Preparation method of heavy gas turbine GH4706 alloy turbine disc forge piece fine grains

Abstract

The invention relates to the technical field of metal heat treatment, in particular to a heavy gas turbine GH4706 alloy turbine disc forge piece fine grain preparation method. The bar is heated to the first temperature, and heat preservation is conducted for the first time at the first temperature; raising the temperature to a second temperature and keeping the temperature for a second time; upsetting deformation is conducted on the heated bar on a press, the deformation amount is controlled to range from 20% to 70%, and the bar is immediately returned to a furnace after upsetting deformation; heating the blank: heating the blank to a third temperature, and keeping the temperature for a third time at the third temperature; performing die forging deformation: performing die forging deformation on the heated blank on a press, controlling the deformation amount to be 20-70%, and performing air cooling on a forge piece formed after die forging deformation; the forge piece is heated to a fourth temperature for solution treatment, then discharged out of the furnace and air-cooled to a fifth temperature, and then water-cooled immediately; and the forge piece water-cooled to the room temperature is reheated to the sixth temperature, heat preservation is conducted for 8-9 h, then furnace cooling is conducted to the seventh temperature, heat preservation is conducted for 8-9 h, and then the forge piece is air-cooled to the room temperature.

Description

Technical Field

[0001] The invention relates to the technical field of metal heat treatment, in particular to a method for preparing fine grains of a heavy-duty gas engine GH4706 alloy turbine disk forging. Background Art

[0002] Advanced heavy-duty gas turbines represent the overall level of the country's major equipment manufacturing industry, and their independent development is of great significance to the country's energy adjustment and environmental protection strategy. As the power of F-class and above heavy-duty gas turbines continues to develop in depth, the size, shape complexity, and strength grade of turbine disks continue to increase. The high alloying of materials and large size of components have put forward extremely high requirements for high purity, homogeneity, fine grains, and stable organizational performance in the preparation, forging, and heat treatment of ingots and billets. As one of the key hot end components of heavy-duty gas turbines, the preparation technology of super-large-sized GH4706 alloy turbine disks is at the forefront and commanding heights of today's industrial manufacturing technology.

[0003] In recent years, China has explored the research and development of super-large GH4706 alloy turbine disc forgings for heavy-duty gas turbines, and trial-produced large-scale turbine disc forgings with a diameter of 2000mm and a weight of 6 tons for heavy-duty gas turbines. Although the turbine disc forgings that meet the shape and size are obtained, there are still a series of problems such as coarse grains and serious mixed crystals in some areas. Due to the high price of large GH4706 high-temperature alloy turbine disc die forgings (each piece is worth hundreds of thousands to millions of yuan), once the organizational performance is not in line with the situation, it will cause great waste. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing fine grains of heavy-duty gas turbine GH4706 alloy turbine disk forgings, which is used to reduce the grain size of the forgings after forming.

[0005] The technical solution adopted by the present invention to solve the technical problem is a method for preparing fine grains of heavy-duty gas turbine GH4706 alloy turbine disk forgings, comprising the following steps:

[0006] S1. Heating the bar: firstly heat the bar to a first temperature and keep it at the first temperature for a first time T1=a1*d, where a1=0.2min / mm~0.4min / mm, d=effective thickness of the bar; then heat it to a second temperature, which is higher than the first temperature, and keep it at the second temperature for a second time T2=a2*d, where a2=0.6min / mm~0.8min / mm;

[0007] S2. Upsetting deformation: The heated bar is subjected to upsetting deformation on a press, and the deformation amount is controlled at 20-70%. The blank formed after the bar is upsetting is immediately returned to the furnace;

[0008] S3, heating the blank: heating the blank to a third temperature, and keeping the blank at the third temperature for a third time T3=a3*d3, wherein a3=0.1min / mm-0.2min / mm, d3=effective thickness of the blank;

[0009] S4, die forging deformation: the heated blank is die forged on a press, the deformation amount is controlled at 20-70%, and the forging formed after die forging deformation is air cooled;

[0010] S5. Heat treatment of forgings: heat the forgings to a fourth temperature for solution treatment and keep them warm for a fourth time T4=a4*d4, wherein a4=0.4min / mm~0.5min / mm, d4=effective thickness of the forgings, then air-cool them to a fifth temperature and immediately water-cool them; heat the forgings that have been water-cooled to room temperature again to a sixth temperature and keep them warm for 8~9h, the sixth temperature is lower than the fifth temperature, then furnace-cool them to a seventh temperature and keep them warm for 8~9h, the seventh temperature is lower than the sixth temperature, then air-cool the forgings to room temperature.

[0011] Further, the first temperature is 820-840°C, the second temperature is 950-970°C; the third temperature is 950-970°C; the fourth temperature is 960-980°C; the fifth temperature is 810-820°C; the sixth temperature is 720-740°C; and the seventh temperature is 615-625°C.

[0012] Furthermore, the press is an 800MN large die forging press.

[0013] The beneficial effects of the present invention are as follows: 1) the rod material is heated by a double-step heating process, which can shorten the heating time by more than 50% and reduce the heating energy consumption compared with the traditional three-step heating process; 2) the method of immediately returning to the furnace for heating after roughening deformation is adopted, which avoids the resource consumption caused by reheating the billet after air cooling, and also shortens the long-term residence time of the GH4706 alloy turbine disk forging in a high temperature state, further avoiding the growth of grains; 3) the low-temperature heating method is adopted to avoid the excessive growth of the GH4706 alloy turbine disk forging during the heating process. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a flow chart of the present invention; DETAILED DESCRIPTION

[0015] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0016] like Figure 1 As shown, the present invention provides a method for preparing fine grains of a heavy-duty gas engine GH4706 alloy turbine disk forging, comprising the following steps:

[0017] S1. Heating the bar: first heat the bar to a first temperature, and keep it at the first temperature for a first time T1=a1*d, where a1=0.2min / mm~0.4min / mm, d=effective thickness of the bar; then heat it to a second temperature, which is greater than the first temperature, and keep it at the second temperature for a second time T2=a2*d, where a2=0.6min / mm~0.8min / mm; Heating to the first temperature (820~840℃) and keeping it warm have two main functions: 1. Under this temperature condition, it is in the peak precipitation temperature range of the η phase of the precipitation phase of the GH4169 high-temperature alloy, and a certain amount of η phase precipitates to play a pinning role at the grain boundary, inhibiting the growth of grains when keeping warm at the second step, i.e., the second temperature (950~970℃); 2. Keeping warm at this location can build a temperature difference between the core and the surface of the billet when it is heated, avoiding the risk of cracking of large-sized billets due to temperature stress. Heating to the second temperature (950-970°C) for insulation has two main functions: 1. Under this temperature condition, GH4169 high-temperature alloy has good high-temperature plasticity, which is conducive to forging deformation; 2. This temperature is lower than the traditional heating deformation temperature. Under this temperature condition, the η phase is not completely dissolved, and a certain amount of η phase plays a pinning role at the grain boundary, inhibiting the growth of grains during insulation, and obtaining a fine-grained structure; the effective thickness of the bar refers to the diameter of the inscribed circle at the thickest position of the bar.

[0018] S2. Upsetting deformation: The heated bar is subjected to upsetting deformation on a press, and the deformation amount is controlled at 20-70%. The blank formed after the bar is upsetting is immediately returned to the furnace;

[0019] S3. Heating the blank: heat the blank to a third temperature (950-970°C), and keep it at the third temperature for a third time T3=a3*d3, wherein a3=0.1min / mm-0.2min / mm, d3=effective thickness of the blank; the effective thickness of the blank refers to the diameter of the inscribed circle of the thickest position of the blank.

[0020] S4, die forging deformation: the heated blank is die forged on a press, the deformation amount is controlled at 20-70%, and the forging formed after die forging deformation is air cooled;

[0021] S5. Heat treatment of forgings: heat the forgings to a fourth temperature (960-980°C) for solution treatment and keep them warm for a fourth time T4=a4*d4, wherein a4=0.4min / mm-0.5min / mm, d4=effective thickness of the forging, which refers to the diameter of the inscribed circle at the thickest position of the forging. Then, air-cool the forgings to a fifth temperature (810-820°C) and immediately water-cool them. The forgings cooled to room temperature by water are heated again to a sixth temperature (720-740°C) and kept warm for 8-9h, the sixth temperature being lower than the fifth temperature. Then, furnace-cool the forgings to a seventh temperature (615-625°C) and kept warm for 8-9h, the seventh temperature being lower than the sixth temperature. Then, air-cool the forgings to room temperature.

[0022] The process of solution treatment and furnace cooling during heat treatment is mainly to obtain the final mechanical properties. During solution treatment, all the precipitated phases of the material are dissolved back into the solid solution, and then the material is taken out of the furnace and air-cooled to the fifth temperature. At this time, a certain amount of η phase can be obtained at the grain boundary, and then it is immediately water-cooled to room temperature. The precipitation amount and size of the η phase can be controlled, that is, to avoid too little η phase and too much η phase. The appropriate amount of η phase helps to improve the high-temperature durability of GH4706. The subsequent furnace cooling to the sixth and seventh temperatures is to further precipitate a certain amount of η phase and γ', γ″ strengthening phases to obtain the final mechanical properties.

[0023] Furthermore, the press is an 800MN die forging press.

[0024] Example 1

[0025] First, heat the rod with a diameter of Φ700mm and a length of 2000mm to 820℃ and keep it at 820℃ for 140min; then heat it to 950℃ and keep it at 950℃ for 420min;

[0026] S2. Upsetting deformation: The heated bar is subjected to upsetting deformation on a press, and the deformation amount is controlled at 20%. The blank formed after the bar is upset is immediately returned to the furnace, and the outer contour size of the blank after upsetting is Φ780×1600mm;

[0027] S3, heating the blank: heating the blank to 950°C and keeping the temperature at 950°C for 78 minutes;

[0028] S4. Die forging deformation: The heated blank is die forged on a press, and the strain field distribution of the forging can be 20% to 70%. The forging formed after die forging deformation is air cooled, and the outer contour size of the forging after die forging deformation is Φ2000×280mm;

[0029] S5. Heat treatment of forgings: Heat the forgings to 960°C for solution treatment and keep them warm for 112 minutes; then furnace cool them to 720°C and keep them warm for 8 to 9 hours, then furnace cool them to 615°C and keep them warm for 8 to 9 hours, and then air cool the forgings to room temperature; the final large-sized turbine disk forgings have a grain size that meets ASTM standard level 4.

[0030] Example 2

[0031] First, heat the rod with a diameter of Φ700mm and a length of 2000mm to 840℃ and keep it at 840℃ for 280min; then heat it to 970℃ and keep it at 970℃ for 560min;

[0032] S2. Upsetting deformation: The heated bar is subjected to upsetting deformation on a press, and the deformation amount is controlled at 70%. The blank formed after the bar is upset and deformed is immediately returned to the furnace. The outer contour size of the blank after upsetting is Φ780×1600mm;

[0033] S3, heating the blank: heating the blank to 970°C and keeping the temperature at 970°C for 156 minutes;

[0034] S4. Die forging deformation: The heated blank is die forged on a press, and the strain field distribution of the forging can be 20% to 70%. The forging formed after die forging deformation is air cooled, and the outer contour size of the forging after die forging deformation is Φ2000×280mm;

[0035] S5. Heat treatment of forgings: Heat the forgings to 980°C for solution treatment and keep them warm for 140 minutes; then furnace cool them to 740°C and keep them warm for 8 to 9 hours, then furnace cool them to 625°C and keep them warm for 8 to 9 hours, and then air cool the forgings to room temperature; the final large-sized turbine disk forgings have a grain size that meets ASTM standard level 5.

[0036] The embodiments of this specific implementation method are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, all equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing fine grains of heavy-duty gas turbine GH4706 alloy turbine disk forgings, characterized in that: The following steps are included: S1. Heating the bar: firstly heat the bar to a first temperature and keep it at the first temperature for a first time T1=a1*d, where a1=0.2min / mm~0.4min / mm, d=effective thickness of the bar; then heat it to a second temperature, which is higher than the first temperature, and keep it at the second temperature for a second time T2=a2*d, where a2=0.6min / mm~0.8min / mm; S2. Upsetting deformation: The heated bar is subjected to upsetting deformation on a press, and the deformation amount is controlled at 20-70%. The blank formed after the bar is upsetting is immediately returned to the furnace; S3, heating the blank: heating the blank to a third temperature, and keeping the blank at the third temperature for a third time T3=a3*d3, wherein a3=0.1min / mm-0.2min / mm, d3=effective thickness of the blank; S4, die forging deformation: the heated blank is die forged on a press, the deformation amount is controlled at 20-70%, and the forging formed after die forging deformation is air cooled; S5. Heat treatment of forgings: heat the forgings to a fourth temperature for solution treatment and keep them warm for a fourth time T4=a4*d4, wherein a4=0.4min / mm~0.5min / mm, d4=effective thickness of the forgings; then take them out of the furnace and air-cool them to a fifth temperature and immediately water-cool them to room temperature; heat the forgings that have been water-cooled to room temperature again to a sixth temperature and keep them warm for 8~9h, the sixth temperature is lower than the fifth temperature, then furnace-cool them to a seventh temperature and keep them warm for 8~9h, the seventh temperature is lower than the sixth temperature, and then air-cool the forgings to room temperature.

2. A method for preparing fine grains of heavy-duty gas turbine GH4706 alloy turbine disk forgings according to claim 1, characterized in that: The first temperature is 820-840°C, the second temperature is 950-970°C; the third temperature is 950-970°C; the fourth temperature is 960-980°C; the fifth temperature is 810-820°C; the sixth temperature is 720-740°C; and the seventh temperature is 615-625°C.

3. A method for preparing fine grains of heavy-duty gas turbine GH4706 alloy turbine disk forgings according to claim 1, characterized in that: The press is an 800MN die forging press.

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