An oxidation-resistant high-speed steel roll and a method for manufacturing the same

Abstract

This invention discloses an anti-oxidation high-speed steel roll and its preparation method, relating to the field of high-quality stainless steel processing technology. The method first pre-treats the high-speed steel roll substrate with sandblasting and ultrasonic cleaning; then, a mixed diffusion agent of alumina, aluminum powder, chromium powder, ammonium chloride, and sodium fluoride is used to embed the roll, followed by heating and heat preservation co-diffusion, pickling, quenching, and tempering to obtain an aluminum-chromium co-diffusion diffusion layer on the surface; next, SiO2 sol and Al2O3 sol are prepared separately, mixed in a certain proportion, and polyvinylpyrrolidone, γ-aminopropyltriethoxysilane, and boric acid are added to form a composite sol; this sol is coated onto the roll surface using the dip-coating method, repeated multiple times, and then heat-treated and sintered to obtain the finished product. This invention forms a metallurgically bonded aluminum-chromium enriched diffusion layer and a dense SiO2-Al2O3 composite ceramic coating on the surface of the high-speed steel roll. These two layers achieve close synergistic protection through chemical bonding and interface defect filling, significantly improving the roll's anti-oxidation performance and service life under high-temperature operating conditions.

Description

Technical Field

[0001] This invention relates to the field of high-quality stainless steel processing technology, specifically to an antioxidant high-speed steel roll and its preparation method. Background Technology

[0002] High-speed steel rolls are widely used in hot strip mills due to their excellent red hardness, wear resistance, and high-temperature strength. However, under hot rolling conditions, the roll surface is exposed to a harsh environment of alternating high temperatures (700–1100℃) and water vapor, which easily leads to the formation of loose, porous iron oxide scale. This uneven growth and repeated peeling of the scale not only accelerates the wear of the roll matrix but also indents into the surface of the rolled material, forming defects and severely affecting the surface quality of the strip steel and the service life of the rolls. Current technologies for improving the oxidation resistance of high-speed steel rolls mainly focus on optimizing the matrix alloy composition, such as adjusting the proportions of alloying elements like Cr, V, W, and Mo to enhance the inherent oxidation resistance of the matrix. However, this method is limited by the influence of alloying elements on the overall mechanical properties of the matrix, making it difficult to significantly improve oxidation resistance without sacrificing hardness and toughness. In addition, there are also technologies using single-coating protection, but single-layer coatings are prone to cracking and peeling under thermal cycling due to mismatched coefficients of thermal expansion, making the protective effect unsustainable. Summary of the Invention

[0003] The purpose of this invention is to provide an antioxidant high-speed steel roll and its preparation method to solve the technical problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing an antioxidant high-speed steel roll includes the following steps: 1) Select high-speed steel rolls as the substrate, use brown corundum sand to sandblast their surface, immerse them in a cleaning solution prepared by mixing acetone and anhydrous ethanol for ultrasonic cleaning, take them out and blow them dry with nitrogen to obtain pretreated high-speed steel rolls. 2) Mix alumina powder, aluminum powder, chromium powder, ammonium chloride and sodium fluoride and ball mill them. After ball milling, sieve the mixture to obtain penetrant powder. 3) Place the pretreated high-speed steel roll in the diffusion chamber, fill and cover it layer by layer with the diffusion agent powder, seal the diffusion chamber with water glass, and then perform heating and heat preservation co-diffusion treatment; after cooling in the furnace, take out the roll to remove the residual powder on the surface, immerse the roll in citric acid aqueous solution to clean the surface, and after washing and drying, perform high temperature quenching and multiple tempering heat treatments on the roll in sequence to obtain a roll with an aluminum-chromium co-diffusion diffusion layer on the surface. 4) Add tetraethyl orthosilicate to anhydrous ethanol and stir to mix. Add deionized water and concentrated hydrochloric acid dropwise and continue stirring to obtain a clear SiO2 sol. 5) Dissolve aluminum isopropoxide in anhydrous ethanol, slowly add deionized water mixed with concentrated nitric acid, and continue stirring to obtain Al2O3 sol. 6) Mix the SiO2 sol and Al2O3 sol and stir, then add polyvinylpyrrolidone, γ-aminopropyltriethoxysilane and boric acid in sequence, and stir until completely dispersed and dissolved to obtain SiO2-Al2O3 composite sol; 7) After cleaning and drying the rolls processed in step 3), immerse them at a uniform speed into the SiO2-Al2O3 composite sol for dip-coating. After being pulled out, allow them to stand and age to form a dry gel film. Repeat the dip-coating and aging process multiple times. 8) Heat-treat the coated and aged rolls from step 7) to remove solvents and organic matter from the film and to produce densification sintering. After cooling, the antioxidant high-speed steel rolls are obtained.

[0005] In the technical solution of this invention, the oxidation resistance of high-speed steel rolls is improved synergistically from the following aspects: (1) An aluminum-chromium enriched diffusion layer is constructed on the surface of the high-speed steel roll and is metallurgically bonded to the substrate. During subsequent high-temperature service, the aluminum and chromium elements in this diffusion layer can selectively migrate to the surface preferentially over iron elements and combine with oxygen in the environment, forming a dense mixed oxide film mainly composed of α-Al2O3 and Cr2O3 on the outermost surface of the roll. This film has fine grains and a dense structure with an extremely low oxygen ion diffusion coefficient, which can effectively block the continuous penetration of external oxygen atoms and water vapor molecules into the substrate, fundamentally inhibiting the excessive growth of loose iron oxides. At the same time, since the diffusion layer and the high-speed steel substrate are connected by an atomic diffusion gradient transition, the bonding strength between the two is much higher than the physical adhesion of traditional external coatings, which significantly reduces the risk of coating peeling caused by repeated thermal shock and mechanical wear during hot rolling, ensuring the long-term service stability of the anti-oxidation protective layer. (2) The SiO2-Al2O3 composite ceramic coating prepared by the sol-gel method serves as the outermost protective barrier. Its mechanism of action lies in the formation of a continuous, pore-free, dense ceramic film on the roll surface using an amorphous and partially crystallized silicon-aluminum oxide network structure. This ceramic film has extremely high chemical inertness and thermal stability. It does not undergo harmful chemical changes with water vapor or oxidizing atmospheres that come into contact with the roll surface at high temperatures, thus providing additional physical isolation protection for the underlying aluminum-chromium co-diffusion layer. In addition, the introduction of the SiO2 component effectively modulates the relatively high elastic modulus of the pure Al2O3 coating, giving the composite coating a certain degree of flexibility and stress buffering capacity. When the roll experiences rapid temperature fluctuations during hot rolling, the coating can adapt to the changes in thermal stress through its own micro-elastic deformation, without generating penetrating network cracks, thereby maintaining the integrity of the coating structure and its continuous protection of the underlying layer.

[0006] Preferably, in step 1), the sandblasting treatment uses No. 46 brown corundum sand and is carried out under a compressed air pressure of 0.5 MPa; the volume ratio of acetone to anhydrous ethanol in the cleaning solution is 1:1, and the ultrasonic cleaning frequency is 40 kHz, the power is 500 W, and the time is 25 min.

[0007] Preferably, in step 2), the raw materials of the penetrant powder include, by mass parts: 40-45 parts alumina powder, 15-18 parts aluminum powder, 8-10 parts chromium powder, 3-5 parts ammonium chloride, and 1-2 parts sodium fluoride.

[0008] Preferably, in step 3), the conditions for the heating and heat preservation co-infiltration treatment are: heating to 940-950℃ at a rate of 6℃ / min and holding for 7-9 hours.

[0009] Preferably, in step 3), the concentration of the citric acid aqueous solution is 8-10% (w / v), and the soaking and washing time is 6-10 min.

[0010] Preferably, in step 4), the volume ratio of tetraethyl orthosilicate to anhydrous ethanol is (18-22):70.

[0011] Preferably, in step 5), the ratio of aluminum isopropoxide to anhydrous ethanol is (10-15) g: 90 mL.

[0012] Preferably, in step 6), the volume ratio of SiO2 sol to Al2O3 sol is 3:(1-2).

[0013] Preferably, in step 6), the mass ratio of γ-aminopropyltriethoxysilane to boric acid is 1:(0.6-0.8).

[0014] After high-temperature co-diffusion and subsequent pickling, the aluminum-chromium co-diffusion layer forms a dense passivated oxide film mainly composed of Al2O3 and Cr2O3 on its surface. This film has very few chemically active sites and low surface energy, resulting in insufficient wetting and spreading ability of the subsequent sol on it. The gel film and the surface of the co-diffusion layer are mainly bonded by weak physical adsorption forces. During the subsequent high-temperature sintering process, the thermal stress easily produces interfacial debonding areas and microscopic pinhole defects, allowing the high-temperature oxidizing atmosphere to penetrate the coating along these weak channels and reach the surface of the co-diffusion layer, greatly weakening the synergistic protective effect of the two. To address this technical problem, this invention synergistically introduces γ-aminopropyltriethoxysilane and boric acid into a composite sol. One end of the γ-aminopropyltriethoxysilane molecule contains a hydrolyzable ethoxy group, which hydrolyzes in the sol system to generate a silanol group. This silanol group can then undergo a condensation reaction with the hydroxyl groups on the oxide film of the co-permeation layer to form a stable metal-oxygen-silicon covalent bond, firmly bridging the coating and the co-permeation layer through chemical bonds. Simultaneously, the amino group at the other end of the γ-aminopropyltriethoxysilane molecule can form hydrogen bonds and coordination interactions with the hydroxyl groups on the surface of the sol particles, achieving a molecular bridge chemical bonding connection between the coating and the substrate. This fundamentally upgrades the interfacial bonding from weak physical adsorption to strong chemical bonding. The molten B2O3 oxide formed by the dehydration of boric acid during sol gelation and subsequent heat treatment has excellent flow and filling capabilities, allowing it to penetrate into the microscopic voids and pinhole defects between the coating and the co-permeation layer. After cooling and solidification, it forms a dense borooxy glass phase filling layer, effectively sealing the penetration channels of oxidizing atmospheres. The synergistic effect of the two substances addresses both the interfacial chemical bonding force and the repair of interfacial physical defects, ensuring a tight and defect-free interfacial bond between the composite ceramic coating and the aluminum-chromium co-diffusion layer. This allows the two treatments to fully exert their synergistic protective effect, thereby enhancing the oxidation resistance of the high-speed steel roll to its optimal state.

[0015] An antioxidant high-speed steel roll is prepared by the method described above.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. A dense mixed oxide film mainly composed of α-Al2O3 and Cr2O3 is formed on the surface, which has an extremely low oxygen ion diffusion coefficient and can effectively block the penetration of high-temperature oxidizing atmosphere into the substrate; at the same time, the diffusion layer is metallurgically bonded to the substrate, with strong anti-stripping ability, ensuring long-term service stability.

[0017] 2. The outermost SiO2-Al2O3 composite ceramic film has high chemical inertness and is dense and non-porous, which can isolate water vapor and oxidizing atmosphere; its flexibility can buffer the thermal stress during hot rolling, prevent coating cracking, and maintain structural integrity.

[0018] 3. By forming chemical bonds between the coating and the co-diffusion layer through γ-aminopropyltriethoxysilane, and combining the B2O3 molten phase generated by boric acid to fill the micro-defects at the interface, a tight and gapless interface bond is formed, giving full play to the synergistic effect of the double-layer protection. Attached Figure Description

[0019] Figure 1 This is a low-magnification SEM image of the surface of the antioxidant high-speed steel roll prepared in Example 4 of the present invention.

[0020] Figure 2 This is a medium-magnification SEM image of the surface of the antioxidant high-speed steel roll prepared in Example 4 of the present invention.

[0021] Figure 3 This is a high-magnification SEM image of the surface of the antioxidant high-speed steel roll prepared in Example 4 of the present invention.

[0022] Figure 4 The image shows the XRD pattern of the antioxidant high-speed steel roll prepared in Example 4 of this invention. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1 A method for preparing an antioxidant high-speed steel roll includes the following steps: Step 1: Select W6Mo5Cr4V2 high-speed steel roll as the substrate, and perform sandblasting treatment with No. 46 brown corundum sand under 0.5MPa compressed air pressure to achieve a surface roughness Ra of 2.0μm; immerse the roll in a cleaning solution prepared by mixing equal volumes of 500mL acetone and 500mL anhydrous ethanol, and ultrasonically clean it for 25min at 40kHz and 500W. After removal, it is purged and dried with high-purity nitrogen to obtain the pretreated high-speed steel roll.

[0025] Step 2: Weigh 44g of alumina powder (200 mesh), 17g of aluminum powder (300 mesh), 9.5g of chromium powder (300 mesh), 4.5g of ammonium chloride and 1.8g of sodium fluoride according to the mass fractions, add them to a stainless steel ball mill jar, ball mill at 350r / min for 2.5h, and then pass through a 100-mesh sieve to obtain a uniformly dispersed penetrant powder.

[0026] Step 3: Place the pretreated roll vertically in the center of the stainless steel diffusion chamber, and fill it with diffusion agent powder layer by layer until the thickness in each direction is not less than 35mm. After sealing the diffusion chamber with water glass, place it in a box-type resistance furnace and heat it to 945℃ at a rate of 6℃ / min and hold it for 8 hours for aluminum-chromium co-diffusion treatment. After cooling to room temperature in the furnace, take out the roll and blow off the residual powder on the surface with compressed air. Immerse the roll in a 9% (w / v) citric acid aqueous solution at room temperature for 9 minutes. After taking it out, rinse it three times with deionized water and dry it at 80℃ for 2 hours. Then, put the roll into a vacuum heat treatment furnace and heat it to 1200℃ at a rate of 10℃ / min and hold it for 25 minutes. Then, oil quench it and temper it three times at 560℃ (holding it for 2 hours each time and then air cooling it) to obtain a roll with an aluminum-chromium co-diffusion diffusion layer on the surface.

[0027] Step 4: Measure 21 mL of tetraethyl orthosilicate and add it to 70 mL of anhydrous ethanol and stir to mix. Add 12 mL of deionized water dropwise at a rate of 1.5 mL / min, and add 0.8 mL of concentrated hydrochloric acid as a catalyst. Stir the mixture in a 60 °C water bath at 300 r / min for 2.5 h to obtain a clear and transparent SiO2 sol (solution A).

[0028] Step 5: Add 14g of aluminum isopropoxide to 90mL of anhydrous ethanol and stir at 400r / min for 30min in a 70℃ water bath until completely dissolved; separately, add 10mL of deionized water to 0.4mL of concentrated nitric acid and mix well, then slowly add the mixture dropwise to the above solution at a rate of 0.8mL / min. Continue stirring the reaction at 70℃ for 3h to obtain a translucent Al2O3 sol (solution B).

[0029] Step 6: Mix solution A and solution B at a volume ratio of 3:1.8 and stir. Then, add 2% polyvinylpyrrolidone (PVP K30), 1.0% γ-aminopropyltriethoxysilane (KH550), and 0.75% boric acid by mass of the mixture. Stir magnetically at 500 r / min for 1.5 h at room temperature until completely dispersed and dissolved to obtain SiO2-Al2O3 composite sol.

[0030] Step 7: After ultrasonic cleaning of the roller treated in step 3 with anhydrous ethanol for 5 minutes and drying with nitrogen, immerse it in the composite sol at a uniform speed and let it stand for 1.5 minutes. Then, pull it up at a uniform speed of 60 mm / min. After taking it out, age it at 25°C and 50% relative humidity for 24 hours to form a dry gel film. Repeat the immersion, pulling and aging operation 4 times (each time with an interval of 12 hours of aging).

[0031] Step 8: Place the coated and aged roll from Step 7 in a tube furnace and perform gradient heat treatment in an air atmosphere: heat to 200℃ at 5℃ / min and hold for 1h to remove residual solvent; heat to 400℃ at 2℃ / min and hold for 1h to decompose organic matter and dehydrate boric acid into B2O3 solid phase; then heat to 550℃ at 3℃ / min and hold for 3h to promote low-temperature densification sintering by utilizing the molten viscous flow of B2O3; cool to room temperature with the furnace to obtain an anti-oxidation high-speed steel roll with a SiO2-Al2O3 composite ceramic coating on the surface.

[0032] Example 2 A method for preparing an antioxidant high-speed steel roll includes the following steps: Step 1: Select W6Mo5Cr4V2 high-speed steel roll as the substrate, and perform sandblasting treatment with No. 46 brown corundum sand under 0.5MPa compressed air pressure to achieve a surface roughness Ra of 2.0μm; immerse the roll in a cleaning solution prepared by mixing equal volumes of 500mL acetone and 500mL anhydrous ethanol, and ultrasonically clean it for 25min at 40kHz and 500W. After removal, it is purged and dried with high-purity nitrogen to obtain the pretreated high-speed steel roll.

[0033] Step 2: Weigh 42g of alumina powder (200 mesh), 16g of aluminum powder (300 mesh), 8.5g of chromium powder (300 mesh), 3.5g of ammonium chloride and 1.2g of sodium fluoride according to the mass fractions, add them to a stainless steel ball mill jar, ball mill at 350r / min for 2.5h, and then pass through a 100-mesh sieve to obtain a uniformly dispersed penetrant powder.

[0034] Step 3: Place the pretreated roll vertically in the center of the stainless steel diffusion chamber, and fill it with diffusion agent powder layer by layer until the thickness in each direction is not less than 35 mm. After sealing the diffusion chamber with water glass, place it in a box-type resistance furnace and heat it to 945℃ at a rate of 6℃ / min and hold it for 8 hours for aluminum-chromium co-diffusion treatment. After cooling to room temperature in the furnace, take out the roll and blow off the residual powder on the surface with compressed air. Immerse the roll in a 9% (w / v) citric acid aqueous solution at room temperature for 7 minutes. After taking it out, rinse it three times with deionized water and dry it at 80℃ for 2 hours. Then, put the roll into a vacuum heat treatment furnace and heat it to 1200℃ at a rate of 10℃ / min and hold it for 25 minutes. Then, oil quench it and temper it three times at 560℃ (holding it for 2 hours each time and then air cooling it) to obtain a roll with an aluminum-chromium co-diffusion diffusion layer on the surface.

[0035] Step 4: Measure 19 mL of tetraethyl orthosilicate and add it to 70 mL of anhydrous ethanol and stir to mix. Add 12 mL of deionized water dropwise at a rate of 1.5 mL / min, and add 0.8 mL of concentrated hydrochloric acid as a catalyst. Stir the mixture in a 60 °C water bath at 300 r / min for 2.5 h to obtain a clear and transparent SiO2 sol (solution A).

[0036] Step 5: Add 11g of aluminum isopropoxide to 90mL of anhydrous ethanol and stir at 400r / min for 30min in a 70℃ water bath until completely dissolved; separately, add 10mL of deionized water to 0.4mL of concentrated nitric acid and mix well, then slowly add the mixture dropwise to the above solution at a rate of 0.8mL / min. Continue stirring the reaction at 70℃ for 3h to obtain a translucent Al2O3 sol (solution B).

[0037] Step 6: Mix solution A and solution B at a volume ratio of 3:1.2 and stir. Then, add 2% polyvinylpyrrolidone (PVP K30), 1.0% γ-aminopropyltriethoxysilane (KH550), and 0.65% boric acid by mass of the mixture. Stir magnetically at 500 r / min for 1.5 h at room temperature until completely dispersed and dissolved to obtain SiO2-Al2O3 composite sol.

[0038] Step 7: After ultrasonic cleaning of the roller treated in step 3 with anhydrous ethanol for 5 minutes and drying with nitrogen, immerse it in the composite sol at a uniform speed and let it stand for 1.5 minutes. Then, pull it up at a uniform speed of 60 mm / min. After taking it out, age it at 25°C and 50% relative humidity for 24 hours to form a dry gel film. Repeat the immersion, pulling and aging operation 4 times (each time with an interval of 12 hours of aging).

[0039] Step 8: Place the coated and aged roll from Step 7 in a tube furnace and perform gradient heat treatment in an air atmosphere: heat to 200℃ at 5℃ / min and hold for 1h to remove residual solvent; heat to 400℃ at 2℃ / min and hold for 1h to decompose organic matter and dehydrate boric acid into B2O3 solid phase; then heat to 550℃ at 3℃ / min and hold for 3h to promote low-temperature densification sintering by utilizing the molten viscous flow of B2O3; cool to room temperature with the furnace to obtain an anti-oxidation high-speed steel roll with a SiO2-Al2O3 composite ceramic coating on the surface.

[0040] Example 3 A method for preparing an antioxidant high-speed steel roll includes the following steps: Step 1: Select W6Mo5Cr4V2 high-speed steel roll as the substrate, and perform sandblasting treatment with No. 46 brown corundum sand under 0.5MPa compressed air pressure to achieve a surface roughness Ra of 2.0μm; immerse the roll in a cleaning solution prepared by mixing equal volumes of 500mL acetone and 500mL anhydrous ethanol, and ultrasonically clean it for 25min at 40kHz and 500W. After removal, it is purged and dried with high-purity nitrogen to obtain the pretreated high-speed steel roll.

[0041] Step 2: Weigh 43g of alumina powder (200 mesh), 16.5g of aluminum powder (300 mesh), 9g of chromium powder (300 mesh), 4g of ammonium chloride and 1.5g of sodium fluoride according to the mass fractions, add them to a stainless steel ball mill jar, ball mill at 350r / min for 2.5h, and then pass through a 100-mesh sieve to obtain a uniformly dispersed penetrant powder.

[0042] Step 3: Place the pretreated roll vertically in the center of the stainless steel diffusion chamber, and fill it with diffusion agent powder layer by layer until the thickness in each direction is not less than 35mm. After sealing the diffusion chamber with water glass, place it in a box-type resistance furnace and heat it to 945℃ at a rate of 6℃ / min and hold it for 8 hours for aluminum-chromium co-diffusion treatment. After cooling to room temperature in the furnace, take out the roll and blow off the residual powder on the surface with compressed air. Immerse the roll in a 9% (w / v) citric acid aqueous solution at room temperature for 8 minutes. After taking it out, rinse it three times with deionized water and dry it at 80℃ for 2 hours. Then, put the roll into a vacuum heat treatment furnace and heat it to 1200℃ at a rate of 10℃ / min and hold it for 25 minutes. Then, quench it in oil and temper it three times at 560℃ (holding it for 2 hours each time and then air cooling it) to obtain a roll with an aluminum-chromium co-diffusion diffusion layer on the surface.

[0043] Step 4: Measure 20 mL of tetraethyl orthosilicate and add it to 70 mL of anhydrous ethanol and stir to mix. Add 12 mL of deionized water dropwise at a rate of 1.5 mL / min, and add 0.8 mL of concentrated hydrochloric acid as a catalyst. Stir the mixture in a 60 °C water bath at 300 r / min for 2.5 h to obtain a clear and transparent SiO2 sol (solution A).

[0044] Step 5: Add 13g of aluminum isopropoxide to 90mL of anhydrous ethanol and stir at 400r / min for 30min in a 70℃ water bath until completely dissolved; separately, add 10mL of deionized water to 0.4mL of concentrated nitric acid and mix well, then slowly add the mixture dropwise to the above solution at a rate of 0.8mL / min. Continue stirring the reaction at 70℃ for 3h to obtain a translucent Al2O3 sol (solution B).

[0045] Step 6: Mix solution A and solution B at a volume ratio of 3:1.5 and stir. Then add polyvinylpyrrolidone (PVP K30) at 2% of the total mass of the mixture, γ-aminopropyltriethoxysilane (KH550) at 1.0% of the total mass, and boric acid at 0.7% of the total mass. Stir magnetically at 500 r / min for 1.5 h at room temperature until completely dispersed and dissolved to obtain SiO2-Al2O3 composite sol.

[0046] Step 7: After ultrasonic cleaning of the roller treated in step 3 with anhydrous ethanol for 5 minutes and drying with nitrogen, immerse it in the composite sol at a uniform speed and let it stand for 1.5 minutes. Then, pull it up at a uniform speed of 60 mm / min. After taking it out, age it at 25°C and 50% relative humidity for 24 hours to form a dry gel film. Repeat the immersion, pulling and aging operation 4 times (each time with an interval of 12 hours of aging).

[0047] Step 8: Place the coated and aged roll from Step 7 in a tube furnace and perform gradient heat treatment in an air atmosphere: heat to 200℃ at 5℃ / min and hold for 1h to remove residual solvent; heat to 400℃ at 2℃ / min and hold for 1h to decompose organic matter and dehydrate boric acid into B2O3 solid phase; then heat to 550℃ at 3℃ / min and hold for 3h to promote low-temperature densification sintering by utilizing the molten viscous flow of B2O3; cool to room temperature with the furnace to obtain an anti-oxidation high-speed steel roll with a SiO2-Al2O3 composite ceramic coating on the surface.

[0048] Example 4 A method for preparing an antioxidant high-speed steel roll includes the following steps: Step 1: Select W6Mo5Cr4V2 high-speed steel roll as the substrate, and perform sandblasting treatment with No. 46 brown corundum sand under 0.5MPa compressed air pressure to achieve a surface roughness Ra of 2.0μm; immerse the roll in a cleaning solution prepared by mixing equal volumes of 500mL acetone and 500mL anhydrous ethanol, and ultrasonically clean it for 25min at 40kHz and 500W. After removal, it is purged and dried with high-purity nitrogen to obtain the pretreated high-speed steel roll.

[0049] Step 2: Weigh 45g of alumina powder (200 mesh), 18g of aluminum powder (300 mesh), 10g of chromium powder (300 mesh), 5g of ammonium chloride and 2g of sodium fluoride according to the mass fractions, add them to a stainless steel ball mill jar, ball mill at 350r / min for 2.5h, and then pass through a 100-mesh sieve to obtain a uniformly dispersed penetrant powder.

[0050] Step 3: Place the pretreated roll vertically in the center of the stainless steel diffusion chamber, and fill it with diffusion agent powder layer by layer until the thickness in each direction is not less than 35mm. After sealing the diffusion chamber with water glass, place it in a box-type resistance furnace and heat it to 950℃ at a rate of 6℃ / min and hold it for 9h for aluminum-chromium co-diffusion treatment. After cooling to room temperature in the furnace, take out the roll and blow off the residual powder on the surface with compressed air. Immerse the roll in a 10% (w / v) citric acid aqueous solution at room temperature for 10min. After taking it out, rinse it three times with deionized water and dry it at 80℃ for 2h. Then, put the roll into a vacuum heat treatment furnace and heat it to 1200℃ at a rate of 10℃ / min and hold it for 25min. Then, oil quench it and temper it three times at 560℃ (holding it for 2h each time and then air cooling it) to obtain a roll with an aluminum-chromium co-diffusion diffusion layer on the surface.

[0051] Step 4: Measure 22 mL of tetraethyl orthosilicate and add it to 70 mL of anhydrous ethanol and stir to mix. Add 12 mL of deionized water dropwise at a rate of 1.5 mL / min, and add 0.8 mL of concentrated hydrochloric acid as a catalyst. Stir the mixture in a 60 °C water bath at 300 r / min for 2.5 h to obtain a clear and transparent SiO2 sol (solution A).

[0052] Step 5: Add 15g of aluminum isopropoxide to 90mL of anhydrous ethanol and stir at 400r / min for 30min in a 70℃ water bath until completely dissolved; separately, add 10mL of deionized water to 0.4mL of concentrated nitric acid and mix well, then slowly add the mixture dropwise to the above solution at a rate of 0.8mL / min. Continue stirring the reaction at 70℃ for 3h to obtain a translucent Al2O3 sol (solution B).

[0053] Step 6: Mix solution A and solution B at a volume ratio of 3:2 and stir. Then, add 2% polyvinylpyrrolidone (PVP K30), 1.0% γ-aminopropyltriethoxysilane (KH550), and 0.8% boric acid by mass of the mixture. Stir magnetically at 500 r / min for 1.5 h at room temperature until completely dispersed and dissolved to obtain SiO2-Al2O3 composite sol.

[0054] Step 7: After ultrasonic cleaning of the roller treated in step 3 with anhydrous ethanol for 5 minutes and drying with nitrogen, immerse it in the composite sol at a uniform speed and let it stand for 1.5 minutes. Then, pull it up at a uniform speed of 60 mm / min. After taking it out, age it at 25°C and 50% relative humidity for 24 hours to form a dry gel film. Repeat the immersion, pulling and aging operation 4 times (each time with an interval of 12 hours of aging).

[0055] Step 8: Place the coated and aged roll from Step 7 in a tube furnace and perform gradient heat treatment in an air atmosphere: heat to 200℃ at 5℃ / min and hold for 1h to remove residual solvent; heat to 400℃ at 2℃ / min and hold for 1h to decompose organic matter and dehydrate boric acid into B2O3 solid phase; then heat to 550℃ at 3℃ / min and hold for 3h to promote low-temperature densification sintering by utilizing the molten viscous flow of B2O3; cool to room temperature with the furnace to obtain an anti-oxidation high-speed steel roll with a SiO2-Al2O3 composite ceramic coating on the surface.

[0056] Example 5 A method for preparing an antioxidant high-speed steel roll includes the following steps: Step 1: Select W6Mo5Cr4V2 high-speed steel roll as the substrate, and perform sandblasting treatment with No. 46 brown corundum sand under 0.5MPa compressed air pressure to achieve a surface roughness Ra of 2.0μm; immerse the roll in a cleaning solution prepared by mixing equal volumes of 500mL acetone and 500mL anhydrous ethanol, and ultrasonically clean it for 25min at 40kHz and 500W. After removal, it is purged and dried with high-purity nitrogen to obtain the pretreated high-speed steel roll.

[0057] Step 2: Weigh 40g of alumina powder (200 mesh), 15g of aluminum powder (300 mesh), 8g of chromium powder (300 mesh), 3g of ammonium chloride and 1g of sodium fluoride according to the mass fractions, add them to a stainless steel ball mill jar, ball mill at 350r / min for 2.5h, and then pass through a 100-mesh sieve to obtain a uniformly dispersed penetrant powder.

[0058] Step 3: Place the pretreated roll vertically in the center of the stainless steel diffusion chamber, and fill it with diffusion agent powder layer by layer until the thickness in each direction is not less than 35mm. After sealing the diffusion chamber with water glass, place it in a box-type resistance furnace and heat it to 940℃ at a rate of 6℃ / min and hold it for 7h for aluminum-chromium co-diffusion treatment. After cooling to room temperature in the furnace, take out the roll and blow off the residual powder on the surface with compressed air. Immerse the roll in an 8% (w / v) citric acid aqueous solution at room temperature for 6min. After taking it out, rinse it three times with deionized water and dry it at 80℃ for 2h. Then, put the roll into a vacuum heat treatment furnace and heat it to 1200℃ at a rate of 10℃ / min and hold it for 25min. Then, oil quench it and temper it three times at 560℃ (holding it for 2h each time and then air cooling it) to obtain a roll with an aluminum-chromium co-diffusion diffusion layer on the surface.

[0059] Step 4: Measure 18 mL of tetraethyl orthosilicate and add it to 70 mL of anhydrous ethanol and stir to mix. Add 12 mL of deionized water dropwise at a rate of 1.5 mL / min, and add 0.8 mL of concentrated hydrochloric acid as a catalyst. Stir the mixture in a 60 °C water bath at 300 r / min for 2.5 h to obtain a clear and transparent SiO2 sol (solution A).

[0060] Step 5: Add 10g of aluminum isopropoxide to 90mL of anhydrous ethanol and stir at 400r / min for 30min in a 70℃ water bath until completely dissolved; separately, add 10mL of deionized water to 0.4mL of concentrated nitric acid and mix well, then slowly add the mixture dropwise to the above solution at a rate of 0.8mL / min. Continue stirring the reaction at 70℃ for 3h to obtain a translucent Al2O3 sol (solution B).

[0061] Step 6: Mix solution A and solution B at a volume ratio of 3:1 and stir. Then, add 2% polyvinylpyrrolidone (PVP K30), 1.0% γ-aminopropyltriethoxysilane (KH550), and 0.6% boric acid by mass of the mixture. Stir magnetically at 500 r / min for 1.5 h at room temperature until completely dispersed and dissolved to obtain SiO2-Al2O3 composite sol.

[0062] Step 7: After ultrasonic cleaning of the roller treated in step 3 with anhydrous ethanol for 5 minutes and drying with nitrogen, immerse it in the composite sol at a uniform speed and let it stand for 1.5 minutes. Then, pull it up at a uniform speed of 60 mm / min. After taking it out, age it at 25°C and 50% relative humidity for 24 hours to form a dry gel film. Repeat the immersion, pulling and aging operation 4 times (each time with an interval of 12 hours of aging).

[0063] Step 8: Place the coated and aged roll from Step 7 in a tube furnace and perform gradient heat treatment in an air atmosphere: heat to 200℃ at 5℃ / min and hold for 1h to remove residual solvent; heat to 400℃ at 2℃ / min and hold for 1h to decompose organic matter and dehydrate boric acid into B2O3 solid phase; then heat to 550℃ at 3℃ / min and hold for 3h to promote low-temperature densification sintering by utilizing the molten viscous flow of B2O3; cool to room temperature with the furnace to obtain an anti-oxidation high-speed steel roll with a SiO2-Al2O3 composite ceramic coating on the surface.

[0064] Comparative Example 1: The difference from Example 4 is that only aluminum-chromium co-diffusion treatment is performed, and the sol-gel composite ceramic coating preparation process is omitted, that is, steps 4 to 8 are omitted.

[0065] Comparative Example 2: The difference from Example 4 is that the preparation of the infiltrator powder and the aluminum-chromium co-infiltration process in steps 2 and 3 are omitted. The rolls after the pretreatment in step 1 are directly subjected to standardized heat treatment (quenching at 1200℃ + tempering three times at 560℃), and then the sol-gel composite ceramic coating preparation in steps 4 to 8 is carried out directly.

[0066] Comparative Example 3: The difference from Example 4 is that in step 6, when preparing the composite sol, γ-aminopropyltriethoxysilane (KH550) and boric acid are not added, but only polyvinylpyrrolidone (PVP K30) accounting for 2% of the total mass of the mixture is added as a dispersant and stabilizer.

[0067] Comparative Example 4: The difference from Example 4 is that in step 6, when preparing the composite sol, γ-aminopropyltriethoxysilane (KH550) is not added, but only polyvinylpyrrolidone accounting for 2% of the total mass of the mixture and boric acid accounting for 0.8% of the total mass are added.

[0068] Comparative Example 5: The difference from Example 4 is that in step 6, when preparing the composite sol, boric acid is not added, but only polyvinylpyrrolidone accounting for 2% of the total mass of the mixture and γ-aminopropyltriethoxysilane (KH550) accounting for 1.0% of the total mass are added.

[0069] Comparative Example 6: As a blank control group, W6Mo5Cr4V2 high-speed steel rolls from the same batch as in Example 4 were selected and subjected to only standardized heat treatment (quenching at 1200℃ + tempering three times at 560℃) without any surface modification treatment.

[0070] Performance testing: (1) High-temperature isothermal oxidation test: Square samples with dimensions of 10mm×10mm×5mm were cut from the rolls prepared in Examples 1-5 and Comparative Examples 1-6, respectively. After ultrasonic cleaning with anhydrous ethanol for 10min and drying with high-purity nitrogen, the initial mass m0 of each sample was accurately weighed on an analytical balance and recorded. The dimensions of each surface of the sample were accurately measured with vernier calipers and the total exposed surface area S was calculated. All samples were placed in numbered corundum ceramic crucibles and sent into a muffle furnace. The temperature was increased to 1000℃ at a rate of 10℃ / min under static air atmosphere and the timing was started to carry out the isothermal oxidation test. Every 20h, the sample was taken out with the crucible and placed in a desiccator containing silica gel desiccant to cool naturally to room temperature and the mass m was weighed. t Record the results, then immediately return the sample to the muffle furnace for further oxidation, with a cumulative oxidation time of 100 hours; the weight gain from oxidation is Δm / S (unit: mg / cm³). 2 The core evaluation index is Δm / S, with a smaller Δm / S indicating better antioxidant performance. The test results are shown in Table 1.

[0071] (2) Matrix hardness test: Samples were cut from the rolls prepared in Examples 1-5 and Comparative Examples 1-6, respectively. The side surface (matrix cross-section) of the sample was polished with sandpaper until smooth and flat. A Rockwell hardness tester was used, with a 120° diamond cone indenter and a total test force of 1471 N (150 kgf). Five different locations were evenly selected on the matrix cross-section of each sample for testing. The HRC hardness value was read, and the arithmetic mean of the five measurements was taken as the matrix hardness of the sample. The test results are shown in Table 1.

[0072] (3) Coating adhesion test (only for samples with coating): An automatic coating adhesion scratch tester was used, with a 120° diamond conical indenter with a radius of curvature of 200 μm. The scratch length was set to 5 mm, the loading rate to 100 N / min, and the scratch speed to 4 mm / min. The load was linearly increased from 0.5 N to 30 N. The acoustic emission signal during the scratching process was monitored in real time by the acoustic emission sensor equipped with the instrument, and the scratch morphology was observed by optical microscope. The normal load corresponding to the first continuous peeling of the coating or the complete exposure of the substrate was taken as the critical load Lc (unit N). The larger the Lc value, the stronger the adhesion between the coating and the substrate. Each sample was tested 3 times and the average value was taken. The test results are shown in Table 1.

[0073] (4) Thermal shock resistance test (only for coated samples): The sample was placed in a box-type resistance furnace preheated to 800℃ and kept at that temperature for 15 minutes to ensure thorough heating. Then, it was quickly removed and immediately immersed in 25℃ deionized water for rapid cooling to room temperature. After removal, it was dried with compressed air, and the surface condition of the coating was observed and recorded under a stereomicroscope. The above heating-rapid cooling operation was repeated as one thermal shock cycle. The cumulative number of cycles when the coating surface showed continuous through cracks visible to the naked eye or the area of ​​coating peeling exceeded 5% of the total area was taken as the thermal shock resistance life N (cycles). The larger the N, the better the thermal shock resistance of the coating. The test results are shown in Table 1.

[0074] Table 1:

[0075] From the above test results, we can conclude that: The oxidative weight gain of Comparative Example 1 (co-diffusion layer only) was 7.5 mg / cm³. 2 Comparative Example 2 (coating only) had a concentration of 9.2 mg / cm³. 2 All were significantly higher than the 2.3 mg / cm³ in Example 4. 2 The coating adhesion strength (Lc) of Comparative Example 2 was only 8.6 N, and the thermal shock resistance life was only 6 cycles. This indicates that without the aluminum-chromium co-diffusion layer as a transition substrate, the ceramic coating and the high-speed steel substrate are difficult to bond effectively due to the large difference in their coefficients of thermal expansion. In contrast, the coating in Example 4 achieved an Lc of 21.3 N and a thermal shock resistance life of 32 cycles, fully demonstrating the crucial supporting role of the aluminum-chromium co-diffusion layer as an intermediate transition layer in the interfacial bonding and thermal shock resistance performance of the coating.

[0076] The synergistic introduction of γ-aminopropyltriethoxysilane and boric acid significantly enhanced interfacial bonding. The coating Lc of Comparative Example 3 (without KH550 and boric acid) was only 10.2 N, with a thermal shock resistance of 12 cycles and an oxidation weight gain as high as 5.1 mg / cm³. 2This indicates that even with the combined effect of the aluminum-chromium co-diffusion layer and the coating, the synergistic protective effect is significantly reduced due to poor interfacial bonding. The Lc value of Comparative Example 4 (boric acid only) increased to 12.8 N, and that of Comparative Example 5 (KH550 only) further increased to 15.6 N, while the Lc value of Example 4 (both added synergistically) reached the highest value of 21.3 N. This demonstrates that both the chemical bonding force provided by KH550 and the physical filling and repair of B2O3 generated by boric acid are indispensable; only through their synergistic cooperation can the optimal interfacial bonding effect be achieved.

[0077] The matrix hardness of all embodiments and comparative examples remained stable within the range of HRC63.8 to 64.8, with no significant differences between groups. This indicates that the process route adopted in this invention, which involves co-diffusion, standardized quenching and tempering, and finally low-temperature sintering of the coating at 550°C, successfully preserved all the core service performance of the W6Mo5Cr4V2 high-speed steel rolls without sacrificing the hardness of the matrix due to surface modification treatment.

[0078] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the essence and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an antioxidant high-speed steel roll, characterized in that, Includes the following steps: 1) Select high-speed steel rolls as the substrate, use brown corundum sand to sandblast their surface, immerse them in a cleaning solution prepared by mixing acetone and anhydrous ethanol for ultrasonic cleaning, take them out and blow them dry with nitrogen to obtain pretreated high-speed steel rolls. 2) Mix alumina powder, aluminum powder, chromium powder, ammonium chloride and sodium fluoride and ball mill them. After ball milling, sieve the mixture to obtain penetrant powder. 3) Place the pretreated high-speed steel roll in the diffusion chamber, fill and cover it layer by layer with the diffusion agent powder, seal the diffusion chamber with water glass, and then perform heating and heat preservation co-diffusion treatment; after cooling in the furnace, take out the roll to remove the residual powder on the surface, immerse the roll in citric acid aqueous solution to clean the surface, and after washing and drying, perform high temperature quenching and multiple tempering heat treatments on the roll in sequence to obtain a roll with an aluminum-chromium co-diffusion diffusion layer on the surface. 4) Add tetraethyl orthosilicate to anhydrous ethanol and stir to mix. Add deionized water and concentrated hydrochloric acid dropwise and continue stirring to obtain a clear SiO2 sol. 5) Dissolve aluminum isopropoxide in anhydrous ethanol, slowly add deionized water mixed with concentrated nitric acid, and continue stirring to obtain Al2O3 sol. 6) Mix the SiO2 sol and Al2O3 sol and stir, then add polyvinylpyrrolidone, γ-aminopropyltriethoxysilane and boric acid in sequence, and stir until completely dispersed and dissolved to obtain SiO2-Al2O3 composite sol; 7) After cleaning and drying the rolls processed in step 3), immerse them at a uniform speed into the SiO2-Al2O3 composite sol for dip-coating. After being pulled out, allow them to stand and age to form a dry gel film. Repeat the dip-coating and aging process multiple times. 8) Heat-treat the coated and aged rolls from step 7) to remove solvents and organic matter from the film and to produce densification sintering. After cooling, the antioxidant high-speed steel rolls are obtained.

2. The method for preparing an antioxidant high-speed steel roll according to claim 1, characterized in that, In step 1), the sandblasting treatment uses No. 46 brown corundum sand and is carried out under a compressed air pressure of 0.5 MPa; the volume ratio of acetone to anhydrous ethanol in the cleaning solution is 1:1, and the ultrasonic cleaning frequency is 40 kHz, the power is 500 W, and the time is 25 min.

3. The method for preparing an antioxidant high-speed steel roll according to claim 1, characterized in that, In step 2), the raw materials of the penetrant powder include, by mass parts: 40-45 parts alumina powder, 15-18 parts aluminum powder, 8-10 parts chromium powder, 3-5 parts ammonium chloride, and 1-2 parts sodium fluoride.

4. The method for preparing an antioxidant high-speed steel roll according to claim 1, characterized in that, In step 3), the conditions for the heating and heat preservation co-infiltration treatment are: heating to 940-950℃ at a rate of 6℃ / min and holding for 7-9 hours.

5. The method for preparing an antioxidant high-speed steel roll according to claim 1, characterized in that, In step 3), the concentration of the citric acid aqueous solution is 8-10% (w / v), and the soaking and washing time is 6-10 min.

6. The method for preparing an antioxidant high-speed steel roll according to claim 1, characterized in that, In step 4), the volume ratio of tetraethyl orthosilicate to anhydrous ethanol is (18-22):

70.

7. The method for preparing an antioxidant high-speed steel roll according to claim 1, characterized in that, In step 5), the ratio of aluminum isopropoxide to anhydrous ethanol is (10-15) g: 90 mL.

8. The method for preparing an antioxidant high-speed steel roll according to claim 1, characterized in that, In step 6), the volume ratio of SiO2 sol to Al2O3 sol is 3:(1-2).

9. The method for preparing an antioxidant high-speed steel roll according to claim 1, characterized in that, In step 6), the mass ratio of γ-aminopropyltriethoxysilane to boric acid is 1:(0.6-0.8).

10. An antioxidant high-speed steel roll, characterized in that, It is prepared by the method described in any one of claims 1 to 9 above.

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