Part to be subjected to laser quenching, pretreatment method of part to be subjected to laser quenching, method for preparing quenching strengthened layer and part machining method

Abstract

The invention relates to the technical field of laser processing, in particular to a part to be subjected to laser quenching and a pretreatment method thereof, a method for preparing a quenching strengthened layer and a part processing method, and the method comprises the following steps: carrying out nanosecond laser irradiation treatment on the part to be quenched, so that a microstructure is formed on the surface of the part; according to the method, the contradiction between the light energy utilization efficiency and the quenching depth in the traditional technology is broken through through the microstructure regulation and control cooperated laser quenching method, meanwhile, the surface hardness, the high-temperature stability and the damage resistance are considered, and an efficient and reliable surface strengthening solution is provided for long-life service of the F92 steel under the extreme working conditions of supercritical thermal power, nuclear power and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of laser processing, and particularly to a part to be laser quenched, a pretreatment method thereof, a method for obtaining a quenched strengthening layer, and a part processing method. Background Art

[0002] Due to its excellent low-cycle thermal fatigue resistance and high-temperature creep fracture strength, martensitic heat-resistant F92 steel has become an ideal material for high-temperature and high-pressure extreme working conditions such as valves and pump bodies in ultra (ultra) supercritical thermal power units, and is widely used in key parts such as main steam regulating valves, reheater valves, and nuclear power main feed water valves. However, when it serves in extreme environments of high temperature, high pressure, and corrosion for a long time, its surface is prone to oxidation, wear, and thermal fatigue crack propagation, resulting in seal failure, which seriously restricts the reliability and service life of the equipment.

[0003] Although the traditional quenching process can increase the hardness of F92 steel within a limited range, the quenching time is long (>10 hours), and it cannot meet the processing requirements of complex geometric structure parts (such as the inner cavity of the valve body). Although the performance can be improved by laser cladding Stellite 6 to form a wear-resistant layer, its hardness is usually about 400 Hv, and additional processes are required for secondary treatment of the workpiece.

[0004] Due to the advantages of high precision and low heat-affected zone of laser surface quenching technology, it has attracted wide attention. However, traditional laser quenching relies on surface pretreatment such as phosphating and spraying to improve the laser absorption rate. Although the thickness of the coating formed by pretreatment can increase the absorption rate, it may cause excessive energy consumption on the surface layer, limiting the extension of the quenching depth into the matrix. In addition, the difference in thermal expansion coefficients between the coating and the matrix is likely to cause interfacial stress concentration, affecting the bonding strength of the strengthening layer. Summary of the Invention

[0005] In order to solve the above technical problems, embodiments of the present invention provide a part to be laser quenched, a pretreatment method thereof, a method for obtaining a quenched strengthening layer, and a part processing method.

[0006] To achieve the above object, the embodiments of the present invention adopt the following technical solutions:

[0007] On the one hand, the present invention provides a pretreatment method before laser quenching, including the following steps: performing nanosecond laser irradiation treatment on the part to be quenched so that a microstructure is formed on the surface of the part.

[0008] In some embodiments, the power of the nanosecond laser is 5 W to 20 W.

[0009] In some embodiments, the scanning speed of the nanosecond laser is 25 mm / s to 100 mm / s.

[0010] In some embodiments, the microstructure includes cross grooves with a pitch of 0.04 mm to 0.05 mm.

[0011] In some embodiments, before the nanosecond laser irradiation treatment, the following steps are further included: placing the part in ethanol, performing ultrasonic cleaning, and drying it in vacuum after cleaning.

[0012] In some embodiments, the ultrasonic cleaning time is 30 min to 60 min, the temperature of the vacuum drying is 80 °C to 120 °C, and the drying time is 1 h to 3 h.

[0013] On the other hand, the present invention also provides a part to be laser quenched, which is obtained by treating with the above pretreatment method.

[0014] On another aspect, the present invention also provides a method for preparing a quenched and strengthened layer by laser quenching, including performing nanosecond laser irradiation treatment on the part to be quenched with the above pretreatment method before laser quenching, and then performing laser quenching treatment on the surface of the part after pretreatment; or performing laser quenching treatment on the surface of the above part to be laser quenched after pretreatment.

[0015] In some embodiments, the laser power of the laser quenching is 5000 W to 10000 W, and the scanning speed is 5 mm / s to 30 mm / s.

[0016] On another aspect, the present invention also provides a processing method for parts, including the method for preparing a quenched and strengthened layer by laser quenching as described above.

[0017] The beneficial effects of the present invention are as follows:

[0018] Through the method of microstructure regulation combined with laser quenching, the present invention breaks through the contradiction between the light energy utilization efficiency and the quenching depth in the traditional technology, and at the same time takes into account the surface hardness, high-temperature stability and anti-damage performance, providing an efficient and reliable surface strengthening solution for the long-term service of F92 steel under extreme working conditions such as supercritical thermal power and nuclear power; specifically, through nanosecond laser irradiation treatment, a microstructure is formed on the surface of the part. On the one hand, it is beneficial to the rapid formation of a steep temperature gradient after the laser energy accumulates briefly on the surface of the part, driving the austenitized region to extend deep into the matrix; on the other hand, while the rough surface introduced by the nanosecond laser irradiation treatment increases the laser absorption area, it also provides a high-density nucleation site for martensitic transformation, enabling the austenitization depth to break through the limitations of traditional processes. Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the nanosecond laser etching pattern of this application;

[0020] Figure 2 It is a schematic microstructural diagram of the surface of the part pretreated by nanosecond laser in Example 1 of this application;

[0021] Figure 3 Schematic diagram of the microstructure of the surface of the part after nanosecond laser pretreatment in Example 2 of this application;

[0022] Figure 4 Schematic diagram of the microstructure of the surface of the part after nanosecond laser pretreatment in Example 3 of this application;

[0023] Figure 5 Macroschematic diagram of the heat affected zone after quenching in Example 1 of this application;

[0024] Figure 6 Macroschematic diagram of the heat affected zone after quenching in Example 2 of this application;

[0025] Figure 7 Macroschematic diagram of the heat affected zone after quenching in Example 3 of this application;

[0026] Figure 8 Macroschematic diagram of the heat affected zone after quenching in Comparative Example 4 of this application;

[0027] Figure 9 Schematic diagram of the hardness change with depth in Comparative Example 1 of this application;

[0028] Figure 10 Schematic diagram of the hardness change with depth in Comparative Example 2 of this application;

[0029] Figure 11 Schematic diagram of the hardness change with depth in Comparative Example 3 of this application;

[0030] Figure 12 Schematic diagram of the hardness change with depth in Comparative Example 4 of this application;

[0031] Figure 13 Schematic diagram of the hardness change with depth in Example 1 of this application;

[0032] Figure 14 Schematic diagram of the hardness change with depth in Example 2 of this application;

[0033] Figure 15 Schematic diagram of the hardness change with depth in Example 3 of this application;

[0034] Figure 16 Schematic diagram of the hardness change with depth in Example 4 of this application;

[0035] Figure 17 Schematic diagram of the hardness change with depth in Example 5 of this application;

[0036] Figure 18 Schematic diagram of the hardness change with depth in Example 6 of this application;

[0037] Figure 19Schematic diagram of the hardness change with depth in Embodiment 7 of the present application;

[0038] Figure 20 Schematic diagram of the hardness change with depth in Embodiment 8 of the present application;

[0039] Figure 21 Schematic diagram of the hardness change with depth in Embodiment 9 of the present application;

[0040] Figure 22 Surface reflectivity result graph of Embodiment 2 of the present application;

[0041] Figure 23 Surface reflectivity result graph of Comparative Example 4 of the present application;

[0042] Figure 24 Surface reflectivity result graph of Comparative Example 5 of the present application;

[0043] Figure 25 Schematic diagram of the hardness change with depth in Comparative Example 5 of the present application.

[0044] Figure 26 Microscopic structure schematic diagram of the surface of the part after nanosecond laser pretreatment in Comparative Example 6 of the present application;

[0045] Figure 27 Microscopic structure schematic diagram of the surface of the part after nanosecond laser pretreatment in Comparative Example 7 of the present application;

[0046] Figure 28 Microscopic structure schematic diagram of the surface of the part after nanosecond laser pretreatment in Comparative Example 2 of the present application;

[0047] Figure 29 Microscopic structure schematic diagram of the surface of the part after nanosecond laser pretreatment in Comparative Example 8 of the present application. Detailed implementation manners

[0048] Next, the technical solutions in some embodiments of the present disclosure will be clearly and completely described in conjunction with the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments provided by the present disclosure fall within the protection scope of the present disclosure.

[0049] Due to advantages such as high precision and low heat affected zone of laser surface hardening technology, it has attracted wide attention. However, traditional laser hardening relies on surface pretreatment such as phosphating and spraying to improve the laser absorption rate. Although the thickness of the coating formed by the pretreatment can increase the absorption rate, it may cause excessive energy consumption on the surface layer, restricting the extension of the hardening depth into the matrix. In addition, the difference in thermal expansion coefficient between the coating and the matrix is likely to cause interfacial stress concentration, affecting the bonding strength of the hardened layer.

[0050] To solve the above technical problems, on the one hand, the present invention provides a pre-treatment method before laser quenching, including the following steps: irradiating the part to be quenched with nanosecond laser to form a microstructure on the surface of the part, and the microstructure has a periodic array and a high light absorption rate. Among them, Figure 22 and Figure 24 respectively show the microstructure reflectivity of Example 2 and Comparative Example 5, and it is found that the reflectivity of the microstructure prepared by nanosecond laser is lower than that prepared by femtosecond laser, indicating that the microstructure prepared by nanosecond laser has a higher absorption rate.

[0051] In some embodiments, the power of the nanosecond laser is 5W to 20W.

[0052] Exemplarily, the power of the nanosecond laser can be any point value among 5W, 6W, 7W, 8W, 9W, 10W, 11W, 12W, 13W, 14W, 15W, 16W, 17W, 18W, 19W, 20W or the range value between any two of them. The embodiments of the present application do not make specific limitations on this.

[0053] In some embodiments, the scanning speed of the nanosecond laser is 25mm / s to 100mm / s.

[0054] Exemplarily, the scanning speed of the nanosecond laser can be any point value among 25mm / s, 30mm / s, 35mm / s, 40mm / s, 45mm / s, 50mm / s, 55mm / s, 60mm / s, 65mm / s, 70mm / s, 75mm / s, 80mm / s, 85mm / s, 90mm / s, 95mm / s, 100mm / s or the range value between any two of them. The embodiments of the present application do not make specific limitations on this.

[0055] If the power of the nanosecond laser is greater than 20W or the scanning speed of the nanosecond laser is lower than 25mm / s, it will cause excessive ablation on the surface of the part and damage the periodic microstructure; if the power of the nanosecond laser is less than 5W or the scanning speed of the nanosecond laser is greater than 100mm / s, it will cause the surface of the part not to absorb enough laser energy, resulting in insufficient or non-existent microstructure depth.

[0056] In some embodiments, the microstructure includes cross grooves with a spacing of 0.04mm to 0.05mm.

[0057] In some embodiments, before the nanosecond laser irradiation treatment, the following steps are further included: placing the part in ethanol, performing ultrasonic cleaning, and drying it in vacuum after cleaning.

[0058] In some embodiments, the ultrasonic cleaning time is 30min to 60min, the temperature of the vacuum drying is 80°C to 120°C, and the drying time is 1h to 3h.

[0059] On the other hand, the present invention also provides a part to be laser quenched, which is obtained by treating with the above-mentioned pretreatment method.

[0060] In yet another aspect, the present invention also provides a method for obtaining a quenched and strengthened layer by laser quenching. After treating the part to be quenched with nanosecond laser irradiation by the above-mentioned pretreatment method before laser quenching, then performing laser quenching treatment on the surface of the part after pretreatment; or performing laser quenching treatment on the surface of the above-mentioned part to be laser quenched after pretreatment.

[0061] In some embodiments, the laser power of the laser quenching is 5000W - 10000W, and the scanning speed is 5mm / s - 30mm / s.

[0062] Exemplarily, the laser power of the laser quenching can be any point value among 5000W, 6000W, 7000W, 8000W, 9000W, 10000W or the range value between any two of them. The embodiments of the present application do not make specific limitations on this.

[0063] Exemplarily, the scanning speed can be any point value among 5mm / s, 8mm / s, 10mm / s, 13mm / s, 14mm / s, 15mm / s, 16mm / s, 17mm / s, 20mm / s, 25mm / s, 30mm / s or the range value between any two of them. The embodiments of the present application do not make specific limitations on this.

[0064] In yet another aspect, the present invention also provides a processing method for a part, including the method for obtaining a quenched and strengthened layer by laser quenching as described above.

[0065] In order to objectively evaluate the technical effects of the embodiments of the present disclosure, the technical solutions provided by the present disclosure will be described in detail and exemplarily through experimental examples below.

[0066] To make the present application easier to understand, the present invention will be described in detail below in conjunction with embodiments. These embodiments are only illustrative and are not limited to the application scope of the present invention.

[0067] Unless otherwise specified, the operations and processing methods involved in the present application belong to the conventional methods in the art.

[0068] Unless otherwise specified, the instruments used in the present application are conventional instruments in the art.

[0069] Example 1

[0070] (1) Place the part (F92 valve) in ethanol and perform ultrasonic cleaning for 30 minutes.

[0071] (2) Dry the parts cleaned in step (1) at 120 °C for 3 hours in a vacuum environment;

[0072] (3) Perform nanosecond laser irradiation treatment on the parts dried in step (2) to form a microstructure on the surface of the parts. The nanosecond laser power is 16 W, the scanning speed is 50 mm / s, and the scanning pattern is a cross groove with a pitch of 0.04 mm;

[0073] (4) Then perform laser quenching treatment. The laser power used for laser quenching is 7500 W, and the scanning speed is 18 mm / s.

[0074] Example 2

[0075] Example 2 is the same as Example 1, except that the scanning speed in step (3) is 25 mm / s.

[0076] Example 3

[0077] Example 3 is the same as Example 1, except that the scanning speed in step (3) is 100 mm / s.

[0078] Example 4

[0079] Example 4 is the same as Example 1, except that the scanning speed in step (3) is 25 mm / s, the scanning speed in step (4) is 18 mm / s, and the laser power is 5000 W.

[0080] Example 5

[0081] Example 5 is the same as Example 1, except that the scanning speed in step (3) is 50 mm / s, the scanning speed in step (4) is 18 mm / s, and the laser power is 5000 W.

[0082] Example 6

[0083] Example 6 is the same as Example 1, except that the scanning speed in step (3) is 100 mm / s, the scanning speed in step (4) is 18 mm / s, and the laser power is 5000 W.

[0084] Example 7

[0085] Example 7 is the same as Example 1, except that the scanning speed in step (3) is 25 mm / s, the scanning speed in step (4) is 18 mm / s, and the laser power is 10000 W.

[0086] Example 8

[0087] Example 8 is the same as Example 1, except that in step (3), the scanning speed is 50 mm / s, in step (4), the scanning speed is 18 mm / s, and the laser power is 10000 W.

[0088] Example 9

[0089] Example 9 is the same as Example 1, except that in step (3), the scanning speed is 100 mm / s, in step (4), the scanning speed is 18 mm / s, and the laser power is 10000 W.

[0090] Comparative Example 1

[0091] In this Comparative Example 1, the heat treatment of the part is carried out using a traditional quenching process. Specifically, the F92 steel is placed in a tubular furnace, the heating temperature is 1000 °C, the holding time is 3 hours, and then it is cooled in water.

[0092] Comparative Example 2

[0093] This Comparative Example 2 is the same as Example 1, except that in step (3), the scanning speed is 500 mm / s.

[0094] Comparative Example 3

[0095] In this Comparative Example 3, Stellite 6 is cladded on the surface of the part by laser cladding technology, the laser power is 10 kW, and the scanning speed is 18 mm / s.

[0096] Comparative Example 4

[0097] In this Comparative Example 4, only laser quenching is used without nanosecond laser pretreatment. The specific parameters are continuous laser scanning, the power is 7500 W, and the scanning speed is 18 mm / s.

[0098] Comparative Example 5

[0099] In this Comparative Example 5, the type of laser used is a femtosecond laser for surface light-trapping structure etching of the part, the laser power is 0.5 W, and the scanning speed is 50 mm / s. The power of the continuous laser used for laser quenching is 7500 W, and the scanning speed of the continuous laser is 18 mm / s.

[0100] Comparative Example 6

[0101] It is the same as Example 1, except that the nanosecond laser power is 30 W.

[0102] Comparative Example 7

[0103] It is the same as Example 1, except that the scanning speed of the nanosecond laser is 10 mm / s.

[0104] Comparative Example 8

[0105] Same as Example 1, except that the power of the nanosecond laser is 2W.

[0106] As Figure 26 and Figure 27 shown, the too high laser power in Comparative Example 6 or the too low scanning speed in Comparative Example 7 cannot form periodic microstructures on the surface because the thermal accumulation effect of the nanosecond laser will cause excessive ablation of the microstructures. In addition, as Figure 28 and Figure 29 shown, the too small power in Comparative Example 8 or the too fast laser etching speed in Comparative Example 2 also cannot form periodic microstructures on the surface because the laser cannot effectively remove the material at this time.

[0107] Figure 1 shows the scanning path of the nanosecond laser. The nanosecond laser first etches along the x direction and then patterns in the y direction. Figure 2 、 Figure 3 、 Figure 4 correspond to the changes in the microstructural morphology of Examples 1, 2, and 3 respectively, and their depth gradually increases with the decrease of the scanning speed. Figures 5 - 8 shows the macroscopic morphology of the heat affected zone of laser quenching for Examples 1-3 and Comparative Example 4. It is found that the heat affected zone with microstructures is significantly deeper than that without microstructures. By Figure 9 comparing with Figures 13 - 21 , it is found that laser quenching has a higher hardness than traditional quenching; comparing Figures 10 - 12 with Figures 13 - 21 , only by etching microstructures within the power and scanning parameter ranges defined in the embodiments of the present application can the laser quenching strength and depth be effectively improved; comparing Figure 11 with Figures 13 - 21 , laser quenching has a better hardness than the Stellite 6 cladding strengthening layer; comparing Figure 12 with Figures 13 - 21 , the laser quenching depth is limited without microstructures; comparing Figures 13 - 21 with Figure 25 , laser quenching after nanosecond laser pretreatment has better hardness performance than that after femtosecond laser pretreatment.

[0108] Comparing Figure 22 and Figure 23 , this method can significantly improve the light absorption ability of F92 steel; comparing Figure 22 and Figure 24 , the microstructures prepared by nanosecond laser have better light absorption ability than those prepared by femtosecond laser.

[0109] In the description of this specification, specific features, structures, materials, or characteristics may be combined in any one or more embodiments or examples in a suitable manner.

[0110] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims described above.

Claims

1. A pretreatment method before laser quenching, characterized in that: The following steps are involved: The part to be quenched is treated with nanosecond laser irradiation to form a microstructure on the surface of the part.

2. A pretreatment method before laser quenching according to claim 1, characterized in that: The power of the nanosecond laser is 5W to 20W.

3. The method for pretreatment before laser quenching according to claim 1, characterized in that: The scanning speed of the nanosecond laser is 25 mm / s to 100 mm / s.

4. The method for pretreatment before laser quenching according to claim 1, characterized in that: The microstructure includes cross grooves with a spacing of 0.04 mm to 0.05 mm.

5. A pretreatment method before laser quenching according to any one of claims 1 to 4, characterized in that: Before the nanosecond laser irradiation treatment, the following steps are also included: placing the parts in ethanol, performing ultrasonic cleaning, and vacuum drying after cleaning.

6. A pretreatment method before laser quenching according to claim 5, characterized in that: The ultrasonic cleaning time is 30 min to 60 min, the vacuum drying temperature is 80° C. to 120° C., and the drying time is 1 h to 3 h.

7. A part to be laser quenched, characterized in that: The method is obtained by using the pretreatment method according to any one of claims 1 to 6.

8. A method for obtaining a quenching strengthening layer by laser quenching, characterized in that: The method comprises: performing nanosecond laser irradiation treatment on a part to be quenched by the laser pretreatment method according to any one of claims 1 to 6, and then performing laser quenching treatment on the pretreated surface of the part; or performing laser quenching treatment on the pretreated surface of the part to be laser quenched according to claim 7.

9. The method according to claim 8, characterized in that The laser power of the laser quenching is 5000W-10000W, and the scanning speed is 5mm / s-30mm / s.

10. A method for processing a part, characterized in that: The method comprises the method for obtaining a quenching-strengthened layer by laser quenching as claimed in claim 8 or 9.

Images