A method for preparing a shaft member with double-property structure by reverse extrusion and a reverse extrusion device

Abstract

The application discloses a shaft member reverse extrusion double-property structure preparation method and a reverse extrusion device and belongs to the technical field of metal material processing forming. The shaft member reverse extrusion double-property structure preparation method comprises the following steps: pretreating a blank and assembling the pretreated blank in a jacket; after assembly, the blank is subjected to partition temperature control reverse extrusion through a reverse extrusion device; and after extrusion, the blank is subjected to pressure maintaining and demolding to obtain a formed shaft member. Through partition temperature control design, the shaft member cross-section structure differentiation regulation is successfully realized in the reverse extrusion process, the double-property member with excellent comprehensive performance is obtained, and the application has remarkable industrial application value.

Description

Technical Field

[0001] This application belongs to the field of metal material processing and forming technology, and specifically relates to a method for preparing a dual-performance structure of shaft components by reverse extrusion and a reverse extrusion device. Background Technology

[0002] Shaft components (such as automotive half-shafts, drive shafts, and pins) are key parts in mechanical transmission systems. They often require high surface hardness and wear resistance to withstand friction and contact stress, while the core needs high toughness and fatigue strength to withstand alternating loads and impacts. Traditional manufacturing processes typically employ combined heat treatment methods such as "tempering and tempering + surface hardening" or "carburizing and quenching," which are lengthy, energy-intensive, and difficult to control deformation. Furthermore, they pose a risk of abrupt changes in the properties of the interface between the hardened layer and the core.

[0003] Reverse extrusion is a highly efficient near-net-shape forming technology for shaft components. However, traditional reverse extrusion mainly focuses on shape forming, with limited control over the spatial distribution of the final component's properties. How to simultaneously achieve differentiated control of the microstructure on the cross-section of the component during this plastic forming process, thereby directly obtaining components with dual properties, is a current research hotspot and challenge. Summary of the Invention

[0004] The purpose of this invention is to provide a method and apparatus for preparing dual-performance structures by reverse extrusion of shaft components, which solves the technical problems of complex process flow, high energy consumption and unsatisfactory interface bonding performance in the existing manufacturing of shaft components with graded performance.

[0005] To achieve the above objectives, one embodiment of the present invention provides a method for preparing a dual-performance microstructure for shaft-type components under reverse extrusion, comprising the following steps: The billet is pretreated and then placed in a sleeve for assembly. After assembly, the billet is subjected to zoned temperature-controlled reverse extrusion through a reverse extrusion device; After extrusion, the billet is held under pressure and demolded to obtain the formed shaft component; After assembly, the billet is subjected to zoned temperature-controlled reverse extrusion by a reverse extrusion device, including: heating the outer surface area of ​​the billet to a first temperature by heating the sleeve, and contacting the inner surface and / or core area of ​​the billet to a second temperature by contacting the reverse extrusion rod with an internal channel in the reverse extrusion device, wherein the first temperature is greater than the second temperature.

[0006] One preferred embodiment of the present invention involves pre-treating the billet and placing the pre-treated billet in a sleeve for assembly, including: surface treatment of the billet and preheating it to the initial deformation temperature; after heating, placing the billet in a sleeve for assembly.

[0007] In one preferred embodiment of the present invention, the temperature of the outer surface region of the billet is higher than the initial deformation temperature, while the temperature of the inner surface and / or core of the billet is not higher than the initial deformation temperature.

[0008] In one preferred embodiment of the present invention, the billet is an alloy steel or aluminum alloy bar, the sheath is made of alloy steel or copper alloy, and the sheath wall thickness is 5%-15% of the billet diameter.

[0009] In one preferred embodiment of the present invention, the shape of the inner wall of the sleeve matches the outer contour of the blank.

[0010] In one preferred embodiment of the present invention, the first temperature is above the austenitizing temperature or recrystallization temperature of the billet material, and the second temperature is below the martensitic transformation start temperature or within the bainitic transformation temperature range of the billet material.

[0011] In one preferred embodiment of the present invention, after extrusion, the billet is subjected to pressure holding and demolding to obtain a shaped shaft component, including: after extrusion, the billet is subjected to pressure holding, demolding, stress-relief annealing or surface finishing to obtain a shaped shaft component.

[0012] The present invention also discloses a reverse extrusion device, including a mold body, a mold cavity for placing a sleeve, a reverse extrusion rod connected to the blank and a heating device for heating the sleeve are provided in the mold cavity, and a channel is provided inside the reverse extrusion rod, through which a heat-conducting medium flows.

[0013] In one preferred embodiment of the present invention, the channel is an axial hole channel, a spiral winding groove, or a multi-loop channel.

[0014] In one preferred embodiment of the present invention, the anti-extrusion rod is also connected to a temperature control unit.

[0015] Compared with the prior art, this application has the following advantages: 1. The method for preparing shaft components with dual-performance microstructure through reverse extrusion in this invention achieves independent and precise temperature difference control on the outer and inner surfaces of the component through the design of the external sleeve and the special treatment of the reverse extrusion rod in the reverse extrusion device. The external sleeve keeps the outer surface area of ​​the component at a high temperature, promoting grain refinement or phase transformation strengthening. At the same time, the heat preservation or cooling treatment of the internal reverse extrusion rod keeps the core or inner hole surface area of ​​the component at a relatively low temperature, inhibiting grain growth or preserving tough microstructure. This allows for the direct acquisition of shaft components with dual-performance microstructure of "hard outside and tough inside" in a one-time forming process, with high strength and high wear resistance on the outer layer and high toughness and high fatigue resistance on the core or inner layer. This eliminates the need for subsequent complex combined heat treatment processes, improving production efficiency and material utilization.

[0016] 2. The reverse extrusion dual-performance microstructure preparation method for shaft components of the present invention realizes integrated manufacturing, combining plastic forming and gradient heat treatment into one, which significantly shortens the process flow, improves production efficiency, and reduces energy consumption.

[0017] 3. The reverse extrusion dual-performance microstructure preparation method of the shaft component of the present invention can directly obtain an ideal dual-performance microstructure with high strength and high wear resistance in the outer layer and high toughness in the core. Moreover, the combination of the inner and outer microstructures is a metallurgical bond with a natural transition, avoiding the risk of interface peeling that may occur in subsequent assembly processing.

[0018] 4. In the method for preparing dual-performance microstructure by reverse extrusion of shaft components of the present invention, the size and depth of the internal and external temperature difference can be flexibly controlled by adjusting the heating power of the cladding and the temperature and flow rate of the cooling medium of the reverse extrusion rod, thereby achieving precise control over the thickness and degree of the performance gradient layer. Furthermore, the preparation method of the present invention is applicable to various shaft components such as alloy steel and aluminum alloy that can be strengthened by thermomechanical treatment.

[0019] Other features and advantages of this application will be set forth in the following description 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 the accompanying drawings. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic flowchart of a method for preparing a dual-performance microstructure of a shaft component under reverse extrusion in one embodiment of the present invention; Figure 2 This is a schematic diagram of the anti-extrusion device in one embodiment of the present invention.

[0022] Among them, 1-mold body, 2-mold cavity, 3-channel, 4-anti-extrusion rod, 5-temperature control unit, 6-heating device, 7-billet. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0025] This invention discloses a method for preparing a dual-performance microstructure for shaft-type components under reverse extrusion, such as... Figure 1 As shown, it includes the following steps: Step (1): Pre-treat the billet and place the pre-treated billet in a sleeve for assembly; specifically, select alloy steel or aluminum alloy bars suitable for thermomechanical treatment as the billet, perform surface cleaning and preheat to the initial deformation temperature T0 (when the billet is alloy steel, T0 is 900℃-1100℃; when the billet is aluminum alloy, T0 is 500℃-800℃), and place the preheated billet in a sleeve for assembly; wherein, the material of the sleeve is alloy steel or copper alloy, and the sleeve wall thickness is 5%-15% of the billet diameter; preferably, the inner wall shape of the sleeve matches the outer contour of the billet; Furthermore, the sheath material is heat-resistant alloy steel or high thermal conductivity copper alloy; Step (2): The assembled billet is subjected to zoned temperature-controlled back extrusion by a back extrusion device; specifically, the assembled billet is placed into the back extrusion device for zoned temperature-controlled back extrusion, that is, the billet with the assembled sleeve is placed into the mold cavity 2, and the outer surface of the sleeve is surrounded by a heating device 6 (such as an induction coil) to ensure that the outer surface of the sleeve and the billet can be continuously heated to T during the extrusion process. H In this process, the outer surface area of ​​the billet is heated to a first temperature T by the heating device in the reverse extrusion apparatus. H The billet's inner surface and / or core region are heated to a second temperature T by contacting a reverse extrusion rod with an internal channel in the reverse extrusion device. L Temperature T of the outer surface area of ​​the billet H >T0, the temperature of the inner surface and / or core of the billet is ≤T0; Preferably, the first temperature T on the outer surface region of the billetH The second temperature T of the billet inner surface and / or core is above the austenitizing temperature or recrystallization temperature of the billet material. L The martensitic transformation start temperature Ms of the billet material is below or within the bainitic transformation temperature range. Step (3): After extrusion, the billet is held under pressure and demolded to obtain the formed shaft component. Specifically, after the billet reaches the target extrusion deformation amount (i.e., the billet deformation amount is 40%-70%), it is held under pressure for 0.5h-2h and the temperature is continuously controlled in different zones so that the inner and outer regions of the component complete the differentiated microstructure transformation while plastically deforming. Then, the temperature control is stopped, the pressure is unloaded, and the formed component along with the sleeve is taken out of the mold. The sleeve is separated, and the component is subjected to necessary stress-relieving annealing or surface finishing to obtain the formed shaft component.

[0026] The reverse extrusion dual-performance microstructure preparation method of the present invention is a short-process and high-efficiency preparation method that can integrate plastic forming and microstructure performance control to achieve a "hard outside and tough inside" dual-performance microstructure in the cross section of shaft components.

[0027] The present invention also discloses a reverse extrusion device for implementing the above-described preparation method, such as... Figure 2 As shown, the mold includes a mold body 1, and a mold cavity 2 for placing the sleeve is provided on the mold body. During the zoned temperature-controlled reverse extrusion process, the assembled blank 7 and the sleeve are placed in the mold cavity 2. The mold cavity 2 is also provided with a reverse extrusion rod 4 connected to the blank 7 and a heating device 6 for heating the sleeve.

[0028] Preferably, the heating device 6 is an induction heating coil that surrounds the entire interior of the mold cavity 2, used for rapid heating and heat preservation of the outer surface of the sleeve and the blank 7; specifically, the blank with the sleeve assembled is placed into the mold cavity 2, and the outer surface of the sleeve is surrounded by the heating device 6 (such as an induction coil) to ensure that the outer surface of the sleeve and the blank can be continuously heated to T during the extrusion process. H ; Preferably, the reverse extrusion rod 4 has a channel 3 inside. The channel 3 is an axial hole channel, a spiral groove, or a multi-loop channel. The channel 3 is filled with a heat-conducting medium, which is a circulating coolant, compressed air, or high-temperature oil. The reverse extrusion rod 4 actively controls the temperature of the inner surface area of ​​the billet 7 in contact with the end of the reverse extrusion rod 4 through the heat-conducting medium inside the channel 3. Specifically, when the billet contacts the reverse extrusion rod 4, the inner surface and / or core of the billet are heated by the heat-conducting medium in the channel 3 inside the reverse extrusion rod 4.

[0029] Preferably, the reverse extrusion rod is also connected to a temperature control unit 5, which is used to provide a heat transfer medium to the channel 3 of the reverse extrusion rod 4. The temperature control unit includes a pump, a heat exchanger, pipelines, etc.

[0030] During the temperature-controlled reverse extrusion process, the heating device 1 continuously heats the jacket, causing the outer surface layer of the billet 7 in close contact with it to rapidly heat up and maintain a high temperature (T). H This promotes dynamic recrystallization and grain refinement in the region, or austenitization or even quenching (depending on the cooling rate) during subsequent holding pressure, resulting in martensite and other strengthened structures. Simultaneously, by pumping a low-temperature heat-conducting medium into the channel 3 inside the reverse extrusion rod 4, the center or inner hole region of the billet 7 in contact with the end of the reverse extrusion rod 4 is directly cooled, maintaining its temperature at a low level (T). L This simulates an "internal boiling" (actually internal cooling) process, inhibiting grain growth in the region or transforming it into tougher structures such as bainite or sorbite. This is achieved through precise control of T... H and T L Parameters such as temperature, extrusion deformation, and holding time can be independently controlled to regulate the outer layer and core structure, ultimately forming a continuous or stepped performance gradient from the surface to the inside on the cross-section of the formed part.

[0031] Example 1: Dual-performance fabrication of solid 40Cr steel half-shafts for automobiles Billet preparation: Select 40Cr steel bar with a diameter of φ60mm, remove the surface oxide scale by turning, heat to the initial deformation temperature of 850℃ (T0), and hold for 1 hour; Packaging assembly: The heated billet is placed into a 304 heat-resistant stainless steel sleeve with a wall thickness of 6mm (10% of the billet diameter), and the inner diameter of the sleeve is interference-fitted with the outer diameter of the billet. System preparation: Assemble the mold, the inside of the reverse extrusion rod is a spiral cooling channel, connect the induction heating coil to the outer edge of the sleeve, and connect the temperature control unit to supply 25℃ circulating cooling water to the extrusion rod channel; Zoned temperature-controlled reverse extrusion: The induction heating coil is activated to heat the outer layer of the casing and billet to 920℃ (T). H (in the fully austenitic region) and maintained; Start the extrusion press, and the counter-extrusion bar extrudes the billet at a speed of 5 mm / s, with a deformation of 60%. During the extrusion process, cooling water is continuously supplied to maintain the temperature of the core region of the billet in contact with the end face of the extrusion rod at approximately 300°C (T). L It is located in the bainite transformation region.

[0032] Pressure holding and temperature control: After reaching the target size, hold the pressure for 30 seconds, maintaining the above temperature field during this period; Demolding and post-processing: Stop heating and cooling, unload, eject the workpiece, let the workpiece cool to room temperature in air, remove the sleeve, and perform low-temperature stress-relieving annealing (200℃, 2h).

[0033] Comparative Example 1: Traditional isothermal reverse extrusion + overall quenching and tempering treatment Using the same 40Cr steel billet as in Example 1, the billet was heated to 850°C and then subjected to reverse extrusion forming with the same parameters without using a heating sleeve or a reverse extrusion rod for cooling. After forming, the workpiece was subjected to overall quenching and tempering treatment (850°C quenching + 550°C tempering).

[0034] Performance comparison analysis: Cross-sectional performance tests were performed on the half-shaft samples obtained in Example 1 and Comparative Example 1.

[0035] Hardness gradient: In Example 1, the hardness distribution of the workpiece from the surface to the core is as follows: surface hardness HRC 55±2, transitioning to approximately HRC 45 at 15mm from the surface, and core hardness (radius center) HRC 35±2. A smooth hardness gradient is observed. In Comparative Example 1, the workpiece cross-section exhibits a uniform hardness distribution, approximately HRC 28-30.

[0036] Impact toughness: A Charpy V-notch impact test was performed on a sample taken from the core of the workpiece. The core impact energy of Example 1 was 80 J, and the overall impact energy of Comparative Example 1 was 60 J.

[0037] Abrasion resistance: Abrasion tests were conducted on the surface of the workpiece. The relative abrasion resistance of the surface in Example 1 was more than 2.5 times that of Comparative Example 1.

[0038] Metallographic structure: In Example 1, the surface layer of the workpiece is fine tempered martensite, and the core is a mixture of bainite and ferrite; in Comparative Example 1, the whole structure is uniform tempered sorbite.

[0039] Example 2: Preparation of dual internal and external properties of aluminum alloy hollow drive shaft Billet preparation: Select 7075 aluminum alloy hollow billet and preheat to 420℃ (T0); Package configuration: The blank is placed into a pure copper sleeve (high thermal conductivity); System preparation: High-temperature oil (200℃) is introduced into the internal channel of the reverse extrusion rod to achieve a "heat preservation" effect on the surface of the inner hole of the billet; Zoned temperature-controlled reverse extrusion: External induction heating heats the outer surface of the casing and billet to 480℃ (T H (above the solution treatment temperature). During the extrusion process, the internal high-temperature oil circulation maintains the surface temperature of the inner bore at approximately 380°C (T). L ); Extrusion deformation amount 70%; Pressure holding and temperature control: maintaining pressure and temperature; Demolding and aging: After the pressure holding is completed, heating is stopped and the workpiece (along with the sleeve) is quickly removed from the mold and immediately subjected to water quenching to achieve solid solution treatment in the high-temperature outer layer, followed by graded aging treatment.

[0040] Comparative Example 2: Conventional reverse extrusion + single aging The same billet is formed by conventional reverse extrusion (without zoned temperature control) and then subjected to the same solution quenching and aging treatment.

[0041] Performance comparison: Due to high temperature deformation and rapid cooling, the outer surface of the workpiece in Example 2 has extremely fine grains, resulting in high strength and hardness; the inner hole area has slightly larger grains but good plasticity due to the lower temperature. The overall bending fatigue life of the component is about 40% higher than that of Comparative Example 2.

[0042] In summary, this invention, through zoned temperature control design, successfully achieves differentiated control of the cross-sectional microstructure of shaft components during the reverse extrusion process, resulting in dual-performance components with excellent overall performance and significant industrial application value.

[0043] 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 method for preparing a dual-performance microstructure through reverse extrusion of shaft-type components, characterized in that, Includes the following steps: The billet is pretreated and then placed in a sleeve for assembly. After assembly, the billet is subjected to zoned temperature-controlled reverse extrusion through a reverse extrusion device; After extrusion, the billet is held under pressure and demolded to obtain the shaped shaft component; The assembled billet is subjected to zoned temperature-controlled reverse extrusion by a reverse extrusion device, including: heating the outer surface area of ​​the billet to a first temperature by heating the sleeve, and contacting the inner surface and / or core area of ​​the billet to a second temperature by contacting the reverse extrusion rod with an internal channel in the reverse extrusion device, wherein the first temperature is greater than the second temperature.

2. The method for preparing a dual-performance microstructure of a shaft-type component by reverse extrusion as described in claim 1, characterized in that: The process of pre-treating the billet and placing the pre-treated billet in a sleeve for assembly includes: surface treatment of the billet and preheating it to the initial deformation temperature; after heating, placing the billet in a sleeve for assembly.

3. The method for preparing a dual-performance microstructure of a shaft-type component by reverse extrusion as described in claim 2, characterized in that: The temperature of the outer surface region of the billet is higher than the initial deformation temperature, while the temperature of the inner surface and / or core of the billet is not higher than the initial deformation temperature.

4. The method for preparing a dual-performance microstructure of a shaft-type component by reverse extrusion as described in claim 1, characterized in that: The billet is an alloy steel or aluminum alloy bar, and the sheath is made of alloy steel or copper alloy, with a sheath wall thickness of 5%-15% of the billet diameter.

5. The method for preparing a dual-performance microstructure of a shaft-type component by reverse extrusion as described in claim 1, characterized in that: The shape of the inner wall of the sleeve matches the outer contour of the blank.

6. The method for preparing a dual-performance microstructure of a shaft-type component by reverse extrusion as described in claim 1, characterized in that: The first temperature is above the austenitizing temperature or recrystallization temperature of the billet material, and the second temperature is below the martensitic transformation start temperature or within the bainitic transformation temperature range of the billet material.

7. The method for preparing a dual-performance microstructure of a shaft-type component by reverse extrusion as described in claim 1, characterized in that: After the extrusion is completed, the billet is subjected to pressure holding and demolding to obtain a shaped shaft component, including: after the extrusion is completed, the billet is subjected to pressure holding, demolding, stress-relief annealing or surface finishing to obtain a shaped shaft component.

8. A reverse extrusion apparatus for implementing the reverse extrusion dual-performance microstructure preparation method for shaft-type components according to any one of claims 1-7, characterized in that: The device includes a mold body, which has a mold cavity for placing a sleeve. The mold cavity has a reverse extrusion rod connected to the blank and a heating device for heating the sleeve. The reverse extrusion rod has a channel inside, and the channel is filled with a heat-conducting medium.

9. The reverse extrusion device as described in claim 8, characterized in that: The channel is an axial hole channel, a spiral groove, or a multi-loop channel.

10. The reverse extrusion device as described in claim 8, characterized in that: The anti-extrusion rod is also connected to a temperature control unit.

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