A forging method of large-size high-toughness S32750 super duplex stainless steel

Abstract

The present application takes the steel ingot circulation link, how to realize the compression ratio, the overall uniformity and the surface quality to reach the optimum in the forging and blooming, how to transition from the intermediate billet to the finished product specification, how to match the finished product heating and forging process as the starting point, designs the steel ingot heat treatment process, reasonably distributes the compression ratio in the upsetting and drawing process, successfully realizes that each index of large specification S32750 duplex stainless steel forging material meets the standard requirements, and meets the market demand.

Description

Technical Field

[0001] This invention relates to the field of pressure processing and rolling, and more particularly to a forging method for large-size, high-toughness S32750 super duplex stainless steel. Background Technology

[0002] With the deepening of human exploration of the ocean and the gradual development of industries such as carbon capture and geothermal energy, the demand for duplex steel, especially super duplex steel, is showing a year-on-year growth trend. Among them, S32750 is the main representative of super duplex steel. S32750 will be widely used in industries such as offshore platforms, carbon capture, geothermal energy, and natural gas pipelines. The demand for specifications is developing towards φ300mm and above, while higher requirements are being placed on the toughness and uniformity of the product. For example, the -46℃ transverse low-temperature impact test requires testing three points at each end, for a total of six groups, and the average impact value of each group must not be less than 200J. Conventional forging processes can only achieve about 40J, which is difficult to meet the application requirements.

[0003] To meet market demand and support the development of new energy in China, it is imperative to develop large-size, high-toughness S32750 super duplex stainless steel.

[0004] This invention designs and develops a forging process for large-scale, high-toughness S32750 super duplex stainless steel, which enables the overall performance uniformity and surface quality of the product to meet standard requirements and satisfy market demand. Summary of the Invention

[0005] The purpose of this invention is to address the above-mentioned problems by providing a forging method for large-size, high-toughness S32750 super duplex stainless steel.

[0006] The objective of this invention is achieved as follows: A forging method for large-size, high-toughness S32750 super duplex stainless steel, comprising the following steps: Step 1: Ingot cooling: The ingot is heated in a trolley annealing furnace at a heating rate of <100℃ / h for 3-4 hours to 1100±10℃ and held for 6-7 hours. After holding, it is removed from the furnace and immersed in water for 30-40 minutes, with the time from removal from the furnace to immersion in water being less than 2 minutes; Step 2: Upsetting and drawing forging: Two upsetting and two drawing processes are adopted, i.e., the first upsetting to... After the original steel ingot height is 2 / 3-3 / 4, the length is drawn to 3 / 4-4 / 5 of the original length. Then, it is returned to the reheat furnace for 1.5-2 hours at 1250±10℃. It is then removed from the furnace for a second upsetting, reducing the ingot height to 1 / 2-2 / 3 of the original height, before being drawn again to 2 / 3-3 / 4 of the original height. It is then returned to the furnace for another 1.5-2 hours at 1250±10℃. After this, normal forging production can begin, with a final forging temperature of 900-950℃. ℃, the diameter of the entire billet is consistent when returning to the furnace; Step 3: Solution treatment of intermediate billets: After the billets are opened, they are immediately hot-charged into the annealing furnace for offline solution treatment. The billets are heated to 1100±10℃ with the furnace and held for 4-4.5 hours, then immediately dipped in water for 30-40 minutes. After offline solution treatment, surface defects are ground off, and then the billets are loaded into the heating furnace to prepare for radial forging; Step 4: Radial forging: When heating the radial forgings, the holding time is 4-5 hours, the temperature is 1250±10℃, and the number of billets loaded into the furnace is 6-8. After the holding time is completed, the billets are... After the material is burned evenly and thoroughly, it is immediately taken out of the furnace for forging. The final forging temperature is required to be 900-950℃. The first forging reduction is 70-80mm, and the reduction from the third forging onwards is reduced by 10-20mm each time. The reduction in the last forging is <10mm to ensure a smooth surface. Step 5: Solution treatment of finished product: After forging, the billet is immediately hot-charged into the annealing furnace for offline solution treatment. After the billet is heated to 1100±10℃ in the furnace, it is immediately dipped in water for 30-40 minutes. After offline solution treatment, surface defects are machined off, and the billet is inspected and delivered to the warehouse.

[0007] In step two, after both upsetting processes, the billet is drawn and rolled laterally. After the second drawing, the requirement for normal drawing and forging is a final forging temperature of 900-950℃, and the diameter of the entire billet is consistent when it is returned to the furnace.

[0008] In step two, during the two drawing processes, it is required that the diameter of the entire billet be consistent when it is returned to the furnace after each firing, so as to ensure that the deformation amount is the same for each firing.

[0009] In step two, during the two drawing operations, ensure that the compression ratio from the intermediate billet to the finished product is 2-2.5. During the drawing operation, the first pass should have a reduction of 80mm-100mm, and the reduction should decrease by 20-25mm for each subsequent pass to ensure that the final forging temperature is 900-950℃.

[0010] In step four, increase the forging speed to 3.5-4 m / min during diaphragm forging. Control the reduction in the first pass to 70-80 mm, and reduce it by 10-20 mm in subsequent passes to ensure that the final forging temperature of the diaphragm forging material is 900-950℃.

[0011] The beneficial effects of this invention are: through the development and design of the steel ingot circulation process, forging process and solution treatment process, the overall performance uniformity and surface quality meet the standard requirements, realizing the mass production of large-size S32750 duplex stainless steel forgings and meeting market demand. Attached Figure Description

[0012] The present invention will now be further described with reference to the accompanying drawings.

[0013] Figure 1 This is a process diagram of the solution treatment of steel ingots according to the present invention. Detailed Implementation

[0014] Conventional fast forging or radial forging processes cannot meet this requirement; an upsetting and drawing process is necessary to ensure a total forging ratio >5. To meet this requirement, the following challenges exist: 1. Due to the characteristics of this steel grade, harmful phases are easily generated during cooling, leading to cracking or fracture; 2. This steel grade is extremely sensitive to temperature. Upsetting and drawing require fast forging, but fast forging is inefficient. Maintaining the final forging temperature requires multiple forging passes, which are detrimental to the microstructure of the finished product. Finding the balance point is difficult; 3. The finished product requires testing the impact energy at three points at both ends, demanding high uniformity of material properties, which is challenging to meet.

[0015] Conventional forging processes employ either hot-charging furnace for rapid forging or direct radial forging of steel ingots. This invention provides a solution-cooling process for steel ingots when a hot-charging furnace is unavailable.

[0016] Conventional forging processes employ either fast forging or radial forging. This invention utilizes a combined fast forging and radial forging method. Through numerous trials and explorations, a reasonable upsetting and drawing method was determined, namely, two upsettings and two drawings. The first upsetting is 1 / 3, followed by a transverse drawing of 1 / 12. The second upsetting is 1 / 4, followed by a transverse drawing of 1 / 6.

[0017] Conventional forging is highly arbitrary, with control only based on the final forging temperature. This invention clarifies that while ensuring the final forging temperature during each drawing process, it is also necessary to ensure that the diameter of the entire billet is consistent when it is returned to the furnace, thus ensuring uniform performance of the entire billet.

[0018] This invention specifies that the compression ratio from intermediate billet specifications to finished product specifications is 2-2.5, ensuring that the performance meets the requirements while guaranteeing the surface quality of the intermediate billet, and ensuring that the overall yield reaches the optimal level.

[0019] Based on the production difficulties, the following technical solutions were developed: 1. Overcome the challenges in the cooling process of steel ingots. According to past production experience, 5-ton steel ingots have cracked after cooling. Forging materials of about 400mm can be solution treated to prevent cracking. Therefore, the following steel ingot solution treatment process was developed: use a 4.5-ton hot-charged annealing furnace for solution treatment. After the steel ingot is heated to 1100℃ in the furnace and held for 6 hours, it is taken out of the furnace and immersed in water for more than 30 minutes. During the production process, it is essential to ensure rapid turnover, with less than 2 minutes between taking it out of the furnace and immersing it in water to avoid excessive temperature drop that could cause cracking.

[0020] 2. To ensure a forging ratio greater than 5 and no severe surface cracking, an upsetting + drawing forging method is adopted for billet preparation + radial forging to form finished products. Considering that excessive upsetting in a single operation can easily cause bending and folding on the surface, and the folds will tear and form cracks during drawing, a two-upsetting and two-drawing method is adopted. That is, after the first upsetting to 1 / 3 of the original ingot height, the length is drawn to 3 / 4 of the original length. Then, it is put back into the furnace for 1.5 hours for holding. After taking it out of the furnace again, the ingot is upsetting to 1 / 2 of the original ingot height and then drawn to 2 / 3 of the original ingot height. After putting it back into the furnace for 2 hours for holding, normal drawing production can begin.

[0021] 3. To ensure the uniformity of billet properties and forging penetration, the billet is stretched and rolled laterally after both upsetting processes. After the second rolling, it is then stretched and forged normally.

[0022] 4. To ensure the uniformity of the performance of the entire billet, during the drawing process, the diameter of the entire billet must be consistent when it is returned to the furnace after each of the three drawing cycles, so as to ensure that the deformation amount is the same for each drawing cycle.

[0023] 5. To avoid the adverse effects of repeated heating on the finished product performance and to ensure surface quality, while reserving a certain amount of deformation for the radial forging, the billet specifications are calculated based on the finished product size during drawing to ensure that the compression ratio from intermediate billet to finished product is 2-2.5. During drawing, the first pass reduction is required to be 80mm-100mm, and the reduction in each subsequent pass (a total of 3-4 passes) is reduced by 20mm to ensure that the final forging temperature is greater than 900℃ and less than 950℃.

[0024] 6. Immediately after billet preparation, charge it into the annealing furnace for offline solution treatment. Heat the billet to 1100℃ in the furnace and hold it for 4 hours (the temperature should not be too long to avoid grain growth). (The holding time should be consistent with the diameter of the steel, i.e., the diameter is a certain number of millimeters and the holding time is a certain number of minutes). Immediately after holding, wet it for at least 30 minutes. After offline solution treatment, grind off surface defects and then charge it into the furnace, ready for radial forging.

[0025] 7. To avoid the adverse effects of prolonged heating on performance, the holding time and the number of billets in the furnace should be strictly controlled during the heating of radial forgings. The billets should be heated evenly and thoroughly after holding for 4 hours, and then taken out of the furnace for forging.

[0026] 8. When forging radial forging, increase the forging speed to 3.5-4m / min. Control the reduction in the first pass to 70-80mm, and reduce it by 10-20mm in subsequent passes (a total of 5 passes) to ensure that the final forging temperature of the radial forging material is 900-950℃.

[0027] This invention utilizes a solution treatment process to achieve cooling of S32750 steel ingots. Upsetting followed by transverse drawing results in a denser, more uniform internal structure and a surface less prone to tearing. After upsetting, the ingot is transversely drawn to the required intermediate billet size, ensuring a final compression ratio of 2-2.5. This guarantees the surface quality and density of the intermediate billet, provides sufficient compression for radial forging, and allows for one-fire forging. By optimizing the forging process, large-diameter S32750 ingots (φ300mm and above) achieve an impact energy exceeding 200J at -46℃. Example 1

[0028] This method uses die-casting steel ingots and radial forging to produce large-size, high-toughness S32750 with a diameter of φ300mm or more. It meets the requirement of achieving an impact energy of 200J at -46℃ while achieving a comprehensive yield of over 70%.

[0029] Step 1: Ingot Cooling: The ingot is heated in the annealing furnace at a rate of <100℃ / h for 4 hours to 1105℃ and held for 6 hours. After holding, it is removed from the furnace and immersed in water for 30 minutes. The time between removing from the furnace and immersion in water is 1.5-2 minutes. Step 2: Upsetting and Drawing Forging: Two upsetting and two drawing processes are used. The first upsetting is performed to 2 / 3 of the original ingot height, followed by drawing to 3 / 4 of the original length. The ingot is then returned to the heating furnace and held at 1250℃ for 2 hours. After exiting the furnace, the ingot undergoes a second upsetting process, upsetting it to half its original height before drawing it to two-thirds of its original height. It is then returned to the furnace and held at 1250℃ for 2 hours, followed by normal drawing and production. The final forging temperature is 912℃, and the diameter of the entire billet upon return is Φ552mm. Step 3: Intermediate Billet Solution Treatment: Immediately after billet preparation, it is hot-charged into the annealing furnace for offline solution treatment. The billet is heated to 1102℃ in the furnace and held for 4 hours, then immediately dipped in water for 30 minutes for offline solution treatment. After melting and cleaning the surface defects, the billet is immediately loaded into a heating furnace to prepare for radial forging. Step 4: Radial forging: The radial forging is held at a temperature of 4 hours during heating, with 6 billets loaded into the furnace. After the holding period, the billet is heated evenly and thoroughly, and then removed from the furnace for forging. The final forging temperature is 905℃. The first pass reduction is 70mm, the second pass reduction is 70mm, the third pass reduction is 55mm, the fourth pass reduction is 40mm, and the fifth pass reduction is 10mm. The surface is smooth after forging, the final forging temperature is 915℃, and the finished product diameter is Φ370mm. Step 5: Finished product solution treatment: After forging, the billet is immediately loaded into an offline annealing furnace for solution treatment. The billet is heated to 1102℃ with the furnace and held for 370 minutes, then immediately wetted for 30 minutes. After offline solution treatment, the surface defects are machined to remove imperfections. The finished product diameter is Φ360mm. The three-point impact energy is tested at 205J (core) / 218J (1 / 4 diameter) / 221J (edge). The billet is then delivered to the warehouse and shipped normally.

[0030] The above description is only a specific embodiment of the present invention, but the structural features protected by the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A forging method for large-size, high-toughness S32750 super duplex stainless steel, characterized in that: Includes the following steps: Step 1: Cooling the steel ingot: The steel ingot is heated in the annealing furnace at a heating rate of <100℃ / h for 3-4 hours to 1100±10℃ and held for 6-7 hours. After holding, it is taken out of the furnace and immersed in water for 30-40 minutes. The time from taking out of the furnace to immersing in water is less than 2 minutes. Step Two: Upsetting and Drawing Forging: Two upsetting and two drawing processes are adopted. The first upsetting is carried out to 2 / 3-3 / 4 of the original ingot height, and then the length is drawn to 3 / 4-4 / 5 of the original length. Then, it is returned to the heating furnace for 1.5-2 hours at a temperature of 1250±10℃. After that, it is taken out of the furnace for a second upsetting, upsetting the ingot to 1 / 2-2 / 3 of the original ingot height, and then drawing it to 2 / 3-3 / 4 of the original ingot height. It is then returned to the furnace for 1.5-2 hours at a temperature of 1250±10℃. After that, it can be drawn into production normally. The final forging temperature is required to be 900-950℃. When returning to the furnace, the diameter of the entire billet is consistent. Step 3: Solution treatment of intermediate billet: After the billet is opened, it is immediately charged into the annealing furnace for offline solution treatment. The billet is heated to 1100±10℃ with the furnace and held for 4-4.5h. Then it is immediately dipped in water for 30-40min. After offline solution treatment, the surface defects are ground off and then loaded into the heating furnace to prepare for radial forging. Step 4: Radial forging: When heating the radial forging material, the holding time is 4-5 hours, the temperature is 1250±10℃, and the number of billets in the furnace is 6-8. After the holding time is completed, the billet is heated evenly and thoroughly, and then taken out of the furnace for forging. The final forging temperature is required to be 900-950℃. The first pass reduction is 70-80mm, and the reduction from the third pass onwards decreases by 10-20mm each time. The reduction in the last pass is <10mm to ensure a smooth surface. Step 5: Solution treatment of finished product: After forging, the billet is immediately hot-charged into the annealing furnace for offline solution treatment. After the billet is heated to 1100±10℃ in the furnace, it is immediately dipped in water for 30-40 minutes. After offline solution treatment, surface defects are machined off, and the billet is inspected and delivered to the warehouse.

2. The forging method for large-size, high-toughness S32750 super duplex stainless steel according to claim 1, characterized in that: In step two, after both upsetting processes, the billet is drawn and rolled laterally. After the second drawing, the requirement for normal drawing and forging is a final forging temperature of 900-950℃, and the diameter of the entire billet is consistent when it is returned to the furnace.

3. The forging method for large-size, high-toughness S32750 super duplex stainless steel according to claim 1, characterized in that: In step two, during the two drawing processes, it is required that the diameter of the entire billet be consistent when it is returned to the furnace after each firing, so as to ensure that the deformation amount is the same for each firing.

4. The forging method for large-size, high-toughness S32750 super duplex stainless steel according to claim 1, characterized in that: In step two, during the two drawing operations, ensure that the compression ratio from the intermediate billet to the finished product is 2-2.

5. During the drawing operation, the first pass should have a reduction of 80mm-100mm, and the reduction should decrease by 20-25mm for each subsequent pass to ensure that the final forging temperature is 900-950℃.

5. The forging method for large-size, high-toughness S32750 super duplex stainless steel according to claim 1, characterized in that: In step four, increase the forging speed to 3.5-4 m / min during diaphragm forging. Control the reduction in the first pass to 70-80 mm, and reduce it by 10-20 mm in subsequent passes to ensure that the final forging temperature of the diaphragm forging material is 900-950℃.

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