Heat treatment process for large diameter 17-4PH thin-walled short ring

Abstract

This invention relates to a heat treatment process for large-diameter 17-4PH thin-walled short rings with diameters of 800mm to 1300mm, wall thicknesses of 20mm to 40mm, and lengths ≤800mm. After forging, controlled-temperature cooling promotes partial microstructural transformation and prevents grain regeneration in the thin-walled short rings. Solution annealing ensures uniform and refined microstructure and grain size in the forged billet. After solution annealing, high-temperature tempering and slow, rate-limited cooling in the furnace to a certain temperature removes structural stress, diffuses hydrogen, and softens the billet hardness, facilitating subsequent rough machining. High-temperature solution cooling employs a combination of pre-cooling, oil cooling, and air cooling to minimize thermal and structural stress, preventing cracking of the thin-walled short rings and ensuring complete microstructural transformation to obtain fine lath martensite. During solution removal from the furnace, slow hoisting prevents deformation of the large-diameter 17-4PH thin-walled short rings due to their own weight. The produced large-diameter 17-4PH thin-walled short rings exhibit uniform overall quality, are free of cracks, and have low ellipticity after heat treatment.

Description

Technical Field

[0001] This invention belongs to the field of 17-4PH material production technology, and specifically relates to a heat treatment process for large-diameter 17-4PH thin-walled short rings with a diameter between 800mm and 1300mm, a wall thickness between 20mm and 40mm, and a length ≤800mm. The large-diameter 17-4PH thin-walled short rings produced according to this invention have uniform overall quality, no cracking, and low ellipticity after heat treatment, which can ensure subsequent processing and use. Background Technology

[0002] 17-4PH material belongs to precipitation hardening martensitic stainless steel, which has good high strength and ductility, and therefore has a wide range of applications. Currently, the 17-4PH material produced in existing technologies consists of thin-walled short rings with diameters between Φ800mm and Φ1300mm, wall thicknesses between 20mm and 40mm, and lengths ≤800mm. These are delivered in a heat-treated solution-treated state. Due to the large size and short length of these products, to save manufacturing costs, they are produced as multiple-size parts in the process design, requiring larger ingots. Furthermore, because this material has a high alloy content and strong deformation resistance, it requires multiple reheating cycles and prolonged high-temperature residence times during forging, resulting in uneven microstructure or coarseness. Additionally, the thin wall thickness makes the products prone to cracking and large elliptical deformation during solution heating, lifting, and cooling due to thermal stress during heating, the weight of the rings during lifting, and microstructure transformation stress during cooling. This can render them unusable and scrapped. Conventional annealing + solution heat treatment processes are insufficient to address these issues of uneven microstructure, cracking, and deformation, failing to effectively guarantee product quality. Therefore, a heat treatment process is needed to solve these problems. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a heat treatment process for large-diameter 17-4PH thin-walled short rings. After heat treatment, not only is the overall quality control uniformity guaranteed, but the risk of cracking, deformation and scrapping of thin-walled short rings after solution treatment is also avoided.

[0004] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A heat treatment process for large-diameter 17-4PH thin-walled short rings is carried out according to the following steps: Step 1) Temperature Control and Cooling: After forging, place the thin-walled short rings in the air cooling zone. The thin-walled short rings are scattered and air-cooled until the surface temperature of the thin-walled short rings reaches 500℃~550℃. Then, the thin-walled short rings are loaded into the horizontal heating furnace to prepare for Step 2). Step 2) Solution annealing: The thin-walled short rings are placed in a horizontal heating furnace at a temperature of 500℃~550℃ for waiting. After waiting, the temperature is increased to 810℃~1040℃ at a heating rate of ≤100℃ / h and held for 1h~5h. After being removed from the furnace, the rings are air-cooled until the surface temperature of the thin-walled short rings is below 40℃ and left to stand for 1h~5h. Then, the thin-walled short rings are placed in a horizontal heating furnace to prepare for step 3). Step 3) High-temperature tempering: When loading the furnace, the horizontal heating furnace temperature is ≤400℃. The temperature is increased to 650℃~700℃ at a heating rate of ≤60℃ / h and held for 5h~15h. Then, the temperature is slowly cooled with the furnace to below 400℃ at a cooling rate of ≤30℃ / h. The furnace is then removed and air-cooled to room temperature. After air cooling, the thin-walled short ring is loaded into the horizontal heating furnace to prepare for step 4). Step 4) High-temperature solution treatment: When loading the furnace, the temperature of the pit-type heating furnace should be ≤450℃. Heat the furnace to 600℃~700℃ at a heating rate of ≤80℃ / h and hold for 0.5h~2h. After holding, heat the furnace to 800℃~900℃ at a heating rate of ≤90℃ / h and hold for 0.5h~2h. After holding, heat the furnace to 1020℃~1050℃ at full power and hold for 0.5h~3h. After holding, remove the furnace and cool for solution treatment.

[0005] The large-diameter 17-4PH thin-walled short ring is suitable for thin-walled short rings with diameters between Φ800mm and Φ1300mm, wall thicknesses between 20mm and 40mm, and lengths ≤800mm.

[0006] In step 4), after heat preservation, the ring is removed from the furnace and cooled by solution treatment. The cooling method is as follows: first, pre-cool for 100s~300s, then slowly lift it using hoisting equipment. During the lifting and transportation to the oil tank, no bumping is allowed. Then, the thin-walled short ring is placed in an oil tank with an initial temperature of 20℃~60℃ and cooled for 10min~30min. After oil cooling, the thin-walled short ring is lifted out of the oil tank and air-cooled to room temperature.

[0007] Compared with the prior art, the process of this invention has the following advantages: The present invention provides a heat treatment process for large-diameter 17-4PH thin-walled short rings, applicable to thin-walled short rings with diameters of Φ800mm~Φ1300mm, wall thicknesses of 20mm~40mm, and lengths ≤800mm. Its advantages are as follows: 1. After forging, temperature-controlled cooling should be performed first to promote partial microstructure transformation and avoid grain growth in thin-walled short rings due to high final temperature after forging and long residence time at high temperature. 2. After temperature-controlled cooling, solution annealing is performed to ensure uniform and refined microstructure and grain size of the forging billet; 3. To avoid cracking due to excessive structural stress, high-temperature tempering is performed after solution annealing, followed by furnace cooling to a certain temperature using a limited-rate slow cooling method. This effectively removes structural stress, diffuses hydrogen, and softens the hardness of the billet, facilitating subsequent rough machining. 4. During high-temperature solution cooling, a pre-cooling + oil cooling + air cooling method is adopted to ensure that the thermal stress and structural stress are minimized during the solution cooling process to avoid cracking of thin-walled short rings, while ensuring complete structural transformation and obtaining fine lath martensite structure. 5. When the solution is removed from the furnace, it should be slowly lifted by equipment to avoid large-diameter 17-4PH thin-walled short rings deforming due to their own weight, resulting in large ovality and making them unprocessable and scrapped.

[0008] The large-diameter 17-4PH thin-walled short rings produced according to this invention have uniform overall quality, no cracking, and low ellipticity, ensuring their processing and use. Detailed Implementation

[0009] Example 1: A heat treatment process for a large-diameter 17-4PH thin-walled short ring, steel grade: 17-4PH, specifications: outer diameter φ1255mm * inner diameter φ1180mm * length 770mm; the heat treatment process is as follows: Step 1) Temperature control and cooling: After forging, place the thin-walled short rings in the air cooling zone. The thin-walled short rings are scattered and air-cooled until the surface temperature of the thin-walled short rings reaches 520℃~540℃. Step 2) After the air cooling in Step 1) is completed, the thin-walled short ring is placed in a horizontal heating furnace at a furnace temperature of 530℃ for waiting. After waiting, solution annealing is performed: the thin-walled short ring is placed in a horizontal heating furnace at a furnace temperature of 530℃ for waiting. After waiting, the temperature is increased to 1020℃ at a heating rate of 100℃ / h and held for 1.5h. It is then removed from the furnace and air-cooled until the surface temperature of the thin-walled short ring is 38℃ and left to stand for 3.5h. Step 3) After the air cooling in step 2) is completed, the thin-walled short ring is loaded into the horizontal heating furnace for high-temperature tempering: the furnace temperature of the horizontal heating furnace is 100℃ when loading into the furnace, and the temperature is increased to 680℃ at a heating rate of 60℃ / h and held for 8 hours. Then, the temperature is slowly cooled to 398℃ with the furnace at a cooling rate of 30℃ / h before being removed from the furnace and air-cooled to room temperature. Step 4) After the air cooling in Step 3) is completed, the thin-walled short ring is loaded into a horizontal heating furnace for high-temperature solution treatment: the furnace temperature of the pit heating furnace is 150℃ when loading into the furnace, and the temperature is increased to 650℃ at a heating rate of 80℃ / h and held for 1 hour. After holding, the temperature is increased to 820℃ at a heating rate of 90℃ / h and held for 1 hour. After holding, the temperature is increased to 1040℃ at full power and held for 1 hour. After holding, the ring is removed from the furnace for solution cooling. The cooling method is as follows: first, pre-cool for 200 seconds, and then slowly lift the ring using equipment. During the lifting process, no bumps or knocks are allowed. The thin-walled short ring is placed in an oil tank with an initial temperature of 35℃ and cooled for 20 minutes. After oil cooling, the thin-walled short ring is lifted out of the oil tank and air-cooled to room temperature.

[0010] After production using the above heat treatment process, the thin-walled short rings did not crack or deform, and their hardness met the technical requirements. The test results are shown in Table 1. Table 1 Test Results Technical Requirements Surface hardness ≤38HRC Surface quality: Cracking is not allowed. Actual testing 32、33、32 The surface quality is acceptable, and no cracks have occurred. After production using the large-diameter 17-4PH thin-walled short ring heat treatment process of this invention, the hardness test results meet the requirements.

[0011] Example 2: A heat treatment process for a large-diameter 17-4PH thin-walled short ring, steel grade: 17-4PH, specifications: outer diameter φ1255mm * inner diameter φ1180mm * length 770mm; the heat treatment process is as follows: Step 1) Temperature control and cooling: After forging, place the thin-walled short rings in the air cooling zone. The thin-walled short rings are scattered and air-cooled until the surface temperature of the thin-walled short rings reaches 520℃~540℃. Step 2) After the air cooling in Step 1) is completed, the thin-walled short ring is placed in a horizontal heating furnace at a furnace temperature of 530℃ for waiting. After waiting, solution annealing is performed: the thin-walled short ring is placed in a horizontal heating furnace at a furnace temperature of 530℃ for waiting. After waiting, the temperature is increased to 1020℃ at a heating rate of 100℃ / h and held for 1.5h. It is then removed from the furnace and air-cooled until the surface temperature of the thin-walled short ring is 37℃ and left to stand for 3.5h. Step 3) After the air cooling in step 2) is completed, the thin-walled short ring is loaded into the horizontal heating furnace for high-temperature tempering: the furnace temperature of the horizontal heating furnace is 100℃ when loading into the furnace, and the temperature is increased to 680℃ at a heating rate of 60℃ / h and held for 8 hours. Then, the temperature is slowly cooled to 399℃ with the furnace at a cooling rate of 30℃ / h before being removed from the furnace and air-cooled to room temperature. Step 4) After the air cooling in Step 3) is completed, the thin-walled short ring is loaded into a horizontal heating furnace for high-temperature solution treatment: the furnace temperature of the pit heating furnace is 140℃ when loading into the furnace, and the temperature is increased to 650℃ at a heating rate of 80℃ / h and held for 1 hour. After holding, the temperature is increased to 820℃ at a heating rate of 90℃ / h and held for 1 hour. After holding, the temperature is increased to 1040℃ at full power and held for 1 hour. After holding, the ring is removed from the furnace for solution cooling. The cooling method is as follows: first, pre-cool for 210 seconds, and then slowly lift it using equipment. During the lifting and transportation to the oil tank, no bumping is allowed. The thin-walled short ring is placed in the oil tank with an initial temperature of 37℃ and cooled for 20 minutes. After oil cooling, the thin-walled short ring is lifted out of the oil tank and air-cooled to room temperature.

[0012] After production using the above heat treatment process, the thin-walled short rings did not crack or deform, and their hardness met the technical requirements. The test results are shown in Table 2. Table 2 Test Results Technical Requirements Surface hardness ≤38HRC Surface quality: Cracking is not allowed. Actual testing 31、33、32.5 The surface quality is acceptable, and no cracks have occurred. After production using the heat treatment process of a large-diameter 17-4PH thin-walled short ring according to the present invention, the hardness test results meet the requirements.

Claims

1. A heat treatment process for large-diameter 17-4PH thin-walled short rings, characterized in that: The process is carried out according to the following steps: Step 1) Temperature Control and Cooling: After forging, place the thin-walled short rings in the air cooling zone. The thin-walled short rings are scattered and air-cooled until the surface temperature of the thin-walled short rings reaches 500℃~550℃. Then, the thin-walled short rings are loaded into the horizontal heating furnace to prepare for Step 2). Step 2) Solution annealing: The thin-walled short rings are placed in a horizontal heating furnace at a temperature of 500℃~550℃ for waiting. After waiting, the temperature is increased to 810℃~1040℃ at a heating rate of ≤100℃ / h and held for 1h~5h. After being removed from the furnace, the rings are air-cooled until the surface temperature of the thin-walled short rings is below 40℃ and left to stand for 1h~5h. Then, the thin-walled short rings are placed in a horizontal heating furnace to prepare for step 3). Step 3) High-temperature tempering: When loading the furnace, the horizontal heating furnace temperature is ≤400℃. The temperature is increased to 650℃~700℃ at a heating rate of ≤60℃ / h and held for 5h~15h. Then, the temperature is slowly cooled with the furnace to below 400℃ at a cooling rate of ≤30℃ / h. The furnace is then removed and air-cooled to room temperature. After air cooling, the thin-walled short ring is loaded into the horizontal heating furnace to prepare for step 4). Step 4) High-temperature solution treatment: When loading the furnace, the temperature of the pit-type heating furnace should be ≤450℃. Heat the furnace to 600℃~700℃ at a heating rate of ≤80℃ / h and hold for 0.5h~2h. After holding, heat the furnace to 800℃~900℃ at a heating rate of ≤90℃ / h and hold for 0.5h~2h. After holding, heat the furnace to 1020℃~1050℃ at full power and hold for 0.5h~3h. After holding, remove the furnace for solution treatment and cooling. The cooling method is as follows: first, pre-cool for 100s~300s, then slowly lift the ring using equipment. During the lifting process, no bumps or collisions are allowed. Place the thin-walled short ring in an oil tank with an initial temperature of 20℃~60℃ and cool for 10min~30min. After oil cooling, lift the thin-walled short ring out of the oil tank and air cool it to room temperature.

2. The heat treatment process for a large-diameter 17-4PH thin-walled short ring according to claim 1, characterized in that: The large-diameter 17-4PH thin-walled short ring is suitable for thin-walled short rings with diameters between Φ800mm and Φ1300mm, wall thicknesses between 20mm and 40mm, and lengths ≤800mm.

3. The heat treatment process for a large-diameter 17-4PH thin-walled short ring according to claim 1, characterized in that: In step 4), after heat preservation, the ring is removed from the furnace and cooled by solution treatment. The cooling method is as follows: first, pre-cool for 100s~300s, then slowly lift it using hoisting equipment. During the lifting and transportation to the oil tank, no bumping is allowed. Place the thin-walled short ring in the oil tank with an initial temperature of 20℃~60℃ and cool for 10min~30min. After oil cooling, lift the thin-walled short ring out of the oil tank and air cool it to room temperature.