A spheroidizing annealing process special for an ultra-long partition gas-lock spheroidizing annealing furnace

Abstract

The application belongs to the technical field of heat treatment, and particularly relates to a spheroidizing annealing process special for an ultra-long partition air-lock spheroidizing annealing furnace. The spheroidizing annealing process special for the ultra-long partition air-lock spheroidizing annealing furnace is characterized in that, in order to meet the spheroidizing annealing process under various conditions, different temperatures and different main transmission frequencies can be set in 11 independent temperature control zones, in order to reduce the oxidation phenomenon on the surface of the bearing steel pipe in the spheroidizing annealing process, the spheroidizing furnace is filled with nitrogen 4 hours before work, and meanwhile, the air pressure in the furnace is slightly higher than that outside, the material is first put into the air-lock chamber during the feeding and discharging process, the inside of the furnace body is not directly contacted with the outside air during the feeding and discharging process, the air tightness of the furnace body is ensured, meanwhile, multiple batches of materials can be simultaneously subjected to the spheroidizing annealing treatment, and the production efficiency is relatively high.

Description

Technical Field

[0001] This invention belongs to the field of heat treatment technology, specifically relating to a spheroidizing annealing process for an ultra-long partitioned air-lock spheroidizing annealing furnace. Background Technology

[0002] Currently, common spheroidizing annealing processes for bearing steel tubes suffer from limitations. Spheroidizing furnaces are typically short with limited temperature zones, resulting in a narrow range of annealing options and insufficient process flexibility. Furthermore, common spheroidizing annealing processes often exhibit poor internal temperature uniformity, leading to uneven microstructure and properties in the bearing steel tubes. Additionally, the long spheroidizing annealing time and poor airtightness under conventional processes result in severe surface oxidation and decarburization of the bearing steel tubes. Therefore, based on an ultra-long, partitioned, air-locked spheroidizing annealing furnace (107m in length), a dedicated spheroidizing annealing process for this furnace is proposed. Summary of the Invention

[0003] To address the aforementioned issues, this invention provides a spheroidizing annealing process specifically designed for an ultra-long partitioned airlock spheroidizing annealing furnace. This process offers controllable holding temperature and time, high operability and flexibility, excellent airtightness, and higher production efficiency.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: the furnace door in step two includes two feeding furnace doors and two discharging furnace doors. The feeding and discharging furnace doors are composed of a furnace frame, furnace door, chain, lifting shaft, pressing shaft, etc. When opening and closing the furnace door, pneumatic lifting and pressing of the furnace door are used to ensure the airtightness of the furnace body.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: in step three, the main drive frequency set during spheroidizing annealing is 21Hz to 28Hz according to the different specifications of the bearing steel pipe, which can ensure different holding times and heating / cooling rates during the spheroidizing annealing process of steel pipes of different specifications.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: Step three is divided into 11 independently temperature-controlled furnace zones. Each zone has a different temperature during the spheroidizing annealing process, which can ensure different holding temperatures during the spheroidizing annealing of steel pipes of different specifications. The heating zone 1 is 9.688m long, the heating zone 2 is 8.304m long, the holding zone 3 is 6.228m long, the holding zone 4 is 6.228m long, the holding zone 5 is 6.228m long, the rapid cooling zone 6 is 8.304m long, the isothermal zone 7 is 8.304m long, the isothermal zone 8 is 8.304m long, the isothermal zone 9 is 8.304m long, the slow cooling zone 10 is 8.304m long, and the slow cooling zone 11 is 8.304m long.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: according to the different requirements of spheroidizing annealing processes, during the spheroidizing annealing treatment in step three, the temperature of heating zone 1 is 740℃~760℃, the temperature of heating zone 2 to holding zone 5 is 790℃~810℃, the temperature of rapid cooling zone 6 is 740℃~760℃, the temperature of isothermal zone 7 is 720℃~740℃, the temperature of isothermal zones 8 and 9 is 710℃~730℃, the temperature of slow cooling zone 10 is 700℃~720℃, and the temperature of slow cooling zone 11 is 680℃~700℃.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: the heating method in step four is natural gas radiation heating, which is low in cost and can ensure that the internal temperature of the spheroidizing furnace is uniform during the operation of the spheroidizing furnace, thus ensuring that the bearing steel pipe has high uniformity in structure and properties after spheroidization.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: in step five, nitrogen is introduced 4 hours before the spheroidizing furnace is put into operation, the oxygen display value is not higher than 25% VOL, and the gas pressure inside the furnace is slightly higher than outside the furnace, so that the material hardly comes into contact with air during the entire spheroidizing annealing process, thereby reducing the oxidation and decarburization phenomenon on the inner and outer surfaces of the bearing steel tube.

[0010] To achieve the above objectives, the present invention adopts the following technical solution. The specific feeding process in step six is ​​as follows: the material is dried before being loaded into the furnace. When loading, ensure that the same specifications are in the same frame. The material is strictly parallel to the axis of the spheroidizing furnace. The material is neatly arranged on the side closest to the furnace, with a length not exceeding 50mm. The first layer must be filled. The second to fifth layers are reduced by one piece each time. Double iron wires are used to bind the material 1m away from the head and tail.

[0011] To achieve the above objectives, the present invention adopts the following technical solution. The specific feeding process in step six is ​​as follows: 1# feeding furnace door opens → (fast forward) transmission starts → material enters the airlock chamber → 1# feeding furnace door closes → (fast forward) transmission stops → 2# feeding furnace door opens → material moves forward → 2# feeding furnace door closes. Throughout the process, the furnace is not in contact with the outside air, ensuring the airtightness of the furnace body.

[0012] To achieve the above objectives, the present invention adopts the following technical solution. The specific process of material discharge in step seven is as follows: 1# discharge furnace door opens → (fast forward) transmission starts → material enters the airlock chamber → 1# discharge furnace door closes → (fast forward) transmission stops → 2# discharge furnace door opens → material advances → 2# discharge furnace door closes. Throughout the entire process, the furnace interior does not come into contact with outside air, ensuring the airtightness of the furnace body. The material after spheroidizing annealing is pushed off the discharge platform before the next batch of material is discharged. Attached Figure Description

[0013] Figure 1 This is the microstructure of the steel pipe in Example 1.

[0014] Figure 2This is the microstructure of the steel pipe in Example 2. Implementation Example

[0015] Step 1: Check the gas pressure, switch the furnace to manual mode, and turn on the main power switch and all other switches.

[0016] Step 2: Manually close all four furnace doors.

[0017] Step 3: Using GCr15 bearing steel pipes with dimensions of 72mm × 5.5mm, set the main drive frequency to 27Hz and the pipe forward speed to 7449mm / h. Turn on the main drive and check if the main chain is rotating. Set the temperatures of each furnace zone according to the process requirements: Zone 1 heating temperature is 760℃, Zones 2 to 5 holding temperature is 800℃, Zone 6 rapid cooling temperature is 750℃, Zone 7 isothermal temperature is 735℃, Zones 8 and 9 isothermal temperature is 730℃, Zone 10 slow cooling temperature is 715℃, and Zone 11 slow cooling temperature is 690℃.

[0018] Step 4: Open the natural gas valve and check that the pressure is above 7 kPa. If it is correct, ignite the gas.

[0019] Step 5: Fill the spheroidizing furnace with nitrogen using a nitrogen generator, adjusting the flow rate to approximately 135 m³ / h. The oxygen reading should not exceed 25% VOL. Open the main nitrogen inlet valve of the furnace. The flow meter for each nitrogen protection device should be set to 20 m³ / h. 3 / h or more.

[0020] Step 6: After bundling the materials, place them on the feeding platform, switch the furnace to automatic mode, press the feeding button, and start feeding.

[0021] Step 7: After the material is spheroidized and annealed, it is taken out of the furnace and placed on the discharge platform for a period of time before being pushed off the discharge platform. Example

[0022] Step 1: Check the gas pressure, switch the furnace to manual mode, and turn on the main power switch and all other switches.

[0023] Step 2: Manually close all four furnace doors.

[0024] Step 3: Using GCr15 bearing steel pipes with dimensions of 102mm × 8.8mm, set the main drive frequency to 26Hz and the pipe forward speed to 7725mm / h. Turn on the main drive and check if the main chain is rotating. Set the temperatures of each furnace zone according to the process requirements: Zone 1 heating temperature is 770℃, Zones 2 to 5 holding temperature is 810℃, Zone 6 rapid cooling temperature is 750℃, Zone 7 isothermal temperature is 740℃, Zones 8 and 9 isothermal temperature is 730℃, Zone 10 slow cooling temperature is 715℃, and Zone 11 slow cooling temperature is 690℃.

[0025] Step 4: Open the natural gas valve and check that the pressure is above 7 kPa. If it is correct, ignite the gas.

[0026] Step 5: Fill the spheroidizing furnace with nitrogen using a nitrogen generator, adjusting the flow rate to approximately 135 m³ / h. The oxygen reading should not exceed 25% VOL. Open the main nitrogen inlet valve of the furnace. The flow meter for each nitrogen protection device should be set to 20 m³ / h. 3 / h or more.

[0027] Step 6: After bundling the materials, place them on the feeding platform, switch the furnace to automatic mode, press the feeding button, and start feeding.

[0028] Step 7: After the material is spheroidized and annealed, it is taken out of the furnace and placed on the discharge platform for a period of time before being pushed off the discharge platform.

[0029] Samples were taken from the spheroidized GCr15 bearing steel tubes, and the microstructure and decarburization layer depth of the samples were observed and measured using an optical microscope. The spheroidized microstructure was rated by comparing it with the standard diagram. The hardness of the spheroidized GCr15 bearing steel tubes was measured using a Brinell hardness tester. The results are shown in Table 1.

[0030] Table 1 Test Results of the Example

[0031] Spheroidization grade Average hardness Hardness difference Example 1 Grade 3 HB 18 7.26 HB 8 Example 2 Grade 3 HB 18 2.33 HB 6

Claims

1. A spheroidizing annealing process specifically for an ultra-long zoned air-lock spheroidizing annealing furnace, comprising the following steps: Step 1: Check the gas pressure, switch the furnace to manual mode, and turn on the main power switch and all other switches, large and small. Step 2: Manually close all four furnace doors; Step 3: Set the main drive frequency, turn on the main drive, check if the main chain is rotating, and set the temperature, alarm value, and cooling value for each furnace zone according to the process requirements. Based on the different specifications of the bearing steel pipes, the main drive frequency set during spheroidizing annealing is 25Hz~28Hz: For steel pipes with a wall thickness of 9.1mm or more, the frequency is set to 25Hz, and the pipe forward speed is 6898mm / h; for steel pipes with a wall thickness between 8.1mm and 9.0mm, the frequency is set to 26Hz, and the pipe forward speed is 7173mm / h; for steel pipes with a wall thickness between 4.6mm and 8.0mm, the frequency is set to 27Hz, and the pipe forward speed is 7449mm / h; for steel pipes with a wall thickness of 4.0mm... The frequency for spheroidizing annealing of steel pipes with a diameter between 4.5mm and 5.5mm was set to 28Hz, and the pipe's forward running speed was 7725mm / h. The furnace body was divided into 11 independently temperature-controlled zones, each with a different temperature during the spheroidizing annealing process. The lengths of the zones are as follows: Heating Zone 1: 9.688m; Heating Zone 2: 8.304m; Holding Zone 3: 6.228m; Holding Zone 4: 6.228m; Holding Zone 5: 6.228m; Rapid Cooling Zone 6: 8.304m; Isothermal Zone 7: 8.304m; Isothermal Zone 8: 8.304m; Isothermal Zone 9: 8.304m; Slow Cooling Zone 10: 8.304m; Slow Cooling Zone 11: 8.304m. During spheroidizing annealing, the temperature in Heating Zone 1 was 740℃~760℃, and the temperature in Heating Zone 2 to Holding Zone 5 was... The temperature ranges from 790℃ to 810℃ in Zone 6, from 740℃ to 760℃ in Zone 6, from 720℃ to 740℃ in Zone 7, from 710℃ to 730℃ in Zones 8 and 9, from 700℃ to 720℃ in Zone 10, and from 680℃ to 700℃ in Zone 11. Step 4: Open the natural gas valve, check the pressure, and ignite the gas if it is correct. Step 5: Fill the spheroidizing furnace with nitrogen using a nitrogen generator; Step 6: After bundling the materials, place them on the feeding platform, switch the furnace to automatic mode, press the feeding button, and start feeding. Step 7: After the material is spheroidized and annealed, it is taken out of the furnace and placed on the discharge platform for a period of time before being pushed off the discharge platform.

2. The spheroidizing annealing process according to claim 1, characterized in that: The furnace doors in step two include two feed furnace doors and two discharge furnace doors. The feed and discharge furnace doors are composed of a furnace frame, furnace door, chain, lifting shaft, and pressing shaft. When opening and closing the furnace doors, pneumatics is used to pull up and press the furnace doors to ensure the airtightness of the furnace body.

3. The spheroidizing annealing process according to claim 1, characterized in that: In step four, the heating method is radiant heating with natural gas heating pipes, which can ensure that the internal temperature of the spheroidizing furnace is uniform during operation.

4. The spheroidizing annealing process according to claim 1, characterized in that: In step five, nitrogen is introduced 4 hours before the spheroidizing furnace is put into operation. The oxygen display value is not higher than 25% VOL, and the gas pressure inside the furnace is slightly higher than outside the furnace. This ensures that the material is almost not in contact with air during the entire spheroidizing annealing process, thereby reducing the oxidation and decarburization of the inner and outer surfaces of the bearing steel tube.

5. The spheroidizing annealing process according to claim 1, characterized in that: In step six, the materials are dried before being loaded into the furnace. When loading, ensure that the materials are of the same specification and in the same frame. The materials are strictly parallel to the axis of the spheroidizing furnace and are arranged neatly on the side closest to the furnace. The length should not exceed 50mm. The first layer must be full. The second to fifth layers should each reduce one piece. Use double iron wires to bind the materials 1m from the beginning and end.

6. The spheroidizing annealing process according to claim 1, characterized in that: The specific feeding process in step six is ​​as follows: 1# feed furnace door opens → transmission starts → material enters the airlock chamber → 1# feed furnace door closes → transmission stops → 2# feed furnace door opens → material moves forward → 2# feed furnace door closes. Throughout the entire process, the furnace is not in contact with the outside air, ensuring the airtightness of the furnace body.

7. The spheroidizing annealing process according to claim 1, characterized in that: The specific process of material discharge in step seven is as follows: 1# discharge furnace door opens → transmission starts → material enters the airlock chamber → 1# discharge furnace door closes → transmission stops → 2# discharge furnace door opens → material moves forward → 2# discharge furnace door closes. Throughout the process, the furnace is not in contact with the outside air to ensure the airtightness of the furnace body. The material after spheroidizing annealing is pushed off the discharge platform before the next batch of material is discharged.

8. The spheroidizing annealing process according to claim 1, characterized in that: The spheroidizing grade of GCr15 bearing steel pipe after spheroidizing annealing is 2 to 4, and the hardness is HB162 to 192. The hardness difference of steel pipes in the same batch is not higher than HB15, and the hardness difference of the same steel pipe is not higher than HB10.

9. The spheroidizing annealing process according to claim 1, characterized in that: Multiple batches of materials were subjected to spheroidizing annealing treatment simultaneously.

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