A hot working method for producing high uniformity ultrafine-grained nickel-based high-temperature alloy

Abstract

The present invention relates to the field of hot working of nickel-based high-temperature alloys, specifically a hot working method for producing high-uniformity ultrafine-grained nickel-based high-temperature alloys, which can be used in the field of high-temperature alloy forging. The method includes the following process steps: first, the nickel-based high-temperature alloy forging is placed in a heating furnace and heated to 700-750°C, and kept warm for a period of time; then the high-temperature alloy is heated to 850-950°C, and kept warm for a period of time; the high-temperature alloy is further heated to 950-1020°C, and kept warm for a period of time; finally, the high-temperature alloy is taken out and subjected to upsetting, extrusion or die forging, and the total deformation is controlled to be above 40%. The nickel-based high-temperature alloy microstructure refinement process of the present invention is simple, and a three-step heating process is adopted during the heating process. By adjusting the precipitation order of the precipitated phase in the alloy, a uniformly distributed precipitated phase is obtained, which solves the problem that the current traditional forging process cannot eliminate the coarse grains and mixed grains in the nickel-based high-temperature alloy.

Description

Technical Field

[0001] The invention relates to the field of hot working of nickel-based high-temperature alloys, in particular to a hot working method for producing highly uniform ultrafine-grained nickel-based high-temperature alloys, which can be used in the field of high-temperature alloy forging. Background Art

[0002] In the conventional hot deformation process of GH4169 steel ingot to bar, a hot working method called Delta Process (DP) can successfully eliminate the occasional large grains and effectively refine the grains. In this process, the intentional precipitation phase δ phase and subsequent hot mechanical processing are used to produce uniform fine-grained bars. At present, GH4169 alloy turbine disk forgings with a grain size grade of more than 8 can be obtained through the DP process, but due to the precipitation of more δ phases in the DP process, a large amount of lamellar δ phases will still exist in the alloy after heat treatment, and the excessive δ phase will reduce the strength of the alloy as a channel for crack initiation and development. In addition, the DP process requires aging at around 900℃ for 24h or longer, and the long-term aging treatment causes the δ phase to easily aggregate and precipitate at the grain boundaries, which not only easily causes uneven distribution of precipitation phases in the organization, but also causes Nb element enrichment at the grain boundaries, resulting in uneven alloy composition. It is difficult to obtain uniform and fine grains in the subsequent hot deformation process. Summary of the invention

[0003] The object of the present invention is to provide a hot working method for producing a highly uniform ultrafine-grained nickel-based high-temperature alloy, by which a uniformly distributed δ phase is obtained through a method of transforming a high-temperature γ″ phase into a δ phase, so as to solve the problem of uneven grain size distribution after hot working caused by the disadvantage that the δ phase is easily segregated at the grain boundary when directly precipitating.

[0004] The technical solution of the present invention:

[0005] A hot working method for producing a highly uniform ultrafine-grained nickel-based high-temperature alloy comprises the following process steps:

[0006] 1) Place the nickel-based high-temperature alloy forging in a heating furnace and heat it to 700-750°C, keep it warm for 5-10 hours, and evenly precipitate the γ″ phase;

[0007] 2) heating the nickel-based high-temperature alloy treated in step 1) to 850-950° C. and keeping the temperature for 5-10 hours to transform the γ″ phase into the δ phase;

[0008] 3) heating the nickel-based high-temperature alloy treated in step 2) to 950-1020° C. and keeping the temperature for 5 min-2 h;

[0009] 4) The nickel-based high-temperature alloy treated in step 3) is subjected to upsetting, extrusion or die forging, and the total deformation is controlled to be above 40%.

[0010] The hot working method for producing high-uniformity ultrafine-grained nickel-based high-temperature alloy comprises the following steps: step 1) selecting a holding temperature of 720° C. for a holding time of 8 hours to ensure that the volume fraction of the γ″ phase in the structure reaches 50% to 80%.

[0011] In the thermal processing method for producing highly uniform ultrafine-grained nickel-based high-temperature alloy, step 2) the holding temperature is selected to be 900° C. and the holding time is 8 hours to ensure that the volume fraction of the δ phase reaches 60% to 90%.

[0012] In the thermal processing method for producing highly uniform ultrafine-grained nickel-based high-temperature alloy, in step 3), the holding temperature is selected to be 960° C. and the holding time is 1 hour to ensure that the volume fraction of the δ phase remains at 40% to 60%.

[0013] The thermal processing method for producing highly uniform ultrafine-grained nickel-based high-temperature alloy comprises placing the nickel-based high-temperature alloy in a heat treatment furnace in step 1), step 2) and step 3), and starting the timing after the temperature reaches the set temperature and is kept for 10 minutes, and the heating rate is not higher than 200°C / h.

[0014] In the thermal processing method for producing highly uniform ultrafine-grained nickel-based high-temperature alloy, step 1), step 2) and step 3) are implemented continuously, and the heating rate is not higher than 200° C. / h.

[0015] In the hot working method for producing high-uniformity ultrafine-grained nickel-based high-temperature alloy, preferably, step 4) is one-time forming, and the total deformation is controlled at 40%.

[0016] The thermal processing method for producing highly uniform ultrafine-grained nickel-based high-temperature alloy obtains a nickel-based high-temperature alloy with uniform ultrafine grain structure, and the grain size is 8 to 10 levels.

[0017] The design idea of ​​the present invention is:

[0018] The present invention provides a hot working method for producing a highly uniform ultrafine-grained nickel-based high-temperature alloy. The method creatively introduces the step of keeping the alloy at 720°C for 8 hours, and changes the precipitation mode of the δ phase from direct precipitation from austenite to transformation from the γ″ phase to the δ phase. Thus, under the premise of ensuring the mass fraction of the δ phase, a uniformly distributed δ phase is obtained, and the effect of the δ phase in promoting recrystallization nucleation during the hot deformation process is utilized, thereby ensuring effective grain refinement.

[0019] The advantages and beneficial effects of the present invention are:

[0020] The microstructure refinement process of the nickel-based high-temperature alloy of the present invention is simple. A three-step heating process is adopted during the heating process. By adjusting the precipitation order of the precipitated phases in the alloy, a uniformly distributed precipitated phase is obtained. During the hot working and forging process, the uniformly distributed precipitated phase can provide a recrystallization nucleation position to increase the nucleation rate; secondly, it can pin the grain boundary, hinder the movement of the grain boundary, and reduce the grain growth rate, thereby obtaining a high-temperature alloy with a uniform ultrafine grain structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the metallographic picture obtained in Example 1.

[0022] Figure 2 This is the metallographic picture obtained in Comparative Example 1. DETAILED DESCRIPTION

[0023] In the specific implementation process, the present invention provides a hot working method for producing a highly uniform ultrafine-grained nickel-based high-temperature alloy, wherein step 1) is to uniformly precipitate γ″, step 2) is to transform the γ″ phase into the δ phase, and step 3) is to control the thermal deformation of the structure containing the δ phase. First, the material is heated to 700-750°C and kept warm for 5-10 hours to obtain a nickel-based high-temperature alloy with fine and uniformly distributed γ″ phase particles. Then, the nickel-based high-temperature alloy is placed in a heat treatment furnace, and the temperature of the heat treatment furnace is raised to 850-950°C and kept warm for 5-10 hours to transform the uniformly distributed γ″ phase into a stable, uniformly distributed δ phase. Finally, deformation (such as upsetting, extrusion or die forging) is performed at 950-1020°C and kept warm for 0.5-2 hours to prevent the temperature from being too high and the δ phase from being completely dissolved. The total deformation is controlled to be above 40% to prevent the deformation from being too small and failing to achieve the refinement effect.

[0024] Preferably, in step 1 of the heat treatment process, 700-750°C is the precipitation temperature of γ″, and keeping it warm at 720°C for 8 hours can obtain a uniform and fine γ″ phase. In step 2 of the heat treatment process, 850-950°C is the δ phase transformation temperature range, and keeping it warm at 900°C for 8 hours is its transformation peak. In step 3 of the heat treatment process, 950-1020°C is the optimal deformation temperature range, and keeping it warm at 960°C for 1 hour can retain more δ phases.

[0025] The present invention is further described in detail below through examples and drawings.

[0026] Example 1

[0027] In this embodiment, a hot working method for producing a highly uniform ultrafine-grained GH4169 alloy comprises the following steps:

[0028] (1) The alloy to be treated was processed into a sample of φ8×12 mm, and the processed sample was placed in a heat treatment furnace and kept at 720°C for 8 h. After the temperature rose to the set temperature and kept for 10 min, the timing was started, and the heating rate was 50°C / h, so that the volume fraction of the γ″ phase in the structure reached 80%.

[0029] (2) The sample treated in step (1) was kept at 900° C. for 8 h. After the temperature reached the set temperature and was kept for 10 min, the timing was started, and the heating rate was 100° C. / h, so that the volume fraction of the δ phase reached 80%.

[0030] (3) The sample treated in step (2) was heated to 960° C. and kept at this temperature for 1 h. After the temperature reached the set temperature and was kept at this temperature for 10 min, the timing was started, and the heating rate was 150° C. / h, so that the volume fraction of the δ phase remained at 50%.

[0031] (4) The sample treated in step (3) is upset and formed to a height of 6 mm in one fire.

[0032] like Figure 1 As shown in the figure, after mechanical polishing and chemical corrosion, the metallographic structure of the treated sample was observed, and the grains were small and uniform, without coarse grains, the grain size reached level 8, and contained a small amount of δ phase.

[0033] Comparative Example 1

[0034] In this comparative example, the hot working method for grain refinement of GH4169 alloy comprises the following steps:

[0035] (1) The alloy to be treated is processed into a specimen of φ8×12 mm and the processed specimen is kept at 900°C for 24 h.

[0036] (2) The sample treated in step (1) was heated to 950°C and kept at this temperature for 5 minutes, and then deformed to a height of 6 mm.

[0037] like Figure 2 As shown in Figure 2, after mechanical polishing and chemical corrosion, the metallographic structure of the treated sample was observed, and the grain size distribution was uneven, still containing coarse grains and a large amount of undissolved δ phase.

[0038] In the preparation methods described in Example 1 and Comparative Example 1, the GH4169 alloy billet material can be prepared according to the method for preparing GH4169 alloy disclosed in the prior art, or can be purchased commercially.

[0039] The results of the embodiments and comparative examples show that compared with the conventional method of directly precipitating the δ phase, the present invention obtains the δ phase by transforming the high-temperature γ″ phase to the δ phase. This method has more advantages in grain refinement and solves the problem that the conventional forging process cannot eliminate the coarse grains and mixed grains in the nickel-based high-temperature alloy.

Claims

1. A hot working method for producing high uniformity ultrafine crystallized nickel-based high temperature alloy GH4169, characterized in that: The process steps include: (1) The alloy to be treated is processed into a sample of φ8×12 mm, and the processed sample is placed in a heat treatment furnace and kept at 720°C for 8 h. After the temperature rises to the set temperature and is kept for 10 min, the timing is started, and the heating rate is 50°C / h, so that the volume fraction of the γ″ phase in the structure reaches 80%; (2) The sample treated in step (1) was kept at 900° C. for 8 h, and the temperature was kept at the set temperature for 10 min before timing was started, with a heating rate of 100° C. / h, until the volume fraction of the δ phase reached 80%; (3) heating the sample treated in step (2) to 960° C. and keeping the temperature for 1 h. When the temperature reaches the set temperature and keeps the temperature for 10 min, start timing, and heat up at a rate of 150° C. / h until the volume fraction of the δ phase remains at 50%; (4) The sample treated in step (3) is subjected to upsetting and forming to a height of 6 mm in one fire; After mechanical polishing and chemical corrosion, the metallographic structure of the treated samples was observed, and the grains were fine and uniform, without coarse grains, the grain size reached level 8, and contained a small amount of δ phase.

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