A method of forming a semi-blind hole forging of duplex stainless steel

Abstract

The application relates to a forming method of a duplex stainless steel semi-blind hole forging, which comprises the following steps: step 1) electric ingot finishing, step 2) forging pre-homogenization heat treatment, step 3) two-up and two-down cogging, step 4) upsetting, step 5) punching, step 6) blank making and hole expanding, step 7) blank making and mandrel drawing, step 8) reducing mandrel hole expanding, and step 9) product cooling. The forming method can effectively form a large-size super duplex stainless steel semi-blind hole forging with excellent performance, improves material utilization, reduces machining time, improves production efficiency, and reduces production cost.

Description

Technical Field

[0001] This invention belongs to the field of metal plastic processing technology, and specifically relates to a forming method for duplex stainless steel semi-blind hole forgings with excellent effective forming performance, which can reduce forging machining time, improve production efficiency, and reduce production costs. Background Technology

[0002] Due to the microstructure of duplex stainless steel, where ferrite and austenite phases each account for approximately equal volume fractions, it is possible to control the chemical composition and heat treatment to achieve both the excellent toughness of austenitic stainless steel and the high strength and resistance to chloride stress corrosion of ferritic stainless steel. This advantage has led to the increasingly widespread application of duplex stainless steel in marine, petroleum, and chemical industries. Despite these inherent advantages, the different deformation mechanisms of the ferrite and austenite phases during high-temperature plastic deformation make this type of steel highly susceptible to cracking during forming, with rapid crack propagation leading to product scrap. Super duplex stainless steel, due to its high content and variety of alloying elements, is prone to precipitate formation under improper heat treatment. The precipitation of the σ phase significantly reduces the material's impact toughness and also affects its tensile properties and hardness.

[0003] Semi-blind hole forgings refer to a special type of hollow forging where the inner hole is not completely penetrated, with openings at both ends. One end has a large-diameter inner hole, and the other end has a small-diameter inner hole, falling between a through hole and a blind hole. Currently, semi-blind hole forgings are formed using the following three methods: 1. After heating to the forging temperature, perform one upsetting and one drawing or two upsetting and two drawing to open the blank, forging the forging into a solid forging, and then machining to hollow out the semi-blind hole; 2. After heating to the forging temperature, perform one upsetting and one drawing or two upsetting and two drawing to open the blank, using the small inner hole diameter of the semi-blind hole as a reference, adding forging allowance, and then forging to a through hole forging, and then machining to form the large-diameter inner hole portion. 3. After heating to the forging temperature, perform one upsetting and one drawing or two upsetting and two drawing to open the billet. The forging is forged to the through hole state with the large diameter inner hole as the reference, but the outer diameter of the small diameter inner hole is left with sufficient allowance. The subsequent through hole forging is closed, and the outer diameter of the small diameter inner hole and the inner hole are forged to the finished size. Although the above three forming methods can effectively shape the finished product in terms of size and shape, the first and second forming methods require the removal of a large amount of material through machining, resulting in low material utilization, high production costs, and poor continuity of metal flow lines. The third forming method has the advantages of high material utilization and good continuity of metal flow lines, but this method is suitable for metal materials with good plasticity. However, due to the different deformation mechanisms of ferrite and austenite in the high-temperature plastic deformation process of duplex stainless steel, the steel has poor high-temperature plasticity. When forming small-diameter inner holes by hole closing, folding defects are easily formed in the inner hole at this location. Moreover, during the hole closing process, the surface of the inner hole is in a state of free deformation tensile stress, which makes it very easy for the microcracks in the inner hole to expand and extend rapidly, resulting in defects that are too deep and scrapped. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a forming method for duplex stainless steel semi-blind hole forgings, which can effectively improve material utilization, reduce machining time, increase production efficiency, and reduce production costs.

[0005] This invention achieves the above objective through the following technical solution: a forming method for duplex stainless steel semi-blind hole forgings, comprising the following forming steps: Step 1) Finishing of electroslag ingots: After cooling, the electroslag ingots are finished by rough turning or grinding with a grinding wheel until there are no defects such as pores, steel scale, slag grooves, or cracks on the circumference of the ingot, and the height-to-diameter ratio of the electroslag ingot is controlled between 1.7 and 2.2. Step 2) Homogenization heat treatment before forging: The electroslag ingots completed in Step 1) are loaded into a heating furnace, preheated at 400℃~450℃ for 3~6 hours, then heated to 800℃~950℃ and held for 4~6 hours, then rapidly heated to 1150℃~1250℃ and held for 15~20 hours to ensure uniform heating. Step 3) Two upsetting and two drawing: The electroslag ingot from Step 2) is placed on a hydraulic press with the riser facing upwards and the ingot plate reversed. A first upsetting is performed using an upper reverse extrusion upsetting plate and a lower upsetting platform, with an upsetting deformation of 50%~65% and a height-to-diameter ratio of 0.60~0.75. A first drawing is then performed using upper and lower V-anvils or an upper flat anvil and lower V-anvil, resulting in a height-to-diameter ratio of 1.7~2.2 for the forging. A second upsetting is then performed with the ingot tail facing upwards using a reverse extrusion upsetting plate and a lower upsetting platform, with an upsetting deformation of 50%~65% and a height-to-diameter ratio of 0.60~0.75 for the forging. A second drawing is then performed using upper and lower V-anvils or an upper flat anvil and lower V-anvil. Step 4) Upsetting: The electroslag ingot completed in step 3) is upset on a hydraulic press using an upsetting plate and a lower upsetting platform. The upsetting deformation is 50%~65%, and the height-to-diameter ratio of the upset electroslag ingot is 0.50~0.65. Step 5) Punching: Place the electroslag ingot from Step 4) on a hydraulic press and punch it using an upper flat anvil, a slotted plate, and a punch. The ratio of the punch diameter to the diameter of the upset billet should be ≤0.30. First, punch the billet from one end to a blind hole 1 / 2 to 2 / 3 deep after upsetting. Then, rotate the billet 180 degrees and punch it from the other end to a through hole to reduce the thickness of the material being pulled and punched. Step 6) Blanking and Hole Enlargement: Place the electroslag ingot that has completed Step 5) on a hydraulic press and enlarge the hole using an upper flat anvil, lever, and frame until the diameter of the hole is 10-30mm larger than the maximum diameter of the mandrel used in Step 7). Step 7) Mandrel drawing: After the electroslag ingot from Step 6) is removed from the furnace, the iron oxide scale inside the hole is knocked off. The mandrel is then drawn on a hydraulic press using a flat anvil on top, a V-shaped anvil on the bottom, and a 0.5-1.5° tapered mandrel. The minimum diameter of the mandrel is 10-30mm larger than the maximum diameter of the variable diameter mandrel used in Step 8). During the mandrel drawing process, the forging is rotated and forged at a rotation angle of 30-60°, a reduction of 60-100mm, and a feed rate of 300-350mm until the length of the forging is 50-100mm greater than the finished length of the forging. During the forging process, the forging is rotated and forged within the range of the above-mentioned rotation angle, reduction, and feed rate parameters according to the actual situation. If the parameters are too large, the roundness and surface quality of the forging may be poor, and if they are too small, the production efficiency will be low. Step 8) Hole Enlargement with Variable Diameter Anvil: After the electroslag ingot from Step 7) is removed from the furnace, the iron oxide scale inside the hole is knocked off. The hole is then enlarged on a hydraulic press using an anvil, variable diameter strut, and frame. In the early stages of the enlargement process, the forging is rotated at a 30-60° rotation angle and a reduction of 60-100mm. During the finishing stage of the enlargement process, the forging is rotated at a 15-25° rotation angle and a reduction of 10-30mm to refine the outer diameter and inner hole to the finished dimensions. Reducing the rotation angle and reduction during the finishing process helps ensure the final surface quality and dimensional accuracy of the forging. Step 9) Finished product cooling: Place the forgings that have completed step 8) into a heating furnace at 1000~1150℃, hold for 1.5-4.5 hours, and then quickly remove them from the furnace and water cool to room temperature.

[0006] The forming method uses double-length forging, with the small hole located in the middle of the forging.

[0007] The variable diameter lever used has the large diameter part at both ends of the lever and the small diameter part in the middle of the lever. The large diameter and small diameter of the variable diameter lever are connected by a 30-60 degree inclined platform. The 25 mm rounded transition between the inclined platform and the straight platform increases the strength at the connection between the large diameter and small diameter of the lever, while facilitating material flow and allowing the small inner hole to be fully formed.

[0008] After the forging is forged to the finished size, it is placed in a heating furnace at 1000~1150℃ and held for 1.5-4.5 hours. Then it is quickly taken out of the furnace and water-cooled to room temperature. This effectively suppresses excessive grain coarsening and prevents the precipitation of harmful σ phase.

[0009] The beneficial effects of this invention are as follows: This invention involves homogenizing the electroslag ingot before forging using a pre-forging heat treatment. High-temperature diffusion improves internal segregation within the ingot, mitigating coarse-grained mixed crystals and uneven mechanical properties caused by compositional segregation. A hydraulic press is used for large-deformation upsetting and drawing to fully deform the ingot core, breaking down the as-cast core structure and welding together the loose shrinkage cavities. High temperature and large deformation allow for dynamic recrystallization, sub-dynamic recrystallization, and post-deformation static recrystallization, thoroughly refining the core grains. Octagonalization and rounding further deform the surface of the ingot, refining the surface grains and resulting in a uniformly deformed intermediate billet.

[0010] The semi-blind hole forging of this invention utilizes a variable-diameter lever forging process to expand the hole, effectively shaping the semi-blind hole. Furthermore, the expanding process, compared to the shrinking process, places the inner hole under compressive stress, effectively suppressing the generation and propagation of internal wall cracks. Forging the semi-blind hole reduces the increased production costs associated with machining blind holes and improves material utilization. Simultaneously, the semi-blind hole forging is integrally formed by forging, ensuring smooth metal flow and avoiding excessive machining that could interrupt the metal flow and degrade the overall mechanical properties of the forging.

[0011] The method for forging duplex stainless steel semi-blind hole parts of the present invention can forge large-size duplex stainless steel semi-blind hole forging parts effectively, while improving material utilization, reducing machining time, increasing production efficiency, and reducing production costs. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the forming method of a duplex stainless steel semi-blind hole forging according to the present invention.

[0013] Figure 2This is an example of the forming method of a duplex stainless steel semi-blind hole forging according to the present invention, and the finished forging dimension drawing is shown.

[0014] Figure 3 This is a schematic diagram of a variable-diameter lever, which is an implementation example of a forming method for a duplex stainless steel semi-blind hole forging according to the present invention. Detailed Implementation

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other. Example 1: This example provides a forming method for a duplex stainless steel blind hole flange. The steel grade is 2507 (UNSS32750), the ingot specifications are Φ790 / Φ830*1440mm, and the finished forging dimensions are as follows. Figure 2 As shown, the forming steps are as follows: Step 1) Finishing of electroslag ingots: After cooling, the electroslag ingots are finished by rough turning or grinding with a grinding wheel until there are no defects such as pores, steel scale, slag grooves, cracks, etc. on the circumferential surface of the ingots, and the height-to-diameter ratio of the electroslag ingots is between 1.78. Step 2) Homogenization heat treatment before forging: The electroslag ingot that has completed step 1) is loaded into the heating furnace, preheated at 400℃~450℃ for 3.0 hours, then heated to 800℃~950℃ and held for 4.0 hours, then rapidly heated to 1180~1200℃ and held for 15 hours to ensure uniform heating; Step 3) Two upsetting and two drawing: The electroslag ingot completed in Step 2) is placed on a hydraulic press with the riser facing upwards and the ingot plate reversed. It is then upset once using an upper reverse extrusion upsetting plate and a lower upsetting platform to upset the height to 740mm. After that, it is drawn once using an upper and lower V-anvil or an upper flat anvil and a lower V-anvil to draw the diameter to Φ820mm. With the ingot tail facing upwards, it is upset a second time using a reverse extrusion upsetting plate and a lower upsetting platform to upset the height to 740mm. After that, it is drawn a second time using an upper and lower V-anvil or an upper flat anvil and a lower V-anvil to draw the diameter to Φ820mm. Step 4) Upsetting: The electroslag ingot completed in step 3) is upset on a hydraulic press using an upsetting plate and a lower upsetting platform, upsetting to a height of 720mm; Step 5) Punching: Place the electroslag ingot that has completed step 4) on a hydraulic press and punch it with an upper flat anvil, a slotted plate, and a Φ300mm punch. First, punch the blank from one end to a blind hole 1 / 2 to 2 / 3 deep after upsetting. Then, turn the blank 180 degrees and punch the through hole from the other end to reduce the thickness of the material being pulled and punched. Step 6) Blanking and Hole Enlargement: The electroslag ingot that has completed Step 5) is enlarged on a hydraulic press using an upper flat anvil, lever, and frame to enlarge the hole to an inner diameter of Φ330mm. Step 7) Mandrel drawing: After the electroslag ingot from Step 6) is removed from the furnace, the iron oxide scale inside the hole is knocked off. The mandrel is then drawn on a hydraulic press using a flat anvil on top, a V-shaped anvil on the bottom, and a Φ375mm mandrel with a taper of 0.5~1.5 degrees. During the mandrel drawing process, the forging is rotated and forged at a rotation angle of 30~60°, a reduction of 60~100mm, and a feed of 300~350mm, until the forging reaches ~Φ695*Φ375*2600mm. During the forging process, the forging is rotated and forged within the range of the above-mentioned rotation angle, reduction, and feed parameters according to the actual situation. If the parameters are too large, it may result in poor roundness and surface quality of the forging; if they are too small, the production efficiency will be low. Step 8) Hole enlargement with a variable diameter lever: After the electroslag ingot from step 7) is taken out of the furnace, the iron oxide scale inside the hole is knocked off. The hole is enlarged and shaped on a hydraulic press using an anvil, a variable diameter lever, and a frame. In the early stage of the hole enlargement process, the forging is rotated at a rotation angle of 30~60° and a reduction of 60~100mm. In the finishing stage of the hole enlargement process, the forging is rotated at a rotation angle of 15~25° and a reduction of 10~30mm to finish the outer diameter and inner hole of the forging to the finished size. Step 9) Finished product cooling: The forgings that have completed step 8) are placed in a heating furnace at 1030℃ and held for 3.0 hours. They are then quickly removed from the furnace and water-cooled to room temperature.

Claims

1. A method for forming a duplex stainless steel semi-blind hole forging, characterized in that, It includes the following steps: Step 1) Finishing of electroslag ingots: After cooling, the electroslag ingots are finished by rough turning or grinding with a grinding wheel until there are no defects such as pores, steel scale, slag grooves, or cracks on the circumference of the ingot, and the height-to-diameter ratio of the electroslag ingot is controlled between 1.7 and 2.

2. Step 2) Homogenization heat treatment before forging: The electroslag ingots completed in Step 1) are loaded into a heating furnace, preheated at 400℃~450℃ for 3~6 hours, then heated to 800℃~950℃ and held for 4~6 hours, then rapidly heated to 1150℃~1250℃ and held for 15~20 hours to ensure uniform heating. Step 3) Two upsetting and two drawing: Place the electroslag ingot from Step 2) on a hydraulic press. With the riser facing upwards, perform a first upsetting using an upper reverse extrusion upsetting plate and a lower upsetting platform. The upsetting deformation is 50%~65%, and the height-to-diameter ratio of the upset forging is 0.60~0.

75. Perform a first drawing using upper and lower V-anvils or an upper flat anvil and lower V-anvil. After drawing, the height-to-diameter ratio of the forging is 1.7~2.

2. With the ingot tail facing upwards, perform a second upsetting using a reverse extrusion upsetting plate and a lower upsetting platform. The upsetting deformation is 50%~65%, and the height-to-diameter ratio of the upset forging is 0.60~0.

75. Perform a second drawing using upper and lower V-anvils or an upper flat anvil and lower V-anvil. Step 4) Upsetting: Place the electroslag ingot completed in step 3) on a hydraulic press and upset it using an upsetting plate and a lower upsetting platform. The upsetting deformation is 50%~65%, and the height-to-diameter ratio of the upset electroslag ingot is 0.50~0.

65. Step 5) Punching: Place the electroslag ingot from Step 4) on a hydraulic press and punch it using an upper flat anvil, a slotted plate, and a punch. The ratio of the punch diameter to the diameter of the upset billet should be ≤0.

30. First, punch the billet from one end to a blind hole 1 / 2 to 2 / 3 deep after upsetting. Then, rotate the billet 180 degrees and punch it from the other end to a through hole to reduce the thickness of the material being pulled and punched. Step 6) Blanking and Hole Enlargement: Place the electroslag ingot that has completed Step 5) on a hydraulic press and enlarge the hole using an upper flat anvil, lever, and frame until the diameter of the hole is 10-30mm larger than the maximum diameter of the mandrel used in Step 7). Step 7) Mandrel drawing: After the electroslag ingot from Step 6) is taken out of the furnace, the iron oxide scale inside the hole is knocked off. The mandrel is drawn on a hydraulic press using a flat anvil on the top and a V-shaped anvil on the bottom, and a 0.5~1.5° tapered mandrel. The minimum diameter of the mandrel is 10~30mm larger than the maximum diameter of the variable diameter rod used in Step 8). During the mandrel drawing process, the forging is rotated and forged at a rotation angle of 30~60°, a reduction of 60~100mm, and a feed of 300~350mm until the length of the forging is 50~100mm larger than the finished length of the forging. During the forging process, the forging is rotated and forged within the range of the above-mentioned rotation angle, reduction, and feed parameters according to the actual situation. If the parameters are too large, the roundness and surface quality of the forging will be poor, and if they are too small, the production efficiency will be low. Step 8) Hole Enlargement with Variable Diameter Anvil: After the electroslag ingot from Step 7) is removed from the furnace, the iron oxide scale inside the hole is knocked off. The hole is then enlarged on a hydraulic press using an anvil, variable diameter strut, and frame. In the early stage of the hole enlargement process, the forging is rotated at a rotation angle of 30-60° and a reduction of 60-100mm. In the finishing stage of the hole enlargement process, the forging is rotated at a rotation angle of 15-25° and a reduction of 10-30mm to finish the outer diameter and inner hole of the forging to the finished size. Reducing the rotation angle and reduction of the forging during the finishing process helps to ensure the surface quality and dimensional accuracy of the final forging. Step 9) Finished product cooling: Place the forgings that have completed step 8) into a heating furnace at 1000~1150℃, hold for 1.5-4.5 hours, and then quickly remove them from the furnace and water cool to room temperature.

2. The forming method of a duplex stainless steel semi-blind hole forging according to claim 1, characterized in that: The forming method uses double-length forging, with the small hole located in the middle of the forging.

3. The forming method of a duplex stainless steel semi-blind hole forging according to claim 1, characterized in that: In step 8) of this forming method, the variable diameter lever has the large diameter part at both ends and the small diameter part in the middle. The large diameter and small diameter of the variable diameter lever are connected by a 30-60 degree inclined platform. The inclined platform and the straight platform have a ≥5 mm rounded transition. This increases the strength at the connection between the large diameter and small diameter of the lever and facilitates material flow so that the small inner hole can be fully formed.

4. The forming method of a duplex stainless steel semi-blind hole forging according to claim 1, characterized in that: In this forming method, step 9) after the forging is forged to the finished size, it is placed in a heating furnace at 1000~1150℃ and held for 1.5-4.5 hours. Then it is quickly taken out of the furnace and water-cooled to room temperature. This effectively suppresses excessive grain coarsening and prevents the precipitation of harmful σ phase.

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