Iron-based welding wire and method for austenitic stainless steel / carbon steel composite pipe CMT welding

Abstract

The invention discloses an iron-based welding wire for austenitic stainless steel / carbon steel composite pipe CMT welding, the iron-based welding wire comprises powder and a welding skin, the powder comprises the following components in percentage by mass: 23.0-28.0% of Cr, 28.0-32.0% of Ni, 15.0-18.0% of Mo, 2.0-4.0% of Nb, 3.0-5.0% of Co, 0.4-0.8% of Y2O3 and La2O3, and the balance of Fe, and the sum of the mass percentages of the components is 100%. The welding wire solves the problems that when an existing stainless steel composite material is welded, a high hard phase occurs, and the corrosion resistance is insufficient. The invention further discloses a preparation method of the iron-based welding wire for the CMT welding of the austenitic stainless steel / carbon steel composite pipe and a welding method for the austenitic stainless steel / carbon steel composite pipe by adopting the welding wire.

Description

Technical Field

[0001] This invention belongs to the field of metal materials technology, specifically relating to iron-based welding wire for CMT welding of austenitic stainless steel / carbon steel composite pipes, and also to the preparation method of iron-based welding wire for CMT welding of austenitic stainless steel / carbon steel composite pipes and the welding method of using such welding wire for welding austenitic stainless steel / carbon steel composite pipes. Background Technology

[0002] With rapid economic development and continuous urbanization in China, urban drinking water supply has become a key focus of urban management. The newly implemented "Standards for Drinking Water Quality" and "Urban Water Supply Engineering Planning Code" have set higher requirements for water quality and pipeline planning, driving the construction and renovation of municipal pipeline networks. Currently, widely used carbon steel pipes face challenges in internal corrosion prevention. Common methods such as spraying epoxy water tank paint and centrifugal cement mortar both suffer from insufficient durability and are prone to cracking and peeling. Failure of the protective layer leads to steel pipe corrosion, causing secondary pollution and resulting in water quality problems such as yellow or black water.

[0003] To ensure water quality and prevent secondary pollution, developed cities in China have gradually adopted composite pipes to replace traditional pipe materials. Abroad, stainless steel pipes or composite pipes are commonly used. Stainless steel metallurgical composite pipes combine the corrosion resistance of stainless steel with the mechanical properties of carbon steel, offering advantages such as corrosion resistance of the inner wall, long service life, and reliable operation. They are a promising new type of pipe material for urban water supply and drainage networks and long-distance drainage networks.

[0004] However, due to the significant compositional differences between the base layer and cladding layer of austenitic stainless steel composite pipes, the welding process can easily lead to issues such as dilution of alloying elements in the cladding layer weld and excessive incorporation of alloying elements into the base layer weld. This results in the formation of high-hardness phases in both the inner and outer welds, thereby reducing the mechanical properties and corrosion resistance of the welded joint. The overall performance of austenitic stainless steel composite pipe welded joints largely depends on the welding materials used. Currently, ER309L or ER309LMo welding wire is commonly used for welding this type of composite pipe. Its high chromium and nickel content can compensate to some extent for the decrease in corrosion resistance caused by the incorporation of the base layer. However, the excessively high chromium and nickel content in this type of welding wire can also cause the corrosion resistance of the weld area to exceed that of the cladding base material, potentially leading to galvanic corrosion of the joint. Summary of the Invention

[0005] The first objective of this invention is to provide an iron-based welding wire for CMT welding of austenitic stainless steel / carbon steel composite pipes, thereby solving the problems of high hard phase and insufficient corrosion resistance in the welding of existing stainless steel composite materials.

[0006] The second objective of this invention is to provide a method for preparing iron-based welding wire for CMT welding of austenitic stainless steel / carbon steel composite pipes.

[0007] A third objective of this invention is to provide a welding method for austenitic stainless steel / carbon steel composite pipes.

[0008] The first technical solution adopted in this invention is an iron-based welding wire for CMT welding of austenitic stainless steel / carbon steel composite pipes, comprising flux powder and welding scale, wherein the flux powder comprises the following components by mass percentage: Cr 23.0~28.0%, Ni 28.0~32.0%, Mo 15.0~18.0%, Nb 2.0~4.0%, Co 3.0~5.0%, Y2O3+La2O3 0.4~0.8%, with the remainder being Fe, and the sum of the mass percentages of the above components is 100%.

[0009] The invention is further characterized in that:

[0010] The purity of each powder is ≥99.9%.

[0011] The particle size of each powder is 100-200 mesh.

[0012] The weld bead is made of 304 stainless steel strip, with a thickness of 0.4 mm and a width of 7 mm.

[0013] The amount of flux filling material in the welding wire is controlled between 20wt% and 24wt%.

[0014] The second technical solution adopted in this invention is a method for preparing iron-based welding wire for CMT welding of austenitic stainless steel / carbon steel composite pipes. According to the above-mentioned formula of iron-based welding wire for CMT welding of austenitic stainless steel / carbon steel composite pipes, the flux powder is weighed and the welding wire is prepared by flux-cored welding wire drawing equipment. Among them, 304 steel strip is used as the welding skin and the filling amount of flux powder in the welding wire is controlled at 20wt%~24wt%.

[0015] The invention is further characterized in that: The preparation method of iron-based welding wire for CMT welding of austenitic stainless steel / carbon steel composite pipes is as follows: Step 1: Weigh out the following components by mass percentage: Cr 23.0~28.0%, Ni 28.0~32.0%, Mo 15.0~18.0%, Nb 2.0~4.0%, Co 3.0~5.0%, Y2O3+La2O3 0.4~0.8%, with the remainder being Fe. The sum of the mass percentages of the above components should be 100%. Step 2: Place the weighed medicinal powder from Step 1 into a vacuum heating furnace and heat it at a temperature of 220℃~250℃ for 1h~3h. After drying, place the medicinal powder into a powder mixer for thorough mixing for 1h~2h. Step 3: Using 304 steel strip as the welding skin, use alcohol to remove the grease on the surface of the 304 steel strip, and wrap the flux powder prepared in step 2 inside the 304 steel strip using a flux-cored wire drawing device. The diameter of the first drawing die is 2.6mm. Step 4: After the first drawing process is completed, the die hole diameter is reduced in sequence to finally obtain flux-cored welding wire with a diameter of 1.0mm~1.2mm.

[0016] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0017] The third technical solution adopted in this invention is a welding method for austenitic stainless steel / carbon steel composite pipes, specifically as follows: First, an asymmetrical X-shaped bevel is made at the welding area of ​​the austenitic stainless steel / carbon steel composite plate. Then, the austenitic stainless steel / carbon steel composite plate is rolled up. Next, the austenitic stainless steel layer is welded using the aforementioned welding wire, with a welding current of 150A~180A, a welding voltage of 22V~24V, and a welding shielding gas of 97vol%Ar+3vol%O2. Finally, the carbon steel layer is welded using ER50-6 welding wire, with a welding current of 180A~220A, a welding voltage of 23V~26V, and a welding shielding gas of 80vol%Ar+20vol%CO2.

[0018] The invention is further characterized in that: The specific parameters for the asymmetric X-shaped bevel at the weld joint of the austenitic stainless steel / carbon steel composite plate are as follows: the thickness of the austenitic stainless steel / carbon steel composite pipe base material is 5mm~10mm, the bevel angle of the austenitic stainless steel layer is 50°~60°, and the bevel angle of the carbon steel layer is 45°~55°; the thickness of the austenitic stainless steel layer is 0.5mm~2mm, the distance from the austenitic stainless steel / carbon steel interface to the bottom of the bevel is 1.0mm~2.0mm, and the assembly gap is 0~1.5mm.

[0019] The beneficial effects of this invention are: (1) The welding wire of the present invention has a high Cr and Ni content, thereby ensuring the excellent corrosion resistance of the austenitic stainless steel layer weld after the carbon steel layer is incorporated.

[0020] (2) The present invention ensures the excellent corrosion resistance and mechanical properties of the austenitic stainless steel layer weld through reasonable element design: high Cr and high Mo design effectively ensures the corrosion resistance of the weld in a chlorine-containing environment; the addition of Nb element inhibits the coarsening of weld grains and fixes carbides; the composite addition of rare earth elements purifies the grain boundaries and improves the weld's resistance to intergranular corrosion.

[0021] (3) CMT (Cold Metal Transfer) technology, as an advanced process for welding austenitic stainless steel composite pipes, can achieve precise control of weld metal composition through high-precision matching of welding materials and welding methods. Based on this, the welding method of this invention aims to develop special welding materials suitable for CMT welding process of austenitic stainless steel metallurgical composite pipes, thereby effectively controlling weld composition, avoiding the occurrence of high-hardness phases and galvanic corrosion, further improving the product quality of composite pipes, and ensuring the cleanliness of water supply and the long-term safe operation of pipelines.

[0022] (4) The welding method of the present invention is based on CMT welding process and welding wire composition, and reasonably designs X-type groove form. The austenitic stainless steel layer and carbon steel base layer are welded separately, which not only ensures the corrosion resistance of the austenitic stainless steel layer, but also inhibits the formation of high hard phase in the carbon steel layer, reduces the precipitation of high hard phase in the weld, and improves the strength and toughness of the stainless steel composite plate joint.

[0023] (5) The welding wire of the present invention, through the reasonable addition of alloying elements, results in a weld structure mainly composed of austenitic structure (γ-Fe) and supplemented by ferrite structure (δ-Fe). This composite structure distribution ensures the excellent crack resistance of the weld.

[0024] (6) The welding wire preparation process of the present invention is simple, and it can be welded using either TIG or MIG / MAG, making it highly applicable to engineering projects. Attached Figure Description

[0025] Figure 1 The bevel form is for austenitic stainless steel / carbon steel composite plates; Figure 2 Metallographic structure of the austenitic stainless steel layer weld in the butt joint of the austenitic stainless steel composite plate prepared using Example 2; Figure 3 The metallographic structure of the carbon steel layer weld in the butt joint of the austenitic stainless steel composite plate prepared using Example 2; Figure 4 The microstructure of the austenitic stainless steel layer of the butt joint of the austenitic stainless steel composite plate prepared in Example 2 after being etched with 3.5% NaCl solution for 24 hours. Figure 5 The microstructure of the carbon steel layer of the butt joint of the austenitic stainless steel composite plate prepared in Example 2 after being corroded with 3.5% NaCl solution for 24 hours. Detailed Implementation

[0026] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0027] This invention provides an iron-based welding wire for CMT welding of austenitic stainless steel / carbon steel composite pipes, comprising flux powder and welding scale. The flux powder comprises the following components by mass percentage: Cr 23.0~28.0%, Ni 28.0~32.0%, Mo 15.0~18.0%, Nb 2.0~4.0%, Co 3.0~5.0%, Y2O3+La2O3 0.4~0.8%, with the remainder being Fe. The sum of the mass percentages of the above components is 100%.

[0028] The purity of each powder is ≥99.9%.

[0029] The particle size of each powder is 100-200 mesh.

[0030] The weld bead is made of 304 stainless steel strip, with a thickness of 0.4 mm and a width of 7 mm.

[0031] The amount of flux filling material in the welding wire is controlled between 20wt% and 24wt%.

[0032] The welding wire designed in this invention has the following main components and their functions: (1) The main alloying element of the welding wire cladding metal is Fe: The welding wire of this invention is used for welding austenitic stainless steel / carbon steel composite plates. The main alloying element of both austenitic stainless steel and carbon steel is Fe. Therefore, the welding wire is designed with Fe as the main element, which can ensure excellent metallurgical bonding performance with the stainless steel layer and the carbon steel layer. In addition, the fact that the welding wire is mainly Fe greatly reduces the cost of the welding wire and has wide applicability.

[0033] (2) The cladding metal of the welding wire contains a large amount of Cr: Cr is a ferrite-forming element (δ-Fe) and an important element for ensuring corrosion resistance. During use, Cr forms a dense Cr2O3 protective film, preventing further penetration of corrosive media. The welding wire of this invention is designed to add 23.0~28.0% Cr to the flux powder according to the CMT process, bevel form, and thickness of the austenitic stainless steel layer of the base material, thereby ensuring that the Cr alloying element in the austenitic stainless steel layer weld is close to that of the base austenitic stainless steel. If the Cr content is added below 23.0%, the Cr element in the welded stainless steel layer is lower than that in the base material; if the Cr content is added above 28.0%, the Cr element in the welded stainless steel layer is much higher than that in the base material, the δ-Fe content in the weld structure increases, the weld brittleness increases, and the higher Cr content also leads to better corrosion resistance of the weld than the base material, making it easy to form galvanic corrosion in the heat-affected zone. Excessive Cr content can also lead to the formation of brittle σ phase during service, resulting in failure.

[0034] (3) The welding wire cladding metal contains a certain amount of Ni element: Ni is an austenite (γ-Fe) forming element. In austenitic stainless steel, a reasonable combination of Cr and Ni elements is the key to ensuring the austenitic phase. The welding wire of this invention is an austenitic stainless steel welding wire, and its main phase composition is γ-Fe phase. The main phase composition of the base metal austenitic stainless steel layer is also γ-Fe phase, so the phase composition of the weld is consistent with that of the base metal, which can ensure uniform corrosion resistance. This invention adds 28.0~32.0% Ni element to the flux powder: if the Ni content is less than 28.0%, the γ-Fe content in the obtained stainless steel layer weld structure is too low, which affects the corrosion resistance; if the Ni content is higher than 32.0%, the γ-Fe content in the obtained stainless steel layer weld structure is too high, which will also lead to a reduction in δ-Fe content. Too little or no δ-Fe structure will result in the weld being mainly composed of pure γ-Fe structure, which has high cracking sensitivity.

[0035] (4) The welding wire cladding metal contains a certain amount of Mo: When the content of each alloying element is constant, the main factor affecting its corrosion resistance is the intergranular Cr of austenite. 23 The formation of C6 carbides. Since these carbides form at grain boundaries, a Cr-depleted zone appears near the interface, leading to intergranular corrosion. For austenitic stainless steel welding wire, simply increasing the Cr content is detrimental to its corrosion resistance. Excessive Cr content generates excessive δ-Fe and brittle σ phases during service, which are detrimental to weld performance. Mo is also an element that improves the corrosion resistance of austenitic stainless steel, especially its resistance to pitting corrosion in chloride-containing environments. Mo reacts with C to form Mo6C-type carbides, thus preventing C from reacting with Cr to form Cr. 23 C6 prevents the formation of Cr-depleted regions in the intergranular space, thus avoiding intergranular corrosion. The combined addition of Cr and Mo improves corrosion resistance better than the addition of a single element, exhibiting a synergistic effect in enhancing corrosion resistance.

[0036] (5) The welding wire cladding metal contains a certain amount of Nb: Nb reacts with C to form Nb6C type carbides. Since stainless steel composite plates are usually connected by multi-layer and multi-pass welding, the welding of subsequent weld passes will have a thermal effect on the preceding weld passes, which will lead to the coarsening of the grains of the preceding weld passes. After adding Nb to the welding wire, the presence of Nb6C type carbides during the welding process significantly inhibits the growth of austenite grains in the weld by pinning the austenite grain boundaries, thereby ensuring the excellent mechanical properties of the weld.

[0037] (6) The welding wire cladding metal contains a certain amount of Co: Co is an excellent high-temperature resistant element. The addition of Co to the welding wire can ensure the structural stability of the austenitic weld during the welding process. Co is dissolved in the austenitic cell and improves the strength and toughness of the weld metal through solid solution strengthening. The presence of Co will inhibit the precipitation of brittle σ phase and, together with Ni, play a role in improving the service stability of the austenitic weld.

[0038] (7) The welding wire contains composite rare earth oxides Y2O3 and La2O3: Adding rare earth oxides such as Y2O3 (yttrium trioxide) and La2O3 (lanthanum oxide) to the weld metal of austenitic stainless steel is an advanced material modification technology. It mainly improves the comprehensive performance of the weld by regulating the microstructure and purifying the weld. Y2O3 and La2O3 particles can act as heterogeneous nucleation points in the molten pool, promoting the nucleation of austenite grains while inhibiting grain growth. More importantly, they will accumulate at the solidification interface front, causing "compositional supercooling", breaking the growth of columnar crystals and promoting the transformation of coarse columnar crystals into fine equiaxed crystals. The rare earth elements yttrium (Y) and lanthanum (La) are chemically very active and have a strong affinity for impurities such as oxygen, sulfur, and phosphorus. They preferentially react with these impurities to form fine rare earth oxides, sulfides, or oxysulfides with high melting points (such as Y2O2S, La2O2S). These stable rare earth compounds "capture" harmful sulfur and phosphorus elements, preventing them from agglomerating at grain boundaries to form low-melting-point or corrosion-sensitive areas, thereby greatly enhancing the weld's ability to resist intergranular corrosion.

[0039] This invention also provides a method for preparing the above-mentioned iron-based welding wire for CMT welding of austenitic stainless steel / carbon steel composite pipes. The method involves weighing the flux powder according to the above-mentioned formula for the iron-based welding wire for CMT welding of austenitic stainless steel / carbon steel composite pipes, and preparing the welding wire using a flux-cored welding wire drawing device. Specifically: Step 1: Weigh out the following components by mass percentage: Cr 23.0~28.0%, Ni 28.0~32.0%, Mo 15.0~18.0%, Nb 2.0~4.0%, Co 3.0~5.0%, Y2O3+La2O3 0.4~0.8%, with the remainder being Fe. The sum of the mass percentages of the above components should be 100%. In step 1, the purity of each powder is ≥99.9%; the particle size of each powder is 100 mesh to 200 mesh. Step 2: Place the weighed powder from Step 1 into a vacuum heating furnace and heat it at a temperature of 220℃~250℃ for 1h~3h to remove the water of crystallization from the powder; place the dried powder into a powder mixer for thorough mixing for 1h~2h. Step 3: Using 304 steel strip as the welding skin, use alcohol to remove the grease on the surface of the 304 steel strip, and wrap the flux powder prepared in step 2 inside the 304 steel strip using a flux-cored wire drawing device. The diameter of the first drawing die is 2.6mm. In step 3, the welding skin is made of 304 stainless steel strip, with a thickness of 0.4 mm and a width of 7 mm; the filling amount of flux in the welding wire is controlled between 20 wt% and 24 wt%. Step 4: After the first drawing process is completed, the die hole diameter is reduced in sequence to finally obtain flux-cored welding wire with a diameter of 1.0mm~1.2mm.

[0040] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0041] This invention also provides a welding method for austenitic stainless steel / carbon steel composite pipes, specifically: first, an asymmetrical X-shaped bevel is made at the weldable area of ​​the austenitic stainless steel / carbon steel composite plate, such as... Figure 1 As shown, the austenitic stainless steel / carbon steel composite plate is then rolled up. Next, the austenitic stainless steel layer is welded using the aforementioned welding wire. The welding current is 150A~180A, the welding voltage is 22V~24V, and the welding shielding gas is 97vol%Ar+3vol%O2. Finally, the carbon steel layer is welded using ER50-6 welding wire. The welding current is 180A~220A, the welding voltage is 23V~26V, and the welding shielding gas is 80vol%Ar+20vol%CO2.

[0042] The specific parameters for the asymmetric X-shaped bevel at the weld joint of the austenitic stainless steel / carbon steel composite plate are as follows: the thickness of the austenitic stainless steel / carbon steel composite pipe base material is 5mm~10mm, the bevel angle of the austenitic stainless steel layer is 50°~60°, and the bevel angle of the carbon steel layer is 45°~55°; the thickness of the austenitic stainless steel layer is 0.5mm~2mm, the distance from the austenitic stainless steel / carbon steel interface to the bottom of the bevel is 1.0mm~2.0mm, and the assembly gap is 0~1.5mm.

[0043] Example 1 Step 1: Weigh out the following components by mass percentage: 23.0% Cr, 28.0% Ni, 15.0% Mo, 2.0% Nb, 3.0% Co, 0.2% Y2O3, 0.2% La2O3, with the remainder being Fe. The sum of the mass percentages of the above components is 100%.

[0044] In step 1, the purity of each powder is ≥99.9%; the particle size of each powder is 100 mesh. Step 2: Place the powder weighed in Step 1 into a vacuum heating furnace and heat it at 220℃ for 1 hour to remove the water of crystallization from the powder; place the dried powder into a powder mixer for thorough mixing for 1 hour. Step 3: Using 304 steel strip as the welding skin, use alcohol to remove the grease on the surface of the 304 steel strip, and wrap the flux powder prepared in step 2 inside the 304 steel strip using a flux-cored wire drawing device. The diameter of the first drawing die is 2.6mm. In step 3, the welding skin is made of 304 stainless steel strip, with a thickness of 0.4 mm and a width of 7 mm; the flux filling amount in the welding wire is controlled at 20 wt%. Step 4: After the first drawing process is completed, the die hole diameter is reduced in sequence to finally obtain flux-cored welding wire with a diameter of 1.0~1.2mm.

[0045] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0046] The austenitic stainless steel composite pipe prepared in Example 1 was used to weld 304 / Q235B composite plates using iron-based welding wire for CMT welding. The composite plates were processed with the following beveling: the austenitic stainless steel / carbon steel composite plate base material thickness was 5mm, with an X-shaped beveling, the beveling angle of the austenitic stainless steel layer was 50°, and the beveling angle of the carbon steel layer was 45°; the thickness of the austenitic stainless steel layer was 0.5mm, the distance from the austenitic stainless steel / carbon steel interface to the bottom of the beveling was 1.0mm, and the assembly gap was 0mm.

[0047] Then, the austenitic stainless steel / carbon steel composite plate is rolled up, and CMT welding of the austenitic stainless steel composite pipe is carried out using the above-mentioned iron-based welding wire and the opened X-shaped groove. During welding, the austenitic stainless steel layer is welded first, using the welding wire of this invention, the welding current is 150A, the welding voltage is 22V, and the welding shielding gas is 97vol%Ar+3vol%O2; then the carbon steel layer is welded, using ER50-6 welding wire, the welding current is 180A, the welding voltage is 23V, and the welding shielding gas is 80vol%Ar+20vol%CO2.

[0048] The butt joints of 304 / Q235B composite plates welded using the above process parameters were subjected to non-destructive, metallographic, and mechanical property tests. The test results are as follows: (1) The welds of the above-mentioned welded test plates were subjected to penetrant testing in accordance with the NB / T 47013.5-2015 "Non-destructive testing of pressure equipment - Part 5: Penetrant testing". The results showed that the quality level of the stainless steel side welds and carbon steel side welds was Grade I qualified.

[0049] (2) Radiographic testing was performed on the above-mentioned welded test plate in accordance with NB / T 47013.2 "Non-destructive testing of pressure equipment - Part 2: Radiographic testing". The results showed that the radiographic testing technology level was AB and the quality level was I qualified.

[0050] (3) Prepare 4t bending specimens (t is the specimen thickness, 4t is the diameter of the pressure head used for bending) in accordance with NB / T 47014-2023 "Welding Procedure Qualification for Pressure Equipment" and conduct a three-point bending test on the joint. The test results show that the joint did not crack after bending 180°.

[0051] (4) Prepare microhardness test specimens for joints. The test results show that the hardness of 304 stainless steel weld is 210HV0.3 and the hardness of carbon steel weld is 202HV0.3.

[0052] (5) A corrosion test was conducted on the weld surface of 304 stainless steel with 3.5% NaCl solution. No defect morphology was observed after 24 hours of corrosion.

[0053] Example 2 Step 1: Weigh out the following components by mass percentage: 28.0% Cr, 32.0% Ni, 18.0% Mo, 4.0% Nb, 5.0% Co, 0.4% Y2O3, 0.4% La2O3, and the remainder Fe. The sum of the mass percentages of the above components is 100%.

[0054] In step 1, the purity of each powder is ≥99.9%; the particle size of each powder is 100 mesh. Step 2: Place the weighed powder from Step 1 into a vacuum heating furnace and heat it at 250℃ for 3 hours to remove the water of crystallization from the powder; place the dried powder into a powder mixer for thorough mixing for 2 hours. Step 3: Using 304 steel strip as the welding skin, use alcohol to remove the grease on the surface of the 304 steel strip, and wrap the flux powder prepared in step 2 inside the 304 steel strip using a flux-cored wire drawing device. The diameter of the first drawing die is 2.6mm. In step 3, the welding skin is made of 304 stainless steel strip, with a thickness of 0.4 mm and a width of 7 mm; the flux filling amount in the welding wire is controlled at 24 wt%. Step 4: After the first drawing process is completed, the die hole diameter is reduced in sequence to finally obtain flux-cored welding wire with a diameter of 1.0~1.2mm.

[0055] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0056] The austenitic stainless steel composite pipe prepared in Example 2 was used to weld 304 / Q235B composite plates using iron-based welding wire for CMT welding. The composite plates were processed with the following beveling: the austenitic stainless steel / carbon steel composite plate base material thickness was 10mm, with an X-shaped beveling, the beveling angle of the austenitic stainless steel layer was 60°, and the beveling angle of the carbon steel layer was 55°; the austenitic stainless steel layer thickness was 2mm, the distance from the austenitic stainless steel / carbon steel interface to the bottom of the beveling was 2.0mm, and the assembly gap was 1.5mm.

[0057] Then, the austenitic stainless steel / carbon steel composite plate is rolled up, and CMT welding of the austenitic stainless steel composite pipe is carried out using the above-mentioned iron-based welding wire and the X-shaped groove. During welding, the austenitic stainless steel layer is welded first, using the welding wire of this invention, with a welding current of 180A, a welding voltage of 24V, and a welding shielding gas of 97vol%Ar + 3vol%O2. Next, the carbon steel layer is welded, using ER50-6 welding wire, with a welding current of 220A, a welding voltage of 26V, and a welding shielding gas of 80vol%Ar + 20vol%CO2.

[0058] The butt joints of 304 / Q235B composite plates welded using the above process parameters were subjected to non-destructive, metallographic, and mechanical property tests. The test results are as follows: (1) The welds of the above-mentioned welded test plates were subjected to penetrant testing in accordance with the NB / T 47013.5-2015 "Non-destructive testing of pressure equipment - Part 5: Penetrant testing". The results showed that the quality level of the stainless steel side welds and carbon steel side welds was Grade I qualified.

[0059] (2) Radiographic testing was performed on the above-mentioned welded test plate in accordance with NB / T 47013.2 "Non-destructive testing of pressure equipment - Part 2: Radiographic testing". The results showed that the radiographic testing technology level was AB and the quality level was I qualified.

[0060] (3) Prepare 4t bending specimens (t is the specimen thickness, 4t is the diameter of the pressure head used for bending) in accordance with NB / T 47014-2023 "Welding Procedure Qualification for Pressure Equipment" and conduct a three-point bending test on the joint. The test results show that the joint did not crack after bending 180°.

[0061] (4) Prepare microhardness test specimens for joints. The test results show that the hardness of 304 stainless steel weld is 212HV0.3 and the hardness of carbon steel weld is 201HV0.3.

[0062] (5) A corrosion test was conducted on the weld surface of 304 stainless steel with 3.5% NaCl solution. No defect morphology was observed after 24 hours of corrosion.

[0063] Figure 2The image shows the metallographic structure of the austenitic stainless steel layer weld in the butt joint of the austenitic stainless steel composite plate prepared in Example 2. As can be seen from Figure 2, the weld is mainly composed of austenite (γ-Fe) + ferrite (δ-Fe).

[0064] Figure 3 The image shows the metallographic structure of the carbon steel layer weld in the butt joint of the austenitic stainless steel composite plate prepared in Example 2. As can be seen from Figure 3, the carbon steel weld mainly consists of proeutectoid ferrite and acicular ferrite.

[0065] Figure 4 The figures show the microstructure of the austenitic stainless steel layer in the butt joint of the austenitic stainless steel composite plate prepared in Example 2 after corrosion with 3.5% NaCl solution for 24 hours. As can be seen from Figure 4, no defects were observed on the surface of the austenitic stainless steel weld, indicating its excellent corrosion resistance.

[0066] Figure 5 The figures show the microstructure of the carbon steel layer in the butt joint of the austenitic stainless steel composite plate prepared in Example 2 after corrosion with 3.5% NaCl solution for 24 hours. As can be seen from Figure 5, the surface of the carbon steel weld exhibits severe pitting corrosion, indicating its poor corrosion resistance.

[0067] Example 3 Step 1: Weigh out the following components by mass percentage: 25.0% Cr, 30.0% Ni, 17.0% Mo, 3.0% Nb, 4.0% Co, 0.3% Y2O3, 0.3% La2O3, with the remainder being Fe. The sum of the mass percentages of the above components is 100%.

[0068] In step 1, the purity of each powder is ≥99.9%; the particle size of each powder is 150 mesh. Step 2: Place the weighed powder from Step 1 into a vacuum heating furnace and heat it at 235℃ for 2 hours to remove the water of crystallization from the powder; place the dried powder into a powder mixer for thorough mixing for 1.5 hours. Step 3: Using 304 steel strip as the welding skin, use alcohol to remove the grease on the surface of the 304 steel strip, and wrap the flux powder prepared in step 2 inside the 304 steel strip using a flux-cored wire drawing device. The diameter of the first drawing die is 2.6mm. In step 3, the welding skin is made of 304 stainless steel strip, with a thickness of 0.4 mm and a width of 7 mm; the flux filling amount in the welding wire is controlled at 22 wt%. Step 4: After the first drawing process is completed, the die hole diameter is reduced in sequence to finally obtain flux-cored welding wire with a diameter of 1.0~1.2mm.

[0069] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0070] The austenitic stainless steel composite pipe prepared in Example 3 was used to weld 304 / Q235B composite plates using iron-based welding wire for CMT welding. The composite plates were processed with the following beveling: the austenitic stainless steel / carbon steel composite plate base material thickness was 8mm, with an X-shaped beveling, the beveling angle of the austenitic stainless steel layer was 55°, and the beveling angle of the carbon steel layer was 50°; the austenitic stainless steel layer thickness was 1.5mm, the distance from the austenitic stainless steel / carbon steel interface to the bottom of the beveling was 1.5mm, and the assembly gap was 0.8mm.

[0071] Then, the austenitic stainless steel / carbon steel composite plate is rolled up, and CMT welding of the austenitic stainless steel composite pipe is carried out using the above-mentioned iron-based welding wire and the X-shaped groove. During welding, the austenitic stainless steel layer is welded first, using the welding wire of this invention, with a welding current of 170A, a welding voltage of 23V, and a welding shielding gas of 97vol%Ar+3vol%O2; then the carbon steel layer is welded, using ER50-6 welding wire, with a welding current of 200A, a welding voltage of 24V, and a welding shielding gas of 80vol%Ar+20vol%CO2.

[0072] The butt joints of 304 / Q235B composite plates welded using the above process parameters were subjected to non-destructive, metallographic, and mechanical property tests. The test results are as follows: (1) The welds of the above-mentioned welded test plates were subjected to penetrant testing in accordance with the NB / T 47013.5-2015 "Non-destructive testing of pressure equipment - Part 5: Penetrant testing". The results showed that the quality level of the stainless steel side welds and carbon steel side welds was Grade I qualified.

[0073] (2) Radiographic testing was performed on the above-mentioned welded test plate in accordance with NB / T 47013.2 "Non-destructive testing of pressure equipment - Part 2: Radiographic testing". The results showed that the radiographic testing technology level was AB and the quality level was I qualified.

[0074] (3) Prepare 4t bending specimens (t is the specimen thickness, 4t is the diameter of the pressure head used for bending) in accordance with NB / T 47014-2023 "Welding Procedure Qualification for Pressure Equipment" and conduct a three-point bending test on the joint. The test results show that the joint did not crack after bending 180°.

[0075] (4) Prepare microhardness test specimens for joints. The test results show that the hardness of 304 stainless steel weld is 207HV0.3 and the hardness of carbon steel weld is 206HV0.3.

[0076] (5) A corrosion test was conducted on the weld surface of 304 stainless steel with 3.5% NaCl solution. No defect morphology was observed after 24 hours of corrosion.

[0077] Example 4 Step 1: Weigh out the following components by mass percentage: Cr 24.0%, Ni 29.0%, Mo 16.0%, Nb 2.1%, Co 3.1%, Y2O3 0.2%, La2O3 0.3%, with the remainder being Fe. The sum of the mass percentages of the above components is 100%.

[0078] In step 1, the purity of each powder is ≥99.9%; the particle size of each powder is 100 mesh. Step 2: Place the weighed powder from Step 1 into a vacuum heating furnace and heat it at 225℃ for 1.1 hours to remove the water of crystallization from the powder; place the dried powder into a powder mixer for thorough mixing for 1.1 hours. Step 3: Using 304 steel strip as the welding skin, use alcohol to remove the grease on the surface of the 304 steel strip, and wrap the flux powder prepared in step 2 inside the 304 steel strip using a flux-cored wire drawing device. The diameter of the first drawing die is 2.6mm. In step 3, the welding skin is made of 304 stainless steel strip, with a thickness of 0.4 mm and a width of 7 mm; the flux filling amount in the welding wire is controlled at 23 wt%. Step 4: After the first drawing process is completed, the die hole diameter is reduced in sequence to finally obtain flux-cored welding wire with a diameter of 1.0~1.2mm.

[0079] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0080] The austenitic stainless steel composite pipe prepared in Example 4 was used to weld 304 / Q235B composite plates using iron-based welding wire for CMT welding. The composite plates were processed with the following beveling: the austenitic stainless steel / carbon steel composite plate base material thickness was 6mm, with an X-shaped beveling, the beveling angle of the austenitic stainless steel layer was 52°, and the beveling angle of the carbon steel layer was 46°; the austenitic stainless steel layer thickness was 1mm, the distance from the austenitic stainless steel / carbon steel interface to the bottom of the beveling was 1.1mm, and the assembly gap was 0.11mm.

[0081] Then, the austenitic stainless steel / carbon steel composite plate is rolled up, and CMT welding of the austenitic stainless steel composite pipe is carried out using the above-mentioned iron-based welding wire and the opened X-shaped groove. During welding, the austenitic stainless steel layer is welded first, using the welding wire of this invention, the welding current is 155A, the welding voltage is 22.5V, and the welding shielding gas is 97vol%Ar+3vol%O2; then the carbon steel layer is welded, using ER50-6 welding wire, the welding current is 190A, the welding voltage is 23.5V, and the welding shielding gas is 80vol%Ar+20vol%CO2.

[0082] The butt joints of 304 / Q235B composite plates welded using the above process parameters were subjected to non-destructive, metallographic, and mechanical property tests. The test results are as follows: (1) The welds of the above-mentioned welded test plates were subjected to penetrant testing in accordance with the NB / T 47013.5-2015 "Non-destructive testing of pressure equipment - Part 5: Penetrant testing". The results showed that the quality level of the stainless steel side welds and carbon steel side welds was Grade I qualified.

[0083] (2) Radiographic testing was performed on the above-mentioned welded test plate in accordance with NB / T 47013.2 "Non-destructive testing of pressure equipment - Part 2: Radiographic testing". The results showed that the radiographic testing technology level was AB and the quality level was I qualified.

[0084] (3) Prepare 4t bending specimens (t is the specimen thickness, 4t is the diameter of the pressure head used for bending) in accordance with NB / T 47014-2023 "Welding Procedure Qualification for Pressure Equipment" and conduct a three-point bending test on the joint. The test results show that the joint did not crack after bending 180°.

[0085] (4) Prepare microhardness test specimens for joints. The test results show that the hardness of 304 stainless steel weld is 204HV0.3 and the hardness of carbon steel weld is 206HV0.3.

[0086] (5) A corrosion test was conducted on the weld surface of 304 stainless steel with 3.5% NaCl solution. No defect morphology was observed after 24 hours of corrosion.

[0087] Example 5 Step 1: Weigh out the following components by mass percentage: 23.5% Cr, 28.5% Ni, 16.5% Mo, 2.5% Nb, 3.5% Co, 0.2% Y2O3, 0.3% La2O3, with the remainder being Fe. The sum of the mass percentages of the above components is 100%.

[0088] In step 1, the purity of each powder is ≥99.9%; the particle size of each powder is 100 mesh. Step 2: Place the weighed powder from Step 1 into a vacuum heating furnace and heat it at 222℃ for 1.2 hours to remove the water of crystallization from the powder; place the dried powder into a powder mixer for thorough mixing for 1.3 hours. Step 3: Using 304 steel strip as the welding skin, use alcohol to remove the grease on the surface of the 304 steel strip, and wrap the flux powder prepared in step 2 inside the 304 steel strip using a flux-cored wire drawing device. The diameter of the first drawing die is 2.6mm. In step 3, the welding skin is made of 304 stainless steel strip, with a thickness of 0.4 mm and a width of 7 mm; the flux filling amount in the welding wire is controlled at 24 wt%. Step 4: After the first drawing process is completed, the die hole diameter is reduced in sequence to finally obtain flux-cored welding wire with a diameter of 1.0~1.2mm.

[0089] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0090] A 304 / Q235B composite plate was welded using an iron-based welding wire for CMT welding of austenitic stainless steel composite pipe prepared in Example 5. The composite plate was processed with the following beveling: the austenitic stainless steel / carbon steel composite plate base material thickness was 6.5 mm, with an X-shaped beveling; the beveling angle of the austenitic stainless steel layer was 56°, and the beveling angle of the carbon steel layer was 47°; the austenitic stainless steel layer thickness was 1.8 mm; the distance from the austenitic stainless steel / carbon steel interface to the bottom of the beveling was 1.3 mm; and the assembly gap was 1.1 mm.

[0091] Then, the austenitic stainless steel / carbon steel composite plate is rolled up, and CMT welding of the austenitic stainless steel composite pipe is carried out using the above-mentioned iron-based welding wire and the X-shaped groove. During welding, the austenitic stainless steel layer is welded first, using the welding wire of this invention, with a welding current of 175A, a welding voltage of 23.4V, and a welding shielding gas of 97vol%Ar+3vol%O2. Next, the carbon steel layer is welded, using ER50-6 welding wire, with a welding current of 201A, a welding voltage of 25.1V, and a welding shielding gas of 80vol%Ar+20vol%CO2.

[0092] The butt joints of 304 / Q235B composite plates welded using the above process parameters were subjected to non-destructive, metallographic, and mechanical property tests. The test results are as follows: (1) The welds of the above-mentioned welded test plates were subjected to penetrant testing in accordance with the NB / T 47013.5-2015 "Non-destructive testing of pressure equipment - Part 5: Penetrant testing". The results showed that the quality level of the stainless steel side welds and carbon steel side welds was Grade I qualified.

[0093] (2) Radiographic testing was performed on the above-mentioned welded test plate in accordance with NB / T 47013.2 "Non-destructive testing of pressure equipment - Part 2: Radiographic testing". The results showed that the radiographic testing technology level was AB and the quality level was I qualified.

[0094] (3) Prepare 4t bending specimens (t is the specimen thickness, 4t is the diameter of the pressure head used for bending) in accordance with NB / T 47014-2023 "Welding Procedure Qualification for Pressure Equipment" and conduct a three-point bending test on the joint. The test results show that the joint did not crack after bending 180°.

[0095] (4) Prepare microhardness test specimens for joints. The test results show that the hardness of 304 stainless steel weld is 216HV0.3 and the hardness of carbon steel weld is 200HV0.3.

[0096] (5) A corrosion test was conducted on the weld surface of 304 stainless steel with 3.5% NaCl solution. No defect morphology was observed after 24 hours of corrosion.

[0097] Example 6 Step 1: Weigh out the following components by mass percentage: 27.9% Cr, 31.5% Ni, 17.9% Mo, 3.9% Nb, 4.9% Co, 0.4% Y2O3, 0.4% La2O3, with the remainder being Fe. The sum of the mass percentages of the above components is 100%.

[0098] In step 1, the purity of each powder is ≥99.9%; the particle size of each powder is 100 mesh. Step 2: Place the weighed powder from Step 1 into a vacuum heating furnace and heat it at 229℃ for 2.9 hours to remove the water of crystallization from the powder; place the dried powder into a powder mixer for thorough mixing for 1.9 hours. Step 3: Using 304 steel strip as the welding skin, use alcohol to remove the grease on the surface of the 304 steel strip, and wrap the flux powder prepared in step 2 inside the 304 steel strip using a flux-cored wire drawing device. The diameter of the first drawing die is 2.6mm. In step 3, the welding skin is made of 304 stainless steel strip, with a thickness of 0.4 mm and a width of 7 mm; the flux filling amount in the welding wire is controlled at 24 wt%. Step 4: After the first drawing process is completed, the die hole diameter is reduced in sequence to finally obtain flux-cored welding wire with a diameter of 1.0~1.2mm.

[0099] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0100] A 304 / Q235B composite plate was welded using an iron-based welding wire for CMT welding of austenitic stainless steel composite pipe prepared in Example 6. The composite plate was processed with the following beveling: the austenitic stainless steel / carbon steel composite plate base material thickness was 9mm, with an X-shaped beveling; the beveling angle of the austenitic stainless steel layer was 50~60°, and the beveling angle of the carbon steel layer was 54°; the thickness of the austenitic stainless steel layer was 1.9mm, the distance from the austenitic stainless steel / carbon steel interface to the bottom of the beveling was 1.9mm, and the assembly gap was 1.45mm.

[0101] Then, the austenitic stainless steel / carbon steel composite plate is rolled up, and CMT welding of the austenitic stainless steel composite pipe is carried out using the above-mentioned iron-based welding wire and the X-shaped groove. During welding, the austenitic stainless steel layer is welded first, using the welding wire of this invention, with a welding current of 179A, a welding voltage of 23.9V, and a welding shielding gas of 97vol%Ar+3vol%O2. Next, the carbon steel layer is welded, using ER50-6 welding wire, with a welding current of 219A, a welding voltage of 25.9V, and a welding shielding gas of 80vol%Ar+20vol%CO2.

[0102] The butt joints of 304 / Q235B composite plates welded using the above process parameters were subjected to non-destructive, metallographic, and mechanical property tests. The test results are as follows: (1) The welds of the above-mentioned welded test plates were subjected to penetrant testing in accordance with the NB / T 47013.5-2015 "Non-destructive testing of pressure equipment - Part 5: Penetrant testing". The results showed that the quality level of the stainless steel side welds and carbon steel side welds was Grade I qualified.

[0103] (2) Radiographic testing was performed on the above-mentioned welded test plate in accordance with NB / T 47013.2 "Non-destructive testing of pressure equipment - Part 2: Radiographic testing". The results showed that the radiographic testing technology level was AB and the quality level was I qualified.

[0104] (3) Prepare 4t bending specimens (t is the specimen thickness, 4t is the diameter of the pressure head used for bending) in accordance with NB / T 47014-2023 "Welding Procedure Qualification for Pressure Equipment" and conduct a three-point bending test on the joint. The test results show that the joint did not crack after bending 180°.

[0105] (4) Prepare microhardness test specimens for joints. The test results show that the hardness of 304 stainless steel weld is 213HV0.3 and the hardness of carbon steel weld is 207HV0.3.

[0106] (5) A corrosion test was conducted on the weld surface of 304 stainless steel with 3.5% NaCl solution. No defect morphology was observed after 24 hours of corrosion.

Claims

1. Iron-based welding wire for CMT welding of austenitic stainless steel / carbon steel composite pipes, characterized in that, It includes flux powder and solder coating. The flux powder comprises the following components by mass percentage: Cr 23.0~28.0%, Ni 28.0~32.0%, Mo 15.0~18.0%, Nb 2.0~4.0%, Co 3.0~5.0%, Y2O3+La2O3 0.4~0.8%, and the remainder is Fe. The sum of the mass percentages of the above components is 100%.

2. The iron-based welding wire for CMT welding of austenitic stainless steel / carbon steel composite pipes according to claim 1, characterized in that, The purity of each powder is ≥99.9%.

3. The iron-based welding wire for CMT welding of austenitic stainless steel / carbon steel composite pipes according to claim 1, characterized in that, The particle size of each powder is 100-200 mesh.

4. The iron-based welding wire for CMT welding of austenitic stainless steel / carbon steel composite pipes according to claim 1, characterized in that, The weld bead is made of 304 stainless steel strip, with a thickness of 0.4 mm and a width of 7 mm.

5. The iron-based welding wire for CMT welding of austenitic stainless steel / carbon steel composite pipes according to claim 1, characterized in that, The amount of flux filling material in the welding wire is controlled between 20wt% and 24wt%.

6. A method for preparing iron-based welding wire for CMT welding of austenitic stainless steel / carbon steel composite pipes, characterized in that, According to claim 1, the formulation of the iron-based welding wire for CMT welding of austenitic stainless steel / carbon steel composite pipe is prepared by weighing the flux powder and using a flux-cored welding wire drawing device; wherein, 304 steel strip is used as the welding skin, and the amount of flux powder in the welding wire is controlled at 20wt%~24wt%.

7. The method for preparing iron-based welding wire for CMT welding of austenitic stainless steel / carbon steel composite pipes according to claim 6, characterized in that, Specifically: Step 1: Weigh out the following components by mass percentage: Cr 23.0~28.0%, Ni 28.0~32.0%, Mo 15.0~18.0%, Nb 2.0~4.0%, Co 3.0~5.0%, Y2O3+La2O3 0.4~0.8%, with the remainder being Fe. The sum of the mass percentages of the above components should be 100%. Step 2: Place the weighed medicinal powder from Step 1 into a vacuum heating furnace and heat it at a temperature of 220℃~250℃ for 1h~3h. After drying, place the medicinal powder into a powder mixer for thorough mixing for 1h~2h. Step 3: Use alcohol to remove the grease from the surface of the 304 steel strip, and use a flux-cored wire drawing device to wrap the flux powder prepared in step 2 inside the 304 steel strip. The diameter of the first drawing die is 2.6mm. Step 4: After the first drawing process is completed, the die hole diameter is reduced in sequence to finally obtain flux-cored welding wire with a diameter of 1.0mm~1.2mm; Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

8. A welding method for austenitic stainless steel / carbon steel composite pipes, characterized in that, Specifically: First, an asymmetrical X-shaped bevel is made at the weldable area of ​​the austenitic stainless steel / carbon steel composite plate. Then, the austenitic stainless steel / carbon steel composite plate is rolled up. Next, the austenitic stainless steel layer is welded using the welding wire described in any one of claims 1-5, with a welding current of 150A~180A, a welding voltage of 22V~24V, and a welding shielding gas of 97vol%Ar+3vol%O2. Finally, the carbon steel layer is welded using ER50-6 welding wire, with a welding current of 180A~220A, a welding voltage of 23V~26V, and a welding shielding gas of 80vol%Ar+20vol%CO2.

9. The welding method for the austenitic stainless steel / carbon steel composite pipe according to claim 8, characterized in that, The specific parameters for the asymmetric X-shaped bevel at the weld joint of the austenitic stainless steel / carbon steel composite plate are as follows: the thickness of the austenitic stainless steel / carbon steel composite pipe base material is 5mm~10mm, the bevel angle of the austenitic stainless steel layer is 50°~60°, and the bevel angle of the carbon steel layer is 45°~55°; the thickness of the austenitic stainless steel layer is 0.5mm~2mm, the distance from the austenitic stainless steel / carbon steel interface to the bottom of the bevel is 1.0mm~2.0mm, and the assembly gap is 0~1.5mm.

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