Preparation method for improving grain uniformity of 38crmoala ring-shaped forgings

Abstract

The application discloses a preparation method for improving the grain uniformity of a 38CrMoAlA ring-shaped forge piece, and comprises the following steps: S100, heating a cylindrical blank to an initial forging temperature to form an initial forging blank; S200, sequentially performing Y-axis lengthening, Y-axis upsetting, X-axis lengthening, X-axis upsetting, Z-axis lengthening and Z-axis upsetting on the square blank on a free forging hammer to form a square forging blank; S300, heating the square forging blank to a forging temperature in a furnace; S400, sequentially performing chamfering, rounding, punching and ring binding on the re-furnace forging blank on the free forging hammer to form a ring-shaped blank; S500, performing shot blasting on the ring-shaped blank; S600, performing heat stabilization treatment on the ring-shaped blank processed in the step S500, so that the grains of the ring-shaped blank meet the requirements of uniformity and smallness; and S700, performing rough turning on the ring-shaped blank processed in the step S600 to form a ring-shaped forge piece.

Description

Technical Field

[0001] This invention relates to the technical field of structural steel ring forging, and in particular, to a method for improving the uniformity of grain size in 38CrMoAlA ring forgings. Background Technology

[0002] 38CrMoAlA steel is a commonly used nitriding steel with excellent carburizing and mechanical properties. After nitriding, the surface exhibits high wear resistance and fatigue strength. For 38CrMoAlA gear ring parts used in engines, the grain size must be no less than grade 5 before nitriding. The ring gear ring forging is upset on a free forging hammer, punched, then expanded and forged. The heat treatment process is normalizing (930℃, air cooling) + high-temperature tempering (730℃, air cooling) + quenching (930℃, oil cooling) + tempering (630℃, oil cooling). The ring gear ring undergoes multiple heat treatments on a free forging hammer, and the forming process is manual. The deformation varies significantly across different parts of the forging, leading to uneven grain size. Since the driving force for grain growth increases with increasing grain inhomogeneity, the austenite grain growth tendency is significant during the high-temperature heating (quenching heating) process. Therefore, the grain size of the gear ring forging shows the following characteristics during grain size inspection: Figure 1 The uneven grain size shown indicates an unqualified grain size. Due to the uneven grain size, the durability and fatigue resistance of the parts are poor, making it difficult to meet the requirements of nitriding treatment. Summary of the Invention

[0003] This invention provides a method for improving the uniformity of grain size in 38CrMoAlA ring forgings, thereby solving the technical problem of how to improve the uniformity of grain size in 38CrMoAlA ring forgings so that the grain size meets the requirements of nitriding treatment.

[0004] According to one aspect of the present invention, a method for improving the grain size uniformity of 38CrMoAlA ring forgings is provided, for preparing 38CrMoAlA ring forgings and improving the grain size uniformity of 38CrMoAlA ring forgings, comprising the following steps:

[0005] S100: A cylindrical billet made of 38CrMoAlA steel raw material is placed in a heating furnace and heated to the initial forging temperature to form an initial forging billet;

[0006] S200: The initial forging billet is forged into a square billet on a free forging hammer. Then, the square billet is sequentially drawn along the Y-axis, upset along the Y-axis, drawn along the X-axis, upset along the X-axis, drawn along the Z-axis, and upset along the Z-axis to form a square forging billet.

[0007] S300: The square forging billet is placed back into the heating furnace and heated to the forging temperature to form a recycled forging billet;

[0008] S400: The forged billet is chamfered, rolled, punched and circumferentially rolled on a free forging hammer to form a ring-shaped billet.

[0009] S500: Shot blasting of ring-shaped billets to remove surface oxide scale;

[0010] S600: Perform heat stabilization treatment on the annular billet processed in step S500 so that the grains of the annular billet meet the requirements of uniformity and fineness.

[0011] S700: The annular blank processed in step S600 is rough-machined to form an annular forging that meets the design requirements.

[0012] Further, step S100 includes the following steps:

[0013] S101: A cylindrical billet made of 38CrMoAlA steel raw material is placed in a heating furnace for preheating. The preheating temperature is 850±20℃, and the holding time is t0 = heating coefficient δ0×D0, where D0 is the cross-sectional diameter of the cylindrical billet, and the heating coefficient δ0 = 0.6.

[0014] S102: The preheated cylindrical billet is heated at a high temperature in a heating furnace. The high temperature is 1120±20℃, and the holding time is t1 = heating coefficient δ1×D0, where the heating coefficient δ1 = 0.4.

[0015] Step S200 includes the following steps:

[0016] S201, the initial forging billet is forged into a square billet on a free forging hammer, and then... Where D0 is the diameter of the initial forging billet, H0 is the length of the initial forging billet, and L... x1 L y1 L z1 These represent the length dimensions of the square blank in the X, Y, and Z directions, respectively.

[0017] S202, elongate the square blank from step S201 along the Y-axis direction, and make... elongated L y2 For free dimensions, where, when When μ∈[0.6,0.7], when When μ∈[0.7,0.8]; H is the height dimension of the annular blank after ring binding in step S400; L x2 L y2 L z2 The length of the square billet in the X, Y, and Z directions after it has been drawn along the Y-axis.

[0018] S203, the billet that has been elongated along the Y-axis in step S202 is upset along the Y-axis, and the size of the billet upset along the Y-axis is equivalent to the size of the square billet in step S201.

[0019] S204, the billet after being upset along the Y-axis in step S203 is drawn out along the X-axis, and the size of the billet after being drawn out along the X-axis is equivalent to the size of the billet after being drawn out along the Y-axis in step S202.

[0020] S205, the billet that has been elongated along the X-axis in step S204 is upset along the X-axis, and the size of the billet upset along the X-axis is equivalent to the size of the square billet in step S201.

[0021] S206, elongate the billet after upsetting along the X-axis in step S205 along the Z-axis, and make L... x6 ≈L y6 =γ L z6 For free dimensions, where, when When γ∈[0.45,0.5], when When γ∈[0.5,0.55], L x6 L y6 L z6 The length of the billet drawn along the Z-axis in the X, Y, and Z directions;

[0022] S207, the billet elongated along the Z-axis in step S205 is upset along the Z-axis, and... L z7 =1.05H, L x7 L y7 L z7 The length of the square forging billet in the X, Y, and Z directions.

[0023] Furthermore, in step S300, the temperature for reheating in the furnace is 1120±20℃, and the holding time t2 = heating coefficient δ2×L z7 The heating coefficient δ2 = 0.2.

[0024] Further, step S400 includes the following steps:

[0025] S401, the edges of the forged billet in the Z-axis direction are rounded on the forging hammer to form a cylindrical initial billet;

[0026] S402, the cylindrical blank is rolled into a cylindrical forging blank;

[0027] S403, punching holes along the central axis of the cylindrical forging billet to form an annular rough billet;

[0028] S404 involves ring-binding the annular rough billet to form an annular billet.

[0029] Further, step 600 includes the following steps:

[0030] S601, the annular billet processed in step S500 is normalized at a temperature of 930±10℃, held for 150 minutes and then cooled.

[0031] S602, the annular billet cooled in step S601 is subjected to initial tempering at a tempering temperature of 730±10℃, held for 120 minutes and then cooled.

[0032] Step S603: The annular billet cooled in step S602 is subjected to low-temperature quenching at a temperature of 790±10℃, and then cooled after holding at that temperature for 180 minutes.

[0033] Step S604: The annular billet cooled in step S603 is subjected to a second tempering at a tempering temperature of 610±10℃, held for 90 minutes, and then cooled.

[0034] Step S605: Quench the annular billet cooled in step S604 at a quenching temperature of 930±10℃, hold for 150 min and then cool.

[0035] Step S606: The annular billet cooled in step S605 is tempered three times at a tempering temperature of 630±10℃, held for 120 minutes, and then cooled.

[0036] Furthermore, in steps S601 and S602, static air cooling is adopted after the heat preservation is completed.

[0037] Furthermore, in steps S603, S605, and S606, oil cooling is used after the heat preservation is completed.

[0038] Furthermore, in step S604, water cooling is used after the heat preservation is completed.

[0039] Furthermore, in step S700, the surface roughness of the annular billet after rough turning reaches Ra1.6.

[0040] The present invention has the following beneficial effects:

[0041] In the preparation method of improving the uniformity of grain size of 38CrMoAlA ring forgings of the present invention, the initial forging billet is subjected to elongation and upsetting forging along the three axes of the spatial rectangular coordinate system on a free forging hammer in sequence, so that the deformation in each direction is sufficient, thereby making the grain structure uniform. Then, after reheating in the furnace, the chamfering, rounding, punching and ring rolling of the reheated forging billet are completed in one go. The ring making and ring rolling are completed in one reheating, which can reduce the energy consumption of multiple heatings and avoid the defects of uneven grain structure caused by multiple heating of billet and gas induced by manual forging. Subsequently, the ring billet is subjected to heat stabilization treatment to obtain uniform and fine initial grains, ensuring the uniformity of grain size of the forging and the grain size level meeting the technical specifications.

[0042] In actual operation, the cylindrical billet of 38CrMoAlA is first heated to the initial forging temperature. Then, the billet is sequentially drawn along the Y-axis, upset along the Y-axis, drawn along the X-axis, upset along the X-axis, drawn along the Z-axis, and upset along the Z-axis on a free forging hammer to form a square billet. The square billet is then reheated in the furnace. The reheated billet is then sequentially chamfered, rounded, punched, and ring-rolled on a free forging hammer to form a ring billet. The ring billet is then shot-blasted to remove the surface oxide scale. Finally, the ring billet undergoes heat stabilization treatment, specifically including the following steps. The process involves: first, normalizing the billet at 930±10℃; second, high-temperature tempering at 730±10℃; third, low-temperature quenching at 790±10℃; fourth, secondary tempering at 610±10℃; fifth, quenching at 930±10℃; and sixth, tertiary tempering at 630±10℃. Finally, the heat-treated annular billet is rough-machined to form an annular forging that meets the design requirements.

[0043] In summary, by performing multi-directional forging on cylindrical billets and rationally designing the billet dimensions during the forging process, the initial forging billets are elongated and upsetting in all directions, ensuring sufficient deformation in each direction. This results in uniform grain structure. Furthermore, the use of ring rolling technology instead of manual free forging reduces the number of forming heats and promotes a more uniform microstructure. Simultaneously, adjusting the heat treatment process and optimizing the low-temperature quenching and secondary tempering processes yields uniform and fine initial grains, reducing the tendency for austenite grain growth during subsequent quenching and heating. This ensures uniform grain size in the forgings, and the grain size level meets technical specifications.

[0044] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0045] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0046] Figure 1 This is a schematic diagram showing that the grain size of the existing 38CrMoAlA ring forging is substandard.

[0047] Figure 2 This is a flowchart of a preferred embodiment of the preparation method for improving the uniformity of grain size in 38CrMoAlA ring forgings according to the present invention;

[0048] Figure 3 This is a process flow diagram of step S200 in a preferred embodiment of the present invention;

[0049] Figure 4 This is a process flow diagram of step S400 in a preferred embodiment of the present invention;

[0050] Figure 5 This is a schematic diagram of the improved grain size structure of the 38CrMoAlA ring forging prepared by the preferred embodiment of the present invention, after improving the uniformity of grain size. Detailed Implementation

[0051] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered below.

[0052] like Figures 2-5 As shown in this embodiment, a method for improving the grain size uniformity of 38CrMoAlA ring forgings is used to prepare 38CrMoAlA ring forgings and improve the grain size uniformity of 38CrMoAlA ring forgings, including the following steps:

[0053] S100: A cylindrical billet made of 38CrMoAlA steel raw material is placed in a heating furnace and heated to the initial forging temperature to form an initial forging billet;

[0054] S200: The initial forging billet is forged into a square billet on a free forging hammer. Then, the square billet is sequentially drawn along the Y-axis, upset along the Y-axis, drawn along the X-axis, upset along the X-axis, drawn along the Z-axis, and upset along the Z-axis to form a square forging billet.

[0055] S300: The square forging billet is placed back into the heating furnace and heated to the forging temperature to form a recycled forging billet;

[0056] S400: The forged billet is chamfered, rolled, punched and circumferentially rolled on a free forging hammer to form a ring-shaped billet.

[0057] S500: Shot blasting of ring-shaped billets to remove surface oxide scale;

[0058] S600: Perform heat stabilization treatment on the annular billet processed in step S500 so that the grains of the annular billet meet the requirements of uniformity and fineness.

[0059] S700: The annular blank processed in step S600 is rough-machined to form an annular forging that meets the design requirements.

[0060] In this embodiment, the initial forging billet is sequentially elongated and upsetting along the three axes of a Cartesian coordinate system on a free forging hammer, ensuring sufficient deformation in each direction and resulting in uniform grain structure. After reheating in the furnace, the forged billet undergoes chamfering, rounding, punching, and ring rolling in a single process. This ring-making and ring rolling are completed within a single reheat cycle, reducing energy consumption per heating cycle and avoiding the uneven grain structure defects caused by multiple heating cycles and gas induced during manual forging. Subsequent heat stabilization treatment of the ring-shaped billet yields uniform and fine initial grains, ensuring uniform grain size in the forging and meeting technical specifications, achieving a grain size grade of 6-7. The resulting grain structure is referenced below. Figure 5 The improved crystals obtained by this method are uniform and free from mixed crystals, and their grain size also meets the requirements of nitriding treatment.

[0061] In actual operation, the cylindrical billet of 38CrMoAlA is first heated to the initial forging temperature. Then, the billet is sequentially drawn along the Y-axis, upset along the Y-axis, drawn along the X-axis, upset along the X-axis, drawn along the Z-axis, and upset along the Z-axis on a free forging hammer to form a square billet. The square billet is then reheated in the furnace. The reheated billet is then sequentially chamfered, rounded, punched, and ring-rolled on a free forging hammer to form a ring billet. The ring billet is then shot-blasted to remove the surface oxide scale. Finally, the ring billet undergoes heat stabilization treatment, specifically including the following steps. The process involves: first, normalizing the billet at 930±10℃; second, high-temperature tempering at 730±10℃; third, low-temperature quenching at 790±10℃; fourth, secondary tempering at 610±10℃; fifth, quenching at 930±10℃; and sixth, tertiary tempering at 630±10℃. Finally, the heat-treated annular billet is rough-machined to form an annular forging that meets the design requirements.

[0062] In summary, by performing multi-directional forging on cylindrical billets and rationally designing the billet dimensions during the forging process, the initial forging billets are elongated and upsetting in all directions, ensuring sufficient deformation in each direction. This results in uniform grain structure. Furthermore, the use of ring rolling technology instead of manual free forging reduces the number of forming heats and promotes a more uniform microstructure. Simultaneously, adjusting the heat treatment process and optimizing the low-temperature quenching and secondary tempering processes yields uniform and fine initial grains, reducing the tendency for austenite grain growth during subsequent quenching and heating. This ensures uniform grain size in the forgings, and the grain size level meets technical specifications.

[0063] Further, step S100 includes the following steps:

[0064] S101: A cylindrical billet made of 38CrMoAlA steel raw material is placed in a heating furnace for preheating. The preheating temperature is 850±20℃, and the holding time is t0 = heating coefficient δ0×D0, where D0 is the cross-sectional diameter of the cylindrical billet, and the heating coefficient δ0 = 0.6.

[0065] S102: The preheated cylindrical billet is heated at a high temperature in a heating furnace. The high temperature is 1120±20℃, and the holding time is t1 = heating coefficient δ1×D0, where the heating coefficient δ1 = 0.4.

[0066] In this embodiment, in step S101, the cylindrical billet of 38CrMoAlA is preheated in a heating furnace to ensure that the external and internal temperatures of the billet are consistent, preventing direct high-temperature heating and the resulting temperature inconsistency between the external and internal temperatures, which could lead to deformation and cracking of the forging. Preheating also improves the plasticity of the metal and reduces its resistance to deformation.

[0067] In step S102, the preheated cylindrical billet is heated to a high temperature to reach the initial forging temperature, which further improves the plasticity of the metal and reduces the deformation resistance, so as to facilitate the initial forging process of the cylindrical billet in step S200.

[0068] refer to Figure 2 Here is a process flow diagram for step S200, which includes the following steps:

[0069] S201, the initial forging billet is forged into a square billet on a free forging hammer, and then... Where D0 is the diameter of the initial forging billet, H0 is the length of the initial forging billet, and L... x1 L y1 L z1 These represent the length dimensions of the square blank in the X, Y, and Z directions, respectively.

[0070] S202, elongate the square blank from step S201 along the Y-axis direction, and make... elongated L y2For free dimensions, where, when When μ∈[0.6,0.7], when When μ∈[0.7,0.8]; H is the height dimension of the annular blank after ring binding in step S400; L x2 L y2 L z2 The length of the square billet in the X, Y, and Z directions after it has been drawn along the Y-axis.

[0071] S203, the billet that has been elongated along the Y-axis in step S202 is upset along the Y-axis, and the size of the billet upset along the Y-axis is equivalent to the size of the square billet in step S201.

[0072] S204, the billet after being upset along the Y-axis in step S203 is drawn out along the X-axis, and the size of the billet after being drawn out along the X-axis is equivalent to the size of the billet after being drawn out along the Y-axis in step S202.

[0073] S205, the billet that has been elongated along the X-axis in step S204 is upset along the X-axis, and the size of the billet upset along the X-axis is equivalent to the size of the square billet in step S201.

[0074] S206, elongate the billet after upsetting along the X-axis in step S205 along the Z-axis, and make L... x6 ≈L y6 =γ L z6 For free dimensions, where, when When γ∈[0.45,0.5], when When γ∈[0.5,0.55], L x6 L y6 L z6 The length of the billet drawn along the Z-axis in the X, Y, and Z directions;

[0075] S207, the billet elongated along the Z-axis in step S205 is upset along the Z-axis, and... L z7 =1.05H, L x7 L y7 L z7 The length of the square forging billet in the X, Y, and Z directions.

[0076] In this embodiment, the specific steps include:

[0077] Step S201: The cylindrical initial forging billet is machined into an approximately square square billet using a forging hammer, with a length of... Where D0 is the diameter of the initial forging billet and H0 is the length of the initial forging billet. The purpose of this step is to facilitate the subsequent drawing and upsetting of the billet in various directions.

[0078] Step S202 involves elongating the square billet from step S201 along the Y-axis. The elongation length is variable. Since elongation along the Y-axis will also change the lengths of the square billet in the X and Z directions, it is necessary to ensure [the desired length] during the elongation process. Among them, when When μ∈[0.6,0.7], when When μ∈[0.7,0.8]; H is the height dimension of the annular blank after ring binding in step S400.

[0079] Step 203: The billet that has been elongated along the Y-axis in step S202 is upset along the Y-axis, and the size of the billet upset along the Y-axis is comparable to the size of the square billet in step S201. The forging after this step is upset is convenient for elongation and upset along the X-axis.

[0080] Steps S204 to S205 are used to elongate and upset the forging along the X-axis.

[0081] Steps S206 and S207 involve elongating and upsetting the forging along the Z-axis to process it into a square billet, ensuring that the final dimensions of the square billet match the specified values.

[0082] In summary, elongating and upsetting the initial forging billet in all directions ensures uniform deformation in each direction, resulting in a uniform grain structure and providing a good foundation for subsequent forging into a ring shape.

[0083] Furthermore, in step S300, the temperature for reheating in the furnace is 1120±20℃, and the holding time t2 = heating coefficient δ2×L z7 The heating coefficient δ2 = 0.2. In this embodiment, compared with the initial forging heating, reducing the heating coefficient of the reheating can shorten the holding time after reheating, ensure uniform temperature throughout the billet and save time, while also preventing excessive heating time from causing grain growth.

[0084] refer to Figure 2 Here is a process flow diagram for step S400. Further, step S400 includes the following steps:

[0085] S401, the edges of the forged billet in the Z-axis direction are rounded on the forging hammer to form a cylindrical initial billet;

[0086] S402, the cylindrical blank is rolled into a cylindrical forging blank;

[0087] S403, punching holes along the central axis of the cylindrical forging billet to form an annular rough billet;

[0088] S404 involves ring-binding the annular rough billet to form an annular billet.

[0089] In this embodiment, the forging process is completed after one reheating in the furnace. This processing flow can reduce the number of reheatings, thereby reducing energy consumption. At the same time, it can also avoid the problem of uneven structure caused by multiple heating of billets and manual forging.

[0090] Further, step 600 includes the following steps:

[0091] S601, the annular billet processed in step S500 is normalized at a temperature of 930±10℃, held for 150 minutes and then cooled.

[0092] S602, the annular billet cooled in step S601 is subjected to initial tempering at a tempering temperature of 730±10℃, held for 120 minutes and then cooled.

[0093] Step S603: The annular billet cooled in step S602 is subjected to low-temperature quenching at a temperature of 790±10℃, and then cooled after holding at that temperature for 180 minutes.

[0094] Step S604: The annular billet cooled in step S603 is subjected to a second tempering at a tempering temperature of 610±10℃, held for 90 minutes, and then cooled.

[0095] Step S605: Quench the annular billet cooled in step S604 at a quenching temperature of 930±10℃, hold for 150 min and then cool.

[0096] Step S606: The annular billet cooled in step S605 is tempered three times at a tempering temperature of 630±10℃, held for 120 minutes, and then cooled.

[0097] In this embodiment, for step S601, 38CrMoAlA steel is a hypoeutectoid steel with a normalizing temperature of Ac3+30℃~50℃, and its Ac3 is 885℃. Therefore, a normalizing temperature of 930℃ can be selected, which can help to quickly homogenize the austenite composition. The holding time is calculated based on an effective thickness of 30+4~4.5min / mm. The effective thickness of the forging is 28mm, and the holding time is 150min, which can make the forging fully cooked and obtain a relatively uniform austenite.

[0098] Step S602: The initial tempering can eliminate the internal stress generated by normalizing. For parts with an effective thickness of 25mm to 30mm, the holding time is calculated as 120min.

[0099] In step S603, the Ac1 temperature of 38CrMoAlA is 760℃. Heating is carried out at 30℃ above Ac1. The holding time is calculated based on the effective thickness of 60+4~4.5min / mm. The effective thickness of the workpiece is 28mm. The holding time is 180min. Due to the low heating temperature, the austenitic structure is fine.

[0100] In step S604, tempering is performed at 630°C below Ac1, and the heating time is controlled at 90 minutes to obtain fine starting grains.

[0101] In step S605, the Ac3 temperature of 38CrMoAlA is 885℃, and the heating temperature is Ac3+30℃~50℃. 930℃ is selected to accelerate austenitization. The holding time is calculated based on an effective thickness of 30+4~4.5min / mm. The effective thickness of the workpiece is 28mm, and the holding time is controlled at 150min to avoid coarsening of the austenite grains.

[0102] In step S606, the Ac1 temperature of 38CrMoAlA is 760℃. Tempering can be carried out below Ac1. In order to avoid temper brittleness (within the range of 100℃~400℃), tempering at 630℃ is selected, and the heating time is controlled at 120min. This can obtain a uniform fine-grained structure and good comprehensive performance.

[0103] In this embodiment, to refine the grains of the forging, the heat treatment process is adjusted compared to the prior art, with the addition of steps 603 and 604. After normalizing and initial tempering, low-temperature quenching and secondary tempering are employed to obtain uniform and fine initial grains. Further quenching and tempering are then performed to achieve the desired grain structure. This is because low-temperature quenching and secondary tempering result in more uniform and finer grains. Since the driving force for grain growth increases with increasing grain inhomogeneity, uniform and fine initial grains can reduce the tendency for austenite grain growth during subsequent high-temperature heating processes, i.e., normal quenching heating. This ensures that the grain size and uniformity after heat stabilization treatment meet the requirements.

[0104] Furthermore, both steps S601 and S602 involve static air cooling after the heat preservation process. In this embodiment, air cooling is used for both normalizing and initial tempering to refine the grains, improve the toughness of the forging, and reduce the risk of cracking.

[0105] Furthermore, oil cooling is used in steps S603, S605, and S606 after the heat preservation process. In this embodiment, after the low-temperature quenching in step S603, the forging is rapidly cooled by oil cooling. Because the low-temperature quenching heating temperature results in a fine austenitic structure, oil cooling can make the microstructure of the forging more uniform. Oil cooling in step S605 can reduce the deformation and cracking tendency of the forging. In step S606, oil cooling after three tempering processes can obtain a uniform fine-grained microstructure and achieve better overall performance.

[0106] Furthermore, in step S604, water cooling is used after the heat preservation is completed. In this embodiment, water quenching is used for the secondary tempering, which helps the forging to obtain more uniform and fine initial grains.

[0107] Furthermore, in step S700, the surface roughness of the annular billet after rough machining reaches Ra1.6. In this embodiment, the annular billet after heat treatment is rough machined to ensure that the surface roughness of the forging meets the design requirements, thus forming an annular forging that meets the design requirements.

[0108] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for improving the grain size uniformity of 38CrMoAlA ring forgings, used to prepare 38CrMoAlA ring forgings and improve the grain size uniformity of 38CrMoAlA ring forgings, characterized in that, Includes the following steps: S100: A cylindrical billet made of 38CrMoAlA steel raw material is placed in a heating furnace and heated to the initial forging temperature to form an initial forging billet; S200: The initial forging billet is forged into a square billet on a free forging hammer. Then, the square billet is sequentially drawn along the Y-axis, upset along the Y-axis, drawn along the X-axis, upset along the X-axis, drawn along the Z-axis, and upset along the Z-axis to form a square forging billet. S300: The square forging billet is placed back into the heating furnace and heated to the forging temperature to form a recycled forging billet; S400: The forged billet is chamfered, rolled, punched and circumferentially rolled on a free forging hammer to form a ring-shaped billet. S500: Shot blasting of ring-shaped billets to remove surface oxide scale; S600: Perform heat stabilization treatment on the annular billet processed in step S500 so that the grains of the annular billet meet the requirements of uniformity and fineness. S700: The annular blank processed in step S600 is rough-machined to form an annular forging that meets the design requirements; Step 600 includes the following steps: S601, the annular billet processed in step S500 is normalized at a temperature of 930±10℃, held for 150 minutes and then cooled. S602, the annular billet cooled in step S601 is subjected to initial tempering at a tempering temperature of 730±10℃, held for 120 minutes and then cooled. Step S603: The annular billet cooled in step S602 is subjected to low-temperature quenching at a temperature of 790±10℃, and then cooled after holding at that temperature for 180 minutes. Step S604: The annular billet cooled in step S603 is subjected to a second tempering at a tempering temperature of 610±10℃, held for 90 minutes, and then cooled. Step S605: Quench the annular billet cooled in step S604 at a quenching temperature of 930±10℃, hold for 150 min and then cool. Step S606: The annular billet cooled in step S605 is tempered three times at a tempering temperature of 630±10℃, held for 120 minutes, and then cooled.

2. The preparation method for improving the uniformity of grain size in 38CrMoAlA ring forgings according to claim 1, characterized in that, Step S100 includes the following steps: S101: A cylindrical billet made of 38CrMoAlA steel raw material is placed in a heating furnace for preheating. The preheating temperature is 850±20℃, and the holding time is t0 = heating coefficient δ0×D0, where D0 is the cross-sectional diameter of the cylindrical billet, and the heating coefficient δ0 = 0.

6. S102: The preheated cylindrical billet is heated at a high temperature in a heating furnace. The high temperature is 1120±20℃, and the holding time is t1 = heating coefficient δ1×D0, where the heating coefficient δ1 = 0.

4.

3. The preparation method for improving the uniformity of grain size in 38CrMoAlA ring forgings according to claim 1, characterized in that, Step S200 includes the following steps: S201, the initial forging billet is forged into a square billet on a free forging hammer, and L... L L =0.9 Where D0 is the diameter of the initial forging billet, H0 is the length of the initial forging billet, and L... L L These represent the length dimensions of the square blank in the X, Y, and Z directions, respectively. S202, elongate the square blank from step S201 along the Y-axis direction, and make L... L =μ The elongated L For free dimensions, where, when H > When μ∈[0.6,0.7], when H≤ When μ ∈ [0.7, 0.8]; L represents the height dimension of the annular blank after ring rolling in step S400. L L The length of the square billet in the X, Y, and Z directions after it has been drawn along the Y-axis. S203, the billet that has been elongated along the Y-axis in step S202 is upset along the Y-axis, and the size of the billet upset along the Y-axis is equivalent to the size of the square billet in step S201. S204, the billet after being upset along the Y-axis in step S203 is drawn out along the X-axis, and the size of the billet after being drawn out along the X-axis is equivalent to the size of the billet after being drawn out along the Y-axis in step S202. S205, the billet that has been elongated along the X-axis in step S204 is upset along the X-axis, and the size of the billet upset along the X-axis is equivalent to the size of the square billet in step S201. S206, elongate the billet after upsetting along the X-axis in step S205 along the Z-axis, and make L... L = γ L For free dimensions, where, when H > When γ∈[0.45,0.5], when H≤ When γ∈[0.5,0.55], L L L The length of the billet drawn along the Z-axis in the X, Y, and Z directions; S207, Upset the billet that has been elongated along the Z-axis in step S205 along the Z-axis, and make L L =0.85 L =1.05H, L L L The length of the square forging billet in the X, Y, and Z directions.

4. The preparation method for improving the uniformity of grain size in 38CrMoAlA ring forgings according to claim 3, characterized in that, In step S300, the reheating temperature is 1120±20℃, and the holding time t2 = heating coefficient δ2×L The heating coefficient δ2 = 0.

2.

5. The preparation method for improving the uniformity of grain size in 38CrMoAlA ring forgings according to claim 1, characterized in that, Step S400 includes the following steps: S401, the edges of the forged billet in the Z-axis direction are rounded on the forging hammer to form a cylindrical initial billet; S402, the cylindrical blank is rolled into a cylindrical forging blank; S403, punching holes along the central axis of the cylindrical forging billet to form an annular rough billet; S404 involves ring-binding the annular rough billet to form an annular billet.

6. The preparation method for improving the uniformity of grain size in 38CrMoAlA ring forgings according to claim 1, characterized in that, Both steps S601 and S602 involve static air cooling after the heat preservation is completed.

7. The preparation method for improving the uniformity of grain size in 38CrMoAlA ring forgings according to claim 1, characterized in that, After the heat preservation is completed, oil cooling is used in steps S603, S605 and S606.

8. The preparation method for improving the uniformity of grain size in 38CrMoAlA ring forgings according to claim 1, characterized in that, In step S604, water cooling is used after the heat preservation is completed.

9. The preparation method for improving the uniformity of grain size in 38CrMoAlA ring forgings according to claim 1, characterized in that, In step S700, the surface roughness of the annular billet after rough machining reaches Ra1.6.

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