Large-inner-diameter thick-wall inner-step cylindrical forge piece and preparation method thereof

Abstract

The invention relates to a large-inner-diameter thick-wall inner-step cylindrical forge piece and a preparation method thereof, and belongs to the technical field of forging machining. The preparation method of the large-inner-diameter thick-wall inner-step cylindrical forge piece comprises the steps that S1, a riser presses a jaw, and pre-stretching is conducted; s2, upsetting and drawing out are carried out; s3, upsetting and punching are carried out; s4, drawing out the core rod; s5, overall flattening is carried out; s6, pre-broaching is conducted on the saddle; s7, single-side leveling is carried out; s8, an inner hole step is collected through a collecting table sleeve; and S9, chambering and the like. According to the preparation method, the inner-step cylindrical forge piece with the step height being 200 mm or above and the maximum wall thickness being 1000 mm or above can be successfully prepared, the formability of the obtained inner-step cylindrical forge piece is high, no defect exists, the material utilization rate is high, and the subsequent machining time is shortened.

Description

Technical Field

[0001] The invention relates to the technical field of forging processing, and in particular to a large inner diameter, thick wall, inner step cylindrical forging and a preparation method thereof. Background Art

[0002] Internal step cylindrical forgings are a common type of forgings, mainly used in nuclear power, steam turbines, petrochemicals and other fields. According to relevant research, there is a method for preparing internal step cylindrical forgings, including upsetting process, punching process, first drawing process (after the first drawing, the blank is a frustum, corresponding to the blank wall thickness on the side of the inner hole with the step), first hole expansion process (after the hole expansion, the blank is a conical cylinder), second drawing process (collecting the inner hole boss), second hole expansion process and forging forming steps. This preparation method is used to arrange the metal of the inner boss on the outside of the blank, which is suitable for forgings with a short straight section of the inner hole step and a small step height.

[0003] There is another method for preparing inner step cylindrical forgings, which mainly includes the steps of steel ingot upsetting, drawing, gas cutting, billet upsetting, punching large hole end hole, rolling forging and drawing (flattening the bulge on the outer side of the billet due to punching large hole end hole) and flattening the end surface, turning over and punching small hole end hole and trimming the finished product. When using a large diameter solid punch to punch the hole diameter, especially for preparing a larger inner hole (blind hole), the forming force required is large, and the equipment requirements are high. This preparation method is suitable for small and medium-sized forgings, but not for large thick-walled cylindrical forgings.

[0004] The two currently disclosed preparation methods cannot be used to prepare cylindrical forgings with a large inner diameter, a thick wall thickness and a large inner step height difference. Therefore, a preparation method is urgently needed for preparing cylindrical forgings with a large inner diameter, a thick wall thickness and a large inner step height difference. Summary of the invention

[0005] In view of the above analysis, the present invention aims to provide a large inner diameter, thick wall, inner step cylindrical forging and a preparation method thereof, which are used to prepare cylindrical forgings with a large inner diameter, thick wall thickness and large inner step drop, so that the amount of post-processing machining is reduced.

[0006] The purpose of the present invention is mainly achieved through the following technical solutions:

[0007] In one aspect, the present invention provides a method for preparing a large inner diameter, thick wall, inner step cylindrical forging, comprising the following steps:

[0008] S1: Riser jaw pressing and pre-drawing: The steel ingot is heated to press the jaws, pre-draw the ingot body to obtain the billet;

[0009] S2: Upsetting and drawing: The obtained billet is heated and upset, and then drawn after upsetting, and drawn to a height-to-diameter ratio of 2-2.3 to obtain a forging billet;

[0010] S3: Upsetting and punching: The obtained forging blank is heated and upset to a height of L3 and an outer diameter of D3; then a hollow punch with an outer diameter of Dc is used for punching to obtain a hollow blank;

[0011] S4: mandrel drawing: heating the obtained hollow blank and drawing it to a height L4 to obtain a drawn blank;

[0012] S5: Overall flattening: heating the obtained drawn billet and flattening it to a height of L5 to obtain a flat forging billet;

[0013] S6: pre-expansion of the forging bar: heating the obtained flat forging blank to pre-expand the forging blank, the outer diameter of the forging blank after pre-expansion is D, and the inner diameter of the forging blank is d;

[0014] S7: Single-side leveling: heating the leveled forging blank after pre-expansion and leveling it on one side to a height of L6;

[0015] S8: collecting the inner hole step by collecting the table sleeve: heating the blank obtained after single-side flattening, and drawing it to the forging blank length L0 by using the collecting table sleeve mandrel to obtain a semi-finished forging blank;

[0016] S9: Hole expansion: After the hole is expanded and the receiving sleeve is removed, an inner step cylindrical forging is obtained.

[0017] In the present invention, a steel ingot is prepared according to the existing smelting process, and the size of the steel ingot is: φ (2900-3200mm) × 3500mm. The obtained steel ingot is heated and forged, and the forging steps include riser pressure jaws, pre-drawing, upsetting, drawing, upsetting, punching, mandrel drawing, overall flattening, horse bar pre-expansion, single-side flattening, collecting the inner hole step and expanding the hole. Forging is carried out strictly in accordance with the above steps, and the preparation steps shall not be replaced, especially the order of step S5 overall flattening, step S6 horse bar pre-expansion and step S7 single-side flattening cannot be replaced, and the obtained step cylindrical forging has high formability and can ensure the integrity of the step cylindrical forging.

[0018] Furthermore, in step S1, the steel ingot is heated to 1150-1250°C to press the jaws and pre-draw the long ingot body to obtain the blank.

[0019] In the process of preparing steel ingots, the upper pouring method is generally adopted. After the steel ingot is formed, the upper end of the steel ingot is the riser position, which is used to press into a jaw for clamping by the forging hydraulic press; and the lower end of the steel ingot is the sprue position, which needs to be cut off to prevent impurities from entering the ingot body during the forging process, thereby ensuring the quality of subsequent flaw detection.

[0020] The steel ingot is pre-drawn by a forging hydraulic press to obtain a billet. The main function of pre-drawing is to deform the surface through a small deformation, changing the surface metal from a cast state to a forged state. After pre-drawing, the high-temperature plasticity is significantly improved, the generation of cracks is reduced, and the normal progress of subsequent work is ensured.

[0021] Furthermore, in step S2, the obtained blank is heated to 1150-1250°C for upsetting and drawing, and is drawn to a height-to-diameter ratio of 2-2.3, and the jaws are removed to obtain a forging blank.

[0022] In the present invention, the blank is upset and stretched so that the blank has good deformation from the surface to the core, ensuring forging and compaction of the blank, thereby ensuring consistent structure from the surface to the core of the blank, uniform grain size, and better mechanical properties.

[0023] When the upsetting and drawing are carried out at a heating temperature of 1150-1250°C, the deformation and cracking tendency of the blank is small, and defects such as cracks are not easy to appear. At the same time, the deformation amount of the blank can be appropriately increased to ensure that the core can be deformed during the upsetting and drawing process, and the core and surface of the blank are deformed synchronously.

[0024] Furthermore, in step S3, the obtained forging blank is heated to 1150-1250°C for upsetting, and the upsetting is performed to a height of L3 and an outer diameter of D3.

[0025] Preferably, in step S3, L3 is 2200-2600 mm, and D3 is φ3000-3500 mm.

[0026] More preferably, in step S3, a hollow punch with an outer diameter of Dc is used for punching to obtain a hollow blank, wherein the outer diameter of the hollow punch needs to meet the requirement of D3 / Dc≥2.5.

[0027] In the present invention, the forging blank is upset to the required size, which is convenient for the subsequent punching of the forging blank. If the height of the blank is too high, the punching is easy to be eccentric. Punching is performed on the forging blank after upsetting to prepare for the mandrel rod to be drawn, which is convenient for the insertion and operation of the mandrel rod. The punching process uses a hollow punch, which is convenient for removing the central part of the large ingot where segregation exists, and ensuring the uniform structure inside the ingot body.

[0028] Furthermore, in step S4, the obtained hollow blank is heated to 1150-1250°C and drawn to a height L4, and the forging ratio L4 / L3=1.1-1.3.

[0029] In the present invention, the mandrel lengthening step uses a solid mandrel to pass through the hollow blank, and the pressure of the forging hydraulic press acts on the surface of the hollow blank. Under the dual action of the mandrel and the forging hydraulic press, the hollow blank is continuously squeezed, thereby achieving the drawing of the hollow blank.

[0030] Preferably, the solid core rod is conical and has a certain slope, and the inclination angle is 1:100.

[0031] Furthermore, in step S5, the obtained drawn billet is heated to 1150-1250°C and flattened to a height L5, where L5=L4-(500-1000mm), to obtain a flat forging billet.

[0032] In the present invention, the drawn blank is flattened as a whole, and the drawn blank is placed vertically on an anvil, with the central axis of the drawn blank perpendicular to the horizontal plane. Under the action of the forging hydraulic press, the height of the drawn blank is reduced, the wall thickness is increased, the inner diameter is reduced, and the outer diameter is increased, so that the upper and lower end surfaces of the drawn blank are flattened.

[0033] Furthermore, in step S6, the obtained flat forging blank is heated to perform pre-expansion, and the outer diameter of the forging blank after pre-expansion is D, and the inner diameter of the forging blank is d.

[0034] In the present invention, in order to ensure that the inner hole of the blank is large enough to allow the receiving sleeve to be smoothly placed, and at the same time, to trim the shape of the blank, especially to avoid local concave center in the inner hole, it is necessary to perform a pre-expansion operation. After the pre-expansion of the forging blank by the horse bar, the outer diameter of the forging blank must satisfy D≥D0, and the inner diameter d must satisfy d≈Dsd+50mm, where Dsd is the outer diameter of the large end of the receiving sleeve.

[0035] Furthermore, in step S7, the flattened forging blank after pre-expansion is heated to 1150-1250°C for single-side flattening to a height of L6, where L5 / L6=1.2-1.5 and L0 / L6=1.3-1.8.

[0036] In the present invention, the pre-expanded forging blank is placed on a turntable, and a flat anvil is used to flatten the upper end surface of the forging blank on one side, so that the metal on one side flows toward the inner wall of the forging blank as much as possible, ensuring the formability of the subsequent inner hole step process and sufficient metal surplus.

[0037] Furthermore, in step S8, the blank obtained after single-side flattening is heated to 1150-1250°C, and is drawn to the forging blank length L0 using a mandrel rod to obtain a semi-finished forging blank.

[0038] In the present invention, a wide flat anvil, a lower V anvil, and a special mandrel are used to draw the forging blank to a length L0. When closing the inner hole step, the single hammer is pressed down as much as possible, controlled at 100-150mm, forcing the metal to flow toward the inner wall of the forging blank.

[0039] The receiving sleeve is a truncated cone with a cylindrical through hole. The through hole coincides with the central axis of the receiving sleeve. The opening of the through hole facilitates the insertion of the core rod. The outer diameter of the large end of the receiving sleeve is Dsd, and the outer diameter of the small end of the receiving sleeve is dsd.

[0040] Furthermore, in step S9, the pressing amount is controlled to be below 50 mm.

[0041] After the closing sleeve has received the inner hole step, the inner hole of the forging blank is completely fitted with the closing sleeve, so that the closing sleeve cannot be removed. It is necessary to expand the hole after receiving the inner hole step, and take out the closing sleeve after the diameter of the inner hole of the forging blank increases.

[0042] Furthermore, the steel grade of the steel ingot is SA508-3, and its chemical composition, by mass percentage, is: C≤0.22%, Mn: 1.15%~1.6%, Si: 0.10%~0.30%, Ni: 0.50%~0.80%, Mo: 0.43%~0.57%, P≤0.020%, S≤0.012%, V≤0.01%, Cu≤0.20%, Al≤0.40%, and Co≤0.03%.

[0043] Furthermore, the maximum outer diameter of the inner step cylindrical forging is D0, the length is L0, the minor diameter of the inner step is D1, the length is L1; the major diameter of the inner step is D2, the length is L2;

[0044] The step height is (D2-D1) / 2, which is more than 200 mm, and the maximum wall thickness is (D0-D1) / 2, which is more than 1000 mm.

[0045] On the other hand, the present invention provides a large inner diameter, thick wall, inner step cylindrical forging, which is obtained by the preparation method of the present invention.

[0046] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0047] 1. The present invention provides a method for preparing a large inner diameter thick wall inner step cylindrical forging, including the steps of riser pressing jaws, pre-drawing, upsetting, drawing, upsetting, punching, mandrel drawing, overall flattening, horse bar pre-expansion, single-side flattening, collecting the inner hole step and expanding the hole. According to the above operation sequence, the operation process of each step is controlled, and a cylindrical forging with a step height of more than 200mm and a maximum wall thickness of more than 1000mm can be successfully produced, and the cylindrical forging has high formability and material utilization, which reduces the time of subsequent mechanical processing and shortens the production cycle.

[0048] 2. The present invention provides a method for preparing a large inner diameter, thick wall, inner step cylindrical forging, including upsetting and drawing steps. The blank is subjected to multiple upsetting and multiple drawing processes, so that the grains from the surface to the core of the blank are crushed and recrystallized, ensuring the forging penetration and compaction of the blank. After multiple upsetting and multiple drawing processes, the structure from the surface to the core of the blank is relatively uniform, ensuring the mechanical properties of the material after forming.

[0049] 3. The present invention provides a method for preparing a large inner diameter, thick wall, inner step cylindrical forging, which includes a collecting sleeve for collecting the inner hole step. Compared with the solution in which the collecting sleeve and the horse lever are made as a whole, the separate collecting sleeve has strong versatility and can not only be applied to cylinders with different inner step lengths; but also can be used in combination with a universal horse lever, which has a lower cost.

[0050] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0052] Figure 1 It is a schematic diagram of a large inner diameter, thick wall, inner step cylindrical forging;

[0053] Figure 2 It is a schematic diagram of the forging blank before single-side flattening;

[0054] Figure 3 It is a schematic diagram of the forging blank after single-side flattening;

[0055] Figure 4 This is a schematic diagram of the receiving set structure;

[0056] Figure 5 This is a working diagram of the steps of collecting the inner hole step of the sleeve;

[0057] Figure 6 This is a schematic diagram of the position of the missing piece after forging of Comparative Example 1;

[0058] Figure 7 It is a solid picture of the inner step cylindrical forging after hole expansion;

[0059] In the figure, 1. flat anvil; 2. forging blank; 3. rotary table; 4. blank after single-side flattening; 5. collecting table cover; 6. horse lever; 7. horse frame. DETAILED DESCRIPTION

[0060] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0061] With the continuous development of society, the specifications of equipment are constantly increasing, especially for large inner diameter thick wall inner step cylindrical forgings, the existing preparation methods are not applicable. Therefore, the present invention provides a preparation method for large inner diameter thick wall inner step cylindrical forgings, comprising the following steps:

[0062] S1: Riser jaw pressing and pre-drawing: The steel ingot is heated to press the jaws, pre-draw the ingot body to obtain the billet;

[0063] S2: Upsetting and drawing: The obtained blank is heated and upset, and then drawn after upsetting, until the height-to-diameter ratio is 2 to 2.3, and the forging blank is obtained after the jaws are removed;

[0064] S3: Upsetting and punching: The obtained forging blank is heated and upset to a height of L3 and an outer diameter of D3; then a hollow punch with an outer diameter of Dc is used for punching to obtain a hollow blank;

[0065] S4: mandrel drawing: heating the obtained hollow blank and drawing it to a height L4 to obtain a drawn blank;

[0066] S5: Overall flattening: heating the obtained drawn billet and flattening it to a height of L5 to obtain a flat forging billet;

[0067] S6: pre-expansion of the forging bar: heating the obtained flat forging blank to pre-expand the forging blank, the outer diameter of the forging blank after pre-expansion is D, and the inner diameter of the forging blank is d;

[0068] S7: Single-side leveling: heating the leveled forging blank after pre-expansion and leveling it on one side to a height of L6;

[0069] S8: collecting the inner hole step by collecting the table sleeve: heating the blank obtained after single-side flattening, and drawing it to the forging blank length L0 by using the collecting table sleeve mandrel to obtain a semi-finished forging blank;

[0070] S9: Hole expansion: After the hole is expanded and the receiving sleeve is removed, an inner step cylindrical forging is obtained.

[0071] Compared with the prior art, the preparation method provided by the present invention is suitable for preparing inner step cylindrical forgings with a step height of more than 200 mm and a maximum wall thickness of more than 1000 mm. It has high formability, the shape of the inner step cylindrical forgings is complete, the subsequent machining amount is less, the preparation cycle of the inner step cylindrical forgings is short, and the delivery is faster.

[0072] Specifically, in step S1, the size of the steel ingot is φ (2900-3200mm) × 3500mm. Pre-drawing can improve the surface structure of the steel ingot, even forge the tiny cracks on the surface, and greatly alleviate the cracking tendency of the steel ingot surface during the subsequent large forging ratio upsetting and other deformation processes. The pre-drawing ratio in S1 is controlled at 1.1-1.3.

[0073] Specifically, in the process of upsetting and drawing in step S2, the microstructures on the surface and the core of the forging blank are ensured to be fully broken. The upsetting and drawing processes in S2 are both high forging ratio deformations of the steel ingot under high temperature. Different from improving the microstructure of the steel ingot surface in S1, S2 mainly improves the microstructure of the core of the steel ingot. Therefore, the forging ratio in S2 is controlled at 2 to 2.3.

[0074] Specifically, in step S3, the obtained forging blank is heated and upset to a height of L3 and an outer diameter of D3, where L3 is 2200-2600 mm and D3 is φ3000-3500 mm. A hollow punch with an outer diameter of Dc is used for punching, and the requirement of D3 / Dc≥2.5 must be met. The use of a hollow punch has several advantages: (1) During use, the forging blank is mainly cut rather than deformed, so the forming force is small and the microstructure of the forging blank is not changed; (2) The metal with poor quality in the core of the forging blank can be removed to ensure the performance of the final product without defects.

[0075] After upsetting, the forging blank is in a drum shape, with small diameters at both ends and large diameters in the middle. In order to reduce the influence of the drum degree on the forging forming, a mandrel drawing process is arranged to draw the drum degree. Specifically, in step S4, the obtained hollow blank is heated and drawn to a height L4. The length L4 after drawing is 1.1 to 1.3 times the length before drawing, which can meet the subsequent overall flattening and unilateral flattening operation requirements.

[0076] Specifically, in step S5, the obtained drawn blank is heated and flattened to a height L5, and the overall reduction amount is 500 to 1000 mm, so that the height in the vertical direction decreases and the diameter in the horizontal direction increases.

[0077] Specifically, in step S6, the obtained flat forging blank is heated for hole expansion. The outer diameter of the forging blank after hole expansion is D, and the inner diameter of the forging blank is d. In order to smoothly insert the receiving sleeve, the outer diameter of the forging blank after pre-expansion of the horse bar must satisfy the requirement of D≥D0, and the inner diameter d must satisfy the requirement of d≈Dsd+50mm, where Dsd is the outer diameter of the large end of the receiving sleeve.

[0078] During the overall leveling process, the blank is compressed as a whole, and then during the horse bar pre-expansion process, the compressed blank is extended. Under the joint action of overall leveling and horse bar pre-expansion, the wall thickness at the large diameter of the inner step can be guaranteed, and preparations can be made for subsequent single-sided leveling to ensure that there is enough metal to move at the large diameter of the inner step to ensure formability.

[0079] Specifically, in step S7, the flattened forging blank after pre-expansion is flattened on one side, and the size requirements of L5 / L6=1.2~1.5 and L0 / L6=1.3~1.8 need to be met. After overall flattening and pre-expansion of the horse bar, there is sufficient metal to flow. During the flattening on one side, the metal at one end of the forging blank is mainly controlled to deform downward, and the metal is moved toward the central axis of the forging blank to ensure that there is enough metal flowing radially when the inner hole step is closed; while the other end of the forging blank is basically not deformed or the deformation is small, which has little effect on the size.

[0080] When performing single-side flattening, it is necessary to use a flat anvil to press the flat forging blank, and the width of the flat anvil is 850-1200mm, which can ensure the size of the L1 section of the cylindrical forging, and the size of the L1 section has a smaller processing amount.

[0081] It should be noted that in order to ensure that the material has a high deformation capacity and a low tendency to crack during deformation during the overall forging process, it is necessary to heat the material before each forging operation at a heating temperature of 1150-1250°C, and ensure that the final processing temperature of steps S1-S9 is not less than 700°C. When the heating temperature is too high, the high-temperature plasticity of the forging blank is improved, but the structure of the final forging becomes coarser and the mechanical properties are poorer.

[0082] It should be noted that the present invention provides a preparation method capable of preparing large inner diameter, thick wall, inner step cylindrical forgings. The preparation method of the present invention is suitable for materials with moderate plasticity, such as alloy with grade SA508-3.

[0083] In order to describe the present invention more clearly, it is further illustrated by the following examples and comparative examples.

[0084] The present invention and the comparative example prepare inner step cylindrical forgings, such as Figure 1 As shown, the maximum outer diameter D0 is φ3800mm, the length L0 is 2500mm, the small diameter D1 of the inner step is φ1800mm, and the length L1 is 1000mm; the large diameter D2 of the inner step is φ2200mm, and the length L2 is 1500mm; the step height is (D2-D1) / 2, the step height is 200mm, the maximum wall thickness is (D0-D1) / 2, and the maximum wall thickness is 1000mm.

[0085] Example 1

[0086] The preparation of inner step cylindrical forgings includes the following steps:

[0087] S1: Riser jaw pressing and pre-drawing: The steel ingot is heated to 1250℃ to press the jaws and pre-draw the ingot body to obtain the billet;

[0088] The grade of the steel ingot is SA508-3, and the chemical composition by mass percentage is: C: 0.18%, Mn: 1.4%, Si: 0.17%, Ni: 0.79%, Mo: 0.51%, P: 0.005%, S: 0.003%, V: 0.005%, Cu: 0.04%, Al: 0.02%, Co: 0.015%;

[0089] The specification of the steel ingot is 229t, and the specification after pre-drawing is φ2600mm×4400mm;

[0090] S2: Upsetting and drawing: The obtained billet is heated to 1250°C for upsetting, and then drawn after upsetting to obtain a forging billet;

[0091] The diameter of the forging blank is φ2400mm, the height is 4800mm, and the height-to-diameter ratio is 2;

[0092] S3: Upsetting and punching: The obtained forging blank is heated to 1250°C for upsetting to a height of L3 and an outer diameter of D3; then a hollow punch with an outer diameter of Dc is used for punching to obtain a hollow blank;

[0093] The height L3 is 2250mm, the outer diameter D3 is φ3500mm, and the outer diameter Dc of the hollow punch is φ1400mm;

[0094] S4: mandrel drawing: heating the obtained hollow blank to 1250°C and drawing it to a height L4 of 2900 mm to obtain a drawn blank;

[0095] S5: Overall flattening: The drawn billet is heated to 1250° C. and flattened to a height L5 of 2400 mm to obtain a flat forging billet;

[0096] S6: Pre-expansion of the horse bar: The obtained flat forging blank is heated to 1250°C for pre-expansion. The outer diameter D of the forging blank after pre-expansion is φ3800mm, and the inner diameter d of the forging blank is φ2050mm;

[0097] S7: Single-side leveling: Heat the pre-expanded leveled forging blank to 1250°C, and use a flat anvil with a width of 1200mm to level the blank on one side to a height of L6, where L6 is 1850mm; Figure 2 and Figure 3 As shown;

[0098] S8: Collecting the inner hole step: The blank obtained after single-side flattening is heated to 1250°C, and the forging blank is drawn to a length L0 of 2500mm using a collecting sleeve mandrel to obtain a semi-finished forging blank; Figure 4 and Figure 5 As shown;

[0099] The receiving sleeve is a frustum-shaped sleeve, with an outer diameter Dsd of φ2000mm at the large end and a length of 2000mm, and an outer diameter dsd of φ1600mm at the small end and a length of 1500mm;

[0100] S9: Hole expansion: After hole expansion and removal of the receiving sleeve, the inner step cylindrical forging is obtained. Figure 7 .

[0101] Example 2

[0102] The preparation of inner step cylindrical forgings includes the following steps:

[0103] S1: Riser jaw pressing and pre-drawing: The steel ingot is heated to 1250℃ to press the jaws and pre-draw the ingot body to obtain the billet;

[0104] The grade of the steel ingot is SA508-3, and the chemical composition by mass percentage is: C: 0.18%, Mn: 1.4%, Si: 0.17%, Ni: 0.79%, Mo: 0.51%, P: 0.005%, S: 0.003%, V: 0.005%, Cu: 0.04%, Al: 0.02%, Co: 0.015%;

[0105] The specification of the steel ingot is 229t, and the specification after pre-drawing is φ2600mm×4400mm;

[0106] S2: Upsetting and drawing: The obtained billet is heated to 1250°C for upsetting, and then drawn after upsetting to obtain a forging billet;

[0107] The diameter of the forging blank is φ2400mm, the height is 4800mm, and the height-to-diameter ratio is 2;

[0108] S3: Upsetting and punching: The obtained forging blank is heated to 1250°C for upsetting to a height of L3 and an outer diameter of D3; then a hollow punch with an outer diameter of Dc is used for punching to obtain a hollow blank;

[0109] The height L3 is 2250mm, the outer diameter D3 is φ3500mm, and the outer diameter Dc of the hollow punch is φ1400mm;

[0110] S4: mandrel drawing: heating the obtained hollow blank to 1250°C and drawing it to a height L4 of 2900 mm to obtain a drawn blank;

[0111] S5: Overall flattening: The drawn billet is heated to 1250° C. and flattened to a height L5 of 2400 mm to obtain a flat forging billet;

[0112] S6: Pre-expansion of the horse bar: The obtained flat forging blank is heated to 1250°C for pre-expansion. The outer diameter D of the forging blank after pre-expansion is φ3800mm, and the inner diameter d of the forging blank is φ2050mm;

[0113] S7: Single-side leveling: Heat the pre-expanded leveled forging blank to 1250°C, and use a flat anvil with a width of 850mm to level the blank on one side to a height of L6, where L6 is 1850mm; Figure 2 and Figure 3 As shown;

[0114] S8: Collecting the inner hole step: The blank obtained after single-side flattening is heated to 1250°C, and the forging blank is drawn to a length L0 of 2500mm using a collecting sleeve mandrel to obtain a semi-finished forging blank; Figure 4 and Figure 5 As shown;

[0115] The receiving sleeve is a frustum-shaped sleeve, with an outer diameter Dsd of φ2000mm at the large end and a length of 2000mm, and an outer diameter dsd of φ1600mm at the small end and a length of 1500mm;

[0116] S9: Hole expansion: After the hole is expanded and the receiving sleeve is removed, an inner step cylindrical forging is obtained.

[0117] Example 3

[0118] The preparation steps of the inner step cylindrical forging in Example 3 are substantially the same as those in Example 1, except that the amount of overall flattening and single-side flattening in Example 3 is different. The specific steps are as follows:

[0119] S5: Overall flattening: The drawn billet is heated to 1250° C. and flattened to a height L5 of 2100 mm to obtain a flat forging billet;

[0120] S6: Pre-expansion of the forging bar: heating the obtained flat forging blank to 1250°C for hole expansion, the outer diameter D of the forging blank after hole expansion is φ3980mm, and the inner diameter d of the forging blank is φ2050mm;

[0121] S7: Single-side leveling: Heat the pre-expanded leveled forging blank to 1250°C and level it on one side to a height of L6, where L6 is 1650mm; Figure 2 and Figure 3 As shown;

[0122] S8: Collecting the inner hole step by the sleeve: Heat the blank obtained after single-side flattening to 1250°C, and use the collecting sleeve mandrel to draw it to a forging blank length L0 of 2500mm to obtain a semi-finished forging blank.

[0123] Example 4

[0124] The preparation steps of Example 4 are substantially the same as those of Example 1, except that, in Step S8 of Example 4: the platform sleeve is collected in the inner hole step, and the heating temperature is 1150°C.

[0125] Example 5

[0126] The preparation steps of Example 5 are substantially the same as those of Example 1, except that, in Step S8 of Example 5: the platform sleeve is collected in the inner hole step, and the heating temperature is 1200°C.

[0127] Comparative Example 1

[0128] The preparation steps of the inner step cylindrical forging of Comparative Example 1 are substantially the same as those of Example 1, except that Comparative Example 1 includes: pre-expansion of the horse bar, overall flattening and single-side flattening; the specific steps are as follows:

[0129] S5: Pre-expansion of the forging bar: The obtained flat forging blank is heated to 1250°C for pre-expansion. The outer diameter D of the forging blank after pre-expansion is φ3600mm, and the inner diameter d of the forging blank is φ2050mm;

[0130] S6: Overall flattening: heating the obtained drawn billet to 1250° C. and flattening it to a height L5 of 2400 mm to obtain a flat forging billet;

[0131] S7: Single-side leveling: Heat the pre-expanded leveled forging blank to 1250°C and level it on one side to a height of L6, where L6 is 1850mm. Figure 2 and Figure 3 As shown;

[0132] S8: Collecting the inner hole step: The blank obtained after single-side flattening is heated to 1250°C, and the forging blank is drawn to a length L0 of 2500mm using a collecting sleeve mandrel to obtain a semi-finished forging blank; Figure 4 and Figure 5 shown.

[0133] Reference Figure 6 In comparative example 1, the order of the preparation steps was changed, and the order of pre-expansion of the hole with a horse bar, overall flattening, and single-side flattening was adopted. The resulting cylindrical forging had a problem of missing dimensions.

[0134] Comparative Example 2

[0135] The preparation steps of Comparative Example 2 are substantially the same as those of Example 1. In step S7 of Comparative Example 2, in single-side leveling, the width of the flat anvil is 1400 mm.

[0136] Integrity (shape and size) inspection

[0137] The integrity (shape and size) of the above-mentioned Examples 1-5 and Comparative Examples 1-2 was tested, and the specific test results are shown in Table 1.

[0138] Table 1 Integrity (shape and size) test results

[0139]

[0140] Reference Figure 5 In the L1 segment, a larger deformation is required to move toward the center, and the problem of missing length often occurs. Therefore, the length of the L1 segment is an important detection indicator.

[0141] It can be seen from Table 1 that when the preparation methods described in Examples 1-5 of the present invention are used, the length of the straight section L1 is greater than 1000 mm, which can meet the requirements. In addition, the difference between the length of the section L1 of the cylindrical forgings obtained in Examples 1-5 and the required value of 1000 mm is small, the subsequent processing amount is small, and the processing time is short. When the preparation methods described in Comparative Examples 1-2 of the present invention are used, although the minor diameter D1 and the maximum outer diameter D0 of the inner step of the cylindrical forgings finally obtained meet the requirements, the length of the section L1 is less than 1000 mm, and the problem of missing length occurs.

[0142] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a large inner diameter, thick wall, inner step cylindrical forging. It is characterized in that The following steps are involved: S1: Riser jaw pressing and pre-drawing: The steel ingot is heated to press the jaws, pre-draw the ingot body to obtain the billet; S2: Upsetting and drawing: The obtained billet is heated and upset, and then drawn after upsetting. The billet height-to-diameter ratio after drawing is 2-2.3, and the forging billet is obtained after the jaws are removed; S3: Upsetting and punching: The obtained forging blank is heated and upset to a height of L3 and an outer diameter of D3; then a hollow punch with an outer diameter of Dc is used for punching to obtain a hollow blank; S4: mandrel drawing: heating the obtained hollow blank and drawing it to a height L4 to obtain a drawn blank; S5: Overall flattening: heating the obtained drawn billet and flattening it to a height of L5 to obtain a flat forging billet; S6: pre-expansion of the forging bar: heating the obtained flat forging blank to pre-expand the forging blank, the outer diameter of the forging blank after pre-expansion is D, and the inner diameter of the forging blank is d; S7: Single-side leveling: heating the leveled forging blank after pre-expansion and leveling it on one side to a height of L6; S8: collecting the inner hole step by collecting the table sleeve: heating the blank obtained after single-side flattening, and drawing it to the forging blank length L0 by using the collecting table sleeve mandrel to obtain a semi-finished forging blank; S9: Hole expansion: After the hole is expanded and the receiving sleeve is removed, an inner step cylindrical forging is obtained.

2. The method for preparing a large inner diameter, thick wall, inner step cylindrical forging according to claim 1, It is characterized in that The steel grade of the steel ingot is SA508-3, and its chemical composition by mass percentage is: C≤0.22%, Mn: 1.15%~1.6%, Si: 0.10%~0.30%, Ni: 0.50%~0.80%, Mo: 0.43%~0.57%, P≤0.020%, S≤0.012%, V≤0.01%, Cu≤0.20%, Al≤0.40%, and Co≤0.03%.

3. The method for preparing a large inner diameter, thick wall, inner step cylindrical forging according to claim 1, It is characterized in that In S1-S9, the heating temperature is 1150-1250°C.

4. The method for preparing the large inner diameter, thick wall, inner step cylindrical forging according to claim 1, It is characterized in that In S3, L3 is 2200~2600mm and D3 is 3000~3500mm.

5. The method for preparing a large inner diameter, thick wall, inner step cylindrical forging according to claim 4, It is characterized in that In S3, D3 / Dc≥2.

5.

6. The method for preparing the large inner diameter, thick wall, inner step cylindrical forging according to claim 1, It is characterized in that In S4, the forging ratio L4 / L3=1.1-1.

3.

7. The method for preparing the large inner diameter, thick wall, inner step cylindrical forging according to claim 1, It is characterized in that In S5, L5=L4-(500~1000mm).

8. The method for preparing the large inner diameter, thick wall, inner step cylindrical forging according to claim 1, It is characterized in that In S7, L5 / L6=1.2~1.

5.

9. The method for preparing the large inner diameter, thick wall, inner step cylindrical forging according to claim 1, It is characterized in that The maximum outer diameter of the large inner diameter thick wall inner step cylindrical forging is D0, the length is L0, the minor diameter of the inner step of the inner hole is D1, the length is L1; the major diameter of the inner step of the inner hole is D2, the length is L2; The step height is (D2-D1) / 2, which is more than 200 mm, and the maximum wall thickness is (D0-D1) / 2, which is more than 1000 mm.

10. A large inner diameter thick wall inner step cylindrical forging, It is characterized in that The method is prepared by any one of claims 1 to 9.

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