Preparation method of a stop valve for a 650 DEG C and above grade unit boiler

Abstract

The application belongs to the technical field of high-temperature metal material processing and preparation, and particularly relates to a preparation method of a stop valve for a 650 DEG C and above grade unit boiler. The preparation method comprises (1) first processing of each component of the stop valve for the unit boiler; (2) first heat treatment and second processing of the valve body, throttling sleeve, valve rod, valve flap, packing seat ring and stand column respectively; (3) surfacing of the valve seat, second heat treatment and third processing; and the specific steps of the first heat treatment and the second heat treatment are limited. The stop valve prepared by the preparation method has stable structure stability and good comprehensive performance, has low risk of cracking of the surfacing sealing surface, and simplifies the heat treatment process. The two heat treatment methods are adopted to effectively control the structure of the prepared stop valve, simplify the heat treatment process, reduce the requirement of the stop valve on the heat treatment process, and reduce the risk of cracking of the sealing surface after surfacing.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature metal material processing and preparation technology, specifically relating to a method for preparing a shut-off valve for boilers of 650℃ and above. Background Technology

[0002] Improving the parameters of coal-fired power units can increase thermal efficiency and reduce carbon emissions. Further developing coal-fired power units with temperatures of 650℃ and above is a strategic measure to further consolidate my country's leading position in coal-fired power technology and reduce carbon emissions from power generation. Valves, as key components of the unit, play a crucial role in protecting equipment safety. Valves are characterized by complex internal structures, harsh operating conditions, and difficult sealing, necessitating ensuring uniform internal structure and stress distribution to guarantee high-temperature sealing and structural integrity. In units with temperatures of 650℃ and above, high-temperature valves face stringent requirements regarding the high-temperature durability, oxidation resistance, processability, and weldability of materials.

[0003] Nickel-iron-based precipitation-strengthened superalloys possess excellent comprehensive high-temperature performance and cost-effectiveness, making them suitable as high-temperature components for valves in next-generation units operating at 650℃ and above. To ensure the service performance requirements of high-temperature valves, nickel-iron-based superalloys reduce the use of costly solid solution strengthening elements and incorporate higher levels of precipitation strengthening elements. While reducing material costs, this places higher demands on microstructure control, requiring appropriate heat treatment to guarantee long-term service performance. As the core of the seal, the valve sealing surface requires high wear resistance, corrosion resistance, oxidation resistance, and high-temperature resistance. However, the material for valve sealing surfaces is typically cobalt-based superalloys. The significant difference in thermal expansion coefficients between cobalt-based and nickel-iron-based superalloys can easily generate substantial residual stress during the multi-pass welding thermal cycles of the welding process. Using nickel-iron-based superalloys as the material for gate valves and cobalt-based superalloys as the sealing surface material, the significant difference in thermal expansion coefficients and the high precision required for microstructure control will impact valve manufacturing and operation, placing higher demands on the welding and heat treatment processes. In addition, the stress concentration of the weld overlay on the valve seat and the weld overlay on the valve body is relatively large and subject to impact, which often becomes the main location for cracking and failure during valve service, and is prone to cracking and other problems. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a shut-off valve for boilers of 650℃ and above, which can effectively control the microstructure, simplify the heat treatment and heat treatment process after valve seat welding, reduce the requirements for heat treatment process and the risk of cracking of weld sealing surface.

[0005] To this end, the present invention provides the following technical solution.

[0006] This invention provides a method for manufacturing a shut-off valve for boilers in units with a capacity of 650℃ and above. The shut-off valve for boilers includes components such as a valve body, valve seat, throttling sleeve, valve stem, valve disc, packing ring, and column. The manufacturing method includes the following steps:

[0007] (1) Perform the first processing on each component of the shut-off valve for the boiler of the unit;

[0008] (2) The valve body, throttling sleeve, valve stem, valve disc, packing ring and column are subjected to a first heat treatment and a second machining, respectively;

[0009] (3) The valve seat is subjected to welding, a second heat treatment, and a third machining;

[0010] The specific steps of the first heat treatment include heating to 450℃-550℃ at a rate of 1℃ / min-5℃ / min, holding at that temperature for no more than 1 hour, then heating to 600℃-750℃ at a rate of 1℃ / min-5℃ / min, holding at that temperature for 8-16 hours and then air cooling, then heating to 800℃-900℃, holding at that temperature for 3-6 hours, and then air cooling to room temperature.

[0011] The temperature difference between the second heat treatment and the Ni3Al solution temperature is 50-250℃, and the second heat treatment temperature is lower than the Ni3Al solution temperature. The second heat treatment time does not exceed 5 hours.

[0012] The valve body, throttling sleeve, valve seat, valve stem, valve disc, packing ring, and column are made of the same material;

[0013] Preferably, the valve body, throttling sleeve, valve seat, valve stem, valve disc, packing ring, and column are all made of nickel-iron-based high-temperature alloy.

[0014] According to the preparation method, the nickel-iron-based superalloy comprises, by weight percentage: Fe: 35%-45%, Cr: 15%-21%, Mo: 0.5%-1.4%, W: 0.1%-0.8%, Ti: 1.8%-2.5%, Al: 0.8%-2.5%, Mn: ≤1.0%, Nb: ≤0.1%, Co: ≤2%, Si: ≤0.05%, C: 0.03%-0.10%, B: 0.001%-0.005%, P: ≤0.01%, with the balance being Ni; wherein the weight percentage of Cr+Ni is greater than 50%, and the weight percentage of W+Mo is 0.6%-1.5%.

[0015] The welding material used for the overlay welding is a cobalt-based high-temperature alloy.

[0016] Furthermore, the hardness value of the component after the first heat treatment is HRC≥28;

[0017] Preferably, the hardness difference between the first heat-treated component and the second heat-treated cobalt-based superalloy is HRC≥5.

[0018] The first processing is machining;

[0019] Preferably, the second processing is machining;

[0020] Preferably, the third processing is machining.

[0021] After the first heat treatment, the volume fraction of intragranular Ni3Al precipitates in the nickel-iron-based superalloy is not less than 15%, the volume fraction of carbides is less than 3%, the maximum size of a single carbide is not more than 10 μm, the room temperature elongation and reduction of area are not less than 15% and 20% respectively, the elongation and reduction of area at 650℃ are not less than 15% and 20% respectively, and the average coefficient of linear expansion at 750℃ does not exceed 18.0 × 10⁻⁶. -6 / ℃.

[0022] After the second heat treatment, the volume fraction of intragranular Ni3Al precipitates in the nickel-iron-based superalloy is not less than 15%; the room temperature elongation and reduction of area are not less than 15% and 20% respectively, the elongation and reduction of area at 650℃ are not less than 13% and 15% respectively, and the average coefficient of linear expansion at 750℃ does not exceed 17.8 × 10⁻⁶. -6 / ℃.

[0023] The present invention also provides a shut-off valve prepared by the above method.

[0024] After the valve seat is welded, the resulting weld layer becomes the sealing surface.

[0025] The technical solution of this invention has the following advantages:

[0026] 1. The present invention provides a method for preparing a shut-off valve for boilers of 650℃ and above, comprising: (1) performing a first processing on each component of the shut-off valve; (2) performing a first heat treatment and a second processing on the valve body, throttling sleeve, valve stem, valve disc, packing seat ring, and column respectively; (3) performing welding, a second heat treatment, and a third processing on the valve seat; and specifying the specific steps of the first and second heat treatments. The shut-off valve prepared by this method has good structural stability and comprehensive performance, low risk of cracking of the welded sealing surface, and simplifies the heat treatment process. Cobalt-based and nickel-iron-based superalloys, due to the demanding operating conditions, often contain high levels of elements such as Cr, Al, and Ti. The influence of element size causes the coefficient of thermal expansion to exhibit a non-linear change with temperature, resulting in significant thermal stress during the welding process and a susceptibility to cracking during service. Post-weld heat treatment (the second heat treatment step after the valve seat weld) is necessary to eliminate this thermal stress. However, post-weld heat treatment processes often need to consider the significant performance differences between the two materials (valve seat and weld material), each with its optimal heat treatment process. Existing technologies cannot effectively match the optimal heat treatment process, thus failing to fully utilize the performance advantages of both cobalt-based and nickel-based superalloys, resulting in the alloys not reaching their optimal performance state. This invention employs a combination of two heat treatment methods, resulting in a gate valve that effectively controls the microstructure, simplifies the heat treatment process, reduces the requirements for heat treatment, and minimizes the risk of cracking on the welded sealing surface. The gate valve produced by this invention is less prone to cracking and failure during operation, and the invention simplifies the process and improves the yield rate.

[0027] The present invention employs a first heat treatment, which, by reasonably controlling the size and volume of the precipitated phase, brings the alloy close to the peak state of aging, effectively improving the alloy hardness while maintaining reasonable ductility and toughness. At the same time, the components after the first heat treatment and the cobalt-based superalloy after the second heat treatment can form a reasonable hardness difference, ensuring that no wear occurs during the opening and closing process of the sealing surface.

[0028] Before the second heat treatment, a nickel-iron-based superalloy containing Ni3Al in solid solution is used as the raw material, ensuring that the intragranular Ni3Al content in the superalloy is below 5% to avoid cracking during welding due to excessive material strength. Simultaneously, since the intragranular precipitates absorb heat and reduce the coefficient of thermal expansion during precipitation above 600℃, residual stress during welding can be reduced to some extent. By rationally selecting the second heat treatment, the microstructure of the base material can be adjusted, the overall strength of the alloy can be improved, and a reasonable match between the weld sealing surface and the base material can be achieved. Attached Figure Description

[0029] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the shut-off valve in a specific embodiment of the present invention;

[0031] Figure label:

[0032] 1-Valve body, 2-Spiral wound gasket, 3-Valve seat, 4-Throttle sleeve, 5-Valve stem, 6-Packing seat ring, 7-Gasket, 8-Packing, 9-Graphite ring, 10-Packing gland, 11-Packing pressure plate, 12-First bolt, 13-First nut, 14-Column, 15-Transition head, 16-Second nut, 17-Electric actuator, 18-Slotted cone end set screw, 19-Washer, 20-Second bolt, 21-Stop ring, 22-Oil cup, 23-Valve stem nut, 24-One-way thrust ball bearing, 25-Guide plate, 26-Hex socket head cap screw, 27-Key. Detailed Implementation

[0033] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0034] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0035] The structure of the shut-off valve mentioned in the following embodiments is as follows: Figure 1 As shown, the shut-off valve includes 1-valve body, 2-winding gasket, 3-valve seat, 4-throttle sleeve, 5-valve stem, 6-packing seat ring, 7-gasket, 8-packing, 9-graphite ring, 10-packing gland, 11-packing pressure plate, 12-first bolt, 13-first nut, 14-column, 15-transition head, 16-second nut, 17-electric actuator, 18-slotted cone end set screw, 19-washer, 20-second bolt, 21-stop ring, 22-oil cup, 23-valve stem nut, 24-one-way thrust ball bearing, 25-guide plate, 26-internal hexagonal head screw, 27-key.

[0036] The nickel-iron-based superalloy used in the following embodiments comprises, by weight percentage: Fe: 35%-45%, Cr: 15%-21%, Mo: 0.5%-1.4%, W: 0.1%-0.8%, Ti: 1.8%-2.5%, Al: 0.8%-2.5%, Mn: ≤1.0%, Nb: ≤0.1%, Co: ≤2%, Si: ≤0.05%, C: 0.03%-0.10%, B: 0.001%-0.005%, P: ≤0.01%, with the balance being Ni; the weight percentage of Cr+Ni is greater than 50%, and the weight percentage of W+Mo is 0.6%-1.5%.

[0037] More specifically, the nickel-iron-based superalloy used in the following embodiments comprises, by weight percentage: Fe: 40%, Cr: 16%, Mo: 0.6%, W: 0.3%, Ti: 2.2%, Al: 1.6%, Mn: 0.1%, Co: 1.0%, Si: 0.025%, C: 0.05%, B: 0.002%, with the balance being Ni. According to test results, the solution temperature of this precipitation-strengthened nickel-iron-based superalloy Ni3Al is 922℃.

[0038] Cobalt-based superalloys can be selected from solid solution strengthened superalloys such as Stellite 6 and Stellite 21 and their derivative alloys.

[0039] Example 1

[0040] This embodiment provides a method for manufacturing a shut-off valve for a power plant boiler. The structure of the shut-off valve for the power plant boiler is as follows: Figure 1 As shown, the valve body, valve seat, throttling sleeve, valve stem, valve disc, packing ring, and column are all made of nickel-iron-based high-temperature alloy, while other components are made of heat-resistant stainless steel. The preparation method includes the following steps:

[0041] (1) Forging and machining of each component of the shut-off valve for the boiler unit.

[0042] (2) The valve body, throttling sleeve, valve stem, valve disc, packing seat ring and column are subjected to the first heat treatment respectively. The first heat treatment specifically includes: heating to 450°C at a rate of 5°C / min, holding for 1 hour, heating to 650°C at a rate of 5°C / min, holding for 8 hours and then air cooling, then heating to 800°C, holding for 5 hours and then air cooling to room temperature.

[0043] (3) Machining of valve body, throttling sleeve, valve stem, valve disc, packing ring and column.

[0044] (4) The valve seat is welded using Stellite6 alloy as the welding material. After the welding is completed, a second heat treatment is performed at 800℃ for 4 hours. After the treatment, the valve seat is air-cooled and then machined.

[0045] (5) Arrange all components according to Figure 1 As shown in the assembly diagram.

[0046] In this embodiment, the volume fraction of intragranular Ni3Al precipitates in the nickel-iron-based superalloy after the first heat treatment is not less than 15%, the volume fraction of carbides is less than 3%, the maximum size of a single carbide is not more than 10 μm, the room temperature elongation and reduction of area are not less than 15% and 20% respectively, the elongation and reduction of area at 650℃ are not less than 15% and 20% respectively, and the average coefficient of linear expansion at 750℃ is not more than 18.0 × 10⁻⁶. -6 The hardness value is HRC 28 at ℃. After the second heat treatment, the volume fraction of intragranular precipitates in the nickel-iron-based superalloy is higher than 15%, the room temperature elongation and reduction of area are not less than 15% and 20% respectively, the elongation and reduction of area at 650℃ are not less than 13% and 15% respectively, and the average coefficient of linear expansion at 750℃ does not exceed 17.8×10. -6 / ℃, the hardness value of the cobalt-based superalloy is HRC 38.

[0047] Example 2

[0048] This embodiment provides a method for manufacturing a shut-off valve for a power plant boiler. The structure of the shut-off valve for the power plant boiler is as follows: Figure 1 As shown, the valve body, valve seat, throttling sleeve, valve stem, valve disc, packing ring, and column are all made of nickel-iron-based high-temperature alloy, while other components are made of heat-resistant stainless steel. The preparation method includes the following steps:

[0049] (1) Forging and machining of each component of the shut-off valve for the boiler unit.

[0050] (2) The valve body, throttling sleeve, valve stem, valve disc, packing seat ring and column are subjected to the first heat treatment respectively. The first heat treatment specifically includes: heating to 450℃ at a rate of 3℃ / min, holding for 0.5h, heating to 700℃ at a rate of 3℃ / min, holding for 10h and then air cooling, then heating to 900℃, holding for 3h, and then air cooling to room temperature.

[0051] (3) Machining of valve body, throttling sleeve, valve stem, valve disc, packing ring and column.

[0052] (4) The valve seat is welded using Stellite21 alloy as the welding material. After the welding is completed, a second heat treatment is performed at 870℃ for 2 hours. After the treatment, the valve seat is air-cooled and then machined.

[0053] (5) Arrange all components according to Figure 1 As shown in the assembly diagram.

[0054] In this embodiment, after the first heat treatment, the volume fraction of intragranular Ni3Al precipitates in the nickel-iron-based superalloy is not less than 15%, the volume fraction of carbides is less than 3%, the maximum size of a single carbide is not more than 10 μm, the room temperature elongation and reduction of area are not less than 15% and 20% respectively, the elongation and reduction of area at 650℃ are not less than 15% and 20% respectively, and the average coefficient of linear expansion at 750℃ is not more than 18.0 × 10⁻⁶. -6 The hardness value is HRC 29 at ℃. After the second heat treatment, the volume fraction of intragranular precipitates in the nickel-iron-based superalloy is higher than 15%, the room temperature elongation and reduction of area are not less than 15% and 20% respectively, the elongation and reduction of area at 650℃ are not less than 13% and 15% respectively, and the average coefficient of linear expansion at 750℃ does not exceed 17.8 × 10⁻⁶. -6 / ℃, the hardness value HRC of the cobalt-based superalloy is 39.

[0055] Example 3

[0056] This embodiment provides a method for manufacturing a shut-off valve for a power plant boiler. The structure of the shut-off valve for the power plant boiler is as follows: Figure 1 As shown, the valve body, valve seat, throttling sleeve, valve stem, valve disc, packing ring, and column are all made of nickel-iron-based high-temperature alloy. The preparation method includes the following steps:

[0057] (1) Forging and machining of each component of the shut-off valve for the boiler unit.

[0058] (2) The valve body, sleeve, throttling sleeve, valve stem, valve disc, packing seat and column are subjected to the first heat treatment respectively. The first heat treatment specifically includes: heating to 550°C at a rate of 1°C / min, holding for 1 hour, heating to 600°C at a rate of 1°C / min, holding for 16 hours and then air cooling, then heating to 800°C, holding for 6 hours and then air cooling to room temperature.

[0059] (3) Machining of valve body, throttling sleeve, valve stem, valve disc, packing ring and column.

[0060] (4) The valve seat is welded using Stellite6 alloy as the welding material. After the welding is completed, a second heat treatment is performed at 800℃ for 5 hours. After the treatment, the valve seat is air-cooled and then machined.

[0061] (5) Arrange all components according to Figure 1 As shown in the assembly diagram.

[0062] In this embodiment, the volume fraction of intragranular Ni3Al precipitates in the nickel-iron-based superalloy after the first heat treatment is not less than 15%, the volume fraction of carbides is less than 3%, the maximum size of a single carbide is not more than 10 μm, the room temperature elongation and reduction of area are not less than 15% and 20% respectively, the elongation and reduction of area at 650℃ are not less than 15% and 20% respectively, and the average coefficient of linear expansion at 800℃ is not more than 18.0 × 10⁻⁶. -6 / ℃, hardness value HRC 30. After the second heat treatment, the volume fraction of intragranular precipitates after stress relief treatment is higher than 15%, the room temperature elongation and reduction of area are not less than 15% and 20% respectively, the elongation and reduction of area at 650℃ are not less than 13% and 15% respectively, and the average linear expansion coefficient at 750℃ does not exceed 17.8×10 -6 / ℃, the hardness value HRC of the cobalt-based superalloy is 39.

[0063] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for manufacturing a shut-off valve for boiler units with a capacity of 650℃ and above, wherein the shut-off valve for boiler units comprises a valve body, a valve seat, a throttling sleeve, a valve stem, a valve disc, a packing ring, and a column, characterized in that, The preparation method includes the following steps: (1) The various components of the shut-off valve for the boiler unit are first processed; the valve body, throttling sleeve, valve seat, valve stem, valve disc, packing ring and column are all made of nickel-iron-based high-temperature alloy; the composition of the nickel-iron-based high-temperature alloy by weight percentage includes: Fe: 35%-45%, Cr: 15%-21%, Mo: 0.5%-1.4%, W: 0.1%-0.8%, Ti: 1.8%-2.5%, Al: 0.8%-2.5%, Mn: ≤1.0%, Nb: ≤0.1%, Co: ≤2%, Si: ≤0.05%, C: 0.03%-0.10%, B: 0.001%-0.005%, P: ≤0.01%, with the balance being Ni; the weight percentage of Cr+Ni is greater than 50%, and the weight percentage of W+Mo is 0.6%-1.5%; (2) The valve body, throttling sleeve, valve stem, valve disc, packing ring and column are subjected to a first heat treatment and a second machining, respectively; The first heat treatment specifically includes heating to 450℃-550℃ at a rate of 1℃ / min-5℃ / min, holding at that temperature for no more than 1 hour, then heating to 600℃-750℃ at a rate of 1℃ / min-5℃ / min, holding at that temperature for 8-16 hours, followed by air cooling, then heating to 800℃-900℃, holding at that temperature for 3-6 hours, and then air cooling to room temperature. After the first heat treatment, the volume fraction of intragranular Ni3Al precipitates in the nickel-iron-based superalloy is not less than 15%, the volume fraction of carbides is less than 3%, the maximum size of a single carbide is no more than 10 μm, the elongation and reduction of area at room temperature are not less than 15% and 20% respectively, the elongation and reduction of area at 650℃ are not less than 15% and 20% respectively, and the average linear expansion coefficient at 750℃ is no more than 18.0 × 10⁻⁶. -6 / ℃; (3) The valve seat is subjected to overlay welding, a second heat treatment, and a third processing; the welding material for overlay welding is a cobalt-based high-temperature alloy; Before the second heat treatment, a nickel-iron-based superalloy containing Ni3Al in solid solution is used as the raw material, ensuring that the intragranular Ni3Al content in the nickel-iron-based superalloy is less than 5%. The difference between the temperature of the second heat treatment and the Ni3Al solid solution temperature is 50-250℃, and the second heat treatment temperature is lower than the Ni3Al solid solution temperature. The duration of the second heat treatment does not exceed 5 hours. After the second heat treatment, the volume fraction of intragranular Ni3Al precipitates in the nickel-iron-based superalloy is not less than 15%, and the average linear expansion coefficient at 750℃ does not exceed 17.8 × 10⁻⁶. -6 / ℃.

2. The preparation method according to claim 1, characterized in that, The hardness value of the part after the first heat treatment is HRC≥28.

3. The preparation method according to claim 2, characterized in that, The hardness difference between the component after the first heat treatment and the cobalt-based superalloy after the second heat treatment is HRC≥5.

4. The preparation method according to any one of claims 1-3, characterized in that, The first processing is machining.

5. The preparation method according to claim 4, characterized in that, The second processing is machining.

6. The preparation method according to claim 4, characterized in that, The third processing step is machining.

7. The preparation method according to any one of claims 1-3, characterized in that, The nickel-iron-based superalloy after the second heat treatment has a room temperature elongation and a reduction of area of ​​not less than 15% and 20%, respectively, and a 650℃ elongation and reduction of area of ​​not less than 13% and 15%, respectively.

8. A shut-off valve prepared by the method according to any one of claims 1-7.

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