A process for improving the distribution of non-metallic inclusions in 13Cr15Ni4Mo3N

Abstract

This invention relates to the field of stainless steel forging technology, specifically to a process for improving the distribution of non-metallic inclusions in 13Cr15Ni4Mo3N stainless steel. The invention includes the following steps: S1, Material preparation: 13Cr15Ni4Mo3N stainless steel material is cut, ground, and then its surface is cleaned; S2, Preheating: The heating temperature is 1115–1145℃, and the holding time is 50–110 min; S3, Free forging: The heat-cooled material described in S2 is subjected to free forging, with a deformation of no less than 40% per forging pass and a final forging temperature of no less than 850℃. After forging, the material is cooled to obtain a forging billet. This invention uses high-pressure water jet cleaning at a specific pressure during material preparation, which effectively removes impurities from the billet surface; preheating ensures a uniform internal structure before forging; controlling the final forging temperature range ensures good plasticity of the material, reduces forging defects, and facilitates better handling of inclusions under high temperature and large deformation, thereby improving the inclusion content within the material.

Description

Technical Field

[0001] This invention relates to the field of stainless steel forging technology, specifically to a process for improving the distribution of non-metallic inclusions in 13Cr15Ni4Mo3N stainless steel. Background Technology

[0002] 13Cr15Ni4Mo3N is a semi-austenitic precipitation-hardening stainless steel with good plasticity and processing properties, widely used in the aerospace field. 13Cr15Ni4Mo3N stainless steel has a complex composition. Low-carbon martensitic strengthening and age hardening methods are commonly used to improve its toughness and strength. After solution treatment and cold treatment, the room temperature microstructure is martensite with a small amount of retained austenite. After aging treatment, dispersed precipitates form on the martensitic matrix, achieving the required strength and toughness.

[0003] However, existing technologies have limitations when processing 13Cr15Ni4Mo3N stainless steel. During heat treatment, the focus is often on improving mechanical properties such as strength and toughness, while neglecting the microstructure and inclusions of the forgings after heat treatment.

[0004] In fact, the mechanical properties of forgings are closely related to their microstructure. The uniformity of the microstructure, grain size, and the content and distribution of inclusions all affect the final mechanical properties of the material. For example, inclusions may become stress concentration points, reducing the fatigue performance of the material, while an unreasonable microstructure may lead to premature failure during use. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a process for improving the distribution of non-metallic inclusions in 13Cr15Ni4Mo3N.

[0006] The technical solution of this invention is: a process for improving the distribution of non-metallic inclusions in 13Cr15Ni4Mo3N, comprising the following steps by mass percentage:

[0007] S1. Material preparation

[0008] By mass percentage, 13Cr15Ni4Mo3N stainless steel material is taken, cut and polished, and then the surface is cleaned with high-pressure water jet. After drying, a blank is obtained; the pressure of the high-pressure water jet is 200-300MPa.

[0009] S2, Preheating

[0010] The billet described in S1 is preheated in a heating furnace at a temperature of 1115-1145°C for 50-110 minutes, and then cooled in the furnace to obtain a fire-cooled material.

[0011] S3, Free Forging

[0012] The heat-cooled material described in S2 is subjected to free forging, with the deformation amount per forging cycle not less than 40%, the final forging temperature not less than 850℃, and the material is cooled after forging to obtain a forging billet.

[0013] S4, Annealing

[0014] The forging described in S3 is placed in a mold and held at 880–900°C for 8–14 hours, then air-cooled to room temperature; then the temperature is raised to 650–670°C, held for 5–8 hours, and then air-cooled to room temperature; then the temperature is raised to 765–795°C, held for 10–14 hours, and then air-cooled to room temperature; finally the temperature is raised to 590–610°C, held for 8–10 hours, and then air-cooled to room temperature to obtain a fire-cooled part.

[0015] S5, Solution treatment

[0016] The fire-cooled part described in S4 is introduced into a heating furnace for solution treatment, held at 840-860°C for 1-1.5 hours, then heated to 1025-1045°C and held for 2-3 hours, followed by water or oil cooling to room temperature; the fire-cooled part after solution treatment is subjected to ice-cooling treatment within 0-2 hours, then held at 840-860°C for 1-1.5 hours, then heated to 945-965°C and held for 0.5-1 hour, and then subjected to ice-cooling treatment again within 0-2 hours after the second solution treatment to obtain the solution-treated part;

[0017] S6, Tempering treatment

[0018] The solution-treated part described in S5 is introduced into a heating furnace and heated to 525-545°C. After holding at this temperature for 4-6 hours, it is air-cooled to room temperature to obtain a low-impurity forging.

[0019] Note: Dirt and scale on the stainless steel surface may react with the material at high temperatures or be trapped inside. High-pressure water jet cleaning can reduce this risk, thus helping to improve the purity of 13Cr15Ni4Mo3N material and reduce the content of non-metallic inclusions. Inhomogeneous microstructure may lead to uneven stress distribution during subsequent forging, thereby promoting the formation or aggregation of inclusions. Preheating to homogenize the microstructure makes the material more conducive to the dispersion and distribution of inclusions during forging, reducing their adverse effects, and also facilitates the process of obtaining fire-cooled material through furnace cooling. It is also a slow cooling process that helps stabilize the internal structure of the material and avoid the formation of new defects or inclusions. Inclusions are usually weak points in the material. Reducing their content will reduce stress concentration when the material is subjected to external forces, thereby improving the strength and toughness of the material. The reduction of non-metallic inclusions helps to improve its corrosion resistance. Inclusions may damage the passivation film on the material surface and become the starting point of corrosion. When the inclusion content is reduced, the passivation film on the material surface is more complete and can better resist the erosion of corrosive media, thereby improving the service life of the material in corrosive environments.

[0020] Multiple heat treatments at different temperatures and subsequent air cooling help eliminate residual stress inside the forging, making the microstructure more stable. Heat treatment in different temperature ranges can promote the rearrangement of internal atoms, reduce crystal defects, and lay a good microstructure foundation for subsequent processing steps. Timely ice cooling after solution treatment can further refine the grains and improve the hardness and wear resistance of the material. The subsequent heating and heat treatment helps to adjust the microstructure of the material, making the material properties more uniform and stable, and further reducing the adverse effects of inclusions. Tempering can eliminate the internal stress caused by solution treatment and ice cooling, improve the plasticity and toughness of the material, reduce the brittleness of the material, and make the internal microstructure of the material more uniform.

[0021] Further, the free forging method of the cold-pressed material described in S3 is as follows: the cold-pressed material is subjected to ultrasonic vibration treatment, the vibration frequency is 25-35 kHz, and the vibration time is 3-5 min; then the cold-pressed material after ultrasonic vibration treatment is subjected to at least one upsetting operation, the upsetting ratio is 1.5-1.7, and then an annular heating device is used to perform annular heating on the outer periphery of the cold-pressed material at a speed of 10-15℃ / min, so that the temperature of the outer periphery of the cold-pressed material is 10-15℃ higher than the temperature of the center, and the outer periphery thickness is 0.2-0.25 times the cross-sectional radius of the cold-pressed material; subsequently, the cold-pressed material after the outer periphery is heated is subjected to one drawing operation, and after forging, it is stacked and cooled to obtain a forging billet.

[0022] Explanation: Controlling the frequency and duration of ultrasonic vibration treatment helps refine the internal grains of the material and improve the uniformity of the microstructure. During this process, the energy generated by ultrasonic vibration promotes grain boundary migration and adjustment, resulting in grain refinement. The acoustic flow and cavitation effects of ultrasonic vibration can positively influence non-metallic inclusions within the material. The acoustic flow can drive inclusions to move within the material, and the impact force generated by cavitation can break up larger inclusions, making them more dispersed throughout the material. This improves the state of inclusions and increases the purity of the material from the initial stage. Upsetting can improve the density of the material and the distribution of streamlines. Since inclusions are usually weak points in the material, their accumulation at the center can seriously affect the material's performance. The stress effect and plastic deformation caused by the temperature difference generated by annular heating will cause inclusions to migrate from the center to the periphery during upsetting, dispersing the inclusions accumulated in the center of the stainless steel outward.

[0023] Furthermore, in the drawing process described in S3, a spiral drawing path is adopted, with a pitch of 0.1 to 0.3 times the length of the forging, a spiral diameter range of 0.8 to 1.2 times the diameter of the forging, and a feed amount of 0.02 to 0.05 times the diameter of the forging each time during drawing.

[0024] Explanation: A suitable helix pitch ensures uniform deformation of the forging along its length during the drawing process. This allows the material's internal grains to be uniformly elongated and refined, improving its strength and toughness. It also prevents internal defects such as cracks caused by excessive localized grain deformation differences. Controlling the helix diameter within the range of 0.8 to 1.2 times the forging diameter ensures a more reasonable stress distribution during drawing. If the helix diameter is too small, stress tends to concentrate locally, potentially leading to cracks or excessive localized deformation during drawing. Conversely, if the helix diameter is too large, stress distribution may be too dispersed, hindering effective drawing. A suitable helix diameter ensures stress is evenly distributed throughout the forging, guaranteeing a smooth drawing process. A smaller feed rate allows for gradual deformation, preventing sudden deformation due to excessive single feeds, which could damage the internal structure or reduce surface quality. Precise control of the deformation degree ensures the stability of the material's internal structure and improves the quality of the forging.

[0025] Furthermore, in S3, when the upsetting process is not less than two times, after the first upsetting process is completed, high-speed hot air is used for reheating in the furnace to rapidly raise the billet temperature to 1115-1145℃ before continuing the next upsetting process until the upsetting process is completed.

[0026] Explanation: Determining the number of forging passes based on the final dimensions allows for precise control of the forging process, ensuring that the billet gradually reaches the required size with higher dimensional accuracy. Repeated free forging operations in each pass help to uniformly improve the internal structure of the material, continuously refining and homogenizing the grains, and enhancing the overall performance of the material. Meanwhile, high-speed hot air reheating allows the billet to quickly reach the target temperature, reducing heating time and improving production efficiency.

[0027] Furthermore, the temperature of the hot air used for high-speed hot air reheating is 1115–1255℃, and the wind speed is 8–15 m / s.

[0028] Explanation: Controlling the hot air temperature within the target range efficiently provides heat to the billet, ensuring rapid heating, reducing heating waiting time, and improving production efficiency. A suitable heating rate helps maintain the billet's good plasticity during forging, which is beneficial for subsequent forging operations. Higher air velocity allows the hot air to circulate rapidly within the furnace, ensuring that heat is evenly transferred to all parts of the billet, avoiding localized overheating or underheating. This results in uniform heating of the billet as a whole, which helps improve the forging quality of the billet and reduces problems such as internal stress and uneven deformation caused by uneven heating.

[0029] Furthermore, in the stacking cooling process described in S3, the forging is placed on a platform with temperature control function for natural cooling. An infrared thermometer is used to detect the temperature of the forging. The temperature control platform is activated to ensure that the bottom temperature of the forging is always 5-10°C lower than the top temperature. During the stacking cooling process, a negative ion generator is placed around the forging, and the concentration of negative ions is 1000-1500 ions / cm³. 3 Once the temperature at the top of the forging has dropped to room temperature, turn off the temperature control platform and the negative ion generator.

[0030] Note: Using an infrared thermometer allows for precise acquisition of the forging temperature, enabling better monitoring of the cooling process. Adjusting the platform temperature and activating the temperature control platform ensures the bottom temperature of the forging is always 5-10°C lower than the top temperature. This promotes further migration and uniform distribution of inclusions under the influence of the temperature gradient. During the stacking cooling process, the negative ion generator is activated. Negative ions adsorb onto the surface of inclusions, altering their surface properties and making them less prone to aggregation. This also reduces impurity adsorption on the forging surface. Once the top temperature of the forging drops to room temperature, the relevant equipment is shut off to ensure sufficient cooling of the forging.

[0031] Furthermore, the method of the cryogenic treatment is as follows: the solution-treated fire-cooled part is placed in a cooling water tank with a temperature not higher than -70°C, and kept warm for 6 to 8 hours before being air-cooled to room temperature; the water tank is equipped with a stirring device with a stirring speed of 80 to 100 rpm, and the stirring is continuous during the cryogenic insulation process.

[0032] Note: By placing the solution-treated fire-cooled parts in a cooling water tank at a temperature not higher than -70℃ and keeping them at that temperature for 6 to 8 hours before air-cooling them to room temperature, the hardness, strength, and wear resistance of the material can be significantly improved. The stirring device in the water tank continuously stirs the parts at a speed of 80 to 100 rpm, which helps to ensure the uniformity of cooling, reduce internal stress, and thus improve the dimensional stability and fatigue resistance of the material.

[0033] The beneficial effects of this invention are:

[0034] This invention employs high-pressure water jet cleaning at a specific pressure during the material preparation process, effectively removing impurities from the billet surface. If these impurities are not removed, they may become part of the material during subsequent forging and heat treatment, becoming a source of non-metallic inclusions. Preheating at 1115–1145℃ for 50–110 minutes ensures a more uniform internal structure of the billet. Controlling the deformation amount per forging pass to be no less than 40% and the final forging temperature to be no less than 850℃ helps to break up larger inclusions in the structure. During the forging process… As the material deforms, inclusions are also subjected to stress, causing them to deform, break, or even disperse. Controlling the final forging temperature range ensures that the material has good plasticity, making the forging process smoother and reducing forging defects. It also helps to better handle inclusions under high temperature and large deformation, thereby improving the inclusion content inside the material. Post-forging cooling also helps to reduce the thermal stress generated during the cooling process, avoiding internal defects and inclusion aggregation caused by thermal stress. Due to the improved content of non-metallic inclusions, the mechanical properties of the material, such as strength and toughness, are improved. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the forging billet forming structure of Embodiment 1 of the present invention;

[0036] Figure 2 This is a schematic diagram of the low-impurity forging forming structure of Embodiment 1 of the present invention;

[0037] Figure 3 This is an optical microscope image of inclusions in the low-impurity forging of Embodiment 1 of the present invention, magnified 100 times.

[0038] Figure 4 This is an optical microscope image of the grain size of the billet in Embodiment 1 of the present invention at 100x magnification;

[0039] Figure 5 This is an optical microscope image of the grain size of the low-impurity forging in Embodiment 1 of the present invention at 100x magnification;

[0040] Figure 6 This is an optical microscope image of the free ferrite in the low-impurity forging of Embodiment 1 of the present invention, magnified 100 times. Detailed Implementation

[0041] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0042] Example 1: A process for improving the distribution of non-metallic inclusions in 13Cr15Ni4Mo3N, comprising the following steps:

[0043] S1. Material preparation

[0044] By mass percentage, 13Cr15Ni4Mo3N stainless steel material is taken, cut and polished, and then the surface is cleaned with high-pressure water jet. After drying, a blank is obtained; the pressure of the high-pressure water jet is 250MPa.

[0045] S2, Preheating

[0046] The billet described in S1 is preheated in a heating furnace at a temperature of 1130°C for 80 minutes, and then cooled in the furnace to obtain a fire-cooled material.

[0047] S3, Free Forging

[0048] The cold-pressed material described in S2 is subjected to free forging: the cold-pressed material is subjected to ultrasonic vibration treatment at a frequency of 30 kHz for 4 min; then, the cold-pressed material after ultrasonic vibration treatment is subjected to a single upsetting operation with an upsetting ratio of 1.6; then, an annular heating device is used to heat the outer periphery of the cold-pressed material at a rate of 12.5℃ / min, so that the temperature of the outer periphery of the cold-pressed material is 12.5℃ higher than the temperature of the center, and the outer periphery thickness is 0.225 times the cross-sectional radius of the cold-pressed material; subsequently, the cold-pressed material after the outer periphery is heated in one drawing operation, and then cooled after forging to obtain a forging billet; the deformation amount of each forging is 47.5%, and the final forging temperature is 870℃; the dimensions of the cold-pressed material after upsetting are Ф120×337mm and the weight is 30.4Kg; the dimensions of the forging billet after drawing are Ф217×120mm at the left fixed end and Ф229×87mm at the right drawn end;

[0049] During the stacking cooling process, the forging is placed on a DB-type stainless steel temperature control plate for natural cooling. An infrared thermometer is used to monitor the temperature of the forging. The DB-type stainless steel temperature control plate ensures that the bottom temperature of the forging is always 7.5°C lower than the top temperature when it falls below 300°C. During the stacking cooling process, a negative ion generator is placed around the forging, with a negative ion concentration of 1250 ions / cm³. 3 Once the temperature at the top of the forging has dropped to room temperature, turn off the DB-type stainless steel temperature control plate and the negative ion generator.

[0050] S4, Annealing

[0051] The forging described in S3 is placed with the narrower end (the longer end) facing down into the mold, i.e., the mold CY-551-407, and held at 890°C for 11 hours, then air-cooled to room temperature; then the temperature is raised to 660°C, held for 6.5 hours, and air-cooled to room temperature; then the temperature is raised to 780°C, held for 12 hours, and air-cooled to room temperature; finally, the temperature is raised to 600°C, held for 9 hours, and air-cooled to room temperature to obtain the fire-cooled part;

[0052] S5, Solution treatment

[0053] The fire-cooled part described in S4 is introduced into a heating furnace for solution treatment, held at 850°C for 1.25 hours, then heated to 1035°C and held for 2.5 hours, followed by water or oil cooling to room temperature; after 0.8 hours, the fire-cooled part after solution treatment is subjected to ice-cooling treatment, then held at 850°C for 1.25 hours, then heated to 955°C and held for 0.75 hours, and then subjected to ice-cooling treatment again within 1 hour after the second solution treatment to obtain the solution-treated part;

[0054] The method of cryogenic treatment is as follows: the fire-cooled part after solidification is placed in a cooling water tank at a temperature of -50°C, and after being kept at the temperature for 7 hours, it is air-cooled to room temperature; the water tank is equipped with a stirring device, and the stirring speed is 90 rpm, and stirring is carried out continuously during the cryogenic insulation process;

[0055] S6, Tempering treatment

[0056] The solution-treated part described in S5 is introduced into a heating furnace and heated to 535°C. After holding at that temperature for 5 hours, it is air-cooled to room temperature to obtain a low-impurity forging with dimensions of Ф225×60mm at the top and Ф89×178mm at the bottom.

[0057] Example 2: The difference between this example and Example 1 is that a spiral drawing path is used in the drawing process, the pitch is 0.1 times the length of the forging, the diameter of the spiral is 0.8 times the diameter of the forging, and the feed amount during drawing is 0.02 times the diameter of the forging each time.

[0058] Example 3: The difference between this example and Example 1 is that a spiral drawing path is used in the drawing process, the pitch is 0.3 times the length of the forging, the diameter of the spiral is 1.2 times the diameter of the forging, and the feed amount during drawing is 0.05 times the diameter of the forging each time.

[0059] Example 4: This example differs from Example 1 in that: the method for free forging of the cold-rolled material described in S3 is as follows: the cold-rolled material is subjected to ultrasonic vibration treatment at a frequency of 25 kHz for 3 minutes; then, the cold-rolled material after ultrasonic vibration treatment is subjected to two upsetting operations. After the first upsetting operation, high-speed hot air is used for reheating to rapidly raise the temperature of the billet to 1115°C before continuing the next upsetting operation until the upsetting is completed. The upsetting ratio is 1.5. Then, a ring heating device is used to perform ring heating on the outer periphery of the cold-rolled material at a speed of 10°C / min, so that the temperature of the outer periphery of the cold-rolled material is 10°C higher than the temperature of the center. The outer periphery thickness is 0.2 times the cross-sectional radius of the cold-rolled material; subsequently, a single elongation operation is performed on the heated cold-rolled material to ensure that the deformation amount of each operation reaches 45%. After forging, the material is cooled to obtain a forging billet; the length of the cold-rolled material after upsetting is 286 mm.

[0060] Example 5: This example differs from Example 1 in that: the free forging method of the cold-rolled material described in S3 is as follows: the cold-rolled material is subjected to ultrasonic vibration treatment at a frequency of 35 kHz for 5 minutes; then, the cold-rolled material after ultrasonic vibration treatment is subjected to three upsetting operations. After the first upsetting operation, high-speed hot air is used for furnace heating to rapidly raise the temperature of the billet to 1145°C before continuing the next upsetting operation until the upsetting is completed. The upsetting ratio is 1.7. Then, a ring heating device is used to perform ring heating on the outer periphery of the cold-rolled material at a speed of 15°C / min, so that the temperature of the outer periphery of the cold-rolled material is 15°C higher than the temperature of the center. The outer periphery thickness is 0.25 times the cross-sectional radius of the cold-rolled material. Subsequently, the cold-rolled material after the outer periphery heating is subjected to a single elongation operation to ensure that the deformation amount of each operation reaches 50%. After forging, the material is cooled to obtain a forging billet. The length of the cold-rolled material after upsetting is 237 mm.

[0061] Example 6: The difference between this example and Example 1 is that the temperature of the hot air for high-speed hot air return heating is 1115℃ and the wind speed is 8m / s.

[0062] Example 7: The difference between this example and Example 1 is that the temperature of the hot air for high-speed hot air return heating is 1255℃ and the wind speed is 15m / s.

[0063] Example 8: This example differs from Example 1 in that: during the stacking cooling process described in S3, the forging is placed on a DB-type stainless steel temperature control plate for natural cooling. An infrared thermometer is used to detect the temperature of the forging. The temperature control platform is activated to ensure that the bottom temperature of the forging is always 5°C lower than the top temperature when it drops below 200°C. During the stacking cooling process, a negative ion generator is placed around the forging, and the negative ion concentration is 1000 ions / cm³. 3 Once the temperature at the top of the forging has dropped to room temperature, turn off the temperature control platform and the negative ion generator.

[0064] Example 9: This example differs from Example 1 in that: during the stacking cooling process described in S3, the forging is placed on a DB-type stainless steel temperature control plate for natural cooling. An infrared thermometer is used to detect the temperature of the forging. The temperature control platform is activated to ensure that the bottom temperature of the forging is always 10°C lower than the top temperature when it drops below 350°C. During the stacking cooling process, a negative ion generator is placed around the forging, and the negative ion concentration is 1500 ions / cm³. 3 Once the temperature at the top of the forging has dropped to room temperature, turn off the temperature control platform and the negative ion generator.

[0065] Example 10: The difference between this example and Example 1 is that the method of the cryogenic treatment is as follows: the fire-cooled part after solidification is placed in a cooling water tank at a temperature of -30°C, and after being kept warm for 6 hours, it is air-cooled to room temperature; the water tank is equipped with a stirring device, and the stirring speed is 80 rpm, and stirring is carried out continuously during the cryogenic heat preservation process.

[0066] Example 11: The difference between this example and Example 1 is that the method of the cryogenic treatment is as follows: the fire-cooled part after solidification is placed in a cooling water tank at a temperature of -70°C, and after being kept warm for 8 hours, it is air-cooled to room temperature; the water tank is equipped with a stirring device, and the stirring speed is 100 rpm, and the stirring is continuous during the cryogenic heat preservation process.

[0067] Example 12: The difference between this example and Example 1 is that the pressure of the high-pressure water jet in S1 is 200 MPa.

[0068] Example 13: The difference between this example and Example 1 is that the pressure of the high-pressure water jet in S1 is 300 MPa.

[0069] Example 14: The difference between this example and Example 1 is that the heating temperature in S2 is 1115℃ and the holding time is 50min.

[0070] Example 15: The difference between this example and Example 1 is that the heating temperature in S2 is 1145℃ and the holding time is 110min.

[0071] Example 16: The difference between this example and Example 1 is that the deformation amount per forging in S3 is 40%, and the final forging temperature is 850℃.

[0072] Example 17: The difference between this example and Example 1 is that the deformation amount per forging in S3 is 60%, and the final forging temperature is 880℃.

[0073] Example 18: This example differs from Example 1 in that: the forging described in S3 is placed in a mold, held at 880°C for 8 hours, and then air-cooled to room temperature; then the temperature is raised to 650°C, held for 5 hours, and then air-cooled to room temperature; then the temperature is raised to 765°C, held for 10 hours, and then air-cooled to room temperature; finally the temperature is raised to 590°C, held for 8 hours, and then air-cooled to room temperature to obtain a fire-cooled part.

[0074] Example 19: This example differs from Example 1 in that: the forging described in S3 is placed in a mold and held at 900°C for 14 hours, then air-cooled to room temperature; then the temperature is raised to 670°C, held for 8 hours, and then air-cooled to room temperature; then the temperature is raised to 795°C, held for 14 hours, and then air-cooled to room temperature; finally the temperature is raised to 610°C, held for 10 hours, and then air-cooled to room temperature to obtain a fire-cooled part.

[0075] Example 20: This example differs from Example 1 in that: the fire-cooled part described in S4 is introduced into a heating furnace for solution treatment, held at 840°C for 1 hour, then heated to 1025°C and held for 2 hours, and then cooled to room temperature by water or oil; the fire-cooled part after solution treatment is immediately subjected to ice-cooling treatment, then held at 840°C for 1 hour, then heated to 945°C and held for 0.5 hours, and then the fire-cooled part after the second solution treatment is immediately subjected to ice-cooling treatment again to obtain the solution-treated part.

[0076] Example 21: This example differs from Example 1 in that: the fire-cooled part described in S4 is introduced into a heating furnace for solution treatment, held at 860°C for 1.5 hours, then heated to 1045°C and held for 3 hours, and then cooled to room temperature by water or oil; after 1.5 hours, the fire-cooled part after solution treatment is subjected to ice-cooling treatment, then held at 860°C for 1.5 hours, then heated to 965°C and held for 1 hour, and then the fire-cooled part after the second solution treatment is subjected to ice-cooling treatment again within 2 hours to obtain the solution-treated part.

[0077] Example 22: This example differs from Example 1 in that the solution-treated part described in S5 is introduced into a heating furnace and heated to 525°C. After holding at that temperature for 4 hours, it is air-cooled to room temperature to obtain a low-impurity forging.

[0078] Example 23: This example differs from Example 1 in that the solution-treated part described in S5 is introduced into a heating furnace and heated to 545°C. After holding at that temperature for 6 hours, it is air-cooled to room temperature to obtain a low-impurity forging.

[0079] Comparative Example 1: Referring to Example 1, the heating temperature in S2 was 1100℃ and the holding time was 40min.

[0080] Comparative Example 2: Referring to Example 1, the deformation amount per forging in S3 was 30%, and the final forging temperature was 750°C.

[0081] Comparative Example 3: Referring to Example 1, the forging described in S3 was placed in a mold and held at 950°C for 18 hours, then air-cooled to room temperature; then the temperature was raised to 680°C, held for 9 hours, and then air-cooled to room temperature; then the temperature was raised to 800°C, held for 15 hours, and then air-cooled to room temperature; finally the temperature was raised to 650°C, held for 15 hours, and then air-cooled to room temperature to obtain a fire-cooled part.

[0082] Comparative Example 4: Referring to Example 1, the fire-cooled part described in S4 was introduced into a heating furnace for solution treatment, held at 830°C for 0.5 hours, then heated to 1011°C and held for 1 hour, and then cooled to room temperature by water or oil. After 2.5 hours, the fire-cooled part after solution treatment was subjected to ice-cooling treatment, then held at 880°C for 1.8 hours, then heated to 985°C and held for 1.5 hours, and then after 2.5 hours, the fire-cooled part after the second solution treatment was subjected to ice-cooling treatment again to obtain the solution-treated part.

[0083] Comparative Example 5: Referring to Example 1, the solution-treated part described in S5 was introduced into a heating furnace and heated to 555°C. After holding at that temperature for 7 hours, it was air-cooled to room temperature to obtain a low-impurity forging.

[0084] To investigate the performance of stainless steel forgings in some embodiments and control examples, the main materials were determined according to the experimental formula and samples were prepared for testing. The stainless steel forging experimental samples were tested, and the free ferrite content in the field of view was the free ferrite content in 10 arbitrary fields of view under a 100x microscope.

[0085] The test results are shown in Tables 1 to 3 below.

[0086] 1. Investigate the influence of preheating parameters in S2 on the properties of stainless steel forgings:

[0087] Table 1. Performance test results of samples from Examples 1, 14, 15 and Control Example 1

[0088]

[0089] As shown in Table 1, a comparison of Examples 1, 14, and 15 with Control Example 1 reveals that: the grain size of Example 1 is grade 7, while the grain size of Control Example 1 is grade 5, which is lower than that of Examples 1, 14, and 15; it can be seen that the grain size is optimal under the preheating parameter range of this scheme; the brittle inclusion level of Examples 1, 14, and 15 is grade 1, while the brittle inclusion level of Control Example 1 is grade 1, indicating that the parameter range of these examples and control examples does not have a significant impact on the brittle inclusion level; the plastic inclusion level of Examples 1, 14, and 15 is grade 1, while the plastic inclusion level of Control Example 1 is grade 1.5, indicating that under the parameter conditions of Examples 1, 14, and 15, compared with Control Example 1, it is more helpful to control the plastic inclusion level at grade 1, among which the grain size prepared using the parameters of Example 1 is the finest and the inclusion distribution is the most uniform.

[0090] 2. Investigate the influence of forging process parameters in S3 on the properties of stainless steel forgings:

[0091] Table 2. Sample performance test results of Examples 4 and 5 and Control Example 2

[0092]

[0093]

[0094] As shown in Tables 1 and 2, comparing Examples 1, 4, and 5 with Comparative Example 2 reveals that: the grain size of Example 1 is grade 7, the grain size of Example 4 is grade 6, the grain size of Example 5 is grade 7, and the grain size of Comparative Example 2 is grade 5. It can be seen that the grain size of Examples 1, 4, and 5 is generally finer than that of Comparative Example 2. This indicates that in the S3 forging process, the selection of process parameters within the scope of this scheme is beneficial to grain size refinement. Compared with Examples 1 and 5, the parameters in Example 4 result in the lowest grain size.

[0095] In Examples 1, 4, and 5, the brittle and ductile inclusion levels were all Grade 1, while in Comparative Example 2, the brittle and ductile inclusion levels were Grade 1.5. This indicates that under the S3 forging process, the process parameters of Examples 1, 4, and 5 help to control the inclusion level to Grade 1. In contrast, the process parameters of Comparative Example 2 may be detrimental to inclusion optimization.

[0096] The free ferrite content in Example 1 was 0.6%, in Example 4 it was 0.7%, in Example 5 it was 0.9%, and in Control Example 2 it was 1.1%. It can be seen that in the S3 forging process, the process parameters of Examples 1, 4, and 5 can reduce the free ferrite content compared with Control Example 2. With the change of process parameters in Example 5, the free ferrite content increased to a certain extent, but it was still lower than that of Control Example 2.

[0097] 3. Investigate the influence of annealing process parameters in S4 on the properties of stainless steel forgings:

[0098] Table 3. Sample performance test results of Examples 18, 19 and Control Example 3

[0099]

[0100] As shown in Tables 1 and 3, comparing Examples 1, 18, and 19 with Comparative Example 3, it can be seen that the grain size of Example 1 is level 7, the grain size of Example 18 is level 6, the grain size of Example 19 is level 7, and the grain size of Comparative Example 3 is level 5.

[0101] It can be seen that the grain size of Examples 1, 18, and 19 is generally finer than that of Comparative Example 3. This indicates that adjusting the relevant process parameters in the S4 annealing process helps to refine the grain size. The parameters in Example 18 resulted in a lower grain size. The brittle inclusion level of Examples 1, 18, and 19 is all grade 1, while the brittle inclusion level of Comparative Example 3 is grade 1.5. This shows that under the S4 annealing process, the process parameters of Examples 1, 18, and 19 help to control the brittle and ductile inclusion levels to grade 1. In contrast, the process parameters of Comparative Example 3 may be unfavorable for the optimization of brittle and ductile inclusions.

[0102] 4. Investigate the influence of S5 solution treatment process parameters on the properties of stainless steel forgings:

[0103] Table 4. Performance test results of samples from Examples 20 and 21 and Control Examples 4 and 5.

[0104]

[0105]

[0106] As shown in Tables 1 and 4, comparing Examples 1, 20, and 21 with Control Examples 4 and 5 reveals that the grain size of Examples 20 and 21 is better than that of Control Examples 4 and 5. This indicates that the process parameters of the S5 solution treatment within the scope of this scheme can effectively refine the grains and improve the strength and toughness of the material. The brittle inclusion levels of Examples 20 and 21 are lower than those of Control Example 4, and the ductile inclusion levels of Examples 20 and 21 are lower than those of Control Examples 4 and 5. This indicates that the process parameters of the S5 solution treatment within the scope of this scheme have a certain positive impact on the inclusion distribution.

Claims

1. A process for improving the distribution of non-metallic inclusions in 13Cr15Ni4Mo3N, characterized in that, Includes the following steps: S1. Material preparation By mass percentage, 13Cr15Ni4Mo3N stainless steel material is taken, cut and polished, and then the surface is cleaned with high-pressure water jet. After drying, a blank is obtained; the pressure of the high-pressure water jet is 200~300MPa. S2, Preheating The billet described in S1 is preheated in a heating furnace at a temperature of 1115~1145℃ and held for 50~110 minutes. Then it is cooled in the furnace to obtain the fire-cooled material. S3, Free Forging The cold-pressed material described in S2 is subjected to free forging, with a deformation of not less than 40% per forging pass and a final forging temperature of not less than 850℃. After forging, it is cooled in a pile to obtain a forging billet. The method for free forging of the cold-pressed material is as follows: the cold-pressed material is subjected to ultrasonic vibration treatment, with a vibration frequency of 25~35kHz and a vibration time of 3~5min; then the ultrasonically vibrated cold-pressed material is subjected to at least one upsetting operation, with an upsetting ratio of 1.5~1.7; and then a ring heating device is used on the outer periphery of the cold-pressed material at 10~15℃. The material is heated in a ring at a speed of min, so that the temperature of the outer periphery of the cold material is 10-15°C higher than that of the center. The outer periphery thickness is 0.2-0.25 times the cross-sectional radius of the cold material. Then, the cold material with the outer periphery heated is subjected to a single drawing operation. After forging, it is stacked and cooled to obtain a forging billet. During the drawing process, a spiral drawing path is used, the pitch is 0.1-0.3 times the length of the forging, the diameter of the spiral is 0.8-1.2 times the diameter of the forging, and the feed rate during drawing is 0.02-0.05 times the diameter of the forging each time. During the stacking cooling process, the forging is placed on a platform with temperature control function for natural cooling. An infrared thermometer is used to detect the temperature of the forging. The temperature control platform is activated to ensure that the bottom temperature of the forging is always 5~10℃ lower than the top temperature. S4, Annealing The forging described in S3 is placed in a mold and held at 880~900℃ for 8~14h, then air-cooled to room temperature; then the temperature is raised to 650~670℃, held for 5~8h, and then air-cooled to room temperature; then the temperature is raised to 765~795℃, held for 10~14h, and then air-cooled to room temperature; finally the temperature is raised to 590~610℃, held for 8~10h, and then air-cooled to room temperature to obtain a fire-cooled part. S5, Solution treatment The fire-cooled part described in S4 is introduced into a heating furnace for solution treatment, held at 840~860℃ for 1~1.5h, then heated to 1025~1045℃ and held for 2~3h, and then cooled to room temperature by water or oil. The fire-cooled part after solution treatment is subjected to ice-cooling treatment within 0~2h, then held at 840~860℃ for 1~1.5h, then heated to 945~965℃ and held for 0.5~1h, and then subjected to ice-cooling treatment again within 0~2h to obtain the solution-treated part. S6, Tempering treatment The solution-treated part described in S5 is introduced into a heating furnace and heated to 525~545℃. After holding at this temperature for 4~6 hours, it is air-cooled to room temperature to obtain a low-impurity forging.

2. The process for improving the distribution of non-metallic inclusions in 13Cr15Ni4Mo3N as described in claim 1, characterized in that, In S3, when the upsetting process is not less than two times, after the first upsetting is completed, high-speed hot air is used to reheat the billet in the furnace to rapidly raise the temperature to 1115~1145℃ before continuing the next upsetting process until the upsetting is completed.

3. The process for improving the distribution of non-metallic inclusions in 13Cr15Ni4Mo3N as described in claim 2, characterized in that, The hot air temperature for high-speed hot air reheating is 1115~1255℃, and the wind speed is 8~15m / s.

4. The process for improving the distribution of non-metallic inclusions in 13Cr15Ni4Mo3N as described in claim 1, characterized in that, The method of cryogenic treatment is as follows: the fire-cooled part after solidification is placed in a cooling water tank with a temperature not higher than -70°C, and then kept warm for 6 to 8 hours before being air-cooled to room temperature; the water tank is equipped with a stirring device with a stirring speed of 80 to 100 rpm, and the stirring is continuous during the cryogenic heat preservation process.

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