Heat treatment process for improving medium-temperature brittleness of GH4698 wrought superalloy

Abstract

The invention discloses a heat treatment process for improving medium-temperature brittleness of GH4698 wrought superalloy, which comprises the following steps: carrying out solution treatment on rolled and deformed nickel-based wrought superalloy to obtain equiaxed grains; slowly cooling to the temperature below the gamma'phase precipitation temperature, and then carrying out water cooling to obtain a bent crystal boundary; a bimodal gamma'phase is obtained in the crystal by adopting low-temperature aging treatment, and the bimodal gamma 'phase comprises a large-size gamma' phase with the average size not less than 100nm and a small-size gamma 'phase with the average size not more than 50nm. According to the heat treatment process, the steps are simplified, the traditional heat treatment time is effectively shortened, more energy is saved, more efficiency is achieved, after the alloy generating medium-temperature brittleness under the traditional heat treatment process is subjected to the heat treatment process, the tensile percentage elongation after fracture at 750 DEG C is increased to 2-4 times, and meanwhile the tensile strength meets the alloy mechanical property standard requirement.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloy heat treatment technology, and in particular relates to a heat treatment process for improving the mid-temperature brittleness of GH4698 deformed high-temperature alloy. Background Technology

[0002] Nickel-based wrought superalloys, due to their ability to maintain high strength at high temperatures and their excellent mechanical properties, oxidation resistance, corrosion resistance, and structural stability, have become widely used high-temperature materials in aerospace, energy, and chemical industries. However, in practical applications, nickel-based wrought superalloys are prone to a sharp decrease in plasticity in the mid-temperature range (600~900℃), a phenomenon known as mid-temperature brittleness. Within this temperature range, the tensile elongation is significantly lower than at other temperatures, often less than 10%, or even as low as 5%. Metal components operating within this temperature range may fail, posing a significant safety hazard.

[0003] GH4698 alloy, a nickel-based wrought superalloy widely used in high-temperature load-bearing components such as turbine disks and fasteners in gas turbines and aero engines, has 750℃ as its critical service temperature range. However, after conventional standard heat treatment and four-stage heat treatment processes, the elongation after tensile fracture at 750℃ is often less than 5%, exhibiting mid-temperature brittleness due to insufficient plasticity. This invention improves the heat treatment process by forming bent grain boundaries between alloy grains to enhance grain boundary strength, thus coordinating intragranular and grain boundary strength. This approach improves the mid-temperature brittleness of the alloy while ensuring its high strength. Summary of the Invention

[0004] The purpose of this invention is to provide a heat treatment process for nickel-based wrought high-temperature alloys that improves plasticity and reduces the mid-temperature brittleness of GH4698 alloy while maintaining its tensile strength at 750 °C.

[0005] The technical solution adopted by this invention to solve its technical problem is: a heat treatment process for improving the intermediate-temperature brittleness of GH4698 deformed high-temperature alloy, comprising the following steps:

[0006] The rolled and deformed nickel-based wrought superalloy was subjected to solution treatment to obtain equiaxed grains;

[0007] Slowly cooled to below the γ′ phase precipitation temperature and then water-cooled, resulting in a curved grain boundary;

[0008] Low-temperature aging treatment is used to obtain a dual-mode γ′ phase in the crystal. The dual-mode γ′ phase includes a larger γ′ phase with an average size of not less than 100 nm and a smaller γ′ phase with an average size of not more than 50 nm.

[0009] Furthermore, the volume fraction of the dual-modal γ′ phase is not less than 20%, the larger γ′ phase is flower-shaped or square, and the smaller γ′ phase is spherical.

[0010] Furthermore, the solution treatment temperature is 0–200°C above the recrystallization temperature, and the holding time is 0.5–2.0 hours;

[0011] The slow cooling process involves cooling the alloy, after solution treatment and heat preservation, to 800-930°C at a rate of 0.1-10°C / min, followed by water cooling.

[0012] The low-temperature aging treatment involves heating the alloy, which has been cooled to room temperature, to 650-800°C, holding it at that temperature for 8-16 hours, and then air-cooling it to room temperature.

[0013] Furthermore, the composition of the GH4698 alloy, by mass percentage, includes: Cr: 13.0~16.0%, Mo: 2.8~3.2%, Nb: 1.8~2.2%, Ti: 2.35~2.75%, Al: 1.3~1.7%, Fe: ≤2.0%, Cu: ≤0.07%, Mn: ≤0.4%, Zr: ≤0.05%, Mg: ≤0.008%, Si: ≤0.60%, C: ≤0.08%, B: ≤0.005%, with the balance being Ni.

[0014] The beneficial effects of this invention are: by heating to a temperature 0-200°C above the recrystallization temperature for solution treatment, a large amount of residual internal stress in the nickel-based superalloy after rolling deformation is eliminated, and the γ′ phase is dissolved into the matrix to prepare for the precipitation of the γ′ phase in the subsequent aging process. The holding time is adjusted to 0.5-2.0 hours to obtain a suitable grain size.

[0015] Bending grain boundaries were achieved in the GH4698 alloy by slowly cooling it below the γ′ phase precipitation temperature after solution treatment, followed by water cooling to room temperature. This improved the grain boundary strength, harmonizing the strength within the grains and between grain boundaries, effectively preventing crack propagation, and thus improving the alloy's mid-temperature brittleness. Cooling to 800–930°C at a rate of 0.1–10°C / min inhibited premature nucleation of the γ′ phase while forming bending grain boundaries, promoting the full precipitation of the γ′ phase during subsequent aging, thereby maintaining the alloy's mechanical properties. Subsequent low-temperature aging treatment at 650–800°C precipitated small-sized γ′ phases (average size not exceeding 50 nm) while retaining the bending grain boundaries, enabling the alloy to achieve the same strength level in the mid-temperature brittle region as standard heat treatment.

[0016] Compared with the traditional heat treatment process for GH4698 alloy, the heat treatment process of this invention simplifies the steps, effectively reduces the traditional heat treatment time, and is more energy-efficient. For alloys that exhibit intermediate-temperature brittleness under traditional heat treatment processes, the elongation at fracture at 750℃ increases by 2 to 4 times after applying the heat treatment process of this invention, while the tensile strength meets the alloy mechanical property standards. Attached Figure Description

[0017] Figure 1 This is a backscattered scanning electron microscope image of the alloy after heat treatment in Example 1 of the present invention.

[0018] Figure 2 The images show the morphology of intragranular and grain boundary precipitates in the alloy after heat treatment in Example 2 of this invention.

[0019] Figure 3 The images show the morphology of intragranular and grain boundary precipitates in the alloy after heat treatment in Example 3 of this invention.

[0020] Figure 4 The image shows the straight grain boundary morphology of the alloy after heat treatment in Comparative Example 1. Detailed Implementation

[0021] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0022] A heat treatment process for improving the intermediate-temperature brittleness of GH4698 deformed high-temperature alloy includes the following steps:

[0023] Step 1: Take the rolled and deformed nickel-based wrought superalloy, which, by mass percentage, includes: Cr: 13.0~16.0%, Mo: 2.8~3.2%, Nb: 1.8~2.2%, Ti: 2.35~2.75%, Al: 1.3~1.7%, Fe: ≤2.0%, Cu: ≤0.07%, Mn: ≤0.4%, Zr: ≤0.05%, Mg: ≤0.008%, Si: ≤0.60%, C: ≤0.08%, B: ≤0.005%, with the balance being Ni;

[0024] Specifically, the above are the conventional composition mass percentages of the existing GH4698 alloy;

[0025] Step 2 Solution treatment: Hold at 0–200°C above the recrystallization temperature for 0.5–2.0 hours;

[0026] After step 2, the alloy grains obtained are equiaxed grains;

[0027] Step 3: Slow cooling process: The alloy after solution treatment and heat preservation is cooled to 800~930℃ at a rate of 0.1~10℃ / min, and then water-cooled.

[0028] After step 3, the grain boundaries of the alloy are curved.

[0029] Step 4: Low-temperature aging treatment: Heat the alloy that has been cooled to room temperature to 650~800℃, hold for 8~16 hours, and then air cool to room temperature;

[0030] After step 4, two types of bimodal γ′ phases with different morphologies are precipitated in the alloy, with a volume fraction of not less than 20%. The larger γ′ phase is flower-shaped or square, with a size greater than 100 nm; the smaller γ′ phase is spherical, with a size less than 50 nm.

[0031] The following are specific embodiments and comparative examples:

[0032] Example 1

[0033] The GH4698 alloy within the composition range specified in the invention comprises, by mass percentage: Cr: 14.44%, Mo: 3.03%, Nb: 2.04%, Ti: 2.64%, Fe: 0.57%, Al: 1.62%, Si: 0.11%, C: 0.048%, Mn: 0.072%, Zr: 0.041%, with the balance being Ni; the recrystallization temperature of the alloy is 970℃, and the γ′ dissolution temperature is 948℃.

[0034] The deformed nickel-based superalloy sample was subjected to solution treatment. The recrystallization temperature of the alloy was 1000℃, the solution treatment temperature was 1030℃, and the holding time was 1 hour. After the solution treatment, the sample was cooled to 900℃ at a cooling rate of 3℃ / min and then water-cooled. Subsequently, the sample was heated to 700℃ and held for 16 hours for low-temperature aging treatment, and then air-cooled to room temperature.

[0035] The obtained sample has a large γ′ phase size of about 150 nm and a shape between flower-shaped and square. The small γ′ phase size is about 14 nm and the shape is spherical. The total volume content of the γ′ phase is about 30%. The grain boundaries exhibit a curved morphology and there are irregularly shaped γ′ phase precipitates. Figure 1 The grain boundary morphology after heat treatment in Example 1 is shown.

[0036] Example 2

[0037] The GH4698 alloy, which falls within the composition range specified in the invention, has the same composition as in Example 1. The deformed nickel-based superalloy sample was subjected to solution treatment. The recrystallization temperature of the alloy was 1000°C, the solution treatment temperature was 1030°C, and the holding time was 0.5 hours. After completion, the sample was cooled to 810°C at a cooling rate of 3°C / min and then water-cooled. Subsequently, the sample was heated to 700°C and held for 16 hours for low-temperature aging treatment, and then air-cooled to room temperature.

[0038] The obtained sample has a large γ′ phase size of about 160 nm and a shape between flower-shaped and square. The small γ′ phase size is about 12 nm and the shape is spherical. The total volume content of the γ′ phase is about 33%. The grain boundaries exhibit a curved morphology and there are irregularly shaped γ′ phase precipitates. Figure 2 The morphology of intragranular and grain boundary precipitates after heat treatment in Example 2 is shown.

[0039] Example 3

[0040] The GH4698 alloy, which falls within the composition range specified in the invention, has the same composition as in Example 1. The deformed nickel-based superalloy sample was subjected to solution treatment. The recrystallization temperature of the alloy was 1000°C, the solution treatment temperature was 1150°C, and the holding time was 0.5 hours. After solution treatment, the sample was cooled to 850°C at a cooling rate of 1°C / min and then water-cooled. Subsequently, the sample was heated to 760°C and held for 16 hours for low-temperature aging treatment, and then air-cooled to room temperature.

[0041] The obtained sample has a large γ′ phase size of about 290 nm and a flower-like shape, and a small γ′ phase size of about 24 nm and a spherical shape. The total volume content of the γ′ phase is about 38%. The grain boundaries exhibit a curved morphology and there are irregularly shaped γ′ phase precipitates. Figure 3 The morphology of intragranular and grain boundary precipitates after heat treatment in Example 2 is shown.

[0042] Example 4

[0043] The GH4698 alloy, which falls within the composition range specified in the invention, has the same composition as in Example 1. The deformed nickel-based superalloy sample was subjected to solution treatment. The recrystallization temperature of the alloy was 1000°C, the solution treatment temperature was 1150°C, and the holding time was 0.5 hours. After completion, the sample was cooled to 810°C at a cooling rate of 3°C / min and then water-cooled. Subsequently, the sample was heated to 760°C and held for 16 hours for low-temperature aging treatment, and then air-cooled to room temperature.

[0044] The obtained sample has a large γ′ phase size of about 200 nm and a shape between flower-shaped and square. The small γ′ phase size is about 27 nm and the shape is spherical. The total volume content of the γ′ phase is about 36%. The grain boundaries exhibit a curved morphology and there are irregularly shaped γ′ phase precipitates.

[0045] Example 5

[0046] The GH4698 alloy, which falls within the composition range specified in the invention, has the same composition as in Example 1. The deformed nickel-based superalloy sample was subjected to solution treatment. The recrystallization temperature of the alloy was 1000°C, the solution treatment temperature was 1030°C, and the holding time was 0.5 hours. After completion, the sample was cooled to 810°C at a cooling rate of 3°C / min and then water-cooled. Subsequently, the sample was heated to 700°C and held for 8 hours for low-temperature aging treatment, and then air-cooled to room temperature.

[0047] The obtained sample has a large γ′ phase size of about 195 nm and a shape between flower-shaped and square. The small γ′ phase size is about 25 nm and the shape is spherical. The total volume content of the γ′ phase is about 31%. The grain boundaries exhibit a curved morphology and there are irregularly shaped γ′ phase precipitates.

[0048] Comparative Example 1

[0049] The GH4698 alloy, which is within the composition range of the invention, has the same composition as in Example 1. The deformed nickel-based high-temperature alloy sample was subjected to solution treatment. The recrystallization temperature of the alloy was 1000°C, the solution treatment temperature was 1030°C, the holding time was 1 hour, and then it was air-cooled to room temperature. Subsequently, the standard heat treatment process of GH4698 alloy was carried out, which involved holding at 1000°C for 4 hours and air-cooling to room temperature, followed by aging treatment at 775°C for 16 hours and then air-cooling.

[0050] The obtained sample has a large γ′ phase size of about 180 nm and a small γ′ phase size of about 35 nm. Both are spherical in shape, and the total volume content of the γ′ phase is about 30%. The grain boundaries are straight, and there are no irregularly shaped γ′ phase precipitates. Figure 4 The grain boundary morphology of Comparative Example 1 after heat treatment is shown.

[0051] Comparative Example 2

[0052] The GH4698 alloy within the composition range of the invention was selected. The composition of the alloy was the same as that in Example 1. The deformed nickel-based high-temperature alloy sample was subjected to solution treatment. The recrystallization temperature of the alloy was 1000℃, the solution treatment temperature was 1030℃, the holding time was 1 hour, and then it was air-cooled to room temperature. Subsequently, the traditional four-stage heat treatment process of GH4698 alloy was carried out. First, it was held at 1000℃ for 4 hours and then air-cooled to room temperature. Then, it was subjected to aging treatment at 775℃ for 16 hours and then air-cooled. Finally, it was subjected to a second aging treatment at 700℃ for 16 hours and then air-cooled.

[0053] The obtained sample has a large γ′ phase size of about 200 nm and a small γ′ phase size of about 40 nm, both of which are spherical in shape. The total volume content of the γ′ phase is about 33%. The grain boundaries are straight and there are no irregularly shaped γ′ phase precipitates.

[0054] Comparative Example 3

[0055] The GH4698 alloy, which falls within the composition range specified in the invention, has the same composition as in Example 1. The deformed nickel-based superalloy sample was subjected to solution treatment. The recrystallization temperature of the alloy was 1000°C, the solution treatment temperature was 1030°C, and the holding time was 0.5 hours. After the solution treatment, the sample was cooled to 810°C at a cooling rate of 3°C / min, and then held at 810°C for 6 hours before being air-cooled to room temperature.

[0056] The obtained sample has a large γ′ phase size of about 312 nm, with a shape between flower-shaped and square, and the total volume content of the γ′ phase is about 25%. The grain boundaries exhibit a curved morphology, with irregularly shaped γ′ phase precipitates, but no fine γ′ phase precipitates.

[0057] Table 1 shows the tensile properties of Examples 1, 2, 3, 4, and 5, and Comparative Examples 1 and 2 at 750°C after heat treatment.

[0058] Table 1 Performance characteristics of the embodiments and comparative examples

[0059] Serial Number 750℃ tensile strength / MPa Elongation after fracture at 750℃ / % Example 1 821 11.5 Example 2 785 24.6 Example 3 741 27.2 Example 4 758 37.5 Example 5 725 28.6 Comparative Example 1 819 3.7 Comparative Example 2 832 5.4 Comparative Example 3 662 15.3

[0060] As can be seen from Table 1, the alloys treated with traditional heat treatment processes exhibit good strength at 750℃, but all show signs of mid-temperature brittleness. In contrast, the alloys treated with the heat treatment process of this invention exhibit good plasticity at 750℃, with significant improvement in mid-temperature brittleness and high tensile strength.

[0061] The above specific embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A heat treatment process for improving the intermediate-temperature brittleness of GH4698 deformed high-temperature alloy, characterized in that, Includes the following steps: The rolled and deformed nickel-based wrought superalloy was subjected to solution treatment to obtain equiaxed grains; Slowly cooled to below the γ′ phase precipitation temperature and then water-cooled, resulting in a curved grain boundary; Low-temperature aging treatment is used to obtain a dual-mode γ′ phase in the crystal. The dual-mode γ′ phase includes a larger γ′ phase with an average size of not less than 100 nm and a smaller γ′ phase with an average size of not more than 50 nm.

2. The heat treatment process according to claim 1, characterized in that: The volume fraction of the dual-modal γ′ phase is not less than 20%, with the larger γ′ phase appearing as a flower or square shape, and the smaller γ′ phase appearing as a sphere.

3. The heat treatment process according to claim 1, characterized in that: The solution treatment temperature is 0–200°C above the recrystallization temperature, and the holding time is 0.5–2.0 hours. The slow cooling process involves cooling the alloy, after solution treatment and heat preservation, to 800-930°C at a rate of 0.1-10°C / min, followed by water cooling. The low-temperature aging treatment involves heating the alloy, which has been cooled to room temperature, to 650-800°C, holding it at that temperature for 8-16 hours, and then air-cooling it to room temperature.

4. The heat treatment process according to claim 1, characterized in that: The composition of GH4698 alloy, by mass percentage, includes: Cr: 13.0~16.0%, Mo: 2.8~3.2%, Nb: 1.8~2.2%, Ti: 2.35~2.75%, Al: 1.3~1.7%, Fe: ≤2.0%, Cu: ≤0.07%, Mn: ≤0.4%, Zr: ≤0.05%, Mg: ≤0.008%, Si: ≤0.60%, C: ≤0.08%, B: ≤0.005%, with the balance being Ni.

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