A method of heat treating a cast nickel-base superalloy

Abstract

The application relates to a heat treatment method of a cast nickel-based superalloy, which comprises the following steps: solid solution treatment of the cast nickel-based superalloy part; first aging treatment of the solid solution treated cast nickel-based superalloy part, the temperature of the first aging treatment being 950-1080 DEG C; second aging treatment of the first aging treated cast nickel-based superalloy part, the temperature of the second aging treatment being 825-925 DEG C; third aging treatment of the second aging treated cast nickel-based superalloy part, the temperature of the third aging treatment being 650-750 DEG C. By adopting four-stage heat treatment, submicron size gamma' phase particles and M 23 C6 carbide particles are formed at the grain boundary of the cast nickel-based superalloy, and nano gamma' phase is further precipitated in the gap of the M 23 C6 carbide, so that the grain boundary strength is improved, the tensile plasticity of the cast nickel-based superalloy is improved, the alloy strength is not reduced, and finally the high-temperature strength and plasticity of the cast nickel-based superalloy are obviously improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of casting nickel-based superalloy, and particularly relates to a heat treatment method for casting nickel-based superalloy, which is used for improving tensile strength and plasticity of the casting nickel-based superalloy. BACKGROUND

[0002] The superalloy is an important metal structural material in the development of aviation industry in the world due to excellent high-temperature mechanical properties. The superalloy can be stably served for a long time under high-temperature conditions, can reliably bear the coupling of complex stress, oxidation, corrosion and other adverse conditions, and is widely applied to key hot end parts such as a combustion chamber, a turbine disc, a blade and a casing of an aero-engine. With the development of aviation technology, the performance requirements of the engine on the material are higher and higher, and the types and contents of alloy elements in the superalloy are gradually increased. High alloying increases the strength and reduces the plasticity of the superalloy, and the deformation resistance of the alloy is significantly increased, so the casting superalloy is developed on the basis of the deformed superalloy.

[0003] The casting superalloy does not need cold and hot deformation, can add more alloy elements, and can obtain more excellent alloy strength and higher use temperature. However, with the increase of the strength of the casting superalloy, the plasticity and toughness of the casting superalloy are generally low due to the limitation of the coarse grain size of the solidification structure. Since no deformation is performed, the reasonable design of the heat treatment process is very important for the mechanical properties of the casting superalloy (that is, the grain size of the casting alloy is coarse, which is not conducive to the plasticity of the alloy. Meanwhile, the casting alloy cannot be deformed by cold and hot working to adjust the grain size and microstructure, and can only rely on the heat treatment to adjust the structure, so the heat treatment process is very important).

[0004] Therefore, how to effectively control the microstructure of the casting superalloy by the heat treatment parameter, optimize the deformation behavior of the alloy (that is, the deformation behavior of the alloy under external force in the service or test process), and then improve the tensile plasticity of the casting superalloy is very important for the safe use of the casting superalloy. SUMMARY

[0005] Therefore, the present application provides a heat treatment method for casting nickel-based superalloy, and the main purpose is to effectively improve the tensile plasticity of the alloy by heat treatment structure regulation without reducing the strength of the casting nickel-based superalloy, so as to improve the tensile strength and plasticity of the casting nickel-based superalloy.

[0006] In order to achieve the above purpose, the present application mainly provides the following technical scheme:

[0007] In one aspect, the embodiment of the present application provides a heat treatment method for casting nickel-based superalloy, which comprises the following steps:

[0008] solution treatment: heating the cast nickel-based superalloy piece to 1140℃+A, and solution treating for 6~10h, and then cooling at a first set cooling rate to obtain a solution treated cast nickel-based superalloy piece; wherein A is the maximum thickness of the cast superalloy piece x (3~5℃ / mm); wherein the cooling at the first set cooling rate is used to avoid precipitation of γ' phase particles during the cooling of the cast nickel-based superalloy piece;

[0009] first aging treatment: first aging treating the solution treated cast nickel-based superalloy piece, and cooling at a second set cooling rate to obtain a first aged cast nickel-based superalloy piece; wherein the first aging treatment is at a temperature of 950~1080℃, and the first aging treatment is for a time of 1~6h;

[0010] second aging treatment: second aging treating the first aged cast nickel-based superalloy piece, and cooling to obtain a second aged cast nickel-based superalloy piece; wherein the second aging treatment is at a temperature of 825~925℃, and the second aging treatment is for a time of 10~20h;

[0011] third aging treatment: third aging treating the second aged cast nickel-based superalloy piece, and cooling to obtain a heat treated cast nickel-based superalloy piece; wherein the third aging treatment is at a temperature of 650~750℃, and the third aging treatment is for a time of 15~25h.

[0012] Preferably, the cast nickel-based superalloy has the following chemical composition in weight percent: C 0.08-0.13wt%, Cr 16-19wt%, Co 8-11wt%, W 1.0-2.7wt%, Mo 1.0-2.5wt%, Al 1.5-2.2wt%, Ti 3.2-4.0wt%, Nb 1.5-2.5wt%, B 0.008-0.015wt%, Zr≤0.1wt%, and Ni is the balance.

[0013] Preferably, in the step of solution treating: the solution treating is at a temperature of 1140℃~1250℃; and / or the maximum thickness is≤20mm.

[0014] Preferably, the first aging treatment causes sub-micron sized γ' phase particles to precipitate at the grain boundaries of the cast nickel-based superalloy piece. It is noted that sub-micron sized means less than 1 micron, and is typically 0.1-1 micron.

[0015] Preferably, the second aging treatment causes sub-micron sized M 23C6 carbide particles.

[0016] Preferably, by the third aging treatment, nano-sized gamma prime phase particles continue to precipitate at the grain boundaries of the cast nickel-base superalloy piece. Here, nano-sized is generally 10-100 nanometers.

[0017] Preferably, in the solid solution treatment step: during cooling, when the temperature of the alloy piece is above 600℃, the first set cooling rate is 500-3000℃ / min.

[0018] Preferably, in the first aging treatment step: during cooling, when the temperature of the alloy piece is above 600℃, the second set cooling rate is 500-3000℃ / min.

[0019] Preferably, in the second aging treatment step, the third aging treatment step: the cooling rate is not less than 100℃ / min; preferably, the cooling mode is furnace-out cooling or furnace-in gas cooling; further preferably, the furnace-out cooling is air cooling or gas cooling; further preferably, the furnace-in gas cooling is inert gas cooling.

[0020] In still another aspect, the embodiments of the present application provide a heat-treated cast nickel-base superalloy piece, wherein the cast nickel-base superalloy piece has sub-micron-sized gamma prime phase particles and M 23 C6 carbide particles at the grain boundaries of the cast nickel-base superalloy piece, and further precipitate nano-sized gamma prime phase particles in the interstices of the C6 carbide particles, M 23 C6 carbide particles; preferably, the heat-treated cast nickel-base superalloy piece has a room temperature tensile yield strength of 904-943MPa, a tensile strength of 1167-1194MPa, an elongation after fracture of 6.0-7.5%, a high temperature tensile yield strength of 729-782MPa, a tensile strength of 872-919MPa, and an elongation after fracture of 7-8%; preferably, the cast nickel-base superalloy piece has the following chemical composition in terms of weight percentage: C 0.08-0.13wt%, Cr 16-19wt%, Co 8-11wt%, W 1.0-2.7wt%, Mo 1.0-2.5wt%, Al 1.5-2.2wt%, Ti 3.2-4.0wt%, Nb 1.5-2.5wt%, B 0.008-0.015wt%, Zr≤0.1wt%, and Ni is the balance; preferably, the heat-treated cast nickel-base superalloy piece is prepared by the heat treatment method of any one of the above-described cast nickel-base superalloy.

[0021] Compared with the prior art, the heat treatment method of the cast nickel-base superalloy of the present application has at least the following beneficial effects:

[0022] The application provides a heat treatment method for improving cast nickel-based superalloy, in particular, a four-stage heat treatment process. First, through solid solution treatment and high-temperature aging treatment (the first aging treatment is high-temperature aging treatment), the solidification element segregation in the cast nickel-based superalloy part is fully eliminated, and submicron-sized γ' phase particles are formed at the grain boundaries of the alloy. After the cast superalloy is fully solid-solved, the alloy has a high element supersaturation and does not have a significant amount of nucleation particles. Under high-temperature aging conditions, the γ' phase has a low precipitation driving force, and because there are no nucleation particles in the grains, it will preferentially nucleate and precipitate at the grain boundaries. The temperature of the high-temperature aging heat treatment is also important. If the temperature is too high, the amount of γ' phase precipitated at the grain boundaries is insufficient, and the grain boundary strengthening effect cannot be achieved. If the temperature is too low, the γ' phase will change from grain boundary precipitation to intragranular precipitation. After high-temperature aging treatment, the main purpose of the medium-temperature aging treatment (the second aging treatment) is to precipitate M 23 C6 carbide particles in the gaps of the submicron-sized γ' phase at the grain boundaries. 23 The treatment temperature of the medium-temperature aging treatment needs to be determined according to the initial precipitation temperature of the M 23 C6 carbide, so as to obtain a large M 23 C6 carbide precipitation undercooling degree, and reduce the M 23 C6 carbide precipitation size. Generally, the M 23 C6 carbide has a micron-level size. The medium-temperature aging temperature in the application is 100-200℃ lower than the M 23 C6 carbide precipitation temperature, so as to ensure that the M 23 C6 carbide and the grain boundary γ' phase have a similar particle size, and can have a better synergistic strengthening effect. Because the medium-temperature aging treatment (the second aging treatment) has a high temperature for the aging treatment of general cast superalloys, the γ' phase is not fully precipitated. Therefore, in order to ensure the microstructure stability, size stability and performance stability of the alloy, the application needs to combine a low-temperature aging treatment (the third aging treatment) after the medium-temperature aging treatment. In the low-temperature aging treatment, the γ' phase will continue to precipitate. They will further fill the gaps between the M 23 C6 carbide and the γ' phase at the grain boundaries, thereby improving the grain boundary strength.

[0023] If the wall thickness, plate thickness or diameter size of the cast nickel-based superalloy part is large, a higher solid solution temperature should be used. If the solid solution temperature is too low, the dendritic segregation in the alloy cannot be fully eliminated, and in the subsequent high-temperature aging treatment, the γ' phase particles will preferentially precipitate in the interdendritic region, weakening the precipitation advantage of the γ' phase at the grain boundaries.

[0024] The cooling rate after the solid solution treatment should be relatively fast under the premise that the cast nickel-based superalloy part does not deform by stress. If the cooling rate after the solid solution treatment is insufficient, the gamma prime phase will precipitate during the cooling process of the alloy, which will also reduce the precipitation of the gamma prime phase at the grain boundaries during the high-temperature aging process.

[0025] Preferably, the cooling rate of the first aging treatment step also has an effect on the structure, and should be fast to avoid the precipitation of the gamma prime phase during the cooling process.

[0026] In summary, the heat treatment method provided by the application can form a multi-stage precipitated phase combination of "sub-micron size gamma prime phase particles + sub-micron size M 23 The multi-stage precipitated phase combination can effectively improve the grain boundary strength and inhibit the crack propagation at the grain boundaries, while not damaging the strength of the alloy, so that the high-temperature tensile strength and plasticity of the cast nickel-based superalloy are significantly improved.

[0027] The above description is only a summary of the technical solutions of the application. In order to more clearly understand the technical means of the application, and to implement the content of the description, the following preferred embodiments of the application are described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 Figure 1 is an SEM microstructure morphology photograph of a cast nickel-based superalloy test bar after heat treatment in Example 1.

[0029] Figure 2 Figure 2 is an SEM microstructure morphology photograph of a cast nickel-based superalloy test bar after heat treatment in Example 2.

[0030] Figure 3 Figure 3 is an SEM microstructure morphology photograph of a cast nickel-based superalloy test bar after heat treatment in Example 3.

[0031] Figure 4 Figure 4 is an SEM microstructure morphology photograph of a cast nickel-based superalloy test bar after heat treatment in Example 4.

[0032] Figure 5 Figure 5 is an SEM microstructure morphology photograph of a cast nickel-based superalloy test bar after heat treatment in Comparative Example 1.

[0033] Figure 6 Figure 6 is an SEM microstructure morphology photograph of a cast nickel-based superalloy test bar after heat treatment in Comparative Example 2.

[0034] Figure 7 Figure 7 is an SEM microstructure morphology photograph of a cast nickel-based superalloy test bar after heat treatment in Comparative Example 3.

[0035] Figure 8is the SEM microstructure morphology photo of the cast nickel-based superalloy test bar after solution treatment in Comparative Example 4. DETAILED DESCRIPTION

[0036] To further clarify the technical means and effects taken by the present application to achieve the intended purpose, the following describes the specific embodiments, structures, features and effects according to the present application in detail with reference to the accompanying drawings and preferred embodiments. In the following description, different "an embodiment" or "embodiments" do not necessarily refer to the same embodiment. In addition, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0037] The present application provides a heat treatment method of a cast nickel-based superalloy, which mainly comprises the following steps:

[0038] Solution treatment: heat the cast nickel-based superalloy part to 1140℃+A, and perform solution treatment for 6-10h, and then cool at a first set cooling rate to obtain a cast nickel-based superalloy part after solution treatment; wherein A is the maximum thickness of the cast superalloy part x (3-5℃ / mm); wherein cooling at the set cooling rate is used to avoid the precipitation of γ' phase particles during the cooling process of the cast nickel-based superalloy part.

[0039] Preferably, the solution treatment temperature is 1140℃-1250℃ to ensure that the solidification element segregation in cast parts of different sizes is fully eliminated.

[0040] In this step, during the cooling process, when the temperature of the alloy part is above 600℃, the first set cooling rate is 500-3000℃ / min. At this point, on the one hand, the cooling process of the alloy part when the temperature is above 600℃ is a key control process, and fast cooling can avoid the precipitation of γ' phase. When the alloy part cools to below 600℃, it has already exceeded the precipitation temperature of γ' phase, so it does not matter whether fast cooling is performed below 600℃. On the other hand, the cooling process is to cool fast at high temperature and slow at low temperature. The same is blowing by the fan, but the cooling rate at high temperature and low temperature is different.

[0041] The cooling method is an out-of-furnace cooling method; the out-of-furnace cooling adopts forced convection cooling of non-oxidizing gas phase medium.

[0042] First aging treatment: the cast nickel-based superalloy part after solution treatment is subjected to first aging treatment, and is cooled at a second set cooling rate to obtain a cast nickel-based superalloy part after first aging treatment; wherein the first aging treatment temperature is 950-1080℃, and the first aging treatment time is 1-6h.

[0043] In this step, the first aging treatment temperature is 5-50℃ below the strengthening phase γ' phase precipitation temperature and higher than M 23 C6 carbide precipitation temperature, to precipitate sub-micron size γ' phase particles on the grain boundaries.

[0044] In this step, during the cooling process, when the temperature of the alloy piece is above 600℃, the second set cooling rate is 500-3000℃ / min. The cooling method is an out-of-furnace cooling method; the out-of-furnace cooling adopts forced convection cooling of non-oxidizing gas phase medium.

[0045] Second aging treatment: the cast nickel-based superalloy piece after the first aging treatment is subjected to a second aging treatment, and after cooling, a cast nickel-based superalloy piece after the second aging treatment is obtained; wherein the temperature of the second aging treatment is 825-925℃, and the time of the second aging treatment is 10-20h.

[0046] In this step, the temperature of the second aging treatment is M 23 C6 carbide precipitation temperature, to ensure M 23 C6 has sufficient nucleation undercooling and precipitation driving force, and precipitates in the gap between the sub-micron size γ' phase particles on the grain boundaries with similar particle size.

[0047] In this step, the cooling rate is not less than 100℃ / min; wherein the cooling method is an out-of-furnace cooling or in-furnace gas cooling method; the out-of-furnace cooling selects air cooling or gas cooling; wherein the in-furnace gas cooling selects inert gas cooling.

[0048] Third aging treatment: the cast nickel-based superalloy piece after the second aging treatment is subjected to a third aging treatment, and after cooling, a heat-treated cast nickel-based superalloy piece is obtained; wherein the temperature of the third aging treatment is 650-750℃, and the time of the third aging treatment is 15-25h.

[0049] In this step, the third aging treatment temperature is 300-400℃ below the γ' phase precipitation temperature, and during the low-temperature and long-time heat treatment process, nanometer size γ' phase continues to precipitate on the grain boundaries.

[0050] In this step, the cooling rate is not less than 100℃ / min; wherein the cooling method is an out-of-furnace cooling or in-furnace gas cooling method; the out-of-furnace cooling selects air cooling or gas cooling; wherein the in-furnace gas cooling selects inert gas cooling.

[0051] The cast superalloy prepared by the existing "solid solution + aging" heat treatment process has grain boundaries generally containing only coarse M 23 C6 carbide. At high temperatures, the grain boundary strength of the alloy is weakened, and the coarse M 23C6 cannot provide enough strength to the grain boundary, which shows that the alloy is prone to cracking along the grain at high temperature and the plasticity is low. Unlike the prior art, the heat treatment method provided by the application can form a multi-level precipitated phase combination of "sub-micron size γ' phase particles + sub-micron size M 23 The multi-level precipitated phase combination of C6 carbide particles + nanometer size γ' phase particles can effectively improve the grain boundary strength and inhibit the crack propagation of the grain boundary, while not damaging the strength of the alloy, so that the high-temperature tensile strength and plasticity of the cast nickel-based high-temperature alloy are significantly improved.

[0052] In addition, it should be noted that the "high strength and plasticity" refers to a good match between the strength and plasticity of the alloy. Generally, the plasticity and the strength are inversely related, and it is difficult to improve both at the same time.

[0053] The application will be further described below through specific examples as follows:

[0054] Example 1

[0055] In this example, a Φ7mm cast nickel-based high-temperature alloy rod is heat treated, and the chemical composition of the nickel-based cast high-temperature alloy test rod is as follows: C 0.13wt%, Cr 18.8wt%, Co 11wt%, W 2.7wt%, Mo 1.7wt%, Al 2.26wt%, Ti 3.55wt%, Nb 1.75wt%, B 0.011wt%, and Ni balance. The heat treatment steps are as follows:

[0056] Solution treatment: the cast nickel-based high-temperature alloy test rod is placed in a heating furnace and heated to 1170℃, and the solution treatment is carried out for 8 hours, and then the furnace is taken out after the heat preservation is over, and fast cooling is carried out by using double fans with large air volume (to ensure that the cooling speed of the alloy part is about 1700℃ / min at a temperature above 600℃), to obtain the cast nickel-based high-temperature alloy test rod after solution treatment.

[0057] First aging treatment: the cast nickel-based high-temperature alloy test rod after solution treatment is placed in a heating furnace and heated to 1080℃, and the first aging treatment is carried out for 2 hours, and then the furnace is taken out after the heat preservation is over, and fast cooling is carried out by using double fans with large air volume (to ensure that the cooling speed of the alloy part is about 1500℃ / min at a temperature above 600℃), to obtain the cast nickel-based high-temperature alloy test rod after the first aging treatment.

[0058] Second aging treatment: the cast nickel-based high-temperature alloy test rod after the first aging treatment is placed in a heating furnace and heated to 850℃, and the second aging treatment is carried out for 15 hours, and then air cooling is carried out outside the furnace after the heat preservation is over, to obtain the cast nickel-based high-temperature alloy test rod after the second aging treatment.

[0059] Third aging treatment: the cast nickel-based superalloy test bar after the second aging treatment is heated to 750 DEG C in a heating furnace, and aged for 15 hours to perform the third aging treatment. After the aging treatment is completed, the test bar is air cooled outside the furnace to obtain the heat-treated cast nickel-based superalloy test bar.

[0060] After the above steps, the mechanical properties of the heat-treated cast superalloy test bar are detected, and the results are shown in Table 1.

[0061] Figure 1 is a SEM microstructure morphology photo of the heat-treated cast nickel-based superalloy test bar in Example 1. From Figure 1 It can be seen that the microstructure of the heat-treated cast nickel-based superalloy test bar in the example is as follows: submicron-sized γ' phase particles and M 23 C6 carbide particles are precipitated between the γ' phase particles, M 23 C6 carbide particles, and further precipitate nano-sized γ' phase particles in the gap between the γ' phase particles, M

[0062] Example 2

[0063] In this example, a Φ10mm cast nickel-based superalloy rod is heat treated. The chemical composition of the nickel-based cast superalloy test bar, by weight percentage, is as follows: C 0.13wt%, Cr 18.9wt%, Co 10.5wt%, W 2.7wt%, Mo 1.7wt%, Al 1.89wt%, Ti 3.69wt%, Nb 1.89wt%, B 0.012wt%, Ni balance. The heat treatment steps are as follows:

[0064] Solution treatment: the cast nickel-based superalloy test bar is heated to 1180 DEG C in a heating furnace, and aged for 6 hours to perform the solution treatment. After the aging treatment is completed, the test bar is taken out of the furnace and air cooled outside the furnace to obtain the solution-treated cast nickel-based superalloy test bar.

[0065] First aging treatment: the solution-treated cast nickel-based superalloy test bar is heated to 1060 DEG C in a heating furnace, and aged for 4 hours to perform the first aging treatment. After the aging treatment is completed, the test bar is taken out of the furnace and air cooled outside the furnace to obtain the first aging-treated cast nickel-based superalloy test bar.

[0066] Second aging treatment: the first aging-treated cast nickel-based superalloy test bar is heated to 830 DEG C in a heating furnace, and aged for 20 hours to perform the second aging treatment. After the aging treatment is completed, the test bar is air cooled outside the furnace to obtain the second aging-treated cast nickel-based superalloy test bar.

[0067] Third aging treatment: the cast nickel-based superalloy test bar after the second aging treatment is placed in a heating furnace and heated to 700℃, and aged for 20 hours to perform the third aging treatment. After the aging is completed, the furnace is cooled outside to obtain the heat-treated cast nickel-based superalloy test bar.

[0068] After the above steps, the mechanical properties of the heat-treated cast superalloy test bar are detected, and the results are shown in Table 1.

[0069] Figure 2 is an SEM microstructure morphology photograph of the heat-treated cast nickel-based superalloy test bar in Example 2. From Figure 2 It can be seen that the microstructure of the heat-treated cast nickel-based superalloy test bar in this example is as follows: submicron-sized γ' phase particles and M 23 C6 carbide particles are intergranularly precipitated, and further nanoscale γ' phase particles are precipitated in the gaps between the γ' phase particles, M 23 C6 carbide particles.

[0070] Example 3

[0071] In this example, a 3mm thick cast nickel-based superalloy test plate is heat treated, and the chemical composition of the nickel-based cast superalloy test plate is as follows: C 0.13wt%, Cr 18.8wt%, Co 11wt%, W 2.7wt%, Mo 1.7wt%, Al 2.26wt%, Ti 3.55wt%, Nb 1.75wt%, B 0.011wt%, and Ni balance, in terms of weight percentage. The heat treatment steps are as follows:

[0072] Solution treatment: the cast nickel-based superalloy test plate is placed in a heating furnace and heated to 1150℃, and aged for 6 hours to perform the solution treatment. After the aging is completed, the furnace is taken out, and a large amount of air is used for fast cooling (to ensure that the cooling rate of the alloy part is about 1600℃ / min at a temperature above 600℃), to obtain the solution-treated cast nickel-based superalloy test plate.

[0073] First aging treatment: the solution-treated cast nickel-based superalloy test plate is placed in a heating furnace and heated to 1070℃, and aged for 4 hours to perform the first aging treatment. After the aging is completed, the furnace is taken out, and a large amount of air is used for fast cooling (to ensure that the cooling rate of the alloy part is about 1400℃ / min at a temperature above 600℃), to obtain the first aging-treated cast nickel-based superalloy test plate.

[0074] Second aging treatment: the cast nickel-based superalloy test plate after the first aging treatment is placed in a heating furnace and heated to 850℃, and aged for 15 hours to perform the second aging treatment. After the aging treatment is completed, air cooling is performed outside the furnace to obtain the cast nickel-based superalloy test plate after the second aging treatment.

[0075] Third aging treatment: the cast nickel-based superalloy test plate after the second aging treatment is placed in a heating furnace and heated to 700℃, and aged for 20 hours to perform the third aging treatment. After the aging treatment is completed, air cooling is performed outside the furnace to obtain the cast nickel-based superalloy test plate after the heat treatment.

[0076] After the above steps, the mechanical properties of the heat-treated cast superalloy test plate are detected, and the results are shown in Table 1.

[0077] Figure 3 is an SEM microstructure morphology photograph of the cast nickel-based superalloy test rod after heat treatment in Example 3. From Figure 3 It can be seen that the microstructure of the cast nickel-based superalloy test rod after heat treatment in this example is as follows: submicron size γ' phase particles and M 23 C6 carbide particles are precipitated between the γ' phase particles, M 23 C6 carbide particles, and further precipitate nano-sized γ' phase particles in the gap between the γ' phase particles, M

[0078] Example 4

[0079] In this example, a Φ14mm cast nickel-based superalloy rod is heat treated. The chemical composition of the nickel-based cast superalloy test rod, by weight percentage, is as follows: C 0.13wt%, Cr 18.8wt%, Co 11wt%, W 2.7wt%, Mo 1.7wt%, Al 2.16wt%, Ti 3.55wt%, Nb 1.75wt%, B 0.011wt%, Ni balance. The heat treatment steps are as follows:

[0080] Solution treatment: the cast nickel-based superalloy test rod is placed in a heating furnace and heated to 1200℃, and aged for 8 hours to perform the solution treatment. After the aging treatment is completed, the furnace is taken out, and fast cooling is performed using double-fan large air volume (to ensure that the cooling rate of the alloy part is about 1900℃ / min at a temperature above 600℃), to obtain the cast nickel-based superalloy test rod after the solution treatment.

[0081] First aging treatment: the cast nickel-based superalloy test rod after the solution treatment is placed in a heating furnace and heated to 1050℃, and aged for 6 hours to perform the first aging treatment. After the aging treatment is completed, the furnace is taken out, and fast cooling is performed using double-fan large air volume (to ensure that the cooling rate of the alloy part is about 1300℃ / min at a temperature above 600℃), to obtain the cast nickel-based superalloy test rod after the first aging treatment.

[0082] Second aging treatment: the cast nickel-based superalloy test bar after the first aging treatment was placed in a heating furnace and heated to 850℃, and aged for 15 hours to perform the second aging treatment. After the aging treatment was completed, the test bar was air-cooled outside the furnace to obtain the cast nickel-based superalloy test bar after the second aging treatment.

[0083] Third aging treatment: the cast nickel-based superalloy test bar after the second aging treatment was placed in a heating furnace and heated to 700℃, and aged for 20 hours to perform the third aging treatment. After the aging treatment was completed, the test bar was air-cooled outside the furnace to obtain the cast nickel-based superalloy test bar after the heat treatment.

[0084] After the above steps, the mechanical properties of the heat-treated cast superalloy test bar were detected, and the results are shown in Table 1.

[0085] Figure 4 is an SEM microstructure morphology photograph of the cast nickel-based superalloy test bar after heat treatment in Example 4. From the photograph, it can be seen that the microstructure of the cast nickel-based superalloy test bar after heat treatment in this example is as follows: the grain boundaries have submicron-sized γ' phase particles and M Figure 4 It can be seen that: the microstructure of the cast nickel-based superalloy test bar after heat treatment in this example is as follows: the grain boundaries have submicron-sized γ' phase particles and M 23 C6 carbide particles, and further nanoscale γ' phase particles are precipitated in the gaps between the γ' phase particles, M 23 C6 carbide particles.

[0086] Comparative Example 1

[0087] Comparative Example 1: a cast nickel-based superalloy bar with a diameter of Φ7 mm was heat-treated, and the chemical composition of the cast nickel-based superalloy test bar, by weight percentage, was as follows: C 0.13wt%, Cr 18.9wt%, Co 10.5wt%, W 2.7wt%, Mo 1.7wt%, Al 1.89wt%, Ti 3.69wt%, Nb 1.89wt%, B 0.012wt%, and Ni balance. The heat treatment steps were as follows:

[0088] Solution treatment: the cast nickel-based superalloy test bar was placed in a heating furnace and heated to 1170℃, and aged for 8 hours to perform the solution treatment. After the aging treatment was completed, the test bar was taken out of the furnace and subjected to fast cooling using a double-fan large air volume (to ensure that the cooling rate of the alloy part at a temperature above 600℃ is about 1700℃ / min) to obtain the cast nickel-based superalloy test bar after the solution treatment.

[0089] Aging treatment: the cast nickel-based superalloy test bar after the solution treatment was placed in a heating furnace and heated to 850℃, and aged for 20 hours to perform the first aging treatment. After the aging treatment was completed, the test bar was cooled outside the furnace to obtain the cast nickel-based superalloy test bar after the heat treatment.

[0090] After the above steps, the mechanical properties of the cast high-temperature alloy test bar were detected, and the results are shown in Table 1.

[0091] Figure 5 is a SEM microstructure morphology photo of the cast nickel-based high-temperature alloy test bar after heat treatment in Comparative Example 1. From the photo, it can be seen that the microstructure of the cast nickel-based high-temperature alloy test bar after heat treatment in the comparative example is as follows: there are no sub-micron size γ' phase particles on the grain boundary, only micron size, long strip-shaped M Figure 5 C6 carbide and uniform size γ' phase. The interphase precipitation state of γ' phase and M 23 C6 carbide is not formed on the grain boundary, which leads to the coarse size of M 23 C6 carbide and limited strengthening effect on the grain boundary. 23

[0092] Comparative Example 2

[0093] Comparative Example 2

[0094] Solution treatment: the cast nickel-based high-temperature alloy test bar was placed in a heating furnace and heated to 1170℃ for 8 hours for solution treatment, and after the end of the heat preservation, the furnace was taken out and fast cooled with a large air volume of double fans (to ensure that the cooling rate of the alloy part is about 1700℃ / min at a temperature above 600℃), to obtain the cast nickel-based high-temperature alloy test bar after solution treatment.

[0095] First aging treatment: the cast nickel-based high-temperature alloy test bar after solution treatment was placed in a heating furnace and heated to 900℃ for 6 hours for first aging treatment, and after the end of the heat preservation, the furnace was taken out and fast cooled with a large air volume of double fans, to obtain the cast nickel-based high-temperature alloy test bar after first aging treatment.

[0096] Second aging treatment: the cast nickel-based high-temperature alloy test bar after first aging treatment was placed in a heating furnace and heated to 850℃ for 15 hours for second aging treatment, and after the end of the heat preservation, the furnace was taken out and air cooled outside the furnace, to obtain the cast nickel-based high-temperature alloy test bar after second aging treatment.

[0097] Third aging treatment: the cast nickel-based high-temperature alloy test bar after second aging treatment was placed in a heating furnace and heated to 750℃ for 15 hours for third aging treatment, and after the end of the heat preservation, the furnace was taken out and air cooled outside the furnace, to obtain the cast nickel-based high-temperature alloy test bar after heat treatment. ​

[0098] After the above steps, the mechanical properties of the heat-treated cast high-temperature alloy test bar were detected, and the results are shown in Table 1.

[0099] Figure 6 is a SEM microstructure morphology photograph of the cast nickel-based high-temperature alloy test bar after heat treatment in Comparative Example 2. From Figure 6 It can be seen that: the microstructure of the cast nickel-based high-temperature alloy test bar after heat treatment in the present comparative example is as follows: the number of submicron size γ' phase in the alloy crystal is too much, which greatly reduces the precipitation of γ' phase in the subsequent aging process, and significantly reduces the strength of the alloy.

[0100] Comparative Example 3

[0101] In the present embodiment, a Φ7 mm cast nickel-based high-temperature alloy rod is heat treated, wherein the chemical composition of the cast nickel-based high-temperature alloy test bar is as follows: C 0.13wt%, Cr 18.9wt%, Co 10.5wt%, W 2.7wt%, Mo 1.7wt%, Al 1.89wt%, Ti 3.69wt%, Nb 1.89wt%, B 0.012wt%, Ni balance, in terms of weight percentage. The heat treatment steps are as follows:

[0102] Solution treatment: the cast nickel-based high-temperature alloy test bar is placed in a heating furnace and heated to 1170℃, and heat treated for 8 hours to perform solution treatment. After the heat preservation is over, the furnace is taken out and air cooled on the ground (the cooling rate of the alloy part is about 400℃ / min at a temperature above 600℃), to obtain the cast nickel-based high-temperature alloy test bar after solution treatment.

[0103] First aging treatment: the cast nickel-based high-temperature alloy test bar after solution treatment is placed in a heating furnace and heated to 1060℃, and heat treated for 4 hours to perform first aging treatment. After the heat preservation is over, the furnace is taken out and air cooled on the ground (the cooling rate of the alloy part is about 300℃ / min at a temperature above 600℃), to obtain the cast nickel-based high-temperature alloy test bar after first aging treatment.

[0104] Second aging treatment: the cast nickel-based high-temperature alloy test bar after first aging treatment is placed in a heating furnace and heated to 850℃, and heat treated for 15 hours to perform second aging treatment. After the heat preservation is over, the furnace is taken out and air cooled outside the furnace, to obtain the cast nickel-based high-temperature alloy test bar after second aging treatment.

[0105] Third aging treatment: the cast nickel-based high-temperature alloy test bar after second aging treatment is placed in a heating furnace and heated to 750℃, and heat treated for 15 hours to perform third aging treatment. After the heat preservation is over, the furnace is taken out and air cooled outside the furnace, to obtain the cast nickel-based high-temperature alloy test bar after heat treatment.

[0106] After the above steps, the mechanical properties of the heat-treated cast high-temperature alloy test bar were tested, and the results are shown in Table 1.

[0107] Figure 7 These are SEM micrographs of the heat-treated cast nickel-based superalloy test bar from Comparative Example 3. Figure 7 It can be seen that the microstructure of the heat-treated cast nickel-based superalloy test bar in this comparative example is as follows: abnormally sized γ′ phase particles precipitate in large quantities within the alloy grains. These particles cause the γ′ phase to change from fine and dispersed nucleation and precipitation to coarse growth of the precipitated γ′ phase during subsequent aging treatment, increasing the average size of the γ′ phase within the grains and reducing the alloy strength.

[0108] Comparative Example 4

[0109] This embodiment describes the heat treatment of a Φ30mm cast nickel-based superalloy rod. The chemical composition of the nickel-based cast superalloy rod, by weight percentage, is as follows: C 0.13wt%, Cr 18.8wt%, Co 11wt%, W 2.7wt%, Mo 1.7wt%, Al 2.16wt%, Ti 3.55wt%, Nb 1.75wt%, B 0.011wt%, Ni balance. The heat treatment steps are as follows:

[0110] Solution treatment: The cast nickel-based superalloy test bar is placed in a heating furnace and heated to 1180℃ and held for 8 hours for solution treatment. After the holding period, it is taken out of the furnace and rapidly cooled with a large air volume using a dual-fan system (ensuring that the cooling rate of the alloy part in the temperature range above 600℃ is about 1800℃ / min) to obtain the solution-treated cast nickel-based superalloy test bar.

[0111] First aging treatment: The solution-treated cast nickel-based superalloy test bar was placed in a heating furnace and heated to 1060℃, and held for 2 hours for the first aging treatment. After the holding period, the test bar was removed from the furnace and rapidly cooled with a large air volume using a dual-fan system (ensuring that the cooling rate of the alloy part in the temperature range above 600℃ is about 1400℃ / min) to obtain the cast nickel-based superalloy test bar after the first aging treatment.

[0112] Second aging treatment: The cast nickel-based superalloy test bar after the first aging treatment is placed in a heating furnace and heated to 850°C, and held for 15 hours for the second aging treatment. After the holding period, it is air-cooled outside the furnace to obtain the cast nickel-based superalloy test bar after the second aging treatment.

[0113] Third aging treatment: The cast nickel-based superalloy test bar after the second aging treatment is placed in a heating furnace and heated to 750°C, and held for 15 hours for the third aging treatment. After the holding period, it is air-cooled outside the furnace to obtain the heat-treated cast nickel-based superalloy test bar.

[0114] After the above steps, the mechanical properties of the heat-treated cast high-temperature alloy test bar were detected, and the results are shown in Table 1.

[0115] Figure 8 is a SEM microstructure morphology photo of the heat-treated cast nickel-based high-temperature alloy test bar in Comparative Example 4. From the photo, it can be seen that the microstructure of the heat-treated cast nickel-based high-temperature alloy test bar in the present comparative example is as follows: submicron-sized γ' phase is only precipitated in the interdendritic region where the element segregation is relatively serious, and is not precipitated in the dendrite trunk region. This makes the alloy not form a uniform and dispersed submicron-sized γ' phase distribution, and a good intragranular and grain boundary strengthening structure is not obtained. Figure 8

[0116] Table 1 is the mechanical properties of the heat-treated cast high-temperature alloy of Examples 1-4 and Comparative Examples 1-4

[0117] Table 1

[0118]

[0119] From the above Examples 1-4 and Comparative Examples 1-4, it can be seen that:

[0120] 1) The heat-treated cast nickel-based high-temperature alloy obtained in Examples 1-4 has a room temperature tensile yield strength of 904-943 MPa, a room temperature tensile strength of 1167-1194 MPa, and a room temperature elongation of 6.0-7.5%. The high-temperature tensile yield strength is 729-782 MPa, the high-temperature tensile strength is 872-919 MPa, and the high-temperature elongation is 7-8%.

[0121] 2) Comparative Example 1 is a heat treatment method of "solid solution + aging" of the prior art. Compared with Comparative Example 1, the strength of the cast alloy after heat treatment in Examples 1-4 does not decrease significantly, and the room temperature and high-temperature tensile plasticity is improved by more than 50%, which significantly improves the tensile strength and plasticity of the cast alloy.

[0122] 3) Compared with Example 1, the high-temperature aging treatment temperature in Comparative Example 2 is too low. Although the tensile plasticity of the alloy is significantly improved, the tensile strength is significantly reduced.

[0123] 4) In Comparative Example 3, no fast cooling measures are taken in the solid solution treatment step and the high-temperature aging treatment step, resulting in a large amount of γ' phase particles precipitating in the alloy intragranular and grain boundary during the cooling process. These γ' phase precipitated during cooling affect the precipitation state of γ' phase during subsequent aging treatment in the intragranular, and pre-occupy the precipitation position of M 23 C6 carbide at the grain boundary, which reduces the intragranular and grain boundary strength of the alloy, resulting in a low alloy strength and no performance optimization effect.

[0124] ​5) The solution treatment system of Comparative Example 4 is not good, which does not meet the solution treatment temperature requirement of 1140℃+A, and fails to eliminate element segregation, resulting in failure of high-temperature aging treatment (first aging treatment), the alloy performance is similar to that of the prior art in Comparative Example 1, and no alloy performance optimization effect is produced.

[0125] In conclusion, the heat treatment method for the cast nickel-based superalloy provided by the application can form submicron-sized γ' phase and M 23 C6 carbide phase, and further precipitate nano γ' phase in the gap of the C6 carbide phase, improve the grain boundary strength, thereby improve the tensile plasticity of the cast nickel-based superalloy, without reducing the alloy strength, and finally realize the significant improvement of the high-temperature strength and plasticity of the cast nickel-based superalloy. 23 C6 carbide phase, and further precipitate nano γ' phase in the gap of the C6 carbide phase, improve the grain boundary strength, thereby improve the tensile plasticity of the cast nickel-based superalloy, without reducing the alloy strength, and finally realize the significant improvement of the high-temperature strength and plasticity of the cast nickel-based superalloy.

Claims

1. A heat treatment method for cast nickel-based superalloys, characterized in that, It includes the following steps: Solution treatment: The cast nickel-based superalloy part is heated to 1140℃+A and solution treated for 6~10 hours. Then, it is cooled at a first set cooling rate to obtain the solution-treated cast nickel-based superalloy part. Wherein, A is the maximum thickness of the cast nickel-based superalloy part × (3~5℃ / mm). The first set cooling rate is used to prevent precipitation during the cooling process of the cast nickel-based superalloy part. Phase particles; First aging treatment: The cast nickel-based superalloy part after solution treatment is subjected to a first aging treatment, and cooled at a second set cooling rate to obtain the cast nickel-based superalloy part after the first aging treatment; wherein, the temperature of the first aging treatment is 950~1080℃, and the time of the first aging treatment is 1~6h. Second aging treatment: The cast nickel-based superalloy part after the first aging treatment is subjected to a second aging treatment, and after cooling, the cast nickel-based superalloy part after the second aging treatment is obtained; wherein, the temperature of the second aging treatment is 825~925℃, and the time of the second aging treatment is 10~20h. Third aging treatment: The cast nickel-based superalloy parts after the second aging treatment are subjected to a third aging treatment, and after cooling, the heat-treated cast nickel-based superalloy parts are obtained; wherein, the temperature of the third aging treatment is 650~750℃, and the time of the third aging treatment is 15~25h. The chemical composition of the cast nickel-based superalloy, by weight percentage, is as follows: C 0.08-0.13wt%, Cr 16-19wt%, Co 8-11wt%, W 1.0-2.7wt%, Mo 1.0-2.5wt%, Al 1.5-2.2wt%, Ti 3.2-4.0wt%, Nb 1.5-2.5wt%, B 0.008-0.015wt%, Zr≤0.1wt%, Ni is the balance; In the solution treatment step: during the cooling process, when the temperature of the alloy part is above 600°C, the first set cooling rate is 500-3000°C / min. In the first aging process: during the cooling process, when the temperature of the alloy part is above 600°C, the second set cooling rate is 500-3000°C / min.

2. The heat treatment method for cast nickel-based superalloys according to claim 1, characterized in that, In the solution treatment step: The solution treatment temperature is 1140℃~1250℃; and / or The maximum thickness is ≤20mm.

3. The heat treatment method for cast nickel-based superalloys according to claim 1, characterized in that, The first aging treatment causes submicron-sized precipitates to form at the grain boundaries of the cast nickel-based superalloy parts. Phase particles.

4. The heat treatment method for cast nickel-based superalloys according to claim 1, characterized in that, Through the second aging treatment, submicron-sized γ′ phase particles precipitate in the interstices of submicron-sized γ′ phase particles at the grain boundaries of the cast nickel-based superalloy parts. Carbide particles.

5. The heat treatment method for cast nickel-based superalloys according to claim 1, characterized in that, Through the third aging treatment, nano-sized precipitates continue to form at the grain boundaries of the cast nickel-based superalloy parts. Phase particles.

6. The heat treatment method for cast nickel-based superalloys according to claim 1, characterized in that, In the steps of solution treatment and first aging treatment, the cooling method is external furnace cooling.

7. The heat treatment method for cast nickel-based superalloys according to claim 6, characterized in that, In the steps of solution treatment and first aging treatment: external cooling adopts forced convection cooling with a non-oxidizing gaseous medium.

8. The heat treatment method for cast nickel-based superalloys according to claim 1, characterized in that, In the second and third aging processes, the cooling rate is not less than 100°C / min.

9. The heat treatment method for cast nickel-based superalloys according to claim 8, characterized in that, In the second and third aging processes, the cooling method is either external furnace cooling or internal furnace air cooling.

10. The heat treatment method for cast nickel-based superalloys according to claim 9, characterized in that, In the second and third aging processes: the external cooling is either air cooling or gas cooling.

11. The heat treatment method for cast nickel-based superalloys according to claim 9, characterized in that, In the second and third aging processes: the furnace cooling is performed using inert gas.

12. A heat-treated cast nickel-based superalloy part, characterized in that, The cast nickel-based superalloy parts have submicron-sized γ′ phase particles and M at the grain boundaries. 23 The interphase precipitation state of C6 carbide particles, and in the γ′ phase particles, M 23 Nano-sized particles further precipitate within the interstitial spaces of the C6 carbide particles. Phase particles; wherein the heat-treated cast nickel-based superalloy part is prepared by the heat treatment method of the cast nickel-based superalloy according to any one of claims 1-11.

13. The heat-treated cast nickel-based superalloy part according to claim 12, characterized in that, The heat-treated cast nickel-based superalloy parts have a room temperature tensile yield strength of 904-943 MPa, a tensile strength of 1167-1194 MPa, and an elongation after fracture of 6.0-7.5%; a high temperature tensile yield strength of 729-782 MPa, a tensile strength of 872-919 MPa, and an elongation after fracture of 7-8%.

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