Flux-cored wire for low-cost duplex stainless steel and preparation method of flux-cored wire

Abstract

The invention relates to the technical field of stainless steel flux-cored wires, in particular to a flux-cored wire for low-cost duplex stainless steel and a preparation method of the flux-cored wire. At present, no stainless steel flux-cored wire for all-position welding of the S32001 duplex stainless steel pipe is developed on the market. In order to solve the technical problems, the low-cost flux-cored wire for the duplex stainless steel is provided, a duplex stainless steel flux-cored wire all-position welding material matched with an S32001 duplex stainless steel pipe is developed through component research and analysis of the S32001 duplex stainless steel pipe and a large number of experimental researches, and the material is low in Ni content, low in cost and good in welding effect. The S32001 duplex stainless steel pipe is simple in structure, good in welding stability and excellent in comprehensive mechanical property, the innovation powerfully promotes wide application of the S32001 duplex stainless steel pipe in urban underground pipeline construction, and extremely high practical value is shown.

Description

Technical Field

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

[0002] The urban underground sewage pipeline system is an important infrastructure for ensuring the urban ecological safety and sustainable development. The performance of its pipe materials directly affects the service life of the pipe network, maintenance costs, and environmental risks. The current mainstream pipe materials are mainly ductile iron and PVC (polyvinyl chloride), but their performance defects under complex working conditions are becoming increasingly prominent. Due to its comprehensive performance advantages, duplex stainless steel has gradually become the preferred solution for a new generation of pipe materials. The differences between different pipe materials are analyzed below from the perspectives of technical defects and market demands.

[0003] Ductile iron improves toughness through graphite spheroidization technology, but its essence is still an iron-based material, with the following inherent defects: Corrosion protection depends on external coatings: In sewage containing Cl⁻, H 2 S or acidic medium (pH < 5), the cement mortar or epoxy coating is prone to peeling and pitting corrosion, resulting in rapid rusting of the matrix (annual corrosion rate > 0.1 mm), leading to leakage risks; high density and installation complexity: The density is as high as 7.3 g / cm³, requiring heavy machinery for hoisting; the socket joint depends on rubber gaskets, which are prone to relaxation and failure under long-term pressure, and the leakage rate is as high as 5% - 10%.

[0004] Although PVC pipes have the characteristics of light weight and low cost, their performance limitations severely restrict the application scenarios: Insufficient mechanical properties: The elastic modulus is only 2 - 4 GPa, and it is prone to buckling deformation (deformation rate < 5%) under a buried depth > 3 m or dynamic loads (such as traffic vibration); significant low-temperature brittleness (impact strength decreases by 70% at -5°C), unable to adapt to cold regions; narrow chemical tolerance: sensitive to hydrocarbon, ester organic solvents, and concentrated sulfuric acid (concentration > 50%), and the wall swelling rate reaches 8% - 12% after contact, resulting in structural failure; the upper limit of the long-term service temperature is 60°C, and high-temperature sewage (> 70°C) will cause thermal creep.

[0005] Duplex stainless steel (DSS) exhibits significant advantages due to its two-phase (austenite + ferrite) microstructure: Excellent corrosion resistance: High Cr (22%-25%), Mo (3%-4%) and N content, maintaining the passivation film stability (corrosion rate < 0.01mm / a) in extreme media with Cl⁻ concentration > 20000ppm and pH = 2 - 12; High strength and lightweight: Tensile strength ≥ 620MPa (twice that of ductile iron), density 7.8g / cm³, reducing the wall thickness by more than 30% and reducing the material consumption; Wide temperature range adaptability: No significant attenuation of mechanical properties in the range of -50°C to 250°C, avoiding the risks of thermal deformation or low-temperature brittle fracture.

[0006] However, the raw material price of duplex stainless steel is 4 - 5 times that of ductile iron, and the high cost seriously restricts the development of duplex stainless steel pipeline technology.

[0007] S32001 duplex stainless steel has good corrosion resistance, strength and impact toughness; compared with traditional duplex stainless steel, S32001 duplex stainless steel has a low Ni element content in its composition and is relatively cheap, and has the potential to be used as the base material of sewage pipes in urban underground sewage pipeline systems. At present, the only welding material suitable for S32001 duplex stainless steel is stainless steel electrodes (which cannot achieve all-position welding of pipe-shaped base materials), and stainless steel flux-cored wires for all-position welding of S32001 duplex stainless steel pipes have not been developed on the market. Summary of the Invention

[0008] The problem existing in the prior art is that: At present on the market, no stainless steel flux-cored wire for all-position welding of S32001 duplex stainless steel pipes has been developed. In view of the above technical problems, the present invention provides a low-cost flux-cored wire for duplex stainless steel, the structure of which includes an iron skin and a flux core, the filling rate of the flux core in the iron skin is 22 - 28%, the iron skin is a stainless steel strip, and the flux core, by mass percentage, includes 16 - 20% rutile powder, 3 - 5% alumina powder, 1 - 5% iron oxide powder, 3 - 4% fluoride powder, 2.5 - 5% silica powder, 1 - 2% titanium dioxide powder, 1 - 2% ferrozirconium alloy powder, 0.3 - 0.6% bismuth oxide powder, 24 - 28% manganese powder, 3 - 4.5% arc stabilizing agent, 3 - 5% nickel powder, 18% chromium powder, 3 - 4.5% ferromolybdenum alloy powder, 1 - 1.5% magnesium powder, 1.8 - 2% marble, 1.5 - 3% feldspar, and the balance is iron powder.

[0009] Preferably, the stainless steel strip, by mass percentage, includes the following elemental components: 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%; The balance is iron.

[0010] Preferably, the fluoride powder is a mixture composed of cryolite and cerium fluoride in a mass ratio of 3:1.

[0011] Preferably, the iron oxide powder is a mixture composed of ferric oxide and ferroferric oxide in a mass ratio of 1:2.

[0012] Preferably, the mass ratio of zirconium to iron in the zirconium - iron alloy powder is 4:1.

[0013] Preferably, the arc - stabilizing agent is composed of TiO 2 , K 2 O, and MgO in a mass ratio of 5:3:2.

[0014] Preferably, the mass ratio of molybdenum to iron in the ferromolybdenum alloy powder is in the range of 4:1.

[0015] Preferably, the rare - earth alloy powder is a mixture composed of cryolite and cerium fluoride in a mass ratio of 3:1.

[0016] A preparation method of a flux - cored wire for low - cost duplex stainless steel, which comprises the following preparation steps: (1) Roll the stainless - steel steel strip into a U - shape, and add the formula amount of flux - cored components into the U - shaped groove; (2) Close the U - shaped groove and roll it into an O - shaped steel pipe, and then successively carry out roll forming, sizing drawing, bright annealing, drawing and reducing, and surface mechanical cleaning to obtain a low - cost duplex stainless - steel flux - cored wire with a diameter of Φ = 1.2 - 1.6 mm.

[0017] The present invention has the following beneficial effects: (1) The low - cost duplex stainless - steel flux - cored 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 - clad metal obtained can both meet the required welding standards; (2) By reasonably designing the formula of the flux - cored wire, the low - cost duplex stainless - steel flux - cored wire obtained by the present invention has good welding stability during high - temperature welding, small spatter, and excellent mechanical properties of the obtained weld. Specific embodiments

[0018] The present invention will be described in detail below in conjunction with embodiments. However, it should be understood that the following embodiments are only illustrative examples of the implementation modes of the present invention, rather than limiting the scope of the present invention.

[0019] In the following embodiments of the present invention, the raw materials used are all commonly commercially available, and the purity of the raw materials is 99.9%.

[0020] The fluoride powder used in the following embodiments of the present invention is a mixture composed of cryolite and cerium fluoride in a mass ratio of 3:1.

[0021] The iron oxide powder used in the following embodiments of the present invention is a mixture composed of ferric oxide and ferroferric oxide in a mass ratio of 1:2.

[0022] In the zirconium-iron alloy powder used in the following embodiments of the present invention, the mass ratio of zirconium to iron is 4:1.

[0023] The arc stabilizing agent used in the following embodiments of the present invention is composed of TiO 2 , K 2 O, and MgO in a mass ratio of 5:3:2.

[0024] In the ferromolybdenum alloy powder used in the following embodiments of the present invention, the mass ratio of molybdenum to iron is 4:1.

[0025] The elemental composition of the stainless steel strip used in the following embodiments of the present invention is as follows: Carbon 0.015%; Silicon 0.3%; Manganese 1.5%; Sulfur 0.012%; Phosphorus 0.002%; Nickel 9.8%; Chromium 18.2%; Molybdenum 0.015%; Aluminum 0.013%; Nitrogen 0.25%; The balance is iron.

[0026] Example 1 A flux-cored wire for low-cost duplex stainless steel, whose structure is composed of an iron skin and a flux core. The filling rate of the flux core in the iron skin is 23%. The iron skin is a stainless steel strip with a thickness of 0.4 mm. The flux core is composed of the following components by mass percentage:

[0027] 16% rutile powder, 3% alumina powder, 5% iron oxide powder, 4% fluoride powder, 2.5% silica powder, 1% titanium dioxide powder, 2% ferrozirconium alloy powder, 0.6% bismuth oxide powder, 28% manganese powder, 4% arc stabilizing agent, 4% nickel powder, 18% chromium powder, 3% ferromolybdenum alloy powder, 1.5% magnesium powder, 2% marble, 1.5% feldspar, balance iron powder.

[0028] The preparation method of the low-cost duplex stainless steel flux-cored wire is as follows: (1) Roll the stainless steel strip into a U shape, and add the formula amount of flux-cored components into the U-shaped groove. The average particle size of the flux-cored powder is 500 mesh; (2) Close the U-shaped groove and roll it into an O-shaped steel pipe. The filling rate of the flux-cored powder in the O-shaped steel pipe is 23%; (3) The O-shaped steel pipe is rolled by 6 groups of 30 roller dies, drawn by 1 sizing die, and annealed by a wire annealing machine to make a Φ2.0mm stainless steel flux-cored wire; (4) The wire obtained in step (3) is further drawn through 10 drawing processes and surface mechanically cleaned to make a Φ1.2 stainless steel flux-cored wire.

[0029] Example 2 A flux-cored wire for low-cost duplex stainless steel, its structure is composed of iron skin and flux core. The filling rate of the flux core in the iron skin is 25%. The iron skin is a stainless steel strip with a thickness of 0.4mm. The flux core is composed of the following components by mass percentage:

[0030] 17% rutile powder, 5% alumina powder, 1% iron oxide powder, 3% fluoride powder, 5% silica powder, 2% titanium dioxide powder, 1% ferrozirconium alloy powder, 0.3% bismuth oxide powder, 26% manganese powder, 4.5% arc stabilizing agent, 3% nickel powder, 18% chromium powder, 4% ferromolybdenum alloy powder, 1% magnesium powder, 1.8% marble, 2% feldspar, balance iron powder.

[0031] The preparation method of the low-cost duplex stainless steel flux-cored wire is as follows: (1) Roll the stainless steel strip into a U shape, and add the formula amount of flux-cored components into the U-shaped groove. The average particle size of the flux-cored powder is 500 mesh; (2) Close the U-shaped groove and roll it into an O-shaped steel pipe. The filling rate of the flux-cored powder in the O-shaped steel pipe is 25%; (3) The O-shaped steel pipe is rolled by 6 groups of 30 roller dies, drawn by 1 sizing die, and annealed by a wire annealing machine to make a Φ2.0mm stainless steel flux-cored wire; (4) The wire obtained in step (3) is further drawn through 10 drawing processes and surface mechanically cleaned to make a Φ1.2 stainless steel flux-cored wire.

[0032] Example 3 A flux-cored wire for low-cost duplex stainless steel, whose structure consists of iron skin and flux core. The filling rate of the flux core in the iron skin is 28%. The iron skin is a stainless steel strip with a thickness of 0.4 mm. The flux core is composed of the following components by mass percentage: 20% rutile powder, 3% alumina powder, 2% iron oxide powder, 3% fluoride powder, 3% silica powder, 2% titanium dioxide powder, 2% ferrozirconium alloy powder, 0.35% bismuth oxide powder, 24% manganese powder, 3% arc stabilizing agent, 5% nickel powder, 18% chromium powder, 4.5% ferromolybdenum alloy powder, 1% magnesium powder, 1.8% marble, 3% feldspar, and the balance is iron powder.

[0033] The preparation method of the low-cost duplex stainless steel flux-cored wire is as follows: (1) Roll the stainless steel strip into a U shape, and add the flux core components in the U-shaped groove. The average particle size of the flux core powder is 500 mesh. (2) Close the U-shaped groove and roll it into an O-shaped steel pipe. The filling rate of the flux core powder in the O-shaped steel pipe is 28%. (3) The O-shaped steel pipe is rolled by 6 groups of 30 roller dies, drawn by 1 sizing die, and annealed by a wire annealing machine to form a Φ2.0 mm stainless steel flux-cored wire. (4) The wire obtained in step (3) is further drawn through 10 drawing processes and surface mechanically cleaned to form a Φ1.2 stainless steel flux-cored wire.

[0034] Comparative Example 1 is the same as Example 2, except that the flux core in Comparative Example 1 is composed of the following components by mass percentage: 13% rutile powder, 2% alumina powder, 2% iron oxide powder, 1.5% fluoride powder, 2% silica powder, 2% titanium dioxide powder, 2% ferrozirconium alloy powder, 0.3% bismuth oxide powder, 29% manganese powder, 5% arc stabilizing agent, 2% nickel powder, 22% chromium powder, 1.2% magnesium powder, and the balance is iron powder.

[0035] Comparative Example 2 is the same as Example 1, except that the flux core in Comparative Example 2 is composed of the following components by mass percentage: 33% manganese powder, 4% arc stabilizing agent, 45% chromium powder, 5% magnesium powder, 1% manganese nitride, and the balance is iron powder.

[0036] Comparative Example 3 is the same as Example 2, except that the flux core in Comparative Example 3 is composed of the following components by mass percentage: 15% rutile powder, 2% alumina powder, 4% iron oxide powder, 2% fluoride powder, 3% silica powder, 1% titanium dioxide powder, 1% ferrozirconium alloy powder, 0.3% bismuth oxide powder, 33% manganese powder, 3% arc stabilizing agent, 20% chromium powder, and the balance is iron powder.

[0037] Comparative Example 4 is the same as Example 2, except that in Comparative Example 4, the flux-cored wire, by mass percentage, is composed as follows: 10% rutile powder, 2% alumina powder, 3% iron oxide powder, 2% fluoride powder, 5% silica powder, 1% titanium dioxide powder, 1% ferrozirconium alloy powder, 0.3% bismuth oxide powder, 30% manganese powder, 3% arc stabilizing agent, 2% nickel powder, 20% chromium powder, 1% ferromolybdenum alloy powder, 1% magnesium powder, 4% marble, 2% feldspar, and the balance is iron powder.

[0038] Comparative Example 5 is the same as Example 2, except that in Comparative Example 5, the flux-cored wire, by mass percentage, is composed as follows: 17% rutile powder, 3% alumina powder, 2% iron oxide powder, 2% fluoride powder, 4% silica powder, 2% titanium dioxide powder, 1% ferrozirconium alloy powder, 0.3% bismuth oxide powder, 27% manganese powder, 4% arc stabilizing agent, 4% nickel powder, 19% chromium powder, 1% ferromolybdenum alloy powder, 1% magnesium powder, 1% marble, 2% feldspar, and the balance is iron powder.

[0039] Comparative Example 6 is the same as Example 2, except that in Comparative Example 6, the fluoride powder is a mixture composed of cryolite and cerium fluoride in a mass ratio of 1:1.

[0040] Comparative Example 7 is the same as Example 2, except that in Comparative Example 7, the fluoride powder is a mixture composed of cryolite and cerium fluoride in a mass ratio of 1:3.

[0041] Comparative Example 8 is the same as Example 2, except that in Comparative Example 8, the iron oxide powder is a mixture composed of ferric oxide and ferroferric oxide in a mass ratio of 1:1.

[0042] Comparative Example 9 is the same as Example 2, except that in Comparative Example 9, the iron oxide powder is a mixture composed of ferric oxide and ferroferric oxide in a mass ratio of 2:1.

[0043] Comparative Example 10 is the same as Example 2, except that in Comparative Example 10, the arc stabilizing agent is composed of TiO 2 , K 2 O, and MgO in a mass ratio of 5:1:4.

[0044] Comparative Example 11 is the same as Example 2, except that in Comparative Example 11, the arc stabilizing agent is composed of TiO 2 , K 2 O, and MgO in a mass ratio of 2:5:3.

[0045] Comparative Example 12 is the same as Example 2, except that in Comparative Example 12, the iron sheet is a commercially available 304L stainless steel strip.

[0046] Performance Test Using the flux-cored wires obtained in Examples 1-3 and Comparative Examples 1-12 of the present invention, surfacing was carried out on the S32001 duplex stainless steel base metal for 5 layers, with three passes for each layer. After the surfacing was completed, relevant performance tests were carried out on the obtained weld cladding metals respectively. Each group of parallel experiments was tested 10 times, and the average value was taken. The specific test results are shown in Tables 1, 2, and 3. The flux-cored wires obtained in Examples 1-3 and Comparative Examples 1-12 of the present invention were used for surfacing under CO 2 After surfacing under the protection gas, the composition of the obtained weld cladding metal was sampled and analyzed respectively. The analysis results are shown in Table 3. When analyzing the element composition of the weld cladding metal, the weld was first ground 2 mm downward along its surface and then the element composition analysis was carried out.

[0047] Tensile strength: The test standard is GB / T 228-2021.

[0048] Elongation at break: The test standard is GB / T 228-2121.

[0049] Impact energy: The test standard is GB / T 229-2020.

[0050] Bending property: The test standard is GB / T 232-2010.

[0051] Spatter property: The test standard is GB / T25776-2010.

[0052] Table 1

[0053]

[0054] Table 2

[0055] Table 3

[0056] .

[0057] According to the analysis of Tables 1-3, in Comparative Example 1, ferromolybdenum alloy powder was not added, and the grain structure of the tissue could not be refined, resulting in poor toughness of the weld; as a ferrite-forming element, the lack of Mo easily led to a decrease in the ferrite content in the weld.

[0058] In Comparative Example 2 and Comparative Example 3, nickel powder and ferromolybdenum alloy powder were not added, and the weld structure could not be regulated through the synergistic effect of Ni, Cr, and Mo elements, and rare earth alloy powder was not added, resulting in a significant reduction in the comprehensive mechanical properties.

[0059] . In Comparative Example 4, a small amount of ferromolybdenum alloy powder was added, making the chemical composition and mechanical properties of the weld unable to meet the standard requirements; and an excessive amount of marble powder was added, increasing the spatter during the welding process.

[0060] In Comparative Example 5, a small amount of ferromolybdenum alloy powder was added, making the chemical composition and mechanical properties of the weld unable to meet the standard requirements.

[0061] In Comparative Example 6 and Comparative Example 7, the ratio of cryolite to cerium fluoride in the added fluoride did not reach the appropriate range, resulting in an increase in spatter during welding, but having no impact on the mechanical properties.

[0062] In Comparative Example 8 and Comparative Example 9, the ratio of ferric oxide to ferroferric oxide in the added iron oxide powder did not reach the appropriate range, resulting in an increase in spatter during welding, but having no impact on the mechanical properties.

[0063] In Comparative Example 10 and Comparative Example 11, the ratio of TiO 2 , K 2 O, and MgO in the added arc stabilizing agent was changed, making the arc unstable during welding and resulting in a slight increase in spatter.

[0064] In Comparative Example 12, ordinary commercially available 304L stainless steel strip was used, and the content of N element in it was low, resulting in a significant decrease in strength compared with that.

[0065] In the present invention, by increasing the addition amount of Mo element in the flux-cored wire composition, the content of ferrite in the weld cladding metal was effectively ensured, and by adding N element and rare earth elements, the mechanical properties of the weld were also effectively guaranteed. At the same time, the slag system formula was adjusted to improve the surface tension of the molten pool, obtaining the ability of all-position welding, a lower spatter rate, and being applicable to the welding of S32001 pipes, meeting the 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% alumina 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 remainder is iron powder.

2. A low-cost flux-cored welding wire for duplex stainless steel according to claim 1, characterized in that: The stainless steel strip includes 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.

3. 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.

4. A 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 ferrous oxide in a mass ratio of 1:

2.

5. The low-cost flux-cored welding wire for duplex stainless steel according to claim 1, characterized in that: The arc stabilizer is a mixture of TiO2, K2O and MgO in a mass ratio of 5:3:

2.

6. 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.

7. 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.

8. 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 7, 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, sizing, bright annealed, drawn and reduced, 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.

9. 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 7 is used as a flux-cored welding wire for S32001 duplex stainless steel pipes.

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