Preparation method of GH706 high-temperature alloy large-size bar billet

Abstract

The invention provides a preparation method of a GH706 high-temperature alloy large-size bar billet, which comprises the following five steps: (1) a GH706 high-temperature alloy ingot prepared by a triple smelting process of vacuum induction melting, protective atmosphere electroslag remelting and vacuum consumable remelting comprises the following chemical components in percentage by weight: 0.025%-0.060% of C, 14.50%-17.50% of Cr, 39.00%-44.00% of Ni, 1.50%-2.00% of Ti, 2.50%-3.30% of Nb + Ta, 0.15%-0.50% of Al and the balance of Fe and inevitable impurities; the balance is Fe and other micro trace elements; (2) high-temperature homogenization treatment; (3) cogging and forging: carrying out high-temperature cogging and forging on the cast ingot for 2-3 heating numbers, wherein the forging modes are upsetting and drawing-out; (4) intermediate billet forging: performing medium-temperature multi-heating-number upsetting and octagonal drawing on the intermediate billet subjected to cogging forging; according to the preparation method of the GH706 high-temperature alloy large-size bar billet, the technical problem that the structure uniformity is difficult to control due to end face cracking, low forging yield and severe temperature rise in the cogging process of a large-size cast ingot is solved, and the preparation method has high application value in industrial actual production.

Description

Technical Field

[0001] The invention belongs to the technical field of nonferrous metal processing methods, and in particular relates to a method for preparing a large-size high-temperature alloy bar blank. Background Art

[0002] GH706 alloy is a precipitation-strengthened Fe-Ni-based high-temperature alloy. Its composition is derived from the widely used GH4169 alloy, with reduced Ni, Cr, and Nb content, removed Mo, and increased Fe and Ti content. It has the advantages of low segregation tendency, excellent hot working performance, and low cost. It is suitable for the preparation of ultra-large turbine disk forgings for heavy-duty gas turbines.

[0003] GH706 alloy requires billeting before die forging. Due to the relatively large size and weight of ultra-large turbine disk forgings for heavy-duty gas turbines—the largest GH706 turbine disk forgings in the world can weigh up to 6 tons and exceed 2000mm in diameter—high requirements are placed on the weight and specifications of the pre-die forging billet. As the weight of the ingot billet increases, controlling the forging yield and microstructure uniformity of the billet becomes a significant challenge. Currently, domestic production technology for large-sized GH706 alloy billets is still in the exploratory stage, necessitating the design of a process solution that achieves high yield and microstructure uniformity. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing large-size GH706 high-temperature alloy billets to solve the problems raised in the above-mentioned background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for preparing a large-size GH706 high-temperature alloy billet, comprising the following steps:

[0006] Step (1), adopting vacuum induction melting + protective atmosphere electroslag remelting + vacuum consumable remelting triple smelting process to prepare ingot, the ingot diameter is 800mm~900mm; the chemical composition percentage of the ingot is: C: 0.025%~0.060%, Cr: 14.50%~17.50%, Ni: 39.00%~44.00%, Ti: 1.50%~2.00%, Nb+Ta: 2.50%~3.30%, Al: 0.15%~0.50%, and the balance is Fe and other trace elements;

[0007] Step (2), the ingot is subjected to high-temperature homogenization heat treatment in a desktop natural gas furnace;

[0008] Step (3), the ingot that has undergone homogenization heat treatment is subjected to 2-3 rounds of high-temperature forging in an 80MN fast forging machine, and a continuous re-melting method is adopted, and the hot material after forging is returned to the furnace for the next round of forging;

[0009] Step (4), after the high-temperature blanking is completed, the intermediate blank is subjected to medium-temperature multi-fire upsetting and eight-way stretching on an 80MN fast forging machine, and a continuous re-melting method is adopted, and the hot material after forging is returned to the furnace for the next fire forging;

[0010] Step (5) is to perform 1 to 3 rounds of low-temperature large deformation upsetting on the octagonal cross-section billet after forging the intermediate billet, and adopt a continuous remelting method. After forging, the hot material is returned to the furnace for the next round of forging. After the last round of upsetting, the edges are chamfered and rounded, and the billet is air-cooled after forming.

[0011] Preferably, the heating and cooling method in step (3) is:

[0012] The homogenized ingot is heated. After the furnace temperature is cooled to below 500°C, the material is loaded into the furnace and heated to 650°C with a thermal insulation coefficient of 0.6 min / mm. Then the temperature is increased to 1100°C~1120°C at a heating rate of 1~2°C / min, and the thermal insulation time is 15~20h. The thermal insulation coefficient of the hot material is continuously returned to the furnace with a coefficient of 0.2 min / mm. After forging is completed, the hot material is returned to the furnace.

[0013] Preferably, the heating and cooling method in step (4) is:

[0014] The hot material after high-temperature blanking is returned to the furnace with a heating temperature of 1040℃~1080℃ and a thermal insulation coefficient of 0.2min / mm. The thermal insulation coefficient of the subsequent continuous returning hot material is 0.2min / mm. The hot material is returned to the furnace after forging is completed.

[0015] Preferably, the heating and cooling method in step (5) is:

[0016] The hot material of the intermediate billet after forging is returned to the furnace, the heating temperature is 1000-1020℃, the insulation coefficient is 0.2min / mm, and then the temperature is quickly raised to 1040-1060℃. After keeping it for 20min-30min, it is taken out of the furnace for forging. The heating system of each subsequent fire is the same as above. After the last fire forging is completed, the material is air-cooled.

[0017] Preferably, the forging method in step (3) is:

[0018] The forging method for each fire is upsetting and drawing. The end face is mortised before upsetting, and the end face is flattened after drawing. The upsetting deformation is 15% to 30%, and the drawing deformation is 10% to 30%. At the end of each fire, an intermediate billet with an octagonal cross section is obtained.

[0019] Preferably, the forging method in step (4) is:

[0020] The forging method for each fire is upsetting and drawing. The end face is mortised before upsetting, and the end face is flattened after drawing. The upsetting deformation is 20% to 30%, and the drawing deformation is 15% to 35%. At the end of each fire, an intermediate billet with an octagonal cross section is obtained.

[0021] Preferably, the forging method in step (5) is:

[0022] The forging method for each fire is upsetting and drawing. The material is soft-wrapped after being taken out of the furnace. The end face is mortised before upsetting. The end face is lightly tapped after drawing. The deformation amount of upsetting is 20% to 35%, and the deformation amount of drawing is 25% to 40%. After the last fire of drawing, chamfering and rounding are performed. The deformation amount of chamfering and rounding is 1% to 10%. At the same time, the pressing rate of the fast forging machine is required to be set to high gear during chamfering and rounding.

[0023] Preferably, the weight of the high-temperature alloy ingot in step (1) is 7 to 9 tons, and the specification is Φ840 mm.

[0024] Preferably, the specification of the finished high-temperature alloy bar in step (5) is Φ650 to Φ850 mm.

[0025] Preferably, the core, middle and edge grain sizes of the finished high-temperature alloy bar blank are all 3.5 or above, the structure is uniform, and the yield rate reaches more than 75%.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The ingot is prepared by a triple smelting process of vacuum induction melting + protective atmosphere electroslag remelting + vacuum consumable remelting, which has low inclusions and gas element content and high purity;

[0028] (2) For high-temperature alloy ingots with large unit weight and large size, in the process of blanking and forging, in order to ensure that the cast dendritic structure is fully broken, the single pressing amount must be large. However, the conventional upsetting and drawing method easily leads to stress concentration cracking at the end face fillet and serious end face concavity, thereby reducing the forging yield rate. The process of upsetting before upsetting and flattening the end face after drawing of the present invention can effectively solve such end face cracking and concavity problems, thereby reducing the amount of material head and tail removed and improving the forging yield rate.

[0029] (3) The final forming fire can effectively solve the problem of mixed crystals caused by edge temperature drop by compensating the surface temperature for a short time before forging and soft coating. In addition, combined with low-temperature and large-deformation forging, the core temperature rise can be effectively controlled on the basis of ensuring forging through, so that different parts of the billet can obtain sufficient energy for dynamic recrystallization, thereby effectively solving the problem of poor microstructure uniformity of large-sized bar billets. By using the forging method of the present invention, large-sized high-temperature alloy bar billets with good microstructure uniformity and high yield can be obtained.

[0030] The core of the present invention is to propose a method for preparing large-size GH706 high-temperature alloy bar billets, which solves the technical problems of low forging yield caused by end face cracking and concave core during the billeting process of large-size bar billets, as well as difficulty in controlling microstructure uniformity. It has high application value in actual industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a flow chart of the method for preparing large-size GH706 high-temperature alloy billets of the present invention;

[0032] Figure 2 This is a physical picture of a GH706 high-temperature alloy Φ680mm large-size bar billet according to Example 1 of the present invention;

[0033] Figure 3 This is a photo of the head of the GH706 high-temperature alloy Ø680 mm bar after forging according to Example 1 of the present invention;

[0034] Figure 4 This is a photo of the tail of the GH706 high-temperature alloy Ø680 mm bar after forging according to Example 1 of the present invention;

[0035] Figure 5 This is the high-magnification microstructure at the center of the head end of the GH706 high-temperature alloy Ø680mm bar blank of Example 1 of the present invention;

[0036] Figure 6 This is the macrostructure at the R / 2 position of the head end of the GH706 high-temperature alloy Ø680 mm bar of Example 1 of the present invention;

[0037] Figure 7 This is the high-magnification microstructure at the edge of the head end of the GH706 high-temperature alloy Ø680mm bar in Example 1 of the present invention;

[0038] Figure 8 This is the high-magnification microstructure at the center of the tail end of the GH706 high-temperature alloy Ø680mm bar billet of Example 1 of the present invention;

[0039] Figure 9 This is the macrostructure at the R / 2 position at the tail end of the GH706 high-temperature alloy Ø680 mm bar of Example 1 of the present invention;

[0040] Figure 10 This is the high-magnification microstructure at the tail end edge of the GH706 high-temperature alloy Ø680mm rod in Example 1 of the present invention. DETAILED DESCRIPTION

[0041] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0042] See also Figure 1-Figure 4 The present invention provides a technical solution: Example 1

[0043] A method for preparing a large-size GH706 high-temperature alloy bar billet comprises the following steps:

[0044] Step (1), preparing an ingot: adopting a triple smelting process of vacuum induction melting + protective atmosphere electroslag remelting + vacuum consumable remelting to prepare an ingot, the chemical composition percentage of the ingot is: C: 0.025% to 0.060%, Cr: 14.50% to 17.50%, Ni: 39.00% to 44.00%, Ti: 1.50% to 2.00%, Nb+Ta: 2.50% to 3.30%, Al: 0.15% to 0.50%, the balance is Fe and other trace elements, the ingot weight is 8t, and the diameter is 840mm;

[0045] Step (2), subjecting the ingot prepared by the triple smelting process to a high-temperature homogenization treatment;

[0046] Step (3), blank forging: an 80MN fast forging machine is used to perform three-fire high-temperature blank forging on the ingot, and the forging method for each fire is upsetting and drawing. The heating temperature of the first fire is 1120°C. After the furnace temperature is cooled to below 500°C, the material is loaded into the furnace, heated to 650°C, and kept warm for 8.5 hours. Then the temperature is raised to 1120°C at a heating rate of 2°C / min, kept warm for 20 hours after reaching the temperature, and then taken out of the furnace for forging. Before upsetting, the end face is mortised, and after drawing, the end face is patted flat. The upsetting deformation is 17%, and the drawing deformation is 16%. After forging is completed, the hot material is returned to the furnace for the next fire forging. The heating temperature of the second and third fires is 1100°C. After reaching the temperature, the holding time is 3 hours. Before upsetting, the end face is mortised, and after drawing, the end face is patted flat. The upsetting deformation is 25%, and the drawing deformation is 29%. The split-forging process is conducted at a higher temperature and with a smaller deformation. The goal is to fully break up the original coarse dendritic structure in the ingot without cracking the billet, thereby improving the billet's plasticity and providing a billet with good plasticity for subsequent intermediate billet forging. After split-forging, an intermediate billet with an octagonal cross-section is obtained. After forging is completed, the hot material is returned to the furnace for the next intermediate billet forging process.

[0047] Step (4), intermediate billet forging: the billet after the open forging is returned to the furnace for two rounds of intermediate billet forging, using an 80MN fast forging machine, and the forging method for each round is upsetting and drawing. The fourth and fifth rounds are heated to 1060℃, and after reaching the temperature, they are kept warm for 3 hours before being forged. The end faces are mortised before upsetting, and the end faces are flattened after drawing. The upsetting deformation is 23%, and the drawing deformation is 30%. The purpose of intermediate billet forging is to further improve the plasticity of the billet and obtain an intermediate billet with relatively uniform structure. After the intermediate billet forging is completed, a billet with an octagonal cross section is obtained. After forging is completed, the hot material is returned to the furnace for the next round of finished product forging;

[0048] Step (5), finished product forging: the hot intermediate billet after forging is returned to the furnace for the final fire forging of the finished product. The heating temperature is 1010℃, and the temperature is kept for 3 hours after reaching the temperature. Then the temperature is quickly raised to 1060℃, kept for 20 minutes, and then taken out of the furnace for forging. After the material is taken out of the furnace, it is soft-packaged. An 80MN fast forging machine is used. The forging method is upsetting and drawing. The end face is mortised before upsetting. After drawing, the end face is gently tapped flat. The upsetting deformation is 27%, and the drawing deformation is 31%. After the drawing is completed, the edges are chamfered and rounded. The deformation of chamfering and rounding is 1% to 10%. At the same time, the fast forging machine is required to set the pressing rate of the high gear during chamfering and rounding. After the final fire forging is completed, the material is air-cooled. Finally, a large-sized GH706 high-temperature alloy billet with a specification of Φ680mm is obtained.

[0049] Example 2

[0050] A method for preparing a large-size GH706 high-temperature alloy bar billet comprises the following steps:

[0051] Step (1), preparing an ingot: adopting a triple smelting process of vacuum induction melting + protective atmosphere electroslag remelting + vacuum consumable remelting to prepare an ingot, the chemical composition percentage of the ingot is: C: 0.025% to 0.060%, Cr: 14.50% to 17.50%, Ni: 39.00% to 44.00%, Ti: 1.50% to 2.00%, Nb+Ta: 2.50% to 3.30%, Al: 0.15% to 0.50%, the balance is Fe and other trace elements, the ingot weighs 8.5t and has a diameter of 840mm;

[0052] Step (2), subjecting the ingot prepared by the triple smelting process to a high-temperature homogenization treatment;

[0053] Step (3), blank forging: an 80MN fast forging machine is used to perform three-fire high-temperature blank forging on the ingot. The forging method for each fire is upsetting and drawing. The heating temperature of the first fire is 1120℃. After the furnace temperature is cooled to below 500℃, the material is loaded into the furnace, heated to 650℃, and kept warm for 8.5 hours. Then the temperature is raised to 1120℃ at a heating rate of 2℃ / min. After reaching the temperature, it is kept warm for 20 hours before being taken out of the furnace for forging. The end face is mortised before upsetting, and the end face is flattened after drawing. The upsetting deformation is 21%, and the drawing deformation is 21%. 12%. After forging is completed, the hot material is returned to the furnace for the next forging. The second heating temperature is 1100℃. The holding time after reaching the temperature is 3 hours. The end face is mortised before upsetting. After drawing, the end face is tapped flat. The upsetting deformation is 26%, and the drawing deformation is 26%. After forging is completed, the hot material is returned to the furnace for the next forging. The third heating temperature is 1100℃. The holding time after reaching the temperature is 3 hours. The end face is mortised before upsetting. After drawing, the end face is tapped flat. The upsetting deformation is 23%, and the drawing deformation is 31%. The forging temperature of the blanking fire is high and the deformation is small. The purpose is to fully break the original coarse cast dendrite structure in the ingot without cracking the blank, thereby improving the plasticity of the blank and providing a blank with good plasticity for the subsequent intermediate blank forging. After blanking forging, an intermediate blank with an octagonal cross section is obtained. After forging, the hot material is returned to the furnace for the next intermediate blank forging.

[0054] Step (4), intermediate billet forging: the billet after the open forging is returned to the furnace for two-fire intermediate billet forging, using an 80MN fast forging machine, the forging method for each fire is upsetting and drawing, the heating temperature of the fourth fire is 1060℃, after reaching the temperature, it is kept warm for 3 hours and then forged out of the furnace, the end face is mortised before upsetting, and the end face is lightly tapped after drawing, the upsetting deformation is 31%, and the drawing deformation is 31%. After forging is completed, the hot material is returned to the furnace for the next fire forging, the heating temperature of the fourth fire is 1060℃, after reaching the temperature, it is kept warm for 3 hours and then forged out of the furnace, the end face is mortised before upsetting, and the end face is lightly tapped after drawing, the upsetting deformation is 31%, and the drawing deformation is 22%. The purpose of forging the intermediate billet is to further improve the plasticity of the billet and obtain an intermediate billet with relatively uniform structure. After the intermediate billet is forged, a billet with an octagonal cross section is obtained. After forging, the hot material is returned to the furnace for the next step of finished product forging.

[0055] Step (5), finished product forging: the hot intermediate billet after forging is returned to the furnace for the final fire forging of the finished product. The heating temperature is 1010℃, and the temperature is kept for 3 hours after reaching the temperature. Then the temperature is quickly raised to 1060℃, kept for 20 minutes, and then taken out of the furnace for forging. After the material is taken out of the furnace, it is soft-packaged. An 80MN fast forging machine is used. The forging method is upsetting and drawing. The end face is mortised before upsetting. After drawing, the end face is gently tapped flat. The upsetting deformation is 22%, and the drawing deformation is 39%. After the drawing is completed, the edges are chamfered and rounded. The deformation of chamfering and rounding is 1% to 10%. At the same time, the fast forging machine is required to set the pressing rate of the high gear during chamfering and rounding. After the final fire forging is completed, the material is air-cooled. Finally, a large-sized GH706 high-temperature alloy billet with a specification of Φ750mm is obtained.

[0056] Example 3

[0057] A method for preparing a large-size GH706 high-temperature alloy bar billet comprises the following steps:

[0058] Step (1), preparing an ingot: adopting a triple smelting process of vacuum induction melting + protective atmosphere electroslag remelting + vacuum consumable remelting to prepare an ingot, the chemical composition percentage of the ingot is: C: 0.025% to 0.060%, Cr: 14.50% to 17.50%, Ni: 39.00% to 44.00%, Ti: 1.50% to 2.00%, Nb+Ta: 2.50% to 3.30%, Al: 0.15% to 0.50%, the balance is Fe and other trace elements, the ingot weighs 9 tons and has a diameter of 840 mm;

[0059] Step (2), subjecting the ingot prepared by the triple smelting process to a high-temperature homogenization treatment;

[0060] Step (3), blank forging: an 80MN fast forging machine is used to perform three-fire high-temperature blank forging on the ingot. The forging method for each fire is upsetting and drawing. The heating temperature of the first fire is 1120℃. After the furnace temperature is cooled to below 500℃, the material is loaded into the furnace, heated to 650℃, and kept warm for 8.5 hours. Then the temperature is raised to 1120℃ at a heating rate of 2℃ / min. After reaching the temperature, it is kept warm for 20 hours before being taken out of the furnace for forging. The end face is mortised before upsetting, and the end face is flattened after drawing. The upsetting deformation is 17%, and the drawing deformation is 17%. 16%. After forging is completed, the hot material is returned to the furnace for the next forging. The second heating temperature is 1100℃. The holding time after reaching the temperature is 3 hours. The end face is mortised before upsetting. After drawing, the end face is tapped flat. The upsetting deformation is 17%, and the drawing deformation is 17%. After forging is completed, the hot material is returned to the furnace for the next forging. The third heating temperature is 1100℃. The holding time after reaching the temperature is 3 hours. The end face is mortised before upsetting. After drawing, the end face is tapped flat. The upsetting deformation is 21%, and the drawing deformation is 15%. The forging temperature of the blanking fire is high and the deformation is small. The purpose is to fully break the original coarse cast dendrite structure in the ingot without cracking the blank, thereby improving the plasticity of the blank and providing a blank with good plasticity for the subsequent intermediate blank forging. After blanking forging, an intermediate blank with an octagonal cross section is obtained. After forging, the hot material is returned to the furnace for the next intermediate blank forging.

[0061] Step (4), intermediate billet forging: the billet after the open forging is returned to the furnace for two-fire intermediate billet forging, using an 80MN fast forging machine, the forging method for each fire is upsetting and drawing, the heating temperature of the fourth fire is 1060℃, after reaching the temperature, it is kept warm for 3 hours and then forged out of the furnace, the end face is mortised before upsetting, and the end face is lightly tapped after drawing, the upsetting deformation is 25%, and the drawing deformation is 25%. After forging is completed, the hot material is returned to the furnace for the next fire forging, the heating temperature of the fourth fire is 1060℃, after reaching the temperature, it is kept warm for 3 hours and then forged out of the furnace, the end face is mortised before upsetting, and the end face is lightly tapped after drawing, the upsetting deformation is 25%, and the drawing deformation is 25%. The purpose of forging the intermediate billet is to further improve the plasticity of the billet and obtain an intermediate billet with relatively uniform structure. After the intermediate billet is forged, a billet with an octagonal cross section is obtained. After forging, the hot material is returned to the furnace for the next step of finished product forging.

[0062] Step (5), finished product forging: the hot material of the intermediate billet after forging is returned to the furnace for the final fire forging of the finished product. The heating temperature is 1010℃, and the temperature is kept for 3.5 hours after reaching the temperature. Then the temperature is quickly raised to 1060℃, kept for 20 minutes, and then taken out of the furnace for forging. After the material is taken out of the furnace, it is soft-packaged. An 80MN fast forging machine is used. The forging method is upsetting and drawing. The end face is mortised before upsetting. After drawing, the end face is gently tapped flat. The upsetting deformation is 20%, and the drawing deformation is 30%. After the drawing is completed, the edges are chamfered and rounded. The deformation of chamfering and rounding is 1% to 10%. At the same time, the fast forging machine is required to set the pressing rate of the high gear during chamfering and rounding. After the final fire forging is completed, the material is air-cooled. Finally, a large-sized GH706 high-temperature alloy billet with a specification of Φ820mm is obtained.

[0063] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing large-size GH706 high-temperature alloy billets, characterized in that: The following steps are involved: Step (1), adopting vacuum induction melting + protective atmosphere electroslag remelting + vacuum consumable remelting triple smelting process to prepare ingot, the ingot diameter is 800mm~900mm; the chemical composition percentage of the ingot is: C: 0.025%~0.060%, Cr: 14.50%~17.50%, Ni: 39.00%~44.00%, Ti: 1.50%~2.00%, Nb+Ta: 2.50%~3.30%, Al: 0.15%~0.50%, and the balance is Fe and other trace elements; Step (2), the ingot is subjected to high-temperature homogenization heat treatment in a desktop natural gas furnace; Step (3), the ingot that has undergone homogenization heat treatment is subjected to 2-3 rounds of high-temperature forging in an 80MN fast forging machine, and a continuous re-melting method is adopted, and the hot material after forging is returned to the furnace for the next round of forging; Step (4), after the high-temperature blanking is completed, the intermediate blank is subjected to medium-temperature multi-fire upsetting and eight-way stretching on an 80MN fast forging machine, and a continuous re-melting method is adopted, and the hot material after forging is returned to the furnace for the next fire forging; Step (5) is to perform 1 to 3 rounds of low-temperature large deformation upsetting on the octagonal cross-section billet after forging the intermediate billet, and adopt a continuous remelting method. After forging, the hot material is returned to the furnace for the next round of forging. After the last round of upsetting, the edges are chamfered and rounded, and the billet is air-cooled after forming.

2. The method for preparing a large-size GH706 high-temperature alloy bar according to claim 1, characterized in that: The heating and cooling method in step (3) is: The homogenized ingot is heated. After the furnace temperature is cooled to below 500°C, the material is loaded into the furnace and heated to 650°C with a thermal insulation coefficient of 0.6 min / mm. Then the temperature is increased to 1100°C~1120°C at a heating rate of 1~2°C / min, and the thermal insulation time is 15~20h. The thermal insulation coefficient of the hot material is continuously returned to the furnace with a coefficient of 0.2 min / mm. After forging is completed, the hot material is returned to the furnace.

3. The method for preparing a large-size GH706 high-temperature alloy billet according to claim 1, characterized in that: The heating and cooling method in step (4) is: The hot material after high-temperature blanking is returned to the furnace with a heating temperature of 1040℃~1080℃ and a thermal insulation coefficient of 0.2min / mm. The thermal insulation coefficient of the subsequent continuous returning hot material is 0.2min / mm. The hot material is returned to the furnace after forging is completed.

4. The method for preparing a large-size GH706 high-temperature alloy bar according to claim 1, characterized in that: The heating and cooling method in step (5) is: The hot material of the intermediate billet after forging is returned to the furnace, the heating temperature is 1000-1020℃, the insulation coefficient is 0.2min / mm, and then the temperature is quickly raised to 1040-1060℃. After keeping it for 20min-30min, it is taken out of the furnace for forging. The heating system of each subsequent fire is the same as above. After the last fire forging is completed, the material is air-cooled.

5. The method for preparing a large-size GH706 high-temperature alloy bar according to claim 1, characterized in that: The forging method in step (3) is: The forging method for each fire is upsetting and drawing. The end face is mortised before upsetting, and the end face is flattened after drawing. The upsetting deformation is 15% to 30%, and the drawing deformation is 10% to 30%. At the end of each fire, an intermediate billet with an octagonal cross section is obtained.

6. The method for preparing a large-size GH706 high-temperature alloy bar according to claim 1, characterized in that: The forging method in step (4) is: The forging method for each fire is upsetting and drawing. The end face is mortised before upsetting, and the end face is flattened after drawing. The upsetting deformation is 20% to 30%, and the drawing deformation is 15% to 35%. At the end of each fire, an intermediate billet with an octagonal cross section is obtained.

7. The method for preparing large-size GH706 high-temperature alloy billets according to claim 1, characterized in that: The forging method in step (5) is: The forging method for each fire is upsetting and drawing. The material is soft-wrapped after being taken out of the furnace. The end face is mortised before upsetting. The end face is lightly tapped after drawing. The deformation amount of upsetting is 20% to 35%, and the deformation amount of drawing is 25% to 40%. After the last fire of drawing, chamfering and rounding are performed. The deformation amount of chamfering and rounding is 1% to 10%. At the same time, the pressing rate of the fast forging machine is required to be set to high gear during chamfering and rounding.

8. The preparation method according to claim 1, characterized in that In the step (1), the weight of the high-temperature alloy ingot is 7 to 9 tons, and the specification is Φ840 mm.

9. The preparation method according to claim 1, characterized in that The specifications of the high-temperature alloy finished bar billet in step (5) are Φ650 to Φ850 mm.

10. The method for preparing large-size GH706 high-temperature alloy billets according to claim 1, characterized in that: The core, middle and edge grain sizes of the finished high-temperature alloy rods are all level 3.5 or above, the structure is uniform, and the yield rate reaches more than 75%.

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