A method for preparing a high-plasticity and toughness 1CrMo alloy repair layer by laser additive and post-heat treatment composite process

Abstract

The invention discloses a method for preparing a high-plasticity and toughness 1CrMo alloy repair layer by a composite process of laser additive manufacturing and post-heat treatment. The method first prepares the 1CrMo alloy repair layer under the coordination of laser additive manufacturing parameters, and the repair layer has the characteristics of metallurgical bonding with a substrate, uniform structure, no pores, crack defects, low hardness, and a bainite-like structure; then, the repair layer is subjected to tempering heat treatment to obtain a tempered bainite structure, thereby obtaining a high-performance repair layer with both high strength and high plasticity; the invention solves the problem that it is difficult to achieve matching of high strength and high plasticity and toughness in laser additive manufacturing alloys, eliminates the boundary existence phenomenon of laser additive manufacturing, and the method is simple and practical, has high production efficiency, is pollution-free, and is economical.

Description

Technical Field

[0001] The present invention relates to the field of metal material science and laser additive repair technology, and in particular to a method for preparing a high-plasticity and toughness 1CrMo alloy repair layer by a laser additive and post-heat treatment composite process. Background Art

[0002] Steam turbine rotor parts in the field of energy and power engineering are large in size and have a long production cycle. Once damaged during operation, the cost of replacing a new shaft is high and the cycle is long, which will lead to production interruptions and cause huge economic losses. If they can be repaired, the economic losses will be recovered and production will be resumed quickly. The operating conditions of rotor parts are complex. They often run at high speed under high temperature, high pressure, and complex stress conditions. They are prone to wear, burrs, and fractures. Therefore, the mechanical properties of the repaired rotors are required to be high, and the plasticity and strength are required to meet the matrix performance requirements. In addition, fracture toughness is an important indicator to measure the toughness performance of materials. Meeting the fracture toughness standards after matrix repair can avoid sudden instability and fracture of parts during operation and avoid accidents. Therefore, it is very important to ensure that the fracture toughness performance of the repaired material meets the standards.

[0003] Traditional repair technologies such as welding, thermal spraying, and brush plating have disadvantages such as large heat-affected zones, low efficiency, and low bonding strength, making it difficult to meet repair requirements. Laser additive repair technology (LAM) based on laser cladding or laser metal deposition technology uses a high-energy laser beam as a heat source and adopts synchronous powder feeding to achieve three-dimensional forming of parts through a layer-by-layer stacking method. Combining LAM technology with traditional subtractive (milling) technology can achieve the repair of metal parts. This technology has the characteristics of high flexibility, flexible process, small thermal impact on the repaired parts, high strength recovery of the repaired parts, short cycle, and high efficiency. It is particularly suitable for the repair of large rotor shafts that are subjected to various stress composite effects during operation and have high requirements for repair quality and construction period.

[0004] Currently, the types of materials used for laser repair of turbine rotor steel on the market are very rare and expensive, and the fracture toughness performance after repair is poor. In addition, it is difficult to achieve high strength and high plasticity matching in laser additive manufacturing alloys, that is, it is difficult to achieve both at the same time, generally high strength and poor plasticity, or high plasticity and low strength. The present invention uses a reasonable laser additive and post-heat treatment composite process to provide an ideal solution for the high plasticity and toughness of the material after laser additive. The method also has the characteristics of simple and practical method, high production efficiency, no pollution, economical and practical, and application value. At present, after laser additive repair of turbine rotor shaft, the method of using reasonable post-heat treatment means to adjust the organizational structure and mechanical properties has not been seen, and a reasonable heat treatment process remains to be studied. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a high-plasticity and toughness 1CrMo alloy repair layer by a composite process of laser additive manufacturing and post-heat treatment. By optimizing the parameters of laser additive manufacturing such as laser power, scanning speed, powder feeding amount, powder feeding carrier gas flow rate, shielding gas flow rate, overlap rate, etc., and combining with a reasonable subsequent heat treatment process to control the organization, an alloy material with both high strength and high plasticity is finally prepared.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing a high-plasticity and toughness 1CrMo alloy repair layer by a laser additive and post-heat treatment composite process, the method comprising:

[0008] The iron-based alloy powder is dried (100-200°C) and then placed in a powder feeder, and the sample to be repaired is placed under the laser for laser additive repair operation, followed by heat treatment to complete the repair;

[0009] The process parameters of the laser additive repair operation are: laser power 1900-2700W, laser scanning speed 240-440mm / min, spot diameter 4mm, powder feeding amount 8-12g / min, the powder feeding method of the iron-based alloy powder is synchronous coaxial feeding, the powder feeding carrier gas is high-purity argon (Ar, 99%), and the protective gas is high-purity argon (Ar, 99%); the thickness of the single-layer repair layer is between 0.5 and 1.5mm;

[0010] The process parameters of the heat treatment are: quenching temperature 970°C, quenching time 10min, quenching cooling method oil cooling; tempering temperature 580-680°C, tempering time 15min-2h, tempering cooling method air cooling; by changing the tempering heating temperature and holding time of the quenching and tempering heat treatment, the tempered troostite structure can be obtained, and the grain size of the equiaxed ferrite can be adjusted to improve the plasticity;

[0011] The iron-based alloy powder is composed of: carbon C: 0.05-0.15%, chromium Cr: 1.0-1.5%, silicon Si: 0.5-1.0%, manganese Mn: 0.6-1.0%, molybdenum Mo: 0.5-1.5%, oxygen O: ≤0.05%, phosphorus P: ≤0.015%, sulfur S: ≤0.03%, and the balance Fe;

[0012] Preferably, the composition of the iron-based alloy powder is: carbon C: 0.15%, chromium Cr: 1.5%, silicon Si: 0.8%, manganese Mn: 0.8%, molybdenum Mo: 1.5%, oxygen O: 0.02%, phosphorus P: 0.01%, sulfur S: 0.03%, iron Fe: 95.19%;

[0013] Also preferably, the composition of the iron-based alloy powder is: carbon C: 0.08%, chromium Cr: 1.0%, silicon Si: 0.5%, manganese Mn: 0.8%, molybdenum Mo: 0.7%, oxygen O: 0.02%, phosphorus P: 0.01%, sulfur S: 0.03%, iron Fe: 96.86%;

[0014] The iron-based alloy powder can be obtained by vacuum induction melting-inert gas atomization; the obtained alloy powder is subjected to vibration screening or airflow classification to prepare alloy powder for laser cladding additive repair process;

[0015] The iron-based alloy powder has an oxygen content of less than 600 ppm, a hollow powder rate based on quantity of less than 3%, a powder particle size between -140 and +325 meshes, and a powder bulk density between 3 and 6 g / cm 2 The liquidity is between 12 and 18 seconds.

[0016] The method of the present invention can be used to repair damaged surfaces of turbine rotor parts. By properly optimizing laser additive manufacturing parameters such as laser power, scanning speed, powder feeding amount, powder feeding carrier gas flow rate, shielding gas flow rate, overlap rate, etc., a repair layer can be obtained that is metallurgically bonded to the substrate, has a uniform structure, is free of pores and crack defects, and has a low hardness.

[0017] The repair layer laser additive manufacturing 1CrMo alloy structure is troostite (acicular ferrite + carbide), and there is a boundary morphology. The existence of the boundary morphology will have an adverse effect on the mechanical properties. Then, combined with a reasonable subsequent heat treatment process, the temperature can be raised to A C3 In the above, the boundary structure is eliminated, and finally an alloy material with both high strength and high plasticity is prepared.

[0018] The microhardness range of the alloy repair layer sample is: 240~270HV 0.3 , tensile strength range: 744 ~ 903MPa, elongation range: 16.3 ~ 21.9%, section shrinkage range: 31 ~ 48%, impact absorption energy range: 148 ~ 197J, fracture toughness range: 179 ~ 246kJ / m 2 .

[0019] After heat treatment, the tensile strength ranges from 618 to 780 MPa, the elongation after fracture ranges from 16.1 to 23.3%, the cross-sectional shrinkage ranges from 45 to 59%, and the fracture toughness ranges from 179 kJ / m 2 Increased to 240kJ / m 2 .

[0020] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in:

[0021] 1. The present invention adopts the alloy powder and the application method thereof, and can obtain a repair layer containing specific alloy elements, free of pore crack defects, good comprehensive mechanical properties, especially good fracture toughness performance under a wide range of process parameters. The laser additive operation process is flexible, repeatable and efficient. Compared with traditional technologies such as submerged arc cladding, it has great advantages and can be fully used for laser additive repair of turbine rotor equipment.

[0022] 2. The process parameters selected in the heat treatment process of the present invention can effectively eliminate the boundary morphology characteristics common to conventional laser additive manufacturing alloys. The existence of the boundary will have an adverse effect on the performance of the sample.

[0023] 3. The present invention obtains tempered martensite structure after heat treatment. By increasing the tempering time and tempering temperature, the structure can be adjusted, the ferrite size can be coarsened, and the plasticity of the alloy can be improved. The problem of high strength and high plasticity of conventional laser additive manufacturing alloys is difficult to match, and the plasticity and toughness of laser additive manufacturing alloys are improved while ensuring strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the uncorroded metallographic structure of the iron-based alloy powder described in Example 3.

[0025] Figure 2 This is the organizational morphology of the iron-based alloy powder described in Example 4.

[0026] Figure 3 This is the XRD of the iron-based alloy powder described in Example 4.

[0027] Figure 4 This is an optical microscope metallographic structure picture of the three-layer repair layer in Example 3.

[0028] Figure 5 This is the microhardness of the three-layer repair layer in Example 3.

[0029] Figure 6 This is a picture of the metallographic structure of the three-layer repair layer of Example 6 after heat treatment.

[0030] Figure 7 This is the boundary morphology of the repair layer in Example 6 before and after heat treatment. DETAILED DESCRIPTION

[0031] The present invention is further described below by means of specific embodiments, but the protection scope of the present invention is not limited thereto.

[0032] Example 1

[0033] The alloy powder elements in this embodiment are as follows:

[0034] Carbon C: 0.15%, chromium Cr: 1.5%, silicon Si: 0.8%, manganese Mn: 0.8%, molybdenum Mo: 1.5%, oxygen O: 0.02%, phosphorus P: 0.01%, sulfur S: 0.03%, iron Fe: 95.19%.

[0035] Example 2

[0036] The alloy powder elements in this embodiment are as follows:

[0037] Carbon C: 0.08%, chromium Cr: 1.0%, silicon Si: 0.5%, manganese Mn: 0.8%, molybdenum Mo: 0.7%, oxygen O: 0.02%, phosphorus P: 0.01%, sulfur S: 0.03%, iron Fe: 96.86%.

[0038] Example 3 Laser additive manufacturing of the iron-based alloy powder described in Example 1

[0039] The iron-based alloy powder for laser additive surface modification described in Example 1 was used for metallographic and scanning electron microscopic observations. Figure 1 As shown, the powder has fewer pores, and the laser spot used subsequently is a circular spot with a diameter of 4 mm. The alloy powder is fed by synchronous coaxial conveying.

[0040] The iron-based alloy powder for laser additive surface modification described in Example 1 is placed in an oven at 100-200° C. for heat preservation until dried and then placed in a powder feeder;

[0041] Place the sample block after overall cutting under the laser and adjust the laser position to the area to be processed;

[0042] The laser process parameters are set as follows:

[0043] The laser power is set to 1900W, the scanning speed is 240mm / min, the powder feeding amount is 8g / min, the powder feeding carrier gas flow rate is 800L / h, the protective gas flow rate is 12L / min, and the overlap rate is 45%.

[0044] The laser power is set to 2100W, the scanning speed is 280mm / min, the powder feeding amount is 9g / min, the powder feeding carrier gas flow rate is 800L / h, the protective gas flow rate is 12L / min, and the overlap rate is 45%.

[0045] The laser power is 2300W, the scanning speed is 340mm / min, the powder feeding amount is 10g / min, the powder feeding carrier gas flow rate is 800L / h, the protective gas flow rate is 12L / min, and the overlap rate is 45%.

[0046] The laser power is 2500W, the scanning speed is 380mm / min, the powder feeding amount is 11g / min, the powder feeding carrier gas flow rate is 800L / h, the protective gas flow rate is 12L / min, and the overlap rate is 45%.

[0047] The laser power is 2700W, the scanning speed is 440mm / min, the powder feeding amount is 12g / min, the powder feeding carrier gas flow rate is 800L / h, the protective gas flow rate is 12L / min, and the overlap rate is 45%.

[0048] Through sample preparation and observation, the repair layer has a dense structure, a troostite-like structure, and no defects such as pores, inclusions, and cracks. Figure 4 shown.

[0049] The hardness of the repair layer was tested using a Hv-1000 Vickers microhardness tester. The test results are as follows: Figure 5 As shown in the figure, in the single-pass and single-layer additive test, the hardness of the repair layer is in an unstable state. After reaching three layers, it gradually stabilizes. Starting from the substrate surface, as the distance increases, the hardness of the repair layer gradually decreases. The hardness of the three-layer laser additive repair layer is 240HV 0.3 ~270HV 0.3 Between, in line with the design standards.

[0050] After a large number of experiments, the laser additive process parameters were selected as described in Table 1. Satisfactory repair layers could be obtained under the laser additive process parameters described in Table 1.

[0051] Table 1 Optimal process parameters for laser additive manufacturing

[0052]

[0053] Example 4 Laser additive manufacturing of the iron-based alloy powder described in Example 2

[0054] The powder used in this embodiment is the alloy powder of Embodiment 2, and the additive process parameters are the same as those of Embodiment 3, except for the alloy element content.

[0055] The alloy powder of Example 2 was prepared metallographically, and the metallographic structure of the powder was as follows: Figure 2 As shown, the presence of ferrite can be found from the figure.

[0056] The alloy powder of Example 2 was subjected to XRD test, and its XRD diffraction pattern is as follows: Figure 3 As shown in the graph, it is found that the repair layer is mainly composed of α-Fe, Fe 19 It is composed of Mn, (Fe-Cr), CrSi4, CrFeSSi, etc.

[0057] Example 5

[0058] The process parameters are selected as laser power 2300W, scanning speed 340mm / min, powder feeding amount 10g / min, repair layer thickness 0.7mm, and spot size 4mm. The iron-based alloy powder of Example 1-2 was subjected to tensile and impact tests after material addition. The specific values ​​are as follows: Samples were taken from the workpiece after material addition, and the tensile and impact toughness tests of the repair layer were tested respectively. The results are shown in Table 2 and Table 3 respectively. They are all taken from the control experiment conducted under the same parameters above.

[0059] Table 2 Repair layer tensile test results

[0060]

[0061] Table 3 Repair layer impact test results

[0062]

[0063] According to the test results, the average tensile strength of the repair layer of Example 1 is 880MPa, and the average tensile strength of the repair layer of Example 2 is 764MPa; the average elongation after fracture of the repair layer of Example 1 is 17.9%, and the average elongation after fracture of the repair layer of Example 2 is 20.4%; the average cross-sectional shrinkage rate of the repair layer of Example 1 is 33%, and the average cross-sectional shrinkage rate of the repair layer of Example 2 is 42%. From the above data, it can be seen that the repair layers of Example 1 and Example 2 ensure their plasticity indicators while ensuring strength. The average impact absorption energy of the repair layer material of Example 1 reaches 154J, and the average impact absorption energy of the repair layer material of Example 2 reaches 191J. In addition, the troostite-like structure of the repair layer has good toughness and plasticity, as well as high strength, enabling it to work under more complex load conditions.

[0064] Example 6

[0065] The iron-based alloy powder of Example 1 was heat treated after laser additive repair. By adjusting the heat treatment parameters reasonably, the tensile properties of the sample after heat treatment and the fracture toughness properties before and after heat treatment were tested and analyzed.

[0066] The heat treatment process parameters are set as follows:

[0067] The quenching temperature is 970℃, the quenching time is 10min, the quenching cooling method is oil cooling, the tempering temperature is 580℃, the tempering time is 15min, and the tempering cooling method is air cooling.

[0068] The quenching temperature is 970℃, the quenching time is 10min, the quenching cooling method is oil cooling, the tempering temperature is 640℃, the tempering time is 15min, and the tempering cooling method is air cooling.

[0069] The quenching temperature is 970℃, the quenching time is 10min, the quenching cooling method is oil cooling, the tempering temperature is 680℃, the tempering time is 15min, and the tempering cooling method is air cooling.

[0070] The quenching temperature is 970℃, the quenching time is 10min, the quenching cooling method is oil cooling, the tempering temperature is 640℃, the tempering time is 1H, and the tempering cooling method is air cooling.

[0071] The quenching temperature is 970℃, the quenching time is 10min, the quenching cooling method is oil cooling, the tempering temperature is 640℃, the tempering time is 2H, and the tempering cooling method is air cooling.

[0072] Through sample preparation and observation, the repair layer has a dense structure, a tempered martensite structure, and no defects such as pores, inclusions, and cracks. Figure 6 As shown in the figure, with the increase of tempering temperature and tempering time, the equiaxed ferrite in the tempered troostite complex structure recovers and the ferrite grain size increases. Small carbide particles dissolve, large carbide particles aggregate and grow, the carbide dispersion strengthening effect on the matrix is ​​weakened, the plasticity of the laser additive manufacturing alloy increases, and the strength decreases. Through heat treatment, the boundary morphology of the laser additive manufacturing alloy disappears. The boundary morphology before and after heat treatment is as follows: Figure 7 The tensile properties after heat treatment are shown in Table 4, and the fracture toughness before and after heat treatment are shown in Table 5. T1' to T5' are the results obtained after the above heat treatment of the samples under the parameters in Example 5. The I3' sample is obtained after the heat treatment at 680℃+15min under the parameters in Example 5.

[0073] Table 4 Test results of tensile properties of repaired layer after heat treatment

[0074]

[0075] Table 5 Fracture toughness test results of repaired layer before and after heat treatment

[0076]

[0077] According to the test results, the tensile strength of the tensile specimen after heat treatment is in the range of 618-780 MPa, the elongation after fracture is in the range of 16.1-23.3%, and the reduction of area is in the range of 45-59%. 1C =179kJ / m 2 , the fracture toughness J of the repair layer material of Example 2 1C =246kJ / m 2 Example 1 was heat treated, and the fracture toughness J of Example 1 after heat treatment was 1C =240kJ / m 2 , the repair layer specimens were all broken, meeting the matrix repair requirements.

Claims

1. A method for preparing a high-plasticity and toughness 1CrMo alloy repair layer by a laser additive and post-heat treatment composite process for repairing damaged surfaces of steam turbine rotor parts, characterized in that: The method is: After drying the iron-based alloy powder, put it into the powder feeder, place the sample to be repaired under the laser for laser additive repair operation, and then perform heat treatment to complete the repair; The process parameters of the laser additive repair operation are: laser power 1900-2700W, laser scanning speed 240-440mm / min, spot diameter 4mm, powder feeding amount 8-12g / min, iron-based alloy powder feeding method is synchronous coaxial feeding, powder feeding carrier gas is high-purity argon gas, and protective gas is high-purity argon gas; the thickness of a single-layer repair layer is between 0.5 and 1.5mm; The process parameters of the heat treatment are: quenching temperature 970°C, quenching time 10min, quenching cooling method oil cooling; tempering temperature 580-680°C, tempering time 15min-2h, tempering cooling method air cooling; The iron-based alloy powder comprises: carbon C: 0.05-0.15%, chromium Cr: 1.0-1.5%, silicon Si: 0.5-1.0%, manganese Mn: 0.6-1.0%, molybdenum Mo: 0.5-1.5%, oxygen O: ≤0.05%, phosphorus P: ≤0.015%, sulfur S: ≤0.03%, and the balance Fe.

2. The method for preparing a high-plasticity and toughness 1CrMo alloy repair layer by a laser additive and post-heat treatment composite process for repairing damaged surfaces of steam turbine rotor parts as claimed in claim 1, characterized in that: The iron-based alloy powder has the following composition: carbon C: 0.15%, chromium Cr: 1.5%, silicon Si: 0.8%, manganese Mn: 0.8%, molybdenum Mo: 1.5%, oxygen O: 0.02%, phosphorus P: 0.01%, sulfur S: 0.03%, and iron Fe: 95.19%.

3. The method for preparing a high-plasticity and toughness 1CrMo alloy repair layer by a laser additive and post-heat treatment composite process for repairing damaged surfaces of steam turbine rotor parts as claimed in claim 1, characterized in that: The iron-based alloy powder has the following composition: carbon C: 0.08%, chromium Cr: 1.0%, silicon Si: 0.5%, manganese Mn: 0.8%, molybdenum Mo: 0.7%, oxygen O: 0.02%, phosphorus P: 0.01%, sulfur S: 0.03%, and iron Fe: 96.86%.

4. The method for preparing a high-plasticity and toughness 1CrMo alloy repair layer by a laser additive and post-heat treatment composite process for repairing damaged surfaces of steam turbine rotor parts as claimed in claim 1, characterized in that: The iron-based alloy powder has an oxygen content of less than 600 ppm, a hollow powder rate based on quantity of less than 3%, a powder particle size between -140 and +325 meshes, and a powder bulk density between 3 and 6 g / cm 2 The liquidity is between 12 and 18 seconds.

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