A method of press forming a thick-walled super duplex stainless steel head

Abstract

The application discloses a kind of thick-walled super duplex stainless steel head's press forming method, by the process steps in the present application: design determines the size of container, shape and material thickness, number material, blanking, using stamping die to be formed to the sheet, solid solution, wherein stamping forming and solid solution process are specially capable of being adapted to the process that thick-walled super duplex stainless steel is made head, can improve forming quality, by strict detection and control process flow, ensure the quality and performance of head, avoid the situation that head is cracked and scrapped using traditional forming mode and the problem that ferrite and hardness cannot meet the requirements, can shorten manufacturing cycle, can reduce material loss and labor cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of head forming process, and particularly relates to a pressing forming method of thick-wall super duplex stainless steel head. BACKGROUND

[0002] With the development of chemical, petrochemical, papermaking and petroleum industries, the demand for corrosion-resistant and high-strength materials is increasing. S25073 as a high-performance super duplex stainless steel is widely used in the manufacture of pressure vessels due to its excellent corrosion resistance and mechanical properties. However, the traditional head forming method has problems of low material utilization, long manufacturing cycle and high cost, which limits its application in industry, and the super duplex stainless steel head is subjected to 1050 DEG C hot pressing + 1050 DEG C solid solution treatment by traditional process, and the head cracks immediately after hot pressing or cracks during solid solution. Using traditional warm forming and hot forming process, cracking occurs in different degrees after head forming, which is due to that the performance requirements of stainless steel itself are not high when the traditional process is used to process general stainless steel, such as hardness, ferrite, whether there is a defect, etc., and the process and process parameter control in the stamping process. These traditional processes cannot be applied to the forming process of stainless steel head of S25073 material. SUMMARY

[0003] The purpose of the application is to provide a pressing forming method of head which can adapt to super duplex stainless steel (S25073 material), and can avoid the problems of head cracking and deformation.

[0004] The technical scheme adopted by the application is as follows:

[0005] A pressing forming method of thick-wall super duplex stainless steel head, comprising the following steps:

[0006] The design determines the container's size, shape, and material thickness. For thicknesses greater than 20mm, S25073 steel plates are selected. The steel plates undergo 100% PT testing to achieve Grade I qualification, requiring 45-55% ferrite content, a hardness ≤310HBW, and a thickness greater than 20mm to qualify as the back wall. The reason for using these steel plates is that uneven strength and phase balance in the original steel plate material can lead to excessively high local stress concentrations during initial pressing, causing cracks in stress concentration areas such as the R-section. Primarily to improve mechanical properties, super duplex steel is composed of austenitic and ferritic phases. At phase equilibrium, the austenitic phase provides high strength and hardness, while the ferrite phase imparts good plasticity and toughness. Super duplex steel achieves a good balance between strength and toughness, possessing high yield strength, tensile strength, and impact strength, while maintaining good ductility and fatigue resistance, allowing it to withstand heavy loads and impacts. Phase balance also enhances corrosion resistance. The optimal distribution of alloying elements such as chromium, molybdenum, and nitrogen in the two phases is crucial for corrosion resistance. Chromium increases the pitting potential and reduces the corrosion rate; molybdenum inhibits anodic dissolution and improves the stability of the passivation film; nitrogen combines with hydrogen to form ammonium ions, promoting pit repassivation. At phase equilibrium, these elements work synergistically in the austenite and ferrite phases, giving the steel excellent resistance to pitting corrosion, crevice corrosion, intergranular corrosion, and stress corrosion cracking, and enabling it to resist corrosion from various inorganic acids, organic acids, and alkalis. Phase equilibrium also significantly impacts the machinability of super duplex steels. A balanced duplex structure reduces the work hardening rate, making the material easier to deform during cold forming, hot working, and welding, reducing cracking and defects, and improving processing efficiency and product quality.

[0007] (2) Marking the material: Mark the blanking dimension line, processing line and inspection line of the top elliptical head on the steel plate. According to the corresponding material sheet layout dimension, the size of the head during and after the stamping process can be guaranteed. For minor defects at the edge, they can be directly removed by secondary cutting of the remaining material to ensure the size and quality of the head.

[0008] (3) Cutting: Cut large pieces of material into the required size and shape to ensure the final overall size of the end cap and the rapid removal of micro-defects.

[0009] (4) The blank is formed by stamping using a stamping die. The blank needs to be gradually formed by multiple stamping, and the curvature and diameter of the blank are gradually adjusted. The number of stamping is ≤4 times. Before the first stamping, the blank is heated in the furnace. After the blank is put into the furnace, the heating rate is fast, the heating rate is 140℃ / h, the holding temperature is 270-295℃, and the holding time is 20-30min. After the blank is taken out of the furnace, it is sent into the stamping die for pressing. The bulging height of the blank after the first pressing is 1 / 3 of the overall height of the head. Before the second to fourth stamping, the blank is heated in the furnace while it is hot. The heating rate is fast, the heating rate is 140℃ / h, the holding temperature is 270-295℃, and the holding time is 20-30min. After each heating, the blank is taken out of the furnace for pressing. The bulging height of the blank after the second and third pressings is 1 / 3 of the overall height of the head. The fourth pressing is for trimming. The hardness increases before and after each stamping. The ferrite decreases before and after each stamping. Because the super duplex steel material, the austenite phase provides high strength and hardness, and the ferrite phase gives good plasticity and toughness. It achieves a good balance between strength and toughness, has high yield strength, tensile strength and impact strength, while maintaining good ductility and fatigue resistance, and can withstand heavy load and impact. If the temperature and number of times do not meet the standards, the strength and toughness will affect the quality of the head.

[0010] (5) Solid solution, weld the support ring on the stamped head, use E2594 welding rod for solid ring welding, prevent the size of the head port from changing during solid solution, stress relief of the head, detect the residual stress level after stress relief, and it is available when the residual stress distribution is uniform. The head is buckled on the solid solution tooling. A thermocouple is placed on the head. The temperature is measured by the thermocouple. Natural gas furnace is used for heating. Heat treatment is carried out according to the solid solution process. The furnace temperature is >850℃ during solid solution. The furnace temperature rises rapidly, the heating rate is 200℃ / h, the holding temperature is 1150-1180℃, the holding time is 25-30min, and the blank is water-cooled after being taken out of the furnace. The water entering time is less than 1min. After solid solution, the ferrite and hardness are detected. The hardness after solid solution is ≤330HBW, and the ferrite is ≥40%. Because the head is deformed after cold forming, restraint force is generated, which causes large stress concentration. The stress generated during the forming of the head must be released through recovery performance heat treatment (solid solution) to ensure the quality of the head and the performance of the product in the process device.

[0011] (6) The head is detected for ferrite. The ferrite content in the metallographic structure of the formed head is 45%-55%, which is qualified.

[0012] The further technical scheme is that if the size of the head after step 4 stamping does not meet the design requirements, it can only be molded and trimmed. During the molding and trimming, the furnace temperature is >850℃, the furnace temperature rises, the holding temperature is 1150-1180℃, the holding time is 30-40min, and the blank is water-cooled after being taken out of the furnace. The water entering time is ≤1min.

[0013] Further technical solutions are that the hole in the center of the bottom of the head is less than or equal to φ150 mm in step (5), which plays a role in exhaust during solid solution heat treatment.

[0014] Further technical solutions are that the surface of the steel sheet is ensured to be free of oil stains, impurities and damage in step (1).

[0015] Further technical solutions are that the burrs and hard objects on the edges of the sheet are cleaned after cutting in step (3), small gaps must be polished and smoothed, and a 3 mm hardened layer is polished and removed, after polishing and cleaning, the end bevel is detected by PT to confirm that there is no surface defect, the deformation caused by cutting is corrected to ensure the flatness and straightness of the material.

[0016] Further technical solutions are that stress relief is performed using a vibration aging device or a thermal aging device in step (5).

[0017] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present application are:

[0018] 1. Improve the forming quality: through the process steps in the present application: design to determine the size, shape and material thickness of the container, material selection, cutting, using a stamping die to stamp the sheet and the process of solid solution, among which the stamping forming and solid solution process is a process specially suitable for making head from thick-walled super duplex stainless steel, which can improve the forming quality, through strict detection and control of the process flow, the quality and performance of the head are ensured, and the problems of head cracking and scrap and the problem that the ferrite and hardness do not meet the requirements are avoided.

[0019] 2. Shorten the manufacturing cycle: simplify the head forming process and reduce the manufacturing time.

[0020] 2. Reduce cost: ensure the quality of head forming, which can reduce material loss and labor cost. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a physical picture of the thick-walled super duplex stainless steel head formed by the method of the present application;

[0022] Figure 2 is a physical picture after the first stamping;

[0023] Figure 3 is a physical picture after the second stamping;

[0024] Figure 4 is a physical picture after the third stamping;

[0025] Figure 5 is a physical picture after the fourth stamping;

[0026] Figure 6 is the metallographic structure of the head after forming;

[0027] Figure 7 is the ferrite and hardness change table of four times stamping process;

[0028] Figure 8 is the picture of cracking after forming of thick-walled super duplex stainless steel head made by using existing stamping process;

[0029] Figure 9 is the picture of cracking after forming of thick-walled super duplex stainless steel head made by using existing stamping process

[0030] Figure 10 is the picture of cracking after forming of thick-walled super duplex stainless steel head made by using existing stamping process;

[0031] Figure 11 is the picture of welding support ring on the stamped head;

[0032] Figure 12 is the picture of the head buckled on the solid solution tool. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples.

[0034] As shown in Figures 1-12 .

[0035] A pressing forming method of thick-walled super duplex stainless steel head, comprising the following steps:

[0036] (1) Design to determine the size, shape and material thickness of the container, the thickness is greater than 20mm, select S25073 material steel plate, the steel plate piece is 100% PT detection I class qualified, the requirement ferrite 45-55%, hardness ≤310HBW,

[0037] (2) Marking, marking the blanking size line, processing line and inspection line of the top elliptical head on the steel plate piece,

[0038] (3) Blanking, cutting the bulk material into the required size and shape,

[0039] (4) The blank is formed by stamping using a stamping die. The blank is gradually formed by multiple stamping, and the curvature and diameter of the blank are gradually adjusted. The number of stamping is less than or equal to 4. Before the first stamping, the blank is heated in the furnace. After the blank is put into the furnace, the heating rate is fast, the heating rate is 140°C / h, the holding temperature is 270-295°C, and the holding time is 20-30 min. After the blank is taken out of the furnace, it is sent into the stamping die. The bulging height of the blank after the first pressing is 1 / 3 of the overall height of the head. Before the second to fourth stamping, the blank is heated in the furnace while it is hot. The heating rate is fast, the heating rate is 140°C / h, the holding temperature is 270-295°C, and the holding time is 20-30 min. After each heating, the blank is taken out of the furnace and pressed. The bulging height of the blank after the second and third pressing is 1 / 3 of the overall height of the head. The fourth pressing is a trimming process. The hardness of the blank increases before and after each stamping. The ferrite content of the blank decreases before and after each stamping, as shown in FIG. 6. Natural gas furnace is used for heating. Figure 7

[0040] (5) Solid solution. The support ring is welded on the stamped head. E2594 welding rod is used for solid ring welding to prevent the size of the head port from changing during solid solution. The head is subjected to stress relief. The residual stress level after stress relief is detected. When the residual stress distribution is uniform, the head is buckled on the solid solution tool. A thermocouple is placed on the head. The temperature is measured by the thermocouple. The head is heated by a natural gas furnace. The head is heat treated according to the solid solution process. The furnace temperature is greater than 850°C. The heating rate is fast, the heating rate is 200°C / h, the holding temperature is 1150-1180°C, the holding time is 25-30 min, and the blank is water-cooled after being taken out of the furnace. The water entering time is less than 1 min. The ferrite and hardness of the blank after solid solution are detected. The hardness of the blank after solid solution is less than or equal to 330 HBW, and the ferrite content of the blank is greater than or equal to 40%.

[0041] (6) The ferrite content of the formed head is detected. The ferrite content in the metallographic structure is 45%-55%, which is qualified.

[0042] If the size of the head after step 4 stamping does not meet the design requirements, it can only be molded and trimmed. During the molding and trimming process, the furnace temperature is greater than 850°C, the furnace temperature is increased, the holding temperature is 1150-1180°C, the holding time is 30-40 min, and the blank is water-cooled after being taken out of the furnace. The water entering time is less than 1 min.

[0043] Mold trimming is required to avoid local residual stress concentration caused by spinning. The mold trimming process is as follows:

[0044] Check the mold: Ensure that the mold cavity, mold core and other parts are not damaged or deformed, the surface finish meets the requirements, and the parts are firmly connected.

[0045] ​Preparation of materials: according to the material and requirements of the parts to be repaired, prepare the appropriate blank, check its size, surface quality, etc. whether it meets the starting processing conditions. At the same time, prepare lubricant and other auxiliary materials to reduce friction during die pressing.

[0046] Debugging equipment: debug the die pressing equipment such as hydraulic machine, etc., to ensure that its pressure, stroke, etc. Parameters can be accurately controlled and meet the process requirements:

[0047] Clean the blank: clean the oil stains, dust and other impurities on the surface of the blank to prevent them from entering the mold and affecting the repair quality.

[0048] Position the blank: accurately place the blank in the cavity of the mold, and ensure that the blank does not shift during die pressing through positioning pins, positioning blocks and other devices to ensure the accuracy of the repair position.

[0049] Clamp: start the die pressing equipment, slowly lower the upper die and close the lower die, and apply pressure to the blank. During clamping, control the clamping speed to avoid impact on the blank and mold due to excessive speed.

[0050] Apply pressure: gradually increase the die pressing pressure to the set value according to the material, thickness of the blank and the requirements of the repair, and keep it for a period of time to make the blank plastic deformation under the action of the mold to achieve the purpose of repair. During the pressure application process, pay close attention to the change of pressure to ensure stable pressure.

[0051] Pressure holding and cooling: after reaching the set pressure, keep the pressure for a period of time to let the blank fully form in the mold. Then cool down, which can be done by natural cooling or forced cooling (such as cooling water) to cool and shape the part in the mold, improve the size accuracy and surface quality.

[0052] Demoulding: after cooling, start the demoulding device of the die pressing equipment to make the upper die rise and take out the formed part from the mold. Carefully operate during demoulding to avoid damaging the repaired part and the mold.

[0053] Trimming: use trimming tools such as scissors, punch, grinding wheel, etc. To trim the flash, burr and other parts of the edge to make the edge of the repaired part more smooth and neat, which meets the design requirements.

[0054] In step (5), a hole with a diameter of ≤φ150mm is opened in the center of the bottom of the head, which plays a role in exhaust during solid solution heat treatment.

[0055] In step (1), ensure that the surface of the steel sheet is free of oil stains, impurities and damage.

[0056] In step (3), the burrs on the edges of the material sheet are cleaned after discharging, small gaps must be polished and smoothed, and 3mm hardened layer of the cut is polished and removed. After polishing and cleaning, the end bevel is subjected to PT detection to confirm that there is no surface layer defect, the deformation generated during cutting is corrected, and the flatness and straightness of the material are ensured.

[0057] In step (5), a stress relief device or a thermal aging device is used for stress relief.

[0058]

[0059]

[0060] The above is only a preferred embodiment of the present application.

Claims

1. A method of press forming a thick-walled super-duplex stainless steel head, characterized in that, The method comprises the following steps: (1) design to determine the size, shape and material thickness of the container, the thickness is greater than 20 mm, select S25073 material steel plate, the steel plate sheet is detected by 100% PT, grade I is qualified, the ferrite content is 45-55%, and the hardness is less than or equal to 310HBW, (2) number, the steel plate sheet is numbered to form the lower blanking size line, the processing line and the inspection line of the top elliptical head, (3) blanking, cutting the large material into the required size and shape, (4) using the stamping die to stamp the sheet, which needs to be gradually formed by multiple stamping, and the curvature and diameter of the sheet are gradually adjusted, the stamping times are less than or equal to 4 times, before the first stamping forming, the sheet is heated in the furnace, after the sheet is put into the furnace, the heating speed is 140 ℃ / h, the holding temperature is 270-295 ℃, the holding time is 20-30 min, then the sheet is sent into the stamping die for pressing after being taken out of the furnace, the first pressing sheet bulge height is 1 / 3 of the overall height of the head, before the second to fourth stamping, the sheet is heated in the furnace while being hot, the heating speed is 140 ℃ / h, the holding temperature is 270-295 ℃, the holding time is 20-30 min, the sheet is pressed after being taken out of the furnace after each heating, the bulge height of the second and third pressing is 1 / 3 of the overall height of the head, the fourth pressing is for repairing, the hardness increases before and after each stamping, and the ferrite content decreases before and after each stamping, (5) solution, welding a supporting ring on the stamped head, using E2594 welding rod for ring welding to prevent the size of the head port from changing during solution, stress relief is performed on the head, the residual stress level after stress relief is detected, and the head is buckled on the solution tool, a thermocouple is placed on the head, the actual temperature is measured by the thermocouple, a natural gas furnace is used for heating, and heat treatment is performed according to the solution process, the solution temperature is greater than 850 ℃, the furnace is rapidly heated, the heating speed is 200 ℃ / h, the holding temperature is 1150-1180 ℃, the holding time is 25-30 min, and the sheet is water-cooled after being taken out of the furnace, the water entering time is less than 1 min, the ferrite and hardness of the sheet after solution are detected, the hardness after solution is less than or equal to 330HBW, and the ferrite content is greater than or equal to 40%, (6) after the head is formed, the ferrite content is detected, and the ferrite content in the metallographic structure is 45%-55% to be qualified.

2. A method of press forming a thick-walled super-duplex stainless steel head according to claim 1, characterized in that, If the head size after step 4 stamping forming does not meet the design requirements, the head can only be repaired by mold pressing, when mold pressing, the furnace temperature is greater than 850 ℃, the furnace is heated, the holding temperature is 1150-1180 ℃, the holding time is 30-40 min, the furnace is taken out and water-cooled, and the water entering time is less than 1 min.

3. A method of press forming a thick-walled super-duplex stainless steel head according to claim 1, characterized in that, In step (5), the hole in the center of the bottom of the head is less than or equal to φ150 mm, which plays a role in exhaust during solution heat treatment.

4. A press forming method of a thick-walled super-duplex stainless steel head according to claim 1, characterized in that, In step (1), it is ensured that the surface of the steel plate sheet is free of oil stains, impurities and damage.

5. A method of press forming a thick-walled super-duplex stainless steel head according to claim 1, characterized in that, In step (3), the burrs and hard objects on the edges of the sheet after blanking are cleaned, small notches are polished and smoothed, 3 mm hardened layer of the cutting edge is polished and removed, after polishing and cleaning, the end bevel is detected by PT to confirm that there is no surface defect, the deformation generated in the cutting process is corrected, and the flatness and straightness of the material are ensured.

6. A method of press forming a thick-walled super-duplex stainless steel head according to claim 1, characterized in that, The stress relief in step (5) is performed using a vibratory stress relief apparatus or a thermal stress relief apparatus. The stress relief in step (5) is performed using a vibratory stress relief apparatus or a thermal stress relief apparatus.

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