Surfacing material for steam turbine valve and surfacing method of surfacing material

Abstract

The invention relates to the technical field of steam turbine valves, and discloses a surfacing material for a steam turbine valve and a surfacing method thereof.The surfacing material comprises, by weight, less than or equal to 0.6% of C, less than or equal to 1% of Si, less than or equal to 1% of Mn, less than or equal to 0.05% of P, less than or equal to 0.05% of S, 24%-27% of Cr, 9%-12% of Ni, 6%-9% of W, less than or equal to 3% of Fe, less than or equal to 0.5% of Mo and the balance Co and inevitable impurities. The service performance of the surfacing layer can be improved, and the defect occurrence rate is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steam turbine valves, in particular to a steam turbine valve surfacing material and a surfacing method thereof. BACKGROUND

[0002] In order to ensure the sealing and sliding reliability of the valve, a surfacing layer is usually arranged on the sealing surface and sliding surface of the valve core to improve the wear resistance. The current surfacing layer is mainly formed by surfacing Stellite No. 6 Co-based alloy. The main components of Stellite No. 6 Co-based alloy are Co, Cr and W. However, the Stellite No. 6 Co-based alloy is prone to martensitic transformation in long-term high-temperature service, which increases the hardness, reduces the plasticity and impact fatigue resistance, and thus defects, especially linear defects, are prone to occur. Since the Stellite No. 6 Co-based alloy has poor welding process and high local repair difficulty, the valve core can only be replaced as a whole or processed according to the new product manufacturing process after defects occur, which results in high repair cost and long repair cycle. SUMMARY

[0003] The technical purpose of the present application is to provide a steam turbine valve surfacing material and a surfacing method thereof, which can improve the service performance of the surfacing layer and reduce the defect rate.

[0004] The technical solution adopted by the present application is as follows: A steam turbine valve surfacing material, by weight percentage, the surfacing material comprises the following components: C≤0.6%, Si≤1%, Mn≤1%, P≤0.05%, S≤0.05%, Cr: 24%-27%, Ni: 9%-12%, W: 6%-9%, Fe≤3%, Mo≤0.5%, the balance being Co and unavoidable impurities.

[0005] The above technical measures add Ni element to the components of the surfacing material. Ni element is a strong austenite stabilizing element, which can stabilize the austenite structure. During long-term high-temperature service of the surfacing layer formed by the surfacing material, Ni element can inhibit martensitic transformation, thereby maintaining the stability of the hardness of the surfacing layer, avoiding cracking and other problems caused by the decrease of plasticity and impact fatigue resistance due to hardening, improving the service performance of the surfacing layer and reducing the defect rate. Meanwhile, the weight percentage of W element is controlled at 6%-9%, and the appropriate amount of C element is combined with W element, which can ensure the number of hard carbides, thereby improving the wear resistance.

[0006] Further, by weight percentage, the surfacing material comprises the following components: C: 0.03%~0.08%, Si: 0.2%~0.5%, Mn: 0.05%~0.2%, P: ≤0.05%, S: ≤0.05%, Cr: 24.5%~26%, Ni: 10%~11%, W: 7%~8%, Fe: ≤1%, Mo: 0.2%~0.4%, the balance of Co and inevitable impurities.

[0007] Further, the surfacing material is a wire or a powder.

[0008] The above technical measures can select different forms of surfacing materials according to different needs.

[0009] The second technical solution adopted by the application is as follows: A surfacing method of the surfacing material for the turbine valve as in the first technical solution, The surfacing method comprises the following steps: S1, preheating the sealing surface and sliding surface of the valve core; S2, surfacing the surfacing material on the preheated sealing surface and sliding surface to form a surfacing layer; S3, post-heating the surfacing area; S4, stress relief heat treatment of the surfacing area.

[0010] The above technical measures can reduce the temperature difference and thermal stress through preheating, which is beneficial to prevent cracking and the like; through post-heating, hydrogen can be diffused and escaped, reducing the risk of cracking; through stress relief heat treatment, the generated residual stress can be eliminated, thereby improving the welding quality and service life.

[0011] Further, the specific steps of the preheating are: The sealing surface and sliding surface of the valve core are heated to 300~500 DEG C and kept for ≥1h.

[0012] The above technical measures keep the temperature for ≥1h, which is beneficial to realize temperature homogenization and avoid cracking caused by large temperature difference.

[0013] Further, the temperature between layers during surfacing is ≤550 DEG C.

[0014] The above technical measures control the temperature between layers to ≤550 DEG C, which can ensure that each layer is completed at an ideal temperature, thereby avoiding organization coarsening and preventing interlayer cracks caused by overheating.

[0015] Further, the thickness of the surfacing layer is ≤5mm.

[0016] The above technical measures control the thickness of the surfacing layer, which can reduce residual stress and reduce the generation of cracks and peeling risk.

[0017] Further, the specific step of the post-heat treatment is: The surfacing area is heated to 400-550 DEG C at a rate of ≤50 DEG C / h, and after holding for ≥2h, it is cooled to room temperature at a rate of ≤50 DEG C / h.

[0018] The above technical measures can prevent new stress from being generated due to too fast temperature change, and reduce the generation of cracks, by controlling the temperature change rate; by heating to 400-550 DEG C, hydrogen can obtain kinetic energy to diffuse to the surface and escape, and holding for ≥2h ensures sufficient escape of hydrogen.

[0019] Further, the specific step of the stress relief heat treatment is: The surfacing area is heated to 600-750 DEG C at a rate of ≤50 DEG C / h, and after holding for 4-8h, it is cooled to room temperature at a rate of ≤50 DEG C / h.

[0020] The above technical measures can release stress by heating to 600-750 DEG C to reduce the yield strength of the material, and holding for 4-8h ensures sufficient elimination of stress.

[0021] Further, the surfacing method for performing surfacing is one of tungsten inert gas arc welding, plasma spray welding and laser cladding.

[0022] The above technical measures can select different surfacing methods according to different requirements.

[0023] The one or more technical solutions provided by the present application have at least the following technical effects or advantages: The present application adds Ni element in the components of the surfacing material, the Ni element is a strong austenite stabilizing element, and the Ni element can stabilize the austenite structure; during long-term service at high temperature, the Ni element can inhibit martensite transformation, thereby maintaining the stability of the hardness of the surfacing layer, avoiding cracking and other problems caused by the decrease of plasticity and impact fatigue resistance due to hardening, and improving the service performance of the surfacing layer and reducing the defect occurrence rate; at the same time, the weight percentage of W element is controlled to be 6-9%, and the appropriate amount of C element is combined with the W element, which can ensure the number of hard carbides, thereby improving the wear resistance.

[0024] The surfacing method in the present application can reduce temperature difference and thermal stress by preheating, which is beneficial to prevent cracking and the like; hydrogen can diffuse and escape by post-heat treatment, thereby reducing the risk of cracking; residual stress can be eliminated by stress relief heat treatment, thereby improving the welding quality and service life. BRIEF DESCRIPTION OF DRAWINGS

[0025] The accompanying drawings, which are included to provide a further understanding of the embodiments of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the principles of the application. Figure 1 is a flow chart of the overlaying method of the overlaying material for the steam turbine valve in the application. DETAILED DESCRIPTION

[0026] In order to enable a clearer understanding of the above-mentioned objects, features and advantages of the application, the application will be further described in detail below with reference to the drawings and specific embodiments. It should be noted that the embodiments of the application and the features in the embodiments can be combined with each other without conflict.

[0027] In the following description, a large number of specific details are set forth in order to facilitate a thorough understanding of the application, however, the application can also be implemented in other ways different from the scope described herein, therefore, the protection scope of the application is not limited by the specific embodiments disclosed below.

[0028] Embodiment 1 The embodiment provides an overlaying material for a steam turbine valve, the overlaying material comprises the following components in percentage by weight: C: 0.05%, Si: 0.35%, Mn: 0.1%, P: 0.01%, S: 0.01%, Cr: 24.6%, Ni: 10.5%, W: 7.5%, Fe: 0.8%, Mo: 0.25%, the balance being Co and inevitable impurities.

[0029] The overlaying material is a wire material.

[0030] Based on the overlaying material for the steam turbine valve, the embodiment further provides an overlaying method based on the overlaying material for the steam turbine valve, referring to Figure 1 , the overlaying method comprises the following steps: S1, preheating the sealing surface and the sliding surface of the valve core; The specific steps of preheating are: The sealing surface and the sliding surface of the valve core are heated to 300 DEG C, and the temperature is kept for 1 h.

[0031] S2, overlaying the overlaying material on the preheated sealing surface and sliding surface to form an overlaying layer; The temperature between layers is 550 DEG C during overlaying. The thickness of the overlaying layer is 5 mm. The overlaying method for overlaying is plasma spray welding.

[0032] S3, post-heating treatment is performed on the overlaying area; The specific steps of post-heating treatment are: The overlaying area is heated to 400 DEG C at a speed of 50 DEG C / h, and then cooled to room temperature at a speed of 50 DEG C / h after keeping the temperature for 2 h.

[0033] S4, stress relief heat treatment is performed on the surfacing area.

[0034] The specific steps of the stress relief heat treatment are as follows: The surfacing area is heated to 600℃ at a rate of 50℃ / h, and then cooled to room temperature at a rate of 50℃ / h after holding for 4h.

[0035] The surfacing area refers to the sealing surface and sliding surface of the valve core after surfacing.

[0036] The valve core is made of FB2 martensitic heat-resistant steel forge piece.

[0037] After surfacing, the surfacing performance is inspected. Hardness inspection: the hardness of the surfacing layer is 350HV-400HV at room temperature, and the cross-sectional structure remains stable after high-temperature aging and thermal cycle test at 650℃, and no defects are found.

[0038] A mutual abrasion test is performed between Stellite No. 6 Co-based alloy and the surfacing material in this embodiment (hereinafter referred to as new Co-based alloy): At 620℃, a load of 50N is applied, and the speed is maintained at 200r / min for one hour, and a pin-on-disc friction and wear test with a friction track diameter of 10mm is performed, and the wear results are shown in Table 1: SX refers to the combination of Stellite No. 6 Co-based alloy (disc) and new Co-based alloy (pin), and XS refers to the combination of Stellite No. 6 Co-based alloy (pin) and new Co-based alloy (disc).

[0039] The friction coefficient refers to the average friction coefficient after the friction curve stabilizes from the 500th second, and is rounded to four decimal places.

[0040] Weight wear rate = (average original mass - average mass after wear) / average original mass Volume wear amount = π * (actual wear area major diameter - actual wear area minor diameter) / 4 * (wear cross-sectional area / cross-sectional width).

[0041] From Table 1, it can be concluded that the wear resistance of Stellite No. 6 Co-based alloy is not as good as that of the new Co-based alloy.

[0042] Example 2 The other contents of this embodiment are the same as those of Example 1, except that: The surfacing material includes the following components in terms of weight percentage: C: 0.03%, Si: 0.2%, Mn: 0.05%, P: 0.05%, S: 0.05%, Cr: 24.5%, Ni: 10%, W: 7%, Fe: 1%, Mo: 0.2%, balance Co and inevitable impurities.

[0043] The surfacing material is a powder.

[0044] Based on the surfacing material for the steam turbine valve, the embodiment further proposes a surfacing method based on the surfacing material for the steam turbine valve, and the surfacing method comprises the following steps: S1, preheating the sealing surface and sliding surface of the valve core; The specific steps of preheating are: The sealing surface and sliding surface of the valve core are heated to 500 DEG C and kept for 1.5 hours.

[0045] S2, surfacing the surfacing material on the preheated sealing surface and sliding surface to form a surfacing layer; The temperature between layers is 500 DEG C during surfacing. The thickness of the surfacing layer is 2mm. The surfacing method for surfacing is tungsten electrode argon arc welding.

[0046] S3, post-heating treatment is performed on the surfacing area; The specific steps of post-heating treatment are: The surfacing area is heated to 550 DEG C at a speed of 45 DEG C / h, kept for 2.5 hours, and then cooled to room temperature at a speed of 45 DEG C / h.

[0047] S4, stress relief heat treatment is performed on the surfacing area.

[0048] The specific steps of stress relief heat treatment are: The surfacing area is heated to 750 DEG C at a speed of 45 DEG C / h, kept for 8 hours, and then cooled to room temperature at a speed of 45 DEG C / h.

[0049] Example 3 The other contents of the embodiment are the same as those of example 1, and the difference is that: The surfacing material comprises the following components in percentage by weight: C: 0.6%, Si: 1%, Mn: 1%, P: 0.05%, S: 0.05%, Cr: 24%, Ni: 9%, W: 6%, Fe: 3%, Mo: 0.5%, balance Co and inevitable impurities.

[0050] Based on the surfacing material for the steam turbine valve, the embodiment further proposes a surfacing method based on the surfacing material for the steam turbine valve, and the surfacing method comprises the following steps: S1, preheating the sealing surface and sliding surface of the valve core; The specific steps of preheating are as follows: The sealing surface and sliding surface of the valve core are heated to 400°C and kept for 2 hours.

[0051] S2, the surfacing material is surfacing on the preheated sealing surface and sliding surface to form a surfacing layer; The temperature between layers during surfacing is 350°C. The thickness of the surfacing layer is 3mm. The surfacing method is laser cladding.

[0052] S3, the surfacing area is post-heated; The specific steps of post-heating are as follows: The surfacing area is heated to 500°C at a rate of 40°C / h, kept for 3 hours, and then cooled to room temperature at a rate of 40°C / h.

[0053] S4, the surfacing area is stress relief heat treated.

[0054] The specific steps of stress relief heat treatment are as follows: The surfacing area is heated to 650°C at a rate of 40°C / h, kept for 6 hours, and then cooled to room temperature at a rate of 40°C / h.

[0055] Example 4 The other contents of this embodiment are the same as those of Example 1, except that: The surfacing material includes the following components in percentage by weight: C: 0.08%, Si: 0.5%, Mn: 0.2%, P: 0.05%, S: 0.05%, Cr: 26%, Ni: 11%, W: 8%, Fe: 1%, Mo: 0.4%, the balance of Co and inevitable impurities.

[0056] Example 5 The other contents of this embodiment are the same as those of Example 1, except that: The surfacing material includes the following components in percentage by weight: C: 0.6%, Si: 1%, Mn: 1%, P: 0.05%, S: 0.05%, Cr: 27%, Ni: 12%, W: 9%, Fe: 3%, Mo: 0.5%, the balance of Co and inevitable impurities.

[0057] Although the preferred embodiments of the present application have been described, those skilled in the art can make further changes and modifications to these embodiments once they know the basic inventive concept. Therefore, the appended claims are intended to be interpreted as including all changes and modifications falling within the scope of the present application.

[0058] It will be apparent to those skilled in the art that various modifications and variations can be made to the present application without departing from the spirit or scope of the application. Thus, it is intended that the present application cover modifications and variations of this application provided they come within the scope of the appended claims and their equivalents.

Claims

1. A welding overlay material for steam turbine valves, characterized in that: The weld overlay material comprises the following components by weight percentage: C≤0.6%, Si≤1%, Mn≤1%, P≤0.05%, S≤0.05%, Cr: 24%~27%, Ni: 9%~12%, W: 6%~9%, Fe≤3%, Mo≤0.5%, with the balance being Co and unavoidable impurities.

2. The surfacing material for turbine valves according to claim 1, characterized in that: The weld overlay material comprises the following components by weight percentage: C: 0.03%~0.08%, Si: 0.2%~0.5%, Mn: 0.05%~0.2%, P≤0.05%, S≤0.05%, Cr: 24.5%~26%, Ni: 10%~11%, W: 7%~8%, Fe≤1%, Mo: 0.2%~0.4%, with the balance being Co and unavoidable impurities.

3. The surfacing material for turbine valves according to claim 1, characterized in that: The welding material is either wire or powder.

4. A method for overlaying welding material for turbine valves according to any one of claims 1 to 3, characterized in that: The welding method includes the following steps: S1. Preheat the sealing and sliding surfaces of the valve core; S2. Weld the welding material onto the preheated sealing surface and sliding surface to form a welding layer; S3. Perform post-heat treatment on the weld overlay area; S4. Perform stress-relieving heat treatment on the weld overlay area.

5. The welding method for the surfacing material for turbine valves according to claim 4, characterized in that: The specific steps for preheating are as follows: Heat the sealing and sliding surfaces of the valve core to 300℃~500℃ and keep them at that temperature for ≥1 hour.

6. The welding method for the surfacing material for turbine valves according to claim 4, characterized in that: The interpass temperature during the welding process is ≤550℃.

7. The welding method for the surfacing material for turbine valves according to claim 4, characterized in that: The thickness of the weld overlay is ≤5mm.

8. The welding method for the surfacing material for turbine valves according to claim 4, characterized in that: The specific steps of the post-heat treatment are as follows: The weld overlay area is heated to 400℃~550℃ at a rate of ≤50℃ / h, held at that temperature for ≥2h, and then cooled to room temperature at a rate of ≤50℃ / h.

9. The welding method for the surfacing material for turbine valves according to claim 4, characterized in that: The specific steps of the stress-relieving heat treatment are as follows: The weld overlay area is heated to 600℃~750℃ at a rate of ≤50℃ / h, held at that temperature for 4h~8h, and then cooled to room temperature at a rate of ≤50℃ / h.

10. The welding method for the surfacing material for turbine valves according to claim 4, characterized in that: The welding method used for cladding is one of tungsten inert gas welding, plasma spraying, and laser cladding.

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