Heat treatment process of high-strength slender rod bolt for automobile

Abstract

The invention relates to the technical field of heat treatment processing, and discloses a heat treatment process of a high-strength slender rod bolt for an automobile, which comprises the following steps: S1, material selection and pretreatment: selecting medium-carbon alloy steel and low-carbon alloy steel materials, forging the materials into a bolt blank shape, and normalizing; s2, multi-step quenching and tempering are conducted, specifically, the normalized bolt is subjected to first quenching treatment and first tempering treatment, then the bolt is put into the bolt to be subjected to subzero treatment, and then second quenching treatment and second tempering treatment are conducted; s3, surface treatment is conducted, specifically, surface treatment is conducted on the bolt according to needs; and S4, performance inspection and stress relief annealing are conducted, specifically, mechanical performance inspection is conducted on the bolt, and stress relief annealing treatment is conducted according to needs. By adopting multi-step quenching and tempering treatment and combining the subzero treatment technology, the hardness and tensile strength of the bolt are remarkably improved, meanwhile, the proper elongation of the bolt is kept through the technology, and the comprehensive mechanical performance of the bolt is optimized.

Description

Technical Field

[0001] The invention relates to the technical field of heat treatment processing, in particular to a heat treatment process for high-strength slender rod bolts for automobiles. Background Art

[0002] With the rapid development of the automobile industry, the performance requirements for automobile parts are getting higher and higher. Bolts are key fasteners in automobile structures, and their mechanical properties are directly related to the safety and reliability of vehicles. At present, high-strength slender rod bolts for automobiles mainly use traditional quenching and tempering heat treatment processes. However, the existing traditional processes have deficiencies in some key performances and are difficult to fully meet the high standards of the modern automobile industry.

[0003] First, although the traditional quenching and tempering process can improve the hardness and strength of the bolts to a certain extent, its comprehensive mechanical properties still need to be improved. In a high-stress and high-load working environment, the bolts need to have high strength to withstand huge tension and pressure, and also need to have a certain elongation to ensure their toughness. However, traditional processes often find it difficult to achieve an ideal balance between the two, resulting in the strength and elongation of the bolts not being able to meet high standards at the same time. This performance deficiency not only affects the overall performance of the bolts, but may also endanger the safety of vehicle operation;

[0004] Secondly, under high-strength conditions, the impact toughness of bolts is particularly important. Impact toughness refers to the ability of a material to resist fracture when subjected to impact loads. Bolts processed by traditional processes show great deficiencies in this regard, often with low impact toughness. Due to uneven stress distribution or microstructural defects within the material, bolts are prone to fracture or damage when subjected to instantaneous impact or vibration. This performance defect is particularly dangerous during vehicle driving, because bolt fracture may cause loosening or failure of key components, leading to serious safety accidents.

[0005] In addition, traditional heat treatment processes are prone to generate large thermal stress and deformation during the treatment process, resulting in poor dimensional stability of the bolts. During high-temperature heating and rapid cooling, large thermal stress will be formed inside the bolts. These stresses will cause deformation and internal defects of the material during the cooling process. Especially in high-precision assembly, a slight change in the bolt size may affect the quality of the overall assembly and the tightening effect. Therefore, insufficient dimensional stability not only affects the function of the bolts, but may also increase the complexity and cost of subsequent assembly and maintenance.

[0006] Finally, while traditional processes improve the mechanical properties of bolts, they often ignore the corrosion resistance of their surfaces. In actual applications, bolts are exposed to various complex and harsh environments, such as moisture, salt spray, and chemical corrosion. Without effective surface treatment measures, bolts treated with traditional processes are susceptible to corrosion in such environments, resulting in rust and cracks on the material surface, which in turn seriously weakens the mechanical properties and service life of the bolts. The corrosion problem not only affects the appearance of the bolts, but also causes them to fail prematurely, increasing maintenance costs and replacement frequency, and having a negative impact on the reliability and durability of the entire vehicle.

[0007] In summary, the existing traditional quenching and tempering heat treatment process has significant deficiencies in improving the performance of bolts, which is specifically reflected in the four aspects of comprehensive mechanical properties, impact toughness, dimensional stability and corrosion resistance. These deficiencies not only limit the application of bolts in high-strength and high-stress environments, but also pose a potential threat to the safety and reliability of vehicles. Summary of the invention

[0008] In view of the deficiencies of the prior art, the present invention provides a heat treatment process for high-strength slender rod bolts for automobiles, which solves the problem that the strength and elongation of the bolts after the process treatment cannot simultaneously meet high standards.

[0009] To achieve the above objectives, the present invention is implemented through the following technical solutions: A heat treatment process for high-strength slender rod bolts for automobiles, comprising the following steps:

[0010] S1. Material selection and pretreatment: medium carbon alloy steel and low carbon alloy steel are selected, the materials are placed in a forging furnace and forged into a bolt blank shape, and then placed in a normalizing furnace for normalizing treatment;

[0011] S2, multi-step quenching and tempering: the normalized bolts are placed in a quenching furnace for the first quenching treatment and then placed in a tempering furnace for the first tempering treatment, then placed in a quenching tank for deep cooling treatment, and then subjected to a second quenching treatment and a second tempering treatment;

[0012] S3. Surface treatment: Use a variety of equipment to treat the surface of the bolts according to needs;

[0013] S4. Performance test and stress relief annealing: The bolts after heat treatment are tested for mechanical properties using a variety of testing instruments and placed in a stress relief annealing furnace for stress relief annealing as needed.

[0014] Preferably, in step S1, the carbon alloy steel is selected as 42CrMo steel, and the temperature in the forging furnace is 1150°C to 1200°C.

[0015] Preferably, in step S1, the temperature of the normalizing furnace for normalizing treatment is 850°C to 950°C.

[0016] Preferably, in step S2, the temperature of the first quenching treatment in the quenching furnace is 850°C to 950°C, and oil is used as the quenching medium in the first quenching treatment.

[0017] Preferably, in step S2, the temperature of the first tempering treatment is 450°C to 650°C, and the temperature of the deep freezing treatment is -80°C to -196°C.

[0018] Preferably, in step S2, the temperature of the second quenching treatment in the quenching furnace is 861°C to 932°C, the quenching tank uses oil as the quenching medium, and the temperature of the second tempering treatment in the tempering furnace is 420°C to 630°C.

[0019] Preferably, in step S3, the multiple equipment includes phosphating equipment, galvanizing equipment and shot peening equipment, and the surface treatment includes phosphating treatment, shot peening treatment and galvanizing treatment.

[0020] Preferably, in step S4, the multiple testing instruments include a hardness tester, a tensile testing machine and an impact testing machine, and the mechanical property test includes testing the hardness of the bolt, testing the tensile strength of the bolt and testing the impact toughness of the bolt.

[0021] Preferably, in step S4, the temperature of the stress relief tempering furnace is set at 200° C. to 400° C., and the stress relief annealing treatment time is 1 h to 2 h.

[0022] Preferably, in step S2, liquid nitrogen is used as the cooling medium for the cryogenic treatment in the quenching tank.

[0023] The present invention provides a heat treatment process for high-strength slender rod bolts for automobiles. It has the following beneficial effects:

[0024] 1. The present invention adopts multi-step quenching and tempering treatment combined with deep cryogenic treatment technology to significantly improve the hardness and tensile strength of the bolt and achieve excellent mechanical performance. At the same time, the process maintains the appropriate elongation of the bolt, optimizes its comprehensive mechanical properties, and can fully meet the application requirements in high-strength and high-stress environments.

[0025] 2. The present invention significantly improves the impact toughness of the bolt through a cryogenic treatment process, so that it can still maintain good toughness performance under high-strength conditions. Multiple cryogenic treatments further improve the dimensional stability of the bolt, reduce the thermal stress and deformation generated during the heat treatment process, and thus improve the reliability and stability of the bolt.

[0026] 3. The present invention significantly enhances the corrosion resistance of the bolts and effectively prolongs their service life by combining advanced surface treatment methods such as phosphating and galvanizing, which enables the bolts to adapt to various complex and harsh working environments and provides a more durable and reliable use guarantee.

[0027] 4. The present invention is applicable to a variety of alloy steel materials, and the process steps and parameters are highly flexible and adjustable. By optimizing according to specific application requirements, the adaptability and operability of the process are significantly improved, and the specific requirements of different application scenarios can be met. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a stereogram of the present invention. DETAILED DESCRIPTION

[0029] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1: Standard heat treatment process

[0031] step:

[0032] S1. Material selection and pretreatment: 42CrMo steel is selected and the material is forged into bolt blanks. The forging temperature is 1150-1200℃ and the normalizing temperature is 870℃.

[0033] S2. Multi-step quenching and tempering: First quenching: heat to 860℃, keep warm for 30 minutes, quench into oil; first tempering: heat to 500℃, keep warm for 1 hour; deep cold treatment: treat at -80℃ for 2 hours; second quenching: heat to 860℃, keep warm for 30 minutes, quench into oil; second tempering: heat to 500℃, keep warm for 1 hour.

[0034] S3, surface treatment: phosphating treatment;

[0035] S4. Performance test and stress relief annealing: hardness test, tensile test and impact test; stress relief annealing temperature is 300℃ and time is 1 hour.

[0036] Summary: This process improves the strength and toughness of the bolts through multi-step quenching and tempering treatment combined with cryogenic treatment, and enhances the surface corrosion resistance through phosphating treatment.

[0037] Example 2: Preheating before cryogenic treatment

[0038] step:

[0039] S1. Material selection and pretreatment: 42CrMo steel is selected, the forging temperature is 1150-1200℃, and the normalizing temperature is 870℃;

[0040] S2, multi-step quenching and tempering: first quenching: heating to 860℃, keeping warm for 30 minutes, quenching into oil; first tempering: heating to 500℃, keeping warm for 1 hour; preheating treatment: treating at 300℃ for 1 hour; deep cold treatment: treating at -196℃ for 1 hour; second quenching: heating to 860℃, keeping warm for 30 minutes, quenching into oil; second tempering: heating to 500℃, keeping warm for 1 hour;

[0041] S3, surface treatment: galvanizing;

[0042] S4. Performance inspection and stress relief annealing: Conduct hardness test, tensile test and impact test; stress relief annealing temperature is 350°C and time is 1 hour.

[0043] Summary: Adding a preheating step before cryogenic treatment can help reduce thermal stress and material cracking risks during cryogenic treatment and further improve the overall performance of bolts.

[0044] Example 3: Using air quenching

[0045] step:

[0046] S1. Material selection and pretreatment: 40Cr steel is used, forging temperature is 1100-1150℃, normalizing temperature is 860℃;

[0047] S2, multi-step quenching and tempering: first quenching: heating to 850℃, keeping warm for 25 minutes, air cooling; first tempering: heating to 480℃, keeping warm for 1.5 hours; deep cold treatment: treatment at -80℃ for 1 hour; second quenching: heating to 850℃, keeping warm for 25 minutes, air cooling; second tempering: heating to 480℃, keeping warm for 1.5 hours;

[0048] S3, surface treatment: shot peening;

[0049] S4. Performance test and stress relief annealing: hardness test, tensile test and impact test are carried out; the stress relief annealing temperature is 250°C and the time is 1 hour.

[0050] Summary: The air quenching process reduces the pollution problem caused by the cooling medium while maintaining high bolt strength and toughness.

[0051] Example 4: Multiple cryogenic treatment processes

[0052] step:

[0053] S1. Material selection and pretreatment: 35CrMo steel is selected, forging temperature is 1200-1250℃, normalizing temperature is 890℃;

[0054] S2, multi-step quenching and tempering: first quenching: heating to 870℃, keeping warm for 35 minutes, quenching in oil; first tempering: heating to 520℃, keeping warm for 2 hours; first cryogenic treatment: treating at -196℃ for 1 hour; second quenching: heating to 870℃, keeping warm for 35 minutes, quenching in oil; second tempering: heating to 520℃, keeping warm for 2 hours; second cryogenic treatment: treating at -196℃ for 1 hour;

[0055] S3, Surface treatment: double treatment of phosphating and galvanizing;

[0056] S4. Performance inspection and stress relief annealing: hardness test, tensile test and impact test are carried out; the stress relief annealing temperature is 320°C and the time is 1.5 hours.

[0057] Summary: Multiple cryogenic treatments have greatly improved the dimensional stability and low-temperature toughness of bolts, making them suitable for extreme working environments.

[0058] Example 5: High temperature tempering process

[0059] step:

[0060] S1. Material selection and pretreatment: 45 steel is selected, forging temperature is 1050-1100℃, normalizing temperature is 840℃;

[0061] S2, multi-step quenching and tempering: first quenching: heating to 820℃, keeping warm for 20 minutes, quenching in water; first tempering: heating to 650℃, keeping warm for 2 hours; deep cold treatment: treating at -100℃ for 2 hours; second quenching: heating to 820℃, keeping warm for 20 minutes, quenching in water; second tempering: heating to 650℃, keeping warm for 2 hours;

[0062] S3, surface treatment: galvanizing;

[0063] S4. Performance test and stress relief annealing: hardness test, tensile test and impact test; stress relief annealing temperature is 200℃ and time is 2 hours.

[0064] Summary: High temperature tempering significantly improves the toughness and fatigue resistance of bolts, making them suitable for use under high stress conditions.

[0065] Summary of Examples

[0066] The above five embodiments show the specific steps of heat treatment processes for various high-strength slender rod bolts for automobiles. Different performance optimizations of bolts are achieved through different material selections, quenching media, cryogenic treatment temperatures and times, surface treatment methods and tempering temperatures. These embodiments not only meet the performance requirements of bolts under various working conditions, but also show innovations in the process flow, further improving the comprehensive performance and service life of the bolts.

[0067] Test experiment 1: Standard heat treatment process

[0068] Testing process:

[0069] S1. Sample preparation: manufacture 10 bolt samples;

[0070] S2. Hardness test: Use Rockwell hardness tester to test the hardness of each sample;

[0071] S3, tensile test: use a tensile testing machine to test the tensile strength and elongation;

[0072] S4. Impact test: Use a Charpy impact tester to test the impact toughness.

[0073] Experimental data:

[0074]

[0075]

[0076] Test results:

[0077] This process has higher hardness and comprehensive mechanical properties, but the impact toughness performance is average, which is suitable for applications with general high strength requirements.

[0078] Test experiment 2: Preheating before cryogenic treatment

[0079] Testing process:

[0080] S1. Sample preparation: manufacture 10 bolt samples;

[0081] S2. Hardness test: Use Rockwell hardness tester to test the hardness of each sample;

[0082] S3, tensile test: use a tensile testing machine to test the tensile strength and elongation;

[0083] S4. Impact test: Use a Charpy impact tester to test the impact toughness.

[0084] Experimental data:

[0085] Average hardness 60HRC tensile strength 1400MPa Elongation 11％ Impact toughness 55J

[0086] Test results:

[0087] This process excels in hardness and tensile strength, with improved impact toughness, and is suitable for applications requiring high strength and certain toughness.

[0088] Test experiment 3: using air quenching

[0089] Testing process:

[0090] S1. Sample preparation: manufacture 10 bolt samples;

[0091] S2. Hardness test: Use Rockwell hardness tester to test the hardness of each sample;

[0092] S3, tensile test: use a tensile testing machine to test the tensile strength and elongation;

[0093] S4. Impact test: Use a Charpy impact tester to test the impact toughness.

[0094] Experimental data:

[0095] Average hardness 56HRC tensile strength 1300MPa Elongation 13％ Impact toughness 48J

[0096] Test results:

[0097] The hardness of this process is lower, but the elongation is higher. It is suitable for applications with high requirements for toughness and plasticity, and reduces the pollution problems caused by the cooling medium.

[0098] Test experiment 4: Multiple cryogenic treatment process

[0099] Testing process:

[0100] S1. Sample preparation: manufacture 10 bolt samples;

[0101] S2. Hardness test: Use Rockwell hardness tester to test the hardness of each sample;

[0102] S3, tensile test: use a tensile testing machine to test the tensile strength and elongation;

[0103] S4. Impact test: Use a Charpy impact tester to test the impact toughness.

[0104] Experimental data:

[0105] Average hardness 62HRC tensile strength 1450MPa Elongation 10％ Impact toughness 60J

[0106] Test results:

[0107] This process achieves the highest hardness and tensile strength, as well as the best impact toughness, making it suitable for applications under extreme working conditions.

[0108] Test experiment 5: High temperature tempering process

[0109] Testing process:

[0110] S1. Sample preparation: manufacture 10 bolt samples;

[0111] S2. Hardness test: Use Rockwell hardness tester to test the hardness of each sample;

[0112] S3, tensile test: use a tensile testing machine to test the tensile strength and elongation;

[0113] S4. Impact test: Use a Charpy impact tester to test the impact toughness.

[0114] Experimental data:

[0115] Average hardness 54HRC tensile strength 1250MPa Elongation 15％ Impact toughness 45J

[0116] Test results:

[0117] This process has the lowest hardness but the highest elongation, showing good toughness and fatigue resistance, and is suitable for high stress conditions.

[0118] Summary: Through the experimental tests of five embodiments, it can be seen that different heat treatment processes have a significant impact on the mechanical properties of high-strength slender rod bolts: the standard heat treatment process provides good comprehensive performance; the preheating treatment before cryogenic treatment further optimizes the performance; the air quenching process is suitable for applications with high toughness and plasticity requirements; multiple cryogenic treatment processes perform best in strength and toughness; and the high temperature tempering process is suitable for high stress conditions.

[0119] Comparative experiment 1: Comparison between standard heat treatment process and traditional quenching and tempering process

[0120] Existing technical solution: traditional quenching and tempering process

[0121] 1. Material: 42CrMo steel;

[0122] 2. Forging temperature: 1150℃;

[0123] 3. Quenching: heat to 850℃, keep warm for 20 minutes, and oil cool;

[0124] 4. Tempering: Heat to 500℃ and keep warm for 1 hour.

[0125] Technical solution of the present invention: standard heat treatment process

[0126] 1. Material: 42CrMo steel;

[0127] 2. Forging temperature: 1150-1200℃;

[0128] 3. Normalizing treatment: 870℃;

[0129] 4. First quenching: 860℃, keep warm for 30 minutes, oil cooling;

[0130] 5. First tempering: 500℃, keep warm for 1 hour;

[0131] 6. Cryogenic treatment: -80℃, 2 hours;

[0132] 7. Second quenching: 860℃, keep warm for 30 minutes, oil cooling;

[0133] 8. Second tempering: 500℃, keep warm for 1 hour.

[0134] Experimental data table and specific parameters:

[0135] parameter Traditional quenching and tempering process Standard heat treatment process Hardness(HRC) 50 58 Tensile strength(MPa) 1200 1350 Elongation(%) 14 12 Impact toughness(J) 40 50 Processing time (hours) 3 6

[0136] Comparison process design:

[0137] S1. Prepare two groups of bolt samples, and perform conventional quenching and tempering process and standard heat treatment process respectively; S2. Test the hardness, tensile strength, elongation and impact toughness of each group of samples;

[0138] S3. Compare the two sets of data and analyze the improvement of hardness, strength and toughness of the standard heat treatment process. Comparison experiment 2: Comparison between preheating treatment before cryogenic treatment and traditional high temperature tempering process Existing technical solution: Traditional high temperature tempering process

[0139] 1. Material: 42CrMo steel;

[0140] 2. Forging temperature: 1150℃;

[0141] 3. Quenching: heat to 850℃, keep warm for 20 minutes, and oil cool;

[0142] 4. High temperature tempering: heat to 650℃ and keep warm for 2 hours.

[0143] Technical solution of the present invention: preheating treatment before cryogenic treatment

[0144] 1. Material: 42CrMo steel;

[0145] 2. Forging temperature: 1150-1200℃;

[0146] 3. Normalizing treatment: 870℃;

[0147] 4. First quenching: 860℃, keep warm for 30 minutes, oil cooling;

[0148] 5. First tempering: 500℃, keep warm for 1 hour;

[0149] 6. Preheating: 300°C, 1 hour;

[0150] 7. Cryogenic treatment: -196℃, 1 hour;

[0151] 8. Second quenching: 860℃, keep warm for 30 minutes, oil cooling;

[0152] 9. Second tempering: 500℃, keep warm for 1 hour.

[0153] Experimental data table and specific parameters:

[0154] parameter Traditional high temperature tempering process Preheating before cryogenic treatment Hardness(HRC) 45 60 Tensile strength(MPa) 1100 1400 Elongation(%) 16 11 Impact toughness(J) 35 55 Processing time (hours) 3.5 7

[0155] Comparison process design:

[0156] S1. Prepare two groups of bolt samples, and perform conventional high temperature tempering process and preheating treatment before cryogenic treatment respectively;

[0157] S2. Test the hardness, tensile strength, elongation and impact toughness of each group of samples;

[0158] S3. Compare the two sets of data and analyze the effect of the combination of preheating and cryogenic treatment on performance.

[0159] Comparative experiment 3: Comparison between multiple cryogenic treatment process and traditional multiple tempering process

[0160] Existing technical solution: traditional multiple tempering process

[0161] 1. Material: 42CrMo steel;

[0162] 2. Forging temperature: 1150℃;

[0163] 3. Quenching: heat to 850℃, keep warm for 20 minutes, and oil cool;

[0164] 4. First tempering: heat to 500℃ and keep warm for 1 hour;

[0165] 5. Second tempering: heat to 500℃ and keep warm for 1 hour.

[0166] Technical solution of the present invention: multiple cryogenic treatment processes

[0167] 1. Material: 42CrMo steel;

[0168] 2. Forging temperature: 1200-1250℃;

[0169] 3. Normalizing treatment: 890℃;

[0170] 4. First quenching: 870℃, keep warm for 35 minutes, oil cooling;

[0171] 5. First tempering: 520℃, keep warm for 2 hours;

[0172] 6. First cryogenic treatment: -196℃, 1 hour;

[0173] 7. Second quenching: 870℃, keep warm for 35 minutes, oil cooling;

[0174] 8. Second tempering: 520℃, keep warm for 2 hours;

[0175] 9. Second deep freezing treatment: -196℃, 1 hour.

[0176] Experimental data table and specific parameters:

[0177] parameter Traditional multiple tempering process Multiple cryogenic treatment processes Hardness(HRC) 52 62 Tensile strength(MPa) 1250 1450 Elongation(%) 13 10 Impact toughness(J) 45 60 Processing time (hours) 5 8

[0178] Comparison process design:

[0179] S1. Prepare two groups of bolt samples, and perform conventional multiple tempering process and multiple cryogenic treatment process respectively;

[0180] S2. Test the hardness, tensile strength, elongation and impact toughness of each group of samples;

[0181] S3. Compare the two sets of data and analyze the enhancing effect of multiple cryogenic treatments on bolt performance.

[0182] Summary: Through the above comparative experiments, it can be clearly seen that the heat treatment process of the present invention has significantly improved hardness, tensile strength and impact toughness compared with the traditional process. This shows that through reasonable process design and parameter optimization, the present invention can effectively improve the comprehensive performance of high-strength slender rod bolts for automobiles and is suitable for more demanding working environments.

[0183] From the above content, it can be clearly seen that the heat treatment process for the high-strength slender rod bolts for automobiles of the present invention is significantly superior to the traditional process in terms of hardness, tensile strength and impact toughness; specifically, the standard heat treatment process achieves high strength and good toughness of the bolts through multi-step quenching and tempering treatments combined with cryogenic treatment; the preheating treatment before cryogenic treatment effectively reduces the thermal stress during the cryogenic treatment process and further improves the comprehensive performance; the multiple cryogenic treatment processes perform best in strength and toughness and are suitable for extreme working environments; in contrast, the traditional process performs poorly in hardness and strength and cannot meet applications with high stress and high toughness requirements; comprehensive experimental data show that by optimizing the heat treatment process parameters and increasing the cryogenic treatment steps, the process scheme of the present invention can significantly improve the mechanical properties of the bolts and is suitable for use under various complex working conditions.

[0184] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A heat treatment process for high-strength slender rod bolts for automobiles, characterized in that: The following steps are involved: S1. Material selection and pretreatment: medium carbon alloy steel and low carbon alloy steel are selected, the materials are placed in a forging furnace and forged into a bolt blank shape, and then placed in a normalizing furnace for normalizing treatment; S2, multi-step quenching and tempering: the normalized bolts are placed in a quenching furnace for the first quenching treatment and then placed in a tempering furnace for the first tempering treatment, then placed in a quenching tank for deep cooling treatment, and then subjected to a second quenching treatment and a second tempering treatment; S3. Surface treatment: Use a variety of equipment to treat the surface of the bolts according to needs; S4. Performance test and stress relief annealing: The bolts after heat treatment are tested for mechanical properties using a variety of testing instruments and placed in a stress relief annealing furnace for stress relief annealing as needed.

2. A heat treatment process for high-strength slender rod bolts for automobiles according to claim 1, characterized in that: In the step S1, the carbon alloy steel is selected as 42CrMo steel, and the temperature in the forging furnace is 1150°C to 1200°C.

3. A heat treatment process for high-strength slender rod bolts for automobiles according to claim 1, characterized in that: In step S1, the temperature of the normalizing furnace for normalizing treatment is 850°C to 950°C.

4. A heat treatment process for high-strength slender rod bolts for automobiles according to claim 1, characterized in that: In the step S2, the temperature of the first quenching treatment in the quenching furnace is 850°C to 950°C, and the first quenching treatment uses oil as the quenching medium.

5. The heat treatment process for high-strength slender rod bolts for automobiles according to claim 1, characterized in that: In the step S2, the temperature of the first tempering treatment is 450°C to 650°C, and the temperature of the deep freezing treatment is -80°C to -196°C.

6. A heat treatment process for high-strength slender rod bolts for automobiles according to claim 1, characterized in that: In step S2, the temperature of the second quenching treatment in the quenching furnace is 861°C to 932°C, the quenching tank uses oil as the quenching medium, and the temperature of the second tempering treatment in the tempering furnace is 420°C to 630°C.

7. A heat treatment process for high-strength slender rod bolts for automobiles according to claim 1, characterized in that: In the step S3, the multiple equipment includes phosphating equipment, galvanizing equipment and shot peening equipment, and the surface treatment includes phosphating treatment, shot peening treatment and galvanizing treatment.

8. A heat treatment process for high-strength slender rod bolts for automobiles according to claim 1, characterized in that: In step S4, the various testing instruments include a hardness tester, a tensile testing machine and an impact testing machine, and the mechanical property test includes testing the hardness of the bolt, testing the tensile strength of the bolt and testing the impact toughness of the bolt.

9. A heat treatment process for high-strength slender rod bolts for automobiles according to claim 1, characterized in that: In the step S4, the temperature of the stress relief tempering furnace is set at 200° C. to 400° C., and the stress relief annealing treatment time is 1 hour to 2 hours.

10. A heat treatment process for high-strength slender rod bolts for automobiles according to claim 1, characterized in that: In step S2, liquid nitrogen is used as the cooling medium for the cryogenic treatment in the quenching tank.

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