Preparation method and die of variable cross-section asymmetric arc-shaped complex stainless steel forging

Abstract

The present application relates to a kind of preparation method and die of variable cross-section asymmetric arc complex stainless steel forgings, belong to stainless steel forging manufacturing technical field, solve the problem of low material utilization rate, low efficiency of existing method.The preparation method includes: step 1: to steel ingot breakdown forging;Step 2: slab forging, forge a pair of slab, each slab has multi-step structure on one side, and the other side is plane;Step 3: the face with multi-step structure of two slabs is placed oppositely, and the step corresponding to the maximum cross section of two slabs is welded, and the assembly after welding is symmetric assembly;Step 4: the symmetric assembly is bent and formed;Step 5: the step corresponding to the maximum cross section of two slabs is split, then the multi-step structure of each slab is processed into the structure required by part, and two variable cross-section asymmetric arc complex stainless steel forgings are obtained.The method has high material utilization rate and high preparation efficiency.

Description

Technical Field

[0001] This invention relates to the field of stainless steel forging technology, and in particular to a method and mold for preparing a complex arc-shaped stainless steel forging with variable cross-section and asymmetry. Background Technology

[0002] Stainless steel forgings are widely used in mechanical equipment and other fields. For complex arc-shaped stainless steel forgings with variable cross-section and asymmetry, which are made of low-temperature non-magnetic austenitic materials, on the one hand, the forging process is quite difficult due to their complex shape; on the other hand, austenitic stainless steel itself has the characteristics of high deformation resistance and poor thermoplasticity, which makes it difficult to achieve the goal of precise forming of irregularly shaped complex austenitic stainless steel forgings.

[0003] Existing methods for forging complex, asymmetrical, arc-shaped stainless steel forgings with variable cross-sections employ a large-margin, overlay forging process. First, a rectangular steel ingot is prepared, then bent into an arc shape. Next, the ingot is forged to create the asymmetrical, variable cross-section structure of the target part. The resulting forged blank has a simple shape, and excess material is removed by machining. However, this method suffers from large ingot margins, low material utilization, and high costs. Furthermore, it only produces one forging at a time, resulting in low efficiency. Summary of the Invention

[0004] In view of the above analysis, the present invention aims to provide a method and mold for preparing a complex arc-shaped stainless steel forging with variable cross-section asymmetry, in order to solve at least one of the following problems of the existing methods: (1) large machining allowance, low material utilization rate and high cost, (2) only one forging is made at a time, resulting in low efficiency.

[0005] On one hand, embodiments of the present invention provide a method for preparing a complex arc-shaped stainless steel forging with a variable cross-section and asymmetry, the method comprising:

[0006] Step 1: Forging the steel ingot;

[0007] Step 2: Slab forging, forging a pair of slabs, each slab having a multi-step structure on one side and a flat surface on the other side;

[0008] Step 3: Place the two slabs with multi-step structures facing each other, and weld the steps corresponding to the largest cross-sections of the two slabs together. The assembled component is a symmetrical component.

[0009] Step 4: Bend and shape the symmetrical component;

[0010] Step 5: Divide the steps corresponding to the maximum cross-section of the two slabs, and then process the multi-step structure of each slab into the structure required for the part, to obtain two variable cross-section asymmetrical arc-shaped complex stainless steel forgings.

[0011] Preferably, in step 1, the steel ingot is subjected to homogenization heat treatment before forging.

[0012] Preferably, the homogenization heat treatment adopts a stepped heating method, including: a first temperature step of 840-860℃, a second temperature step of 1050-1060℃, and a third temperature step of 1200-1220℃.

[0013] Preferably, in step 1, the forging process includes at least one upsetting deformation and at least one drawing deformation;

[0014] The forging ratio for upsetting deformation is not less than 1.7, and the forging ratio for drawing deformation is not less than 1.7.

[0015] Preferably, in step 2, the multi-step structure is a multi-step structure that gradually decreases or gradually increases in height, extending from one end of the slab to the other.

[0016] Preferably, in step 2, the forging ratio of each step in the multi-step structure is not less than 1.3.

[0017] Preferably, in step 4, before bending the symmetrical forging, the symmetrical component is kept at a temperature below the secondary recrystallization temperature.

[0018] Preferably, step 3 further includes welding lifting lugs to both ends of the two slabs that make up the symmetrical component.

[0019] On the other hand, the present invention also provides a mold for the bending and forming step in the above-described preparation method, the mold comprising an upper mold and a lower mold;

[0020] The side of the upper mold opposite to the lower mold is an arc surface;

[0021] The lower mold includes a square base and columns disposed at the four corners of the base, with a groove provided on each column.

[0022] Preferably, the curvature of the arc surface of the upper die is the same as the arc curvature of the complex arc-shaped stainless steel forging with variable cross-section and asymmetry.

[0023] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0024] 1. The method of the present invention first forges a steel ingot into a slab with a multi-step structure on one side, then welds two slabs together to form a symmetrical assembly, then bends the symmetrical assembly into shape, and finally disassembles it to process the multi-step structure of each slab into the structure required for the part. The multi-step structure of the slab is closer to the shape of the final part, which can effectively improve material utilization and reduce subsequent machining allowances. The machining allowance at each part is less than 40mm, and in a preferred embodiment, the machining allowance at each part is less than 20mm.

[0025] 2. In the method of the present invention, two forgings can be prepared in one bending and forming process, which improves production efficiency. In particular, for the need to prepare a pair of complex stainless steel forgings with variable cross-section and asymmetric arc shape, the method of the present invention can prepare a pair of forgings in one bending and forming process, thereby improving the production efficiency of parts.

[0026] 3. The present invention welds two single asymmetrical slabs into a symmetrical component, and then performs bending forming, which can effectively solve the problem of bending instability of a single asymmetrical slab.

[0027] 4. This invention improves the grain refinement of forgings (the grain size in the microstructure is grade 1-3, and in a preferred embodiment, the grain size in the microstructure is grade 4-5) by performing a stepped homogenization heat treatment on the forgings, limiting the upsetting and drawing parameters, and heating and holding the forgings at a temperature below the secondary recrystallization temperature before bending and forming. This gives the forgings better thermoplasticity and thus improves the forging accuracy.

[0028] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0029] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0030] Figure 1 This refers to the ingot homogenization heat treatment process in step 1 of this invention;

[0031] Figure 2 This refers to the forging process in step 1 and the multi-step slab forging process in step 2 of the present invention.

[0032] Figure 3 This refers to the slab forging with a multi-step structure obtained in step 2 of the present invention.

[0033] Figure 4This refers to the symmetrical component obtained by welding two slabs together in step 3 of the present invention.

[0034] Figure 5 This refers to step 4 of the present invention, which involves bending and shaping the symmetrical component.

[0035] Figure 6 This is a schematic diagram of step 5 of the present invention, which involves separating the two slabs.

[0036] Figure 7 This is a schematic diagram of the structure required for forging the multi-step structure of the slab into the part in step 5 of the present invention.

[0037] Figure 8 This is a schematic diagram of the final part;

[0038] Figure 9 This is a schematic diagram of the mold structure of the present invention.

[0039] Figure 10 A flowchart of a method for preparing complex arc-shaped stainless steel forgings with variable cross-section and asymmetric shape in the prior art;

[0040] Figure 11 Schematic diagram of slab assembly welding in step 3 of this invention;

[0041] Figure 12 Metallographic photographs of the forgings were obtained in Embodiment 2 of the present invention.

[0042] Figure label:

[0043] 1-Upper mold; 2-Lower mold; 201-Square base; 202-Column; 203-Groove. Detailed Implementation

[0044] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0045] On the one hand, this invention provides a method for preparing complex arc-shaped stainless steel forgings with variable cross-section and asymmetry, such as... Figures 1-7 As shown, the preparation method includes:

[0046] Step 1: Forging the steel ingot;

[0047] Step 2: Slab forging, forging a pair of slabs, each slab having a multi-step structure on one side and a flat surface on the other side;

[0048] Step 3: Place the two slabs with multi-step structures facing each other, and weld the steps corresponding to the largest cross-sections of the two slabs together. The assembled component is a symmetrical component.

[0049] Step 4: Bend and shape the symmetrical component;

[0050] Step 5: Divide the steps corresponding to the maximum cross-section of the two slabs, and then process the multi-step structure of each slab into the structure required for the part, to obtain two variable cross-section asymmetrical arc-shaped complex stainless steel forgings.

[0051] Compared with existing technologies, the method of this invention first forges a steel ingot into a slab with a multi-step structure on one side, then welds two slabs together to form a symmetrical assembly, then bends the symmetrical assembly into shape, and finally disassembles it, forging the multi-step structure of each slab into the structure required for the part. The multi-step structure of the slab is closer to the final part shape, which can effectively improve material utilization and reduce subsequent machining allowances. In the method of this invention, two forgings can be produced in one bending and forming process, which improves production efficiency. Especially for the production of a pair of complex stainless steel forgings with asymmetrical arc shape and variable cross-section, the method of this invention can produce a pair of forgings in one bending and forming process, improving part production efficiency. The pair of forgings refers to two symmetrical forgings, for example, as shown in the figure. Figure 8 The two opposite side forgings of the box shown can be produced in one step using the method of this invention. This invention welds two single asymmetrical slabs into a symmetrical assembly, and then performs bending forming, effectively solving the problem of bending instability in a single asymmetrical slab.

[0052] For example, the stainless steel forging is a low-temperature resistant non-magnetic austenitic stainless steel forging.

[0053] Due to the inherent characteristics of austenitic stainless steel, such as high resistance to deformation and poor thermoplasticity, it is difficult to achieve precise forming of irregularly shaped and complex austenitic stainless steel forgings.

[0054] In this invention, in order to promote the precise forming of complex arc-shaped stainless steel forgings with variable cross-section and asymmetry, in step 1, the steel ingot is first subjected to homogenization heat treatment before the forging of the steel ingot.

[0055] Specifically, such as Figure 1 As shown, the homogenization heat treatment adopts a stepped heating method, including: a first temperature step of 840-860℃, a second temperature step of 1050-1060℃, and a third temperature step of 1200-1220℃.

[0056] It should be noted that insulation is performed at each temperature step, and the insulation time is determined based on the smallest cross-section. The minimum insulation time is determined as one hour per 80mm, and the maximum insulation time is determined as one hour per 50mm.

[0057] Specifically, the first temperature step is the point of abrupt change in the coefficient of thermal expansion. After holding and homogenizing at this temperature, the temperature is raised to the second temperature step. Holding and homogenizing at the second temperature step does not cause significant grain growth. Then, holding at a high temperature at the third temperature step provides the necessary conditions for sufficient deformation during the initial forging. Furthermore, the homogenization heat treatment uses a stepped heating method, and holding at the first and second temperature steps for a period of time allows segregated elements to pre-diffuse, avoiding initial melting at grain boundaries. Raising to the third temperature step and holding for a certain period of time gradually eliminates segregation and dendrites, improves the thermoplasticity of austenitic stainless steel, reduces forging cracks, and enables precise forging with small allowances.

[0058] Furthermore, removing slag grooves from the surface of the steel ingot before the homogenization heat treatment can effectively prevent subsequent forging cracking caused by slag grooves.

[0059] For example, such as Figure 2 As shown, in step 1, the initial forging includes at least one upsetting deformation and at least one drawing deformation. Initial forging primarily breaks down the as-cast structure of the steel ingot, generating a large number of dislocations and slips, which is more conducive to element diffusion, further eliminates segregation, and further improves the hot plasticity of austenitic stainless steel.

[0060] For example, the forging ratio of the upsetting deformation is not less than 1.7 (e.g., 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, etc.), and the final forging temperature is higher than 900℃ (e.g., 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, 1500℃, etc.). A forging ratio of 1.7 or higher ensures sufficient large deformation and meets the requirement of fine and uniform grains; a final forging temperature higher than 900℃ is to avoid cracking, as the tendency to crack increases if the temperature is lower than 900℃.

[0061] It should be noted that before the forged billet is returned to the furnace after upsetting deformation, it is wrapped with an asbestos anvil. The purpose is to maintain the temperature during forging, prevent the temperature from dropping too quickly during the forging process, and extend the effective forging time. After the heat preservation is completed, a wide and flat anvil is used for elongation deformation.

[0062] For example, the forging ratio for the elongation deformation is not less than 1.7 (e.g., 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, etc.), and the final forging temperature is higher than 900℃ (e.g., 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, 1500℃, etc.). Before returning the billet to the furnace, the forging billet is wrapped with an asbestos anvil to maintain the temperature during forging, prevent the temperature from dropping too quickly during the forging process, and extend the effective forging time. A forging ratio of 1.7 or higher can ensure sufficient large deformation and meet the requirement of fine and uniform grains; a final forging temperature higher than 900℃ is to avoid cracking, as the tendency to crack increases if the temperature is lower than 900℃.

[0063] It should be noted that, Figure 2 and Figure 3 Only one multi-step structure is shown, but the multi-step structure of the present invention is not limited thereto.

[0064] For example, in step 2, the specific shape of the multi-step structure can be determined according to the variable cross-section asymmetric structure of the target part. For example, the multi-step structure is a multi-step structure that gradually decreases or gradually increases from one end of the slab to the other end, or a multi-step structure that first increases and then decreases, or a multi-step structure that first decreases and then increases. Figure 2 and Figure 3 The multi-step structure in the text corresponds to Figure 8 Side panels and Figure 7 The target part features a variable cross-section asymmetric structure, i.e., a sloping structure within the part. Multi-step slab shapes more closely resemble the final part shape, effectively improving material utilization and reducing subsequent machining allowances.

[0065] For example, in step 2, a pair of multi-step shaped slabs are drawn out using upper and lower flat anvils. The forging ratio of each step in the multi-step structure is not less than 1.3, for example, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, etc., to meet the critical deformation amount for dynamic recrystallization of the material and achieve grain refinement.

[0066] For example, in step 3, the welding method includes: machining 10×10mm welding bevels on the four sides of the corresponding welding surface, and then butt-welding the two slabs together, such as... Figure 11 As shown.

[0067] For example, to facilitate hoisting, step 3 further includes welding lifting lugs to both ends of the two slabs that make up the symmetrical assembly.

[0068] For example, in step 4, before bending the symmetrical component, the symmetrical component is first kept at a temperature below the secondary recrystallization temperature, and the holding time is determined as 1 hour for every 80 mm of the thickest section. Heating and holding at a temperature below the secondary recrystallization temperature can effectively avoid the problem of grain growth in austenitic stainless steel and further improve thermoplasticity.

[0069] For example, in step 5, the method of splitting includes: splitting by gouging open the original weld position.

[0070] For example, in step 5, the method for machining the multi-step structure of each slab into the structure required for the part can be a machining method.

[0071] Secondly, the present invention also provides a mold, such as Figure 9As shown, the mold is used in the bending and forming step of the above preparation method, and the mold includes an upper mold 1 and a lower mold 2;

[0072] The side of the upper mold 1 that is opposite to the lower mold 2 is an arc surface;

[0073] The lower mold 2 includes a square base 201 and columns 202 disposed at the four corners of the base 201, with a groove 203 disposed on each column 202.

[0074] Specifically, the curvature of the arc surface of the upper mold 1 is the same as the arc curvature of the complex arc-shaped stainless steel forging with variable cross-section and asymmetry.

[0075] For example, the length of the square base 201 is not less than the length of the symmetrical component, and the width of the square base 201 is not less than the width of the symmetrical component. The groove 203 is used to support the two ends of the two slabs in the symmetrical component; the height of each column 202 provides sufficient space when the symmetrical component bends downward.

[0076] When this mold is applied to step 4 of the preparation method of the present invention, such as Figure 5 As shown, the symmetrical component is placed on the lower mold 2, and the two ends of the two blanks in the symmetrical component are placed in the corresponding grooves 203 respectively. The upper mold 1 is used to press down from the upper surface of the symmetrical component until the bending deformation of the symmetrical component is completed.

[0077] The following specific embodiments further illustrate the preparation method of the variable cross-section asymmetric arc-shaped complex stainless steel forging of the present invention.

[0078] Example 1

[0079] This embodiment provides a mold, the mold including an upper mold 1 and a lower mold 2;

[0080] The side of the upper mold 1 that is opposite to the lower mold 2 is an arc surface;

[0081] The lower mold 2 includes a square base 201 and columns 202 disposed at the four corners of the base 201, with a groove 203 disposed on each column 202.

[0082] The curvature of the arc surface of the upper mold 1 is the same as the arc curvature of the complex arc-shaped stainless steel forging with variable cross-section and asymmetry.

[0083] The length of the square base 201 is not less than the length of the symmetrical component, and the width of the square base 201 is not less than the width of the symmetrical component. The groove 203 is used to support the two ends of the two slabs in the symmetrical component; the height of each column 202 provides sufficient space when the symmetrical component bends downward.

[0084] Example 2

[0085] This embodiment provides a method for preparing a complex arc-shaped stainless steel forging with a variable cross-section and asymmetric shape, wherein the complex arc-shaped stainless steel forging with a variable cross-section and asymmetric shape is as follows: Figure 8 The two side plate forgings of the box shown are made of 316LN. Each side plate forging has a complex, asymmetrical, arc-shaped structure with a variable cross-section, such as... Figure 2 The forging weighs approximately 4 tons and is manufactured using 6-ton electroslag steel ingots.

[0086] 1. Pre-treat the electroslag ingot, and after annealing, process to remove the slag grooves on the surface of the electroslag ingot.

[0087] 2. The electroslag ingot undergoes homogenization heat treatment using a stepped heating method. The first temperature step is 850℃, the second is 1055℃, and the third is 1210℃. Each temperature step is held for one hour every 60 mm.

[0088] 3. Steel ingot forging, such as... Figure 2 As shown, the steel ingot is first upset with an upsetting ratio of 1.7 and a final forging temperature of 1000℃. Before returning it to the furnace, the forging billet is wrapped with an asbestos anvil. After heat preservation, it is drawn with upper and lower wide flat anvils with a drawing ratio of 1.7 and a final forging temperature higher than 1000℃. Before returning it to the furnace, the forging billet is wrapped with an asbestos anvil.

[0089] 4. A pair of slabs are drawn out using an anvil, each slab having a multi-step structure on one side and a flat surface on the other side; the multi-step structure is a gradually decreasing multi-step structure extending from one end of the slab to the other, such as... Figure 2 and Figure 3 As shown; the forging ratio of each step in the multi-step structure is 1.5.

[0090] 5. Place two slabs with multi-step structures facing each other, and weld the steps corresponding to the largest cross-sections of the two slabs together. The resulting assembly is a symmetrical assembly, such as... Figure 4 As shown, lifting lugs are welded to both ends of the two slabs that make up the symmetrical component.

[0091] 6. The symmetrical component is kept at a temperature below the secondary recrystallization temperature. After the holding period, the symmetrical component is bent and shaped using the mold described in Example 1, as follows: Figure 5 As shown, the symmetrical component is placed on the lower mold, and the two ends of the two blanks in the symmetrical component are placed in the corresponding grooves. The upper mold is used to press down from the upper surface of the symmetrical component until the bending deformation of the symmetrical component is completed.

[0092] 7. For example Figure 6 As shown, the steps corresponding to the largest cross-sections of the two slabs are divided, as follows: Figure 7As shown, the multi-step structure of each slab is then machined into a sloping structure to obtain two complex, asymmetrical, arc-shaped stainless steel forgings with varying cross-sections, as shown in the figure. Figure 8 The box shown has two side plate forgings.

[0093] No bending instability occurred during the bending deformation process in this embodiment; the grain size in the microstructure of the forging was grade 4-5, and the grains were fine and uniform. Figure 12 As shown; forging accuracy refers to the machining allowance from the forging blank to the final structural part, and the machining allowance of each part is less than 20mm.

[0094] Example 3

[0095] This embodiment provides a method for preparing a complex arc-shaped stainless steel forging with a variable cross-section and asymmetry, similar to that in Embodiment 2. The difference is that the homogenization heat treatment is not a stepped heating method, but a direct heating to 1210°C.

[0096] The microstructure of the forgings obtained in this embodiment has a grain size of 1-3, with a small amount of mixed grains and coarse grains, and the machining allowance for each part is 30-40 mm.

[0097] Example 4

[0098] This embodiment provides a method for preparing a complex arc-shaped stainless steel forging with a variable cross-section and asymmetry, similar to that in Embodiment 2, except that the final forging temperature for upsetting and drawing is 800°C.

[0099] The forging obtained in this embodiment has a small number of cracks on its surface.

[0100] Example 5

[0101] This embodiment provides a method for preparing a complex arc-shaped stainless steel forging with a variable cross-section and asymmetry, similar to that in Embodiment 2. The difference is that the surface slag grooves of the electroslag ingot are not removed before the homogenization heat treatment.

[0102] The forging obtained in this embodiment has a small number of cracks on its surface.

[0103] Example 6

[0104] This embodiment provides a method for preparing a complex arc-shaped stainless steel forging with a variable cross-section and asymmetry, similar to that in Embodiment 2. The difference is that, before bending the symmetrical component, the symmetrical component is kept at a temperature exceeding the secondary recrystallization temperature.

[0105] The microstructure of the forging obtained in this embodiment has a grain size of 1-3.

[0106] Comparative Example 1

[0107] This comparative example provides a method for preparing existing variable cross-section asymmetric arc-shaped complex stainless steel forgings, such as... Figure 8 The box shown consists of two side plate forgings. The method is as follows: Figure 10 As shown, the process includes: first preparing a rectangular steel ingot, then bending the steel ingot to form an arc shape, then forging the bent steel ingot into a variable cross-section asymmetric structure of the target part, the forged blank finished product having a simple shape structure, and finally removing the excess blank by machining.

[0108] The microstructure of the forgings prepared in this comparative example has a grain size of grade 1-2, and the machining allowance for each part is 20-300 mm.

[0109] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a complex arc-shaped stainless steel forging with variable cross-section and asymmetry, characterized in that, The preparation method includes: Step 1: Forging the steel ingot; Step 2: Slab forging, forging a pair of slabs, each slab having a multi-step structure on one side and a flat surface on the other side; Step 3: Place the two slabs with multi-step structures facing each other, and weld the steps corresponding to the largest cross-sections of the two slabs together. The assembled component is a symmetrical component. Step 4: Bend and shape the symmetrical component; Step 5: Divide the steps corresponding to the maximum cross-section of the two slabs, and then process the multi-step structure of each slab into the structure required for the part, to obtain two variable cross-section asymmetrical arc-shaped complex stainless steel forgings. In step 2, the multi-step structure is a multi-step structure that gradually decreases or gradually increases in height, extending from one end of the slab to the other. In step 2, the forging ratio of each step in the multi-step structure is not less than 1.3; In step 4, before bending the symmetrical component, the symmetrical component is kept at a temperature below the secondary recrystallization temperature.

2. The preparation method according to claim 1, characterized in that, In step 1, before forging the steel ingot, the steel ingot is first subjected to homogenization heat treatment.

3. The preparation method according to claim 2, characterized in that, The homogenization heat treatment adopts a stepped heating method, including: a first temperature step of 840-860℃, a second temperature step of 1050-1060℃, and a third temperature step of 1200-1220℃.

4. The preparation method according to claim 1, characterized in that, In step 1, the forging process includes at least one upsetting deformation and at least one drawing deformation. The forging ratio for upsetting deformation is not less than 1.7, and the forging ratio for drawing deformation is not less than 1.

7.

5. The preparation method according to claim 1, characterized in that, Step 3 also includes welding lifting lugs to both ends of the two slabs that make up the symmetrical component.

6. A mold, said mold being used in the bending and forming step of the preparation method according to any one of claims 1-5, characterized in that, The mold includes an upper mold (1) and a lower mold (2); The side of the upper mold (1) opposite to the lower mold (2) is an arc surface; The lower mold (2) includes a square base (201) and columns (202) set at the four corners of the base (201), with a groove (203) provided on each column (202).

7. The mold according to claim 6, characterized in that, The curvature of the arc surface of the upper mold (1) is the same as the arc curvature of the complex arc-shaped stainless steel forging with variable cross-section and asymmetry.

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