Background technology:
High strength fasteners require quenching and tempering treatment according to technical requirements. Heat treatment quenching and tempering is to improve the comprehensive mechanical properties of fasteners to meet the specified tensile strength and yield ratio of products. The heat treatment process has a crucial impact on the internal quality of high-strength fasteners, especially their internal quality. During the quenching and tempering heat treatment process, some oxidizing gas is usually brought in from outside the furnace. The oxidizing gas will react with the bolt, causing decarburization on the surface of the bolt. Due to the different surface and internal structures, it has different expansion coefficients. During quenching, surface cracks may occur, reducing product quality. The traditional heat treatment process involves directly placing bolts into a quenching furnace for high-temperature quenching. During the quenching and tempering process, problems such as insufficient hardness in the quenched state, uneven hardness in the quenched state, excessive quenching deformation, and quenching cracking are prone to occur. In view of this, it is necessary to make improvements to the traditional heat treatment process.
Technical implementation elements:
To address the shortcomings of existing technology, the aim of the present invention is to provide a heat treatment process for bolts with better quenching effect, improved product quality, and extended product service life.
In order to achieve the above objectives, the present invention adopts the following technical solution:
The heat treatment process of bolts includes the following steps:
S1. Dephosphorization;
S2. Pre treatment: Place the product in a preheating furnace and continuously inject high-temperature nitrogen gas into the preheating furnace. After preheating for 2.5 to 3 hours, remove it and place it in a carburizing furnace for carburization treatment;
S3. Quenching: Place the product in a quenching furnace and continuously inject nitrogen into the quenching furnace. After injecting nitrogen for 30-40 minutes, slowly raise the temperature of the quenching furnace to 460-500 ℃ and maintain it for 15-20 minutes before proceeding with the first stage of quenching treatment; Slowly increase the temperature of the quenching furnace to 550~700 ℃ and maintain it for 20~35 minutes before proceeding with the second stage of quenching treatment; Slowly increase the temperature of the quenching furnace to 750-850 ℃ and maintain it for 30-45 minutes before proceeding with the third stage of quenching treatment;
S4. Oil cooling: Take out the quenched product and place it in the first quenching oil tank for oil cooling, stirring every 15 minutes and maintaining it for 20-30 minutes; After removal, place it in the second quenching oil tank for oil cooling, stir every 15 minutes until the product temperature drops to 100 ℃;
S5. Oil removal: Take out the cooled product and let it stand for 35-45 minutes, and blow off the quenching oil on the surface of the product through cold air;
S6. Tempering: Put the degreased product into a tempering furnace for tempering treatment, adjust the tempering temperature to 110~180 ℃, and the tempering time to 1.5~3 hours. Perform the first stage of tempering treatment; Raise the temperature to 370-410 ℃ and temper for 3-6 hours before proceeding with the second stage of tempering treatment; After tempering treatment, air cool the product to room temperature.
Preferably, in step s1 above, the cleaning solution consists of the following components by mass: 20-36 parts of butyl acetate, 10-13 parts of polyglycolic acid, 16-20 parts of aminoacetic acid, 13-22 parts of ethyl acrylate, 5-9 parts of oleic acid triethanolamine salt, 3-16 parts of ethanolamine, and 18-26 parts of water, which can effectively remove oil stains on the surface of the product and avoid affecting the quenching effect.
More preferably, the aforementioned dephosphorization tank is equipped with a dephosphorization solution, which selects a potassium hydroxide solution with a concentration of 2.2-6.5g/l or a sodium hydroxide solution with a concentration of 2.8-6.9g/l.
More preferably, in the aforementioned step s2, the high-temperature nitrogen gas introduced into the preheating furnace is the nitrogen gas in the quenching furnace in step s3, with a flow rate of 2.5-3.5l/h. By preheating the product, the cleaning solution on its surface can be dried and the sudden increase in temperature in the quenching furnace can avoid affecting product quality.
Further preferably, in step s3 above, the flow rate of nitrogen is 4-5l/h, which can remove air from the preheating furnace, avoid oxidation reaction between oxygen and the product, and avoid decarburization, which may cause failure of threaded fasteners and shorten the service life of the product.
Specifically, in step s3 above, the heating rate of the quenching furnace during the heating period to 460-500 ℃ is 30-40 ℃/min, the heating rate during the heating period to 550-700 ℃ is 50-60 ℃/min, and the heating rate during the heating period to 750-850 ℃ is 70-90 ℃/min. The stage heating quenching treatment can improve the quenching effect of the product and improve the quality of the product.
Preferably, in step s4, the temperature of the quenching oil in the first quenching oil tank is 250-300 ℃, and the temperature of the quenching oil in the second quenching oil tank is 50-70 ℃.
More preferably, in step s5 above, the temperature of the cold air is 30-35 ℃, and the wind speed is 20-25m/s.
The advantages of the present invention are that the heat treatment process of the bolt is simple, easy to operate, and has good quenching effect. By preheating the product, the cleaning solution on its surface can be dried, and the sudden increase in temperature in the quenching furnace can avoid affecting the product quality; The high-temperature nitrogen used in the preheating furnace comes from the quenching furnace, eliminating the heating device in the preheating furnace, which can save energy consumption and reduce production costs; Injecting nitrogen into the preheating and quenching furnaces can remove the air inside, avoiding oxidation reactions between oxygen and the product, thereby avoiding decarburization and causing failure of threaded fasteners, and extending the service life of the product; Stage heating quenching treatment can improve the quenching effect of the product and improve its quality; Staged oil cooling treatment can effectively cool high-temperature products without damaging their quality.
Specific implementation method
The following is a specific introduction to the present invention in conjunction with specific embodiments.
Example 1
The heat treatment process of bolts includes the following steps:
S1. Dephosphorization;
The cleaning solution consists of the following components by mass: 20 parts of butyl acetate, 10 parts of polyglycolic acid, 16 parts of aminoacetic acid, 13 parts of ethyl acrylate, 5 parts of oleic acid triethanolamine salt, 3 parts of ethanolamine, and 18 parts of water; The dephosphorization tank is equipped with dephosphorization solution, which uses a potassium hydroxide solution with a concentration of 2.2g/l;
S2. Pre treatment: Place the product in a preheating furnace and continuously inject high-temperature nitrogen gas into the preheating furnace. After preheating for 2.5 hours, take it out and place it in a carburizing furnace for carburization treatment;
S3. Quenching: Place the product in the quenching furnace and continuously inject nitrogen gas into the quenching furnace. The flow rate of nitrogen gas is 4l/h, and after injecting nitrogen gas for 30 minutes, slowly increase the temperature of the quenching furnace to 460 ℃, with a heating rate of 30 ℃/min, and maintain it for 15 minutes before proceeding with the first stage of quenching treatment; Slowly increase the temperature of the quenching furnace to 550 ℃, with a heating rate of 50 ℃/min, and maintain it for 20 minutes before proceeding with the second stage of quenching treatment; Slowly increase the temperature of the quenching furnace to 750 ℃, with a heating rate of 70 ℃/min, and maintain it for 30 minutes before proceeding with the third stage of quenching treatment;
S4. Oil cooling: Take out the quenched product and place it in the first quenching oil tank for oil cooling. The temperature of the quenching oil is 250 ℃, and stir every 15 minutes for 20 minutes; After removal, place it in the second quenching oil tank for oil cooling, with the quenching oil temperature at 50 ℃ and stir every 15 minutes until the product temperature drops to 100 ℃;
S5. Oil removal: Take out the cooled product and let it stand for 35 minutes. Blow off the quenching oil on the surface of the product with cold air at a temperature of 30 ℃ and a wind speed of 20m/s;
S6. Tempering: Put the degreased product into a tempering furnace for tempering treatment, adjust the tempering temperature to 110 ℃, and the tempering time to 1.5 hours. Perform the first stage of tempering treatment; Raise the temperature to 370 ℃, temper for 3 hours, and proceed with the second stage of tempering treatment; After tempering treatment, air cool the product to room temperature.
The high-temperature nitrogen gas introduced into the preheating furnace in step s2 of this embodiment is the nitrogen gas from the quenching furnace in step s3, and the flow rate of the high-temperature nitrogen gas is 2.5l/h.
Example 2
The process steps in this embodiment are the same as those in Example 1, except for the specific process conditions, which include the following steps:
S1. Dephosphorization: put the product into the cleaning machine and pour in the cleaning solution until the product is completely immersed in the cleaning solution. Adjust the cleaning temperature to 50 ℃ and stir it every 15min. After cleaning for 3h, take out the product and put it into the dephosphorization tank for dephosphorization treatment;
The cleaning solution consists of the following components by mass: 36 parts of butyl acetate, 13 parts of polyglycolic acid, 20 parts of aminoacetic acid, 22 parts of ethyl acrylate, 9 parts of oleic acid triethanolamine salt, 16 parts of ethanolamine, and 26 parts of water; The dephosphorization tank is equipped with dephosphorization solution, which is selected as a potassium hydroxide solution with a concentration of 6.5g/l or a sodium hydroxide solution with a concentration of 6.9g/l;
S2. Pre treatment: Place the product in a preheating furnace and continuously inject high-temperature nitrogen gas into the preheating furnace. After preheating for 3 hours, take it out and place it in a carburizing furnace for carburization treatment;
S3. Quenching: Place the product in the quenching furnace and continuously inject nitrogen gas into the quenching furnace. The flow rate of nitrogen gas is 5l/h, and after injecting nitrogen gas for 40min, slowly increase the temperature of the quenching furnace to 500 ℃, with a heating rate of 40 ℃/min, and maintain it for 20min before proceeding with the first stage of quenching treatment; Slowly increase the temperature of the quenching furnace to 700 ℃, with a heating rate of 60 ℃/min, and hold for 35 minutes before proceeding with the second stage of quenching treatment; Slowly increase the temperature of the quenching furnace to 850 ℃, with a heating rate of 90 ℃/min, and hold for 45 minutes before proceeding with the third stage of quenching treatment;
S4. Oil cooling: Take out the quenched product and place it in the first quenching oil tank for oil cooling. The temperature of the quenching oil is 300 ℃, and stir every 15 minutes for 30 minutes; After removal, place it in the second quenching oil tank for oil cooling, with the quenching oil temperature at 70 ℃ and stir every 15 minutes until the product temperature drops to 100 ℃;
S5. Oil removal: Take out the cooled product and let it stand for 45 minutes. Blow off the quenching oil on the surface of the product with cold air at a temperature of 35 ℃ and a wind speed of 25m/s;
S6. Tempering: Put the degreased product into a tempering furnace for tempering treatment, adjust the tempering temperature to 180 ℃, and the tempering time to 3 hours. Perform the first stage of tempering treatment; Raise the temperature to 410 ℃, temper for 6 hours, and proceed with the second stage of tempering treatment; After tempering treatment, air cool the product to room temperature.
The high-temperature nitrogen gas introduced into the preheating furnace in step s2 of this embodiment is the nitrogen gas from the quenching furnace in step s3, with a flow rate of 3.5l/h for high-temperature nitrogen gas.
Example 3
The process steps in this embodiment are the same as those in Example 1, except for the specific process conditions, which include the following steps:
S1. Dephosphorization;
The cleaning solution consists of the following components by mass: 28 parts of butyl acetate, 12 parts of polyglycolic acid, 18 parts of aminoacetic acid, 18 parts of ethyl acrylate, 7 parts of oleic acid triethanolamine salt, 10 parts of ethanolamine, and 22 parts of water; The dephosphorization tank is equipped with dephosphorization solution, which is selected as a sodium hydroxide solution with a concentration of 4.5g/l;
S2. Pre treatment: Place the product in a preheating furnace and continuously inject high-temperature nitrogen gas into the preheating furnace. After preheating for 2.7 hours, remove it and place it in a carburizing furnace for carburization treatment;
S3. Quenching: Place the product in the quenching furnace and continuously inject nitrogen gas into the quenching furnace. The flow rate of nitrogen gas is 4.5l/h, and after injecting nitrogen gas for 35 minutes, slowly increase the temperature of the quenching furnace to 480 ℃, with a heating rate of 35 ℃/min, and maintain it for 18 minutes before proceeding with the first stage of quenching treatment; Slowly increase the temperature of the quenching furnace to 575 ℃, with a heating rate of 55 ℃/min, and maintain it for 27 minutes before proceeding with the second stage of quenching treatment; Slowly increase the temperature of the quenching furnace to 800 ℃, with a heating rate of 80 ℃/min, and maintain it for 38 minutes before proceeding with the third stage of quenching treatment;
S4. Oil cooling: Take out the quenched product and place it in the first quenching oil tank for oil cooling. The temperature of the quenching oil is 275 ℃, and stir every 15 minutes for 25 minutes; After removal, place it in the second quenching oil tank for oil cooling, with the quenching oil temperature at 60 ℃ and stir every 15 minutes until the product temperature drops to 100 ℃;
S5. Oil removal: Take out the cooled product and let it stand for 40 minutes. Blow off the quenching oil on the surface of the product through cold air, with a temperature of 33 ℃ and a wind speed of 22m/s;
S6. Tempering: Put the degreased product into a tempering furnace for tempering treatment, adjust the tempering temperature to 145 ℃, and the tempering time to 2.2 hours. Perform the first stage of tempering treatment; Raise the temperature to 390 ℃, temper for 4.5 hours, and proceed with the second stage of tempering treatment; After tempering treatment, air cool the product to room temperature.
The high-temperature nitrogen introduced into the preheating furnace in step s2 of this embodiment is the nitrogen in the quenching furnace in step s3, with a flow rate of 3l/h.
Mechanical performance testing
According to the testing results, it can be seen that the strength level of the bolts treated by the heat treatment process of the present invention is above 10.5, which meets the quality requirements.
The heat treatment process of the bolt of the present invention is simple, easy to operate, and has good quenching effect. By preheating the product, the cleaning solution on its surface can be dried, and the sudden increase in temperature in the quenching furnace can avoid affecting product quality; The high-temperature nitrogen used in the preheating furnace comes from the quenching furnace, eliminating the heating device in the preheating furnace, which can save energy consumption and reduce production costs; Injecting nitrogen into the preheating and quenching furnaces can remove the air inside, avoiding oxidation reactions between oxygen and the product, thereby avoiding decarburization and causing failure of threaded fasteners, and extending the service life of the product; Stage heating quenching treatment can improve the quenching effect of the product and improve its quality; Staged oil cooling treatment can effectively cool high-temperature products without damaging their quality.
In the description of this specification, the reference to terms such as “one embodiment”, “some embodiments”, “examples”, “specific examples”, or “some examples” means that the specific features, structures, materials, or features described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiments or examples. Moreover, the specific features, structures, materials, or features described can be combined in an appropriate manner in any one or more embodiments or examples.
The above shows and describes the basic principles, main features, and advantages of the present invention. Technicians in this industry should understand that the above embodiments do not in any way limit the present invention, and any technical solutions obtained through equivalent replacement or equivalent transformation fall within the scope of protection of the present invention.
Post time: Apr-04-2023