Cobalt-chromium-molybdenum-silicon coating and printing plate roller and method for producing the same

Abstract

This invention provides a cobalt-chromium-molybdenum-silicon coating and a printing roller, as well as a method for preparing the same, relating to the field of printing roller manufacturing technology. It aims to at least solve the problems of poor wear resistance, corrosion resistance, and mechanical properties of printing rollers. The preparation method includes: preparing cobalt-chromium-molybdenum-silicon alloy powder, wherein, by weight percentage, the cobalt-chromium-molybdenum-silicon alloy powder contains Cr: 27.0% to 29.0%, Mo: 5.5% to 6.5%, Si: 0.7% to 1.0%, C: 0 to 0.01%, totaling 100%, with the balance being Co; pre-treating the surface of the printing roller substrate by degreasing and derusting; preheating the pre-treated printing roller substrate to 150°C to 200°C; preparing a cobalt-chromium-molybdenum-silicon coating on the surface of the printing roller substrate using the cobalt-chromium-molybdenum-silicon alloy powder via laser cladding; placing the printing roller substrate with the cobalt-chromium-molybdenum-silicon coating in a heating furnace, heating to 750°C to 800°C, holding at that temperature for 3.5 hours to 5 hours, and cooling to room temperature to obtain the printing roller. The printing roller prepared by this method has a uniform and refined coating structure, and possesses high hardness, high toughness, and excellent wear and corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of printing roller manufacturing technology, and more specifically, to a cobalt-chromium-molybdenum-silicon coating and a printing roller and a method for preparing the same. Background Technology

[0002] Printing rollers are a crucial component in printing, enduring printing pressure and friction during operation, while also facing the corrosive effects of the printing medium. Therefore, the roller surface material requires excellent wear resistance, corrosion resistance, and mechanical strength. Currently, the main methods for preparing printing roller materials are electroforming and electroplating. The process involves first electroforming a copper coating layer onto a carbon steel roller substrate, then creating a pattern using laser engraving, and finally electroplating a layer of hard chrome to enhance the roller surface's wear and corrosion resistance. However, the hard chrome plating layer is thin and brittle, prone to micro-cracks. Furthermore, the significant chemical difference at the Cu / Cr (copper / chromium) plating interface allows corrosive media to easily penetrate through surface defects to the Cu / Cr interface region, initiating interfacial corrosion and ultimately leading to plating failure. This issue has become a significant factor affecting the service life of printing rollers. In addition, given the poor environmental friendliness of electroplating processes and increasingly stringent regulations, the development of green alternatives is urgently needed.

[0003] Ultra-high-speed laser cladding utilizes a laser heat source to rapidly clad coating materials onto the surface of a substrate (carbon steel, alloy steel, cast iron, or forged steel rollers), forming a metal or metal-based composite coating that is metallurgically bonded to the substrate. This technology can serve as an alternative to electroplating and can be applied to targeted additive manufacturing of patterned areas on printing rollers. However, the coatings formed by laser cladding typically exhibit typical dendritic structures, with significant differences in composition and microstructure between the pre-solidified and post-solidified regions. This not only makes it difficult to subsequently fabricate high-definition patterns using laser engraving technology but also significantly limits the coating's service life in abrasive environments. Therefore, developing a coating material and corresponding preparation process that combines excellent wear resistance, corrosion resistance, and mechanical properties to eliminate laser cladding dendritic structures and obtain a uniform equiaxed crystal structure is of great significance for advancing the development of printing rollers. Summary of the Invention

[0004] The present invention aims to at least solve the problems of poor wear resistance, corrosion resistance and mechanical properties of conventional printing roller coatings in related technologies.

[0005] The first aspect of the present invention provides a method for preparing a printing roller with a cobalt-chromium-molybdenum-silicon coating, comprising: preparing cobalt-chromium-molybdenum-silicon alloy powder, wherein, by weight percentage, the cobalt-chromium-molybdenum-silicon alloy powder comprises Cr: 27.0% to 29.0%, Mo: 5.5% to 6.5%, Si: 0.7% to 1.0%, C: 0 to 0.01%, totaling 100%, with the balance being Co (wherein Co is cobalt, Cr is chromium, Mo is molybdenum, Si is silicon, and C is carbon); performing a degreasing and derusting pretreatment on the surface of the printing roller substrate; preheating the pretreated printing roller substrate to 150°C to 200°C; and using the cobalt-chromium-molybdenum-silicon alloy powder. A cobalt-chromium-molybdenum-silicon coating is prepared on the surface of a printing roller substrate by laser cladding. During the laser cladding process, the cladding speed is 100 mm / s to 300 mm / s, the current is 230 A to 260 A, the laser frequency is 14 Hz to 20 Hz, the laser power is 2 kW to 2.8 kW, the spot diameter is 2 mm to 2.5 mm, the cladding overlap rate is 50% to 60%, and the thickness of the cobalt-chromium-molybdenum-silicon coating is 0.5 mm to 1.5 mm. The printing roller substrate with the cobalt-chromium-molybdenum-silicon coating is placed in a heating furnace and heated to 750°C to 800°C, held at that temperature for 3.5 hours to 5 hours, and then cooled to room temperature to obtain the printing roller.

[0006] The present invention provides a method for preparing a printing roller with a cobalt-chromium-molybdenum-silicon coating. Through the synergistic effect of optimized CoCrMoSi alloy composition design, specific laser cladding process parameters, and subsequent heat treatment, a coating with an ultra-fine network equiaxed crystal microstructure is ultimately obtained on the roller surface. Its effects are mainly reflected in the following three aspects: First, the laser cladding process is stable, the coating forms well, and it is metallurgically bonded to the substrate; second, the subsequent heat treatment effectively eliminates the internal stress generated by laser cladding and promotes the diffusion of Cr, Mo, and Si elements to the grain boundaries; third, a network of close-packed hexagonal ε-Co solid solution phase is formed at the grain boundaries, with a face-centered cubic γ-Co phase within the network. The network of ε-Co phase provides strength support, while the γ-Co-based solid solution phase with good plasticity can accommodate dislocations and deformation. This ε / γ phase interleaved distribution effectively inhibits grain growth, making the coating structure uniform and refined, eliminating the typical dendritic directional solidification structure obtained after laser cladding, and exhibiting high hardness, high toughness, and excellent wear and corrosion resistance.

[0007] Among them, "cladding speed" refers to the relative scanning speed between the laser head and the substrate surface of the printing roller; "current" refers to the working current of the laser; "cladding overlap rate" refers to the degree of overlap between adjacent cladding passes, which is usually expressed as the ratio of the overlap width to the width of a single cobalt-chromium-molybdenum-silicon coating.

[0008] The CoCrMoSi alloy powder prepared by this invention has Co as the main element, for example, Co: 64.0% to 66.0%, and Cr as the main solid solution element, mainly used to improve the alloy's resistance to electrochemical corrosion. To ensure corrosion resistance, the addition amount is ≥25%, and considering the factors of component segregation and cost, the addition amount is 27.0 wt.%-29.0 wt.%. Mo has a larger atomic radius and plays a solid solution strengthening role in Co-based alloys. During corrosion, the addition of Mo can improve the chemical stability of the passivation film, thereby improving the alloy's... Anti-pitting corrosion performance: Si is a non-metallic element. During coating preparation and heat treatment, Si, Mo, and Cr elements tend to accumulate at grain boundaries, promoting the formation of a network ε-Co-based solid solution phase with a close-packed hexagonal lattice structure in the grain boundary region. Within the network, a γ-Co phase with a face-centered cubic lattice structure (FCC) is formed. The precipitation of the network ε-Co phase at the grain boundaries inhibits the growth of γ-Co phase grains, thereby obtaining an ultrafine network equiaxed microstructure with ε / γ phases distributed alternately. The coating has good microstructure uniformity, high strength, toughness, and wear resistance.

[0009] It is important to understand that preheating the printing roller substrate before laser cladding can significantly reduce the temperature difference between the coating and the roller substrate during the laser cladding process, thereby effectively reducing cladding thermal stress and cold cracking tendency, which is especially crucial for large printing rollers or easily cracked materials. This temperature range provides a good slow cooling effect while avoiding the adverse effects of excessively high temperatures on the performance of the printing roller substrate. The ideal heat treatment temperature is 750℃-800℃, which can remove the coating stress after laser cladding, while promoting the diffusion of Cr, Mo, and Si to the grain boundaries and forming a network of ε-Co solid solution phase with the Co solid solution at the grain boundaries. At the same time, the dendritic structure of the coating after laser cladding obtains a coating structure dominated by equiaxed crystals through element diffusion and recrystallization. If the temperature is too low, the diffusion rate of Mo, Si, and Cr elements is slow, which slows down the precipitation of the intergranular network ε-Co phase. If the temperature is too high, with the diffusion of alloying elements, it is easy to lead to the formation of blocky σ-Co3Mo phases at grain boundaries and within grains.

[0010] Among them, ultra-high-speed laser cladding equipment or ordinary laser cladding equipment can be selected.

[0011] In the above technical solution, the cobalt-chromium-molybdenum-silicon alloy powder is prepared by vacuum melting and gas atomization.

[0012] In this technical solution, high-purity raw materials such as Co, Cr, Mo, and Si are melted in a vacuum induction melting furnace according to a specified ratio, thoroughly stirred and refined to obtain a uniform alloy melt. The melt is then poured into a heat-insulating crucible and, as it flows down through a guide tube, is atomized into tiny droplets by a high-pressure inert gas (such as argon). During the cooling process, the droplets spheroidize and solidify under the action of surface tension, ultimately yielding spherical alloy powder with high sphericity, good fluidity, and low oxygen content. This method provides high-quality raw materials for subsequent laser cladding.

[0013] In the above technical solution, the present invention uses vacuum melting and gas atomization methods to prepare cobalt-chromium-molybdenum-silicon alloy powder, and the sphericity of the cobalt-chromium-molybdenum-silicon alloy powder is ≥90%.

[0014] In the above technical solution, the particle size of the cobalt-chromium-molybdenum-silicon alloy powder is 5μm to 52μm.

[0015] In this technical solution, limiting the powder particle size range is to ensure smooth powder feeding and melting efficiency during the laser cladding process. Particles that are too fine are prone to burning or clogging the powder feeding pipeline, while those that are too coarse are difficult to melt completely, affecting coating quality. Optionally, the powder particle size can be controlled between 15μm and 45μm. Powders within this range have better flowability and laser absorption, which helps to form a denser, smoother cobalt-chromium-molybdenum-silicon coating.

[0016] In the above technical solutions, the degreasing and rust removal pretreatment includes at least one of the following methods: alkaline washing, acid washing, mechanical grinding (e.g., belt or wheel grinding) or sandblasting.

[0017] In this technical solution, thoroughly removing oil, scale, and rust from the surface of the printing roller substrate through pretreatment is a prerequisite for ensuring a good metallurgical bond between the cobalt-chromium-molybdenum-silicon coating and the substrate, thus guaranteeing the smoothness of the coating. For example, alkaline washing can use a 5% to 10% sodium hydroxide solution to remove grease; acid washing can use a 10% to 15% hydrochloric acid or sulfuric acid solution to remove rust; mechanical grinding or sandblasting can simultaneously clean and roughen the surface, further improving the coating's bonding strength.

[0018] In the above technical solution, the step of cooling to room temperature includes: cooling to room temperature in the heating furnace along with the furnace.

[0019] In this technical solution, furnace cooling to room temperature is employed, resulting in an extremely slow cooling rate. This slow cooling process minimizes thermal stress caused by rapid temperature changes, effectively preventing coating cracking or deformation. Simultaneously, it provides more time for the full diffusion of alloying elements (such as Cr, Mo, and Si), promoting the stable precipitation of the network ε-Co phase at grain boundaries and the homogenization of the microstructure. This leads to more thorough stress relief and a more stable microstructure within the coating.

[0020] In the above technical solution, the step of cooling to room temperature includes: after cooling to 350°C in a heating furnace, removing the printing roller substrate with cobalt chromium molybdenum silicon coating from the heating furnace and allowing it to cool naturally to room temperature.

[0021] In this technical solution, cooling the material in the furnace to 350°C followed by air cooling is a compromise that balances production efficiency and performance. Cooling in the furnace above 350°C avoids excessive internal stress caused by rapid cooling; air cooling (natural cooling) below 350°C accelerates production and improves efficiency. At this temperature, the phase transformation of the material is essentially complete, and air cooling does not introduce harmful microstructural transformations, thus shortening the process cycle while ensuring coating performance.

[0022] In the above technical solution, the laser cladding process is carried out in a protective gas environment.

[0023] In this technical solution, the laser cladding process is carried out in a protective gas environment to prevent the molten alloy powder and the substrate surface from reacting chemically with oxygen and nitrogen in the air at high temperatures, causing oxidation, burn-off, or the formation of harmful phases, thereby ensuring the purity, composition accuracy, and metallurgical quality of the coating.

[0024] In the above technical solution, the protective gas includes one of the following: argon, helium, or a mixture of argon and helium.

[0025] In this technical solution, argon is an inert gas with relatively low cost and stable and reliable protective effect; helium has high thermal conductivity, which can bring a stronger cooling effect and help refine grains, but its cost is higher. Selecting argon, helium, or a mixture thereof as the protective gas or powder feeding gas according to actual needs can balance coating performance and production cost.

[0026] In the above technical solution, the cobalt-chromium-molybdenum-silicon coating is formed by at least two laser cladding processes.

[0027] In this technical solution, a multi-layer, multi-pass cladding strategy (for example, for a 0.8 mm thick coating, first cladding a 0.3 mm thick base layer, then cladding a 0.5 mm thick top layer) can be used to construct a thicker functional coating. This method allows for fine-tuning of the process for each layer, helps to disperse heat input, reduces overall thermal stress and deformation, and facilitates control of the dilution rate, ensuring that the surface layer has optimal performance.

[0028] In the above technical solution, after each laser cladding, the oxide scale and spatter on the surface of the layer are removed with a wire brush or grinding tool before the next layer is clad. This can improve the interlayer bonding force and reduce the defect rate.

[0029] In the above technical solution, the cladding speed is 150mm / s to 250mm / s, the current is 240A to 250A, the laser frequency is 16Hz to 18Hz, the laser power is 2.2kW to 2.6kW, the spot diameter is 2.1mm to 2.3mm, the cladding overlap rate is 52% to 58%, and the thickness of the cobalt-chromium-molybdenum-silicon coating is 0.8mm to 1.2mm. For example, the cladding speed is 180mm / s or 220mm / s; the current is 245A; the laser frequency is 17Hz; the laser power is 2.4kW; the spot diameter is 2.2mm; and the overlap rate is 55%. Within this range, the laser energy input is optimally matched with the powder melting and cooling crystallization process, which can further refine the grains, improve the smoothness and uniformity of the coating surface, and achieve a better balance between strength, toughness, and abrasion resistance in the final coating, making it particularly suitable for the manufacture of high-performance printing rollers.

[0030] The second aspect of the present invention provides a printing roller, which is prepared by the method for preparing a printing roller with a cobalt-chromium-molybdenum-silicon coating according to any one of the first aspects of the present invention.

[0031] The third aspect of the present invention provides a cobalt-chromium-molybdenum-silicon coating for use on printing rollers. The cobalt-chromium-molybdenum-silicon coating comprises, by weight percentage: Cr: 27.0% to 29.0%, Mo: 5.5% to 6.5%, Si: 0.7% to 1.0%, C: 0 to 0.01%, totaling 100%, with the balance being Co. Attached Figure Description

[0032] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0033] Figure 1 This is one of the process flow diagrams for preparing the printing plate roller according to an embodiment of the present invention;

[0034] Figure 2 This is the second flowchart illustrating the preparation process of the printing roller according to an embodiment of the present invention;

[0035] Figure 3 The microstructure of the CoCrMoSi coating with a network equiaxed crystal structure is shown in the image.

[0036] Figure 4 This is a distribution diagram of Co, Cr, Mo, and Si elements in the CoCrMoSi coating. Detailed Implementation

[0037] To better understand the above-mentioned objectives, features, and advantages of this application, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0038] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein. Therefore, the scope of protection of this application is not limited to the specific embodiments disclosed below.

[0039] The method for preparing the printing roller with cobalt-chromium-molybdenum-silicon coating in this embodiment is as follows: Figure 1 As shown, it includes the following steps:

[0040] S102: Prepare CoCrMoSi alloy powder;

[0041] Specifically, weigh out the high-purity cobalt, chromium, molybdenum, silicon metal raw materials and intermediate alloys according to the weight percentages shown in Table 1 below, ensuring that the total mass is 100%.

[0042] Table 1

[0043]

[0044] S104: Smelting and gas atomization to obtain spherical alloy powder;

[0045] Specifically, the prepared raw materials are placed in a vacuum induction melting furnace, where they are completely melted and refined under argon protection. The alloy liquid is then introduced into an atomization tower, where it is atomized and cooled by high-pressure argon gas, and spherical alloy powder is collected.

[0046] S106: Pre-treatment of the roller substrate surface for degreasing and rust removal;

[0047] Specifically, sandblasting is used to thoroughly remove oil, scale, and rust from the surface of the printing roller substrate until a clean metal surface is exposed, in order to ensure the bonding strength between the coating and the printing roller substrate.

[0048] S108: CoCrMoSi coating obtained after laser cladding;

[0049] Specifically, the dried alloy powder is conveyed through a powder feeder, and under argon protection, a laser beam is used to clad the surface of the printing roller substrate, which is preheated to 150℃-200℃. A uniform coating is formed by controlling the laser parameters and the overlap rate.

[0050] S110: A network equiaxed crystal structure is obtained after heat treatment.

[0051] Specifically, the coated roller substrate is placed in a heating furnace and kept at 750℃-800℃ to promote element diffusion and phase transformation. Then it is cooled according to a set program, and finally an ideal structure composed of network ε-Co phase and γ-Co equiaxed crystals is obtained in the coating.

[0052] The preparation process of the printing roller of the present invention will be described in more detail below using three specific preparation methods.

[0053] Example 1

[0054] Specifically, the alloy composition is designed as follows: Cr: 27wt.%, Mo: 5.5wt.%, Si: 0.7wt.%, Co: balance. After preparing the mixed powder, spherical CoCrMoSi alloy powder is prepared using a "vacuum melting + gas atomization" method. Powder with a particle size ranging from 5μm to 52μm is screened and dried in an oven for later use. The surface of the printing roller substrate is cleaned with a grinding wheel to remove surface deposits and rust. The dried powder is then clad using an ultra-high-speed laser cladding system. The cladding process parameters are: cladding speed 300mm / s, current 230A, laser frequency 14Hz, laser power 2kW, spot diameter 2.5mm, and cladding overlap rate 50%. The coating thickness is designed to be 0.8mm, using a two-stage cladding method, with each cladding layer being 0.4mm thick. The coated printing roller is placed in a high-temperature electric furnace for overall heat treatment. The furnace is heated to 750°C and held for 5 hours. After cooling to room temperature, a CoCrMoSi coating with a network equiaxed crystal structure is obtained on the surface of the printing roller substrate.

[0055] The method for preparing a printing roller with a cobalt-chromium-molybdenum-silicon coating provided in this embodiment utilizes a "high-speed laser cladding + heat treatment" technique to obtain a network-like equiaxed crystal structure, eliminating the dendritic structure of traditional laser cladding coatings. This method can replace traditional electroplating techniques for preparing printing roller coatings. Furthermore, this invention utilizes the segregation of Mo, Si, and Cr elements at grain boundaries during the laser cladding process to obtain a network-like ε-Co solid solution phase at grain boundaries. The inter-mesh structure consists of a γ-Co phase with good plasticity, forming a microstructure with alternating soft (γ-Co) and hard (ε-Co) phases. The coating exhibits both good strength, toughness, and wear resistance. Its microstructure morphology is shown in the figure below. Figure 3 As shown, clear equiaxed crystals and a network of grain boundary precipitates are visible. The elemental distribution of Co, Cr, Mo, and Si in the coating is shown in the diagram. Figure 4 As shown.

[0056] Example 2

[0057] Specifically, the alloy composition is designed as follows: Cr: 28 wt.%, Mo: 6 wt.%, Si: 0.9 wt.%, Co: balance. After preparing the mixed powder, spherical CoCrMoSi alloy powder is prepared using a "vacuum melting + gas atomization" method. Powder with a particle size ranging from 5 μm to 52 μm is screened and dried in an oven for later use. The surface of the printing roller substrate is cleaned with a sanding belt to remove surface deposits and rust. The dried powder is then clad using an ultra-high-speed laser cladding system. The cladding process parameters are: cladding speed 300 mm / s, current 230 A, laser frequency 14 Hz, laser power 2 kW, spot diameter 2.5 mm, and cladding overlap rate 60%. The coating thickness is designed to be 0.9 mm, using a 3-layer cladding method, with each layer being 0.3 mm thick. The coated printing roller is placed in a high-temperature electric furnace for overall heat treatment. The furnace is heated to 800°C and held for 3.5 hours. After cooling to 350°C, the printing roller substrate is removed and air-cooled. A CoCrMoSi coating with a network equiaxed crystal structure is obtained on the surface of the printing roller substrate.

[0058] Example 3

[0059] Specifically, the alloy composition is designed as follows: Cr: 29 wt.%, Mo: 6.5 wt.%, Si: 1.0 wt.%, Co: balance. After preparing the mixed powder, spherical CoCrMoSi alloy powder is prepared using a "vacuum melting + gas atomization" method. Powder with a particle size ranging from 5 μm to 52 μm is screened and dried in an oven for later use. The surface of the printing roller substrate is cleaned with a sanding belt to remove surface deposits and rust. The dried powder is then clad using a conventional laser cladding system. The cladding process parameters are: cladding speed 100 mm / s, current 260 A, laser power 2.8 kW, spot diameter 2 mm, and cladding overlap rate 60%. The coating thickness is designed to be 1.0 mm, using a three-layer cladding method. The first cladding layer is 0.2 mm thick, and the second and third cladding layers are both 0.4 mm thick. The coated printing roller is placed in a high-temperature electric furnace for overall heat treatment. The furnace is heated to 780°C and held for 4 hours. Then, it is cooled to room temperature. A CoCrMoSi coating with a network equiaxed crystal structure is obtained on the surface of the printing roller substrate.

[0060] The CoCrMoSi coating on the surface of the printing rollers prepared in the above three embodiments was tested. The test methods and results are summarized below:

[0061] The hardness of the coating cross-section was measured using a micro Vickers hardness tester, with the average value at three points exceeding 550 HV, significantly higher than that of traditional chromium plating. Dry sliding friction wear testing using a ball-and-disc wear tester showed a wear rate approximately 40% lower than the control sample, demonstrating excellent wear resistance. Potentiodynamic polarization curve testing in a 3.5% NaCl solution using an electrochemical workstation showed a positive shift in the self-corrosion potential and a decrease in the passivation current density, indicating a significant improvement in corrosion resistance. Metallographic observation revealed that the coarse dendritic structure generated by laser cladding had completely transformed into a uniform and fine equiaxed grain structure, with a continuously distributed network of secondary phase visible at the grain boundaries. These test results fully verify that this invention, through synergistic optimization of composition and process, successfully obtained a coating with excellent wear resistance, corrosion resistance, and high strength and toughness, completely achieving the core objective of eliminating laser cladding dendritic structure and obtaining a uniform equiaxed grain structure.

[0062] The printing rollers prepared in the three embodiments of the present invention have a CoCrMoSi coating with a network equiaxed crystal structure. The grain size of the equiaxed crystals is 2μm to 8μm, the thickness of the network ε-Co phase at the grain boundaries is 0.2μm to 1.0μm, and the network ε-Co phase is distributed in a continuous network.

[0063] like Figure 2 As shown, another embodiment of the present invention provides a method for preparing a printing roller with a cobalt-chromium-molybdenum-silicon coating, comprising:

[0064] S202: Prepare cobalt-chromium-molybdenum-silicon alloy powder, wherein, by weight percentage, the cobalt-chromium-molybdenum-silicon alloy powder contains Cr: 27.0% to 29.0%, Mo: 5.5% to 6.5%, Si: 0.7% to 1.0%, C: 0 to 0.01%, totaling 100%, with the balance being Co;

[0065] S204: Pre-treatment of the printing roller substrate surface for degreasing and rust removal;

[0066] S206: Preheat the pretreated printing roller substrate to 150°C to 200°C;

[0067] S208: Cobalt-chromium-molybdenum-silicon alloy powder is used to prepare a cobalt-chromium-molybdenum-silicon coating on the surface of the printing roller substrate through laser cladding process. During the laser cladding process, the cladding speed is 100mm / s to 300mm / s, the current is 230A to 260A, the laser frequency is 14Hz to 20Hz, the laser power is 2kW to 2.8kW, the spot diameter is 2mm to 2.5mm, the cladding overlap rate is 50% to 60%, and the thickness of the cobalt-chromium-molybdenum-silicon coating is 0.5mm to 1.5mm.

[0068] S210: The printing roller substrate with a cobalt-chromium-molybdenum-silicon coating is placed in a heating furnace, heated to 750°C to 800°C, held at that temperature for 3.5 hours to 5 hours, and then cooled to room temperature to obtain the printing roller.

[0069] The present invention provides a method for preparing a printing roller with a cobalt-chromium-molybdenum-silicon coating. Through the synergistic effect of optimized CoCrMoSi alloy composition design, specific laser cladding process parameters, and subsequent heat treatment, a coating with an ultra-fine network equiaxed crystal microstructure is ultimately obtained on the roller surface. Its effects are mainly reflected in the following three aspects: First, the laser cladding process is stable, the coating forms well, and it is metallurgically bonded to the substrate; second, the subsequent heat treatment effectively eliminates the internal stress generated by laser cladding and promotes the diffusion of Cr, Mo, and Si elements to the grain boundaries; third, a network of close-packed hexagonal ε-Co solid solution phase is formed at the grain boundaries, with a face-centered cubic γ-Co phase within the network. The network of ε-Co phase provides strength support, while the γ-Co-based solid solution phase with good plasticity can accommodate dislocations and deformation. This ε / γ phase interleaved distribution effectively inhibits grain growth, making the coating structure uniform and refined, eliminating the typical dendritic directional solidification structure obtained after laser cladding, and exhibiting high hardness, high toughness, and excellent wear and corrosion resistance.

[0070] Among them, "cladding speed" refers to the relative scanning speed between the laser head and the substrate surface of the printing roller; "current" refers to the working current of the laser; "cladding overlap rate" refers to the degree of overlap between adjacent cladding passes, which is usually expressed as the ratio of the overlap width to the width of a single cobalt-chromium-molybdenum-silicon coating.

[0071] The CoCrMoSi alloy powder prepared by this invention is mainly composed of Co and Cr as the main solid solution element, primarily used to improve the alloy's resistance to electrochemical corrosion. To ensure corrosion resistance, the addition amount is ≥25%, and considering factors such as component segregation and cost, the addition amount is 27.0wt.%-29.0wt.%. Mo has a large atomic radius and plays a solid solution strengthening role in Co-based alloys. During corrosion, the addition of Mo can improve the chemical stability of the passivation film, thereby improving the alloy's resistance to pitting corrosion. Si is a non-metallic element. During coating preparation and heat treatment, Si, Mo, and Cr elements easily accumulate at grain boundaries, promoting the formation of a network ε-Co-based solid solution phase with a close-packed hexagonal lattice structure in the grain boundary region. Within the network, a γ-Co phase with a face-centered cubic lattice structure is formed. The precipitation of the network ε-Co phase at the grain boundaries inhibits the growth of γ-Co phase grains, thereby obtaining an ultrafine network equiaxed microstructure with alternating ε / γ phases. The coating has good microstructure uniformity, high strength, toughness, and wear resistance.

[0072] It is important to understand that preheating the printing roller substrate before laser cladding can significantly reduce the temperature difference between the coating and the roller substrate during the laser cladding process, thereby effectively reducing cladding thermal stress and cold cracking tendency, which is especially crucial for large printing rollers or easily cracked materials. This temperature range provides a good slow cooling effect while avoiding the adverse effects of excessively high temperatures on the performance of the printing roller substrate. The ideal heat treatment temperature is 750℃-800℃, which can remove the coating stress after laser cladding, while promoting the diffusion of Cr, Mo, and Si to the grain boundaries and forming a network of ε-Co solid solution phase with the Co solid solution at the grain boundaries. At the same time, the dendritic structure of the coating after laser cladding obtains a coating structure dominated by equiaxed crystals through element diffusion and recrystallization. If the temperature is too low, the diffusion rate of Mo, Si, and Cr elements is slow, which slows down the precipitation of the intergranular network ε-Co phase. If the temperature is too high, with the diffusion of alloying elements, it is easy to lead to the formation of blocky σ-Co3Mo phases at grain boundaries and within grains.

[0073] Among them, ultra-high-speed laser cladding equipment or ordinary laser cladding equipment can be selected.

[0074] In the above embodiments, the cobalt-chromium-molybdenum-silicon alloy powder was prepared by vacuum melting and gas atomization.

[0075] In this embodiment, high-purity raw materials such as Co, Cr, Mo, and Si are melted in a vacuum induction melting furnace according to a specified ratio, thoroughly stirred and refined to obtain a uniform alloy melt. The melt is then poured into a heat-insulating crucible and, as it flows down through a guide tube, is atomized into tiny droplets by a high-pressure inert gas (such as argon). During the cooling process, the droplets spheroidize and solidify under the action of surface tension, ultimately yielding spherical alloy powder with high sphericity, good fluidity, and low oxygen content. This method provides high-quality raw materials for subsequent laser cladding.

[0076] In the above embodiments, the particle size of the cobalt-chromium-molybdenum-silicon alloy powder is 5 μm to 52 μm.

[0077] In this embodiment, limiting the powder particle size range is to ensure smooth powder feeding and melting efficiency during the laser cladding process. Particles that are too fine are prone to burning or clogging the powder feeding pipeline, while those that are too coarse are difficult to melt completely, affecting coating quality. Optionally, the powder particle size can be controlled between 15μm and 45μm. Powders within this range have better flowability and laser absorption, which helps to form a denser, smoother cobalt-chromium-molybdenum-silicon coating.

[0078] In the above embodiments, the degreasing and rust removal pretreatment includes at least one of the following methods: alkaline washing, acid washing, mechanical grinding (e.g., belt or wheel grinding) or sandblasting.

[0079] In this embodiment, thoroughly removing oil, scale, and rust from the surface of the printing roller substrate through pretreatment is a prerequisite for ensuring a good metallurgical bond between the cobalt-chromium-molybdenum-silicon coating and the substrate, thus guaranteeing the smoothness of the coating. For example, alkaline washing can use a 5% to 10% sodium hydroxide solution to remove grease; acid washing can use a 10% to 15% hydrochloric acid or sulfuric acid solution to remove rust; mechanical grinding or sandblasting can simultaneously clean and roughen the surface, further improving the coating's bonding strength.

[0080] In the above embodiments, the step of cooling to room temperature includes: cooling to room temperature in a heating furnace along with the furnace.

[0081] In this embodiment, after the furnace stops heating, it is cooled to room temperature along with the furnace, and the cooling rate is extremely slow. This slow cooling process can minimize the thermal stress caused by rapid temperature changes, effectively prevent the coating from cracking or deforming, and at the same time provide more time for the full diffusion of alloying elements (such as Cr, Mo, Si), promoting the stable precipitation of the network ε-Co phase at the grain boundaries and the homogenization of the microstructure, so that the internal stress of the coating is eliminated more thoroughly and the microstructure is more stable.

[0082] In the above embodiments, the step of cooling to room temperature includes: after cooling to 350°C in a heating furnace, removing the printing roller substrate with cobalt chromium molybdenum silicon coating from the heating furnace and allowing it to cool naturally to room temperature.

[0083] In this embodiment, cooling the material in the furnace to 350°C followed by air cooling is a compromise that balances production efficiency and performance. Cooling in the furnace above 350°C avoids excessive internal stress caused by rapid cooling; air cooling (natural cooling) below 350°C accelerates production and improves efficiency. At this temperature, the phase transformation of the material is essentially complete, and air cooling does not introduce harmful microstructural changes, thus shortening the process cycle while ensuring coating performance.

[0084] In the above embodiments, the laser cladding process is carried out in a protective gas environment.

[0085] In this embodiment, the laser cladding process is carried out in a protective gas environment to prevent the molten alloy powder and the substrate surface from reacting chemically with oxygen and nitrogen in the air at high temperatures, which could cause oxidation, burn-off, or the formation of harmful phases, thereby ensuring the purity, composition accuracy, and metallurgical quality of the coating.

[0086] In the above embodiments, the protective gas includes one of the following: argon, helium, or a mixture of argon and helium.

[0087] In this embodiment, argon is an inert gas with relatively low cost and stable and reliable protective effect; helium has high thermal conductivity, which can bring a stronger cooling effect and help refine the grains, but its cost is higher. Selecting argon, helium, or a mixture thereof as the protective gas or powder feeding gas according to actual needs can balance coating performance and production cost.

[0088] In the above embodiments, the cobalt-chromium-molybdenum-silicon coating is formed by at least two laser cladding processes.

[0089] In this embodiment, a multi-layer, multi-pass cladding strategy (e.g., for a 0.8 mm thick coating, first cladding a 0.3 mm thick base layer, then cladding a 0.5 mm thick top layer) can be used to construct a thicker functional coating. This method allows for fine-tuning of the process for each layer, helps to disperse heat input, reduces overall thermal stress and deformation, and facilitates control of the dilution rate, ensuring optimal performance of the surface layer.

[0090] In the above embodiments, the cladding speed is 150 mm / s to 250 mm / s, the current is 240 A to 250 A, the laser frequency is 16 Hz to 18 Hz, the laser power is 2.2 kW to 2.6 kW, the spot diameter is 2.1 mm to 2.3 mm, the cladding overlap rate is 52% to 58%, and the thickness of the cobalt-chromium-molybdenum-silicon coating is 0.8 mm to 1.2 mm. For example, the cladding speed is 180 mm / s or 220 mm / s; the current is 245 A; the laser frequency is 17 Hz; the laser power is 2.4 kW; the spot diameter is 2.2 mm; and the overlap rate is 55%. Within this range, the laser energy input is optimally matched with the powder melting and cooling crystallization process, which can further refine the grains, improve the smoothness and uniformity of the coating surface, and achieve a better balance between strength, toughness, and abrasion resistance in the final coating, making it particularly suitable for the manufacture of high-performance printing rollers.

[0091] The printing roller prepared in this embodiment has a cobalt-chromium-molybdenum-silicon coating with a hardness ≥550HV and a wear rate ≤5×10⁻⁶ under dry sliding friction conditions. -6 mm 3 / N·m.

[0092] The second aspect of the present invention provides a printing roller, which is prepared by the preparation method of any embodiment of the first aspect of the present invention.

[0093] The beneficial effects of the printing roller of the present invention are as follows:

[0094] (1) The CoCrMoSi alloy coating of the printing roller of the present invention has a network of ε-Co phase that provides strength support, and a γ-Co-based solid solution phase with good plasticity that can accommodate dislocations and deformation. The coating has excellent strength, toughness and wear resistance.

[0095] (2) In Co-based alloys, by adjusting the content of Cr, Mo and Si alloying elements, combined with laser cladding and heat treatment processes, a fine network equiaxed crystal structure is obtained, which eliminates the typical dendritic directional solidification structure obtained after laser cladding and improves the uniformity of the structure.

[0096] (3) The solute element types of the γ-Co solid solution phase facing the cubic lattice structure and the ε-Co phase facing the close-packed hexagonal structure are the same, but the contents are slightly different. They have similar corrosion potentials and passivation properties in corrosive media, and the coating has excellent corrosion resistance.

[0097] (4) The CoCrMoSi alloy coating has good uniformity and corrosion resistance. It is used to prepare coated printing rollers. The pattern after ultra-short pulse laser engraving has high clarity and good pattern clarity retention.

[0098] The third aspect of the present invention provides a cobalt-chromium-molybdenum-silicon coating for use on printing rollers. The cobalt-chromium-molybdenum-silicon coating comprises, by weight percentage: Cr: 27.0% to 29.0%, Mo: 5.5% to 6.5%, Si: 0.7% to 1.0%, C: 0 to 0.01%, totaling 100%, with the balance being Co.

[0099] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one embodiment or example.

[0100] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing a printing roller with a cobalt-chromium-molybdenum-silicon coating, characterized in that, include: A cobalt-chromium-molybdenum-silicon alloy powder is prepared, wherein, by weight percentage, the cobalt-chromium-molybdenum-silicon alloy powder comprises Cr: 27.0% to 29.0%, Mo: 5.5% to 6.5%, Si: 0.7% to 1.0%, C: 0 to 0.01%, totaling 100%, with the balance being Co; The surface of the printing roller substrate is pretreated for degreasing and rust removal; The pretreated printing roller substrate is preheated to 150°C to 200°C; Using the aforementioned cobalt-chromium-molybdenum-silicon alloy powder, a cobalt-chromium-molybdenum-silicon coating is prepared on the surface of the printing roller substrate by laser cladding. During the laser cladding process, the cladding speed is 100 mm / s to 300 mm / s, the current is 230 A to 260 A, the laser frequency is 14 Hz to 20 Hz, the laser power is 2 kW to 2.8 kW, the spot diameter is 2 mm to 2.5 mm, the cladding overlap rate is 50% to 60%, and the thickness of the cobalt-chromium-molybdenum-silicon coating is 0.5 mm to 1.5 mm. The printing roller substrate with the cobalt-chromium-molybdenum-silicon coating is placed in a heating furnace and heated to 750°C to 800°C, held at that temperature for 3.5 hours to 5 hours, and then cooled to room temperature to obtain the printing roller.

2. The method for preparing a printing roller with a cobalt-chromium-molybdenum-silicon coating according to claim 1, characterized in that, The cobalt-chromium-molybdenum-silicon alloy powder is prepared by vacuum melting and gas atomization; or The cobalt-chromium-molybdenum-silicon alloy powder has a particle size of 5 μm to 52 μm.

3. The method for preparing a printing roller with a cobalt-chromium-molybdenum-silicon coating according to claim 1, characterized in that, The degreasing and rust removal pretreatment includes at least one of the following methods: alkaline washing, acid washing, mechanical grinding, or sandblasting.

4. The method for preparing a printing roller with a cobalt-chromium-molybdenum-silicon coating according to claim 1, characterized in that, The step of cooling to room temperature includes: Cooled to room temperature within the heating furnace; or After cooling to 350°C in the heating furnace, the printing roller substrate with the cobalt-chromium-molybdenum-silicon coating is removed from the heating furnace and allowed to cool naturally to room temperature.

5. The method for preparing a printing roller with a cobalt-chromium-molybdenum-silicon coating according to claim 1, characterized in that, The laser cladding process is carried out in a protective gas environment.

6. The method for preparing a printing roller with a cobalt-chromium-molybdenum-silicon coating according to claim 5, characterized in that, The protective gas includes one of the following: argon, helium, or a mixture of argon and helium.

7. The method for preparing a printing roller with a cobalt-chromium-molybdenum-silicon coating according to claim 1, characterized in that, The cobalt-chromium-molybdenum-silicon coating is formed by at least two laser cladding processes.

8. The method for preparing a printing roller with a cobalt-chromium-molybdenum-silicon coating according to any one of claims 1 to 7, characterized in that, The cladding speed is 150 mm / s to 250 mm / s, the current is 240 A to 250 A, the laser frequency is 16 Hz to 18 Hz, the laser power is 2.2 kW to 2.6 kW, the spot diameter is 2.1 mm to 2.3 mm, the cladding overlap rate is 52% to 58%, and the thickness of the cobalt-chromium-molybdenum-silicon coating is 0.8 mm to 1.2 mm.

9. A printing roller, characterized in that, The printing roller is prepared by the method for preparing a printing roller with a cobalt-chromium-molybdenum-silicon coating as described in any one of claims 1 to 8.

10. A cobalt-chromium-molybdenum-silicon coating, characterized in that, When applied to printing rollers, the cobalt-chromium-molybdenum-silicon coating comprises, by weight percentage: Cr: 27.0% to 29.0%, Mo: 5.5% to 6.5%, Si: 0.7% to 1.0%, C: 0 to 0.01%, totaling 100%, with the balance being Co.

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