A high-strength bolt and its preparation method

Abstract

The present invention relates to the field of alloy steel and provides a high-strength bolt and a method for preparing the same. The high-strength bolt comprises a bolt composed of the following components by mass percentage: C 0.12% to 0.18%, Si 0.25% to 0.4%, Mn 0.4% to 0.7%, Cr 1.2% to 2.8%, Mo 0.25% to 0.55%, W 0.1% to 0.3%, Ti 0.3% to 0.45%, Nb 0.06% to 0.1%, V 0.12% to 0.22%, La 0.05% to 0.12%, Ce 0.05% to 0.12%, Y 0.08% to 0.18%, Er 0.03% to 0.08%, and B 0.002% to 0.005%, with the remainder being Fe and other unavoidable impurities. The high-strength bolt provided by the present invention has certain wear resistance and corrosion resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy steel, and in particular to a high-strength bolt and a preparation method thereof. Background Art

[0002] High-strength bolts are made of high-strength steel and require a high preload. These bolts play a vital role in the connection of bridges, rails, and high- and ultra-high-pressure equipment. In particular, ultra-high-pressure equipment requires significant preload to ensure the tightness of the container. Furthermore, high-strength bolts offer advantages such as simple construction, excellent stress-bearing properties, removability, fatigue resistance, and resistance to loosening under dynamic loads. These bolts are essential connectors in modern engineering structures. Based on this, the present invention proposes a high-strength bolt and a method for its preparation. Summary of the Invention

[0003] The present invention provides a high-strength bolt and a preparation method thereof. The obtained bolt has high strength and certain wear resistance and corrosion resistance.

[0004] The technical solutions of the present invention are as follows:

[0005] In a first aspect, the present invention provides a high-strength bolt, comprising a bolt, wherein the bolt is composed of the following components in mass percentage: C 0.12%-0.18%, Si 0.25%-0.4%, Mn 0.4%-0.7%, Cr 1.2%-2.8%, Mo 0.25%-0.55%, W 0.1%-0.3%, Ti 0.3%-0.45%, Nb 0.06%-0.1%, V 0.12%-0.22%, La 0.05%-0.12%, Ce 0.05%-0.12%, Y 0.08%-0.18%, Er 0.03%-0.08% and B 0.002%-0.005%, with the balance being Fe and other inevitable impurities.

[0006] As a further technical solution, the bolt is composed of the following components in mass percentage: C 0.12%~0.18%, Si 0.25%~0.4%, Mn 0.4%~0.7%, Cr 1.2%~2.8%, Mo 0.25%~0.55%, W 0.1%~0.3%, Ti0.3%~0.45%, Nb 0.06%~0.1%, V 0.12%~0.22%, La 0.05%~0.12%, Ce 0.05%~0.12%, Y 0.08%~0.18%, Er 0.03%~0.08% and B 0.002%~0.005%, the balance being Fe and other inevitable impurities, and the Cr / Mo mass ratio is 4:1~5:1.

[0007] As a further technical solution, the bolt is composed of the following components in mass percentage: C 0.12%-0.18%, Si 0.25%-0.4%, Mn 0.4%-0.7%, Cr 1.2%-2.8%, Mo 0.25%-0.55%, W 0.1%-0.3%, Ti 0.3%-0.45%, Nb 0.06%-0.1%, V 0.12%-0.22%, La 0.05%-0.12%, Ce 0.05%-0.12%, Y 0.08%-0.18%, Er 0.03%-0.08% and B 0.002%-0.005%, with the remainder being Fe and other inevitable impurities, and 0.35%≤V+Ce+Y≤0.45%.

[0008] As a further technical solution, it also includes an AlCr-Y2O3 wear-resistant layer deposited on the surface of the bolt, and the AlCr-Y2O3 wear-resistant layer includes an AlCr layer and a Y2O3 layer in sequence from the substrate to the outside.

[0009] As a further technical solution, the thickness of the AlCr layer is 0.2-0.4 μm; the thickness of the Y2O3 layer is 0.5-0.7 μm.

[0010] As a further technical solution, the mass content of Cr in the AlCr layer is 18%-22%.

[0011] In a second aspect, the present invention provides a method for preparing a high-strength bolt, comprising the following steps:

[0012] S1. Weighing raw materials according to the components in the mass percentages, performing vacuum melting, argon refining, and casting at 1550-1600° C. to obtain bolt blanks;

[0013] S2, heat treating the bolt blank and processing it into a shape to obtain a bolt;

[0014] S3. After depositing an AlCr layer on the surface of the bolt using an AlCr target, a Y2O3 layer is deposited on the surface of the AlCr layer using a Y2O3 ceramic target, ultimately forming an AlCr-Y2O3 wear-resistant layer on the bolt surface. Finally, the high-strength bolt is obtained through post-processing.

[0015] As a further technical solution, the heat treatment step includes maintaining the temperature at 600-700°C for 50-70 minutes, maintaining the temperature at 750-800°C for 30-40 minutes, and maintaining the temperature at 850-900°C for 2-3 hours.

[0016] As a further technical solution, the target current during the deposition of the AlCr layer is 60-70A; the sputtering power during the deposition of the Y2O3 layer is 7-8kW, the temperature is 380-420°C, and the gas atmosphere is oxygen and argon in a volume ratio of 1:3.

[0017] As a further technical solution, the post-processing step includes annealing at a temperature of 400-500° C. in an argon atmosphere for 2-3 hours.

[0018] The working principle and beneficial effects of the present invention are:

[0019] The present invention significantly improves the high-temperature strength and corrosion resistance of bolts by precisely controlling the Cr / Mo mass ratio between 4:1 and 5:1. Cr and Mo are important alloying elements in steel materials and have a significant impact on the mechanical properties and corrosion resistance of the materials. The Cr element can form a stable passivation film, improving the corrosion resistance of the material; the Mo element can refine carbides, improving the strength and toughness of the material. A reasonable Cr / Mo ratio can optimize the distribution of carbides and avoid grain boundary embrittlement caused by carbide coarsening, thereby enhancing the high-temperature strength and corrosion resistance of the material. The upper yield strength of Example 2 (Cr / Mo=4:1) is significantly higher than that of Example 7 (Cr / Mo=7:1), and the salt spray resistance time is also greatly improved to 74h, verifying the effectiveness of the Cr / Mo ratio optimization.

[0020] The present invention significantly improves the wear and corrosion resistance of bolts by introducing rare earth elements (V, Ce, and Y) and controlling their combined content between 0.35% and 0.6%. V refines grains, increasing the material's strength and toughness; while rare earth elements (Ce and Y) purify grain boundaries, inhibit high-temperature oxidation, and promote the formation of a passivation film, thereby enhancing the material's corrosion resistance. The synergistic effect of these elements further refines grains and optimizes the material's microstructure, thereby improving its wear and corrosion resistance. Example 3 (V+Ce+Y = 0.52%) exhibits a 31% improvement in wear resistance compared to Example 8 (total content 0.25%), and its salt spray resistance is also extended to 61 hours, demonstrating the effectiveness of the synergistic effect of the rare earth elements.

[0021] The present invention significantly improves the material stability of the bolt by introducing rare earth elements such as La and Ce. These elements can purify grain boundaries and inhibit high-temperature oxidation, thereby enhancing the material's stability. These elements also promote the formation of a passivation film, improving the material's corrosion resistance. The upper yield strength and hardness of Example 1 are significantly higher than those of Comparative Example 1, demonstrating the effectiveness of the introduction of La and Ce rare earth elements.

[0022] The present invention significantly improves the wear resistance and corrosion resistance of the bolts by depositing an AlCr-Y2O3 wear-resistant layer on the bolt surface. The AlCr layer has good toughness and adhesion, and can provide support as a base layer; the Y2O3 layer has excellent wear resistance and corrosion resistance, and can serve as a protective layer to protect the substrate. This double-layer structure achieves dual protection through the synergistic effect of the tough AlCr base and the dense oxidation protection of Y2O3. The wear rate of Examples 4-6 was only 1 / 7 to 1 / 8 of that of the uncoated group, and the salt spray resistance time exceeded 500 hours without initial rust, verifying the effectiveness of the AlCr-Y2O3 wear-resistant layer.

[0023] The deposition order of the AlCr and Y2O3 layers in this invention significantly impacts the bolt's performance, and this order is irreversible. The AlCr layer, as a base layer, provides excellent adhesion and toughness; the Y2O3 layer, as a protective layer, requires close adhesion to the base layer to achieve optimal results. Depositing the Y2O3 layer before the AlCr layer reduces interfacial bonding strength, thus affecting the coating's performance.

[0024] This invention further improves the performance of the bolt by optimizing heat treatment process parameters. The heat treatment process has a significant impact on the material's microstructure and properties. By optimizing the annealing temperature and holding time, the uniform precipitation of carbides can be promoted, optimizing the material's microstructure and thus improving its strength and toughness.

[0025] Specific implementation methods

[0026] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0027] Example 1

[0028] This embodiment provides a high-strength bolt, including a bolt composed of the following components in percentage by mass: C 0.15%, Si 0.3%, Mn 0.5%, Cr 2.0%, Mo 0.4%, W 0.2%, Ti 0.35%, Nb 0.08%, V 0.18%, La 0.08%, Ce 0.08%, Y 0.12%, Er 0.05%, B 0.003%, and the balance being Fe and other unavoidable impurities;

[0029] A method for preparing a high-strength bolt comprises the following steps:

[0030] S1. Weighing raw materials according to their mass percentages, performing vacuum melting, argon refining, and casting at 1580° C. to obtain bolt blanks;

[0031] S2. heat treating the bolt blank at 650° C. for 60 minutes, 780° C. for 35 minutes, and 880° C. for 2.5 hours, and forming the bolt blank into a shape.

[0032] S3. Finally, the high-strength bolts are obtained by annealing at a temperature of 450°C in an argon atmosphere for 2.5 hours and then post-processing.

[0033] Example 2

[0034] This embodiment provides a high-strength bolt, including a bolt composed of the following components in percentage by mass: C 0.15%, Si 0.3%, Mn 0.5%, Cr 2.2%, Mo 0.55%, W 0.2%, Ti 0.35%, Nb 0.08%, V 0.18%, La 0.08%, Ce 0.08%, Y 0.12%, Er 0.05%, B 0.003%, and the balance being Fe and other unavoidable impurities;

[0035] Among them, Cr / Mo=4:1;

[0036] A method for preparing a high-strength bolt comprises the following steps:

[0037] S1. Weighing raw materials according to their mass percentages, performing vacuum melting, argon refining, and casting at 1580° C. to obtain bolt blanks;

[0038] S2. heat treating the bolt blank at 650° C. for 60 minutes, 780° C. for 35 minutes, and 880° C. for 2.5 hours, and forming the bolt blank into a shape.

[0039] S3. Finally, the high-strength bolts are obtained by annealing at a temperature of 450°C in an argon atmosphere for 2.5 hours and then post-processing.

[0040] Example 3

[0041] This embodiment provides a high-strength bolt, including a bolt composed of the following components in percentage by mass: C 0.15%, Si 0.3%, Mn 0.5%, Cr 2.0%, Mo 0.4%, W 0.2%, Ti 0.35%, Nb 0.08%, V 0.22%, La 0.08%, Ce 0.12%, Y 0.18%, Er 0.05%, B 0.003%, and the balance being Fe and other unavoidable impurities;

[0042] Among them, the total of V+Ce+Y is 0.52%;

[0043] A method for preparing a high-strength bolt comprises the following steps:

[0044] S1. Weighing raw materials according to their mass percentages, performing vacuum melting, argon refining, and casting at 1580° C. to obtain bolt blanks;

[0045] S2. heat treating the bolt blank at 650° C. for 60 minutes, 780° C. for 35 minutes, and 880° C. for 2.5 hours, and forming the bolt blank into a shape.

[0046] S3. Finally, the high-strength bolts are obtained by annealing at a temperature of 450°C in an argon atmosphere for 2.5 hours and then post-processing.

[0047] Example 4

[0048] This embodiment provides a high-strength bolt, including a bolt composed of the following components in percentage by mass: C 0.15%, Si 0.3%, Mn 0.5%, Cr 2.0%, Mo 0.4%, W 0.2%, Ti 0.35%, Nb 0.08%, V 0.18%, La 0.08%, Ce 0.08%, Y 0.12%, Er 0.05%, B 0.003%, and the balance being Fe and other unavoidable impurities;

[0049] A method for preparing a high-strength bolt comprises the following steps:

[0050] S1. Weighing raw materials according to their mass percentages, performing vacuum melting, argon refining, and casting at 1580° C. to obtain bolt blanks;

[0051] S2. heat treating the bolt blank at 650° C. for 60 minutes, 780° C. for 35 minutes, and 880° C. for 2.5 hours, and forming the bolt blank into a shape.

[0052] S3. After depositing an AlCr layer on the bolt surface using an AlCr target, a Y2O3 layer is deposited on the surface of the AlCr layer using a Y2O3 ceramic target, ultimately forming an AlCr-Y2O3 wear-resistant layer on the bolt surface. Finally, a high-strength bolt is obtained after post-processing. The target current during the AlCr layer deposition is 65A. The sputtering power during the Y2O3 layer deposition is 7.5kW, the temperature is 400°C, and the gas atmosphere is an O2 / Ar with a volume ratio of 1:3. Finally, the high-strength bolt is obtained after annealing at a temperature of 450°C in an argon atmosphere for 2.5 hours and post-processing.

[0053] Among them, the thickness of the AlCr layer is 0.3μm; the thickness of the Y2O3 layer is 0.6μm; and the mass content of Cr in the AlCr layer is 20%.

[0054] Example 5

[0055] This embodiment provides a high-strength bolt, including a bolt composed of the following components in percentage by mass: C 0.15%, Si 0.3%, Mn 0.5%, Cr 2.0%, Mo 0.4%, W 0.2%, Ti 0.35%, Nb 0.08%, V 0.18%, La 0.08%, Ce 0.08%, Y 0.12%, Er 0.05%, B 0.003%, and the balance being Fe and other unavoidable impurities;

[0056] A method for preparing a high-strength bolt comprises the following steps:

[0057] S1. Weighing raw materials according to their mass percentages, performing vacuum melting, argon refining, and casting at 1580° C. to obtain bolt blanks;

[0058] S2. heat treating the bolt blank at 650° C. for 60 minutes, 780° C. for 35 minutes, and 880° C. for 2.5 hours, and forming the bolt blank into a shape.

[0059] S3. After depositing an AlCr layer on the bolt surface using an AlCr target, a Y2O3 layer is deposited on the surface of the AlCr layer using a Y2O3 ceramic target, ultimately forming an AlCr-Y2O3 wear-resistant layer on the bolt surface. The high-strength bolt is obtained after post-processing. The target current during the AlCr layer deposition is 70A. The sputtering power during the Y2O3 layer deposition is 8kW, the temperature is 420°C, and the gas atmosphere is an O2 / Ar with a volume ratio of 1:3. Finally, the high-strength bolt is obtained after annealing at a temperature of 450°C in an argon atmosphere for 2.5 hours and post-processing.

[0060] Among them, the thickness of the AlCr layer is 0.4μm; the thickness of the Y2O3 layer is 0.7μm; and the mass content of Cr in the AlCr layer is 22%.

[0061] Example 6

[0062] This embodiment provides a high-strength bolt, including a bolt composed of the following components in percentage by mass: C 0.15%, Si 0.3%, Mn 0.5%, Cr 2.0%, Mo 0.4%, W 0.2%, Ti 0.35%, Nb 0.08%, V 0.18%, La 0.08%, Ce 0.08%, Y 0.12%, Er 0.05%, B 0.003%, and the balance being Fe and other unavoidable impurities;

[0063] A method for preparing a high-strength bolt comprises the following steps:

[0064] S1. Weighing raw materials according to their mass percentages, performing vacuum melting, argon refining, and casting at 1580° C. to obtain bolt blanks;

[0065] S2. heat treating the bolt blank at 700° C. for 70 minutes, 800° C. for 40 minutes, and 900° C. for 3 hours, and forming the bolt blank into a shape.

[0066] S3. After depositing an AlCr layer on the bolt surface using an AlCr target, a Y2O3 layer is deposited on the surface of the AlCr layer using a Y2O3 ceramic target, ultimately forming an AlCr-Y2O3 wear-resistant layer on the bolt surface. The high-strength bolt is obtained after post-processing. The target current during the AlCr layer deposition is 70A. The sputtering power during the Y2O3 layer deposition is 8kW, the temperature is 420°C, and the gas atmosphere is an O2 / Ar with a volume ratio of 1:3. Finally, the high-strength bolt is obtained after annealing at a temperature of 500°C in an argon atmosphere for 3 hours and post-processing.

[0067] Among them, the thickness of the AlCr layer is 0.4μm; the thickness of the Y2O3 layer is 0.7μm; and the mass content of Cr in the AlCr layer is 22%.

[0068] Example 7

[0069] In Example 7, the Cr composition is 2.8% and the Mo composition is 0.4% (Cr / Mo=7:1), and the rest is the same as in Example 1, and the preparation steps are the same as in Example 1.

[0070] Example 8

[0071] In Example 8, V is 0.12%, Ce is 0.05%, and Y is 0.08% (total 0.25%), and the rest is the same as in Example 1, and the preparation steps are the same as in Example 1.

[0072] Example 9

[0073] The components in Example 9 are the same as those in Example 4, but the order of coating deposition is reversed, with the Y2O3 layer deposited first and then the AlCr layer.

[0074] Example 10

[0075] The components in Example 10 are the same as those in Example 4. The preparation is based on Example 4, except that the post-treatment is adjusted to annealing at 600° C. for 2 h.

[0076] Comparative Example 1

[0077] In Comparative Example 1, the components are La 0%, Ce 0%, and the rest are the same as in Example 1.

[0078] Test Example 1: The high-strength bolts prepared in Examples 1-10 and Comparative Example 1 were subjected to the following tests:

[0079] Upper yield strength: Refer to GB / T 228.2-2015 "Metallic Materials High-Temperature Tensile Test Methods" to conduct upper yield strength test at a temperature of 700°C;

[0080] Wear resistance: Tested in accordance with GB / T 12444-2006 Metallic materials wear test methods;

[0081] Hardness: Refer to GB / T 3098.1-2000 and use Rockwell hardness tester (HRC) to test the surface hardness of the bolt;

[0082] Neutral salt spray resistance: Refer to ISO 9227 standard and continuously spray the sample with a 5% mass concentration of NaCl aqueous solution;

[0083] The results are shown in Table 1 below:

[0084] Table 1

[0085]

[0086] Combined with the above content, it can be seen that the upper yield strength of Example 2 is significantly higher than that of Example 7, and the salt spray resistance time is increased to 74h, indicating that a reasonable Cr / Mo ratio can optimize the carbide distribution and enhance high-temperature strength and corrosion resistance. In Example 7, the grain boundary embrittlement is caused by the coarsening of carbides, and the overall performance is greatly reduced. The wear resistance of Example 3 (V+Ce+Y=0.52%) is improved by 31% compared with Example 8, and the salt spray resistance time is extended to 61h, verifying the grain refinement and passivation film formation effects of rare earth elements. Due to insufficient rare earths, Example 8 cannot effectively inhibit the expansion of corrosion. The upper yield strength and hardness of Comparative Example 1 are significantly lower than those of Example 1, indicating that La / Ce significantly improves the stability of the material by purifying the grain boundaries and inhibiting high-temperature oxidation.

[0087] The wear rate of Examples 4-6 was only 1 / 7 to 1 / 8 of that of the uncoated group, and the salt spray resistance time exceeded 500 hours without initial rust. The coating has an outstanding effect on improving wear resistance and corrosion resistance. The coating structure achieves dual protection through the synergistic effect of the tough AlCr substrate and the dense oxidation protection of Y2O3. The hardness and wear resistance of Example 6 are better than those of Example 4, indicating that increasing the Cr content and coating thickness can further enhance performance. The wear rate of Example 9 is much higher than that of Example 4. The reverse coating causes the interface bonding strength to decrease, and the salt spray resistance time is only 124 hours.

[0088] The salt spray resistance time of Example 10 was significantly lower than that of Example 4. High-temperature annealing resulted in oxidation failure of the coating, verifying that the annealing temperature must be strictly controlled within 400-500°C. The upper yield strength and hardness of Example 6 were superior to those of the other examples, indicating that appropriately increasing the heat treatment temperature can promote uniform carbide precipitation and strengthen the matrix.

[0089] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high-strength bolt, characterized in that: The invention relates to a bolt composed of the following components in percentage by mass: C 0.12% to 0.18%, Si 0.25% to 0.4%, Mn 0.4% to 0.7%, Cr 1.2% to 2.8%, Mo 0.25% to 0.55%, W 0.1% to 0.3%, Ti 0.3% to 0.45%, Nb 0.06% to 0.1%, V 0.12% to 0.22%, La 0.05% to 0.12%, Ce 0.05% to 0.12%, Y 0.08% to 0.18%, Er 0.03% to 0.08% and B 0.002% to 0.005%, with the balance being Fe and other unavoidable impurities; and a Cr / Mo mass ratio of 4:1 to 5:1; V+Ce+Y 0.35%≤0.6%; It also includes an AlCr-Y2O3 wear-resistant layer deposited on the surface of the bolt, and the AlCr-Y2O3 wear-resistant layer includes an AlCr layer and a Y2O3 layer in sequence from the substrate to the outside; the thickness of the AlCr layer is 0.2-0.4μm; the thickness of the Y2O3 layer is 0.5-0.7μm.

2. A high-strength bolt according to claim 1, characterized in that: The mass content of Cr in the AlCr layer is 18%-22%.

3. A method for preparing a high-strength bolt according to any one of claims 1 to 2, characterized in that the steps include: S1. Weighing raw materials according to the components in the mass percentages, performing vacuum melting, argon refining, and casting at 1550-1600° C. to obtain bolt blanks; S2, heat treating the bolt blank and processing it into a shape to obtain a bolt; S3. After depositing an AlCr layer on the surface of the bolt using an AlCr target, a Y2O3 layer is deposited on the surface of the AlCr layer using a Y2O3 ceramic target, thereby finally forming an AlCr-Y2O3 wear-resistant layer on the surface of the bolt. Finally, the high-strength bolt is obtained through post-processing.

4. A high-strength bolt according to claim 3, characterized in that: The heat treatment step includes maintaining the temperature at 600-700° C. for 50-70 minutes, maintaining the temperature at 750-800° C. for 30-40 minutes, and maintaining the temperature at 850-900° C. for 2-3 hours.

5. The high-strength bolt according to claim 3, characterized in that: The target current during the deposition of the AlCr layer is 60-70 A; the sputtering power during the deposition of the Y2O3 layer is 7-8 kW, the temperature is 380-420° C., and the gas atmosphere is O2 / Ar with a volume ratio of 1:

3.

6. The method for preparing a high-strength bolt according to claim 3, wherein: The post-processing step includes annealing at a temperature of 400-500° C. in an argon atmosphere for 2-3 hours.

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