Austenitic stainless steel surface wear-resistant strengthened layer and preparation method thereof

Abstract

This invention discloses a wear-resistant reinforcing layer on the surface of austenitic stainless steel and its preparation method. Using nanodiamond as a carbon source, it is generated in situ on the surface of an austenitic stainless steel substrate through slurry coating and vacuum heat treatment, forming a grain-refining region and creating a continuous gradient reinforcing layer between the nanodiamond and the substrate. This invention utilizes nanodiamond as a highly active carbon source, combined with the synergistic diffusion effect of a specific diffusion aid, to form a continuous grain-refining reinforcing layer on the surface of austenitic stainless steel, achieving a good gradient reinforcing layer with the substrate and significantly improving the overall mechanical properties of the austenitic stainless steel surface.

Description

Technical Field

[0001] This invention belongs to the field of high-quality stainless steel surface strengthening processing technology, specifically relating to an austenitic stainless steel surface wear-resistant strengthening layer and its preparation method. Background Technology

[0002] Stainless steel possesses excellent corrosion resistance, superior processability, and stable mechanical properties with temperature, making it one of the most important metallic structural materials. With the rapid development of my country's commercial aerospace industry, the stable performance of stainless steel has also secured a crucial position in this sector. Furthermore, due to its excellent corrosion resistance, stainless steel also holds immense application potential in marine industries, deep-sea oil fields, and mold making.

[0003] Stainless steel can be classified into austenitic stainless steel and martensitic stainless steel according to its microstructure. Generally speaking, austenitic stainless steel has lower strength and hardness, but its properties are more stable. The hardness of martensitic stainless steel can be controlled by heat treatment temperature. However, compared with other high-strength and hard steels, austenitic stainless steel has a relatively low overall hardness. The hardness of fully annealed austenitic stainless steel (such as 316 stainless steel) is generally about 10 HRC, including surface hardness. Therefore, stainless steel has poor wear resistance, which restricts its development in fields such as mold making and aerospace.

[0004] Many methods exist for improving the surface hardness and wear resistance of stainless steel, including mechanical sandblasting, ceramic thermal barrier layers, CVD / PVD hard coatings, high-speed flame spraying, laser cladding, and plasma metal infiltration. However, these technologies suffer from problems such as expensive equipment, complex processes, poor coating bonding strength, and numerous interface defects. Furthermore, they still have shortcomings in areas such as the localization of high-end coating equipment, long-term interface bonding mechanisms, wide-temperature-range service reliability, batch production consistency, and quantitative lifespan assessment. Therefore, there is an urgent need to develop a stainless steel surface modification technology that is simple in process, low in cost, has high bonding strength of the strengthening layer, and exhibits stable performance.

[0005] Several related attempts have been made in the prior art. For example, CN 106381474A discloses a double-layer glow discharge plasma gold infiltration technology for preparing wear-resistant coatings such as W and Mo on stainless steel surfaces; CN 112281155A discloses a process for preparing high-entropy alloy coatings on stainless steel surfaces using powder pre-embedding and electron beam cladding; CN 117684120A discloses a process for preparing composite coatings on stainless steel surfaces using gradient ion nitriding and chromium infiltration; CN 115354275A discloses a process for improving stainless steel surfaces using a combination of infiltration and plating; CN 119662970A provides a technology for strengthening stainless steel surfaces using a process of laser shock and ion carbonitriding; CN 117821894A provides a process for borax salt bath boron-chromium composite co-infiltration on stainless steel surfaces; CN CN121556019A provides a method for improving the corrosion resistance of stainless steel surfaces using a cold spraying process; CN103212713A discloses a technique for preparing wear-resistant coatings on stainless steel surfaces using a hot isostatic pressing powder bonding method; CN112481613A discloses a technique for preparing ultrafine-grained coatings on stainless steel surfaces using laser scanning cladding technology; CN119120859A provides a technique for treating high-hardness stainless steel surfaces using microwave-assisted micro-forging technology; CN105937018A provides a method for low-temperature ion nitriding of austenitic stainless steel; CN114622156A provides a technique for aluminizing a stainless steel substrate surface with a mixed powder of ammonium halide and iron-aluminum alloy powder to form an iron-aluminate layer; CN111979451A provides a laser cladding technology for preparing composite coatings on stainless steel surfaces.

[0006] While the aforementioned existing technologies have achieved some degree of surface strengthening of stainless steel, they all suffer from fundamental drawbacks such as strong equipment dependence, lengthy process flows, poor interfacial bonding reliability, and difficulty in adapting to the mass production of complex components. Physical methods such as mechanical sandblasting are difficult to form a metallurgical bonding layer; high-temperature or vacuum deposition technologies such as CVD / PVD and laser cladding not only require huge equipment investments, but also easily lead to thermal stress cracks or delamination between the coating and the substrate; plasma metal infiltration or salt bath co-infiltration processes can infiltrate elements, but the thickness of the infiltrated layer is difficult to control, the surface quality is unstable, and there are potential environmental pollution risks. Especially in high-end applications such as commercial aerospace and deep-sea equipment, these methods still have significant shortcomings in terms of wide-temperature-range service reliability, batch production consistency, and long-term bonding strength, and cannot meet the high-performance requirements of stainless steel components under extreme working conditions.

[0007] In summary, while there are many existing stainless steel surface strengthening technologies, they generally suffer from problems such as complex processes, high costs, insufficient bonding strength, and limited applicability, making it difficult to simultaneously achieve performance improvement, economy, and versatility. Therefore, developing a strengthening technology that uses nanodiamonds as a carbon source and can achieve surface grain refinement or in-situ ceramic layer formation through simple slurry coating and conventional vacuum heat treatment is of significant practical importance and urgent need. Summary of the Invention

[0008] The purpose of this invention is to overcome the defects of the prior art and provide a wear-resistant strengthening layer for the surface of austenitic stainless steel.

[0009] Another objective of this invention is to provide a method for preparing the aforementioned wear-resistant strengthening layer on the surface of austenitic stainless steel.

[0010] The technical solution of the present invention is as follows:

[0011] A wear-resistant strengthening layer on the surface of austenitic stainless steel is formed in situ on the surface of an austenitic stainless steel substrate by using nanodiamond as a carbon source and with the help of a penetration aid through slurry coating and vacuum heat treatment. It forms a grain refinement region with Al-rich area and a depth of 90-110μm, and forms a continuous gradient strengthening layer between the layer and the austenitic stainless steel substrate.

[0012] The penetration enhancer is composed of Al powder, and at least one of Mo powder, Ta powder, and W powder.

[0013] The aforementioned grain refinement region contains fine compound particles containing at least one of Mo, Ta, and W.

[0014] The method for preparing the wear-resistant strengthening layer on the surface of the above-mentioned austenitic stainless steel includes the following steps:

[0015] (1) Prepare a slurry containing nanodiamonds, the slurry being composed of 15-50 wt% nanodiamonds, 1-5 wt% surfactant, 3-15 wt% penetration enhancer, 13-17 wt% film-forming agent and organic solvent as balance, the penetration enhancer being composed of Al powder and at least one of Mo powder, Ta powder and W powder;

[0016] (2) The slurry containing nanodiamonds is coated on the surface of austenitic stainless steel;

[0017] (3) Place the coated austenitic stainless steel in an oven at 50-120 ℃ for drying and curing for 10-30 min;

[0018] (4) Place the dried and cured austenitic stainless steel in a vacuum furnace and evacuate it to 10°C. -2Below Pa, while maintaining a vacuum, heat to 500-600 ℃ and hold for 1-2 h; then heat to 900-1100 ℃ and hold for 1-3 h, finally cool with the furnace to obtain the product.

[0019] The main mechanism for the formation of the above-mentioned grain refinement region and continuous gradient strengthening layer is as follows: First, the Al powder in the penetration aid has a low melting point, and a small amount of liquid phase is easily generated during vacuum high-temperature heat treatment, which can quickly diffuse with the austenitic stainless steel matrix. The other penetration aid elements are all high-melting-point metal elements with low solid solubility with the austenitic stainless steel matrix. When the Al liquid diffuses with the austenitic stainless steel matrix, these high-melting-point elements can easily enter the metal surface layer and pin the grain boundaries, inhibiting the growth of surface grains, and playing the role of grain refinement strengthening and precipitation strengthening.

[0020] In a preferred embodiment of the present invention, the nanodiamond has a particle size of 100-500 nm.

[0021] In a preferred embodiment of the present invention, the organic solvent is N,N-dimethylformamide or 3-methoxy-3-methylbutanol.

[0022] In a preferred embodiment of the present invention, the surfactant is a silane coupling agent KH550.

[0023] In a preferred embodiment of the present invention, the penetration enhancer is composed of at least one of Al powder with a particle size of 500 nm-2 μm, Mo powder with a particle size of 500 nm-2 μm, Ta powder with a particle size of 500 nm-2 μm, and W powder with a particle size of 500 nm-2 μm.

[0024] In a preferred embodiment of the present invention, the film-forming agent is polyethylene oxide or polyethylene glycol.

[0025] In a preferred embodiment of the present invention, the coating method in step (2) is brush coating or dip coating.

[0026] The beneficial effects of this invention are:

[0027] 1. This invention uses nanodiamond as a highly active carbon source, combined with the synergistic diffusion effect of a specific penetration aid, to form a continuous grain refinement region on the surface of austenitic stainless steel, achieving a good gradient reinforcement layer with the substrate.

[0028] 2. The process of this invention is simple, requiring only slurry preparation, coating, drying and curing, and conventional vacuum heat treatment. It does not require expensive laser, plasma, or high-energy beam equipment, which significantly reduces the production threshold and manufacturing cost, making it suitable for large-scale promotion and application.

[0029] 3. The raw materials of this invention are readily available, the operating parameters are easy to control, and there are no harmful residue emissions throughout the process, which has good environmental protection and meets the requirements of green manufacturing.

[0030] 4. This invention is applicable to various types of austenitic stainless steel and complex components. The thickness of the reinforcing layer is controllable, the performance is improved stably, and it has strong versatility and scalability. It can be widely used in aerospace, marine engineering, mold making and other fields.

[0031] 5. This invention achieves synergistic optimization of carbon diffusion and grain refinement through a dual-temperature-range design of vacuum heat treatment. While maintaining the overall stability of the matrix, it significantly improves surface hardness and wear resistance, and extends the service life of the components. Attached Figure Description

[0032] Figure 1 The macroscopic morphology of 304 stainless steel with a wear-resistant strengthening layer without surface modification according to the present invention (original state, left figure) and 304 stainless steel modified according to Example 2 of the present invention (right figure) are shown.

[0033] Figure 2 The cross-sectional metallographic microstructure of 316 stainless steel in Comparative Examples 1, 2 and 3 of this invention is shown.

[0034] Figure 3 The images show the cross-sectional metallographic image (top), SEM morphology image (bottom left), and enlarged SEM morphology image (bottom right) of 316 stainless steel modified according to Example 3 of this invention.

[0035] Figure 4 The figure shows the Al content distribution of the cross-section of 316 stainless steel modified according to Example 3 of the present invention. The upper figure is a SEM morphology image and a positional image of the composition line scan. The lower figure is a line composition distribution diagram of the corresponding Al content.

[0036] Figure 5 The image shows the cross-sectional SEM morphology of the 316 stainless steel in Comparative Example 4.

[0037] Figure 6 The cross-sectional metallographic structure (left) and cross-sectional microhardness (right) of the 316 stainless steel modified according to Example 4 of the present invention are shown.

[0038] Figure 7 The test result of the friction coefficient of the 316 stainless steel surface in Example 4 of the present invention is 0.47. Detailed Implementation

[0039] The technical solution of the present invention will be further explained and described below with reference to specific embodiments and accompanying drawings.

[0040] Example 1

[0041] The slurry containing nanodiamonds in this embodiment, by weight percentage, comprises: 15% nanodiamond powder with an average particle size of 500 nm, 50% N,N-dimethylformamide, 5% silane coupling agent KH550, 5% Mo powder with an average particle size of 2 μm, 2% Ta powder with an average particle size of 2 μm, 5% Al powder with an average particle size of 2 μm, 3% W powder with an average particle size of 2 μm, and 15% polyethylene oxide.

[0042] The preparation method of the slurry containing nanodiamonds is as follows: First, N,N-dimethylformamide, silane coupling agent KH550, and polyethylene oxide are stirred evenly to form a transparent solution. Then, Mo powder, Ta powder, Al powder, and W powder are added sequentially at a speed of 500 rpm using a dispersing mixer. The speed is increased to 1400 rpm and the mixture is stirred rapidly for 30 min. Then, the speed is reduced to 500 rpm and nanodiamond powder is slowly added. After the nanodiamond powder is completely added, the speed is increased to 1400 rpm and the mixture is stirred rapidly for 30 min to obtain the slurry containing nanodiamonds.

[0043] A slurry containing nanodiamonds was uniformly brushed onto the surface of 316 stainless steel, then dried and cured at 50 °C for 30 min. The cured 316 stainless steel was then placed in a vacuum oven and evacuated to a vacuum level of 7 × 10⁻⁶. -3 Pa, maintain vacuum, heat to 500 ℃ at a heating rate of 20 ℃ / min and hold for 2 h, then heat to 1100 ℃ at a heating rate of 20 ℃ / min and hold for 1 h, finally cool with the furnace to obtain 316 stainless steel with wear-resistant and reinforced surface modification.

[0044] Example 2

[0045] The nanodiamond-containing slurry in this embodiment, by weight percentage, comprises: 50% nanodiamond powder with an average particle size of 100 nm, 15% 3-methoxy-3-methylbutanol, 5% silane coupling agent KH550, 5% Mo powder with an average particle size of 500 nm, 2% Ta powder with an average particle size of 500 nm, 5% Al powder with an average particle size of 500 nm, 3% W powder with an average particle size of 500 nm, and 15% polyethylene glycol.

[0046] The preparation method of the slurry containing nanodiamonds is as follows: First, the above-mentioned 3-methoxy-3-methylbutanol, silane coupling agent KH550 and polyethylene glycol are stirred evenly to a transparent solution. Then, Mo powder, Ta powder, Al powder and W powder are added sequentially at a speed of 300 rpm using a dispersing mixer. The speed is increased to 1000 rpm and the mixture is stirred rapidly for 1 h. Then, the speed is reduced to 300 rpm and nanodiamond powder is slowly added. After the nanodiamond powder is completely added, the speed is increased to 1000 rpm and the mixture is stirred rapidly for 2 h to obtain the slurry containing nanodiamonds.

[0047] A slurry containing nanodiamonds was uniformly brushed onto the surface of 304 stainless steel, then dried and cured at 120 °C for 10 min. The cured 304 stainless steel was then placed in a vacuum oven and evacuated to a vacuum level of 5 × 10⁻⁶. -3 Pa, maintain vacuum, heat to 600 ℃ at a heating rate of 10 ℃ / min and hold for 1 h, then heat to 900 ℃ at a heating rate of 10 ℃ / min and hold for 3 h, finally cool with the furnace to obtain 304 stainless steel with wear-resistant and reinforced surface modification.

[0048] Example 3

[0049] The slurry containing nanodiamonds in this embodiment, by weight percentage, is as follows: 25% nanodiamond powder with an average particle size of 250 nm, 50% 3-methoxy-3-methylbutanol, 1% silane coupling agent KH550, 4% Mo powder with an average particle size of 1 μm, 5% Al powder with an average particle size of 500 nm, and 15% polyethylene glycol.

[0050] The preparation method of the slurry containing nanodiamonds is as follows: First, the above-mentioned 3-methoxy-3-methylbutanol, silane coupling agent KH550 and polyethylene glycol are stirred evenly to a transparent solution. Then, Mo powder is added at a speed of 400 rpm using a dispersing mixer. The speed is increased to 1200 rpm and the mixture is stirred rapidly for 1 h. Then, the speed is reduced to 400 rpm and nanodiamond powder is slowly added. After the nanodiamond powder is completely added, the speed is increased to 1200 rpm and the mixture is stirred rapidly for 1 h to obtain the slurry containing nanodiamonds.

[0051] A slurry containing nanodiamonds was uniformly brushed onto the surface of 316 stainless steel, then dried and cured at 100 °C for 20 min. The cured 316 stainless steel was then placed in a vacuum furnace and evacuated to a vacuum level of 4 × 10⁻⁶. -3Pa, maintain vacuum, heat to 550 ℃ at a heating rate of 15 ℃ / min and hold for 2 h, then heat to 1000 ℃ at a heating rate of 15 ℃ / min and hold for 2 h, finally cool with the furnace to obtain 316 stainless steel with wear-resistant and reinforced surface modification.

[0052] Example 4

[0053] The slurry containing nanodiamonds in this embodiment, by weight percentage, comprises: 30% nanodiamond powder with an average particle size of 250 nm, 50% 3-methoxy-3-methylbutanol, 2% silane coupling agent KH550, 1% Mo powder with an average particle size of 1 μm, 1% Ta powder with an average particle size of 1 μm, 1% Al powder with an average particle size of 500 nm, and 15% polyethylene glycol.

[0054] The preparation method of the slurry containing nanodiamonds is as follows: First, the above-mentioned 3-methoxy-3-methylbutanol, silane coupling agent KH550 and polyethylene glycol are stirred evenly to a transparent solution. Then, Mo powder is added at a speed of 400 rpm using a dispersing mixer. The speed is increased to 1200 rpm and the mixture is stirred rapidly for 1 h. Then, the speed is reduced to 400 rpm and nanodiamond powder is slowly added. After the nanodiamond powder is completely added, the speed is increased to 1200 rpm and the mixture is stirred rapidly for 1 h to obtain the slurry containing nanodiamonds.

[0055] A slurry containing nanodiamonds was uniformly brushed onto the surface of 316 stainless steel, then dried and cured at 100 °C for 30 min. The cured 316 stainless steel was then placed in a vacuum oven and evacuated to a vacuum level of 5 × 10⁻⁶. -3 Pa, maintain vacuum, heat to 600 ℃ at a heating rate of 15 ℃ / min and hold for 1 h, then heat to 950 ℃ at a heating rate of 15 ℃ / min and hold for 3 h, finally cool with the furnace to obtain 316 stainless steel with a wear-resistant and reinforced layer after surface modification.

[0056] Example 5

[0057] The nanodiamond-containing slurry in this embodiment, by weight percentage, comprises: 30% nanodiamond powder with an average particle size of 250 nm, 50% 3-methoxy-3-methylbutanol, 2% silane coupling agent KH550, 1% Mo powder with an average particle size of 1 μm, 1% W powder with an average particle size of 1 μm, 1% Al powder with an average particle size of 500 nm, and 15% polyethylene glycol.

[0058] The preparation method of the slurry containing nanodiamonds is as follows: First, the above-mentioned 3-methoxy-3-methylbutanol, silane coupling agent KH550 and polyethylene glycol are stirred evenly to a transparent solution. Then, Mo powder is added at a speed of 400 rpm using a dispersing mixer. The speed is increased to 1200 rpm and the mixture is stirred rapidly for 1 h. Then, the speed is reduced to 400 rpm and nanodiamond powder is slowly added. After the nanodiamond powder is completely added, the speed is increased to 1200 rpm and the mixture is stirred rapidly for 1 h to obtain the slurry containing nanodiamonds.

[0059] A slurry containing nanodiamonds was uniformly brushed onto the surface of 316 stainless steel, then dried and cured at 120 °C for 10 min. The cured 316 stainless steel was then placed in a vacuum oven and evacuated to a vacuum level of 5 × 10⁻⁶. -3 Pa, maintain vacuum, heat to 600 ℃ at a heating rate of 15 ℃ / min and hold for 1 h, then heat to 1050 ℃ at a heating rate of 15 ℃ / min and hold for 3 h, finally cool with the furnace to obtain 316 stainless steel with a wear-resistant and reinforced layer after surface modification.

[0060] Comparative Example 1

[0061] The nanodiamond-containing slurry from Example 4 was uniformly brushed onto the surface of 316 stainless steel, then dried and cured at 150 °C for 20 min. The dried and cured 316 stainless steel was then placed in a vacuum oven and evacuated to a vacuum level of 5 × 10⁻⁶. -3 Pa, maintain vacuum, heat to 400 ℃ at a heating rate of 15 ℃ / min and hold for 1 h, then heat to 800 ℃ at a heating rate of 15 ℃ / min and hold for 2 h, and finally cool with the furnace.

[0062] The difference between Comparative Example 1 and Example 4 is that the subsequent vacuum heat treatment temperature of the 316 stainless steel after drying and curing is different. In Example 4, the vacuum heat treatment temperature is 600 ℃ for 1 h and then 950 ℃ for 3 h, while in Comparative Example 1, the vacuum heat treatment temperature is 400 ℃ for 1 h and then 800 ℃ for 2 h.

[0063] Comparative Example 2

[0064] The nanodiamond-containing slurry from Example 4 was uniformly brushed onto the surface of 316 stainless steel, then dried and cured at 150 °C for 20 min. The dried and cured 316 stainless steel was then placed in a vacuum oven and evacuated to a vacuum level of 5 × 10⁻⁶. -3 Pa, maintain vacuum, heat to 400 ℃ at a heating rate of 15 ℃ / min and hold for 1 h, then heat to 1200 ℃ at a heating rate of 15 ℃ / min and hold for 2 h, and finally cool with the furnace.

[0065] The difference between Comparative Example 2 and Example 4 is that the subsequent vacuum heat treatment temperature of the 316 stainless steel after drying and curing is different. In Example 4, the vacuum heat treatment temperature is 600 ℃ for 1 h and then 950 ℃ for 3 h, while in Comparative Example 1, the vacuum heat treatment temperature is 400 ℃ for 1 h and then 800 ℃ for 2 h.

[0066] Comparative Example 3

[0067] The slurry containing nanodiamonds in this embodiment, by weight percentage, is as follows: 30% nanodiamond powder with an average particle size of 250 nm, 50% 3-methoxy-3-methylbutanol, 2% silane coupling agent KH550, 3% Fe powder with an average particle size of 1 μm, and 15% polyethylene glycol.

[0068] The preparation method of the slurry containing nanodiamonds is as follows: First, the above-mentioned 3-methoxy-3-methylbutanol, silane coupling agent KH560 and polyethylene glycol are stirred evenly to a transparent solution. Then, Mo powder is added using a dispersing mixer at a speed of 400 rpm. The speed is increased to 1200 rpm and stirred rapidly for 1 h. Then, the speed is reduced to 400 rpm and nanodiamond powder is slowly added. After the nanodiamond powder is completely added, the speed is increased to 1200 rpm and stirred rapidly for 1 h to obtain the slurry containing nanodiamonds.

[0069] A slurry containing nanodiamonds was uniformly brushed onto the surface of 316 stainless steel, then dried and cured at 100 °C for 30 min. The cured 316 stainless steel was then placed in a vacuum oven and evacuated to a vacuum level of 5 × 10⁻⁶. -3 Pa, maintain vacuum, heat to 600 ℃ at a heating rate of 15 ℃ / min and hold for 1 h, then heat to 950 ℃ at a heating rate of 15 ℃ / min and hold for 3 h, finally cool with the furnace to obtain surface-modified 316 stainless steel.

[0070] The difference between Comparative Example 3 and Example 4 is that the penetration aid in the slurry containing nanodiamonds in Example 4 was changed to 3% Fe powder with an average particle size of 1 μm, while the rest of the process and parameters remained unchanged.

[0071] Comparative Example 4

[0072] The nanodiamond-containing slurry in this comparative example, by weight percentage, contains: 25% nanodiamond powder with an average particle size of 250 nm, 50% 3-methoxy-3-methylbutanol, 1% silane coupling agent KH550, 4% Mo powder with an average particle size of 1 μm, 3% Ta powder with an average particle size of 1 μm, 2% W powder with an average particle size of 1 μm, and 15% polyethylene glycol.

[0073] The preparation method of the slurry containing nanodiamonds is as follows: First, the above-mentioned 3-methoxy-3-methylbutanol, silane coupling agent KH550, and polyethylene glycol are stirred evenly to form a transparent solution. Then, Mo powder, Ta powder, and W powder are added using a dispersing mixer at a speed of 400 rpm. The speed is increased to 1200 rpm and the mixture is stirred rapidly for 1 h. Then, the speed is reduced to 400 rpm and nanodiamond powder is slowly added. After the nanodiamond powder is completely added, the speed is increased to 1200 rpm and the mixture is stirred rapidly for 1 h to obtain the slurry containing nanodiamonds.

[0074] A slurry containing nanodiamonds was uniformly brushed onto the surface of 316 stainless steel, then dried and cured at 100 °C for 20 min. The cured 316 stainless steel was then placed in a vacuum furnace and evacuated to a vacuum level of 4 × 10⁻⁶. -3 Pa, maintain vacuum, heat to 550 ℃ at a heating rate of 15 ℃ / min and hold for 2 h, then heat to 1000 ℃ at a heating rate of 15 ℃ / min and hold for 2 h, finally cool with the furnace to obtain surface-modified 316 stainless steel.

[0075] The difference between Comparative Example 4 and Example 3 is that no penetration aid Al was added in Comparative Example 4, only Mo, W and Ta penetration aids were added, and the rest of the process and parameters remained unchanged.

[0076] Figure 1 The images show the macroscopic morphology of 304 stainless steel without surface modification according to this invention (original state, left image) and 304 stainless steel modified according to Example 2 of this invention (right image). Figure 1 It can be observed that the macroscopic morphology of 304 stainless steel treated by the present invention has changed significantly, and the stainless steel surface has lost its metallic luster.

[0077] Figure 2The images show the cross-sectional metallographic microstructure of 316 stainless steel in Comparative Examples 1, 2, and 3 of this invention. In Comparative Example 1, due to insufficient vacuum heat treatment temperature, a dense reinforcing layer was not formed (upper left image, right side is the coated surface), rendering it without practical value. In Comparative Example 2, due to excessively high vacuum heat treatment temperature, the adhesion between the reinforcing layer and the substrate significantly decreased (upper right image, lower side is the coated surface), also rendering it without practical value. In Comparative Example 3, because the penetration enhancer was Fe powder, a grain refinement layer was not formed on the stainless steel surface (lower image, left side is the coated surface).

[0078] Figure 3 The image above shows the cross-sectional metallographic structure of 316 stainless steel modified according to Example 3 of this invention. A distinct grain refinement region appears on the surface coated with the nanodiamond slurry. As can be seen in the lower left image, an Al-rich region also exists on the surface of the grain refinement region. Furthermore, numerous fine Mo-rich compound particles, formed by the penetration enhancer and metallic elements in the substrate, are present in both the Al-rich and grain refinement regions. These particles have a significantly smaller grain size than the austenite grains of the matrix and are mainly concentrated at grain boundaries, thus refining the matrix grain structure (lower right image). The depth of the grain refinement layer can reach 100 μm.

[0079] Figure 4 The compositional distribution of Al content in the cross-section of 316 stainless steel modified according to Example 3 of the present invention is shown below. Figure 4 It can be observed that the Al alloy in the penetration aid forms an Al-rich region on the stainless steel surface. Due to the low melting point of Al, it can quickly diffuse into the substrate, while also bringing the other penetration aid components into the substrate. Excess Al can form an Al-rich layer on the outermost surface of the metal, mixed with other remaining penetration aids, and diffuse with each other at high temperature to form fine Mo-rich compound particles.

[0080] Figure 5 The metallographic microstructure of the cross-section of 316 stainless steel in Comparative Example 4 is shown. From... Figure 5 It can be observed that even without the addition of low-melting-point Al, there is a very narrow grain refinement zone on the surface of stainless steel, with a depth of about 20 micrometers. Moreover, there is no Al-rich zone on the outermost surface, and the corresponding content of fine compound particles rich in Mo, W, or Ta is also very low.

[0081] Figure 6 The images show the cross-sectional metallographic structure (left) and cross-sectional microhardness (right) of 316 stainless steel modified according to Example 4 of this invention. A distinct grain refinement region appears on the surface coated with the nano-diamond slurry. As can be seen from the right image, the microhardness of the grain refinement region is significantly higher than that of the substrate (specific microhardness values ​​are shown in Table 1).

[0082] Figure 7The friction coefficient test of the 316 stainless steel surface in Example 4 of the present invention is shown. The results show that the friction coefficient of the modified 316 stainless steel surface is about 0.47, which is much lower than the friction coefficient of 316 stainless steel itself (0.7-0.8).

[0083] Table 1. Microhardness HRC of the modified 316 stainless steel surface in Example 4 Figure 2 The image on the right shows, from left to right, the three hardness values ​​on the left are the hardness of the grain refinement strengthening layer, and there is a gradient strengthening from the strengthening layer to the stainless steel substrate.

[0084]

[0085] Through the embodiments of the present invention and the technical results obtained, it can be seen that the present invention provides a breakthrough in the surface strengthening technology of stainless steel by using nanodiamond as a carbon source to enhance the surface properties of stainless steel. The surface hardness and wear resistance of stainless steel can be significantly improved through a simple process.

[0086] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A wear-resistant reinforcing layer on the surface of austenitic stainless steel, characterized in that: Using nanodiamond as a carbon source, and with the help of a penetration enhancer, it is generated in situ on the surface of austenitic stainless steel substrate through slurry coating and vacuum heat treatment, forming a grain refinement region with Al-rich area and a depth of 90-110μm, and forming a continuous gradient reinforcement layer between it and the stainless steel substrate. The penetration enhancer is composed of Al powder, and at least one of Mo powder, Ta powder, and W powder. The aforementioned grain refinement region contains fine compound particles containing at least one of Mo, Ta, and W.

2. The method for preparing a wear-resistant strengthening layer on the surface of austenitic stainless steel according to claim 1, characterized in that: Includes the following steps: (1) Prepare a slurry containing nanodiamonds, the slurry being composed of 15-50 wt% nanodiamonds, 1-5 wt% surfactant, 3-15 wt% penetration enhancer, 13-17 wt% film-forming agent and organic solvent as balance, the penetration enhancer being composed of Al powder and at least one of Mo powder, Ta powder and W powder; (2) The slurry containing nanodiamonds is coated on the surface of austenitic stainless steel; (3) Place the coated austenitic stainless steel in an oven at 50-120 ℃ for drying and curing for 10-30 min; (4) Place the dried and cured austenitic stainless steel in a vacuum furnace and evacuate it to 10°C. -2 Below Pa, while maintaining a vacuum, heat to 500-600 ℃ and hold for 1-2 h; then heat to 900-1100 ℃ and hold for 1-3 h, finally cool with the furnace to obtain the product.

3. The preparation method according to claim 2, characterized in that: The nanodiamonds have a particle size of 100-500 nm.

4. The preparation method according to claim 2, characterized in that: The organic solvent is N,N-dimethylformamide or 3-methoxy-3-methylbutanol.

5. The preparation method according to claim 2, characterized in that: The surfactant is a silane coupling agent, KH550.

6. The preparation method according to claim 2, characterized in that: The penetration enhancer is composed of at least one of Al powder with a particle size of 500 nm-2 μm, Mo powder with a particle size of 500 nm-2 μm, Ta powder with a particle size of 500 nm-2 μm, and W powder with a particle size of 500 nm-2 μm.

7. The preparation method according to claim 2, characterized in that: The film-forming agent is polyethylene oxide or polyethylene glycol.

8. The preparation method according to claim 2, characterized in that: The coating method in step (2) is brush coating or dip coating.

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