A method for processing a ni-cr-co based wrought superalloy

Abstract

This invention discloses a method for processing Ni-Cr-Co based difficult-to-deform high-temperature alloys, comprising the following steps: rolling: heating the billet to a set value and holding it at that temperature, rolling the processed billet into a bar; straightening the bar and turning it; rough grinding the turned bar; and fine grinding the rough-ground bar to obtain the finished bar. Compared with traditional processes, this invention reduces the tumbling process and simplifies process costs. This process uses multi-fire, multi-pass hot rolling + turning + grinding to process GH93 alloy. During the heating process, furnace temperature fluctuations are effectively controlled, and the feed rate and single-pass grinding amount are clearly controlled during turning, rough grinding, etc., effectively solving the problem of low-magnification coarse grains in the longitudinal direction after heat treatment, reducing the scrap rate of low-magnification coarse grains to below 10%.

Description

Technical Field

[0001] This invention belongs to the field of metallurgy, and specifically relates to a method for processing Ni-Cr-Co based difficult-to-deform high-temperature alloys. Background Technology

[0002] Nickel-based alloys are a class of alloys that possess high strength and certain resistance to oxidation and corrosion at high temperatures of 650–1000℃. Based on their main properties, they are further subdivided into nickel-based heat-resistant alloys, nickel-based corrosion-resistant alloys, nickel-based wear-resistant alloys, nickel-based precision alloys, and nickel-based shape memory alloys. High-temperature alloys are classified according to their matrix: iron-based high-temperature alloys, nickel-based high-temperature alloys, and cobalt-based high-temperature alloys. Nickel-based high-temperature alloys are simply referred to as nickel-based alloys.

[0003] Ni-Cr alloys, also known as nickel-based heat-resistant alloys, are primarily used in oxidizing media. They are resistant to high-temperature oxidation and corrosion from gases containing sulfur and vanadium, with their corrosion resistance increasing with increasing chromium content. These alloys also exhibit good resistance to hydroxide corrosion (such as NaOH and KOH) and stress corrosion.

[0004] GH93 alloy is a Ni-Cr-Co based precipitation-hardening wrought superalloy with a long-term service temperature below 750℃ and a short-term service temperature up to 800℃. The alloy possesses high high-temperature strength, high high-temperature creep strength, and fatigue resistance, with stable microstructure and good overall performance. It also exhibits good hot-working plasticity and weldability. It is suitable for manufacturing turbine blades for aero-engines, turbine disks for small engines, and fasteners. The main products are plates, bars, and forgings. However, GH93 alloy processed using existing techniques has a low-magnification coarse-grain rate exceeding 70%. This results in dark, speckled low-magnification microstructure at a certain thickness on the surface of forgings, known as low-magnification coarse grains. This microstructure leads to inhomogeneity in the forging microstructure, with locally coarse β-grains. The microscopic characteristics of the low-magnification coarse-grained structure are large β grains with fine equiaxed α grains uniformly distributed inside. The large β grains are not closely adjacent to each other, and the normal low-magnification structure (non-low-magnification coarse-grained) of the forging is distributed between them. It belongs to the typical bimorphic structure, which is characterized by fine equiaxed β grains, and fine equiaxed α grains are also uniformly distributed inside the fine equiaxed β grains. (2) Compared with the normal structure, the low-magnification coarse-grained structure of TB6 titanium alloy forgings has lower tensile strength. However, due to the transformation of the β phase to the orthorhombic martensite α phase during the tensile deformation of the micro-tensile specimen with low-magnification coarse-grained structure, a secondary stress increase phenomenon occurs, which increases the elongation of the material. Low-magnification coarse grains affect the uniformity of the material structure, so it is necessary to explore its generation mechanism and find ways to avoid and eliminate it. This application solves the problem of longitudinal low-magnification coarse grains of GH93 alloy rolled bars for turbine blades of existing aero-engines through a new processing technology. Summary of the Invention

[0005] To address the above problems, the present invention

[0006] A method for processing Ni-Cr-Co based hard-to-deform superalloys includes the following steps:

[0007] Rolling: The billet is heated to a set value and held at that temperature, and then rolled into a bar.

[0008] The bar is straightened and then machined.

[0009] Rough grinding is performed on the machined bar stock;

[0010] The coarsely ground bars are then finely ground to obtain the finished bars.

[0011] A further preferred technical solution is that the heat preservation time is 1-8 hours.

[0012] A further preferred technical solution is as follows: the rolling process includes three rolling processes, wherein the deformation is controlled at 70-83% in the first rolling process, 55-78% in the second rolling process, and 60-80% in the third rolling process.

[0013] A further preferred technical solution is: in the three-stage rolling process, the rolling temperature gradually decreases.

[0014] A further preferred technical solution is that, during the rolling process, the billet heating rate is ≤1.5℃ / min.

[0015] A further preferred technical solution is that the feed rate of the lathe tool used for machining is 0.2-1mm.

[0016] The further preferred technical solution is as follows: the rough grinding process parameters are: 2-4 rough grinding passes, rough grinding to the design size + 0.3mm.

[0017] A further preferred technical solution is as follows: the rough grinding process parameters also include: the rough grinding amount per side is 0.1-0.4 mm.

[0018] The further preferred technical solution is as follows: the fine grinding process parameters are: the amount of polishing on one side per pass is 0.05-0.1mm, and the fine grinding is carried out to the design size.

[0019] A further preferred technical solution is as follows: the chemical composition of the Ni-Cr-Co based hard-deformable high-temperature alloy is as follows by mass percentage: Cr 18.0~21.0%; Al 1.0~2.0%; Ti 2.0~3.0%; Co 15.0~21.0%; C≤0.13%; Cu≤0.2%; Fe≤1.0%; B≤0.02%; Si≤0.80%; Mn≤0.80%; P≤0.013%; S≤0.013%; balance: Ni.

[0020] The beneficial effects of this invention are as follows: Compared with traditional processes, this invention reduces the burnishing process and simplifies process costs. This process uses multi-fire, multi-pass hot rolling + machining + polishing to process GH93 alloy. During the heating process, furnace temperature fluctuations are effectively controlled, and the feed rate and single-pass grinding amount during machining and rough grinding are clearly controlled. This effectively solves the problem of low-magnification coarse grains in the longitudinal direction after heat treatment, reducing the scrap rate of low-magnification coarse grains to below 10%.

[0021] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 The process flow steps of the present invention are shown. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0025] Existing technologies produce low-magnification coarse-grained finished bars with a scrap rate exceeding 70%. The cold working process lacks specific feed rates and single-pass grinding amounts, potentially leading to increased feed rates and grinding amounts to meet production demands. This invention, however, specifies precise feed rates and single-pass grinding amounts, adapting to GH93 alloy raw materials and thus reducing the low-magnification coarse-grained rate. Fluctuations in furnace temperature during the process also contribute to surface coarse grains. This invention addresses this by repeatedly calibrating and altering the furnace temperature, thereby reducing the coarse-grained scrap rate to below 0%.

[0026] Example 1: CH93 was selected as the raw material, and its chemical composition requirements are as follows: Cr 18.0~21.0%; Al 1.0~2.0%; Ti 2.0~3.0%; Co 15.0~21.0%; C≤0.13%; Cu≤0.2%; Fe≤1.0%; B≤0.02%; Si≤0.80%; Mn≤0.80%; P≤0.013%; S≤0.013%; balance: Ni.

[0027] The processing steps are as follows: Select a 120 cubic meter billet, put the billet into a heating furnace, heat it to 1150℃ for the first time, and keep the heating rate ≤1.5℃ / min, hold it for 3 hours, and obtain the heated GH93 billet. The deformation amount of the first heating is 70-83%.

[0028] Existing technologies produce low-magnification coarse-grained finished bars with a scrap rate exceeding 70%. The cold working process lacks specific feed rates and single-pass grinding amounts, potentially leading to increased feed rates and grinding amounts to meet production demands. The method provided by this invention, however, specifies precise feed rates and single-pass grinding amounts, adapting to GH93 alloy raw materials and thus reducing the low-magnification coarse-grained rate. Fluctuations in furnace temperature during the process also contribute to surface coarse grains. The method provided by this invention involves multiple calibrations and adjustments to the furnace temperature, thereby reducing the coarse-grained scrap rate to below 0%.

[0029] The heated GH93 billet is rolled to Φ75mm; after cleaning the surface defects of the billet, it is sent into the heating furnace for secondary heating, and the deformation amount of the second heating is 55-78%.

[0030] The second heating rate is maintained at ≤1.5℃ / min, heated to 1130℃, held for 2 hours, and rolled into a billet to Φ35mm. After cleaning the surface defects of the billet, it is sent into the heating furnace for final heating. The deformation amount of the third heating is 60-80%.

[0031] The final heating is carried out at a rate of ≤1.5℃ / min, heated to 1060℃, held for 3 hours, rolled to Φ22mm, and then annealed at 1070℃ for 8 hours to obtain the finished blank.

[0032] After straightening the finished blank, the blank is then machined five times to make its surface smooth. Five machining passes are performed to obtain a Φ21mm bar with a feed rate of 0.2mm per pass.

[0033] A Φ21mm bar was subjected to four passes of rough grinding, with each pass maintaining a rough grinding thickness of 0.1–0.2mm; resulting in a Φ20.3mm bar.

[0034] The Φ20.3mm bar was finely ground in 6 passes until the finished size Φ20mm was obtained. Each fine grinding pass was 0.05mm, and the finished bar was obtained.

[0035] The finished bar stock passed the low-magnification inspection after heat treatment and its performance was satisfactory.

[0036] Example 2: CH93 was selected as the raw material, and its chemical composition requirements are as follows: Cr 18.0~21.0%; Al 1.0~2.0%; Ti 2.0~3.0%; Co 15.0~21.0%; C≤0.13%; Cu≤0.2%; Fe≤1.0%; B≤0.02%; Si≤0.80%; Mn≤0.80%; P≤0.013%; S≤0.013%; balance: Ni.

[0037] The processing steps are as follows: Select a 120 cubic meter billet, put the billet into a heating furnace, heat it to 1150℃ for the first time, and keep the heating rate ≤1.5℃ / min, hold it for 3 hours, and obtain the heated GH93 billet. The deformation amount of the first heating is 70-83%.

[0038] The heated GH93 billet is rolled to Φ75mm; after cleaning the surface defects of the billet, it is sent into the heating furnace for secondary heating; the deformation amount of the second heating is 55-78%.

[0039] The second heating process involves maintaining a heating rate of ≤1.5℃ / min, heating to 1130℃, holding for 2 hours, and rolling the billet to Φ35mm. After cleaning the surface defects of the billet, it is sent into the heating furnace for final heating. The deformation amount in the third heating process is 60-80%.

[0040] The final heating is carried out at a rate of ≤1.5℃ / min, heated to 1060℃, held for 3 hours, rolled to Φ22mm, and then annealed at 1070℃ for 8 hours to obtain the finished blank.

[0041] After straightening the finished blank, the blank is then machined five times to make its surface smooth. Two machining passes are then performed to obtain a Φ21mm bar with a feed rate of 0.5mm per pass.

[0042] The Φ21mm bar was subjected to two passes of rough grinding, with each pass maintaining a rough grinding thickness of 0.3–0.4mm; a Φ20.3mm bar was obtained.

[0043] As long as the rough grinding process ensures that each pass is within the range of 0.3–0.4 mm, excessive stress accumulation on the surface will not occur. Fine grinding serves two purposes: firstly, it thins the stress layer on the rough-ground surface; secondly, it further reduces the amount of material removed per pass, thus preventing the generation of surface stress. Surface stress promotes grain growth, leading to coarse surface grains, or coarse edge grains.

[0044] The Φ20.3mm bar was finely ground in 3 passes to a finished size of Φ20mm. Each pass of fine grinding was 0.1mm, and the finished bar was obtained.

[0045] Example 3: CH93 was selected as the raw material, and its chemical composition requirements are as follows: Cr 18.0~21.0%; Al 1.0~2.0%; Ti 2.0~3.0%; Co 15.0~21.0%; C≤0.13%; Cu≤0.2%; Fe≤1.0%; B≤0.02%; Si≤0.80%; Mn≤0.80%; P≤0.013%; S≤0.013%; balance: Ni.

[0046] The processing steps are as follows: Select a 130 cubic meter billet, put the billet into a heating furnace, heat it to 1150℃ for the first time, and keep the heating rate ≤1.5℃ / min, hold it for 3 hours, and obtain the heated GH93 billet. The deformation amount of the first heating is 70-83%.

[0047] The heated GH93 billet is rolled to Φ75mm; after cleaning the surface defects of the billet, it is sent into the heating furnace for secondary heating; the deformation amount of the second heating is 55-78%.

[0048] A single pass to 75 / 60mm results in a deformation of approximately 65-80%. Within this range, the billet provides a relatively uniform grain size for the finished product rolling. Insufficient deformation leads to localized undeformed coarse grains at the edges. Excessive deformation requires more passes, resulting in significant temperature drops and rolling cracking.

[0049] The second heating process involves maintaining a heating rate of ≤1.5℃ / min, heating to 1130℃, holding for 2 hours, and rolling the billet to Φ50mm. After cleaning surface defects, the billet is sent to the heating furnace for final heating. The deformation amount in the third heating process is 60-80%.

[0050] The final heating is maintained at a heating rate of ≤1.5℃ / min, heated to 1060℃, held for 3h, rolled to Φ22mm, and the hot-rolled finished blank is annealed at (1070) for (8h) to obtain the finished blank.

[0051] After straightening the finished blank, the blank is then machined five times to make its surface smooth. Two machining passes are then performed to obtain a Φ21mm bar with a feed rate of 0.5mm per pass.

[0052] The Φ21mm bar was subjected to two passes of rough grinding, with each pass maintaining a rough grinding thickness of 0.3–0.4mm; a Φ20.3mm bar was obtained.

[0053] The Φ20.3mm bar was finely ground in 3 passes to a finished size of Φ20mm. Each pass of fine grinding was 0.1mm, and the finished bar was obtained.

[0054] The finished bar stock passed the low-magnification inspection after heat treatment and its performance was satisfactory.

[0055] Example 4: CH93 was selected as the raw material, and its chemical composition requirements are as follows: Cr 18.0~21.0%; Al 1.0~2.0%; Ti 2.0~3.0%; Co 15.0~21.0%; C≤0.13%; Cu≤0.2%; Fe≤1.0%; B≤0.02%; Si≤0.80%; Mn≤0.80%; P≤0.013%; S≤0.013%; balance: Ni.

[0056] The processing steps are as follows: Select a 130 cubic meter billet, put the billet into a heating furnace, heat it to 1150℃ for the first time, and keep the heating rate ≤1.5℃ / min, hold it for 3 hours, and obtain the heated GH93 billet. The deformation amount of the first heating is 70-83%.

[0057] The heated GH93 billet is rolled into a blank to Φ60mm; after cleaning the surface defects of the billet, it is sent into the heating furnace for secondary heating; the deformation amount of the second heating is 55-78%.

[0058] The second heating process involves maintaining a heating rate of ≤1.5℃ / min, heating to 1130℃, holding for 2 hours, and rolling the billet to Φ35mm. After cleaning the surface defects of the billet, it is sent into the heating furnace for final heating. The deformation amount in the third heating process is 60-80%.

[0059] The final heating is carried out at a rate of ≤1.5℃ / min, heated to 1060℃, held for 3 hours, rolled to Φ22mm, and then annealed at 1070℃ for 8 hours to obtain the finished blank.

[0060] After straightening the finished blank, the blank is then machined five times to make its surface smooth. Two machining passes are then performed to obtain a Φ21mm bar with a feed rate of 0.5mm per pass.

[0061] The Φ21mm bar was subjected to two passes of rough grinding, with each pass maintaining a rough grinding thickness of 0.3–0.4mm; a Φ20.3mm bar was obtained.

[0062] The Φ20.3mm bar was finely ground in 3 passes to a finished size of Φ20mm. Each pass of fine grinding was 0.1mm, and the finished bar was obtained.

[0063] The finished bar stock passed the low-magnification inspection after heat treatment and its performance was satisfactory.

[0064] The GH93 alloy processed using existing techniques has a low-magnification coarse-grained content exceeding 70%. This results in dark, speckled low-magnification structures at certain thicknesses on the forging surface, known as low-magnification coarse grains. This structure leads to inhomogeneity in the forging's microstructure, with locally coarse β grains. The microscopic characteristics of this low-magnification coarse-grained structure are characterized by large β grains, within which fine equiaxed α grains are uniformly distributed. These large β grains are not closely adjacent, and the normal low-magnification structure (non-low-magnification coarse grains) of the forging is distributed between them. This is a typical bimodal structure, characterized by fine equiaxed β grains, within which fine equiaxed α grains are also uniformly distributed. Compared to normal microstructure, TB6 titanium alloy forgings with low-magnification coarse-grained microstructure have lower tensile strength. However, due to the transformation of the β phase to the orthorhombic martensite α” phase during tensile deformation, a secondary stress increase occurs, improving the elongation of the material. Low-magnification coarse grains affect the uniformity of the material's microstructure. This invention, compared to traditional processes, reduces the burnishing process, streamlining process costs. This process uses multi-pass hot rolling + machining + grinding to process GH93 alloy. During heating, furnace temperature fluctuations are effectively controlled, and the feed rate and single-pass grinding amount during machining and rough grinding are precisely controlled, effectively solving the problem of longitudinal low-magnification coarse grains in the finished product after heat treatment, reducing the scrap rate of low-magnification coarse-grained products to below 10%.

[0065] The method provided by this invention clarifies the specific feed rate and single-pass grinding amount, adapting to GH93 alloy raw materials, thereby achieving the goal of reducing low-magnification coarse grains. Fluctuations in furnace temperature during process heating can also lead to surface coarse grains. The method provided by this invention involves multiple calibrations and adjustments to the firing temperature, thereby reducing the coarse grain scrap rate to below 0%. In actual production, it has been found that when the billet is opened to 75 / 60 ​​in one firing, the deformation is approximately 65-80%. Within this range, it can provide the finished product with a relatively uniform original billet structure. If the deformation is too low, there will be localized undeformed original coarse grains at the edges. If the deformation is too high, more passes are required, resulting in severe temperature drops and rolling cracks. Therefore, the method provided by this invention involves multiple calibrations and adjustments to the firing temperature, thereby reducing the coarse grain scrap rate to below 0%, achieving better implementation results.

[0066] To reduce the scrap rate of low-magnification coarse-grained products, the inventors discovered that coarse grinding requires each pass to be within the range of 0.3–0.4 mm to prevent excessive stress accumulation on the surface. Fine grinding serves two purposes: first, it thins the stress layer on the coarse-ground surface; second, it further reduces the amount of material removed per pass, thus avoiding the generation of surface stress. Surface stress promotes grain growth, leading to coarse-grained surfaces, i.e., coarse-grained edges.

[0067] It should be noted that the terms "first," "second," etc., used in this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this application described herein. In this application, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," "longitudinal," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings.

[0068] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for processing Ni-Cr-Co based difficult-to-deform superalloys, characterized in that, Includes the following steps: Rolling: The billet is heated to a set value and held at that temperature, and then rolled into a bar. The bar is straightened and then machined. Rough grinding is performed on the machined bar stock; The coarsely ground bars are then finely ground to obtain the finished bars. The feed rate of the lathe tool used for machining is 0.2-1mm; The rough grinding process parameters are as follows: 2-4 rough grinding passes, rough grinding to the design size + 0.3mm; The rough grinding process parameters also include: the amount of polishing per side per pass is 0.1-0.4 mm; The fine grinding process parameters are as follows: the polishing amount per side is 0.05-0.1 mm, and the fine grinding is carried out to the design size; the chemical composition mass percentage of the Ni-Cr-Co based difficult-to-deform superalloy is as follows: Cr 18.0~21.0%; Al 1.0~2.0%; Ti 2.0~3.0%; Co 15.0~21.0%; C≤0.13%; Cu≤0.2%; Fe≤1.0%; B≤0.02%; Si≤0.80%; Mn≤0.80%; P≤0.013%; S≤0.013%; the remainder: Ni.

2. The method for processing Ni-Cr-Co based difficult-to-deform superalloys according to claim 1, characterized in that, The heat preservation time is 1-8 hours.

3. The method for processing Ni-Cr-Co based difficult-to-deform superalloys according to claim 2, characterized in that, The rolling process includes three rolling passes, with the deformation controlled at 70-83% in the first rolling pass, 55-78% in the second rolling pass, and 60-80% in the third rolling pass.

4. The method for processing Ni-Cr-Co based difficult-to-deform superalloys according to claim 3, characterized in that, In the three-stage rolling process, the rolling temperature gradually decreases.

5. The method for processing Ni-Cr-Co based difficult-to-deform superalloys according to claim 4, characterized in that, During the rolling process, the billet heating rate is ≤1.5℃ / min.

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