A flux-cored welding wire for additive repair of rotors of power station unit dynamic equipment, and its preparation method and application

Abstract

The present invention discloses a flux-cored welding wire for additive repair of rotors in power plant units, as well as its preparation method and application. The austenitic stainless steel flux-cored welding wire comprises an outer sheath and a flux-cored powder filled within the outer sheath. The flux-cored powder comprises the following components, calculated as 100% by mass: 4%-6% ferrosilicon, 10%-12% nickel powder, 20%-22% chromium powder, 6%-8% manganese powder, 5%-8% molybdenum powder, 3%-5% rutile, 2%-3.6% micron-sized tungsten-niobium-titanium carbonitride solid solution, and the balance iron powder. By introducing the micron-sized tungsten-niobium-titanium carbonitride solid solution into the welding wire, when used for additive repair, the wire effectively repairs the rotor through the combined effects of grain refinement, solid solution strengthening, precipitation strengthening, and dispersion strengthening, extending the service life of the repair layer.

Description

Technical field:

[0001] The present invention relates to an austenitic stainless steel flux-cored welding wire, a preparation method and applications thereof, and in particular to a flux-cored welding wire for additively repairing rotors of power station unit moving equipment, a preparation method and applications thereof. Background technology:

[0002] Power plant units contain numerous moving equipment, such as steam turbines, generators, various electric pumps, steam pumps, and fans. These moving equipment are core components of power plant units, and their long-term, stable operation is crucial to the safe operation and maintenance of the units. The rotor is a key component in maintaining the long-term operation of these moving equipment. The materials used for moving equipment rotors are quite unique, encompassing a variety of compositions: pump rotors are typically made of carbon steel, while turbine and generator rotors are made of alloy steel. The rotor shaft rotates at high speed within the bearings for a long period of time, causing surface defects such as wear, scratches, and even cracks. This has become a common problem, especially under harsh operating conditions such as oil shortages, oil shortages, and impurities. Damage and defects are more likely to occur, leading to downtime and maintenance. Due to the rotor's large size and weight, high value, manufacturing complexity, long production cycles, and inconvenient transportation, problems can not only cause damage to the equipment itself, but also lead to unplanned downtime, resulting in significant economic losses. However, there is currently a lack of systematic research on online repair of power plant rotors, and the overall level of repair technology is low, making it difficult to ensure safe operation and timely startup and shutdown of the units. Currently, rotor repair materials are mostly Ni-based heterogeneous materials. A lack of materials with physical and chemical properties equal to or similar to the base material, along with high wear resistance and toughness, hinders the maintenance and improvement of the repaired area's performance. Furthermore, most repairs are performed manually, resulting in low automation, unreliable quality, and a short lifespan for the repaired layer. Therefore, the search for more suitable repair materials and highly automated repair solutions is urgent.

[0003] Austenitic stainless steel, with chromium and nickel as its primary alloying elements, is non-magnetic, corrosion-resistant, high-temperature resistant, and easily formable, similar in physicochemical properties to alloy steel rotors. Cold Metal Transfer (CMT) arc additive manufacturing technology, with its advantages of low heat input, stable arc, and excellent formability, is increasingly being used in metal additive manufacturing. Using austenitic stainless steel as the repair material for damaged rotors, and the highly automated CMT arc additive manufacturing method, could theoretically address the current issue of poor rotor repair results in moving equipment.

[0004] Patent publication number CN112899575A discloses an austenitic stainless steel wire and process based on cold metal transfer arc additive manufacturing, which belongs to the field of additive manufacturing technology. The wire composition is: C: 0.01%~0.03%, Si: 0.40%~0.55%, Mn: 1.5%~2.0%, Cr: 18.5%~20.0%, Ni: 9.0%~10.5%, Cu: 0.05%~0.1%, Mo: 0.01%~0.03%, Ti: 0.20%~0.50%, P: 0~0.02%, S: 0~0.015%, and the balance is Fe and unavoidable impurity elements. Wire manufacturing process: Welding current 129A-160A, welding voltage 14V-18V, welding speed 0.45m / min-0.70m / min, wire feed speed 5.0m / min-7.0m / min, shielding gas Ar + 0.5-2.0% CO2, gas flow rate 15-20L / min, interpass temperature ≤150°C. Suitable for additive manufacturing of complex structural parts, deposition efficiency ≥2.50kg / h, tensile strength ≥520MPa, elongation ≥40%, and -40°C impact toughness ≥120J. CN111992923A discloses a metal-type flux-cored welding wire. Using this metal-type flux-cored wire as raw material, austenitic stainless steel structural parts are produced using arc additive manufacturing technology. The resulting thin-walled structural parts exhibit excellent mechanical properties. The flux core alloy composition of the metal-type flux-cored welding wire is composed of the following components in mass percentage: 8% ferrosilicon; 18% to 22% manganese powder; 27% nickel powder; 26% chromium powder; 4% to 8% molybdenum powder; 1% to 3% copper powder; 0.5% titanium powder; 0.2% aluminum powder; 0.5% lanthanum oxide; 1% niobium carbide, and the rest is iron powder, and the sum of the mass percentages of the above components is 100%. The austenitic stainless steel thin-walled structural parts obtained by additive manufacturing have beautiful shape and excellent mechanical properties.

[0005] Currently published research on austenitic stainless steel welding wires and processes for arc additive manufacturing primarily improves the material's microstructure and properties by optimizing the wire composition and additive manufacturing process parameters. However, there are no reports on the development of additive repair wires and repair processes tailored to the characteristics of rotors in moving equipment. Therefore, there is an urgent need for austenitic stainless steel flux-cored welding wire for CMT arc additive repair, as well as its preparation method and application, that can effectively improve the strength of the repaired rotor area and extend the service life of the repair layer. Summary of the invention:

[0006] The purpose of the present invention is to provide a flux-cored welding wire for additive repair of rotors of power plant unit dynamic equipment, as well as its preparation method and application. By introducing a micron-sized tungsten niobium titanium carbonitride solid solution into the welding wire, when the welding wire is used for additive repair, based on the combined effects of fine grain strengthening, solid solution strengthening, precipitation strengthening and dispersion strengthening, effective repair of the rotor is achieved, and the service life of the repair layer is extended.

[0007] The present invention is achieved through the following technical solutions:

[0008] A flux-cored welding wire for additive repair of rotors of dynamic equipment in power station units is an austenitic stainless steel flux-cored welding wire, consisting of an outer sheath and flux-cored powder filled in the outer sheath. The invention is characterized in that the outer sheath is a 316 stainless steel strip, the flux-cored wire filling amount is 26%-30%, the diameter of the flux-cored welding wire ranges from 1.2 to 1.6 mm, and the flux-cored powder composition, based on the total mass percentage being 100%, includes the following components: 4%-6% ferrosilicon, 10%-12% nickel powder, 20%-22% chromium powder, 6%-8% manganese powder, 5%-8% molybdenum powder, 3%-5% rutile, 2%-3.6% micron-sized tungsten niobium titanium carbonitride solid solution, and the remainder is iron powder.

[0009] The rotor is made of alloy steel.

[0010] The average particle size of the micron-sized tungsten niobium titanium carbonitride solid solution is 3 μm.

[0011] Preferably, the outer skin has a width of 14 mm and a thickness of 0.7 mm.

[0012] The preparation method of the flux-cored welding wire comprises the following steps:

[0013] S1: Weigh the core powder with a mesh size higher than 60 mesh according to the required ratio, then mix it in a V-type mixer. After mixing, place it in a tube furnace and keep it at 180℃-240℃ under argon protection for 2-3 hours;

[0014] S2: The cleaned and dried 316 stainless steel strip is processed into a U-shaped groove by forming rollers, and then the mixed powder obtained in S1 is added to the U-shaped groove according to the required filling rate, further rolled into a tube, and then drawn through multiple passes to obtain the flux-cored welding wire of the required diameter.

[0015] The application of the flux-cored welding wire comprises the following steps: using the flux-cored welding wire as a repair material, and performing ultrasonic-assisted CMT arc additive repair on the defective part of the rotor; wherein the process parameters of the CMT arc additive repair are: welding current of 130A to 160A, welding voltage of 24V to 30V, welding speed of 4.0mm / s to 5.5mm / s, shielding gas of 98% Ar + 2% N2, gas flow rate of 20L / min, interpass temperature controlled below 150°C; and ultrasonic frequency of 20-80kHz.

[0016] The beneficial effects of the present invention are as follows:

[0017] (1) When the welding wire is used for additive repair, the micron-sized tungsten niobium titanium carbonitride solid solution in the composition partially dissolves and transfers nitrogen to the molten pool. Nitrogen plays a role in solid solution strengthening. Elements such as carbon, nitrogen, and niobium can diffuse into the repaired matrix and precipitate nano-sized niobium carbonitride near the repair interface, which can further inhibit the occurrence of fatigue cracks at the interface. The residual incompletely dissolved tungsten niobium titanium carbonitride solid solution is nano-sized and dispersed in the matrix, playing a role in dispersion strengthening.

[0018] (2) The additive repair process generates high-amplitude residual compressive stress, which effectively improves the fatigue resistance of the repaired part of the rotor of the dynamic equipment. The tungsten niobium titanium carbonitride dispersed in the repair layer and the niobium carbonitride precipitated at the repair interface can further inhibit the initiation of fatigue cracks and reduce the propagation rate of fatigue cracks. These factors greatly improve the fatigue life of the additive repaired area of ​​the rotor of the dynamic equipment.

[0019] (3) By coupling an ultrasonic energy field during the CMT arc additive repair process, high-energy ultrasound is used to effectively disrupt the epitaxial growth of the austenite structure during the repair process, reducing the possibility of coarse columnar crystal formation and achieving grain refinement. Grain refinement increases the resistance to dislocation slip motion, further improving the yield strength of the material. In addition, as the austenite grain size decreases, the ductile-brittle transition temperature decreases, and the toughness of the repair layer increases.

[0020] In summary, by introducing micron-sized tungsten niobium titanium carbonitride solid solution into the welding wire, the rotor was effectively repaired and the service life of the repair layer was extended based on the combined effects of grain refinement strengthening, solid solution strengthening, precipitation strengthening and dispersion strengthening. Specific implementation method:

[0021] The following is a further description of the present invention, but not a limitation of the present invention.

[0022] Example 1:

[0023] This flux-cored welding wire, used for additive repair of rotors in power plant equipment, is an austenitic stainless steel flux-cored wire consisting of an outer sheath filled with flux-cored powder. The outer sheath is a 316 stainless steel strip with a width of 14 mm and a thickness of 0.7 mm; the flux-cored wire has a flux-cored powder filling of 26%; and the diameter of the flux-cored wire ranges from 1.2 mm. The flux-cored powder, calculated as a total mass percentage of 100%, comprises the following components: 4.0% ferrosilicon, 12.0% nickel powder, 20.0% chromium powder, 8.0% manganese powder, 5.0% molybdenum powder, 5.0% rutile, 3.6% micron-sized tungsten niobium titanium carbonitride solid solution (average particle size 3 μm), and the balance is iron powder.

[0024] The specific steps of the preparation method and application of the flux-cored welding wire of Example 1 are as follows:

[0025] S1: Weigh the core powder with a mesh size higher than 60 mesh according to the required ratio and mix it in a V-type mixer for 0.5 hours. After mixing, place it in a tube furnace and keep it at 180℃ under argon protection for 3 hours.

[0026] S2: The cleaned and dried 316 stainless steel strip is first processed into a U-shaped groove by a forming roller. Then, the mixed powder obtained in S1 is added to the U-shaped groove at a filling rate of 26%, further rolled into a tube, and then subjected to multiple drawing processes to obtain a flux-cored welding wire with a diameter of 1.2 mm.

[0027] S3: Using the flux-cored wire produced in S2 as the repair material, ultrasonic-assisted CMT arc additive repair was performed on the defective rotor. The CMT arc additive repair process parameters were: welding current of 130A, welding voltage of 24V, welding speed of 4.0mm / s, shielding gas of 98% Ar + 2% N2 at a gas flow rate of 20L / min, and interpass temperature controlled below 150°C. The ultrasonic frequency was 20kHz.

[0028] Example 2

[0029] The flux-cored welding wire provided in this embodiment for additive repair of rotors in power plant units is an austenitic stainless steel flux-cored welding wire consisting of an outer sheath and a flux-cored powder filled within the outer sheath. The outer sheath is a 316 stainless steel strip with a width of 14 mm and a thickness of 0.7 mm; the flux-cored powder filling is 30%; and the flux-cored wire diameter ranges from 1.6 mm. The flux-cored powder composition, calculated as a total mass percentage of 100%, comprises the following: 6.0% ferrosilicon, 10.0% nickel powder, 22.0% chromium powder, 6.0% manganese powder, 8.0% molybdenum powder, 3.0% rutile, 2.0% micron-sized tungsten niobium titanium carbonitride solid solution (average particle size 3 μm), and the remainder is iron powder.

[0030] The specific steps of the preparation method and application of the flux-cored welding wire of Example 2 are as follows:

[0031] S1: Weigh the core powder with a mesh size higher than 60 mesh according to the required ratio and mix it in a V-type mixer for 0.5 hours. After mixing, place it in a tube furnace and keep it at 240℃ under argon protection for 2 hours.

[0032] S2: The cleaned and dried 316 stainless steel strip is first processed into a U-shaped groove by a forming roller. Then, the mixed powder obtained in S1 is added to the U-shaped groove at a filling rate of 30%, further rolled into a tube, and then drawn through multiple passes to obtain a flux-cored welding wire with a diameter of 1.6 mm.

[0033] S3: Using the flux-cored wire produced in S2 as the repair material, ultrasonic-assisted CMT arc additive repair was performed on the defective rotor. The CMT arc additive repair process parameters were: welding current of 160A, welding voltage of 30V, welding speed of 5.5mm / s, shielding gas of 98% Ar + 2% N2 at a gas flow rate of 20L / min, and interpass temperature controlled below 150°C. The ultrasonic frequency was 80kHz.

[0034] Example 3

[0035] The flux-cored welding wire provided in this embodiment for additive repair of rotors in power plant equipment is an austenitic stainless steel flux-cored welding wire consisting of an outer sheath and a flux-cored powder filled within the outer sheath. The outer sheath is a 316 stainless steel strip with a width of 14 mm and a thickness of 0.7 mm; the flux-cored powder filling is 28%; and the flux-cored wire diameter ranges from 1.4 mm. The flux-cored powder composition, calculated as a total mass percentage of 100%, comprises the following: 5.0% ferrosilicon, 11.0% nickel powder, 21.0% chromium powder, 7.0% manganese powder, 6.0% molybdenum powder, 4.0% rutile, 3.0% micron-sized tungsten niobium titanium carbonitride solid solution (average particle size 3 μm), and the remainder is iron powder.

[0036] The specific steps of the preparation method and application of the flux-cored welding wire of Example 3 are as follows:

[0037] S1: Weigh core powder with a mesh size greater than 60 mesh according to the required ratio and mix in a V-type mixer for 0.5 h. After mixing, place in a tube furnace under argon protection at 200°C for 2.5 h.

[0038] S2: The cleaned and dried 316 stainless steel strip is first processed into a U-shaped groove by a forming roller. Then, the mixed powder obtained in S1 is added to the U-shaped groove at a filling rate of 28%, further rolled into a tube, and then subjected to multiple drawing processes to obtain a flux-cored welding wire with a diameter of 1.4 mm.

[0039] S3: Using the flux-cored wire produced in S2 as the repair material, ultrasonic-assisted CMT arc additive repair was performed on the defective rotor. The CMT arc additive repair process parameters were: welding current of 150A, welding voltage of 28V, welding speed of 5.0mm / s, shielding gas of 98% Ar + 2% N2 at a gas flow rate of 20L / min, and interpass temperature controlled below 150°C. The ultrasonic frequency was 60kHz.

[0040] Comparative Example 1:

[0041] Refer to Example 3, except that the core powder does not contain micron-sized tungsten niobium titanium carbonitride solid solution.

[0042] Comparative Example 2:

[0043] Referring to Example 3, the difference is that CMT arc additive repair is directly adopted without ultrasonic auxiliary means.

[0044] Comparative Example 3:

[0045] Referring to Example 3, the difference is that the core powder does not contain micron-sized tungsten niobium titanium carbonitride solid solution; and CMT arc additive repair is directly adopted without ultrasonic auxiliary means.

[0046] Comparative Example 4:

[0047] Refer to Example 3, except that the 3.0% micron-sized tungsten niobium titanium carbonitride solid solution in the core powder is replaced by 0.5% titanium powder, 1% niobium carbide, 1% Cu powder, 0.2% aluminum powder, and 0.3% lanthanum oxide.

[0048] Austenitic stainless steel flux-cored welding wires suitable for additive repair of rotors in moving equipment, prepared in Examples 1-3 and Comparative Examples 1-4, were used to perform arc additive repairs on high-alloy rotors with large defects using a CMT arc additive manufacturing machine. The performance of the repaired parts was tested using the mechanical property testing methods described in GB / T 39254-2020, "General Rules for the Evaluation of Mechanical Properties of Additively Manufactured Metal Parts." The test results are shown in Table 1 below.

[0049] Table 1 Performance test results of repaired parts of various embodiments and control examples

[0050]

[0051] From the results in Table 1, it can be concluded that the preparation and application method of the flux-cored welding wire for additive repair of the rotor of the power station unit moving equipment proposed in the present invention can well repair the damaged rotor of the moving equipment and improve the strength of the repaired part.

Claims

1. A flux-cored welding wire for additive repair of rotors of power plant units, which is an austenitic stainless steel flux-cored welding wire, consisting of an outer sheath and a flux-cored powder filled in the outer sheath, characterized in that: The outer skin is a 316 stainless steel strip, and the powder filling amount is 26%-30%. The diameter of the flux-cored welding wire ranges from 1.2 to 1.6 mm. The flux-cored powder composition, based on the total mass percentage being 100%, includes the following components: 4%-6% ferrosilicon, 10%-12% nickel powder, 20%-22% chromium powder, 6%-8% manganese powder, 5%-8% molybdenum powder, 3%-5% rutile, 2%-3.6% micron-sized tungsten niobium titanium carbonitride solid solution, and the remainder is iron powder.

2. The flux-cored welding wire according to claim 1, characterized in that The rotor is made of alloy steel.

3. The flux-cored welding wire according to claim 1, wherein: The average particle size of the micron-sized tungsten niobium titanium carbonitride solid solution is 3 μm.

4. The flux-cored welding wire according to claim 1, wherein: The outer skin is 14mm wide and 0.7mm thick.

5. A method for preparing the flux-cored welding wire according to claim 1, characterized in that: The steps include: S1: Weigh the core powder with a mesh size higher than 60 mesh according to the required ratio, then mix it in a V-type mixer. After mixing, place it in a tube furnace and keep it at 180℃-240℃ under argon protection for 2-3 hours; S2: The cleaned and dried 316 stainless steel strip is processed into a U-shaped groove by forming rollers, and then the mixed powder obtained in S1 is added to the U-shaped groove according to the required filling rate, further rolled into a tube, and then drawn through multiple passes to obtain the flux-cored welding wire of the required diameter.

6. The use of the flux-cored welding wire according to claim 1, characterized in that: The following steps are involved: Flux-cored wire was used as the repair material to perform ultrasonic-assisted CMT arc additive repair on the defective part of the rotor. The process parameters for CMT arc additive repair were as follows: welding current of 130A to 160A, welding voltage of 24V to 30V, welding speed of 4.0mm / s to 5.5mm / s, shielding gas of 98% Ar + 2% N2 at a gas flow rate of 20L / min, and interpass temperature controlled below 150°C. The ultrasonic frequency is 20-80kHz.

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