Laser additive repairing method for 17-4PH turbine blade

Abstract

The invention discloses a laser additive repairing method for 17-4PH steam turbine blades, and relates to a laser repairing method for steam turbine blades. The method aims at solving the technical problem that in existing laser additive 17-4PH turbine blade repairing, the difference between the thermal expansion coefficient of Co-based corrosion-resistant alloy and the thermal expansion coefficient of 17-4PH alloy is large, and consequently the interface performance is reduced after repairing is conducted. According to the laser additive repairing method for the 17-4PH steam turbine blade, due to the fact that 17-4PH is poor in water erosion resistance, Co-based alloy powder is used for preparing a water erosion resistance structure, on the basis, in consideration of the problem that the performance difference of the Co-based alloy powder and the 17-4PH material is large, a powder component gradient transition mode is adopted, and the water erosion resistance of the 17-4PH steam turbine blade is greatly improved. The problem of low interfacial strength during direct transition is solved, the binding capacity of the Co-based water erosion resistant layer and the 17-4PH matrix is improved, and finally the service time of the 17-4PH blade is prolonged.

Description

TECHNICAL FIELD

[0001] The application relates to a laser repair method of a steam turbine blade. BACKGROUND

[0002] As core equipment in the field of power generation and driving, the steam turbine is an expensive and critical power component. The blade is long-term operated under the harsh working conditions of high temperature, high pressure and high speed, and is extremely prone to damage and failure at the blade tip and the inlet edge due to wear, corrosion, erosion and fatigue. The cost of replacing a new blade is extremely high, and the cycle is long, so the development of an efficient and reliable remanufacturing repair technology has great economic and technical value. In this context, laser additive repair technology (mainly laser cladding) emerged as the times require and gradually became a key solution in this field. Laser additive repair technology uses high-energy laser as a heat source, synchronously delivers metal powder matching the composition and performance of the blade substrate, and realizes three-dimensional forming by layer-by-layer cladding in the damaged area. Compared with traditional argon arc welding and other repair methods, the core advantages are: the heat input is extremely small, the energy input can be accurately controlled, the risk of heat-affected zone and deformation of the blade (usually martensitic stainless steel or precipitation-hardened stainless steel) is greatly reduced, and the performance decline caused by overheating is avoided; the metallurgical bonding quality is high, the cladding layer is dense and pore-free, and a firm metallurgical bond is formed with the substrate, and the performance can reach or even exceed that of the original substrate; the forming precision is high, the repair path and shape can be accurately controlled through a digital model, the subsequent mechanical processing allowance is greatly reduced, and the repair efficiency and quality consistency are improved. In the traditional repair of 17-4PH steam turbine blades, the target is usually small-area damage repair, and the repair material is mostly the substrate material. Co-based corrosion-resistant alloy has good corrosion resistance and good application prospect in the repair field of steam turbine blades. Due to the large difference in thermal expansion coefficient between the Co-based corrosion-resistant alloy and the 17-4PH alloy, the interface performance after repair is reduced, which limits the application of the Co-based corrosion-resistant alloy. SUMMARY

[0003] The application aims to solve the technical problem that the thermal expansion coefficient of the Co-based corrosion-resistant alloy is greatly different from that of the 17-4PH alloy in the existing laser additive 17-4PH steam turbine blade repair, resulting in reduced interface performance after repair, and provides a laser additive repair method of a 17-4PH steam turbine blade.

[0004] The laser additive repair method of the 17-4PH steam turbine blade of the application is performed according to the following steps:

[0005] I. Use a polishing tool to polish the surface to be repaired of the steam turbine blade to be flat, and then use alcohol to wipe the polished surface to be repaired clean;

[0006] II. Based on the length and width of the area to be repaired on the turbine blade, select the corresponding laser motion trajectory from the following two different trajectories:

[0007] The first method: When both the length and width of the area to be repaired are ≥10mm, additive repair is performed using a scanning method with adjacent layers rotated 90° (e.g., ...). Figure 1 );

[0008] The second method: When one of the length and width of the area to be repaired is less than 10mm, or both are less than 10mm, additive repair is performed using a unidirectional scanning method (i.e., without changing the scanning direction, such as...). Figure 2 );

[0009] Both of the above methods require further selection of the following process parameters based on the height of the area to be repaired:

[0010] When the height of the area to be repaired is ≤30mm, the repair area uses Co-based powder, brand name Stellite 6, with a powder particle size of 45μm~105μm; the laser power is 1200W, the scanning speed is 0.9mm / s, the single-channel transverse shift is 0.9mm, the single-layer lift is 0.7mm, the powder feed rate is 6.5g / min, the flow rate of the coaxial protective gas is 12L / min, and the flow rate of the powder-carrying gas is 10L / min;

[0011] When the height of the area to be repaired is greater than 30mm, a gradient transition layer is used for repair, specifically:

[0012] Both the first and second layers use a mixture of 17-4 PH and Stellite 6 powders, with particle sizes ranging from 45 μm to 105 μm. The volume ratio of 17-4 PH powder to Stellite 6 powder is 3:1. The process parameters used are: laser power of 900 W, scanning speed of 0.9 mm / s, single-pass transverse shift of 0.8 mm, single-layer lift of 0.7 mm, powder feed rate of 6.5 g / min, coaxial protective gas flow rate of 12 L / min, and powder carrier gas flow rate of 10 L / min.

[0013] The third and fourth layers both use a mixture of 17-4 PH and Stellite 6 powders, with particle sizes ranging from 45 μm to 105 μm. The volume ratio of 17-4 PH powder to Stellite 6 powder is 1:1. The process parameters used are: laser power of 1000 W, scanning speed of 0.9 mm / s, single-pass transverse shift of 0.85 mm, single-layer lift of 0.7 mm, powder feed rate of 6.5 g / min, coaxial protective gas flow rate of 12 L / min, and powder carrier gas flow rate of 10 L / min.

[0014] The fifth and sixth layers both use a mixture of 17-4 PH and Stellite 6 powders, with particle sizes ranging from 45 μm to 105 μm. The volume ratio of 17-4 PH powder to Stellite 6 powder is 1:3. The process parameters used are: laser power of 1100 W, scanning speed of 0.9 mm / s, single-pass transverse shift of 0.9 mm, single-layer lift of 0.7 mm, powder feed rate of 6.5 g / min, coaxial protective gas flow rate of 12 L / min, and powder carrier gas flow rate of 10 L / min.

[0015] Subsequent layers all used only Stellite 6 powder with a particle size of 45μm~105μm. The laser process parameters used were: laser power of 1200W, scanning speed of 0.9mm / s, single-pass transverse shift of 0.9mm, single-layer lift of 0.7mm, powder feed rate of 6.5g / min, coaxial protective gas flow rate of 12L / min, and powder carrier gas flow rate of 10L / min.

[0016] Third, determine the process parameters according to the above requirements, and then start the laser additive repair from the surface to be repaired after step one.

[0017] In this invention, when the length and width of the area to be repaired are both ≥10mm, an additive repair is performed by scanning with adjacent layers rotated by 90° (rotation direction is not restricted). The rotation of adjacent layers is to reduce interlayer stress during the repair process. However, the robot's stability is poor when the robot's stroke is short. Therefore, it is necessary to ensure that the robot's single scan stroke is ≥10mm. So, the scanning method of rotating adjacent layers by 90° can only be performed when the length and width are both ≥10mm. Otherwise, unidirectional scanning can only be performed along the long side.

[0018] In the laser additive repair method for turbine blades of the present invention, when the height of the area to be repaired is >30mm, the proportion of 17-4 PH powder in the mixed powder of 17-4 PH powder and Stellite 6 gradually decreases from the first layer of the repair layer, and different process parameters are applied for powders with different ratios. The presence of the gradient transition layer can significantly reduce the difference in thermal expansion coefficients between the 17-4 PH blade substrate and the Stellite 6 repair layer, thereby ensuring the bonding performance of the repair layer and improving the service performance of the turbine blade. When the height of the area to be repaired is ≤30mm, the interfacial stress during the repair process is small, and the impact on the interfacial bonding is small, so there is no need to use a gradient transition form.

[0019] In the laser additive repair method for 17-4 PH turbine blades of the present invention, since 17-4 PH has poor water erosion resistance, Co-based alloy powder is used to prepare the water erosion resistant structure. On this basis, considering the large difference in performance between Co-based alloy powder and 17-4 PH material, a gradient transition of powder composition is adopted to solve the problem of low interface strength during direct transition, improve the bonding ability between Co-based water erosion resistant layer and 17-4 PH matrix, and ultimately extend the service life of 17-4 PH blades. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the additive repair process performed in step two of the present invention, using a scanning method with adjacent layers rotated by 90°.

[0021] Figure 2 This is a schematic diagram illustrating the additive repair process performed using a unidirectional scanning method in step two of the present invention.

[0022] Figure 3 This is a photograph of the repaired turbine blade after a tensile test along the additive manufacturing direction in Experiment 1.

[0023] Figure 4 The photo shows the turbine blades after they were repaired during the comparison test. Detailed Implementation

[0024] Specific Implementation Method 1: This implementation method is a laser additive repair method for 17-4 PH steam turbine blades, specifically carried out according to the following steps:

[0025] 1. Use a grinding tool to grind the surface of the turbine blade to be repaired until it is smooth, and then wipe the ground surface clean with alcohol.

[0026] II. Based on the length and width of the area to be repaired on the turbine blade, select the corresponding laser motion trajectory from the following two different trajectories:

[0027] The first method: When the length and width of the area to be repaired are both ≥10mm, additive repair is performed by scanning with adjacent layers rotated by 90°.

[0028] The second method: When one of the length and width of the area to be repaired is less than 10mm or both are less than 10mm, additive repair is performed using a unidirectional scanning method.

[0029] Both of the above methods require further selection of the following process parameters based on the height of the area to be repaired:

[0030] When the height of the area to be repaired is ≤30mm, the repair area uses Co-based powder, brand name Stellite 6, with a powder particle size of 45μm~105μm; the laser power is 1200W, the scanning speed is 0.9mm / s, the single-channel transverse shift is 0.9mm, the single-layer lift is 0.7mm, the powder feed rate is 6.5g / min, the flow rate of the coaxial protective gas is 12L / min, and the flow rate of the powder-carrying gas is 10L / min;

[0031] When the height of the area to be repaired is greater than 30mm, a gradient transition layer is used for repair, specifically:

[0032] Both the first and second layers use a mixture of 17-4 PH and Stellite 6 powders, with particle sizes ranging from 45 μm to 105 μm. The volume ratio of 17-4 PH powder to Stellite 6 powder is 3:1. The process parameters used are: laser power of 900 W, scanning speed of 0.9 mm / s, single-pass transverse shift of 0.8 mm, single-layer lift of 0.7 mm, powder feed rate of 6.5 g / min, coaxial protective gas flow rate of 12 L / min, and powder carrier gas flow rate of 10 L / min.

[0033] The third and fourth layers both use a mixture of 17-4 PH and Stellite 6 powders, with particle sizes ranging from 45 μm to 105 μm. The volume ratio of 17-4 PH powder to Stellite 6 powder is 1:1. The process parameters used are: laser power of 1000 W, scanning speed of 0.9 mm / s, single-pass transverse shift of 0.85 mm, single-layer lift of 0.7 mm, powder feed rate of 6.5 g / min, coaxial protective gas flow rate of 12 L / min, and powder carrier gas flow rate of 10 L / min.

[0034] The fifth and sixth layers both use a mixture of 17-4 PH and Stellite 6 powders, with particle sizes ranging from 45 μm to 105 μm. The volume ratio of 17-4 PH powder to Stellite 6 powder is 1:3. The process parameters used are: laser power of 1100 W, scanning speed of 0.9 mm / s, single-pass transverse shift of 0.9 mm, single-layer lift of 0.7 mm, powder feed rate of 6.5 g / min, coaxial protective gas flow rate of 12 L / min, and powder carrier gas flow rate of 10 L / min.

[0035] Subsequent layers all used only Stellite 6 powder with a particle size of 45μm~105μm. The laser process parameters used were: laser power of 1200W, scanning speed of 0.9mm / s, single-pass transverse shift of 0.9mm, single-layer lift of 0.7mm, powder feed rate of 6.5g / min, coaxial protective gas flow rate of 12L / min, and powder carrier gas flow rate of 10L / min.

[0036] Third, determine the process parameters according to the above requirements, and then start the laser additive repair from the surface to be repaired after step one.

[0037] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the material of the turbine blades mentioned in step one is 17-4 PH. Everything else is the same as in Specific Implementation Method One.

[0038] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the grinding tool mentioned in step one is an angle grinder. Everything else is the same as in Specific Implementation Method One or Two.

[0039] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the elemental composition of the Co-based powder mentioned in step two is: 1%~1.4% C, 0.8%~1.2% Si, 28%~32% Cr, 0.8%~1.8% Fe, 2%~3% Ni, 4%~5% W, with the balance being Co. Everything else is the same as in Specific Implementation Methods One to Three.

[0040] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Four in that all protective gases used in step two are argon. Everything else is the same as in Specific Implementation Method Four.

[0041] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Five in that all powder-carrying gases in step two are argon. Everything else is the same as in Specific Implementation Method Five.

[0042] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method Six in that the particle size of all 17-4PH powder and Stellite 6 powder in step two is 60μm~80μm. Everything else is the same as in Specific Implementation Method Six.

[0043] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that the defocusing amount of the laser in step three is +15mm. Everything else is the same as in Specific Implementation Method Seven.

[0044] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Eight in that the wavelength of the laser in step three is 1064nm. Everything else is the same as in Specific Implementation Method Eight.

[0045] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method Nine in that the laser type in step three is a continuous laser. Everything else is the same as in Specific Implementation Method Nine.

[0046] The invention was verified using the following experiments:

[0047] Experiment 1: This experiment demonstrates a laser additive repair method for 17-4 PH steam turbine blades, specifically carried out according to the following steps:

[0048] 1. Use a grinding tool to grind the surface of the turbine blade to be repaired until smooth, and then wipe the ground surface clean with alcohol; the material of the turbine blade is 17-4 PH; the grinding tool is an angle grinder;

[0049] II. The area to be repaired has a height of 45mm, a length of 40mm, and a width of 8mm. Additive repair is performed using a unidirectional scanning method; a gradient transition layer method is used for repair, specifically:

[0050] Both the first and second layers use a mixture of 17-4 PH and Stellite 6 powders, with particle sizes ranging from 45 μm to 105 μm. The volume ratio of 17-4 PH powder to Stellite 6 powder is 3:1. The process parameters used are: laser power of 900 W, scanning speed of 0.9 mm / s, single-pass transverse shift of 0.8 mm, single-layer lift of 0.7 mm, powder feed rate of 6.5 g / min, coaxial protective gas flow rate of 12 L / min, and powder carrier gas flow rate of 10 L / min.

[0051] The third and fourth layers both use a mixture of 17-4 PH and Stellite 6 powders, with particle sizes ranging from 45 μm to 105 μm. The volume ratio of 17-4 PH powder to Stellite 6 powder is 1:1. The process parameters used are: laser power of 1000 W, scanning speed of 0.9 mm / s, single-pass transverse shift of 0.85 mm, single-layer lift of 0.7 mm, powder feed rate of 6.5 g / min, coaxial protective gas flow rate of 12 L / min, and powder carrier gas flow rate of 10 L / min.

[0052] The fifth and sixth layers both use a mixture of 17-4 PH and Stellite 6 powders, with particle sizes ranging from 45 μm to 105 μm. The volume ratio of 17-4 PH powder to Stellite 6 powder is 1:3. The process parameters used are: laser power of 1100 W, scanning speed of 0.9 mm / s, single-pass transverse shift of 0.9 mm, single-layer lift of 0.7 mm, powder feed rate of 6.5 g / min, coaxial protective gas flow rate of 12 L / min, and powder carrier gas flow rate of 10 L / min.

[0053] Subsequent layers all used only Stellite 6 powder with a particle size of 45μm~105μm. The laser process parameters used were: laser power of 1200W, scanning speed of 0.9mm / s, single-pass transverse shift of 0.9mm, single-layer lift of 0.7mm, powder feed rate of 6.5g / min, coaxial protective gas flow rate of 12L / min, and powder carrier gas flow rate of 10L / min.

[0054] In step two, all protective gases are argon; in step two, all powder carrier gases are argon.

[0055] Third, determine the process parameters according to the above requirements, and then start laser additive repair from the surface to be repaired after step one. The defocusing amount is +15mm, the laser wavelength is 1064nm, the type is continuous laser, and the laser is infrared laser.

[0056] A pair of repaired turbine blades were subjected to tensile tests along the additive manufacturing direction. Figure 3 As shown in the figure, the area between the two black dashed lines is the gradient transition layer. Above the gradient transition layer is the Stellite 6 deposited layer, and below is the 17-4 PH matrix. The fracture can be seen on the 17-4 PH side of the matrix (the black arrow in the figure indicates the fracture point), proving that the presence of the gradient transition layer alleviates the difference in thermal expansion coefficients between the two, achieving good metallurgical bonding. The tensile strength is 935 MPa. The figure also shows that no cracks were observed after additive manufacturing when the gradient transition layer was added.

[0057] Comparative Experiment: The difference between this experiment and Experiment 1 is that a gradient transition layer was not used in step 2. Instead, Stellite 6 cobalt-based alloy powder was added to the 17-4PH substrate. The powder particle size was 45μm~105μm. Everything else was the same as Experiment 1. Figure 4 The photograph of the repaired turbine blade reveals that cracks had already formed at the interface between the blade and the substrate due to thermal stress during the additive manufacturing process. Penetrant testing after the additive manufacturing was completed showed color-coded areas at the interface, confirming the presence of the cracks. The results were significantly less effective than using a gradient transition layer.

Claims

1. A laser additive repair method for 17-4 PH steam turbine blades, characterized in that... The method is performed according to the following steps:

1. Use a grinding tool to grind the surface of the turbine blade to be repaired until it is smooth, and then wipe the ground surface clean with alcohol. II. Based on the length and width of the area to be repaired on the turbine blade, select the corresponding laser motion trajectory from the following two different trajectories: The first method: When the length and width of the area to be repaired are both ≥10mm, additive repair is performed by scanning with adjacent layers rotated by 90°. The second method: When one of the length and width of the area to be repaired is less than 10mm or both are less than 10mm, additive repair is performed using a unidirectional scanning method. Both of the above methods require further selection of the following process parameters based on the height of the area to be repaired: When the height of the area to be repaired is ≤30mm, the repair area uses Co-based powder, brand name Stellite 6, with a powder particle size of 45μm~105μm; the laser power is 1200W, the scanning speed is 0.9mm / s, the single-channel transverse shift is 0.9mm, the single-layer lift is 0.7mm, the powder feed rate is 6.5g / min, the flow rate of the coaxial protective gas is 12L / min, and the flow rate of the powder-carrying gas is 10L / min; When the height of the area to be repaired is greater than 30mm, a gradient transition layer is used for repair, specifically: Both the first and second layers use a mixture of 17-4 PH and Stellite 6 powders, with particle sizes ranging from 45 μm to 105 μm. The volume ratio of 17-4 PH powder to Stellite 6 powder is 3:

1. The process parameters used are: laser power of 900 W, scanning speed of 0.9 mm / s, single-pass transverse shift of 0.8 mm, single-layer lift of 0.7 mm, powder feed rate of 6.5 g / min, coaxial protective gas flow rate of 12 L / min, and powder carrier gas flow rate of 10 L / min. The third and fourth layers both use a mixture of 17-4 PH and Stellite 6 powders, with particle sizes ranging from 45 μm to 105 μm. The volume ratio of 17-4 PH powder to Stellite 6 powder is 1:

1. The process parameters used are: laser power of 1000 W, scanning speed of 0.9 mm / s, single-pass transverse shift of 0.85 mm, single-layer lift of 0.7 mm, powder feed rate of 6.5 g / min, coaxial protective gas flow rate of 12 L / min, and powder carrier gas flow rate of 10 L / min. The fifth and sixth layers both use a mixture of 17-4 PH and Stellite 6 powders, with particle sizes ranging from 45 μm to 105 μm. The volume ratio of 17-4 PH powder to Stellite 6 powder is 1:

3. The process parameters used are: laser power of 1100 W, scanning speed of 0.9 mm / s, single-pass transverse shift of 0.9 mm, single-layer lift of 0.7 mm, powder feed rate of 6.5 g / min, coaxial protective gas flow rate of 12 L / min, and powder carrier gas flow rate of 10 L / min. Subsequent layers all used only Stellite 6 powder with a particle size of 45μm~105μm. The laser process parameters used were: laser power of 1200W, scanning speed of 0.9mm / s, single-pass transverse shift of 0.9mm, single-layer lift of 0.7mm, powder feed rate of 6.5g / min, coaxial protective gas flow rate of 12L / min, and powder carrier gas flow rate of 10L / min. Third, determine the process parameters according to the above requirements, and then start the laser additive repair from the surface to be repaired after step one.

2. The laser additive repair method for 17-4 PH turbine blades according to claim 1, characterized in that... The turbine blades mentioned in step one are made of 17-4 PH material.

3. The laser additive repair method for 17-4 PH turbine blades according to claim 1, characterized in that... The grinding tool mentioned in step one is an angle grinder.

4. The laser additive repair method for 17-4 PH turbine blades according to claim 1, characterized in that... The elemental composition of the Co-based powder mentioned in step two is as follows: 1%~1.4% C, 0.8%~1.2% Si, 28%~32% Cr, 0.8%~1.8% Fe, 2%~3% Ni, 4%~5% W, and the balance is Co.

5. The laser additive repair method for 17-4 PH turbine blades according to claim 1, characterized in that... In step two, all protective gases are argon.

6. The laser additive repair method for 17-4 PH turbine blades according to claim 1, characterized in that... In step two, all the powder carrier gases are argon.

7. The laser additive repair method for 17-4 PH turbine blades according to claim 1, characterized in that... In step two, all 17-4 PH powder and Stellite 6 powder have a particle size of 60 μm to 80 μm.

8. The laser additive repair method for 17-4 PH turbine blades according to claim 1, characterized in that... In step three, the laser defocusing amount is +15mm.

9. The laser additive repair method for a 17-4 PH steam turbine blade according to claim 8, characterized in that... In step three, the wavelength of the laser is 1064nm.

10. The laser additive repair method for a 17-4 PH steam turbine blade according to claim 9, characterized in that... The laser type in step three is a continuous laser.

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