A method for preparing a safety valve for boilers of 650℃ and above.

Abstract

This invention belongs to the field of high-temperature metal material processing and preparation technology, specifically relating to a method for preparing a safety valve for boilers of 650℃ and above. The preparation method includes: (1) performing a first processing on each component of the boiler safety valve; (2) performing a first heat treatment on the valve body; performing a second heat treatment on the valve stem, valve disc, and hot valve disc; (3) performing a second processing on the valve body, valve stem, valve seat, valve disc, and hot valve disc; (4) sequentially performing welding, a third heat treatment, and a third processing on the valve seat; (5) assembling the components, then sealing and welding them, and performing a fourth heat treatment and a fourth processing on the sealed and welded parts. The safety valve prepared by this method is less prone to cracking and failure during operation, and has good sealing between components, small differences in the thermal expansion coefficients between the materials used in the components, and low stress.

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 safety valve for boilers of units with a temperature of 650℃ and above. Background Technology

[0002] Valves, as key components of generating units, play a crucial role in protecting equipment safety. Valves are characterized by complex internal structures, harsh operating conditions, and difficult sealing, necessitating the assurance of uniform internal structure and stress distribution to guarantee high-temperature sealing and structural integrity. In generating units operating at 650℃ and above, high-temperature valves face stringent requirements regarding material durability, oxidation resistance, processability, and weldability.

[0003] Nickel-iron-based precipitation-strengthened superalloys possess excellent comprehensive high-temperature performance and superior cost-effectiveness, making them suitable as materials for high-temperature components of valves in next-generation units operating at 650℃ and above. The performance requirements of high-temperature valve components vary significantly. While different alloys may meet mechanical performance requirements, their significant differences in thermal expansion during heating and cooling can lead to sealing defects and internal stress issues. As the core of the seal, the valve sealing surface requires high wear resistance, corrosion resistance, oxidation resistance, and high-temperature resistance. Therefore, cobalt-based superalloys are often used to enhance sealing surface performance. However, due to the significant difference in thermal expansion coefficients between nickel-iron-based and cobalt-based alloys, large residual stresses can easily be generated during the multi-pass welding thermal cycles. Furthermore, the significant difference in thermal expansion coefficients and the high precision required for microstructure control between nickel-iron-based and cobalt-based welding alloys will affect valve manufacturing and operation, placing high demands on welding and heat treatment processes. Moreover, the stress concentration and impact on the weld layers of the valve seat and body of safety valves often make them the primary locations for cracking and failure during valve service. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the problems of cracking, failure, and poor sealing of valves in the prior art during operation and service, as well as the large differences in the thermal expansion coefficients of various components in the valve, which easily generate large stresses, and thus provide a method for preparing a safety valve for boilers of 650℃ and above.

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

[0006] This invention provides a method for manufacturing a safety valve for boilers in units with a capacity of 650℃ and above. The components of the boiler safety valve include a valve body, a valve stem, a valve seat, a valve disc, and a thermal valve disc. The manufacturing method includes the following steps:

[0007] (1) Perform a first processing on each component of the boiler safety valve;

[0008] (2) Perform a first heat treatment on the valve body; perform a second heat treatment on the valve stem, the valve disc, and the hot valve disc;

[0009] (3) Perform a second machining on the valve body, valve stem, valve seat, valve disc, and hot valve disc;

[0010] (4) The valve seat is subjected to welding, third heat treatment and third machining in sequence;

[0011] (5) Assemble the various components, then seal and weld them, and perform a fourth heat treatment and a fourth processing on the sealed and welded parts;

[0012] Specifically, the first heat treatment includes heating to 450℃-550℃ at a rate of 1℃ / min-5℃ / min, holding at that temperature for no more than 3 hours, then heating to 250-350℃ below the Ni3Al solution temperature at a rate of 1℃ / min-5℃ / min, holding at that temperature for 6-16 hours, then air cooling, then heating to 50℃-200℃ below the Ni3Al solution temperature, holding at that temperature for 3-6 hours, and then air cooling to room temperature.

[0013] The second 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 200-300℃ below the Ni3Al solution temperature at a rate of 1℃ / min-5℃ / min, holding at that temperature for 6-16 hours, then air cooling, then heating to 50℃-200℃ below the Ni3Al solution temperature, holding at that temperature for 3-6 hours, and then air cooling to room temperature.

[0014] The temperature difference between the third heat treatment temperature and the Ni3Al solution temperature is 50-250℃, and the third heat treatment temperature is lower than the Ni3Al solution temperature. The duration of the third heat treatment is no more than 5 hours, and the heat treatment is followed by air cooling.

[0015] The temperature difference between the fourth heat treatment temperature and the Ni3Al solution temperature is 0-100℃, and the fourth heat treatment temperature is not higher than the Ni3Al solution temperature. The fourth heat treatment time does not exceed 5 hours. After heat preservation, the components are air-cooled or slowly cooled. Slow cooling is a method of naturally cooling the components by wrapping them in heat insulation material. The heat insulation material can be, but is not limited to, heat insulation cotton.

[0016] The valve body, valve seat, valve stem, valve disc, and thermal valve disc are made of the same material;

[0017] Preferably, the valve body, valve seat, valve stem, valve disc, and hot valve disc are all made of precipitation-strengthened nickel-iron-based high-temperature alloy.

[0018] Further, the composition of the precipitation-strengthened nickel-iron-based superalloy, 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%.

[0019] Furthermore, the welding material used for the aforementioned overlay welding is a cobalt-based high-temperature alloy;

[0020] Preferably, when performing the sealing weld, the welding material is a solution-treated nickel-based superalloy. The fourth heat treatment involves localized heating of the sealing weld area, where the heating targets both the base material and the welding material surrounding the weld.

[0021] Furthermore, the hardness value of the component after the first heat treatment is HRC≥24;

[0022] Preferably, the hardness value of the component after the second heat treatment is HRC≥28.

[0023] Preferably, the hardness difference between the second heat-treated component and the third heat-treated cobalt-based superalloy is HRC≥5.

[0024] Furthermore, the first processing is rough processing;

[0025] Preferably, the second processing is machining;

[0026] Preferably, the third processing is machining;

[0027] Preferably, the fourth processing is machining.

[0028] Furthermore, after the first or second heat treatment, the volume fraction of intragranular Ni3Al precipitates in the precipitation-strengthened 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 × 10⁻⁶. -6 / ℃.

[0029] Furthermore, after the third heat treatment, the volume fraction of intragranular Ni3Al precipitates in the precipitation-strengthened 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 13% and 15% respectively, and the average coefficient of linear expansion at 750℃ is not more than 17.8 × 10⁻⁶. -6 / ℃.

[0030] Furthermore, after the fourth heat treatment, the volume fraction of Ni3Al precipitates in the precipitation-strengthened nickel-iron-based superalloy in the sealed weld area is not less than 10%, the volume fraction of carbides is within 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 18% and 20% respectively, the elongation and reduction of area at 650℃ are not less than 18% and 20% respectively, and the average coefficient of linear expansion at 750℃ is not more than 17.5 × 10⁻⁶. -6 / ℃.

[0031] Furthermore, the present invention also provides a safety valve prepared by the above-described preparation method.

[0032] The technical solution of this invention has the following advantages:

[0033] 1. The present invention provides a method for manufacturing a boiler safety valve, wherein the components of the boiler safety valve include at least a valve body, a valve stem, a valve seat, a valve disc, and a hot valve disc. The manufacturing method includes: (1) performing a first processing on each component of the boiler safety valve; (2) performing a first heat treatment on the valve body; performing a second heat treatment on the valve stem, the valve disc, and the hot valve disc; (3) performing a second processing on the valve body, the valve stem, the valve seat, the valve disc, and the hot valve disc; (4) performing a third heat treatment and a third processing on the valve seat in sequence; (5) assembling each component, then sealing and welding, and performing a fourth heat treatment and a fourth processing on the sealed and welded parts. The safety valve manufactured by this method is less prone to cracking and failure during operation and service, and has good sealing between components, small difference in thermal expansion coefficients between component materials, and low stress. For 600℃ rated valves, heat-resistant steel is typically used, with materials for each component rationally selected based on performance and price factors. However, for units operating at 650℃ and above, heat-resistant steel is insufficient to meet high-temperature performance requirements, necessitating the use of nickel-based superalloys. Nickel-based alloys generally have a significantly higher coefficient of thermal expansion compared to traditional heat-resistant steels. If components are selected using standard materials, the difference in thermal expansion between components becomes even more pronounced. This invention addresses this issue by performing a first heat treatment on the valve body and a second heat treatment on the valve stem, valve disc, and hot valve disc. This effectively solves the problem of poor sealing and high internal stress caused by the large difference in the coefficients of thermal expansion between reinforced nickel-iron-based superalloys and cobalt-based superalloys precipitated during the welding process. Furthermore, it reduces stress, promotes co-contraction, and ensures good sealing between the valve stem, valve disc, hot valve disc, and valve seat, improving the structural stability and overall performance of the safety valve. This reduces the likelihood of cracking and failure during operation, while simultaneously guaranteeing the long-term mechanical properties of the alloy.

[0034] Furthermore, the first, second, third, and fourth heat treatments can achieve different hardnesses for each component, reducing frictional damage. This invention employs the first and second heat treatments, which, by rationally controlling the size and volume of the precipitated phases in the precipitation-strengthened nickel-iron-based superalloy, bring the alloy close to its aging peak state, effectively increasing its hardness while maintaining reasonable ductility and toughness, and improving the uniformity of the alloy microstructure. Simultaneously, the components after the second heat treatment and the cobalt-based alloy after the third heat treatment can form a reasonable hardness difference, ensuring that no wear occurs during the opening and closing of the sealing surface.

[0035] By appropriately selecting the third 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. The fourth heat treatment can effectively reduce residual stress during the welding process, improve the plasticity of the heat-affected zone and the heating-affected zone, and appropriately reduce strength while increasing stress, which is conducive to local plastic deformation of the alloy, ensuring the safety of the sealing position. Through reasonable matching of process steps, the preparation of a 650℃-rated safety valve can be achieved.

[0036] The valve sealing weld is subjected to local post-weld heat treatment (i.e., the fourth heat treatment) to eliminate the stress involved and adjust the properties of the heat-affected zone and the nearby base material, improve the plastic deformation capacity, improve the alloy damage tolerance, and prevent leakage.

[0037] 2. The method for preparing a boiler safety valve provided by this invention uses precipitation-strengthened nickel-iron-based superalloys as the material for each component. The volume fraction of Ni3Al within the crystals of this nickel-iron-based superalloy in its solid solution state is less than 5%, which can avoid cracking tendencies during welding due to excessive material strength. Simultaneously, since the intracrystalline precipitates absorb heat and reduce the coefficient of thermal expansion during precipitation above 600℃, residual stress during welding can be reduced to a certain extent. Attached Figure Description

[0038] 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.

[0039] Figure 1 This is a schematic diagram of the safety valve in a specific embodiment of the present invention;

[0040] Figure label:

[0041] 1-1-Valve body; 1-2-Valve seat; 2-Lower adjusting ring; 3-Lower adjusting rod; 4-Upper adjusting rod; 5-Upper adjusting ring; 6-1-Valve disc; 6-2-Hot valve disc; 7-Valve disc sleeve; 8-Guide sleeve; 9-Cooler; 10-Exhaust chamber; 11-Adjusting sleeve; 12-Spring cover; 13-Spring; 14-Valve stem; 15-Handle. Detailed Implementation

[0042] 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.

[0043] 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.

[0044] The structure of the safety valve mentioned in the following embodiments is as follows: Figure 1As shown, the safety valve includes a valve body, valve seat, lower adjusting ring, lower adjusting rod, upper adjusting rod, upper adjusting ring, valve disc, hot valve disc, valve disc sleeve, guide sleeve, cooler, exhaust chamber, adjusting sleeve, spring cover, spring, valve stem, and handle.

[0045] The precipitation-strengthened 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%. The solution temperature of the precipitation-strengthened nickel-iron-based superalloy Ni3Al is 880-1000℃.

[0046] More specifically, the precipitation-strengthened nickel-iron-based superalloy used in the following embodiments comprises, by weight percentage: Fe: 43%, Cr: 16%, Mo: 0.6%, W: 0.3%, Ti: 2.1%, Al: 1.4%, 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 920℃.

[0047] Cobalt-based superalloys can be selected from superalloys such as Stellite 6 and Stellite 21 and their derivative alloys.

[0048] The welding material used for sealing welding is a solution-treated nickel-based superalloy, such as In617 or In625.

[0049] Example 1

[0050] This embodiment provides a method for manufacturing a safety valve for boilers. The structure of the safety valve for boilers is as follows: Figure 1 As shown, the valve body, valve stem, valve seat, valve disc, and hot valve disc are all made of precipitation-strengthened nickel-iron-based superalloys. The preparation method includes the following steps:

[0051] (1) Perform rough forging on each component of the boiler safety valve.

[0052] (2) Perform a first heat treatment on the valve body. The first heat treatment specifically includes: heating to 450°C at a rate of 5°C / min, holding for 1 hour, then heating to 640°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.

[0053] The valve stem, valve disc, and hot valve disc undergo a second heat treatment, which specifically includes: heating to 450°C at a rate of 5°C / min and holding for 1 hour; then heating to 680°C at a rate of 5°C / min and holding for 8 hours before air cooling; then heating to 800°C and holding for 5 hours before air cooling to room temperature.

[0054] (3) Machining of valve body, valve stem, valve disc and hot valve disc.

[0055] (4) The valve seat is welded using Stellite6 alloy as the welding material. After the welding is completed, a third heat treatment is performed at 800℃ for 4 hours. After the treatment, the valve seat is air-cooled and then machined.

[0056] (5) Arrange all components according to Figure 1 The assembly shown is followed by sealing welding, and a fourth heat treatment to obtain a safety valve. During the sealing welding, the welding material is In617 nickel-based high-temperature alloy, and the fourth heat treatment is performed using localized induction heating. After heating, the valve is air-cooled. The temperature of the fourth heat treatment is 900℃, and the time is 2 hours.

[0057] In this embodiment, the precipitation-strengthened nickel-iron-based superalloy after the first heat treatment exhibits an intragranular Ni3Al precipitate volume fraction of no less than 15%, a carbide volume fraction of no more than 3%, a maximum individual carbide size of no more than 10 μm, and room temperature elongation and reduction of area of ​​no less than 15% and 20%, respectively; elongation and reduction of area at 650℃ of no less than 15% and 20%, respectively; and an average linear expansion coefficient at 750℃ of no more than 18.0 × 10⁻⁶. -6 / ℃, hardness value HRC is 25.

[0058] After the second heat treatment, the volume fraction of Ni3Al precipitates in the precipitation-strengthened nickel-iron-based alloy 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 / ℃, hardness value HRC is 28.

[0059] After the third heat treatment, the volume fraction of intragranular precipitates in the precipitation-strengthened nickel-iron-based superalloy is higher 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 room temperature elongation and reduction of area are no less than 15% and 20% respectively, the elongation and reduction of area at 650℃ are no less than 13% and 15% respectively, and the average coefficient of linear expansion at 750℃ is no more than 17.8 × 10⁻⁶. -6 At ℃, the hardness value of the cobalt-based alloy is HRC 38.

[0060] After the fourth heat treatment, the volume fraction of Ni3Al precipitates in the precipitation-strengthened nickel-iron-based superalloy is not less than 10%, 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 18% and 20% respectively, the elongation and reduction of area at 650℃ are not less than 18% and 20% respectively, and the average coefficient of linear expansion at 750℃ is not more than 17.5 × 10⁻⁶. -6 / ℃.

[0061] Example 2

[0062] This embodiment provides a method for manufacturing a safety valve for boilers. The structure of the safety valve for boilers is as follows: Figure 1 As shown, the valve body, valve stem, valve seat, valve disc, and hot valve disc are all made of nickel-iron-based high-temperature alloy. The preparation method includes the following steps:

[0063] (1) Perform rough forging on each component of the boiler safety valve.

[0064] (2) The valve body is subjected to a first heat treatment, which specifically includes: heating to 450°C at a rate of 3°C / min, holding for 0.5h, then heating to 630°C at a rate of 3°C / min, holding for 6h and then air cooling, then heating to 850°C, holding for 3h and then air cooling to room temperature.

[0065] The valve stem, valve disc, and hot valve disc undergo a second heat treatment, which specifically includes: heating to 450°C at a rate of 5°C / min and holding for 0.5 hours; then heating to 660°C at a rate of 5°C / min and holding for 8 hours before air cooling; then heating to 800°C and holding for 3 hours before air cooling to room temperature.

[0066] (3) Machining of valve body, valve stem, valve disc and hot valve disc.

[0067] (4) The valve seat is welded using Stellite21 alloy as the welding material. After the welding is completed, the valve seat is subjected to a third heat treatment at 860℃ for 3 hours. After the treatment, the valve seat is air-cooled and then machined.

[0068] (5) Arrange all components according to Figure 1The assembly shown is followed by sealing welding, and a fourth heat treatment to obtain a safety valve. During the sealing welding, the welding material is In625 nickel-based high-temperature alloy, and the fourth heat treatment is performed using localized induction heating. After heating, the valve is air-cooled. The temperature of the fourth heat treatment is 880℃, and the time is 4 hours.

[0069] In this embodiment, the precipitation-strengthened nickel-iron-based superalloy after the first heat treatment exhibits an intragranular Ni3Al precipitate volume fraction of no less than 15%, a carbide volume fraction of no more than 3%, a maximum individual carbide size of no more than 10 μm, and room temperature elongation and reduction of area of ​​no less than 15% and 20%, respectively. The hardness value is HRC 24. The elongation and reduction of area at 650℃ are no less than 15% and 20%, respectively, and the average coefficient of linear expansion at 750℃ does not exceed 18 × 10⁻⁶. -6 / ℃.

[0070] After the second heat treatment, the volume fraction of Ni3Al precipitates within the nickel-iron alloy should be no less than 15%, the volume fraction of carbides should be less than 3%, the maximum size of a single carbide should not exceed 10 μm, the room temperature elongation and reduction of area should be no less than 15% and 20% respectively, the elongation and reduction of area at 650℃ should be no less than 15% and 20% respectively, and the average coefficient of linear expansion at 750℃ should not exceed 16.5 × 10⁻⁶. -6 / ℃, hardness value HRC is 28.

[0071] After the third heat treatment, the volume fraction of intragranular precipitates in the nickel-iron-based superalloy is higher 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 room temperature elongation and reduction of area are no less than 15% and 20% respectively, the elongation and reduction of area at 650℃ are no less than 13% and 15% respectively, and the average coefficient of linear expansion at 750℃ is no more than 17.8 × 10⁻⁶. -6 / ℃, the hardness value of the cobalt-based alloy is HRC 40.

[0072] After the fourth heat treatment, the volume fraction of Ni3Al precipitates in the precipitation-strengthened nickel-iron-based superalloy in the sealed weld area is not less than 10%, 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 18% and 20% respectively, the elongation and reduction of area at 650℃ are not less than 18% and 20% respectively, and the average coefficient of linear expansion at 750℃ is not more than 17.5 × 10⁻⁶. -6 / ℃.

[0073] Example 3

[0074] This embodiment provides a method for manufacturing a safety valve for boilers. The structure of the safety valve for boilers is as follows: Figure 1As shown, the valve body, valve stem, valve seat, valve disc, and hot valve disc are all made of nickel-iron-based high-temperature alloy. The preparation method includes the following steps:

[0075] (1) Perform rough forging on each component of the boiler safety valve.

[0076] (2) Perform a first heat treatment on the valve body. The first heat treatment specifically includes: heating to 550°C at a rate of 1°C / min, holding for 1 hour, then heating to 650°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.

[0077] The valve stem, valve disc, and hot valve disc undergo a second heat treatment, which specifically includes: heating to 450°C at a rate of 5°C / min and holding for 1 hour; then heating to 700°C at a rate of 5°C / min and holding for 8 hours before air cooling; then heating to 800°C and holding for 5 hours before air cooling to room temperature.

[0078] (3) Machining of valve body, valve stem, valve disc and hot valve disc.

[0079] (4) The valve seat is welded using Stellite6 alloy as the welding material. After the welding is completed, a third heat treatment is performed at 800℃ for 5 hours. After the treatment, the valve seat is air-cooled and then machined.

[0080] (5) Arrange all components according to Figure 1 The assembly shown is followed by sealing welding, and a safety valve is obtained after post-weld heat treatment. During the sealing welding, the welding material is In625 nickel-based high-temperature alloy, and a fourth heat treatment is performed using localized induction heating. After heating, the valve is air-cooled. The fourth heat treatment temperature is 920℃, and the time is 2 hours.

[0081] 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, and the room temperature elongation and reduction of area are not less than 15% and 20%, respectively. At 650℃, the elongation and reduction of area are not less than 15% and 20%, respectively, and at 750℃, the average coefficient of linear expansion does not exceed 18 × 10⁻⁶. -6 / ℃. Hardness value HRC is 27.

[0082] After the second heat treatment, the volume fraction of Ni3Al precipitates within the nickel-iron alloy should be no less than 15%, the volume fraction of carbides should be less than 3%, the maximum size of a single carbide should not exceed 10 μm, the elongation and reduction of area at room temperature should be no less than 15% and 20% respectively, the elongation and reduction of area at 650℃ should be no less than 15% and 20% respectively, and the average coefficient of linear expansion at 750℃ should not exceed 18.0 × 10⁻⁶.-6 / ℃, hardness value HRC is 28.

[0083] After the third heat treatment, the volume fraction of intragranular precipitates in the nickel-iron-based superalloy is higher 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 room temperature elongation and reduction of area are no less than 15% and 20% respectively, the elongation and reduction of area at 650℃ are no less than 13% and 15% respectively, and the average coefficient of linear expansion at 750℃ is no more than 17.8 × 10⁻⁶. -6 At ℃, the hardness value of the cobalt-based alloy is HRC 39.

[0084] After the fourth heat treatment, the volume fraction of Ni3Al precipitates in the precipitation-strengthened nickel-iron-based superalloy in the sealed weld area is not less than 10%, 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 18% and 20% respectively, the elongation and reduction of area at 650℃ are not less than 18% and 20% respectively, and the average coefficient of linear expansion at 750℃ is not more than 17.5 × 10⁻⁶. -6 / ℃.

[0085] 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 safety valve for boilers of 650℃ and above, wherein the safety valve comprises at least a valve body, a valve stem, a valve seat, a valve disc, and a thermal valve disc, characterized in that, The preparation method includes the following steps: (1) Perform a first processing on each component of the boiler safety valve; (2) Perform a first heat treatment on the valve body; perform a second heat treatment on the valve stem, the valve disc, and the hot valve disc; (3) Perform a second machining on the valve body, valve stem, valve seat, valve disc, and hot valve disc; (4) The valve seat is subjected to welding, third heat treatment and third machining in sequence; (5) Assemble the various components, then seal and weld them, and perform a fourth heat treatment and a fourth processing on the sealed and welded parts; Specifically, the first heat treatment includes heating to 450℃-550℃ at a rate of 1℃ / min-5℃ / min, holding at that temperature for no more than 3 hours, then heating to 250-350℃ below the Ni3Al solution temperature at a rate of 1℃ / min-5℃ / min, holding at that temperature for 6-16 hours, then air cooling, then heating to 50℃-200℃ below the Ni3Al solution temperature, holding at that temperature for 3-6 hours, and then air cooling to room temperature. The second 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 200-300℃ below the Ni3Al solution temperature at a rate of 1℃ / min-5℃ / min, holding at that temperature for 6-16 hours, then air cooling, then heating to 50℃-200℃ below the Ni3Al solution temperature, holding at that temperature for 3-6 hours, and then air cooling to room temperature. The temperature difference between the third heat treatment temperature and the Ni3Al solution temperature is 50-250℃, and the third heat treatment temperature is lower than the Ni3Al solution temperature, and the time of the third heat treatment does not exceed 5 hours. The temperature difference between the fourth heat treatment temperature and the Ni3Al solution temperature is 0-100℃, and the fourth heat treatment temperature is not higher than the Ni3Al solution temperature, and the fourth heat treatment time does not exceed 5h. The valve body, valve seat, valve stem, valve disc, and hot valve disc are all made of precipitation-strengthened nickel-iron-based high-temperature alloy. After the first or second heat treatment, the volume fraction of intragranular Ni3Al precipitates in the precipitation-strengthened nickel-iron-based superalloy shall not be less than 15%, the volume fraction of carbides shall be less than 3%, the maximum size of a single carbide shall not exceed 10 μm, the room temperature elongation and reduction of area shall not be less than 15% and 20%, respectively, the elongation and reduction of area at 650℃ shall not be less than 15% and 20%, respectively, and the average coefficient of linear expansion at 750℃ shall not exceed 18 × 10⁻⁶. -6 / ℃.

2. The preparation method according to claim 1, characterized in that, The precipitation-strengthened 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; the weight percentage of Cr+Ni is greater than 50%, and the weight percentage of W+Mo is 0.6%-1.5%.

3. The preparation method according to claim 2, characterized in that, The welding material used in the aforementioned overlay welding is a cobalt-based high-temperature alloy.

4. The preparation method according to claim 3, characterized in that, When performing the sealing welding, the welding material is a solid solution nickel-based high-temperature alloy.

5. The preparation method according to claim 4, characterized in that, The hardness value of the part after the first heat treatment is HRC≥24.

6. The preparation method according to claim 5, characterized in that, The hardness value of the part after the second heat treatment is HRC≥28.

7. The preparation method according to claim 6, characterized in that, The hardness difference between the second heat-treated component and the third heat-treated cobalt-based superalloy is HRC≥5.

8. The preparation method according to claim 7, characterized in that, The first processing is rough processing.

9. The preparation method according to claim 8, characterized in that, The second processing is machining.

10. The preparation method according to claim 9, characterized in that, The third processing step is machining.

11. The preparation method according to claim 10, characterized in that, The fourth processing step is machining.

12. The preparation method according to claim 2, characterized in that, After the third heat treatment, the volume fraction of intragranular Ni3Al precipitates in the precipitation-strengthened nickel-iron-based superalloy shall not be less than 15%, the volume fraction of carbides shall be less than 3%, the maximum size of a single carbide shall not exceed 10 μm, the room temperature elongation and reduction of area shall not be less than 15% and 20%, respectively, the elongation and reduction of area at 650℃ shall not be less than 13% and 15%, respectively, and the average coefficient of linear expansion at 750℃ shall not exceed 17.8 × 10⁻⁶. -6 / ℃.

13. The preparation method according to claim 2, characterized in that, After the fourth heat treatment, the volume fraction of Ni3Al precipitates in the precipitation-strengthened nickel-iron-based superalloy in the sealed weld area shall not be less than 10%, the volume fraction of carbides shall be less than 3%, the maximum size of a single carbide shall not exceed 10 μm, the room temperature elongation and reduction of area shall not be less than 18% and 20% respectively, the elongation and reduction of area at 650℃ shall not be less than 18% and 20% respectively, and the average coefficient of linear expansion at 750℃ shall not exceed 17.5 × 10⁻⁶. -6 / ℃.

14. A safety valve prepared by the method according to any one of claims 1-13.

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