Forging method of PCrNi3Mo hollow integral forging type extrusion shaft

Abstract

The invention relates to the technical field of metal forging, in particular to a forging method of a PCrNi3Mo hollow integral forging type extrusion shaft. Comprising the steps that a demolded steel ingot is subjected to high-temperature homogenization treatment, and a to-be-forged part is obtained; the to-be-forged part is heated and then subjected to primary upsetting and drawing-out in sequence, and a first intermediate part is obtained; the first middleware is heated and then subjected to secondary upsetting and punching, and a second middleware is obtained; after the second middleware is heated, the second middleware is drawn out to the middle size through a first core rod, then the second middleware is drawn out to the finished product size from the middle size through a second core rod, and a finished product forge piece is obtained; the diameter of the second core rod is smaller than that of the first core rod, and the diameter of the second core rod is smaller than that of an inner hole of the second middle piece. The problems that in the whole-section forging process of the extrusion shaft, the forging ratio of a flange area is insufficient, and deformation is difficult can be solved.

Description

Technical Field

[0001] This invention relates to the technical field of metal forging, and specifically to a forging method for a PCrNi3Mo hollow integral forging extrusion shaft. Background Technology

[0002] PCrNi3Mo extrusion shafts are key components of extrusion presses. They can be divided into two categories according to their uses: solid shafts and hollow shafts. Since extrusion shafts need to withstand huge pressures and complex stresses during operation, their performance requirements are extremely high.

[0003] Currently, the forging process for extruded shafts mainly includes separate manufacturing followed by splicing and integral forging. Separate manufacturing followed by splicing suffers from drawbacks such as poor overall performance, complex forging processes, and low production efficiency. In contrast, integral forging of extruded shafts, by forging raw materials into a complete shaft body in a single operation, effectively avoids the quality risks associated with splicing, significantly improving the strength and reliability of the extruded shaft. However, during integral forging, the structural characteristics of extruded shafts—large flange diameter and short shaft body—can easily lead to insufficient forging ratio and deformation difficulties in the flange area, resulting in structural defects (grass-like undulations). Furthermore, this structural feature makes dimensional control during forging extremely difficult, easily leading to high dimensional non-conformity rates, significantly increased product scrap rates, and a substantial increase in production costs. Summary of the Invention

[0004] The present invention aims to solve the problems of insufficient forging ratio and difficulty in deformation of flange area in the integral forging process of extrusion shaft.

[0005] To address the above problems, this invention provides a forging method for a PCrNi3Mo hollow integral forging extrusion shaft, comprising: The demolded steel ingot is subjected to high-temperature homogenization treatment to obtain the part to be forged; The workpiece to be forged is heated and then subjected to upsetting and drawing in sequence to obtain the first intermediate part; The first intermediate part is heated and then subjected to a second upsetting and punching process to obtain the second intermediate part. After heating the second intermediate part, the first mandrel is used to draw the second intermediate part to the intermediate size, and then the second mandrel is used to draw the second intermediate part from the intermediate size to the finished size to obtain the finished forging; wherein, the diameter of the second mandrel is smaller than the diameter of the first mandrel, and the diameter of the second mandrel is smaller than the inner diameter of the second intermediate part.

[0006] Optionally, the diameter of the first core rod is 1100 to 1200 mm, and the diameter of the second core rod is 900 to 1000 mm.

[0007] Optionally, the step of heating the billet and then sequentially upsetting and drawing to obtain the first intermediate part includes: placing the billet between an upper V-anvil and a lower V-anvil for drawing.

[0008] Optionally, the step of placing the billet between the upper V-anvil and the lower V-anvil for drawing includes: after pressing one pass, rotating it 90° and shifting it halfway between the anvils, and pressing the next pass.

[0009] Optionally, the step of heating the first intermediate part and then performing secondary upsetting and punching to obtain the second intermediate part includes: placing the first intermediate part between a spherical upsetting cover plate and an upsetting stencil for secondary upsetting.

[0010] Optionally, the upsetting ratio of the primary upsetting to the secondary upsetting is (1:5 to 2):1.

[0011] Optionally, the heating temperatures of the workpiece to be forged and the first intermediate part are 1240 to 1260°C, respectively, and the heating temperature of the second intermediate part is 1190 to 1210°C.

[0012] Optionally, after using a second mandrel to elongate the second intermediate part from the intermediate dimension to the finished size to obtain the finished forging, the method further includes: placing the finished forging in a ventilated area to air cool to 600 to 650°C.

[0013] Optionally, the high-temperature homogenization treatment of the demolded steel ingot includes: first holding the steel ingot at 660 to 680°C for a first stage, then raising the temperature to 700 to 750°C at a heating rate of 50 to 60°C / h for a second stage, then raising the temperature to 850 to 900°C at a heating rate of 50 to 60°C / h for a third stage, and finally raising the temperature to 1240 to 1260°C at a heating rate of 70 to 80°C / h for a fourth stage.

[0014] Optionally, the insulation time of the first stage is determined according to 5 min / mm to 0.6 min / mm, the insulation time of the second stage and the insulation time of the third stage are determined according to 0.3 min / mm to 0.4 min / mm respectively, and the insulation time of the fourth stage is determined according to 0.55 min / mm to 0.65 min / mm.

[0015] The advantages of this invention compared to related technologies include: In the integral forging process of PCrNi3Mo hollow extrusion shaft, this invention obtains the finished forging by sequentially subjecting the demolded steel ingot to high-temperature homogenization treatment, first upsetting and drawing, and second upsetting and drawing. While ensuring a sufficient overall forging ratio in the finished forging, in the final forming stage of forging (finished product firing), a first mandrel with a larger diameter is first used to draw the second intermediate part to its intermediate diameter. Then, a second mandrel with a diameter smaller than the inner diameter of the second intermediate part is used to hollow-shrink the entire second intermediate part, reducing its overall wall thickness until the finished size is reached. Because the diameter of the second mandrel is smaller than the inner diameter of the second intermediate part, a uniform annular gap exists between the second mandrel and the inner wall of the second intermediate part. Under this condition, pressure is applied to the outer wall of the second intermediate part, forcing the forging wall thickness to uniformly shrink and thin towards the center, thereby increasing the degree of plastic deformation in the flange area and effectively increasing the forging ratio of the flange area. Furthermore, the increased deformation helps to forge or eliminate internal defects such as grass-like waves caused by insufficient forging ratio; at the same time, through a controllable empty-shrinkage process, the final outer diameter can be controlled more precisely, solving the problem of difficult control of the size of short and thick forgings and reducing the product scrap rate. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of a forging method for a PCrNi3Mo hollow integral forging extrusion shaft in an exemplary embodiment of the present invention. Figure 2 This is a schematic diagram of the high-temperature homogenization process of steel ingots in an exemplary embodiment of the present invention; Figure 3 This is a schematic diagram of the axial structure of the workpiece to be forged when using an upper V-anvil and a lower V-anvil in an exemplary embodiment of the present invention for drawing. Figure 4 This is a schematic diagram of the lateral structure of the workpiece to be forged when the upper V-anvil and the lower V-anvil are used for full anvil drawing in an exemplary embodiment of the present invention. Figure 5 This is a schematic diagram of the lateral structure of the workpiece to be forged when using an upper V-anvil and a lower V-anvil for staggered half-anvil drawing in an exemplary embodiment of the present invention. Figure 6 This is a schematic diagram of a secondary upsetting process for the first intermediate component in an exemplary embodiment of the present invention; Figure 7 This is a schematic diagram of the clamping process performed on the sprue end of the forging part in Embodiment 1 of the present invention; Figure 8 This is a schematic diagram of the structure of the finished forging in Embodiment 1 of the present invention.

[0017] Explanation of reference numerals in the attached drawings: 1. Part to be forged; 11. Riser end; 12. Sprue end; 2. Upper V-anvil; 3. Lower V-anvil; 4. First intermediate part; 5. Spherical upsetting cover plate; 6. Upsetting sprue; 7. Finished forging. Detailed Implementation

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0019] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the description of this application is for the purpose of describing particular embodiments only and is not intended to limit this application. The term "comprising" and its variations as used herein are open-ended, meaning "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; and the term "optionally" means "optional embodiments". Definitions of other terms will be given in the description below. It should be noted that the concepts of "first," "second," etc., mentioned in this invention are used to distinguish different objects, not to describe a specific order or hierarchy. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0020] Due to its structural characteristics of "large flange diameter and short shaft body," the PCrNi3Mo hollow integral forging extrusion shaft is prone to insufficient forging ratio and deformation difficulties in the flange area during the forging process, further leading to the industry-wide problems of structural defects (grass-like ripples) and dimensional deviations. Therefore, the embodiments of the present invention aim to improve the deformation amount in the flange area through precise control of process parameters and innovative process combinations, thereby ensuring the internal quality and dimensional accuracy of the entire forging.

[0021] This invention provides a forging method for a PCrNi3Mo hollow integral forging extrusion shaft, such as... Figure 1 As shown, it includes: Step S1: The demolded steel ingot is subjected to high-temperature homogenization treatment to obtain the forging part. Specifically, the billet of PCrNi3Mo material is first smelted into an electroslag steel ingot by ESR (electroslag remelting), and then the steel ingot is subjected to high-temperature homogenization treatment. Optionally, the billet comprises the following elements by mass percentage: C: 0.32 to 0.42%, Si: 0.17 to 0.37%, Mn: 0.25 to 0.50%, P: 0.015%, S≤0.003%, Cr: 1.20 to 1.50%, Ni: 3.00 to 3.50%, Mo: 0.35 to 0.45%, V: 0.10 to 0.25%, Cu≤0.25%, As≤0.015%, Sn≤0.015%, Pb≤0.01%, Bi≤0.01%, H≤0.00015%, O≤0.0030%, and the balance Fe.

[0022] In some alternative embodiments, such as Figure 2 As shown, the high-temperature homogenization process specifically includes: first, holding the steel ingot at 660-680℃ for the first stage; then, heating it to 700-750℃ at a rate of 30-50℃ / h for the second stage; then, heating it to 850-900℃ at a rate of 30-50℃ / h for the third stage; and finally, heating it to 1240-1260℃ at a rate of 50-70℃ / h for the fourth stage. The holding time for the first stage is determined from 5 min / mm to 0.6 min / mm; the holding times for the second and third stages are determined from 0.3 min / mm to 0.4 min / mm; and the holding time for the fourth stage is determined from 0.55 min / mm to 0.65 min / mm. It can be understood that "min / mm" represents the holding time corresponding to a 1mm increase in the wall thickness of the forging, meaning the holding time for each stage is adjusted according to the actual wall thickness of the forging. More specifically, the heating rate for each segment can be 50℃ / h, 50℃ / h, and 70℃ / h, respectively.

[0023] It is understandable that PCrNi3Mo steel, due to its high alloy element content and relatively poor thermal conductivity, should not be heated too quickly. Therefore, controlling the heating rate during high-temperature homogenization treatment and using a stepped, slow heating method can effectively balance the internal and external temperatures, ensuring uniform deformation of all parts of the billet, avoiding excessive local deformation, and preventing ingot cracking due to excessive thermal stress. Furthermore, prolonged holding at medium and low temperatures promotes the diffusion of alloying elements, thereby reducing or eliminating dendrite segregation in the electroslag ingot, achieving microstructure homogenization, improving the material's processing plasticity, and creating conditions for subsequent large deformation forging.

[0024] Step S2: After heating the workpiece to be forged, perform upsetting and drawing in sequence to obtain the first intermediate part.

[0025] Specifically, before upsetting and drawing, a 100MN hydraulic press can be used to press the end of the steel ingot after high-temperature homogenization, and then 150mm of material is cut from the riser end using gas cutting. It should be understood that gas cutting refers to the process of cutting metal using a gas flame (such as an oxy-acetylene flame); the riser is the upper supplementary structure of the forging, used to compensate for shrinkage during metal solidification and ensure the density of the casting. It is understood that the riser portion of the forging usually needs to be removed after casting. Therefore, approximately 150mm of metal from the end of the riser is removed to eliminate defects or facilitate subsequent processing. In practice, the riser position must first be located, and then gas cutting equipment is used to cut from the riser end, ensuring a 150mm length is removed.

[0026] It should be noted that after gas cutting the riser, the workpiece to be forged is returned to the heating furnace for reheating. The heating temperature of the workpiece is 1240 to 1260℃, and the holding time is determined according to 0.65 min / mm to 0.75 min / mm. After exiting the furnace, it is subjected to a first upsetting on a 150MN hydraulic press. The upsetting ratio for the first upsetting is in the range of (1:5 to 2:1). The first upsetting serves to compact the billet, reducing the billet height and increasing the cross-sectional area, thus providing a suitable cross-sectional size for subsequent drawing.

[0027] In some alternative embodiments, refer to Figure 3 As shown, the forged part, after initial upsetting, is placed between an upper V-anvil and a lower V-anvil for drawing. It should be noted that the basic principle of drawing is to use external force to cause plastic deformation of the billet along its length, reducing its cross-sectional area. During this process, the metal grains inside the billet are compressed and stretched, thereby refining the grain structure and improving the mechanical properties and density of the forging. Figure 3 As shown, the opening angles of the upper and lower V-anvils can both be 135°, and the anvil width ratio (w / d) can be controlled at around 0.6. The KD drawing method features a wide anvil and large reduction. Under high-temperature diffusion heating conditions, the plasticity of the steel ingot is improved, and efficient forging of core defects can be achieved through large reduction forging. Compared with the traditional upper flat anvil and lower platform method, this process can significantly reduce axial tensile stress, and the V-shaped anvil constraint can enhance the compaction effect at the center of the billet, resulting in a more uniform distribution of equivalent strain.

[0028] More specifically, when using an upper V-anvil and a lower V-anvil to draw the workpiece after a single upsetting, the process includes: after one pass, rotating the workpiece 90° and offsetting it by half anvil, then passing it down for another pass, while controlling the reduction in each pass to be 15% to 25% of the billet height. It should be noted that during the drawing process, multiple passes are required to achieve step-by-step control of internal stress and uniform deformation. This can be understood as... Figure 4 and Figure 5As shown, "one pass" refers to a single pressing process; "full anvil" means the width of the upper V-anvil is basically the same as the width of the part of the billet being pressed; "half-anvil offset" means that in the next pressing pass, the upper V-anvil is moved about half anvil width along the length (axial direction) of the billet. In this embodiment, during each pressing pass, the anvil must completely cover the billet along its length to ensure sufficient forging of internal defects and greatly improve the material's density. After each pressing pass, the billet needs to be rotated 90° circumferentially before the next pressing pass. This is to alternate the deformation direction, promoting internal metal flow and defect welding. Controlling the upper and lower V-anvils to perform half-anvil offset pressing in the next pressing pass is to avoid repeated stress on the same area and reduce the risk of cracking.

[0029] Step S3: After heating the first intermediate part, perform a second upsetting and punching to obtain the second intermediate part.

[0030] In this step, the first intermediate component is returned to the heating furnace for heating. The heating temperature of the first intermediate component can be controlled within the range of 1240 to 1260℃, and the holding time is determined according to 0.65 min / mm to 0.75 min / mm. Then... Figure 6 As shown, the heated first intermediate part is placed between the spherical upsetting cover plate and the upsetting stencil for secondary upsetting. After upsetting, a hole is punched, and finally, the punched burrs are removed by gas cutting. It should be noted that the upsetting ratio of the secondary upsetting can also be controlled between (1:5 and 2:1). The purpose of secondary upsetting is to further compact the billet and at the same time provide a suitable cross-sectional size for punching.

[0031] Step S4: After heating the second intermediate part, first use the first mandrel to draw the second intermediate part to the middle size, and then use the second mandrel to shrink the second intermediate part from the middle diameter to the finished size to obtain the finished forging.

[0032] Specifically, the diameter of the second mandrel is smaller than that of the first mandrel. Optionally, the diameter of the first mandrel can range from 1100 to 1200 mm (e.g., 1180 mm), and the diameter of the second mandrel is smaller than the inner diameter of the second intermediate part, specifically from 900 to 1000 mm (e.g., 980 mm). It should be noted that mandrel drawing is a process that uses a mandrel as an internal support tool for a hollow blank, and then processes the blank using a hydraulic press to reduce its outer diameter and increase its length while keeping the inner diameter essentially unchanged. In this embodiment, the main purpose of first mandrel drawing is to increase the length of the second intermediate part by stretching it axially, while the main purpose of second mandrel drawing is to reduce the wall thickness radially along the second intermediate part.

[0033] It is understood that in the final forming stage of forging (finished product firing), the second intermediate part is first drawn to the intermediate diameter (e.g., outer diameter = finished product outer diameter + 150mm) using a first mandrel with a larger diameter (close to the inner diameter of the second intermediate part). Then, a second mandrel with a smaller diameter than the inner diameter of the second intermediate part is used to perform overall shrinkage of the second intermediate part (shrinkage amount is about 150mm) to reduce its overall wall thickness until the finished product size is reached. During the first mandrel drawing process, due to the high metal flow resistance and the large flange diameter with a short axial length, the force during the drawing process is difficult to transmit to the flange area, resulting in a small deformation in the flange area. Therefore, by further using a second mandrel for overall shrinkage, since the diameter of the second mandrel is smaller than the inner diameter of the second intermediate part, a uniform annular gap exists between the second mandrel and the inner wall of the second intermediate part. Under this state, pressure is applied to the outer wall of the second intermediate part, forcing the forging wall thickness to shrink and thin uniformly towards the center, thereby increasing the degree of plastic deformation in the flange area and effectively increasing the forging ratio of this critical area. Furthermore, the increased deformation helps to forge or eliminate internal defects such as grass-like waves caused by insufficient forging ratio; at the same time, through a controllable empty-shrinkage process, the final outer diameter can be controlled more precisely, solving the problem of difficult control of the size of short and thick forgings and reducing the product scrap rate.

[0034] In some optional embodiments, the heating temperature of the second intermediate part is 1190 to 1210°C. In the final firing, a lower furnace temperature helps control the actual starting temperature of the forging after it exits the furnace, avoiding overheating that could lead to coarse grains or overheated structures, thus ensuring a fine and uniform final microstructure. It should be noted that if the forging is not completed in one firing, the finished product must be returned to the furnace for further heating and forging. In this case, the furnace temperature should be controlled at 1140 to 1160°C, and the holding time should be determined based on 0.55 min / mm to 0.8 min / mm.

[0035] Step S5: Place the finished forging in a ventilated area and air-cool it to 600-650℃ before heat treatment to obtain a PCrNi3Mo hollow integral forged extruded shaft. It can be understood that placing the forging in a ventilated area for rapid cooling after production inhibits grain growth, resulting in a finer and more uniform microstructure. At this point, the microstructure of the forging is relatively stable, providing a better initial microstructure for subsequent heat treatment. It should be noted that subsequent heat treatment generally refers to tempering the finished forging through quenching and high-temperature tempering processes.

[0036] The present invention will be described in detail below through a specific embodiment: Example 1 In this embodiment, the billet material is PCrNi3Mo, the ingot shape is 107T, and the steelmaking method is ESR (electroslag remelting). The specific steps for forging this electroslag ingot into an extrusion shaft include: Step (1): After the steel ingot is demolded, it is subjected to high temperature homogenization treatment to obtain the forging part: first, it is held at 670℃ for 20h, then heated to 750℃ at a heating rate of 50℃ / h and held for 15h, then heated to 850℃ at a heating rate of 50℃ / h and held for 15h, and finally heated to 1250℃ at a heating rate of 70℃ / h and held for 20h.

[0037] Step (2): As Figure 7 As shown, a 100MN hydraulic press is used to perform a clamping process on the sprue end of the forging part, forming a clamping jaw of 650mm in length. At the same time, 150mm of the riser end is cut with gas and discarded (including the cutting edge). The forging part is then returned to the heating furnace, with the furnace temperature set at 1250℃ and the holding time set at 25h. After exiting the furnace, it is upset once on a 150MN hydraulic press to a length of 1750mm and a diameter of 2740mm. Then, the forging part is placed between an upper V-anvil and a lower V-anvil and drawn to a diameter of 1940mm and a length of 3490mm, obtaining the first intermediate part.

[0038] Step (3): Return the first intermediate part to the heating furnace. Set the furnace temperature to 1250℃ and hold for 25 hours. After exiting the furnace, perform a second upsetting on the first intermediate part using an upsetting auger and a spherical upsetting cover plate on a 150MN hydraulic press. Upset the part to a length of 1600mm and a diameter of 2820mm, and punch holes to an inner diameter of 1200mm. Finally, use an air cutter to remove the punched burrs to obtain the second intermediate part.

[0039] Step (4): Return the second intermediate part to the heating furnace. Set the furnace temperature to 1200℃ and hold for 10 hours. After exiting the furnace, perform mandrel drawing on a 150MN hydraulic press. First, use a first mandrel with a diameter of 1180mm to draw it to an outer diameter of 2700mm, an inner diameter of 1180mm, and a length of 1930mm. The drawn mandrel is then cut to... Figure 5 As shown; subsequently, a second mandrel with a diameter of 980mm was used to hollow out the workpiece to the finished size, and the end was cut with gas to obtain the finished forging. The dimensions of the finished forging are as follows. Figure 8 As shown.

[0040] Step (5): Place the finished forging in a ventilated area for rapid cooling. When the temperature reaches 650℃, the microstructure is relatively stable. Then, it is put into a heat treatment furnace for further processing.

[0041] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A method of forging a PCrNi3Mo hollow integral-extruded axle, characterized in that, The application relates to a method for manufacturing a large-size steel forging product. The steel ingot after demoulding is subjected to high-temperature homogenization treatment to obtain a to-be-forged piece; The to-be-forged piece is heated and then subjected to primary upsetting and elongation to obtain a first intermediate piece; The first intermediate piece is heated and then subjected to secondary upsetting and punching to obtain a second intermediate piece; The second intermediate piece is heated, elongated to an intermediate size by using a first mandrel, and then elongated to a finished product size by using a second mandrel to obtain a finished product forging; wherein the diameter of the second mandrel is smaller than that of the first mandrel, and the diameter of the second mandrel is smaller than the inner hole diameter of the second intermediate piece.

2. The PCrNi3Mo hollow integral-forged extrusion shaft forging method according to claim 1, characterized in that, The diameter of the first mandrel is 1100-1200 mm, and the diameter of the second mandrel is 900-1000 mm.

3. The PCrNi3Mo hollow integral-forged extrusion shaft forging method according to claim 1, characterized by, The to-be-forged piece is placed between the upper V anvil and the lower V anvil for elongation.

4. The method of claim 3, wherein the PCrNi3Mo hollow integral forged extrusion shaft is characterized by, After one pass is completed, the to-be-forged piece is turned by 90 degrees and is placed in the upper V anvil and the lower V anvil for the next pass.

5. The method of claim 1, wherein the PCrNi3Mo hollow integral forged extrusion shaft is characterized by, The first intermediate piece is placed between the spherical upsetting cover plate and the upsetting leakage disc for secondary upsetting.

6. The PCrNi3Mo hollow integral-forged extrusion shaft forging method according to claim 1, characterized by The upsetting ratio of the primary upsetting and the secondary upsetting is (1:5-2):

1.

7. The PCrNi3Mo hollow integral-forged extrusion shaft forging method according to claim 1, characterized by The heating temperature of the to-be-forged piece and the first intermediate piece is 1240-1260 DEG C respectively, and the heating temperature of the second intermediate piece is 1190-1210 DEG C.

8. The method of claim 1, wherein the PCrNi3Mo hollow integral forged extrusion shaft is characterized by, After the second intermediate piece is elongated to the finished product size by using the second mandrel to obtain the finished product forging, the finished product forging is placed in a ventilated place for air cooling to 600-650 DEG C.

9. The method of claim 1, wherein the PCrNi3Mo hollow integral forged extrusion shaft is characterized by, The high-temperature homogenization treatment of the steel ingot after demoulding comprises the following steps: the steel ingot is first subjected to first stage heat preservation at 660-680 DEG C, then is subjected to second stage heat preservation at 700-750 DEG C at a heating rate of 50-60 DEG C / h, then is subjected to third stage heat preservation at 850-900 DEG C at a heating rate of 50-60 DEG C / h, and finally is subjected to fourth stage heat preservation at 1240-1260 DEG C at a heating rate of 70-80 DEG C / h.

10. The method of claim 9, wherein the PCrNi3Mo hollow integral forged extrusion shaft is characterized by, The time of the first stage heat preservation is determined according to 5 min / mm-0.6 min / mm, the time of the second stage heat preservation and the third stage heat preservation is determined according to 0.3 min / mm-0.4 min / mm respectively, and the time of the fourth stage heat preservation is determined according to 0.55 min / mm-0.65 min / mm.

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