Method and equipment for eliminating residual stress of iron-carbon alloy forge piece

Abstract

The invention belongs to the field of machining, and particularly relates to a method for eliminating residual stress of an iron-carbon alloy forge piece, which comprises the following steps: B1, providing the iron-carbon alloy forge piece; b2, heating the iron-carbon alloy forge piece to a first temperature, wherein the first temperature is higher than the recrystallization temperature of the iron-carbon alloy forge piece; and B3, vibrating the iron-carbon alloy forge piece and quenching. The method has the effect of inhibiting second phase precipitation in thermal aging treatment.

Description

Technical Field

[0001] The present invention relates to the field of mechanical processing, and in particular to a method and a device for eliminating residual stress of an iron-carbon alloy forging. Background Art

[0002] During the processing, forgings will produce plastic deformation due to external forces. Because the force on the forgings only acts on their surfaces, this leads to uneven stress distribution inside them. Some of these uneven stresses remain inside the forgings after the external forces are removed and the forgings rebound, which is called residual stress. The generation of residual stress is usually closely related to factors such as uneven cooling, plastic deformation and phase change. The residual stress in forgings will have a significant effect on their mechanical properties, such as reducing fatigue strength, tensile strength and toughness, and may cause stress corrosion cracking and dimensional deformation, thereby affecting the service life and reliability of the forgings.

[0003] In order to eliminate the residual stress in the forgings and improve their comprehensive performance, thermal aging treatment is a common method, that is, heating the forgings to a certain temperature and keeping it warm for a period of time, so that the stress inside the metal can be released through thermal vibration and diffusion, thereby reducing the residual stress. The specific operation steps include heating the forgings to the specified aging temperature, and then maintaining this temperature for a period of time to ensure that the internal stress is fully released, and then slowly cooling the forgings to avoid the generation of new stress. Thermal aging treatment can effectively reduce the residual stress inside the forgings and improve their mechanical properties.

[0004] However, although thermal aging treatment has a significant effect in eliminating residual stress in forgings and has a wide range of applications, its process has some shortcomings. Since thermal aging treatment requires the forging to be slowly cooled from a higher temperature, and usually even starts from the recrystallization temperature of the forging, this process will inevitably lead to the precipitation of a second phase inside the forging. The precipitation of the second phase will change the crystal structure of the metal, and may form a hard and brittle phase or other structure that is not conducive to mechanical properties, thereby deteriorating the comprehensive performance of the forging. In addition, the slow cooling process is time-consuming, has low production efficiency, and consumes a lot of energy. Therefore, how to effectively eliminate residual stress while avoiding the precipitation of the second phase and improving production efficiency is a problem that urgently needs to be solved in the current technical field. Summary of the invention

[0005] In order to solve the above problems and reduce various defects caused by cooling during thermal aging treatment, in a first aspect, the present application provides a method for eliminating residual stress in iron-carbon alloy forgings.

[0006] The present application provides a method for eliminating residual stress of an iron-carbon alloy forging using the following technical solution: A method for eliminating residual stress of an iron-carbon alloy forging comprises the following steps: B1. Provide iron-carbon alloy forgings; B2. heating the iron-carbon alloy forging to a first temperature greater than 200° C.; B3. Vibrate the iron-carbon alloy forging and cool it.

[0007] Specifically: B1. Provide iron-carbon alloy forgings; B2. heating the iron-carbon alloy forging to a first temperature, wherein the first temperature is greater than a recrystallization temperature of the iron-carbon alloy forging; B3. Vibrate the iron-carbon alloy forging and quench it.

[0008] By adopting the above technical scheme, the iron-carbon alloy forging is rapidly cooled from the first temperature, and the microstructure is solidified before the second phase has time to precipitate. The iron-carbon alloy forging after cooling still retains the fine-grained structure at the first temperature. The thermal stress generated by the vibration and cooling process is compounded. After the composite stress breaks through the yield limit of the iron-carbon alloy forging, the thermal stress is released, and the generation of new residual stress is also reduced.

[0009] Optionally, the step B3 includes: providing a quenching pool, the quenching pool containing a high-frequency vibrating quenching liquid, and immersing the iron-carbon alloy forging in the quenching liquid.

[0010] Optionally, the temperature of the quenching liquid in step B3 does not exceed 120° C. during the entire process.

[0011] By adopting the above technical solution, coarse grains and impurity precipitation caused by excessively high final quenching temperature are avoided.

[0012] Alternatively, the present application provides a method for eliminating residual stress of an iron-carbon alloy forging using the following technical solution: A method for eliminating residual stress of an iron-carbon alloy forging comprises the following steps: B1. Provide iron-carbon alloy forgings; B2. heating the iron-carbon alloy forging to a second temperature, wherein the second temperature is greater than a stress relief annealing temperature of the iron-carbon alloy forging; B3, vibrating the iron-carbon alloy forging at the first temperature and keeping it warm; B4. Maintain vibration and cool the iron-carbon alloy forging, with the cooling rate being slower than air cooling.

[0013] By adopting the above technical solution, during the cooling of the iron-carbon alloy forging from the second temperature, the vibration causes adjacent grains to tend to combine, thereby engulfing impurities on the grain boundaries, destroying the weak surface network inside the iron-carbon alloy forging, and enhancing the performance of the iron-carbon alloy forging.

[0014] Optionally, the step B3 includes: providing a vibration pool, the vibration pool containing a vibration medium preheated to the second temperature, and a vibration generator provided on a wall of the vibration pool; placing the iron-carbon alloy forging in the vibration medium, and starting the vibration generator to vibrate the vibration medium and the iron-carbon alloy forging; The step B4 includes keeping the vibration generator working and cooling the vibration medium and the iron-carbon alloy forging synchronously, with the cooling rate being slower than air cooling.

[0015] Optionally, the second temperature is in the range of 500°C-600°C.

[0016] By adopting the above technical solution, the vibration is transmitted from the vibration generator to the iron-carbon alloy forging via the vibration medium, so that the iron-carbon alloy forging maintains good vibration throughout the entire cooling process.

[0017] In a second aspect, the present application provides a device for eliminating residual stress in iron-carbon alloy forgings.

[0018] The present application provides a device for eliminating residual stress of iron-carbon alloy forgings using the following technical solution: A device for eliminating residual stress of an iron-carbon alloy forging comprises a heating component and a vibration component. The heating component is used to heat the iron-carbon alloy forging, and the vibration component is used to vibrate the iron-carbon alloy forging and cool it down.

[0019] Optionally, the vibration assembly includes a vibration pool, a vibration medium contained in the vibration pool, and a vibration generator arranged on the inner wall of the vibration pool.

[0020] Optionally, the vibration assembly further includes a heater, and the heater is used to preheat the vibration medium.

[0021] By adopting the above technical solution, a device adapted to the method for eliminating residual stress of iron-carbon alloy forgings provided in the first aspect is provided.

[0022] In summary, the present application includes at least one of the following beneficial technical effects: 1. At the first temperature, the energy of the internal particles of the iron-carbon alloy forging increases, the activity is enhanced, and the resistance to dislocation movement decreases, so that the residual stress accumulated during the processing of the iron-carbon alloy forging is released, and the subsequent cooling process takes a short time, so there is no condition for the precipitation of the second phase, and the iron-carbon alloy forging still maintains a stable and uniform fine-grained structure at the first temperature; 2. The iron-carbon alloy forgings are vibrated while being cooled. For the iron-carbon alloy forgings cooled from the first temperature, the vibration causes the thermal stress of the material to exceed its yield limit, and the thermal stress originally generated by quenching is converted into plastic deformation consumption. For the iron-carbon alloy forgings cooled from the second temperature, the vibration causes the crystal lattice inside the material to change, and the impurities originally at the grain boundary are swallowed back into the crystal, reducing the destructiveness of the impurities. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flow chart of a method for eliminating residual stress of an iron-carbon alloy forging according to Example 1 of the present application; Figure 2 This is a flow chart of a method for eliminating residual stress of an iron-carbon alloy forging according to Example 2 of the present application; Figure 3 This is an overall structural diagram of a device for eliminating residual stress in an iron-carbon alloy forging according to Example 3 of the present application.

[0024] Explanation of the reference numerals: 1. Heating component; 2. Vibration component; 21. Vibration pool; 22. Vibration medium; 23. Vibration generator. DETAILED DESCRIPTION

[0025] The following is combined with Figure 1-3 This application is described in further detail.

[0026] Thermal aging treatment is a commonly used method to eliminate residual stress in industrial production. It heats the workpiece to a preset temperature, enhances the grain mobility and even causes grain recrystallization, thereby releasing the residual stress accumulated during the workpiece forming process. However, because thermal aging treatment requires the workpiece to be heated to a higher temperature and then slowly cooled, during the cooling process, as the temperature of the workpiece decreases, its microstructure will also change, especially the precipitation of second phases such as cementite along the grain boundaries will greatly deteriorate the performance of the workpiece.

[0027] Therefore, a new residual stress elimination method is needed to alleviate the above defects.

[0028] The embodiment of the present application discloses a method for eliminating residual stress of an iron-carbon alloy forging.

[0029] Example 1 Reference Figure 1 , the method for eliminating residual stress of iron-carbon alloy forgings comprises the following steps: B1. Provide iron-carbon alloy forgings.

[0030] To avoid procedural waste, the iron-carbon alloy forgings provided in step B1 should be pre-inspected to ensure that they are structurally intact, materially uniform, and free of obvious defects.

[0031] It should be noted that, considering the size limitation of subsequent heating, the iron-carbon alloy forgings of this embodiment are preferably used for small standard parts such as screw sleeves, etc. Moreover, the larger the size of the iron-carbon alloy forgings to be processed, the easier it is to accumulate thermal stress during temperature changes, which will also deteriorate product performance.

[0032] B2. Heating the iron-carbon alloy forging to a first temperature, wherein the first temperature is greater than a recrystallization temperature of the iron-carbon alloy forging.

[0033] Preferably, the first temperature is above the alloy transformation temperature. For carbon steel, the first temperature is preferably greater than the austenite temperature.

[0034] B3. Provide a quenching pool, wherein the quenching pool contains a high-frequency vibrating quenching liquid, and immerse the iron-carbon alloy forging in the quenching liquid.

[0035] Exemplarily, a vibration generator is provided on the wall of the quenching pool. The vibration generator may be one or more of an electromagnetic vibrator, a piezoelectric vibrator, an ultrasonic generator or a resonator, and may be configured according to the size and material of the actual iron-carbon alloy forging.

[0036] When the iron-carbon alloy forging is quenched in step B3, because the quenching liquid is in a high-frequency vibration state, the vibration will also be transmitted to the iron-carbon alloy forging. The iron-carbon alloy forging is in a vibrating state during the entire quenching process until its temperature drops to the same temperature as the quenching liquid and is fished out. It should be noted that for iron-carbon alloy forgings made of carbon steel, in order to avoid low-temperature tempering to produce coarse carbides, the volume of the quenching liquid should be controlled, or a cooling or circulation device should be set for the quenching liquid to ensure that the temperature of the quenching liquid is less than 120°C after the iron-carbon alloy forging is cooled.

[0037] The implementation principle of Example 1 is: In this embodiment, after the iron-carbon alloy forging is heated to the first temperature, the grains inside the iron-carbon alloy forging are recrystallized, and the residual stress is released while having an excellent microstructure. Taking carbon steel as an example, on the one hand, as the temperature rises, the energy of the metal particles increases, the movement intensifies, the grain boundaries melt, the dislocations decrease, and the resistance to dislocation movement is greatly reduced, the grains lose their constraints, and the residual stress accumulated in the previous forming process of the iron-carbon alloy forging is released. On the other hand, at the first temperature, the crystal structure inside the iron-carbon alloy forging is austenite, which has a large solubility for the carbon element in the iron-carbon alloy forging, so there are fewer intergranular impurities.

[0038] It should be noted that the first temperature of this embodiment is set to be above the recrystallization temperature. In fact, since forging is one of the processes with the largest residual stress among all metal forming processes, driven by internal stress, the recrystallization temperature can be lower than the austenite transformation temperature of carbon steel, and the austenite transformation temperature will also change with the carbon content of the iron-carbon alloy forging and the forging process. The above analysis simply equates the recrystallization temperature with a preset fixed carbon steel austenite transformation temperature. If in the implementation method where the first temperature is lower than the austenite transformation temperature, the above description of the change in crystal structure is not valid, but the recrystallization and dislocation movement at the first temperature still exist, and the residual stress can still be released.

[0039] Subsequently, as the iron-carbon alloy forging is immersed in the quenching liquid, the iron-carbon alloy forging is rapidly cooled, the internal lattice structure is rapidly solidified, and the cooling process of the iron-carbon alloy forging is completed in a very short time. Although the carbon element in each unit cell after cooling has exceeded its solubility limit, the energy of various particles inside the iron-carbon alloy forging has been greatly reduced at this time, which is not enough to support the movement of impurities such as cementite to the grain boundary. Therefore, the microscopic state of the entire iron-carbon alloy forging still maintains the regular fine-grained structure in step B2, and does not leave enough time for impurities to be enriched between grains like in the cooling process of thermal aging treatment, which deteriorates the plasticity of the iron-carbon alloy forging and increases its brittleness.

[0040] At the same time, because the entire iron-carbon alloy forging is in continuous high-frequency vibration, the generation of thermal stress will be suppressed in this embodiment. Specifically, the thermal stress caused by the rapid cooling of the iron-carbon alloy forging actually stems from the limitations of the current cooling technology, which can only cool the surface of the iron-carbon alloy forging, and then the heat in the high-temperature area in the center of the iron-carbon alloy forging is transferred outward along the temperature gradient. There must be a critical state in this process, that is, the outer layer of the iron-carbon alloy forging has basically shrunk, while the internal high-temperature area is still in contraction, so the thermal stress of the iron-carbon alloy forging after rapid cooling is usually manifested as compressive stress on the outer layer and tensile stress on the inner layer. In this embodiment, under the above critical state, on the one hand, the formation of dislocations is suppressed due to the effect of vibration on the inside of the iron-carbon alloy forging, so that the internal metal has greater plasticity, and on the other hand, the outer layer of the iron-carbon alloy forging is superimposed with the vibration due to the effect of vibration, breaking through the yield limit of the material, so that the outer layer of the iron-carbon alloy forging, which can only undergo elastic deformation, undergoes plastic deformation, and the internal and external cooperation greatly suppresses the residual thermal stress.

[0041] In summary, compared with heat aging treatment, this embodiment does not provide sufficient precipitation of the second phase. Therefore, the iron-carbon alloy forging after cooling still retains its excellent fine-grained structure at high temperature, while eliminating the residual stress of the iron-carbon alloy forging and avoiding the generation of intergranular defects.

[0042] Taking a hypoeutectoid steel cylindrical forging with a carbon content of 0.72% as an example, the original size of the forging is a cylindrical forging with a height of 200 mm and a diameter of 100 mm. It is longitudinally sectioned along its axis and left static to release stress. The maximum warping height of the cross section is 20.18 mm. The maximum warping height of the cross section of the forging after oil quenching is 37.23 mm. After the processing flow of this embodiment, the maximum warping height of the cross section of the forging is 2.03 mm.

[0043] It should be noted that the above data are average values ​​after multiple measurements, and the maximum warpage height represents the height of the projected bow of the section. It only qualitatively analyzes the elimination of internal stress, and does not use the contour method to accurately measure the residual internal stress.

[0044] The embodiment of the present application also discloses a method for eliminating residual stress of an iron-carbon alloy forging.

[0045] Example 2 Reference Figure 2 In this embodiment, a method for eliminating residual stress of an iron-carbon alloy forging comprises the following steps: B1. Provide iron-carbon alloy forgings.

[0046] B2. Heating the iron-carbon alloy forging to a second temperature, wherein the second temperature is greater than a stress relief annealing temperature of the iron-carbon alloy forging.

[0047] Exemplarily, the second temperature is between 500-600°C.

[0048] B3. Provide a vibration pool, wherein the vibration pool contains a vibration medium preheated to the second temperature, and a vibration generator is provided on the wall of the vibration pool; place the iron-carbon alloy forging in the vibration medium, and start the vibration generator to vibrate the vibration medium and the iron-carbon alloy forging.

[0049] The difference from Example 1 is that: the example needs to control the volume of the quenching liquid, or set a cooling or circulation device for the quenching liquid to ensure that the temperature of the quenching liquid is less than 120°C after the iron-carbon alloy forging is cooled; the vibration medium in this example has no temperature difference with the iron-carbon alloy forging, and is only used to transmit the wave energy generated by the vibration generator to the iron-carbon alloy forging. Therefore, the amount of vibration medium used only needs to ensure that the iron-carbon alloy forging can be immersed therein.

[0050] B4. Keep the vibration generator working and cool down the vibration medium and iron-carbon alloy forgings synchronously. The cooling rate is slower than air cooling.

[0051] Exemplarily, the cooling rate is in the range of 50° C. / h-200° C. / h.

[0052] The implementation principle of Example 2 is: The temperature of the iron-carbon alloy forging in this embodiment is controlled at a second temperature, that is, above the stress relief annealing temperature of the iron-carbon alloy forging. The vibration makes the stress environment inside the iron-carbon alloy forging disordered, the precipitation of the second phase is suppressed, the concentration of the second phase on the grain boundary is reduced, and the performance of the iron-carbon alloy forging is optimized.

[0053] Specifically, stress relief annealing is not easy to generate thermal stress due to its slow cooling rate and small temperature difference between the inside and outside. However, the long cooling time makes the iron-carbon alloy forgings exposed to high temperature environment for a long time. The particles inside the iron-carbon alloy forgings have large energy and strong activity. Therefore, the impurities that cannot be dissolved inside the grains are discharged under the action of concentration gradient and stress field, and enriched between the grains to form a weak surface network. The entire cooling process of this embodiment takes place in a high-frequency vibration environment. On the one hand, the vibration causes the stress environment inside the iron-carbon alloy forging to change all the time, and it is difficult to have a stable stress field to allow impurities to be discharged in a directional manner. This leads to a greatly reduced efficiency in the enrichment of impurities on the grain boundaries. On the other hand, because the grains inside the iron-carbon alloy forging continue to vibrate, and the lattice mismatch between adjacent grains inside the iron-carbon alloy forging is extremely low, as the vibration proceeds, when the crystal orientations of two adjacent grains match, there is a certain probability that the two will fuse, causing the original grain boundaries to be swallowed up, and a small number of impurities that move to the grain boundaries are swallowed back into the crystal. In this case, the impurities originally enriched on the grain boundaries will be retained in the crystal or on dislocations, greatly reducing the destructiveness of the impurities to the performance of the iron-carbon alloy forging.

[0054] The embodiment of the present application also discloses a device for eliminating residual stress of iron-carbon alloy forgings.

[0055] Example 3 Reference Figure 3 The equipment for eliminating residual stress of iron-carbon alloy forgings includes a heating component 1 and a vibration component 2. The heating component 1 is used to heat the iron-carbon alloy forgings, and the vibration component 2 is used to vibrate the iron-carbon alloy forgings and cool them down.

[0056] Exemplarily, the heating component 1 is an induction heater, and the vibration component 2 includes a vibration pool 21, a vibration generator 23 disposed on the inner wall of the vibration pool 21, and a vibration medium 22 contained in the vibration pool 21. The vibration medium 22 in this embodiment is a quenching liquid. The induction heater is located directly above the vibration pool 21 and is hollow in the vertical direction. When the iron-carbon alloy forging is poured from the top of the equipment, the iron-carbon alloy forging is heated to a first temperature during the process of passing through the hollow section of the induction heater, and then falls into the vibration pool 21 to achieve quenching.

[0057] Similar to the precautions in Example 1, the equipment of this embodiment should also consider the temperature change of the quenching liquid. An optional embodiment is that the quenching pool is provided with a water inlet and a water outlet located at the bottom of the pool. The quenching liquid maintains synchronous input and output throughout the entire processing flow, and the iron-carbon alloy forgings falling into the vibration pool 21 are output from the water outlet along with the quenching liquid.

[0058] The implementation principle of Example 3 is: A matching processing equipment is provided for the method of eliminating residual stress of iron-carbon alloy forgings in Example 1.

[0059] Example 4 The difference between this embodiment and the third embodiment is that the vibration assembly 2 of this embodiment further includes a heater, which is disposed in the vibration pool 21 and is used to heat the vibration medium 22 .

[0060] The implementation principle of Example 4 is: A matching processing equipment is provided for the method of eliminating residual stress of iron-carbon alloy forgings in Example 2.

[0061] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for eliminating residual stress in iron-carbon alloy forgings. It is characterized in that The following steps are involved: B1. Provide iron-carbon alloy forgings; B2. heating the iron-carbon alloy forging to a first temperature greater than 200° C.; B3. Vibrate the iron-carbon alloy forging and cool it.

2. The method for eliminating residual stress of an iron-carbon alloy forging according to claim 1, It is characterized in that The step B2 comprises: heating the iron-carbon alloy forging to a first temperature, wherein the first temperature is greater than a recrystallization temperature of the iron-carbon alloy forging; The step B3 includes: vibrating the iron-carbon alloy forging and quenching it.

3. The method for eliminating residual stress of an iron-carbon alloy forging according to claim 2, It is characterized in that The step B3 comprises: providing a quenching pool, wherein the quenching pool contains a high-frequency vibrating quenching liquid, and immersing the iron-carbon alloy forging in the quenching liquid.

4. The method for eliminating residual stress of an iron-carbon alloy forging according to claim 3, It is characterized in that The temperature of the quenching liquid in step B3 does not exceed 120° C. during the entire process.

5. The method for eliminating residual stress of an iron-carbon alloy forging according to claim 1, It is characterized in that The step B2 comprises: heating the iron-carbon alloy forging to a second temperature, wherein the second temperature is greater than a stress relief annealing temperature of the iron-carbon alloy forging; The step B3 comprises: vibrating the iron-carbon alloy forging at the second temperature and keeping the temperature; The method further comprises step B4: maintaining vibration and cooling the iron-carbon alloy forging, wherein the cooling rate is slower than air cooling.

6. The method for eliminating residual stress of an iron-carbon alloy forging according to claim 5, It is characterized in that The step B3 comprises: providing a vibration pool, wherein the vibration pool contains a vibration medium preheated to the second temperature, and a vibration generator is provided on the wall of the vibration pool; placing the iron-carbon alloy forging in the vibration medium, and starting the vibration generator to vibrate the vibration medium and the iron-carbon alloy forging; The step B4 includes keeping the vibration generator working and cooling the vibration medium and the iron-carbon alloy forging synchronously, with the cooling rate being slower than air cooling.

7. The method for eliminating residual stress of an iron-carbon alloy forging according to claim 5, It is characterized in that The second temperature is in the range of 500°C-600°C.

8. A device for eliminating residual stress in iron-carbon alloy forgings. It is characterized in that It comprises a heating component (1) and a vibration component (2), wherein the heating component (1) is used to heat the iron-carbon alloy forging, and the vibration component (2) is used to vibrate the iron-carbon alloy forging and cool it down.

9. The device for eliminating residual stress of an iron-carbon alloy forging according to claim 8, It is characterized in that The vibration component (2) comprises a vibration pool (21), a vibration medium (22) contained in the vibration pool (21), and a vibration generator (23) arranged on the inner wall of the vibration pool (21).

10. The device for eliminating residual stress of iron-carbon alloy forgings according to claim 9, It is characterized in that The vibration component (2) also includes a heater, which is used to preheat the vibration medium (22).

Images