Preparation method of soft and hard alternate wear-resistant reinforced layer

Abstract

The invention provides a preparation method of a soft and hard alternate wear-resistant reinforced layer, and relates to the field of surface treatment, comprising the following steps: step 1, pretreating a matrix; step 2, rare earth salt bath nitriding treatment: firstly preparing a dispersion colloid of bismuth trioxide nano crystal whiskers, a rare earth beta-diketone complex and bis (trifluoromethanesulfonyl) imine tributyl methyl quaternary phosphonium salt, sequentially adding a nitrogen source, sodium carbonate, sodium thiosulfate, potassium fluoborate and the composite rare earth system, and then adding the dispersion colloid and bismuth nitrate to obtain a rare earth salt bath agent; adding the pretreated matrix into a rare earth salt bath agent to obtain a nitrogen oxide layer; and step 3, laser irradiation treatment: in an argon atmosphere, strip-shaped laser irradiation is carried out on the surface of the nitrogen oxide layer at intervals by adopting a laser melting process. According to the method, a soft and hard alternate structure is prepared on the surface of the low-carbon steel through the means of combining rare earth salt bath and laser irradiation, and the wear resistance of the low-carbon steel is effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of surface treatment, and in particular to a method for preparing a soft and hard alternating wear-resistant strengthening layer. Background Art

[0002] Low-carbon steel (such as AF1410 and 17-4PH) boasts excellent ductility and toughness (elongation exceeding 25%), outstanding weldability, good cold-working formability, and adaptability to surface treatments. It is widely used in construction, automotive manufacturing, appliance housings, aerospace, and new energy sectors. However, low-carbon steel suffers from relatively low strength and hardness (yield strength of approximately 195-275 MPa, tensile strength of approximately 315-430 MPa, and annealed strength of approximately 130-180 HBW), resulting in high wear from contact friction and poor machinability (prone to sticking during cutting, resulting in rapid tool wear). Furthermore, due to its low carbon content, conventional quenching cannot be used to increase its surface hardness, severely limiting its service life and range of applications. Laser is an ideal heat source and is often used for processing and strengthening of material surfaces. For alloy steels with high carbon content, such as 40Cr, 40CrNiMo, 5CrNiMo, and 45 steel, laser surface quenching and laser melting are often used. A high-energy laser beam is scanned on the workpiece surface to rapidly increase the surface temperature of the material. The material then rapidly cools down by its own action to form high-carbon martensite, achieving the purpose of strengthening the material and significantly improving the surface hardness, wear resistance and other properties of the material. However, for low-carbon steel, direct laser quenching or laser melting irradiation will instead have a tempering effect, causing the hardness of the laser irradiated area to decrease. Summary of the Invention

[0003] In response to the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing a soft and hard alternating wear-resistant strengthening layer. This method combines a rare earth salt bath with laser irradiation to prepare a "soft and hard" alternating structure on the surface of low-carbon steel, thereby effectively improving the wear resistance of low-carbon steel.

[0004] The purpose of the present invention is achieved through the following technical solutions: A method for preparing a soft and hard alternating wear-resistant strengthening layer, comprising: Step 1: Matrix pretreatment: Clean the surface of the mild steel to remove impurities and grease on the surface of the mild steel; Step 2: Rare earth salt bath nitriding treatment: First, bismuth trioxide nanowhiskers and rare earth β-diketone complexes are added to a liquid of bis(trifluoromethanesulfonyl)imide tributylmethyl quaternary phosphonium salt, ultrasonically dispersed at 55-65°C, and vacuum dried to form a dispersed colloid; then, a nitrogen source, sodium carbonate, sodium thiosulfate, and potassium fluoroborate are added in proportion in a nitriding furnace, the temperature is increased, and the mixture is stirred evenly; then, the composite rare earth system is slowly added to the nitriding furnace, the temperature is increased, and nitrogen is introduced; finally, the dispersed colloid and bismuth nitrate are added to the nitriding furnace and stirred evenly to obtain a rare earth salt bath agent; The pretreated substrate is added to a rare earth salt bath, subjected to rare earth nitriding treatment at 510-540°C for 2-3 hours, and cooled to form a nitrogen oxide layer on the surface of the substrate; Step 3: Laser irradiation treatment: In an argon atmosphere, a laser melting process is used to perform strip laser irradiation on the surface of the nitride oxide layer to obtain a "soft and hard" alternating structure.

[0005] Based on further optimization of the above scheme, the substrate adopts either AF1410 or 17-4PH low carbon steel; the substrate pretreatment is specifically as follows: first, ultrasonic cleaning with acetone for 8 to 12 minutes, pickling with 10% hydrochloric acid for 3 to 5 minutes, rinsing with distilled water for 8 to 12 minutes, and then blowing the substrate surface dry.

[0006] Based on further optimization of the above scheme, the rare earth β-diketone complex uses any one of lanthanum acetylacetonate, cerium acetylacetonate, and neodymium acetylacetonate, the rare earth β-diketone complex accounts for 10% to 15% of the mass of the bismuth trioxide nanowhiskers, and the mass-to-volume ratio of the bismuth trioxide nanowhiskers to bis(trifluoromethanesulfonyl)imide tributylmethyl quaternary phosphonium salt is 1 to 1.2 g: 4.8 to 5.2 mL.

[0007] Based on further optimization of the above solution, the particle size of the bismuth trioxide nanowhiskers is 20 to 50 nm.

[0008] Based on further optimization of the above scheme, the vacuum drying temperature for preparing the dispersed colloid in step 2 is 120-150° C. and the time is 40-60 min to remove trace moisture in the dispersed colloid and avoid hydrolysis during the salt bath process.

[0009] Based on further optimization of the above scheme, the weight percentage of each component in the rare earth salt bath agent is: nitrogen source 48% to 52%, sodium carbonate 16% to 20%, sodium thiosulfate 6% to 10%, potassium fluoroborate 4% to 6%, composite rare earth system 4.5% to 7%, bismuth trioxide whiskers 1.5% to 2%, and bismuth nitrate 0.8% to 1.2%; wherein, the nitrogen source is urea and dicyandiamide, and the mass ratio of urea to dicyandiamide is 5 to 8:1.

[0010] Based on further optimization of the above scheme, the composite rare earth system includes lanthanum titanate, cerium carbonate and neodymium oxide, and their mass ratio is 2:2:0.3-0.5.

[0011] Based on further optimization of the above scheme, after adding the nitrogen source, sodium carbonate, sodium thiosulfate and potassium fluoroborate in step 2, the temperature is rapidly increased to 280°C to 320°C at a heating rate of 4 to 6°C / min and stirred for 8 to 12 minutes to melt the basic salts such as the nitrogen source, sodium carbonate and sodium thiosulfate; after adding the composite rare earth salt system, the temperature is increased to 420 to 450°C at a heating rate of 2 to 3°C / min and kept warm for 25 to 35 minutes, and the nitrogen flow rate introduced is 480 to 520 mL / min; after adding the dispersed colloid and bismuth nitrate, the stirring time is 12 to 15 minutes.

[0012] Based on further optimization of the above scheme, the laser irradiation power is 400-600W, the spot diameter is 2mm, the defocus amount is 2cm, the scanning speed is 5-20mm / s; the width of the laser irradiation area is 2.8mm, and the distance between adjacent strip laser irradiations is 2-4mm.

[0013] Urea and dicyandiamide are used as nitrogen sources for rare earth salt bath nitriding. The different decomposition rates of urea and dicyandiamide are utilized to adapt to the requirements of both hardening layer depth and toughness in the nitriding process of the low carbon steel surface. At the same time, urea, dicyandiamide and rare earth ions in the composite rare earth system form stable complexes to reduce the toxicity of the salt bath and its corrosion to equipment. In addition, the carbon-oxygen groups produced by the decomposition of urea can form a trace carbonitriding effect on the surface of the low carbon steel, increase surface active sites, and promote the adsorption of nitrogen atoms. The nitrogen molecules decomposed by dicyandiamide, under the catalysis of rare earth ions, penetrate into the gaps in the low carbon steel matrix to form a deeper diffusion layer, thereby avoiding the problem of increased brittleness of the nitrided layer of low carbon steel due to insufficient carbon content.

[0014] Using sodium carbonate as a co-stabilizer not only effectively lowers the melting point of the salt bath, improves fluidity, and inhibits volatilization and component depletion, but also effectively promotes the dissolution and ionization of rare earth element oxides. Ionized rare earth elements reduce the nitrogen diffusion activation energy and increase the nitriding rate. The addition of sodium thiosulfate provides sulfur atoms during the salt bath process. The synergistic effect of sulfur and nitrogen atoms refines the nitride grains in the nitride layer, reducing the risk of spalling caused by the brittle nitride phase. Furthermore, the strong reducing properties of sodium thiosulfate inhibit the over-oxidation of rare earth ions in the rare earth system, thereby maintaining the nitrogen-promoting effect of rare earth ions and improving the uniformity and density of the nitride layer. The addition of potassium fluoroborate further reduces the nitrogen diffusion activation energy and improves wear resistance. Fluoride and boron ions simultaneously destroy the oxide film on the mild steel surface, increase vacancy concentration, and promote the diffusion of nitrogen and boron (i.e., the boride layer acts as a supporting framework, while nitrogen fills the gaps). This creates a gentle hardness gradient and enhances the bonding strength of the nitride layer.

[0015] Through a composite rare earth system composed of lanthanum titanate, cerium carbonate and neodymium oxide, lanthanum is used as a Lewis acid site to adsorb and activate nitrogen atoms in the salt bath, prompting them to chemically react with the surface of low-carbon steel; cerium is used to increase the adsorption and diffusion effects of active nitrogen atoms in the nitriding reaction, reduce surface defects, and improve the density and hardness of the nitride layer; the lattice distortion caused by the penetration of neodymium into the surface of low-carbon steel is used to inhibit the coarsening of nitride grains in the salt bath process, thereby promoting a gentle hardness gradient in the diffusion layer; that is, the composite rare earth system effectively promotes the adsorption and diffusion of nitrogen atoms, increases their diffusion rate into the matrix, and thereby enhances the interfacial bonding force. At the same time, the composite rare earth system is combined with sodium carbonate, sodium thiosulfate, potassium fluoroborate, etc. to form a multi-component composite diffusion layer on the surface of low-carbon steel, which not only improves the hardness and wear resistance of the diffusion layer surface, but also avoids problems such as segregation and shallow diffusion layer; and the multi-component composite diffusion layer has a gentle hardness gradient and elastic modulus gradient, forming a thermal expansion gradient during the subsequent laser irradiation process, thereby effectively reducing the problems of cracks and diffusion layer fracture caused by sudden changes in hardness in the process of laser irradiation weakening the nitride layer, ensuring the smooth formation of the "soft and hard" phase structure.

[0016] By adding dispersed colloid and bismuth nitrate, bismuth nitrate is preferentially decomposed to produce Bi 3+It forms a low-melting-point eutectic with the iron element on the surface of low-carbon steel, reducing the softening threshold of the subsequent laser irradiation area. Subsequently, bismuth trioxide nanowhiskers are embedded in the diffusion layer in a monodisperse state, effectively strengthening the nitride layer and forming a nano-scale multi-component composite gradient, avoiding cracks caused by hardness and temperature changes during laser irradiation; at the same time, the nano-reinforced bismuth compound infiltrated into the matrix inhibits the crack propagation in the irradiated and non-irradiated areas during laser irradiation through crack deflection and dislocation accumulation, further avoiding the generation of cracks in the diffusion layer during laser irradiation; in addition, the multi-component composite structure based on bismuth elements can also effectively prevent oxygen atoms from diffusing into the interior, reduce the generation of intergranular oxidation cracks during laser irradiation, and at the same time inhibit the generation of brittle phases in low-carbon steel, ensure a smooth hardness gradient, and avoid stress concentration during laser irradiation.

[0017] The following are the technical effects of the solution of the present invention: The present invention provides a wear-resistant strengthening layer with alternating "soft and hard" layers. First, a high-hardness oxynitride layer is prepared on the surface of a low-carbon steel substrate such as AF1410 or 17-4PH using a specific rare earth salt bath agent. The oxynitride layer is then weakened by intermittent laser irradiation, thereby forming a wear-resistant structure with alternating "soft and hard" layers on the surface of the low-carbon steel substrate. The bonding strength between the oxynitride layer and the substrate is high, and no obvious cracks exist on the surface of the oxynitride layer after laser irradiation. The method not only utilizes local burning caused by laser irradiation to form nano-scale parabolic pits on the surface of the carburized layer, and utilizes the oil storage and grinding storage functions of the pits to reduce wear during friction and wear and improve the wear resistance of the low-carbon steel, but also utilizes a bionic striped structure with alternating "soft and hard" layers (i.e., the hardness of the irradiated area is relatively low and the hardness of the non-irradiated area is relatively high) (such as the back surface of a dung beetle or the surface of a shell) to improve the overall fatigue resistance and wear resistance of the low-carbon steel surface. In addition, after intermittent laser irradiation, the non-irradiated high-hardness area is approximately trapezoidal as a whole. Compared with the traditional parabolic linear shape, the reinforced unit has better load-bearing resistance, stronger hardness and wear resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the "soft and hard" alternating structure in an embodiment of the present invention.

[0019] Figure 2 It is a longitudinal cross-sectional view of the "soft and hard" alternating structure in an embodiment of the present invention.

[0020] Figure 3 This is a cross-sectional microscopic morphology of the surface of AF1410 low-carbon steel after rusting in an embodiment of the present invention.

[0021] Among them, 10, irradiated area; 20, non-irradiated area; 30, low carbon steel substrate. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly described below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0023] Example 1: A method for preparing a soft and hard alternating wear-resistant strengthening layer, wherein the substrate is AF1410 low-carbon steel, comprising: Step 1: Surface pretreatment of the low-carbon steel substrate: Clean the surface of the low-carbon steel substrate to remove impurities and grease on the surface of the low-carbon steel; specifically: first use acetone ultrasonic cleaning for 8 minutes (degreasing), pickling with 10% hydrochloric acid for 3 minutes (rust removal), and rinsing with distilled water for 8 minutes (removing the cleaning agent), and then blow dry the substrate surface.

[0024] Step 2: rare earth salt bath nitriding treatment: The weight percentages of the components in the rare earth salt bath are: nitrogen source 48%, sodium carbonate 20%, sodium thiosulfate 6%, potassium fluoroborate 6%, composite rare earth system 4.5%, bismuth trioxide whiskers 2%, and bismuth nitrate 1.2%.

[0025] First, bismuth trioxide nanowhiskers and a rare earth β-diketone complex were added to a solution of bis(trifluoromethanesulfonyl)imide tributylmethyl quaternary phosphonium salt (CAD: 324575-10-2). The particle size of the bismuth trioxide nanowhiskers was 20-50 nm, and the rare earth β-diketone complex was cerium acetylacetonate (CAS: 15653-01-7). The rare earth β-diketone complex accounted for 10% of the mass of the bismuth trioxide nanowhiskers, and the mass-to-volume ratio of the bismuth trioxide nanowhiskers to the tributylmethyl quaternary phosphonium salt was 1 g:4.8 mL. After ultrasonic dispersion at 55°C, the solution was vacuum dried at 120°C for 60 minutes to remove trace moisture from the dispersed colloid and prevent hydrolysis during the salt bath, thereby forming a dispersed colloid.

[0026] Afterwards, a nitrogen source, sodium carbonate, sodium thiosulfate and potassium fluoroborate were added to the nitriding furnace in proportion. The nitrogen source was urea and dicyandiamide, and the mass ratio of urea to dicyandiamide was 5:1. The temperature was rapidly raised to 280°C at a heating rate of 4°C / min and stirred for 12 minutes to melt the basic salts such as the nitrogen source, sodium carbonate and sodium thiosulfate. Then, a composite rare earth system was slowly added to the nitriding furnace. The composite rare earth system included lanthanum titanate, cerium carbonate and neodymium oxide in a mass ratio of 2:2:0.3. The temperature was raised to 420°C at a heating rate of 2°C / min and kept warm for 35 minutes. Nitrogen was introduced at a nitrogen flow rate of 480 mL / min. Finally, the dispersed colloid and bismuth nitrate were added to the nitriding furnace, stirred evenly for 15 minutes, and a rare earth salt bath was obtained. The pretreated substrate was added to a rare earth salt bath and subjected to rare earth nitriding treatment at 510°C for 5 hours. After cooling, a nitride oxide layer (the thickness of the nitride oxide layer was 50 μm) was formed on the surface of the substrate.

[0027] Step 3: Laser irradiation treatment: In an argon atmosphere, laser melting process is used to perform strip laser irradiation on the surface of the nitride oxide layer at intervals. The laser irradiation power is 600W, the spot diameter is 2mm, the defocus distance is 2cm, and the scanning speed is 5mm / s. The width of the laser irradiation area is 2.8mm, and the distance between adjacent strip laser irradiations (i.e. the width of the non-irradiated area) is 4mm. A "soft and hard" alternating structure (such as Figure 1 or Figure 2 shown).

[0028] Example 2: A method for preparing a soft and hard alternating wear-resistant strengthening layer, wherein the substrate is AF1410 low-carbon steel, comprising: Step 1: Surface pretreatment of the low-carbon steel substrate: Clean the surface of the low-carbon steel substrate to remove impurities and grease on the surface of the low-carbon steel; specifically: first use acetone ultrasonic cleaning for 10 minutes (degreasing), pickling with 10% hydrochloric acid for 4 minutes (rust removal), and rinsing with distilled water for 10 minutes (removing the cleaning agent), and then blow dry the substrate surface.

[0029] Step 2: rare earth salt bath nitriding treatment: The weight percentage of each component in the rare earth salt bath is: nitrogen source 50%, sodium carbonate 18%, sodium thiosulfate 8%, potassium fluoroborate 5%, composite rare earth system 5.75%, bismuth trioxide whiskers 1.75%, and bismuth nitrate 1%.

[0030] First, bismuth trioxide nanowhiskers and a rare earth β-diketone complex were added to a solution of bis(trifluoromethanesulfonyl)imide tributylmethyl quaternary phosphonium salt (CAD: 324575-10-2). The particle size of the bismuth trioxide nanowhiskers was 20-50 nm, and the rare earth β-diketone complex was lanthanum acetylacetonate (CAS: 64424-12-0). The rare earth β-diketone complex accounted for 12% of the mass of the bismuth trioxide nanowhiskers, and the mass-to-volume ratio of the bismuth trioxide nanowhiskers to the tributylmethyl quaternary phosphonium salt was 1.1 g:5 mL. The bismuth trioxide nanowhiskers were ultrasonically dispersed at 55-65°C and then vacuum dried at 135°C for 50 minutes to remove trace moisture from the dispersed colloid and prevent hydrolysis during the salt bath, thereby forming a dispersed colloid.

[0031] Afterwards, a nitrogen source, sodium carbonate, sodium thiosulfate and potassium fluoroborate were added to the nitriding furnace in proportion. The nitrogen source used was urea and dicyandiamide, and the mass ratio of urea to dicyandiamide was 6.5:1. The temperature was rapidly raised to 300°C at a heating rate of 5°C / min and stirred for 10 minutes to melt the basic salts such as the nitrogen source, sodium carbonate and sodium thiosulfate. Then, a composite rare earth system was slowly added to the nitriding furnace. The composite rare earth system included lanthanum titanate, cerium carbonate and neodymium oxide in a mass ratio of 2:2:0.4. The temperature was raised to 435°C at a heating rate of 2.5°C / min and kept warm for 30 minutes. Nitrogen was introduced at a nitrogen flow rate of 500 mL / min. Finally, the dispersed colloid and bismuth nitrate were added to the nitriding furnace, stirred evenly for 13.5 minutes to obtain a rare earth salt bath. The pretreated substrate was added to a rare earth salt bath and subjected to rare earth nitriding treatment at 525°C for 4 hours. After cooling, a nitride oxide layer (the thickness of the nitride oxide layer was 40 μm) was formed on the surface of the substrate.

[0032] Step 3: Laser irradiation treatment: In an argon atmosphere, laser melting process is used to perform strip laser irradiation on the surface of the nitride oxide layer at intervals. The laser irradiation power is 500W, the spot diameter is 2mm, the defocus distance is 2cm, and the scanning speed is 12mm / s. The width of the laser irradiation area is 2.8mm, and the distance between adjacent strip laser irradiations (i.e. the width of the non-irradiated area) is 3mm. A "soft and hard" alternating structure (such as Figure 1 or Figure 2 shown).

[0033] The final microscopic morphology of the "soft and hard" interphase structure and the matrix is ​​shown in the figure. Figure 3 shown.

[0034] Example 3: A method for preparing a soft and hard alternating wear-resistant strengthening layer, wherein the substrate is 17-4PH low-carbon steel, comprising: Step 1: Matrix pretreatment: Clean the surface of the low-carbon steel matrix to remove impurities and grease on the surface of the low-carbon steel; specifically, first use acetone ultrasonic cleaning for 12 minutes (degreasing), pickling with 10% hydrochloric acid for 5 minutes (rust removal), and rinsing with distilled water for 12 minutes (removing the cleaning agent), and then blow dry the matrix surface.

[0035] Step 2: rare earth salt bath nitriding treatment: The weight percentage of each component in the rare earth salt bath is: nitrogen source 52%, sodium carbonate 16%, sodium thiosulfate 10%, potassium fluoroborate 4%, composite rare earth system 7%, bismuth trioxide whiskers 1.5%, and bismuth nitrate 0.8%.

[0036] First, bismuth trioxide nanowhiskers and a rare earth β-diketone complex were added to a solution of bis(trifluoromethanesulfonyl)imide tributylmethyl quaternary phosphonium salt (CAD: 324575-10-2). The bismuth trioxide nanowhiskers had a particle size of 20-50 nm and the rare earth β-diketone complex was neodymium acetylacetonate (CAS: 14589-38-9). The rare earth β-diketone complex accounted for 15% of the bismuth trioxide nanowhiskers' mass. The mass-to-volume ratio of bismuth trioxide nanowhiskers to bis(trifluoromethanesulfonyl)imide tributylmethyl quaternary phosphonium salt was 1.2 g:5.2 mL. The solution was ultrasonically dispersed at 65°C and then vacuum dried at 150°C for 40 minutes to remove trace moisture from the dispersed colloid and prevent hydrolysis during the salt bath, thereby forming a dispersed colloid.

[0037] Afterwards, a nitrogen source, sodium carbonate, sodium thiosulfate and potassium fluoroborate were added to the nitriding furnace in proportion. The nitrogen source used was urea and dicyandiamide, and the mass ratio of urea to dicyandiamide was 8:1. The temperature was rapidly raised to 320°C at a heating rate of 6°C / min and stirred for 8 minutes to melt the basic salts such as the nitrogen source, sodium carbonate and sodium thiosulfate. Then, a composite rare earth system was slowly added to the nitriding furnace. The composite rare earth system included lanthanum titanate, cerium carbonate and neodymium oxide in a mass ratio of 2:2:0.5. The temperature was raised to 450°C at a heating rate of 3°C / min and kept warm for 25 minutes. Nitrogen was introduced at a nitrogen flow rate of 520 mL / min. Finally, the dispersed colloid and bismuth nitrate were added to the nitriding furnace, stirred evenly for 12 minutes, and a rare earth salt bath was obtained. The pretreated substrate was added to a rare earth salt bath and subjected to rare earth nitriding treatment at 540°C for 3 hours. After cooling, a nitride oxide layer (the thickness of the nitride oxide layer was 30 μm) was formed on the surface of the substrate.

[0038] Step 3: Laser irradiation treatment: In an argon atmosphere, laser melting process is used to perform strip laser irradiation on the surface of the nitride oxide layer at intervals. The laser irradiation power is 400W, the spot diameter is 2mm, the defocus distance is 2cm, and the scanning speed is 20mm / s. The width of the laser irradiation area is 2.8mm, and the distance between adjacent strip laser irradiations (i.e. the width of the non-irradiated area) is 2mm. A "soft and hard" alternating structure (such as Figure 1 or Figure 2 shown).

[0039] Comparative Example 1: A method for preparing a wear-resistant layer on the surface of low-carbon steel, wherein the substrate is AF1410 low-carbon steel, comprising: Step 1: Substrate pretreatment: the same as that in Example 2.

[0040] Step 2: rare earth salt bath nitriding treatment: the steps are the same as those in Example 2, except that the potassium fluoroborate in Example 2 is replaced by potassium borate.

[0041] Step 3: Laser irradiation treatment: the same as the steps in Example 2.

[0042] Comparative Example 2: A method for preparing a wear-resistant layer on the surface of low-carbon steel, wherein the substrate is AF1410 low-carbon steel, comprising: Step 1: Substrate pretreatment: the same as that in Example 2.

[0043] Step 2: rare earth salt bath nitriding treatment: the steps are the same as those in Example 2, except that the potassium fluoroborate in Example 2 is replaced by potassium fluoride.

[0044] Step 3: Laser irradiation treatment: the same as the steps in Example 2.

[0045] Comparative Example 3: A method for preparing a wear-resistant layer on the surface of low-carbon steel, wherein the substrate is AF1410 low-carbon steel, comprising: Step 1: Substrate pretreatment: the same as that in Example 2.

[0046] Step 2: rare earth salt bath nitriding treatment: The weight percentages of the components in the rare earth salt bath are: nitrogen source 50%, sodium carbonate 18%, sodium thiosulfate 8%, potassium fluoroborate 5%, composite rare earth system 5.75%, and bismuth trioxide whiskers 1.75%.

[0047] First, bismuth trioxide nanowhiskers and a rare earth β-diketone complex were added to a solution of bis(trifluoromethanesulfonyl)imide tributylmethyl quaternary phosphonium salt (CAD: 324575-10-2). The bismuth trioxide nanowhiskers had a particle size of 20-50 nm and the rare earth β-diketone complex was lanthanum acetylacetonate (CAS: 64424-12-0). The rare earth β-diketone complex accounted for 13% of the bismuth trioxide nanowhiskers' mass. The mass-to-volume ratio of bismuth trioxide nanowhiskers to tributylmethyl quaternary phosphonium salt was 1.1 g:5.2 mL. The bismuth trioxide nanowhiskers were ultrasonically dispersed at 55-65°C and then vacuum dried at 135°C for 50 minutes to remove trace moisture from the dispersed colloid and prevent hydrolysis during the salt bath, thereby forming a dispersed colloid.

[0048] Afterwards, a nitrogen source, sodium carbonate, sodium thiosulfate and potassium fluoroborate were added to the nitriding furnace in proportion. The nitrogen source was urea and dicyandiamide, and the mass ratio of urea to dicyandiamide was 6.5:1. The temperature was rapidly raised to 300°C at a heating rate of 5°C / min and stirred for 10 minutes to melt the basic salts such as the nitrogen source, sodium carbonate and sodium thiosulfate. Then, a composite rare earth system was slowly added to the nitriding furnace. The composite rare earth system included lanthanum titanate, cerium carbonate and neodymium oxide in a mass ratio of 2:2:0.4. The temperature was raised to 435°C at a heating rate of 2.5°C / min and kept warm for 30 minutes. Nitrogen was introduced at a nitrogen flow rate of 500 mL / min. Finally, the dispersed colloid was added to the nitriding furnace and stirred evenly for 13.5 minutes to obtain a rare earth salt bath. The pretreated substrate was added to a rare earth salt bath and subjected to rare earth nitriding treatment at 525°C for 4 hours. After cooling, a nitride oxide layer (the thickness of the nitride oxide layer was 40 μm) was formed on the surface of the substrate.

[0049] Step 3: Laser irradiation treatment: the same as the steps in Example 2.

[0050] Comparative Example 4: A method for preparing a wear-resistant layer on the surface of low-carbon steel, wherein the substrate is AF1410 low-carbon steel, comprising: Step 1: Substrate pretreatment: the same as that in Example 2.

[0051] Step 2: rare earth salt bath nitriding treatment: The weight percentage of each component in the rare earth salt bath agent is: nitrogen source 50%, sodium carbonate 18%, sodium thiosulfate 8%, potassium fluoroborate 5%, composite rare earth system 5.75%, and bismuth nitrate 13.25%.

[0052] A nitrogen source, sodium carbonate, sodium thiosulfate and potassium fluoroborate were added to the nitriding furnace in proportion. The nitrogen source was urea and dicyandiamide, and the mass ratio of urea to dicyandiamide was 6.5:1. The temperature was rapidly increased to 300°C at a heating rate of 5°C / min and stirred for 10 minutes to melt the basic salts such as the nitrogen source, sodium carbonate and sodium thiosulfate. A composite rare earth system was then slowly added to the nitriding furnace. The composite rare earth system included lanthanum titanate, cerium carbonate and neodymium oxide in a mass ratio of 2:2:0.4. The temperature was increased to 435°C at a heating rate of 2.5°C / min and kept warm for 30 minutes. Nitrogen was introduced at a nitrogen flow rate of 500 mL / min. Finally, bismuth nitrate was added to the nitriding furnace and stirred evenly for 13.5 minutes to obtain a rare earth salt bath. The pretreated substrate was added to a rare earth salt bath and subjected to rare earth nitriding treatment at 525°C for 4 hours. After cooling, a nitride oxide layer (the thickness of the nitride oxide layer was 40 μm) was formed on the surface of the substrate.

[0053] Step 3: Laser irradiation treatment: the same as the steps in Example 2.

[0054] Comparative Example 5: A method for preparing a wear-resistant layer on the surface of low-carbon steel, wherein the substrate is AF1410 low-carbon steel, comprising: Step 1: Substrate pretreatment: the same as that in Example 2.

[0055] Step 2: rare earth salt bath nitriding treatment: The weight percentage of each component in the rare earth salt bath is: nitrogen source 50%, sodium carbonate 18%, sodium thiosulfate 8%, potassium fluoroborate 5%, composite rare earth system 5.75%, bismuth trioxide whiskers 1.75%, and bismuth nitrate 1%.

[0056] First, bismuth trioxide nanowhiskers and a rare earth β-diketone complex were added to a solution of bis(trifluoromethanesulfonyl)imide tributylmethyl quaternary phosphonium salt (CAD: 324575-10-2). The particle size of the bismuth trioxide nanowhiskers was 20-50 nm, and the rare earth β-diketone complex was lanthanum acetylacetonate (CAS: 64424-12-0). The rare earth β-diketone complex accounted for 12% of the mass of the bismuth trioxide nanowhiskers, and the mass-to-volume ratio of the bismuth trioxide nanowhiskers to the tributylmethyl quaternary phosphonium salt was 1.1 g:5 mL. The bismuth trioxide nanowhiskers were ultrasonically dispersed at 55-65°C and then vacuum dried at 135°C for 50 minutes to remove trace moisture from the dispersed colloid and prevent hydrolysis during the salt bath, thereby forming a dispersed colloid.

[0057] Afterwards, a nitrogen source, sodium carbonate, sodium thiosulfate and potassium fluoroborate were added to the nitriding furnace in proportion. The nitrogen source used was urea and dicyandiamide, and the mass ratio of urea to dicyandiamide was 6.5:1. The temperature was rapidly raised to 300°C at a heating rate of 5°C / min and stirred for 10 minutes to melt the basic salts such as the nitrogen source, sodium carbonate and sodium thiosulfate. Then, a composite rare earth system was slowly added to the nitriding furnace. The composite rare earth system included lanthanum titanate and cerium carbonate in a mass ratio of 2:2. The temperature was raised to 435°C at a heating rate of 2.5°C / min and kept warm for 30 minutes. Nitrogen was introduced at a nitrogen flow rate of 500 mL / min. Finally, the dispersed colloid and bismuth nitrate were added to the nitriding furnace, stirred evenly for 13.5 minutes, and a rare earth salt bath was obtained. The pretreated substrate was added to a rare earth salt bath and subjected to rare earth nitriding treatment at 525°C for 4 hours. After cooling, a nitride oxide layer (the thickness of the nitride oxide layer was 40 μm) was formed on the surface of the substrate.

[0058] Step 3: Laser irradiation treatment: the same as the steps in Example 2.

[0059] The samples prepared in Examples 1 to 3 and the samples prepared in Comparative Examples 1 to 5 were subjected to hardness tests and wear tests (the hardness test was conducted using a Vickers hardness tester with a load of 0.98 N; the wear test was conducted using a ball-on-disc wear test with a load of 10 N, a rotation speed of 200 rpm, and a stroke of 1000 m, and the worn surface was observed). The test results are shown in the following table:

[0060] It is clear from the above table that the present invention, through a specific rare earth salt bath, can not only provide a nitride oxide layer with high hardness and good wear resistance for the surface of low-carbon steel, but also avoid the stress concentration, microcracks or crack propagation caused by the sudden change in hardness and the influence of temperature during laser irradiation, thereby ensuring the overall wear resistance and avoiding the problems of microcracks extending during wear, such as fracture of the carburized layer and even peeling.

Claims

1. A method for preparing a soft and hard alternating wear-resistant strengthening layer, characterized by: include: Step 1: Matrix pretreatment: Clean the surface of the mild steel to remove impurities and grease on the surface of the mild steel; Step 2: Rare earth salt bath nitriding treatment: First, bismuth trioxide nanowhiskers and rare earth β-diketone complexes are added to a liquid of bis(trifluoromethanesulfonyl)imide tributylmethyl quaternary phosphonium salt, ultrasonically dispersed at 55-65°C, and vacuum dried to form a dispersed colloid; then, a nitrogen source, sodium carbonate, sodium thiosulfate, and potassium fluoroborate are added in proportion in a nitriding furnace, the temperature is increased, and the mixture is stirred evenly; then, the composite rare earth system is slowly added to the nitriding furnace, the temperature is increased, and nitrogen is introduced; finally, the dispersed colloid and bismuth nitrate are added to the nitriding furnace and stirred evenly to obtain a rare earth salt bath agent; The pretreated substrate is added to a rare earth salt bath, subjected to rare earth nitriding treatment at 510-540°C for 2-3 hours, and cooled to form a nitrogen oxide layer on the surface of the substrate; Step 3: Laser irradiation treatment: In an argon atmosphere, laser melting technology is used to perform strip laser irradiation on the surface of the nitride oxide layer at intervals to obtain a "soft and hard" alternating structure.

2. The method for preparing a soft and hard alternating wear-resistant strengthening layer according to claim 1, characterized in that: The substrate is made of either AF1410 or 17-4PH low-carbon steel. The substrate pretreatment is specifically as follows: first, ultrasonic cleaning with acetone for 8 to 12 minutes, pickling with 10% hydrochloric acid for 3 to 5 minutes, rinsing with distilled water for 8 to 12 minutes, and then blowing the substrate surface dry.

3. The method for preparing a soft and hard alternating wear-resistant strengthening layer according to claim 1 or 2, characterized in that: The rare earth β-diketone complex is any one of lanthanum acetylacetonate, cerium acetylacetonate, and neodymium acetylacetonate. The rare earth β-diketone complex accounts for 10% to 15% of the mass of the bismuth trioxide nanowhiskers. The mass-to-volume ratio of the bismuth trioxide nanowhiskers to bis(trifluoromethanesulfonyl)imide tributylmethyl quaternary phosphonium salt is 1 to 1.2 g: 4.8 to 5.2 mL.

4. The method for preparing a soft and hard alternating wear-resistant strengthening layer according to claim 1 or 3, characterized in that: The particle size of the bismuth trioxide nano whisker is 20-50 nm.

5. The method for preparing a soft and hard alternating wear-resistant strengthening layer according to claim 3 or 4, characterized in that: The vacuum drying temperature for preparing the dispersed colloid in step 2 is 120-150° C. and the drying time is 40-60 min.

6. The method for preparing a soft and hard alternating wear-resistant strengthening layer according to claim 1, characterized in that: The weight percentages of the components in the rare earth salt bath agent are: nitrogen source 48% to 52%, sodium carbonate 16% to 20%, sodium thiosulfate 6% to 10%, potassium fluoroborate 4% to 6%, composite rare earth system 4.5% to 7%, bismuth trioxide whiskers 1.5% to 2%, and bismuth nitrate 0.8% to 1.2%; wherein the nitrogen source is urea and dicyandiamide, and the mass ratio of urea to dicyandiamide is 5 to 8:

1.

7. The method for preparing a soft and hard alternating wear-resistant strengthening layer according to claim 1, characterized in that: After adding the nitrogen source, sodium carbonate, sodium thiosulfate and potassium fluoroborate in step 2, the temperature is rapidly increased to 280° C. to 320° C. at a heating rate of 4 to 6° C. / min and stirred for 8 to 12 minutes to melt the basic salts such as the nitrogen source, sodium carbonate and sodium thiosulfate; after adding the composite rare earth salt system, the temperature is increased to 420 to 450° C. at a heating rate of 2 to 3° C. / min and kept warm for 25 to 35 minutes, with the nitrogen flow rate of 480 to 520 mL / min; after adding the dispersed colloid and bismuth nitrate, the stirring time is 12 to 15 minutes.

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