Method for manufacturing wire for fasteners, and method for manufacturing fasteners

Abstract

This invention discloses a wire material for fasteners, a method for manufacturing the same, a fastener, and a method for manufacturing the same. The chemical composition of the wire and fasteners, by mass percentage, is as follows: C 0.25~0.45%, Si 0.15~0.50%, Mn 0.5~0.8%, P≦0.015%, S≦0.005%, Cr 5~12%, Ni 2.0~4.5%, Cu≦0.1%, Ti 0.05~0.10%, Mo 0.25~0.50%, Re 0.01~0.10%, Al 0.015~0.050%, O≦0.001%, N≦0.005%, and at least one of B, Nb, and V, with the remainder being Fe and unavoidable impurities, resulting in [B]+[Nb]+[V]≦0.15%, [Cr] / [Ni] 2.0~3.5, and [Mo] / [Ti] 4~6.

Description

Technical Field

[0001] This application is filed based on the Chinese patent application with application number 202311084987.5 and filing date August 28, 2023, claims the priority of the Chinese patent application, and incorporates all the content of the above patent application by reference into this application.

[0002] The present invention belongs to the technical field of steelmaking, relates to wire rods for fasteners and a manufacturing method thereof, and further relates to fasteners and a manufacturing method of fasteners.

Background Art

[0003] As the source of industry, fasteners are widely applied in fields such as automobiles, machine manufacturing, energy, aerospace, etc. In recent years, with the development of the economy and the progress of science and technology, in industrial applications, there are requirements for high design stress and weight reduction for fastener steels. To meet these requirements, first, it is necessary to improve the strength of fasteners. At the same fastening force, by reducing its own dimensions, the weight can be reduced, the installation space can be increased, and the functions and volume of the connected parts can be optimized to achieve the overall goals of weight reduction and performance optimization. Furthermore, improving the strength of fasteners can improve the fuel efficiency of automobiles, reduce fuel consumption, and achieve ultra-low carbon emissions.

[0004] However, with the improvement of steel strength, especially when the tensile strength exceeds 1200 MPa, the problem of delayed fracture of steel becomes very prominent. High-strength fasteners have very high notch sensitivity, and delayed fracture is likely to occur at notch stress concentration sites such as the transition part between the rod and the head and the root of the thread, leading to serious safety accidents and economic losses. Therefore, while improving the strength of fasteners, improving their ability to resist delayed fracture has become the focus of recent research work at home and abroad. [[ID=​​​​​

[0006] To achieve one of the above objectives, one embodiment of the present invention has a chemical composition in mass percentages of: C 0.25~0.45%, Si 0.15~0.50%, Mn 0.5~0.8%, P≦0.015%, S≦0.005%, Cr 5~12%, Ni 2.0~4.5%, Cu≦0.1%, Ti 0.05~0.10%, Mo 0.25~0.50%, Re 0.01~0.10%, Al We provided a wire material for fasteners containing 0.015~0.050%, O≦0.001%, N≦0.005%, and at least one of B, Nb, and V, with the remainder being Fe and unavoidable impurities, having [B]+[Nb]+[V]≦0.15%, [Cr] / [Ni] 2.0~3.5, and [Mo] / [Ti] 4~6.

[0007] As a further improvement of one embodiment of the present invention, the chemical composition of the fastening wire is as follows, by mass percentage: C 0.30~0.45%, Si 0.20~0.40%, Mn 0.60~0.75%, P≦0.015%, S≦0.005%, Cr 6~11%, Ni 2.5~4.0%, Cu≦0.1%, Ti 0.05~0.10%, Mo 0.25~0.50%, Re 0.01~0.10%, Al It contains 0.015-0.050%, O ≤ 0.001%, N ≤ 0.005%, and at least one of B, Nb, and V, with the remainder being Fe and unavoidable impurities, with [B] + [Nb] + [V] ≤ 0.15%, [Cr] / [Ni] ratio 2.0-3.5, and [Mo] / [Ti] ratio 4-6.

[0008] As a further improvement of one embodiment of the present invention, the chemical composition of the fastening wire is, by mass percentage, C 0.30~0.40%, Si 0.20~0.35%, Mn 0.60~0.70%, P≦0.015%, S≦0.005%, Cr 6.5~10%, Ni 2.5~3.5%, Cu≦0.1%, Ti 0.05~0.10%, Mo 0.25~0.50%, Re 0.01~0.10%, Al It contains 0.015-0.050%, O ≤ 0.001%, N ≤ 0.005%, and at least one of B, Nb, and V, with the remainder being Fe and unavoidable impurities, with [B] + [Nb] + [V] ≤ 0.15%, [Cr] / [Ni] ratio 2.0-3.5, and [Mo] / [Ti] ratio 4-6.

[0009] To achieve one of the above objectives, one embodiment of the present invention further provides a method for manufacturing wire for fasteners as described above. This manufacturing method includes sequentially performing molten steel refining steps, continuous casting steps, slow cooling steps, heating steps, high-speed wire rolling steps, and controlled cooling steps. In the continuous casting process described above, the temperature of the intermediate ladle (intermediate container) is controlled to 1510-1530°C. In the aforementioned slow cooling process, the continuously cast slab obtained in the continuous casting process is cooled to 650-700°C by air cooling, then sent to a heat-insulating pit, where it is slowly cooled at a cooling rate of 5.5-7°C / h until it reaches 200°C or below, and then removed from the heat-insulating pit. The heating process includes a heating stage and a soaking stage, wherein the heating stage has a temperature of 1100-1140°C, a heating rate of 0.3-0.4°C / s, and a heating time of 20-30 mins, and the soaking stage has a temperature of 1150-1190°C and a soaking time of 15-25 mins. In the high-speed wire rolling process, the starting rolling temperature is 1050 to 1090°C, and the ending rolling temperature is 910 to 940°C. In the controlled cooling process described above, the discharge temperature is 890-910°C, the insulating covers of the first and second stage roller tables of the Stermore cooling wire are opened, the insulating covers of all other roller tables are closed, the first to third fans are opened and the fan airflow is set to 60-90%, the other fans are closed, the roller table speed of the first and second stage roller tables is set to 0.25-0.4 m / s, the roller table speed of the other roller tables is set to 0.15-0.3 m / s, and the temperature of the wire when it reaches the third stage roller table is controlled to 750-780°C.

[0010] As a further improvement of one embodiment of the present invention, the molten steel refining process includes a converter refining process and LF refining that are performed sequentially, In the converter refining process, the carbon content in the steel water at the end of the converter refining process is set to 0.05-0.15% and P ≤ 0.012%, the tapping temperature is set to 1620-1660°C, and after 25-30% of the tapping is completed, aluminum ingots, silicon iron, manganese iron, chromium iron, nickel iron, and molybdenum iron are sequentially added to perform deoxidation and alloying, and during the tapping process, argon gas is blown from the bottom of the steel packaging at a flow rate of 400-800 L / min throughout the entire steel packaging process. In the LF refining process, after injecting the steel water tapped in the converter refining process into the LF furnace, lime and fluorite are sequentially added to prepare the white slag. After white slag refining for 5 to 10 minutes, titanium iron and rare earth iron alloys are sequentially added, and then at least one of boron iron, vanadium iron, or niobium iron is added to perform alloying. The flow rate of argon gas blown from the bottom of the steel bag during the alloying period is set to 300 to 450 L / min. After that, the temperature is raised by applying electricity and chemical composition testing is performed by taking samples. Based on the test results, alloy is added to fine-tune the chemical composition. The flow rate of argon gas blown from the bottom of the steel bag during the fine-tuned chemical composition period is set to 150 to 300 L / min. After that, soft stirring is performed for 25 to 35 minutes, and the tapping temperature at the end of LF refining is set to 1530 to 1560°C.

[0011] As a further improvement of one embodiment of the present invention, in the continuous casting process, a ladle long nozzle argon seal, an alkaline intermediate ladle coating agent, and an immersion nozzle are used to perform fully protective casting during the continuous casting process, a medium carbon steel protective slag is used as the protective slag, the intermediate ladle steel water superheating degree is controlled to 25-35°C, the mold molten metal level is set to 80-87% of the mold height, the molten metal level fluctuation range is set to within ±3%, the mold electromagnetic stirring current is set to 700-750A, the stirring frequency is set to 3-5Hz, the secondary cooling specific water amount is controlled to 0.25-0.30 L / Kg, and the drawing speed is set to 2.3-2.5 m / min.

[0012] To achieve one of the above objectives, one embodiment of the present invention further comprises, by mass percentage, C 0.25~0.45%, Si 0.15~0.50%, Mn 0.5~0.8%, P≦0.015%, S≦0.005%, Cr 5~12%, Ni 2.0~4.5%, Cu≦0.1%, Ti 0.05~0.10%, Mo 0.25~0.50%, Re 0.01~0.10%, Al We also provide fasteners containing 0.015-0.050%, O ≤ 0.001%, N ≤ 0.005%, and at least one of B, Nb, and V, with the remainder being Fe and unavoidable impurities, wherein [B] + [Nb] + [V] ≤ 0.15%, [Cr] / [Ni] is 2.0-3.5, and [Mo] / [Ti] is 4-6.

[0013] As a further improvement of one embodiment of the present invention, the chemical composition of the fastener is as follows, by mass percentage: C 0.30~0.45%, Si 0.20~0.40%, Mn 0.60~0.75%, P≦0.015%, S≦0.005%, Cr 6~11%, Ni 2.5~4.0%, Cu≦0.1%, Ti 0.05~0.10%, Mo 0.25~0.50%, Re 0.01~0.10%, Al It contains 0.015-0.050%, O ≤ 0.001%, N ≤ 0.005%, and at least one of B, Nb, and V, with the remainder being Fe and unavoidable impurities, with [B] + [Nb] + [V] ≤ 0.15%, [Cr] / [Ni] ratio 2.0-3.5, and [Mo] / [Ti] ratio 4-6.

[0014] As a further improvement of one embodiment of the present invention, the chemical composition of the fastener is as follows, by mass percentage: C 0.30~0.40%, Si 0.20~0.35%, Mn 0.60~0.70%, P≦0.015%, S≦0.005%, Cr 6.5~10%, Ni 2.5~3.5%, Cu≦0.1%, Ti 0.05~0.10%, Mo 0.25~0.50%, Re 0.01~0.10%, Al It contains 0.015-0.050%, O ≤ 0.001%, N ≤ 0.005%, and at least one of B, Nb, and V, with the remainder being Fe and unavoidable impurities, with [B] + [Nb] + [V] ≤ 0.15%, [Cr] / [Ni] ratio 2.0-3.5, and [Mo] / [Ti] ratio 4-6.

[0015] As a further improvement of one embodiment of the present invention, the fastener has a tensile strength of ≥2000 MPa, a yield strength of ≥1750 MPa, and a delayed fracture strength ratio of ≥0.85.

[0016] To achieve one of the above objectives, an embodiment of the present invention further provides a method for manufacturing the fastener described above. This manufacturing method involves sequentially manufacturing the fastener using a wire for fasteners through the following steps: annealing, pickling and phosphate treatment, drawing, warm upsetting, rolling, tempering, and surface polishing. The annealing process includes a heating stage, a first cooling stage, and a second cooling stage. In the heating stage, the heating rate is set to 4-6°C / min, the temperature is raised to 760-800°C, and then maintained for 3-5 hours. In the first cooling stage, the cooling rate is set to 1-1.5°C / min, the temperature is cooled to 680-720°C, and then maintained for 2-4 hours. In the second cooling stage, the wire is cooled to room temperature by natural cooling in the heating furnace. In the aforementioned warm upsetting process, the drawn wire obtained in the drawing process is heated to 530-570°C and then upset. The aforementioned tempering process includes a quenching process and a tempering process, wherein the quenching process is heated to a temperature of 850-880°C and held for 30-60 minutes, and the tempering process is heated to a temperature of 550-580°C and held for 60-90 minutes, after which the material is cooled to room temperature by air cooling.

[0017] As a further improvement of one embodiment of the present invention, the quenching cooling medium in the quenching process is oil. [Effects of the Invention]

[0018] Compared to the conventional technology, the beneficial effects of the present invention are as follows:

[0019] (1) In the chemical composition design of the present invention, the presence or absence of each element and the magnitude of its content are precisely selected and controlled, after comprehensively considering the effects of each element on the toughness of the steel, its resistance to delayed fracture, and the formability of the fastener. By defining the relationship between the content of Cr, Ni, Mo, and Ti while significantly reducing the content of C, Si, and Mn, Cr and Ni form interstitial solid solutions in the steel, forming clusters that significantly improve the strength, corrosion resistance, and oxidation resistance of the steel, and suppress hydrogen penetration. Furthermore, Ni and Ti combine to generate nano-precipitation phases even finer than carbide dimensions, strengthening the substrate and simultaneously forming stronger hydrogen traps, further improving the delayed fracture resistance of the steel. In addition, Mo segregates at the interface between the precipitate phase and the substrate, promoting and accelerating the precipitation process. As a result, the final manufactured fasteners have a tensile strength of ≥2000 MPa, a yield strength of ≥1750 MPa, and a delayed fracture strength ratio of ≥0.85, possessing excellent toughness, formability, and delayed fracture resistance. This significantly improves the safety of use in industrial applications of fasteners, and further reduces the reliance of high-strength fasteners on valuable elements such as Mo, V, and Co, resulting in substantial cost savings and advantages for industrial production.

[0020] (2) Based on the aforementioned chemical composition design, by adjusting a series of process means, the wire for fasteners has good structure and mechanical performance, the wire structure is a composite structure of fine equiaxed ferrite and martensite, the tensile strength is 1250 to 1350 MPa, and the wire surface quality is excellent.

[0021] (3) Furthermore, by combining with a series of forming processes such as pickling phosphating treatment, drawing, warm upsetting (heading) forming, forging, quenching and tempering treatment, and surface polishing, not only can the cracking in the upsetting forming process of the fastener be avoided, but the microstructure of the finally manufactured fastener is tempered sorbite, with a tensile strength ≥ 2000 MPa, a yield strength ≥ 1750 MPa, a ratio of fatigue fracture strength ≥ 0.85, excellent toughness, forming performance and fatigue fracture resistance performance, greatly improving the use safety of the fastener in industrial applications. Furthermore, compared with the adoption of a numerical control lathe forming process, the production efficiency can be greatly improved, and it is suitable for industrial mass production.

Brief Description of the Drawings

[0022] [Figure 1] It is a schematic diagram of a sample notch when a low strain rate tensile test is performed on the fastener in the present invention.

Embodiments for Carrying Out the Invention

[0023] Hereinafter, the technical solution of the present invention will be further introduced in combination with specific embodiments, but the scope of protection claimed is not limited only to the described content.

[0024] One embodiment of the present invention provides a wire rod for ultra-high strength fasteners, the chemical composition of which is in mass percentage, C 0.25 - 0.45%, Si 0.15 - 0.50%, Mn 0.5 - 0.8%, P ≤ 0.015%, S ≤ 0.005%, Cr 5 - 12%, Ni 2.0 - 4.5%, Cu ≤ 0.1%, Ti 0.05 - 0.10%, Mo 0.25 - 0.50%, Re 0.01 - 0.10%, Al 0.015 - 0.050%, O ≤ 0.001%, N ≤ 0.005%, and contains at least one of B, Nb, and V, the balance being composed of Fe and unavoidable impurities, [B] + [Nb] + [V] ≤ 0.15%, [Cr] / [Ni] is 2.0 - 3.5, and [Mo] / [Ti] is 4 - 6.

[0025] Here, [B] represents the mass percentage of B, [Nb] represents the mass percentage of Nb, [V] represents the mass percentage of V, [Cr] represents the mass percentage of Cr, [Ni] represents the mass percentage of Ni, [Mo] represents the mass percentage of Mo, and [Ti] represents the mass percentage of Ti.

[0026] In the chemical composition design of this invention, the presence or absence of each element and the magnitude of its content are precisely selected and controlled, after comprehensively considering the effects of each element on the toughness of the steel, its resistance to delayed fracture, and the formability of the fasteners. By defining the relationship between the content of Cr, Ni, Mo, and Ti while significantly reducing the content of C, Si, and Mn, Cr and Ni form interstitial solid solutions in the steel, creating clusters that significantly improve the strength, corrosion resistance, and oxidation resistance of the steel, and suppress hydrogen penetration. Furthermore, Ni and Ti combine to generate nano-precipitation phases even finer than carbide dimensions, strengthening the substrate and simultaneously forming stronger hydrogen traps, further improving the delayed fracture resistance of the steel. In addition, Mo segregates at the interface between the precipitate phase and the substrate, promoting and accelerating the precipitation process. As a result, the final manufactured fasteners have a tensile strength of ≥2000 MPa, a yield strength of ≥1750 MPa, and a delayed fracture strength ratio of ≥0.85, possessing excellent toughness, formability, and delayed fracture resistance. This significantly improves the safety of use in industrial applications of fasteners, and further reduces the reliance of high-strength fasteners on valuable elements such as Mo, V, and Co, resulting in substantial cost savings and advantages for industrial production.

[0027] Preferably, the chemical composition of the ultra-high-strength fastener wire is, by mass percentage, C 0.30~0.45%, Si 0.20~0.40%, Mn 0.60~0.75%, P≦0.015%, S≦0.005%, Cr 6~11%, Ni 2.5~4.0%, Cu≦0.1%, Ti 0.05~0.10%, Mo 0.25~0.50%, Re 0.01~0.10%, Al It contains 0.015-0.050%, O ≤ 0.001%, N ≤ 0.005%, and at least one of B, Nb, and V, with the remainder being Fe and unavoidable impurities, with [B] + [Nb] + [V] ≤ 0.15%, [Cr] / [Ni] ratio 2.0-3.5, and [Mo] / [Ti] ratio 4-6.

[0028] More preferably, the chemical composition of the wire material for the ultra-high-strength fastener is, by mass percentage, C 0.30~0.40%, Si 0.20~0.35%, Mn 0.60~0.70%, P≦0.015%, S≦0.005%, Cr 6.5~10%, Ni 2.5~3.5%, Cu≦0.1%, Ti 0.05~0.10%, Mo 0.25~0.50%, Re 0.01~0.10%, Al It contains 0.015-0.050%, O ≤ 0.001%, N ≤ 0.005%, and at least one of B, Nb, and V, with the remainder being Fe and unavoidable impurities, with [B] + [Nb] + [V] ≤ 0.15%, [Cr] / [Ni] ratio 2.0-3.5, and [Mo] / [Ti] ratio 4-6.

[0029] One embodiment of the present invention further provides an ultra-high-strength fastener manufactured using the above-mentioned ultra-high-strength fastener wire as a base material, and having the same chemical composition as the above-mentioned ultra-high-strength fastener wire.

[0030] One embodiment of the present invention further provides a preferred method for manufacturing the ultra-high-strength wire for fasteners. The manufacturing method includes sequentially performing molten steel refining steps, continuous casting steps, slow cooling steps, heating steps, high-speed wire rolling steps, and controlled cooling steps to produce the ultra-high-strength wire for fasteners. The chemical composition of the wire is as described above and will not be repeated here.

[0031] The manufacturing method described above will be explained in detail below, following the production sequence.

[0032] (1) Smelting process This process includes sequential converter refining and LF refining steps.

[0033] a. Converter refining process Scrap iron and blast furnace pig iron are fed into a converter for refining. At the end of the converter refining process, the carbon content in the steel water is set to 0.05-0.15% and P ≤ 0.012%. The tapping temperature is set to 1620-1660°C. After 25-30% of the tapping is complete, aluminum ingots, silicon iron, manganese iron, chromium iron, nickel iron, and molybdenum iron are sequentially added to deoxidize and alloy the steel, reducing oxidative combustion losses and improving the efficiency of alloy use.

[0034] Preferably, during the tapping process, argon gas is blown from the bottom of the steel packaging at a flow rate of 400 to 800 L / min throughout the entire packaging process.

[0035] b. LF refining process After injecting the steel water tapped in the converter refining process into the LF furnace, lime and fluorite are sequentially added to prepare the white slag. After white slag refining for 5-10 minutes, titanium iron and rare earth iron alloys are sequentially added, followed by alloying with at least one of boron iron, vanadium iron, or niobium iron. The flow rate of argon gas blown from the bottom of the steel sack during the alloying period is set to 300-450 L / min. After that, the temperature is raised by applying electricity, and chemical composition analysis is performed by sampling. Based on the test results, alloy is added to fine-tune the chemical composition. The flow rate of argon gas blown from the bottom of the steel sack during the fine-tuning period is set to 150-300 L / min. After that, soft stirring is performed for 25-35 minutes, and the tapping temperature at the end of LF refining is set to 1530-1560°C.

[0036] (2) Continuous casting process In the LF refining process, the resulting steel water is cast into continuous slabs through continuous casting. The temperature of the intermediate ladle (intermediate pack or tundish) is controlled to 1510-1530°C to improve the fluidity of the steel water, thereby improving the poor fluidity of the steel water caused by high Cr, Ni, and Mo content in the steel, and improving the uniformity of the alloying elements.

[0037] Preferably, a ladle long nozzle argon seal, an alkaline intermediate ladle coating agent, and an immersion nozzle are used to perform fully protective casting during the continuous casting process, and a medium carbon steel protective slag is used as the protective slag.

[0038] Preferably, during the continuous casting process, the superheating of the ladle steel water is controlled to 25-35°C, the mold molten metal level is set to 80-87% of the mold height, the molten metal level fluctuation range is within ±3%, the mold electromagnetic stirring current is set to 700-750A, the stirring frequency to 3-5Hz, the secondary cooling specific water volume is controlled to 0.25-0.30 L / Kg, and the drawing speed is set to 2.3-2.5 m / min.

[0039] (3) Slow cooling process The continuously cast slabs obtained in the continuous casting process are cooled to 650-700°C by air cooling, then sent to a heat-insulating pit, where they are slowly cooled at a cooling rate of 5.5-7°C / h until they reach below 200°C, after which they are removed from the heat-insulating pit.

[0040] (4)Heating process The continuous cast slab after the slow cooling process is sent into a heating furnace for heating. The heating process includes a heating stage and a soaking stage. The heating stage temperature is set to 1100-1140°C, the heating rate to 0.3-0.4°C / s, and the heating time to 20-30 mins. The soaking stage temperature is set to 1150-1190°C, and the soaking time to 15-25 mins.

[0041] By controlling the heating temperature, heating rate, and heating time in stages, the temperature of the continuous cast slab can be made uniform, the alloying elements can be sufficiently dissolved in the austenite, and cracks can be prevented from occurring due to excessive thermal stress in the subsequent rolling process. At the same time, the rhythm of rolling production can be improved, and production efficiency can be increased.

[0042] (5) High-speed wire rolling process The continuous cast slab after the heating process is rolled into wire, wound into a coil, with a starting rolling temperature of 1050-1090°C and a finishing rolling temperature of 910-940°C. In this way, the brittle temperature range of the steel of the present invention is avoided, the wire obtained by rolling has good microstructure and mechanical properties, and the surface quality of the wire can be improved.

[0043] Here, the diameter of the wire is 5 to 26 mm.

[0044] (6) Controlled cooling process The resulting coil is sent to a Stermore cooling wire for cooling, and the discharge temperature is set to 890-910°C.

[0045] The insulation covers for the first and second stage roller tables of the Stermore cooling wire are opened, all insulation covers for the other roller tables are closed, the first to third fans are opened and the fan airflow is set to 60-90%, the other fans are closed, the roller table speed for the first and second stage roller tables is set to 0.25-0.4 m / s, and the roller table speed for the other roller tables is set to 0.15-0.3 m / s, and the temperature when the wire reaches the third stage roller table is controlled to 750-780°C. That is, the temperature when the wire enters the first closed insulation cover is controlled to 750-780°C. The above process and parameter settings improve the uniformity of the microstructure of the obtained wire, form a fine equiaxed ferrite and martensitic structure in the wire, which is advantageous for subsequent annealing, drawing, and forming processes when manufacturing fasteners.

[0046] Thus, the manufacturing method of this embodiment, based on the aforementioned chemical composition design, involves adjusting a series of process steps to produce a fastener wire that ultimately possesses good structure and mechanical performance. The wire structure is a composite structure of fine equiaxed ferrite and martensite, with a tensile strength of 1250-1350 MPa and excellent wire surface quality.

[0047] Furthermore, ultra-high-strength fasteners can be manufactured by sequentially processing the above-mentioned wire material for ultra-high-strength fasteners through annealing, pickling and phosphate treatment, drawing, warm upsetting, rolling, tempering, and surface polishing. The specific process is as follows.

[0048] (7) Annealing process The process includes a heating stage, a first cooling stage, and a second cooling stage. The heating stage has a heating rate of 4-6°C / min, raising the temperature to 760-800°C, after which it is held at that temperature for 3-5 hours. The first cooling stage has a cooling rate of 1-1.5°C / min, cooling the temperature to 680-720°C, after which it is held at that temperature for 2-4 hours. In the second cooling stage, the wire is cooled to room temperature by natural cooling in the heating furnace. In this way, the wire is given a spherical pearlite structure, and carbides are uniformly precipitated and distributed within the ferrite matrix, thereby reducing the hardness of the wire and making it advantageous for subsequent drawing and forming processes.

[0049] (8) Pickling phosphoric acid treatment process After annealing, the wire is subjected to acid pickling and phosphate treatment to remove oxide scale from the wire surface, and a phosphate coating is formed on the wire surface to improve lubrication performance and reduce damage to the mold during subsequent drawing and upsetting processes.

[0050] (9) Drawing process After pickling and phosphate treatment, the wire is drawn to the specified diameter, and the amount of diameter reduction during drawing is controlled according to the product requirements of the fastener. The so-called amount of diameter reduction during drawing is the difference between the diameter of the wire and the diameter of the finished wire.

[0051] Preferably, the amount of diameter reduction from drawing is controlled to 0.5 to 1.5 mm.

[0052] (10) Warm upsetting process The drawn wire obtained in the drawing process is heated to 530-570°C and then upscaled. Warm upscaled molding avoids the large drag force and cold work hardening that occur during cold upscaled molding, making it convenient for upscaled fasteners with complex shapes and large deformation amounts.

[0053] (11) Rolling process After warm upsetting, the fasteners are subjected to rolling to form screw threads.

[0054] (12) Tempering treatment process The process includes a quenching process and a tempering process. In the quenching process, the heating temperature is set to 850-880°C and the holding time to 30-60 mins, transforming the entire structure of the fastener into austenite. After cooling, the cooling rate is set to 80-90°C / s, transforming the supercooled austenite into martensite. In the tempering process, the heating temperature is set to 550-580°C and the holding time to 60-90 mins, transforming the structure of the fastener into tempered sorbite. After tempering, the fastener is cooled to room temperature by air cooling. In this way, the strength of the fastener is improved, as well as its plasticity and toughness, making it possible to achieve good overall mechanical performance for the fastener.

[0055] The quenching and cooling medium used in the aforementioned quenching process is oil.

[0056] (13) Surface polishing process The surface of the fastener after the heat treatment process is polished.

[0057] Thus, the fasteners manufactured by further drawing in this embodiment, based on the aforementioned chemical composition design, not only avoid cracking during the upsetting process through a series of forming steps including pickling, phosphate treatment, drawing, warm upsetting, rolling, tempering, and surface polishing, but also have a tempered sorbite microstructure, exhibiting a tensile strength of ≥2000 MPa, a yield strength of ≥1750 MPa, and a delayed fracture strength ratio of ≥0.85, possessing excellent toughness, formability, and resistance to delayed fracture, significantly improving the safety of use in industrial applications of the fasteners. Furthermore, compared to the adoption of numerically controlled lathe forming processes, production efficiency can be significantly improved, making it suitable for industrial mass production.

[0058] The following 10 examples further illustrate specific embodiments of the present invention. Of course, these 10 examples represent only a portion, not all, of the many variations included in this embodiment. Other embodiments based on the above-described embodiments do not depart from the technical spirit of the present invention.

[0059] <Examples> First, Examples 1 to 10 all provide wire rods for ultra-high-strength fasteners, and ultra-high-strength fasteners manufactured by further processes of annealing, pickling and phosphate treatment, drawing, warm upsetting, rolling, tempering, and surface polishing of the wire rods. The chemical composition of the wire rods and fasteners is shown in Table 1, with the remainder being Fe and unavoidable impurities.

[0060] [Table 1]

[0061] The manufacturing method is as follows:

[0062] (1) Smelting process a. Converter refining process Scrap iron and blast furnace pig iron were sent into a converter for refining, and the carbon content in the steel water at the end of the converter refining process was set to 0.05-0.15% and P ≤ 0.012%. The tapping temperature was set to 1620-1660°C, and during the tapping process, argon gas was blown from the bottom of the steel packaging at a flow rate of 400-800 L / min. After 25-30% of the tapping was completed, aluminum ingots, silicon iron, manganese iron, chromium iron, nickel iron, and molybdenum iron were sequentially added to deoxidize and alloy the steel.

[0063] b. LF refining process After injecting the steel water tapped in the converter refining process into the LF furnace, lime and fluorite were sequentially added to prepare the white slag. After 5-10 minutes of white slag refining, titanium iron and rare earth iron alloys were sequentially added, followed by the addition of at least one of boron iron, vanadium iron, or niobium iron to perform alloying. The flow rate of argon gas blown from the bottom of the steel bag during the alloying period was set to 300-450 L / min. After that, the temperature was increased by applying electricity and chemical composition analysis was performed by sampling. Based on the test results, alloy was added to fine-tune the chemical composition. The flow rate of argon gas blown from the bottom of the steel bag during the chemical composition fine-tuning period was set to 150-300 L / min. After that, soft stirring was performed for 25-35 minutes, and the tapping temperature at the end of LF refining was set to 1530-1560°C.

[0064] (2) Continuous casting process In the LF refining process, the resulting steel water was continuously cast into slabs by continuous casting. The temperature of the intermediate ladle was controlled to 1510-1530°C, the superheating degree of the steel water in the intermediate ladle was set to 25-35°C, the mold molten metal height was set to 80-87% of the mold height, and a ladle long nozzle argon seal, alkaline intermediate ladle coating agent, and immersion nozzle were used for complete protective casting during the continuous casting process. Medium carbon steel protective slag was used as the protective slag, the molten metal fluctuation range was kept within ±3%, the mold electromagnetic stirring current was set to 700-750A, the stirring frequency to 3-5Hz, the secondary cooling specific water volume was controlled to 0.25-0.30 L / Kg, and the drawing speed was set to 2.3-2.5 m / min.

[0065] (3) Slow cooling process The continuously cast slabs obtained in the continuous casting process were cooled to 650-700°C by air cooling, then sent to a heat-insulating pit where they were slowly cooled at a cooling rate of 5.5-7°C / h until they reached below 200°C, after which they were removed from the heat-insulating pit.

[0066] (4)Heating process The continuous cast slabs after the slow cooling process were sent into a heating furnace for heating. The heating process included a heating stage and a soaking stage. The heating stage temperature was set to 1100-1140°C, the heating rate to 0.3-0.4°C / s, and the heating time to 20-30 mins. The soaking stage temperature was set to 1150-1190°C and the soaking time to 15-25 mins.

[0067] (5) High-speed wire rolling process The continuous cast slabs after the heating process were rolled into wire rods with a diameter of 5 to 26 mm, wound into coils, with a starting rolling temperature of 1050 to 1090°C and a finishing rolling temperature of 910 to 940°C.

[0068] (6) Controlled cooling process The obtained coil was sent to a Stermore cooling wire for cooling, and the discharge temperature was set to 890-910°C. The insulation covers of the first and second stage roller tables of the Stermore cooling wire were opened, and all insulation covers of the other roller tables were closed. The first to third fans were opened, with the fan airflow set to 60-90%, and the other fans were closed. The roller table speed of the first and second stage roller tables was set to 0.25-0.4 m / s, and the roller table speed of the other roller tables was set to 0.15-0.3 m / s, and the temperature of the wire when it reached the third stage roller table was controlled to 750-780°C.

[0069] (7) Annealing process The process includes a heating stage, a first cooling stage, and a second cooling stage. The heating stage has a heating rate of 4-6°C / min, and the temperature is raised to 760-800°C, after which it is maintained for 3-5 hours. The first cooling stage has a cooling rate of 1-1.5°C / min, and the temperature is cooled to 680-720°C, after which it is maintained for 2-4 hours. In the second cooling stage, the wire is cooled to room temperature by natural cooling within the heating furnace.

[0070] (8) Pickling phosphoric acid treatment process The wire rods were subjected to pickling and phosphate treatment after annealing.

[0071] (9) Drawing process After pickling and phosphate treatment, the wire was drawn to the specified dimensions, and the amount of diameter reduction during drawing was controlled according to the product requirements for the fasteners.

[0072] (10) Warm upsetting process The drawn wire obtained in the aforementioned drawing process was heated to 530-570°C and then upscaled.

[0073] (11) Rolling process After warm upsetting, the fasteners were subjected to a rolling process to form screw threads.

[0074] (12) Tempering treatment process The process included a quenching process and a tempering process. In the quenching process, the heating temperature was set to 850-880°C, the holding time to 30-60 mins, and then the material was cooled. Oil was used as the quenching cooling medium, and the cooling rate was set to 80-90°C / s. In the tempering process, the heating temperature was set to 550-580°C, the holding time to 60-90 mins, and after tempering, the material was cooled to room temperature by air cooling.

[0075] (13) Surface polishing process The surface of the fasteners was polished after the heat treatment process.

[0076] In Examples 1 to 10, no cracks occurred during the upsetting process, meaning the crack rate was 0. During the processing, the average processing time for a single fastener was 0.5 to 1.5 seconds, and the product rate was 95% or higher.

[0077] Samples were taken from each of the 10 fasteners in the examples, and mechanical performance tests and delayed fracture resistance tests were performed.

[0078] Regarding mechanical performance, the yield strength, tensile strength, and elongation after fracture of the fasteners were tested using a tensile testing machine, referring to the standard test methods and definitions for mechanical performance testing of ASTM A370 steel products.

[0079] For delayed fracture resistance, a low-strain-rate tensile test method was adopted, and the test procedure was as follows:

[0080] Step 1: Referring to Figure 1, prepare two sets of fastener samples 10, and make a notch 20 along the circumferential direction in the center of the two sets of fastener samples 10. The notch angle α = 60°, one set of samples will be used as a hydrogen charge test piece, and the other set of samples will be used as a control test piece.

[0081] Step 2: Place the hydrogen charging test specimen in a 4 g / L NaOH solution and perform electrochemical hydrogen charging. The hydrogen charging time is 48 hours, and the current density is 15 A / m². 2 After hydrogen charging is complete, the sample is washed and dried.

[0082] For the control specimen, the procedure in step 2 is omitted.

[0083] Step 3: Both sets of samples are subjected to room temperature tensile testing using a low-strain-rate tensile testing machine. The tensile strain rate is set to 5 × 10⁻⁶. -6 Set the test interval to / s and measure the tensile strength of each of the two sets of samples.

[0084] Step 4: Calculate the delayed fracture strength ratio. The delayed fracture strength ratio is calculated as: tensile strength of the hydrogen-charged specimen / tensile strength of the control specimen. Here, a larger delayed fracture strength ratio indicates better delayed fracture resistance of the sample. A delayed fracture strength ratio of 0.7 or higher is generally considered acceptable, and a ratio of 0.8 or higher is considered excellent.

[0085] The results of the mechanical performance tests and the delayed fracture strength ratio are shown in Table 2.

[0086] [Table 2]

[0087] Based on the above, the fasteners of this invention, by combining chemical composition design with control of the entire production process of the wire and fasteners, avoid cracking during the upsetting process of the fasteners. Furthermore, the manufactured fasteners have a tensile strength of ≥2000 MPa, a yield strength of ≥1750 MPa, and a delayed fracture strength ratio of ≥0.85. They possess extremely high tensile strength, excellent toughness, moldability, and delayed fracture resistance, significantly improving safety in industrial applications of fasteners and greatly improving production efficiency, making them suitable for industrial mass production.

[0088] It should be understood that although this specification is described according to embodiments, each embodiment does not contain only one independent technical solution, and this style of description in the specification is for clarity only, and those skilled in the art can consider the specification as a whole and combine the technical solutions in each embodiment as appropriate to form other embodiments that will be understood by those skilled in the art.

[0089] The series of detailed descriptions listed above are merely specific descriptions of possible embodiments of the present invention and do not limit the scope of protection of the present invention. Equivalent embodiments or modifications made without departing from the technical spirit of the present invention are all included within the scope of protection of the present invention.

Claims

1. The chemical composition, by mass percentage, is as follows: C 0.25–0.45%, Si 0.15–0.50%, Mn 0.5–0.8%, P ≤ 0.015%, S ≤ 0.005%, Cr 5–12%, Ni 2.0–4.5%, Cu ≤ 0.1%, Ti 0.05–0.10%, Mo 0.25–0.50%, Re 0.01–0.10%, Al 0.015–0.050%, O ≤ 0.001%, N ≤ 0.005%, and at least one of B, Nb, and V, with the remainder being Fe and unavoidable impurities, and [B] + [Nb] + [V] ≤ 0.15%, [Cr] / [Ni] is 2.0–3.5, and [Mo] / [Ti] is 4–6. wire rod.

2. The chemical composition, by mass percentage, is as follows: C 0.30-0.45%, Si 0.20-0.40%, Mn 0.60-0.75%, P ≤ 0.015%, S ≤ 0.005%, Cr 6-11%, Ni 2.5-4.0%, Cu ≤ 0.1%, Ti 0.05-0.10%, Mo 0.25-0.50%, Re 0.01-0.10%, Al It contains 0.015–0.050%, O ≤ 0.001%, N ≤ 0.005%, and at least one of B, Nb, and V, with the remainder being Fe and unavoidable impurities, with [B] + [Nb] + [V] ≤ 0.15%, [Cr] / [Ni] being 2.0–3.5, and [Mo] / [Ti] being 4–6. The wire material according to claim 1.

3. The chemical composition, by mass percentage, is as follows: C 0.30-0.40%, Si 0.20-0.35%, Mn 0.60-0.70%, P ≤ 0.015%, S ≤ 0.005%, Cr 6.5-10%, Ni 2.5-3.5%, Cu ≤ 0.1%, Ti 0.05-0.10%, Mo 0.25-0.50%, Re 0.01-0.10%, Al It contains 0.015–0.050%, O ≤ 0.001%, N ≤ 0.005%, and at least one of B, Nb, and V, with the remainder being Fe and unavoidable impurities, with [B] + [Nb] + [V] ≤ 0.15%, [Cr] / [Ni] being 2.0–3.5, and [Mo] / [Ti] being 4–6. The wire material according to claim 1.

4. A method for manufacturing a wire according to claim 1, This process includes sequential molten steel refining, continuous casting, slow cooling, heating, high-speed wire rolling, and controlled cooling processes. 、 In the continuous casting process described above, the temperature of the intermediate ladle is controlled to 1510 to 1530°C. In the aforementioned slow cooling process, the continuously cast slab obtained in the continuous casting process is cooled to 650-700°C by air cooling, then sent to a heat-insulating pit, where it is slowly cooled at a cooling rate of 5.5-7°C / h until it reaches 200°C or below, and then removed from the heat-insulating pit. The heating process includes a heating stage and a soaking stage, wherein the heating stage has a temperature of 1100 to 1140°C, a heating rate of 0.3 to 0.4°C / s, and a heating time of 20 to 30 mins, and the soaking stage has a temperature of 1150 to 1190°C and a soaking time of 15 to 25 mins. In the high-speed wire rolling process, the starting rolling temperature is 1050 to 1090°C, and the ending rolling temperature is 910 to 940°C. A method for manufacturing wire, comprising the above-mentioned controlled cooling step, wherein the discharge temperature is 890 to 910°C, the insulating covers of the first and second stage roller tables of the Stermore cooling wire are opened, the insulating covers of all other roller tables are closed, the first to third fans are opened and the fan airflow is set to 60 to 90%, the other fans are closed, the roller table speed of the first and second stage roller tables is set to 0.25 to 0.4 m / s, the roller table speed of the other roller tables is set to 0.15 to 0.3 m / s, and the temperature of the wire when it reaches the third stage roller table is controlled to 750 to 780°C.

5. The molten steel refining process includes a converter refining process and an LF refining process, which are carried out sequentially. In the converter refining process, the carbon content in the steel water at the end of the converter refining process is set to 0.05-0.15% and P ≤ 0.012%, the tapping temperature is set to 1620-1660°C, and after 25-30% of the tapping is completed, aluminum ingots, silicon iron, manganese iron, chromium iron, nickel iron, and molybdenum iron are sequentially added to perform deoxidation and alloying, and during the tapping process, argon gas is blown from the bottom of the steel packaging at a flow rate of 400-800 L / min throughout the entire steel packaging process. In the LF refining process, after injecting the steel water tapped in the converter refining process into the LF furnace, lime and fluorite are sequentially added to prepare the white slag. After 5 to 10 minutes of white slag refining, titanium iron and rare earth iron alloys are sequentially added, and then at least one of boron iron, vanadium iron, or niobium iron is added to perform alloying. The flow rate of argon gas blown from the bottom of the steel casing during the alloying period is set to 300 to 450 L / min. After that, the temperature is raised by applying electricity and a sample is taken to perform a chemical composition test. Based on the test results, the alloy is replenished and the chemical composition is finely adjusted. The flow rate of argon gas blown from the bottom of the steel casing during the chemical composition fine adjustment period is set to 150 to 300 L / min. After that, soft stirring is performed for 25 to 35 minutes, and the tapping temperature at the end of LF refining is set to 1530 to 1560°C. The method for manufacturing a wire according to claim 4.

6. In the continuous casting process described above, a ladle long nozzle argon seal, an alkaline intermediate ladle coating agent, and an immersion nozzle are used to perform fully protective casting during the continuous casting process. A medium carbon steel protective slag is used as the protective slag. The intermediate ladle steel water superheating temperature is controlled to 25-35°C. The mold molten metal level is set to 80-87% of the mold height, the molten metal level fluctuation range is within ±3%, the mold electromagnetic stirring current is set to 700-750A, the stirring frequency to 3-5Hz, the secondary cooling specific water volume is controlled to 0.25-0.30 L / Kg, and the drawing speed is set to 2.3-2.5 m / min. The method for manufacturing a wire according to claim 4.

7. The chemical composition, by mass percentage, is as follows: C 0.25–0.45%, Si 0.15–0.50%, Mn 0.5–0.8%, P ≤ 0.015%, S ≤ 0.005%, Cr 5–12%, Ni 2.0–4.5%, Cu ≤ 0.1%, Ti 0.05–0.10%, Mo 0.25–0.50%, Re 0.01–0.10%, Al 0.015–0.050%, O ≤ 0.001%, N ≤ 0.005%, and at least one of B, Nb, and V, with the remainder being Fe and unavoidable impurities, and [B] + [Nb] + [V] ≤ 0.15%, [Cr] / [Ni] is 2.0–3.5, and [Mo] / [Ti] is 4–6. Fasteners.

8. The chemical composition, by mass percentage, is as follows: C 0.30-0.45%, Si 0.20-0.40%, Mn 0.60-0.75%, P ≤ 0.015%, S ≤ 0.005%, Cr 6-11%, Ni 2.5-4.0%, Cu ≤ 0.1%, Ti 0.05-0.10%, Mo 0.25-0.50%, Re 0.01-0.10%, Al It contains 0.015–0.050%, O ≤ 0.001%, N ≤ 0.005%, and at least one of B, Nb, and V, with the remainder being Fe and unavoidable impurities, with [B] + [Nb] + [V] ≤ 0.15%, [Cr] / [Ni] being 2.0–3.5, and [Mo] / [Ti] being 4–6. The fastener according to claim 7.

9. The chemical composition, by mass percentage, is as follows: C 0.30-0.40%, Si 0.20-0.35%, Mn 0.60-0.70%, P ≤ 0.015%, S ≤ 0.005%, Cr 6.5-10%, Ni 2.5-3.5%, Cu ≤ 0.1%, Ti 0.05-0.10%, Mo 0.25-0.50%, Re 0.01-0.10%, Al It contains 0.015–0.050%, O ≤ 0.001%, N ≤ 0.005%, and at least one of B, Nb, and V, with the remainder being Fe and unavoidable impurities, with [B] + [Nb] + [V] ≤ 0.15%, [Cr] / [Ni] being 2.0–3.5, and [Mo] / [Ti] being 4–6. The fastener according to claim 7.

10. The tensile strength is ≥ 2000 MPa, the yield strength is ≥ 1750 MPa, and the delayed fracture strength ratio is ≥ 0.

85. The fastener according to claim 7.

11. A method for manufacturing a fastener according to claim 7, The method for manufacturing the fastener involves sequentially performing the following steps using wire as the base material: annealing, pickling and phosphate treatment, drawing, warm upsetting, rolling, tempering, and surface polishing. The annealing step includes a heating step, a first cooling step, and a second cooling step. In the heating step, the heating rate is 4 to 6°C / min, the temperature is raised to 760 to 800°C, and then maintained for 3 to 5 hours. In the first cooling step, the cooling rate is 1 to 1.5°C / min, the temperature is cooled to 680 to 720°C, and then maintained for 2 to 4 hours. In the second cooling step, the wire is cooled to room temperature by natural cooling in a heating furnace. In the aforementioned warm upsetting process, the drawn wire obtained in the drawing process is heated to 530 to 570°C and then upset. A method for manufacturing fasteners, wherein the heat treatment process includes a quenching process and a tempering process, the heating temperature of the quenching process being 850 to 880°C and the holding time being 30 to 60 mins, the heating temperature of the tempering process being 550 to 580°C and the holding time being 60 to 90 mins, and the fastener is cooled to room temperature by air cooling after tempering.

12. The quenching cooling medium in the aforementioned quenching process is oil. A method for manufacturing a fastener according to claim 11.

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