A method for stabilizing the size of super-large components

Abstract

The present invention relates to a method for dimensional stabilization of super-large heterogeneous components. After the forging of the present invention has been subjected to a "solid solution + aging" treatment, the forging is subjected to a three-cycle deep cryogenic treatment by a gas-liquid method, so as to promote the transformation of a portion of unstable reversed austenite, and at the same time improve the stability of the remaining reversed austenite, improve the stability of the material structure, and thus improve the dimensional stability of the forging. By adopting this dimensional stabilization treatment, the austenite structure containing about 35% after the "solid solution + aging" treatment of the forging can be effectively stabilized to an austenite structure containing about 11% that will not transform at -170 to -190°C, which greatly improves the structural stability of the material, and thus improves the dimensional stability of the forging.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgical production technology, in particular to a method for stabilizing the size of an ultra-large heterogeneous component. Background Art

[0002] With the rapid development of my country's heavy equipment manufacturing industry, many large equipment forgings have put forward higher requirements on appearance and material properties. In particular, some multifunctional testing equipment has put forward extremely high requirements on material quality uniformity and shape stability.

[0003] 00Cr12Ni10MoTi is a martensitic aged stainless steel with high strength and excellent low-temperature toughness. It is often used to manufacture rocket parts. The working conditions of forgings are relatively harsh. To ensure the normal operation of the equipment, the forgings need to have good dimensional stability to avoid affecting the operation and evaluation of the equipment. 00Cr12Ni10MoTi forms a certain amount of reversed austenite through aging, thereby obtaining excellent low-temperature toughness, but if the reversed austenite decomposes in the subsequent process, it will affect the size of the forging.

[0004] Therefore, it is urgent to develop an effective dimensional stabilization treatment method for super-large circular arc deformed components. Based on this, the present invention has studied and successfully completed the dimensional stabilization treatment of super-large circular arc deformed components of 00Cr12Ni10MoTi maraging stainless steel, and determined the good dimensional stability of the product through dimensional measurement during subsequent machining and determination of the amount of residual austenite. The present invention introduces a dimensional stabilization treatment method for a large-diameter semi-circular arc component with an outer diameter of R5500mm, an inner diameter of R3500mm, and a thickness of 220mm, the material of which is 00Cr12Ni10MoTi. There is currently no report on the dimensional stabilization treatment method for super-large deformed components of the present invention. Summary of the invention

[0005] The purpose of the present invention is to provide a method for stabilizing the size of an ultra-large heterogeneous component in view of the deficiencies in the prior art.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] In a first aspect, the present invention provides a method for stabilizing the size of an ultra-large component, the method comprising three cycles of cryogenic treatment by a gas-liquid method, comprising the following steps:

[0008] S1: Place the forging as a whole into a cryogenic device, fill the cryogenic tank with liquid nitrogen, and use the gasification method to cool the forging to -170~-190℃ and keep it isothermal for 3 hours;

[0009] S2: After the insulation is completed, open the valve to discharge the liquid nitrogen, and the forging slowly returns to room temperature, completing a deep cryogenic treatment;

[0010] S3: After an interval of 3-6 hours, repeat steps S1 and S2 to complete the second and third cryogenic treatments respectively, wherein the cooling rate in step S1 is 0-15°C / min.

[0011] Further, step S1 is: placing the forging as a whole into a cryogenic device, and filling the cryogenic tank with liquid nitrogen, using a gasification method to cool the forging to -170 to -190°C and isothermally maintaining the temperature for 3 hours / 500mm.

[0012] Furthermore, step S1 also includes using a fan to assist liquid nitrogen gasification.

[0013] Furthermore, step S1 also includes cooling the forging to -170 to -190°C and then isothermally treating the forging for 3 hours / 500 mm.

[0014] Furthermore, step S1 also includes filling with liquid nitrogen before keeping warm.

[0015] Furthermore, step S2 also includes stirring the low-temperature gas in the cryogenic tank by using a circulating fan after discharging the liquid nitrogen, thereby driving internal and external circulation at the same time.

[0016] Furthermore, in step S3, the temperature must be restored before the second and third cryogenic treatments.

[0017] Furthermore, the temperature recovery rate is ≤15°C / min.

[0018] In a second aspect, the present invention provides application of the method as described above in preparing dimensionally stable extra-large heterogeneous components.

[0019] The present invention has the advantages that:

[0020] The present invention can effectively stabilize the austenite structure containing about 35% of the forging after "solid solution + aging" treatment to an austenite structure containing about 11% that will not change at -170 to -190°C by performing three deep cold cycle treatments on the forging made of 00Cr12Ni10MoTi, thereby greatly improving the organizational stability of the material. The experimental results show that after the first deep cold treatment, the maximum deformation size of the forging in the height direction is 10mm compared with that before the deep cold treatment, and the austenite content is reduced from 35% before the deep cold to about 20% after the furnace test block is detected; after the second deep cold treatment, the maximum deformation size of the forging in the height direction is 5mm compared with that before the first deep cold treatment, and the austenite content is reduced from 30% to 11% after the furnace test block is detected; after the third deep cold treatment, the forging size is measured to have no obvious change compared with the end of the second deep cold, and the austenite content of the furnace test block is basically the same as that after the end of the second deep cold. In the subsequent finishing process, the forging has good dimensional stability. This verifies that after the forgings have undergone three deep cryogenic treatments, the austenite structure in the forgings has undergone three cycles of cooling, and the organizational stability is greatly improved, thereby improving the dimensional stability of the forgings.

[0021] Generally, cryogenic treatment is mostly used for smaller forgings. The cryogenic tank required for the forgings used in this article exceeds the largest cryogenic tank equipment currently available. In addition, since the forgings are too large, the conventional cryogenic method (conventionally directly immersing in liquid nitrogen from room temperature) is prone to excessive local stress, causing deformation or possible cracking of the forgings. Therefore, this article uses the gas-liquid method to deep cool the forgings.

[0022] Before reaching the cryogenic temperature, the temperature of the cryogenic tank is gradually reduced by controlling the temperature of the gas entering the cryogenic tank, so that the forging is slowly cooled at a rate of ≤15℃ / min. At the same time, near the cryogenic temperature zone,

[0023] The forging is kept isothermally at -170-190℃ for a long time to make the temperature inside and outside the workpiece consistent, and then liquid nitrogen is poured in to keep the temperature for a long enough time to fully decompose the residual austenite inside the forging.

[0024] That is, for large forgings, the method of limiting speed cooling and setting intermediate isothermal steps can ensure that the forgings can be fully deep cooled, while avoiding deformation or cracking caused by thermal stress and uneven structural stress due to excessive internal and external temperature differences during the deep cooling process.

[0025] Another point of the present invention is that the residual ferrite content of the material can be stabilized only after multiple deep cooling. Generally, forgings only need to be done once. However, the present material needs to gradually reduce the amount of residual austenite in the material through repeated deep cooling. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Attached Figure 1 This is a deep cooling process diagram for large diameter semi-circular arc components. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0028] Example

[0029] 1 Experimental methods

[0030] The dimensional stabilization treatment of the large-diameter semicircular arc-shaped component with an outer diameter of R5500mm, an inner diameter of R3500mm, and a thickness of 220mm and made of 00Cr12Ni10MoTi is specifically implemented as follows:

[0031] Step 1: After the forging is subjected to "750℃ solution treatment + 500℃ aging", the forging is placed flat in a cryogenic equipment with an effective size of 12000×6000×1500mm for cryogenic treatment at -196℃. The cryogenic cooling process adopts a gas-liquid mixing method. A contact thermocouple is placed on the workpiece to measure the workpiece temperature in real time, and a thermocouple is placed on the inner wall of the cryogenic equipment to monitor the ambient temperature in real time for temperature control.

[0032] Step 2: After the workpiece and thermocouple are placed, start to slowly fill the cryogenic tank with liquid nitrogen, and turn on the fan to assist the liquid nitrogen gasification. The speed of filling liquid nitrogen determines the temperature of the space in the cryogenic tank, and the temperature of the space in the tank directly affects the temperature of the workpiece. The speed of filling liquid nitrogen is adjusted by the temperature signal fed back by the cryogenic tank thermocouple and the contact thermocouple;

[0033] Step 3: The workpiece is slowly cooled down under the influence of the temperature of the deep cold tank space, and the cooling rate is ≤15℃ / min. After the temperature of the deep cold tank couple is reduced to -170℃~-190℃, adjust the amount of liquid nitrogen charged, and start isothermal when the temperature of all contact thermocouples is reduced to the range of -170℃~-190℃. The isothermal process lasts for 3 hours. The isothermal process requires continuous replenishment of liquid nitrogen and the use of fans to assist in gasification to keep the workpiece temperature in the range of -170℃~-190℃.

[0034] Step 4: After the isothermal treatment is completed, quickly fill the workpiece with liquid nitrogen to immerse it. After the workpiece is immersed, the insulation timer starts. During the insulation process, the amount of liquid nitrogen filled needs to be controlled to ensure that the liquid nitrogen does not drop due to gasification and the workpiece is exposed to the liquid surface. The entire liquid nitrogen insulation time is 3.5 hours.

[0035] Step 5: After the insulation is completed, open the valve to quickly discharge the liquid nitrogen, use the circulating fan to stir the low-temperature gas in the deep cold tank, and pull the internal and external circulation at the same time to slowly return the workpiece to room temperature. The return speed does not exceed 15℃ / min.

[0036] Step 6: After slowly returning to room temperature, keep warm at room temperature for at least 3 hours before starting the second deep cooling.

[0037] Step 7: Repeat steps 2 to 6 to complete the second deep freezing treatment.

[0038] Step 8: Repeat steps 2 to 5, slowly return the temperature to room temperature, and complete the third deep freezing treatment; the dimensional stabilization treatment is completed.

[0039] 2 Experimental results

[0040] During the deep cryogenic treatment of forgings, the size of the forgings and the austenite content of the furnace test blocks were measured. After the first deep cryogenic treatment, the maximum deformation size of the forgings in the height direction was 10mm compared with that before the deep cryogenic treatment. The austenite content of the furnace test blocks was reduced from 35% before deep cryogenic treatment to about 20% after testing; after the second deep cryogenic treatment, the maximum deformation size of the forgings in the height direction was 5mm compared with that before the first deep cryogenic treatment. The austenite content of the furnace test blocks was reduced from 30% to 11% after testing; after the third deep cryogenic treatment, the size of the forgings was measured to have no significant change compared with the end of the second deep cryogenic treatment. The austenite content of the furnace test blocks was basically the same as that after the end of the second deep cryogenic treatment. In the subsequent finishing process, the dimensional stability of the forgings is good.

[0041] This verifies that after the forgings have undergone three deep-cryogenic treatments at -170 to -190°C, the austenite structure in the forgings has undergone three cycles of cooling, and the organizational stability is greatly improved, thereby improving the dimensional stability of the forgings.

[0042] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the principle of the present invention. These improvements and supplements should also be regarded as the scope of protection of the present invention.

Claims

1. A method for stabilizing the size of an extra-large component, characterized in that: The method is to perform three-cycle cryogenic treatment by gas-liquid method, comprising the following steps: S1: Place the forging as a whole into a cryogenic device, fill the cryogenic tank with liquid nitrogen, and use the gasification method to cool the forging to -170--190°C and keep it isothermal for 3 hours; a contact thermocouple is placed on the workpiece to measure the workpiece temperature in real time, and a thermocouple is placed on the inner wall of the cryogenic device to monitor the ambient temperature in real time for temperature control; After the temperature displayed by the cryogenic tank couple drops to -170℃~-190℃, adjust the amount of liquid nitrogen charged, and when the temperature of all contact thermocouples drops to the range of -170℃~-190℃, start isothermal. During the isothermal process, liquid nitrogen is continuously replenished and gasification is completed with the assistance of a fan to keep the temperature of the workpiece in the range of -170℃~-190℃. After the isothermal treatment, liquid nitrogen is filled to immerse the workpiece. After the workpiece is immersed, the insulation timer starts. During the insulation process, the amount of liquid nitrogen filled needs to be controlled to ensure that the liquid nitrogen does not drop due to gasification and the workpiece is exposed to the liquid surface. The entire liquid nitrogen insulation time is 3.5h; S2: After the insulation is completed, open the valve to discharge the liquid nitrogen, and the forging slowly returns to room temperature, completing a deep cryogenic treatment; S3: After an interval of 3-6 hours, repeat steps S1 and S2 to complete the second and third cryogenic treatments respectively, wherein the cooling rate in step S1 is 0-15°C / min; and In step S3, the temperature must be restored before the second and third cryogenic treatments, and the rate of the temperature restoration is ≤15°C / min.

2. The method according to claim 1, characterized in that Step S1 is: placing the forging as a whole into a cryogenic device, and filling the cryogenic tank with liquid nitrogen, using a gasification method to cool the forging to -170 to -190°C and isothermally holding for 3 hours / 500mm.

3. The method according to claim 1, characterized in that Step S1 also includes using a fan to assist in gasification of liquid nitrogen.

4. The method according to claim 3, characterized in that Step S1 also includes cooling the forging to -170 to -190°C and then isothermally treating the forging for 3 hours / 500 mm.

5. The method according to claim 4, characterized in that Step S1 also includes charging liquid nitrogen before keeping warm.

6. The method according to claim 5, characterized in that Step S2 also includes using a circulating fan to stir the low-temperature gas in the cryogenic tank after discharging the liquid nitrogen, while driving internal and external circulation.

7. Use of the method according to any one of claims 1 to 6 in preparing dimensionally stable extra-large heterogeneous components.

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