Coating for protecting medium-carbon Cr-Ni-Mo-V alloy steel, preparation method thereof and application

Abstract

The present invention provides a coating for protecting medium-carbon Cr-Ni-Mo-V alloy steel, a preparation method thereof and an application thereof. By weight, the coating comprises 15-20 parts of a first glass, 5-10 parts of a second glass, 5-10 parts of a third glass, 36-59 parts of a high-temperature resistant filler and 5-10 parts of a solvent; the first glass, the second glass and the third glass all comprise specific contents of SiO₂, Al₂O₃, MgO, B₂O₃, Na₂O and K₂O; the high-temperature resistant filler comprises SiC, Si₃N₄, SiO₂, ZrO₂, MgO, feldspar and kaolin. The coating of the present invention has good thermal stability, chemical stability and high-temperature resistance, can effectively prevent the alloy steel from being oxidized during heating, significantly reduce the generation of metal oxide scales, has good high-temperature protection effect, and can be easily removed during the water descaling process, and can be used for protecting medium-carbon Cr-Ni-Mo-V alloy steel.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy steel protective coatings, and more particularly, to a coating for protecting medium-carbon Cr-Ni-Mo-V alloy steel, a preparation method thereof, and an application thereof. Background Art

[0002] Medium-carbon Cr-Ni-Mo-V alloy steel belongs to high-performance special alloys and is widely used in various weapons and equipment. During the preparation of weapons and equipment, it is usually necessary to perform hot working processes such as hot extrusion and forging on metal materials such as medium-carbon Cr-Ni-Mo-V alloy steel to complete the preliminary manufacturing.

[0003] During the process of long-term heating of medium-carbon Cr-Ni-Mo-V alloy steel at high temperatures, a thick oxide scale is likely to form, seriously reducing the material utilization rate. In addition, different from other materials, the oxide scale of medium-carbon Cr-Ni-Mo-V alloy steel is firmly bonded to the metal substrate. Even when using high-pressure water descaling and ensuring above the window temperature, the removal amount of the oxide scale does not exceed 30%. The remaining oxide scale will seriously affect the surface quality of the billet after the alloy steel is extruded and formed during the hot extrusion process, bringing difficulties to subsequent processing, and even leading to the scrapping of the entire equipment; moreover, it will also increase the deformation resistance of the material, causing jamming, affecting the service life of the tooling, threatening equipment safety, resulting in waste of special materials and damage to the equipment.

[0004] However, there is no specific protective coating for medium-carbon Cr-Ni-Mo-V alloy steel in the prior art. Moreover, after applying the existing traditional coating on the surface of medium-carbon Cr-Ni-Mo-V alloy steel, a relatively thick oxide scale of the alloy steel still forms after long-term heating at high temperatures. The coating has a poor high-temperature protection effect on the alloy steel and is not easy to peel off, which has an adverse effect on the subsequent processing process. Summary of the Invention

[0005] The main object of the present invention is to provide a coating for protecting medium-carbon Cr-Ni-Mo-V alloy steel, a preparation method thereof, and an application thereof, so as to solve the problems that medium-carbon Cr-Ni-Mo-V alloy steel in the prior art is prone to form a relatively thick oxide scale during long-term heating at high temperatures, the coating has a poor high-temperature protection effect and is not easy to peel off.

[0006] To achieve the above object, according to one aspect of the present invention, there is provided a coating for protecting medium-carbon Cr-Ni-Mo-V alloy steel. By weight, the coating comprises 15-20 parts of a first glass, 5-10 parts of a second glass, 5-10 parts of a third glass, 36-59 parts of a high-temperature resistant filler, and 5-10 parts of a solvent; wherein, by weight, the first glass comprises 35-40 parts of SiO2, 25-30 parts of Al2O3, 3-5 parts of MgO, 3-8 parts of B2O3, 3-8 parts of Na2O, and 3-8 parts of K2O; the second glass comprises 30-35 parts of SiO2, 25-30 parts of Al2O3, 2-4 parts of MgO, 5-10 parts of B2O3, 4-8 parts of Na2O, and 4-8 parts of K2O; the third glass comprises 25-30 parts of SiO2, 20-25 parts of Al2O3, 2-4 parts of MgO, 10-15 parts of B2O3, 10-15 parts of Na2O, and 10-15 parts of K2O; the high-temperature resistant filler comprises SiC, Si3N4, SiO2, ZrO2, MgO, feldspar, and kaolin.

[0007] Further, by weight, the coating comprises 17-20 parts of the first glass, 5-8 parts of the second glass, 6-9 parts of the third glass, 45-59 parts of the high-temperature resistant filler, and 8-10 parts of the solvent; and / or the high-temperature resistant filler comprises 6-10 parts of SiC, 3-5 parts of Si3N4, 8-12 parts of SiO2, 7-12 parts of ZrO2, 3-5 parts of MgO, 6-10 parts of feldspar, and 3-5 parts of kaolin.

[0008] Further, by weight, the first glass comprises 37-40 parts of SiO2, 25-28 parts of Al2O3, 3-4 parts of MgO, 4-6 parts of B2O3, 4-6 parts of Na2O, and 3-5 parts of K2O; and / or the second glass comprises 31-34 parts of SiO2, 26-28 parts of Al2O3, 2-3 parts of MgO, 5-7 parts of B2O3, 5-7 parts of Na2O, and 5-7 parts of K2O; and / or the third glass comprises 25-27 parts of SiO2, 21-23 parts of Al2O3, 3-4 parts of MgO, 11-13 parts of B2O3, 10-13 parts of Na2O, and 12-15 parts of K2O; and / or the high-temperature resistant filler comprises 7-9 parts of SiC, 4-5 parts of Si3N4, 9-11 parts of SiO2, 9-11 parts of ZrO2, 3-4 parts of MgO, 6-8 parts of feldspar, and 3-4 parts of kaolin.

[0009] Further, the total weight parts of SiO2, Al2O3, and MgO in the coating ≥ 210 parts, preferably 185-190 parts; and / or the total weight parts of B2O3, Na2O, and K2O in the coating ≥ 80 parts, preferably 59-69 parts.

[0010] Further, by weight, the coating further comprises 35-40 parts of a binder; preferably, the binder is silica sol and / or alumina sol; and / or by weight, the coating further comprises 1-2 parts of a dispersant; preferably, the dispersant is one or more of an anionic dispersant, a cationic dispersant, and a non-ionic dispersant; and / or the solvent is water.

[0011] According to another aspect of the present invention, there is provided a method for preparing the above-mentioned coating for protecting medium-carbon Cr-Ni-Mo-V alloy steel of the present invention, comprising the following steps: mixing the first glass, the second glass, the third glass, the high-temperature resistant filler and the solvent according to the component ratio to obtain the coating for protecting medium-carbon Cr-Ni-Mo-V alloy steel.

[0012] Further, the mixing method is ball milling and / or stirring; when the mixing is ball milling, the ball milling speed is 50-100 rpm, the ball milling time is 10-30 h, and the ball-to-material ratio is (2-8):1; when the mixing is stirring, the stirring speed is 1200-2000 rpm, the stirring time is 0.5-2 h, and the ball-to-material ratio is (2-7):1.

[0013] Further, when the mixing is ball milling, the ball milling speed is 60-80 rpm, the ball milling time is 20-30 h, and the ball-to-material ratio is (3-7):1; when the mixing is stirring, the stirring speed is 1200-1500 rpm, the stirring time is 0.5-1 h, and the ball-to-material ratio is (5-7):1.

[0014] According to another aspect of the present invention, there is provided a method for protecting medium-carbon Cr-Ni-Mo-V alloy steel, coating the above-mentioned coating for protecting medium-carbon Cr-Ni-Mo-V alloy steel on the surface of the medium-carbon Cr-Ni-Mo-V alloy steel, heating and keeping warm in the furnace with the medium-carbon Cr-Ni-Mo-V alloy steel, and removing the coating after the medium-carbon Cr-Ni-Mo-V alloy steel is taken out of the furnace.

[0015] Further, the medium-carbon Cr-Ni-Mo-V alloy steel is one or more of 30CrMnMoRE, 30CrNi3MoV, 32CrNi3MoVE, and G4335V; and / or the coating thickness is 850-1100 μm; and / or the heat preservation temperature is 700-1300 °C, preferably 1200-1300 °C; and / or the heat preservation time is 8-20 h, preferably 15-20 h.

[0016] Applying the technical solution of the present invention, through the mutual cooperation among the specific components of the three glasses, the thermal stability and chemical stability of each glass at different temperature levels can be effectively improved, thereby enhancing the mechanical properties of the glass. When the coating of the present invention is used for the protection of medium-carbon Cr-Ni-Mo-V alloy steel, the three glasses respectively play the roles of metal protection and air isolation at different temperature segments, which can not only improve the high-temperature durability of the coating, but also effectively control the liquefaction amount of the coating, having the beneficial effect of preventing oxidation of the alloy steel throughout the process, thereby significantly reducing the generation of oxide scale on the medium-carbon Cr-Ni-Mo-V alloy steel at high temperature. In addition, the specific high-temperature resistant filler of the present invention has high stability at high temperature, good wettability with metals, and low expansion coefficient, which not only improves the high-temperature protection performance of the coating, but also enables the protective coating formed by the coating to be easily peeled off during the descaling process, avoiding the influence of coating residue on subsequent processing, thereby improving the surface quality of the alloy steel, effectively reducing the waste of equipment materials while reducing the equipment cost.

[0017] The protective coating of the present invention has excellent thermal stability and chemical stability, can withstand high temperatures for a long time, forms dense film layers at different temperatures in different stages of the alloy heating process, tightly combines with the alloy steel billet, isolates oxygen, effectively prevents the alloy steel from oxidizing during the heating process, and significantly reduces the generation of metal oxide scale. Moreover, the coating of the present invention can further meet the requirements of long-term anti-oxidation at high temperatures and can also continuously protect the medium-carbon Cr-Ni-Mo-V alloy steel during the heat preservation treatment process. Moreover, the coating of the present invention is easy to apply and can form a uniform and dense protective coating. In addition, the coating of the present invention is easy to peel off and can be easily removed during the water descaling process. Compared with traditional coatings, the coating of the present invention can be used as a special high-temperature long-term anti-oxidation coating for medium-carbon Cr-Ni-Mo-V alloy steel, ensuring the surface quality after hot extrusion of the billet. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The schematic drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0019] Figure 1 shows the surface photo of the 30CrMnMoRE alloy after high-temperature treatment and being taken out of the furnace in Example 1 of the present invention;

[0020] Figure 2 shows the surface photo of the 30CrMnMoRE alloy after water descaling in Example 1 of the present invention;

[0021] Figure 3 shows the surface photo of the tube billet after extrusion of the 30CrMnMoRE alloy in Example 1 of the present invention;

[0022] Figure 4 The surface photograph of the 30CrNi3MoV alloy tube blank after extrusion and before machining in Example 2 of the present invention is shown;

[0023] Figure 5 Surface photographs of the finished pipe after machining of 30CrNi3MoV alloy in Example 2 of the present invention are shown;

[0024] Figure 6 The surface photograph of the 30CrMnMoRE alloy after bare firing in Comparative Example 1 is shown;

[0025] Figure 7 The surface photograph of the 30CrMnMoRE alloy in Comparative Example 2 after water descaling and cooling is shown;

[0026] Figure 8 A surface photograph of the 30CrMnMoRE alloy in Comparative Example 9 after water descaling and cooling is shown;

[0027] Figure 9 A surface photograph of the 30CrMnMoRE alloy in Comparative Example 10 after water descaling and cooling is shown;

[0028] Figure 10 Surface photographs of the 30CrMnMoRE alloy in Comparative Example 11 after water descaling and cooling are shown. DETAILED DESCRIPTION

[0029] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0030] As described in the background art of the present invention, in the prior art, there are problems that medium-carbon Cr-Ni-Mo-V alloy steel is prone to form a relatively thick oxide scale during high-temperature long-term heating, the high-temperature protection effect of the coating is poor, and it is not easy to peel off. To solve the above problems, in a typical embodiment of the present invention, a coating for protecting medium-carbon Cr-Ni-Mo-V alloy steel is provided. By weight, the coating includes 15-20 parts of a first glass, 5-10 parts of a second glass, 5-10 parts of a third glass, 36-59 parts of a high-temperature resistant filler, and 5-10 parts of a solvent; wherein, by weight, the first glass includes 35-40 parts of SiO2, 25-30 parts of Al2O3, 3-5 parts of MgO, 3-8 parts of B2O3, 3-8 parts of Na2O, and 3-8 parts of K2O; the second glass includes 30-35 parts of SiO2, 25-30 parts of Al2O3, 2-4 parts of MgO, 5-10 parts of B2O3, 4-8 parts of Na2O, and 4-8 parts of K2O; the third glass includes 25-30 parts of SiO2, 20-25 parts of Al2O3, 2-4 parts of MgO, 10-15 parts of B2O3, 10-15 parts of Na2O, and 10-15 parts of K2O; the high-temperature resistant filler includes SiC, Si3N4, SiO2, ZrO2, MgO, feldspar, and kaolin.

[0031] In the coating composition for protecting medium-carbon Cr-Ni-Mo-V alloy steel of the present invention, it includes a first glass, a second glass, a third glass, a high-temperature resistant filler, and a solvent. During the processing of medium-carbon Cr-Ni-Mo-V alloy steel, the first glass, the second glass, and the third glass can be respectively melted into a dense film at the temperatures in different stages of the high-temperature treatment of the metal to cover the surface of the alloy, isolating the corrosion of gases such as oxygen to the alloy metal and avoiding obvious oxidation of the alloy billet. The present invention combines three glasses, which can not only improve the high-temperature persistence of the coating, but also facilitate the control of the liquefaction amount of the coating, effectively improving the thermal stability, chemical stability, and mechanical properties of the glass, and realizing the whole-process protection of medium-carbon Cr-Ni-Mo-V alloy steel in the heating and heat preservation treatment process. Mixing the high-temperature resistant filler with the base glass composed of the first glass, the second glass, and the third glass can improve the stability of the coating at high temperatures for a long time, enable the coating to remain dense for a long time, and enhance the long-term high-temperature protection effect on medium-carbon Cr-Ni-Mo-V alloy steel.

[0032] Among them, the first glass, the second glass, and the third glass all contain SiO2, Al2O3, MgO, B2O3, Na2O, and K2O. Among them, the addition of SiO2 is conducive to the formation of an irregular network structure in the glass; as a network intermediate, Al2O3 can effectively improve the compactness of the irregular network structure of the glass, thereby improving the high-temperature resistance of the glass; MgO has the characteristic of high melting point and can effectively improve the high-temperature stability of the glass; SiO2, Al2O3, and MgO can react synergistically at high temperatures to produce a crystallization effect, converting the glass into a crystallized glass with cordierite as the main crystal phase. The crystals are sealed on the alloy surface, which can effectively isolate the air. In addition, as network modifiers, B2O3, Na2O, and K2O can change the existence state of network ions in the glass, thereby improving the high-temperature viscosity of the glass and effectively enhancing the plasticity of the glass; B2O3, Na2O, and K2O cooperate with each other synergistically to effectively adjust the softening point of the glass, so that the glass forms a liquid phase at a certain temperature, covering the alloy surface and isolating the alloy from the air, effectively avoiding the oxidation of the alloy surface.

[0033] The inventors unexpectedly found that when the component contents of SiO2, Al2O3, MgO, B2O3, Na2O, and K2O in the third glass are controlled within the range of the present invention, the softening point of the glass is low. Before the alloy blank reaches the low-temperature processing temperature, i.e., the oxidation temperature (such as 750 ± 50 °C), the third glass melts into a dense film on the alloy surface, thereby isolating the corrosion of gases such as oxygen to the alloy metal and effectively avoiding obvious oxidation of the alloy blank at a relatively low heating temperature. When the component contents of SiO2, Al2O3, MgO, B2O3, Na2O, and K2O in the second glass are controlled within the range of the present invention, within the medium-temperature processing temperature range (such as 900 ± 20 °C), the second glass can effectively melt on the alloy surface to protect the alloy material within the medium-temperature heating range. When the component contents of SiO2, Al2O3, MgO, B2O3, Na2O, and K2O in the first glass are controlled within the range of the present invention, within the high-temperature processing temperature range (such as 1000 - 1300 °C), the first glass can produce a crystallization effect and transform into a crystallized glass with cordierite as the main crystal phase. The cordierite crystals can be permanently sealed on the alloy surface, isolating the air and effectively avoiding the oxidation of the alloy blank at high temperatures for a long time. In summary, the protective coating of the present invention can achieve all-round multi-range protection during the entire hot processing process of medium-carbon Cr-Ni-Mo-V alloy steel, significantly reducing the generation of scale on medium-carbon Cr-Ni-Mo-V alloy steel and improving the processing quality of alloy steel.

[0034] In addition, the high-temperature resistant filler of the present invention includes SiC, Si3N4, SiO2, ZrO2, MgO, feldspar and kaolin. Among them, SiC is beneficial to improving the high-temperature stability of the coating; Si3N4 is beneficial to improving the wettability of the coating to the metal blank; at high temperatures, SiC and Si3N4 will react with oxygen to form oxides, which can further enhance the high-temperature protection performance of the coating; SiO2 has a low expansion coefficient, which is beneficial to reducing the expansion coefficient of the coating, so that the coating can easily fall off during the water descaling process after the blank is taken out of the furnace; ZrO2, MgO and feldspar are beneficial to improving the high-temperature stability of the coating; the addition of kaolin is beneficial to improving the suspension performance and easy coating property of the coating. In summary, the high-temperature resistant filler of the present invention can improve the high-temperature protection performance of the coating while facilitating the coating to form a uniform protective coating, and the protective coating is easy to fall off during the descaling process, effectively avoiding the influence of coating residue on subsequent processing. In addition, the addition of the solvent is beneficial to improving the solubility and viscosity among various components of the coating.

[0035] The protective coating of the present invention has excellent thermal stability and chemical stability, can withstand high temperatures for a long time, forms dense film layers at different stages of the alloy heating process at different temperatures, closely combines with the alloy steel blank, isolates oxygen, effectively prevents the oxidation of alloy steel during the heating process, and significantly reduces the generation of metal oxide scales. Moreover, the coating of the present invention can further meet the anti-oxidation requirements for long-term high-temperature insulation (such as maintaining heat at a heating temperature of 1200-1300°C for 8-17 hours), and can also continuously protect medium-carbon Cr-Ni-Mo-V alloy steel during the heat preservation treatment process. Moreover, the coating of the present invention is easy to apply and can form a uniform and dense protective coating. In addition, the coating of the present invention is easy to fall off and can be easily removed during the water descaling process. Compared with traditional coatings, the coating of the present invention can be used as a special high-temperature long-term anti-oxidation coating for medium-carbon Cr-Ni-Mo-V alloy steel, ensuring the surface quality of the blank after hot extrusion.

[0036] In a preferred embodiment, by weight, the coating includes 17-20 parts of the first glass, 5-8 parts of the second glass, 6-9 parts of the third glass, 45-59 parts of the high-temperature resistant filler and 8-10 parts of the solvent. Under the above conditions, the chemical stability and high-temperature resistance persistence of the coating are better, which is more conducive to the dense distribution of the coating on the alloy surface, further reducing the generation of metal oxide scales, and is easier to fall off, with a better protective effect on the alloy blank. For the purpose of further improving the chemical stability of the high-temperature resistant filler and being more conducive to improving the wettability between the high-temperature resistant filler and each metal of medium-carbon Cr-Ni-Mo-V alloy steel, in a preferred embodiment, by weight, the high-temperature resistant filler includes 6-10 parts of SiC, 3-5 parts of Si3N4, 8-12 parts of SiO2, 7-12 parts of ZrO2, 3-5 parts of MgO, 6-10 parts of feldspar and 3-5 parts of kaolin.

[0037] To further improve the chemical stability and high-temperature resistance of the first glass, second glass, third glass, and high-temperature resistant filler, thereby further enhancing the high-temperature durable protection performance and denseness of the coating. In a preferred embodiment, by weight parts, the first glass comprises 37-40 parts of SiO2, 25-28 parts of Al2O3, 3-4 parts of MgO, 4-6 parts of B2O3, 4-6 parts of Na2O, and 3-5 parts of K2O; and / or the second glass comprises 31-34 parts of SiO2, 26-28 parts of Al2O3, 2-3 parts of MgO, 5-7 parts of B2O3, 5-7 parts of Na2O, and 5-7 parts of K2O; and / or the third glass comprises 25-27 parts of SiO2, 21-23 parts of Al2O3, 3-4 parts of MgO, 11-13 parts of B2O3, 10-13 parts of Na2O, and 12-15 parts of K2O; and / or the high-temperature resistant filler comprises 7-9 parts of SiC, 4-5 parts of Si3N4, 9-11 parts of SiO2, 9-11 parts of ZrO2, 3-4 parts of MgO, 6-8 parts of feldspar, and 3-4 parts of kaolin.

[0038] For the purpose of further enhancing the high-temperature stability of the coating, thus being more conducive to the coating being durably sealed on the alloy surface at high temperature and more effectively avoiding alloy oxidation. In a preferred embodiment, the total weight parts of SiO2, Al2O3, and MgO in the coating ≥ 210 parts, preferably 185-190 parts. Correspondingly, the total weight parts of B2O3, Na2O, and K2O in the coating ≥ 80 parts, preferably 59-69 parts. Under the above conditions, the high-temperature viscosity of the coating can be further improved, being more conducive to the coating being sealed on the alloy surface and further isolating the alloy from contact with air. To further make the coating evenly distributed on the alloy surface and be more conducive to improving the protection effect of the coating, it is preferred that the particle size of the solid components of the coating is controlled at 300-600 mesh.

[0039] For the purpose of further improving the bonding effect of the coating and making it more conducive to the firm adhesion of the coating on the surface of the blank, in a preferred embodiment, the coating further includes 35 to 40 parts by weight of a binder. To further improve the uniform dispersion of the coating and make it more conducive to the uniform distribution of the coating on the surface of the blank, in a preferred embodiment, the coating further includes 1 to 2 parts by weight of a dispersant. Common types of binders, dispersants and solvents of the coating can be used. To further improve the bonding effect and dispersion effect of the coating, in a preferred embodiment, the binder is silica sol and / or alumina sol. Preferably, the dispersant is one or more of anionic dispersants, cationic dispersants and non-ionic dispersants; more preferably, the anionic dispersant is one or more of carboxylates and sulfate esters; the cationic dispersant is one or more of amine salts and quaternary amine salts; the non-ionic dispersant is one or more of polyvinyl alcohol and polyvinyl ether; and / or the solvent is water. Under the above conditions, the binder, dispersant and solvent cooperate with the first glass, the second glass, the third glass and the high-temperature resistant filler to form a coating with more uniform distribution of each component and more suitable viscosity, which is more conducive to coating the coating and subsequent peeling, thereby further improving the protection effect on medium-carbon Cr-Ni-Mo-V alloy steel and further reducing the impact on the surface quality of the subsequent extruded tube blank.

[0040] In another typical embodiment of the present invention, a method for preparing the above-mentioned coating for protecting medium-carbon Cr-Ni-Mo-V alloy steel of the present invention is also provided, including the following steps: mixing the first glass, the second glass, the third glass, the high-temperature resistant filler and the solvent according to the component ratio to obtain a coating for protecting medium-carbon Cr-Ni-Mo-V alloy steel. Preferably, the components further include an adhesive and a dispersant.

[0041] The components of the coating of the present invention are weighed according to the component ratio and then mixed to obtain a protective coating for medium-carbon Cr-Ni-Mo-V alloy steel. The preparation process of the coating of the present invention is simple, large-scale production can be realized, the raw materials are simple and easy to obtain, and the prepared coating is uniform, has high repeatability and is inexpensive.

[0042] For the purpose of further improving the uniform dispersion of each component of the coating, making each component in the coating more uniformly distributed on the surface of the alloy, and thus being more conducive to improving the protection effect of the coating on the alloy, in a preferred embodiment, the mixing method is ball milling and / or stirring; when the mixing is ball milling, the ball milling speed is 50 to 100 rpm, the ball milling time is 10 to 30 h, and the ball-to-material ratio is (2 to 8):1; when the mixing is stirring, the stirring speed is 1200 to 2000 rpm, the stirring time is 0.5 to 2 h, and the ball-to-material ratio is (2 to 7):1.

[0043] For similar reasons, further, in a preferred embodiment, when the mixing is carried out by ball milling, the ball milling speed is 60 - 80 rpm, the ball milling time is 20 - 30 h, and the ball-to-material ratio is (3 - 7):1; when the mixing is carried out by stirring, the stirring speed is 1200 - 1500 rpm, the stirring time is 0.5 - 1 h, and the ball-to-material ratio is (5 - 7):1.

[0044] In yet another typical embodiment of the present invention, a method for protecting medium-carbon Cr-Ni-Mo-V alloy steel is also provided. The above-mentioned coating is applied to the surface of the medium-carbon Cr-Ni-Mo-V alloy steel, and it is heated and kept warm in the furnace together with the medium-carbon Cr-Ni-Mo-V alloy steel. After the medium-carbon Cr-Ni-Mo-V alloy steel is taken out of the furnace, the coating is removed. The protection method of the present invention is simple and highly operable, and it provides high-temperature protection for medium-carbon Cr-Ni-Mo-V alloy steel, filling the blank in the prior art that there is no protective coating for medium-carbon Cr-Ni-Mo-V alloy steel. Moreover, it effectively reduces the waste of special materials and further saves the manufacturing cost of weapons and equipment.

[0045] In a preferred embodiment, the medium-carbon Cr-Ni-Mo-V alloy steel is one or more of 30CrMnMoRE, 30CrNi3MoV, 32CrNi3MoVE, and G4335V. Since the surface of the alloy steel is coated with the above-mentioned coating of the present invention, it can more effectively inhibit the oxidation and other conditions of the medium-carbon Cr-Ni-Mo-V alloy steel (alloy with high carbon and molybdenum content) during the high-temperature treatment process, and it is more convenient for the coating and scale to fall off, thus specifically solving the problems of serious high-temperature oxidation and difficult removal of scale of the medium-carbon Cr-Ni-Mo-V alloy steel.

[0046] To further improve the protection effect of the coating on the blank, more effectively avoid alloy oxidation, and at the same time be more conducive to the removal of the coating from the alloy surface to facilitate the smooth progress of the subsequent hot extrusion process, thereby further improving the surface quality of the extruded metal blank, in a preferred embodiment, the coating thickness is 850 - 1100 μm. Correspondingly, the temperature for heat preservation is 700 - 1300 °C, preferably 1200 - 1300 °C; and / or the time for heat preservation is 8 - 20 h, preferably 15 - 20 h. Under the above conditions, the coating has a better protection effect on the medium-carbon Cr-Ni-Mo-V alloy steel, and at the same time can match the processing processes of most medium-carbon Cr-Ni-Mo-V alloy steels, with better universality.

[0047] Typically but not limitedly, by weight, the first glass in the coating is 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts, or a range value composed of any two of these numerical values;

[0048] Typical but non-limiting, by weight, the second glass in the coating is 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts or a range value composed of any two of these values;

[0049] Typical but non-limiting, by weight, the third glass in the coating is 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts or a range value composed of any two of these values;

[0050] Typical but non-limiting, by weight, the high-temperature resistant filler in the coating is 36 parts, 37 parts, 38 parts, 39 parts, 40 parts, 41 parts, 42 parts, 43 parts, 44 parts, 45 parts, 46 parts, 47 parts, 48 parts, 49 parts, 50 parts, 51 parts, 52 parts, 53 parts, 54 parts, 55 parts, 56 parts, 57 parts, 58 parts, 59 parts or a range value composed of any two of these values;

[0051] Typical but non-limiting, by weight, the solvent in the coating is 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts or a range value composed of any two of these values;

[0052] Typical but non-limiting, by weight, the binder in the coating is 35 parts, 36 parts, 37 parts, 38 parts, 39 parts, 40 parts or a range value composed of any two of these values;

[0053] Typical but non-limiting, by weight, the dispersant in the coating is 1 part, 2 parts or a range value composed of any two of these values;

[0054] Typical but non-limiting, the ball milling speed is 50 rpm, 60 rpm, 70 rpm, 80 rpm, 90 rpm, 100 rpm or a range value composed of any two of these values, the ball milling time is 10 h, 15 h, 20 h, 25 h, 30 h or a range value composed of any two of these values, and the ball-to-material ratio is 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1 or a range value composed of any two of these values;

[0055] Typical but non-limiting, the stirring speed is 1200 rpm, 1300 rpm, 1400 rpm, 1500 rpm, 1600 rpm, 1700 rpm, 1800 rpm, 1900 rpm, 2000 rpm or a range value composed of any two of these values, the stirring time is 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1 h, 1.2 h, 1.4 h, 1.6 h, 1.8 h, 2 h or a range value composed of any two of these values, and the ball-to-material ratio is 2:1, 3:1, 4:1, 5:1, 6:1, 7:1 or a range value composed of any two of these values;

[0056] Typically but not limitedly, the coating thickness of the coating is 850μm, 900μm, 950μm, 1000μm, 1050μm, 1100μm or a range value composed of any two of these values;

[0057] Typically but not limitedly, the heat preservation temperature is 700℃, 800℃, 900℃, 1000℃, 1100℃, 1200℃, 1300℃ or a range value composed of any two of these values, and the heat preservation time is 8h, 10h, 12h, 14h, 15h, 16h, 18h, 20h or a range value composed of any two of these values.

[0058] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0059] Example 1

[0060] A protective coating was prepared as required, and its raw material ratio (by weight) is: 18 parts of the first glass, 7 parts of the second glass, 7 parts of the third glass, 47 parts of the high-temperature resistant filler, 37 parts of the binder, 1 part of the dispersant, and 8 parts of the solvent. See Table 1 for details. Among them, the components of the first glass, the second glass, and the third glass are shown in Table 2, and the components of the high-temperature resistant filler are shown in Table 3. The binder is silica sol, the dispersant is polyvinyl alcohol, and the solvent is water. The particle size of the above solid components is controlled within 300 - 400 mesh.

[0061] Weigh the above components proportionally, put the first glass, the second glass, the third glass, the high-temperature resistant filler, the binder, the dispersant, and the solvent into a ball mill tank, and ball mill with a horizontal tank ball mill. The ball-to-material ratio is 5:1, the ball mill rotation speed is 70 revolutions per minute, and the ball mill time is 25h. After ball milling, pour out the coating and brush it on the surface of 30CrMnMoRE alloy. The coating thickness is 1000μm. After the coating is dried, put it into the furnace together with the alloy. After the furnace temperature rises to 1250℃, keep it warm at 1250℃ for 17h. After the alloy steel is taken out of the furnace, use high-pressure water descaling to remove the coating. Then, perform extrusion forming on the alloy steel to prepare a tube blank.

[0062] After verification, after the alloy is taken out of the furnace, no obvious oxidation is seen on its surface, the thickness of the formed scale is only 0.2mm, the coating has good protective performance. During the water descaling process, the coating is easy to peel off, most of the scale can be removed, and the scale removal rate reaches 95%. There is no folding or delamination caused by the scale in the tube blank prepared by the subsequent extrusion forming process. The surface photo of the 30CrMnMoRE alloy after high-temperature treatment and taken out of the furnace is as Figure 1 shown, the surface photo of the 30CrMnMoRE alloy after water descaling is as Figure 2 shown, and the surface photo of the tube blank of the 30CrMnMoRE alloy after extrusion is as Figure 3as shown

[0063] Example 2

[0064] The coating composition and the content of each component are the same as those in Example 1.

[0065] Put the first glass, the second glass, the third glass, the high-temperature resistant filler, the binder, the dispersant, and the solvent into a ball mill tank, and ball mill with a horizontal tank mill. The ball-to-material ratio is 5:1, the ball mill rotation speed is 70 revolutions per minute, and the ball mill time is 25 hours. After ball milling, pour out the coating and brush it on the surface of 30CrNi3MoV alloy. The coating thickness is 1000 μm. After the coating is dried, put it into the furnace together with the alloy. After the temperature in the furnace rises from 500 °C to 1260 °C, keep it at 1260 °C for 14 hours. After the alloy steel is taken out of the furnace, use high-pressure water descaling to remove the coating. Then, extrude the alloy steel to prepare a tube blank.

[0066] After verification, after the alloy is taken out of the furnace, no obvious oxidation is seen on its surface. The thickness of the formed scale is only 0.15 mm. The coating has good protective performance. During the high-pressure water descaling process, the coating is easy to peel off, most of the scale can be removed, and the scale removal rate reaches 96%. The tube blank prepared by the subsequent extrusion forming process does not show folding or delamination caused by scale. The surface photos of the tube blank of 30CrNi3MoV alloy after extrusion and before machining are as Figure 4 shown, and the surface photos of the finished pipe made of 30CrNi3MoV alloy after machining are as Figure 5 shown

[0067] Example 3

[0068] The composition of the coating and the content of each component are the same as those in Example 1.

[0069] Put the first glass, the second glass, the third glass, the high-temperature resistant filler, the binder, the dispersant, and the solvent into a ball mill tank, and ball mill with a horizontal tank mill. The ball-to-material ratio is 5:1, the ball mill rotation speed is 70 revolutions per minute, and the ball mill time is 25 hours. After ball milling, pour out the coating and brush it on the surface of 32CrNi3MoVE alloy. The coating thickness is 1000 μm. After the coating is dried, put it into the furnace together with the alloy. After the temperature in the furnace rises from 500 °C to 1260 °C, keep it at 1260 °C for 14 hours. After the alloy steel is taken out of the furnace, use high-pressure water descaling to remove the coating. Then, extrude the alloy steel to prepare a tube blank.

[0070] After verification, after the alloy is taken out of the furnace, no obvious oxidation is seen on its surface. The thickness of the formed scale is only 0.16 mm. The coating has good protective performance. During the high-pressure water descaling process, the coating is easy to peel off, most of the scale can be removed, and the scale removal rate reaches 96%. The tube blank prepared by the subsequent extrusion forming process does not show folding or delamination caused by scale.

[0071] Example 4

[0072] The components of the coating and the content of each component are the same as those in Example 1.

[0073] Put the first glass, the second glass, the third glass, the high-temperature resistant filler, the binder, the dispersant, and the solvent into a ball mill tank, and ball mill with a horizontal tank mill. The ball-to-material ratio is 5:1, the ball mill rotation speed is 70 revolutions per minute, and the ball milling time is 25 hours. After ball milling, pour out the coating and brush it on the surface of the G4335V alloy. The coating thickness is 1000 μm. After the coating is dried, put it into the furnace together with the alloy. After the temperature in the furnace rises from 500 °C to 1260 °C, keep it at 1260 °C for 12 hours. After the alloy steel is taken out of the furnace, use high-pressure water descaling to remove the coating. Then, perform extrusion forming on the alloy steel to prepare a tube blank.

[0074] After verification, after the alloy is taken out of the furnace, no obvious oxidation is seen on its surface. The thickness of the formed scale is only 0.17 mm. The coating has good protective performance. During the water descaling process, the coating is easy to peel off, most of the scale can be removed, and the scale removal rate reaches 96%. There is no folding or delamination caused by the scale in the tube blank prepared by the subsequent extrusion forming process.

[0075] Examples 5 to 8

[0076] The differences between Examples 5 to 8 and Example 1 are only that the coating components are different, as shown in Table 1 for details.

[0077] After verification, after the alloy is taken out of the furnace, no obvious oxidation is seen on its surface. The thickness of the formed scale is 0.35 mm. The coating has good protective performance. During the water descaling process, the coating is easy to peel off, most of the scale can be removed, and the scale removal rate is 90%.

[0078] Table 1

[0079]

[0080]

[0081] Examples 9 to 14

[0082] The differences between Examples 9 to 14 and Example 1 are only that the components of the first glass, the second glass, and the third glass are different, as shown in Table 2 for details.

[0083] After verification, after the alloy is taken out of the furnace, no obvious oxidation is seen on its surface. The thickness of the formed scale is 0.32 mm. The coating has good protective performance. During the water descaling process, the coating is easy to peel off, most of the scale can be removed, and the scale removal rate is 91%.

[0084] Table 2

[0085]

[0086] Examples 15 to 18

[0087] It is only different from Example 1 in that the composition of the high-temperature resistant filler is different, as shown in Table 3 for details.

[0088] It has been verified that after the alloy is taken out of the furnace, no obvious oxidation is seen on its surface, the thickness of the formed scale is 0.29 mm, the coating has good protective performance, during the water descaling process, the coating is easy to peel off, most of the scale can be removed, and the scale removal rate is 89%.

[0089] Table 3

[0090]

[0091] Example 19

[0092] It is only different from Example 1 in that the ratio of the protective coating (by weight) is: 18 parts of the first glass, 7 parts of the second glass, 7 parts of the third glass, 22 parts of the high-temperature resistant filler, 37 parts of the binder, 1 part of the dispersant and 8 parts of the solvent. Among them, the compositions of the first glass, the second glass, the third glass and the high-temperature resistant filler are the same as those in Example 1, the binder is aluminum sol, the dispersant is amine salt, and the solvent is water. The particle size of the above solid components is controlled at 400 - 500 mesh.

[0093] It has been verified that after the alloy is taken out of the furnace, no obvious oxidation is seen on its surface, the thickness of the formed scale is only 0.28 mm, the coating has good protective performance, during the water descaling process, the coating is easy to peel off, most of the scale can be removed, and the scale removal rate reaches 87%.

[0094] Example 20

[0095] It is only different from Example 1 in that the ratio of the protective coating (by weight) is: 18 parts of the first glass, 7 parts of the second glass, 7 parts of the third glass, 22 parts of the high-temperature resistant filler, 37 parts of the binder, 1 part of the dispersant and 8 parts of the solvent. Among them, the compositions of the first glass, the second glass, the third glass and the high-temperature resistant filler are the same as those in Example 1, the binder is silica sol, the dispersant is sulfate ester salt, and the solvent is water. The particle size of the above solid components is controlled at 500 - 600 mesh.

[0096] It has been verified that after the alloy is taken out of the furnace, no obvious oxidation is seen on its surface, the thickness of the formed scale is only 0.27 mm, the coating has good protective performance, during the water descaling process, the coating is easy to peel off, most of the scale can be removed, and the scale removal rate reaches 87%.

[0097] Example 21

[0098] The difference from Example 1 is only that the protective coating composition does not contain a binder and a dispersant. The particle size of the above solid components is controlled within 300 - 400 mesh.

[0099] It has been verified that after the alloy is taken out of the furnace, no obvious oxidation is seen on its surface, the thickness of the formed scale is only 0.39 mm, the coating has good protective performance, during the water descaling process, the coating is easily peeled off, most of the scale can be removed, and the scale removal rate reaches 80%.

[0100] Example 22

[0101] The difference from Example 1 is that the above components are weighed proportionally, the first glass, the second glass, the third glass, the high-temperature resistant filler, the binder, the dispersant, and the solvent are put into a ball mill tank, and ball milled with a horizontal tank ball mill, the ball-to-material ratio is 3:1, the ball mill rotation speed is 80 revolutions / min, and the ball milling time is 20 h. After ball milling, the coating is poured out and brushed on the surface of the 30CrMnMoRE alloy, the coating thickness is 1100 μm, after the coating is dried, it is put into the furnace together with the alloy, after the furnace temperature rises to 1300 °C, it is kept warm at 1300 °C for 15 h, after the alloy steel is taken out of the furnace, the coating is removed by high-pressure water descaling. Then, the alloy steel is extruded to prepare a tube blank.

[0102] It has been verified that after the alloy is taken out of the furnace, no obvious oxidation is seen on its surface, the thickness of the formed scale is only 0.25 mm, the coating has good protective performance, during the water descaling process, the coating is easily peeled off, most of the scale can be removed, and the scale removal rate reaches 85%.

[0103] Example 23

[0104] The difference from Example 1 is that the above components are weighed proportionally, the first glass, the second glass, the third glass, the high-temperature resistant filler, the binder, the dispersant, and the solvent are put into a ball mill tank, and ball milled with a horizontal tank ball mill, the ball-to-material ratio is 7:1, the ball mill rotation speed is 60 revolutions / min, and the ball milling time is 30 h. After ball milling, the coating is poured out and brushed on the surface of the 30CrMnMoRE alloy, the coating thickness is 850 μm, after the coating is dried, it is put into the furnace together with the alloy, after the furnace temperature rises to 1200 °C, it is kept warm at 1200 °C for 15 h, after the alloy steel is taken out of the furnace, the coating is removed by high-pressure water descaling. Then, the alloy steel is extruded to prepare a tube blank.

[0105] It has been verified that after the alloy is taken out of the furnace, no obvious oxidation is seen on its surface, the thickness of the formed scale is only 0.27 mm, the coating has good protective performance, during the water descaling process, the coating is easily peeled off, most of the scale can be removed, and the scale removal rate reaches 87%.

[0106] Example 24

[0107] The difference from Example 1 is that the above-mentioned components are weighed proportionally, and the first glass, the second glass, the third glass, the high-temperature resistant filler, the binder, the dispersant, and the solvent are put into a ball milling tank and ball milled with a horizontal tank ball mill. The ball-to-material ratio is 2:1, the ball milling speed is 100 revolutions per minute, and the ball milling time is 10 hours. After ball milling, the coating is poured out and brushed on the surface of the 30CrMnMoRE alloy. The coating thickness is 850 μm. After the coating is dried, it is put into the furnace together with the alloy. After the temperature in the furnace rises to 1200 °C, it is kept warm at 1200 °C for 15 hours. After the alloy steel is taken out of the furnace, the coating is removed by high-pressure water descaling. Then, the alloy steel is extruded to prepare a tube blank.

[0108] It is verified that after the alloy is taken out of the furnace, no obvious oxidation is seen on its surface, and the thickness of the formed scale is only 0.23 mm. The coating has good protective performance. During the high-pressure water descaling process, the coating is easy to peel off, most of the scale can be removed, and the scale removal rate reaches 89%.

[0109] Example 25

[0110] The difference from Example 1 is that the above-mentioned components are weighed proportionally, and the first glass, the second glass, the third glass, the high-temperature resistant filler, the binder, the dispersant, and the solvent are put into a ball milling tank and ball milled with a horizontal tank ball mill. The ball-to-material ratio is 8:1, the ball milling speed is 50 revolutions per minute, and the ball milling time is 30 hours. After ball milling, the coating is poured out and brushed on the surface of the 30CrMnMoRE alloy. The coating thickness is 1100 μm. After the coating is dried, it is put into the furnace together with the alloy. After the temperature in the furnace rises to 1300 °C, it is kept warm at 1300 °C for 15 hours. After the alloy steel is taken out of the furnace, the coating is removed by high-pressure water descaling. Then, the alloy steel is extruded to prepare a tube blank.

[0111] It is verified that after the alloy is taken out of the furnace, no obvious oxidation is seen on its surface, and the thickness of the formed scale is only 0.24 mm. The coating has good protective performance. During the high-pressure water descaling process, the coating is easy to peel off, most of the scale can be removed, and the scale removal rate reaches 89%.

[0112] Example 26

[0113] The difference from Example 1 is that the above-mentioned components are weighed proportionally, and the first glass, the second glass, the third glass, the high-temperature resistant filler, the binder, the dispersant, and the solvent are put into a high-speed mixer for stirring. The ball-to-material ratio is 7:1, the stirring speed is 1200 revolutions per minute, and the stirring time is 1 hour. After stirring, the coating is poured out and brushed on the surface of the 30CrMnMoRE alloy. The coating thickness is 1100 μm. After the coating is dried, it is put into the furnace together with the alloy. After the temperature in the furnace rises to 1200 °C, it is kept warm at 1200 °C for 15 hours. After the alloy steel is taken out of the furnace, the coating is removed by high-pressure water descaling. Then, the alloy steel is extruded to prepare a tube blank.

[0114] After verification, no obvious oxidation was seen on the surface of the alloy after it was taken out of the furnace. The thickness of the formed scale was only 0.26 mm, and the coating had good protective performance. During the water descaling process, the coating was easy to peel off, most of the scale could be removed, and the scale removal rate reached 86%.

[0115] Example 27

[0116] The difference from Example 1 was that each of the above components was weighed in proportion. The first glass, the second glass, the third glass, the high-temperature resistant filler, the binder, the dispersant, and the solvent were put into a high-speed mixer for stirring. The ball-to-material ratio was 5:1, the stirring speed was 1500 r / min, and the stirring time was 0.5 h. After stirring, the coating was poured out and brush-coated on the surface of the 30CrMnMoRE alloy. The coating thickness was 850 μm. After the coating was dried, it was put into the furnace together with the alloy. After the furnace temperature rose to 700 °C, it was held at 700 °C for 8 h. After the alloy steel was taken out of the furnace, the coating was removed by high-pressure water descaling. Then, the alloy steel was extruded into shape to prepare a tube blank.

[0117] After verification, no obvious oxidation was seen on the surface of the alloy after it was taken out of the furnace. The thickness of the formed scale was only 0.24 mm, and the coating had good protective performance. During the water descaling process, the coating was easy to peel off, most of the scale could be removed, and the scale removal rate reached 85%.

[0118] Example 28

[0119] The difference from Example 1 was that each of the above components was weighed in proportion. The first glass, the second glass, the third glass, the high-temperature resistant filler, the binder, the dispersant, and the solvent were put into a high-speed mixer for stirring. The ball-to-material ratio was 2:1, the stirring speed was 2000 r / min, and the stirring time was 0.5 h. After stirring, the coating was poured out and brush-coated on the surface of the 30CrMnMoRE alloy. The coating thickness was 850 μm. After the coating was dried, it was put into the furnace together with the alloy. After the furnace temperature rose to 700 °C, it was held at 700 °C for 8 h. After the alloy steel was taken out of the furnace, the coating was removed by high-pressure water descaling. Then, the alloy steel was extruded into shape to prepare a tube blank.

[0120] After verification, no obvious oxidation was seen on the surface of the alloy after it was taken out of the furnace. The thickness of the formed scale was only 0.24 mm, and the coating had good protective performance. During the water descaling process, the coating was easy to peel off, most of the scale could be removed, and the scale removal rate reached 87%.

[0121] Example 29

[0122] The difference from Example 1 is that each of the above components is weighed proportionally, and the first glass, the second glass, the third glass, the high-temperature resistant filler, the binder, the dispersant, and the solvent are put into a high-speed mixer for stirring. The ball-to-material ratio is 7:1, the stirring speed is 1200 revolutions per minute, and the stirring time is 2 hours. After stirring, the coating is poured out and brushed on the surface of the 30CrMnMoRE alloy. The coating thickness is 850 μm. After the coating is dried, it is put into the furnace together with the alloy. After the temperature in the furnace rises to 700 °C, it is kept warm at 700 °C for 8 hours. After the alloy steel is taken out of the furnace, the coating is removed by high-pressure water descaling. Then, the alloy steel is extruded to prepare a tube blank.

[0123] It is verified that after the alloy is taken out of the furnace, there is no obvious oxidation on its surface, and the thickness of the formed scale is only 0.26 mm. The coating has good protective performance. During the water descaling process, the coating is easy to peel off, most of the scale can be removed, and the scale removal rate reaches 89%.

[0124] Comparative Example 1

[0125] The surface of the 30CrMnMoRE alloy was not coated with a coating and was directly put into the furnace. After the temperature in the furnace rose to 1250 °C, it was kept warm at 1250 °C for 17 hours. After the alloy steel was taken out of the furnace, high-pressure water descaling was used.

[0126] It is verified that the surface of the alloy without coating is severely oxidized, forming multiple layers of scale. The average thickness of the scale is 4.5 mm. After water dephosphorization treatment, the scale is difficult to peel off, and the removal rate is only 20%. The state photo of the alloy after bare burning is as Figure 6 shown.

[0127] Comparative Example 2

[0128] The difference between Comparative Example 2 and Example 1 is that the coating composition does not contain the second glass and the third glass. The surface photo of the 30CrMnMoRE alloy with a coating thickness of 400 μm and a heat preservation time of 4 hours after water descaling and cooling is as Figure 7 shown.

[0129] It is verified that most of the surface of the alloy is oxidized, and the average thickness of the formed scale is 3.2 mm. After water dephosphorization treatment, the scale is difficult to peel off, and the removal rate is only 30%. It can be seen that a single glass is difficult to achieve a long-term protection effect. If the designed viscosity is too small, it burns out severely at high temperatures and cannot provide long-term protection; if the designed viscosity is too large, it melts slowly at low temperatures and the film sealing is slow, resulting in oxidation at an early stage.

[0130] Comparative Example 3

[0131] The difference between Comparative Example 3 and Example 1 is that the coating composition does not contain the first glass and the second glass.

[0132] It has been verified that most of the alloy surface is oxidized, and the average thickness of the oxide scale formed is 2.7 mm. After water descaling treatment, the oxide scale is difficult to peel off, and the removal rate is only 35%.

[0133] Comparative Example 4

[0134] The difference between Comparative Example 4 and Example 1 is that the coating composition does not contain the first glass and the third glass.

[0135] It has been verified that most of the alloy surface is oxidized, and the average thickness of the oxide scale formed is 2.3 mm. After water descaling treatment, the oxide scale is difficult to peel off, and the removal rate is only 37%.

[0136] Comparative Example 5

[0137] The difference between Comparative Example 5 and Example 1 is that the coating composition does not contain the second glass and the third glass.

[0138] It has been verified that most of the alloy surface is oxidized, and the average thickness of the oxide scale formed is 1.9 mm. After water descaling treatment, the oxide scale is difficult to peel off, and the removal rate is only 40%.

[0139] Comparative Example 6

[0140] The difference between Comparative Example 6 and Example 1 is that the coating composition does not contain the first glass.

[0141] It has been verified that most of the alloy surface is oxidized, and the average thickness of the oxide scale formed is 1.4 mm. After water descaling treatment, the oxide scale is difficult to peel off, and the removal rate is only 50%.

[0142] Comparative Example 7

[0143] The difference between Comparative Example 7 and Example 1 is that the coating composition does not contain the second glass.

[0144] It has been verified that most of the alloy surface is oxidized, and the average thickness of the oxide scale formed is 1.6 mm. After water descaling treatment, the oxide scale is difficult to peel off, and the removal rate is only 45%.

[0145] Comparative Example 8

[0146] The difference between Comparative Example 8 and Example 1 is that the coating composition does not contain the third glass.

[0147] It has been verified that most of the alloy surface is oxidized, and the average thickness of the oxide scale formed is 1.8 mm. After water descaling treatment, the oxide scale is difficult to peel off, and the removal rate is only 42%.

[0148] Comparative Example 9

[0149] The difference between Comparative Example 9 and Example 1 lies in the coating thickness of the paint and the heat preservation duration. The surface photos of the 30CrMnMoRE alloy after descaling with water and cooling are as Figure 8 shown. Among them, Figure 8 in 8a, the coating thickness is 200 μm and the heat preservation time is 5 h; Figure 8 in 8b, the coating thickness is 200 μm and the heat preservation time is 8 h.

[0150] It is verified that when the coating thickness of the paint is 200 μm and the heat preservation duration is 5 h, as Figure 8 shown in a, no obvious oxidation is seen on the surface of the alloy steel. When the heat preservation duration is extended to 8 h, the oxidation layer on the surface of the alloy steel is obvious, the average thickness of the formed scale is 22.5 mm, and the coating is not easy to peel off. As Figure 8 shown in b, it shows that when the paint thickness is too thin, the long-time high-temperature protection effect on the alloy is poor.

[0151] Comparative Example 10

[0152] The difference between Comparative Example 10 and Example 1 lies in the coating thickness of the paint and the heat preservation duration. The surface photos of the 30CrMnMoRE alloy after descaling with water and cooling are as Figure 9 shown. Among them, Figure 9 in 9a, the coating thickness is 400 μm and the heat preservation time is 5 h; Figure 9 in 9b, the coating thickness is 400 μm and the heat preservation time is 8 h.

[0153] It is verified that when the coating thickness of the paint is 400 μm and the heat preservation duration is 5 h, as Figure 9 shown in a, no obvious oxidation is seen on the surface of the alloy steel. The coating is easy to peel off. When the heat preservation duration is extended to 8 h, the oxidation layer on the surface of the alloy steel is obvious, the average thickness of the formed scale is 0.4 mm, and the coating is easy to peel off. As Figure 9 shown in b, it can be seen that when the paint thickness is too thin, the long-time high-temperature protection effect on the alloy is poor.

[0154] Comparative Example 11

[0155] The difference between Comparative Example 11 and Example 1 lies in the coating thickness of the paint. The surface photos of the 30CrMnMoRE alloy after descaling with water and cooling are as Figure 10 shown.

[0156] It is verified that when the coating thickness of the paint is 800 μm, as Figure 10 shown, the oxidation layer on the surface of the alloy steel is obvious, the average thickness of the formed scale is 0.12 mm, and the coating is easy to peel off. It can be seen that when the paint thickness is too thin, the protection effect on the alloy is poor.

[0157] As can be seen from the above, compared with the comparative examples, when the coatings of the embodiments of the present invention are used for high-temperature protection of the alloy, after the alloy is taken out of the furnace, no obvious oxidation is seen on its surface, the formed oxide scale is thin, the coating has good protection performance, during the water descaling process, the coating is easy to peel off, and the oxide scale removal rate is high, effectively avoiding the folding or delamination of the tube blank caused by the oxide scale in the subsequent extrusion forming process, thereby improving the surface quality of the tube blank after the alloy steel is extruded. Generally speaking, the protective coating of the present invention has excellent thermal stability and chemical stability, can withstand high temperatures for a long time, effectively prevents the oxidation of alloy steel during the heating process, significantly reduces the generation of metal oxide scale. At the same time, it can further meet the anti-oxidation requirements of maintaining heat at a heating temperature of 1200-1300 °C for 8-17 hours, and can also continuously protect medium-carbon Cr-Ni-Mo-V alloy steel during the heat preservation treatment process. Moreover, the coating of the present invention is easy to apply, can form a uniform and dense protective coating, is easy to fall off, and can be easily removed during the water descaling process. Compared with traditional coatings, the coating of the present invention can be used as a special high-temperature long-term anti-oxidation coating for medium-carbon Cr-Ni-Mo-V alloy steel, ensuring the surface quality of the billet after hot extrusion.

[0158] In addition, it can be seen that when the component ratios and process parameters are all within the preferred ranges of the present invention, the protective coating has better thermal stability, chemical stability and high-temperature durability, the prepared protective coating is more uniform, has higher repeatability and lower cost, and has better protection performance when used to protect medium-carbon Cr-Ni-Mo-V alloy steel, and the coating and oxide scale are easier to peel off.

[0159] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A coating for the protection of medium-carbon Cr-Ni-Mo-V alloy steel, characterized in that, By weight, the coating comprises 15 - 20 parts of a first glass, 5 - 10 parts of a second glass, 5 - 10 parts of a third glass, 36 - 59 parts of a high-temperature resistant filler, and 5 - 10 parts of a solvent; wherein, by weight, the first glass comprises 37 - 40 parts of SiO2, 25 - 28 parts of Al2O3, 3 - 4 parts of MgO, 4 - 6 parts of B2O3, 4 - 6 parts of Na2O, and 3 - 5 parts of K2O; the second glass comprises 31 - 34 parts of SiO2, 26 - 28 parts of Al2O3, 2 - 3 parts of MgO, 5 - 7 parts of B2O3, 5 - 7 parts of Na2O, and 5 - 7 parts of K2O; the third glass comprises 25 - 27 parts of SiO2, 21 - 23 parts of Al2O3, 3 - 4 parts of MgO, 11 - 13 parts of B2O3, 10 - 13 parts of Na2O, and 12 - 15 parts of K2O; the high-temperature resistant filler comprises 6 - 10 parts of SiC, 3 - 5 parts of Si3N4, 8 - 12 parts of SiO2, 7 - 12 parts of ZrO2, 3 - 5 parts of MgO, 6 - 10 parts of feldspar, and 3 - 5 parts of kaolin; the medium carbon Cr-Ni-Mo-V alloy steel is 30CrMnMoRE, 30CrNi3MoV, 32CrNi3MoVE or G4335V.

2. The coating according to claim 1, wherein By weight, the coating comprises 17 - 20 parts of the first glass, 5 - 8 parts of the second glass, 6 - 9 parts of the third glass, 45 - 59 parts of the high-temperature resistant filler, and 8 - 10 parts of the solvent.

3. The coating according to claim 1, wherein The total weight parts of SiO2, Al2O3 and MgO in the coating ≥ 210 parts; and / or the total weight parts of B2O3, Na2O and K2O in the coating ≥ 80 parts.

4. The coating according to claim 1, wherein by weight, the coating further comprises 35 - 40 parts of a binder; the binder is silica sol and / or alumina sol; and / or by weight, the coating further comprises 1 - 2 parts of a dispersant; the dispersant is one or more of an anionic dispersant, a cationic dispersant, and a non-ionic dispersant; and / or the solvent is water.

5. The preparation method of the coating for protecting medium-carbon Cr-Ni-Mo-V alloy steel according to any one of claims 1 to 4, characterized in that, Comprising the following steps: Mix the first glass, the second glass, the third glass, the high-temperature resistant filler and the solvent according to the component ratio to obtain the coating for protecting the medium carbon Cr-Ni-Mo-V alloy steel.

6. The preparation method according to claim 5, wherein the mixing method is ball milling and / or stirring; when the mixing is ball milling, the ball milling speed is 50 - 100 rpm, the ball milling time is 10 - 30 h, and the ball-to-material ratio is (2 - 8):1; when the mixing is stirring, the stirring speed is 1200 - 2000 rpm, the stirring time is 0.5 - 2 h, and the ball-to-material ratio is (2 - 7):

1.

7. The preparation method according to claim 5, wherein when the mixing is ball milling, the ball milling speed is 60 - 80 rpm, the ball milling time is 20 - 30 h, and the ball-to-material ratio is (3 - 7):1; When the mixing is stirring, the stirring speed is 1200 - 1500 rpm, the stirring time is 0.5 - 1 h, and the ball-to-material ratio is (5 - 7):

1.

8. A method for protecting medium-carbon Cr-Ni-Mo-V alloy steel, characterized in that the coating for protecting medium-carbon Cr-Ni-Mo-V alloy steel according to any one of claims 1 to 4 is coated on the surface of the medium-carbon Cr-Ni-Mo-V alloy steel, and is heated and kept warm in the furnace together with the medium-carbon Cr-Ni-Mo-V alloy steel, and after the medium-carbon Cr-Ni-Mo-V alloy steel is taken out of the furnace, the coating is removed.

9. The protection method according to claim 8, characterized in that the coating thickness is 850 - 1100 μm; and / or the temperature for heat preservation is 1200 - 1300 °C; and / or the heat preservation time is 8 - 20 h.

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