A synchronous extrusion forming method for improving fatigue performance of thin-walled hole shaft components

Abstract

This application discloses a synchronous extrusion forming method for improving the fatigue performance of thin-walled, fine-hole shaft components, belonging to the field of high-temperature alloy precision plastic forming technology. The method includes: preheating a steel mandrel and an alloy hollow billet with a pre-set central hole; synchronous extrusion forming: fixing the preheated alloy hollow billet, pushing the preheated steel mandrel axially into the central pre-hole of the alloy hollow billet, and driving the alloy hollow billet to undergo radial compression deformation, so that the extrusion process of the steel mandrel and the extrusion deformation process of the alloy hollow billet are completed integrally; after forming, separating the steel mandrel from the alloy hollow billet, and subjecting the alloy hollow billet to subsequent heat treatment and processing. In this application, the synchronously extruded steel mandrel and the flowing inner wall of the alloy hollow billet generate intense relative motion and frictional shearing, allowing the core region, which is most difficult to deform in traditional processes, to bear the maximum degree of shear strain and deformation heat treatment effect, resulting in ultra-fine grains.

Description

Technical Field

[0001] This application belongs to the field of high-temperature alloy precision plastic forming technology, and specifically relates to a synchronous extrusion forming method for improving the fatigue performance of thin-walled, fine-hole shaft components. Background Technology

[0002] GH4169 high-temperature alloy is widely used in the manufacture of key shaft components for high-end equipment such as aero engines and gas turbines due to its excellent high-temperature strength, fatigue resistance, and corrosion resistance. For shaft components with thin walls and slender deep holes, high-cycle fatigue performance is a core indicator determining service reliability and lifespan.

[0003] Currently, the following processes are mainly used for the preparation of blanks for such components: Solid bar reforging and drilling: Solid bars are processed by multi-directional forging or repeated upsetting and drawing, and finally the center hole is machined. In this method, the material deformation degree of the core of the component (the future inner hole area) is low, and the original casting structure or coarse grains are not sufficiently refined, resulting in poor uniformity of the structure from the surface to the core. In addition, the metal flow lines are cut off by the drilling process, which seriously impairs fatigue performance.

[0004] Hollow billet fixed mandrel extrusion: Hollow billets are extruded using an extrusion die with a fixed mandrel in both forward and reverse directions. Although this method can form continuous streamlines, for "thin-walled, fine-pore" structures, the friction between the mandrel and the inner wall of the billet, as well as the rigid constraint of the mandrel itself, limits the deformation of the metal layer adhering to the inner wall. This results in the grain refinement and streamline integrity in the area near the inner wall being inferior to that of the outer wall, and the problem of microstructure inhomogeneity is not fundamentally solved.

[0005] The common drawback of the above-mentioned traditional methods is that the metal in the core or key areas of the inner wall of the component cannot obtain sufficient and uniform plastic deformation similar to that of the outer wall, forming weak areas in terms of structure and performance, which become the preferred locations for fatigue crack initiation, thus restricting the improvement of the overall fatigue performance of the component. Summary of the Invention

[0006] To address the aforementioned issues, this application provides a synchronous extrusion forming method for improving the fatigue performance of thin-walled, fine-hole shaft components.

[0007] The first objective of this application is to provide a synchronous extrusion forming method for improving the fatigue performance of thin-walled, fine-hole shaft components, comprising: Synchronous extrusion forming: The preheated alloy hollow billet is fixed, and the preheated steel mandrel is pushed axially into the central pre-hole of the alloy hollow billet, driving the alloy hollow billet to undergo radial compression deformation, so that the extrusion process of the steel mandrel and the extrusion deformation process of the alloy hollow billet are completed in one step; in this process, the steel mandrel acts as a "moving inner mold", and its extrusion behavior is strongly coupled with the radial flow of the alloy hollow billet, applying continuous and intense radial frictional shear force and axial tensile force to the inner wall of the billet.

[0008] Furthermore, the diameter of the central preset hole is 0.1% to 2% smaller than the diameter of the steel core rod.

[0009] Furthermore, the preheating temperature of the steel core rod is 600℃~850℃.

[0010] Furthermore, the preheating temperature of the alloy hollow billet is 1020℃~1100℃.

[0011] Furthermore, the material of the steel core rod is hot work die steel; Alternatively, the steel core rod may be made of other high-temperature alloy steels to accommodate the temperature of synchronous extrusion forming.

[0012] Furthermore, the steel core rod is made of H13 steel.

[0013] Furthermore, the material of the alloy hollow billet is GH4169.

[0014] Furthermore, reverse extrusion is used in the synchronous extrusion forming process, with an extrusion ratio of 4 to 12.

[0015] Furthermore, the synchronous extrusion forming method for improving the fatigue performance of thin-walled, fine-hole shaft components further includes: after forming, separating the steel mandrel from the alloy hollow billet, and subjecting the alloy hollow billet to subsequent heat treatment and processing.

[0016] Furthermore, the heat treatment and processing include solution treatment and aging treatment.

[0017] Furthermore, the conditions for the solution treatment are: temperature of 940-970℃, holding time of 1-1.5h, and air cooling; the conditions for the aging treatment are: temperature of 700-730℃, holding time of 7-8.5h, and furnace cooling.

[0018] Preferably, the conditions for the solution treatment are: a temperature of 960°C, a holding time of 1-1h, and air cooling; the conditions for the aging treatment are: a temperature of 720°C, a holding time of 8h, and furnace cooling.

[0019] Compared with the prior art, this application has the following advantages: This application discloses a synchronous extrusion forming method for improving the fatigue performance of thin-walled shaft components with fine holes. The method employs a synchronous extrusion forming process and has the following advantages: First, it achieves extreme shear deformation in the core: the synchronously extruded steel mandrel and the inner wall of the flowing alloy hollow billet generate intense relative motion and frictional shear, so that the core area, which is the most difficult to deform in traditional processes, bears the maximum shear strain and deformation heat treatment effect, and the grains are made ultra-fine.

[0020] Secondly, it forms a unique gradient composite streamline: This process not only retains the circumferential fiber streamlines, but also, due to the extrusion of the steel core, forms a strong axial streamline component and a denser three-dimensional streamline network inside the material, which significantly optimizes the stress transmission path.

[0021] Third, it fundamentally improves the uniformity of the structure: the forced, inside-out synchronous deformation mechanism ensures that the deformation amount is distributed extremely uniformly from the inner wall to the outer wall of the billet, thereby obtaining a uniform and fine recrystallized structure that runs through the entire wall thickness and completely eliminating the "weak core area".

[0022] Fourth, significantly improved fatigue performance: The fundamental improvements in microstructure and streamlines directly translate into a leap in fatigue performance. The uniform, fine-grained microstructure inhibits crack initiation, and the optimized multi-directional streamlines effectively hinder crack propagation, resulting in an order-of-magnitude improvement in the fatigue limit and high-cycle fatigue life of the component. Compared to traditional fixed-mandrel extrusion, the component prepared in this application exhibits a fatigue limit increase of over 38% and an order-of-magnitude increase in fatigue life, providing a breakthrough solution for the manufacture of high-performance thin-walled, fine-hole shaft components.

[0023] Highly innovative in process: The "synchronous extrusion" of this application is different from the traditional "pre-placed mandrel" or "fixed mandrel". It is a dynamic and composite new plastic forming process that breaks through the concept of traditional extrusion.

[0024] Other features and advantages of this application will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the application. The objectives and other advantages of this application may be realized and obtained by means of the structures pointed out in the description and claims. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] Example 1 Simultaneous extrusion forming method for improving fatigue properties of thin-walled shaft components with fine holes To prepare a thin-walled shaft of GH4169 alloy, with the following final dimensions: outer diameter φ60mm, inner hole φ15mm, and length 400mm.

[0027] S1. Material Preparation: GH4169 hollow billet (forged and machined) with the following dimensions: outer diameter φ85mm, inner hole φ14.5mm (slightly smaller than the target steel mandrel diameter), and length 250mm. The steel mandrel is made of H13 hot work die steel, machined to a diameter of φ15.05mm (slightly larger than the pre-hole diameter of the billet), a length of 500mm, and surface polished.

[0028] S2. Heating: Heat the GH4169 billet to 1080℃ under a protective atmosphere and hold for 2 hours. Heat the H13 steel mandrel to 750℃ and hold for 1 hour.

[0029] S3. Synchronous Extrusion Forming: The die is preheated to 400℃. The hot GH4169 billet is placed in the extrusion cylinder, and the hot steel mandrel is aligned with the pre-drilled hole at the upper center of the billet and placed under the extrusion punch (i.e., reverse extrusion). The extruder is started, and the punch presses down at a constant speed, pushing the steel mandrel into the center of the GH4169 billet and propelling the billet downwards. Under an extrusion ratio of ~5.0, the steel mandrel and the GH4169 billet deform synchronously, ultimately forming a shaft blank encasing the steel mandrel.

[0030] S4. Separation and Processing: Air cooling after extrusion. Utilizing the difference in thermal expansion coefficients between GH4169 and H13 steel, the steel mandrel is removed through shrinkage separation after cooling, combined with an ejection device. The GH4169 billet undergoes standard heat treatment (960℃×1h / AC +720℃×8h / FC to 620℃×8h / AC) and finishing.

[0031] Comparative Example 1 (Conventional Fixed Mandrel Extrusion) A hollow GH4169 billet with the same material and initial outer diameter (φ85mm) as in Example 1 was used, but its inner hole was machined to φ20mm (to accommodate the mandrel). A reverse extrusion die with a mandrel (φ15mm in diameter) was used. The billet was heated to 1080°C and placed into the die, with the mandrel pre-positioned in the inner hole of the billet. Extrusion was performed, with the extrusion ratio also being ~5.0. Subsequent heat treatment and finishing processes were the same as in Example 1.

[0032] Performance testing and comparative analysis: Organization and Streamline Observation: Macroscopic streamlines: The continuity of streamlines near the inner wall of the component in Comparative Example 1 is significantly weaker than that on the outer wall. The streamlines of the entire cross-section of the component in Example 1 are extremely dense and continuous, and exhibit a unique spiral propagation pattern.

[0033] Microstructure: In Comparative Example 1, the inner wall structure has relatively coarse grains with orientation. In Example 1, the inner wall structure consists of uniform, ultrafine equiaxed crystals with a finer grain size than the outer wall structure.

[0034] Fatigue performance test: In 10 7 Under the same number of cycles, the fatigue strength limit of Comparative Example 1 was approximately 420 MPa. The fatigue strength limit of Example 1 was as high as 580 MPa, an increase of over 38%. At a stress level of 450 MPa, the fatigue life of Example 1 was more than 10 times that of Comparative Example 2.

[0035] Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A synchronous extrusion forming method for improving the fatigue performance of thin-walled, fine-hole shaft components, characterized in that, include: Synchronous extrusion forming: The preheated alloy hollow billet is fixed, and the preheated steel core rod is pushed axially into the central pre-hole of the alloy hollow billet, and the alloy hollow billet is driven to undergo radial compression deformation, so that the extrusion process of the steel core rod and the extrusion deformation process of the alloy hollow billet are completed in one step.

2. The synchronous extrusion forming method for improving the fatigue performance of thin-walled, fine-hole shaft components according to claim 1, characterized in that, The diameter of the central preset hole is 0.1% to 2% smaller than the diameter of the steel core rod.

3. The synchronous extrusion forming method for improving the fatigue performance of thin-walled, fine-hole shaft components according to claim 1, characterized in that, The preheating temperature of the steel core rod is 600℃~850℃.

4. The synchronous extrusion forming method for improving the fatigue performance of thin-walled, fine-hole shaft components according to claim 1, characterized in that, The preheating temperature of the alloy hollow billet is 1020℃~1100℃.

5. The synchronous extrusion forming method for improving the fatigue performance of thin-walled, fine-hole shaft components according to claim 1, characterized in that, The steel core rod is made of hot work die steel.

6. The synchronous extrusion forming method for improving the fatigue performance of thin-walled, fine-hole shaft components according to claim 5, characterized in that, The steel core rod is made of H13 steel.

7. The synchronous extrusion forming method for improving the fatigue performance of thin-walled, fine-hole shaft components according to claim 1, characterized in that, The material of the alloy hollow billet is GH4169.

8. The synchronous extrusion forming method for improving the fatigue performance of thin-walled, fine-hole shaft components according to claim 1, characterized in that, In the synchronous extrusion forming process, reverse extrusion is used, and the extrusion ratio is 4~12.

9. A synchronous extrusion forming method for improving the fatigue performance of thin-walled, fine-hole shaft components according to any one of claims 1-8, characterized in that, Also includes: After forming, the steel core rod is separated from the alloy hollow billet, and the alloy hollow billet undergoes subsequent heat treatment and processing. The heat treatment and processing include solution treatment and aging treatment.

10. A synchronous extrusion forming method for improving the fatigue performance of thin-walled, fine-hole shaft components according to claim 9, characterized in that, The conditions for the solution treatment are: temperature of 940-970℃, holding time of 1-1.5h, and air cooling; the conditions for the aging treatment are: temperature of 700-730℃, holding time of 7-8.5h, and furnace cooling.