A method for forging a 300-ton large-diameter thick cake type martensitic stainless steel forging

Abstract

The application provides a forging method for a 300-ton large-diameter thick cake type martensitic stainless steel forging, and relates to the technical field of forgings. In the application, high-temperature diffusion treatment is performed on the steel ingot, so as to reduce the risk of cracking in the forging process; in the application, the best initial forging temperature and the final forging temperature are determined according to the flow curve and the hot processing diagram of the steel ingot, so as to ensure that the forging is forged in the optimal temperature range, and the risk of cracking in the forging process can be reduced. In addition, in the application, the forging process of wide-narrow anvil combined with double-face alternating rotation edge opening is adopted, so that uneven deformation of the forging can be avoided. In the drawing and compaction process of the application, the suitable anvil type and the single-anvil pressure reduction rate are selected according to the mass of the steel ingot, so that the problem of incomplete compaction of the center of the forging due to insufficient press pressure can be effectively avoided.

Description

Technical Field

[0001] This invention relates to the field of forging technology, and more specifically, to a forging method for 300-ton-class large-diameter thick-disc martensitic stainless steel forgings. Background Technology

[0002] With continuous technological innovation, the demand for large stainless steel forgings in various industries has increased significantly. Among them, 300-ton-class large-diameter thick-disc martensitic stainless steel forgings, due to their special material and large tonnage, are prone to the following problems during the forging process: high deformation resistance, making it difficult to compact the center of the forging; narrow forging temperature range, making it difficult to control the generation and propagation of cracks, and making it easy to crack during the forging process; poor forgeability, making it difficult to control the uniformity of the forming. Summary of the Invention

[0003] The problem solved by this invention is: how to avoid uneven deformation, difficulty in compacting the center of the forging, and easy cracking during the forging process for 300-ton-class large-diameter thick-disc martensitic stainless steel forgings.

[0004] To address the above problems, this invention provides a forging method for 300-ton-class large-diameter thick-disc martensitic stainless steel forgings, comprising:

[0005] Step S1: The steel ingot is subjected to high-temperature diffusion treatment at 1180-1200℃ to obtain a pretreated steel ingot; wherein the mass of the steel ingot is 250-350t;

[0006] Step S2: Press the riser end of the pretreated steel ingot with clamps, and cut off the waste material of the ingot body and the waste material of the riser clamps to obtain the billet;

[0007] Step S3: Perform the first upsetting on the billet to obtain the first preform;

[0008] Step S4: Stretch and compact the first preform to obtain the second preform;

[0009] Step S5: Perform a second upsetting on the second preform and cut off the clamp handle to obtain the third preform;

[0010] Step S6: Perform double-sided alternating rotation with wide and narrow anvils on the third preform to open its edges, thereby obtaining the fourth preform; the height of the fourth preform is H;

[0011] Step S7: After punching the fourth preform, roll the outer circle and flatten the end face to obtain the forging;

[0012] In steps S2-S7, the initial forging temperature of each forging is 1170-1190℃, the final forging temperature is 890-910℃, and a heat preservation treatment is performed before each forging; the heat preservation treatment temperature is 1040-1060℃, and the time is 18-22h.

[0013] When the mass of the steel ingot is 250-299t, in step S4, the drawing anvil used in the drawing and compaction process is a V-shaped anvil with wide upper and lower sides, and the reduction rate of each single anvil pressing is more than 20%; when the mass of the steel ingot is 300-350t, in step S4, the drawing anvil used in the drawing and compaction process is a flat anvil with a platform at the bottom, and the reduction rate of each single anvil pressing is more than 13%.

[0014] In step S6, the step of performing alternating wide and narrow anvil rotation on the third preform includes:

[0015] First, the third preform is opened by alternating double-sided rotation using a wide anvil with a width of 1200mm until its height is h; then, the fourth preform is obtained by continuing to open the edge by alternating double-sided rotation using a narrow anvil with a width of 800mm; where h - H = 200mm.

[0016] Optionally, in step S1, the high-temperature diffusion treatment time is not less than 80 hours.

[0017] Optionally, in step S3, the upsetting ratio of the first upsetting is 1.5-2.5.

[0018] Optionally, in step S4, the elongation ratio during the elongation and compaction process is 2-3.

[0019] Optionally, in step S5, the upsetting ratio of the second upsetting is 1.5-2.5.

[0020] Optionally, in step S6, during the alternating double-sided rotation and opening process of the wide and narrow anvils, the third preform is flipped once every x millimeters when its height decreases, so as to switch the pressure surface, where x is 50-200.

[0021] Optionally, in step S2, the ratio of the mass of the waste material from the sprue to the mass of the steel ingot is not less than 4%.

[0022] Optionally, in step S2, during the process of pressing the riser end clamp of the pretreated steel ingot, the pressing amount during clamping is 8-10% of the billet height.

[0023] Optionally, in step S7, the forging temperature during the flattening process is not higher than 1150°C.

[0024] Optionally, in step S1, the composition of the steel ingot, by weight percentage, includes: C: 0.01-0.04%, Si: 0-0.5%, Mn: 0.60-1.00%, P: 0-0.015%, S: 0-0.002%; Cr: 12.0-13.0%, Ni: 4.50-5.00%, Mo: 0-0.025%, with the balance being Fe and unavoidable impurities.

[0025] Compared with existing technologies, this invention uses high-temperature diffusion treatment on steel ingots to allow elements to diffuse fully, reducing or eliminating microsegregation of various metal elements in the steel, thereby reducing the risk of cracking during forging. Furthermore, this invention determines the optimal initial and final forging temperatures based on the rheological curve and heat treatment diagram of the steel ingot, ensuring that the forging is forged within the optimal temperature range, further reducing the risk of cracking during forging. In addition, this invention employs a forging process using a combination of wide and narrow anvils with alternating double-sided rotation for edge opening. Since the strain distribution differs when using wide and narrow anvils for rotational edge opening, this method can compensate for local deformation, resulting in more uniform and complete forging, thus avoiding uneven deformation. Moreover, in this process, the wide anvil is initially used for alternating double-sided rotational edge opening, and when the height of the forging is 200mm from the target height, the process switches from wide to narrow anvils for alternating double-sided rotational edge opening, ensuring edge material feeding and preventing localized material shortages in the forging, which also helps to avoid uneven deformation. Moreover, during the drawing and compaction process, the present invention selects a suitable anvil type and a suitable single anvil pressing reduction rate according to the quality of the steel ingot, which can effectively avoid the problem of incomplete compaction of the center of the forging due to insufficient press pressure. Attached Figure Description

[0026] Figure 1 This is a schematic flowchart of the forging method for a 300-ton-class large-diameter thick-disc martensitic stainless steel forging in an embodiment of the present invention.

[0027] Figure 2 This is a schematic diagram of the riser end clamping clamp for pre-treated steel ingots in an embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram illustrating the first upsetting of the billet in an embodiment of the present invention;

[0029] Figure 4 This is a schematic diagram of elongation and compaction of the first preform in an embodiment of the present invention;

[0030] Figure 5 This is a schematic diagram of the double-sided alternating rotational opening of the third preform in an embodiment of the present invention using a wide and narrow anvil combination;

[0031] Figure 6This is a schematic diagram of punching holes in the fourth preform in an embodiment of the present invention;

[0032] Figure 7 This is one of the metallographic images of the forging obtained in Example 1;

[0033] Figure 8 The second image shows the metallographic structure of the forging obtained in Example 1.

[0034] Figure 9 This is a schematic diagram of the structure of the forging obtained in Example 1;

[0035] Figure 10 This is a physical image of the third preform obtained in Example 1;

[0036] Figure 11 A physical image of the third preform obtained in Comparative Example 2;

[0037] Figure 12 This is a physical image of the fourth preform obtained in Example 1;

[0038] Figure 13 This is a physical image of the fourth preform obtained in Comparative Example 1. Detailed Implementation

[0039] 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 with reference to the accompanying drawings. Although some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the accompanying drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0040] 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.

[0041] 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.

[0042] It should be noted that the meanings of the relevant limiting terms in the 300-ton-class large-diameter thick disc-shaped martensitic stainless steel forgings in this invention are as follows: "300-ton-class" means that the steel ingot used for forging is 250-350t; "large-diameter thick disc-shaped" means that the forging is a disc-shaped forging with a diameter of not less than 4m and a height of not less than 1m.

[0043] The upper and lower wide V-grooves used in this invention refer to a tool used in the forging process, which has wide V-grooves on both its upper and lower parts. The upper flat anvil and lower platform used in this invention is a mold configuration used in a forging process, wherein the upper mold (upper anvil) is flat, and the lower mold (lower platform) is also flat.

[0044] The wide and narrow anvils used in this invention are flat hammer heads. Double-sided alternating rotational edge opening is a metal forging process that gradually forms the desired edge shape by alternately forging both sides of the workpiece during rotation.

[0045] It should be noted that multiple single-anvil compaction processes are required during the drawing and compaction process. Assuming that the thickness of the billet before a certain single-anvil compaction is M0, and the thickness is reduced to M1 after that single-anvil compaction, the reduction rate of that single-anvil compaction is (M0-M1) / M0.

[0046] It should be noted that the "neck-in phenomenon" refers to a noticeable necking or indentation on a certain cross-section of a workpiece during the forging process due to uneven stress or other factors. This phenomenon often occurs in the middle of the forging, resembling a pinched waist, hence the name. The "localized material shortage" phenomenon refers to a situation where there is insufficient material or uneven thickness in certain parts of the workpiece.

[0047] like Figure 1As shown in the embodiment of the present invention, a forging method for a 300-ton-class large-diameter thick-disc martensitic stainless steel forging includes:

[0048] Step S1: The steel ingot is subjected to high-temperature diffusion treatment at 1180-1200℃ to obtain a pretreated steel ingot; wherein the mass of the steel ingot is 250-350t;

[0049] Step S2, as follows Figure 2 As shown, the riser end of the pretreated steel ingot is clamped and the waste material of the ingot body and the riser clamp are cut off to obtain the billet;

[0050] Step S3, as follows Figure 3 As shown, the billet is subjected to a first upsetting to obtain the first preform;

[0051] Step S4, as follows Figure 4 As shown, the first preform is elongated and compacted to obtain the second preform;

[0052] Step S5: Perform a second upsetting on the second preform and cut off the clamp handle to obtain the third preform;

[0053] Step S6, as follows Figure 5 As shown, the third preform is subjected to alternating wide and narrow anvil rotation on both sides to open its edges, resulting in a fourth preform; the height of the fourth preform is H.

[0054] Step S7, as follows Figure 6 As shown, after punching the fourth preform, the outer circle is rolled and the end face is flattened to obtain the forging;

[0055] In steps S2-S7, the initial forging temperature of each forging is 1170-1190℃, the final forging temperature is 890-910℃, and a heat preservation treatment is performed before each forging; the heat preservation treatment temperature is 1040-1060℃, and the time is 18-22h.

[0056] When the mass of the steel ingot is 250-299t, in step S4, the drawing anvil used in the drawing and compaction process is a V-shaped anvil with wide upper and lower sides, and the reduction rate of each single anvil pressing is more than 20%; when the mass of the steel ingot is 300-350t, in step S4, the drawing anvil used in the drawing and compaction process is a flat anvil with a platform at the bottom, and the reduction rate of each single anvil pressing is more than 13%.

[0057] In step S6, the step of performing alternating wide and narrow anvil rotation on the third preform includes:

[0058] First, the third preform is opened by alternating double-sided rotation using a wide anvil with a width of 1200mm until its height is h; then, the fourth preform is obtained by continuing to open the edge by alternating double-sided rotation using a narrow anvil with a width of 800mm; where h - H = 200mm.

[0059] In this embodiment of the invention, high-temperature diffusion treatment of the steel ingot allows for full diffusion of elements, reducing or eliminating microsegregation of various metallic elements in the steel, thereby lowering the risk of cracking during forging. Furthermore, based on the rheological curve and heat treatment diagram of the steel ingot, the optimal initial and final forging temperatures are determined to ensure that the forging is performed within the optimal temperature range, further reducing the risk of cracking during forging. Additionally, this embodiment employs a forging process using a combination of wide and narrow anvils with alternating double-sided rotation for edge opening. Since the strain distribution differs between wide and narrow anvils during the rotational edge opening process, using a combination of wide and narrow anvils for alternating double-sided rotation can compensate for local deformation, resulting in more uniform and complete forging, thus avoiding uneven deformation. Moreover, in this process, the wide anvil is initially used for alternating double-sided rotation for edge opening, and when the height of the forging is 200mm from the target height, the process switches from wide to narrow anvils for alternating double-sided rotation for edge opening. This ensures material flow at the edges, preventing localized material shortages in the forging and also helping to avoid uneven deformation. In addition, in the drawing and compaction process of this invention, selecting a suitable anvil shape according to the quality of the steel ingot can effectively avoid the problem of incomplete compaction of the center of the forging due to insufficient press pressure.

[0060] In some embodiments of the present invention, in step S1, the high-temperature diffusion treatment time is not less than 80 hours.

[0061] In some embodiments of the present invention, in step S3, the upsetting ratio of the first upsetting is 1.5-2.5.

[0062] In some embodiments of the present invention, in step S4, the elongation ratio during the elongation and compaction process is 2-3.

[0063] In some embodiments of the present invention, in step S5, the upsetting ratio of the second upsetting is 1.5-2.5.

[0064] In some embodiments of the present invention, during step S6, in the process of alternating double-sided rotation and edge opening with wide and narrow anvils, the third preform is flipped once every x millimeters decrease in height to switch the pressure surface, where x is 50-200. This ensures uniform deformation on both sides.

[0065] In some embodiments of the present invention, in step S2, the ratio of the mass of the waste material from the sprue to the mass of the steel ingot is not less than 4%. This removes the defective areas caused by the sprue deposits on the steel ingot.

[0066] In some embodiments of the present invention, in step S2, during the process of pressing the riser end of the pretreated steel ingot with clamps, the pressing amount is 8-10% of the billet height. This better ensures that the center of the clamps coincides with the axis of the steel ingot, and completes the clamping process more quickly and efficiently.

[0067] In some embodiments of the present invention, preferably, the forging temperature during the end-face flattening process in step S7 is not higher than 1150°C. This further improves the grain size of the forging.

[0068] In some embodiments of the present invention, in step S1, the steel ingot comprises, by weight percentage: C: 0.01-0.04%, Si: 0-0.5%, Mn: 0.60-1.00%, P: 0-0.015%, S: 0-0.002%; Cr: 12.0-13.0%, Ni: 4.50-5.00%, Mo: 0-0.025%, with the balance being Fe and unavoidable impurities.

[0069] The present invention will be further described below with reference to specific embodiments.

[0070] Example 1

[0071] A1. A steel ingot is subjected to high-temperature diffusion treatment at 1200℃ to obtain a pretreated steel ingot; wherein the high-temperature diffusion treatment time is 85h, the mass of the steel ingot is 257t, and the height is 3500mm; the composition of the steel ingot by weight percentage includes: C: 0.03%, Si: 0.3%, Mn: 0.8%, P: 0.010%, S: 0.002%; Cr: 12.0%, Ni: 5.00%, Mo: 0.025%, with the balance being Fe and unavoidable impurities.

[0072] A2. Press the riser end of the pretreated steel ingot with clamps and cut off the waste material of the ingot body and the waste material of the riser clamp to obtain a billet; wherein, the mass ratio of the waste material of the ingot body to the mass of the steel ingot is 5%, and the pressing amount when pressing the riser end of the pretreated steel ingot is 9% of the height of the billet.

[0073] A3. The billet is upset for the first time to obtain the first preform; the upset ratio of the first upset is 1.6.

[0074] A4. The first preform is stretched and compacted to obtain the second preform; the stretching and compaction process uses a V-shaped anvil with a top and bottom width, a stretching ratio of 2, and a compaction rate of 20% for each single anvil press.

[0075] A5. The second preform is upset a second time, and the clamp is removed to obtain the third preform; the upset ratio of the second upset is 1.6.

[0076] A6. Double-sided alternating rotation opening with wide and narrow anvils: First, the third preform is opened by alternating rotation with wide anvils with a width of 1200mm until its height is h; then, the double-sided alternating rotation opening is continued with narrow anvils with a width of 800mm to obtain the fourth preform; where h is 1400mm, the height H of the fourth preform is 1200mm, and during the double-sided alternating rotation opening process with wide and narrow anvils, the third preform is flipped once every 50mm decrease in height to switch the pressure surface.

[0077] A7. After punching the fourth preform, roll the outer circle and flatten the end face to obtain a forging; the height of the forging is 1200mm, the outer diameter is 4800mm, and the inner diameter is 1200mm.

[0078] In steps A2-A7, the initial forging temperature of each forging cycle is 1180℃ and the final forging temperature is 900℃. Before each forging cycle begins, a heat preservation treatment is performed. The heat preservation treatment temperature is 1050℃ and the time is 20h.

[0079] Comparative Example 1

[0080] The difference from Example 1 is that step A6 is: using a narrow anvil with a width of 800mm to perform double-sided alternating rotation and opening on the third preform to obtain the fourth preform; wherein, the height H of the fourth preform is 1200mm, and during the double-sided alternating rotation and opening process, the third preform is flipped once every 50mm decrease in height to switch the pressure surface.

[0081] Comparative Example 2

[0082] The difference from Example 1 is that in steps A2-A7, the initial forging temperature of each forging is 1220℃.

[0083] Experimental Example

[0084] The metallographic structure of the forgings obtained in Example 1 was observed, and the results are shown in the figure. Figure 7 and Figure 8 ,from Figure 7 It can be seen that the grain size of this forging is level 2. Figure 8 It can be seen that no ferrite structure is present in this forging. Figure 9To illustrate the structure of the forging obtained in Example 1, samples were taken from positions T1, L1, and T2 of the forging obtained in Example 1 for mechanical property testing. The results are shown in Table 1. As can be seen from Table 1, the performance indicators of the forging meet the requirements of relevant standards, and the mechanical properties of different positions of the forging are not significantly different, indicating that the forging has good uniformity.

[0085] Table 1

[0086] Sampling location Rp0.2 (MPa) <![CDATA[A4(%)]]> Z(％) AKv(J) Standard requirements 620 15 45 ≥90 T1 780 20 65 193 L1 775 18 62 183 T2 720 21 69 198

[0087] It should be noted that in Table 1, Rp0.2 represents the yield strength, AKv is used to characterize the impact toughness, representing the energy absorbed by the material under impact load, A4 represents the elongation after fracture, and Z represents the reduction of area.

[0088] Figure 10 and Figure 11 These are physical images of the third preform in Example 1 and Comparative Example 2, respectively. Figure 10 and Figure 11 It can be seen that the surface of the third preform in Example 1 is free of cracks, while the surface of the third preform in Comparative Example 2 is obviously cracked.

[0089] Figure 12 and Figure 13 These are physical images of the fourth preform in Example 1 and Comparative Example 1, respectively. Figure 12 and Figure 13 It can be seen that the outer circle of the fourth preform in Example 1 is relatively flat and the surface is free of cracks, while the fourth forging in Comparative Example 2 shows a "waist-pinching phenomenon" (…). Figure 13 The Chinese box shows the part).

[0090] 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 forging method for 300-ton-class large-diameter thick-disc martensitic stainless steel forgings, characterized in that, include: Step S1: The steel ingot is subjected to high-temperature diffusion treatment at 1180-1200℃ to obtain a pretreated steel ingot; wherein, the mass of the steel ingot is 250-350t; and the composition of the steel ingot by weight percentage includes: C: 0.01-0.04%, Si: 0-0.5%, Mn: 0.60-1.00%, P: 0-0.015%, S: 0-0.002%; Cr: 12.0-13.0%, Ni: 4.50-5.00%, Mo: 0-0.025%, with the balance being Fe and unavoidable impurities; Step S2: Press the riser end of the pretreated steel ingot with clamps, and cut off the waste material of the ingot body and the waste material of the riser clamps to obtain the billet; Step S3: The billet is upset for the first time to obtain the first preform; the upset ratio of the first upset is 1.5-2.5; Step S4: The first preform is stretched and compacted to obtain the second preform; the stretching ratio during the stretching and compaction process is 2-3. Step S5: Perform a second upsetting on the second preform and cut off the clamp handle to obtain the third preform; the upsetting ratio of the second upsetting is 1.5-2.5; Step S6: Perform double-sided alternating rotation with wide and narrow anvils on the third preform to open its edges, thereby obtaining the fourth preform; the height of the fourth preform is H; Step S7: After punching the fourth preform, roll the outer circle and flatten the end face to obtain the forging; In steps S2-S7, the initial forging temperature of each forging is 1170-1190℃, the final forging temperature is 890-910℃, and a heat preservation treatment is performed before each forging; the heat preservation treatment temperature is 1040-1060℃, and the time is 18-22h. When the mass of the steel ingot is 250-299t, in step S4, the drawing anvil used in the drawing and compaction process is a V-shaped anvil with wide upper and lower sides, and the reduction rate of each single anvil pressing is more than 20%; when the mass of the steel ingot is 300-350t, in step S4, the drawing anvil used in the drawing and compaction process is a flat anvil with a platform at the bottom, and the reduction rate of each single anvil pressing is more than 13%. In step S6, the step of performing alternating wide and narrow anvil rotation on the third preform includes: First, the third preform is opened by alternating double-sided rotation using a wide anvil with a width of 1200mm until its height is h; then, the fourth preform is obtained by continuing to open the edge by alternating double-sided rotation using a narrow anvil with a width of 800mm; where h - H = 200mm.

2. The forging method for 300-ton-class large-diameter thick-disc martensitic stainless steel forgings according to claim 1, characterized in that, In step S1, the high-temperature diffusion treatment time is not less than 80 hours.

3. The forging method for 300-ton-class large-diameter thick-disc martensitic stainless steel forgings according to claim 1, characterized in that, In step S6, during the alternating double-sided rotation and opening process of the wide and narrow anvils, the third preform is flipped once every x millimeters when its height decreases, so as to switch the pressure surface, where x is 50.

4. The forging method for 300-ton-class large-diameter thick-disc martensitic stainless steel forgings according to claim 1, characterized in that, In step S2, the ratio of the mass of the waste material from the sprue to the mass of the steel ingot is not less than 4%.

5. The forging method for 300-ton-class large-diameter thick-disc martensitic stainless steel forgings according to claim 1, characterized in that, In step S2, during the process of pressing the riser end clamp of the pretreated steel ingot, the pressing amount when pressing the clamp is 8-10% of the billet height.

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