An austenitic stainless steel for lead-based reactor fastener having excellent high-temperature microstructure stability and a method for producing the same

Abstract

The application belongs to the field of austenitic stainless steel structural materials for high temperature, and particularly relates to an austenitic stainless steel with excellent high-temperature microstructure stability for lead-based stack fasteners and a preparation method thereof, which is suitable for a new type of fastener structural material facing long-time high-temperature lead-bismuth corrosion environment in the field of nuclear energy. The chemical composition of the steel, by weight percentage, is as follows: C: 0.09-0.12%; Si: 2.4-2.8%; Mn: ≤0.5%; S: ≤0.005%; P: ≤0.1%; Cr: 14.0-16.0%; Ni: 10.0-14.0%; Mo: 0.8-1.6%; Nb: 0.8-1.0%; N: 0.06-0.12%; O: ≤0.005%; and the balance is Fe. Under the premise of guaranteeing excellent lead-bismuth corrosion resistance, the application balances the influence of alloy elements on microstructure stability, and realizes the optimization of the matching of lead-bismuth corrosion resistance, stress relaxation resistance and microstructure thermal stability of the application steel.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature austenitic stainless steel structural materials, specifically relating to an austenitic stainless steel with excellent high-temperature structural stability for lead-based reactor fasteners and its preparation method. It is mainly used as a new type of fastener structural material in the nuclear energy field facing long-term high-temperature lead-bismuth corrosion environment. Background Technology

[0002] One common approach to solving lead-bismuth corrosion problems is to add an appropriate amount of silicon (Si) to existing structural materials. Si forms a stable and dense oxide film on the material surface at high temperatures, isolating the liquid lead-bismuth metal and thus exhibiting good corrosion resistance. Therefore, high-Si austenitic stainless steel is an important structural metal material in small lead-bismuth fast reactors.

[0003] As an alloying element in steel, silicon (Si) not only provides resistance to lead and bismuth corrosion, but also promotes the growth of metals (M) in austenitic stainless steel during high-temperature, long-term service. 23 The precipitation of second phases such as C6, Sigma, ferrite, and G alters long-term microstructure stability, thereby affecting high-temperature strength and toughness. Therefore, while fully utilizing the role of Si in achieving resistance to liquid lead-bismuth corrosion, the influence of Si on the microstructure stability of steel under high-temperature, long-term conditions cannot be ignored. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide an austenitic stainless steel with excellent high-temperature structural stability for lead-based fasteners and its preparation method, which balances the dual effects of Si in austenitic stainless steel on resistance to liquid lead-bismuth corrosion and high-temperature long-term structural stability. The austenitic stainless steel has both excellent structural stability and resistance to lead-bismuth corrosion.

[0005] The technical solution of this invention is:

[0006] An austenitic stainless steel with excellent high-temperature structural stability for lead-based fasteners has the following chemical composition by weight percentage:

[0007] C: 0.09~0.12%; Si: 2.4~2.8%; Mn: ≤0.5%; S: ≤0.005%; P: ≤0.1%; Cr: 14.0~16.0%; Ni: 10.0~14.0%; Mo: 0.8~1.6%; Nb: 0.8~1.0%; N: 0.06~0.12%; O: ≤0.005%; balance Fe.

[0008] The lead-based fasteners are made of austenitic stainless steel with excellent high-temperature structural stability, and the Cr equivalent and Ni equivalent satisfy: Ni equivalent / Cr equivalent ≥ 0.75, wherein:

[0009] Chromium equivalent is calculated according to formula (1):

[0010] Cr equivalent = 100 × (Cr + Mo + 1.5Si + 0.5Nb) (1)

[0011] Nickel equivalent is calculated according to formula (2):

[0012] Ni equivalent = 100 × (Ni + 30 × C + 30 × N + 0.5 × Mn) (2).

[0013] The aforementioned lead-based fasteners are made of austenitic stainless steel with excellent high-temperature structural stability. The initial microstructure of the austenitic stainless steel is austenite and Nb-containing carbides; after aging at 510°C for 3000 hours, the microstructure is still austenite and Nb-containing carbides.

[0014] The method for preparing austenitic stainless steel with excellent high-temperature structural stability for lead-based fasteners includes the following steps:

[0015] Step 1: Obtain steel ingots by vacuum induction smelting or vacuum induction smelting + vacuum consumable melting.

[0016] Step two involves continuous homogenization, forging, and heat treatment of the steel ingot:

[0017] (1) The steel ingot is heated to 1260±10℃ with the furnace and kept at that temperature for no less than 12 hours;

[0018] (2) After the steel ingot is taken out of the furnace and air-cooled to 1100~1150℃, it is forged and the final forging temperature is 850~950℃;

[0019] (3) After forging, the billet is placed in a holding furnace at 1050~1100℃ for 1~2 hours and then cooled with water.

[0020] The method for preparing austenitic stainless steel with excellent high-temperature structural stability for lead-based fasteners, in step (2), forging is carried out in a three-dimensional cyclic forging with large reduction, with a single deformation amount of >10% in one cycle, a cycle number of not less than 6 times, and a total forging ratio of >20.

[0021] The method for preparing austenitic stainless steel with excellent high-temperature structural stability for lead-based fasteners, wherein the performance indicators of the austenitic stainless steel are as follows:

[0022] Room temperature yield strength ≥360MPa, tensile strength ≥750MPa, elongation ≥50.0%; V-cut full-size impact toughness ≥140J;

[0023] Yield strength at 550℃ ≥230MPa, tensile strength ≥540MPa, elongation ≥40.0%.

[0024] The method for preparing austenitic stainless steel with excellent high-temperature structural stability for lead-based fasteners, wherein the oxide film thickness of the austenitic stainless steel does not exceed 20 μm after corrosion in a liquid lead-bismuth alloy (45% Pb-Bi) at 550℃ with saturated oxygen concentration for 3000 hours, exhibiting excellent resistance to liquid lead-bismuth corrosion.

[0025] The method for preparing austenitic stainless steel with excellent high-temperature structural stability for lead-based fasteners, wherein the performance indicators of the austenitic stainless steel after aging at 510℃ for 3000 hours are as follows: yield strength ≥330MPa, tensile strength ≥750MPa, elongation ≥50.0%; V-nose full-size impact toughness value ≥130J, exhibiting excellent structural stability.

[0026] The method for preparing austenitic stainless steel with excellent high-temperature structural stability for lead-based fasteners, wherein the austenitic stainless steel has a residual stress greater than 90 MPa after being held at 510℃ and with an initial stress of 120 MPa for 1000 hours.

[0027] The design concept of this invention is as follows:

[0028] This invention, while ensuring Si's excellent resistance to lead-bismuth corrosion, considers the negative impact of Si on microstructure stability. Through iterative optimization of key elements such as Si, Mo, Ni, Nb, C, and N, and with coordinated microstructure control, the optimal balance between lead-bismuth corrosion resistance, stress relaxation resistance, and thermal stability of the material is achieved. For example, in mitigating ferrite precipitation, a high Ni equivalent (Ni equivalent / Cr equivalent ≥ 0.75) is followed, prioritizing higher initial austenite microstructure stability; in suppressing M... 23 Regarding C6 precipitation, a compositional design system based on Nb to solidify C was adopted to minimize the combination of Cr and C; to mitigate Sigma phase precipitation, the number of electron vacancies Nv in the alloy was strictly controlled to be less than 2.52.

[0029] Furthermore, this invention innovatively employs an appropriate amount of P alloying method. With the help of P, more vacancies can be added during the quenching process of austenitic stainless steel, thereby increasing the precipitation density of NbC in the steel and improving the stress relaxation resistance of the steel.

[0030] The content of the main elements in this invention is described as follows:

[0031] Si: 2.4~2.8wt%

[0032] Si is a key element ensuring the resistance of austenitic stainless steel to lead-bismuth corrosion. At high temperatures, Si preferentially oxidizes to form Si-containing oxides. Since these oxides have extremely low solubility in liquid lead-bismuth metal, they can hinder corrosion from the external liquid lead-bismuth metal environment. Utilizing this effect of Si, adding an appropriate amount of Si to the steel provides excellent resistance to liquid lead-bismuth corrosion. However, considering that Si is a strong ferrite-forming element, and that excessive Si can promote the precipitation of harmful second phases during long-term high-temperature service, impairing the high-temperature microstructure stability, the Si content in the steel of this invention is 2.4~2.8 wt%.

[0033] Cr: 14.0~16.0wt%

[0034] The stainless and corrosion-resistant properties of austenitic stainless steel are primarily due to the passivation effect of Cr, which promotes the steel's corrosion resistance and maintains it in a stable passive state. This effect of Cr results in a continuous and dense Cr₂O₃ passivation film on the steel surface that hinders ion migration and the dissolution of elements into liquid lead and bismuth. This effect of Cr is mutually reinforced with that of Si, thereby improving the steel's resistance to liquid metal corrosion. However, Cr is a ferrite-forming element and readily forms Mg with C. 23 C6 is the second phase. Therefore, the Cr content is controlled at 14.0~16.0 wt%.

[0035] Ni: 10.0~14.0wt%

[0036] Ni is the main element that enables steel to achieve a fully austenitic structure. However, Ni has a high solubility in liquid lead-bismuth alloys, and excessively high content will deteriorate the resistance to liquid metal corrosion. At the same time, increasing the Ni content in the steel will reduce the solubility of C in austenitic stainless steel, thereby increasing the tendency for carbide precipitation. Therefore, taking all factors into consideration, the Ni content in the steel of this invention is controlled at 10.0~14.0 wt%, preferably 10.0~12.0 wt%.

[0037] C: 0.09~0.12wt%

[0038] C is one of the most effective elements for increasing Ni equivalent, with a coefficient 30 times that of Ni. It can significantly expand the austenite phase region and stabilize the austenite structure. Another important role of C in the steel of this invention is to form nano-sized NbC with Nb. This results in high-density, fine, and dispersed NbC particles pinning dislocations, improving the steel's resistance to high-temperature stress relaxation. The C and Nb contents in the steel of this invention follow the principle of ideal stoichiometry, ensuring that the weight percentage of Nb is 8 times that of C. If the C or Nb content is too low, the resulting NbC will have a low density and a smaller effect; while if the C content is too high, it will react with Cr in the steel to form MnO2 early. 23 C6 carbides, on the contrary, worsen the overall performance. Therefore, the C content of the steel of this invention is 0.09~0.12wt%.

[0039] N: 0.06~0.12wt%

[0040] Ni has a nickel equivalent coefficient 30 times that of Ni, effectively increasing the Ni equivalent and exhibiting significant solid solution strengthening in austenitic stainless steel. Furthermore, the carbonitrides it forms are stable, and its solubility in liquid lead-bismuth metal is lower than that of Ni. Therefore, it is the most effective element for simultaneously improving high-temperature structural stability and resistance to lead-bismuth corrosion. However, the Ni content cannot be too high, as excessive Ni readily forms a Cr-N compound second phase with Cr in the steel, affecting corrosion resistance. Considering all factors, the optimal Ni content is 0.06~0.12 wt%.

[0041] Mo: 0.8~1.6wt%

[0042] The main role of Mo in the steel of this invention is to improve the high-temperature strength of the steel. As the Mo content in the steel increases, the high-temperature strength of the steel improves; however, Mo increases the Cr equivalent and promotes the precipitation of intermetallic phases in austenitic stainless steel, such as Sigma and Laves phases, thus reducing the stability of the microstructure. Therefore, considering all factors, the Mo content in the steel of this invention is 0.8~1.6 wt%, preferably 0.8~1.2 wt%.

[0043] Nb: 0.8~1.0wt%

[0044] In the steel of this invention, on the one hand, Nb forms a high-density Nb(C,N) nanoscale precipitate phase with C and N. This precipitate phase pins dislocations, preventing the transformation of elastic strain to plastic strain, thereby improving the high-temperature stress relaxation resistance. On the other hand, the solid-solution Nb also exhibits excellent resistance to lead-bismuth corrosion. However, Nb also increases the Cr equivalent, and it is a segregating element. Excess Nb in the steel will form a Fe2Nb-type Laves phase after long-term aging, deteriorating the performance. Therefore, considering all factors, the maximum Nb content does not exceed 1.0 wt%, and the optimal content is 0.8~1.0 wt%.

[0045] P: ≤0.1 wt%

[0046] This invention innovatively relaxes the restrictions on phosphorus (P) content, allowing a maximum P content of up to 0.1 wt%. Generally, P is considered a harmful impurity in austenitic stainless steel, and lower content is better. However, research has found that appropriately increasing the P content in carbon-containing austenitic stainless steel not only does not impair the steel's mechanical properties, but also promotes the creation of more vacancies during the quenching process. These vacancies provide nucleation sites for NbC precipitation, significantly increasing the NbC precipitation density and thus improving the steel's resistance to stress relaxation. The optimal P content for this effect is 0.1 wt%, therefore, this invention relaxes the P content in the steel to ≤0.1 wt%, preferably 0.01~0.1 wt%. This relaxation of the P content restriction not only improves the overall performance of austenitic stainless steel but also reduces raw material costs.

[0047] The advantages and beneficial effects of this invention are:

[0048] 1. This invention, while ensuring that Si possesses excellent resistance to lead and bismuth corrosion, fully considers the negative impact of Si on microstructure stability, and obtains an austenitic stainless steel that simultaneously possesses excellent microstructure stability and resistance to lead and bismuth corrosion, as well as its preparation method.

[0049] 2. The steel of this invention innovatively relaxes the limit of P content to ≤0.1wt%, which not only improves the high-temperature stress relaxation resistance of austenitic stainless steel, but also reduces the cost of raw materials.

[0050] 3. The steel of this invention is a new type of fastener structural material that can be applied in the nuclear energy field to face high-temperature and long-term lead-bismuth corrosion environments. Attached Figure Description

[0051] Figure 1 The initial microstructure of the steel in Comparative Example 1 is austenite and Nb-containing carbides.

[0052] Figure 2 The microstructure of Comparative Example 1 steel after aging at 510℃ for 3000 hours consists of austenite, Nb-containing carbides, and a second phase precipitated at the grain boundaries.

[0053] Figure 3 The initial microstructure of the steel in Example 4 is austenite and Nb-containing carbides.

[0054] Figure 4 The microstructure of the steel in Example 4 after aging at 510°C for 3000 hours is still austenite and Nb-containing carbides.

[0055] Figure 5 The oxide film morphology of steel in Example 5 after corrosion in a liquid lead-bismuth alloy (45% Pb-Bi) at 550°C and saturated oxygen concentration for 3000 hours is shown.

[0056] Figure 6 The distribution morphology of nano-NbC in steel of Example 1 is shown.

[0057] Figure 7 The distribution morphology of nano-NbC in steel in Example 3 is shown. Detailed Implementation

[0058] In the specific implementation process, the preparation methods of the inventive steel (example) and the comparative steel (comparative example) are as follows:

[0059] (1) Steel ingots are obtained by smelting raw materials with the chemical composition described in this invention using a 200 kg vacuum induction furnace;

[0060] (2) The steel ingot is heated to 1250℃ in the furnace and held for 14 hours. After that, it is taken out of the furnace and air-cooled. When the temperature is cooled to 1150℃, forging begins. The forging is carried out by three-dimensional cyclic forging with large reduction in the longitudinal, transverse and longitudinal directions. The deformation amount per cycle is 15%, the number of cycles is 6, the total forging ratio is 25, and the final forging temperature is 870℃. After forging, the bar is placed in a 1050℃ holding furnace and held for 1 hour, and then water-cooled to room temperature.

[0061] The present invention will now be described through different embodiments and comparative examples. These embodiments are for illustrative purposes only, and the present invention is not limited to these embodiments.

[0062] Comparative Example 1

[0063] The chemical composition of the steel, by weight percentage, is as follows: C: 0.11%; Si: 2.61%; Mn: 0.49%; S: 0.0017%; P: 0.009%; Cr: 14.96%; Ni: 11.21%; Mo: 1.01%; Nb: 0.90%; O: 0.002%; N: 0.005%; balance Fe. The Cr equivalent is 20.34, the Ni equivalent is 14.91, and the Ni equivalent / Cr equivalent ratio is 0.73.

[0064] Comparative Example 2

[0065] The chemical composition of the steel, by weight percentage, is as follows: C: 0.12%; Si: 2.56%; Mn: 0.35%; S: 0.0020%; P: 0.008%; Cr: 15.17%; Ni: 10.02%; Mo: 0.004%; Nb: 0.90%; O: 0.002%; N: 0.0055%; balance Fe. The Cr equivalent is 19.46, the Ni equivalent is 13.96, and the Ni equivalent / Cr equivalent ratio is 0.72.

[0066] Comparative Example 3

[0067] The chemical composition of the steel, by weight percentage, is as follows: C: 0.10%; Si: 2.50%; Mn: 0.50%; S: 0.0019%; P: 0.008%; Cr: 14.77%; Ni: 11.84%; Mo: 1.01%; Nb: 0.87%; O: 0.002%; N: 0.011%; balance Fe. The Cr equivalent is 19.96, the Ni equivalent is 15.39, and the Ni equivalent / Cr equivalent ratio is 0.77.

[0068] Comparative Example 4

[0069] The chemical composition of the steel, by weight percentage, is as follows: C: 0.11%; Si: 2.54%; Mn: 0.53%; S: 0.0019%; P: 0.008%; Cr: 15.05%; Ni: 12.04%; Mo: 1.54%; Nb: 0.90%; O: 0.002%; N: 0.0094%; balance Fe. The Cr equivalent is 20.85, the Ni equivalent is 15.89, and the Ni equivalent / Cr equivalent ratio is 0.76.

[0070] Comparative Example 5

[0071] The chemical composition of the steel, by weight percentage, is as follows: C: 0.11%; Si: 2.54%; Mn: 0.48%; S: 0.0022%; P: 0.007%; Cr: 14.97%; Ni: 14.00%; Mo: 1.52%; Nb: 0.88%; O: 0.002%; N: 0.0076%; balance Fe. The Cr equivalent is 20.74, the Ni equivalent is 17.77, and the Ni equivalent / Cr equivalent ratio is 0.86.

[0072] Example 1

[0073] The chemical composition of the steel, by weight percentage, is as follows: C: 0.11%; Si: 2.61%; Mn: 0.18%; S: 0.0022%; P: 0.007%; Cr: 15.07%; Ni: 11.52%; Mo: 1.03%; Nb: 0.90%; O: 0.002%; N: 0.06%; balance Fe. The Cr equivalent is 20.47, the Ni equivalent is 16.71, and the Ni equivalent / Cr equivalent ratio is 0.82.

[0074] Example 2

[0075] The chemical composition of the steel, by weight percentage, is as follows: C: 0.10%; Si: 2.70%; Mn: 0.22%; S: 0.0022%; P: 0.008%; Cr: 15.12%; Ni: 11.3%; Mo: 1.08%; Nb: 0.91%; O: 0.002%; N: 0.117%; balance Fe. The Cr equivalent is 20.71, the Ni equivalent is 17.92, and the Ni equivalent / Cr equivalent ratio is 0.87.

[0076] Example 3

[0077] The chemical composition of the steel, by weight percentage, is as follows: C: 0.10%; Si: 2.65%; Mn: 0.12%; S: 0.0022%; P: 0.09%; Cr: 15.23%; Ni: 11.43%; Mo: 1.1%; Nb: 0.90%; O: 0.002%; N: 0.087%; balance Fe. The Cr equivalent is 20.76, the Ni equivalent is 17.1, and the Ni equivalent / Cr equivalent ratio is 0.82.

[0078] Example 4

[0079] The chemical composition of the steel, by weight percentage, is as follows: C: 0.09%; Si: 2.78%; Mn: 0.20%; S: 0.002%; P: 0.007%; Cr: 15.97%; Ni: 10.51%; Mo: 1.14%; Nb: 0.93%; O: 0.002%; N: 0.1%; balance Fe. The Cr equivalent is 21.75, the Ni equivalent is 16.31, and the Ni equivalent / Cr equivalent ratio is 0.75.

[0080] Example 5

[0081] The chemical composition of the steel, by weight percentage, is as follows: C: 0.10%; Si: 2.74%; Mn: 0.16%; S: 0.0018%; P: 0.085%; Cr: 15.76%; Ni: 11.36%; Mo: 1.08%; Nb: 0.90%; O: 0.0016%; N: 0.092%; balance Fe. The Cr equivalent is 21.46, the Ni equivalent is 17.2, and the Ni equivalent / Cr equivalent ratio is 0.80.

[0082] Table 1 shows the room temperature mechanical properties of the above embodiments and comparative examples.

[0083] Table 1

[0084]

[0085] As shown in Table 2, the mechanical properties at 550℃ of the above embodiments and comparative examples are as follows.

[0086] Table 2

[0087]

[0088] The results in Tables 1 and 2 show that by adding an appropriate amount of nitrogen (N), the mechanical properties of the invented steel are significantly improved in both room temperature and high temperature conditions. Specifically, the yield strength and tensile strength are greatly increased, while the elongation and impact toughness remain at or even better than those in the comparative examples. It is worth noting that in the invented steel of the examples, a suitable increase in phosphorus (P) content (as shown in the comparison between Examples 4 and 5) also resulted in a certain degree of strength improvement. This demonstrates that phosphorus (P) also contributes to the improvement of strength in the invented steel.

[0089] Figures 1-4 The figures show the original microstructure and the microstructure after aging at 510℃ for 3000 hours for Comparative Example 1 (Ni equivalent / Cr equivalent = 0.73) and Example 4 (Ni equivalent / Cr equivalent = 0.75), respectively. The comparison shows that the Ni equivalent / Cr equivalent ratio of the steel in Comparative Example 1 is less than 0.75, and a second phase appears at the grain boundaries in its microstructure after aging at 510℃ for 3000 hours. In contrast, the microstructure of the steel in Example 4 after aging at 510℃ for 3000 hours remains the same as the initial microstructure, consisting of an austenitic matrix and Nb-containing carbides. Therefore, to ensure excellent microstructural stability, the Ni equivalent / Cr equivalent ratio of the invented steel needs to be no less than 0.75.

[0090] Table 3 shows the mechanical properties of the steels in the examples and comparative examples after aging at 510°C for 3000 hours.

[0091] Table 3

[0092]

[0093] Comparing the mechanical properties in Table 3, it can be seen that the invented steel, after aging at 510℃ for 3000 hours, exhibits a yield strength ≥330MPa, tensile strength ≥750MPa, elongation ≥50.0%, and a V-shaped full-size impact toughness ≥130J. In contrast, the steel in Comparative Example 1 shows a significant decrease in impact toughness after aging at 510℃ for 3000 hours (from 127J in Table 1 to 33J in Table 3), indicating microstructural instability and a deterioration in impact toughness. Therefore, the invented steel possesses excellent microstructural stability.

[0094] Figure 5 The oxide film morphology of the steel in Example 5 after corrosion in a liquid lead-bismuth alloy (45% Pb-Bi) at 550°C and saturated oxygen concentration for 3000 hours is shown. The oxide film thickness is only about 15 μm.

[0095] As shown in Table 4, the oxide film thickness values ​​of the above embodiments and comparative examples after 3000 hours of corrosion in a liquid lead-bismuth alloy (45%Pb-Bi) at saturated oxygen concentration and 550°C.

[0096] Table 4

[0097]

[0098] Comparing the inventive steel and the comparative steel in Table 4, it can be seen that although the Ni equivalent / Cr equivalent ratio of the steels in Comparative Examples 4 and 5 meets the requirement of not less than 0.75, this is achieved by increasing the Ni content. While this may improve the microstructure stability, it reduces the resistance to lead-bismuth corrosion, as shown in the table, resulting in a thicker oxide film. Overall, the inventive steels (Examples 1, 2, 4, and 5) not only possess the aforementioned excellent microstructure stability but also maintain excellent resistance to lead-bismuth corrosion, thus achieving both excellent microstructure stability and resistance to lead-bismuth corrosion.

[0099] As shown in Table 5, the residual stress values ​​of the above embodiments and comparative examples after being maintained at 510°C and with an initial stress of 120 MPa for 1000 hours are shown.

[0100] Table 5

[0101]

[0102] The results in Table 5 show that, in addition to having excellent structural stability and resistance to lead and bismuth corrosion, the invented steel also exhibits significantly improved stress relaxation resistance. This is evidenced by the fact that, after being kept at 510℃ for 1000 hours with an initial stress of 120 MPa, the residual stress value is significantly higher than that of the comparative steel.

[0103] Figure 6 and Figure 7 The distribution of nano-NbC in the steels of Examples 1 and 3 are shown respectively. As can be seen from the comparison, the number density of nano-NbC in the steel of Example 3 is significantly higher than that of Example 1. This is because the steel of Example 3 contains a higher content of P, which promotes the precipitation of more nano-sized NbC during the quenching process, thereby improving the steel's resistance to stress relaxation, i.e., increasing the residual stress by 11 MPa.

[0104] The results show that, while ensuring excellent resistance to lead and bismuth corrosion, the present invention balances the influence of alloying elements on the stability of the microstructure, thus achieving the optimal matching of the steel's resistance to lead and bismuth corrosion, stress relaxation resistance, and thermal stability.

[0105] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. An austenitic stainless steel with excellent high-temperature structural stability for lead-based fasteners, characterized in that, The chemical composition of the steel by weight percentage is as follows: C: 0.11%; Si: 2.61%; Mn: 0.18%; S: 0.0022%; P: 0.007%; Cr: 15.07%; Ni: 11.52%; Mo: 1.03%; Nb: 0.90%; O: 0.002%; N: 0.06%; balance Fe; wherein, the Cr equivalent is 20.47, the Ni equivalent is 16.71, and the Ni equivalent / Cr equivalent = 0.82; Chromium equivalent is calculated according to formula (1): Cr equivalent = 100 × (Cr + Mo + 1.5Si + 0.5Nb) (1) Nickel equivalent is calculated according to formula (2): Ni equivalent = 100 × (Ni + 30 × C + 30 × N + 0.5 × Mn) (2).

2. An austenitic stainless steel with excellent high-temperature structural stability for lead-based fasteners, characterized in that, The chemical composition of the steel, by weight percentage, is as follows: C: 0.10%; Si: 2.70%; Mn: 0.22%; S: 0.0022%; P: 0.008%; Cr: 15.12%; Ni: 11.3%; Mo: 1.08%; Nb: 0.91%; O: 0.002%; N: 0.117%; balance Fe; wherein, the Cr equivalent is 20.71, the Ni equivalent is 17.92, and the Ni equivalent / Cr equivalent = 0.87; Chromium equivalent is calculated according to formula (1): Cr equivalent = 100 × (Cr + Mo + 1.5Si + 0.5Nb) (1) Nickel equivalent is calculated according to formula (2): Ni equivalent = 100 × (Ni + 30 × C + 30 × N + 0.5 × Mn) (2).

3. An austenitic stainless steel with excellent high-temperature structural stability for lead-based fasteners, characterized in that, The chemical composition of the steel, by weight percentage, is: C: 0.10%; Si: 2.65%; Mn: 0.12%. S: 0.0022%; P: 0.09%; Cr: 15.23%; Ni: 11.43%; Mo: 1.1%; Nb: 0.90%; O: 0.002%; N: 0.087%; balance Fe; where Cr equivalent is 20.76, Ni equivalent is 17.1, Ni equivalent / Cr equivalent = 0.82; Chromium equivalent is calculated according to formula (1): Cr equivalent = 100 × (Cr + Mo + 1.5Si + 0.5Nb) (1) Nickel equivalent is calculated according to formula (2): Ni equivalent = 100 × (Ni + 30 × C + 30 × N + 0.5 × Mn) (2).

4. An austenitic stainless steel with excellent high-temperature structural stability for lead-based fasteners, characterized in that, The chemical composition of the steel, by weight percentage, is: C: 0.09%; Si: 2.78%; Mn: 0.20%. S: 0.002%; P: 0.007%; Cr: 15.97%; Ni: 10.51%; Mo: 1.14%; Nb: 0.93%; O: 0.002%; N: 0.1%; balance Fe; wherein, Cr equivalent is 21.75, Ni equivalent is 16.31, Ni equivalent / Cr equivalent = 0.75; Chromium equivalent is calculated according to formula (1): Cr equivalent = 100 × (Cr + Mo + 1.5Si + 0.5Nb) (1) Nickel equivalent is calculated according to formula (2): Ni equivalent = 100 × (Ni + 30 × C + 30 × N + 0.5 × Mn) (2).

5. An austenitic stainless steel with excellent high-temperature structural stability for lead-based fasteners, characterized in that, The chemical composition of the steel, by weight percentage, is as follows: C: 0.10%; Si: 2.74%; Mn: 0.16%; S: 0.0018%; P: 0.085%; Cr: 15.76%; Ni: 11.36%; Mo: 1.08%; Nb: 0.90%; O: 0.0016%; N: 0.092%; balance Fe; wherein, the Cr equivalent is 21.46, the Ni equivalent is 17.2, and the Ni equivalent / Cr equivalent = 0.80; Chromium equivalent is calculated according to formula (1): Cr equivalent = 100 × (Cr + Mo + 1.5Si + 0.5Nb) (1) Nickel equivalent is calculated according to formula (2): Ni equivalent = 100 × (Ni + 30 × C + 30 × N + 0.5 × Mn) (2).

6. The austenitic stainless steel with excellent high-temperature structural stability for lead-based fasteners according to any one of claims 1 to 5, characterized in that, The initial microstructure of austenitic stainless steel is austenite and Nb-containing carbides; after aging at 510℃ for 3000 hours, the microstructure is still austenite and Nb-containing carbides.

7. A method for preparing an austenitic stainless steel with excellent high-temperature structural stability for lead-based fasteners as described in any one of claims 1 to 6, characterized in that, Includes the following steps: Step 1: Obtain steel ingots by vacuum induction smelting or vacuum induction smelting + vacuum consumable melting. Step two involves continuous homogenization, forging, and heat treatment of the steel ingot: (1) The steel ingot is heated to 1260±10℃ with the furnace and kept at that temperature for no less than 12 hours; (2) After the steel ingot is taken out of the furnace and air-cooled to 1100~1150℃, it is forged and the final forging temperature is 850~950℃; (3) After forging, the billet is placed in a holding furnace at 1050~1100℃ for 1~2 hours and then cooled with water.

8. The method for preparing austenitic stainless steel with excellent high-temperature structural stability for lead-based fasteners according to claim 7, characterized in that, In step (2), the forging process involves longitudinal-transverse-longitudinal three-dimensional cyclic forging with a large reduction amount. The deformation amount per cycle is >10%, the number of cycles is not less than 6, and the total forging ratio is >20.

9. The method for preparing austenitic stainless steel with excellent high-temperature structural stability for lead-based fasteners according to claim 7, characterized in that, The performance indicators of austenitic stainless steel are as follows: Room temperature yield strength ≥360MPa, tensile strength ≥750MPa, elongation ≥50.0%; V-cut full-size impact toughness ≥140J; Yield strength at 550℃ ≥230MPa, tensile strength ≥540MPa, elongation ≥40.0%.

10. The method for preparing austenitic stainless steel with excellent high-temperature structural stability for lead-based fasteners according to claim 7, characterized in that, The austenitic stainless steel exhibits excellent resistance to liquid lead-bismuth corrosion. After 3000 hours of corrosion in saturated oxygen concentration and 550℃ liquid lead-bismuth alloy (45% Pb-Bi), the oxide film thickness does not exceed 20 μm.

11. The method for preparing austenitic stainless steel with excellent high-temperature structural stability for lead-based fasteners according to claim 7, characterized in that, The performance indicators of this austenitic stainless steel after aging at 510℃ for 3000 hours are as follows: yield strength ≥330MPa, tensile strength ≥750MPa, elongation ≥50.0%; V-nose full-size impact toughness ≥130J, exhibiting excellent microstructural stability.

12. The method for preparing austenitic stainless steel with excellent high-temperature structural stability for lead-based fasteners according to claim 7, characterized in that, The austenitic stainless steel exhibits a residual stress greater than 90 MPa after being held at 510℃ with an initial stress of 120 MPa for 1000 hours.

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