Coating for 40Ni35Cr25Nb furnace bottom roller, preparation method of coating and furnace bottom roller

Abstract

The invention provides a coating for a 40Ni35Cr25Nb furnace bottom roller, the coating sequentially comprises a bottom layer, a working layer and a sealing layer along the direction far away from a furnace bottom roller base body, and the thickness ratio of the bottom layer to the working layer to the sealing layer is 1: (1.5-2.5): (2.5-3.5); the sealing layer is made of a Cr3C2-NiCr material; the working layer is made of NiCrAlY; based on the total mass of the base layer, the base layer contains 40 to 56 weight percent of Co, 22 to 28 weight percent of Cr, 12 to 18 weight percent of Ta, 6 to 9 weight percent of Al, 3 to 4 weight percent of Y, 0.5 to 1.5 weight percent of Ni and 0.3 to 1 weight percent of W. According to the coating provided by the invention, the base coat can form firm combination on the surface of the substrate, stable support is provided for the working layer and the closing layer, and the hardness and wear resistance of the coating can be ensured.

Description

Technical Field

[0001] The invention relates to the technical field of hearth roller surface treatment, relates to an energetic adhesive, and in particular to a coating for a 40Ni35Cr25Nb hearth roller, a preparation method thereof, and the hearth roller. Background Art

[0002] In the metallurgical industry, hearth rollers are key components of high-temperature equipment such as continuous annealing furnaces and hot-dip galvanizing lines. Their surface properties directly affect the quality and production efficiency of the strip steel. Although the traditional hearth roller base material, 40Ni35Cr25Nb heat-resistant alloy, has good high-temperature strength and oxidation resistance, it still faces the following problems when subjected to long-term high temperatures of 800-1100°C and corrosive atmospheres (such as oxidizing and carburizing environments):

[0003] (1) Surface nodules and steel sticking: Due to the long-term contact between the furnace rollers and the strip, the oxides on the strip surface (such as FeO, MnO) easily react with the roller surface at high temperatures to form spinel nodules such as MnCr2O4 and FeCr2O4, resulting in scratches or indentations on the strip surface, affecting product quality.

[0004] (2) Coating peeling and failure: Although traditional coatings (such as CoCrAlY-CrB2 / Y2O3) can provide certain high temperature resistance and wear resistance, due to the mismatch of the coefficient of thermal expansion (CTE), microcracks are easily generated under thermal cycling conditions, which leads to coating peeling and shortens the service life.

[0005] (3) Insufficient thermal shock resistance: The interlayer bonding strength of the existing coating is low. During the rapid heating and cooling process, delamination failure occurs due to the accumulation of thermal stress, which is particularly obvious on the high nickel-chromium alloy 40Ni35Cr25Nb substrate.

[0006] CN102650028A discloses a coating for preventing nodules and resistant high-temperature furnace bottom rollers. The coating includes a base layer composed of the following components by mass: Co: 35-63%, Cr: 20-30%, Ta: 10-20%, Al: 5-10%, and Y: 2-5%. This method involves explosively spraying a metal-ceramic material onto the roller body, modifying the roller's surface properties. This effectively prevents nodules and increases the roller's high-temperature lifespan. However, this method still suffers from poor adhesion between the coating and the substrate and easy detachment, making it difficult to meet the demanding operating conditions of modern, high-efficiency continuous annealing furnaces. Summary of the Invention

[0007] The main purpose of the present invention is to provide a coating for a 40Ni35Cr25Nb hearth roller, so as to solve the problems of poor bonding between the existing hearth roller coating and the substrate and easy shedding of the coating.

[0008] To achieve the above object, the present invention provides a coating for a 40Ni35Cr25Nb hearth roller, wherein the coating comprises a primer layer, a working layer, and a sealing layer in a direction away from the hearth roller substrate, wherein the thickness ratio of the primer layer, the working layer, and the sealing layer is 1:1.5-2.5:2.5-3.5;

[0009] Based on the total mass of the sealing layer, the sealing layer contains 60-80wt% of Cr3C2 and 20-40wt% of NiCr alloy;

[0010] Based on the total mass of the working layer, the working layer contains 75-85wt% Ni, 10-15wt% Cr, 3-8wt% Al and 1-3wt% Y;

[0011] Based on the total mass of the primer layer, the primer layer contains 40-56wt% Co, 22-28wt% Cr, 12-18wt% Ta, 6-9wt% Al, 3-4wt% Y, 0.5-1.5wt% Ni and 0.3-1wt% W.

[0012] Furthermore, the ratio of the thickness of the sealing layer, the thickness of the working layer and the thickness of the primer layer is 1:1.5-2.0:2.5-3.0.

[0013] Furthermore, the total thickness of the coating is not less than 0.5 mm.

[0014] Furthermore, the hardness of the coating is greater than Hv800, and the surface roughness is not less than Ra10.0 μm.

[0015] The present invention also provides a method for preparing a coating for a 40Ni35Cr25Nb hearth roller, the method comprising:

[0016] (1) performing surface pretreatment on a hearth roller substrate to obtain a hearth roller substrate I;

[0017] (2) forming a base layer on the hearth roller substrate I by using explosion spraying method I, then forming a working layer on the surface of the base layer by using plasma spraying method, and finally forming a sealing layer on the surface of the working layer by using explosion spraying method II to obtain a hearth roller ';

[0018] (3) The hearth roller is subjected to tempering treatment.

[0019] Furthermore, the conditions of the explosion spraying method I include at least: an explosion frequency of 9-13 times / minute, a spraying distance of 100-300 mm, an oxygen pressure of 0.6-1.2 MPa, an acetylene pressure of 0.15-0.2 MPa, and a nitrogen pressure of 0.55-0.85 MPa.

[0020] Furthermore, the plasma spraying method is carried out using a plasma arc, and the conditions of the plasma spraying method include at least: an ion arc current of 300-500A, a spraying distance of 80-120mm, a main gas flow rate of 40-60L / min, a powder feeding gas flow rate of 5-10L / min, and a powder conveying speed of 15-25g / min.

[0021] Optionally, the main gas is argon and the powder feeding gas is hydrogen.

[0022] Furthermore, the conditions of the explosion spraying method II include at least: controlling the explosion frequency to 12-15 times / minute, the spraying distance to 150-250 mm, the oxygen pressure to 1.2-1.5 MPa, the acetylene pressure to 0.25-0.35 MPa, and the nitrogen pressure to 0.7-0.9 MPa.

[0023] Furthermore, the tempering treatment operation steps include: placing the hearth roller in a heat treatment furnace, heating it to 800-900°C at a heating rate of 5-10°C / min, keeping it warm for 2-4 hours, and then cooling it to room temperature at a cooling rate of 3-5°C / min.

[0024] The present invention also provides a hearth roller, comprising a hearth roller base and a coating applied on the hearth roller base, wherein the coating is the coating for the 40Ni35Cr25Nb hearth roller, and the hearth roller base is made of 40Ni35Cr25Nb material.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The coating provided by the present invention adopts a three-layer coating design of a primer layer, a working layer and a sealing layer. According to the characteristics of the 40Ni35Cr25Nb hearth roller material, a specific amount of Ni and W are introduced into the traditional CoCrAlYTa primer layer, so that the primer layer can form a strong bond with the surface of the hearth roller substrate, providing stable support for the working layer and the sealing layer. At the same time, the present invention can ensure the hardness and wear resistance of the coating by adjusting the thickness ratio of the primer layer, the working layer and the sealing layer to 1:1.5-2.5:2.5-3.5.

[0027] Before coating spraying, the present invention performs strict pretreatment on the hearth roller, and then adopts explosion spraying method and plasma spraying method to prepare base layer, working layer and sealing layer respectively. By reasonably setting the spraying parameters and controlling the thickness of each layer within the aforementioned proportional range, the base layer has good density and bonding strength, and at the same time ensures good metallurgical bonding between the base layer and the working layer, and ensures the hardness, wear resistance and oxidation resistance of the coating. DETAILED DESCRIPTION

[0028] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] In addition, in the present invention, descriptions such as "first" and "second" are for descriptive purposes only and should not be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of such features. Moreover, the technical solutions between the various embodiments of the present invention can be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in this field. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0030] It should be noted that the room temperature or normal temperature mentioned in the present invention refers to 25±2°C.

[0031] As mentioned above, the present invention provides a coating for a 40Ni35Cr25Nb hearth roller, wherein the coating comprises a primer layer, a working layer, and a sealing layer in the direction away from the hearth roller substrate, wherein the ratio of the thickness of the primer layer, the thickness of the working layer, and the thickness of the sealing layer is 1:1.5-2.5:2.5-3.5;

[0032] Based on the total mass of the sealing layer, the sealing layer contains 60-80wt% of Cr3C2 and 20-40wt% of NiCr alloy;

[0033] Based on the total mass of the working layer, the working layer contains 75-85wt% Ni, 10-15wt% Cr, 3-8wt% Al and 1-3wt% Y;

[0034] Based on the total mass of the primer layer, the primer layer contains 40-56wt% Co, 22-28wt% Cr, 12-18wt% Ta, 6-9wt% Al, 3-4wt% Y, 0.5-1.5wt% Ni and 0.3-1wt% W.

[0035] The coating provided by the present invention adopts a three-layer coating design including a primer layer, a working layer and a sealing layer. According to the characteristics of the 40Ni35Cr25Nb hearth roller material, a specific amount of Ni and W are introduced into the traditional CoCrAlYTa primer layer, so that the primer layer can form a strong bond with the surface of the hearth roller substrate, providing stable support for the working layer and the sealing layer. At the same time, the present invention can ensure the hardness and wear resistance of the coating by adjusting the thickness ratio of the primer layer, the working layer and the sealing layer to 1:1.5-2.5:2.5-3.5.

[0036] The base layer serves as the connecting layer between the coating and the furnace bottom roller substrate, and its composition design is crucial to the coating's bonding strength and overall performance. The base layer of the present invention contains 40-56wt% Co, 22-28wt% Cr, 12-18wt% Ta, 6-9wt% Al, and 3-4wt% Y, with 0.5-1.5wt% Ni and 0.3-1wt% W added. Among them, Co has good toughness and bonding strength, and can enhance the bonding strength between the coating and the substrate; Cr can improve the coating's oxidation resistance and corrosion resistance; Ta can enhance the coating's high temperature resistance and wear resistance; Al helps to form a dense alumina protective film and enhance oxidation resistance; Y, as a rare earth element, can refine the grains, improve the coating's microstructure, and improve the coating's high temperature stability and thermal shock resistance. In addition, the present invention can further improve the coating's toughness and impact resistance through the additional addition of Ni, while W can enhance the coating's hardness and wear resistance.

[0037] The present invention simultaneously adds Ni and W elements to the traditional CoCrAlYTa base layer. The FCC structure of Ni and the BCC structure of W can form a dual-phase structure, balancing the strength and toughness of the coating. During the high-temperature oxidation process, Ni promotes the formation of Al2O3, while W enhances the spalling resistance of the oxide film, thereby jointly improving the long-term protective capability of the coating.

[0038] The addition of Ni can not only improve the toughness and impact resistance of the coating, but also form a β-NiAl phase, which coexists with the traditional β-CoAl phase to obtain a higher Al diffusion rate, thereby promoting the rapid formation of a protective Al2O3 oxide film, and can also delay the consumption of Al in the coating and extend the antioxidant life. The addition of Ni may change the composition of the oxide film, forming a denser (Ni, Co)(Cr, Al)2O4 spinel structure and improving the anti-stripping ability of the oxide film. The mass percentage of Ni can be, for example, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt% or any value between 0.5-1.5wt%. If the mass percentage of added Ni is too high, the hardness and strength will not be enhanced; if the mass percentage of added Ni is too low, the antioxidant ability of the coating will be reduced.

[0039] The addition of W not only enhances the hardness and wear resistance of the coating, but also works with Ni to improve the toughness of the coating to a certain extent. The mass percentage of W can be, for example, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt% or any value between 0.3-1.0wt%. However, when the mass percentage of added W is too high, the toughness of the coating will be significantly reduced; if the mass percentage of added W is too low, the hardness and wear resistance of the coating will not be effectively enhanced, and it will be easily worn in actual use, shortening the service life of the coating.

[0040] During the research process, the inventors found that by combining the characteristics of the 40Ni35Cr25Nb hearth roller material and the working layer, by controlling the Ni addition amount between 0.5-1.5wt%, the W addition amount within the range of 0.3-1.0wt%, and strictly controlling the Ni / W ratio, it is possible to avoid the induction of brittleness, thereby obtaining a coating with better overall performance.

[0041] The working layer utilizes a NiCrAlY alloy containing 75-85wt% Ni, 10-15wt% Cr, 3-8wt% Al, and 1-3wt% Y. The working layer provided by the present invention exhibits excellent high-temperature oxidation and hot corrosion resistance, serving as a transition between the base layer and the top layer, further enhancing the overall performance and adhesion of the coating. Furthermore, the alloy forms a stable oxide protective film at high temperatures, effectively preventing oxygen atoms from diffusing into the coating and enhancing the coating's oxidation resistance.

[0042] The sealing layer is made of a cermet material, primarily composed of Cr3C2 and NiCr. The Cr3C2 content is 60-80% by weight, and the NiCr alloy content is 20-40% by weight. Cr3C2 exhibits high hardness, wear resistance, and excellent high-temperature resistance, effectively protecting against the wear and high-temperature erosion experienced by the hearth rollers during operation. NiCr, as a binder, firmly bonds the Cr3C2 particles together, enhancing the coating's toughness and impact resistance. The combined Cr3C2-NiCr cermet forms a dense chromium carbide protective film at high temperatures, further enhancing the coating's resistance to oxidation and nodulation.

[0043] In some embodiments, the ratio of the thickness of the sealing layer, the thickness of the working layer, and the thickness of the primer layer is 1:1.5-2.0:2.5-3.0. During research, the inventors found that adopting this preferred embodiment can ensure a good metallurgical bond between the primer layer and the working layer, and ensure the hardness, wear resistance, and oxidation resistance of the coating.

[0044] In some embodiments, the total thickness of the coating is not less than 0.5 mm. It should be noted that the prior art generally recommends a total coating thickness greater than 0.15 mm. Although this can significantly improve anti-nodulation performance and extend the service life of the hearth roller, when the total coating thickness reaches 0.5 mm or more, the excessively thick coating may fail prematurely due to insufficient bonding strength or peel off due to thermal stress. However, the inventors of the present invention unexpectedly discovered that by adopting the three-layer coating design of the present invention, by adjusting the ratio of the components of each layer, and in particular optimizing the ratio of the components of the base layer, a strong bond can still be maintained when the total coating thickness is not less than 0.5 mm.

[0045] In order to obtain a coating with better comprehensive performance, in some specific embodiments, the thickness of the sealing layer is 0.3-0.5 mm, the thickness of the working layer is 0.2-0.3 mm, and the thickness of the primer layer is 0.1-0.25 mm.

[0046] In some embodiments, the coating has a hardness greater than Hv800 and a surface roughness no less than Ra10.0 μm.

[0047] As mentioned above, the present invention also provides a method for preparing a coating for a 40Ni35Cr25Nb hearth roller, the method comprising:

[0048] (1) performing surface pretreatment on a hearth roller substrate to obtain a hearth roller substrate I;

[0049] (2) forming a base layer on the hearth roller substrate I by using explosion spraying method I, then forming a working layer on the surface of the base layer by using plasma spraying method, and finally forming a sealing layer on the surface of the working layer by using explosion spraying method II to obtain a hearth roller ';

[0050] (3) The hearth roller is subjected to tempering treatment.

[0051] Before coating spraying, the present invention performs strict pretreatment on the hearth roller, and then adopts explosion spraying method and plasma spraying method to prepare base layer, working layer and sealing layer respectively. By reasonably setting the spraying parameters and controlling the thickness of each layer within the aforementioned ratio range, the base layer has good density and bonding strength, thereby obtaining a coating with excellent comprehensive properties such as hardness, wear resistance and oxidation resistance.

[0052] In order to further improve the bonding strength between the coating and the substrate, ensure the quality and performance of the coating, and remove surface impurities to prevent coating defects, in some specific embodiments, the pretreatment steps include:

[0053] Step S1: using sandblasting to remove impurities such as oil, rust, and scale on the surface of the hearth roller to achieve a surface roughness of Ra10-15 μm, thereby increasing the mechanical bonding strength between the coating and the substrate;

[0054] Step S2: After the sandblasting treatment, the surface of the furnace bottom roller is immediately cleaned with acetone or anhydrous ethanol to remove residual abrasives and impurities, and stored in a dry environment to prevent the surface from being oxidized again.

[0055] Detonation spraying utilizes the high-temperature and high-pressure shock waves generated by explosive explosions to heat the spraying material to a molten or semi-molten state, and then sprays it onto the surface of the furnace bottom roller at high speed to form a coating. The process parameters of the explosion spraying method have a significant impact on the quality and performance of the coating. By optimizing parameters such as the explosion frequency, spraying distance, and gas pressure, the bonding strength, density, and uniformity of the coating can be significantly improved, thereby meeting the needs of different application scenarios. In some specific embodiments, the conditions of the explosion spraying method I include at least: an explosion frequency of 9-13 times / minute, a spraying distance of 100-300mm, an oxygen pressure of 0.6-1.2MPa, an acetylene pressure of 0.15-0.2MPa, and a nitrogen pressure of 0.55-0.85MPa. The inventors have found that by precisely controlling the aforementioned spraying parameters, the thickness of the base layer can be controlled within the range of 0.15-0.25mm, so that the base layer has good density and bonding strength.

[0056] The explosion frequency can be, for example, 9 times / minute, 10 times / minute, 11 times / minute, 12 times / minute, 13 times / minute, or any value between 9 and 13 times / minute. If the explosion frequency is too low, such as less than 9 times / minute, the energy release interval generated by the explosion is longer, and the sprayed particles have more time to dissipate heat during flight. The temperature and kinetic energy when they reach the substrate surface are relatively low, which will lead to less tight bonding between the particles, a decrease in the density of the coating, and the bonding strength between the coating and the substrate will also be affected, making it easy for the coating to peel off. Conversely, when the explosion frequency is too high, such as greater than 13 times / minute, the particles will overheat, excessive oxidation or gasification will occur, which will also affect the quality of the coating. The inventors have found that setting the explosion frequency between 9 and 13 times / minute allows for more frequent release of explosion energy, allowing the particles to impact the substrate surface with higher temperatures and kinetic energy, which is beneficial for bonding between the particles and between the particles and the substrate, thereby improving the density and bonding strength of the coating.

[0057] The spraying distance refers to the distance from the spray gun outlet to the substrate surface, and can be, for example, 100mm, 120mm, 150mm, 180mm, 200mm, 210mm, 220mm, 230mm, 240mm, 250mm, 260mm, 270mm, 280mm, 290mm, 300mm, or any value between 100-300mm. When the distance is short, the particles encounter less air resistance during flight and reach the substrate surface at a higher speed. However, due to the short flight time, the particles may not fully melt, resulting in a reduction in the smoothness and bonding quality of the coating. When the spraying distance is long, the particles spend more time in contact with the air during flight, resulting in a greater loss of heat and velocity. Upon reaching the substrate surface, they may not be fully spread and bonded, which also reduces the quality of the coating.

[0058] Oxygen plays a combustion-supporting role in explosion spraying, and the oxygen pressure directly affects the intensity of the combustion reaction and the energy released. When the oxygen pressure is low, the combustion reaction is relatively weak, and the energy released is insufficient to fully melt the sprayed particles, resulting in unmelted particles in the coating, affecting the density and performance of the coating. When the oxygen pressure is too high, the particles may overheat, excessively oxidize, and produce oxide inclusions, which reduces the performance of the coating. The inventors have found that within the oxygen pressure range of 0.6-1.2MPa, the oxygen pressure is sufficient to fully promote the combustion reaction, increase the energy released, and better melt the particles, which is conducive to the formation of high-quality coatings.

[0059] Acetylene is the fuel used in explosive spraying. The acetylene pressure and oxygen pressure work together to determine the effectiveness of the combustion reaction. If the acetylene pressure is too low, the fuel supply is insufficient, the combustion reaction is incomplete, and the melting degree and flight speed of the particles are affected, resulting in reduced coating quality. Excessive acetylene pressure can cause excessive combustion, resulting in unstable explosions and even safety issues. Furthermore, excessive acetylene pressure can lead to carbon residue, affecting coating performance.

[0060] Nitrogen plays a major role in explosive spraying, transporting and dispersing the sprayed particles. If the nitrogen pressure is too low, the particles may not be smoothly transported to the substrate surface, or they may agglomerate during transport, resulting in coating defects. Excessive nitrogen pressure may cause the particles to fly too fast, increasing friction between the particles and the air, leading to overheating or oxidation, and also potentially affecting the particle deposition effect on the substrate surface. The inventors have discovered that within a nitrogen pressure range of 0.55-0.85 MPa, the particles can be evenly transported to the spray gun outlet and remain well dispersed during flight.

[0061] After the base layer is sprayed, a plasma spraying method is used to prepare a working layer. Plasma spraying utilizes the high temperature generated by a plasma arc to heat the spraying material to a molten or semi-molten state, and sprays it onto the surface of the base layer at high speed to form a coating. In some specific embodiments, the plasma spraying method is carried out using a plasma arc, and the conditions of the plasma spraying method include at least: an ion arc current of 300-500A, a spraying distance of 80-120mm, a main gas flow rate of 40-60L / min, a powder feeding gas flow rate of 5-10L / min, and a powder conveying speed of 15-25g / min. The inventors found that by reasonably adjusting the spraying process parameters, the thickness of the working layer can be controlled to be 0.2-0.3mm, thereby enabling a good metallurgical bond to be formed between the coating and the base layer.

[0062] In some specific embodiments, the conditions of the explosion spraying method II include at least: controlling the explosion frequency to 12-15 times / minute, the spraying distance to 150-250 mm, the oxygen pressure to 1.2-1.5 MPa, the acetylene pressure to 0.25-0.35 MPa, and the nitrogen pressure to 0.7-0.9 MPa. The inventors have found that, by adopting this preferred embodiment, controlling the thickness of the sealing layer to within the range of 0.3-0.5 mm can ensure that the coating has good hardness, wear resistance, and oxidation resistance.

[0063] It should be noted that after the coating is sprayed, the hearth roller undergoes a high-temperature tempering treatment. In some specific embodiments, the tempering treatment includes placing the hearth roller in a heat treatment furnace, heating it to 800-900°C at a heating rate of 5-10°C / min, holding it at that temperature for 2-4 hours, and then cooling it to room temperature at a cooling rate of 3-5°C / min. High-temperature tempering can eliminate residual stress within the coating, improve the coating's microstructure, and further enhance the coating's adhesion, high-temperature resistance, and impact resistance.

[0064] As mentioned above, the present invention also provides a hearth roller, comprising a hearth roller substrate and a coating applied on the hearth roller substrate, wherein the coating is the aforementioned coating for the 40Ni35Cr25Nb hearth roller, and the hearth roller substrate is made of 40Ni35Cr25Nb material.

[0065] In some embodiments, the chemical composition of the 40Ni35Cr25Nb material is: Ni 35-40 wt%, Cr 24-26 wt%, Nb 24-26 wt%, C≤0.4 wt%, and the balance is Fe.

[0066] The present invention will be described in detail below by way of examples. In the following examples, unless otherwise specified, all raw materials and instruments used are commercially available.

[0067] The hearth roller substrates used in the examples are all made of 40Ni35Cr25Nb material, which consists of the following components by mass percentage: Ni 35wt%, Cr 25wt%, Nb 25wt%, C 0.4wt%, and the balance Fe.

[0068] In the following embodiments, the main gas used in the plasma spraying process is argon, and the powder feeding gas is hydrogen.

[0069] Example 1

[0070] This embodiment provides a method for preparing a coating for a 40Ni35Cr25Nb hearth roller. The coating comprises a primer layer, a working layer, and a sealing layer. The primer layer comprises the following components by mass: Co: 56%, Cr: 22%, Ta: 12%, Al: 6%, Y: 3%, Ni: 0.5%, and W: 0.5%. The working layer comprises a NiCrAlY alloy having the following composition by mass: Ni: 80%, Cr: 15%, Al: 3%, and Y: 2%. The sealing layer comprises a Cr3C2-NiCr metal ceramic material, with a mass fraction of Cr3C2 of 60% and a mass fraction of NiCr of 40%. The method comprises the following specific steps:

[0071] (1) The surface of the furnace bottom roller base body was treated with 120 mesh brown corundum abrasive at a sandblasting pressure of 0.45 MPa to achieve a surface roughness of Ra10 μm, and then cleaned with acetone and dried;

[0072] (2) The base layer is sprayed with explosion frequency of 8 times / min, spraying distance of 300mm, oxygen pressure of 0.8MPa, acetylene pressure of 0.1MPa, nitrogen pressure of 0.5MPa, and thickness controlled at 0.1mm;

[0073] The working layer was sprayed with a plasma arc with an arc current of 300 A, a spraying distance of 120 mm, a main gas flow rate of 40 L / min, a powder feeding gas flow rate of 10 L / min, a powder conveying speed of 25 g / min, and a thickness of 0.2 mm.

[0074] The sealing layer is sprayed by explosion, with an explosion frequency of 10 times / minute, a spraying distance of 250mm, an oxygen pressure of 1.0MPa, an acetylene pressure of 0.15MPa, a nitrogen pressure of 0.6MPa, and a thickness of 0.3mm;

[0075] (3) After the coating is sprayed, the furnace bottom roller is placed in a heat treatment furnace, heated to 800°C at a heating rate of 5°C / min, kept at this temperature for 4 hours, and then cooled to room temperature at a cooling rate of 3°C / min for tempering.

[0076] The final total coating thickness is 0.6 mm, the coating hardness is greater than Hv800, and the final surface roughness of the roller coating is Ra10.0.

[0077] This coating is suitable for quenching furnace environments with a temperature range of 600-900°C and low loads such as strip friction.

[0078] Example 2

[0079] This embodiment provides a method for preparing a coating for a 40Ni35Cr25Nb hearth roller. The coating comprises a primer layer, a working layer, and a sealing layer. The primer layer comprises the following components by mass percentage: Co: 45%, Cr: 25%, Ta: 18%, Al: 6%, Y: 4%, Ni: 1%, and W: 1%. The working layer is a NiCrAlY alloy having the following composition by mass percentage: Ni: 85%, Cr: 10%, Al: 4%, and Y: 1%. The sealing layer is a Cr3C2-NiCr metal ceramic material, with a mass fraction of Cr3C2 of 80% and a mass fraction of NiCr of 20%. The method comprises the following specific steps:

[0080] (1) The surface of the furnace bottom roller base body is treated with 80 mesh brown corundum abrasive at a sandblasting pressure of 0.6 MPa to make the surface roughness reach Ra15 μm, and then cleaned and dried with anhydrous ethanol;

[0081] (2) The base layer is sprayed with explosion frequency of 12 times / min, spraying distance of 200mm, oxygen pressure of 1.2MPa, acetylene pressure of 0.2MPa, nitrogen pressure of 0.8MPa, and thickness of 0.2mm;

[0082] The working layer was sprayed with a plasma arc with an arc current of 500 A, a spraying distance of 80 mm, a main gas flow rate of 60 L / min, a powder feeding gas flow rate of 5 L / min, a powder conveying speed of 15 g / min, and a thickness of 0.3 mm.

[0083] The sealing layer is sprayed by explosion with an explosion frequency of 15 times / minute, a spraying distance of 180mm, an oxygen pressure of 1.5MPa, an acetylene pressure of 0.25MPa, a nitrogen pressure of 0.9MPa, and a thickness of 0.5mm.

[0084] (3) After the coating is completed, the hearth roller is placed in a heat treatment furnace, heated to 900°C at a heating rate of 10°C / min, kept at this temperature for 2 hours, and cooled to room temperature at a cooling rate of 5°C / min for tempering.

[0085] The final coating has a total thickness of 1.0 mm, a hardness greater than Hv800, and a surface roughness of Ra12.0 on the roller surface. This coating is suitable for high-temperature oxidizing environments of 600-1000°C and quenching furnace conditions with contact stresses ≤500 MPa.

[0086] Example 3

[0087] This embodiment provides a method for preparing a coating for a 40Ni35Cr25Nb hearth roller. The coating comprises a primer layer, a working layer, and a sealing layer. The primer layer comprises the following components by mass: Co: 50%, Cr: 23.5%, Ta: 13%, Al: 8%, Y: 3.7%, Ni: 1.5%, and W: 0.3%; the working layer comprises a NiCrAlY alloy, and its composition by mass is: Ni: 77.5%, Cr: 15%, Al: 6%, and Y: 1.5%; and the sealing layer comprises a Cr3C2-NiCr metal ceramic material, with a mass fraction of Cr3C2 of 70% and a mass fraction of NiCr of 30%. The method comprises the following specific steps:

[0088] (1) The surface of the furnace bottom roller base body was treated with 100 mesh brown corundum abrasive at a sandblasting pressure of 0.5 MPa to achieve a surface roughness of Ra12 μm, and then cleaned with acetone and dried;

[0089] (2) The base layer is sprayed with explosion frequency of 10 times / min, spraying distance of 250mm, oxygen pressure of 1.0MPa, acetylene pressure of 0.15MPa, nitrogen pressure of 0.6MPa, and thickness of 0.15mm;

[0090] The working layer was sprayed with a plasma arc with an arc current of 400 A, a spraying distance of 100 mm, a main gas flow rate of 50 L / min, a powder feeding gas flow rate of 8 L / min, a powder conveying speed of 20 g / min, and a thickness of 0.25 mm.

[0091] The sealing layer is sprayed with explosion frequency of 12 times / minute, spraying distance of 220mm, oxygen pressure of 1.2MPa, acetylene pressure of 0.2MPa, nitrogen pressure of 0.7MPa, and thickness of 0.4mm;

[0092] (3) After the coating is completed, the hearth roller is placed in a heat treatment furnace, heated to 850°C at a heating rate of 8°C / min, kept at this temperature for 3 hours, and cooled to room temperature at a cooling rate of 4°C / min for tempering.

[0093] The final coating has a total thickness of 0.8 mm, a hardness greater than Hv800, and a surface roughness of Ra11.0. This coating can be used in a quenching furnace environment with a temperature range of 700-950°C and a contact stress load of 200-400 MPa.

[0094] Example 4

[0095] This embodiment provides a method for preparing a coating for a 40Ni35Cr25Nb hearth roller, which is carried out according to the method of Example 1, except that: the parameters of the plasma spraying are controlled so that the thickness of the working layer is 0.25 mm; wherein the ratio of the thickness of the primer layer, the thickness of the working layer, and the thickness of the sealing layer is 1:2.5:3.

[0096] Example 5

[0097] This embodiment provides a method for preparing a coating for a 40Ni35Cr25Nb hearth roller, which is carried out according to the method of Example 1, except that: the parameters of the plasma spraying are controlled so that the thickness of the sealing layer is 0.35 mm; wherein the ratio of the thickness of the primer layer, the thickness of the working layer, and the thickness of the sealing layer is 1:2.5:3.5.

[0098] Comparative Example 1

[0099] This comparative example provides a method for preparing a coating for a 40Ni35Cr25Nb hearth roller, which is carried out according to the method of Example 1, except that the primer layer does not contain Ni and W; specifically, the primer layer includes the following components in mass percentage: Co: 50%, Cr: 25%, Ta: 15%, Al: 6%, and Y: 4%.

[0100] Comparative Example 2

[0101] This comparative example provides a method for preparing a coating for a 40Ni35Cr25Nb hearth roller, which is carried out by referring to the method of Example 1, except that the base layer includes the following components in mass percentage: Co: 52%, Cr: 22%, Ta: 12%, Al: 9%, Y: 3%, Ni: 1.9%, and W: 0.1wt%.

[0102] Comparative Example 3

[0103] This comparative example provides a method for preparing a coating for a 40Ni35Cr25Nb hearth roller, which is carried out according to the method of Example 1, except that the parameters of the explosion spraying are controlled so that the thickness of the primer layer is 0.2 mm; wherein the ratio of the thickness of the primer layer, the thickness of the working layer, and the thickness of the sealing layer is 1:1.0:1.5.

[0104] Comparative Example 4

[0105] This comparative example provides a method for preparing a coating for a 40Ni35Cr25Nb hearth roller, which is carried out according to the method of Example 1, except that the parameters of the explosion spraying are controlled so that the thickness of the primer layer is 0.05 mm; wherein the ratio of the thickness of the primer layer, the thickness of the working layer, and the thickness of the sealing layer is 1:4:6.

[0106] Analysis example 1

[0107] The properties of the 40Ni35Cr25Nb hearth roller coatings obtained in Examples 1-5 and Comparative Examples 1-4 were tested, including the total coating thickness, coating hardness, and surface roughness. The specific test results are shown in Table 1.

[0108] Table 1

[0109]

[0110]

[0111] As can be seen from the above table, the present invention introduces specific amounts of Ni and W into the traditional CoCrAlYTa base layer, allowing the base layer to form a strong bond with the surface of the hearth roller substrate, providing stable support for the working layer and the sealing layer. At the same time, the present invention also improves the high-temperature oxidation resistance and thermal shock resistance while ensuring anti-nodulation performance by adjusting the thickness ratio of the base layer, working layer, and sealing layer to 1:1.5-2.5:2.5-3.5.

[0112] It should be noted that, in this article, the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements that are inherent to such process, method, article or apparatus.

[0113] The above technical solutions of the present invention are only preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention specification under the technical concept of the present invention, or direct / indirect applications in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A coating for a 40Ni35Cr25Nb hearth roller, characterized in that: The coating comprises a primer layer, a working layer and a sealing layer in the direction away from the hearth roller base body, wherein the thickness ratio of the primer layer, the working layer and the sealing layer is 1:1.5-2.5:2.5-3.5; Based on the total mass of the sealing layer, the sealing layer contains 60-80wt% of Cr3C2 and 20-40wt% of NiCr alloy; Based on the total mass of the working layer, the working layer contains 75-85wt% Ni, 10-15wt% Cr, 3-8wt% Al and 1-3wt% Y; Based on the total mass of the primer layer, the primer layer contains 40-56wt% Co, 22-28wt% Cr, 12-18wt% Ta, 6-9wt% Al, 3-4wt% Y, 0.5-1.5wt% Ni and 0.3-1wt% W.

2. The coating according to claim 1, characterized in that The ratio of the thickness of the sealing layer, the thickness of the working layer and the thickness of the primer layer is 1:1.5-2.0:2.5-3.

0.

3. The coating according to claim 2, characterized in that The total thickness of the coating is not less than 0.5 mm.

4. The coating according to any one of claims 1 to 3, characterized in that The hardness of the coating is greater than Hv800, and the surface roughness is not less than Ra10.0 μm.

5. A method for preparing the coating according to any one of claims 1 to 4, characterized in that: The method includes: (1) performing surface pretreatment on a hearth roller substrate to obtain a hearth roller substrate I; (2) forming a base layer on the hearth roller substrate I by using explosion spraying method I, then forming a working layer on the surface of the base layer by using plasma spraying method, and finally forming a sealing layer on the surface of the working layer by using explosion spraying method II to obtain a hearth roller '; (3) The hearth roller is subjected to tempering treatment.

6. The method according to claim 5, characterized in that The conditions of the explosion spraying method I include at least: an explosion frequency of 9-13 times / minute, a spraying distance of 100-300 mm, an oxygen pressure of 0.6-1.2 MPa, an acetylene pressure of 0.15-0.2 MPa, and a nitrogen pressure of 0.55-0.85 MPa.

7. The method according to claim 5, characterized in that The plasma spraying method is performed using a plasma arc, and the conditions of the plasma spraying method include at least: an ion arc current of 300-500A, a spraying distance of 80-120mm, a main gas flow rate of 40-60L / min, a powder feeding gas flow rate of 5-10L / min, and a powder conveying speed of 15-25g / min; Optionally, the main gas is argon and the powder feeding gas is hydrogen.

8. The method according to claim 5, characterized in that The conditions of the explosion spraying method II include at least: controlling the explosion frequency to 12-15 times / minute, the spraying distance to 150-250 mm, the oxygen pressure to 1.2-1.5 MPa, the acetylene pressure to 0.25-0.35 MPa, and the nitrogen pressure to 0.7-0.9 MPa.

9. The method according to claim 5, characterized in that The tempering treatment process includes placing the hearth roller in a heat treatment furnace, heating it to 800-900°C at a heating rate of 5-10°C / min, keeping the temperature for 2-4 hours, and then cooling it to room temperature at a cooling rate of 3-5°C / min.

10. A hearth roller, characterized in that: It comprises a hearth roller base body and a coating coated on the hearth roller base body, wherein the coating is the coating according to any one of claims 1 to 4, and the hearth roller base body is made of 40Ni35Cr25Nb material.

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