Method for improving as-cast grain boundary of Haynes 214 high-temperature alloy

Abstract

The invention relates to the technical field of high-temperature alloy processing, in particular to a method for improving a Haynes 214 high-temperature alloy as-cast grain boundary, which comprises the following steps: reasonably designing a processing technology of a Haynes 214 high-temperature alloy, introducing a multi-directional forging technology of upsetting and then drawing in the processing process, and combining the synergistic effect of subsequent hot rolling deformation, solution treatment and cold rolling technologies to improve the casting grain boundary of the Haynes 214 high-temperature alloy. The primary as-cast grain boundary in the alloy is physically broken and recrystallized and reconstructed, a loose, thick and non-uniform alloy ingot is converted into a compact, fine and uniform-structure high-quality forging stock, and the conditions of element segregation and brittle phase aggregation at the grain boundary are greatly improved. By the adoption of the method, a recrystallization equiaxed crystal structure which is uniform in structure and fine in grain can be obtained, the risk that cracks are generated due to stress concentration in the thermal deformation process is reduced, and the Haynes 214 high-temperature alloy material which is smooth in surface and uniform in internal structure is obtained.

Description

Technical Field

[0001] This invention relates to the field of high-temperature alloy processing technology, specifically to a method for improving the grain boundaries of Haynes 214 high-temperature alloy in the as-cast state. Background Technology

[0002] Haynes 214 alloy is a Ni-Cr-Al based wrought superalloy. Due to its ability to form a dense and stable Al2O3 protective film under high-temperature conditions, it exhibits excellent resistance to high-temperature oxidation. Furthermore, this alloy demonstrates good corrosion resistance in carburizing, nitriding, and chlorine-containing atmospheres, making it widely used in the manufacture of high-temperature components such as honeycomb sealing structures, flame hoods, and burners.

[0003] However, in actual processing and application, Haynes 214 alloy still faces the following major problems: (1) Due to the high Al content in the alloy, its hot working temperature range is relatively narrow. During hot working and heat treatment, strengthening phase precipitation is likely to occur, which leads to a significant reduction in the plasticity of the material during subsequent cold working and an increase in deformation resistance, thus increasing the difficulty of processing and preparation. (2) During the solidification process of Haynes 214 alloy ingot, due to the slow cooling rate, coarse as-cast grains and obvious primary as-cast grain boundaries are easily formed. The size of such as-cast grains can usually reach 1 to 3 mm, and the corresponding dendrite arm spacing is large. Alloy elements are obviously segregated in the grain boundary and interdendritic region, and brittle phases (such as carbides, γ′ films, etc.) are enriched at the grain boundary and distributed continuously. The above-mentioned primary as-cast grain boundaries and their accompanying segregated structures are prone to stress concentration during subsequent hot deformation, becoming the preferred location for crack initiation and propagation, thus significantly reducing the hot working performance and high-temperature service reliability of the material.

[0004] Therefore, how to effectively improve the as-cast microstructure of Haynes 214 alloy and weaken the adverse effects of primary as-cast grain boundaries during the processing and preparation of this alloy is a problem that needs to be solved to further expand the engineering applications of this alloy. Summary of the Invention

[0005] The technical problem to be solved by this invention is that Haynes 214 high-temperature alloy is prone to forming primary cast grain boundaries during processing and preparation, resulting in uneven microstructure, element segregation at grain boundaries and continuous aggregation of brittle phases. During hot deformation, stress concentration leads to cracking.

[0006] This invention rationally designs the processing technology for Haynes 214 superalloy, introducing a multi-directional forging process of upsetting followed by drawing, combined with the synergistic effects of subsequent hot rolling deformation, solution treatment, and cold rolling. This promotes the physical fragmentation and recrystallization reconstruction of the primary cast grain boundaries within the alloy, transforming the loose, coarse, and inhomogeneous alloy ingot into a dense, fine, and uniform high-quality forging blank, significantly improving elemental segregation and brittle phase aggregation at grain boundaries. Using the method described in this invention, a recrystallized equiaxed crystal structure with uniform microstructure and fine grains can be obtained, reducing the risk of stress concentration and cracking during hot deformation, and resulting in Haynes 214 superalloy material with a smooth surface and uniform internal microstructure.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for improving the as-cast grain boundaries of Haynes 214 high-temperature alloy includes the following steps:

[0009] S1: The Haynes 214 master alloy ingot is subjected to multi-directional free forging, which first upsetting and then drawing, to disrupt the continuity of the primary cast grain boundaries and obtain a free forged slab with recrystallized grain boundaries.

[0010] S2: Hot rolling deformation of free forged slabs to form a uniform recrystallized equiaxed grain structure, resulting in strip billets;

[0011] S3: The strip is solution treated, water cooled, and then subjected to cold rolling-annealing cycle processing to finally obtain Haynes214 high-temperature alloy material.

[0012] Preferably, the process of upsetting and then elongating in step S1 is as follows: first, the Haynes 214 master alloy ingot is placed vertically and radially upset to 60%-70% of its original height, while maintaining a temperature of not less than 980℃; then, the upset blank is laid flat and the axial thickness is reduced so that the blank length is increased to 1 to 2 times the original length.

[0013] Preferably, the thickness of the free forging slab obtained in step S1 is 35~45mm, and the total deformation of the free forging process is 60%~80%.

[0014] Preferably, in step S2, the hot rolling temperature is 1100℃~1200℃, the deformation is 92%~98%, and the thickness of the resulting strip is 3~4mm.

[0015] Preferably, the solution treatment temperature in step S3 is 1100℃~1200℃, and the time is 50~70min.

[0016] Preferably, in step S3, the number of cold rolling-annealing cycles is 5 to 7, the intermediate annealing temperature is 1050℃ to 1150℃, the deformation is 30% to 60%, and the deformation of the last cold rolling cycle is 20% to 25%.

[0017] Any Haynes 214 high-temperature alloy material prepared by the above method has a uniform equiaxed crystal structure and no continuous cast grain boundary structure.

[0018] Applications of Haynes 214 high-temperature alloy materials prepared by any of the above methods in the field of metal material processing and manufacturing.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] (1) By introducing a multi-directional free forging process of upsetting followed by drawing, the continuous primary cast grain boundaries inside the alloy are broken and recrystallized and reconstructed, thereby disrupting the continuity of the cast grain boundaries and reducing the risk of crack initiation.

[0021] (2) Hot rolling triggers dynamic recrystallization by applying larger and continuous plastic deformation, thereby obtaining finer and more uniform equiaxed grains than after multi-directional free forging, and further dissolving or uniformly precipitating the incompletely dissolved precipitates.

[0022] (3) Through the synergistic effect of multi-directional free forging, high deformation hot rolling, solution treatment and multiple cold rolling-annealing cycles, the continuity of the cast grain boundary is destroyed, the element segregation at the grain boundary and the brittle phase aggregation are improved, and the stress is not easy to concentrate during hot deformation, thereby reducing the risk of cracking and obtaining Haynes 214 high temperature alloy material with uniform and dense internal structure and smooth surface. Attached Figure Description

[0023] Figure 1 The thick slab obtained after multi-directional free forging in Example 1;

[0024] Figure 2 This is a diagram of the internal grain structure of the Haynes 214 high-temperature alloy strip obtained in Example 1;

[0025] Figure 3 The internal grain structure of the Haynes 214 high-temperature alloy strip obtained in Comparative Example 1 is shown.

[0026] Figure 4 The image shows the internal grain structure of the Haynes 214 high-temperature alloy strip obtained in Comparative Example 2. Detailed Implementation

[0027] The technical solutions of 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] The Haynes 214 master alloy ingots used in the following examples and comparative examples are all cylindrical ingots of the same size, prepared under the same vacuum induction melting parameters.

[0029] Example 1

[0030] (1) Multi-directional free forging: The Haynes 214 master alloy ingot is free forged at 1150℃. The process involves upsetting followed by drawing. First, the master alloy ingot is placed vertically and radially upset to 65% of its original height. Note that the temperature should not be lower than 980℃ during this process. Then, the upset blank is laid flat, and the axial thickness is reduced to increase the blank length to 1.5 times its original length. After free forging, a 40mm thick slab is obtained (e.g. Figure 1 As shown), the deformation of the entire free forging process is 70%.

[0031] (2) Hot rolling: The thick slab obtained by free forging is heated to 1150℃ and hot rolled into a strip with a thickness of 3.4mm and a deformation of 95%;

[0032] (3) Cold rolling: The hot-rolled strip is solution treated at 1160℃ for 60 minutes, water-cooled, and then cold-rolled and annealed repeatedly 6 times. The intermediate annealing temperature during cold rolling is 1100℃, and the deformation is 40%, of which the deformation in the last rolling pass is 23%, to obtain Haynes 214 high-temperature alloy strip (the internal grain structure of the material is as follows). Figure 2 (As shown).

[0033] Comparative Example 1

[0034] The difference from Example 1 is that multi-directional free forging is not performed; instead, ordinary rotary forging is used.

[0035] (1) Rotary forging: The Haynes 214 master alloy ingot was placed in a heat treatment furnace and held at 1150℃ for 10 minutes. A total of 5 rotary forging processes were carried out. The material was placed in the furnace and held for 5 minutes in the middle of each forging. The deformation after five forgings was 58%, and a slab was obtained.

[0036] (2) Hot rolling: The slab obtained by rotary forging is heated to 1150℃ and hot rolled into a strip with a thickness of 3.4mm and a deformation of 95%;

[0037] (3) Cold rolling: The hot-rolled strip is solution treated at 1160℃ for 60 minutes, water-cooled, and then cold-rolled and annealed repeatedly 6 times. The intermediate annealing temperature during cold rolling is 1100℃, and the deformation is 40%, of which the deformation in the last rolling pass is 23%, to obtain Haynes 214 high-temperature alloy strip (the internal grain structure of the material is as follows). Figure 3 (As shown).

[0038] Comparative Example 2

[0039] The difference from Example 1 is that hot rolling is not performed; only multi-directional free forging and cold rolling processes are used.

[0040] (1) Multi-directional free forging: The Haynes 214 master alloy ingot is free forged at 1150℃. The process involves upsetting followed by drawing. First, the master alloy ingot is placed vertically and radially upset to 65% of its original height. Note that the temperature should not be lower than 980℃ during this process. Then, the upset blank is laid flat, and the axial thickness is reduced to increase the blank length to 1.5 times its original length. After free forging, a 40mm thick slab is obtained (e.g. Figure 1 As shown), the deformation of the entire free forging process is 70%.

[0041] (2) Cold rolling: The thick slab obtained by free forging is subjected to cold rolling and annealing repeatedly for 6 times. The intermediate annealing temperature during cold rolling is 1100℃, and the deformation is 40%, of which the deformation in the last rolling pass is 23%, to obtain Haynes 214 high-temperature alloy strip (the internal grain structure of the material is as follows). Figure 4 (As shown).

[0042] Combination Figures 2-4 It can be seen that after using the multi-directional free forging, hot rolling, and cold rolling-annealing synergistic process of upsetting followed by drawing in Example 1, the resulting material exhibits a fine and uniform recrystallized equiaxed grain structure. The original cast columnar and dendritic morphologies have basically disappeared, and no continuously distributed primary cast grain boundaries were observed. The grain boundaries are clean, and segregation and brittle phases are significantly reduced, resulting in a uniform and dense overall structure. In contrast, Comparative Example 1 uses a unidirectional rotary forging process. Although it undergoes subsequent rolling, the single deformation method and insufficient core deformation result in the retention of cast structure, and coarse deformed grains can still be observed, leading to poor structural uniformity. Comparative Example 2 uses a multi-directional free forging process, but it does not introduce a hot rolling process, lacking the dynamic recrystallization process triggered by high-temperature plastic deformation. The resulting grains are significantly coarser, and the degree of recrystallization is insufficient.

[0043] As can be seen, the present invention performs preliminary crushing of the as-cast microstructure through multi-directional free forging, further refines the grains through hot rolling, and achieves microstructure homogenization through solution treatment and multiple cold rolling-annealing cycles. The various processes work together to effectively achieve the crushing and reconstruction of the as-cast grain boundaries in one step, significantly reducing stress concentration and cracking risk, and demonstrating a microstructure optimization effect that is significantly better than that of the comparative example.

[0044] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for improving the as-cast grain boundaries of Haynes 214 high-temperature alloy, characterized in that, Includes the following steps: S1: The Haynes 214 master alloy ingot is subjected to multi-directional free forging, which first upsetting and then drawing, to disrupt the continuity of the primary cast grain boundaries and obtain a free forged slab with recrystallized grain boundaries. S2: Hot rolling deformation of free forged slabs to form a uniform recrystallized equiaxed grain structure, resulting in strip billets; S3: The strip is solution treated, water cooled, and then subjected to cold rolling-annealing cycle processing to finally obtain Haynes 214 high-temperature alloy material.

2. The method for improving the as-cast grain boundaries of Haynes 214 high-temperature alloy according to claim 1, characterized in that, The process of upsetting and then elongating in step S1 is as follows: First, the Haynes 214 master alloy ingot is placed vertically and radially upset to 60%-70% of its original height, while maintaining a temperature of not less than 980℃; then, the upset blank is laid flat and the axial thickness is reduced so that the blank length is increased to 1 to 2 times the original length.

3. The method for improving the as-cast grain boundaries of Haynes 214 high-temperature alloy according to claim 1, characterized in that, The thickness of the free forging slab obtained in step S1 is 35~45mm, and the total deformation of the free forging process is 60%~80%.

4. The method for improving the as-cast grain boundaries of Haynes 214 high-temperature alloy according to claim 1, characterized in that, In step S2, the hot rolling temperature is 1100℃~1200℃, the deformation is 92%~98%, and the thickness of the resulting strip is 3~4mm.

5. The method for improving the as-cast grain boundaries of Haynes 214 high-temperature alloy according to claim 1, characterized in that, The solution treatment in step S3 is performed at a temperature of 1100℃~1200℃ for 50~70 minutes.

6. The method for improving the as-cast grain boundaries of Haynes 214 high-temperature alloy according to claim 1, characterized in that, In step S3, the number of cold rolling-annealing cycles is 5 to 7, the intermediate annealing temperature is 1050℃ to 1150℃, the deformation is 30% to 60%, and the deformation of the last cold rolling cycle is 20% to 25%.

7. The Haynes 214 high-temperature alloy material prepared by the method according to any one of claims 1 to 6, characterized in that, The Haynes 214 high-temperature alloy material has a uniform equiaxed crystal structure and no continuous cast grain boundary structure.

8. The application of Haynes 214 high-temperature alloy material prepared by any one of claims 1 to 6 in the field of metal material processing and manufacturing.

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