Variable-cross-section high-temperature alloy casting and machining method and application thereof

Abstract

The invention belongs to the technical field of high-temperature alloy material processing, and particularly relates to a variable-cross-section high-temperature alloy casting and a processing method and application thereof. The processing method of the variable-cross-section high-temperature alloy casting comprises the following steps: carrying out vacuum melting, variable-cross-section casting mold processing, integrated low-pressure casting mold filling and staged low-pressure sequential directional solidification on high-temperature alloy to obtain the variable-cross-section high-temperature alloy casting, the single-side thick-wall, medium-wall and thin-wall machining surfaces of the variable-cross-section high-temperature alloy casting are sequentially subjected to simultaneous integrated machining, homogenizing heat treatment, aging treatment, stress annealing treatment, vibration aging treatment and grinding, and a variable-cross-section high-temperature alloy casting product is obtained. According to the method, the problems that an existing variable cross-section high-temperature alloy casting is large in casting solidification stress, uneven in machining stress, large in machining deformation and prone to generating cracks at the variable cross section are solved, and then machining of the large complex variable-wall-thickness integrated casting uniform in directional structure, small in deformation and excellent in quality is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-temperature alloy material processing, and particularly relates to a variable cross-section high-temperature alloy casting and a processing method and application thereof. BACKGROUND

[0002] High-temperature alloys are widely used in the fields of aerospace, energy, chemical industry and the like due to excellent high-temperature strength, oxidation resistance and creep resistance. With the improvement of the performance of an aero-engine, the key components of the aero-engine made of high-temperature alloys are continuously developed in the direction of complexity and thin-walledness. For example, the wall thickness of 80% of castings such as a certain turbine rear casing, diffuser and turbine blade is less than 3 mm, and the castings are in a hollow structure. The minimum wall thickness is only 1 mm. The sudden change in cross-section thickness leads to a difference of more than 10 times in the wall thickness of different parts of the castings. Although such a design helps to reduce weight and improve performance, it brings great challenges to the manufacturing process. In the process of liquid precision forming, from wax mold injection forming, slurry sand coating to alloy pouring, more than ten processes are involved, and thousands of parameters are involved. The size deformation mechanism of the castings is very complex, and the size deformation law is difficult to accurately and quantitatively predict. These factors together lead to the problem of size out-of-tolerance, which reduces the aerodynamic performance of the engine and reduces the assembly precision.

[0003] The large-diameter variable cross-section high-temperature alloy cartridge structure has the following characteristics: the part is composed of a large-diameter rotating conical cylinder, a convex boss on the outer circumference and a hook on the inner circumference, the maximum diameter size is 2100 mm, a plurality of convex bosses are arranged on the outer circumference, the thinnest wall thickness of the convex boss is only 1.8 mm, and the part belongs to a large-diameter ultra-thin-walled part. However, during the casting process of the large and complex variable cross-section high-temperature alloy casting, due to the large diameter size of the casting, the large difference in wall thickness of different parts and the inconsistent cooling rate, the grain size and phase distribution are not uniform, the high-temperature alloy usually has a wide solidification temperature range (more than 150℃), the paste zone in the thick section lasts for a long time, the high-temperature alloy has high high-temperature strength and low thermal conductivity, and the casting bears a large thermal stress (shrinkage stress) during the cooling process, and the shrinkage amount is large, so the thermal cracks (tears) along the grain are easily generated at the hot spots of the casting and the cross-section mutation, resulting in the casting being scrapped. In addition, the high-temperature alloy has high hardness and toughness, the traditional processing method has low efficiency and generates large cutting force, so the surface residual stress value of the part is high, thereby generating large processing deformation. Taking the GH4738 high-temperature alloy casting as an example, the processing difficulties are as follows: 1) high hardness and difficult processing; the part has a large processing diameter, the wall thickness of the convex boss on the outer circumference is ultra-thin, there are many circumferential convex bosses, large stress is easily generated during milling of the convex boss, and the wall thickness of the reinforcing rib, support structure and connecting part is very thick, thereby causing deformation of the part. 2) the upper and lower structures are used to apply pressure to the outer surface of the cartridge, because the wall thickness difference between the upper and lower installation edges and the cone (t=0.8-1.0 mm) is large, the deformation amount is difficult to control during the correction process, and the "misalignment" condition is easily generated, thereby making it difficult to guarantee the wall thickness tolerance, the problem of deformation of the thin-walled part caused by stress is difficult to solve, although long-time aging treatment or heat treatment can release stress to a certain extent, but it cannot meet the stress release requirements of the variable cross-section high-temperature alloy casting.

[0004] Therefore, it is urgent to seek a processing method which can effectively solve the deformation of the variable cross-section high-temperature alloy casting caused by stress. SUMMARY

[0005] In view of the problems existing in the prior art, the purpose of the present application is to provide a variable cross-section high-temperature alloy casting and a processing method and application thereof, so as to solve the problem that the existing processing method of the variable cross-section high-temperature alloy casting easily generates large stress, thereby causing large processing deformation (the maximum can be more than 3 mm); the problem that the grain size and phase distribution of the existing variable cross-section high-temperature alloy casting are not uniform due to the large size of the casting, the inconsistent wall thickness and the inconsistent cooling rate; the problem that the solidification time of the variable cross-section high-temperature alloy casting is inconsistent due to the inconsistent wall thickness, thereby further causing the problems of uneven processing deformation, uneven stress from casting solidification stress to processing stress and easy generation of cracks at the variable cross-section. Further, the large and complex variable wall thickness integrated casting is processed with uniform organization, small deformation and excellent quality.

[0006] The technical scheme of the present application is as follows: The present application provides a processing method of variable cross-section high-temperature alloy castings, comprising the following steps: Step 1: vacuum melting of high-temperature alloy, variable cross-section mold processing, integrated low-pressure casting filling and phased low-pressure sequential directional solidification to obtain variable cross-section high-temperature alloy castings; Step 2: simultaneously and integrally processing the single-sided thick wall and thin wall processing surface of the variable cross-section high-temperature alloy castings, homogenizing heat treatment, aging treatment, stress annealing treatment, vibration aging treatment and grinding to obtain variable cross-section high-temperature alloy casting products.

[0007] Simultaneously and integrally processing the single-sided thick wall and thin wall processing surface of the variable cross-section high-temperature alloy castings, one-time processing of thick wall, medium wall and thin wall, makes the processing efficiency higher. Homogenizing heat treatment of the castings can eliminate composition segregation and ensure uniform organization. Aging treatment of the castings can eliminate internal stress, stabilize organization, improve mechanical properties and processing performance, and improve the dimensional stability, reliability and comprehensive quality of the castings. Stress annealing of the castings can release the residual stress inside the castings. Vibration aging treatment of the castings can further release residual stress and reduce deformation. Further grinding treatment of the castings can ensure the surface precision of the castings. From the casting solidification stress to the processing stress, consistent control is performed. Through careful design of each processing step, stress reduction is carried out throughout the entire processing process, strict implementation of phased stress relief and fine low-stress processing, effective connection of each step, and finally the variable cross-section high-temperature alloy castings with uniform stress are obtained. Effectively solves the problem that the existing variable cross-section high-temperature alloy casting processing method is prone to generate large stress, resulting in large processing deformation (maximum can reach more than 3mm), and the castings are prone to cracks. Also solves the problem that cracks are prone to occur at the variable cross-section, resulting in the rejection of the castings.

[0008] Further, in the step 1, further comprising: performing mold flow analysis on the process of integrated low-pressure casting filling and phased low-pressure sequential directional solidification, judging the local high stress area, and removing the surface stress deformation layer of the local high stress area caused by the solidification process by milling and local annealing process; the high stress area refers to the area with stress > 500MPa.

[0009] Further, in the step 2, the single side refers to the flat surface of one side of the variable cross-section high-temperature alloy casting. The mold flow analysis software is used to analyze the filling and solidification process of the casing casting, to determine the high stress area with stress > 500 MPa, and then the milling and local annealing process is used to remove the surface stress deformation layer caused by the solidification process, so that the tensile stress and compressive stress generated in the casting and machining processes can be offset, thereby effectively controlling the deformation of the high-temperature alloy thin wall after stress release, and the product after machining has good stability and reliability.

[0010] Further, the cross-section thickness of the variable cross-section high-temperature alloy casting changes from 3 mm to 200 mm; the thick wall is the cross-section thickness of the variable cross-section high-temperature alloy casting at 51-200 mm, the medium wall is the cross-section thickness of the variable cross-section high-temperature alloy casting at 6-50 mm, and the thin wall is the cross-section thickness of the variable cross-section high-temperature alloy casting at 3-5 mm. The single-side thick wall and thin wall machining surface of the variable cross-section high-temperature alloy casting is simultaneously and integrally machined, specifically including: first filling the thin wall and medium wall with plaster to make the thickness of the thin wall and medium wall consistent with the thickness of the thick wall, and then simultaneously milling the thick wall, medium wall and thin wall, and using a milling cutter for the milling.

[0011] Further, the cross-section thickness changes in a non-continuous cliff type, forming a clear "step" or "corner", and the non-continuous cliff type change refers to the sudden and discontinuous jump change of the cross-section thickness of the variable cross-section high-temperature alloy casting between adjacent regions.

[0012] During the machining process of the variable cross-section high-temperature alloy casting, the thick wall has small machining strain, the thin wall has large machining strain, the thicker parts and the thinner parts have different stress and deformation degrees, which leads to the problem of overall workpiece deformation. In order to overcome this problem, the lower part of the 3-5 mm thin wall is first filled with plaster to make the thickness consistent with that of the thick wall, and then the thick wall and the thin wall are simultaneously milled. In this way, the stress on the workpiece during machining is uniform, and the machining deformation is also uniform. Filling the thin wall area with plaster can reduce clamping deformation. Simultaneous one-time machining can improve machining efficiency.

[0013] Wherein, during the milling of the thick wall, a hydraulic expansion mandrel is required.

[0014] Further, the milling adopts a layered milling strategy, and the milling depth of each layer is 0.5-1 mm.

[0015] By using the layered milling strategy, the residual stress generated by the machining can be further reduced to reduce the machining deformation.

[0016] Further, the milling machining uses a hard alloy or ceramic cutter.

[0017] By using a hard alloy or ceramic cutter for high-speed milling and by setting the milling speed and feed speed, the residual stress value generated by the large cutting force can be effectively reduced, and the machining deformation can be further reduced.

[0018] Further, the local annealing process uses high-frequency or intermediate-frequency alternating current to generate eddy current in the conductor (castings), and the high-stress area is heated by resistance; millimeter or sub-millimeter local area uses a high-power laser beam to scan the surface of the high-stress area, and local heating is performed by converting light energy into heat energy.

[0019] Among them, the frequency range of the high-frequency alternating current is 100-300Hz, and the frequency range of the intermediate-frequency current is 30-80kHz. The power of the high-power laser beam scanning is 50-80mw.

[0020] Further, the high-power laser beam is generated by a fiber laser or a semiconductor laser.

[0021] Further, in step 1, a three-dimensional scanner is also used to scan the entire solidified variable cross-section superalloy casting to form point cloud data, and then the deformation caused by the casting stress and the actual three-dimensional model size difference are judged.

[0022] Further, before milling and grinding machining of the casting, the residual stress of the casting needs to be detected, and the machining parameters are adjusted according to the detection results, and the areas with high residual stress are preferentially machined. At the same time, during the machining process, online measurement is implemented to measure the size, shape, position accuracy and surface quality of the casting, and the control accuracy is controlled.

[0023] Detecting the distribution of residual stress of the casting and adjusting the machining parameters according to the detection results can avoid the deformation of the casting caused by the release of residual stress; by milling to efficiently remove a large amount of material, grinding to ensure surface accuracy, and online measurement to monitor and correct errors in real time, the combination of the three can significantly improve the size accuracy and surface quality of the casting.

[0024] Preferably, the detection is performed using an X-ray diffractometer or an ultrasonic detector, and the detection selects the thin-walled area, variable cross-section and / or thick-walled part (i.e. thick-walled area) of the casting.

[0025] The residual stress of the casting is detected by using an X-ray diffractometer or an ultrasonic detector, and the specific part of the casting can be accurately detected to provide a reliable basis for subsequent processing parameter adjustment. The thin wall area and / or connecting part of the casting is selected during detection, which can ensure the accuracy of the detection data. The problems of large local machining amount and stress concentration in the subsequent machining process are solved.

[0026] Further, the variable cross-section mold processing comprises: designing a mold, and coating an anti-oxidation coating on the inner wall of the mold. The anti-oxidation coating composition is composed of aluminum oxide, zirconium oxide and boron nitride, and the mass percentage of the aluminum oxide, zirconium oxide and boron nitride is 20%:10%:70%. The thickness of the anti-oxidation coating is 0.1-0.2mm.

[0027] By coating the anti-oxidation coating on the inner wall of the mold, the alloy liquid can be prevented from reacting with the mold. The anti-oxidation coating made of a mixture of aluminum oxide, zirconium oxide and boron nitride can be uniformly distributed on the surface of the casting, ensuring the uniform thickness of the coating, thereby providing uniform protection and avoiding performance differences caused by too thin or too thick local coating, and improving the overall protection effect of the casting.

[0028] Further, in step 1, the process temperature of the vacuum melting is 1500-1600℃, and the holding time is 2-3h.

[0029] Further, the vacuum melting adopts vacuum induction melting (VIM) and vacuum arc remelting (VAR) double technology.

[0030] Further, the integrated low-pressure casting filling adopts a bottom pouring low-pressure pouring system, the temperature of the integrated low-pressure casting filling is 1450-1550℃, and the pressure of the low pressure is 0.2-0.5MPa.

[0031] Further, the staged low-pressure sequential directional solidification specifically comprises: controlling the pressure of the low pressure to be 0.2-0.5 MPa, increasing a shape cooling channel on one side of the variable cross-section mold, and embedding a heating cable on the other side of the variable cross-section mold; controlling the cooling water flow rate of the thick wall of the variable cross-section superalloy casting to be 1000-2000 L / h, and first performing directional solidification on one side of the thick wall; simultaneously, first controlling the heating temperature of the thin wall, the medium wall and the next thin wall area of the variable cross-section superalloy casting to be 600-1000 DEG C; simultaneously, performing temperature measurement at the variable cross-section position, when the temperature measurement at the variable cross-section position reaches the solid-liquid phase line of the variable cross-section superalloy, controlling the cooling water flow rate of the thin wall and the medium wall of the variable cross-section superalloy casting to be 800-1000 L / h, slowing down the directional solidification rate at the thin wall and the medium wall, and simultaneously performing temperature measurement at the next variable cross-section position, when the temperature measurement at the next variable cross-section position reaches the solid-liquid phase line of the variable cross-section superalloy, starting the cooling water on one side of the next thin wall area, and controlling the cooling water flow rate to be 600-800 L / h, so that the solid-liquid interface moving rate of the next thin wall area, the thin wall and the medium wall and the moving rate of the thick wall area are kept consistent; finally, the solid-liquid interface of the next thin wall area, the thin wall and the medium wall is moved to keep consistent with the solid-liquid interface of the thick wall area, and so on, and finally the solid-liquid interfaces at various positions of the thick wall, the medium wall, the thin wall and the next thin wall area reach the other side at the same time.

[0032] Further, the next thin wall area is named in the order of gradually thinning thickness of the variable cross-section superalloy casting; the wall thickness (cross-section thickness) of the next thin wall area is within the range of the wall thickness (cross-section thickness) of the thin wall.

[0033] The heating cable is embedded on the other side of the variable cross-section mold, the heating temperature of the thin wall, the medium wall and the next thin wall area of the variable cross-section superalloy casting is controlled to be 600-1000 DEG C, and the purpose is to reduce the melt cooling rate on this side.

[0034] Further, the solidification rate of the staged low-pressure sequential directional solidification is controlled to be 50-60 DEG C / min.

[0035] The staged low-pressure sequential directional solidification refers to: staged filling in the low pressure, and sequentially solidifying from the thick wall to the thin wall and from one side to the other side. In the process of directional solidification, the reinforced cooler of the thick wall is first started, the thick wall is first directionally solidified from one side to the other side, and the melt solid-liquid interface position is moved to the next variable cross-section position (such as the thin wall area, the medium wall area and the next thin wall area). Figure 1), and then the next stage of the variable cross-section thin wall cooler is started, and the melt of the next stage of the wall thickness is simultaneously directionally solidified, so that the solid-liquid interface remains flush, and when the melt solid-liquid interface position of the two thickness positions is pushed to the next variable cross-section position, the next stage of the variable cross-section thin wall cooler is started, and the melt of the next stage of the wall thickness is simultaneously directionally solidified, so that the solid-liquid interface remains flush, and so on, so that when the melt moves from one side to the other side, the final solidification end time of different wall thickness positions is basically consistent. In this way, the casting solidification time of the same section at different positions is basically consistent, the stress is released more, the stress is uniformly released, and the deformation and cracks caused by the difference in casting stress at different positions are reduced.

[0036] The integrated low-pressure casting filling and staged low-pressure sequential solidification technology uses gas pressure (0.2-0.5 MPa) to smoothly inject molten metal from the bottom of a sealed crucible through a riser tube into a mold, and complete crystallization and solidification under pressure. The low-pressure pressure control of the integrated low-pressure casting filling and staged low-pressure sequential solidification is 0.2-0.5 MPa, because the density of the high-temperature alloy melt is about 8.8 g / cm 3 Therefore, low-pressure casting at about 2-5 atmospheres is required to make the melt fill from the bottom to the top smoothly and without turbulence.

[0037] By controlling the process temperature and holding time of vacuum melting, the composition can be homogenized, the removal of impurities and gas can be promoted, the flowability can be improved, and the integrated low-pressure casting filling temperature can be accurately controlled, thereby improving the alloy liquid purity and the casting forming quality and performance. Using vacuum induction melting (VIM) and vacuum arc remelting (VAR) technologies to melt the high-temperature alloy can ensure the purity of the alloy liquid, reduce the content of gas and inclusions, and also ensure the uniformity of the alloy composition. Setting the integrated low-pressure casting filling temperature to 1450-1550℃ and using a bottom pouring system can effectively reduce oxidation and inclusions during the flow of the alloy liquid. Coating the inner wall of the pouring channel with refractory material can prevent the alloy liquid from reacting with the channel. Because the cooling rates of the thick and thin walls of the continuously variable cross-section high-temperature alloy casting are not consistent, the solidification rates are also not consistent, with the solidification rate of the 3-5mm thin wall reaching more than 125℃ / min and the solidification rate of the 51-200mm thick wall reaching less than 5℃ / min, with the difference in solidification rates of the thick and thin walls reaching more than 120℃ / min. In the process of phased low-pressure sequential directional solidification, the thick wall is first solidified by starting the reinforcement cooler, and then the melt solid-liquid interface position is moved to the next variable cross-section position, and the cooler of the next stage variable cross-section thin wall is started to solidify the melt of the next stage wall thickness synchronously, and when the melt solid-liquid interface position of the two thicknesses is moved to the next variable cross-section position, the cooler of the next stage variable cross-section thin wall is started, and so on, so that the solidification time of different positions is basically consistent when the melt moves from one side to the other side. In this way, the casting solidification time of different positions at the same cross-section is basically consistent, the stress is released more, and the deformation and cracks caused by the difference in casting stress of different positions are reduced. Thus, the problems of uneven grain size and phase distribution due to the large size of the existing variable cross-section high-temperature alloy casting, the inconsistency of wall thickness, and the inconsistency of cooling time during casting are effectively solved, and the problem of uneven machining deformation and uneven stress from casting solidification to machining is further solved.

[0038] Among them, the way to change the directional solidification rate of different wall thicknesses is to add a shaped cooling channel on one side of the variable cross-section mold and pre-embed a heating cable at the other position of the variable cross-section mold; by increasing or decreasing the water cooling intensity, the directional solidification rate is changed, the cooling water flow of the thick wall is increased, and the solidification rate of the thick wall is accelerated; the heating cable in the thin wall is started first, and then the cooling water flow in the thin wall is reduced to slow down the directional solidification rate of the thin wall.

[0039] Further, in step 2, the homogenization heat treatment comprises: placing the variable cross-section superalloy casting in an inert atmosphere, then heating to 800℃ at a first heating rate, and then heating to 1040-1160℃ at a second heating rate, and then holding for treatment; the first heating rate is greater than the second heating rate. Further, the aging treatment comprises: heating the variable cross-section superalloy casting to 700-800℃, holding for treatment, and then cooling. Further, the stress annealing treatment comprises: heating the variable cross-section superalloy casting to 500-600℃, holding for treatment, and then cooling to room temperature in stages. Further, the vibration aging treatment has a frequency of 50-100Hz and a vibration time of 30-60min. Further, the grinding has a grinding speed of 30-50m / s and a feed speed of 0.01-0.02mm / turn.

[0040] The homogenization heat treatment is performed in stages, which can effectively avoid thermal stress concentration; the inert gas is introduced during the homogenization heat treatment, which can prevent the oxidation of the casting surface. When the casting is subjected to aging treatment, heating to 700-800℃, holding for 2-4 hours, and then cooling can further improve the strength and toughness of the alloy. The stress annealing treatment can effectively eliminate internal stress, improve the uniformity of the structure, avoid new stress generated during cooling, and improve the performance and stability of the casting. The vibration aging treatment has a frequency of 50-100Hz and a vibration time of 30-60min, which can ensure uniform stress release. The grinding speed is set to 30-50m / s, which can disperse the grinding force, reduce the grinding force acting on the casting per unit time, thereby reducing the residual stress, and also helps to obtain better surface finish and reduce surface roughness. The feed speed is set to 0.01-0.02mm / turn, which can reduce vibration during grinding and further reduce machining deformation.

[0041] Further, the inert gas is argon.

[0042] Further, the grinding process adopts a step-by-step grinding strategy. In the rough grinding stage, a larger back engagement and feed amount are used, and the engagement amount can reach 0.3-0.4mm each time. In the fine grinding stage, the engagement amount is 0.001-0.002mm each time, and size measurement and calibration are performed after each grinding step.

[0043] Through step-by-step grinding and multiple measurements, the machining precision can be ensured and the machining deformation can be reduced.

[0044] Further, the grinding process adopts a cubic boron nitride grinding wheel.

[0045] The cubic boron nitride grinding wheel has extremely high hardness and wear resistance, can maintain good performance at high temperature, and can realize high-precision grinding processing.

[0046] Further, the first heating rate is 10℃ / min.

[0047] Further, the second heating rate is 5℃ / min.

[0048] Further, the holding time of the homogenization heat treatment is 4-6h.

[0049] Further, the holding time of the aging treatment is 2-4h.

[0050] Further, the cooling adopts air cooling or oil cooling, the cooling speed of the air cooling is 100℃ / min, and the oil cooling adopts quenching oil cooling.

[0051] Further, the holding time of the stress annealing treatment is 2-3h.

[0052] Further, the segmented cooling to room temperature comprises: cooling to 300℃ at a cooling rate of 100℃ / min, and then cooling to room temperature at a cooling rate of 10℃ / min.

[0053] By controlling the cooling speed to be 5-10℃ / min, the uniform cooling can be ensured.

[0054] Further, the high-temperature alloy is a nickel-based high-temperature alloy GH4738, and comprises the following components in percentage by mass: Ni≥72%, Cr is 14%-17%, Fe is 6%-10%, C≤0.15%, Si≤0.5%, Mn≤1.0%, S≤0.015%, Cu≤0.5% and Ti≤0.5%.

[0055] Further, the high-temperature alloy is a nickel-based high-temperature alloy K4169, and comprises the following components in percentage by mass: Ni is 50%-55%, Cr is 17%-21%, Nb is 4.7-5.5%, Mo is 2.8-3.3%, Ti is 0.65-1.15%, Al is 0.2-0.8%, C≤0.08%, Si≤0.35%, Mn≤0.35%, S≤0.015%, Cu≤0.3%, and the rest is Fe.

[0056] Further, the high-temperature alloy is GH2132, and comprises the following components in percentage by mass: Ni is 24%-27%, Cr is 13.5%-16%, Mo is 1-1.5%, Ti is 1.7-2.3%, V is 0.1-0.5%, Al is 0.2-0.3%, C≤0.08%, Si≤1%, Mn≤2%, S≤0.03%, P≤0.03%, and the rest is Fe.

[0057] The application further provides the variable cross-section high-temperature alloy casting prepared by the processing method.

[0058] The application further provides application of the processing method in preparation of an integrated casing casting, a diffuser and / or a turbine disc-blade.

[0059] The application has the following beneficial effects: First, the cooling rate is optimized by computer simulation, so that the cooling of each part of the casting is uniform, and thermal stress is reduced; the integrated low-pressure casting filling temperature is set to 1450-1550 DEG C, and a bottom pouring system is used, so that oxidation and inclusions in the alloy liquid during flow can be effectively reduced; the inner wall of the pouring channel is coated with refractory material, so that the alloy liquid can be prevented from reacting with the channel. Since the cooling time and solidification rate of the thick wall, the medium wall and the thin wall of the variable cross-section high-temperature alloy casting are inconsistent, in the process of phased low-pressure sequential solidification, a conformal cooling channel is added on one side of the variable cross-section casting, and a heating cable is pre-embedded on the other side; the cooling water flow rate of the thick wall is controlled to be 1000-2000 L / h, so that the thick wall is sequentially solidified; at the same time, the heating temperature of the thin wall, the medium wall and the next thin wall of the variable cross-section high-temperature alloy casting is controlled to be 600-1000 DEG C; at the same time, the temperature at the variable cross-section position is measured, and when the temperature at the variable cross-section position reaches the solid-liquid phase line of the variable cross-section high-temperature alloy, the cooling water flow rate of the thin wall and the medium wall of the variable cross-section high-temperature alloy casting is controlled to be 800-1000 L / h, so that the solidification rate of the thin wall and the medium wall is slowed down. That is, the cooling intensity of the thick wall is controlled to be large, and the cooling intensity of the medium wall and the thin wall is controlled to be small, so that the solidification rate of the thick wall, the medium wall and the thin wall casting at the same horizontal plane is consistent, the casting solidification time of different positions at the same cross-section is basically consistent, stress release is more, stress release is uniform, and deformation and cracks caused by the difference in casting stress of different positions are reduced.

[0060] Second, the variable cross-section casting is subjected to segmented uniform heat treatment, so that thermal stress concentration can be effectively avoided; the thickness difference between the thick wall position and the thin wall position is calculated, so that the time required for homogenization annealing of the thick wall and the thin wall position is controlled in segments; inert gas is introduced during the homogenization heat treatment process, so that the surface of the casting can be prevented from being oxidized; when the casting is subjected to aging treatment, the strength and toughness of the alloy can be further improved by heating to 700-800 DEG C, holding for 2-4 hours, and then air cooling or oil cooling; the cooling speed is controlled to be 100 DEG C / min, so that uniform cooling can be ensured. The casting is subjected to stress annealing, so that the residual stress in the casting can be released.

[0061] Third, process the material, and perform flexible clamping to synchronously and integrally process the thick wall and the thin wall. The thick wall position adopts a hydraulic expansion mandrel, and the thin wall area is filled with gypsum to reduce clamping deformation. The milling speed is 280 m / min, the feed speed is 0.1-0.2 mm / tooth, the high-speed milling adopts a layered milling strategy, and the milling depth of each layer is 0.5-1 mm. The precision grinding process adopts a cubic boron nitride grinding wheel, the thin wall area grinding speed is 30-50 m / s, the feed speed is 0.01-0.02 mm / time, and the precision grinding process needs to be step-by-step ground and measured multiple times. The distribution of the residual stress of the casting is detected, and the processing parameters are adjusted according to the detection results, so that the deformation of the casting caused by the release of the residual stress can be avoided. The high-speed milling efficiently removes a large amount of material, the precision grinding guarantees the surface precision, the online measurement monitors and corrects the error in real time, and the combination of the three can significantly improve the size precision and the surface quality of the casting. The thin wall area and / or the connecting part of the casting is selected during the detection, so that the accuracy of the detection data can be ensured.

[0062] Fourth, the layered milling strategy can further reduce the residual stress generated during processing to reduce the processing deformation. The grinding speed is set to 30-50 m / s, the grinding force can be dispersed, the grinding force acting on the casting in a unit time can be reduced, the residual stress can be reduced, and better surface smoothness can be obtained and the surface roughness can be reduced. The feed speed is set to 0.01-0.02 mm / time, the vibration during grinding can be reduced, and the processing deformation can be further reduced. The grinding speed and the feed speed set during the precision grinding process can ensure the processing precision and reduce the processing deformation through step-by-step grinding and multiple measurements.

[0063] Fifth, the casting is subjected to vibration aging treatment after the machining is completed, the residual stress can be further released, and the deformation can be reduced. The vibration aging treatment frequency is set to 50-100 Hz, and the vibration time is set to 30-60 min, so that the stress release can be uniform.

[0064] In summary, the casting, heat treatment and machining process are more reasonable, the uniformity of the microstructure, the consistency of the performance, the excellent quality and the small processing deformation of the variable cross-section high-temperature alloy casting are realized. In the manufacturing process of the variable cross-section high-temperature alloy casting, the stress accumulation throughout the casting, heat treatment and machining chain is effectively controlled through strict implementation of the stage-by-stage stress release and fine low-stress processing strategy, so that the deformation risk of the final product is significantly reduced, the size precision and the performance stability are ensured, and the product quality and reliability are improved. The processing method is suitable for the manufacturing of complex variable cross-section high-temperature alloy castings, and has remarkable economic benefits and application prospects in the high-temperature alloy material processing technical field. BRIEF DESCRIPTION OF DRAWINGS

[0065] Figure 1A local view of the variable cross-section superalloy casting during integrated casting filling and solidification; Figure 2 A schematic view of the variable cross-section superalloy casting after filling with gypsum; Figure 3 A schematic view of the influence of cutting speed on milling stress, (a) shows the residual stress distribution when the cutting speed is 1000, (b) shows the residual stress distribution when the cutting speed is 1500, and (c) shows the residual stress distribution when the cutting speed is 2000; wherein, 1-milling cutter, 2-variable cross-section superalloy casting, 3-machining surface, 4-thick wall, 5-thin wall, 6-gypsum, 7-contoured cooling channel, 8-heating cable, 9-variable cross-section superalloy casting mold (variable cross-section mold), 10-liquid lifting pipe, 11-melt, 12-low-pressure casting furnace, 13-heat preservation crucible, 14-pressurizing system, 15-intermediate wall. DETAILED DESCRIPTION

[0066] The application will be further described in detail below by way of examples, but the application is not limited in any way by the examples.

[0067] In the following examples, as shown in Figure 1 and Figure 2 , the variable cross-section superalloy casting has the following characteristics: The cross-sectional thickness of the variable cross-section superalloy casting 2 varies from 3 mm to 200 mm, and the cross-sectional thickness wall thickness varies discontinuously in the form of a cliff, that is, the cross-sectional thickness suddenly and discontinuously jumps between adjacent regions, forming a clear "step" or "edge". When the cross-sectional thickness of the variable cross-section superalloy casting is 51-200 mm, it refers to a thick wall 4, when the cross-sectional thickness of the variable cross-section superalloy casting is 6-50 mm, it refers to an intermediate wall 15, and when the cross-sectional thickness of the variable cross-section superalloy casting is 3-5 mm, it refers to a thin wall 5. Large stress is easily generated at the variable cross-section, so staged low-pressure sequential directional solidification is adopted, and the thick wall 4 is allowed to solidify first, and when the solid-liquid interface solidifies to the intermediate wall 15 and the thin wall 5 of the next stage, the melt of the intermediate wall 15 and the thin wall 5 of the next stage is allowed to solidify again. In this way, when the solid-liquid interface of different wall thicknesses is pushed, the solid-liquid interfaces are all flush.

[0068] For example, Figure 1 , the cross-sectional thickness variation of the variable cross-section superalloy casting 2 in Figure 2 corresponds to Figure 1 , the cross-sectional thickness variation of the variable cross-section mold 9, which varies in the horizontal direction from left to right. For example, Figure 2 , the cross-sectional thickness variation of the variable cross-section superalloy casting 2 refers to a variation in the vertical direction from top to bottom.

[0069] The experimental materials used in the following examples of the application are as follows: A nickel-based superalloy GH4738, comprising the following components in mass percentage: Ni≥72%, Cr 14%-17%, Fe 6%-10%, C≤0.15%, Si≤0.5%, Mn≤1.0%, S≤0.015%, Cu≤0.5% and Ti≤0.5%.

[0070] A nickel-based superalloy K4169, comprising the following components in mass percentage: Ni 50%-55%, Cr 17%-21%, Nb 4.7-5.5%, Mo 2.8-3.3%, Ti 0.65-1.15%, Al 0.2-0.8%, C≤0.08%, Si≤0.35%, Mn≤0.35%, S≤0.015%, Cu≤0.3%, and the rest is Fe.

[0071] A superalloy GH2132, comprising the following components in mass percentage: Ni 24%-27%, Cr 13.5%-16%, Mo 1-1.5%, Ti 1.7-2.3%, V 0.1-0.5%, Al 0.2-0.3%, C≤0.08%, Si≤1%, Mn≤2%, S≤0.03%, P≤0.03%, and the rest is Fe.

[0072] The next thin-walled zone in the following embodiment 1 means: the next thin-walled zone is named in the order of gradually thinning thickness of the variable cross-section superalloy casting 2; the wall thickness (cross-section thickness) of the next thin-walled zone is within the wall thickness (cross-section thickness) range of the thin-walled zone 5.

[0073] Embodiment 1 A processing method of a variable cross-section superalloy K4169 machine case casting, comprising the following steps: 1. Vacuum melting of the superalloy by vacuum induction melting (VIM) and vacuum arc remelting (VAR) double technology; the process temperature of the vacuum melting is 1500-1600℃, and the holding time is 2-3h; the solid-liquid phase line of the alloy is 1254-1339℃, 1254℃ is the solidus, and 1339℃ is the liquidus.

[0074] 2. Processing of the variable cross-section mold 9 (variable cross-section superalloy casting mold 9): designing the mold, preparing the mold according to the design, and coating an oxidation-resistant coating on the inner wall of the mold; the oxidation-resistant coating is composed of aluminum oxide, zirconium oxide and boron nitride, and the mass percentage of aluminum oxide, zirconium oxide and boron nitride is 20%:10%:70%; the thickness of the oxidation-resistant coating is 0.1-0.2mm; 3. Integrated low-pressure casting filling: as Figure 1As shown, the low-pressure casting furnace 12 adopts a bottom pouring low-pressure pouring system for integrated low-pressure casting filling, the pressurizing system 14 adopts a low pressure of 0.3 MPa, and the temperature of the integrated low-pressure casting filling is 1450-1550℃; the low-pressure casting furnace 12 includes a pouring opening, a pouring channel and a pouring cup, and the inner wall of the pouring channel is coated with refractory material; The melt 11 of the molten metal is smoothly poured into the variable cross-section superalloy casting mold 9 from the bottom of the holding crucible 13 through the riser tube 10, and the low-pressure pressure control is 0.3 MPa, because the density of the superalloy melt 11 is about 8.8 g / cm 3 Therefore, low-pressure casting at about 2-5 atmospheres is required to make the melt 11 fill from the bottom to the top smoothly without turbulence. 4. Staged low-pressure sequential directional solidification: as shown in Figure 1 As shown, the staged low-pressure sequential directional solidification technology is adopted to perform staged sequential directional solidification under a low pressure of 0.2-0.5 MPa. A conformal cooling channel 7 is added to one side of the variable cross-section casting mold 9, and a heating cable 8 is pre-embedded on the other side of the variable cross-section casting mold 9. The cooling water flow rate of the thick wall 4 of the variable cross-section superalloy casting 2 is controlled to be 1000 L / h, one side of the thick wall 4 is first subjected to directional solidification, and the solidification rate is accelerated. At the same time, the heating temperature of the thin wall 5, the medium wall 15 and the next thin wall area of the variable cross-section superalloy casting 2 is controlled to be 900℃. At the same time, temperature measurement is performed at the variable cross-section position of the variable cross-section superalloy casting 2. When the temperature measurement at the variable cross-section position reaches the solid-liquid phase line 1254-1339℃ (1254℃ is the solidus and 1339℃ is the liquidus) of the variable cross-section superalloy, the cooling water flow rate of the thin wall 5 and the medium wall 15 of the variable cross-section superalloy casting 2 is controlled to be 800 L / h, the directional solidification rate at the thin wall 5 and the medium wall 15 is slowed down, and the moving rate of the solid-liquid interface of the thick wall area, the thin wall area and the medium wall area is kept consistent. At the same time, temperature measurement is performed at the next variable cross-section position. When the temperature measurement at the next variable cross-section position reaches the solid-liquid phase line 1254-1339℃ (1254℃ is the solidus and 1339℃ is the liquidus) of the variable cross-section superalloy, the cooling water at one side of the next thin wall area is started, and the cooling water flow rate is controlled to be 600 L / h, the water flow rate is weakened, the moving rate of the solid-liquid interface at the next thin wall area, the thin wall 5 and the medium wall 15 is kept consistent with the moving rate of the thick wall area. Finally, the solid-liquid interface at the next thin wall area, the thin wall 5 and the medium wall 15 is moved to keep consistent with the solid-liquid interface of the thick wall area, and so on, until the solid-liquid interfaces at all positions of the thick wall 4, the medium wall 15, the thin wall 5 and the next thin wall area reach the other side at the same time, as shown in Figure 1 .

[0075] The superalloy undergoes vacuum melting, variable-section casting, integrated low-pressure casting, and staged low-pressure sequential directional solidification to create a variable-section superalloy casting. A 3D scanner is used to scan the solidified superalloy casting as a whole, generating point cloud data. This data then allows for the determination of deformation caused by casting stress and discrepancies between the actual 3D digital model dimensions.

[0076] 5. Simultaneous integrated processing of thick-walled, medium-walled and thin-walled machining surfaces on one side of variable-section high-temperature alloy castings: Figure 2 As shown, mold flow analysis was performed during the integrated low-pressure casting process of mold filling and staged low-pressure sequential directional solidification to identify localized high-stress areas (high stress areas are defined as those with stresses greater than 500 MPa). Milling and local annealing were then used to remove the surface stress and deformation layer caused by the solidification process. First, the lower portions of the thin wall 5 and the medium wall 15 of the variable-section high-temperature alloy casting were filled with plaster 6 until their thickness matched that of the thick wall 4. Milling cutter 1 was then used for simultaneous milling. A layered milling strategy was employed, with each layer milling to a depth of 0.5 to 1 mm. The milling speed of milling is 200~300m / min, and the feed speed is 0.1~0.2mm / tooth; the local annealing process is to use high-frequency or medium-frequency alternating current to generate eddy current in the casting, and heat the high-stress area through resistance; the high-power laser beam is used to scan the surface of the high-stress area in the millimeter or sub-millimeter local area, and local heating is performed by converting light energy into heat energy; the high-power laser beam is generated by a fiber laser or a semiconductor laser.

[0077] 6. Perform homogenization heat treatment on variable-section high-temperature alloy castings: Place the variable-section high-temperature alloy castings in an inert atmosphere, then heat them to 800°C at a first heating rate, then heat them to 1040-1160°C at a second heating rate, and keep them warm for 4-6 hours; the first heating rate is greater than the second heating rate; the first heating rate is 10°C / min; the second heating rate is 5°C / min; 7. Perform aging treatment on variable-section high-temperature alloy castings: heat the variable-section high-temperature alloy castings to 700-800°C, keep warm for 2-4 hours, and then cool; use air cooling or oil cooling, the cooling rate of air cooling is 100°C / min, and oil cooling uses quenching oil cooling; 8. Stress annealing the variable-section high-temperature alloy casting: heat the variable-section high-temperature alloy casting to 500-600°C, keep it at this temperature for 2-3 hours, and then cool it down to room temperature in stages; the staged cooling to room temperature includes: cooling it down to 300°C at a cooling rate of 100°C / min, and then cooling it down to room temperature at a cooling rate of 10°C / min.

[0078] 9. Perform vibration aging treatment on variable-section high-temperature alloy castings: the frequency of vibration aging treatment is 50~100Hz, and the vibration time is 30~60min; 10. Grinding the variable cross-section high-temperature alloy casting: cubic boron nitride grinding wheel is used for grinding. The grinding speed of the grinding is 30-50 m / s, and the feed speed is 0.01-0.02 mm / turn; a step-by-step grinding strategy is used during grinding, the coarse grinding stage: the coarse grinding uses a larger back engagement and feed, and the engagement can reach 0.3-0.4 mm each time; the fine grinding stage: the fine grinding engagement is 0.001-0.002 mm each time, and size measurement and calibration are performed after each step of grinding.

[0079] Note: Before milling and grinding the casting, the residual stress of the casting needs to be detected by using an X-ray diffractometer or an ultrasonic detector. During detection, the thin-walled area, variable cross-section and thick-walled part (i.e. thick-walled area) of the casting are selected; and the processing parameters are adjusted according to the detection results, and the areas with high residual stress are processed first. At the same time, online measurement is implemented during processing to measure the size, shape, position accuracy and surface quality of the casting to control the accuracy.

[0080] The variable cross-section high-temperature alloy casting K4169 machine case casting is finally obtained by sequentially performing homogenization heat treatment, aging treatment, stress annealing treatment, vibration aging treatment and grinding on the variable cross-section high-temperature alloy casting.

[0081] Results: The influence of cutting speed on milling stress is shown in Figure 3 As the feed per tooth increases, the milling stress also shows a significant upward trend. First, analyze the residual stress distribution of the machined surface. When v=1000 r / min, the residual stress is about 337 MPa and is relatively uniform. When the cutting speed increases to v=1500 r / min, the distribution of the milling stress changes, and the residual stress value decreases to 310.8 MPa. The overall stress distribution pattern changes. The range of the high-stress area decreases, and the degree of stress concentration in some parts decreases. This indicates that as the cutting speed increases, the mechanical state during cutting changes, resulting in a change in stress distribution. When the cutting speed v=2000, the stress value also decreases, and the surface residual stress is about 298 MPa.

[0082] Example 2 The blade thin wall (3 mm), medium wall (40 mm) and disc thick wall (> 150 mm) transition area of the high-temperature alloy turbine disc-blade integrated casting have a large stiffness difference, are prone to vibration deformation, are difficult to control residual stress, have a high gradient residual stress caused by thermal-mechanical coupling effect during milling / turning, reduce fatigue life (especially in the mortise and tenon part), require a blade profile tolerance of less than or equal to 0.05 mm, a disc runout of less than or equal to 0.03 mm, and need to overcome processing deformation.

[0083] The method for casting forming and processing of a variable cross-section GH4738 high-temperature alloy turbine disc-blade integrated casting comprises the following steps: 1. Vacuum induction melting (VIM) and vacuum arc remelting (VAR) double-technology is used to vacuum melt the high-temperature alloy GH4738; the process temperature of the vacuum melting is 1500℃, the holding time is 3h, and a high-temperature alloy liquid is obtained; the solidus temperature of the alloy is 1260℃, and the liquidus temperature is 1350℃.

[0084] 2. Variable cross-section casting (variable cross-section high-temperature alloy casting mold) processing: a casting mold is designed for the variable cross-section GH4738 high-temperature alloy turbine disc-blade integrated casting, a ceramic shell mold is used as the casting mold, the casting mold is prepared according to the design, and an anti-oxidation coating is coated on the inner wall of the casting mold; the anti-oxidation coating is composed of aluminum oxide, zirconium oxide and boron nitride, and the mass percentage of aluminum oxide, zirconium oxide and boron nitride is 20%:10%:70%; the thickness of the anti-oxidation coating is 0.15mm; a conformal cooling channel is added to one side of the variable cross-section casting mold, and a heating cable is pre-embedded on the other side of the variable cross-section casting mold, which is used for subsequent staged low-pressure sequential directional solidification; 3. Integrated low-pressure casting filling: a bottom injection low-pressure pouring system is used in a low-pressure casting furnace for integrated low-pressure casting filling, the pressure system uses a low-pressure of 0.2MPa, and the temperature of the integrated low-pressure casting filling is 1500℃; the low-pressure casting furnace comprises a pouring port, a pouring channel and a pouring cup, and the inner wall of the pouring channel is coated with refractory material; The melt of the molten metal is smoothly poured into the variable cross-section high-temperature alloy casting mold from the bottom of the holding crucible through the riser pipe, and the low-pressure pressure is controlled to be 0.2MPa, because the density of the high-temperature alloy melt is about 8.8g / cm 3 Therefore, low-pressure casting at about 2~5atm is needed to make the melt fill from the bottom to the top smoothly without turbulence; 4. The low-pressure sequential directional solidification in stages is adopted to carry out directional solidification in stages under a low pressure of 0.2 MPa. A cooling channel is added to one side of the variable cross-section casting mold, and a heating cable is embedded in the other side of the variable cross-section casting mold. The cooling water flow rate of the thick wall (160 mm in thickness) of the variable cross-section superalloy casting is controlled to be 1200 L / h. The thick wall is first subjected to directional solidification, and the solidification rate is accelerated. At the same time, the heating temperature of the medium wall (40 mm in thickness) and the thin wall (3 mm in thickness) of the variable cross-section superalloy casting is controlled to be 1000℃. The temperature at the variable cross-section position of the variable cross-section superalloy casting is measured. When the temperature at the variable cross-section position reaches the solid-liquid phase line 1260-1350℃ of the variable cross-section superalloy (1260℃ is the solidus, and 1350℃ is the liquidus), the cooling water flow rate of the medium wall of the variable cross-section superalloy casting is controlled to be 900 L / h, and the temperature at the next variable cross-section position is measured. When the temperature at the next variable cross-section position reaches the solid-liquid phase line 1260-1350℃ of the variable cross-section superalloy, the cooling water flow rate of the thin wall is controlled to be 700 L / h. The directional solidification rate of the medium wall and the thin wall is slowed down, so that the migration rate of the solid-liquid interface of the thin wall region, the medium wall and the thick wall region is kept consistent. Finally, the solid-liquid interface of the medium wall and the thin wall is pushed to be consistent with the solid-liquid interface of the thick wall. In this way, the solid-liquid interfaces of the thick wall, the medium wall and the thin wall are simultaneously pushed to the other side.

[0085] After vacuum melting, variable cross-section casting mold processing, integrated low-pressure casting filling and low-pressure sequential directional solidification in stages, the variable cross-section superalloy casting is obtained. The variable cross-section superalloy casting obtained by solidification is scanned by a three-dimensional scanner to form point cloud data, and then the deformation caused by casting stress and the actual three-dimensional model size difference are judged.

[0086] 5. Simultaneous and integrated machining of the single-thick wall, medium wall and thin wall machining surface of the variable cross-section high-temperature alloy casting: during the process of integrated low-pressure casting and phased low-pressure sequential solidification, the mold flow is analyzed to determine the local high-stress area, the high-stress area refers to the area with stress > 500 MPa, and the surface stress deformation layer caused by the solidification process is removed by milling and local annealing process. The machining equipment is flexible clamping, the disc body uses hydraulic expansion mandrel, the blade area is filled with plaster to reduce clamping deformation, the lower part of the thin wall and medium wall of the variable cross-section high-temperature alloy casting is filled with plaster until the thickness of the thin wall and medium wall is consistent with the thickness of the thick wall (the thickness of the thick wall of the variable cross-section high-temperature alloy casting is 160 mm), and then synchronous milling is performed using a milling cutter; the milling strategy is layered milling, and the milling depth of each layer is 0.5 mm. The milling speed is 280 m / min, and the feed speed is 0.1 mm / tooth; the local annealing process is to generate eddy current in the casting by using high-frequency or medium-frequency alternating current, and heat the high-stress area through resistance; millimeter or sub-millimeter local area is scanned on the surface of the high-stress area by using a high-power laser beam, and local heating is performed by converting light energy into heat energy; the high-power laser beam is generated by a fiber laser or a semiconductor laser.

[0087] 6. Homogenization heat treatment of the variable cross-section high-temperature alloy casting: the variable cross-section high-temperature alloy casting is placed in an inert atmosphere, then heated to 800℃ at a first heating rate, and then heated to 1100℃ at a second heating rate, and held for 5h; the first heating rate is greater than the second heating rate; the first heating rate is 10℃ / min; the second heating rate is 5℃ / min; 7. Aging treatment of the variable cross-section high-temperature alloy casting: the variable cross-section high-temperature alloy casting is heated to 750℃ and held for 3h, and then cooled; the cooling is air cooling or oil cooling, the cooling speed of air cooling is 100℃ / min, and the oil cooling uses quenching oil cooling; 8. Stress annealing treatment of the variable cross-section high-temperature alloy casting: the variable cross-section high-temperature alloy casting is heated to 550℃ and held for 2h, and then cooled to room temperature in stages; the cooling to room temperature in stages includes: cooling to 300℃ at a cooling rate of 100℃ / min, and then cooling to room temperature at a cooling rate of 10℃ / min.

[0088] 9. Vibration aging treatment of the variable cross-section high-temperature alloy casting: the frequency of the vibration aging treatment is 80Hz, and the vibration time is 50min; 10. Grinding of variable-section high-temperature alloy castings: A cubic boron nitride grinding wheel is used for grinding. The grinding speed is 30 m / s, with a feed rate of 0.01 mm / pass. A step-by-step grinding strategy is employed: During the rough grinding phase, a larger back-cut and feed rate are used, with each pass reaching 0.3 mm. During the fine grinding phase, each pass is 0.001 mm deep, with dimensional measurement and calibration performed after each step. Precision grinding utilizes a cubic boron nitride grinding wheel, with a grinding speed of 30 m / s and a feed rate of 0.01 mm / pass in thin-walled areas. This precision grinding process requires step-by-step grinding and multiple measurements.

[0089] Note: Before milling or grinding castings, it is necessary to use an X-ray diffractometer or ultrasonic detector to test the casting's residual stress. During testing, select thin-walled areas, variable cross-sections, and thick-walled areas (i.e., thick-walled areas). Based on the test results, adjust machining parameters, prioritizing areas with high residual stress. During machining, perform online measurements to measure the casting's size, shape, positional accuracy, and surface quality to control precision.

[0090] The variable cross-section high temperature alloy casting is subjected to homogenization heat treatment, aging treatment, stress annealing treatment, vibration aging treatment and grinding in sequence, and finally a variable cross-section GH4738 high temperature alloy turbine disk-blade integrated casting is obtained. The high-temperature alloy blade disk is subjected to investment casting, turning, milling and annealing. During this process, the dimensions and residual stress of each part are monitored. Machining is performed on areas with dimensional deviations, and then residual stress monitoring is performed. If the residual stress is large, residual stress removal is performed. In this way, during the manufacturing process of high-temperature alloy castings, more residual stress is eliminated and dimensional accuracy is controlled. This process can increase the qualified rate of turbine disk-blade integrated components from 45% of the traditional process to more than 80%. At a cutting speed of v=2000m / min, the stress value is also reduced, and the surface residual stress is about 50MPa.

[0091] Example 3 The steps of the integrated casting-machining-aging forming method for the complex variable cross-section diffuser of GH2132 high-temperature alloy are as follows: 1. Vacuum melting the high-temperature alloy GH2132 using vacuum arc remelting (VAR) technology; the vacuum melting process temperature is 1580°C, the holding time is 3 hours, and a high-temperature alloy liquid is obtained; the solidus temperature of the alloy is 1350°C, and the liquidus temperature is 1390°C.

[0092] 2. Processing of variable cross-section casting mold (variable cross-section high-temperature alloy casting mold): A variable cross-section GH2132 high-temperature alloy complex variable cross-section diffuser casting mold is designed, ceramic shell or graphite mold is used as the casting mold, the casting mold is prepared according to the design, and an anti-oxidation coating is coated on the inner wall of the casting mold; the anti-oxidation coating is composed of aluminum oxide, zirconium oxide and boron nitride, and the mass percentage of aluminum oxide, zirconium oxide and boron nitride is 20%:10%:70%; the thickness of the anti-oxidation coating is 0.2mm; a conformal cooling channel is added to one side of the variable cross-section casting mold, and a heating cable is pre-embedded on the other side of the variable cross-section casting mold, which is used for subsequent staged low-pressure sequential solidification; 3. Integrated low-pressure casting: An integrated low-pressure casting is performed in a low-pressure casting furnace using a bottom pouring low-pressure pouring system, and the pressure system uses a low-pressure of 0.5MPa, and the temperature of the integrated low-pressure casting is 1550℃; the low-pressure casting furnace includes a pouring port, a pouring channel and a pouring cup, and the inner wall of the pouring channel is coated with a refractory material; The melt of the molten metal is smoothly injected into the variable cross-section high-temperature alloy casting mold from the bottom of the holding crucible through the riser pipe, and the low-pressure is controlled to be 0.5MPa, because the density of the high-temperature alloy melt is about 8.8g / cm 3 Therefore, low-pressure casting at about 2~5atm is required to make the melt fill from the bottom to the top smoothly without turbulence; 4. Staged low-pressure sequential directional solidification: A staged low-pressure sequential directional solidification technology is used to perform staged sequential directional solidification under a low-pressure of 0.5MPa. A conformal cooling channel is added to one side of the variable cross-section casting mold, and a heating cable is pre-embedded on the other side of the variable cross-section casting mold; the cooling water flow rate of the thick wall (the wall thickness is 110mm) of the variable cross-section high-temperature alloy casting is controlled to be 1000L / h, one side of the thick wall is first subjected to directional solidification, and the solidification rate is accelerated; at the same time, the heating temperature of the medium wall (the wall thickness is 45mm) and the thin wall (the wall thickness is 4mm) of the variable cross-section high-temperature alloy casting is controlled to be 1000℃; at the same time, the temperature at the variable cross-section position of the variable cross-section high-temperature alloy casting is measured, when the temperature at the variable cross-section position reaches between the solid-liquid phase line 1350~1390℃ of the variable cross-section high-temperature alloy (1350℃ is the solid phase line and 1390℃ is the liquid phase line), the cooling water flow rate of the medium wall and the thin wall of the variable cross-section high-temperature alloy casting is controlled to be 800L / h, the directional solidification rate of the medium wall and the thin wall is slowed down, so that the moving rate of the solid-liquid interface of the medium wall zone, the thin wall zone and the thick wall zone is kept consistent; finally, the solid-liquid interface of the medium wall and the thin wall is moved to keep consistent with the solid-liquid interface of the thick wall, and so on, until the solid-liquid interfaces of the thick wall, the medium wall and the thin wall reach the other side at the same time.

[0093] The high-temperature alloy is vacuum melted, a variable cross-section casting mold is processed, integrated low-pressure casting is filled, and a variable cross-section high-temperature alloy casting is obtained after stage low-pressure sequential solidification. A three-dimensional scanner is used to scan the variable cross-section high-temperature alloy casting obtained after solidification as a whole to form point cloud data, and then the deformation caused by casting stress and the actual three-dimensional model size difference are judged.

[0094] The cooling rate is optimized by computer simulation to ensure uniform cooling of each part of the casting and reduce thermal stress; the cooling rate is controlled at 50℃ / min to ensure uniform grain size and avoid local overheating or undercooling.

[0095] 5. The variable cross-section high-temperature alloy casting is simultaneously and integrally processed on one side of the thick wall, medium wall and thin wall processing surface: mold flow analysis is performed during the process of integrated low-pressure casting filling and stage low-pressure sequential solidification to determine the local high stress area, which refers to the area with stress > 500 MPa, and the surface stress deformation layer caused by the solidification process is removed by milling and local annealing process. First, fill the variable cross-section high-temperature alloy casting with gypsum at the lower part of the thin wall and medium wall until the thickness of the thin wall is consistent with the thickness of the thick wall (the thickness of the thick wall of the variable cross-section high-temperature alloy casting is 110 mm), and then use a milling cutter for synchronous milling; the milling adopts a layered milling strategy, and the milling depth of each layer is 0.5 mm. The milling speed is 200 m / min, and the feed speed is 0.1 mm / tooth; the local annealing process is to generate eddy current in the casting by using high-frequency or intermediate-frequency alternating current to heat the high stress area through resistance; millimeter or sub-millimeter local area is used to scan the surface of the high stress area by using a high-power laser beam, and local heating is performed by converting light energy into heat energy; the high-power laser beam is generated by a fiber laser or a semiconductor laser.

[0096] 6. Homogenization heat treatment is performed on the variable cross-section high-temperature alloy casting: the variable cross-section high-temperature alloy casting is placed in an inert atmosphere, then heated to 800℃ at a first heating rate, then heated to 1100℃ at a second heating rate, and held for 6h, and then air cooled; the first heating rate is greater than the second heating rate; the first heating rate is 10℃ / min; the second heating rate is 5℃ / min; 7. Aging treatment is performed on the variable cross-section high-temperature alloy casting: the variable cross-section high-temperature alloy casting is heated to 750℃, held for 4h, and then cooled; air cooling is used for cooling, and the cooling speed of air cooling is 100℃ / min; 8. Stress annealing treatment is performed on the variable cross-section high-temperature alloy casting: the variable cross-section high-temperature alloy casting is heated to 550℃, held for 2h, and then cooled to room temperature in stages; the cooling to room temperature in stages includes: cooling to 300℃ at a cooling rate of 100℃ / min, and then cooling to room temperature at a cooling rate of 10℃ / min.

[0097] 9. Vibration aging treatment is performed on the variable cross-section high-temperature alloy casting: the frequency of the vibration aging treatment is 100 Hz, and the vibration time is 60 min; 10. Grinding is performed on the variable cross-section high-temperature alloy casting: cubic boron nitride grinding wheel is used for grinding. The grinding speed of the grinding is 50 m / s, and the feed speed is 0.02 mm / time; a step-by-step grinding strategy is used during grinding: in the rough grinding stage, a larger back engagement amount and feed amount are used, and the engagement amount can reach 0.4 mm each time; in the fine grinding stage, the engagement amount of the fine grinding is 0.002 mm each time, and size measurement and calibration are performed after each step of grinding; the cubic boron nitride grinding wheel is used for the precision grinding processing, the thin-wall area grinding speed is 50 m / s, and the feed speed is 0.02 mm / time, and the precision grinding processing needs step-by-step grinding and multiple measurements.

[0098] Note: Before milling and grinding processing is performed on the casting, an X-ray diffractometer or an ultrasonic detector needs to be used to detect the residual stress of the casting, and during detection, the thin-wall area, the variable cross-section, and the thick-wall part (i.e., the thick-wall area) of the casting are selected; and according to the detection results, the processing parameters are adjusted, and the areas with high residual stress are preferentially processed. At the same time, online measurement is implemented during processing to measure the size, shape, position accuracy, and surface quality of the casting, and the control accuracy is controlled.

[0099] The variable cross-section high-temperature alloy casting is sequentially subjected to homogenization heat treatment, aging treatment, stress annealing treatment, vibration aging treatment, and grinding, and finally a GH2132 high-temperature alloy complex variable cross-section diffuser is obtained.

[0100] The process can increase the qualified rate of complex diffuser castings from 40% in the traditional process to more than 85%. At a cutting speed v=2000 m / min, the stress value is also reduced, and the surface residual stress is about 60 MPa.

Claims

1. A method for processing a variable cross-section high-temperature alloy casting, characterized in that: The steps include: Step 1: vacuum melting the high-temperature alloy, processing the variable-section casting, integrated low-pressure casting filling and staged low-pressure sequential directional solidification to obtain a variable-section high-temperature alloy casting; Step 2: performing simultaneous integrated processing, homogenization heat treatment, aging treatment, stress annealing treatment, vibration aging treatment and grinding on the single-side thick-wall, medium-wall and thin-wall processing surfaces of the variable-section high-temperature alloy casting in sequence to obtain a variable-section high-temperature alloy casting product.

2. The processing method according to claim 1, characterized in that: In step 1, the method further includes: performing mold flow analysis on the integrated low-pressure casting filling and staged low-pressure sequential directional solidification process to determine local high stress areas, and using milling and local annealing processes to remove surface stress deformation layers in the local high stress areas caused by the solidification process; the high stress areas are areas with stresses greater than 500 MPa; And / or, in step 2, the single side refers to the flush surface on one side of the variable-section high-temperature alloy casting.

3. The processing method according to claim 2, characterized in that: The cross-sectional thickness of the variable-section high-temperature alloy casting varies from 3 mm to 200 mm; the thick wall is the cross-sectional thickness of the variable-section high-temperature alloy casting at 51 to 200 mm, the medium wall is the cross-sectional thickness of the variable-section high-temperature alloy casting at 6 to 50 mm, and the thin wall is the cross-sectional thickness of the variable-section high-temperature alloy casting at 3 to 5 mm; The thick-walled and thin-walled machined surfaces on one side of the variable-section high-temperature alloy casting are simultaneously and integrally processed, specifically comprising: first filling the thin and medium walls with gypsum to make the thickness of the thin and medium walls consistent with the thickness of the thick wall, and then simultaneously milling the thick, medium, and thin walls using a milling cutter; the milling speed is 200-300 m / min, and the feed rate is 0.1-0.2 mm / tooth; And / or, the local annealing process is to use high-frequency or medium-frequency alternating current to generate eddy currents in the casting, and heat the high-stress area through resistance; use a high-power laser beam to scan the surface of the high-stress area in the millimeter or sub-millimeter local area, and perform local heating by converting light energy into heat energy.

4. The processing method according to claim 1, characterized in that: The variable cross-section casting process includes: designing a casting mold and coating an anti-oxidation coating on the inner wall of the casting mold; The anti-oxidation coating composition is composed of aluminum oxide, zirconium oxide and boron nitride, and the mass percentage of aluminum oxide, zirconium oxide and boron nitride is 20%:10%:70%; The thickness of the anti-oxidation coating is 0.1-0.2 mm.

5. The processing method according to claim 1, characterized in that: In step 1: the process temperature of the vacuum melting is 1500-1600°C, and the holding time is 2-3 hours; And / or, the vacuum melting adopts vacuum induction melting (VIM) and vacuum arc remelting (VAR) dual technology; And / or, the integrated low-pressure casting filling adopts a bottom-injection low-pressure pouring system, the integrated low-pressure casting filling temperature is 1450-1550° C., and the low-pressure pressure is 0.2-0.5 MPa; And / or, the staged low-pressure sequential directional solidification specifically includes: controlling the low pressure to 0.2~0.5MPa, adding a conformal cooling channel on one side of the variable-section mold, and pre-burying a heating cable on the other side of the variable-section mold; controlling the cooling water flow rate of the thick wall of the variable-section high-temperature alloy casting to 1000~2000L / h, and first directionally solidifying the thick wall side; at the same time, first controlling the heating temperature of the thin wall, medium wall and next thin wall area of ​​the variable-section high-temperature alloy casting to 600~1000℃; at the same time, measuring the temperature at the variable-section position, and when the variable-section temperature measurement temperature reaches between the solid-liquid phase line of the variable-section high-temperature alloy casting, then controlling the thin wall and medium wall of the variable-section high-temperature alloy casting to heat the variable-section high-temperature alloy casting to a temperature between 600~1000℃; The cooling water flow rate is 800~1000L / h, which slows down the directional solidification rate at the thin wall and medium wall, and measures the temperature at the next variable section position at the same time. When the temperature of the next variable section reaches the solid-liquid phase line of the variable section high-temperature alloy, start the cooling water on the side of the next thin-wall area, control the cooling water flow rate to 600~800L / h, and weaken the water flow rate so that the solid-liquid interface movement rate of the next thin-wall area, thin wall and medium wall is consistent with the movement rate of the thick-wall area; finally, the solidification solid-liquid interface at the next thin-wall area, thin wall and medium wall is moved to the same level as the solid-liquid interface of the thick wall area, and so on. Finally, the solid-liquid interfaces at the thick wall, medium wall, thin wall and next thin-wall area reach the other side at the same time.

6. The processing method according to claim 1, characterized in that: In step 2, the homogenization heat treatment includes: placing the variable-section high-temperature alloy casting in an inert atmosphere, then heating it to 800° C. at a first heating rate, then heating it to 1040-1160° C. at a second heating rate, and then holding the temperature; the first heating rate is greater than the second heating rate; And / or, the aging treatment comprises: heating the variable-section high-temperature alloy casting to 700-800° C., holding the casting at this temperature, and then cooling the casting; And / or, the stress annealing treatment comprises: heating the variable cross-section high-temperature alloy casting to 500-600° C., holding the casting at this temperature, and cooling the casting in stages to room temperature; And / or, the frequency of the vibration aging treatment is 50-100 Hz, and the vibration time is 30-60 min; And / or, the grinding speed is 30-50 m / s, and the feed speed is 0.01-0.02 mm / time.

7. The processing method according to claim 6, characterized in that: The first heating rate is 10°C / min; And / or, the second heating rate is 5°C / min; And / or, the holding time of the homogenization heat treatment is 4 to 6 hours; And / or, the holding time of the aging treatment is 2 to 4 hours; And / or, the cooling adopts air cooling or oil cooling, the cooling rate of the air cooling is 100°C / min, and the oil cooling adopts quenching oil cooling; And / or, the holding time of the stress annealing treatment is 2 to 3 hours; And / or, the stepwise cooling to room temperature includes: cooling to 300° C. at a cooling rate of 100° C. / min, and then cooling to room temperature at a cooling rate of 10° C. / min.

8. The processing method according to claim 1, characterized in that: The high-temperature alloy is a nickel-based high-temperature alloy GH4738, comprising the following components by mass percentage: Ni ≥ 72%, Cr 14% to 17%, Fe 6% to 10%, C ≤ 0.15%, Si ≤ 0.5%, Mn ≤ 1.0%, S ≤ 0.015%, Cu ≤ 0.5% and Ti ≤ 0.5%; Alternatively, the high-temperature alloy is a nickel-based high-temperature alloy K4169, comprising the following components in mass percentage: Ni is 50% to 55%, Cr is 17% to 21%, Nb is 4.7% to 5.5%, Mo is 2.8% to 3.3%, Ti is 0.65% to 1.15%, Al is 0.2% to 0.8%, C≤0.08%, Si≤0.35%, Mn≤0.35%, S≤0.015%, Cu≤0.3%, and the remainder is Fe; Alternatively, the high-temperature alloy is GH2132, comprising the following components in mass percentage: Ni is 24% to 27%, Cr is 13.5% to 16%, Mo is 1 to 1.5%, Ti is 1.7 to 2.3%, V is 0.1 to 0.5%, Al is 0.2 to 0.3%, C≤0.08%, Si≤1%, Mn≤2%, S≤0.03%, P≤0.03%, and the rest is Fe.

9. A variable-section high-temperature alloy casting produced according to the processing method according to any one of claims 1 to 8.

10. Use of the processing method according to any one of claims 1 to 8 in the preparation of integrated casing castings, diffusers and / or turbine disks and blades.

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