Hot working method for significantly increasing the volume fraction of dynamic recrystallization of nickel-based superalloys

Abstract

The application provides a hot working method for significantly improving the dynamic recrystallization volume fraction of a nickel-based superalloy, which comprises the following steps: firstly, placing Inconel 625 alloy into a heat treatment furnace at 1000-1100 DEG C and keeping it for 30-90 min for solid solution treatment, and then water cooling; secondly, increasing the temperature of the Inconel 625 alloy after the solid solution treatment to 700-750 DEG C and keeping it for 50-100 h, and then water cooling while applying a stress of 100-160 MPa, so as to uniformly precipitate a delta phase; and finally, increasing the temperature of the Inconel 625 alloy after the aging heat treatment to 870-950 DEG C and keeping it for 2-10 min, and then hot deforming the alloy at a strain rate of 0.1-0.001 s ‑1 The application can obtain a large amount of uniformly distributed delta phase with appropriate size in a short time by applying an external stress, avoids the problem of the delta phase being distributed along the grain and being coarse in size caused by traditional aging heat treatment, ensures that the delta phase fully plays a role in the subsequent hot deformation process by using appropriate process parameters, greatly improves the dynamic recrystallization volume fraction, and has obvious advantages in grain refinement and uniform structure in the hot working process of the nickel-based superalloy.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of hot working of nickel-based superalloys, and particularly relates to a hot working method for significantly improving the dynamic recrystallization volume fraction of a nickel-based superalloy. BACKGROUND

[0002] Nickel-based superalloys are widely used in the manufacture of high-temperature structural components in the fields of aerospace, petrochemical engineering, etc. due to their good creep resistance, fatigue resistance, corrosion resistance and oxidation resistance. In recent years, the continuous development of processes, structures and properties of large equipment such as aircraft engines has put forward more and more stringent requirements on the organization control of the forming process of nickel-based superalloys.

[0003] The pre-precipitated δ phase can effectively promote the dynamic recrystallization during the forging process of the nickel-based superalloy, thereby assisting in refining the grains, which is called Delta Process. This process has been applied to the industrial production of nickel-based superalloys. However, since the δ phase usually tends to precipitate along the grain boundaries during aging, dynamic recrystallization cannot be fully carried out, resulting in the formation of a non-uniform organization of fine recrystallized grains surrounding the original coarse deformed grains in the nickel-based superalloy prepared by the Delta Process, which is difficult to achieve the ideal grain refinement effect.

[0004] Although sufficient intragranular δ phase can be formed by long-term peak aging, it inevitably leads to excessively large δ phase size, and the excessive and oversized residual δ phase after hot working can deteriorate the mechanical properties of the nickel-based superalloy. Long-term heat treatment also increases the process cost. In addition, the δ phase cannot effectively promote the nucleation of dynamic recrystallized grains when the δ phase size is too small. Therefore, there is an urgent need for a method that can obtain a dispersed distribution of δ phase with appropriate size and sufficient quantity in a relatively short time to further promote the dynamic recrystallization of the nickel-based superalloy for refining and uniform organization. SUMMARY

[0005] In order to solve the problems existing in the prior art, the present application provides a method for significantly improving the dynamic recrystallization volume fraction of a nickel-based superalloy, which controls the uniform precipitation of δ phase at grain boundaries and intragranularly through pre-stress aging heat treatment, avoids the occurrence of dynamic recrystallization only at grain boundaries during subsequent hot working, thereby promoting the more complete occurrence of intragranular dynamic recrystallization, and finally making the grain size more uniform and fine.

[0006] The specific technical solutions of the present application are as follows:

[0007] The present application provides a hot working method for significantly improving the dynamic recrystallization volume fraction of a nickel-based superalloy, comprising the following steps:

[0008] Step 1, solution heat treatment: the temperature of the heat treatment furnace is raised to 1000-1100 DEG C, Inconel 625 alloy is put in for solution heat treatment, heat preservation is 30-90 min, and water cooling is carried out;

[0009] Step 2, aging heat treatment: the Inconel 625 alloy after solution heat treatment is heated to 700-750 DEG C and heat preserved for 50-100 h, and pre-stressed aging treatment is carried out by applying stress of 100-160 MPa, and water cooling is carried out;

[0010] Step 3, hot deformation: the Inconel 625 alloy after aging heat treatment is heated to 870-950 DEG C and heat preserved for 2-10 min, hot deformation is carried out at strain rate of 0.1-0.001 s -1 , and the total deformation is more than 60%.

[0011] As a further illustration of the application, in step 2, the pre-stressed aging heat treatment temperature is selected as 750 DEG C, and the heat preservation time is 90 h.

[0012] As a further illustration of the application, after pre-stressed aging treatment in step 2, the delta phase in the Inconel 625 alloy is dispersedly distributed, the volume fraction is more than 40%, and the average long axis size can be maintained between 1-3 mu m.

[0013] As a further illustration of the application, in step 3, the hot deformation treatment is specifically any one of forging, hot rolling or hot compression.

[0014] As a further illustration of the application, in step 3, the hot deformation temperature is 900 DEG C, and the heat preservation time is specifically 5 min.

[0015] As a further illustration of the application, in step 3, the strain rate is specifically 0.01 s -1 .

[0016] Compared with the prior art, the application has the following beneficial technical effects:

[0017] The application controls the distribution, size and quantity of the delta phase by applying external stress, overcomes the difficulty in controlling the characteristics of the delta phase, and the uniformly distributed micron-level delta phase can significantly promote the dynamic recrystallization in the original grain, thereby avoiding the problems of the delta phase distribution along the crystal and the non-uniform structure in the subsequent hot deformation process caused by the traditional aging heat treatment.

[0018] The application accelerates the precipitation of the delta phase based on the external stress regulation, reduces the time required for precipitating sufficient delta phase, avoids the excessive coarsening of the delta phase caused by the long heat treatment time, and the appropriate hot deformation process parameters also ensure that the residual delta phase which is not completely dissolved after hot deformation will also be dispersedly distributed in the form of fine particles, so that the mechanical properties of the nickel-based superalloy will not be deteriorated.

[0019] Other features and advantages of the present technical solution will be set forth in the following description, and, in part, will be apparent from the description, or can be learned by practice of the present technical solution. The objects and other advantages of the present technical solution will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

[0020] The technical solution of the present application will be further described in detail below with the help of drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0021] The accompanying drawings are included to provide a further understanding of the present technical solution and are incorporated in and constitute a part of the specification, illustrate embodiments of the present technical solution and serve to explain the present technical solution, and do not limit the present technical solution.

[0022] Figure 1 Microstructure of Inconel 625 alloy in Example 1 of the present application after pre-stress aging at 750℃ for 60h.

[0023] Figure 2 Microstructure of Inconel 625 alloy in Example 2 of the present application after pre-stress aging at 750℃ for 90h.

[0024] Figure 3 Microstructure of Inconel 625 alloy in Comparative Example 1 after conventional aging at 750℃ for 200h.

[0025] Figure 4 Microstructure of Inconel 625 alloy in Example 1 of the present application after pre-stress aging for 60h heat treatment and hot deformation at 900℃.

[0026] Figure 5 Microstructure of Inconel 625 alloy in Example 2 of the present application after pre-stress aging for 90h heat treatment and hot deformation at 900℃.

[0027] Figure 6 Microstructure of Inconel 625 alloy in Comparative Example 1 after conventional aging for 200h heat treatment and hot deformation at 900℃.

[0028] Figure 7 Statistical diagram of δ phase volume fraction after aging and recrystallized grain volume fraction after hot deformation of Inconel 625 alloy in Example 1, Example 2 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0029] The preferred embodiments of the technical solution are described below in conjunction with the drawings, and it should be understood that the preferred embodiments described herein are only used to illustrate and explain the technical solution, and are not used to limit the technical solution.

[0030] At present, sufficient intracrystalline δ phase can be formed by long-time peak aging, but it will inevitably lead to excessively coarse δ phase size, and the excessive and oversized residual δ phase after hot working will deteriorate the mechanical properties of the nickel-based superalloy, and the long-time heat treatment also increases the process cost. In addition, the δ phase size is too small to effectively promote the dynamic recrystallization grain nucleation. Therefore, a method for obtaining a dispersed distribution, suitable size and sufficient number of δ phase in a shorter time is urgently needed to further promote the dynamic recrystallization of the nickel-based superalloy for refining and uniformizing the structure.

[0031] Based on this, the present application provides a hot working method for significantly improving the dynamic recrystallization volume fraction of a nickel-based superalloy, comprising the following steps:

[0032] Step 1, solution heat treatment: the temperature of the heat treatment furnace is raised to 1000-1100℃, and Inconel 625 alloy is put in for solution heat treatment, and the temperature is kept for 30-90min, and then water-cooled, so that the alloy matrix composition is homogenized and the primary carbide is dissolved.

[0033] Specifically, the temperature of the above-mentioned solution heat treatment can be set to 1000℃, 1030℃, 1050℃, 1070℃, 1100℃, etc.; and the holding time can be set to 30min, 40min, 50min, 60min, 70min, 90min, etc.

[0034] Step 2, aging heat treatment: the Inconel 625 alloy after solution heat treatment is heated to 700-750℃ and kept for 50-100h, and at the same time, a stress of 100-160MPa is applied for pre-stress aging treatment, and then water-cooled to uniformly precipitate δ phase.

[0035] Specifically, the pre-stress aging heat treatment temperature can be selected as 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, etc., and preferably 750℃; and the holding time can be 50h, 60h, 70h, 80h, 90h, 100h, etc., and preferably 90h. The aging heat treatment temperature is preferably 750℃, and the holding time is preferably 90h, which can ensure that the volume fraction of δ phase is more than 40%, and the long axis size is greater than 1μm. Specifically, the δ phase in the Inconel 625 alloy after pre-stress aging treatment is dispersedly distributed, the volume fraction is more than 40%, and the average long axis size can be maintained between 1-3μm.

[0036] Step 3, hot deformation: the Inconel 625 alloy after aging heat treatment is heated to 870-950℃ for 2-10 min, and hot deformation is performed at a strain rate of 0.1-0.001 s -1 , and the total deformation is more than 60%.

[0037] The hot deformation treatment is any one of forging, hot rolling or hot compression.

[0038] Specifically, the hot deformation temperature can be, for example, 870℃, 900℃, 920℃, 950℃, etc., and is preferably 900℃, so as to prevent the δ phase from dissolving too quickly at a too high temperature or from not being able to fully perform dynamic recrystallization at a too low temperature; the hot deformation holding time can be, for example, 2 min, 5 min, 7 min, 10 min, etc., and is preferably 5 min, so as to prevent the δ phase from dissolving too early at a too long time or the Inconel 625 alloy from not being uniform in temperature at a too short time. The hot deformation strain rate can be, for example, 0.1 s -1 , 0.05 s -1 , 0.01 s -1 , 0.005 s -1 , 0.001 s -1 , etc., and is preferably 0.01 s -1 , so as to ensure that there is enough time for dynamic recrystallization to occur during hot deformation and to prevent the δ phase from dissolving and the cost from increasing due to a too long time.

[0039] The application will be described in detail below in conjunction with specific embodiments and the accompanying drawings. Example 1

[0040] In this embodiment, the method for significantly increasing the dynamic recrystallization volume fraction of a nickel-based high-temperature alloy includes the following steps:

[0041] The temperature of the heat treatment furnace is raised to 1050℃ at a rate of 6℃ / min, and after the furnace temperature is stabilized for 5 min, the Inconel 625 alloy sample is placed in the furnace for solid solution heat treatment, with a holding time of 60 min, and water cooling, so that the primary carbides are redissolved.

[0042] The Inconel 625 alloy after solid solution heat treatment is reheated to 750℃ at a rate of 6℃ / min and subjected to a stress of 150 MPa, and a pre-stressed aging heat treatment is performed with a holding time of 60 h, and water cooling, so that the δ phase is uniformly distributed.

[0043] The Inconel 625 alloy after pre-stressed aging treatment is heated to 900℃ at a rate of 10℃ / min, and after being held at 900℃ for 5 min, hot compression deformation is performed at a strain rate of 0.01 s -1 , and the deformation amount is 60%, and water cooling is performed.

[0044] As shown in Figure 1 Prestress aging formed a dispersed distribution of δ phase in Inconel 625 alloy, with a volume fraction of about 41% and an average size of about 1 μm.

[0045] As shown in Figure 4 The volume fraction of dynamic recrystallization grains in Inconel 625 alloy after hot deformation was about 56%. Example 2

[0046] In this embodiment, the method for significantly increasing the volume fraction of dynamic recrystallization of nickel-based superalloys comprises the following steps:

[0047] The temperature of the heat treatment furnace was raised to 1050℃ at a rate of 6℃ / min, and after 5 min of holding to stabilize the furnace temperature, the Inconel 625 alloy sample was placed in the furnace for solid solution heat treatment, with a holding time of 60 min and water cooling to dissolve the primary carbides.

[0048] The Inconel 625 alloy after solid solution heat treatment was re-heated to 750℃ at a rate of 6℃ / min and subjected to a stress of 150 MPa, with a holding time of 90 h for pre-stress aging heat treatment, and water cooling to obtain a uniform distribution of δ phase.

[0049] The Inconel 625 alloy after pre-stress aging was heated to 900℃ at a rate of 10℃ / min, held for 5 min at 900℃, and then hot compressed, with a strain rate of 0.01 s -1 and a deformation of 60%, and water cooling.

[0050] As shown in Figure 2 Prestress aging formed a dispersed distribution of δ phase in Inconel 625 alloy, with a volume fraction of about 43% and an average size of about 2 μm.

[0051] As shown in Figure 5 The volume fraction of dynamic recrystallization grains in Inconel 625 alloy after hot deformation was about 68%, with only a few residual deformation grains due to insufficient recrystallization within the original deformation grains.

[0052] Comparative Example 1

[0053] The temperature of the heat treatment furnace was raised to 1050℃ at a rate of 6℃ / min, and after 5 min of holding to stabilize the furnace temperature, the Inconel 625 alloy sample was placed in the furnace for solid solution heat treatment, with a holding time of 60 min and water cooling to dissolve the primary carbides.

[0054] The solution-treated Inconel 625 alloy was reheated to 750℃ at a heating rate of 6℃ / min, held for 200h for conventional aging heat treatment, and then water-cooled to obtain the grain boundary δ phase.

[0055] The conventionally aged Inconel 625 alloy was heated to 900℃ at a heating rate of 10℃ / min, held at that temperature for 5 minutes, and then subjected to hot compression deformation at 900℃ with a strain rate of 0.01s. -1 The deformation is 60%, and it is water-cooled.

[0056] In this comparative example, the aging time was chosen to be 200h because the precipitation kinetics of the δ phase during traditional aging is slow. Therefore, the time was extended to ensure that sufficient grain boundary δ phases were formed in the Inconel 625 alloy.

[0057] like Figure 3 As shown, the δ phase formed in Inconel 625 alloy by conventional aging is concentrated near the grain boundaries, with only a very small amount of δ phase existing inside the grains. The volume fraction of the δ phase is about 9%, and the average size is about 4 μm.

[0058] like Figure 6 As shown, after conventional aging, Inconel 625 alloy undergoes hot deformation, dynamic recrystallization only occurs near the grain boundaries of the original deformed grains. Most of the original deformed grains remain without dynamic recrystallization, and the volume fraction of dynamically recrystallized grains is only about 14%.

[0059] Obviously, as Figure 7 As shown, the results of the examples and comparative examples indicate that, compared with obtaining grain boundary δ by traditional long-term aging heat treatment, the present invention obtains a large number of uniformly distributed δ phases in a shorter time by applying external stress, which provides more dynamic recrystallization nucleation sites in the grain during subsequent hot deformation, thus significantly increasing the dynamic recrystallization volume fraction. This method has obvious advantages in refining grains and homogenizing the microstructure during the hot working of nickel-based superalloys.

[0060] Obviously, those skilled in the art can make various modifications and variations to this technical solution without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this technical solution and their equivalents, this technical solution also intends to include these modifications and variations.

Claims

1. A hot working method for significantly improving the dynamic recrystallization volume fraction of nickel-based superalloys, characterized in that, Includes the following steps: Step 1: Raise the temperature of the heat treatment furnace to 1000~1050℃, put in Inconel 625 alloy for solution heat treatment, hold for 30~90 minutes, and then water cool; Step 2: Heating the solution-heat-treated Inconel 625 alloy to 700~750℃ and holding for 50~100h, while applying a stress of 150~160MPa for prestress aging treatment, followed by water cooling; After the prestress aging treatment in Step 2, the δ phase in the Inconel 625 alloy is dispersed, with a volume fraction of 40%-43%, and the average major axis dimension can be maintained between 1~3μm; Step 3: Heat the aged Inconel 625 alloy to 870~900℃ and hold for 2~10 minutes, with an induction rate of 0.01~0.001s. -1 The strain rate was used for hot deformation, and the total deformation was over 60%; after hot deformation, the volume fraction of dynamically recrystallized grains in the alloy could reach over 56%.

2. The hot working method for significantly increasing the dynamic recrystallization volume fraction of nickel-based superalloys as described in claim 1, characterized in that, In step 2, the prestressed aging heat treatment temperature is selected as 750℃, and the holding time is 90h.

3. The hot working method for significantly increasing the dynamic recrystallization volume fraction of nickel-based superalloys as described in claim 1, characterized in that, The hot deformation treatment in step 3 can be any one of forging, hot rolling, or hot compression.

4. The hot working method for significantly increasing the dynamic recrystallization volume fraction of nickel-based superalloys as described in claim 1, characterized in that, In step 3, the heat distortion temperature is 900℃; the holding time is 5 minutes.

5. The hot working method for significantly increasing the dynamic recrystallization volume fraction of nickel-based superalloys as described in claim 1, characterized in that, The strain rate in step 3 is specifically 0.01 s. -1 .

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