High-strength bolt and preparation method thereof

Abstract

The invention relates to the field of alloy steel, and provides a high-strength bolt and a preparation method thereof. The high-strength bolt comprises a bolt body, and the bolt body is composed of, by mass, 0.12%-0.18% of C, 0.25%-0.4% of Si, 0.4%-0.7% of Mn, 1.2%-2.8% of Cr, 0.25%-0.55% of Mo, 0.1%-0.3% of W, 0.3%-0.45% of Ti, 0.06%-0.1% of Nb, 0.12%-0.22% of V, 0.05%-0.12% of La, 0.05%-0.12% of Ce, 0.08%-0.18% of Y, 0.03%-0.08% of Er, 0.002%-0.005% of B and the balance Fe and other inevitable impurities. The high-strength bolt provided by the invention has certain wear resistance and corrosion resistance.

Description

Technical Field

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

[0002] A high-strength bolt is a bolt made of high-strength steel or requiring a large pre-tightening force. Such bolts play an important role in the connection of bridges, rails, and high-pressure and ultra-high-pressure equipment. Especially in ultra-high-pressure equipment, in order to ensure the sealing performance of the container, high-strength bolts need to apply huge prestress. In addition, high-strength bolts also have the advantages of simple construction, good mechanical properties, detachable, fatigue resistance, and no loosening under dynamic load, and are important indispensable connectors in modern engineering structures. Based on this, the present invention proposes a high-strength bolt and a preparation method thereof. Summary of the Invention

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

[0004] The technical solution of the present invention is as follows: In a first aspect, the present invention proposes a high-strength bolt, including a bolt, and the bolt is composed of the following components by 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%, and the balance is Fe and other inevitable impurities.

[0005] As a further technical solution, the bolt is composed of the following components by 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%, and the balance is Fe and other inevitable impurities, and the mass ratio of Cr / Mo is 4:1 - 5:1.

[0006] As a further technical solution, the bolt is composed of components with the following mass percentages: 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%, the balance being Fe and other inevitable impurities, and 0.35% ≤ V + Ce + Y ≤ 0.45%.

[0007] As a further technical solution, it further includes an AlCr - Y2O3 wear - resistant layer deposited on the surface of the bolt, and the AlCr - Y2O3 wear - resistant layer sequentially includes an AlCr layer and a Y2O3 layer from the substrate outwards.

[0008] 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.

[0009] As a further technical solution, the mass content of Cr in the AlCr layer is 18% - 22%.

[0010] In the second aspect, the present invention proposes a preparation method of a high - strength bolt, and the steps include: S1. Weigh raw materials according to the components with the above - mentioned mass percentages, and then carry out vacuum melting, argon refining, and casting molding at 1550 - 1600 °C to obtain a bolt blank; S2. Heat - treat the bolt blank and process it into a bolt; S3. Deposit an AlCr layer on the surface of the bolt using an AlCr target, and then deposit a Y2O3 layer on the surface of the AlCr layer using a Y2O3 ceramic target, finally forming an AlCr - Y2O3 wear - resistant layer on the surface of the bolt, and then obtaining the high - strength bolt after post - treatment.

[0011] As a further technical solution, the heat - treatment step includes holding for 50 - 70 min at 600 - 700 °C, holding for 30 - 40 min at 750 - 800 °C, and holding for 2 - 3 h at 850 - 900 °C.

[0012] As a further technical solution, 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 a volume ratio of 1:3 of oxygen and argon.

[0013] As a further technical solution, the post-treatment step includes annealing for 2 - 3 h in an argon atmosphere at a temperature of 400 - 500 °C.

[0014] The working principle and beneficial effects of the present invention are as follows: By precisely controlling the Cr / Mo mass ratio between 4:1 and 5:1, the present invention significantly improves the high-temperature strength and corrosion resistance of the bolts. Cr and Mo are important alloying elements in steel materials, which have a significant impact on the mechanical properties and corrosion resistance of the materials. The Cr element can form a stable passivation film to improve the corrosion resistance of the material; the Mo element can refine carbides to improve 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 increased to 74 h, verifying the effectiveness of the optimized Cr / Mo ratio.

[0015] By introducing rare earth elements such as V, Ce, and Y and controlling their total content between 0.35% and 0.6%, the present invention significantly improves the wear resistance and corrosion resistance of the bolts. The V element can refine grains to improve the strength and toughness of the material; rare earth elements such as Ce and Y can purify grain boundaries, inhibit high-temperature oxidation, and promote the formation of a passivation film, thereby improving the corrosion resistance of the material. The synergistic effect of these elements can further refine grains and optimize the microstructure of the material, thereby improving its wear resistance and corrosion resistance. The wear resistance of Example 3 (V + Ce + Y = 0.52%) is 31% higher than that of Example 8 (total 0.25%), and the salt spray resistance time is also extended to 61 h, verifying the effectiveness of the synergistic effect of rare earth elements.

[0016] By introducing rare earth elements such as La / Ce, the present invention significantly improves the material stability of the bolts. Rare earth elements such as La / Ce can purify grain boundaries and inhibit high-temperature oxidation, thereby improving the stability of the material. These elements can also promote the formation of a passivation film and improve the corrosion resistance of the material. The upper yield strength and hardness of Example 1 are significantly higher than those of Comparative Example 1, verifying the effectiveness of the introduction of La / Ce rare earth elements.

[0017] By depositing an AlCr-Y2O3 wear-resistant layer on the surface of the bolt, the wear resistance and corrosion resistance of the bolt are significantly improved. 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 protect the substrate as a protective layer. This double-layer structure realizes dual protection through the synergistic effect of the tough base of AlCr and the dense oxidation protection of Y2O3. The wear amount in Examples 4-6 is only 1 / 7 to 1 / 8 of that of the uncoated group, and the salt spray resistance time exceeds 500h without initial rust, verifying the effectiveness of the AlCr-Y2O3 wear-resistant layer.

[0018] In the present invention, the deposition sequence of the AlCr layer and the Y2O3 layer has a significant impact on the performance of the bolt, and the sequence is irreversible. The AlCr layer, as the base layer, can provide good adhesion and toughness; the Y2O3 layer, as the protective layer, needs to adhere tightly to the base layer to achieve the best effect. If the Y2O3 layer is deposited first and then the AlCr layer, the interfacial bonding force will decrease, thereby affecting the performance of the coating.

[0019] By optimizing the heat treatment process parameters, the performance of the bolt is further improved. The heat treatment process has a significant impact on the microstructure and performance of the material. By optimizing the annealing temperature and holding time, the uniform precipitation of carbides can be promoted, and the microstructure of the material can be optimized, thereby improving its strength and toughness.

[0020] Specific Embodiments The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of the present invention.

[0021] Example 1 A high-strength bolt is provided in this embodiment, including a bolt, and the bolt is composed of the following components by mass percentage: 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 is Fe and other inevitable impurities; The preparation method of the high-strength bolt includes the following steps: S1. Weigh the raw materials according to the components by mass percentage, and then carry out vacuum melting, argon refining, and casting at 1580 °C to obtain a bolt blank; S2. Keep the bolt blank at 650 °C for 60 min, at 780 °C for 35 min, and at 880 °C for 2.5 h for heat treatment, then process and form it to obtain the bolt; S3. Finally, anneal it at 450 °C in an argon atmosphere for 2.5 h, and obtain the high-strength bolt after post-treatment.

[0022] Example 2 In this example, a high-strength bolt is provided, including a bolt, and the bolt is composed of the following components by mass percentage: 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 is Fe and other inevitable impurities; Among them, Cr / Mo = 4:1; The preparation method of the high-strength bolt includes the following steps: S1. Weigh the raw materials according to the components by mass percentage, then carry out vacuum melting, argon refining, and casting at 1580 °C to obtain the bolt blank; S2. Keep the bolt blank at 650 °C for 60 min, at 780 °C for 35 min, and at 880 °C for 2.5 h for heat treatment, then process and form it to obtain the bolt; S3. Finally, anneal it at 450 °C in an argon atmosphere for 2.5 h, and obtain the high-strength bolt after post-treatment.

[0023] Example 3 In this example, a high-strength bolt is provided, including a bolt, and the bolt is composed of the following components by mass percentage: 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 is Fe and other inevitable impurities; Among them, the total of V + Ce + Y is 0.52%; The preparation method of the high-strength bolt includes the following steps: S1. Weigh the raw materials according to the components by mass percentage, then carry out vacuum melting, argon refining, and casting at 1580 °C to obtain the bolt blank; S2. Keep the bolt blank at 650 °C for 60 min, at 780 °C for 35 min, and at 880 °C for 2.5 h for heat treatment, then process and form it to obtain the bolt; S3. Finally, anneal at 450 °C in an argon atmosphere for 2.5 h, and obtain the high-strength bolt after post-treatment.

[0024] Example 4 In this example, a high-strength bolt is provided, including a bolt, and the bolt is composed of the following components by mass percentage: 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 is Fe and other inevitable impurities. The preparation method of the high-strength bolt includes the following steps: S1. Weigh the raw materials according to the components by mass percentage, and then carry out vacuum melting, argon refining and casting at 1580 °C to obtain the bolt blank. S2. Keep the bolt blank at 650 °C for 60 min, at 780 °C for 35 min, and at 880 °C for 2.5 h for heat treatment and processing to obtain the bolt. S3. After depositing the AlCr layer on the bolt surface using an AlCr target, then deposit the Y2O3 layer on the surface of the AlCr layer using a Y2O3 ceramic target to finally form the AlCr-Y2O3 wear-resistant layer on the bolt surface. Finally, obtain the high-strength bolt after post-treatment; the target current during the deposition of the AlCr layer is 65 A; the sputtering power during the deposition of the Y2O3 layer is 7.5 kW, the temperature is 400 °C, and the gas atmosphere is O2 / Ar with a volume ratio of 1:3; finally, anneal at 450 °C in an argon atmosphere for 2.5 h, and obtain the high-strength bolt after post-treatment. Among them, the thickness of the AlCr layer is 0.3 μm; the thickness of the Y2O3 layer is 0.6 μm; the mass content of Cr in the AlCr layer is 20%.

[0025] Example 5 In this example, a high-strength bolt is provided, including a bolt, and the bolt is composed of the following components by mass percentage: 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 is Fe and other inevitable impurities. The preparation method of the high-strength bolt includes the following steps: S1. Weigh the raw materials according to the components by mass percentage, and then carry out vacuum melting, argon refining and casting at 1580 °C to obtain the bolt blank. S2. Keep the bolt blank at 650 °C for 60 min, at 780 °C for 35 min, and at 880 °C for 2.5 h for heat treatment, and then process and form it to obtain a bolt; S3. After depositing an AlCr layer on the bolt surface using an AlCr target, deposit a Y2O3 layer on the surface of the AlCr layer using a Y2O3 ceramic target, and finally form an AlCr - Y2O3 wear - resistant layer on the bolt surface. After post - treatment, a high - strength bolt is obtained; the target current during the deposition of the AlCr layer is 70 A; the sputtering power during the deposition of the Y2O3 layer is 8 kW, the temperature is 420 °C, and the gas atmosphere is O2 / Ar with a volume ratio of 1:3; finally, anneal at 450 °C in an argon atmosphere for 2.5 h and obtain a high - strength bolt after post - treatment; Among them, the thickness of the AlCr layer is 0.4 μm; the thickness of the Y2O3 layer is 0.7 μm; the mass content of Cr in the AlCr layer is 22%.

[0026] Example 6 In this example, a high - strength bolt is provided, including a bolt. The bolt is composed of the following components by mass percentage: 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 is Fe and other inevitable impurities; The preparation method of the high - strength bolt includes the following steps: S1. Weigh the raw materials according to the mass percentage of the components, then carry out vacuum melting, argon refining, and casting at 1580 °C to obtain a bolt blank; S2. Keep the bolt blank at 700 °C for 70 min, at 800 °C for 40 min, and at 900 °C for 3 h for heat treatment, and then process and form it to obtain a bolt; S3. After depositing an AlCr layer on the bolt surface using an AlCr target, deposit a Y2O3 layer on the surface of the AlCr layer using a Y2O3 ceramic target, and finally form an AlCr - Y2O3 wear - resistant layer on the bolt surface. After post - treatment, a high - strength bolt is obtained; the target current during the deposition of the AlCr layer is 70 A; the sputtering power during the deposition of the Y2O3 layer is 8 kW, the temperature is 420 °C, and the gas atmosphere is O2 / Ar with a volume ratio of 1:3; finally, anneal at 500 °C in an argon atmosphere for 3 h and obtain a high - strength bolt after post - treatment; Among them, the thickness of the AlCr layer is 0.4 μm; the thickness of the Y2O3 layer is 0.7 μm; the mass content of Cr in the AlCr layer is 22%.

[0027] Example 7 In Example 7, the component Cr is 2.8% and Mo is 0.4% (Cr / Mo = 7:1), and the rest is the same as in Example 1. The preparation steps are the same as in Example 1.

[0028] Example 8 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. The preparation steps are the same as in Example 1.

[0029] Example 9 In Example 9, the components are the same as in Example 4, but the coating deposition sequence is reversed. First, the Y2O3 layer is deposited, and then the AlCr layer is deposited.

[0030] Example 10 In Example 10, the components are the same as in Example 4. On the basis of Example 4, the post-treatment is adjusted to annealing at 600 °C for 2 h.

[0031] Comparative Example 1 In Comparative Example 1, the components La is 0% and Ce is 0%, and the rest is the same as in Example 1.

[0032] Test Example 1: The high-strength bolts prepared in the foregoing Examples 1-10 and Comparative Example 1 were tested as follows: Upper yield strength: Refer to GB / T 228.2-2015 "Metallic materials - Tensile testing at elevated temperatures" for the upper yield strength test at a temperature of 700 °C. Wear resistance: Refer to "GB / T 12444-2006 Test methods for wear of metallic materials" for testing. Hardness: Refer to "GB / T 3098.1-2000", and use a Rockwell hardness tester (HRC) to detect the surface hardness of the bolts. Neutral salt spray resistance: Refer to ISO 9227 standard and continuously spray the specimens with a 5% NaCl aqueous solution by mass concentration. The results are shown in Table 1 below: Table 1

[0033] Combined with the foregoing 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 74 h, indicating that a reasonable Cr / Mo ratio can optimize the carbide distribution and enhance the high-temperature strength and corrosion resistance. In Example 7, the grain boundary embrittlement is caused by carbide coarsening, resulting in a significant decrease in comprehensive performance. The wear resistance of Example 3 (V + Ce + Y = 0.52%) is 31% higher than that of Example 8, and the salt spray resistance time is extended to 61 h, verifying the grain refinement and passivation film formation effects of rare earth elements. In Example 8, due to insufficient rare earth, the corrosion propagation cannot be effectively inhibited. 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 material stability by purifying the grain boundary and inhibiting high-temperature oxidation.

[0034] The wear amount of Examples 4-6 is only 1 / 7 to 1 / 8 of that of the uncoated group, and the salt spray resistance time exceeds 500 h without initial rust, indicating that the coating has a prominent effect on improving wear resistance and corrosion resistance. The coating structure realizes double protection through the synergistic effect of the tough substrate of AlCr 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 strengthen the performance. The wear amount of Example 9 is much higher than that of Example 4. The reverse coating causes a decrease in the interfacial bonding force, and the salt spray resistance time is only 124 h.

[0035] The salt spray resistance time of Example 10 is significantly lower than that of Example 4. High-temperature annealing causes the coating to oxidize and fail, verifying that the annealing temperature needs to be strictly controlled at 400-500 °C. The upper yield strength and hardness of Example 6 are better than those of other examples, indicating that appropriately increasing the heat treatment temperature can promote the uniform precipitation of carbides and strengthen the matrix.

[0036] The above are only the 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 principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high-strength bolt, characterized in that: The invention comprises 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%, and the balance is Fe and other inevitable impurities.

2. A high-strength bolt according to claim 1, characterized in that: 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%, the balance is Fe and other inevitable impurities, and the Cr / Mo mass ratio is 4:1-5:

1.

3. A high-strength bolt according to claim 2, characterized in that: 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%, Ce0.05%-0.12%, Y 0.08%-0.18%, Er 0.03%-0.08% and B 0.002%-0.005%, the balance is Fe and other inevitable impurities, and 0.35%≤V+Ce+Y≤0.45%.

4. A high-strength bolt according to claim 1, characterized in that: 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.

5. The high-strength bolt according to claim 1, characterized in that: The thickness of the AlCr layer is 0.2-0.4 μm; the thickness of the Y2O3 layer is 0.5-0.7 μm.

6. A high strength bolt according to claim 5, characterized in that: The mass content of Cr in the AlCr layer is 18%-22%.

7. A method for preparing a high-strength bolt according to any one of claims 1 to 6, characterized in that the steps include: S1. Weighing raw materials according to the components in the mass percentage, 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, and finally an AlCr-Y2O3 wear-resistant layer is formed on the surface of the bolt, and finally the high-strength bolt is obtained through post-processing.

8. The method for preparing a high-strength bolt according to claim 7, 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.

9. The method for preparing a high-strength bolt according to claim 7, characterized in that: 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.

10. The method for preparing a high-strength bolt according to claim 7, characterized in that: The post-treatment step includes annealing at a temperature of 400-500° C. in an argon atmosphere for 2-3 hours.

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