Heat treatment process for improving overall quality of large-size 1Cr11MoV thick-wall pipe

Abstract

The present application relates to a kind of heat treatment processes for improving the overall quality of large specification 1Cr11MoV thick-walled pipe, which adopts temperature control cooling after forging, low-temperature spheroidizing annealing, low-temperature quenching, high-temperature tempering, high-temperature tempering and semi-fine plus high-temperature tempering process, to ensure the uniformity of thick-walled pipe quality and internal stress removal, realize the hardness deviation control within 15HB from surface to core, and ensure the core temperature drop of thick-walled pipe forging blank after forging by temperature control cooling, to avoid the precipitation of core reticular carbide and grain recovery and re-growth. The quenching heating temperature is controlled to avoid grain size growth, and the intermittent quenching cooling and different stirring speeds during cooling process are adopted to ensure the quenching effect of thick-walled pipe and avoid uneven cooling due to long length and thickness of thick-walled pipe during quenching. Two continuous high-temperature tempering is adopted to remove the thermal stress and organizational stress generated during quenching cooling. Semi-fine plus high-temperature tempering is performed again to effectively remove the processing and internal residual stress, to ensure the stability of thick-walled pipe.

Description

Technical Field

[0001] This invention belongs to the field of metal material production technology, and specifically relates to a heat treatment process that can not only solve the problem of uneven structure and hardness from the surface to the core of 1Cr11MoV thick-walled tubes, but also effectively remove thermal stress, structural stress, processing stress and internal residual stress, thereby improving the overall quality of large-size 1Cr11MoV thick-walled tubes. Background Technology

[0002] 1Cr11MoV is a martensitic heat-resistant steel with a high alloy content and a wide range of applications. Currently, it is mainly used in the manufacture of forgings for photovoltaic glass. The future development trend of both centralized and distributed photovoltaic power generation is evident, driving demand for thick-walled tubes, a key component in photovoltaic glass manufacturing. However, due to intense market competition, the photovoltaic glass manufacturing industry is currently designing thick-walled tubes with outer diameters of φ470 mm to φ510 mm, wall thicknesses of 80 mm to 140 mm, and lengths of 4500 mm to 5500 mm to increase production capacity and reduce manufacturing costs.

[0003] With the increased outer diameter and length of thick-walled tubes, larger ingots are used during manufacturing, which easily leads to problems such as uneven internal structure, poor or uneven quenching and cooling effects from the surface to the core, and incomplete stress removal. This results in a significant reduction in high-temperature fatigue resistance and a high susceptibility to cracking and deformation during high-temperature use, failing to meet application requirements. Furthermore, there is no domestic or international experience in producing large-specification thick-walled tubes with outer diameters of φ470 mm to φ510 mm, wall thicknesses of 80 mm to 140 mm, and lengths of 4500 mm to 5500 mm; this is a pioneering effort both domestically and internationally. In view of the above, there is an urgent need to innovate the process and develop a heat treatment process to improve the overall quality of large-specification 1Cr11MoV thick-walled tubes, ultimately achieving the goal of developing high-quality, large-specification thick-walled tubes, thereby improving the overall quality of thick-walled tubes and ensuring their stability in machine operation. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a heat treatment process to improve the overall quality of large-size 1Cr11MoV thick-walled tubes, thereby solving the problem of uneven structure and hardness of 1Cr11MoV thick-walled tubes from the surface to the core, and effectively removing problems such as thermal stress, structural stress, processing stress and internal residual stress, thus improving the overall quality of thick-walled tubes and ensuring the stability of their service in machinery.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A heat treatment process for improving the overall quality of large-diameter 1Cr11MoV thick-walled tubes, characterized by the following steps: Step 1) Post-forging temperature control and cooling: After forging, the thick-walled tube forging billet is placed on the material rack, and fans are placed on both sides for air cooling. After air cooling to the surface temperature of the thick-walled tube forging billet of 450℃~650℃, it is air-cooled to the surface temperature of the thick-walled tube forging billet of 350℃~550℃. After completing Step 1), the thick-walled tube forging billet is loaded into the box furnace for low-temperature spheroidizing annealing. Step 2) Low-temperature spheroidizing annealing: The tube is placed in a box-type heating furnace with a furnace temperature of 450℃~650℃, heated to 850℃~870℃ at a heating rate of ≤80℃ / h, and held for 10h~20h. After the holding is completed, the tube is cooled with the furnace at a cooling rate of ≤30℃ / h. The tube is then removed from the furnace and air-cooled to room temperature. After completing Step 2), the thick-walled tube is placed in a pit-type heating furnace and subjected to low-temperature quenching using a vertical hanging method. Step 3) Low-temperature quenching: Heat to 600℃~700℃ at a rate of ≤100℃ / h, hold for 1h~3h, then heat to 995℃~1010℃ at full power, hold for 1h~5h, and then remove from the furnace for quenching and cooling. First, pre-cool in air for 100s~250s, then place the thick-walled tube into a quenching cooling water-based liquid bath with a mass percentage concentration of 6%~11% and an initial liquid temperature of 20℃~50℃ for 3min~15min. After cooling, lift the thick-walled tube out of the quenching cooling water-based liquid bath and air-cool for 30s~100s, then... The thick-walled tube is placed back into the quenching and cooling water-based liquid tank for 3 to 15 minutes. During the quenching and cooling process of the quenching and cooling water-based liquid, the compressed air rotary stirring valve should be turned on. The valve should be opened 1 / 4 to 1 / 2 turn to stir the quenching and cooling water-based liquid with compressed air. After cooling, the thick-walled tube is lifted out of the quenching and cooling water-based liquid tank and transferred to the quenching oil tank with an initial temperature ≤60℃ for 20 to 60 minutes of cooling. After oil cooling, the temperature of the thick-walled tube is controlled at 70℃ to 180℃. After completing step 3), the thick-walled tube is placed into the pit-type heating furnace and subjected to a high-temperature tempering using a vertical hanging method. Step 4) First high-temperature tempering: The furnace temperature is controlled at ≤450℃, and the temperature is increased to 650℃~750℃ at a heating rate of ≤100℃ / h. The temperature is held for 2h~8h. Then, the thick-walled tube is taken out of the furnace and placed on a 1000t~1500t straightening machine for hot straightness testing. The straightness is controlled at ≤3mm. After hot straightness testing, the tube is air-cooled to room temperature. After completing Step 4), the thick-walled tube is put into a pit-type heating furnace and subjected to a second high-temperature tempering using a vertical hanging method. Step 5) Secondary high-temperature tempering: The furnace temperature is controlled at ≤450℃, and the temperature is increased to 600℃~700℃ at a heating rate of ≤100℃ / h. The temperature is held for 2h~8h. Then, the thick-walled tube is taken out of the furnace and placed on a 1000t~1500t straightening machine for hot straightness testing. The straightness is controlled at ≤3mm. After hot straightness testing, the tube is air-cooled to room temperature. After completing Step 5), semi-finishing is performed. After semi-finishing, the thick-walled tube is put into a box-type heating furnace for a third high-temperature tempering. Step 6) Three-stage high-temperature tempering: The furnace temperature is controlled at ≤450℃, and the temperature is increased to 500℃~600℃ at a heating rate of ≤100℃ / h. The temperature is held for 2h~15h, and then the furnace is removed and air-cooled to room temperature.

[0006] Suitable for thick-walled pipes with outer diameter Φ470mm~Φ510mm, wall thickness 80mm~140mm, and length 4500mm~5500mm.

[0007] The large-size 1Cr11MoV thick-walled tube comprises the following components by mass percentage: C=0.12%, Si=0.33%, Mn=0.40%, Cr=10.42%, Ni=0.33%, S=0.002%, P=0.012%, Mo=0.55%, V=0.34%.

[0008] Compared with existing technologies, the heat treatment process of this invention, which improves the overall quality of large-diameter 1Cr11MoV thick-walled tubes, is applicable to thick-walled tubes with an outer diameter of Φ470mm~Φ510mm, a wall thickness of 80mm~140mm, and a length of 4500mm~5500mm. This invention has the following positive effects: 1. For the first time, a composite process of temperature-controlled cooling after forging + low-temperature spheroidizing annealing + low-temperature quenching + high-temperature tempering + high-temperature tempering after semi-finishing was invented. This ensured the overall quality uniformity and internal stress removal of the large-size thick-walled tubes that were promoted for the first time in the photovoltaic glass manufacturing field. It also achieved a hardness deviation from the surface to the core within 15HB, which met the stability requirements for machine operation. 2. After forging, temperature control cooling is used to ensure that the core temperature of the thick-walled tube billet drops, thus avoiding the core from remaining at high temperature for too long, which promotes the precipitation of network carbides and the regeneration of grains. 3. This material is highly sensitive to heating temperature and is prone to rapid grain growth at high temperatures. Therefore, controlling the quenching heating temperature can effectively avoid the problem of grain growth. 4. By using a low-concentration water-soluble medium for intermittent quenching and cooling, and by adjusting different stirring speeds during the cooling process, the quenching effect of the thick-walled tube is ensured, and the uneven cooling caused by the long length and thickness of the thick-walled tube during quenching is avoided. 5. Two consecutive high-temperature tempering processes are adopted to better remove the thermal stress and structural stress generated by quenching and cooling while ensuring performance indicators; 6. The high-temperature tempering process following semi-finishing effectively removes processing stress and internal residual stress, ensuring the quality stability of the thick-walled tube. Large-size 1Cr11MoV thick-walled tubes produced according to this invention exhibit uniform overall quality, with hardness deviation from the surface to the core controlled within 15 HB, resolving the issue of uneven quality. Simultaneously, it effectively removes thermal stress, structural stress, processing stress, and internal residual stress, ensuring stability during machine operation. Detailed Implementation

[0009] Example 1: A heat treatment process for improving the overall quality of large-diameter 1Cr11MoV thick-walled tubes, comprising the following components by mass percentage: C=0.12%, Si=0.33%, Mn=0.40%, Cr=10.42%, Ni=0.33%, S=0.002%, P=0.012%, Mo=0.55%, V=0.34%; specifications: outer diameter Φ480 mm * inner diameter Ø260 mm * length 5320 mm; the heat treatment process is carried out according to the following steps: Step 1) Post-forging temperature control and cooling: After forging, place the thick-walled tube forging billet on the material rack, and place fans on both sides for air cooling. After air cooling to the surface temperature of the thick-walled tube forging billet of 450℃~550℃, air cooling is carried out until the surface temperature of the thick-walled tube forging billet of 350℃~450℃. Step 2) After the air cooling in Step 1) is completed, the thick-walled tube forging billet is loaded into a box-type heating furnace for low-temperature spheroidizing annealing: it is loaded into a box-type heating furnace with a furnace temperature of 600℃, heated to 860℃ at a heating rate of 80℃ / h and held for 11h. After the holding is completed, it is cooled with the furnace at a cooling rate of 30℃ / h until it reaches 298℃. It is then removed from the furnace and air-cooled to room temperature. Step 3) After the air cooling in Step 2) is completed, the thick-walled tube is placed into a pit-type heating furnace for low-temperature quenching: the temperature is increased to 650℃ at a rate of 100℃ / h and held for 2 hours, then increased to 1000℃ at full power and held for 1.5 hours. After holding, the tube is removed from the furnace for quenching and cooling. It is first pre-cooled in air for 230 seconds, and then placed in a quenching and cooling water-based liquid bath with a concentration of 9.5% and an initial liquid temperature of 35℃ for 7 minutes. After cooling, the thick-walled tube is lifted out of the quenching furnace. The thick-walled tube is air-cooled in a water-based quenching solution for 40 seconds. Then, it is placed back into the water-based quenching solution for 5 minutes. During the quenching process, the compressed air rotary stirring valve is turned on, and the valve is opened 1 / 4 to 1 / 2 turn to stir the water-based quenching solution with compressed air. After cooling, the thick-walled tube is lifted out of the water-based quenching solution and transferred to a quenching oil tank with an initial temperature of 40℃ for 40 minutes. After oil cooling, the temperature of the thick-walled tube is controlled at 105℃. Step 4) After the cooling in Step 3) is completed, the thick-walled tube is put into the pit-type heating furnace for a high-temperature tempering: the furnace temperature is controlled at 280℃, and the temperature is increased to 690℃ at a heating rate of 100℃ / h. The temperature is held for 3 hours, and then the tube is taken out of the furnace and placed on a 1500t straightening machine for hot straightness testing. The straightness is controlled at 2.5mm. After hot straightness testing, the tube is air-cooled to room temperature. Step 5) After the air cooling in step 4) is completed, the thick-walled tube is put into the pit-type heating furnace for secondary high-temperature tempering: the furnace temperature is controlled at 220℃, and the temperature is increased to 660℃ at a heating rate of 100℃ / h. The temperature is held for 3 hours, and then the tube is taken out of the furnace and placed on a 1500t straightening machine for hot straightness testing. The straightness is controlled at 2.5mm. After hot straightness testing, the tube is air-cooled to room temperature. Step 6) After the air cooling in step 5) is completed, perform semi-finishing. After semi-finishing, put the thick-walled tube into a box-type heating furnace for three high-temperature temperings: the furnace temperature is controlled at 95℃, and the temperature is increased to 580℃ at a rate of 100℃ / h. Hold for 8 hours, and then remove from the furnace and air cool to room temperature.

[0010] After production according to the above process, the test results are shown in Table 1: Table 1 Test Results Actual testing 223、227、230 After the heat treatment process of this invention improves the overall quality of large-diameter 1Cr11MoV thick-walled tubes, the hardness test results along the entire length meet the requirements.

[0011] Example 2: A heat treatment process for improving the overall quality of large-diameter 1Cr11MoV thick-walled tubes, Chemical composition: C=0.12%, Si=0.33%, Mn=0.40%, Cr=10.42%, Ni=0.33%, S=0.002%, P=0.012%, Mo=0.55%, V=0.34%; Specifications: Outer diameter Φ480 mm * Inner diameter Ø260 mm * Length 5320 mm; Heat treatment process is as follows: Step 1) Post-forging temperature control and cooling: After forging, place the thick-walled tube forging billet on the material rack, and place fans on both sides for air cooling. After air cooling to the surface temperature of the thick-walled tube forging billet of 450℃~550℃, air cooling is carried out until the surface temperature of the thick-walled tube forging billet of 350℃~450℃. Step 2) After the air cooling in Step 1) is completed, the thick-walled tube forging billet is loaded into a box-type heating furnace for low-temperature spheroidizing annealing: it is loaded into a box-type heating furnace with a furnace temperature of 600℃, heated to 860℃ at a heating rate of 80℃ / h and held for 11h. After the holding is completed, it is cooled with the furnace at a cooling rate of 30℃ / h until it reaches 299℃. It is then removed from the furnace and air-cooled to room temperature. Step 3) After the air cooling in Step 2) is completed, the thick-walled tube is placed into a pit-type heating furnace for low-temperature quenching: the temperature is increased to 650℃ at a rate of 100℃ / h and held for 2 hours, then increased to 1000℃ at full power and held for 1.5 hours. After holding, the tube is removed from the furnace for quenching and cooling. It is first pre-cooled in air for 231 seconds, and then placed in a quenching and cooling water-based liquid bath with a concentration of 9.5% and an initial liquid temperature of 35℃ for 7 minutes. After cooling, the thick-walled tube is lifted out of the quenching furnace. The thick-walled tube is air-cooled in a water-based quenching liquid tank for 40 seconds. Then, it is placed back into the water-based quenching liquid tank for 5 minutes. During the quenching process, the compressed air rotary stirring valve is turned on, and the valve is opened 1 / 4 to 1 / 2 turn to stir the water-based quenching liquid with compressed air. After cooling, the thick-walled tube is lifted out of the water-based quenching liquid tank and transferred to a quenching oil tank with an initial temperature of 40℃ for 40 minutes. After oil cooling, the temperature of the thick-walled tube is controlled at 95℃. Step 4) After the cooling in Step 3) is completed, the thick-walled tube is put into the pit-type heating furnace for a high-temperature tempering: the furnace temperature is controlled at 283℃, and the temperature is increased to 690℃ at a heating rate of 100℃ / h. The temperature is held for 3 hours, and then the tube is taken out of the furnace and placed on a 1500t straightening machine for hot straightness testing. The straightness is controlled at 2.5mm. After hot straightness testing, the tube is air-cooled to room temperature. Step 5) After the air cooling in step 4) is completed, the thick-walled tube is put into the pit-type heating furnace for secondary high-temperature tempering: the furnace temperature is controlled at 225℃, and the temperature is increased to 660℃ at a heating rate of 100℃ / h. The temperature is held for 3 hours, and then the tube is taken out of the furnace and placed on a 1500t straightening machine for hot straightness testing. The straightness is controlled at 2.5mm. After hot straightness testing, the tube is air-cooled to room temperature. Step 6) After the air cooling in step 5) is completed, perform semi-finishing. After semi-finishing, put the thick-walled tube into a box-type heating furnace for three high-temperature temperings: the furnace temperature is controlled at 60℃, and the temperature is increased to 580℃ at a rate of 100℃ / h. Hold for 8 hours, and then remove from the furnace and air cool to room temperature.

[0012] After production according to the above process, the test results are shown in Table 2: Table 2 Test Results Actual testing 231、228、229 After the heat treatment process of this invention improves the overall quality of large-diameter 1Cr11MoV thick-walled tubes, the hardness test results along the entire length meet the requirements.

Claims

1. A heat treatment process for improving the overall quality of large-diameter 1Cr11MoV thick-walled tubes, characterized in that: The process is implemented according to the following steps: Step 1) Post-forging temperature control and cooling: After forging, the thick-walled tube forging billet is placed on the material rack, and fans are placed on both sides for air cooling. After air cooling to the surface temperature of the thick-walled tube forging billet of 450℃~650℃, it is air-cooled to the surface temperature of the thick-walled tube forging billet of 350℃~550℃. After completing Step 1), the thick-walled tube forging billet is loaded into the box furnace for low-temperature spheroidizing annealing. Step 2) Low-temperature spheroidizing annealing: The tube is placed in a box-type heating furnace with a furnace temperature of 450℃~650℃, heated to 850℃~870℃ at a heating rate of ≤80℃ / h, and held for 10h~20h. After the holding is completed, the tube is cooled with the furnace at a cooling rate of ≤30℃ / h. The tube is then removed from the furnace and air-cooled to room temperature. After completing Step 2), the thick-walled tube is placed in a pit-type heating furnace and subjected to low-temperature quenching using a vertical hanging method. Step 3) Low-temperature quenching: Heat to 600℃~700℃ at a rate of ≤100℃ / h, hold for 1h~3h, then heat to 995℃~1010℃ at full power, hold for 1h~5h, and then remove from the furnace for quenching and cooling. First, pre-cool in air for 100s~250s, then place the thick-walled tube into a quenching cooling water-based liquid bath with a mass percentage concentration of 6%~11% and an initial liquid temperature of 20℃~50℃ for 3min~15min. After cooling, lift the thick-walled tube out of the quenching cooling water-based liquid bath and air-cool for 30s~100s, then... The thick-walled tube is placed back into the quenching and cooling water-based liquid tank for 3 to 15 minutes. During the quenching and cooling process of the quenching and cooling water-based liquid, the compressed air rotary stirring valve should be turned on. The valve should be opened 1 / 4 to 1 / 2 turn to stir the quenching and cooling water-based liquid with compressed air. After cooling, the thick-walled tube is lifted out of the quenching and cooling water-based liquid tank and transferred to the quenching oil tank with an initial temperature ≤60℃ for 20 to 60 minutes of cooling. After oil cooling, the temperature of the thick-walled tube is controlled at 70℃ to 180℃. After completing step 3), the thick-walled tube is placed into the pit-type heating furnace and subjected to a high-temperature tempering using a vertical hanging method. Step 4) First high-temperature tempering: The furnace temperature is controlled at ≤450℃, and the temperature is increased to 650℃~750℃ at a heating rate of ≤100℃ / h. The temperature is held for 2h~8h. Then, the thick-walled tube is taken out of the furnace and placed on a 1000t~1500t straightening machine for hot straightness testing. The straightness is controlled at ≤3mm. After hot straightness testing, the tube is air-cooled to room temperature. After completing Step 4), the thick-walled tube is put into a pit-type heating furnace and subjected to a second high-temperature tempering using a vertical hanging method. Step 5) Secondary high-temperature tempering: The furnace temperature is controlled at ≤450℃, and the temperature is increased to 600℃~700℃ at a heating rate of ≤100℃ / h. The temperature is held for 2h~8h. Then, the thick-walled tube is taken out of the furnace and placed on a 1000t~1500t straightening machine for hot straightness testing. The straightness is controlled at ≤3mm. After hot straightness testing, the tube is air-cooled to room temperature. After completing Step 5), semi-finishing is performed. After semi-finishing, the thick-walled tube is put into a box-type heating furnace for a third high-temperature tempering. Step 6) Three-stage high-temperature tempering: The furnace temperature is controlled at ≤450℃, and the temperature is increased to 500℃~600℃ at a heating rate of ≤100℃ / h. The temperature is held for 2h~15h, and then the furnace is removed and air-cooled to room temperature.

2. The heat treatment process for improving the overall quality of large-diameter 1Cr11MoV thick-walled tubes according to claim 1, characterized in that: Suitable for thick-walled pipes with outer diameter Φ470mm~Φ510mm, wall thickness 80mm~140mm, and length 4500mm~5500mm.

3. The heat treatment process for improving the overall quality of large-diameter 1Cr11MoV thick-walled tubes according to claim 1, characterized in that: The large-size 1Cr11MoV thick-walled tube comprises the following components by mass percentage: C=0.12%, Si=0.33%, Mn=0.40%, Cr=10.42%, Ni=0.33%, S=0.002%, P=0.012%, Mo=0.55%, V=0.34%.