Spheroidal graphite cast iron-based composite laser cladding material and preparation method therefor

Abstract

The present invention provides a spheroidal graphite cast iron-based composite laser cladding material, composed of a spheroidal graphite cast iron substrate, a laser-remelted layer composited on the surface of the spheroidal graphite cast iron substrate, a nickel-based transition cladding layer composited on the surface of the laser-remelted layer, and a cobalt-based cladding layer composited on the surface of the nickel-based transition cladding layer. The present invention further provides a method for preparing the spheroidal graphite cast iron composite-based laser cladding material. In the spheroidal graphite cast iron composite-based laser cladding material, the laser-remelted layer is conducive to achieving good metallurgical bonding between the cladding layer and the substrate. Furthermore, by means of the nickel-based transition cladding layer, which has the advantage of high mutual solubility with the substrate, the problems of crack defects and cladding layer falling off can be avoided. Finally, by using cobalt-based alloy powder as a cladding material to form the cobalt-based cladding layer, which has the characteristics of excellent high-temperature resistance, wear resistance, and corrosion resistance, the surface of the spheroidal graphite cast iron substrate can be repaired, and the purpose of prolonging the service life is achieved.

Description

A composite laser cladding material for ductile iron and its preparation method

[0001] This application claims priority to Chinese Patent Application No. 202410989626.3, filed on July 23, 2024, entitled "A Composite Laser Cladding Material for Ductile Iron and Its Preparation Method", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to the field of laser cladding technology, and in particular to a ductile iron composite laser cladding material and its preparation method. Background Technology

[0003] With the continuous development of industrialization, surface damage failure of cast iron parts is very common in manufacturing sectors such as wind power, mining, shipbuilding, and rail transportation. These failures mainly include wear failure, corrosion failure, and fatigue failure. Surface damage failure can lead to overall structural failure, resulting in the scrapping of the entire part and causing incalculable safety hazards and economic losses. Conventional surface repair methods for aging surface damage include electroplating, high-speed spraying, and welding. Electroplating, however, causes severe environmental pollution and cannot produce thick coatings; the electroplated layer is prone to peeling. High-speed spraying is a non-metallurgical bonding method based on the principle of high-speed impact and plastic deformation mechanical interlocking, resulting in low adhesion between the cladding layer and the substrate, and the repair layer is only at the micrometer level, failing to meet the thickness requirements for part repair. Welding, due to its high heat input, can affect the properties of the substrate, easily causing deformation and cracking. Therefore, selecting appropriate methods to repair surface damage is of great significance for improving part lifespan, achieving energy conservation and emission reduction, and saving economic costs.

[0004] Laser cladding, a relatively new surface repair technology, utilizes a high-energy laser beam to melt cladding powder that has been pre-placed or synchronously delivered to the repair area, thereby forming a metallurgical bond with the substrate. It offers advantages such as high efficiency, low heat input, and minimal environmental pollution. Self-fluxing alloy powders are a widely used type of cladding material, among which cobalt-based self-fluxing alloy powders exhibit good wettability, high-temperature resistance, and excellent wear and corrosion resistance.

[0005] Building upon this, cobalt-based self-fluxing alloy powder has been applied in laser cladding technology. For example, Chinese patent CN117845208A uses cobalt-based self-fluxing alloy powder mixed with carbon fiber powder as the cladding material, producing a cladding layer with good corrosion resistance and wear resistance. Another example is Chinese patent CN116426921A, which uses cobalt-based alloy powder as the cladding material to prepare a well-formed cladding layer with high hardness. These existing technologies all utilize cobalt-based self-fluxing alloys directly clad onto the substrate for repair, improving the surface hardness and wear resistance of parts. However, they overlook the fact that ductile iron surfaces are prone to free graphite, and the significant difference in thermal expansion coefficients between ductile iron and the cobalt-based cladding layer can lead to poor adhesion between the substrate and the cladding layer, resulting in defects such as microcracks at the joint. When parts are subjected to significant impact, the cladding layer may crack and detach, thus limiting its industrial application.

[0006] Summary of the Invention

[0007] The technical problem solved by this invention is to provide a ductile iron composite laser cladding material, which can effectively repair the surface of ductile iron substrate and extend its service life.

[0008] In view of this, this application provides a ductile iron composite laser cladding material, which is composed of a ductile iron substrate, a laser remelting layer composited on the surface of the ductile iron substrate, a nickel-based transition cladding layer composited on the surface of the laser remelting layer, and a cobalt-based cladding layer composited on the surface of the nickel-based transition cladding layer.

[0009] The raw materials for preparing the nickel-based transition cladding layer, by mass percentage, include: C 0.2-0.5%, Si 2.8-3.5%, B 2.0-3.0%, Cr 9.0-13.0%, and Ni balance;

[0010] The raw materials for preparing the cobalt-based cladding layer, by mass percentage, include: C 0.7-1.2%, Si 1.5-2.0%, B 1.5-2.0%, Mn 0.4-0.6%, Cr 24-26%, Mo 1.0-2.0%, and Co balance.

[0011] Preferably, the thickness of the laser remelting layer is 1-3 mm, the thickness of the nickel-based transition cladding layer is 1-2 mm, and the thickness of the cobalt-based cladding layer is 2-3 mm.

[0012] Preferably, the ductile iron substrate is QT400 ductile iron damaged parts.

[0013] The present invention also provides a method for preparing the aforementioned ductile iron composite laser cladding material, comprising the following steps:

[0014] C powder, Si powder, B powder, Cr powder and Ni powder are mixed in a certain mass ratio to obtain nickel-based alloy powder;

[0015] C powder, Si powder, B powder, Mn powder, Cr powder, Mo powder and Co powder are mixed in a certain mass ratio to obtain cobalt-based alloy powder;

[0016] Laser remelting is performed on the surface of the ductile iron substrate to obtain a laser remelted layer;

[0017] The nickel-based alloy powder is placed into the powder feeding device of a laser cladding machine, and laser cladding is performed on the surface of the laser remelting layer to obtain a nickel-based transition cladding layer.

[0018] The cobalt-based alloy powder is fed into the powder feeding device of a laser cladding machine, and laser cladding is performed on the surface of the nickel-based transition cladding layer to obtain a cobalt-based cladding layer.

[0019] Preferably, the nickel-based alloy powder has a sphericity ≥95% and a particle size distribution of 45–150 μm; the cobalt-based alloy powder has a sphericity ≥95% and a particle size distribution of 45–150 μm.

[0020] Preferably, during the preparation of the laser remelting layer, the laser power is 1000-1200W, the remelting speed is 18-20mm / s, the protective gas is pure argon, and the gas flow rate is 5-10L / min.

[0021] Preferably, during the preparation of the nickel-based transition cladding layer, the laser power is 1400-1600W, the cladding speed is 18mm / s, the powder feeding speed is 20-25g / min, and the overlap rate is 30-35%; the protective gas is pure argon with a flow rate of 10-15L / min; and the powder carrier gas is pure nitrogen with a flow rate of 8-10L / min.

[0022] Preferably, during the preparation of the cobalt-based cladding layer, the laser power is 1500-1700W, the cladding speed is 14-20mm / s, the powder feeding speed is 20-25g / min, and the overlap rate is 40-50%; the protective gas is pure argon with a flow rate of 5-8L / min, and the powder carrier gas is pure nitrogen with a flow rate of 8-10L / min.

[0023] Preferably, in the preparation process of the nickel-based alloy powder and the cobalt-based alloy powder, the mixing is carried out in a planetary ball mill, the planetary ball mill has a revolution speed of 10-20 r / min and a rotation speed of 50-70 r / min, and the mixing time is 1-3 h.

[0024] Preferably, after the laser remelting layer is prepared and before the nickel-based transition cladding layer is prepared, the process further includes:

[0025] The surface is polished without damaging the laser remelted layer, and then rinsed.

[0026] After the preparation of the nickel-based transition cladding layer and before the preparation of the cobalt-based cladding layer, the following steps are also included:

[0027] The surface of the nickel-based transition cladding layer is polished;

[0028] After the cobalt-based cladding layer is prepared, the following steps are also included:

[0029] The surface of the cobalt-based cladding layer is polished.

[0030] This invention provides a ductile iron composite laser cladding material, comprising a ductile iron substrate, a laser remelting layer laminated to the surface of the ductile iron substrate, a nickel-based transition cladding layer laminated to the surface of the laser remelting layer, and a nickel-based cladding layer laminated to the surface of the nickel-based transition cladding layer. The laser remelting layer on the surface of the ductile iron substrate reduces free graphite on the substrate surface, homogenizes the surface microstructure and elemental distribution, and facilitates a good metallurgical bond between the cladding layer and the substrate. The nickel-based transition cladding layer has good adhesion and high toughness. Fusing the nickel-based transition layer onto the surface of the ductile iron substrate effectively avoids problems such as cracking defects and cladding layer detachment at the joint due to the large difference in thermal expansion coefficients between the cobalt-based cladding layer and the ductile iron. Finally, cobalt-based alloy powder is fused onto the surface of the ductile iron, preparing a cobalt-based cladding layer with good high-temperature resistance, wear resistance, and corrosion resistance. This effectively repairs the surface of cast iron parts, extending their service life. Attached Figure Description

[0031] Figure 1 is a schematic diagram of the cross-section of the ductile iron composite laser cladding material;

[0032] Figure 2 shows the effect of repairing the QT400 ductile iron parts;

[0033] Figure 3 is a microstructure photograph of the cladding layer after laser remelting in Comparative Example 1;

[0034] Figure 4 shows microscopic photographs of the cobalt-based alloy powder and cladding layer in Example 1 of the present invention and the cobalt-based alloy powder and cladding layer in Comparative Example 2. Detailed Implementation

[0035] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention.

[0036] In view of the problems of poor adhesion between the laser cladding layer and the substrate in the prior art, resulting in microcracks at the bonding interface, this invention provides a ductile iron composite laser cladding material and its preparation method. In the ductile iron composite laser cladding material, the laser remelting layer can reduce the free graphite on the substrate surface, homogenize the surface structure and element distribution, and facilitate a good metallurgical bond between the cladding layer and the substrate. The selection of nickel-based alloy powder in the nickel-based transition cladding layer gives it good wettability, high toughness, and strong adhesion to the cobalt-based cladding layer and the substrate, effectively preventing the direct melting of cobalt-based powder into the ductile iron surface. The large difference in thermal expansion coefficients between the two leads to cracks and defects at the joint and cladding layer peeling. It exhibits good metallurgical bonding. The selection of cobalt-based alloy powder in the cobalt-based cladding layer gives it excellent high-temperature resistance, wear resistance, and corrosion resistance, effectively repairing ductile iron substrates. Specifically, this invention discloses a ductile iron composite laser cladding material, composed of a ductile iron substrate, a laser remelting layer composited on the surface of the ductile iron substrate, a nickel-based transition cladding layer composited on the surface of the laser remelting layer, and a cobalt-based cladding layer composited on the surface of the nickel-based transition cladding layer.

[0037] The raw materials for preparing the nickel-based transition cladding layer, by mass percentage, include: C 0.2-0.5%, Si 2.8-3.5%, B 2.0-3.0%, Cr 9.0-13.0%, and Ni balance;

[0038] The raw materials for preparing the cobalt-based cladding layer, by mass percentage, include: C 0.7-1.2%, Si 1.5-2.0%, B 1.5-2.0%, Mn 0.4-0.6%, Cr 24-26%, Mo 1.0-2.0%, and Co balance.

[0039] In this invention, the ductile iron substrate is specifically QT400 cast iron, and more specifically, QT400 cast iron surface-damaged parts.

[0040] Since cylinders, shafts, and other parts made of QT400 cast iron are subjected to frictional forces and often bear impact loads, the impact toughness of the cladding layer is required to be high under such conditions. Therefore, the design principle of the composite cladding layer of this invention is: the outermost cladding layer has high hardness and high wear resistance, and also has a certain high temperature resistance; the transition layer has a certain strength and hardness, and has good bonding performance and high toughness, which can absorb the impact force on the workpiece to a certain extent; however, there are metallurgical bonding problems between the outermost cladding layer, the transition layer, and the substrate. How to achieve good metallurgical bonding while giving full play to the effect of each layer is the key and difficult point of this invention.

[0041] The outermost layer of the substrate of this invention is composited with a cobalt-based cladding layer. By adjusting the composition and content of the cobalt-based alloy powder in the cobalt-based cladding layer, the cobalt-based cladding layer has high strength, good resistance to thermal fatigue, resistance to thermal corrosion and wear corrosion. The cobalt-based alloy powder includes the following elements in mass percentage: C 0.7-1.2%, Si 1.5-2.0%, B 1.5-2.0%, Mn 0.4-0.6%, Cr 24-26%, Mo 1.0-2.0%, and Co balance.

[0042] In the raw materials for preparing cobalt-based cladding layers, carbon (C) has very low solubility in cobalt (Co). Therefore, adding higher amounts of chromium (Cr) and carbon (C) allows the formation of carbides during the cladding process, which act as a second reinforcing phase, improving the strength and hardness of the cobalt-based cladding layer. However, when the C content is greater than 1.5% and the Cr content is greater than 30%, the cladding layer becomes very brittle and stress cracks may occur. Therefore, the C content is 0.7%–1.2%, and the Cr content is 24%–26%. Specifically, the C content is 0.8%–1.1%, for example, 0.8%, 0.9%, 1.0%, or 1.1%, and the Cr content is 24%, 25%, or 26%.

[0043] Bo (B) and silicon (Si) have deoxidizing and slag-forming effects, and also lower the melting point of alloys, making them essential elements in self-fluxing alloys. However, excessive content increases the tendency of the cladding layer to crack and significantly enhances its brittleness. Therefore, the content of B is 1.5–2.0%, and the content of Si is 1.5–2.0%. Specifically, the content of B is 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0%, and the content of Si is 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0%.

[0044] 1.0% to 2.0% Mo can improve the thermodynamic and chemical properties of the cladding layer; specifically, the Mo content is 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0%.

[0045] Mn, at a content of 0.4% to 0.6%, plays a role in deoxidation and desulfurization and is a beneficial element in cobalt-based alloy systems; specifically, the Mn content is 0.4%, 0.5%, or 0.6%.

[0046] Nickel-based alloy powders are designed with specific components and their contents to achieve good wettability, good bonding properties, and moderate toughness and strength.

[0047] B and Si elements have deoxidizing and slag-forming effects, while also lowering the alloy's melting point and improving wettability. However, excessive B content leads to a significant increase in the eutectic phase, resulting in intergranular cracking within the cladding layer and reducing its lifespan. Excessive Si content, on the other hand, reduces the ductility and toughness of the cladding layer. Therefore, the contents of B and Si are set at 2.0%–3.0% and 2.8%–3.5%, respectively. Specifically, the Si content is 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, or 3.5%, and the B content is 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, or 3.0%.

[0048] Cr has a solid solution strengthening effect and can form carbides with C during the cladding process as a second reinforcing phase, improving the strength and hardness of the nickel-based transition cladding layer. However, since a large amount of carbides will significantly reduce the plasticity and toughness of the cladding layer, and the transition layer has higher requirements for plasticity and toughness than strength, the Cr and C contents of the nickel-based transition layer are reduced to 9%–13% and 0.2–0.5%, respectively, compared to the high Cr and C contents in the outermost cobalt-based cladding layer, to ensure the plasticity and toughness of the nickel-based transition layer. Specifically, the Cr content is 9%, 10%, 11%, 12%, or 13%, and the C content is 0.2%, 0.3%, 0.4%, or 0.5%.

[0049] The nickel-based transition layer powder designed in this invention has a microhardness of 35-40 HRC, which is comparable to that of conventional Ni60 alloy powder (20% Cr and 8% Fe) with a cladding layer hardness of 58-60 HRC. It has both strength and toughness, and its coefficient of thermal expansion is similar to that of the substrate. Therefore, it has good adhesion to the substrate and is less prone to cracking.

[0050] In the ductile iron composite laser cladding material of the present invention, the thickness of the laser remelting layer is 1-3 mm, the thickness of the nickel-based transition cladding layer is 1-2 mm, and the thickness of the cobalt-based cladding layer is 2-3 mm; the specific structural schematic diagram is shown in Figure 1.

[0051] Furthermore, the present invention also provides a method for preparing ductile iron composite laser cladding materials, comprising the following steps:

[0052] C powder, Si powder, B powder, Cr powder and Ni powder are mixed in a certain mass ratio to obtain nickel-based alloy powder;

[0053] C powder, Si powder, B powder, Mn powder, Cr powder, Mo powder and Co powder are mixed in a certain mass ratio to obtain cobalt-based alloy powder;

[0054] Laser remelting is performed on the surface of the ductile iron substrate to obtain a laser remelted layer;

[0055] The nickel-based alloy powder is placed into the powder feeding device of a laser cladding machine, and laser cladding is performed on the surface of the laser remelting layer to obtain a nickel-based transition cladding layer.

[0056] The cobalt-based alloy powder is fed into the powder feeding device of a laser cladding machine, and laser cladding is performed on the surface of the nickel-based transition cladding layer to obtain a cobalt-based cladding layer.

[0057] In the preparation process of ductile iron composite laser cladding material, the present invention first prepares nickel-based alloy powder and cobalt-based alloy powder. The alloying elements and their proportions in the nickel-based alloy powder and the cobalt-based alloy powder have been described in detail above and will not be repeated here.

[0058] The nickel-based alloy powder and the cobalt-based alloy powder are preferably obtained by ball milling. More specifically, the ball milling is carried out in a planetary ball mill with a revolution speed of 10-20 r / min and a rotation speed of 50-70 r / min, and the mixing time is 1-3 h. Further, the revolution speed of the planetary ball mill is 15 r / min and the rotation speed is 65 r / min, and the mixing time is 2 h. After the above mixing is completed, drying is carried out at a temperature of 100-150°C for 1-3 h, and more specifically, at a temperature of 120-130°C for 2 h.

[0059] In this invention, the nickel-based alloy powder has a sphericity ≥95% and a particle size distribution of 45–150 μm; the cobalt-based alloy powder has a sphericity ≥95% and a particle size distribution of 45–150 μm. The high sphericity of both the nickel-based and cobalt-based alloy powders improves their fluidity in the molten pool, ensuring complete melting, enhancing pool spreadability, and reducing cladding defects. In other words, sphericity affects powder melting and pool morphology during subsequent laser cladding, and also influences crack inclination. Particle size distribution affects heat input and melting efficiency. Factors such as the yield and high-temperature dwell time can have an impact. Furthermore, non-spherical nickel-based alloy powders and cobalt-based alloy powders present the following problems: 1) Reduced forming quality: Compared to spherical powders, non-spherical powder particles have larger gaps, making them prone to porosity, defects, and other quality issues; 2) Slowed forming speed: The complex shape and large coverage area of ​​non-spherical powders can easily clog nozzles, thus reducing forming speed; 3) Unstable molten pool shape: Due to their irregular shape, non-spherical powders can easily cause problems such as eccentricity and uneven forming in the molten pool. Excessively large cladding powder particle size can lead to melting difficulties, making it hard to flow in the molten pool and easily causing unmelted defects; excessively small cladding powder particle size can easily agglomerate, clogging the powder feeding pipes and causing powder feeding difficulties.

[0060] According to the present invention, laser remelting is performed on the surface of the ductile iron substrate to obtain a laser remelted layer; the laser remelting is preferably performed under an argon atmosphere, and during the preparation of the laser remelted layer, the laser power is 1000-1200W, the remelting speed is 18-20mm / s; the protective gas is pure argon, and the gas flow rate is 5-10L / min; more specifically, the laser power is 1150-1180W, the remelting speed is 19-20mm / s, and the gas flow rate is 6-8L / min.

[0061] The present invention then places the nickel-based alloy powder into the powder feeding device of a laser cladding machine, and performs laser cladding on the surface of the laser remelted layer to obtain a nickel-based transition cladding layer; in order to avoid the influence of the oxide layer on the nickel-based transition layer, the invention further includes the following steps before preparing the nickel-based transition cladding layer:

[0062] Use 1000-grit sandpaper to sand away the surface oxide layer without damaging the remelted layer, then rinse the surface of the part with anhydrous ethanol and blow it dry.

[0063] In the process of preparing the nickel-based transition cladding layer, the preferred steps are as follows:

[0064] Place the nickel-based cladding powder into the powder feeder and set the appropriate powder feeding amount and powder feeding air flow rate;

[0065] In the robot program, the stepping distance is set according to the overlap rate, the water cooler and protective gas are set, the powder feeder is turned on, and the laser is turned on when the powder is uniformly discharged from the powder outlet pipe, so that the nickel-based powder is uniformly melted on the surface of the laser cladding layer to form a nickel-based transition cladding layer.

[0066] In the above process, the laser power is 1400-1600W, the cladding speed is 18mm / s, the powder feeding speed is 20-25g / min, and the overlap rate is 30-35%; the protective gas is pure argon with a flow rate of 10-15L / min; the powder carrier gas is pure nitrogen with a flow rate of 8-10L / min; specifically, the laser power is 1450-1500W, the powder feeding speed is 21-23g / min, the overlap rate is 32-33%, the gas flow rate is 11-13L / min, and the powder carrier gas is pure nitrogen with a flow rate of 9-10L / min.

[0067] The present invention then prepares a cobalt-based cladding layer on the surface of the nickel-based transition cladding layer. To avoid the influence of the oxide layer, it is preferable to polish the nickel-based transition cladding layer before preparing the cobalt-based cladding layer. The preparation of the cobalt-based cladding layer specifically involves:

[0068] Replace the powder in the powder feeder with cobalt-based alloy powder and reset appropriate parameters such as laser power and powder feeding amount;

[0069] The cobalt-based alloy powder is uniformly melted onto the nickel-based transition cladding layer to form a cobalt-based cladding layer.

[0070] In the preparation of the cobalt-based cladding layer, the laser power is 1500–1700 W, the cladding speed is 14–20 mm / s, the powder feeding speed is 20–25 g / min, and the overlap rate is 40–50%. The protective gas is pure argon with a flow rate of 5–8 L / min, and the powder carrier gas is pure nitrogen with a flow rate of 8–10 L / min. Specifically, the laser power is 1600–1700 W, the cladding speed is 16–18 mm / s, the powder feeding speed is 22–24 g / min, and the overlap rate is 42–45%. The protective gas is pure argon with a flow rate of 5–6 L / min, and the powder carrier gas is pure nitrogen with a flow rate of 9–10 L / min.

[0071] The preparation method provided by this invention is used for the repair of ductile iron parts, and specifically includes the following steps:

[0072] Step 1: Select appropriate parameters and perform laser remelting on the surface of QT400 cast iron parts under argon atmosphere protection to obtain a remelted layer with uniform microstructure and composition distribution and a thickness of 1-3 mm.

[0073] Step 2: Use 1000-grit sandpaper to sand away the oxide layer on the surface of the part without damaging the remelted layer. Rinse the surface of the part with anhydrous ethanol and blow it dry.

[0074] Step 3: Place the elemental powders of the aforementioned mass fractions into a planetary ball mill and mix and ball mill them at a revolution speed of 15 r / min and a rotation speed of 60 r / min for 2 hours. Then place them in a drying oven at 120°C for 2 hours to dry them, thus preparing nickel-based alloy powder and cobalt-based alloy powder respectively.

[0075] Step 4: Place the nickel-based alloy powder into the powder feeder and set the appropriate powder feeding amount and powder feeding air flow rate;

[0076] Step 5: In the robot program, set the stepping distance according to the overlap rate, set the water chiller and protective gas, turn on the powder feeder, and turn on the laser when the powder is evenly discharged from the powder outlet pipe, so that the nickel-based powder is evenly melted on the surface of the part to be repaired to form a nickel-based transition cladding layer.

[0077] Step 6: Polish the nickel-based transition cladding layer to remove the surface oxide layer;

[0078] Step 7: Replace the powder in the powder feeder with the prepared cobalt-based alloy powder, and reset the appropriate laser power, powder feeding amount and other parameters;

[0079] Step 8: The cobalt-based alloy powder is uniformly melted onto the nickel-based transition cladding layer to form a cobalt-based cladding layer;

[0080] Step 9: Perform surface processing or grinding on the parts repaired by laser cladding to complete the repair process.

[0081] This invention provides a composite laser cladding material for ductile iron and its preparation method. The specific process includes: before cladding, using a laser beam to laser remelt the surface of ductile iron to reduce free graphite on the material surface, homogenize the surface structure and element distribution, which is conducive to achieving good metallurgical bonding between the cladding layer and the substrate; then using a nickel-based alloy powder obtained by preparation to clad a nickel-based transition cladding layer on the surface of the laser remelted layer; finally, using cobalt as the base and adding other alloy components to prepare cobalt-based alloy powder as the cladding material to repair the surface of ductile iron. This invention employs a laser remelting process and utilizes the excellent wettability, high toughness, and strong adhesion of nickel-based powder to cobalt-based cladding layers and ductile iron substrates. This effectively avoids problems such as cracking defects and cladding layer detachment at the interface caused by the large difference in thermal expansion coefficients between cobalt-based powder and the substrate when directly cladding cobalt-based powder onto the ductile iron surface. It achieves a good metallurgical bond between the substrate and the transition layer, and between the transition layer and the cladding layer. Simultaneously, it leverages the excellent high-temperature resistance, wear resistance, and corrosion resistance of the cobalt-based cladding layer. The method provided by this invention can effectively repair surface failures in QT400 ductile iron parts, thereby extending the service life of the parts.

[0082] To further understand the present invention, the following detailed description of the ductile iron composite laser cladding material and its preparation method provided by the present invention is provided in conjunction with embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0083] Example 1

[0084] A QT400 ductile iron part operates in a high-temperature environment, and the reciprocating grinding motion with mating parts easily leads to wear and failure of the mating surface. This invention uses cladding powder and a cladding process to repair the surface wear of this part, thereby extending its service life.

[0085] A) Under the protection of an argon atmosphere with a gas flow rate of 6L / min, a laser remelting power of 1000W and a remelting speed of 20mm / s were selected. The laser beam was used to perform laser remelting on the surface of QT400 ductile iron parts to obtain a remelted layer with uniform microstructure and composition distribution and a thickness of 2mm.

[0086] Use 1000-grit sandpaper to polish the oxide layer on the laser-remelted surface, rinse it with anhydrous ethanol and blow it dry;

[0087] B) Prepare nickel-based transition layer cladding powder and cobalt-based cladding powder respectively. The nickel-based transition layer cladding powder is prepared by mixing other alloying element powders with nickel powder as the matrix in a planetary ball mill. The powder sphericity is ≥95%, the particle size distribution is 45-150μm, and it mainly includes the following elements by mass percentage: C 0.3%, Si 2.8%, B 2.2%, Cr 13%, Ni balance;

[0088] Cobalt-based cladding powder is prepared by mixing cobalt powder as the matrix with other alloying element powders in a planetary ball mill. The powder has a sphericity ≥95% and a particle size distribution of 45-150μm. It mainly includes the following elements by mass percentage: C 1.2%, Si 1.8%, B 1.5%, Mn 0.6%, Cr 25%, Mo 1.5%, and Co balance.

[0089] C) Place the nickel-based transition layer cladding powder into the powder feeder, set the powder feeding speed to 20g / min, the overlap rate to 35%, the protective gas type to pure argon, the gas flow rate to 15L / min, and the powder carrier gas to pure nitrogen, the gas flow rate to 10L / min; turn on the robot and laser, set the laser power to 1600W, and the robot travel speed and cladding speed to 18mm / s, so that a nickel-based transition cladding layer is formed on the surface of the remelted QT400 ductile iron parts;

[0090] After the parts have cooled, use 1000-grit sandpaper to polish the obtained nickel-based transition cladding layer to remove the surface oxide layer, clean with anhydrous ethanol and blow dry.

[0091] D) Place the cobalt-based cladding powder into the powder feeder, set the powder feeding speed to 25g / min, the overlap rate to 45%, the protective gas type to pure argon with a flow rate of 5L / min, and the powder carrier gas to pure nitrogen with a flow rate of 10L / min; turn on the robot and laser, set the laser power to 1700W, and the robot travel speed and cladding speed to 18mm / s, so that a cobalt-based cladding layer is formed on the surface of the QT400 ductile iron parts after remelting, as shown in Figure 2. Figure 2 is an effect diagram of the repaired QT400 ductile iron parts. As can be seen from the figure, the cobalt-based cladding layer of the repaired parts is uniform in macroscopic terms, and there are no cracks on the surface.

[0092] After the repair preparation was completed, metallographic samples were cut from the cladding layer for microstructure observation. No defects such as cracks or lack of fusion were found. Furthermore, the fusion zone between the cladding layer, transition layer, and substrate had a dense microstructure, forming a good metallurgical bond. Rockwell hardness testing showed that the hardness of the QT400 ductile iron part substrate was 26 HRC, the nickel-based transition layer was 35 HRC, and the outermost cobalt-based cladding layer was 58 HRC, representing a 123% increase in hardness compared to the substrate. Simultaneously, wear resistance was improved by 78%, and the cobalt-based cladding layer improved the high-temperature fatigue performance of the part by 37%, extending the service life of the QT400 ductile iron part in high-temperature environments.

[0093] Example 2

[0094] During the installation and disassembly of a certain QT400 ductile iron part, excessive wear on the assembly surface can easily lead to its scrapping. The cladding powder and cladding process provided by this invention can repair the worn areas of the assembly surface of this part, enabling it to be reused and extending its service life.

[0095] A) Under the protection of an argon atmosphere with a gas flow rate of 7L / min, a laser remelting power of 1150W and a remelting speed of 18mm / s were selected. The wear parts of QT400 ductile iron were laser remelted using a laser beam to obtain a remelted layer with uniform microstructure and composition distribution and a thickness of 2.5mm.

[0096] Use 1000-grit sandpaper to polish the oxide layer on the laser-remelted surface, rinse it with anhydrous ethanol and blow it dry;

[0097] B) Prepare nickel-based transition layer cladding powder and cobalt-based cladding powder respectively. The nickel-based transition layer powder is prepared by mixing other alloying element powders with nickel powder as the matrix in a planetary ball mill. The powder sphericity is ≥95%, the particle size distribution is 45-150μm, and it mainly includes the following elements by mass percentage: C 0.35%, Si 3%, B 2.5%, Cr 12%, Ni balance.

[0098] Cobalt-based cladding powder is prepared by mixing cobalt powder as the matrix with other alloying element powders in a planetary ball mill. The powder has a sphericity ≥95% and a particle size distribution of 45-150μm. It mainly includes the following elements by mass percentage: C 1.1%, Si 1.8%, B 1.7%, Mn 0.6%, Cr 26%, Mo 1.5%, and Co balance.

[0099] C) Place the nickel-based transition layer cladding powder into the powder feeder, set the powder feeding speed to 20g / min, the overlap rate to 35%, the protective gas type to pure argon, the gas flow rate to 15L / min, and the powder carrier gas to pure nitrogen, the gas flow rate to 10L / min; turn on the robot and laser, set the laser power to 1500W, and the robot travel speed and cladding speed to 18mm / s, so that a nickel-based transition cladding layer is formed on the surface of the remelted QT400 ductile iron parts;

[0100] After the parts have cooled, use 1000-grit sandpaper to polish the obtained nickel-based transition cladding layer to remove the surface oxide layer, clean with anhydrous ethanol and blow dry.

[0101] D) Place the cobalt-based cladding powder into the powder feeder, set the powder feeding speed to 25g / min, the overlap rate to 45%, the protective gas type to be pure argon, the gas flow rate to be 5L / min, the powder carrier gas to be pure nitrogen, and the gas flow rate to be 10L / min; turn on the robot and the laser, set the laser power to 1600W, the robot travel speed and the cladding speed to 18mm / s, so that a cobalt-based cladding layer is formed on the surface of the remelted QT400 ductile iron parts;

[0102] After the repair was completed, metallographic samples were cut from the cladding layer for microstructure observation. No defects such as cracks or lack of fusion were found. The fusion zone between the cladding layer, transition layer, and substrate was dense, forming a good metallurgical bond. Rockwell hardness testing showed that the QT400 ductile iron part had a substrate hardness of 28 HRC, the nickel-based transition layer hardness of 36 HRC, and the outermost cobalt-based cladding layer hardness of 60 HRC, representing a 114% increase in hardness compared to the substrate. Simultaneously, wear resistance was improved, and the service life was extended by more than double compared to the original part.

[0103] Comparative Example 1

[0104] In this comparative example, cobalt-based powder was directly clad onto the assembly surface of the aforementioned QT400 ductile iron parts after laser remelting.

[0105] A) Under the protection of an argon atmosphere with a gas flow rate of 7L / min, a laser remelting power of 1150W and a remelting speed of 20mm / s were selected. The wear-removed parts of QT400 ductile iron were laser remelted using a laser beam to obtain a remelted layer with uniform microstructure and composition distribution and a thickness of 2.5mm.

[0106] The oxide layer on the laser remelted surface was polished with 1000-grit sandpaper, rinsed with anhydrous ethanol, and dried.

[0107] B) Cobalt-based alloy powder is prepared by mixing cobalt powder as the matrix with other alloying element powders in a planetary ball mill. The powder has a sphericity ≥95% and a particle size distribution of 45-150μm. It mainly includes the following elements by mass percentage: C 1.1%, Si 1.8%, B 1.7%, Mn 0.6%, Cr 26%, Mo 1.5%, and Co balance.

[0108] Cobalt-based cladding powder is placed into a powder feeder, with a feeding speed of 25g / min, an overlap rate of 45%, a protective gas type of pure argon with a flow rate of 5L / min, and a powder carrier gas of pure nitrogen with a flow rate of 10L / min. The robot and laser are turned on, with the laser power set to 1600W, and the robot travel speed and cladding speed set to 18mm / s, so that a cobalt-based cladding layer is formed on the surface of the remelted QT400 ductile iron parts.

[0109] After the cladding was completed, metallographic samples were cut from the cladding layer for observation. It was found that there were obvious cracks and pore defects at the junction of the cladding layer and the substrate, as shown in Figure 3.

[0110] Comparative Example 2

[0111] The preparation method is the same as in Example 1, except that the sphericity of the nickel-based alloy powder is 80% and the sphericity of the cobalt-based alloy powder is 80%.

[0112] As shown in Figure 4, Figure 4 is a microscopic photograph of the cobalt-based alloy powder and cladding layer in Example 1 and a microscopic photograph of the cobalt-based alloy powder and cladding layer in Comparative Example 2. (a) Figure is a microscopic photograph of the cobalt-based alloy powder and cladding layer in Example 1, and (b) Figure is a microscopic photograph of the cobalt-based alloy powder and cladding layer in Comparative Example 2. As can be seen from the figures, the cladding layer prepared in Example 1 has a dense and defect-free structure, while the cladding layer prepared in Comparative Example 2 has defects such as cracks and pores.

[0113] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0114] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A nodular cast iron composite laser cladding material, comprising a nodular cast iron base material, a laser remelted layer combined on the surface of the nodular cast iron base material, a nickel-based transition cladding layer combined on the surface of the laser remelted layer, and a cobalt-based cladding layer combined on the surface of the nickel-based transition cladding layer. The raw material for preparing the nickel-based transition cladding layer comprises, in mass percentage: C 0.2-0.5%, Si 2.8-3.5%, B 2.0-3.0%, Cr 9.0-13.0%, and Ni balance. The cobalt-based cladding layer is prepared from raw materials including, in mass percentage, C 0.7-1.2%, Si 1.5-2.0%, B 1.5-2.0%, Mn 0.4-0.6%, Cr 24-26%, Mo 1.0-2.0%, and Co balance.

2. The ductile cast iron composite laser cladding material according to claim 1, characterized in that, The thickness of the laser remelted layer is 1-3 mm, the thickness of the nickel-based transition cladding layer is 1-2 mm, and the thickness of the cobalt-based cladding layer is 2-3 mm.

3. The ductile cast iron composite laser cladding material according to any one of claims 1 to 2, characterized in that, The nodular cast iron base material is a QT400 nodular cast iron damaged part. 4.A method for preparing the nodular cast iron composite laser cladding material of claim 1, comprising the following steps: mixing C powder, Si powder, B powder, Cr powder, and Ni powder according to mass ratio to obtain a nickel-based alloy powder; mixing C powder, Si powder, B powder, Mn powder, Cr powder, Mo powder, and Co powder according to mass ratio to obtain a cobalt-based alloy powder; laser remelting on the surface of the nodular cast iron base material to obtain a laser remelted layer; putting the nickel-based alloy powder into a powder feeding device of a laser cladding machine to perform laser cladding on the surface of the laser remelted layer to obtain a nickel-based transition cladding layer; putting the cobalt-based alloy powder into a powder feeding device of a laser cladding machine to perform laser cladding on the surface of the nickel-based transition cladding layer to obtain a cobalt-based cladding layer.

5. The preparation method according to claim 4, characterized in that, The nickel-based alloy powder has a sphericity of ≥95% and a particle size distribution of 45-150 μm; and the cobalt-based alloy powder has a sphericity of ≥95% and a particle size distribution of 45-150 μm.

6. The preparation method according to claim 4, characterized in that, During the preparation of the laser remelted layer, the laser power is 1000-1200 W, the remelting speed is 18-20 mm / s, the protective gas type is pure argon, and the gas flow rate is 5-10 L / min.

7. The preparation method according to claim 4, characterized in that, During the preparation of the nickel-based transition cladding layer, the laser power is 1400-1600 W, the cladding speed is 18 mm / s, the powder feeding speed is 20-25 g / min, the overlap rate is 30-35%, the protective gas type is pure argon, the gas flow rate is 10-15 L / min, and the powder carrying gas is pure nitrogen with a gas flow rate of 8-10 L / min.

8. The preparation method according to claim 4, characterized in that, During the preparation of the cobalt-based cladding layer, the laser power is 1500-1700 W, the cladding speed is 14-20 mm / s, the powder feeding speed is 20-25 g / min, the overlap rate is 40-50%, the protective gas type is pure argon with a gas flow rate of 5-8 L / min, and the powder carrying gas is pure nitrogen with a gas flow rate of 8-10 L / min.

9. The preparation method according to claim 4, characterized in that, In the preparation of the nickel-based alloy powder and the cobalt-based alloy powder, the mixing is respectively carried out in a planetary ball mill, the planetary ball mill has an orbital speed of 10-20 r / min and a self-rotation speed of 50-70 r / min, and the mixing time is 1-3 h.

10. The method of any one of claims 4 to 9, wherein the method further comprises, After the preparation of the laser remelted layer and before the preparation of the nickel-based transition cladding layer, the method further comprises: polishing the surface without damaging the laser remelted layer, and then rinsing; After the preparation of the nickel-based transition cladding layer and before the preparation of the cobalt-based cladding layer, the method further comprises: polishing the surface of the nickel-based transition cladding layer; After the preparation of the cobalt-based cladding layer, the method further comprises: polishing the surface of the cobalt-based cladding layer.

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