Wear-resistant nut and preparation process thereof

Abstract

The invention relates to the technical field of nuts, and provides a wear-resistant nut and a preparation process thereof. The preparation technology of the corrosion-resistant nut comprises the steps that raw materials are taken and placed in a vacuum induction furnace to be smelted; lF refining is conducted, 80-100 kg of lime is added into an LF refining furnace for desulfurization, 30-40 kg of calcium carbide is added into the LF refining furnace for deep deoxidation in the later period, and the total refining time is 60-80 min; then argon blowing stirring is carried out; the molten steel is subjected to square billet continuous casting to form steel billets; heating the steel billet to 1250-1300 DEG C for melting, pouring into a mold under the protection of argon, pre-cooling in the mold to 600-700 DEG C, and demolding to obtain a nut rough blank; and performing heat treatment after demolding, cladding the coating material on a nut rough blank through surface laser cladding, and performing post-treatment at 450-550 DEG C for 4-5 hours to obtain the wear-resistant nut. According to the wear-resistant nut provided by the invention, the corrosion resistance is improved, and the wear resistance of the nut is effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of nuts, and specifically, to a wear-resistant nut and its preparation process. Background Art

[0002] In mechanical engineering, nuts, as a basic and crucial fastener, are widely used in the connection and fixation of various mechanical equipment. Its function is to generate a pre-tightening force through cooperation with bolts, so that the connected parts are tightly combined, ensuring the stability and reliability of the mechanical structure. However, in the actual working environment, nuts often face complex mechanical actions, friction and wear, as well as harsh environmental conditions, such as high temperature, high pressure, corrosive media, etc. These factors will cause the wear of nuts to intensify, thereby affecting their fastening performance and service life.

[0003] Wear-resistant nuts are widely used in various fields with high requirements for the wear resistance of fasteners, such as aerospace, automotive manufacturing, petrochemical industry, mining machinery, etc. In the aerospace field, during the high-speed flight of aircraft, nuts will be affected by strong vibrations, impacts and high-temperature environments, and need to have extremely high wear resistance to ensure flight safety; in the automotive manufacturing industry, nuts in key components such as engines and transmissions will bear large frictional forces and alternating loads during long-term operation. The use of wear-resistant nuts can effectively extend the service life of components and improve the reliability and safety of vehicles; in the petrochemical and mining machinery fields, equipment usually operates under harsh working conditions, such as high temperature, high pressure, strong corrosion and a large amount of dust. Wear-resistant nuts can adapt to these extreme environments and ensure the normal operation of equipment.

[0004] In some special working conditions, such as chemical and marine environments, nuts will come into contact with various corrosive media. Existing wear-resistant nut materials have certain defects in corrosion resistance, are prone to corrosion, resulting in a decrease in the mechanical properties of nuts and a corresponding reduction in wear resistance. Corrosion not only damages the surface structure of nuts but also accelerates the deterioration of the internal structure, shortening the service life of nuts. In addition, for nuts working in high-temperature environments, existing materials are prone to problems such as softening and oxidation at high temperatures. The hardness and strength of the materials will decrease significantly with the increase in temperature, resulting in a sharp reduction in wear resistance. For example, in some high-temperature furnace equipment, ordinary wear-resistant nuts will quickly lose their original fastening function under the action of high temperature and cannot meet the requirements of long-term stable operation of the equipment. Based on this, the present invention proposes a wear-resistant nut and its preparation process. Summary of the Invention

[0005] The present invention provides a wear-resistant nut and its preparation process, which improves the corrosion resistance of the existing wear-resistant nut materials in corrosive environments such as chemical industry and ocean, avoids the decline of the mechanical properties and wear resistance of the nut due to corrosion, prevents the destruction of the surface structure and the deterioration of the internal structure, so as to extend the service life of the nut; it also improves the performance stability of the existing wear-resistant nut materials in high-temperature environments, avoids problems such as softening and oxidation of the materials at high temperatures, and then maintains the wear resistance of the nut, ensuring that it can stably perform the fastening function for a long time in high-temperature equipment (such as high-temperature furnace equipment).

[0006] The technical solution of the present invention is as follows: In the first aspect, the present invention provides a preparation process for a wear-resistant nut, and the steps include: (1) Take the raw materials and place them in a vacuum induction furnace for melting, with the vacuum degree ≤ 10 -3 Pa, the melting temperature is 1550 - 1600 °C, keep warm for 1 - 2 h, and the oxygen content < 50 ppm; (2) Conduct LF refining. First, add 80 - 100 kg / lot of lime to the LF refining furnace for desulfurization, and later add 30 - 40 kg / lot of calcium carbide for deep deoxidation. The total refining time is 60 - 80 min; then conduct argon blowing and stirring; (3) Carry out continuous casting of square billets for the molten steel, adjust the drawing speed to 2.5 - 3 m / min, the specific water volume is 1.2 L / kg, the tundish temperature is 1150 - 1200 °C, and continuously cast into 150 mm × 150 mm steel billets; (4) Heat the steel billet to 1250 - 1300 °C for melting, pour it into the mold under argon protection, and demold after pre-cooling the mold to 600 - 700 °C to obtain the rough nut; (5) After demolding, conduct heat treatment. Use Al2O3 - TiO2 nanoparticles as the coating material and perform surface laser cladding on the rough nut, and conduct post-treatment at 450 - 550 °C for 4 - 5 h to obtain the wear-resistant nut.

[0007] In the present invention, a high vacuum degree can effectively reduce the mixing of gases during the melting process, reduce the gas content in the molten steel, and avoid the formation of defects such as pores. Precise melting temperature and holding time contribute to the full melting and uniform mixing of the raw materials, enabling the full diffusion of each element and forming a uniform alloy structure. Strictly controlling the oxygen content can prevent the oxidation of the molten steel, reduce oxide inclusions, improve the purity of the molten steel, and provide a good foundation for subsequent processes.

[0008] Stage-by-stage desulfurization and deoxidation can more effectively remove sulfur and oxygen in the molten steel according to the requirements of different stages. Lime reacts with sulfur in the molten steel to form calcium sulfide, thus achieving the purpose of desulfurization; calcium carbide has a stronger deoxidizing ability and can further reduce the oxygen content in the molten steel. Precise refining time can ensure the full progress of the desulfurization and deoxidation reactions. Argon blowing and stirring promotes the floating and removal of inclusions in the molten steel through the stirring action of argon, making the composition of the molten steel more uniform and improving the quality of the molten steel.

[0009] An appropriate drawing speed can ensure the formation of a stable solidification shell in the mold for the molten steel, avoiding defects such as breakout. The control of the specific water volume affects the cooling intensity in the mold, and an appropriate specific water volume helps to obtain a uniform solidification structure and good surface quality. Precise control of the tundish temperature can ensure the fluidity of the molten steel during continuous casting, make the internal structure of the billet uniform, and reduce the generation of internal defects.

[0010] Heating the billet to an appropriate temperature can fully melt the billet, ensure the fluidity of the molten steel, and facilitate pouring and forming. Argon protection can prevent the molten steel from contacting air and oxidizing during pouring, improving the quality of the rough nut blank. Pre-cooling in the mold can initially solidify the rough nut blank in the mold, and controlling the demolding temperature can avoid defects such as deformation of the rough nut blank due to too high temperature or cracks due to too low temperature.

[0011] Solution treatment can fully dissolve alloying elements in the matrix to form a supersaturated solid solution, providing a tissue basis for subsequent aging treatment. During the aging treatment, alloying elements in the supersaturated solid solution precipitate in the form of fine precipitate phases, playing a role of precipitation strengthening and improving the strength and hardness of the nut. Molten salt quenching treatment refines the surface structure of the nut through rapid cooling, further improving the surface strength and hardness. At the same time, the composition and proportion of the molten salt have an important impact on the quenching effect, and appropriate molten salt composition can ensure the stability of the quenching process and the quenching effect.

[0012] As a further technical solution, the argon flow rate for the argon blowing and stirring is 10 - 15 L / min, and the stirring time is 30 - 40 min.

[0013] As a further technical solution, the composition of the billet is as follows: C 0.3% - 0.5%, Si 0.2% - 0.3%, Cr 3.5% - 4.5%, Ni 2.4% - 2.8%, Mo 1.5% - 2.5%, Nb 0.1% - 0.3%, B 0.1% - 0.2%, Ce 0.05% - 0.1%, Co 0.06% - 0.12%, Ti 0.03% - 0.07%, P ≤ 0.03%, S ≤ 0.02%, and the balance is Fe and other inevitable impurities.

[0014] As a further technical solution, the heat treatment step includes: first, solution treatment is carried out at 1100 - 1200 °C for 2 - 3 h, and then water-cooled to room temperature; aging treatment is carried out at 700 - 800 °C for 5 - 6 h, and then air-cooled to room temperature; subsequently, it is heated to 800 - 900 °C and held for 15 - 20 min, quenched into a molten salt at 240 - 260 °C and held for 10 - 12 min, and then air-cooled to room temperature.

[0015] As a further technical solution, the molten salt includes KNO3 and NaNO2 with a weight ratio of 5 - 6:4 - 5.

[0016] As a further technical solution, the preparation method of the Al2O3-TiO2 nanoparticles includes: adding polyvinyl alcohol to deionized water to prepare a polyvinyl alcohol solution, adding Al2O3 nanopowder and TiO2 nanopowder and mixing them, obtaining a mixed solution after ultrasonic dispersion for 60 - 80 min, and spray-drying the mixed solution; subsequently, heating it at a heating rate of 5 - 10 °C / min to 1100 - 1200 °C, calcining for 2 - 4 h, and then cooling with the furnace to obtain the product.

[0017] As a further technical solution, the feeding rate of the spray drying is 10 - 20 mL / min, the inlet air temperature is controlled at 450 - 550 °C, and the outlet air temperature is 80 - 120 °C.

[0018] As a further technical solution, the dosage ratio of polyvinyl alcohol, deionized water, Al2O3 nanopowder and TiO2 nanopowder is (2 - 3):(70 - 80):(1 - 1.4):(20 - 24).

[0019] As a further technical solution, in the surface laser cladding step, the laser power is 3 - 4 kW, the scanning speed is 8 - 10 mm / s, the overlapping rate is 30 - 40%, and finally a coating thickness of 100 - 150 μm is obtained under the condition of argon protection with a flow rate of 15 - 20 L / min.

[0020] In the second aspect, the present invention provides a corrosion-resistant nut prepared by the foregoing preparation process.

[0021] The working principle and beneficial effects of the present invention are as follows: The present invention adopts a Cr-Ni-Mo-Nb multi-element composite strengthening system. Among them, the Cr element plays a dual strengthening role in the alloy system: firstly, through the solid solution strengthening mechanism, it occupies the lattice interstitial sites of the Fe matrix, forming a lattice distortion field, which significantly hinders the movement of dislocations; secondly, it forms M7C3-type carbides with the C element, and nano-scale hard phases precipitate at grain boundaries and dislocation lines, generating a second-phase strengthening effect. When the Cr content is 3.5 - 4.5, the volume fraction of carbides increases and the distribution uniformity improves. It can not only pin the grain boundaries to inhibit recrystallization, but also strengthen the matrix through dispersion distribution. The Cr content forms a dynamic balance with the C element, avoiding excessive Cr from causing carbide coarsening or the precipitation of brittle phases, and ensuring the coordinated optimization of strength and toughness.

[0022] In addition, the addition of the Ni element can reduce the stacking fault energy, promote dislocation multiplication and cross-slip, and cooperate with the Mo element to achieve grain refinement. The Nb element inhibits the growth of austenite grains during the heat treatment process by forming NbC particles, forming a fine grain strengthening effect. The B element segregates at grain boundaries, enhancing the grain boundary binding energy, and the Ce element, as a micro-alloying element, purifies the grain boundaries, further blocking the crack propagation path. This multi-element synergistic effect breaks through the performance bottleneck of a single strengthening mechanism and achieves the balance between matrix strength and toughness.

[0023] In the present invention, a gradient treatment process of solution-aging-salt bath quenching is constructed. In the solution treatment stage, alloying elements are fully dissolved to form a supersaturated solid solution; the aging treatment produces a dispersion strengthening effect. The salt bath quenching process uses a KNO3-NaNO2 eutectic salt system, and the cooling rate is precisely controlled by adjusting the proportion of the salt bath components. During the salt bath quenching process, the eutectic temperature of the salt bath decreases, ensuring the uniformity of heat transfer during quenching. + and Na + The difference in ionic radii leads to lattice distortion, promotes the non-diffusive phase transformation of austenite to martensite, refines the surface layer structure, generates a dense passivation layer, and significantly improves the corrosion resistance.

[0024] In addition, during the quenching process, the temperature difference between the surface layer and the core causes a thermal stress gradient, which promotes dislocation multiplication and forms a high-density dislocation wall; at the same time, O 2- in the salt bath selectively oxidizes with the surface layer Fe atoms to form a Fe3O4 / Fe2O3 composite oxide film with a thickness of about 50 nm. This oxide film forms a metallurgical bond with the matrix, which can not only act as a diffusion barrier to inhibit the penetration of corrosive media, but also increase the crack propagation resistance through residual compressive stress.

[0025] The corrosion-resistant nut of the present invention introduces Al2O3-TiO2 nanoparticles into the coating. The composite design of Al2O3 and TiO2 is based on the principle of complementary material properties: Al2O3 has high hardness and low friction coefficient, and can effectively resist abrasive wear and adhesive wear; TiO2 has excellent chemical stability and the ability to form a passivation film, and preferentially combines with O 2 ⁻ in the corrosive medium to form a passivation layer, blocking the penetration of the corrosive medium. After the two are combined, the Al2O3 skeleton structure bears the main load, TiO2 fills the gaps and forms a lubricating phase, and a TiO2-FeO solid solution is formed through in-situ reaction during the friction process, realizing the self-lubricating effect. This synergistic effect between the hard phase and the lubricating phase endows the coating with both wear resistance and corrosion resistance.

[0026] When preparing the coating raw materials, the polyvinyl alcohol solution can be used as a dispersant to uniformly disperse the Al2O3 nano-powder and TiO2 nano-powder in the solution. Ultrasonic dispersion can further promote the dispersion of the nano-powder and reduce the agglomeration phenomenon. Spray drying can convert the mixed solution into dry particles. Controlling the feeding rate, inlet air temperature and outlet air temperature can ensure the morphology and performance of the particles, realize the spheroidization granulation of the nano-particles, and ensure the powder fluidity during laser cladding. When the inlet air temperature is 500 °C, the solvent evaporation rate and the surface tension of the particles reach a dynamic equilibrium, forming hollow spherical particles, ensuring the uniform dispersion of the nano-particles during the cladding process; too low temperature (such as 400 °C) leads to solvent residue and causes particle agglomeration; too high temperature (such as 600 °C) makes the particle surface harden and hinders the diffusion of the internal solvent, forming shell-core structure defects.

[0027] Detailed implementation mode Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present invention. It should be noted that the polyvinyl alcohol in the present invention has a CAS number: 9002-89-5, product number: 341584, and is purchased from Merck Chemical.

[0028] Example 1 In this embodiment, a wear-resistant nut is provided, and the preparation process steps include: (1) Take the raw materials and place them in a vacuum induction furnace for melting. The vacuum degree is 10 -3 Pa, the melting temperature is 1570 °C, keep warm for 1.5 h, and the oxygen content is 40 ppm; (2)Perform LF refining. First, add 90 kg / lot of lime to the LF refining furnace for desulfurization, and then add 35 kg / lot of calcium carbide for deep deoxidation in the later stage. The total refining time is 70 min. Subsequently, perform argon blowing and stirring with an argon flow rate of 12 L / min and a stirring time of 35 min; (3)Carry out continuous casting of square billets for the molten steel. Adjust the casting speed to 2.7 m / min, the specific water ratio to 1.2 L / kg, and the tundish temperature to 1170 °C, and continuously cast square billets of 150 mm × 150 mm. The composition of the billets is as follows: C 0.4%, Si 0.25%, Cr 4%, Ni 2.6%, Mo 2%, Nb 0.23%, B 0.15%, Ce 0.07%, Co 0.09%, Ti 0.05%, P 0.03%, S 0.02%, and the balance is Fe and other inevitable impurities; (4)Heat the billets to 1270 °C for melting, pour them into the mold under argon protection, and demold after pre-cooling the mold to 650 °C to obtain the rough nut blanks; (5)After demolding, perform heat treatment. First, carry out solution treatment at 1150 °C for 2.5 h and cool it to room temperature with water. Carry out aging treatment at 750 °C for 5.5 h and air-cool it to room temperature. Subsequently, heat it to 850 °C and hold for 17 min, then quench it into a molten salt of KNO3 and NaNO2 with a weight ratio of 5.5:4.5 at 250 °C and hold for 11 min, and then air-cool it to room temperature. Use Al2O3-TiO2 nanoparticles as the coating material and deposit it on the rough nut blanks by surface laser cladding. The laser power is 3.5 kW, the scanning speed is 9 mm / s, the overlapping rate is 35%, and finally, under the condition of argon protection with a flow rate of 17 L / min, a coating thickness of 120 μm is obtained. Subsequently, carry out post-treatment at 500 °C for 4.5 h to obtain the wear-resistant nut.

[0029] Among them, the preparation method of Al2O3-TiO2 nanoparticles includes: adding polyvinyl alcohol to deionized water to prepare a polyvinyl alcohol solution, adding Al2O3 nanopowder and TiO2 nanopowder and mixing them, and obtaining a mixed solution after ultrasonic dispersion for 70 min. Spray-dry the mixed solution with a feeding rate of 15 mL / min, control the inlet air temperature at 500 °C, and the outlet air temperature at 100 °C. Subsequently, heat it to 1150 °C at a heating rate of 7 °C / min, calcine for 3 h, and cool it with the furnace to obtain it. The dosage ratio of polyvinyl alcohol, deionized water, Al2O3 nanopowder, and TiO2 nanopowder is 2.5:75:1.2:22.

[0030] Example 2 In this example, a wear-resistant nut is provided, and the preparation process steps include: (1)Take the raw materials and place them in a vacuum induction furnace for melting, with a vacuum degree of 10 -3Pa, the melting temperature is 1550 - 1600 °C, keep warm for 1 - 2 h, and the oxygen content is 40 ppm; (2) Conduct LF refining. First, add 80 kg / lot of lime to the LF refining furnace for desulfurization, and add 30 kg / lot of calcium carbide for deep deoxidation in the later stage. The total refining time is 60 min; then conduct argon blowing and stirring, the argon gas flow rate is 10 L / min, and the stirring time is 30 min; (3) Continuously cast the molten steel into square billets, adjust the drawing speed to 2.5 m / min, the specific water ratio is 1.2 L / kg, the tundish temperature is 1150 °C, and continuously cast into 150 mm × 150 mm steel billets; the composition of the steel billets is as follows: C 0.3%, Si 0.2%, Cr 3.5%, Ni 2.4%, Mo 1.5%, Nb 0.1%, B 0.1%, Ce 0.05%, Co 0.06%, Ti 0.03%, P 0.03%, S 0.02%, and the balance is Fe and other inevitable impurities; (4) Heat the steel billet to 1250 °C for melting, pour it into the mold under argon protection, and demold after pre-cooling the mold to 600 °C to obtain the rough nut blank; (5) Conduct heat treatment after demolding. First, conduct solution treatment at 1100 °C for 2 h and cool it to room temperature with water; conduct aging treatment at 700 °C for 5 h and air-cool it to room temperature; then heat it to 800 °C and keep it warm for 15 min, quench it into a molten salt of KNO3 and NaNO2 with a weight ratio of 5:5 at 240 °C and keep it warm for 10 min, and then air-cool it to room temperature; Use Al2O3 - TiO2 nanoparticles as the coating material and deposit it on the rough nut blank by surface laser cladding. The laser power is 3 kW, the scanning speed is 8 mm / s, the overlapping rate is 30%, and finally, under the condition of argon protection with a flow rate of 15 L / min, a coating thickness of 120 μm is obtained. Then, conduct post-treatment at 450 °C for 4 h to obtain the wear-resistant nut.

[0031] Among them, the preparation method of Al2O3 - TiO2 nanoparticles includes: adding polyvinyl alcohol to deionized water to prepare a polyvinyl alcohol solution, adding Al2O3 nanopowder and TiO2 nanopowder and mixing them. After ultrasonic dispersion for 60 min, a mixed solution is obtained. Spray-dry the mixed solution, the feeding rate is 10 mL / min, control the inlet air temperature to be 450 °C, and the outlet air temperature to be 80 °C; then heat it to 1100 °C at a heating rate of 5 °C / min, calcine for 2 h, and cool it with the furnace to obtain; the dosage ratio of polyvinyl alcohol, deionized water, Al2O3 nanopowder and TiO2 nanopowder is 2:70:1:20.

[0032] Example 3 In this example, a wear-resistant nut is provided, and the preparation process steps include: (1) Take the raw materials and place them in a vacuum induction furnace for melting, and the vacuum degree is 10 -3Pa, the melting temperature is 1600 °C, keep warm for 2 h, and the oxygen content is 45 ppm; (2) Conduct LF refining. First, add 100 kg / lot of lime to the LF refining furnace for desulfurization, and later add 40 kg / lot of calcium carbide for deep deoxidation. The total refining time is 80 min; then conduct argon blowing and stirring, the argon gas flow rate is 15 L / min, and the stirring time is 40 min; (3) Continuously cast the molten steel into square billets. Adjust the casting speed to 3 m / min, the specific water ratio is 1.2 L / kg, the tundish temperature is 1200 °C, and continuously cast into 150 mm×150 mm steel billets; the composition of the steel billets is as follows: C 0.5%, Si 0.3%, Cr 4.5%, Ni 2.8%, Mo 2.5%, Nb 0.3%, B 0.2%, Ce 0.1%, Co 0.12%, Ti 0.07%, P 0.03%, S 0.02%, and the balance is Fe and other inevitable impurities; (4) Heat the steel billet to 1300 °C for melting, pour it into the mold under argon protection, and demold after pre-cooling the mold to 700 °C to obtain the rough nut blank; (5) Conduct heat treatment after demolding. First, conduct solution treatment at 1200 °C for 3 h, and cool it to room temperature with water; conduct aging treatment at 800 °C for 6 h, and air-cool it to room temperature; then heat it to 900 °C and keep warm for 20 min, quench it into a molten salt of KNO3 and NaNO2 with a weight ratio of 6:4 at 260 °C and keep warm for 12 min, and then air-cool it to room temperature; Use Al2O3-TiO2 nanoparticles as the coating material and deposit it on the rough nut blank by surface laser cladding. The laser power is 4 kW, the scanning speed is 10 mm / s, the overlapping rate is 40%, and finally obtain a coating thickness of 120 μm under the condition of argon protection with a flow rate of 20 L / min. Then conduct post-treatment at 550 °C for 5 h to obtain the wear-resistant nut.

[0033] Among them, the preparation method of Al2O3-TiO2 nanoparticles includes: adding polyvinyl alcohol to deionized water to prepare a polyvinyl alcohol solution, adding Al2O3 nanopowder and TiO2 nanopowder and mixing them. After ultrasonic dispersion for 80 min, a mixed solution is obtained. Spray-dry the mixed solution, the feeding rate is 20 mL / min, control the inlet air temperature to 550 °C, and the outlet air temperature to 120 °C; then heat it to 1200 °C at a heating rate of 10 °C / min, calcine for 4 h, and cool it with the furnace to obtain; the dosage ratio of polyvinyl alcohol, deionized water, Al2O3 nanopowder and TiO2 nanopowder is 3:80:1.4:24.

[0034] Example 4 In this example, a wear-resistant nut is provided, and the preparation process steps include: (1) Take the raw materials and place them in a vacuum induction furnace for melting, and the vacuum degree is 10 -3Pa, melting temperature is 1600 °C, holding for 1 h, oxygen content is 45 ppm; (2) Conduct LF refining. First, add 80 kg / lot of lime to the LF refining furnace for desulfurization, and later add 40 kg / lot of calcium carbide for deep deoxidation. The total refining time is 60 min. Subsequently, conduct argon blowing and stirring, with the argon flow rate being 15 L / min and the stirring time being 30 min; (3) Continuously cast the molten steel into square billets, adjust the casting speed to 3 m / min, specific water ratio to 1.2 L / kg, tundish temperature to 1150 °C, and continuously cast into 150 mm × 150 mm steel billets. The composition of the steel billets is as follows: C 0.5%, Si 0.2%, Cr 4.5%, Ni 2.4%, Mo 2.5%, Nb 0.1%, B 0.2%, Ce 0.05%, Co 0.12%, Ti 0.03%, P 0.03%, S 0.02%, and the balance is Fe and other inevitable impurities; (4) Heat the steel billets to 1250 °C for melting, pour them into the mold under argon protection, and demold after pre-cooling the mold to 700 °C to obtain rough nut blanks; (5) Conduct heat treatment after demolding. First, conduct solution treatment at 1100 °C for 3 h and cool it to room temperature with water. Conduct aging treatment at 700 °C for 6 h and air-cool it to room temperature. Subsequently, heat it to 800 °C and hold for 20 min, then quench it into a molten salt of KNO3 and NaNO2 with a weight ratio of 6:4 at 240 °C and hold for 12 min, and then air-cool it to room temperature. Use Al2O3-TiO2 nanoparticles as the coating material and deposit it on the rough nut blanks through surface laser cladding. The laser power is 3 kW, the scanning speed is 10 mm / s, the overlapping rate is 30%, and finally, a coating thickness of 120 μm is obtained under the condition of argon protection with a flow rate of 20 L / min. Subsequently, conduct post-treatment at 450 °C for 5 h to obtain the wear-resistant nuts.

[0035] Among them, the preparation method of Al2O3-TiO2 nanoparticles includes: adding polyvinyl alcohol to deionized water to prepare a polyvinyl alcohol solution, adding Al2O3 nano-powder and TiO2 nano-powder and mixing them. After ultrasonic dispersion for 60 min, a mixed solution is obtained. Spray-dry the mixed solution, with the feeding rate being 20 mL / min, control the inlet air temperature to 450 °C, and the outlet air temperature to 120 °C. Subsequently, heat it to 1200 °C at a heating rate of 5 °C / min and calcine for 2 h, and then cool it with the furnace to obtain it. The dosage ratio of polyvinyl alcohol, deionized water, Al2O3 nano-powder, and TiO2 nano-powder is 3:80:1:24.

[0036] Comparative Example 1 In Comparative Example 1, the Cr content in the steel billets is reduced to 2.5%, and the rest is the same as in Example 1. The preparation steps are the same as in Example 1.

[0037] Comparative Example 2 In Comparative Example 2, the weight ratio of Al2O3 nanopowder to TiO2 nanopowder in the coating material was adjusted to 0.5:24.5, and the rest was the same as in Example 1. The preparation steps were the same as in Example 1.

[0038] Comparative Example 3 In Comparative Example 3, the Al2O3-TiO2 nanoparticles in the coating material were replaced with Al2O3 nanoparticles, and the rest was the same as in Example 1. The preparation steps were the same as in Example 1.

[0039] Comparative Example 4 In Comparative Example 4, the Al2O3-TiO2 nanoparticles in the coating material were replaced with TiO2 nanoparticles, and the rest was the same as in Example 1. The preparation steps were the same as in Example 1.

[0040] Comparative Example 5 In Comparative Example 5, the weight ratio of KNO3 to NaNO2 in the molten salt was adjusted to 4:6, and the rest was the same as in Example 1. The preparation steps were the same as in Example 1.

[0041] Comparative Example 6 In Comparative Example 6, the step of quenching and holding in the molten salt was not included; the rest was the same as in Example 1. The preparation steps were the same as in Example 1.

[0042] Comparative Example 7 In Comparative Example 7, the inlet air temperature of spray drying was increased to 600 °C, and the rest was the same as in Example 1. The preparation steps were the same as in Example 1.

[0043] Test Example 1: The corrosion-resistant nuts prepared in the foregoing Examples 1-4 and Comparative Examples 1-7 were tested as follows: Tensile strength: Refer to GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature" to detect the tensile strength of the nuts at room temperature; Salt spray resistance: Refer to ASTM B117 standard, conduct a salt spray test using a 5% mass concentration of NaCl solution at 60 °C, and record the time when red rust appears on the surface; Acid resistance: Immerse the nuts in a 10% weight concentration of sulfuric acid aqueous solution for 30 days, and observe and record the outer surface of the nuts; Alkali resistance: Immerse the nuts in a 10% weight concentration of sodium hydroxide aqueous solution for 30 days, and observe and record the outer surface of the nuts; Wear resistance: Refer to ASTM G99-23, use a pin-on-disk wear tester, with a load of 50 N, a sliding speed of 0.5 m / s, and a wear time of 60 min, to measure the wear volume; The results are shown in Table 1 below: Table 1

[0044] As can be seen from the foregoing, the Cr element significantly improves the matrix strength through solid solution strengthening and carbide formation. In Examples 1-4, the Cr content is ≥3.5%, and the tensile strength is ≥1200 MPa. In Comparative Example 1, the tensile strength drops sharply to 980 MPa, a decrease of 22%. Elements such as Ni, Mo, and Nb further optimize the mechanical properties through grain refinement and precipitation strengthening. Among them, Example 3 (Cr 4.5%, Mo 2.5%, Nb 0.3%) has the highest tensile strength. The high hardness of Al2O3 and the chemical stability of TiO2 act synergistically to form a dense protective layer, achieving a red rust time of ≥800 h in Examples 1-4; there is no corrosion in both 10% sulfuric acid and NaOH; the salt spray resistance of Comparative Example 3 and Comparative Example 4 drops to about 500 h, and the wear resistance decreases by more than 50%. In Example 1, the surface layer structure is also refined by molten salt quenching, and the tensile strength reaches 1250 MPa; in Comparative Example 5 with a ratio of 4:6, due to the decrease in molten salt stability, the tensile strength decreases to 1050 MPa, and the salt spray resistance decreases synchronously. In Comparative Example 6, molten salt quenching is not carried out, and both the tensile strength and corrosion resistance are significantly lower than those of the examples, and the wear volume increases to 0.45 mm 3 , indicating insufficient coating adhesion. In addition, in Example 1, the inlet air temperature of 500 °C ensures uniform dispersion of nanoparticles and a dense coating; in Comparative Example 7, the inlet air temperature of 600 °C leads to particle agglomeration due to the too high temperature, and the salt spray resistance drops to 650 h, and the wear volume increases to 0.28 mm 3 .

[0045] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A process for preparing a wear-resistant nut, characterized in that the steps include: (1) Place the raw materials in a vacuum induction furnace for smelting, with a vacuum degree of ≤10 -3 Pa, melting temperature 1550-1600℃, heat preservation 1-2h, oxygen content <50ppm; (2) LF refining: first add 80-100 kg / furnace of lime to the LF refining furnace for desulfurization, then add 30-40 kg / furnace of calcium carbide for deep deoxidation, and the total refining time is 60-80 min; then argon blowing and stirring are performed; (3) The molten steel is continuously cast into square billets, the casting speed is adjusted to 2.5-3 m / min, the specific water content is 1.2 L / kg, the tundish temperature is 1150-1200 °C, and the billets are continuously cast into 150 mm × 150 mm billets; (4) The steel billet is heated to 1250-1300°C to melt, poured into the mold under argon protection, pre-cooled to 600-700°C in the mold, and then demolded to obtain a rough nut blank; (5) After demolding, heat treatment is performed, and Al2O3-TiO2 nanoparticles are used as a coating material by surface laser cladding on the nut blank, and post-treatment is performed at 450-550°C for 4-5h to obtain the wear-resistant nut.

2. The preparation process of a wear-resistant nut according to claim 1, characterized in that: The argon flow rate of the argon blowing stirring is 10-15 L / min, and the stirring time is 30-40 min.

3. The preparation process of a wear-resistant nut according to claim 1, characterized in that: The composition of the steel billet is as follows: C 0.3%-0.5%, Si 0.2%-0.3%, Cr 3.5%4.5%, Ni 2.4%-2.8%, Mo 1.5%-2.5%, Nb 0.1%-0.3%, B 0.1%-0.2%, Ce 0.05%-0.1%, Co 0.06%-0.12%, Ti 0.03%-0.07%, P≤0.03%, S≤0.02%, and the balance is Fe and other inevitable impurities.

4. According to the preparation process of a wear-resistant nut according to claim 1, the heat treatment step comprises: First, solution treatment is performed at 1100-1200°C for 2-3h, and then water-cooled to room temperature; Carry out aging treatment at 700-800℃ for 5-6h, air cool to room temperature; then heat to 800-900℃ and keep warm for 15-20min, quench into 240-260℃ molten salt and keep warm for 10-12min, and then air cool to room temperature.

5. The process for preparing a wear-resistant nut according to claim 4, characterized in that: The molten salt includes KNO3 and NaNO2 in a weight ratio of 5-6:4-5.

6. The process for preparing a wear-resistant nut according to claim 1, characterized in that: The preparation method of the Al2O3-TiO2 nanoparticles comprises: adding polyvinyl alcohol to deionized water to prepare a polyvinyl alcohol solution, adding Al2O3 nanopowder and TiO2 nanopowder to mix, ultrasonically dispersing for 60-80 minutes to obtain a mixed solution, spray-drying the mixed solution; then heating to 1100-1200°C at a heating rate of 5-10°C / min, calcining for 2-4 hours, and cooling in the furnace to obtain the obtained product.

7. The process for preparing a wear-resistant nut according to claim 6, characterized in that: The feed rate of the spray drying is 10-20 mL / min, the air inlet temperature is controlled to be 450-550°C, and the air outlet temperature is controlled to be 80-120°C.

8. The process for preparing a wear-resistant nut according to claim 6, characterized in that: The dosage ratio of the polyvinyl alcohol, deionized water, Al2O3 nanopowder and TiO2 nanopowder is (2-3): (70-80): (1-1.4): (20-24).

9. The process for preparing a wear-resistant nut according to claim 1, characterized in that: The surface laser cladding step has a laser power of 3-4kW, a scanning speed of 8-10mm / s, an overlap rate of 30-40%, and finally obtains a coating thickness of 100-150μm under argon protection conditions with a flow rate of 15-20L / min.

10. A corrosion-resistant nut, characterized in that: The corrosion-resistant nut is prepared by using the preparation process of the corrosion-resistant nut according to any one of claims 1 to 9.

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