation film stability (corrosion rate <0.01mm / a) in extreme media with Cl⁻ concentration >20,000ppm and pH = 2-12; High strength and lightweight: Tensile strength ≥620MPa (twice that of ductile iron) and density 7.8g / cm³ can reduce wall thickness by more than 30%, reducing material usage; Wide temperature range adaptability: No significant degradation of mechanical properties within the range of -50°C to 250°C, avoiding the risk of thermal deformation or low-temperature brittle cracking.

[0009] However, the price of duplex stainless steel raw materials is 4-5 times that of ductile iron, and the high cost has seriously restricted the development of duplex stainless steel pipeline technology.

[0010] S32001 duplex stainless steel offers excellent corrosion resistance, strength, and impact toughness. Compared to traditional duplex stainless steel, S32001 duplex stainless steel has a lower nickel content and is relatively inexpensive, making it a promising candidate for use as a base material for sewage pipes in urban underground sewage systems. Currently, the only welding material suitable for S32001 duplex stainless steel is stainless steel electrodes (which cannot achieve full-position welding of the tubular base material). Stainless steel flux-cored wire specifically designed for full-position welding of S32001 duplex stainless steel pipes has not yet been developed on the market. Summary of the Invention

[0011] The problem existing in the prior art is that currently on the market, no stainless steel flux-cored welding wire has been developed for all-position welding of S32001 duplex stainless steel pipes. In response to the above technical problems, the present invention provides a low-cost flux-cored welding wire for duplex stainless steel, which comprises an iron sheet and a flux core. The filling rate of the flux core in the iron sheet is 22-28%, the iron sheet is a stainless steel strip, and the flux core comprises, by mass percentage, 16-20% rutile powder, 3-5% aluminum oxide powder, 1-5% iron oxide powder, 3-4% fluoride powder, 2.5-5% silicon dioxide powder, 1-2% titanium dioxide powder, 1-2% zirconium-iron alloy powder, 0.3-0.6% bismuth oxide powder, 24-28% manganese powder, 3-4.5% arc stabilizer, 3-5% nickel powder, 18% chromium powder, 3-4.5% molybdenum-iron alloy powder, 1-1.5% magnesium powder, 1.8-2% marble, 1.5-3% feldspar, and iron powder as the balance.

[0012] Preferably, the stainless steel strip comprises the following elements in percentage by mass:

[0013] Carbon 0.01-0.02%;

[0014] Silicon 0.1-0.5%;

[0015] Manganese 1-2%;

[0016] Sulfur ≤ 0.02%;

[0017] Phosphorus ≤ 0.004%;

[0018] Nickel 8-10%;

[0019] Chromium 18-20%;

[0020] Molybdenum 0.01-0.02%;

[0021] Aluminum 0.01-0.03%;

[0022] Nitrogen 0.2-0.4%;

[0023] Iron balance.

[0024] Preferably, the fluoride powder is a mixture of cryolite and cerium fluoride in a mass ratio of 3:1.

[0025] Preferably, the iron oxide powder is a mixture of ferric oxide and ferrosoferric oxide in a mass ratio of 1:2.

[0026] Preferably, the mass ratio of zirconium to iron in the zirconium-iron alloy powder is 4:1.

[0027] Preferably, the arc stabilizer is composed of TiO2, K2O, and MgO in a mass ratio of 5:3:2.

[0028] Preferably, the mass ratio of molybdenum to iron in the molybdenum-iron alloy powder is in the range of 4:1.

[0029] Preferably, the rare earth alloy powder is a mixture of cryolite and cerium fluoride in a mass ratio of 3:1.

[0030] A method for preparing a low-cost flux-cored welding wire for duplex stainless steel comprises the following steps:

[0031] (1) Roll the stainless steel strip into a U-shape and add the formulated core component into the U-shaped groove;

[0032] (2) The U-shaped groove is rolled into an O-shaped steel pipe, and then rolled, sized, drawn, bright annealed, reduced in diameter, and mechanically cleaned to obtain a low-cost duplex stainless steel flux-cored welding wire with a diameter of Φ = 1.2-1.6 mm.

[0033] The present invention has the following beneficial effects:

[0034] (1) The low-cost duplex stainless steel flux-cored welding wire obtained by the present invention can realize all-position welding of S32001 duplex stainless steel pipes, and the strength and impact toughness of the weld cladding metal obtained can meet the required welding standards;

[0035] (2) By rationally designing the formula of the flux-cored welding wire, the low-cost duplex stainless steel flux-cored welding wire obtained by the present invention has good welding stability during high-temperature welding, small spatter, and excellent mechanical properties of the obtained weld. DETAILED DESCRIPTION

[0036] The present invention will be described in detail below with reference to the following examples. However, it should be understood that the following examples are merely illustrative of the embodiments of the present invention and are not intended to limit the scope of the present invention.

[0037] The raw materials used in the following examples of the present invention are all commercially available, and the purity of the raw materials is 99.9%.

[0038] The fluoride powder used in the following examples of the present invention is a mixture of cryolite and cerium fluoride in a mass ratio of 3:1.

[0039] The iron oxide powder used in the following examples of the present invention is a mixture of ferric oxide and ferrosoferric oxide in a mass ratio of 1:2.

[0040] The mass ratio of zirconium to iron in the ferro-zirconium alloy powder used in the following examples of the present invention is 4:1.

[0041] The arc stabilizer used in the following embodiments of the present invention is composed of TiO2, K2O, and MgO in a mass ratio of 5:3:2.

[0042] The mass ratio of molybdenum to iron in the ferromolybdenum alloy powder used in the following examples of the present invention is 4:1.

[0043] The elemental composition of the stainless steel strip used in the following embodiments of the present invention is as follows:

[0044] Carbon 0.015%;

[0045] Silicon 0.3%;

[0046] Manganese 1.5%;

[0047] Sulfur 0.012%;

[0048] Phosphorus 0.002%;

[0049] Nickel 9.8%;

[0050] Chromium 18.2%;

[0051] Molybdenum 0.015%;

[0052] Aluminum 0.013%;

[0053] Nitrogen 0.25%;

[0054] The balance is iron.

[0055] Example 1

[0056] A low-cost flux-cored welding wire for duplex stainless steel, comprising an iron sheet and a flux core. The flux core has a filling rate of 23% in the iron sheet. The iron sheet is a stainless steel strip with a thickness of 0.4 mm. The flux core is composed of the following components in percentage by mass:

[0057] 16% rutile powder, 3% alumina powder, 5% iron oxide powder, 4% fluoride powder, 2.5% silicon dioxide powder, 1% titanium dioxide powder, 2% zirconium-iron alloy powder, 0.6% bismuth oxide powder, 28% manganese powder, 4% arc stabilizer, 4% nickel powder, 18% chromium powder, 3% molybdenum-iron alloy powder, 1.5% magnesium powder, 2% marble, 1.5% feldspar, and iron powder as the balance.

[0058] The preparation method of the low-cost duplex stainless steel flux-cored welding wire is as follows:

[0059] (1) Roll the stainless steel strip into a U-shape, add the formulated amount of core powder into the U-shaped groove, and the average particle size of the core powder is 500 mesh;

[0060] (2) The U-shaped groove is rolled into an O-shaped steel tube, and the filling rate of the core powder in the O-shaped steel tube is 23%;

[0061] (3) The O-shaped steel pipe is rolled through 6 groups of 30 roller dies, drawn through 1 sizing die, and then annealed by a wire to produce Φ2.0mm stainless steel flux-cored wire;

[0062] (4) The welding wire obtained in step (3) is subjected to 10 drawing processes and mechanical surface cleaning to be made into a Φ1.2 stainless steel flux-cored welding wire.

[0063] Example 2

[0064] A low-cost flux-cored welding wire for duplex stainless steel, comprising an iron sheet and a flux core. The flux core has a filling rate of 25% in the iron sheet. The iron sheet is a stainless steel strip with a thickness of 0.4 mm. The flux core has the following composition, calculated by mass percentage:

[0065] 17% rutile powder, 5% alumina powder, 1% iron oxide powder, 3% fluoride powder, 5% silicon dioxide powder, 2% titanium dioxide powder, 1% zirconium-iron alloy powder, 0.3% bismuth oxide powder, 26% manganese powder, 4.5% arc stabilizer, 3% nickel powder, 18% chromium powder, 4% molybdenum-iron alloy powder, 1% magnesium powder, 1.8% marble, 2% feldspar, iron powder as balance.

[0066] The preparation method of the low-cost duplex stainless steel flux-cored welding wire is as follows:

[0067] (1) Roll the stainless steel strip into a U-shape, add the formulated amount of core powder into the U-shaped groove, and the average particle size of the core powder is 500 mesh;

[0068] (2) The U-shaped groove is rolled into an O-shaped steel tube, and the filling rate of the core powder in the O-shaped steel tube is 25%;

[0069] (3) The O-shaped steel pipe is rolled through 6 groups of 30 roller dies, drawn through 1 sizing die, and then annealed by a wire to produce Φ2.0mm stainless steel flux-cored wire;

[0070] (4) The welding wire obtained in step (3) is subjected to 10 drawing processes and mechanical surface cleaning to be made into a Φ1.2 stainless steel flux-cored welding wire.

[0071] Example 3

[0072] A low-cost flux-cored welding wire for duplex stainless steel, comprising an iron sheet and a flux core. The flux core has a filling rate of 28% in the iron sheet. The iron sheet is a stainless steel strip with a thickness of 0.4 mm. The flux core has the following composition, calculated by mass percentage:

[0073] 20% rutile powder, 3% alumina powder, 2% iron oxide powder, 3% fluoride powder, 3% silicon dioxide powder, 2% titanium dioxide powder, 2% zirconium-iron alloy powder, 0.35% bismuth oxide powder, 24% manganese powder, 3% arc stabilizer, 5% nickel powder, 18% chromium powder, 4.5% molybdenum-iron alloy powder, 1% magnesium powder, 1.8% marble, 3% feldspar, iron powder as balance.

[0074] The preparation method of the low-cost duplex stainless steel flux-cored welding wire is as follows:

[0075] (1) Roll the stainless steel strip into a U-shape, add the formulated amount of core powder into the U-shaped groove, and the average particle size of the core powder is 500 mesh;

[0076] (2) The U-shaped groove is rolled into an O-shaped steel tube, and the filling rate of the core powder in the O-shaped steel tube is 28%;

[0077] (3) The O-shaped steel pipe is rolled through 6 groups of 30 roller dies, drawn through 1 sizing die, and then annealed by a wire to produce Φ2.0mm stainless steel flux-cored wire;

[0078] (4) The welding wire obtained in step (3) is subjected to 10 drawing processes and mechanical surface cleaning to be made into a Φ1.2 stainless steel flux-cored welding wire.

[0079] Comparative Example 1 is the same as Example 2, except that the drug core in Comparative Example 1 is composed of the following components in terms of mass percentage:

[0080] 13% rutile powder, 2% alumina powder, 2% iron oxide powder, 1.5% fluoride powder, 2% silicon dioxide powder, 2% titanium dioxide powder, 2% zirconium-iron alloy powder, 0.3% bismuth oxide powder, 29% manganese powder, 5% arc stabilizer, 2% nickel powder, 22% chromium powder, 1.2% magnesium powder, and iron powder as the balance.

[0081] Comparative Example 2 is the same as Example 1, except that the medicinal core in Comparative Example 2 is composed of the following components in terms of mass percentage:

[0082] 33% manganese powder, 4% arc stabilizer, 45% chromium powder, 5% magnesium powder, 1% manganese nitride, and iron powder as balance.

[0083] Comparative Example 3 is the same as Example 2, except that the medicinal core in Comparative Example 3 is composed of the following components in terms of mass percentage:

[0084] 15% rutile powder, 2% alumina powder, 4% iron oxide powder, 2% fluoride powder, 3% silicon dioxide powder, 1% titanium dioxide powder, 1% zirconium-iron alloy powder, 0.3% bismuth oxide powder, 33% manganese powder, 3% arc stabilizer, 20% chromium powder, and iron powder as the balance.

[0085] Comparative Example 4 is the same as Example 2, except that the medicinal core in Comparative Example 4 is composed of the following components in terms of mass percentage:

[0086] 10% rutile powder, 2% alumina powder, 3% iron oxide powder, 2% fluoride powder, 5% silicon dioxide powder, 1% titanium dioxide powder, 1% zirconium-iron alloy powder, 0.3% bismuth oxide powder, 30% manganese powder, 3% arc stabilizer, 2% nickel powder, 20% chromium powder, 1% molybdenum-iron alloy powder, 1% magnesium powder, 4% marble, 2% feldspar, iron powder as balance.

[0087] Comparative Example 5 is the same as Example 2, except that the core in Comparative Example 5 is composed of the following components in terms of mass percentage:

[0088] 17% rutile powder, 3% alumina powder, 2% iron oxide powder, 2% fluoride powder, 4% silicon dioxide powder, 2% titanium dioxide powder, 1% zirconium-iron alloy powder, 0.3% bismuth oxide powder, 27% manganese powder, 4% arc stabilizer, 4% nickel powder, 19% chromium powder, 1% molybdenum-iron alloy powder, 1% magnesium powder, 1% marble, 2% feldspar, iron powder as balance.

[0089] Comparative Example 6 is the same as Example 2, except that the fluoride powder in Comparative Example 6 is a mixture of cryolite and cerium fluoride in a mass ratio of 1:1.

[0090] Comparative Example 7 is the same as Example 2, except that the fluoride powder in Comparative Example 7 is a mixture of cryolite and cerium fluoride in a mass ratio of 1:3.

[0091] Comparative Example 8 is the same as Example 2, except that the iron oxide powder in Comparative Example 8 is a mixture of ferric oxide and ferrosoferric oxide in a mass ratio of 1:1.

[0092] Comparative Example 9 is the same as Example 2, except that the iron oxide powder in Comparative Example 9 is a mixture of ferric oxide and ferrosoferric oxide in a mass ratio of 2:1.

[0093] Comparative Example 10 is the same as Example 2, except that the arc stabilizer in Comparative Example 10 is composed of TiO2, K2O, and MgO in a mass ratio of 5:1:4.

[0094] Comparative Example 11 is the same as Example 2, except that the arc stabilizer in Comparative Example 11 is composed of TiO2, K2O, and MgO in a mass ratio of 2:5:3.

[0095] Comparative Example 12 is the same as Example 2, except that the iron sheet in Comparative Example 12 is a common commercially available 304L stainless steel strip.

[0096] Performance Testing

[0097] Five layers of S32001 duplex stainless steel base material were overlay-welded using the flux-cored welding wires obtained in Examples 1-3 of the present invention and Comparative Examples 1-12, respectively, with three passes per layer. After the overlay welding, the resulting weld cladding metals were subjected to relevant performance tests. Each parallel experiment was tested 10 times, and the average value was taken. The specific test results are shown in Tables 1, 2, and 3. After overlay welding under CO2 shielding gas using the flux-cored welding wires obtained in Examples 1-3 of the present invention and Comparative Examples 1-12, the composition of the weld cladding metals was sampled and analyzed. The analysis results are shown in Table 3. For the elemental composition analysis of the weld cladding metals, the weld was first ground 2 mm downward along its surface before the elemental composition analysis was performed.

[0098] Tensile strength: The test standard is GB / T 228-2021.

[0099] Elongation at break: The test standard is GB / T 228-2121.

[0100] Impact energy: The test standard is GB / T 229-2020.

[0101] Bending performance: The test standard is GB / T 232-2010.

[0102] Splash performance: The test standard is GB / T25776-2010.

[0103] Table 1

[0104]

[0105] Table 2

[0106]

[0107] Table 3

[0108] .

[0109] According to the analysis of Tables 1-3, in Comparative Example 1, no molybdenum-iron alloy powder was added, and the grain structure of the organization could not be refined, resulting in poor toughness of the weld; as a ferrite-forming element, not adding Mo easily leads to a decrease in the ferrite content in the weld.

[0110] In Comparative Examples 2 and 3, nickel powder and molybdenum-iron alloy powder were not added, and the weld structure could not be regulated by the synergistic effect of the three elements Ni, Cr, and Mo. In addition, rare earth alloy powder was not added, resulting in a significant decrease in the comprehensive mechanical properties.

[0111] In Comparative Example 4, a small amount of molybdenum-iron alloy powder was added, so that the chemical composition and mechanical properties of the weld could not meet the standard requirements; and excessive addition of marble powder increased the spattering during welding.

[0112] In Comparative Example 5, a small amount of molybdenum-iron alloy powder was added, so that the chemical composition and mechanical properties of the weld could not meet the standard requirements.

[0113] In Comparative Examples 6 and 7, the ratio of cryolite to cerium fluoride in the fluoride added did not reach the appropriate range, resulting in increased spatter during welding, but did not affect the mechanical properties.

[0114] In Comparative Examples 8 and 9, the ratio of ferric oxide to ferrosoferric oxide in the iron oxide powder added did not reach the appropriate range, resulting in increased spatter during welding, but did not affect the mechanical properties.

[0115] In Comparative Examples 10 and 11, the ratio of TiO2, K2O, and MgO in the arc stabilizer was changed, which made the arc unstable during welding and caused a slight increase in spatter.

[0116] Comparative Example 12 uses common commercially available 304L stainless steel strip, which has a lower nitrogen content and a significantly lower strength.

[0117] The present invention effectively ensures the ferrite content in the weld cladding metal by increasing the amount of Mo added to the flux-cored welding wire, and effectively ensures the mechanical properties of the weld by adding N and rare earth elements. At the same time, the slag system formula is adjusted to improve the surface tension of the molten pool, thereby achieving all-position welding capability and a lower spatter rate and being suitable for S32001 pipe welding, thereby meeting welding requirements.

Claims

1. A low-cost flux-cored welding wire for duplex stainless steel, characterized in that: The invention comprises an iron sheet and a flux core, wherein the filling rate of the flux core in the iron sheet is 22-28%, the iron sheet is a stainless steel strip, and the flux core comprises, by weight percentage, 16-20% rutile powder, 3-5% aluminum oxide powder, 1-5% iron oxide powder, 3-4% fluoride powder, 2.5-5% silicon dioxide powder, 1-2% titanium dioxide powder, 1-2% zirconium-iron alloy powder, 0.3-0.6% bismuth oxide powder, 24-28% manganese powder, 3-4.5% arc stabilizer, 3-5% nickel powder, 18% chromium powder, 3-4.5% molybdenum-iron alloy powder, 1-1.5% magnesium powder, 1.8-2% marble, 1.5-3% feldspar, and the balance is iron powder; The stainless steel strip comprises the following elements in terms of mass percentage: Carbon 0.01-0.02%; Silicon 0.1-0.5%; Manganese 1-2%; Sulfur ≤ 0.02%; Phosphorus ≤ 0.004%; Nickel 8-10%; Chromium 18-20%; Molybdenum 0.01-0.02%; Aluminum 0.01-0.03%; Nitrogen 0.2-0.4%; Iron balance; the arc stabilizer is a mixture of TiO2, K2O, and MgO in a mass ratio of 5:3:

2.

2. The low-cost flux-cored welding wire for duplex stainless steel according to claim 1, characterized in that: The fluoride powder is a mixture of cryolite and cerium fluoride in a mass ratio of 3:

1.

3. The low-cost flux-cored welding wire for duplex stainless steel according to claim 1, characterized in that: The iron oxide powder is a mixture of ferric oxide and ferrosoferric oxide in a mass ratio of 1:

2.

4. The low-cost flux-cored welding wire for duplex stainless steel according to claim 1, characterized in that: The mass ratio of zirconium to iron in the zirconium-iron alloy powder is 4:

1.

5. The low-cost flux-cored welding wire for duplex stainless steel according to claim 1, characterized in that: The mass ratio of molybdenum to iron in the molybdenum-iron alloy powder is 4:

1.

6. A method for preparing a low-cost flux-cored welding wire for duplex stainless steel, characterized in that: The method comprises the following preparation steps: (1) According to any one of claims 1 to 5, the low-cost flux-cored welding wire for duplex stainless steel is rolled into a U-shape as required, and a flux-cored component in a prescribed amount is added into the U-shaped groove; (2) The U-shaped groove is rolled into an O-shaped steel pipe, and then rolled, sized, drawn, bright annealed, reduced in diameter, and mechanically cleaned to obtain a low-cost duplex stainless steel flux-cored welding wire with a diameter of Φ = 1.2-1.6 mm.

7. Application of a low-cost flux-cored welding wire for duplex stainless steel, characterized in that: The low-cost flux-cored welding wire for duplex stainless steel according to any one of claims 1 to 5 is used as the flux-cored welding wire for S32001 duplex stainless steel pipes.

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