A vacuum heat treatment method for tubing encapsulated in 304 stainless steel tubing

Abstract

This invention belongs to the field of metal processing technology and aims to provide a low-cost vacuum heat treatment method specifically for pipe processing, solving the problems of high initial investment and high maintenance costs of general-purpose pipe vacuum heat treatment equipment. The method described in this invention involves vacuum-sealing the pipe to be treated in a device made of 304 stainless steel tubing, and then heat-treating the entire encapsulation device under normal pressure to achieve vacuum heat treatment of the pipe product. This method is characterized by low cost and ease of quality assurance. This invention can be used in processes such as vacuum furnace cooling, vacuum air cooling, and vacuum oil (water) quenching, and is particularly suitable for vacuum oil (water) quenching, effectively ensuring the transfer time from high temperature to room temperature.

Description

Technical Field

[0001] This invention belongs to the field of metal processing technology, and specifically provides a low-cost vacuum heat treatment method for pipes, suitable for pipes with an outer diameter range of ≤φ80mm. Background Technology

[0002] Pipes are a major industrial product, typically manufactured through multi-pass rolling (or drawing) deformation processing. For pipes in production, multiple intermediate annealing heat treatments are required during rolling to restore the material's plasticity; for finished pipes, a finishing heat treatment is required to achieve the required performance.

[0003] In the production of high-quality titanium alloy, copper alloy, stainless steel, and high-temperature alloy pipes, high-vacuum heat treatment is required to prevent surface oxidation, whether during intermediate annealing or finished product heat treatment. Vacuum heat treatment equipment for pipes is typically long and slender with a large furnace volume, requiring multiple vacuum systems. Furthermore, the loading and unloading of the pipes necessitates a complex motion device, thus the price of vacuum heat treatment furnaces for pipes is generally high. Especially for pipes requiring vacuum water quenching or vacuum oil quenching, the heat treatment equipment needs two vacuum chambers, in which the pipes must be transferred between hot and vacuum states, further increasing the complexity of the equipment and resulting in a substantial investment. Summary of the Invention

[0004] This invention encapsulates the pipe to be treated in a vacuum chamber made of 304 stainless steel pipe, and completes vacuum heat treatment in an atmospheric pressure furnace. It does not require complicated furnace loading and unloading and transfer devices, making it a low-cost vacuum heat treatment method. It is particularly suitable for the research and development and small-batch production stages of pipe materials, and can ensure product quality while maintaining low cost.

[0005] The technical solution of this invention is as follows: 1) Use a stainless steel tube (hereinafter referred to as tube 1) with a suitable length and inner diameter (meaning that a certain number of tubes to be processed can be placed inside it, i.e., a certain number of tubes to be processed can be completely placed inside it) and closed at one end as a vacuum chamber, and put the tubes to be processed into tube 1. 2) Use a stainless steel pipe with a smaller inner diameter than pipe 1 (hereinafter referred to as pipe 2) as a vacuum pipe. One end of pipe 2 is sealed to a vacuum quick-connect flange pipe, and the other end is sealed to the other open end of pipe 1. 3) Vacuum sealing: A. First, connect the vacuum quick-connect flange connected to one end of pipe 2 to the vacuum leak detection unit in a sealed manner. Detect leaks in the entire device of pipes 1 and 2 connected together to ensure that there are no leaks in pipes 1, 2 and all connections between them. Then, connect the vacuum quick-connect flange connected to one end of pipe 2 to the vacuum pumping unit in a sealed manner. Vacuum pipe 1 is evacuated, and at the same time, pipe 1 is heated to 350℃~450℃. B. When the vacuum degree reaches ≤1×10 -3 Pa, and after holding the heating temperature for ≥15 minutes, maintain the vacuum inside the device of tube 1 and tube 2 connected together, flatten and cut off the middle part of tube 2, and weld the cut surface near tube 1 with argon arc welding, thereby sealing the tube to be processed in the vacuum cavity formed by tube 1 and tube 2 to form a vacuum device. 4) Then heat-treat the entire vacuum device; after the heat treatment is completed, cut off tube 1 at the end where it connects to tube 2 and remove the treated tube.

[0006] This invention provides a low-cost vacuum heat treatment method specifically for pipe processing, solving the problems of high initial investment and high maintenance costs of general-purpose pipe vacuum heat treatment equipment. The method involves vacuum-sealing the pipe to be treated within a device made of 304 stainless steel tubing, and then heat-treating the entire encapsulation device under normal pressure to achieve vacuum heat treatment of the pipe product. This method is characterized by low cost and ease of quality assurance. This invention can be used in processes such as vacuum furnace cooling, vacuum air cooling, and vacuum oil (water) quenching, and is particularly suitable for vacuum oil (water) quenching, effectively ensuring the transfer time from high temperature to room temperature. Attached Figure Description

[0007] Figure 1 This is a schematic diagram of a 304 stainless steel pipe with one end closed.

[0008] Figure 2 A schematic diagram showing the pipe to be processed being placed inside a 304 stainless steel pipe.

[0009] Figure 3 This is a schematic diagram showing the connection between a vacuum-sealed 304 stainless steel pipe and a quick-connect flange.

[0010] Figure 4 This is a schematic diagram showing the connection between pipe 1 and pipe 2 via a reducing diameter.

[0011] Figure 5 This is a schematic diagram showing the flattening of two parts of tube 2.

[0012] Figure 6 This is a schematic diagram of flattening the middle part of tube 2.

[0013] Figure 7 A schematic diagram showing the cutting and welding of the cut end at the flattened part of pipe 2.

[0014] Figure 8 This is a B30 cupronickel tube that has undergone vacuum water quenching heat treatment using this method.

[0015] Figure 9 This is a schematic diagram of the present invention. Detailed Implementation Example

[0017] 1) 26 B30 white copper tubes with an outer diameter of φ22mm, a wall thickness of 3mm, and a length of 3m require vacuum water quenching treatment.

[0018] 2) The sealing tube is a 304 stainless steel tube (tube 1) with an outer diameter of φ108mm, a wall thickness of 2mm, and a length of 4m. A 3mm thick 304 stainless steel plate is welded to one end of tube 1 for sealing. See [link to documentation]. Figure 1 Place half of the pipes to be processed (13 pieces) into pipe 1, which is closed at one end. See below. Figure 2 .

[0019] The vacuum tube is a 304 stainless steel tube (tube 2) with an outer diameter of φ40mm, a wall thickness of 2mm, and a length of 300mm; one end of it is welded to a KF40 vacuum quick-connect flange tube made of 304 stainless steel. (See attached image.) Figure 3 .

[0020] 3) According to the method of the present invention, Figure 2 The unclosed end of tube 1 shown is... Figure 3 The other end of pipe 2 shown, which is not connected to a flange, is welded together via a reducer with a wall thickness of 2mm. See [reference needed]. Figure 4 .

[0021] Will Figure 4 The flange of the device shown is connected to a leak detection unit (model ZQJ-530 helium mass spectrometer leak detector manufactured by Beijing Zhongke Instrument Technology Development Co., Ltd.). Vacuum leak testing is performed on all welds of the device. If a leak is found, it is cut open and re-welded. After ensuring that all parts of the device are leak-free, the flange is then connected to a vacuum pumping unit (model ZJ-700F high-vacuum molecular pump vacuum pumping unit manufactured by Shenyang Guoshun Vacuum Equipment Co., Ltd.). The ultimate vacuum of the vacuum pumping unit should be able to reach 5 × 10⁻⁶. -4 Pa, while heating tube 1 to 400℃ and keeping it warm with a heating jacket.

[0022] When the vacuum degree of tube 1 reaches ≤1×10 -3 After maintaining the temperature at 400℃ for ≥15 minutes, continue evacuation and turn off heating. First, use two cylinders with a diameter of φ57mm to flatten tube 2 at two points 70mm apart in the middle of tube 2 with a pressure of 80 tons. See [link to relevant documentation]. Figure 5 .

[0023] Then, use two 70mm wide flat plates and apply 80 tons of pressure to flatten the middle of pipe 2. See [link / reference]. Figure 6 .

[0024] Finally, using two φ57mm cylinders, apply 80 tons of pressure to continuously press down on the flattened end of tube 2 near tube 1. Then, shut off the vacuum unit, cut the flattened section of tube 2 in the middle, and weld the cut end with argon arc welding. (See below) Figure 7 .

[0025] Two opposing φ57mm cylinders are separated to achieve vacuum sealing of the pipe to be processed in pipe 1.

[0026] 4) Then, place the vacuum device in an atmospheric pressure bar furnace and heat it to 800°C. After holding it at that temperature for 90 minutes, remove the vacuum device and place it in a water tank for water quenching to complete the vacuum water quenching heat treatment process.

[0027] 5) After heat treatment, cut off the end of pipe 1 that connects to pipe 2, and remove the treated pipe. See below. Figure 2 .

[0028] 6) The treated pipe is bright silver, and the subsequent rolling deformation proceeds smoothly, achieving the effect of vacuum water quenching heat treatment. See [link / reference]. Figure 8 .

Claims

1. A vacuum heat treatment method for tubular materials encapsulated with 304 stainless steel tubing, characterized in that: 1) Use a stainless steel tube (hereinafter referred to as tube 1) with a suitable length and inner diameter (meaning that a certain number of tubes to be processed can be placed inside it, i.e., a certain number of tubes to be processed can be completely placed inside it) and closed at one end as a vacuum chamber, and put the tubes to be processed into tube 1. 2) Use a stainless steel pipe with a smaller inner diameter than pipe 1 (hereinafter referred to as pipe 2) as a vacuum pipe. One end of pipe 2 is sealed to a vacuum quick-connect flange pipe, and the other end is sealed to the other open end of pipe 1. 3) Vacuum sealing: A. First, connect the vacuum quick-connect flange connected to one end of pipe 2 to the vacuum leak detection unit in a sealed manner. Detect leaks in the entire device of pipes 1 and 2 connected together to ensure that there are no leaks in pipes 1, 2 and all connections between them. Then, connect the vacuum quick-connect flange connected to one end of pipe 2 to the vacuum pumping unit in a sealed manner. Vacuum pipe 1 is evacuated, and at the same time, pipe 1 is heated to 350℃~450℃. B. When the vacuum degree reaches ≤1 x 10 -3 Pa, and after keeping the heating temperature for ≥15 min, the vacuum inside the connected-together pipe 1 and pipe 2 device is maintained, the middle part of pipe 2 is partially flattened and cut off, and the cut surface near the side of pipe 1 is welded by argon arc welding, so as to realize the sealing of the pipe to be processed in the vacuum cavity formed by pipe 1 and pipe 2, and form a vacuum device. 4) Then heat-treat the entire vacuum device; after the heat treatment is completed, cut off tube 1 at the end where it connects to tube 2 and remove the treated tube.

2. The vacuum heat treatment method according to claim 1, characterized in that: The pipe to be treated is encapsulated in a high-vacuum 304 stainless steel pipe, and then the encapsulated stainless steel pipe is used as a carrier for heating and cooling under normal pressure to achieve vacuum heat treatment of the pipe product. This method can ensure that the pipe product is under high vacuum throughout the heat treatment process and can achieve vacuum water quenching heat treatment at low cost. The maximum heating temperature of this method is 1100℃. Step 4) involves the following heat treatment process: the entire vacuum device is placed in an atmospheric pressure heat treatment furnace for heating and heat preservation. After the heat preservation is completed, the entire vacuum device is cooled according to the process requirements.

3. The vacuum heat treatment method according to claim 1, characterized in that: Pipe 1 is a 304 stainless steel round pipe with an outer diameter of φ60~φ200mm, a wall thickness of 2~4mm, and a length of 1~6m; one end of pipe 1 is sealed by a circular 304 stainless steel plate with a thickness of 3~4mm through an argon arc welding process to form a closed end.

4. The vacuum heat treatment method according to claim 1, characterized in that: Pipe 2 is a 304 stainless steel round pipe with an outer diameter of φ39~φ40mm, a wall thickness of 2~3mm, and a length of 250~350mm; One end of pipe 2 is connected to the open end of pipe 1 by an "reducer" through argon arc welding. The other end of pipe 2 is connected to a "KF40 vacuum quick-connect flange" through argon arc welding. The entire device is sealed to the vacuum leak detection unit or vacuum pumping unit through the aforementioned quick-connect flange.

5. The vacuum heat treatment method according to claim 4, characterized in that: The "variable diameter" is a truncated cone-shaped tube made of 304 stainless steel with a wall thickness of 2~4mm. Its outer diameter at the end connected to tube 2 is the same as that of tube 2, and its outer diameter at the end connected to tube 1 is the same as that of tube 1. The "KF40 vacuum quick-connect flange pipe" is a standard part that can be easily purchased from local hardware stores. The pipe part has an inner diameter of φ40mm, a wall thickness of 2mm, and a length of 50mm; the flange part has an outer diameter of φ55mm and a thickness of 3mm.

6. The vacuum heat treatment method according to claim 1, characterized in that: During step 3)B, when the vacuum level inside tube 1 is ≤1×10 -3 After holding the tube at the heating temperature for ≥15 minutes, maintain vacuum and turn off the heating. First, use two cylinders with a diameter of φ50~φ65mm to flatten the tube 2 at two points 50~80mm apart in the middle. The flattening process is as follows: the two cylinders are placed on opposite sides of the middle of the tube 2, with the axis of the cylinders perpendicular to the axis of the tube 2, and the two cylinders are positioned opposite each other on the two sides of the tube 2. The two cylinders move towards each other along the radial direction of the tube 2 towards the axis of the tube 2. Then, use two flat plates 50~80mm wide to flatten the area between the two flattened points in the middle of the tube 2, ensuring that the tube walls on both sides of the flattened area are completely in contact. The flattening process is as follows: the two flat plates are placed on opposite sides of the middle of the tube 2, with the surface of the flat plates parallel to the axis of the tube 2. Two flat plates are positioned opposite each other on both sides of tube 2. The two plates move towards each other along the radial direction of tube 2 towards the axis of tube 2. Finally, two cylinders with a diameter of φ50~φ65mm are used to continuously clamp or press the flattened part of tube 2 near the end of tube 1. The pressure is adjusted to ensure a leak-proof seal. The clamping or pressing process is as follows: the two cylinders are placed on two opposite plane surfaces on the flattened part of tube 2, the axis of the cylinders is perpendicular to the axis of tube 2, and the two cylinders are positioned opposite each other on both sides of tube 2. A pressure is applied between the two cylinders. The pressure is maintained, the vacuum unit is turned off, the middle of the flattened part of tube 2 is cut off, and the cut is welded with argon arc welding. The two opposing cylinders are separated, thus achieving vacuum sealing of the tube to be processed in tube 1.

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