Delayed fracture resistant bolt and manufacturing method thereof

Abstract

The invention relates to a delayed fracture resistant bolt and a manufacturing method thereof, and relates to the field of fasteners, the delayed fracture resistant bolt comprises a bolt head and a screw rod, a stress dispersion structure is arranged at the joint of the bolt head and the screw rod, the surface of the bolt is sequentially coated with an alloy co-permeation layer and an anti-corrosion coating from inside to outside, and the bolt is formed by machining high-strength bolt steel. The high-strength bolt steel comprises the following chemical components in percentage by mass: 0.38%-0.43% of C, 0.05%-0.10% of Si, 0.2%-0.35% of Mn, 0.95%-1.28% of Cr, 0.45%-0.65% of Mo, 0.13%-0.27% of W, 0.1%-0.25% of Ti, 0.02%-0.06% of B, less than or equal to 0.01% of P, less than or equal to 0.005% of S and the balance of Fe and other inevitable impurities. The bolt is high in delayed fracture resistance, high in stability and long in service life.

Description

Technical Field

[0001] The present invention relates to the field of fasteners, and in particular to a delayed fracture resistant bolt and a manufacturing method thereof. Background Art

[0002] Bolts are widely used accessories, serving as fasteners for connecting two components or tightening a part. They perform various functions in mechanical structures, including connection, fastening, positioning, and sealing. Bolts must be tightened during installation and withstand static tensile loads. During operation, they are often subjected to additional axial and lateral alternating loads. These additional axial alternating loads can cause fatigue fracture in bolts, while axial alternating loads can also cause delayed fracture in the presence of environmental media.

[0003] Delayed fracture occurs when a bolt is subjected to continuous or alternating loads, which accumulate over time and eventually lead to a sudden break. This is a brittle fracture that occurs at room temperature and constant stress. Delayed fracture is caused by hydrogen intrusion, which leads to hydrogen enrichment at the brittle fracture site. When bolts are used in environments such as seawater or de-icing salt, the increased hydrogen intrusion caused by salt adhesion increases the likelihood of delayed fracture. Delayed fracture can compromise the safety of bolts and pose a serious threat to the safety of equipment or components.

[0004] At present, although there are some studies on delayed fracture resistant bolts, the delayed fracture resistance effect is limited, and there are problems such as poor performance stability and short service life, which are difficult to meet the use requirements. Summary of the Invention

[0005] In order to provide a bolt with strong delayed fracture resistance, strong stability and long service life, the present application provides a delayed fracture resistant bolt and a manufacturing method thereof.

[0006] The present application provides a delayed fracture resistant bolt and a manufacturing method thereof using the following technical solutions: In a first aspect, the present application provides a delayed fracture resistant bolt, comprising a bolt head and a screw rod, wherein a stress dispersion structure is provided at the connection between the bolt head and the screw rod, and the surface of the bolt is coated with an alloy co-diffusion layer and an anti-corrosion coating in sequence from the inside out. The bolt is made of high-strength bolt steel, and the high-strength bolt steel contains the following chemical compositions in mass percentage: C 0.38%-0.43%, Si 0.05%-0.10%, Mn 0.2%-0.35%, Cr 0.95%-1.28%, Mo 0.45%-0.65%, W 0.13%-0.27%, Ti 0.1%-0.25%, B 0.02%-0.06%, P≤0.01%, S≤0.005%, and the balance is Fe and other unavoidable impurities.

[0007] By adopting the above technical solution, a stress dispersion mechanism is provided at the connection between the bolt head and the screw, thereby reducing stress concentration and lowering the risk of delayed fracture; the alloy co-diffusion layer and the anti-corrosion coating are provided on the surface of the bolt, which plays an anti-corrosion protection role, which is beneficial to improving the corrosion resistance of the bolt, while reducing the amount of hydrogen intruding into the bolt surface, preventing hydrogen penetration and enrichment, improving the delayed fracture resistance of the bolt, and increasing the service life of the bolt.

[0008] Bolt steel utilizes specific components to control the P and S contents, reduce grain boundary segregation, and increase the Mo and W contents. This creates carbides that enhance the bolt's strength through enhanced precipitation and serve as hydrogen traps, improving delayed fracture resistance. Ti refines the grains and acts as a hydrogen trap to inhibit hydrogen diffusion. B improves workability while reducing fracture notch sensitivity. This specific combination of components enhances hydrogen catalytic resistance, resulting in bolts with high strength, excellent delayed fracture resistance, strong stability, and a long service life.

[0009] Optionally, the chemical composition of the high-strength bolt steel further includes one or more of V 0.04%-0.07%, Nb 0.03%-0.05%, Cu 0.07%-0.11%, and Ce 0.004%-0.009%.

[0010] By adopting the above technical solution, V and Nb can combine with N and C to form carbonitrides, thereby refining the grains, Cu improves corrosion resistance, and Ce is beneficial to suppressing crack extension, all of which are beneficial to improving the stability of the bolt.

[0011] Optionally, the alloy co-diffusion layer includes the following raw materials in parts by mass: 80-100 parts of zinc powder, 11-17 parts of molybdenum powder, 4-8 parts of aluminum powder, 2-5 parts of rare earth oxide, 0.4-0.9 parts of ammonium chloride, and 3-5 parts of hydrogen peroxide.

[0012] By employing this technical solution, zinc, molybdenum, and aluminum powders diffuse into the bolt steel during the heat-co-infiltration process, forming a zinc-aluminum-molybdenum-iron multi-element co-infiltration layer. Rare earth oxides accelerate the infiltration process, improving the hardness and wear resistance of the co-infiltration layer. The addition of ammonium chloride powder activates the workpiece surface, enhancing bonding and promoting co-infiltration. Hydrogen peroxide oxidizes the original divalent iron in the bolt steel into trivalent iron, making it easier to bond with the alloy co-infiltration layer. This zinc-aluminum-molybdenum-iron multi-element co-infiltration layer improves the bolt steel's hardness, salt spray corrosion resistance, and delayed fracture resistance.

[0013] Optionally, the anti-corrosion coating comprises the following raw materials in parts by mass: 40-55 parts of bisphenol A epoxy resin, 15-23 parts of modified glass flakes, 4-7 parts of polyphenylene sulfide, 10-14 parts of diluent, 5-10 parts of titanium dioxide, and 10-23 parts of curing agent.

[0014] By adopting the above technical solution, the modified glass flakes and bisphenol A epoxy resin are tightly combined, and polyphenylene sulfide and titanium dioxide are used as fillers to fill the gaps, making the coating system structure denser; modified glass flakes and polyphenylene sulfide are used to modify the epoxy resin coating, thereby enhancing the corrosion resistance and anti-penetration properties of the coating, effectively blocking the penetration of hydrogen ions, and improving the delayed fracture resistance of the bolts.

[0015] Optionally, the modified glass flakes are prepared from the following raw materials in parts by weight: 10-15 parts of glass flakes; 43-48 parts of silane coupling agent KH-560.

[0016] By adopting the above technical solution, the silane coupling agent KH-560 is selected to modify the glass flakes and introduce epoxy groups. The epoxy groups can react with the hydroxyl groups of the epoxy resin to enhance the bonding tightness with the resin coating.

[0017] Optionally, the stress dispersion structure includes a transition groove opened at the connection between the screw and the bolt head, the bolt is connected with a gasket, and the gasket is provided with a protrusion, and the protrusion fits with the transition groove.

[0018] By adopting the above technical solution, the setting of the transition groove makes the connection between the screw and the bolt head present an arc-shaped transition, which effectively reduces the stress at the connection and reduces the stress concentration phenomenon at the connection, which is beneficial to improving the delayed fracture resistance of the bolt.

[0019] In a second aspect, the present application provides a method for manufacturing a delayed fracture resistant bolt, comprising the following steps: Weighing the chemical components of the high-strength bolt steel, adding them into an electric furnace, heating them to 1500-1600° C., taking them out of the furnace, pouring them, and forming them to obtain high-strength bolt steel raw materials; The high-strength bolt steel raw material is pickled for rust removal and air-dried, and then the air-dried raw material is subjected to spheroidizing annealing, phosphating treatment and wire drawing; The processed high-strength bolt steel raw material is formed into the desired shape of the bolt under the action of upsetting force, and the semi-finished bolt is obtained by turning, milling grooves and thread rolling; The outer thread of the semi-finished bolt is quenched at 740-790°C, the semi-finished bolt is tempered at 490-520°C for 100-120 minutes, the polished rod of the bolt is quenched at 750-800°C with an aqueous quenching liquid, kept at this temperature for 50-70 minutes, the tempering process is repeated, and then the semi-finished bolt is naturally cooled to room temperature; The alloy co-infiltration layer raw material is prepared, the semi-finished bolt is subjected to degreasing and shot blasting surface treatment, and then placed in a co-infiltration furnace, the alloy co-infiltration layer raw material is added to the co-infiltration furnace, and the alloy co-infiltration layer is formed by co-infiltration; The anti-corrosion coating raw material is prepared and applied to the surface of the semi-finished bolt. After solidification, the anti-corrosion coating is formed to obtain a delayed fracture resistant bolt.

[0020] By adopting the above technical solution, the process and related parameters for preparing bolts are optimized, so that the prepared bolts meet the requirements of strength and delayed fracture resistance, reduce costs and save energy.

[0021] Optionally, the preparation of the alloy co-diffusion layer raw material includes the following steps: Zinc powder, molybdenum powder, aluminum powder, rare earth oxide and hydrogen peroxide are mixed evenly, and preheated at 200-220° C. for 40-60 minutes to obtain a co-penetrating agent. The co-penetrating agent is mixed evenly with ammonium chloride to obtain a raw material for an alloy co-penetrating layer.

[0022] By adopting the above technical solution, the raw materials for the alloy co-diffusion layer are obtained by heating and mixing, and the preparation method is simple.

[0023] Optionally, the preparation of the anti-corrosion coating raw material includes the following steps: Weigh bisphenol A epoxy resin and disperse and stir for 20-30 minutes, add titanium dioxide, polyphenylene sulfide and diluent, stir at a speed of 1000-1200 r / min for 25-35 minutes, grind the mixture in a conical mill to a fineness of less than 40 μm, then add modified glass flakes, stir evenly and age for 23-24 hours to prepare component A; The curing agent is used as component B to obtain the anti-corrosion coating raw material.

[0024] By adopting the above technical solution, the two-component anti-corrosion coating raw material is prepared, the process is simple, and it is convenient to use at any time.

[0025] Optionally, the preparation of the modified glass flakes comprises the following steps: Soak the glass flakes in a 5%-10% NaOH solution for 30-35 minutes, wash with deionized water to pH = 7-8, dry at room temperature, place the glass flakes in a 10% xylene solution of silane coupling agent KH-560, soak all of it for 20-30 minutes, and dry it in a 90-100°C oven to obtain modified glass flakes.

[0026] By adopting the above technical solution, the glass flakes are pretreated in advance, which facilitates the combination of glass flakes and silane coupling agent KH-560 and improves the grafting rate.

[0027] In summary, this application has the following beneficial effects: 1. A stress dispersion mechanism is set at the connection between the bolt head and the screw to reduce stress concentration and the risk of delayed fracture; the alloy co-diffusion layer and anti-corrosion coating are set on the bolt surface to play an anti-corrosion protection role, which is beneficial to improving the corrosion resistance of the bolt. At the same time, it reduces the amount of hydrogen intruding into the bolt surface, prevents hydrogen penetration and enrichment, improves the delayed fracture resistance of the bolt, and increases the service life of the bolt.

[0028] Bolt steel utilizes specific components to control the P and S contents, reduce grain boundary segregation, and increase the Mo and W contents. This creates carbides that enhance the bolt's strength through enhanced precipitation and serve as hydrogen traps, improving delayed fracture resistance. Ti refines the grains and acts as a hydrogen trap to inhibit hydrogen diffusion. B improves workability while reducing fracture notch sensitivity. This specific combination of components enhances hydrogen catalytic resistance, resulting in bolts with high strength, excellent delayed fracture resistance, strong stability, and a long service life.

[0029] 2. During the heat-co-infiltration process, zinc, molybdenum, and aluminum powders diffuse into the bolt steel, forming a zinc-aluminum-molybdenum-iron alloy co-infiltration layer. Rare earth oxides accelerate the infiltration process, improving the hardness and wear resistance of the co-infiltration layer. The addition of ammonium chloride powder activates the workpiece surface, enhancing bonding and promoting co-infiltration. Hydrogen peroxide oxidizes the original divalent iron in the bolt steel into trivalent iron, making it easier to bond with the alloy co-infiltration layer. The zinc-aluminum-molybdenum-iron alloy co-infiltration layer improves the bolt steel's hardness, salt spray corrosion resistance, and delayed fracture resistance.

[0030] 3. The modified glass flakes and bisphenol A epoxy resin are tightly combined, and polyphenylene sulfide and titanium dioxide are used as fillers to fill the gaps, making the coating system structure more dense; modified glass flakes and polyphenylene sulfide are used to modify the epoxy resin coating, thereby enhancing the corrosion resistance and anti-penetration properties of the coating, effectively blocking the penetration of hydrogen ions, and improving the delayed fracture resistance of the bolts. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a structural schematic diagram of the delayed fracture resistant bolt of the present application.

[0032] Description of reference numerals: 1. Bolt head; 2. Screw; 3. Transition groove; 4. Gasket; 5. Protrusion. DETAILED DESCRIPTION

[0033] The present application is further described in detail below in conjunction with Examples 1-7 and Comparative Examples 1-3.

[0034] Preparation Example Preparation Example 1 Preparation of high-strength bolt steel A high strength bolt steel comprising the following chemical compositions in percentage by mass: C 0.38%, Si 0.05%, Mn 0.2%, Cr 0.95%, Mo 0.45%, W 0.13%, Ti 0.1%, B 0.02%, P ≤ 0.01%, S ≤ 0.005%, and the balance is Fe and other inevitable impurities.

[0035] The preparation method of high-strength bolt steel includes the following steps: The above chemical components were weighed and added into an electric furnace, heated to 1500°C for smelting, and after being discharged from the furnace, the molten steel was cast into 142 mm × 142 mm square billets; The produced billet is transported to a heating furnace for heating to heat the billet to 1000° C. The heated billet is output from the heating furnace and subjected to high-speed wire rolling, while the final rolling temperature is controlled at 920°C and the high-speed wire drawing temperature is controlled at 880°C.

[0036] The Stelmore line is processed according to conventional technology and air-cooled by a Stelmore blower to obtain the corresponding wire rod and obtain high-strength bolt steel raw material.

[0037] Preparation Example 2 Preparation of high-strength bolt steel A high strength bolt steel comprising the following chemical compositions in percentage by mass: C 0.43%, Si 0.10%, Mn 0.35%, Cr 1.28%, Mo 0.65%, W 0.27%, Ti 0.25%, B 0.06%, P ≤ 0.01%, S ≤ 0.005%, and the balance is Fe and other inevitable impurities.

[0038] The preparation method of high-strength bolt steel includes the following steps: The above chemical components were weighed and added into an electric furnace, heated to 1600°C for smelting, and after being discharged from the furnace, the molten steel was cast into 142 mm × 142 mm square billets; The produced billet is transported to a heating furnace for heating to heat the billet to 1050° C. The heated billet is output from the heating furnace and subjected to high-speed wire rolling, while the final rolling temperature is controlled at 970°C and the high-speed wire drawing temperature is controlled at 900°C.

[0039] The Stelmore line is processed according to conventional technology and air-cooled by a Stelmore blower to obtain the corresponding wire rod and obtain high-strength bolt steel raw material.

[0040] Preparation Example 3 Preparation of high-strength bolt steel A high strength bolt steel comprising the following chemical compositions in percentage by mass: C 0.38%, Si 0.05%, Mn 0.2%, Cr 0.95%, Mo 0.45%, W 0.13%, Ti 0.1%, B 0.02%, P ≤ 0.01%, S ≤ 0.005%, V 0.04%, Cu 0.07%, and the balance is Fe and other inevitable impurities.

[0041] The preparation method of the high-strength bolt steel is the same as that in Preparation Example 1.

[0042] Preparation Example 4 A high strength bolt steel comprising the following chemical compositions in percentage by mass: C 0.43%, Si 0.10%, Mn 0.35%, Cr 1.28%, Mo 0.65%, W 0.27%, Ti 0.25%, B 0.06%, P ≤ 0.01%, S ≤ 0.005%, Nb 0.05%, Ce 0.009%, and the balance is Fe and other inevitable impurities.

[0043] The preparation method of the high-strength bolt steel is the same as that in Preparation Example 1.

[0044] Preparation Example 5 Preparation of raw materials for alloy co-diffusion layer The alloy co-diffusion layer includes the following raw materials in parts by mass: 80 parts of zinc powder, with an average particle size of 50μm; 11 parts of molybdenum powder, with an average particle size of 50μm; 4 parts of aluminum powder, with an average particle size of 50μm; 2 parts of rare earth oxide, specifically lanthanum oxide, with an average particle size of 50μm; 0.4 parts of ammonium chloride, and 3 parts of hydrogen peroxide.

[0045] The preparation method of the alloy co-diffusion layer raw material comprises the following steps: Zinc powder, molybdenum powder, aluminum powder, rare earth oxide and hydrogen peroxide are mixed evenly, and preheated at 200° C. for 60 minutes to obtain a co-penetrating agent. The co-penetrating agent is mixed evenly with ammonium chloride to obtain a raw material for an alloy co-penetrating layer.

[0046] Preparation Example 6 Preparation of raw materials for alloy co-diffusion layer The alloy co-diffusion layer includes the following raw materials in parts by mass: 100 parts of zinc powder, with an average particle size of 40μm; 17 parts of molybdenum powder, with an average particle size of 40μm; 8 parts of aluminum powder, with an average particle size of 40μm; 5 parts of rare earth oxide, specifically neodymium oxide, with an average particle size of 40μm; 0.9 parts of ammonium chloride and 5 parts of hydrogen peroxide.

[0047] The preparation method of the alloy co-diffusion layer raw material comprises the following steps: Zinc powder, molybdenum powder, aluminum powder, rare earth oxide and hydrogen peroxide are mixed evenly, and preheated at 220° C. for 40 minutes to obtain a co-penetrating agent. The co-penetrating agent is mixed evenly with ammonium chloride to obtain a raw material for an alloy co-penetrating layer.

[0048] Preparation Example 7 Preparation of anti-corrosion coating raw materials The anti-corrosion coating includes the following raw materials in parts by mass: 40 parts of bisphenol A epoxy resin with an average molecular weight of 4500; 15 parts of modified glass flakes, prepared from 10 parts of glass flakes with a particle size of 200 mesh and 43 parts of silane coupling agent KH-560; 4 parts of polyphenylene sulfide, with an average molecular weight of 20,000; 10 parts of diluent, specifically 7 parts of benzyl alcohol and 3 parts of ethyl acetate; 5 parts of titanium dioxide, with a particle size of 20-30 μm; 10 parts of curing agent, the curing agent is curing agent 7016, which comes from Wuxi Honghui New Materials Technology Co., Ltd.

[0049] The preparation method of the anti-corrosion coating raw material comprises the following steps: Preparation of modified glass flakes: Soak the glass flakes in 5% NaOH solution for 30 minutes, wash with deionized water to pH = 7, dry at room temperature, place the glass flakes in 10% xylene solution of silane coupling agent KH-560, soak all of them and wait for 20 minutes, dry in a 90°C oven to obtain modified glass flakes.

[0050] Preparation of coating: Weigh bisphenol A epoxy resin and disperse and stir for 20 minutes, add titanium dioxide, polyphenylene sulfide and diluent, stir at 1000 r / min for 25 minutes, grind the mixture in a conical mill to a fineness of less than 40 μm, then add modified glass flakes, stir evenly and age for 23 hours to prepare component A; The curing agent is used as component B to obtain the anti-corrosion coating raw material.

[0051] Preparation Example 8 Preparation of anti-corrosion coating raw materials The anti-corrosion coating comprises the following raw materials in parts by weight: 55 parts of bisphenol A epoxy resin with an average molecular weight of 4500; 23 parts of modified glass flakes, prepared from 10 parts of glass flakes with a particle size of 200 mesh and 43 parts of silane coupling agent KH-560; 7 parts of polyphenylene sulfide, with an average molecular weight of 20,000; 14 parts of diluent, specifically 10 parts of benzyl alcohol and 4 parts of ethyl acetate; 10 parts of titanium dioxide, particle size 20-30 μm; 23 parts of curing agent, the curing agent is curing agent 7016, which comes from Wuxi Honghui New Materials Technology Co., Ltd.

[0052] The preparation method of the anti-corrosion coating raw material comprises the following steps: Preparation of modified glass flakes: Soak the glass flakes in 10% NaOH solution for 35 minutes, wash with deionized water to pH = 8, dry at room temperature, place the glass flakes in 10% xylene solution of silane coupling agent KH-560, soak all of them and wait for 30 minutes, dry in an oven at 100°C to obtain modified glass flakes.

[0053] Preparation of coating: Weigh bisphenol A epoxy resin and disperse and stir for 30 minutes, add titanium dioxide, polyphenylene sulfide and diluent, stir at 1200 r / min for 35 minutes, grind the mixture in a conical mill to a fineness of less than 40 μm, then add modified glass flakes, stir evenly and age for 24 hours to prepare component A; The curing agent is used as component B to obtain the anti-corrosion coating raw material.

[0054] Preparation Example 9 Preparation of anti-corrosion coating raw materials The difference between this preparation example and preparation example 7 is that 15 parts of modified glass flakes are prepared from 15 parts of glass flakes with a particle size of 200 mesh and 48 parts of silane coupling agent KH-560.

[0055] The preparation method of the anti-corrosion coating raw material is the same as that of Preparation Example 7. Example

[0056] Example 1 Preparation of a delayed fracture resistant bolt The delayed fracture resistant bolt of this embodiment is shown in FIG. Figure 1 , including a bolt head, a screw and a gasket. A transition groove is provided at the connection between the bolt head and the screw, and the transition groove is set biased towards the bolt head. The gasket is provided with a protrusion, which fits in the transition groove, thereby keeping the bolt flat during use.

[0057] The raw materials of the delayed fracture resistant bolts of this embodiment include: High-strength bolt steel raw material: the high-strength bolt steel raw material prepared in Preparation Example 1; Alloy co-penetration layer raw material: the alloy co-penetration layer raw material prepared in Preparation Example 5; Anti-corrosion coating raw material: the anti-corrosion coating raw material prepared in Preparation Example 7 was used.

[0058] The preparation method of the delayed fracture resistant bolt comprises the following steps: The high-strength bolt steel raw materials are pickled, derusted, air-dried, and then spheroidized annealed at 800℃. After constant temperature treatment for 5 hours, phosphating treatment and wire drawing; The processed high-strength bolt steel raw material is formed into the required shape of the bolt under the action of upsetting force, and the semi-finished bolt is obtained through turning, milling and thread rolling; The outer thread of the semi-finished bolt is quenched at 740°C, and the semi-finished bolt is tempered at 490°C for 120 minutes. The polished rod of the bolt is quenched at 750°C with an aqueous quenching liquid, kept at this temperature for 70 minutes, and the tempering process is repeated, and then naturally cooled to room temperature. The alloy co-infiltration layer raw materials are prepared, and the semi-finished bolts are subjected to degreasing and shot blasting surface treatment and then placed in a co-infiltration furnace. The alloy co-infiltration layer raw materials are added to the co-infiltration furnace, and the co-infiltration furnace is evacuated to a pressure of -0.1 MPa, heated to 700°C and kept warm for 2 hours, then heated to 850°C and kept warm for 3 hours, and then cooled to 300°C at a rate of 5°C / min and kept warm for 40 minutes, and then cooled to room temperature, thereby forming the alloy co-infiltration layer by co-infiltration; The raw materials for anti-corrosion coating are prepared and applied to the surface of the semi-finished bolt. After curing, the anti-corrosion coating is formed to obtain a delayed fracture resistant bolt.

[0059] Example 2 Preparation of a delayed fracture resistant bolt The delayed fracture resistant bolt of this embodiment includes a bolt head, a screw rod and a gasket. A transition groove is provided at the connection between the bolt head and the screw rod, and the transition groove is set biased towards the bolt head. The gasket is provided with a protrusion, which fits in the transition groove, thereby keeping the bolt flat during use.

[0060] The raw materials of the delayed fracture resistant bolts of this embodiment include: High-strength bolt steel raw material: the high-strength bolt steel raw material prepared in Preparation Example 2; Alloy co-penetration layer raw material: the alloy co-penetration layer raw material prepared in Preparation Example 6; Anti-corrosion coating raw material: the anti-corrosion coating raw material prepared in Preparation Example 8 was used.

[0061] The preparation method of the delayed fracture resistant bolt comprises the following steps: The high-strength bolt steel raw materials are pickled, derusted, air-dried, and then spheroidized annealed at 820℃. After 6 hours of constant temperature treatment, phosphating and wire drawing; The processed high-strength bolt steel raw material is formed into the required shape of the bolt under the action of upsetting force, and the semi-finished bolt is obtained through turning, milling and thread rolling; The outer thread of the semi-finished bolt is quenched at 790℃, and the semi-finished bolt is tempered at 520℃ for 100 minutes. The polished rod of the bolt is quenched at 800℃ with aqueous quenching liquid, kept at this temperature for 50 minutes, and the tempering process is repeated, and then naturally cooled to room temperature. The raw materials for the alloy co-infiltration layer are prepared, and the semi-finished bolts are subjected to degreasing and shot blasting surface treatment and then placed in a co-infiltration furnace. The raw materials for the alloy co-infiltration layer are added to the co-infiltration furnace, and the co-infiltration furnace is evacuated to a pressure of -0.08 MPa, heated to 650°C and kept warm for 3 hours, then heated to 780°C and kept warm for 4 hours, and then cooled to 250°C at a rate of 5°C / min and kept warm for 60 minutes, and then cooled to room temperature, thereby forming the alloy co-infiltration layer by co-infiltration; The raw materials for anti-corrosion coating are prepared and applied to the surface of the semi-finished bolt. After curing, the anti-corrosion coating is formed to obtain a delayed fracture resistant bolt.

[0062] Example 3-Example 7 The difference between Examples 3-7 and Example 1 is that the raw materials of the delayed fracture resistant bolts are different. The specific raw materials are shown in Table 1.

[0063] The preparation method of the delayed fracture resistant bolt is the same as that in Example 1. Table 1 Sample Example 3 Example 4 Example 5 Example 6 Example 7 High-strength bolt steel Preparation Example 1 Preparation Example 2 Preparation Example 3 Preparation Example 4 Preparation Example 3 Alloy co-diffusion layer Preparation Example 6 Preparation Example 5 Preparation Example 6 Preparation Example 6 Preparation Example 5 Anti-corrosion coating Preparation Example 8 Preparation Example 9 Preparation Example 8 Preparation Example 8 Preparation Example 9

[0064] Comparative Example Comparative Example 1 The difference between this comparative example and Example 1 is that the delayed fracture resistant bolt of this comparative example is not provided with a stress dispersion structure, and does not have a transition groove and a gasket.

[0065] The preparation method of the delayed fracture resistant bolt is the same as that in Example 1.

[0066] Comparative Example 2 The difference between this comparative example and Example 1 is that the delayed fracture resistant bolt of this comparative example is not provided with an alloy co-penetration layer.

[0067] The preparation method of the delayed fracture resistant bolt is the same as that in Example 1.

[0068] Comparative Example 3 The difference between this comparative example and Example 1 is that the delayed fracture resistant bolts in this comparative example are not provided with an anti-corrosion coating.

[0069] The preparation method of the delayed fracture resistant bolt is the same as that in Example 1.

[0070] Performance Testing The tensile strength, delayed fracture performance, salt spray resistance time, and atmospheric corrosion resistance of the delayed fracture resistant bolts prepared in Examples 1-7 and Comparative Examples 1-3 were tested.

[0071] 1. Tensile strength: Test according to the national standard GB / T 228-2002 "Metallic Materials Room Temperature Tensile Test Method" and record the test results in Table 2.

[0072] 2. Delayed fracture strength ratio: Refer to ISO / FDIS16573:2014 "Test and evaluation method for hydrogen-induced delayed fracture resistance of high-strength steel" and use a constant load tensile testing machine to determine the critical fracture stress σ of the sample under the corrosion action of the corrosion inhibitor solution of hydrochloric acid + sodium acetate + deionized water with a pH of 3.5. NC ,σ f is the minimum stress for fracture within 200h, σ n is the maximum stress without fracture within 200h, then the critical fracture stress σ NC =(σ n +σ f ) / 2.

[0073] Delayed fracture strength ratio = σ NC / tensile strength, and record the results in Table 2.

[0074] 3. Salt spray resistance time: The test temperature is 35℃. A 5% mass concentration sodium chloride aqueous solution is sprayed in the test chamber to simulate the accelerated corrosion environment. The resistance time of the bolts, that is, the time they remain rust-free, is recorded to determine the quality of their corrosion resistance. The results are recorded in Table 2.

[0075] 4. Weight loss corrosion rate: Refer to TB / T 2375-1993 "Cyclic Immersion Corrosion Test Method for Weathering Steel for Railway Use" and conduct a cyclic immersion accelerated corrosion test. The solution used is 0.01 mol / L NaHSO3, with a pH value of 4.4; the test temperature is 45°C; the test humidity is 72% RH, the cycle period is 60 minutes, of which the immersion time is 12 minutes. The corrosion rate over 72 hours is recorded in Table 2.

[0076] Table 2 According to Table 2, the tensile strength of the delayed fracture resistant bolts prepared in this application after treatment is greater than 1300 MPa, the delayed fracture strength ratio is greater than 1.55, the salt spray resistance time can reach more than 1100 hours, and the weight loss corrosion rate of 72 hours is less than 0.7g / m 2 h, has good strength, excellent delayed fracture resistance and good corrosion resistance.

[0077] According to Comparative Examples 1-3, the lack of any one of the stress dispersion structure, the alloy co-diffusion layer and the anti-corrosion coating will reduce the delayed fracture resistance and corrosion resistance of the bolt.

[0078] This specific implementation manner is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the specific implementation manner as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A delayed fracture resistant bolt, characterized in that: The bolt includes a bolt head and a screw rod, a stress dispersion structure is provided at the connection between the bolt head and the screw rod, the surface of the bolt is coated with an alloy co-infiltration layer and an anti-corrosion coating in sequence from the inside out, and the bolt is made of high-strength bolt steel, and the high-strength bolt steel contains the following chemical components in mass percentage: C 0.38%-0.43%, Si 0.05%-0.10%, Mn 0.2%-0.35%, Cr 0.95%-1.28%, Mo 0.45%-0.65%, W 0.13%-0.27%, Ti 0.1%-0.25%, B 0.02%-0.06%, P≤0.01%, S≤0.005%, and the balance is Fe and other inevitable impurities.

2. The delayed fracture resistant bolt according to claim 1, characterized in that: The chemical composition of the high-strength bolt steel further includes one or more of V 0.04%-0.07%, Nb 0.03%-0.05%, Cu 0.07%-0.11%, and Ce 0.004%-0.009%.

3. The delayed fracture resistant bolt according to claim 1, characterized in that: The alloy co-diffusion layer includes the following raw materials in parts by mass: 80-100 parts of zinc powder, 11-17 parts of molybdenum powder, 4-8 parts of aluminum powder, 2-5 parts of rare earth oxide, 0.4-0.9 parts of ammonium chloride, and 3-5 parts of hydrogen peroxide.

4. The delayed fracture resistant bolt according to claim 1, characterized in that: The anti-corrosion coating comprises the following raw materials in parts by mass: 40-55 parts of bisphenol A epoxy resin, 15-23 parts of modified glass flakes, 4-7 parts of polyphenylene sulfide, 10-14 parts of diluent, 5-10 parts of titanium dioxide, and 10-23 parts of curing agent.

5. The delayed fracture resistant bolt according to claim 4, characterized in that: The modified glass flakes are prepared from the following raw materials in parts by weight: 10-15 parts of glass flakes; 43-48 parts of silane coupling agent KH-560.

6. The delayed fracture resistant bolt according to claim 1, characterized in that: The stress dispersion structure includes a transition groove opened at the connection between the screw rod and the bolt head. The bolt is connected with a gasket, and the gasket is provided with a protrusion. The protrusion fits with the transition groove.

7. The method for manufacturing a delayed fracture resistant bolt according to any one of claims 1 to 6, characterized in that: The steps include: Weighing the chemical components of the high-strength bolt steel, adding them into an electric furnace, heating them to 1500-1600° C., taking them out of the furnace, pouring them, and forming them to obtain high-strength bolt steel raw materials; The high-strength bolt steel raw material is pickled for rust removal and air-dried, and then the air-dried raw material is subjected to spheroidizing annealing, phosphating treatment and wire drawing; The processed high-strength bolt steel raw material is formed into the desired shape of the bolt under the action of upsetting force, and the semi-finished bolt is obtained by turning, milling grooves and thread rolling; The outer thread of the semi-finished bolt is quenched at 740-790°C, the semi-finished bolt is tempered at 490-520°C for 100-120 minutes, the polished rod of the bolt is quenched at 750-800°C with an aqueous quenching liquid, kept at this temperature for 50-70 minutes, the tempering process is repeated, and then the semi-finished bolt is naturally cooled to room temperature; The alloy co-infiltration layer raw material is prepared, the semi-finished bolt is subjected to degreasing and shot blasting surface treatment, and then placed in a co-infiltration furnace, the alloy co-infiltration layer raw material is added to the co-infiltration furnace, and the alloy co-infiltration layer is formed by co-infiltration; The anti-corrosion coating raw material is prepared and applied to the surface of the semi-finished bolt. After solidification, the anti-corrosion coating is formed to obtain a delayed fracture resistant bolt.

8. The method for manufacturing a delayed fracture resistant bolt according to claim 7, wherein: The preparation of the alloy co-diffusion layer raw material comprises the following steps: Zinc powder, molybdenum powder, aluminum powder, rare earth oxide and hydrogen peroxide are mixed evenly, and preheated at 200-220° C. for 40-60 minutes to obtain a co-penetrating agent. The co-penetrating agent is mixed evenly with ammonium chloride to obtain a raw material for an alloy co-penetrating layer.

9. The method for manufacturing a delayed fracture resistant bolt according to claim 7, wherein: The preparation of the anti-corrosion coating raw material comprises the following steps: Weigh bisphenol A epoxy resin and disperse and stir for 20-30 minutes, add titanium dioxide, polyphenylene sulfide and diluent, stir at a speed of 1000-1200 r / min for 25-35 minutes, grind the mixture in a conical mill to a fineness of less than 40 μm, then add modified glass flakes, stir evenly and age for 23-24 hours to prepare component A; The curing agent is used as component B to obtain the anti-corrosion coating raw material.

10. The method for manufacturing a delayed fracture resistant bolt according to claim 9, wherein: The preparation of the modified glass flakes comprises the following steps: Soak the glass flakes in a 5%-10% NaOH solution for 30-35 minutes, wash with deionized water until the pH is 7-8, dry at room temperature, place the glass flakes in a 10% xylene solution of silane coupling agent KH-560, soak them completely for 20-30 minutes, and dry them in a 90-100°C oven to obtain modified glass flakes.

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