A laser cladding method using alloy powder to improve the self-lubricity and reduce the hardening sensitivity of the large steam turbine rotor journal

Abstract

This invention belongs to the field of laser cladding processing, specifically disclosing a laser cladding method for improving the self-lubricating properties and reducing the hardening sensitivity of large steam turbine rotor journals using alloy powder. The alloy powder comprises: C: 0.140–0.160 wt%; Mo: 2.90–3.10 wt%; B: 0.25–0.35 wt%; Si: 0.45–0.55 wt%; Mn: ≤0.30 wt%; Cu: 19.2–19.6 wt%; Ni: 38.1–38.5 wt%; Fe as the balance, and unavoidable impurities. Compared with existing non-laser cladding technologies, laser cladding using the aforementioned alloy powder solves the problems of long processing cycles, poor adhesion between the cladding layer and the substrate, and large thermal deformation. Compared with existing laser cladding technologies, it improves the lubricity of the turbine rotor journal and reduces hardening sensitivity, solving the problem of downtime caused by turbine wear. This invention reduces the frequency of turbine rotor downtime and safety accidents through laser cladding, lowers the overall cost of the industry, improves production efficiency, and extends the service life of the rotor.

Description

Technical Field

[0001] This invention belongs to the field of laser cladding processing, and specifically discloses a laser cladding method that uses alloy powder to improve the self-lubrication of the journal of a large steam turbine rotor and reduce its hardening sensitivity. Background Technology

[0002] Thermal power plants typically use 25Cr2Ni4MoV steel to manufacture large steam turbine rotors. These large turbine rotors generally operate at speeds of several thousand revolutions per minute and weigh tens to hundreds of tons. The blades on the turbine rotor rotate suspended in the air, and the journals at both ends of the rotor directly contact the bearings for support. Under such high-speed, heavy, and high-pressure steam erosion conditions, for safety reasons, thermal power plants must immerse the turbine rotor journals in an oil bath. The continuous replenishment and flow of lubricating oil cools the journals and reduces friction and wear. However, even with the most stringent safety measures, wear can still pose safety hazards. For example, operator error leading to insufficient oil supply can disrupt the turbine's dynamic balance. The result is that the substrate of the turbine rotor's journal is rapidly worn down. The temperature of the worn journal rises rapidly, and the residual lubricating oil in the oil sump quickly cools the substrate, causing it to harden rapidly. This hardened substrate further wears down the bearing, creating a vicious cycle. Because the turbine rotates at excessively high speeds, by the time staff notice the abnormality, it is often too late.

[0003] Some manufacturers have repaired worn journals by installing bushings, thermal spraying, or plasma beam cladding. However, these methods have been phased out due to their long processing time; the semi-metallurgical bonding between thermal spraying and the substrate, resulting in insufficient pressure resistance and wear resistance, and short service life; and the high heat output and difficulty in controlling stress deformation during plasma beam cladding. Currently, the industry commonly uses laser cladding, which offers lower heat output and controllable deformation, to repair turbine journals. Figure 1 As shown. However, when using laser cladding for repair, the first problem to be faced is that there is no alloy powder with self-lubricating and hardening-reducing properties that can reduce the friction and hardening of the substrate when the journal is worn, prevent the turbine journal and bearing from exceeding the tolerance of the fit dimensions, reduce the risk of safety accidents, and extend the service life of the turbine.

[0004] Chinese invention patent CN 104858423A discloses a composite solid self-lubricating alloy powder for scraper conveyor chutes and its preparation method. According to the alloy powder information provided in the patent, the authors used an iron-based alloy material. In addition to elements commonly used in laser cladding such as Cr, Ni, Mn, Mo, B, and Si, 1%–3.5% rare earth oxides, 2%–8% tungsten carbide, 2%–8% hexagonal boron nitride, and a high concentration of 2%–8% carbon were added. The technical method used was laser cladding. It is certain that this alloy powder belongs to the iron-based ceramic composite powder category. The purpose of adding a total of 7%–27.5% rare earth oxides, tungsten carbide, hexagonal boron nitride, and carbon is to improve wear resistance and self-lubricating properties. However, this powder is unsuitable for repairing turbine rotor journals because: First, turbine rotor journals are used in conjunction with bearings, and the hardness of the bearings is generally comparable to that of the journals. If one is too hard, it will lead to wear and dimensional deviations in the other. The industry standard for journal hardness is no higher than 38 HRC, while this patent provides a hardness of 45–58 HRC. This is clearly unacceptable. Second, turbine rotors operate under conditions of heavy weight, high speed, and high-pressure steam erosion, making their safety paramount. Therefore, the materials used for journals and bearings prioritize toughness and ductility in terms of mechanical properties, rather than high strength / hardness. The 5%–19.5% hard particles and 2%–8% carbon added to the alloy powder in this patent will not only severely embrittle the cladding layer, but the worn-off hard particles will also accelerate the turbine's failure. Using this powder for laser treatment would be disastrous for the turbine rotor. The technical solution provided by this patent not only has no reference value, but is also detrimental to the development of the steam turbine industry.

[0005] Chinese invention patent CN 112063934A discloses a laser-clad iron-based alloy powder for repairing turbine rotor journals and its preparation and application. The alloy powder solution provided in this patent is a low-carbon alloy steel self-fluxing alloy powder, aiming to solve problems such as wear and scoring that occur on turbine rotor shafts during operation. This invention provides a wear-resistant solution, but does not mention the technical requirements for lubrication, friction reduction, and prevention of hardening. Summary of the Invention

[0006] To address the above issues, this invention discloses a laser cladding method that utilizes alloy powder to improve the self-lubricating properties of the journal section of a large steam turbine rotor and reduce its hardening sensitivity. After laser cladding, this powder can reduce frictional wear on the turbine rotor journal section and the occurrence of substrate hardening, thus ensuring normal power plant production and extending the service life of the turbine rotor.

[0007] The technical solution of the present invention is as follows:

[0008] An alloy powder comprising the following components:

[0009] C: 0.140~0.160wt%;

[0010] Mo: 2.90–3.10 wt%;

[0011] B: 0.25–0.35 wt%;

[0012] Si: 0.45–0.55 wt%;

[0013] Mn: ≤0.30wt%

[0014] Cu: 19.2–19.6 wt%;

[0015] Ni: 38.1–38.5 wt%;

[0016] Fe is the balance, along with unavoidable impurities.

[0017] Preferably, the alloy powder comprises the following components:

[0018] C: 0.145~0.155wt%;

[0019] Mo: 2.95–3.05 wt%;

[0020] B: 0.27–0.32 wt%;

[0021] Si: 0.47–0.52 wt%;

[0022] Mn: 0.05~0.25wt%

[0023] Cu: 19.3–19.5 wt%;

[0024] Ni: 38.2–38.4 wt%;

[0025] Fe is the balance, along with unavoidable impurities.

[0026] Preferably, the above alloy powder comprises the following components: C: 0.155 wt%;

[0027] Mo: 3.05 wt%;

[0028] B: 0.32wt%;

[0029] Si: 0.52 wt%;

[0030] Mn: 0.25wt%

[0031] Cu: 19.5 wt%;

[0032] Ni: 38.4 wt%;

[0033] Fe is the balance, along with unavoidable impurities;

[0034] Or may include the following ingredients:

[0035] C: 0.145 wt%;

[0036] Mo: 2.95 wt%;

[0037] B: 0.27wt%;

[0038] Si: 0.47wt%;

[0039] Mn: 0.05wt%

[0040] Cu: 19.3 wt%;

[0041] Ni: 38.2 wt%;

[0042] Fe is the balance, along with unavoidable impurities.

[0043] Furthermore, the aforementioned alloy powder was prepared in advance and then produced by vacuum nitrogen atomization powder preparation method, with a particle size of 53–150 micrometers.

[0044] Furthermore, the method for preparing the above-mentioned alloy powder includes the following steps:

[0045] S1 Batching: The composition of the alloy powder is designed according to the working environment and technical requirements, and the batching is carried out according to the composition;

[0046] S2 smelting: The prepared alloy raw materials are added to the resistance crucible furnace and heated to 1490℃ to melt them into a liquid state. Then, slag removal and degassing are carried out.

[0047] S3 gas atomization and cooling: The above liquid metal is heated to 1530℃, stirred thoroughly, and kept at this temperature for 12 minutes. Then it is poured into a ladle. When the liquid alloy flows to the liquid guide pipe below the ladle, it is broken up and atomized into solid powder by a nitrogen pressure spray gun with a pressure of 4.6 MPa.

[0048] S4 grading: After the powder cools to room temperature, use a grading sieve to sieve out alloy powder of 80-300 mesh, and then repackage and pack it.

[0049] Furthermore, the aforementioned alloy powder is used to improve the self-lubricating properties of the journal section of a large steam turbine rotor and reduce its hardening sensitivity, and the alloy powder is used as a raw material in laser cladding.

[0050] Furthermore, a laser cladding method for improving the self-lubricating properties and reducing hardening sensitivity of large steam turbine rotor journals using alloy powder, employing any of the aforementioned alloy powders, includes the following steps:

[0051] 1) Remove the fatigue layer from the journal of the large steam turbine rotor by turning, and chamfer 30-60° at the beginning and end of turning.

[0052] 2) The alloy powder is clad onto the surface of the rotor journal using a side-shaft feeding method. During laser cladding, the laser power is 9000-10000w, the linear speed is 10-11mm / s, the overlap rate is 38-42%, and the cladding thickness is controlled at 1.50-1.60mm.

[0053] 3) After completing one layer of laser cladding, stop the laser, use a polishing wheel to brush away the slag on the cladding layer, and perform dye penetrant testing. If defects are found, the existing cladding layer needs to be machined off, and then return to step 2) to continue cladding.

[0054] 4) If no defects are found during the flaw detection, the turbine rotor is sent to a heat treatment furnace for high-temperature tempering. The tempering temperature is 580-620℃, with a temperature fluctuation of ±12℃, and the tempering time is 280-300 minutes. After tempering, it is air-cooled to room temperature. Then, the journal is subjected to dye penetrant testing again. If no defects are found during the flaw detection, the cladding layer of the turbine rotor journal is machined to the required dimensional and positional tolerances, and the hardness is tested.

[0055] Preferably, in the above method, the laser cladding spot size in step 2) is 3x26mm.

[0056] Preferably, in the above method, when laser multilayer cladding is performed, dye penetrant testing is performed after the previous layer of cladding is completed, and the next layer of cladding is performed only after confirming that there are no defects.

[0057] Preferably, in the above method, the thickness of the decarburized layer of the cladding layer is less than or equal to 0.50 mm.

[0058] The design concept of the alloy powder of this invention and the basis for selecting the range of each component are as follows:

[0059] (1) Design concept of alloy powder

[0060] To achieve the technical effects of reducing friction and wear and minimizing hardening of the substrate, the overall design concept of the alloy powder is "connection first, then precipitation and lubrication." The specific steps are as follows: First, Fe and Ni are infinitely soluble in solids, and Ni and Fe mutually act as the aforementioned "connectors." Selecting Fe+Ni as the main alloy serves two purposes: firstly, to create the basic framework of the alloy powder; secondly, to act as a connecting link—ensuring better metallurgical bonding between the cladding layer and the substrate, improving weldability, and preventing cracking and peeling of the cladding layer. Secondly, Ni can dissolve more Cu, and the combination of Ni and Fe can also promote the precipitation of Cu, forming "almost elemental Cu." Here, Ni acts as the "connector" for Cu. Thirdly, the combination of Ni, Cu, Mo, and Si promotes the graphitization of C. The process involves the formation of cementite after laser cladding, followed by graphitization during high-temperature tempering (a mandatory requirement in the steam turbine industry). Here, Fe acts as the "connector" between the four elements and C (graphite). Finally, the precipitated "elemental Cu" and MC(B) type compounds also strengthen the matrix, ensuring that the hardness of the cladding layer does not decrease excessively after high-temperature tempering. Here, M specifically refers to Fe and Mo elements. The above discussion is based on the following... Figure 2 As shown.

[0061] On the other hand, the matrix phase of the cladding layer is austenitic. It is well known that alloys with an austenitic matrix do not undergo phase transformation during heating and cooling, meaning that the hardness of this type of alloy does not change significantly during temperature changes. However, under conditions of high wear and poor thermal conductivity, its work hardening efficiency increases dramatically, macroscopically manifested as a hardness increase to over 420 HB after processing. However, according to the solution provided in this patent application, no work hardening phenomenon occurred during the machine simulation test, based on the fact that the hardness of the cladding layer is concentrated below 320 HB. Figure 5 and Figure 6 As shown. This also means that when the turbine's oil pumping system is under-supply, the rotor journal will not experience substrate hardening. This also indirectly demonstrates that the cladding layer has the ability to reduce friction and wear, that is, the self-lubricating and high thermal conductivity technologies have achieved the expected results. This may be related to the precipitation of copper, graphite, and carbide.

[0062] To further explain the design concept of "connecting first, then precipitation for lubrication": The solution provided in this patent application mainly revolves around improving the self-lubricating properties of the laser cladding layer and reducing its hardenability. To achieve the aforementioned technical effects, the design of the precipitated phase is particularly important. The existence of the precipitated phase requires that the cladding layer be free of quality defects; therefore, "connection (solid solution)" is also crucial. Only under the design concept of "connecting first, then precipitation for lubrication" can the alloy powder of this patent application achieve the technical effect of self-lubrication.

[0063] (2) Basis for selecting the composition range of alloy powder

[0064] The technical specifications are as follows: (1) When the cladding thickness is less than 3mm, no cracks shall be found in the cladding layer after penetrant testing; (2) The hardness of the cladding layer after machining shall be between 280HB and 320HB; (3) The lubricity of the cladding layer is 1.62 times that of the prior art, and the hardening sensitivity is only 66.7% of that of the prior art.

[0065] The combination of Ni, Fe, and Cu elements: When the Ni:Fe weight percentage is close to 1:1 and the copper precipitation reaches 10-15 wt%, the crack resistance, hardness, and self-lubricating effect of the cladding layer can meet the above technical requirements. Here, when the Ni content is below 38.1 wt%, the Cu solid solution content decreases, the precipitation increases, and the frequency of "copper embrittlement" in the cladding layer increases by 72%. When the Ni content is above 38.5 wt%, the cladding layer has a high work hardening tendency, and the hardness after machining is around 400 HB. At this point, when the Cu addition is 19.2-19.6 wt%, the above technical requirements are met.

[0066] The five elements Ni, Cu, Mo, Si, and C work together: C's main role is to increase hardness and form graphite. When the carbon content is higher than 0.160 wt%, the cladding layer has a high tendency to crack and excessive hardness, hindering widespread industrial application. When the C content is lower than 0.140 wt%, the self-lubricating effect of the cladding layer is poor. The amount of Mo added is closely related to the C content. When the Mo content is higher than 3.10 wt%, the amount of carbon in solid solution is low, the amount of graphitized carbon is high, and the cladding layer has a high tendency to crack. When the Mo content is lower than 2.90 wt%, high-temperature tempering brittleness is high. Although Si can promote carbon graphitization, if the amount added is higher than 0.55 wt%, the ferrite content in the cladding layer will exceed the standard and deteriorate the quality of the cladding layer. When the Si content is lower than 0.45 wt%, the continuous casting performance of the cladding layer deteriorates. In addition, the amount of Si added is also closely related to the amount of B.

[0067] The combination of boron (B) and silicon (Si) primarily serves to remove oxygen and form slag. Additionally, it helps to supplement the hardness of the cladding layer when the carbon content is insufficient. Due to the brittleness and high susceptibility to hot cracking of boron, the less boron added, the better, provided that the cladding layer does not exhibit porosity or inclusions. With a Si content of 0.45–0.55 wt%, an optimal boron addition of 0.25–0.35 wt% is considered optimal.

[0068] Mn element: The main function of Mn is desulfurization. Since the sulfur content in the alloy powder is below 0.01wt%, the maximum theoretical addition of Mn is 0.22wt%. Considering the burn-off rate of Mn element during laser cladding, the maximum addition of Mn element is increased to 0.3wt%.

[0069] The present invention has the following beneficial effects:

[0070] 1. In cases of wear on the turbine rotor journal, particularly when the turbine pump oil system experiences insufficient oil supply, the solution provided in this patent application offers advantages over existing non-laser cladding technologies. It features a shorter processing cycle, stronger adhesion between the cladding layer and the substrate, and less thermal deformation. Compared to existing laser cladding technologies, by improving the self-lubricating properties of the turbine rotor journal and reducing hardening sensitivity, it mitigates safety issues caused by frictional wear and substrate hardening in the turbine rotor. The self-lubricating performance is 1.62 times that of existing technologies, and the hardening sensitivity is only 66.7% of existing technologies, extending the service life of the turbine rotor. Figures 3-4 and Figures 5-6 As shown.

[0071] 2. The laser cladding solution provided in this patent application has an alloy powder cost comparable to that of existing technologies, and the overall production time is only 13% to 90% of that of existing technologies. The service life is about 1.5 times that of existing technologies, significantly reducing production costs. Attached Figure Description

[0072] Figure 1 A physical image of laser cladding repair of the turbine rotor journal according to Embodiment 1 provided in the present invention patent application;

[0073] Figure 2 A phase transformation simulation diagram of laser cladding alloy powder was calculated according to the scheme of Embodiment 1 provided in the present invention patent application; wherein, LIQUID: liquid; AUSTENITE: austenitic phase; M3B2: boride; M23C6: carbide; CU: copper phase or "copper-like phase"; CEMENTITE: cementite.

[0074] Figure 3The friction and wear test conducted at room temperature using existing laser cladding technology yielded an average friction coefficient of 0.503.

[0075] Figure 4 According to the embodiment 1 provided in the present invention patent application, a friction and wear test conducted at room temperature yielded an average friction coefficient of 0.311.

[0076] Figure 5 To utilize existing laser cladding technology, a physical image is shown of a substrate used for testing the hardness of the journal section of a steam turbine rotor under wear conditions.

[0077] Figure 6 According to Embodiment 1 provided in this patent application, a physical image shows the hardness of the substrate at the journal section of a turbine rotor under wear conditions. Detailed Implementation

[0078] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0079] Unless otherwise specified, all reagents or instruments used in the embodiments of this invention are commercially available conventional reagent products.

[0080] The method for preparing the alloy powder includes the following steps:

[0081] S1 Batching: The composition of the alloy powder is designed according to the working environment and technical requirements, and the batching is carried out according to the composition;

[0082] S2 smelting: The prepared alloy raw materials are added to the resistance crucible furnace and heated to 1490℃ to melt them into a liquid state. Then, slag removal and degassing are carried out.

[0083] S3 gas atomization and cooling: The above liquid metal is heated to 1530℃, stirred thoroughly, and kept at this temperature for 12 minutes. Then it is poured into a ladle. When the liquid alloy flows to the liquid guide pipe below the ladle, it is broken up and atomized into solid powder by a nitrogen pressure spray gun with a pressure of 4.6 MPa.

[0084] S4 grading: After the powder cools to room temperature, use a grading sieve to sieve out alloy powder of 80-300 mesh, and then repackage and pack it.

[0085] It should be specifically noted that in the alloy powder solution provided in this patent application, the technical term "Fe as balance" does not mean that the alloy powder is an iron-based material. The inventors believe that this material should be called nickel-iron (or iron-nickel) based alloy powder, or more accurately, nickel-iron-copper (or iron-nickel-copper) based alloy powder. Furthermore, the "and unavoidable impurities" mentioned in the above alloy powder specifically refer to the three elements O, S, and P, with contents of less than 0.02 wt%, less than 0.01 wt%, and less than 0.03 wt%, respectively. These elements, due to their extremely low content and lack of intentional addition, will not be further discussed in this patent application. As for harmful elements such as Pb, Sn, As, Sb, and Bi, the inventors have not detected them in the alloy powder.

[0086] Example 1

[0087] An alloy powder for improving the self-lubrication and reducing the hardening sensitivity of large steam turbine rotor journals, comprising the following components:

[0088] C: 0.150 wt%;

[0089] Mo: 3.00 wt%;

[0090] B: 0.30 wt%;

[0091] Si: 0.50 wt%;

[0092] Mn: 0.15wt%

[0093] Cu: 19.4 wt%;

[0094] Ni: 38.4 wt%;

[0095] Fe is the balance, along with unavoidable impurities.

[0096] The alloys of the above components were pre-prepared and then prepared by vacuum nitrogen atomization powder preparation method, and the resulting powder had a particle size of 53-150 micrometers.

[0097] A laser cladding method for improving the self-lubrication and reducing the hardening sensitivity of large steam turbine rotor journals, based on the aforementioned alloy powder for improving the self-lubrication and reducing the hardening sensitivity of large steam turbine rotor journals, includes the following steps:

[0098] 1) Remove the fatigue layer from the journal of the large steam turbine rotor by turning, and chamfer 45° at the beginning and end of turning.

[0099] 2) The alloy powder is clad onto the surface of the rotor journal using a side-shaft feeding method. During laser cladding, the laser power is 9500w, the spot size is 3x26mm, the linear speed is 10.5mm / s, the overlap rate is 40%, and the cladding thickness is controlled at 1.55mm.

[0100] 3) After completing one layer of laser cladding, stop the laser, use a polishing wheel to brush away the slag on the cladding layer, and perform dye penetrant testing. If defects are found, the existing cladding layer needs to be machined off, and then return to step 2) to continue cladding.

[0101] 4) If no defects are found during the flaw detection, the turbine rotor is sent to a heat treatment furnace for high-temperature tempering at a temperature of 600℃ with a temperature fluctuation of ±7℃ and a tempering time of 290min. After tempering, it is air-cooled to room temperature. Then, the journal is subjected to dye penetrant testing again. If no defects are found during the flaw detection, the cladding layer of the turbine rotor journal is machined to the required dimensional and positional tolerances and the hardness is tested.

[0102] It should be noted that if the fatigue layer of the rotor journal substrate is very deep and requires laser multi-layer cladding, dye penetrant testing should be performed after the previous layer of cladding is completed. If no defects are found, the next layer of cladding can be performed. After the cladding is completely completed, high-temperature tempering should be performed. When tempering at a high temperature below 607 degrees Celsius and within 290 minutes, the decarburized layer thickness of the cladding layer should be less than or equal to 0.48 mm.

[0103] Example 2

[0104] An alloy powder for improving the self-lubrication and reducing the hardening sensitivity of large steam turbine rotor journals, comprising the following components:

[0105] C: 0.160 wt%;

[0106] Mo: 3.10 wt%;

[0107] B: 0.35wt%;

[0108] Si: 0.55wt%;

[0109] Mn: 0.30wt%

[0110] Cu: 19.6 wt%;

[0111] Ni: 38.5 wt%;

[0112] Fe is the balance, along with unavoidable impurities.

[0113] The alloys of the above components were pre-prepared and then prepared by vacuum nitrogen atomization powder preparation method, and the resulting powder had a particle size of 53-150 micrometers.

[0114] A laser cladding method for improving the self-lubrication and reducing the hardening sensitivity of large steam turbine rotor journals, based on the aforementioned alloy powder for improving the self-lubrication and reducing the hardening sensitivity of large steam turbine rotor journals, includes the following steps:

[0115] 1) Remove the fatigue layer from the journal of the large steam turbine rotor by turning, and chamfer 60° at the beginning and end of turning.

[0116] 2) The alloy powder is clad onto the surface of the rotor journal using a side-shaft feeding method. During laser cladding, the laser power is 10000w, the spot size is 3x26mm, the linear speed is 11.0mm / s, the overlap rate is 42%, and the cladding thickness is controlled at 1.60mm.

[0117] 3) After completing one layer of laser cladding, stop the laser, use a polishing wheel to brush away the slag on the cladding layer, and perform dye penetrant testing. If defects are found, the existing cladding layer needs to be machined off, and then return to step 2) to continue cladding.

[0118] 4) If no defects are found during the flaw detection, the turbine rotor is sent to a heat treatment furnace for high-temperature tempering at a temperature of 620℃ with a temperature fluctuation of ±12℃ and a tempering time of 300 minutes. After tempering, it is air-cooled to room temperature. Then, the journal is subjected to dye penetrant testing again. If no defects are found during the flaw detection, the cladding layer of the turbine rotor journal is machined to the required dimensional and positional tolerances and the hardness is tested.

[0119] It should be noted that if the fatigue layer of the rotor journal substrate is very deep and requires multi-layer laser cladding, dye penetrant testing should be performed after the previous layer is completed. If no defects are found, the next layer can be clad. After the cladding is completely completed, high-temperature tempering should be performed. When tempering at a high temperature below 632 degrees Celsius and within 300 minutes, the decarburized layer thickness of the cladding layer should be less than or equal to 0.50 mm.

[0120] Example 3

[0121] An alloy powder for improving the self-lubrication and reducing the hardening sensitivity of large steam turbine rotor journals, comprising the following components:

[0122] C: 0.140 wt%;

[0123] Mo: 2.90 wt%;

[0124] B: 0.25wt%;

[0125] Si: 0.45 wt%;

[0126] Mn: 0.05wt%

[0127] Cu: 19.2 wt%;

[0128] Ni: 38.1 wt%;

[0129] Fe is the balance, along with unavoidable impurities.

[0130] The alloys of the above components were pre-prepared and then prepared by vacuum nitrogen atomization powder preparation method, and the resulting powder had a particle size of 53-150 micrometers.

[0131] A laser cladding method for improving the self-lubrication and reducing the hardening sensitivity of large steam turbine rotor journals, based on the aforementioned alloy powder for improving the self-lubrication and reducing the hardening sensitivity of large steam turbine rotor journals, includes the following steps:

[0132] 1) Remove the fatigue layer from the journal of the large steam turbine rotor by turning, and chamfer 30° at the beginning and end of turning.

[0133] 2) The alloy powder is clad onto the surface of the rotor journal using a side-shaft feeding method. During laser cladding, the laser power is 9000w, the spot size is 3x26mm, the linear speed is 10.0mm / s, the overlap rate is 38%, and the cladding thickness is controlled at 1.50mm.

[0134] 3) After completing one layer of laser cladding, stop the laser, use a polishing wheel to brush away the slag on the cladding layer, and perform dye penetrant testing. If defects are found, the existing cladding layer needs to be machined off, and then return to step 2) to continue cladding.

[0135] 4) If no defects are found during the flaw detection, the turbine rotor is sent to a heat treatment furnace for high-temperature tempering at a temperature of 580℃ with a temperature fluctuation of ±3℃ and a tempering time of 280min. After tempering, it is air-cooled to room temperature. Then, the journal is subjected to dye penetrant testing again. If no defects are found during the flaw detection, the cladding layer of the turbine rotor journal is machined to the required dimensional and positional tolerances and the hardness is tested.

[0136] It should be noted that if the fatigue layer of the rotor journal substrate is very deep and requires laser multi-layer cladding, dye penetrant testing should be performed after the previous layer of cladding is completed. If no defects are found, the next layer of cladding can be performed. After the cladding is completely completed, high-temperature tempering should be performed. When tempering at a high temperature below 583 degrees Celsius and within 280 minutes, the decarburized layer thickness of the cladding layer should be less than or equal to 0.46 mm.

[0137] Example 4

[0138] An alloy powder for improving the self-lubrication and reducing the hardening sensitivity of large steam turbine rotor journals, comprising the following components:

[0139] C: 0.155 wt%;

[0140] Mo: 3.05 wt%;

[0141] B: 0.32wt%;

[0142] Si: 0.52 wt%;

[0143] Mn: 0.25wt%

[0144] Cu: 19.5 wt%;

[0145] Ni: 38.4 wt%;

[0146] Fe is the balance, along with unavoidable impurities.

[0147] The alloys of the above components were pre-prepared and then prepared by vacuum nitrogen atomization powder preparation method, and the resulting powder had a particle size of 53-150 micrometers.

[0148] A laser cladding method for improving the self-lubrication and reducing the hardening sensitivity of large steam turbine rotor journals, based on the aforementioned alloy powder for improving the self-lubrication and reducing the hardening sensitivity of large steam turbine rotor journals, includes the following steps:

[0149] 1) Remove the fatigue layer from the journal of the large steam turbine rotor by turning, and chamfer 45° at the beginning and end of turning.

[0150] 2) The alloy powder is clad onto the surface of the rotor journal using a side-shaft feeding method. During laser cladding, the laser power is 9750w, the spot size is 3x26mm, the linear speed is 10.7mm / s, the overlap rate is 41%, and the cladding thickness is controlled at 1.57mm.

[0151] 3) After completing one layer of laser cladding, stop the laser, use a polishing wheel to brush away the slag on the cladding layer, and perform dye penetrant testing. If defects are found, the existing cladding layer needs to be machined off, and then return to step 2) to continue cladding.

[0152] 4) If no defects are found during the flaw detection, the turbine rotor is sent to a heat treatment furnace for high-temperature tempering at a temperature of 610℃ with a temperature fluctuation of ±10℃ and a tempering time of 295 minutes. After tempering, it is air-cooled to room temperature. Then, the journal is subjected to dye penetrant testing again. If no defects are found during the flaw detection, the cladding layer of the turbine rotor journal is machined to the required dimensional and positional tolerances and the hardness is tested.

[0153] It should be noted that if the fatigue layer of the rotor journal substrate is very deep and requires multi-layer laser cladding, dye penetrant testing should be performed after the previous layer of cladding is completed. If no defects are found, the next layer of cladding can be performed. After the cladding is completely completed, high-temperature tempering should be performed. When tempering at a high temperature below 620 degrees Celsius and within 295 minutes, the decarburized layer thickness of the cladding layer should be less than or equal to 0.49 mm.

[0154] Example 5

[0155] An alloy powder for improving the self-lubrication and reducing the hardening sensitivity of large steam turbine rotor journals, comprising the following components:

[0156] C: 0.145 wt%;

[0157] Mo: 2.95 wt%;

[0158] B: 0.27wt%;

[0159] Si: 0.47wt%;

[0160] Mn: 0.05wt%

[0161] Cu: 19.3 wt%;

[0162] Ni: 38.2 wt%;

[0163] Fe is the balance, along with unavoidable impurities.

[0164] The alloys of the above components were pre-prepared and then prepared by vacuum nitrogen atomization powder preparation method, and the resulting powder had a particle size of 53-150 micrometers.

[0165] A laser cladding method for improving the self-lubrication and reducing the hardening sensitivity of large steam turbine rotor journals, based on the aforementioned alloy powder for improving the self-lubrication and reducing the hardening sensitivity of large steam turbine rotor journals, includes the following steps:

[0166] 1) Remove the fatigue layer from the journal of the large steam turbine rotor by turning, and chamfer 30° at the beginning and end of turning.

[0167] 2) The alloy powder is clad onto the surface of the rotor journal using a side-shaft feeding method. During laser cladding, the laser power is 9250w, the spot size is 3x26mm, the linear speed is 10.2mm / s, the overlap rate is 39%, and the cladding thickness is controlled at 1.52mm.

[0168] 3) After completing one layer of laser cladding, stop the laser, use a polishing wheel to brush away the slag on the cladding layer, and perform dye penetrant testing. If defects are found, the existing cladding layer needs to be machined off, and then return to step 2) to continue cladding.

[0169] 4) If no defects are found during the flaw detection, the turbine rotor is sent to a heat treatment furnace for high-temperature tempering at a temperature of 590℃ with a temperature fluctuation of ±5℃ and a tempering time of 285 minutes. After tempering, it is air-cooled to room temperature. Then, the journal is subjected to dye penetrant testing again. If no defects are found during the flaw detection, the cladding layer of the turbine rotor journal is machined to the required dimensional and positional tolerances and the hardness is tested.

[0170] It should be noted that if the fatigue layer of the rotor journal substrate is very deep and requires multi-layer laser cladding, dye penetrant testing should be performed after the previous layer of cladding is completed. If no defects are found, the next layer of cladding can be performed. After the cladding is completely completed, high-temperature tempering should be performed. When tempering at a high temperature below 595 degrees Celsius and within 285 minutes, the decarburized layer thickness of the cladding layer should be less than or equal to 0.47 mm.

[0171] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this patent application and are not intended to limit them. For those skilled in the art, modifications can be made to the specific technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. However, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions protected by this patent application.

Claims

1. The application of an alloy powder in improving the self-lubricating properties and reducing hardening sensitivity of large steam turbine rotor journals, characterized in that, The alloy powder is used as a raw material in laser cladding; The alloy powder comprises the following components: C: 0.140~0.160wt% Mo: 2.90~3.10 wt% B: 0.25~0.35wt%; Si: 0.45~0.55wt% Mn: ≤0.30wt% Cu: 19.2~19.6 wt% Ni: 38.1~38.5 wt% Fe is the balance, along with unavoidable impurities; The alloy powder was prepared in advance and then atomized by vacuum nitrogen gas to produce powder with a particle size of 80-300 mesh.

2. The application according to claim 1, characterized in that, The alloy powder comprises the following components: C: 0.145~0.155wt% Mo: 2.95~3.05 wt% B: 0.27~0.32wt%; Si: 0.47~0.52wt% Mn: 0.05~0.25wt% Cu: 19.3~19.5 wt% Ni: 38.2~38.4 wt% Fe is the balance, along with unavoidable impurities.

3. The application according to claim 1, characterized in that, The alloy powder comprises the following components: C: 0.155wt% Mo: 3.05 wt% B: 0.32wt% Si: 0.52wt% Mn: 0.25wt% Cu: 19.5 wt% Ni: 38.4 wt% Fe is the balance, along with unavoidable impurities; Or may include the following ingredients: C: 0.145wt% Mo: 2.95 wt% B: 0.27wt% Si: 0.47wt% Mn: 0.05wt% Cu: 19.3 wt% Ni: 38.2 wt% Fe is the balance, along with unavoidable impurities.

4. A method for preparing alloy powder for use as described in any one of claims 1-3, characterized in that, Includes the following steps: S1 Batching: The composition of the alloy powder is designed according to the working environment and technical requirements, and the batching is carried out according to the composition; S2 smelting: The prepared alloy raw materials are added to a resistance crucible furnace and heated to 1490℃ to melt them into a liquid alloy. Then, slag removal and degassing are performed. S3 gas atomization and cooling: The above liquid alloy is heated to 1530℃, stirred thoroughly and kept at that temperature for 12 minutes; then it is poured into a ladle. When the liquid alloy flows to the liquid guide pipe below the ladle, it is broken up and atomized into solid powder by a nitrogen pressure spray gun with a pressure of 4.6 MPa. S4 Grading: After the powder cools to room temperature, use a grading sieve to sieve out alloy powder of 80~300 mesh, and then repackage and pack it.

5. A laser cladding method for improving the self-lubricating properties and reducing hardening sensitivity of large steam turbine rotor journals using alloy powder, characterized in that, Using the alloy powder as described in any one of claims 1-3, the steps include: 1) Remove the fatigue layer from the journal of the large steam turbine rotor by turning, and chamfer 30~60° at the beginning and end of turning; 2) The alloy powder is clad onto the surface of the rotor journal using a side-shaft powder feeding method. During laser cladding, the laser power is 9000~10000W, the linear speed is 10~11mm / s, the overlap rate is 38~42%, and the cladding thickness is controlled at 1.50~1.60mm. 3) After completing one layer of laser cladding, stop the laser, use a polishing wheel to brush away the slag on the cladding layer, and perform dye penetrant testing. If defects are found, the existing cladding layer needs to be machined off, and then return to step 2) to continue cladding. 4) If no defects are found during the flaw detection, the turbine rotor is sent to a heat treatment furnace for high-temperature tempering at a temperature of 580~620℃ for 280~300min. After tempering, it is air-cooled to room temperature. Then, the journal is subjected to dye penetrant testing again. If no defects are found, the cladding layer of the turbine rotor journal is machined to the required dimensional and positional tolerances and its hardness is tested.

6. The method according to claim 5, characterized in that, When performing laser multilayer cladding, dye penetrant testing must be performed after the previous layer is completed. Only after confirming that there are no defects can the next layer be claddinged.

7. The method according to claim 6, characterized in that, The thickness of the decarburized layer of the cladding layer is less than or equal to 0.50 mm.

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