A method for improving the surface of a ship steel with a rare earth oxide by means of an iron-based cladding coating

Abstract

The application relates to a method for improving the surface performance of high-strength ship structure steel, and the method comprises the following steps: using 316L stainless steel powder as a powder material for laser repair, using rare earth oxide as a protective layer, and using fluoride as a covering layer material; in the preparation process of the corrosion-resistant coating, the stainless steel powder, the composite rare earth oxide and the fluoride powder are coated on the to-be-repaired part of the ship steel material in layers by using water-resistant glue; then, underwater laser cladding is performed on the to-be-repaired base by using a laser cladding process; after the multi-element composite rare earth oxide, the thickness of the heat-affected zone is reduced, because the multi-element composite rare earth oxide particles provide more nucleation sites; the coating of the multi-element composite rare earth oxide has excellent wear resistance, and the wear rate is 0.435*10 ‑15 m 3 N ‑1 m ‑1 The main wear mechanism is abrasive wear. The improved microhardness and the multi-element composite rare earth oxide particle addition are key factors for improving the wear resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for improving the surface properties of high-strength ship structural steel, in particular to a method for improving the surface iron-based cladding coating of ship steel using rare earth oxides. BACKGROUND

[0002] Ship steel is commonly used to manufacture structural components of marine vessels, such as hulls, decks, and other ship components. This steel material has high yield strength and tensile strength, which is suitable for resisting harsh conditions in marine environments, such as seawater corrosion and strong wind and waves. Ship steel usually meets relevant international standards and specifications to ensure its quality and performance meet specific requirements, such as those of ship classification societies. As a high-strength marine steel material, ship structural steel is widely used in marine engineering due to its high toughness, strength, and weldability, and is an important functional and structural material for various marine engineering equipment and platforms. However, the high salinity, oxygen-rich, and constant erosion in the marine environment can easily lead to corrosion, wear, and other damage to ship structural steel. This will pose a serious threat to the long-term safe use of marine engineering equipment and bring huge losses to the development of the marine economy. Therefore, ensuring the durability and safety of marine engineering equipment, reducing the occurrence of major disaster accidents, and prolonging the service life are key issues and common problems that need to be addressed.

[0003] Ship structural steel is immersed in seawater for many years and must withstand various harsh sea conditions. Therefore, the technical indicators of offshore platform steel are extremely high. Not only must it have high resistance to atmospheric corrosion and seawater corrosion, but it must also have good mechanical and processing properties. The performance requirements of offshore platform steel include: (1) high strength to resist wind and flow impact above the water surface; good resistance to lamellar tearing to prevent tearing of the steel when subjected to external forces in the thickness direction; (2) good low-temperature impact performance, with some offshore platform steel requiring good impact performance at -60°C to serve in extremely cold environments; (3) good welding performance, with the mechanical properties of the welded joint being the same as or similar to those of the base material to ensure the safety of the overall structure of the offshore platform; (4) steel purity requirements. The steel must have very low impurity element content, such as P and S, and have high requirements for the morphology, type, and distribution of inclusions to prevent fatigue failure of the offshore platform when affected by typhoons and water flow, ensuring the safety of life and property; (5) high corrosion resistance. Due to the long-term exposure of offshore steel structures to salt spray, moisture, and seawater, they are subjected to severe electrochemical corrosion, paint film saponification, and aging, resulting in severe structural corrosion. Not only does this reduce the mechanical properties of the structural material and shorten its service life, but also because it is far from the coast, it cannot be regularly maintained and repaired like a ship. Therefore, the corrosion resistance requirements are even higher.

[0004] Various types of surface cracks are prone to occur on the surface of ship hulls after long-term service, which need to be repaired in time. Traditional ship maintenance is carried out in the dock, which has high economic cost and low sailing rate. In recent years, underwater repair technology has become the main means of emergency maintenance for marine engineering equipment such as ships, offshore platforms and offshore pipelines. Introducing laser cladding technology for underwater in-situ repair can effectively utilize the advantages of high automation and high repair efficiency. Therefore, many researchers have studied underwater laser wet cladding technology. However, since the underwater wet cladding process is carried out in seawater environment, the molten pool will inevitably be attacked by water, which will greatly reduce the formability of the cladding layer, and many studies have tried to solve this problem.

[0005] For example, Chinese invention patent CN202310049426.5 relates to a process for preparing high-performance high-nitrogen steel by underwater laser cladding. A local dry zone is constructed on the processing surface of the substrate workpiece. A nitrogen atmosphere is constructed in the local dry zone. A high-nitrogen steel powder is cladded on the processing surface of the substrate workpiece to form a molten pool according to the scanning trajectory at the initial cladding height. The nitrogen atmosphere promotes nitrogen infiltration at the gas-liquid interface near the molten pool to increase the solubility of nitrogen in the molten pool. Through the cooling effect of the water environment, an initial high-nitrogen steel deposition sample is obtained on the processing surface of the substrate workpiece.

[0006] Studies have shown that the addition of titanium can increase the surface tension of the molten pool, slow down the impact of high-speed water jet on the molten pool, and reduce the formation of defects such as pores.

[0007] Studies by Zhang X et al. (Int. J. Hydrogen Energy, 2022, 47(11): 7362-7367) have shown that compared with traditional water environments, the glycerol environment can greatly reduce the content of diffusible hydrogen and obtain a cladding layer with a dense structure and no pore defects when glycerol is used as a liquid protective agent. In order to obtain a dense coating, the formability of the cladding layer also plays an important role. Studies have shown that appropriate additives can reduce the supercooling degree during the cladding process and effectively optimize the microstructure characteristics of the cladding layer. Previous studies have shown that protecting the molten pool during underwater wet laser cladding can improve the formability stability of the cladding layer to some extent. Although constructing a surface dry zone and using a liquid protective agent can improve the underwater formability stability of the cladding layer, it is relatively cumbersome for underwater online cladding, especially for underwater online cladding of large components.

[0008] As a material with excellent corrosion resistance and wear resistance, metal matrix nanocomposite is widely used in technologies such as plasma spraying and laser cladding. Metal matrix nanocomposites usually contain a matrix phase (Fe-based, Ni-based, Co-based alloy) and nanoparticles.

[0009] Murmu AM et al. introduced a TiC-ZrO2 composite laser cladding coating during the laser cladding process of Ti6Al4V material (J. Mater. Eng. Perform, 2021, 30 (3): 1748-1758). In the TiC-ZrO2 composite cladding layer, they found that nano ZrO2 can promote the formation of dendritic microstructure and significantly improve the wear resistance of the TiC-ZrO2 composite cladding layer.

[0010] Chang Y. C et al. introduced nano-WC during the laser cladding process of Al7075 aluminum alloy (MaterialsCharacterization, 2022, 191, 112124). The Al2Cu and MgZn2 phases formed on the surface of the nano-WC exhibited an enhanced layered microstructure, resulting in an enhanced cladding layer with excellent mechanical properties. In the 316L / nano-TiN laser cladding layer, the introduction of nano-TiN particles refined the grains and promoted the transformation of grains from columnar to equiaxed, which is the main reason for the improved mechanical properties. However, in addition to providing nucleating particles, the introduction of nanoparticles also causes changes in the melting behavior, solidification mechanism, and solidification sequence of the molten pool. The introduction of metal matrix nanocomposites is currently mainly used for online laser cladding of non-ferrous alloys such as titanium and aluminum, and its application in marine steel plates is relatively limited. Summary of the Invention

[0011] The purpose of this invention is to provide a method for improving the iron-based cladding coating on the surface of marine steel using rare earth oxides. This invention successfully prepares an underwater wet laser Fe-based cladding layer on the surface of marine steel by applying nano-composite rare earth oxides, exhibiting good forming quality and ideal performance. The introduction of a nano-rare earth oxide protective layer increases the viscosity of the molten pool surface, which can resist the impact force generated by high-speed water jets. In this invention, the contradiction between the forming quality and performance of the underwater Fe-based cladding layer is resolved by introducing nanoparticles to regulate melting and solidification behavior. By adding rare earth composite oxides and fluorides as protective layers, the formability, phase composition, and microstructure of the underwater laser Fe-based cladding layer are significantly improved.

[0012] The objective of this invention is achieved through the following technical solution:

[0013] A method for improving iron-based cladding coatings on ship steel surfaces using rare earth oxides, the method comprising the following steps:

[0014] (1) Ship structural steel is used as the base material to be repaired;

[0015] (2) 316L stainless steel powder is used as the powder material for laser repair, fluoride powder is used as the coating material, and composite rare earth oxide is used as the protective layer material.

[0016] (3) Apply stainless steel powder, composite rare earth oxides and fluoride powder in layers to the marine steel to be repaired using water-resistant adhesive;

[0017] (4) A corrosion-resistant protective layer is formed using underwater laser cladding equipment;

[0018] The aforementioned 316L stainless steel powder, fluoride coating material, composite rare earth oxide material, and marine steel repair substrate are first mixed with water-resistant adhesive, then coated with 316L stainless steel powder, followed by composite rare earth oxide powder, and finally coated with the coating material. The fluoride is one or a mixture of several of sodium fluoride, silicon tetrafluoride, boron trifluoride, and calcium fluoride, with calcium fluoride being the preferred coating material. The weight composition of the fluoride coating, rare earth oxide protective layer, and 316L stainless steel powder is (5~10)%: (5~20)%: (70~90)%. The composite rare earth oxide is a mixture of yttrium oxide, lanthanum oxide, and cerium oxide, wherein the weight proportion of yttrium oxide is 50~70%, lanthanum oxide is 20~25%, and the remainder is cerium oxide.

[0019] The method for improving the iron-based cladding coating on the surface of ship steel using rare earth oxides, wherein the water-resistant adhesive is composed of ethyl 2-cyano-2-acrylate (C6H7NO2); the proportion of the water-resistant adhesive added accounts for 5-20% of the weight of the solid powder.

[0020] The method for improving the iron-based cladding coating on the surface of ship steel using rare earth oxides, wherein during laser cladding, the laser power is 1000~4000W, the welding speed is 1~10mm / s, the spot diameter is 2~8mm, and the defocusing amount is +2~5mm. The laser cladding process is carried out online underwater.

[0021] The method described above utilizes rare earth oxides to improve the iron-based cladding coating on the surface of ship steel. The method is applicable to ship structural steel of strength grades A, B, D, and E, as well as high-strength ship structural steel of grades AH32, DH32, EH32, AH36, DH36, and EH36.

[0022] The advantages and effects of this invention are:

[0023] This invention utilizes a method to improve the wear resistance and corrosion resistance of iron-based cladding coatings on the surface of high-strength marine structural steel using composite rare earth oxides and fluorides. Marine structural steel possesses high yield strength and tensile strength, making it suitable for withstanding harsh conditions in marine environments, such as seawater corrosion and strong waves. The underwater stability of the cladding layer primarily depends on the viscosity of the molten pool surface; a high-viscosity molten pool significantly enhances resistance to the impact force generated by water jets, contributing to the stability of the molten pool during the underwater laser cladding process.

[0024] This invention successfully prepared an underwater wet laser coating for the surface of ship structural steel using multi-component nano-composite rare earth oxides and fluorides, exhibiting excellent forming quality and ideal performance. The introduction of nano-rare earth oxide and fluoride protective layers increases the viscosity of the molten pool surface to resist the impact of high-speed water jets. 316L stainless steel powder was used as the powder material for laser repair, composite rare earth oxides as the protective layer, and fluorides as the coating material. 1. The addition of fluorides and nano-multi-component rare earth oxide particles increases the depth of the molten pool and reduces the depth of the heat-affected zone. The addition of the multi-component composite rare earth oxide and fluoride protective layer effectively improves the coating's resistance to seawater corrosion. The corrosion potential and corrosion current density of the protective layer are -0.25V and 1.87×10⁻⁶, respectively. -7 A·cm −2 This results in better resistance to pitting corrosion. The coating, incorporating multi-component rare earth oxides and fluorides, exhibits excellent wear resistance. Therefore, this invention provides a laser cladding method for emergency maintenance of marine engineering equipment such as ships, offshore platforms, and offshore pipelines. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the pre-treatment coating structure of the steel plate before laser cladding in Embodiment 1 of the present invention;

[0026] Figure 2 This is a scanning electron microscope (SEM) schematic diagram of the microstructure of the heat-affected zone cross section in Embodiment 1 of the present invention.

[0027] Figure 3 This is a scanning electron microscope (SEM) schematic diagram of the microstructure of the heat-affected zone cross section in Comparative Example 1 of the present invention.

[0028] Figure 4 This is a comparison of the thickness of the heat-affected zone in Embodiment 1 and Comparative Example 1 of the present invention;

[0029] Figure 5 The microhardness distribution of the heat-affected zone in Embodiment 1 and Comparative Example 1 of the present invention;

[0030] Figure 6 The friction coefficients of five materials (Example 1, Example 2, Example 3, Comparative Example 1, and Comparative Example 2) in 4.0 wt% NaCl solution are compared. Implementation

[0031] In practical implementation, to improve the seawater corrosion resistance of ship structural steel, this invention proposes an underwater laser cladding repair technology. Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods. Unless otherwise specified, the reagents and materials are commercially available.

[0032] In the implementation of this invention, firstly, taking high-strength ship structural EH 32 steel as an example, EH32 steel serves as the base material to be repaired, possessing excellent mechanical properties and seawater corrosion resistance. 316L stainless steel powder is used as the powder material for laser repair, rare earth oxides as the protective layer material, and fluorides as the coating layer material. In the preparation of the corrosion-resistant coating, stainless steel powder, composite rare earth oxides, and fluoride powder are first layered and coated onto the part of the ship EH32 steel to be repaired using a water-resistant adhesive. Then, a corrosion-resistant coating is obtained through a laser cladding process.

[0033] from Figure 1 It can be seen that before laser cladding of the steel plate, the pre-treatment coating consists of three layers. The marine EH32 steel plate to be repaired has three layers: the bottom layer is 316L stainless steel powder, the middle layer is a composite rare earth oxide protective layer, and the top layer is a fluoride layer.

[0034] Figure 2 This is a scanning electron microscope (SEM) schematic diagram of the microstructure of the heat-affected zone cross-section in Embodiment 1 of the present invention. As can be seen from the figure, the heat-affected zone is tightly bonded to the substrate, without pores or inclusions, indicating that the substrate has been effectively repaired.

[0035] Figure 3 This is a scanning electron microscope (SEM) schematic diagram of the microstructure of the heat-affected zone cross-section in Comparative Example 1 of this invention. As can be seen from the figure, compared to the coating with added rare earth oxides, the heat-affected zone of the coating without added rare earth oxides is more pronounced, and larger particles appear in the transition zone.

[0036] Figure 4 To compare the thickness of the heat-affected zone in Example 1 and Comparative Example 1 of the present invention, a coating of composite rare earth oxides was added, which significantly reduced the thickness of the heat-affected zone from 800 micrometers to 400 micrometers.

[0037] Figure 5 The images show the microhardness distribution of the heat-affected zones in Example 1 and Comparative Example 1 of this invention. Both exhibit the same hardness variation trend, with the coating and transition zone showing significantly higher hardness than the substrate. Furthermore, the microhardness of Example 1 is significantly higher than that of Comparative Example 1. This is mainly because the composite rare earth oxides are distributed at the grain boundaries, hindering grain growth and increasing the hardness of the laser cladding coating.

[0038] Figure 6 This section compares the wear rates of six materials (Examples 1, 2, 3, Comparative Examples 1 and 2) in a 4.0 wt% NaCl solution. After adding the composite rare earth oxide and fluoride, the wear rate of Example 1 was significantly reduced to 0.435 × 10⁻⁶. -15 m 3 N -1 m -1 .

[0039] Table 1 shows the corrosion potentials obtained from the polarization curves. E corr ) and corrosion current density ( I corr (Comparison) The corrosion current density shows that, after adding the composite rare earth oxide and the fluoride, the corrosion current density of Example 1 is 1.87 × 10⁻⁶. -7 A . cm -2 The corrosion potential of Example 1 was significantly lower than that of the substrate to be repaired, indicating a significant improvement in corrosion resistance. The corrosion potential of Example 1 was -0.25V, which was significantly higher than that of Comparative Example 1 and Comparative Example 2, indicating that the addition of composite rare earth oxides and fluorides improved the corrosion resistance.

[0040] Table 1

[0041] Sample name Corrosion potential Corrosion current (A / cm 2 )]]> Example 1 -0.25 1.87 x 10 -7 ]] Example 2 -0.27 2.87 x 10 -7 <!-- 4 -->]]> Example 3 -0.30 3.99 x 10 -7 ]] Comparative Example 1 -0.54 4.89 x 10 -6 ]]> Comparative Example 2 -0.38 2.12 x 10 -6 ]]> Example 1

[0042] In this embodiment, a method for enhancing the wear resistance of underwater laser cladding coatings includes the following steps:

[0043] Step 1: Substrate Treatment

[0044] High-strength marine structural steel EH32 was used as the base material to be repaired, and the area to be repaired on the surface of the base was removed by grinding with a grinding wheel.

[0045] Step 2: Weighing and mixing materials

[0046] Mix 1700g of 316L stainless steel powder with 85g of ethyl 2-cyano-2-acrylate (C6H7NO2) water-based adhesive;

[0047] 180g of rare earth oxides were mixed with 9g of ethyl 2-cyano-2-acrylate (C6H7NO2) aqueous adhesive. Of the rare earth oxides, 126g was Y2O3, 45g was La2O3, and 9g was CeO2.

[0048] 100g of CaF2 powder is mixed with 5g of ethyl 2-cyano-2-acrylate (C6H7NO2) aqueous adhesive;

[0049] Step 3: Pre-treatment of the repair area

[0050] The area to be repaired was sequentially coated with 316L stainless steel powder, rare earth oxide powder, and CaF2 powder.

[0051] Step 4: Laser Cladding

[0052] Laser cladding technology is used to perform surface repair on the area to be repaired underwater by adjusting process parameters. The laser power of this process is 2500W, the welding speed is 2mm / s, the spot diameter is 3mm, and the defocusing amount is +2mm.

[0053] Step 5: Sample Post-processing

[0054] The surface of the repair area is machined and polished using an automatic mechanical grinding and polishing machine until it meets the required precision for use, resulting in a high-performance surface cladding layer. Example 2

[0055] In this embodiment, a method for enhancing the wear resistance of underwater laser cladding coatings, compared to Example 1, uses single-phase Y2O3 as the rare earth oxide, and includes the following steps:

[0056] Step 1: Substrate Treatment

[0057] High-strength marine structural steel EH32 was used as the base material to be repaired, and the area to be repaired on the surface of the base was removed by grinding with a grinding wheel.

[0058] Step 2: Weighing and mixing materials

[0059] Take 1700g of 316L powder and mix it with 85g of ethyl 2-cyano-2-acrylate (C6H7NO2) water-based adhesive;

[0060] 180g of Y2O3 was mixed with 9g of ethyl 2-cyano-2-acrylate (C6H7NO2) aqueous adhesive.

[0061] 100g of CaF2 powder is mixed with 5g of ethyl 2-cyano-2-acrylate (C6H7NO2) aqueous adhesive;

[0062] Step 3: Pre-treatment of the repair area

[0063] 316L stainless steel powder, rare earth oxide Y2O3 powder, and CaF2 powder were sequentially coated onto the area to be repaired.

[0064] Step 4: Laser Cladding

[0065] Laser cladding technology is used to perform surface repair on the area to be repaired underwater by adjusting process parameters. The laser power of this process is 2500W, the welding speed is 2mm / s, the spot diameter is 3mm, and the defocusing amount is +2mm.

[0066] Step 5: Sample Post-processing

[0067] The surface of the repair area is machined and polished using an automatic mechanical grinding and polishing machine until it meets the required precision for use, resulting in a high-performance surface cladding layer. Example 3

[0068] In this embodiment, a method for enhancing the wear resistance of underwater laser cladding coatings, compared to Example 1, uses NaF as the fluoride and includes the following steps:

[0069] Step 1: Substrate Treatment

[0070] High-strength marine structural steel EH32 was used as the base material to be repaired, and the area to be repaired on the surface of the base was removed by grinding with a grinding wheel.

[0071] Step 2: Weighing and mixing materials

[0072] Take 1700g of 316L powder and mix it with 85g of ethyl 2-cyano-2-acrylate (C6H7NO2) water-based adhesive;

[0073] 180g of rare earth oxides were mixed with 9g of ethyl 2-cyano-2-acrylate (C6H7NO2) aqueous adhesive. The rare earth oxides contained 126g of Y2O3, 45g of La2O3, and 9g of CeO2.

[0074] 100g of NaF powder is mixed with 5g of ethyl 2-cyano-2-acrylate (C6H7NO2) aqueous adhesive;

[0075] Step 3: Pre-treatment of the repair area

[0076] 316L stainless steel powder, rare earth oxide powder, and NaF powder were sequentially coated onto the area to be repaired.

[0077] Step 4: Laser Cladding

[0078] Laser cladding technology is used to perform surface repair on the area to be repaired underwater by adjusting process parameters. The laser power of this process is 2500W, the welding speed is 2mm / s, the spot diameter is 3mm, and the defocusing amount is +2mm.

[0079] Step 5: Sample Post-processing

[0080] The surface of the repair area is machined and polished using an automatic mechanical grinding and polishing machine until it meets the required precision for use, resulting in a high-performance surface cladding layer.

[0081] Comparative Example 1

[0082] In this comparative example, a method for enhancing the wear resistance of an underwater laser cladding coating, compared to Example 1, does not have a composite rare earth oxide protective layer. Comparative Example 1 includes the following steps:

[0083] Includes the following steps:

[0084] Step 1: Substrate Treatment

[0085] High-strength marine structural steel EH32 was used as the base material to be repaired, and the area to be repaired on the surface of the base was removed by grinding with a grinding wheel.

[0086] Step 2: Weighing and mixing materials

[0087] Take 1700g of 316L powder and mix it with 85g of ethyl 2-cyano-2-acrylate (C6H7NO2) water-based adhesive;

[0088] 100g of CaF2 powder is mixed with 5g of ethyl 2-cyano-2-acrylate (C6H7NO2) aqueous adhesive;

[0089] Step 3: Pre-treatment of the repair area

[0090] 316L stainless steel powder and CaF2 powder were sequentially applied to the area to be repaired.

[0091] Step 4: Laser Cladding

[0092] Laser cladding technology is used to perform surface repair on the area to be repaired underwater by adjusting process parameters. The laser power of this process is 2500W, the welding speed is 2mm / s, the spot diameter is 3mm, and the defocusing amount is +2mm.

[0093] Step 5: Sample Post-processing

[0094] The surface of the repair area is machined and polished using an automatic mechanical grinding and polishing machine until it meets the required precision for use, resulting in a high-performance surface cladding layer.

[0095] Comparative Example 2

[0096] In this comparative example, a method for enhancing the wear resistance of an underwater laser cladding coating, compared to Example 1, does not have a CaF2 coating layer. Comparative Example 2 includes the following steps:

[0097] Step 1: Substrate Treatment

[0098] High-strength marine structural steel EH32 was used as the base material to be repaired, and the area to be repaired on the surface of the base was removed by grinding with a grinding wheel.

[0099] Step 2: Weighing and mixing materials

[0100] Take 1700g of 316L powder and mix it with 85g of ethyl 2-cyano-2-acrylate (C6H7NO2) water-based adhesive;

[0101] 180g of rare earth oxides were mixed with 9g of ethyl 2-cyano-2-acrylate (C6H7NO2) aqueous adhesive. Of the rare earth oxides, 126g was Y2O3, 45g was La2O3, and 9g was CeO2.

[0102] Step 3: Pre-treatment of the repair area

[0103] 316L stainless steel powder and rare earth oxide powder were sequentially coated onto the area to be repaired.

[0104] Step 4: Laser Cladding

[0105] Laser cladding technology is used to perform surface repair on the area to be repaired underwater by adjusting process parameters. The laser power of this process is 2500W, the welding speed is 2mm / s, the spot diameter is 3mm, and the defocusing amount is +2mm.

[0106] Step 5: Sample Post-processing

[0107] The surface of the repair area is machined and polished using an automatic mechanical grinding and polishing machine until it meets the required precision for use, resulting in a high-performance surface cladding layer.

[0108] The results demonstrate that this invention proposes a method to enhance the wear resistance of underwater laser cladding coatings. The addition of a multi-component composite rare earth oxide and fluoride laser cladding protective layer effectively improves the coating's resistance to seawater corrosion. Surface hardness is significantly increased, and the corrosion potential and corrosion current density of the protective layer are -0.25 V and 1.87 × 10⁻⁶ V, respectively. -7 A·cm −2 It exhibits better resistance to pitting corrosion. The coating with added multi-component rare earth oxides and fluorides demonstrates excellent wear resistance, with a wear rate of 0.435 × 10⁻⁶. -5 mm 3 N -1 m -1 The wear resistance is significantly better than that of the untreated substrate, with the main wear mechanism being abrasive wear. Increased microhardness, grain refinement, and fine multi-component rare earth oxide particles are key factors in improving wear resistance. This invention provides a laser cladding method for emergency maintenance of marine engineering equipment such as ships, offshore platforms, and offshore pipelines, with broad application prospects.

[0109] The surface morphology of the laser-clad alloy coating was analyzed using a FEI NOVA 430 scanning electron microscope. The hardness of the samples was measured using an HV-1000A microhardness tester with a load of 100g and a loading time of 15s. Electrochemical measurements were performed using a three-electrode workstation (SOLARTRON 1287 / 1260) in a 4.0% (w / w) NaCl solution. Friction corrosion tests were conducted using a wear testing machine (HT-1000). The test conditions were: 4.0% (w / w) NaCl solution, a friction radius of 2 mm, a loading force of 10 N, and a duration of 60 minutes. GCr15 bearing steel grinding balls with a diameter of 4 mm were used in the experiment.

Claims

1. A method for improving iron-based cladding coatings on ship steel surfaces using rare earth oxides, characterized in that, The method is performed according to the following steps: (1) Ship structural steel is used as the base material to be repaired; (2) 316L stainless steel powder is used as the powder material for laser repair, fluoride powder is used as the coating material, and composite rare earth oxide is used as the protective layer material. (3) Apply stainless steel powder, composite rare earth oxides and fluoride powder in layers to the marine steel to be repaired using water-resistant adhesive; (4) A corrosion-resistant protective layer is formed using underwater laser cladding equipment; The aforementioned 316L stainless steel powder, fluoride coating material, composite rare earth oxide material, and marine steel repair substrate are first mixed with water-resistant adhesive, then coated with 316L stainless steel powder, then with composite rare earth oxide powder, and finally with coating material; the fluoride is calcium fluoride, and the preferred coating material is calcium fluoride; the weight composition of the fluoride coating layer, rare earth oxide protective layer, and 316L stainless steel powder is (5~10)%: (5~20)%: (70~90)%; the composite rare earth oxide is a mixture of yttrium oxide, lanthanum oxide, and cerium oxide, wherein the weight proportion of yttrium oxide is 50~70%, lanthanum oxide is 20~25%, and the remainder is cerium oxide.

2. The method for improving iron-based cladding coatings on ship steel surfaces using rare earth oxides according to claim 1, characterized in that, The water-resistant adhesive is composed of ethyl 2-cyano-2-acrylate (C6H7NO2); the proportion of water-resistant adhesive added accounts for 5-20% of the weight of the solid powder.

3. The method for improving iron-based cladding coatings on ship steel surfaces using rare earth oxides according to claim 1, characterized in that, During the laser cladding process, the laser power is 1000~4000W, the welding speed is 1~10mm / s, the spot diameter is 2~8mm, and the defocusing amount is +2~5mm; the laser cladding process is carried out online underwater.

4. The method for improving iron-based cladding coatings on ship steel surfaces using rare earth oxides according to claim 1, characterized in that, The method is applicable to ship structural steel of strength grades A, B, D, and E, and high-strength ship structural steel of grades AH32, DH32, EH32, AH36, DH36, and EH36.

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