Iron-based welding wire for resisting cavitation damage of turbine runner, preparation method and surfacing method

Abstract

The invention relates to the technical field of metal materials, and discloses an iron-based welding wire for resisting cavitation damage of a water turbine runner, a preparation method and a surfacing method.The welding wire comprises powder and a welding skin used for wrapping the powder, and the powder comprises, by mass, 10.0%-20.0% of an additional hard phase and the balance metal alloy powder; the additional hard phase comprises 20%-30% of WC powder, 20%-30% of TiC powder and the balance VC powder. The preparation method comprises the following steps: mixing the powder, carrying out ball milling, wrapping with a 430 belt, and drawing. According to the welding wire disclosed by the invention, through compound addition of various hard phases and cooperation with a low-heat-input CMT process, the Rockwell hardness of a surfacing layer is 40-50 HRC, the cavitation resistance of the surfacing layer is 3.5 times or above that of 0Cr13Ni5Mo base metal, and the cavitation resistance of the surfacing layer is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal materials, and particularly relates to an iron-based welding wire for resisting cavitation damage of a water turbine runner, a preparation method and a surfacing method. Background Art

[0002] By virtue of the advantages of rapid start-stop, fast power regulation response and large regulation scale, hydropower units play an indispensable role in peak shaving and frequency modulation in the power grid, especially providing key support for primary frequency modulation and secondary frequency modulation of the power grid. However, the frequent response to frequency modulation commands forces hydropower units to operate for a long time under off-design conditions, especially at low loads. This change in the operation mode deteriorates the water flow conditions, significantly increasing the occurrence frequency and intensity of cavitation erosion in the runner area. Cavitation damage has become a prominent hidden danger threatening the safe operation of hydropower units.

[0003] Regarding the damage of water turbine runners, the existing repairs mainly rely on factory processing after returning or on-site surfacing. The former involves equipment disassembly, transportation and factory processing, with a long cycle and high cost, making it difficult to meet the urgent repair needs; the latter can be implemented in-situ, but the commonly used repair materials have insufficient cavitation resistance, and defects such as cracks and spalling are prone to occur in the surfacing layer, resulting in poor repair effects.

[0004] Super low-carbon martensitic stainless steel 0Cr13Ni5Mo has become a preferred material for water turbine runners due to its excellent comprehensive mechanical properties (high strength, high toughness), corrosion resistance and good weldability. However, it is still difficult to completely resist the continuous impact cutting of high-speed cavitation microjets during service, which is prone to induce microcracks and exacerbate local failure.

[0005] Chinese Patent CN119733990A proposes a cavitation-resistant martensitic welding wire for a water turbine runner and a preparation method, including a powder and a welding skin. The powder includes the following components by mass percentage: 20.0 - 25.0% Cr powder, 25.0 - 30.0% Ni powder, 5.0 - 8.0% Mo powder, 3.0 - 5.0% Nb powder, 3.0 - 5.0% W powder, 0.5 - 1.0% C powder, 4.0 - 6.0% B powder, 0.8 - 1.0% Y2O3 powder, and the rest is Fe powder. As the only hard phase in the above powder, B powder combines with elements such as Cr, Mo, and W during the fusion welding process to in-situ generate boride hard phases. Although it can improve the hardness of the surfacing layer, its toughness, fatigue resistance and cavitation resistance are weakened. And in complex areas such as the runner curved surface and narrow gaps, due to the limitation of the adaptability of the welding process, it is difficult to form a uniform, dense and tightly bonded cladding layer with the substrate. This results in unstable cavitation resistance and a high recurrence rate of damage for the repaired runner under alternating hydraulic loads, making it difficult to ensure its long-term service safety under the harsh conditions of peak shaving and frequency modulation. Summary of the Invention

[0006] The object of the present invention is to overcome the above problems and provide an iron-based welding wire for resisting cavitation damage of a hydraulic turbine runner, a preparation method and a surfacing method, so as to obtain a surfacing layer with synergistically optimized hardness and toughness and ensure the long-term service safety under the peak load regulation and frequency modulation conditions of a hydropower unit.

[0007] To achieve the above object, the present invention adopts the following technical solutions: In the first aspect, the present invention provides an iron-based welding wire for resisting cavitation damage of a hydraulic turbine runner, which includes a powder and a welding skin for wrapping the powder. The powder includes an externally added hard phase and a metal alloy powder. Among them, in terms of mass percentage, the externally added hard phase is 10% - 20%, and the rest is the metal alloy powder; In terms of mass percentage, the externally added hard phase includes: 20% - 30% of WC powder, 20% - 30% of TiC powder, and the rest is VC powder.

[0008] A further improvement of the present invention is that, in terms of mass percentage, the metal alloy powder includes: 6.0% - 8.0% of Cr powder, 8.0% - 10.0% of Ni powder, 4.0% - 6.0% of Mo powder, 2.0% - 3.0% of B powder, and the rest is Fe powder.

[0009] A further improvement of the present invention is that the powder particle size of the externally added hard phase is all 200 - 250 mesh.

[0010] A further improvement of the present invention is that the powder particle size of the metal alloy powder is all 100 - 150 mesh.

[0011] A further improvement of the present invention is that the filling rate of the powder in the welding skin is controlled at 28% - 32%.

[0012] A further improvement of the present invention is that the welding skin is a 430 strip with a thickness of 0.4 mm and a width of 10 mm.

[0013] In the second aspect, the present invention also provides a preparation method of an iron-based welding wire for resisting cavitation damage of a hydraulic turbine runner, including the following steps: Step 1, respectively weigh 10.0% - 20.0% of the externally added hard phase in terms of mass percentage, and the rest is the metal alloy powder; Step 2, perform ball milling and mixing on the weighed externally added hard phase and metal alloy powder to obtain a powder; Step 3, wrap the powder prepared in Step 2 in the welding skin and perform the first drawing process. The aperture of the drawing die used in the first drawing process is 2.6 mm; Step 4: After the first drawing process is completed, several drawing processes are sequentially set, and the aperture diameters of the drawing dies corresponding to each drawing process decrease sequentially, so that the finally obtained wire diameter is 1.2 - 1.4 mm, and an iron-based wire for resisting cavitation damage of a water turbine runner is prepared.

[0014] A further improvement of the present invention lies in that in the step 1, the weighed metal alloy powders are mixed, vacuum melted, and subjected to gas atomization treatment to obtain metal alloy powders; Among them, N2 is used as the atomizing gas for the gas atomization treatment, the atomizing pressure is 6 - 7 MPa, and the superheat degree of the melt is maintained at 100 - 150 °C during the atomization process.

[0015] A further improvement of the present invention lies in that in the step 2, the ball milling speed is 250 - 300 r / min, and the ball milling time is 1 - 2 h.

[0016] In a third aspect, the present invention also provides a surfacing method, using a CMT power source to perform surfacing on the iron-based wire for resisting cavitation damage of a water turbine runner; The process parameters of the surfacing are as follows: The welding current is 160 - 190 A, the short-circuit transfer mode is adopted for the molten droplets during the surfacing process, and the dilution rate is controlled at 3% - 5%; the surfacing layer thickness is 1.8 - 2.4 mm, the swing width is 15 - 20 mm, the overlap amount is 5 - 8 mm, the surfacing layer is 1 layer, and the shielding gas is 30% He + 70% Ar.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides an iron-based welding wire for resisting cavitation damage of a hydraulic turbine runner. The welding wire includes a powder and a welding skin for wrapping the powder. The powder includes an externally added hard phase and a metal alloy powder. By accurately controlling the content of the externally added hard phase in the powder within the range of 10% - 20% and synergistically acting with the metal alloy powder, it can ensure that on the basis of obtaining a high-hardness surfacing layer, the risk of stress concentration caused by excessive brittle phases is effectively avoided, so that the obtained surfacing layer has high strength, good toughness, and strong cavitation resistance. Specifically, the externally added hard phase includes WC, TiC, and VC. WC powder has high hardness and good wear resistance, and can be evenly distributed on the substrate during surfacing to form small and hard particles. These particles can effectively resist wear when subjected to cavitation impact, improving the hardness of the surfacing layer; TiC powder has ultra-high hardness and oxidation resistance, can form a strengthening phase in the surfacing layer, enhance the cavitation resistance of the surfacing layer, and synergistically act with WC powder to further improve the hardness and wear resistance of the surfacing layer; the addition of VC powder can not only improve the hardness of the surfacing layer, but also improve the toughness of the surfacing layer to a certain extent, making the surfacing layer not prone to cracking and spalling when subjected to cavitation impact. The three hard phases work together in parallel. Compared with the traditional single hard phase, the addition of multiple hard phases significantly improves the hardness, wear resistance, and toughness of the surfacing layer, thus effectively improving the cavitation resistance of the surfacing layer, meeting the cavitation damage protection and repair of the surface of the hydraulic turbine runner in a hydropower plant, and the performance requirements under the rapid peak shaving condition of the hydropower plant.

[0018] Furthermore, the metal alloy powder in the welding wire is added with elements such as Cr, Ni, Mo, and B, which has both solid solution strengthening effect and precipitation strengthening effect. Therefore, the strengthening and toughening effect on the surfacing layer is significantly improved. At the same time, the main alloy element Cr in the welding wire matches the commonly used material of the hydraulic turbine (0Cr13Ni5Mo), that is, their linear expansion coefficients are close, thus ensuring excellent metallurgical bonding performance between the surfacing layer and the hydraulic turbine substrate and lower welding residual stress.

[0019] The present invention also provides a preparation method of an iron-based welding wire for resisting cavitation damage of a hydraulic turbine runner. By ball-milling and mixing the weighed externally added hard phase and metal alloy powder to obtain a powder, then wrapping the powder in a welding skin, and then through a drawing process with gradually decreasing die apertures in multiple passes, accurately controlling the wire diameter of the welding wire, the uniform dispersion of the powder is realized, and finally an iron-based welding wire for resisting cavitation damage of a hydraulic turbine runner with excellent hardness and toughness is obtained, ensuring the deposition efficiency during the surfacing process.

[0020] Furthermore, the preparation of the metal alloy powder by the gas atomization process makes the formed metal alloy powder have higher purity and more excellent metallurgical transition effect during surfacing.

[0021] The present invention also provides a surfacing method. By using a CMT power source with low heat input to perform surfacing on an iron-based wire for resisting cavitation damage of a water turbine runner, not only the decomposition of WC, TiC, and VC added hard phases during the welding process is reduced, but also the molten pool residence time is decreased, and the settlement and aggregation of the added hard phases are inhibited. Description of the Drawings

[0022] The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the disclosure of the present invention in any way. Additionally, the shapes and proportional dimensions of the components in the figures are only schematic and are used to assist in understanding the present invention, rather than specifically defining the shapes and proportional dimensions of the components of the present invention.

[0023] Figure 1 It is a schematic diagram of the metallographic structure of the surfacing layer after surfacing an iron-based wire for resisting cavitation damage of a water turbine runner prepared in Example 2 on a 0Cr13Ni5Mo base material; Figure 2 It is a schematic diagram of the cavitation damage on the surface of the surfacing layer after a 4-hour cavitation test on the surfacing layer obtained by surfacing an iron-based wire for resisting cavitation damage of a water turbine runner prepared in Example 2 on a 0Cr13Ni5Mo base material; a comparison diagram with the base material; Figure 3 It is a schematic diagram of the cavitation damage on the surface of a 0Cr13Ni5Mo base material after a 4-hour cavitation test. Detailed Embodiments

[0024] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and phrases mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art for the present invention. In case of conflict, the definition in this specification shall prevail.

[0025] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0026] In this article, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of simplicity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values within the range (including integers and fractions).

[0027] In this text, unless otherwise specified, the terms "include", "comprise", "contain", "have" or similar terms cover the meanings of "consist of" and "consist essentially of". For example, "A includes a" covers the meanings of "A includes a and others" and "A only includes a".

[0028] In this text, for the sake of brevity of description, not all possible combinations of all technical features in each embodiment or example are described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as the scope described in this specification.

[0029] The present invention provides an iron-based welding wire for resisting cavitation damage of a water turbine runner, which includes welding powder and a welding skin for wrapping the welding powder. The welding powder includes an externally added hard phase and a metal alloy powder. Among them, in terms of mass percentage, the externally added hard phase is 10% - 20%, and the rest is the metal alloy powder.

[0030] In terms of mass percentage, the externally added hard phase includes: 20% - 30% of WC powder, 20% - 30% of TiC powder, and the rest is VC powder.

[0031] In terms of mass percentage, the metal alloy powder includes: 6.0% - 8.0% of Cr powder, 8.0% - 10.0% of Ni powder, 4.0% - 6.0% of Mo powder, 2.0% - 3.0% of B powder, and the rest is Fe powder.

[0032] The powder particle size of the externally added hard phase is all 200 - 250 mesh.

[0033] The powder particle size of the metal alloy powder is all 100 - 150 mesh.

[0034] The filling rate of the welding powder in the welding skin is controlled at 28% - 32%.

[0035] The welding skin is 430 strip, with a thickness of 0.4 mm and a width of 10 mm.

[0036] The functions and roles of the main alloy components in the welding wire of the present invention are as follows: (1) The externally added hard phases WC, TiC and VC in the welding wire all have the characteristics of high hardness. Specifically: 1) WC has high hardness (~2400 HV) and wear resistance, and can provide strong support for the matrix; secondly, compared with other carbides, WC also has good toughness and can reduce crack propagation.

[0037] 2) TiC has ultra-high hardness (~3200 HV) and oxidation resistance, and can form a TiO2 protective layer at high temperature; furthermore, TiC can also inhibit grain growth, refine grains, and improve high-temperature strength.

[0038] 3) In the WC-Ni system, VC can hinder the dissolution-recrystallization process of WC grains, that is, VC has a strong effect on inhibiting grain growth. In addition, VC can also improve the hot hardness retention, namely the red hardness.

[0039] The multi-component composite addition has the following synergistic advantages: Firstly, the balance of hardness and toughness: WC provides the basic toughness for the matrix, and TiC and VC synergistically compensate for the hardness loss of WC at high temperatures. Secondly, the optimization of flexural strength: VC refines grains to reduce stress concentration and alleviate the brittle tendency of single TiC. In addition, the wear forms: WC resists abrasive wear, TiC inhibits adhesive wear, and VC reduces fatigue wear, and the service life can be increased by 30% - 50%.

[0040] In summary, the composite addition of WC-TiC-VC realizes the comprehensive improvement of hardness, toughness, and abrasion resistance (wear + cavitation) through the synergy of multiple mechanisms, which is one of the core strategies for high-end alloy design.

[0041] (2) Cr element is added to the welding wire metal alloy powder. The Cr element matches the commonly used material 0Cr13Ni5Mo of the water turbine runner, thus ensuring high metallurgical bonding strength and low residual stress between the two during the surfacing repair of the runner surface.

[0042] (3) Ni and Mo elements are added to the welding wire metal alloy powder: Ni and Mo elements can dissolve in the α-Fe matrix of the surfacing layer to achieve the effect of solid solution strengthening; Ni element is an austenite-forming element. The addition of Ni can regulate the content of austenite in the surfacing layer. In this invention, the addition of 8.0% - 10.0% of Ni powder ensures about 3% - 5% of retained austenite in the surfacing layer, thus effectively improving the toughness of the matrix structure of the surfacing layer. The toughness and hardness of the surfacing layer are two key indicators for cavitation resistance. Therefore, the addition of Ni improves the toughness and strength of the surfacing layer, and the addition of Mo improves the strength of the surfacing layer.

[0043] (4) B element is added to the welding wire metal alloy powder: B element improves the performance mainly through mechanisms such as grain boundary strengthening, microstructure refinement, and improvement of hardenability, and the specific manifestations are as follows: 1) Grain boundary strengthening and improvement of hardenability: The matrix structure of the surfacing layer is martensitic α-Fe. B atoms are preferentially adsorbed on the austenite grain boundaries, reducing the grain boundary energy, inhibiting the precipitation of ferrite and carbides at the grain boundaries, and at the same time delaying the phase transformation process at high temperatures, thus significantly improving the hardenability of the surfacing layer; Inhibition of grain boundary brittleness: B combines with impurity elements (such as S, P) at the grain boundaries, reducing the precipitation of harmful phases such as sulfides and reducing the tendency of temper brittleness.

[0044] 2) Refined microstructure: B forms BN or M2B (M is Cr, Fe, etc.) particles at high temperature, pinning grain boundaries to inhibit austenite grain coarsening and refining the martensite laths after quenching; Microstructure homogenization: reducing local coarse martensite and improving the matching of strength and toughness.

[0045] 3) Carbide regulation: B preferentially combines with Cr to form Cr2B, reducing the consumption of Cr carbides, avoiding Cr depletion at grain boundaries, and improving the corrosion resistance of the weld heat-affected zone.

[0046] 4) Other effects: B cooperates with Cr and Mo, which can enhance the hardenability effect of B.

[0047] In summary, the composite addition of Cr, Ni, Mo, and B elements realizes the strength-toughness matching of the surfacing layer through the synergy of multiple mechanisms, thereby improving the cavitation resistance of the surfacing layer.

[0048] The present invention also provides a preparation method of an iron-based welding wire for resisting cavitation damage of a water turbine runner, comprising the following steps: Step 1, weighing 10.0% - 20.0% of an external hard phase by mass percentage, and the rest is metal alloy powder; Step 2, ball-milling and mixing the weighed external hard phase and metal alloy powder to obtain a powder; Step 3, wrapping the powder prepared in Step 2 in a welding skin and performing the first drawing process, and the aperture of the drawing die used in the first drawing process is 2.6 mm; Step 4, after the first process drawing is completed, arranging several drawing processes in sequence, and the aperture of the drawing die corresponding to each drawing process decreases in sequence, so that the diameter of the finally obtained welding wire is 1.2 - 1.4 mm, and an iron-based welding wire for resisting cavitation damage of a water turbine runner is prepared.

[0049] In Step 1, the weighed metal alloy powder is mixed, vacuum melted, and subjected to gas atomization treatment to obtain metal alloy powder; Among them, N2 is used as the atomizing gas for gas atomization treatment, the atomizing pressure is 6 - 7 MPa, and the superheat of the melt is maintained at 100 - 150 °C during the atomization process.

[0050] In Step 2, the ball-milling speed is 250 - 300 r / min, and the ball-milling time is 1 - 2 h.

[0051] The present invention also provides a surfacing method, using a CMT power source to perform surfacing on the above-mentioned iron-based welding wire for resisting cavitation damage of a water turbine runner; The process parameters of the surfacing are as follows: The welding current is 160 - 190 A. During the surfacing process, the molten droplets adopt the short - circuit transfer mode, and the dilution rate is controlled within 3% - 5%. The thickness of the surfacing layer is 1.8 - 2.4 mm, the oscillation width is 15 - 20 mm, the overlap amount is 5 - 8 mm, the surfacing layer is 1 layer, and the shielding gas is 30% He + 70% Ar.

[0052] The following will further elaborate on the present invention in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0053] In the following embodiments, conventional instrument and equipment in the art are used. For the experimental methods without specific conditions indicated in the following embodiments, they are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. In the following embodiments, various raw materials are used. Unless otherwise stated, all are commercially available products with conventional specifications in the art. In the specification of the present invention and the following embodiments, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0054] All the following embodiments of the present invention are carried out by arc surfacing on the 0Cr13Ni5Mo base metal.

[0055] Example 1 This embodiment provides a preparation method of an iron - based welding wire for resisting cavitation damage of a water turbine runner, including the following steps: Step 1: Weigh the following metal alloy powders by mass percentage. Among them, Cr powder is 6.0%, Ni powder is 8.0%, Mo powder is 4.0%, B powder is 2.0%, and the rest is Fe powder; Step 2: Mix the metal alloy powders weighed in Step 1, then carry out vacuum melting, use the gas atomization method to prepare metal alloy powders, and perform particle size screening on the gas - atomized metal alloy powders so that the particle size of the screened metal alloy powders is 125 ± 25 mesh; Step 3: Weigh 20% WC powder and 20% TiC powder by mass percentage, and the rest is VC powder, and mix them to obtain an additional hard phase; Step 4: Weigh 10% of the additional hard phase and the rest is metal alloy powder by mass percentage; Step 5: Put the weighed additional hard phase and metal alloy powder into a planetary ball mill for ball milling. The ball - milling speed is 250 r / min, and the ball - milling time is 1 h, so that the above - mentioned additional hard phase and metal alloy powder are fully mixed and locally mechanically welded to obtain the powder; Step 6: Remove the grease on the surface of the 430 strip with alcohol, wrap the powder prepared in Step 6 with the flux-cored wire drawing equipment inside the 430 strip, and perform the first drawing process. The aperture of the drawing die used in the first drawing process is 2.6 mm. Step 7: After the first drawing process is completed, set several drawing processes in sequence. The aperture of the drawing die corresponding to each drawing process decreases in sequence, and finally a wire with a diameter of 1.2 mm is obtained. Step 8: After the wire drawing is completed, wind it on a wire spool by a wire winding machine, and finally seal it in a wire vacuum packaging bag for standby.

[0056] Arc surfacing is carried out on the surface of the 0Cr13Ni5Mo matrix using the iron-based wire for resisting cavitation damage of the water turbine runner prepared in Example 1. The CMT power source is adopted, the welding current is 160 A, the short-circuit transfer mode is adopted for the molten droplets during the surfacing process, and the dilution rate is controlled at 3%; the surfacing layer thickness is 1.8 mm, the swing width is 15 mm, the overlap amount is 5 mm, and one layer is surfaced. The shielding gas is a helium-argon mixture (30% He + 70% Ar).

[0057] After testing: (1) The Rockwell hardness of the surfacing layer is 41 HRC. (2) After 18 h of cavitation test on the surfacing layer, its weight loss is 0.5 mg. After the same time of cavitation test on the base material 0Cr13Ni5Mo, its weight loss is 1.75 mg. Therefore, the cavitation resistance of the surfacing layer is 3.5 times that of the base material.

[0058] Example 2 This example provides a preparation method of an iron-based wire for resisting cavitation damage of a water turbine runner, including the following steps: Step 1: Weigh the following metal alloy powders by mass percentage, where Cr powder is 8.0%, Ni powder is 10.0%, Mo powder is 6.0%, B powder is 3.0%, and the rest is Fe powder. Step 2: Mix the metal alloy powders weighed in Step 1, then carry out vacuum melting, prepare metal alloy powders by gas atomization method, and perform particle size screening on the gas atomized metal alloy powders to make the particle size of the screened metal alloy powders be 125 ± 25 mesh. Step 3: Weigh 30% of WC powder and 30% of TiC powder by mass percentage, and the rest is VC powder, and mix them to obtain an external hard phase. Step 4: Weigh 20% of the external hard phase by mass percentage, and the rest is metal alloy powder. Step 5: Put the weighed additional hard phase and metal alloy powder into a planetary ball mill for ball milling. The ball milling speed is 300 r / min and the ball milling time is 2 h to fully mix and locally mechanically bond the above-mentioned additional hard phase and metal alloy powder, obtaining the powder. Step 6: Use alcohol to remove the grease on the surface of the 430 strip. Wrap the powder prepared in Step 6 with the 430 strip through a flux-cored wire drawing device and perform the first drawing process. The aperture of the drawing die used in the first drawing process is 2.6 mm. Step 7: After the first drawing process is completed, set several drawing processes in sequence. The aperture of the drawing die corresponding to each drawing process decreases in sequence, and finally a wire with a diameter of 1.2 mm is obtained. Step 8: After the wire drawing is completed, wind the wire around a wire reel by a wire winding machine and finally seal it in a wire vacuum packaging bag for standby.

[0059] Use the iron-based wire for resisting cavitation damage of the water turbine runner prepared in Example 2 to perform arc surfacing on the surface of the 0Cr13Ni5Mo substrate. Use a CMT power source, the welding current is 190 A, the short-circuit transfer mode is adopted for the molten droplets during the surfacing process, and the dilution rate is controlled at 5%; the surfacing layer thickness is 2.4 mm, the swing width is 20 mm, the overlap amount is 8 mm, and one layer of surfacing is performed. The shielding gas is a helium-argon mixture (30% He + 70% Ar).

[0060] After testing: (1) The Rockwell hardness of the surfacing layer is 43 HRC. (2) After an 18-hour cavitation test on the surfacing layer, its weight loss is 0.45 mg. After the same cavitation test for the same time on the base material 0Cr13Ni5Mo, its weight loss is 1.75 mg. Therefore, the cavitation resistance of the surfacing layer is 3.8 times that of the base material.

[0061] Figure 1 It is a schematic diagram of the metallographic structure of the surfacing layer after using the iron-based wire for resisting cavitation damage of the water turbine runner prepared in Example 2 to perform surfacing on the 0Cr13Ni5Mo base material. It can be seen from the figure that the surfacing layer is mainly composed of martensite structure, and the base material is also martensite structure, with a matching tissue phase.

[0062] Figure 2 It is a surface cavitation damage diagram of the surfacing layer after a 4-hour cavitation test after using the iron-based wire for resisting cavitation damage of the water turbine runner prepared in Example 2 to perform surfacing on the 0Cr13Ni5Mo base material; Figure 3 It is a surface cavitation damage diagram of the 0Cr13Ni5Mo base material after a 4-hour cavitation test. From Figure 2 and Figure 3It can be seen that the surfacing layer formed by the welding wire of the present invention has significantly fewer cavitation pits on the surface than those on the surface of the 0Cr13Ni5Mo base material.

[0063] Example 3 This example provides a preparation method for an iron-based welding wire for resisting cavitation damage of a water turbine runner, including the following steps: Step 1, weigh the following metal alloy powders by mass percentage, wherein Cr powder is 7.0%, Ni powder is 9.0%, Mo powder is 5.0%, B powder is 2.5.0%, and the rest is Fe powder; Step 2, mix the metal alloy powders weighed in Step 1, then carry out vacuum melting, prepare metal alloy powders by gas atomization method, and perform particle size screening on the gas atomized metal alloy powders to make the particle size of the screened metal alloy powders be 125 ± 25 mesh; Step 3, weigh 25% of WC powder and 25% of TiC powder by mass percentage, and the rest is VC powder, and mix to obtain an additional hard phase; Step 4, weigh 15% of the additional hard phase by mass percentage, and the rest is metal alloy powder; Step 5, put the weighed additional hard phase and metal alloy powder into a planetary ball mill for ball milling, the ball milling speed is 280 r / min, and the ball milling time is 1.5 h, so that the above additional hard phase and metal alloy powder are fully mixed and locally mechanically welded to obtain a powder; Step 6, use alcohol to remove the grease on the surface of the 430 strip, wrap the powder prepared in Step 6 in the 430 strip through a flux-cored wire drawing device, and perform the first drawing process, and the aperture of the drawing die used in the first drawing process is 2.6 mm; Step 7, after the first process drawing is completed, set several drawing processes in sequence, the aperture of the drawing die corresponding to each drawing process decreases in sequence, and finally a welding wire with a diameter of 1.2 mm is obtained; Step 8, after the welding wire drawing is completed, wind it on a welding wire reel by a wire winding machine, and finally seal it in a welding wire vacuum packaging bag for standby.

[0064] The iron-based welding wire for resisting cavitation damage of a water turbine runner prepared in Example 3 is used for arc surfacing on the surface of a 0Cr13Ni5Mo substrate. A CMT power source is adopted, the welding current is 180 A, the short-circuit transfer mode is adopted for the molten droplets during the surfacing process, and the dilution rate is controlled at 4%; the surfacing layer thickness is 2.1 mm, the swing width is 17 mm, the overlap amount is 7 mm, one layer is surfaced, and the shielding gas is a helium-argon mixture (30% He + 70% Ar).

[0065] After testing: (1) The Rockwell hardness of the surfacing layer is 44 HRC; (2) After 18 hours of cavitation test, the weight loss of the surfacing layer is 0.41 mg, and the weight loss of the base material 0Cr13Ni5Mo after the same cavitation test is 1.75 mg. Therefore, the cavitation resistance of the surfacing layer is 4.2 times that of the base material.

[0066] Example 4 This example provides a preparation method for an iron-based welding wire for resisting cavitation damage of a water turbine runner, including the following steps: Step 1: Weigh the following metal alloy powders by mass percentage. Among them, Cr powder is 6.8%, Ni powder is 8.1%, Mo powder is 4.6%, B powder is 2.3%, and the rest is Fe powder; Step 2: Mix the metal alloy powders weighed in Step 1, then conduct vacuum melting, use the gas atomization method to prepare metal alloy powders, and perform particle size screening on the gas atomized metal alloy powders so that the particle size of the screened metal alloy powders is 125 ± 25 mesh; Step 3: Weigh 26% of WC powder and 26% of TiC powder by mass percentage, and the rest is VC powder, and mix to obtain an additional hard phase; Step 4: Weigh 16% of the additional hard phase by mass percentage, and the rest is metal alloy powder; Step 5: Put the weighed additional hard phase and metal alloy powder into a planetary ball mill for ball milling. The ball milling speed is 260 r / min, and the ball milling time is 1.2 h, so that the above-mentioned additional hard phase and metal alloy powder are fully mixed and locally mechanically welded to obtain welding powder; Step 6: Use alcohol to remove the grease on the surface of the 430 strip, wrap the welding powder prepared in Step 6 in the 430 strip through a flux-cored wire drawing device, and perform the first drawing process. The aperture of the drawing die used in the first drawing process is 2.6 mm; Step 7: After the first process drawing is completed, set several drawing processes in sequence. The aperture of the drawing die corresponding to each drawing process decreases in sequence, and finally a welding wire with a diameter of 1.2 mm is obtained; Step 8: After the welding wire drawing is completed, wind it on a welding wire reel by a wire winding machine, and finally seal it in a welding wire vacuum packaging bag for standby.

[0067] The iron-based welding wire for resisting cavitation damage of a water turbine runner prepared in Example 4 is used for arc surfacing on the surface of a 0Cr13Ni5Mo substrate. A CMT power source is used, the welding current is 170 A, the short-circuit transfer mode is adopted for the molten droplets during the surfacing process, and the dilution rate is controlled at 3.5%; the surfacing layer thickness is 2.0 mm, the swing width is 16 mm, the overlap amount is 6 mm, and one layer of surfacing is performed. The shielding gas is a helium-argon mixture (30% He + 70% Ar).

[0068] After testing: (1)The Rockwell hardness of the surfacing layer is 42.5 HRC; (2)After 18 hours of cavitation test on the surfacing layer, the weight loss is 0.44 mg. For the base material 0Cr13Ni5Mo after the same cavitation test for the same time, the weight loss is 1.75 mg. Therefore, the cavitation resistance of the surfacing layer is 3.9 times that of the base material.

[0069] Example 5 This example provides a preparation method for an iron-based welding wire for resisting cavitation damage of a water turbine runner, including the following steps: Step 1: Weigh the following metal alloy powders by mass percentage. Among them, Cr powder is 7.9%, Ni powder is 9.9%, Mo powder is 5.9%, B powder is 2.9%, and the rest is Fe powder; Step 2: Mix the metal alloy powders weighed in Step 1, then carry out vacuum melting, use the gas atomization method to prepare metal alloy powders, and perform particle size screening on the gas-atomized metal alloy powders so that the particle size of the screened metal alloy powders is 125 ± 25 mesh; Step 3: Weigh 29% of WC powder and 29% of TiC powder by mass percentage, and the rest is VC powder, and mix them to obtain an external hard phase; Step 4: Weigh 19% of the external hard phase by mass percentage, and the rest is metal alloy powder; Step 5: Put the weighed external hard phase and metal alloy powder into a planetary ball mill for ball milling. The ball milling speed is 290 r / min, and the ball milling time is 1.9 h, so that the above external hard phase and metal alloy powder are fully mixed and locally mechanically welded to obtain welding powder; Step 6: Use alcohol to remove the grease on the surface of the 430 strip, wrap the welding powder prepared in Step 6 in the 430 strip through a flux-cored wire drawing device, and perform the first drawing process. The aperture of the drawing die used in the first drawing process is 2.6 mm; Step 7: After the first process drawing is completed, set several drawing processes in sequence. The aperture of the drawing die corresponding to each drawing process decreases in sequence, and finally a welding wire with a diameter of 1.2 mm is obtained; Step 8: After the welding wire drawing is completed, wind it on a welding wire reel by a wire winding machine, and finally seal it in a welding wire vacuum packaging bag for standby.

[0070] The iron-based welding wire for resisting cavitation damage of a water turbine runner prepared in Example 5 is used for arc surfacing on the surface of the 0Cr13Ni5Mo substrate. The CMT power supply is used, the welding current is 180 A, the short-circuit transfer mode is adopted for the molten droplets during the surfacing process, and the dilution rate is controlled at 3.2%; the surfacing layer thickness is 1.9 mm, the swing width is 19 mm, the overlap amount is 6.5 mm, one layer of surfacing is carried out, and the shielding gas is a helium-argon mixture (30% He + 70% Ar).

[0071] After testing: (1) The Rockwell hardness of the surfacing layer is 47 HRC; (2) After 18 hours of cavitation test on the surfacing layer, the weight loss is 0.38 mg. For the base material 0Cr13Ni5Mo after the same time of cavitation test, the weight loss is 1.75 mg. Therefore, the cavitation resistance of the surfacing layer is 4.6 times that of the base material.

[0072] Example 6 This example provides a preparation method of an iron-based welding wire for resisting cavitation damage of a water turbine runner, including the following steps: Step 1: Weigh the following metal alloy powders by mass percentage. Among them, Cr powder is 6.1%, Ni powder is 8.3%, Mo powder is 4.3%, B powder is 2.1%, and the rest is Fe powder; Step 2: Mix the metal alloy powders weighed in Step 1, then carry out vacuum melting, use the gas atomization method to prepare metal alloy powders, and perform particle size screening on the gas-atomized metal alloy powders to make the particle size of the screened metal alloy powders be 125 ± 25 mesh; Step 3: Weigh 22% of WC powder and 22% of TiC powder by mass percentage, and the rest is VC powder, and mix them to obtain an external hard phase; Step 4: Weigh 12% of the external hard phase by mass percentage, and the rest is metal alloy powder; Step 5: Put the weighed external hard phase and metal alloy powder into a planetary ball mill for ball milling. The ball milling speed is 255 r / min, and the ball milling time is 1.1 h, so that the above-mentioned external hard phase and metal alloy powder are fully mixed and locally mechanically welded to obtain a powder; Step 6: Use alcohol to remove the grease on the surface of the 430 strip, wrap the powder prepared in Step 6 in the 430 strip through a flux-cored wire drawing device, and carry out the first drawing process. The aperture of the drawing die used in the first drawing process is 2.6 mm; Step 7: After the first process drawing is completed, set several drawing processes in sequence. The aperture of the drawing die corresponding to each drawing process decreases in sequence, and finally a welding wire with a diameter of 1.2 mm is obtained; Step 8: After the welding wire drawing is completed, wind it on a welding wire reel by a wire winding machine, and finally seal it in a welding wire vacuum packaging bag for standby.

[0073] The iron-based welding wire for resisting cavitation damage of the water turbine runner prepared in Example 6 was used for arc surfacing on the surface of the 0Cr13Ni5Mo matrix. The CMT power source was adopted, the welding current was 185 A, the short-circuit transfer mode was adopted for the molten droplets during the surfacing process, and the dilution rate was controlled at 4.5%. The thickness of the surfacing layer was 2.2 mm, the oscillation width was 15.5 mm, the overlap amount was 7.5 mm, and one layer of surfacing was carried out. The shielding gas was a helium-argon mixture (30% He + 70% Ar).

[0074] After testing: (1) The Rockwell hardness of the surfacing layer was 43.5 HRC (2) After the 18-hour cavitation test of the surfacing layer, its weight loss was 0.39 mg. After the same-time cavitation test of the base material 0Cr13Ni5Mo, its weight loss was 1.75 mg. Therefore, the cavitation resistance of the surfacing layer was 4.4 times that of the base material.

[0075] Example 7 This example provides a preparation method of an iron-based welding wire for resisting cavitation damage of a water turbine runner, including the following steps: Step 1: Weigh the following metal alloy powders by mass percentage. Among them, the Cr powder was 6.35%, the Ni powder was 9.75%, the Mo powder was 5.88%, the B powder was 2.78%, and the rest was Fe powder; Step 2: Mix the metal alloy powders weighed in Step 1, then carry out vacuum melting, adopt the gas atomization method to prepare metal alloy powders, and perform particle size screening on the gas-atomized metal alloy powders to make the particle size of the screened metal alloy powders be 125 ± 25 mesh; Step 3: Weigh 29.5% of WC powder and 29.5% of TiC powder by mass percentage, and the rest was VC powder, and mix them to obtain an external hard phase; Step 4: Weigh 18.5% of the external hard phase by mass percentage, and the rest was metal alloy powder; Step 5: Put the weighed external hard phase and metal alloy powder into a planetary ball mill for ball milling. The ball milling speed was 287 r / min, and the ball milling time was 1.7 h, so that the above external hard phase and metal alloy powder were fully mixed and locally mechanically welded to obtain a powder; Step 6: Use alcohol to remove the grease on the surface of the 430 strip, wrap the powder prepared in Step 6 in the 430 strip through a flux-cored wire drawing device, and carry out the first drawing process. The aperture of the drawing die used in the first drawing process was 2.6 mm; Step 7: After the first process drawing was completed, several drawing processes were set up in sequence. The aperture of the drawing die corresponding to each drawing process decreased in sequence, and finally a welding wire with a diameter of 1.2 mm was obtained; Step 8: After the wire drawing of the welding wire is completed, it is wound on a welding wire reel by a wire winding machine and finally sealed in a vacuum packaging bag for the welding wire for standby.

[0076] The iron-based welding wire for resisting cavitation damage of the water turbine runner prepared in Example 7 is used for arc surfacing on the surface of the 0Cr13Ni5Mo matrix. A CMT power source is adopted, the welding current is 188 A, the short-circuit transfer mode is adopted for the molten droplets during the surfacing process, and the dilution rate is controlled at 3.1%; the thickness of the surfacing layer is 2.3 mm, the swing width is 15.6 mm, the overlap amount is 7.5 mm, and one layer of surfacing is carried out. The shielding gas is a helium-argon mixed gas (30% He + 70% Ar).

[0077] After testing: (1) The Rockwell hardness of the surfacing layer is 49 HRC; (2) After 18 h of cavitation test on the surfacing layer, the weight loss is 0.31 mg. After the same time of cavitation test on the base material 0Cr13Ni5Mo, the weight loss is 1.75 mg. Therefore, the cavitation resistance of the surfacing layer is 5.6 times that of the base material.

[0078] The above content is only to illustrate the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention fall within the protection scope of the claims of the present invention.

Claims

1. An iron-based welding wire for resisting cavitation damage of a water turbine runner, characterized in that, It includes powder and a welding skin for wrapping the powder. The powder includes an externally added hard phase and a metal alloy powder. Among them, by mass percentage, the externally added hard phase is 10% - 20%, and the rest is the metal alloy powder; By mass percentage, the externally added hard phase includes: 20% - 30% WC powder, 20% - 30% TiC powder, and the rest is VC powder.

2. The iron-based welding wire for resisting cavitation damage of a hydraulic turbine runner according to claim 1, wherein, By mass percentage, the metal alloy powder includes: 6.0% - 8.0% Cr powder, 8.0% - 10.0% Ni powder, 4.0% - 6.0% Mo powder, 2.0% - 3.0% B powder, and the rest is Fe powder.

3. A ferrous-based welding wire for resisting cavitation damage of a hydraulic turbine runner according to claim 1, characterized in that, The powder particle size of the externally added hard phase is all 200 - 250 mesh.

4. A ferrous-based welding wire for resisting cavitation damage of a water turbine runner according to claim 1, characterized in that, The powder particle size of the metal alloy powder is all 100 - 150 mesh.

5. A ferrous-based welding wire for resisting cavitation damage of a hydraulic turbine runner according to claim 1, characterized in that, The filling rate of the powder in the welding skin is controlled at 28% - 32%.

6. A ferrous-based welding wire for resisting cavitation damage of a water turbine runner according to claim 1, characterized in that, The welding skin is a 430 strip, with a thickness of 0.4 mm and a width of 10 mm.

7. A preparation method of an iron-based welding wire for resisting cavitation damage of a water turbine runner as described in claim 1, characterized in that, It includes the following steps: Step 1, by mass percentage, respectively weigh 10.0% - 20.0% of the externally added hard phase, and the rest is the metal alloy powder; Step 2, ball-mill and mix the weighed externally added hard phase and metal alloy powder to obtain powder; Step 3, wrap the powder prepared in Step 2 in the welding skin and perform the first drawing process. The aperture of the drawing die used in the first drawing process is 2.6 mm; Step 4, after the first process drawing is completed, set several drawing processes in sequence. The aperture of the drawing die corresponding to each drawing process decreases in sequence, so that the diameter of the finally obtained welding wire is 1.2 - 1.4 mm, and an iron-based welding wire for resisting cavitation damage of a water turbine runner is prepared.

8. The preparation method of an iron-based welding wire for resisting cavitation damage of a water turbine runner according to claim 7, characterized in that, In Step 1, mix, vacuum melt, and perform gas atomization treatment on the weighed metal alloy powder to obtain metal alloy powder; Among them, N2 is used as the atomization gas for gas atomization treatment, the atomization pressure is 6 - 7 MPa, and the superheat degree of the melt is maintained at 100 - 150 °C during the atomization process.

9. The preparation method of an iron-based welding wire for resisting cavitation damage of a water turbine runner according to claim 7, characterized in that, In Step 2, the ball-milling speed is 250 - 300 r / min, and the ball-milling time is 1 - 2 h.

10. A surfacing method, characterized in that, Use a CMT power source to build up the weld of the iron-based welding wire for resisting cavitation damage of a water turbine runner as described in any one of claims 1 - 6; The process parameters of the build-up welding are as follows: The welding current is 160 - 190 A. The short-circuit transfer mode is adopted for the molten droplets during the build-up welding process, and the dilution rate is controlled at 3% - 5%; the thickness of the build-up welding layer is 1.8 - 2.4 mm, the swing width is 15 - 20 mm, the overlap amount is 5 - 8 mm, the build-up welding layer is 1 layer, and the shielding gas is 30% He + 70% Ar.

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