A grain refinement method for free forging nickel-based high-temperature alloy

Abstract

The present invention provides a grain refinement method for a free forging nickel-based high-temperature alloy, comprising the following steps: step 1: forging and deforming a nickel-based high-temperature alloy forging blank into a forging, wherein during the forging and deformation process: the temperature needs to be between 950°C and 1150°C, the deformation amount is between 20% and 34%, and the forging ratio is ≥4; step 2: directly hot-sending the forging to a furnace for a short-time high-temperature annealing heat treatment, wherein the annealing heat treatment process is: the annealing temperature is between 1100°C and 1150°C, the holding time is between 10 and 40 minutes; after the annealing is completed, the furnace is cooled; step 3: performing a standard performance heat treatment on the forging, including: solution treatment, stabilization treatment and aging treatment. The present invention utilizes the re-refining effect of static / metadynamic recrystallization on the coarse-grained / mixed-grained structure formed during the forging process, so that the mixed-grained structure of the forging obtained after deformation under small deformation and medium-high strain rate becomes uniform again, thereby achieving the purpose of improving the uniformity of the structure of the nickel-based alloy forging.

Description

Technical Field

[0001] The invention relates to a heat treatment technology, in particular to a grain refinement method of a free forging nickel-based high-temperature alloy. Background Art

[0002] GH4080A is a high-temperature alloy based on Ni-Cr. It is strengthened by adding a certain amount of Al and Ti and performing aging treatment to form a strengthening phase. At the same time, the grain boundary is greatly strengthened due to the addition of trace B elements. It has good creep resistance and oxidation resistance in the range of 600-850℃. It has the best load-bearing capacity when working for a long time above 760℃, and has resistance to high-temperature fatigue and medium corrosion. It is widely used in aerospace and steam turbine power generation equipment and other fields to manufacture various high-temperature key components such as blades, bolts, sealing rings and valve stems.

[0003] Usually, nickel-based alloy parts are in high temperature and alternating load conditions for a long time. In order to ensure its reliability, durability and safety in harsh service conditions, the final grain size of nickel-based alloys must be small and uniform. This is because nickel-based alloy forgings with coarse grains and serious mixed crystals not only have large internal residual stress and poor hot workability, but also fail to meet the standards for long-term durability, fatigue resistance, corrosion resistance and impact resistance. Hot forging deformation process is an important way to obtain nickel-based alloy forgings with uniform and fine grain structure. However, during the forging process, due to the influence of factors such as friction and billet shape, there is inevitably a serious deformation unevenness phenomenon, resulting in complete dynamic recrystallization in the large deformation area and incomplete dynamic recrystallization in the small deformation area. As a result, the final forging structure has serious coarse grains and mixed crystals, which seriously reduces the mechanical properties and performance of the forging. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide a method for grain refinement of free forging nickel-based high-temperature alloys, so as to solve the problem of coarse-grained / mixed-grained structure of nickel-based high-temperature alloy forgings in the prior art.

[0005] To achieve the above-mentioned object and other related objects, the present invention provides a method for grain refinement of a free forging nickel-based high-temperature alloy, characterized in that it comprises the following steps:

[0006] Step 1: forging and deforming the nickel-based high-temperature alloy forging blank into a forging, wherein during the forging and deformation process: the temperature needs to be between 950° C. and 1150° C., the deformation amount needs to be between 20% and 34%, and the forging ratio needs to be ≥4;

[0007] Step 2: directly hot-send the forgings to the furnace for short-time high-temperature annealing heat treatment. The annealing heat treatment process is as follows: annealing temperature 1100℃~1150℃, holding time 10~40 minutes; after annealing, furnace cooling is performed, and the furnace cooling speed is ≤50℃ / h;

[0008] Step 3: Performing standard performance heat treatment on the forging, including: solution treatment, stabilization treatment and aging treatment.

[0009] Preferably, the last forging heating temperature in step 1 is 1080-1120° C., and the deformation is controlled at 20%-25%.

[0010] Preferably, the short-time high-temperature annealing heat treatment in step 2 is as follows: the temperature is raised to 1100°C to 1150°C in the furnace, and the holding time is t=((0.2-0.4)min / mm×H+20)min,

[0011] Where H is the effective thickness of the forging, in mm; t is in min; after the insulation is completed, the furnace is cooled to ≤600℃, the furnace cooling rate is ≤50℃ / h, and then it is air-cooled to room temperature.

[0012] Preferably, the temperature of the solution treatment is between 1050°C and 1080°C, and needs to be kept warm for 8 hours, followed by air cooling.

[0013] Preferably, the stabilization treatment temperature is 850±10° C. and needs to be kept warm for 24 hours, followed by air cooling.

[0014] Preferably, the aging treatment temperature is within 700±10°C and needs to be kept warm for 16 hours, followed by air cooling.

[0015] As described above, the free forging nickel-based high-temperature alloy grain refinement method of the present invention has the following beneficial effects:

[0016] The present invention utilizes the re-refining effect of static / meta-dynamic recrystallization on the coarse crystal / mixed crystal structure formed in the forging process, so that the mixed crystal structure of the forging obtained after deformation at small deformation and medium-high strain rate becomes uniform again, thereby achieving the purpose of improving the uniformity of the structure of the nickel-based alloy forging. In addition, during the annealing process, the structure of the final small deformation area will also be completely recrystallized, and the entire structure will become a uniform recrystallized structure, thereby avoiding the existence of coarse crystal / mixed crystal structure in the nickel-based high-temperature alloy forging and refining the grains. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A time-temperature coordinate diagram showing a method for grain refinement of a free forging nickel-based high-temperature alloy according to the present invention;

[0018] Figure 2The original grain size state of the forging of the free forging nickel-based high-temperature alloy grain refinement method of the present invention is shown. (Macro coarse grain, 20% 6 grade);

[0019] Figure 3 It shows the grain structure of the forging after short-time high-temperature annealing heat treatment of a free forging nickel-based high-temperature alloy grain refinement method of the present invention; (level 4). DETAILED DESCRIPTION

[0020] The following is a description of the implementation of the present invention by means of specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0021] See also Figures 1 to 3 . It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the effects and purposes that can be achieved by the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" quoted in this specification are only for the convenience of description, and are not used to limit the scope of the implementation of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the implementation of the present invention without substantially changing the technical content.

[0022] like Figure 1 As shown, the present invention provides a method for grain refinement of a free forging nickel-based high-temperature alloy, comprising the following steps:

[0023] Step 1: forging and deforming the nickel-based high-temperature alloy forging blank into a forging, wherein during the forging and deformation process: the temperature needs to be between 950° C. and 1150° C., the deformation amount needs to be between 20% and 34%, and the forging ratio needs to be ≥4;

[0024] Step 2: directly hot-send the forgings to the furnace for short-time high-temperature annealing heat treatment. The annealing heat treatment process is as follows: annealing temperature 1100℃~1150℃, holding time 10~40 minutes; after annealing, furnace cooling is performed, and the furnace cooling speed is ≤50℃ / h;

[0025] Step 3: Performing standard performance heat treatment on the forging, including: solution treatment, stabilization treatment and aging treatment.

[0026] The present invention utilizes the re-refining effect of static / meta-dynamic recrystallization on the coarse crystal / mixed crystal structure formed in the forging process, so that the mixed crystal structure of the forging obtained after deformation at small deformation and medium-high strain rate becomes uniform again, thereby achieving the purpose of improving the uniformity of the structure of the nickel-based alloy forging. In addition, during the annealing process, the structure of the final small deformation area will also be completely recrystallized, and the entire structure will become a uniform recrystallized structure, thereby avoiding the existence of coarse crystal / mixed crystal structure in the nickel-based high-temperature alloy forging and refining the grains.

[0027] Due to the complete dynamic recrystallization in the large deformation area, the deformation energy is almost exhausted, the grain boundary driving force is relatively low, and the grains only grow slightly during the annealing process; while the small deformation area undergoes incomplete recrystallization, and the organization contains residual deformation energy and dislocation energy; static / meta-dynamic recrystallization is now carried out by nucleation through grain boundaries and annealing subgrains during the annealing process. As the annealing time increases, the organization of the small deformation area will eventually recrystallize completely, and the entire organization will become a uniformly recrystallized organization.

[0028] In order to improve the uniformity of the structure of nickel-based alloy forgings. This method only adds an annealing heat treatment process after the forging is deformed, and uses recrystallization during the annealing process to improve the uniformity of the forging structure; after the performance heat treatment is completed, the forging is subjected to metallographic testing, and the results are as follows Figure 3 As shown, the grain size is level 4, which meets the grain size assessment requirements in the technical standards. Figure 2 and Figure 3 It can be seen that in the embodiment, the deformed nickel-based alloy forging is subjected to a short-term high-temperature annealing heat treatment, so that the deformed structure is recrystallized again, and the original coarse deformed grains are gradually swallowed up and replaced by recrystallized grains, and finally the Figure 2 The necklace-shaped mixed crystals produced by the uneven deformation make the original mixed crystal structure become a recrystallized structure with high uniformity. Compared with other methods of improving the uniformity of forging structure by forging the alloy billet multiple times at high temperature, this method has the advantages of simple operation, high efficiency, low cost, easy implementation and can greatly reduce the requirements for forging process.

[0029] In order to further make the grain size finer, furnace cooling is adopted after annealing is completed in step 2; the grain size of the forgings after furnace cooling is finer than that of direct air cooling.

[0030] In this embodiment, the forging used is GH4080A, the chemical composition of the forging is shown in Table 1, and the grain structure after solution aging treatment is as follows; Figure 2 As shown, the grain size is judged to be macroscopically coarse grains, of which 20% is grade 6 and needs to be refined by forging deformation.

[0031] Table 1 Chemical composition of forgings

[0032] C Si Mn P S Ni Cr 0.051 0.057 0.008 0.002 0.001 margin 19.40 Ti Al Co Fe Cu B Ti+Al 2.49 1.67 0.021 0.78 0.005 0.0044 4.16

[0033] The last forging heating temperature in step 1 is 1080-1120° C., and the deformation is controlled at 20%-25%.

[0034] The standard performance heat treatment in step 3 is as follows: the temperature of the solution treatment is within the range of 1050°C to 1080°C, and it needs to be kept warm for 8 hours, followed by air cooling; the temperature of the stabilization treatment is within the range of 850±10°C, and it needs to be kept warm for 24 hours, followed by air cooling; the temperature of the aging treatment is within the range of 700±10°C, and it needs to be kept warm for 16 hours, followed by air cooling.

[0035] After completing the above work, the final product is obtained, and the performance of the finished product is excellent at room temperature and high temperature, as shown in Table 2 below:

[0036] Table 2 Mechanical properties at room temperature

[0037]

[0038] High temperature endurance performance and grain size grade are shown in Table 3:

[0039] Table 3 High temperature durability and grain size

[0040]

[0041] In summary, the present invention can make the mixed crystal structure of the forging obtained after deformation under small deformation and medium to high strain rates become uniform again, thereby achieving the purpose of improving the uniformity of the structure of the nickel-based alloy forging, and static / sub-dynamic recrystallization will occur through grain boundary nucleation and annealing of subgrains during the annealing process.

[0042] Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

[0043] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for grain refinement of free forging nickel-based high-temperature alloy, characterized in that: The following steps are involved: Step 1: forging and deforming the nickel-based high-temperature alloy GH4080A forging blank into a forging, wherein during the forging and deformation process: the temperature needs to be between 950° C. and 1150° C., the deformation amount needs to be between 20% and 34%, and the forging ratio needs to be ≥4; Step 2: directly hot-send the forgings to the furnace for short-time high-temperature annealing heat treatment. The annealing heat treatment process is as follows: annealing temperature 1100℃~1150℃, holding time 10~40 minutes; after annealing, furnace cooling is performed, and the furnace cooling speed is ≤50℃ / h; Step 3: Perform standard performance heat treatment on the forging, including: solution treatment, stabilization treatment and aging treatment; the temperature of the solution treatment is between 1050°C and 1080°C, and it needs to be kept warm for 8 hours, followed by air cooling; the temperature of the stabilization treatment is between 850±10°C, and it needs to be kept warm for 24 hours, followed by air cooling; the temperature of the aging treatment is between 700±10°C, and it needs to be kept warm for 16 hours, followed by air cooling.

2. The method for grain refinement of free forging nickel-based high-temperature alloy according to claim 1, characterized in that: The last forging heating temperature in step 1 is 1080-1120°C, and the deformation is controlled at 20%-25%.

3. The method for grain refinement of free forging nickel-based high-temperature alloy according to claim 1, characterized in that: The short-time high-temperature annealing heat treatment in step 2 is as follows: the temperature is raised to 1100°C-1150°C in the furnace, and the holding time is t=(0.2-0.4)min / mm×H+20min, wherein H is the effective thickness of the forging, in mm; the unit of t is min; after the holding is completed, the furnace is cooled to ≤600°C, and the furnace cooling rate is ≤50°C / h, and then the furnace is taken out and air-cooled to room temperature.

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