Processing method of steel for automobile fastener and fastener produced by using method

Abstract

The invention relates to the technical field of automobile part production equipment, in particular to an automobile fastener steel machining method which comprises the following steps: S1, cold machining forming; s2, preparing high-purity nitrogen; s3, high-temperature heat treatment; s4, surface strengthening treatment; s5, carrying out precise straightening treatment; the raw materials of the fastener for the automobile are obtained by adopting the method. A nut is arranged at the upper end of the screw, an annular table is arranged on the upper surface of the nut, a circular table is arranged in the center of the inner side face of the annular table, positioning grooves are annularly and evenly distributed in the edge of the inner side face of the annular table, and slopes are arranged on the edges of the positioning grooves. A composite molecular sieve catalytic deoxidation technology is used for replacing a traditional high-temperature carbon adsorption method, so that the energy consumption of nitrogen purification is remarkably reduced; the cyclic regeneration mechanism of the copper component in the molecular sieve improves the utilization efficiency of the material, and the multistage stretching process accurately controls the reduction of area, effectively inhibits the generation of defects in the steel, and guarantees the performance of the basic material.

Description

Technical Field

[0001] This application relates to the field of automotive parts manufacturing equipment technology, specifically to a method for processing steel for automotive fasteners and fasteners produced using this method. Background Technology

[0002] Currently, automotive fastener manufacturing commonly employs either cold heading or hot heading processes. Cold heading relies on multi-stage stretching to control material plasticity; however, existing technologies have limited control over reduction of area, leading to microcracks and stress concentration within the steel, exacerbating center segregation and porosity. While hot heading reduces deformation resistance, heating to over 1000℃ results in an oxide scale formation of up to 35g / m² on the steel surface. 2 Currently, oxide scale removal mainly relies on pickling or mechanical sandblasting. Residual oxide scale is pressed into the forging during the upsetting process, forming inclusion defects and significantly reducing fatigue life. Furthermore, traditional decarburization processes, such as shot peening, do not thoroughly remove the surface carbon layer, hindering the consistency of subsequent nitriding treatment.

[0003] In high-temperature environments, fastener steel readily reacts with oxygen to produce oxides, leading to surface degradation and oxidative corrosion. Using a nitrogen atmosphere during heat treatment effectively eliminates oxygen, reducing oxidation and preventing further oxidation of the fastener steel. Simultaneously, high-temperature heat treatment causes phase transformations and stress release within the fastener steel, resulting in changes in shape and size. Nitrogen provides an inert atmosphere, reducing contact between the fastener steel and air, lowering the likelihood of surface oxidation and deformation, and thus maintaining the geometric and dimensional stability of the fastener steel. During high-temperature heat treatment, nitrogen can form a layer of nitrides on the surface of the fastener steel, such as iron nitride and molybdenum nitride. These nitrides possess high hardness and wear resistance. Therefore, using nitrogen can increase the hardness of the fastener steel, improve its wear resistance, and extend its service life.

[0004] High-purity nitrogen used in the high-temperature heat treatment of fastener steel is mostly prepared through air fractionation. However, the crude nitrogen prepared by fractionation still contains about 5% oxygen, which cannot be completely removed. To remove the oxygen from the crude nitrogen, existing technology usually involves passing the crude nitrogen product into a carbon adsorbent and then adjusting the ambient temperature to 800℃, so that the oxygen reacts directly with the carbon to produce carbon dioxide gas. The generated carbon dioxide is an atmospheric gas and will not harm the high-temperature heat treatment process of fastener steel. However, this treatment method is energy-intensive, and traditional treatment equipment has a small contact area between carbon and oxygen, resulting in reduced treatment efficiency.

[0005] Meanwhile, most fasteners produced using existing technology are ordinary bolts, which are prone to loosening under prolonged vibration. In addition, during the installation of existing fasteners, in order to prevent bolt yielding deformation and crushing of connecting parts caused by over-tightening, electronic torque wrenches are mostly used. However, in installation scenarios with limited operating space, electronic torque wrenches cannot be used, and workers can only rely on experience to install fasteners. Summary of the Invention

[0006] This application provides a method for processing steel for automotive fasteners and fasteners produced using this method, which can effectively solve the problems in the background art.

[0007] To achieve the above objectives, this application provides the following technical solution: a method for processing steel for automotive fasteners, comprising the following steps:

[0008] S1. Cold forming:

[0009] S1.1 The steel coil is decarburized to remove the surface carbon layer;

[0010] S1.2 Perform multi-stage tensile testing on decarburized steel to control the reduction of area to ≤15%;

[0011] S1.3 The drawn material is formed into a fastener blank on a cold heading machine;

[0012] S1.4 Cut the billet to obtain steel sections of standard size;

[0013] S2. Preparation of high-purity nitrogen:

[0014] S2.1 Obtain crude nitrogen gas from air fractionation, with an oxygen content of 35 vol%.

[0015] S2.2 Pass crude nitrogen gas into a purification device filled with composite molecular sieves;

[0016] S2.3 undergoes a catalytic deoxygenation reaction at 250-350℃, with the following process:

[0017] ① Oxygen reacts with the copper component in the molecular sieve: 2Cu + O2 → 2CuO

[0018] ② Reduction of copper oxide with carbon support: 2CuO + C → 2Cu + CO2↑

[0019] S2.4 Collect deoxygenated nitrogen gas with an oxygen content ≤0.05%;

[0020] S3. High-temperature heat treatment:

[0021] S3.1 Place the steel section obtained in S1 into a heat treatment furnace;

[0022] S3.2 introduces the high-purity nitrogen obtained from S2 at a flow rate of 510 L / min;

[0023] S3.3 was heat-treated at 800-1100℃ for 1060 minutes;

[0024] S4. Surface strengthening treatment:

[0025] S4.1 The steel section after high-temperature heat treatment is placed in an ion nitriding furnace, and a mixture of ammonia and nitrogen is introduced, wherein the ammonia accounts for 30-50%;

[0026] S4.2 is subjected to ion nitriding treatment at 500-600℃ and 0.1-0.3MPa pressure for 36 hours;

[0027] S5. Precision straightening process:

[0028] S5.1 A laser measuring instrument is used to detect the straightness of the steel section;

[0029] S5.2 Based on the test results, use a hydraulic straightening machine to straighten the steel section at multiple points in stages, with each straightening amount controlled within 0.01-0.03 mm.

[0030] Preferably, the composite molecular sieve is composed of copper nanoparticles supported on a honeycomb carbon carrier, and the mass ratio of copper to carbon is 1:(0.8-1.5).

[0031] Preferably, the deoxidation reaction temperature in step S2.3 is 280-320℃, and the reaction pressure is 0.2-0.5 MPa.

[0032] Preferably, the copper component of the molecular sieve is recycled during the reaction, and a single regeneration cycle can process ≥1000m³ of crude nitrogen gas. 3 / ton of molecular sieve.

[0033] Preferably, in step S3.2, the nitrogen gas needs to undergo deep drying treatment with a dew point ≤60℃ before being introduced.

[0034] Preferably, the multi-stage stretching in step S1.2 includes: first, rough stretching with a deformation rate of 20-30%, and then fine stretching with a deformation rate of 5-10%.

[0035] Preferably, the flow rate of the mixed gas in step S4.1 is calculated using the following formula:

[0036] Q = k × V × (1 + α × T)

[0037] Where Q is the mixed gas flow rate (L / h), k is a coefficient with a value range of 1.2-1.5; V is the effective volume of the ion nitriding furnace (L); α is the temperature coefficient with a value of 0.003 / ℃; and T is the ion nitriding treatment temperature (℃).

[0038] Preferably, the straightness error after straightening in step S5.2 is evaluated using the following formula:

[0039] δ=(L1L2) / L0×100%

[0040] Where δ is the straightness error (%); L1 is the maximum bending length of the steel section before straightening (mm); L2 is the maximum bending length of the steel section after straightening (mm); L0 is the standard length of the steel section (mm), and δ is required to be ≤0.05%.

[0041] An automotive fastener, the raw material of which is obtained by the above method.

[0042] It also includes a screw, the upper end of which is provided with a nut, the upper surface of which is provided with an annular platform, the center of the inner side of the annular platform is provided with a truncated cone, and the inner side edge of the annular platform is provided with a circumferentially distributed positioning groove, the edge of which is provided with a slope.

[0043] The lower end of the outer side of the screw is threaded with nut two and nut one from top to bottom. The upper end of the outer side of nut one is provided with a frustum sleeve. Both the outer side of nut one and the frustum sleeve are provided with strip grooves. The lower end of the inner side of nut two is provided with a frustum positioning groove that corresponds to the insertion of the frustum sleeve.

[0044] Preferably, it also includes a disassembly sleeve for disassembling fasteners. The disassembly sleeve includes a cylinder body, and the inside of the cylinder body is provided with a secondary cavity and a primary cavity from top to bottom. The primary cavity has a cylindrical cross-section, and the secondary cavity has a polygonal cross-section. A slider is slidably connected to the inner side of the secondary cavity. The lower end face of the slider is provided with positioning teeth. The upper end of the inner side of the secondary cavity is connected to the upper end face of the slider through a strong spring. The positioning teeth are correspondingly set to engage with the positioning groove. The primary cavity is correspondingly set to sleeve the annular platform.

[0045] Compared with the prior art, the beneficial effects of the present invention are:

[0046] 1. By replacing the traditional high-temperature carbon adsorption method with composite molecular sieve catalytic deoxygenation technology, the energy consumption of nitrogen purification is significantly reduced; the recycling mechanism of copper components in the molecular sieve improves the material utilization efficiency, while the multi-stage stretching process precisely controls the section reduction rate, effectively suppressing the generation of internal defects in steel and ensuring the performance of basic materials.

[0047] 2. High-temperature heat treatment under high-purity nitrogen protection combined with ion nitriding surface strengthening significantly reduces oxide inclusions and forms a uniform and dense hardened layer, which significantly improves the fatigue resistance and wear resistance of fasteners; subsequent precision straightening process ensures controllable micro-deformation and achieves high stability of product dimensions.

[0048] 3. The fasteners innovatively adopt a double-nut linkage structure and annular positioning groove design, combined with the elastic engagement mechanism of a special disassembly and assembly sleeve, which not only prevents the risk of deformation caused by over-tightening, but also enables precise disassembly and assembly in confined spaces, effectively overcoming the problem of traditional installation relying on electronic torque wrenches. Attached Figure Description

[0049] Figure 1 This is a flowchart of the application process;

[0050] Figure 2 This is a schematic diagram of the structure of a fastener used in automobiles.

[0051] Figure 3 A front view of an automotive fastener;

[0052] Figure 4 A top view of an automotive fastener;

[0053] Figure 5 This is a schematic diagram showing the connection between an automotive fastener and a disassembly sleeve.

[0054] Figure 6 This is a cross-sectional view of the disassembly and assembly sleeve.

[0055] In the diagram: 1. Frustum, 2. Positioning groove, 3. Annular platform, 4. Nut, 5. Screw, 6. Strip groove, 7. Frustum sleeve, 8. Nut 1, 9. Nut 2, 10. Frustum positioning groove, 11. Ramp, 12. Disassembly sleeve, 121. Secondary cavity, 122. Strong spring, 123. Cylinder body, 124. Slider, 125. Positioning tooth, 126. Primary cavity. Detailed Implementation

[0056] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0057] In the description of this application, if directional descriptions are involved, such as "up," "down," "front," "back," "left," "right," etc., indicating directional or positional relationships, they are based on the appendix. Figure 3 The orientations or positional relationships shown are for the convenience of describing this application and simplifying the description only, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. When a feature is referred to as "set", "fixed", or "connected" to another feature, it can be directly set, fixed, or connected to the other feature, or it can be indirectly set, fixed, or connected to the other feature.

[0058] Please see Figure 1-6 This application provides the following technical solution: a method for processing steel for automotive fasteners, comprising the following steps:

[0059] S1. Cold forming:

[0060] S1.1 The steel coil is decarburized to remove the surface carbon layer;

[0061] S1.2 Perform multi-stage tensile testing on decarburized steel to control the reduction of area to ≤15%;

[0062] S1.3 The drawn material is formed into a fastener blank on a cold heading machine;

[0063] S1.4 Cut the billet to obtain steel sections of standard size.

[0064] Specifically, mechanical decarburization, such as shot peening or pickling, thoroughly removes the carbon layer on the steel surface to avoid carbon residue hindering the uniformity of subsequent nitriding; multi-stage stretching adopts a "coarse first, fine later" strategy: coarse stretching for rapid forming, and fine stretching for precise control of the section reduction rate ≤15% to suppress internal micro-cracks; after cold heading, it is cut into standardized billets.

[0065] Furthermore, the multi-stage stretching process avoids stress concentration caused by large single deformation, reducing the risk of center segregation; strict control of the reduction of area improves the plasticity of the material, providing highly consistent blanks for subsequent cold heading and reducing the scrap rate.

[0066] S2. Preparation of high-purity nitrogen:

[0067] S2.1 Obtain crude nitrogen gas from air fractionation, with an oxygen content of 35 vol%.

[0068] S2.2 Pass crude nitrogen gas into a purification device filled with composite molecular sieves;

[0069] S2.3 undergoes a catalytic deoxygenation reaction at 250-350℃, with the following process:

[0070] ① Oxygen reacts with the copper component in the molecular sieve: 2Cu + O2 → 2CuO

[0071] ② Reduction of copper oxide with carbon support: 2CuO + C → 2Cu + CO2↑

[0072] S2.4 Collect deoxygenated nitrogen gas with an oxygen content ≤0.05%;

[0073] Specifically, a composite molecular sieve is constructed by using nano-copper particles (Cu:C = 1:0.8~1.5) supported on a honeycomb carbon carrier; when crude nitrogen passes through, oxygen reacts with copper at 280-320℃ / 0.2-0.5MPa to generate CuO, which is then reduced and regenerated into copper by the carbon carrier, while releasing CO2. The copper component is recycled and regenerated to achieve continuous deoxygenation.

[0074] More specifically, the honeycomb structure increases the gas-solid contact area, resulting in a higher catalytic deoxygenation efficiency compared to the traditional high-temperature carbon adsorption method; the low-temperature operation at 250-350℃ is more energy-efficient; copper recycling extends the molecular sieve lifespan, and reducing the oxygen content to below 0.05% ensures the purity of the heat treatment.

[0075] S3. High-temperature heat treatment:

[0076] S3.1 Place the steel section obtained in S1 into a heat treatment furnace;

[0077] S3.2 introduces the high-purity nitrogen obtained from S2 at a flow rate of 510 L / min;

[0078] S3.3 was heat-treated at 800-1100℃ for 1060 minutes;

[0079] Specifically, deep-dried nitrogen with a dew point ≤60℃ is introduced into a heat treatment furnace at 800-1100℃ to form an inert atmosphere that isolates oxygen; the nitrogen also participates in surface pre-nitriding to form a primary nitriding layer on the steel surface.

[0080] More specifically, ultra-low dew point nitrogen eliminates the risk of hydrogen embrittlement; a nitrogen atmosphere reduces the amount of oxide scale generated, avoiding acid pickling contamination; and the pre-nitrided layer provides a uniform substrate for subsequent ion nitriding, improving hardening efficiency.

[0081] S4. Surface strengthening treatment:

[0082] S4.1 The steel section after high-temperature heat treatment is placed in an ion nitriding furnace, and a mixture of ammonia and nitrogen is introduced, wherein the ammonia accounts for 30-50%;

[0083] S4.2 is subjected to ion nitriding treatment at 500-600℃ and 0.1-0.3MPa pressure for 36 hours;

[0084] Specifically, an ammonia-nitrogen mixture is introduced into an ion nitriding furnace, where an electric field ionizes the gas to generate highly active nitrogen. + Ions bombard the steel surface; the gas flow rate is dynamically adjusted according to the formula Q=k×V×(1+0.003T) (k=1.2~1.5) to ensure stable pressure inside the furnace when the temperature changes; nitrogen ions penetrate at 500-600℃ to form a dense nitrided layer.

[0085] More specifically, the flow rate formula precisely controls the atmosphere concentration, avoiding uneven diffusion caused by traditional empirical methods; ion bombardment increases the nitriding rate, increases the depth of the hardened layer and reduces the porosity, thereby improving wear resistance.

[0086] S5. Precision straightening process:

[0087] S5.1 A laser measuring instrument is used to detect the straightness of the steel section;

[0088] S5.2 Based on the test results, use a hydraulic straightening machine to straighten the steel section at multiple points in stages, with each straightening amount controlled within 0.01-0.03 mm.

[0089] Specifically, a laser measuring instrument scans the steel section to generate a three-dimensional deformation map, and a hydraulic straightening machine applies pressure at multiple points based on the map data; the straightness error is quantitatively controlled according to the formula δ=(L1L2) / L0×100% (δ≤0.05%).

[0090] More specifically, laser detection achieves micron-level precision, which, combined with step-by-step straightening, eliminates internal residual stress; formulaic error assessment ensures consistent product straightness, avoids stress concentration during assembly, and extends the fatigue life of fasteners.

[0091] Preferably, the composite molecular sieve is composed of copper nanoparticles supported on a honeycomb carbon carrier, and the mass ratio of copper to carbon is 1:(0.8-1.5).

[0092] Preferably, the deoxidation reaction temperature in step S2.3 is 280-320℃, and the reaction pressure is 0.2-0.5 MPa.

[0093] Preferably, the copper component of the molecular sieve is recycled during the reaction, and a single regeneration cycle can process ≥1000m³ of crude nitrogen gas. 3 / ton of molecular sieve.

[0094] Preferably, in step S3.2, the nitrogen gas needs to undergo deep drying treatment with a dew point ≤60℃ before being introduced.

[0095] Preferably, the multi-stage stretching in step S1.2 includes: first, rough stretching with a deformation rate of 20-30%, and then fine stretching with a deformation rate of 5-10%.

[0096] Preferably, the flow rate of the mixed gas in step S4.1 is calculated using the following formula:

[0097] Q = k × V × (1 + α × T);

[0098] Where Q is the mixed gas flow rate (L / h), k is a coefficient with a value range of 1.2-1.5; V is the effective volume of the ion nitriding furnace (L); α is the temperature coefficient with a value of 0.003 / ℃; and T is the ion nitriding treatment temperature (℃).

[0099] Preferably, the straightness error after straightening in step S5.2 is evaluated using the following formula:

[0100] δ=(L1L2) / L0×100%

[0101] Where δ is the straightness error (%); L1 is the maximum bending length of the steel section before straightening (mm); L2 is the maximum bending length of the steel section after straightening (mm); L0 is the standard length of the steel section (mm), and δ is required to be ≤0.05%.

[0102] An automotive fastener, the raw material of which is obtained by the above method.

[0103] It also includes a screw, the upper end of which is provided with a nut, the upper surface of which is provided with an annular platform, the center of the inner side of the annular platform is provided with a truncated cone, and the inner side edge of the annular platform is provided with a circumferentially distributed positioning groove, the edge of which is provided with a slope.

[0104] The lower end of the outer side of the screw is threaded with nut two and nut one from top to bottom. The upper end of the outer side of nut one is provided with a frustum sleeve. Both the outer side of nut one and the frustum sleeve are provided with strip grooves. The lower end of the inner side of nut two is provided with a frustum positioning groove that corresponds to the insertion of the frustum sleeve.

[0105] Specifically, the anti-loosening structure involves inserting the frustum sleeve 7 of nut 1 (8) into the frustum positioning groove 10 of nut 2 (9), with the two nuts mechanically interlocked to resist vibration and loosening.

[0106] Preferably, it also includes a disassembly sleeve for disassembling fasteners. The disassembly sleeve includes a cylinder body, and the inside of the cylinder body is provided with a secondary cavity and a primary cavity from top to bottom. The primary cavity has a cylindrical cross-section, and the secondary cavity has a polygonal cross-section. A slider is slidably connected to the inner side of the secondary cavity. The lower end face of the slider is provided with positioning teeth. The upper end of the inner side of the secondary cavity is connected to the upper end face of the slider through a strong spring. The positioning teeth are correspondingly set to engage with the positioning groove. The primary cavity is correspondingly set to sleeve the annular platform.

[0107] Specifically, the primary cavity 126 of the disassembly sleeve 12 covers the annular platform 3, the spring 122 in the secondary cavity 121 pushes the slider 124 to make the positioning teeth 125 engage the positioning groove 2, and the ramp 11 guides the rapid positioning.

[0108] The double-nut interlocking structure eliminates the need for additional washers and increases the anti-loosening torque by 35%. The splice sleeve achieves precise force application in confined spaces through mechanical engagement, replacing electronic torque wrenches, increasing installation efficiency by 50% and eliminating the risk of over-tightening.

[0109] When using:

[0110] I. Processing methods for steel used in automotive fasteners:

[0111] Key steps and operational points:

[0112] 1. Cold forming

[0113] S1.1 Decarburization treatment: Shot blasting or pickling is performed on the steel coil to thoroughly remove the surface carbon layer (to avoid affecting the uniformity of subsequent nitriding).

[0114] S1.2 Multi-stage Tension:

[0115] First, perform rough stretching with a deformation rate of 2030%;

[0116] Then, perform precision stretching at a deformation rate of 510%.

[0117] Control the reduction of area to ≤15% (to prevent internal microcracks).

[0118] S1.3 Cold heading: The drawn material is processed into fastener blanks on a cold heading machine.

[0119] S1.4 Cutting: Obtain steel sections of standard size.

[0120] 2. Preparation of high-purity nitrogen

[0121] S2.1 Obtain crude nitrogen gas (oxygen content 35 vol%) from air fractionation.

[0122] S2.2 Pass crude nitrogen gas into a composite molecular sieve purification device (molecular sieve structure: honeycomb carbon carrier loaded with nano-copper, copper-carbon mass ratio 1:0.8-1.5).

[0123] S2.3 catalytic deoxygenation:

[0124] Temperature 280-320℃, pressure 0.2-0.5MPa;

[0125] Reaction principle:

[0126] ①2Cu + O₂ → 2CuO

[0127] ②2CuO+C→2Cu+CO2↑

[0128] Copper components are recycled and regenerated, with a single processing capacity of ≥1000m³. 3 / ton of molecular sieve.

[0129] S2.4 Collects high-purity nitrogen gas with an oxygen content ≤0.05% and deeply dries it to a dew point ≤60℃.

[0130] 3. High-temperature heat treatment

[0131] S3.1 steel sections are placed into a heat treatment furnace.

[0132] S3.2 Introduce dry, high-purity nitrogen at a flow rate of 510 L / min (to isolate oxygen and form a pre-nitrided layer).

[0133] S3.3 is held at 800-1100℃ for 1060 minutes (to relieve stress and refine grains).

[0134] 4. Surface strengthening treatment (ion nitriding)

[0135] S4.1 steel material section is placed into ion nitriding furnace and a mixture of ammonia and nitrogen is introduced (ammonia content 30-50%).

[0136] S4.2 was kept at 500-600℃ and 0.1-0.3MPa for 36 hours.

[0137] Flow control formula:

[0138] Q = k × V × (1 + 0.003 × T)

[0139] Q: Mixed gas flow rate (L / h);

[0140] k: coefficient (1.2~1.5);

[0141] V: Effective furnace volume (L);

[0142] T: Processing temperature (°C).

[0143] 5. Precision alignment

[0144] S5.1 Use a laser measuring instrument to check the straightness of the steel section.

[0145] S5.2 hydraulic straightening machine performs step-by-step straightening (each straightening step is 0.01-0.03mm).

[0146] Straightness error formula:

[0147] δ=(L1L2) / L0×100%≤0.05%

[0148] L1: Maximum bending length before straightening (mm);

[0149] L2: Maximum bending length after straightening (mm);

[0150] L0: Standard length (mm).

[0151] II. Fastener Usage Instructions (Installation and Removal);

[0152] The screw 5 is passed through the part to be connected, and the screw 5 and nut 9 are locked together by the disassembly sleeve 12. When using the disassembly sleeve 12, the first-stage cavity 126 is first placed on the outer side of the annular platform 3, and a certain downward pressure is applied to the disassembly sleeve 12 so that the lower surface of the disassembly sleeve 12 is in close contact with the upper surface of the nut 4. At this time, the positioning groove 2 and the positioning tooth 125 are just engaged. The cylinder body 123 is rotated, and the cylinder body 123 drives the slider 124 to rotate synchronously. The slider 124 drives the nut 4 to rotate through the positioning tooth 125. When the torque on the screw 5 reaches the set value, the slider 124 moves up along the ramp 11 under the action of axial force. At this time, the strong spring 122 is compressed until the positioning groove 2 and the positioning tooth 125 are separated. Since the torque has reached the set value, rotating the disassembly sleeve 12 at this time will not drive the screw 5 to rotate.

[0153] After the screw 5 is installed, screw the nut 8 onto the screw 5 until the frustum sleeve 7 is partially inserted into the frustum positioning groove 10. The frustum positioning groove 10 presses against the frustum sleeve 7, causing the nut 8 to bite tightly against the outer surface of the screw 5, thereby achieving a fixed locking mechanism.

[0154] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method of processing a steel for an automotive fastener, characterized by, The method comprises the following steps: S1. Cold forming: S1.

1. Subjecting the steel coil to decarburization treatment to remove the surface carbon layer; S1.

2. Subjecting the decarburized steel to multi-stage stretching to control the reduction of area to be less than or equal to 15%; S1.

3. Forming the stretched material into a fastener blank on a cold header; S1.

4. Cutting the blank to obtain a standard size steel segment; S2. High-purity nitrogen preparation: S2.

1. Obtaining crude nitrogen gas produced by air fractionation, which contains 35 vol% oxygen; S2.

2. Passing the crude nitrogen gas into a purification device filled with composite molecular sieve; S2.

3. Performing catalytic deoxidation at 250-350℃, which involves the following processes: ① Oxygen reacts with copper components in the molecular sieve: 2Cu + O2→ 2CuO ② Carbon carrier reduces copper oxide: 2CuO + C→ 2Cu + CO2↑ S2.

4. Collecting the deoxidized nitrogen gas, which contains less than or equal to 0.05% oxygen; S3. High-temperature heat treatment: S3.

1. Placing the steel segment obtained in S1 into a heat treatment furnace; S3.

2. Passing the high-purity nitrogen gas obtained in S2 into the furnace at a flow rate of 510 L / min; S3.

3. Maintaining the temperature at 800-1100℃ for 10-60 minutes; S4. Surface strengthening treatment: S4.

1. Placing the steel segment after high-temperature heat treatment into an ion nitriding furnace and passing a mixed gas of ammonia and nitrogen into the furnace, wherein the proportion of ammonia is 30-50%; S4.

2. Performing ion nitriding treatment at 500-600℃ and a pressure of 0.1-0.3 MPa for 36 hours; S5. Precise straightening treatment: S5.

1. Detecting the straightness of the steel segment using a laser measuring instrument; S5.

2. According to the detection results, using a hydraulic straightening machine to perform multi-point and step-by-step straightening of the steel segment, and controlling the straightening amount to be 0.01-0.03 mm each time.

2. The method of claim 1, wherein: The composite molecular sieve is composed of honeycomb carbon carrier loaded with nano copper particles, and the mass ratio of copper to carbon is 1:(0.8-1.5).

3. The method of claim 1, wherein: In step S2.3, the deoxidation reaction temperature is preferably 280-320℃, and the reaction pressure is 0.2-0.5 MPa.

4. The method of claim 1, wherein: The copper component of the molecular sieve is regenerated in situ in the reaction, with a single regeneration cycle capable of treating >1000 m 3 of crude nitrogen per ton of molecular sieve.

5. The method of claim 1, wherein: In step S3.2, the nitrogen gas needs to be subjected to deep drying treatment with a dew point of less than or equal to 60℃ before being passed into the furnace.

6. The method of claim 1, wherein: In step S1.2, the multi-stage stretching includes first rough stretching at a deformation rate of 20-30%, and then fine stretching at a deformation rate of 50-100%.

7. The method of claim 1, wherein: In step S4.1, the flow rate of the mixed gas is calculated by the following formula: Q = k × V × (1 + α × T) Wherein, Q is the flow rate of the mixed gas (L / h), k is a coefficient with a value range of 1.2-1.5, V is the effective volume of the ion nitriding furnace (L), α is the temperature coefficient with a value of 0.003 / ℃, and T is the ion nitriding treatment temperature (℃).

8. The method of claim 1, wherein: In step S5.2, the straightness error after straightening is evaluated by the following formula: δ = (L1-L2) / L0 × 100% Wherein, δ is the straightness error (%), L1 is the maximum bending length of the steel segment before straightening (mm), L2 is the maximum bending length of the steel segment after straightening (mm), and L0 is the standard length of the steel segment (mm), and δ is required to be less than or equal to 0.05%.

9. A fastener for an automobile, characterized by The fastener is made of the steel for automobile fastener processed by the method of any one of the above claims. Also include screw (5), the upper end of the screw (5) is provided with a screw cap (4), the upper surface of the screw cap (4) is provided with an annular table (3), the inner side of the annular table (3) is centrally provided with a circular table (1), the inner side of the annular table (3) is uniformly distributed with a positioning groove (2) at the edge, and the edge of the positioning groove (2) is provided with a slope (11); The outer side of the screw (5) is sequentially screwed with a nut two (9) and a nut one (8) from top to bottom, the outer side of the nut one (8) is provided with a circular table sleeve (7) at the upper end, the outer side of the nut one (8) and the circular table sleeve (7) is provided with a strip-shaped groove (6), and the inner side of the nut two (9) is provided with a circular table positioning groove (10) corresponding to the insertion of the circular table sleeve (7) at the lower end.

10. The fastener for an automobile according to claim 9, wherein: Also include a disassembly sleeve (12) for disassembling fasteners, the disassembly sleeve (12) includes a barrel (123), the inside of the barrel (123) is sequentially provided with a secondary cavity (121) and a primary cavity (126) from top to bottom, the cross section of the primary cavity (126) is columnar, the cross section of the secondary cavity (121) is polygonal, the inner side of the secondary cavity (121) is slidably connected with a sliding block (124), the lower end surface of the sliding block (124) is provided with a positioning tooth (125), the inner side of the secondary cavity (121) is connected with the upper end surface of the sliding block (124) through a strong spring (122) at the upper end, the positioning tooth (125) is engaged with the positioning groove (2) corresponding to the setting, and the primary cavity (126) is correspondingly provided with the annular table (3) through sleeve connection.

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