Method for improving low-temperature toughness of fastener

Abstract

The invention discloses a method for improving the low-temperature toughness of a fastener, which comprises the following steps of: S1, adopting alloy structural steel 35CrMoA (meeting the requirement of GB / T 3077) or 40CrNi2MoA (meeting the requirement of ASME or ASTM standard A 320L43) as a raw material for manufacturing the fastener, and controlling the content of phosphorus, sulfur and manganese in the raw material and the macrostructure defect of the raw material; s2, a fastener is manufactured through raw materials; and S3, the fastener is subjected to heat treatment, and the fastener subjected to heat treatment meets the conditions that the hardness is HRC26-30, the impact toughness AKV is larger than or equal to 27 J, and the lateral expansion value is larger than or equal to 0.38 mm. The low-temperature impact performance of the material can be effectively improved by controlling the metallurgical quality of the raw materials, reasonably matching the hardness, controlling the heat treatment technological process, modulating the compounding of the alloy powder and other technical means, and the product meeting the mechanical performance requirement can be obtained.

Description

Technical Field

[0001] The invention relates to the field of fastener materials, and in particular to a method for improving the low-temperature toughness of fasteners. Background Art

[0002] In recent years, low-temperature fasteners have been widely used in many major petrochemical engineering projects and major equipment factories. The so-called low-temperature fasteners mainly refer to: 35CrMoA-L studs (with -70℃, -80℃, -101℃ impact toughness requirements) produced according to national standards with working temperatures below -20℃ and A 320Gr.L43 studs (with -101℃ impact toughness requirements) produced according to ASME / ASTM standards. The average impact toughness of three impact specimens at low temperatures is A KV ≥27J, the impact toughness of one of the samples is allowed to be less than the specified value, but not less than 70% of the specified value, and the lateral expansion value is ≥0.38mm. This type of pressure pipe fastener has harsh service conditions, both under high pressure and in a low temperature state. In order to prevent the stud from undergoing brittle transformation at low temperatures and instantaneous fracture failure, the relevant standards have made stricter regulations on the materials and low-temperature impact properties of this type of fasteners. Users attach great importance to this, but meeting its low-temperature impact performance of -101℃ has always been a difficult problem to solve in the fastener industry.

[0003] The carbon content and the contents of various alloying elements in the chemical composition of the material directly affect the mechanical property indexes of the parts after heat treatment. Among them, the contents of impurity elements such as phosphorus and sulfur affect the quantity and distribution of inclusions in the material. At the same time, if the sulfur and phosphorus contents exceed the standard, it will also affect the plasticity and toughness of the material under different service conditions. Especially when the phosphorus content is too high, it will make the material brittle at low temperature. There are many types of macrostructure defects in steel, and the common ones are porosity, segregation, bubbles, inclusions, white spots, and plastic and brittle inclusions, etc. Severe macrostructure defects will also reduce the plasticity and toughness of steel. Therefore, when purchasing raw materials, for the raw materials used to manufacture low-temperature fasteners, it is necessary to strictly control the phosphorus and sulfur contents and control the macrostructure defects of the steel. And the mechanical properties of the material can be improved through appropriate heat treatment. Strength represents the load-bearing capacity of the parts, plasticity is the ability of the material to undergo plastic deformation, and impact toughness is the ability of the material to resist impact loads. For the same kind of steel, after quenching and tempering, strength, plasticity, and toughness are in an inverse relationship. It is necessary to determine a reasonable hardness range to ensure a good match between the strength and plasticity and toughness of the material. In addition, the size of the grains after heat treatment has a great relationship with the strength and toughness of the steel. Refining the grains can improve both the strength and toughness of the steel. Compared with ordinary heat treatment, critical-region heat treatment can significantly improve toughness without reducing strength. Therefore, when formulating the heat treatment process, the quenching heating temperature is selected near the upper part of the critical region, and the holding time is sufficient but not too long to avoid causing coarse martensite structure after quenching. At the same time, the tempering holding time should be sufficient to fully release the internal stress after quenching. Through reasonable coordination of several aspects, the low-temperature impact toughness of the fasteners can be improved. But now there is a lack of a reliable solution to improve the low-temperature impact performance of fasteners. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for improving the low-temperature toughness of fasteners in view of the above-mentioned deficiencies in the prior art. Through a combination of various technical means such as controlling the metallurgical quality of raw materials, reasonable hardness matching, control of the heat treatment process, and compounding of modulated alloy powders, the present invention can effectively improve the low-temperature impact performance of the material and obtain products that meet the mechanical property requirements.

[0005] To solve the above technical problem, the technical solution adopted by the present invention is: A method for improving the low-temperature toughness of fasteners, comprising the following steps:

[0006] S1. Use alloy structural steel 35CrMoA or 40CrNi2MoA as the raw material for manufacturing fasteners, and control the phosphorus, sulfur, and manganese contents of the raw material and the macrostructure defects of the raw material; wherein, the chemical composition of 35CrMoA meets the requirements of GB / T 3077, and the chemical composition of 40CrNi2MoA meets the requirements of ASME or ASTM standard A 320L43.

[0007] S2. Manufacture fasteners using raw materials;

[0008] S3. Heat-treat the fasteners so that the heat-treated fasteners meet the requirements: the hardness is HRC26 - 30, the impact toughness A at -101°C KV ≥27 J, and the lateral expansion value ≥0.38 mm;

[0009] The steps of the heat treatment include:

[0010] S3-1. Quenching heating: The quenching heating adopts stepped heating. The first heating is to a temperature of 300°C - 400°C, and the second heating is to the quenching temperature. The quenching temperature is 810°C - 870°C, and the quenching holding time is 15 - 40 minutes;

[0011] S3-2. Cooling: Cool the fasteners with oil or a brine solution;

[0012] S3-3. Tempering: Heat to the tempering temperature. The tempering temperature is 590°C - 670°C, the holding time is 90 - 120 minutes, and then air-cool to room temperature.

[0013] Preferably, the steps of the heat treatment in step S3 include:

[0014] S3-1. Quenching heating: The quenching heating adopts stepped heating. The first heating is carried out in an oven with 30 Kw, heating to 300°C - 400°C; the second heating is carried out in a medium-temperature salt bath furnace with 50 Kw, the loading capacity ≤50 Kg, heating to the quenching temperature. The quenching temperature is 810°C - 870°C, and the quenching holding time is 15 - 40 minutes;

[0015] S3-2. Cooling: Cool the fasteners with 10# or 20# mechanical oil or a brine solution. The brine solution contains sodium chloride with a mass fraction of 6% - 10%; the temperature of the cooling medium: the brine solution ≤40°C, 10# or 20# mechanical oil ≤80°C;

[0016] S3-3. Tempering: Tempering is carried out in a pit furnace with 35 Kw, the loading capacity ≤120 Kg, heating to the tempering temperature. The tempering temperature is 590°C - 670°C, the holding time is 90 - 120 minutes, and air-cool to room temperature.

[0017] Preferably, in step S1, the phosphorus content in the raw materials 35CrMoA and 40CrNi2MoA is controlled below 0.012% by mass fraction, and the sulfur content is controlled below 0.006% by mass fraction.

[0018] Preferably, in step S1, the manganese content in the raw material 40CrNi2MoA is 0.65% - 0.80% by mass fraction.

[0019] Preferably, the macrostructure defects of the raw materials 35CrMoA and 40CrNi2MoA meet the following requirements: general looseness and square segregation are below grade 0.5, and central looseness is below grade 1.0; plastic inclusions and brittle inclusions are both not greater than grade 2.5, and the sum of the two is not greater than grade 4.5.

[0020] Preferably, in step S2, the raw materials are subjected to composite treatment with a modulated alloy powder and then manufactured into fasteners. The specific steps are as follows: completely melt the raw materials 35CrMoA or 40CrNi2MoA and then add the modulated alloy powder, melt, cast, and machine process to obtain fasteners;

[0021] Among them, the modulated alloy powder is obtained by coating boron powder with an alloy.

[0022] Preferably, the mass ratio of the modulated alloy powder to the raw materials is: 0.05 - 0.24:99.95 - 99.76;

[0023] The chemical composition of the raw material 35CrMoA by mass percentage is: C: 0.32 - 0.40%, Mn: 0.40 - 0.70%, Si: 0.17 - 0.37%, Cr: 0.80 - 1.10%, Mo: 0.15 - 0.25%, P: ≤0.012%, S: ≤0.006%, and the balance is Fe and inevitable impurity elements;

[0024] The chemical composition of the raw material 40CrNi2MoA by mass percentage is: C: 0.38 - 0.43%, Mn: 0.65 - 0.80%, Si: 0.17 - 0.37, Cr: 0.70 - 0.90%, Ni: 1.65 - 2.00%, Mo: 0.20 - 0.30%, P: ≤0.012%, S: ≤0.006%, and the balance is Fe and inevitable impurity elements.

[0025] Preferably, the modulated alloy powder is prepared by the following method:

[0026] S2-1. Pretreatment of B powder;

[0027] S2-2. Sensitization treatment of B powder:

[0028] S2-3. Activation treatment of B powder:

[0029] S2-4. Coating the activated B powder with an alloy:

[0030] S2-4-1. Mix nickel nitrate, yttrium nitrate, lanthanum nitrate, iron nitrate, and the activated B powder to obtain a precursor;

[0031] S2-4-2. Add the precursor into an ammonia aqueous solution, then add ammonium sulfate, sodium citrate, PdCl 2 , disperse it by ultrasonic wave. Transfer the obtained mixture to a reaction kettle, introduce hydrogen gas, and react under stirring and heating. After the reaction is completed, cool it. Centrifuge, wash, and dry the product under vacuum, then grind it to obtain the modulated alloy powder.

[0032] Preferably, the modulated alloy powder is prepared by the following method:

[0033] S2-1. Pretreatment of B powder: B powder with a particle size of 2-10 μm is boiled in a NaOH solution with a mass concentration of 5-20% for 5-30 min, taken out, rinsed with deionized water, and then soaked in a 30-50 wt% HNO 3 solution for 2-10 min, taken out, rinsed with deionized water until neutral, and dried to obtain the pretreated B powder;

[0034] S2-2. Sensitization treatment of B powder: Dissolve 0.5-2 g of SnCl 2 ·2H 2 O in 25-100 mL of ethanol to obtain a sensitizing solution; Take 0.5-2 g of the pretreated B powder prepared in step S1 and add it to the sensitizing solution, ultrasonically treat for 10-30 min, centrifuge and separate, and wash the solid product with ethanol and deionized water in sequence to obtain the sensitized B powder;

[0035] S2-3. Activation treatment of B powder: Take 0.5-2 g of the sensitized B powder and add it to 25-100 mL of a PdCl 2 hydrochloric acid solution with a mass fraction of 0.025-0.1%, ultrasonically treat for 10-40 min, centrifuge and separate, wash the solid product with ethanol, and then dry it under vacuum at 40-65 °C for 4-16 h to obtain the activated B powder;

[0036] S2-4. Coating the B powder with an alloy:

[0037] S2-4-1. Mix nickel nitrate, yttrium nitrate, lanthanum nitrate, iron nitrate and the activated B powder to obtain a precursor, and the mass ratio of Ni:Fe:La:Y:B in the precursor is 5.5-7.5:3.8-6:1-4:0.75-3:1;

[0038] S2-4-2. Take 2.5-10 g of the precursor and add it to 50-200 mL of an ammonia aqueous solution with a mass concentration of 2.5-10%, then add ammonium sulfate with a concentration of 5-20 g / L, sodium citrate with a concentration of 0.06-0.25 g / L, and PdCl with a concentration of 0.03-0.12 g / L 2, ultrasonically disperse for 5 - 20 min, transfer the obtained mixture to a reaction kettle, introduce hydrogen, react at 150 - 170 °C with stirring at 250 - 100 rpm for 0.5 - 2 h, control the hydrogen partial pressure at 2 - 3 MPa during the reaction, after the reaction, cool to below 50 - 65 °C, then release the gas and unload the kettle, centrifuge the product, wash it with ethanol, and vacuum dry it at 80 - 100 °C for 6 - 24 h, and grind to obtain the modulated alloy powder.

[0039] Preferably, the mass ratio of Ni:Fe:La:Y:B in the precursor is 6:4.5:2:1.5:1.

[0040] The beneficial effects of the present invention are as follows:

[0041] The present invention provides a method for improving the low-temperature toughness of fasteners. In the method of the present invention, by controlling the metallurgical quality of raw materials, reasonable hardness matching, and the control of the heat treatment process, the low-temperature impact performance and mechanical properties (-101 °C) of the obtained products can meet the requirements, and the method is simple, easy to produce, and has broad application prospects; specifically, the present invention reasonably controls the metallurgical quality of raw materials, especially the content of trace elements and the grade of inclusions, controls a reasonable hardness range, controls the quenching heating temperature near the upper part of the critical region, and has an appropriate quenching holding time (too short, the free ferrite is not fully dissolved, too long, it will cause grain coarsening), and has a sufficient tempering holding time.

[0042] In a further optimized embodiment of the present invention, the raw materials are also subjected to composite treatment by using the modulated alloy powder. Elements B, La, and Y that can be uniformly dispersed are added to the fastener raw material system, which can further improve the low-temperature toughness of the fasteners; the modulated alloy powder has a core-shell structure, with B powder as the core and a NiFe alloy doped with La and Y as the shell. By coating the B powder with the alloy shell, on the one hand, it can solve the problems of poor wettability between the B powder and the fastener metal matrix and difficulty in uniform dispersion, and at the same time, it can also achieve the uniform dispersion of trace elements La and Y in the fastener metal matrix (the density differences between La, Y and the molten steel are relatively large, and trace amounts of La and Y are not easily uniformly dispersed in the molten steel), so that B, La, and Y play a synergistic strengthening effect in improving the low-temperature toughness and other aspects. Description of the Drawings

[0043] Figure 1 XRD pattern of the modulated alloy powder prepared in Example 3;

[0044] Figure 2 Impact toughness test results of the specifications of M20×L prepared in Examples 1 - 4 and the control group. Detailed Embodiments

[0045] The following further elaborates on the present invention in conjunction with embodiments, so that those skilled in the art can implement it with reference to the text of the specification.

[0046] It should be understood that terms such as "having", "comprising", and "including" used herein do not exclude the presence or addition of one or more other elements or their combinations.

[0047] Unless otherwise specified, the test methods used in the following embodiments are all conventional methods. The materials, reagents, etc. used in the following embodiments can all be obtained from commercial channels unless otherwise specified. For those not specifying specific conditions in the following embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0048] In a first aspect of the present invention, a method for improving the low-temperature toughness of fasteners is provided, including the following steps:

[0049] S1. Use alloy structural steel 35CrMoA or 40CrNi2MoA as the raw material for manufacturing fasteners, and control the phosphorus, sulfur, and manganese contents of the raw material and the macrostructure defects of the raw material; among them, the chemical composition of 35CrMoA meets the requirements of GB / T 3077, and the chemical composition of 40CrNi2MoA meets the requirements of ASME or ASTM standard A 320L43.

[0050] In a preferred embodiment, specifically, the requirements met by the chemical composition of the raw material are shown in Table 1 below:

[0051] Table 1

[0052]

[0053] As shown in Table 2 below, in a preferred embodiment, the macrostructure defects of the raw materials 35CrMoA and 40CrNi2MoA meet the following requirements: general looseness and square segregation are below grade 0.5, and central looseness is below grade 1.0; plastic inclusions and brittle inclusions are both not greater than grade 2.5, and the sum of the two is not greater than grade 4.5.

[0054] Table 2

[0055]

[0056] S2. Use the raw material to manufacture fasteners, and the manufacturing process is a conventional process, which is not specifically limited in the present invention; in a preferred embodiment, the fasteners are selected as bolts or studs, and their specifications can be metric M20 - M39, American standard 0.75" - 1.75", etc.

[0057] S3. Heat-treat the fasteners so that the heat-treated fasteners meet the following requirements: the hardness is HRC26 - 30, the impact toughness A at -101°C KV ≥27 J, and the lateral expansion value ≥0.38 mm;

[0058] The steps of the heat treatment include:

[0059] S3-1. Quenching and heating: The quenching and heating adopt stepped heating. For the first heating, use an oven with 30 Kw to heat to 300°C - 400°C; for the second heating, use a medium-temperature salt bath furnace with 50 Kw, the loading capacity ≤50 Kg, heat to the quenching temperature, the quenching temperature is 810°C - 870°C, and the quenching holding time is 15 - 40 minutes; the specific holding time can be calculated at about 1 minute per millimeter of the cross-sectional diameter of the bolt or stud blank;

[0060] S3-2. Cooling: Cool the fasteners with 10# or 20# mechanical oil or with a brine solution, and the brine solution contains sodium chloride with a mass fraction of 6% - 10%; the temperature of the cooling medium: the brine solution ≤40°C, 10# or 20# mechanical oil ≤80°C;

[0061] S3-3. Tempering: Tempering is carried out in a pit furnace with 35 Kw, the loading capacity ≤120 Kg, heat to the tempering temperature, the tempering temperature is 590°C - 670°C, the holding time is 90 - 120 minutes, and air-cool to room temperature. The obtained product is a fastener blank, and further finish machining and other treatments are carried out according to requirements later.

[0062] In the second aspect of the present invention, there is also provided a method for further improving the low-temperature toughness of fasteners. The difference from the above is that in step S2, the raw materials are subjected to composite treatment with a modulated alloy powder and then made into fasteners. The specific steps are as follows: completely melt the raw materials 35CrMoA or 40CrNi2MoA and then add the modulated alloy powder, melt, cast, and machine process to obtain fasteners;

[0063] Among them, the modulated alloy powder is obtained by coating boron powder with an alloy.

[0064] In a preferred embodiment, the mass ratio of the modulated alloy powder to the raw materials is: 0.05 - 0.24:99.95 - 99.76.

[0065] In a preferred embodiment, the modulated alloy powder is prepared by the following method:

[0066] S2-1. Pretreatment of B powder: B powder with a particle size of 2 - 10 μm is boiled in a NaOH solution with a mass concentration of 5 - 20% for 5 - 30 min, taken out, rinsed with deionized water, and then treated with 30 - 50 wt% HNO 3Soak in the solution for 2 - 10 min, take out, rinse with deionized water until neutral, and dry to obtain the pretreated B powder;

[0067] S2 - 2. Sensitization treatment of B powder: Take 0.5 - 2 g of SnCl 2 ·2H 2 O and dissolve it in 25 - 100 mL of ethanol to obtain a sensitizing solution; Take 0.5 - 2 g of the pretreated B powder prepared in step S1 and add it to the sensitizing solution, perform ultrasonic treatment for 10 - 30 min, carry out centrifugal separation, and wash the solid product with ethanol and deionized water in sequence to obtain the sensitized B powder;

[0068] S2 - 3. Activation treatment of B powder: Take 0.5 - 2 g of the sensitized B powder and add it to 25 - 100 mL of a hydrochloric acid solution with a mass fraction of 0.025 - 0.1% of PdCl 2 Perform ultrasonic treatment for 10 - 40 min, carry out centrifugal separation, wash the solid product with ethanol, and then perform vacuum drying at 40 - 65 °C for 4 - 16 h to obtain the activated B powder;

[0069] S2 - 4. Coating the B powder with an alloy:

[0070] S2 - 4 - 1. Mix nickel nitrate, yttrium nitrate, lanthanum nitrate, iron nitrate and the activated B powder to obtain a precursor, and the mass ratio of Ni:Fe:La:Y:B in the precursor is 5.5 - 7.5:3.8 - 6:1 - 4:0.75 - 3:1;

[0071] S2 - 4 - 2. Take 2.5 - 10 g of the precursor and add it to 50 - 200 mL of an ammonia water solution with a mass concentration of 2.5 - 10%, then add ammonium sulfate with a concentration of 5 - 20 g / L, sodium citrate with a concentration of 0.06 - 0.25 g / L, and PdCl 2 , perform ultrasonic dispersion for 5 - 20 min, transfer the obtained mixture to a reaction kettle, introduce hydrogen, react at 250 - 100 rpm of stirring and 150 - 170 °C for 0.5 - 2 h, control the hydrogen partial pressure to be 2 - 3 MPa during the reaction, after the reaction, cool to below 50 - 65 °C and then release the gas and unload the kettle, centrifuge the product, wash with ethanol, perform vacuum drying at 80 - 100 °C for 6 - 24 h, and grind to obtain the modulated alloy powder.

[0072] In a preferred embodiment, the mass ratio of Ni:Fe:La:Y:B in the precursor is 6:4.5:2:1.5:1.

[0073] In the present invention, by using a modulated alloy powder to perform composite treatment on raw materials and adding elements B, La, and Y that can be evenly dispersed to the raw material system of fasteners, the low-temperature toughness of fasteners can be effectively improved; the modulated alloy powder has a core-shell structure, with B powder as the core and a NiFe alloy doped with La and Y as the shell. By coating the B powder with the alloy shell, on the one hand, the problem of poor wettability between the B powder and the fastener metal matrix and difficulty in uniform dispersion can be solved, and at the same time, the uniform dispersion of trace elements La and Y in the fastener metal matrix can be achieved (the density differences between La, Y and the molten steel are relatively large, and trace amounts of La and Y are not easily uniformly dispersed in the molten steel), enabling B, La, and Y to play a synergistic strengthening effect in improving low-temperature toughness and other aspects.

[0074] The main preparation mechanism of the modulated alloy powder: First, the micron B powder is pretreated by alkali immersion and acid immersion in sequence, then sensitization treatment and activation treatment are carried out in sequence, and then the activated B powder is alloy-coated by the hydrothermal hydrogen reduction method. During the coating process, nickel nitrate, yttrium nitrate, lanthanum nitrate, and iron nitrate are used as raw materials for the alloy coating layer, hydrogen provides a reducing atmosphere, and sodium citrate is used as a complexing agent, which can effectively slow down the grain growth rate, thereby making the grains refined and obtaining a uniform and dense coating layer; PdCl 2 As a catalyst, it reduces the energy barrier during the reaction process and promotes the deposition and coating of the alloy.

[0075] In the alloy coating layer, Ni and Fe are the main coating elements, which can significantly improve the wettability between the modulated alloy powder and the steel matrix, and can make the density of the modulated alloy powder closer to that of the molten steel. Further through mechanical entrainment and other effects, the modulated alloy powder can be uniformly dispersed in the molten steel.

[0076] It has been confirmed that trace amounts of boron can improve the low-temperature toughness of steel, and its mechanism of action includes: (1) improving toughness through grain refinement; (2) grain boundary strengthening. The segregation of boron at the grain boundaries can inhibit the grain boundary segregation of sulfur and phosphorus and the resulting low-temperature brittle fracture. Boron can improve the grain boundary bonding force, thereby improving the low-temperature toughness (Zhong Hao, Li Zhanwei, Li Wenying, etc. Influence of Microalloying on the Low-Temperature Impact Resistance of Alloy Cold Heading Steel SCM440 [C] / / 2014 National Steel Rolling Production Technology Conference. 0 [2025-01-23]. DOI: ConferenceArticle / 5af171f6c095d71bc8c2a071.).

[0077] La and Y can play the role of desulfurization and deoxidation in steel to purify the molten steel. Y can reduce the critical nucleation work, increase the crystallization nuclei, inhibit the growth of coarse grains, refine the as-cast structure of steel, reduce alloy segregation, and strengthen the grain boundaries. The finer the grains, the more grain boundaries there are, and the more obvious the effect of hindering the movement of dislocations, resulting in improved toughness. The mixed addition of La and Y can achieve a compound enhancement effect in improving the toughness of steel.

[0078] The above is the general concept of the present invention. The following provides detailed examples and comparative examples on this basis to further illustrate the present invention.

[0079] Example 1

[0080] A method for improving the low-temperature toughness of fasteners, comprising the following steps:

[0081] S1. Use 35CrMoA from Jiangyin Xingcheng Special Steel Co., Ltd. as the raw material for manufacturing fasteners, and control the phosphorus, sulfur, and manganese contents of the raw material and the low-magnification structure defects of the raw material; among them, the chemical composition of 35CrMoA meets the requirements of GB / T 3077.

[0082] In this embodiment, the prepared fastener is a bolt, and its specifications include metric M20 - M39 and American standard 0.75” - 1.75”; the specific chemical composition is shown in Table 3 below, and the low-magnification structure defect situation is shown in Table 4 below:

[0083] Table 3

[0084]

[0085]

[0086] Table 4

[0087]

[0088] S2. Use the raw material to manufacture fasteners through conventional processes such as melting, casting, forging, and machining.

[0089] S3. Heat-treat the fasteners so that the heat-treated fasteners meet the following requirements: the hardness is HRC26 - 30, the impact toughness A KV ≥27 J at -101 °C, and the lateral expansion value ≥0.38 mm;

[0090] The steps of heat treatment include:

[0091] S3-1. Quenching Heating: Step heating is adopted for quenching heating. For the first heating, an oven with 30 Kw is used to heat to 300°C - 400°C. For the second heating, a medium-temperature salt bath furnace with 50 Kw is used. When the loading capacity ≤ 50 Kg and the bolt diameter specification made of 35CrMoA ≤ M22 or 7 / 8", the quenching temperature is 850°C - 870°C; when the bolt diameter specification made of 35CrMoA ≥ M24 or 1", the quenching temperature is 830°C - 850°C. The quenching holding time is 15 - 40 minutes, and the holding time is calculated at about 1 minute per millimeter of the bolt cross-sectional diameter.

[0092] S3-2. Cooling: 20# mechanical oil or a brine solution is used to cool the fasteners. The brine solution contains sodium chloride with a mass fraction of 6% - 10%. The temperature of the cooling medium: for the brine solution ≤ 40°C, for 10# or 20# mechanical oil ≤ 80°C.

[0093] S3-3. Tempering: A pit furnace with 35 Kw is used for tempering. The loading capacity ≤ 120 Kg, heated to the tempering temperature. The tempering temperature is 590°C - 670°C, the holding time is 90 - 120 minutes, and it is air-cooled to room temperature. The obtained product is a fastener blank (bolt), and subsequent further finishing and other treatments are carried out according to requirements.

[0094] The specific heat treatment process parameters of bolts of each specification are shown in Table 5 below:

[0095] Table 5

[0096]

[0097] Performance Test:

[0098] A low-temperature impact test is carried out on the furnace-following specimens. In the national standard GB / T 3098.1, it is stipulated that the sampling position is along the axial direction and as close to the outer surface as possible. In the American standard A320, for products with a diameter less than or equal to 1", the specimen is taken from the axis line; for products with a diameter greater than 1", the specimen should be taken at 1 / 2 radius. In this embodiment, following the principle of strictness, for test specimens with a diameter less than or equal to M24 or 1", they are taken from the center of the blank; for those with a diameter greater than M24 or 1", they are taken from 1 / 2 radius. The specimens comply with the provisions of GB / T 229 or A 370. The test equipment is a PIT452D-2 impact testing machine, the low-temperature medium is liquid nitrogen plus analytical alcohol, the heat preservation is carried out with a self-made low-temperature tank for impact testing, the test temperature is -101°C, the degree of supercooling is -3°C, the heat preservation time is 20 minutes, and the test results are shown in Table 6 below.

[0099] Table 6

[0100]

[0101] In the table, the impact toughness and lateral expansion value are measured in three groups, and the average value is finally taken as the result.

[0102] Example 2

[0103] Provide a method for improving the low-temperature toughness of fasteners, including the following steps:

[0104] S1. Use 40CrNi2MoA from Jiangyin Xingcheng Special Steel Co., Ltd. as the raw material for manufacturing fasteners, and control the phosphorus, sulfur, and manganese contents of the raw material and the macrostructure defects of the raw material; among them, the chemical composition of 40CrNi2MoA meets the requirements of ASME or ASTM standard A 320 L43;

[0105] In this example, the prepared fasteners are bolts, and their specifications include metric M20 - M39 and American standard 0.75" - 1.75"; the specific chemical compositions are shown in Table 7 below, and the macrostructure defect conditions are shown in Table 8 below:

[0106] Table 7

[0107]

[0108]

[0109] Table 8

[0110]

[0111] S2. Use the raw material to manufacture fasteners through conventional processes such as melting, casting, forging, and machining;

[0112] S3. Heat-treat the fasteners so that the heat-treated fasteners meet the following requirements: the hardness is HRC26 - 30, the impact toughness A KV ≥27 J at -101 °C, and the lateral expansion value ≥0.38 mm; the steps of heat treatment include:

[0113] S3-1. Quenching heating: Quenching heating adopts stepped heating. The first heating uses an oven with 30 Kw and heats to 300 °C - 400 °C; the second heating uses a medium-temperature salt bath furnace with 50 Kw, the loading capacity ≤50 Kg, the quenching temperature for studs made of 40CrNi2MoA with a diameter specification ≤M22 or 7 / 8" is 830 °C - 850 °C; for studs made of 40CrNi2MoA with a diameter specification ≥M24 or 1", the quenching temperature is 810 °C - 830 °C, and the quenching holding time is 15 - 40 minutes, and the holding time is calculated at about 1 minute per millimeter of the stud cross-sectional diameter;

[0114] S3-2. Cooling: Cool the fasteners with 20# mechanical oil or a brine solution, and the brine solution contains 6% - 10% sodium chloride by mass fraction; the temperature of the cooling medium: the brine solution ≤40 °C, 10# or 20# mechanical oil ≤80 °C;

[0115] S3-3, Tempering: The tempering is carried out in a pit furnace with a power of 35 Kw. The loading capacity is ≤120 Kg. Heat it to the tempering temperature, which is 590°C to 670°C, keep it warm for 90 - 120 minutes, and then air-cool it to room temperature. The obtained product is a fastener blank (bolt), and further finishing and other treatments are carried out according to requirements later.

[0116] The specific heat treatment process parameters of bolts of each specification are shown in Table 9 below:

[0117] Table 9

[0118]

[0119] Performance test:

[0120] The test method is the same as that in Example 1, and the test results are shown in Table 10 below.

[0121] Table 10

[0122]

[0123] In the table, the impact toughness and lateral expansion values were measured in three groups, and the average value was finally taken as the result.

[0124] Example 3

[0125] Based on the further improvement of Example 1, the difference in the method for improving the low-temperature toughness of fasteners provided in this example is that: in step S2, the raw material is subjected to composite treatment with a modulated alloy powder and then manufactured into a fastener. The specific steps are as follows:

[0126] Add the raw material 35CrMoA into an electric melting furnace, melt it at 1580°C for 20 min, then add the modulated alloy powder and continue melting for 5 min. Carry out LF refining outside the furnace, with a refining temperature of 1650°C and a refining time of 10 min. Carry out VD vacuum degassing, pour the obtained molten steel, forge and form the ingot, cool it, and carry out machining to obtain the fastener. The mass ratio of the modulated alloy powder to the raw material 35CrMoA is 0.1:99.9.

[0127] The modulated alloy powder is prepared by the following method:

[0128] S2-1, Pretreatment of B powder: B powder with an average particle size of 5 μm is boiled in a NaOH solution with a mass concentration of 10% for 15 min, taken out, rinsed with deionized water, and then soaked in a 40 wt% HNO 3 solution for 5 min, taken out, rinsed with deionized water until neutral, and dried to obtain the pretreated B powder;

[0129] S2-2, Sensitization treatment: Take 1 g of SnCl 2 ·2H2 O is dissolved in 50 mL of ethanol to obtain a sensitizing solution; 1 g of the pretreated B powder prepared in step S1 is added to the sensitizing solution, ultrasonic treatment is carried out for 15 min, centrifugal separation is carried out, and the solid product is washed successively with ethanol and deionized water to obtain sensitized B powder;

[0130] S2-3. Activation treatment: Take 1 g of sensitized B powder and add it to 50 mL of a PdCl 2 hydrochloric acid (35 wt% concentrated hydrochloric acid) solution, ultrasonic treatment is carried out for 20 min, centrifugal separation is carried out, the solid product is washed with ethanol, and then vacuum dried at 50 °C for 8 h to obtain activated B powder;

[0131] S2-4. Coating the B powder with an alloy:

[0132] S2-4-1. Mix nickel nitrate, yttrium nitrate, lanthanum nitrate, iron nitrate and activated B powder to obtain a precursor, and the mass ratio of Ni:Fe:La:Y:B in the precursor is 6:4.5:2:1.5:1;

[0133] S2-4-2. Take 5 g of the precursor and add it to 100 mL of an ammonia water solution with a mass concentration of 5%, then add ammonium sulfate with a concentration of 10 g / L, sodium citrate with a concentration of 0.125 g / L, and PdCl 2 , ultrasonic dispersion is carried out for 10 min, the obtained mixture is transferred to a reaction kettle, hydrogen is introduced, and the reaction is carried out at 500 rpm under stirring, hydrogen atmosphere and 160 °C for 1 h. During the reaction process, the hydrogen partial pressure is controlled at 2.5 MPa. After the reaction is completed, it is cooled to below 60 °C and then the gas is released and the kettle is unloaded. The product is centrifuged, washed with ethanol, vacuum dried at 90 °C for 12 h, and ground to obtain a modulated alloy powder.

[0134] Refer to Figure 1 for the XRD pattern of the modulated alloy powder.

[0135] As an example, in this embodiment, bolts with a specification of M20×L are prepared. Their heat treatment method and specimen size are the same as those in Example 1, and the impact toughness test is carried out according to the same method as in Example 1.

[0136] Example 4

[0137] Based on the further improvement of Example 2, the difference in the method for improving the low-temperature toughness of fasteners provided in this embodiment is that: in step S2, the raw materials are compounded with a modulated alloy powder and then manufactured into fasteners. The specific steps are as follows:

[0138] Add the raw material 40CrNi2MoA into an electric furnace, melt it at 1600 °C for 25 min, then add the modulating alloy powder and continue melting for 5 min. Refine it outside the LF furnace, with the refining temperature being 1650 °C and the refining time being 10 min. Conduct VD vacuum degassing, pour the obtained molten steel, forge and shape the ingot, cool it, and perform machining to obtain the fastener. The mass ratio of the modulating alloy powder to the raw material 40CrNi2MoA is 0.1:99.9.

[0139] The preparation method of the modulating alloy powder is the same as that in Example 3 and will not be elaborated here.

[0140] Control group A of comparative examples

[0141] This control group of comparative examples is based on Example 3 and provides several examples for comparison, as follows.

[0142] Comparative example A-1

[0143] The difference from Example 3 is only that: in this example, the modulating alloy powder is prepared by the following method:

[0144] Under nitrogen protection, mix nickel, yttrium, lanthanum, and iron evenly according to the mass ratio of Ni:Fe:La:Y being 6:4.5:2:1.5 to obtain the modulating alloy powder.

[0145] Comparative example A-2

[0146] The difference from Example 3 is only that: in this example, step S2-4 of the preparation of the modulating alloy powder is specifically as follows:

[0147] S2-4-1. Mix nickel nitrate, lanthanum nitrate, iron nitrate, and activated B powder to obtain a precursor, and the mass ratio of Ni:Fe:La:B in the precursor is 6:4.5:2:1;

[0148] S2-4-2. Take 5 g of the precursor and add it to 100 mL of an ammonia water solution with a mass concentration of 5%, then add ammonium sulfate with a concentration of 10 g / L, sodium citrate with a concentration of 0.125 g / L, and 0.06 g / L of PdCl 2 , ultrasonically disperse for 10 min, transfer the obtained mixture to a reaction kettle, introduce hydrogen, react at 500 rpm under stirring, in a hydrogen atmosphere, and at 160 °C for 1 h. During the reaction, control the hydrogen partial pressure to be 2.5 MPa. After the reaction, cool it to below 60 °C and then release the gas and unload the kettle. Centrifuge the product, wash it with ethanol, vacuum dry it at 90 °C for 12 h, and grind it to obtain the modulating alloy powder.

[0149] Comparative example A-3

[0150] The difference from Example 3 is only that: in this example, step S2-4 of the preparation of the modulating alloy powder is specifically as follows:

[0151] S2-4-1. Mix nickel nitrate, yttrium nitrate, iron nitrate and activated B powder to obtain a precursor, where the mass ratio of Ni:Fe:Y:B in the precursor is 6:4.5:1.5:1;

[0152] S2-4-2. Take 5 g of the precursor and add it to 100 mL of an ammonia water solution with a mass concentration of 5%, then add ammonium sulfate with a concentration of 10 g / L, sodium citrate with a concentration of 0.125 g / L, and PdCl 2 , ultrasonically disperse for 10 min, transfer the obtained mixture to a reaction kettle, introduce hydrogen, react at 500 rpm under stirring, in a hydrogen atmosphere and at 160 °C for 1 h, control the hydrogen partial pressure to be 2.5 MPa during the reaction, after the reaction, cool to below 60 °C and then release the gas and unload the kettle, centrifuge the product, wash it with ethanol, and vacuum dry it at 90 °C for 12 h, and grind it to obtain the modulated alloy powder.

[0153] Comparative Example A-4

[0154] The difference from Example 3 is only that: in this example, the modulated alloy powder is prepared by the following method:

[0155] Under nitrogen protection, mix nickel, yttrium, lanthanum, iron, and B powder evenly according to the mass ratio of Ni:Fe:La:Y:B of 6:4.5:2:1.5:1 to obtain the modulated alloy powder.

[0156] Comparative Example Group B

[0157] This comparative example group is based on Example 3 and provides several examples for comparison, as follows.

[0158] Comparative Example B-1

[0159] The difference from Example 4 is only that: in this example, the modulated alloy powder is prepared by the following method:

[0160] Under nitrogen protection, mix nickel, yttrium, lanthanum, and iron evenly according to the mass ratio of Ni:Fe:La:Y of 6:4.5:2:1.5 to obtain the modulated alloy powder.

[0161] Comparative Example B-2

[0162] The difference from Example 4 is only that: in this example, the preparation step S2-4 of the modulated alloy powder is specifically:

[0163] S2-4-1. Mix nickel nitrate, lanthanum nitrate, iron nitrate and activated B powder to obtain a precursor, where the mass ratio of Ni:Fe:La:B in the precursor is 6:4.5:2:1;

[0164] S2-4-2: Add 5 g of the precursor into 100 mL of an ammonia water solution with a mass concentration of 5%, then add ammonium sulfate with a concentration of 10 g / L, sodium citrate with a concentration of 0.125 g / L, and PdCl 2 , ultrasonically disperse for 10 min, transfer the obtained mixture to a reaction kettle, introduce hydrogen, react at 500 rpm under stirring, in a hydrogen atmosphere and at 160 °C for 1 h. During the reaction process, control the hydrogen partial pressure to be 2.5 MPa. After the reaction, cool to below 60 °C, then release the gas and unload the kettle. Centrifuge the product, wash it with ethanol, vacuum dry it at 90 °C for 12 h, and grind it to obtain the modulated alloy powder.

[0165] Comparative Example B-3

[0166] The difference from Example 4 is only that: in this example, the preparation step S2-4 of the modulated alloy powder is specifically as follows:

[0167] S2-4-1: Mix nickel nitrate, yttrium nitrate, iron nitrate and activated B powder to obtain a precursor, and the mass ratio of Ni:Fe:Y:B in the precursor is 6:4.5:1.5:1;

[0168] S2-4-2: Add 5 g of the precursor into 100 mL of an ammonia water solution with a mass concentration of 5%, then add ammonium sulfate with a concentration of 10 g / L, sodium citrate with a concentration of 0.125 g / L, and PdCl 2 , ultrasonically disperse for 10 min, transfer the obtained mixture to a reaction kettle, introduce hydrogen, react at 500 rpm under stirring, in a hydrogen atmosphere and at 160 °C for 1 h. During the reaction process, control the hydrogen partial pressure to be 2.5 MPa. After the reaction, cool to below 60 °C, then release the gas and unload the kettle. Centrifuge the product, wash it with ethanol, vacuum dry it at 90 °C for 12 h, and grind it to obtain the modulated alloy powder.

[0169] Comparative Example B-4

[0170] The difference from Example 4 is only that: in this example, the modulated alloy powder is prepared by the following method:

[0171] Under nitrogen protection, mix nickel, yttrium, lanthanum, iron and B powder evenly according to the mass ratio of Ni:Fe:La:Y:B of 6:4.5:2:1.5:1 to obtain the modulated alloy powder.

[0172] The summary of the impact toughness test results of Example 3-4 and the comparative examples is shown in Table 11 below. For the convenience of comparison, the impact toughness test results of the specifications of M20×L in Examples 1-2 are incorporated into Table 11, and the details are as follows:

[0173] Table 11

[0174]

[0175]

[0176] According to the test results in the above table:

[0177] From the comparison between Example 3 and Example 1, it can be seen that compound treatment of the raw material 35CrMoA with the modulated alloy powder can improve the low-temperature toughness of the obtained bolt fasteners;

[0178] From the comparison between Example 4 and Example 2, it can be seen that compound treatment of the raw material 40CrNi2MoA with the modulated alloy powder can improve the low-temperature toughness of the obtained bolt fasteners;

[0179] The result comparison between Comparative Example A-1 and Example 3 shows that for the raw material 35CrMoA, adding a small amount of boron powder can improve the low-temperature toughness. The toughness of Comparative Example A-4 is lower than that of Example 3, mainly because trace elements such as boron, yttrium, and lanthanum in the directly mixed modulated alloy powder are difficult to be uniformly dispersed in the matrix;

[0180] The result comparison between Comparative Examples A-2, A-3 and Example 3 shows that for the raw material 35CrMoA, the compound addition of yttrium and lanthanum has an obvious improvement effect on the low-temperature toughness.

[0181] The result comparison between Comparative Example B-1 and Example 4 shows that for the raw material 40CrNi2MoA, adding a small amount of boron powder can also improve the low-temperature toughness. The toughness of Comparative Example B-4 is lower than that of Example 4, mainly because trace elements such as boron, yttrium, and lanthanum in the directly mixed modulated alloy powder are difficult to be uniformly dispersed in the matrix;

[0182] The result comparison between Comparative Examples B-2, B-3 and Example 4 shows that for the raw material 40CrNi2MoA, the compound addition of yttrium and lanthanum also has an obvious improvement effect on the low-temperature toughness.

[0183] Although the embodiments of the present invention have been disclosed as above, it is not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details.

Claims

1. A method for improving the low temperature toughness of a fastener, characterized in that: The steps include: S1. Use alloy structural steel 35CrMoA or 40CrNi2MoA as raw materials for manufacturing fasteners, and control the phosphorus, sulfur and manganese content of the raw materials and the macrostructural defects of the raw materials; the chemical composition of 35CrMoA meets the requirements of GB / T 3077, and the chemical composition of 40CrNi2MoA meets the requirements of ASME or ASTM standard A 320L43; S2. Manufacturing fasteners using raw materials; S3. Heat treat the fasteners to ensure that the fasteners meet the following requirements: hardness HRC26-30, impact toughness A at -101°C KV ≥27J, lateral expansion value ≥0.38mm; The heat treatment steps include: S3-1, quenching heating: quenching heating adopts step heating, the first heating to the temperature of 300 ℃ ~ 400 ℃, the second heating to the quenching temperature, the quenching temperature is 810 ℃ ~ 870 ℃, and the quenching holding time is 15 to 40 minutes; S3-2, Cooling: Cool the fasteners with oil or saline solution; S3-3. Tempering: Heat to the tempering temperature, the tempering temperature is 590℃~670℃, the heat preservation time is 90~120 minutes, and then air cool to room temperature.

2. The method for improving the low temperature toughness of a fastener according to claim 1, characterized in that: The heat treatment steps in step S3 include: S3-1, quenching heating: quenching heating adopts step heating, the first heating uses a 30Kw oven, heated to 300℃~400℃; the second heating uses a 50Kw medium-temperature salt bath furnace, the furnace load is ≤50Kg, heated to the quenching temperature, the quenching temperature is 810℃~870℃, and the quenching holding time is 15~40 minutes; S3-2, Cooling: Use 10# or 20# machine oil or saline solution to cool the fasteners, the saline solution contains 6% to 10% sodium chloride by mass; cooling medium temperature: saline solution ≤ 40°C, 10# or 20# machine oil ≤ 80°C; S3-3, Tempering: Tempering adopts 35Kw pit furnace, furnace load ≤120Kg, heating to tempering temperature, tempering temperature 590℃~670℃, insulation time 90~120 minutes, air cooling to room temperature.

3. The method for improving the low temperature toughness of a fastener according to claim 1, characterized in that: In step S1, the phosphorus content in the raw materials 35CrMoA and 40CrNi2MoA is controlled to be less than 0.012% by mass, and the sulfur content is controlled to be less than 0.006% by mass.

4. The method for improving the low temperature toughness of a fastener according to claim 1, characterized in that: In step S1, the mass fraction of manganese content in the raw material 40CrNi2MoA is 0.65% to 0.80%.

5. The method for improving the low temperature toughness of a fastener according to claim 1, characterized in that: The macrostructure defects of raw materials 35CrMoA and 40CrNi2MoA meet the following requirements: general porosity and square segregation are below level 0.5, and central porosity is below level 1.0; both plastic inclusions and brittle inclusions are not greater than level 2.5, and the sum of the two is not greater than level 4.

5.

6. The method for improving low temperature toughness of a fastener according to claim 1, characterized in that: In step S2, the raw materials are composited with the modulated alloy powder and then manufactured into fasteners. The specific steps are: the raw materials 35CrMoA or 40CrNi2MoA are completely melted and then the modulated alloy powder is added, smelting, casting, and machining are performed to obtain the fasteners; The prepared alloy powder is obtained by coating boron powder with alloy.

7. The method for improving the low temperature toughness of a fastener according to claim 6, characterized in that: The mass ratio of the alloy powder to the raw material is: 0.05-0.24:99.95-99.76; The chemical composition of the raw material 35CrMoA is as follows by mass percentage: C: 0.32-0.40%, Mn: 0.40-0.70%, Si: 0.17-0.37%, Cr: 0.80-1.10%, Mo: 0.15-0.25%, P: ≤0.012%, S: ≤0.006%, and the balance is Fe and unavoidable impurity elements; The chemical composition of the raw material 40CrNi2MoA is as follows by mass percentage: C: 0.38-0.43%, Mn: 0.65-0.80%, Si: 0.17-0.37, Cr: 0.70-0.90%, Ni: 1.65-2.00%, Mo: 0.20-0.30%, P: ≤0.012%, S: ≤0.006%, and the balance is Fe and unavoidable impurity elements.

8. The method for improving the low temperature toughness of a fastener according to claim 7, characterized in that: The alloy powder was prepared by the following method: S2-1, B powder pretreatment; S2-2, B powder sensitization treatment: S2-3, B powder activation treatment: S2-4. Use alloy to coat the activated B powder: S2-4-1, mixing nickel nitrate, yttrium nitrate, lanthanum nitrate, iron nitrate and activated B powder to obtain a precursor; S2-4-2. Take the precursor and add it into an ammonia solution, then add ammonium sulfate, sodium citrate and PdCl2, and disperse it ultrasonically. The obtained mixture is transferred to a reactor, hydrogen is introduced, and the mixture is reacted under stirring and heating. After the reaction is completed, the mixture is cooled, the product is centrifuged, washed, vacuum dried, and ground to obtain a modulated alloy powder.

9. The method for improving the low temperature toughness of a fastener according to claim 8, characterized in that: The alloy powder was prepared by the following method: S2-1. Pretreatment of B powder: B powder with a particle size of 2-10 μm is boiled in a 5-20% NaOH solution for 5-30 min, taken out and rinsed with deionized water, and then soaked in a 30-50wt% HNO3 solution for 2-10 min, taken out and rinsed with deionized water until neutral, and dried to obtain the pretreated B powder; S2-2, B powder sensitization treatment: 0.5-2g SnCl2·2H2O is dissolved in 25-100mL ethanol to obtain a sensitizing solution; 0.5-2g of the pretreated B powder prepared in step S1 is added to the sensitizing solution, ultrasonically treated for 10-30min, centrifuged, and the solid product is washed with ethanol and deionized water in sequence to obtain a sensitized B powder; S2-3, B powder activation treatment: take 0.5-2g of sensitized B powder and add it to 25-100mL of PdCl2 hydrochloric acid solution with a mass fraction of 0.025-0.1%, ultrasonically treat for 10-40min, centrifuge and separate, wash the solid product with ethanol, and then vacuum dry at 40-65°C for 4-16h to obtain activated B powder; S2-4, using alloy to coat B powder: S2-4-1. Mix nickel nitrate, yttrium nitrate, lanthanum nitrate, iron nitrate and activated B powder to obtain a precursor, wherein the mass ratio of Ni:Fe:La:Y:B in the precursor is 5.5-7.5:3.8-6:1-4:0.75-3:1; S2-4-2. Take 2.5-10g of the precursor and add it into 50-200mL of 2.5-10% ammonia solution, then add 5-20g / L ammonium sulfate, 0.06-0.25g / L sodium citrate and 0.03-0.12g / L PdCl2, and disperse ultrasonically for 5-20min. Transfer the mixture to a reactor, introduce hydrogen, and react at 250-100rpm and 150-170℃ for 0.5-2h. During the reaction, control the hydrogen partial pressure to 2-3MPa. After the reaction, cool to below 50-65℃ and vent the air to unload the reactor. Centrifuge the product, wash with ethanol, and vacuum dry at 80-100℃ for 6-24h. Grind to obtain the modulated alloy powder.

10. The method for improving the low temperature toughness of a fastener according to claim 9, characterized in that: The mass ratio of Ni:Fe:La:Y:B in the precursor is 6:4.5:2:1.5:1.

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