Heat treatment process for large-size ultralow-expansion alloy forgings

Abstract

The invention provides a heat treatment process for a large-size ultralow-expansion alloy forge piece. The heat treatment process comprises the following steps: S1, finishing a workpiece; s2, supplementing meat; s3, clamping the workpiece; s4, secondary heat treatment including medium-temperature solution treatment and low-temperature stabilizing treatment; due to the two-stage heat treatment mode including medium-temperature solution treatment and low-temperature stabilizing treatment, the 4J32B oversized special-shaped expansion alloy forging is subjected to heat treatment, and the ultralow expansion coefficient, namely the expansion coefficient # imgabs0 #, within the ultra-wide temperature range of-55 DEG C to 100 DEG C can be obtained.

Description

Technical Field

[0001] The invention belongs to the field of heat treatment of metal functional materials, and in particular relates to a heat treatment process for large-sized ultra-low expansion alloy forgings. Background Art

[0002] Invar 4J36 and Super Invar 4J32 are both low expansion alloys. Their notable feature is that they have a very low thermal expansion coefficient within a specific temperature range. The expansion coefficient of Invar 4J36 is Expansion coefficient of super-Invar alloy 4J32 It is widely used to make instrument parts with high precision requirements and approximately constant dimensions.

[0003] The thermal expansion coefficients of these two low expansion alloys are obtained after heat treatment. The heat treatment system specified in YB / T5241-2005 "Low Expansion Iron-Nickel, Iron-Nickel-Cobalt Alloys" is: heat the semi-finished sample to 840±10℃, keep it warm for 1h, water quench, and then process the sample into a finished sample, keep it warm at 315±10℃ for 1h, and cool it in the furnace or in the air.

[0004] According to the user's demand for ultra-low expansion alloys, it is necessary to develop an alloy material with an ultra-low expansion coefficient in an ultra-wide temperature range of -55℃~100℃. However, both of the above alloys cannot meet the requirements.

[0005] Therefore, those skilled in the art are committed to developing a method to achieve a desired expansion coefficient. Heat treatment process for large-size ultra-low expansion alloy forgings. Summary of the invention

[0006] The purpose of the present invention is to provide a method for achieving the expansion coefficient required by the prior art. Heat treatment process for large-size ultra-low expansion alloy forgings.

[0007] The object of the present invention is achieved by adopting the following scheme: A heat treatment process for large-sized ultra-low expansion alloy forgings comprises the following steps:

[0008] S1. Finishing the workpiece: remove the oxide scale on the workpiece surface caused by high temperature forging to ensure that the workpiece surface is heated more evenly and the temperature measurement is more accurate.

[0009] S2. Filling: Mix the high temperature mud with water glass and fill the pits where the workpiece is missing meat, fill and compact the pits; water glass increases the viscosity of the high temperature mud, and controls the dryness and wetness of the mixture, so that it can be manually kneaded into a ball without falling apart and without liquid seepage. Fill the mixture into the pits where the workpiece is missing meat, fill and compact the pits;

[0010] S3. Workpiece clamping: Place the workpiece on a flat material tray, hoist it and place it in the effective heating area of ​​the heat treatment furnace, and use refractory spacers to separate the workpiece from the flat material tray;

[0011] S4. Secondary heat treatment: including medium-temperature solution treatment and low-temperature stabilization treatment. During heat treatment, the temperature is raised with the furnace to ensure that the inside and surface of the workpiece are heated evenly;

[0012] S4.1. Medium-temperature solution treatment: The holding temperature of medium-temperature solution treatment is 750-800℃, the holding time is not less than 4 hours, and the cooling method after furnace removal is water cooling;

[0013] S4.2. Low temperature stabilization treatment: The temperature of low temperature stabilization treatment is 280-300°C, the holding time is 4 hours, and the furnace discharge method is air cooling;

[0014] Further, step S1 includes the following two steps:

[0015] S1.1. Milling: Milling is used to remove the surface oxide scale produced during the high temperature forging process of the workpiece;

[0016] S1.2. Grinding: Grind the areas that cannot be milled and where the workpiece is lacking in meat to remove the surface oxide scale.

[0017] Furthermore, in step S4.1, the time from when the workpiece is taken out of the furnace to when it enters the water is controlled to be no more than 3 minutes, and the cooling time is no less than 4 hours.

[0018] Furthermore, in step S4.1, the cooling water is circulating cooling water, and the water temperature is less than or equal to 30°C.

[0019] Furthermore, in step S3, an external thermocouple is connected to the workpiece to accurately measure the temperature of the workpiece.

[0020] Furthermore, in step S2, the high temperature mud and water glass are uniformly mixed in a weight ratio of 2:1.

[0021] Furthermore, the chemical composition of the large-size ultra-low expansion alloy forging is calculated by weight percentage as follows: C: ≤0.05; Si: ≤0.10; Mn: ≤0.30; S: ≤0.010; P: ≤0.010; Al: 0-0.40; Ti: 0-0.40; Nb: 0.4-0.8; Ni: 31.5-34.0; Co: 3.20-4.50; the remainder is Fe and unavoidable impurities, and the alloy forging is named 4J32B alloy forging.

[0022] Furthermore, the large-size ultra-low expansion alloy forging has specifications of 900 mm in height, 1080 mm in width, and 1480 mm in length, with a hollow interior with an envelope diameter of 800 mm, a maximum wall thickness of 260 mm, and a minimum wall thickness of 150 mm.

[0023] The invention has the advantages that the heat treatment process of the large-sized ultra-low expansion alloy forgings of the invention includes a two-stage heat treatment method of medium-temperature solution treatment and low-temperature stabilization treatment, and the heat treatment of the 4J32B ultra-large-sized special-shaped expansion alloy forgings can obtain an ultra-low expansion coefficient in an ultra-wide temperature range of -55°C to 100°C, that is, the expansion coefficient BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the implementation structure of the workpiece clamping of the present invention;

[0025] Figure 2 The average linear expansion coefficient value and curve diagram at the maximum wall thickness in Example 1 of the present invention;

[0026] Figure 3 The figure shows the average linear expansion coefficient value and curve diagram at the minimum wall thickness in Example 1 of the present invention. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to understand the characteristics and effects of the present application, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein have the common meanings understood by those skilled in the art for the present application. In case of conflict, the definitions in this specification shall prevail.

[0028] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present application in any way, that is, the content of the present application can be implemented without being limited by any specific theory or mechanism.

[0029] As used herein, "this application" means "the present invention" or "the present disclosure".

[0030] The use of "one", "an", "a kind" or similar expressions to describe the components and technical features described in this application is merely for the convenience of expression and to provide a general meaning to the scope of this application. Therefore, such description should be understood to include one or at least one, and the singular also includes the plural, unless it is obvious that it refers to another meaning.

[0031] In this document, "or its combination" means "or any combination thereof", and "any one", "any one" means "any one", "any one" or "any one".

[0032] As used herein, the terms "comprises," "including," "having," "containing," or any other similar terms are open-ended transitional phrases that are intended to cover non-exclusive inclusions. For example, a composition or article containing multiple elements is not limited to the elements listed herein, but may also include other elements that are not explicitly listed but are generally inherent to the composition or article. In addition, unless otherwise expressly stated, the term "or" refers to an inclusive "or" rather than an exclusive "or." For example, any of the following situations satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), and both A and B are true (or exist). In addition, in this article, the terms "comprising", "including", "having", and "containing" should be interpreted as being specifically disclosed and simultaneously covering closed connections such as "consisting of", "consisting of", "the remainder of", and "substantially consisting of", "mainly consisting of", "mainly consisting of", "basically containing", "essentially consisting of", "essentially consisting of", "essentially containing", and other connecting words.

[0033] In this article, all features or conditions such as numerical values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are only for simplicity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be deemed to have covered and specifically disclosed all possible sub-ranges and individual values ​​within the range (including integers and fractions), especially integer values. For example, the range description of "1.0 to 8.0" or "between 1.0 and 8.0" or "between 1.0 and 8.0" should be deemed to have specifically disclosed all sub-ranges such as 1.0 to 8.0, 1.0 to 7.0, 2.0 to 8.0, 2.0 to 6.0, 3.0 to 6.0, 4.0 to 8.0, 3.0 to 8.0, etc., and should be deemed to cover endpoint values, especially sub-ranges defined by integer values, and should be deemed to have specifically disclosed individual values ​​such as 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, etc. Unless otherwise indicated, the foregoing method of interpretation applies to all contents of the entire application, regardless of whether the scope is broad or not.

[0034] If the quantity, concentration or other numerical value or parameter is expressed as a range, a preferred range (or a better range) or a series of upper and lower limits, it should be understood that all ranges consisting of any pair of the upper limit or preferred value (or a better value) of the range and the lower limit or preferred value (or a better value) of the range have been specifically disclosed herein, regardless of whether these ranges are disclosed separately. In addition, if a numerical range is mentioned herein, unless otherwise specified, the range should include its endpoints and all integers and fractions within the range.

[0035] In this document, numerical values ​​should be understood to have the accuracy of the number of significant digits of the numerical value, provided that the purpose of the invention can be achieved. For example, the number 40.0 should be understood to cover the range of 39.50 to 40.49.

[0036] It should be understood that the features disclosed in the various embodiments herein may be arbitrarily combined to form the technical solution of the present application, as long as there is no contradiction in the combination of these features.

[0037] The present application will be described below with specific implementations and examples. It should be understood that these specific implementations and examples are merely illustrative and are not intended to limit the scope of the present application and its use.

[0038] Unless otherwise specified, the methods, reagents and conditions used in the preparation examples, comparative examples and examples below are conventional methods, reagents and conditions in the art. The high-temperature mud in the following examples is dura-tab mortar produced by United Minerals (Tianjin) Co., Ltd. of the United States; the water glass is a sodium silicate solution produced by Wuhan Jiyesheng Chemical Co., Ltd., CAS No.: 1344-09-8, molecular formula: Na2O3Si, purity 99%.

[0039] Example 1

[0040] A large-size ultra-low expansion alloy forging, with specifications of 900mm in height, 1080mm in width, 1480mm in length, with a hollow interior with an envelope diameter of 800mm, a maximum wall thickness of 260mm, and a minimum wall thickness of 150mm. Its chemical composition by weight percentage is: C: 0.05; Si: 0.08; Mn: 0.30; S: 0.001; P: 0.006; Al: 0.20; Ti: 0.20; Nb: 0.5; Ni: 33.0; Co: 4.0; the balance is Fe and unavoidable impurities.

[0041] C: 0.05, Si: 0.10, Mn: 0.30, S: 0.010, P: 0.010, Al: 0.2, Ti: 0.4, Nb: 0.8, Ni: 31.5, Co: 4.5, and the balance is Fe and inevitable impurities.

[0042] The preparation process includes the following steps:

[0043] S1. Finishing the workpiece: remove the oxide scale on the workpiece surface caused by high temperature forging to ensure that the workpiece surface is heated more evenly and the temperature measurement is more accurate.

[0044] S1.1. Milling: Milling is used to remove the surface oxide scale produced during the high temperature forging process of the workpiece;

[0045] S1.2. Grinding: Use conventional grinding wheels to grind the areas that cannot be milled and where the workpiece is lacking in meat, and remove the surface oxide scale;

[0046] S2. Filling: Mix the high temperature mud with water glass and fill it into the pits where the workpiece lacks meat. The high temperature mud and water glass are evenly mixed in a weight ratio of 2:1. Water glass increases the viscosity of the high temperature mud and controls the dryness and wetness of the mixture so that it can be manually kneaded into a ball without falling apart and without liquid seepage. Fill the mixture into the pits where the workpiece lacks meat and fill and compact the pits.

[0047] S3. Workpiece clamping: Use a flat plate with a thickness of 80 to 100 mm. The flat plate is made of high-temperature material castings that can withstand long-term high-temperature heating of 800°C without deformation. Figure 1 , place the workpiece 1 on a flat material tray 2, hoist it into the effective heating zone of the heat treatment furnace, and separate the workpiece 1 from the flat material tray 2 with a refractory spacer 3; connect an external thermocouple 4 to the workpiece 1 to accurately measure the temperature of the workpiece.

[0048] S4. Secondary heat treatment: including medium-temperature solution treatment and low-temperature stabilization treatment. During heat treatment, the temperature is raised with the furnace to ensure that the inside and surface of the workpiece are heated evenly;

[0049] S4.1. Medium-temperature solution treatment: The holding temperature of medium-temperature solution treatment is 750-800℃, and the holding time is not less than 4 hours. The holding time is determined according to the heating temperature and the maximum thickness of the workpiece. The cooling method after the workpiece is taken out of the furnace is water cooling, and the cooling water is circulating cooling water with a water temperature of 25℃. The time from the workpiece being taken out of the furnace to entering the water is controlled to be 2.5 minutes, and the cooling time is 4.5 hours. After the workpiece is cooled, it is lifted out and the water is drained.

[0050] S4.2. Low temperature stabilization treatment: The workpiece after draining the water is subjected to low temperature stabilization treatment. The temperature of low temperature stabilization treatment is 280-300℃, the insulation time is 4 hours, and the furnace removal method is air cooling.

[0051] The average linear expansion coefficient is tested at the maximum wall thickness and minimum wall thickness of the workpiece after heat treatment. The test method is as follows: 1. Drill a round bar (test bar) with a diameter of 20 mm at the corresponding position of the forging;

[0052] 2. Take a small sample from the test rod and process it into an expansion performance sample with a diameter of 6mm and a length of 25mm;

[0053] 3. Hitachi thermomechanical analyzer TMA7100 is used to test the expansion coefficient.

[0054] The test results are: (See attached Figure 2 ), minimum wall thickness (See attached Figure 3), expansion coefficient

[0055] Example 2

[0056] A large-size ultra-low expansion alloy forging, with specifications of 900mm in height, 1080mm in width, 1480mm in length, with a hollow interior with an envelope diameter of 800mm, a maximum wall thickness of 260mm, and a minimum wall thickness of 150mm. Its chemical composition by weight percentage is: C: 0.05, Si: 0.10, Mn: 0.30, S: 0.010, P: 0.010, Al: 0.2, Ti: 0.4, Nb: 0.8, Ni: 31.5, Co: 4.5, and the balance is Fe and unavoidable impurities.

[0057] The preparation process includes the following steps:

[0058] S1. Finishing the workpiece: remove the oxide scale on the workpiece surface caused by high temperature forging to ensure that the workpiece surface is heated more evenly and the temperature measurement is more accurate.

[0059] S1.1. Milling: Milling is used to remove the surface oxide scale produced during the high temperature forging process of the workpiece;

[0060] S1.2. Grinding: Use conventional grinding wheels to grind the areas that cannot be milled and where the workpiece is lacking in meat, and remove the surface oxide scale;

[0061] S2. Filling: Mix the high temperature mud with water glass and fill it into the pits where the workpiece lacks meat. The high temperature mud and water glass are evenly mixed in a weight ratio of 2:1. Water glass increases the viscosity of the high temperature mud and controls the dryness and wetness of the mixture so that it can be manually kneaded into a ball without falling apart and without liquid seepage. Fill the mixture into the pits where the workpiece lacks meat and fill and compact the pits.

[0062] S3. Workpiece clamping: Use a flat plate with a thickness of 80 to 100 mm. The flat plate is made of high-temperature material castings that can withstand long-term high-temperature heating of 800°C without deformation. Figure 1 , place the workpiece 1 on a flat material tray 2, hoist it into the effective heating zone of the heat treatment furnace, and separate the workpiece 1 from the flat material tray 2 with a refractory spacer 3; connect an external thermocouple 4 to the workpiece 1 to accurately measure the temperature of the workpiece.

[0063] S4. Secondary heat treatment: including medium-temperature solution treatment and low-temperature stabilization treatment. During heat treatment, the temperature is raised with the furnace to ensure that the inside and surface of the workpiece are heated evenly;

[0064] S4.1. Medium-temperature solution treatment: The holding temperature of medium-temperature solution treatment is 750-800℃, and the holding time is not less than 4 hours. The holding time is determined according to the heating temperature and the maximum thickness of the workpiece. The cooling method after the workpiece is out of the furnace is water cooling, and the cooling water is circulating cooling water with a water temperature of 30℃. The time from the workpiece out of the furnace to the water entry is controlled to be 3 minutes, and the cooling time is 5 hours. After the workpiece is cooled, it is lifted out and the water is drained;

[0065] S4.2. Low temperature stabilization treatment: The workpiece after draining the water is subjected to low temperature stabilization treatment. The temperature of low temperature stabilization treatment is 280-300℃, the insulation time is 4 hours, and the furnace removal method is air cooling.

[0066] The average linear expansion coefficient was tested at the maximum wall thickness and minimum wall thickness of the workpiece after heat treatment, respectively, in the same way as in Example 1, and the test results were: Minimum wall thickness Expansion coefficient

[0067] Example 3

[0068] A large-size ultra-low expansion alloy forging, with specifications of 900mm in height, 1080mm in width, 1480mm in length, with a hollow interior with an envelope diameter of 800mm, a maximum wall thickness of 260mm, and a minimum wall thickness of 150mm. Its chemical composition by weight percentage is: C: 0.04, Si: 0.092, Mn: 0.28, S: 0.0085, P: 0.0092, Al: 0.4, Ti: 0.2, Nb: 0.4, Ni: 34.0, Co: 3.2, and the balance is Fe and unavoidable impurities.

[0069] The preparation process includes the following steps:

[0070] S1. Finishing the workpiece: remove the oxide scale on the workpiece surface caused by high temperature forging to ensure that the workpiece surface is heated more evenly and the temperature measurement is more accurate.

[0071] S1.1. Milling: Milling is used to remove the surface oxide scale produced during the high temperature forging process of the workpiece;

[0072] S1.2. Grinding: Use conventional grinding wheels to grind the areas that cannot be milled and where the workpiece is lacking in meat, and remove the surface oxide scale;

[0073] S2. Filling: Mix the high temperature mud with water glass and fill it into the pits where the workpiece lacks meat. The high temperature mud and water glass are evenly mixed in a weight ratio of 2:1. Water glass increases the viscosity of the high temperature mud and controls the dryness and wetness of the mixture so that it can be manually kneaded into a ball without falling apart and without liquid seepage. Fill the mixture into the pits where the workpiece lacks meat and fill and compact the pits.

[0074] S3. Workpiece clamping: Use a flat plate with a thickness of 80 to 100 mm. The flat plate is made of high-temperature material castings that can withstand long-term high-temperature heating of 800°C without deformation. Figure 1 , place the workpiece 1 on a flat material tray 2, hoist it into the effective heating zone of the heat treatment furnace, and separate the workpiece 1 from the flat material tray 2 with a refractory spacer 3; connect an external thermocouple 4 to the workpiece 1 to accurately measure the temperature of the workpiece.

[0075] S4. Secondary heat treatment: including medium-temperature solution treatment and low-temperature stabilization treatment. During heat treatment, the temperature is raised with the furnace to ensure that the inside and surface of the workpiece are heated evenly;

[0076] S4.1. Medium-temperature solution treatment: The holding temperature of medium-temperature solution treatment is 750-800℃, and the holding time is not less than 4 hours. The holding time is determined according to the heating temperature and the maximum thickness of the workpiece. The cooling method after the workpiece is taken out of the furnace is water cooling, and the cooling water is circulating cooling water with a water temperature of 28℃. The time from the workpiece being taken out of the furnace to entering the water is controlled to be 2.8 minutes, and the cooling time is 4.8 hours. After the workpiece is cooled, it is lifted out and the water is drained.

[0077] S4.2. Low temperature stabilization treatment: The workpiece after draining the water is subjected to low temperature stabilization treatment. The temperature of low temperature stabilization treatment is 280-300℃, the insulation time is 4 hours, and the furnace removal method is air cooling.

[0078] The average linear expansion coefficient was tested at the maximum wall thickness and minimum wall thickness of the workpiece after heat treatment, respectively, in the same way as in Example 1, and the test results were: Minimum wall thickness Expansion coefficient

[0079] Example 4

[0080] A large-size ultra-low expansion alloy forging, with specifications of 900mm in height, 1080mm in width, 1480mm in length, with a hollow interior with an envelope diameter of 800mm, a maximum wall thickness of 260mm, and a minimum wall thickness of 150mm. Its chemical composition by weight percentage is: C: 0.03, Si: 0.081, Mn: 0.25, S: 0.0083, P: 0.0091, Al: 0.4, Ti: 0.2, Nb: 0.6, Ni: 32.5, Co: 4.0, and the balance is Fe and unavoidable impurities.

[0081] The preparation process includes the following steps:

[0082] S1. Finishing the workpiece: remove the oxide scale on the workpiece surface caused by high temperature forging to ensure that the workpiece surface is heated more evenly and the temperature measurement is more accurate.

[0083] S1.1. Milling: Milling is used to remove the surface oxide scale produced during the high temperature forging process of the workpiece;

[0084] S1.2. Grinding: Use a conventional grinding wheel to grind the areas that cannot be milled and where the workpiece is lacking in meat, and remove the surface oxide scale.

[0085] S2. Filling: Mix the high temperature mud with water glass and fill it into the pits where the workpiece lacks meat. The high temperature mud and water glass are evenly mixed in a weight ratio of 2:1. Water glass increases the viscosity of the high temperature mud and controls the dryness and wetness of the mixture so that it can be manually kneaded into a ball without falling apart and without liquid seepage. Fill the mixture into the pits where the workpiece lacks meat and fill and compact the pits.

[0086] S3. Workpiece clamping: Use a flat plate with a thickness of 80 to 100 mm. The flat plate is made of high-temperature material castings that can withstand long-term high-temperature heating of 800°C without deformation. Figure 1 , place the workpiece 1 on a flat material tray 2, hoist it into the effective heating zone of the heat treatment furnace, and separate the workpiece 1 from the flat material tray 2 with a refractory spacer 3; connect an external thermocouple 4 to the workpiece 1 to accurately measure the temperature of the workpiece.

[0087] S4. Secondary heat treatment: including medium-temperature solution treatment and low-temperature stabilization treatment. During heat treatment, the temperature is raised along with the furnace to ensure uniform heating inside and on the surface of the workpiece.

[0088] S4.1. Medium-temperature solution treatment: The holding temperature of medium-temperature solution treatment is 750-800℃, and the holding time is not less than 4 hours. The holding time is determined according to the heating temperature and the maximum thickness of the workpiece. The cooling method after the workpiece is taken out of the furnace is water cooling, and the cooling water is circulating cooling water with a water temperature of 27℃. The time from the workpiece being taken out of the furnace to entering the water is controlled to be 2 minutes, and the cooling time is 5.1 hours. After the workpiece is cooled, it is lifted out and the water is drained.

[0089] S4.2. Low temperature stabilization treatment: The workpiece after draining the water is subjected to low temperature stabilization treatment. The temperature of low temperature stabilization treatment is 280-300℃, the insulation time is 4 hours, and the furnace removal method is air cooling.

[0090] The average linear expansion coefficient was tested at the maximum wall thickness and minimum wall thickness of the workpiece after heat treatment, respectively, in the same way as in Example 1, and the test results were: Minimum wall thickness Expansion coefficient

[0091] The above embodiments illustrate that heat treatment of 4J32B super-large shaped expansion alloy forgings can obtain an ultra-low expansion coefficient in an ultra-wide temperature range of -55°C to 100°C, that is, the expansion coefficient

[0092] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification made to the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A heat treatment process for large-size ultra-low expansion alloy forgings, characterized in that: The following steps are involved: S1. Finishing workpiece: remove the oxide scale on the workpiece surface caused by high temperature forging; S2. Filling: Mix high temperature mud and water glass and fill the pits where the workpiece is lacking meat, fill and compact the pits; S3. Workpiece clamping: Place the workpiece on a flat material tray, hoist it and place it in the effective heating area of ​​the heat treatment furnace, and use refractory spacers to separate the workpiece from the flat material tray; S4. Secondary heat treatment: including medium temperature solution treatment and low temperature stabilization treatment; S4.

1. Medium-temperature solution treatment: The holding temperature of medium-temperature solution treatment is 750-800℃, the holding time is not less than 4 hours, and the cooling method after furnace removal is water cooling; S4.

2. Low temperature stabilization treatment: The temperature of low temperature stabilization treatment is 280-300℃, the insulation time is 4 hours, and the furnace removal method is air cooling.

2. The heat treatment process for large-size ultra-low expansion alloy forgings according to claim 1 is characterized in that: Step S1 includes the following two steps: S1.

1. Milling: Milling is used to remove the surface oxide scale produced during the high temperature forging process of the workpiece; S1.

2. Grinding: Grind the areas that cannot be milled and where the workpiece is lacking in meat to remove the surface oxide scale.

3. The heat treatment process for large-size ultra-low expansion alloy forgings according to claim 1 is characterized in that: In step S4.1, the time from when the workpiece leaves the furnace to when it enters the water is controlled to be no more than 3 minutes, and the cooling time is no less than 4 hours.

4. The heat treatment process for large-size ultra-low expansion alloy forgings according to claim 1 is characterized in that: In step S4.1, the cooling water is circulating cooling water, and the water temperature is less than or equal to 30°C.

5. The heat treatment process for large-size ultra-low expansion alloy forgings according to claim 1, characterized in that: In step S3, an external thermocouple is connected to the workpiece to accurately measure the temperature of the workpiece.

6. The heat treatment process for large-size ultra-low expansion alloy forgings according to claim 1, characterized in that: In step S2, the high temperature mud and water glass are uniformly mixed in a weight ratio of 2:

1.

7. The heat treatment process for large-size ultra-low expansion alloy forgings according to claim 1, characterized in that: The chemical composition of the large-size ultra-low expansion alloy forging is calculated by weight percentage: C: ≤0.05; Si: ≤0.10; Mn: ≤0.30; S：≤0.010； P: ≤0.010; Al: 0~0.40; Ti: 0~0.40; Nb: 0.4~0.8; Ni: 31.5~34.0; Co: 3.20-4.50; the balance is Fe and inevitable impurities.

8. The heat treatment process for large-size ultra-low expansion alloy forgings according to claim 1, characterized in that: The large-size ultra-low expansion alloy forging has specifications of 900 mm in height, 1080 mm in width, and 1480 mm in length, with a hollow interior having an envelope diameter of 800 mm, a maximum wall thickness of 260 mm, and a minimum wall thickness of 150 mm.

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