Method for carrying out heat treatment on fastener

Abstract

The invention provides a method for carrying out heat treatment on a fastener, and relates to the technical field of heat treatment of metal products. The method comprises the steps that S100, after smelting and forging, the fastener is subjected to heat preservation for 3 h to 6 h under the temperature condition of 900 DEG C to 980 DEG C, the temperature is reduced to 580 DEG C to 700 DEG C, heat preservation continues to be conducted for 4 h to 8 h, and a green body is obtained; s200, the blank is subjected to oil cooling to the room temperature so as to be subjected to quenching treatment; s300, the green body is subjected to heat preservation for 2 h to 3 h under the temperature condition of 300 DEG C to 340 DEG C so as to be subjected to tempering treatment; s400, the green body is subjected to heat preservation for 4 h to 6 h under the temperature condition of 140 DEG C to 160 DEG C, and then the green body is air-cooled to the room temperature so as to be subjected to aging treatment; and S500, the blank is subjected to laser cladding treatment through cladding powder, and the fastener is obtained. According to the heat treatment method, the wear resistance and corrosion resistance of the fastener can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal product heat treatment, and in particular to a method for heat treating fasteners. BACKGROUND

[0002] Fasteners are a large category of hardware elements used to mechanically join, secure or fasten two or more components (usually objects or materials) together, including bolts, studs, screws, nuts, washers, pins, rivets, etc. The main role of fasteners is to provide reliable connection and fixation, which is embodied in: combining two or more separate components into a whole structure or assembly; preventing relative movement (sliding, rotating, separating) between connected components; transmitting force (tension, shear), torque and vibration between connection points; providing means to adjust component position, clearance or pre-tightening force. Fasteners are widely used in many fields including energy, electronics, electrical appliances, machinery, chemical industry, metallurgy, mold, hydraulic, etc.

[0003] The choice of fastener material is crucial, as it directly affects the strength, hardness, toughness, corrosion resistance, temperature resistance, electrical conductivity, and cost of the fastener. Common materials for fasteners include carbon steel, stainless steel, alloy steel, non-ferrous metals and their alloys. In stainless steel fasteners, austenitic stainless steel (such as 304, 316) is most commonly used, with excellent corrosion resistance, no magnetism, and moderate strength and hardness. 316 steel is more resistant to acid, alkali and salt mist corrosion than 304 due to the presence of molybdenum. Austenitic stainless steel is mainly used in food, chemical industry, medical devices, marine environment, etc. Martensitic stainless steel (such as 410, 420) has some corrosion resistance, but is inferior to austenitic stainless steel, and is usually magnetic. Martensitic stainless steel is used in applications that require strength and some corrosion resistance, such as cutlery, valve parts, high-strength screws. Ferritic stainless steel (such as 430) has general corrosion resistance and low strength, but also has low cost, so it can be used in decorative or less demanding environments.

[0004] For stainless steel fasteners, heat treatment is a key process step to improve mechanical properties, optimize internal structure, and meet specific service requirements. In particular, for martensitic stainless steel (such as 410, 420, 440C, 17-4PH, etc.), the core characteristic of this type of stainless steel is that it can be significantly hardened through heat treatment (quenching + tempering). Quenching (rapid cooling after high-temperature austenitizing) helps to form a high-hardness martensitic structure. Tempering can reduce the brittleness and internal stress after quenching, balance the toughness and hardness, and obtain the target strength grade (such as meeting ISO 8.8, 10.9, 12.9 requirements). Therefore, martensitic stainless steel after heat treatment can be used as high-strength bolts, automobile engine fasteners, and heavy load-bearing structural parts.

[0005] One of the deficiencies existing in the prior art is that for some special scenarios with relatively harsh application environment, such as aviation equipment, flight equipment, engine, marine equipment and the like, higher requirements are required for the wear resistance and corrosion resistance of the fastener, and the conventional martensitic stainless steel fastener is often difficult to meet the above requirements. SUMMARY

[0006] One of the problems solved by the present application is how to provide a martensitic stainless steel fastener with wear resistance and corrosion resistance.

[0007] To solve at least one of the above problems, the present application provides a method for heat treating a fastener, the method comprising:

[0008] S100, after smelting and forging, the fastener is kept at a temperature of 900-980 DEG C for 3-6 hours, cooled to 580-700 DEG C, and kept at the temperature for 4-8 hours to obtain a blank;

[0009] S200, the blank is oil-cooled to room temperature for quenching treatment;

[0010] S300, the blank is kept at a temperature of 300-340 DEG C for 2-3 hours for tempering treatment;

[0011] S400, the blank is kept at a temperature of 140-160 DEG C for 4-6 hours and then air-cooled to room temperature for aging treatment;

[0012] S500, laser cladding treatment is performed on the blank by using cladding powder to obtain a fastener.

[0013] In any of the above technical solutions, the composition of the fastener comprises silicon, manganese, cobalt, chromium, nickel, molybdenum, vanadium, and the balance of iron and unavoidable impurities.

[0014] In any of the above technical solutions, the composition of the fastener comprises vanadium: 0.1%-0.2%; nickel: 0.2%-0.3%; manganese: 0.4%-0.6%; molybdenum: 0.8%-1.2%; silicon: 0.8%-1.0%; cobalt: 2.2%-3.0%; and chromium: 12%-14%.

[0015] In any of the above technical solutions, the composition of the fastener further comprises nitrogen: 0.005% or less; sulfur: 0.03% or less; phosphorus: 0.03% or less; and carbon: 0.05% or less.

[0016] In any of the above technical solutions, the laser cladding treatment specifically comprises:

[0017] S510, the blank is cleaned, rusted and polished;

[0018] S520, send the blank into the laser cladding device, and preheat at a temperature of 280-320 DEG C for 0.5-1 h;

[0019] S530, send the cladding powder into the laser cladding device, and perform single-layer strip reciprocating scanning on the blank by laser to obtain the fastener.

[0020] In any of the above technical solutions, the laser power used in the laser cladding treatment is 2.5-4.0 KW, the laser beam spot diameter used in the laser cladding treatment is 2.0-3.0 mm, and the laser scanning rate used in the laser cladding treatment is 12-16 mm / s.

[0021] In any of the above technical solutions, the delivery rate of the cladding powder is 15-20 g / min; the delivery medium of the cladding powder is nitrogen or argon, and the gas flow rate is 4-5 L / min.

[0022] In any of the above technical solutions, the cladding powder comprises magnesium oxide, praseodymium oxide, chromium nitride, boron carbide, and aluminum oxide.

[0023] In any of the above technical solutions, the preparation method of the cladding powder comprises:

[0024] S610, using magnesium chloride, praseodymium chloride, and aluminum chloride as raw materials, adding water and a complexing agent to prepare a precursor solution;

[0025] S620, mixing the precursor solution with chromium nitride and boron carbide, and adding a precipitant to prepare a precursor sol by coprecipitation;

[0026] S630, aging, washing, spray drying, and sintering the precursor sol to obtain the cladding powder.

[0027] In any of the above technical solutions, in S610, the complexing agent: magnesium chloride: praseodymium chloride: aluminum chloride: water = (0.5-1): (4-6): (1.5-2): (20-22): 100 by mass ratio; in S620, the addition amount of chromium nitride is 20-30% of the addition amount of magnesium chloride in S610 by mass ratio; and in S620, the addition amount of boron carbide is 15-20% of the addition amount of magnesium chloride in S610 by mass ratio.

[0028] Advantages

[0029] The application provides a method for heat treatment of a fastener, and the method comprises the following steps: after smelting and forging, the fastener is kept at a temperature of 900-980 DEG C for 3-6 hours, is cooled to 580-700 DEG C, is kept at the temperature for 4-8 hours, and a blank is obtained; the blank is oil-cooled to room temperature for quenching treatment; the blank is kept at a temperature of 300-340 DEG C for 2-3 hours for tempering treatment; the blank is kept at a temperature of 140-160 DEG C for 4-6 hours and is air-cooled to room temperature for aging treatment; the blank is subjected to laser cladding treatment by using cladding powder, and the fastener is obtained. By the method, the wear resistance and corrosion resistance of the martensitic stainless steel fastener can be improved, and the fastener can be applied to special application scenarios such as aviation equipment, flight equipment, engines and marine equipment. DETAILED DESCRIPTION

[0030] In order to make the above objectives, characteristics and advantages of the application more obvious and easy to understand, the following will be described in detail in combination with specific embodiments of the application.

[0031] Unless otherwise specified, the reagents and raw materials used in the application can be purchased through commercial channels. The experimental methods in the following examples are selected according to conventional methods and conditions, or according to the product instructions.

[0032] The application provides a method for heat treatment of a fastener, and the method comprises the following steps:

[0033] S100, after smelting and forging, the fastener is kept at a temperature of 900-980 DEG C for 3-6 hours, is cooled to 580-700 DEG C, is kept at the temperature for 4-8 hours, and a blank is obtained;

[0034] S200, the blank is oil-cooled to room temperature for quenching treatment;

[0035] S300, the blank is kept at a temperature of 300-340 DEG C for 2-3 hours for tempering treatment;

[0036] S400, the blank is kept at a temperature of 140-160 DEG C for 4-6 hours and is air-cooled to room temperature for aging treatment;

[0037] S500, the blank is subjected to laser cladding treatment by using cladding powder, and the fastener is obtained.

[0038] The present invention is applicable to the treatment of martensitic stainless steel fasteners. Martensitic stainless steel is a type of stainless steel that can have its mechanical properties (such as hardness, strength, and toughness) adjusted through heat treatment, with the core characteristic being that its crystal structure can undergo a martensitic phase transformation during heating and cooling. The heat treatment of martensitic stainless steel mainly includes two processes: quenching and tempering. In the annealed state, martensitic stainless steel usually exhibits an austenitic structure. After quenching, the structure is transformed into martensite, which has high hardness and high strength. Tempering can eliminate quenching stress, improve toughness and corrosion resistance, while maintaining certain hardness and strength. Therefore, quenching and tempering can cause the structure of stainless steel to undergo a martensitic phase transformation, thereby improving its hardness and strength. High hardness and high strength make martensitic stainless steel have good wear resistance, suitable for manufacturing wear-resistant parts and tools. The high hardness and good wear resistance of martensitic stainless steel make it an ideal material for manufacturing knives, such as surgical knives, scissors, and kitchen knives. In addition, martensitic stainless steel is also suitable for manufacturing mechanical parts such as bearings and valves, as well as products such as molds, springs, and pipes. Martensitic stainless steel is particularly suitable for manufacturing fastener products.

[0039] The present invention provides a method for heat treating fasteners, aiming to significantly improve the mechanical properties of martensitic stainless steel fasteners, especially corrosion resistance, by precisely controlling the temperature, time, and cooling method during heat treatment.

[0040] Before heat treatment, the stainless steel raw material needs to be melted and cast into ingots and forged into shape. The melting process is carried out in a vacuum induction furnace, the purpose of which is to melt the raw material into a uniform alloy. Through forging, the fastener can be given a preliminary shape and certain density. The temperature range for melting and casting stainless steel raw materials is 1500°C to 1600°C. The initial forging temperature for forging is not more than 1200°C, and the final forging temperature is not less than 900°C.

[0041] After melting and forging, the fastener is placed in a high-temperature furnace at a temperature of 900°C to 980°C for heat preservation, so that the elements can fully diffuse, eliminate forging stress, and promote austenite homogenization. Cooling to 580°C to 700°C and continuing to heat preservation can improve the subsequent processing performance and final structure uniformity of stainless steel, and reduce the risk of quenching cracks.

[0042] The purpose of quenching treatment is to induce martensitic transformation, thereby increasing the hardness and strength of the blank. Compared with water quenching, oil quenching can more gently control the cooling speed, reduce thermal stress and reduce the risk of cracking. The purpose of tempering treatment is to eliminate the residual stress generated by quenching, stabilize the microstructure, and improve the toughness and fatigue resistance of the blank. Aging treatment can be carried out in an air circulation furnace to ensure temperature uniformity. The purpose of aging treatment is to optimize the dimensional stability of the stainless steel product and reduce its dimensional change during long-term use. Laser cladding can form a dense and high-hardness cladding layer on the surface of the blank, thereby enhancing the wear resistance and corrosion resistance of the fastener surface, prolonging the service life of the fastener, and making it particularly suitable for use in harsh environments.

[0043] In terms of chemical composition, the characteristic of martensitic stainless steel is the addition of chromium and / or nickel. Among them, martensitic chromium stainless steel mainly includes 410, 420, 440 series stainless steel. In martensitic chromium stainless steel, the content of chromium is usually between 12% and 18%. In the present application, the composition of the fastener includes silicon, manganese, cobalt, chromium, nickel, molybdenum, vanadium, and the balance of iron and unavoidable impurities. Preferably, the composition of the fastener includes vanadium: 0.1% to 0.2%; nickel: 0.2% to 0.3%; manganese: 0.4% to 0.6%; molybdenum: 0.8% to 1.2%; silicon: 0.8% to 1.0%; cobalt: 2.2% to 3.0%; chromium: 12% to 14%. In addition, the composition of the fastener also includes nitrogen: 0.005% or less; sulfur: 0.03% or less; phosphorus: 0.03% or less; carbon: 0.05% or less. The addition of chromium can significantly improve the corrosion resistance of stainless steel, strongly promote the martensitic transformation, and improve the hardenability. Nickel and vanadium elements can further improve the performance of stainless steel and improve its wear resistance. Molybdenum can enhance the stability of the passivation film and significantly improve the resistance to pitting and crevice corrosion. In addition, molybdenum can form secondary hardening carbides (Mo2C) with carbon and improve high-temperature strength and tempering stability. Manganese and silicon elements can inhibit temper brittleness, improve high-temperature oxidation resistance and hardenability. In addition, it should be noted that although carbon can stabilize martensite and significantly improve the hardness and strength of stainless steel, too high a carbon content will reduce the toughness and corrosion resistance of martensitic stainless steel. Therefore, the content of carbon needs to be controlled.

[0044] Martensitic stainless steel has considerable corrosion resistance in oxidizing media, but its corrosion resistance is still not as good as that of austenitic stainless steel and ferritic stainless steel. In order to further improve its corrosion resistance, the present application performs laser cladding treatment on the martensitic stainless steel fastener after aging treatment. Laser cladding treatment specifically includes:

[0045] S510, cleaning, rust removal and polishing of the blank;

[0046] S520, sending the blank into the laser cladding equipment and preheating at a temperature of 280-320℃ for 0.5-1h;

[0047] S530, feeding the cladding powder into the laser cladding equipment and performing single-layer strip reciprocating scanning on the blank by laser to obtain the fastener.

[0048] The purpose of cleaning is to remove oil stains and particle contaminants on the surface of the fastener, and preferably, an alkaline degreasing solution comprising sodium hydroxide, sodium bicarbonate and a surfactant is prepared, and the fastener is ultrasonically cleaned. Nitric acid corrosion inhibitor can be used for rust removal. Polishing can be performed by ceramic grinding wheel or diamond file. In addition to polishing, the fastener can also be polished.

[0049] The laser cladding treatment can form a laser cladding layer on the surface of the fastener, and the laser cladding layer forms a dense metallurgical bond with the substrate, which can impart excellent barrier properties to the fastener and improve the corrosion resistance of the martensitic stainless steel fastener.

[0050] Preferably, the laser cladding treatment uses a laser power of 2.5-4.0KW, a laser beam spot diameter of 2.0-3.0mm, and a laser scanning speed of 12-16mm / s. The delivery rate of the cladding powder is 15-20g / min; the delivery medium of the cladding powder is nitrogen or argon, and the gas flow rate is 4-5L / min.

[0051] It should be noted that the laser cladding powder formulation has a decisive influence on the treatment effect of the martensitic stainless steel fastener, and the composition design directly determines the microstructure, performance and compatibility with the substrate of the cladding layer. In the present application, the cladding powder comprises magnesium oxide, praseodymium oxide, chromium nitride, boron carbide and aluminum oxide. Specifically, the preparation method of the cladding powder comprises:

[0052] S610, using magnesium chloride, praseodymium chloride and aluminum chloride as raw materials, adding water and a complexing agent to prepare a precursor solution;

[0053] S620, mixing the precursor solution with chromium nitride and boron carbide and adding a precipitant to prepare a precursor sol by coprecipitation;

[0054] S630, aging, washing, spray drying and sintering the precursor sol to obtain the cladding powder.

[0055] In S610, the complexing agent: magnesium chloride: praseodymium chloride: aluminum chloride: water = (0.5-1): (4-6): (1.5-2): (20-22): 100 by mass ratio; in S620, the addition amount of chromium nitride is 20% to 30% of the addition amount of magnesium chloride in S610 by mass ratio; in S620, the addition amount of boron carbide is 15% to 20% of the addition amount of magnesium chloride in S610 by mass ratio.

[0056] In S610, first weigh the ingredients by mass ratio, then add the above-mentioned metal chloride raw materials in sequence, and add deionized water and a complexing agent. The complexing agent is preferably citric acid.

[0057] In S620, the precursor solution can be heated to 45-55°C first, then chromium nitride and boron carbide are added, and stirred or ultrasonically mixed uniformly under heat preservation, and then a precipitant is added, and stirring is continued until the metal chlorides form metal carbonate or metal hydroxide precipitates. Preferably, the precipitant is mixed and prepared from concentrated ammonia water, ammonium carbonate and water in a mass ratio of 8:10:100. In the co-precipitation reaction, the addition amount of the precipitant is such that the pH value of the reaction system reaches 10-11. In the co-precipitation reaction, rapid stirring is required to ensure that all metal ion components are precipitated synchronously to obtain a precursor sol. After obtaining the precursor sol, the precursor sol is soaked in anhydrous ethanol for 24 h for aging. After aging, the sol is aged into a gel, and the gel is washed with water twice, then dispersed in a 10wt% polyvinyl alcohol aqueous solution at 85-90°C, spray dried, and sintered to obtain a cladding powder. The inlet temperature of spray drying is 160-180°C, and the outlet temperature is 90-100°C. The atomization pressure is 0.3-0.5 MPa. The sintering after spray drying uses a stepwise temperature rising mode, first heat preservation at 300°C for 2 h to remove bound water and polyvinyl alcohol, then heat preservation at 600°C for 2 h to decompose the carbonate, and then heat preservation at 1000°C for 2 h. After natural cooling, the cladding powder is obtained.

[0058] The reason for using the above steps to prepare the cladding powder is that chromium nitride and boron carbide can form a wear-resistant network in situ with iron during laser cladding, magnesium ions and aluminum ions form a MgAl2O4 spinel framework after precipitation and sintering, the cladding layer with MgAl2O4 spinel structure can improve the thermal shock stability and high temperature toughness of martensitic stainless steel, praseodymium ions form praseodymium oxide after precipitation and sintering, which can be adsorbed on the grain boundaries to reduce the interfacial energy and eliminate thermal cracks that may occur during heat treatment. Therefore, laser cladding treatment of martensitic stainless steel fasteners using the cladding powder prepared by the above steps can further improve the performance of martensitic stainless steel fasteners.

[0059] Example 1

[0060] A series of cladding powder samples are prepared in this example, whose component proportions are listed in Table 1, and the preparation method comprises the following steps:

[0061] S1, according to the mass ratio of Table 1, magnesium chloride, praseodymium chloride, aluminum chloride are mixed, and deionized water and citric acid are added and mixed uniformly to prepare a precursor solution;

[0062] S2, according to the mass ratio of 8:10:100, concentrated ammonia, ammonium carbonate and water are mixed to prepare a precipitant;

[0063] S3, according to the mass ratio of Table 1, first heat the precursor solution to 50°C, then mix the precursor solution with chromium nitride and boron carbide, and gradually add the precipitant and stir synchronously until the pH value of the reaction system reaches 10, stop adding, continue stirring for 1h, and prepare a precursor sol;

[0064] S4, after soaking the precursor sol in anhydrous ethanol for 24h, wash it twice, then prepare a 10wt% polyvinyl alcohol aqueous solution, heat it to 90°C, and stir until the polyvinyl alcohol is completely dissolved, then add 20% of the precursor sol with a mass of 20% of the polyvinyl alcohol aqueous solution, mix uniformly, and spray dry at an inlet temperature of 160°C, the atomization pressure of spray drying is 0.3 MPa, to obtain a raw powder;

[0065] S5, the raw powder is sent into a resistance furnace, first heat treated at 300°C for 2h, then heat treated at 600°C for 2h, and finally heat treated at 1000°C for 2h, and naturally cooled to room temperature with the furnace, to obtain a cladding powder sample.

[0066] Table 1

[0067] No. Cladding powder sample 1 Cladding powder sample 2 Cladding powder sample 3 Cladding powder sample 4 Citric acid: magnesium chloride: praseodymium chloride: aluminum chloride: water 0.5：5：1.5：22：100 0.5：5：2：20：100 1：4：1.5：22：100 1：6：2：20：100 Added amount of chromium nitride 20% of added amount of magnesium chloride 20% of added amount of magnesium chloride 30% of added amount of magnesium chloride 30% of added amount of magnesium chloride Added amount of boron carbide 20% of added amount of magnesium chloride 20% of added amount of magnesium chloride 15% of added amount of magnesium chloride 15% of added amount of magnesium chloride

[0068] Example 2

[0069] A series of fastener samples are prepared in this example, whose component proportions are listed in Table 2, and the preparation method comprises the following steps:

[0070] S1, according to the proportions of Table 2, the raw materials are sent into a vacuum induction furnace, melted at a temperature range of 1550°C to 1580°C, then forged, heat treated at a temperature of 940°C to 950°C for 4h, then cooled to 620°C, and heat treated for another 4h, to obtain a blank;

[0071] S2, after oil cooling the blank to room temperature, heat it at a temperature of 320°C for 2h, and then heat it at a temperature of 145°C for 4h, and then air cool to room temperature;

[0072] S3, using sodium hydroxide, sodium bicarbonate and surfactant and deionized water in a mass ratio of 4:12:2:100, mixing uniformly to prepare an alkaline degreasing solution, and using the same to ultrasonically clean the fasteners;

[0073] S4, using an aqueous nitric acid solution, adding a small amount of triethanolamine and benzotriazole to prepare an inhibitor, using the inhibitor to remove rust from the fasteners, and then polishing to obtain samples 1 to 8 of the fastener blanks.

[0074] Table 2

[0075] No. Fastener sample 1 Fastener sample 2 Fastener sample 3 Fastener sample 4 Vanadium 0.1% 0.1% 0.2% 0.2% Nickel 0.3% 0.3% 0.2% 0.2% Manganese 0.4% 0.45% 0.5% 0.6% Molybdenum 1.2% 1.0% 1.0% 0.8% Silicon 0.8% 0.8% 1.0% 1.0% Cobalt 3.0% 2.6% 2.4% 2.2% Chromium 13% 13% 13% 13% Carbon 0.04% 0.04% 0.04% 0.04% Balance Iron and unavoidable impurities of nitrogen, phosphorus, sulfur, etc. Iron and unavoidable impurities of nitrogen, phosphorus, sulfur, etc. Iron and unavoidable impurities of nitrogen, phosphorus, sulfur, etc. Iron and unavoidable impurities of nitrogen, phosphorus, sulfur, etc. No. Fastener sample 5 Fastener sample 6 Fastener sample 7 Fastener sample 8 Raw material ratio Same as fastener sample 1 Same as fastener sample 2 Same as fastener sample 3 Same as fastener sample 4

[0076] Example 3

[0077] In this example, samples 1 to 8 of the fastener blanks obtained in Example 2 were subjected to laser cladding treatment. The source of the cladding powder used in the laser cladding treatment of samples 1 to 8 of the fastener blanks is shown in Table 3. The treatment method of the laser cladding treatment was as follows:

[0078] Samples 1 to 8 of the fastener blanks were fed into a laser cladding device, preheated at a temperature of 300℃ for 0.5h, and then the cladding powder was fed into the laser cladding device at a powder delivery rate of 15g / min and a gas delivery rate of 4L / min using nitrogen as the medium. A 2.5KW laser power was used to perform single-layer strip-shaped reciprocating scanning on the blank, with a laser beam spot diameter of 2.0mm and a laser scanning rate of 12mm / s to obtain the fastener.

[0079] Table 3

[0080] No. Fastener sample 1 Fastener sample 2 Fastener sample 3 Fastener sample 4 Cladding powder source Cladding powder sample 1 Cladding powder sample 2 Cladding powder sample 3 Cladding powder sample 4 No. Fastener sample 5 Fastener sample 6 Fastener sample 7 Fastener sample 8 Cladding powder source Cladding powder sample 4 Cladding powder sample 3 Cladding powder sample 1 Cladding powder sample 1

[0081] Performance test

[0082] According to the accelerated test method of YY / T 0149-2006, the fastener samples 1 to 8 without laser cladding treatment were subjected to pressure steam test, and the corrosion grade of the sample surface was checked. The fastener samples 1 to 8 subjected to laser cladding treatment were subjected to pressure steam test, and the corrosion grade of the sample surface was checked. The corrosion grade of the fastener samples 1 to 8 without laser cladding treatment was all grade c, and the corrosion grade of the fastener samples 1 to 8 subjected to laser cladding treatment was all grade b.

[0083] Although the present application is disclosed as above, the present application is not limited thereto. Any person skilled in the art, without departing from the spirit and scope of the present application, can make various changes and modifications, and therefore the scope of protection of the present application should be limited by the scope defined in the claims.

Claims

1. A method of heat treating a fastener, characterized by, The method of the heat treatment comprises: S100, after smelting and forging, the fastener is kept at a temperature of 900-980 DEG C for 3-6 hours, cooled to 580-700 DEG C, kept for 4-8 hours, and a blank is obtained; S200, the blank is oil-cooled to room temperature for quenching treatment; S300, the blank is kept at a temperature of 300-340 DEG C for 2-3 hours for tempering treatment; S400, the blank is kept at a temperature of 140-160 DEG C for 4-6 hours and then air-cooled to room temperature for aging treatment; S500, the blank is treated by laser cladding with cladding powder, and the fastener is obtained.

2. The method of claim 1, wherein, The composition of the fastener comprises silicon, manganese, cobalt, chromium, nickel, molybdenum, vanadium, and the balance of iron and inevitable impurities.

3. The method of claim 2, wherein, The composition of the fastener comprises vanadium 0.1-0.2%, nickel 0.2-0.3%, manganese 0.4-0.6%, molybdenum 0.8-1.2%, silicon 0.8-1.0%, cobalt 2.2-3.0%, and chromium 12-14%.

4. The method of claim 3, wherein, The composition of the fastener further comprises nitrogen 0.005% or less, sulfur 0.03% or less, phosphorus 0.03% or less, and carbon 0.05% or less.

5. The method according to any one of claims 1 to 4, characterized in that, The laser cladding treatment specifically comprises: S510, the blank is cleaned, rusted and polished; S520, the blank is sent into a laser cladding device and preheated at a temperature of 280-320 DEG C for 0.5-1 hour; S530, the cladding powder is delivered into the laser cladding device, and the blank is scanned by laser in a single-layer strip-shaped reciprocating manner, and the fastener is obtained.

6. The method of claim 5, wherein, The laser cladding treatment adopts a laser power of 2.5-4.0 KW, a laser beam spot diameter of 2.0-3.0 mm, and a laser scanning speed of 12-16 mm / s.

7. The method of claim 5, wherein, The delivery rate of the cladding powder is 15-20 g / min, and the delivery medium of the cladding powder is nitrogen or argon with a gas flow of 4-5 L / min.

8. The method of claim 5, wherein, The cladding powder comprises magnesium oxide, praseodymium oxide, chromium nitride, boron carbide and aluminum oxide.

9. The method of claim 8, wherein, The preparation method of the cladding powder comprises: S610, using magnesium chloride, praseodymium chloride and aluminum chloride as raw materials, a precursor solution is prepared by adding water and a complexing agent; S620, the precursor solution is mixed with the chromium nitride and the boron carbide, and a precipitant is added to prepare a precursor sol by a co-precipitation reaction; S630, the precursor sol is aged, washed, spray-dried and sintered to obtain the cladding powder.

10. The method of claim 9, wherein, in S610, the complexing agent, magnesium chloride, praseodymium chloride, aluminum chloride and water are in a mass ratio of (0.5-1):(4-6):(1.5-2):(20-22):

100. ​ In S620, the chromium nitride is added in an amount of 20% to 30% of the amount of the magnesium chloride added in S610, in terms of mass ratio; In S620, the boron carbide is added in an amount of 15% to 20% of the amount of the magnesium chloride added in S610, in terms of mass ratio.