A composite coating for improving the lifespan of copper plates in crystallizers and its preparation method by plasma spraying.

Abstract

This invention relates to the fields of materials surface engineering and metallurgical equipment technology. Specifically, it relates to a composite coating for improving the lifespan of copper plates in crystallizers and its plasma spraying preparation method. The chemical composition, by mass percentage, includes: 35%-55% chromium, 20%-55% nickel, 5%-10% titanium diboride, 0.1%-0.3% niobium, with the balance being chromium carbide and unavoidable trace impurities. In this invention, titanium diboride and chromium carbide are used as the main hard reinforcing phases, enabling the coating to exhibit excellent wear resistance at both room temperature and high temperature. During the spraying process, a hollow graphite electrode is used, generating a plasma arc. Simultaneously, the ablation products (carbon) provide a carbon source for the formation of chromium carbide. Titanium powder and boron powder undergo an in-situ reaction in the plasma arc to generate titanium diboride. This in-situ synthesis technology results in fine and uniformly distributed hard phase particles, forming a strong interface with the metal binder phase, avoiding the problems of interface contamination and weak bonding caused by externally added hard phases.

Description

Technical Field

[0001] This invention relates to the fields of material surface engineering and metallurgical equipment technology, specifically to a composite coating for improving the lifespan of copper plates in crystallizers and its plasma spraying preparation method. Background Technology

[0002] The continuous casting crystallizer is a core component in the continuous casting of steel. Its inner copper plate is in direct contact with high-temperature molten steel, and the working conditions are extremely harsh. The surface of the copper plate is not only subjected to the thermal shock and thermal corrosion of the high-temperature molten steel, but also to the friction and wear of the solidified billet shell. These factors make the copper plate of the crystallizer prone to problems such as hot cracking, wear, deformation and coating peeling, which ultimately reduces its service life and affects the smooth operation of continuous casting and the quality of the cast billet.

[0003] Currently, the main method to improve the lifespan of crystallizer copper plates is to prepare various protective coatings on their surface, such as electroplated chromium, thermal spraying of nickel-based or cobalt-based alloys, etc. However, although electroplated chromium layers have high hardness and good wear resistance, they have problems such as microcracks, limited adhesion to the substrate, and insufficient thermal shock resistance, and they are prone to softening at high temperatures. Although traditional thermal spray coatings can improve certain performance, their density, bonding strength, and the types and distribution of hard phases in the coating often cannot meet the long-term protection requirements under extreme working conditions, resulting in limited improvement in the "steel overload" of crystallizer copper plates. In view of this, we propose a composite coating for improving the lifespan of crystallizer copper plates and its plasma spraying preparation method. Summary of the Invention

[0004] The purpose of this invention is to provide a composite coating for improving the lifespan of copper plates in crystallizers and its plasma spraying preparation method, in order to solve the problems mentioned in the background art, such as microcracks, insufficient bonding with the substrate, poor thermal shock resistance, low density, and uneven distribution of hard phases, which make it difficult to achieve long-term reliable protection under extreme working conditions, resulting in limited improvement in the "over-steel" of the copper plates in crystallizers.

[0005] This invention provides a composite coating for improving the lifespan of copper plates in crystallizers. The coating is formed on the surface of a copper plate substrate and has a thickness of 0.10-0.25 mm. Its chemical composition by mass percentage includes: 35%-55% chromium, 20%-55% nickel, 5%-10% titanium diboride, 0.1%-0.3% niobium, with the balance being chromium carbide and unavoidable trace impurity elements.

[0006] The coating is a metal-ceramic composite structure containing dispersed titanium diboride and chromium carbide hard phases.

[0007] The coating is formed by the deposition of powder raw materials of nickel, boron, iron, titanium, aluminum, silicon, chromium and niobium after reaction and melting in a plasma arc. The coating contains a titanium diboride hard phase generated by the in-situ reaction of titanium powder and boron, and a chromium carbide hard phase generated by the in-situ reaction of chromium powder and carbon (mainly from the ablation of hollow graphite electrodes). These hard phases are uniformly dispersed in a metal binder phase mainly composed of chromium and nickel, forming a metal-ceramic composite structure.

[0008] Preferably, the unavoidable trace impurity elements are boron, iron, aluminum, and silicon.

[0009] On the other hand, the present invention provides a composite coating for improving the lifespan of a crystallizer copper plate and a method for preparing the same by plasma spraying. The method for preparing the aforementioned composite coating for improving the lifespan of a crystallizer copper plate includes the following steps:

[0010] S1.1 The surface of the copper plate substrate of the crystallizer is degreased, derusted and roughened by sandblasting to obtain a pretreated copper plate;

[0011] S1.2. Chromium powder, nickel powder, boron powder, titanium powder, aluminum powder, silicon powder and niobium powder are placed in a three-dimensional mixer and thoroughly mixed to obtain a mixed powder;

[0012] S1.3. A hollow graphite electrode plasma arc spraying equipment is used, with argon as the working gas and powder feeding gas. The mixed powder is fed into the plasma arc, where it melts and is sprayed onto the pretreated copper plate surface to deposit and form a composite coating.

[0013] S1.4. Perform fine grinding and polishing on the composite coating after spraying.

[0014] The mixed powder is rapidly heated to a molten or semi-molten state in a high-temperature plasma arc (temperatures can reach over 10,000°C). Titanium powder and boron powder react in situ to form titanium diboride, while chromium powder reacts with carbon provided by the graphite electrode to form chromium carbide. The molten particles are accelerated by the argon gas flow and impact the copper plate surface at high speed, spreading, flattening, and rapidly cooling and solidifying, layer by layer to form a dense composite coating.

[0015] Preferably, in step S1.1, the degreasing treatment is performed by ultrasonic cleaning with acetone at a power of 300-600W for 10-30 minutes.

[0016] Rust removal involves soaking the surface in a 5-15% hydrochloric acid solution for 5-10 minutes to remove oxides and rust.

[0017] The sandblasting roughening treatment uses 16-60 mesh brown corundum gravel as the sandblasting medium, the sandblasting air pressure is 0.4-0.8MPa, the sandblasting angle is 70-90°, and the surface roughness Ra after treatment reaches 6-8μm.

[0018] Preferably, in step S1.2, the mass percentage composition of the mixed powder is: 35%-55% chromium powder, 20%-55% nickel powder, the total amount of titanium powder and boron powder corresponds to the formation of 5%-10% titanium diboride, 0.5%-2% aluminum powder, 0.5%-2% silicon powder, and 0.1%-0.3% niobium powder.

[0019] Preferably, in step S1.3, the power of the plasma arc is 20-45kW.

[0020] Preferably, in step S1.3, the spraying distance is 80-150mm and the spray gun moving speed is 300-800mm / s.

[0021] Preferably, in step S1.3, the flow rate of the working gas is 35-45 L / min, and the flow rate of the powder feeding gas is 5-10 L / min.

[0022] Preferably, in step S1.3, the arc current of the plasma spraying is 400-600A and the voltage is 50-70V.

[0023] Preferably, in step S1.4, the fine grinding and polishing step is as follows: the coating is planar ground using a diamond grinding wheel to a depth of 0.005-0.020 mm, so that the coating thickness reaches 0.10-0.25 mm; the surface after fine grinding is coarsely polished and finely polished sequentially using diamond polishing paste with grit sizes of W10-W20 and W1-W5; and the polished copper plate is ultrasonically cleaned with anhydrous ethanol at a power of 300-600W for 5-15 minutes.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] In the composite coating for improving the lifespan of copper plates in crystallizers and its plasma spraying preparation method of the present invention, by precisely designing the coating composition, titanium diboride and chromium carbide are used as the main hard reinforcing phases. Their synergistic effect enables the coating to exhibit excellent wear resistance at both room temperature and high temperature. During the spraying process, hollow graphite electrodes are used, generating a plasma arc while its ablation products (carbon) provide a carbon source for the formation of chromium carbide. Titanium powder and boron powder undergo an in-situ reaction in the plasma arc to generate titanium diboride. This in-situ synthesis technology results in fine and uniformly distributed hard phase particles, forming a strong interface with the metal binder phase, avoiding the interface contamination and weak bonding problems caused by the addition of an external hard phase. The key features of titanium diboride and chromium carbide are their high melting points and ability to maintain sufficient strength and oxidation resistance at high temperatures. When the coating surface is rich in chromium, a dense chromium carbide protective film can be formed, giving the coating excellent corrosion resistance. By introducing elements such as aluminum and silicon as fluxes, the surface tension of the molten pool is reduced, and wettability is improved. At the same time, the solid solution formed by these elements helps to adjust the matching of the thermal expansion coefficients between the coating and the copper substrate, alleviate thermal stress, and thus significantly improve the thermal shock resistance of the coating, preventing cracking and peeling under rapid heating and cooling conditions. The high energy density of the plasma arc causes the powder to melt slightly with the substrate surface, forming a local quasi-metallurgical bond, the bonding strength of which is much higher than that of traditional spraying methods. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0027] This invention provides a composite coating for improving the lifespan of copper plates in crystallizers. The coating is formed on the surface of a copper plate substrate and has a thickness of 0.10-0.25 mm. Its chemical composition by mass percentage includes: 35%-55% chromium, 20%-55% nickel, 5%-10% titanium diboride, 0.1%-0.3% niobium, with the balance being chromium carbide and unavoidable trace impurity elements.

[0028] The coating is a metal-ceramic composite structure containing dispersed titanium diboride and chromium carbide hard phases.

[0029] Chromium powder (CAS No.: 7440-47-3, purity ≥99.8%), nickel powder (CAS No.: 7440-02-0, purity ≥99.9%), and silicon powder (CAS No.: 69012-64-2, purity ≥99%) were all purchased from Anhui Kerun Nanotechnology Co., Ltd.

[0030] Titanium powder (CAS No.: 7440-32-6, titanium powder purity ≥99.5%) was purchased from Nanjing Chemical Reagent Co., Ltd.

[0031] Boron powder (CAS No.: 7440-42-8, purity ≥95%) was purchased from Sichuan Juchun Materials Technology Co., Ltd.

[0032] Niobium powder (CAS No.: 7440-03-1, ≥99.8%) was purchased from Yumu (Ningbo) New Materials Co., Ltd.

[0033] All powders have a particle size range of 15-45 μm and a particle size distribution D50 of 30 μm.

[0034] Example 1: A composite coating for improving the lifespan of copper plates in crystallizers and its preparation method by plasma spraying, comprising the following steps:

[0035] S1.1 Select a copper plate from a continuous casting crystallizer and perform degreasing, rust removal, and sandblasting roughening treatment on its surface to obtain a pretreated copper plate;

[0036] Degreasing treatment: Use acetone for ultrasonic cleaning at 400W for 20 minutes;

[0037] Rust removal treatment: Soak in 10% dilute hydrochloric acid for 10 minutes to remove surface oxides and rust;

[0038] Sandblasting roughening treatment: 50-mesh brown corundum gravel was used as the sandblasting medium, the sandblasting air pressure was 0.5MPa, the sandblasting angle was 80°, and the surface roughness Ra after treatment reached 7μm.

[0039] S1.2 Weigh the following powders (all with a particle size of 30μm):

[0040] Chromium powder: 50kg

[0041] Nickel powder: 35kg

[0042] Titanium powder: 4.2 kg (corresponding to the formation of 8% titanium diboride)

[0043] Boron powder: 1.8 kg (corresponding to the formation of 8% titanium diboride)

[0044] Aluminum powder: 1kg

[0045] Silicon powder: 1kg

[0046] Niobium powder: 0.2kg

[0047] The total weight is approximately 93.2 kg, which is then mixed in a mixer for 4 hours.

[0048] S1.3. Plasma spraying is performed using hollow graphite electrode plasma arc spraying equipment:

[0049] Working gas: Argon, flow rate 40 L / min;

[0050] Powder delivery gas: Argon, flow rate 8L / min;

[0051] The power of the plasma arc is 30kW;

[0052] The arc current is 500A and the voltage is 60V;

[0053] The spraying distance is 120mm, and the spray gun moving speed is 500mm / s;

[0054] The mixed powder is fed into the plasma arc and sprayed repeatedly on the surface of the copper plate until the coating thickness reaches 0.20 mm.

[0055] S1.4. Use a diamond grinding wheel to perform surface grinding on the coating to a depth of 0.005mm, so that the coating thickness reaches 0.20mm; use diamond polishing paste with grit size W15 and W3 to perform coarse polishing and fine polishing on the surface after fine grinding in sequence; use anhydrous ethanol to ultrasonically clean the polished copper plate at a power of 400W for 10 minutes.

[0056] Example 2: A composite coating for improving the lifespan of copper plates in crystallizers and its preparation method by plasma spraying, comprising the following steps:

[0057] S1.1 Select a copper plate from a continuous casting crystallizer and perform degreasing, rust removal, and sandblasting roughening treatment on its surface to obtain a pretreated copper plate;

[0058] Degreasing treatment: Use acetone for ultrasonic cleaning at 400W for 20 minutes;

[0059] Rust removal treatment: Soak in 10% dilute hydrochloric acid for 10 minutes to remove surface oxides and rust;

[0060] Sandblasting roughening treatment: 50-mesh brown corundum gravel was used as the sandblasting medium, the sandblasting air pressure was 0.5MPa, the sandblasting angle was 80°, and the surface roughness Ra after treatment reached 7μm.

[0061] S1.2 Weigh the powder according to the following specifications:

[0062] Chromium powder: 50kg

[0063] Nickel powder: 35kg

[0064] Titanium powder: 2.5 kg (corresponding to the formation of 5% titanium diboride)

[0065] Boron powder: 1.1 kg (corresponding to the formation of 5% titanium diboride)

[0066] Aluminum powder: 1kg

[0067] Silicon powder: 1kg

[0068] Niobium powder: 0.2kg

[0069] The total weight is approximately 90.8 kg, which is then mixed in a mixer for 4 hours.

[0070] S1.3. Plasma spraying is performed using hollow graphite electrode plasma arc spraying equipment:

[0071] Working gas: Argon, flow rate 40 L / min;

[0072] Powder delivery gas: Argon, flow rate 8L / min;

[0073] The power of the plasma arc is 30kW;

[0074] The arc current is 500A and the voltage is 60V;

[0075] The spraying distance is 120mm, and the spray gun moving speed is 500mm / s;

[0076] The mixed powder is fed into the plasma arc and sprayed repeatedly on the surface of the copper plate until the coating thickness reaches 0.20 mm.

[0077] S1.4. Use a diamond grinding wheel to perform surface grinding on the coating to a depth of 0.005mm, so that the coating thickness reaches 0.20mm; use diamond polishing paste with grit size W15 and W3 to perform coarse polishing and fine polishing on the surface after fine grinding in sequence; use anhydrous ethanol to ultrasonically clean the polished copper plate at a power of 400W for 10 minutes.

[0078] Example 3: A composite coating for improving the lifespan of copper plates in crystallizers and its preparation method by plasma spraying, comprising the following steps:

[0079] S1.1 Select a copper plate from a continuous casting crystallizer and perform degreasing, rust removal, and sandblasting roughening treatment on its surface to obtain a pretreated copper plate;

[0080] Degreasing treatment: Use acetone for ultrasonic cleaning at 400W for 20 minutes;

[0081] Rust removal treatment: Soak in 10% dilute hydrochloric acid for 10 minutes to remove surface oxides and rust;

[0082] Sandblasting roughening treatment: 50-mesh brown corundum gravel was used as the sandblasting medium, the sandblasting air pressure was 0.5MPa, the sandblasting angle was 80°, and the surface roughness Ra after treatment reached 7μm.

[0083] S1.2 Weigh the powder according to the following specifications:

[0084] Chromium powder: 50kg

[0085] Nickel powder: 35kg

[0086] Titanium powder: 5.3 kg (corresponding to the formation of 10% titanium diboride)

[0087] Boron powder: 2.3 kg (corresponding to the formation of 10% titanium diboride)

[0088] Aluminum powder: 1kg

[0089] Silicon powder: 1kg

[0090] Niobium powder: 0.2kg

[0091] The total weight is approximately 94.8 kg, which is then mixed in a mixer for 4 hours.

[0092] S1.3. Plasma spraying is performed using hollow graphite electrode plasma arc spraying equipment:

[0093] Working gas: Argon, flow rate 40 L / min;

[0094] Powder delivery gas: Argon, flow rate 8L / min;

[0095] The power of the plasma arc is 30kW;

[0096] The arc current is 500A and the voltage is 60V;

[0097] The spraying distance is 120mm, and the spray gun moving speed is 500mm / s;

[0098] The mixed powder is fed into the plasma arc and sprayed repeatedly on the surface of the copper plate until the coating thickness reaches 0.20 mm.

[0099] S1.4. Use a diamond grinding wheel to perform surface grinding on the coating to a depth of 0.005mm, so that the coating thickness reaches 0.20mm; use diamond polishing paste with grit size W15 and W3 to perform coarse polishing and fine polishing on the surface after fine grinding in sequence; use anhydrous ethanol to ultrasonically clean the polished copper plate at a power of 400W for 10 minutes.

[0100] Example 4: A composite coating for improving the lifespan of copper plates in crystallizers and its preparation method by plasma spraying, comprising the following steps:

[0101] S1.1 Select a copper plate from a continuous casting crystallizer and perform degreasing, rust removal, and sandblasting roughening treatment on its surface to obtain a pretreated copper plate;

[0102] Degreasing treatment: Use acetone for ultrasonic cleaning at 400W for 20 minutes;

[0103] Rust removal treatment: Soak in 10% dilute hydrochloric acid for 10 minutes to remove surface oxides and rust;

[0104] Sandblasting roughening treatment: 50-mesh brown corundum gravel was used as the sandblasting medium, the sandblasting air pressure was 0.5MPa, the sandblasting angle was 80°, and the surface roughness Ra after treatment reached 7μm.

[0105] S1.2 Weigh the powder according to the following specifications:

[0106] Chromium powder: 50kg

[0107] Nickel powder: 35kg

[0108] Titanium powder: 4.2 kg (corresponding to the formation of 8% titanium diboride)

[0109] Boron powder: 1.8 kg (corresponding to the formation of 8% titanium diboride)

[0110] Aluminum powder: 1kg

[0111] Silicon powder: 1kg

[0112] Niobium powder: 0.2kg

[0113] The total weight is approximately 93.2 kg, which is then mixed in a mixer for 4 hours.

[0114] S1.3. Plasma spraying is performed using hollow graphite electrode plasma arc spraying equipment:

[0115] Working gas: Argon, flow rate 40 L / min;

[0116] Powder delivery gas: Argon, flow rate 8L / min;

[0117] The power of the plasma arc is 35kW;

[0118] The arc current is 500A and the voltage is 60V;

[0119] The spraying distance is 120mm, and the spray gun moving speed is 500mm / s;

[0120] The mixed powder is fed into the plasma arc and sprayed repeatedly on the surface of the copper plate until the coating thickness reaches 0.10 mm.

[0121] S1.4. Use a diamond grinding wheel to perform surface grinding on the coating to a depth of 0.005mm, so that the coating thickness reaches 0.10mm; use diamond polishing paste with grit size W15 and W3 to perform rough polishing and fine polishing on the surface after fine grinding in sequence; use anhydrous ethanol to perform ultrasonic cleaning on the polished copper plate at a power of 400W for 10 minutes.

[0122] Example 5: A composite coating for improving the lifespan of copper plates in crystallizers and its preparation method by plasma spraying, comprising the following steps:

[0123] S1.1 Select a copper plate from a continuous casting crystallizer and perform degreasing, rust removal, and sandblasting roughening treatment on its surface to obtain a pretreated copper plate;

[0124] Degreasing treatment: Use acetone for ultrasonic cleaning at 400W for 20 minutes;

[0125] Rust removal treatment: Soak in 10% dilute hydrochloric acid for 10 minutes to remove surface oxides and rust;

[0126] Sandblasting roughening treatment: 50-mesh brown corundum gravel was used as the sandblasting medium, the sandblasting air pressure was 0.5MPa, the sandblasting angle was 80°, and the surface roughness Ra after treatment reached 7μm.

[0127] S1.2 Weigh the powder according to the following specifications:

[0128] Chromium powder: 50kg

[0129] Nickel powder: 35kg

[0130] Titanium powder: 4.2 kg (corresponding to the formation of 8% titanium diboride)

[0131] Boron powder: 1.8 kg (corresponding to the formation of 8% titanium diboride)

[0132] Aluminum powder: 1kg

[0133] Silicon powder: 1kg

[0134] Niobium powder: 0.2kg

[0135] The total weight is approximately 93.2 kg, which is then mixed in a mixer for 4 hours.

[0136] S1.3. Plasma spraying is performed using hollow graphite electrode plasma arc spraying equipment:

[0137] Working gas: Argon, flow rate 40 L / min;

[0138] Powder delivery gas: Argon, flow rate 8L / min;

[0139] The power of the plasma arc is 30kW;

[0140] The arc current is 500A and the voltage is 60V;

[0141] The spraying distance is 120mm, and the spray gun moving speed is 500mm / s;

[0142] The mixed powder is fed into the plasma arc and sprayed repeatedly on the surface of the copper plate until the coating thickness reaches 0.25 mm.

[0143] S1.4. Use a diamond grinding wheel to perform surface grinding on the coating to a depth of 0.005mm, so that the coating thickness reaches 0.25mm. Then, use diamond polishing paste with grit size W15 and W3 to perform coarse polishing and fine polishing on the surface after fine grinding. Use anhydrous ethanol to ultrasonically clean the polished copper plate at a power of 400W for 10 minutes.

[0144] Example 6: A composite coating for improving the lifespan of a crystallizer copper plate and its preparation method by plasma spraying, comprising the following steps:

[0145] S1.1 Select a copper plate from a continuous casting crystallizer and perform degreasing, rust removal, and sandblasting roughening treatment on its surface to obtain a pretreated copper plate;

[0146] Degreasing treatment: Use acetone for ultrasonic cleaning at 300W for 10 minutes;

[0147] Rust removal treatment: Soak in 5% dilute hydrochloric acid for 5 minutes to remove surface oxides and rust;

[0148] Sandblasting roughening treatment: 16-mesh brown corundum gravel was used as the sandblasting medium, the sandblasting air pressure was 0.4MPa, the sandblasting angle was 70°, and the surface roughness Ra after treatment reached 6μm.

[0149] S1.2 Weigh the powder according to the following specifications:

[0150] Chromium powder: 35kg

[0151] Nickel powder: 20kg

[0152] Titanium powder: 4.2 kg (corresponding to the formation of 8% titanium diboride)

[0153] Boron powder: 1.8 kg (corresponding to the formation of 8% titanium diboride)

[0154] Aluminum powder: 0.5kg

[0155] Silicon powder: 0.5kg

[0156] Niobium powder: 0.1kg

[0157] The total weight is approximately 62.1 kg, which is then mixed in a mixer for 4 hours.

[0158] S1.3. Plasma spraying is performed using hollow graphite electrode plasma arc spraying equipment:

[0159] Working gas: Argon, flow rate 35 L / min;

[0160] Powder delivery gas: Argon, flow rate 5L / min;

[0161] The power of the plasma arc is 20kW;

[0162] The arc current is 400A and the voltage is 50V;

[0163] The spraying distance is 80mm, and the spray gun moving speed is 300mm / s;

[0164] The mixed powder is fed into the plasma arc and sprayed repeatedly on the surface of the copper plate until the coating thickness reaches 0.20 mm.

[0165] S1.4. Use a diamond grinding wheel to perform surface grinding on the coating to a depth of 0.005mm, so that the coating thickness reaches 0.20mm; use diamond polishing paste with grit size W10 and W1 to perform coarse polishing and fine polishing on the surface after fine grinding in sequence; use anhydrous ethanol to ultrasonically clean the polished copper plate at a power of 300W for 5 minutes.

[0166] Example 7: A composite coating for improving the lifespan of a crystallizer copper plate and its preparation method by plasma spraying, comprising the following steps:

[0167] S1.1 Select a copper plate from a continuous casting crystallizer and perform degreasing, rust removal, and sandblasting roughening treatment on its surface to obtain a pretreated copper plate;

[0168] Degreasing treatment: Use acetone for ultrasonic cleaning at 600W for 30 minutes;

[0169] Rust removal treatment: Soak in 15% dilute hydrochloric acid for 10 minutes to remove surface oxides and rust;

[0170] Sandblasting roughening treatment: 60-mesh brown corundum gravel was used as the sandblasting medium, the sandblasting air pressure was 0.8MPa, the sandblasting angle was 90°, and the surface roughness Ra after treatment reached 8μm;

[0171] S1.2 Weigh the powder according to the following specifications:

[0172] Chromium powder: 55kg

[0173] Nickel powder: 55kg

[0174] Titanium powder: 4.2 kg (corresponding to the formation of 8% titanium diboride)

[0175] Boron powder: 1.8 kg (corresponding to the formation of 8% titanium diboride)

[0176] Aluminum powder: 2kg

[0177] Silicon powder: 2kg

[0178] Niobium powder: 0.3kg

[0179] The total weight is approximately 120.3 kg, which is then mixed in a mixer for 4 hours.

[0180] S1.3. Plasma spraying is performed using hollow graphite electrode plasma arc spraying equipment:

[0181] Working gas: Argon, flow rate 45 L / min;

[0182] Powder delivery gas: Argon, flow rate 10L / min;

[0183] The power of the plasma arc is 42kW;

[0184] The arc current is 600A and the voltage is 70V;

[0185] The spraying distance is 150mm, and the spray gun moving speed is 800mm / s;

[0186] The mixed powder is fed into the plasma arc and sprayed repeatedly on the surface of the copper plate until the coating thickness reaches 0.20 mm.

[0187] S1.4. Use a diamond grinding wheel to perform surface grinding on the coating to a depth of 0.020mm, so that the coating thickness reaches 0.20mm; use diamond polishing paste with grit size W20 and W5 to perform rough polishing and fine polishing on the surface after fine grinding in sequence; use anhydrous ethanol to perform ultrasonic cleaning on the polished copper plate at a power of 600W for 15 minutes.

[0188] The coating bond strength was determined according to ASTM C633, "Standard Test Method for Adhesion or Bond Strength of Thermally Sprayed Coatings": Two cylindrical substrates with a diameter ≥25.4 mm (one end face is the surface to be sprayed) were taken, and the material was the same as or had a similar coefficient of thermal expansion to the copper plate of the crystallizer; one end face of one of the substrates was sprayed according to the method of this invention, while the other was left unsprayed; a high-strength structural adhesive (such as FM-1000 series) was used to bond and align the coated surface with the unsprayed end face of the specimen to form a butt tensile specimen; the adhesive layer was ensured to be uniform and free of bubbles, and cured under standard conditions; the prepared butt specimen was mounted on a special fixture of a universal testing machine; a tensile load was applied at a constant rate (usually 1.0-1.5 mm / min) until the specimen failed; the maximum tensile load (F) was recorded; the bond strength (σ) was calculated as F / A, where A is the cross-sectional area of ​​the coating.

[0189] The microhardness of the coating was determined according to the standard ASTM E384, "Standard Test Method for Microhardness of Materials": Metallographic specimens of the coating section were prepared. The coated samples were mounted, coarsely ground, finely ground, and polished to obtain a scratch-free mirror-like cross-section. A micro Vickers hardness tester was used, with a test force of 2.942 N (0.3 kgf) and a holding time of 15 seconds. Indentation tests were performed at at least five different locations within the coating section, ensuring the indentations were located within the coating and sufficiently far from interfaces or other indentations. The lengths of the two diagonals of the indentation were measured using the hardness tester's built-in optical system. The hardness tester automatically calculated the Vickers hardness value (HV) based on the diagonal lengths and the test force. The arithmetic mean of all valid measurements was taken as the average microhardness of the coating.

[0190] High-temperature oxidation performance was determined according to standard ASTM G54 "Simple Static Oxidation Test": the coated sample was cut into specified dimensions (e.g., 20mm × 10mm × thickness), and its surface area was recorded; the sample was ultrasonically cleaned with acetone, dried, and its initial mass was weighed using an analytical balance with an accuracy of 0.1mg. The sample was placed in a muffle furnace preheated to 800°C with a static air environment; it was held at 800°C for 100 hours; after the time was up, the sample was removed from the furnace and cooled to room temperature in a dry environment; the loose oxide scale was carefully removed with a soft brush, and then the mass of the sample was weighed again. ); Result calculation: Weight gain per unit area = ( - ) / A, where A is the total surface area of ​​the sample.

[0191] Thermal shock resistance test: Place the sample in a muffle furnace preheated to 800℃ and hold for 5 minutes to ensure the entire sample reaches the furnace temperature; quickly remove the sample with preheated crucible tongs and immediately immerse it in a 20℃ flowing tap water bath, ensuring the sample is completely submerged and holding for 30 seconds; remove the sample and inspect the coating surface and edges for cracks, peeling, or flaking with the naked eye or a 10x magnifying glass; after drying with compressed air or at low temperature, repeat the above steps to start the next cycle; the result determination of the thermal shock resistance cycle number refers to the maximum number of cycles that the coating of each sample does not crack or peel.

[0192] Actual steel throughput comparison measurement: Under the same continuous casting machine, casting the same steel grade, using the same billet pulling speed and cooling intensity, crystallizer copper plates with the coating of this invention and conventional electroplated chromium coating were installed respectively; the total tonnage of molten steel cast was recorded from the time the new copper plate was put into service until its coating failed due to wear, burning or cracking and needed to be taken offline for repair; the average steel throughput of multiple copper plates with the coating of this invention and conventional electroplated chromium coating (1.0 times the benchmark) was calculated respectively.

[0193] Relative content determination of chromium carbide: X-ray diffraction (XRD) analysis was used to determine the relative content of the chromium carbide phase in the coating.

[0194] Table 1 Performance data of composite coatings used to improve the lifespan of copper plates in crystallizers

[0195] ;

[0196] As can be seen from the comparison of Examples 1-3 in Table 1, as the titanium diboride content increases from 5% to 10%, the coating hardness increases significantly (from 890HV0.3 to 1010HV0.3); this is because titanium diboride is an ultra-high hardness ceramic phase, and the higher its content, the stronger the dispersion strengthening effect.

[0197] As can be seen from the comparison of Examples 1-3 in Table 1, as the relative content of chromium carbide in the coating increases from 7% to 13%, the microhardness of the coating shows a significant upward trend; this is because chromium carbide and titanium diboride together act as hard reinforcing phases, and the increase in their content directly enhances the dispersion strengthening effect of the coating.

[0198] Example 3 (10% titanium diboride) performed best; this is because the denser titanium diboride phase hindered the inward diffusion of oxygen ions.

[0199] The bonding strength of Examples 1-3 remained at a high level (>70MPa); the bonding strength of Example 2 (5% titanium diboride) was slightly lower because the content of the hard phase was low, which had a limited strengthening effect on the overall coating; the bonding strength of Example 3 (10% titanium diboride) (75MPa) was slightly lower than that of Example 1 (78MPa), but it still remained at a high level. This is because while the high content of the hard phase increased the hardness, it also slightly increased the brittleness of the coating, which restricted further improvement of the bonding strength.

[0200] Example 1 (8% titanium diboride) showed a balance between hardness and toughness; higher hardness resulted in better wear resistance, so Example 3 had the highest steel content (2.8 times).

[0201] From Table 1, comparing Examples 1 and 4-5, it can be seen that Example 4 (0.10 mm) has the lowest bonding strength. This is because the thinner coating has a poorer ability to release internal stress. Although its chromium carbide content (8%) is similar to that of Example 1 (9%), the thinner coating has insufficient ability to release internal stress and protect the substrate.

[0202] Example 5 (0.25mm) showed the highest bonding strength, indicating that within a certain range, increasing the thickness is beneficial for forming a more stable layered structure and improving the bonding force.

[0203] Example 4 (0.10 mm) failed after 130 cycles, while thicker coatings could withstand more than 150 cycles; this is because the stress at the interface between the coating and the substrate is huge during thermal cycling, and thicker coatings can better buffer and redistribute these stresses.

[0204] The thinner coating (0.10 mm) offers limited protection and relatively low steel penetration (2.0 times); while the 0.20 mm and 0.25 mm coatings provide more durable and effective protection and higher steel penetration.

[0205] The 0.20 mm thickness in Example 1 is a preferred thickness that balances economy and superior performance.

[0206] Based on the above measurements, Example 1 is selected as the optimal example.

[0207] Comparative Example 1: The difference between this example and Example 1 is that a chromium plating layer with a thickness of 0.05 mm is prepared on the same copper plate using a traditional electroplating process.

[0208] Comparative Example 2: The difference between this example and Example 1 is that a conventional hollow tungsten electrode plasma spraying equipment is used.

[0209] Table 2 Performance data of composite coatings used to improve the lifespan of copper plates in crystallizers

[0210] ;

[0211] Compared to the conventional electroplated chromium layer (Comparative Example 1, thickness 0.05 mm), the bonding strength of Example 1 (thickness 0.20 mm) is more than three times that of the conventional electroplated chromium layer. This demonstrates that the bonding formed by plasma spraying is far superior to that of electroplating. At the same time, although the coating of Example 1 is thicker, its thermal shock resistance (>150 cycles) is still far superior to that of the electroplated chromium layer (40 cycles). This is due to its unique metal-ceramic composite structure, which can effectively release thermal stress. The electroplated chromium layer, due to its inherent brittleness, will quickly crack and peel off under severe thermal cycling, even at the optimal thickness. The amount of steel in the coating of Example 1 is 2.5 times that of Comparative Example 1, demonstrating a significant improvement in its overall performance.

[0212] Comparative Example 2 uses a hollow tungsten electrode, which lacks a continuous and controllable carbon source. It can only rely on the premixed carbon in the powder or the trace amount of carbon in the atmosphere to carry out the reaction, resulting in a significantly lower in-situ chromium carbide generation amount than in Example 1. The lack and uneven distribution of chromium carbide leads to a decrease in coating hardness and insufficient structural density, thereby affecting its oxidation resistance and bonding strength.

[0213] The difference in hardness between Comparative Example 2 and Example 1 indicates that hollow graphite electrodes can generate high-hardness chromium carbide more efficiently and uniformly; the efficiency of decomposition and reaction of externally introduced hydrocarbon gas in the plasma arc is low and difficult to control precisely, resulting in a small amount of chromium carbide generated and uneven distribution; poor oxidation resistance also indirectly proves that the coating structure is not dense enough and that the presence of free carbon promotes oxidation.

[0214] The decrease in bonding strength in Comparative Example 2 is related to the higher amount of unreacted chromium and the change in stress distribution within the coating; the significant reduction in thermal shock resistance is due to insufficient toughness of the coating itself and insufficient bonding strength with the substrate, leading to earlier failure under repeated thermal stress impacts.

[0215] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A composite coating for improving the life of a crystallizer copper plate formed on the surface of a copper plate substrate, characterized by, The coating has a thickness of 0.10-0.25 mm and contains, by mass percent, Cr 35-55%, Ni 20-55%, TiB2 5-10%, Nb 0.1-0.3%, and the balance of CrC and inevitable trace impurities. The coating is a cermet composite structure containing dispersed TiB2 and CrC hard phases.

2. The composite coating for improving the life of crystallizer copper plate according to claim 1, wherein, The inevitable trace impurities are B, Fe, Al, and Si.

3. A method for the production of a composite coating plasma sprayed for increasing the lifetime of crystallizer copper plates, for the production of a composite coating for increasing the lifetime of crystallizer copper plates according to any one of claims 1-2, characterized in that, The preparation method is as follows: S1.1, the surface of the crystallizer copper plate substrate is subjected to oil removal, rust removal, and sand blasting roughening treatment to obtain a pretreated copper plate; S1.2, the chromium powder, nickel powder, boron powder, titanium powder, aluminum powder, silicon powder, and niobium powder are mixed in a three-dimensional mixer to obtain a mixed powder; S1.3, a hollow graphite electrode plasma arc spraying device is used, argon is used as the working gas and the powder feeding gas, the mixed powder is fed into the plasma arc, and the mixed powder is melted and sprayed onto the surface of the pretreated copper plate to form a composite coating; S1.4, the sprayed composite coating is finely ground and polished.

4. The method of claim 3, wherein the method further comprises the step of: applying a plasma sprayed coating of a composite material to the copper plate of the mold. In S1.1, the oil removal treatment is ultrasonic cleaning with acetone at a power of 300-600 W for 10-30 min; The rust removal treatment is soaking in dilute hydrochloric acid with a mass concentration of 5-15% for 5-10 min to remove the surface oxides and rust; The sand blasting roughening treatment uses 16-60 mesh brown corundum grit as the sand blasting medium, the sand blasting pressure is 0.4-0.8 MPa, the sand blasting angle is 70-90°, and the surface roughness Ra after treatment reaches 6-8 μm.

5. The method of claim 3, wherein the method further comprises the step of: applying a plasma sprayed coating of a composite material to the copper plate of the mold. In S1.2, the mass percentage composition of the mixed powder is: chromium powder 35-55%, nickel powder 20-55%, the total amount of titanium powder and boron powder corresponds to the generation of 5-10% of titanium diboride, aluminum powder 0.5-2%, silicon powder 0.5-2%, and niobium powder 0.1-0.3%.

6. The method of claim 3, wherein the method further comprises the step of: applying a plasma sprayed coating of a composite material to the copper plate of the mold. In S1.3, the power of the plasma arc is 20-45 kW.

7. The method of claim 3, wherein the method further comprises the step of: applying a plasma sprayed coating of a composite material to the copper plate of the mold. In S1.3, the spraying distance is 80-150 mm, and the gun moving speed is 300-800 mm / s.

8. The method of claim 3, wherein the method further comprises the step of: applying a plasma sprayed coating of a composite material to the copper plate of the mold. In S1.3, the flow rate of the working gas is 35-45 L / min, and the flow rate of the powder feeding gas is 5-10 L / min.

9. The method of claim 3, wherein the method further comprises the step of: applying a plasma sprayed coating of a composite material to the copper plate of the mold. In S1.3, the arc current of the plasma spraying is 400-600 A, and the voltage is 50-70 V.

10. The method of claim 3, wherein the method is characterized by: In S1.4, the steps of fine grinding and polishing are as follows: a diamond grinding wheel is used to plane grind the coating, the grinding depth is 0.005-0.020 mm, the coating thickness reaches 0.10-0.25 mm, and then W10-W20 and W1-W5 diamond polishing paste is used for rough polishing and fine polishing, respectively, and the polished copper plate is ultrasonically cleaned with anhydrous ethanol at a power of 300-600 W for 5-15 min.