Duplex stainless steel metal type flux-cored wire and method for 3D printing flange structural component

Abstract

The invention discloses a duplex stainless steel metal type flux-cored wire for a 3D printing flange structural part and a method. Flux core alloy components in the metal type flux-cored wire comprise, by mass, 22%-28% of chromium powder, 1%-2% of titanium powder, 2%-4% of aluminum powder, 6%-8% of molybdenum powder, 2%-3% of copper powder, 5%-7% of niobium powder, 0.03% of carbon powder, 1%-2% of manganese powder, 0.3%-0.6% of silicon powder, 0.1%-0.2% of chromium nitride and the balance iron powder, and the sum of the mass percentages of the components is 100%. The duplex stainless steel structural part obtained through 3D printing is attractive in shape, excellent in mechanical property and good in corrosion resistance, and the use requirements of flange structural parts are completely met.

Description

Technical Field

[0001] The present invention belongs to the technical field of wire 3D printing, and in particular relates to a duplex stainless steel metal-type flux-cored welding wire and a method for 3D printing flange structural parts. Background Art

[0002] The "duplex" in duplex stainless steel refers to the coexistence of austenite and ferrite in its structure, which makes duplex stainless steel achieve a good balance between strength and corrosion resistance. This material is widely used in the automotive industry, chemical equipment, marine engineering and other fields, mainly in situations requiring high strength and excellent corrosion resistance.

[0003] Flange components are widely used in the fields of petrochemical, marine engineering, power equipment, shipbuilding, etc. These industries have extremely high requirements for the corrosion resistance, strength and reliability of materials, especially in the environment of high temperature, high pressure and highly corrosive media. Ordinary materials are difficult to meet the requirements, so the selection of high-performance materials is particularly important.

[0004] Currently, 3D printing technology has been widely used in the manufacture of complex structural parts because it can achieve geometric complexity and material utilization that are difficult to achieve with traditional manufacturing methods. As a high-performance material, duplex stainless steel is widely used in many industrial fields due to its excellent mechanical properties and outstanding corrosion resistance. However, due to its complex metallographic structure and high processing difficulty, the use of traditional manufacturing methods to produce duplex stainless steel parts, especially parts with complex internal structures, often faces challenges such as high cost, long cycle, and serious material waste.

[0005] Flux-cored welding wire is a special welding material, which is made of an outer metal skin wrapped with metal powder or other additives filled inside. Flux-cored welding wire can provide a more stable arc, better droplet transition and higher deposition efficiency during welding, and can also control the chemical composition and properties of the weld metal by adjusting the flux core composition. The application of self-developed duplex stainless steel flux-cored welding wire in 3D printing technology, especially for the manufacture of flange structural parts, has the following technical background and advantages: superior material performance, flexibility of 3D printing technology, advantages of flux-cored welding wire, cost-effectiveness, technological innovation and industrial upgrading. Therefore, the application of self-developed duplex stainless steel flux-cored welding wire in 3D printing flange structural parts can not only meet the market demand for high-performance and high-reliability components, but also promote technological innovation and industrial upgrading in related fields.

[0006] Currently, the existing technology mainly uses commercial solid welding wire for duplex stainless steel 3D printing technology. There is no flux-cored wire for arc 3D printing and remanufacturing of duplex stainless steel. The solid welding wire has a long manufacturing cycle, causes great environmental pollution, and has a single wire variety. The existing welding wire on the market often cannot meet the requirements of 3D printing.

[0007] Therefore, how to develop a new type of duplex stainless steel flux-cored welding wire is the current problem. Summary of the invention

[0008] The first object of the present invention is to provide a duplex stainless steel flux-cored welding wire that can be used as a raw material for 3D printing of flange structural parts. The preparation process of the flux-cored welding wire is simple and pollution-free, and the composition is easy to control.

[0009] A second object of the present invention is to provide a 3D printing method for duplex stainless steel structural parts, which is used for 3D printing of flange structural parts.

[0010] The first technical solution adopted by the present invention is: a duplex stainless steel flux-cored welding wire, comprising a flux core and an outer sheath, wherein the flux core is composed of the following components in mass percentage: chromium powder 22-28%, titanium powder 1-2%, molybdenum powder 6-8%, copper powder 2-3%, niobium powder 5-7%, aluminum powder 2-4%, carbon powder 0.03%, manganese powder 1-2%, silicon powder 0.3-0.6%, chromium nitride 0.1-0.2%, and the rest is iron powder.

[0011] The outer skin is 0Cr18Ni9 austenitic stainless steel strip, and the filling amount of the core powder is 20wt%-25wt%. (The composition is shown in Table 1).

[0012] The second technical solution adopted by the present invention is a 3D printing method for duplex stainless steel structural parts, which is specifically carried out according to the following steps: Step 1, weigh the following raw materials according to mass percentage: chromium powder 22-28%, titanium powder 1-2%, molybdenum powder 6-8%, copper powder 2-3%, niobium powder 5-7%, aluminum powder 2-4%, carbon powder 0.03%, manganese powder 1-2%, silicon powder 0.3-0.6%, chromium nitride 0.1-0.2%, and the rest is iron powder; Step 2: heating and keeping the raw material powder weighed in step 1 in an inert gas atmosphere to remove moisture; Step 3, placing the outer skin on the unwinding machine of the welding wire forming machine, rolling the outer skin into a U-shaped groove through the pressing groove of the forming machine, keeping the raw material powder obtained in step 2 warm and then cooling it to room temperature with the furnace, then filling the powder into the U-shaped groove, the filling rate of the flux core powder is controlled at 20wt%-25wt%, and after closing the forming rollers, a 2.10mm welding wire is made, and a 1.20mm metal-type flux-cored welding wire is finally made by a step-by-step reduction method; Step 4: Assemble the prepared metal flux-cored welding wire onto the fully automatic welding robot, determine that the height of each layer is 2-3 mm, write the corresponding program and input it into the welding robot, run the welding machine command, and use MIG welding as the heat source to 3D print the structural parts.

[0013] In step 2, the inert protective atmosphere is argon gas with a purity of 99.999%; in step 3, the outer skin is a 0Cr18Ni9 austenitic stainless steel strip.

[0014] In step 2, the heating temperature is 150-200°C and the insulation time is 2-2.5h.

[0015] In step 4, the process parameters of MIG welding are welding speed 0.2m / min-0.3m / min; the welding gun is raised 2mm-3mm for each layer, and the shielding gas is argon with a purity of 99.999%; interlayer cooling is adopted in step 4 cooling, and the interlayer temperature is controlled between 100℃ and 150℃.

[0016] The beneficial effects of the present invention are: 1. The duplex stainless steel flux-cored welding wire of the present invention has a short preparation cycle and high production efficiency. The performance can be improved by adjusting the flux core composition and ratio. Meanwhile, the flux-cored welding wire is pollution-free in production and has high cladding efficiency in the welding process.

[0017] 2. The strengthening effect of the duplex stainless steel flux-cored welding wire of the present invention is that a variety of precipitation phase elements are added to the welding wire, with Cr and Ni elements as the main alloying components, and a certain amount of trace alloying elements such as Cu, Al, Mo, Nb, Ti, CrN, etc. are added, and the proportion of each element is strictly controlled. The phase structure is predicted by Jmatpro thermodynamic software. When the ferrite: austenite ratio is 1:1, the duplex steel has the best performance and can significantly improve the mechanical properties.

[0018] 3. The 3D printing method of duplex stainless steel structural parts of the present invention is a method for preparing duplex stainless steel by 3D printing technology using MIG welding as a heat source and metal-type flux-cored welding wire as a raw material; the present invention places the uniformly mixed flux-cored powder in a tubular furnace, continuously introduces argon gas, and keeps the temperature at 150°C to 200°C for 2h to 2.5h. The present invention uses a fully automatic welding robot programming to realize 3D printing of duplex stainless steel structural parts, which is highly efficient; the arc is stable during the printing process, the weld is beautifully formed, the weld surface is smooth, and there are no pores or slag inclusions.

[0019] 4. The duplex stainless steel structural parts obtained by 3D printing of the present invention have beautiful shape and excellent mechanical properties, and perfectly meet the use requirements of flanges. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a stress-strain curve diagram of duplex stainless steel prepared by flux-cored welding wire in Example 4 of the present invention; Figure 2 It is the microstructure diagram of Example 4 of the present invention. DETAILED DESCRIPTION

[0021] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] The invention provides a duplex stainless steel flux-cored welding wire, comprising a flux core and an outer sheath, wherein the flux core is composed of the following components in percentage by mass: 22-28% chromium powder, 1-2% titanium powder, 6-8% molybdenum powder, 2-3% copper powder, 5-7% niobium powder, 2-4% aluminum powder, 0.03% carbon powder, 1-2% manganese powder, 0.3-0.6% silicon powder, 0.1-0.2% chromium nitride, and the remainder is iron powder.

[0023] The metal-type flux-cored welding wire of the present invention has simple composition control, a more accurate chemical composition range, and no waste water or waste gas is discharged during the whole process. The composition adjustment range is large, which is suitable for the research and development of new materials, has greater flexibility, and can easily meet various performance requirements.

[0024] The role and function of each component in the welding wire are as follows: Cr element: As one of the main alloying elements of duplex stainless steel, Cr element also plays an important role in improving the strength and corrosion resistance of cladding alloy. Cr element can be added into carbides (such as M 23 C6), replaces with Fe atoms to form composite phases, such as (Fe,Cr)7C3 and (Fe,Cr) 23 C6, etc. In addition, the Cr element in the surfacing alloy can be dissolved in γ-Fe and α-Fe, improving the high-temperature strength and hardness of the alloy and improving the corrosion resistance of the material.

[0025] Mo (molybdenum) element: Mo element added within an appropriate range helps to promote the formation of dual-phase (ferrite + austenite) structure, which is not only conducive to improving the comprehensive mechanical properties of the material, but also to improving its corrosion resistance. The ferrite phase in the dual-phase structure can improve the plasticity and toughness of the material, while the austenite phase helps to maintain high strength and corrosion resistance.

[0026] Ni (nickel) element: The alloying element Ni in the steel strip can significantly inhibit the migration of carbon elements, effectively reduce the stability of carbides and the binding ability of carbide-forming elements to carbon, promote the formation of austenite and ferrite dual-phase structure, inhibit the growth of carbides, and improve the overall mechanical properties.

[0027] Cu element: Cu can improve the strength and hardness of duplex stainless steel through the solid solution strengthening effect. Especially under appropriate heat treatment conditions, Cu element has a regulating effect on the phase transformation and microstructure formation of duplex stainless steel, which can optimize the mechanical properties and wear resistance of stainless steel.

[0028] Nb (niobium) element: Nb can be dissolved in the iron matrix and improve the strength and hardness of stainless steel through solid solution strengthening. At the same time, Nb can be used as a grain boundary strengthening element to promote grain refinement, improve the toughness and tensile strength of the material, affect the phase change behavior of stainless steel, and help optimize the microstructure and performance of duplex stainless steel.

[0029] Ti (titanium) element: The strengthening effect of Ti element is mainly reflected in two aspects: fine grain strengthening and precipitation strengthening. The appropriate amount of Ti addition can serve as a nucleation site during the solidification process of the molten pool, promoting the refinement of the structure. The presence of a large number of fine grain boundaries can effectively hinder the movement of dislocations, thereby limiting deformation and crack propagation, and improving the yield strength and impact toughness of steel.

[0030] Al (aluminum) element: Al combines with other alloying elements in steel to form the following main precipitation phases: γ' phase (Ni3Al, (Ni,Co)3(Al,Ti)), β phase (NiAl) and η phase (Ni3(A1,Ti)). Among them, the γ' phase has high strength and plastic toughness, and with the increase of temperature, the strength of the γ' phase will also show an upward trend, while it can also ensure a certain plasticity, which makes it an ideal choice for strengthening stainless steel. The β phase has a relatively high hardness, but it is a hard and brittle phase; in Fe-based alloys, nickel (Ni) and aluminum (Al) first tend to form NiA1 phase, rather than Ni3Al phase. Only after adding Ti and A1 can the γ'-Ni3(Ti,Al) phase with significant strengthening effect be generated. The strengthening effect of the η phase depends on the difference in its precipitation morphology at different precipitation temperatures and its orientation relationship with the matrix. However, when the aluminum content in the flux-cored wire is too high, it will greatly affect the process performance of the wire, resulting in increased spatter and cracking tendency during welding, which will have an adverse effect on the toughness of the deposited metal.

[0031] Mn and Si elements: During the welding process, the main functions of Mn and Si are deoxidation and desulfurization, which can reduce the content of oxygen and sulfur in the surfacing alloy and prevent defects such as pores from being generated in the surfacing metal, resulting in a decrease in forming quality.

[0032] CrN element: The role of CrN in duplex stainless steel is mainly reflected in enhancing its corrosion resistance and mechanical properties. As a hard and wear-resistant compound, CrN can effectively improve the surface hardness and wear resistance of stainless steel and extend its service life. In addition, CrN can also improve the corrosion resistance of stainless steel, making it more resistant to corrosion in harsh environments, thereby expanding its application range in industry and manufacturing.

[0033] The outer skin is a 0Cr18Ni9 austenitic stainless steel strip, and the filling amount of the core powder is controlled at 20wt%-25wt%.

[0034] The present invention also provides a 3D printing method for duplex stainless steel structural parts, which is specifically prepared according to the following steps: Step 1, weigh the following raw materials according to mass percentage: chromium powder 22-28%, titanium powder 1-2%, molybdenum powder 6-8%, copper powder 2-3%, niobium powder 5-7%, aluminum powder 2-4%, carbon powder 0.03%, manganese powder 1-2%, silicon powder 0.3-0.6%, chromium nitride 0.1-0.2%, and the rest is iron powder; Step 2: heating and keeping the raw material powder weighed in step 1 in an inert gas atmosphere to remove moisture; In step 2, the heating temperature is 150°C to 200°C, and the insulation time is 2h to 2.5h.

[0035] Step 3, placing the outer skin on the unwinding machine of the welding wire forming machine, rolling the outer skin into a U-shaped groove through the pressing groove of the forming machine, keeping the raw material powder obtained in step 2 warm and then cooling it to room temperature with the furnace, then filling the powder into the U-shaped groove, the filling rate of the flux core powder is controlled at 20wt%-25wt%, and after closing the forming rollers, a 2.10mm welding wire is made, and a 1.20mm metal-type flux-cored welding wire is finally made by a step-by-step reduction method; In step 3, the inert atmosphere is argon gas with a purity of 99.999%; in step 3, the outer skin is a 0Cr18Ni9 austenitic stainless steel strip.

[0036] Step 4: Assemble the prepared metal flux-cored welding wire onto the fully automatic welding robot, determine that the height of each layer is 2-3 mm, write the corresponding program and input it into the welding robot, and use MIG welding as the heat source to perform 3D printing to obtain the structural parts.

[0037] In step 4, the process parameters of MIG welding are welding speed 0.2m / min-0.3m / min; the welding gun is raised 2mm-3mm for each layer, and the shielding gas is argon with a purity of 99.999%; interlayer cooling is adopted in step 4 cooling, and the interlayer temperature is controlled between 100℃ and 150℃.

[0038] The duplex stainless steel structural part obtained by 3D printing of the present invention is prepared by the above method.

[0039] Example 1 Step 1: Weigh 22% chromium powder, 1% titanium powder, 6% molybdenum powder, 2% copper powder, 5% niobium powder, 2% aluminum powder, 0.03% carbon powder, 1% manganese powder, 0.3% silicon powder, 0.1% chromium nitride, and the rest iron powder, and the sum of the mass percentages of the above components is 100%; Step 2: Mix all the raw materials weighed in step 1 evenly and place them in a tube furnace. Keep the mixture at 200° C. for 2.5 h while continuously introducing argon.

[0040] Step 3: Place a 0Cr18Ni9 austenitic stainless steel strip (the composition is shown in Table 1) with a width of 7 mm and a thickness of 0.3 mm on the unwinding machine of the welding wire forming machine, roll the steel strip into a U-shaped groove through the pressing groove of the forming machine, put the flux core powder obtained in step 2 into the U-shaped groove, and control the filling rate of the flux core powder to 21wt%. Then, use the forming machine to roll and close the U-shaped groove, wipe it clean with acetone or anhydrous ethanol, and draw it into a welding wire with a diameter of 2.1 mm, then reduce the diameter to 1.20 mm, wipe the oil stains on the welding wire with a cotton cloth dipped in acetone or anhydrous ethanol, and finally straighten the welding wire through the wire drawing machine, coil it into a disc, and seal it to obtain a duplex stainless steel metal-type flux-cored welding wire for 3D printing.

[0041] Step 4: Load the prepared duplex stainless steel metal flux-cored welding wire for 3D printing into the fully automatic welding robot, determine that the height of each layer is 2-3mm, write a program and input it into the welding machine, run the welding machine command, and use MIG welding as the heat source to 3D print the structural parts; the specific parameters of the welding process are: welding speed is 0.2m / min-0.3m / min; each layer of welding gun is lifted 2mm-3mm; the shielding gas is 99.999% argon.

[0042] The duplex stainless steel molded parts prepared in this example have beautiful molding, no obvious spatter, tensile strength can reach 783.6MPa, and elongation is 19.5%.

[0043] Example 2 Step 1: Weigh 24% chromium powder, 1% titanium powder, 6.5% molybdenum powder, 2.5% copper powder, 5.5% niobium powder, 2.5% aluminum powder, 0.03% carbon powder, 1.5% manganese powder, 0.4% silicon powder, 0.15% chromium nitride, and the rest iron powder according to mass percentage; Step 2: Mix all the raw materials weighed in step 1 evenly and place them in a tube furnace. Keep the mixture at 200° C. for 2.5 h while continuously introducing argon.

[0044] Step 3: Place a 0Cr18Ni9 austenitic stainless steel strip (the composition is shown in Table 1) with a width of 7 mm and a thickness of 0.3 mm on the unwinding machine of the welding wire forming machine, roll the steel strip into a U-shaped groove through the pressing groove of the forming machine, put the flux core powder obtained in step 2 into the U-shaped groove, and control the filling rate of the flux core powder to 24wt%. Then, use the forming machine to roll and close the U-shaped groove, wipe it clean with acetone or anhydrous ethanol, and draw it into a welding wire with a diameter of 2.1 mm, then reduce the diameter to 1.20 mm, wipe the oil stains on the welding wire with a cotton cloth dipped in acetone or anhydrous ethanol, and finally straighten the welding wire through the wire drawing machine, coil it into a disc, and seal it to obtain a duplex stainless steel metal-type flux-cored welding wire for 3D printing.

[0045] Step 4: Load the prepared duplex stainless steel metal flux-cored welding wire for 3D printing into the fully automatic welding robot, determine that the height of each layer is 2-3mm, write a program and input it into the welding machine, run the welding machine command, and use MIG welding as the heat source to 3D print the structural parts; the specific parameters of the welding process are: welding speed is 0.2m / min-0.3m / min; each layer of welding gun is lifted 2mm-3mm; the shielding gas is 99.999% argon.

[0046] The duplex stainless steel molded parts prepared in this example have good mechanical properties, no obvious spatter, a tensile strength of up to 815.2 MPa, and an elongation of 17.6%.

[0047] Example 3 Step 1: Weigh 26% chromium powder, 1.5% titanium powder, 7.5% molybdenum powder, 2.5% copper powder, 6% niobium powder, 3% aluminum powder, 0.03% carbon powder, 2% manganese powder, 0.4% silicon powder, 0.2% chromium nitride, and the rest iron powder by mass percentage. The sum of the mass percentages of the above components is 100%; Step 2: Mix all the raw materials weighed in step 1 evenly and place them in a tube furnace. Keep the mixture at 200° C. for 2.5 h while continuously introducing argon.

[0048] Step 3: Place a 0Cr18Ni9 austenitic stainless steel strip (the composition is shown in Table 1) with a width of 7 mm and a thickness of 0.3 mm on the unwinding machine of the welding wire forming machine, roll the steel strip into a U-shaped groove through the pressing groove of the forming machine, put the flux core powder obtained in step 2 into the U-shaped groove, and control the filling rate of the flux core powder at 23wt%. Then, use the forming machine to roll and close the U-shaped groove, wipe it clean with acetone or anhydrous ethanol, and draw it into a welding wire with a diameter of 2.1 mm, then reduce the diameter to 1.20 mm, wipe the oil stains on the welding wire with a cotton cloth dipped in acetone or anhydrous ethanol, and finally straighten the welding wire through the wire drawing machine, coil it into a disc, and seal it to obtain a duplex stainless steel metal-type flux-cored welding wire for 3D printing.

[0049] Step 4: Load the prepared duplex stainless steel metal flux-cored welding wire for 3D printing into the fully automatic welding robot, determine that the height of each layer is 2-3mm, write a program and input it into the welding machine, run the welding machine command, and use MIG welding as the heat source to 3D print the structural parts; the specific parameters of the welding process are: welding speed is 0.2m / min-0.3m / min; each layer of welding gun is lifted 2mm-3mm; the shielding gas is 99.999% argon.

[0050] The duplex stainless steel formed parts prepared in this example have no cracks or pores on the surface, no obvious spatter during the welding process, the tensile strength can reach 824.2 MPa, and the elongation is 20.8%.

[0051] Example 4 Step 1: Weigh 28% chromium powder, 2% titanium powder, 8% molybdenum powder, 3% copper powder, 7% niobium powder, 4% aluminum powder, 0.03% carbon powder, 2% manganese powder, 0.6% silicon powder, 0.2% chromium nitride, and the rest iron powder, and the sum of the mass percentages of the above components is 100%; Step 2: Mix all the raw materials weighed in step 1 evenly and place them in a tube furnace. Keep the mixture at 200° C. for 2.5 h while continuously introducing argon.

[0052] Step 3: Place a 0Cr18Ni9 austenitic stainless steel strip (the composition is shown in Table 1) with a width of 7 mm and a thickness of 0.3 mm on the unwinding machine of the welding wire forming machine, roll the steel strip into a U-shaped groove through the pressing groove of the forming machine, put the flux core powder obtained in step 2 into the U-shaped groove, and control the filling rate of the flux core powder to 25wt%. Then, use the forming machine to roll and close the U-shaped groove, wipe it clean with acetone or anhydrous ethanol, and draw it into a welding wire with a diameter of 2.1 mm, then reduce the diameter to 1.20 mm, wipe the oil stains on the welding wire with a cotton cloth dipped in acetone or anhydrous ethanol, and finally straighten the welding wire through the wire drawing machine, coil it into a disc, and seal it to obtain a duplex stainless steel metal-type flux-cored welding wire for 3D printing.

[0053] Step 4: Load the prepared duplex stainless steel metal flux-cored welding wire for 3D printing into the fully automatic welding robot, determine that the height of each layer is 2-3mm, write a program and input it into the welding machine, run the welding machine command, and use MIG welding as the heat source to perform 3D printing to obtain structural parts; the specific parameters of the welding process are: welding speed is 0.2m / min-0.3m / min; the welding gun is lifted 2mm-3mm per layer; the shielding gas is 99.999% argon. Based on the duplex stainless steel flux-cored welding and 3D printing structural parts method of the present invention, the duplex stainless steel components obtained in this example are beautifully formed, and the macroscopic morphology shows that the deposited parts show obvious stratification, the metallurgical bonding between the layers is good, and there are no defects such as pores and inclusions. Its microstructure is as follows Figure 2 As shown in the figure, the microstructure is austenite (A) + ferrite (δ-F). The light-colored part in the figure is austenite, the dark-colored part is ferrite, and the ratio of austenite to ferrite is close to 1:1, which is completely consistent with the microstructure of duplex stainless steel. After mechanical property testing, its stress-strain curve is as follows Figure 1 As shown, the tensile strength of the formed part of this example can reach 847.8MPa, and the elongation is 21.5%. In summary, the duplex stainless steel obtained by the present invention has good mechanical performance indicators and fully meets the use requirements of flange structural parts.

[0054] Table 1 shows the chemical composition (mass fraction%) of the 0Cr18Ni9 austenitic stainless steel strip used. element C Cr Ni Mn Si S P Fe content 0.06 18.67 8.53 1.51 0.42 0.014 0.032 Bal. Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A duplex stainless steel metal cored welding wire for 3D printing flange structural parts, comprising a core and a sheath, characterized in that: The flux core is composed of the following components in mass percentage: 22-28% chromium powder, 1-2% titanium powder, 2-4% aluminum powder, 6-8% molybdenum powder, 2-3% copper powder, 5-7% niobium powder, 0.03% carbon powder, 1-2% manganese powder, 0.3-0.6% silicon powder, 0.1-0.2% chromium nitride, and the rest is iron powder, and the sum of the mass percentages of the above components is 100%.

2. The duplex stainless steel flux-cored welding wire according to claim 1, characterized in that: The outer skin is a 0Cr18Ni9 austenitic stainless steel strip, and the filling rate of the core powder is controlled at 20wt%-25wt%.

3. A 3D printing method for duplex stainless steel structural parts, characterized in that: Using the duplex stainless steel metal cored welding wire for 3D printing flange structural parts as described in any one of claims 1-2, specifically following the steps: Step 1, weighing 22-28% chromium powder, 1-2% titanium powder, 2-4% aluminum powder, 6-8% molybdenum powder, 2-3% copper powder, 5-7% niobium powder, 0.03% carbon powder, 1-2% manganese powder, 0.3-0.6% silicon powder, 0.1-0.2% chromium nitride, and the rest iron powder, respectively, according to mass percentage, and the sum of the mass percentages of the above components is 100%; Step 2: heating and keeping the alloy powder weighed in step 1 in an inert gas atmosphere to remove moisture; Step 3, the alloy powder obtained in step 2 is kept warm and then cooled to room temperature with the furnace, and then the powder is filled into a U-shaped groove of a low-carbon steel strip, and is made into a 2.10 mm welding wire after passing through a closed forming roller, and finally a 1.20 mm metal-type flux-cored welding wire is made by a step-by-step reduction method; Step 4: Assemble the prepared metal flux-cored welding wire to the fully automatic welding robot, plan the welding path, determine the layer height, write a program and input it into the welding robot, run the welding machine command, and use MIG welding as the heat source to perform 3D printing to obtain the structural parts.

4. The 3D printing method of duplex stainless steel structural parts according to claim 3, characterized in that: In step 2, the inert atmosphere is 99.999% argon.

5. The 3D printing method of duplex stainless steel structural parts according to claim 3, characterized in that: In step 2, the heating temperature is 150-200°C and the insulation time is 2-2.5h.

6. The 3D printing method of duplex stainless steel structural parts according to claim 3, characterized in that: The process parameters of the MIG welding are as follows: a welding speed of 0.2-0.3 m / min; a welding gun lift of 2-3 mm per layer; and a shielding gas of 99.999% argon.

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