CN115852226B - Low-expansion alloy for ultra-supercritical steam turbine fastener and preparation method thereof - Google Patents
Low-expansion alloy for ultra-supercritical steam turbine fastener and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a low expansion alloy for a ultra-supercritical turbine fastener and a preparation method thereof, wherein the low expansion alloy comprises the following elements in percentage by mass: 5.00-6.00%, ti 0.10-0.40%, nb 2.50-3.50%, Y0.01-0.02%, fe:24.0 to 27.0 percent, and the balance of Co and unavoidable impurities. The low-expansion alloy is prepared by designing alloy components, adding and adjusting alloy elements, adopting vacuum induction, vacuum consumable remelting, high-temperature homogenizing diffusion and forging, has excellent high-temperature mechanical property at the temperature of more than 600 ℃, can meet the requirements of oxidation resistance and high-temperature strength in a high-temperature environment, and meets the requirement of selecting materials of a main valve fastener of an ultra-supercritical steam turbine.
Description
Technical Field
The invention relates to the field of low expansion alloy, in particular to low expansion alloy for a super-supercritical turbine fastener and a preparation method thereof, wherein the low expansion alloy for the super-supercritical turbine fastener still has excellent high-temperature mechanical properties at the temperature of more than 600 ℃.
Background
The low expansion alloy is widely applied to electric power energy transmission lines and high-temperature gap structures by virtue of low expansion characteristicsA component. In recent years, with the development of ultra-supercritical coal-fired generator sets in China, higher requirements are put forward on the use temperature of low-expansion alloy. The ultra-supercritical coal-fired generator set is the most advanced coal-fired generator set at present internationally, and all industrial developed countries are developing new generation metal materials so as to adapt to the requirement of the ultra-supercritical generator set for further development of ultra-high parameters. The main technical characteristics of the ultra-supercritical unit are that as the steam parameters are greatly improved, new materials are needed to be adopted for each steam operation part and the like so as to improve the high temperature resistance and the strength of bearing ultra-supercritical pressure. Because the ultra-supercritical steam parameters are high, the heat content of the unit kilogram steam is about 1/4 higher than that of the subcritical parameter steam, the use temperature of the subcritical parameter steam is 540 ℃, and the use temperature of the ultra-supercritical steam is 600 ℃. Meanwhile, cold and hot state starting in the operation of the main valve of the steam turbine of the ultra-supercritical unit is considered, once the thermal expansion coefficient of a fastener is high, the thermal stress of peripheral thick-wall elements is easily increased in the temperature cycle lifting cold and hot scaling process, and the looseness and even the influence on the air tightness of the main valve and the unit peak regulation can be caused. Therefore, the material selected for the main valve portion fastener must not only have excellent high temperature strength and durability, but also satisfy a linear low expansion coefficient of 650 ℃ of 13.5X10 or less -6 The requirements are quite high at/deg.C.
In general, low expansion alloys for electric power are usually controlled by adding no Cr or by controlling the thermal expansion coefficient of the alloy to a Cr content of less than 5%, but there is a problem that the use temperature of the low Cr alloy is very limited and is usually difficult to reach 600 ℃ or higher in order to avoid oxidation of the alloy in a high temperature environment. The alloy is applied to the high-temperature environment and needs to be loaded, and the iron-based, nickel-based or cobalt-based high-temperature alloy with the Cr content of more than 15% is often adopted as the material so as to ensure the high-temperature oxidation resistance of the alloy. The data shows that the addition of Cr element can reduce the average atomic magnetic moment of each Fe-Ni-Co base alloy, and directly result in the improvement of the thermal expansion coefficient.
GH2036 alloy is one of high-temperature alloys with larger fastener consumption in China at present, and comprises the following components in percentage by weight: c is 0.34 to 0.40 percent; cr is 11.5-13.5%; si is 0.3-0.8%; mo is 1.10-1.40%; b is less than or equal to 0.010 percent; v is 1.25-1.55%; mn is 7.5-9.5%; ni is 7.0-9.0%; nb is 0.25-0.50%; the balance being Fe. The Cr content is 11.5-13.5%, the VC strengthening phase is mainly formed for precipitation strengthening, and although the VC strengthening phase has better physical and mechanical properties at 600-650 ℃, relevant data show that when the service temperature is 600-650 ℃, the thermal expansion coefficient is 22.49-22.85 multiplied by 10 < -6 >/DEG C, and obviously, the material selection requirement of the main valve fastener cannot be met. Therefore, the high-quality high-temperature-resistant low-expansion fastener material is developed, the operation reliability of the main valve of the ultra-supercritical coal-fired generator set is ensured, and the method has great significance for realizing the localization of materials of important technical equipment in the key field of China.
Chinese patent CN1400330 a describes a high strength low expansion alloy steel material comprising the following components (in weight%): c is 0.51-2.50%; ni is 32.0-45.0%; v is 1.21-3.0%; cr is 0.5-5.0%; si is less than or equal to 0.60 percent; mn is less than or equal to 2.0 percent; cu is less than or equal to 5.0 percent; mg is less than or equal to 0.2 percent; ca is less than or equal to 0.01 percent; RE is less than or equal to 0.2 percent; mo, W, nb, zr, the sum of any one or two or more than two of the Mo, W, nb, zr is 0.5-5.0%; the balance being Fe. The patent increases alloy strength by adding C, V to form a carbide VC strengthening phase, increases oxidation corrosion resistance of the alloy by a small amount of Cr and a large amount of Ni, and simultaneously adds W, mo to carry out solid solution strengthening and precipitates a part of Nb to carry out aging strengthening. The alloy has low Cr content of only 0.5-2.2 wt% and no other antioxidant element or antioxidant phase, and has room temperature strength up to 1200MPa but no high temperature use condition. Therefore, the application of the alloy on the main valve of the coal-fired generator set is severely limited.
Chinese patent CN1275630a describes a low cost low expansion nickel base alloy having the chemical composition (wt%) C0.15-0.35, ni 32-40, mo 0.3-0.95, mn 0.1-0.6, si 0.15-0.6, b 0.003-0.15, zr 0.005-0.01, and the balance Fe. The patent increases the alloy strength by adding Mo element and removes Cr to reduce the expansion coefficient, and the patent obviously cannot meet the requirements of oxidation resistance and high-temperature strength in a high-temperature environment although the cost is very low due to the fact that the strengthening elements are very few and no Cr exists at all.
In view of the above, there is a need to develop a new low expansion alloy and a preparation method thereof, which can meet the requirements of oxidation resistance and high temperature strength in high temperature environment, ensure the feasibility of engineering application of the alloy, and meet the application requirements in the field of electric power energy.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a low expansion alloy for a ultra-supercritical turbine fastener and a preparation method thereof, and the low expansion alloy is prepared by designing alloy components, adding and adjusting alloy elements, and adopting vacuum induction, vacuum consumable remelting, high-temperature homogenization diffusion and forging; the low-expansion alloy for the ultra-supercritical turbine fastener has a high-temperature thermal expansion coefficient greatly superior to that of GH2036 alloy, has excellent high-temperature mechanical property above 600 ℃, can meet the requirements of oxidation resistance and high-temperature strength in a high-temperature environment, and meets the requirement of selecting materials of the ultra-supercritical turbine main valve fastener.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
the invention provides a low expansion alloy for a fastening piece of an ultra-supercritical steam turbine, which comprises the following elements in percentage by mass: 5.00-6.00%, ti 0.10-0.40%, nb 2.50-3.50%, Y0.01-0.02%, fe:24.0 to 27.0 percent, and the balance of Co and unavoidable impurities.
Preferably, the low expansion alloy for the ultra-supercritical turbine fastener has a thermal expansion coefficient of less than or equal to 13.0x10 at the temperature of 650 DEG C -6 ℃。
Preferably, the low expansion alloy for the ultra-supercritical turbine fastener has fracture durability plasticity delta under the conditions of temperature 650 ℃ and pressure 586MPa 5 14 to 40 percent.
According to the second aspect of the invention, the preparation method of the low expansion alloy for the ultra-supercritical turbine fastener is provided, raw materials are proportioned according to the components of the low expansion alloy for the ultra-supercritical turbine fastener, and then the low expansion alloy for the ultra-supercritical turbine fastener is prepared by vacuum induction smelting, vacuum consumable remelting, high-temperature homogenization diffusion and forging in sequence.
Preferably, the vacuum induction smelting comprises the following steps:
(11) Adding a main material element Ni, cr, co, fe, adding C, vacuumizing to below 2.7Pa, raising the power to 300-600 kw for material conversion, and raising the power to 600-1000 kw and the temperature to 1520-1580 ℃ for refining after the main material element is clear;
(12) Reducing the power and the temperature of molten steel, and adding alloying elements Al, ti and Nb to carry out alloying smelting;
(13) Analyzing the components of molten steel, charging argon after Ni, cr, co, fe, al, ti, nb is in a target range, adding Y element, smelting at 200-500 kw power, tapping and pouring an electrode.
Preferably, in the step (11), the refining time is 30-60 min; and/or
In the step (12), the power is controlled to be 100-600 kw, and the temperature of molten steel is 1400-1470 ℃; and/or
In the step (13), the smelting time after adding the Y element is 5-10 min.
Preferably, in the vacuum consumable remelting process, the melting speed is controlled to be 2.0-5.0 kg/min, the current is 4000-6500A, and the voltage is 20-25V.
Preferably, in the high-temperature homogenizing diffusion process, the steel ingot obtained by vacuum consumable remelting is heated and kept at the temperature of 1050-1200 ℃ for more than 100 hours, and the heating rate of heating is controlled to be 30-70 ℃/h.
Preferably, in the forging process, the steel ingot subjected to high-temperature homogenization diffusion is heated to 1050-1150 ℃, firstly, the steel ingot is upset to half of the original height of the steel ingot, then the steel ingot is returned to the furnace to be heated to 1050-1150 ℃, and the temperature is kept for 60-120 min, and then the steel ingot is forged.
Preferably, in the forging process, the forging temperature is more than or equal to 900 ℃, and the forging stopping temperature is more than or equal to 850 ℃.
The design idea of the low expansion alloy composition for the ultra-supercritical turbine fastener is mainly based on the following points: (1) Co is used for replacing part of Fe, and the content of Co is increased to reduce the content of Fe, so that the high-temperature oxidation corrosion resistance of the alloy is improved on one hand, the high-temperature structure stability of the alloy is improved on the other hand, and the temperature bearing capacity of the alloy is improved. (2) The Cr is controlled to be 2.5-3.5 wt percent, so that the oxidation resistance of the alloy is improved; the Cr content should not be too high, otherwise the decrease in the coefficient of thermal expansion of the alloy would be adversely affected. (3) Al is added in a compound way, and the Al and the Ni are combined to form an intragranular crystal boundary strengthening phase; meanwhile, the oxidation brittleness of the grain boundary can be improved under a high-temperature environment, so that the high-temperature oxidation resistance of the alloy is greatly improved. (4) Nb element is added in a composite way, and the precipitated precipitation strengthening phase can improve the high-temperature strength and the durability of the alloy in the aging process of the alloy. (5) And trace Y elements are added in a compound way, so that alloy grain boundaries are purified, and the alloy hot working plasticity is improved.
The low expansion alloy for the ultra-supercritical turbine fastener has the following composition design principle:
c:0.01 to 0.03 percent, wherein C is an essential element for forming carbide in the nickel-based superalloy, and the content of C is lower than 0.01 percent, so that the carbide is less, the grain structure refinement and the performance are unfavorable, and the vacuum smelting deoxidation is also unfavorable; an excessive carbide formation with a C content of more than 0.03 causes excessive inclusion and segregation tendency, resulting in non-uniformity of grains and deterioration of alloy plasticity.
Cr:2.50 to 3.50 weight percent, and the addition amount of Cr element considers two factors, namely, the oxidation resistance of the alloy is improved, and the high-temperature plasticity of the alloy is improved; cr is one of the most effective elements for improving the oxidation of the alloy, but comprehensively considers the requirement of low expansion coefficient, and the Cr content is controlled to be 2.5-3.5 wt%.
Nb:2.50 to 3.50 weight percent, and adding a proper amount of Nb can improve the tensile strength of the alloy, thereby improving the high-temperature tissue stability of the material; however, excessive Nb element can lead to segregation during the smelting process, such as the creation of Laves-like brittle phase defects; the control range of Nb content in the invention is 2.50-3.50%.
Ti:0.10 to 0.40 weight percent, and adding a proper amount of Ti can improve the ageing strengthening effect of the material and the high-temperature strength of the alloy; however, the oxidation resistance of the material is affected by too high Ti content, and Ti is easy to form a low-melting-point phase, so that the melting point of the alloy is reduced, and the high-temperature service performance of the alloy is greatly limited; therefore, the control range of the Ti content of the invention is Ti:0.10-0.40%.
Al:5.00 to 6.00 weight percent of Al element is added, which is a bright spot designed by the composition of the invention; al and Ni combine to form an intragranular, grain boundary strengthening phase; the reinforced phase can reduce the oxidation brittleness of the grain boundary and improve the oxidation resistance of the material under a high-temperature environment; under the interaction with Cr element, the high-temperature-resistant and oxidation-resistant capabilities of the low-expansion alloy are greatly improved; however, the Al content is too high, and a large particle strengthening phase appears in the alloy, which affects the hot working plasticity of the alloy. Therefore, al is controlled to 5.00-6.00%.
Y:0.01 to 0.02 weight percent, and Y is taken as a rare earth element to be added into a second bright point designed for the composition of the patent; researches show that the addition of a proper amount of Y element can improve the plasticity of the alloy, in particular the high-temperature surface shrinkage; however, excessive Y element is adversely worse; comprehensively considering that the content of the Y element is controlled to be 0.01-0.02 wt%.
Co: the rest is that Co element can form an austenite matrix with Ni, cr and other elements, and the alloy heat intensity and the structure stability can be improved by reducing the stacking fault energy of the alloy, so that the precipitation of harmful phases can be avoided.
Compared with the prior art, the invention has the beneficial effects that:
the low expansion alloy for the ultra-supercritical turbine fastener and the preparation method thereof are prepared by designing alloy components, adding and adjusting alloy elements, and adopting vacuum induction, vacuum consumable remelting, high-temperature homogenization diffusion and forging; the low-expansion alloy for the ultra-supercritical turbine fastener has a high-temperature thermal expansion coefficient greatly superior to that of GH2036 alloy, has excellent high-temperature mechanical property above 600 ℃, can meet the requirements of oxidation resistance and high-temperature strength in a high-temperature environment, and meets the requirement of selecting materials of the ultra-supercritical turbine main valve fastener.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the present invention, but are not intended to limit the invention in any way.
The invention provides a low expansion alloy for a fastening piece of an ultra-supercritical steam turbine, which comprises the following components in percentage by mass: 0.01 to 0.0.3 percent of C, 2.50 to 3.50 percent of Cr, 26.0 to 30.0 percent of Ni, and Al: 5.00-6.00%, ti 0.10-0.40%, nb 2.50-3.50%, Y0.01-0.02%, fe:24.0 to 27.0 percent, and the balance of Co and unavoidable impurities.
The low expansion alloy for the ultra-supercritical turbine fastener has a thermal expansion coefficient less than or equal to 13.0x10 at the temperature of 650 DEG C -6 The temperature is lower than the temperature; fracture durability plasticity delta under the condition of loading temperature 650 ℃ and loading load tau=586 MPa 5 14-40%, and the duration time of the low expansion alloy for the ultra-supercritical turbine fastener is 20-200 h.
The low-expansion alloy for the ultra-supercritical turbine fastener is prepared from raw materials according to the components of the low-expansion alloy for the ultra-supercritical turbine fastener, and then sequentially carrying out vacuum induction smelting, vacuum consumable remelting, high-temperature homogenization diffusion and forging to prepare the low-expansion alloy for the ultra-supercritical turbine fastener; the method specifically comprises the following steps:
(1) Vacuum induction smelting, namely adding the prepared raw materials into a vacuum induction furnace to perform smelting, tapping and pouring electrodes; wherein the raw materials adopt selected high-purity metal Ni, cr, co, fe, al, ti, nb, Y raw material lump material surfaces for rust removal, cleaning and no greasy dirt. Alloying element Al, ti, nb, Y
The specific process is as follows:
(11) Adding a main material element Ni, cr, co, fe into a vacuum induction furnace, adding C, vacuumizing to below 2.7Pa, raising the power to 300-600 kw for material melting, and raising the power to 600-1000 kw for refining after the full molten liquid level keeps calm and no bubbles overflow, namely the main material element is clear, wherein the refining time is controlled to be 30-60 min; in the process, the C-O reaction is utilized to carry out degassing, so that the gas content in the molten steel is ensured to be reduced to the control requirement, for example, the O content is less than or equal to 0.005wt%.
(12) Reducing the power and the temperature of molten steel, and adding alloying elements Al, ti and Nb to carry out alloying smelting; wherein the power is reduced to 100-600 kw, and the temperature of molten steel is reduced to 1400-1470 ℃;
(13) Analyzing the molten steel component, charging argon after Ni, cr, co, fe, al, ti, nb is in a target range (namely the target range is the content range required by the low expansion alloy for the ultra-supercritical turbine fastener), controlling the pressure to be 25-35 kPa, adding Y element, smelting at the power of 200-500 kw, wherein the smelting time is 5-10 min, tapping and pouring the electrode.
(2) Vacuum consumable remelting
And carrying out consumable remelting on one end of the annealed electrode with the shrinkage cavity upwards, wherein the surface of the electrode needs to be cleaned, and dirt such as dirt, oxide skin, water stain and the like cannot be produced. Selecting a self-consuming crystallizer with the diameter of phi 423mm, smelting the electrode head by shrinkage cavity upwards, setting the smelting speed to be 2.0-5.0 kg/min, and controlling the current to be 4000-6500A and the voltage to be 20-25V. Breaking vacuum and stripping after remelting is finished for 90-180 min to obtain the steel ingot.
(3) High temperature homogenizing diffusion
Heating the steel ingot obtained by vacuum consumable remelting to 1050-1200 ℃ and preserving heat for more than 100 hours to perform high-temperature homogenization diffusion, wherein a certain heating rate is required to be adopted in the heating process for heating so as to avoid the generation of micro-molten pool defects in the steel ingot tissue; wherein the heating rate of heating is 30-70 ℃/h. After the steel ingot surface is cleaned, the subsequent processing is carried out.
(4) Forging
Heating the steel ingot subjected to high-temperature homogenization diffusion to 1050-1150 ℃, and upsetting to half the height of the steel ingot to increase the forging ratio and improve the uniformity of the steel, wherein the number of times of upsetting is 1-5 times, and the upsetting is specific according to actual conditions; and then the steel ingot is returned to the furnace and heated to 1050-1150 ℃, the temperature is kept for 60-120 min, and then forging is carried out, wherein the forging start temperature is more than or equal to 900 ℃, and the forging stop temperature is more than or equal to 850 ℃.
The low expansion alloy for ultra-supercritical turbine fasteners and the method for preparing the same according to the present invention will be further described with reference to specific examples; wherein the low expansion alloy for the ultra-supercritical turbine fastener in the embodiment comprises the following elements in percentage by weight: 0.01 to 0.0.3 percent of C, 2.50 to 3.50 percent of Cr, 26.0 to 30.0 percent of Ni, and Al: 5.00-6.00%, ti 0.10-0.40%, nb 2.50-3.50%, Y0.01-0.02%, fe:24.0 to 27.0 percent, and the balance of Co and unavoidable impurities.
Examples
The specific preparation process of the low expansion alloy for the ultra-supercritical turbine fastener in the embodiment is as follows:
(1) Vacuum induction smelting: the surfaces of the raw material blocks of the selected high-purity metal Ni, cr, co, fe are derusted, clean and free of greasy dirt. Main material element Ni, cr, co, fe is distributed according to the target components, vacuumized to below 2.7Pa, and power-up material melting is started, and the power is controlled at 300-600 KW. After the full-melting liquid level is kept calm and no bubbles overflow, namely the full-melting is carried out, the power is increased to 600-1000 kW, the temperature is increased to 1520-1580 ℃ for refining, and the refining time is about 30-60 min. Then the power value is reduced to 100-600 kW, the temperature of molten steel is reduced to 1400-1470 ℃, and elements such as Ti, al, nb and the like are added for alloying smelting. Taking a finished product sample for analysis, charging 25-30 kPa Ar when the content of all chemical elements is within the index range, adding Y element, smelting for 5-10 min at 200-500 KW power, and tapping and casting an electrode.
(2) Vacuum consumable remelting: and (3) carrying out consumable remelting on one end of the electrode with the shrinkage cavity upwards, wherein the electrode must be cleaned up and cannot be rusted, oil and dirt. A self-consuming crystallizer with the diameter of 423mm is selected, the melting speed is set to be 2.0-5.0 kg/min, the current is controlled to be 4000-6500A, and the voltage is controlled to be 20-25V. Breaking vacuum and stripping after remelting is finished for 90-180 min.
(3) Homogenizing and diffusing at high temperature: the steel ingot is heated and kept at the temperature of 1050-1200 ℃ for more than 100 hours to carry out high-temperature diffusion annealing, and the heating rate is controlled to be 30-70 ℃/h in the heating process. After the surface of the steel ingot is cleaned, the subsequent processing is carried out.
(4) Forging: the steel ingot is heated to 1050-1150 ℃, upsetting is carried out on the steel ingot for 1-5 times, and the upsetting is carried out to half of the original height of the steel ingot, so that the forging ratio is increased. And then returning the steel ingot to the furnace, heating to 1050-1150 ℃, preserving heat for 60-120 min, and forging to obtain the low expansion alloy for the ultra-supercritical turbine fastener, wherein the forging temperature is controlled to be more than or equal to 900 ℃ and the forging stopping temperature is controlled to be 850 ℃.
The low expansion alloy for the 5-furnace ultra-supercritical turbine fastener is produced according to the method, the specific components of the alloy are shown in table 2, part of parameters in the preparation process are shown in table 3, then the 5-furnace ultra-supercritical turbine fastener is sampled, and mechanical property tests are carried out respectively, and the results are shown in tables 4 and 5; as can be seen from tables 4 and 5, the low-expansion alloy for the ultra-supercritical turbine fastener has a high-temperature thermal expansion coefficient obviously superior to that of GH2036 alloy, has good high-temperature mechanical properties at 650 ℃, and can completely meet the material selection requirement of the ultra-supercritical turbine main valve fastener.
Table 2 elemental content (wt%) of furnace alloy 5 in the example
| C | Cr | Ni | Al | Ti | Nb | Y | Fe | Co | |
| 1 | 0.021 | 2.71 | 28.3 | 5.30 | 0.23 | 2.83 | 0.019 | 24.8 | Remainder of the process |
| 2 | 0.012 | 2.85 | 28.6 | 5.60 | 0.26 | 2.95 | 0.013 | 25.6 | Remainder of the process |
| 3 | 0.022 | 3.10 | 29.1 | 5.55 | 0.29 | 2.88 | 0.016 | 25.2 | Remainder of the process |
| 4 | 0.016 | 3.06 | 27.5 | 5.43 | 0.16 | 3.10 | 0.019 | 26.1 | Remainder of the process |
| 5 | 0.015 | 2.95 | 28.9 | 5.56 | 0.32 | 3.06 | 0.012 | 25.3 | Remainder of the process |
Table 3 parameters during the preparation of the 5 furnace alloy of the example
Table 4 high temperature thermal expansion coefficient of 5 furnace alloys in examples
Table 5 high temperature durable mechanical properties of the 5 furnace alloys of the examples
In view of the foregoing, the embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solution of the present invention may be modified or substituted without departing from the spirit and scope of the technical solution of the present invention, and the scope of the claims of the present invention should be covered.
Claims (3)
1. The low expansion alloy for the ultra-supercritical turbine fastener is characterized by comprising the following elements, by mass, 0.01-0.03% of C, 2.50-3.50% of Cr, 26.0-30.0% of Ni and Al: 5.00-6.00%, ti 0.10-0.40%, nb 2.50-3.50%, Y0.01-0.02%, fe:24.0 to 27.0 percent, the balance being Co and unavoidable impurities,
the low expansion alloy for the ultra-supercritical turbine fastener is prepared by the following preparation method:
the raw materials are proportioned according to the components of the low expansion alloy for the ultra-supercritical turbine fastener, and then the low expansion alloy for the ultra-supercritical turbine fastener is prepared by vacuum induction smelting, vacuum consumable remelting, high-temperature homogenizing diffusion and forging in sequence,
the vacuum induction smelting comprises the following steps:
(11) Adding a main material element Ni, cr, co, fe, adding C, vacuumizing to below 2.7Pa, raising the power to 300-600 kW for material conversion, and raising the power to 600-1000 kW and the temperature to 1520-1580 ℃ for refining after the main material element is clear;
(12) Reducing the power and the temperature of molten steel, and adding alloying elements Al, ti and Nb to carry out alloying smelting;
(13) Analyzing the composition of molten steel, charging argon after Ni, cr, co, fe, al, ti, nb is within a target range, adding Y element, smelting at 200-500 kW power, tapping, pouring electrodes,
in the step (11), the refining time is 30-60 min;
in the step (12), the power is controlled to be 100-600 kW, and the temperature of molten steel is 1400-1470 ℃;
in the step (13), the smelting time after adding the Y element is 5-10 min,
in the vacuum consumable remelting process, the melting speed is controlled to be 2.0-5.0 kg/min, the current is 4000-6500A, the voltage is 20-25V,
in the high-temperature homogenizing diffusion process, the steel ingot obtained by vacuum consumable remelting is heated and kept at the temperature of 1050-1200 ℃ for more than 100 hours, and the heating rate of heating is controlled to be 30-70 ℃/h
In the forging process, the steel ingot subjected to high-temperature homogenization diffusion is heated to 1050-1150 ℃, firstly, the steel ingot is upset to half of the original height of the steel ingot, then the steel ingot is returned to the furnace to be heated to 1050-1150 ℃, the temperature is kept for 60-120 min, and then the forging is carried out,
in the forging process, the forging temperature is not less than 900 ℃, the forging stopping temperature is not less than 850 ℃,
the low expansion alloy for the ultra-supercritical turbine fastener has the fracture durability plasticity delta under the conditions that the loading temperature is 650 ℃ and the loading load is 586MPa 5 14 to 40 percent.
2. The low expansion alloy for a fastener for a super supercritical turbine as claimed in claim 1, wherein said low expansion alloy for a fastener for a super supercritical turbine has a thermal expansion coefficient of 13.0x10 or less at 650 ℃ -6 ℃。
3. A preparation method of the low expansion alloy for the ultra-supercritical turbine fastener is characterized in that raw materials are proportioned according to the components of the low expansion alloy for the ultra-supercritical turbine fastener according to claim 1, and then the low expansion alloy for the ultra-supercritical turbine fastener is prepared by vacuum induction smelting, vacuum consumable remelting, high-temperature homogenization diffusion and forging in sequence,
the vacuum induction smelting comprises the following steps:
(11) Adding a main material element Ni, cr, co, fe, adding C, vacuumizing to below 2.7Pa, raising the power to 300-600 kW for material conversion, and raising the power to 600-1000 kW and the temperature to 1520-1580 ℃ for refining after the main material element is clear;
(12) Reducing the power and the temperature of molten steel, and adding alloying elements Al, ti and Nb to carry out alloying smelting;
(13) Analyzing the composition of molten steel, charging argon after Ni, cr, co, fe, al, ti, nb is within a target range, adding Y element, smelting at 200-500 kW power, tapping, pouring electrodes,
in the step (11), the refining time is 30-60 min;
in the step (12), the power is controlled to be 100-600 kW, and the temperature of molten steel is 1400-1470 ℃;
in the step (13), the smelting time after adding the Y element is 5-10 min,
in the vacuum consumable remelting process, the melting speed is controlled to be 2.0-5.0 kg/min, the current is 4000-6500A, the voltage is 20-25V,
in the high-temperature homogenizing diffusion process, the steel ingot obtained by vacuum consumable remelting is heated and kept at the temperature of 1050-1200 ℃ for more than 100 hours, the heating rate of heating is controlled to be 30-70 ℃/h,
in the forging process, the steel ingot subjected to high-temperature homogenization diffusion is heated to 1050-1150 ℃, firstly, the steel ingot is upset to half of the original height of the steel ingot, then the steel ingot is returned to the furnace to be heated to 1050-1150 ℃, the temperature is kept for 60-120 min, and then the forging is carried out,
in the forging process, the forging temperature is not less than 900 ℃, the forging stopping temperature is not less than 850 ℃,
the low expansion alloy for the ultra-supercritical turbine fastener has the fracture durability plasticity delta under the conditions that the loading temperature is 650 ℃ and the loading load is 586MPa 5 14 to 40 percent.
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