Nickel-based welding wire for 700 DEG C ultra-supercritical steam turbine cylinder and application of nickel-based welding wire

Abstract

The invention discloses a homogeneous welding wire of a nickel-based heat-resistant alloy for a 700 DEG C ultra-supercritical steam turbine cylinder and application of the homogeneous welding wire, and belongs to the technical field of metal materials (welding materials). The welding wire comprises the following chemical components in percentage by weight: 0.03 to 0.07 percent of C, less than or equal to 0.05 percent of Si, 0.3 to 1.1 percent of Ti, 0.8 to 1.3 percent of Al, 20 to 23 percent of Cr, 8 to 10 percent of Mo, 9 to 12 percent of Co, 0.03 to 0.08 percent of Zr, 0 to 0.3 percent of Nb, 0 to 0.003 percent of B and the balance of Ni and inevitable impurities (P is less than 0.005 percent and S is less than 0.002 percent). A welding joint obtained through welding of the welding wire has excellent strength and plasticity under the condition of postweld heat treatment (such as 750 DEG C / 8 h / air cooling) at 700 DEG C, the heat crack resistance sensitivity is good, the welding wire is suitable for repair welding of 700 DEG C grade nickel-based heat-resisting alloy large castings, and the manufacturing quality and the service safety of high-temperature components are guaranteed.

Description

Technical Field

[0001] This invention relates to the field of metal materials (welding materials), specifically to a nickel-based welding wire for nickel-based heat-resistant alloys used in 700℃ ultra-supercritical steam turbine cylinders. This welding wire is suitable for repair welding of large nickel-based heat-resistant alloy castings to ensure their mechanical properties and crack resistance under high-temperature service environments, and to meet the high-temperature mechanical properties, durability and thermal crack resistance requirements of 700℃-class cylinder components. Background Technology

[0002] 700℃-class ultra-supercritical steam turbine technology is a crucial route to improving the thermal efficiency of coal-fired power plants and reducing carbon emissions. Its key pressure-bearing components (such as cylinders) operate under near-700℃ high-temperature and high-pressure environments for extended periods, placing extremely high demands on the materials' high-temperature strength, thermal stability, oxidation / corrosion resistance, and crack resistance. Therefore, high-alloy nickel-based heat-resistant alloys are widely used to manufacture large castings. To obtain structurally intact large castings, welding repair is necessary during manufacturing or repair. However, currently available commercial nickel-based welding materials (such as commercial 617 nickel-based high-temperature alloys) are not perfectly matched to the high-temperature base materials in terms of composition and solidification behavior. Welding often exhibits a fully austenitic solidification mode and has a high susceptibility to hot cracking, especially under the high-constraint conditions of large castings, making it difficult to simultaneously meet the requirements of 700℃ high-temperature strength and good toughness. Therefore, developing a welding filler material with high strength and strong crack resistance at 700℃ is of paramount importance for ensuring the manufacturing quality and service safety of 700℃ ultra-supercritical steam turbine cylinders. Summary of the Invention

[0003] This invention provides a homogeneous nickel-based welding wire for repairing large castings made of nickel-based heat-resistant alloys with a temperature range of 700℃. By limiting the key alloying elements (such as Ti, Zr, Nb, B, C, Co, Mo, etc.) in the welding wire and strictly controlling the content of impurities such as P and S, the goal of achieving both 700℃ strength and resistance to hot cracking susceptibility under post-weld heat treatment conditions is achieved.

[0004] To achieve the above objectives, the technical solution adopted by this invention is as follows: A homogeneous nickel-based welding wire for a 700℃ ultra-supercritical steam turbine cylinder, the chemical composition of which, by weight percentage, is as follows: C: 0.03-0.07%, Si: ≤0.05%, Ti: 0.3-1.1%, Al: 0.8-1.3%, Cr: 20-23%, Mo: 8-10%, Co: 9-12%, Zr: 0.005-0.08%, Nb: 0.01-0.3%, B: 0.0005-0.003%, with the balance being Ni and unavoidable impurities (wherein P < 0.005%, S < 0.002%). This welding wire can be produced by vacuum induction furnace smelting or by electric furnace smelting with ladle refining, provided that the final chemical composition of the welding wire meets the above requirements.

[0005] This welding wire is used for repair welding of large nickel-based heat-resistant alloy castings for 700℃ ultra-supercritical steam turbine cylinders. The welding process is as follows: take welding wire with a specification of Φ 1.2 mm or Φ 2.0 mm, use tungsten inert gas (TIG) welding, the joint type is butt joint, and the welding parameters are: welding current 160-200 A, current type / polarity DC positive, welding speed 1.5-2.5 mm / s, wire feed speed 15-20 mm / s, arc protection using high purity argon gas with a purity ≥99.995%, gas flow rate 15-20 L / min.

[0006] The welded joint obtained by welding with the welding wire of the present invention has excellent strength and plasticity at 700°C after post-weld heat treatment (e.g., 750°C / 8h / air cooling), and good resistance to hot cracking. It is suitable for repair welding of large nickel-based heat-resistant alloy castings of 700°C grade, ensuring the manufacturing quality and service safety of high-temperature components.

[0007] The present invention has the following advantages: 1. Experimental verification shows that the welding wire of this invention can be used for repair welding of large nickel-based heat-resistant Ni-based alloy castings such as K317. The welding process is simple and highly feasible, and welding can be carried out using the commonly used tungsten inert gas welding method.

[0008] 2. When using the nickel-based welding wire of this invention for welding, the welding process is stable, with few defects and good process performance.

[0009] 3. The nickel-based welding wire of the present invention can produce welds that meet the required performance. In particular, after post-weld heat treatment, the welds exhibit excellent high-temperature strength at 700°C and good resistance to hot cracking.

[0010] 4. The weld obtained by welding with the welding wire of this invention, after aging heat treatment, exhibits the following tensile properties at 700℃: yield strength > 450 MPa, tensile strength > 660 MPa, elongation after fracture > 15%; in the cross-lap weld crack test, the hot cracking rate is < 20%; and the room temperature V-shaped Charpy impact toughness of the weld metal is > 90 J / cm². 2 .

[0011] The main ideas and mechanisms of this invention are as follows: This invention addresses the homogeneous welding requirements of nickel-based heat-resistant alloys (such as K317) used in 700℃ ultra-supercritical steam turbine cylinders, and designs a nickel-based welding wire with adjustable composition. The design concept is as follows: First, by adjusting key elements such as C, Ti, Zr, Nb, and B, two representative composition schemes with excellent performance are obtained. Scheme 1 (as claimed in claim 2) focuses on adding a suitable trace amount of Zr (0.04-0.06%) to achieve excellent 700℃ strength through solid solution strengthening and grain boundary strengthening mechanisms, while reducing the C and Ti content to ensure high ductility and toughness and low hot cracking sensitivity of the weld. Scheme 2 (as claimed in claim 3) increases the Ti and Nb content to enhance γ′ phase strengthening, introduces a suitable amount of B to improve grain boundary strengthening, and simultaneously controls the upper limits of Zr, C, and B content to improve ductility and toughness and reduce hot cracking sensitivity, ultimately achieving excellent room temperature impact toughness, elongation, hot crack resistance, and matching high-temperature strength. This invention effectively reduces the tendency for welding hot cracking by controlling the content of impurity elements S and P. The welding wire of this invention combines the two excellent performance schemes mentioned above, which can meet the requirements of working conditions with extreme high-temperature strength and scenarios with higher requirements for toughness and crack resistance, providing a flexible and reliable solution for the repair welding of large nickel-based castings. Attached Figure Description

[0012] Figure 1 Dimensions of the cross-lapped cracked specimen and the specimen before the experiment; Figure 2 Photograph of Example 1 after the cross-lap crack test; Figure 3 Comparative example 3 photographs after the cross-lap crack test. Detailed Implementation

[0013] The nickel-based welding wire in this invention can be produced by vacuum induction furnace smelting or by electric furnace refining, as long as the final chemical composition of the welding wire meets the above-mentioned requirements. Furthermore, the entire smelting and processing of the welding wire is not significantly different from that of ordinary nickel-based alloy welding wire, and there are no additional special technical requirements. The base material used in welding in this invention is K317 nickel-based heat-resistant alloy, which is used to manufacture cylinders for 700℃ ultra-supercritical steam turbines.

[0014] The following are preferred embodiments of the present invention. In the following embodiments and comparative examples, the welding wire was produced by vacuum induction furnace smelting. The resulting ingot was subjected to high-temperature homogenization treatment at 1160–1170℃ for 10 hours, followed by multi-directional forging into a 35mm × 35mm square bar. The final forging temperature was >950℃. After air cooling to room temperature, the oxide scale was removed by grinding. The forged square billet was held at 1160–1170℃ for 5 hours and then hot-rolled on a continuous hot rolling mill to… 8.5 mm wire rod; after solution treatment at 1150℃ / 1 h / air cooling, the wire rod is subjected to multiple cold drawing passes combined with intermediate annealing (vacuum online annealing at 1050℃) to finally draw to the required diameter. 1.2 mm finished welding wire, with a bright, clean, and defect-free surface. Manual tungsten inert gas (TIG) welding was used for all welding. Butt welding with a V-groove and a single-sided angle of 22.5° was used for preparing the weld metal for tensile and impact specimens. The base plate dimensions were 300×150×15 mm. Cross lap welding was used for hot crack sensitivity testing; the dimensions are shown in the diagram. Figure 1 The welding parameters used in the test were as follows: welding current 180A, DC positive polarity, welding speed 2.0 mm / s, wire feed speed 17 mm / s, arc shielding atmosphere argon with a purity ≥99.995%, and shielding gas flow rate 18 L / min. After welding, all samples underwent post-weld heat treatment: 750℃ / 8h / air cooling.

[0015] After post-weld heat treatment and cooling, tensile and impact specimens of the entire weld were taken from the butt joint test plate and tested. The tensile specimen dimensions (M10) and test methods were in accordance with GB / T 228.2-2015 "Metallic materials, tensile testing - Part 2: High temperature test method". The V-shaped impact specimens (55×10×10 mm) and tests were in accordance with GB / T 229-2020 "Metallic materials, Charpy pendulum impact test method", with three parallel specimens for each test.

[0016] The hot crack susceptibility of welding materials with different compositions was evaluated using the cross-lap joint crack test method (Li Yajiang, Wang Juan, et al. Weldability Testing and Analysis Methods [M]. Beijing: Chemical Industry Press, 2014:102). The shape and dimensions are shown in Figure 1. Two thin plates were first tack welded together and then continuously welded according to the sequence and direction shown in Figure 1. Within 2 hours after welding, the crack tendency of the weld and heat-affected zone was checked. The crack rate was defined as the percentage of crack length to the total weld length, and the welding hot crack tendency level was assessed. The welding process parameters were consistent with the butt welding parameters described above, and three tests were conducted for each type of welding material.

[0017] The weld seam after post-weld heat treatment was cut by wire cutting for microstructure characterization. The cut weld seam samples were polished with 150-2000# sandpaper from coarse to fine, and then polished with 2.5μm diamond polishing paste. The samples were then immersed in an etching solution (5ml concentrated sulfuric acid + 150ml concentrated hydrochloric acid + 20g copper sulfate + 80ml water) for 40s. After washing and drying, the microstructure was characterized using a field emission scanning electron microscope.

[0018] Example 1 The basic chemical composition (by weight) of this homogeneous nickel-based welding wire used in 700℃ ultra-supercritical steam turbine cylinders is as follows: C: 0.068%, Si: 0.035%, Ti: 0.35%, Al: 1.22%, Cr: 21.8%, Mo: 8.98%, Co: 11.6%, Zr: 0.057%, Nb: 0.013%, B: 0.0005%, P: 0.0004%, S: 0.0018%, with the balance being Ni and unavoidable impurity elements (including one or more of Fe, Cu, etc.). The composition range of this embodiment meets the preferred scheme A. The tensile properties at 700℃, room temperature impact toughness, and crack rate all meet the design requirements. Fine carbides with a size of approximately 2-5 μm are visible in the weld microstructure.

[0019] Example 2 The basic chemical composition (by weight) of this homogeneous nickel-based welding wire used in 700℃ ultra-supercritical steam turbine cylinders is as follows: C: 0.038%, Si: 0.028%, Ti: 1.02%, Al: 1.04%, Cr: 22.0%, Mo: 9.13%, Co: 10.2%, Zr: 0.015%, Nb: 0.19%, B: 0.0028%, P: 0.0005%, S: 0.0013%, with the balance being Ni and unavoidable impurity elements (including one or more of Fe, Cu, etc.). The composition range of this embodiment meets the preferred scheme B. The tensile properties at 700℃, room temperature impact toughness, and crack rate all meet the design requirements. Fine carbides with a size of approximately 1-4 μm are visible in the weld microstructure.

[0020] Comparative Example 1 The basic chemical composition of this nickel-based welding wire is (by weight): C: 0.067%, Si: 0.033%, Ti: 0.35%, Al: 1.22%, Cr: 21.8%, Mo: 8.98%, Co: 11.6%, Zr: 0.12%, Nb: 0.020%, B: 0.0006%, P: 0.0004%, S: 0.0014%, with the balance being Ni. This comparative example is an adjustment based on the preferred scheme A, with the Zr content exceeding the range of claim 1. This results in a maximum weld carbide size of 12 μm, a decrease in impact toughness, elongation, and tensile strength, and the excessive Zr significantly increases the crack rate to 28%.

[0021] Comparative Example 2 The basic chemical composition of this nickel-based welding wire is (by weight): C: 0.060%, Si: 0.011%, Ti: 0.87%, Al: 1.19%, Cr: 21.9%, Mo: 9.04%, Co: 11.7%, Zr: 0.12%, Nb: 0.025%, B: 0.0006%, P: 0.0006%, S: 0.0013%, with the balance being Ni. This comparative example is an adjustment based on the preferred scheme A. The Zr content is higher than that of claim 1. Although the Ti content does not exceed the range of claim 1, it exceeds the upper limit of preferred scheme A. Although the yield strength is high, the maximum carbide size in the weld reaches 18 μm, resulting in premature fracture during tensile testing, a decrease in elongation and tensile strength. At the same time, the excessive Zr significantly increases the impact toughness and crack rate.

[0022] Comparative Example 3 The basic chemical composition of this nickel-based welding wire is (by weight): C: 0.064%, Si: 0.03%, Ti: 0.33%, Al: 1.21%, Cr: 22.34%, Mo: 8.84%, Co: 10.8%, Zr: 0.0005%, Nb: 0.09%, B: 0.0075%, P: 0.001%, S: 0.0021%, with the balance being Ni. This comparative proportion is an adjustment based on the preferred scheme A, with the Zr content lower than that required in claim 1 and the B content higher than that required in claim 1. Due to the lower Zr content, the yield strength and tensile strength are lower, while the excessive B content causes a decrease in impact toughness and a significant increase in the crack rate.

[0023] Comparative Example 4 The basic chemical composition of this nickel-based welding wire is (by weight): The composition is as follows: C 0.038%, Si 0.028%, Ti 1.02%, Al 1.04%, Cr 22.0%, Mo 9.13%, Co 10.2%, Zr 0.005%, Nb 0.05%, B 0.001%, P 0.0005%, S 0.0013%, with the balance being Ni. This comparative example has an excessively low Nb content compared to the preferred embodiment B. Although still within the composition range of this invention, it deviates from the preferred embodiment B. It exhibits a lower crack rate and higher impact toughness, but due to the lack of Nb strengthening effect, its strength is too low to meet design requirements.

[0024] Comparative Example 5 The basic chemical composition of this nickel-based welding wire is (by weight): The comparative example contains 0.035% C, 0.030% Si, 1.11% Ti, 1.07% Al, 22.3% Cr, 9.13% Mo, 10.4% Co, 0.004% Zr, 0.35% Nb, 0.001% B, 0.0005% P, and 0.0010% S. This Nb content is increased compared to the preferred embodiment B, exceeding the upper limit of the claims. Although the strength is improved due to Nb promoting γ′ formation, Nb is a strongly segregating element, thus increasing the crack rate to 22% and decreasing the elongation at 700°C and room temperature impact toughness.

[0025] Comparative Example 6 The basic chemical composition of this nickel-based welding wire is (by weight): The composition of this comparative example is C 0.082% (significantly higher than Scheme B), Si 0.033%, Ti 1.04%, Al 1.00%, Cr 22.2%, Mo 9.13%, Co 10.4%, Zr 0.005%, Nb 0.20%, B 0.001%, P 0.0005%, S 0.0010%, with the balance being Ni. This comparative example increases the C content compared to the preferred Scheme B, exceeding the upper limit of the claims. Although the strength is improved due to the solid solution strengthening effect of C, C is a strong interdendritic segregating element, resulting in a significant increase in the crack rate to 25%, while also impairing the elongation at 700°C and room temperature impact toughness.

[0026] The tensile properties at 700℃, room temperature impact properties, and hot cracking rate of the cross-lap joints of the above embodiments and comparative examples are shown in Table 1.

[0027] Table 1. Performance test results of welds in the examples and comparative examples. (The number of parallel samples in each test experiment was 3, and the average value was taken.)

[0028] By rationally controlling key elements such as Ti, Zr, Nb, and B, and strictly controlling the content of P and S impurities, the welding wire of this invention achieves high strength, high plasticity, and low hot cracking sensitivity at a high temperature of 700℃ under recommended welding and post-weld heat treatment conditions. It is suitable for repair welding of large nickel-based heat-resistant alloy castings at 700℃. The above embodiments are merely preferred embodiments, and the scope of protection of this invention is defined by the claims.

Claims

1. A nickel-based welding wire, characterized in that: The chemical composition of this welding wire, by weight percentage, is as follows: C: 0.03-0.07%, Si: ≤0.05%, Ti: 0.3-1.1%, Al: 0.8-1.3%, Cr: 20-23%, Mo: 8-10%, Co: 9-12%, Zr: 0.005-0.08%, Nb: 0.01-0.3%, B: 0.0005-0.003%, with the balance being Ni and unavoidable impurities; And P < 0.005%, S < 0.002%.

2. The nickel-based welding wire according to claim 1, characterized in that: The preferred composition scheme A of this welding wire, by weight percentage, is: C: 0.05-0.07%, Si: ≤0.05%, Ti: 0.3-0.5%, Al: 0.8-1.3%, Cr: 20-23%, Mo: 8-10%, Co: 9-12%, Zr: 0.04-0.06%, Nb: 0.01-0.1%, B: 0.0005-0.001%, with the balance being Ni and unavoidable impurities; And P < 0.005%, S < 0.002%.

3. The nickel-based welding wire according to claim 1, characterized in that: The preferred composition scheme B of the welding wire, by weight percentage, is: C: 0.03-0.05%, Si: ≤0.05%, Ti: 0.9-1.1%, Al: 0.8-1.3%, Cr: 20-23%, Mo: 8-10%, Co: 9-12%, Zr: 0.01-0.03%, Nb: 0.1-0.2%, B: 0.001-0.003%, with the balance being Ni and unavoidable impurities; and P < 0.005%, S < 0.002%.

4. The welding wire according to any one of claims 1-3, characterized in that: The diameter of the welding wire is Φ1.2 mm or Φ2.0 mm; The welding wire is produced by vacuum induction furnace smelting or electric furnace smelting, supplemented by ladle refining process, to ensure that the impurity and oxide content meets the requirements of P < 0.005% and S < 0.002%.

5. An application of the welding wire according to any one of claims 1-4, characterized in that: The welding wire is used for repair welding of large nickel-based heat-resistant alloy castings with a temperature of 700℃, and is preferably used as a homogeneous nickel-based welding wire for 700℃ ultra-supercritical steam turbine cylinders. The welding method is tungsten inert gas (TIG) welding, and the welding parameters are as follows: welding current 160-200 A, DC positive polarity, welding speed 1.5-2.5 mm / s, wire feed speed 15-20 mm / s, shielding gas is argon with a purity ≥99.995% and a gas flow rate of 15-20 L / min.

6. The application according to claim 5, characterized in that: The post-weld heat treatment conditions are 750℃±10℃ / 8 h±2 h / air cooling.

7. The welding wire according to any one of claims 1-4, characterized in that: When the weld seam welded with the aforementioned welding wire and subjected to post-weld heat treatment is subjected to tensile testing at 700℃ (test according to GB / T 228.2-2015), the yield strength is >450 MPa, the tensile strength is >660 MPa, and the elongation after fracture is >15%.

8. The welding wire according to any one of claims 1-4, characterized in that: When the weld seam, after welding with the welding wire and post-weld heat treatment, is subjected to a room temperature V-shaped Charpy impact test according to GB / T 229-2020, the specimen shall be prepared according to standard dimensions (55×10×10 mm) with an average absorbed energy >90 J / cm². 2 When evaluating the hot cracking rate of the welding wire through the cross-lap hot cracking test, the hot cracking rate is <20%.

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