Corrosion-resistant fastener and process for making same

Abstract

This invention relates to the field of fastener technology and proposes a corrosion-resistant fastener and its preparation process. The preparation process of a corrosion-resistant fastener includes the following steps: a steel ingot undergoes homogenization treatment, annealing treatment, stamping, turning, and threading, followed by quenching and tempering treatment, and cooling to obtain the corrosion-resistant fastener; the tempering process involves first heating to 150-200℃ for a first-stage tempering treatment, then performing a second-stage tempering treatment at 350-450℃, and finally performing a third-stage tempering treatment at 600℃. The fastener of this invention possesses high tensile strength and salt spray resistance, and can better meet the long-term use requirements under complex corrosive environments and high load conditions.

Description

Technical Field

[0001] This invention relates to the field of fastener technology, and more specifically, to a corrosion-resistant fastener and its manufacturing process. Background Technology

[0002] Fasteners, as indispensable basic connecting components in the industrial field, are widely used in machinery manufacturing, construction engineering, marine engineering, chemical equipment, rail transportation, and many other fields. Their performance directly determines the connection stability, safety, and service life during application. In actual service, fasteners not only need to withstand mechanical forces such as assembly preload and working loads, but are also often exposed to complex corrosive environments such as the atmosphere, seawater, acid and alkali media, and high humidity, facing the dual challenges of corrosion and mechanical loads. Therefore, corrosion resistance and mechanical properties are core key indicators for evaluating fastener quality.

[0003] However, the corrosion resistance and mechanical properties of current fasteners cannot adequately meet the long-term use requirements under complex corrosive environments and high load conditions. Therefore, there is a need to provide a corrosion-resistant fastener with good mechanical properties. Summary of the Invention

[0004] This invention proposes a corrosion-resistant fastener and its manufacturing process, which has high corrosion resistance and tensile strength.

[0005] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a process for preparing corrosion-resistant fasteners, comprising the following steps: after homogenization treatment, annealing treatment, stamping, turning, and threading of steel ingots, quenching treatment, tempering treatment, and cooling, corrosion-resistant fasteners are obtained; the tempering treatment process is as follows: firstly, the temperature is raised to 150~200℃ for the first stage of tempering treatment, then the temperature is raised to 350~450℃ for the second stage of tempering treatment, and finally the temperature is raised to 600℃ for the third stage of tempering treatment.

[0006] In one embodiment, the tempering process specifically involves: first, heating to 150-200°C at a rate of 5-10°C / h for the first stage of tempering; then heating to 350-450°C at a rate of 10°C / h for the second stage of tempering; and finally heating to 600°C at a rate of 10-15°C / h for the third stage of tempering.

[0007] In one implementation, the first tempering process takes 0.5 hours, the second tempering process takes 1 to 2 hours, and the third tempering process takes 1 to 2 hours.

[0008] In one embodiment, the homogenization treatment temperature is 1100~1200℃, and the homogenization treatment time is 12~16h.

[0009] In one embodiment, the annealing process is as follows: first, a first-stage annealing process is performed at 600~750℃, followed by a second-stage annealing process at 950~1100℃.

[0010] In one implementation, the first annealing process takes 1 to 1.5 hours, and the second annealing process takes 1.4 to 1.5 hours.

[0011] In one embodiment, the steel ingot comprises the following components by weight percentage: C 0.06%~0.07%, Si 0.20%~0.35%, Mn 0.30%~0.70%, P 0.008%~0.010%, S 0.004%~0.008%, Al 0.20%~0.30%, Cr 2.0%~2.5%, Mo 0.30%~0.50%, V 0.2%~0.3%, Cu 0.1%~0.20%, Ni 0.02%~0.80%, N 0.004%~0.006%, with the balance being Fe and unavoidable impurities.

[0012] In one embodiment, the mass ratio of Cr to Mo in the steel ingot composition is: Cr / Mo = 4.2~9.4.

[0013] In one embodiment, the quenching process is as follows: after heating to 900~930℃, water cooling is performed to room temperature.

[0014] Secondly, the present invention provides a corrosion-resistant fastener prepared by the above-mentioned preparation process.

[0015] To improve the corrosion resistance and mechanical properties of fasteners, this invention employs a three-stage gradient tempering process in the preparation of corrosion-resistant fasteners, which has the following beneficial effects: The three-stage gradient tempering process first eliminates residual internal stress from quenching and stabilizes the matrix structure through low-temperature tempering, then optimizes the strength-toughness ratio of the material through medium-temperature tempering, and finally further refines the grains, reduces grain boundary defects and micropores through high-temperature tempering, effectively reducing the initiation sites of electrochemical corrosion. This process not only improves the overall mechanical properties of fasteners but also significantly enhances their corrosion resistance, achieving a simultaneous improvement in both mechanical and corrosion resistance. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0017] Currently available fasteners struggle to balance high mechanical strength with long-term corrosion resistance, making them unsuitable for complex corrosive environments such as marine salt spray, chemical acids and alkalis, humid and hot mining areas, and high-altitude and heavy-load conditions, as well as for high-load, long-term service conditions in engineering machinery, wind power, rail transportation, and pressure vessels. To address the issues of low mechanical strength and corrosion resistance in fasteners, this invention provides a corrosion-resistant fastener and its manufacturing process. By employing a three-stage tempering process, a two-stage annealing process, and further optimization of the fastener's chemical composition, the mechanical strength and corrosion resistance of the fastener are improved.

[0018] Specifically, in order to better understand the technical solution of the present invention, it is described in the following parts.

[0019] Part One This invention provides a process for preparing corrosion-resistant fasteners, comprising the following steps: A steel ingot undergoes homogenization, annealing, stamping, turning, and threading, followed by quenching and tempering. After cooling, the corrosion-resistant fastener is obtained. The tempering process involves first heating to 150-200℃ for a first-stage tempering, then performing a second-stage tempering at 350-450℃, and finally a third-stage tempering at 600℃. The 150-200℃ temperature can be, for example, 150℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 200℃, etc.; the 350-450℃ temperature can be, for example, 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, etc.

[0020] In some embodiments of the present invention, the tempering process specifically includes: firstly, a first-stage tempering process is performed by heating to 150-200°C at a rate of 5-10°C / h; secondly, a second-stage tempering process is performed by heating to 350-450°C at a rate of 10°C / h; and finally, a third-stage tempering process is performed by heating to 600°C at a rate of 10-15°C / h. The 5-10°C / h rate can be, for example, 5°C / h, 6°C / h, 7°C / h, 8°C / h, 9°C / h, 10°C / h, etc., and the 10-15°C / h rate can be, for example, 10°C / h, 11°C / h, 12°C / h, 13°C / h, 14°C / h, 15°C / h, etc.

[0021] In some embodiments of the present invention, the first tempering treatment time is 0.5 hours, the second tempering treatment time is 1 to 2 hours, for example, 1 hour, 1.2 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.8 hours, 2.0 hours, etc., and the third tempering treatment time is 1 to 2 hours, for example, 1 hour, 1.2 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.8 hours, 2.0 hours, etc.

[0022] In some embodiments of the present invention, the homogenization temperature is 1100~1200℃, for example, 1100℃, 1110℃, 1120℃, 1130℃, 1140℃, 1150℃, 1160℃, 1170℃, 1180℃, 1190℃, 1200℃, etc., and the homogenization time is 12~16h, for example, 12h, 13h, 14h, 15h, 16h, etc.

[0023] In some embodiments of the present invention, the annealing process is as follows: a first-stage annealing treatment is performed at 600~750℃, followed by a second-stage annealing treatment at 950~1100℃; wherein 600~750℃ can be, for example, 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, 660℃, 670℃, 680℃, 690℃, 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, etc.; wherein 950~1100℃ can be, for example, 950℃, 960℃, 970℃, 980℃, 990℃, 1000℃, 1050℃, 1100℃, etc.

[0024] In this invention, the first stage of annealing is carried out at 600~750℃, which can improve the preferential diffusion of C and Mo, and the early precipitation of carbides without coarse agglomeration. It can also eliminate residual stress in the steel ingot, laying the foundation for further annealing. The second stage of annealing at 950~1100℃ can further release residual stress, reduce corrosion-sensitive sites, and improve corrosion resistance.

[0025] In some embodiments of the present invention, the steel ingot is composed of the following components by weight percentage: C 0.06%~0.07%, Si 0.20%~0.35%, Mn 0.30%~0.70%, P 0.008%~0.010%, S 0.004%~0.008%, Al 0.20%~0.30%, Cr 2.0%~2.5%, Mo 0.30%~0.50%, V 0.2%~0.3%, Cu 0.1%~0.20%, Ni 0.02%~0.80%, N 0.004%~0.006%, with the balance being Fe and unavoidable impurities.

[0026] In some embodiments of the present invention, the mass relationship between Cr and Mo in the steel ingot composition is: Cr / Mo = 4.2~9.4, for example, it can be 4.2, 5, 6, 7, 8, 9, 9.4, etc. In some embodiments of the present invention, the mass relationship between Cr and Mo in the steel ingot composition is: Cr / Mo = 5.

[0027] In this invention, Mo in the steel ingot combines with C in the steel to precipitate M2C type carbides. Cr can enhance the secondary hardening effect and improve hardenability, allowing for more uniform carbide precipitation, thereby achieving simultaneous improvement in corrosion resistance and mechanical properties. Furthermore, the mass relationship between Cr and Mo is limited to Cr / Mo = 4.2~9.4, which can better leverage the effects of Cr and Mo in the composition and improve corrosion resistance and mechanical properties.

[0028] In some embodiments of the present invention, the quenching process is as follows: after heating to 900~930℃, for example, 900℃, 905℃, 910℃, 915℃, 920℃, 925℃, 930℃, etc., water cooling is performed to room temperature.

[0029] Part Two, The present invention also provides a corrosion-resistant fastener, which is prepared by the above-described corrosion-resistant fastener preparation process.

[0030] method The following methods are used to determine the performance defined in the examples and comparative examples.

[0031] Tensile strength was determined according to the method in GB / T 228.1-2021 "Metallic Materials - Tensile Testing", with a test rate of 0.008 s. -1 ; Corrosion resistance was tested using a spray test chamber. During the experiment, the spray salt solution was a 5% wt sodium chloride aqueous solution, and the salt spray deposition rate was 2 mL / (80 cm²). 2 (·h), test temperature 35℃, test duration 30 days; The measurement results are shown in Tables 4 and 5.

[0032] A process for manufacturing corrosion-resistant fasteners includes the following steps: After homogenization, annealing, stamping, turning, and threading, steel ingots are quenched, tempered, and cooled to obtain corrosion-resistant fasteners. The chemical composition and weight percentage of each chemical component of the steel ingots in each embodiment and comparative example are shown in Table 1, and the preparation process parameters are shown in Tables 2 and 3.

[0033] Table 1 Chemical composition and weight percentage of steel ingots in Examples 1-5

[0034] The chemical composition and weight percentage of the steel ingots in Examples 6-10 and Comparative Examples 1-3 were the same as those in Example 1.

[0035] Table 2 Tempering process

[0036] Table 3 Process parameters for quenching and tempering treatments

[0037] Table 4 Tensile strength test results

[0038] Compared with Example 1, Comparative Examples 1-3 changed the tempering process, and the tensile strength of Comparative Examples 1-3 was lower than that of Example 1. This shows that the limitation of the tempering process in the present invention can improve the tensile strength of fasteners by synergistically improving the composition of steel ingots. Compared with Example 2, Examples 4-5 changed the mass relationship of Cr and Mo in the composition of steel ingots, and the tensile strength of Example 2 was higher than that of Examples 4-5.

[0039] Table 5 Results of corrosion resistance test

[0040] As shown in Table 5, compared with Example 1, Comparative Examples 1-3 changed the tempering process, and the corrosion resistance of Example 1 was higher than that of Comparative Examples 1-3. This indicates that the limitation of the tempering process in this invention can synergistically improve the corrosion resistance of fasteners by modifying the composition of the steel ingot. Compared with Examples 9-11, Examples 1 and 7-8 changed the annealing process, and the corrosion resistance of Examples 9-11 was higher than that of Examples 1 and 7-8. This indicates that the limitation of the annealing process in this invention can further improve the corrosion resistance of fasteners.

[0041] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A manufacturing process for corrosion-resistant fasteners, characterized in that, Includes the following steps: After homogenization, annealing, stamping, turning, and threading, the steel ingot undergoes quenching and tempering, and is then cooled to obtain corrosion-resistant fasteners. The tempering process is as follows: first, the temperature is raised to 150~200℃ for the first stage of tempering, then the temperature is raised to 350~450℃ for the second stage of tempering, and finally the temperature is raised to 600℃ for the third stage of tempering.

2. The manufacturing process of a corrosion-resistant fastener according to claim 1, characterized in that, The tempering process is as follows: first, the temperature is raised to 150-200℃ at a rate of 5-10℃ / h for the first stage of tempering; then, the temperature is raised to 350-450℃ at a rate of 10℃ / h for the second stage of tempering; and finally, the temperature is raised to 600℃ at a rate of 10-15℃ / h for the third stage of tempering.

3. The manufacturing process of a corrosion-resistant fastener according to claim 2, characterized in that, The first tempering process takes 0.5 hours, the second tempering process takes 1 to 2 hours, and the third tempering process takes 1 to 2 hours.

4. The manufacturing process of a corrosion-resistant fastener according to claim 1, characterized in that, The homogenization process is carried out at a temperature of 1100~1200℃ for 12~16 hours.

5. The manufacturing process of a corrosion-resistant fastener according to claim 1, characterized in that, The annealing process is as follows: first, a first-stage annealing process is carried out at 600~750℃, and then a second-stage annealing process is carried out at 950~1100℃.

6. The manufacturing process of a corrosion-resistant fastener according to claim 5, characterized in that, The first annealing process takes 1 to 1.5 hours, and the second annealing process takes 1.4 to 1.5 hours.

7. The manufacturing process of a corrosion-resistant fastener according to claim 1, characterized in that, The steel ingot is composed of the following components by weight percentage: C 0.06%~0.07%, Si 0.20%~0.35%, Mn 0.30%~0.70%, P 0.008%~0.010%, S 0.004%~0.008%, Al 0.20%~0.30%, Cr 2.0%~2.5%, Mo 0.30%~0.50%, V 0.2%~0.3%, Cu 0.1%~0.20%, Ni 0.02%~0.80%, N 0.004%~0.006%, with the balance being Fe and unavoidable impurities.

8. The manufacturing process of a corrosion-resistant fastener according to claim 7, characterized in that, In the steel ingot composition, the mass relationship between Cr and Mo is: Cr / Mo = 4.2~9.

4.

9. The manufacturing process of a corrosion-resistant fastener according to claim 1, characterized in that, The quenching process is as follows: after heating to 900~930℃, water cooling is used to bring it to room temperature.

10. A corrosion-resistant fastener, characterized in that, It is prepared by the preparation process described in any one of claims 1 to 9.

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