Heat treatment method for improving the endurance performance of large in 718 alloy parts

Abstract

The present application relates to the field of IN718 alloy piece processing, and discloses a kind of IN718 alloy piece heat treatment method.The method comprises the following steps: S1, the forging of material IN718 is loaded into heating furnace, heating temperature is raised to solid solution temperature 950~980 DEG C, and is kept at 950~980 DEG C for 1~1.5h;S2, the forging after keeping warm is immediately water cooled;S3, the forging after water cooling is placed into heating furnace and is aged, and the heating rate is controlled 40~60 DEG C / h, and is raised to 690-730 DEG C, and is kept at 690~730 DEG C for 7~9h after furnace cooling to 614~630 DEG C / h, and is kept at 614~630 DEG C for 7~8h after furnace cooling, and is discharged and cooled.The IN 718 alloy piece heat treated by this method can be stable to reach 650 DEG C, 760Mpa condition, and the endurance time is not less than 25h.This method can not only be used for the heat treatment of IN718 alloy turbine disc, but also can be used for the heat treatment of other large IN 718 alloy pieces.

Description

Technical Field

[0001] This invention relates to the field of IN718 alloy parts processing, and particularly to a heat treatment method for IN718 alloy parts. Background Technology

[0002] Jet engines are the preferred power source for aircraft, and the gas turbine disk is the core component of a jet engine. Jet engines are characterized by their light weight, high power, and relatively simple structure.

[0003] One effective way to improve jet engine performance is to increase turbine inlet temperature, which requires high-performance turbine disks. Improving the durability of turbine disks can reduce engine weight and increase engine efficiency. Currently, jet engine turbine disks mainly use IN718 alloy, an Inconel 718 alloy, a precipitation-hardening nickel-chromium-iron alloy containing niobium and molybdenum. It possesses high strength, good toughness, and corrosion resistance in both high and low temperature environments below 650°C. Currently, IN718 alloy turbine disks are produced through forging and heat treatment. The turbine disk forging diameter is approximately Φ600mm, weighs about 500kg, and has a durability of no less than 25 hours at 650°C / 690MPa. However, when the stress condition is increased from 690MPa to 760MPa, the durability cannot reach 25 hours. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a heat treatment method for improving the creep performance of large IN718 alloy parts. The creep performance of forgings obtained by this heat treatment method can be stably maintained at 650℃ and 760MPa, with a creep time of not less than 25h.

[0005] The heat treatment method for improving the creep rupture properties of large IN718 alloy parts disclosed in this invention includes the following steps:

[0006] S1. Place the forging of IN718 material into the heating furnace, heat it to the solution temperature of 950-980℃, and hold it at 950-980℃ for 1-1.5 hours.

[0007] S2. Immediately after the heat preservation is completed, the forgings are water-cooled;

[0008] S3. Place the water-cooled forgings into a heating furnace for aging treatment. Control the heating rate to 40-60℃ / h, raise the temperature to 690-730℃, hold at 690-730℃ for 7-9h, then furnace cool to 614-630℃, hold at 614-630℃ for 7-8h, and then remove from the furnace for cooling.

[0009] Preferably, before step S1, surface defects of the forging are removed, and the step transition is smoothly transitioned by machining.

[0010] Preferably, the forging is a disc-shaped forging with a central hole. Before step S1, the excess material of the forging is removed, and the outer contour and the central hole of the forging retain an allowance of 3-5 mm.

[0011] Preferably, the forging is a disc-shaped forging, and in steps S1 and S3, the forging is placed at an angle of 15 to 30° with respect to the horizontal plane.

[0012] Preferably, in steps S1 and S3, the surface temperature of the turbine disk is actually measured by contacting the forging with a thermocouple.

[0013] Preferably, in steps S1 and S3, the heating rate of the forging is controlled at 50–80 °C / h.

[0014] Preferably, in steps S1 and S3, the furnace is preheated to 450–500°C before the forgings are loaded into the furnace.

[0015] Preferably, in step S2, the interval between the forging exiting the furnace and water cooling is no more than 50 seconds.

[0016] Preferably, in step S2, the cooling water temperature is controlled below 30°C.

[0017] Preferably, in step S2, the cooling water is circulated and stirred to achieve a water flow rate of 3-5 m / s.

[0018] Preferably, in step S3, the forging is furnace cooled to 614-630°C at a rate of 40-60°C / h.

[0019] Preferably, in step S3, the sum of the holding time at 690–730°C, the furnace cooling time, and the holding time at 614–630°C for the entire aging process should be 18 hours.

[0020] The beneficial effects of this invention are as follows: When IN 718 alloy parts are heat-treated using this method, the holding time and temperature are precisely controlled during the heat treatment process. Under the condition that part of the δ phase is dissolved back, the forgings also maintain ultra-fine grains and maintain fine grain strengthening. Subsequently, through a cooling method that is faster than that of traditional heat treatment, the re-precipitation of the δ phase is suppressed to the greatest extent. The composition of the dissolved δ phase is the same as that of the γ" and γ' phases. The dissolved δ phase is used to increase the content of the γ" and γ' phases during the subsequent aging process, thereby increasing the high-temperature creep performance of the disc. This method can not only be used for the heat treatment of IN 718 alloy turbine discs, but also for the heat treatment of other large IN 718 alloy parts. Detailed Implementation

[0021] The present invention will be further described below.

[0022] The large IN718 alloy parts in this invention refer to forgings with a diameter of Φ600~Φ1000mm, a thickness of 55~220mm, and a weight of 200~1000kg. Their heat treatment method includes the following steps:

[0023] S1. Place the forging of IN718 material into the heating furnace, heat it to the solution temperature of 950-980℃, and hold it at 950-980℃ for 1-1.5 hours.

[0024] S2. Immediately after the heat preservation is completed, the forgings are water-cooled;

[0025] S3. Place the water-cooled forgings into a heating furnace for aging treatment. Control the heating rate to 40-60℃ / h, raise the temperature to 690-730℃, hold at 690-730℃ for 7-9h, then furnace cool to 614-630℃, hold at 614-630℃ for 7-8h, and then remove from the furnace for cooling.

[0026] After the IN718 forging is die-forged, the distribution of the internal strengthening phases γ' and γ'" is uneven, with most precipitating along grain boundaries and some δ phase present. The strengthening effect of this phase is weaker than that of the γ' and γ'" phases, so solution treatment is required to dissolve the γ', γ'" and δ phases. The solution treatment effect of the above-mentioned precipitated phases is directly related to the cooling rate of the turbine disk. In step S1, the γ', γ'" and δ phases dissolve into the γ matrix at 950-980℃. However, rapid cooling is necessary during the cooling process to suppress the precipitation of the γ', γ'" and δ phases, because the size of the γ', γ'" and δ phases precipitated during continuous cooling is uneven, which is not conducive to improving performance. In step S2, through extensive experiments, the inventors controlled the solution treatment holding time to 1-1.5 hours. The cooling rate of water cooling is greater than that of the previous oil cooling, which can enhance the solution treatment effect. In step S3, a step-by-step aging method is adopted, with the precipitation of the γ' phase at 690–730℃ and the precipitation of the γ'" phase at 614–630℃. By adjusting the curing heating rate, the temperature gradient on the surface and core of the turbine disk is made uniform, that is, the precipitation time of the strengthening phase inside and outside is basically the same, thereby making the performance of each part of the forging basically consistent.

[0027] Surface defects and stepped transitions in forgings may cause stress cracking during heat treatment. Therefore, before step S1, surface defects such as folds, cracks, and fissures in the forging are removed, and stepped transitions are smoothly machined to prevent stress cracking during heat treatment.

[0028] Based on actual production experience, removing excess material from the forging before step S1 helps reduce the heat treatment cross-section and improve the cooling rate. For disc-shaped forgings with a center hole, similar to turbine disks, the center hole also needs to be machined. Only 3-5 mm of allowance should be retained on both the outer contour of the forging and the center hole; the rest should be removed.

[0029] When placing disc-shaped forgings, it is preferable to place them at an angle of 15 to 30 degrees to the horizontal plane. The principle of tilting is that when water flows and impacts the forging, a vortex is formed on the inclined surface of the lower surface of the forging, which carries away the bubble film in the high-temperature stage, advances the "film breaking" stage, improves the cooling rate of the lower surface of the forging, and reduces the difference in cooling rate between the upper and lower surfaces.

[0030] To ensure maximum temperature accuracy, steps S1 and S3 involve contacting a thermocouple with the forging to accurately measure the surface temperature of the turbine disk. Specifically, a forging is placed vertically below the temperature sensor port of the heating furnace. A 10-meter N-type thermocouple is used. After the forging is loaded into the furnace, the thermocouple is inserted directly above it, ensuring contact between the thermocouple and the forging to accurately measure its surface temperature. The connected external thermocouple precisely measures the turbine disk temperature, preventing temperature deviations caused by improper precipitate distribution. Accurately measuring the time it takes for the turbine disk to reach its target temperature ensures consistent heating times for each batch, guaranteeing batch stability.

[0031] In steps S1 and S3, the heating rate of the forging is preferably controlled at 50–80 °C / h. To better control the heating rate, the furnace is preheated to 450–500 °C before the forging is loaded into the furnace. Preheating improves the temperature field distribution inside and outside the forging and reduces its non-uniformity.

[0032] After the heat treatment in step S1, water cooling should be performed as soon as possible. In step S2, the interval between the forging exiting the furnace and water cooling should not exceed 50 seconds, and preferably not exceed 30 seconds. Because a cooling rate higher than conventional oil cooling is required, the cooling water temperature should be further controlled below 30°C. The inventors discovered that generating a fluid field by stirring the water tank during the cooling process can further enhance the solution treatment effect. Therefore, in step S2, the cooling water is circulated and stirred to achieve a flow rate of 3-5 m / s, resulting in a better solution treatment effect. The turbine disk temperature should be reduced to 10-30°C from room temperature. The turbine disk should then be lifted out of the water surface to remove surface moisture, facilitating the next step.

[0033] Step S3 employs a step-by-step aging method. After the precipitation of the γ' phase at 690–730℃, it is preferable to furnace cool to 614–630℃ at a rate of 40–60℃ / h to precipitate the γ'" phase. Throughout the entire aging process, the sum of the holding time at 690–730℃, the furnace cooling time, and the holding time at 614–630℃ should be 18–20 hours.

[0034] In steps S1 and S3, stirring fans should be added to the solution heating furnace and aging heating furnace to ensure heating uniformity. The temperature uniformity of the solution heating furnace should meet the AMS 2750 requirement of ±10℃, and the temperature uniformity of the aging heating furnace should meet the AMS 2750 requirement of ±5℃.

[0035] The present invention was used to perform heat treatment on a certain type of turbine disk in a certain factory. The turbine disk has a size of Φ600×100mm.

[0036] Example 1:

[0037] 1. Roughly machine the turbine disk forging formed by die forging to remove surface defects such as folds, cracks, and fissures. Smooth the transition part of the forging with steps by machining. Machining the center hole with a radial allowance of 3-5mm and the outer contour also with a allowance of 3-5mm.

[0038] 2. Place a total of two turbine discs on a special material tray, and specifically place one turbine disc vertically below the temperature measuring hole of the heating furnace to complete the material preparation.

[0039] 3. Prepare a 10-meter N-type thermocouple (accuracy ±3℃). Install the turbine disk into the heating furnace, inserting the thermocouple directly above the heating element to ensure contact between the thermocouple and the turbine disk, and accurately measure the surface temperature of the turbine disk. Close the furnace door and turn on the power for heating.

[0040] 4. Raise the temperature to 970℃±10℃, using an external thermocouple as the reference. Hold at 970℃±10℃ for 1 hour, then immediately remove the turbine disk from the furnace for water cooling.

[0041] 5. Place the turbine disk in a heating furnace for aging treatment. Control the heating rate at 50±10℃ / h, raise it to 720℃±10℃, and use an external thermocouple as the reference temperature. Hold it at 720℃±10℃ for 8 hours, then furnace cool it to 622±8℃ at 50±10℃ / h. Hold it at 622±8℃ for 8 hours, and then remove the turbine disk from the furnace for cooling.

[0042] After heat treatment, the turbine disk forging was subjected to physical and chemical tests, and the creep performance of each part tested was better than that of Comparative Example 1.

[0043] Example 2:

[0044] 1. Roughly machine the turbine disk forging formed by die forging to remove surface defects such as folds, cracks, and fissures. Smooth the transition part of the forging with steps by machining. Machining the center hole with a radial allowance of 3-5mm and the outer contour also with a allowance of 3-5mm.

[0045] 2. Place a total of two turbine disks on the same special material tray as in Example 1. Specifically, place one turbine disk vertically below the temperature measuring hole of the heating furnace to complete the material preparation. The turbine disk plane is placed at a 15° angle to the material tray.

[0046] 3. Prepare a 10-meter N-type thermocouple (accuracy ±3℃). Install the turbine disk into the heating furnace, inserting the thermocouple directly above the heating element to ensure contact between the thermocouple and the turbine disk, and accurately measure the surface temperature of the turbine disk. Close the furnace door and turn on the power for heating.

[0047] 4. Raise the temperature to 960±10℃, using an external thermocouple as the reference. Hold at 960±10℃ for 1.5 hours, then immediately remove the turbine disk from the furnace for water cooling.

[0048] 5. Place the turbine disk in a heating furnace for aging treatment. Control the heating rate at 50±10℃ / h, raise it to 700±10℃, and use an external thermocouple as the reference temperature. Hold it at 700±10℃ for 8 hours, then furnace cool it to 622±8℃ at 50±10℃ / h. Hold it at 622±8℃ for 8 hours, and then remove the turbine disk from the furnace for cooling.

[0049] After heat treatment, the turbine disk forging was subjected to physical and chemical tests, and the creep performance of each part tested was better than that of Comparative Example 1.

[0050] Comparative Example 1

[0051] 1. The turbine disk forging formed by die forging is not rough machined, but only polished to remove forging defects such as folds and cracks that are visible to the naked eye.

[0052] 2. Place two turbine discs flat on the same special material tray as in Example 1. Specifically, place one turbine disc vertically below the temperature measuring hole of the heating furnace to complete the material preparation.

[0053] 3. Prepare a 10-meter N-type thermocouple (accuracy ±3℃). Install the turbine disk into the heating furnace, inserting the thermocouple directly above the heating element to ensure contact between the thermocouple and the turbine disk, and accurately measure the surface temperature of the turbine disk. Close the furnace door and turn on the power for heating.

[0054] 4. Raise the temperature to 970±10℃, using an external thermocouple as the reference. Hold at 970±10℃ for 1 hour, then immediately remove the turbine disk from the furnace for oil cooling.

[0055] 5. Place the turbine disk in a heating furnace for aging treatment. Control the heating rate at 100±10℃ / h, raise it to 720±10℃, hold it at 720±10℃ for 8 hours, then furnace cool it to 620±8℃, hold it at 620±8℃ for 8 hours, and then remove the turbine disk from the furnace for cooling.

[0056] The turbine disk forgings after heat treatment according to the above embodiments were subjected to a creep rupture test, and the results are as follows:

[0057]

Claims

1. A heat treatment method for improving the creep rupture performance of large IN718 alloy parts, characterized in that, Includes the following steps: S1. Place the forging of IN718 material into the heating furnace, heat it to the solution temperature of 950-980℃, and hold it at 950-980℃ for 1-1.5 hours. S2. Immediately after the heat preservation is completed, the forgings are water-cooled; the interval between the forgings coming out of the furnace and water cooling is no more than 50 seconds, the cooling water temperature is controlled below 30℃, and the cooling water is circulated and stirred so that the water flow rate reaches 3-5m / s. S3. Place the water-cooled forgings into a heating furnace for aging treatment. Control the heating rate to 40-60℃ / h, raise the temperature to 690-730℃, hold at 690-730℃ for 7-9h, then furnace cool to 614-630℃, hold at 614-630℃ for 7-8h, and then remove from the furnace for cooling. The forging is a disc-shaped forging with a central hole. Before step S1, the excess material of the forging is removed, and the outer contour and the central hole of the forging are both left with an allowance of 3 to 5 mm. When placing disc-shaped forgings, the forgings should be placed at an angle of 15 to 30 degrees to the horizontal plane. In step S3, the forgings are furnace cooled to 614-630℃ at a rate of 40-60℃ / h.

2. The heat treatment method for improving the creep rupture performance of large IN718 alloy parts as described in claim 1, characterized in that: Before step S1, surface defects of the forging are removed, and the step transition is smoothly smoothed by machining.

3. The heat treatment method for improving the creep rupture performance of large IN718 alloy parts as described in claim 1, characterized in that: In steps S1 and S3, the surface temperature of the turbine disk is measured by contacting the forging with a thermocouple.

4. The heat treatment method for improving the creep rupture performance of large IN718 alloy parts as described in claim 1, characterized in that: In steps S1 and S3, the furnace is preheated to 450-500°C before the forgings are loaded into the furnace.

5. The heat treatment method for improving the creep rupture performance of large IN718 alloy parts as described in claim 1, characterized in that: In step S3, the sum of the holding time at 690–730℃, the furnace cooling time, and the holding time at 614–630℃ should be 18–20 hours.

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