Method for regulating and controlling structure of Inconel 625 alloy and Inconel 625 alloy obtained through method

Abstract

The embodiment of the invention provides a structure regulation and control method for Inconel 625 alloy, and belongs to the technical field of special alloy processing and manufacturing. The structure regulation and control method comprises the steps that cold drawing is conducted, specifically, an Inconel 625 alloy bar is subjected to primary cold drawing till the sectional area of the Inconel 625 alloy bar is reduced by 10%-30%, and a treated Inconel 625 alloy bar is obtained; aging heat treatment is conducted, specifically, the treated Inconel 625 alloy bar is placed in a heating device at the temperature of 750-800 DEG C to be heated for 50-70 minutes, then the temperature is reduced to 600-700 DEG C, and heat preservation is conducted for 10-100 hours; after cold drawing, crystal grain orientation distribution in the cold-drawn steel plate is changed, formed texture dislocation proliferation is carried out to improve the yield strength and the tensile strength of the cold-drawn steel plate, then the texture dislocation density is reduced through aging heat treatment, and meanwhile the gamma ''phase precipitation amount is increased to strengthen the internal organization structure and release stress of the cold-drawn steel plate. According to the structure regulation and control method, cold drawing and aging heat treatment are combined, so that the alloy strength is improved, the phenomenon of non-uniform section strengthening is improved, residual stress is reduced, plasticity after cold machining is improved, and the long-term service stability of the alloy is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of special alloy processing and manufacturing, and particularly relates to a method for controlling the microstructure of Inconel 625 alloy and the Inconel 625 alloy obtained thereby. Background Art

[0002] As a typical nickel-based austenitic wrought superalloy, Inconel 625 alloy has good high-temperature mechanical properties, structural stability, and hot and cold working properties. Since the internal crystal structure of Inconel 625 alloy is face-centered cubic, it can withstand complex and harsh environmental conditions. For example, it has good corrosion resistance in chloride media, especially in harsh service environments such as petroleum and petrochemical industries. For another example, Inconel 625 alloy is also widely used in aeroengine components under ultra-high temperature environments, nuclear reactor cooling systems under strong radiation environments, and 3D printing laser powder melting components with high plasticity requirements. The microstructure and properties of Inconel 625 alloy depend on its chemical composition and the microstructure evolution during plastic processing, especially the plastic processing has an important effect on the change of its microstructure.

[0003] On the one hand, when cold working Inconel 625 alloy, such as cold rolling or cold drawing, although the cold deformation process has the advantages of high precision and good continuity of the deformation process. However, for Inconel 625 alloy after cold deformation treatment, especially rod-shaped Inconel 625 alloy, the strengthening effects at different positions on the cross-section of the specimen are not uniform, resulting in residual stress, which affects its structural stability and service life.

[0004] On the other hand, when hot working Inconel 625 alloy, the hot deformation resistance of nickel-based alloy is relatively large, it is sensitive to hot working processes, it is difficult to control the alloy microstructure, and the grain growth rate becomes fast, resulting in excessive grain growth. Usually, the microstructure defects after forging are difficult to eliminate by heat treatment.

[0005] In view of this, based on cold working and hot working processes, a new method for controlling the microstructure of Inconel 625 alloy and the Inconel 625 alloy obtained thereby are proposed to fully or partially solve the above problems. Summary of the Invention

[0006] To address at least one of the above problems and defects in the prior art, embodiments of the present invention provide a method for microstructure control of Inconel 625 alloy and Inconel 625 alloy obtained thereby. By combining cold drawing and age heat treatment on Inconel 625 alloy bars, while significantly enhancing the strength of the alloy, it improves the defect of uneven cross-section strengthening effect caused by cold drawing deformation, greatly reduces residual stress, improves the plasticity of the alloy after cold working, and enhances the stability of the alloy during long-term service. The technical solution is as follows:

[0007] According to one aspect of the present invention, a method for microstructure control of Inconel 625 alloy is provided. The microstructure control method includes:

[0008] Cold drawing: Cold draw an Inconel 625 alloy bar once until its cross-sectional area is reduced by 10% - 30% to obtain a processed Inconel 625 alloy bar;

[0009] Age heat treatment: Place the processed Inconel 625 alloy bar in a heating device at a temperature of 750 - 800 °C and heat for 50 - 70 minutes, then lower the temperature of the heating device to 600 - 700 °C and hold for 10 - 100 hours;

[0010] Wherein, after the Inconel 625 alloy bar is cold drawn, the distribution of grain orientations inside it changes, and the formed texture dislocations multiply to increase its yield strength and tensile strength. After age heat treatment, the texture dislocation density is reduced, and at the same time, the precipitation amount of γ" phase increases to strengthen its internal microstructure and release stress.

[0011] In some embodiments, the preparation steps of the Inconel 625 alloy bar specifically include:

[0012] Obtain an Inconel 625 alloy steel ingot by melting an Inconel 625 alloy raw material;

[0013] Obtain an Inconel 625 alloy steel billet by heating and forging the Inconel 625 alloy steel ingot;

[0014] Obtain an Inconel 625 alloy bar by successively performing rolling treatment, annealing treatment, and polishing treatment on the Inconel 625 alloy steel billet.

[0015] In some embodiments, specifically, the Inconel 625 alloy steel billet is a square steel billet with a size of 80 mm * 80 mm - 120 mm * 120 mm; the cross-sectional diameter range of the Inconel 625 alloy bar is 15 - 25 mm.

[0016] In some embodiments, alternatively, a cold drawing device is used to cold-draw an Inconel 625 alloy bar. Preferably, the cold-drawing speed range of the cold drawing device is 8-15 m / min, and the cross-sectional diameter range of the Inconel 625 alloy bar after cold drawing is 15-17 mm.

[0017] In some embodiments, preferably, when the cross-sectional area of the Inconel 625 alloy bar after cold drawing is reduced by 30%, the yield strength of the Inconel 625 alloy bar is 2.4-2.7 times that before cold drawing; the tensile strength of the Inconel 625 alloy bar is 1.4-1.6 times that before cold drawing.

[0018] In some embodiments, alternatively, the heating speed range of the heating device is 12-17 °C / min; the cooling speed range of the heating device is 8-12 °C / min.

[0019] In some embodiments, preferably, the heating temperature of the Inconel 625 alloy bar during aging heat treatment after cold drawing is 760 °C, the heating time is 1 hour, and the yield ratio of the Inconel 625 alloy bar after heating drops from 100% before heating to 90%-93%.

[0020] In some embodiments, preferably, during aging heat treatment, when the holding temperature is 650 °C and the holding time is 24 hours, the yield strength of the Inconel 625 alloy bar is increased by 100-105 MPa compared to before holding. When the holding temperature is 650 °C and the holding time is 96 hours, the yield strength of the Inconel 625 alloy bar is increased by 90-95 MPa compared to before holding.

[0021] In some embodiments, preferably, during aging heat treatment, when the holding temperature is 650 °C and the holding time is 24 hours, the tensile strength of the Inconel 625 alloy bar is increased by 75-80 MPa compared to before holding; when the holding temperature is 650 °C and the holding time is 96 hours, the tensile strength of the Inconel 625 alloy bar is increased by 80-85 MPa compared to before holding.

[0022] According to another aspect of the present invention, an Inconel 625 alloy is provided. The Inconel 625 alloy is obtained by cold-drawing and aging heat treatment of an Inconel 625 alloy raw material using the above-mentioned microstructure control method. The yield strength, tensile strength, and plasticity of the Inconel 625 alloy are all improved.

[0023] An Inconel 625 alloy microstructure regulation method provided by an embodiment of the present invention and the Inconel 625 alloy obtained thereby have at least one or a part of at least one of the following advantages:

[0024] (1) By cold drawing an Inconel 625 alloy bar, the strength of the alloy is improved, and then the stability of the alloy during long-term service is obtained through aging heat treatment;

[0025] (2) By combining cold drawing and aging heat treatment of the Inconel 625 alloy bar, the defect of uneven strengthening effect at different positions of the cross-section caused by cold drawing deformation is improved, the residual stress is greatly reduced, and the alloy structure stability is improved;

[0026] (3) By directly cold drawing an Inconel 625 alloy bar to reach the required cross-sectional diameter at one time, multiple drawing operations are not required and the reduction ratio is high. The maximum drawing deformation degree can reduce the cross-sectional area by 30%, thus avoiding the defect of uneven strengthening caused by a small reduction ratio;

[0027] (4) By cold drawing an Inconel 625 alloy bar, the degree of anisotropy inside it can be effectively increased, thereby changing the grain orientation distribution inside it, which helps the accumulation of texture dislocations and generates new texture dislocation sources, thus enabling the proliferation and accumulation of texture dislocations, and significantly improving the yield strength and tensile strength of the alloy;

[0028] (5) By cold drawing before aging heat treatment, the precipitation temperature and precipitation rate of the γ'' phase can be effectively reduced, and the temperature range for γ'' phase precipitation can be effectively expanded, so that the aging heat treatment can be completed under the conditions of lower temperature and shorter time;

[0029] (6) Through the heating process of aging heat treatment, it helps to increase the combined precipitation of γ'' phase and various carbides in the Inconel 625 alloy, and can effectively improve its yield strength and tensile strength;

[0030] (7) Through the heat preservation process of aging heat treatment, the residual stress can be effectively released and it helps to reduce the texture dislocation density inside the Inconel 625 alloy, so as to achieve the improvement of alloy strength and alloy hardness while also taking into account better plasticity. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] These and / or other aspects and advantages of the present invention will become apparent and be readily understood from the following description of the preferred embodiments in conjunction with the accompanying drawings, wherein:

[0032] Figure 1Process flow diagram of the microstructure regulation method of Inconel 625 alloy according to an embodiment of the present invention;

[0033] Figure 2 Schematic diagram of the physical state photos of Inconel 625 alloy bars of Comparative Examples 1-4 according to the present invention;

[0034] Figure 3 Diffraction peak curve diagram of the internal texture dislocation accumulation of Inconel 625 alloy bars of Comparative Examples 1-4 according to the present invention;

[0035] Figure 4 Curve diagram of the strength of the engineering strain of Inconel 625 alloy bars of Comparative Examples 1-4 according to the present invention;

[0036] Figure 5 Curve diagram of the strength of the engineering strain of Inconel 625 alloy bars of Examples 1, 2, 4, 5 and Comparative Example 4 according to the present invention;

[0037] Figure 6 Schematic diagram of the test results of the yield strength of Inconel 625 alloy bars of Examples 1-7 and Comparative Examples 1-5 according to the present invention;

[0038] Figure 7 Schematic diagram of the test results of the tensile strength of Inconel 625 alloy bars of Examples 1-7 and Comparative Examples 1-5 according to the present invention;

[0039] Figure 8 Schematic diagram of the test results of the yield ratio of Inconel 625 alloy bars of Examples 1-7 and Comparative Examples 1-5 according to the present invention;

[0040] Figure 9 Microstructure diagram of Inconel 625 alloy bar before cold drawing according to Example 5 of the present invention;

[0041] Figure 10 Microstructure diagram of Inconel 625 alloy bar after cold drawing according to Example 5 of the present invention;

[0042] Figure 11 TEM diagram of Inconel 625 alloy bar after cold drawing according to Example 5 of the present invention;

[0043] Figure 12 Microstructure diagram of Inconel 625 alloy bar after cold drawing and aging heat treatment according to Example 5 of the present invention. Detailed implementation manners

[0044] The technical solution of the present invention will be further specifically described below through embodiments in conjunction with the accompanying drawings. In the specification, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall inventive concept of the present invention and should not be construed as a limitation of the present invention.

[0045] Inconel 625 alloy is widely used in special environments and special equipment. For example, load-bearing components in oil collection equipment are usually selected to be made of Inconel 625 alloy material. In order to ensure that Inconel 625 alloy can have corresponding mechanical properties and mechanical performance in different application scenarios, it is necessary to specifically strengthen the performance of Inconel 625 alloy through further processing.

[0046] The tissue regulation method of Inconel 625 alloy provided by the embodiment of the present invention first uses a cold deformation process (preferably a cold drawing process) to obtain an improvement in the mechanical properties of Inconel 625 alloy, and then obtains an improvement in the mechanical properties and long-term stable service performance of Inconel 625 alloy through a heat treatment process (preferably aging heat treatment).

[0047] Specifically, the tissue regulation method of the Inconel 625 alloy preferably combines the cold drawing and aging heat treatment process methods, and adjusts the internal tissue structure of the Inconel 625 alloy through texture dislocation strengthening and γ'' phase precipitation supplementary strengthening, thereby improving the mechanical properties and mechanical performance of the Inconel 625 alloy. Cold drawing is to cold draw an Inconel 625 alloy bar once to reduce its cross-sectional area by 10% - 30% to obtain a processed Inconel 625 alloy bar. Aging heat treatment is to place the cold-drawn Inconel 625 alloy bar in a heating device at a temperature of 750 - 800 °C and heat it for 50 - 70 minutes, and then reduce the temperature of the heating device to 600 - 700 °C and keep it warm for 10 - 100 hours. After the Inconel 625 alloy bar is cold-drawn, the distribution of grain orientations inside it changes, and the formed texture dislocations proliferate to increase its yield strength and tensile strength. After aging heat treatment, the texture dislocation density is reduced, and at the same time, the amount of γ'' phase precipitation increases to strengthen its internal tissue structure and release stress.

[0048] In order to illustrate in detail the method for controlling the microstructure of Inconel 625 alloy of the present invention, the following specific embodiments and each example are described by taking Inconel 625 alloy bars as an example. Those skilled in the art can understand that Inconel 625 alloy bars are only an illustrative example, and other shapes of Inconel 625 alloy, such as Inconel 625 alloy plates and sheets, can also be manufactured by other cold working forms, and the optimization of the mechanical properties, mechanical properties, long-term service stability, etc. of the alloy can be achieved through the microstructure control method combined with aging heat treatment.

[0049] See Figure 1 , which shows the complete process flow of the method for controlling the microstructure of Inconel 625 alloy. The complete processing process that needs to be experienced to obtain Inconel 625 alloy bars meeting the performance requirements successively includes: smelting, forging, rolling, polishing, cold drawing, aging heat treatment and natural cooling. Among them, the core process also includes obtaining Inconel 625 alloy bars with different initial strengths through cold drawing. After completing cold drawing, the texture dislocation density inside the Inconel 625 alloy bars is reduced through aging heat treatment, the residual stress is released, and the plasticity of the alloy is improved. At the same time, the precipitation strengthening of γ'' phase is used to supplement the decrease in mechanical strength caused by the decrease in texture dislocation density. Through the combined action of texture dislocation strengthening and γ'' phase precipitation strengthening, the mechanical properties of Inconel 625 alloy bars are improved and the internal residual stress is released to improve the machining performance and structural stability. The steps of this process flow specifically include:

[0050] Step S100: Melting the Inconel 625 alloy raw material to obtain an Inconel 625 alloy steel ingot.

[0051] Step S200: Heating and forging the Inconel 625 alloy steel ingot to obtain an Inconel 625 alloy steel billet.

[0052] Preferably, the Inconel 625 alloy steel billet after heating and forging is a square steel billet, and the size range of the square steel billet is 80mm * 80mm to 120mm * 120mm.

[0053] More preferably, the size of the square steel billet is 100mm * 100mm.

[0054] Step S300: Sequentially subjecting the Inconel 625 alloy steel billet to rolling treatment, annealing treatment and polishing treatment to obtain Inconel 625 alloy bars.

[0055] Preferably, a square steel billet of 100mm*100mm is rolled into a cylindrical Inconel625 alloy bar with a diameter ranging from 15 to 25mm.

[0056] More preferably, the diameter of the Inconel 625 alloy bar is 20mm. After stress relief annealing, it is ground and polished into an Inconel 625 alloy bar with a diameter of 18mm.

[0057] Step S400: Cold drawing. The Inconel 625 alloy bar is cold drawn once using a cold drawing device until its cross-sectional area is reduced by 10% - 30%.

[0058] Preferably, the cold drawing device uses a double-chain cold drawing machine with a cold drawing speed ranging from 8 to 15m / min.

[0059] More preferably, the Inconel 625 alloy bar with a diameter of 18mm is cold drawn on the double-chain cold drawing machine at a speed of 10 - 12m / min until the cross-sectional diameter is 15 - 17mm, corresponding to a reduction rate of 10% - 30%.

[0060] Step S500: Aging heat treatment. The cold-drawn Inconel 625 alloy bar is placed in a heating device at a temperature of 750 - 800°C and heated for 50 - 70 minutes, and then the temperature of the heating device is reduced to 600 - 700°C and held for 10 - 100 hours.

[0061] Preferably, the heating device is an electric resistance furnace, and the heating speed range of the electric resistance furnace is 12 - 17°C / min, and the cooling rate range is 8 - 12°C / min.

[0062] More preferably, the electric resistance furnace is heated to 760°C at a speed of 15°C / min, then the Inconel 625 alloy bar is put in and heated for 1h. Then the electric resistance furnace reduces the heating temperature of 760°C to 650°C at a speed of 10°C / min and holds for 12h - 96h.

[0063] Step S600: Take out the Inconel 625 alloy bar that has completed aging heat treatment from the heating device and place it in a room temperature environment for natural cooling.

[0064] Among them, the cold drawing process in step S400 is mainly used to improve the strength and hardness of Inconel 625 alloy bars. During the cold drawing process, the diameter of the Inconel 625 alloy bars can be reduced to varying degrees, and the internal crystal structure will also change during the cold drawing process. For example, the amount of texture dislocations in the crystal structure tissue gradually increases, thereby improving the yield strength and tensile strength of the Inconel 625 alloy bars. The aging heat treatment process in step S500 is mainly used to improve the plasticity of the Inconel 625 alloy bars and release the residual stress accumulated during the cold drawing process.

[0065] In order to be able to elaborate in detail the process and effect of the embodiment of the present invention on the microstructure control of Inconel 625 alloy. It particularly relates to the process flow, process parameters of cold drawing and aging heat treatment, as well as the mechanical properties and mechanical properties that the Inconel 625 alloy can achieve after cold drawing and aging heat treatment. The following takes the processing of Inconel 625 alloy bars as an example and is described through Examples 1-7 and Comparative Examples 1-5.

[0066] Referring to Table 1, it shows the cross-sectional diameter and reduction ratio of the Inconel 625 alloy bars obtained during the cold drawing process in Examples 1-7 and Comparative Examples 1-5, as well as the aging heat treatment system.

[0067] Table 1 Processing parameters of Inconel 625 alloy bars in each example and comparative example

[0068]

[0069]

[0070] Inconel 625 alloy can be prepared by using pure metals such as metallic chromium, niobium bars, nickel plates, molybdenum, aluminum, and titanium, and adopting the vacuum induction melting method (VIM) and the vacuum arc remelting method (VAR) to obtain Inconel 625 alloy steel ingots. Among them, the content distribution of each element component in the Inconel 625 alloy steel ingot is shown in Table 2.

[0071] Table 2 Content of each element component in Inconel 625 alloy steel ingot

[0072]

[0073] In each example and each comparative example, the cross-sectional diameter of the initial Inconel 625 alloy bars obtained through steps S100 - S300 is 18 mm. Among them, referring to Figure 2, showing photos of Inconel 625 alloy bars of Comparative Examples 1-4, where Comparative Examples 1-4 respectively correspond to no cold drawing (cross-sectional diameter 18 mm), cold drawing to a cross-sectional diameter of 17 mm (area reduction rate 10%), cold drawing to a cross-sectional diameter of 16 mm (area reduction rate 20%), and cold drawing to a cross-sectional diameter of 15 mm (area reduction rate 30%). At the same time, no aging heat treatment was carried out on Comparative Examples 1-4.

[0074] In one example, specifically, during the cold drawing process, the cold drawing deformation of the Inconel 625 alloy bar is formed in one step, and the required cross-sectional size of the Inconel 625 alloy bar is directly achieved through one-time cold drawing.

[0075] For example, the cross-sectional diameter of the initial Inconel 625 alloy bar after preliminary forging, rolling, and polishing is 18 mm, and the required cross-sectional diameter of the processed Inconel 625 alloy bar is 15 mm. Then, through one-time cold drawing, the cross-sectional diameter can be directly reduced from 18 mm to 15 mm. At this time, relative to the cross-sectional area of the initial Inconel 625 alloy bar, the cross-sectional area of the Inconel 625 alloy bar after one-time cold drawing is reduced by 30%, that is, the area reduction rate reaches 30%.

[0076] See Figure 3 , showing the diffraction peak curves of the cumulative amount of texture dislocations in the Inconel 625 alloy bars of Comparative Examples 1-4. From Figure 3 Analysis shows that with the increase of the area reduction rate, the accumulation of texture dislocations in the Inconel 625 alloy bar gradually increases. Along with cold drawing, texture dislocations pile up and new texture dislocation sources are generated, forming texture dislocation multiplication. This strengthening of texture dislocation multiplication helps to improve the yield strength and tensile strength of the Inconel 625 alloy bar.

[0077] After cold drawing, from microscopic structure observation and analysis, it can be seen that cold drawing deformation significantly increases the deformation texture of the Inconel 625 alloy bar, making the anisotropy inside it more obvious and changing the distribution of grain orientations. Further, through measurement, the amount of texture dislocations inside the Inconel 625 alloy bar can increase by about 90 times, and the dislocation strengthening effect is significantly enhanced. In particular, cold drawing deformation significantly improves the yield strength and tensile strength of the Inconel 625 alloy bar. And, with the increase of the area reduction rate, the increase in yield strength and tensile strength also increases.

[0078] See Figure 4 , showing the strength curves of engineering strain of the Inconel 625 alloy bars of Comparative Examples 1-4. From Figure 4Analysis shows that after cold drawing deformation, the plasticity of Inconel 625 alloy bars will decrease. In particular, with the increase of the reduction ratio, the uniform elongation cross-section of Inconel 625 alloy bars becomes smaller. As Figure 4 shown, the Inconel 625 alloy bar with a reduction ratio of 30% quickly reaches the maximum strain strength and then fractures. This is because the uniform expansion of texture dislocations is related to the ability of texture dislocation growth and movement. After cold drawing deformation, a large number of texture dislocation tangles and accumulations have been generated in the internal microstructure of Inconel 625 alloy bars. These texture dislocation tangles and accumulations seriously hinder the further movement of texture dislocations, thus hindering the generation of new work-hardening phenomena. Therefore, aging heat treatment needs to be carried out after cold drawing to improve the uniform distribution of internal elements and the stability of the microstructure of Inconel 625 alloy bars by strengthening the precipitation of γ'' phase.

[0079] The cold deformation process refers to the processing technology of plastic deformation of metals at temperatures below the recrystallization temperature. Work-hardening phenomena will occur during the cold deformation process, which helps to improve the mechanical strength of metal materials.

[0080] For example, for rod-shaped and tubular metal materials, cold rolling processes, cold drawing processes, etc. are usually used to complete cold deformation processing. During the cold deformation processing, with the deformation of the metal material, texture dislocation pile-ups and texture dislocation bands will be formed inside it. Further, with the gradual increase of the deformation amount of the metal material, the texture dislocation bands inside it will also bend, and then new texture dislocation walls will be generated in the bent texture dislocation bands.

[0081] Although the above-mentioned texture dislocation pile-ups or texture dislocation bands have a significant strengthening effect on many mechanical properties of Inconel 625 alloy, for example, the yield strength and tensile strength of Inconel 625 alloy bars after cold deformation treatment can be greatly improved. However, due to the limited reduction ratio (the percentage of cross-sectional area reduction) during the cold deformation process, the strengthening effect of Inconel 625 alloy bars at different positions on its cross-section is not uniform, and residual stresses will be accumulated inside it. The remaining residual stresses will deform due to structural instability during its service life, thus affecting its service life.

[0082] Therefore, after completing the cold deformation process, continue to carry out heat treatment on Inconel 625 alloy bars, so that Inconel 625 alloy bars can effectively release internal residual stresses while retaining the strengthened mechanical properties, improve the internal structural stability, and enhance the stability of the alloy during long-term service.

[0083] The heat treatment process refers to a processing technology that heats metal materials, alloy materials, etc. in a certain medium to a certain temperature, maintains them at this temperature for a certain period of time, and then cools them at different speeds in different media to control their properties by changing the microscopic structure on their surface or inside.

[0084] Furthermore, age hardening heat treatment refers to a heat treatment process in which alloy materials, after undergoing processing technologies such as solution treatment, cold plastic deformation, casting, forging, etc., are then placed at a certain temperature, and their properties, shape, and size change with the placement time. The purpose of age hardening heat treatment is to release the internal stress of alloy materials, stabilize their internal organizational structure, and improve the mechanical properties of alloy materials.

[0085] For example, when the temperature setting of age hardening heat treatment is in the range of 649 - 871 °C, γ'' phase and various carbides will precipitate inside the Inconel 625 alloy during the placement process. The combined precipitation of γ'' phase and carbides can significantly increase the yield strength and tensile strength of the Inconel 625 alloy.

[0086] Furthermore, during the age hardening heat treatment process, by adjusting the age hardening heat treatment regime, the residual stress accumulated inside the cold - deformed Inconel 625 alloy can be effectively released, thereby improving its mechanical properties, such as processing plasticity, service performance, service life, etc.

[0087] In one example, through experiments and measurement and analysis, it is known that inside the Inconel 625 alloy bar, γ'' particles are formed in the form of metastable phase within the temperature range of 595 - 760 °C. When it is aged at 760 °C for 1 hour, its alloy plasticity can be improved, and at the same time, the elements in its organizational structure can be evenly distributed, and the strengthening non - uniformity caused by cold drawing can be reduced as much as possible.

[0088] Since the Inconel 625 alloy bar has only undergone aging at 760 °C for 1 hour, the γ'' phase inside it cannot be effectively precipitated, and its internal microstructure basically remains similar to that of the solution - annealed alloy, showing a decrease in overall hardness, especially in the cross - section center area. To strengthen the precipitation amount of the γ'' phase, according to the isothermal transformation curve (TTT curve) of the alloy material, if the heating temperature is slightly reduced (for example, cooled to 600 - 700 °C) and continued aging treatment for a certain time after aging at 760 °C for 1 hour, the precipitation rate of the γ'' phase can be increased.

[0089] Furthermore, through measurement, when the Inconel 625 alloy bar continues to age at a temperature of 600 - 700 °C for more than 10 hours, the equilibrium precipitation amount of the γ'' phase is approximately 10%. As the aging time prolongs, the precipitation amount of the γ'' phase gradually tends to equilibrium and enters the equilibrium state after 100 hours. During the precipitation process of the γ'' phase, its phase radius also gradually increases, and the phase radius of the γ'' phase can reach 16 nm after aging for 100 hours. During the complete aging heat treatment process, the texture dislocation amount of the Inconel 625 alloy bar will significantly decrease, but as the aging time prolongs, the texture dislocation density rebounds to maintain the improvement effect of the yield strength and tensile strength obtained through cold drawing.

[0090] In one example, during cold drawing, a reduction ratio of 30% is achieved in a single cold drawing pass. Through Examples 1 - 5, the aging heat treatment regime is adjusted to further analyze the effect of different aging heat treatment regimes on improving the mechanical properties of the Inconel 625 alloy bar. Among them, after completing cold drawing, Example 1 only undergoes a treatment of aging at a heating temperature of 760 °C for 1 hour, and Examples 2 - 5 continue to age at a heating temperature of 650 °C for 12 hours, 24 hours, 48 hours, and 96 hours respectively after aging at a heating temperature of 760 °C for 1 hour.

[0091] See Figure 5 , which shows the curves of the strength change of the engineering strain of the Inconel 625 alloy bars in Examples 1, 2, 4, 5 and Comparative Example 4. When the reduction ratio of cold drawing all reaches 30%, further aging heat treatment significantly improves the stress - strain performance of the Inconel 625 alloy bar. Through heat treatment, the uniform elongation length of the Inconel 625 alloy bar can be improved. Moreover, continuing the aging treatment at a heating temperature of 650 °C in Examples 2, 4, 5 can increase the γ'' precipitation phase, making the Inconel 625 alloy bar gradually strengthen.

[0092] From the microscopic structure analysis, cold drawing can significantly increase the texture dislocations inside the structure of the Inconel 625 alloy bar, generate dislocation strengthening, and improve the mechanical strength. However, the continuous accumulation of texture dislocations will cause a decrease in plasticity. To balance the mechanical strength and plasticity, at this time, aging heat treatment of the Inconel 625 alloy bar can not only maintain the improvement of the mechanical properties obtained through cold drawing in the early stage but also release stress to improve plasticity.

[0093] During the cold drawing process, as the reduction ratio increases continuously, the yield strength of Inconel 625 alloy bars increases with the increase of the texture dislocation density, reaches a peak at the maximum stress strain, decreases after a short heat treatment, but increases and gradually stabilizes after continuing to extend the aging time. The calculation results show that for every 10% increase in the deformation amount of Inconel 625 alloy bars during the cold drawing process, its yield strength can be increased by 300 - 700 MPa.

[0094] Furthermore, the texture dislocation density can be calculated by formulas (1) and (2):

[0095]

[0096] where D is the crystallite size, k is the Scherrer constant, β is the measured width at the maximum of the full width at half maximum of the diffraction peak, θ is the Bragg diffraction angle, and λ is the X-ray wavelength.

[0097] Meanwhile, cold drawing before aging heat treatment can also effectively expand the temperature range for the precipitation of strengthening γ'' phase. For example, when the cold drawing deformation amount, i.e., the reduction ratio, is 30%, its tensile strength and yield strength are increased by approximately 500 MPa and 800 MPa respectively. This large degree of plastic deformation can effectively reduce the precipitation temperature and precipitation rate of the γ'' phase, which enables the subsequent aging heat treatment to complete the γ'' phase precipitation strengthening without using too high a temperature. That is to say, the requirements for mechanical properties and mechanical performance can be met at a lower temperature and in a shorter time.

[0098] By measuring the mechanical property parameters of the Inconel 625 alloy bars obtained in Examples 1 - 5, and comprehensively considering their yield strength, tensile strength, and yield ratio, the Inconel 625 alloy bars obtained under the aging heat treatment system of Example 5 have the best comprehensive performance.

[0099] In one example, further, on the basis of the aging heat treatment system of Example 5, the mechanical property parameters of Inconel 625 alloy bars with different reduction ratios during the cold drawing process under the same aging heat treatment system conditions were measured in Comparative Example 5 and Examples 6 - 7 respectively. Among them, Comparative Example 5 directly entered the aging heat treatment without cold drawing, and Examples 6 and 7 corresponded to reduction ratios of 10% and 20% after cold drawing respectively.

[0100] See Figures 6 - 8 , which respectively show the test results of the yield strength, tensile strength, and yield ratio of the Inconel 625 alloy bars obtained from all the above comparative examples and all the examples.

[0101] As Figure 6 and Figure 7As shown, for the Inconel 625 alloy bar after cold drawing, when its cross-sectional area is reduced by 30%, the yield strength of the Inconel 625 alloy bar is 2.4 - 2.7 times that before cold drawing, and the tensile strength of the Inconel 625 alloy bar is 1.4 - 1.6 times that before cold drawing.

[0102] After cold drawing, aging heat treatment is continued, such as Figure 6 As shown, the influence of aging heat treatment on the yield strength of the Inconel 625 alloy bar is as follows: after aging for 1 hour at a heating temperature of 760°C, when the holding temperature is 650°C and the holding time is 24 hours, the yield strength of the Inconel 625 alloy bar is increased by 100 - 105 MPa compared with that before holding (after aging for 1 hour at a heating temperature of 760°C). When the holding temperature is 650°C and the holding time is 96 hours, the yield strength of the Inconel 625 alloy bar is increased by 90 - 95 MPa compared with that before holding.

[0103] Furthermore, as Figure 7 As shown, the influence of aging heat treatment on the tensile strength of the Inconel 625 alloy bar is as follows: after aging for 1 hour at a heating temperature of 760°C, when the holding temperature is 650°C and the holding time is 24 hours, the tensile strength of the Inconel 625 alloy bar is increased by 75 - 80 MPa compared with that before holding; when the holding temperature is 650°C and the holding time is 96 hours, the tensile strength of the Inconel 625 alloy bar is increased by 80 - 85 MPa compared with that before holding.

[0104] As Figure 8 As shown, for the Inconel 625 alloy bar after cold drawing, when its cross-sectional area is reduced by 30%, the yield ratio can be decreased from 100% before heating to 90% - 91% by aging for 1 hour at a heating temperature of 760°C. By continuing the aging heat treatment at a heating temperature of 650°C, the yield ratio will increase, but will not exceed 93%.

[0105] From Figures 6 - 8 the test results, it can be seen that after cold drawing, the yield strength and tensile strength of the Inconel 625 alloy bar are both significantly improved, but at the same time, the yield ratio also increases. After continuing the aging heat treatment, although the yield strength and tensile strength decrease after aging for 1 hour at a heating temperature of 760°C, the yield ratio also decreases significantly. Then, continuing to age for a certain time (such as 96 hours) at a holding temperature of 650°C can promote the recovery of the yield strength and tensile strength. Finally, an Inconel 625 alloy bar with both enhanced mechanical properties and good plasticity is obtained.

[0106] From the microstructure and theoretical analysis, it can be known that during the stage of aging at 760 °C for 1 hour, the precipitation amount of γ'' phase in the Inconel 625 alloy bar gradually increases, but the total precipitation amount in this stage does not reach the peak. Then it enters the stage of aging for a certain time at 650 °C for heat preservation. In this stage, with the extension of the heat preservation time, the precipitation rate of γ'' phase first increases and then tends to be stable. Usually, after 48 hours of heat preservation, the volume fraction of γ'' phase tends to be balanced, and the precipitation strengthening effect of γ'' phase reaches the equilibrium value.

[0107] In one example, the microstructure of the Inconel 625 alloy bar with the optimal comprehensive performance strengthening effect obtained in Example 5 was characterized.

[0108] See Figure 9 , which shows the microstructure diagram of the Inconel 625 alloy bar in Example 5 before cold drawing. At this time, the interior of the Inconel 625 alloy bar presents a cast structure. It can be observed that its overall structure is relatively uniform, and the average grain size is less than 20 μm. At the same time, there are a small amount of carbides in the microstructure, and granular δ phase is distributed at the grain boundaries.

[0109] See Figure 10 and Figure 11 , which respectively show the microstructure diagram and TEM diagram of the Inconel 625 alloy bar in Example 5 after cold drawing. It can be observed that cold drawing deformation only slightly refines the grain size inside the Inconel 625 alloy bar, and the change in grain size is not obvious. At the same time, cold drawing deformation has a great tensile effect on the carbides inside it, and some larger carbide particles fracture under the action of strain. The degree of cold drawing deformation increases the number of twins and the number of substructures inside the grains. Especially in Figure 11 , it can also be observed that the texture dislocations inside the Inconel 625 alloy bar increase significantly, as well as obvious texture dislocation pile-ups.

[0110] See Figure 12 , which shows the microstructure diagram of the Inconel 625 alloy bar in Example 5 after completing age hardening heat treatment. At this time, compared with the metallographic state of Figure 9 , while the internal grains of the Inconel 625 alloy bar are refined, the situation of texture dislocation pile-ups is significantly improved.

[0111] The organization control method of an Inconel 625 alloy provided by the embodiment of the present invention and the Inconel 625 alloy obtained through it have at least one or a part of at least one of the following advantages:

[0112] (1) The strength of the Inconel 625 alloy bar is enhanced by cold drawing, and then the stability of the alloy during long-term service is obtained through aging heat treatment;

[0113] (2) By using a processing method that combines cold drawing and aging heat treatment of the Inconel 625 alloy bar, the defect of uneven strengthening effect at different positions of the cross-section caused by cold drawing deformation is improved, the residual stress is greatly reduced, and the structural stability of the alloy is enhanced;

[0114] (3) By directly cold drawing the Inconel 625 alloy bar to the required cross-sectional diameter in one step, multiple drawing operations are not required and the reduction ratio is high. The maximum drawing deformation degree can reduce the cross-sectional area by 30%, thus avoiding the defect of uneven strengthening caused by a small reduction ratio;

[0115] (4) By cold drawing the Inconel 625 alloy bar, the degree of anisotropy inside it can be effectively increased, thereby changing the distribution of grain orientations inside it, which helps the accumulation of texture dislocations and generates new texture dislocation sources, resulting in the proliferation and accumulation of texture dislocations, and significantly improving the yield strength and tensile strength of the alloy;

[0116] (5) By cold drawing before aging heat treatment, the precipitation temperature and precipitation rate of the γ'' phase can be effectively reduced, and the temperature range for the precipitation of the γ'' phase can be effectively expanded, so that the aging heat treatment can be completed under the conditions of lower temperature and shorter time;

[0117] (6) Through the heating process of aging heat treatment, it helps to increase the combined precipitation of the γ'' phase and various carbides in the Inconel 625 alloy, and can effectively improve its yield strength and tensile strength;

[0118] (7) Through the heat preservation process of aging heat treatment, the residual stress can be effectively released and it helps to reduce the texture dislocation density inside the Inconel 625 alloy, so as to achieve the improvement of the alloy strength and hardness while also taking into account better plasticity.

[0119] Although some embodiments of the general inventive concept have been shown and described, those of ordinary skill in the art will understand that changes can be made to these embodiments without departing from the principles and spirit of the general inventive concept. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for microstructure control of Inconel 625 alloy, characterized in that, The described tissue regulation method includes: Cold drawing: Cold drawing an Inconel 625 alloy bar once to reduce its cross-sectional area by 10% - 30% to obtain a processed Inconel 625 alloy bar; Aging heat treatment: Placing the processed Inconel 625 alloy bar in a heating device at a temperature of 750 - 800 °C and heating for 50 - 70 minutes, then reducing the temperature of the heating device to 600 - 700 °C and holding for 10 - 100 hours; Among them, after the Inconel 625 alloy bar undergoes the cold drawing, the grain orientation distribution inside it changes, and the formed texture dislocations proliferate to increase its yield strength and tensile strength. Then, through the aging heat treatment, the texture dislocation density is reduced, and at the same time, the precipitation amount of γ" phase increases to strengthen its internal tissue structure and release stress.

2. The tissue regulation method according to claim 1, wherein The preparation steps of the Inconel 625 alloy bar include: Melting the Inconel 625 alloy raw material to obtain an Inconel 625 alloy steel ingot; Heating and forging the Inconel 625 alloy steel ingot to obtain an Inconel 625 alloy steel billet; Successively subjecting the Inconel 625 alloy steel billet to rolling treatment, annealing treatment, and polishing treatment to obtain the Inconel 625 alloy bar.

3. The tissue regulation method according to claim 2, wherein The Inconel 625 alloy steel billet is a square steel billet with dimensions of 80mm * 80mm - 120mm * 120mm; The cross-sectional diameter range of the Inconel 625 alloy bar is 15 - 25mm.

4. The tissue regulation method according to any one of claims 1 - 3, wherein Using a cold drawing device to cold draw the Inconel 625 alloy bar, the cold drawing speed range of the cold drawing device is 8 - 15m / min, and the cross-sectional diameter range of the Inconel 625 alloy bar after the cold drawing is 15 - 17mm.

5. The tissue regulation method according to claim 4, wherein After the Inconel 625 alloy bar undergoes the cold drawing, when its cross-sectional area is reduced by 30%, The yield strength of the Inconel 625 alloy bar is 2.4 - 2.7 times that before the cold drawing; The tensile strength of the Inconel 625 alloy bar is 1.4 - 1.6 times that before the cold drawing.

6. The tissue regulation method according to claim 4, wherein The heating speed range of the heating device is 12 - 17 °C / min; The cooling speed range of the heating device is 8 - 12 °C / min.

7. The tissue regulation method according to claim 6, wherein The heating temperature of the Inconel 625 alloy bar after the cold drawing during the aging heat treatment process is 760 °C, the heating time is 1 hour, and the yield strength ratio of the Inconel 625 alloy bar after heating drops from 100% before heating to 90% - 93%.

8. The microstructure control method according to claim 7, characterized in that during the aging heat treatment process when the holding temperature is 650 °C and the holding time is 24 hours, the yield strength of the Inconel 625 alloy bar is increased by 100 - 105 MPa compared to before holding; when the holding temperature is 650 °C and the holding time is 96 hours, the yield strength of the Inconel 625 alloy bar is increased by 90 - 95 MPa compared to before holding.

9. The microstructure control method according to claim 7, characterized in that during the aging heat treatment process when the holding temperature is 650 °C and the holding time is 24 hours, the tensile strength of the Inconel 625 alloy bar is increased by 75 - 80 MPa compared to before holding; when the holding temperature is 650 °C and the holding time is 96 hours, the tensile strength of the Inconel 625 alloy bar is increased by 80 - 85 MPa compared to before holding.

10. An Inconel 625 alloy obtained by subjecting an Inconel 625 alloy raw material to cold drawing and aging heat treatment using the microstructure control method according to any one of claims 1-9, characterized in that, The yield strength, tensile strength and plasticity of the Inconel 625 alloy are all improved.

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