CN114574765B

CN114574765B - Preparation method of high-performance fastener for lead-based pile

Info

Publication number: CN114574765B
Application number: CN202210210872.5A
Authority: CN
Inventors: 燕春光; 严伟; 徐海涛; 史显波; 乔鹏瑞; 单以银; 韩丽青; 戎利建; 杨红义; 李依依
Original assignee: Institute of Metal Research of CAS; China Institute of Atomic of Energy
Current assignee: Institute of Metal Research of CAS; China Institute of Atomic of Energy
Priority date: 2022-03-04
Filing date: 2022-03-04
Publication date: 2023-07-14
Anticipated expiration: 2042-03-04
Also published as: CN114574765A

Abstract

The invention belongs to the field of high-temperature fasteners, and particularly relates to a high-performance fastener resistant to liquid lead (lead bismuth) corrosion for a high-temperature lead-based pile and a preparation method thereof. The fastener material comprises the following chemical components in percentage by weight: c: 0.06-0.12%; si:2.0 to 3.0 percent; mn:0 to 1.0 percent; s:0 to 0.005 percent; p:0 to 0.01 percent; cr:13.0 to 17.0 percent; ni:8.0 to 15.0 percent; cu:0 to 1.0 percent; mo:0.5 to 2.0 percent; nb: 8X 100C-1.0%; o:0 to 0.003 percent; n:0 to 0.03 percent; fe balance. The invention obtains the high-performance fastener which integrates the comprehensive performances of excellent lead-bismuth corrosion resistance, high strength, high endurance resistance, high fatigue performance, excellent stress relaxation resistance and the like, and can be used for connecting structural materials which are in the nuclear energy field and are exposed to a high-temperature lead (lead-bismuth) corrosion environment.

Description

Preparation method of high-performance fastener for lead-based pile

Technical Field

The invention belongs to the field of high-temperature fasteners, and particularly relates to a high-performance fastener resistant to liquid lead (lead bismuth) corrosion for a high-temperature lead-based pile and a preparation method thereof.

Background

The lead (lead bismuth) cooled nuclear reactor, abbreviated as lead-based reactor, is one of the six main types of the fourth generation nuclear reactor. The lead-based stack can well meet the target requirements of safety, economy, sustainability and non-diffusion of nuclei, is subjected to international important attention, and has a wide development space in the future.

The fastener is one of the structural components in the lead-based stack and is responsible for the extremely critical connection that is involved in the safe operation of the components in the stack. The bolt connection by adopting the fastener has the advantages of compact structure, easy assembly and disassembly, large connecting force, reusability and the like, and is widely applied to various mechanical structures. Screw bolts are commonly used in the improved three-loop pressurized water reactor (CPR 1000) internal member connecting structure in China. The number of the screw bolts of the first-stage internal components of the turning-plate-ridge Australian nuclear power station reaches as many as thousands. It can be seen that the use of fasteners in nuclear reactors is widespread and important.

However, the role of the fasteners within the nuclear reactor is critical. Historically, there have been many incidents of bolt loosening and breakage that have caused significant damage to the operation of the reactor. If the secondary support of the lower part of the first-stage reactor internals and the instrument sleeve assembly in Qinshan in 1988 have a plurality of broken instrument sleeves, the connecting screws between the plurality of instrument sleeves and the grid plate and between the plurality of instrument sleeves and the reactor core support plate are loosened and broken; in 1998, after the thermal state function test of the pakistan C1 project, the phenomenon that 5 bolts are loosened on a hanging basket of a pile inner member was found.

Therefore, the fastener serving in the lead-based pile with more severe use environment has special performance requirements of high heat resistance (fracture resistance), high-temperature stress relaxation resistance (anti-loosening), fatigue fracture resistance (fracture resistance) and the like besides good liquid metal corrosion resistance. At present, the high-performance fastener which has the comprehensive integration of liquid lead (lead bismuth) corrosion resistance, stress relaxation resistance, fatigue fracture resistance and high heat strength is not available at home and abroad.

Disclosure of Invention

The invention aims to provide a high-performance fastener which is integrated with liquid lead (lead bismuth) corrosion resistance, stress relaxation resistance, fatigue fracture resistance, high durability and high heat intensity and a preparation method thereof, and meets the use requirements of severe service environments such as high temperature, strong corrosion, vibration and the like in a lead-based pile.

The technical scheme of the invention is as follows:

a high-performance fastener for a lead-based pile comprises the following chemical components in percentage by weight: c: 0.06-0.12%; si:2.0 to 3.0 percent; mn:0 to 1.0 percent; s:0 to 0.005 percent; p:0 to 0.01 percent; cr:13.0 to 17.0 percent; ni:8.0 to 15.0 percent; cu:0 to 1.0 percent; mo:0.5 to 2.0 percent; nb: 8X 100C-1.0%; o:0 to 0.003 percent; n:0 to 0.03 percent; fe balance.

The preparation method of the high-performance fastener for the lead-based pile comprises the following steps:

(1) Raw material preparation: proportioning according to the designed components;

(2) Double vacuum smelting: adopting a duplex vacuum smelting process of vacuum induction smelting and vacuum consumable to obtain an ingot;

(3) Homogenizing: homogenizing the cast ingot at a high temperature;

(4) Forging an ingot: carrying out hot forging on the homogenized cast ingot to obtain a forged rod;

(5) Heat treatment of steel bars: the forged steel bar is subjected to solution treatment, and the treatment process comprises the following steps: preserving heat for 0.5-2 hours at 1000-1150 ℃, and air-cooling to room temperature;

(6) Cold drawing of steel bars: cold drawing the steel bar subjected to solution treatment, wherein the cold drawing deformation is not less than 30%;

(7) And (3) secondary heat treatment of the steel bar: preserving the temperature of the steel bar at 800-900 ℃ for 2-4 hours after cold drawing, and air cooling to room temperature;

(8) Slicing the steel bar: cutting the steel bar subjected to cold drawing secondary heat treatment to a required length, and slicing the cut bolt bar, wherein the slicing amount of each pass is not more than 0.16mm, and the surface roughness of the sliced bolt is not more than Ra0.4mu m;

(9) And (3) forming a nut: heating one end of the sliced bolt by using an induction coil for 10-30 s, and then placing the bolt into a steel mould to be pressed and forged into a nut;

(10) Thread rolling: and rolling threads on the processed bolts to form finished fastener products.

In the preparation method of the high-performance fastener for the lead-based pile, in the step (1), the design components of the raw materials need to satisfy: cr equivalent <20; ni equivalent >14, the alloy formed is single austenite in room temperature structure;

chromium equivalent is calculated according to formula (1):

cr equivalent = 100× (cr+mo+1.5si+0.5nb) (1)

The nickel equivalent is calculated according to formula (2):

ni equivalent = 100× (ni+30×c+0.5×mn+0.5×cu) (2).

In the preparation method of the high-performance fastener for the lead-based pile, in the step (3), the homogenization treatment process comprises the following steps: the furnace loading temperature of the cast ingot is less than 700 ℃, the temperature is increased to 1200-1280 ℃ along with the furnace, the heat preservation time is not less than 12 hours, and the cast ingot is discharged from the furnace and cooled to the room temperature.

The preparation method of the high-performance fastener for the lead-based pile comprises the following steps of: the furnace charging temperature of the cast ingot is less than 700 ℃, the temperature is increased to 1150-1200 ℃ along with the furnace, and the heat preservation time is not less than 8 hours; the initial forging temperature is 1080-1180 ℃, the final forging temperature is 850-950 ℃, the forging is performed by repeatedly pressing the steel plate in a longitudinal-transverse-longitudinal direction under a large pressure, the number of times of the forging is not less than 6, the single deformation is more than 10%, the total forging ratio is more than 20, and the steel plate is air-cooled to room temperature after the forging.

In the step (6), the cold drawing deformation of each pass of the steel bar is not less than 10%, the intermediate annealing times are not more than 2, the annealing temperature is 900-1000 ℃, and the heat preservation time is 300-600 seconds.

The preparation method of the high-performance fastener for the lead-based pile has the following room temperature performance indexes: the yield strength is more than or equal to 300MPa, the tensile strength is more than or equal to 700MPa, and the impact energy is more than or equal to 160J; the high-temperature performance index at 550 ℃ is as follows: the yield strength is more than or equal to 200MPa, the tensile strength is more than or equal to 480MPa, and the elongation is more than or equal to 40.0%.

The preparation method of the high-performance fastener for the lead-based pile has the advantages that the thickness of the oxide film is not more than 20 mu m after the fastener is corroded in liquid lead-bismuth alloy (45% Pb-Bi) with saturated oxygen concentration and 550 ℃ for 2000 hours, and the fastener has excellent liquid lead-bismuth corrosion resistance.

The preparation method of the high-performance fastener for the lead-based pile has the advantage that the lasting fracture time is more than 2000 hours under the stress of 260MPa at 550 ℃.

According to the preparation method of the high-performance fastener for the lead-based pile, the initial stress is 80MPa at 550 ℃, and the residual stress after 1000 hours is more than 60MPa; the cycle number of the fatigue test is not less than 17000 times under the conditions that the temperature is 550 ℃, the strain amplitude is +/-0.3%, the strain ratio is-1, the loading waveform is triangular wave and the strain rate is 0.001 mm/s.

The design idea of the invention is as follows:

the precondition of meeting the requirements of the high-performance fastener under the severe working conditions such as high temperature, strong corrosion, vibration and the like in the lead-based pile is that the material used for manufacturing the fastener has excellent comprehensive performance. The material for the fastener consists of Cr, ni, si, mo, C, nb, cu and other key alloy elements. Si can enhance the oxidation resistance of Cr in the alloy, so that a compact Cr-rich and Si-rich oxide layer is generated under the high temperature condition, and the excellent liquid lead-bismuth corrosion resistance of the steel is ensured; mo can improve the heat resistance of the alloy, and ensure the high initial high-temperature strength and long-term good lasting resistance of the steel; nb and Cu form high-density nano-sized NbC and Cu-rich precipitated phases, so that excellent stress relaxation resistance and creep property of the steel are ensured; the alloy material with extremely high purity can be obtained by adopting double vacuum purification smelting and combining high temperature homogenization and hot and cold processing, so that the alloy material has excellent fatigue fracture resistance.

The structure regulation of the fastener alloy material is a guarantee for further improving various performances. The structure parameters such as grain size, carbide number density, cu-rich phase number density and dislocation density are regulated and controlled by means of high-temperature homogenization, heat treatment, cold processing, heat treatment and the like, so that the further improvement of each performance of alloy materials used for the fastener is ensured.

In the preparation process of the fastener bolt, the processing streamline generated by slicing, hot heading and thread rolling has an important influence on the comprehensive performance of the finished fastener bolt. The invention improves the comprehensive performance of the fastener by the precise slicing, high-temperature rapid hot forging and thread rolling process, and improves the process guarantee.

The contents of key elements for component design in the alloy material used for the fastener are described as follows:

C：0.06～0.12wt％

c can enlarge the austenite phase region and stabilize the austenite structure. Another important function of C in the alloy is to form nano-sized NbC with Nb, and form high-density fine dispersed NbC particles in a tissue to pin dislocation, so that the high-temperature stress relaxation resistance and creep strength of the alloy are improved. The content of C and the content of Nb in the alloy follow the principle of ideal chemical proportion, and the content of Nb is ensured to be 8 times of the content of C. The NbC formed by the too low content of C or Nb has low density and smaller effect; while too high a C content can form M with Cr element in the alloy at an early stage ₂₃ C ₆ Carbides, on the contrary, deteriorate the overall properties. Therefore, the C content of the alloy is 0.06 to 0.12wt%.

Si：2.0～3.0wt％

Si has strong bonding force with O. Therefore, the thermal stability of the oxide of Si is extremely strong. Si first combines with O in the environment to form an oxide of Si in an oxygen-containing environment. Si is added into the alloy, and Si is preferentially oxidized to form an oxide barrier containing Si in a high-temperature environment, so that further corrosion of the external environment can be prevented. By utilizing the effect of Si, the alloy is added with a proper amount of Si to play a role in resisting the corrosion of liquid lead bismuth. Si has a high solid solubility in austenite, and more than 2.0wt% of Si can be added to form a continuous dense corrosion-resistant 'barrier' with stronger binding force, but Si is a stronger ferrite forming element, and excessive Si can embrittle steel. Therefore, comprehensively considering, the Si content in the alloy is 2.0 to 3.0wt%.

Cr：13.0～17.0wt％

Cr may promote passivation of the alloy and maintain the alloy in a stable passive state. Again, this action of Cr causes the formation of a continuous dense Cr on the alloy surface ₂ O ₃ The passivation film can prevent ion migration and dissolution of elements into liquid lead bismuth, so that the liquid metal corrosion resistance of the alloy is improved, the effect of Cr and Si are mutually enhanced, and the liquid lead bismuth corrosion resistance is better. However, cr and C are liable to form M ₂₃ C ₆ . Therefore, the Cr content in the alloy is controlled to be 13.0 to 17.0wt%.

Ni：8.0～15.0wt％

The Ni mainly acts to form and stabilize austenite, so that the alloy obtains a complete austenitic structure and the thermodynamic stability of the alloy is improved. However, the solubility of Ni in the liquid lead bismuth alloy is large, and the excessively high content can deteriorate the corrosion resistance of liquid metal; meanwhile, an increase in Ni content in steel decreases the solubility of C in the alloy, thereby enhancing the carbide precipitation tendency. Therefore, comprehensively considering, the Ni content in the alloy is controlled to be 8.0-15.0 wt%.

Cu：0～1.0wt％

Cu is a non-carbide forming element, and the addition of Cu into the austenitic alloy can separate out a nano-sized Cu-rich phase in the heat treatment and long-term service process, and the nano-sized Cu-rich phase has smaller coarsening rate and can play a role in pinning dislocation so as to improve stress relaxation resistance and durability. Meanwhile, the addition of Cu into the alloy can obviously reduce the cold work hardening tendency of the alloy and improve the cold working forming performance. However, excessive Cu deteriorates the hot workability of the material. Therefore, the preferable Cu content in the alloy is 0 to 1.0wt%.

Mo：0.5～2.0wt％

Mo is an element that forms and stabilizes and enlarges the ferrite phase region, and in order to maintain a single austenite structure, mo is added to the alloy while increasing the Ni content. The main role of Mo in the alloy is to improve the high temperature strength. As the Mo content in the alloy increases, the high temperature endurance resistance increases, but Mo promotes intermetallic phases in the alloy, such as: precipitation of sigma phase and Laves phase reduces tissue stability. Therefore, comprehensively considering, the Mo content in the alloy is 0.5-2.0 wt%.

Nb：8×100C～1.0wt％

Nb is a key element in the alloy and is a basis for guaranteeing excellent stress relaxation resistance. Nb and C in the alloy for the fastener form a high-density NbC nano-sized precipitated phase, and the elastic strain is prevented from changing into plastic strain transformation by pinning dislocation of the precipitated phase, so that higher residual stress is maintained. According to the rough calculation, the Nb content required to fix all the C in austenite to NbC is 7.78 times the C content. Considering that Nb also forms a corresponding nitride with a trace amount of N in the steel to be partially consumed, the minimum Nb content in the alloy is 8 times the C content. Since Nb is an element liable to segregation, and excessive Nb in the alloy forms Fe after aging for a long period of time ₂ Nb type Laves phase deteriorates performance. Thus, in combination, the maximum content of Nb is not more than 1.0 wt.%.

The invention has the advantages and beneficial effects that:

1. the invention breaks through the technical barriers of the fastener for the lead-based pile, and obtains the high-performance fastener which has the comprehensive properties of excellent lead-bismuth corrosion resistance, high strength, high endurance resistance, high fatigue performance, excellent stress relaxation resistance and the like.

2. The fastener can be applied to the connection of structural materials in the nuclear energy field, which are exposed to a high-temperature lead (lead bismuth) corrosion environment.

Drawings

FIG. 1 is a microstructure of example 1.

FIG. 2 is a microstructure of example 2.

FIG. 3 is a graph of residual stress versus time for the steels of example 5 and comparative example 1 at 550℃under an initial stress of 80 MPa.

FIG. 4 is a graph showing the morphology of the oxide film of comparative example 1 after etching in a liquid Pb-Bi alloy (45% Pb-Bi) at 550℃for 2000 hours at a saturated oxygen concentration.

FIG. 5 is a graph showing the morphology of the oxide film of example 5 after 2000 hours of corrosion in a liquid Pb-Bi alloy (45% Pb-Bi) at 550℃with saturated oxygen concentration.

Detailed Description

In the practice of the present invention, the principal methods of manufacture of the fastener of the present invention are described below, and the differences between the individual examples and the comparative examples are described in additional detail for comparison purposes. Notably, all experimental samples from which performance data was obtained were cut on finished fastener products.

(1) Raw material preparation: and (5) proportioning according to the designed components.

(2) Double vacuum smelting: vacuum induction smelting and pouring are carried out on the raw materials to obtain an ingot; removing surface oxide skin of an ingot obtained by vacuum induction smelting, and cutting off two ends to prepare a consumable electrode rod; and (3) further purifying and smelting the consumable electrode rod in a vacuum consumable smelting furnace to obtain the high-purity consumable ingot.

(3) Homogenizing: cold-charging the cast ingot into a furnace, heating to 1220 ℃ along with the furnace, homogenizing at high temperature, preserving heat for 20 hours, discharging from the furnace after treatment, and air-cooling to room temperature.

(4) Forging an ingot: cold-charging the homogenized cast ingot into a furnace, heating to 1180 ℃ along with the furnace, preserving heat for 10 hours, forging, wherein the initial forging temperature is 1125 ℃, and performing cyclic repeated large-reduction forging in the longitudinal, transverse and longitudinal directions for 7 times, wherein the deformation of each forging is about 13%, and the total forging ratio is about 24; and forging into round bars, wherein the final forging temperature is about 935 ℃, and air cooling to room temperature after forging.

(5) Heat treatment of steel bars: the forged steel bar is subjected to solution treatment, and the treatment process comprises the following steps: preserving heat for 1.5 hours at 1080 ℃, and air-cooling to room temperature.

(6) Cold drawing of steel bars: the steel bar after solution treatment is subjected to 3 times of cold drawing, the deformation amount of the 1 st time cold drawing is about 18%, the deformation amount of the 2 nd time cold drawing is about 14%, the steel bar is annealed for 1 time at 920 ℃ after heat preservation for 480 seconds after the 2 nd time of cold drawing, and the steel bar is cooled to room temperature along with a furnace. The 3 rd pass cold drawing deformation is about 12%, and the total cold drawing deformation is about 44%.

(7) And (3) secondary heat treatment of the steel bar: and (3) preserving the temperature of the steel bar after cold drawing at 870 ℃ for 3 hours, and air-cooling to room temperature.

(8) Slicing the steel bar: cutting the steel bar subjected to the cold drawing secondary heat treatment; the cut bolt bar is sliced on a lathe, the slicing amount of each pass is 0.10mm, and the surface roughness of the sliced bolt is Ra0.1μm.

(9) And (3) forming a nut: one end of the sliced bolt is heated in an induction coil for 18 seconds, and then the bolt is put into a steel die for manufacturing the bolt to be hot-forged into a nut.

(10) Thread rolling: and rolling threads on the treated steel bar on an oil-cooled rolling machine to form a fastener finished product with the diameter of 30 mm.

Hereinafter, the present invention will be described by comparison of various examples and comparative examples, which are for illustrative purposes only, and the present invention is not limited to these examples.

Example 1

In this embodiment, the alloy raw materials used are as follows: c:0.065%; si:2.17%; mn:0.43%; s:0.0017%; p:0.009%; cr:14.55%; ni:9.5%; mo:0.05%; nb:0.68%; o:0.002%; n:0.005%; fe balance. Wherein Cr equivalent is 18.20<20, and Ni equivalent is 11.96-14.

Example 2

In this embodiment, the alloy raw materials used are as follows: c:0.081%; si:2.58%; mn:0.60%; s:0.0016%; p:0.008%; cr:14.70%; ni:12.75%; cu:0.64; mo:0.56%; nb:0.80%; o:0.002%; n:0.005%; fe balance. Wherein Cr equivalent is 19.53<20, and Ni equivalent is 15.80>14.

Example 3

In this embodiment, the alloy raw materials used are as follows: c:0.09%; si:2.47%; mn:0.58%; s:0.0017%; p:0.008%; cr:14.60%; ni:14.75%; mo:1.06%; nb:0.85%; o:0.002%; n:0.005%; fe balance. Wherein Cr equivalent is 19.79<20, and Ni equivalent is 17.74>14.

Example 4

In this embodiment, the alloy raw materials used are as follows: c:0.12%; si:2.57%; mn:0.51%; s:0.0015%; p:0.008%; cr:14.73%; ni:10.26%; mo:0.03%; nb:0.96%; o:0.0016%; n:0.004%; fe balance. Wherein Cr equivalent is 19.09<20 and Ni equivalent is 14.12>14.

Example 5

In this embodiment, the alloy raw materials used are as follows: c:0.11%; si:2.3%; mn:0.81%; s:0.0015%; p:0.008%; cr:14.2%; ni:12.24%; cu:0.90; mo:1.53%; nb:0.90%; o:0.0016%; n:0.004%; fe balance. Wherein Cr equivalent is 19.63<20, and Ni equivalent is 16.39>14.

Example 6

In this embodiment, the alloy raw materials used are as follows: c:0.11%; si:2.44%; mn:0.61%; s:0.0014%; p:0.007%; cr:14.3%; ni:11.22%; mo:1.03%; nb:0.42%; o:0.0017%; n:0.004%; fe balance. Wherein Cr equivalent is 19.2<20, and Ni equivalent is 14.82>14.

Comparative example 1

In the comparative example, the alloy raw material adopted is commercial 316 austenitic stainless steel, and the chemical components are as follows: c: 0.022; si:0.34%; mn:1.36%; s: 0.023; p:0.03%; cr:18.24%; ni:12.36%; mo:2.53%; n:0.12%; fe balance.

Comparative example 2

In the comparative example, the alloy raw materials used had the following chemical composition: c:0.11%; si:2.3%; mn:0.81%; s:0.0015%; p:0.008%; cr:14.2%; ni:12.24%; cu:0.90; mo:1.53%; nb:0.90%; o:0.0016%; n:0.004%; fe balance. Wherein Cr equivalent is 19.63<20, and Ni equivalent is 15.94>14.

Comparative example 2 is different from example 5 in that comparative example 2 is not cold drawn and other preparation processes are the same.

Comparative example 3

Comparative example 3 is different from example 5 in that comparative example 3 was not subjected to the homogenization process, and other preparation processes were the same.

The mechanical properties at room temperature and 550℃of the above examples and comparative examples are shown in Table 1.

TABLE 1

The results in table 1 show that the inventive steel obtains a single austenite structure by regulating and controlling the Cr equivalent and the Ni equivalent, and obtains higher room temperature and high temperature mechanical properties, and the fastener prepared in example 1 has a dual-phase structure and reduced high temperature strength because the Ni equivalent fails to meet the requirements. From the results of examples 2, 3 and 5, it can be seen that the strength at 550 c is improved and the strength is increased as the Mo content is increased after the desired Mo is added to the fastener. Comparative example 1, although containing a higher Mo content, did not contain C, nb and Cu and did not reach the level of the fastener of the present invention in strength.

As shown in fig. 1, the microstructure of example 1 is a two-phase structure.

As shown in fig. 2, the microstructure of example 2 is a single austenitic structure.

The endurance fracture times of the above examples and comparative examples at 550℃under 260MPa stress are shown in Table 2.

TABLE 2

As can be seen from the results of examples 2, 3 and 5, after the required Mo is added into the fastener, the durable breaking time of 260MPa and 550 ℃ is more than 2000 hours, and the breaking time is longer as the Mo content is increased; however, if cold drawing or high temperature homogenization treatment is not used, or the Nb content is too low, the duration of fracture is greatly reduced (see example 5 and comparative examples 2 and 3). It can be seen that the optimum performance is achieved by combining the composition design and tissue control of the fastener stock itself.

The residual stress values after 1000 hours at 550℃under an initial stress of 80MPa are shown in Table 3.

TABLE 3 Table 3

	Example 2	Example 5	Example 6	Comparative example 1	Comparative example 2	Comparative example 3
							Residual stress/MPa	49	62	35	17	26	22

The results in Table 3 show that the inventive fasteners exhibit significantly higher residual stresses after Nb, C and Cu additions than the steel of comparative example 1, which does not require Nb, C and Cu additions, and that the inventive steels exhibit excellent stress relaxation resistance. However, the low Nb (example 6) or no cold drawing or high temperature homogenization treatment (comparative examples 2 and 3) also did not achieve the optimum effect of stress relaxation resistance.

As shown in fig. 3, the steels of example 5 and comparative example 1 had initial stresses of 80MPa at 550 c, and it can be seen from the plot of residual stress versus time that the stress of example 5 was reduced to a much lower extent over time than that of comparative example 1, i.e., example 5 had higher residual stress and exhibited more excellent stress relaxation resistance than comparative example 1.

The results of the fatigue test under conditions of 550 ℃ and strain amplitude of + -0.3%, strain ratio-1, triangular wave as loading waveform and strain rate of 0.001mm/s are shown in Table 4.

TABLE 4 Table 4

	Example 5	Comparative example 2	Comparative example 3
				Cycle times	17621	11373	7853

The results in Table 4 show that the fasteners prepared from the same component materials have different fatigue lives due to different preparation processes (comparative example 2 is not cold drawn and comparative example 3 is not homogenized), and that the effects of high temperature homogenization and cold drawing on fatigue life are very significant, i.e., it is demonstrated that the optimum fatigue life can be obtained by combining the component design and the structure control of the fastener materials of the present invention.

The oxide film thickness values after 2000 hours of corrosion in a liquid lead bismuth alloy (45% Pb-Bi) at 550℃at a saturated oxygen concentration in the above examples and comparative examples are shown in Table 5.

TABLE 5

As shown in fig. 4 and 5, the oxide film morphology of the steels of comparative example 1 and example 5 after being corroded in a liquid lead bismuth alloy (45% pb-Bi) with saturated oxygen concentration and 550 ℃ for 2000 hours is evident that the oxide film thickness of comparative example 1 is the thickest, the corrosion resistance of the liquid lead bismuth alloy is poor, the oxide film thickness of example 5 is the thinnest, and the corrosion resistance of the lead bismuth alloy of example 5 is the best.

The results in Table 5 show that the lead-bismuth corrosion resistance of the fastener of the invention is significantly improved after Si is added (comparative example 1 does not require Si as a raw material); the lead-bismuth corrosion resistance of the fastener disclosed by the invention is related to alloying of Si element, and Mo is found to have an important effect on improving the liquid lead-bismuth corrosion resistance for the first time. The addition of Mo has the property of improving the resistance to corrosion by liquid lead bismuth metal (examples 2 and 4), which makes example 5, although Si content is not the highest value, have the thinnest oxide layer and exhibit the best resistance to corrosion by lead bismuth.

The above embodiments are provided to illustrate 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 the same, and are not intended to limit the scope of the present invention. All equivalent changes or modifications made in accordance with the spirit of the present invention should be construed to be included in the scope of the present invention.

Claims

1. The preparation method of the high-performance fastener for the lead-based pile is characterized by comprising the following chemical components in percentage by weight: c: 0.081-0.12%; si:2.0 to 2.58 percent; mn:0.43 to 1.0 percent; s:0 to 0.005 percent; p:0 to 0.01 percent; cr:13.0 to 17.0 percent; ni:10.26 to 15.0 percent; cu:0 to 1.0 percent; mo:0.5 to 2.0 percent; nb: 8X 100C-0.96%; o:0 to 0.003 percent; n:0 to 0.03 percent; fe balance;

(3) Homogenizing: homogenizing the cast ingot at a high temperature;

(10) Thread rolling: rolling threads on the processed bolts to form fastener finished products;

in the step (1), the design components of the raw materials need to satisfy: cr equivalent <20; ni equivalent >14, the alloy formed is single austenite in room temperature structure;

chromium equivalent is calculated according to formula (1):

cr equivalent = 100× (cr+mo+1.5si+0.5nb) (1)

The nickel equivalent is calculated according to formula (2):

ni equivalent = 100× (ni+30×c+0.5×mn+0.5×cu) (2)

In the step (3), the homogenization treatment process is as follows: the furnace loading temperature of the cast ingot is less than 700 ℃, the temperature is increased to 1200-1280 ℃ along with the furnace, the heat preservation time is not less than 12 hours, and the cast ingot is discharged from the furnace and cooled to room temperature;

in the step (4), the forging process is as follows: the furnace charging temperature of the cast ingot is less than 700 ℃, the temperature is increased to 1150-1200 ℃ along with the furnace, and the heat preservation time is not less than 8 hours; the initial forging temperature is 1080-1180 ℃, the final forging temperature is 850-950 ℃, the forging is performed by repeatedly pressing the steel plate in a longitudinal-transverse-longitudinal direction under a large pressure, the number of times of the forging is not less than 6, the single deformation is more than 10%, the total forging ratio is more than 20, and the steel plate is air-cooled to room temperature after the forging;

in the step (6), the cold drawing deformation of each pass of the steel bar is not less than 10 percent, the intermediate annealing times are not more than 2 times, the annealing temperature is 900-1000 ℃, and the heat preservation time is 300-600 seconds.

2. The method of producing a high-performance fastener for lead-based stacks according to claim 1, wherein the room temperature performance index is as follows: the yield strength is more than or equal to 300MPa, the tensile strength is more than or equal to 700MPa, and the impact energy is more than or equal to 160J; the high-temperature performance index at 550 ℃ is as follows: the yield strength is more than or equal to 200MPa, the tensile strength is more than or equal to 480MPa, and the elongation is more than or equal to 40.0%.

3. The method for producing a high-performance fastener for lead-based stacks according to claim 1, wherein the oxide film thickness after corrosion in a liquid lead bismuth alloy (45% pb-Bi) at 550 ℃ for 2000 hours at a saturated oxygen concentration is not more than 20 μm, and has excellent resistance to corrosion by liquid lead bismuth.

4. The method of making a high performance fastener for lead-based stacks as claimed in claim 1, wherein the duration of fracture is greater than 2000 hours at 550 ℃ under 260MPa stress.

5. The method of producing a high-performance fastener for lead-based stacks according to claim 1, wherein the initial stress is 80MPa at 550 ℃, and the residual stress after 1000 hours is more than 60MPa; the cycle number of the fatigue test is not less than 17000 times under the conditions that the temperature is 550 ℃, the strain amplitude is +/-0.3%, the strain ratio is-1, the loading waveform is triangular wave and the strain rate is 0.001 mm/s.