Production process of weathering resistant steel bolt

Abstract

The invention discloses a production process of a weathering resistant steel bolt. The production process comprises the following steps: S1, spheroidizing annealing; steel is heated, the temperature is set to be 760-775 DEG C above AC1, heat preservation is conducted, furnace cooling is conducted to 700 DEG C, the temperature is kept constant for 6-8 h, furnace cooling is conducted to 450 DEG C, furnace discharging is conducted, the hardness is detected to be 74-78 HRB, and the spheroidization rate is larger than or equal to 70%; s2, acid pickling; the bolt is placed in an acid solution, the surface of the bolt is completely acidified, after acid pickling is finished, washing is conducted again, and the acid solution on the surface of the bolt is cleaned away; s3, removing oxide skin; oxide generated by reaction of the steel surface and oxygen in air during high-temperature treatment is removed through a mechanical, chemical or thermal method; s4, phosphating is conducted; soaking the steel in a phosphoric acid solution to form a layer of phosphate film on the surface of the steel; s5, drawing and cold heading; and drawing the steel to a specified size by stretching the steel. According to the technical scheme, the corrosion resistance of the steel structure is improved, the surface quality is improved, and the cold heading performance of the steel structure is improved.

Description

Technical Field

[0001] This invention relates to the technical field of steel structure manufacturing processes, and in particular to a manufacturing process for weather-resistant steel bolts. Background Technology

[0002] High-strength bolts are used in steel structures for connections due to their simplicity, replaceability, fatigue resistance, stability, and safety. Large-scale building projects require even higher strength from the bolts used for connections. In my country, most high-strength bolts are made of alloy structural steels such as ML20MnTiB, 35VB, and ML40Cr, which are not resistant to atmospheric corrosion. Even with phosphate treatment, they still exhibit significant uniform corrosion and crevice corrosion. Furthermore, ordinary high-strength bolts are susceptible to stress corrosion and corrosion fatigue, posing a risk of sudden brittle fracture and low-stress failure, thus creating significant safety hazards for steel structures such as bridges. Summary of the Invention

[0003] The main objective of this invention is to provide a production process for weathering steel bolts, which aims to improve the corrosion resistance of steel structures, enhance surface quality, and improve their cold heading properties.

[0004] To achieve the above objectives, the present invention proposes a manufacturing process for weathering steel bolts, comprising the following steps;

[0005] S1: Spheroidizing annealing;

[0006] By heating the steel, the temperature is set at A. C1 The sample is kept at a temperature between 760 and 775°C, then furnace-cooled to 700°C for 6 to 8 hours, and then furnace-cooled to 450°C before being removed from the furnace. The hardness is tested to be 74 to 78 HRB and the spheroidization rate is ≥70%.

[0007] S2: Pickling;

[0008] The bolts are placed in an acid solution to completely acidify their surface. After the acid pickling is complete, they are washed with water again to remove the acid from the bolt surface.

[0009] S3: Remove oxide scale;

[0010] Remove oxides generated on the surface of steel by mechanical, chemical, or thermal methods when they react with oxygen in the air during high-temperature treatment;

[0011] S4: Phosphating;

[0012] The steel is immersed in a phosphoric acid solution, which forms a thin film of phosphate on the surface of the steel.

[0013] S5: Drawing and cold heading;

[0014] By stretching steel to a specified size, and utilizing the plasticity of metal, the precision wire is forged through a multi-station cold forging machine to achieve the shape and length of the bolt semi-finished product.

[0015] S6: Heat treatment;

[0016] Through ladle refining, the content of major alloying elements such as carbon, chromium, nickel, and manganese in steel is controlled within a smaller range than that of ordinary steel, the content of impurity elements (oxygen, sulfur, phosphorus, nitrogen, etc.) is reduced and controlled, and then the steel is quenched and tempered.

[0017] S7: Hydrogen removal treatment;

[0018] After the heat treatment process is completed, hydrogen removal treatment should be carried out. The temperature in the hydrogen removal furnace should be controlled at 170±10℃ and maintained for more than 8 hours.

[0019] S8: Packaging;

[0020] After the hydrogen removal treatment is completed, the bolts are blackened by the residual heat of tempering and then coated with anti-rust oil, while the nuts and washers are directly packaged after phosphating and saponification.

[0021] In one possible implementation, during the S6 heat treatment, the copper content is between 0.20% and 0.40%, the chromium + nickel + copper ratio should be greater than 1.30%, phosphorus is controlled at ≤0.015%, sulfur is controlled at ≤0.010%, and the phosphorus + sulfur ratio should be ≤0.020%.

[0022] In one possible implementation, in the S6 heat treatment, the quenching temperature is selected to be 860℃~900℃, and the tempering temperature is selected to be 430℃~470℃.

[0023] In one possible implementation, the heating and holding time of the quenched sample is controlled according to the operating speed of the mesh belt heating furnace, which is 120 and 90 minutes respectively. After heating, it is cooled with PAG aqueous solution, and the water temperature is controlled at 35±2℃. The tempering temperature holding time is controlled according to the operating speed of the mesh belt heating furnace, which is 135 minutes.

[0024] In one possible implementation, the nickel content is 0.30%.

[0025] In one possible implementation, the same batch of bolted assemblies in the S8 package should undergo a set of process inspections according to standards.

[0026] In one possible implementation, in the S8 package, the same batch of bolted assemblies should be supplied according to the guaranteed torque coefficient. The torque coefficient test of the assemblies should be conducted, and the average torque coefficient of the same batch of assemblies should be 0.110 to 0.150, and the standard deviation of the torque coefficient should not be greater than 0.010.

[0027] This invention utilizes ladle refining to control the content of major alloying elements such as carbon, chromium, nickel, and manganese in steel within a narrower range than ordinary steel. This results in steel with better structural uniformity, smaller fluctuations in mechanical properties, and reduced and controlled content of impurity elements (oxygen, sulfur, phosphorus, nitrogen, etc.), thereby lowering the content of non-metallic inclusions, improving surface quality, and enhancing cold heading properties. Compared to ordinary steel, weathering steel exhibits superior corrosion resistance because the trace alloying elements in weathering steel reduce the electrical conductivity of the rust layer, hindering further electrochemical reactions. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the chemical composition of XG295N steel, which is resistant to atmospheric corrosion and is used in the production process of weathering steel bolts according to the present invention.

[0030] Figure 2 This is a schematic diagram illustrating the mechanical requirements of NH8.8S bolts after heat treatment, representing the production process of weather-resistant steel bolts according to the present invention.

[0031] Figure 3 This is a schematic diagram illustrating the mechanical properties of XG295N steel M16 bolts after quenching and tempering, representing a production process for weather-resistant steel bolts according to the present invention.

[0032] Figure 4 This is a schematic diagram illustrating the microstructure of a weathering steel bolt produced by heat treatment at 860℃ during quenching, as described in this invention.

[0033] Figure 5 This is a schematic diagram illustrating the microstructure of a weathering steel bolt manufactured using a process described in this invention, involving quenching at 880℃.

[0034] Figure 6 This is a schematic diagram illustrating the microstructure of a weathering steel bolt produced by quenching at 900℃, as part of the manufacturing process of this invention.

[0035] Figure 7 This is a schematic diagram showing the microstructure after quenching and tempering, highlighting the production process of weathering steel bolts according to the present invention.

[0036] Figure 8 This is a schematic diagram of the four-stage spheroidized annealing microstructure of a weathering steel bolt manufacturing process according to the present invention. Figure 1 ;

[0037] Figure 9 This is a schematic diagram of the four-stage spheroidized annealing microstructure of a weathering steel bolt manufacturing process according to the present invention. Figure 2 ;

[0038] Figure 10 This is a production process flow diagram of a weathering steel bolt according to the present invention.

[0039] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0041] Example 1

[0042] This invention proposes a manufacturing process for weather-resistant steel bolts;

[0043] Reference Figures 1 to 10 It includes the following steps:

[0044] S1: Spheroidizing annealing;

[0045] By heating the steel, the temperature is set at A. C1 The sample is kept at a temperature between 760 and 775°C, then furnace-cooled to 700°C for 6 to 8 hours, and then furnace-cooled to 450°C before being removed from the furnace. The hardness is tested to be 74 to 78 HRB and the spheroidization rate is ≥70%.

[0046] S2: Pickling;

[0047] The bolts are placed in an acid solution to completely acidify their surface. After the acid pickling is complete, they are washed with water again to remove the acid from the bolt surface.

[0048] S3: Remove oxide scale;

[0049] Remove oxides generated on the surface of steel by mechanical, chemical, or thermal methods when they react with oxygen in the air during high-temperature treatment;

[0050] S4: Phosphating;

[0051] The steel is immersed in a phosphoric acid solution, which forms a thin film of phosphate on the surface of the steel.

[0052] S5: Drawing and cold heading;

[0053] By stretching steel to a specified size, and utilizing the plasticity of metal, the precision wire is forged through a multi-station cold forging machine to achieve the shape and length of the bolt semi-finished product.

[0054] S6: Heat treatment;

[0055] Through ladle refining, the content of major alloying elements such as carbon, chromium, nickel, and manganese in steel is controlled within a smaller range than that of ordinary steel, the content of impurity elements (oxygen, sulfur, phosphorus, nitrogen, etc.) is reduced and controlled, and then the steel is quenched and tempered.

[0056] S7: Hydrogen removal treatment;

[0057] After the heat treatment process is completed, hydrogen removal treatment should be carried out. The temperature in the hydrogen removal furnace should be controlled at 170±10℃ and maintained for more than 8 hours.

[0058] S8: Packaging;

[0059] After the hydrogen removal treatment is completed, the bolts are blackened by the residual heat of tempering and then coated with anti-rust oil, while the nuts and washers are directly packaged after phosphating and saponification.

[0060] XG295NH weathering steel is a premium wire rod produced by Xingtai Iron & Steel Co., Ltd. according to its enterprise standard "Weathering Cold Heading Steel Wire Rod". XG295N steel undergoes ladle refining, which allows for control of the content of major alloying elements such as carbon, chromium, nickel, and manganese within a narrower range than ordinary steel. This results in better uniformity of the steel's microstructure, smaller fluctuations in mechanical properties, and reduced and controlled content of impurity elements (oxygen, sulfur, phosphorus, nitrogen, etc.), thereby lowering the content of non-metallic inclusions, improving surface quality, and enhancing cold heading properties. Compared to ordinary steel, weathering steel exhibits superior corrosion resistance because the trace alloying elements in it reduce the electrical conductivity of the rust layer, hindering further electrochemical reactions. This corrosion-resistant property typically becomes apparent only after long-term use.

[0061] XG295N steel wire rod is used to produce large hexagonal head bolts for building steel structures. This steel is a low-carbon alloy steel containing alloying elements such as chromium and nickel. If the cooling rate is too fast after rolling, bainite structure is easily formed. Generally, the hot-rolled structure is mainly ferrite + pearlite + a small amount of bainite. The yield strength of the wire rod is greater than 500 MPa, and the elongation after fracture is greater than 10%, which has a certain impact on the drawing and cold heading of the wire rod. Therefore, the wire rod must undergo pre-spheroidizing annealing to obtain more ferrite and spheroidized pearlite structure. The temperature is set at A... C1 The furnace was held at 760℃~775℃, then furnace-cooled to 700℃ for 6h~8h isothermally for 4h, and then removed from the furnace at 450℃. The hardness was tested to be 74~78HRB, the spheroidization rate ≥70%, and the spheroidization structure grade approximately 4 (see...). Figures 8-9 The φ16mm wire is drawn to φ14.45mm, with a hardness of 86.2HRB~91.5HRB, which can meet the cold heading performance of XG295N steel.

[0062] Then, mechanical property tests were conducted on the finished bolts. The tests showed that for samples with a diameter ≤φ10, when using rapid quenching oil and a cooling rate greater than 90℃ / s, the microstructure of the samples consisted of acicular martensite and lath martensite, with proeutectoid ferrite decreasing as the cooling rate increased. For samples with a diameter >φ10, when using rapid quenching oil and a cooling rate less than 85℃ / s, the microstructure of the samples gradually transformed from bainite + martensite to martensite. In production practice, to ensure that the microstructure fully meets the GB / T3098.1 standard, a 3%–4% PAG aqueous solution quenching agent should be selected, and the cooling rate should be increased to greater than 100℃ / s to reduce the presence of undissolved ferrite in the core and avoid insufficient hardening, which would affect the mechanical properties.

[0063] Then, after heat treatment, XG295N steel wire rod can automatically form a dense protective rust layer on the surface of the steel structure, preventing further rust corrosion. After medium-temperature tempering at the optimal quenching temperature, XG295N steel can meet the mechanical properties of GB / T43151 steel structural bolts.

[0064] Moreover, generally speaking, the higher the atmospheric corrosion resistance index, the better the weather resistance. According to the American ASTM G101-04 "Guideline for the Evaluation of Atmospheric Corrosion Resistance of Low Alloy Steels", when the atmospheric corrosion resistance index of steel is greater than 6.0, the steel is considered to be corrosion-resistant steel and can be used without coating. According to calculations, the corrosion resistance index of XG295N steel is greater than 6.69, so it can be used without coating.

[0065] Reference Figures 1 to 5 In the S6 heat treatment, the copper content is between 0.20% and 0.40%, the chromium + nickel + copper ratio should be greater than 1.30%, the phosphorus content is controlled at ≤0.015%, the sulfur content is controlled at ≤0.010%, and the phosphorus + sulfur content should be ≤0.020%.

[0066] Considering the influence of chemical composition, the elements such as carbon, silicon, manganese, chromium, and nickel were optimized and controlled. The chemical composition of XG295N steel samples was analyzed using a LABSPARK 750A nanocrystal direct-reading spectrometer. Carbon is a major element in steel, forming a solid solution to increase strength. It is the most important element for ensuring the hardenability and martensitic strength of bolts. Its content has a significant impact on impact toughness. To improve toughness, the lower-middle limit of carbon content for medium-carbon steel was selected to refine the final microstructure. To ensure resistance to atmospheric corrosion, chromium is often added to steel. Chromium not only improves the corrosion resistance of steel but also significantly increases its strength, hardness, and wear resistance, but it also reduces plasticity and toughness. Adding a small amount of nickel can improve the occurrence of type II temper brittleness. The addition of chromium and copper is primarily to ensure that its atmospheric corrosion resistance meets standards. After adding copper, the corrosion resistance of XG295N steel is significantly improved, and a protective rust layer can quickly form on the surface. This rust layer is also denser and more protective. The copper content is controlled between 0.20% and 0.40%. To prevent copper from forming defects such as cracks on the steel surface, a certain amount of nickel is also added. The chromium + nickel + copper ratio should be greater than 1.30. Nickel can accumulate on the oxidized surface of the steel to form a protective film that hinders hydrogen intrusion. Adding a small amount of Ni can improve the atmospheric corrosion resistance of low-alloy steel. Nickel is also the most effective toughening element; it not only improves the fracture toughness of the steel, but the increased nickel content also increases the strength of bolts at the same tempering temperature. The main chemical composition of the XG295N steel used in the experiment is shown below. Figure 1 The requirements are as shown.

[0067] The test specimens were made from φ16 wire rod, which was drawn to φ15.45±0.02 after spheroidizing annealing. Utilizing the plasticity of the metal, the fine wire was forged using a multi-station cold forging machine to achieve the shape and length of an M16 bolt semi-finished product. Samples of the bolt manufacturing material were taken and treated with the same heat treatment process as in bolt manufacturing to prepare standard specimens for tensile testing.

[0068] Furthermore, the tensile test was conducted using actual bolts for wedge load testing, and the values ​​measured in the impact test and hardness test were also within the specified range. (See...) Figure 2 ;

[0069] according to Figure 1 as well as Figure 2 In summary, chromium, nickel, and molybdenum alloying elements can increase the diffusion activation energy of carbon in γ-Fe (austenite), reduce the diffusion rate of carbon, and delay the diffusion decomposition process of γ-Fe (austenite), making it easier to form martensitic structure after quenching. Since XG295N steel has a low carbon content and contains certain amounts of chromium and nickel alloying elements, using PAG aqueous solution quenching for heat treatment will improve the hardenability.

[0070] Reference Figures 3 to 9In the S6 heat treatment, the quenching temperature is selected as 860℃~900℃ and the tempering temperature is selected as 440℃~480℃.

[0071] Chromium, nickel, and molybdenum alloying elements can increase the diffusion activation energy of carbon in γ-Fe (austenite), reduce the diffusion rate of carbon, and delay the diffusion decomposition process of γ-Fe (austenite), making it easier to form martensitic structure after quenching. Since XG295N steel contains certain chromium and nickel alloying elements, a PAG aqueous solution cooling quenching test was conducted for heat treatment. Table 3 shows the test results of the mechanical properties of XG295N steel after quenching and tempering. From the three sets of test results listed, the mechanical properties of the steel structure bolts after tempering are basically within the standard range. The impact energy data obtained from samples with quenching temperatures of 860℃~900℃ and tempering temperatures of 440℃~480℃ are all good, and these are all within the ideal quenching heating temperature range.

[0072] Reference Figures 1 to 10 The nickel content is 0.30%;

[0073] The structural steel used in this application is named XG295N steel. Microstructure analysis after quenching shows that adding approximately 0.30% nickel to XG295N steel improves the austenite grain size. Austenite grain size refers to the size of individual grains in the austenite structure, usually expressed as the average grain diameter. Austenite is a face-centered cubic iron-based alloy phase that typically forms at high temperatures and is an important phase state after steel is heated. Grain size has a significant impact on the mechanical properties, processing properties, and heat treatment effects of materials, and refining the grain size also improves hardenability.

[0074] Reference Figures 1 to 10 In the S8 package, the same batch of bolt connections should undergo a set of process inspections according to the standard;

[0075] Batch inspection significantly improves inspection efficiency because bolt assemblies within the same batch typically share similar materials, manufacturing processes, and specifications. Batch inspection allows for sampling to represent the quality of the entire batch, avoiding individual inspection of each bolt and saving time and labor costs. Furthermore, inspecting bolts within the same batch helps ensure consistent quality and performance across all assemblies. If all bolts in a batch meet standards during inspection, it indicates that the bolt assemblies in the entire batch are consistent in performance, guaranteeing structural stability and reliability. Standardized batch inspection ensures quality control at every stage of production, reducing the risk of overall connection failure due to a single bolt's quality issue. This is especially crucial for large projects, ensuring batch consistency for long-term connection reliability. In summary, inspecting bolt assemblies in batches according to standards not only improves inspection efficiency and reduces costs but also guarantees consistency and reliability, enhancing product quality control, facilitating compliance with standards and regulations, and increasing customer trust.

[0076] Reference Figures 1 to 10 In the S8 package, the same batch of bolt connection pairs should be supplied according to the guaranteed torque coefficient. The torque coefficient test of the connection pairs should be conducted, and the average torque coefficient of the same batch of connection pairs should be 0.110 to 0.150, and the standard deviation of the torque coefficient should not be greater than 0.010.

[0077] The torque coefficient refers to the relationship between the applied torque and the bolt force during bolt tightening. Ensuring a consistent torque coefficient across bolt assemblies from the same batch guarantees that each bolt experiences a similar preload during installation, contributing to a consistent level of tightness. This consistency ensures that the preload of each bolt meets design requirements, thereby guaranteeing the safety and long-term stability of the connection. The average torque coefficient for assemblies from the same batch is 0.110–0.150, while the traditional range is typically between 0.12 and 0.20. A lower torque coefficient generally indicates lower friction during tightening. This allows for lower torque application during bolt tightening, reducing the effort required by workers and the burden on equipment. Lower friction also results in a smoother tightening process, reducing the risk of overtightening.

[0078] Example 2

[0079] Reference Figure 4 M16 bolts were used for the samples. The heating temperature was 860℃. The heating and holding time of the samples were controlled according to the operating speed of the mesh belt heating furnace for 120 and 90 minutes respectively. After heating, the samples were cooled with PAG aqueous solution with the water temperature controlled at 35±2℃. The tempering temperature was 430℃ and the holding time was controlled according to the operating speed of the mesh belt heating furnace for 135 minutes.

[0080] The microstructure after quenching at 860℃ consists of lath martensite + acicular martensite + a significant amount of undissolved ferrite, see [reference needed]. Figure 4 It can be seen that the quenched state exhibits a typical lath martensite structure, with clearly visible original austenite grain boundaries. The lath martensite is arranged in parallel lath bundles, with clear lath boundaries. After quenching and medium-temperature tempering, XG295N steel yields a tempered troostite structure, inheriting the morphology of the quenched martensite, partially exhibiting a lath-like structure. As the tempering temperature further increases, the lath structure gradually widens and disappears. The addition of the microalloying element nickel to XG295N steel enhances its tempering stability. When the tempering temperature rises to 500℃, thin film-like carbide precipitation occurs at the grain boundaries of XG295N steel, while fine granular carbide precipitation exists in the matrix. The thin film-like carbide precipitation at the grain boundaries gradually breaks off, resulting in a decrease in mechanical properties such as tensile strength and hardness.

[0081] Example 3

[0082] Reference Figure 5 M16 bolts were used for the samples. The heating temperature was 880℃. The heating and holding times of the samples were controlled according to the operating speed of the mesh belt heating furnace for 120 and 90 minutes respectively. After heating, the samples were cooled with PAG aqueous solution with the water temperature controlled at 35±2℃. The tempering temperature was 450℃ and the holding time was controlled according to the operating speed of the mesh belt heating furnace for 135 minutes.

[0083] The microstructure after quenching at 880℃ consists of lath martensite + fine acicular martensite + a small amount of undissolved ferrite, see [reference needed]. Figure 5 It can be seen that the quenched state exhibits a typical lath martensite structure, with clearly visible original austenite grain boundaries. The lath martensite is arranged in parallel lath bundles, with clear lath boundaries. After quenching and medium-temperature tempering, XG295N steel yields tempered troostite, inheriting the morphology of the quenched martensite, partially exhibiting a lath-like structure. As the tempering temperature further increases, the lath structure gradually widens and disappears. Due to the addition of the microalloying element nickel to XG295N steel, the tempering stability of the steel is enhanced. During tempering at 450℃, no significant change in microstructure size was observed. The tempered troostite structure after quenching and tempering (see...) Figure 7 When the tempering temperature rises to 500℃, thin film-like carbide precipitation occurs at the grain boundaries of XG295N steel, and fine particulate carbide precipitation exists in the matrix. The thin film-like carbide precipitation at the grain boundaries gradually breaks apart, resulting in a decrease in mechanical properties such as tensile strength and hardness.

[0084] Example 4

[0085] Reference Figure 6M16 bolts were used for the samples. The heating temperature was 900℃. The heating and holding time of the samples were controlled according to the operating speed of the mesh belt heating furnace, which was 120 min and 90 min respectively. After heating, the samples were cooled with PAG aqueous solution, and the water temperature was controlled at 35±2℃. The tempering temperature was 470℃ and the holding time was controlled according to the operating speed of the mesh belt heating furnace, which was 135 min.

[0086] The microstructure after quenching at 900℃ consists of fine acicular martensite + lath martensite + trace amounts of dot-like ferrite, see [reference needed]. Figure 6 It can be seen that the quenched state exhibits a typical lath martensite structure, with clearly visible original austenite grain boundaries. The lath martensite is arranged in parallel lath bundles, with clear lath boundaries. After quenching and medium-temperature tempering, XG295N steel yields tempered troostite, inheriting the morphology of the quenched martensite, partially exhibiting a lath-like structure. As the tempering temperature further increases, the lath structure gradually widens and disappears. Due to the addition of the microalloying element Ni to XG295N steel, the tempering stability of the steel is enhanced. During tempering at 450℃, no significant change in microstructure size was observed. The tempered troostite structure after quenching and tempering (see...) Figure 7 When the tempering temperature rises to 500℃, thin film-like carbide precipitation occurs at the grain boundaries of XG295N steel, and fine particulate carbide precipitation exists in the matrix. The thin film-like carbide precipitation at the grain boundaries gradually breaks apart, resulting in a decrease in mechanical properties such as tensile strength and hardness.

[0087] In the accompanying drawings of this embodiment, the same or similar reference numerals correspond to the same or similar components. In the description of this application, it should be understood that if terms such as "upper," "lower," "left," and "right" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, they are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the accompanying drawings are only for illustrative purposes and should not be construed as limiting this patent. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0088] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A manufacturing process for weathering steel bolts, characterized in that, Includes the following steps: S1: Spheroidizing annealing; By heating the steel, the temperature is set at A. C1 The sample is kept at a temperature between 760 and 775°C, then furnace-cooled to 700°C for 6 to 8 hours, and then furnace-cooled to 450°C before being removed from the furnace. The hardness is tested to be 74 to 78 HRB and the spheroidization rate is ≥70%. S2: Pickling; The bolts are placed in an acid solution to completely acidify their surface. After the acid pickling is complete, they are washed with water again to remove the acid from the bolt surface. S3: Remove oxide scale; Remove oxides generated on the surface of steel by mechanical, chemical, or thermal methods when they react with oxygen in the air during high-temperature treatment; S4: Phosphating; The steel is immersed in a phosphoric acid solution, which forms a thin film of phosphate on the surface of the steel. S5: Drawing and cold heading; By stretching steel to a specified size, and utilizing the plasticity of metal, the precision wire is forged through a multi-station cold forging machine to achieve the shape and length of the bolt semi-finished product. S6: Heat treatment; Through ladle refining, the content of major alloying elements such as carbon, chromium, nickel, and manganese in steel is controlled within a smaller range than that of ordinary steel, the content of impurity elements (oxygen, sulfur, phosphorus, nitrogen, etc.) is reduced and controlled, and then the steel is quenched and tempered. S7: Hydrogen removal treatment; After the heat treatment process is completed, hydrogen removal treatment should be carried out. The temperature in the hydrogen removal furnace should be controlled at 170±10℃ and maintained for more than 8 hours. S8: Packaging; After the hydrogen removal treatment is completed, the bolts are blackened by the residual heat of tempering and then coated with anti-rust oil, while the nuts and washers are directly packaged after phosphating and saponification.

2. The manufacturing process of weathering steel bolts according to claim 1, characterized in that, In the S6 heat treatment, the copper content is between 0.20% and 0.40%, the chromium + nickel + copper ratio should be greater than 1.30%, the phosphorus content is controlled at ≤0.015%, the sulfur content is controlled at ≤0.010%, and the phosphorus + sulfur content should be ≤0.020%.

3. The manufacturing process of weathering steel bolts according to claim 1, characterized in that, In the S6 heat treatment, the quenching temperature is selected as 860℃~900℃, and the tempering temperature is selected as 430℃~470℃.

4. The manufacturing process of weathering steel bolts according to claim 3, characterized in that, The heating and holding time of the quenched sample is controlled according to the operating speed of the mesh belt heating furnace, which is 120 and 90 min respectively. After heating, it is cooled with PAG aqueous solution, and the water temperature is controlled at 35±2℃. The holding time of the tempering temperature is controlled according to the operating speed of the mesh belt heating furnace, which is 135 min.

5. The manufacturing process of weathering steel bolts according to claim 1, characterized in that, The nickel content is 0.30%.

6. The manufacturing process of weathering steel bolts according to claim 1, characterized in that, In the S8 package, the same batch of bolt connections should undergo a set of process inspections according to the standard.

7. The manufacturing process of weathering steel bolts according to claim 6, characterized in that, In the S8 package, the same batch of bolted assemblies should be supplied according to the guaranteed torque coefficient. The torque coefficient test of the assemblies should be conducted, and the average torque coefficient of the same batch of assemblies should be 0.110 to 0.150, and the standard deviation of the torque coefficient should not be greater than 0.010.

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