Laser cladding layer material of nodular cast iron and method for preparing corrosion-resistant layer on surface of nodular cast iron

Abstract

The application discloses a nodular cast iron laser cladding layer material and a nodular cast iron surface corrosion-resistant layer preparation method. The cladding layer material is a nickel-based powder, and the nickel-based powder comprises the following components in percentage by mass: C: 0.02% to 0.15%, Cr: 16.6 to 17.5%, Mo: 13 to 17, Fe: 2.5 to 3.8%, Mn: 0.7 to 1.6%, V: 0.6 to 0.8%, Si: 0.3 to 0.7%, S: 0.01%, O: 0.05%, W: 3.0 to 5.0%, and the balance is Ni. The preparation method comprises the following steps: drying treatment is performed on the cladding layer nickel-based powder; laser cladding is performed to prepare the cladding layer; and during the laser cladding, the cladding powder is fed by using a carrier gas type powder feeder, and the powder feeding mode is coaxial powder feeding. The application can avoid defects such as cracking and falling of the cladding layer, effectively improves the corrosion resistance of the nodular cast iron base body, and takes into account the bonding strength, the compactness of the structure and the wear resistance.

Description

Technical Field

[0001] This invention belongs to the field of laser surface engineering technology, specifically relating to laser cladding materials for ductile iron and methods for preparing corrosion-resistant layers on ductile iron surfaces. Background Technology

[0002] Ductile iron possesses high strength, good toughness, and excellent plasticity. Combined with the lubricating effect of graphite spheres, it is widely used in the manufacture of high-strength and tough parts such as screw pump housings and bases. However, ductile iron is prone to shrinkage cavities and sand holes during the casting process. Furthermore, cast iron parts are frequently subjected to corrosive gas corrosion, alternating thermal stress, and wear during service. Without surface treatment, they cannot meet the required performance.

[0003] Laser cladding uses a high-energy laser beam to melt cladding powder and solidify it on the material surface. Through a metallurgical reaction with the base material, a cladding layer is formed, significantly improving the material's corrosion resistance, wear resistance, oxidation resistance, and heat resistance. It is an efficient and high-quality method for surface modification and repair / remanufacturing. Compared with traditional coating preparation methods such as spraying, electroplating, and arc welding, laser cladding has advantages such as high coating-substrate bonding strength, good density, controllable thickness, and low dilution rate, showing promising application prospects in the preparation of coatings for ductile iron surfaces. Currently, the cladding powders used on ductile iron workpieces are mostly iron-based or cobalt-based, primarily used to improve the hardness of the cladding layer and consider its wear resistance, with less consideration given to the corrosion resistance of the cladding layer. For ductile iron workpieces used in acidic environments (containing chloride ions), such as pump ductile iron workpieces, the corrosion resistance of the cladding layer needs to be considered.

[0004] Currently, there is limited research on methods for preparing corrosion-resistant layers on the surface of ductile iron. The research focus is on how to eliminate defects such as cracking and peeling of the corrosion-resistant layer on the surface of ductile iron in acidic environments and improve the corrosion resistance of the ductile iron matrix.

[0005] Therefore, this patent application is filed. Summary of the Invention

[0006] To address the above issues, this patent application aims to provide a laser cladding material for ductile iron and a method for preparing a corrosion-resistant layer on the surface of milled cast iron. This method can avoid defects such as cracking and peeling of the cladding layer on the surface of milled cast iron, effectively improve the corrosion resistance of the ductile iron matrix, and take into account the bonding strength, density, and wear resistance.

[0007] This invention is achieved through the following technical solution:

[0008] The first objective of this invention is to provide a laser cladding material for ductile iron, wherein the cladding material is a nickel-based powder comprising the following components in the indicated mass percentages: C: 0.02%–0.15%, Cr: 16.6–17.5%, Mo: 13–17%, Fe: 2.5–3.8%, Mn: 0.7–1.6%, V: 0.6–0.8%, Si: 0.3–0.7%, S: 0.01%, O: 0.05%, W: 3.0–5.0%, with the balance being Ni.

[0009] Currently, most cladding powders used on ductile iron workpieces are iron-based or cobalt-based, primarily used to improve the hardness of the cladding layer. Considering the need for acidic environments and improved corrosion resistance, the cladding powder used in this embodiment is nickel-based. However, since nickel-based powders combine with ductile iron to form intermetallic compounds, hot cracks easily form in the cladding metal when nickel-based alloy materials are deposited on the surface of QT500 cast iron. This is because the high content of S and P in the cast iron mixes into the high-nickel cladding layer, forming Ni3S2 nickel sulfide. The Ni-Ni3S2 eutectic temperature is very low (644℃), and nickel combines with phosphorus to form Ni3P, which also has a very low Ni-Ni3P eutectic temperature (880℃). Both of these eutectics reduce the high-temperature strength of the weld metal. In addition, the single-phase austenitic cladding layer has coarse grains, and low-melting-point eutectics are prone to accumulate at grain boundaries. Ultimately, under stress, hot cracks occur in the cladding layer. This leads to poor metallurgical compatibility. Therefore, in this embodiment of the invention, nickel-based powder is rationally designed by adding vanadium, manganese, and tungsten elements to provide grain nucleation points, refine the cladding layer structure, and inhibit the formation of intermetallic compounds, thereby improving the toughness and ductility of the cladding layer and overcoming the technical problem of poor metallurgical compatibility when nickel-based powder is combined with ductile cast iron.

[0010] In some optional embodiments, the nickel-based powder has a particle size of 20–50 μm. Using nickel-based powder with a particle size of 20–50 μm can achieve the technical objective of ensuring the density of the cladding layer and reducing the generation of porosity and inclusion defects.

[0011] The second objective of this invention is to provide a method for preparing a corrosion-resistant layer on the surface of ductile iron, comprising the following steps:

[0012] The nickel-based powder of the cladding layer is dried.

[0013] Laser cladding is used to prepare the cladding layer;

[0014] During the laser cladding process, a carrier gas-type powder feeding method is used to feed the cladding powder, and the powder feeding method is coaxial powder feeding.

[0015] The nickel-based cladding powder comprises the following components in the indicated weight percentages: C: 0.02%–0.15%, Cr: 15.6%–16.5%, Mo: 14%–18%, Fe: 2.5%–3.8%, Mn: 0.7%–1.6%, V: 0.3%–0.8%, Si: 0.3%–0.7%, S: 0.01%, O: 0.05%, W: 3.0%–5.0%, with the balance being Ni.

[0016] In this invention, a laser cladding method is used to obtain a corrosion-resistant layer (i.e., a cladding layer). Nickel-based powder and the ductile iron substrate melt under the action of a laser heat source, forming a metallurgical bond. The cladding layer and substrate exhibit high bonding strength and good density, with no delamination, wear resistance, and controllable thickness, eliminating the problem of cladding layer detachment during machining. The rational design of the nickel-based powder improves the corrosion resistance of the cladding layer and enhances the substrate's resistance to chloride ion corrosion, preventing cracking and detachment even in acidic environments. The laser cladding process described in this patent also effectively reduces the dilution rate of the substrate, minimizing the influence of the substrate on the chemical composition of the cladding layer and preserving its original good properties. Furthermore, the heat input of the laser cladding method is significantly lower than that of arc welding, significantly reducing substrate deformation.

[0017] Furthermore, the coaxial powder feeding method has good powder utilization and spatial adaptability, and can realize the preparation of corrosion-resistant layers on complex surface and internal pore structures.

[0018] In some optional embodiments, the particle size of the nickel-based powder is 20–50 μm.

[0019] In some optional embodiments, the drying process is drying at a temperature of 100–120°C for 1–1.5 hours.

[0020] In some optional embodiments, the laser used for laser cladding is a fiber laser, and the laser spot is a circular spot with a diameter of 1 to 3 mm. The matching selection of the circular spot and the spot diameter can effectively ensure that the fed powder melts uniformly and forms a continuous and beautiful cladding layer.

[0021] In some optional embodiments, the process parameters of the laser cladding process are as follows: laser power: 1600-2100W, powder feeding rate: 10-15g / min, powder carrier gas flow rate: 2.0-3.5L / min, and scanning rate: 250-350mm / min.

[0022] In some optional embodiments, the cladding layer is prepared by a single-layer multi-pass cladding method, with an overlap rate of 30-50% between passes, an inter-pass temperature controlled at 100-150°C, and the laser scanning direction of each cladding pass remaining consistent.

[0023] In this embodiment of the invention, by reasonably controlling the process parameters and overlap rate, the obtained cladding layer is well bonded to the substrate, and no defects such as voids or interface microcracks appear. The cladding layer has a uniform structure and fine grains.

[0024] In some alternative embodiments, the thickness of the cladding layer is 0.8–1.5 mm.

[0025] In some optional embodiments, the weld bead layer is thinned by milling, and the thickness of the weld bead layer after milling is 0.4 to 0.5 mm, and the surface roughness is Ra 0.8.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0027] The laser cladding material for ductile iron provided in this invention is nickel-based powder. By rationally designing the nickel-based powder, the formation of intermetallic compounds when nickel-based powder and ductile iron are bonded is eliminated, thus overcoming the technical problem of poor metallurgical compatibility between nickel-based powder and ductile iron.

[0028] The present invention provides a method for preparing a corrosion-resistant layer on the surface of ductile cast iron. By utilizing cleverly designed nickel-based powder and laser cladding technology, and by reasonably controlling the laser cladding process parameters, the cladding layer and the substrate have high bonding strength, good density, no delamination, wear resistance, and strong corrosion resistance. The corrosion-resistant layer will not crack or peel off even in acidic environments.

[0029] Specifically:

[0030] (1) Compared with existing spraying methods, the present invention enables the powder and ductile iron substrate to melt and generate metallurgical bonding under the action of laser heat source. The bonding strength between the cladding layer and the substrate is high, and the thickness of the cladding layer is controllable. There is no problem of the cladding layer falling off during machining.

[0031] (2) Compared with the traditional electric arc welding method, the laser cladding method used in the embodiments of the present invention can effectively reduce the dilution rate of the substrate. Therefore, the chemical composition of the cladding layer is less affected by the substrate, ensuring its original good performance. Moreover, the heat input of the laser cladding method is much lower than that of electric arc welding, which can significantly reduce the degree of substrate deformation.

[0032] (3) Compared with the existing pre-placed powder laser cladding method, the coaxial powder feeding method of the present invention has better powder utilization and spatial adaptability, and can realize the preparation of corrosion-resistant layers on complex structural surfaces and internal holes.

[0033] (4) By reasonably controlling the process parameters and overlap rate, the cladding layer obtained in the embodiment of the present invention has a good bond with the substrate and no defects such as voids or interface microcracks appear. The cladding layer has a uniform structure and fine grains.

[0034] (5) The cladding layer obtained in the embodiments of the present invention has good density and no delamination phenomenon. The hardness of the cladding layer reaches 400Hv, which is much higher than the substrate's 200Hv, and can effectively improve the wear resistance of the substrate material.

[0035] (6) The embodiments of the present invention use nickel-based powder to prepare a corrosion-resistant layer, which significantly improves the substrate’s resistance to chloride ion corrosion and meets the requirements of actual working conditions. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0037] Figure 1 This is a macroscopic structural diagram of the cladding layer before machining obtained in Example 1.

[0038] Figure 2 This is a macroscopic metallographic image of the cladding layer before machining obtained in Example 1.

[0039] Figure 3 This is a microstructure image of the interface of the cladding layer before machining obtained in Example 1.

[0040] Figure 4 This is a metallographic diagram of the surface of the cladding layer before machining obtained in Example 1.

[0041] Figure 5 This is a chemical composition distribution diagram of the cladding layer and the substrate at the interface chemistry obtained in Example 1 before machining.

[0042] Figure 6 The image shows the hardness test results of the cladding layer before machining obtained in Example 1.

[0043] Figure 7 The image shows the corrosion resistance test results of the cladding layer before machining obtained in Example 1.

[0044] Figure 8 The image shows the typical morphology of the dendritic structure of the cladding coating before machining obtained in Example 1. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. The illustrative embodiments and descriptions of this invention are only used to explain this invention and are not intended to limit this invention.

[0046] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other embodiments, well-known methods have not been specifically described in order to avoid obscuring the invention.

[0047] Throughout this specification, references to "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases "an embodiment," "an example," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination.

[0048] In the description of this invention, the terms "front," "rear," "left," "right," "upper," "lower," "vertical," "horizontal," "high," "low," "inner," and "outer," etc., indicating orientation or positional relationships, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention.

[0049] Example 1:

[0050] The nickel-based powder has the following composition: C: 0.02%, Cr: 15.6%, Mo: 16%, Fe: 2.5%, Mn: 0.9%, V: 0.3%, Si: 0.3%, S: 0.01%, O: 0.05%, W: 3.0%, with the balance being Ni. The particle size of the nickel-based powder is 20 micrometers.

[0051] The method for preparing a corrosion-resistant layer on the surface of ductile cast iron comprises the following steps:

[0052] (1) Place the nickel-based powder into a drying equipment for drying treatment. The drying temperature is 110℃ and the drying time is 60min. After drying, seal and store for later use.

[0053] (2) Use a grinding device to grind the surface of the substrate and wipe it with anhydrous ethanol to remove surface rust and oil stains.

[0054] (3) Set the laser cladding parameters as follows:

[0055] Laser power: 1700W; laser spot diameter: 3mm; powder feeding rate: 10g / min; powder carrier gas flow rate: 3.5L / min; scanning rate: 250mm / min; powder carrier gas is high-purity argon (99.999%). A coaxial powder feeding method with carrier gas is adopted.

[0056] (4) A single-layer, multi-pass cladding method was used to prepare the cladding layer. The overlap rate between passes was set to 40%, the inter-pass temperature was controlled at 150℃, and the laser scanning direction of each cladding pass remained consistent. The desired result was as follows: Figure 1 The cladding layer shown is 0.8 mm thick.

[0057] (5) The cladding layer is thinned by milling. After milling, the thickness of the cladding layer is 0.4 mm, the surface is smooth and there are no traces of machining. The surface roughness is controlled to Ra0.8 level.

[0058] Example 2:

[0059] The nickel-based powder has the following composition: C: 0.15%, Cr: 16.5%, Mo: 18%, Fe: 3.8%, Mn: 0.7%, V: 0.8%, Si: 0.7%, S: 0.01%, O: 0.05%, W: 5.0%, with the balance being Ni. The particle size of the nickel-based powder is 40 micrometers.

[0060] The method for preparing a corrosion-resistant layer on the surface of ductile cast iron comprises the following steps:

[0061] (1) Place the nickel-based powder into a drying equipment for drying treatment. The drying temperature is 120℃ and the drying time is 90min. After drying, seal and store for later use.

[0062] (2) Use a grinding device to grind the surface of the substrate and wipe it with anhydrous ethanol to remove surface rust and oil stains.

[0063] (3) Set the laser cladding parameters as follows:

[0064] Laser power: 1600W; laser spot diameter: 1mm; powder feeding rate: 15g / min; powder carrier gas flow rate: 2.0L / min; scanning rate: 300mm / min; powder carrier gas is high-purity argon (99.999%). A coaxial powder feeding method with carrier gas is adopted.

[0065] (4) A single-layer, multi-pass cladding method was used to prepare the cladding layer. The overlap rate between passes was set to 30%, the inter-pass temperature was controlled at 130℃, and the laser scanning direction of each cladding pass remained consistent. The desired result was as follows: Figure 1 The cladding layer shown is 1.5 mm thick.

[0066] (5) The cladding layer is thinned by milling. After milling, the thickness of the cladding layer is 0.45 mm, the surface is smooth and there are no machining marks. The surface roughness is controlled to Ra0.8 level.

[0067] Example 3:

[0068] The nickel-based powder has the following composition: C: 0.1%, Cr: 16.0%, Mo: 14%, Fe: 3.5%, Mn: 1.6%, V: 0.5%, Si: 0.45%, S: 0.01%, O: 0.05%, W: 4.1%, with the balance being Ni. The particle size of the nickel-based powder is 40 micrometers.

[0069] The method for preparing a corrosion-resistant layer on the surface of ductile cast iron comprises the following steps:

[0070] (1) Place the nickel-based powder into a drying equipment for drying treatment. The drying temperature is 115℃ and the drying time is 80min. After drying, seal and store for later use.

[0071] (2) Use a grinding device to grind the surface of the substrate and wipe it with anhydrous ethanol to remove surface rust and oil stains.

[0072] (3) Set the laser cladding parameters as follows:

[0073] Laser power: 2100W; laser spot diameter: 1.5mm; powder feeding rate: 15g / min; powder carrier gas flow rate: 3.0L / min; scanning rate: 350mm / min; powder carrier gas is high-purity argon (99.999%). A coaxial powder feeding method with carrier gas is adopted.

[0074] (4) A single-layer, multi-pass cladding method was used to prepare the cladding layer. The overlap rate between passes was set to 30%, the inter-pass temperature was controlled at 150℃, and the laser scanning direction of each cladding pass remained consistent. The desired result was as follows: Figure 1 The cladding layer shown is 1.2 mm thick.

[0075] (5) The cladding layer is thinned by milling. After milling, the thickness of the cladding layer is 0.45 mm, the surface is smooth and there are no machining marks. The surface roughness is controlled to Ra0.8 level.

[0076] Test example:

[0077] 1. Conduct a penetration test

[0078] The clad ductile iron workpiece obtained in Example 1 was subjected to a penetrant test, a conventional non-destructive testing method. The results are shown below. Figure 1 As shown.

[0079] The results show that the cladding layer on the workpiece obtained in the example has no defects such as cracks or pores.

[0080] 2. Perform metallographic examination

[0081] The clad spheroidal cast iron workpiece obtained in Example 1 was subjected to metallization experiments.

[0082] Example 1: Macroscopic metallographic image of the cross-section of the cladding layer before machining (see example 1). Figure 2 As shown, the weld plating layer is approximately 1.5 mm thick, and the microscopic metallographic image at the interface is as follows. Figure 3 As shown, the cladding layer is well bonded to the substrate, and no cracks or defects were found. The metallographic structure of the cladding layer surface is shown below. Figure 4 This indicates that the cladding layer has a typical dendritic morphology with fine grains and no defects such as pores, cracks, or inclusions.

[0083] The chemical composition distribution at the interface between the cladding layer and the substrate was also studied, see [reference needed]. Figure 5 It can be seen that there is a gradual transition of Fe, Ni, Mo and Cr elements at the interface.

[0084] 3. Hardness test

[0085] The clad ductile iron workpiece obtained in Example 1 was subjected to a hardness test. The results of Example 1 are shown below. Figure 6 As shown in the figure, the hardness of the weld layer is higher than 350 Hv, which is much higher than the hardness of the substrate (150 Hv). It has high bonding strength and good wear resistance.

[0086] 4. Corrosion resistance test

[0087] The galvanized cast iron workpiece from Example 1 was subjected to a salt spray test, with the uncoated cast iron base material used as a control sample. The results are as follows: Figure 7 As shown, under the same corrosion conditions, the corrosion weight gain of the base material sample was much higher than that of the welded sample, indicating that the presence of the welded layer can significantly improve the substrate's resistance to chloride ion corrosion.

[0088] The dendritic structure of the coating was observed using a scanning electron microscope, and the results are as follows: Figure 8 As shown in Table 1, the elemental energy dispersive spectroscopy (EDS) results of typical morphologies (sp1, sp2, sp3) in the dendritic structure are presented. It can be seen that the dendritic structure in the cladding layer mainly consists of a Ni-rich solid solution matrix (sp1) and a network eutectic structure (sp2 and sp3). The network eutectic structure is composed of Ni-rich solid solution and Mo-rich carbides. This microstructure has a good promoting effect on improving the corrosion resistance of the material.

[0089] Table 1: Elemental energy spectrum (wt%) results of typical morphologies (sp1, sp2, sp3) in dendritic structures.

[0090]

[0091] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A laser cladding material for ductile iron, characterized in that, The cladding layer material is nickel-based powder, which comprises the following components in the indicated mass percentages: C: 0.02%–0.15%, Cr: 16.6–17.5%, Mo: 13–17%, Fe: 2.5–3.8%, Mn: 0.7–1.6%, V: 0.6–0.8%, Si: 0.3–0.7%, S: 0.01%, O: 0.05%, W: 3.0–5.0%, with the balance being Ni.

2. The laser cladding material for ductile iron according to claim 1, characterized in that, The nickel-based powder has a particle size of 20–50 μm.

3. A method for preparing a corrosion-resistant layer on the surface of ductile iron, characterized in that, Includes the following steps: The nickel-based powder of the cladding layer is dried. Laser cladding is used to prepare the cladding layer; During the laser cladding process, a carrier gas-type powder feeding method is used to feed the cladding powder, and the powder feeding method is coaxial powder feeding. The nickel-based cladding powder comprises the following components in the indicated weight percentages: C: 0.02%–0.15%, Cr: 16.6–17.5%, Mo: 13–17%, Fe: 2.5–3.8%, Mn: 0.7–1.6%, V: 0.6–0.8%, Si: 0.3–0.7%, S: 0.01%, O: 0.05%, W: 3.0–5.0%, with the balance being Ni.

4. The method for preparing a corrosion-resistant layer on the surface of ductile iron according to claim 3, characterized in that, The particle size of the nickel-based powder is 20–50 μm.

5. The method for preparing a corrosion-resistant layer on the surface of ductile iron according to claim 3, characterized in that, The drying process is called drying, with a drying temperature of 100-120℃ and a holding time of 1-1.5h.

6. The method for preparing a corrosion-resistant layer on the surface of ductile iron according to claim 3, characterized in that, The laser used in laser cladding is a fiber laser with a circular laser spot diameter of 1–3 mm.

7. The method for preparing a corrosion-resistant layer on the surface of ductile iron according to claim 3, characterized in that, The process parameters for laser cladding are as follows: laser power: 1600~2100W, powder feeding rate: 10~15g / min, powder carrier gas flow rate: 2.0~3.5L / min, scanning rate: 250~350mm / min.

8. The method for preparing a corrosion-resistant layer on the surface of ductile iron according to claim 3, characterized in that, The cladding layer is prepared by a single-layer multi-pass cladding method, with an overlap rate of 30-50% between passes, and the interpass temperature is controlled at 100-150℃. The laser scanning direction of each cladding pass is kept consistent.

9. The method for preparing a corrosion-resistant layer on the surface of ductile iron according to claim 3, characterized in that, The thickness of the cladding layer is 0.8–1.5 mm.

10. The method for preparing a corrosion-resistant layer on the surface of ductile iron according to claim 9, characterized in that, The weld bead layer is thinned by milling. After milling, the thickness of the weld bead layer is 0.4-0.5 mm and the surface roughness is Ra0.8.

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